The distribution behavior of iodide complex of Cd(II) in the propyl-alcohol ammonium sulfate aqueous biphasic extraction systems was experimentally investigated in this study. In the presence of NH4I and HCl medium, Cd(II) was found to be extracted into the propyl-alcohol phase as a result of the formation of ion pair [CdI42-.(PrOH2+)(2)]. The experimental results indicated that cadmium can be quantitatively extracted by the proposed method, and an extraction percentage of 99.2% can be achieved under the suggested optimal extraction conditions. The potential applications of the proposed method to the separation of cadmium from base metals, such as Fe2+, Ca2+, Mg2+, Mn2+, Al3+, Pb2+ and Zn2+ in synthetic samples, and to the separation of cadmium from Cd contaminated soils were also investigated in this work. (C) 2005 Elsevier B.V. All rights reserved.