EXTRACTION AND CHARACTERIZATIONOF HIGH-PURITYSILICA AND α-ALUMINA FROMNAPASOIL(WESTSUMATERA, INDONESIA)

Napa soil (NS), a naturally abundant material from West Sumatra, Indonesia, presents significant potential as asustainable raw source for advanced material synthesis due to its high silica and alumina content. This study focuseson the extraction and characterisation of high-purity silica and α-alumina from NS through a combined calcination–alkali fusion–hydrothermal acid process. Calcination at 750 °C effectively transformed crystalline phases into morereactive amorphous forms, enhancing the SiO₂ and Al2O3 content. Silica extraction using NaOH achieved optimumyield at 4M, producing a material containing quartz and cristobalite phases as confirmed by XRD and FTIRanalyses, with particle sizes ranging from