Thermodynamics of alkaline-earth metals reduction from slag melts

Abstract

Based on the state diagrams of two–component silicate systems SrO – SiO2 , BaO – SiO2 , CaO – SiO2 , the authors have determined the activity of components in invariant (eutectic and monotectic) points of the systems under consideration. Crystallization processes at invariant eutectic points l1 and l2 are considered as chemical reactions le1 (KSiO2 (l) + lMeO(l)) → CSiO2 (sol) + α(MeO·SiO2 )(sol), le2 (mSiO2 (l) + nMeO(l)) → (MeO·SiO2 )(sol) + b(2MeO·SiO2 )(sol), for which the values ΔG°T and the equilibrium constants were established. The values of aMeO in the slags were determined at given temperatures and known values of the component activities in metal melts in equilibrium with slag. In homogeneous slag melts, the activity of alkaline-earth metal (AEM) oxides was defined from the constants of equilibrium reactions of reduction of these metals from slags by silicon of iron-silicon metal melts. In the zone of homogeneous slag melts, the dependences aSiO2 = f (x(SiO2 )) were constructed at temperatures of 1600 and 1700 °C, and when using data on the activities of AEM (Sr, Ba, Ca) in metallic high-silicon melts, the dependences lga(SrO) = f (x(SiO2 ) , x(Si)) at 1493 °C and lga(BaO) = f (x(SiO2 ) , x(Si)) at 1450 °C were determined. On a three-parameter diagram in coordinates a[Si] – a(SiO2 ) – a(MeO) (for AEM), the dependencies a(SrO) = f (a[Si] , a(SiO2 ) ) at 1493 °C and a(BaO) = f (a[Si] , a(SiO2 ) ) at 1450 °C were constructed. It is shown that low equilibrium values of a(SrO) and a(BaO) , lga(SrO) = f (a(SiO2 ) , a[Si] ) ≤ (–4) and lga(BaO) = f (a(SiO2 ) , a[Si] ) ≤ (–3), can be achieved at equilibrium values of silicon activity in metal melts a[Si] > 0,5 during strontium reduction and a[Si] > 0,7 during barium reduction.