Effect of Fluorspar and Industrial Wastes (Red Mud and Ferromanganese Slag) on Desulfurization Efficiency of Molten Steel

Fluorspar (CaF₂) has been widely used to control the physicochemical properties of slag in steelmaking processes. However, it is very important to reduce the CaF₂ consumption because it causes various environmental problems. In the current study, therefore, the effect of industrial waste materials such as red mud (RM) and ferromanganese slag (FMS) on the desulfurization behavior of molten steel was investigated to find potential substitutes for fluorspar. Compared to conventional 10 pct CaF₂-containing ladle slag, when excess industrial wastes were added (i.e., more than 10 mass pct), the composition of the slag was dramatically changed (SiO₂ increases, while Fe_tO and MnO decrease). Therefore, the sulfide capacity of the slag decreased, and the viscosity of the slag increased. Thus, the desulfurization efficiency was also reduced. However, when the RM or FMS were added not more than 10 mass pct to lean-CaF₂ (3 pct) slag, the sulfide capacity of the slag was equivalent to 10 pct CaF₂-containing ladle slag; thus, the desulfurization efficiency was also equivalent with lower melting point and higher fraction of liquid phase. Consequently, it was confirmed that a small amount (less than 10 mass pct) of industrial wastes can be added as a desulfurization fluxing agent as a partial substitute for fluorspar.