Study of Operational Parameters on Indium Electrowinning Using a Ti Cathode

Indium, widely used as indium-tin oxide (ITO), has been recognized as a strategical metal for audiovisual, optoelectronic systems, semiconductors and photovoltaic fields. An increasing shortage and unflexible mineral supply have led indium to be recovered from secondary sources, such as waste electrical and electronic equipment (WEEE). The main step for indium hydrometallurgical recovery from WEEE is the electrowinning process using sulfate baths, giving lower environmental impact and improved workplace safety conditions. In this investigation, a titanium cathode has been employed for the study of the indium electrowinning process in a sulfate-based bath. This study was focused on analyzing current efficiency (CE), specific energy consumption (SEC) and deposit morphology and structure as the temperature, current density, pH and electrolyte composition were varied. Prior to conducting electrowinning tests, a conventional three-electrode cell was used to perform cyclic voltametric assessments of the electrodeposition reactions on the Ti electrode at room temperature. The indium electrowinning tests on Ti cathodes presented CE values higher than 90%, with low energy consumption at low current densities, showing a negligible influence of additive agents in the bath, different from results obtained with other cathodes in other works. Moreover, the increase of the current density beyond 75 A/m² produced significant effects by etching the electrode surface with 1M HF. In particular, at the conclusion of this investigation, good results are obtained without additives, by etching the titanium cathode and operating at higher current density between 100 and 200 A/m² at pH 2.3 and different temperatures (40 °C and 60 °C). Finally, indium deposits were analyzed by XRD and SEM in order to determine the influence of operative conditions on the structure and surface morphology.