Vanadium distribution in melts intermediate to ferroalloy production from vanadiferous slag
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I.
INTRODUCTION
V A N A D I F E R O U S slags originate from iron-making operations in which titanomagnetite is used as the primary ore. Hot metal from the reduction process contains vanadium, which can be recovered by an interstage oxygen blow to form a slag containing around 15 to 20 pet V203. At the completion of the oxygen blow, the hot metal contains typically 0.07 to 0.1 pet vanadium, 0.01 pet silicon, and 0.1 pet manganese, tl,21 Blowing operations are ceased at this vanadium level due to the onset of rapid carbon oxidation. Vanadiferous slags are used as a feedstock in the manufacture of V203, the majority of which is converted by metallothermic smelting into high-grade ferrovanadium. In order to satisfy the requirements of the V2Os salt roast and leach process, the uptake of CaO and MgO during slag production is limited to around 1.5 pet total, in order to minimize the formation of insoluble vanadates during roasting, t3] Conventional vanadiferous slags are, therefore, highly acid in nature. The value of reducible metal oxides contained in many vanadiferous slags is sufficient to warrant consideration of pyrometallurgical processing. However, from an examination of a typical composition, shown in Table I, it can be seen that a single-stage reduction would result in a ferroalloy containing only 15 to 20 pet vanadium. Removal of FeO from the slag is, therefore, desirable for ferroalloy production by this route. Cagnon and Castonguay I41 have shown that iron can be partitioned from vanadium during smelting of hightitania slags. In pilot plant-smelting trials, the FeO concentration was reduced from around 85 to 30 pet, before vanadium metallization losses became significant. In their work, a 40 pet TiO2 slag was produced, containing 8 pet V203. R.L. HOWARD, formerly with Industrial Research Ltd., Wellington, New Zealand, is Consultant Metallurgist, African Mining and Trust Co., Johannesburg, South Africa. S.R. RICHARDS, Group Manager, is with Industrial Research Ltd., Wellington, New Zealand. B.J. WELCH, Professor, is with the Department of Chemical and Materials Engineering, University of Auckland, New Zealand. J.J. M O O R E , P r o f e s s o r and Head, is with the D e p a r t m e n t of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO 80401. Manuscript submitted January 12, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS B
The production of a 45 pet vanadium ferroalloy from vanadiferous slag has been described in a patent for a two-stage silicothermic process, lsJ Using a basic slag composition, 75 pet FeSi was used to reduce the FeO content of the slag in preparation for a final reduction using 90 pet FeSi. In order to increase vanadium recovery into the alloy, considerable lime additions were made to give a CaO/SiO2 ratio of 2.0. The increase in slag basicity was reported to be required for both prereduction and final reduction stages.
A. Vanadium Recovery into Basic Slags Recently, new producers of vanadiferous slags have appeared, and new production and processing option
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