Vanadium requirement

Flame methods are the conventional atomization sources used in MS for industrial hygiene (Table I). Air/acetylene at 2150-2400°C is used for the easily atomized elements like lead, cadmium, and zinc. Refractory metals such as tungsten or vanadium require hotter nitrous oxide/acetylene atomization at 2600-2800 C. The need for greater sensitivity and multielement analysis from a single filter has increased the use of electrothermal atomization for tin, vanadium, nickel, and other difficult elements. Formation of hydrides combined with flame atomization has been used in some cases to increase sensitivity. 

The postulated vanadium requirement of adults of < 10 jg per day is met by foodstuffs and beverages (Anke et al. 1989, Nielsen and Uthus 1990, Illing-Giinther et al. 1997b). 

Vanadium deficiency has not been investigated in humans. Most diets supply > 10 pg V per day, which suggests that a daily dietary intake of < 10 pg probably meets any postulated vanadium requirement. 

It is difficult to suggest a vanadium requirement for animal species, including humans. However, at least four Independent laboratories have found that diets with less than 25 ng of vanadlum/g adversely affect rats and chicks under certain conditions. If animal data could be extrapolated to humans, then a 70 kg man consuming 1 kg of diet per day (dry basis) would have a daily requirement of about 25 yg of vanadium under certain dietary conditions. 

The vanadium requirements of humans have not been established because the evidence for requirements and essentiality is weak. However, if requirements do exist they are very low and easily met by the levels naturally occurring in food, water and air [21]. The daily intake of vanadium may vary widely but has been established to be 2 mg in a well-balanced diet for a 75-kg person [22]. One study found that nine institutional diets supplied 12.4-30.1 p.g of vanadium daily, with intakes averaging 20 p.g [23]. Sources of vanadium are bread, some grains and nuts, vegetable oils, fish, meat, and a few vegetables. The amounts vary from less than 0.1 ng/g in peas, beets, and carrots to 52 ng/g in radishes. Liver, fish, and meat contain up to 10 ng/g [23]. 

The catalyst used in the production of maleic anhydride from butane is vanadium—phosphoms—oxide (VPO). Several routes may be used to prepare the catalyst (123), but the route favored by industry involves the reaction of vanadium(V) oxide [1314-62-1] and phosphoric acid [7664-38-2] to form vanadyl hydrogen phosphate, VOHPO O.5H2O. This material is then heated to eliminate water from the stmcture and irreversibly form vanadyl pyrophosphate, (V(123,124). Vanadyl pyrophosphate is befleved to be the catalyticaHy active phase required for the conversion of butane to maleic anhydride (125,126). 

Fluidized-bed reactor systems put other unique stresses on the VPO catalyst system. The mixing action inside the reactor creates an environment that is too harsh for the mechanical strength of a vanadium phosphoms oxide catalyst, and thus requires that the catalyst be attrition resistant (121,140,141). To achieve this goal, vanadium phosphoms oxide is usually spray dried with coUoidal siUca [7631-86-9] or polysiUcic acid [1343-98-2]. Vanadium phosphoms oxide catalysts made with coUoidal sUica are reported to have a loss of selectivity, while no loss in selectivity is reported for catalysts spray dried with polysUicic acid (140). 

The oxidative dehydration of isobutyric acid [79-31-2] to methacrylic acid is most often carried out over iron—phosphoms or molybdenum—phosphoms based catalysts similar to those used in the oxidation of methacrolein to methacrylic acid. Conversions in excess of 95% and selectivity to methacrylic acid of 75—85% have been attained, resulting in single-pass yields of nearly 80%. The use of cesium-, copper-, and vanadium-doped catalysts are reported to be beneficial (96), as is the use of cesium in conjunction with quinoline (97). Generally the iron—phosphoms catalysts require temperatures in the vicinity of 400°C, in contrast to the molybdenum-based catalysts that exhibit comparable reactivity at 300°C (98). 

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

The a—and P-aHoys are used where higher strengths are required, such as in shafts, oil and gas weUs, and medical implants. Again, Pd and Ru variations of the basic alloys are available where improved corrosion resistance is needed. Several of the Hsted P-aHoys were developed for implants. These alloys were designed to be free of aluminum and vanadium, which have created some concern related to potential toxicity when used in implants (50). 

Vanadium metal can be prepared either by the reduction of vanadium chloride with hydrogen or magnesium or by the reduction of vanadium oxide with calcium, aluminum, or carbon. The oldest and most commonly used method for producing vanadium metal on a commercial scale is the reduction of V20 with calcium. Recently, a two-step process involving the alurninotherniic reduction of vanadium oxide combined with electron-beam melting has been developed. This method makes possible the production of a purer grade of vanadium metal, ie, of the quaUty required for nuclear reactors (qv). 

Because no process has been developed for selectively removing impurities in vanadium and vanadium alloys in the metallic state, it is essential that all starting materials, in aggregate, be pure enough to meet final product purity requirements. In addition, the consoHdation method must be one that prevents contamination through reaction with air or with the mold or container material. 

The toxicity of vanadium alloys may depend on other components in the alloy. For example, the V Ga alloy requires precautions related to both vanadium and gaUium, and gallium is highly toxic. Similarly, alloys with chromium may require precautions associated with that metal. 

Catalytic uses result in Htde consumption or loss of vanadium. The need to increase conversion efficiency for pollution control from sulfuric acid plants, which require more catalyst, and expanded fertilizer needs, which require more acid plants, were factors in the growth of vanadium catalyst requirements during the mid-1970s. Use was about evenly divided between initial charges to new plants and replacements or addition to existing plants. 

The typical amounts of sodium and vanadium in the fuel should be less than 1 ppm. Figure 29-42 shows the effect of sodium and vanadium on the life of the blade and on the combustor life. Figure 29-43 shows the reduction in firing temperature required to maintain design life (hrs) of a typical turbine (IN718) blade due to sodium and vanadium in the fuel. 

Liquid fuels require atomization and treatment to inhibit sodium and vanadium content. Liquid fuels can drastically reduce the life of a unit if not properly treated. A typical fuel system is shown in Figure 4-7. The effect of fuels on gas turbines and the details of types of fuel handling systems is given in Chapter 12. 

The water washing of the hot seetion of the turbine is required for fuels with high vanadium eontents. The addition of magnesium salts to eneounter the eorrosive aetion of the vanadium ereates ash, whieh deposits on the... 

Failure to consider listed chemical qualifier. Aluminum, vanadium and zinc are qualified as fume or dust." Isopropyl alcohol and saccharin have manufacturing qualifiers. Ammonium nitrate and ammonium sulfate are qualified as solutions. Phosphorus is qualified as yellow or white. Asbestos is qualified as friable. Only chemicals meeting the qualifiers require reporting under section 313 and should be reported on Form R with the appropriate qualifier in parenthesis. 

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... 

The elements of Group 5 are in many ways similar to their predecessors in Group 4. They react with most non-metals, giving products which are frequently interstitial and nonstoichiometric, but they require high temperatures to do so. Their general resistance to corrosion is largely due to the formation of surface films of oxides which are particularly effective in the case of tantalum. Unless heated, tantalum is appreciably attacked only by oleum, hydrofluoric acid or, more particularly, a hydrofluoric/nitric acid mixture. Fused alkalis will also attack it. In addition to these reagents, vanadium and niobium are attacked by other hot concentrated mineral acids but are resistant to fused alkali. 

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