Thermodynamic Model and Database for Sulfides Dissolved in Molten Oxide Slags
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UCTION
VARIOUS gaseous species like S, N, C, and H dissolve in molten oxide slags as sulfide, sulfate, nitride, carbide, carbonate, and so on. Knowledge of the solubility of these gaseous species in slags is important. For example, control of the sulfur level in many grades of commercial products, such as steel, copper, and lead, can be achieved by control of the distribution ratio of sulfur between the liquid metals and the molten slags. In steel, a low sulfur content is usually desired because of the detrimental effect of sulfur on many types of final products. However, relatively high sulfur content is desired in some steel grades, such as fast-cutting steels. Approaches have been proposed to correlate the sulfide solubility with the optical basicity[1] or bulk composition[2] of slags. These approaches generally require several empirical model parameters; that is, they have low predictive ability. A more fundamental approach was proposed by Gaye and Lehmann,[3] who included sulfide solubility in the IRSID cell model. This approach has been more successful but still requires several empirical parameters. In the model of Reddy and Blander,[4] which was later modified by Pelton et al.,[5] the activity of sulfide in the slag is calculated from considerations of its configurational entropy of mixing with the silicate structural units, whereas the activities of the oxide components of YOUN-BAE KANG, Research Associate, and ARTHUR D. PELTON, Professor and Co-director, are with the Centre de Recherche en Calcul Thermochimique (CRCT), De´partement de Ge´nie Chimique, E´cole Polytechnique, P.O. Box 6079, Station ‘‘Downtown,’’ Montre´al, Quebec, Canada H3C 3A7. Contact e-mail: [email protected], [email protected]. Manuscript submitted February 13, 2009. Article published online August 25, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
the slag are taken from existing evaluated databases. This model yields good predictions of sulfide solubility in multicomponent slags, with no adjustable model parameters. The model has been extended[6] with equal success to the dissolution of other species (SO42, CO32, I, etc.). In the current article, we report on a new model for the solubility of gaseous species in molten slags within the framework of the modified quasichemical model (MQM) in the quadruplet approximation.[7] This model is similar to the Reddy–Blander–Pelton (RBP) model inasmuch as the sulfide activities are calculated from considerations of the configurational entropy of structural units, whereas the oxide activities are taken from existing extensive evaluated thermodynamic databases, which we have developed during the last 30 years. Like the RBP model, the model involves no adjustable empirical parameters. It is superior to the RBP model inasmuch as it applies even in highly acidic slags and even at high sulfide contents, and its predictive ability is generally even better. The model has been incorporated into the FactSage[8,9] databases and software (ThermFact Ltd., Montreal, Canada and GTT-Technologies, Herzogenr
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