From coal biodesulfurization to mine-soil remediation: a critical review of microbial sulfur transformation in coal-impacted environments.

Coal biodesulfurization has traditionally been regarded as a pre-combustion clean-coal technology; however, its connections to sulfur cycling and remediation in coal-impacted soils have not been sufficiently integrated. This review addresses this gap by examining microbial sulfur transformations in coal, coal gangue, mine spoil, acid mine drainage systems, and reclaimed soils. The discussion encompasses pyritic sulfur biooxidation, organic sulfur biotransformation, sulfate reduction and metal sulfide precipitation, rhizosphere-mediated sulfur cycling, and the reuse of coal mine solid wastes in reclamation contexts. Drawing on these lines of evidence, the review proposes a systems-level, risk-controlled sulfur management framework that conceptualizes coal treatment and mine-soil remediation as interconnected microbial, mineral, hydrological, and ecological processes. The synthesis demonstrates that sulfur-transforming microorganisms may facilitate sulfur removal, waste stabilization, and vegetation recovery, or alternatively promote acidification, sulfate export, and metal mobilization. These outcomes depend on factors such as matrix accessibility, oxygen exposure, redox stability, hydrologic connectivity, buffering capacity, sulfur loading, and labile carbon availability. Future research should progress beyond isolated microbial screening and instead prioritize matrix-aware, field-validated, and risk-based strategies that integrate sulfur mass balance, contaminant mobility, and long-term reclamation performance.