Study On Adsorption Mechanism Of U(?) On Clay Mineral Surface

The clay rock is considered as one of the most important surrounding rocks for the research of Chinese high-level radioactive waste repository.Alxa area in Inner Mongolia is one of the primary sites of clay rock disposal repository for high-level radioactive waste?HLW?in China.Although many researches have been done on the adsorb-ability of granite,there are few researches on the disposal of the clay rock and its research system is relatively simple.Therefore,this paper takes the clay rock in Alxa area,Inner Mongolia as the research object.By studying the adsorption mechanism between radionuclide U???and mineral surface of the clay rock in different physical and chemical conditions,the paper is supposed to provide references for the site selection,design and safety performance evaluation of the clay rock to be high-level radioactive waste repository.The main researches are as follows.?1?With the help of various testing methods and apparatus,the clay rock in Alxa area,Inner Mongolia were analyzed and found containing illite,calcite,chlorite and other clay mineral composition.Analysis shows that there are many holes in the surface of the clay rock and its structure is quite loose.There are kinds of active functional groups like hydroxyl,carboxyl,carbonyl,Al-O,Si-O and others in the surface of the clay rock.The specific surface area is46.13 46.13 m²/g.?2?Static experiment was used to research the impacts of different conditions,including contact time,PH value,ion concentration,solid-liquid ratio,initial concentration of nuclide,temperature and so on.The results of adsorption experiment shows that on the surface of the clay rock,U can reach adsorption equilibrium within 24 hours.The optimal solid-liquid ratio is 1:20,and the initial concentration is 160?g·m L^-1.The adsorption of the clay rock for U???is significantly affected by PH,greatly influenced by ionic species but less affected by ion concentration,which demonstrates that the adsorption process has both inner complexation and outer complexation and the former is given priority to;Compared with the adsorption properties of clay minerals such as illite,chlorite and kaolinite,the adsorption capacity of the clay rock for U???is much higher than that of the other three clay minerals;U???exists in the form of UO₂?CO₃?₂^2-and UO₂?CO₃?₃^4-in groundwater environment in Alxa area,Inner Mongolia.?3?The fitting results of isotherm models of dynamics,thermodynamics and adsorption shows that the four models all can be used to describe the adsorption process,but the Freundlich model and Slip model are more suitable,which illustrates that the adsorption process belongs to multi-layer covering?between bi-layer and multilayer?and adsorption reaction mainly occurs on the surface of heterogeneous adsorbent;The quasi-second-order kinetic equation can accurately describe the adsorption process in which the adsorption mainly lies in ion exchange;the reaction process can be spontaneous;and the increasing temperature is conducive to the adsorption reaction.?4?By means of spectrum and energy spectrum,the adsorption morphology and microstructure of U???were analyzed.The results show that the adsorption reaction occurs in the inner holes on the surface of the clay rock.The hydroxyl and carbonyl on the surface of minerals can react with–OH?-C=O and Al₂O₃?SiO₂ forming=Al/-OH??Si-OH.The hydroxyl groups of-C-C-?-C-O-?-C=O-?Al-O and Si-O on the surface of minerals mainly are involved in the adsorption reaction;U???reacts with the surface of the clay minerals and forms a variety of surface complexes,such as?Al/SiO-UO₂⁺,?Al/SiO-CO₂UO₂?CO₃?₂^4-,?Al/SiO-?UO₂?₂?OH?₂CO₃^-,etc.