Detoxification of heavy metal ions from aqueous solutions using a novel lignocellulosic multi-metal binding biosorbent
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Since, the availability of a biomass at a low cost is a key factor dictating its selection for a biosorption, thus agro–industrial wastes and by–products are considered as alternatives for heavy metal biosorption development. Utilizing potentials of combination of common agro–industrial wastes and by–products let us have different kinds of active binding sites at same time in wastewater treatment. In order to make the biosorption process more suitable for heavy metal removal, both batch and continuous systems have been studied. Two breakthrough multi–metal binding biosorbent made from a combination of tea wastes, maple leaves and mandarin peel (MMBB1) and a mixture of tea waste, sawdust and corncob (MMBB2) were applied to evaluate their biosorptive potential of heavy metal removal from synthetic multi–metal solutions. FTIR and SEM were conducted, before and after biosorption, to explore the intensity and position of the available functional groups and changes in adsorbent surface morphology. Carboxylic and hydroxyl groups were found to be the principal functional groups for the sorption of metals. MMBB1 exhibited better performance at pH 5.5 with maximum sorption capacities of 41.48, 39.48, 94.0 and 27.23 mg/g for Cd(II), Cu(II), Pb(II) and Zn(II), respectively. In batch system, MMBB1 was selected for further process optimization, modification, characterization and thermodynamic studies. The data indicated that Langmuir isotherm and pseudo–second order kinetics model describe the experimental data very well. The maximum amounts of biosorption capacity of modified MMBB increased to 69.56, 127.70, 345.20 and 70.55 mg/g for Cd(II), Cu(II), Pb(II) and Zn(II), respectively. Then a continuous fixed–bed study was carried out by utilizing the modified MMBB for cadmium, copper, lead and zinc removal from synthetic solution and real wastewater. The effect of operating conditions i.e. influent flow rate, metal concentration and bed depth was investigated at optimal pH (5.5±0.1) for a synthetic wastewater. Results confirmed that the total amount of metal adsorption decreased with increasing influent flow rate and also increased with increasing each metal concentration. The maximum biosorption capacity of 38.25, 63.37, 108.12 and 35.23 mg/g for Cd, Cu, Pb and Zn, respectively, were attained at 31 cm bed height, 10 mL/min flow rate and 20 mg/L initial concentration. The Thomas model found better describing the whole dynamic behaviour of the column. Finally, desorption studies indicated that metal–loaded biosorbent could be used after three consecutive sorption, desorption and regeneration cycles by applying a semi−simulated real wastewater.
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