Chemical modification of four lignocellulosic materials to improve the Pb2+ and Ni2+ ions adsorption in aqueous solutions

The water contamination by metal ions arising from industrial, mining and agricultural activities increase is a recurring problem that makes necessary new research for effective and low-cost water treatments. This study aimed to increase the adsorption capacity of Pb2+ and Ni2+ ions for different lignocellulosic materials (banana peel (BP), eucalyptus bark (EB), maize cob (MC) and maize leaf (ML) by alkali and acidic hydrolysis chemical treatments. The fibers chemical modifications were evaluated using the FTIR and the Boehm method. The Pb2+ and Ni2+ ions concentrations in the solutions were quantified by the Energy-Dispersive X-ray Fluorescence Spectrometer. The results demonstrated that the alkali-treatment was the most efficient in increasing the adsorption capacity of Pb2+ and Ni2+ ions for all the fibers. The kinetics and isotherms adsorption of the alkali-modified eucalyptus bark (BEB) and alkali-modified banana peel (BBP) were studied due to their highest adsorption capacity compared to the other fibers. The Ni2+ ions adsorption reached equilibrium after 6 and 30 min, while the Pb2+ ions after 1 min, for the BBP and BEB fibers respectively. The single-element isotherm that best fitted the experimental data was Langmuir. The highest maximum adsorption capacity values obtained for Pb2+ and Ni (2+) ions were 65.9 +/- 13.8 (BBP) and 17.1 +/- 1.0 (BBP) mg g(-1), respectively. The main active sites responsible for adsorption are the basic sites (predominantly carboxylates ions). The lignocellulosic fibers demonstrated higher adsorption affinity with Pb2+ ions.