Immobilization of uranium in contaminated sediments by hydroxyapatite addition
- Univ. of Georgia, Aiken, SC (United States)
Batch equilibrations were performed to investigate the ability of hydroxyapatite (Ca{sub 5}(PO{sub 4}){sub 3}OH) to chemically immobilize U in two contaminated sediment samples having different organic carbon contents. Apatite additions lowered aqueous U to near proposed drinking water standards in batch equilibrations of two distinct sediment strata having total U concentrations of 1703 and 2100 mg kg{sup {minus}1}, respectively. Apatite addition of 50 g kg{sup {minus}1} reduced the solubility of U to values less than would be expected if autunite was the controlling solid phase. A comparison of the two sediment types suggests that aqueous phase U may be controlled by both the DOC content through complexation and the equilibrium pH for a given apatite application rate. Sequential chemical extractions demonstrated that apatite amendment transfers U from more chemically labile fractions, including water-soluble, exchangeable, and acid-soluble fractions, to the Mn-occluded fraction. This suggests that apatite amendment redirects solid-phase speciation with secondary U phosphates being solubilized due to the lower pH of the Mn-occluded extractant, despite the lack of significant quantities of Mn oxides within these sediments. Energy dispersive X-ray (EDX) analysis conducted in a transmission electron microscope (TEM) confirmed that apatite amendment sequesters some U in secondary Al/Fe phosphate phases.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FC09-96SR18546
- OSTI ID:
- 318754
- Journal Information:
- Environmental Science and Technology, Vol. 33, Issue 2; Other Information: PBD: 15 Jan 1999
- Country of Publication:
- United States
- Language:
- English
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