期刊
JOURNAL OF HAZARDOUS MATERIALS
卷 377, 期 -, 页码 315-320出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jhazmat.2019.05.101
关键词
Uranium; Groundwater; Remediation; Metaschoepite; Uranophane
资金
- EPA through its Office of Research and Development
Understanding the factors that govern aqueous solubility of uranyl minerals is important for predicting uranium mobility in groundwater and for designing effective remediation strategies. The uranyl-containing minerals metaschoepite [UO3 center dot(2H(2)O)] and uranophane [Ca(UO2)(2)(SiO3OH)(2)center dot 5H(2)O] were synthesized and evaluated in batch solubility experiments conducted in the presence of common groundwater ions: calcium, bicarbonate/carbonate, and dissolved silica. Solid-phase characterization revealed the expected structural and thermogravimetric properties of metaschoepite and uranophane. Metaschoepite solubility in carbonate-free water followed a u-shaped pH dependency with minimum solubility near pH 8.5; uranium concentrations at pH greater than or similar to 8.5 were approximately equivalent to the reference value for safe drinking water established by the EPA (30 mu g/L). With increasing bicarbonate/carbonate concentration (1 mM - 50 mM) the solubility of metaschoepite increased, presumably due to the formation of uranyl-carbonate complexes. However, the experimental concentrations of uranium were lower than concentrations predicted from accepted complexation constants. For uranophane, equilibrium uranium concentrations were < 75 mu g/L at typical groundwater concentrations of calcium and dissolved silica (pH > 7). The diversity of uranyl minerals that possibly form in the presence of common groundwater species: Ca-Mg-Na-K-Si-bicarbonate/carbonate-sulfate-chloride, has not been fully explored with respect to understanding potential mineral transformations and impacts on uranium solubility and mobility.
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