Synthesis of N-2-Ethylhexylurea and Its Selective Extraction Equilibria of Palladium(II) and Gold(III)

N-2-Ethylltexylurea (EHU) was synthesized to develop a selective extractant for precious metals over base metals and to separate individual precious metals. The extraction selectivity for precious metals from hydrochloric acid was investigated using EHU in chloroform at 303 K. EHU exhibited a high selectivity for gold(III) and palladium(II) over base metals such as copper(II), mercury(II), nickel(II), cadmium(II), zinc(II), cobalt(II) and iron(III). Furthermore, gold(III) was extracted selectively over palladium(II) at high hydrochloric acid concentrations. In order to understand the high selectivity, the extraction equilibria of palladium(II) and gold(III) were quantitatively studied by examining the concentration dependence of chloride and hydrogen ions on the extraction equilibria. Stripping of palladium(II) and gold(III) were performed by a single contact batch method using I mol dm(-3) aqueous thiourea solution or 1 mol dm(-3) aqueous thiourea solution containing 1 mol dm(-3) hydrochloric acid.