Recovery of uranium (VI) from concentrated phosphoric acid by mixtures of new bis(1,3- dialkyloxypropan-2-yl) phosphoric acids and tri-n-octylphosphine oxide

Three new extractants, namely bis(1,3-dihexyloxypropan-2-yl) phosphoric acid, bis(1,3-dioctyloxypropan-2-yl) phosphoric acid and bis(1,3-di-2-ethylhexyloxypropan-2-yl) phosphoric acid, were synthesized and tested in mixture with tri-n-octyl phosphine oxide (TOPO) in Isane IP 185 for the recovery of uranium (VI) from 5.3 mol L− 1 synthetic phosphoric acid and 30% wt P2O5 industrial wet phosphoric acid. The results were compared with those previously obtained with bis(1,3-dibutoxypropan-2-yl) phosphoric acid (BiDiBOPP), under similar experimental conditions. The increase of the length of the alkyloxy chains of bis(1,3-dialkyloxypropan-2-yl) phosphoric acid is responsible for an increase of the distribution coefficients of both uranium (VI) and iron (III) whereas steric hindrance effect arising from the increase of branching improves the selectivity for uranium (VI) against iron (III). A quantitative relationship between the distribution coefficients of uranium (VI) measured for the series of 7 extractants and two molecular descriptors has been developed. This opens a way for computer-guided design of new phosphoryl-containing extractants.