Application of ionic theory to calculate sulfide capacity of slags

The article considers the issues of sulfur removal in the ladle-furnace unit. The sulfur distribution coefficient depends on sulfide capacity of the slag, sulfur activity coefficient, oxidizing potential of the medium and equilibrium constant. The sulfide capacity CS of slags is one of the most important characteristics of refining capacity of the slags used in extra-furnace steel processing. One of the factors affecting the sulfide capacity is temperature. The formula was proposed showing the dependence of sulfide capacity on the optical basicity and temperature, in the temperature range of 1650 – 1400 °C and when the optical basicity Λ is not more than 0.75; the error of the presented formula does not exceed 6 %. The formula for calculating the optical basicity is proposed, which takes into account the influence of basic, acidic oxides and amphoteric oxide Al2O3. It is shown that slags, completely consisting of a homogeneous phase, have an increased optical basicity of aluminum oxide. Heterogeneous slags have a reduced optical basicity of Al2O3 in comparison with homogeneous slags. Perhaps, this fact can be explained by the fact that in homogeneous slags there is a deficiency of the basic oxide CaO and in the conditions under consideration Al2O3 compound begins to exhibit more basic properties than acidic ones, thus, in homogeneous slags, the optical basicity of aluminum oxide is increased and approaches optical basicity of CaO oxide. Calculations carried out on the basis of real heats have shown that with an increase in the content of Al2O3 oxide in the slag, its optical basicity decreases. Known value of the optical basicity makes it possible to determine sulfide capacity of the slag, sulfur distribution coefficient between metal and slag, and, accordingly, final sulfur content in the metal. The research results have shown that it is advisable to apply the ionic theory of slags for the sulfide capacity determination.

Effect of slag composition on desulfurization during recycling rejected electrolytic manganese metal by electroslag remelting

To reduce the Mn vaporization during recycling rejected electrolytic manganese metal by electroslag remelting, it is proposed to reduce the temperature of molten slag pool, but which leads to the degradation of slag desulfurization. The desulfurization by interaction between CaF2–CaO–Al2O3–Na2O slag and rejected electrolytic manganese metal scrap was studied from the view of thermodynamics in this study. The results show that sulfur distribution ratio decreases with increase of CaF2 content, and increases with the increase of Na2O content and temperature. Na2O increases sulfur distribution ratio of slag by increasing CaO activity. Na2O addition in CaF2–CaO–Al2O3–Na2O slag can enhance desulfurization ability of slag due to the larger sulfur distribution ratio and lower viscosity. Thus, sulfur content in test of slag T3 bearing 45.8 wt% CaF2-23.2 wt% CaO-22.7 wt% Al2O3-8.3 wt% Na2O is much lower than that of slag without Na2O, implying that 45.8 wt% CaF2-23.2 wt% CaO-22.7 wt% Al2O3-8.3 wt%Na2O slag is the promising slag for recycling rejected electrolytic manganese metal by ESR.