Electrochemical production of cobalt powder by using a modified hydrocyclone with ultrasonic assistance

Abstract

The effect of ultrasound on the production of cobalt powder was analysed. The experiments were carried out with a standardised hydrocyclone, whose internal cylindrical stainless-steel wall acted as a cathode and the vortex finder as an anode, made of Pb-0.75%Ag alloy. The electrolyte was a synthetic solution containing 1.9–3.8 g dm−3 Co in 36.7 g dm−3 (NH4)2SO4 and 30 g dm−3 H3BO3 at pH 5.5 as the supporting electrolyte. Ultrasound application was very effective to detach the dendritic deposits from the cathode surface and also to improve the reactor performance in comparison with a silent system. The best working conditions were achieved at a current of 15 A and 60 °C, where the partial current of hydrogen evolution is acceptably low. Under these conditions, the current efficiency was 58.3%, 11.7 kW h kg−1 the specific energy consumption, 63.7 kg m−3 h−1 the space time yield and 61% the cobalt fraction obtained from the spigot. The volumetric kinetic constants under ultrasound or silent conditions were calculated from the experimental data, corroborating the beneficial effect of ultrasound for the production of cobalt powder. The particles have a globular shape with a dendritic characteristic featuring an average length of 31.7 μm.