department commerce national technical information service · 2018. 6. 13. · cooperative...

PB 8 4- 1 7 0 6 6 1

E v a l u a t i o n of P r o c e s s S y s t e m s for E f f e c t i v e Management o f A l u m i n u m F i n i s h i n g Waste wa te r s and S 1 udg e s

I

i

G e o r g i a I n s t . of T e c h . , A t l a n t a

P r e p a r e d for

I n d u s t r i a l Env i ronmen ta l R e s e a r c h Lab . R e s e a r c h T r i a n g l e P a r k , NC

Mar 8 4

U.S. DEPARTMENT OF COMMERCE National Technical Information Service

EPA-600/2-84-077 March 1984

FM P- 00 27 L-

EVALUATION OF PROCESS SYSTEMS FOR EFFECTIVE MANAGEMENT OF ALUMINUM FINISHING WASTEWATERS AND SLUDGES

F. Michael Saunders, Edward S. K. Chian, C . B lake Harmon, K u r t L. K ra tz ,

Jesus M. Medero, Michael E. P i s a n i , Rey R. Ramirez and Mesut Sezgin

School o f C i v i l Engineer ing Georgia I n s t i t u t e o f Technology

Cooperat ive Agreement CR 807512-01

P r o j e c t O f f i c e r

A l f r e d B. C r a i g Jr. Nonferrous Meta ls and Minera ls Branch

I n d u s t r i a l Environmental Research Laboratory C i n c i n n a t i , OH 45268

OFFICE OF RESEARCH AND DEVELOPMENT U.S. ENVIRONMENTAL PROTECTION AGENCY

CINCINNATI, OH 45268

Co-Sponsored by

ALUMINUM EXTRUDERS COUNCIL

ROLLING MEADOWS, I L 60008 4300-L LINCOLN AVENUE

INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY OFFICE OF RESEARCH AND DEVELOPMENT

U.S. ENVIRONMENTAL PROTECTION AGENCY CINCINNATI, O H I O 45268

TECHNICAL REPORT DATA /Plcorr read lnrrruci:oir on iiic ~ C I ( E ~ S C brJorc w m p l c r i n ~ j

13. RECIP IENT 'S ACCESSION N O -

1. R E P O R T N O . 12.

L

R e s u l t s of t h e research can be immediate iy implemented a t many a lum inum- f i n i sh ing p l a n t s where s ludge d i sposa l r e s t r i c t i o n s and c o s t s a r e i n c r e a s i n g . Segregated n e u t r a l i z a t i o n and recove ry o f spent c a u s t i c e t c h can be used t o i n c r e a s e t h e n e t s o l i d s c o n t e n t of dewatered-sludge a v a i l a b l e f o r d i s p o s a l . s ludge s o l i d s u s i n g a c i d e x t r a c t i o n f o r p r o d u c t i o n o f l i q u i d alum has p o t e n t i a l f o r

Reclamat ion o f dewatered- , 1

EPA-600/2-84-077 PB84-30661

I 15. S U P P L E M E N T A R Y N O T E S

4. T I T E A N D S U 8 T l T L E Eva \ua t ion of Process Systems f o r E f f e c t i v e

and Sludges

F.M. Saunders, E.S.K. Chian, C.B. Harmon, K.L. K r a t z , J.M. Medero, M.E. P i s a n i , R.R. Ramierz, and M. Sezqin

Georg ia I n s t i t u t e o f Technology

A t l a n t a , GA 30332

Management o f Aluminum F i n i s h i n g Wastewaters

7 A U T H O R I S 1

3 P E R F O R M I N G O R G A N I Z A T I O N N A M E A N D ADDRESS

School o f C i v i l Eng ineer ing

1 6 . A B S T ACT Pnnovat ive processes f o r use i n t r e a t m e n t o f wastewaters and sludges produced

Segregated n e u t r a l i z a t i o n o f spent c a u s t i c e t c h and spent anodize a c i d s a t tem- i n anod iz ing , e t c h i n g and p a i n t i n g ex t ruded aluminum were i n v e s t i g a t e d .

p e r a t u r e s o f 60 t o 90'C and pH values o f 5.5 t o 10 were examined. i n t h i c k e n i n g and dewa te r ing p r o p e r t i e s were ach ieved w i t h i n c r e a s i n g va lues o f n e u t r a l z a t i o n pH w h i l e n e u t r a l i z a t i o n temperature had minimal impact . Recovery o f spent c a u s t i c e t c h by p r e c i p i t a t i o n o f aluminum w i t h c a l c i u m ( i . e . , l i m e ) a d d i t i o n was s tud ied . achieved a t Ca/A1 r a t i o s o f 4 t o 5.5 (mass b a s i s ) . Recovery o f a l u m i n u m - f i n i s h i n g s ludges u s i n g s u l f u r i c - a c i d e x t r a c t i o n t o produce l i q u i d alum ( i .e. , A12(S04)3.14 H7O) was examined w i t h numerous t w e s o f s ludges.

Major improvements

S t o i c h i o m e t r i c p r e c i p i t a t i o n o f aluminum a t temperatures o f 25 t o 60°C was

5 REPORT D A T E

March 1984 6 P E R F O R M I N G O R G A N I Z A T I O N CODE

8 P E R F O R M I N G O R G A N I Z A T I O N REPORT N O

EPA/600

C33BlB

CR807512

1 0 P R O G R A M E L E M E N T N O

1 1 C O N T R A C T I G R A N T N O

P N S Q R I N G A G N Y A M A N A D D ESS '65 hi ronmenta? Pro€ec€'ion FAgency

C i n c i n n a t i , OH 45268 I n d u s t r i a l Environmental Research Labora to ry

13. T Y P E O F R E P O R T A N D P E R I O D C O V E R E D F i n a l

14 . SPONSORING A G E N C Y CODE

EPA/600/12

- ~~ ~~ ~-

v i r t u a l e l i m i n a t i o n o f t h e need f o r s ludge d i s p o s a l w h i l e p roduc ing a n e t income f rom t h i s s l udge-rec lamat ion process. i

17.

a. DESCRIPTORS b . l D E N T I F I E R S I O P E N E N D E D T E R M S E . COSATI FicldlCraup K E Y WORDS A N D D O C U M E N T A N A L Y S I S

A I umi num Sludge Reclamat ion Meta l Recovery Sludge D isposa l Dewater ing

18. D I S T R I B U T I O N S T A T E M E N T 1 9 , S E C U R I T Y CLASS ( T h i s R r p o r f l 21. N O . O F PAGES

p - b ---____ 20. S E C U R I T Y CLASS (TI ! i .spq<, , 22. PRICE UNCLASSIFIED

I

€ P A Form 2220-1 (Rev. 4-77) P R E V I O U S E D ~ T ~ O N I S O B S O L E T E

NOTICE

This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved fo r publication. or commercial products does not constitute endorse- ment or recommendation for use.

Mention of trade names

FORWARD

When energy and m a t e r i a l resources a re e x t r a c t e d , processed, conver ted, and used, t h e r e l a t e d p o l l u t i o n a l impacts on o u r env i ronment and even on our h e a l t h o f t e n r e q u i r e t h a t new and i n c r e a s i n g l y more e f f i c i e n t p o l l u t i o n con- t r o l methods be used. The I n d u s t r i a l Env i ronmenta l Research Labora to ry - C i n c i n n a t i ( IERL-Ci) a s s i s t s i n deve lop ing and demonst ra t ing new and improved methodologies t h a t w i l l meet these needs bo th e f f i c i e n t l y and economica l l y .

T h i s r e p o r t desc r ibes research under taken t o e v a l u a t e t h e performance o f conven t iona l and i n n o v a t i v e systems used i n t h e development o f t rea tmen t s t r a t e g i e s t o m in im ize c u r r e n t s ludge d i sposa l problems assoc ia ted w i t h aluminum e t c h i n g and anod iz ing processes. Resu l t s o f t h i s research can be. implemented a t many aluminum f i n i s h i n g p l a n t s where s ludge d i sposa l r e s t r i c t i o n s and cos ts a r e i n c r e a s i n g .

David G. Stephan D i r e c t o r

I n d u s t r i a l Environmental Research Labora to ry C i n c i n n a t i

iii

CONTENTS

1.

2.

3.

4.

5.

6.

-

iii

v i i

x i

9 11 11

12

12 13 18 18 18 18 18 21 21 25 26 27 30 30 30 32

..

i v

CONTENTS (con t ' d )

Sec t ion

32 33 33 '

34

37

37 40 40 41 41 41 49 49 52 52 52 52 64 64 73 77 77 30 80 80 83 86 88 88 92 95

98

98 98 99 99 99

101

Section

CONTENTS (con t ' d )

x

v i

FIGURES

Number

7.1

7.2

7.3

7.4

7.5

7.6

7.7

7.8

7.9

7.10

7.11

7.12

7.13

Schematic Diagram of Laboratory-Scale Reac

In t e r f ac i a l S e t t l i n g Velocity Data f o r Sludge Produced

In t e r f ac i a1 S e t t l i n g Velocity Data f o r 51 udge Produced


Effect of Temperature on S e t t l i n g Charac te r i s t ics of Sludges Produced a t Elevated Temperatures and Neutral pH ---------- 45

System Used for Segregated Neutralization Studies ---------------- 39

42 i n Run 1 ..................................................

43 i n Run 2 ___---___-__---__________________________---------

44 i n Run 3 ____________-___________________________----------



Effect of Neutral izat ion pH on Thickening Charac te r i s t ics

Batch Flux Curves a t pH Values of 8.5 ( # l ) , 7.9 ( # 2 ) and

Variation of Spec i f ic Resistance, F i l t e r Yield and CST w i t h Suspended Sol ids Concentration in Run 1 ------------------- Evaluation of Compressibility Coeff ic ient , So , a t Suspended Sol ids Concentration of 20.8 g/ l f o r Run 1 ---------------- Effect of Vacuum on F i l t e i Yield a t a Suspended Solids CoTiWntration o f 112.1 g / l in Run 1 ....................... Variation of Specif ic Resistance, F i l t e r Yield and CST w i t h Suspended S o l i d s Concentration i n Run 2 --------------

vi i

in Run 4 ..................................................

i n Run 5 ..................................................

of Sludges Produced a t 80°C __________--_______-___________

5.5 (#3) ____-_______-___________________________----------

46

47

48

50

54

55

56

58

FIGURES (cont 'd )

Number

7.14

7.15

7.16

7.17

7.18

7.19

7.20

7.21

7.22

7.23

7.24

7.25

7.26

7.27

7.28

Evaluation of Compressibility Coeff ic ient , So, a t Various Suspended Sol ids Concentrations f o r Run 2 ----------------- Effec t of Applied Vacuum Pressure on F i l t e r Yield a t a Suspended Sol ids Concentration of 151.1 g/1 and a t Room Temperature i n Experimental Run 2 ......................... Effect of Time of Cake Formation on Filter Yield a t a Suspended Sol ids Concentration of 151.1 g/1 and a t Room Temperature i n Experimental Run 2 ......................... Variation of Spec i f i c Resistance, F i l t e r Yield and CST w i t h Suspended Sol i d s Concentration i n Run 3 ------------------- Evaluation of Compressibility Coeff ic ient , So, a t Various Suspended Sol ids Concentrations i n Run 3 ------------------ Effec t of Applied Vacuum on F i l t e r Yield a t a Suspended So l ids Concentration of 157.3 g/1 i n Run 3 ---------------- Effec t of Time of Cake Formation on F i l t e r Yield a t a Suspended Sol ids Concentration of 157.5 g/ i i n Ftun 3 ------ Variation of Spec i f i c Resistance, F i l t e r Yield and CST w i t h Suspended Sol ids Concentration i n Run 4 ------------------- Evaluation of Compressibility Coeff ic ient , So , a t Various Suspended Sol ids Concentrations i n Experimental Run 4 ---- Effect of Applied Vacuum on F i l t e r Yield a t a Suspended Sol ids Concentrationof 184.4 g/l i n R u n 4 ----------------- Effec t of Time of Cake Formation on Filter Yield a t a Suspended Sol ids Concentration of 184.4 g / l i n Run 4 ------ Variation of Spec i f i c Resistance, F i l t e r Yield a n d Capi l lary CST w i t h Suspended Soi ids Concentration i n Run 5

E f fec t of Time of Cake Formation on F i l t e r Yield a t a Suspended Sol ids Concentration of 159.6 g/1 i n Run 5 ---.--

Batch F l u x Curves f o r Sludges Produced by Conventional and Segregated Neutral izat ion of Aluminum-Finishing Wastes

Variation of Spec i f i c Resistance w i t h Suspended Sol ids Concentration Produced a t Various pH Values ---------------

59

60

61

63

65

66

67

69

70

71

72

75

76

78

81

v i i i

FIGURES ( c o n t ' d )

Number

7.29

7.30

7.31

7.32

7.33

7.34

7.35

a. 1

8.2

8.3

8.4

8.5

8.6

a. 7

Variation of CST with Suspended Sol ids Concentration a t

Variation of CST with Suspended Sol ids Concentration a t

Variation o f F i l t e r Yield with Suspended Sol ids Concen-

Effec t of Suspended Sol ids Concentration on Cake Sol ids Concentration i n F i l t e r - l e a f Analyses fo r Various Neutral izat ion pH Values -_-_____----______-______________ 87

Effect of Sludge Neutral izat ion pH on Sludge Compressibil-

Ef fec t of Applied Vacuum on F i l t e r Yield a t Various pH

Effec t of Applied Vacuum on Cake Sol ids Concentration ---- Relationship Between Residual Soluble Aluminum and Reaction Time a t a Constant Ca/A1 Molar Ratio of 2/i ----- 100

Relationship Between Residual Soluble Aluminum and Ap.plied Ca/A1 Dose ....................................... 103

Relationship Between Residual Dissolved Sol ids and Residual Soluble Aluminum fo r Various Ca/Al Ratios and a Reaction Temperature of 30°C ............................. 104

Relationship Between Measured Dry-Cake Sol ios and Corresponding Aluminum and Calcium Composition as Calcu- l a t ed from I n i t i a l and Final Concentrations in Treated

Relationship Between Spec i f ic Resistance and Reaction Time for Temperatures of 2 5 O C and 60°C a t Ca/A1 of 3 g /g - 107

Relationship Between Spec i f i c Resistance and Applied Ca/A1 Ratios f o r Reaction Temperatures of 25, 42, and

Relationship Between Applied Calcium t o Aluminum Ratio and Dewatered Cakes Sol ids Content a t Reaction Tempera-

82 Various pH Values _______________--_______________________

84 Various pH Values ........................................

t r a t i o n a t Various pH Values ____----_____--______________ 85

d9 i t y Coeff ic ien ts ________________________________________-

90

9 i

Values ...................................................

105 Etch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

109 60°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

110 tu re s of 25 and 6O0C ____________________--------- - - - - - - - -

ix

FIGURES (cont'd)

Number

a. a Relationship Between Vacuum Filter Yields and Soiution Temperature for an Applied Ca/A1 Mass Ratio o f 2.5jl ----- 1 1 1

Fiitrate Aluminum Concentrations in Direct-Acidification 125

9.2 Schematic Diagram o f an Alum Production Facility --------- 131

. . . 9.1 of Aluminum-Finisning Sludges ............................

X

TABLES

Number

5.1

6.1 '

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

6.10

6.11

6.12

. 6.13

6.14

6.15

D e s c r i p t i o n o f P a r t i c i p a t i n g A1 umi num- F i n i s h i ng p l a n t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P a i n t L i n e Process a t P l a n t A 1 _- - - -__- - - -_L- - - - - - - - - - - - - -

D e s c r i p t i o n o f Anodiz ing Process L i n e a t P l a n t A1 -------- Wastewater Treatment Systems a t P l a n t A2 ----------------- Wastewater Flow Rate For Anodize L i n e .................... Wastewater C h a r a c t e r i s t i c s f o r Anodize and P a i n t L i n e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Meta l Composi t ion o f Wastewater Sources ------------------ Meta l Composi t ion o f Anod iz ing Process S o l u t i o n s --------- Mass Flow o f Me ta l s from Wastewater Sources -------------- Meta l Composi t ion o f P a i n t - L i n e Wastewater and

Meta l Composi t ion o f Anodize and N e u t r a l i z e d

F i n i s h i n g S o l u t i o n s ......................................

P l a n t Wastewaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aluminum Produc t ion Data f o r P l a n t A I .................... Anod iz ing Processes U t i l i z e d Dur ing t h e

Chemical Composi t ion L i m i t s o f Wrought Aluminum A l l o y s (Aluminum Assoc ia t i on , 1979) ...................... R e l a t i v e Trace Metal Composi t ion o f Apod iz ing Rinsewaters and F i n i s h i n g Solut ion------------------------

R e l a t i v e Trace Metal Composi t ion o f P a i n t i n g Rinsewaters and F i n i s h i n g S o l u t i o n s ......................

Survey Per iod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

l a

12

14

17

1 9

20

22

23

24

25

26

28

29

30

31

32

x i

TABLES (Cont. 'd)

Number

6.16

6.17

6.18

7.1

7 . 2

7.3

7.4

7.5

7.6

7.7

7.8

7.9

7.10

7.11

7.12

Drag in Rate f o r Anodize-L ine Rinsewaters ----------------- Summary o f Wastewater and Metal Flows f o r Anod iz ing

Wastewater and Metal Flows Normal ized t o

L i n e a t P l a n t A1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Produc t ion of F in i shed Meta l . ............................ Range o f C h a r a c t e r i s t i c s o f Spent Anodize and

C h a r a c t e r i s t i c s o f Waste S o l u t i o n s Used i n

E t c h Wastes from P l a n t A3 ................................

Phase 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exper imenta l Cond i t i ons Dur ing Runs i n Phase 1 ----------- C h a r a c t e r i s t i c s o f Waste S o l u t i o n s Used i n

Exper imenta l Cond i t i ons Dur ing Runs i n Phase 2 ----------- E f f e c t o f Suspended Sol i d s Concen t ra t i on on S p e c i f i c Resistance, F i l t e r Y i e l d and CST i n

E f f e c t o f Suspended S o l i d s Concen t ra t i on on S p e c i f i c Resis tance, F i l t e r Y i e l d and CST i n

E f f e c t o f Suspended S o l i d s Concen t ra t i on on S p e c i f i c Resistance, F i l t e r Y i e l d and CST i n



Phase 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Run 1 a t pH 8 5-------------------------------------------

Run 2 a t pH 7.0-------------------------------------------

Run 3 a t pH 5 5-------------------------------------------

Run 4 a t pH lo- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Run 5 a t pH 8 5-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

R e s u l t s f o r S p e c i f i c Resis tance Tests i n Run 6 ----------- D e s c r i p t i o n o f Aluminum-Finishing P l a n t Used i n E v a l u a t i o n o f Impact o f Segregated N e u t r a l i z a t i o n on Thickened Sludge Volume ...............................

33

34

35

38

40

40

49

51

53

57

62

68

74

77

79

x i i

TABLES (Cont’d)

Number

7.13

7.14

7.15

7.16

8.1

8.2

8.3

9.1

9.2

9.3

9.4

9 .5

9.6

Comparison of the Use of Conventional and Segregated Neut ra l iza t ion a t a Typical A l u m i n u m Ext rus ion/

Impact o f Segregated Neutral izat ion o f Spent Process Solut ions on Sludge Dewatering Characterist ics------------

Impact of a Segregated Neutral izat ion of Spent Process Wastes a t Plant A3 on Required Vacuum F i l t e r Area and Mass o f Wet Sludge f o r Disposal ----------------- Physical Charac te r i s t ics o f Selected A l u m i n u m

Charac t e r i s t i c s of Spent Etch blaste From Plant A3 a s Used i n Experimental Invest igat ion ----------------- Speci f ic Resistance of Lime-Treated Spent Etch

Sludge Quant i t ies a t Plant A1 W i t h a n d Without Etch Recovery Using Lime A d d i t i o n ........................ Charac te r i s t i c s of Sol ids Extracted by Direct

Anodize Plant---------------------------------------------

p r e c i p i t a t e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sludges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Acidi f ica t ion w i t h Sul fur ic Acid __--_-_____-_______-_____ Chemical Additives i n A l u m Extractions ------------------- Composition o f Extracted L i q u i d Alum Products ------------ Trace Metal Composition o f Liquid Alum ------------------- Description of Equipment Required f o r an A l u m Reclamation F a c i l i t y ..................................... Equipment Costs f o r an Alum Reclamation F a c i l i t y ---------

79

93

94

96

1.01

108

11.5

122

124

127

127

132

132

x i i i

SECTION 1

INTRODUCTION

Treatment and d i soosa l o wastewaters and 5 idaes pro1 ced a s a r e s u l t o f c lean ing , m i l l i n g , e t ch ing , anod iz ing and p a i n t i n g aluminum a r e major problems i n t h e a lum inum- f i n i sh ing i n d u s t r y due t o the l a r g e q u a n t i t i e s and g e l a t i n o u s p r o p e r t i e s o f s ludge s o l i d s produced. A t many aluminum f i n i s h i n g p l a n t s , t h e mass o f w e t s ludge s o l i d waste approaches the mass o f f i n i s h e d aluminum products, r e p r e s e n t i n g a major s o l i d s d i s p o s a l problem. examinat ion o f t h e c h a r a c t e r i s t i c s o f a lum inum- f i n i sh ing wastes produced i n anod iz ing , e t c h i n g and p a i n t i n g processes as w e l l as t h e processes c o n v e n t i o n a l l y u t i l i z e d i n t rea tmen t o f these wastes. t o be u t i l i z e d i n improv ing conven t iona l t rea tment p r a c t i c e s t o min imize s ludge volume and t rea tmen t and d i sposa l cos ts . The r e s u l t s o f t he i n i t i a l n o r t i o n of t h e i n v e s t i g a t i o n o f wastewater t rea tmen t p r a c t i c e s were presented i n a r e p o r t en- t i t l e d " C h a r a c t e r i z a t i o n , Reclamation and F i n a l D isposa l o f Aluminum Bear ing Sludges" by Saunders Th is document served as an i n i t i a l r e p o r t on t h e ove ra l l p r o j e c t focused on t r e a t - ment and d i s p o s a l o f a lum inum- f i n i sh ing wastes and i s t o be u t i l i z e d as a ma jor re fe rence source he re in .

Prev ious research was focused on

I n v e s t i g a t i o n s were conducted on techniques

(1982) and submi t ted t o The Aluminum A s s o c i a t i o n I n c .

I n t h i s second phase o f t h e o v e r a l l p r o j e c t , research was focused on examina- t i o n o f i n n o v a t i v e t rea tmen t processes w i t h p o t e n t i a l f o r a c h i e v i n g major reduc t i ons i n s ludge q u a n t i t i e s o r rec lamat ion o f wastewater o r waste meta l . The i n i t i a l focus was p laced on an i n -dep th a n a l y s i s o f waste sources and q u a n t i t i e s assoc ia ted w i t h aluminum e t c h i n g and anod iz ing processes u s i n q a comprehensive i n d u s t r i a l survey. From t h i s survey and f rom examinat ion o f p rev ious exper imenta l i n v e s t i q a t i o n s (Saunders e t c., 1982), t h r e e i n n o v a t i v e processes were i d e n t i f i e d f o r f u r t h e r study.

a t a lum inum- f i n i sh ing p l a n t s . i n v e s t i g a t e d f o r t rea tmen t o f concent ra ted wastes a t e leva ted temperatures t o i m - prove sludge h a n d l i n g p r o p e r t i e s and reduce sludge volume. recovery system was a l s o i n v e s t i g a t e d f o r use i n t r e a t i n g waste aluminum con ta ined i n c a u s t i c e t c h i n g s o l u t i o n s . o f aluminum and rec lamat ion o f c a u s t i c f o r use i n f i n i s h i n g aluminum. T o t a l r e - c lamat ion o f waste aluminum i n a luminum- f i n i sh ing sludges was i n v e s t i g a t e d u s i n g d i r e c t a c i d i f i c a t i o n o f sludges w i t h s u l f u r i c a c i d . of aluminum s u l f a t e s o l u t i o n s f rom dewatered sludges was es tab l i shed .

r e p o r t o f Saunders e t a l . (1982) was used as a source document f o r t h i s s tudy and should be consul t e d f o F b a c k g r o u n d i n f o r m a t i o n .

Spent f i n i s h i n g s o l u t i o n s c o n t a i n a major p o r t i o n o f t h e waste aluminum t r e a t e d Acco rd ing l y , a segregated n e u t r a l i z a t i o n process was

An i n n o v a t i v e e t c h

Lime a d d i t i o n t o spent e t c h was examined f o r removal

The f e a s i b i l i t y o f p r o d u c t i o n

The r e s u l t s o f these i n v e s t i g a t i o n s a re presented h e r e i n . The i n i t i a l p r o j e c t

Sponsors o f t he research presented

2

herein included the Indus t r ia l Environmental Research Laboratory o f the U. S. Environmental Protect ion Agency and the A l u m i n u m Extruders Council. The Aluminum Association Inc. , i n addi t ion , was a p a r t i c i p a n t i n the overal l Pro jec t as presented i n the report by Saunders e t _. - a l . (1982) and i n th i s repor t .

SECTION 2

CONCLUSIONS

The r e s u l t s o f t he research on innovative treatment processes ind ica t e tha t they have exce l len t potent ia l for achieving major reductions i n quant i - t i e s o f sludge f o r disposal and recovery of spent c a u s t i c e tching so lu t ions as well as economical reclamation of a l l waste aluminum as a commercially marketable product.

f i c a t i o n for pursuit of the th ree innovative processes inves t iga ted . the survey i t was concluded t h a t :

The r e s u l t s o f an i n i t i a l i ndus t r i a l plant survey provided t h e j u s t i - From

1 . The majori ty o f waste metal from an anodiLe l ine was aluminum removed from a l l o y sur faces d u r i n g etching and anodizing w i t h f in i sh ing-so lu t ion addi t ives providing minor metal loadings. Waste metal q u a n t i t i e s i n paint-1 ine wastes were s i g n i f i c a n t l y lower than those i n anodize l i n e s and were equal ly a t t r i b u t a b l e t o aluminum removed from a l l o y surfaces and chromium discharged from f in i sh ing so lu t ions .

2 . In anodize l i n e s , r insewaters contributed the bulk o f t he wastewater discharged while spent caus t i c e tch , spent anodize acids and dragout from etching tanks were the sources o f more than 90 percent of waste aluminum.

l a t e r use based on sur face area o f f in i shed metal was 73.4m3/1000m2 a n d 4.2 m3/lOOOm2 on t h e anodize and pa in t l i n e s , respec t ive ly . Water use ranged from 27.8 m3/ton t o 2.5 m3/ton, based on mass of f in i shed aluminum, f o r anodize and paint 1 ines , respec t ive ly .

Dragin r a t e s on an anodize l i n e ranged from 0.092 t o 2.87 m 3 / d w i t h c a u s t i c e tch , desmut, anodize and c leaner so lu t ions having r a t e s o f from 1 to 2.87 m3/d.

W i t h respec t t o f in i shed aluminum q u a n t i t i e s , waste aluminum was discharged a t r a t e s o f 77.7 kg/1000m2 and 29.5 kg/ton on the anodize l i n e and was discharged on t h e pa in t l i n e a t r a t e s of 0.21 kg/1000m2 and 0.10 kg/ton.

6. The t o t a l mass quant i ty of chromium, cadmium and nickel discharged from an anodize l i n e was l e s s than 0.15 percent o f t he mass quant i ty o f waste aluminum. The to t a l metal , as the sum o f aluminum, chromium,

3 .

4.

5.

3

4

cadmium and n i c k e l , d i scha rged from a p a i n t l i n e was equal t o less than 0.5 pe rcen t o f t h e mass q u a n t i t y o f waste aluminum discharged from an anodize l i n e .

Recovery o f spent c a u s t i c e t c h by p r e c i p i t a t i o n o f aluminum w i t h l i m e was i n v e s t i g a t e d . From r e s u l t s o f t hese s t u d i e s , i t was concluded t h a t :

1.

2.

3.

4.

5.

Removal o f aluminum f rom c a u s t i c e t c h s o l u t i o n s was achieved b y p r e c i p i t a t i o n o f ca l c ium a lumina te u s i n g l i m e a d d i t i o n a t r e a c t i o n temperatures o f 25 t o 60°C.

React ion k i n e t i c s were a f f e c t e d by r e a c t i o n temperature, r e a c t i o n t i m e and ca l c ium t o aluminum r a t i o . For a r e a c t i o n t i m e o f s i x hours,a m o l a r ca l c ium t o aluminum dose o f 2.75 a t 6OoC and 3.7 a t 25°C was r e q u i r e d .

Sludge s o l i d s produced a t c a l c i u m t o aluminum molar r a t i o s o f 1.5 t o 3 and temperatures o f 25 t o 6OoC had e x c e l l e n t dewater ing c h a r a c t e r i s t i c s as i n d i c a t e d by s p e c i f i c r e s i s t a n c e va lues o f 4.0 t o 9.6 x 1Olo m/kg.

Dewatered s ludge s o l i d s f o l l o w i n g aluminum p r e c i p i t a t i o n a t molar ca l c ium t o aluminum r a t i o s o f 1.0 t o 3.0 and temperatures o f 25 t o 60°C ranged from 48 t o 53 pe rcen t s o l i d s .

A n a l y s i s o f the impac t o f implementat ion o f e t c h r e c o v e r y w i t h l i m e a d d i t i o n a t a f u l l - s c a l e a n o d i z i n g p l a n t i n d i c a t e d a 25 p e r c e n t r e d u c t i o n i n wet s ludge mass was achieved as w e l l as a p o t e n t i a l chemical s a v i n g of $500/day through recove ry o f spent e t c h i n g s o l u t i o n .

Segregated n e u t r a l i z a t i o n o f concen t ra ted f i n i s h i n g s o l u t i o n s was i n v e s t i g a t e d as a means o f r e d u c i n g t h e volume o f s ludge s o l i d s produced. It was concluded t h a t :

1. Segregated n e u t r a l i z a t i o n o f concentrated spent e t c h and a c i d s o l u t i o n s c o u l d be achieved a t temperatures o f 65 t o 90°C i n a p e r i o d o f 9 t o 10 minutes.

Th icken ing p r o p e r t i e s o f s ludges produced were n o t a f f e c t e d by tempera tu reo f n e u t r a l i z a t i o n o r by 24 hours o f ag ing a t ambient temperature.

T h i c k e n i n g p r o p e r t i e s were improved s i g n i f i c a n t l y by a l k a l i n e n e u t r a l i z a t i o n (e.g., pH = 8.5) o v e r n e u t r a l o r a c i d i c n e u t r a l i - z a t i o n (e.g., pH = 7.0 and pH = 5.5).

2 .

3.

4. Batch f l u x a n a l y s i s i n d i c a t e d t h a t t h i ckened s ludge concen t ra t i ons o f 4 t o 5 pe rcen t s o l i d s c o u l d be r o u t i n e i y achieved i n sedimenta- t i o n bas ins c o n v e n t i o n a l l y u s e d i n t h e i n d u s t r y as compared t o c o n v e n t i o n a l - n e u t r a l i z a t i o n s ludge c o n c e n t r a t i o n s o f 1 t o 2 percen t .

5

5.

6.

7.

8 .

f iewater ing p r o p e r t i e s o f s ludges produced by segregated n e u t r a l i z a t i o n were improved by use o f a l k a l i n e pH values o f 8.5 and 10.0 as con f i rmed by s p e c i f i c resistance,CST and f i l t e r - l e a f y i e l d measurements. Cake s o l i d s c o n c e n t r a t i o n s f rom 35 t o 54 pe rcen t s o l i d s were achieved a t a l k a l i n e pH va lues i n d i c a t i n g a ma jo r r e d u c t i o n i n f i n a l s ludge volume.

Sludge c o m p r e s s i b i l i t y c o e f f i c i e n t s , S , were t y p i c a l l y below 0.5 and were i n d i c a t i v e o f h i g h l y i n c o f i p r e s s i b l e s ludge s o l i d s which was conf i rmed by improved f i l t e r y i e l d s w i t h i n c r e a s i n g a p p l i e d vacuum.

E v a l u a t i o n o f implementat ion o f segregated n e u t r a l i z a t i o n t o t r e a t spent f i n i s h i n g s o l u t i o n s a t p l a n t A3 i n d i c a t e d t h a t p r e d i c t e d r e d u c t i o n s i n wet s ludge mass ranged from 73 t o 80 p e r c e n t r e s u l t i n g i n a m a j o r r e d u c t i o n i n s ludge d i s p o s a l c o s t s .

Segregated n e u t r a l i z a t o n o f concen t ra ted e t c h and anodize wastes a t a l k a l i n e pH and e l e v a t e d temperatures r e s u l t e d i n f o r m a t i o n o f a c r y s t a l i i n e - l i k e s ludge c o n s i s t e n t w i t h f o r m a t i o n o f , f o r example, pseudoboehmite, g i b b s i t e and b a y e r i t e forms as opposed t o amorphous n o n - c r y s t a l l i n e aluminum hydrox ide.

D i r e c t a c i d i f i c a t i o n o f dewatered a lum inum- f i n i sh ing sludges f o r reclama- t i on o f waste aluminum as aluminum s u l f a t e s o l u t i o n s was i n v e s t i g a t e d . t h i s research i t was concluded t h a t :

From

1 .

2.

3 .

5.

Anodize s ludge s o l i d s produced w i t h conven t iona l and segregated n e u t r a l i z a t i o n and a lum inum- t r i hyd ra te s ludges produced from e tch - recove ry systems r e a c t e d r a p i d l y w i t h s u l f u r i c a c i d t o form s o l u t i o n s o f aluminum s u l f a t e which meet q u a l i t y c r i t e r i a f o r commercial -grade products .

A s ludge s o l i d s c o n t e n t o f 21 pe rcen t o r h i g h e r i s r e q u i r e d t o produce a commerc ia l -s t rength aluminum s u l f a t e s o l u t i o n w i t h a minimum aluminum c o n c e n t r a t i o n o f 8.3 pe rcen t as A1203.

Aluminum t r i h y d r a t e s ludge produced w i t h e tch - recove ry systems i s b e s t e x t r a c t e d a t a c i d c o n c e n t r a t i o n s above s t o i c h i o m e t r i c requi rements t o achieve commercial s t r e n g t h . These s ludge s o l i d s appear t o be an e x c e l l e n t feedstock f o r p r o d u c t i o n o f i r o n - f r e e l i q u i d alum.

D i r e c t a c i d i f i c a t i o n o f aluminum f i n i s h i n g sludges r e s u l t s i n s o l u b i l i z a t i o n o f v i r t u a l l y a l l s’udge sol i d s t h e r e b y . e l i m i n a t i n g s ludge d i sposa l requi rements f o r a l l b u t a m i n o r r e s i d u e f o l l o w i n g alum p roduc t i on .

Reclamat ion o f a lum inum- f i n i sh ing s ludge as an aluminum s u l f a t e s o l u t i o n i s an economical a l t e r n a t i v e t o s ludge d i sposa l w i t h an e s t i m a t e d pay-back p e r i o d o f 14 t o 21 months.

SECTION 3

RECOMMENDATIONS

The exp r i n n t a l r e s u l t t r o n g ba t h e i n d

Recommendations-reaardinq t h e i n d i v i d u a l processes a r e presented t:

presented h e r e i n p r o v i d e a f u r t h e r i nves t i qa t i o n o f i n n o v a t i v e t reatmen t processes i

e f o r s t ry . 1 ow

fo l lowed by those r e g a r d i n g i n t e g r a t i o n o f i n n o v a t i v e and conven t iona l systems .

Segregated n e u t r a l i z a t i o n should be examined i n l abo ra to ry -and p i l o t -

A combrehensive i n v e s t i g a t i o n s c a l e systems t o de te rm ine t h e op t ima l pH and temperature va lues f o r t r e a t - i n g concentrated e t c h and a n o d i z i n g wastes. should be made u s i n g a broad range o f pH va lues. Emphasis shou ld be p l a c e d e v a l u a t i n g e f f e c t s on t h i c k e n i n g and dewater ing p r o p e r t i e s as w e l l as examina- t i o n o f t h e f a t e o f waste me ta l s i n c l a r i f i e d e f f l uen ts and dewatered f i l t r a t e . E levated pH values would improve removal o f heavy meta l contaminants b u t decrease removal o f aluminum. Sludges produced by segregated n e u t r a l i z a t i o n can be t r e a t e d s e p a r a t e l y b u t would r e q u i r e redundant systems o r mu l t i - phase o p e r a t i o n o f e x i s t i n g systems. Therefore, t h e e f f e c t s o f m i x i n g segregated- n e u t r a l i z a t i o n suspensions w i t h o t h e r conven t iona l wastes should be examined. These n e u t r a l i z e d wastes cou ld , f o r example, be mixed w i t h r i n s e w a t e r s i n a conven t iona l n e u t r a l i z a t i o n system, c l a r i f i e r i n f l u e n t o r t h i c k e n e d s ludge . The impact o f making these m i x t u r e s should be i n v e s t i g a t e d .

Lime a d d i t i o n f o r r e c o v e r y o f spent e t c h proved t o be a successfu l means o f r e d u c i n g s ludge volume and r e c o v e r i n g spent e t c h f o r reuse i n f i n i s h i n g aluminum. The r e s u l t s r e g a r d i n g r e a c t i o n t ime, temperature, and l i m e dose, however, a r e n o t s u f f i c i e n t t o de te rm ine t h e op t ima l c o n d i t i o n s f o r i n s t a l l a - t i o n o f such a system. A comprehensive p i l o t - s c a l e s t u d y should be pursued i n t h i s rega rd . I n a d d i t i o n , d i s p o s a l o f ca l c ium-a lumina te s ludge s o l i d s which a r e s a t u r a t e d w i t h a c a u s t i c soda s o l u t i o n w i l l be d i f f i c u l t and c o s t l y . Research shou ld be conducted t o determine i f these s o l i d s can be washed p r i o r t o d i s p o s a l t o remove r e s i d u a l e t c h i n g s o l u t i o n . E v a l u a t i o n o f a batch- ope ra ted p e r f o r a t e - b a s k e t c e n t r i f u g e , s i m i l a r t o t h a t employed i n t h e Fugi Sash e t c h r e c o v e r y system (Brown, 1982), should be considered t o e l i m i n a t e t h e hazardous p r o p e r t i e s o f t h e s ludge due t o t h e presence o f c a u s t i c soda.

t o e s t a b l i s h t h e minimum s o l i d s c o n t e n t r e q u i r e d t o achieve commercial-grade s tandards. I n a d d i t i o n , a d d i t i o n a l a lum inum- f i n i sh ing sludges should be examined t o assure t h e widespread a p p l i c a b i l i t y o f t h e process. s i v e me ta l a n a l y s i s should be i n c l u d e d i n t h i s program t o assu re t h e q u a l i t y

Research on r e c o v e r y o f a lum inum- f i n i sh ing sludges should be conducted

A comprehen-

6

7

o f t h e alum produced has maximum u t i l i t y .

A luminum-t r ihydrate s ludges appear t o have e x c e l l e n t p o t e n t i a l f o r p ro - d u c t i o n o f i r o n - f r e e alum. F u r t h e r i n v e s t i g a t i o n should be pursued t o assure t h a t t h i s p roduc t can be c o n s i s t e n t l y used t o meet requi rements fo r t h i s h i g h - q u a l i t y feedstock.

W i th r e g a r d t o i n t e g r a t i o n o f i n n o v a t i v e and conven t iona l t r e a t m e n t systems, i t i s recommended t h a t a comprehensive p i l o t - s c a l e system be developed t o i n v e s t i g a t e t h e concur ren t use o f e t c h r e c o v e r y w i t h l i m e a d d i t i o n o r a lum inum- t r i hyd ra te fo rma t ion , segregated n e u t r a l i z a t i o n o f concen t ra ted f i n i s h i n g wastes and d i r e c t a c i d i f i c a t i o n o f s ludges t o produce l i q u i d alum w i t h conven t iona l n e u t r a l i z a t i o n and s ludge t rea tmen t processes. The p r i m a r y o b j e c t i v e f o r such a system would be t o e s t a b l i s h t h o s e process combinat ions which would p r o v i d e f o r maximum r e d u c t i o n i n s ludge volume and those com- b i n a t i o n s which r e s u l t i n maximum economical r e c o v e r y o f waste meta l and waste f i n i s h i n g s o l u t i o n s .

SECTION 4

BACKGROUND

The research reported herein i s the second phase of a pro jec t j o i n t l y funded by The Aluminum Association Inc. , the Aluminum Extruders Council and the Indus t r ia l Environmental Research Laboratory of the U . S. Environmental Protection Agency. The r e s u l t s o f the i n i t i a l phase were reported e a r l i e r (Saunders _ _ e t a l . , 1982). review of previous research re la ted t o treatment and disposal o f aluminum- f in i sh inq wastes and wil l no t be reoeated here. In a d d i t i o n , l i t e r a t u r e n o t c i t ed in the e a r l i e r report b u t of importance t o the nrocess research reoorted herein i s oresented in the i n i t i a l oortions of the aporopriate sec t ions .

The e a r l i e r report included r e s u l t s of a n indus t r ia l plant wastewater survey conducted a t a oar t ic ipa t inq plant s i t e and the r e s u l t s of an extensive paper-survey conducted by The Aluminum Association, Inc. Research conducted on thickening, dewatering, conditioning,gravit.v drainaqe and leaching of conven- t iona l wastewaters from f i v e aluminum-finishing plants a r e reported in the e a r l i e r report . formation presented herein s ince they provided the f o u n d a t i o n from which manv of the reported s tudies were formulated, The reader i s therefore referred t o the report by Saunders -- e t a l . (1982) f o r de ta i led background information.

The i n i t i a l repor t included an extensive l i t e r a t u r e

These r e s u l t s a r e extremely important w i t h resDect t o the i n -

8

SECTION 5

EXPERIMENTAL METHODS AND PROCEDURE5

I n conduc t ing i n v e s t i g a t i o n s o f t rea tmen t processes f o r use i n t h e a lum inum- f i n i sh ing i n d u s t r y , i t was i m p e r a t i v e t h a t wastewaters, s ludges and f i n i s h i n g s o l u t i o n s be r e p r e s e n t a t i v e o f t hose encountered i n p r a c t i c e . assure t h i s , waste samples used i n t h e s t u d i e s r e p o r t e d h e r e i n were o b t a i n e d f rom a luminum- f i n i sh ing p l a n t s t h a t had p a r t i c i p a t e d i n t h e i n i t i a l p o r t i o n o f t h i s s tudy and as desc r ibed i n d e t a i l by Saunders -- e t a l . (1982).

To

PARTICIPATING ALUMINUM-FINISHING PLANTS

The r e p o r t e d research was focused on p l a n t s u s i n g anod iz ing , etchin'g and p a i n t i n g processes t o f i n i s h ex t ruded aluminum. i n t h e research on i n n o v a t i v e t rea tmen t processes r e p o r t e d h e r e i n . o f these p l a n t s a r e presented i n Table 5.1. and p a i n t i n g l i n e s , i n each o f which approx ima te l y 400 t o n s o f aluminum were f i n i s h e d monthly. T h i s p l a n t served as t h e s i t e o f an i n t e n s i v e i n d u s t r i a l waste survey so t h a t r e l a t i v e q u a n t i t i e s o f wastes generated i n a n o d i z i n g and p a i n t i n g l i n e s c o u l d be e s t a b l i s h e d .

P l a n t A2 had an anodize l i n e w i t h a c a p a c i t y s i m i l a r t o t h a t o f p l a n t A1 b u t d i d n o t have a p a i n t l i n e . Waste s ludge suspensions c o l l e c t e d f rom t h i s p l a n t were examined w i t h respec t t o r e c l a m a t i o n o f waste aluminum as an aluminum s u l f a t e s o l u t i o n . P l a n t A3 had conven t iona l and i n t e g r a l - c o l o r a n o d i z i n g l i n e s w i t h a month ly c a p a c i t y o f 680 tons o f f i n i s h e d aluminum. Waste s ludge suspensions and spent e t c h and a n o d i z i n g wastes were c o l l e c t e d f rom t h i s f a c i l i t y f o r use i n i n v e s t i g a t i n g i n n o v a t i v e t rea tmen t processes.

D e t a i l e d i n f o r m a t i o n r e g a r d i n g wastewater q u a n t i t i e s and compos i t i on and t h i c k e n i n g , dewater ing and g r a v i t y - d r a i n a g e p r o p e r t i e s o f wastewater suspensions from these p l a n t s a re presented i n an e a r l i e r r e p o r t (Saunders _ - e t a l . , 1982). I n fo rma t ion on t r a c e meta l and p r i o r i t y - p o l l u t a n t me ta l s and E P - t o x i c i t y d a t a a r e a l s o i n c l u d e d i n t h e e a r l i e r r e p o r t .

ANALYTICAL PROCEDURES

Three p l a n t s were employed D e s c r i p t i o n s

P l a n t A1 had separate a n o d i z i n g

Numerous a n a l y t i c a l procedures were performed i n conduc t ing t h e research . Chemical c h a r a c t e r i z a t i o n was focused on measurement o f c o n c e n t r a t i o n s o f numerous meta ls w h i l e p h y s i c a l c h a r a c t e r i z a t i o n i n c l u d e d measurements o f s ludge t h i c k e n i n g and dewater ing p r o p e r t i e s . used throughout t h e s t u d y a r e presented below w h i l e o t h e r procedures s p e c i f i c t o a p a r t i c u l a r s p e c i f i c process a r e presented i n l a t e r sec t i ons .

Numerous procedures commonly

9

Tab1 e 5.1 Description of Participating A1 umi num-Fi ni shi ng P1 ants

Sludge Production Rate,

Dry Basis __ Plant Finishing Lines ' Wastewater and Sludge kg/mo

Desiqnation and Production Rates Treatment Systems Wet Basis

6.8~1 O4 3.4~1 O5 5 A1 Paint Line: 3.6-4.5~10 kg/mo. Paint Line: Two-stage chrome reduction followed by lime neutralization

(20% solids)

Anodize Line (clear-coat Anodize Line: Wastewater mixed and integral-color with lime-neutralized paint- anodize with bright dip and line wastewater; 3-stage pH gold d eing lines): 4.0 - neutralization, sedimentation, 4.5~10 t: kg/mo. series of lagoons and stream

-discharge; sludge: stored in 1 agoons.

Total anodize/paint- iqe waste-

mgd). (Anodize-flow to paint-line water flow = 1.5~10- 4 m-/s (0.35

flow = 7.3)

A2 Anodize Line (clear-coat pH neutralization; polyelectrolyte 1 .8x105 3.6~10~ anodize w/brig t dip and dye flocculation; sedimentation with

effluent discharge to surface stream and sludge dewatered on a vacuum filter and landfilled.

(20% solids) lines): 3 x10 kl kg/mo.or 1.24~10 5 m 4 /mo.

A3 Anodize Line (including 3-stage pH neutralization; 1.45~1 O6 1 .7x1 O5 integral-color and clear- coat anodize): 6.8x105kg/mo.

pol ye1 ectrolyte. flocculation; sedimentation with effluent discharge to stream; sludge dewatering on 2 filter presses and cake disposal to land on plant site.

1 1

Chemical Analyses

sol ids were conducted in accordance with Standard Methods (1980). were prepared for metal analyses by digestion with ultrapure nitric acid (EPA, 1979). Aluminum, calcium, potassium, magnesium, nickel, and iron were determined using a Perkin-Elmer Model 303 atomic absorption spectrophotometer. Lanthanum was added to all calcium solutions at 1 percent to prevent anionic interferences. Standard calibration curves were prepared for use in establishing metal concentrations. Perkin-Elmer Model 703 atomic spectrophotometer. A graphite-furnace accessory was used in conjunction with the method of standard addition as presented in detail by Saunders _ - et a1 . (1982). Physical Analyses

Thickening measurements were conducted in 1-1 itre graduated cy1 inders at suspension heights of 0.4 m. A stirrer located at the wall of the cylinder was rotated at a tip velocity of 0.31 cm/s to minimize wall effects. Tests were initiated by pouring a suspension into a cylinder and mixing the suspension by inverting the cylinder several times. The stirring apparatus was placed in the column and started and interface height was recorded with time.

Measurements o f pH, alkalinity, acidity, and total, suspended and dissolved Waste samples

Measurements of chromium and cadmium were made using a

Dewatering properties of suspensions were established with measurements of capillary suction time (CST), specific resistance and filter-leaf yield. CST is the time required for the liquid portion of a sludge sample to travel 1 cm between two concentric circles on a filter paper by capillary action (Baskerville and Gale, 1968). A type 92/1 CST Apparatus (Triton Electronics Limited) and two hollow, cylindrical, metal reservoirs o f 10 mm and 18 mm in diameter were used. chromatography-grade paper.

by O'Connor (1975). under a vacuum of 38 cm Hg (50 kPa) using No. 1 Whatman filter paper placed in a 9-cm diameter Buchner funnel with an effective filtering diameter of 7.5 cm. The volume of filtered liquid was recorded with time and the test was terminated when a crack in the sludge surface caused a sudden drop in vacuum. measurements are used to obtain design and performance data for vacuum filters and were utilized to measure filter yields. equipped with NY-319F 3/1 Br Twill multifilament cloth and a filtration area of 92 cm2, was operated under a vacuum of 6.6'~ lo4 N/mZ(20 in. of Hg) with a drying time o f one minute and a form time of two minutes. formed in accordance with the method described by O'Connor (1975).

The CST filter paper (7 cm x 9 cm) was Whatman 17

Specific resistance was measured using the Buchner funnel procedure presented For a typical test, a 300 ml volume of sludge was filtered

Filter-leaf

An Eimco filter-leaf apparatus,

The test was per-

SECTION 6

SOURCES OF WASTEWATER CONSTITUENTS

Development and inves t iga t ion of innovative approaches t o reduction or reclamation o f aluminum f i n i s h i n g wastewaters and sludges required a detailed examination of the sources of the major wastewater cons t i tuents . Since the research program was focused on wastewaters produced i n conjunction w i t h e tch ing , anodizing and p a i n t i n g aluminum, p lan t A1 was se l ec t ed f o r de t a i l ed examination.

PLANT DESCRIPTION

P l a n t A1 had segregated p a i n t and anodize l i nes w i t h production capac i t ies of 3.6-4.5~105 kg/mo and 4.0-4.5~105 kg/mo, respec t ive ly , a s ind ica ted i n Table 5.1. The p a i n t l ine was an automated process used t o pa in t aluminum strips. Pre-painting process steps included: ( i ) spray wash w i t h an a lka l ine cleaner; ( i i ) spray rinse; ( i i i ) conversion-coat formation using a dichromate- fluoride-phosphate process; ( i v ) spray r i n s e and ( v ) a c i d u l a t i n g r in se as presented i n Table 6.1. The a lka l ine cleaner and conversion-coat so lu t ions were not discharged t o waste. was ca r r i ed i n t o the spray r in ses w h i c h continuously overflowed t o a wastewater treatment sys tem.

Dragout from these f i n i s h i n g so lu t ions however

Table 6.1. Paint Line Process a t Plant A1

Tank Number PL-1

PL-2

PL-3

PL-4

PL-5

Finishing Step Spray Wash

Rinse

Conversion Coat Formation

Rinse

Acidulating Rinse ~~

~

Des cri p t i on Alkaline c leaner , dumped t o waste twice a year

Tap water rinse w i t h continuous overflow t o waste

Solution of Aladine 47 (5.5g/1) and Aladine 407

Tap water r in se w i t h continuous overflow t o waste

Dilute chromic acid (0 .4g/ l ) ; Discharged t o waste on a weekly basis.

( 5 8 . W )

13

The anodize l i n e was a semi-batch system i n which racked aluminum ex t rus ions were plac,ed i n a s e r i e s o f f i n i s h i n g s o l u t i o n s and r i n s e s .

. f i n i s h i n g s teps i n c l u d e d ( i ) a l k a l i n e de tergent c leaner ; ( i i ) a c i d d e t e r g e n t c leaner ; ( i i i ) c o l d c a u s t i c e tch ; ( i v ) h o t c a u s t i c e t ch ; ( v ) desmut; ( v i ) b r i g h t d i p ; ( v i i ) i n t e g r a l - c o l o r anodize (Duranodic) ; ( v i i i ) convent iona l s u l f u r i c - a c i d anodize; and ( i x ) g o l d dye as descr ibed i n Table 6.2. s tep was f o l l o w e d by a s i n g l e o r double c o u n t e r - c u r r e n t r i n s e which was d i s - charged c o n t i n u o u s l y t o waste, except f o r t he b r i g h t - d i p r i n s e w a t e r s which were rec la imed and so ld .

The

Each f i n i s h i n g

The i n t e g r a l - c o l o r anodize s o l u t i o n was c o n t i n u o u s l y c i r c u l a t e d through a c a t i o n exchanger a t 3.7 l / m i n t o c o n t r o l t he accumulat ion o f aluminum.. The c a t i o n exchange r e s i n was regenerated us ing 18 percent s u l f u r i c a c i d when aluminum l e v e l s exceeded approx imate ly 1 g /1 i n the anodize tank. Concentra- t e d regenerant waste .was d ischarged t o a s to rage tank from which i t was d i s - charged a t a slow r a t e t o the waste t rea tment system. d ischarge of a c i d i c regenerant wastes, p l a n t personnel p laced siphons i n t h e c a u s t i c e t c h tanks (AL-5, A L - 7 ) and c a u s t i c e t ch was d ischarged t o the waste t r e a t m e n t system t o , i n p a r t , n e u t r a l i z e t h e a c i d i c regenerant p r i o r t o d i s c h a r g e t o the waste t rea tment system.

t o p r e t r e a t p a i n t l i n e wastelrlaters p r i o r t o combinat ion w i t h anodize l i n e wastewaters and (ii) a system c o n s i s t i n g o f n e u t r a l i z a t i o n , polymer c o n d i t i o n - ’ i n g and sed imenta t ion used t o t r e a t combined anodize-and p a i n t - l i n e wastewaters. These two systems a re descr ibed i n Table 6.3.

anodize wastewaters cons is ted o f r i nsewa te rs , chemical s p i l l s , b r i g h t - d i p s t r i p p i n g - t o w e r blowdown, a c i d i c ion-exchange regenerant and spent c a u s t i c e tch. Fo l l ow ing chrome r e d u c t i o n o f p a i n t - l i n e wastewater, a l l wastewaters were com- b ined i n a f o u r - s t a g e n e u t r a l i z a t i o n system t o p r e c i p i t a t e aluminum as an aluminum hydrox ide. 5 t o 12 p e r c e n t o f t h e t o t a l wastewater f l o w w i t h anodize wastewater c o n t r i b u t i n g t h e remainder.

t he wastewater by g r a v i t y sed imenta t ion and disposed o f i n s ludge lagoons. C l a r i f i e d e f f l u e n t was d ischarged t o two ponds i n s e r i e s w i t h f i n a l d ischarge t o a stream.

SURVEY TECHNIQUES

q u a n t i t i e s o f Al, Cd, C r and N i d ischarged from each process ing l i n e as w e l l as t he volume o f water d ischarged. i d e n t i f y t he q u a n t i t y of each contaminant d ischarged from each major zgurce.

channel and segregat ion o f these sources was n o t possib1.e. however, a l l r i n s e w a t e r over f lows were separated and cou ld be sampled.

Concurrent w i t h t h e

Wastewater t rea tment a t p l a n t A1 cons is ted o f ( i ) a chrome-reduct ion s y s t e m

P a i n t - l i n e wastewaters cons is ted o f two cont inuous r i n s e over f lows w h i l e

P a i n t - l i n e wastewater was i n d i c a t e d t o be approx imate ly

Fo l l ow ing n e u t r a l i z a t i o n , p r e c i p i t a t e d aluminum s o l i d s were separated from

The o b j e c t i v e o f t he survey o f t h e p l a n t was t o determine the sources and

The survey was, fu r thermore , designed t o

. .. . . ~.~ On t h e p a i n t l i n e , t h e two r i nsewa te r overf lows d ischarged t o a common

The On t h e anodize l i n e ,

14

Table 6.2. Description of Anodizing Process Line a t Plant A 1

F i n i s h i n g Process Tank Number Description Contents Comments

AL-1

AL-2

AL- 3

AL- 4

AL- 5

AL- 6

AL- 7

AL- 8

AL- 9

A1 ka l ine C1 eaner

Rinse

Acid Cleaner

Rinse . Cold Caustic Etch

Rinse

Hot Caust ic Etch

Rinse

Desmut

SC-61 @ 5 g / l ; T = 60 t o 66'C

Tap water rinse w i t h continuous overflow t o waste

H3P04 @ 58-65 g/1; Dowanol EB and T r i t o n DF 12 @ 35 g / l ; T = 60'C; Air a g i t a t i o n

Tap water r in se w i t h continuous overflow t o waste

NaOH @ 36 g/1, Sorbi tol @ 70 g/l ; Alt3 = 38-60 g / l ; T = 43°C; Air a g i t a t i o n

Tap water r i n s e w i t h continuous overflow t o waste

NaOH 0 90-98 g / l , Sorbi tol @ 70 g / l , Hailand ND-68E @

86.4-93.6 g / l ; Alf3 = 38-60 g / l ; T = 60°C; Air a g i t a t i o n

Tap water r i n s e w i t h continuous overflow t o waste

N i t r i c acid @ 20 g/1; T = Ambient; Air a g i t a t i o n

Rinse f o r Tank.AL-1

Rinse f o r Tank AL-3 -

Etch for in t eg ra l - co lo r anodize. Rinse step performed rap id ly t o e l iminate "run-down"; Approximately 3 m3/d i s siphoned o f f t o neu t r a l i ze acid from regeneration of i o n exchange resin used t o remove A1 from in tegra l -co lor anodize tank.

First rinse following h o t and cold etc'h.

+3

Etch for c lear -coa t anodize. Approximately 3 m3/d i s siphoned o f f t o neu t r a l i ze acid from r e enerat ion of r e s in t o remove

t a n k . A 1 9 3 from in tegra l -co lor anodize

Second r in se following hot and cold etch.

15

Table 6.2 (cont inued)

F i n i s h i n g Process Tank Number D e s c r i p t i o n Con t e n t s Comments

AL -1 0 Rinse

AL-11 B r i g h t D ip

AL-12 Rinse

AL-13 Rinse

AL-14 Storage/Rinse

AL-15 T r a n s f e r Rinse

AL- 16 Storage

AL- 17 I n t e g r a l - C o l o r Anodize

AL-18&20 C lea r Anodize

AL- 19 Rinse

Tap water r i n s e w i t h cont inuous o v e r f l o w t o waste

HNO, @ 3.2 g / l ,

Rinse f o r tank AL-9

Rapid t r a n s f e r (<30 sec) t o J

H3P04 t o achieve r i n s e t o min imize a i r - e t c h . Oragout i s h igh .

s p e c i f i c g r a v i t y ~ 1 . 7 2 ; T = 93OC; A i r a g i t a t i o n

Batch water r i n s e F i r s t r i n s e f o r b r i g h t d i p . Tank conten ts a r e rec la imed when s p e c i f i c g r a v i t y reaches 1.3-1.35 (35% H3P04). Tank conten ts a re rec la imed once every 10 days.

Second r i n s e f o r b r i g h t d i p . Tank conten ts a r e t r a n s f e r r e d t o tank AL-12 when dumped, and t a p water i s used t o f i l l tank AL-13.

Used f o r s torage.

Batch w a t e r r i n s e

Tap water r i n s e w i t h cont inuous o v e r f l o w t o waste

Tap water r i n s e w i t h cont inuous o v e r f l o w one s i d e o f l i n e t o o t h e r . t o waste

Tap water r i n s e w i t h Used f o r s to rage and as r i n s e cont inuous o v e r f l o w f o r i n t e g r a l - c o l o r anodize. t o waste

0-300 @ 65-85 g / l , H2S04 @ 5 g / l ; des i red . Tank conten ts a re

T = 10 t o 21OC

Used t o t r a n s f e r aluminum from

Tank conten ts vary w i t h shade

regenerated w i t h ion-exchange r e s i n t o m a i n t a i n A1 5 0.9-1.0 g/1.

T h i s a c i d i s used t o regenera te ion-exchange r e s i n .

F i r s t r i n s e f o r c l e a r anodize

H2S04 @ 200 g / l ; T = 2 1 O C

Tap water r i n s e w i t h cont inuous o v e r f l o w tanks AL-18&20. t o waste

16

Tab le 6 . 2 ( con t inued)

F i n i s h i n g Process Tank Number D e s c r i p t i o n Contents Comments

AL -21

AL-24*

AL-25&26

AL-27

AL-28

Rinse Tap wa te r r i n s e w i t h cont inuous o v e r f l o w t o waste.

Seal Rinse Deminera l ized water r i n s e

Seal Eloxan s a l t @ 5 ga l / t ank ;

pH @ 6.6 (pH ad jus ted w i t h NaOH and a c e t i c a c i d ) ; T = 99°C; No m i x i n g

o x a l a t e @ 14 /l; pH = 3.8-4.5 9 o x a l i c a c i d and aqua-ammonia added t o a d j u s t pH); T = 99°C

Dye lCoo l ing Tap water r i n s e w i t h r i n s e cont inuous o v e r f l o w

Dye F e r r i c ammonium

t o waste.

Second r i n s e f o r c l e a r anodize tanks AL-18&20.

..

Continuous r e c y c l e o f wa te r th rough demine ra l i ze r ; Flow z 2.3 m3/h.

Tank con ten ts dumped t o waste on weekends.

Tank con ten ts a r e dumped approx imate ly once i n 4-6 months. I n c r e a s i n g anodize t i m e increases dye uptake. Time i n tank i s determined by dye matching.

Used as r i n s e t o coo l aluminum a f t e r sea l tank and dye process.

*Tanks AL-22 and AL-23 were n o t i n use d u r i n g survey.

17

Table 6.3. Wastewater Treatment Systems a t P l a n t A2

Treatment Step D e s c r i p t i o n

P a i n t L i n e Wastewater

Chrome Reduct ion Two-stage system t o reduce hexavalent chrome t o t r i v a l e n t chrome; Stage 1: a d j u s t pH t o 2.2 and ORP t o 150-175 mw and

H,SO, and SO, a d d i t i o n t o

reduce hexavalent chromium t o t r i v a l e n t chromium. Stage 2: H o l d i n g tank f o r pumping system; Waste pumped t o s tage 1 o f n e u t r a l i - z a t i o n system and combined w i t h anodize wastewater.

Anodize L i n e and P a i n t L i n e Wastewaters

N e u t r a l i z a t i o n Mixed, f ou r -s tage system w i t h 4.7 m3/stage. Stage I : Wastewaters f rom p a i n t - l i n e

chrome-reduct ion system and anodize l i n e a r e combined. P o r t i o n o f s e t t l e d s ludge i s r e c y c l e d .

Stage 2-3: pH i s a d j u s t e d t o w i t h i n range o f 5-8 (Stage 2 ) and then t o pH = 6.2 (Stage 3 ) .

S ta e 4:

p i t a t e d aluminum.

- -

A d d i t i o n o f a n i o n i c p o l y e l e c - -5. t r o y t e and f l o c c u l a t i o n o f p r e c i -

Sedimentat ion Continuous- fl ow , s o l i ds-con tac t c l a r i f i e r w i t h d iameter = 15.3111 and depth = 3.7m; Average o v e r f l o w v e l o c i t y = 14.5 m/d (355 gpd/sq. f t . ) and h y d r a u l i c r e t e n t i o n t i m e = 3h ( i . e . , s ludge depth o f 1 .Em).

C l a r i f i e d e f f l u e n t i s d ischarged t o two ponds i n s e r i e s w i t h f i n a l d i scha rge t o a stream.

Under f low from c l a r i f i e r i s d ischarged t o one o f f o u r lagoons f o r ambient- a i r dewa te r in . T o t a l a v a i l a b l e pond

P o l i s h i n g Ponds

Sludge Lagoons

.. volume = 9x1 0 t m 3 .

-.

survey was conducted f o r a 24-h p e r i o d on a Wednesday s t a r t i n g w i t h the t h i r d s h i f t o f opera t ion . The p a i n t l i n e was operated f o r two s h i f t s . f o r a t o t a l o f 16 h w h i l e t h e anodize l i n e was operated c o n t i n u o u s l y d u r i n g t h e 24-h survey.

Sampling p o i n t s were i d e n t i f i e d i n c o n j u n c t i o n w i t h p l a n t personnel t o c o l l e c t samples o f a l l wastewaters d ischarged from t h e process l i n e s t o t h e wastewater t rea tment system. water t r e a t m e n t systems t o use t o c o n f i r m va lues o b t a i n e d w i t h samples c o l l e c t e d from w i t h i n t h e process l i n e s . 24-h p e r i o d and used t o make equal-volume composites f o r each sample l o c a t i o n . Sampl ing o f t h e cat ion-exchange system used t o remove aluminum f rom the i n t e g r a l - c o l o r anod iz ing system was conducted d u r i n g a r e g e n e r a t i o n c y c l e a t 1-5 min i n t e r v a l s and examined on an i n d i v i d u a l bas is . wastewater, as d ischarged t o a h o l d i n g - t a n k p r i o r t o d ischarge t o the wastewater t rea tment system, were c o l l e c t e d .

Sampling p o i n t s were a l s o l o c a t e d i n t h e waste-

Samples were c o l l e c t e d on an h o u r l y bas i s f o r a

A l s o samples o f a c i d regenerant

RESULTS

Wastewater Flow

Anodize L ine- -

s e t a t f i x e d va lues p r i o r t o t h e survey and u m l t e r e d throughout the 24-hour sampl ing p e r i o d where poss ib le . and ion-exchange wastewaters, were mon i to red d i r e c t l y d u r i n g pe r iods of f l o w .

Average f low ra tes f o r wastewater sources a re presented i n Table 6.4. waters c o n s t i t u t e d t h e m a j o r i t y (83 pe rcen t ) o f t he measured f l o w from the anodize l i n e . tower ove r f l ow , d i l u t e wastewaters c o n s t i t u t e d more than 97 percent of t he t o t a l wastewater f l o w w h i l e concent ra ted ac ids ( ion-exchange regenerant a c i d ) and bases (spent e t ch ) conta ined t h e remainder o f t h e f l ow .

P a i n t L ine- -

o f o p e r a t i o n or.43.3m3/d. charge pumps f rom t h e chrome r e d u c t i o n system and h o u r l y m o n i t o r i n g o f t he cumula t ive t ime o f pumping. t i o n system and combined w i t h anodize wastewater f o r t reatment .

The f l o w r a t e s o f i n d i v i d u a l sources o f wastewater i n t h e anodize l i n e were

I n t e r m i t t e n t wastewater f lows, e.g., spent e t ch

Rinse

I n c o n j u n c t i o n w i t h c o o l i n g water, backwash water and s t r i p p i n g

The average f l o w o f wastewater f rom t h e p a i n t l i n e was 2.71m3/h f o r 16 h Th is f l o w was measured by c a l i b r a t i o n o f t he d i s -

The wastewater was pumped t o a fou r -s tage n e u t r a l i z a -

Wastewater C h a r a c t e r i s t i c s

To e s t a b l i s h wastewater c h a r a c t e r i s t i c s d u r i n g the survey, each hour ly-sample was analyzed f o r temperature and pH p r i o r t o i n c o r p o r a t i o n i n t o a composite sample. f o r pH and a l k a l i n i t y , a c i d i t y and suspended s o l i d s concentrat ions,which a r e presented i n Tab le 6.5. dnOdiZe l i n e (i.e*., 17 t o 2 6 O C ) w i t h an average r i n s e w a t e r temperature o f 23OC and a measured temperature o f 22°C f o r t h e combined a n o d i z e - l i n e wastewater.

waters had a l k a l i n e pH values and f i l t r a t e - a l k a l i n i t y concent ra t ions o f 225, 8742 and 151 mg/ l (as CaC03), r e s p e c t i v e l y .

Fo l l ow ing t r a n s p o r t t o t h e l a b o r a t o r y , composite samples were analyzed

Wastewater temperatures d i d n o t va ry d r a s t i c a l l y f o r t he

A l k a l i n e c l e a n e r (AL-2), c a u s t i c e t c h (AL-6) and d y e l c o o l i n g (AL-28) r i n s e -

These r insewaters , fu r thermore , were

1 9

Table 6.4. Wastewater Flow Rate f o r Anodize Line

Description Wastewater Tank Number F1 ow

m3/d Rinsewaters

AL-2 Alkal ine Cleaner . . . . . . . , . . . . . . . . . 29.3 AL-4 Acid Cleaner . . . . . . . . . . . . . . . . . . . 18.6 AL-6 Caus t i c Etch-1 . . . . . . . . . . . . . . . . . . 83.5 AL-8 Caus t i c Etch-2 . . . . . . . . . . . . . . . . . . 47.1 AL-10 Desmut . . . . . . . . . . . . . . . . . . . . . . 35.5 AL-14 S to rage . . . . . . . . . . . . . . . . . . . . . 24.5 AL-15 Transfer . . . . . . . . . . . . . . . . . . . . . 121.5 AL-16 I n t e g r a l - c o l o r anodize . . . . . . . . . . . . . . 23.6 AL-19 Anodize . . . . . . . . . . . . . . . . . . . . . 21.4

18.0 20.5

Subtotal 443.5

AL-21 Anodize . . . . . . . . . . . . . . . . . . . . . AL-28 DyelCool i n g . . . . . . . . . . . . . . . . . . . -

Other - Bri ght-di p s t r i p p i n g tower . . . . . . . . . . . . Pump coo l ing water . . . . . . . . . . . . . . . .

51 .3 7 . 5

Ion exchange Backwash water . . . . . . . . . . . . . . . 16.3 -

1

- Regenerant a c i d . . . . . . . . . . . . . . . 9.5 6.3

Subtotal 90.9 - AL-5,-7 Spent E t c h . . . . . . . . . . . . . . . . . . . .

I_

TOTAL WASTEWATER FLOW 534.4

TABLE 6.5. Wastewater C h a r a c t e r i s t i c s f o r Anodize and P a i n t Lines

Descr ipt ion

ANODIZE LINE Rinsewaters:

AL-2 AL-4 AL-6 AL-8 AL-10 AL-14 AL-15 AL-16

AL-19 AL-21 AL-28

Alka l ine Cleaner Acid Cleaner Caus t ic Etch-1 Caus t ic Etch-2 Desmut Storage Transfer In t eg ra l Color

Anodize Anodize DyelCool i ng

Anodize

pH** Composite F i 1 t r a t e F i 1 t r a te Temperature* A1 k a l i n i t y Acid i ty Suspended Sol ids

O C mg/l ( a s CaCo3) mg/l ( a s CaCO3) mgll -

7.4 25 225 20 910 , 2.7 23 - 2,584 -

12.0 24 8742 - 1105 2.2 24 - 938 - 1 . 8 22 - 5,262 - 3.2 21 - 552 - 3.5 23 - 333 -

2.8 23 - 1,229 - 1 .3 22 18,978 - 2.4 22 - 1,698 - 7.7 26 151 13 942

-

Others: Bright-dip S t r ipp ing

Tower 2.6 17 1,381

Anodize Wastewater 6 .9 22 158 94 3716 PAINT LINE

Rinsewater overflow 5.1 31 10 224 955 Chrome Reduction

Eff 1 uent 2.3 28 - BO2 - *Average temperature u s i n g values of ind iv idua l samples taken a t time of sampling. **Value measured 4 days a f t e r survey.

21

t h e o n l y ones which had measurable l e v e l s o f suspended s o l i d s . r i n s e w a t e r s and c o o l i n g tower o v e r f l o w wastewater were a c i d i c (pH = 1.3 - 3 .5 ) w i t h a c i d i t y values o f 333 -18,978 mg/l (as CaCOJ). The combined a n o d i z e - l i n e wastewater had a near -neu t ra l pH, low l e v e l s o f a c i d i t y and a l k a l i n i t y and a suspended s o l i d s c o n c e n t r a t i o n o f 3,716 mg/l.

o v e r f l o w ) and e f f l u e n t t o the chrome r e d u c t i o n system. was s l i g h t l y a l k a l i n e and had a r e l a t i v e l y h i g h temperature o f 31°C and a suspended s o l i d s c o n c e n t r a t i o n o f 955 mg/ l . As a r e s u l t o f chromate r e d u c t i o n u s i n g s u l f u r i c a c i d , t r e a t e d e f f l u e n t f rom t h e p a i n t - l i n e system was h i g h l y a c i d i c and had no measurable l e v e l o f suspended s o l i d s .

The rema in ing

P a i n t - l i n e wastewater samples were taken a t t h e i n f l u e n t ( i . e . , r i n s e w a t e r P a i n t - 1 i n e r i n s e w a t e r

Waste Meta ls

A ma jor o b j e c t i v e o f t h e study, i n a d d i t i o n t o d e t e r m i n a t i o n o f t he sources and q u a n t i t i e s o f wastewater flow,was t o determine t h e p r i n c i p l e sources o f waste aluminum, t h e major component c o n t r i b u t i n g t o t h e p r o d u c t i o n o f s ludge s o l i d s . I n a d d i t i o n , s i n c e approx imate ly 50 pe rcen t o f t h e aluminum f i n i s h e d a t t h e p l a n t was p a i n t e d f o l l o w i n g a p p l i c a t i o n o f a chrome convers ion coa t ing , chrome. concen t ra t i ons and mass f l o w s were o f i n t e r e s t . N i c k e l and cadmium con- c e n t r a t i p n s h a d been shown t o be o f s i g n i f i c a n c e i n a lum inum- f i n i sh ing wastewaters (Saunders - e t _' a1 3 1982) and, as major t o x i c contaminants w i t h r e s p e c t t o p l a n t s and human and animal h e a l t h , concen t ra t i ons and mass f low r a t e s o f these me ta l s were t o be examined. There fore , metal analyses were focused on aluminum ( A l ) , chromium ( C r ) , cadmium (Cd) and n i c k e l ( N i ) .

.

Anodi ze-L i ne--

t h e anodize l i n e a r e presented i n Table 6 . 6 . r i n s e s f o l l o w i n g c a u s t i c e t c h and anodize processes, i .e . , tanks AL-6 and A1-19 r e s p e c t i v e l y , con ta ined t h e h i g h e s t concen t ra t i ons o f aluminum. c o n t a i n i n g s i g n i f i c a n t concen t ra t i ons o f aluminum i n c l u d e d a c i d c leaner , desmut, second-stage c a u s t i c e t c h (AL-8) and second-stage anodize (AL-21) r i nsewa te rs .

con f i rm t h a t c a u s t i c e t c h and anodize s o l u t i o n s were p r i n c i p a l sources o f waste aluminum. (51 g / l ) as d i d t h e two subsequent r i n s e s (22 and 6.54 g/1, r e s p e c t i v e l y ) . ever, no wastewater d ischarges were made f rom t h e tanks s i n c e t h e s t a g e - l r i n s e i s rec la imed and s o l d f o r i t s phosphorus con ten t . There fore , o n l y d ragout from t h e stage-2 r i n s e and vapors t rapped i n the s t r i p p i n g tower a re d ischarged t o the wastewater system f rom t h e b r i g h t d i p process.

The wastewater w i t h t h e h i g h e s t c o n c e n t r a t i o n o f chromium on the anodize l i n e was dragout f rom the a l k a l i n e c leaner (AL-l), as con ta ined i n a l k a l i n e c leaner r i n s e w a t e r (AL-2). t a i n e d more than approx imate ly 8 0 - f o l d h i g h e r c o n c e n t r a t i o n of chromium than any o t h e r f i n i s h i n g s o l u t i o n on the anodize l i n e . l e v e l s o f chromium i n c l u d e d i o n exchange regenerant a c i d and b r i g h t - d i p - s t r i p p i n g - tower o v e r f l o w f o l l o w e d by ac id -c leaner , desmut and f i r s t - s t a g e anodize r i n s e - waters.

Meta l c o n c e n t r a t i o n s o f r i nsewa te rs and o t h e r wastewaters d ischarged from Ion-exchange regenerant and i n i t i a l

Other tanks

Data presented i n Tab le 6 . 7 f o r metal compos i t ion o f m e t a l - f i n i s h i n g s o l u t i o n s

The b r i g h t d i p s o l u t i o n (AL-11) a l s o conta ined h i g h aluminum l e v e l s How-

A t a c o n c e n t r a t i o n of 475 mg/l, t h e c l e a n i n g s o l u t i o n con-

Other wastewaters w i t h s i g n i f i c a n t

22

Table 6.6. Metal Composition o f Wastewater Sources

A1 Description mq/i

Rinsewaters AL-2 A1 ka l ine Cleaner AL-4 Acid Cleaner AL-6 Caustic Etch-1 A L - 8 Caustic Etch-2 AL-10 Desmut AL-14 Storage AL-15 Transfer AL-16 In tegra l Color Anodize AL-19 Anodize

. AL-21 Anodize ‘AL-i4 Seal AL-28 DyelCool i n g

2.5 325.0

1,900.0 115.7 195.0 37.5 16.2 28.5

575 98.5 1 .o 5.33

Other - Bright Dip S t r ipp ing Tower 19

- backwash-1 18.91 - backwash-2 1.92 - regenerant ac id 3,824

Ion Exchange

Spent Etch AL-5 Cold E t c h AL-7 Hot Etch

47,7 00 59,600

Cr mq/l

17.3 0.6 0.17 2.3 0 . 2 0.013 0.014 0.03 0.126 0.009 0.005 0.004

0.854

0.0142 0.0126 0.98

0.63 0.47

Cd w 11

0.37 1.19 0.67 0.36 0.23 0.20 0.08 0.48 5.81 0.53 0.02 0.59

1.7

0.15 0.08

14.4

14,600 29,100

Ni mg/l

<0.02 <o. 02

0.22 < o . 02

0.54 <o. 02 <0.02

<0.02 0.15 0.04

<o. 02 0.03

0.05

<0.02 <0.02

0.72

1 .o 0.4

23

Table 6 .7 . Metal Composition o f Anodizing Process Solut ions

Tank Number

AL-1 AL-3 AL-5 AL-7 AL-9 AL-11 AL-12 AL- 13 AL-17

AL- 18 AL-20 AL-25 AL-26 AL-27

A1 -- Description - 9/1

Alkaline c leaner 0.059 Acid c leaner 3.8 Cold etch 47.7 Hot etch 59.6 Desmut 3.2 B r i g h t d ip 51 .O B r i g h t d i p r inse-1 22.0 Bright d i p r inse-2 6.54 In tegra l co lo r

anodize 0.75 Conventional anodize 5.8 Conventional anodize 5.2 Seal 0.003 Seal 0.012 DY e 0.425

Cr mg/l

475. 4.92 0.63 0.47 3.0 3.0 6.0 6.05

4.58 1.42 0.45 0.004 0.035 0.34

Cd !W!L

13.8 20.2 14.6 29.1 6.2 4.5

118.0 58.2

91.3 26.3 37.8 0.17 0.37

13.6

N i E!fL 0.22 0.51 1 .o 0.4 1 .o 1.25 2.8 2.63

1.20 0.6 1.3

co.02 0.05 0.29

Cadmium concentrat ions were l e s s than 15 pg/l for a l l anodize wastewater samples presented i n Table 6.6. Nickel concentrations were below de tec t ion limits ( i . e . , 0.02 mg/l) f o r more t h a n ha l f of t he rinsewater samples and less than 0.54 mg/l for the others.

Evalua t ion of the mass flow of metal was determined w i t h metal concentration data i n Tables 6.6 and 6.7 and flow r a t e da ta i n Table 6.4 and a r e presented i n Table 6.8. The pr incipal source of aluminum was the etching process w i t h a t o t a l of 334.64 kg/d of aluminum discharged i n spent etch and 164.16 kg/d discharged i n caus t i c e tch r insewaters . The combined flows accounted for 498.8 kg/d, o r 88.1 percent of t he t o t a l of 565.96 kg/d of waste a luminum discharged from the anodize line. The anodize process was the next major source of aluminum w i t h 36.23 kg/d and 13.1 kg/d i n ion-exchange regenerant and anodize r insewaters , respec t ive ly . Wastewater discharges resulting d i r e c t l y from anodizing and etching therefore cons t i tu ted over 96 percent of t o t a l waste aluminum from the anodize l ine.

As re f l ec t ed by rinsewater concentrat ions, a1 kal ine cle'aner rinsewater was the major source o f chromium a t 507.47 g /d on the anodize l ine. Elimination of the use of a chromate-based --_---.l-- a lka l ine ~ c leaner , therefore , would result in a 75.6 percent reduction i n the mass flbw of"c-tirGiium. chromium appeared t o be the second-stage c a u s t i c rinsewater (AL-8). However, evaluat ion of data f o r chromium content of c a u s t i c etch so lu t ions (Table 6 .7)

.. .

A second major source of

24

and fo r f i r s t - s t a g e c a u s t i c rinsewater (AL-6) placed th i s value i n quest ion. All other chromium sources ranged from 0.08 t o 14.12 g /d .

Table 6.8. Mass Flow o f Metals from Wastewater Sources

Description

Ri nsewaters : AL-2 AL-4 AL-6 AL-8 A-10 AL-14 AL-15 AL-16 AL-19 AL-21 AL-28

Other: --

Alkaline cleaner Acid c leaner Caustic etch-1 Caust ic etch-2 Desmut Storage Transfer Integral Color Anodize Anodize Anodize

DY e Subtotal

Br ight Dip S t r ipp ing tower

Ion Exchange Backwash Regenerant

AL-5,-7 Spent Etch Subtotal

TOTAL

A1 kg/d

. 0.07 6.05

158.72 5.44 6.93 0.92 1.97 0.67

11.33 1.77 0.11

193.98

0.98

0.13 36.23

334.64 371.98

Cr 9!!3

507.47 11.17 14.12

108.17 6.99 0.31

. 1.69 0.74 2.69 0.17 0.08

653.6

4.38

0.22 9.27

3.48 17.35

Cd !!!Y@

11 22 56 17 8 5 9

11 124

10 12

285 -

87

2 136

134 359 - -

565.96 670.95 644

N i g/d

* *

17.96 *

19.26 * * *

3.22 0.72 0.51

41.67

2.57

* 6.79

4.47 13.83 - 55.5

*Ni below de tec t ion l i m i t of 0.02 mg/l.

Cadmium was discharged i n anodize rinsewater (AL-19), ion exchange regenerant and spent e tch a t 124, 136 and 134 mg/d, respec t ive ly , accounting f o r 61 percent o f the t o t a l cadmium mass flow. Other major sources included the br ight-dip stripping-tower overflow and c a u s t i c e tch rinsewater (AL-6). Cadmium discharge r a t e s were below 22 mg/d for a l l o the r wastewater sources. Nickel discharge t o t a l l e d 55.5 g /d w i t h c aus t i c e tch (AL-6) and desmut (AL-10) r insewaters being major sources a t 17.96 g/d and 19.26 g / d , respec t ive ly . Seven of the 16 wastewater sources included i n Table 6 .8 contained nickel a t l eve l s below the

25

detec t ion l i m i t ( i . e . , 0.02 mg/ l ) of the procedure used (flame atomic adsorp t ion) .

discharge was the pr incipal metal a t 565.96 kg /d . this mass o f aluminum t o a p rec ip i t a t ed form as aluminum hydroxide (A1(OHI3) would result i n predict ion of a suspended s o l i d s mass flow 1635 kg/d and a suspended s o l i d s concentrat ion of 3060 mg/l . cadmium and nickel equalled 727 g/d or 0.13 percent o f the mass of aluminum discharged. These metals, therefore ,contr ibuted only a minor portion of the metal to be t reated and precipitation of them would only c o n s t i t u t e a minor increase i n sludge inventor ies .

Paint-Line-- The flow r a t e of pa in t l i n e wastewater was measured using the pumps w h i c h

t r ans fe r r ed paint- l ine wastewater from the chrome-reduction system t o a neut ra l iza- t i o n system receiving a l l p lan t wastewaters. a period of 16 hours of operat ion and the t o t a l da i ly discharge of wastewater from the paint-line was 43.3 m3/d.

Metal concentrat ions for the wastewater flow and f i n i s h i n g so lu t ions a r e presented i n Table 6.9. Metal concentrat ions for the pa in t - l ine wastewater and chrome reduction effluent were v i r t u a l l y ident ica l s ince nothing was done i n the chrome reduction system t o a l t e r the t o t a l metal content of the wastewaters and no d i s t i n c t i o n was made i n Table 6.9 between trivalent and hexavalent forms of chromium nor f o r various forms of the o the r metals. Chromium and aluminum were the major metals w i t h concentrations between 40 and 47 m g / l . concentrat ions were much lower a t 0.02 - 0.03 mg/l and 0.44 - 0.48 u g / i , respec t i vely .

With respec t t o overal l discharge of metals from the anodize l ine , aluminum Mathematical conversion o f

The t o t a l discharge of chromium,

The flow r a t e averaged 2.7 m3/h f o r

Nickel and cadmium

Table 6.9. Metal Composition of Paint-Line Wastewater and F i n i s h i n g Solut ions

Description A1 Cr Cd Ni "g/l mg/l mg/l

Wastewater P a i n t - l i n e r insewaters 40 47 0.48 0.02 Chrome reduction e f f l u e n t 40.2 43 0.44 0.03

F i n i s h i n g Solut ions A1 kal i ne Rinse 168 9.5 0.47 <o. 02 Chromate Conversion Coat <1 5240.0 14.85 0.32 Acidulating Rinse 20 51.5 19.43 <0.02

Examination of t he composition of f i n i s h i n g so lu t ions indicated t h a t a lka l ine rinsewaters and chrome-conversion-coat r insewaters were, respec t ive ly , the major sources of aluminum and chromium. cadmium concentration b u t i t was not discharged t o wastewater d u r i n g the survey.

The ac idula t ing rinse so lu t ion had the highest

26

Using a flow rate of 43.3m?/d and the metal concentration data for the chrome-reduction effluent, metal discharge rates for the plant-line were 1.74 kg/d for aluminum, 1.86 kg/d for chromium, 19.05 mg/d for cadmium and 1.30 g/d for nickel.

Combined Wastewaters--

anodize and paint lines and that discharged from the neutralization basin used t o treat the combined flow of anodizing and painting wastewaters. samples of individual wastewaters were collected within the paint-line system, metal data were only collected for the combined paint-line wastewater and are presented in Table 6.9. However, numerous sources of wastewater were examined within the anodize line (see Tables 6.6 and 6.8) as well as a composite sample of the combined discharge from the anodize line. wastewaters are presented in Table 6.10.

Combined wastewaters which were sampled included those discharged from the

Since no

Metal data for combined anodize

Table 6.10. Metal Composition of Anodize and Neutralized Plant Wastewaters

Description A1 Cr Cd Ni !!!dl ms/l ug/l u

Combined Anodize Wastewater. . . . . . . 850 2.2 0.98 0.08

Neutralization Basin Effluent

Total . . . . . . 875 6.2 0.97 0.12 Filtrable . . . . 7.8 0.32 1.17 0.04

Neutralization Basin Effluent*

Monday. . . . . . 1000 3.45 1.78 0.1 Tuesday . . . . . 1420 3.45 3.80 0.1 Wednesday**. . . . 1110 6.65 1.60 0.15 Thursdav. . . . . 1500 6.50 2.01 0.23 " Friday. . . . . . 770 Average . . . . . 1182

- 1 .o 4.21

1.55 2.15 - 0.15

0.15 ~

* Composite samples collected by plant personnel on first shift (2-hour grab samples combined on equal-volume basis for 8-hour period).

** Date on which full 24-hour survey was conducted. As predicted from characteristics of individual wastewater sources, aluminum

was the major metal contained in the combined anodize-line wastewater and the metal data were in general agreement with those presented in Tables 6.6 and 6.8. For example, predicted metal concentrations for the anodize effluent using data in Tables 6.6 and 6.8 were A1 = 1059 mg/l, Cr = 1.3 mg/l, Cd = 1.21 ug/l and Ni = 0.104 mg/l. Predicted aluminum levels were higher than measured aluminum

27

by 20 percent. ( i . e . , 59 percent) of the waste aluminum as spent etch (see Table 6 .8) during the f i r s t s h i f t w i t h no adjustment in composite-sampling frequency due t o this flow.

Data f o r the neut ra l iza t ion basin e f f luen t i n Table 6.10 r e f l e c t the combined metal flows o f anodize- and pa in t - l ine wastewaters. 6.4,6.8 and 6.9, predicted metal concentrations were: A 1 = 983 mg/l; Cr = 1.17 mg/l; Cd = 1.15 pg/l and Ni = 0.098 mg/l . in exce l len t agreement, considering the low l eve l s of several metals and the unsteady discharge of some wastewaters. F i l t r a b l e metal data indicated t h a t aluminum, chromium and nickel were e f f ec t ive ly prec ip i ta ted w i t h dissolved res idua ls of 7.8 mg/l, 0.32 mg/l and 0.04 mg/l, respec t ive ly . t ion d i d not occur due, most probably, t o the extremely low l eve l s (--1 pg / l ) of the metal in the wastewater.

personnal developed 8-hour composite samples ( i . e . , g r a b samples taken a t 2-hour i n t e rva l s during the f irst shif t ) f o r t e s t i n g during the f i r s t s h i f t f o r f i v e days. Results of metal analyses f o r these samples a r e presented in Table 6.10. Since spent etch was rout ine ly discharged d u r i n g t h i s s h i f t and s ince the paint line was operational during this s h i f t ( b u t only 16 hours of the 24-hour survey) metal concentrat ions, espec ia l ly aluminum, were expected t o be s l i g h t l y higher t h a n those of the 24-hour composite sample. This was the case b u t the samples co l lec ted d u r i n g the week of the survey were i n general agreement w i t h the samples co l lec ted d u r i n g the survey.

Aluminum Production

T h i s e r r o r was a t t r i b u t a b l e t o the discharge of the bulk

Using d a t a in Tables

The predicted and measured data were

Cadmium prec ip i ta -

To r e l a t e the r e s u l t s of the survey t o other days of operat ion, p l a n t

Production records f o r the week of the study were col lec ted and examined with respect t o survey r e s u l t s . Aluminum a l loys processed during the week of the survey were 6063 and 6463 (see Table 6.13) with the majority of the metal being 6063, i . e . , 86.3 percent of the t o t a l surface area f inished f o r the day of the survey. Production data f o r the plant a re presented in Table 6.11 f o r the week of the survey. (i.e., Wednesday) included data from the t h i r d s h i f t of Tuesday and the f i r s t and second s h i f t s of Wednesday and a r e , therefore , n o t cons is ten t with the values recorded f o r t he 24-hour period of the survey.

The quan t i t i e s of aluminum f in ished on the anodize- and pa in t - l ines were approximately equal with the material painted having a higher surface area per un i t mass, i . e . , 0.48 m2/kg vs 0.38 m2/kg . Total production was 36.8 T/d or 1.57 x l o 4 m2/d and was ind ica t ive of monthly production rates of approximately 736 T/mo o r 3.14 x l o 5 m2/mo ( i . e . , f o r 20 day/mo), which were s l i g h t l y below indicated production capac i t i e s . was cons is ten t with production l eve l s t h r o u g h o u t the survey week, which averaged 18.9 T/d and 8.14 x lo3 m2/d. reduced t o t h a t f o r one hour of operation on Thursday and r7 production on Friday due t o a mechanical breakdown. survey was near the average l eve l s of production f o r the three days of f u l l operation f o r the survey week ( i . e . , 15.8 T /d and 8.6 x l o 3 m 2 / d ) .

The data presented f o r the 24-hour period of the survey

Product ion on the anodize l i n e d u r i n g the survey

Paint- l ine production during the survey week was

However, production on the day of the

28

Table 6.11. Aluminum Production Data f o r P lan t A1

Finished Aluminum Surface

Descri p ti on

Survey Day Anodize Line P a i n t Line

Week of Survey Anodize Line:

Monday Tuesday Wednesday Thursday Friday

Pa in t Line: Monday Tuesday Wednesday Thursday Friday

Lencjth Area 10 m i o 3 m2

32.6 30.0

7.3 8.4

38.5 8.7 41.3 10.7 30.2 6.7 31.8 7.7 30.7 6.9

38.2 9.7 63.9 7.8 30.0 8 .4

2.3 0.8 0 0

Mass Ton -

19.2 17.6

18.2 23.5 17.2 18.0 17.7

16.4 13.4 17.6

1.8 0

Area/Mass m2/kg

0.38 0.48

0.48 0.46 0.39 0.43 0.39

. 0.59 0.48 0.48 0.44 -

With respec t t o the s p e c i f i c f i n i s h i n g operations u t i l i z e d , the pa in t l i n e was an automated system and a l l aluminum was f in i shed u s i n g the same iden t i ca l processes, However, several f i n i s h i n g sequences were u t i l i z e d on the anodize l ine resulting i n va r i a t ions i n use of t he ava i l ab le f i n i s h i n g processes as included i n Table 6.2. survey u s i n g the var ious processes a r e included i n Table 6.12. process was not used d u r i n g the survey and the c o l d e tch and b r i g h t d i p processes were only used on 70.5 - 72.8 percent and 29.5 - 27.2 percent of the aluminum f i n i s h e d , respec t ive ly . All a luminum was anodized (conventional c lear -coa t su l fur ic -ac id anodize = 80-86 percent and in tegra l -co lor su l fur ic -ac id anodize = 14-20 percent) and a l l o the r processes were used i n f i n i s h i n g the aluminum processed during the survey.

The portions of aluminum which were finished d u r i n g t he The hot e tch

29

Table 6.12. Anodizing Processes Ut i l ized during the Survey Period

Tank Description Number

Percent o f Total Finished Cumulative

time o f treatment

- Mass hour

AL-1 A1 kal i ne C1 eaner 100 100 10.5

AL-3 Acid Cleaner 100 100 *

Surface Area -

AL-5 Cold Etch

AL-9 Desmut

70.5 72.8 21.6

100 100 3

AL-11 Bright Dip 29.5 27.2 1.2

AL-17 Integral-Color Anodize 14.4 19.7 24

AL-18&20 Clear Anodize

AL-24 Seal Rinse

85.6 80.3 31.5

100 100 0.75

AL-25&26 Seal 100 100 30

AL-28 Dye/Cooling Rinse 100 100 0.75

*time not available

30

D I S C U S S I O N

Sources o f Waste Me ta l s

Waste meta ls a t P l a n t A1 were e i t h e r a d d i t i v e s i n the' f i n i s h i n g s o l u t i o n s o r c o n s t i t u e n t s o f t h e a l l o y s be ing f i n i s h e d . The a l l o y s f i n i s h e d d u r i n g t h e s tudy were s i m i l a r i n compos i t ion as i n d i c a t e d i n Tab le 6.13. t y p i c a l l y c o n t a i n no n i c k e l o r cadmium, a l though cadmium would be expected t o be a l o w - l e v e l contaminant o f z i n c added t o 6063. Chromium i s con ta ined i n 6063 a t a maximum o f 0.1 percent o r - < 1,000 mg Cr/kg A l .

The a l l o y s

Tab le 6.13. Chemical Composit ion L i m i t s o f Wrought Aluminum A 1 l o y s (Aluminum A s s o c i a t i o n , 1979)

Meta l Content A l l o y Percent o f A l l o y Mass*

Fe Cu Mn Mg C r Zn T i Others A1 _ _ - --- S i

6063 0.2-0.6 0.35 0.1' 0.1 0.45-0'.9 0.1 0.1 0.1 0.05-0.15 Remainder I, (0.4) - - - (0.67) - - - -

6463 0.2-0.6 0.15 0.2 0.05 0.45-0.9 - - - 0.05-0.15 Remainder I, (0.4) - - - (0 .7 ) - - - -

*Values i n b racke ts a r e nominal compos i t ion l i m i t s .

Anodize L ine- -

f i n i s h i n g , t h e l e v e l s o f cadmium, chromium and n i c k e l removed from a l l o y su r faces would be smal l i n comparison t o t h e q u a n t i t y o f aluminum removed. cadmium, chromium and n i c k e l t o f i n i s h i n g s o l u t i o n s would r e s u l t i n h ighe r l e v e l s o f these meta ls i n a f i n i s h i n g s o l u t i o n , r e l a t i v e t o aluminum, and would n o t be p r o p o r t i o n a l t o aluminum removal r a t e s . To determine t h e sources of meta ls examined, the compos i t ion o f r i nsewa te rs and f i n i s h i n g s o l u t i o n s were expressed w i t h r e s p e c t t o aluminum concen t ra t i ons and a re presented i n Tab le 6.14 f o r t h e anodize l i n e . Wi th r e s p e c t t o chromium, a l k a l i n e c l e a n e r was the p r i n c i p a l source w i t h l e v e l s o f 6.92 kg Cr /kg A l , s i n c e chromium was an a d d i t i v e i n t h e process tank . The a c i d c leaner , w i t h a chromium l e v e l o f 1.85 g/kg, may a l s o have c o n t a i n - ed a low l e v e l o f chromium-based c leaner . However, a l l o t h e r r i nsewa te rs c o n t a i n - ed chromium a t l e v e l s i n d i c a t i v e o f those a t t r i b u t a b l e t o chromium removal f rom a l l o y s .

S ince e t c h i n g and anod iz ing r e s u l t i n t h e removal o f s u r f a c e metal d u r i n g

A d d i t i o n o f

Cadmium compos i t ion o f a c i d c l e a n e r r i n s e w a t e r was equal t o 3.66g/kg b u t t h i s va lue was n o t con f i rmed by the 5.3 mg/kg va lue f o r t h e a c i d c l e a n e r f i n i s h i n g s o l u t i o n . A l l o t h e r sources were < 353 mg/kg w i t h t h e m a j o r i t y be ing < 20 mg/kg, i n d i c a t i n g maximum a l l o y compos i t ion l e v e l s o f 0.035 pe rcen t and 0.002 p e r c e n t , r e s p e c t i v e l y (assuming Cd l e v e l s were a t t r i b u t a b l e t o a l l o y i m p u r i t i e s ) . l e v e l s i n t h i s range, i .e . , 0.002 t o 0.035 percent , a re reasonable w i t h r e s p e c t t o a l l o y con ten t . source o f cadmium.

Cadmium

Removal o f cadmium from a l l o y s be ing f i n i s h e d was t h e apparent

31

Table 6.14. R e l a t i v e Trace Meta l Composi t ion o f Anod iz ing Rinsewaters and F i n i s h i n g S o l u t i o n

Cr/A1 Cd/A1 Ni/A1

D e s c r i p t i o n m& m s L k s ~FlI!!sL

Rinsewaters

AL-2 AL-4 AL-6 AL-8 AL-10 AL-14 AL-15 AL-16 AL-19 AL-21 AL-28

A1 k a l i ne C1 eaner 6,920,000 148. Ac id Cleaner 1,850 3,660 Caust ic Etch-1 89.5 353 Caus t i c Etch-2 (19,900) 3.1 Desmut 1,030 1.2 Storage 347 5.3 T r a n s f e r 864 4.9 I n t e g r a l C o l o r Anodize 1,053 16.8 Convent ional Anodize 219 10.0 Convent ional Anodize 91 5.4 Dye/Cooling , 750 111

-- F i n i s h i n g S o l u t i o n s

8,000

116 173

2,770 533

61.5

1,230 702 260 406

5,630

AL-1 A l k a l i n e Cleaner 8,050,000 234 3,700 AL-3 A c i d Cleaner 1,295 5.3 134 AL-5 Cold E tch 13.2 0.3 21 AL-7 Hot E tch 7.9 0.5 6.7 AL-9 Desmut 938 1.9 31 3 AL-11 B r i g h t - D i p 59 0.009 24.5 AL-12 B r i g h t D i p Rinse-1 272 5.4 127. AL-13 B r i g h t D i p Rinse-2 925 8.9 402 AL-17 I n t e g r a l Co lo r Anodize 6,110 122 1,600 AL-18 Convent ional Anodize 245 4.5 103 AL-20 Convent ional Anodize 87 7.3 250 AL-25 Seal 1,330 56.7 ~ 6 , 7 0 0 AL-25 Seal 8,750 92.5 . 12,500 AL-27 Dye 3,200 128. 2.730

N i c k e l c o n t e n t o f a l k a l i n e c leaner , desmut and d y e l c o o l i n g r i nsewa te rs ranged f rom 2770 t o 8000 mg/kg. apparent t h a t n i c k e l was a chemical a d d i t i v e i n t h e assoc ia ted f i n i s h i n g s o l u t i o n s . N i c k e l l e v e l s i n t h e s e a l i n g s o l u t i o n s (AL-25 & 26) were a t t r i b u t a b l e t o n i c k e l a d d i t i v e s ( e l o x a l s a l t ) used t o assure proper s e a l i n g o f anodized sur faces . N i c k e l con ta ined i n t h e a l k a l i n e c leaner s o l u t i o n was a p p a r e n t l y a contaminant assoc ia ted w i t h t h e chromate a d d i t i v e . Data f o r t h e n i c k e l c o n t e n t of t h e desmut s o l u t i o n d i d n o t c o n f i r m desmut r i n s e w a t e r as a major source o f n i c k e l a d d i t i v e s . Other sources o f n i c k e l ranged f rom 61.5 t o 1230 mg/kg which, i f a t t r i b u t a b l e t o a l l o y composi t ion, i n d i c a t e d n i c k e l l e v e l s i n t h e a l l o y s o f 0.006 percent t o 0.12 percent . r e q u i r e d n i c k e l a d d i t i v e s b u t a l l o y contaminants cou ld have c o n t r i b u t e d t o t h e n i c k e l l oad ings .

S ince n i c k e l was n o t an a l l o y a d d i t i v e , i t i s

These l e v e l s appeared t o be r e l a t i v e l y h i g h f o r a l l o y s w i t h no

3 2

I n summary, w i t h t h e excep t ion o f chromium and n i c k e l a d d i t i v e s i n the a l k a l i n e c l e a n e r and n i c k e l a d d i t i v e s i n the s e a l i n g s o l u t i o n s , removal o f cadmium, chromium and n i c k e l c o n c u r r e n t l y w i t h aluminum from a l l o y sur faces was' t h e ma jo r means by which these me ta l s en tered wastewaters. There fo re , meta l con taminat ion i s i n h e r e n t t o e t c h i n g and anod iz ing processes and w i t h the excep t ion o f a d d i t i v e s t o the a l k a l i n e c l e a n e r and s e a l i n g s o l u t i o n s , can o n l y be c o n t r o l l e d w i t h changes i n a l l o y compos i t ion o r f i n i s h i n g procedures.

P a i n t L ine- - P a i n t - l i n e wastewaters i n c l u d e d r i n s e w a t e r d ischarges f o l l o w i n g a l k a l i n e

c l e a n e r and chromate-convers ion s o l u t i o n s . These r i nsewa te rs c o u l d n o t be separated f o r sampl ing and were sampled c o l l e c t i v e l y as one d ischarge. Metal compos i t ion da ta f o r p a i n t - l i n e r i n s e w a t e r and f i n i s h i n g s o l u t i o n s a r e presented i n Tab le 6.15. Chromium was o b v i o u s l y the major metal d ischarged f rom t h e p a i n t l i n e and i t s presence was due t o d r a g i n f rom t h e a l k a l i n e c l e a n e r and chromate convers ion s o l u t i o n s . Cadmium and n i c k e l d i scha rges were fu r the rmore s i g n i f i c a n t l y a f f e c t e d by compos i t i on o f t h e chromate-convers ion s o l u t i o n . Meta l d ischarges f rom t h e p a i n t - l i n e were, t h e r e f o r e , due p r i m a r i l y t o d r a g i n o f a d d i t i v e s con- t a i n e d i n f i n i s h i n g s o l u t i o n s as opposed t o removal o f meta l f rom aluminum s u r - faces d u r i n g f i n i s h i n g .

Tab le 6.1 5. R e l a t i v e Trace Meta l Composi t ion o f P a i n t i n g . - - Rinsewaters and F i n i s h i n g S o i u t i o n s

D e s c r i p t i o n Cr/A1 Cd/A1 Ni/A1

mg/kg mg/kg mg/kg - - P a i n t l i n e Rinsewater* 1.18 x i o 6 12 500

F i n i s h i n g S o l u t i o n s :

A l k a l i n e C leaner 5.65 l o 4 2.8 <119

A c i d u l a t i n g Rinse 2.68 x i o 6 970 <I l o 3

3 Chromate Convers ion 5.24 l o 9 1.49 x l o 4 >3 .2 x 10

*Combined d ischarge o f a l k a l i n e - c l e a n e r r i n s e w a t e r and chromate-conversion r i nsewater.

D rag in Rates

taminants , t h e ma jo r source o f wastewater was r i nsewa te r . meta l compos i t ion o f r i nsewa te rs and f i n i s h i n g s o l u t i o n s , i t was p o s s i b l e t o d e t e r - mine d r a g i n f l ows , QD, f o r each f i n i s h i n g tank accord ing t o the fo rmula QD = QR CR CD-', where QR = r i n s e w a t e r f l o w ; CR = contaminant c o n c e n t r a t i o n i n r i n s e - water; and CD = contaminant c o n c e n t r a t i o n i n d r a g i n ( i . e . , c o n c e n t r a t i o n i n preceeding t a n k ) .

A l though concen t ra ted f i n i s h i n g s o l u t i o n s were major sources o f wastewater con- Using da ta f o r f l o w and

33

Anodize L ine - - D rag in values a re presented i n Tab le 6.16 f o r a n o d i z e - l i n e r i n s e w a t e r s .

D r a g i n values based on n i c k e l were n o t c a l c u l a t e d due t o l i m i t e d da ta f o r r i n s e - wa te r n i c k e l concen t ra t i ons . With the excep t ion o f t h r e e abnormal ly h i g h values and one low value, d r a g i n f l o w r a t e s ranged from 0.053 m3/d t o 3.08 m3/d. expected, v iscous f i n i s h i n g s o l u t i o n s r e s u l t e d i n the h i g h e s t d r a g i n r a t e s . Caus t i c e t c h (AL-6 & 8 ) , anodize (AL-19 & 21), desmut (AL-10) and a c i d c l e a n e r (AL-4) r i n s e w a t e r s had d r a g i n r a t e s rang ing from 2.87 t o 1.38 m3/d (based on average va lues ) . A low d r a g i n r a t e o f 0.34 m3/d f o r t h e i n t e g r a l - c o l o r anodize system was a t t r i b u t e d t o low usage o f t h i s s o l u t i o n d u r i n g t h e survey. l owes t d r a g i n r a t e was f o r t h e dye /coo l i ng r i n s e which was due t o t h e decreased v i s c o s i t y o f t h e h igh- temperature s e a l i n g s o l u t i o n .

As

The

Table 6.16. D rag in Rate f o r Anodize-L ine Rinsewaters

Q , Drag in Din3/d

Tank D e s c r i p t i o n A1 C r Cd Average Number

AL-2 A l k a l i n e Cleaner 1.24 1.07 0.79 1.03

AL-4 Ac id Cleaner 1.59 2.27 1.10 1.65

AL-6 Caus t i c Etch-1 1.48 (12.8)* 1.28 1.38

- - -

AL-8 Caus t i c Etch-2 2.87 ** (25.3)* 2.87

AL-10 Desmut 2.16 2.37 1.32 1.95

AL-14 Storage 0.14 0.053 0.084 0.092

AL-16 I n t e g r a l C o l o r Anodize 0.90 0.0015 0.12 0.34

AL-19 Convent ional Anodize 1.12 1.44 1.94 1.62

AL-21 Convent ional Anodize 3.08 1.29 1.64 2.00

AL-28 Dye/Cool 0.26 0.24 0.89 0.46

*High values exc luded from i n d i c a t e d averages. * *Ca lcu la ted d r a g i n f l o w was g r e a t e r than r i n s e w a t e r f l o w .

P a i n t L ine- -

s i n c e f l o w r a t e s f o r t h e i n d i v i d u a l r i n s e w a t e r s were n o t c o l l e c t e d . examinat ion o f chemical compos i t ion da ta i n Tables 6.9 and 6.15 i n d i c a t e d t h a t t h e t o t a l r i n s e w a t e r d ischarge had a chemical compos i t ion which was i n t e r m e d i a t e between t h e a l k a l i n e c l e a n e r and chromate-convers ion s o l u t i o n s . water was added t o t h e r i n s e w a t e r tanks , i f i t was assumed t h a t no t a p water a d d i t i o n occurred, t he d r a g i n r a t e f o r t h e a l k a l i n e c leaner s o l u t i o n would account f o r more than 99 percent o f t he r i n s e w a t e r f l o w . p o s s i b l e t o c o n f i r m t h i s s i n c e the r e l a t i v e f l o w s o f r i n s e w a t e r were unknown and d r a g i n r a t e s c o u l d n o t be c a l c u l a t e d .

Examinat ion o f d r a g i n r a t e s f o r i n d i v i d u a l r i nsewa te rs was n o t p o s s i b l e However,

A l though t a p

However, i t was n o t

34

Wastewater Summary

l i n e . cen t ) of t he wastewater f rom the anodize l i n e was conta ined i n d i l u t e r i n s e - water w i t h concent ra ted ac idsand a l k a l i c o n t a i n i n g t h e remainder. e f f o r t s t o reduce water use should be focused on m i n i m i z i n g r i n s e w a t e r f l o w by, f o r example, use o f ex tens i ve c o u n t e r c u r r e n t r i n s i n g and reuse o f t r e a t e d wastewater e f f l u e n t f o r r i n s e s f o l l o w i n g c lean ing and e tch ing .

The major source o f wastewater and waste metal a t p l a n t A1 was the anodize As shown i n t h e da ta summary i n Table 6.17, t he m a j o r i t y ( i , e . , 94 pe r -

There fore ,

Table 6.17. Summary o f Wastewater and Meta l Flows f o r Anodiz ing L i n e a t P l a n t A1

Wastewater Flow Meta l Flow D e s c r i p t i o n A1 C r Cd N i

m3/d kg/d g/d mg/d g/d

Rinsewaters 502.3 195.0 658.0 372 44.2

I o n Exchange Wastewater 25.8 36.4 9.5 138 6.8

Spent E tch 6.3 334.6 3.5 134 - - - 4.5

Average Metal Concent ra t ion 1059mg/1 1.26mg/l l . zNg/ l 0.104mg/l

Wi th r e s p e c t t o waste meta1,aluminum accounted f o r the m a j o r i t y , i . e . , 99.9 percent , o f t h e t o t a l o f t he f o u r meta ls mon i to red and t h e r e f o r e accounted f o r t h e m a j o r i t y o f t h e suspended s o l i d s t r e a t e d a t t h e p l a n t . However, u n l i k e t h e wastewater f l ow , the major sources o f waste aluminum were spent e t ch and i o n exchange regenerant , which were minor sources o f wastewater, Reduct ion i n the mass f l o w o f aluminum should t h e r e f o r e be focused on reduc ing t h e q u a n t i t y o f spent e t c h and t h e c o n c e n t r a t i o n o f aluminum i n etch. Reduct ion o f aluminum c o n c e n t r a t i o n i n spent e t ch would f u r t h e r m o r e reduce alumimum mass f l ows f o r e t c h r i nsewa te rs . The mass f l o w s o f chromium, cadmium and n i c k e l were ve ry low as i n d i c a t e d by average wastewater c o n c e n t r a t i o n s o f 1.26 mg/ l , 1.2 p g / l and 0.104 m g / l , r e s p e c t i v e l y , and as compared t o 105 mg/l f o r aluminum.

min imize wastewater f l o w s . ope ra t i on ) w h i l e meta l f l o w r a t e s were 1.74 kg/d, 1.86 kg/d, 19.05 mg/d, and 1.3 g/d, r e s p e c t i v e l y , f o r aluminum, chromium, cadmium and n i c k e l . These l e v e l s were s i g n i f i c a n t l y l e s s than those f o r t he anodize l i n e , except f o r chromium.

As d iscussed e a r l i e r , t h e p a i n t - l i n e system was automated and was operated t o T o t a l wastewater f l o w was 43.3m3/d ( f o r 16 hours o f

The use

35

of a chromate-based conversion-coat process resu l ted i n a chromium mass flow w h i c h was more than 2.7 times higher than t h a t for the anodize l i n e . a l l mass flow of metals examined was 3.6 kg/d which was 0.64 percent of t h a t for the anodize l i n e .

The over-

A n ana lys i s of wastewater flows w i t h respect t o f in i shed metal i s presented i n Table 6.18. With the exception of chromium, the anodize l i n e had the highest waste-metal flow r a t e , a s well as t he highest wastewater flow r a t e . In addi t ion , waste aluminum from the anodize l ine t o t a l l e d 2.95 percent of aluminum produced, on a mass bas i s , while t h a t from the pa in t l i n e t o t a l l e d 0.01 percent. Anodizing processes therefore include more aggressive f in i sh ing steps r e su l t i ng i n the re - moval of considerably more sur face metal and the consequent production of i n - creased quantit ies o f prec ip i ta ted metals for disposal .

Table 6.18. Wastewater and Metal Flows Normalized t o Production of Finished Metal

Surface Area . Mass of Finished Wastewater of Finished Metal Metal Const i tuent

Anodize Line Paint Line Anodize Line Paint . L i ne

F1 ow 73.4 m3/1000m2 4.2 l;i3/1000m2 27.8 m3/ton* 2.5 m3/ton*

A1

Cr

Cd

77.7 kg/1000m2 0.21 kg/1000m2 29.5 kg/ton 0.10 kg/ton

91.9 g/1000m2 221 g/1000m2 34.9 g / t o n 105.7 g/ton

0.088 g/1000m2 0.0023 g/1000m2 0.03 g/ton 0.001 g / t o n

Ni 7.6 g/1000m2 0.9 g/1000m2 2.9 g/ton 0.074 g / t o n

*metric ton (1000 k g )

Note: lm3/1000m2 = 24.5 ga1/1000 f t 2 lm3/ton = 0.12 g a l / l b

The t o t a l wastewater flow d u r i n g the survey period was estimated t o be 577.7 m3/d from anodize- and pa in t - l ine flows. percent of t he measured water flow used i n the two l i n e s and was therefore con- s idered t o be s a t i s f a c t o r y . The suspended s o l i d s concentration of the combined e f f l u e n t from the neu t r a l i za t ion basin was 3387 mg/l which was then ind ica t ive of .a suspended s o l i d s mass flow of 1956.7 kg/d . Examination of this value w i t h respect t o sludge production was not possible s ince sludge was n o t mechanically dewatered a t the p lan t b u t was per iodica l ly pumped t o sludge lagoons. However, from data i n Table 6.10, the aluminum content of the sludge solids were estimated t o be 0.258 g Al/gSS, which was w i t h i n the range of 0.206 t o 0.381 g Al/gSS presented by Saunders _ _ e t a l . (1982) f o r aluminum f i n i s h i n g sludges. inert suspended s o l i d s concentrat ion was not determined, using a typical r a t i o

T h i s value was equal t o 97.13

Although

36

of inert suspended sol ids t o t o t a l suspended s o l i d s of 0 .75, the aluminum content o f sludge s o l i d s was 0.344 g Al/gISS (ISS = inert suspended s o l i d s ) . This l a t t e r value was i n exce l l en t agreement w i t h a theore t ica l value for aluminum hydroxide of 0.346 g A l / g Al(OH), ind ica t ing i t t o be the major sludge p r e c i p i t a t e . sludge produced from the f a c i l i t y was therefore typical o f other a luminum-f in i sh - i n g sludges examined e a r l i e r (Saunders -- e t a l . , 1982) and was considered t o be typica l of those produced by a n o d i z i n g p lan ts . In addi t ion , research conducted by Kratz (1981) indicated t h a t sludges produced from pa in t - l i ne wastewaters had thickening proper t ies s imi l a r t o those produced i n anodizing p lan ts .

r a t e s were 124.6 kg/1000m2 and 53.17 k g / t o n . be 16 percent s o l i d s , wet sludge production r a t e s were estimated t o be 778.9 kg/1000m2 a n d 332.3 kg/ton. t o be equal t o 33.2 percent of the t o t a l mass o f f in i shed aluminum products. Considering t h a t the pa in t - l i ne wastewater contained only 0.3 percent ( (1 .74 k g / d ) / (567.7 k g / d ) ) of the t o t a l aluminum discharged, t he dewatered s ludge production was estimated t o be 1675 kg/lOOOmz and 636.9 k g / t o n . Therefore, t he estimated quan t i ty o f wet dewatered sludge was 63.69 percent of anodized metal , ind ica t ing the magnitude of t he sludge disposal problem associated w i t h anodizing processes.

The

With respect t o finished-metal production r a t e s , suspended s o l i d s production I f dewatered sludge was assumed t o

Dewatered sludge production therefore was estimated

SECTION 7

SEGREGATED NEUTRALIZATION OF CONCENTRATED ALUMINUM-FINISHING WASTES

A s i n d i c a t e d i n s e c t i o n 6 and by Saunders, st. (1982), concen t ra ted f i n i s h i n g s o l u t i o n s and wastewaters c o n t a i n a ma jo r p o r t i o n o f waste aluminum produced i n aluminum e t c h i n g and anod iz ing p l a n t s . e t ch , spent anod iz ing ac ids and ion-exchange r e enerants ( i n t e g r a l - c o l o r ano- d i z i n g ) . I n i t i a l r e s u l t s presented by Ledfore 9 1955) and Fukuyama _ _ e t a l . (1974) i n d i c a t e d t h a t n e u t r a l i z a t i o n o f concen t ra ted f i n i s h i n g s o l u t i o n s on a ba tch b a s i s r e s u l t e d i n f o r m a t i o n o f sludges w i t h i nc reased c r y s t a l l i n e s t r u c t u r e . These sludges, fu r thermore , were i n d i c a t e d t o have improved t h i c k e n i n g and de- w a t e r i n g p r o p e r t i e s . i n d i c a t e d improved t h i c k e n i n g and dewater ing p r o p e r t i e s were achieved w i t h s ludge suspensions produced by p e r i o d i c t rea tmen t o f concent ra ted a luminum- f in ish ing wastes a t h i g h temperature, i .e . , t h a t produced from hea t o f n e u t r a l i z a t i o n , a t a f u l l - s c a l e anod iz ing p l a n t . The s ludge produced through n e u t r a l i z a t i o n of con- c e n t r a t e d e t c h and a c i d i c anodize wastes had t h i c k e n i n g p r o p e r t i e s which were b e t t e r than those o f t h e conven t iona l a lum inum- f i n i sh ing s ludge examined and cou ld be dewatered t o a f i n a l s o l i d s c o n t e n t which was approx imate ly t w i c e t h a t achieved w i t h conven t iona l a lum inum- f i n i sh ing sludges.

From these pub l i shed r e s u l t s , i t was apparent t h a t n e u t r a l i z a t i o n o f spent, concent ra ted f i n i s h i n g s o l u t i o n s a t a lum inum- f i n i sh ing p l a n t s c o u l d have bene f i ca l impact on s ludge t rea tmen t and d i sposa l p r a c t i c e s . S ince temperature and pH of n e u t r a l i z a t i o n were p r i n c i p l e var i .ables, t hey were examined w i t h respec t t o i m - p a c t on s ludge t h i c k e n i n g and dewater ing p r o p e r t i e s . p r i o r t o t rea tmen t was t o be avoided and s i n c e an e leva ted suspension temperature was c r i t i c a l , t h e hea t generated by n e u t r a l i z a t i o n o f concent ra ted a c i d and a l k a l i was t o be used as the s o l e source o f hea t . To do t h i s , t h e a c i d i c and a l k a l i n e wastes were n o t t o be d i l u t e d and c o n c u r r e n t l y n e u t r a l i z e d w i t h l a r g e volumes o f r i n s e w a t e r s b u t were t o be segregated from a l l o t h e r waste so as t o a l l o w f o r t he development o f e l e v a t e d temperatures. Hence "segregated" n e u t r a l i z a t i o n o f con- c e n t r a t e d f i n i s h i n g wastes was pursued t o determine t h e e f f e c t s o f pH and temperature on s ludge c h a r a c t e r i s t i c s . p r o j e c t was t o i n v e s t i g a t e processes f o r use i n r e d u c t i o n i n o r rec lamat ion o f waste s ludges, t h e s tudy was focused on t h i c k e n i n g and dewater ing o f sludges pro- v i d e d by segregated n e u t r a l i z a t i o n .

EXPERIMENTAL REACTOR SYSTEM

These wastes i n c l u d e spent

I n a d d i t i o n , i n f o r m a t i o n presented by Saunders et al. (1982)

Since h e a t i n g o f spent wastes

Since t h e p r imary o b j e c t i v e o f t he research

I n v e s t i g a t i o n of segregated n e u t r a l i z a t i o n o f concent ra ted a1 uminum- f in ish ing wastes was conducted i n a continuous-flow,laboratory-scale r e a c t o r system shown

37

38

s c h e m a t i c a l l y i n F i g u r e 7.1. A double-wal led g lass r e a c t o r was used as t h e n e u t r a l i z a t i o n bas in. An e x t e r n a l c o o l i n g system was used t o c o n t r o l tempera ture b y c i r c u l a t i o n o f c o o l a n t th rough an o u t e r j a c k e t o f t h e r e a c t o r . was s t i r r e d w i t h a s i n g l e f l a t - b l a d e paddle and pH was mon i to red and c o n t r o l l e d w i t h an au tomat ic p H - c o n t r o l l e r system. were pumped i n t o t h e r e a c t o r u s i n g p e r i s t a l t i c pumps. a l k a l i n e e t c h s o l u t i o n was s e t a t a cons tan t va lue w h i l e t h e f l o w r a t e o f t h e a c i d i c anodize s o l u t i o n was r e g u l a t e d b y a p H - c o n t r o l l e r system t o m a i n t a i n a s e t pH va lue . on a b a t c h t i t r a t i o n r u n such t h a t t h e t o t a l f l o w r a t e was equal t o app rox ima te l y 76ml/min. Wi th a r e a c t o r volume of 0.7 l i t r e , t h e r e t e n t i o n t i m e i n t h e r e a c t o r was approx imate ly 8-10 min.

s t o r a g e vessel which was ma in ta ined a t t h e temperature o f t h e n e u t r a l i z e d suspen- s i o n . The r e a c t o r was opera ted f o r app rox ima te l y 4 hours t o c o l l e c t 18 l i t r e s o f n e u t r a l i z e d suspension. Fo l l ow ing comple t ion o f an exper imenta l run , t he suspen- s i o n was concent ra ted b y g r a v i t y and immedia te ly examined and, t h e i , q r a v i t v s e t t l e d f o r a 24-hour p e r i o d and examined again.

a t e l y p r i o r t o each exper imenta l r u n f rom p l a n t A3. t a i n e d i n separate, mixed r e s e r v o i r s a t room temperature and pumped i n t o t h e n e u t r a l i z a t i o n vessel a t c o n t r o l l e d r a t e s . C h a r a c t e r i s t i c s o f t h e wastes v a r i e d w i t h each exper imenta l run, however, da ta p resented i n Tab le 7.1 i n d i c a t e ranges o f va lues f o r t h e c h a r a c t e r i s t i c s o f t h e wastes used.

p laced on d e t e r m i n a t i o n o f process f e a s i b i l i t y and examinat ion o f t h e e f f e c t s o f temperature and pH on s ludge t h i c k e n i n g p r o p e r t i e s . d e t a i l e d e v a l u a t i o n o f s ludge dewater ing p r o p e r t i e s and t h e assoc ia ted e f f e c t s o f

The r e a c t o r

A l k a l i n e e t c h and a c i d i c anodize s o l u t i o n s The f l o w r a t e f o r t h e

I n d i v i d u a l f l o w r a t e s were s e t p r i o r t o each exper imenta l r u n based

N e u t r a l i z e d con ten ts were c o n t i n u o u s l y removed th rough a vacuum l i n e t o a

Samples o f a l k a l i n e e t c h and a c i d i c anodize s o l u t i o n s were c o l l e c t e d immedi- These s o l u t i o n s were main-

Exper imenta l s t u d i e s were conducted i n two phases w i t h emphasis i n phase 1

Phase 2 was focused on a

PH *

Tab le 7.1. Range o f C h a r a c t e r i s t i c s o f Spent Anodize and Etch Wastes f rom P l a n t A3

Parameter

Temperature*, O C

Aluminum, g/1 A l k a l i n i t y , g/1 (as CaC03) A c i d i t y

PH C o l o r

Sul f u r i c - A c i d Anodize S o l u t i o n

21-25

7.5-15

340-400

0.3-0.6 l i g h t brown

A l k a l i n e E tch S o l u t i o n

50-60 35.6-65

275-520 -

13.3-1 3.8

b lue-green

*Temperature o f s o l u t i o n a t t ime o f c o l l e c t i o n .

II

ACID ANODIZE

w u3

w

Figure 7.1. Schematic Diagram o f Laboratory-Scale Reactor System used for Segregated Neutralization Studies.

WASTE RESERVOIR

40

PHASE 1 - THICKENING

Experimental Techniques

Anodize and etch so lu t ions obtained from plan t A3 had c h a r a c t e r i s t i c s a s presented i n Table 7.2. highly viscous suspensions which were d i f f i c u l t t o mix and c o l l e c t . s tud ie s were therefore conducted w i t h one-tenth d i l u t i o n s o f the so lu t ions i n Table 7.2.

I n i t i a l s tud ies conducted w i t h these so lu t ions produced Subsequent

Table 7.2. Cha rac t e r i s t i c s o f Waste Solut ions Used i n Phase 1

Parameter

Temperature*, " C A l u m i n u m , g/1 Alka l in i ty , g/1 ( a s CaC03) Acidi ty , g/1 ( a s CaC03)

PH Color

Sul furic-Acid Anodize

Solut ion

25 15

400 0.3

l i g h t brown

Spent Etch

Solut ion

60 65

275 -

13.3 blue-green

*Temperature a t time of sampling.

Neutralized suspensions were co l l ec t ed a t o r near the temperature of neu t r a l i za t ion and analyzed immediately following co l l ec t ion . In t e r f ac i a l s e t t l i n g v e l o c i t i e s were determined using s t i r r e d (0 .3 cm/s), 1 - l i t r e graduated cy l inders ( in t e rna l diameter = 6 cm, i n i t i a l sludge h e i g h t = 0.4 m ) over a range o f suspended sol ids concentrat ions. A t o t a l of f ive experimental runs were made, as summarized fn Table 7.3.

Table 7.3. Experimental Conditions During Runs i n Phase 1

Experimental R u n 3

Parameter 5 - 4 - - 2 - 1 -

Neutral izat ion pH . . . . . . . . 7.1 7.0 7.3 5.5 8.5 Neutral izat ion Temperature, "C . 65 80 90 80 80

S e t t l i n g Analysis Temperature,'C I n i t i a l . . . . . . . . . . 48 80 72 80 80 After 24-hour s torage . . . 22 23 24 23 23

Waste Flow Rate Anodize Acid, m l / m i n . . . . 36 36 36 37.5 41.5 S p e n t Etch, m l / m i n . . . . . 40 40 40 38.5 34.5

41

Experimental Results

Two groups of experiments were conducted t o determine the e f f e c t s of ,

temperature and the e f f ec t s of neut ra l iza t ion pH on sludge thickening proper t ies .

Effects of Neutralization Temperature-- Since etch and anodize so lu t ions a r e typ ica l ly maintained a t temperatures of

50 t o 6OoC and 21 t o 25OC, respec t ive ly , and s ince the heat re leased during neut ra l iza t ion of concentrated etch and anodize wastes was calculated t o be s u f f i c i e n t t o r a i s e suspension temperature by 30"C, a range of temperatures of from 65 t o 90°C was chosen for ana lys i s . Experimental runs 1-3 were therefore conducted a t a neutral pH and 'neutral izat ion temperatures of 65, 80 and 90°C. I n i t i a l d i f f i c u l t i e s did no t allow f o r an analysis of sludge thickening proper t ies a t these temperatures f o r runs 1 and 3 . were, however, conducted immediately following co l lec t ion of 1 8 - l i t r e s of neutra- l ized sludge f o r a l l runs a t sludge temperatures of 48, 80 and 72°C f o r runs 1,2, and 3, respect ively. These data a re presented in Figures 7.2, 7.3, and 7.4. In addi t ion t o s e t t l i n g analyses conducted immediately following neu t r a l i za t ion , a l l sludges were s tored a t ambient temperature (22-24'C) f o r 24 hours and examined with respect t o thickening propert ies using i n t e r f a c i a l s e t t l i n g analyses. These d a t a a r e presented in Figures 7.2-7.4 with data col lected a t the elevated temperatures.

Examination o f data co l lec ted immediately following waste neu t r a l i za t ion , as presented in Figure 7.5, indicated t h a t neut ra l iza t ion temperature d i d n o t have a major impact on sludge thickening properties. Although var ia t ions were noted i n in t e r f ac i a l s e t t l i n g ve loc i t i e s a t s imi l a r concentrat ions, these were considered t o be within the range of reproducib i l i ty of the s e t t l i n g ana lys i s and ind ica t ive o f v i r tua l i den t i ca l responses. Data presented in Figures 7.2, 7.3 and 7.4 indicated t h a t analyses conducted a f t e r 24 hours of s torage and a t temperatures which were 33 t o 6OoC lower than temperatures of neut ra l iza t ion and 22 t o 57°C lower t h a n those of i n i t i a l s e t t l i n g analyses did n o t change appreciable from those conducted immediately following neut ra l iza t ion . In t e r f ac i a l s e t t l i n g veloci ty data f o r r u n 2 showed the g r e a t e s t divergence following storage for 24 hours. Data f o r t h i s r u n were a l so co l lec ted with the g rea t e s t temperature d i f fe rence (57OC) and the increased e f f e c t s of v i scos i ty d i f fe rences would be expected t o have had the g rea t e s t impact on these data .

d i d not have a major impact on sludge thickening propert ies over the range o f 65-90°C. neut ra l iza t ion temperatures of 65-9OoC d i d not change due t o aging f o r a 24-hour period a t ambient temperature a n d appeared t o r e t a in physical propert ies s imi l a r t o those developed immediately upon p rec ip i t a t ion .

Effects of Neutral izat ion pH--

were made a t pH values of 5.5 and 8.5 a t a neut ra l iza t ion temperature of 80°C as indicated in Table 7.3. following neut ra l iza t ion a t 80°C and a f t e r a 24-hour storage period a t 23°C and are presented i n Figures 7.6 and 7.7. temperature on thickening propert ies were s imi la r t o those demonstrated a t neut ra l iza t ion temperatures o f 65 a n d 90°C a t neutral pH. d i f ferences resu l ted from var ia t ions in neut ra l iza t ion DH.

Analyses of i n t e r f a c i a l s e t t l i n g ve loc i t i e s

A n i n i t i a l conclusion from these data was t h a t temperature o f neut ra l iza t ion

In addi t ion , the cha rac t e r i s t i c s of the sludge so l id s produced a t

To examine the e f f e c t s of pH on thickening proper t ies , two experimental runs

In t e r f ac i a l s e t t l i n g d a t a were col lected immediately

The e f f e c t s of neut ra l iza t ion and ambient

However, considerable

Using data presented f o r r u n 2 (Figure 7.3) with those f o r runs 4 and 5, the e f f e c t of neut ra l iza t ion pH i s indicated in Figure 7.8. resul ted in s iqn i f i can t increases in in t e r f ac i a l s e t t l i n g ve loc i t i e s a t a l l

Increased pH values

42

1 -

- ,-

RUN NO. 1 0 0 SETTLING

TEMP., OC 22 48

SUSPENDED SOLIDS CONCENTRATION, G/L

Fiqure 7.2. Interfacial Settlinq Velocity Data for Sludge Produced in Run 1.

43

10-1 1

SE'JTLING fEh?P., ' C 22.5 80


F i g u r e 7.3. I n t e r f a c i a l S e t t l i n g V e l o c i t y Data f o r Sludge Produced i n Run 2.

44

I I # I 1

I

1 10 100


Figure 7.4. Interfacial Settling Velocity Data for Sludge Produced i n Run 3.

45

10 I I I I I 1 - -

1 10 100


J 0 0

Figure 7.5. Effect o f Temperature on Settling Characteristics o f S1 udges Produced at Elevated Temperatures .and Neutral PH .

46

10-3

1 10 100


RUN NO. 4

SETTLING TEMP., "C

0 0 22.5 80

Figure 7.6. Interfacial Settling Velocity Data for Sludge Produced in Run 4.

..

47

1

TEMP., 'C

10-2 I 1 I l l I 1 , I

1 10 100


Figure 7.7. Interfacial Settling Velocity Data for Sludge Produced in Run 5.

48

..

SUSPENDED SOLIDS CONCENTRATION, GIL

Figure 7.8. Effect of Neutralization pH on Thickening Characteristics of Sludges Produced at 80'C.

49

suspended s o l i d s concen t ra t i ons . For example, a t a suspended so l i d s c o n c e n t r a t i o n o f approx imate ly 11 g/1, an inc rease i n n e u t r a l i z a t i o n pH f rom 5.5 t o 7.0 r e s u l t e d i n more than a 1 0 - f o l d inc rease i n s e t t l i n g v e l o c i t y and an inc rease o f pH f rom 5.5 t o 8.5 r e s u l t e d i n a 100- fo ld inc rease i n s e t t l i n g ve1ocit.v. pH then was a c r i t i c a l v a r i a b l e i n segregated n e u t r a l i z a t i o n systems and had more impact than d i d changesin n e u t r a l i z a t i o n temperature f rom 65 t o 90'C.

D i f f e r e n c e s i n s ludge t h i c k e n i n g p r o p e r t i e s , as i n d i c a t e d by i n t e r f a c i a l s e t t l i n g data, a r e w e l l e s t a b l i s h e d w i t h respec t t o des ign i m p l i c a t i o n s th rough use o f ba tch f l u x data, i .e. , t h e produc t o f i n t e r f a c i a l s e t t l i n g v e l o c i t y and suspended so l i d s concen t ra t i on . S ince i n t e r f a c i a l s e t t l i n g da ta f o r n e u t r a l pH va lues were s i m i l a r a t a l l temperatures, va lues a t 8OoC were used i n examining d i f f e r e n c e s i n ba tch f l u x da ta . As shown i n F igu re 7.9, improved t h i c k e n i n g p r o p e r t i e s were apparent f o r i n c r e a s i n g n e u t r a l i z a t i o n pH. For example, a sed imenta t ion b a s i n loaded w i t h a s o l i d s l o a d i n g r a t e o f 2 kg/m2.h (9.8 l b / f t 2 . d ) would produce a under f low suspension w i t h a s o l i d s c o n c e n t r a t i o n o f 4.1 percent , 2.8 percent and l e s s than 1.0 percent f o r suspensions n e u t r a l i z e d a t 80°C and pH values o f 8.5, 7.0 and 5.5, r e s p e c t i v e l y . Therefore, n e u t r a l i z a t i o n o f concentra- t e d f i n i s h i n g wastes a t an a l k a l i n e pH would r e s u l t i n the p roduc t i on o f a concen t ra ted under f low suspension from a g r a v i t y t h i c k e n e r w i t h an e f f e c t i v e area l e s s than t h a t r e q u i r e d f o r suspensions n e u t r a l i z e d a t lower pH values.

N e u t r a l i z a t i o n

PHASE 2 - DEWATERING

Exper imental Techniques

A s e r i e s o f dewater ing exper iments was conducted us inq one sample o f a c i d i c anodize waste and f i v e samples o f a l k a l i n e e t c h waste. r e q u i r e d s i n c e s t o r a g e f o r 7 t o 10 days r e s u l t e d i n s i g n i f i c a n t changes i n e tch p r o p e r t i e s which caused cons iderab le v a r i a t i o n i n t h e p r o p e r t i e s o f p r e c i p i t a t e s formed d u r i n g n e u t r a l i z a t i o n . w i t h respec t t o analyses conducted. o f spent e t c h w i t h one anodize waste sample were acceptable s ince i t would, i n p a r t , s i m u l a t e some o f t h e i n - p l a n t v a r i a t i o n s exoected w i t h f u l l imolementat ion o f

M u l t i p l e e tch samples were

The a c i d i c anodize waste was s t a b l e d u r i n g s to rage V a r i a t i o n s caused by use o f numerous samples

segregated n e u t r a l i z a t i o n . a r e oresented i n Table 7.4.

C h a r a c t e r i s t i c s ' o f t h e concent ra ted f i n i s h i n g wastes

Table 7.4. C h a r a c t e r i s t i c s o f Waste S o l u t i o n s Used i n Phase 2

Sul f u r i c - A c i d Spent E tch So lu t i ons Parameter Anodize

S o l u t i o n

Exper imenta l Run 1-5 1 2 3 4 5 Temperature, "C 21 50 50 50 50 50 Aluminum, g/1 7.5 51 45.8 28.2 35.6 41.3 A l k a l i n i t y , g/1 ( a s CaCD3) - 405 454 489 454 528 A c i d i t y , g/1 (as CaC03) 340 - - - - - PH 0.6 13.5 13.5 13.7 13.3 13.8 Co lo r L i g h t brown Dark Dark Dark Dark Oark

green green green green green *Temperature a t t ime o f sampling.

50

5

4

3

2

1

0

0 10 20 30 40


Figure 7 . 9 . Batch Flux Curves at pH Values o f 8.5 ( # l ) , 7.0 ( # 2 ) and 5.5 ( # 3 ) .

51

Spent etch c h a r a c t e r i s t i c s did n o t vary d r a s t i c a l l y and spent etch and ac id i c anodize solut ion cha rac t e r i s t i c s were s imi l a r to those used in phase 1 . concentrations were, however, t yp ica l ly lower than those of the i n i t i a l phase.

i n Table 7 . 5 , neut ra l iza t ion temperature was not a major process var iab le , 8 O o C was used as the neut ra l iza t ion temperature for a l l runs during phase 2 . major process var iab le and ranged from 5.5 t o 10.0. varied between 9 . 2 and 10.2 m i n which was s imi l a r t o phase 1 . experimental runs made d u r i n g phase 1 , i n f luen t concentrated wastes were not d i lu t ed b u t were used f u l l strength.

A l u m i n u m

Operational parameters used d u r i n g the f i v e experimental runs are presented Since r e s u l t s obtained in the i n i t i a l phase indicated t h a t

Hydraulic re ten t ion time pH was, futhermore,the

However, unlike

...

Table 7.5. Experimental Conditions During Runs i n Phase 2

Parameter Experimental Run

Neutral izat ion pH 8.5 7.0 5.5 10.0 8.5 Neutralization temperature, "C 80 80 80 80 80 Waste Flow [ la te

Anodize Acid, ml/min 28 32 35 28 29 Spent Etch, ml/min 60 66 63 60 60

5 - 4 - 3 - 2 - 1 -

Hydraulic Retention time, m i n 10.2 9.2 9.2 10.2 10.2 Suspended Solids*, g/1 101 97 100 86 91

*concentration i n neutral ized e f f luen t .

I n i t i a l examination of s p e c i f i c r e s i s t ance , f i l t e r y i e l d , and CST values f o r sludges generated i n run 1 was focused on determination of the e f f e c t s of s torage fo r 24 hours a t ambient temperature of the suspension produced by neut ra l iza t ion a t 80°C. propert ies resu l ted from s tor ing neutral ized suspensions f o r 24 hours (Medero, 1981). Since storage allowed f o r g rea t e r f l e x i b i l i t y and expansion of experimental inves t iga t ions f o r each r u n , a l l sludges generated in subsequent runs were examined only a t ambient temperature, 2 5 O C .

Experimental evaluations conducted f o r each sludge suspension produced in runs 1 t h r o u g h 5 were focused on s ludge dewatering proper t ies . f i l t e r y i e l d , and cap i l l a ry suction time (CST) measurements were used throughout t o e s t ab l i sh sludge dewatering propert ies as a function of suspended so l id s concentra- t ion . In addition,experimental examinations f o r runs 1-4 included invest igat ion of the e f f e c t s of vacuum on s p e c i f i c resistance aid f i l t e r y i e l d values f o r one suspended so l id s concentration. y i e l d were examined during runs 2 t h r o u g h 5.

The r e s u l t s indicated t h a t no appreciable differences in sludge dewatering

Spec i f ic r e s i s t ance ,

Final ly , the e f f e c t s o f time of cake formation on f i l t e r

52

Experimental Results

Run 1-- In t h i s r u n , sludge so l id s were produced a t a pH of 8.5 and a temperature of

8OoC and sludge dewatering analyses were conducted a t t he neut ra l iza t ion temperature and a t room temperature, i . e . , 25OC. Data co l lec ted a t 8OoC were s imi la r t o those co l lec ted a t 25OC and are presented elsewhere (Medero, 1981). Spec i f ic res i s tance var ied w i t h suspended so l id s concentration from 1.33 x 1O1O t o 2.95 x 10'O m/kg, as i l l u s t r a t e d in Table 7.6 and Figure 7.10. Cake so l id s concent ra t ion averaged 35.0 percent i n s p e c i f i c res i s tance analyses. The var ia t ion of specific res i s tance with applied vacuum was examined a t a suspended so l id s concentration of 20.8 g / l , from which a compressibi l i ty coe f f i c i en t ( S o ) of 1.23 was determined, as i l l u s t r a t e d in Figure 7.11.

In f i l t e r l eaf analyses , f i l t e r y i e ld f luc tua ted w i t h suspended so l id s concentration from 1.94 kg/m2.h a t 8 g/1 t o 104.8 kg/m2.h a t 157.8 g/ l as i l l u s t r a t e d in Table 7 . 6 and Figure 7.10, while cake so l id s concentration averaged 41.1 percent . The var ia t ion of f i l t e r y i e ld with applied vacuum was obtained a t a suspended so l id s concentration of 112.1 g/1 and i s presented in Figure 7.12. A l i n e a r correlation was used t o descr ibe the var ia t ion of f i l t e r y ie ld with vacuum a t a constant suspended so l id s concentration. A l i n e with a slope o f 1 . 4 2 x 10-7 kg/N.s and a least-squares cor re la t ion coe f f i c i en t o f 0.975 was obtained f o r t h i s re la t ionship . However, according t o f i l t r a t i o n theory, var ia t ion of f i l t e r y i e ld w i t h vacuum shouTd be a exponential function and data in Figure 7 .12 tend t o follow such a r e l a t ionsh ip . This i s discussed in d e t a i l in a l a t e r sec t ion .

as shown i n Table 7 . 6 and Figure 7.10.

Run 2-- In this r u n , sludge was generated a t a

Specific res i s tance varied between 2.33 x l oyo m/kg and 3.18 x 1 O ' O m/kg while cake so l id s concentration averaged 32.9 percent. Table 7.7 and Figure 7.13. vacuum were obtained a t suspended so l id s concentrations of 77.9 and 151.1 g / l , fo r which compressibi l i ty coe f f i c i en t s of 0.57 and 0.31, respec t ive ly , were obtained as i l l u s t r a t e d i n Figure 7.14. F i l t e r y i e ld varied from 20.7 kg/m2.h a t 16.4 g/1 t o 146.2 kg/mZ.h a t 151.1 g/1 as indicated in Tab le 7 . 7 and Figure 7.13. Cake so l id s concentration averaged 34.6 percent so l id s in these t e s t s . of vacuum and time of cake formation on f i l t e r y i e l d were examined a t a suspended so l id s concentration of 151.1 g / l , as i l l u s t r a t e d in Figures 7.15 and 7.16. Least- squares co r re l a t ion coe f f i c i en t s of 0.989 and 0.952 were obtained between f i l t e r y i e ld and applied vacuum and between f i l t e r y ie ld and time of cake formation, respect ively, ind ica t ing t h a t l i n e a r re la t ionships adequately described these f i l t e r y ie ld var ia t ions .

Run 3-- In t h i s experimental run, sludge was generated a t a pH of 5 . 5 and a tempera-

ture o f 8OoC and analyzed a t room temperature. Variations in spec i f i c res i s tance w i t h suspended so l id s concentration are presented i n Table 7.8 and Figure 7.17. Specif ic res i s tance varied from 2.25 x 1011 m/kg t o 3.1 x 10l1 m/kg and dewatered cakes averaged 31.3 percent so l id s in these t e s t s . on s p e c i f i c res i s tance was examined and comoressibi l i ty coef f ic ien ts of 0.42, 0.54 and 0.48 were determined a t suspended so l id s concentrations of 12.8,

CST values varied with suspended so l id s concentration from 23.7 t o 59.8 s

H of 7.0 and a temperature of 80°C.

These data a re presented in Relationships between s p e c i f i c res i s tance and applied

The e f f e c t s

The e f f e c t of applied vacuum

".

Table 7.6. Effect of Suspended Solids Concentation on Specific Resistance, Filter Yield and CST in Run 1 at pH 8.5

Suspended Specific Resistance Filter Yield CST Sol ids r ' Cake Solids Y Cake Solids (g/l) (lolo m/kg) (percent) (kg/m2.h) (percent) (second)

20.8 2.09 35.5 1.94 42.9 23.7

64.9 2.95 35.3 15.5 40.7 29.5

112.1 2.00

135.0 1.33 34.6 27.8 41.3 36.0 ul

w

34.6 53.6 40.4 41.8

157.8 1.56 34.9 104.8 40.0 59.8

54

0 SPECIFIC RESISTANCE

FILTER YIELD A

N I W Y

. 5- W - > a W

0 50 100 150 200


F i g u r e 7.10. V a r i a t i o n o f S p e c i f i c Resistance, F i l t e r Y i e l d and CST w i t h Suspended S o l i d s Concent ra t ion i n Run 1.

..

5 5

VACUUM PRESSURE, 104 NIM~

F i g u r e 7.11. E v a l u a t i o n o f C o m p r e s s i b i l i t y C o e f f i c i e n t , So, a t Suspended S o l i d s Concen t ra t i on o f 20.8 g / l for Run 1.

56

z

i

6

v)

N . z 5

b

W Y n

F

4 4

5 3 -

w - > K w

U

2

1

LEAST SQUARES CORRELATION COEFFICIENT = 0.975 -

-

I I 0 1 2 3 4 5 6 7 8

VACUUM PRESSURE, 104 N J M ~

F i g u r e 7.12. E f f e c t o f Vacuum on F i l t e r Y i e l d a t a Suspended S o l i d s Concentrat ion o f 112.1 g/1 i n Run 1.

..

57

U

L'?

h

h

W

7

n

m

c

... .

N

N

N

m

m

d

h

0

N

W

m

m

m

7

m

d

W

,.-

e

a, N

m

*

m

W

d a

In

m

m

e- W

N

W

* a

N

d

m

W

0

m

h

N

h

m

m

- u3 h

N

m

h

h

m

01

*

Ln

6.

m

m

7

P 0

a, N

m

m

m

N

a, N

- 7

0

h

- u3

d

m

N

W

d

- m

m

N

h

m

N

- 7

Ln

7

58

60 fn - a 5 2 w 5 0 - fn w K I

40 ' 1 s

30

1 200

- E 80 I ' 60 W' 0 z

. al

a - ?z 3 40 K 0 Y

8 0 w -

8ol 70 t 100

20

* O t

10

I I lo-' I


A FILTER YIELD

0 CST

i I 1 - 0 50 100 150 200


Figure 7.13. Variation o f Speci f ic Resistance, F i l t e r Yield and CST with Suspended Solids Concentration in Run 2

59

loo s so -- SS (G/L)

77.9 0.57

10 I I I t I I 1 1 1

1 2 4 6 8 10

VACUUM PRESSURE, i o 4 NIM~

E v a l u a t i o n o f C o m p r e s s i b i l i t y C o e f f i c i e n t , Sp,at Var ious Suspended S o l i d s Concentra- t i o n s for Run 2.

F i g u r e 7.14.

60

UJ

N I 0 Y r .

4 w > a w

-

5 - Y

0 1 2 3 4 5 6 7 8

VACUUM PRESSURE, io4 N / M ~ ..

Figure 7.15. Effect o f Applied Vacuum Pressure on F i l t e r Yield a t a Suspended Solids Concentration o f 151.1 g/ l and a t Room Temperature i n Experimental Run 2.

61

Figure'7.16. Effect o f Time o f Cake Formation on Filter Yield at a Suspended Solids Concentration of 151.1 g/1 and at Room Temperature in Experimental Run 2.

20 40 60 80 100

TIME OF CAKE FORMATION, S

Table 7.8. E f f e c t o f Suspended S o l i d s Concentrat ion on S p e c i f i c Resistance, F i l t e r Y i e l d and CST i n Run 3 a t pH 5.5

Suspended S p e c i f i c Resistance F i l t e r Y i e l d Sol I d s r Cake S o l i d s Y Cake S o l i d s CST

( lOlOm/kg) (percent ) (kq/m2.h) (percent ) (second) .-hLu.- 12.8 3.10 32.1 3.55 33.3 38.2

37.1 2.61 32.1 11.6 34.0 64.3

86.5 2.25 30.9 17.4 33.5 123.6

U> N 122.8 2.38 30.5 29.1 34.3 170.3

157.5 2.32 46.1 46.1 34.0 255.9

63

300

250

v)

a 200

> E w

5

3 a

$

t;

150

- 0

100

50

c3 Y I \

r r

rii 0 z a t; w a 0 Y 0 w n v)

10

8

6

4

2

1


A FILTER YIELD

0 CST

0 50 100 'I 50 200


F i g u r e 7.17. V a r i a t i o n o f S p e c i f i c Res is tance, F i l t e r Y i e l d and CST w i t h Susoended S o l i d s Con- c e n t r a t i o n i n Run 3.

64

86.5 and 157.5 g /1 , respect ively, as presented i n Figure 7.18. varied with suspended so l id s from 3.55 t o 46.1 kg/m2.h and dewatered cakes from f i l t e r l eaf tes ts had an average so l id s content of 33.8 percent. Variations of f i l t e r , y i e l d with vacuum and time of cake formation were b o t h obtained a t a suspended so l id s concentration of 157.5 g/1 and a re presented in Figures 7.19 and 7.20. As shown in the f igu res , least-squares co r re l a t ion coe f f i c i en t s of 0.958 and 0.933 were obtained f o r the re la t ionship of f i l t e r y i e ld with applied vacuum and for f i l t e r y i e ld and time of cake formation, respect ively. observed t o vary with feed suspended so l id s concentration from 38.2 t o 255.9 s , as presented i n Table 7.8.

Poor dewatering c h a r a c t e r i s t i c s were observed f o r t h i s sludge with a neut ra l iza t ion pH o f 5.5 when compared t o those obta ined f o r sludges in runs 1 and 2. Since dewaterincl oroperties de te r iora ted a t t h i s lower pH, a pH of 10.0

F i l t e r y i e l d

CST was

was se lec ted f o r sludge-neutral i za t ion t o evaluate the e f f e c t of an elevated pH on dewatering c h a r a c t e r i s t i c s .

Run 4-- In t h i s experimental run, sludge was generated a t a pH of 10.0 and a tempera-

Spec i f ic ture of 80°C and dewatering analyses were conducted a t room temperature. res i s tance varied w i t h suspended so l id s concentration from 3.36 x 109 t o 8.73 x l o 9 m/kg, as i l l u s t r a t e d in Table 7.9 and Figure 7.21. on spec i f i c res i s tance was examined and compressibi l i ty coe f f i c i en t s of 0.41, 0.07 and 0.55 were determined a t suspended so l id s concentrations o f 25.4, 74.3 and 184.4 g / l , respec t ive ly , as presented i n Figure 7.22.

Results from f i l t e r l ea f t e s t s showed a var ia t ion of f i l t e r y i e ld with suspended so l id s concentration of from 2.26 t o 91.4 kg/m2.h, as i l l u s t r a t e d in Table 7 .9 and Figure 7.21. dewatered sludge cakes a r i s i n g from these t e s t s . T h e e f f e c t of applied vacuum on f i l t e r y ie ld was examined a t a suspended so l id s concentration of 184.4 g / l . A l i n e a r r e l a t ionsh ip adequately described the var ia t ion of f i l t e r y ie ld w i t h applied vacuum a t a suspended so l id s concentration of 184.4 g / l , as i l l u s t r a t e d i n Figure 7.23. A least-squares co r re l a t ion coe f f i c i en t of 0.957 was obtained from t h i s r e l a t ionsh ip . y i e ld was examined a t a suspended so l id s concentration of 184.4 g / 1 . However, as opposed t o o ther sludges generated a t 8 0 T , no d e f i n i t e re la t ionship was observed between these two parameters. However, as i l l u s t r a t e d i n Figure 7.24, th ree of the four points presented tended t o follow a curve s imi l a r t o the ones observed i n runs 2 and 3 f o r the re la t ionship of f i l t e r y i e ld .wi th cake formation time. t o 51.0 seconds as indicated i n Table 7 .9 .

The e f f e c t of applied vacuum

A n average value of 48.7 percent so l id s was obtained f o r

The e f f e c t of time of cake formation on f i l t e r

The var ia t ion of CST w i t h suspended so l id s concentration was from 23.1

As observed from d a t a f o r t h i s and previous runs, the sludge produced a t a pH of 10.0 and 80°C showed the bes t f i l t r a t i o n propert ies in terms of s p e c i f i c res i s tance and CST. However, i t ' i s i n t e re s t ing t o observe t h a t the sludge from run 4 exhibited the lowest f i l t e r y ie ld values o f a l l the sludges generated i n the f i rs t four experimental runs. This f a c t suggested t h a t probably the dewatering c h a r a c t e r i s t i c s of the suspension generated a t the high pH of 10.0 and 80°C

- ~ ~ ~ - were somewhat a f fec ted by the sludge p a r t i c l e s i z e s , as well as other s ludge properties.

Run 5--

ture of 8OoC as in r u n 1,with the main purpose being t o obtain information a b o u t In t h i s experimental r u n , sludge was generated a t a pH of 8.5 and a tempera-

65

8 -

I I I I I I l l - . SS (G/L) - so -

0 12.8 0.42

- A 86.5 0.54

0 157.5 0.48

- -

- -

4t 1

1 2 4 6 8 i o VACUUM PRESSURE, 104 N / M ~

F i g u r e 7.18. E v a l u a t i o n o f C o m p r e s s i b i l i t y Co- e f f i c i e n t , So, a t Var ious Suspended S o l i d s Concen t ra t i ons i n Run 3,

66

1,

1:

1:

11

1c

9

8

7

LEAST SQUARES CORRELATION COEFFICIEN' = 0.958

/ 0 1 2 3 4 5 6 7 8

VACUUM PRESSURE, io4 N / M ~

F i g u r e 7.19. E f f e c t o f ADp l ied Vacuum on F i l t e r Y i e l d a t a Suspended S o l i d s Concen t ra t i on o f 157.5 g/1 i n Run 3.

67

1.7

1.6

1.5

v)

N 1.4 I c3 Y

ru

. k 5-

1.3

w - > 5 1.2 5 - LL

1.1

1.0

I

LEAST SQUARES CORRELATION COEFFICIENT = 0.933

0 , 1 I I

0 20 40 60 80 100


F i g u r e 7.20. E f f e c t o f Time o f Cake Format ion on F i l t e r Y i e l d a t a Suspended S o l i d s Concen t ra t i on o f 157.5 g/1 i n Run 3.

Table 7.9. Effect of Suspen--d Sol ids Concentration on Spec Resistance, Filter Yie d and CST i n Run 4 a t pH

C

Suspended Spec i f ic Resistance - Filter Yield

0 (1 03m/kq) (percent ) (ks/m2- h r (percent) (second) Sol ids r Cake Sol ids Y Cake Sol ids CST

25.4 8.73 40.0 2.26 53.8 23.1

74.3 3.85 39.4 - - 30.7

124.2 3.36 39.0 15.2 44.8 33.6

184.4 4.12 38.8 34,6 48.9 41.5

256.3 5.60 39.5 91.4 47.3 51 .O

m m

69

70

60

50

40

30

20

10

v)

- -

- 0 Y - I . ol z W'

z". a k tz a - 0

a

- w

; w

-

-

Figure 7 .21 .


A FILTER YIELD

1 0 100 200 300


Variation o f Speci f ic Resistance, F i l t e r Yield and CST w i t h Suspended Sol ids Concentration i n Run 4.

70

0 Y I . A 74.3 0.07

VACUUM PRESSURE, lo4 NIM2

Figure 7.22. Evaluation of Compressibility Coefficient, Sp. at Various Suspended Solids Concentra- tions in Experimental Run #4.

71

0 1 2 3 4 5 6 7 a

VACUUM PRESSURE, i o 4 NIM~

F i g u r e 7.23. E f f e c t o f Vacuum Pressure on F i l t e r Y i e l d a t a Suspended S o l i d s Concen t ra t i on o f 184.4 g/1 i n Run 4.

72

4 Y >

0 20 40 60 80 100


Figure 7.24. Effect of Time of Cake Formation on Filter Yield at a Suspended Solids Concentration o f 184.4 g/l in Run 4.

73

the v a r i a t i o n o f f i l t e r y i e l d

w i t h suspended s o l i d s s ludge generated i n r u n 1 was ob- t a i n e d a t a vacuum o f 6.8 x o f Hg), as opposed t o runs 2, 3 and 4 i n which a vacuum o f 5.1 x o f Hg) was u t i l i z e d . Therefore, i n f o r m a t i o n f rom run 5 a l lowed f o r comparison between f i l t e r y i e l d values ob- t a i n e d f o r t h e s ludge generated a t a pH o f 8.5 and a temperature o f 8OoC w i t h the values ob ta ined f o r o t h e r sludges generated a t o t h e r pH va lues . i n f o r m a t i o n about the v a r i a t i o n o f s p e c i f i c r e s i s t a n c e and CST w i t h suspended s o l i d s c o n c e n t r a t i o n was ob ta ined t o compare them w i t h t h e ones ob ta ined pre- v i o u s l y . S p e c i f i c r e s i s t a n c e v a r i e d w i t h suspended s o l i d s c o n c e n t r a t i o n f rom 2.87 x l o 9 t o 8.45 x l o 9 m/kg, as p resented i n Table 7.1Q and i n F igu re 7 . 2 5 . Dewatered cakes averaged 37.4 pe rcen t s o l i d s i n these t e s t s .

i t h suspended s o l i d s c o n c e n t r a t i o n a t a vacuum p r e s s u r e o f 5 .1 x i 0 4 N/m Y (15 i n . o f Hg). The v a r i a t i o n o f f i l t e r y i e l d

I n a d d i t i o n ,

The v a r i a t i o n o f f i l t e r y i e l d w i t h suspended s o l i d s c o n c e n t r a t i o n was observed t o be f rom 18.7 t o 525.6 kg/m2.h as i l l u s t r a t e d i n Tab le 7.10 and F i g u r e 7.25. An average o f 40.7 percent s o l i d s was observed f o r dewatered cakes a r i s i n g f rom these t e s t s . The v a r i a t i o n o f f i l t e r y i e l d w i t h cake f o r m a t i o n t ime was ob ta ined a t a cons tan t suspended s o l i d s c o n c e n t r a t i o n o f 159.6 g / l . A l i n e a r r e l a t i o n s h i p was observed t o be adeauate t o desc r ibe the i nc rease of f i l t e r y i e l d with i n c r e a s i n g cake f o r m a t i o n t imes a t c o n s t a n t suspended s o l i d s c o n c e n t r a t i o n , as i l l u s t r a t e d i n F i q u r e 7.26. t i o n c o e f f i c i e n t o f 0.946 was determined f r o m t h e r e l a t i o n s h i p ob ta ined between these two parameters. However, t he p o i n t s i l l u s t r a t e d i n t h e f i g u r e a l s o tended t o f o l l o w a s i m i l a r curve t o t h e ones observed i n runs 2 and 3 f o r t he r e l a t i o n - s h i p between f i l t e r y i e l d and cake f o r m a t i o n t ime. The v a r i a t i o n o f CST w i t h suspended s o l i d s c o n c e n t r a t i o n was observed t o be f rom 16.4 t o 37.2 s, as i l l u s t r a t e d i n Tab le 7.10. These were t h e l owes t CST values observed f o r a l l t h e sludges examined i n t h i s s tudy .

Run 6-- I n t h i s exper imenta l run, an a t tempt was made t o eva lua te t h e e f f e c t o f

p a r t i c l e s i z e on dewater ing c h a r a c t e r i s t i c s o f t h e aluminum f i n i s h i n g sludges generated a t h i g h temperature i n t h i s study. w i t h sludges generated i n runs 1 t o 4 u s i n q the s o e c i f i c r e s i s t a n c e t e s t w i t h some m o d i f i c a t i o n s . The usua l f i l t e r medium u t i l i z e d f o r runn ing s p e c i f i c r e s i s t a n c e t e s t s ( i . e . , Whatman #l f i l t e r paper) was rep laced by the f i l t e r - l e a f media u t i l i z e d i n f i l t e r l e a f analyses. t h e f i l t r a t e was c o l l e c t e d and analyzed f o r suspended s o l i d s concen t ra t i on . The s p e c i f i c r e s i s t a n c e va lues ob ta ined i n t h i s r u n a r e presented i n Tab le 7.11 and w e c o m p a r a b l e t o s p e c i f i c r e s i s t a n c e values ob ta ined p r e v i o u s l y w i t h Whatman #1 f i l t e r media.

A Teast-squares c o r r e l a -

T h i s exper imenta l r u n was conducted

A f t e r f i l t r a t i o n o f samples,

Table 7.10. E f f e c t o f Suspended So l i ds Concentrat ion on S p e c i f i c Resistance, F i l t e r Y i e l d and CST i n Run 5 a t pH 8.5

Suspended S p e c i f i c Resistance F i l t e r Y i e l d S o l i d s Cake S o l i d s Y Cake S o l i d s CST (4/1) ( 1O9m7kq) (percent ) ( kq/m2. h ) (percent ) ( second)

21 .o 2.87 37.0 18.7 41.7 16.4

67.5 - - 33.3 43.3 18.4

113.1 8.45 35.6 69.1 42.4 24.6

- - 159.6 142.6 39.3 29.9

288.9 4.05 39.7 525.6 36.7 37.2

75

40

35

30

25

20

15

10

VJ

-

-

-

-

-

-

-

m


F i g u r e 7.25. V a r i a t i o n o f S p e c i f i c Res is tance, F i l t e r Y i e l d and C a p i l l a r y CST w i t h Suspended S o l i d s Con- c e n t r a t i o n i n Run 5 .

76

IW I /o I I I

I- 30

LEAST SQUARES CORRELATION COEFFICIENT = 0.946

20 0 20 40 60 80 100


F i g u r e 7.26. E f f e c t o f Time o f Cake Format ion on F i l t e r Y i e l d a t a Suspended Solids Concen t ra t i on o f 159.6 g/1 i n Run 5.

77

Table 7.11. Results f o r Specif ic Resistance Tests in Run 6

Suspended Sol ids Sample - Concentration Spec i f ic Resistance

From Feed F i 1 t r a t e r Cake Solids Run U (mq/l) (1 O l o m / k q ) (percent )

1 157.8 28.0 1.43 37.8

2 112.8 43.4 3.38 32.8

3 " 157.5 15.3 16.2 41.7

4 184.4 32.2 0 . 4 2 40.4

DISCUSSION

Thickeni nq

f a c i l i t a t e d by use of batch f lux d a t a i n Figure 7.9, i n conjunction w i t h s imi l a r d a t a f o r a conventional sludge produced a t p lant A3 t h r o u g h neut ra l iza t ion of a l l anodizing wastewaters a t ambient temperature and a pH of 7.2. Since the sludge produced by neut ra l iza t ion a t pH of 8 .5 exhibited the bes t s e t t l i n g propert ies o f . the sludges examined, batch-flux data f o r t h i s s ludge and a conventional sludge from plant A3 (Saunders -- e t a l . , 1982) a re presented i n Figure 7.27. f lux values f o r the segregated neut ra l iza t ion sludge indicated improved thickening performance as compared t o a conventional sludge.

To evaluate the impact of implementation of segregated neut ra l iza t ion ,on thickened s ludge quantit ies, an example i s presented f o r a typical extrusion and anodizing p lan t . and i s based on data included i n Section 6 and as presented by Saunders - _ e t a l . (1982). To determine the impact of segregated neut ra l iza t ion on sludge volume, an i n i t i a l ana lys i s was made assuming t h a t a l l wastewaters were t rea ted by conventional neut ra l iza t ion and t h a t the batch-flux curve f o r plant A3 in Figure 7.27 was ind ica t ive of thickening propert ies of t h i s sludge. A second analysis was then conducted assuming t h a t only rinsewater was t rea ted d u r i n g two s h i f t s and t h a t spent f in i sh ing so lu t ions were s tored f o r treatment d u r i n g a t h i r d s h i f t . Therefore, neutral ized rinsewater was thickened during two s h i f t s and neutral ized spent f in i sh ing so lu t ions were thickened i n the same sedimentation b a s i n during the th i rd s h i f t . As indicated i n Table 7.13, implementation o f segregated neut ra l iza t ion r e s u l t s i n improved thickening of conventional sludge s o l i d s , due t o decreased f lux rates on the sedimentation basin, and an overal l reduction i n sludge volume. Using conventional neut ra l iza t ion alone resu l ted in da i ly p lo-

neut ra l iza t ion for concentrated f in i sh ing wastewaters resul ted in da i ly production of 33.9111~ of sludge a t 44.2 g / l . Al though the same mass of sludge so l ids were produced ( i . e . , 1 .5T/d of dry suspended s o l i d s ) in each a l t e r n a t i v e , implementa- t i o n of segregated neut ra l iza t ion resul ted i n a 72 percent reduction in sludge volume.

Evaluation of the impact of segregated neut ra l iza t ion on sludge thickening i s

The h igher

The descr ipt ion o f the example p l a n t i s presented in Table 7.12

7. .. ~ duction ion of lZOm3 of s ludge a t 12.5 g/l while implementation of segregated

Therefore,provision of 56m3 of s torage f o r concentrated f in i sh ing solut ion

3.0

2.0

1.0

0

7a

I I 1 I I I 1 1 I

HIGH TEMP. SLUDGE pH 8.5, T = 80°C

1 \ I 1 \ 1 t 1 1 I

20 30 40


0 10

Figure 7.27. Batch Flux Curves for Sludges Produced by Conventional and Segregated Neutralization of Aluminum-Finishing Wastes.

79

and n e u t r a l i z a t i o n o f these s t o r e d wastes d u r i n g a t h i r d s h i f t would s i g n i f i c a n t l y reduce s ludge volume.

Tab le 7.12. D e s c r i p t i o n o f A luminum-Fin ish ing P l a n t Used i n E v a l u a t i o n o f Impact o f Segregated N e u t r a l i z a t i o n on Thickened Sludge Volume '

F i n i s h e d Meta l Capaci ty: 20T/d(400T/mo) P1 a n t Opera t i on: two 8- hour s h i f t s l d a y Wastewater Composi t ion

Aluminum Losses: Sludge Aluminum con ten t : Water Use :

Wastewater: 90% = r i n s e w a t e r

Waste Meta l ( A l ) : 30% = r i n s e w a t e r

30g/kg o f f i n i s h e d meta l 0.4 kg/kg suspended s o l i d s

28m3/T o f f i n i s h e d metal

Water Sources

10% = spent f i n i s h i n g s o l u t i o n s

70% = spent f i n i s h i n g s o l u t i o n s

Wastewater Treatment N e u t r a l i z a t i o n Bas in Sed imenta t ion Basin: Sur face Area = 65m2

-

Table 7.13. Comparison o f t he Use o f Convent ional and Segregated N e u t r a l i z a t i o n a t a T y p i c a l Aluminum Ex t rus ion lAnod ize P l a n t

Thickened Sludge Storage Volume Concen t ra t i on Volume

m3 q / 1 m3

I. Convent ional N e u t r a l i z a - 0

11. Convent ional N e u t r a l i z a -

t i o n

t i o n w i t h Segregated N e u t r a l i z a t i o n o f Concentrated Wastes

A. Rinsewater 0 B. Concentrated

12.5 120

54.0 8.3

Was t e s - 56 - 41 .O 25.6 __ C . T o t a l Combined -.

Wastes 56 44.2 33.9

80

The above example serves t o ind ica te the potent ia l impact of the use of segregated neu t r a l i za t ion . In the example, concentrated wastes were neutral ized da i ly . However, t h i s could be performed weekly by providing addi t ional s torage volume o r could be performed continuously by providing a separa te neut ra l iza t ion system. This separate neut ra l iza t ion system would, however, contain only about 10 percent of the volume of a conventional system. Crys ta l l ine so l id s produced during segregated neut ra l iza t ion could be mixed w i t h conventional r insewaters and set t led concurrently. Therefore, the benef i t s of decreased sludge volumes could be rea l ized a t aluminum-finishing plants using numerous treatment s t r a t e g i e s . The ul t imate benef i t in a l l such cases would be decreased sludge volume which would, f o r example, decrease sludge t ranspor ta t ion cos t s , decrease volume requirements for sludge lagoons or increase performance of mechanical dewatering systems.

Dewatering

Dewatering proper t ies of sludges produced by segregated neut ra l iza t ion were examined using s p e c i f i c res i s tance , CST and f i l t e r y ie ld measurements, as well as dewatered cake s o l i d s , and compressibi l i ty coe f f i c i en t measurements. Process var iables w h i c h were invest igated included neut ra l iza t ion pH and pressure vacuum leve l s . I n i t i a l inves t iga t ions confirmed t h a t measurements of dewaterabi l i ty taken immediately following waste neut ra l iza t ion a t neut ra l iza t ion temperature (80°C) were v i r t u a l l y ident ica l t o those co l lec ted a f t e r 24 hours of s toraqe a t ambient temperature (Medero, 1981). Therefore, a l l experimental inves t iga t ions were based on measuremenfs taken a f t e r s torage for 24 hours a t ambient temperature (25OC).

Neutralization nH--

The e f f e c t s of other process var iables a r e examined below.

-. . - - - . Speci f ic R k i s t a n c e and CST-- The re la t ionships obtained between s p e c i f i c

res i s tance and c a p i l l a r y suction time (CST) and suspended so l id s concentrations f o r a l l sludges a r e i l l k t r a t e d i n Figures.7.28 and'7.29. shown in each f igu re f o r a 'pH of 8.5, i .e., runs 1 and 5.

pended so l id s concentration a t a l l neut ra l iza t ion pH values. This response was typical of such measurements s ince s p e c i f i c res i s tance values a r e normalized t o the dry mass o f dewatered cake. A decrease in spec i f i c r e s i s t ance , however, was observed with increasing neut ra l iza t ion pH values. exhibited the highest s p e c i f i c res i s tance w i t h values in the range of 2.25 x 10I1 t o 3.10 x lo1' m/kg . Sludges generated a t pH values of 7.0 and 8.5 ( r u n 1) exhibi ted lower s p e c i f i c res i s tance values than those observed a t pH 5.5.

m/kg. Therefore, sludge neutral ized a t a pH of 5.5 exhibi ted spec i f i c res i s tance values which were approximately 10-fold g rea t e r t h a n those observed f o r sludges a t pH values of 7.0 and 8.5. A f u r t h e r decrease in spec i f i c res i s tance was observed when neut ra l iza t ion pH was increased t o 10.0. ,Specific res i s tance values a t t h i s pH varied between 3.36 x l o 9 and 8.73 x l o 9 m/kg and were from 72 t o 75 percent lower than those obtained a t pH values of 7.0 and 8.5 in runs 2 and 1 , respect ively.

-observed f o r s p e c i f i c r e s i s t ance , as shown in Figure 7.29. Although no s i g n i f i c a n t d i f fe rences i n CST values were observed a t low suspended so l ids concentrat ions, d e f i n i t e decreases i n CST values were observed with increasing neut ra l iza t ion pH values a t high suspended so l id s concentrations. The highest CST values observed were those f o r a neut ra l iza t ion pH of 5.5.

Two relationshiDs a r e

Specif ic res i s tance values remained r e l a t i v e l y s t a b l e w i t h increased S W S -

Sludge generated a t pH 5.5

S e c i f i c res i s tance values f o r these sludges ranged between 1.33 x 1OIo and 3.18 x 10 P o

The e f f e c t of neut ra l iza t ion pH on c a p i l l a r y suction time was s imi la r t o t h a t

A s ign i f i can t decrease in CST of

81

1012

101’

:: . I W’ 0 z a & Gj w K 0 - 5 10’0 w a

109

I I I I I - - - - - -

-Q’ pH 5.5 - - - - - - - - -

- -

pH 8.5 (RUN NO. 1) - - - - - - - -

- PH 8.5 (RUN NO. 5 ) -

I I I I I

Figure 7.28. Variation o f Speci f ic Resistance w i t h Suspended Sol ids Conrentration Produced a t Various pH Values.

a2

200

v)

2 100 a 80 >

w 60 a I I

- 5 v)

40 - 5

20

10

pH 8.5 (F JN IO.

pH 7.0 pH 10.0

pH 8.5 (RUN NO. 5)

0 50 100 150 200 250 300


Figure 7.29. Variation o f CST w i t h Suspended Sol ids Concentration a t Various pH Values.

83

between 42 and 72 percent was observed when sludge neut ra l iza t ion pH was increased t o 7.0. Sludges produced a t pH values of 7 .0 , 8.5 a n d 10.0 in runs 2 , 1 and 4 , respec t ive ly , exhibited s imi la r CST values a t low suspended so l id s concentrations whereas, a t high suspended so l id s concentrat ions, a decrease in CST was observed with increasing neut ra l iza t ion pH. lowest CST values of the l a t t e r three s ludges, indicat ing the best dewatering propert ies of the sludges examined. CST increased w i t h increasing suspended so l id s concentration and the r a t e of increase in CST increased with suspended so l id s concen t r a t ion , indicat ing a n exponential re la t ionship . A l i n e a r re la t ionship was observed in the semilogaritmic p lo t i n Figure 7.30 o f CST and suspended so l id s concent ra t ion and was corroborated by the least-squares cor re la t ion coe f f i c i en t s ( r ) presented i n the f igu re .

As i l l u s t r a t e d in Figures 7.28 and 7.29, s i g n i f i c a n t d i f fe rences were observed f o r sludges produced a t pH 8.5 i n runs 1 and 5. The sludge i n r u n 5 had improved dewatering c h a r a c t e r i s t i c s , in terms of spec i f i c res i s tance and CST, over those i n run 1 . Also, the sludge in run 5 exhibited the best dewatering c h a r a c t e r i s t i c s in terms of CST f o r a l l the sludges examined. These differences were a t t r i b u t e d t o changes i n waste c h a r a c t e r i s t i c s s ince a new etch wastewater sample was used i n each one of the runs. However, i t i s apparent t h a t improved dewateri.ng performance was achieved a t pH values of 8 .5 (runs 1 and 5) and 10.0 in a l l cases , when compared t o r e s u l t s achieved a t lower pH values, Alkaline pH values were therefore indicated t o be preferred over neutral and ac id ic pH values for segregated neutral- i za t i on.

F i l t e r Yield-- The re la t ionships between f i l t e r y ie ld and suspended so l id s

Sludge produced a t a pH. of 10.0 showed the

concentration are presented in Figure 7.31. f i l t e r y ie ld analyses were conducted a t a vacuum of 6.8 x 104 /m2(20 i n . of Hgj

used d u r i n g f i l t e r y i e l d analyses.

from 5 . 5 t o neutral and s l i g h t l y a lka l ine pH values, crease i n neut ra l iza t ion pH caused a decrease in f i l t e r y ie ld . viously, s p e c i f i c res i s tance and CST values f o r these sludges decreased w i t h neu t ra l iza t ion pH, indicat ing t h a t improved f i l t r a b i l i t y could be achieved by increasing neut ra l iza t ion pH values. T h i s would ind ica te t h a t higher f i l t e r y i e lds could be obtained when increasing neut ra l iza t ion pH under prac t ica l conditions. However, s ince f i l t e r l eaf t e s t s provide a r e a l i s t i c approximation of vacuum f i l t e r operat ion, f i l t e r - l e a f data were used in se lec t ing optimum neut ra l iza t ion pH f o r improving sludge dewatering c h a r a c t e r i s t i c s a t the reference plant .

values increased with suspended so l ids concentration a n d the highest f i l t e r y ie ld values were observed f o r sludges neutral ized a t pH values of 7.0 and 8.5. sludge generated a t a pH of 5.5, f i l t e r y i e lds were 68 t o 91 percent lower t h a n those observed a t pH values of 7.0 and 8 .5 .

The sludge produced by neut ra l iza t ion a t a pH of 10.0 exhibited the lowest - f i l t e r y ie ld values f o r a l l the sludges examined. F i l t e r y ie ld values for t h i s sludge ranged frm 2.3 t o 91.4 kg/m2.h . This sludge, however, showed exce l len t f i l t , r a t i o n propert ies i n terms of spec i f i c res i s tance and CST when compared t o other sludges examined, indicat ing t h a t high f i l t e r y i e lds would have been expected. Therefore, f i l t e r y i e ld data obtained f o r t h i s sludge suggested

No d a t a a r e presented f o r r u n 1 s ince

as opposed t o other sludges in which a vacuumof. 5.1 x lo4 N/m ! (15 i n . " of Hg) was

. .

A n increase in f i l t e r y ie ld was observed when increasing neut ra l iza t ion pH However, a subsequent in-

As discussed pre-

As observed i n Figure 7.31, f i l t e r y ie ld values of sludges a t various pH

For the

~

a4

- I I 1 I I

RUN NO. R - 1000 - 0 1 0.962

A 2 0.996

- 3 0.991 0

- 0 4 0.989 -

- - - - - - - -

- 5 0.991 0 - - -

Figure 7.30. Variation o f CST with Suspended Sol ids Concentration a t Various pH Values.

a5

d

Figure 7.31. Variation o f F i l t e r Yield w i t h Suspended Solids Concentration a t Various DH Values.

86

t h a t f i l t r a t i o n c h a r a c t e r i s t i c s m i g h t have been affected by small p a r t i c l e s causing blinding of the f i l t e r - l e a f medium during f i l t r a t i o n . I f t h i s were the case, however , spec i f i c res i s tance o f the sludge wou ld increase as a r e s u l t of blinding during f i l t e r - l e a f ana lys i s . media typ ica l ly used w i t h the s p e c i f i c res i s tance t e s t ( i . e . , Whatman No. 1 paper) with s p e c i f i c res i s tance r e s u l t s obtained with the media used on the f i l t e r - l e a f apparatus ( i . e . , NY-319F 3/1 Br Twill multif i lament c l o t h ) indicated t h a t media blinding was n o t an apparent cause of the unusually low f i l t e r y i e ld data (Medero, 1981). Low f i l t e r y i e lds observed for the sludge a t a neut ra l iza t ion pH of 10.0 could a l s o be a t t r i bu ted t o s e t t l i n g of the sample during f i l t e r - l e a f ana lys i s . Good s e t t l i n g c h a r a c t e r i s t i c s were expected f o r the sludge, which showed exce l len t f i l t r a t i o n propert ies i n terms of spec i f i c res i s tance and CST. provided in the f i l t e r - l e a f ana lys i s could have been i n s u f f i c i e n t t o keep the so l id s i n suspension resu l t ing i n blinding of the f i l t e r by small p a r t i c l e s and decreased accumulation o f sol ids on the f i l t e r surface. Therefore, i t i s apparent t h a t a t a neut ra l iza t ion pH o f 10.0, a sludge t h a t exh ib i t s good dewatering pro- pe r t i e s may be otained b u t , unfortunately, the sludge would probably cause operational problems d u r i n g vacuum f i l t r a t i o n e i t h e r by s e t t l i n g or other unknown condi t ions, r e su l t i ng in low f i l t e r y i e l d s . Consequently, l a rge r vacuum-filter surface areas would be required t o dewater the sludge.

The optimum neut ra l iza t ion pH for improved sludge dewatering propert ies by segregated neut ra l iza t ion of spent e tch and anodize wastewaters an an aluminum- f in i sh inq plant appeared t o be in the range of 7.0 t o 8.5. these of the cake s o l i d s produced by dewatering.

Comparison of spec i f i c res i s tance r e s u l t s obtained with

Slow ag i t a t ion

Select ion between values of neut ra l iza t ion pH i s a f fec ted by the so l id s or moisture content

Cake Solids-- The re la t ionship between cake so l id s concentration and suspended

Cake so l id s concentrations ranged from 33 percent t o 53 percent so l id s and so l id s concentration obtained from f i l t e r - l e a f analyses a re presented in Figure 7.32. were much higher than cake sol ids concentrations t,ypical l y achieved with conventional aluminum-finishing sludges. neut ra l iza t ion pH increased. duced a t a neut ra l iza t ion pH of 10.0 were enhanced by a h i g h cake so l id s concentra- t ion a f t e r dewatering, with cake so l id s content f luc tua t ing between 45 and 53 oercent , which were the highest values observed. Sludge produced a t a neut ra l iza t ion pH of 7.0 had cake so l id s concentrations of 34 t o 35 percent. These were only s l i g h t l y higher than those f o r sludge produced a t a neut ra l iza t ion pH of 5.5,which was the sludge with the poorest dewatering proper t ies of a l l the sludges examined. Sludge produced a t a neut ra l iza t ion pH of 8 .5 had cake so l id s concentrations ranging from 37 t o 43 percent and were grea te r t h a n those observed f o r the sludge produced a t a neutral pH.

examined, the s ludge produced a t a neut ra l iza t ion pH of 8.5 exhibited the best over- a l l dewatering c h a r a c t e r i s t i c s , espec ia l ly when f i l t e r y ie ld values and cake so l id s content were considered. Sludges produced a t a higher pH had increased so l id s con- t e n t s b u t lower f i l t e r y i e lds while sludges produced a t lower pH values had lower dewatering r a t e s and lower cake so l id s contents. sented herein, i t i s apparent t h a t a neut ra l iza t ion pH of 8.5 produced the best sludge proper t ies a n d should be more c lose ly examined i n a p i lo t - sca l e system.

In a d d i t i o n , cake so l id s contents increased as The exce l len t dewatering propert ies of the sludge pro-

Examination of Figures 7.28, 7.30 and 7.32 indicated t h a t of a l l sludges

Therefore, from the s tudies pre-

a7

55

50

W Y

35 2

30

I I I

0 50 100 150 200 250 300


F i g u r e 7.32. E f f e c t o f Suspended S o l i d s Concent ra t ion on Cake S o l i d s Concen t ra t i on i n F i l t e r - l e a f Analyses f o r Var ious N e u t r a l i z a t i o n pH Values.

88

S1 udge Compressibi 1 i tp-Compressi b i l i ty coe f f i c i en t s ( S O ) were obtained for segregated neut ra l iza t ion sludges a t various suspended so l ids concentrations using spec i f i c res i s tance measurements t o o b t a i n average values f o r each suspension. of compressibi l i ty coe f f i c i en t s reported f o r alum sludges resu l t ing from the treatment of surface waters f o r drinking purposes (Novak and Montgomery, 1975; Novak and Langford, 1977; Glenn -- e t a l . , 1973; Bal l , 1978).

Compressibility coe f f i c i en t s are measures of var ia t ions of sludge spec i f i c res i s tance withvacuum pressure. pervious cake a t high vacuum due t o squeezing and compaction of the sludge cake during sludge f i l t r a t i o n , therefore , increasing sludge r e s i s t ance t o f i l t r a t i o n and decreasing sludge y i e ld on a mechanical f i l t e r . i b i l i t y should decrease with a n improvement in dewatering propert ies of the sludge.

Average compressibi l i ty coe f f i c i en t s obtained f o r sludges produced a t the four neut ra l iza t ion pH values examined are presented in Figures 7.33. exception of the .value of SQ = 1.23 a t a pH v a l u e of 8.5 ( r u n l ) , coe f f i c i en t s of compressibi l i ty decreased w i t h increasing neut ra l iza t ion pH. in r u n 1 was f o r a s ing le , d i l u t e (20.8 g / l ) suspension while a l l other values were determined using two t o th ree concentrated suspensions. associated with determination of s p e c i f i c res i s tance of d i l u t e suspensions could therefore account f o r t h i s s ing le extraneous value. Using the do t t ed l i n e in Figure 7.33,a cor re la t ion coe f f i c i en t of 0.999 was obtained. apparent t h a t sludge compressibi l i ty decreased with increasing neut ra l iza t ion pH values and t h a t the low values were indica t ive of sludges w i t h exce l len t dewatering proper t ies .

Vacuum Pressure-- As indicated in Figure 7.34, f i l t e r y ie ld increased w i t h vacuum pressure f o r

a l l sludges a t constant i n i t i a l suspended so l id s concentrations. The increase was well described by a l i nea r re la t ionship as indicated by least-squares co r re l a t ion coe f f i c i en t s of 0.956 t o 0.989. Therefore, f i l t e r y i e ld increased in d i r e c t pro- portion t o the vacuum pressure indicat ing t h a t g rea te r so l id s capture could be achieved by increasing vacuum pressurewith a subsequent decrease in the vacuum- f i l t e r surface area required t o dewater these sludges a t a constant i n i t i a l suspended so l id s concentration.

The var ia t ion of cake so l id s concentrations with vacuum obtained from f i l t e r l eaf t e s t s f o r each sludge i s presented in Figure 7.35. A n increase i n cake so l id s concentration was observed w i t h increased vacuum and the r a t e of increase o f cake s o l i d s with vacuum pressurewas constant f o r a l l sludges examined. Therefore, a t a constant i n i t i a l suspended so l id s concentration an increase i n vacuum pressureincreased sludge so l id s content making the sludges more manageable and amenable t o u l t imate d isposa l .

Comparison of data i n Figure 7.35 developed with f i l t e r - l e a f analyses w i t h those i n Figure 7.32 from s p e c i f i c res i s tance analyses indicated t h a t sludges produced a t a neu t r a l i za t ion pH of 10 had the highest so l id s content following de-

In addi t ion , sludge produced a t a neut ra l iza t ion pH of 8.5 had the next highest cake so l id s content followed by those produced a t pH values o f 5.5 and 7 . 0 . . Therefore, increased neut ra l iza t ion pH resul ted in production o f dewatered cakes with higher so l id s contents which could be more e f f ec t ive ly dewatered with increases i n vacuum pressure.

Compressibility values ranged from 0.34 t o 1 .23 and were i n the range

A sludge of high compressibi1it.v produced a n im-

Therefore, sludge compress-

With the

The value determined

D i f f i c u l t i e s

I t was therefore

---watering in bo th analyses.

1.5

vp 5 1.0 z

E Lu

2 8 I

Y 0 I- z w 2 0.5 Y U w

-

8

0

89

I I

r2 = 0.999 (See text p. 88)

5 6 7 a 9 10 11

SLUDGE NEUTRALIZATION pH

Figure 7.33. Effect of Sludge Neutralization pH on Sludge Compressibility Coefficients.

90

50

40

v)

"I 30 0 Y

. 0

*:

5-

k- 2c 3

Y >

it

10

C

I I I ~ I J N .'pH S'S (GIL) ' R

o - - 1 8.5 112.1 0.975

A 2 7.0 151.1 0.989

0 3 5.5 157.5 0.958 /d 0 4 10.0 184.4 0.956

A/

0 1 2 3 4 5 6 7 8

VACUUM PRESSURE, 104 N I M ~

..

Figure 7.34. Effect o f Vacuum Pressure on F i l t e r Yield a t Various pH Values.

91

VACUUM PRESSURE, i o 4 N I M ~

Figure 7 . 3 5 . Effec t o f Aoolied Vacuum on Cake Solids Concentration.

92

Summary--

so lu t ions on sludge dewatering c h a r a c t e r i s t i c s , data i n Table 7.14 are presented. Since the concentrated f in i sh inq so lu t ions were obtained from plan t A3, data f o r sludges produced by conventional neu t r a l i za t ion a t p l a n t A3 a r e included f o r comparison purposes. s e l ec t ed t o compare f i l t e r y i e l d and CST values of segregated neu t r a l i za t ion sludges w i t h corresponding values a t 36.1 g / l fo r conventional sludge from p l a n t A3 which was produced a t a pH of 7.0 and a t room temperature. This was required since, unl ike s p e c i f i c r e s i s t ance values, f i l t e r y i e l d and CST Measurements a r e not normalized t o i n i t i a l suspended sol ids concentration.

Def in i te improvements i n sludge dewatering c h a r a c t e r i s t i c s were apparent w i t h segregated neu t r a l i za t ion o f spent f i n i s h i n g so lu t ions a t p lan t A3. r e s i s t ance values f o r conventional neu t r a l i za t ion were g r e a t e r than those observed for the sludges neut ra l ized a t 80'C. I t was a l s o apparent t h a t a n approximate 100-fold reduction i n specific r e s i s t ance could be achieved by the appl ica t ion of segregated neu t r a l i za t ion of spent e tch and anodize wastes a t p lan t A3 a t 8 O o C and a pH of 8.5. Segregated neu t r a l i za t ion made dewatered sludge more amenable t o disposal by decreasing sludge moisture content s ince a l l sludges produced a t 80°C had higher cake s o l i d s contents after dewatering than those for conventional neu t r a l i za t ion . For example, sludge produced a t pH of 8 .5 and a temperature o f 80°C was dewatered t o a concentrat ion of 42.2 percent sol ids as compared t o a concen t r a t ion of 9 . 2 percent s o l i d s observed for the conventional sludge from plan t A3, ind ica t ing t h a t a reduction of about 36 percent i n sludqe cake moisture can be achieved by the appl ica t ion of segregated neu t r a l i za t ion .

To f u r t h e r i l l u s t r a t e the impact of segregated neu t r a l i za t ion on sludge dewatering c h a r a c t e r i s t i c s , data i l l u s t r a t i n g vacuum-fil ter sur face areas required t o dewater each o f the segregated neu t r a l i za t ion and conventional neu t r a l i za t ion sludges a r e presented i n Table 7.15. Total masses of wet dewatered sludges f o r disposal are a l s o presented. t o t a l waste-aluminum mass-flow of 938 kg/d , which was estimated t o be t h a t t r ea t ed by segregated neu t r a l i za t ion of spent e tch and anodize wastewaters a t p lan t A3 from an indus t r i a l waste survey (Saunders -- e t a l . , 1982). T h i s mass of aluminum was assumed t o be t o t a l l y prec ip i ta ted as aluminum hydroxide as a r e s u l t of waste neu t r a l i za t ion and was assumed t o be t o t a l l y removed by s e t t l i n g as a thickened sludge of 15 percent sol ids (150 g / l ) f o r t he sludges produced u s i n g segregated neu t r a l i za t ion . sludge dewatering i n these ca l cu la t ions , F ina l ly , f i l t e r y i e ld and cake s o l i d s concentrat ion values for conventional sludge i n Table 7.14 were the highest values observed f o r these sludges (Saunders -- e t a l . , 1982).

pact of segregated neu t r a l i za t ion on sludge treatment and disposal a t the reference p lan t . w i t h t h i s technique. sludges, a lower sur face area was required f o r dewatering by vacuum f i l t r a t i o n than t h a t required t o dewater conventional sludge. For sludqe produced a t a temperature

segregated-neutral izat ion sludge, ascompared t o the f i l t e r area o f 22 m 2 required t o dewater t he conventional sludge. I n add i t ion , appl ica t ion o f ?e regated neu t r a l i za t ion

thereby reducing the volume of wet sludge f o r disposal . A mass reduction of 77 percent was achieved by laboratory simulation of segregated neut ra l iza t ion a t a

To evaluate the impact of segregated neu t r a l i za t ion of spent e tch and anodize

A suspended s o l i d s concentrat ion of 35 g/1 was a r b i t r a r i l y

Spec i f i c

The values presented i n Table 7.15 a r e based upon a

Also, a 6-hour s h i f t of vacuum f i l t e r operation was assumed f o r

The r e s u l t s presented i n Table 7.15 c l e a r l y demonstrated the s i g n i f i c a n t im-

A s i g n i f i c a n t reduction i n required vacuum-filter area can be achieved As shown i n the t a b l e for a l l the segregated neu t r a l i za t ion

-of 80°C and a pH o f 8 .5 , a f i l t e r area of approximately 3.7 m 2 was reouired t o dewater -.

r e s u l t s i n production of sludge which can be dewatered t o a h i g i! e r s o l i d s conten t ,

Table 7.14. Impact of Segregated Neutralization of Spent Process Solutions on Sludge Dewatering Characteristics

Neutralization Conditions Specific Resistance Filter Yield CST Y** Cake Solids SS* CST PH Temperature ss* r SS*

"C (J/1 1 0I0m/ kq - g/l kg/m2. h percent 3 2 s SEGREGATED NEUTRALIZATION

5.5 80 12.8 - 157.5 22.5 - 31.0 35.0 2.8 34.0 35.0 63.0

7.0 80 16.4 - 151.1 2.33 - 3.18 35.0 9.6 34.6 35.0 25.0

8.5l 80 20.8 - 157.8 1.33 - 2.95 35.0 6.2 42.2 35.0 25.0

10.0 80 25.4 - 256.3 0.34 - 0.87 35.0 0.78 52.8 35.0 25.0

W CONVENTIONAL NEUTRALIZATION w

7.02 25 3.4 - 36.1 28 - 38 3.4-36.1 0.70-5.71 8.5-9.2 3.4-36.1 18.1-53.7

*SS = suspended solids concentration **approximate values from Figures 7,10, 7.13, 7.17 and 7.21 'Filter yield data from run 5 *Conventional sludge data from Saunders _ _ et ai. (1982) for plant A3.

l .?- .2 7. 5. Impact o f a Segregated Neutralization o f Spent Process Wastes at Plant A3 on Required Vacuum Filter Area and Mass o f Wet Sludge for Disposal

Neutralization PH Temperature

"C -

SEGREGATED NEUTRALIZATION

5.5 ao

7.0 80

8.5 80

10.0 80

Fi 1 ter Cake Solids Vacuum Filter Mass of Wet Yield Area Sludge for Disposal kg/m2. h percent m2 k d d

39.6 34.2 11.4 7,925

144

122.4

21.6

CONVENTIONAL NEUTRALIZATION

7.0 25 20.6

34.8

40.0

46.7

3.1

3.7

20.9

7,790

6,775

5,800

9.2 22.0 29,460

u3 P

!

95

pH o f 8 . 5 and a temperature o f 80'C.

i n v a c u u m - f i l t e r area requi rements, decreased q u a n t i t i e s of wet s l u d g e c f o r d i s p o s a l and an improved s ludge-hand l ing c h a r a c t e r i s t i c s . spent e t c h and anodize wastes f o r t rea tmen t when p l a n t p r o d u c t i o n i s reduced, s i g n i f i c a n t r e d u c t i o n s i n l o a d i n g o f conven t iona l sludges t o t h i c k e n i n g and de- w a t e r i n g equipment w i l l be achieved on days i n which wastes a re t r e a t e d by con- v e n t i o n a l means, s i n c e approx imate ly 75 percent o f t o t a l waste aluminum can be t r e a t e d by segregated n e u t r a l i z a t i o n o f these concent ra ted spent s o l u t i o n s (Saunders c., 1982). The p o t e n t i a l f o r imp lementa t ion o f segregated n e u t r a l i z a - t i o n a t p l a n t A3 and o t h e r s i m i l a r p l a n t s was t h e r e f o r e e s t a b l i s h e d by t h e above a n a l y s i s .

Therefore, use o f segregated n e u t r a l i z a t i o n r e s u l t s . i n s i g n i f i c a n t r e d u c t i o n s

Also,by s to rage o f concent ra ted

SUMMARY AND ENGINEERING SIGNIFICANCE

Th icken ing and dewater ing p r o p e r t i e s o f a lum inum- f i n i sh ing sludges a r e i n - f lue.nced by many f a c t o r s i n c l u d i n g suspension temperature, age o f t h e suspension and t y p e of aluminum hydrox ide formed upon n e u t r a l i z a t i o n o f t he waste. Temperature may a f f e c t suspension c h a r a c t e r i s t i c s th rough the i n f l u e n c e o f l i q u i d v i s c o s i t y . L i q u i d v i s c o s i t y a f f e c t s p a r t i c l e drag f o r c e s d u r i n g t h i c k e n i n g and dewater ing. With r e s p e c t t o t h i c k e n i n g , a t h i g h suspended s o l i d s concen t ra t i ons , i n t e r p a r t i c l e f o r c e s predominate. changes i n a n a l y s i s temperature would r e s u l t i n d i v e r g i n g s e t t l i n g curves ob ta ined a t d i f f e r e n t temperatures. s ludge t h i c k e n i n g da ta ob ta ined a t t h e temperatures examined. be concluded t h a t under the c o n d i t i o n s o f t h i s s tudy , l i q u i d v i s c o s i t y d i d n o t a p p r e c i a b l y i n f l u e n c e t h e t h i c k e n i n g d a t a ob ta ined f o r t h e sludges examined.

duced a t a n e u t r a l i z a t i o n temperature o f 80°C. da ta c o l l e c t e d 25OC and 8OoC (Medero, 1981) i n d i c a t e d t h a t temperature e f f e c t s were i n c o r p o r a t e d i n t o c a l c u l a t i o n s o f s p e c i f i c r e s i s t a n c e through i n c l u s i o n o f f i l t r a t e v i s c o s i t y b u t n o t w i t h f i l t e r y i e l d and CST values; and chemical c h a r a c t e r i s t i c s o f segregated n e u t r a l i z a t i o n were n o t s i g n i f i c a n t l y a f fec ted by v a r i a t i o n s i n suspension temperature.

The e f f e c t s of chemical s t r u c t u r e and ag ing on sludge p r o p e r t i e s a r e dependant on t h e chemis t r y of aluminum hyd rox ide f o r m a t i o n d u r i n g n e u t r a l i z a t i o n ; upon pH and temperature,numerous forms o f aluminum p r e c i p i t a t e s a re formed i n - c l u d i n g , f o r example, amorphous, pseudoboehmite and t r i h y d r o x i d e forms. Amorphous aluminum p r e c i p i t a t e s ( 1 .e., aluminum hyd rox ide p repara t i ons which a r e X-ray i n - a c t i v e and c o n t a i n numerous t r i h y d r o x i d e and ox ide-hydrox ide fo rms) a re h y d r o p h i l i c , amphoteric forms w i t h low c r y s t a l l i n e o r d e r (Papee and T e r t i a n , 1963: Maczura - e t _ * a1 9 1978). P r e c i p i t a t i o n o f aluminum a t pH values below 7 r e s u l t s i n f o r m a t i o n of these amorphous forms which c o n t a i n h i g h l e v e l s o f c0ntaminan.t anions (e.g., Sob=, C1-) and have an average wa te r c o n t e n t o f 3 moles H20/mole A1,03 ( l laczura - e t _. a1 3 1979). I n a d d i t i o n , H e r b i l l i o n and Gastuche (1970) i n d i c a t - d t h a t o n l y

2- ... ~. ~~~ . ~~ ~ amorphous and pseudoboehmite would be formed i n t h e presence o f h i g h concen t ra t i ons of c h l o r i d e , n i t r a t e and s u l f a t e anions, r e g a r d l e s s o f pH. the amorphous forms a re e a s i l y coagu la ted i n t o g e l s which upon ag ing may be con- v e r t e d i n t o v a r i o u s t r i h y d r o x i d e forms. I t i s apparent f rom the p r o p e r t i e s o f sludges formed by conven t iona l n e u t r a l i z a t i o n a t a lumi.num-f in ishing p l a n t s t h a t amorphous forms a r e the predominate aluminum species p r e c i p i t a t e d and t h a t t he

Therefore, as suspended s o l i d s concen t ra t i ons decrease,

Such a d i v e r g e n t r e l a t i o n s h i p d i d n o t occur f o r t he There fore , i t may

The m a j o r i t y o f t he dewater ing da ta were c o l l e c t e d a t 25°C f o r sludges p ro - Comparison o f dewater ing

However, t he p h y s i c a l

Depending

A t h i g h concen t ra t i ons ,

96

poor thickening and dewatering proper t ies a r e a t t r i b u t a b l e t o the ge la t inous nature of the p r e c i p i t a t e s .

W i t h regard t o t r ihydroxide forms, i t i s reported t h a t a t room temperature g ibbs i t e i s formed i n a c i d i c s o l u t i o n , nords t randi te i s formed i n s l i g h t l y acid t o neutral so lu t ion and bayer i te i s formed i n a l k a l i n e so lu t ion (Barnhisel and Rich, 1965; Hsu, 1966; Hem and Roberson, 1967; and Schoen and Roberson, 1970). Herbil lon and Gastuche (1970) observed t h a t following removal of contaminant anions from aluminum solu t ions by d i a l y s i s , g ibbs i t e p rec ip i t a t ion occurred a t pH 4.6 while p rec ip i t a t ion of mixed bayer i te and pseudoboehmite occurred a t pH 6.5. Hayden and R u b i n (1974) ind ica ted t h a t upon hea t ing an aluminum n i t r a t e so lu t ion f o r 5 days a t 65°C and a t low pH values ( i . e . , i n i t i a l pH = 5.5; f i n a l pH = 4 .1 ) , g ibbs i t e was formed. a l u m i n u m hydroxide was formed and pseudoboehmite was observed a t a f i n a l pH of 7.25,

t a t e d a t pH values below 7 , a gel-type boehmite (pseudoboehmite) was formed a t pH 9 which had a lower water content ( i . e . , 1.5 - 2 mole HZO/mole A1 03) than

(e .g . , nonstrandi te and g ibbs i t e ) were a l s o formed. t r ihydroxide forms t y p i c a l l y had lower water contents than the amorphous forms, as indicated i n Tab le 7.16. forms would r e s u l t i n production of a suspension composed of c r y s t a l l i n e s o l i d s w i t h a water content l e s s than t h a t of amorphous sludge conventionally produced.

In addi t ion , mixed g ibbs i t e and bayer i te were formed a t pH 8.

However,when the f i n a l pH was 4.42 ( i n i t i a l pH = 5 . 5 ) , amorphous

Papee and Tert ian (1963) reported t h a t , while amorphous forms were prec ip i -

amorphous forms. A t pH values g rea t e r than 10, f i n e l y c r y s t a l l i z e d F; y r a t e s In addi t ion , the c r y s t a l l i n e

Therefore, p rec ip i t a t ion o f non-amorphous t r ihydroxide

Table 7.16. Physical Charac te r i s t ic~s of Selected Aluminum Prec io i t a t e s

AI umi num P r e c i p i t a t e

Amorphous

Gibbsi te

Bayeri t e

In. i t ia1 Water Content a t Room Temperature Mole H 0 Reference d ; 0 q

3 1 4 2

3 3 2.5-3 1

3.15 3 2.5-3 1

Density* g/cm3

2.42

2.53

- Nordstrandi t e 2.5-3 1

Boehmite 1.5-2 1 3.01 1.15 1 .5

References: 1 . Popee and Te r t i an , 1963; 2. Wefers and Be l l , 1972;

"Maczura e t a l . , 1978 3 . Newsome fig., 1960

_ _

r,

97

I t i s apparent t h a t bo th n e u t r a l i z a t i o n pH and temperature g r e a t l y a f f e c t t he chemical composi t ion o f n e u t r a l i z e d aluminum suspensions. Increased temperature tends t o reduce the o v e r a l l water c o n t e n t o f aluminum p r e c i p i t a t e s w h i l e inc reased pH values r e s u l t i n the fo rma t ion o f more c r y s t a l l i n e forms, which a l s o have lower water con ten t va lues. I n v iew o f t h e h i g h s u l f a t e c o n t e n t o f n e u t r a l i z e d wastes examined he re in , i t i s apparent t h a t amorphous forms o f .a luminum hydrox ide were pre- c i p i t a t e d d u r i n g h i g h temperature exper imenta l runs, e s p e c i a l l y a t a pH o f 5.5. As pH was increased t o n e u t r a l and a l k a l i n e va lues, c r y s t a l l i n e aluminum tri- hydrox ide and aluminum ox ide hydrox ide forms were a p p a r e n t l y produced which tended. t o i nc rease s ludge d e n s i t y and decrease s ludge water con ten t (Hsu, 1967).

Aluminum suspensions produced a t temperatures rang ing f rom 65 t o 90°C and a t n e u t r a l pH va lues f o r t h i c k e n i n g analyses were a p p a r e n t l y composed o f s i m i l a r aluminum forms, That i s , v a r i a t i o n s i n n e u t r a l i z a t i o n temperature o f up t o 2 5 O C d i d n o t s i g n i f i c a n t l y a f f e c t t h i c k e n i n g p r o p e r t i e s , d ramat ic e f f e c t on bo th t h i c k e n i n g and dewater ing p r o p e r t i e s , i n c r e a s i n g pH values appeared t o c o n t a i n an inc reased p r o p o r t i o n o f c r y . s t a l l i n e - l i k e p r e c i p i t a t e s , a p p a r e n t l y c r y s t a l l i n e t r i h y d r o x i d e forms, which accounted f o r t h e enhancement of t h i c k e n i n g and dewater ing p r o p e r t i e s . However, regard less o f mechanism, segregated n e u t r a l i z a t i o n o f concent ra ted a luminum- f in ish ing wastes r e s u l t s I n ma jor imprwements i n the performance o f s ludge t rea tment systems and has a major impact on r e d u c t i o n o f t h e volume o f s ludge f o r d i sposa l due t o decreases i n s ludge m o s i t u r e conten t .

p o s s i b l e approaches. sed imenta t ion and dewater ing systems p rov ided t o t r e a t s ludges produced by con- v e n t i o n a l n e u t r a l i z a t i o n and segregated n e u t r a l i z a t i o n . ' success fu l b u t would be c o s t i n t e n s i v e due t o t h e requi rements f o r redundant t h i c k e n i n g and dewater ing systems. anod iz ing p l a n t ( p l a n t A2) employing a v e r s i o n o f segregated n e u t r a l i z a t i o n i n d i c a t e s t h a t o t h e r op t i ons a r e a v a i l a b l e , A t p l a n t A2, o n l y r i nsewa te rs a r e t r e a t e d by n e u t r a l i z a t i o n and sed imenta t ion i n a s o l i d s - c o n t a c t c l a r i f i e r d u r i n g pe r iods when aluminum i s a c t i v e l y be ing f i n i s h e d , u s u a l l y 5 o r 6 days/week. aluminum i s n o t be ing f i n i shed , concent ra ted f i n i s h i n g s o l u t i o n s a re d ischarged t o t h e n e u t r a l i z a t i o n system r e s u l t i n g i n ma jor increases i n suspension temperature. Massive q u a n t i t i e s o f waste s o l i d s a r e p r e c i p i t a t e d and s t o r e d i n the so l ids -con- t a c t c l a r i f i e r f o r dewater ing d u r i n g a p e r i o d o f normal p l a n t ope ra t i on . Examina- t i o n o f t he s ludge produced d u r i n g t h i s l a t t e r p e r i o d when "segregated n e u t r a l i z a - t i o n " was be ing p r a c t i c e d i n d i c a t e d t h a t t h e s ludge had s u p e r i o r t h i c k e n i n g and dewater ing p r o p e r t i e s when comapred t o those produced c o n v e n t i o n a l l y . I n a d d i t i o n , us ing a.vacuum f i l t e r f o r dewater ing t h e combined s ludge s o l i d s a t t h e p l a n t s i t e , cake s o l i d s conten ts o f 20 percent and h i g h e r are r o u t i n e l y achieved. No o t h e r p l a n t i n v e s t i g a t e d by Saunders -- e t a l . (1982) was a b l e t o .achieve t h i s l e v e l of dewater ing . Therefore, i t would appear t h a t t h e improved t h i c k e n i n g and dewater ing p r o p e r t i e s o f s ludges produced by segregated n e u t r a l i z a t i o n can be used t o improve t h e p r o p e r t i e s of convent iona l sludges by m i x i n g t h e two toge the r . N e u t r a l i z a t i o n o f concent ra ted f i n i s h i n g s o l u t i o n s would be conducted w i t h a segregated system,with

convent iona l n e u t r a l i z a t i o n . f o r f u r t h e r t rea tment . Segregated n e u t r a l i z a t i o n s o l i d s c o u l d a l s o be blended w i t h convent iona l s ludge f o l l o w i n g t h i c k e n i n g b u t p r i o r t o dewater ing t h e m i x t u r e . Exper imental r e s u l t s i n d i c a t e t h a t these a l t e r n a t i v e s a re f e a s i b l e . these and o t h e r a l t e r n a t i v e s as w e l l as e s t a b l i s h the op t ima l a l t e r n a t i v e .

Changes i n pH, however, had a Sludges produced a t

As t o implementat ion o f segregated n e u t r a l i z a t i o n t h e r e a r e a number of A comple te ly separate system c o u l d be implemented w i t h two

T h i s a l t e r n a t i v e should, be

Data presented by Saunders -- e t a l . (1982) f o r an ' -

On a day when

.. ~. ~~ .. ... t he e f f l u e n t s o l i d s be ing mixed w i t h d i l u t e r i nsewa te r wastes p r i o r t o o r f o l l o w i n g

F u r t h e r i n v e s t i g a t i o n i s , however, r e q u i r e d t o c o n f i r m the bene f i t s o f

SECTION 8

RECLAMATIOIi OF SPENT CAUSTIC ETCH B Y LIME ADDITION

The ma jo r source o f waste aluminum from an aluminum a n o d i z i n g p l a n t S tud ies conducted a t p l a n t s A l and A3 i n d i c a t e d t h a t

I n a d d i t i o n , aluminum i n spent e t c h i s i n a concen t ra ted

i s spent c a u s t i c e t c h . 73 and 59 pe rcen t o f t o t a l waste aluminum was con t inued i n spent e t ch , r e s p e c t i v e l y . form s ince, f o r example, spent e t c h accounted f o r o n l y 1.2 and 1 .5 percen t o f t h e t o t a l wastewater f l o w a t p l a n t s A1 and A3, r e s p e c t i v e l y . Treatment o f t h e ma jo r p o r t i o n o f a waste contaminant i n a concen t ra ted form p r o v i d e s an e x c e l l e n t o p p o r t u n i t y t o reduce waste t rea tmen t c o s t s .

New techno logy presented by Alcoa, Inc . and Fugi Sash, I n c . p r o v i d e s a means o f removing aluminum as a l ow-mo is tu re aluminum-hydrate p r e c i p i t a t e and r e c o v e r i n g c a u s t i c e t c h f o r t h e use i n t h e f i n i s h i n g process (Brown, 1982; Meyer etal., 1979). p e r i o d i c a l l y c i r c u l a t e d through a c r y s t a l l i z e r c o n t a i n i n g aluminum-hydrate c r y s t a l s and aluminum i s p r e c i p i t a t e d and removed f rom suspension by g r a v i t y sed imen ta t i on . w h i l e t h e aluminum-hydrate suspension is p e r i o d i c a l l y dewatered t o recove r p r e c i p i t a t e d aluminum-hydrate s o l i d s . systems have found favorable a p p l i c a t i o n i n t h e aluminum f i n i s h i n g i n d u s t r y .

Data presented by Schaezler (1978) ,Kel ly (1960) and Holmes (1982) i n d i c a t e d a l i m i t e d s o l u b i l i t y f o r aluminum i n presence o f c a l c i u m i o n s a t e l e v a t e d pH va lues . A t s u f f i c i e n t c a l c i u m l e v e l s , aluminum i s v i r t u a l l y i n s o l u b l e as a c a l c i u m a lumina te (Schaezler , 1978; Holmes, 1982), u n l i k e t h e p r o p r i e t a r y e t c h recove ry systems i n which s o l u b l e aluminum l e v e l s i n recovered e t c h s o l u t i o n s remains between 16 and 24 g / l (Brown, 1982). I n a d d i t i o n , t h e process o f ca l c ium a d d i t i o n i s n o t p r o p r i e t a r y i n nature, and appears t o be s i m p l e r technoloay w i t h p o t e n t i a l f o r a p o l i c a t i o n i n t h e aluminum f i n i s h i n g i n d u s t r y . Therefore, i n i t i a l s t u d i e s were conducted t o determine t h e f e a s i b i l i t y o f t h e process w i t h r e s p e c t t o waste t rea tmen t c o n s i d e r a t i o n s .

EXPERIMENTAL TECHNIQUES

Exper imental Reactor System

which were mixed w i t h a s i n g l e - b l a d e (7.7cm x 2.4 cm) s t a i n l e s s - s t e e l paddle a t 100 rpm. Constant temperatures were ma in ta ined by p l a c i n g

Caus t i c e t c h i n g s o l u t i o n s a r e c o n t i n u o u s l y o r

C l a r i f i e d e t c h i s reused i n t h e e t c h i n g process

These p r o p r i e t a r y e tch - recove ry

-

A l l expe r imen ta l s t u d i e s were conducted i n o n e - l i t r e g lass beakers

98

99

r e a c t i o n beakers (up t o a maximum o f f i v e ) i n a cons tan t - tempera tu re ba th .

I n d i v i d u a l exper iments were conducted by p l a c i n g 200 mi o f a spent c a u s t i c s o l u t i o n i n a beaker and we igh ing t h e beaker and c a u s t i c s o l u t i o n ( t o t h e n e a r e s t 0 . l g ) . t h e constant - temperature bath. Lime ( reagent-grade hyd ra ted l ime , Ca(0H) ) was then added t o t h e spent e t c h s o l u t i o n as a d r y powder o v e r a 90-seconi i n t e r v a l and t h e r e a c t i o n was a l lowed t o proceed f o r r e a c t i o n pe r iods o f 15 minutes t o 10 hours. beakers were removed from t h e 'constant- temperature bath, towel d r i e d and weighed t o determine t h e n e t evapora t i on l oss . A t r e a c t i o n temperatures a t and above 6OoC, evapora t i on l osses were c o r r e c t e d by a d d i t i o n o f d i s t i l l e d , d e i o n i z e d wa te r t o each beaker. Water a d d i t i o n was accomplished by p i p e t t i n g 3.5 m l o f preheated water i n t o a beaker a t 30-minute i n t e r v a l s . A t complet ion o f an exper iment, no a d d i t i o n a l wa te r was added b u t i n i t i a l and f i n a l r e a c t o r we igh ts were used t o compute a d i l u t i o n f a c t o r which was used i n c o r r e c t i n g subsequent a n a l y t i c a l data.

con ten ts o f a beaker were f i l t e r e d on a Buchner funnel apparatus t o determine s p e c i f i c r e s i s t a n c e , s o l i d s y i e l d , cake volume, and f i l t r a t e c h a r a c t e r i s t i c s . p r i o r t o a n a l y s i s f o r r e s i d u a l s o l u b l e ca l c ium and aluminum, pH, d i s s o l v e d sol i d s and a1 k a l i n i t y .

The beaker was a l lowed t o e q u i l i b r a t e f o r 1 0 m i n u t e s i n

A t t h e end o f each r e a c t i o n pe r iod , i n d i v i d u a l

F o l l o w i n g comp le t i on o f a s p e c i f i e d r e a c t i o n pe r iod , t h e e n t i r e

F i l t r a t e was passed th rough a 0.45 um membrane f i l t e r

Spent E tch Waste

Spent e t c h f rom p l a n t A3 was c o l l e c t e d from a spacer-etch tank f o r use

The con ten ts o f i n t h e s tudy. l i n e and was used t o c lean spacers used on aluminum racks. t h e spacer-etch tank were c o n t i n u a l l y d ischarged t o a h o l d i n g tank f o r use i n n e u t r a l i z a t i o n o f p l a n t wastewaters.

The spacer-etch t a n k r e c e i v e d spent e t c h from t h e anodize

C h a r a c t e r i s t i c s o f t h e spent e t c h s o l u t i o n used i n t h e s t u d y a r e presented i n Table 8.1. The m a j o r i t y o f t h e aluminum i n t h e sample was i n t h e d i s s o l v e d form as were t h e m a j o r i t y o f t h e s o l i d s con ta ined i n t h e e t c h s o l u t i o n . The c h a r a c t e r i s t i c s o f t h e e t c h s o l u t i o n were i n a d d i t i o n s i m i l a r t o those presented by o t h e r s (Brown, 1982; Ramirez, 1979; Saunders et., 1982) f o r spent c a u s t i c e t c h s o l u t i o n s .

EXPERIMENTAL RESULTS

I n examinat ion o f t h e use o f l i m e a d d i t i o n f o r r e c l a m a t i o n o f spent c a u s t i c e tch, p r i m a r y a t t e n t i o n was p laced on r e q u i r e d r e a c t i o n t i m e and c a l c i u m l e v e l s t o achieve aluminum removal and on c h a r a c t e r i s t i c s o f p r e c i p i t a t e d s o l i d s f o l l o w i n g l i m e a d d i t i o n .

React ion Time

I n i t i a l d u p l i c a t e t e s t s w i t h r e a c t i o n t imes v a r y i n g from 45 t o 90 m inu tes f a i l e d t o produce c o n s i s t e n t r e s u l t s . Subsequent i n v e s t i g a t i o n s i n t o t h e e f f e c t s o f r e a c t i o n t i m e and temperature revea led t h a t b o t h had s i g n i f i c a n t impact on aluminum removal , as i n d i c a t e d i n F igu re 8.1.

100

d u 0 (D

II

I.

..

101

Table 8.1 Charac te r i s t ics o f Spent Etch Waste From Plant A3 as Used i n Experimental Invest igat ion

PARAMETER CONCENTRATION

Sol i d s Total , g / l . . . . . . . . . . . . . . 190.4 Dissolved, g/1. . . . . . . . . . . . 189.3

. . . . . . . . Solution Density, k g / l . 1.15

pH . . . . . . . . . . . . . . . . . . Alkal in i ty , g/1 ( a s CaC03). . . . . . . A l u m i n u m

Tota l , g / l . . . . . . . . . . . . . Dissolved, g / l . . . . . . . . . . .

13.6

15.6

37.5 36.5

. . . . . . . . . . . . Calcium, m g / l . 1

Data i n Figure 8.1 indicated t h a t no s i g n i f i c a n t aluminum prec ip i t a t ion occurred i n an i n i t i a l 45-minute period a t temperatures of 30 and 6OoC f o r a mass dosage of Ca/A1=3/1. However, following react ion periods of between 45 and 90 minutes,rapid aluminum prec ip i t a t ion occurred. For a react ion temperature o f 6OoC, the to t a l aluminum removal following a 90-minute reac t ion period was 68 percent while a t a reac t ion temperature o f 3OoC, aluminum removal was 45 percent. period, the r a t e o f aluminum prec ip i t a t ion decreased and remained constant through a 10-hour period a t both tem e ra tu re s . The approximate r a t e s o f

respec t ive ly , over the react ion time period o f 1 .5 t o 10 hours.

temperature, i t was necessary to e s t a b l i s h a constant value for one o f t h e parameters t o remain w i t h i n r e a l i s t i c experimentation l i m i t s . time of 6 hours was therefore chosen f o r a l l subsequent experiments. 6-hour react ion period was considered reasonable f o r a fu l l - s ca l e system and would assure process s t a b i l i t y . indicated t h a t f o r react ion times g rea t e r than 90 minutes, changes i n residual aluminum were s l i g h t compared t o those f o r react ion times of 90 minutes o r l e s s . dupl icat ion o f experimental r e s u l t s when u s i n g react ion times o f 6 hours.

Reaction Stoichiometry

s tud ie s were conducted a t ambient temperature (25OC) and 6OoC, w i t h 6OoC

After a 90-minute react ion

aluminum prec ip i t a t ion f o r 30 and 60 8 C were 1.2 g/1 .h and 0.75 g / l . h ,

Since process performance was a f fec ted by both react ion time and

A react ion A

Data presented i n Figure 8.1

Therefore, t he low r a t e o f change allowed f o r cons is tan t

Using a react ion time o f 6 hours following lime addi t ion , a s e r i e s of

102

b e i n g t y p i c a l o f t h a t used f o r e t c h i n g s o l u t i o n s on aluminum a n o d i z i n g l i n e s . Incrementa l i nc reases i n ca l c ium a d d i t i o n were used t o determine t h e e f f e c t on r e s i d u a l aluminum. As i n d i c a t e d i n F i g u r e 8.2, i nc reased a d d i t i o n o f l i m e r e s u l t e d i n a p r o p o r t i o n a l decrease i n r e s i d u a l s o l u b l e aluminum, i n d i c a t i n g a c o n s t a n t r e l a t i o n s h i p between l i m e ( i .e. , ca l c ium) a d d i t i o n and aluminum removal. Furthermore, r e s i d u a l s o l u b l e ca l c ium i n f i l t r a t e samples f o l l o w i n g a 6-hour r e a c t i o n p e r i o d remained between 1 t o 5 mg/l a t c a l c i u m t o aluminum m o l a r r a t i o s o f 1 t o 5. Calcium t h e r e f o r e r e a c t e d w i t h aluminum o r o t h e r species t o form p r e c i p i t a t e s and was o n l y s l i g h t l y s o l u b l e i n t h e e t c h s o l u t i o n .

E x t r a p o l a t i o n o f d a t a i n F igu re 8.2 t o zero r e s i d u a l aluminum i n d i c a t e d t h a t t h e r e q u i r e d m o l a r r a t i o s o f ca l c ium t o aluminum were 2.75/1 and 3.7/1 f o r 6OoC and 25OC, r e s p e c t i v e l y . 25OC were 4.1/1 and 5.4/1. Lime requi rements a t ambient temperature ( i .e., 25OC) were 34 pe rcen t h i g h e r than those a t 6OoC f o r t h e 6-hour r e a c t i o n p e r i o d examined. i n d i c a t e d , however, t h a t s i m i l a r aluminum removals c o u l d be achieved a t two temperatures u s i n g a c o n s t a n t Ca/A1 r a t i o i f r e a c t i o n t i m e was extended a t t h e l ower temperature.

W i th r e s p e c t t o f i l t r a t e q u a l i t y f o r exper iments conducted a t ca l c ium t o aluminum m o l a r r a t i o s r a n g i n g from 1 t o 3 a t 25 and 60OC, a l k a l i n i t y and pH values remained cons tan t . D isso lved s o l i d s , however, decreased w i t h i n c r e a s i n g c a l c i u m a d d i t i o n due t o removal o f s o l u b l e aluminum. I n F i g u r e 8.3, r e s i d u a l d i s s o l v e d s o l i d s c o n c e n t r a t i o n i s presented as a f u n c t i o n o f r e s i d u a l s o l u b l e aluminum . f o r a r e a c t i o n temperature o f 3OoC a t v a r i o u s c a l c i u m t o aluminum r a t i o s . The removal o f l g o f aluminum by a d d i t i o n o f l i m e r e s u l t e d i n a n e t r e d u c t i o n i n d i s s o l v e d s o l i d s o f 1.259. Residual d i s s o l v e d so , l i ds c o n c e n t r a t i o n f o l l o w i n g removal o f a l l aluminum was 147 g/1, wh ich was a t t r i b u t a b l e t o sodium hyd rox ide and e t c h a d d i t i v e s . There fo re , complete removal o f aluminum by l i m e a d d i t i o n c o u l d be success- f u l l y achieved w i t h o u t a r e d u c t i o n i n t h e s t r e n g t h o f t h e e t c h i n g s o l u t i o n , as i n d i c a t e d b y a l k a l i n i t y and d i s s o l v e d s o l i d s l e v e l s .

The r e s p e c t i v e mass r a t i o s f o r 6OoC and

Th is was c o n s i s t e n t w i t h da ta i n F igu re 8.1 which

The q u a n t i t y o f s ludge s o l i d s produced by a d d i t i o n o f l i m e was examined b y a n a l y s i s o f t h e q u a n t i t i e s o f c a l c i u m and aluminum added. For a g i v e n Ca/A1 r a t i o , i n i t i a l and f i n a l aluminum and ca l c ium c o n c e n t r a t i o n s o f a t r e a t e d e t c h s o l u t i o n , w e r e used t o determine t h e q u a n t i t y o f ca l c ium and aluminum removed as p r e c i p i t a t e d s o l i d s . These c a l c u l a t e d va lues a r e compared w i t h measured v a l u e s f o r cake s o l i d s i n F igu re 8.4. For a range o f Ca/A1 r a t i o s , c a l c i u m and aluminum accounted f o r app rox ima te l y 46 p e r c e n t o f t h e d r y s o l i d s produced. o b v i o u s l y p r e c i p i t a t e d w i t h ca l c ium and aluminum.

Sludge C h a r a c t e r i s t i c s

Other c a t i o n s and assoc ia ted anions were

A d d i t i o n o f l i m e t o spent e t c h produced a suspension which con ta ined a h i g h c o n c e n t r a t i o n o f suspended s o l i d s r e s u l t i n g f rom the p r e c i p i t a t i o n o f ca l c ium and aluminum. I n i t i a l i n v e s t i g a t i o n i n d i c a t e d t h a t t h e suspensions were d i r e c t l y amenable t o dewater ing and t h a t i n i t i a l t h i c k e n i n g was n o t r e q u i r e d . t h e r e f o r e focused on measures of s ludge dewa te r ing p r o p e r t i e s .

Analyses o f s ludge c h a r a c t e r i s t i c s were

103

.

0 0 0 0 N

V a,

0. Q a -0 8 m E 3 c

.r 7

.r

5 - a a

3

0 (0

m U m a, PI

c a,

+J a,

c n - - a .r

% m a .r . L a , m v l c o Om

+- 7..

PIV

.r

m a a m

N

m a, L 3 m U .r

104

220

180 . 0 vi n i 8 El 3 8 - n

3 140 n G a

-I

w

100

10 20 30 40 50 60 0

RESIDUAL SOLUBLE ALUMINUM, G/L

Figure 8.3. Relat ionship Between Residual Dissolved Sol ids and Residual Soluble Aluminum for Various Ca/A1 Ratios and a Reaction Temperature o f 3OOC.

105

120

100

0 vi 80 P - i w Y

Y 60 > K P

a

9 2 a

3 40 I

20

0

p o 1 . 0

/

I I 1 I I 20 30 40 50 10

CALCULATED DRY-CAKE CONSTITUENTS, G

Figure 8.4. Relationship Between Measured Dry-Cake Sol ids and Corresponding A l u m i n u m and Calcium Composition as Calculated from I n i t i a l and Final Concentrations i n Treated Etch

106

S p e c i f i c Resistance-- To examine s ludge dewater ing c h a r a c t e r i s t i c s , numerous exper iments

were conducted a t temperatures o f 25, 43 and 6OoC and a p p l i e d c a l c i u m t o aluminum mass r a t i o s of 1 t o 3. V i s u a l obse rva t i ons made d u r i n g these exper iments i n d i c a t e d t h a t t h e s ludges t y p i c a l l y had a coa rse -g ra in t e x t u r e s i m i l a r t o t h a t f o r wet sand f o r r e a c t i o n temperatures o f 25OC and a smoother t e x t u r e as r e a c t i o n temperatures were i nc reased t o 43 and 6OoC. I n general , s ludges produced a t l o w e r temperatures and Ca/A1 r a t i o s had poor cake-re lease c h a r a c t e r i s t i c s d u r i n g t e s t i n g f o r s p e c i f i c res i s tance , w h i l e those produced a t h i g h e r temperatures and Ca/A1 r a t i o s e x h i b i t e d e x c e l l e n t cake-re lease c h a r a c t e r i s t i c s . Sludges produced a t low temperatures and Ca/A1 r a t i o s r e t a i n e d t h e green c o l o r which was c h a r a c t e r i s t i c o f t h e o r i g i n a l spent e t c h s o l u t i o n w h i l e those produced a t i n c r e a s i n g temperatures and h i g h Ca/A1 r a t i o s had an o f f - w h i t e c o l o r . a d d i t i o n t o these general s ludge c h a r a c t e r i s t i c s , s p e c i f i c r e s i s t a n c e measurements were used t o e v a l u a t e t h e e f f e c t s o f r e a c t i o n t ime, Ca/A1 r a t i o and r e a c t i o n temperature.

r e a c t i o n temperatures, i t was suspected t h a t s p e c i f i c r e s i s t a n c e v a r i e d w i t h r e a c t i o n t ime. S p e c i f i c r e s i s t a n c e r e s u l t s a t v a r i o u s r e a c t i o n t imes a r e presented i n F igu re 8.5. 25OC r e a c t i o n temperature, s p e c i f i c r e s i s t a n c e was a t a minimum and d i d n o t s i g n i f i c a n t l y change d u r i n g t h e f i r s t 1.5 hours o f r e a c t i o n . t ime o f 1.5 t o 6 hours, s p e c i f i c r e s i s t a n c e jacreased by an o r d e r o f magnitude, i .e . , from 5 x l o 9 m/kg t o 6 x 1 0 dewater ing b e i n g a t a minimum d u r i n g t h e i n i t i a l 1.5-hour p e r i o d corresponded t o e a r l i e r d a t a ( F i g u r e 8.1) i n d i c a t i n g 1 i m i t e d aluminum removal d u r i n g t h i s pe r iod .

f rom 5.7 x l O l o m/kg t o 1.5 x 1 O 1 O m/kg a t 6OoC. 1.5 t o 6 hours, s p e c i f i c r e s i s t a n c e inc reased from 1.5 t o l o T o m/kg t o a maximum of 6.1 x 1 O l o m/kg. t h a t a d d i t i o n a l s ludge s o l i d s were b e i n g produced (see F igu re 8.1) and t h a t t h e r e s i s t a n c e o f those s o l i d s t o the passage o f e t c h d u r i n g mechanical dewater ing i nc reased f o r a r e a c t i o n temperature o f 25OC and remained r e l a t i v e l y c o n s t a n t a t 60OC (see F i g u r e 8.5) .

Calc ium t o Aluminum Rat io- - To e v a l u a t e t h e e f f e c t s o f c a l c i u m t o aluminum r a t i o on s ludge dewa te r ing p r o p e r t i e s , a cons tan t r e a c t i o n t i m e o f 6 hours was employed, as i n d i c a t e d p r e v i o u s l y . S p e c i f i c r e s i s t a n c e va lues o b t a i n e d f o r t h e s ludges produced a t temperatures o f 25, 43 and 6OoC ranged between 2.8 x 1 O l o m/kg and 47.5 x 1 O ’ O m/kg, as i n d i c a t e d i n Table 8.2. o b t a i n e d by Saunders -- e t a l . (1982) f o r u n c o n d i t i o n a l a lum inum- f i n i sh ing s ludges produced by conven t iona l n e u t r a l i z a t i o n (e.g., 1 .8 - 51 x 1 0 l 1

-m/kg), i n d i c a t i n g improved dewater ing p r o p e r t i e s o v e r conven t iona l aluminum- f i n i s h i n g s ludges. on v i s c o s i t y va lues f o r wa te r a t t h e temperature o f t h e exper iment. The v i s c o s i t y o f t h e spent e t c h s o l u t i o n was, however, h i g h e r than t h a t f o r wa te r b u t was n o t measured f o r i n c l u s i o n i n t h e c a l c u l a t i o n . Therefore,

I n

Reac t ion Time-- Owing t o c o l o r and t e x t u r e changes no ted f o r i nc reased

A n a l y s i s o f these da ta i n d i c a t e d t h a t f o r a

For a r e a c t i o n

m/kg. The r e s i s t a n c e t o

For r e a c t i o n t imes o f 0.5 t o 1.5 h o u r s , s p e c i f i c r e s i s t a n c e decreased For r e a c t i o n t imes o f

In genera l , i nc reased r e a c t i o n t i m e i n d i c a t e d

These va lues were approx ima te l y 1 0 - f o l d l e s s than those

I n a d d i t i o n , t h e va lues r e p o r t e d i n Table 8.2 a r e based

107

I I

L 0 + W E + S 0

.r

._ c, V

w m w-. -0 r m

+ w o u

v) S- m a U-.

K m m 3 .r u 0 w o I

w m W' V U .r 0

I U - 0 .r w F

z V aJn ns 0 m m T U W O

W W L D 3 N W ' c m o QY) .r w .cL t A 3 su o m .r L u w m a - E a J W wl-

m .

m

m

VI

E a K c ,

i 08

Table 8.2 S p e c i f i c Resis tance o f L ime-Treated Spent E t c h Sludges

SPEC I FI C RES I STANCE 1O1O m/kg

React ion Temperature

01: A p p l i e d Ca/A1 R a t i o (>lass b a s i s ) *

3 .O 2.0 - 2.5 - - 1.5 - 1 .o - 25 2.8 6.4 6.8 4.3 4.0

43 14. 9.6 6.4 5.2 5.6

60 47.5 8.4 5.0 4.0 5.4

* Ca/A1 (molar b a s i s ) = [Ca/A1 (mass b a s i s ) ] x 0.675

t h e r e p o r t e d va lues shou ld be f u r t h e r reduced b y a f a c t o r equal t o t h e r a t i o o f t h e v i s c o s i t y o f water, p ~ + , t o t h e v i s c o s i t y of spent e tch, ~ N ~ O H . For 2 t o 8 p e r c e n t e t c h s o l u t i o n s a t temperatures o f 25 t o 6OoC, the v i s c o s i t y r a t i o i s app rox ima te l y 0.67, i n d i c a t i n g t h a t a c t u a l s p e c i f i c r e s i s t a n c e va lues shou ld be reduced by approx ima te l y o n e - t h i r d .

The e f f e c t o f Ca/Al r a t i o a t a r e a c t i o n p e r i o d o f 6 hours on s p e c i f i c r e s i s t a n c e i s presented g r a p h i c a l l y i n F igu re 8.6. For r e a c t i o n temperatures o f 43OC and 6OoC, t h e r e s i s t a n c e t o dewa te r ing decreased w i t h i nc reased c a l c i u m dosages. For a r e a c t i o n temperature o f 25OC, t h e r e s i s t - ance t o dewater ing i nc reased as t h e mass Ca/A1 dosage inc reased f rom 1: l t o 1 .5 : l b u t remained r e l a t i v e l y c o n s t a n t f o r a d d i t i o n a l i nc reases i n t h e Ca/A1 r a t i o . r e s i s t a n c e . Except f o r t h e v a l u e a t a Ca/A1 mass r a t i o o f 1.0 a t 25"C, s p e c i f i c r e s i s t a n c e va lues i n F i g u r e 8.6 f o l l o w e d s i m i l a r r e l a t i o n s h i p s a t a i l temperatures.

i n a d d i t i o n , r e a c t i o n temperature had a m i n o r impact on s p e c i f i c

Dewatered Cake S o l i d s Content-- The r e l a t i o n s h i p s between a p p l i e d Ca/A1 r a t i o and s o l i d s c o n t e n t o f dewatered cakes produced i n s p e c i f i c r e s i s t a n c e t e s t s a re shown i n F i g u r e 8.7 a t r e a c t i o n temperatures o f 25OC and 6OoC. Dry cake s o l i d s d i d n o t s i g n i f i c a n t l y change ove r t h e range o f a p p l i e d doses f o r each o f t h e r e a c t i o n temperatures. However, t h e r e was a s i g n i f i c a n t d i f f e r e n c e between t h e s o l i d s c o n t e n t a t r e a c t i o n temperatures o f 6OoC and 25OC. temperature o f 6OoC was 52.5 pe rcen t w h i l e t h e average d r y s o l i d s c o n t e n t a t a r e a c t i o n temperature o f 25OC was 48 p e r c e n t d r y s o l i d s . Thus, f o r a r e a c t i o n temperature o f 6OoC, app rox ima te l y 8.5 p e r c e n t l e s s dewatered s ludge mass r e s u l t e d as compared t o r e a c t i o n temperatures o f 25OC f o r e q u i v a l e n t Ca/A1 dosag, r a t i o s .

F i l t e r - L e a f Y i e l d - -

l i m i t e d q u a n t i t i e s of s ludge a v a i l a b l e f o r l a b o r a t o r y s tudy and t h e q u a n t i t y o f s ludge r e q u i r e d f o r l e a f t e s t i n g , o n l y l i m i t e d t e s t i n g was conducted. Data f o r t h r e e temperatures a t a Ca/A1 mass r a t i o o f 3.5/1 a r e

The average d r y s o l i d s c o n t e n t a t a r e a c t i o n

__

Resu l t s o f f i l t e r l e a f t e s t i n g a r e shown i n F i g u r e 8.7. Due t o

1.

25°C

-f-A- 43OC

-5-----U- 60°C

0 0.5 1 .o 1.5 2.0 2.5 3.0

CalAl RATIO, GIG

0 (D

F i g u r e 8.6. R e l a t i o n s h i p Between S p e c i f i c Resis tance and App l i ed Ca/A1 Ra t ios f o r React ion Temperatures of 25, 42 and 60°C.

110

Y N

R

Y F

9 c

2

0

0 W

0 U

vi W Y

0

U W L W +J m 3 W n

m

n W .r +J L E v i 0 S U 0

r. a3 W L 3 m

L L .-

111

0 0 N

I I I

0 W

0 m

0 P

0 m

,::

z

0

0

112

presented i n F i g u r e 8.8. 48.8, 133.3 and 146.4 kg/m ah, r e s p e c t i v e l y . Cake r e l e a s e f o r t he 25OC f i l t r a t i o n temperature was poor and t h e cake had t o be removed from t h e f i l t e r w i t h a k n i f e edge. A t f i l t r a t i o n temperatures of-45OC and 60OC, cakes s e l f - d i s c h a r g e d from t h e media w i t h r e l e a s e o f vacuum. F i g u r e 8.8 i n d i c a t e d t h a t f i l t e r y i e l d s were d r a s t i c a l l y reduced a t a s ludge temperature o f 25'C. I n f a c t , t h e d a t a i n d i c a t e d a 200 p e r c e n t decrease i n f i l t e r y i e l d f o r a s ludge f i l t r a t i o n temperature o f 25OC as opposed t o f i l t r a t i o n temperatures o f 43 and 6OoC.

DISCUSSION

S i l t e r - l e a f y i e l d s f o r 25, 43 and 60oC were

A n a l y s i s o f

Resu l t s o f l a b o r a t o r y exper iments i n d i c a t e d t h a t r e c l a m a t i o n o f spent e t c h c o u l d be achieved by p r e c i p i t a t i o n o f aluminum w i t h l i m e . Mechanical f i l t r a t i o n o f t h e suspension c o u l d be s u c c e s s f u l l y employed t o remove p rec ip i t a ted -a lum inum s o l i d s and recove r t h e c a u s t i c e t c h s o l u t i o n f o r reuse. D iscuss ion o f t h e r e s u l t s o f t h e s t u d y a r e focused on r e a c t i o n chemis t r y , s ludge t rea tmen t and d i sposa l and process a p p l i c a t i o n .

Reac t ion Chemistry

t h e c o n c u r r e n t p r e c i p i t a t i o n o f aluminum and c a l c i u m a t temperatures o f 25 t o 6OoC. aluminum, sodium and c a l c i u m f o l l o w e d by a l l oy -con taminan t meta ls w h i l e p r i n c i p a l an ions were hyd roxy l i ons . A t t h e extreme a l k a l i n e c o n d i t i o n s o f spent c a u s t i c e t c h wastes, t h e most probable chemical p r e c i p i t a t e s formed upon l i m e a d d i t i o n were c a l c i u m a lumina tes .

Accord ing t o K e l l y (19601, c a l c i u m forms f o u r w e l l - d e f i n e d anhydrous a luminates and approx ima te l y t e n hydrated a lum ina tes . The f o u r anhydrous forms a r e presented as Ca0.A1203; 3CaO.Al 0 ( K e l l y , 1960). The most w e l l -known hydra?ediforms are238a0.A1203.6H26i 2Ca0.A1203.8H20; .3CaO.A1 0 .12H20;and 4Ca0.A1203.12H 0, a l t hough 3CaO.Al 0 .6H 0 i s g e n e r g l j y agreed t o be t h e o n l y ssab le a lum ina te a t temperafu9es getween 20 and 215OC ( K e l l y , 1960; Car lson, 1958). c a l c i u m a lumina te f o r m a t i o n i n m i n e r a l i z e d mun ic ipa l waters and found p r e c i p i t a t e compos i t i on t o be represented b y 3.4 CaO-A1 03.8.8H20, 4.2CaO.Al 0 .13.2H20 and 1.7 Ca0.A1203*5.7H20 a t i n i t i a ? ca l c ium t o aluminum ?a?ios (molar) o f 3, 4 and 2, r e s p e c t i v e l y .

A d d i t i o n o f hyd ra ted l i m e t o a spent c a u s t i c e t c h s o l u t i o n r e s u l t e d i n

The p r i n c i p a l c a t i o n s i n l i m e - t r e a t e d e t c h s o l u t i o n s were

3CaO.5A1 0 ;and 5CaO.Al O3

Pepples and Wel ls , 1954; I n a d d i t i o n , Schaezler (1978) examined t h e c h e m i s t r y o f

Calc ium a p p l i c a t i o n r a t e s , expressed as a molar r a t i o o f c a l c i u m t o aluminum, o f 2.75 and 3.7 were r e q u i r e d t o remove aluminum from spent e t c h i n a 6-hour p e r i o d a t temperatures o f 60 and 25OC, r e s p e c t i v e l y . va lues were w i t h i n t h e range o f va lues presented by Schaezler (1978). M o l a r c a l c i u m t o aluminum r a t i o s f o r t h e ca l c ium a luminates presented by K e l l y (1960) ranged- f rom 0.3 t o 1.5 and 1 t o 2 f o r anhydrous and hydrated

r e l a t i v e t o aluminum. o b t a i n e d h e r e i n t o t h a t presented b y K e l l y (1960) i s , however, n o t p o s s i b l e . As i n d i c a t e d i n F i g u r e 8.1, e q u i l i b r i u m c o n d i t i o n s were n o t reached w i t h i n t h e r e a c t i o n t i m e o f 6 hours used th roughou t t h e s t u d y and aluminum p r e c i p i t a t i o n con t inued t o occu r a t a l l c a l c i u m t o aluminum r a t i o s .

These

-forms, r e s p e c t i v e l y . These va lues were l ower than t h e l e v e l s o f c a l c i u m a p p l i e d D i r e c t comparison o f chemical composi t ion d a t a

113

However, i t i s apparent t h a t t h e r e s u l t s ob ta ined a r e c o n s i s t e n t w i t h those presented b y Schaezler (1978) f o r ca l c ium t o aluminum r a t i o s and t h a t t h e most probable chemical p r e c i p i t a t e s formed were hyd ra ted c a l c i u m a luminates. S ince n o n - e q u i l i b r i u m c o n d i t i o n s were moni tored th roughou t t h e study, i t i s imposs ib le t o p r e d i c t t h e e x a c t form of t h e aluminum p r e c i p i t a t e s .

Labora to ry r e s u l t s i n d i c a t e d t h a t t h e ca l c ium a lumina te r e a c t i o n was enhanced by i nc reases i n r e a c t i o n temperature and r e a c t i o n t ime. Increases i n temperature f rom 3OoC t o 6OoC decreased t h e molar Ca/A1 r a t i o from 4.5 t o 2.75 f o r a r e a c t i o n t i m e o f 6 hours. Thus, f o r equal amounts o f aluminum i n s o l u t i o n , a 3OoC i n c r e a s e i n r e a c t i o n temperature r e s u l t e d i n a 29 pe rcen t r e d u c t i o n i n l i m e requi rements. r e d u c t i o n i n raw chemical consumption would a l s o r e s u l t i n a r e d u c t i o n i n t h e mass o f s ludge f o r d i sposa l and thus a r e d u c t i o n i n u l t i m a t e s ludge dewater ing and d i sposa l cos ts . Cons ide r ing t h e b e n e f i c i a l e f f e c t s o f h i g h r e a c t i o n temperature on r e a c t i o n s tochiometry , scale-up o f an e t c h recove ry system shou ld be designed f o r h i g h temperatures. t a n k used i n f i n i s h i n g aluminum i s main ta ined a t temperatures o f 55 t o 65OC, e t c h recove ry systems c o u l d be e f f e c t i v e l y employed a t these temperamres t o m in im ize chemical requirements. As presented i n F igu re 8.1, l o n g e r r e a c t i o n pe r iods p rov ided f o r more e f f e c t i v e p r e c i p i t a r i o n a t a g i ven i i m e a p p l i c a t i o n r a t e . temperature o f t h e suspension must be considered when i n c l u d i n g t h i s v a r i a b l e i n t o t h e des ign o f a p r o t o t y p e system.

Sludge Treatment and Disposal

and maximum values f o r cake s o l i d s c o n t e n t s a t r e a c t i o n temperatures o f 6OoC and m o l a r Ca/A1 doses equal t o o r exceeding 2.0 a t a r e a c t i o n t ime o f 6 hours. These s ludge had c h a r a c t e r i s t i c s p e c i f i c r e s i s t a n c e va lues o f app rox ima te l y 5.4 x l o f o m/kg and cake s o l i d s con ten ts t y p i c a l l y exceeding 52 percent . These d a t a compare v e r y f a v o r a b l y w i t h conven t iona l s ludges produced a t P l a n t A3 which have t y p i c a l s p e c i f i c r e s i s t a n c e va lues f o r uncond i t i oned s ludges r a n g i n g from 2.8 t o 3.8 x 1011 m/kg and d r y s o l i d s o f 8 t o 1 4 pe rcen t (Saunders e t a l . , 1982). Calc ium a lumina te s ludges produced i n e t c h recove ry had s p e c i f i c r e s i s t a n c e va lues which were 1 0 - f o l d l o w e r than those f o r conven t iona l s ludges (when c o r r e c t i n g f o r v i s c o s i t y d i f ferences i n c a l c i u m a lumina te s ludges) and dewatered t o a d r y s o l i d s c o n t e n t which was 3.7- t o 6.5- fo ld h i g h e r than t h a t f o r conven t iona l s ludges produced a t t h e p l a n t .

For a p r o t o t y p e u n i t , t h i s

S ince an e t c h

However, t h e e f f e c t o f i nc reased r e a c t i o n t i m e on t h e

Calc ium a lumina te s ludges e x h i b i t e d minimum s p e c i f i c r e s i s t a n c e va lues

Reac t ion temperature i nc reased t h e e x t e n t o f aluminum p r e c i p i t a t i o n a t a g i ven Ca/A1 r a t i o b u t d i d n o t s i g n i f i c a n t l y a f f e c t s ludge dewater ing c h a r a c t e r i s t i c s . s i m i l a r a t v i r t u a l l y , a l l Ca/A1 values, a l t hough s o l i d s con ten ts o f

As presented i n F i g u r e 8.6, s p e c i f i c r e s i s t a n c e da ta were

__ ~-. dewatered cakes d i d i n c r e a s e w i t h r e a c t i o n temperature.

L i m i t e d f i l t e r l e a f t e s t s conducted a t a r e a c t i o n temperature o f 6OoC and a molar Ca/A1 r a t ' o o f 1 .7 r e s u l t e d i n s imu la ted v a c u u m - f i l t e r y i e l d s

f o r uncond i t i oned conven t iona l s ludges produced i n a lum inum- f i n i sh ing p l a n t s -- o f 48.8 t o 146.4 kg/m 3 -h. F i l t e r y i e l d s r e p o r t e d by Saunders e t a l . (1982)

114

ranged from 0.37 t o 20.54 kg/m2.h. s ludges were a t t r i b u t a b l e t o increased i n i t i a l suspended s o l i d s concentra- t i o n s and t o improved s ludge dewater ing p r o p e r t i e s .

The improved y i e l d s f o r ca lc ium-aluminate

Process A p p l i c a t i o n and Eng ineer ing S i g n i f i c a n c e

I n c o n s i d e r a t i o n o f a p p l i c a t i o n o f t h e e t c h recove ry process, i t i s assumed t h a t an o p e r a t i o n a l temperature o f 60°C and r e a c t i o n t i m e o f s i x hours a r e p r a c t i c a l . For purposes o f examinat ion, t h e i n f o r m a t i o n i n S e c t i o n 6 a r e t o be used i n c o n s i d e r i n g use o f e t c h recove ry on t h e anodize l i n e a t p l a n t A l . L ' i t h a spent e t c h p r o d u c t i o n r a t e o f 6.3m3/d, a r e a c t i o n vessel f o r l i m e a d d i t i o n w i t h a volume o f app rox ima te l y 1.6m3 would be r e q u i r e d (e.g., d iamete r = l m and depth = 3m [ i n c l u d i n g 0.8m3 o f f reeboard volume)). would be r e q u i r e d . The i n s t a l l a t i o n , t h e r e f o r e , would n o t be a major one and would occupy o n l y a smal l p o r t i o n o f a p l a n t s i t e .

i n S e c t i o n 6 i n d i c a t e d t h e t o t a l aluminum wastage r a t e a t p l a n t A1 was 566 kg/d. i t was assumed t h a t t h i s q u a n t i t y o f aluminum would be p r e c i p i t a t e d as

. Al(OH), and dewatered t o a s o l i d s c o n t e n t o f 12 pe rcen t f o r normal o p e r a t i o n a l c o n d i t i o n s . t i o n , it was assumed t h a t a l l spent e t c h was removed as c a l c i u m a lumina te u s i n g l i m e a d d i t i o n a t a mass a p p l i c a t i o n r a t e o f 4/1(Ca/A1) a t a temperature o f 60OC. Furthermore, i t was assumed t h a t t h e aluminum c o n c e n t r a t i o n i n e t c h was reduced by 80 percent, thereby r e d u c i n g t h e q u a n t i t y o f aluminum i n d ragou t f rom t h e e t c h tank . q u a n t i t y o f s ludge produced d u r i n g e t c h recove ry was es t ima ted t o be 8.7 kg d r y s o l i d s / k g aluminum removed. q u a n t i t i e s were e s t i m a t e d f o r p l a n t A1 w i t h and w i t h o u t an e t c h recove ry system u s i n g l i m e a d d i t i o n and a r e presented i n Table 8.3. The es t ima ted q u a n i t y o f wet s ludge s o l i d s u s i n g conven t iona l n e u t r a l i z a t i o n w i th an e t c h recove ry system was 13.5 T/d. Convent ional t rea tmen t w i t h o u t an e t c h r e -

. cove ry system would produce approx ima te l y 18.1 T/d, o r 34 p e r c e n t more wet s ludge s o l i d s . Implementat ion o f t h e e t c h recove ry system u s i n g l i m e a d d i t i o n , t h e r e f o r e , would have a p o s i t i v e impact on s ludge q u a n t i t i e s .

c a n t chemical sav ings. C o n t i n u i n g w i t h t h e use o f p l a n t A1 as an example, t h e f l o w o f spent e t c h was 6.3m3/d as shown i n Tab le 6.4. was r e q u i r e d t o c o n t r o l t h e accumulat ion o f aluminum ( A i t 3 ) i n t h e e t c h tank , would be e l i m i n a t e d , as would be t h e need f o r r o u t i n e a d d i t i o n o f v i r g i n c a u s t i c . v i r g i n c a u s t i c would be approx ima te l y $500/d. The c o s t o f l i m e would be approx ima te l y $100/d (Ca(OH)2 a t $38/ ton (1982). c o s t s would be approx ima te l y $400/d o r $110,00O/year. chemical c o s t s would be o f f s e t i n i t i a l l y by t h e c a p i t a l and i n s t a l l a t i o n c o s t s f o r a l i m e s t o r a g e and dos ing system, a dewater ing system and assoc ia ted h y d r a u l i c systems. The p r e l i m i n a r y chemical c o s t data, however, i n d i c a t e t h a t t h e process i s f e a s i b l e and wor thy o f f u r t h e r c o n s i d e r a t i o n . research i s r e q u i r e d b e f o r e t h e process can be implemented.

I n add i t i on , a l i m e a d d i t i o n system and vacuum f i l t e r

I n c o n s i d e r a t i o n o f t h e impact on s ludge p roduc t i on , da ta presented

To determine t h e impact o f e t c h recove ry on s ludge p roduc t i on ,

F o r imp lemen ta t i on o f a.n e t c h recove ry system u s i n g l i m e a d d i -

From da ta i n F igures 8.2 and 8.4, t h e

Based on these assumptions, s ludge

Imp lemen ta t i on o f an e t c h recove ry system would a l s o r e s u l t i n s i g n i f i -

T h i s f l o w , which

Using a c o s t f o r NaOH o f $180/ton (1982), t h e chemical sav ings f o r

The n e t sav ings i n chemical T h i s sav ings i n

. ~

A d d i t i o n a l

i15

Table 8.3 Sludge Quan t i t i e s a t Plant A1 w i t h and without Etch Recovery Using Lime Addition

Sludge Sol ids

A1 u m i n u m Sol ids Wet Sludge Treated Content

Description T/d Percent T/d

Conventional Neutral izat ion

All wastewaters 0.566 1 2 18.1

Conventional Neutral izat ion with E tch Recovery System

Conventional Neutral izat ion o f Rinsewaters 0.270 1 2 8.6

Spent Etch Recovery System (Lime Addition)

0.296 52.5 4 .9

TOTAL 13.5

Although t h e calcium aluminate sludge can e a s i l y be dewatered, the moisture i n the sludge s o l i d s is c a u s t i c soda. T h i s places the sludge i n a hazardous category, requir ing addi t ional disposal cos ts over those typ ica l ly required f o r conventional sludges. A perforate-basket cen t r i fuge may, however,' allow for a means o f removing caus t i c soda associated w i t h sludge s o l i d s w i t h a water wash p r io r t o disposal . T h i s should be examined i n d e t a i l . Additional information regarding process k ine t ics and s to ich io- r i e t r y i s required. recovered etch i s c r i t i c a l t o implementation o f t he process and must be f i n a l l y es tab l i shed w i t h fu r ther research.

In addition, information regarding u t i l i t y of the

F ina l ly , the f e a s i b i l i t y o f t h e e tch recovery process has been es tab l i shed herein. Additional laboratory-scale and p i lo t - sca l e t e s t i n g i s required t o e s t ab l i sh the fu l l - s ca l e u t i l i t y of the process.

SECTION 9

RECLAMATION OF ALUMINUM-FINISHING SLUDGE AS LIQUID ALUM

INTRODUCTION

Sludges produced i n t h e aluminum-finishing indus t ry , e spec ia l ly i n e tching and anodizing p l an t s , contain aluminum hydroxide a s t he primary chemical cons t i tuent . An overa l l ob jec t ive o f this pro jec t was to examine techniques which had t h e poten t ia l f o r e l iminat ion of sludge disposal problems through reclamation o f sludge a s useful products. Direct ac id i - f i c a t i o n o f aluminum-finishing sludge w i t h s u l f u r i c acid t o produce aluminum s u l f a t e so lu t ions was therefore inves t iga ted .

f i n i sh ing sludges i s minimal. However, alum sludges from water treatment p l an t s , have been used f o r t he recovery o f aluminum, a s aluminum s u l f a t e , f o r reuse as a coagulant. Since sludges from aluminum-finishing industries and alum sludges contain the same primary cons t i t uen t , i . e . , aluminum hydroxide (Saunders -- e t a l . , 1982), i t i s possible t h a t aluminum recovery technology used w i t h alum sludges may a l so be applied to.aluminum f i n i s h i n g sl udges.

Recovery o f Water Treatment Plant S1 udges

Recovery of aluminum from alum sludges w i t h s u l f u r i c acid i s a well known process. As ea r ly as 1903, aluminum recovery was pract iced i n t he United S t a t e s (Roberts and Roddy, 1960). Later , the process found widespread appl ica t ion i n Japan, Great Br i ta in and Poland (Chen gal., 1976).

A l t h o u g h some va r i a t ions i n the ac id ex t rac t ion process a r e encountered i n p rac t i ce , t he process general ly cons is t s of a rapid-mix u n i t followed by a separa tor . flow sludge i s mixed w i t h s u l f u r i c acid i n a rapid mix tank. sludge i s t r ans fe r r ed t o a separa tor i n which supernatant l i qu id i s recovered f o r reuse as a coagulant i n t h e water treatment process. from t h e underflow o f t he separa tor i s neut ra l ized w i t h l ime, dewatered and disposed t o a lagoon or a l a n d f i l l .

hydroxide sludge sol i d s proceeds a s follows:

Pub1 ished l i t e r a t u r e on recovery o f aluminum s u l f a t e from aluminum-

A l u m sludge i s gravi ty thickened and under-

S l u d g e

Acidified

In the rapid-mix tank, reac t ion between s u l f u r i c acid and aluminum-

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As i s apparent from t h e s t o i c h i o m e t r i c r e l a t i o n s h i p , t h e amount o f a lum i - num recovered v a r i e s w i t h the q u a n t i t y o f a c i d added. Chen e t a l . (1976) observed t h a t most alum s ludge samples e x h i b i t e d an a c i d -demand which c o u l d be p r e d i c t e d from s t o i c h i o m e t r i c c o n s i d e r a t i o n s f o r up t o about 80 pe rcen t aluminum recovery. mined from s t o i c h i o m e t r i c r e l a t i o n s h i p s . 80 pe rcen t e f f e c t i v e , suspension pH was 3.0 f o r most o f t h e s ludge samples. Cornwell and Susan (1 979) r e p o r t e d t h a t aluminum recovery v a r i e d between 50 t o 90 I n a d d i t i o n , t h e o p t i m a l a c i d dose o c c u r r e d a t a s u l f u r i c a c i d t o t o t a l aluminum mo la r r a t i o o f 1.5: l which was approx ima te l y equal t o t h e s t o i c h i o m e t r i c r a t i o . However, f u r t h e r i nc reases i n a c i d a d d i t i o n d i d n o t appear t o i nc rease aluminum recovery s i g n i f i c a n t l y . Exper ience a t f u l l - s c a l e aluminum r e c o v e r y p l a n t s i n Japan i n d i c a t e d t h a t 50 t o 70 pe rcen t aluminum recovery a t pH 2-2.5 was observed w i t h alum sludges (Gruninger, 1975). Gruninger (1975) observed i n p i l o t - p l a n t s t u d i e s t h a t about 75 pe rcen t o f i n f l u e n t aluminum hyd rox ide was recovered as alum a t pH 2. Tongkasame (1975) r e p o r t e d 98 pe rcen t aluminum e x t r a c t i o n a t pH 2. (1966) found t h a t aluminum recovery was about 80 pe rcen t complete a t pH 3 .

W i th m o s t a h m sludges, complete aluminum recovery i s p o s s i b l e . How- ever, t o x i c me ta l s and o t h e r contaminants a r e d i s s o l v e d i n t h e e x t r a c t i o n process and may accumulate t o u n d e s i r a b l e l e v e l s w i t h con t inued r e c y c l i n g of recove red alum. a d d i t i o n , r e p o r t e d t h a t superna tan t c o l o r a t i o n i nc reased s i g n i f i c a n t l y a t pH l e v e l s below pH 3. c o l o r e x t r a c t e d from s ludge had an adverse e f f e c t on t h e e f f i c i e n c y of recovered alum as a coagu lan t .

Wide v a r i a t i o n s observed i n aluminum recovery may be due t o d i f f e r i n g s ludge c h a r a c t e r i s t i c s and exper imenta l c o n d i t i o n s employed. For example, Webster (1966) employed a s l o w - s t i r r e d s e t t l i n g u n i t w i t h a d e t e n t i o n t i m e o f 24 hours i n p lace o f a rap id-mix u n i t . m i x i n g u n i t w i t h a 30-minute d e t e n t i o n t i m e and s t i r r i n g r a t e o f 30 rpm. Cornwel l and Susan (1979) a p p l i e d a d e t e n t i o n p e r i o d o f 15 m inu tes w h i l e Wes te rho f f and Da ly (1974) r e p o r t e d t h e use o f a 25-minute d e t e n t i o n t i m e f o r t h e a c i d u l a t o r i n a p i l o t - p l a n t s t u d y and 10 minutes i n f u l l - s i z e p l a n t s i n Japan. minutes i n an a c i d u l a t o r and Gruninger (1975) found t h a t l o n g e r d e t e n t i o n t imes c o n t r i b u t e d t o h i g h aluminum recover ies . There was a l s o an i n d i c a - t i o n t h a t recovered alum c o n c e n t r a t i o n i nc reased l i n e a r l y w i t h i n c r e a s i n g s o l i d s c o n c e n t r a t i o n .

D e t e n t i o n t imes employed i n p r a c t i c e f o r separa to rs v a r y w i d e l y .

--

Beyond t h i s l e v e l , a c i d demand c o u l d n o t be d e t e r - When aluminum recovery was

p e r c e n t a t pH 3 w l t h f i v e alum sludges.

However, L indsey and Nebster

Webster (1966) and I saac and Vah id i (1961), i n

I saac and Vah id i (1961) observed t h a t t h e amount o f

Chen -- e t a l . (1976) used a

Goldman and Watson (1975) used a d e t e n t i o n t i m e o f 1 0

The d e t e n t i o n t i m e employed by Chen e t a l . (1976) was one hour f o r s e t t l i n g t e s t s conducted i n a 1 - l i t r e g r a d u a t a G l i n d e r . Cornwell and Susan (1979) used a 1 - l i t r e gradua'ted c y l i n d e r as a s e t t l i n g column and a 2:hour s e t t l i n g t ime. t h r e e sludges (Cornwel l and Susan, 1979). However, p r i o r t o a c i d i f i c a t i o n , s ludge volume r e d u c t i o n s o f o n l y 7 pe rcen t were achieved. s ludge volume r e d u c t i o n , a r e d u c t i o n i s achieved i n t h e d r y w e i g h t o f r e s i d u a l s o l i d s . I saac and Vah id i (1961) observed t h a t t h e sludge volume c o u l d be reduced by 67 pe rcen t a t pH 3 a f t e r a 24-hour s e t t l i n g p e r i o d i n

A volume r e d u c t i o n o f app rox ima te l y 80 pe rcen t was observed w i t h . ...~. ~~

I n a d d i t i o n t o

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a 250-1111 as l o w e r pH values. However, i n t h i s case, c o l o r a t i o n o f superna tan t occu r red v e r y r a p i d l y . Goldman and Watson (1975) found t h a t s ludge volume c o u l d be reduced from 890 m l t o 435 m l by l o w e r i n g pH from 7.1 t o 3.0 and employing a s e t t l i n g p e r i o d o f one hour i n a 1 - l i t r e graduated c y l i n d e r . hour d e t e n t i o n t imes f o r t h e separa to r i n p i l o t - p l a n t s t u d i e s . D e t e n t i o n t imes r a n g i n g from 14 t o 60 hours d i d n o t i n f l u e n c e t h e c o n c e n t r a t i o n o f recovered alum. F i n a l l y , Webster (1966) used a d e t e n t i o n p e r i o d o f f i v e days i n a separator .

t rea tmen t p l a n t s ludges i s p r a c t i c a l ,' i n d i c a t i n g t h e p o t e n t i a l f o r a p p l i c a t i o n o f alum recove ry i n t h e a lum inum- f i n i sh ing i n d u s t r y . I t i s t h e r e f o r e o f b e n e f i t t o examine c u r r e n t p r a c t i c e s used i n t h e i n d u s t r y f o r p r o d u c t i o n o f commercial-grade l i q u i d alum.

A1 uminum Sul f a t e I n d u s t r y

where i t i s used i n c l a r i f i c a t i o n of process waters , pH c o n t r o l o f p u l p s l u r r i e s , s e t t i n g o f dyes and s e t t i n g o f s i z e on p u l p f i b e r s . Other uses i n c l u d e c o a g u l a t i o n o f wa te r and wastewaters, phosphorus removal from - domest ic and i n d u s t r i a l wastewaters, p r o d u c t i o n o f f i r e e x t i n g u i s h e r s , t rea tmen t o f w h i t e l e a t h e r s , a s an a s t r i n g e n t i n drugs and cosmetics, and as a mordant t o f i x dyes on t e x t i l e s .

P r o d u c t i o n o f commercial-grade aluminum s u l f a t e e q u a l l e d 1.05 x l o 6 m e t r i c t o n s and i r o n - f r e e aluminum s u l f a t e p r o d u c t i o n e q u a l l e d 1.3 x l o 5 m e t r i c t ons i n 1981 (U. S . Department o f Commerce, 1982). The m a j o r i t y o f t h e commercial-grade aluminum s u l f a t e i s produced by e x t r a c t i o n o f b a u x i t e o r c l a y w i t h excess s u l f u r i c a c i d a t 100 t o 120'C. The h o t supersa tu ra ted suspension i s c l a r i f i e d and mixed w i t h water used t o wash excess sludge s o l i d s t o make l i q u i d alum,whi le the c l a r i f i e d s o l u t i o n i s concen t ra ted by e v a p o r a t i o n p r i o r t o format ion o f g r a n u l a r aluminum sul fa te. . I r o n - f r e e (<0.005 percend Fe,O-,) aluminum s u l f a t e i s produced f rom a c i d i f i c a t i o n o f a lumina t r i h y d r a t e (A1203.3H20), due t o t h e h i g h l e v e l o f i r o n t y p i c a l l y p resen t i n b a u x i t e and c l a y s .

EXPERIMENTAL TECHNIQUES

A1 uminum-Finishinq S1 udges

a lum inum- f i n i sh ing i n d u s t r y as commercial-grade s o l u t i o n s o f aluminum s u l f a t e (i . e . , 1 i q u i d alum), s ludge samples were ob ta ined from numerous sources. The sludges examined i n c l u d e d conven t iona l anod iz ing s ludges, s ludges produced b y segregated n e u t r a l i z a t i o n o f spent e t c h and anodize a c i d , and e tch - recove ry sludge,as w e l l as a b a u x i t e sample.

Convent ional Sludges--

were c o l l e c t e d f rom p l a n t A2 immed ia te l y

graduated c y l i n d e r , and h i g h e r volume r e d u c t i o n s were p o s s i b l e

Wes te rho f f and Da ly (1974) r e p o r t e d on t h e use o f 14- t o 20-

Recovery o f aluminum as an aluminum s u l f a t e s o l u t i o n f rom wa te r

The m a j o r u s e r o f aluminum s u l f a t e i s t h e p u l p and paper i n d u s t r y

To e v a l u a t e t h e p o t e n t i a l f o r r e c l a m a t i o n o f s ludges produced i n t h e

Sludge samples from two a n o d i z i n g p l a n t s were examined. Sludge samples f o l l o w i n g d i scha rge f rom a r o t a r y

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vacuum f i l t e r . Sludges a t t h i s plant were produced by conventional neu t r a l i za t ion o f rinsewaters d u r i n g t he week and by segregated neu t r a l i - za t ion o f concentrated f in i sh ing waste o n a weekend day. The sludge cake co l l ec t ed on t h e vacuum f i l t e r was therefore a mixture o f t he two sludge suspensions.

on a plate-and-frame f i l t e r press. Conventional neu t r a l i za t ion was u t i l i z e d t o t r e a t a l l wastewaters, including spent e tch and anodize ac ids , followed by g rav i ty sedimentation. Sludge s o l i d s , i n both ins tances , were t ransported t o t h e labora tory i n a i r - t i g h t containers t o prevent mois- t u r e l o s s e s .

Segregated Neutral izat ion Sludge-- The potent ia l f o r production o f l i q u i d alum from a sludge produced

by segregated neu t r a l i za t ion o f spent caus t i c e tch and anodize acid was examined u s i n g a sludge produced i n t he laboratory. acid from plant A3 was used t o produce a sludge cake u s i n g a neut ra l iza ton temperature o f 8OoC and a neut ra l iza t ion pH of 8.5, i n accdrd procedures indicated i n Sect ion 7.

Etch Recovery Sludge--

a calcium aluminate sludge. sludge was not amenable t o the production o f a commercial-grade l i qu id alum. Two propr ie ta ry processes f o r etch recovery have been presented by Fugi Sash Inc. and Alcoa, Inc. (Meyer -- e t a l . , 1978; Brown, 1982) which r e s u l t i n production an aluminum-trihydrate sludge. ma te r i a l s , personnel a t p lan t A2 co l lec ted representa t ive samples of sludges from plants u s i n g the two processes and forwarded them t o t he labora tory i n a i r - t i g h t containers f o r i nves t iga t ion .

Bauxite-- To compare product q u a l i t y and r e l a t i v e r e a c t i v i t y of aluminum-finishing

sludges t o t h a t typical o f t h e alum indus t ry , a sample o f bauxite from a lo- cal producer o f aluminum s u l f a t e was obtained. The material was co l lec ted immediately p r i o r t o ac id i f ioa t ion w i t h s u l f u r i c acid a t t h e production s i t e .

Experimental Reactor

I n i t i a l experimental inves t iga t ions were conducted i n covered, 2 - l i t r e , g l a s s beakers which were mixed b u t not insu la ted o r heated. made under these condi t ions were incomplete and unsa t i s fac tory due primarily t o the extensive heat l o s s from t h e low-volume and high-surface-area beaker. In conjunction w i t h d iscussions w i t h representa t ives from numerous producers

~~~~ of l i q u i d alum, an a l t e r n a t i v e ex t r ac t ion system was devised which was con- s i s ten t w i t h t h a t used i n indus t ry t o eva lua te the qua l i t y of bauxi te , c lay and o the r mater ia l s for production of l i q u i d alum.

Sludge s o l i d s were a l so co l lec ted from plan t A3 following dewatering

Spent e tch and anodize

w i t h

The recovery of spent e tch w i t h lime addi t ion (Sect ion 8) produced However, due t o h i g h l e v e l s of calcium, t h i s

To examine these

Extract ions

, - ~

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The r eac to r vessel was a 2 - l i t r e Pyrex beaker w i t h a high-temperature

The r eac to r was placed on a hot p l a t e d u r i n g an ex t r ac t ion and

p l a s t i c cover t o minimize moisture l o s s d u r i n g reac t ion . mixed w i t h a s ing le lb lade Teflon s t i r r e r a t tached t o a variable-speed motor, heated to maintain a near-boiling temperature throughout a react ion period. Su l fu r i c acid addi t ion was cont ro l led u s i n g a 100-ml g lass bure t te . Sample co l l ec t ion and acid addi t ion were achieved t h r o u g h small holes i n t he cover on t h e r eac to r .

The r eac to r was

Experimental Procedures

To examine the potent ia l f o r production o f l i q u i d alum from a sludqe sample, t he sludge was i n i t i a l l y charac te r ized . both t o t a l and i n e r t A 10- to 20-9 sludge sample was dr ied a t 103OC for 24 hours t o deter- minetotal s o l i d s content and then combusted a t 550°C for 30 minutes t o determine the i n e r t ( o r nonvola t i le ) s o l i d s content . determined s ince Saunders e t a l . (1982) determined t h a t t he composition o f the i n e r t s o l i d s was bes t approximated by the formula Al(0H) f o r aluminum-

A l u m i n u m composition was determined on each sample. repeatedly ac id i f i ed t o pH-2 w i t h n i t r ic acid and boiled u n t i l a l l s o l i d s were so lubi l ized or the ex t rac t ion was complete.

The s o l i d s content , s o l i d s , o f t he sludge was determined a t 103°C and 550°C.

I n e r t s o l i d s were

f in i sh ing sludges. 3

Sludges were

The next s t e p i n the ex t rac t ion procedure required the determination o f t h e quant i ty of s u l f u r i c acid t o be added. s o l i d s concentrat ion a s a measure o f t he A l ( O H ) , content o f the sludge, acid requirementswere estimated u s i n g Equation 9.1. A ten percent reduction i n s u l f u r i c acid was usual ly made t o avoid formation o f a p roduc t containing excess acid. I n addi t ion , t he predicted f ina l s t rength o f t he alum product was determined u s i n g Equation 9.1, i n conjunction w i t h t he water content o f the sludge determined i n s o l i d s analyses. I f the predicted s t rength ,of the product exceeded s o l u b i l i t y limits, t he quant i ty o f water required t o avoid supersa tura t ion condi t ions was ca lcu la ted .

Using the i n e r t suspended

To i n i t i a t e an ex t r ac t ion , t he complete r eac to r system was placed i n a vented hood due t o t h e poten t ia l f o r production o f noxious gases d u r i n g an ex t r ac t ion . acid addi t ion was i n i t i a t e d . Due t o the vigorous nature o f t he reac t ion , acid addi t ion was r e s t r i c t e d t o flows of 10-15 m l / m i n . An excessive r a t e o f acid addi t ion resu l ted i n production o f extremely h i g h react ion tempera- t u re s and production o f excessive quan t i t i e s of foam which would overflow the r eac to r . Slow addi t ion o f acid decreased the r a t e of foam production and minimized overflows.

W i t h i n f i v e minutes of i n i t i a t i n q the ex t r ac t ion w i t h acid addi t ion ,

Wet sludge samples were then placed i n the r eac to r and

s t i r r ing was i n i t i a t e d a t 15 rpm. impossible due t o the th ick gelat inous nature of sludge so l id s . of the ex t r ac t ion mixtures were maintained near boiling f o r the durat ion o f t he ex t rac t ion u s i n g t he heater p l a t e .

I n i t i a l l y , s t i r r i n g was v i r t u a l l y Temperature

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F o l l o w i n g a c i d a d d i t i o n and i n i t i a l m i x i n g o f t h e e x t r a c t i o n suspension, samples o f 1 0 - t o 15-1111 volume were c o l l e c t e d and immed ia te l y f i l t e r e d through a 0.45 pm g l a s s - f i b e r f i l t e r . The f i l t r a t e was analyzed f o r f r e e a c i d t o determine t h e progress o f t h e r e a c t i o n . c o n t e n t was l e s s t h a n 0.1%, t h e r e a c t i o n was cons ide red t o be complete and t h e e x t r a c t i o n was terminated. The c o n t e n t s o f t h e r e a c t i o n was then s t o r e d f o r f u r t h e r a n a l y s i s .

EXPERIMENTAL RESULTS

When f r e e - a c i d

The exper imen ta l i n v e s t i g a t i o n o f d i r e c t a c i d i f i c a t i o n o f aluminum- f i n i s h i n g sludges was focused on d e t e r m i n a t i o n o f process f e a s i b i l i t y and on process requi rements t o assure p r o d u c t i o n o f a comnercial-grade p roduc t . Severa l b a t c h e x t r a c t i o n s were conducted on f i v e s ludge samples and a b a u x i t e sample.

Sludge C h a r a c t e r i s t i c s

F i v e s ludge samples were examined i n t h e exper imenta l s t u d i e s . The two s ludges from a n o d i z i n g p l a n t s A2 and A3 were des ignated A2 and A3 h e r e i n . I n a d d i t i o n , s i n c e t h e s o l i d s c o n t e n t f o r t h e s ludge sample c o l l e c t e d a t p l a n t A3 was r e l a t i v e l y low, a p o r t i o n o f t h i s sample was a i r - d r i e d a t a s l i g h t l y e l e v a t e d temperature t o ach ieve a s o l i d s c o n t e n t near t h a t o f sample A2. The o r i g i n a l s ludge sample was des ignated A3-1 w h i l e t h e d r i e d sample was des igna ted A3-2.

Sludge p roduced in t h e l a b o r a t o r y by segregated n e u t r a l i z a t i o n o f con- c e n t r a t e d f i n i s h i n g wastes (see S e c t i o n 8) was des igna ted SN. r e c o v e r y s ludges were des igna ted ER-1 and ER-2 w i t h no d i s t i n c t i o n made t o i d e n t i f y t h e source o f t h e m a t e r i a l s .

The two e t c h

F i n a l l y , b a u x i t e was r e f e r r e d t o as 6.

C h a r a c t e r i s t i c s o f t h e f i v e s ludge samples as used i n t h e e x t r a c t i o n s a r e presented i n Table 9.1. A2 s ludge sample had a s o l i d s c o n t e n t o f 21.3 percent , which was e x c e p t i o n a l f o r anod iz ing p l a n t s . A3-1 s ludge was 13.5 pe rcen t and was t y p i c a l o f t h e s o l i d s c o n t e n t s achieved by t h e m a j o r i t y o f t h e a luminum-f in ish ing p l a n t s surveyed by The Aluminum Assoc ia t i on , I n c . (Saunders _- e t - al., 1982). D ry ing o f a p o r t i o n o f sample A3-1 produced a sample (A3-2) w i t h a s o l i d s c o n t e n t nea r t h a t o f sample A2. The aluminum con ten t , based on i n e r t s o l i d s (IS) was 35.2 and 33.8 percent , r e s p e c t i v e l y , f o r samples A2 and A3. These va lues were s i m i l a r t o t h e t h e o r e t i c a l v a l u e f o r Al(OH), o f 34.6 p e r c e n t and were t y p i c a l o f aluminum f i n i s h i n g s ludges (Saunders -- e t a1 ., 1982).

The s o l i d s c o n t e n t o f

As t y p i c a l o f segregated n e u t r a l i z a t i o n s ludges (see S e c t i o n 7 ) , s ludge sample SN had a h i g h s o l i d s c o n t e n t , i .e., 32.9 percent . t e n t was t h e l o w e s t o f t hose examined, however, i t was n o t s i g n i f i c a n t l y

-below t h a t f o r a lum inum- f i n i sh ing s ludges and was acceptable as a feeds tock f o r p r o d u c t i o n o f l i q u i d alum.

The aluminum con-

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Table 9.1 Charac te r i s t ics of Sol ids Extracted by Direct .Acidification w i t h Su l fur ic Acid

Dry Cake Sol ids A l u m i n u m Content

Total I n e r t Sample (percent ) (percent )

A2 21.3 16.8 0.352

A3-1 13.5 9 .6 0.338

A3-2 21.1 15.5 0.338

SN 32.9 27.1 0.322

ER-1 95.1 94.2 0.373

ER-2 90.4 99.7 0.378

B 94.8 94.4 0.325

* IS = I n e r t Sol ids

Etch recovery sludge samples had extremely h i g h so l id s contents o f 90.4 and 95.4, ind ica t ing t h a t t he samples contained l e s s than 10 percent moisture. These values were, i n addi t ion , i n agreement w i t h those presented by Brown (1982). Vola t i le mater ia l s accounted f o r approximately 1 percent of sludge so l id s , s ince i n e r t s o l i d s ranged from 89.7 t o 94.2 percent s o l i d s . The aluminum contents of t he e tch recovery s o l i d s ranged from 37.3 t o 37.8 percent. the poten t ia l f o r t h e presence o f crys ta l1 ine aluminum prec ip i t a t e s w i t h decreased water contents and aluminum-oxide forms. This potent ia l d i f fe rence i n chemical composition could a f f e c t aluminum ex t r ac t ion w i t h acid addi t ion and was inves t iga ted .

cen t aluminum. The r e s u l t s i n Table 9.1 f o r aluminum content , however, do not r e f l e c t t he nonreactive port ion of bauxite. of the i n e r t s o l i d s were r e f r ac to ry and could not be ex t rac ted . The value for a luminum of 32.5 percent is based on the r eac t ive port ion of the i n e r t solids alone. based on t o t a l inert so l id s .

These values were t h e highest o f a l l those examined and indicated

F ina l ly , the bauxi te sample was low i n moisture and contained 32.5 per-

Approximately 40 percent

The aluminum content was approximately 19.5 percent , when

123

I n general , a lum inum- f i n i sh ing sludges con ta ined h i g h l e v e l s o f aluminum r e l a t i v e t o b a u x i t e and appeared t o be e x c e l l e n t feedstocks f o r p r o d u c t i o n o f l i q u i d alum. sludges, however, i n d i c a t e d p o t e n t i a l f o r d i l u t i o n o f t h e f i n a l p r o d u c t b e l ow acceptable 1 eve ls .

The r e l a t i v e l y h i g h m o i s t u r e c o n t e n t s f o r anod iz ing

Chemical Balance f o r Alum E x t r a c t i o n s

I n i n i t i a t i n g a c i d e x t r a c t i o n s o f s ludge samples, t he p r i m a r y o b j e c t i v e was t o produce a l i q u i d alum w i t h t h e h i g h e s t s t r e n g t h p o s s i b l e w i t h o u t exceeding s a t u r a t i o n c o n c e n t r a t i o n s a t ambient temperatures. Commercial- grade l i q u i d alum t y p i c a l l y c o n t a i n s aluminum a t c o n c e n t r a t i o n s o f 7.5 t o 8.5 pe rcen t as A1203 ( i .e . , 43.7 t o 49.5 pe rcen t as A12(S04)3 14H20). To e s t a b l i s h s t i - ingent requi rements f o r l i q u i d alum produced from aluminum- f i n i s h i n g sludge, i n i t i a l es t ima ted c o n c e n t r a t i o n s o f 8.2 t o 8.5 p e r c e n t as A1203were e s t a b l i s h e d t o determine chemical q u a n t i t i e s f o r e x t r a c t i o n exper iments. However, i f w a t e r con ta ined i n s ludge samples would n o t a l l o w f o r p r o d u c t i o n o f t h i s c o n c e n t r a t i o n , then t h e maximum p o s s i b l e c o n c e n t r a t i o n was used i n t h e e x t r a c t i o n s . Using Equat ion 9.1 and i n c l u d i n g t h e m o i s t u r e c o 3 t a i n e d i n t h e wet s ludge samples, chemical requi rements f o r e x t r a c t i o n exper iments were e s t a b l i s h e d . a c i d c o n c e n t r a t i o n due p r i m a r i l y t o t h e r e f r a c t o r y n a t u r e o f these s o l i d s .

a d d i t i v e s u s e d i n t h e e x t r a c t i o n s a r e presented i n Table 9.2. A l l anodize and segregated n e u t r a l i z a t i o n s ludges were e x t r a c t e d a t 8.2-8.3 p e r c e n t A1203 except sample A3-1. Due t o t h e l o w s o l i d s c o n t e n t o f t h i s s ludge, i .e . , 13.5 p e r c e n t s o l i d s , s ludge m o i s t u r e d i l u t e d t h e e x t r a c t i o n m i x t u r e and an e s t i m a t e d maximum o f 5.3 pe rcen t A1203 was achievable. The h i g h s o l i d s c o n t e n t s o f t h e SN sample, on t h e c o n t r a r y , r e s u l t e d i n an a d d i t i o n a l r e - quirement f o r water, i . e . , 0.56g/g o f wet s ludge s o l i d s , o r 2779. r e c o v e r y s ludge samples were e a s i l y e x t r a c t e d u s i n g est imated A1203 con- c e n t r a t i o n s o f 8.3 and 11.0 pe rcen t . T h i s was achieved by e i t h e r adding the r e q u i r e d d i l u t i o n b e f o r e o r a f t e r conduc t ing t h e e x t r a c t i o n . I n b o t h cases, however, t h e es t ima ted f i n a l A1203 c o n c e n t r a t i o n was 8.3 p e r c e n t and wa te r was added a t t h e r a t e o f 2.1-2.39 H20/g wet s ludge. was e x t r a c t e d a t a h i g h a c i d c o n c e n t r a t i o n b u t water was added a t t h e r a t e o f 4.69 H20/g b a u x i t e f o l l o w i n g e x t r a c t i o n t o reduce t h e s t r e n g t h o f t h e l i q u i d alum s o l u t i o n from 1 4 t o 8.3 p e r c e n t as Al,O,.

Baux i te was e x t r a c t e d u s i n g a h i g h e r r e l a t i v e

Based on t h e above e s t i m a t i n g procedures, t h e chemical and s ludge

Etch

Gaux i te

Sludge E x t r a c t i o n by D i r e c t A c i d i f i c a t i o n

Batch a1 um e x t r a c t i o n s were conducted and samples were taken p e r i o d i c a l l y t o determine t h e e x t e n t o f r e a c t i o n u s i n g f r e e - a c i d measurements. t i o n , samples were c o l l e c t e d p e r i o d i c a l l y t n m o n i t o r t he r e a c t i o n f o r a l l samples except baux i te . be f i l t e r e d w i t h i n a reasonable t i m e p e r i o d t o m o n i t o r t h e e x t r a c t i o n r e a c t i o n . F i l t r a t e samples were n o t c o l l e c t e d f o r samples ER-l(B) and ER-Z(B) due t o t h e supersa tu ra ted c o n d i t i o n s under which these exper iments were conducted.

I n addi -

. B a u x i t e samples were ex t reme ly v iscous and c o u l d n o t

124

Table 9.2 Chemical A d d i t i v e s i n Alum Ex t rac - t i ons

E x t r a c t i o n A d d i t i v e s Pos t - Es t imated I n e r t Sludge D i l u t i o n E x t r a c t i o n

H,SOI, Sludge Water Water D i l u t i o n Sol i d s Water

A1 Z03

Sample ( p e r c e n t ) 0 ( 9 ) M 0 ( 9 )

A2 8.3 31 7 168 83 2 0 0

A3- 1 5.3 181 96 904 0 0

A3-2 8.2 285 151 804 0 0

SN 8.3 243 129 3 69 277 0

ER-1 (A) 8.3 242 106 6 665 0

ER-Z(A) 8.3 256 112 12 695 0

ER-1 ( E ) 11.0 242 106 6 41 1 254*

ER-Z(B) 11 .o 256 1 1'2 12 43 2 263-

B 14.0 144 83 5 160 406*

* D i l u t i o n water added a f t e r e x t r a c t i o n t o achieve f i n a l A1,03concentrations

o f 6.3 percent .

F i l t r a t e aluminum c o n c e n t r a t i o n s f o r severa l samples a re presented i n F i g u r e 9.1. A l i q u i d alum c o n c e n t r a t i o n o f 6.3 t o 8.5 pe rcen t as A1203 i s r e f l e c t i v e o f s a t u r a t i o n c o n d i t i o n s and maximum p r a c t i c a l concen t ra t i ons f o r l i q u i d alum. There fore , w i t h i n approx imate ly a 40-minute pe r iod , aluminum concen t ra t i ons f o r samples A2, A3-2, and SN were a t s a t u r a t i o n l e v e l s . E x t r a c t i o n o f samples ER-1(A) and ER-2(A) were v i r t u a l l y i d e n t i c a l and a re presented i n F i g u r e 9.1 w i t h an ER des igna t ion . The s o l i d s i n t h e e t c h recovery sludges were more d i f f i c u l t t o e x t r a c t s i n c e a 120-minute p e r i o d was r e q u i r e d t o reach aluminum c o n c e n t r a t i o n s above 7.5 pe rcen t as A1203. Data f o r e x t r a c t i o n o f sample A3-2

_ f o l l o w e d t h e same t r e n d as sample A3-1 w i t h t h e excep t ion t h a t t h e maximum aluminum c o n c e n t r a t i o n was 5.8 pe rcen t as A1203. Data cou ld n o t be c o l l e c t e d f o r t h e b a u x i t e sample b u t t h e e x t r a c t i o n was n o t complete u n t i l a f t e r t h r e e hours a t an e l e v a t e d a c i d c o n c e n t r a t i o n .

I.

125

10 I I I I I I

8

6

4

2

0

40 60 80 100 120 140 0 20

TIME, MINUTES

Figure 9.1 Filtrate Aluminum Concentrations in Direct-Acidification o f Aluminum-Finishing Sludges.

126

'Therefore, s ludge samples f rom a luminum- f i n i sh ing p l a n t s were r e a d i l y e x t r a c t a b l e u s i n g s t o i c h i o m e t r i c a d d i t i o n o f s u l f u r i c a c i d w i t h i n a two-hour pe r iod . b a u x i t e , t h e common feedstock f o r alum p roduc t i on .

a c i d and f r e e A1 a r e presented i n Table 9.3. t r a t i o n s i n Tab le 9.3 were those presented i n Table 9.2 ( f o l l o w i n g pos t - e x t r a c t i o n d i l u t i o n ) . A1203 c o n c e n t r a t i o n s exceeded es t ima ted va lues by 0.1 t o 0.6 pe rcen t , i n d i - c a t i n g e x c e l l e n t p r o d u c t q u a l i t y . I n ' a d d i t i o n , w i t h excep t ion o f A3-1, t h e A1203 c o n c e n t r a t i o n s were w i t h i n o r s l i g h t l y above t h e t y p i c a l range o f va lues f o r commercial-grade l i q u i d alum ( i , e . , 7.5 t o 8.5 pe rcen t as A1,0,). c o n c e n t r a t i o n s o f 8.3 pe rcen t . was n o t as r a p i d f o r these samples as i t was f o r o t h e r a lum inum- f i n i sh ing sludges. However, when d i l u t i o n water was added a f t e r comp le t i on o f t h e e x t r a c t i o n w i t h samples ER-1(B) and E R - Z ( B ) , and n o t a t t h e beginning, t h e h i g h e r a c i d c o n c e n t r a t i o n a c c e l e r a t e d t h e e x t r a c t i o n o f aluminum and A1203 c o n c e n t r a t i o n s o f 8.5-8.7 pe rcen t were achieved. T h i s o p t i o n o f p o s t - e x t r a c t i o n d i l u t i o n i s o b v i o u s l y one which c o u l d be p r a c t i c e d i n pro- t o t y p e systems, the reby i n d i c a t i n g e x c e l l e n t p o t e n t i a l f o r use o f e t c h recove ry s o l i d s f o r alum p r o d u c t i o n .

Sample A3-1 was e x t r a c t e d t o a c o n c e n t r a t i o n o f 5.8 p e r c e n t A1203 which was below accep tab le l e v e l s f o r f u l l - s t r e n t h l i q u i d alum. i n i t i a l s o l i d s c o n t e n t o f t h i s sample was too l o w t o a l l o w f o r p r o d u c t i o n o f a commercial-grade m a t e r i a l . appear t h a t a s o l i d s c o n t e n t o f app rox ima te l y 21 pe rcen t i s r e q u i r e d t o be a b l e t o achieve commercial-grade l e v e l s . The va lues o f f r e e A1 i n c l u d e d i n Tab le 9.3 a r e i n d i c a t i v e of s l i g h t l y s a t u r a t e d c o n d i t i o n s . c o r r e c t e d by t h e a d d i t i o n o f w a t e r t o t h e e x t r a c t i o n m i x t u r e and may have, i n fac t , been caused b y t h e l o s s of m o i s t u r e d u r i n g t h e e x t r a c t i o n pe r iod .

The s ludge samples were, i n a d d i t i o n , more e a s i l y e x t r a c t e d than

Wi th r e s p e c t t o q u a l i t y o f t h e f i n a l product , da ta f o r A1203, f r e e The e s t i m a t e d A1,0, concen-

W i t h t h e excep t ion o f ER-1 ( A ) and ER-2(A), measured

Samples ER-1(A) and ER-Z(A) were e x t r a c t e d a t es t ima ted A1203 As i n d i c a t e d i n F i g u r e 9.1, t h e e x t r a c t i o n

The

From da ta f o r samples A2 and A3-1, i t would

Th is c o u l d be

Due t o t h e predominant use o f l i q u i d alum by t h e p u l p and paper indus- try, t h e p r i n c i p l e concern w i t h r e s p e c t t o alum q u a l i t y i s n o t f o r t o x i c meta ls , f o r example, b u t f o r c o n s t i t u e n t s which r e s u l t i n poor p roduc t q u a l i t y . potassium ( K ) , c a l c i u m (Ca), magnesium (Mg), t i t a n i u m ( T i ) , ammonia (NH4) as w e l l as t o t a l heavy m e t a l s . Analyses o f a lum inum- f i n i sh ing sludges i n - d i c a t e d t h a t ammonia and t o t a l heavy me ta l s were n o t o f m a j o r concern (Saunders - e t _ * a1 3 1982). warranted. presented i n Tab le 9.4. w i t h i n t y p i c a l i n d u s t r i a l l i m i t s as e x t r a c t e d from numerous i n d u s t r i a l sources (Note: t h e r e a r e no f i x e d l i m i t s which a r e en fo rced by a regu la - t o r y o r i n d u s t r i a l -users group) , on aluminum c o n t e n t and on t h e m a j o r contaminant c a t i o n s and should be o f accep tab le i n d u s t r i a l q u a l i t y . I n a d d i t i o n , t h e e t c h recove ry s ludges were below t h e l i m i t s e t f o r i r o n - f r e e l i q u i d alum, i .e . , 3 5 mg/l as Fe.

These contaminants o f concern i n d u s t r i a l l y i n c l u d e i r o n (Fe) ,

However, analyses f o r Fe, Ca, K, and Mg were Concen t ra t i ons o f t hese me ta l s i n l i q u i d alum s o l u t i o n s a r e

A l l o f t h e alum samples produced i n t h e s tudy were

The p roduc ts t h e r e f o r e met s p e c i f i c a t i o n s

127

Table 9'.3 Composition o f Extracted Liquid Alum Products

A1 20 3 (percent ) Free Free

Acid A1 Sample Estimated Measured (percent ) (percent )

A2

A3-1

A3-2

SN

ER-1 ( A )

ER-l(8)

E R - Z ( A )

ER-Z(B)

B

8.3

5.3

8.2

8.3

8.3

8.3

8.3

8.3

8.3

8.9

5.8

8.4

8.5

7.6

8.7

7.9

8.5

8.4

-- 0.62

-- 0.52

-- 0.61

-- 0.37

0.38 -- -- 0.67

0.26 -- -- 0.42

-- 0.04

Table 9.4 Trace Metal Composition o f Liquid A l u m

Fe Ca K Mg Sample m g l l mg/l m g l l mgll

A2 543 22 16 102

A3-1 1135 166 11 401

A3-2 1923

SN 233

ER-1 30

ER-2 28

B 822

Typical Indus t r ia l <2100 Standard

* -~ -

....................

278 15 670

10 44 252

<1 <1 54

<1 <1 31

40 23 2

<300 <125 < 800

128

S ince i r o n - f r e e l i q u i d alum i s s o l d f o r about t w i c e t h e p r i c e o f commercial- grade l i q u i d alum, implementat ion of e t c h recove ry systems a t a n o d i z i n g p l a n t s may r e s u l t i n p r o d u c t i o n o f sludges which c o u l d be used t o produce an alum p r o d u c t o f h i g h e r commercial va lue.

D I S C U S S I O N

To examine t h e p o t e n t i a l f o r r e c l a m a t i o n o f a lum inum- f i n i sh ing sludges by d i r e c t a c i d i f i c a t i o n , d a t a presented by Saunders -- e t a l . (1982) f o r numerous a n o d i z i n g and e t c h i n g sludges were examined.

Sludge Reclamat ion by D i r e c t A c i d i f i c a t i o n

Dry i n e r t s o l i d s i n a lum inum- f i n i sh ing sludges c o n t a i n app rox ima te l y 35 p e r c e n t aluminum and a r e b e s t rep resen ted by t h e fo rmu la Al(OH),. The r e a c t i o n assoc ia ted w i t h t h e a d d i t i o n o f s u l f u r i c a c i d t o wet aluminum- f i n i s h i n g s ludge s o l i d s i s t h e r e f o r e rep resen ted by:

A1 (OH), + X H20 + 1.5 H2S04 .+ 0.5 AI,(SO4)3 + ( 3 + X ) H2O (9.2)

where X i s i n d i c a t i v e o f t h e m o l a r q u a n t i t y o f water assoc ia ted w i t h wet s ludge s o l i d s . S u l f u r i c a c i d requi rements t h e r e f o r e a r e equal t o 1.8 kg/kg d r y i n e r t s ludge s o l i d s and alum p r o d u c t i o n r a t e s a r e equal t o 2.4 kg A1,(S04),/kg d r y i n e r t s ludge s o l i d s o r 0.72 kg Al,O,/kg d r y i n e r t s ludge s o l i d s . The compos i t i on o f commercial-grade l i q u i d alum i s app rox ima te l y 8.3 p e r c e n t as A1,03, o r 27 p e r c e n t as A12(SD4),. i n Equa t ion 9.2, a s ludge c o n t a i n i n g 16.8 pe rcen t Al(OH), i s r e q u i r e d as a minimum t o produce an accep tab le c o m e r c i a l - g r a d e l i q u i d alum. However, s i n c e a lum inum- f i n i sh ing s ludges c o n t a i n app rox ima te l y 70 t o 80 p e r c e n t i n e r t s o l i d s (Saunders, e t a1 ., 1982), a more r e a l i s t i c e s t i m a t e f o r minimum s o l i d s c o n c e n t r a t i o n s i s b e t w e e n 21 and 24 pe rcen t d ry -so l i d s (measured a t 105OC).

'

Us ing these l a t t e r va lues

Data presented i n Tables 9.1 and 9.3 f o r s ludge samples A2 and A3-2 i n d i c a t e d t h a t commercial-grade alum c o u l d be produced w i t h s ludges con- t a i n i n g i n e r t s o l i d s o f 16.8 and 15.5 percent , r e s p e c t i v e l y , and t o t a l s o l i d s o f 21.3 and 21.1 pe rcen t , r e s p e c t i v e l y . These measured values, i n c o n j u n c t i o n w i t h es t ima ted va lues above,s t rongly i n d i c a t e t h a t s ludge s o l i d s c o n c e n t r a t i o n s i n excess o f 21 p e r c e n t a r e r e q u i r e d t o e f f e c t i v e l y produce l i q u i d alum w i t h a conven t iona l aluminum f i n i s h i n g sludge. The q u a n t i t y o f wa te r assoc ia ted w i t h s ludges a t l o w e r s o l i d s con ten ts r e s u l t i n d i l u t i o n o f t h e p roduc t , as i n d i c a t e d b y r e s u l t s w i t h sample A3-1.

~ Data f rom a s t u d y conducted b y The Aluminum A s s o c i a t i o n I n c . (Saunders _ _ e t a1 ., 1982) i n d i c a t e d t h a t conven t iona l s ludges f o l l o w i n g dewater ing Rad s o l i d s con ten ts rang ing f rom 7.4 t o 20 pe rcen t and l a b o r a t o r y data presented by Saunders _ - e t a l . (1982) i n d i c a t e d a range o f 8.5 t o 20.1 pe rcen t s o l i d s . These da ta t h e r e f o r e s t r o n g l y i n d i c a t e t h a t r e c l a m a t i o n o f a lum inum- f i n i sh ing s ludge can o n l y be achieved i f s ludge m o i s t u r e con- t e n t o f conven t iona l s ludges i s reduced.

129

Data presented f o r s ludge s o l i d s produced b y segregated n e u t r a l i z a t i o n and by recove ry o f spent e t c h as an aluminum t r i h y d r a t e i n d i c a t e d t h e y were e x c e l l e n t sources f o r p r o d u c t i o n o f l i q u i d alum. The m o i s t u r e c o n t e n t o f t hese sludges, i n a d d i t i o n , r e q u i r e d t h a t wa te r be added t o produce a commercial-grade l i q u i d alum. F i n a l l y , segregated n e u t r a l i z a t i o n and e t c h r e c o v e r y processes a r e bo th focused on t rea tmen t o f t h e ma jo r source o f waste aluminum a t f i n i s h i n g p l a n t s , i .e., spent etchnand have e x c e l l e n t p o t e n t i a l f o r a p p l i c a t i o n i n conven t iona l a lum inum- f i n i sh ing p l a n t s . I m - p lemen ta t i on o f e i t h e r process would t h e r e f o r e r e s u l t i n s i g n i f i c a n t s ludge v o l - ume r e d u c t i o n as w e l l as enhance the p o t e n t i a l f o r p r o d u c t i o n of l i q u i d alum u s i n g a m i x t u r e o f s e g r e g a t e d - n e u t r a l i z a t i o n o r e t ch - recove ry s ludge and conven t iona l a lum inum- f i n i sh ing sludge. I n a d d i t i o n , u t i l i z a t i o n o f an e t c h r e c o v e r y system has p o t e n t i a l f o r p r o d u c t i o n o f an i r o n - f r e e l i q u i d alum which has a h i g h market va lue.

Eng ineer ing S i g n i f i c a n c e

Recovery o f a lum inum- f i n i sh ing s ludges as commercial-grade 1 i q u i d alum w i l l t y p i c a l l y r e q u i r e a l t e r a t i o n s i n e x i s t i n g t rea tmen t systems t o m in im ize s ludge m o i s t u r e c o n t e n t and an a d d i t i o n a l r e a c t o r system t o produce l i q u i d alum b y d i r e c t a c i d i f i c a t i o n . A l t e r a t i o n s i n e x i s t i n g techno logy v a r y f rom r e l a t i v e l y m i n o r changes, such as improv ing performance of e x i s t i n g dewater ing systems and a d d i t i o n o f a s e g r e g a t e d - n e u t r a l i z a t i o n system, t o such ma jo r changes as i n s t a l l a t i o n o f an e t c h r e c o v e r y system. These changes, however, a r e p l a n t - s p e c i f i c and encompass numerous o t h e r advantages, i n c l u d i n g chemical sav ing, and changes i n f i n i s h i n g techniques. Therefore, to e v a l u a t e t h e e n g i n e e r i n g s i g n i f i c a n c e o f an alum p r o d u c t i o n system t o r e c l a i m s ludge s o l i d s , t h e a n a l y s i s i s t o be conducted w i t h t h e assumption t h a t t h e s u b j e c t s ludge i s amenable t o rec lamat ion , i .e., i t has a s o l i d s con ten t g r e a t e r t h a n 21 pe rcen t .

mine t h e q u a n t i t y t o be produced and t h e c o s t o f p r o d u c t i o n . For a p l a n t w i th an aluminum p r o d u c t i o n r a t e o f 500 ton/month, app rox ima te l y 2 t o 4 per- c e n t o f aluminum p roduc t i on , o r 10 t o 20 ton/month, w i l l be d i scha rged t o wastewater t rea tmen t r e s u l t i n g i n t h e p r o d u c t i o n o f app rox ima te l y 29 t o 58 ton/month o f d r y i n e r t s ludge s o l i d s ( S e c t i o n 6 and Saunders e t a l . (1982)) . I n accord w i th Equa t ion 9.2, d i r e c t a c i d i f i c a t i o n would r e s u l T i r t h e p r o d u c t i o n o f app rox ima te l y 70 t o 140 ton/month o f A12(S04).,. alum i s t y p i c a l l y shipped i n t a n k - t r u c k q u a n t i t i e s o f 4000 g a l l o n s , o r 22 tons o f 8.3 p e r c e n t (as A1,03) l i q u i d alum, app rox ima te l y 11 t o 22 t a n k - t r u c k l oads o f l i q u i d alum would be shipped on a mon th l y bas is .

eva lua ted on a t a n k - t r u c k l o a d bas i s . The p r o d u c t i o n o f a l o a d o f l i q u i d

o f dry s ludge s o l i d s . $85/ton ( v i r g i n 100% H,SO,) w h i l e c u r r e n t c o s t s o f l i q u i d alum range from $130-$135/ton (as 1 7 pe rcen t A1204) (Chemical M a r k e t i n g Repor ter , 1982). Therefore, t h e chemical c o s t t o produce a l o a d o f l i q u i d alum i s $300-$450

To examine t h e v i a b i l i t y o f alum p roduc t i on , i t i s necessary t o d e t e r -

S ince l i q u i d

. Wi th r e s p e c t t o t h e c o s t s o f p roduc t i on , chemical c o s t s a r e e a s i l y

_ _ alum r e q u i r e s t h e a d d i t i o n o f 5.3 t o n o f H2S04 t o app rox ima te l y 3.9 t o n Cur ren t c o s t s o f s u l f u r i c a c i d range from $57 t o

_.

130

w h i l e t h e market va lue o f t h e alum i s app rox ima te l y $1 ,400. due t o t h e r e l a t i v e l y smal l volume o f l i q u i d alum produced a t a p l a n t , i t i s most probable t h a t t h e l i q u i d alum w i l l be marketed th rough a chemical s u p p l i e r and l i q u i d alum would p robab ly be s o l d a t a l ower r a t e than c u r r e n t market value. alum ( i . e . , 60 p e r c e n t o f market va lue) , t h e purchase p r i c e o f a t a n k - t r u c k l o a d o f l i q u i d alum would be reduced t o $850. The n e t payback would be f rom $350 t o $550 f o r each l o a d o f l i q u i d alum. For a p l a n t wi th a m e t a l - p r o d u c t i o n c a p a c i t y o f 500 ton/month, t h e revenue generated by pro- d u c i n g and s e l l i n g l i q u i d alum would range from $3,85O/month t o $12,10O/month ($46,200 t o $145,20O/year). aluminum l o s s e s d u r i n g aluminum f i n i s h i n g as w e l l as v a r i a t i o n s i n chemical c o s t s . Alum p r o d u c t i o n f rom aluminum s ludges i s t h e r e f o r e favo rab le w i t h r e s p e c t t o chemical c o s t s .

s ludge t rea tmen t systems remain i n o p e r a t i o n and t h a t a dewatered s ludge w i t h a minumum o f 21 p e r c e n t s o l i d s be produced. To e v a l u a t e t h e o v e r a l l v i a b i l i t y o f a r e c l a m a t i o n system he re in , i t i s assumed t h a t an e x i s t i n g system can meet t h e minimum s o l i d s c o n t e n t requi rement .

9;2. ( i ) an ac id -s to rage f a c i l i t y ; ( i i ) a s ludge conveyor f rom a s ludge dewater ing system t o t h e r e c l a m a t i o n f a c i l i t y ; ( i i i ) a r e a c t i o n vessel w i t h s t i r r e r ; ( i v ) m u l t i p l e alum-storage tanks; ( v ) an alum t r a n s f e r f a c i l i t y t o l o a d alum o n t o t a n k e r ca rs and ( v i ) a piping-pump network t o t r a n s f e r alum from t h e r e a c t i o n t o s to rage tanks and t h e t r a n s f e r f a c i l i t y . To e v a l u a t e t h e c a p i t a l c o s t s assoc ia ted w i t h such a f a c i l i t y , i t i s assumed t h a t an average o f 11 t a n k - t r u c k l o a d s o f l i q u i d alum a r e t o be produce month ly o r t h a t an average o f 29 tons/month of d r y i n e r t s ludge s o l i d s a r e t o be t r e a t e d . The c a p a c i t y and d e s c r i p t i o n s o f t h e r e a c t o r systems r e q u i r e d f o r such an alum p r o d u c t i o n f a c i l i t y a r e presented i n Tab le 9.5 and t h e es t ima ted c o s t s assoc ia ted w i t h c o n s t r u c t i o n o f t h e f a c i l i t y a r e presented i n Table 9.6. The t o t a l c o s t o f $80,000 i s a c o n s e r v a t i v e e s t i m a t e which c o u l d be lowered c o n s i d e r a b l y when e x i s t i n g s t o r a g e f a c i l i t i e s , s i t e c o n s t r u c t i o n and p l a n t eng inee r ing c a p a b i l i t i e s a r e considered, S ince e x i s t i n g s ludge d i s p o s a l f a c i l i t i e s and s e r v i c e s w i l l be v i r t u a l l y e l i m i n a t e d (excep t f o r smal l and, more i m p o r t a n t l y , s i n c e personnel assoc ia ted w i t h s ludge t r a n s p o r t and d i s p o s a l w i l l n o t be r e q u i r e d , no a d d i t i o n a l o p e r a t i o n a l s t a f f w i l l be r e q u i r e d upon i n s t a l l a t i n o f t h e s ludge r e c l a m a t i o n system.

t h a t equipment c o s t s would be $80,000 w h i l e t h e n e t payback f o r chemicals i s $46,200 t o $72,6'00/year f o r a p l a n t p roduc ing 11 t a n k - t r u c k l oads o f l i q u i d alum on a mon th l y bas i s . Therefore, a s ludge r e c l a m a t i o n f a c i l i t y c o u l d be i n s t a l l e d a t a t r e a t m e n t p l a n t w i t h a pay-back p e r i o d o f app rox ima te l y 14 t o 21 months.

However,

Therefore, assuming a va lue o f $80/ton f o r l i q u i d

T h i s range o f va lues i n c l u d e s v a r i a t i o n s i n

Imp lemen ta t i on o f a s ludge r e c l a m a t i o n system w i l l r e q u i r e t h a t e x i s t i n g

A schematic diagram o f an alum r e c l a m a t i o n system i s presented i n F i g u r e The components o f t h e system i n c l u d e :

f r a c t i o n s o f bot tom r e s i d u a l s )

The o v e r a l l economic assessment f o r a s ludge r e c l a m a t i o n system i n d i c a t e d

T h i s range i s based on c o n s e r v a t i v e f i g u r e s f o r equipment and n e t

131

LC 0 .

z L m

m

.r 0

132

Table 9.5 Descr ip t ion o f Equipment Required f o r an A l u m Reclamation F a c i l i t y

Component Volume (m3) Desc r ip t ion

Acid-Storage Tank 1 5 Lined f i b e r g l a s s o r CPVC .

Reactor Tanks ( 2 ) In su la t ed and l i n e d f i b e r l a s s o r CPVC; 2-10 HP mixer and p and temperature probes r equ i r ed ; pump t o remove s o l u t i o n from r e a c t o r r equ i r ed .

t? 1 5

Alum-Storage Tanks ( 2 ) 40 Lined f i b e r g l a s s o r CPVC

-- ' Transfer F a c i l i t y Platform w i t h f l e x i b l e

connec tors r equ i r ed t o f i l l tank car.

Table 9.6 Equipment Costs f o r an Alum Reclamation F a c i l i t y

Item c o s t s -.

Equipment

..

1 3 3

chemical revenues i n d i c a t i n g a p o t e n t i a l f o r a s h o r t e r pay-back p e r i o d . I n a d d i t i o n t o t h e d i r e c t economic p o t e n t i a l , s l udge r e c l a m a t i o n would a l s o e l i m i n a t e t h e need f o r expansion o f s ludge d i s p o s a l f a c i l i t i e s and a l l o w f o r g a i n f u l development o f p resen t d i s p o s a l s i t e s . I t would a l s o m in im ize f u t u r e environmental concerns assoc ia ted w i t h l ong - te rm s to rage / d i s p o s a l o f s ludge i n a l a n d d i sposa l f a c i l i t y . I t i s apparent t h a t t h e r e c l a m a t i o n o f aluminum-bearing s ludges produced a t aluminum f i n i s h i n g p l a n t s (e.g., e t c h i n g and anod iz ing p l a n t s ) i s p r a c t i c a l and i s wor thy o f f u r t h e r i n v e s t i g a t i o n b y t h e i n d u s t r y .

The r e and disposa

SECTION 10

ENGINEER1 NG S I G N 1 FICANCE AND APPLICATIONS

earch presented on c h a r a c t e r i z a t i o n , t rea tmen t , 31 o f a lum inum- f i n i sh ina wastewaters i n t h i s and an i n

mat ion t i a l p r o j e c t

Improve- r e p o r t p r o v i d e a b a s i s f o r improv ing waste t rea tmen t p r a c t i c e s i n s m a l l , medium and l a r g e i n d u s t r i a l p l a n t s i n which aluminum i s f i n i s h e d . ments can i n c l u d e m ino r changes i n conven t iona l t rea tmen t p r a c t i c e s o r i n - c o r p o r a t i o n o f numerous i n n o v a t i v e t rea tmen t systems t o s i g n i f i c a n t l y reduce o r e l i m i n a t e s ludge d i sposa l problems. u s i n g a c t u a l wastewaters, s ludges and f i n i s h i n g s o l u t i o n s f rom f i v e e t c h i n g , a n o d i z i n g and p a i n t i n g p l a n t s i n t h e U n i t e d S ta tes , t h e r e s u l t s a r e d i r e c t l y a p p l i c a b l e t o wastewater t rea tmen t systems i n many a lum inum- f i n i sh ing p l a n t s . The r e s u l t s , however, a r e based on l a b o r a t o r y i n v e s t i g a t i o n s o f wastewater t rea tmen t systems. Whi le much o f t h e i n f o r m a t i o n i s c o n c l u s i v e enough t o war ran t development o f f u l l - s c a l e systems, w i t h o u t excep t ion , p i l o t - s c a l e i n v e s t i g a t i o n o f many o f t h e comprehensive t r e a t m e n t systems i s warranted t o determine t h e u l t i m a t e impact on t h e f i n i s h i n g o f t h e aluminum p roduc t as w e l l as t h e success o f t h e waste t rea tmen t process.

S ince t h e research has been conducted

CONVENTIONAL TREATMENT SYSTEMS

I n e t c h i n g and a n o d i z i n g p l a n t s , spent c a u s t i c e t c h and dragout from

Implementat ion o f water con- c a u s t i c e t c h tanks a r e t h e major sources o f waste aluminum w h i l e r i n s e - waters a r e t h e major sources o f wastewater. s e r v a t i o n p r a c t i c e s and repeated use o f r i nsewa te rs i n c o u n t e r - c u r r e n t r i n s e systems w i l l serve t o reduce wastewater d ischarges. However, t h e ma jo r problem i n t r e a t m e n t o f a lum inum- f i n i sh ing wastes i s t h e d i sposa l o f th ickened o r dewatered s ludge s o l i d s . Surveys o f two p l a n t s i n t h e s tudy i n d i c a t e d t h a t wet dewatered-sludge q u a n t i t i e s were p o t e n t i a l l y equal t o 33 t o 90 per- c e n t o f t h e mass o f f i n i s h e d aluminum product . Reduct ion i n o r r e c l a m a t i o n o f t h i s q u a n t i t y o f s ludge i s t h e r e f o r e t h e major waste t rea tmen t t a s k f a c i n g t h e i n d u s t r y .

Resu l t s presented i n an e a r l i e r r e p o r t (Saunders gal-:, 1982) i n d i c a t e d p r i o r i t y - p o l l u t a n t meta ls were p resen t i n convent ional alumlnum f i n i s h i n g sludges a t r e l a t i v e l y low l e v e l s b u t were n o t r e a d i l y e x t r a c t e d from dewatered sludges, even i n t h e aggress ive environment Lyp ica l o f s a n i t a r y l and - f i l l s . Issues o f s ludge t o x i c i t y are, t he re fo re , n i n o r and t h e ma jo r i s s u e i s assoc ia ted w i t h t h e g e l a t i n o u s , voluminous n a t u r e o f aluminum hydrox ide suspensions produced upon conven t iona l n e u t r a l i z a t i o n o f a lum inum- f i n i sh ing wastewaters.

134

135

Convent ional t rea tmen t o f t h e m a j o r i t y o f a lum inum- f i n i sh ing wastewaters i n c l u d e s m u l t i - s t a g e n e u t r a l i z a t i o n o f r i n s e w a t e r s u s i n g spent e t c h and a c i d s t o a d j u s t suspension pH t o nea r -neu t ra l va lues. t i o n i n a g r a v i t y sedimentat ion bas in f o l l o w s n e u t r a l i z a t i o n w i t h t h e c l a r i - f i e d e f f l u e n t b e i n g d ischarged t o a r e c e i v i n g s t ream o r mun ic ipa l sewer f o r f u r t h e r t rea tmen t . systems o r dewatered w i t h mechanical systems o r g r a v i t y - d r a i n a g e beds p r i o r t o l a n d d i s p o s a l . t h e area where ma jo r improvements a r e requ i red .

wa te r suspensions i s p o s s i b l e w i t h use o f p o l y e l e c t r o l y t e a d d i t i o n . a r e so dramat ic t h a t p o l y e l e c t r o l y t e use i s a l l b u t r e q u i r e d t o e f f e c t i v e l y c l a r i f y these wastewaters (Saunders _ _ e t a l . , 1982). P o l y e l e c t r o l y t e condi - t i o n i n g , i n a d d i t i o n , r e s u l t s i n s i g n i f i c a n t improvements i n s ludge t h i c k e n i n g p r o p e r t i e s . The improvements i n t h i c k e n i n g p r o p e r t i e s a r e among t h e most d ramat i c which can be achieved i n convent ional t rea tmen t systems. F i e l d obse rva t i ons a t i n d u s t r i a l p l a n t s i n d i c a t e t h a t c o n t r o l l e d a d d i t i o n o f p o l y e l e c t r o l y t e s i s n o t commonly achieved and t h a t many waste t rea tmen t problems p robab ly r e s u l t f rom l a c k o f t h i s c o n t r o l . and c o n t r o l o f p o l y e l e c t r o l y t e a d d i t i o n shou ld be p r a c t i c e d .

C l a r i f i c a -

Thickened under f low s ludge i s d ischarged t o lagoon

T h i s ' l a t t e r s t e p o f s ludge t rea tmen t and d i sposa l i s

Improvements i n c l a r i f i c a t i o n c h a r a c t e r i s t i c s o f conven t iona l waste- Resu l t s

P rec i se m o n i t o r i n g

Wi th r e s p e c t t o dewater ing, p o l y e l e c t r o l y t e a d d i t i o n r e s u l t e d i n ma jo r improvements i n r a t e s a t which wa te r c o u l d be removed from th i ckened sludges. However, r e d u c t i o n i n s ludge m o i s t u r e c o n t e n t c o u l d n o t be achieved and no r e d u c t i o n i n wet s ludge volume was poss ib le .

Techniques f o r ma jo r improvements i n conven t iona l t rea tmen t systems beyond use o f p o l y e l e c t r o l y t e c o n d i t i o n i n g a r e n o t a v a i l a b l e . i n c u r r e n t o p e r a t i o n a l procedures should be pursued b u t p resen t t rea tmen t p r a c t i c e s a r e commonly w i t h i n l i m i t s o f c u r r e n t s t a t e - o f - t h e - a r t technology. Ma jo r i n n o v a t i v e changes i n waste t rea tmen t p r a c t i c e s a r e r e q u i r e d .

INNOVATIVE TREATMENT SYSTEMS

Refinements

In -dep th i n d u s t r i a l surveys a t p l a n t A1 and A3 i n d i c a t e d t h a t waste s ludge s o l i d s were a t t r i b u t a b l e t o aluminum removal from t h e su r faces o f a l l o y s f i n i s h e d . p o s s i b l e w i t h changes i n t h e f i n i s h i n g process u t i l i z e d i n t h e i n d u s t r y . I n a d d i t i o n , t h e q u a n t i t i e s o f wastes produced i n p a i n t i n g l i n e s were approx i m a t e l y 50 - fo ld l e s s than those f rom a n o d i z i n g l i n e s . Chromium i n d ragou t f r o m f i n i s h i n g s o l u t i o n s and aluminum removed from a l l o y sur faces were t h e ma jo r contaminants i n p a i n t - l i n e wastes. Again, changes i n t h e f i n i s h i n g process a r e r e q u i r e d t o f u r t h e r reduce t h i s minor source o f s ludge s o l i d s .

I n v e s t i g a t i o n o f new techniques t o be used i n a l t e r i ng*a luminum- f i n i s h i n g processes was w e l l beyond t h e scope o f t h i s p r o j e c t . Therefore, emphasis was p iaced on i n v e s t i g a t i o n o f i n n o v a t i v e processes which had p o t e n t i a l f o r r e d u c t i o n i n t h e volume o f s ludge s o l i d s produced and reclama- t i o n o f s ludge s o l i d s as a p roduc t f o r reuse.

Reduct ion i n waste s ludge s o l i d s a r e t h e r e f o r e o n l y

136

Sludge Volume Reduction

Moisture contents of conventiona? aluminum f inishing sludges a re typ ica l ly equal t o or g rea t e r than 80 percent. moisture content i s therefore an obvious way i n which sludge volume, and therefore sludge mass, can be reduced. Although not examined herein due to the lack o f a p i lo t - sca l e system, f i i t e r presses t y p i c a l i y produce sludges w i t h lower moisture contents than o the r mechanical systems ana should be examined f o r treatment o f aluminum-finishing wastes. An a l t e r n a t i v e technique t o reducing sludge moisture content was t o a l t e r the chemicai composition o f t he siudge s o l i d s and avoid formation o f amorphous, gelat inous aluminum-hydroxide so l id s . To achieve t h i s ob jec t ive , waste sources had t o be i so l a t ed t o provide f o r control over t he conditions o f chemical precipi- t a t i o n .

Reduction i n sludge

The major source o f waste a l u m i n u m was shown t o be spent caus t i c e tch suspensions and i so l a t ion o f t h i s waste source i s e a s i l y achieved. To produce a c r y s t a l l i n e p r e c i p i t a t e a s opposed t o a n amorphous one, two innovative processes were inves t iga ted .

Removal o f aluminum from spent e tch was possible u s i n g lime addi t ion to heated so lu t ions o f caus t i c e tch . A calcium aluminate suspension was formed w h i L h could e a s i l y be dewatered t o s o l i d s contents of 48 t o 52 percent. This a l t e r a t i o n i n t he form of the aluminum p r e c i p i t a t e resu l ted i n reduction i n sludge volume through reduced moisture content o f the dewatered sludge. I n addi t ion , t he process provided f o r the addi t ional economic benef i t o f recovery o f the c a u s t i c e tch so lu t ion . Waste reclamation i s , t he re fo re , possible as i s t h e concurrent reduction i n sludge volume.

Application o f e tch recovery w i t h lime addi t ion may be most e f f ec t ive ly applied i n small f i n i s h i n g p lan ts where r e l a t i v e l y small quan t i t i e s of waste do not allow f o r appl ica t ion o f cap i t a l - in t ens ive recovery systems, b u t disposal c o s t s a r e prohib i t ive . I n s t a l l a t i o n o f a small heated react ion vessel and a mechanical dewatering system (e .g . , per fora te basket cen t r i fuge , f i l t e r press o r vacuum f i l t e r ) would provide f o r recovery o € a l l spent e tch while producing a low-volume sludge f o r d i sposa l . Reduced disposal cos ts for spent etch as well as chemical saving f o r make-up c a u s t i c soda could prove t o make the process cos t - e f f ec t ive . These benef i t s a r e , furthermore, not t o be l imi ted t o small-scale systems b u t could prove t o be extremely bene f i c i a l , e spec ia l ly i f sludge s o l i d s could be co l lec ted without being sa tura ted w i t h spent etch u s i n g a system t o wash the dewatered sludge, e .g . , perforate-basket cen t r i fuge w i t h a water-spray.

aluminum prec ip i t a t e s and thereby reduce sludge volume was segregated , :eu t ra l iza t ion of concentrated f in i sh ing wastes. anodize-acid regenerant a r e major sources of waste aluminum and a r e , respec t ive ly , highly a l k a l i n e and ac id i c . Controlled neu t r a l i za t ion o f these concentrated wastes a t a l k a l i n e pH values produced dewatered suspensions which had s o l i d s contents of from 33 t o 53 percent. The so l id s produced were s imi l a r t o c r y s t a l l i n e forms, e.g. , g ibbs i t e , bayer i te , and pseudoboehmite, and had improved sludge handllng proper t ies . This option a l so allowed f o r treatment of approximately 70 t o 80 percent of the t o t a l waste

A second process inves t iga ted t o a l t e r the chemical c h a r a c t e r i s t i c s of

Spent caus t i c e tch a n d

137

meta l i n a smal l volume o f wastewater u s i n g a smal l n e u t r a l i z a t i o n system. Furthermore, d a t a c o l l e c t e d f o l l o w i n g a 24-hour p e r i o d o f ag ing a t ambient temperature and those o b t a i n e d from p l a n t A2 r e g a r d i n g segregated n e u t r a l i - z a t i o n i n d i c a t e d t h a t t h e improved h a n d l i n g p r o p e r t i e s o f these s o l i d s were n o t a l t e r e d w i t h t i m e o r upon m i x i n g w i t h conven t iona l , amorphous s ludge suspensions. Therefore, segregated n e u t r a l i z a t i o n shou ld have p o t e n t i a l f o r a p p l i c a t i o n a t a l l a lum inum- f i n i sh ing p l a n t s i n which concen t ra ted a l k a l i n e and a c i d i c f i n i s h i n g wastes can be i s o l a t e d f o r segregated t r e a t - ment. z a t i o n t o a conven t iona l n e u t r a l i z a t i o n system o r c l a r i f i e r i n f l u e n t o r mixed w i t h th i ckened conven t iona l s ludge s o l i d s shou ld improve t h e u l t i m a t e s o l i d s c o n t e n t achieved f o l l o w i n g dewater ing and t h e r e b y reduce s l udge v o l ume.

Recl amat ion o f A1 uminum- F i n i s h i n g Wastes

p e r c e n t o f t he aluminum t o r i n s e w a t e r s and f i n i s h i n g s o l u t i o n s . o f t h e waste meta l o r contaminated f i n i s h i n g s o l u t i o n s would reduce o v e r a l l f i n i s h i n g c o s t s and m in im ize waste t rea tmen t and d i sposa l problems. Two i n n o v a t i v e processes were examined i n t h i s regard.

D ischarge o f concen t ra ted suspensions f o l l o w i n g segregated n e u t r a l i -

F i n i s h i n g o f ext ruded aluminum r e s u l t s i n t h e loss o f from 2 t o 5 Recovery

- - Treatment o f s p e l t e t c h w i t h l i m e r e s u l t s i n p r e c i p i t a t i o n o f aluminum

as a c a l c i u m a l u m i n a t e which can be removed b y d i r e c t f i l t r a t i o n o f t h e suspension. Complete removal o f aluminum i s p o s s i b l e and i s c o n t r o l l e d by r e a c t i o n t ime , temperature and q u a n t i t y o f l i m e added. t h e f i l t r a t e e t c h s o l u t i o n can be r e t u r n e d t o a process e t c h tank. soda a d d i t i o n would be reduced t o t h a t equal t o d ragou t a n d t h a t con ta ined i n ca l c ium-a lumina te s ludge s o l i d s . i n a l l m e t a l - f i n i s h i n g o p e r a t i o n s e s p e c i a l l y those i n which n e u t r a l i z e d wastewaters a r e d i scha rged t o a m u n i c i p a l sewer. T h i s would a l l o w f o r separa te t r e a t m e n t o f a suspension which i s d i f f i c u l t t o d i scha rge and recove ry o f t h e spent etch.

The i n n o v a t i v e process which has p o t e n t i a l f o r e l i m i n a t i o n o f a l l a lum inum- f i n i sh ing waste s o l i d s and recove ry o f waste aluminum as a marketable p roduc t i s d i r e c t a c i d i f i c a t i o n t o produce l i q u i d alum ( i .e. , an aluminum s u l f a t e s o l u t i o n ) . Sludges produced b y conven t iona l and segregated n e u t r a l i - z a t i o n were e x t r a c t e d w i t h s u l f u r i c a c i d t o form commercial-grade l i q u i d alum w i t h a q u a l i t y equal t o t h a t formed commerc ia l ly f rom b a u x i w . a d d i t i o n , s ludges produced w i t h t h e Fugi Sash and Alcoa e tch - recove ry systems were e x c e l l e n t feedstocks f o r p r o d u c t i o n o f l i q u i d alum.

Fo l l ow ing f i l t r a t i o n ,

T h i s r e c l a m a t i o n process has a p p l i c a t i o n

Caust ic

i n

_I Implementat ion o f a system t o r e c l a i m waste-aluminum was shown t o be c o n t i n g e n t upon p r o d u c t i o n of a dewatered s ludge suspension w i t h a s o l i d s c o n t e n t o f app rox ima te l y 21 pe rcen t o r h ighe r . Convent ional t rea tmen t systems do n o t r o u t i n e l y r e s u l t i n p r o d u c t i o n o f such a dewatered s ludge and one o f numerous techniques must be employed t o reduce s ludge m o i s t u r e c o n t e n t . Opt ions i n c l u d e , f o r example, segregated n e u t r a l i z a t i o n o f concen t ra ted f i n i s h i n g s o l u t i o n s and i n s t a l l a t i o n o f an e t c h recove ry system producing an a lum inum- t r i hyd ra te s ludge. W i th such systems, a l l waste aluminum can be conver ted i n t o a commerc ia l ly marke tab le p roduc t .

, .. .

138

Implementation of such a reclamation system, therefore , requi res i n s t a l l a t i o n of 3 system t o increase sludge sol ids content and a sludge ex t r ac t ion and alum s torage system. Chemical composition data ind ica t e t h a t chemical qua l i t y of th le l i q u i d alum so lu t ions produced were o f acceptable qua l i ty . However, var ia t ions i n sludge qua l i t y and composi t ion could a f f e c t product q u a l i t y as well as product c l a r i t y . Finally, p i lo t - sca l e v e r i f i c a t i o n o f laboratory r e s u l t s must be pursued before i t is t o be implemented i n fu l l - s ca l e systems. l4ajor i s sues as y e t unresolved include heat requirements d u r i n g ex t r ac t ion , c l a r i t y of ex- t r ac t ed suspensions and procedures required t o assure acceptable c l a r i t y , and cont ro l systems required t o opera te t h e ex t r ac t ion system.

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SECTION 11

REFERENCES

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<

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