Effects of certain impurities on zinc electrowinning in high-purity synthetic solutions

Abstract

The individual effects of lead, copper, nickel, cobalt and antimony on zinc electrowinning were evaluated by measurements in high-purity synthetic solutions, free from additives. The coulombic efficiency (QE) of zinc electrodeposition was determined over 2h under mass transfer-controlled conditions at a temperature of 35°C and a current density of 400 A m−2 in a solution of 0.8 M ZnSO4+1.07 M H2SO4. Antimony had a very detrimental effect on QE causing decrease of ∼ 5 and 50% at 4 and 14 μg l−1, respectively. Antimony also exerted a strong grain-refining effect and changed the deposit orientation from random to (112) to (004) with increasing concentration. Lead had a small beneficial effect on QE at the electrode rotation rate employed (20 s−1). It also exerted a grain-refining effect and changed the deposit orientation from random to (102), (103), (104), to strong basal (004), (002) with increasing concentration. Copper, nickel and cobalt had minor effects on QE, with reductions at 5 mg l−1 of 0.8, 0.3 and 0.3%, respectively. The effects of copper on morphology and orientation were very concentration dependent, but with a general trend towards grain-refining and random orientation. Nickel promoted coarse-grained deposits and changed the orientation from random to (114), (102) to (204), (102) with increasing concentration. Cobalt had the least effect on the morphology of the deposit, although it gradually increased the basal plane orientation with increasing concentration.