Activated carbon Freundlich isotherm model

Abstract Removal of the pesticide metobromuron from aqueous solutions by adsorption at the high area activated carbon cloth was investigated. Kinetics of adsorption was followed and adsorption isotherms of the pesticide was also be determined. In kinetic studies a special V-shaped cell with an UV cuvette attached to it was used for adsorption processes. With this cell it was possible to follow the concentration of pesticide molecule by in situ UV spectroscopy as it is adsorbed at the activated carbon cloth. The obtained absorbance vs time data were converted into concentration vs time data and these data were treated according to pseudo-first-order and psendo-second-order kinetic models. Adsorption of that pesticide was fonnd to follow second-order kinetic model with k 87.35 g mol min. Adsorption isotherms were derived at 25°C on the basis of batch analysis. Isotherm data were treated according to Langmuir and Freundlich models. The fits of experimental data to these equations were examined and founded that the adsorption isotherm was well represented by Frenndlich model. 

The capacity and intensity with which either GAC or PAC adsorbs a given solute has been modeled in several ways. The most commonly applied method is referred to as a Freundlich isotherm. The capacity of the activated carbon is defined as a function of the intrinsic characteristics of the carbon itself, the nature of the solute, and the final equilibrium concentration of the solute. The eapacity is defined as ... 

Due to the effects of molecular size and shape and pore structure on the kinetics, the model cannot be used for general predictive purposes. In practice, in order to predict PAC adsorption, a series of experiments must first be carried out using the compound of interest, the activated carbon to be applied, and the water in which it is to be used. Equilibrium parameters, determined from the Freundlich adsorption isotherm equation, are used as input into a computer-based HSDM, which uses the method of least squares to minimize the difference between the experimental kinetic data points and the HSDM fit of the data [10]. When the best fit is achieved, the resultant kinetic parameters (liquid film mass transfer coefficient, k(, and the surface diffusion coefficient, DJ can then be used for the prediction of adsorption behavior under different conditions. 

Kitagara ° nsed two commercial granular activated carbons for the adsorption of phenol, p.nitrophenol, and 2,4 dichlorophenol from aqueous solutions, and found that the adsorption data could be explained by the Freundlich isotherm equation. The adsorption at a given concentration decreased with increase in the temperature of adsorption, although the rate of adsorption increased with increase in the adsorption temperature. Scharifov derived a mathematical model for the adsorption of phenols by activated carbons from aqueous solutions and obtained an equation for the static adsorption isotherm, which could help in the calculation of adsorption of phenol at any concentration. Chakravorti and Weber used batch and fixed-bed systems for the removal of phenol from aqueous solutions by activated carbons. The pore-diffusion model and a homogenous solid model were used to explain the results. 

Reed, B.E., and Matsumoto, M.R.. Modeling cadmium adsorption by activated carbon using the Langmuir and Freundlich isotherm expressions, Sep. Sci. Technol., 28(13). 2179-2196 (1993). 

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