tin electrolysis
TRANSCRIPT
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Report of Investigations 8887
Electrolytic Stripping of Tin
inan
AcidFlu
oborateEle
ctrolyte
By J. G Groetsch Jr. R C Gabler Jr.
and D A. Wilson
UNITED STATES DEPARTMENT OF THE INTERIOR
William P Clark Secretary
BUREAU OF MINES
Robert C Horton Director
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Library of Congress Cataloging n Publication Data:
Groetsch, J. G. (John G.)
.Elecrrolyric srripping of rin in an acid fluoborare elecrrolyre.
(Reporr of invesrigarions ; 8887)
Bi bliography: p. 9.
Supr. of Docs. no.: I 28.23:8887.
1. Tin plare-Derinning. 2. Fluoborares. 3. Elecrrolyres. I.
Gabler, Roberr C II. Wilson, D. A. (Donald A.). III. Tirle. IV. Se
ries: Reporr of invesrigarions (Unired Srares. Bureau of Mines) ; 8887.
TN 23. U 43 TS590] 622s [669 .6] 84-600092
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CONTENTS
Abstract •• I I I I •••••••••• I . . . . .
Introduction .
and experimental P I ~ O C I d u l r eexper imen t s . .
electrolyte composition • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
Effect of impurities in the electrolyte ••••••••••••••••••••••••••••••••••••••
t es t program .
Results of
Results of
postconsumer scrap • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
municipal sol id waste af ter various
P ] ~ e,t r t 11Em. t s • .. .. • .. • .. .. • .. • • • • . • • . .. .. .. .. • • • .. .. • ......... I .
SUnl lD ary . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . .
References • • ••
1 .
2.3.
1.
2.
3.
4
5.
6.
ILLUSTRATIONS
versus currentversus current density:
acid concentrationlow acid concentration.
Cathode currentCathode currentShredded MSW m , a ~ n . e it cs
TABLES
Effect of on cathode current efficiency at 60Composition scrap
Composition shredded MSW W 1)<,11<:: ....... 'cc'
Effects of different on elect ro ly t ic of Sn fromshredded MSW I'i, 11 <:: •• -'-...... '
Copper and SnImpurities in
treated and untreated
for s tee l scrap • • •• •• •• •• • • • •
during elect ro ly t ic of
m :ljl;ne lti cs •••••••••••••••••••••••••• •••
1
2
3
33
45
5
69
9
3
46
55
7
7
8
8
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UNIT OF ME SURE BBREVI TIONS USED IN THIS REPORT
A ampere L l i t e r
A ft2 ampere per square foot Ib pound
° degree Celsius Ib d pound per day
cm centimeter Ib f t 3 pound per cubic foot
g gram min minute
g Aoh gram per ampere hour min h minute per hour
g cm3 gram per cubic centimeter MMton yr million tons per year
giL gram perl i t e r
pct percent
gal gallon ton yr ton per year
h hour V volt
in inch wt pct weight percent
kg kilogram
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ELECTROLYTIC STRIPPING OF TIN IN N CID FLUOBORATE ELECTROLYTE
By J. G Groetsch, Jr., R. C. Gabler, Jr., 2 and D. A. Wilson3
ABSTRACT
Municipal so l id waste MSW) contains about 8 pct fer rous metal l ics
which are typ ica l ly recovered by magnetic separators a t municipal re
source recovery f a c i l i t i e s . At present , only about 182,500 ton/yr of
MSW magnetics are being processed for remelt ing out of the MMton/yr
discarded. The Sn in MSW magnetics makes th i s mater ia l d i f f i cu l t to re cycle to the s t ee l indust ry . An e l ec t r o l y t i c method using stannous
f luoborate- f luobor ic ac id for removing Sn was evalua ted . Optimum con-
cent ra t ions of Sn in the e lec t ro ly te and the e f fec t s of impur i t i e s such
as AI, Cu, Fe, and Pb on Sn recovery from the e lec t ro ly te were evalu
ated . Operat ing parameters were 60 to 65 giL f luobor ic ac id and 20 to
30 giL Sn using s ta in les s s t ee l elect rodes a t a current dens i ty of 60
A/f t 2 • Tests were run with postconsumer scrap4 and MSW magnet ics .
Good r esu l t s were obtained with MSW magnet ics , a f t e r pre t rea tment by
reshredding , magnetic separat ion , and a i r c las s i f i ca t ion . The f ina l Sn
conten t of the MSW magnetics scrap was reduced from 0.18 to 0.017 wt
pct . Heat and solvent t rea tments o f MSW magnetics to remove coatings
did not s igni f i cant ly improve Sn removal beyond t ha t obtained with ma -t e r i a l t ha t had only been mechanical ly pret reated .
Chemical engineer .
2Research chemist .
3Research chemist r e t i r ed ) .
Avondale Research Center , Bureau of Mines, Avondale, MD.
P o s t c o n s u m e ~ scrap for th i s study cons is ted of cleaned t i n cans.
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2
INTRODUCTION
At present , in the United Sta tes , mu
nic ipa l SQlid waste (MSW) i s generated a t
a ra t e Qf 3 to 5 lb /d per persQn. I t
cQntains abQut 8 pct ferrQus meta l l ics .
PrQjectiQns ind ica te ~ 1 1 MMtQn/yr Qf t h i s
valuable ferrQus scrap i s being discarded
1) .5 Discarded MSW magnetics are equiv
a lent to apprQximately 15 pct Qf the tQ
t a l U.S. 1982 s t ee l prQductiQn 1). I t
i s d i f f i c u l t to recycle t h i s ferrQUS
scrap by di rec t remelt ing because the
cQntaminants crea te prQblems in the
steelmaking furnaces and the s t ee l end
prQduct. CQPper and Sn are the majQr
meta l l i c cQntaminants in MSW magnetics
t ha t are re ta ined in the s t ee l . They
harden and s t rengthen s t ee l s , but alsOdecrease duc t i l i t y and cause sur face hQt
shQrtness (cracking in hQt-rQlled s t ee l
prQducts) 3) . Lead cQntaminatiQn frQm
the Pb-Sn sQlder causes prQblems with
furnace re f rac tQries . These cQntaminants
fQrce any recyc l ing Qf MSW magnetics in
twO PQssible direct iQns: di lut iQn with
blas t furnace pig irQn Qr clean scrap in
a 10:1 ratiO , Qr remQval Qf the CQntam
inants befQre remel t ing .
The det inning indust ry CQuld t r ea t MSW
magnetics to remQve the Sn and prQduceacceptable scrap , but mQst det inners ,
using the cQnventiQnal NaOH leach, pre
fe r nQt to use t h i s Sn SQurce because Qf
cQntaminatiQn by Qrganic mater ia l and Al.
Organics absQrb Sn-cQntaining leach SQlu
t iQn and cQntaminate the prQduct s tee l
by carrYQver Qf the leach sQlutiQn.
Aluminum in bimeta l l ic cans) CQnsumes
the NaOH det inning sQlutiQn by fQrming
NaAl02. The fQrmatiQn Qf NaAl02 alsO
increases sQlutiQn visCQsity and causes
fQaming, sp i l lQver , and Al cQntaminatiQn
Qf the Sn prQduct.
An addi t iQnal prQblem
reSQurce recQvery plants
i n eCQnQmical shipping
i s tha t many
are nQt with
dis tances Qf
5Underl ined numbers in parentheses re
fe r to i tems in the l i s t of re ferences a t
the end of t h i s repor t .
curren t ly Qperating det inning plants .
This prQblem can prQbably Qnly be ad
dressed by de t inning technQlQgy tha t is
wQrkable Qn a small sca le I , 4) . In
resPQnse to these prQblems, the BUreau of
Mines has s tudied nQncQnventiQnal de t in
ning technQlQgy.
A Bureau-funded study by Arthur D. Li t
t l e , Inc . (1) reviewed exis t ing technQl
Qgy and examined new cQncepts. I t CQn
cluded tha t - -
1. CQnventiQnal det inning technQlQgy
i s nQt adequate (fQr the reaSQns d i s
cussed abQve) to prQcess MSW magnetics Qn
a small sca le .
2. I t i s unl ike ly tha t nQnupgraded MSW
magnetics can be detinned eCQnQmically.
3. I f MSW magnetic scrap i s upgraded
to reduce the nQnmetall ics to reasQnably
lQW l evels ~ 1 . 5 pct ) , t may be det inned
Qn a small sca le eCQnQmically by a number
Qf proce-s·se-s-, including aqueQus chemical
QxidatiQn and e lec t rQlys i s .
StannQus fluQbQrate-fluQbQric acid , the
sQlutiQn used to make e lec t rQly t ic t i n pla te 5) , can alsO be used fQr elec t rQ
l y t i c Sn s t r ipp ing . A study Qf t h i s prQ
cess and i t s effec t iveness in det inning
MSW magnetics was i n i t i a t e d . This e lec
t rQly t ic prQcess can be Qperated a t rQQm
temperature in a wide range Qf Sn and
f luQbQric acid cQncentratiQns and between
current densi t ies Qf 20 and 120 A/ft 2
6) . I t was chQsen to aVQid the high
temperatures and the cQntaminatiQn prQb
lems Qf the NaOH l each. Optimum Sn CQn
centratiQn and current densi ty were de
termined, as were the ef fec t s Qf impurit i e s present in MSW magnetics. Testing
began with pure Sn, and then prQceeded to
PQstcQnsumer scrap (peS) and f i na l l y to
MSW magnetics. In t es t ing with MSW mag
net i cs , at tempts were made to remQve
lacquer cQatings, as suggested by anQther
study Cl .
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The Sn recovered from any det inning
operat ion replaces a por t ion of import
requirements. The United States cur ren t
ly imports about 80 pct of i t s Sn, and
3
the est imated po ten t ia l recovery from
processing about 11 MMton/yr of MSW mag-
ne t ic s i s about 30,000 ton/yr , or about
half the U.S. consumption (l ,
CELL DESIGN AND EXPERIMENTAL PROCEDURE
The mater ia l to be detinned was divided
equal ly and placed in two s ta t ionary
s ta in les s s t ee l wire mesh baskets tha t
served as anodes. Two baskets were used
to obtain a uniform Sn depos i t on the en
t i r e cathode, which cons is ted of a sol id
piece of s ta in les s s t ee l l i t h a known ex
posed area for determining cathode cur
ren t densi ty . The two wire baskets were
1 in 2.5 cm) apar t , and the cathode was
between them. The t o t a l e lec t ro ly te vo l
ume was 0.53 gal 2 L), and the so lu t ion
was circula ted with a s ta in les s s t ee l
s t i r r ing rod. The c e l l s po ten t ia l
var ied between 1 and 3 V depending on the
type of mater ia l tes ted . The ce l l op
era ted a t room temperature. In i n i t i a l
t es t ing , the mater ia l used was pure Sn,
but l a t e r t e s t s used pes and SW magnetic
scrap . Tests were conducted for the time
necessary for complete Sn removal as ca l
cula ted by- -
Tmln
where Tmln
60) Xg ) C cs )
1) 2 .21409) ,
s t r ipp ing t ime min),
1)
I
weight scrap (g) ,
Sn content of scrap ex
pressed as g Sn/g metal ,
cur r ent A),
2.21409 electrochemical equivalent
for Sn in the +2 valence
s t a t e g/A·h) ,
and 60 conversion h to min
min/h) .
For example, for a PCS samp l e ,
Tm I n =60 min/h) 187.4 g) 0 .003 gig)
1.5 A) 2.21409 g/A·h)
10.16 min.
The f ina l Sn content of the scrap was
computed by subt ract ing the amount of
pure Sn deposited from the amount of Sn
i n i t i a l l y present in the scrap and cor rec t ing for the Sn concentrat ion in the
e lec t ro ly te .
ELECTROLYTE EXPERIMENTS
DETERMINING ELECTROLYTE COMPOSITION
Elec t ro ly t i c removal of Sn using an
aqueous stannous f luoborate- f luobor ic
ac id e lec t ro ly te was evaluated using op
e ra t ing condi t ions s imilar to those used
to p la te Sn on s tee l (9) . Th e ce l l us es
a pure Sn anode. The-var iables s tudiedwere cathode current eff ic iency, current
densi ty , and e lec t ro ly te composition.
The tes ted f luobor ic acid concentrat ion
in the e lec t ro ly te was var ied between
28 and 174 giL, and the Sn concentrat ion
was var ied between 12 . 1 and 40.0 giL.
Good Sn depos i ts were obtained cathode
current eff ic iency >90 pct and minimal
amounts of sponge and powder) when Sn
1 0 0 r
.
ti 90zw
ou::W
Z
80a::::J
u
.
: - .- - ..... .......... . .
-
KEY
- 12 .9 giL Sn
27 .3 gIL Sn
. .... 40 .0 giL Sn
.
7 L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ L L____20 40 60 80 100 120
CURRENT DENSITY , Alft '
FIGURE Cathode cu rrent efficiency ve rsuS cur
rentdensity: h igh acid concentration ( 174 gi H BF4 ).
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4
concentrat ion was greater than 5 giL
with current dens i t i e s a t or below 60
A/f t 2 • Gassing occurred a t the higher
current dens i t i e s and low Sn l eve l s .
This i s re f lec ted in lower cathode cur
rent ef f i c i enc ies ( f igs . 1-2 . The acid
concentrat ion had l i t t l e ef fec t on cath
ode current eff ic iency; a t a l l acid lev
e l s tes ted , cathode current ef f ic iency
was above 90 pct when the Sn concentra
t ion and the current densi ty were in ac
ceptable ranges. Tests were also con
ducted using gela t in and beta naphthol
addi t ions to the e lec t ro ly te ; these
addi t ives are used commercially to obtain
good throwing power and good t inp la te
appearance. Based on these resu l t s , the
following e lec t ro ly te composition was
chosen:
HBF 4
Sn • •• • •
Gelat in • • • • • • • • • •
Beta naphthol • • • .
giL
60-65
25-30
6
1
Since acid concentrat ion had l i t t l e e f
fec t on cathode current eff ic iency, a
moderately low acid concentrat ion was se
lec ted from the concentrat ions used in
commercial Sn pla t ing . The gela t in and
beta naphthol concentrat ions used are a l
so representa t ive of commercial pract ice .
EFFECTS OF IMPURITIES
IN THE ELECTROLYTE
Impuri t ies were invest igated to deter
mine the i r ef fec t on cathode current
ef f ic iency and the qua l i ty of the Sn
deposi t . The ce l l used a pure Sn anode.
The impuri t ies Al, Cu, and Fe were dis
solved in to the e lec t ro ly te using the
elemental metal or oxide; Pb was dis
solv-ed as PbC03. The anode current ef f i
ciency was assumed to be 100 pct because
the e l ec t ro ly t e s Sn concentrat ion in
creased. Any change in cathode current
ef f ic iency was caused by the impuri ty .
The e f fec t of impur i t ies on current e f
f ic iency at 60 A/ft2 i s summarized in
tab le 1
1 0 0 . - - - - - - - - - - - - r - - - - - - - - - - - - . - - - - - - - - - - - ~ ~ ~ - - - - _ _ - - - - - - - - _ _ .
-Ja-
UZwULL
LL
W
Zwa
a
l
U
~ - - - --• . ~ ~ ~ .............................................- ........ .
-
, .•
80
',
60KEY
12.1 gIL n
. 18.2 gIL n
·27 4 gIL n
40
2 0 ~ - - - - - - - - - - ~ - - - - - - - - - - - - ~ - - - - - - - - - - - - L - - - - - - - - - - - ~ - - - - - - - - - - - - ~20 40 60 80 100 120
CURRENT DENSITY A/fF
FIGURE - Cathode current efficiency versus current density low acid concentration (28 giL HBF4 .
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T BLE 1. - Effect of impur i t ies on cath
ode current eff ic iency a t 60 A/ft2
Impuri ty v Sn Cathode
Impurity conc, conc, current
giL giL eff ic iency,
pctNone • • • • • • . N p 36.5 96.9
Ai . . • • • • • • • 12.5 31.9 97.1
4.7 30.9 96.3
Fe . • • • • • • • . 32.0 30.9 96.1
11.0 31.6 95.6
b 9.0 34.0 94.9
6.7 32.0 95.1
u .86 30.0 95.6
N p Not appl icable .
5
Copper and Pb codeposited with Sn to
a much greater degree than Al and Fe.
The impuri ty levels were, in weight
percent Cu, up to 3; Pb, up to 10; Al,
<0.02; and Fe, <0.40. These impur i t ies
had l i t t l e i f any ef fec t on the cathode
current ef f ic iency at the concentrationstes ted. Aluminum in concentrations
above 12.5 giL forms a sludge containing
AlF3 and AlF3·3H20. The concentrat ionof Al in the e lec t ro ly te is therefore
se l f - l im i t ing .
DETINNING TEST PROGR M
RESULTS OF DETINNING
POSTCONSUMER SCR P
PCS was shredded in a hammer mill with
1/2-in 1.27-cm) gra tes . The shredded
PCS contained many balled pieces r e su l t
ing from too long a res idence t ime in
the mill ing zone before passing through
the gra tes . A shearer- type shredder
would produce a bet t e r sample for de
t inning, but one was not avai lable . To
t a l shredded sample weight was about
11 lb 5,000 g) with an average bulk den
s i ty of 89.8 l b / f t
3
1.44 g/cm
. Theshredded scrap was s p l i t using a r i f f l e
s p l i t t e r from which ana ly t ica l samples
were taken as well as samples for de t in
ning. The analysis i s l i s t ed in tab le 2.
T BLE 2. - Composition of postconsumer
scrap
Sample Sample Concentrat ion, w pct
weight , g Al Cu Pb Sn
PCS 1 4.4 0.02 0.02 1.32 0.32
PCS 2 4.5 .02 .03 .30 .-36
PCS 3 7.5 .02 .04 .65 .25PCS 4 6.9 .01 .03 .35 .27
Sample preparat ion and ce l l operat ion
with PCS were as fol lows: Material for
t es t ing was r i f f l e - s p l i t in to samples be
tween 150 and 200 g. Before the scrap
was detinned, t was screened to 100 pct
plus 20 mesh to prevent the f ines from
f a l l ing through the wire mesh basket .
The f ines « 1 wt pct of the sample) were
discarded. S tr ipping time equation 1)
was based on the Sn content of the post
screened weight, assuming an average of
0.30 w pct Sn C cs ) and a current den
s i ty of 60 A/ f t2 . The f inal Sn content
of the detinned scrap var ied between
0.035 and 0.009 w pct with an average of
0.014 for 32 t e s t s . The t rea ted sc rap s
Sn content did not increase great ly as
the t es t s proceeded, showing no ine f f i
ciency with t ime.
Impurity buildup from det inning PCS was
also s tudied during these t e s t s . Theconcentrat ions of Cu, .Fe, and Pb were
determined in the e lec t ro ly te and in the
Sn deposi t . Lead was the highes t Sn
depos i t impuri ty , present up to 0.15 w
pct . This value remained r e la t ive ly con
s tan t , while the lead in the e lec t ro ly te
increased l inear ly up to 0.223 giL dur
ing the 32 det inning t e s t runs. The same
trend was observed with Fe. The Fe con
tamination of the Sn depos i t never ex
ceeded 0.05 wt pct , while the Fe con
cent-ration in the e lec t ro ly te increased
l inear ly up to 1.62 giL during the 32runs. Copper was detected in very small
quan t i t i e s 0.0007 giL in the e lec t ro
ly te . The small level present « 0 . 2 w
pct) in the Sn depos i t would s ig
n i f i cant ly a f fec t the value of the Sn
product .
The ce l l operated on a problem-free ba
s i s with PCS for 32 consecutive t e s t s ,
approximately 5 h of operat ion. During
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6
th i s t ime, cathode current ef f ic iency re
mained a t approximately 9 pet . Gassing
was minimized, and a l l Sn depos i ts were
ra ted good to f a i r on the bas is of ap-
pearance. A good depos i t i s smooth and
contains no spongy or powdery areas . The
Sn e lec t ro ly te concentrat ion remained a t
28±2 giL throughout the t e s t s , i nd ica t ing
Sn was not being s t r ipped from the
e lec t ro ly te .
RESULTS OF DETINNING MUNICIPAL
SOLID WASTE MAGNETICS AFTER
VARIOUS PRETREATMENTS
About 100 lb 45.5 kg) of
scrap was obtained from the
covery Unit of the Ontario
MSW magnetic
Resource Re-
Ministry of
the Environment in Toronto, Canada. The
scrap had already been shredded, mag-
net i ca l ly separated, and a i r - c l a s s i f i ed .
I t was reshredded in the same manner as
PCS, then again subjected to magnetic
separat ion and a i r c l a s s i f i ca t i on to r e
move Al and organic wastes entrapped in
the or ig ina l sample. Rif f le sp l i t t i ng
was then done to ob ta in samples for ana l
ys i s . Their composition i s l i s t ed in
table 3. The Al and Cu content var ied
great ly from sample to sample. The var i
at ions in Pb and Sn content were smal l ,
consider ing the heterogeneous nature of
the mater ia l f ig . 3). The average bulk
dens i ty for th i s mater ia l was 101 I b / f t 3
1.62 gl cm 3 •
FIGURE 3 - Shredded SW magnetics.
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TABLE 3. - Composition of shredded MSW
MSW-1
MSW-2
MSW-3
g
Concentration, wtAl Cu Pb
0.01 0.02 0.39
2.91 .11 .37
.01 .04 .46
Sn
0.16
.16
.22
The scrap was blended, coned. and quar-
tered. Then, to have sam-, portions were taken
for the individual t es t s .
size and prep current
MSW
aration60 A/f
whenSn content0.18 wt pet.
comident ical to that used
PCS. The in i t ia l average
C cs for equation 1 was
The tes of MSW
vided into four parts .periments, the shredded
were given no furtherthan
and air classif icat ion.
was d i
In the f i r s t exMSW
treatment other
In the second,
7
they were chemically delacquered by soak
in acetone for 4 followed
thinner for 2 days, washed with
fresh acetone, and then air dried. In
the th ird , the MSW magnetics were roastedfor 30 min a t 350° C. Finally, the MSW
were flash-roasted; i . e .
cold in a furnace
to 400°, 500°, or 600° C for res i
dence times of 2, 5, 10, or 15 min, andthen removed and allowed to cool. Treatments, Sn content, and cathode currentefficiencies are l is ted in table 4.
Theferent
the di f -
were good,producingscrap for
these t es t s cathode current
was above or close to 90 pct, and Snwere of quali ty.
average f inal Sn content of MSW
de
The
that had only been shredded and magnetical ly separated with no furthertreatment was 0.017 wt pet. None of the
appear to
affect Sn removal.
TABLE 4. - Effects of different on elec-str ipping of Sn from shredded MSW
of pretreatment
None. . . «, ,thinner •••••
Roast at 350° C for 30 min ••
Roast at 400 0 C for - -
2 min. , , . , ,
5 min. . . , , . , ,
10 min . , , III •
15 min • • . ,, •• ,,Roast at C for--
2 min •• . . .,, ,,.,,
5 min •• . ,,.,, ,,.
10 min , , . , ,
15 min . , , . , ,Roast at 600 0 C for--
2 min. .,,,,
5 min. . , , , , . , ,
10 min. . , , , , . . . .
15 m i n . , , . , ,
Av Sncontent of
detinned MSW
magnetics,
wt pct
0.017
.016
.015
.022
.026
.020
.013
.025
.027
.021
.014
.026
.020
.017
.Oll
Av cathode
current
eff
90.6
91.1
91.6
87.8
85.5
88.8
92.7
86.1
85.0
88.3
92.2
85.6
88.9
90.6
.9
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8
Table 5 l i s t s Cu and Sn values for some
of the grades of s tee l scrap tha t are
current ly marketed lQ). The f luoborate
detinned SW appears comparable to de
t inned bundle or No. 2 bundle scrap. A
representa t ive Pb analysis for shredded
auto scrap i s 0.01 wt pct . Detinned SW
would contain l a rge r amounts of Pb.
T BLE 5. - Copper and Sn analyses for
s t ee l scrap
Scrap type
N o . 1 heavy melting • • • • • • • •
N o . 1 factory bundle • • • • • • •
Shredded auto • • • • • • • • • • • • • •
Detinned bundle • • • • • • • • • • • •
N o . 2 bundle nonauto) •••••
N o . 2 bundle auto) • • • • • • • •
N Not avai lable .
Conc,
Cu
0.16
.06
.22
N
.38
.48
w pct
Sn
O.Oll
.005
.021
.04
._038
.08
Analyt ical da ta for the Sn depos i t and
e lec t ro ly te are l i s t ed in tab le 6. The
impuri ty l eve l s var ied depending on the
type of pretreatment . All Sn depos i ts
contained less than 1.0 pct to ta l impuri
t i e s . Aluminum and Pb were the most
abundant elements in the Sn depos i ts but
were found in lower concen tra t ions than
Fe in the e lec t ro ly te . Copper content
was small in both the Sn deposits and the
e lec t ro ly te , but the deposi ts Cu content
was s ign i f ican t consider ing the amount of
Cu in the e lec t ro ly te .
Pretreatment of the SW with acetone
lacquer th inner before det inning did
not s ign i f ican t ly a f fec t e i ther the Sn
depos i t or the e lec t ro ly te . Roasting
did not appear to s ign i f ican t ly improve
depos i t qual i ty , and many of the roasts
were dele ter ious . The Fe content in
the e lec t ro ly te increased when roasted
scrap is used, probably owing to the for
mation of rus t ( i ron oxide) . Also, Pb
concentrat ion increased in both the elec
t ro ly te and the Sn depos i t when roasted
scrap was detinned.
The metal produced met the STM speci
f i ca t ion for Grade E Sn 99 pct Sn).
This mater ia l i s used in cast bronzes,
bear ings , and Pb-base al loys . I t s Al
content makes t unacceptable for use in
s-Older_ and i nning- U1- -._
T BLE 6. - Impuri t ies in Sn depos i ts and e lec t ro ly tes during e l ec t r o l y t i c
s t r ipp ing of t rea ted and un t rea ted shredded SW magnetics
Type of pre t rea tment Tin depos i t impur i t ies , wt pct Electro ly te impur i t ies , giL
Ai Cu Fe Pb Al Cu Fe Pb
None • • • • • • • • • • • • • • • • • . • • 0.141 0.010 0.043 0.139 0.146 0.002 0.668 0.064
Acetone-lacquer th inner . .206 .012 .042 .098 .160 .0014 .608 .054
Roast a t 3500
C for
30 min • • • • • • • • • • • • • • • • • .099 .010 .032 .197 .154 .0018 1.64 .160
Roast a t 4000
C for - -
2 min .122 .005 .025 .045 .042 .0010 .200 .022
5 min • • .143 .007 .062 .078 .086 .0009 .760 .069
1 min • .107 .009 .027 .159 .148 .0013 1.05 .130
5 min •• • •• .107 .010 .024 .224 .210 .0014 1.85 .178
Roast a t 5000
C for - -
2 min • .058 .008 .036 .066 .063 .0009 .400 .02385 min • • • • .064 .007 .104 .147 .176 .0010 1.10 .0854
10 min • • • • • • • • • • • • • . • • .076 .010 . l lO .371 .250 .0010 2.60 .210
5 min • • • .063 .Oll .034 .412 .358 .0009 11.3 .256
Roast a t 6000
C for - -
2 m 1n .085 .006 .057 .098 .051 .0008 1.34 .030
5 m 1 n .071 .006 .032 .243 .133 .0010 11.3 .16
10 min •• •• .073 .008 .039 .381 .220 .0008 21.9 .41
5 min• • • .043 .007 .043 .773 .270 .0008 29.8 .57
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s
SUMM RY
Samples of PCS and SW magnetics were
detinned using an e lec t ro ly t ic process .
The e lec t ro ly te composition chosen for
the research was 60 to 65 giL HBF 4 25 to
3 giL Sn, 6 giL gela t in and 1 giL beta
naphthol. At a current densi ty of 60
A/f t2 the cathode current eff ic iency was
usual ly above 90 pct . Aluminum, Cu, Fe,
and Pb impur i t ies had l i t t l e or no ef fec t
on cathode current eff ic iency but s ig-
n i f i cant amounts of Cu and Pb codeposited
with the Sn. The detinned scrap appeared
comparable to severa l commercial grades
of s tee l scrap . The Sn recovered met the
ASTM speci f icat ion for Grade E Sn. Addi
t iona l pretreatment to remove lacquer
coat ing did not improve Sn qual i ty or de
t inned product qual i ty.
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INT . BU.OF MIN ES PGH. PA . 27561