Methomyl Adsorption onto Cotton Stalks Activated Carbon (CSAC): Equilibrium and Process Design

Equilibrium studies were carried out for adsorption of an insecticide (Methomyl) form aqueous solutions onto a prepared cotton stack activated carbon (CTAC) in a batch adsorption system. Parameters affecting adsorption capacity including contact time, adsorbent size (dp =355:800 μm) and temperature (T=25:60 °C) were investigated. Three mathematical models, Langmuir, Freundlich and Redlich-Peterson were employed for fitting the equilibrium data. Linear regression was used to determine the best fit and was found that the equilibrium data are best represented by Langmuir model thus suggesting the monolayer sorption of methomyl. The Langmuir constants (qmax = KL/aL) decreases with the increasing of temperature as well as decreasing the particle size of adsorbent. The adsorption capacity was found 72.85 mg/g at 25 °C and decreased to 47.36 mg/g when temperature increased to 60 °C . The value of enthalpy change was calculated (H = -2.35 kJ/mol) indicating that the removal process was exothermic and physical in nature. A single stage batch adsorber was designed for the adsorption of methomyl onto CSAC based on the optimum isotherm.