Selective separation of cobalt and nickel using a stable supported ionic liquid membrane

The selective separation of cobalt from nickel is of major importance for the recovery of cobalt from primary or secondary sources, as well as for analytical purposes. In this paper, the extraction of cobalt from the mixtures was examined using a supported liquid membrane employing the undiluted hydrophobic ionic liquid, namely tri (hexyl)tetradecyl phosphonium chloride [P-66614][Cl], as a carrier and polyvinylidene difluoride (PVDF) as a membrane material. In the preliminary study, the efficiency of this supported ionic liquid membrane (SILM) for the cobalt extraction was evaluated by conventional static mode sorption experiments. Up to 86% of cobalt can be recovered under optimal conditions (by contacting SILM with 9.8 cm(2) in 5 mL of aqueous phase for 1 h at 100 rpm, with 9 mol.L-1 HCl in the aqueous phase). Next, metal ion transport through a flat sheet SILM was investigated with pure water as a receiving phase. Permeation coefficients values of 2.2 x 10-6 m.s(-1) and 8.0 x 10(-6) m.s(-1) were obtained with a hydrophobic and a hydrophilic membrane, respectively. The SILM showed selectivity for cobalt over nickel with separation factors as high as 218. Membrane stability was proven to be excellent, since the same SILM was used three times without losses of performances.