REPUBLICA DEL PERU

SECTOR ENERGIA Y MINAS

INSTITUTO GEOLOGICO MINERO Y METALURGICO

BOLETIN No.1

Serie G. Metalurgia

- Fenómenos de Oxidación e Hidrolización del Sulfato Ferroso. - Por: Jorge Rodríguez Velarde y Mary Herrera Maldonado

- Some Recent Developments in the Electro- refining and Electrowinning of Copper.

-Por: W. Charles Cooper

- Aspects of the Leaching of Oxide Copper Minerals and Ores.

-Por: W. Charles Cooper

NOVIEMBRE 1980

Editado por el Instituto Geológico Minero y Metalúrgico

LIMA - PERU

. ,_,-

.·,

.-:_.

'

SOME RECENT DEVELOPMENTS IN THE

ELECTROREFINING AND ELECTROWINNING OF COPPER

By: Prof. W.Charles Copper

THE NATURE AND STRIPPABILITY OF COPPER

ELECTRODEPOSITS ON DIFFERENT FILM-COVERED SURFACES

By: Kevin S. Fraser and W.Charles Cooper

Department of Metallurgical Englneering, Quenn's Unlversfty,. Kfnsston, Ontarlo, Canada.

Presented at Seminario Internacional sobre Procesos Etpacialas de Metalurgia Extrae ti va del Cobre - Truj 111 o -Perú

2 - 20 November - 1979.

'

ALGUNOS DESARROLLOS RECIENTES EN LA

ELECTROREFINACION Y ELECTRODEPOSICION DE COBRE

R E S U M E N

En vista de la necesidad de minimizar los costos de

producci6n en la electrorref'inaci6n y electrodeposici6n

de Cobre, se ha considerado varios ensayos. Estos ~nclu­

yen burbujeo de gas, corriente peri6dica reversible, eles

tr6lisie en lecho :f'luidizado y la reducci6n del inventa­

rio en la casa de celdas de cobre como en el proceso Ona

hama. Trabajos recientes han demostrado que la electrod;

posici6n directa de soluciones diluidas procedentes de­

lixiviaci6n utilizando el burbujeo de S02 tiene algunas

posibilidades interesantes para la producci6n de coore a

un costo reducido

Estudios sobre la electrodeposici6n de cobre sobre

superficies de metal recubiertas de una película y .La f~

cil.~dad de desprender tales dep6sitos han demostrado la

aplicabilidad de planchas madre de titanio en relaciónal

"stripping" automático. Sin embargo el alto costo del ~i

tanio es un :factor que debe tenerse en cuenTa.

SOME RECENT DEVELOPMENTS IN THE

ELECTROREFINING AND ELECTROWINNING OF COPPER

ABSTRACT

Various approaches to copper electrorefining and

electrowinning are considered in the light of the need w minimize production costs, These approaches include gas

sparging, periodic current reversal, fluid bed elecTrolz

sis, and the reduction of copper cell house inventory as

in the Onahama process. Recent work has shown that the -

direct electrowinning of copper from dilute leachliquors

using so2 sparging has sorne interesting possibilities for

copper production at reduced cost.

Studies on the electrodeposition of copper on film­

covered metal surfaces and the strippability of such de­

posits have demonstrated the suitability of titanium

blanks especially in relation to automated stripping.Ho:::

ever, the high cost of titanium is a :factor which must -

be considerad.

pu~J- t..;:, .l.J.i:LV't;:: "-"o:;:;UIV.I..I.O ................... ....._ ...-": ... 'ª3...,-__ -------hlAnks esueciallv in relation to automated strippin~Ho:::

INTRODUCTION

The rapidly increasing costa of power and of plant construction

are important considerations in both the electrorefining and electrowinning

of copper. Consequently metallurgical engineers associated with these

operations, should be concerned with the means whereby refinery production

and efficiency can be increased without plant expansion. The question

which must be resolved is: how to increase the current density without

unduly affecting power consumption and, at the same time, maintain the

quality of the copper cathodes. This paper focusas on recent davelopmenta

in the electrorefining and electrowinning of copper which have attempted

to address this queation. These approaches include periodic current

raversal, reduction of copper cell house inventory as in the Onahama

procesa, forced electrolyte circulation, gas aparging, and fluid bed

electrolysis. Particular attention is given to recent work in the

writer's laboratory which has shown that the direct electrowinning of

copper from dilute leach liquors using S02 sparging, has some interesting

possibilities for copper production at reduced cost.

In the second part of this paper consideration is given to studies

on the electrodeposition of copper on film-covered metal surfaces and the

strippability of such deposita. This work has demonstrated the suitability

of titanium blanks especially in relation to automated stripping. It

sbould be noted that due to the high cost of titanium, no copper refinery

in Japsn is currently using titanium blanks.

* * * * * *

- 85 -* * * * * *

..

PART I

COPPER ELECTROREFINING

Periodic Current Reversa1

In copper e1ectrorefining the different cost components are

related to current density in the manner shown in Figure l. These data

serve to indicate the cost advantage which can accrue through the use of

periodic current reversa1 (PCR) in copper refining.

20 ,-----~-

r

15 ;

r t

~ 10~ f ~

5

100

:

lobour ---Cu lnventorv lnt.

Eledrical Power

~ 200 300

C.D., A/m 2 400

Figure 1- Refining cost componente, (after Ette1 (1)).

Power - l~kWh

Steam $5/ton

Interest - 10%

Deprec. , 15 years

Copper - price - $2000/t

linear Labour - $10/manhour

Although PCR resu1ts in a higher power consumption due to the current

which flows for short periods in the reverse direction in the cell(e.g.,

200 seconds forward and 9 seconds reverse) • the smoothing effect of this

reverse current on the electrodeposit does permit the use of significantly

higher current densities with a resultant increase in productivity.

- 87 -

Figure 2 presents a comparison of the energy componente in conventional

copper refining and refining using PCR.

Álthough periodic current reversa! was introduced into the platirig

industry many years ego, its application in copper refining has come

about only recently. The pioneering work here was carried out at the

refinery of the G. Damjanov Smelting Works Bulgaria (2). PCR is used or

has been used at refineries in Bulgaria, Canada, and Japan (3).

COHVEHTIONAl PCR

Cl

e~ il '~.l!i .. l

1 ¡¡ /1 \ ,. :1

: . . ~,--0,: 11

;:::- "' 11.~ :. 1.. '.: lj

--u, ¡¡:·¡¡ e :'---UH • 1' 1 .... ti i 1 1 ~ lj .

•j.. . . 1

Lli.i U_ll l k. o 25

(V 0 :.!:l

( D ~it.­

CE '17!':

0.1 V

Symbols and Abbreviations

E.R. T.E.R. C.I. C.E. s.c .. CD. c.v .. e R nA nC UE U¡¡ F EMF

= Energy reqúirement = Thel"lllodynamic energy requi remen t

= Current inefficiency of a process = Current efficiency of a process • Stray currents = Current density = Cell voltage = Current reversal = Anodic overpotential = Cathodic overpotential = Ohmic potential drop in the electrolyte

= Ohmic potential drop in the cell hardware

= Faraday constant = Electro-motive force

Figure 2 - Components of cell voltage

and energy requirements in copper electrorefining, (a:fter Ettel(l))

Reduction of Copper Cell House Inventory

An importGt component of refining cost is the capital and accrued

interest which are tied up in the copper which is being processed in the

tal\khouse. This. factor has becoae of greater importance recently due to

the lllSrked increase in interest rates. This particular proble111 has been

resolved by the Onahama Smelting and Refining Co. Ltd., in the Onahama No.

3 tankhouse which c0111111enced operation in 1973 (4). In this refinery the

-. ... ... -. , -- ---- -------

-tlll -

•

SOME RECENT DEVELOPMEN'!;S IN THE ELEC'J.'ROi.!WINING AND ELECTROONNING OF CoPPER

_,ventorv cost has been reduced by approximate1y 60% by decreasing the

chickness of the anodes from the conventiona1 45 mm to 13 mm. The anode-

anode spacing is 80 mm as opposed to 100 mm in a conventiona1 tankhouse.

The cornparison of refining costs presented in Table l shows that at

d power cost of 1c/kwh the costs for refining copper by the PCR and Onahama

, rocesses ,gre approximate1y equa1 whereas at 2~ /kwh, the Onahama procesa is

'avoured. The inferiority of conventiona1 practice is indicated clearly

especia1ly with regard to the copper inventory interest cost.

Tab1e I - Componente of Refining Cost in $/t, (after Ettel (1)). 1

ronventional PCR 1 Onahama 1/3 · Practiee 1

1 (210 A/m2) (350 A/m2)! (200 A/m2) Energy at lc/kWh ..••••.. : 2.3 4.0 2.8 Steam at $5/t ........... 3.0 1.5 3 .o Tankhouse deprec. + int. 15.5 11.5 13.0 Cu inventory int .••.•..• 15.0 9.5 7.5

TOTAL ........... 36.3 26.5 26.3

' S ame but energy at 2c/kWhi

TOTAL 38.8 30.5 28.8 1

lt wi11 be interesting to follow the progress of the new Onahama-type

refinery which should be on stream in 1981 at Texasgulf Canada Ltd., Timmins,

Ontario.

COPPER ELECTROWINNING

The cost of copper e1ectrowinning is a major factor in the recovery

of copper from hydrometa11urgica1 so1utions. These so1utions may be 1iquors

from the direct su1furic acid 1eaching of oxide and/or sulfide copper ores

or concentrates or solutions arising from the stripping of copper from the

organic phase in a solvent extraction operation. Since the power requirement

in copper electrowinning is 8 to 10 times that in copper refining (2.0

kwh/kg Cu vs 0.25 kwh/kg Cu), the reduction of this power dernand is an

important objective in lowering the cost of metal production by e1ectrowinning.

kwh/kg Cu vs 0.25 kwh/kg Cu), the reduction of this power dernand is an - !!~-

. tNSTIWO GKQLOOICO MTWQ .Y.M!i!TNIJB.GICO

The various componente of the. cell voltage whích contribute to copper

electrowinning are indicated in Figure 3. s.c ....

C.l.

2~------~--------~

o .E ::- 1 -4

· e E MF

2

VOLTS

Fi~ure 3 - Componente of cell voltage and energy requirements in conventional copper electrowinning, (af.ter Ettel(l)) E.R. - 2.0kWh/kg C.D. - 300A/m~ C.V. - 2.0V C.E. - 85%

In conventional copper electrowinning the high oxygen overvoltage

is a major component of the overall cell voltage. This overvoltage which

is in the arder of 700 mv at a normal operating current density (200 amp/m2 )

can be reduced through the addition of cobalt te the electrolyte. A much

greater reduction in anodic overveltage can be realized through the use

ef titanium anodes ceated with ruthenium dioxide (the se-called dimensionally

stable anedes or DSA anodes) in place of the cenventional Pb-Sb anedes.

However, at present the cest ef these anodes is prohibitiva when related te

the power saved through their use. The relationship between the anedic

evervoltage and the current density for these three anedes is shown in Figure 4.

Enhancement ef Masa Transfer in Cepper Electrowinning

In metal electrodepesitien the limiting diffusion current density is

given by the fellowing equatien:

= -~nF ó

[~+)bulk (1 - ~n+)

D = diffusion coefficient

ó (1 - t •• n+)

- 90 -

Jf

> E

o = thickness of Nernst boundary layer

n = no. of electrons involved in electrode reaction

F = Faraday

¡MF+)bulk = concentration of metal cation in body of solution or bulk concentration.

transport no. of ~+ (can be equated to zero in regular electrowinning electrolytes)

800 '¡ --- -~----~-- - ---~- ---------1

600 v-=----:------j:, Pb/Sb anode, 2g/l Co in eleclrolyte

l

Pb/Sb anodo 1

! 400

OSA onode {Eiectrode Corp.)

1

200 c---~-~-~---c-' _____ . ______ j____~ _ _j o 200 400 600 800

C.D., A./m 2

Figure 4- Overpotentials of insoluble anodes in Cu electrolytes, (after Ettel (1)).

Although it is clearly impossible to operate a commercial electrowinning

cell at the limiting current density, any increase in the limiting current

density is reflected in an increase in the operating current density of the

commercial cell. One of the most effective ways to realize this objective is

to increase the value of D which is commonly known as the mass transfer o

coefficient. Two means of increasing D which have been investigated in recent ¿-

years are forced electrolyte circulation and gas sparging. The relative

merita of these two methods will now be considered.

years are forced electrolyte circulaiion and gas sparging. The relative - 91 -

.¡:'

Forced Electrolyte Circulation

In work sponsored by Continental Copper and Steel Industries Inc.,

llalberyszski & co-workera (S) at the Colorado School of Minesdeveloped a

copper electrowinning cell based on the forced circulation of electrolyte.

In this cell electrolyte is injected into the cell through a series of

orifices (6.4 llllll in di-ter) 50 1IID apart in a 50 !IIDdiameter pipe located

along the centre line of the cell. The electrolyte leaves the cell through

50 mm diameter pipes which are parallel to the inlet pipe. The inlet and

outlet pipes are connected in closed circuit to a centrifuga! pump and an

electrolyte storage tank. A number of cells can be operated in series using

one pump and one solution head tank. The electrolyte flow-distribution in

density cell,(after Balberyszski e~ al (5 )) •

According to Balberyszski et al (5) satiafa,ctory commercial size

cathodes were obtained using this cell at current densities exceeding

According to Balberyszski et al (5) satisfa,ctory commercial siz.e - 92 -

•

SOME REcmfT DEVEIP!:'MENTS IN THE ELj!iCTB.OREFINING AND ELECTROWINNING OF COPPER

750 amp/m2. However, the pumping costa associated with the cell constitute

a major disadvantage in the procesa. In addition, as will be shown later,

air sparging provides a much higher and more uniform mass transfer coefficient

o•ter the -.ntire cathode surface. This fact together wiü" the modest cost of

air sparging effectively eliminate the consideration of forcrd electrolyte

eirculation in any industrial copper "electrowinning plant.

Gas Sparging

Air sparging in copper electrowinning has been shown to be decidedly

beneficial in enhancing the mass transfer of copper in the solution,

producing a thinner and more uniform Nernst boundary layer on the e"' thode

surface and thereby permitting cell operation at a higher than normal current

density.

In a comparison of copper electrowinning using electrolyte injection

and air sparging, Ettel et al (6) demonstrated through the use of added silver

i.onS", that the mass transfer coefficient of these ions, kAg+ is definitely

superior and more uniform in the case, of ¡lir "sparging (Figures 6 and 7) .

CATHODE 1'

(front view)

1

: 1 k 1\\

~ ELECTROL VTE

INLET ELECTROlYTE

OUTLET

1 , CATHODE

1 (front view)

1

1 !

i j j j ~ SPA~GER

Figure 6 - Diagram of electrolyte jetted and air sparged operation

n~

sparged operation - "'7.:J -

INSTITIJTO GEOLOGICQ MINEBO Y METALI!RGICQ

'E' o

E :: 100 o o 4 " .e 25'c - ~ 80 e "' 4 25g/l Cu ~ 2 amp/dm

2 • 100 g/1 HzSO• ~ 60~ • 23 'V ELECTROl YTE ~ i omp/dm2

JETTED

40f • AIR

-'Z y ~ SPARGED <o 20 u--1-

o' 1--a:r/l 100 200 300 400 wo o >a.

kAg+ x105 (::)

Figure 7 - Vertical distribution of kA2+

jetted and air sparged copp~r (after Ettel et al (6)).

in electrolyte electrowinning cell,

lt should also be observed that the current density in the air sparged cell was

higher (400 amp/m2).

Ettel et al (7) have also shown using silver ions in a copper electro-

winning cell, the greatly reduced thickness and marked uniformity of the

Nernst boundary layer, 8Ag+• when air sparging is employed (Figure 8) .

---BOrTOM (cm)

• A

No Alt --.....

O IU Cl2 Q.J

- CIIO SN.Ag·C-

Figure 8 - Diffusion layer profiles, in copper electrowinning, (after Ettel et al (7)).

The favourable results afforded by air sparging in copper electro-

winning are demonstrated by the data obtained by Ettel el al (7) and shown

in Table li.

winnin~ are demonstrated by the data obtained by Ettel el al (7) and shown

- 94 -

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SOME RECENT DEVELOPM.ENTS IN THE ELECTROREFINING AND ELECTROWINNING OF COPPER

Table II- Electrowinning in Half S cale Cell, (after Ettel et al (7))

' 1 1 ¡ Cell electrolyte-Cu g/1 45 45 2 i Cell electrolyte-HzS04 g/1 150 150 S , Cell electrolyte-Fe g/1 • 1 o ; Cell electrolyte-Jaguar+ y es y es no ' Current Density A/dm 2 10 20 o. 75 iAir Flow/Cathode Face 1/min 8 8 6 l Power Consumption kwhr/kgCu 2.5 3.1 2.0 ¡ Cathode Thickness mmn 2.5 2.0 1.0 1

Cathode-Pb ppm :3 3 3 i Ca t hpd.,- S PPill ~ 5 10 1

'

According to these investigators since agitation by air ¡¡p¡¡,rging !i\.~lows the

electrowinning to be carried out with considerably redueed e;n!lde-<~athode

spacing, the power consumption at 10 amp/dm2 (or 1000 amp/m2 ) was onlv lO~

higher than in a conventiona.l operation.

Since the power consumption at current densities above 1000 amp/111~

is no longer economically to¡erab!e and incremental savings in capital

investment decrease rapidly as the current density approaches this va1ue,

1000 amp/m2 would appear to be a practica! operating limit for the current

density in copper electrowinning using air sparging.

In the Sherritt-Cominco procesa for the hydrometallurgical treatment

of copper concentrates, very favourable resulta were obtained in pilot plant

work on the electrowinnning of copper at 650 amp/m2 using air sparging. As

shown in Table III the quality of the electrowon copper appeared to be excellent.

i 1

1 2 Current Densi ty (A/ m ) ...•.••••.•..•.

Sparge Air(m 3 /ce11) ..... , .......... ..

ICell Temperature( °C) .................. . Cell Vol tage •..•.•.•••.••.•.•••..••..

IFeed Solution Cu(gpl) .•....••••• Cell Solution Cu(gpl) .....••••••

Fe(gpl) .•.•.•.•••• H2S04 (gpl) •.•..... Se(mgpl). •\• .•..•••

Bank I

650 0.57

54 2.4

85 30 1.5

130 0.4

H?SOu(gpl)........ 130 - 95 -

Bank 2

330 0.57

49 2.0

20 20

2.5 130

0.4

130

INSTITUTO GE()LOGtcQ MiliD!l Y MEIALt!RplCO

Table lii - E1ectrowinning of Copper in Sherritt-Cominco (cont'd) Copper Procese, (aftar Kawu1ka et al (8))

Cell Solution Co(mgpl) •••••••••• Separan(mgp1) •••••

Current Efficiancy(%) •••••••••••• Cathode Copper S (ppm) ••••••••••••

Pb (ppm) •••••••••.• Se(ppm). ~ •........ *SEV(DIDl) ......... . Conductivity(%IACS)

Bank I

100 15 95 10

3 0.2

400 102

Bank 2

100

80 15

1 0.2

360 101.5

*Spring Elongation Va1ue - a measure of ductility.

The rising costa of mining and beneficiation together with the need

to procesa economic:ally large tonnages of low-grade ores, have led, partic:ularly

in the Unicted States, to a growing and substantial tortnage of copper produc:tion

via the treatment of low-grade material or what was forlll8rly c:on.sidered as

mine waste or tailings, by heap, dump or in-situ leac:hing. The low c:oncentration

of c:opper in the resulting leach solutions is rec:overed at present by c:ementation

or by solvent extrac:tion and electrowinning.

A considerable cost saving would result if it were possible to electro-

win copper directly from such dilute laach liquors thereby eliminating the

solvent extraction procesa. This saving would be enhsnced if the cost of

electrowinning could be reduced significantly.

One approach to achieving this two-fold objective (i .e., eliminating

the solvent extraction step and reduc:ing the power requirement in copper

electrowinning) is through the use of eulfur dioxide sparging in the electro-

chemical ce11. In the presence of sulfur dioxide the anode reaction becomes the

oxidation of su1fur dioxide to sulfate:

ZH20 + so2 • so42• + 4H+ + 2e-

as opposed to the oxidation of water to form oxYgen in the conventional electro-

winning procese:

as opposed to the oxidation of water to form oxYgen in the conventional electro­- 96 -

•

SOME RECENT DEVELOPMENTS IN THE ELEC'l'ROREFINING AND EJ.RCTROWINNING OF ~

The net cell reactions for the SOz procesa (a) and in the conventional process

(b) are given below: o

(a) CuS04 + HzS0 3 + H20 = Cu + 2HzS04 o

~H = -18.47 kcal/mole Cu o

~G = 7.59 kcal/mole Cu o

(b) CuSo4 + HzO = Cu + ~2 + HzS04 o

~H = 52.93 kcal/mo1e Cu o

6G = 41.16 kcal/mole Cu

The enthalpy difference between the two reactions amounts to 71.40

kcal/mo1e of Cu in favour of the S02 reaction. This va1ue works out to

be 1.30 kwh/kg Cu less for the SO¿ teaction. From the free energies of

reaction, it can be shown that the SOz reaction takes place at a theoretical

potentia1 which is 1.05 volts less than for the conventional electrowinning

process.

Pace and Stauter (9) succeeded in electrowinning copper direct1y from

synthetíc pregnant 1each liquors utilizing the SOz reaction. They were able

to demonstrate that copper cathodes can be produced at c.urrent efficiencies

much higher than those encountered in conventiona1 electrowinning practice for

e1ectrolytes in which the copper is plated down from 10 gp1 to 2 gp1 in the

presence of 10 gpl iron. Thus Pace and Stauter demonstrated the viabi1ity

of this modified e1ectrowinning procesa in the recovery of copper direct1y

from 1each so1utions at a reduced power requirement and without the necessity

of purification and concentration of the solution by solvent extraction prior

to electrowinning.

Since many 1each liquors especia11y those from heap and dump leaching

operations contain much less than 10 gpl of copper, it is important to know

the applicability of the S02 process to such dilute so1utions and to indicate

ooerations contain much less than 10 gol of coooer. it is imoortant to know - 97 -

INSTITUTO Gsoy>GICO KINliRO Y KETALUBGICO

the lower limit to which the copper concentration can be reduced ·'oncomitant

with the production of acceptable cathodes and a favourable power yield.

Jackson (10) in a study of the direct electrowinning of copper from

dilute leach liquors using SOz sparging established that it is possible to

apply the so2 procesa directly to leach liquors, both synthetic and actual,

ccntaining less than 2 gpl of copper. Thus Jackson obtained excellent resulta

on the percolation leach liquors from a sample of medium- to low-grade ore

assaying 1.04% copper from the Ray Mines Division of the Kennecott Copper

Corporation. Sulfur dioxide gas made it possible to obtain high quality

deposita at high current efficiency (93%) and low power consumption (1.1

kwh/kg copper) at copper levels as low as 0 •. 6 gpl in these liquor~. lt

should be noted that in this leach solution the iron amounted to only 0.2 gpl

and that the coppet was plated down from 7.8 to 0.6 gpl.

In the preaence of a .significant iron concentration such as encountered

in the leach solutions from a sample of low-grade oxide copper ore (0.2% Cu)

f~ Gasp' Copper Mines Ltd., viz. 5.7 gpl Fe, the electrowinning behaviour

was less favourable. Thus in the plating ckJwn of copper from 1.6 to l. O gpl in

a Gasp' leach solution containing 5.7 gpl Pe, there was a decided tendency for

the copper to be deposited in powder fon. However, in experimenta on the

Gaspé leach liquor the current efficiency was high (90 to 95%) and the power

consumption was quite favourable viz 0.7 to 0.9 kwh/kg Cu. The important

findings from this part of Jackson'" investigation -re the higher limiting

copper concentration viz. 1.6 gpl Cu 8Dd the somewhat lower cell voltage,

O. 8 volt in the case of the iron-bearing leadl solutions.

ln order to establish the c-Tdal villhility of the S02 procesa, it

is necessary to extend the experi~tal work which has been carried out to

date. This further work would define .-re elearly the limiting factors in

the procesa and determine the conditions uade.r which the procesa could be

- 98 -

•

expected to opera te successfully on a commerci~ll scale.

Fluidized-Bed Electrowinning of Copper

The electrowinning of copper by deposition onto copper particles which

are fluidized by the upward flow of electrolyte through a bed of particles,

has been studied by a nurnber. of investigators, (11-14). In this procesa the

)Jatticle bed is made cathodic by a "feeder" electrode which is inserted in the

bed and the circuit is completad by an inert anode immersed in the electrolyte.

Different cell configurations have been desigried in an effo:c.t; to talte advantage

of the possibilities inherent in this type of·electrolysis for a truly continuous

electrowinning proceás. It appears that as yet no one has succeeded in

developing a commercially viable cell for metal electrowinning by the fluidized

bed rnethod. The process suffers the serious disadvantages of a cell voltage

and power consurnption well above the values experienced in conventional copper

electrowinning. Unless the cell chemistry and configuration can be modified to

overcorne these disadvantages and to provide a continuous electrowinning procesa,

there is little expectation that fluidized-bed electrolysis of copper will b.e

utilizad on a cornrnercial scale.

REFERENCES

l. Ettel, V.A., "Energy Requirementa.in EZ.ei!tro1-ytia Winning and Refining of Meta 'Le "• CIM Bull. 70 (No. 783), pp 179-187, July 1977.

2. Encev, Ivan, "Inten,sifiaation of the Eleatro1-ytie Production of Meta1-s frcm Aqueous Sotutions by Using AUernating PoZarity Current," Hutnicke Listy, No. 11, pp. 820-823 (1971) (English translation).

3. Kitamura, T., Kawakita, T., Sakoh, Y. and Sasaki, K., "Design, Construation and Opera#on of Reverse CuiTent I:?roaess at Tamano," Volurne 1, Extractive Metallurgy of Copper, Editora: J.C. Yannopoulos and J.C. Agarwal, Chapt. 26, pp. 525-538, AlliE, New York, 1976.

4. Ikida, H. and Matsubara, Y., "No. 3 Tankhouse at Onahama Smelter and Refinery", Vol. 1, 'Extractive MetaHurgy of Copper, Editora: J.C. Yannopoulos and J.C. Agarwal, Chapt. 30, pp. 588-608, AIME, New York, 1976.

S. Balberyszski, T., Andersen, A.K., and Eaman, R.H., "CeU Devewpment for the EZ.ectrodeposi tion of Copper at High Cui'I'ent Densi ties "• in Copper Metallurgy, Editor: R.P. Ehrlich, pp. 314-332, AIME, New York, 1970.

S. Balberyszski, T., Andersen, A.K., and Eaman, R.H., "CeU Devewpment for - 99 -

6. Ettel, V.A., Tilak, B. V. and Gendron, A.S., "Measurement of CathodS Mass

Transfer Coeffiaients in EZect7'C11JJinning CeZZs." J. Electrochem. Soc.,

121, pp. 867-872 (1974).

7. Ettel, V.A., Gendron, A.S. and Tilak, B. V., "EZectrObJinning Copper at lligh Current Dens,ities". Metal!. Trans. 6B, pp. 31-36, March 1975.

8. Kawulka, P., Kirby, C.R. and Bolton, G.L., "1'118 SheZ'Z'itt-Cominoo.COpper Procesa - Part II: Pitot-PZant Operation. 11 C!M.BulL, 71 (No. 790),

pp. 122•130, February 1978.

9. Pace, G. F. and Stauter, J.C. "Direct EZect7'C11JJinning of Copper from Synthetic Pregnant Leach Sotutions UtiZising Sutfur Dioa:ide and Gt'aphite Anodes -PiZot-PZant Resu'Lts"• ibid, &7, (No, 741), pp. IS-91, January 1974.

10. Jackson, J.R., "The Direc.t EZectrObJinning of Copper from DiZute .Leach ~iquors Using S02 Sparging". B.Sc. Thesis, Queen's University, Kingston,

Ontario, .May 1978.

11. Flet::, D.S., "1'118 EtectrObJinning of CoppeP from DiZute Copper SuZphate Sotutions with a Kluidised-Bed Electro&." Chemistry and Industry, 51, pp. 300-302 (1971). . -

12. Flett, D .S., "1'118 FZuidised-Bed El-ectrode in E:z:tractive Metatl-urgy". ibid, 52, pp. 983-988 ( 19 72) •

13. Wilkinson, J.A.E. and Raines, K.P., "Feasibitity Study on the EtectrObJinning of Copper with FZuidised-Bed Etectrodes." Trans. !.M. M., 81, Cl57-C162 {1972).

14. Monhemius, A.J. and Costa, P .L.N., "IntePaCtions of Variabl-es in the FZuidised-Bed EZect7'C11JJinning of Copper''. Hydrometallurgy, 1, pp.

183-203, (1975). -

* * * * * *

- lOO -

•

Part II

THF. :"ATl'RE AND STRIPPARILITY OF COPPER F.LECTRODEPOSITS

ON DJFFERENT FILM-COVEREO SURFACES

Summary

.. \ romrarativf' st.ucl:y of t.hr> pctrtin!! :U!<'Ilt~. CCH Pmut .. inn nnd 2-lwnz.o­

thiazolethiol IBTATI. and <·old-rolh•d m0chanieall)' ahra<lP<l tit.anium

cathodes was carried out to mak0 a critieal evaluation of the effectiveness of

the various film-covered metal suhst.rates in the production of cop(lf'r

refinery starter sheets. The following factors were considered in the evalua­

tion: 11) the type and quality of th0 final starter sheet, (2) the ease of

stripping, t 31 the type of crystal growth a~<ocialr'd with t.he deposit.

The study wa< conducted under commercial conditions of curren\

density. temperature and electrolyte flow rate. In addition, stripper electro·

lyte ohtained from a commercial tankhouse was used in the study.

The parting agents, CCR emulsion and 2-benzothiazolethiol, and mecha­

nirally abraded titanium were all found lo yicld a high quality produet. Thc

copper starter sheet.< obtained wrrr dens~', cohPrent and polycrystallin<· ai1d

exhibited superior surface quality. No si¡¡nificant differences were observed

in the crystal structures and thl' growth pattems of the copper elertro.­

deposits on the emulsion-coated copper. the BTAT-coated copper or the

abraded titanium. The relative stripping strrngths for the éopper el~ctrodPposits were

found to be !in descending ord~r and in ordPr of increasing Pase of stripping)

BTAT 3.9, CCR emulsion 2.3 and cold-rollrd m<'chanically abraded titanium

1.0. This arder of strippability conforms precisely to the prPviously observed

increasing cathodic deposition potential on the differ<'nt substrates.

l . Introduction

In the preparation of copper cathode starter shepts u sed in the electro­

refining of copper it has been the practice to electrodeposit copper on a

smooth cold-rolled copper blank that has beén coated with a thin film of a

parting agent. The essential functions of this parting agent are to provide a

su'itable surface for the electrodeposition of copper, to prevent adhesion of

the electrodeposited copper to the copper blank and to facilitate the !'emoval

or stripping of the electrodPposited copper from the copper blank in the

form of a dense, coherent and suhstantially nodular-free sheet. In recent years numerous copper refineries havP come to use titanium

blanks instead of copper blanks covered with an extraneous film. The

titanium used for this purpose has a surface oxide film which serves as a

permanent parting agpnt. Problen1S that m ay be encount.,red in the production of starter shePts

include the formation of nodules, which affect adversely the quality of the

sheet. on the surfacP of the electrodPposit. and inconsistent parting aciion. 1

• - 101 - . include the formation of nodules, which affect adversely the quality of the

INSTITUTO GEOLQGICO MINERO Y METALURGICO

The latter condition can be quite serious, especially if the refinery is aiming

towards or actually Pngaged in automated stripping. \\'ith the ahove factors in mind we undprtook Uw prescnt sturly to

make a critica! evaluation of ex isting parling agent.s, selPded as heing the

most promising, and to compare these parting agents with the performance

of a typical titanium hlank. In this evaluat.ion the most important considera­

tions in the selection of the hest acceptahte parting agent or substrate were

as follows. (1) The start.er sheets produced should have relatively easy stripping

charact.eristics with no prernature release and should be arnenable to auto·

mated stripping. (2) The starter sheets should have high surfacP quality, i.e. the electro­

deposit should have a rninirnal amount of nodulation and should be dense

and compact with unidirectional columnar growth perpendicular to the

substrate. f 31 Tlw starter sheets should have good mechanical properties, especially

stiffness and rigidity.

2. Experimental conditions

This investigation consisted of determining the effect of different

parting agents and substrates on ( 1) the forrn of the electrodeposited copper

and (2) the strippability of the deposit. The PxperimPntal conditions were kept as close as possible to those

encountered in commercial opPrating practice and were as follows: current

density 200 A m 2 ; electrolyte ternperature 6.0 "C: flow rate of electrolyte

4.4 mi min- 1 in the laboratory cell, corresponding to 4.5 USGPM in a corn­

mercial cell: electrolyte composition (CCR stripper dectrolyte, section

1027), Cu 49 g 1-1 , H 2 S04 154 g 1-1 , Cl 0.019 g 1-1 , Ni 6.90 g J-l

The e!Pctrodeposition expPrinlf'nts were carried out in a scaled-down

version of a cornrnercial e!Pctrorefining cel!. The dimensions of the

laboratory cell (Model 266 from Bdl Engineering, Tucson, Arizona) were

18.10 cm X 9.53 cm X 6.99 cm. with an anode-to-cathode spacing of 1.27

cm. Cold-rolled copper plato was userl l.o form the eoppPr anodes whieh had

the approximate dimensions R.89 cm·,; 7.1>2 r·m X 0.07 cm. ThP copper and

titanium blanks were masked with a plastic to preven! copper dPposit.ion at

the edges, which would inlPrfere with stripping tests. In addition this pro­

cedure served to control the area of the cathode immPrsed in the electrolyte.

Two types of partinJ! agent for coppf'r Wf:lff' consid<~rf'd:

(1 1 2-benzothiazol<>thiol (BTATl* (l•:astman Kodak¡ in a so!ution of

0.5 wt.% BTAT in aqueous sodium hydroxide tOH !RTAT"' 1.11 [11:

(2) Canadian Copper Refincrs emulsion tan aquPous emulsion) [ 21

(cornposition: 5.0 wt.% n-hexadecyl alcohol ICH,(CII 2 ) 150H), 1.5 wt.%

sodiurn n-dodecylhenzene sulfonate. which SPrves asan ernulsifying agent,

0.1 wt.% ~-m~rcaptopropionic acid (!IS-Cil 2-CH 2 -COOH), 9.1.4 wt.%

water).

*2-benzothiazolethiol (BTAT)

- 102 -

•

S<ME REC~T DeyELOPMENTS IN THE ELI!.CTR.OREFINING AND RLECTROWINNING OF COPPBR

The partín~ a~ent.s wcre heawd to a lemporalur<' of GO °C ond were subscqucnUy applied by immrrsinl! Lhe copper slartrr hlnnks in thr pnrlin~: ftj!l'lll (soluhon or rmul•ion) ror ~pproximalrly 4 . 5' ond lhcn r~isin~ lhr blanks Md pennttc.inl! lhr cxccss parting agenl lo drain.

Thr tilanium hlanks from Kobc Steel Lld., Tokyo, J~ran had a surra~-e whtch had bren mrchanically ahradcd toa su rface roughnes~ or 90 ¡Jtn. Thr pronlc o( th~ •urfn•·e •howed strialions oricnled rrom thr lOJllO the bollom or thr blnnk Thr roxh.le !ayer on thesc blanks was formcd in ni r Lo o lhlck· MM or ap¡troximatcly 30 A.

The cnthodes were lowcrcd in Lo t he eJedrolytc firs~ tmd then con tucL with ~h~ currcnt-carry ing bus·bar was made, lhe total time botween immcr· slon 811d contllct being npproxirnately 1· 2 s. Coppcr clectrodeposi tion wns carrled ottl on bolh thc copper and the lltanium blank~ for a 24 h JlOriod, as in commercial star\.cr •he~l production, Suhsrqucn~ly: lhr •urf;w~ <¡unliiy or the deposiled copper was examined togclher wilh the microslruclure of cross ~ectiot\s or lhc calhodes.

1'he str1¡1ping sb·cnglh ror each dcposit was measured uslng an lnstron tt>nstle lcsl~r as shown in fig. l. This property is a mcasure of the force,ln ktloi(Tl)m>-force per centimetre w1dLh of bond, requtred to strip the copper stllrtcr sheet from the substrate onto which it has bcen electrodcposited ( 3) The Lell cons1sts of measuring lhe force requtred to stnp or pcel the

Fic. l . (A) Tht ln¡\ro n ltnsllt' ·~lt'r ~lmwin~ 3 s.amplr in u·-tina t•m:hlon: (h) A Jlllrlt"r ahtN htmr A~tlp¡.;"d ftom a tnppcr lltan'k

\ S(t,.r·All(ltn•.IC. Mt•S

\--7 _tN'TIA\. '!1RIPP'·'lti 'Off \1./ / APJ!U(..Ati!)N 0r- .(,.IIJP';

~ . / ro-!'ll'l tllC t"*tt'l(f'O':)t

"'L[\1 -~.':;;:,~~--' ~.~.... ..;¡,.---.-J

-«~TCH $;95~-r ....... Ft.: 2. Thtt !J() stnppang •trt.•ngth l~l.

- 103 -

INSTITUTO GEOLQGICQ-MINERO Y METALURGICO

starter sheet at an angle of 90° from the deposition suhstratl'_ The magni­

tude of the force that causes failure at either the interface hetween the

elN·trodeposit and the parting agent or within the parting agent film is

recorded. The 90" stripping strength tl'st is shown in Figs. l(b) and 2.

3. Results

3.1. The nat.,re o{ the copper rlcctrodepo<it< 011 rlif{erent substrates

The cathodt' deposit producen hy a 24 h electrolysis in comm<·rcial

Plectrolyte using the pmulsion partin¡¡ agent was dt•nsc. coherent and vir­

tually nodular-free copper which <howed high hrightness and a polycrystal­

line growth form. 'fhere were small-distind area.• of nodulation at the edges

of the t>lectrodeposit, especially at th<• bottom edgi'_ However, the nodules

were rounded owing to the effect of the addition agPnt. thiourea, and did

not stand out from the cathode surfaee. The quality ohtainPd using the

emulsion parting agent was excellent and exceeded commercially accepred

quality standards. The surface quality of the enp¡wr rlPp<l'it grown fnr 24 h on a copper

blank eoated with a film of the fiTAT parting a~ent was vPry similar to that

of the emulsion¡copper <>lectrodeposit._ The bright copper deposit exhihited

a very fine polycrystalline structurP with few distinct areas of nodulation.

Also there appeared to he less nodulation at the bottom of thP deposit as

compared \Vith the emulsion rleposit. This is thought to be duP to the

quick and even draining of the BT,\T solution across the surface of the

roppPr hlank after immersion. In contra•t, thP emulsion drained unevenly,

with glohules of heavy oil draining tn the bot.tom edge to produce minutl'

oily patches where no nucleation of copper occurred. The surface quality

of the copper electrodeposil ~rown on a eop¡wr substrate roated with the

BTA'f parting agent was exc(•JIPnt ami would easily pass commercial tank­

house standards for coppPr starter sheets_ The electrolytir copper dPpositPd on a Kohe titanium hlank using

commerdal électrolyt(' wa"' <'X('f'IIPI"'t. hf'ing VPf)' tlf'ns<\ cohPrr>tlt and frf'f'

from any -kind of surfacP rol-t~luwss or noclulatinn. Tlw eop1wr was vrcy

hright with a fine polycrystallinr st.rttdure and was similar in appearance to

hoth the emulsion ami thc RT.\T dPposits. On visual examination it

appeared that this deposit was superior f.o the deposits obtained on emulsion

and BT AT -covered suhslrates. !'i<'VNtlwl<>" the latter d('posits were found to

he most acreptable as far as commrreial tankhouse standards are concerned.

However, hefore any judgemPnt roukl he mad(' asto the most acceptable

su bstrate. it was necessary to det<•rmin•• the stripping or peel strength of each

of the deposit.•.

3. 2. Slrippíng strtm{flh mea.<ur<•mrn ts

Relativeo slrip"ping stren¡zth mPUSltf('nll'llts w•~rP mafl('·f<•r l.hP n·moval

of the copper deposit.• from all thr<'e suhstrates. TahlP 1 ami l'ig . .1 show

typical lnstron strip chart data from the test.<. The absolute and relative

stripping strengths are given in Tahle 2. Jt should h<' notro that in tlw <'ase of the BTAT-covered copper

hlanks the copper electrodeposits oecasionally exhihited very large

stripping strengths in the range 2. 75 · 4.1 O kilograms-force per centimetre

width of bond.

~lllpptut; ;,w.o..ut;"u"' ,., .... ,.,._ ~~··l"- -·· -- _,.."\.~.

width of bond. - 1UQ -

)

•

•

SOME RECEN'T DEVELOPMENTS IN THE ELECTROREFINING AND ELECTROWINNING OF COPPER

4. Discussion

4 l. llnnding o{ the electrod~pmil lo the suh.•trale and the relationship

between bonding and .• tripping strenath The force required to renHwc an eiPrtrodeposit from a substrate

depends on tlw degree of physieal and ch<>mical interaction betwPen the

pair. Thus for deposits that. have lw<'n formPd on copper hlanks coated

with partin¡¡ agents such as emulsion ancl BT/\T we expPct. the stripping

stren¡¡th to he related to the extt'nt of the chemical interaction hctween

the partin¡¡ ag<>nt and the Plectrodcposit. Cook et al. [ l] found that the

hest parting agents are those that intcraet with the copp<'r surface.

TABI,E !

Instron strip chart data

CCR e-mulsion strain ratf' = 0.1 in min- 1

Ti m,• {min)

Loa O (lhf)

BTAT :;;train mtr = 0.5 in min- 1

Ti m('

(minJ Loafl (lhf)

Kohf' t.ilanium st.rain ratr> '"' 0.5 in min- 1

Ti m(> (min)

Load llhf\

-------·----0.5 O.ñ 1.0 1.6 ! .5 2.1 2.0 3.1 2.:=. 3.1 3.0 4.0 3.5 ·1.! 4.0 36 4.5 :1.2 5.0 2.I"l

ñ.11 2.5

6.0 2.5

1

! 2.f>

• 15.2 . c:tripped

TABLE 2

0.:!;; o.r~o

1 .o t.;l 2.0 2.!í 3 o

·:J.::O 1.0 ·1.!1

2.li o. 1

:l.í 0.2 :J,!i 0.3 1.0 0.1 1.3 n . .s 1.3 n fi

.u 1.0 c1,3 l.."l

1.:1 2.0 l'll_rip(wd :J.S

.. ---·---·------

0.1 O.R 1.! 1.! 1.! 1.1 . l.! 1.1 1.1 si rippNI

Sfrippínu strencth.-~; for cop(l*'r PIC'clrodepo.~;if.s on different suhstr3tP~

Suh~irate R.\rippin~ s1 n•ngth (k~f PN cm wid!.h of honrl)

lV•Iativf• stripping str,.ngth

. ---·--- ----------· ----·-----BTAT--eovere-d coppe.,. b1ank

Emulsion-.covered coppPr

blank

Kobe titaniurn blank

0.296

0.172

0.076

3.9

2.3

1.0

In the case of parting a¡!Pnt,; that cont.ain m<"rcaptans this chemical

intemction can be considered to involve the ehelation T<'action between

the -SH radical of the part.ing a¡¡ent and copper. RPactions bt>tween

copper and compounds such as benzotriazolc ( 4] and benzothiazolethiol

or, as it is somPtimes called, mercaptohenzothiazole [ 5·- 7] to form

- 105 -

copper and compounds such as benzotriazolc ( 4] and benzothiazolethiol

INSTITUTO GEOLOGICO MINERO Y METALURGICO

0-0 BTA~ ;(')Pf>fll

6 ~ 4~ P~o_IL$1()>,¡/COPC(o:;¡

o-o KQSE ,.,,.A~IUM

o J..---- _l __ , 2 3

TIMF:,

! -·-- '·· ! 1

• 5 6 7

~"

Fig. 3. Load vs. time plot.s in strippintZ IP~Is for eop¡wr drpositrd on difff'r('lll .... uhstr:lirs.

surface films which actas corrosion inhihitors are well known. Thus on

application of the ( -SH )·containing parting agents to the surface of the

copper blank, chelation tak<>s place at active sites on the copper surface.

It is reasonahle to assume that reactions involving the -·SH groups also

take place during the process of copper nucleation on the emulsion and

B I'AT parting agents. Thus slripping strengths for these agents can be asso·

dated with the strength of the bond ing at the parting agent -electrodeposit

interface. It then follows that the adhesive forees between the deposit and

the substrate are dependen t. on the copper nucleation density on the suh·

strate. If we assume that the bonding is stronger nearer the point of

nucleation than between nuclei where lateral growth has occurred, an

increased density of nuclei, as in the case of the BTAT deposits, will almost

certainly increase the stripping strPn~th. ;\nother factor of importancP is l.lw l'ffp!'( of tlw pnrtin¡! agenl.s on th<'

cathode polarization. Thus Cook rl al. 111 founrl that the strippin!( stren¡(th

of the deposit decreased as the deposition potential hecatne more eathodie.

This observation is corroborated by the results ohtained in the present study

and in the electrochemical data of Hao and Cooper [ 8]. These authors found

the deposition potentials to he as in Table 3.

TABLE 3

-----------·--·-Substrate

Copp(!r BTAT-covered copper Emulsion--coverPd copper Kobe titanium

--so -()()

--1:20 --LíO

In the case of BTAT, Cook el al. [1] found a substantial increase in

the peel strength with decreasing BTNf concentration in the parting agent

solution. This result corresponrls to the less cathodic deposition poten tia!

notcd by these investigators with decreased BTAT concentration. In this

solution. This result corresponrls to the less cathodic deposition potent.Jal . ... io . T'HT". oTO -------""--"":~~ t ...... k ...

- 6 -

•

SCJom RECENT DmJ.tm!FNTS IN 1'HE ID,RcntOREFINING AND ELECTB.QWINNING OF COPPER

connection it is interesting to nolt' that Fiaud <'1 al. 1 S 1 fnund thal lhe

potential of cop¡wr in 0.07 M II"S04 snlution hecanw more cathodie with

inereased concentration of henzothiazolethiol; the effect ht>eoming more

pronounced with increac;ing tirrw of imnwrsion.

Thr adhPsion of thfl coppf'r PIPctrodPpnsit to t.itanium incorroratf's

the effects of mechanical or physical intPrad ion or honding. This mt-chanical

honding depends on the roughneS< anrl prvfile of tlw surface of the suhstrate.

Clearly, larger adhesive forces will exist. if tht> stripping of the copper ele<·tro.

deposits entai!s the removal of cnpper !ocated in finP fissures of Uw titanium

suhstrate, i.e. mechanically kPyt>d <·oppN. ,\s a result, modifieation of thP

surface can change th;• strength nf t.lw mechanical honc!B. The pffeets of

various degrees of surface modifieation ar~ illus\ratPd hy the diffPrPñcP

~wtwf'en -thc rPprPS{'IltatiV(l strippinl! /'t.rf'tH!ths of clwmically ('01\ditionN:I

titanium. which possesses a fairly smooth oxidP surfaet', and physieally

abraded titanium, whieh has a high hul mntrolhed dPgTP<' of roughowss that

incorporntes mf'rhani(';ll k{'yinf.!. Control of t.lw surfact• ¡·ondit.inn of tit.anium ,·athod,•s ap¡H'ars lo he

a C"ritical step in attempting to gPnPratf' strípping forc<'s suitahlt• for the.

application considered. This ohservation is suhstantiatPd hy !he data

ITahle 4) compiled hy !ves r/ al. 191 on tlw st.ripping force for coppPr

declrodeposits on titanium surfaees that have IH•<•n prepared (chemically

etchPd) in various ways_ A final poinl worth noling hNP is that tlw honding lwtween copper and

the surface reactive organie-hasPd parting agents was dí'finitdy stronger than

the mechanical keyin¡¡ or physi<·al honding of the copper electrodeposits on

titanium suhstrates.

TABLE 1

Thf' effe('t of chemic<JI f'khinc of tlw surfaC'r> on tlw strippinc friorc•t·

for Coppe-r eleclrodeposits on 1 itan ium su hstrale1-i ( nftPr Ivt:>!'O t'l ni. ) f 9j

Et<•hant Stt·ippina force (twwtotJs p('r ml"trP witlth)

H2 S04 ~oo

HCI ! :;o

Oxalic acid ~~~-,

,\mmonium bifluoridr ~-,o

HF ~;,

Alkali-ne t>trh H_OO

4.2. Cathode starter sheet qualily Starter sheets grown on the emulsion-coated ami BTAT-coated copper

and titanium substratPs displaypd an overall superior quality, rPsulting in

fully continuous sheets of dense and particulnrly hright electrolytic copper.

The stiffness and rigiditv of t.lw sheets. of mainr import.anre in the

prevention of warping in the clPdrolytic cP!Is, pr<w<•d to h<' exce!lent for

both the emulsion and BTAT shpets: howe,er, the Kohe titanium sheets did

not reach the same standard and could be severely flexed without much

difficu!ty. Reproduction of tlw surfa<.'<' of tlw hlank hy the p]ectrodeposits was

demonstrated quitP WPII in al! th<• deposit.s. In particular, t.h<' RTAT deposit

showed a finish t.hat was somewhat. superior to that of the emulsion deposit.

Reproduction of tlw surfa<.'<' of tlw hlank hy the p]ectrodeposits was • ·• ~-- _____ _._: __ ._J __ '-'--- OT ~'T' --1~.--....,..,;,t.

-107-

hl>ing a mucfi more htilliant cop¡lf'r sur!'~. Thl' dppmit on tht> ahraded titanium hlank Mearly rosst>Sst'C.I tht• least SfltOOtll fmhoh. This surfacl' n.su1tt>d from the reprodudion of thti-stnatiOfls (caused hy physical !lbrasion 1 on the surface of th .. titaniurit bürrilt. However, this ''roughrwu" ili not ruch as to pryelu<l~ the ohtainiftll of a-tllftoottl electrodeposi~ in cum­mercial ct'll5;

Thus the .copper cathO<lP start<>r ~ prMI!t'l'd with hoth thl' t'rnul­$1on and R'f..\ T parhn~ aJtt>nts as wdl ns with th..- mrc·harrkally ahrndl'd lllanium arr al\ oflllíll!lntandard :mcl r¡uitr capahk df prn;sing any •·om­llll'l'Mal tan"khou~ $t;lndards in -effect todái/.

4.3. Srrurtural a"a/;v.m o{ thf' ropper depo.•ilst . Micl'OSI'eti<>ns taken of llll' correr deposits j¡Town on the l'mulsion/

eopper. BT AT /correr l!fld K o he titanium substrates are shown in Figs. 4 •. 6. The copper depo~t.~ on all ihe su!mnttes illustmte very well t~ \)rf!!f oJ

pofycrystalline growth referrl'd to- hy Winand {lOt and Fiscl\er { 111 as a twinn-lnl! inreTTO<!diate type z. 1ñ.e modetate current demity Bllom oefft. cient tltne for ~ lareral growth !)r ~· yet the poedorninant g¡-oowth." it in the columnAr.-~stals- wkie& l(mW éutwatdirfi'Ofl> tfle. $U~- -

coupper crystallization in tll<"!!l' r!<-c·lro~O$it..• is th<• ffiOf utitl'ltll4111t. resulting from the fact that thl' erystallil!l*tion ovetvoftage is rninimized for a (110) -orienred deposit. The Z-type electrodeposits afe characteri~ed hy the crystal CT058-sectional ar!'as, whkh W!Ot>ra!ly ar<' ahout tZO !lll!2

, anrl Uw hi¡¡hly twinned copp<'r crystals. The <'X isteMt• of twill!Wd érystals in the~ deposits has been ex['lained hy tl-¡e facttha~ tht> [110! orient11ti~.,_ tN> most favourable to the phenomPnon or twinnjng, w!lích occu~ \11 the ~f .alo.ng the intersection betwPPn the 11 Hlllnd the 1 iOOJ planes.

There are no markt>d <liff<'r<'n<'<'S in-the OV<'rillt Cl'Y"tal strudl,l1'8 !1t the dl'posits. However, se>tne importan!. diffl'fent!I!S wiore noted in the physica.J ii!PJ>earance of the interfacP h!•lwren tllf> de¡X>$it and !he partí._ lll(l!n\.

Cop¡>E'r electrodeposits .:rown on a RT AT suhstrat<' exhihit V<'TY hroad colurnnar crystal growfh incorporatin!l exceptionally large copper crystals togeth"er with crystal twinning which ap¡>E'ars sporadically througt¡out the deposít. The parting a¡¡ent interface, shown in the fi!(Uff'S as a dar!( line lying betwl'<'n the copper blank and Uw coppereleí'trodeposit, is very sharp and well dPfined and devoid of any defects or-imperfectitms. Thus a complere and unifonn surface coveraJ!P of t hl' copper hlank <'an h<' obtaineq !ro m tht> LIS(' Qf BTAT-., parting agent. How!'Ver, it~hould hl' noted that Of'\e'particu­lar problem that did occur during the studws ofl 81'AT was an incomplete surfae<> cover8J!e--<>n isolatt>d patehPs of- the copp,.r hlank: Althouflh this $ítuation oecurrl'd infrequPntly. it is nonethel<>i<S undt'Sirahle as it results in a copper on co¡Jper deposit ( Fig. 6Jh f that rl'<'fulres an Pxeessiv<' strippin¡! force to effect the separation of the deposit from tllf' substratc. Caution then is :warrantro in this case as pro6k'ln5 of this knnHn a CQmm!!Fial ~;trípping operatioh could be critica!. -

In th...- t·opper E'lect-rodeposits growiú>nan etnulsion substratl' thPrP is an initialstrikl' or-lluéleation layN of'l'!qlúaxed ~í'ains fTom which th<' columnar copper crystals grow, Oncf. tliilrl'IUcléátión lay..Y has b<oen fonned, the coppe¡: depositi<illl!ppears to occurlls· ifttre subs(nl.te wE>re cor>per. For comparison. thE' cólumnar growt.h ••xhmlts a· si¡¡Ífi-fkantly srnaller amount of lateral growth in tñP Pmujsion dcposil·$ than in tlw B'rt\T dPposits. The copper ·el('ctrodei>osit seerns al so to ro"'~ a signit'ii'ant amount of twinning throughout thf.- crystál stÍ'ilcturP. ThP: <"mulsion·intrrface ( Fii!S. 4(h) and 51aH clearljl•hoWllt!te el<istenr" ora patchy or Ufl('VE'n surface coverage of

copper :;.l('ctrodei>osit ,.;,.~. al so ~~ ro"'~ a signit'ii'ant amount of twinning . . - 108 ...

•

~~·

(ut .. - . '

fle 4, ~el ion¡ throu¡:h coPPN drpo~~oiU ¡row• (a) on J BT AT/copper JUhÍ\.nlt.e ahowlnQ cotumnar st..rueturc-; (b} on an f'muiJinn/c-nppaf auba.Lnl~ s.howing eohamnar strueturo 1nd cryatal Lwinning: (e) on a tU.anlum (KoiJr) tulnlreU' a.howing tht" tlf'velopmenl of a tolumner slrudu.t(l' on top of an tquu1x~d •Hi&c-e IA)'t"t. (Ma¡rnilicetion 70X .)

1• 1

Ffg. !l, St'clions throu¡:h eopp,.r ¡·l ••(l(HI\,'\ ~ruwn on nn cmulsio.n/ropprr substrale ~howln~ f!vidcmct> o( (n} de ndritic ¡.::rowt..h onj!UH1lllll! frmn r)lly patches on thc coppcr suhs\rtlttt

(m3Jlnificallon, 1 4fJX) llnd (b) ,;mnllcuu,l rtiiiiiVt'ly flltf!E! oíly pnlchcs o f parlÍn(t agttH Of'l th~ &urfact or the coppar hlnnk (mttgnl(¡c:ntlol1, 350'lt: )

- 109 -

(el

(b)

!NSTIMQ GBOLQGICO MJN J!RO Y METALURGICO

Flg. 6 . ( a ) A 1tc•clion thro ugh copJl<'r d<'poslt..·nrnwn o rt 3 BTAT/copper ¡sut)s trat.e show¡ng wh::at wns nn ov~n n¡1plicatiqn o f Jl<lrlir1g :agenl o n lhc surfocé oC th~ cóppr:t blonk (m••tr· niricalion. 140:.. ). (b) A $Cclio n lhrou¡th a COI'P""' deposil g-rown on 11 BTA1'/c:oppf"r subslrall'! which posseued ttn unusu-ally hiRh strippin¡: fo rcr o( 26.3 kgf ot 4 . 10 kilo¡:Timu~ force per «nlimtt~ or bond widlh. Thc ngurt! lihOW$ the evidente of incompiC!le turface covtrage or lht co¡1~r blank by tbe )'Jnrtinc a¡:eM which resulta in a copper on c:opper depos.il (ma,niOcaLion. 35Óx ).

the copp<'r blnnk by th e parLint: ugent. Thcso oily patchcs nre the rcsult of di fficult ics cncountered in ohlaining un c mu lsiou which is suWcicnlly slnble du rin ~ thr uppllcnlion period and prior lo the e leclrolysis in lhe Ct'li , Figure 5 illua\ratcs thc finding that hi¡:hly dcndritic ~owlhs o[ copper crnnnatc I rom the.<e pnlchrs o f oil owinJ! lo the hr~h rrsistno~P of llw putchrs to current now nnd hcnce to lhe existenc" of high current densilrcs allheir perimNcr.

The copper deposit.on thc Kohc tit.anrurn substrate (Frg.1(C)) has a crystal growt.h similar to lhat foro copp!'r t.leposil on an emulsion substrate as well ·~ on ul)am copper substrall' . T lw fi¡:ure shows the relatrvely lar~~ in itial nuclonf.ion !ayer of fin ~ equ i:tXNI ~rains on wh rch a very fincly 5l.ruc­lurccl columnar crystal growlh is l)as~d. Cryslal twm ning rs cxtensrve throughoul the slructure, as in the ~rnuls.ion deposrt.

5. Conclusions

In summary, lhis invesli¡!nlron hos r('vralrd severa! im¡1ortanl finclrni!S relatcd lo the sclcction nnd evalual ion <rf lhr. hcst nct·rpl~hlr pnrtln¡: a~<'lll or subslrolc for Lh~ proé!uc lion uf <01'1" ' ' st:rrl~r sht•,•ls.

(1) Thc sur faces of the coppcr clcctrodeposils growri on lht• c rnu lsio n and f.he B1'AT flarlí ng ugents ns woll ns on Lhe m~chan ically ubraded tit.n. ni u m were all round lo be of very acccpl.ohlc' quality as far as commcrcial tartkhous~ stnndnrds are conccrncd.

(2) Thc relalive slripping strrn~ths for lhe coppcr clcctrodcposit.~ wcre found Lo be (in descending arder) BTAT 3 .9, emulsion 2 .3 and Kobe litanium 1.0.

(3) Copper calhode starter shect.s p roduced by usmg Lhe emulsron and BTAT pnrting a¡rent.s were of equally hi~h quality and were qurl~ cnpoble of passing commcrcial tankhous~ slnnnard s . '!'he qualily o f thc s la rtcr shccl5 from Lhr mcchn11ically ahratlt•d tit:mium was of a somt•whnllt>wN slunclnn.l

(b)

.

t

Sct!E RECENT DEVELOPMENTS IN TBE ELECTROREI!'INll{G AND ELECTROWINNING OF COl'PER

with respect to rigidity and possihiP warping of thP sheet hut was slill '

an acceptahle commPrcial standard. 14) No significant differen.,es werc ohserved in the cryslal structures

and growth patterns of thc copper eleclrodeposils on the three substratcs.

\Ve can therefore draw thP following conclusions from these studi~s.

11) CCR emulsion is su¡wrior a' a parting agent to BTAT. especially

with regard to the stripping strength. (2) Commercialtankhouses contemplating the mechanization of their

stripping operations should considcr carefully the possihlc up¡.iJcation of

physically abraded titanium cathodes asan alternative to the use of extra­

neous parting agents. Of particular interest is the significantly · JlallPr

stripping force that is required in lhe case of the titanium substrate.

Acknowledgments

The authors would like to acknowledge the receipt of stripper

electrolyle· and parting agent emulsion from Canadian CoppPr Refiners

Ltd., Montreal East, Quebec and of tilanium blanks from Kobe Stoel Ltd ..

Titanium Metals Division, Tokyo. Japan. The copp<'r sheet u sed for ano<lp

and cathode fahrication was kíndly supplied by Noranda Metal Industries

Ltd.; Montreal East, Quebec. The authors would also like to acknowledge theír appreciation of the

assistance provided by Dr. S. Saimoto, Dr. G. M. Rao and G. B. Hobbs and

of the photography done by Mr. Harry Holland.

Reft'rences

! (; \t l'ook. \V. E. Galin and .J. Zak, A partinR agent for improved starter sheets,

1 03rd ,\nnual Mt>etin5!, AlME, TlaiJ¡:¡r.;, Tc>xas, 197 4.

2 E.M. 1-:Jkin, Canadian Patent 830,,1H1 (Decemher 23, 1969), to Canadian Copper

Refiners Ltd. 3 R. S. H. Parker and P. Taylor. A(lhrsion and Adhesives, PN~amnn PrPss, New York,

1966, pp. 40. 11. 4 l. C. G. O~tle and U. \V. Poi in!!:. <'orro~ion inhibilinn of <>oppPr wilh ht>nzol.riazole,

Can. ~letal!. Q .. 14 (1) (197!\) :)7.

5 C. fiaud, C. Aucouturier, S .. Jeannin amt J. Talhot, Application de_ différt>ntes

méthodes électrochimiques ñ \'~tude dP 1 'inhihiti<m de 1" corrosion _du cui'lre par le

mercaptobenzothiazole, Rull. Snc-. Chim. Fr., 2 {1970) 465.

6 S. Thibault and J. Talhot, U1 ilisat.ion dt• la !<pectrométrie infrarouge dans 1 'étude des

phénomimes de corrosion: appli<.'ation a la détermination de composés a la surface du

cuh,re, Bull. Soc. Chim. Fr., 4 { 1972) 13·t8_

7 S .• Jeannin, Y. Jeannin and G. Lavi~ne. On sorne complexes of mercaptobenzolhia·

zolt in relatlon with corrosion inhihition, Proc. 16th In t. Con f. on Coordination

Chemistry, 1974, Department of Chf'mistry, Universíty College, Duhlin. 1976, R20.

8 G. M. Raó and W. C. Cooper, ThE" electrodeposition of copper on film·covered metal

su.rfaces, HydrometalluntY, 4 (1979) 185.

9 A. G. Jves, J. R. B. Gilberl and .J. r. ,\. Wnrlll"y. Nud<'lllion and ~rowth of copper

electrocieposits on titanium, l O:lnl Annual 1\.leetin~. AIJ\11-:, Dalias. Texas, 1974.

10 R. Winand, ElectTocrystallization of copper, Trans. Inst. Min. Metall., 84C (1975)

C6i · 75. 11 H. Fischer, Elektrolytische Abschf'idung und Elektrokristallisation von Metallen,

Springer, Berlín, 1954.

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