Microstructural modification of Ni electrodeposit in an acidic NiCl2 solution

Abstract

Electrowinning is an important process to extract Ni from aqueous solutions. In this work, the characteristics of electro-deposited Ni were modified by employing magnetic agitation and flowing bubbles in an acidic chloride solution. The nucleation and growth of Ni grains were analyzed in the electro-crystallization. Phase compositions and morphologies of the modified deposits were characterized. As well, the positive effects of magnetic agitation and flowing bubbles on the electrowinning process were discussed. Mass transportation of Ni 2+ ions was efficiently accelerated by magnetic agitation and upwards flowing bubbles. The preferential growth of Ni deposit was also facilitated along the (111) orientation. The nucleation and growth of Ni crystals proceeded in the instantaneous nucleation mode and the lateral growth mode, respectively. The introduction of magnetic agitation and upwards flowing bubbles can promote the detachment of hydrogen gas and be available for the enhancement of current efficiency. • Microstructure of Ni deposit was modified by magnetic agitation and flowing bubbles. • Mass transfer of Ni 2+ ions during electrowinning was accelerated. • Nucleation mode of Ni was transformed from instantaneous to progressive. • Preferential growth of (111) plane orientationally was promoted. • Compact deposit consisting of bar grains was formed in the lateral growth mode.