Kaixian Ke, Wenfa Tan, Mingchao Zhang, Yufei Chen, Boying Li
This study investigated the removal of U(VI) from multi-ion simulated groundwater using a uranium-tolerant indigenous strain Leifsonia sp. coupled with natural kaolinite and montmorillonite binary clay composites. Batch static experiments were performed to systematically quantify the independent and interactive effects of key variables (pH, reaction duration, initial U(VI) concentration, bacterial dry biomass dosage) and common groundwater coexisting ions on U(VI) immobilization efficiency. The binary clay-bacteria composite achieved optimal U(VI) removal performance, with a maximum removal efficiency of 94.23% under the optimized conditions of pH 6, 20 h reaction time, 10 mg·L-¹ initial U(VI) concentration, and 0.6 g·L-¹ bacterial biomass. Kinetic studies were further conducted to elucidate the adsorption behaviour, and the PSO model exhibited the best fitting performance, confirming the dominant chemisorption mechanism. Multi-technique characterizations including SEM-EDS, FTIR and XPS were applied to reveal the synergistic immobilization mechanism. Clay minerals significantly promoted bacterial cell attachment, alleviated bacterial aggregation and uranium cytotoxicity, and supplied abundant extra inorganic ion-exchange adsorption sites. FTIR spectra verified that hydroxyl, carboxyl, alkoxy and carbonyl functional groups from bacterial extracellular polymeric substances and clay lattices jointly coordinated uranyl ions. XPS high-resolution U4f spectra and quantitative peak fitting detected coexisting U(VI) and U(IV) species in solid reaction precipitates, realizing differentiation of passive surface adsorption (∼73%) and metabolism-dependent microbial bioreduction (∼21%) contributions to U(VI) immobilization. Overall, the natural binary clay-indigenous Leifsonia composite exhibited prominent cascade synergistic effects and shows promising application potential for in-situ remediation of uranium-contaminated groundwater.