Electrowinning of Nickel from Dilute Sulfate Solution

Electrowinning is one of the methods for recovery of nickel metal from pregnant leach solutions. In industrial practice, the Ni content in electrolytes is usually above 80 g/L. However, many nickel solutions obtained from processing of secondary nickel resources are much less concentrated and this makes the electrowinning of such solutions difficult. In the present study, Nickel electrowinning from 30 g/L sulfate solutions has been investigated and the effect of the parameters such as current density (CD), temperature (T) and boric acid concentration (BA) on the current efficiency and nickel deposit quality has been determined using a central composite design methodology. The statistical analysis of experimental results revealed the significant factors and a proper model was obtained for each response variable. The results revealed two important negative interaction effects of T´BA and CD´BA which means that increasing temperature and current density could result in a higher current efficiency and satisfactory Ni deposit quality only at lower boric acid concentrations. By using overlaid contour plot method for multiple response optimization, the optimum condition for attaining current efficiencies of >95% and a smooth and compact Ni deposit quality was determined as CD = 2-2.5 A/dm2, T = 25-30 °C, and BA = 10 g/L.