Equilibria of Co(II) and Ni(II) extraction from sulphate solutions with Cyanex 301

The extraction equilibria of Co(II) and Ni(II) extraction from the sulphate solutions with di(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301) dissolved in an aliphatic kerosene have been studied. The obtained results prove that the stoichiometry of Co(II) and Ni(II) complexes extracted with Cyanex 301 (HA) corresponds to the following formulae CoA2(HA)2 and NiA2(HA)4, respectively.The logarithmic values of corresponding extractions constants (log Kex,Co and log Kex,Ni) are equal to 2.47±0.03 and 4.73±0.02, respectively. The observed changes of electronic absorption spectra of the organic phases containing cobalt complexes have been attributed to the oxidation of Co(II) in contact with air.