METHOD OF SOLVENT EXTRACTION OF NICKEL SULFATE

摘要

Provided is an economical method of solvent extraction of a nickel sulfate solution to purify nickel sulfate, in which the organic phase obtained is prevented from being contaminated with impurities such as sodium and ammonium, and a high-purity nickel sulfate solution is obtained with ease. The method uses a multi-stage, counter-current, organic solvent extraction system composed of at least two extractors as connected in series, and comprises a first extraction step of feeding a crude nickel sulfate solution that contains impurities of essentially sodium and ammonium into a second-stage extractor, followed by processing therein the crude nickel sulfate solution with an organic extractant having been fed into the second-stage extractor from the first-stage extractor, within a pH range falling between 6.5 and 7.0 in a manner of counter-current extraction reaction therebetween to thereby make a part of nickel existing in the crude nickel sulfate solution extracted out into the organic extractant; and a second extraction step of transferring the nickel-containing, organic phase to an organic phase-scrubbing step of scrubbing it to remove sodium and ammonium from the thus-transferred, nickel-containing organic phase, while transferring the crude nickel sulfate solution, which has been processed in the first extraction step and from which a part of nickel has been removed, to the first-stage extractor, followed by further processing therein the thus-transferred crude nickel sulfate solution with a fresh organic extractant, within a pH range falling between 5.5 and 6.5 in a manner of counter-current extraction reaction therebetween to thereby make the remaining part of nickel still existing in the crude nickel sulfate solution extracted out into the organic extractant. In the method, the nickel-containing organic phase as separated in the second extraction step is divided into two portions, and one of these portions is used as the organic extractant to be fed into the second-stage extractor while the other is transferred to a by-pass, organic phase-scrubbing step of scrubbing it to remove sodium and ammonium from the thus-transferred, nickel-containing organic phase.