The extraction of trivalent f-elements by 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) is at the core of lanthanide hydrometallurgy for recovery from minerals and in the Advanced TALSPEAK and the ALSEP processes for lanthanide/actinide separations. To broaden the state of knowledge of the basic features of HEH[EHP] interactions, the role of the organic diluent in f-elements separations has been investigated. This study presents the results of an investigation of the trivalent f-element separations by HEH[EHP] in 22 different diluents from dilute nitric acid solutions. The study used the basic techniques of liquid-liquid extraction slope analysis of selected lanthanide radiotracers (obtained by neutron activation at the WSU Nuclear Science Center) to characterize the apparent metal:extractant stoichiometry. The results demonstrate that the coefficient of extractions are impacted by the diluent effect, with a log Kex ranging from -0.29 ± 0.02 in iso-octane to -6.05 ± 0.02 in chloroform. The apparent stoichiometries of the extracted metal complex is also seen to vary over the range of LnA3(HA)2 in n-decane to LnA3(HA)4 in methyl isobutyl ketone. This solvent effect on the Kex and the stoichiometries will be discussed.

Exploring the effect of the diluent on trivalent f-element extraction by the di-alkyl acidic organophosphorus extractant HEH[EHP]

255th National Meeting (2018)

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