Preparation And Characterization Of Organoclays And The Mechanisms To Adsorb DDT Analog From Water

This paper presents a summary of the advances in application of organoclay minerals to the sorption of the environmental organic pollutants. The sorption properties, mechanisms and rules of DDT to organozeolite, organomontmorillonite and organoattapulgite from water were reviewed.A series of organoclays are synthesized by exchanging cation surfactants such as hexadecyltrimethylammonium (HDTMA) and benzyltrimethylammonium (BTMA) on zeolite, montmorillonite and attapulgite. These organoclays were characterized by FT-IR spectroscopic analysis and investigated by scanning electron microscope. The sorption properties, rules and mechanisms for organoclays to sorb DDT and its metabolites DDD and DDE in water are investigated in detail. The results indicate that:1) FT-IR measurements indicate that HDTMA and BTMA have entered interlayer spacing of clays. Total OC content of organoclay is more than that of original clay. From the scanning electron micrographs, the surface of the modified clays are smoother, the degree of stretches are big, and have the crystal characteristic. In addition, the pellet of the modified clay is bigger than the unmodified clay particles.2) The sorption isotherms indicate that the unmodified clays have a low concentration of DDT sorption, but the sorption of DDT on the organoclays increased dramatically. Adsorptive capacity of the HDTMA organoclays increased in the order of atta-H < mont-H< zeo-H, and adsorptive capacity of the BTMA organoclays increased in the order of atta-B< mont-B< zeo-B. For four kinds of DDT analogues, there is negative correlation between adsorptive capacity of the HDTMA organoclays and solubility of them; there is a big change of adsorptive capacity of the BTMA organoclays because of different kinds of clay.3) The results of desorption experiment indicate that the rates of desorption of DDE on organoclays and clays increased with increasing of initial concentrations, and the rates of desorption on clay is much greater than that of organoclay. The rates of desorption on the HDTMA organoclay is the smallest in all. The order of amount of DDE retention on organoclays and clays is BTMA-clay>HDTMA-clay>clay.4) The sorption of HDTMA-montmorillonite for DDT and DDE are related to the amounts of surfactants and the property of organic compounds. With the amounts of surfactants increasing, the adsorptive capacity increased. Sorption isotherms of DDT and DDE are linear. Partition occurs to the sorption for DDT and DDE to HDTMA-montmorillonite. The proportion of partition in the total sorption for DDT to HDTMA-montmorillonite is more than that to soil. So the sorption of DDT to HDTMA-montmorillonites is better than that to soil. It is one of the necessary conditions to control and recover contaminated environment.5) The results of kinetics of adsorption process for DDT and DDE on organomontmorillonite indicated that the adsorption followed pseudo-second-order kinetics with a small energy of activation, which led to large kinetic rate constant and small time to reach adsorption equilibrium. With the temperature increasing, the kinetic rate constant increased, but the adsorptive capacity decreased. And the adsorptive capacity of HDTMA-Montmorillonite for DDE enhanced with the concentration of CaCl₂ increasing.