Optimization of Silica Extraction Method from Rice Husk Ash using Taguchi Method

This study presents a systematic investigation of silica extraction from rice husk ash (RHA) using Taguchi L27 orthogonal array optimization. With global rice production generating 31–39 million tonnes of RHA annually, valorization of this agricultural waste addresses both environmental disposal challenges and sustainable silica production needs. The extraction process involved controlled calcination, acid leaching with hydrochloric acid, alkali solubilization using sodium hydroxide, and acid precipitation. Three process parameters — heating temperature (600–800°C), heating time (2–6 hours), and chemical concentration (1–3 M) — were evaluated across 27 experimental runs. Optimal conditions were identified at 700°C, 4 hours, and 3 M chemical concentration, yielding 7.02 g of silica per 10 g RHA (70.2% extraction efficiency). Among the parameters studied, chemical concentration had the greatest effect on yield, followed by temperature, which peaked at 700°C, and heating time, which showed a positive correlation with yield. The extracted product exhibited white appearance, near-neutral pH, bulk density of 180–200 kg/m³, and 3.1% moisture content. Silica presence was confirmed by NaOH/CuSO₄ test, and the absence of HCl reaction indicated product purity. The yields obtained compare favourably with those reported for alkali hydrothermal extraction (52.8%) and fall within the range reported for acid leaching methods (70–90%). The Taguchi approach reduced experimental runs by 66% relative to a full factorial design. These findings suggest that the proposed methodology may offer an efficient route for converting agricultural waste into silica suitable for construction, ceramics, and environmental remediation applications.