Adsorption dynamics of phenol on activated carbon produced from Salvinia molesta Mitchell by single-step steam pyrolysis

The kinetics of phenol adsorption with Salvinia molesta Mitchell based activated carbon is reported here by examining the efficacy of single-step steam pyrolysis as cheaper activation process for the production of low-cost activated carbon. The extent of removal of phenol has been found to be dependent on concentration, pH and temperature of the solution. This adsorption reaction can be approximated to first-order reversible kinetics. Also, the intraparticle diffusion of phenol through pores in the adsorbent has been found to be the main rate-limiting step. The surface mass transfer coefficients have been determined for the process under the influence of a number of variables including initial concentration, temperature, agitation speed and adsorbent particle size. With an initial concentration of phenol at 25 mg/L at 30 degrees C and pH 6.0, its removal has been found to be 88%. Phenol adsorption by carbon can be interpreted by Langmuir and Freundlich isotherm models. With the Langmuir model, an adsorption capacity of 100.12 mg/g at 40 degrees C and 177.66 mg/g at 10 degrees C is obtained. Thermodynamic parameters show that the adsorption of phenol by activated carbon is an exothermic process and is spontaneous at low temperatures. Regeneration with hot water has been investigated for several cycles with a view to recover the adsorbed phenol and also to restore the sorbent to its original state.