Phosphoric acid actinides, effect

Di(2-ethylhexyl) phosphoric acid (HDEHP) is an extractant molecule used for An(III)/Ln(III) separation. Used in TALSPEAK-type processes in a mixture with TBP, or in the DIAMEX-SANEX process in a mixture with a malonamide (154-157), it has also been proposed, in a mixture with TBP, to remove strontium from PUREX acid waste solution in the Hanford B plant (158). Therefore, numerous studies have focussed on the radiolytic degradation of HDEHP and its effects on the extraction of Sr(II), lanthanides(III), and actinides(III) (10, 158-163). 

Another possibility is to take advantage of the effect of various supporting electrolytes (in a wide sense) that act as luminescence enhancers, as discussed in sect. 3.3, such as phosphoric acid. This method has been investigated in details both for lanthanides and actinides... 

The addition of an ether linkage in the alkyl chains of dialkylphosphoric acids has been found to increase its extractive power for trivalent actinides, resulting in an extractant that is more effective from acid solutions than is HDEHP (69). Bis(hexoxy-ethyl)phosphoric acid (HDHqEP) is a compound of this type that has been studied extensively (70,71). The ether linkage may contribute to the coordination of the metal ion, resulting in the formation of a seven-membered ring. 

The results obtained by Ansari etal. (2007) and by Singh et a/. (2010) suggest that the separation of minor actinides and U(VI) from the HLW solutions and phosphoric acid medium, respectively, is technically feasible as application of SLM. Despite the encouraging results described in this section, in order to effectively use the SLM system for the separation of metal ions from HLW, it is fundamental to consider the problems related to the radiol)dic stability of the liquid membrane phase. 

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