Electrowinning of zinc from alkaline solutions

The objective of this work was to determine the best conditions for minimizing energy consumption in Zn electrowinning from alkaline solutions. The effects of several variables, i.e. hydroxide concentration (300-500 g/l), current density (50-1000 A /m exp 2 ), temperature (24-74 deg C), cathode material (Mg, Ni, Pb, stainless steels 304 and 316) and impurities (Cu and arsenide), on current efficiency and cell voltage were investigated. The current efficiency was always 100% on magnesium except in the presence of arsenide (78% at 100 mg/l). With cathode materials such as stainless steels 304 and 316 nickel and lead, hydrogen evolution was observed at the beginning of electrolysis. Hydroxide concentration did not have a significant effect on cell voltage. Specific energy was low, even at 1000 A/m exp 2 , and decreased with rising temperature, being only 2.17 kW h/kg at 74 deg C. No redissolution of the deposit was observed. Decreasing distance between electrodes and using active anodes permitted a further reduction of specific energy to 1.75 kW h/kg. Decreasing space between electrodes was possible as no dendritic deposits were observed. 48 ref.--AA