Carvão ativado a partir de resíduo têxtil: síntese, caracterização e aplicação na remoção de corante reativo em efluente sintético

Abstract

The textile industry demands an enormous amount of water resources, thence generates large volumes of wastewater with a high polluting potential. Among these contaminants, textile dyes, since they give color to water bodies, appear to have a distinctive role in the environmental approach. Regarding this, the present work proposes a cyclical reuse of the solid textile waste, whose usual destinations point to low added value products, for the synthesis of activated carbon and removal of dyes from textile wastewater. Therefore, 100% cotton fibers (RFA), which are the main natural matrix of the textile industry, were used. The RFA was impregnated with H3PO4 and pyrolyzed in a vertical tubular oven at a rate of 5 °Cmin-1 and remained for 3 h at 500 ° C under N2(g) flow, obtaining the activated carbon (CAT). A commercial activated carbon (CAC) was used as a direct comparison parameter. Novacron Red S-B was used as adsorbate for fitting in categories that are widely used in that sector. The RFA showed low fixed carbon content (Cfixo = 2.98%), semi-crystalline structure (IC = 77.88%) of type Iα cellulose and flat twisted ribbon morphology with no pores on its surface. On the other hand, RFA+H3PO4 showed an increase in its stability and carbon availability for the synthesis of activated carbon by the appearance of phosphate bridges that promoted crosslinking of cellulose chains, resulting in a satisfactory pyrolysis yield (ηpir = 60.145 %). CAT and CAC coals showed irregular morphologies, amorphous structures and close isoelectric points (pHiso = 2.62 and 2.29, respectively), with CAT showing better textural properties (SBET=1096 m2 g-1; VTP = 0.81 cm3 g-1; dPm = 1.5 nm) when compared to CAC. The adsorption tests reached a maximum removal of 75.41% and 65.36% for CAT and CAC, respectively, at 12 h (pH = 2, [VSB]0 = 50 ppm, INaCl = 0,05 molL-1). Both systems fitted better to pseudo-second order kinetic model (R2 CAT = 0.995 and R2 CAC = 0.997) with k2,CAT = 2194.163 gmg-1 min-1 and k2,CAC = 2167.879 gmg-1 min-1. The equilibrium isotherm data denoted a physical and favorable adsorption process with maximum adsorption capacities of qmax,CAT = 131.238 mgg-1 and qmax,CAC = 58.915 mgg-1. A better fit was obtained for the Freundlich model for CAT (R2 = 0.991) and for Langmuir for CAC (R2 = 0.999), indicating heterogeneous and homogeneous adsorptions sites, respectively. Therefore, these results suggest the viability of those residues as carbon sources for activated carbon production and its suitability for dye removal.