Studies on Hydrolysis and Complexation Reactions of Transuranium Elements

Ne等超铀元素的迁移行为对于高放废物地质处置的性能评价具有重要意义。然而，一般而言，这些元素表现出复杂的化学行为，而且这种行为还没有完全被理解。由于超铀元素的化学性质，对氧化还原条件非常敏感，在水溶液中可能参与水解和络合反应，为了了解地质处置条件下超铀元素在水溶液中的化学行为，本文研究了超铀元素的水解和络合反应。研究结果如下：(1)测定了碳酸盐离子对Np(VI)的溶解度的影响，得到了Np(VI)的水解物和羟基碳酸酯络合物物种形成的新结果。(2)提出了一个简单的硬球模型来研究超铀离子的水解和碳酸盐络合的热力学常数。该模型可用于检验实验值和预测未知值。(3)用商品腐植酸测定了Np(V)的腐植酸络合度。用双电层模型对Np(V)和Cs在石英上的吸附行为进行了测量和分析。分析是成功的，通过考虑石英表面的一些吸附反应，很好地解释了pH和离子强度对分配系数的依赖关系。

Migration behavior of transuranium elements such as neptunium is very important for the performance assessment of geologic disposal of high level radioactive wastes. Generally speaking, however, the elements show complex chemical behavior, and the behavior is not completely understood yet. Because of their chemical nature, transuranium elements are very sensitive to redox conditions, and are likely involved in hydrolysis and complexation reactions in aqueous solutions.In the present study, the hydrolysis and complexation reactions of transuranium elements were studied in order to know the chemical behavior of transuranium elements in aqueous solutions under the conditions of geologic disposal. Obtained results are as follows :(1) The effect of carbonate ions on the solubility of Np (VI) was measured, and a new result was obtained for the formation of hydrolysis and hydroxycarbonate complex species of Np (VI).(2) A simple hard sphere model was presented to study the systematics for the termodynamic constants of hydrolysis and carbonate complexation of transuranium ions. The model was found to be useful to check the experimental values and to predict the unknown ones.(3) With the use of commercial humic acids, humate complexation of Np (V) was measured. The results were found to be successfully interpreted by a multi-site model.(4) Adsorption behavior of Np (V) and Cs onto quartz was measured and analyzed by an electric double layr model. The analysis was successful, and the pH and ionic strength dependences of distribution coefficients were well interpreted by considering a number of adsorption reactions on the quartz surface.