Synergistic Effects in Separation of Cobalt(II) and Lithium(I) from Chloride Solutions by Cyphos IL-101 and TBP

This work reports on the extraction and separation of Co(II) and Li(I) ions from chloride solutions using a synergistic mixture, namely Cyphos IL 101 (trihexyl(tetradecyl)phosphonium chloride[R4PCl] and TBP (tributylphosphate). This system has not been described up to now. The aim of this research was to compare the extraction efficiency (%E) and the extraction selectivity of Co(II) over Li(I) (SCo/Li) using single extractants and their equimolar mixture. Co(II) extraction with Cyphos IL 101 and TBP depends strongly on hydrochloric acid concentration in the aqueous phase. The separation coefficient of the studied metal ions was determined depending on the hydrochloric acid concentrations in the aqueous phase. The significance of the work is in the examination of the re-extraction of cobalt(II) from the organic phase after extraction. For this purpose, inorganic acids were investigated as the stripping agents, i.e., HCl (hydrochloric acid), H2SO4 (sulfuric acid) and HNO3 (nitric acid). Finally, optimal conditions for the separation of Co(II) and Li(I) were established by using a synergistic mixture. A highly selective and effective solvent extraction of cobalt(II) over lithium(I) from 5 mol∙dm−3 hydrochloric acid has been achieved with the synergistic mixture of 0.1 mol∙dm−3 Cyphos IL 101 and 0.1 mol∙dm−3 TBP in kerosene. The selectivity coefficients of Co(II) over Li(I) (CCo/Li) in the solvent extraction with 0.1 mol∙dm−3 Cyphos IL 101, 0.1 mol∙dm−3 TBP, and with their equimolar mixture were found to be equal: 73.1, 3.7 and 225.5, respectively. Efficient Co(II) stripping was achieved using 0.5 mol∙dm−3 sulfuric acid.