Effect of different factors on the Adsorption of Endosulfan on Soils

The effects of exchangeable ions (H⁺ and Na⁺), organic matter, surfactants (anionic and non-ionic) and temperatures (10, 20 and 40°C) on the adsorption of endosulfan on 3 different soil types (silt loam, loam and sandy loam) at fixed volume fraction of methanol (f_s = 0.25) has been studied. The measured equilibrium adsorption isotherms for all the effects/treatments were in close agreement with the Freundlich isotherms and yielded S-shaped isotherms. The adsorption of endosulfan in all cases was higher in silt loam soil followed by loam and sandy loam soil and was related to the organic matter, clay, CaCO₃ contents and surface area of the soils. Adsorption on soils follows the order H⁺ -soil > Na⁺ -soil > Natural soil at 10°C > Natural soil at 20°C > Non-ionic surfactant > Organic matter removed soil > Anionic surfactant > Natural soil at 40°C and was in accordance with the Freundlich constant K and distribution coefficient K_D values. The adsorptive capacity of the endosulfan for organic matter and clay content of the soils was evaluated by calculating K_om and K_c values and it was found that endosulfan adsorption was better correlated with the clay content than organic matter content of the soils. The thermodynamic equilibrium constant (K_o), standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes were calculated in order to predict the nature of adsorption.