Avaliação do potencial de cascas residuais como biossorventes para o tratamento de efluentes de simulados têxteis

Abstract

Industrial activities are the main causal agents in the contamination of waste water by dyes, due to the large amount of organic pollutants released in the effluents. In this scenario, adsorption has been pointed out as a promising technique in dye removal. Associating this process with the use of low cost adsorbents, such as waste from agroindustries and other alternative materials, we have an inexpensive, efficient and easily executed technique. In this sense, the peels of Pecan nut (Carya illinoensis), Chestnut (Parakeet) (Bertholletia excelsa) and Avocado (Persea americana) generate a high amount of residues when used in the manufacture of various products. Thus, this work had as objective, to develop adsorbent materials from residues of vegetal origin for the removal of industrial dyes. Pecan, Parana nut and Abacate hulls were used as biosorbents for the removal of methylene blue, crystal violet and reactive red (RR141) dyes as a model contaminant system. Both materials were characterized by the DRX, MEV and FT-IR techniques, after which pH, adsorbent mass, kinetic, equilibrium, thermodynamic studies were carried out and the adsorption capacity of the material was tested by simulation of a textile effluent. The adsorbent formed from Nóz pecã bark obtained better adsorption capacity at pH 2, from 45 mg g-1 for crystal violet and 8.5 mg g-1 for methylene blue. The pseudo-first order model was adequate to represent the kinetic data, and the equilibrium was best represented by the Sips model. Actual effluent tests revealed a 65% removal percentage of the dyes. For the nut shell the best adsorption capacity for both dyes was better in acid pH, the pseudo-first order model represented satisfactorily the kinetic curves, whereas Freundlich's model represented the best equilibrium curves. Maximum biosorption capacities were 83.6 and 83.8 mg g-1 for Violta crystal and Methylene blue, respectively. In the simulation of the textile effluent the nut shell removed 90% of the color. Finally, the bark of the avocado treated with H2SO4 and HNO3, obtained better adsorption capacities at pH 6.5, where more than 90% of Red procion was removed from the solution. The general order model was the one that best represented the adsorption kinetics, since the Sips model was adequate to represent the isotherm data, with the maximum adsorption capacities of 167.0 and 212.6 mg g-1 for the material treated with H2SO4 and HNO3, respectively. The adsorption processes were thermodynamically spontaneous, favorable and exothermic. In the simulation of the textile effluent the removal was 82 and 75%, for the adsorvent treated with H2SO4 and HNO3, respectively. It is concluded that these materials possess a great potential in the removal of dyes.