Indium electrowinning on Al cathode: Tuning of operating parameters and obtained deposits characterization

In this investigation, the indium electrowinning process using Al cathode and a sulfate-based electrolytic bath have been studied. In particular, current efficiency (CE), specific energy consumption (SEC) and deposit quality, in terms of morphology and structure, have been evaluated and optimized considering the operative parameters such as temperature, current density, pH and electrolyte composition. Cyclic voltametric assessments were conducted to have a preliminary electrochemical characterization of the indium electrodeposition reaction on the Al cathode at room temperature using a conventional three-electrode cell configuration. Subsequently, galvanostatic tests were performed on Al cathode without a surface pretreatment obtaining at 100 A/m2 for CE and SEC values higher than 90 % and 1.6 kWh/kg, respectively. The presence of boric acid and sodium sulfate within the electrolytic bath showed insignificant improvements, different from results obtained with other cathodes in other works. Furthermore, the use of cathode surface pretreatment, namely chemical etching with 1 M HF, allowed operating at a current density of 150 A/m2, increasing productivity and achieving CE and SEC values of 86.6 % and 2.7 kWh/kg, respectively. The use of chemical etching by preventing the indium deposit detachment allowing for higher CD values. Finally, XRD and SEM analysis were used to evaluate indium deposits to address the influence of operative conditions on the structure and surface morphology.