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<p>Rice husk (RH) offers a low-cost, silica‐rich feedstock, yet conventional extraction relies on concentrated mineral acids and high solid‐to‐liquid ratios, generating excessive waste. This work demonstrates that leaching with dilute citric acid (5% v/v of 2&#xa0;M, 1&#xa0;g:5 mL solid-to-liquid ratio) achieves ultra-high silica purity (&gt; 95%). Using a three-factor half-fractional factorial design, we evaluated particle size (0.125–0.25&#xa0;mm vs. 0.5–1&#xa0;mm), water and citric acid leaching at 90&#xa0;°C for 2&#xa0;h, additional hydrothermal activation (200&#xa0;°C, 3&#xa0;h), and carbonization (550–750&#xa0;°C; 2–6&#xa0;h). Citric acid leaching alone boosted coarse RH silica purity to 96.2% with a modest yield penalty (~ 20.5 wt %), outperforming water leaching in P<sub>2</sub>O<sub>5</sub> and alkali metal removal. When coupled with hydrothermal treatment (HT) and carbonization at 550&#xa0;°C for 2&#xa0;h, the 0.5–1&#xa0;mm fraction achieved 98.3% SiO<sub>2</sub> purity and an 18.2% overall yield. Regression analysis identifies citric acid leaching as the strongest predictor of silica purity (β = 9.58, <i>p</i> &lt; 0.001), whereas thermal parameters exert minimal linear effects. This green, organic-acid – based protocol not only aligns with sustainable chemistry principles but also offers a scalable route to high-purity silica suitable for industrial applications.</p> Graphical abstract <p></p>

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Fractional Factorial Design for Process Optimization in Rice Husk Valorization: Integrating Citric Acid Leaching and Hydrothermal Treatment

  • 期刊论文

  • 发表日期：

    2026年7月16日

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  • Ibrahim Hamidu,
  • Benjamin Afotey,
  • Bright Kwakye-Awuah,
  • Daniel Adjah Anang

摘要

Rice husk (RH) offers a low-cost, silica‐rich feedstock, yet conventional extraction relies on concentrated mineral acids and high solid‐to‐liquid ratios, generating excessive waste. This work demonstrates that leaching with dilute citric acid (5% v/v of 2 M, 1 g:5 mL solid-to-liquid ratio) achieves ultra-high silica purity (> 95%). Using a three-factor half-fractional factorial design, we evaluated particle size (0.125–0.25 mm vs. 0.5–1 mm), water and citric acid leaching at 90 °C for 2 h, additional hydrothermal activation (200 °C, 3 h), and carbonization (550–750 °C; 2–6 h). Citric acid leaching alone boosted coarse RH silica purity to 96.2% with a modest yield penalty (~ 20.5 wt %), outperforming water leaching in P2O5 and alkali metal removal. When coupled with hydrothermal treatment (HT) and carbonization at 550 °C for 2 h, the 0.5–1 mm fraction achieved 98.3% SiO2 purity and an 18.2% overall yield. Regression analysis identifies citric acid leaching as the strongest predictor of silica purity (β = 9.58, p < 0.001), whereas thermal parameters exert minimal linear effects. This green, organic-acid – based protocol not only aligns with sustainable chemistry principles but also offers a scalable route to high-purity silica suitable for industrial applications.

Graphical abstract