砂岩含水介质中铀的吸附和迁移行为研究

地浸铀矿山退役后,含水层中残留的含铀浸出液随着地下水的运动向下游迁移扩散,存在对周边地下水污染的风险。本文设计了若干组批实验和柱实验,研究铀在北方某地浸铀矿山砂岩含水介质中的吸附和迁移行为。实验结果表明,砂岩对铀的吸附在12 h以内达到平衡,铀初始浓度越高,砂岩的铀吸附容量越大;砂岩对铀的吸附为吸热反应,温度升高有利于吸附反应的进行。溶液pH值和共存 {\mathrm{HCO}}_3^{-}浓度会对铀的吸附作用产生强烈的影响:pH值在7左右时,铀的吸附量最高; {\mathrm{HCO}}_3^{-}浓度越高,铀的吸附量越低。这些影响是通过改变溶液中铀的络合形态和砂岩矿物表面的电荷性质实现的。柱实验表明,pH值、铀浓度、流速和 {\mathrm{HCO}}_3^{-}浓度是影响铀在饱和砂岩含水介质中迁移的重要因素。pH值≤7时,pH值越高,砂岩柱越不易被铀穿透;而铀浓度、流速、 {\mathrm{HCO}}_3^{-}浓度越高,砂岩柱越易被铀穿透。两点非平衡模型可以很好地拟合不同条件下铀在砂岩柱中的迁移过程。批实验获得的分配系数是柱实验的1.16.6倍。通过对比实验条件、含水层特性和地下水化学特征,确定分配系数为48.1 mL/g时,较适合描述研究区内砂岩含水层中的铀迁移。上述认识为地浸铀矿山地下水铀的反应运移过程和天然自净化机理提供了理论依据。

Adsorption and transport of uranium in porous sandstone media

After the decommissioning of a in-situ leach uranium mining site, residual uranium leaching fluid in the aquifer migrates and diffuses downstream posing pollution risks to the surrounding groundwater. In this study, a series of batch and column experiments were designed to investigate the adsorption and migration behavior of uranium in aquifer sandstone in an in-situ leach uranium mining area in northern China. In batch experiments, uranium adsorption on sandstone reached equilibrium within 12 h, and in the process a positive correlation between the initial uranium concentration and sandstone’s uranium adsorption capacity was observed. It was found that the uranium adsorption process was endothermic and the increase in temperature was beneficial for uranium adsorption. The pH of the eluent and {\mathrm{HCO}}_3^{-} concentration have a strong influence on uranium adsorption. Maximum uranium adsorption was reached at around neutral pH, and higher {\mathrm{HCO}}_3^{-} concentration led to lower level of adsorption. These effects are due to the alteration of uranium complexation in the solution and the surface charge properties of sandstone. In column experiments, pH, uranium concentration, flow rate, and {\mathrm{HCO}}_3^{-} concentration were the most important factors affecting uranium migration. Weaker acidity (pH≤7) was found to be associated with fewer late uranium breakthrough in the sandstone column; whereas higher uranium concentration, flow rate, and {\mathrm{HCO}}_3^{-} concentration might cause early uranium breakthrough. The two-point non-equilibrium model could well describe the uranium migration process in the sandstone column under variable conditions. The partition coefficients obtained from batch experiments were 1.1-6.6 fold higher than those obtained from column experiments. According to the aquifer characteristics and hydrogeochemical characteristics, we suggest that the distribution coefficient of 48.1 mL/g would be suitable for describing uranium migration in sandstone aquifers in the study area. Overall, this study provided a theoretical basis for the reactive transport process and for the natural remediation of polluted groundwater in the in-situ leaching uranium mining areas.