Caracterização do resíduo da siderurgia pó de aciaria elétrica e aplicação em fotocatálise para degradação de contaminante orgânico

Abstract

Steel is a metal alloy widely used in the automobile industry, civil construction, manufacture of mechanical equipment and household appliances, among others. Moreover, steel is considered an essential material for the development of the country. In the last decade, the world production of steel increased by up to 60% in relation to the production in 2009. Thus, generation of solid waste, such as powders, sludge and slag, also increases – as a result. During the manufacture of steel using electric arc furnace, electric arc furnace dust (PAE) is generated as a by-product, which has a complex chemical composition, that vary with the applied operational parameters and raw materials. Its disposal must be carried out in appropriate places, especially because it contains heavy metals in its constitution. Thus, destination to hazardous waste landfills is the most common practice nowadays. In order to reuse, recycle and reduce costs to contribute to sustainability, PAE has been used to recover metals that present market value, such as zinc and iron, and also incorporated into other products and industrial processes. In this work, a sample of PAE generated in a steel mill in the southern region of Minas Gerais was characterized and used as a photocatalyst for degradation of the remazol black B textile dye (PR). The results of the characterizations by X-Ray Fluorescence (FRX), X-Ray Diffraction (XRD) and Spectroscopy in the Infrared Region by Fourier Transform (FTIR) showed that the main components of PAE are zinc oxide (ZnO), oxide of magnesium (MgO), iron oxide (Fe2O3) and silica (SiO2). The Scanning Electron Microscopy (SEM) and mapping images showed that the particles present different shapes and sizes, with a predominance of zinc, magnesium and spherical iron particles. The specific surface area of PAE, which was determined by the B.E.T. method, is extremely low value (2 m2 g-1). Bandgap studies showed that the energy of PAE is similar to the energy of ZnO. The thermogravimetric curve showed the excellent stability of PAE at high temperatures, with a loss of 2.85% of the total mass. An experimental design was used to determine the conditions of the photocatalytic reactions carried out with different masses of PAE (20, 70 and 120 mg), pH values (4, 7 and 10) and UV radiation power (15, 36 and 51 watts). All reactions followed zero pseudo-order kinetics and the rate constants increased with the catalyst mass and the applied UV radiation, since the pH of the solution was the least significant parameter of the process. The best result was obtained with 120 mg of PAE and 51 watts, showing efficiency of 84% of discoloration of PR. Reuse was investigated in ten consecutive reactions (40 hours) from the same sample of PAE and the result showed that it can be reused in several reactions without loss of activity. The matrix effect was investigated using river water and distilled water in the preparation of the PR solution. It was observed that the difference in the percentage of PR degradation is due to the different characteristics of the matrices. The obtained results showed that the use of PAE as a photocatalyst added value to the residue, since it presented high potential for application in photocatalytic processes for the degradation of organic contaminants.