ON THE HOT METAL DESULFURIZATION

Although there is no thermodynamic limitation to the desulfurization o f carbon-saturated iron with CaO, the process is well-known to be slow . Consequently, the desulfurization of carbon-saturated Fe-S, Fe-S-Si, Fe-S-Si-Al, Fe-S-Zr alloys be CaO, and Fe-S-Si alloys by CaO-10 % CaF 2 were investigated to determine the reaction mechanism. For this purp ose, dense CaO and CaO-10 % CaF2 discs were cemented to the bottoms of graphite crucibles containing the carbon-saturated alloys. The desulf urization experiments were run at 1450 degrees C in an SiC resistance furnace under argon gas atmosphere. The results indicate that the desu lfurization of hot metal by CaO is greatly improved by prior addition of aluminum to the hot metal. The addition of 10 % CaF2 to CaO also in creases the rate of desulfurization. Ziroonium, which has a stronger a ffinity for oxygen than aluminum did not increase the rate. SEM and X- ray diffraction studies on the surfaces of CaO discs used to desulfuri ze carbon-saturated Fe-S, and Fe-S-Si alloys showed that solid CaS, an d solid CaS plus small amount of solid 2 CaO . SiO2 compounds form on the limo surface, respectively. The slow reaction rate with CaO is att ributed to the solid reaction products which block the reaction by pre venting the occurrence of interfacial turbulence.