Liquidus surface of FeO-Fe2O3-SiO2-CaO slag containing Al2O3, MgO, and Cu2O at intermediate oxygen partial pressures

Abstract

The liquidus surface of the FeO-Fe 2 O 3 -SiO 2 -CaO system is of special importance in general pyrometallurgy. 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.

Liquidus Surface of FeO-Fe<SUB>2</SUB>O<SUB>3</SUB>-SiO<SUB>2</SUB>-CaO Slags at Constant CO<SUB>2</SUB>/CO Ratios

“…Second, lime does not decrease, but instead, increases the liquidus temperature of the slag at spinel saturation area and consequently increases the risk of the magnetite (spinel) precipitation which makes lime not a good flux in terms of the liquidus temperature. This effect is much more pronounced in this kind of diagrams compared to the diagrams at constant p O 2 presented previously 4) and this reflects the sensitivity of the liquidus temperature toward changes on the oxygen potentials. It should be mentioned however that lime decreases the liquidus temperature only in the region of newly proposed FCS slag 5,6) where it may be used as a good flux.…”

“…This difference has not been always understood and one of the reasons for that is that the experiments have always been carried out in equilibrium with metallic iron and in air where the oxygen potential does not change (in air) or change only slightly (in equilibrium with metallic iron). This is clearly reflected on the difference that exists between the diagrams at constant oxygen potentials 4) and those at constant CO 2 /CO, as given in this work.…”

“…As stated in previous work [4][5][6][7] oxygen potentials during matte smelting and blister making converting at 1573 K can be respectively approximated as 10 À8 and 10 À6 . This is illustrated in Fig.…”

“…They have been constructed by FLOGEN TM software 9) through a new thermophysicochemical model, 4) which was already verified against all available experimental data on liquidus temperatures as well as other thermodynamic properties at several oxygen potentials. 3.…”

“…In our previous work the liquidus surface of some iron oxide slags has been quantified at low oxygen potentials, characteristic of reductive processes [1][2][3] and at intermediate oxygen potentials, characteristic of oxidative processes [4][5][6][7] such as direct smelting and continuous converting. This was carried out by the means of a new type of multicomponent phase diagrams 1) at constant oxygen potentials and deducted from the use of a new thermophysicochemical model.…”