Electrochemical codeposition of copper-antimony and interactions with electrolyte additives: towards the use of electronic waste for sustainable copper electrometallurgy

The use of electronic waste or low grade materials as feedstock for the electrolytic production of copper is challenging because impurity metals such as Sb(III) are introduced in the electrolyte. In this work, the mechanisms that lead to antimony contamination in electrolytic copper are studied. Linear sweep voltammetry experiments indicate that the reduction of Sb(III) is kinetically slow in the absence of Cu(II). In the presence of Cu(II), however, reduction of Sb(III) can occur readily by the codeposition of Cu(II) and Sb(III) as demonstrated by chronoamperometry. The ToF-SIMS analyses confirmed the codeposition of antimony in the very first micrometer of the copper deposit, enabled by the nucleation overpotential for galvanostatic copper electrodeposition under conditions relevant for the commercial production of copper. Based on potentiostatic electrodeposition experiments, we suggest that a copper concentration of ≥40 g L−1 Cu(II) in Sb(III) containing electrolytes is beneficial to obtain high purity copper. Codeposition reactions were impacted by the presence of additives (thiourea, glue and chloride ions). In particular, the addition of 0.02 g L−1 chloride mitigated the codeposition of antimony (0.02 g L−1 Sb(III)) to produce grade A copper. For optimal removal of Sb(III) from bleed electrolytes, a molar ratio of ~3 Cu(II)/Sb(III) should be maintained (e.g. 0.3 g L−1 Cu(II) for a typical concentration of 0.2 g L−1 Sb(III)).