Reaction mechanism for the CaO-Al and CaO-CaF₂ desulfurization of carbon-saturated iron

Abstract

The desulfurization of carbon-saturated iron with CaO is inefficient due to the formation of solid reaction products on the CaO particles which inhibit sulfur transfer. It has been shown in full scale and pilot plant studies that Al improves desulfurization with CaO. The present results indicate that Al affects the rate at 1450 °C, but not at 1350 °C, and that zirconium, which has a stronger affinity for oxygen than Al, does not increase the rate as much as aluminum. Alternate methods of producing a liquid reaction surface, such as desulfurization with CaO-CaF₂ or a premelted calcium aluminate flux, also increase the rate. From these results, it is concluded that it is critical to have a liquid reaction surface for effective desulfurization. Aluminum in the metal, reacting with oxygen and CaO, provides a liquid calcium aluminate surface. An optimum aluminum level of about 0.1 to 0.3 pct was found. At lower levels, the Al is consumed and eventually solid calcium silicate forms, and at higher levels, possibly an alumina-rich solid phase forms.