Comparison of the efficiency of unmodified and chemically modified low-cost biosorbents in the removal of lead from aqueous solutions.

Abstract

The application of residues of agricultural products as low-cost biosorbents for removing heavy metal from water, is particularly appropriate for developing countries. This study was conducted to compare the removal efficiency of lead (Pb (II)) from aqueous solutions with initial concentration of lead (0- 100 mg/L) by some raw (unmodified) biosorbents (sunflower stalks, wheat straw and corn stalks) and chemically modified of these biosorbents with NaHCO3 0.5 mol/L and NaOH 0.5 mol L. Also in this study, lead adsorption isotherms and lead removal efficiency by these biosorbents was investigated. Biochemical composition analysis of the studied biosorbents showed that sunflower stalks had the highest cellulose, lignin and ash content. Hemicellulose were highest in wheat straw but lowest in sunflower stalks. Langmuir and Freundlich models had a better fitness than the Temkin model for removal of lead by unmodified and modified biosorbents. The removal efficiency (RE) for unmodified sunflower stalks, wheat straw and corn stalks were obtained 94-99%, 85-97% and 55-95%, respectively. Also, by modification of biosorbents with NaHCO3, the removal efficiency (RE) of sunflower stalks, wheat straw and corn stalks were 94-99%, 85-97% and 55-95%, respectively. Maximum mono layer adsorption (qmax) of modified sunflower stalks, wheat straw and corn stalks increased 293, 305, 394 and 226, 265 and 363 percent compared to unmodified biosorbents, respectively. Separation factor of Langmuir (RL) increased from 0.014-0.73 (for unmodified biosorbents) to 0.065-0.93 (for modified biosorbents by NaHCO3) and 0.023-0.56 (for modified biosorbents by NaOH), indicated that the sorption reaction of lead by studied biosorbents are favorable. Chemical modification of the biosorbents with NaHCO3 could significantly increase the efficiency and capacity removal of lead from aqueous solutions. The ease of preparation of these chemically modified low-cost biosorbents and its high removal capacity for lead makes these biosorbents a good practical candidate for removal of lead from aqueous solutions.