Adsorption Of Organic Matter On Clay Minerals And The Stability Of The Organo-clay Composites

The adsorption of organic matter on clay minerals is an important process in sediments and sedimentary rocks. In the sediment deposition, burial and diagenesis process, clay minerals and organic matter are interdependent, interwovenness and intergration. Clay minerals preservation of organic matter has a very important role in studies of soil and marine sediment. It is also of great significance for deepening the hydrocarbon-generating theory and the evaluation of oil and gas resources. But the study on the interaction of organic matter and clay minerals as well as the evolution process is still in a relatively weak phase.For this purpose, alkyl ammonium salt and two typical kinds of natural organic matter, lysine(L) and chitosan, are intercalated in montmorillonite and under detail characterization. The stability of the complexes are studied in different solutions at room temperature and pressure as well as in hydrothermal conditions. The adsorption of diesel on montmorillonite, smectite-illite minerals, illite and organoclay complexes was studied afterwards. The main results are given bellow:1. The adsorption of the organic matter on montmorillonite is dominated by cation exchange and then by adsorption of electrically neutral forms. The organic matter first enters in the interlayer of the montmorillonite by cation exchange. But with the increasing of concentration, the organic matter is adsorbed in electrically neutral forms by van der Waals force and hydrogen bond into the interlayer of montmorillonite when the cationic exchange capacity of the clay is balanced. 2. The adsorption of hexadecyltrimethylammonium bromide (HDTMA) montmorillonite is mainly dominated by cation exchange. At low concentration, alkylammonium ions form a monolayer; when the amount of modifier is high, alkylammonium ions may tilt in the interlayer of montmorillonite, and it is possible to form a double-layer or pseudotrimolecular layer structure. Lysine has three kinds of configuration arrangement in the interlayer of montmorillonite. With increasing concentration of lysine, the molecules are first inclined in the interlayer, and then orientate perpendicular to the montmorillonite layers, maybe a zig-zag arrangement, finally form second rows and may generate simple peptide by lysine polymerization. The net charge of amino acids, which depends on the pH in both the bulk solution and in the proximity of the clay layer or the interlayer space, is an important factor affecting the adsorption process. For chitosan, a layered structure can form in the interlayer of montmorillonite. The first chitosan layer is adsorbed through a cationic exchange procedure, while the second layer is adsorbed in the acetate salt form. The pH of the solution and the presence of the inorganic salt will affect the adsorption process.3. The stability of the complex is related to the nature of the organic matter itself and its form combined with montmorillonite. At room temperature and pressure,18HD-montmorillonite and chitosan-montmorillonite complexes in different solutions are stable, but lysine-montmorillonite complexes are unstable under the same condition. Under hydrothermal conditions, lysine and chitosan can promote the illitization of smectite, but when alkyl ammonium salt is intercalated into montmorillonite, the conversion rate seems to be reduced.4. Clay minerals can adsorb diesel effectively, smectite-illite mixed-layer sequence seems to have a higher adsorption capacity with the increase of illitization. Adsorption capacity of chitosan-montmorillonite complex is close to smectite, but the adsorption capacity of18HD-montmorillonite complex is far higher than the other samples. The majority of adsorption amount of diesel on clay minerals and complexes are in the micropores and on the external surface. Only a small amount of diesel can enter into interlayer of the clay minerals and complexes.