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ABSTRACT
To investigate the structural modification of Guizhou anthracite through the application of hydrofluoric acid and its corresponding response in terms of enhanced gas desorption and permeability, we utilized Guizhou anthracite from a mining area as the focal point of our study. We conducted a series of experiments encompassing X-ray diffraction (XRD), initial gas release velocity measurements, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR). Our investigation identified hydrofluoric acid as the primary acid solution, with an optimal concentration of 6% and a soaking duration of 12 hours. Furthermore, our theoretical analysis unveiled the physicochemical structural evolution of Guizhou anthracite under the influence of hydrofluoric acid and its subsequent response to enhanced gas desorption and permeability within the coal. Regarding chemical structure, hydrofluoric acid effectively dissolves inorganic minerals in anthracite and reduces the condensation of its regular basic structural units. Peak fitting of functional groups on the surfaces of the experimental coal samples revealed that hydrofluoric acid induces side chain reactions in the molecular structure of anthracite, promoting the gradual ordering of the aromatic structure. Simultaneously decreasing the content of cyclically closely bonded and self-associated hydroxyl hydrogen bonds. These alterations in irregular basic structural units can diminish coal’s adsorption capacity for gas, thereby enhancing gas desorption. Regarding the physical structure, treatment with hydrofluoric acid leads to the dissolution of minerals within specific pores and fissures of the coal samples, generating numerous dissolution pores. These pores and fissures expand and interconnect. The surface morphology quantified by fractal dimension has decreased by about 25.8%, indicating that pore and fracture structures often become relatively simple, which is conducive to gas flow and desorption in coal. Furthermore, the effective porosity and total porosity of the coal samples increase, as does the total movable fluid porosity. This enhances pore connectivity within the coal seam. Calculations reveal that after acidification, the permeability of the experimental coal samples increases by approximately 1.37 times, confirming the permeability-enhancing effect of hydrofluoric acid on anthracite.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Supplementary material
Supplemental data for this article can be accessed online at https://doi.org/10.1080/15567036.2024.2334924.
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Notes on contributors
Lian Chen
Lian Chen was born in Guizhou, China in 1996. Graduated from Guizhou University with a Master’s degree in Safety Engineering in June 2021. The research focuses on coal and gas safety prevention and control.
Mei Yuan
Mei Yuan a professor and master’s supervisor at Guizhou University, specializing in coal seam modification, solubilization, and transparency enhancement.
Bobo Li
Bobo Li is currently the Vice Dean of the School of Mining Engineering at Guizhou University in China.
Chaolin Zhang
Chaolin Zhang, Associate Professor and Doctoral supervisor at China University of Mining and Technology. Deputy Director of the Institute of Safety Monitoring and Emergency Management, Secretary of the Second Party Branch, and Member of the Youth Teacher Development Committee.
Qing Lv
Qing Lv is currently an associate professor at the School of Resources and Environment, Guizhou University.
Shiqing Xu
Shiqing Xu is a senior researcher at the Laboratory of the School of Mining and Technology, Guizhou University, China.
Jiabo Geng
Jiabo Geng, Associate Professor, master’s supervisor. Main research directions: Emergency technology for slope disasters, prevention and control of mining disasters, etc.