Effect of citric acid on uranyl(VI) solution speciation, gas-phase chemistry and surface interactions with alumina

Persistent Link:
http://hdl.handle.net/10150/280730
Title:
Effect of citric acid on uranyl(VI) solution speciation, gas-phase chemistry and surface interactions with alumina
Author:
Pasilis, Sofie Portia
Issue Date:
2004
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Activities related to nuclear weapons production have left a legacy of uranium contamination in the United States. Understanding the chemical interactions that uranium undergoes in the environment is important for prediction of uranium mobility and development of remediation strategies. A detailed spectroscopic examination of the pH-dependent behavior of the UO₂²⁺-citrate system in aqueous solution was completed using Raman, ATR-FTIR, and NMR spectroscopies, combined with ESI-MS. Three structurally-distinct UO₂²⁺-citrate complexes, {(UO₂)₂Cit2}²⁻, {(UO₂)₃Cit₃}³⁻, and (UO₂)₃Cit₂ exist in dynamic equilibrium over a pH range from 2 to 9. ¹⁷O and ¹³C NMR data confirm the previously published structure of {(UO₂)₂Cit₂}²⁻ and indicate that {(UO₂)₃Cit₃}³⁻ is a symmetric, fluxional molecule. The (UO₂)₃Cit₂ complex was found to have a rigid structure and two structural isomers. Chemical interactions of U(VI), citric acid and Al₂O₃ were investigated using ATR-FTIR spectroscopy to examine how complexation of U(VI) by citrate affects adsorption of U(VI) to Al₂O₃. Participation in UO₂²⁺-citrate complexes does not significantly affect the ability of citrate to chemisorb to Al₂O₃. The UO₂²⁺-citrate complexes dissociate upon adsorption, with hydrolysis of UO₂²⁺. Adsorption isotherms developed from ATR-FTIR data indicate enhanced citrate adsorption to Al₂O₃ in the presence of UO₂²⁺ , suggesting that UO₂²⁺ acts as a central link between two citrate ligands, one of which is complexed to Al₂O₃. UO₂²⁺-citrate complexes can physisorb to citrate-saturated Al₂O₃. This study demonstrates how an in-depth infrared spectroscopic analysis of UO₂²⁺-ligand complexes both in solution and adsorbed to oxide surfaces can be used to understand the adsorption mechanisms of these complexes. ESI-MS was investigated for the characterization of U(VI) species in groundwater. Both ion trap and FTICR instruments were used. UO₂²⁺ forms complexes with ligands such as acetate, trifluoroacetate, and nitrate, which readily react with CH₃CN, CH₃OH, and H₂O to form solvated gas-phase species of the form [(UO₂L)Sn]⁺, where L represents the ligand, S represents solvent, and 1 ≤ n ≤ 4. n is directly related to the number of available coordination sites on UO₂²⁺, providing insight into the coordination environment of UO₂²⁺. Solvent exchange and addition reactions readily occur. UO₂²⁺ also forms coordinately saturated negatively-charged complexes with nitrate. UO₂²⁺-carbonate complexes were also investigated.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Geochemistry.; Chemistry, Inorganic.; Geochemistry.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Pemberton, Jeanne E.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleEffect of citric acid on uranyl(VI) solution speciation, gas-phase chemistry and surface interactions with aluminaen_US
dc.creatorPasilis, Sofie Portiaen_US
dc.contributor.authorPasilis, Sofie Portiaen_US
dc.date.issued2004en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractActivities related to nuclear weapons production have left a legacy of uranium contamination in the United States. Understanding the chemical interactions that uranium undergoes in the environment is important for prediction of uranium mobility and development of remediation strategies. A detailed spectroscopic examination of the pH-dependent behavior of the UO₂²⁺-citrate system in aqueous solution was completed using Raman, ATR-FTIR, and NMR spectroscopies, combined with ESI-MS. Three structurally-distinct UO₂²⁺-citrate complexes, {(UO₂)₂Cit2}²⁻, {(UO₂)₃Cit₃}³⁻, and (UO₂)₃Cit₂ exist in dynamic equilibrium over a pH range from 2 to 9. ¹⁷O and ¹³C NMR data confirm the previously published structure of {(UO₂)₂Cit₂}²⁻ and indicate that {(UO₂)₃Cit₃}³⁻ is a symmetric, fluxional molecule. The (UO₂)₃Cit₂ complex was found to have a rigid structure and two structural isomers. Chemical interactions of U(VI), citric acid and Al₂O₃ were investigated using ATR-FTIR spectroscopy to examine how complexation of U(VI) by citrate affects adsorption of U(VI) to Al₂O₃. Participation in UO₂²⁺-citrate complexes does not significantly affect the ability of citrate to chemisorb to Al₂O₃. The UO₂²⁺-citrate complexes dissociate upon adsorption, with hydrolysis of UO₂²⁺. Adsorption isotherms developed from ATR-FTIR data indicate enhanced citrate adsorption to Al₂O₃ in the presence of UO₂²⁺ , suggesting that UO₂²⁺ acts as a central link between two citrate ligands, one of which is complexed to Al₂O₃. UO₂²⁺-citrate complexes can physisorb to citrate-saturated Al₂O₃. This study demonstrates how an in-depth infrared spectroscopic analysis of UO₂²⁺-ligand complexes both in solution and adsorbed to oxide surfaces can be used to understand the adsorption mechanisms of these complexes. ESI-MS was investigated for the characterization of U(VI) species in groundwater. Both ion trap and FTICR instruments were used. UO₂²⁺ forms complexes with ligands such as acetate, trifluoroacetate, and nitrate, which readily react with CH₃CN, CH₃OH, and H₂O to form solvated gas-phase species of the form [(UO₂L)Sn]⁺, where L represents the ligand, S represents solvent, and 1 ≤ n ≤ 4. n is directly related to the number of available coordination sites on UO₂²⁺, providing insight into the coordination environment of UO₂²⁺. Solvent exchange and addition reactions readily occur. UO₂²⁺ also forms coordinately saturated negatively-charged complexes with nitrate. UO₂²⁺-carbonate complexes were also investigated.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectGeochemistry.en_US
dc.subjectChemistry, Inorganic.en_US
dc.subjectGeochemistry.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorPemberton, Jeanne E.en_US
dc.identifier.proquest3158135en_US
dc.identifier.bibrecord.b48028629en_US
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