Research into the Influence of Process Parameters on the Efficiency of Zinc Electrolysis from Alkaline Solutions

Abstract

The effect of the main zinc electrolysis parameters from an alkaline zincate solution on the current efficiency and power consumption is studied in laboratory conditions. The zinc concentration (initial and final), current density, and temperature are chosen as variable parameters. Both model (prepared from standard reagents) and actual electrolytes are used. The latter is prepared by leaching the calcined middling product of zinc-bearing dusts processing of ferrous metallurgy. It is shown that the current efficiency can be rather high (higher than 90%) even at the initial zinc concentration in the alkaline electrolyte of 10 g/dm3. However, low current loads (100–400 A/m2) are required in this case, the use of which is unreasonable for industrial electrolysis with the formation of powdered metal, because the actual current density decreases with the development of a cathode deposit surface even lower than the limiting diffusion current of complex ions. The growth of enlarged dendrites with the formation of short-circuited segments in the interelectrode space is expected in this case, which will decrease the current efficiency of zinc. Large-scale laboratory studies on zinc electrolysis from the actual zincate solution make it possible to determine the most power-efficient (with the highest current efficiency of zinc and lowest power consumption) process parameters; notably, the current density is 1000–2000 A/m2, the electrolyte temperature is 50–80°C, the initial zinc concentration is 20–50 g/dm3, and the residual zinc concentration is no lower than 15 g/dm3. A high current efficiency (85–95%) and applied power consumption (2.28–3.20 kW h/kgZn) will be provided under these conditions. The maximal current efficiency (higher than 90%) for the “depleted” zincate solution with a zinc content of 10 g/dm3 is implemented at current density j = 125 A/m2 close to the diffusion current density (of about 95.7 A/m2). The current efficiency considerably decreases at j > 500 A/m2, which is caused by intense hydrogen evolution. When performing studies for the enlarged electrolysis cell, the formed cathode deposit is evaluated qualitatively (by visible crystal sizes).