Use of catalytic anodes for zinc electrowinning at high current densities from purified electrolytes

Substantial energy savings are possible in zinc electrowinning by substituting catalytic oxygen evolution anodes for conventional lead-silver anodes. However, it is well known that the harmful effects of impurities usually present in zinc electrolyte solutions limit the service life of catalytic anodes, though their purification by solvent extraction could obviate such problems. Laboratory scale zinc deposition experiments with synthetic electrolytes have been performed to determine the effects of current density, temperature and electrolyte composition on cell voltages and current efficiencies. These data sets were used in an assessment of the optimum design parameters of the tank house. Zinc electrowinning at high current densities (higher than 2000 A/m(2)) using catalytic anodes and purified solutions (by solvent extraction) is proposed as an alternative to the conventional process, which is based on lead-silver anodes working at relatively low current densities (ca. 500 A/m(2)). Finally, a system for continuous deposition and stripping of the metal is discussed.