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To investigate the effect of impurities in solution on the lightness, surface morphology and current efficiency of deposited Ni, Ni electrodeposition was performed at a current density of 300 A/m2 and 7.2×105 C・m-2 of charge, in an unagitated chloride solution containing Mn2+, Cr3+ and SO4 ions as impurity with pH 1 to 3, at 333 K. In solution containing 10 g・dm-3 of Mn2+, the current efficiency for Ni deposition decreased slightly, and crystal size of deposited Ni became small. The lightness of deposited Ni decreased when the concentration of Mn2+ exceeded 1 g・dm-3. When the Ni deposition was performed using soluble Ni anode to prevent the formation of MnO2 at anode, the lightness of Ni was higher than that using insoluble anode, which suggesting that MnO2 resulting from insoluble anode caused the decrease in lightness of Ni. In solution containing Cr3+, the current efficiency of Ni gradually decreased with increasing concentration of Cr3+, and significantly decreased above the Cr3+ concentration of 0.1 g・dm-3. The lightness of deposited Ni greatly decreased with increasing concentration of Cr3+ above 0.001 g・dm-3. In solution containing Cr3+, it is presumed that Cr(OH)3 formed at cathode layer suppresses the Ni deposition, resulting in some codeposition of NiO and Ni(OH)2 with Ni, which causes the decrease in current efficiency and lightness of Ni. On the other hand, in solution containing SO4, the current efficiency of Ni somewhat decreased at SO4 concentration above 50 g・dm-3, and significantly decreased above 100 g・dm-3. The lightness of deposited Ni somewhat increased at SO4 concentration of 20 g・dm-3, and greatly increased above 20 g・dm-3. Since the overpotential for Ni deposition increases with increasing concentration of SO4, the surface of deposited Ni becomes smooth, resulting in increase in lightness. [doi:10.2320/jinstmet.J2016030]

Effect of Impurities in Solution on the Lightness and Surface Morphology of Ni Deposited from Chloride Electro-Winning Solutions