Redox of Vanadium?

Ammonium metavanadate, NH4VO3 will be the source of the +5 oxidation state. Treatment of the ammonium metavanadate with hot hydrochloric acid partly reduces the vanadium to the +4 oxidation state in the form of the VO2+ ion. The two species are separated using an ion exchange resin. The VO2+ ion is then treated with mossy zinc generating the V3+ and V2+ which also are separated by ion exchange chromatography.