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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 -
•
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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