Ferrochromium, production

Occupational exposure to chromium(VI) and/or chromium(III) in other chromium-related industries has also been associated with respiratory effects. These industries include chromate and dichromate production, stainless steel welding, and possibly ferrochromium production and chromite mining. 

Occupational exposure to chromium(III) or chromium(O) does not appear to be associated with renal effects. No renal impairment based on urinary albumin, retinol binding protein, and renal tubular antigens was found in 236 workers employed in the ferrochromium production industry where ferrochromite is reduced with coke, bauxite, and quartzite. The mean airborne concentration of chromium in various sample locations was 0.075 mg chromium(III)/m3 chromium(VI) was below the detection limit of 0.001 mg chromium(VI)/m3 at all locations (Foa et al. 1988). Workers employed in an alloy steel plant with a mean exposure of 7 years to metallic chromium at 0.61 mg chromium(0)/m3 and to other metals had normal urinary levels of total protein and p2-microglobulin, enzyme activities of alanine-aminopeptidase, N-acetyl-P-D-glucosaminidase, gammaglutamyl-transpeptidase, and P-galactosi-dase (Triebig et al. 1987). In boilermakers exposed to chromium(O), no increase in urinary levels of... 

Ferrochromium Production. Studies of workers in the ferrochromium alloy industry are inconclusive. No significant increase in the incidence of lung cancer was found among 1,876 employees who worked in a ferrochromium plant in Sweden for at least 1 year from 1930 to 1975 compared with the expected rates for the county in which the factory was located. The workers had been exposed mainly to metallic chromium and chromium(III), but chromium(VI) was also present. The estimated levels ranged from 0 to 2.5 mg chromium(O) and chromium(III)/m3 and 0 to 0.25 mg chromium(VI)/m3 (Axelsson et al. 1980). 

Ferrochromium is an alloy of iron and chromium. More than 80% of all chromite ore is consumed in manufacturing this alloy. It is mainly used as the chromium source for the manufacture of stainless steels and other chromium steels. HC ferrochromium with high carbon content (5-6%) is manufactured in electric furnaces with coke as the reducing agent. The process has a high energy consumption, 4000 kWh per tonne of chromium metal. Plants for ferrochromium production have therefore been located in areas with low energy prices. This was one reason why Sweden, without its own chromium deposits, was a pioneer country in this field and in the production of stainless steels. 

Refractories for Electric Reduction Furnaces. Carbon hearth linings are used in submerged-arc, electric-reduction furnaces producing phosphoms, calcium carbide, all grades of ferrosilicon, high carbon ferrochromium, ferrovanadium, and ferromolybdenum. Carbon is also used in the production of beryllium oxide and beryllium copper where temperatures up to 2273 K ate requited. 

Occupational exposure to chromium(VI) compounds in a number of industries has been associated with increased risk of respiratory system cancers, primarily bronchogenic and nasal. Among the industries investigated in retrospective mortality studies are chromate production, chromate pigment production and use, chrome plating, stainless steel welding, ferrochromium alloy production, and leather tanning. 

Studies of chromate production workers, who are exposed to a variety of chromium compounds both hexavalent and trivalent, and chromate pigment industries, where exposure is mainly to chromium(VI), have consistently demonstrated an association with respiratory system cancer. Studies in chrome platers, who are exposed to chromium(VI) and other agents, including nickel, generally support the conclusion that certain chromium(VI) compounds are carcinogenic. Studies in stainless steel welders exposed to chromium(VI) and other chemicals, and in ferrochromium alloy workers, who are exposed mainly to chromium(O) and chromium(III), but also to some chromium(VI), were inconclusive. Studies in leather tanners, who are exposed to chromium(III), were consistently negative. 

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... 

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 %. 

Table 24.2 Production of high-carbon grade ferrochromium in the year 2000...

Chromium steel became available in 1870 when Julius Braun established the Chrome Steel Works in Brooklyn for manufacturing structural and tool steels (not stainless). Chromium became of great importance from the metallurgical point of view around 1910, when the alloy ferrochromium was introduced and the production of stainless steels started. 

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