2020 Hideaki Sasaki Electrorefining of copper and anode passivation journalofmmij.136.14

In the process of electrorefining of copper, application of higher current density increases the tendency of anode passivation. The passivation disrupts the sound operation of the electrorefining process, reducing the current efficiency and the quality of copper deposited on the cathode. Therefore, anode passivation should be avoided in industrial electrolytic cells. Anode passivation is attributed to the precipitation of copper sulfate, which is saturated locally in the vicinity of the anode surface. When a copper anode contains high concentrations of insoluble impurities that form slime on the anode surface, the tendency of anode passivation increases. Because e-waste often contains such elements that induce anode passivation as well as the harmful elements from the concentrate, the operation of the electrorefining process becomes difficult when the feeding ratio of secondary materials (scraps) is increased. To promote the recycling of metals and reduce energy consumption in the process, it is essential to develop a passivation-prevention technology for low-grade copper anodes.