title: Phosphate-Induced Immobilization of Uranium in Hanford Sediments.
abstract: Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred only at high initial U(VI) (>25 μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Zezhen
authors.initials: Z
authors.lastname: Pan
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Daniel E
authors.identifier: 0000-0002-4634-5640
authors.initials: DE
authors.lastname: Giammar
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Vrajesh
authors.initials: V
authors.lastname: Mehta
authors.affiliation: Department of Earth and Planetary Science, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Lyndsay D
authors.initials: LD
authors.lastname: Troyer
authors.affiliation: Department of Earth and Planetary Science, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Jeffrey G
authors.identifier: 0000-0001-9311-977X
authors.initials: JG
authors.lastname: Catalano
authors.affiliation: Department of Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Zheming
authors.initials: Z
authors.lastname: Wang
mesh_terms: D000327:Adsorption; D019015:Geologic Sediments / Q000737:chemistry*; D060587:Groundwater / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D014501:Uranium / Q000737:chemistry*; D014875:Water Pollutants, Radioactive
chemical_list: D010710:Phosphates; D014875:Water Pollutants, Radioactive; D014501:Uranium