The effect of exchangeable ions (Wand Na+), organic matter, surfactants (non-ionic and anionic) and temperature on the adsorption of endosulphan on two different soil types (loam and sandy loanl) at fixed volume fraction of methanol (0.25 fs) has been studied by batch, equilibrium technique. The measured equilibrium adsorption isotherms for all the equilibrium effects/treatments were in close agreement with the Freundlich isotherms. The adsorption was higher on loam soil than on sandy loam soil and was related to the organic matter content, clay content, CaCO3 content, CEC and surface area of the soils. Adsorption on both the soils follows the order as: H -soil > Na-soil natural soil at 10°C> natural soil at 20°C> non-ionic surfactant> organic matter-removed soil> anionic surfactants > natural soil at 40°C and was in accordance with the Freundlich constant K and distribution coefficient Kd values. The adsorptive capacity of the endosulphan for organic matter and clay content of the soils was evaluated by calculating Kom and KC values and it was found that endosulphan adsorption was better correlated with clay content than organic matter content of the soils. The thermodynamic equilibrium constant (K0), standard free energy (ΔGO), enthalpy (ΔHO) and entropy (ΔSO) changes were calculated in order to predict the nature of adsorption.
Adsorption, endosulphan, Freundlich isotherms, free energy, enthalpy, entropy
