Waste Slime of the V2O5 Production according to the Lime–Sulfuric Acid Technology as a Technical Raw Material for Vanadium Recovery

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Representative samples of the waste slime of the vanadium pentoxide V₂O₅ production from converter slags according to the lime–sulfuric acid technology are studied to develop its effective reclamation with vanadium recovery. The phase composition of the slime consists of gypsum, hematite, quartz, cristobalite, pseudo-brookite, complex ferrite, and various calcium-containing silicates. The residual vanadium content in the waste slime that is based on V₂O₅ is 2–7%, the major part of which is sealed (insoluble) vanadium and the minor part is acid-soluble vanadium. A high vanadium content in the slime is found to be related to the disadvantages of oxidizing roasting of a vanadium slag with a lime addition in a rotary kiln and sulfuric acid leaching of a cinder under industrial conditions. To study the vanadium recovery from the slime, we analyzed direct sulfuric acid leaching of the slime and its leaching after preliminary oxidizing roasting. The optimum parameters of oxidizing roasting and sulfuric acid leaching are determined. Oxidizing roasting of the slime in the temperature range 925–1050°C is shown to substantially increase the vanadium recovery during subsequent leaching of the roasting product by weak sulfuric acid solutions. To exclude the formation of aggressive compounds SO₂ and SO₃ in roasting, it is necessary to separate a fine gypsum-containing fraction from the slime before oxidizing roasting in order to perform acid leaching.