TRATAMENTO TERMOQUÍMICO PARA A PRODUÇÃO DE SÍLICA BIOGÊNICA A PARTIR DA FOLHA DA CANA-DE-AÇÚCAR

Abstract

Vegetables absorb the silicon present in the soil in the form of monosilicic acid (H4SiO4) through their roots and deposit it in other plant organs. Forming structures called biogenic silica. This silica has been used as a deflocculating agent, a controlled release vehicle for biocides and as a source for obtaining sodium silicate, among other applications. The objective of this work is to use sugarcane leaves to produce amorphous biogenic silica using a thermochemical method that uses organic acid. The biomass samples were leached with 5%, 7.5% and 10% w/w by citric acid, and 5%, 7.5% and 10% w/w sulfuric acid at 100 °C for 2 h, before being rinsed, dried and carbonized using a four-step program ranging from room temperature to 873 K in a rotary kiln. The characterization of pretreated biomass samples was carried out using thermogravimetric analysis (TG), X-ray diffraction (XRD) and surface analysis (BET). Pretreatment with citric acid has proven to be an attractive alternative to mineral acids, such as sulfuric and hydrochloric acid, which in addition to posing health risks, their disposal can affect the environment. Good quality biogenic amorphous silica was produced from sugarcane leaves with excellent textural properties, such as a surface area of up to 176 m2 g−1 and average pore diameter of 20 nm. Samples pretreated with sulfuric acid had their most pronounced degradation between 240 °C and 557 °C, while samples pretreated with citric acid suffered greater degradation between 450 °C and 700 °C, making it possible to obtain a greater amount of silica with samples pretreated with H2SO4. Although leaching with sulfuric acid resulted in a greater yield of silica, the option for citric acid is healthier and more viable in economic terms. This study demonstrated that the production of biogenic silica from sugar cane leaves, an abundant residue in our country, will be a differentiator in solving disposal and burning, minimizing environmental problems.