Abstract
The effect of exchangeable cations (H+ and Na+). autoclaving, organic matter, anionic surfactants and temperature on the adsorption of phosphamidon on two different types of Indian soil was studied. The adsorption isotherms for all the effects/treatments were in close agreement with the Freundlich equation and yielded S-shaped isotherms. The amount of phosphamidon adsorbed in all cases was higher in medium black (silt loam) soil than alluvial soil (sandy loam) and was related to the organic matter content, clay content, CaCO3 content, surface area and cation-exchange capacity of the soils. The adsorption on both types of soil follows the order H+-soil > Na+-soil > natural soil at 10°C > natural soil at 20°C > autoclaved soil > organic matter-removed soil > anionic surfactant > natural soil at 40°C, which was in accordance with the Freundlich constant, KF, and distribution coefficient, Kd, values. The adsorption capacity of phosphamidon for organic matter and clay content for both the soils was evaluated by calculating the Kom and Kc values when it was found that phosphamidon adsorption was better correlated with the clay content than with the orgnic matter content on the basis of adsorption isotherms. Various thermodynamic parameters such as the thermodynamic equilibrium constant (K0), the standard free energy (ΔG0), the standard enthalpy (ΔH0) and the standard entropy (ΔS0) changes have been calculated as a means of predicting the nature of the isotherms.
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