Vanadium oxidant, pentavalent

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). 

Wadsley A.D. Crystal chemistry of non-stoichiometric pentavalent vanadium oxides crystal structure of Li ,V 0. ActaCryst. 1957 10 261-67. 

The mean vanadium oxidation state in equilibrated (NH4)2(V0)3(P207)2-based catalysts is 4.12 [6], That means half of the vanadium ions in the amorphous phase should be pentavalent. Taking also into account the stoichiometry of the dehydration reaction the follorving equation can be written formally ... 

Oxidation of pentavalent neptunium by pentavalent vanadium. Oxidation of pentavalent neptunium by pentavalent vanadium proceeds at a practical rate without catalyst. Dukes [D4] found that the rate of reaction could be represented by... 

Process selection. The processes just described recovered neptunium only partially and in variable yield because of the difficulty in controlling the distribution of neptunium valence between 5 and 6 in the primary extraction step with nitrite-catalyzed HNO3 and the incomplete reduction of neptunium from valence 5 to 4 in the partitioning step with feirous ion. This section describes a modified Purex process that could be used if more complete recovery of neptunium were required. It is based on process design studies by Tajik [Tl]. The principal process steps are shown in the material flow sheet Fig. 10.32. In the primary decontamination step, pentavalent vanadium oxidizes neptunium to the extractable hexavalent state. In the partitioning step, tetravalent uranium reduces plutonium to the inextractable trivalent state while converting neptunium to the still-extractable tetravalent state. 

Environmental studies [17] of urban airsheds in several areas of the country have shown that high levels of atmospheric vanadium oxide are associated with industrialized areas, especially those areas where fossil fuels are burned or where vanadate steel is being produced. In addition, vanadium has been shown to exhibit increased tissue levels in fish and other marine animals associated with oil rigs in the Santa Barbara basin of the United States [18]. Blotcky et al. [19] determined the vanadium content in shrimp, crab, and oyster from four ocean sites off and near Galveston Island, Texas. They found that the vanadium content was greater in marine biological samples taken in waters near industrialized areas as compared to samples taken in waters near the nonindustrialized sections. Speciation of the vanadium is very important since the two oxidation states, i.e., IV or V, have different nutritional and toxic properties [14]. Orvini et al. [20] applied a preirradiation speciation method to freshwaters from the Italian Ticino and Po rivers and found out that vanadium was present in various tetravalent cationic and pentavalent anionic as well as in natural complexed forms. 

In commercial units today, it is preferred to use the alkali metal metavanadates, particularly potassium metavanadate (KVO3). If de.sired, vanadium pentoxide (V2O5) can be added directly to the potassium carbonate solution, forming potassium metavanadate by reaction with potassium carbonate. For the corrosion inhibitor to be effective, the plant must be designed so that exposed carbon steel surfaces are wetted by the inhibited solution. In order to maintain the metavanadate in its fully oxidized (pentavalent) state, the licensors of the Benfield process recommend that potassium nitrite be injected into the solution on a carefully controlled basis (Sorell, 1990). 

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. 

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. 

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. ... 

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],... 

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. 

Titanium is the only member of its family forming +3 compounds of appreciable stability (Zr, Hf, and Th are almost exclusively tetravalent). In group Va, only vanadium assumes a +4 oxidation state (its congeners almost invariably are pentavalent). In Group VIII, osmium and ruthenium can assume a valence of + 8, but their lighter congener, iron, apparently does not. 

A number of V complexes of various nuclearities are now known that contain persulfide groups in either terminal or bridging modes, mostly in the III and IV oxidation states, but at least two pentavalent vanadium compounds have been characterized,33 namely (Me3NCH2Ph)2[VS2(S2)(SPh)] and (NEt4)[VO(S2)2(bipy)]. 

Recently the large pore vanadium containing molecular sieve, V-NCL-1 with a pore size of 7 A, has been shown to be an active catalyst for the oxidation of larger molecules, such as napthalenes, 1,4-napthoquinones and phthalic anhydride (Scheme 22)[187]. The as synthesised form of V-NCL-1 contains atomically dispersed V4+ ions located in fiamework postions although not neccessarily in tetrahedral coordination. The vandium ions can be oxidised to the pentavalent state by calcination, as evidenced by ESR [157], with some... 

A laboratory study was undertaken to determine the behaviour of neptunium in the WAK flowsheet, and to devise a procedure for its recovery. Based on static ( ) and counter-current experiments (J5), the conclusion was reached that about half of the Np is co-extracted with the U and Pu in the HA-HS mixer-settlers of WAK while the other half is rejected to the HAW, see Fig.1. It could also be shown that an increase of the aqueous acidity, or the addition of pentavalent vanadium as an oxidant into the lower stages of the HA mixer-settler (6), would increase the Np yield in the organic solvent. In the 1BX-1BS mixer-settlers where the partitioning of U and Pu is carried out by use of uranium (IV)nitrate - hydrazine nitrate, a splitting of the coextracted Np between the two product streams was observed the proportions of the (co-extracted) Np which ended up in the 1CU (uranium product) stream fluctuated from 30 to 93 % while the difference amount (from 7 to 70 %) ended up in the 1 BP (plutonium product) stream. 

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