Geothermal effects on the release and molecular evolution of dissolved organic matter from coking coal

Coal-derived dissolved organic matter (Coal-DOM) plays a critical role in subsurface carbon migration and pollutant transport in groundwater systems. However, its release behavior under deep subsurface thermal conditions remains poorly understood,despite the increasing trend of coal mining at greater depths. In this study,coking coal was used to establish coal-water microcosm systems at 25 ℃ and 50 ℃. Dissolved organic carbon (DOC) analysis,excitation-emission matrix (EEM) spectroscopy,and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were employed to systematically characterize the optical properties and molecular composition of JM-DOM. The results showed that elevated temperature significantly promoted DOM release and molecular complexity. At 50 ℃, the DOC concentration increased by 43% compared with that at 25 ℃. EEM spectra shifted toward humic-like components,while FT-ICR MS revealed that DOM was dominated by CHO and CHON formulas,with structural types mainly distributed in lignin-like,lipid-like,and condensed aromatic-like regions. Overall,DOM exhibited enhanced aromaticity and polarity under higher temperature. These findings highlight the regulatory role of geothermal conditions on the release behavior and molecular characteristics of Coal-DOM,providing a theoretical basis for the resource utilization of mine water,risk assessment of organic matter migration,and investigation of subsurface carbon cycling in coal mining areas.