Microstructure Characteristic and Phase Evolution of Refractory Siderite Ore during Sodium-carbonate-added Catalyzing Carbothermic Reduction

Thermodynamic analysis of refractory siderite ore during carbothermic reduction was conducted. Microstructure characteristics and phase transformation of siderite ore during sodium-carbonate-added catalyzing carbothermic reduction were investigated. X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive analysis of X-rays were used to characterize the reduced samples. Results indicate that the solid reaction between FeO and SiO2 is inevitable during carbothermic reduction and the formation of fayalite is the main hindrance to the rapid reduction of siderite. The phase transformation of present siderite ore can be described as: siderite-magnetite-metallic iron, complying with the formation of abundant fayalite. Improving the reduction temperature (≤ 1050 °C) and duration is helpful for the formation and aggregation of metallic iron. The iron particle size in the reduced ore was below 20 μm, and fayalite was abundant in the absence of sodium carbonate. With 5% Na2CO3 addition, the iron particle size in the reduced ore was generally above 50 μm, and the diffraction intensity associated with metallic iron in the XRD pattern increased. The Na2O formed from the dissociation of Na2CO3 can catalyze the carbothermic reduction of the siderite. This catalytic activity may be mainly caused by an increase in the reducing reaction activity of FeO.