SOLVENT EXTRACTION PROCESS

Loss of thiocyanate ions used in solvent extraction processes is minimized by adjusting the acid concentrations of aqueous process solutions to repress substantially completely ionization of the thiocyanate and contacting the aqueous process solutions with a liquid organic solvent to incorporate the thiocyanate therein as hydrogen thiocyanate. In a specific example, cobalt is separated from a nickel process solution by contacting the process solution with an organic extractant of methyl isobutyl ketone having hydrogen thiocyanate dissolved therein. The cobalt-loaded organic extractant is stripped of its cobalt values by contact with a concentrated sulfuric acid solution, which minimizes losses of thiocyanate to the stripping solution, and produces a sulfuric acid solution containing cobalt, which can be treated to crystallize cobalt sulfate and to regenerate a concentrated sulfuric acid solution that can be recycled to the stripping operation. Concentrated sulfuric acid is added to the nickel-containing raffinate which is then contacted with the stripped organic extractant to scavenge hydrogen thiocyanate from the raffinate. The thiocyanate-free raffinate is treated for nickel and sulfuric acid recovery. (1)