Some Aspects of the Chemistry of Slags Containing Cr and V

The present paper provides some pioneering experimental information regarding the chemistry of steelmaking slags containing Cr and V. Initially, the thermodynamic activities of CrO and VO1.5 in slags at very low oxygen potentials were determined by gas-equilibration technique involving CO-CO2-Ar gas mixtures at 1600 ℃. While the activity of CrO as a function of XCrO showed a positive deviation from ideality, the trend in the case of VO1.5 was found to be the opposite. In the case of Cr-slags, it is important to determine the valence states of Cr in the slag as a function of basicity, oxygen partial pressure prevailing and temperature. In view of the contradictory results in the literature, experiments were conducted by XANES (X-ray Absorption Near-Edge Spectroscopy) as well as the high temperature Knudsen cell mass spectroscopy (pioneering experiment). The ratio of Cr2+ /Cr3+ as functions of basicity, pO2 and temperature were determined. Cr emission from slags were determined by a thin film method, using SHTT (Single Hot Thermocouple Technique) set-up. It was found that at CrO3 emissions are significant in air at steelmaking temperatures. In the case of V-containing slags, the ratio of the valence states of vanadium was determined as functions of temperature and basicity by the same methods as in the case of Cr. The kinetics of evaporation of pure V2O5 was examined by thermogravimetry. Thin film experiments showed that vanadium losses as V2O5 are significant in oxidizing atmospheres. Further experiments were conducted by simultaneously applying vacuum and oxygen purging in order to force the micro bubbles of V2O5 formed and entrapped in the viscous slag. These experiments demonstrated the potential of this method to extract vanadium from slags, low grade ores and even pet-coke ash.