<p>This study explores nano-scale silica extraction from mixed biomass ash through a two-step process involving alkaline digestion followed by CO₂ precipitation. Digestion conditions were optimized for maximum silica yield using Central Composite Design (CCD). Results from 20 experimental runs showed that extended reaction time and moderate NaOH concentrations (0.5 M) achieved the highest 180 g/kg yield. ANOVA indicated temperature as a significant factor (<i>p</i> &lt; 0.0001, <i>F</i> = 577.07), with an R² of 0.9756. The optimized condition resulted in 65% silica recovery with 97.5% purity, confirmed by Ion Chromatography (IC). Thermogravimetric analysis (TGA) indicated excellent thermal stability with minimal weight loss up to 800 °C. FTIR spectra showed characteristic Si–O–Si stretching at 1100 cm⁻¹ and bending at 800 cm⁻¹ and 460 cm⁻¹, confirming silica’s structural integrity. X-ray diffraction (XRD) revealed an amorphous structure, confirming successful alkali treatment and precipitation. Field emission scanning electron microscopy (FESEM) showed smooth, clustered nanoparticles (90–150 nm) suitable for high-surface-area applications. Energy-dispersive X-ray spectroscopy (EDS) confirmed the composition as silica with 48.5% silicon and 51.5% oxygen. BET surface area analysis revealed a specific surface area of 195.36 m²/g and a pore volume of 0.211 cm³/g, comparable to mesoporous materials. The pore size distribution showed an average diameter of 4.33 nm, making the silica suitable for catalytic and adsorption applications. These results demonstrate the potential of the process to make silica from biomass ash for industrial applications like catalysts and adsorbents.</p> Graphical Abstract <p></p>