NOTE THERMAL STABIL ITY OF CHLORDIMEFORM- MONTMORILLONITE COMPLEX

Studies of the thermal stability of organic compounds adsorbed on clay minerals are of interest from several points of view, e.g. the type and strength of bonding forces between the organics and the clay surfaces (Chou & McAtee, 1969; Yariv et al., 1971; Lacher et al., 1981), and the effect of the clay surface on stability or degradation mechanism of the organic compounds adsorbed on clays (Bodenheimer et al., 1966; Yariv et al., 1971; Durand et al., 1972). Interactions between clay minerals and organic pesticides are important to studies of environmental pollution, the thermal stability of pesticide-clay complexes being of particular elevance. Chlordimeform is a cationic pesticide which is strongly adsorbed on montmorillonite, ssentially by cation exchange (Hermosin & Perez-Rodriguez, 1981), and the chlordimeform-montmorillonite complex is highly stable under normal conditions (Hermosin, 1978). This note describes the thermal stability of the chlordimeform-montmorillonite exchange complex as studied by infrared spectroscopy (IR), X-ray powder diffraction (XRD) and thermal analysis (DTA and TG) in order to assess the effect of the clay surface on the fate of this cationic pesticide. Materials and methods The clay used was Na-montmorillonite from Crock County, Wyoming (SWy-1) obtained from the CMS Source Clays Repository. Homoionic Mg:+-montmorillonite was prepared by saturating the clay with MgCl 2 solution and washing with water until chloride-free. The chlordimeform used was the technical product supplied by Shering Agro SA (Barcelona, Spain) of purity>99%. The molecular structure of chlordimeform is