Effect of Oxide Additives on Desulfurization Efficiency of Hot Metal by CaO-based Powders

Utilization of CaO-CaF2 fluxes provides an efficient and inexpensive method for the dusulfurization of hot metal and has been used extensively. However, it is an urgent necessity to develop an effective desulfurization treatment without CaO-CaF2 fluxes from the environmental point of view. Experiments were carried out mainly at 1400°C to clarify the effect of oxide additives on the desulfurization behavior of hot metal by using CaO-based powders and synthesized CaO-Al2O3 slags. The desulfurization efficiency of CaO-based powders increased by the addition of Al2O3 and Na2CO3. However, as the amount of Al2O3 addition increased up to 30 mass%, the initial desulfurization rate was decreased, although the formation of liquid slag at the early stage of reaction was promoted. CaO-Al2O3-TiO2 fluxes were found to have the largest promoting effect on the desulfurization, due to low melting point and low viscosity of such slags. According to the EPMA mapping analysis, it was found that the flux powders near the slag-metal interface were sintered or partly melted, and that the sulfur removed was concentrated in this flux. As the result, the desulfurization rate was considered to be considerably accelerated by Ar blowing into the metal bath. Consequently, CaO-Al2O3-TiO2 fluxes was regarded to be very useful for hot metal treatment.