Thermodynamic Modeling of Sulfide Capacity of Na 2 O-Containing Oxide Melts
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E sulfur solubility in oxide melts at high temperatures is important for ironmaking, steelmaking, combustion, glassmaking, and geochemistry. Particularly, there is currently a strong demand for the production of high-quality steels with very low levels of impurities for line pipes, electrical tools, and advanced automotive applications. The desulfurization process of hot metal is often carried out prior to decarburization in the basic oxygen furnace, and further desulfurization of steel can be conducted in the ladle furnace in the secondary steelmaking process. As a result, the sulfide segregation and inclusions of steel are reduced, and the surface quality is improved, which decreases the need for subsequent surface treatments.[1] Various desulfurizers, such as mixtures of CaO (lime), CaC2 (calcium carbide), Na2CO3 (soda ash), metallic Mg, etc., have been widely used in hot metal pretreatment. Lime is a strong desulfurization agent often used in the Kanbara Refining (KR) station. To accelerate the desulfurization kinetics, a small amount of CaF2 is mixed. However, the CaF2 consumption has raised serious concerns regarding the corrosion of refractories, health, and environment.[2,3] The desulfurization operation using CaC2 and Mg is rather costly, and cares must be given to the storage and transport due to possible explosion.[4] Therefore, Na2O-containing fluxes from Na2CO3 have regained interest as desulfurization agents in ironmaking and steelmaking. However, to optimize the sulfur removal efficiency, accurate knowledge of sulfide capacities of the fluxes is essential. Sulfide capacities of Na2O-containing silicate melts,[5–13] and the sulfur partition ratio between the ELMIRA MOOSAVI-KHOONSARI, Ph.D. Student, and IN-HO JUNG, Associate Professor, are with the Department of Mining and Materials Engineering, McGill University 3610 University Street, Montreal, QC, H3A 0C5, Canada. Contact e-mail: in-ho.jung@ mcgill.ca. Manuscript submitted August 16, 2015. Article published online July 14, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
slag and liquid Fe[10–12,14–22] were experimentally studied. However, experimental data are inconsistent and limited to specific composition and temperature ranges. This is attributed to difficulties in performing experiments involving Na2O-containing slags: (i) the high vapor pressure of Na in slags and subsequent loss of Na, especially those slags with high Na2O contents,[10,11,13,17] (ii) very hygroscopic nature of slags, and (iii) the absorption of CO2 and other gaseous species from the atmosphere by slags.[13,16] The main objective of the present study is to develop a thermodynamic database to predict sulfide capacities of slags, especially those of Na2O-containing slags. In the past, the modified quasi-chemical model (MQM) was used to explain the dissolution of gaseous species in slags.[23–26] For example, the dissolution of H (H2O and hydroxyl ion), N (various nitrides), and C (carbonates and carbides) in steelmaking slags was described using the MQM and simplified Blander–Reddy capacity mo
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