Mawardi Mawardi, Illyas Md Isa, Syamsurizal, Okta Suryani, Fadlurrahman Mawardi, Fiqrhatul Ilmi, Salsabilla Yuswilia, Feliska Amanda
Napa soil (NS), a naturally abundant material from West Sumatra, Indonesia, presents significant potential as a sustainable raw source for advanced material synthesis due to its high silica and alumina content. This study focuses on 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 more reactive amorphous forms, enhancing the SiO₂ and Al2O3 content. Silica extraction using NaOH achieved optimum yield at 4M, producing a material containing quartz and cristobalite phases as confirmed by XRD and FTIR analyses, with particle sizes ranging from <14 nm to 134 nm observed under SEM. XRF analysis indicated a silica purity of 69.85% with minor alumina residues. Alumina extraction using HCl (1.0–2.5 M) achieved a maximum yield of 86.8% at 1.5 M, yielding α-alumina with a hexagonal corundum structure confirmed by XRD, Al–OH and Al–O vibrations in FTIR spectra, and agglomerated morphologies with heterogeneous porosity observed by SEM. TGA results supported the formation stability of α-alumina at 750 °C. These findings demonstrate that Napa soil can serve as a sustainable and low-cost precursor for producing high-purity silica and α-alumina suitable for applications in ceramics, catalysts, and environmental remediation. The study contributes to the valorisation of natural minerals in Indonesia and provides a scalable route toward developing advanced functional materials from locally available resources. © 2026, Rasayan Journal of Chemistry, c/o Dr. Pratima Sharma. All rights reserved.
Department of Chemistry, Universitas Negeri Padang, Padang, 25173, Indonesia; Department of Biology, Universitas Negeri Padang, Padang, 25173, Indonesia; Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Andalas, Padang, 2516, Indonesia; Department of Chemistry, Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, Perak, Tanjong Malim, 35900, Malaysia
