Removal of vanadium from titanium tubes by chemical method

The vanadium impurities in the titanium tube are mainly VOCl3 and a tiny amount of VCI4. Their presence makes the TC4 titanium alloy tube yellow. The purpose of vanadium removal is not only for decoration, but also for oxygen removal. This is a particularly critical part of the refining process.

The boiling point difference and relative volatility of Welded Titanium Tube and vanadium impurity are relatively tiny. For example, the boiling point difference of Titanium tube and VOCl3 is 10℃, and the relative volatility d = 1.22. The difference between the two boiling points of TC4 titanium alloy tube and VCl4 series is 14 degrees Celsius. In theory, however, it is possible to remove vanadium impurities by physical methods, such as extreme efficiency rectification towers. The advantages of this method are that chemical reagents are not needed, the refining process is continuous production, easy to realize automation, and the separated VOCl3 and VCl4 can be used directly. The disadvantage is that the energy consumption is large, the equipment investment is large, and the structure of the high-power kettle needs to be solved, so it has not been applied in industry.

In addition, TC4 titanium alloy tube - V0Cl3 system two components of the freezing point difference is large, about 54 degrees Celsius difference, so it can also be used to remove VOCI3 frozen crystallization method, but the freezing energy consumption is extremely large, so it has not been used in industrial applications.

For this reason, chemical removal of vanadium is frequently used, chemical removal of vanadium is in the titanium tube to add a chemical agent, so that VOCl3 (or VCl4) impurity selective reduction or selective precipitation generated insoluble alum compounds and TC4 titanium alloy tube separation or selective adsorption of VoCl3 (or VCl4), so that vanadium impurities and TC4 titanium alloy tube separation; ​or selectively dissolved VOCl2, so that the alum impurities and 7icld mutually separated.

It can be said that a higher ideal process of vanadium removal, which is simple in equipment, low in cost, excellent in working conditions and easy to realize continuous operation, has not been established. This is also the TC4 titanium alloy tube refining process needs to be studied.

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