Changes in Uranium Speciation through a Depth Sequence of Contaminated Hanford Sediments

• Published in: Environmental science & technology Vol. 40; no. 8; pp. 2517 - 2524
• Main Authors: Catalano, Jeffrey G, McKinley, James P, Zachara, John M, Heald, Steve M, Smith, Steven C, Brown, Gordon E
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15-04-2006
• Subjects: Adsorption; Applied sciences; CALCITE; CLAYS; Contaminated sediments; COPRECIPITATION; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; GEOCHEMISTRY; Geologic Sediments - analysis; GROUND WATER; Groundwater; Groundwater pollution; Groundwaters; HANFORD RESERVATION; MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; Natural water pollution; Phosphates - analysis; Phosphates - chemistry; Pollution; Pollution, environment geology; Ponds; Radioactive Waste; RADIOACTIVE WASTE DISPOSAL; Radioactive wastes; RADIONUCLIDE MIGRATION; SEDIMENTS; SETTLING PONDS; Sorption; Uranium; Uranium - analysis; Uranium - chemistry; URANIUM COMPOUNDS; Uranium Compounds - analysis; Uranium Compounds - chemistry; Washington; Wastes; Water Pollutants, Radioactive - analysis; Water treatment and pollution; United States; North America; Washington; America; USA, Washington, Hanford; USA, Washington, Hanford Site; Radioactive waste; Radioactive pollution; Pollutant behavior; Geochemistry; Mobility; Hazardous waste; Liquid waste; Plume; Radioisotope; Heavy metal; Unsaturated zone; Depth profile; Nuclear installation; Uranium VI; Water pollution; Speciation; Ground water
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es0520969

The disposal of basic sodium aluminate and acidic U(VI)−Cu(II) wastes in the now-dry North and South 300 A Process Ponds at the Hanford site resulted in a groundwater plume of U(VI). To gain insight into the geochemical processes that occurred during waste disposal and those affecting the current and future fate and transport of this uranium plume, the solid-phase speciation of uranium in a depth sequence of sediments from the base of the North Process Pond through the vadose zone to groundwater was investigated using standard chemical and mineralogical analyses, electron and X-ray microprobe measurements, and X-ray absorption fine structure spectroscopy. Near-surface sediments contained uranium coprecipitated with calcite, which formed due to overneutralization of the waste ponds with base (NaOH). At intermediate depths in the vadose zone, metatorbernite [Cu(UO2PO4)2·8H2O] precipitated, likely during pond operations. Uranium occurred predominantly sorbed onto phyllosilicates in the deeper vadose zone and groundwater; sorbed uranium was also an important component at intermediate depths. Since the calcite-bearing pond sediments have been removed in remediation efforts, uranium fate and transport will be controlled primarily by desorption of the sorbed uranium and dissolution of metatorbernite.