Vanadium-bearing ores

The principal vanadium-bearing ores are generally cmshed, ground, screened, and mixed with a sodium salt, eg, NaCl or Na2C02- This mixture is roasted at ca 850°C and the oxides are converted to water-soluble sodium metavanadate, NaVO. The vanadium is extracted by leaching with water and precipitates at pH 2—3 as sodium hexavanadate, Na V O, a red cake, by the addition of sulfuric acid. This is then fused at 700°C to yield a dense black product which is sold as technical-grade vanadium pentoxide. This product contains a minimum of 86 wt % V20 and a maximum of 6—10 wt % Na20. 

For industrial purposes vanadium is not required in the elemental state. More than 90 per cent, of the world s production of vanadium is used in the manufacture of special steels, for which purpose an iron-vanadium alloy, known as ferrovanadium, containing from 80 to 40 per cent, of vanadium, is marketed. The method of manufacture of this alloy from vanadium-bearing ores varies considerably with the composition of the ore and the value of the by-products. The process is conveniently divided into two stages ... 

Vanadium is recovered from several sources vanadium minerals, vanadium-bearing phosphates, boder residues, and spent vanadium catalysts. One major vanadium mineral is patronite, a greenish-black, amorphous sulfide ore used extensively for many years to produce vanadium. This mineral, found in Peru, has depleted gradually. The metal also is recovered commercially from carnotite and roscoelite. 

The lead-chamber process supplied the world s need for sulfuric acid for a century and a half. In the late nineteenth century, the contact process replaced the lead-chamber process. The contact process utilized sulfur dioxide, SOj, which was produced as a byproduct when sulfur-bearing ores were smelted. The contact process was named because the conversion of sulfur dioxide to sulfur trioxide, SO3, takes place on contact with a vanadium or platinum catalyst during the series of reactions ... 

III. 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 (6) sulphur or hydrogen sulphide on a fairly porous rock which has been impregnated with a vanadium compound. 

The Koenig procoas consists in treating the crushed ore with a 20 per cent solution of sulfuric or hydrochloric acid at a temperature of 200° and a pressure of 225 pounds per square inch. After several hours the liquid is filtered, evaporated, and the Halts ignited to expel excess acid, then roasted with sodium carbonate. The mass is leached with boiling water, and curiam dioxide bubbled in to precipitate alumina. This method is recommended for roscoelite and vanadium-bearing sandstone. 

Other sources of vanadium are the vanadium-bearing phosphate ores of Idaho, by-product slags of lead mining operations in South West Africa, and bauxite operations in France. Significant quantities of vanadium are also available in boiler scale and other residues resulting from the combustion of vanadiumbearing fuels for power generation. 

Vanadium is widely distributed in the earth s crust having an abundance of 0.02% by weight. It is found combined in various minerals, coal, and petroleum. It is present in phosphate rock, in some iron ores, and in certain cmde oils in the form of organic complexes. An important source of the vanadium-bearing mineral patronite, which was found in coal at Mina Raga, Peru, has been materially depleted [12]. The world leaders in vanadium production are the United States, the former Soviet Union, South Africa, Namibia, Finland, Norway, and Chile [13]. 

There are two other aspects that should be mentioned here that may directly affect the choice of the milling process. First, the uranium ore often contains other metals that have commercial value, like vanadium or niobium, for example, and their recovery may influence the process selected for uranium recuperation. Second, uranium itself may be a by-product of other processes like gold extraction, niobium, and tantalum production or phosphoric acid manufacture. Thus, recovery of low levels of uranium from phosphates, columbite, or gold-bearing minerals may not be economical in itself, but extracting uranium as a by-product from the waste streams of these operations could be commercially sensible. 

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