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<p>The pore mechanism of coal under acidic treatment is a critical factor for optimizing pore structure and enhancing effective gas extraction. This study aims to provide a comprehensive and comparative understanding of pore structure evolution across different coal ranks (Datong lignite, Ordos bituminous coal, and Zhaogu anthracite) treated with an optimized mixed-acid system (sulfuric, nitric, and acetic acids). Using low-temperature nitrogen adsorption (LTNA) and fractal dimension analysis, we quantified the changes in adsorption capacity and pore morphology. Results show that the tailored acid treatments significantly reduced the specific surface area (e.g., up to 90% reduction in lignite) and the volume of adsorption pores (&lt; 100&#xa0;nm). Conversely, the dissolution of embedded minerals facilitated the coalescence of isolated micropores into interconnected mesopores and macropores, which expanded the migration space and decreased the pore structural complexity. Consequently, the effective porosity increased, suggesting a strong potential for enhanced permeability. This study provides a novel multi-rank perspective on the microscopic physical modifications induced by mixed-acid systems, laying a robust theoretical foundation for permeability-enhancing technologies in coalbed methane recovery.</p>

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Experimental research on evolution characteristics of coal pore systems under acidification–modification conditions

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年6月15日

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  • Jun Nian,
  • Lei Zhang,
  • Bo Zhao,
  • Xiaobo Lv,
  • Chunsheng Deng

摘要

The pore mechanism of coal under acidic treatment is a critical factor for optimizing pore structure and enhancing effective gas extraction. This study aims to provide a comprehensive and comparative understanding of pore structure evolution across different coal ranks (Datong lignite, Ordos bituminous coal, and Zhaogu anthracite) treated with an optimized mixed-acid system (sulfuric, nitric, and acetic acids). Using low-temperature nitrogen adsorption (LTNA) and fractal dimension analysis, we quantified the changes in adsorption capacity and pore morphology. Results show that the tailored acid treatments significantly reduced the specific surface area (e.g., up to 90% reduction in lignite) and the volume of adsorption pores (< 100 nm). Conversely, the dissolution of embedded minerals facilitated the coalescence of isolated micropores into interconnected mesopores and macropores, which expanded the migration space and decreased the pore structural complexity. Consequently, the effective porosity increased, suggesting a strong potential for enhanced permeability. This study provides a novel multi-rank perspective on the microscopic physical modifications induced by mixed-acid systems, laying a robust theoretical foundation for permeability-enhancing technologies in coalbed methane recovery.