High-purity nickel is mainly produced by electrowinning from sulphate and chloride solutions in the presence of high concentrations of boric acid as a buffer. The generally used pH is in the range 3-4 if Ni concentration in the electrolyte is higher than 10 g/l. Lower Ni concentration, as in the case of either industrial liquid effluents and in situ low grade Ni ore leaching, needs pH values ranging from 10 to 11 in order to hinder the evolution of hydrogen. Ni electrowinning from acidic and alkaline solutions is studied to determine in both cases the best operative conditions. Particularly Ni concentration, additive presence, pH values, temperatures, cathode material, current density and voltage, to be used in the case of low Ni concentration, have been considered to obtain low energy requirements together with pure nickel having a good morphology. (C) 2006 Elsevier Ltd. All rights reserved.