(CIP) M514 Meio Ambiente em Foco-Volume 13/ SUMÁRIO Capítulo 1: O papel das unidades de conservação na educação ambiental por meio do uso público ..

Rice is among the main foods produced in the world and is part of the daily diet of most families. The main waste from rice processing is rice husk (RH), which has been used as biomass for energy generation through combustion. In this process, rice husk ash (RHA) is generated as a residue, and its silica (SiO 2 ) content varies from 85-98%. The present work describes the study of the extraction of silica from RHA by the ultrasoundassisted sol-gel method. An experimental design based on the Response Surface Methodology (RSM) with the symmetrical, second-order Rotational Central Composite Design (RCCD) was applied to determine the best extraction conditions considering extraction time and molar ratio (n) as variables = n NaOH / n Silica ). These optimal conditions were then applied to three ash samples, two obtained by the combustion process in a boiler furnace, with a mobile grate system (RHAC 1 and RHAC 2 ), and one obtained by the pyrolysis process (RHAP) carried out in a xed bed reactor. Results showed that a molar ratio of 4.4, and an extraction time of 107 minutes were the best extraction conditions, leading to a yield of 73.3% for RHAP, 43.9% for RHAC 1 , and 31.1% for RHAC 2 . It was found that the extraction yield and textural properties of the silica obtained depend on the characteristics of the ash used. The silica extracted from RHAC 1 presented a surface area of 465 m 2 .g − 1 , mesopores of 4.69 nm, purity greater than 95%, and an ultra-ne granulometric distribution, reaching nanoparticle dimensions, characteristics comparable to commercially available silicas.

Rice is among the main foods produced in the world and is part of the daily diet of most families. The main waste from rice processing is rice husk (RH), which has been used as biomass for energy generation through combustion. In this process, rice husk ash (RHA) is generated as a residue, and its silica (SiO2) content varies from 85–98%. The present work describes the study of the extraction of silica from RHA by the ultrasound-assisted sol-gel method. An experimental design based on the Response Surface Methodology (RSM) with the symmetrical, second-order Rotational Central Composite Design (RCCD) was applied to determine the best extraction conditions considering extraction time and molar ratio (n) as variables = nNaOH / nSilica). These optimal conditions were then applied to three ash samples, two obtained by the combustion process in a boiler furnace, with a mobile grate system (RHAC1 and RHAC2), and one obtained by the pyrolysis process (RHAP) carried out in a fixed bed reactor. Results showed that a molar ratio of 4.4, and an extraction time of 107 minutes were the best extraction conditions, leading to a yield of 73.3% for RHAP, 43.9% for RHAC1, and 31.1% for RHAC2. It was found that the extraction yield and textural properties of the silica obtained depend on the characteristics of the ash used. The silica extracted from RHAC1 presented a surface area of ​​465 m2.g− 1, mesopores of 4.69 nm, purity greater than 95%, and an ultra-fine granulometric distribution, reaching nanoparticle dimensions, characteristics comparable to commercially available silicas.

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 .

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