Selective separation of cadmium from cobalt, copper, iron (III) and zinc by water-based two-phase system of tetrabutylammonium bromide

An aqueous two-phase system of tetrabutylammonim. bromide (TBAB) and (NH4)2SO4mixture is proposed for the selective extraction of trace Cd2+ from large amounts of Co2+, Cu2+, Fe3+ and Zn2+. Transparent two-phase system is prepared by mixing 3 ml of 1.0 mol/l TBAB, and 2 ml of sample solution and 1.1g of (NH4)2SO4, the two-phase system thus obtained is of 1.5 ml upper phase and 4.1 ml bottom phase. TBAB was distributed between the upper and bottom phases respectively, but the concentration in upper phase is much higher than that of the bottom phase. The results showed that Cd2+ is selectively extracted into the upper phase in the pH ranges 1.0–9.0, while Co2+ Cu2+ and Fe3+ ions were little extracted (<1%) at pH 3.0. Zinc ion was extracted to upper phase by about 24%, but it did not interfere the extraction of Cd2+. The interaction between CdBr42− and TBA+ plays an important role in the extraction process.