Vanadium pentavalent

Vanadium Sulfates. Sulfate solutions derived from sulfuric acid leaching of vanadium ores are industrially important in the recovery of vanadium from its raw materials. Vanadium in quadrivalent form may be solvent-extracted from leach solutions as the oxycation complex (VO) ". Alternatively, the vanadium can be oxidized to the pentavalent form and solvent-extracted as an oxyanion, eg, (V O ) . Pentavalent vanadium does not form simple sulfate salts. 

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. 

For vanadium solvent extraction, Hon powder can be added to reduce pentavalent vanadium to quadrivalent and trivalent Hon to divalent at a redox potential of —150 mV. The pH is adjusted to 2 by addition of NH, and an oxyvanadium cation is extracted in four countercurrent stages of mixer—settlers by a diesel oil solution of EHPA. Vanadium is stripped from the organic solvent with a 15 wt % sulfuric acid solution in four countercurrent stages. Addition of NH, steam, and sodium chlorate to the strip Hquor results in the precipitation of vanadium oxides, which are filtered, dried, fused, and flaked (22). Vanadium can also be extracted from oxidized uranium raffinate by solvent extraction with a tertiary amine, and ammonium metavanadate is produced from the soda-ash strip Hquor. Fused and flaked pentoxide is made from the ammonium metavanadate (23). 

Pentavalent antimony compounds, 20 56 Pentavalent plutonium cations, 19 692 Pentavalent tungsten, 25 386 Pentavalent vanadium aqueous, 25 533... 

When Roscoe investigated them he found that vanadium is a tri- and pentavalent element of the phosphorus group. He also discovered that what Berzelius had taken for the metal was really the mononitride, VN, and that most of the vanadium compounds studied by the Swedish chemists had contained oxygen. 

Mg (OH) 2 is exclusively basic in its properties. Zn(OH)2, on the other hand, is amphoteric, while arsenious acid, H3As04, is considerably stronger than the acid derived from pentavalent vanadium. 

Hexavalent molybdenum and tungsten, pentavalent vanadium and, to a more limited extent, niobium and tantalum form a very large number of polyoxoanions ( heteropolyanions such as [PW12O40]3- and isopolyanions such as [M07O24]6-). Unlike the polyoxoanions of the post transition elements the heteropolyanions for the most part are discrete, compact species of high... 

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. 

J ADA Isomer Selection. Limited attention is often given in refineries to the isomer of ADA used (Lorton 1988). 2,6-ADA is a commonly used isomer, although it has been found inferior to 2,7-ADA in converting vanadium to its pentavalent form. If this conversion is not performed efficiently, elemental sulfur production rate will fall, and thiosulfate formation will increase. More attention to procuring only 2,7-ADA could augment the efficiency of the Stretford process. 

Trivalent Compounds.—In trivalent vanadium compounds the basic character of the element is well developed, and both normal and oxy-salts of the sesquioxide V203 are well defined, e.g. vanadous sulphate, V2(S04)3, and vanadium oxymonochloride, VOC1. It has been previously mentioned that resemblances between the elements of the A and B Subdivisions of Group V. are mainly restricted to the pentavalent compounds it is of interest to note that the oxychloride has analogues in the trivalent antimony and bismuth basic chlorides, SbOCl and BiOCl. Trivalent vanadium also displays considerable analogy, however, with other trivalent transitional elements, as shown by the following —... 

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. ... 

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... 

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. 

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

Detection.—Apart from naturally occurring ores of vanadium, vanadium steels, and ferrovanadium, the commonest compounds of vanadium are those which contain the element in the pentavalent state, viz. the pentoxide and the various vanadates. The analytical reactions usually employed are, therefore, those which apply to vanadates. Most vanadium ores can be prepared for the application of these reactions by digesting with mineral acids or by alkaline fusion with the addition of an oxidising agent. When the silica content is high, preliminary treatment with hydrofluoric acid is recommended. Vanadium steels and bronzes, and ferrovanadium, are decomposed by the methods used for other steels the drillings are, for instance, dissolved in sulphuric acid and any insoluble carbides then taken up in nitric acid, or they are filtered off and submitted to an alkaline fusion. Compounds of lower valency are readily converted into vanadates by oxidation with bromine water, sodium peroxide, or potassium permanganate. 

Maritidine. It was observed that a variety of alkoxyl or silyloxy phenols 340 (Scheme 51), on oxidation with the non-toxic pheny 1 iodo-tos-trifluoroacetate, instead of customary heavy metal reagents such as trivalent thallium or pentavalent vanadium salts, in the weakly nucleophilic solvent, trifluoroethanol at low temperature, furnished consistently improved yields of cyclisation products 341 [89],... 

Abbasi [243] described a spectrophotometric method based on N(-pN, N-dimethyl anilo-3-methoxy-2-naphtho)hydroxaminic acid for the determination of vanadium in soil. The soil sample was digested with 8 M hydrochloric acid and potassium permanganate (to oxidise vanadium to the pentavalent state). This extract was retrieved with a chloroform solution of the chromogen and the violet colour was evaluated spectrophotometrically. 

Sakurai, H., Shimomura, S., Fukuzawa, K., and Ishizu, K. (1980). Detection of oxovanadium(IV) and characterization of its ligand environment in subcellular fractions of the liver of rats treated with pentavalent vanadium(V). Biochem. Biophys. Res. Commun. 96, 293. 

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... 

Another class of 12-heteropoly anions involves the replacement of molybdenum by pentavalent vanadium. The molybdovanadophosphoric acids,... 

As a last example of a 1 1 structure derived from a cubic close-packed anion sublattice we mention that of the mineral sulvanite CU3VS4. Here, the copper atoms occupy three of the four positions of one set of tetrahedral holes, while the vanadium atom is located at one position of the other set. Thus, the anion is no longer tetrahedrally coordinated but has all four cation neighbours on the same side. In C113VS4 vanadium may be replaced by Nb and Ta and the sulphur by Se and Te (178). These compounds all are diamagnetic semiconductors containing monovalent copper and a pentavalent transition element, as does CuTaS3 (179) where Ta, however, is octahedrally coordinated. 

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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