Adsorção de amarelo tartrazina e alaranjado de metila em carvão ativo preparado a partir de cinzas de caldeira: cinética, isoterma e caracterização do material

Abstract

Nowadays the most commonly boilers fuel used is biomass. Various materials are used as such fuels, like pine and eucalyptus chips, rice hulls and sugarcane bagasse. However, the burning of biomass provides a large volume of a by-product known as ash or boiler residue, which, without eminent use ends up having industrial landfills as its destination, and may therefore present risks to the environment. The present work aimed at the use of these materials as precursors to produce activated carbon via alkaline activation using sodium hydroxide (NaOH) in two different proportions, thus adding value to the material besides offering a use to it. The characterization of activated carbons was performed by scanning electron microscopy (SEM), the presence of functional groups was elucidated by Fourier transform infrared spectroscopy (FTIR) in addition to dispersive energy spectroscopy (DES) and thermal stability was evaluated by means of thermogravimetric analysis (TG / DTG) which showed constancy of materials at high temperatures. Surface area, volume and pore diameter were measured by nitrogen adsorption and desorption, where the surface areas were determined from 355,026 to 1072,505 m2 g-1, all of them were classified as mesoporous. Effects like activating agent proportion, pH and contact time in adsorption process through the batch method were studied. The kinetics of reaction were made using tartrazine yellow and methyl orange dyes as contaminants and the data approach was obtained using the pseudo first order, pseudo second order, Elovich and intraparticle diffusion models, where data obtained with Pseudo second order model presented better fit through the correlation coefficient (R2 = 0.9996). The materials adsorption capacity was evaluated using linear models of adsorption isotherms of Langmuir and Freundlich, with electrochemical monitoring and compared by molecular absorption spectrometry. Langmuir was the best fit model, which showed adsorption capacity values of 161.8123, 36.9004 and 77.1010 mg g-1 for the active charcoal 1: 3 (CA1: 3), activated charcoal 1 : 1 (CA1: 1) and commercial active charcoal (CACOM), respectively. The results show that the prepared coals can be used satisfactorily as adsorbents of contaminants tested in aqueous medium.