Extraction of Silica from the residue of Thermoelectric Power Plants

Abstract

Brazil presents the second largest coal reserves in Latin America, whose exploration is mainly focused on electricity generation. The present study was carried out to systematically evaluate the influence of various physical and chemical factors on the extraction of pure amorphous silica precipitated from coal-fired bottom ash. The coal bottom ashes (CBA) is a disposable waste from thermoelectric plants, which basically consists of oxides of silicon (80-60%), aluminium (25-20%) and iron (10-2%), being considered as raw material for silica production, by the sol-gel process. The CBA characterization was carried out by determining moisture, elemental composition (XRF), amorphism (XRD) and granulometry.The process evaluation tookplace in two stages: the quantitative evaluation that wasrelated to the quantification of the amount of silica obtained and the process variables (NaOH concentration and temperature); and the qualitative evaluationof the silica extracted. The extracted silica particles were characterized by TG, BET, XRD.Silica and aluminium contents were obtained by gravimetric analysis. Among the factors analysed, the concentration of sodium hydroxide and temperature interference were the most important. Likewise, the repeat process for the same ash sample (sequential extraction) proved to be more effective than increasing the NaOH concentration. The obtained yield was 51.34%. The silica is 89.4% pure, when 5,63% of impurities are related to aluminium oxide .