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Phosphate controls uranium release from acidic waste-weathered Hanford sediments
Angélica Vázquez-Ortega1, Nicolas Perdrial2, Estela Reinoso-Maset3
1Department of Environmental Science, University of Arizona, 1177 East Fourth Street, Tucson, ARI 85721, USA; School of Earth, Environment and Society, Bowling Green State University, 190 Overman Hall, Bowling Green, OH 43403, USA.
Journal of Hazardous Materials
|September 8, 2021
Summary
Phosphate addition stabilizes uranium (U) in contaminated sediments by forming recalcitrant uranyl minerals. This prevents U release when exposed to infiltrating water, crucial for managing radioactive waste sites.
Area of Science:
- Environmental Science
- Geochemistry
- Radiochemistry
Background:
- Contaminant fate in soils and sediments is governed by mineral dissolution and precipitation.
- Aggressive solutions can transform native minerals, releasing incorporated contaminants via water percolation.
Purpose of the Study:
- To evaluate uranium (U) release from Hanford sediments after reaction with U-containing liquid waste.
- To investigate the influence of phosphate on U release and mineral transformation.
Main Methods:
- Flow-through column experiments using Hanford sediments reacted with U-containing solutions (with/without phosphate) at pH 2 and 3.
- Simulated background porewater (BPW; pH ~7) leaching for 22 days.
- Uranium LIII-edge EXAFS spectroscopy and thermodynamic calculations.
Main Results:
- Up to 5% U release from phosphate-free sediments due to becquerelite and boltwoodite dissolution.
- Negligible U release from phosphate-reacted sediments, with meta-ankoleite as the main U-mineral phase.
- Becquerelite and meta-ankoleite transformed into schoepite and phosphuranylite-type phases, respectively.
Conclusions:
- Phosphate addition stabilizes U in sediments by forming recalcitrant uranyl minerals.
- This stabilization significantly reduces U release upon exposure to infiltrating porewater.
- Phosphate plays a key role in controlling U mobility and release at contaminated sites.
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