Chemical Behavior of Transuranium Elements in Underground Environments

实验研究了镎的形态、胶体行为、溶解/沉淀和缓凝现象。这对于澄清与高水平放射性废物安全评估有关的地质介质中的TRU迁移至关重要。纸电泳是一种有效的方法，可用于研究在低浓度下相互带相反电荷的物种的形态，也可用于研究溶解的带电荷的沉淀物的溶解度。用纸电泳法测定了NpO_2OH^O和NpO_2(OH)^-_的水解常数。在缺氧条件下，还得到了未溶解的Np（IV）的溶解度。采用超滤和离心技术研究了中性Np(V)在氧化条件下的化学行为，以及SiO_2OH^O和Fe（III）胶体共存的影响；(1)NpO_2OH^O、NpO_2OH^O和NpO_2OH^O+Fe（III）被超滤捕获，捕获分数随时间增加而增加。(2)超滤捕获馏分高于离心沉淀馏分，这表明有可能吸附在过滤器上或形成未离心的小颗粒。(3)形成Np-FE（III）伪胶体，Fe（III）浓度越高，捕获率越高。在还原条件下，研究了未溶解的非晶态NpO_2.H_2O（am）的化学行为。由于超滤在滤网上的吸附和一些未溶解的物质无法捕获，因此超滤是研究化学行为的一种困难的方法。通过石英粉柱实验，得到以下结论：(1)明确了NpO^+_的吸附机理。NpO_2被认为是静电吸附在石英表面的。(2) NpO_2OH^O的释放与NpO^+_不同。研究发现，团聚体的过滤作用在保留机理中起重要作用。此外，NpO_2OH^O的吸附也被认为是有效的。(3)带负电的碳酸盐配合物的缓蚀作用很小。(4)与Np(V)溶解态相比，NpO_2.xH_2O（am）的不溶态反应速率较慢，且随着pH的增加和石英粒径的减小，反应速率减慢。少

Speciation, colloidal behavior, solubility/precipitation, and retardation phenomena of neptunium were experimentally studied. These are essential to clarify TRU migration in geologic media relating to safety assessment of high level radioactive wastes.1. Paper electrophoresis was found to be a useful method for studying speciation of the species which had opposite charge each other at low concentration and also for studying solubility of precipitate if the dissolved species had a charge. Using paper electrophoresis, hydrolysis constants for NpO_2OH^O and NpO_2(OH)^-_ were obtained. Solubility product of undissolved Np(IV) species was also obtained from experiments under anoxic conditions.2. Chemical behavior of neutral Np(V) species, under oxidizing conditions, and effects of coexisting SiO_2OH^O and Fe(III) colloids were studied using ultrafiltration and centrifugation; (1)NpO_2OH^O,NpO_2OH^O, and NpO_2OH^O+Fe(III) were partially trapped by ultrafiltration with the trappea fractions i … More ncreasing with respect to time. (2)Ultrafiltration trapped fractions were found to be higher than centrifuging precipitated fractions which indicates the possibility of adsorption onto the filter or the formation of small particles that were not centrifuged. (3)A Np-FE(III) pseudocolloid was formed and the trapped ratio was higher at increased Fe(III) concentrations.Under reducing conditions the chemical behavior of undissolved amorphous NpO_2.H_2O(am) was studied. Ultrafiltration was determined to be a difficult method to study the chemical behavior because of adsorption on the filter and the non-trapping of some undissolved species.3. From column experiments using quartz powder, the following conclusions were obtained; (1)The adsorption mechanism of NpO^+_ was made clear. NpO_2 is thought to be adsorbed electrostatically on the quartz surface. (2)Reiardation of NpO_2OH^O was found to be different from that of NpO^+_. Filtration of aggromeate was found to play an important role in the retention mechanism. In addition, sorption of NpO_2OH^O is also thought to be effective. (3)Retardation of megatively charged carbonate complexes was found to be little. (4)Neptunium(IV) undissolved species (NpO_2.xH_2O(am)) retarded in comparison with the Np(V) dissolved species, and the retardation factor increased with increasing pH and with decreasing particle size of quartz. Less