Vanadate minerals

P.A. Wood, in Contaminated Land and its Reclamation (R.E. Hester and R.M. Harrison, eds.), p. 47, Vol. 7, The Royal Society of Chemistry, Cambridge, 1997. J.W. Anthony, R.A. Bideaux, K.W. Bladh and M.C. Nichols, Handbook of Mineralogy, Vol. IV. Arsenates, Phosphates, Vanadates, Mineral Data Publishing, Tucson, 2000. M. Fleischer and J.A. Mandarine, Glossary of Mineral Species, The Mineralogical Record, Inc., Tucson, 1995. 

Fig. IS Complex vanadate ions found in uranyl vanadate minerals, (a) (top), (VaOg) " unit of carnotite family. After Cesbron and Borene. (b) (bottom), (V10O28) " ion as found in rauvite. After Swallow and co-workers ...

Dreyerite is a bismuth vanadate mineral with composition Bi(V04). It is polymorphous with pucherite and chnobisvanite q.v) and is ftie tetragonal form. It occurs as relatively soft orange-yeUow to yellow-brown microscopic or lamellar crystals and its occurrence was first reported by Dreyer and TiUmanns in 1981 from Hirschom (Germany). Collier and Phmer (2002) have shown ftiat at Lively s Mine (Australia) dreyerite may be replaced by clinobisvanite during weathering. 

The ore is ordinarily ground to pass through a ca 1.2-mm (14-mesh) screen, mixed with 8—10 wt % NaCl and other reactants that may be needed, and roasted under oxidising conditions in a multiple-hearth furnace or rotary kiln at 800—850°C for 1—2 h. Temperature control is critical because conversion of vanadium to vanadates slows markedly at ca 800°C, and the formation of Hquid phases at ca 850°C interferes with access of air to the mineral particles. During roasting, a reaction of sodium chloride with hydrous siUcates, which often are present in the ore feed, yields HCl gas. This is scmbbed from the roaster off-gas and neutralized for pollution control, or used in acid-leaching processes at the mill site. 

Some oxide-type minerals have been found to luminesce when irradiated. A simple example is ruby (aluminium oxide with chromium activator), which emits bright-red light. The phosphors are incorporated into colour television screens to emit the colours blue (silver-activated zinc sulphide), green (manganese-activated zinc orthosilicate), and red (europium-activated yttrium vanadate). 

Vanadium occurs in soils predominantly as the +5 vanadate species (VO(OH)3°, V02(0H)2 and V03(0H) ) and under reducing conditions as the +4 vanadyl cation (VO +). Less commonly V + may also form and substitute for Fe in minerals. Interchange between these oxidation states with redox conditions greatly alters the solubility of V in soils. 

Natural fibrous materials are identified somewhat by chance. For example, there are seven vanadate and seven vanadium oxysalt minerals on the list of fibrous minerals. These species are composed of a rare element, vanadium, but the fibrous samples may have attracted attention because they are often brightly colored. Vanadinite [Pb5(V04)3Cl] for example, is bright orange-red. Further, the list of natural mineral fibers we have compiled contains seventy-seven phosphate species. So many phosphates are listed because detailed descriptions of these mostly quite rare minerals were readily available (Nriagu and Moore, 1984). 

Vibrational spectra of some vanadate salts " and several mineral species containing condensed vanadate ions have been reported. 

Vanadium usually is recovered from its ores by one of two processes, (1) leaching raw mineral with hot dilute sulfuric acid, and (2) roasting ore with common salt to convert vanadium into water soluble sodium vanadates. In the sulfuric acid leaching process, vanadium is extracted from acid leach liquors by solvent extraction with an aliphatic amine or an alkyl phosphoric acid in kerosene. The organic solvent extract then is treated with an aqueous solution of ammonia in the presence of ammonium chloride to convert vanadium into ammonium metavanadate. Alternatively, the organic extract is treated with dilute sulfuric acid or an aqueous solution of soda ash under controlled conditions of pH. Vanadium is precipitated from this solution as a red cake of sodium polyvanadate. 

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. 

By addition of mineral acids to solutions of vanadates, or by the hydrolysis of vanadium oxytrichloride, a reddish-brown, gelatinous precipitate of hydrated vanadium pentoxide is obtained. This is very... 

Colloidal Vanadium Pentoxide.11—When a soluble vanadate is treated with mineral acids, a red, curdy form of vanadium pentoxide is precipitated, which, on being shaken with water, appears to dissolve to a red liquid. This reaction gives rise to the following usual method for making a colloidal solution Ammonium metavanadate, NH4V03, is made into a paste with 10 per cent, hydrochloric acid of 10 per cent, concentration, and the resulting gel of vanadium pentoxide is washed repeatedly on the filter with distilled water until it assumes the colloidal form, i.e. until it is peptised, and in consequence passes through the... 

Lead Metavanadate, Pb(VOg)2.—Acid solutions of vanadates on being treated with lead salts give rise to yellow basic vanadates the composition of which varies with the conditions. The precipitation of normal lead vanadate is, therefore, difficult. It has been accomplished by the addition of lead acetate to ammonium metavanadate solution in the presence of acetic acid.2 The lead precipitates contain all the vanadic acid originally present in solution, and precipitation of vanadates with lead salts has, therefore, been employed for the quantitative estimation of vanadium.3 The mineral deschenite consists chiefly of lead metavanadate a portion of the lead is, however, frequently replaced by zinc.4... 

Vanadium Ferrocyanides.—Solutions of vanadates, when treated with potassium ferrocyanide, yield a precipitate of doubtful composition.1 The compound is insoluble in mineral acids of high concentration, and a method involving its precipitation has recently been suggested for the estimation of vanadium in steels.2... 

Detection.—Apart from naturally occurring ores of vanadium, vanadium steels, and ferrovanadium, the commonest compounds of vanadium are those which contain the element in the pentavalent state, viz. the pentoxide and the various vanadates. The analytical reactions usually employed are, therefore, those which apply to vanadates. Most vanadium ores can be prepared for the application of these reactions by digesting with mineral acids or by alkaline fusion with the addition of an oxidising agent. When the silica content is high, preliminary treatment with hydrofluoric acid is recommended. Vanadium steels and bronzes, and ferrovanadium, are decomposed by the methods used for other steels the drillings are, for instance, dissolved in sulphuric acid and any insoluble carbides then taken up in nitric acid, or they are filtered off and submitted to an alkaline fusion. Compounds of lower valency are readily converted into vanadates by oxidation with bromine water, sodium peroxide, or potassium permanganate. 

CARNOTITE, This mineral is a vanadate of potassium and uranium with small amounts of radium. Its formula may be written K (UCL) (VOah JHsO. The amount of water, however, seems to be variable. It occurs as a lemon-yellow earthy powder disseminated through cross-bedded sandstones with rich concentrations around petrified and carbonized trees. Soft sp gr 4.7. It was mined in Colorado and Utah as a source of radium. Other localities are in Arizona. Pennsylvania, and Zaire. 

VANADINITE. The mineral vanadimte corresponds to the formula Pb VO Cl, being composed of lead chloride and lead vanadate in the proportion of 90.2% of the former and 9.8% of the latter. It crystallizes in the hexagonal system, is usually prismatic, but the ciystals are often skeletal or cavernous it may be found in crusts. Its fracture is uneven brittle hardness. 2.75-3 specific gravity. 6.86 fresh fractures show a resinous luster color, yellow, yellowish-brown, reddish-brown, and red streak, white to yellowish translucent to opaque. Vanadinite, not a common mineral, occurs as an alteration product in lead deposits. It is found in the Ural Mountains, Austria, Spain, Scotland, Morocco, the Transvaal, Argentina, and Mexico, In the United States it occurs in Arizona, New Mexico, and South Dakota, It is used as an ore of vanadium and to some extent of lead as well. It is interesting to note that this mineral was first described as a chromate upon its discovery in Mexico in 1801, It was not until the discovery of the element vanadium in 1830 that the true nature of this compound was known. 

Acid and alkaline phosphatases with phosphorylated intermediates are inhibited by vanadate. This has been exploited in the study of the role of alkaline phosphatase in mineralization.1069 Vanadate also inhibits the ATP-dependent degradation of proteins in reticulocytes.1070... 

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