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Uranium Release from Acidic Weathered Hanford Sediments: Single-Pass Flow-Through and Column Experiments.
Guohui Wang1, Wooyong Um1,2, Zheming Wang1
1Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
Environmental Science & Technology
|September 9, 2017
Summary
Radioactive waste reactions with sediments can alter uranium mineralogy. Phosphate addition promotes meta-ankoleite formation, strongly retaining uranium and aiding remediation strategies.
Area of Science:
- Geochemistry
- Environmental Science
- Radiochemistry
Background:
- Acidic radioactive waste reactions with sediments influence contaminant mobility.
- Simulating waste disposal conditions at Hanford's cribs is crucial for understanding contaminant fate.
Purpose of the Study:
- Investigate sediment weathering by synthetic uranium-acid solutions.
- Determine the influence of phosphate on uranium mineralogy and retention.
- Assess uranium release rates under simulated waste disposal conditions.
Main Methods:
- Bench-scale experiments simulating Hanford crib conditions.
- Spectroscopic and diffraction-based techniques for mineral identification.
- Single-pass flow-through and column leaching experiments.
Main Results:
- Phosphate presence led to meta-ankoleite [K(UO2)(PO4)·3H2O] precipitation, strongly retaining uranium (release rate: 2.67 × 10⁻¹² mol g⁻¹ s⁻¹).
- In phosphate-free systems, uranium oxyhydroxides (compreignacite-type) formed, showing higher uranium release rates (1.05-2.42 × 10⁻¹⁰ mol g⁻¹ s⁻¹).
- Identified distinct uranium mineral phases based on phosphate presence.
Conclusions:
- Uranium mineralogy is significantly controlled by phosphate availability during acid weathering.
- Phosphate minerals enhance uranium retention in sediments, suggesting potential for remediation.
- Study findings support accurate U-release models for contaminant transport prediction.