RESPONSE SURFACE METHODOLOGY TO OPTIMIZE ADSORPTION PARAMETERS FOR NAPHTHALENE REMOVAL IN AQUEOUS SOLUTIONS BY ACTIVATED CARBON

The adsorption characteristics of naphthalene from aqueous solutions on coconut husk-activated carbon (AC) were evaluated. Batch adsorption studies were conducted to study the effects of various parameters, such as initial concentration, agitation time and adsorbent dosage, on naphthalene adsorption. The kinetic data were analyzed using pseudo first-order, pseudo second-order and intra-particle diffusion equations. The experimental data fitted very well the pseudo second-order kinetic model. The equilibrium data were analyzed by the Langmuir and Freundlich adsorption isotherm models. The adsorption isotherm data fitted well to Langmuir isotherm, and the monolayer adsorption capacity was found to be 15.60 mg/g at 20 degrees C. In this study, the central composite face-centered experimental design matrix and response surface methodology (RSM) were applied to design the experiments and evaluate the interactive effects of the 3 most important operating variables, adsorbent dosage (1.0-3.0 g/L), agitation time (10.0-25.0 min) and initial naphthalene concentration (10.0-30.0 mg/L), on adsorption of naphthalene with AC. A total of 20 experimental runs were set, and the experimental data fitted to the empirical second-order polynomial model of a suitable degree for the maximum adsorption of naphthalene from aqueous solutions by AC. An initial concentration of 10 mg/L, adsorption time of 25 min and carbon dosage of 3 g/L were found to be optimal for the maximum removal of naphthalene (97.8%) from aqueous solutions. Analysis of variance of the quadratic model showed that the model was highly significant (R-2 = 0.970, predicted R-2 = 0.766 for q(t) as well as R-2 = 0.989, predicted R-2 = 0.917 for Re %).