Americium diluent effects, extraction

Srinivasan, T.G., Vasudeva Rao, P.R., Sood, D.D. 1998. Diluent and extractant effects on the enthalpy of extraction of uranium(VI) and americium(in) nitrates by trialkyl phosphates. Solvent Extraction and Ion Exchange 16(6) 1369-1387. 

On the other hand, Dyrssen and Liem (1960) report (table 7) greater variation in both distribution ratios [for americium and europium extraction by dibutyl phosphoric acid (HDBP)] and in separation factors as a function of diluent. The separation factors and distribution coefficients are correlated (more or less consistently) inversely with the distribution ratio of the extractant between the phases. In this system, the largest separation factors are observed in n-hexane, chloroform, and carbon tetrachloride. Diluents capable of direct coordination (i.e., those possessing potential oxygen-donor atoms) are correlated with reduced distribution ratios and separation factors. The observations of greater separation factors in non-complexing diluents suggest that more effective separation is observed when the inner-coordination sphere of the hydrophobic complex is not disturbed. 

Most of the studies focused on the influence of CMPO radiolysis on two important steps of the TRUEX process for americium recovery extraction and stripping. The effect of radiolysis on CMPO-diluent solutions was extremely different under these two process conditions (see Table 8.5), with a major increase in Z)Am values at pH 2, but a moderate decrease for 2-3 mol L 1 HN03. 

In a recent study, Retegan compared the radiolytic stability of C5-BTBP and CyMe4-BTBP in hexanol or in cyclohexanone (242). No protective effect of a cyclic diluent was observed on europium extraction, whereas surprising results were obtained with americium. The behavior needs to be more precisely defined. 

For the removal of americium from nuclear waste streams, Muscatello and Navratil (61) employed dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP) as the extractant without a diluent in a supported liquid membrane. They removed more than 95% of americium from the waste streams. The DHDECMP extractant and a surfactant, e.g., SPAN 80 or LMS-2, with 0.25M oxalic acid as the internal phase could constitute an effective ELM system for americium removal. 

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