Pelletization of rolling mill scale waste: Thermodynamic insights into sintering mechanisms

Mill scale, a by-product from hot rolling of steel, contains a high iron content (68–72 wt%) primarily as wustite, magnetite, and hematite, making it an attractive material for recycling in steelmaking processes. This study investigates the pelletization of mill scale using two different binders: Na-bentonite and carboxymethyl cellulose. The produced pellets were sintered at temperatures between 800 and 1200 °C, and their physical properties, including compressive strength and porosity, were evaluated. The evolution of mineral phases during sintering was analyzed using X-ray diffraction and Mössbauer spectroscopy. Thermodynamic modeling with FactSage 8.3 software, employing Reaction, Predom, Equilib, and Phase Diagram modules, was conducted to understand phase transformations and equilibrium conditions. Special attention was given to the formation of calcium ferrite, whose presence was confirmed and thermodynamically justified. The study demonstrates that optimized sintering conditions significantly improve the mechanical strength of the pellets, enhancing their suitability for recycling applications in steelmaking. • Rolling mill scale waste was successfully processed by pelletization. • Thermodynamic study revealed phase evolution during pellet sintering. • Optimized sintering parameters enhanced mechanical strength of pellets. • High mechanical strength promotes industrial application of recycled pellets. • Energy-efficient recycling process supports circular economy goals.