Vanadium recovery is a measure of how much of the vanadium that enters a process actually ends up where it is wanted. In steelmaking the term usually means the fraction of the vanadium in the ferrovanadium addition that dissolves into the steel rather than reporting to the slag. In the ferroalloy and slag-processing business the same words mean the fraction of vanadium extracted from a converter slag or an ore. Both numbers are quoted as percentages and both are sensitive to operating practice, which is why two plants using the same alloy can report yields several points apart.
Recovery of Ferrovanadium into Steel
Vanadium has a high affinity for oxygen, so the controlling variable is the oxygen potential of the bath at the moment of addition. In normal ladle practice, with the addition made after deoxidation and with argon stirring, a recovery of 90–95% is achievable. Recovery falls when:
the addition is made while the bath is still oxidising, for example before aluminium or silicon deoxidation is complete;
the slag is oxidising or high in iron oxide, which returns vanadium to the slag as V2O5;
the material is added too early and is exposed to the furnace atmosphere for a long time;
fine powder is charged by hand or allowed to sit on the slag rather than being injected below the surface;
stirring is inadequate, so undissolved particles are carried into the slag with the first slag cut.
Typical plant figures, stated as the yield of the vanadium added as FeV, are about 85–90% for a furnace addition and about 92–96% for a properly stirred ladle addition. These are operating ranges, not limits fixed by any standard: ASTM A102/A102M and GB/T 4139 specify the alloy, not the process yield.
Why Vanadium Ends Up in the Slag
Slag is not simply waste in a vanadium heat; it is a parallel vanadium stream. Basic oxygen furnace slag from vanadium-bearing hot metal typically carries 12–20% V2O5, and electric arc furnace slag from alloy steel heats can carry 2–5% V2O5 depending on the scrap mix and the practice. Vanadium distributes between metal and slag according to the oxygen potential and the basicity of the slag, so the same heat will lose more vanadium to the slag when the slag is oxidising and less when it is strongly reducing.
Recovering Vanadium from Slag and Residues
Salt roasting and leaching. The standard industrial route. Slag or ore is roasted with sodium carbonate or sodium chloride at roughly 750–850 °C to convert the vanadium into water-soluble sodium vanadate, then leached with water. Vanadium is precipitated from the leach liquor as ammonium vanadate and calcined to V2O5. Plant recoveries of the vanadium in the feed are typically in the 80–90% range, with the losses spread across roasting conversion, leaching and precipitation.
Reductive recovery from slag into an alloy. Because vanadium in slag is present as an oxide, it can be reduced back to the metal. Adding aluminium or calcium to molten slag reduces the oxide, and the vanadium reports to the metal phase, where it alloys with the reductant carrier and can be tapped off. Silicon and carbon can perform the same duty at higher temperature.
Electric arc furnace and converter treatment. Slag is melted in an electric arc furnace, or treated in a converter where oxygen is blown to shift the slag chemistry and liberate vanadium, and the vanadium-bearing phase is separated for return to the steelmaking route. The recovered material is then used as a substitute for purchased ferrovanadium.
Residue and spent catalyst processing. Spent V2O5-based catalysts and vanadium-bearing residues from the chemical industry are leached in alkaline or acid media and returned to the same precipitation route used for slag.
Controlling and Measuring Recovery
Reliable recovery figures come from a mass balance, not from a single analysis. Weigh and assay the alloy charged, weigh and assay the steel at tap, and assay the slag, then reconcile the three. Standard practice for the supporting analyses includes ASTM A370 for the mechanical property verification of the finished steel and ASTM E1019 for carbon, sulphur, nitrogen and oxygen determinations, with vanadium itself normally measured by inductively coupled plasma or X-ray fluorescence against certified reference materials. At least two of the three streams should be sampled on the same heat so that the balance closes within a defined tolerance.
Frequently Asked Questions
Q: What is the recovery of ferrovanadium in steelmaking?
A: Typically 90–95% when the alloy is added to a deoxidised, well-stirred ladle, and about 85–90% for a furnace addition where the bath and slag are more oxidising.
Q: Why is vanadium lost to the slag?
A: Vanadium has a strong affinity for oxygen. When the slag is oxidising or high in iron oxide, vanadium reports to the slag as V2O5 instead of dissolving in the steel.
Q: How much V2O5 does converter slag contain?
A: Basic oxygen furnace slag produced from vanadium-bearing hot metal typically contains 12–20% V2O5, which is why it is processed as a vanadium ore rather than discarded.
Q: How is vanadium recovered from slag?
A: The usual industrial route is salt roasting at about 750–850 °C with sodium carbonate or sodium chloride, water leaching of the sodium vanadate, precipitation of ammonium vanadate and calcination to V2O5. Reductive recovery in an arc furnace or converter is used where an alloy product is wanted.
Q: What recovery is expected from slag processing?
A: Around 80–90% of the vanadium in the feed is a realistic plant figure, with losses split between incomplete roasting conversion, leaching and precipitation.
Q: How should recovery be measured?
A: By mass balance across the alloy charged, the steel at tap and the slag, with each stream sampled and assayed on the same heat and the vanadium analysis bracketed with certified reference materials.