Vanadium

History

Vanadium was originally discovered by Andrés Manuel del Río (a Spanish mineralogist) in Mexico City, in 1801. He called it "brown lead" (now named vanadinite). Through experimentation, its colors reminded him of chromium, so he named the element panchromium. He later renamed this compound erythronium, since most of the salts turned red when heated. The French chemist Hippolyte Victor Collet-Descotils incorrectly declared that del Rio's new element was only impure chromium. Del Rio thought himself to be mistaken and accepted the statement of the French chemist that was also backed by Del Rio's friend Baron Alexander von Humboldt.

In 1831, Sefström of Sweden rediscovered vanadium in a new oxide he found while working with some iron ores and later that same year Friedrich Wöhler confirmed del Rio's earlier work. Later, George William Featherstonhaugh, one of the first US geologists, suggested that the element should be named "rionium" after Del Rio, but this never happened.

Metallic vanadium was isolated by Henry Enfield Roscoe in 1867, who reduced vanadium(III) chloride VCl₃ with hydrogen. The name vanadium comes from Vanadis, a goddess in Scandinavian mythology, because the element has beautiful multicolored chemical compounds.

Biological role

In biology, a vanadium atom is an essential component of some enzymes, particularly the vanadium nitrogenase used by some nitrogen-fixing micro-organisms. Vanadium is essential to ascidians or sea squirts in vanadium chromagen proteins. The concentration of vanadium in their blood is more than 100 times higher than the concentration of vanadium in the seawater around them. Rats and chickens are also known to require vanadium in very small amounts and deficiencies result in reduced growth and impaired reproduction.

Administration of oxovanadium compounds has been shown to alleviate diabetes mellitus symptoms in certain animal models and humans. Much like the chromium effect on sugar metabolism, the mechanism of this effect is unknown.

Mineral supplement in drinking water

Vanadium pentoxide V₂O₅ is marketed in Japan as a good mineral health supplement naturally occurring in drinking water. The source of this drinking water is mainly the slopes of Mount Fuji. The water's vanadium pentoxide content ranges from about 80 to 130 μg/liter. It is marketed as being effective against diabetes, eczema, and obesity. There is no mention of its toxicity in the marketing of these products.

Occurrence

Vanadium is never found unbound in nature but it does occur in about 65 different minerals among which are patronite VS₄, vanadinite Pb₅(VO₄)₃Cl, and carnotite K₂(UO₂)₂(VO₄)₂.3H₂O. Vanadium is also present in bauxite, and in carbon containing deposits such as crude oil, coal, oil shale and tar sands. Vanadium has also been detected spectroscopically in light from the Sun and some other stars.

Much of the vanadium metal being produced is now made by calcium reduction of V₂O₅ in a pressure vessel. Vanadium is usually recovered as a by-product or co-product, and so world resources of the element are not really indicative of available supply.

Isolation

Vanadium is available commercially and production of a sample in the laboratory is not normally required. Commercially, routes leading to metallic vanadium as main product are not usually required as enough is produced as byproduct in other processes.

In industry, heating of vanadium ore or residues from other processes with salt NaCl or sodium carbonate Na₂CO₃ at about 850°C gives sodium vanadate NaVO₃. This is dissolved in water and acidified to give a red solid which in turn is melted to form a crude form of vanadium pentoxide V₂O₅. Reduction of vanadium pentoxide with calcium gives pure vanadium. An alternative suitable for small scales is the reduction of vanadium pentachloride VCl₅ with hydrogen or magnesium. Many other methods are also in use.

Industrially, most vanadium is used as an additive to improve steels. Rather than proceed via pure vanadium metal it is often sufficient to react the crude of vanadium pentoxide V₂O₅ with crude iron. This produces ferrovanadium suitable for further work.

Compounds

Vanadium pentoxide V₂O₅ is used as a catalyst principally in the production of sulfuric acid. It is the source of vanadium used in the manufacture of ferrovanadium. It can be used as a dye and colour-fixer.

Vanadyl sulfate VOSO₄, also called vanadium(IV) sulfate oxide hydrate, is used as a relatively controversial dietary supplement, primarily for increasing insulin levels and body-building. Whether it works for the latter purpose has not been proven, and there is some evidence that athletes who take it are merely experiencing a placebo effect.

Vanadium(IV) chloride VCl₄ is a soluble form of vanadium that is commonly used in the laboratory. V(IV) is the reduced form of V(V), and commonly occurs after anaerobic respiration by dissimilatory metal reducing bacteria. VCl₄ reacts violently with water.

Toxicity of vanadium compounds

The toxicity of vanadium depends on its physico-chemical state; particularly on its valence state and solubility. Pentavalent VOSO₄ has been reported to be more than 5 times as toxic as trivalent V₂O₃ (Roschin, 1967). Vanadium compounds are poorly absorbed through the gastrointestinal system. Inhalation exposures to vanadium and vanadium compounds result primarily in adverse effects to the respiratory system (Sax, 1984; ATSDR, 1990). Quantitative data are, however, insufficient to derive a subchronic or chronic inhalation.

There is little evidence that vanadium or vanadium compounds are reproductive toxins or teratogens. There is also no evidence that any vanadium compound is carcinogenic; however, very few adequate studies are available for evaluation. Vanadium has not been classified as to carcinogenicity by the U.S. EPA (1991a).

Isotopes

Naturally occurring vanadium is composed of one stable isotope ⁵¹V and one radioactive isotope ⁵⁰V with a half-life of 1.5×10¹⁷ years. 24 artificial radioisotopes have been characterized (in the range of mass number between 40 and 65) with the most stable being ⁴⁹V with a half-life of 330 days, and ⁴⁸V with a half-life of 15.9735 days. All of the remaining radioactive isotopes have half-lives shorter than an hour, the majority of them below 10 seconds. In 4 isotopes, metastable excited states were found (including 2 metastable states for ⁶⁰V).

The primary decay mode before the most abundant stable isotope ⁵¹V is electron capture. The next most common mode is beta decay. The primary decay products before ⁵¹V are element 22 (titanium) isotopes and the primary products after are element 24 (chromium) isotopes.

Precautions

Powdered metallic vanadium is a fire hazard, and unless known otherwise, all vanadium compounds should be considered highly toxic. Generally, the higher the oxidation state of vanadium, the more toxic the compound is. The most dangerous one is vanadium pentoxide.

The Occupational Safety and Health Administration (OSHA) has set an exposure limit of 0.05 mg/m³ for vanadium pentoxide dust and 0.1 mg/m³ for vanadium pentoxide fumes in workplace air for an 8-hour workday, 40-hour work week.

The National Institute for Occupational Safety and Health (NIOSH) has recommended that 35 mg/m³ of vanadium be considered immediately dangerous to life and health. This is the exposure level of a chemical that is likely to cause permanent health problems or death.