Recovery of vanadium oxide from steelmaking slag is of great interest for Swedish steel producers and the technique for assessing the oxidation state of vanadium is crucial in the optimization of vanadium recovery. There is a large spread in the reported values of published V2p 3/2 binding energy values for various oxidation states of vanadium. Therefore, an extensive analysis of vanadium oxide standards was performed aimed at obtaining reliable data and improved methods for the preparation of representative oxide standards. Powdered oxide standards of V 2 O 5 , VO 2 , V 2 O 3 , and VO, with purity better than 99%, were chosen. In their as-received state, all of the standards are covered by a thin layer of vanadium pentoxide that does not allow accurate evaluation of X-ray photoelectron spectroscopy spectra for vanadium oxides at lower oxidation states. Therefore, different methods for obtaining a representative surface for vanadium oxide standards were tested. The experimental results show high sensitivity of vanadium oxide standards to argon ion etching. Hence, a method to obtain a representative surface of standards by special heat treatment is proposed. Such approach was developed using a preparation chamber (furnace) attached to an X-ray photoelectron spectroscopy instrument. The annealing was performed in a vacuum at defined temperatures from 400 to 900 C for 4-24 h; the annealing parameters were selected based on thermodynamic equilibrium data for vanadium oxides. Experimental fitting parameters (peak position E and full width of half maximum of the peak) for vanadium V2p 3/2 and oxygen O1s peaks are thus obtained for stoichiometric vanadium oxides.
Experiments on a vanadium recovery method from vanadium containing BOF‐slag using both a Tamman furnace (3 kg scale) and an induction furnace (150 kg scale) were conducted. The vanadium was extracted into the slag phase by bubbling oxidation gas into a metal bath consisting mainly of V (1–10 mass%), Si (less than 1 mass%) and P (about 1 mass%). The first experiments revealed that the slag formed during oxidation reaction had considerably high phosphate capacity. High phosphorus content would rule out the possibility of using the slag as a raw material for the production of ferrovanadium of high quality. In order to reduce the P‐content in the slag, addition of slag former to reduce phosphate capacity was necessary. A suitable slag system (having the initial composition 40 mass% Al2O3 ‐ 25 mass% CaO ‐ 35 mass% SiO2) and a suitable atmosphere, by using CO2, that enhanced the oxidation of vanadium, but limit the oxidation of iron and phosphorus was found. However, more efforts should be put forward, e.g. study of the phase diagram, the viscosity of the slag and even oxide activities to gain more insight into the slag formed by selective oxidation.
Swedish steel producers are particularly interested in the recovery of vanadium oxide from the steelmaking slag because of its high content in the LD‐converter slag. Hence, optimization of the vanadium recovery has strong economic and environmental impact. Solving the problem with vanadium recovery from the slag requires development of reliable technique for assessing the oxidation state of vanadium. This paper summarizes methodology for the robust analysis of the Ca‐Si‐based slag materials containing vanadium oxide in different oxidation states utilizing XPS. The measurements show that because of high oxygen affinity of vanadium oxides and number of oxidation states, only fracturing of machined specimens in an ultra‐high vacuum chamber, connected to XPS, allows accurate evaluation of oxidation state of vanadium in slag. Proper charge compensation, required due to non‐conductive nature of the slag specimens, is considered to be the main problem faced during analysis. As neither carbon nor oxygen signals were proven to be appropriate reference point for charge referencing in this material, the calcium 2p peak position at 347.0 eV, characteristic for CaSiO3, shown to be the most stable and reliable binding energy calibration reference and was used during the charge compensation. Results indicated that in the case of the studied slags, vanadium oxides present are formed preferably by mixture of V2O3 and VO2, depending on the reducing potential of the controlled atmosphere applied during the slag synthesis. Copyright © 2014 John Wiley & Sons, Ltd.
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