Roles and influencing mechanisms of Fe2+ and Lix984 in copper electrodeposition

In the copper (Cu) hydrometallurgical process, the extractant, and impurity ions in the leaching process would inevitably enter the electrolyte in the electrodeposition with the process cycle. And with the recycling of electrolyte, the impurities would continue to accumulate. When the accumulation of impurities exceeds a certain limit, it could have a large negative impact on the deposited Cu. In this paper, the effects of the ferrous ion (Fe²⁺) and the commonly used extractant Lix984 (5-nonylsalicylaldehyde oxime and 2-hydroxy-5-nonylacetophenone oxime 1:1 mixture) on the morphology, current efficiency (CE) and energy consumption of Cu cathodes were investigated. In addition, the electrochemical mechanisms were investigated using electrochemical methods such as cyclic voltammetry (CV), linear scanning voltammetry (LSV), Tafel linear fitting and chronopotentiometry (CP). When the Fe²⁺ concentration was 2.0 g/L, the CE decreased sharply to 93.63%, which was 6.21% lower than normal. And the Lix984 at 50 mg/L reduced the CE from 5.88% to 93.99%. The energy consumption increased by up to 89 kWh/ (t Cu). Electrochemical studies showed that high concentrations of Fe²⁺ and/or Lix984 in the electrolyte significantly inhibited Cu deposition by increasing the overpotential, decreasing the deposition rate, and covering the electrode surface, resulting in larger Cu coating roughness and larger grain size. Therefore, the concentration of Fe²⁺ and organic impurities in the electrolyte should be appropriately controlled before proceeding to Cu electrodeposition to obtain a favorable quality Cu cathode.