Purificação de cinzas de cascas de castanha de cajú para obtenção de sílica orgânica de alta pureza

Abstract

After the cashew nuts processing, the husks rich in silicon are used as fuel in boilers where they are burned at temperatures above 1000 °C. In this study was investigated a form of silicon extraction from the ashes taken from the boiler using a chemical-thermal route. At first, the ashes were bathed with an aqua regia solution (3H₂ SO₄ + 1H₂O₂), then it were bathed with sulfuric acid (3HCl + 1HNO₃) and taken to the oven at 600 °C for two hours. X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS) analysis were performed to characterize the material. XRF results indicated percentages of silicon up to 52% in the materials analyzed without purification and treatment for up to 82% in the treated samples. EDS results indicate, by mapping chemical composition, the overlapping of the elements silicon and oxygen, indicating that both are attached forming oxides. The presence of silicon oxide was also shown in XRD analysis, which showed the presence of hexagonal quartz in the final samples. It can be concluded that is possible to purify the ashes to use a waste of cashew nuts processing industry as a source of obtaining silicon dioxide in quartz format.