Element Vanadium, V, Transition Metal

The three elements, vanadium, niobium, and tantalum resemble those of the nitrogen group in that they chiefly form compounds belonging to the pentavalent type, and that their higher oxygen compounds have an acid character. In the elementary state they have the properties of metals; their halogen compounds are readily volatile. All three are only sparingly found in the earth's crust, although the first mentioned, vanadium, occurs in small quantities widely distributed.

Vanadium is obtained from the mixtures containing it by fusing these with soda and saltpetre. It is thereby converted into soluble sodium vanadate, and can be extracted with water. After the admixtures have been removed as far as possible, pieces of solid ammonium chloride are placed in the liquid. Ammonium vanadate is then formed, which is practically insoluble in the concentrated solution of ammonium chloride, and separates out as a crystalline powder. By heating the ammonium salt in the air vanadium pentoxide, V₂O₅, the anhydride of vanadic acid, is obtained as a yellow or brown powder, which dissolves in water with a red colour. The solution appears, however, to be essentially of a colloidal nature, as it is precipitated by neutral salts.

Various acids can be derived from vanadium pentoxide. Metavanadic acid, HVO₃, in the form of its salts, is the best known. The above-mentioned ammonium salt is a metavanadate (NH₄)VO₃. Ortho- and pyro-vanadates also exist. Besides these acids, " condensed " acids, containing several combining weights of vanadium, are readily formed. Thus, for example, the salts of hexavanadic acid, H₂V₆O₁₆, are known. They are formed on acidifying the simple vanadates, and are of a yellow-red to dark red colour, while the simple vanadates are white, or sometimes yellow. Little is known, however, of the conditions of formation and of mutual transformation of these various forms.

Vanadium pentoxide is capable also of uniting with strong acids to form salt-like compounds, hydroxyl being split off instead of the acid hydrogen. Such compounds, more especially with sulphuric acid, are known even in the solid state.

By reducing the pentoxide with hydrogen, or with charcoal at a high temperature, vanadium trioxide, V₂O₃, is obtained as a grey-black powder with metallic lustre. This was formerly regarded as metallic vanadium, since, besides having a metallic lustre, it is also a good conductor of electricity. It dissolves in acids to form dark-green salts, containing the trivalent, green trivanadion V^•••, and which are also obtained by reducing acid solutions of the pentoxide with zinc.

Besides these two oxides, the compounds V₂O, V₂O₂, V₂O₄, and some intermediate compounds have also been prepared. They have all a metallic appearance. The dioxide dissolves in dilute acids to form blue liquids, which evolve hydrogen, and have strong reducing properties. They contain, presumably, a divalent, violet blue divanadion V^••.

The compounds with the halogens, especially with chlorine, exhibit as great variety as the oxygen compounds. Strange to say, a pentachloride, which would be expected, corresponding to the pentoxide, does not exist; the highest chloride stage is the tetrachloride, VCl₄. An oxychloride, however, viz. vanadyl chloride, VOCl₃(VO = vanadyl), belonging to the pentavalent type, is known. It is obtained by first passing hydrogen and then chlorine over a heated mixture of vanadium pentoxide and charcoal. It is a bright yellow liquid, boiling at 127°, which reacts with water with great rise of temperature, and fumes in the air. From this VOCl₂ and VOCl are obtained by reduction with hydrogen; they are both solid, crystalline substances, the former being green, the latter brown.

If a mixture of vanadyl trichloride vapour and chlorine is passed over red-hot charcoal, the tetrachloride, VCl₄, is obtained as a brown liquid, boiling at 154°. On being more strongly heated it decomposes into chlorine and vanadium trichloride, VCl₃, which forms lustrous, violet-red crystals, which recall chromic chloride. They attract moisture from the air and deliquesce to a brown liquid. On heating the vapour with hydrogen the tetrachloride is converted into vanadium dichloride, VCl₂. This forms apple-green, difficultly volatile crystals with a micaceous lustre, which deliquesce in the air to a violet-blue liquid.

Finally, on strongly heating the dichloride in a current of hydrogen, metallic vanadium is obtained as an unmelted, grey mass, which acquires a metallic lustre on being rubbed, and does not dissolve in dilute acid. It burns readily in a current of nitrogen, forming vanadium nitride, VN, a yellow-brown powder with a metallic lustre. On fusion with caustic potash the nitride is converted into vanadic acid with evolution of ammonia.

On passing sulphuretted hydrogen into a solution of ammonium vanadate in ammonia a precipitate is produced which, on continuing to pass the gas, dissolves, forming a fine, violet-red coloured liquid.

From this solid ammonium thiovanadate, resembling potassium permanganate in appearance, crystallises out. The salt has the composition (NH₄)₃VS₄, and therefore belongs to the ortho series. On adding acids, sulphuretted hydrogen is evolved, and a brown precipitate is formed, which, however, does not appear to be pure vanadium penta-sulphide. The latter is obtained as a black powder by fusing the trisulphide with sulphur. The trisulphide, in its turn, is obtained by heating the pentoxide in a current of sulphuretted hydrogen, or, better, of carbon disulphide. It is grey-black in colour, and dissolves in alkali sulphides, especially in such as contain excess of sulphur, forming a red-violet solution of thio vanadate.

Vanadic acid has the property of catalytically accelerating certain oxidation processes (e.g. the oxidation of aniline to aniline black, with sodium chlorate), and is therefore employed for that purpose in the arts and manufactures. Even very small quantities of the acid are sufficient to effect a great acceleration.

In 1801 Manuel del Rio discovered the presence of a new metallic substance, which was subsequently called erythronium, in a lead ore found at Zimapan in Mexico. The discovery was communicated to the Academie des Sciences de Paris, and the ore was examined by Collet-Descostils, who reported, however, that the new metal was impure chromium. In 1830 Sefstrom definitely established the presence of a new element in a remarkably tenacious and ductile specimen of wrought iron which had been prepared from Taberg (SmMand) ore. To this Sefstrom gave the name vanadium, from Vanadis, a cognomen of the Scandinavian goddess Freia. About the same time Wohler re-examined the Zimapan ore and found del Rio's erythronium to be identical with vanadium. Considerable numbers of vanadium compounds were then prepared and examined by Berzelius, who formed the conclusion that vanadium belonged to the same family as chromium and molybdenum. This conclusion was subsequently shown by Roscoe to be in error, because Berzelius had been handling the oxide or nitride when he thought he was dealing with the free metal. This error was due to the extreme difficulty experienced in reducing vanadium compounds to the metal. Roscoe conducted some classical researches on vanadium from 1868 to 1870, and found that the metal forms an oxide, VO, which enters into reactions as the vanadyl radical [VO]^••, in an analogous manner to the uranyl radical [UO₂]^••. He also established the intimate relation that exists between vanadium and the members of the nitrogen family.15 Ditte continued the work by his extensive investigations into the preparation and behaviour of a large number of vanadium compounds.

Roscoe obtained his vanadium from the residual lime precipitate which was thrown down during the extraction of cobalt from the copper deposits at Alderley Edge and Mottram St. Andrews in Cheshire, England. Although the total amount of vanadium in the ore was only small (the lime precipitate contained about 2 per cent, of vanadium), these deposits for a long time formed an important source of supply of Vanadium compounds. Until the year 1900 the only industrial applications of vanadium compounds lay in their employment as catalysts in the manufacture of aniline-black, and in their use as mordants in dyeing and calico-printing. The Cheshire source for these purposes was supplemented and later displaced by supplies obtained from the Spanish lead mines and from the basic steel slags produced at Le Creusot Steel Works in France. It was found that these slags contained over 1 per cent, of vanadium.

The industrial application of vanadium received its main impetus, however, when the metal entered the domain of metallurgy. In 1893 Moissan applied his electric furnace to the making of alloys of vanadium, and produced ferrovanadium in large quantity. The mechanical properties of vanadium steels were noted by Helouis in 1896, but were first thoroughly investigated at Sheffield, England, by Professor Arnold in 1900, whose work was followed by that of Sankey and Smith in 1904. The discovery of the vast Peruvian deposits in 1905 was followed by the successful preparation from them of a ferrovanadium alloy which could readily be employed in the manufacture of vanadium steels. This process now absorbs nearly all the world's production of vanadium.

Although vanadium does not occur free in nature, compounds of vanadium occur widely distributed in small quantities in many rocks, and even in the ashes of plants. According to Clarke, the amount of vanadium in the earth's crust is 0.017 per cent. The corresponding figures for copper, zinc, and lead are 0.0104 per cent., 0.0039 per cent., and 0.0020 per cent, respectively, so that it is incorrect to refer to vanadium as a " rare " element, although it is true that vanadium ores from which the metal can be economically extracted occur in only a few localities. The principal industrial deposit is an impure vanadium sulphide, containing considerable quantities of free sulphur and carbonaceous matter, known as patronite, after its discoverer, and found in Peru. Analysis gave the following composition (per cent.) - S, 58.79; V, 19.53; SiO₂, 6.88; C, 3.47; Fe, 2.92; Al₂O₃ and P₂O₅, 2.00; TiO₂, 1.53; Ni, 1.87; Fe₂O₃, 0.20; Mo, 0.18; O, 0.38; H₂O, 1.90. Total = 99.65 per cent. Particulars of the most important ores are set out in the table on the next page.

Vanadium ores are mainly of igneous origin. The vanadium sources which are of present or potential economic value can be classified under several headings.

1. In association with titaniferous magnetites and ilmenites. The best known deposit of this type is the Taberg iron ore in Sweden, where vanadium was first definitely discovered.
2. In veins of hydrothermal origin, where the vanadium is associated with either uranium or gold. This division includes roscoelite and mottramite.
3. In sulphide ores in which the mineral is associated with hydrocarbons. This class includes the patronite deposits of Peru and various vanadium-bearing asphaltites. It is probable that these asphaltites are the residuary seepage of petroleum deposits, and that they have been formed by the action of (a) hydrocarbons and (b) sulphur or hydrogen sulphide on a fairly porous rock which has been impregnated with a vanadium compound.
4. In the oxidised upper levels of certain veins of lead and copper. This class is numerous and widely distributed, and includes the various vanadates of lead, copper, zinc, etc. They may have been formed by the action of percolating vanadiferous waters on compounds of lead, but their origin is doubtful.
5. V. In sedimentary rocks. These minerals also contain oxidised vanadium, and consist of vanadates of iron, aluminium, lead, copper, etc. The carnotite deposits of Colorado are of this type.

Minerals containing Vanadium

Name.	Locality.	Density.	Proximate Formula.
Patronite.	Peru	2.65	V2S5 + nS
Carnotite.	Colorado, Utah, Australia.	4.14	2U2O3.V2O5.K2O.3H2O
Roscoelite	Colorado, California, W. Australia.	2.90	(A Muscovite containing about 28.6 per cent. V2O5.)
Vanadinite	Arizona, Mexico, Argentine, Spain, Transvaal, Scotland, Ireland.	6.60-7.23	3Pb3(VO4)2.PbCl2
Descloizite	La Plata, Nevada, N.W., Rhodesia.	5.9-6.2	2Pb(Zn)O.V2O5
Desehenite	Germany	5.6-5.81	Pb(Zn)VO4
Mottramite	Cheshire, England	5.89	3(PbCu)(VO4)2
Chileite.	Chili	. . .	3Cu2O.3PbO.V2O5
Psittacinite	Montana	. . .	3(PbCu)(VO4)2.3Cu(OH)2.6H2O
Volborthite	Urals	3.55	3(CuCa)(VO4)2.H2O
Sulvanite	S. Australia	4.0	3Cu2S.V2S5

In Great Britain vanadium has been found associated with the lead ores at Wanlockhead, in the Lead Hills, Dumfriesshire, as vanadinite, and associated with the copper deposits at Alderley Edge and at Mottram St. Andrews, Cheshire, as mottramite. The latter was at one time mined and treated for its vanadium, but commercially profitable supplies of this ore have now given out. Vanadium has also been reported to occur in titaniferous iron ores at Antrim, and in rocks at Wicklow and Giant's Causeway.

The foregoing account deals with the main distribution of vanadium; the presence of this element in very small quantities has also been established in a variety of substances. Among these the following may be mentioned - Clays and shales, bauxite, cryolite, rutile and pitchblende. Vanadium is absorbed by plants from the soil, and hence is found in the ash of some coals and lignites; a lignite from San Rafael, Argentine, gave 0.63 per cent, of ash which contained 38.22 per cent, of vanadium estimated as the pentoxide, and the flue dust from the burning of a South Yorkshire coal contained an appreciable proportion of vanadium. The presence of vanadium has been observed in petroleum hydrocarbons, asphalt, volcanic sublimations on Mount Vesuvius, and meteorites; in technical products, e.g. caustic potash, sodium carbonate; and in the blood-cells of certain ascidia, where it apparently replaces iron.

Commercial Sources of Vanadium

The world's most important vanadium supply comes from the deposits of patronite in Peru. The ore occurs in the coal deposits at Minas Raga, and is essentially a sulphide of vanadium containing 10 per cent, or more of vanadium and 30 per cent, or more of free sulphur. The substance is hard, and has the appearance of a black, slaty coal. The surrounding earth is impregnated with vanadates or other vanadium compounds, and contains numerous deposits of asphaltites, the ash from which yields from 20 to 40 per cent, of vanadium pentoxide. The patronite deposits are supposed to have been formed by the upward movement of asphaltic petroleum and its subsequent evaporation, the vanadium being derived from the vegetable matter which gave rise to the petroleum. The mines at Minas Raga are the highest in the world, and are about 16,000 feet above sea-level. The ore is here submitted to a preliminary roasting, whereby the vanadium content is increased to about 20 per cent, with almost total elimination of sulphur. The mines are connected by rail to Callao, whence shipment of the material takes place to the United States for further treatment.

A secondary source of supply lies in the carnotite deposits of Colorado and Utah. The vanadium content in these is very low, being only about 1 per cent, or even less, and the ore is really worked for its radium and uranium content, the vanadium forming a by-product. The deposits of carnotite are considerable.

Commercial sources of vanadium which are now disused are the roscoelite deposits in Colorado, the vanadinite deposits near Santa Marta in Spain, and the mottramite deposits in Cheshire and Shrewsbury. It is of some interest to note that efforts are being made to extract the vanadium from the Taberg iron ores or slags, in which vanadium was originally discovered, and from the Rhodesian deposits.