Complexation of neptunium(V) by salicylate,phthalate and citrate ligands in a pH 7.5 phosphate buffered system |
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| Authors: | Terry F Rees Stephen R Daniel |
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| Institution: | Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401, U.S.A. |
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| Abstract: | Conditional stability constants, enthalpies and entropies of complexation at pH 7.5 and ionic strength 0.1 have been determined for neptunium(V) complexes of phosphate, salicylate, phthalate and citrate. Phosphate forms a complex with log β = 2.36 ± 0.42 at 25°C, ΔH°c = ? 69.9 kJ/mole and ΔS°c = ? 188 J/mole-K. At pH 7.5 salicylate does not form a complex with neptunium(V) due to the low charge density of the NpO2+ ion and incomplete ionization of the salicylate ion. Phthalate forms a complex with log β = 3.43 ± 0.33 at 25°C, ΔH°c = 33.5 kJ/mole and ΔS°c = 182 J/mole-K. Citrate forms a complex with log β = 4.84 ± 0.72 at 25°C, ΔH°c = 14.0 kJ/mole and ΔS°c = 140 J/mole-K. In all cases, only 1:1 complexes were identified. |
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| Keywords: | Author to whom correspondence should be addressed Present address: U S Geological Survey Lakewood Colorado U S A |
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