Evolution of the Structure of Different-Rank Coals under Acidic Conditions
DOI:
https://doi.org/10.54691/vkp7zp34Keywords:
Acidic Water, pH, Temperature, Coal Structure, Different Coal Ranks.Abstract
Acidic mine drainage (AMD) present in coal seam roof and floor strata significantly modifies coal structure. To investigate the modification patterns of AMD on different coal ranks, coal samples of varying ranks (lignite, bituminous coal, anthracite) were selected. Changes in elemental content, molecular structure, functional groups, pore structure, and microcrystalline structure of the coal samples after immersion in acidic water (pH=4, 35°C) were studied. Fourier Transform Infrared (FTIR) spectroscopy analysis revealed that under the influence of acidic water, the coal samples exhibited a decrease in aromatic structures, disappearance of aliphatic structures, transformation of hydroxyl structures, and redistribution of oxygen-containing functional groups. However, these effects weakened with increasing coal rank. X-ray Photoelectron Spectroscopy (XPS) results indicated a significant reduction of oxygen-containing functional groups (e.g., C-O and C=O) in low-rank coal, while in high-rank coal, the content of C=O groups (such as carbonyl and carboxyl) decreased. BET adsorption experiments showed that the impact of acidic water on the specific surface area and openness of pores in low-rank coal was far greater than in high-rank coal. X-ray Diffraction (XRD) analysis results indicated that the Full Width at Half Maximum (FWHM) of the coal samples gradually increased under acidic water influence, suggesting a decrease in crystallite size. The interlayer spacing (d₀₀₂) of aromatic layers decreased, and the molecular structure of the coal exhibited higher condensation and orderliness. All findings consistently demonstrate that the influence of acidic water weakens with increasing coal rank, although functional group transformation and structural reorganization still occur. Through the aforementioned characterization techniques, the modifying effects of acidic mine drainage on coal quality and structure were clarified, providing a reference for understanding the transformation mechanism of acidic water on coal reservoir physical properties.
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