Chromium metal production

The total heat requirement is thus around 599.98 kj, which is about 548.81 kj more than the heat available from the reaction. This calculation, however, does not take into account the inevitable heat losses due to the nonadiabatic conditions in the reactor. An estimate of these heat losses can be made by considering the industrial practice for aluminothermic chromium metal production. The charge is preheated to about 500 °C before loading into the aluminothermic crucible. This operation adds about 96.65 kj (i.e., 48.9 cal deg-1 475) of heat to the system. It, therefore, appears that around 41.84 kj (96.65 kj - 54.81 kj) of heat is lost due to radiation and convection for every mole of chromium sesquioxide reduced to the metal by the aluminothermic process. 

Chromium 50d X X The leather tanning industry manufacture of catalysts pigments and paints fungicides the ceramics and glass industries photography chrome alloy chromium metal production chrome plating corrosion control 111, 23,3231, 3512,3521,3522, 361,362,372, 38, 94... 

Metallic chromium is also produced by an electrolytic method. Ferrochromium is crushed and dissolved at a temperature near the boiling point in a mixture of sulfuric acid and used anolyte. In a crystallizer the iron is separated as iron ammonium sulfate at a temperature of 5°C. The temperature in the electrolytic cells is 53°C. In the process sulfuric add and hexavalent chromium are formed in the anolyte. Because of that it must be prevented from mixing with the catholyte. Otherwise the divalent chromium there wiU be oxidized and the chromium predpitation disturbed. The cathode material is 316-type molybdenum-alloyed stainless steel, the anode material silver-alloyed lead or titanium covered with iridium. For environmental reasons dichromate plants are dosed and the aluminothermic part of the chromium metal production increases. About 1990 it was 60 % and in the begiiming of the 2000s 90 %. 

Chromic Acid Electrolysis. Alternatively, as shown in Figure 1, chromium metal may be produced electrolyticaUy or pyrometaUurgicaUy from chromic acid, CrO, obtained from sodium dichromate by any of several processes. Small amounts of an ionic catalyst, specifically sulfate, chloride, or fluoride, are essential to the electrolytic production of chromium. Fluoride and complex fluoride catalyzed baths have become especially important in recent years. The cell conditions for the chromic acid process are given in Table 7. 

Water-Soluble Trivalent Chromium Compounds. Most water-soluble Cr(III) compounds are produced from the reduction of sodium dichromate or chromic acid solutions. This route is less expensive than dissolving pure chromium metal, it uses high quaHty raw materials that are readily available, and there is more processing fiexibiHty. Finished products from this manufacturing method are marketed as crystals, powders, and Hquid concentrates. 

The main use of the chromium metal so produced is in the production of non-ferrous alloys, the use of pure chromium being limited because of its low ductility at ordinary temperatures. Alternatively, the Cr203 can be dissolved in sulphuric acid to give the electrolyte used to produce the ubiquitous chromium-plating which is at once both protective and decorative. 

The carbothermic reduction processes outlined so far apply to relatively unstable oxides of those metals which do not react with the carbon used as the reductant to form stable carbides. There are several metal oxides which are intermediate in stability. These oxides are less stable than carbon monoxide at temperatures above 1000 °C, but the metals form stable carbides. Examples are metals such as vanadium, chromium, niobium, and tantalum. Carbothermic reduction becomes complicated in such cases and was not preferred as a method of metal production earlier. However, the scenario changed when vacuum began to be used along with high temperatures for metal reduction. Carbothermic reduction under pyrovacuum conditions (high temperature and vacuum) emerged as a very useful commercial process for the production of the refractory metals, as for example, niobium and tantalum, and to a very limited extent, of vanadium. 

The production of chromium metal by the aluminothermic reduction of chromium sesquioxide can be represented by the equation ... 

Figure 9.4. Measured and fitted world annual metal production. The measured world annual metal production data were collected from U.S. Geological Survey-Minerals Information, 1997 Adriano, 1986 Woytinsky and Woytinsky, 1953. Chromium production was calculated from chromite production assuming an average of 27.0% Cr. The fitted Cd data before 1963, were calculated from the world annual Zn production (Cd mainly as a by-product) (after Han et al., 2002a. Reprinted from Naturwissenschaften, 89, Han F.X., Banin A., Su Y., Monts D.L., Plodinec M.J., Kingery W.L., Triplett G.B., Industrial age anthropogenic inputs of heavy metals into the pedosphere, p 499, Copyright (2002), with kind permission of Springer Science and Business Media)...

Although it has been known since 19051 that very pure chromium metal reacts with acids, under oxygen-free conditions, to produce large quantities of chromium (II), this approach to the preparation of chromium(II) compounds has not been developed. Rather, syntheses generally involved (1) reduction of chro-mium(III), either by electrolytic means or by chemical agents (for example Zn/Hg), or (2) metathetical procedures. Both methods are inefficient and often lead to impure products. Recently2-8 extensive use of reactions between electrolytic chromium and various acids has led to the synthesis of a wide variety of chromium (II) complexes which would be considerably more difficult to prepare by other methods.9-11... 

Alkenyl Fischer carbene complexes can serve as three-carbon components in the [6 + 3]-reactions of vinylchro-mium carbenes and fulvenes (Equations (23)—(25)), providing rapid access to indanone and indene structures.132 This reaction tolerates substitution of the fulvene, but the carbene complex requires extended conjugation to a carbonyl or aromatic ring. This reaction is proposed to be initiated by 1,2-addition of the electron-rich fulvene to the chromium carbene followed by a 1,2-shift of the chromium with simultaneous ring closure. Reductive elimination of the chromium metal and elimination/isomerization gives the products (Scheme 41). 

Preparation. Oxidation of the chromite ore by air in molten alkali gives sodium chromate, Na2Cr04 that is then converted to Cr203. The oxide is further reduced with aluminium or silicon to form chromium metal. Solutions suitable for electrolytic production of chromium (for plating) can be obtained from ore by oxidative roasting in alkali or by dissolution of chromite in H2S04 and especially by dissolving ferro-chromium in sulphuric acid. 

Chromium atoms also react with butadiene to give a product that yields predominately d2-but-l-ene together with cis- and trans-d2-but-2-ene on deuterolysis. This can also be interpreted in terms of cr-bonded organo-metallic products. However, it is also possible to isolate a 7r-complex of butadiene by ligand stabilization of the low-temperature condensate (115, 138, 140) ... 

The reduction of aqueous chromium(III) solutions can be carried out electrolytically o chemically with zinc amalgam, zinc and acid or a Jones reductor.2,24 Electrolytic procedures ca be cumbersome, and with chemical reductants contamination with other products can occur Chromium metal and acid can be used to reduce chromium(III) salts, and this requires less c the metal than in the method described in Section 35.3.1.1.i. 

Metallurgy aluminothermic production of chromium metal by reaction of aluminum powder and Cr203... 

The industrial significance of chromium oxide is due to its chemical and physical properties. Its high purity makes it suitable as a starting material for the alu-minothermic production of very pure chromium metal. 

Metals that are almost completely corrosion resistant, as for instance stainless steel uf the 18/8 type, chromium plate products, monel, and gold. 

Many of the finishes applied to other types of metal products can also be applied to zinc die castings, although some differences in formulation as well as occasional differences in method of application may be desirable. The types of finishes applicable to zinc die castings include mechanical finishes (buffed, polished, brushed, and tumbled) electrodeposited finishes (copper, nickel, chromium, brass, silver, and black nickel) chemical finishes (chromale, phosphate, molybdate and black nickel) and organic finishes (enamel, lacquer, paint and varnish, and plastic finishes). Electrodeposited coatings of virtually any metal capable of electrodeposition can be applied to zinc die castings. 

To prevent corrosion and make paints adhere better, some aluminum products are treated with chromium(III) phosphate before finishing. Chromium(III) phosphate (CrP04) is commercially produced by treating chromium metal with orthophosphoric acid (H3P04). 

Inc., Ward Hill, Massachusetts (16) chromium potassium sulfate McGean-Rohco, Inc., Cleveland, Ohio and (17) chromium-silicon monoxide Cerac Incorporated, Milwaukee, Wisconsin (SRI 1997). Besides these producers of chromium metal alloys and chromium compounds, Table 4-1 reports the number of facilities in each state that manufacture and process chromium, the intended use of the products, and the range of maximum amounts of chromium products that are stored on site. The data reported in Table 4-1 are derived from the Toxic Release Inventory (TRI) of EPA (TRI97 1999). The TRI data should be used with caution since only certain types of facilities were required to report. Hence, this is not an exhaustive list. 

Apart from the utilization of large quantities of ferrochrome (produced by reducing chromite with coal) in the manufacture of alloys containing iron and chromium, smaller quantities of chromium metal are used in, for example, the manufacture of turbine blades, the production of iron-free alloys and cermets (metal ceramics e.g. 23% by weight aluminum oxide, 77% by weight chromium). 

Chromium metal (26.0 g, 0.50 mol) was dissolved in 4M HCl (240 mL, 0.96 mol) under a Nj atmosphere to give a blue solution of CrClj. After 4 h, when evolution of H2 had ceased and most of the metal had dissolved, a solution of l,5,6,7-tetrachloro-8,8-dimethoxy-c rfo-tricyclo[3.2.1.0 ]oct-6-ene (12.16g, 0.040 mol) and ethylenediamine (120 g, 2.0 mol) in DMF (800 mL) was added dropwise and the mixture was stirred magnetically for 36 h under Nj. The maroon-colored mixture was then poured into HjO and the product extracted into EtjO (3 x lOOmL). The combined EtjO extracts were washed thoroughly with HjO, dried, and evaporated to give a clear oil, which solidified when cooled to — 10°C. The solid was crystallized from pentane (at — 20°C) to give the product as chunky white crystals mp 22.5-23.5°C. 

Chromium is a refractory metal having a melting point of 3375°F (1857°C). Neither chromium metal nor chromium-based alloys are widely in the hydrocarbon or chemical industries. Chromium plating is useful for aesthetic purposes, and hard chromium plating finds some use in hardface applications. It is extensively used as an alloy addition to low-alloy steels (usually for the purpose of stabilizing carbides) and in cast irons (to produce wear-resistant products) and nickel alloys (for increased corrosion resistance). Chromium is the main alloying addition in the 400-series stainless steels and is used extensively in the 200- and 300-series stainless steels. 

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