Calcium vanadate

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used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate.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... 

H. 8-Hydroxyquinaldine (XI). The reactions of 8-hydroxyquinaldine are, in general, similar to 8-hydroxyquinoline described under (C) above, but unlike the latter it does not produce an insoluble complex with aluminium. In acetic acid-acetate solution precipitates are formed with bismuth, cadmium, copper, iron(II) and iron(III), chromium, manganese, nickel, silver, zinc, titanium (Ti02 + ), molybdate, tungstate, and vanadate. The same ions are precipitated in ammoniacal solution with the exception of molybdate, tungstate, and vanadate, but with the addition of lead, calcium, strontium, and magnesium aluminium is not precipitated, but tartrate must be added to prevent the separation of aluminium hydroxide. 

Phosphate, arsenate, and vanadate interfere. Borate, fluoride, and large amounts of aluminium, calcium, magnesium, and the alkali metals have no effect in the determination, but large amounts of iron (> 5 per cent) appear to produce slightly low results. 

Vanadate, dioxybis(oxamato)-bond-length ratios, 1,57 Vanadate, heptacyano-potassium salt structure, I, 72 Vanadate, hexafluoro-dipotassium salt history, I, 21 potassium salt history, 1,21 tripotassium salt history, 1,21 Vanadate, pentachloro-stereochemistry, 1,40 Vanadate, pentafluorooxy-stereochemistry, I, 50 Vanadates biochemistry, 3,456 calcium/magnesium ATPase inhibition, 6, 567 competition with phosphates physiology, 6,665 protonation, 3,1026 sodium pump, 6, 557 in uranium purification from ore, 6, 899 Vanadates, hexafluoro-, 3. 482,531 Vanadates, oxoperoxo-, 3,501 Vanadates, pentacarbonyl-, 3, 457 Vanadium biology, 6,665 determination, 1. 548 extraction... 

The T2 site also became protected from tryptic hydrolysis after phosphorylation of the native or solubilized sarcoplasmic reticulum vesicles with inorganic phosphate in a calcium free medium in the presence of dimethylsulfoxide or glycerol [121,252]. Under these conditions the Ca -ATPase is converted into a covalent E2-P intermediate, that is analogous in conformation to the E2V intermediate formed in the presence of vanadate. In contrast to this, the T2 site in the stable phosphorylated Ca2E P intermediate generated by the reaction of the Ca -ATPase with chro-mium-ATP in the presence of Ca [178,253] was fully exposed to trypsin, just as it was in the nonphosphorylated Ca2Ei form. Therefore the phosphorylated intermediates show the same sensitivity to trypsin at the T2 site as the corresponding nonphosphorylated enzyme forms. 

The photocleavage is accompanied by loss of ATPase activity and inhibition of the crystallization of Ca -ATPase both processes are accelerated by Ca [104,105]. The faster loss of ATPase activity during illumination in the presence of calcium is consistent with simultaneous binding of vanadate and calcium to the Ca -ATPase [259-261]. 

As examples of some water-soluble salts, mention may be made of potassium chloride, copper sulfate, and sodium vanadate. As examples of some water-insoluble salts, mention may be made of some typical ones such as lead chloride, silver chloride, lead sulfate, and calcium sulfate. The solubilities of most salts increases with increasing temperature. Some salts possess solubilities that vary very little with temperature or even decline. An interesting example is provided by ferrous sulfate, the water solubility of which increases as temperature is raised from room temperature, remains fairly constant between 57 and 67 °C, and decreases at higher temperatures to below 12 g l-1 at 120 °C. Table 5.2 presents the different types of dissolution reactions in aqueous solutions, and Table 5.3 in an indicative way presents the wide and varied types of raw materials that different leaching systems treat. It will be relevant to have a look at Table 5.4 which captures some of the essential and desirable features for a successful leaching system. 

Two general approaches to syntheses seem to exist. In one method, exemplified in Section A for the sodium salt, a solution of a simple vanadate is acidified in a controlled way to produce the condensed [V100M] 6 ion, which is then crystallized as the salt of the original cation. This method has somewhat limited applicability inasmuch as the solubilities of many simple vanadates (e.g., of calcium and ammonium) are too low. 

In 1927 J. W. Marden and M. N. Rich of the research staff of the Westinghouse Lamp Company obtained metallic vanadium 99.9 per cent pure by heating a mixture of vanadic oxide, metallic calcium, and calcium chloride in an electric furnace for an hour at a temperature of about 1400° Fahrenheit. When the resulting mass was cooled and stirred into cold water, beads of pure metallic vanadium separated out (35). 

B. Wet Processes.—These vary considerably in detail according to the nature and amount of constituents other than vanadium in the ore. An outline of the operations involved in the case of patronite is as follows The ore is roasted with common salt or sodium carbonate and then extracted either (a) with water to give an alkaline solution of sodium vanadate and soluble vanadates of other metals, any lead, zinc, copper, etc., being left in the residue or (b) with sulphuric acid to produce a solution of vanadyl sulphate. Acid extraction is usually employed when the vanadium content of the material is low. The alkaline extract from (a) is treated with excess of sodium carbonate in order to precipitate calcium and aluminium, after removal of which,... 

It is possible to measure the formation of various radicals such as reactive oxygen species in cells. Reactive oxygen species (ROS) activate the nuclear factor of activated T cell transcription factor (NFAT), which is associated with its dephosphorylation, nuclear translocation, and increased affinity for DNA binding. Vanadium activation of nuclear factor of activated T cells (NFAT) was found to correlate with formation of the ROS H202 and was dependent upon the activity of calcium channels [39], In activated human neutrophiles, vanadium(II), (III), and (IV) increased hydroxyl radical formation and attenuation of myeloperoxidase activity, whereas V(V) did not show these effects. Similar results were seen in a cell-free system [40], Increased lipid peroxidation in liver but not in kidneys was found in normal rats treated with vanadate [41]. 

Calcium seems to have a significant effect on the accumulation and transport of the vanadate anion. Morrell et al. (1983) found that low levels of Ca in the nutrient solution resulted in less vanadate accumulation in the root and proportionally more of it being transported to the shoot. These results agree with the hypothesis of Cannon (1963) who suggested that V was immobilised in the root as the sparingly soluble calcium vanadate. 

The results of the studies with Na+, K+-ATPases prompted workers to examine other ATPases for effects of vanadate(V). Ca2+-ATPase of red cell membranes, which is coupled to the calcium pump, is also strongly inhibited by vanadate86"88 , but early work suggested that Ca2+-ATPase from the sarcoplasmic reticulum of muscle is not89 . The... 

Chemical Vapor Deposition of CaO and Calcium Vanadate Films... 

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