Aqueous Uranium(VI) Concentrations Controlled by Calcium Uranyl Vanadate Precipitates

作者：Tokunaga Tetsu K^*; Kim Yongman; Wan Jiamin; Yang Li

来源：Environmental Science & Technology, 2012, 46(14): 7471-7477.

DOI：10.1021/es300925u

Elevated concentrations of U in contaminated environments necessitate understanding controls on its solubility in groundwaters. Here, calculations were performed to compare U(VI) concentrations expected in typical oxidizing groundwaters in equilibrium with different U(VI) minerals. Among common U(VI) minerals, only tyuyamunite (Ca(UO2)(2)V2O8 center dot 8H(2)O), uranophane (Ca(UO2)(2)(SiO3OH)(2)center dot 5H(2)O), and a putative well-crystallized becquerelite (Ca(UO2)(6)O-4(OH)(6)center dot 8H(2)O) were predicted to control U concentrations around its maximum contaminant level (MCL = 0.13 mu M), albeit over narrow ranges of pH. Given the limited information available on uranyl vanadates, room temperature Ca-U-V precipitation experiments were conducted in order to compare aqueous U concentrations with tyuyamunite equilibrium predictions. Measured U concentrations were in approximate agreement with predictions based on Langmuir's estimated Delta G(f)degrees, although the precipitated solids were amorphous and had wide ranges of Ca/U/V molar ratios. Nevertheless, high initial U concentrations were decreased to below the MCL, over the pH range 5.5-6.5 in the presence of newly formed CaUV solids, indicating that such solids can be important in controlling U in some environments.

• 出版日期2012-7-17