Extraction of halide and thiocyanate complexes of cadmium by tributylphosphate from sulfuric acid solutions

Extraction of the halide and thiocyanate complexes of cadmium from H2SO4-KX solutions, where X=Cl, Br, I, or SCN, by solutions of tributyl phosphate (TBP) in benzene has been examined as a function of the acidity of the medium, halide ion and TBP concentration, and also of the temperature. Optimal conditions have been established for extraction. Cadmium is extracted as CdX2.2TBP at low halide-ion concentrations (less than or equal to 0.1 g-ion I-/liter, and less than or equal to 1 g-ion Br-, Cl-, and SCN-/liter). The extraction constants and the thermodynamic extraction characteristics of the cadmium complexes have been determined. In order of their extractability by tributyl phosphate the cadmium halide complexes follow the order: iodide > bromide > chloride > thiocyanate. Extraction of cadmium as its iodide complex by tributyl phosphate enables cadmium to be separated from indium and zinc