Interactions of variables in the fluidised-bed electrowinning of copper

Abstract

The effects of certain variables on the current efficiency and power consumption of a small fluidised-bed electrowinning cell treating dilute copper sulphate solutions have been studied. A factorial experimental design in two levels has been used to investigate the effects of cell current, sulphuric acid concentration, temperature and the presence of iron in the electrolyte, and the results have been analysed by the Yates technique. It is shown that an increase in temperature and the presence of iron in solution both decrease the current efficiency, while an increase in the cell current increases the current efficiency, for conditions where the cathode is not polarized with respect to copper ions. Significant interaction effects on the current efficiency are shown to exist for the case of cell current and iron concentration and for cell current and temperature. These main effects and interactions can be accounted for by a model in which three simultaneous reduction reactions occur at the cathode involving cupric ions, ferric ions and oxygen, with the latter two occurring at their diffusion limited rates. Significant main effects on the power consumption of the cell are shown to exist for cell current, iron concentration and acid concentration. Increasing either of the former two variables increases the power consumption whereas an increase in the latter causes a marked decrease in power consumption, and significant interactions occur between cell current and iron concentration and cell current and acid concentration. An increase in temperature is shown to lead to an increase in the amount of metal deposited on the feeder electrode. The paper concludes with a discussion of the application of fluidised-bed cathodes to the recovery of copper by electrowinning from various types of solutions.