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

AbstractEquilibrium 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 =355:800μm) 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

Removal of an insecticide (methomyl) from aqueous solutions using natural clay

Adsorption of an insecticide (methomyl) onto natural clay have been investigated as a possible alternative method for its removal from aqueous solutions. The study was aimed to use low cost material as a step towards cleaner environment. The influence of system variables, such as particle size (dp) and temperature on the adsorption capacity have been studied. It was found that natural clay reached equilibrium with methomyl solution in time less than 3 h. The experimental data were fitted to equilibrium isotherm models, Langmuir, Freundlich and Redlich–Peterson. A dimensionless separation factor, R^, was used to judge the favorable adsorption. The results indicated that percentage of insecticide removal ranged from 27.6 to 32.9 for initial concentration varied from 43.71 to 19.99 mg/l. The effect of temperature showed the exothermic nature of the process. The enthalpy change (ΔH) of adsorption has been evaluated and it has a value of, −17.54 kJ/mol. The Langmuir model fit the experimental data significantly better than Freundlich and Redlich–Peterson models. A chart based on material balance using single batch adsorber was constructed for different percentage of methomyl removal using the Langmuir isotherm where the mass of natural clay required to treat a specified volume of solution is calculated

Adsorption Equilibrium of a Herbicide (Pendimethalin) onto Natural Clay

The equilibrium adsorption of a herbicide (pendimethalin) onto natural clay from aqueous solutions was studied experimentally using different system variables. The influence of such variables, such as particle size (d p ), pH and temperature, on the adsorption capacity was studied. Equilibrium modelling was carried out using the Langmuir, Freundlich and Redlich—Peterson models with the corresponding constants being calculated for the different system variables. The results indicate that the maximum adsorption capacity (q max ) at an acidic pH value (3.44) was approximately double that observed at an alkaline pH value (9.62). It was also found that the effect of particle size was significant and that the temperature plays an interesting role in the adsorption process. The enthalpy change (ΔH) for adsorption was evaluated as −29.36 kJ/mol. It is clear from the results of this study that the Freundlich model fitted the experimental adsorption data significantly better than the Langmuir or the Redlich—Peterson models