8 - Liquidus Surface of FeO-Fe2O3-SiO2-CaO Slag Containing...

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Liquidus Surface of FeO-Fe 2 O 3 -SiO 2 -CaO Slag Containing Al 2 O 3 , MgO, and Cu 2 O at Intermediate Oxygen Partial Pressures FLORIAN KONGOLI and AKIRA YAZAWA The liquidus surface of the FeO-Fe 2 O 3 -SiO 2 -CaO system is of special importance in general pyrometal- lurgy. It determines several industrial slags, such as “fayalite” slag, calcium ferrite slag, acidic and basic steelmaking slags, as well as the newly proposed “ferrous calcium silicate slags” (FCS), which are all nominally based on this system. Nevertheless, the liquidus surface of this system has been studied only in equilibrium with metallic iron or in air, and the data at intermediate oxygen partial pressures are almost missing. In reductive smelting processes, the aforementioned slags were based on the liquidus surface of the FeO-Fe 2 O 3 -SiO 2 -CaO system in equilibrium with metallic iron. In oxidative matte smelting and in today’s modern trends of nonferrous smelting, such as continuous converting or white metal production, the characterization of the liquidus surface of this system at intermediate oxygen partial pressures becomes imperative. Furthermore, the effect of minor oxides on the liquidus surface of this system has not been studied at higher oxygen potentials and confusing conclusions are found in literature even for low oxygen potentials. In this work, a quantitative description of the liquidus surface of FeO-Fe 2 O 3 -SiO 2 -CaO slag containing Al 2 O 3 , MgO, and Cu 2 O is carried out by means of a thermodynamic model at various intermediate oxygen partial pressures. Through a new type of easy-to-understand multicomponent phase diagram, it is shown that important differences exist between the liquidus surfaces of this system in reductive and oxidative conditions. It is also shown that minor components can have fundamentally different effects in reductive and oxidative conditions. I. INTRODUCTION literature and industrial practice about the problem of “mag- netite” precipitation, which most of the time has been only T HE FeO-Fe 2 O 3 -SiO 2 -CaO system is of special impor- empirically explained. tance in general extractive metallurgy. Many existing indus- Most of the industrial slags also contain different amounts trial slags such as the “fayalite” slag, calcium ferrite slag, of minor oxides, which are introduced through the mineral acidic and basic steelmaking slags, as well as the newly concentrates, fluxes, dissolved refractories, etc. These oxides proposed “ferrous calcium silicate slags” (FCS) are nomi- significantly affect the liquidus surface of the FeO-Fe 2 O 3 - nally based on this system. The liquidus surface of this SiO 2 -CaO system and the operational windows of the slags. system determines the operational windows of existing slags
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8 - Liquidus Surface of FeO-Fe2O3-SiO2-CaO Slag Containing...

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