Thermodynamics of alkaline-earth metals reduction from slag melts

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 l_e1 (KSiO₂(l) + lMeO(l)) → CSiO₂ (sol) + α(MeO·SiO₂)(sol), l_e2(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 a_MeO 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 a_SiO2 = 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.

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