Electrowinning of cobalt from sulphate solutions contaminated with organic impurities

The electrowinning (EW) of cobalt from sulphate solution contaminated with organic impurities: tri-n-butyl phosphate (TBP), 2-hexylmethyl decanoic acid (VERSATIC 10), 2-hydroxy-5-nonyl acetophenone oxime (LIX 84), di-2-ethylhexyl phosphoric acid (D2EHPA) and di-2,4,4-trimethylpentyl phosphinic acid (CYANEX 272) has been investigated at 60 degreesC. Both cyclic voltammetry and flow cell electrolysis have been used. The effect of organic impurities on the cathodic reduction of cobalt is compared with the blank solution. The current efficiency is more than 90% in most cases and is highest in the case of D2EHPA (96%) and lowest with VERSATIC 10 (86%). The cathodic polarization from cyclic voltammetry indicates that the exchange current density (i(0)) value is higher in the presence of organic impurities than in solutions containing no organic impurities. The organic impurities indicate an inhibition of electrocrystallization process due to suppression of nucleation. Cathodic polarization also indicates that Co2+ reduction occurs slightly at less negative potential in solution containing organic impurities. (C) 2002 Published by Elsevier Science B.V.