Vanadium tetravalent

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. 

This view is supported by the types of compounds that can be prepared. Group IVa metals in the tetravalent state have no d electrons and tetra-valent vanadium has one. Compounds with a large number of d electrons, e.g., nickel, do not form benzyl compounds readily and attempts to synthesize Ni (benzyl) 2 have not succeeded. 

Another application of an isomerisation reaction can be found in the production of the third monomer that is used in the production of EPDM rubber, an elastomeric polymerisation product of Ethene, Propene and a Diene using vanadium chloride catalysts. The starting diene is made from vinylnorbomene via an isomerisation reaction using a titanium catalyst. The titanium catalyst is made from tetravalent salts and main group hydride reagents, according to patent literature. 

In studies of the concentrations of arsenic, bromine, chromium, copper, mercury, lead and zinc in south-eastern Lake Michigan, it was shown that these elements concentrated near the sediment water interface of the fine-grained sediments. The concentration of these elements was related to the amount of organic carbon present in the sediments (161). However, it was not possible to correlate the concentration of boron, berylium, copper, lanthanum, nickel, scandium and vanadium with organic carbon levels. The difficulty in predicting the behaviour of cations in freshwater is exemplified in this study for there is no apparent reason immediately obvious why chromium and copper on the one hand and cobalt and nickel on the other exhibit such variations. However, it must be presumed that lanthanium might typify the behaviour of the trivalent actinides and tetravalent plutonium. 

Takahashi et al. [25] reported that the dispersed tetravalent vanadium (l 7/2) showed a hyperfine structure but broad band could be observed in the agglomerated vanadium. Miyamoto et al. [8] and Jhung et al. [7] reported that EPR spectra of VAPO -S showed hyperfine structure. Miyamoto et al. [8] suggested that the hyperfine structure indicated atomically dispersion of vanadium in VAPO -S molecular sieve, in other words, vanadium was substituted in the framework of AIPO -S. 

The valence state of vanadium in as synthesized VAPO -S was mainly the tetravalent state, in which... 

For vanadium and chromium the first ionization energies are much lower than the first ionization energies of phosphorus and sulphur, respectively. This explains the high heats of formation of VC13 and CrCl3. In uranium, the tetravalent state is more stable than that in tungsten because uranium as an actinide has a different electron configuration. 

Stretford plants have been in operation for 30 years. There are hundreds of such plants worldwide, used in a variety of sulfur removal operations (Dalrymple 1989). In a Stretford process, the hydrogen sulfide in the feed gas stream is absorbed and oxidized to elemental sulfur in aqueous phase, using pentavalent vanadium which is subsequently reduced from a pentavalent form to a tetravalent form. Later in the process, the vanadium is re-oxidized back again, using anthraquinone disulfonic acid (ADA) as a catalyst, and the elemental sulfur is floated to the surface of the solution and removed. 

Increasing Vanadium and ADA Content. Raising the concentration of vanadium in the Stretford solution can increase the rate of elemental sulfur formation in the absorber/reactor, and thus lower the concentration of sulfur compounds that are converted to thiosulfate in the oxidizer (Moyes 1974 and Nicklin 1977). It may also be necessary to increase the ADA concentration as well, in order to convert the additional tetravalent vanadium that will be formed back into its pentavalent state. 

Hypovanadic Oxide, V02, is amphoteric, and dissolves both in alkalis and acids. In passing from trivalent to tetravalent vanadium, however, the basic character of the oxide becomes less pronounced and... 

Vanadyl salts are salts of tetravalent vanadium, and contain the divalent [VO]- radical. Many vanadium compounds are known which appear to contain a [VO] group, but the vanadium is either trivalent or pentavalent. Throughout this book the term vanadyl is restricted to compounds of tetravalent vanadium, that is, to salts of the oxide V02. Hence, for example, the compound VOCI3, which contains pentavalent vanadium, is called vanadium oxytrichloride, and not by the more usual but less logical name vanadyl chloride. ... 

Vanadium predpitates the metal from solutions of salts of gold, silver, platinum, and iridium, and reduces solutions of mercuric chloride, cupric chloride and ferric chloride to mercurous chloride, cuprous chloride, and ferrous chloride, respectively. In these reactions the vanadium passes into solution as the tetravalent ion. No precipitation or reduction ensues, however, when vanadium is added to solutions of divalent salts of zinc, cadmium, nickel, and lead. From these reactions it has been estimated that the electrolytic potential of the change, vanadium (metal)—>-tetravalent ions, is about —0 3 to —0 4 volt, which is approximately equal to the electrolytic solution pressure of copper. This figure is a little uncertain through the difficulty of securing pure vanadium.5... 

When an electrolyte which is without action on vanadium at ordinary temperatures (for example, dilute solutions of mineral acids, of oxalic acid, or of potassium halides) is electrolysed with a vanadium anode, a complex tetravalent vanadium ion is produced. Similarly, electrolysis at 100° C. and in molten chlorides of sodium or zinc gives rise to complex tetravalent vanadium ions. The E.M.F. in each case is found to be independent of the nature of the electrolyte. When, however, solutions of caustic soda or of caustic potash are employed, the vanadium dissolves as a pentavalent ion, irrespective of variations... 

In 1898, Cowper-Coles 2 claimed to have successfully effected the electrolytic reduction of an acid solution of vanadium pentoxide to metallic vanadium, but the product was subsequently shown by Fischer 3 to have been a deposit of platinum hydride. Fischer, in a series of over three hundred experiments, varied the temperature, current density, cathode material, concentration, electrolyte, addition agent, and construction of cell, but in not one instance was the formation of any metallic vanadium observed. In most cases reduction ceased at the tetravalent state (blue). At temperatures above 90° C. reduction appeared to proceed to the divalent state (lavender). The use of carbon electrodes led to the trivalent state (green), but only lead electrodes produced the trivalent state at temperatures below 90° C. Platinum electrodes reduced the electrolyte to the blue vanadyl salt below 90° C. using a divided cell and temperatures above 90° C. the lavender salt was obtained. 

Electrolytic reduction of pentavalent and tetravalent vanadium salts has frequently been employed for the preparation of vanadium compounds of lower valency.4 Bleecker5 has also prepared vanadium pentoxide and several vanadates electrolytically. 

With more water, it passes into solution dilute solutions, which are brownish-yellow or red, according to the concentration, evolve chlorine and become blue on standing, undergoing reduction to the tetravalent state. On evaporation to dryness, aU the chlorine is evolved and the residue consists of the. pentoxide. Vanadium oxytrichloride is also soluble in ether and alcohol. It dissolves chlorine, bromine, iodine, yellow phosphorus, and sulphur, and is miscible with various liquid hydrocarbons and chlorinated hydrocarbons its use as an industrial solvent has therefore been suggested. ... 

Hydrogen also reduces pentavalent and tetravalent vanadium salts to the trivalent state in the presence of spongy platinum.1... 

Concentrated acid solutions of vanadium pentoxide are reduced to the tetravalent state by hydrogen peroxide, the peroxides of sodium, barium, magnesium, and by persulphates of potassium and ammonium.4 Acid solutions of vanadium pentoxide give rise to pervanadic acid with hydrogen peroxide. 

Reduction of add solutions of vanadium pentoxide to the tetravalent state also takes place with bismuth amalgam 5 magnesium gives the trivalent salts of vanadium, while by using zinc, zinc coated with cadmium, electrolytically deposited cadmium, or sodium amalgam in the absence of air, divalent vanadium salts are obtained in solution.7 Vanadous salts and hypovanadous salts are, however, much more conveniently prepared by electrolytic reduction of acid solutions of vanadium pentoxide in an atmosphere of carbon dioxide.8... 

Vanado-tellurites.—These compounds are of interest in that they are the only heteropoly-acid compounds containing tetravalent tellurium. They are prepared by mixing hydrochloric acid solutions of tellurium dioxide with solutions of vanadium pentoxide in caustic soda and then neutralising with more hydrochloric acid, or by mixing strongly alkaline... 

A sulphide in which the vanadium is tetravalent, corresponding to the oxide V02, has not hitherto been prepared. 

Vanadyl Sulphites.—Normal sulphites containing tetravalent vanadium have not hitherto been prepared in consequence of the readiness with which hydrolysis takes place. A considerable number of vanadyl sulphites are, however, known, as well as their double salts, which, no doubt, are heteropoly-acid compounds. 

Estimation of Vanadium.1—Volumetric Methods.—The most convenient and the usual method for the estimation of vanadium is a volumetric process. The vanadium is first obtained in acid solution as vanadate, and reduced to the tetravalent state by one of several reducing agents which are available. The solution is then titrated in the presence of sulphuric acid with hot potassium permanganate solution, which quantitatively oxidises the lower vanadium salt to the vanadate. Using sulphur dioxide to effect the reduction, the following reactions take place —... 

The estimation of a vanadate solution by direct titration with ferrous sulphate or ferrous ammonium sulphate solution has been worked out, and is found to be specially applicable to the analysis of vanadium alloys. The vanadate is again reduced to tire tetravalent state by the ferrous salt, the end point being obtained by the use of potassium ferricyanide as internal indicator alternatively, a known excess of the ferrous salt solution is added to the vanadate, the amount unused... 

Most tetravalent vanadium complexes contain the V02+ unit which leads to a strong low-symmetry ligand field component. Three ligand field bands with 20 commonly occur, one — 13000 cm-1, one 17000 and one 25000-30000 cm-1, in VOL4 units, but their classification in formal C4v. symmetry is not clear, in spite of the availability of polarized light results.38-138-139 However, the ground term is accepted to be 2B2. 

In conclusion, the EPR results demonstrate the presence of tetravalent vanadium atoms in some sites of the sample. The Vlv atoms could be included in a new compound, as in the NaV5vV,vC>15 vanadate identified in the sample by X-ray spectroscopy. They could also interact with the zeolite surface as reported for V205 supported on silica or n alumina (22) and titania surfaces (23). 

NaY zeolite and V205 react at temperatures as low as 700 K, although both compounds are stable at this temperature. For low R values, the V2C>5 structure disappears, whereas that of the zeolite does not seem to be damaged nor is the cavity size reduced. However some cavity entrances are blocked by a compound containing vanadium atoms and, in particular, a few tetravalent vanadium atoms. Some tetravalent vanadium atoms have also been observed by Occelli and Stencel (25, 26) in much more complex reaction mixtures. 

Liochev, S. and I. Fridovitch. 1987. The oxidation of NADH by tetravalent vanadium. Biochim. Biophys. Acta 255 274-278. 

An ion exchange chromatographic method has been described [16] for the determination of the various forms of vanadium in fresh water. These include tetravalent cationic, pentavalent anionic and neutral complexed forms of vanadium. Separation is achieved on two columns in series involving the absorption of the sample on Chelex 100 and Dowex 1x8 columns followed by the selective elution of the different vanadium species and their assay by neutron activation analysis. Experiments were carried out using vanadium-48... 

Aqueous pentavalent vanadium is readily reduced to the tetravalent state by iron powder or by S02 gas. A stronger reducing agent, eg, zinc amalgam, is needed to yield divalent vanadium. Divalent and tfivalent vanadium compounds are reducing agents and require storage under an inert atmosphere to avoid oxidation by air. 

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