Chromium chemicals

High-temperature calcination of chromite ore and soda ash leads to oxidation of chromium to sodium chromate, which is leached out by water. After acidifying, sodium dichromate, the basic material for chromium chemicals, is formed. Chromium trioxide CrOj, chromic add, prepared from sodium dichromate, is used for preparing the baths for chromium plating. Hexavalent chromium chemicals are also still used to some extent in pigments, for corrosion protection and for timber treatment Chromic add is also used for video/audio tapes although iron-based tapes have taken over more than 90% of this market. 

As color pigments, chromium compounds have had varied use. Chrome green is CrjOj, chrome yellow is PbCrO, and thus has the same composition as the mineral 

1) Dressing (concentration) of chromite ore gives dressed ore, an ore concentrate. For dressed ore see Chapter 1 Introduction, 

Siberian red lead. Chrome red is Pb CrOj, lead oxide chromate. In our day the use of color pigments containing lead and hexavalent chromium is of course restricted for environmental reasons. 

Different trivalent chromium products, chromium oxide, chromium hydroxide and chromium sulfate, are made by reduction of dichromate. Chromium sulfate is used in leather tanning. Skins are mainly derived from animals that are butchered for the food industry. To protect the skin from putrefaction it is transformed to leather by the tanning process. The tanning agent is fixed to the reactive groups of collagen, the protein in the sldn. That stops the spontaneous decomposition of collagen. 

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The prices of some important chromium chemicals are given ia Table 4, and production and shipment data for sodium chromate and dichromate are given ia Table 5. Data for the productioa and shipment of chromic acid have not been available siace 1972. However, traditionally CrO has held at about 30—35% of sodium dichromate production. The estimated capacity for domestic production of sodium dichromate is 150,000 to 200,000 t/yr. 

Drilling Muds in the Petroleum and Natural Gas Industry. Since 1941, chromium chemicals have been used in the drilling of wells to combat fatigue corrosion cracking of drill strings, with about one metric ton of sodium chromate being used aimuaHy for an average West Texas well. Other early uses were in gas-condensate wells in Louisiana and East Texas. 

Reagent-Grade Chemicals. Potassium dichromate is an important analytical standard, and other chromium chemicals, in reagent grades, find considerable laboratory use (90,91). This use, though small, is most important in wet analyses. 

The sodium chromate produced in the isolation of chromium is itself the basis for the manufacture of all industrially important chromium chemicals. World production of chromite ores approached 12 million tonnes in 1995. 

Hexavalent chromium (Cr+6) is the most biologically active chromium chemical species, although little is known about the properties of organochromium compounds, water-soluble species, or their interactions in complex mixtures... 

However, emission control dust or sludge from ferrochromium and ferrochromium-silicon production is listed as hazardous waste by EPA (1988b). The processed wastes from several chromium chemical industries are designated as hazardous wastes as well (EPA 1981), and disposal of process wastes is regulated by the EPA. Land filling appears to be the most important method for the disposal of chromium wastes generated by chemical industries. Of the total chromium released in the environment by chemical industries, 82.3% is released on land. An equally large amount of chromium waste is transferred off-site (see Section 5.2). It is anticipated that most of this off-site waste will be disposed of in landfills after proper treatment. It is important to convert chromium wastes into forms of chromium... 

Hayes RB. 1988. Review of occupational epidemiology of chromium chemicals and respiratory cancer. Sci Total Environ 71 331-339. 

Hayes RB, Lilienfeld AM, Snell LM. 1979. Mortality in chromium chemical production workers A prospective study. Int J Epidemiol 8(4) 365-374. 

Hill WJ, Ferguson WS. 1979. Statistical analysis of epidemiological data from a chromium chemical manufacturing plant. J Occup Med 21 103-106. 

Fig. 2. Chromium chemical state plot for chromium oxide and fluoride samples before and after activation with halocarbons (static charge reference C Is 284.8 eV) (reproduced with permission from J. Catal., 159 (1996) 270 (39]).

The only statistics available over the production of chromium chemicals sites concern the production of sodium dichromate (see Table 3.3-1). 

The raw material for all chromium chemicals is chrome iron ore, so-called chromite, which is a spinel. It contains magnesium and aluminum as minor constituents and has the approximate composition (Fe, Mg)[Cr,Al,Fe(III)]204. Calcium, silicon dioxide and, in some cases, vanadium are also present in small quantities. 

Only alkaline oxidative digestion is suitable for the industrial conversion of chromite to chromium chemicals. This results in alkali (sodium) chromates ... 

Synonyms Chrome Chromium Chemical/Pharmaceutical/Other Class Metals Chemical Formulas Cr " " Cr " "... 

In 1798, Lowitz and Klaproth independently discovered chromium in a sample of a heavy black rock found further north from the Beresof Mines and in 1799 Tassaert identified chromium in the same mineral from a small deposit in the Var region of South-Eastern France. The chromite ore deposits discovered in the Ural Mountains greatly increased the supplies of chromium to the growing paint industry and even resulted in a chromium chemicals factory being set up in Manchester, England around 1808. In 1827, Isaac Tyson identified deposits of chromite ore on the Maryland-Pennsylvania border and the United States became the monopoly supplier for a number of years. 

The roasted clinker is then leached out with hot water and the resulting liquor filtered to remove insoluble silica, along with aluminum and iron oxides present as impurities in the original chromite ore. Pure sodium dichromate is then crystallized and dried. The anhydrous sodium chromate can then be reduced to chromium trioxide by simple carbothermic reduction. Note that the sodium chromate produced can be converted into the dichromate by dissolving it in sulfuric acid and is the basis for the manufacture of all industrially important chromium chemicals. Once produced, chromium trioxide is mixed with aluminum powder and lime and placed inside a refractory-lined steel vessel. The exothermic reaction is started by igniting a pyrotechnic mixture made of barium peroxide and aluminum powder or potassium chlorate aluminum powder ... 

In 1799, Tassierf a German chemist active in France, discovered chromium in an iron mineral from the Var region of southeastern France. This interested Fourcroy, who anticipated that iron-chromium ores might be source materials for a diversified manufacture of chromium chemicals. Due to the richness of color of the metal s compounds the minerals could be used for painting and for manufacturing colored glass and china. 

Dates and subpart identifiers in parendieses are those expected by EPA as of August 3,2000, per the EPA OAQPS TI N web site. The following categories were also delisted on die date listed in parentheses asbestos processing (10/30/95) electric arc furnace, stainless and nonstainless steel (06/04/96) chromium chemical manufacturing (06/04/96) nylon 6 production (02/12/98) wood treatment (06/04/96) lead-acid battery manufacturing (5/17/96). 

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