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Use of marble waste and boron oxide in desulfurizing synthetic slags for steels.

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Author(s):
Jorge Luís Coleti
Total Authors: 1
Document type: Master's Dissertation
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
Defense date:
Examining board members:
Jorge Alberto Soares Tenório; Jean Carlo Camasmie de Paola; Claudio Geraldo Schön
Advisor: Jorge Alberto Soares Tenório
Abstract

The present market requires from steel industry better quality of steel that was produced by processes that cause less impact to the environment. Thus, this study aims to recycle the marble waste generated from the industry of ornamental rocks, which has in its composition calcium oxide (CaO) and magnesium oxide (MgO). Using this waste in the steel production process, the amount of CaO is enough to replace the lime in the slag whereas the MgO contributes to reduce the wear of the refractory material. Furthermore, it was part of this study to test the replacement of the fluorite by boron oxide as desulfurizing flux into the composition of mixtures. The marble waste was characterized using the following techniques: chemical analysis (EDXFR), particle size analysis with a light scattering method, specific surface area by BET method, Xrays diffraction (XRD), scanning electron microscopy (SEM), analysis of micro-regions by energy dispersive spectroscopy (EDS) and thermogravimetry analysis (TG) with mass spectrometer coupled (MS). In order to verify the efficiency of desulfurization, mixtures were formulated using conventional lime or marble waste, and fluorite or boron oxide. The blends were prepared using the computational thermodynamics programs, Thermo-Calc and FactSage. These mixtures were added into the molten steel under an argon atmosphere and the metallic bath stirred by a rotor of alumina at the temperature of 1600ºC. Metal Samples were removed periodically in order to verify the variation of sulfur content during the experiments. The characterization of marble waste showed in its composition the amount of 40% CaO and 14% MgO in a CaCO3 and MgCO3 carbonates forms. It was also observed a mass loss of 42.1%, in the form of CO2 at a temperature of 780 ° C. The experiments showed that the tested mixtures desulfurization efficiency was above 60%, in most cases. (AU)