Chemical and Thermogravimetric Analyses of Raw and Saturated Agave Bagasse Main Fractions with Cd(II), Pb(II), and Zn(II) Ions: Adsorption Mechanisms

Abstract

Agave salmiana bagasse has proved to be a good biosorbent for heavy metal ions in aqueous solutions. However, more information about its chemical structure and the interaction with metal ions remains to be understood. Raw bagasse and its fractions hemicellulose, cellulose, and lignin were characterized by acid–base titrations, Attentuated Total Reflectance Fourier Transform Infrared Spectroscopy and thermogravimetric analysis (TGA), before and after they were tested to remove Cd(II), Pb(II), and Zn(II) from aqueous solution. Oxygen, sulfur, and nitrogen containing groups were identified in both raw bagasse and its fractions. TGA of the exhausted biosorbent demonstrated that Cd(II) and Pb(II) ions shifted the pyrolisis temperature of the neutral detergent fiber (NDF) fraction while Zn(II) decreased it. Carboxylic and strong acid groups were mainly responsible for metal removal. Lignin contributes the most to metal uptake in the NDF adsorption process. Finally, the higher or lower pyrolisis temperature of exhausted NDF fraction was related to decarboxylation reactions and elimination of hydroxyl groups.