Experiment And Simulation Study On Water-Rock Reaction Between GMZ Na-Bentonite And Beishan Groundwater

Based on the design requirements for engineered barrier of high-level radioactive waste（HLW）disposal repository,this thesis took GMZ Na-Bentonite sampled from Xinghe County of Inner Mongolia and Beishan groundwater of Gansu Province as research objects,and uses the methods of theoretical analysis,mechanical tests and numerical simulation.The experiment and simulation of Water-Rock Reaction between Na-Bentonite and Beishan Groundwater were studied using indoor tests and analysis,theoretical calculating as well as numerical simulating.The major conclusions obtained from this study were summarized as follows.The L₂₅（5⁵）orthogonal tests between GMZ Na-Bentonite and different salt solutions were established.The impact of pH,concentrations of ion,temperature,solid-to-liquid ratio as well as reaction time on pH of system,exchangeable cations,and ion composition were revealed.The main ion exchange reactions occurring under different conditions were found out.The results showed that Bentonite had fine buffer capacity to pH and could keep the system in alkaline range.Experimental technical processof interactions between GMZ Na-Bentonite and Beishan groundwater were established.The variation characteristics of pH and Eh of Bentonite-Groundwater system with time were investigated lasting 1 year in ambient temperature and 150 days in high temperature through experiments respectively.The concentrations of key cations in liquid were obtained.Chemical composition,exchangeable cations and chemical composition of Bentonite after reaction were determined.The types of ion exchange reactions occurred in Bentonite and Groundwater were ascertained and whose thermodynamics models were conducted.The results showed that Bentonite-Groundwater system could maintain a relatively stable state in experimental condition and time range.The findings could provide scientific information and basis for bringing to linght geochemical environment and evaluating chemical properties of Bentonite.The effect of Siderite and Na₂CO₃ as additives to pH and Eh of Bentonite-groundwater system,critical ionic component in liquid,mineral composition,as well as exchangeable cations was studied by experiment in anaerobic and normal temperature condition.The results showed that adding Na₂CO₃ could not only maintain the system in alkaline range,but also prevent Na-Bentonite from transforming into Ca-Bentonite.Siderite could lower the Eh effectively,keep the system in reducing condition and stabilize at-158mV eventually.The mineral composition of Bentonite did not change too much because of adding siderite and Na₂CO₃.The optimal ratio of Bentonite,Siderite and Na₂CO₃ improving chemical buffer capacity of GMZ Na-Bentonite was determined at last.By means of the geochemical software PHREEQC,the geochemical evolution of Na-montmorillonite and Gaomiaozi bentonite in Beishan groundwater under anaerobic conditions were investigated at different temperature（25^oC,60℃,90^oC）based on experiment datas.The dissolution kinetics of Na-montmorillonite and GMZ Bentonite in purified water and Beishan groundwater were investigated over a time scale of 100 000 years.The time of key minerals reaching saturation or starting to precipitate,and the time when the system reached equilibrium were catulated.The achievements chould provide references and basis for evaluating long term capacities of Bentonite as buffer material of HLW geological disposal in China.