The study of adsorption efficiency of rice husk ash for removal of phenol from wastewater with low initial phenol concentration

Abstract

This research work aimed to assess the adsorption efficiency of rice husk ash for removal of phenol from wastewater. The authors studied the morphology and characterization of rice husk ash using SEM, FTIR, XRD and BET analyzers and carried out the batch experiments to evaluate the removal percentage of phenol with variation of pH (3–11), adsorption time (30–270 min), adsorbent dose (0.5–4.0 gm/L), phenol concentration (5–20 mg/L) and temperature (25–35 °C). It was observed that the maximum removal reached as high as 95%. The testing of kinetic models showed that the second-order model was better than the first-order model. Elovich model showed that the adsorption process was chemical, Reichenberg model showed that adsorption occurred because of film diffusion, Furusawa and Smith model showed that phenol moved faster from bulk to solid stage, Boyd model indicated that the process supported chemisorptions, and Fick’s model implied that film and intraparticle diffusion took 45 min and 135 min, respectively. Testing of isotherm models indicated that Langmuir, Freundlich and Temkin models were all supportive of equilibrium data. The Dubinin–Radushkevich isotherm indicated that the process was explained by feeble physical adsorption. The isothermal study indicated that the process was random, endothermic and spontaneous. Although some studies had been done for removal of phenol using rice husk ash in the past, this research had covered the extensive works on the characterization of the adsorbent, extent of phenol removal with the variation of several process variables, and testing of several models in the areas of kinetics, isotherms, and thermodynamics. Further, the novelty of this research was that the experiments were carried out for treatment of wastewater exclusively with low initial phenol concentrations so that the results can be effectively applied in several small- and medium-scale industries at lesser costs, particularly in the Third World countries.