地浸铀矿山地下水U污染问题是国际社会广泛关注的环境地质问题,准确预测地浸铀矿山采区外围地下水中U的运移范围对辐射风险评估至关重要。本文以我国某酸法地浸铀矿山为研究对象,利用数值模拟方法定量模拟和预测了不同生产时间地下水中U的运移范围。数值模拟结果表明,地浸生产会明显改变采区流场形态,形成指向采区内部的水力梯度,生产井的抽注是改变流场形态的主控因素。在流场模拟的基础上,建立了不考虑吸附作用的地下水U运移模型与基于K_d值的U阻滞运移模型。根据采区内生产井及采区外围不同距离处监测井地下水pH情况,对阻滞运移模型中的K_d进行了分区赋值。对比两个模型的模拟结果可以发现,当考虑含水介质对地下水中U的吸附阻滞作用后,模拟结果能够跟现场监测数据更好拟合,表明地浸采区外围地下水中U的运移范围受含水介质的吸附阻滞作用明显;这种情况下,U在地下水中的运移距离缩短了53%,运移范围缩小了41%;阻滞运移模型预测的投产5年后采区外围地下水中U迁移距离为50 m。该结果与现场监测结果基本一致,证明数值模拟手段可以为地浸铀矿山地下水U分布范围预测提供科学依据。

Uranium (U) contamination of groundwater at in-situ leaching uranium mines is a global environmental geological problem. Accurately predicting the transport range of U in the groundwater outside the in-situ leaching mining areas is crucial to radiation risk assessment. In this study, the migration range of groundwater U at different production times was quantitatively simulated and predicted by numerical simulation method from an acid in-situ leaching uranium mine. The numerical simulation results showed that the mining activities of in-situ leaching uranium significantly changed the groundwater flow field in the mining area, and depression cones were induced by the high ratio of pumping to injection inside the mining area. On the basis of flow modeling, the transport model of groundwater U without considering adsorption and the retardation transport model based on K_d value were established. According to the groundwater pH of production well and monitoring wells at different distances outside the mining area, different K_d value was assigned by regions. By comparing the simulation results of the two models, it could be found that when considering the adsorption-retardation effect of aqueous medium on groundwater U, the simulation results could be better fitted with the field monitoring data, indicating that the migration of U in groundwater was significantly retarded by the aqueous medium. The U reactive transport model showed that the migration distance and range were reduced by 53% and 41%, respectively. Besides, the model predicted that the migration distance of groundwater U in the mining area was 50 m after 5 years of mining, which was consistent with the monitoring results. It was proven that the numerical simulation method, as an effective tool, could be successfully used to predict the impact of in-situ mining on groundwater environment at the uranium mining site.