PURIFICATION OF NICKEL SULFATE-SOLUTIONS CONTAINING IRON, COPPER, COBALT, ZINC AND MANGANESE

Abstract

Acidic nickel-bearing solution containing iron, cobalt, manganese, zinc and copper was processed through a solvent extraction and precipitation technique to obtain a pure nickel sulphate solution. Iron was extracted using 0.2M Cyanex-272 (partially neutralised) as the extractant. Stripping of iron from the loaded organic has also been studied. After iron recovery through solvent extraction the raffinate still contained 0.25 g dm-3 of iron which was quantitatively separated by a lime precipitation technique. During this iron precipitation there was no loss of cobalt and nickel but copper, manganese and zinc were coprecipitated to some extent. From the iron-free nickel sulphate solution the other impurities were extracted using the same extractant (Cyanex-272) in a single stage. The metal ions from the loaded organic were stripped using a 0.5% (v/v) H2SO4 solution in a single stage. The entire operation needs only seven stages: two stages for iron extraction, three stages for iron stripping from the loaded organic, and one stage each for extraction and stripping of other impurities. In the entire operation the loss of nickel was less than 0.5%.