THE EFFECT OF CO2+, CU2+, FE2+ AND FE3+ DURING ELECTROWINNING OF NICKEL

The effects of the impurities Co2+, Cu2+, Fe2+, Fe3+ on the current efficiency, physical appearance, purity, crystallographic orientation and surface morphology of the deposit and on nickel deposition polarization behaviour during nickel electrowinning were determined. The current efficiency did not change significantly in the presence of these impurities over the concentration range studied, but certain changes in the purity and physical appearance of the deposit were observed. Based on the physical appearance of the electrodeposited nickel, the tolerance limits of the impurities in the electrolyte are reported. The tolerance limit of Co2+ was a maximum at 500 p.p.m. and a minimum at 5 p.p.m. in the case of Fe2+. No deviation of nickel structure from fcc was observed in the presence of any of these impurities but the peak height values for different orientations showed variations with all the impurities and the values also changed with increase in the impurity concentrations. The surface morphology of electrodeposited nickel also changed in the presence of the impurities. The potentio-dynamic scan curves for electrodeposition of nickel showed deviations in the presence of all the impurities except Cu2+. Based on the results, an attempt is made to correlate the effects of the various factors investigated.