Avaliação da biomassa da Terminalia catappa Linn (amendoeira) como adsorvente: estudo cinético e termodinâmico

Abstract

The textile industries are responsible for the disposal of large volumes of effluents, damaging aquatic life and human health. The disposal of wastewater without treatment can modify the natural color of water resources, causing some problems, such as the formation of foams on the surface and an increase in the concentration of toxic substances as dyes. There are different technologies that have been studied to solve this problem, but the adsorption has been an attractive and promising for dye removal due to its advantages such as the possibility to reuse biomaterials, low operating cost, among others. Moreover, the application of alternative adsorbents of residues from biomasses has been increasingly studied. Terminalia catappa Linn (TCL), for example, generates an organic waste such as their fruits, which fall to the ground, and cause manhole clogging in the cities of Rio de Janeiro. Therefore, in this work, it was evaluated the efficiency of the endocarp of the almond fruit as adsorbent in the adsorption process of an organic dye, methyl orange. The adsorption studies were carried out by analyzing the equilibrium and kinetics. The endocarp were evaluated in its natural form, calcinated at 400 °C, and chemical activated with phosphoric acid (H3PO4). It was observed that the material treated with acid showed the best results with 100% removal of the dye. So, the experiments were done using the activated carbon with H3PO4 varying the initial concentration (200 – 800 mg.L- 1), temperature (25, 35 and 45 °C), contact time (0 - 150 min), pH (1 - 11) and addition of sodium chloride (0.5, 0.7, 1.0 and 1.2 g.100 mL-1). The highest adsorptive capacity, 197.87 mg.g-1, was reached at pH 3, at 25 °C, 800 mg.L-1 and a contact time of 150 min, removing 99.67% of the dye. The pseudo-second order model was, in general, the best that described the adsorption process, wich indicates that adsorption is limited by chemisorption process. The Freundlich isotherm best describes the adsorption of dye, which implies that the adsorption is heterogeneous with multi-layers. The thermodynamic study indicated that the process is endothermic, spontaneous, and the results indicated an affinity between the adsorbent and the adsorbate. Therefore, the activated carbon of the almond endocarp had a good performance, making it a promising adsorbent for the removal of methyl orange.