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1 Polish Journal of Applied Chemistry

1 2001

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Trials on zinc electrowinning from sulphate-type electrolytes replenished with waste zinc hydroxide

Stefanowicz T., Napieralska-Zagozda S., Osińska M., Skotarczyk A.

Polish Journal of Applied Chemistry

2001

Vol. 45, nr 1-2

33-40

Zinc electrowinning was performed with insoluble graphite anodes at current density of Dk = 5 A/dm2 in 3 sulphate-type electrolytes. During electrolysis the pH value decreased below pH 0.8. To rise pH and to replenish zinc concentration the waste Zn(OH)2 was batched to electrolyte. The zinc layers of approx. 800 mm were deposited with the average efficiency of 90%. Trials evidenced that in case of iron-sheet cathodes due to different hydrogen overvoltage on zinc and on iron, the deposited zinc layer, depending on zinc concentration in electrolytes may be covered on the whole surface with cavities either drop-like convexities. Such abnormal shape of zinc layer did not appear in case of zinc-sheet cathode. During the electrowinning trials in continuous-flow electrolysis cell with zinc cathode the smooth, flat zinc deposit layer was obtained. In spite of low pH, the added zinc hydroxide dissolves slowly and the periodical batching of Zn(OH)2 with continuous filtration of electrolyte was required. After 100 Ah some erosion traces on graphite anodes were noticed.