Fused vanadium pentoxide

The general method of preparation of these double salts consists in fusing vanadium pentoxide with excess of the halide of the metal. Except in the case of the sodium compound, the residue is simply washed with water, in which the double salts are insoluble. The following have been described —... 

Pyrovanadates, R 4V207 or 2R a0.Va05.—The alkali pyrovana-dates are prepared by dissolving the equivalent quantity of vanadium pentoxide in solutions of alkalis, or by the spontaneous decomposition in solution of the alkali orthovanadates. Pyrovanadates of other metals are obtained by fusing vanadium pentoxide with the salts or hydroxides of the metals in molecular proportions, or, when they are sufficiently insoluble, by double decomposition between an alkali pyro-vanadate and a salt of the metal required. 

Metavanadates, R VOs or R 20.V205.—These salts are more stable than either the ortho- or pyro-vanadates. Solutions of the latter yield metavanadates on being evaporated or by treatment with carbon dioxide. The alkali metavanadates are prepared directly by dissolving vanadium pentoxide in the calculated quantity of alkali hydroxide. The metavanadates of other metals are prepared by fusing vanadium pentoxide with the oxide or carbonate of the metal in calculated quantity,11 or by the action of a soluble salt of the metal... 

Vanadates.—Ortho-vanadates are prepared by fusing vanadium pentoxide with the required amount of a carbonate ... 

Many modifications of the vanadium catalysts have been developed. Thus, by fusing vanadium pentoxide with infusorial earth a more active... 

Stratcor process (Durango, CO). In Durango, US Vanadium Corp. recovers vanadium as a coproduct with uranium by leaching the ore concentrate for 24 h with hot sulfuric acid and an oxidant such as sodium chlorate (NaClOj). After removal of solids, the leachate is fed into a solvent-extraction circuit, where the uranium is extracted in an organic solvent consisting of 2.5%-amine-2.5%-isodecanol-95%-kerosene. Vanadium remains in the raffinate, which is fed into a second solvent-extraction circuit. There vanadium in turn is extracted in the organic phase, stripped with a 10 wt.% soda-ash solution, and precipitated with ammonium sulfate. The ammonium metavanadate precipitate is filtered, dried, and calcined to yield flakes of black (fused) vanadium pentoxide. 

Up to about 1945 the typical naphthalene oxidation catalyst was fused vanadium pentoxide, sometimes combined with molybdenum trioxide, on an inert support. At that time US production of phthalic anhydride was probably less than 60,000 tonnes year and catalyst quality was not very important. 

The principal vanadium-bearing ores are generally cmshed, ground, screened, and mixed with a sodium salt, eg, NaCl or Na2C02- This mixture is roasted at ca 850°C and the oxides are converted to water-soluble sodium metavanadate, NaVO. The vanadium is extracted by leaching with water and precipitates at pH 2—3 as sodium hexavanadate, Na V O, a red cake, by the addition of sulfuric acid. This is then fused at 700°C to yield a dense black product which is sold as technical-grade vanadium pentoxide. This product contains a minimum of 86 wt % V20 and a maximum of 6—10 wt % Na20. 

For solvent extraction of a tetravalent vanadium oxyvanadium cation, the leach solution is acidified to ca pH 1.6—2.0 by addition of sulfuric acid, and the redox potential is adjusted to —250 mV by heating and reaction with iron powder. Vanadium is extracted from the blue solution in ca six countercurrent mixer—settler stages by a kerosene solution of 5—6 wt % di-2-ethyIhexyl phosphoric acid (EHPA) and 3 wt % tributyl phosphate (TBP). The organic solvent is stripped by a 15 wt % sulfuric acid solution. The rich strip Hquor containing ca 50—65 g V20 /L is oxidized batchwise initially at pH 0.3 by addition of sodium chlorate then it is heated to 70°C and agitated during the addition of NH to raise the pH to 0.6. Vanadium pentoxide of 98—99% grade precipitates, is removed by filtration, and then is fused and flaked. 

The usual extraction procedure is to roast the crushed ore, or vanadium residue, with NaCl or Na2C03 at 850°C. This produces sodium vanadate, NaV03, which is leached out with water. Acidification with sulfuric acid to pH 2-3 precipitates red cake , a polyvanadate which, on fusing at 700°C, gives a black, technical grade vanadium pentoxide. Reduction is then necessary to obtain the metal, but, since about 80% of vanadium produced is used as an additive to steel, it is usual to effect the reduction in an electric furnace in the presence of iron or iron ore to produce ferrovanadium, which can then be used without further refinement. Carbon was formerly used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate. If pure vanadium metal is required it can... 

Sulphates, which form part of the ash from the combustion of many fuels, are not harmful to high-alloy steels, but can become so if reduction to sulphide occurs. This leads to the formation of low melting point oxide-sulphide mixtures and to sulphide penetration of the metal. Such reduction is particularly easy if the sulphate can form a mixture of low melting point with some other substance. Reduction can be brought about by bad combustion, as demonstrated by Sykes and Shirley , and it is obviously important to avoid contact with inefficiently burnt fuels when sulphate deposits may be present. Reduction can also be brought about in atmospheres other than reducing ones and the presence of chlorides or vanadium pentoxide has been shown to be sufficient to initiate the reaction. It has also been shown that it can be initiated by prior cathodic polarisation in fused sodium sulphate. The effect of even small amounts of chloride on oxidation in the presence of sulphate is illustrated in Fig. 7.33 . 

V02.V206 also results as deep blue crystals on heating ammonium metavanadate which has previously been fused and cooled. It is stated that the fused substance does not furnish vanadium pentoxide on being decomposed.10 The residue is extracted with concentrated ammonium hydroxide solution and the oxide precipitated by addition of water. 

The red, amorphous form of vanadium pentoxide is the form most frequently met with in the laboratory. Its preparation has been described above. It melts at 658°10 or 675° C.u to a dark red liquid, but is not volatile even at high temperatures it can be vaporised only in the electric furnace.18 The fused solid conducts electricity, with formation of hypovanadic oxide, V02 18 the electrical conductivity has been measured.14 The oxide absorbs water on exposure to the air, the... 

Molten vanadium pentoxide is a corrosive substance and attacks most containers even when made of platinum, fused silica, or graphite.10... 

Manganese Pyrovanadate, MnaV207, is obtained in large, brilliant brown needles by fusing together a mixture of vanadium pentoxide, sodium bromide and manganese bromide.4... 

Thallium Pyrovanadate, T14V20 is precipitated as a light yellow powder by the addition of thallium sulphate to a cold, saturated solution of sodium orthovanadate. It also results on fusing a mixture of vanadium pentoxide and thallium carbonate.14 It melts at 454°15 or 416° C.,16 and is soluble in about 5000 parts of water at 14° C. 

Zinc Pyrovanadate, Zn2V207, forms orange-red prisms when vanadium pentoxide is fused with a mixture of sodium bromide and zinc bromide.2 It is appreciably soluble in water. 

Lead Polyvanadate, Pb0.2Va06, can be obtained as yellow, transparent needles by fusing a mixture of vanadium pentoxide, sodium iodide, and lead iodide.11... 

Sodium Orthoxytrithiovanadate, Na8VS30.5H20, is obtained in dark, reddish-brown, deliquescent crystals by the action of sodium hydrosulphide on sodium pyrovanadate. The anhydrous salt is formed when vanadium pentoxide, sulphur and sodium carbonate are fused together,4 or by the action of hydrogen sulphide on sodium orthovanadate at 500° to 700° C.5... 

Vanadium Disilicide, VSia, is prepared by reducing a mixture of vanadium trioxide and silicon with magnesium vanadium pentoxide can also be employed with the addition of fluorspar to the mixture.12 Gin used a mixture of the pentoxide, silica, and coke.18 Vanadium disilicide is a very stable compound it forms metallic prisms which melt at 1655° C., have a specific gravity of 4-42, and are hard enough to scratch glass. It is attacked by hydrofluoric acid, hydrogen chloride gas, and fused alkalis. 

W. Muthmann and co-workers also reported that finely divided vanadium reacts with nitrogen at a red-heat. The reaction is so slow that 20-24 hrs. are needed for the increase in weight to become constant nitrogen is also absorbed at dull redness, but the action is still slower. In contradistinction to H. E. Roscoe, the composition of the product approximated vanadium heminitride, V2N. R. E. Slade and G. I. Higson found that vanadium nitride dissociates at 1203° and 02 mm. press. According to N. Whitehouse, at a white-heat vanadium forms the mononitride. The velvety-black powder is unchanged in air when heated in air, however, it forms vanadium pentoxide water, and dil. hydrochloric acid, hot or cold, have no action, but it dissolves in cold dil. nitric acid. G. Gore found that vanadium nitride is insoluble in liquid ammonia. It is not affected by alkali-lye, but with fused potassium hydroxide, ammonia is evolved. 

In oxide materials [2] which are fused for catalytic applications, two additional factors contribute to the unique features of this preparation route. Many oxides in their liquid states are thermodynamically unstable with respect to the oxygen partial pressure present in ambient air, i.e. they decompose into lowcr-valcnt oxides and release molecular oxygen into the gas phase. This process can be fast on the time-scale of the fusion process, such as with vanadium pentoxide or man-... 

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