A critical review of geochemical contributions, anthropogenic emissions and environmental impacts of iron ion in coal seam from antiquity to the present

The current studies lack a coherent cognitive framework for the evolution of Fe in coal seams, spanning from natural geological processes to anthropogenic perturbation. In particular, the understanding of the coupling mechanism between iron-bearing minerals and exogenous iron in the mining environment, as well as their multi-media environmental effects, remains unsystematic. This lack of systematic understanding restricts the overall comprehension and risk control. Therefore, this paper introduces the concept of dual-source iron and systematically constructs a theoretical framework for the iron cycle that links geological evolution and human disturbances. The core findings suggest that the enrichment and transformation of iron under natural geological processes are primarily governed by the biogeochemical processes and temperature-pressure-fluid driving mechanisms during the sedimentary diagenetic stage. Large-scale mining significantly modifies the geochemical behavior of iron. The introduction of exogenous iron and the formation of primary iron establish a coupled system, which serves as a crucial turning point for iron activation and migration. Based on this, we have revealed the environmental impacts of iron in water, soil, and air, including its dual characteristics of pollution effects and remediation potential. Moreover, the continuous impact of iron-driven corrosion and coal spontaneous combustion risk on engineering safety is clarified. This framework offers a new perspective for understanding the biogeochemical cycle of Fe in coal, guiding the environmental governance of abandoned mines and the control of engineering safety.