1
25-097
Use of Chemical Additives to Improve Copper Electrowinning
Wayne Dickinson
Kemira, Atlanta, GA
Matias Pentinnen
Kemira, Helsinki, Finland
INTRODUCTION
Electrowinning is a key process for copper production
contributing roughly twenty percent globally and thirty to
forty percent of production in the Americas1. Copper grade
is assessed largely on deposit smoothness and on level of
impurities in the metal. Smoothing aids are essential to cre-
ate dense, low porosity deposits and guar has long been the
material of choice for this purpose. Guar is, however, poorly
stable under the strongly acidic electrowinning conditions,
underlying ongoing research to identify an effective, acid-
tolerant replacement. Current efficiency is also a critical
factor in controlling copper production costs and chemical
additives should ideally improve current efficiency as well
as improving deposit smoothness.
BACKGROUND
Copper electrowinning is used to deposit copper from
acidic, copper-rich solution onto stainless steel cathodes.
Typically, modern tankhouses use lead-calcium-tin anodes
at which water is oxidized to generate oxygen and protons,
releasing electrons. The electrons travel through the polariz-
ing circuit to reduce cupric ions to elemental copper at the
cathode. In the absence of smoothing aids, copper plates
where the chemical potential is highest, that is, at protru-
sions on the cathode surface. The result is dendrite forma-
tion which can short-circuit to adjacent electrodes, reducing
current efficiency and raising electrical costs2. Perhaps more
important is that the high porosity of untreated copper
deposits trap solute electrolytes leading to elevated levels of
impurities such as iron, nickel, zinc and sulfate that lower
the copper purity and reduce it’s value.
Smoothing aids function by adsorbing to surface pro-
trusions to prevent dendrite growth and by promoting crys-
tal nucleation to enable finer, less porous deposits to form3.
The effect is to generate denser, lower impurity deposits
that retain maximum copper value.
MATERIALS AND METHODS
Electrolye solution comprised 160 g/L sulfuric acid, 35
g/L cupric ion, 100 mg/L cobalt ion, and 25 ppm chlo-
ride4. The cell operated at 330 amps/m2 and a tempera-
ture of 65°C with mild stirring to reduce mass-transport
limitations.
The polarizing circuit (Figure 1) used a commercial
potentiostat/galvanostat (PG) modified with a current
booster to provide the higher current needed for electro-
plating. Data was captured using a data-logging ammeter
and voltmeter and with the unamplified signal from the
commercial PG system. Following the galvanostatic run,
the cathode was removed from solution, rinsed with deion-
ized water, dried overnight at 65°C and weighed to deter-
mine moles of copper deposited. All tests were run for 240
minutes.
Deposit characteristics were assessed microscopically
at 40, 100 and 200x and current efficiency was calculated
based on the moles of copper deposited divided by the theo-
retical moles derived from the coulombs of charge applied2.
Figure 2 illustrates the current-time behavior of the sys-
tem. The data shows a roughly 5 percent increase in current
during the first hour of deposition followed by steady-state
current. As the electrochemical system was run in galva-
nostatic mode, the initial rise in current is surprising. It
may be explained, however, if the overvoltage limits are
exceeded during copper plating onto stainless steel, after
which overvoltage is within limits when plating onto the
copper deposit. Regardless of the validity of this explana-
tion, the amperage vs. time behavior allows coulombs of
charge to be quantified, as needed in calculating current
efficiency.
25-097
Use of Chemical Additives to Improve Copper Electrowinning
Wayne Dickinson
Kemira, Atlanta, GA
Matias Pentinnen
Kemira, Helsinki, Finland
INTRODUCTION
Electrowinning is a key process for copper production
contributing roughly twenty percent globally and thirty to
forty percent of production in the Americas1. Copper grade
is assessed largely on deposit smoothness and on level of
impurities in the metal. Smoothing aids are essential to cre-
ate dense, low porosity deposits and guar has long been the
material of choice for this purpose. Guar is, however, poorly
stable under the strongly acidic electrowinning conditions,
underlying ongoing research to identify an effective, acid-
tolerant replacement. Current efficiency is also a critical
factor in controlling copper production costs and chemical
additives should ideally improve current efficiency as well
as improving deposit smoothness.
BACKGROUND
Copper electrowinning is used to deposit copper from
acidic, copper-rich solution onto stainless steel cathodes.
Typically, modern tankhouses use lead-calcium-tin anodes
at which water is oxidized to generate oxygen and protons,
releasing electrons. The electrons travel through the polariz-
ing circuit to reduce cupric ions to elemental copper at the
cathode. In the absence of smoothing aids, copper plates
where the chemical potential is highest, that is, at protru-
sions on the cathode surface. The result is dendrite forma-
tion which can short-circuit to adjacent electrodes, reducing
current efficiency and raising electrical costs2. Perhaps more
important is that the high porosity of untreated copper
deposits trap solute electrolytes leading to elevated levels of
impurities such as iron, nickel, zinc and sulfate that lower
the copper purity and reduce it’s value.
Smoothing aids function by adsorbing to surface pro-
trusions to prevent dendrite growth and by promoting crys-
tal nucleation to enable finer, less porous deposits to form3.
The effect is to generate denser, lower impurity deposits
that retain maximum copper value.
MATERIALS AND METHODS
Electrolye solution comprised 160 g/L sulfuric acid, 35
g/L cupric ion, 100 mg/L cobalt ion, and 25 ppm chlo-
ride4. The cell operated at 330 amps/m2 and a tempera-
ture of 65°C with mild stirring to reduce mass-transport
limitations.
The polarizing circuit (Figure 1) used a commercial
potentiostat/galvanostat (PG) modified with a current
booster to provide the higher current needed for electro-
plating. Data was captured using a data-logging ammeter
and voltmeter and with the unamplified signal from the
commercial PG system. Following the galvanostatic run,
the cathode was removed from solution, rinsed with deion-
ized water, dried overnight at 65°C and weighed to deter-
mine moles of copper deposited. All tests were run for 240
minutes.
Deposit characteristics were assessed microscopically
at 40, 100 and 200x and current efficiency was calculated
based on the moles of copper deposited divided by the theo-
retical moles derived from the coulombs of charge applied2.
Figure 2 illustrates the current-time behavior of the sys-
tem. The data shows a roughly 5 percent increase in current
during the first hour of deposition followed by steady-state
current. As the electrochemical system was run in galva-
nostatic mode, the initial rise in current is surprising. It
may be explained, however, if the overvoltage limits are
exceeded during copper plating onto stainless steel, after
which overvoltage is within limits when plating onto the
copper deposit. Regardless of the validity of this explana-
tion, the amperage vs. time behavior allows coulombs of
charge to be quantified, as needed in calculating current
efficiency.