Removal mechanism of endosulfan sorption onto wood charcoal

Endosulfan is among the most widely used pesticides in developing countries and other parts of the world and has been found to contaminate various par ts of the environment, including drinking water sources. In an earlier stud y to find a suitable adsorbent to remove endosulfan, wood charcoal was foun d to give promising results. In the present study, the process controlling the rate of endosulfan sorption onto wood charcoal and the mechanism of rem oval were examined using various methodologies. Both film and pore diffusio n coefficients were determined, and the linearity of the rate constants of adsorption with initial endosulfan concentrations revealed the process to b e controlled by film diffusion. This was supported by the linear fit of the rate constants with the inverse of the diameter of adsorbent particles and the change in adsorption rates with agitation speed. Multiple interruption tests also revealed that endosulfan sorption onto wood charcoal is control led by film diffusion. The increase in reaction rate constant with temperature and isosteric heat of adsorption in the range of -2.655 to 5.185 kcal/mol implied that the end osulfan removal process was endothermic in nature. The activation energy of 2.33 kcal/mol, which was less than 12 kcal/mol, revealed that the removal mechanism could be attributed to physisorption with a major contribution of van der Waals and electrostatic forces.