Study On Preparation, Structure And Adsorption Performance Of Al-Pillared Montmorillonite

Al-pillared montmorillonite is a kind of new mineral material with good adsorption performance, the structure and performance of which is closely related to the structure and property of pillared reagents and the preparation parameters. Therefore, thorough investigation of the formation mechanism, variation laws of structure and properties have important significance to improve the application performance of Al-pillared montmorillonite. Using surfactant as structure regulators, based on the study about the structure and properties of hydroxyl-aluminum pillared-agent, this thesis systematically studies the preparation, formation mechanism of Al-pillared montmorillonite, and the influence of surfactant on the structure and properties of Al-pillared montmorillonite. Subsequently the laws and mechanism of adsorption of Cr6+ onto Al-pillared montmorillonite are discussed.Based on the preparation research of aluminum polyhydroxy cation(Keggin ion), the optimum parameters are put forward. A high efficient pillared reagent, in which the content of Ala (usually regarded as mononuclear species), Alb (usually regarded as polymeric species) and Alc (usually including high polymeric or colloidal Al species) is 2.21%,87.51% and 10.28% respectively, can be prepared when the basicity is 2.4, temperature is 80℃, sampling speed is 1 mL/min, stirring rate is 300 r/min, the concentration of aluminum chloride and sodium carbonate is 0.2 mol/L and 0.4 mol/L respectively and aging time (at room temperature) is 1 day.The interlayer spacing, specific surface area and pore structure of the prepared Al-pillared montmorillonite samples are detected by XRD, TG-DTA, FTIR, SEM and EDS, and the structure variation laws of the samples are discussed. Al3+/clay, calcination temperature and drying method have significant influence on the interlayer spacing, specific surface area, pore structure and surface property of Al-pillared montmorillonite, and the product prepared air-dried at room temperature has the maximum d(001) and specific surface area value; BET specific surface area, surface fractal dimensions and surface roughness of Al-pillared montmorillonite are much larger than those of unpillared Na-montmorillonite, and have a positive correlation to d(001) value. Their pore structure is characterized as parallel plate slit or "house-of-cards-like" wedge-shaped pore which is formed by novel meso-microporous delaminated structure and fragments. The most probable pore size is about 2 nm, which is mesopore; The influence of pillared reagents on the Al-pillared montmorillonite is suggested as the interaction of the pillared effect, the new pore and surface area effect, the clogging effect and smoothing and sealing effect, which are closely related to the dosage of hydroxyl-aluminum pillared-agent.The structure and property control of Al-pillared montmorillonite modified by surfactant is systematically investigated. The results suggest that the interlayer spacing, specific surface area and surface properties are affected evidently by category and dosage of surfactant, if the surfactant is preadsorbed in the preparation of Al-pillared montmorillonite. With the increase in the addition content of dodecylamine (DA) and dodecyl trimethyl ammonium chloride (DTAC), the hydrophobicity of Al-pillared montmorillonite preadsorbed by DA (DA-Al-M samples) or DTAC (DTAC-Al-M samples) increases, their weight loss increases, while their interlayer spacing, specific surface area and pore volume increases firstly and then decrease. The interlayer spacing and specific surface area value of Al-pillared montmorillonite reached to maximum when the dosage of DA and DTAC are 0.5CEC and 0.75CEC respectively, while their interlayer spacing and specific surface area value decreases with the increase in the addition content of DA and DTAC when the dosage of DA and DTAC is more than 0.5CEC and 0.75CEC respectively, in which the clogging effect plays a leading role. The interlayer spacing and specific surface area of DA-Al-M samples is much larger than that of DTAC-Al-M samples with the same dosage. The interlayer of DA-Al-M and DTAC-Al-M samples has both the structure of DA or DTAC and Keggin ion. Their thermal stability highly depends on the density of interlayer pillars. Compared to the Al-pillared montmorillonite without preadsorption of surfactant, the surface fractal dimensions of DA-Al-M and DTAC-Al-M samples is lower while their surface is relatively smooth.Results of thermodynamics and kinetics research indicate that the adsorption of aluminum polyhydroxy cation onto montmorillonite can be better described by pseudo-second-order kinetic model, while the isotherm is in accordance with Redlich-Peterson model. The adsorption, which is an endothermic process, is the interaction of hydrogen bonding force, dipole force and Van der Waals force.The results of adsorption research indicate that the adsorption amounts of Cr6+ onto Al-pillared montmorillonite increase with the increase of the initial concentration of Cr6+and adsorption time. The adsorption amounts of Cr6+ onto Al-pillared montmorillonite with surfactant modification (DA-Al-M and DTAC-Al-M samples) are significantly larger than those without surfactant modification. The adsorption amount of DA-Al-M samples is much larger than that of DTAC-Al-M samples with the same dosage. The adsorption process of Cr6+ can be better described by pseudo-second-order kinetic model, which is controlled by both intraparticle diffusion and film diffusion, while the isotherm is in accordance with Redlich-Peterson model.