160 functions of chloride in copper-refining electrolyte.pdf

8/10/2019 160 Functions of chloride in copper-refining electrolyte.pdf

1/12

A paper presented at the Eiohty-Sixth Gen-

eral Meetino held at Buffalo N. Y.

October 14 1944 F. A. Lowenheim pre-

siding.

F U N C T I O N S O F C H L O R I D E I N C O P P E R - R E F I N I N G E L E C T R O LY T E ]

By Y U - L I N YAO.J:

A B S T R A C T

T h e c h l o ri d e c o n c e n t r a t i o n o f c o p p e r - r e f in i n g e l e c t r o l y t e is c o r r e l a te d

w i t h t h e c a t h o d e p o l a r i z a t i o n a n d a l s o w i t h t h e g r a i n s i z e a n d t h e

h a r d n e s s o f t h e c o p p e r d e p o s it . I t i s s h o w n t h a t t h e cu r v e s h a v e a

b r e a k a t t h e c h lo r i d e c o n c e n t r a t io n o f a b o u t 15 m g . / L . T h e v a r i a t i o n o f

t h e c a t h o d e p o l a r i z a t i o n i s e x p l a i n e d o n t h e a s s u i n p t i o n t h a t t h e e l e c t r o -

chem ica l r e ac t ion C u + + -[- e ~=t C u + i s a s low pr ocess and tha t t he

e l e ct r o ch e m i c a l r e a c t io n C u + + + 2 C 1 - + e --> C u C 1 2 - m a y t a k e

p la c e. T h e v a r i a t i o n s o f t h e h a r d n e s s a n d t h e g r a i n si ze a r e e x p l a in e d

a c c o r d i n g l y b y t h e p o l a r i z a ti o n p h e n o m e n a .

I N T R O D U C T I O N

C h l o r i d e i s a n e s s e n ti a l c o n s t i t u e n t o f t h e c o p p e r - r e fi n i n g e l e c t r o l y t e ? *

T h e f u n c t i o n s o f c h l o r i d e h a v e b e e n r e p o r t e d a s f o l l o w s : c h e m i c a ll y i t

p r e c ip i t at e s s i l v er a s s i lv e r c h l o r id e , a n d a n t i m o n y a n d b i s m u t h a s

ox yc h lo r ide s ; e l e c t r ochem ica l ly i t a c ts a s a c a thod e dep o la r i z e r ;8 phy s i -

ca l ly i t re f ine s the g r a in s i z e o f t he copp e r depo s i t . * I t i s we l l kn ow n tha t

ch lo r ide r educes t he s il ve r l os s i n t he r e fined coppe r . H ow ev e r , the

o t h e r s t a t e m e n t s a r e n o t s o w e l l e s ta b l is h e d . I n a p r e v i o u s p a p e # t h e

a u t h o r h a s s h o w n t h a t i t i s v e r y i m p r o b a b l e t h a t a n t i m o n y p r e c i p i t a t e s

a s o x y c h l o r id e . O n e o f t h e l a rg e c o p p e r r e fi n e ri e s h a s f o u n d in a

l a r ge - sca l e expe r imenta l c e l l t ha t t he r e i s a dec ided d r op in t he ca thode

po ten t i a l when the e l ec t r o ly t e i s p r ac t i c a l ly dech lo r id i zed . 6 A c c o r d i n g

t o R o u s e a n d A u b e P t h e c r y s t a l s i z e o f c o p p e r d e p o s i t s f r o m a n e l e c t r o -

l y t e c o n t a i n i n g 2 0 m g . / L c h l o r i d e i s m u c h l a r g e r t h a n t h e c r y s t a l s i z e

f r o m a n e l e c t ro l y t e c o n t a i n i n g o n l y 5 m g . / L c h l o ri d e . T h u s i t i s s e e n

t h a t t h e r e h a s b e e n n o a d e q u a t e a n d c o n s i s t e n t e x p l a n a t i o n f o r s o m e o f

the e f f ec t s o f ch lo r ide i n t he coppe r - r e f in ing e l ec t r o ly t e .

T h e p u r p o s e o f t h e p r e s e n t w o r k w a s t o i n v e s t i g a t e t h e r o l e o f

ch lo r ide i n t he coppe r - r e f in ing e l ec t r o ly t e i n t he absence o f add i t i on

a g e n t s a n d i m p u r i t i e s .

t M a n u s c r i p t r e c e iv e d J u n e 1 9 , I 9 4 4 .

:~ G r a d u a t e S t u d e n t , D e p t . o f M e t a l l u r g y , L e h i g h U n i v e r s i t y , B e t h l e h em , P a .

1 L a w r e n c e A d d l c k s , T r a n s . l ~ l e c t r o c h e m . S o c . g S , 2 6 6 ( 1 9 1 3 ) .

2 , , L e a r n i n g H o w to R e f i ne a n d C a s t C o p p e r . b y A . L . W a l k e r , i n C h o i c e o f M e t h o d s in

M i n i n g a n d M e t a l l u r g y . L i s t e d i n A m . I n st . M i n i n g E n g r s . S e r ie s , p u b l . b y M c G r a w - H i l l

B o o k C o m p a n y , N e w Y o r k ( 1 9, 3 2) .

E d w i n W . R o u s e a n d P a u l K . A u b e t . T r a n s . E l e e tr o e h em . S o e. $ 2 , 1 8 9 ( 1 9 2 7 7 .

4 K u r t A r n d t , T e e h n i s e h e E l e k t r o e h e m i e , p .

297.

V e r L ag F . E n k e , S t u t t g a r t ( 1 9 2 9 ) .

Y . L . Y a o , T r a n s . E l e c t r o c h e m . S o c . , p , 3 6 5 , t h i s v o l u m e .

6 P r i v a t e c o m m u n i c a t io n .

371


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3 7 2 Y U - L I N Y A O

E X P E R I M E N T A L

A rectangular glass jar holding about 10 liters of electrolyte was

used as an experimental cell. This was placed in a large water bath,

the temperature of which was maintained thermostatically so that the

temperature of the electrolyte was held at 37 ~ C (99 ~ F). There

were separate motor stirrers in the cell and in the water bath. The

speed of the stirrer in the cell was about 2,000 r.p.m.

The electrolyte used was a synthetic one, made from C.P. chemicals.

The composition was: Cu, 40 g./L; H2SO4, 184 g. /L . The electrolyte

was frequently analyzed for copper and acid by the usual methods and

minor adjustments were made to maintain this composition. The

evaporation loss was compensated by repeated additions of distilled

water.

Current was supplied by a small motor generator set capable of de-

livering 15 amp. at 30 v. Proper resistance was connected in the circuit

to maintain the cathode current density at 15 arap./sq, ft. (1.6

amp./d.m.~).

There were two anodes and one cathode. The anodes were cast

electrolytic copper and the cathode was cast commercial lead. Lead

was selected as the cathode to facilitate the stripping of the copper

deposit without using oil. The immersed area ~)f the cathode was

52 sq. in. (340 cm?).

Attention had been paid to the possibility of the crystal orientation

of the cathode basis metal being copied by the deposit. At the begin-

ning of the electrolysis, the current was interrupted three or {our times.

The cathode was taken out of the cell and washed with 1.0N sulfuric

acid and distilled water. Then electrolysis was resumed. This had

been shown ~ to have the effect of minimizing the continuity of the

crystal structure. The duration of electrolysis in each run was 12 hr.

It was improbable that the influence of the basis metal extended very

deep into the deposited copper. As a final check,.a portion of the

deposit perpendicular to the depositing surface was examined micro-

scopically. In each case the deposit was found to be freely oriented.

In each run the operating conditions were maintained constant, as

specified above. The only variable was the chloride concentration of

the electrolyte. Chloride was determined potentiometrically.8 Start-

ing with C.P. hydrated copper sulfate, which was practically chloride-

free, and C.P. sulfuric acid, which was chloride-free, the original solu-

tion was found to contain 2.74mg./L of chloride (Expt. No. 1, Table I) .

This chloride concentration was reduced to 0.7 5 mg ./L by agitating the

solution with copper powder for 8 hr. and filtering off the precipitated

CuC1 (Expt. No. 2). The chloride concentration was further reduced

to a negligible amount ,by adding an equivalent amount of silver nitrate

to the solution (Expt. No. 3). Later the chloride concentration was

gradually increased by adding sodium chloride to the solution until a

concentration of 84.8 mg./L was reached (Expt. No. 9).

After the electrolysis, the copper deposit was stripped from the lead

cathode. Small specimens were mounted in bakelite and polished. One

~ A l l i s o n B u t t s a n d V i t t o r i o d e N o r a , T r a n s . E l e c t ro c h e m . S ~ c . 7 9 , 17 1 ( 1 9 4 1 ) .

a y . L . Y a o , T r a n s . E l e c t r o c h e m . S o c . 85 , 2 1 3 ( 1 9 4 4 ) .


3/12

C H L O R I D E I N C O P P E R - R E F I N I N G E L E C T R O L Y T E

373

s a m p l e w a s u s e d t o d e t e r m i n e t h e h a r d n e s s a n d a n o t h e r w a s u s e d f o r

t h e e s t i m a t i o n o f t h e g r a i n s i z e .

A H a t i n g c e lP w a s u s ed t o d e t e r m i n e t h e c a t h o d e p o l a r i z a ti o n . T h e

o p e r a t i n g c o n d i t i o n s , s u c h a s c o m p o s i t i o n o f t h e e l e c t r o l y t e , c u r r e n t

d e n s i t y , a n d t e m p e r a t u r e , w e r e t h e s a m e a s t h o s e i n t h e l a r g e e x p e r i -

m e n t a l c e l l e x c e p t t h a t i n t h e H a r i n g c e l l t h e d i s t a n c e f r o m t h e a n o d e

f a c e t o t he c a t h o d e f a c e w a s e x a c t l y i 5 c m . ( 5 . 9 i n . ) a n d t h e e l e c t ro l -

y s is w a s c a r ri e d o u t f o r s e v e r al m i n u t e s w i t h o u t s ti r r in g . O n l y t h e

h a l i d e c o n c e n t r a t i o n w a s v a r i e d ; o t h e r c o n d i t i o n s w e r e m a i n t a i n e d c o n -

s t an t . T h e h a l i de s u se d w e r e s o d i u m f l u o r id e , s o d i u m c h l o r i d e ,

p o t a s s i u m b r o m i d e a n d p o t a s s i u m i o d i d e .

R E S U L T S

T h e d a t a c o r r e l a t i n g t h e c h l o r id e c o n c e n t r a t i o n o f t h e e l e c t ro l y t e a n d

t h e h a r d n e s s a n d t h e g r a i n s i ze o f t h e d e p o s i t a r e c o l le c t e d i n T a b l e I .

TABLE I

Hardness and Grain Size of the Copper Deposit

E x p t . N o .

C h l o r i d e C o n c e n t r a t i o n , m g . / L

B e f o r e

E l e c t r o l -

y s i s

0.00

0.75

2.74

5.72

18.5

32.2

49.5

63.3

84.8

A f t e r

E lec t ro l -

y s i s

A v e r .

C o n c n .

o f t h e

B u l k

0.20

0.79

2.63

5.52

16.5

30.2

43.9

42.5

40.0

0.10

0.77

2.69

5.62

17.5

31.2

46.7

52.9

62.4

A v e r .

C o n c h .

o f C a t h o d e

F i l m

0.23

0.95

2.80

5.84

21.9

30.6

44.3

46.4

54.7

E x p t . N o .

A v e r a g e

V i c k e r s

H a r d n e s s

N u m b e r

A v e r a g e

G r a i n S i z e .

sq. in . x 10 - s

72.1

66.9

72.6

75.473.3

72.4

71.0

68.5

66.4

113

123

64

43

52

60

66

60

72

P h o t o -

m i c r o -

g r a p h

( F i g . 3 )

o H . E . H a r i n g , T r a n s . E l e c t r o ch e m , S o c . 4 9 , 4 1 7 ( 1 9 2 6 ) .


4/12

374 YU-L IN YAO

The four th co lumn o{ Tab le I r e cords the ave rage o f the ch lo r ide

concen t ra t ions b e fore and a f te r e lect ro lys i s , which repre sen ts the ave rage

ch lor ide concen t ra tion o f the bu lk o f the e lec t ro ly te . T he f i f th co lumn

records the ave rage ch lo r ide concen t ra t ion o f the ca thode f i lm de te r -

mined f rom the compo s i te sample s t aken du r ing the e lect ro lysi s by the

so-ca l led d ra inag e me thod . 1~ Th e s ix th co lumn records the V icke rs

ha rdness num ber , which i s an ave rage o f five o r s ix read ings. Th e

seve nth colu m n record s the avera ge gra in s ize in sq . in . X 1() s . Th is

w a s e s t im a t e d b y c u t t i n g 1 0 0 g r a i n s f r o m m i c r o g r a p h s t a k e n a t a m a g -

n i f i c a t i o n o f 1 0 0 , w e i g h i n g t h e m a n d c o m p a r i n g t h e w e i g h t w k h t h a t

o f one squa re inch o f the sam e pho tog raph ic pape r . F re sh ly p rep a red

ammoniaca l hydrogen pe rox ide so lu t ion was used a s the e tehan t .

I I ] i I

T

f

I]0_

8 0 _ I

. _ . 7 .

~ I00_ E

~ j

~8o_ 7o

o

[Jl l

1

= 6 o _ - ~

I ; \ = _

4O_ II \

6 o / I

0 I0 70

T m

T

= I

I I

I I

I I

~ s s T

I I , 9 _

' , ;

I

I

L

r [ 1 i 1

Z0 t0 4O 50 60

Mg IL of Chloride in C o p p e r - R e f i n i n g E l e c t r o l y t e

~o. 1. Variation of hardness and grain size of copper with chloride con-

centration in copper-refining electrolyte.

Composition of electrolyte: Cu, 40 g./L; H~SO*, 184 g./L. Current

density: 15 amp./sq, ft. (I .6 amp,/dm3). Temperature: 37 o C. Stirring:

about 2 000 r.p.m, No addition agents.

Th e ha rdness and the g ra in s ize da ta a re p lo t ted in F ig . 1 . Th e da ta

f rom Expt . No . 3 ( ze ro in i t i a l ch lo r ide concen t ra t ion) a re omi t ted

because o f the i r appa ren t anom a ly . Th e re i s an inc rea se o f ch lo r ide

concen t ra t ion o f 0 .20 mg./L a f te r elec tro lys is . P ro bab ly some s i lve r

f rom s i lve r ch lo r ide (due to the add i t ion o f s i lve r n i t r a te ) was co-

depos i ted wi th coppe r and an equ iva len t amount o f ch lo r ide was

l ibe ra ted in the e lec t ro ly te . The ha rdness curve i s d rawn th rough the

po in t s o f the ave rage ha rdness , and the bands show the range o f va lue s

recorded .

lOAbner Brenner, Proc. Am. Electroplaters' Sot., p. 28 (1941).


5/12

C t t L O R I D E I N C O P P E R - R E F I N I N G E L E C T R O L Y T E

375

T h e p o l a r i z a ti o n d a t a a r e p l o tt e d i n F i g . 2 . T h e o r d i n a t e s a r e t h e

e x c e s s c at h o d e p o l a r i z a t i o n o v e r t h a t o f t h e o r i g i n a l e l e c tr o l y t e w i t h o u t

a n y a d d i t i o n o f h a l i d e . T h e o r i g i n a l e l e c t r o l y t e c o n t a i n s n o f l u o r i d e ,

b r o m i d e o r i o d id e , b u t c o n t a i n s 1 .3 6 m g . / L o f c h l o ri d e . P o l a r i z a t i o n

i s a f u n c t i o n o f t h e s m o o t h n e s s o f t h e e l e c tr o d e . I t i s v e r y d i ff ic u l t

t o d u p l i ca t e t h e s m o o t h n e s s o f t h e e l e c tr o d e . B y o u r m e t h o d o f

p l o t t i n g , a l l c u r v e s a r e s h i f t e d v e r t i c a l l y t o c o i n c i d e a t t h e p o l a r i z a t i o n

a t z e r o h a l i d e c o n c e n t r a t i o n ( i n c a s e o f c h l o r i d e , t h e e x c e s s c a t h o d e

p o l a r i z a t i o n i s r e f e r r e d t o a c h l o r i d e c o n c e n t r a t i o n o f 1 . 3 6 m g . / L a n d

t h e ab s ci ss a s a r e s h i f t e d 1 .3 6 m g . / L t o th e l e f t a l s o ) a n d t h e r e b y t h e

c o m p a r i s o n i s f a c i l i t a t e d .

s o i o I I

.4{ i d

30

.

e

1 I [ I I

~ 1

o r i d e

t .~ I z t _ _ . _

0 - - ~ ~ % , , q [ 7 1 0 i e

t ~

i c I I I I T I I r

0 IS 50

1 0 0 1 5 0

200 250 300 350 400

M g./i. oF H alide in CQp per.R efinin Elec~rol~lie

F Z G . 2 . V a r i a t i o n o f c a t h o d e p o l a r i z a t i o n w i t h h a l i d e c o n c e n t r a t i o n .

C o m p o s i t i o n o f el e c t r o ly t e : C u , 4 0 g . / L ; H ' 2S O 4 , 1 8 4 g . / L . C u r r e n t d e n s i t y :

1 5 a m p . / s q , f t . (1 . 6 a m p . / d m . S ) . T e m p e r a t u r e : 3 7 * C . D i s t a n c e f r o m a n o d e f a c e

t o c a t h o d e f a c e : 1 5 e r a. N o a d d i t i o n a g e n t s .

T A B L E I I

Solubilit ies of Cuprous H alides a t ab ou t 20~

C o m p o u n d

CttF

CuCI

Cu r

CuI

S o l u b i l i t y P r o d u c t

i n ( t o o l / L ) 2

?

3.4 x 10

4.6 x 10--*

S. x l 0 - n

S o l u b i l i t y o f H a l i d e i n m g , / L

i n C o p p e r - R e f i n i n g E l e c t r o ly t e

24.0

0.7

0.0001

R e f e r e n c e

( 1 1 )

( 1 1 )

I Z )


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376

Y U - L I N Y A O

D I S C U S S I O N O F R E S U L T S

I t i s s e e n f r o m t h e p o l a r i z a t i o n c u r v e s t h a t b r o m i d e i s a m o r e p o w e r -

f u l p o l a r i z i n g a g e n t t h a n c h l o r id e . T h i s i s l i n k e d w i t h t h e f a c t t h a t

C u B r is m o r e i n s o lu b l e t h a t C u C 1 . T h e s o l u b i li ti e s o f c u p r o u s h a l i d e s

a r e co l l e c t ed in Tab le I I .

T h e s o l u b i l i t y p r o d u c t o f t h e r e s p e c t i v e h a l i d e i s c a l c u l a t e d o r t a k e n

f r o m t h e r e f e r e n c e m a r k e d i n t h e l a s t c o l u m n o f t h is t ab l e. I n m a k i n g

t h e c a lc u l a t io n s f o r t h e t h i r d c o l u m n , t h e f o l l o w i n g v a l u e s ( w h i c h a r e

a p p r o x i m a t e o n l y ) a r e a s s u m e d :

c u + ) ~

0 .S x 10 - 4 a n d ( C u + + ) = 0 .5 M

(Cu++)

T h e m a x i m u m o f t h e f l u o ri d e p o l a r iz a t io n c u r v e o c c u rs a t a h i g h e r

c o n c e n t r a t io n o f f l u o ri d e t h a n t h a t o f b r o m i d e o r ch l o ri d e . A l t h o u g h

no d a t a on the so lub i l i t y o f C u F a r e ava i l ab l e , i t i s r e a sonab le t o be l ieve

t h a t C u F h a s a h i g h e r so l u b il it y t h a n C u C I .

A f t e r a t t a i n i n g c e r ta i n / n a x i m u m c o n c e n t ra t io n s o f b r o m i d e a n d

c h l o ri d e ( f o r c h l o ri d e, a b o u t 1 5 m g . / L ; f o r b r o m i d e , a b o u t 1 0 r e g . / L ) ,

t h ey ac t a s depo la r i z e r s . Th i s m ay be e :< p la ined b y the i nc r ea se i n

so lub i l i t y o f t he l ha l ide due to t he f o r ma t ion o f a complex ion such a s

C u C 1 2 - .

H o w e v e r , C u I i s m o r e i n s o l u b l e t h a n C u B r , y e t t h e p o l a r i z i n g e f f e c t

o f th e f o r m e r is r e l a ti v e l y w e a k . M o r e o v e r , w h e n sm a l l a m o u n t s o f

s i l v e r n i t r a t e s o l u t i o n a r e a d d e d t o a n e l e c t r o l y t e c o n t a i n i n g 1 . 3 6 m g . / L

o f c h l o r i d e , w e f o u n d t h a t a t f i r s t t h e r e i s a d e c i d e d d r o p i n c a t h o d e

p o l a r iz a t i o n . A s m o r e s i lv e r n i t r a t e s o lu t i o n is a d d e d , t h e r e i s n o

s i g n i f ic a n t c h a n g e in p o l ar i z a ti o n . S i l v e r c h l o r i d e ' i s m o r e i n so l u b le

t h a n t h e c u p r o u s h a l id e s , e x c e p t c u p r o u s i o d id e . T h u s w e c a n n o t e x -

p l a i n t h e p o l a r i z a t i o n b y m e r e l y a t t r i b u t i n g i t t o t h e p r e c i p i t a t i o n o f a n

i n s o lu b l e c o m p o u n d o n t h e s u r f a c e o f t h e c a th o d e .

T h e t h r e e e l e c t r o c h e m i c a l r e a c t i o n s o c c u r r i n g a t t h e c a t h o d e o f a

coppe r - r e f in ing ce l l a r e :

C u + + + 2 e --> C u . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 1 )

C u + + -'k e --> C u + . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 2 )

C u + + e - - > C u . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 3 )

T h e s e m u s t p r o c e e d i n s u c h a w a y t h a t t h e r e la t iv e a a n o u n ts o f C u + +

a n d C u + i o n s d e p o s i t e d s a t i s f y t h e e q u i li b r iu m c o n s t a n t K o f t h e f o l -

l ow ing r eac t ion :

C u + + q - C u ~ 2 C u + -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 4 )

i f equ i l i b r ium i s r e ached and pe r s i s t s . 13

I f e q u i l i b r i u m i s d i s t u r b e d , t h a t e l e c t r o c h e m i c a l r e a c t i o n w h i c h t e n d s

t o re s t o r e e q u i l i b r iu m w i I 1 p r o c e e d t o t h e g r e a t e r e x t e n t . A n d t h a t

r e a c t i o n w i l l b e t h e p r e d o m i n a n t o n e , b u t w i l l n o t n e c e s s a r i l y p r o c e e d

m o s t q u i c k l y .

T o e x p l a i n t h e p o l a r i z a t i o n p h e n o m e n a , w e a s s u m e t h a t r e a c t i o n

( 2 ) a b o v e is a sl o w o n e . I f C u + is r e m o v e d ,

e . g . ,

as an inso lub le

G. B~d l / i nde r and O. S to rbeck , Z . anorg . Chem . 01o

22,

4 6 0 ( 1 9 0 2 ) .

z t Ot to Ruf f , Z . ano rg , a l l gem . Chem. 185, 387 ( 1929 ) .

A . J . A i l m a n d a n d H . J . T . E l l i n g h a m , P r i n c i p l e s of A p p l i e d E l e c t r o c h e m i s t r y , p . 262.

L o n g m a n s , G r e e n a n d C o . , N e w Y o r k ( 1 9 2 4 ) .


7/12


377

h a l i d e , t o a n a m o u n t l a r g e r t h a n t h a t d e m a n d e d b y t h e C u + + i o n

c o n c e n t r a t io n a n d t h e c o n s t a n t K , r e a c t io n ( 2 ) w i ll p r e d o m i n a t e . T h i s

a s s u m p t i o n i n v o l v e s a h i g h e r p o l a r i z a t i o n e f f e c t . I n o t h e r w o r d s ,

t he low er t he so lub i l i t y o f t he ha l ide , t he h ig he r the po la r i z a t ion . T h i s

e x p l a i n s w h y f l u o r i d e , c h l o r i d e , a n d b r o m i d e a t l o w e r c o n c e n t r a t i o n s

ac t as pola r ize rs .

T h e a s s u m p t i o n t h a t r e a c t i o n ( 2 ) i s a s l o w p r o c e s s i s n o t n e w .

M . d e K a y T h o m p s o n 14 a s s u m e d t h a t i n t h e a n o d i c s o l u t i o n o f c o p p e r,

x I 0 0

F I G . 3 . - - E l e c t r o l y t i c c o p p e r , e t c h e d w i t h a m m o n l a c a l h y d r o g e n p e r o x i d e .

a I C o n c e n t r a t i o n o f c h l o r i d e , 0 .

b - - C o n c e n t r a t i o n o f c h l o r i d e , 0 , 7 ; ' m g . / L .

c - - C o n c e n t r a t l o n o f c h l o ri d e , 2 . 69 m g . / L .

C u - * C u + + + 2 e h a s a g r e a t e r p o l a r i z a t i o n e f f ec t t h a n

C u --+ C u + + e . T h e r e is t o o m u c h C u + d i s s o lv e d a n d t h e r e f o r e t h e

r e a c ti o n 2 C u + --~ C u + + q - C u t a k e s p l a ce w i t h t h e p r e c i p i t a ti o n o f

c o p p er p o w d e r . T h i s is a n o t h e r w a y o f s a y i n g t h a t C u + - *

Cu + + + e i s a s low pr ocess , a s o the r w i se t he excess Cu + can be r e -

m o v e d b y t h i s r e a c t i o n .

14 M . d e K . T h o m p s o n , C h e m . & M e t . E n g . $ 3 , 2 9 8 ( t 9 2 6 ) ,


8/12

3 7 8 Y U - L I N Y A O

T h e a n o m a l o u s b e h a v i o r o f i o d i d e is d u e t o th e f o l l o w i n g tw o c o n -

se c u t ive r e a c t ion s :

2 C u + + - I- 2 I - - -) 2 C u + + I2

2 C u + - I - 2 I - ~ 2 C u I

2 C u + + n - 4 I - ---) 2 C uI ~ -F I 2

T h i s i n v o l v e s n o r e d u c t i o n i n C u + i o n . T h u s , e v e n w h e n i o d i d e i s

a d d e d , r e a c t i o n ( 2 ) w i ll p r o c e e d to a lm o s t t h e s am e e x t e n t a s i f n o

i o d i d e w e r e p r e s e n t , a n d t h e r e f o r e t h e p o l a r i z a t i o n e f f e c t i s n o t

s ign i f ican t .

x I 0 0

F i o . 3 ( c o n t i n u e d ) . - - E l e c t r o l y t i e c o p p e r, e tc h e d w i t h a m m o n i a c a l

h y d r o g e n p e r o x i d e .

d - - C o n c e n t r a t i o n o f c h l o r i d e , 5 . 6 2 m g . / L .

e - - C o n c e n t r a t i o n o f c h l o r i d e , 1 7 . 5 m g . / L

f - - C o n c e n t r a t i o n o f c h l o r i d e , 3 1 . 2 m g . / L .

I n c o n t r a s t t o w h a t h a p p e n s a t t h e a n o d e , t h e r e a c t i o n C u + + +

C u - -~ 2 C u + w i ll n o t p r e d o n f i n a t e a t t h e c a t h o d e , s i n ce o n e o f t h e

r e a c t a n t s is a s o li d . P r o b a b l y b e c a u s e o f t h is , t h e c a t h o d e p o l a r i z a t i o n

i s a l w a y s h i g h e r t h a n t h e a n o d e p o l a r i z a t i o n . A s c h l o r i d e o r b r o m i d e

c o n c e n t r a t i o n i n c r e a s e s a b o v e a c e r t a i n v a l u e , c o r r e s p o n d i n g t o t h e s a t u -


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CtILORIDE IN COPPER-REFINING ELECTROLYTE

379

ra t ion concen t ra t ion o f the r e spec t ive cupro us ha lide , the fo l low ing

e lec trochemica l reac t ion wil l par t ly replace reac t ion (2) .

C u + + -+- 2 C l - %- e ---> C u C l ~ - . . . . . . . . . . . . . . . . . . . . . . ( 5 )

I t i s conce ivab le tha t r e ac t ion (5 ) t akes p lace mo re read i ly than re -

ac t ion (2 ) , a s C u+ has a na tu ra l t endency to fo rm a com plex ion . Con -

sequen t ly the fo l lowing tw o consecu t ive reac tions wi l l sh i f t f ro m the

r igh t to the l e f t :

C u + %- C 1 - ~ C uC 1 ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 6 )

C uC I ~ %- C 1 - ~ C u C I2 -. . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 7 )

T h u s l e s s C u + i s r e m o v e d a s c o m p a r e d w i t h t h e r e m o v a l o f C u + b y

x 1

FIG. 3 (eont inued) .--Elect rolyt ie copper, etched with amrnoniaeal

hydrogen peroxide.

g--Concentration of chloride, 46 .7 mg./L.

h--Coneentra tlon of chloride, 52.9 mg./ L.

i--Concentration of chloride, 62.4 mg./L.

r e a ct io n ( 6 ) a lo n e. T h u s w e e x p l ai n h o w ch l o ri d e ( o r b r o m i d e ) a c t s

a s a c a thode depo la r iz e r a t h ighe r concen t ra t ions .

Ap ply ing the se cons ide ra tions to the anode , in the absence o f ch lo ride ,

reae t ion (4 ) t akes p lace in the r eve r se d i rec t ion , wi th the depos i t ion

of coppe r pow de r . A s ch lo r ide concen t ra t ion is inc reased , the r eve r se


10/12

3 8 0 Y U - L I N Y A O

r eac tion o f ( 5 ) wi l l no t p redo m ina te ; bu t the fo rward reac t ions o f ( 6 )

and (7 ) wi l l comp e te wi th the r eve r se r eac t ion o f ( 4 ) . A s a r e su l t,

cuprous ch lo r ide wi l l be p rec ip i ta ted wi th coppe r powde r in the v ic in i ty

of the anode .

Blum and H og abo om 1 ~ have modi f ied the s ta tement o f W . D . Ban-

c rof t tha t inc rea s ing the po ten tia l d i f fe rence a t the ca thode dec rea se s

the s ize of the c rys ta ls to increas ing the ca thode pola r iza t ion usua l ly

decreases the c rys ta l s ize . I t is seen f rom Fig . 1 and 2 tha t the re is

such a corre la t ion be tween the gra in s ize and the ca thode pola r iza t ion.

Inden ta t ion ha rdness inc rea se s wi th the inc rea s ing f ineness o f the

gra ins in polycrys ta l l ine me ta ls ) ~ I t is seen f rom Fig. 1 tha t th ere is

such a corre la t ion.

Referr ing to Table I , i t i s seen tha t there is a decrease of chlor ide

conc entra t ion a f te r 12 hr . e lec trolys is . T he decrease is not s ignificant

unt i l the in it ia l chlor ide concen tra t ion is a t or above 18.5 m g. /L . Th is

is due to the prec ipi ta t ion of CuC1 in the vic ini ty of the anode , which

grad ua l ly se t t les to the bot tom o f the cel l. A s to the chlor ide con-

cen t ra t ion o f the ca thode f i lm , i t i s in te re s t ing to no te tha t the ave rage

ch lor ide concen t ra t ion o f 17 .5 mg. /L a l so fo rms a demarca t ion po in t .

At o r be low tha t concen t ra t ion the ca thode f i lm has a h ighe r concen-

t ra t ion than the bu lk o f the e lec t ro ly te , bu t the r eve r se i s t rue above

tha t concen t ra tion . As was ment ioned be fore , when the ch lo r ide con-

cen t ra t ion i s above the sa tu ra t ion concen t ra t ion o f CuC1 in the coppe r -

re f in ing ~ lect ro ly te , the reac t ions (6 ) and (7 ) a re sh i f ted f rom the

r igh t to the l e f t , and the re fore CuC 1 i s p rec ip i tated in the v ic in i ty o f the

ca thode .

C O N C L U S I O N S

Up to abou t 15 mg. /L ch lo r ide ac t s a s a c a thode po la r iz e r in the

copp er- re f ining e lec trolyte . I t re fines the copper c rys ta l size and in-

c rea se s the ha rdness o f the coppe r depos it . Ab ove tha t -conc en t ra t ion

chlor ide ac ts as a ca thode depola r ize r , wi th s imultaneous reversa l in

effec ts on gra in s ize and hardne ss . Th is concentr~ .t ion pro bab ly repre -

sen ts the sa tu ra t ion concen t ra t ion o f CuCI in coppe r - re f in ing e lec t ro ly te .

I t mus t be emphas ized tha t our expe r iments we re ca r r ied ou t in a

synthe t ic e lec trolyte in the absence of impur i t ies and addi t ion agents .

In our expe r iments the ch ie f e f fec t o f ch lo r ide i s to r educe the c rys ta l

s iz e o f the coppe r depos it . Th is e f fec t i s ove r sh adow ed by the p re sence

of g lue o r o the r add i t ion agem in the o rd ina ry coppe r - re f in ing e lec t ro -

lyte .

A C K N O W L E D G M E N T

T h e a u t h o r w i s h e s t o t h a n k L e h i g h U n i v e r s i t y f o r a g r a n t o f t h e

Gotscha l l Scho la r sh ip , P rofe s sor Al l i son But t s fo r h i s gu idance and

c o u n se l t h r o u g h o u t t h e i n v es ti g at io n , D r . W . W . E w i n g a n d M r . S .

S k o w r o n s k i f o r t h e r e v i e w o f t h e m a n u s c r i p t , a n d M e s s r s . S i d n e y L i u

a n d C . P . S u n f o r h e l p w i t h c u r v e s a n d p h o t o g r a p h s r e s p e c t i v e l y .

W i n . B l u m a n d G . B . H o g a b o o m , P r i n c i p l e s o f E le c t ro p la t in g a n d E l e e t r o f o r m i n g , p. 98,

l~fe( }raw-HiU B .ook Com pany , N ew Yo rk ( 19 . ] 0 ) .

11 W . H.

B a s s e t t a n d

C . H . D a v i s, T r a n s . A m . I n s t . M i n i n g M e t.

E n g r s . a 0 ,

,~28 ( 1919) .

H . T . A n g a s a r f d P . F . S u m m e r s , J ' . I n s t , M e t a l s 3 8 , 1 1 5 ( 1 9 2 5 ) .


11/12


381

R e s u m e n d e l a r t f c u lo : L a s F u n c i o n e s d e l C l o r u r o e n e l B a A o p a r a

R e f i n a r C o b r e .

Se ha n investigado los efectos debidos a la presencia de haldgenos en el

bafio corrie nte para refinar cobre. Se emple6 una densidad de corr iente

catddica de 1.6 amper ios por dm. 2 a 37 ~ C. Se ut iliz 6 sulfato de c o b r e

y/Lcido sulffirico puros y se separ6 el cloro que habia con cobre met~.lico

y nitrato de plata.

Se comprob6 que hay un a conce ntrac idn critica de cloro de 15 mgm ./ 1.

Si hay menos en el bafio se polariza el c~itodo, produciendo un dep6sito

duro de cristales finos. Si hay m/Ls ocurre Io contrari o. Est a con-

centraci6n probablemente representa la solubilidad de CuCI en el ba~o.

DISCUSSION

F. C. MATHERS~7: It might be worth while to consider another possible theory.

We know that various substances in the baths are either adsorbed or co-deposited

with the me~al at the cathode. We know these various substances in the bath will

change the properties of the cathode enormously. Addition agents reduce the size

of the cathode crystals. There is no question as to the presence of these foreign

substances in the cathode deposit. Most of the experiments reported on have been

carried out with halogens because the halogens can be tested for and deposited with

more accuracy than can sulfates or colloids. Accordingly, if you do add halides

to a bath, you will find that the analysis of the cathode material will show the

chlorides (and the bromides and iodides) to an even greater extent. The copper

deposits are influenced by the presence of these halides. That is especially true

of lead. If you want to spoil a lead bath, put a lit tle iodide in it, and you will

get no smooth lead deposit until the iodide ~is exhausted. It is possible that the

author's theory may not adequately account for the change in properties of the

copper deposit. The change may be due to the fact that the chloride or other

halogen is present in the cathode and is affecting the grain size, hardness, and

other properties.

F. E. LATHE;~ Commurdcated): This interesting paper throws new light on

the important function of chlorine (as chloride) in copper refining electrolytes.

The experimental work described deals with electrolytes made from C.P. chem-

icals; it may therefore be of interest to call attention to the use of sodium chloride

in an electrolyte of unusually impure grade.

During the operation of the British American Nickel refinery at Deschenes,

Quebec, some 20 years ago, the copper electrolyte always carried considerable

n~ckel, derived from leaching the roasted Ni-Cu matte with sulfuric acid, in spite

of which this solution was used in making starting sheets. Ordinarily, the feed to

the starting sheet tanks contained 45 to 50 g./L Cu and 50 to 60 g./L HsSO,,

with 40 or more g./L Ni, present as sulfate. As long as the nickel content did

not exceed 50 to 55 g./L, good starting sheets were made with an electrolyte

chlorine con~ent of 0.015 to 0.020 g./L, derived wholIy from ~he chlorlna~ed river

water used. As the nickel in solution increased from 60 to 80 g./L, however,

the percentage of good starting sheets fell rapidly to zero. Under these conditions

practically every sheet was weak and full of holes, as from the adherence of

bubbles of hydrogen. By. the addition of sufficient salt to raise the chlorine con-

tent to 0.035 to 0.040 g./L, however, the percentage of good sheets was raised in

48 hours from zero to 100, and was readily maintained at about that point. T'he

only practical limit on the nickel in the electrolyte then became the concentration

at which nickel sulfate began to crystallize out in the circulation lines. Further

details have been given in a published paper3'

1 , P r o f e s s o r o f C h e m i s t r y , I n d i a n a U n i v e r s i t y , B ' l o o m i ng t o u , I n d .

x s N a t i o n a l R e s e a r c h C o u n c i l , O t t a w a , C a n ac l~ .

ao F . E . L a t h e , 3 . S o c . C h e m . I n d . 4 4 , 4 3 3 T . 4 3 8 T a n d 4 4 3 T - 4 4 4 T ( 1 9 2 5 ) .


12/12

382 DlSCOSSION

Y. L . YAO: Re p ly ing t o D r . M a the r s , we f i nd i t d if fi cul t t o exp l a in t he e r r a t i c

e f f ec t s o f ha l i de ions on po l a r i z a t i on ( F ig . 1 ) by m ere ly a t t r i bu t i n g t he se t o d i f f e r -

ences o f depos i t i on o r adso rp t i on o f ha l i de i ons on t he su r f ace o f t he depos i t .

A s t o .th e p e c u l ia r p h e n o m e n o n m e n t i o n e d b y D r . L a t h e , w e v e n t u r e t h e f o l l o w -

ing gues s : T he pos s ib le c ry s t a l l i z a t i on o f n i cke l sul f at e , when t he n i cke l in so lu -

t i on i nc r ea se s ~ rom 60 t o 80 g . /L , m ay ca r ry ch lo r ide w i th i t ; t hus t he bene f ic i a l

e f f ec t o f ch lo r ide i s l o s t un l e s s t he ch lo r ide con t en t i s i nc r ea sed a l so .

160 functions of chloride in copper-refining electrolyte.pdf

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