Reduction of metal oxides with carbon

The free energy line for the formation of carbon monoxide and carbon dioxide are included in this plot, as the reduction of metal oxides with carbon monoxide is common in smelting operations ... 

Metals above carbon in the activity series, such as sodium and aluminium, cannot be produced by reduction of metal oxides with carbon instead electrolysis has to be used. Metals below carbon, such as iron and zinc, can be produced by reduction of metal oxides with carbon. 

Tantalum. Numerous methods developed to extract tantalum metal from compounds included the reduction of the oxide with carbon or calcium the reduction of the pentachloride with magnesium, sodium, or hydrogen and the thermal dissociation of the pentachloride (30). The only processes that ever achieved commercial significance are the electrochemical reduction of tantalum pentoxide in molten K TaF /KF/KCl mixtures and the reduction of K TaF with sodium. 

Molybdenum was first identified as a distinct element by Swedish chemist Karl Wilhelm Scheele in 1778. The metal was isolated by Hjelm in 1782 by reduction of its oxide with carbon. Moissan in 1895 isolated the metal in highly purified form by electrolytic reduction of its oxide and studied many of its physical and chemical properties. The element derived its name in 1816 from the word molybdos, meaning a soft mineral that appeared like lead. 

In 1792 Anton Rupprecht prepared impure magnesium (contaminated with iron) by reduction of magnesium oxide with carbon and called the metal austrium in honor of Austria (68). 

S) Reduction of the Oxide with Carbon Monoxide.—Reduction of cobalto-cobaltic oxide to the metal takes place rapidly, and is quite complete at 900° C. Between 350° and 450° C. the reaction is very interesting. At first some oxide is reduced to metallic cobalt after a time the finely divided metal decomposes the carbon monoxide, depositing solid carbon, presumably in the same way as its analogue, iron, namely ... 

Tin and Pb are obtained from the ores in various ways, commonly by reduction of their oxides with carbon. Further purification is usually effected by dissolving the metals in acid and depositing the pure metals electrolytically. 

Carbothermal reduction of tungsten oxides with carbon monoxide [3.47], or gas mixtures of CO/CO2, CO/H2, CH4/H2 [3.50], C2H4/H2, and C2H4/H2 [3.51], as well as by reaction between metal oxide vapor and solid carbon [3.52] have recently attracted attention for producing high surface area tungsten carbides (up to lOOm /g), for use as catalyst (see Section 10.4), and for nanophase WC/Co composite powders (see also Section 9.2.1.4) [3.53]. 

Berzelius, Johnston and others tried in vain to isolate the metal itself. The substances they thought were metallic vanadium, obtained by reduction of vanadium oxide with carbon or potassium, or of vanadium chlorides (VCI3, VOCI3) with potassium or ammonia, all turned out to be carbides, silicides, nitrides (VN) or low-valent oxides (VO).[ l The first apparently successful generation of metallic vanadium was accomplished by Sir Henry Enfield Roscoe in 1869 by reduction of VCI2 with hydrogen in a lengthy experiment [ 1... 

Many metals are extracted by reduction of their oxides with carbon. Under these circumstances the carbon can be regarded as competing with the metal to bind oxygen ... 

Throughout the whole period of discovery, the first three decades of the 19 century, vanadium minerals had been found and vanadium compounds been prepared. The metal itself, however, had not been isolated. BerzeHus showed early that it was impossible to prepare vanadium metal by reduction of the oxide with carbon. This gave vanadium carbide. Nor did reduction with metaUic potassium give the pure metal. 

The reduction of metal oxides with solid carbon could also be a true solid-solid reaction, provided it is carried out at very low absolute pressures ... 

Jn the general case the system of Eqs. (5.4.28), (5.4.32), and (5.4.33) must be solved numerically [25]. The solutions for the cases Er = Ep = 3 and 1 t>e presented subsequently. One of the more important reactions between solids through gaseous intermediates is the reduction of metal oxides with solid carbon, in which case, a = 2 and c = 1 the following solutions will correspond to these values of a and c. 

Preparation. Uranium metal may be prepared by several methods the reduction of uranium oxides with carbon In an arc-melting furnace reduction of uranium oxides with magnesium, aluminum, calcium or calcium hydride the reduction of uranium halides with alkali or alkaline-earth metals electrolytic reduction of uranium halides and the themal decomposition of uranium Iodide. 

The text mentions that scandium metal is obtained from its molten chloride by electrolysis, and that titanium is obtained from its chloride by reduction with magnesium. Why are these metals not obtained by the reduction of their oxides with carbon (coke), as are metals such as zinc and iron ... 

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). 

Metafile arsenic can be obtained by the direct smelting of the minerals arsenopyrite or loeUingite. The arsenic vapor is sublimed when these minerals are heated to about 650—700°C in the absence of air. The metal can also be prepared commercially by the reduction of arsenic trioxide with charcoal. The oxide and charcoal are mixed and placed into a horizontal steel retort jacketed with fire-brick which is then gas-fired. The reduced arsenic vapor is collected in a water-cooled condenser (5). In a process used by Bofiden Aktiebolag (6), the steel retort, heated to 700—800°C in an electric furnace, is equipped with a demountable air-cooled condenser. The off-gases are cleaned in a sembber system. The yield of metallic arsenic from the reduction of arsenic trioxide with carbon and carbon monoxide has been studied (7) and a process has been patented describing the gaseous reduction of arsenic trioxide to metal (8). 

Stable oxides, such as those of chromium, vanadium and titanium cannot be reduced to the metal by carbon and the production of these metals, which have melting points above 2000 K, would lead to a refractory solid containing carbon. The co-reduction of the oxides with iron oxide leads to the formation of lower melting products, the ferro-alloys, and this process is successfully used in industrial production. Since these metals form such stable oxides and carbides, the process based on carbon reduction in a blast furnace would appear to be unsatisfactory, unless a product saturated with carbon is acceptable. This could not be decarburized by oxygen blowing without significant re-oxidation of the refractory metal. 

A new production technique fully cost competitive with current processes could be the reduction of magnesium oxide by carbon to produce magnesium metal as a vapour and carbon monoxide gas this technique, according to Brooks et al. (2006), will involve rapid quenching of the Mg vapour through a nozzle at supersonic velocity to avoid Mg reversion to magnesium oxide. 

It is not possible to obtain titanium metal by the usual method of reduction of the dioxide with carbon, because a very stable carbide is formed. Moreover the metal is reactive towards nitrogen and oxygen at elevated temperatures, and hydrogen at 900 °C only reduces Ti02 as far as Ti3Os. Reduction of the dioxide with most reducing metals, e.g. Na, Al, Ca or Mg, seldom seems to yield a pure product the most common contaminants, and in some cases the principal products, are lower oxides of titanium. Reduction of the tetrachloride is, therefore, the basis of the preferred methods. 

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