Spectrophotometric and Calorimetric Studies of U(VI) Complexation with Sulfate at 25-70oC

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Sulfate, one of the inorganic constituents in the groundwater of nuclear waste repository, could affect the migration of radioactive materials by forming complexes. Spectrophotometric and microcalorimetric titrations were performed to identify the U(VI)/sulfate complexes and determine the equilibrium constants and enthalpy of complexation at 25-70 C. Results show that U(VI) forms moderately strong complexes with sulfate, i.e., UO{sub 2}SO{sub 4}(aq) and UO{sub 2}(SO{sub 4}){sub 2}{sup 2-}, in this temperature range and the complexes become stronger as the temperature is increased: 2-fold and 10-fold increases in the stability constants of UO{sub 2}SO{sub 4}(aq) and UO{sub 2}(SO{sub 4}{sub 2}{sup 2-}), respectively, when ... continued below

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Tian, Guoxin & Rao, Linfeng October 30, 2008.

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Sulfate, one of the inorganic constituents in the groundwater of nuclear waste repository, could affect the migration of radioactive materials by forming complexes. Spectrophotometric and microcalorimetric titrations were performed to identify the U(VI)/sulfate complexes and determine the equilibrium constants and enthalpy of complexation at 25-70 C. Results show that U(VI) forms moderately strong complexes with sulfate, i.e., UO{sub 2}SO{sub 4}(aq) and UO{sub 2}(SO{sub 4}){sub 2}{sup 2-}, in this temperature range and the complexes become stronger as the temperature is increased: 2-fold and 10-fold increases in the stability constants of UO{sub 2}SO{sub 4}(aq) and UO{sub 2}(SO{sub 4}{sub 2}{sup 2-}), respectively, when the temperature is increased from 25 C to 70 C. The complexation is endothermic and entropy-driven, showing typical characteristics of inner-sphere complexation and 'hard acid'/'hard base' interactions. The thermodynamic trends are discussed in terms of dehydration of both the cation (UO{sub 2}{sup 2+}) and the anion (SO{sub 4}{sup 2-}) as well as the effect of temperature on the structure of water.

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  • Journal Name: Journal of Chemical Thermodynamics

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  • Report No.: LBNL-1408E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 959416
  • Archival Resource Key: ark:/67531/metadc932696

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  • October 30, 2008

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  • Nov. 13, 2016, 7:26 p.m.

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  • Nov. 18, 2016, 3:58 p.m.

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Tian, Guoxin & Rao, Linfeng. Spectrophotometric and Calorimetric Studies of U(VI) Complexation with Sulfate at 25-70oC, article, October 30, 2008; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc932696/: accessed September 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.