Studies on Hydrolysis and Complexation Reactions of Transuranium Elements

镎等超铀元素的迁移行为对高放废物地质处置效果评价具有重要意义。然而，一般来说，这些元素表现出复杂的化学行为，并且这些行为尚未完全理解。超铀元素由于其化学性质，对氧化还原条件非常敏感，在水溶液中很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，对超铀元素的水解和络合反应进行了研究。（1）测定了碳酸根离子对Np（VI）溶解度的影响，得到了Np（VI）水解形成羟基碳酸根络合物的新结果。(2)提出了一个简单的硬球模型，用于研究超铀离子水解和碳酸根络合的热力学常数。该模型被发现是有用的检查实验值和预测未知的。(3)用商品腐殖酸测定了腐殖酸与Np（V）的络合作用。结果被认为是成功地解释了一个多站点模型。(4)用双电层模型研究了Np（V）和Cs在石英表面的吸附行为。分析是成功的，和pH值和离子强度的依赖性的分配系数被很好地解释，考虑了一些吸附反应的石英表面上。

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.