Equilibrium slag losses in ferrovanadium production

Ferrovanadium is sometimes produced from V₂O₃ in electric arc furnaces, using aluminum as a reductant. The CaO fluxes the alumina, which forms during reduction of the vanadium oxide. Incomplete reduction of vanadium oxide from the slag is a significant cause of vanadium losses. To quantify factors that can affect the equilibrium vanadium loss, the vanadium oxide activity coefficient was measured experimentally for different slag compositions. Hydrogen-water mixtures were used to control the partial oxygen pressure (approximately 10⁻¹³ atm) ove CaO-Al₂O₃ slags contained in vanadium crucibles at 1700 °C; gas-phase mass transfer was controlled by jetting the gas mixture onto the slag surface. Manipulation of the redox conditions at a single slag composition and temperature showed that, as expected, the vanadium is present in the trivalent state in the slag. The slag basicity (CaO-Al₂O₃ ratio) was found to have a very strong effect on the activity coefficient of VO_1.5, with clear implications for the effect of plant practice on vanadium loss. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.