Equilibrium distribution of boron between metal of fe–C–Si–Al system and boron slag

Abstract

Using the HSC 6.1 Chemistry software package (Outokumpu) and simplex-lattice planning, the thermodynamic modeling of the boron equilibrium distribution between iron containing 0.2 % of C, 0.35 % of Si, 0.028 % of Al (in the terms and hereinafter indicated mass. %) and slag of the system СаО – SiO2 – Аl2O3 – 8 % МgO – 4 % В2O3 was carried out in a wide range of chemical composition and at temperatures of 1550 °С and 1600 °С. Adequate mathematical models in the form of III degree polynomial obtained for each temperature, describes the equilibrium distribution of boron between slag and metal depending on the slag composition. Mathematical modeling results are presented graphically in the form of diagrams of composition – boron equilibrium distribution. It is shown that slag basicity affects on the boron distribution coefficient. Thus, increasing the slag basicity from 5 to 8 at temperature of 1550 °С reduces the boron distribution coefficient from 160 to 120 and, as a consequence, increase the boron content in the metal from 0.021 % at LB = 159 to 0.026 % at LB = 121, that is, growth slag basicity is beneficial to the development of boron recovery process. The positive effect of the slag basicity on boron recovery process in the researched range of the chemical composition can be explained according to the slag phase composition and thermodynamics of boron reduction reactions. The temperature growth of the metal negatively affects the boron recovery. Equilibrium boron distribution coefficient increases by an average of 10 units with an increase in temperature to 1600 °C. The diagrams contain marked field of slag chemical composition with 53 – 58 % of CaO, 8.5 – 10.5 % of SiO2 and 20 – 27 % of Al2O3, providing boron distribution coefficients at level of 140 – 170 at temperature range of 1550 – 1600 °C and allowing to expect boron concentration in the metal at the level of 0.020 % at LB = 168 % and 0.023 % at LB = 139 at the 4 % of B2O3 in the slag initial. © 2017 National University of Science and Technology MISIS. All rights reserved.