Extraction of Th(IV) as a mixed complex, nitrate or chloride, by 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate

Abstract

The extraction of Th(IV) from aqueous perchlorate, chloride and nitrate aqueous phases into a solution of an acidic phosphonate, generally represented as (GO)(G)PO(OH), dissolved in a carrier diluent is reported for the first time. Specifically, 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate, (EHO)(EH)PO(OH), dissolved in toluene has been employed as the extractant phase. From a nitrate phase, Th(IV), in tracer level concentration, is extracted as two mono-nuclear species containing one and two nitrate groups per atom of Th(IV), respectively. The extraction of the two-nitrate entity is favoured, with respect to that of the one-nitrate entity, as the acidity of the aqueous phase increases. The K for each of these species appears to be third-power dependent upon the concentration of the (EHO)(EH)PO(OH), which is dimeric in the diluent employed. The extraction of a nitrate-free entity is negligible under the conditions of the investigation. In saturation experiments, the empirical composition of the extract, as determined by gross analyses, is Th(NO 3) 1·9 (EH[EHP]) 2·2. From a chloride phase, the extract in tracer-level studies contained a chloride-free and a one-chloride species. The K values for these two species are third-power and 2·5-power extractant dependent, respectively. In saturation experiments, the empirical composition of the extract, as determined by gross analyses, is Th(Cl) 0·9(EH[EHP]) 2·9. The perchlorate behaviour parallels that of the chloride system, except that the extractant dependency is third-power. The empirical composition of the extract, in saturation experiments, is Th(ClO 4) 0·4 (EH[EHP]) 3·7.