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 <14 nm to 134 nm observed under SEM. XRF analysis indicated a silica purityof 69.85% with minor alumina residues. Alumina extraction using HCl (1.0–2.5 M) achieved a maximumyieldof 86.8% at 1.5 M, yielding α-alumina with a hexagonal corundum structure confirmed by XRD, Al–OHand Al–Ovibrations in FTIR spectra, and agglomerated morphologies with heterogeneous porosity observed by SEM. TGAresults supported the formation stability of α-alumina at 750 °C. These findings demonstrate that Napa soil can serveas a sustainable and low-cost precursor for producing high-purity silica and α-alumina suitable for applications inceramics, catalysts, and environmental remediation. The study contributes to the valorisation of natural minerals inIndonesia and provides a scalable route toward developing advanced functional materials fromlocally availableresources.
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