Temperature effects in the extraction of metal ions by dialkyl-substituted diphosphonic acids. Part 1 : The Am(III) case.
The extraction of Am(III) from HNO{sub 3} by o-xylene solutions of P,P'-di(2-ethylhexyl) methylene- (H{sub 2}DEH[MDP]), ethylene- (H{sub 2}DEH[EDP]), and butylene- (H{sub 2}DEH[BuDP]) diphosphonic acids has been investigated. Thermodynamic parameters of the extraction process were determined by the temperature coefficient of the metal distribution ratio in the 25.0 to 60.0 {sup o}C temperature range. The extractant aggregation and the extraction stoichiometries with the different diphosphonic acids did not exhibit any significant temperature dependence. Extraction of Am(III) by H{sub 2}DEH[MDP] is favored by both enthalpy and entropy variations. When Am(III) is extracted by either H{sub 2}DEH[EDP] or H{sub 2}DEH[BuDP] the process is entropy controlled. The enthalpy variation for Am(III) extraction exhibited a trend along the series H{sub 2}DEH[MDP], H{sub 2}DEH[EDP], H{sub 2}DEH [BuDP], with the reaction being exothermic for the first, thermoneutral for the second, and endothermic for the third extractant, respectively. This trend was explained as arising from the formation of progressively less stable chelate rings along the diphosphonic acids series. The zero or positive enthalpy variation with a concomitant favorable entropy variation confirm for H{sub 2}DEH[EDP] and possibly for H{sub 2}DEH[BuDP] a micellar-like type of extraction process.
- Research Organization:
- Argonne National Laboratory (ANL)
- Sponsoring Organization:
- SC
- DOE Contract Number:
- AC02-06CH11357
- OSTI ID:
- 943242
- Report Number(s):
- ANL/CHM/JA-38565
- Journal Information:
- Solvent Extr. Ion Exch., Journal Name: Solvent Extr. Ion Exch. Journal Issue: 5 ; 2001 Vol. 19; ISSN 0736-6299; ISSN SEIEDB
- Country of Publication:
- United States
- Language:
- ENGLISH
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