INDIVIDUAL AND COMPETITIVE ADSORTION OF NITROBENZENE AND HUMIC ACID

Abstract

The present study aims to investigate the suitability of using commercial activated carbon (ACC) for individual and simultaneous adsorption of Nitrobenzene (NB) and Humic Acid (HA) from aqueous solution. The physico-chemical characterization of the ACC before and after adsorption of NB and HA has been done using various methods like X-ray diffraction, energy dispersive and scanning electron microscopy, FTIR spectroscopy, etc. The X-ray spectra of the ACC reflected the presence some characteristic components in ACC. FTIR spectra of the ACC indicated the presence of various types of functional groups. Thermo-gravimetric analysis exhibited the thermal stability of the ACC up to 300 °C temperature. The influence of various experimental parameters viz. initial pH (p1-1,), adsorbent dose, contact time and temperature on the adsorptive removal of NB and HA from aqueous solution by commercial grade activated carbon (ACC) were investigated. Equilibrium contact time for both the adsorbates were found to be 5 h for Co < 100 mg/1 and 12 h for 100 mg/1 < Co < 500 mg/I. Optimum removal of NB and HA onto ACC occurred at respective natural pH of 5 and 2, respectively. Optimum adsorbent was found to be 10 g/I for both the adsorbates. The NB and HA adsorption following pseudo-second-order kinetics. NB and HA adsorption onto ACC was found to be best represented by the Redlich-Peterson and Temkin isotherms, respectively. The positive values of the change in entropy (AS°) and heat of adsorption (AH°); and negative value of change in Gibbs free energy (AG) indicated feasible, endothermic nature of NB and HA adsorption onto ACC. This also utilized Taguchi optimization methodology (L27 orthogonal array) to optimize various parameters for the simultaneous removal of NB and HA from aqueous solutions using ACC as an adsorbent. The effect of such parameters as initial adsorbate concentrations (C0,1), temperature, adsorbent dosage (m) and contact time on the III adsorption of the NB and HA has been studied at three levels to see their effect on the selected response characteristic (total amount of adsorbate adsorbed on ACC in mg/g of ACC (qt.,). The Pareto analysis of variance shows that m is the most significant parameter. The contribution of interactions between Co,i's is also significant. Confirmation experiments haVe been performed to prove the effectiveness of the Taguchi technique after the optimum levels of process parameters are determined. The equilibrium adsorption data for competitive adsorption of NB and HA onto ACC from binary systems were also obtained at different initial concentrations ( C0=25- 500 mg/1), 12 h contact time, 30 °C temperature, ACC dosage of 10 mg/I. The adsorption capacities of ACC in the binary mixtures are in the order NB > HA. The equilibrium NB and HA removal decreased with increasing concentration of the other adsorbate and the combined action of NB and HA on ACC was found to be antagonistic. The extended-Langmuir model satisfactory represented the binary adsorption equilibrium data of NB and HA onto ACC. NB and HA loaded ACC regeneration was studied by using various solvents as well as by heating the spent ACC at 350 °C. Solvent aided regeneration of ACC was found to be very less with maximum desorption efficiency shown by acetone (around 25%) NB-ACC system. However, with thermal regeneration ACC showed good efficiency for NB and HA removal in five subsequent desorption-adsorption cycles.