Uptake of heavy metals in batch systems by sulfurized steam activated carbon prepared from sugarcane bagasse pith

In this work, sorption of Pb(II), Hg(II), Cd(II), and Co(II) on sulfurized steam activated carbon (SSAC) has been studied by using a batch technique. The SSAC has been prepared from sugarcane bagasse pith by single-step steam pyrolysis in the presence of SO2 and H2S at 400 degreesC. The adsorption of metal ions on SSAC has been found to be time-, concentration-, pH-, and temperature-dependent. The kinetic data obtained at different temperatures have been analyzed using a pseudo-second-order equation. Kinetic and thermodynamic parameters have been determined based on the rate constants using Arrhenius and Eyring equations. The adsorption of heavy metal ions from aqueous solutions increased with increasing pH, and maximum removal [99.2% for Pb(II), 97.2% for Hg(II), 93.1% for Cd(II), and 81.9% for Co(II)] was observed in the pH range of 4.0-8.0 with an initial concentration of 100 mg/L. The selectivity order of the adsorbent is Pb(II) > Hg(II) > Cd(II) > Co(II). The H-type adsorption isotherm obtained for the adsorbent indicated a favorable process. The applicability of the Langmuir and Freundlich adsorption isotherm models has been tested. The SSAC had maximum adsorption capacities (evaluated from fits of the Langmuir isotherm to batch adsorption data for a contact time of 4 h at 30 degreesC) for Pb(II), Hg(II), Cd(II), and Co(II) of 200.00, 188.68, 153.85, and 128.70 mg/g, respectively. The competitive adsorption capacities of the SSAC for all metal ions were found to be lower than noncompetitive conditions. Heavy metal adsorption from synthetic wastewaters was also studied to demonstrate its efficiency in removing metals from wastewaters containing other cations and anions. Metal ions, which are bounded to the SSAC, could be stripped by acidic solutions (0.2 M HCl) so that SSAC can be recycled. Surface modification of activated carbon using steam pyrolysis in the presence of SO2 and H2S greatly enhanced metal removal and resulted in a product with possible commercial potential for wastewater treatment.