SOLVENT-EXTRACTION OF TRIVALENT YTTRIUM, HOLMIUM, AND ERBIUM BY NOVELTYPES OF ACIDIC ORGANOPHOSPHONATES

New types of acidic organophosphonates, HR with different hydrophobic groups, were synthesized in order to investigate their extraction beha vior for heavy rare earth elements (Y3+, Ho3+, and Er3+) from aqueous acidic chloride media. Their physicochemical properties, such as aggre gation in an organic diluent and the acid dissociation constants (K(a) ) in the aqueous phase, were examined. These rare earth elements were supposed to be extracted according to the stoichiometric relation, M3 + 3(HR)2 half arrow right over half arrow left MR3.3HR + 3H+. This id ea and the extraction equilibrium constants (K(ex)) for each metal ion were evaluated. Both the extraction equilibrium constants and the sep aration factors (beta) between these metal ions were found to be great er than those of commercial extractants. The correlation between the e xtractability of heavy rare earth elements, the selectivity among thes e elements and the chemical structures of these extractants are discus sed from a qualitative perspective.