THE EFFECT OF SOME TRACE-METAL IMPURITIES ON THE ELECTROWINNING OF ZINC FROM KIDD CREEK ELECTROLYTE

The single and combined effects of cobalt (0.15-5 mg/l), arsenic (0.01-5 mg/l ) and iron (2.5-50 mg/l) on zinc deposition current efficiency (CE ) and polarization behaviour and on the deposit morphology and orientation of 24 h zinc deposits were studied. The in-plant additive mix of 1 mg/l Saponin, 5 mg/l Dowfroth, 13 mg/l sodium silicate and 0.01 5 mg/l antimony was employed under the conditions of 60 g/l Zn2+, 200 g/l H2SO4, 500 A/m2 and 38-degrees-C with conditioned Pb-Ag anodes and SrCO3 additions in bench scale electrolysis (cell volume 300 ml). The CE was sensitive to increasing concentrations of cobalt and arsenic both alone and in combination. Iron alone and cobalt little effect on CE. Iron concentrations greater than 20 mg/l, in combination with arsenic and cobalt, significantly lowered the CE. The nucleation overpotential (NOP) determined from cyclic voltametry did nol correlate with the CE results. A prewave in the voltammograms in thc presence of some impurities, particularly arsenic, made the determinations of the NOP difficult. Most of the deposits were intermediate (e.g. [101][112][102]) in orientation. The surface of the deposit darkened in appearance as the arsenic concentration increased. At higher cobalt concentrations, the solution side of the deposit appeared normal although significant corroded dark areas starting on the edges were noted on the electrode side.