Metal-solvate stoichiometry evaluation in extractions by solvating type neutral extractants - A novel approach

This paper reports a novel approach for the evaluation of the stoichiometry of the metal-solvate formed during the macro level extraction of metal salts from neutral media by neutral solvating type extractants. This method involves the measurement of the distribution coefficient for the extraction of the metal ion from neutral medium as a function of the concentration of the metal ion in the organic phase, and finding the organic loading at which the distribution coefficient is a maximum. This new approach has been verified by a study of the uranyl nitrate extraction by tri-n-butyl phosphate and di-n-butyl octanamide, as well as cerium(III) nitrate extraction by TBP. In all these cases the solvation number measured by the new method was in agreement with the value reported by other techniques. The method was extended to a study of the thorium nitrate extraction by trialkyl phosphates, which yielded a solvation number of 3 for all the trialkyl phosphates studied.