Isothermal reduction kinetics of beneficiated tungsten mine tailings using boiler-grade coal

Extensive, continuous mining has depleted most tungsten deposits, leaving vast quantities of tailings that now represent a potential lean-grade hematite resource. The isothermal reduction kinetics of beneficiated tungsten mine tailings using boiler-grade coal as a reductant were investigated in the temperature range of 1273–1373 K. Reduction experiments demonstrated that both temperature and holding time strongly influence the extent of reduction, with a maximum fractional conversion (α) of 0.854 achieved after 60 min at 1373 K. XRD and SEM analyses confirmed sequential phase transformations from hematite to magnetite, wüstite, and ultimately metallic iron, with crack formation and spherical iron particles observed on the briquette surfaces. Kinetic modeling indicated a mixed-control mechanism: the contracting geometry (CG3) model predominated in the initial stages, while diffusion (D1) governed the later stages. The apparent activation energies were calculated to be 52.18 kJ/mol (CG3 stage) and 65.81 kJ/mol (D1 stage), indicating a higher energy demand for diffusion through the product layer. The findings provide the intrinsic mechanism for the reduction behaviour of beneficiated tungsten mine tailings-coal composite briquettes and demonstrate the potential of utilizing industrial boiler coal as a reductant in solid-state ironmaking.