To achieve a completed burning of untreated rice husk it is necessary to achieve about 500 ◦C. This temperature increased up to 620 ◦C when the rice husk became more thermally stable due to the chemical treatment. The results found for T3 are smaller than the result found in the literature, proving that it is possible to obtain silica from rice husk in an economic way. Table 3 shows composition of volatile, organic and inorganic compounds data, and also three important temperatures on the burning process of agulhinha and cateto rice husk. The reported data was obtained by the mean of each four heat rate TGA analysis using descriptive statistics. TGA was performed with all samples at constant heating rates of 5, 10,15 and 20 ◦C min−1.