Strong electrolyte, the copper rich aqueous phase from the solvent extraction strip stage, is continually added to to the circulating elelctrolyte to maintain the copper concentration about 45 grams per liter. For proper operation in electrowinning the copper and acid concentrations must be keep within a narrow concentration range. The overall reaction takes place in the electrowinning cells as the electrolyte is circulated through the circuit and an electrical current is passed between the anodes and cathodes. The ampheres of the an electrowinning circuit is a function of the capacity of the electrowinning cells and the voltage is a function of the number of cells. If copper production is greater than the output of a single cell, additional cells are added in series and the cell voltages are additive. The unit processes of solvent extraction combine with electrowinning to form a single, continuous process that can be illustrated as: These resistances are combined and require a voltage between 1.8 and 2.5 volts per cell. A detailed explanation of these individual resistances which comprise the electrowinning system are beyond the scope of this paper, but can generally classified as the reaction potential as determined by the electromotive force of the electrowinning reaction, over voltage due to chemical and physical reactions at the surfaces of the anodes and cathodes, electrolyte and hardware resistances. The voltage required is determined by the electrical resistance of the electrowinning cell and the electrical system providing electricity to the cell. The amount of copper from a single electrolytic cell is determined by the number and size of anode/cathode pairs in the cell and the time that electrical current is applied to the cell. It is important to note that copper deposited at the cathode is not a function of voltage, but of time and ampheres. The electrochemical equivalent for copper is 0.02846 kilogram per ampere day. One faraday or 96489 ampere seconds (coulombs) will deposit the atomic weight of an element measured in grams divided by the valance of the metal. The amount of copper that is deposited in the reaction is defined as an electrochemical equivalent. The overall reaction is the combination of two electrochemical half reactions. Electrowinning is defined as the cathodic deposition of metal, in this example copper, from a copper bearing solution by the passage of an electric current current using an insoluble anode.įor copper the electrowinning reaction reaction is:
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