DRI from Recycled Iron Bearing Wastes for Lower Carbon in the Blast Furnace

Abstract

Reduction of Fe-bearing FINEX process waste and carbon composite pellets from 1373 K to 1573 K to produce DRI (direct reduced iron) for use in the blast furnace was investigated using a modified thermo-gravimetric analyzer. Reduction from the initial Fe₂O₃ was not uniform throughout the composite pellet. Oxygen removal from the Fe₂O₃ rich composite pellets over 84% was only observed at 1573 K. Lower temperatures resulted in significantly un-reduced FeO_t due to the premature consumption of the carbon. A peripheral boundary of FeO_t·Al₂O₃ and 2FeO·SiO₂ phases surrounding the reducible FeO_t was observed in some of the partially reduced cross-sectional SEM (scanning electron microscope) images that could hinder reduction. From the apparent activation energy, interfacial reaction seems to affect the kinetics of the Fe-bearing process waste composite pellets. Bursting of pre-dried composite pellets containing less than 2 mass% moisture was simulated in a RHF hearth simulator. From direct observation of pellets charged between 1173 K to 1573 K, medium-sized pellets between 9.4 to 12.4 mm diameter showed less bursting of the pellet, when charged below 1273 K. In addition, modification of the physical strength of the hard bedrock formed from pellet bursting could be softened with additions of SiO₂.