Chemical modification of the angico gum (Anadenanthera macrocarp Benth): use as adsorbent of heavy metal.
Red angico gum is a heteropolysaccharide (arabinogalactan) obtained from Anadenanthera macrocarpa trees. Carboxymethylation of angico gum (AG) with monochloroacetic acid (MCA) in alkaline aqueous medium resulted in samples which were characterized by infrared, 13C nuclear magnetic resonance spectroscopy and gel permeation chromatography. The effects of reactional parameters, such as alkali concentration, MCA/angico gum ratio and temperature on the reaction yield and degree of substitution (DS) were investigated. The DS and MCA total efficiency values increase up to 2 h reaction time and then decrease. The DS varied from 0.11 to 1.10 depending onNaOH/MCA/AG ratio and temperature. Higher DS value was obtained for molar ratio of 9:3:1 at 70°C, although with low yield and MCA total efficiency (7.5% and 0.03 respectively). Polymer degradation was observed in all samples, but in different degree. The best carboxymethylated sample from angico gum was obtained with NaOH/MCA/AG molar ratio equal to 3:1:1, at 70 °C. (DS = 0.63, yield = 91.0%). Crosslinked AG and Carboxymethylated AG chemical gels (GAGel and GAGMGel respectively) were alsoobtained using epichlorohydrin (E) as crosslinking agent. Crosslinked AG gel was further carboxymethylated resulting in GAGelCM sample. The products obtained were characterized by IR spectroscopy and swelling degree (W). The swelling degree decreases as the E/AG ratio increase from GAGel. Carboxymethyalted gels possess higher waterabsorption than GAGel (16 times higher). The gels obtained by crosslinking were tested as adsorbent of heavy metal (Pb, Cd and Cu). Adsorption isothermal studies were carried out and interpreted by the Langmuir and Freundlich equations. The sorption of individual metals followed the sequence Cu gt; Cd gt;Pb. The best Cu adsorbent was GACMGel (20.32 mmol/g). In equimolar metal mixture sorption experiment the best Cu adsorbent was GAGelCM (9.79 mmol/g).
Advisor:Regina Célia Monteiro de Paula; Judith Pessoa de Andrade Feitosa; Márcia Rodrigues Pereira
School:Universidade Federal do Ceará
Source Type:Master's Thesis
Date of Publication:07/13/2005