Obtenção de silício metálico a partir da cinza da casca do arroz

Abstract

Brazil is one of the largest rice producers in the world and consequently of the waste generated by it. These wastes can harm the environment if incorrectly disposed of what often happens. Furthermore, this is a residue that can have high added value if processed correctly, due to its high content of amorphous silica. In this context, the present work aims to obtain metallic silicon through an aluminothermic reduction of amorphous silica extracted from rice husk ash, adding value to what was previously a residue. At the beginning of the work, the characterization of the received CCA was carried out, after submitting it to a physical separation to remove husks and other large solids, getting 92.06% of SiO2 most of it amorphous, and a small part crystalline, with an average diameter of 42 µm, specific mass of 1.969 g/cm³ and specific surface area of 57,744 m²/g, in accordance with the CCA used by other authors. From this separated CCA with a homogeneous aspect, it was leached with hydrochloric acid to remove oxides which are impurities for the original silica, followed by an alkaline digestion of the leached CCA to extract the silica. After obtaining the silica gel, it was washed with deionized water to remove salts and dried to obtain xerogel. The silica obtained was washed then once more, obtaining 99.31% SiO2, completely amorphous, with an average particle diameter of 36.33 µm and a real specific mass of 2.305 g/cm³, which was very similar to the one obtained by other authors. Silicon was obtained by submitting the obtained silica (xerogel) to a reduction, using aluminum as a reducing agent in a conventional forging furnace, without controlled atmosphere. Although the reaction requires oxygen absence to convert the silica into silicon, its consumption by the burning gas in the furnace were sufficient to an provide the atmosphere poor in O2. Silicon was obtained and its formation was proven, through the joint use of micrographs, which gave evidence of its formation, with the X-ray diffraction analysis carried out on the sample, showing the metallic silicon peaks.