COMPARATIVE-STUDIES ON THE SOLVENT-EXTRACTION OF PD(II) USING ALKANE-1,OMEGA-DIYL BIS(O,O-DIISOBUTYL PHOSPHORODITHIOATE)S

A series of new bis-type derivatives of O,O-diisobutyl phosphorodithio ate, namely, the alkane-1,omega-diyl bis(O,O-diisobutyl phosphorodithi oate)s (ADBDiBPDT), were synthesized for use in the solvent extraction of precious metals. These compounds having the general formula (i-BuO )(2)P(S)S(CH2)(n)S(S)P(Oi-Bu)(2), have considerable selectivity for ex traction of Pd(II) over Au(III), Ag(I), and Pt(IV) when extracted from 0.1 M (1 M = 1 mol dm(-3)) perchlorate, nitrate, and chloride media. The extractability of individual metal ions increases with the increas e in the length of the alkane-1,omega-diyl chain (n = 1-4), joining th e two phosphorodithioate groups in the bis-structure. The extraction o f palladium(II) from 1.0 M chloride solution at pH 3 in 1,2-dichloroet hane (DCE) proceeds through the formation of either a 1:2 (n = 1) or a 1:1 (n = 2,3,4) palladium-ligand complex involving ligand displacemen t in PdCl42- species. When compared with the monofunctional triisobuty lphosphine sulfide (TIBPS) and dihexyl sulfide (DHS), the new reagents were found to provide higher Pd(II) extraction and better extraction selectivity, under identical conditions. The higher members of the ADB DiBPDT series acting as bidentate ligands are also characterized by be tter stripping properties compared with those of the monodentate sulfu r ligands. The metal loading capability, the extraction constants, and the kinetic properties of palladium extraction using these reagents a re discussed.