Vanadium aluminothermic reduction

The vanadium alloy is purified and consoHdated by one of two procedures, as shown in the flow diagram of the entire aluminothermic reduction process presented in Figure 1. In one procedure, the brittle alloy is cmshed and heated in a vacuum at 1790°C to sublime most of the aluminum, oxygen, and other impurities. The aluminum faciHtates removal of the oxygen, which is the feature that makes this process superior to the calcium process. Further purification and consoHdation of the metal is accompHshed by electron-beam melting of pressed compacts of the vanadium sponge. 

Vanadium forms numerous oxides, the most important of which are vanadium monoxide, vanadium sesquioxide, vanadium dioxide and vanadium pentoxide. In the earlier examples (e.g., oxides of chromium and of niobium) the enthalpy values for the aluminothermic reduction of each of the oxides was given for the purpose of illustration. Normally, the consideration can be restricted to only those oxides which are readily obtained and which can be handled freely without any special or cumbersome precautions. In the case of vanadium for example, it is sufficient to consider the reduction of the sesquioxide (V203) and the pentoxide (V2Os). The pertinent reactions are ... 

In practice, the production of vanadium by aluminothermic reduction is also governed by some other considerations. The reduction has to be carried out under an inert atmosphere (helium or argon) to avoid nitrogen pick-up from the air by vanadium metal. The composition of the oxide-aluminum charge has to be so chosen that the thermit (metal obtained by aluminothermic reduction) contains between 11 and 19% aluminum. This is necessary for the subsequent refining step in the vanadium metal production flowsheet. Pure vanadium pentoxide and pure aluminum are used as the starting materials, and the reduction is conducted in a closed steel bomb as shown in Figure 4.17 (C). 

Figure 4.17 C Schematic of the closed-bomb reactor for aluminothermic reduction of vanadium pentoxide.

Ferrovanadium stands as a major industrially used form of vanadium. Similarly, it is in the form of ferroniobium that the bulk of niobium is used industrially. Aluminothermic reduction is an elegant metallurgical process for the production of these ferroalloys in their practically carbon-free forms. 

Preparation. Commercially it is prepared mainly as ferro-vanadium alloy. It can be obtained by aluminothermic reduction of the oxide. Pure V may be obtained through the de Boer-Van Arkel process by iodide thermal decomposition (vanadium iodide is decomposed on an electrical heated W wire). 

Vanadium metal can be prepared either by the reduction of vanadium chloride with hydrogen or magnesium or by the reduction of vanadium oxide with calcium, aluminum, or carbon. The oldest and most commonly used method for producing vanadium metal on a commercial scale is the reduction of V2Os with calcium. Recently, a two-step process involving the aluminothermic reduction of vanadium oxide combined with electron-beam melting has been developed. This method makes possible the production of a purer grade of vanadium metal, ie, of the quality required for nuclear reactors (qv). 

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