tin electrolysis

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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



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



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



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



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.



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 .



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 ).



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 .



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



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.



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



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



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.

REFERENCES

1. Kusik, C. L . P. Tsantr izos , J .

Valentine, S. C. Malhotra, and F. Harr i-

son. Sm all-Scale Detinning of Municipal

Solid Waste Magnetics. Final repor t on

Bureau of Mines contract JOl13039 withArthur D. Li t t l e I nc . March 1983,

75 pp.; avai lable from J . G. Groetsch,

J r . BuMines, Avondale, MD.

2. Schottman, F. J . I ron and Steel .

Sec. in BuMines Mineral Commodity Sum-

maries 1983, p. 78.

3. Kaplan, R. S. Deterrents to the

Recycling of Ferrous Scrap From Urban

Refuse. Paper in Resource Recovery and

Uti l i za t ion; Proceeding of the Nation

a l Mater ia ls Conservation Symposium,Gaithersburg, MD, Apri l 29, 1974 to May

I , 1974 ASTM Spec. Tech. Publ. 592).

ASTM, Phi ladelphia , PA 1975, pp. 91-105.

4. Banks, K. C. Tin and I t s Alloys.

Ch. in Kirk-Othmer Encyclopedia of Chem-

i c a l Technology, ed. by H. F. Mark, J . J .

McKetta, J r . D. F. Othmer, and A.

Standen. Wiley, v. 20, 2d ed . 1969,

pp. 294-303.

5. Hoore, W. E . E. S. Hedges, and

T. K. Barry. The Technology of Tinpla te .St . Mart in s Press , 1965, p. 250.

6. Tin Research I n s t i tu te .

s t ruc t ions for Elect rodeposi t ing

In-

Tin.

In ternat ional Tin

Greenford, Middlesex,

1971, p. 19.

Research

England,

Council ,

5th ed .

7. Linley, B. D. Recycling of Tinand Tinpla te . Paper in Proceedings,

Fi r s t In ternat ional Tinplate Conference,

In ternat ional Tin Research In s t i t u t e

London, October 5-8, 1976. Perry and

Rout lef f , Ltd . London, 1976, pp. 427-

440.

8. Car l in , J . F . J r . Tin. Ch. in

Mineral Facts and Problems, 1980 Edit ion.

BuMines B 671, 1981, pp. 947-959.

9. Spi l io t i s N. Tinplat ing From the

Fluoborate Bath. Metal Finishing 49thGuidebook and Directory, v . 79, No. lA,

1981, p. 327.

10. Makar, H. V., B. J . Wiegard, J r .

and E. L. Gresh I I I . Detinning Ferrous

Products From Urban Waste for Use in

Steelmaking. BuMines RI 8404, 1979,

16 pp.

11. American Society for Testing and

Mater ia ls . Standard Class i f ica t ion of

Pig Tin. B 339-72 in 1977 Annual Book

of ASTM Standards: Par t 8, NonferrousMetals--Nickel, Lead, and Tin Alloys,

Precious Metals, Primary Metals; Reac

t ive Metals. Phi ladelphia , PA 1977,

pp. 251-253.

INT . BU.OF MIN ES PGH. PA . 27561

tin electrolysis

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