How is high-purity vanadium pentoxide purified from red cake?

To purify high-purity vanadium pentoxide ($V_2{O}_5$) from red cake (sodium hexavanadate), the red cake is first dissolved in an aqueous solution of sodium carbonate. During this process, impurities such as iron, aluminum, and silicon precipitate out of the solution when the acidity is adjusted.

Following the removal of these impurities, ammonium chloride is added to the solution to precipitate the vanadium as ammonium metavanadate. This precipitate is then filtered and calcined, resulting in vanadium pentoxide with a purity level greater than 99.8 percent.1