RESEARCH OF THE INFLUENCE OF TECHNOLOGICAL PARAMETERS ON EFFICIENCY OF ZINC ELECTROLYSIS FROM ALKALINE SOLUTIONS

Abstract

The effect that the main parameters of zinc electrolysis from an alkaline zincate solution have on current efficiency and power con­sumption was studied in laboratory conditions. Zinc concentration (initial and final), current density and temperature were chosen as variable parameters. The study used both model electrolytes (prepared using standard reagents) and real ones produced by leaching the calcined middling product obtained when processing zinc-bearing dusts of ferrous metallurgy. It was shown that the current efficiency of zinc can be quite high (more than 90 %) even at an initial zinc concentration in the alkaline electrolyte of 10 g/dm 3 . However, this requires low current loads (100—400 A/m 2 ) that are impractical in industrial electrolysis used to produce powdered metal, since the actual current density decreases as the cathode deposit surface develops and may fall below the limiting diffusion current of complex ions. In this case, the growth of enlarged dendrites is expected with the formation of «short-circuited» sections in the interelectrode space, which as a whole will reduce the zinc current efficiency. Larger-scale laboratory studies focused on zinc electrolysis from a real zincate solution made it possible to determine the most energy-efficient (with the highest zinc current efficiency and the lowest power consumption) process parameters: current density — 1000—2000 A/m 2 ; electrolyte temperature — 50—80 °С; initial zinc concentra­tion — 20—50 g/dm 3 ; residual zinc concentration — not less than 15 g/dm 3 . These conditions will ensure high current efficiency (85 — 95 %) and electric power consumption (2,28—3,20 kW-h/kg Zn ). For the «depleted» zincate solution with a zinc content of 10 g/dm 3 , the highest current efficiency (more than 90 %) is achieved at a current density of 125 A/m 2 , close to the diffusion current density j = = 95,7 A/m 2 . With j > 500 A/m 2 , the current efficiency is significantly lower due to the intensive hydrogen release. A qualitative evalu­ation of the resulting cathode deposit was made (by the visible dimensions of crystals) in studies on an enlarged electrolytic cell.