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 consumpution in the process, it is essential to develop a passivationprevention technology for low-grade copper anodes. This article outlines the physicochemical basis of anode passivation and reviews earlier research with a focus on experimental techniques. Past research on anode passivation of pure Cu anodes, which was carried out to understand the precipitation of copper sulfate quantitatively, is also reviewed to explain the relationship between passivation and current density.
