Potential Remediation Approach for Uranium-Contaminated Groundwaters Through Potassium Uranyl Vanadate Precipitation

摘要

Methods for remediating groundwaters contaminated with uranium (U) through precipitation under oxidizing conditions are needed because bioreduction-based approaches require indefinite supply of electron donor. Although strategies based on precipitation of some phosphate minerals within the (meta)autunite group have been considered for this purpose, thermodynamic calculations for K- and Ca-uranyl phopsphates, meta-ankoleite and autunite, predict that U concentrations will exceed the Maximum Contaminant Level (MCL = 0.13 μM for U) at any pH and pCO_2, unless phosphate is maintained at much higher concentrations than the sub-μM levels typically found in groundwaters. We hypothesized that potassium uranyl vanadate will control U(VI| concentrations below regulatory levels in slightly acidic to neutral solutions based on thermodynamic data available for camotite, K_2(UO_2)_2V_2O_8. The calculations indicate that maintaining U concentrations below the MCL through precipitation of camotite will be sustainable in some oxidizing waters having pH in the range of 5.5 to 7, even when dissolution of this solid phase becomes the sole supply of sub-μM levels of V. Batch experiments were conducted in solutions at pH 6.0 and 7.8, chosen because of their very different predicted extents of U(VI) removal. Conditions were identified where U concentrations dropped belowthe MCL within 1 -5 days of contact with oxidizing solutions containing 0.2-10 mM K, and 0.1 -20 μM V(V). This method may also have application in extracting (mining) U and Vfrom groundwaters where they both occur at elevated concentrations.