Modelling pyrometallurgical kinetics: ladle desulphurization

Ladle desulphurization of aluminium-deoxidized steel by means of a syntheti c slag is an example of a mass-transfer-controlled pyrometallurgical operat ion. Literature data Indicate that mass transfer of sulphur in the liquid s teel is rate-determining. In this work, the rate of desulphurization in an argon-stirred ladle was calculated, incorporating literature correlations f or the mass-transfer coefficient of sulphur in the liquid metal, and thermo dynamic data on the activities of relevant species dissolved in the liquid steel and synthetic slag. The desulphurization rate was calculated using th e Metsim package, assuming local equilibrium at the slag-metal interface. T his process serves as an example of the modelling - within Metsim - of a ba tch process, with mass-transfer control (and hence local equilibrium at the reaction interface). The results of the simulation are compared with a sim ple analytical solution for this system; the analytical solution is an appr oximation in that it neglects changes in the dissolved aluminium content of the steel, and changes in the slag composition, as the reaction proceeds. It is shown that the simple analytical model yields results that are genera lly satisfactorily close to the more rigorous model - which means that the analytical model can be used as a general tool to control this step of seco ndary metallurgy.