Síntese e caracterização de carvões ativados e compósitos C/Fe produzidos a partir de tortas de biodiesel para remoção de Cr (VI) em meio aquoso

Abstract

The by-products generated from biodiesel production need to be critically assessed because they can be a relevant factor in the economic viability of this biofuel production. The reuse the biodiesel press-cake for activated carbon production is a challenge in the inquiry for alternatives to improve the treatment efficiency of contaminated effluent. The aim of this work was the production of different materials in order to be used in the Cr (VI) removal from aqueous environment using some biodiesel press-cake: Brassica napus, Helianthus annuus, Jatropha curcas L., Lupinus albus L., Raphanus sativus and Ricinus communis L.) as raw materials. Non-oxidized, oxidized and activated carbons with HNO3 were produced, besides carbon/Fe composite with different iron concentrations (19, 35 and 45 wt.%) and pyrolyzed at different temperatures (400, 600 and 800 °C) in a conductive oven. The materials were characterized by specific surface analysis, scanning electron microscopy, chemical composition, elemental analysis, ash content, thermal analysis, X-ray diffraction, IR spectroscopy, potentiometric titration, pH at point of zero charge, Raman spectroscopy, Mössbauer and saturation magnetization. Oxidized carbon exhibit acidic character (pHpcz 3.4 to 4.4), while the composite showed basic nature (pHpcz 6.0 - 10.8). For all the materials it was verified carboxylic and phenolic groups and, especially for the composites, it is also noted iron oxides. The specific surface area ranged from 3 to 491 m2 g-1. Mössbauer spectra of a series of composite showed the presence of reducing phase iron as Fe3O4, Feo and Fe3C, essential for the Cr (VI) reduction process. The saturation magnetization values for the composites ranged from 6 to 84 emu g -1 indicating the feasibility of their separation from aqueous solutions by a simple magnetic process. The adsorption capacity Cr (VI) was verified for all materials and removal up to 97% of the pollutant in aqueous environment had been achieved using oxidized carbon at pH 4 after 20h reaction. Langmuirs and Freundlichs isotherms were used to fit the experimental data from the removal of Cr (VI) by the composites and both models showed coefficients of determination above 0.90. Maximum adsorption capacities up to 459 ± 33 mg g-1 were observed for the series of composites containing 45 wt.% Fe. These results are considerably better than those reported in the literature for similar materials used in the removal of Cr (VI), indicating that the materials produced in this study are attractive for environmental applications.