EXTRACTION OF ALKALINE EARTH AND ACTINIDE CATIONS BY MIXTURES OF DI(2-ETHYLHEXYL) ALKYLENEDIPHOSPHONIC ACIDS AND NEUTRAL SYNERGISTS

Abstract

ABSTRACT The synergistic extraction of alkaline earth (Ca2+, Sr2+, Ba2+ and Ra2+) and actinide (Am3+, UO2 2+ and Th4+) cations from aqueous nitric acid solutions by mixtures of P,P′-di(2-ethylhexyl) methylene-(H2DEH[MDP]), ethylene-(H2DEH[EDP]), and butylene-(H2DEH[BuDP]) diphosphonic acids and neutral extractants in o-xylene has been investigated. The cis-syn-cis and cis-anti-cis stereoisomers of dicyclohexano-18-crown-6 (DCH18C6), the unsubstituted 21-crown-7 (21C7) and dicyclohexano-21-crown-7 (DCH21C7) were used as neutral synergists of the crown ether type. For Am(III) synergistic effects were also investigated using neutral organophosphorus esters, such as, tri-n-butylphosphate (TBP), diamyl amylphosphonate (DA[AP]) and tri-n-octylphosphine oxide (TOPO) as co-extractants. In all systems investigated, no synergistic extraction enhancement was observed for actinide ions. For the alkaline earth cations, synergistic effects were only observed when mixtures of H2DEH[EDP] or H2DEH-[BuDP] with DCH18C6 were used to extract Sr2+, Ba2+ and Ra2+. No synergistic effects were observed for the extraction of alkaline earth cations by H2DEH[MDP] or for the extraction of Ca2+ by any of the diphosphonic acids studied. The synergistic effects obtained with DCH18C6 were significantly higher for the cis-syn-cis than for the cis-anti-cis stereoisomer.