Use of a residue containing chromium(VI) for dye decomposition using an advanced oxidative process

Abstract

In this study, a Cr2O3 catalyst was produced from a sulfochromic residue (SCR) generated in the analysis of soil organic matter. The Cr2O3 obtained from the residue was then characterized by techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (DRS), and scanning electron microscopy (SEM). To evaluate the applicability of Cr2O3 as a catalyst, methylene blue (MB) dye was evaluated as a model molecule in discoloration and degradation tests. The catalytic tests were performed in the absence (Cr2O3/H2O2) and in the presence of UV radiation (Cr2O3/H2O2/UV) at room temperature (25 ± 1 °C) under constant agitation at 200 rpm. The H2O2 dose, catalyst mass, initial concentration, and pH of the MB solution were optimized for each treatment. The optimized conditions were applied in dye degradation/discoloration. The results showed that Cr2O3 has high catalytic activity, with discoloration and degradation rates of 97% and 60%, respectively, at an equilibrium time of 6 h for both treatments. The catalyst reuse performance was evaluated, and discoloration greater than 80% was observed for MB concentrations of 50 and 100 mg L-1 after 7 cycles. These results showed that SCR treatment minimized the environmental impact by ensuring adequate properties for disposal in accordance with the current Brazilian legislation, in addition to recovering Cr2O3, which was demonstrated to be an efficient catalyst in the degradation of organic compounds via advanced oxidative processes (AOPs).