Obtenção de nanopartículas de óxido de ferro a partir do resíduo do beneficiamento do carvão mineral

Abstract

Mineral coal is the most abundant mineral in the world and the main fuel source for global energy. However, its processing generates waste that presents economic problems, such as adequate logistics and disposal, and environmental concerns because it is a contamination source. This residue, called Coal gangue, has considerable amounts of iron and other elements, such as silicon, aluminum, magnesium, and sulfur. This work aims to develop routes for producing iron oxide nanoparticles from coal gangue, adding value and contributing to the sustainability of a waste material that is usually discarded. Iron oxide nanoparticles have unique properties, such as high reactivity and adsorption capacity, which have aroused great interest due to the wide range of applications. Through the steps of grinding, sieving and dissolving in hydrochloric acid, it was possible to extract 16,11% of the available iron in 2 hours of acid extraction, under stirring at 1500 rpm 17,26% when the time was increased to 4 hours, enough for developed syntheses needs. Iron oxide nanoparticles were synthesized using the 4 hours extract for acid extraction. The main steps were pH neutralization and passivation using dihydrate sodium citrate. The material obtained has spherical nanoparticles and plates resembling crumpled sheets with much larger dimensions. A second synthesis was carried out by adding the passivating sodium citrate before pH correction, resulting in a material composed of misshapen plaques, probably resulting from the coalescence of particles. It has spherical particles of reduced dimensions between the plaques on a nanometric scale. This same synthesis was carried out with the 2-hour extract, resulting in ellipsoidal coalesced plaques with spherical nanoparticles of significantly reduced dimensions in the spaces between the coalesced plaques. The analyzes by X-ray diffraction, infrared spectroscopy and UV-Vis absorption spectroscopy indicated the formation mainly of iron oxides mixed with small amounts of iron hydroxide and aluminum oxide. Raman spectroscopy showed only iron oxide formation. The processes added value to discarded waste, transforming it into a technological material with great potential for environmental treatment.