Comparison of iron desulphurisation using calcium carbide and lime-magnesium mixtures

Experiments were carried out to compare the desulphurisation behaviour of commercial calcium carbide mixtures with that of lime-magnesium mixtures by injection into 400 kg heats of hot metal. It was found that the rate was higher for the lime-magnesium mixtures, while the utilisations based on stoichiometry were higher with the calcium carbide mixtures. The reaction rates for both types of reagent were improved by predeoxidation with aluminium. The fundamental kinetic mechanisms of reaction were examined for CaO, CaC2, CaCO3, Mg, CaO-Mg, and CaC2-Mg reagents. For the calcium carbide reagents, only a fraction (approximately one third) of the particles was estimated to contact the melt. The calcium carbide desulphurisation rate was sensitive to the oxygen activity in the melt, because the commercial reagent used contained CaO and CaCO3. For lime-magnesium mixtures, magnesium acts primarily as a deoxidiser, whereas lime acts as a desulphuriser. The implications for full scale practice are discussed, particularly with respect to oxygen control to achieve low sulphur contents.