黄陵矿区是陕北侏罗纪煤田主要矿区之一，年产煤炭2800余万吨，煤炭开发伴生200余万吨的固体废弃物-煤矸石，长期以来区内矸石的主要利用途径集中在制砖、制陶粒、回填、发电等低值领域。本文在对区内煤矸石基本性质充分认识基础上，以其富集的硅源(SiO2达60%)为对象，通过常压干燥技术制备了具有高附加值的纳米多孔SiO2气凝胶。作为硅基纳米多孔材料的典型代表，SiO2气凝胶因其独特的结构特征引起学界广泛关注，从材料构效关系分析，SiO2气凝胶通过溶胶-凝胶法制备形成的三维网络结构，呈现出显著的三维孔隙分布特征和纳米级孔道结构（孔隙率＞90%）。这种特殊拓扑形态使其同时具备多重功能特性：低导热系数和低密度等优异性能，在保温隔热、光能材料和吸附等方面有着广阔的应用价值。本研究是区内煤矸石绿色、低碳、高效和高值化利用新途径的有益尝试。
本研究煤矸石样品取自陕西黄陵矿区中侏罗世延安组2号煤层夹矸，其主要矿物组成为石英、高岭石、伊利石和蒙脱石等，其灰成分主要由SiO2(61.31%)和Al2O3(27.87%)组成，黄陵矿区煤矸石高硅含量为其提取Al2O3和制备SiO2气凝胶提供了理论基础。
采用Na2CO3 助剂对区内煤矸石煅烧活化，继而通过HCl酸浸和NaOH碱浸提取SiO2，以浸出的SiO2为硅源，正硅酸乙酯作为前驱体，通过溶胶-凝胶法和常压干燥制得SiO2气凝胶。在Na2CO3 助剂煅烧活化-HCl浸取阶段，系统考察了物料比、煅烧温度、酸浓度、液固比等因素对区内矸石Al2O3浸出效率的影响。结果显示：对Al2O3浸出率影响最大的因素是煅烧温度；煤矸石中Al2O3的最佳浸出条件是：煅烧温度850 ℃、液固比10:1 mL·g-1、物料比5:6、酸浓度8 mol·L-1，此条件下Al2O3的浸出率为94.27%。NaOH碱浸法浸取SiO2阶段，系统考察了碱浓度、固液比、反应温度和反应时间等参数对SiO2浸出率的影响。结果表明，煤矸石中SiO2的最佳浸出条件为：反应温度100 ℃、碱浓度4 mol·L-1、固液比1:10 mL·g-1，反应时间30 min，此条件下SiO2的浸出率为 96.57%。在制备SiO2气凝胶过程中，发现酸催化剂种类、酸浓度是影响气凝胶性能的关键因素。最佳条件下制备得到的煤矸石基SiO2气凝胶最大疏水角为141.3 °，耐热温度为750 ℃，最小密度为0.125 g·cm-3，孔隙率为94.32%，最大比表面积为455 m2·g-1。
为提高气凝胶的力学性能，设计在溶胶阶段引入羟基封端聚二甲基硅氧烷(PDMS)进行改性，通过溶胶-凝胶、无水乙醇老化和常压阶梯干燥制备得到了高性能的SiO2气凝胶。最短凝胶时间为5 min，疏水角最高为151.3°，耐热温度为800 ℃，密度最小为0.131 g·cm-3，孔隙率为94.05%，比表面积最大为379 m2·g-1。
采用傅里叶变换红外光谱(FTIR)、X射线衍射分析(XRD)、比表面积测试(BET)、热重分析仪(TGA5500)、扫描电镜(SEM)、氮气吸附、接触角测试等方法研究了SiO2气凝胶的性能。结果表明，SiO2气凝胶中均含疏水特征基团-CH3；气凝胶为典型的非晶材料；气凝胶的吸附特性主要与材料的孔隙结构和外观形貌有关；改性后的SiO2气凝胶具有更加丰富的纳米三维网络结构；改性前后的气凝胶均有良好的热稳定性，改性后的气凝胶耐热温度更高，达800 ℃；改性后的气凝胶接触角更大，最大可达151.3 °。
 

The Huangling Mining Area, as one of the principal production zones in the Jurassic coalfield of Northern Shaanxi, yields an annual coal output exceeding 28 million metric tons, concomitantly generating over 2 million metric tons of coal gangue solid waste. Historically, the utilization of this byproduct within the region has been predominantly restricted to low-value applications including brick manufacturing, ceramsite production, backfilling, and power generation. Based on comprehensive characterization of the intrinsic properties of local coal gangue, this study focuses on its silicon-rich composition (SiO₂ content up to 60%) to synthesize high-value-added nano-porous SiO₂ aerogels through ambient pressure drying technology.
As a representative silicon-based nanoporous material, SiO₂ aerogels have attracted extensive academic attention due to their unique structural characteristics. Structure-property relationship analysis reveals that the three-dimensional network architecture formed via sol-gel processing exhibits significant porosity (>90%) and nanoscale pore channels. This distinctive topology endows the material with multifunctional properties, including ultralow thermal conductivity and density, thereby demonstrating broad application potential in thermal insulation, photonic materials, and adsorption technologies. The present research represents a pioneering endeavor toward green, low-carbon, and high-value utilization of coal gangue resources in the Huangling region.
The investigated coal gangue samples were obtained from the Middle Jurassic Yan’an Formation No.2 coal seam in Huangling, with mineralogical composition dominated by quartz, kaolinite, illite, and montmorillonite. Ash composition analysis identified SiO₂ (61.31%) and Al₂O₃ (27.87%) as primary constituents, providing a theoretical foundation for both Al₂O₃ extraction and SiO₂ aerogel synthesis.
A sequential processing methodology was implemented, beginning with Na₂CO₃-assisted calcination activation of coal gangue, followed by HCl acid leaching for Al₂O₃ extraction, and subsequent NaOH alkaline leaching for SiO₂ recovery. The extracted SiO₂ served as a silicon source, with tetraethyl orthosilicate as the precursor, enabling sol-gel synthesis of SiO₂ aerogels under ambient pressure drying conditions. Systematic investigation of Al₂O₃ leaching parameters identified calcination temperature as the most influential variable, with optimal conditions achieving 94.27% leaching efficiency at 850 °C calcination temperature, 10:1 mL·g⁻¹ liquid-solid ratio, 5:6 material ratio, and 8 mol·L⁻¹ HCl concentration. For SiO₂ extraction, maximum recovery efficiency of 96.57% was attained under conditions of 100°C reaction temperature, 4 mol·L⁻¹ NaOH concentration, 1:10 mL·g⁻¹ solid-liquid ratio, and 30-minute duration. Acid catalyst selection and concentration were identified as critical factors governing aerogel performance, with optimized specimens exhibiting a maximum hydrophobicity contact angle of 141.3°, thermal stability up to 750 °C, minimal density of 0.125 g·cm⁻³, porosity of 94.32%, and specific surface area of 455 m²·g⁻¹.
To enhance mechanical properties, hydroxyl-terminated polydimethylsiloxane (PDMS) was introduced during the sol phase for material modification. The resultant aerogels demonstrated accelerated gelation within 5 minutes, superior hydrophobicity with a contact angle of 151.3°, enhanced thermal resistance up to 800 °C, preserved porosity of 94.05%, and specific surface area of 379 m²·g⁻¹.
Comprehensive characterization through Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), nitrogen adsorption isotherms, and contact angle measurements confirmed the following: the presence of hydrophobic -CH₃ functional groups in all aerogel specimens; amorphous microstructure characteristics; adsorption properties predominantly governed by pore architecture and surface morphology; enhanced three-dimensional nanoporous networks in modified aerogels; exceptional thermal stability in both pristine and modified aerogels, with the latter exhibiting increased thermal resistance up to 800 °C; and maximized hydrophobicity with PDMS modification, achieving a maximum contact angle of 151.3°.
 

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