The extraction of Cr(III) from aqueous thiocyanate solutions and its separation from Co(II) and Ni(II)

For the system liquid anion-exchanger—Cr(III)−NCS⁻, an investigation has been made of the dependence of the percentage extraction of Cr(III) on parameters such as standing time of the Cr(III)−NCS⁻ solution, temperature, pH and type of exchanger. Quantitative extraction of e.g. 4·10⁻⁴ M Cr(III) by 0.1M Aliquat in CCl₄ is easily achieved at room temperature, using 4.75M KNCS−0.05N HCl as aqueous phase. At high Cr(III) concentrations, the complex anion present in the organic phase is Cr(NCS) ₆ ³⁻ ; when working with dilute metal ion solutions, the species extracted is Cr(NCS)₄ (H₂O) ₂ ⁻ . Separations of mixtures containing 10⁻²−10⁻⁴ M Co(II), Ni(II) and Cr(III) have successfully been accomplished.