Estimation of Sulfide Capacity of Slags Using Ionic Theory

Abstract

Abstract This article discusses the issues of sulfur removal in a ladle–furnace unit. The coefficient of sulfur distribution depends on sulfide capacity of slag, the coefficient of sulfur activity, as well as oxidation potential of medium and equilibrium constant. The sulfide capacity of slags C S is one of the most important properties of refining power of slags used upon extra furnace steel processing. One of the factors influencing on sulfide capacity is temperature. The equation is proposed to determine the sulfide capacity as a function of optical basicity and temperature in the range of 1400–1650°C. At optical basicity Λ not higher than 0.75, the error of the equation does not exceed 6%. The equation for estimation of optical basicity is proposed, which accounts for the influence of basic, acidic oxides and amphoteric oxide Al 2 O 3 . It is demonstrated that the slags comprised totally of homogeneous phase are characterized by higher optical basicity of aluminum oxide. The heterogeneous slags are characterized by lower optical basicity of Al 2 O 3 in comparison with homogeneous slags. Most likely, this can be attributed to the fact that the homogenous slags are characterized by deficit of basic oxide CaO and, under the considered conditions, the compound Al 2 O 3 starts to exert more basic properties than acidic ones. Therefore, in homogeneous slags, the optical basicity of aluminum oxide is higher and approaches the optical basicity of the oxide CaO. The estimations performed on real heats demonstrate that its optical basicity decreases upon increase in Al 2 O 3 content in slag. A known value of optical basicity allows to determine sulfide capacity of slag, distribution coefficient of sulfur between metal and slag, and, respectively, final content of sulfur in metal. Theoretical estimations carried out for actual heats demonstrate that the sulfide capacity can be reasonably determined by ionic theory of slags.