Efeito do tratamento ácido nas propriedades superficiais de rejeito da mineração de ferro: obtenção de catalisadores eficientes para a remoção de corantes de meio aquoso

Abstract

In the present work, a study was carried out with the objective of better understanding the effect of acid treatment on the modification of the surface properties of the flotation mud from iron mining (LM). Adsorbents/catalysts materials were prepared from the modification of LM with sulfuric acid or ρ-toluenesulfonic acid at different concentrations (1.0; 1.5 and 3.0 mol L-1) and heat treatments (300 and 600 °C). The materials obtained were characterized by Xray diffractometry (XRD), Mössbauer spectroscopy, infrared spectroscopy (IR) and thermogravimetric analysis (TG). In addition, the surface properties of the materials produced were studied using three processes: (i) adsorption of methylene blue (cationic) and indigo carmine (anionic) probe dyes, (ii) decomposition of hydrogen peroxide (H2O2) and (iii) evaluation of the kinetic oxidation of methylene blue (AM) and indigo carmine (IC) dyes by H2O2. The sludge treated at 300 °C (LM300) and, especially at 600 °C (LM600), showed, on its surface, the predominance of negative charges, indicated by the strong adsorption of the cationic AM dye. Treatment with H2SO4 clearly shows the generation of positive surface charges which leads to increased adsorption of the negative IC dye. The positive charges are probably related to surface iron hydroxide species Fe(OH)x n+ type. The modified materials showed activity for both reactions, i.e., decomposition of H2O2 and oxidation of the dyes. In general, it was observed that the treatment with H2SO4 at different concentrations caused significant changes in the decomposition rate of H2O2. However, this acid treatment did not significantly alter the oxidation activity of the dyes. This behavior was discussed based on a possible mechanism of decomposition mainly heterogeneous H2O2 that occurs on the surface of materials containing Fe-OH species without the diffusion of radicals to the aqueous solution. Comparative experiments were also performed with a less strong acid, ρ-toluenessulfonic acid, which indicated a less significant modification of the tailings surface.