DERIVATIVES OF IMIDOPYROPHOSPHORIC ACIDS AS EXTRACTANTS .6. DETERMINATION OF METAL-ION EXTRACTION MECHANISM OF N,N-N',N'-OCTABUTYLIMIDODIPHOSPHOTETRAMIDE BY POTENTIOMETRY

Extraction of tri-, tetra- and hexavalent metal ions by N,N-N',N'-octa butylimidodiphosphotetramide has been investigated. Imidodiphosphoryl extractants show promise for treatment of nuclear waste but the optimu m extractant structure must still be determined. Extraction of rare ea rths was investigated using two-phase potentiometric titrations as the more conventional slope analysis techniques could not be applied. The data thus obtained were analysed by the ESTA library of programs whic h was designed for modeling solution equilibria in aqueous phases. Res ults obtained showed that ESTA may be used for modeling two-phase syst ems providing corrections are made. Models were obtained for the extra ction of Nd(III), Eu(III), Y(III) and Yb(III). Extraction equilibrium constants could be calculated as well as distribution ratios showing t hat imidodiphosphoryl extractants are promising as rare earth extracta nts. Extraction mechanisms were complicated with a number of species b eing formed proving that traditional slope analysis techniques for mec hanistic determination would not have been successful here.