Chemical Behavior of Transuranium Elements in Underground Environments

实验研究了Nb的形态、胶体行为、溶解/沉淀和滞留现象。这些对于澄清TRU在与高放射性废物安全评估有关的地质介质中的迁移至关重要。纸片电泳法是研究低浓度下相互带相反电荷的物种形态的有效方法，也是研究溶解物种带电荷时的溶解度的有效方法。用纸电泳法测定了NPO_2OH^O和NPO_2(OH)^-_的水解常数。实验还得到了未溶解的Np(IV)物种在缺氧条件下的溶解度积。用超滤和离心法研究了中性Np(V)物种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)通过超滤组分I…被部分捕获随着时间的推移而增加。(2)超滤捕获组分高于离心沉淀组分，这表明有可能吸附在过滤器上或形成未离心的小颗粒。(3)形成了Np-Fe(III)拟胶体，且随着Fe(III)浓度的增加，Np-Fe(III)的捕获率增大。超滤是研究化学行为的一种困难的方法，因为超滤在过滤器上的吸附和一些不溶物质的非捕集。通过石英粉的吸附实验，得出以下结论：(1)明确了NPO^_2的吸附机理。NPO_2被认为是以静电方式吸附在石英表面。(2)NPO_2OH^O与NPO^_2的复氧作用不同。研究发现，过滤在滞留机制中起着重要作用。此外，对NPO_2OH^O的吸附也被认为是有效的。(3)巨电荷碳酸盐络合物的缓凝作用很小。(4)与Np(V)溶解物种相比，Nb(IV)难溶物种(NPO_2·xH_2O(Am))对Np(V)有抑制作用，且滞后因子随pH的升高和石英粒度的减小而增大。较少

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