Microscopic Study On The Adsorption Mechanism Of Montmorillonite

The large deformation and failure of deep soft rock roadway is an important engineering problem.The property of water and metal adsorbed in soft clay mineral are the important factors that affect the large deformation and failure of the roadway.In this paper,using the first principles calculation method,the atomic and electronic structures,the mechanism of metal doping,the properties of adsorbed water and heavy metals were simulated from the microscopic point of view.It is hoped that the research results can provide theoretical guidance for solving the problem of large deformation of soft rock road.The calculation results of atomic and electronic structure of montmorillonite shows that with the increase of pressure,the tetrahedral structure of montmorillonite crystal will change irregularly,Al-O and Si-O were significantly decreased and the H-O bond length is almost unchanged,crystal energy increases linearly,the band gap from 5.425ev?0Gpa?to 7.054ev?100Gpa?,the band gap will distortion as the press for 6.1Gpa and 55.6Gpa.Analysis of density of states shows that the cationic and oxygen atoms are main in ionic bond into montmorillonite,also parts of covalent bond,and pressure can enhance two kind of bonds.The mechanism of metal doping in montmorillonite shows that the lattice constant C increases obviously with the increase of the interlayer cation radius,and the lattice angle and the length of the bond around the replacement ion are changed.The VBM of two kinds of replacement patterns appears the impurity band,the band gap decreases,the density of states of O atoms combined with replacement atoms is higher than that of O atoms..The results of the calculation of the adsorption properties of water molecules in the interlayer of montmorillonite indicate that the interlayer cations are the main factors affecting the adsorption of montmorillonite.The adsorption energy is the largest in the cation site,and is better than that in bridge,hollow and top site.When the cation radius increases gradually,the water adsorption is weaken relatively effect by cations,and adsorption distance increased;in bridge,hollow and top site was increased relatively,adsorption distance becomes small.With the increase of the number of water molecules,the change trend of the adsorption energy and the cell layer spacing in the cation site of montmorillonite increases.When the pressure parameters are taken into account,the increase of pressure will lead to the decrease of adsorption energy and the increase of adsorption distance,and the pressure has the greatest influence on these two data at 6Gap.The inner structure of montmorillonite adsorption results show that the formation energy of Cr is minimum,As and Pb followed,indicating that these heavy metals were easily adsorbed in the octahedral?tetrahedron?inner structure,the formation energy of Cd is very high,it is difficult to enter the two inner structures.The transition energy of Cr is minimum,indicating that Cr most likely to enter octahedral?tetrahedron?inner structure and had negative chargeing;transition energy of As and Pb are relatively small,in the two kinds of structure are easier to exist and had negative chargeing,transition energy of Cd is deep,difficult to enter the structure to produce negative chargeing.The calculation of montmorillonite interlayer adsorption of heavy metal atoms shows that the effect of adsorption of heavy metals is the worst in the cation site,bridge,hollow and top site were better,larger interlayer cations have enhanced the adsorption effect of bridge,hollow and top site,and adsorption effect:Cr>As>Pb>Cd.Analysis the state of density of the adsorbed As,it is found that the adsorption effect of As in the interlayer cation is the worst,and in the bridge site is relatively stable,the adsorption of AS in bridge site had more extensive overlap region with O_As,which is easier to form the AS-O bond.