GB735791A - Treatment of nickel and cobalt solutions - Google Patents

Abstract

Nickel ammonium sulphate and cobalt ammonium sulphate and ammonium sulphate are prepared from an acid sulphate solution of nickel and cobalt by reducing the acidity of the solution to a pH between 3 and 7 with ammonia, arranging to have at least one mol. of ammonium sulphate per each mol. of nickel and cobalt sulphate, concentrating the solution by evaporation to completely p precipitate the nickel as mixed crystals of nickel ammonium sulphate and cobalt ammonium sulphate and discontinuing the evaporation at a point where the precipitated crystals contain from 1.2 to 3 mols. of ammonium sulphate for each mol. of nickel and cobalt sulphate, separating the precipitated crystals from the mother liquor and then evaporating the major part, but not all of the water from the mother liquor, thereby forming ammonium sulphate crystals which are separated, after which the final mother liquor is recycled to the first evaporation step. Such mother liquor still contains dissolved cobalt. Both evaporation steps are preferably conducted at 20 DEG to 60 DEG C. and the second evaporation step is preferably stopped when the cobalt content of the ammonium sulphate crystals is not more than 0.1 per cent and the cobalt concentration in the mother liquor is between 2.5 and 4 grams per litre. The mixed crystals of nickel ammonium sulphate and cobalt ammonium sulphate are preferably redissolved in water and the solution saturated with ammonia to form complex amine salts of the metal, which solution on heating to 230 DEG C. under pressure in the presence of an oxidizing gas forms a precipitate of crystalline cobaltic amine salt free from nickel. The cobalt salt is separated and the nickel solution further processed in known manner. The sulphate solutions to which the invention is applied are preferably freed from lead, copper and iron before treatment, the iron being removed from the lead-free solution preferably as in Specification 695,517 and the copper removed next. The original feed solution may contain about 6 per cent free sulphuric acid. According to a typical example a solution of cobalt and nickel is treated with anhydrous ammonia until the pH is brought to 4 and the solution evaporated at 60 DEG C. until the crystals separated shows a molar ratio of ammonium sulphate to nickel and cobalt sulphate of 2.14 to 1. The separated crystals contained 99.96 per cent of the nickel and 97.1 per cent of the cobalt. The mother liquor was then evaporated at 50 DEG C. to crystallize ammonium sulphate containing 0.05 per cent cobalt and bring the cobalt concentration in the solution to 3.5 g.p.l. The ammonium sulphate crystals were separated and the mother liquor recycled to the first evaporator.