Obtenção e caracterização da sílica precipitada de cascas de arroz

Abstract

Rice husk is an agricultural biomass which contains silica and can be used in a range of applications based on its potential characteristics. Some characteristics are related to increased strength and durability when applied to cement paste, for example by filling the pores and accelerating the cement hydration process. Silica can also be applied in the composition of ceramic materials, such as in porcelain prostheses. In this work, the objective was to use rice husks from previous hydrolysis processing through an integrated study to obtain micrometric silica. The hydrolysis was performed at different water/solid ratios and at different temperatures, and the remaining solid residue was used to obtain silica. The chemical precipitation of silica was done with NaOH and HCl, while the acid was used for the formation of silica gel. The pH values of the solution before adding HCl were monitored, which the values remained between 12 - 13. The results demonstrated a silica yield in the range of 10 - 20%. The silica samples were characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that silica has amorphous characteristics and a purity in the range of 87 - 97%, which is in agreement with the scientific literature. The samples obtained from fresh rice husks and those processed by transient hydrolysis have slightly higher purity when compared to the other samples. The results also show that silica obtained from rice husks has micrometering or submicrometering sizes.