Thermodynamics of desulphurization reactions during the treatment of hot metal with calcium and calcium compounds

Basic discussions on the desulphurization reactions when treating hot metal with calcium and calcium compounds shall contribute to a better understanding of the results of this process where mixtures of lime and calcium carbide are added by means of the submerged lance process. From the thermodynamic equilibrium of sulphur and oxygen with calcium carbide it can be concluded that in commercial-scale operation with a submerged lance the use of pulverized calcium carbide leads to a considerable conversion of calcium carbide into calcium oxide due to the dissolution of the oxygen contained in the hot metal. The desulphurization reaction is predominantly a secondary reaction with the calcium oxide which is turned into calcium sulfide. Additions of aluminium into the hot metal rush the lime desulphurization reaction by decreasing the oxygen activity in the hot metal and by suppressing the passive dicalciumsilicate formation on the lime surface by formation of calcium aluminate during the desulphurization reaction.