Removal of lead ions from aqueous solutions by adsorption onto chemically modified silk cotton hulls by different oxidizing agents

In the present study, the removal of lead ions from aqueous solutions was studied using activated carbons prepared from silk cotton hulls by three different acid activation methods; they are named as concentrated (conc.) H2SO4 (AC), mixture of conc. H2SO4+H2O2 (AC1), and mixture of conc.H2SO4+NH4S2O8 (AC2). The surface properties of the adsorbent materials were determined by the Fourier Transform infrared spectroscopy, thermogravimetric analysis, BrunauerEmmetteTeller, scanning electron microscope, and energy dispersive X-ray analyses. From the thermogravimetric analysis result, the formation of carboxylic acid and lactones are present in the order AC2>AC1>AC. BrunauerEmmetteTeller result shows that the activated carbons are macroporous in nature. Batch adsorption experiments were performed as a function of pH, adsorbent dose, contact time, initial metal ion concentration, and temperature. The experimental equilibrium adsorption data fits well for the Langmuir, Freundlich, and Tempkin equations. The maximum adsorption capacities were 40.00mgg1 for AC and 83.33mgg1 for AC1 and AC2, respectively. Adsorption kinetic data were modeled using the pseudo-first-order and pseudo-second-order, and intraparticle diffusion equations and its rate constants were evaluated. The adsorption process followed the pseudo-second-order reaction kinetics, suggesting that it is presumably chemisorption. The calculations of the thermodynamic parameters revealed that the adsorption process was endothermic, but it is feasible and spontaneous under natural conditions. The reversibility of the process has been studied in a qualitative manner, and it shows that the spent activated carbons can be effectively regenerated for further use easily. (c) 2012 Curtin University of Technology and John Wiley & Sons, Ltd.