Method for purifying a nickel sulfate solution by solvent extraction

Abstract

A method of purifying a crude nickel sulfate solution to give pure nickel sulfate through solvent extraction, in which the impurities such as cobalt, calcium, magnesium, iron, zinc, copper, sodium, ammonia and others to be in the crude solution are removed while, if necessary, effectively recovering cobalt, and for which the amount of a neutralizer to be used is reduced and the cost of treating wastewater is also reduced includes an extraction step of adding an organic acid extractant to a crude nickel sulfate solution to thereby extract nickel into the extractant to give a nickel-loaded organic phase, followed by a scrubbing step of scrubbing the organic phase as obtained in the previous extraction step with a nickel-containing scrub solution to thereby remove sodium and ammonia from the organic phase; and a second purifying step of adding a crude nickel sulfate solution to the nickel-retaining organic phase as obtained in the previous first purifying step so as to exchange the nickel in the organic phase with the impurities except sodium and ammonia existing in the crude nickel sulfate solution added in this step, thereby giving a purified nickel sulfate solution and an organic phase containing impurities; and optionally a third purifying step of recovering nickel from the organic the organic phase containing impurities as obtained in the second purifying step, and a step of recovering a valuable metal, cobalt from the organic phase containing impurities.