Adsorption of Phenolic Compounds onto the Activated Carbon Synthesized fromPulp and Paper Mill Sludge: Equilibrium Isotherm, Kinetics, Thermodynamics andMechanism Studies

New activated carbon was produced from pulp and paper mill sludge as a low cost precursor viachemical activation by zinc chloride. The activated carbon was successfully used for the adsorption ofphenol and two of its derivatives, i.e. 2-chlorophenol and 4-nitrophenol from aqueous solutions. Thecharacterization of the prepared activated carbon demonstrated high textural properties for thesynthesized activated carbon. The results revealed superior adsorption performance of the preparedactivated carbon in this study compared to the commercial one. The effect of main affecting parameterssuch as pH, contact time, concentration and temperature on adsorption of phenolic compounds wasexperimentally investigated in discontinuous system. The adsorption capacities followed the order of4-nitrophenol > 2-chlorophenol >phenol which was attributed to the property of substituent groups intheir chemical structure. Amongst the isotherm models used to describe experimental equilibrium data,the best match was obtained by Sips isotherm which revealed the heterogeneous behavior of theadsorption sites on the adsorbent surface. Kinetic study demonstrated that the adsorption kineticsfollowed pseudo-second-order kinetic model. Based on thermodynamical analysis, the negative valuesobtained for Gibbs free energy, enthalpy and entropy indicated spontaneous, exothermic and randombehavior of the adsorption process