Adsorption of Oxamyl and Dimecron by Cu-, Gd-, Zn-, Mn-, Co- and Ni- Montraorillonites

Adsorption of two pesticides namely, Oxamyl and Dimecron on montmorill-onite saturated with transition metal ions under variable conditions of pH, humic acid, temperature and solution ionic strength was studied. Oxamyl was found to be more adsorbed than Dimecron. Maximum adsorption of both occurred at pH 6. The adsorption isotherms were of ‘S’ type. The adsorption varied directly with the effective ionic radii of the exchangeble cations and inversely with increase in temperature, organic matter and metal ionic concentration up to 0.25 M after which it became constant. The enthalpy change (ΔH) indicated the process to be exothermic and adsorption of pesticides on montmorillonite gave rise to on entropy loss. Various studies viz, IR, X-ray, thermodynamic parameters and Freundlich adsorption isotherms revealed the existence of protonation andjor coordination between exchangeable cations of clay and oxygen of C = O group of the pesticides.