Solvent extraction of zinc(II)- and cadmium (II)-O, O'-dialkyldithiophosphate complexes

Abstract

The extraction behavior of zinc(II) and cadmium(II) complexes of O, O'-dialkyldithiophosphate(R₂dtp^-) with chloroform was investigated in a medium with constant ionic strength at 25°C. Four kinds of R₂dtp^- were examined, i.e., dimethyl(Me₂dtp^-), diethyl(Et₂dtp^-), dipropyl(Pr₂dtp^-) and dibutyl(Bu₂dtp^-) derivatives. The distribution ratio, D, of metal ion was calculated from the extracted metal ion concentration which was determined by AAS after the oxidative decomposition of the extracted complex with an NH₄I-I₂ solution. The composition, overall formation constant(β₂), and distribution constant(K_D) of the complex extracted were determined by analyzing a logarithmic plot of D vs. [R₂dtp^-] by a curve-fitting method. The species extracted was [M(R₂dtp)₂](M=Zn, Cd) in all cases. The values of K_D increased in the order Me₂dtp^-<Et₂dtp^-<Pr₂dtp^-≈Bu₂dtp^- and the values of β₂ increased in the order Me₂dtp^-<Et₂dtp^-<Pr₂dtp^-<Bu₂dtp^-.The cadmium complex was always more stable than the corresponding zinc complex.