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<p>Coal fly ash (CFA) is a low-cost silicon source for silica (SiO<sub>2</sub>) aerogels, but conventional synthesis methods face challenges like low conversion efficiency, complex processes, and difficulty in incorporating Si–F bonds. This study introduces a novel HCl-HF mixed-acid leaching process, in which SiF<sub>4</sub> gas produced from CFA is directly converted into high-purity fluorinated SiO<sub>2</sub> aerogels via hydrolysis and polycondensation. Key parameters affecting SiO<sub>2</sub> conversion were optimized, achieving 35 wt% conversion under 4 mol/L HCl, 5 mol/L HF, 95°C, 90 min, and a 9:1 L/S ratio. The resulting aerogel showed high purity (99.32 wt.%), a specific surface area of 580 m<sup>2</sup>/g, and 89.8% porosity. Successful incorporation of Si-F bonds endowed the aerogel with a low thermal conductivity of 0.029–0.056 W/(m·K) (comparable to commercial glass wool) and a low dielectric constant of 2.45 (significantly lower than the ~ 4.0 of dense silica). This work offers a feasible route for high-value utilization of CFA and the development of high-performance fluorinated SiO<sub>2</sub> aerogel functional materials.</p>

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Preparation of Fluorinated SiO2 Aerogels from Coal Fly Ash via HCl-HF Leaching: Formation Mechanism, Microstructure, and Properties

  • 期刊论文

  • 发表日期：

    2026年3月5日

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  • Cunquan Wang,
  • Zhiming Shi,
  • Yu Yang

摘要

Coal fly ash (CFA) is a low-cost silicon source for silica (SiO2) aerogels, but conventional synthesis methods face challenges like low conversion efficiency, complex processes, and difficulty in incorporating Si–F bonds. This study introduces a novel HCl-HF mixed-acid leaching process, in which SiF4 gas produced from CFA is directly converted into high-purity fluorinated SiO2 aerogels via hydrolysis and polycondensation. Key parameters affecting SiO2 conversion were optimized, achieving 35 wt% conversion under 4 mol/L HCl, 5 mol/L HF, 95°C, 90 min, and a 9:1 L/S ratio. The resulting aerogel showed high purity (99.32 wt.%), a specific surface area of 580 m2/g, and 89.8% porosity. Successful incorporation of Si-F bonds endowed the aerogel with a low thermal conductivity of 0.029–0.056 W/(m·K) (comparable to commercial glass wool) and a low dielectric constant of 2.45 (significantly lower than the ~ 4.0 of dense silica). This work offers a feasible route for high-value utilization of CFA and the development of high-performance fluorinated SiO2 aerogel functional materials.