CaO-enhanced mechanism of oxidized consolidation of chromite pellets

The production of chromite pellets is a low-energy route for stainless steel manufacturing, but chromite ores suffer from low reactivity and poor consolidation during induration. This study aims to improve the oxidizability and consolidation of chromite pellets by adding CaO-containing additive (CE), thereby promoting structural reinforcement. Laboratory-scale oxidation firing tests and thermodynamic calculations were conducted to investigate the effects of CE on the oxidation behavior and consolidation mechanism. Results show that under optimum conditions of preheating at 950 °C for 8 min and roasting at 1280 °C for 12 min, the cold compressive strength (CCS) of fired pellets with 2% CE reaches 3598 N/p, compared to only 2364 N/p for those without CE. When targeting a CCS of approximately 2500 N/p, the required roasting temperature for chromite pellets with CE can be reduced to about 1200 °C. Thermodynamic analysis reveals that CaO reduces the Gibbs free energy for the oxidation decomposition reaction of chromite spinel. The coexistence of CaSiO 3 , CaAl 2 Si 2 O 8 and SiO 2 forms a stable low-melting-point phase (1184.29 °C). Mechanism analysis reveals that CE accelerates the oxidation rate and enhances the oxidation degree of chromite spinel, and consequently reduces the FeO content in fired pellets by 46.70%. The addition of CE promotes sesquioxide formation, strengthening solid-state consolidation. Meanwhile, the liquid phase derived from low-melting-point phases increases contact points among mineral particles and provides assisted bonding. These improvements enhance the strength of chromite fired pellets. Overall, incorporating CE not only improves pellet strength but also lowers the roasting temperature, offering better economic efficiency.