Preparation Of Clay Minerals Treated By Hydroxyl Aluminum And Adsorption Of Sr,Cs And U

In this paper,montmorillonite and kaolinite with high content are selected as the representative research objects of clay minerals.After optimizing the modification conditions such as modification basicity,modification time,modification temperature and calcination temperature,hydroxyl aluminum ion is used to modify the two kinds of clay minerals,and the clay minerals before and after modification are tested by XRF,XRD,FT-IR,SEM,TEM and TG-DSC Analysis and characterization,explore the mechanism of modification.The static adsorption experiment was used to explore the influence of pH value,contact time,solid-liquid ratio,initial concentration,temperature and ion type on the adsorption of Sr,CS and u by the modified clay minerals.At the same time,the experimental data were used to fit the adsorption kinetic model and isothermal adsorption model,and the following conclusions were drawn:?1?The clay minerals represented by montmorillonite and kaolinite are laminated,with high surface pores and negative charges;the main components are SiO₂,Al₂O₃ and Fe₂O₃,with sufficient cation exchange capacity;they have the basis of modification and ion exchange,and are one of the excellent adsorbents for radionuclides.?2?The best modification conditions of montmorillonite and kaolinite are as follows:alkalinity(OH^-/Al³⁺mole ratio)is 2.4,mixing time is 3 h,modification temperature is338.15K and calcination temperature is 623.15K.XRD results show that the pillared montmorillonite can be achieved in the process of modification,and the interlayer spacing increases from 14.93?to 19.04?;kaolinite can only be intercalated in the interlayer,and the interlayer spacing increases from 7.18?to 7.69?;the increase of interlayer spacing is one of the direct reasons for the increase of adsorption capacity.FT-IR results show that the increase of adsorption sites is due to the attachment or exposure of more metal ion exchange sites on the surface of clay minerals.The SEM results show that the edge profile of the original montmorillonite flake is fuzzy,the number of pores per unit area is limited,the flake peeling phenomenon appears after the modification,the surface irregularity and the number of pores increase obviously,and the edge profile is obvious,which directly proves the formation of pillared modification.Because of the large area of the original kaolinite lamellae and the loose structure,only intercalation can be carried out.After modification,the number of pores per unit area and the number of two-dimensional tubular nanostructures increase significantly;the change of surface structure is one of the reasons for the increase of adsorption efficiency.TEM results show that the original montmorillonite lamellae are closely stacked,the edge of lamellae structure is dense,the modified montmorillonite is loosely stacked,and the edge of lamellae structure is scattered obviously;the poor light transmittance of the original kaolinite indicates that the crystal surface is thick,and the stacking order and crystal surface thickness decrease after modification,meanwhile,it is proved that the two-dimensional tubular nanostructure is hollow;the change of stacking structure is one of the reasons for the increase of adsorption efficiency.The results of TG-DSC show that the modified montmorillonite and kaolinite have good thermal stability and can be used as radionuclide adsorbents.?3?The optimal pH of Sr adsorption by modified montmorillonite and kaolinite is 6,the contact time is 12 h and 8 h,the solid-liquid ratio is 1:150 g·mL^-11 and 1:100 g·mL^-1,the initial concentration is 100 mg·L^-11 and 80 mg·L^-1,and the temperature is 318.15 K and328.15K.The adsorption behavior of SR is in accordance with the quasi second-order kinetic model,and the saturated adsorption capacity q_e22 is 17.39 mg·g^-11 and 11.49 mg·g^-1.The adsorption behavior of SR is in accordance with Freundlich isotherm adsorption model,and the adsorption index 1/n is between 0.1 and 0.5,indicating that the modified clay mineral is very suitable for Sr²⁺.?4?The optimal pH value of Cs⁺adsorption by modified montmorillonite and kaolinite is 4,the contact time is 8h,the solid-liquid ratio is 1:150 g·mL^-11 and 1:100 g·mL^-1,the initial concentration is 120 mg·L^-11 and 100 mg·L^-1,and the temperature is 328.15 K.The adsorption behavior of Cs⁺is in accordance with the quasi second-order kinetic model,and the saturated adsorption capacity q_e22 is 18.66 mg·g^-11 and 14.93 mg·g^-1.The adsorption behavior of Cs⁺is in accordance with Freundlich isotherm adsorption model,and the adsorption index 1/n is between 0.1⁰.5 and 0.5¹.0,indicating that the modified clay mineral is suitable for Cs⁺adsorption.?5?The optimal pH of U?VI?adsorption by modified montmorillonite and kaolinite is 6 and8,the contact time is 8h,the solid-liquid ratio is 1:200 g·mL^-11 and 1:100 g·mL^-1,the initial concentration is 120 mg·L^-11 and 100 mg·L^-1,and the temperature is 328.15 K.The adsorption behavior of U?VI?is in accordance with the quasi second-order kinetic model,and the saturated adsorption capacity q_e22 is 17.44 mg·g^-11 and 15.78 mg·g^-1.The adsorption behavior of U?VI?is in accordance with Freundlich isotherm adsorption model,and the adsorption index 1/n is between 0.1 and 0.5,indicating that the modified clay mineral is very suitable for U?VI?adsorbent.