The vanadium impurities in the titanium tube are mainly VOCl3 and a small amount of VCI4, which cause the TC4 titanium alloy tube to appear yellow. The purpose of refining vanadium is not only to decolorize, but also to remove oxygen. This is an extremely important step in the refining process.

The boiling point difference and relative volatility of titanium tube and vanadium impurities are relatively small. For example, the boiling point difference between the two components in the titanium tube VOCl3 system is 10 ℃, and the relative volatility is d=1.22; The boiling point difference between TC4 titanium alloy tube and VCl4 system is 14 degrees Celsius. However, theoretically, it is possible to remove vanadium impurities using physical methods, such as using efficient distillation columns. The advantage of this method is that it does not require the use of chemical reagents, the refining process is continuous, easy to achieve automation, and the separated VOCl3 and VCl4 can be directly used. The disadvantages are high energy consumption, large equipment investment, and the need to solve the structure of high-power kettles, which have not yet been applied in industry.

In addition, there is a significant difference in the solidification points of the two components in the TC4 titanium alloy tube-V0Cl3 system, with a difference of about 54 degrees Celsius. Therefore, the freezing crystallization method can also be used to remove VOCI3, but the energy consumption of freezing is high, so it has not been industrially applied. Chemical methods are often used to remove vanadium for this purpose. Chemical vanadium removal involves adding a chemical reagent to a titanium tube to selectively reduce or precipitate VOCl3 (or VCl4) impurities, resulting in insoluble alum compounds that separate from TC4 titanium alloy tubes. Alternatively, VoCl3 (or VCl4) is selectively adsorbed to separate vanadium impurities from TC4 titanium alloy tubes; Alternatively, VOCl2 was selectively dissolved to separate alum impurities from 7icld. It can be said that a more ideal vanadium removal process with simple equipment, low cost, good working conditions, and ease of continuous operation has not yet been established. This is also a topic that needs to be studied in the refining process of TC4 titanium alloy tubes.