铀在放射性废物处置场周边土壤中的吸附行为及机理研究

Behavior and Mechanism of Uranium Adsorption on Soil Medium Nearby Radioactive Waste Disposal Sites

放射性核元素在土壤介质中的吸附特征是放射性废物处置场地选址及安全评价中最重要的考虑因素之一。为探讨核素铀在放射性废物处置场预选场址周边土壤介质中的吸附行为与机理,实验以深圳市蛇山顶(SSD)及阳江市大尖山(YJ)表层土壤为研究对象,采用批式实验法研究不同铀初始质量浓度及离子强度对其吸附核素铀行为的影响,并通过吸附动力学模型及吸附等温线模型对实验数据进行拟合,分析吸附机理。结果表明:当铀初始质量浓度增大时,SSD及YJ土壤对U(VI)的平衡吸附量也增大,但去除率则分别从97.07%、91.56%下降至88.55%、87.93%;离子强度对SSD土壤吸附U(VI)的影响并不显著,表明U(VI)在SSD土壤上的吸附可能以内层络合反应为主;准二级动力学方程及Langmuir吸附等温模型能够很好地拟合吸附动力学及平衡吸附实验结果,相关系数R2均在0.99以上。实验获取的这些参数为核素铀在土壤介质上的吸附模型的建立提供了重要依据,且为推测核素铀在环境中的迁移行为提供了研究基础。

The adsorption of radionuclides in soil media has become one of the key considerations in both site selection and safety evaluation of geological repository.In order to understand the adsorption behavior and mechanism of uranium on soil media from pre-selected sites of radioactive waste disposal sites,batch adsorption experiments were adopted to study the adsorption of U(VI)on mineralogical components in Shenzhen(SSD)soil and Yangjiang(YJ)soil.The effects of initial concentration of U(VI)and ionic strength were studied in detail and the adsorption mechanisms were discussed by kinetic model and isothermal adsorption model.The results show that the equilibrium absorption capacity of U(VI)on both SSD soil and YJ soil increase when the initial concentration of U(VI)increase,while the removal rates of U(VI)on SSD soil and YJ soil decrease from 97.07%and 91.56%to 88.55%and 87.93%,respectively.The adsorption of uranium is not sensitive to ionic strength,which indicates the major species form on SSD soil might be inner-sphere surface complexes.The pseudo-second-order kinetic model and Langmuir isothermal adsorption equation can be used to describe the adsorption of U(VI)on both SSD and YJ soil media,and all the relation coefficients are higher than 0.99.This work provides some guidance for further study of actinides adsorption model on the soil medium,and offers the basis to speculate the transport behavior of uranium in the environment.