Characteristics and influencing factors of uranium adsorption by sandstones outside an acid in situ leaching uranium mining area

Uranium (U) contamination in groundwater of the uranium mines exploited using the in situ leaching (ISL) technology (also referred to as the ISL uranium mines) has attracted wide international attention. Since the adsorption of U in groundwater by aquifer media influences the migration scope of U, understanding the U adsorption by aquifer media is of great significance for accurately predicting the influencing scope of ISL uranium mines on groundwater. This study collected sandstone samples from the ore-bearing aquifer outside a typical mining area in a uranium mine exploited using the acid ISL (AISL) technology (also referred to as an AISL uranium mine) in northern China. Using these sandstone samples, this study conducted batch adsorption experiments and column experiments of U to reveal the characteristics and major influencing factors of U adsorption under different conditions. The results show that the adsorption of U by sandstones in the ore-bearing aquifer outside a mining area satisfies the pseudo-second-order kinetic equation and the linear isothermal adsorption model. In the batch U adsorption experiments, the adsorption efficiency and capacity for U reached maxima of 77.45% and 0.069 mg/g at pH 7, respectively. As shown by column experiments, the sandstones showed a significant increase in the U adsorption and retardation as pH increased. The SO42− concentration has minor effects on U adsorption under experimental conditions. Sandstones from different monitoring wells exhibited different U adsorption characteristics. Sandstone cores with relatively high contents of clay minerals such as illite showed strong U adsorption. Under the same experimental conditions, the U distribution coefficient Kd (6.91 × 10–2 L/g) obtained from column experiments is much less than that (0.14 L/g) obtained from the batch U adsorption experiments. These results suggest that it is necessary to take into account the U adsorption and retardation by aquifer media in predicting the impacts of ISL uranium mines on the groundwater environment.