Caracterização de serpentinito e esteatito ocorrentes em Nova Lima/MG, antes e após processo de moagem, calcinação e separação magnética

Abstract

Serpentinite and steatite are existing rocks in various parts of the world with relevant industrial applications. In Nova Lima / MG there is an important deposit of these rocks, they are used in several areas; agriculture, steel and polymer industry, and its characterization is a fundamental tool in the study of the characteristics of these materials and in the understanding of their functional performance. In this work, the two lithotypes were characterized, before and after the milling process and thermal treatment at 1200ºC, this was done to understand the mineralogical phase changes at this temperature. Magnetic separation tests were also carried out to evaluate the behavior of the materials under the influence of a low-intensity 800 Gauss field before and after calcination. The characterization was carried out by means of the following techniques: grain size analysis, quantitative chemical analysis, phase analysis by X-ray diffraction and Mössbauer spectrometry, thermogravimetric analysis, microstructural analysis by SEM and EDS; this latter analysis also complemented the determination of the phase composition. The result of the magnetic separation of the in natura materials showed a much larger presence of magnetic materials in the serpentinite sample (16%) when compared to the steatite sample (1.9%). This magnetic characteristic had a great reduction in the serpentinite sample when calcined at 1200ºC, reaching 2.7% of magnetic material, while in the steatite sample it remained stable. The results of X-ray diffraction analysis indicated the presence of some common minerals in the two rocks, such as lizardite, talc and magnetite. The sample of steatite presented in its mineralogy mainly the talc, serpentines and small amounts of tremolite, besides traces of hematite. The serpentinite sample had the lizardite as the main mineral, and talc and magnetite in medium and low quantities respectively. Steatite presented a narrower particle size curve for both the fine material and ultrafine material. The d90 of the steatite for the thin material was 0.48 mm versus 0.65 mm of the serpentinite. For the ultrafine material, the result was 11.3ìm versus 19.4ìm respectively. The specific surface area of steatite was 15.3 m2/g, slightly lower than that of the serpentinite, 16.3 m2/g. In thermogravimetry up to 1450 ° C (TG and DTG), a mass loss of 12.15% was verified in the serpentinite, in addition to two peaks of mass loss: for lizardite at 645°C and for talc at 729°C. The steatite curve presented three main peaks, being: at 630ºC forlizardite, at 733ºC for talc, and at 783ºC for tremolite;the total mass loss was 9.45%. To analyze the iron-rich phases, Mössbauer spectroscopy was used, with spectra recorded at room temperature. The steatite presented as main alteration the appearance of maghemite in the calcined sample, replacing magnetite and hematite. In addition, the calcined serpentinite sample was also analyzed at the very low temperature of 25K. These results completed the phase composition of both calcined samples, with the decrease of the amount of magnetite and the significant presence of magnesioferrite. The dominant phases were forsterite and enstatite, both containing iron, in low amount, in their composition. The microstructural analysis with SEM and EDS complemented the other techniques used, confirming the phase and structural changes. By the same analysis, the morphological change of the particles was observed, with expressive decrease of the fine fibers, for more rounded forms of rods, in both serpentinite and steatite. The beginning of the sintering process at 1200°C was also noted. It is expected that, with these results, new uses will be developed for these rocks, as well as the understanding of the success in already consolidated applications