Electrochemical codeposition of arsenic from acidic copper sulfate baths: The implications for sustainable copper electrometallurgy

Abstract

• The main source of arsenic contamination is codeposition during the nucleation stage. • Convection and concentrated Cu(II) electrolytes mitigate arsenic contamination. • The reduction of As(III) to metallic As does not occur readily. • Fast removal of As(III) possible by copper-arsenic codeposition. Copper producers face increased demand associated with increasing complexity in feedstock composition, including high amounts of impurity metals. In this work, linear sweep voltammetry was used to study the electrodeposition behavior of copper and arsenic, define strategies for the production of grade A copper, and the removal of arsenic from complex electrolytes. Our results show that the copper concentration is a key parameter to control in the electrodeposition process. The continuous deposition of arsenic from the electrolyte requires copper in solution (≤10 g L −1 Cu(II) for 2 g L −1 As(III)) to form copper arsenides . The deposition of metallic arsenic does not occur readily. Conversely, the use of a concentrated Cu(II) solution (e.g. 40 g L −1 ) resulted in grade A copper from an electrolyte with a maximum of 2 g L −1 As(III) under galvanostatic control at a current density of – 42 mA cm −2 . Time-of-Flight Secondary Ion Mass Spectrometry depth profile measurements on copper deposits revealed that arsenic contamination was entirely concentrated near the substrate side of the deposit and progressively decreased further into the deposit. The codeposition of arsenic occurred along with the initial copper nucleation, when the electrochemical potential for electrodepostion under galvanostatic control is temporarily lower. These findings provide important insights for future sustainable copper electrodeposition technologies from complex feedstocks.