The Study Of Kaolinite Adsorption

In the engineering of deep soft rock tunnel,the main problem is the large deformation of soft rock,which comes from the clay minerals in the soft rock interaction with water molecules.In order to reveal the mechanism of water absorption and swelling of soft rock,it is necessary to study the adsorption characteristics of kaolinite.In this paper,the first principles calculation method is used to simulate the microstructure,high pressure and water absorption of kaolinite.Furthermore,the adsorption characteristics of heavy metal is studied.Firstly,the research status of clay mineral kaolinite adsorption experiment of heavy metal and water are introduced.Under the influence of experimental conditions and external impurities,the experimental result is always unsatisfactory,and theoretical research of kaolinite is less.In order to reveal adsorption mechanism of kaolinite from the microscopic view,study the internal information of kaolinite by the first principles method.The theoretical basis and method of the research are introduced briefly.Secondly,set up the structure model of clay mineral kaolinite and carry on the calculation by the first principles method,and get the state density and band structure of clay mineral kaolinite.In order to simulate the high pressure environment for soft rock engineering,this paper had studied the influence of stress conditions on the structure of kaolinite.The results show that the pressure will change the lengths of ionic bonds,and the width of band gap get bigger with the increase of stress through the analysis the density of state and band structure of kaolinite.The band structure of kaolinite converts an indirect gap with a direct gap when the pressures are 0.6GPa,66.3GPa and 76.5GPa.With the increase of pressure,the peak of DOS decreases and electron delocalization enhances for Al and O atoms,which means that the exchange Al ions in kaolinite with some low-valent is weakened.Thirdly,considering the high stress conditions in engineering,this paper has studied kaolinite water absorption under the high pressure.By studying the water molecules adsorbed in the different adsorption sites such as top,bridge and hollow sites,it is found that the stable adsorption distance is different at the different adsorption site.The adsorption of water molecules at the bridge sites is the best,followed by the top sites and hollow sites.This paper has studied the adsorption of multiple water molecules on the surface of kaolinite on the basis of the single water molecule adsorption,and it is found that the adsorption structure of kaolinite is more stable with the increase of water absorption.The effect on the adsorption of water molecules is best when the pressure is 4?6GPa.Lastly,the adsorption characteristics of four heavy metals,As,Cd,Cr and Pb,were studied by the surface,internal and interstitial adsorption of kaolinite respectively.The results show that the adsorption effect of the three kinds of adsorption is the best,and the adsorption of the four heavy metal ions on the surface of clay mineral kaolinite is Cr>As>Pb>Cd.The adsorption of heavy metal Cr in kaolinite is the best,and the adsorption of heavy metal Pb and Cd in kaolinite is the worst.The heavy metal Pb could be adsorbed stably under high temperature.All of the four kinds of heavy metal are di–cult to be adsorbed steadily in the interstitial spaces of kaolinite.The results show that the adsorption effect of clay mineral kaolinite for Cr and As is the better,and the adsorption of heavy metal Pb and Cd is the worst.