The Interfacial Characteristics Of Mineral-Water System And The Study Of Their Adsorption Mechanism

Reactions at the mineral-water interface play an important role in the cycling of matter in aquatic systems even at the Earth's surface as well as the geochemical processes of elements, and are of significance to the environment. Kaolinite, as the most important clay mineral in soils and sediments and a main component of suspended particles in atmosphere and aquatic systems, controls the transport, fate and bioavailability of inorganic ions and organic molecules in atmosphere, aquatic systems and sediments vitally. Focusing on the reactions at the mineral-water interface, this dissertation at first gave a brief review of the theoretical basis and models of the reactions, and then investigated the surface acid-base properties of kaolinite and metal ions adsorption behavior with nonelectrostatic model (NEM). Also, the study was presented on interfacial physicochemical characteristics of humic acid-kaolinite systems.This study was supported by National Natural Science Foundation of China (NO 40373042) and Guangdong Province Natural Science Foundation (NO 031504). The workloads of this paper can be summarized as follows. Conclusions of this work were drawn as follows:1. The proton adsorption on kaolinite under different pH conditions was described with nonelectrostatic mode (NEM). Relative parameters of proton adsorption/desorption were calculated by nonlinear fit based on the experimental data which were corrected with consideration to the kaolinite dissolution, also, the reactions at every sites were discussed. The overall surface is neutral in a narrow pH range close to the overall PZNPC (-5.2), where the positive and negative charges are balanced, irrespective of the nature of sites. At this pH, the uncharged species are however dominant.2. Dielectric relaxation spectroscopy of the kaolinite suspension in NaCl solution ianalysis shows that the frequency dependence of the response of kaolinite suspension in NaCl can be well explained by the use of the properties of the EDL. The dielectric relaxation mechanism of this system is not merely single-mechanism relaxation which involves translational motion, interfacial polarization, electrode polarization, solution diffusion and low-frequency dielectric dispersion.3. Multi-modes sorption mechanisms of Cu(II) onto kaolinite coexisted: the ion exchange model, surface complexation model and surface precipitation.4. The sorption mechanism of humic acid onto the kaolinite depended on surface sites or functional groups and their surface charge. The major mechanism by which humic acid adsorbed onto kaolinite involved ligand exchange, hydrophobicadsorption and surface complexation. The adsorption of humic acids on kaolinitesurface increases with the decreases of solution pH.Furthermore, detailed information about the adsorption mechanisms have beenmentioned and discussed in this study in order to clear the interfacial behavior ofkaolinite.