Abstract Amorphous silica (SiO2) was extracted from the rice husk ashes (RHAs) of the agulhinha and cateto varieties. Optimized time, temperature, extractor concentration, and reaction time for a sustainable and cleaner production of SiO2 from RHAs were studied. Textural and internal structures were analyzed by N2 adsorption-desorption isotherms. The percentage of SiO2 in the treated rice husks (RHs) increased by approximately 11 and 12% for the agulhinha and cateto varieties, respectively. The silica present in the RHAs remained predominantly amorphous for all of the times and temperatures investigated. The optimum parameters for calcination of the RHs were: 2 h at 700 °C. Type IV isotherms with type H1 hysteresis and good specific surface area values were observed. The optimum parameters for extraction of the amorphous silica were: concentration of 4 mol L−1 NaOH and 4 h of reaction. The extraction yield values were 80–99% and 83–97% for the agulhinha and cateto RHAs, respectively.