Adsorption of phenol and 4-nitrophenol on granular activated carbon in basal salt medium: equilibrium and kinetics

Batch studies were carried out for studying the adsorption behaviour of phenol and 4-nitrophenol on granular activated carbon from a basal salt medium (BSM) at pH approximately 7.1 and temperature approximately 30 degrees C. The literature review was done in order to review the information for comparison purposes on equilibrium models of phenol and 4-nitrophenol adsorption on activated carbon. The units for measurements reported in these models were found to be diverse, thus making the comparison difficult. These units have been converted into similar units for easy reference. In all, six models of Freundlich, Langmuir, Redlich-Peterson, Radke-Prausnitz, Toth and Fritz-Schlunder as reported in the literature have been fitted to the data of phenol/activated carbon and 4-nitrophenol/activated carbon systems of the present studies using nonlinear regression technique. Based on maximum deviations and correlation coefficients, Langmuir gave the poorest fit for both compounds; Redlich-Peterson, Radke-Prausnitz, and four parameter model of Fritz-Schlunder could represent the data with similar accuracy, i.e. with R2-value of 0.98 and maximum deviation approximately 12%. However, for phenol, two parameter model of Freundlich may be recommended because of ease in its parameter estimation and better accuracy. 4-Nitrophenol was found to be more adsorbed than phenol, which is consistent with the result found in literature. The kinetics of the adsorption was found to be intra-particle diffusion controlled with diffusion coefficient values of the order of 10(-13)m2/s. Three distinct phases of kinetics--rapid, medium, and slow--have been observed in this study.