Resumo: O silício grau metalúrgico (SiGM) é largamente produzido através da carboredução do quartzo (Si02) a altas temperaturas, em processo sob fomo de arco submerso. Entretanto, para se obter uma composição química de 98% a 99,5% em. peso, toma-se necessário submeter a uma ou mais etapas de refino através da injeção de nitrogênio e/ou oxigênio ao silício em estado fundente. Desta forma, conduz-se a reações entre estas impurezas presentes no material fundido e os gases, originando as denominadas escórias, que correspondem ao volume de ~10% do volume total de SiGM produzido. No Brasil, a geração anual destas escórias é de ~20,000 toneladas. Normalmente, estas escórias contêm 50% de silício total e 25-30% de Si livre (sendo o restante encontrado disperso sob a forma de óxidos, carbetos, silicatos e silicetos, tais como: SiO2, CaSiO4, SiC, CaSi, CaO, e FeO). A caracterização da composição química e da estrutura cristalina da escória de silício foi realizada aplicando-se as técnicas de espectroscopia de fluorescência de raios-X (FRX) e difração de raios-X (DRX). Observou-se que os elementos majoritários são Si (39-45%), Ca (5-11%), Fe (1-2%), e Al (1-8%). As principais fases cristalinas detectadas foram: silício, siliceto de ferro e silicato de cálcio. As concentrações destas fases foram determinadas por DRX usando o método de padrão interno. Outra contribuição relevante desta pesquisa foi o desenvolvimento de um processo de extração do silício metálico a partir das escorias por plasma térmico, que resulta na obtenção de um silício com pureza equivalente ao silício grau metalúrgico (SiGM) Ver menos

Abstract: Metallurgieal Grade Silicon (MGSi) is produced by a well-established industrial process that consists of the carbo-reduction of quartz in a submerged are fumace under high temperature. The process is an intensive energy consumption method (13 - 15 kWh to each kilogram of produced MGSi). After tapered, the MGSi is submitted to some purification stages in order to archive the commereial chemieal purity (98% to 99.5% of silicon). These purification stages consist of the injection of reactive gases, mostly nitrogen or oxygen, in order to remove the most reactive impurities like aluminum, calcium, magnesium, and with minor effectiveness iron. The material formed on these chemical reactions involving the impurities and the gas-stream constitutes the slag. The total slag amount formed in the silicon process ranges from 7% to 10% of the total silicon produced. In Brazil, the amount of produced slag ranges about 20,000 t/y. Afier the refining stage, the silicon is left to cooling, being mechanically separated from slag. These slags usually have about 50% of total silicon and 25% to 30% of free-silicon. Silicon is presented in other forms mainly oxides, carbides, silicates and silicides like SiO2, CaSiO4, SiC, CaSi, and FeSi. The chemical composition and the crystalline structure of silicon slag were characterized by X-ray fluorescence spectrometry (XRF) and X-ray Diffraction (XRD), respectively. It was observed that the major elements of silicon slags are: Si (39-45%), Ca (5-11%), Fe (1-2%), and Al (1-8%) and the main crystalline phases are: silicon, iron silicide and calcium silicate. Their concentrations were determined by XRD with the internal standard method in several samples. This research work presents also the results of a thermal plasma process employed to recover the free-silicon present in the process slag. The process consists of a laboratory-scale closed reactor, lined with refractory and insulating materials, a cooled anode at the fumace bottom and a DC arc-transferred plasma torch. The furnace feed could be continuous or in batch mode. The overall recovering of silicon and the material's quality presented here points to a very promising technology that could help to avoid wasting non-renewable raw materials (like quartz), charcoal and energy Ver menos