Ammonium decavanadate

Savan. [Kerr-McGee] Sodium ammonium decavanadate. 

For solvent extraction of pentavalent vanadium as a decavanadate anion, the leach solution is acidified to ca pH 3 by addition of sulfuric acid. Vanadium is extracted in about four countercurrent mixer—settler stages by a 3—5 wt % solution of a tertiary alkyl amine in kerosene. The organic solvent is stripped by a soda-ash or ammonium hydroxide solution, and addition of ammoniacal salts to the rich vanadium strip Hquor yields ammonium metavanadate. A small part of the metavanadate is marketed in that form and some is decomposed at a carefully controlled low temperature to make air-dried or fine granular pentoxide, but most is converted to fused pentoxide by thermal decomposition at ca 450°C, melting at 900°C, then chilling and flaking. 

Averbuch-Pouchot, M.T. 1995. Crystal structure of hexakis(2-ammonium-2-methyl-1-propanol) decavanadate (C4H12NO)6(V10O28). Z. Krist. 210 371-372. 

Two metastable aqueous polyvanadates have been identified. Acidification of neutral vanadate solutions yields a solution with the expected V and O NMR spectra of the decavanadate anion and with additional resonances (two V, 1 12 three O, 1 1 1) that decay with a half-life of 80 min at 25 °C. The spectra are consistent with either a protonated a-Keggin anion or its e-isomer, [II12V13O40]3, 8 9 Reaction of V02+ with 50% H202 and subsequent treatment with tetramethyl-ammonium ion leads to black (NMe -jI I6[V, 5O4J in 36% yield. The anion has a trans bicapped Keggin structure analogous to that of [PV 4042]9 (see below) and has the expected four-line 51V NMR spectrum (1 2 8 4). At pH 3.5, solutions of the anion are stable for a week at room temperature, and exhibit an initial reduction potential of 0.23 V vs. Ag/AgCl. Acidification leads irreversibly to VO2+.X0... 

During the titration of sodium or ammonium vanadate at a high ionic strength, no solid phase is formed around H /V = 3 corresponding to the existence of the zero-charge species. The decavanadate is in equilibrium with the non-condensed cation [V02(OH2)4] and the kinetic phenomena are such that there is a direct transition from one form to the other [2,50]. 

To obtain vanadia-titania catalysts ammonium vanadate is dissolved in that standard solution. After 1 h stirring the dark brown solution shows a pH of about 6, indicating the presence of decavanadate ions [9]. In the case of quaternary oxides an aqueous solution of ammonium metatungstate is added. 

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