Hydration behaviour of uranyl chloride: from fundamental chemistry to environmental applications

In water uranium exists almost exclusively as the uranyl ion [UO2]2+. In the presence of halides these can form complexes of the type [UO2(H2O)nClx]2-x, whose thermodynamics and structures in solution are not fully understood. This is important as high halide concentrations are expected to be found in spent nuclear fuels or under certain environmental conditions. In this work we propose to study the reaction of uranyl chloride [UO2(H2O)5][Cl]2 with LiCl under increasing halide concentrations to determine the structures and formation constants. The latter are important as these feed into thermodynamic databases but are experimentally unknown. These databases are used as prediction tools that underpin safety cases for storage of spent nuclear fuels so it is of importance to have robust, experimentally determined values.

水溶液中，铀几乎仅以铀酰离子（uranyl ion）[UO₂]²⁺的形式存在。在卤化物（halides）存在的条件下，铀酰离子可形成形如[UO₂(H₂O)ₙClₓ]²⁻ˣ的配合物，目前学界对这类配合物在水溶液中的热力学行为与分子结构尚未完全厘清。这一研究方向具有重要意义，因为高浓度卤化物环境常见于乏核燃料（spent nuclear fuels）或特定自然环境中。本研究拟通过调控卤化物浓度梯度，探究氯化铀酰（uranyl chloride，化学式为[UO₂(H₂O)₅][Cl]₂）与氯化锂（LiCl）的反应过程，以明确上述配合物的分子结构与形成常数（formation constants）。这类形成常数是热力学数据库（thermodynamic databases）的关键输入参数，但目前尚无可靠的实验测定值。此类数据库被用作预测工具，为乏核燃料储存的安全论证提供核心支撑，因此获取稳健且经实验确证的形成常数数值至关重要。