Comparative Studies on the Solvent Extraction of Pd(II) Using Alkane-1,ω-diyl Bis(O,O-diisobutyl phosphorodithioate)s

Article abstract of DOI:10.1246/bcsj.70.601

A series of new bis-type derivatives of O,O-diisobutyl phosphorodithioate, namely, the alkane-1,ω-diyl bis(O,O-diisobutyl phosphorodithioate)s (ADBDiBPDT), were synthesized for use in the solvent extraction of precious metals. These compounds having the general formula (i-BuO)₂P(S)S(CH₂)_nS(S)P(Oi-Bu)₂, have considerable selectivity for extraction 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 increase in the length of the alkane-1,ω-diyl chain (n = 1 - 4), joining the two phosphorodithioate groups in the bis-structure. The extraction of palladium(II) from 1.0 M chloride solution at pH 3 in 1,2-dichloroethane (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 displacement in PdCl₄^2- species. When compared with the monofunctional triisobutylphosphine 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 ADBDiBPDT series acting as bidentate ligands are also characterized by better stripping properties compared with those of the monodentate sulfur ligands. The metal loading capability, the extraction constants, and the kinetic properties of palladium extraction using these reagents are discussed.