Potassium metavanadate

Prepare 10 g. of potassium metavanadate, KVO 3, either by heating a solution of vanadium pentoxide, V2O5, with the necessary amount of a solution of potassium hydroxide or by boiling the necessary amount of ammonium metavanadate (difficultly soluble) with the required quantity of potassium hydroxide. In either case, obtain the white, needle-shaped crystals by evaporation. 

In an excess of concentrated (30 per cent) hydrogen peroxide to which a little sulfuric acid has been added to insure acidity, dissolve the potassium metavanadate, observing that the color changes to an intense yellow. To this solution, well cooled, add 95 per cent alcohol until the pervanadate has been precipitated as a microcrystalline powder. Filter off the product, wash with alcohol, and dry in a desiccator over calcium chloride. 

Metavanadates of the alkalis are white or colourless, and give colourless aqueous solutions which rapidly become yellow, and, on addition of acids, red or orange. These coloured solutions contain polyvanadates, the formation of which is comparable to that of the polychromates and other salts formed by condensation of weakly acid oxides of metals, e.g. molybdates and borates. Thus, under definite conditions of temperature and concentration, potassium metavanadate is converted into the acid salt 2K20.3Va05, in accordance with the equation ... 

Basic Potassium Metavanadate, 5K20.4V20S.7H20 or K20. KV03. 7H20, separates in white crystals when a solution of potassium pyrovanadate, K4V207, is acidified with acetic acid and concentrated.4... 

Calcium Metavanadate, Ca(V03)2.3H20, gives rise to bright yellow needles when a solution of ammonium metavanadate is boiled with calcium chloride solution and precipitated with alcohol.6 The tetra-hydrate, Ca(V03)2.4H20, is prepared by allowing a mixture of potassium metavanadate and calcium chloride to evaporate for several days.7 Anhydrous calcium metavanadate is a white, porous substance, which is unaffected by strong heating, but is readily decomposed by acids to yield vanadium pentoxide.8 It is much more soluble in water than strontium metavanadate. 

Strontium Metavanadate, Sr(V03)ss.4H20, is obtained as colourless, monoclinic prisms by the action of strontium chloride on potassium metavanadate. It is only sparingly soluble in water and undergoes dehydration at 280° C.14... 

Ammonium Orthothiovanadate, (NH4)3VS4, is obtained in rhombic crystals by the action of ammonium hydrosulphide on potassium metavanadate or sodium pyrovanadate solution. It also separates out slowly from an ice-cold saturated solution of ammonium metavanadate in concentrated ammonium hydroxide which has been previously treated with hydrogen sulphide. 

SYNS POTASSIUM METAVANADATE POTASSIUM VANADIUM TRIOXIDE V.ANADIC ACID, POTASSIUM SALT... 

At a pH near 6, manganese(II) metavanadate precipitates and does not react further, whereas at a pH near 2, other heteropoly species are formed. Inasmuch as commercial potassium metavanadate is not suitable for the syntheses of the 13-vanadomanganate(IV) and nickelate(IV), directions for the preparation of this compound are included in the syntheses below, which are modified from the method of Flynn and Pope.5 The preparation of the yellow-tinged green reduced form of potassium 13-vanadomanganate(IV) is also included.5... 

If commercial potassium metavanadate has been used, precipitation occurs at this point, and only a poor yield of product will be obtained. 

The procedure is the same as that for potassium 13-vanado-manganate(IV) (Sec. B), with the substitution of commercial ammonium metavanadate (15.20 g., 0.130 mole) for potassium metavanadate and ammonium peroxydisulfate (4.56 g., 0.020 mole) for potassium peroxydisulfate. At the end of the reaction (ca. 6 hours, volume of reaction mixture ca. 75 ml.), after the reaction mixture has been filtered, 1.54 g. (0.020 mole) of ammonium acetate is added with stirring. The filtrate is transferred to a 9-cm. evaporating dish and set aside for ca. 3 days or until the volume has decreased to ca. 25 ml. The crystals of bright red crude product are collected by suction filtration on a 9-cm. Buchner funnel and air-dried (ca. 

EINECS 237-388-8 K-Van Potassium m-vanadate Potassium metavanadate Potassium trioxovanadate Potassium vanadate Potassium vanadate(V) (KVO3) Potassium vanadium trioxide UN2854 Vanadate (V03 ), potassium Vanadic acid, potassium salt. Crystals mp = 520" d = 2,840, Kerr-McGee. 

This salt is obtained from solutions of commercial potassium metavanadate (1.04 KgO VsOs 0.78 H3O) by addition of 1.4 moles of acetic acid per mole of vanadate. 

Commercial potassium metavanadate (7 g.) is dissolved in 25 ml. of water in a beaker placed in a large heating bath (75°C). The hot solution, which is about 2M in vanadium, is then treated with 70 ml. of IM acetic acid added from a burette whose tip is immersed in the vanadate solution (vigorous mechanical stirring). The acetic acid is introduced at the rate of 1 ml./minute. The red solution is allowed to remain in the heating bath xmtil the latter cools to room temperature (about 15 hours). The clear solution is then cooled to 0 C to induce crystallization. The crystals are filtered off and washed with some ice-cold water, then with acetone. 

Ano er line of research that is arousing great interest in this area of research is the incorporation of corrosion inhibitors capable of playing an active role in protecting against corrosion similar to that of Cr +. Thus, studies are to be found that incorporate a wide variety of compounds such as cerium acetate, cerium oxalate, calcium borate, potassium metavanadate and cerium vanadate. 

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). 

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