腐殖酸对Tc价态影响研究

Studies of Tc Oxidation States in Humic Acid Solutions

在模拟高放废物深地质处置环境的低氧(O2含量小于5×10-6)、低Tc(Ⅶ)初始浓度(10-8 mol/L)条件下,研究腐殖酸浓度对Tc(Ⅶ)价态影响。结果显示,腐殖酸对99Tc液闪测定存在淬灭效应,但当腐殖酸浓度在40 mol/L以下,保持闪烁液体积为样品体积20倍可消除影响;在此基础上分别用四苯砷氯-氯仿萃取法和LaCl3沉淀腐殖酸法独立进行腐殖酸-Tc(Ⅶ)体系中锝价态研究,所得Tc(Ⅳ)和Tc(Ⅶ)价态分布结果基本吻合,表明两种研究方法均可用于腐殖酸-Tc(Ⅶ)体系中低浓度Tc价态研究;研究发现平衡350天的不同浓度Fluka腐殖酸-Tc(Ⅶ)体系中,Tc(Ⅶ)浓度长期保持稳定,而Tc(Ⅳ)浓度很低,表明即使在低氧气氛中,Fluka腐殖酸也未对Tc(Ⅶ)表现出明显还原行为,腐殖酸在地下水中的存在可能是高放废物地质处置中Tc(Ⅶ)阻滞的不利因素。

The oxidation state of Tc is an important aspect of the speciation in groundwater which contained organic substances due to it control the precipitation, complexation, sorption and colloid formation behavior of the Tc under HWL geological disposal conditions. In present work, the oxidation states of Tc were investigated using the LaCl3 coagulation method and solution extraction method in aqueous solutions in which the humic acid concentration range is from 0 to 20 mg/L and the Tc （ Ⅶ ） concentration is about 10^-8 mol/L. The radioacounting of ^99Tc was determined using liquid scintillation spectrometry. The humic acid will influence the radiocounting ratio of ^99Tc apparently, however, the quenching effect can be restrained once keep the volume of the cocktail to about twenty times of the sample volume. The LaCl3 coagulation method was carried out for the investigation of Tc oxidation states in humic acid aqueous systems at about pH 8. The tetraphenylarsonium chloride （TPA）-chloroform extraction method was used also simultaneously to investigation the concentrations of Tc （ Ⅳ ） and Tc （ Ⅶ ） for the availability of the LaCl3 precipitation method, and the experimental results demonstrate that tetravalent technetium and pertechnetate concentrations are well agreement with the LaCl3 precipitation method. These two experimental results demonstrated that Tc （Ⅶ） is very stable in the Tc （Ⅶ）-humic acid system during a 350 days experimental period, and the Tc（ Ⅳ ） concentrations are very lower, that is indicate that there didn＇t oxidizing reactions between the Fluka humic acid and Tc （ Ⅶ） in aqueous solutions under anaerobic conditions. That means the presence of humic acids even in anaerobic groundwater is disadvantage for the retardance of radionuclides.