The Characterization、thermal Activation And Kinetics For Reactions Of Bentonite From Kerjian In Xinjiang

Bentonite is a kind of nonmetallic minerals whose main mineral component is montmorillonite, and montmorillonite is hydrous aluminum silicate minerals with layered structure. Montmorillonite has been widely used in the inudstry, agriculture, medicine and scientific research because of its excellent physical and chemical performances. Although bentonite has been reseached systematically and broadly, properties of bentonite from different places have great difference because they have strong adsorption, ion exchange and hygroscopicity. In this paper, using bentonite from Kerjian in Xinjiang as the research object, its composition, structure, and physicochemical properties were characterized, and its thermal activation and kinetics for reactions were investigated. The study has important academic and practical meaning to fully understand physical and chemical behavior of this kind of bentonite.In this paper, the chemical structural formula of montmorillonite is [(Na, Ca, Mg, K)0.4](Al3+1.58(Fe3+, Fe2+)0.07Mg0.31) Si4O10(OH)2·nH2O, which is calculated by the chemical constituents of bentonite.The structure of bentonite was characterized and properties of bentonite were determined by Brunauer- Emmett-Teller(BET) nitrogen sorption, Zetapotential, X-ray diffraction(XRD), Scanning electron cicroscopy(SEM), Fourier transform infrared spectrometer(FTIR) spectra, and Thermogravimetric Analysis and Differential scanning calorimeter(TG-DSC) technology.The thermal decomposition processes of bentonite from Kerjian, Xin jiang have been studied in dynamic air using a simultaneous thermal analysis instrument. It is found that montmorillonite dehydrate interlayerwater when the temperature is between 98℃ to 450℃, and the hydroxyl in octahedral sheet dehydrate when the thermal treatment temperature is from 500℃ to 750℃.Thermogravimetric data was used to carry out the kinetic analysis. First, the exact activation energy was calculated by the iterative method. Then, the activation energy was used in the Malek method to infer the reaction mechanism. Finally, the above data were used to obtain the pre-exponential factor A. The dehydroxylation of montmorillonite in the temperature range 98 ~ 450 ℃ followed the model of chemical reaction. The functions are nnf))1(1(-14)(n)(--=ααα and n)-1-1)(Gn=αα)((, where α is the transformation degree and the reaction order n is 1/2. The apparent activation energy is 32.81 kJ/mol, and the range of the lgA is from 4.876 to 4.8821s-. The dehydroxylation of montmorillonite in the temperature range 500 ~ 750 ℃ followed the model of chemical reaction. The functions are f(α) =(1-α)n 和 G(α) =(1-(1-α)1-n)/(1-n), where α is the transformation degree and the reaction order n is 2.1. The apparent activation energy is 201.85 kJ/mol, and the range of the lgA is from 11.210 to11.2311s-.