Influence of arsenic on copper anode dissolution in electrorefining processes

Abstract

Over the past four decades, the average arsenic content in copper anodes has increased. Arsenic is known as one of the anode components that can help prevent anode passivation. This study challenges the proposed mechanism of acid generation in a boundary layer of the passive layer and aims to expand the effect of arsenic both before and after the generation of the passive layer. The novel mechanism proposed in this study explains why samples with higher arsenic content have a higher dissolution rate before the passive layer forms. It also accounts for the longer time to passivation values observed in higher arsenic-containing anodes. The proposed mechanism also describes the passive layer dissolution rate as a function of arsenic content. The study investigated the impact of arsenic on the passivation mechanism of copper anodes at different arsenic concentrations using chronopotentiometry (CP) and contact angle experimental methods. The CP and ICP results confirm that the time to passivation increases and the electrolyte cupric concentration rises as the anode arsenic content increases from 500 to 1500 ppm. The higher dissolution rate of the anodes containing more arsenic was attributed to their fine, dendritic structure and higher wettability before the formation of the passive layer. Interestingly, the fastest dissolution rate after the formation of the passive layer was observed in the 1000 ppm arsenic sample. This was attributed to the counter effect of the electrolyte on surface accessibility caused by the passive layer microstructure and the wettability of the anode surface.