{"id":{"repo_id":"wustl","oai_identifier":"oai:openscholarship.wustl.edu:etd-1323"},"canonical_url":"https://search.dev.ndltd.org/etd/wustl/oai:openscholarship.wustl.edu:etd-1323","repository":{"repo_id":"wustl","name":"Washington University in St. Louis","base_url":"https://openscholarship.wustl.edu/do/oai/"},"display":{"title":"Geochemical Conditions Affecting Uranium(VI) Fate And Transport In Soil And Groundwater In The Presence Of Phosphate","abstract":"Soil and groundwater contamination with actinides like uranium is a serious environmental concern. Phosphate addition to uranium-contaminated soil and groundwater can potentially provide long-term in-situ U(VI) immobilization by precipitation of low solubility U(VI)-phosphates. Reactions at the iron: oxy)hydroxide-water interface can control macroscopic transport and long-term stability of uranium. First, the interactions among phosphate, U(VI), and goethite: alpha-FeOOH) were investigated in a year-long batch experimental study. Dissolved U(VI) and phosphate concentrations were interpreted within a reaction-based modeling framework. U(VI) uptake mechanism varied with the aqueous composition. For most initially supersaturated conditions, chernikovite, H3O(UO2)(PO4)*3H2O(s), nucleated homogeneously, but heterogeneous nucleation probably occurred in cases of mild supersaturation. For conditions undersaturated with respect to chernikovite, phosphate-enhanced U(VI) adsorption indicated the formation of a U(VI)-phosphate-Fe(III) oxide ternary surface complex. Second, molecular-scale structures of adsorbed and precipitated U(VI) from batch experiments were probed using X-ray absorption fine-structure: XAFS) spectroscopy for different total U(VI) concentrations over a pH range 4-7 in the absence and presence of phosphate. The structure of precipitated U(VI) fit the meta-autunite group structure. While U(VI) adsorbed as bidentate edge-sharing =Fe(OH)2UO2 and bidentate corner-sharing: =FeOH)2UO2 surface complexes in the absence of phosphate, it formed a ternary surface complex: =FeO)2UO2PO4 in the presence of phosphate. Third, the effect of transport on U(VI) uptake and remobilization mechanisms and rate was examined. Continuous-flow stirred tank reactor: CFSTR) experiments at pH 4 were conducted under conditions supersaturated and undersaturated with respect to chernikovite and analyzed using a combination of measured dissolved concentrations, microscopy, and XAFS spectroscopy. The rates of dominant U(VI) and phosphate uptake and remobilization mechanisms in the absence and presence of goethite were quantified using a flow-through reactor model. Finally, the effects of simultaneous Fe(III) uptake on iron: oxy)(hydr)oxides on U(VI) and phosphate uptake and remobilization were investigated at pH 4. Goethite-coated sand packed columns and goethite-containing CFSTRs were used to simulate environmental conditions favoring the growth of iron: oxy)(hydr)oxide. While the presence of co-influent Fe(III) increased the extent and rate of phosphate uptake its presence not only decreased U(VI) uptake on goethite but also limited the formation of stable phosphate-induced uranium surface species.","abstract_html":"Soil and groundwater contamination with actinides like uranium is a serious environmental concern. Phosphate addition to uranium-contaminated soil and groundwater can potentially provide long-term in-situ U(VI) immobilization by precipitation of low solubility U(VI)-phosphates. Reactions at the iron: oxy)hydroxide-water interface can control macroscopic transport and long-term stability of uranium. First, the interactions among phosphate, U(VI), and goethite: alpha-FeOOH) were investigated in a year-long batch experimental study. Dissolved U(VI) and phosphate concentrations were interpreted within a reaction-based modeling framework. U(VI) uptake mechanism varied with the aqueous composition. For most initially supersaturated conditions, chernikovite, H3O(UO2)(PO4)*3H2O(s), nucleated homogeneously, but heterogeneous nucleation probably occurred in cases of mild supersaturation. For conditions undersaturated with respect to chernikovite, phosphate-enhanced U(VI) adsorption indicated the formation of a U(VI)-phosphate-Fe(III) oxide ternary surface complex. Second, molecular-scale structures of adsorbed and precipitated U(VI) from batch experiments were probed using X-ray absorption fine-structure: XAFS) spectroscopy for different total U(VI) concentrations over a pH range 4-7 in the absence and presence of phosphate. The structure of precipitated U(VI) fit the meta-autunite group structure. While U(VI) adsorbed as bidentate edge-sharing =Fe(OH)2UO2 and bidentate corner-sharing: =FeOH)2UO2 surface complexes in the absence of phosphate, it formed a ternary surface complex: =FeO)2UO2PO4 in the presence of phosphate. Third, the effect of transport on U(VI) uptake and remobilization mechanisms and rate was examined. Continuous-flow stirred tank reactor: CFSTR) experiments at pH 4 were conducted under conditions supersaturated and undersaturated with respect to chernikovite and analyzed using a combination of measured dissolved concentrations, microscopy, and XAFS spectroscopy. The rates of dominant U(VI) and phosphate uptake and remobilization mechanisms in the absence and presence of goethite were quantified using a flow-through reactor model. Finally, the effects of simultaneous Fe(III) uptake on iron: oxy)(hydr)oxides on U(VI) and phosphate uptake and remobilization were investigated at pH 4. Goethite-coated sand packed columns and goethite-containing CFSTRs were used to simulate environmental conditions favoring the growth of iron: oxy)(hydr)oxide. While the presence of co-influent Fe(III) increased the extent and rate of phosphate uptake its presence not only decreased U(VI) uptake on goethite but also limited the formation of stable phosphate-induced uranium surface species.","abstract_has_math":false,"creators":["Singh, Abhas"],"institution":null,"degree_name":"Doctor of Philosophy (PhD)","degree_level":"Dissertation","degree_discipline":"Energy, Environmental and Chemical Engineering","degree_department":null,"school":null,"contributors":["Daniel Giammar"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2010,"date_issued":"2010-01-01T08:00:00Z","date_published":"2010-01-01T08:00:00Z","updated_at":"2026-07-24T06:12:48Z","subjects":["Engineering","Environmental","Geochemistry","Environmental Sciences","Adsorption","Goethite","Phosphate","Precipitation","Ternary surface complex","Uranium"],"languages":["English (en)"],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.7936/K7R20ZF5"],"render_values":[{"text":"https://doi.org/10.7936/K7R20ZF5","href":"https://doi.org/10.7936/K7R20ZF5","code":true}]}]},"links":{"outbound_url":"https://openscholarship.wustl.edu/etd/324","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Daniel Giammar"]},{"key":"dc:creator","label":"Author","values":["Singh, Abhas"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2010-01-01T08:00:00Z"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Energy, Environmental and Chemical Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Engineering","Environmental","Geochemistry","Environmental Sciences","Adsorption","Goethite","Phosphate","Precipitation","Ternary surface complex","Uranium"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["English (en)"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://openscholarship.wustl.edu/etd/324"]},{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.7936/K7R20ZF5"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Soil and groundwater contamination with actinides like uranium is a serious environmental concern. Phosphate addition to uranium-contaminated soil and groundwater can potentially provide long-term in-situ U(VI) immobilization by precipitation of low solubility U(VI)-phosphates. Reactions at the iron: oxy)hydroxide-water interface can control macroscopic transport and long-term stability of uranium. First, the interactions among phosphate, U(VI), and goethite: alpha-FeOOH) were investigated in a year-long batch experimental study. Dissolved U(VI) and phosphate concentrations were interpreted within a reaction-based modeling framework. U(VI) uptake mechanism varied with the aqueous composition. For most initially supersaturated conditions, chernikovite, H3O(UO2)(PO4)*3H2O(s), nucleated homogeneously, but heterogeneous nucleation probably occurred in cases of mild supersaturation. For conditions undersaturated with respect to chernikovite, phosphate-enhanced U(VI) adsorption indicated the formation of a U(VI)-phosphate-Fe(III) oxide ternary surface complex. Second, molecular-scale structures of adsorbed and precipitated U(VI) from batch experiments were probed using X-ray absorption fine-structure: XAFS) spectroscopy for different total U(VI) concentrations over a pH range 4-7 in the absence and presence of phosphate. The structure of precipitated U(VI) fit the meta-autunite group structure. While U(VI) adsorbed as bidentate edge-sharing =Fe(OH)2UO2 and bidentate corner-sharing: =FeOH)2UO2 surface complexes in the absence of phosphate, it formed a ternary surface complex: =FeO)2UO2PO4 in the presence of phosphate. Third, the effect of transport on U(VI) uptake and remobilization mechanisms and rate was examined. Continuous-flow stirred tank reactor: CFSTR) experiments at pH 4 were conducted under conditions supersaturated and undersaturated with respect to chernikovite and analyzed using a combination of measured dissolved concentrations, microscopy, and XAFS spectroscopy. The rates of dominant U(VI) and phosphate uptake and remobilization mechanisms in the absence and presence of goethite were quantified using a flow-through reactor model. Finally, the effects of simultaneous Fe(III) uptake on iron: oxy)(hydr)oxides on U(VI) and phosphate uptake and remobilization were investigated at pH 4. Goethite-coated sand packed columns and goethite-containing CFSTRs were used to simulate environmental conditions favoring the growth of iron: oxy)(hydr)oxide. While the presence of co-influent Fe(III) increased the extent and rate of phosphate uptake its presence not only decreased U(VI) uptake on goethite but also limited the formation of stable phosphate-induced uranium surface species."]},{"key":"dc:title","label":"Title","values":["Geochemical Conditions Affecting Uranium(VI) Fate And Transport In Soil And Groundwater In The Presence Of Phosphate"]}]}],"canonical_facts":{"dc:contributor":["Daniel Giammar"],"dc:creator":["Singh, Abhas"],"dc:date.available":["2010-01-01T08:00:00Z"],"dc:description.abstract":["Soil and groundwater contamination with actinides like uranium is a serious environmental concern. Phosphate addition to uranium-contaminated soil and groundwater can potentially provide long-term in-situ U(VI) immobilization by precipitation of low solubility U(VI)-phosphates. Reactions at the iron: oxy)hydroxide-water interface can control macroscopic transport and long-term stability of uranium. First, the interactions among phosphate, U(VI), and goethite: alpha-FeOOH) were investigated in a year-long batch experimental study. Dissolved U(VI) and phosphate concentrations were interpreted within a reaction-based modeling framework. U(VI) uptake mechanism varied with the aqueous composition. For most initially supersaturated conditions, chernikovite, H3O(UO2)(PO4)*3H2O(s), nucleated homogeneously, but heterogeneous nucleation probably occurred in cases of mild supersaturation. For conditions undersaturated with respect to chernikovite, phosphate-enhanced U(VI) adsorption indicated the formation of a U(VI)-phosphate-Fe(III) oxide ternary surface complex. Second, molecular-scale structures of adsorbed and precipitated U(VI) from batch experiments were probed using X-ray absorption fine-structure: XAFS) spectroscopy for different total U(VI) concentrations over a pH range 4-7 in the absence and presence of phosphate. The structure of precipitated U(VI) fit the meta-autunite group structure. While U(VI) adsorbed as bidentate edge-sharing =Fe(OH)2UO2 and bidentate corner-sharing: =FeOH)2UO2 surface complexes in the absence of phosphate, it formed a ternary surface complex: =FeO)2UO2PO4 in the presence of phosphate. Third, the effect of transport on U(VI) uptake and remobilization mechanisms and rate was examined. Continuous-flow stirred tank reactor: CFSTR) experiments at pH 4 were conducted under conditions supersaturated and undersaturated with respect to chernikovite and analyzed using a combination of measured dissolved concentrations, microscopy, and XAFS spectroscopy. The rates of dominant U(VI) and phosphate uptake and remobilization mechanisms in the absence and presence of goethite were quantified using a flow-through reactor model. Finally, the effects of simultaneous Fe(III) uptake on iron: oxy)(hydr)oxides on U(VI) and phosphate uptake and remobilization were investigated at pH 4. Goethite-coated sand packed columns and goethite-containing CFSTRs were used to simulate environmental conditions favoring the growth of iron: oxy)(hydr)oxide. While the presence of co-influent Fe(III) increased the extent and rate of phosphate uptake its presence not only decreased U(VI) uptake on goethite but also limited the formation of stable phosphate-induced uranium surface species."],"dc:identifier":["https://openscholarship.wustl.edu/etd/324"],"dc:identifier.doi":["https://doi.org/10.7936/K7R20ZF5"],"dc:language":["English (en)"],"dc:subject":["Engineering","Environmental","Geochemistry","Environmental Sciences","Adsorption","Goethite","Phosphate","Precipitation","Ternary surface complex","Uranium"],"dc:title":["Geochemical Conditions Affecting Uranium(VI) Fate And Transport In Soil And Groundwater In The Presence Of Phosphate"],"thesis:degree_discipline":["Energy, Environmental and Chemical Engineering"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T06:12:48Z"}