Industrial steel waste recovery pathway: Production of innovative supported catalyst and its application on hexavalent chromium reduction studies.

Mill scale is the metallurgical waste produced by the rolling mill in the steel hot rolling process. This hazardous waste is mainly composed of oxide iron, such as hematite, magnetite and wustite. It may have a different and alternative final destination by becoming a catalyst for wastewater treatment. In this work, the catalytic potential of mill scale (MS) from a steel plant was evaluated for hexavalent chromium reduction from synthetic and real matrices under slurry conditions (MS particles dispersed in the solution) or immobilized in Raschig rings. Experiments were conducted in an annular photoreactor irradiated by UVA light. Raschig rings were coated with MS by electrostatic link with polyethylene-grafted-maleic anhydride copolymer (PEGMA) film, and further packed in the annular zone of the UV photoreactor. SEM, XRD and FTIR analysis showed a homogeneous film of MS firmly attached on Raschig rings surface. In this way, the iron-rich industrial steel waste acted as both source of iron and photocatalyst, allowing the reduction of Cr(VI) to Cr(III) in the bulk solution and MS surface, respectively, in the presence of tartaric acid as hole and hydroxyl scavenger and Fe-complexing agent. The Raschig rings (248 g) coated with MS (23 g) achieved total Cr(VI) reduction (below detection limit) after 45 min of reaction (k = 2.0 × 10-2 mg L-1 min- 1) under UVA radiation, considering the following initial conditions: [Cr(VI)]0 = 10 mg L-1, [tartaric acid]0/[Cr(VI)]0 molar ratio = 6:1, pH = 3.0, T = 25 °C. The same system was tested for the treatment of a real effluent from a galvanic industry containing 6 mg L-1 of Cr(VI). Using the same tartaric acid/Cr(VI) molar ratio (6:1) and pH 3.0, the Cr(VI) present in the effluent was totally reduced (below detection limit) in 360 min (k = 1.93 × 10-2 mg L- 1 min- 1), showing similar kinetic behavior as the process with the synthetic matrix. In all experiments, the concentrations of dissolved iron (Fe(II) and Fe(total)) were below the disposal limit established by Brazilian legislation, and total chromium removal was achieved by Cr(III) precipitation after the photocatalytic reaction.

The application of textile sludge adsorbents for the removal of Reactive Red 2 dye.

Sludge from the textile industry was used as a low-cost adsorbent to remove the dye Reactive Red 2 from an aqueous solution. Adsorbents were prepared through the thermal and chemical treatment of sludge originating from physical-chemical (PC) and biological (BIO) effluent treatment processes. The adsorbent characterization was carried out through physical-chemical analysis, X-ray fluorescence (XRF) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, pHPZC determination, Boehm titration method, Brunauer-Emmett-Teller (BET) surface area analysis and scanning electron microscopy (SEM). Batch kinetic experiments and adsorption isotherm modeling were conducted under different pH and temperature conditions. The results for the kinetic studies indicate that the adsorption processes associated with these systems can be described by a pseudo-second-order model and for the equilibrium data the Langmuir model provided the best fit. The adsorption was strongly dependent on the pH but not on the temperature within the ranges studied. The maxima adsorption capacities were 159.3 mg g(-1) for the BIO adsorbent and 213.9 mg g(-1) for PC adsorbent at pH of 2 and 25 °C.