Calcium oxide is one of the major fluxing agents used for steel refining. Because unreacted CaO remains in slag in most cases, discharged slag is difficult to be recycled smoothly. With the growth of environmental concerns, improving utilization efficiency of CaO is required to reduce the amount of discharged slag and energy consumption. The authors have reported a resource and energy-saving process by using multi-phase flux for dephosphorization. Reaction behavior of phosphorus in multi-phase CaO-FeO_x-SiO_2-P_2O_5 flux system was investigated. Formation mechanism of P_2O_5-rich phases was clarified at the interface between solid CaO or 2CaO·SiO_2 and molten CaO-FeO_x-SiO_2-P_2O_5 slag. Phase relationship and thermodynamic properties of 2CaO; SiO_2-3CaO·P_2O_5 solid solution were observed to confirm the condensation of P_2O_5 in solid phase. Based on these results, reduction of CaO consumption, discharged slag curtailment, and energy-saving effects in the novel refining process by using multi-phase flux were discussed.
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