Nickel(II) and Cobalt(II) Extraction from Chloride Solutions with Quaternary Phosphonium Salts

Trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101), trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate (Cyphos IL 104) are used as extractants for Ni(II) and Co(II) from chloride solutions. Such a system has not been described up to now. Co(II) extraction to Cyphos IL 101 depends on HCl concentration in the feed. Co(II) extraction with Cyphos IL 104 is the most efficient (> 95%) for feed without HCl. UV/Vis spectra analysis is employed to explain the extraction of both metal ions. Co(II), extracted from acidic HCl solutions, forms in the organic phase tetrahedral anionic complexes that allow phosphonium salts easily to form (R3R'P)HCoCl4. However, Co(II) extraction with Cyphos IL 104 from feed without HCl proceeds according to another mechanism - cation exchange - resulting in CoA(2) formation. Successful separation of Co(II) over Ni(II) is achieved with Cyphos IL 104.