Cd(II) extraction in PEG (1550)-(NH4)2SO4 aqueous two-phase systems using halide extractants

Abstract

The extraction of Cd(II) was studied in an aqueous PEG-(NH 4)2SO4 two-phase system, formed from a water-soluble polymer (poly(ethylene glycol), PEG) and an inorganic salt ((NH4)2SO4), in the presence of halide ions. In the absence of a suitable extracting agent, Cd(II) remains predominantly in the salt-rich phase of the extraction system. By addition of halide ions as extractants, Cd(II) is extracted into the PEG-rich phase due to the formation of cadmium halide species. The efficiency of the extractants increased in the order: Cl- < Br- < I-. From the distribution coefficients determined as a function of the concentration of the halide ions, the compositions of the extracted species were assumed and the "conditional" extractions constants calculated. The experimental results indicate that the extractability of Cd(II) in such extraction systems depends on the type of Cd(II) halide species (which is mainly determined by the acidity of salt stock solution) and of their stability.