Estéreis em minas de minério de ferro: sua caracterização como material pozolânico após calcinação em forno flash

Abstract

The waste material displaced to enable mining of a mineralized body is usually deposited in the form of heaps, which require constant monitoring and generate visual changes in the environment. In this work, two types of rocks were considered to be waste in an iron ore mine located in the Quadrilátero Ferrífero, MG, Brazil: a weathered metabasic and a phyllite, before and after passing through the process of calcination in a flash furnace, at a temperature of 770ºC. The aim of the research was to validate the use of these wastes as raw material for the production of artificial pozzolans by the flash calcination process and to determine the physical and morphological changes after calcination. The chemical analysis, mainly by X-ray fluorescence, showed that both wastes have SiO2, Fe2O3 and Al2O3 as main components; the latter component was high in the weathered metabasic (29.22%) and lower in the phyllite (6.28%). The mineralogical composition determined by X-ray diffraction and confirmed by thermogravimetry, showed abundant presence of kaolinite and gibbsite, medium hematite and low goethite and muscovite; for the phyllite, quartz and goethite were abundant, medium kaolinite, and low hematite. After calcination, most of the material was amorphous, with only some residual kaolinite, quartz and hematite as significant crystalline phases. The specific surface areas of the raw samples are about 60.00 m2 /g; after calcination this value decreased significantly, indicating incipient sintering; the average particle sizes consistently increased after burning. Microstructural research, by scanning electron microscope (SEM) with the support of EDS microanalysis, confirmed the extensive formation of metakaolinite after flash calcination, maintaining the lamellar morphology of the original kaolinite. Tests of mechanical resistance in molded test pieces with the addition of hydrated lime to the calcined materials showed good values, proving that the pozzolanic activity was achieved.