Conversion-resolved kinetics and phase transformation of Zn–Fe separation from zinc-bearing dust during hydrogen reduction

Zinc-bearing dust (ZBD), a complex secondary resource generated from ironmaking and steelmaking processes, contains considerable amounts of zinc and iron but remains challenging to recycle because of its multiphase structure and overlapping reaction pathways. The non-isothermal reduction behaviour of ZBD was systematically investigated using an integrated experimental and analytical framework comprising thermogravimetric analysis, thermodynamic assessment, conversion-resolved kinetic modelling, Rietveld-refined phase analysis, SEM–EDS elemental mapping, and XRF-based bulk elemental quantification. The apparent activation energy (E α ) remains mainly within 100–110 kJ·mol −1 in the principal conversion region and shows a V-shaped minimum at α = 0.55–0.65. Under 30 vol% H 2 /Ar, model discrimination indicates an apparent transition from D3 type diffusion control at α = 0.01–0.55 to F2 type reaction control at α ≥ 0.55. Rietveld refinement indicates progressive metallic Fe phase development, while SEM–EDS mapping reveals heterogeneous Zn depletion in the quenched products. XRF analysis shows that the estimated Zn removal increases from 9.97% at α = 0.20 to 55.23% at α = 0.60 and 90.12% at α = 0.90, with the bulk Fe/Zn ratio increasing from 9.36 in the raw ZBD to 94.36 at α = 0.90. Because conversion is defined from total mass loss, the derived kinetic parameters describe the apparent kinetics of overlapping reduction, decomposition, volatilisation, and transport processes. These findings provide a conversion-resolved interpretation of the coupling among reaction progress, phase transformation, and Zn–Fe separation during hydrogen reduction of a complex industrial residue.