How Current Density and Temperature Affect the Zinc Electrowinning Efficiency

Oct 21, 2021

How Current Density and Temperature Affect the Zinc Electrowinning Efficiency?

Generally, the higher current density promotes a random growth of electrodeposits which loosely adhere to the cathodes and are readily dislodged by the greater evolution of hydrogen gas. Meanwhile, the higher current density can enhance the current efficiency of MnO2 generation, and therefore decreases the current efficiency of Zn deposition. Low current density electrowinning carries the opposite way.

The zinc deposit mass increased significantly with increasing current density from 450to 650 Am‐2 while it increased very little with further increasing current density to 650 A m‐2. Hydrogen evolution was the main cathodic side reaction. In the current density ranging from 450 to 750 Am‐2, the current efficiency of hydrogen evolution increased with increasing current density. At a higher cathodic current density, hydrogen evolution was facilitated more than zinc deposition, resulting in a lower zinc current efficiency.

An optimum temperature range of 30°-40° C is maintained by cooling because ampere efficiency suffers at higher temperatures. In addition, lead contamination of the zinc cathode, originating from the conventional anode, increases with temperature. The theoretical decomposition voltage of zinc sulfate is 2.35 volts, but the commercial value with lead anodes is about 2.67 volts. Due to the existence of overpotential, the actual applied voltage is in excess of 3 volts and increases with current density. But maintaining the cells at 30°-40° C. usually requires expensive cooling; and operating at currents higher than about 40 ASF(amps per square foot), which is very desirable indeed to reduce the high tankhouse capital cost, is commonly ruled out because it results in excessive lead contamination of the zinc, due to anodic lead dissolution.