铀与蒙脱石-细菌交联界面的分子作用机制研究

The environmental risk of uranium is largely influenced by its interaction with soils composed with biotic and abiotic components. Active clay minerals and bacteria are mostly combined to form mineral-bacteria aggregate, altering their native surface property and biological activity, and consequently influencing the chemical behavior and bioavailability of uranium. There have been extensive studies done on the interaction of uranium with single minerals or bacteria. However, as far as we are known, little is known about the molecular interaction mechanism between uranium and mineral-bacteria aggregate. Herein, Bacillus cereus and Shewanella putrefaciens, isolated from a uranium ore in China, will be chosen as model bacteria, and bentonite will be chosen as a model clay mineral. Simulate the montmorillonite-bacteria aggregate over different time scale, and investigate the sorption, reduction and mineralization of uranyl on montmorillonite-bacteria mutual interface. Explore and compare uranium thermodynamics and dynamics behavior on montmorillonite, bacteria, and montmorillonite-bacteria aggregates under different environmental conditions by batch sorption t and column experiments. Identify the microstructure of uranium on multi phase interface, and elucidate the uranium species and its transformation on montmorillonite-bacteria mutual interface, and reveal the interaction mechanism between uranium and montmorillonite-bacteria composites. Expected result not only reflects the binding character of uranium in soils more accurately, but also has theoretical and practical significance in predicting the fate and ecological effects of uranium. Additionally, it could also provide theory basis for remediation and risk assessment of soils contaminated by uranium.

铀在环境中的化学行为取决于其与环境介质的反应。活跃的粘土矿物与细菌及其分泌物常以团聚交联体形式存在，前期工作多关注单介质的模拟研究，关于介质之间交互作用对铀所产生的环境效应，尤其是分子水平上的机理研究较少。本项目以某铀矿区分离的蜡样芽孢杆菌和希瓦氏菌为细菌代表，蒙脱石为粘土矿物代表，模拟不同时间尺度下的蒙脱石-细菌交联体，研究其对铀酰离子的吸附、还原和矿化，及作用过程中蒙脱石和细菌组分的关联机制；深入探究和比较铀在不同界面上的反应热力学及动力学行为；进一步利用EXAFS技术在分子水平上分析铀在多相界面上的微观结构。查明铀在蒙脱石-细菌交联界面的化学形态和转化规律，揭示蒙脱石-细菌交联体对铀的固定机制。预期成果不仅能更真实反映铀元素在土壤中的结合特征，而且对揭示铀在环境中的归趋和生态效应具有重要的理论和实际意义，同时为评估和分析核废料地质处置提供理论指导。

铀在环境中的生态行为取决于其与土壤各组分之间的反应。活跃的粘土矿物组分与细菌及其分泌物在土壤中常以团聚交联体形式存在，前期工作过多关注单组分的模拟研究，忽视了组分交互作用对铀所产生的环境效应，尤其是分子水平上的机理研究。本项目以蒙脱石为粘土矿物代表，模拟不同时间尺度下的蒙脱石-细菌交联体，研究其对铀酰离子的吸附和矿化，及作用过程中蒙脱石和细菌组分的关联机制。研究发现当蒙脱石与细菌的相互作用时，对铀吸附的影响并非简单的促进或抑制作用，一般情况下低pH范围内，二者的交互作用抑制了对铀的吸附，高pH范围内抑制作用不仅不明显，反而促进了铀的吸附，促进作用主要来源于细菌分泌的一些可溶性有机小分子会扦插到蒙脱石的有机片层，或吸附结合在蒙脱石的表面及边缘，为铀提供新的吸附位点，而抑制作用来源于细菌和蒙脱石的包裹和吸附，从空间上阻隔对铀的吸附，同时导致部分位点被占据。铀在菌体、菌体-蒙脱石复合体上的存在形式主要以类氢铀云母矿物为主，而细菌是诱导铀矿物形成的主要原因。本成果发现细菌分泌的活性小分子趋向于与矿物颗粒结合，进而影响其对铀的延申滞固或释放行为等，对揭示铀在土壤中的归趋和生态效应具有重要的理论和实际意义，同时为铀污染土壤的修复和风险评价提供理论依据。