The Modification Of Montmorillonite And Its Adsorption Of Arsenate And Molecular Simulation Of Hydrates

Montmorillonite is a naturally occurring clay mineral that exhibits ability to swell. It plays very important roles in many industrial processes. This thesis focuses on two main aspects of simulation and experiments. Molecular dynamics simulation can be very useful in the study of the montmorillonite-cations-water system for understanding the swelling properties of montmorillonite. Titanium pillared montmorillonite prepared by fluorine treating have effective adsorption of arsenate in water which provide a new application field of montmorillonite.First, for a better understanding of the effect of different interlayer counterions on the swelling properties of montmorillonite, the former simulations has been investigated further and MD has been introduced in the comparative studies between Na-/Mg-montmorillonite (a small quantity of Mg2+ replaces Na+ as interlayer counterions in the montmorillonite), which contain mixed univalent and bivalent counterions, and Na-montmorillonite. The montmorillonite-cations-water systems were simulated and swelling patterns of montmorillonite that have different interlayer counterions were investigated. Therefore, the structures and movements of interlayer species has been studied further and the underlying reasons for variations in diffusion modes of Na+ and Mg2+ have been investigated.The simulation results show that Na/Mg-montmorillonite exhibits a higher swellability compared with that of Na-montmorillonite for given water content. Especially with 48～72 water molecules of interlayer, the expansion of layer spacings of Na/Mg-montmorillonite is greater than those of Na-montmorillonite. Interlayer water molecules have a stronger tendency to solvate Mg2+ compared to that of Na+. Inner-sphere complexes and outer-sphere complexes of Mg2+ with water are observed, whereas only planar inner-sphere complexes of Na+ with water are found for two-layer Na/Mg-montmorillonite hydrates. The results also indicate the different diffusion modes of Na+ and Mg2+ for Na/Mg montmorillonite: Na+ remains close to the surfaces of the sheets, whereas Mg2+ is easily hydrated and is located in the middle of the interlayer. Comparatively, Na+ has a wider diffusion range and higher self-diffusion coefficient than Mg2+. Moreover, self-diffusion coefficient of interlayer water is higher for Na-montmorillonite than that for Na/Mg-montmorillonite at the same water content. Most of the results obtained in this study can be understood in terms of the strong solvation of Mg2+ with water molecules, and Mg2+ and Na+ have different influences on the structure of interlayer. It can therefore be assumed that the replacement of a relatively small amount of interlayer Na+ cations by Mg2+ in Na-montmorillonite during the initial stage can substantially change the swelling and diffusion properties of interlayer species. This study demonstrates that both the type and the property of interlayer cations can influence the swelling properties and the structure of interlayer water in montmorillonite.Second, The synthesis of pillared interlayered clays have led to the development of a new class of microporous materials of potential interst as adsorbents, which provide a new way to remove arsenic from groundwater. In the work, titanium pillared montmorillonite by fluorine treating with TiCl4 as the precursors were prepared by hydrothermal method and were characterized using XRD, FT-IR, DTA-TGA, XPS, TEM and N2 adsorption-desorption. Furthermore, the adsorption of trace arsenate in water on titanium pillared montmorillonite by fluorine treating was conducted.The experiments results show that materials have different properties and effects on adsorption of arsenate prepared by different drying methods and/or different different fluorine treating dosage. The 20HF-Ti-MMT has good homogeneous particle size, high crystallization integrity and good stability. TiO2 particles were deposited on the surface of 20HF-Ti-MMT flakes with well-crystallized anatase. The 20HF-Ti-MMT has better effect on adsorption of arsenate in water than the others with high specific surface areas and surface hydroxyl contents. It is also found that, as the thermal treatment temperature and fluorine treating dosage of titanium pillared montmorillonite increase, the adsorption of arsenate in water obviously decrease. Furthermore, during of adsorption, pH, illumination intensity and initial aresnate concentration have effects on adsorption of arsenate by materials.