腐殖酸对Np胶体行为的影响

在模拟高放废物深地质处置的低氧低浓条件下,探讨用膜过滤法研究Np胶体行为的可行性。实验研究结果表明:无腐殖酸存在时,在pH=1～13条件下,无机离子对237Np的测定无明显影响,237Np的液闪探测效率可达100%;增加闪烁液用量可消除腐殖酸对237Np的淬灭效应,过滤器对237Np的吸附可忽略不计,说明将过滤法应用于Np的胶体行为研究准确、可靠,操作简便。应用该方法对Np的不同价态和腐殖酸存在下的胶体行为进行了研究。Np(Ⅴ)无明显胶体行为,Np(Ⅳ)以真胶体形态存在,其浓度显著影响胶体行为;腐殖酸与Np(Ⅳ)能形成假胶体,从而提高了Np(Ⅳ)在溶液中的含量,有利于Np的迁移。腐殖酸是核素迁移研究必须考虑的重要影响因素。

Colloidal Behavior of Neptunium in Present of Humic Acids

The colloidal-borne facilitated transport of actinides is an important aspect of radionuclide migration investigation in high-level waste geological disposal. In the present study, colloidal behavior of Np in the presence of humic acids was investigated by using micro- and ultra-filtration methods under simulated disposal conditions. All experiments were performed in argon atmosphere glove-box and at ambient temperature. No significantly effect of acidity, inorganic irons and filter wall and membrane adsorption on the detection of Np was found in these research systems. It is indicated that the counting efficiency for ²³⁷Np should be close to 100%. The humic acids would be the apparent influence factor for the ²³⁷Np counts ratios due to its quenching efficiency, however, the sample quenching induced by humic acids can be depressed by increasing the volume of liquid scintillation cocktail to 16 mL under the condition that the humic acids concentration is lower than 66.6 mg/L. The formation of neptunium colloids was observed, and the influences of oxidation states of Np, initial concentrations of Np and the present of humic acids on Np colloidal behaviors were investigated. The intrinsic colloids of Np were found in Np(Ⅳ) solutions at pH=8 under anaerobic conditions, while the formation of the colloidal species was less observed in Np(Ⅴ) solutions under the same conditions. The initial concentration of Np(Ⅳ) would influence the Np(Ⅳ) colloidal behavior, and the amount of Np(Ⅳ) colloids would be very lower under the higher Np(Ⅳ) initial concentration. The radioactive pseudo colloids of Np(Ⅳ) were formed in the presence of humic acids in aqueous solution. It is indicated that the Np(Ⅳ)-humates pseudocolloids are generated through adsorption and complexation of Np(Ⅳ) by humic acids. In this work, we found that humic acids will enhance the Np(Ⅳ) concentrations in solutions, the results demonstrate that some Np(Ⅳ) can be bound to low molecular weight humic acids and thus the 10 kDa membrane can not retard these Np(Ⅳ)-humate compounds. It can be concluded that the present of humic acids will facilitate the migration of Np(Ⅳ) even under anaerobic conditions.