A generalized shrinking-core model for iron ore pellet reduction under H₂ and mixed-gas atmospheres

Hydrogen-based direct reduction requires models that connect pellet chemistry and structure with reduction kinetics under different gas atmospheres. A generalized shrinking-core model is presented for single-pellet reduction under H₂, CO and mixed H₂-CO-H₂O-CO₂ atmospheres. The formulation couples an equilibrium-corrected gas driving force with surface reaction, product-layer diffusion and evolving pellet structure. Gangue composition affects both apparent reducibility and internal gas transport, allowing their combined influence to be examined within one model. The source database contains 144 standardized records from 14 literature sources; 140 quality-screened trajectories were retained for comparison. For these retained curves, the median coefficient of determination was 0.9977 and the median root-mean-square error in reduction degree was 0.0143. The extracted reaction coefficients, effective diffusivities and high-conversion times place heterogeneous experiments in a common reaction-transport space. Controlled calculations distinguish the effects prescribed for gas composition, transport quality and acidic or basic gangue. The contribution is a common calibration and comparison framework that translates literature reduction curves into apparent descriptors suitable for pellet assessment and subsequent data-driven or reactor-scale modelling.