Reduction of iron oxide with polypropylene and polyurethane by thermogravimetric analysis for ironmaking processing

Abstract

This study investigates the reduction kinetics and thermal degradation behavior of hematite (Fe₂O₃) mixed with recycled polypropylene (PP) and polyurethane (PU) using non-isothermal thermogravimetric analysis (TGA). Kinetic parameters were derived via the Coats-Redfern solid-state reaction model. Our findings demonstrate that PP and PU exhibit fundamentally different degradation mechanisms when utilized as reductants. Pure PP degrades in a sharp, single step around 480–490°C due to random chain scission, whereas PU decomposition is a complex multi-stage process initiating at lower temperatures (250–280°C) but ultimately leaving a resilient char residue. Kinetic evaluations of the polymer-iron oxide composites reveal that the PP composite undergoes rapid devolatilization with an activation energy of 192 kJ/mol, effectively promoting early indirect reduction through the rapid release of light hydrocarbons and hydrogen. Conversely, the PU composite exhibits a pronounced dual-stage kinetic profile: an initial low-energy devolatilization (134.3 kJ/mol) followed by a high-energy barrier (335.9 kJ/mol) representing carbothermic reduction between 850°C and 950°C. The delayed high-temperature reactivity and stable char formation characteristic of PU make it highly advantageous as a resilient internal reductant, capable of supporting rapid metallization. Ultimately, both polymer wastes offer distinct kinetic advantages, reinforcing their viability as strategic metallurgical resources for green ironmaking.