Investigation of the Thermodynamic Properties of Vanadium Oxides in the CaO–VOx–Al2O3–SiO2 Slag at 1873 K

Abstract In order to minimize the vanadium oxide concentration in slag during the basic oxygen furnace process, the mixed-valence states and activity coefficients of vanadium oxides in the CaO–VO x –Al 2 O 3 –SiO 2 slag were investigated at 1873 K in the present study. At the oxygen partial pressures of 1.94 × 10 −11 and 1.90 × 10 −7 atm, the mixed-valence states of VO, VO 1.5 , VO 2 , and VO 2.5 in the slag were measured by using XPS analysis. V 2+ /V 3+ and V 3+ /V 4+ were the major redox pairs at 1.94 × 10 −11 atm, and the V 3+ /V 4+ redox pair was major at 1.90 × 10 −7 atm. With respect to the increase of slag basicity and oxygen partial pressure, vanadium oxides in the slag showed oxidizing tendency. Simultaneously, the activity coefficients of VO, VO 1.5 , and VO 2 in the slag were measured at the oxygen partial pressure of 7.91 × 10 −11 atm. When the slag basicity increased, the activity coefficients of VO and VO 1.5 increased, while those of VO 2 decreased. With increasing alumina concentration, the activity coefficients of VO and VO 1.5 decreased, and those of VO 2 increased. Then, the activity coefficients of VO x in the slag were integrated. With respect to the increase of slag basicity, the integrated activity coefficients of VO x in the slag increased in the low slag basicity region. They decreased in the high slag basicity region, showing a downward concave trend. When the alumina concentration increased, the integrated activity coefficients decreased. To minimize the vanadium oxide concentration during the BOF process, it is preferable to maintain the slag basicity near 1 and to decrease the alumina concentration in the slag.