Effect of the Carbon Mixing Ratio on Mineral Evolution and Gasification Dephosphorization during the Pre-reduction Sintering Process of Bayan Obo Iron Ore Concentrate

Abstract

The pre-reduction sintering process is an effective measure to fundamentally solve the detrimental circulating accumulation of phosphorus in iron- and steel-making procedures. The effect of the carbon mixing ratio on the mineral evolution, gasification dephosphorization and pre-reduction degree of sintering products was primarily investigated based on the phosphorus occurrence status in Bayan Obo iron ore concentrate. The obtained results indicated that iron oxide was dominantly transformed from magnetite into wüstite, and metallic iron was basically not detected. Regarding silicate slag, the precipitated dendritic phase accounted for a higher content of FeO and MgO and a lower content of Na₂O + K₂O and SiO₂ over the vitreous matrix phase. Moreover, as the carbon mixing ratio was increased from 5 to 25 wt%, the gasification dephosphorization and pre-reduction degree first increased from 11.3% and 30.7%, respectively, to 70.0% and 67.4%, respectively, due to the enhanced reducing atmosphere and then decreased to 45.0% and 59.0%, respectively, led by the increased content of liquid slag and the reduced permeability of the burden layer. Both maximum values were obtained at a 20 wt% carbon mixing ratio. Furthermore, the pre-reduction sintering products as raw materials for blast furnaces could not only largely reduce the phosphorus content in hot metal but could also dramatically decrease coke usage and carbon dioxide emissions, which could be highly beneficial to realize carbon peaking and carbon neutrality.