Computing of liquid-liquid equilibria. I. Application of a general chemical model to the extraction of uranium from phosphoric acid by a hydroxyalkyldiphosphonic acid

A microcomputer program - MODEX - has been developed to model equilibrium data for the liquid-liquid extraction of metals, even when redox equilibria and precipitation occur. The calculations, based on chemical interactions, require the total concentrations of the introduced components and the formation constants of the species as parameters. Its flexibility makes it able to treat numerous problems. However, the use of conditional constants, valid in not too different ionic media, restricts its applicability. As an illustration, the program has been applied to the analysis of potentiometric, spectrophotometric and shake-out test data relating to the solvent extraction of uranium from phosphoric acid. The new extractant investigated - a diphosphonic compound R(HO)C-(PO₃H₂)₂ where R is a C-17 alkyl group - was dissolved in a hydrocarbon diluent with octanol as modifier, and various aqueous phase parameters (Fe(II)/Fe(III) ratio, H₃PO₄ concentration) were considered.