GEPA

Issues and Options

Volume 111

Waste Minimization Issues and ODtions Volume 3: Appendices C through K

Submitted by:

Versar, Inc. 6850 Versar Center

P. 0. Box 1509 Springfield, Virginia 22 15 1

and

Jacobs Engineering Group 251 S. Lake Avenue

Pasadena, California 9 1 10 I

S u b m i t t e d t o :

Elaine E b y Off ice o f Solid Was:?

Waste Treatment aranch U.S. Environmental Protection Agency

401 M Street, S.W. Washington, D.C. 20460

In Response to:

EPA Contract No. 68-01-7053 Work Assignment No. 17

October I , 1986

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3 DISCLAIMER

This d o c u m e n t has been r ev iewed and approved f o r publ icat ion by t h e O f f i c e of Soiid Waste, O f f i c e o f Solid Waste and E m e r g e n c y Response , U.S. E n v i r o n m e n t a l P r o t e c t i o n Agency. Approval d o e s n o t s ignify t ha t the c o n t e n t s necessar i ly r e f i e c t the v i ews a n d pol ic ies o f the Env i ronmen ta l P r o t e c t i o n Agency, nor does r b e men t ion o f t r a d e n a m e s or c o m m e r c i a l p r o d u c t s c o n s t i t u t e endorsemen; or r e c o m m e n d a t i o n f o r use.

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LIST OF APPENDICES

C. RECYCLING TECHNOLOGIES AND PRACTICES

C. 1 Solvent Recycl ing Technologies C.2 C.3 M e t a l Recovery Technologies . C.4 Recycl ing Technologies fo r Corrosive Wastes . . C.5 Cyanides and Other Reactives C.6 Summary Data on O f f s i t e Recycl ing Prac t ices C.7 References

Halogenated Organics (Nonsolvent) Recycl ing Technologies

D. NORTHEAST INDUSTRIAL WASTE EXCHANGE’S ON-LINE COMPUTER SYSTEM

E. CONDUCTING A PROJECT PROFITABILITY ANALYSIS

F. EPA’S DEFINITION OF SOLID WASTE

G. CORRESPONDENCE FROM EPA ON WASTE MINIMIZATION ACTIVITIES

H. COMPILATION OF INDUSTRIAL WASTE REDUCTION CASES

3. DESCRIPTIONS OF STATE PROGRAMS

3. 1 3.2 3.3 3.4 3.5 3.6 J. 7 J.8 J.9 J. 10 J.l I

Cal i forn ia Georgia I l l ino is Massachusetts Minnesota New Jersey New York N o r t h Carol ina Pennsylvania Tennessee Washington

K. TWO PROPOSED REGULATIONS ON HAZARDOUS WASTE MANAGEMENT B Y TWO COUNTIES IN CALIFORNIA

K.l Sacramento County K.2 Santa Cruz County

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APPENDIX C

RECYCLING TECHNOLOGIES AND PRACTICES

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3 RECVCLING TEC+NCLOGIES A N D PRACTICES c. 1 Solvent Recycl ing Technologies

Solvent w a s t e s are r e c y c l e d by Various uni t t r e a t m e n t opera t ions , w h i c h may be p e r f o r m e d singly or in sequence . These ope ra t ions a r e grouped in to the following technology ca tegor ies : d i s t i l l a t ion ; so l ids removal ; liquid-liquid phase sepa ra t ion ;

'emulsion/dispers ion breaking; dissolved and emuls i f i ed o rgan ic s r ecove ry ; and o rgan ic s vapor recovery . The recyc lab le p roduc t o f t h e ope ra t ion m a y b e t h e so lven t or the i so la ted c o n t a m i n a n t s , or both. Appl ica t ions and l imi t a t ions o f use of so lven t recyc l ing ope ra t ions are p resen ted in Tab le C-1 and discussed below.

Dis t i l l a t ion

Sepa ra t ion t echn iques t ha t r e ly on the boiling poin t d i f f e r e n c e s o f t he c o m p o n e n t s o f a liquid w a s t e a r e ca l l ed d is t i l l a t ions and include pot d i s t i l l a t i on , s t e a m dis t i l l a t ion , f r a c t i o n a l d i s t i l l a t ion , f i lm evapora t ion , and j ry ing techniques . Pu r i f i ca t ion o f o rgan ic so lven t s f o r recyc l ing in p rocess app l i ca t ions u s u a l l y r e q u i r e s a t l e a s t one d is t i l l a t ion s tep KO r e m o v e w a s t e s o f l o w volat i l i ty . Dist i : la t ion is t h e dominan t recyc l ing technology f o r so lven t wastes .

P o t Dis t i l l a t ion describes the p rocess o f hea t ing liquid ind i rec t ly t o boiling in a po t and t h e n r ecove r ing b y condensa t ion o f t h e vapors t h a t a r e in equi l ibr ium wi th the r ema in ing liquid. Nonvola t i le residues r e m o v e d f r o m the po t a lso a r e r e c l a i m e d (e.g., by d rye r s ) f o r use a s fuel or f o r disposal. P o t d i s t i l l a t ion c a n be p e r f o r m e d in a b a t c h o r con t inuous mode o f o p e r a t i o n under vacuum or a t m o s p h e r i c pressure. Opera t ion unde r vacuum e n h a n c e s r e m o v a l o f o rgan ic s f r o m h e a v y residues.

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P o t d is t i l l a t ion is e f f e c t i v e l y used t o r ec l a im ha logena ted a s wel l a s nonha logena ted s o l v e n t s f r o m wastes . For e x a m p l e , a c e t o n e used as a p a i n t c l e a n e r is commonly r e c o v e r e d f r o m nonvola t i le oils, resins. p igmen t , etc., by pot dis t i l la t ion. T h e tecnnology is widely used by ; o f f s i t e ) c o m m e r c i a l so lven t r e c o v e r y opera t ions .

c-1

1208s

Table C-1 Su*ury o f Recycling Technologies fo r Solvent Waste Streams

lype of process Descr ipt ion o f technology Appl icat ions l i m i t a t i o n s o f use

f l ash d i s t i l l a t i o n D i s t i l l a t i o n i n which an appreciable Allows f o r solvent recovery. (Also used f o r proport ion of a l i q u i d i s qu ick ly converted t o vapor i n such a way that the f i l i a l vapor i s i n equ i l ib r ium w i t h the f i n a l l i q u i d (Condensed Chemical Dict ionary 1985). Nonvolat i le residues are removed f o r fue l reuse o r disposal.

desal inat ion of sea water.) Widely used.

Frac t i orial d i s t i l l a t i o n

0 I N

D i s t i l l a t i o n i n which the product i s co l lec ted i n a ser ies o f separate solvent. Widely used. components of s i m i l a r b o i l i n g range. Part o f the vapor i s condensed, and the resu l t i ng l i q u i d i s contacted w i t h more vapor, usual ly i n a column w i th p la tes o r packing (Condensed Chemical D i c t i oiiary 1985 1.

Allows f o r recovery o f reasonably pure

F i l m evaporation A set of r o t a t i n g blades ins ide a cy l inder moves the waste mater ia l so used. tha t the mater ia l i s evaporated.

Same as above, except less frequently

Steam d i s t i l l a t i o n Heating accomplished by steam in jec ted D i s t i l l a t i o n a t lower temperatures.

d i r e c t l y i n t o the solvent. . .

Dryers

L

Dryers achieve removal by d i s t i l l a t i o n o f r m i n i r i g solvents from heavy v is - cous organic wastes. Solverit vaporized o f f of two hor izontal c y l i n d r i c a l drums heated i n te rna l l y . Solverit vapors are conderised drld recovered; so1 i ds scraped o l t drum arid packaged f o r disposal.

Allows f o r dry product recovery; frequently used.

Solvent must not be t h e m a l l y unstable.

Not appl icable t o areotropic mixtures.

Same as above. Cap i ta l costs are higher than f o r other d i s t i l l a t i o n methods.

Problems w i t h product s t a b i l i t y . ' corrosion, foaming. and condensate water disposal.

Requi res condensat ion equ i pterlt to recover solvents.

t 1208s

I

Table C - l (continued)

___-_ -_ ~

L im i ta t ions o f use type o f process Descr ipt ion of technology Appl icat ions

--

Sedimentation Ihe s e t t l i n g out by g rav i t y of s o l i d Prel iminary p u r i f i c a t i o n step; al lows p a r t i c l e s suspended i n a ' l i qu id discharge o f water contained i n waste. (Condensed Chemical D ic t ionary 1985). and f o r recovery o f recyclable materia Oversize and heavy so l ids drop out l h i s i s a widely used technulogy. read i l y un standing.

F i l t r a t i o n

c) I w

Cent r i t ugat i on

Separation o f suspended so l ids from a Same as above. l i q u i d (o r gas) by fo rc ing the mixture through a porous b a r r i e r (Condensed Chemical Dict ionary 1985). Sol ids l a rge r than the pore openings i n the f i l t e r media are removed.

A separation technique based on the app l ica t ion of cent r i fuga l torce t o a mixture o r suspension o f mater ia ls o f c lose ly s im i la r dens i t i t es (Condensed Chemical O i c t iotiary 1985). The s e t t l i n g force created by the cen- t r i t u g e enhances separation ot small p a r t i c l e s and less dense sol ids.

Same as above, except the technology i s less frequently used.

o r

5 . remove by sedimentation o r

f i n e l y div ided so l ids o r emulsi t ied mater ia ls sometimes d i f t i c u l t t o

f i l t r a t i o n .

Because o f the array of t i l t r a t i o n equipment. costs vary widely.

Power requirements are high, and - operat ing supervi s i on arid ma intrrtance costs nay be high.

Uecant tank L iqu id phases w i l l separate i n storage Allows f o r recovery of spent solvents f o r so that one phase ran be pu l led 0 1 I reprocessing. I h i s i s a widely used, the top and one o t t the bottom. inexpensive technology. fu r ther treatment before i't.irse.

Separated nonaqueous l i q u i d w i l l be saturated w i t h water anal way require

API separator Rsle 01 sepdraliori ot l i q u i d phases i s Allows l o r recovery ot o i l y o r petrolewn- Sane as above: also. retuvrred increased i n an open basin w i th large surtase area. the petroleum industry. suhstances.

based mater ia ls. l h i s i s widely used i n mater ia ls may contain some t a r - l i h e

1208s

Table C-1 (continued)

Type o f process Descr ipt ion o f technology Appl icat ions L imi ta t ions of use

(continued)

T i l l e d p l a t e The add i t ion o f t i l t e d p la tes Same as above. This technology i s less Separated nonaqueous l i q u i d w i l l separator t o an open basin fu r the r increases

the r a t e of separation i n proport ion processes. reuse. t o the projected hor izon ta l surface area.

f requent ly used than the above two require fu r ther processing before

&-ion break-

Coalescence The union of d rop le ts of a l i q u i d t o form Prel iminary separation o f aqueous-phase waste Some emulsions are d i f t i c u l l t o a la rqer droplet , brought about when the droplets approach one another c lose ly betore reuse. This e t h o d i s infrequent ly surfactants.

surface tensions (Condensed Chemical Dict ionary 1985). L iquids are pumped through a f i n e mesh t o which entrained droplets tend t o c l ing ; an o leoph i l i c medium can be used t o eohacice r t t r a c t i o n ol entrained drop- l e t s .

t o be treated by b io log i ca l methods handle, p a r t i c u l a r l y those containing

c)

P I enough t o overcome t h e i r ind iv idua l used.

Centr i fugat ion complete1 y

Chemi cal de-emulsifying agenl s

Used t o remove small amounts o f water Same as above; a lso used f o r recovery

as we l l a5 so l ids trom recovered tue l . o f nonaqueous mater ia l .

Addi t ion ot chemical agents t o ra i se o r lower pH o r t o change a t t r a c t i v e forces belween p a r t i c l e s causes some solvents and o i l s t o separate out o f water i n t o a l i q u i d organic phase.

Same as above; however, i t i s used only w i th emulsions.

. Fine dispersants MY not be

separated by t h i s wt l iod .

Some emulsions may requ i re Id rye amounts o f chemicals. Ctiemicrl emulsi fy ing agents are more eNpetisive than the a i r f l o t a t i o n process.

G 1208,

Table C-1 (continued)

Type of process Descr ipt ion o f technology Appl icat ions L imi ta t ions o f use

A i r f l o t a t i o n Fine organic droplets and/or Same as f o r cen t r i fugat ion . p a r t i c l e s are removed frqm water by introducing a i r bubbles which at tach themselves t o the droplets and are then car r ied t o the surface and skinmned.

U l v e c l a nd emuls-nics recorlpry

Steam o r a i r s t r i pp ing

Carbon absorption

Solvent ex t rac t ion

Waste i s pumped t o top 0 . a packed Discharge a. t reated wastewater; recovery column. Steam o r a i r i s fed through the column from the bottom, p ick ing This i s widely used t o remove annonia from up v o l a t i l e organics. Organics are water. recovered from the condensate.

o f str ipped mater ia ls i s also possible.

Water w i t h dissolved ory r i i i cs i s pumped through bed of ac t i va ted . wastewater. l l i i s i s more cos t l y than carbons which absorb the organics. steam s t r ipp ing . I t i s widely used

Removes la rye va r ie t y o f organics from

from wastewater. Bed reyewrated w i t h steam o r t o ce r ta in solvents t o recover organics.

Water and organic contaminants percolated A I

remove trace oryani cs

ows f o r recovery o f d ssolved organics through a pdckrd column; preselected solvetit, pumped i n counter-current, used tlidn above two methods. dissulves tlie contaminant. Spent sulvei i t i s r e d i s t i l l e d leaving organic waste residue.

from an aqueous so lu t ion . l ess frequently

Recovered organics requ i re considerable processing belore they can be reused.

Hay cause a i r emissions problems i f s t r ipped mater ia ls are vented t o atmosphere. Limited t o use w i th v o l a t i l e mater ia ls.

High cost o f regenerating t l ie carbon o r inc inera t ing i t . Requires t ra ined operators and close monitor ing f o r e f f i c i e n t operation. Nut

. e f f e c t i v e on ethylene (Condensed Chemical D ic t ionary 1985).

,Solvent losses t o water Need l o r f u r the r prucessi iq t o recover mater ia ls.

1208s

Table C-1 (continued)

lype of process Descr ipt ion o f technology Appl icat ions l i m i t a t i o n s o f use

Qi-lfisied d- (continued)

Supercr i t i ca l f l u i d ex t rac t ion

Membrane separation

0 I 01

Condensation

S imi la r t o above, except solvent i s Substantial energy savings over a t a temperature above ' i t s c r i t i c a l d i s t i l l a t i o n processes, but po in t so acts as a f l u i d . C02 i s high-pressure operat ing equipment being tested on t h i s appl icat ion; i s higher i n cost than conventional se lec t i ve ly ex t rac ts organic solvents processing equipment. Requires from wastewater. t ra ined operators: must be wel l

designed t o prevent explosions.

No commercial appl icat ions were i d e n t i f i e d dur ing t h i s study.

Highly e l f i t i e n t f i l t r a t i o n system. Hem- Recovery ot some dissolved organics. Membranes Membrane technology i s I i iy l ier i n cost brane pore openings are submicron s ize o f celtuphdrie. col lodion, asbestos f i be r , etc.. than older technology. f a i r l y cos t l y (0.0025-0.010 u). Molecules o f water are used i n waste l i q u o r recovery, desal inat ion, and low molecular weight compounds and e lec t ro l ys i s . pass readi ly; la rger organic molecules and c o l l o i d a l p a r t i c l e s b u i l d up i n the rec i r cu la t i on stream u n t i l i t can be used as fue l .

cocnpared t o other processes.

Solvent vapors recovered by beiny fed Ilirouyh a condenser cooler.

Recovery of solvent and reduct ion o f evaporative losses.

. For some mater ia ls. condensers 8 MY require re f r i ge ra t i on ,

which i s expensive.

k

c 1208s

Table C-1 (continued)

lype of process Descr ipt ion of technology Appl icat ions L i r i t a t i o n s o f use

nic v m e r n r e r y (continued)

Carbon adsorption Beds of ac t i va ted carbon are used t o Removal of organics from a i r emissions. se lec t i ve l y adsorb organic vapors from gas streams. Spent carbon regenerated with steam; steam and concentrated organics are recondensed and separaled.

Carbon regeneration o r inc iner - a t i on i s cost ly. Process requires close control and wel l - t ra ined operators.

Absorpt i on Gas and l i q u i d streams f low counter- current t o each other; gaseous mater ia l confined, such as pa in t overspray. s o l u b i l i t y i n water. Host i s t ransferred t o the l i q u i d streams.

Recovery uf gaseous organics not eas i l y

Limited use.

Host organics do not have high

appl icable t o high-temperature gas streams.

0 S t e a m Dis t i l l a t ion is s imi la r t o pot d i s t i l l a t ion except t h a t keat is sucp i i ce by direct s t e a m inject ion vvhicn r eouces the d is t i l i a t ion t e m c e r s t i i r e . S t e a r d i s t i l l a t ion is appl icabie t o the recove ry o f s o l v e n t s t h a t a r e water insoiubie (i.e., a l l water - inso luble nonhalogenated s o l v e n t s and water- :nsolubie ha logena ted solvents) . However , p roduc t ins tab i l i ty , cor ros ion , foaming, . a n c c o n d e n s a t e w a t e r disposal may Cause p rob lems wi th t h i s process .

One r e s t r i c t i o n on the use o f s t e a m dis t i l l a t ion is that t h e r e c o v e r e d so lven t mus t h a v e a s ign i f i can t vapor pressure a t or be low the boiling poin t w i t h wa te r . A s e c o n d r e s t r i c t ion is that the s u b s t a n c e to b e r e c o v e r e d m u s t b e s t a b l e unde r d is t i l l a t ion conditions. Desp i t e these t w o l imi t a t ions , S t e a m dis t i l l a t ion has been used to r ecove r s e v i - v o l a t i l e o r g a n i c s f r o m a v a r i e t j of process w a s t e s t r e a m s in the organic c h e m i c a l s industry..

0 F r a c t i o n a l Dis t i l l a t ion is genera l ly used to s e p a r a t e individual c o m p o n e n t s o f w a s t e s o l v e n t m i x t u r e s in cases where t h e boiling po in t s of individual c o n s t i t u e n t s are fairly c lose to one another . In t h i s p rocess , the feed stream e n t e r s a d is t i l l a t ion co lumn which con ta ins plates on packing w h i c h provide a high s u r f a c e a r e a o f vapor-liquid c o n t a c t . Vapors f r o m t h e t o p of t h e co lumn a r e c o l l e c t e d and condensed , and a por t ion o f these is re turned t o the column.

Boiling poin t d i f f e r e n c e s among the var ious c o n s t i t u e n t s s t rongly a f f e c t t h e design (Le., n u m b e r o f s t a g e s ) of a f r ac t iona l d i s t i l l a t ion column. T h e c l o s e r the boiling po in t s o f the compounds be ing s e p a r a t e d , the g r e a t e r t he n u m b e r o f s t a g e s required to ach ieve e f f i c i e n t separa t ion .

Individual apo l i ca t ions o f f r ac t iona l d i s t i l l a t ion t o r ecove ry o f s o l v e n t s f r o r w a s t e s t r e a m s include: r ecove ry of a c e t o n e f r o m w a s t e w a t e r g e n e r a t e d f r o m p r i n t e d circuit board c leaning opera t ions ; ons l t e r e c o v e r y o f isopropanol f r o m w a s t e w a t e r s g e n e r a t e d by the o rpan ic c h e m i c a l industry: and r e c o v e r y of so lven t s f r o m aqueous and nonaqueous m i x t u r e s in t h e specialty o rgan ic s indus t ry (Versar 1980). A case in poin t is the s e p a r a t i o n and r e c o v e r y o f acetic acid and benzene separately from t e r n a r y m i x t u r e s o f these compounds wi th water .

Azeot ropes . So lven t s fo rming a z e o t r o p e s c a n a l so be r e c o v e r e d by f r a c t i o n a l d i s t i l l a t ion with s o m e mod i f i ca t ions (an a z e o t r o p e is a liquitl m i x t u r e wi th a c o n s t a n t boiling point; a z e o t r o p e s e x h i b i t a min imum or m a x i m u m boi l ing poin t r e l a t ive to the boiling po in t s of sur rounding m i x t u r e composi t ions) . T h e mos t c o m m o n me thod to break a binary a z e t r o p e is t o add a th i rd c o m p o n e n t ( a l so ca l l ed en t r a ine r ) , w h i c h forms a te rnar j azeo t rope . T h e t e r n a r y a z e o t r o p e separates in t w o layers, one o f which is enriched in o n e o f the f e e d components . This l aye r is d e c a n t e d w h i l e t h e o t h e r layer, con ta in ing mos t o f the e n t r a i n e r , is r e in t roauced in to t h e d is t i l l a t ion co lumn (i.e., ref luxed) . For e x a m p l e , w a t e r c a n De r e m o v e d f r o m a 9 5 o e r c e n t e t h a n o l / 5 p e r c e n t w a t e r m i x t u r e using s z e o t r o p i c d is t i l l a t ion wi th benzene .

C-8 i

A n o t h e r me tnod o f oreaking a z e o t r o p e s is by changing t h e p r e s s Y r i 2' dist i l la t ion. The me thy l e t h y l k e t o n e - w a t e r a z e o t r o p e , w h i c n con:s!ns 3 j p e r c e n t w a t e r a t a tmospne r i c p re s su re and 50 percen: w a t e r a t lG2 psl p re s su re , c a n be broken by dis t i l l ing the m i x t u r e first a t a t m o s p h e r i c p re s su re and then a t a higher pressure.

Viscous was te s , including so lvents / res in mix tu res , c a n be recoverec uslng f i lm evapora t ion . Wiped- and scraped-f i lm e v a p o r a t o r s h a v e a set o f r o t a t i n g blades housed in a s t e a m - j a c k e t e d cyl inder . As t he w a s t e is h e a t e d , the b lades move the m a t e r i a l so t h a t heat t r a n s f e r a t the j a c k e t s u r f a c e is main ta ined . The b o t t o m re s idue m u s t f low to r e m o v e i t f r o m t h e equipment . This technology g e n e r a l l y . is m o r e expens ive to ins ta l l t h a n o t h e r d i s t i l l a t ion techniques and is n o t widely used.

D r y e r s handle d is t i l l a t ion residues and s e p a r a t e so lven t s f r o m heavy viscous o rgan ic was tes . T h e drum cons i s t s o f t w o hor izonta l , in te rna l ly n e a t e d cy l indr ica l d r u m s t h a t r o t a t e in c o n t a c t wi th each o ther . Viscous s o l v e n t waste is f e d in to the annulus b e t w e e n the drums: the so lvent is vapor i zed , and the re s ins and o t h e r nonvola t i les are pressed in to a f la t sheet as t h e y pas s down b e t w e e n the drums. The so lven t vapor s a r e condensed and recovered, while t he sol ids a r e s c r a p e d o f f the d rum and p a c k a g e d f o r a isposal . Drying technologies have p o t e n t i a l aopl ica t ion to semi-sol id , viscous, nonpumpable , or bare ly pumpab le s ludges t h a t c u r r e n t l y are landfi l led.

-

Solids Remova l (Liquid-Solid Phase Separa t ion!

El imina t ion o f suspended sol ids is a necessary p r e t r e a t m e n t f o r c e r t a i n r ecyc l ing t echno log ie s (e.g., f racz iona l d i s t i l l a t ion) t o r e d u c e fouling. R e m o v a l o f f i n e s t ao i l i z ing sol ids , which c a u s e o i l l w a t e r emuls ions , e n h a n c e s the subsequen t s e p a r a t i o n o f liquid phases. Techn iques f o r the r e m o v a l of suspended so l ids f r o m liquid s o l v e n t s include sed imen ta t ion , f i l t r a t ion , and cen t r i fuga t ion . F i l t r a t i o n or c e n t r i f u g a t i o n are requi red f o r r emova l o f f i n e par t ic les .

0 Sed imen ta t ion is accompl ished in t a n k s or holding ponds where heavy sol ids f a l l out of t h e suspension by gravi ty .

F i l t r a t i o n inc ludes any me thod b y which soiids l a r g e r than t3e oore o c e n i n p o f a f i l t e r med ium are r e t a ined b y t h e f i l t e r . Spec i f i ca i ions and C O S ~ S o f f i 1 t e r eq u ip men t vary wide 1 y . C e n t r i f u q a t i o n is c o m m o n l j u sed to d e w a t e r sludses and t c r emove oil 3nd di r t f r o m m e t a l Parts. ? h e s e t t l i ng f o r c e cre3te3 by a c e n t r i f u g e e n n a n c e s s e p a r a t i o n o f sma l l and low sDecific g rav i ty solids. R t q u i r e m e n t s f o r e n e r g y , ma in tenance , and ope ra t ing supervis ion may be high.

c- 9

Y Liquid-Liquid Phase Separation

Water-insoluble solvents can be separated from wastewater in one or more organic liquid phases, and then reclaimed or reused. For example, nitrobenzene a n d aniline are separated from the wastewater resulting from aniline production. The aniline is recycled to the process.

Types of equipment available for liquid-liquid phase separation include decant tanks, API separators, and tilted-plate separators. API separators ,enhance the rate o f separation achievable in a decant t a n k b y using an open basin w i t h a large surface area. The addition o f tilted plates to an open basin further increases the rate of separation in proportion to the horizontal surface area.

Emulsion/Disoersion Breaking

Dispersions of solvent or oil droplets in water or o f water droplets in oil can be separated by the use o f a coalescer, centrifuge, or air flotation equipment, or by the addi t ion o f chemical de-emulsifying agents.

'\

Coalescence. When emulsions are pumped through a fine mesh, oil dropiets w i l l coalesce i n t o large drops that separate readily. Attraction o f the o i l droplets can be enhanced b y the use o f an oleophilic medium.

Centrifugation can be used t o remove smal l amounts o f water (as well as solids) from recovered fuel. T h i s technology has been applied to the shipboard removal of oil from ballast water and, b y the electric utilities industry, t o separate impurities from spent dielectric fluids processed for reuse.

Air Flotation. Oil droplets (or particles) also may be removed from water by dissolved or diffused air flotation. Air for the process first is dissolved under pressure in a recycle stream, which then is released directly or through a fine diffuser into an air flotation tank. The air bubbles become attached to the droplets or particles, float to the surface, and are skimmeo. Chemical agents often are added to improve flocculation. In oetroleum refineries, dissolved air flotation is commonly used t o remove oil from oil-in-water emulsions. Recovered oil is recycled t o tne Fefinery Drocess (Jacobs Engineering 1975).

Chemical De-emulsifvinq Agents added t o l iquid wastes raise or lower the p H of the liquid or change the attractive forces between the particles. These processes separate solvents and oil from the water phase i n t o a l iquid organic phase.

c-10

Dissolved and Emulsified Orqanics Recoverv

Organics separation techniques such as steam or air strigpins, carbon adsorption, and solvent extraction are generally considered wastewater treatment methods. The organics that are removed are concentrated and amenable t o recovery.

0 Steam Stripping. In steam stripping, steam (or air) fed t o the bottom o f a packed column picks u p volatile organics from wastes pumped onto the t o p of the column. The organic vapors recovered a t the t o p of the column are condensed, and the organics are recovered from the condensate. T h l s process is used commonly to remove chlorinated solvents (e.g., methylene chloride) from wastewater.

Carbon Adsorption. Wastewaters with dissolved organic solvents i n l ow concentrations (less than 1 percent) can be pumped through a packed bed o f activated carbon, which preferentially absorbs the solvent. When tne zarbon becomes loaded w i t h the solvent, the bed can be regenerated w i t h steam or another solvent. Although carbon adsorotion has been used successfully t o remove low concentrations o f halogenated solvents (such as Zhlorcethane, chloroform, 1,l-dicnloroethane, 1,2-dichloroethane, I ,2-dichlcropropane, l,!,l-tricnloroethane, 1,1,2-trichloroethane, and p h e n o l ) from organic chemical industry wastewaters, the solvents evolved as gases during the regeneration o f the carbon are not recovered f o r reuse. Instead, tr,e evcivecj gases are incinerated (USEPA - Effluent Gtiidellnes Development Documerrt Organic Chemicals 198 1 ).

Solvent Extraction. Separation o f l iqu id waste constituents is achieved more commonly by solvent extraction. The wastewater is mixed 'with a solvent that extracts certain components o f the waste stream, b u t is immiscible w i t h the remainder of the waste. Then the solvent is recovered and recycled to the process, leaving the residual organic waste.

The principal use of solvent extraction technology is in the organic chemical industry (USEPA - Effluent Guidelines Development Document - Crganic Chemicals' 198 I ). Phenol from wastewater is commercially recovered by extraction w i t h isopropyl ether followed by distillation. The recDvere:! phenol is recycled t o the process or sold as a chemic81. Solvent extracticn ( w i t h water as the solvent) is used to recover water-soluble organics from halogenated hydrocarbon solvents.

Suoercritical Fluid Extraction is similar t o solvert extrac'icr, b u t uses an extracting solvent whose temoerature has been raisea abcve irs critics: point (where i t n o longer exists as a solid, liqbid, o r gas, b u t sinpl! as a f lu id) . Critical Fluid Systems inc, is testing supercritical camon dioxioe (COz), which exhibits unique solvent properties in t h i s range. Super critical

c-11

c

'i CO2 s e l e c t i v e l y e x t r a c t s organic s o l v e n t s (e.g., i sopropanci i frDm w a s t e w a t e r . Then the C 0 2 / s o l v e n t m i x t u r e is d e c o m p r e s s e s , s l iowizg toe C 0 2 t o vapor ize , and leaving the e x t r a c t e d o r g a n i c solvent res idue. F ina l ly , the vapor ized CO2 is recompressed a b o v e its c r i t i c a l point and rec t .c ied t o the process . No c o m m e r c i a l appl ica t ions o f s u p e r c r i t i c a l f luid e x t r a c t i o n t o recovery of hazardous masks w e r e ident i f ied during t h i s s tudy.

M e m b r a n e S e p a r a t i o n is accompl ished by applying e x t e r n a l pressure t o o n e side o f a m e m b r a n e so that so lvent in a liquid w a s t e s t r e a m will f low in t h e opposite d i rec t ion . Molecules o f w a t e r and low molecular weight compounds readi ly p a s s through the m e m b r a n e , while the l a r g e r o r g a n i c molecules bui ld up in t he r e c i r c u l a t i o n s t r e a m , becoming. c o n c e n t r a t e d .

0

E i t h e r u l t r a f i l t r a t i o n o r reverse osmosis c a n be use.d ' to a c h i e v e m e m b r a n e separa t ion . U l t r a f i l t r a t i o n uni ts have m e m b r a n e openings ranging f r o m 0.0025 t o 0.010 micron and o p e r a t e at a b o u t S O psig. R e v e r s e osmosis u n i t s h a v e s m a l l e r m e m b r a n e openings (0.0005 to 0.0025 micron) t h a n the u l t r a f i l t r a t i o n uni ts , bu t o p e r a t e a t much higher pressures ( s e v e r a l hundred pounds). U l t r a f i l t r a t i o n is appl ied in b o t h o n s i t e and o f f s i t e r e c o v e r y o p e r a t i o n s t o c o n c e n t r a t e w a s t e organics.

R e c o v e r y of O r a a n i c Vapor f r o m C a s e o u s Waste S t r e a m s

Solvent vapors are r e c o v e r e d f r o m gaseous w a s t e s t r e a m s by c o n d e n s a t i o n , carbon adsorp t ion , o r absorp t ion in to a liquid s t r e a m .

0 Condensa t ion c a n be used alone (e.g., t o r e c o v e r volat i le s o l v e n t s f r o m s t o r a g e t a n k s ) o r in conjunct ion with such uni t o p e r a t i o n s a s d i s t i l l a t ion , carbon adsorp t ion , and a i r o r s t r e a m stripping. Solvent vapors a r e r e c o v e r e d through a c o n d e n s e r cooled by r e c i r c u l a t e d cool ing w a t e r , chi l led water, o r a r e f r i g e r a n t . T h e c h o i c e of coolan t is o n e of e c o n o m i c s and p e r f o r m a n c e (i.e., a d e q u a t e vola t i le organic c h e m i c a l removal) .

C a r b o n A d s o m t i o n , descr ibed previously f o r nquid-liquid phase s e p a r a t i o n , has b e e n used t o r e c o v e r low c o n c e n t r a t i o n s o f so lvent (e.g., a c e t o n e ) v a p o r s f r o m g a s s t r e a m s . G e n e r a l appl ica t ion o f c a r b o n adsorp t ion technology to r e c o v e r y of s o l v e n t s f o r r e u s e has been l i m i t e d f o r s a f e t y reasons. A c t i v a t e d c a r b o n c a n c a t a l y z e the decomposi t ion o f s o m e o r g a n i c s , resu l t ing in hot s p o t s and possible bed fires. (However , t h e technology is widely used in the organic c h e m i c a l industry to l i m i t a x b o r r e emiss ions o f t o x i c vapors.)

0 Liauid Phase Absorpt ion is t h e t r a n s f e r of a so lvent f r o m the gaseous s t r e a m in to a l iquid s t r e a m . Continuous c o n t a c t o f g a s and liquid is required. T h e

c-12

3 absorption aoparacus may be a tower f i l led w i t h solid pacu:ng mate:.ai. qn e m p t y tower mt3 ,Nhicn the liauid is sorayed and th rous I : whicr the 3 a s flows, or a tower containing a number o f plates f o r increased surface area. The gas and liquid streams are maintained in countercurrent flow, thereby achieving maximum concentration driving force and the highest possibie ra te of absorption of gas by the liquid phase. A n e w aDsorption arocess recovers volatile organic chemical emissions from paint spray booths using an oil-in-water emulsion. After absorption, the emulsion is separated into clean water and a solvent-oil rich phase. The water is recycled t o the paint booth, and the solvent-oil rich phase is processed to recover the solvent and recycle oil to the absorption loop.

3 C-13

c.2 Halogenated Organics (Nonsolvent) Recvcling Technolooies

Halogenated organic wastes that are n o t solvents include the chlorinated hydrocarbon pesticides and intermediates (e.g., chlorinated phenols, halogenated aliphatic pesticides, aldrin, and toxaphene); polychlorinated biphenyls (PCBs); and other chlorinated organic wastes such as epoxy strippers and still bottom residues from recovery of halogenated solvents.

Recycling opportunities are generally more restricted for this.class of material for two reasons: (1) some o f these wastes, particulary those containing polyhalogenated aromatics, may be contamined w i t h dioxins, and ( 2 ) markets f o r some possible.products, such as carbon tetrachloride, have been declining sharply i n recent years.

Technologies available for recycling nonsolvent halogenated wastes, either for reuse or heat recovery, are discussed below. The uses and limitations o f each technology are summarized in Table C-2.

Pesticide Dusts ;I

Halogenated organic pesticides and pesticide intermediates usually are recycled onsite. Dusts and particulates generated either from product drying during pesticide manufacture or from blending operations during pesticide formulation are collected by baghouse filters and recycled to the process.

Pesticide Wastewater

Recycling of wastewater from pesticide production also is practiced commonly in conjunction with solvent extraction, steam stripping, and distillation operations (see Table 4 - 2 ) .

C- 14

Li' 1208s

Table C-2 Summary o f Recycling Technologies f o r Halogenated Organics Waste Streams

Type of process Descr ipt ion of technology Appl icat ions L imi ta t ions o f Use

Halogenated oryanic wastes are used as fue l i n cement k i l ns . Energy i s recovered as we l l as ac id gas, which reacts w i t h f ree a l k a l i i n the cement t o produce a low-alkal i cement.

SQ~Y& e x t r a c t i m Dimethylformamide (DHF) solvent ex t rac ts PCBs from waste o i l s : water washing i n second stage t o separate out solverit and leave a PCB concentrate.

,

c) I

Recovers heat dur ing tliernial destruct ion o f organics. Method i s widely used. loading per ton of cement. A t h igh

L im i ta t i on imposed by maximum haloyen

halogen loadings. s a l t s formed by reac t ion of ac id gases and a l k d l i i n the cement w i l l begin t o fuse i n t o a mol ten r ing. operation o f the k i l n .

I n te r fe res w i tli

Process y ie lds a decontaminated o i l . which could be fu r ther processed t o g ive a r e l a t i v e s o l u b i l i t i e s of PCB n DMF recyclable product. and other media; i n some case , nay

Ex t rac t ion e f f i c i ency depends un

not g ive a completely decocitamindted f l u i d .

i

Exhausiive Chlorination

A commercial process that involves h igh temperature (600O C) and exhaustive chlorination converts chlorinated hydrocarbon wastes to a salable product, caroon tetrachloride. This process has been used by DOW Chemical Corporation a t their Freeport, Texas, facility (Versar 1975). However, portions of the process at Freeport have been discontinued (Chemical Week 1985). Exhaustive chlorination can be used t o convert h igh ly chlorinated still bottoms generated from distillation o f crude halogenated solvents to carbon tetrachloride. Such reclamation operations also have practiced b y Ethyl Corporation and Vulcan Materials (Versar Inc., 1975; Versar Inc., 1980; personal communication with Mr. John Huguet, E t h y l Corooraticn, February 1980).

Reclamation o f PCB-Contaminated Waste Oil

Polychlorinated biphenyls can be removed from waste oil b y extraction or the waste oil can be dechlorinated. B o t h processes are available commercially for offs i te or onsite applications.

1 De c h I o rin a t ion. Stat e -0 f - t he-ar t dechlorination processes rec 1 ai m N as: e oils contaminated with PCBs at concentrations between 50 and 10.000 opm so that the oil can be reused. These processes use sodium compoumis 10 dechlorinate the PCB molecules and produce a nonhalogenated oqan ic compound and a sodium salt. The new processes are patented ~y PPM, Acurex, and Sunohio, and are improvements over the original dechlorination process investigated b y Goodyear Tire and Rubber Company. Dechlorination process equipment is mounted on mobile equipment, which can be brought t o the site of the generator's facility (usually a transformer requiring service).

Solvent Extraction. Another new process, based on solvent extraction, is suitable f o r removing PCBs from waste oil. This process, dimethylformamide (DMF) extraction, also reduces the volume of PCB waste by a factor o f IO. The steps of the process are: extraction of PCSs with DMF; extraction w i t h water o f the' DMF from the DLIF-PC3 mixture; and recovery and purification o f the DMF by distillation. The ourified DMF is recycled t o the process, and the decontaminate0 oil can be reLses. i h e concentrated PCB-containing residue requires crisoosal 3s a hszsrdobs Nasf?.

C-16

->

H e a t R e c o v e r v f r o m Ha looena ted Organ ic Was te s

H a l o g e n a t e d o r g a n i c w a s t e s can be i n c i n e r a t e d f o r h e a t r ecove ry du r ing t h e m a n u f a c t u r e of o t h e r ch lo r ina t ed o rgan ic s o r in cemeq t kilns. A new p r o c e s s ca t a ly t i ca l ly d e s t r o y s the ch lo r ina t ed hydrocarbon byproduc t s of vinyl c h l o r i d e m o n o m e r p roduc t ion a n d r e c o v e r s heat and ch lo r ine value without e n v i r o n m e n t a l pollution (Benson 1979). In c e m e n t kilns, t h e t e m p e r a t u r e and e x t e n d e d resideclce t i m e r equ i r ed f o r a d e q u a t e ca l c ina t ion o f Cement e n s u r e eff ic ient d e s t r u c t i o n of ha logena ted o r g a n i c was te s . In addi t ion t o r ecove r ing e n e r g y value f r o m the w a s i e during its d e s t r u c t i o n , t h e acid g a s g e n e r a t e d reacts w i t h f ree a lka l i in the c e m e n t t o p roduce a low-alkali c e m e n t . This p roduc t is desirable in a n u m b e r o f m a r k e t applications.

The p r i m a r y l i m i t a t i o n t o the use o f ha logena ted o rgan ic w a s t e in cem.ent kilns is the m a x i m u m halogen loading p e r t on o f c e m e n t . C e m e n t kilns t y p i c a l l y l i m i t chlor ine c o n t e n t o f the w a s t e fuel to a maximum r a n g e o f 5 t o 10 p e r c e n t , a l t h o u g h a kiln equipped to blend t h e w a s t e with o t h e r f u e l pr ior t o burning 'can hand le h ighe r levels. A t high halogen loadings ( g r e a t e r t h a n 10 percent) salts f o r m e d by r e a c t i o n begin to fuse in to a m o l t e n ring. The mol t en salts i n t c r f e r e w i t h p rope r cpe rac ion cf the kiin aod c3n cause shutdown i f a l lowed t o build U P excessive!y. Also, na lcgen acid g a s e s are co r ros ive t 3 any m e t a l p a r t s o f the k i l n system (Stoddard e t i!. i 98 I j.

R e c o v e r y o f Hydrochlor ic Ac id

Hydroch lo r i c acid is c o m m e r c i a l l y produced th rough d e s t r u c t i o n o f c h l o r i n a t e d byproduc t s or w a s t e s b y i nc ine ra t ion and subsequent scrubbing o f combus t ion g a s e s with w a t e r . F o r e x a m p i e , at one f ac i l i t y , ch lo r ina t ed o r g a n i c c o m p o u n d s are inc ine ra t ed in a high p e r f o r m a n c e bu rne r , and the resul t ing hydrochlor ic acid g a s is abso rbed in w a t e r t o p roduce a 2 1 percent hydrocplor ic acid, 79 percent w a t e r a z e o t r o p i c mixture . A m o r e c o n c e n t r a t e d acid (35 t o 36 p e r c e n t nydroc-ior ic ac:d) is t h e n p roduced b y e x t r a c t i v e d is t i l l a t ion (Fox 1972). A t t w o C)ther f ac i l i t i e s . o v e r

C-17

90 percent o f organic wastes are inc inerated and the hydrochloric ac id is r e c o v e r e c . -) A t o n e plant , the a c i d is used t o neutral ize o t h e r wastes, and at another p lant the a c i d is to ld as a product.

C- 18

3

c.3 Meta l Recoue ry Technoioqies

M e t a l r ecove ry p rocesses c a n b e divided in to the fol lowing c a t e g o r i e s , r ep resen t ing a va r i e ty of un i t t r e a t m e n t opera t ions : m e t a l concen t r a t ion , m e t a l reduct ion , m e t a l subs t i tu t ion , and agglomera t ion . Many o f t h e c o n c e n t r a t i o n , reduct ion , and subs t i t u t ion p rocesses are widely used. Agglomera t ion t echn iques , however , have no t been widely employed. Al though many m e t a l r ecove ry ope ra t ions are p e r f o r m e d ons i t e ( f o r recyc l ing t o a' m a n u f a c t u r i n g o r finishing process) , c o m m e r c i a l o f f s i t e recyc l ing f ac i l i t i e s a l so are ava i l ab le ' (see CTffsite Recyc l ing , Sec t ion 4.3 and Appendix C-6).

Aqqlomera t ion

Agglomera t ion is a t e r m descr ib ing any p r o c e s s o f ga the r ing o f sma l l p a r t i c l e s i n to l a r g e r pa r t i c l e s , where the sma l l p a r t i c l e s s t i l l c a n be ident i f ied . Mill s c a l e , s ludges, and dus t s g e n e r a t e d by var ious indus t r i e s (e.g., iron and steel indus t ry) are a g g l o m e r a t e d t o be used for their m e t a l va lues in blast or induct ion fu rances . Agglomera t ion avoids p a r t i c u l a t e c a r r y o v e r f r o m furances . T h e agg1omera:ion t echn iques commonly used fo r w a s t e recyc i ing inc!lJJde :ow t e m p e r a t u r e bonding, hot b r i aue t t i ng , direct r educ t ion , and g reen balling.

e

e

0

e -

Low T e m p e r a t u r e Bonding. In t h i s p rocess , :he w a s t e s t e a m is blended w i t h a b inde r and t h e m i x t u r e is f o r m e d in to p e l l e t s by h e a t a n d / o r pressure. L o w t e m p e r a t u r e bonding p rocesses differ in the t y p e o f b inder used (see Tab le C-3).

H o t Br iaue t t inq . S o m e m e t a l w a s t e s c a n be h e a t e d t o a t e m p e r a t u r e b e t w e e n 1,6OO0F and 1,800"F in a f lu id ized bed and pressed in to briquettes. These b r i q u e t t e s a r e cooled by h e a t e x c h a n g e with tno feed (Frankl in Assoc ia t e s 1982a). This p rocess is n o t widely used in the U.S.

D i r e c t Reduct ion. Wastes conta in ing m e t a l ox ides can be T i x e d w i t h c o k e breeze (coue particles having a d i a m e t e r s m a i l e r t han 0.5 incn ) f r o m iron and s t e e l mil ls and f o r m e d in to pel le ts . By a p rocess ca i l ea direct reduct ion , these p e l l e t s a r e p r e h e a t e d on a g r a t e , t h e n reduced ci.e., :he m e t a l ox ides in the p e l l e t s are c o v e r t e d t o m e t a l s ) in a ro:ary k i i n , a t a t e m p e r a t u r e o f abou t l,lOO°C, using c o k e a s t h e reducing a s e n t . The d i r e c t r educ t ion p rocess is used c o m m e r c i a l l y only in J a p a n (Frankl in Assoc ia t e s 1982a).

3 c-19

1420s

Table C-3 Surmary o f Recycling Technologies f o r Metals-Bearing Waste Streams

Type o f process Descr ipt ion Appl icat ions l i m i t a t i o n s o f Use -

Hydrometallurgical processing ( leaching)

Metals can be leached aut o f so l ids and sludges by extended contact w i th spec i f i c acids.

Solvent ex t rac t ion Select ive solvents used t o ex t rac t and concentrate metal cat ions from aqueous solut ions such as leachate. n

I N 0

loci exchange

Prec ip i t a t i on

Ion exchange resins a re produced which w i l l se lec t i ve ly remove ce r ta in metal ions but pe rn i t others t o pass wlieci wastewater i s pumped through the packed bed.

Metals dissolved i n wastewater are p rec ip i ta ted out o f so lu t ion by re- ac t i ng them t o form insoluble c o n ~ poullcls.

Chemical reduction Addi t ion of reducing ayents t o waste so I ut i 00 c o d a i ni ng tonic met a1 s causes p rec ip i t a t i on o f elemental s i l v e r and mercury, o r the reduct ion 01 t o C r + B .

Ex t rac t ion of metals from hazardous sludges, b r ine muds.

Concentration o f desirable metals must be reasonably high (over 5,000 ppm) t o make leaching a t t rac t i ve . Moderate cost o f acids used i s an economic constraint inposing lower l i m i t s on contents of waste t o be handled.

Economically feasible f o r recovery o f vanadium pentoxide. Evaporation o f the some v o l a t i l e solvents. High cost i s amine solvent leads t o recovery o f reasonably pure annonium vanadate. wastes.

Solvent losses can be a problem w i th

not feas ib le f o r many metal-bearing

Same as above

Same as above; frequently used.

Expected l i f e o f res ins i s a concern i n that frequent r e s i n replacement w i l l make the process more cos t ly . Puisoning of r e s i n w i t h nonremovable i n p u r i t i e s i s a lso a major concern. For many app l ica t ions the process i s cost 1 y .

Recovered sludges need fu r ther processing to recover metal values.

Recovery ot s i l v e r o r mercury in useable l o r n from wastes. Converts eas i l y reducible tox i c const i tuents. hdrdrduus CR+6 t o nonhazardous Cr+3.

Useful only f o r wastes cori tdini i ig

d

L, 1420s

l ab le C-3 (continued)

Type of process Descr ipt ion Appl icat ions L imi ta t ions o f Use

n e l s \ n ! w t r a t i o n m” (continued)

Crys ta l l i za t i on

Calc inat ion

Evaporation

Membrane separation

Adsofpt ion

.

Sol id metal compounds rembved from so lu t ion by cool ing i t . t o lower s o l u b i l i t y o f metal sa l ts .

Consists of reac t ing metal-bearing sludges a t h igh temperatures to dr i ve o f f water and other vo la t i l es . inc inera te residual organics, and ox id ize remaining inorganic compounds inc lud ing metals.

Concentration t o r recovery by evapor- at ion. tanks. Also used on r i nse water from other p l a t i n g operations.

Widely used f o r chrome r inse

Sol ids la rger than pore openings i n the l i l t e r media are removed. Ihe openings must be smaller to achieve metal separations thaii those used i n oryaii i c s .

Simi lar tu i on exchanges i n select- i v e l y removing mater ia ls when waste- w d t r r i s passed through a colunm o f adsorptive media. Various natural mater ia ls including redwood bark and sphagnum moss are i n comercia1 use to r removal o t various metals.

Same as above. Used only i n l i n i t e d cases i n which recovered mater ia l i s saleable.

Converts waste t o oxide tha t i s eas i l y handled as feedstocd by a smelter. only i n l i m i t e d cases.

Used

Allows fo r recovery o f concentrated solut ions.

Allows f o r recovery o f concentrated solut ions. Rarely used because of higher costs.

Removes metals Iron wastewaters. Not frequently used due t o higher costs.

Practiced only f o r reasonably concentrated solut ions. ( i .e., above 20 percent concentration).

Not appl icable t o wastes containing arsenic o r selenium. which f o m v o l a t i l e oxides.

Energy costs place lower l i m i t s on concentrations to which technoloyy i s appl icable. Used only i n l i m i t e d cases.

Membrane mater ia ls must be selected based on t h e i r a b i l i t y to withstand degradation by the waste; chromic ac id and high pH cyanide baths have been p a r t i c u l a r l y d i CCicul t streams to t rea t w i t h . t h i s operation. Rarely used because of higher costs. ,

Recovery ot metals f rom adsorbents such as high surface area c lay o r s i l i c a i s d i f f i c u l t . Not f requett t ly used due t o higher costs.

1420s

Table C-3 (continued)

Appl icat ions L ia i t a t i ons o f Use lype o f process Descr ipt ion

Foam f l o t a t i o n Involves a i r t l o t a t i o n of foams a f t e r add i l i on of po l ye lec t ro l y te and ad- j u s t i n g pH. Relat ively.new process - no connerical i n s t a l l a t i o n s t o date.

E lec t ro l y te recovery

Sodium borohydride

Reduction i n furnaces

01 her reducing processes

Current passed through electrodes innersed i n the metal solut ion. Metal ions migrate t o the electrode where they give up an e lec t ron and are p la ted out.

Addi t ion of sodium borohydride t o neutral o r a l ka l i ne solut ions o f metals w i l l r e s u l t i n p r e c i p i t a t i o n o f the me ta l l i c powders out o f so l ut ion.

Sludye i s mixed w i th coke o r other reducing agent and heated.

Copper can be removed from e lec t ro less solut ions i n me ta l l i c form by addi t - ion of formaldehyde and r a i s i n g the

pti- i n ac id ic copper baths.

Copper w i l l p l a t e onto steel

E f f e c t i v e l y removes copper, zinc, chromium, and lead. Rarely used due to ore-l ike. Many waste types higher costs. unacceptable as feeds. Rarely used

Raw mater ia l t o process must be

due t o higher costs.

Recovery o f precious metals.

Recovery of mercury from ch lo ra l ka l i production.

Metal r e f i n i n g

Process becones i n e f f i c i e n t when handling d i l u t e so lu t ions (concentrations below 100 n g / l . )

Process l i m i t e d t o recovering more noble metals. i.e.. precious metals, n i c k e l l cobalt. copper, and m e r c u r y . Process l i m i t e d t o s a l t s f o r which metals are eas i l y formed by reduct ion and t o neutral o r a l k a l i n e solut ions. Used in l i m i t e d cases due t o h igher operating costs.

High cost l i m i t s t h i s process t o + ta l re f in ing .

Recovery of mater ia l i n me ta l l i c form. Metal s a l t must be eas This l i m i t s process t o metals. n icke l , cobal t and mercury. Value o t

d

l y reducible. prec i ous copper.

there covered mater ia l must j u s t i f y cost of using the process. l i a t i t r d cases due t o higher costs.

Used on ly i n

ir'

t 1420s

Table C-3 (continued)

Type of process Descr ipt ion Appl icat ions l i m i t a t i o n s o f Use -__ - - ___-

Par t icu la te recovery

Select ive adsorbetits

0 I 1u w

Wet scrubbers

Retor t iny

Fine s o l i d pa r t i c l es . entrained i n baghouses and e lec t ros ta t i c p rec ip i - t a to rs (used i n a i r p o l l u t i o n cont ro l ) are recycled as feed i n s tee l m i l l s , o r as source O F t race metals to other industr ies.

Adsorbent media are ava i lab le comner- c i a l l y which se lec t ive ly t i e up spec i t i c metals. Adsorbents can be regenerated o r destroyed t o recover the metals. An example i s the recovery ot gold from cyanide- bearing solut ions; gold i s adsorbed from so lu t ion onto a resin. Inc inera t ion o f the res in produces yo ld i n u w f u l lorn.

Vapors rnd extremely f i n e p a r t i c l e s can be recovered by wet systems such as packed scrubbing columns and i mf) i nymtent p 1 a l e scrubbers .

Process used to recovery mercury trom sludges; waste i s heated i n an ox id i z ing environment. Mercury i s recovered by condensation.

Closed loop rerovery system invo lv ing a replacement react ion between ralciunt arid s a l t . added t o Na-sludye i n healed react ion vessel.

Reduction of a i r emissions. c h i e f l y t o r con t ro l o f a i r pa r t i cu la te emissions from meta l lu rg ica l industr ies.

Widely used,

Reduction of a i r emissions.

Reduction of a i r emissions.

Recuvery of mercury and minimization o f hazardous waste. I t r e t o r t i n g i s done properly. residue may be nonhazardous.

Recuvery of sodium from waste sludge i n sodium manufacture.

Hater ia l recovered i s dry; wet mater ia l may be desired. Requires reasonably dry gas stream f o r su i tab le recovery.

k e d t o regenerate adsorbents or t o dispose o f sludges generated by spent adsorbent p u r i f i c a t i o n . Not widely used due t o higher costs.

Need.to t rea t o r handle wastewater genera ted.

Energy-intensive operation. Value of recovered mercury may be i n s u t t i c i e n t t o cover costs unless wastes w i t h h igh mercury content are processed.

Oiily appl icable to waste sludyrb l rom elemental sodium production.

1420s

Table C-3 (continued)

lype o f process Descr ipt ion Appl icat ions L imi ta t ions o f Use

low temperature bond i ng

Hot b r i que t t i ng

0

h) P

Direc t reduction

Waste stream mixed w i t h a binder; b r iquet tes o r p e l l e t s pressed out, which are then used as feedstock i n metals operations (steelmaking. i ron) .

Feed mater ia l heated between 1600°F and 1800°F i n f l u id i zed bed, then pressed i n t o br iquettes.

The process nixes. pe l l e t i zes . and pre- heats the waste stream on a grate and reduces the p e l l e t s on a ro ta ry k i l n by making use o f the carbon i n the p e l l e t s as the reduclant.

t , I lows f o r reuse of co l lec ted pa r t i cu la te Br iquettes prepared by t h i s method may mater ia ls. not have desired i n t e g r i t y a t elevated

temperatures. procedure i s probably preferable t o any ons i te use o f such a process.

Use of waste by metals

Same as above. Applicable only t o so l i ds w i t h low vapor pressure a t b r i que t t i ng temperature. Process i s not widely used.

Sone oxide/hydroxide wastes from p l a t i n g operations, i f kept segregated by metals could be a useful feedstock f o r a smelter using such a process t o convert ore t o ne ta l .

Useful only w i t h eas i l y reducible substances (i.e.. s w metal oxides). Recovered ne ta l nust j u s t i f y cost. Process i s used as pa r t o f smelt ing industry t o reduce ores t o metals. Shipment o f waste t o smeller i n l i e u o f ons i te processing i s probably preterred

.

-3 I

0 Green Ballinq. The green balling process, another agglcmeration tecnnlpue. recycles bagnouse and electrostatic CreClPitatOr dusc ,a:r D C i l b t i O n 2 3 n t r 3 1 devices) from electric and open hearth furnaces o f the iron a n a s:ee: industry. The collected dust is wetted and formed in to balls, whicn then are fed back in to the furnace as a material feedstock.

Particulate and Vapor Recovery from Gases

Metals and metal compounds are recovered from air or gas streams usually as fine particles; however, more volatile metals (such as mercury, lead, cadmium, and zinc), which tend to vaporize in high-temperature processes, are recovered from the vapor phase.

0 Particulate Recovery. Baghouses, electrostatic precipitators, and wet scrubbers are used in many industries to capture fine solid particles. These particles may be recycled to feed streams as in steel mills or may be a source of trace metals to other industries such as smelters in the nonferrous metals industries. Cadmium dust generated from cadmium batteries or pigment plants can be recycled (Versar 1980).

VaDor Recovery. Metal vapors can be recovered b y adsorbents that seiectively tie up metals from gas streams. These commercially svailabie adsorbents are regenerated or destroyed to recover the metals. Mecal vapors also can be recovered by wet systems such as packed scrubbing columns or impingement plate scrubbers.

The metals recovered by adsorption generally are disposed o f rather than reused (personal communication w i t h Or. M. Caprini, M o d u x Corp., 1935). For example, in the production o f phenol mercuric acetate, the process ta i l gases are passed through a carbon adsorption column for the removal o f mercury, and the spent carbon (containing the mercury) is sent offs i te t o hazardous waste landfills or offs i te reclaims.

Retorting. This process is used in the chloralkali industry (Sic 2 8 1 2 ) t o recover mercury from mercury-bearing sludges and solid wastes. The waste is heated in an oxidizing environment. As elemental mercury forms, i t distills from the waste and is collerted by condensation. The residues from the retorting are shipped offs i te as hazardous wastes. (Personal communication w i t h Mr. Paul Tobia, Plant Manager, 3nd Mr. George Gissell, Plant Environmental Coordinator, Vulcan Materials inc., July 16, 1985).

C-25

M e t a l C o n c e n t r a t i o n Processes

T h e r e are d iverse m e t h o d s ava i lab le t o c o n c e n t r a t e m e t a l compounds f r o m a bulk solid or l iquid i n t o a s ludge or solution. Unit o p e r a t i o n s f o r c o n c e n t r a t i n g m e t a l s include hydrometa l lurg ica l processing (leaching), so lvent e x t r a c t i o n , ion exchange , c h e m i c a l prec ip i ta t ion , ca lc ina t ion , evapora t ion , m e m b r a n e s e p a r a t i o n , adsorpt ion, a n d f o a m f lo ta t ion . These Processes have been developed either to r e c y c l e the m e t a l s or t o treat the bulk s t r e a m t o r e n d e r it nonhazardous. T h e m e t a l c o n c e n t r a t e s f o r m e d m u s t b e t r e a t e d further to r e c o v e r the m e t a l s in a usable (salable) form.

0 H y d r o m e t a l l u r s i c a l Processinq. T h e p r i m a r y appl ica t ion of hydro- m e t a l l u r g i c a l processing ( leaching) is for m e t a l s r e c o v e r y f r o m ores , b u t leaching technology a l so h a s b e e n appl ied t o the e x t r a c t i o n of m e t a l s f r o m h a z a r d o u s sludges. M e t a l s are l e a c h e d f r o m sol ids and s ludges by e x t e n d e d c o n t a c t wi th inorganic solvents . T h e n t h e dissolved m e t a l s a r e r e c o v e r e d by uni t o p e r a t i o n s such as e lec t ro lys i s , c h e m i c a l reduct ion , o r c h e m i c a l p r e c i p i t a t i o n fo l lowed by f i l t r a t i o n , e lec t ro lys i s , and ion exchange . S o l v e n t s used in hydrometa l lurg ica l l eaching include s u l f u r i c acid, hydrocnlor ic ac id , n i t r i c ac id , a m m o n i a , a m m o n i u m c a r b o n a t e , ferric ch lor ide , a n d s u l f u r dioxide ( M e h t a 1981).

Although the leaching o f m e t a l s f r o m hazardous s ludges is not p r a c t i c e d widely, o n e such appl ica t ion is in the r e m o v a l of mercury f r o m c o n t a m i n a t e d br ine m u d s g e n e r a t e d f r o m m e r c u r y cell ch lora lka l i plants . Vulcan M a t e r i a l s Inc. (one f a c i l i t y a t P o r t Edwaros, Wisconsin) l e a c h e s c o n t a m i n a t e d muds wi th s u l f u r i c acid t o c o n v e r t the sol ids t o n o n h a z a r d o u s gypsum and t o r e c o v e r the mercury. Subsequent t r e a t m e n t o f t h e leaching solut ion g e n e r a t e s a m u c h r e d u c e d volume o f mercury-bearing wastes wnich is r e t o r t e d to r e c o v e r m e r c u r y (Personal c o m m u n i c a t i o n w i t h Mr. P. Tobiz , Vulcan Mater ia l s , 1985).

+)

Solvent Ext rac t ion . O r g a n i c s o l v e n t s c a n be used similar ly t o e x t r a c t a n d concent ra t -e m e t a l c a t i o n s f r o m aqueous o r nonaqueous so lu t ions (e.g., l eacha tes ) . C o m m e r c i a l appl ica t ion o f organic so lvent e x t r a c t i o n t o r e c o v e r y o f m e t a l s is n o t c o m m o n because o f t h e high cost . O n e e x c e p t i o n is t h e r e c o v e r y of vanadium pentoxide f r o m s p e n t su l fur ic ac id c a t a l y s t s ( a t t w o plants). T h e vanadium is leached f r o m the c a t a l y s t s , t h e n s e l e c t i v e l y e x t r a c t e d f r o m a q u e o u s s o l u t i o n with a high molecular weight a m i n e . Evapora t ion o f t h e a m i n e so lvent leads t o recovery o f reasonably pure a m m o n i u m v a n a d a t e ( p e r s o n a l communica t ion with Dr. T. qurst, Kerr-McGee Corp. 1980).

C-26

Ion Exchanae . Ion e x c h a n g e co lumns a r e used eXtenSiveiy in i a r g e a l a t i p g shops t o r e m o v e m e t a l s such a s c a d m i u m , nickel , s i iver , ana goid ?Tom w a s t e w a t e r s (Ploos Van Anste l and F r a m p t o n 1977). 'dherl m e t a i - o e a r i n g w a s t e w a t e r is pumped through the co lumn, t h e resins in t h e c o l u m n r e m o v e c e r t a i n m e t a l ions b u t p e r m i t o t h e r s t o pass. The t r e a t e d was:ewa:er is r e c y c l e d t o t h e p r o c e s s as rinse water . The resin is r e g e n e r a t e d w i t h s t r o n g acid, which, in t u r n , is t r e a t e d t o r e c o v e r the m e t a l s b e f o r e reuse. By removing dissolved m e t a l s f r o m a n e l e c t r o p l a t i n g b a t h , t h e ion e x c h a n g e co lumn e x t e n d s the service life o f t h e bath.

Prec ip i ta t ion . Toxic m e t a l s dissolved in w a s t e w a t e r s c a n be p r e c i p i t a t e d by addi t ion of c h e m i c a l s , usually l ime or c a u s t i c soda. This c o n v e n t i o n a l technology (hydroxide prec ip i ta t ion) has been improved upon b y p r o c e s s e s such as s u l f i d e prec ip i ta t ion , which r e d u c e the c o n c e n t r t i o n of t o x i c m e t a l s in t h e t r e a t e d w a s t e w a t e r .

O n e c o m m e r c i a l p r e c i p i t a t i o n process r e m o v e s m e t a l s f r o m w a s t e w a t e r s th rough addi t ion of a f e r r o u s s a l t fol lowed by n e u t r a l i z a t i o n a n d a i r oxidat ion. T h e ferrites f o r m e d f r o m t h i s t r e a t m e n t are insoluble o v e r a wide p H r a n g e a n d easy t o s e p a r a t e because of their m a g n e t i c p r o p e r t i e s and the size o f t h e p r e c i p i t a t e crystals . I n f o r m a t i o n on c o m m e r c i a l appl ica t ions o f t h i s p r o c e s s w a s not ava i lab le during t h i s s t u d y .

Nickel-plat ing so lu t ions and spent-nickel c a t a l y s t a r e commonly recycled b y the e l e c t r o o i a t i n g and inorganics c h e m i c a l (SIC 2 8 19) industries. Nickel-plat ing so lu t ions a r e r e a c t e d with soda ash t o p r e c i p i t a t e n icke l c a r b o n a t e , which t h e n is c c l l e c t e d and r e a c t e d with su l fur ic i c i d :o g e n e r a t e an i m p u r e n icke l -su l fa te solution. This solut ion is p u r i f i e d f r o m iron salts b y addi t ion o f s m a l l q u a n t i t i e s o f sodium su l f ide (iron s a l t s a r e P r e c i p i t a t e d as iron sulf ide) . Tne solut ion is q e x t s e c a r s t e d f r o m iron s u l f i d e by f i l t r a t i o n and e v a p o r a t e d to r e c o v e r pure nickel s u l f a t e . Soent-nickel c a t a l y s t s , a f t e r being dissolved with a minera l ac id t o f o r m a nickel s a l t solut ion, are treated the s a m e w a y a s t h e nickel-plat ing solutions. This r e c o v e r y technology is c u r r e n t l y used by a t least t w o m a n u f a c t u r e r s o f p la t ing chemica ls , Harshaw-Fil t rol (personal c o m m u n i - c a t i o n wi th Mr. David Wilson, Manager o f Envi ronmenta l Affairs and Mr. Fred Kaplan, Business M a n a g e r of Industr ia l C h e m i c a l P r o d u c t s Division, Harshaw-Fil t rol , Inc., Cleve land , Ohio, J u l y 16, 1985) and C-P C h e m i c a l (personal . c o m m u n i c a t i o n wi th Mr. Vincent Krajewski , D i r e c t o r of E n v i r o n m e n t a l A f f a i r s , C-P C h e m i c a l Co., Sewaren , New Jersey, :uly 16, 1985).

A n o t h e r p r e c i p i t a t i o n p r o c e s s uses cross-linked s t a r c h x a n t h a t e as the c n e m i c a l addi t ive. T h i s o r o c e s s h a s a f a s t r e a c t i o n r a t e and h i g n r e m o v a l rates o f m e t a l s f r o m w a s t e solutions. I t r e a c t s rapidly t o tie up the m e t a l s and l e a v e s very low leve ls of most m e t a l s in the solut ion. Tne f!3c :hat s e t t l e s rapidly c a n be d e w a t e r e d t o m u c h lower !evels than c a n De x t a i n e d

C-27

I

with m e t a l hydroxides. Subseouent t r e a t m e n t o f the P r e c i p i t a t e with a c i d r e l e a s e s t h e m e t a l s reaaiiy. Tnis process is effective ove r a p i l r a n g e f r o m 3 t o 1 1 . T h e U.S. D e p a r t m e n t o f Agr i cu l tu re holds s o m e p a t e n t s , but O the r s are also developing p a t e n t e d or P ropr i e t a ry i m p r o v e m e n t s ove r t h i s process .

Ano the r app l i ca t ion o f chemica l p rec ip i t a t ion is f o r the r e c o v e r y o f spent hydrofluoric a c i d e t ch ing solut ions at the Conse rva t ion C h e m i c a l C o m p a n y , St. Louis, Missouri , faci l i ty . The s p e n t e t c h i n g solut ion is n e u t r a l i z e d w i t h po tass ium hydroxide, convert ing the heavy m e t a l f l uo r ides p r e s e n t in to the cor responding insoluble hydroxides, which p r e c i p i t a t e f r o m t h e solut ion. T h e r e su l t i ng potass ium f luoride s ludges a r e f i l t e r e d to r e m o v e t h e hydroxide s ludge which is disposed o f ( landfi l led) as a haza rdous waste . T h e r ema in ing solut ion is e v a p o r a t e d to yield t e c h n i c a l g r a d e po ta s s ium f luo r ide f o r resale . Approx ima te ly 2,000 t o n s p e r y e a r o f t h i s p roduc t are produced by th i s p r o c e s s (personal communica t ion with H. Kaiser, C o n s e r v a t i o n C h e m i c a l Company , July 16, 1985).

0 C h e m i c a l Reduct ion . In c e r t a i n in s t ances , c h e m i c a l r educ t ion is r equ i r ed pr ior to p r e c i p i t a t i o n o f metals . F o r e x a m p l e , t o p r e c i p i t a t e silver o r m e r c u r y a s m e t a l , a reducing a g e n t is added t o t he w a s t e solut ion con ta in ing t h e s e m e t a l ions. Hexava len t ch romium is r e d u c e d to a t r i v a l e n t s t a t e w i t h a reducing a g e n t such a s sodium bisulf ide o r sodium metab i su l f ide . T h e t r i v a l e n t c h r o m i u m c a n then be p r e c i p i t a t e d in t h e f o r m o f a hydroxide. I t has been proposed t h a t t h e hydroxide s ludge c a n be t r e a t e d with. su l fu r i c ac id to r e c o v e r chromium s u l f a t e , which c a n t h e n be used in t he l e a t h e r tanning industry. P rec ip i t a t ion p rocesses a r e widely used in t h e ino rgan ic c h e m i c a l , e l e c t r o p l a t i n g , and metal-f inishing industries.

Crys t a l l i za t ion . Crys t a l l i za t ion o f m e t a l ions f r o m a w a s t e solut ion o c c u r s a s the t e m p e r a t u r e o f t h e solution is lowered . This t r a n s f o r m a t i o n t a k e s p l a c e b e c a u s e m e t a l compounds have lower solubili ty a t c o l d e r t e m p e r a t u r e s . Crys t a l l i za t ion commonly is used to r e c o v e r f e r r o u s s u l f a t e f r o m w a s t e pickle l iquors o r f r o m s u l f a t e p rocess t i t an ium dioxide w a s t e ac id solutions. The acid is pumped t o a c r y s t a l l i z e r where the t e m p e r a t u r e is ma in ta ined at approx ima te ly 35" t o 40°F to c rys t a l l i ze f e r r o u s s u l f a t e h e p t a h y d r a t e (FeSOa7H20) f r o m t h e solution. Crys t a l l i za t ion also is used to r e g e n e r a t e coDper e t ch ing b a t h s for reuse. T h e b a t h s (with hydrogen peroxide and su l fu r i c ac id) a r e r e g e n e r a t e d by r e f r i g e r a t i o n and f r e e z i n g of the c o p p e r s u l f a t e c r y s t a l s ou t of the solution.

Calcinat ion. Ca lc ina t ion drives o f f w a t e r and o t h e r vo la t i l e s f r o m meta l -bear ing s ludges b y exposure t o high ( inc ine ra t ion ) t e m p e r a t u r e s . T h e residual o r g a n i c s in t h e sludge a r e combus ted during t h e process , and any r ema in ing ino rgan ic compounds (including m e t a l s ) a r e oxidized. Leaded t a n k b o t t o m s a r e t r e a t e d b y ca l c ina t ion t o r e c o v e r l ead oxide (Stoddard et 31. 1981).

C-28

Evaoora t ion . Evapora t ion is used t o c o n c e n t r a t e r inse Ha te r ' rom 3ia t i -g ope ra t ions (n icke l , c a d m i u m , copper , c h r o m i u m , s i lver . golc. a n a z inc . yielding dis t i l led w a t e r and a m e t a l c o n c e n t r a t e t h a t a r e r e c y c l e 0 tc tne r inse t anks and p la t ing tanks, r e spec t ive ly (Warnke e t ai. 1977 , S h a t i z a n d J u m p 19.77, El icker r and Lacy 1978, and Capr io e t al. 1977). Addi t iona l m e t a l r ecove ry steps may be necessary . F o r example , so lu t ions f r o m chromium r inse t anks t h a t a r e first c o n c e n t r a t e d by evapora t ion are passed through ion e x c h a n g e co lumns to r e c o v e r the c h r o m i u m tha t IS r e c y c l e d t o the plat ing baths.

M e m b r a n e Separa t ion . Membrane s e p a r a t i o n processes include r e v e r s e osmosis , u l t r a f i l t r a t ion , and e lec t rodia lys i s . T h e m e m b r a n e s serve a s a medium f o r s epa ra t ing m e t a l s and o t h e r dissolved species f r o m w a t e r and small molecu la r species. In r eve r se osmosis and u l t r a f i l t r a t ion s e p a r a t i o n processes , the was te solut ion is f o r c e d through the m e m b r a n e b y pumping. In e lec t rodia lys i s , an e l e c t r i c a l po ten t i a l is appl ied a c r o s s the m e m b r a n e , caus ing the t r anspor t o f either c a t i o n s o r an ions through t h e m e m b r a n e .

R e v e r s e osmosis m e m b r a n e s have s m a l l e r p o r e openings and o p e r a t e a t h igher pressures . M e m b r a n e m a t e r i a l s m u s t be s e l e c t e d based on their ab i l i ty t o wi ths tand degrada t ion by (cor ros ive) was tes . P r e t r e a t m e n t o f t h e w a s t e is n e e d e d to r educe plugging and foul ing o f the membrane . R e , t r s e osmosis is f r equen t ly appl ied t o the recove ry o f m e t a l s f r o m copper and z inc p la t ing so lu t ions , . s i lver-bear ing photoprocess ing so lu t ions (Daigp3ul t 1977), and mixed p la t ing was tes . U l t r a f i l t r a t ion m e m b r a n e s used f o r organ ic s c a n r e m o v e suspended, col loidal , and l a rge molecu la r dissolved solids. This s epa ra t ion technique can , t h e r e f o r e , s e r v e a s a p r e t r e a t m e n t f o r meta!s.

Adsorot ion is s imi la r t o ion exchange in se l ec t ive ly removing mace r i a i s w5en w a s t e w a t e r is passed through a co lumn o f adso rp t ive meoia; horvever, t h i s p rocess involves a looser bond b e t w e e n tne s u r f a c e o f the media and :ne m e t a l being removed. (In ion e x c h a n g e resins , t h e r e is an a c t u a l c h e m i c a i group r e p l a c e m e n t in the complex molecular s t r u c t u r e o f t h e resin.)

Various n a t u r a l ma te r i a l s , including redwood bark and sphagnum moss, are used c o m m e r c i a l l y f o r adsorbing m e t a l s f r o m solut ion, and synthetic adsorbents , first c o m m e r c i a l i z e d i n J apan , a r e a l so used in the U.S.

Syn the t i c adso rben t s a r e r e g e n e r a t e d by passing an ac id through t h e column. 'Al te rna t ive ly , the adso rben t may be inc ine ra t ed , leaving 'an ash-meta l oxide c o n c e n t r a t e .

F o a m f lo ta t ion is a new process , w h i c h involves a i r f l o t a t i o n o f f o a m s a f t e r addi t ion o f po lye lec t ro ly t e and pH ad jus tmen t . F o a m f lo t a t ion effectiveiy r e m o v e s coppe r , z inc , c h r a m i u m , and lead f r o m was te so lu t ions "IPSF 1983). Although t h e e c o n o m i c s o f t h i s p rocess a r e c la imed K O De favorab le (WPCF 19831, no c o m m e r c i a l ins ta l la t ions w e r e i o e l t i f i e d aur in9 t ~ i s TeDort.

C-29

Metals Reduction and Metals Recovery

Metals reduction and recovery operations include e1ec:rolytic recovery, chemical recovery with sodium borohydride, and reduction in metal furnaces end through other processes. Wastes must be concentrated by one of the methods described above prior to application o f reduction and recovery operations.

0 Electrolytic Recovery is t h e most conventional commercial metals reduction process, where current is passed through electrodes immersed in the metal solution. Metal ions migrate to the cathode (negative terminal) t o be reduced to their elemental form (by giving up an electron) and are plated out. The reaction a t the anode (positive terminal) generates oxygen to complete the oxidation-reduction reaction. The deposited metal can be peeled o f f t h e cathode and sent t o a refiner or, if the cathode is made o f stainless steel, it can be directly used as an anode in a plating tank. Battelle Columbus Laboratories and Rolla Metallurgy Center have developed an electrolytic process that removes copper f r o m a mixed-metals leachate. After removal of copper, the chromium and zinc which remain in t h e leachate are recovered by roasting. Silver has also been electrolytically recovered from spent photographic development solutions (Daiqnault 1977).

Chemical recovery w i t h Sodium Borohydride. A recently developed process involves addition of sodium borohydrate t o neutral or alkaline solutions of metals, and precipitation o f metals by recLction in their eiemental form. No additional treatment is required except 'or filtration o f the grecipitated metals from the solution. The metals a f t e r filtration can be sold airectly t o scrap metal dealers.

1

Chemical recovery with the sodium borohydride process is acquiring wide acceptance for treatment and recycling o f metals in various industries. This process has been used to recover mercury from chlor-alkali production wastes, and precious metals from spent photograohic fixer and plating solutions (Business Week 1971, Medding and Lander 1981).

This process has a very l o w capital requirement, but is relatively h i g h in operating costs because of the cost o f sodium borohydride. The use of this process is limited to neutral or alkaline solutions, because sodium borohydride may cause an explosive reaction in acidic solutions (Business Week 1974).

Reduction in Furnaces. Metal refiners recover metals directly f r o m certain sludges in reduction furnaces. This operation is very similar to :he recovery o f metals from ores in furnaces.

-

C-30

the

The s ludge is mixed w i t h a reducing a g e n t (usually ccKej m d c n a r g e d t h e fu rnace . The m e t a l l i c compound is reduced t o the me ta l , wni;e :re c3Ne is ox id ized t o c a r b o n monoxide and c a r b o n dioxide. T h e hlgh capital i n v e s t m e n t l i m i t s app l i ca t ion o f t h i s t echno logy to m e t a l ref iners .

0 O t h e r R e d u c t i o n Processes . O t h e r r educ t ion p rocesses are a i so c o m m e r c i a l l y ava i l ab le in l imi t ed appl icat ions. F o r example , c o p p e r c a n be r e m o v e d f r o m a lka lone e l e c t r o l e s s so lu t ions in m e t a l l i c f o r m by a d d i t i o n o f fo rma ldehyde . Copper c a n a l so be r e m o v e d as m e t a l f r o m acidic c o p p e r b a t h s i f s t e e l sheets are p laced in to the solution. In this app l i ca t ion , iron c a t i o n s r e p l a c e c o p p e r in the solution.

M e t a l Subs t i t u t ion a n d R e c o v e r y

A byproduc t s ludge con ta in ing sodium, c a l c i u m , and their oxides, r e s u l t s f r o m m a n u f a c t u r e o f sodium meta l . T h e sodium m e t a l is r e c o v e r e d f r o m t h e s ludge

using a closed loop r e c o v e r y s y s t e m a n d r e t u r n e d t o the sodium p rocess as usable finished p r o d u c t ( D u P o n t 1985).

The r e c o v e r y p r o c e s s involves a r e p l a c e m e n t r e a c t i o n b e t w e e n c a l c i u m a n d salt, which is added t o the s ludge in a heated r e a c t i o n vessel. The r e a c t i o n c o n v e r t s t h e ca l c ium in to c a l c i u m ch lo r ide and yields r e c o v e r s b l e sodium me:al.

-3 The sodium r e c o v e r y p r o c e s s a t DuPont resulcs in approxima:ely 1,100 t o n s of

usable sodium being r e c o v e r e d p e r year. Additionally, app rox ima te ly ! ,200 t o n s of R C R A h a z a r d o u s w a s t e s are e l i m i n a t e d per year. T h e p rocess r e s u l t s in t he g e n e r a t i o n o f 800 t o n s per year o f nonhaza rdous w a s t e , which is disposed o f in a n approved s a n i t a r y landfil l .

A s o m e w h a t d i f f e r e n t , p r o p r i e t a r y p rocess is used a t the R M I sodium fac i l i t y . The re , a l so , w a s t e sodium-bearing s ludge is r ep rocessed t o r e c o v e r tne metal .

P r o c e s s Subs i t u :ion

3

!n a f e w c a s e s , i t is possible t o substitute the use o f a n e w x o c e s s t o entirei, avoid g e n e r a t i o n o f n a z a r d o u s was te . T h e p r e m i e r c3se o f t h i s s i t ua t ion e x i s t s in

C- 31

the chloralkali industry. Up until 1980, all high-purity sodium hydroxide was produced by the mercury-cell process, wh ich generates mercury-bearing solid wastes. A new process, the membrane cell, has been developed b y DuPont. The process also produces high-grade caustic soda a t lower cost than the old mercury-cell process. In the membrane cell, chlorine is formed a t the anode and sodium ions migrate through a membrane to undergo further electrolytic reaction with water in the cathode compartment, t h u s forming sodium hydroxide and hydrogen. Five membrane cell plants have been built since 1980 in t h e U.S. All of them are fairly small and use either evaporated salt or salt recovered for onsite diaphragm cell operations as feedstock. In April Ish, DuPont announced construction o f a new 1,000 ton-per-day membrane cell plant a t Niagara Falls, New York, to open in mid-1987. According to data supplied by DuPont (personal communication and material submitted by Dr. John Cooper, Petrochemicals Department, E. I. duPont de Nemours, Inc., Delaware, October 2, 1985). The plant design calls for the following features:

0 Zero production of hazardous waste;

0 Total recycling of spent brines to the brine wells for solution min ing o f raw salt material;

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Production of hydrochloric acid from chlorine present in process tail gases; and

Total sale o f the spent sulfuric acid used in chlorine drying.

The e f f e c t o f the construction of this new plant on the industry has already manifested itself. Recently, Olin Corporation (Wall Street Journal, September 27, 1985) announced the closure o f their mercury cell plant located in Niagara Falls, New Y o r k , because they do not feel their plant can be competitive with the new DuPont facility under construction. Should the new facility meet industry expectations, a further expansion of membrane cell capacity is to be expected. This may be accompanied b y a further decline in the amounts o f mercury-bearing hazardous wastes generated.

C- 32

The number o f cases in wPich new process deve1oDmeqts nave :?e 2o:ep;ia; :z

eiiminate hazardous waste has beer: srnail. In cases in wniccl :her c3 G c x r , SUC- is

for the membrane cell, their e f fect on future hazardous waste genetat-on ma:! t e

subst an rial.

c-33

I

C.b Recycling Technoioqies for Corrosive Wastes

Corrosive. wastes that are recycled include spent acids and alkaiis from chemical manufacture and petroleum refining processes, and also the acid from spent pickle liquor. Technologies commonly used t o recycle corrosive wastes include thermal decomposition, evaporation, crystallization, ion exchange, and oxidation. The limitations and uses of each of these technologies are presented in Table C-4 and discussed below.

Thermal Decomposition

Thermal decomposition is used in the recovery of sulfuric acid from spent acid sludges to recover ferric chloride from acidic titanium dioxide waste and for the recovery o f hydrochloric acid from spent pickle liquor or halogenated organic residues.

Recovery o f Sulfuric Acid. Thermal decomposition is widely used in petroleum refineries to recover concentrated sulfuric acid from speqt alkylating acid sludges contaminated w i t q hydrocarbons and concaining water. The acid sludges are recyucles by spen t acid processars i n evaporators a t temperatures ranging from 2,000' to 2,300°F. Mixed sulfur dioxide and water vapors produced from aecomposition o f the siudge are passed through a dust collection chamber fo r particulate colleccion, a waste-heat boiler f o r heat recovery, and a heat exchanger to lower the temperature to 700OF. The water vapor is removed from t h e gas b y 93 percent acid and t h e sulfur dioxide is oxidized to sulfur trioxide in the presence o f vanadium catalyst. Finally, the sulfur trioxide gas is scrubbed w i t h strong acid in an absorption tower t o yeild 98 to 99 percent sulfuric acid (Versar 1980).

Recovery of Hydrochloric Acid from Pickle Liquor. Iron and steel mills (SICS 331 and 332) generate a spent pickle liquor ( R C R A Code KO621 that contains approximately 20 percent ferrous chloride and 5 percent hydrochloric acid. Recovery o f t he hydrochloric acid b y thermal decomposition could be practiced by many of these facilities.

The first step in the recovery process is the preheating and concent:afion o f the spent pickle !iquor in evaporators. This concentrated sc.ution is introduced into a hydrolysis reactor. The reactor, ooerating a t approximately 1470°F to 183OoF, creates an oxidizing environment f o r the reaction between ferrous chloride and water. Ferric oxide solids are produced and precipitate out of the solution.

c- 34

Li 1410s

Table C-4 Summary o f Recycling Technologies f o r Corrosive Waste Streams

L imi ta t ions o f Use Type of process Descri p t ion Appl icat ions

. . mal derornPPrltlon

Recovery o f HCl l l yd ro ih lo r ic ac id contai'niny dissolved Recovery of HCl f o r reuse. Hydrolysis o f FeC12 requires a considerable input o f energy; i r o n oxide becomes a waste. needing disposal. Use o f FeC12 t o produce ferrous/ f e r r i c chlor ides f o r sale, where v iable, is preferred. (Not widely used due t o higher cost.)

ferrous ch lo r ide from p i c k l i n g i s re- acted w i th water i n the presence o f heat t o y i e l d hydrochlor ic acid and f e r r i c oxide.

Recovery o f H2SO4 Concentrated s u l f u r i c acids contamin- ated by water and hydrocarbons are

are passed through dust co l l ec t i on chamber. d r ied by 93% acid. and the SO2 present i s oxidized t o SO3 in the presence o f a vanadium catalyst . Ihe 503 i s scrubbed w i t h acid t