CHROMIUM AND CHROMIUM COMPOUNDS

Chromium was first isolated and identified as a metal by the French chemist, Vauquelin, in , working with a rare mineral, Siberian red lead (crocoite, PbCrO4).

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A generalized flow diagram for the production processes used now to lead from chromite ore to the major products containing chromium is shown in .

Simplified flow chart for the production of metallic chromium, chromium compounds and selected products from chromite ore. Processes for which occupational exposure levels to chromium are available are indicated by ' a

Although chromium is found in various minerals, chromite is the sole source of chromium used commercially ( Stern, ). From until , chromite from the Ural Mountains of Russia was the principal source of world supply, primarily for chemical use. After chromite ore was discovered in the USA in , that country became the principal source for the limited world demand; it no longer produces it. Large Turkish deposits were developed in to supply the world market. presents world production figures by region in , and .

Eight US companies produced chromium alloys in , but separate data on the quantity of cobalt-chromium alloys produced were not available ( Morning, ). Stellite (usually 53% Co, 35% Cr and the remainder tungsten) has been produced by one company in the UK ( Roskill Information Services, ).

Cobalt-chromium alloys were first made in by fusion of cobalt with 10'60% chromium ( Haynes, ). Commercial production began shortly thereafter, and since more than 75% of the cobalt used in the USA has been for the manufacture of alloys with chromium ( Sibley, ).

Chromium alloys are produced by technology very similar to that used for steel production, except that the melting and decarburizing units are generally smaller and greater use is made of vacuum melting and remelting ( Warner, ). No data were available on production volumes of these alloys.

Chromium-containing steels (stainless steels and others) are produced by melting cast iron and adding ferrochromium and/or steel scraps in large electric furnaces. The melt is transferred to a refining vessel to adjust the carbon content and impurity levels and is then cast into ingots or continuously into casting shapes. Defects in the cast steel are repaired by cutting or scarfing or by chipping or grinding. The desired shapes are produced primarily by rolling, and their surfaces are conditioned by a variety of operations, including grinding, polishing and pickling ( Warner, ).

Ferrochromium is produced by treatment of chromite ore in electric furnaces using coke as a reducing agent. Worldwide production figures for all grades of ferrochromium are summarized in .

Chromium metal has been produced in Japan since , where it is manufactured by two companies by electrolysis of an ammonium chromic sulfate solution. About tonnes were produced in ; there were no reported imports or exports ( IARC, a ).

In , US production of chromium metal and metal alloys, other than ferrochromium alloys, was 14 thousand tonnes (about 75% by the electrolytic method; IARC, a ); this had increased to 18 thousand tonnes by ( Morning, ). Production included chromium briquets, exothermic chromium additives and miscellaneous chromium alloys, in addition to chromium metal. By , US production of chromium metal and ferrochromium-silicon (including exothermic chromium additives and other miscellaneous chromium alloys) had dropped to tonnes ( Papp, ).

Chromium metal is made commercially in the USA by two processes: (i) an electrolytic method in which a chromium-containing electrolyte, prepared by dissolving a high-carbon ferrochromium in a solution of sulfuric acid and chromium potassium sulfate, is subjected to electrolysis; and (ii) an aluminothermic reduction method in which chromic oxide is reduced with finely divided aluminium ( Bacon, ; Papp, ).

Potassium chromic sulfate is also produced by one company in Brazil and one company in Czechoslovakia ( Chemical Information Services Ltd, ).

Potassium chromic sulfate dodecahydrate (potassium chrome alum) is produced commercially by the reduction of potassium dichromate with sulfur dioxide ( Copson, ). One company in the USA currently produces potassium chromic sulfate, but no data on volumes were available ( Chemical Information Services Ltd, ). It was produced commercially in Japan before . Production reached about 20'30 tonnes in ; subsequently, the annual quantity produced decreased rapidly, and only about one tonne was produced in ( IARC, a ).

Chromium sulfate is also produced by one company each in Brazil, France, India and New Zealand, two each in the Federal Republic of Germany and Spain and three in the UK. Basic chromic sulfate is also produced by one company each in Australia, Brazil, Colombia, Italy, Mexico, Pakistan, Turkey and the USSR, two each in China and India and three in the UK ( Chemical Information Services Ltd, ).

Both chromium sulfate and basic chromic sulfate have been produced in Japan since about , by reduction of sodium dichromate with glucose. The combined production of the two producers in (which are still operating) was about tonnes basic chromic sulfate and about 120 tonnes chromium sulfate ( IARC, a ).

Two companies in the USA produce chromium sulfate and one produces basic chromic sulfate, but no data on volumes were available ( Chemical Information Services Ltd, ).

Solutions of mixed hydrated chromic sulfates are obtained by dissolving chromic oxide in concentrated sulfuric acid and allowing it to stand until crystals of the hydrated chromic sulfate separate. The anhydrous form is produced by heating any of the hydrates to 400°C in air or to 280°C in a stream of carbon dioxide ( IARC, a ). Mixtures of basic chromic sulfates (containing mainly Cr(OH)SO 4 ) with sodium sulfate are produced commercially by the organic reduction (with such substances as molasses) of a solution of sodium dichromate in the presence of sulfuric acid or by reduction of dichromate solutions with sulfur dioxide ( Copson, ).

Chromic phosphate is produced by two companies in the USA and one each in Australia, Austria, the Federal Republic of Germany, India, Japan and the UK ( Chemical Information Services Ltd, ).

A violet hexahydrate form of chromic phosphate is formed by mixing cold solutions of potassium chromium sulfate (chrome alum) with disodium phosphate. A green crystalline dihydrate is obtained by boiling the violet hexahydrate with acetic anhydride or by heating it in dry air ( Udy, ).

Chromic oxide was produced by six companies in the USA in . US production of the most important type of chromic oxide, chromic oxide green, was reported to be about tonnes in ( IARC, a ), about tonnes in and tonnes in ( Hartford, ). It is now produced by one company in the USA ( Chemical Information Services Ltd, ). Chromic oxide has been produced in Japan by two companies, either by heating hydrous chromic oxide or chromium trioxide or by reducing sodium dichromate with carbon. An estimated tonnes were produced in ( IARC, a ). It is also produced by two companies each in the Federal Republic of Germany and the UK and one each in France, India, Italy, Spain and Switzerland ( Chemical Information Services Ltd, ).

Anhydrous chromic oxide is produced commercially by heating chromic hydroxide, by heating dry ammonium dichromate, or by heating sodium dichromate with sulfur and washing out the sodium sulfate ( Sax & Lewis, ). The hydrated material is made commercially by calcining sodium dichromate with boric acid and hydrolysing chromic borate ( IARC, a ).

Chromic nitrate may be produced by the action of nitric acid on chromium hydroxide ( Sax & Lewis, ). It is produced by three companies each in Japan, the UK and the USA, two each in Italy and Spain and one in the Federal Republic of Germany ( Chemical Information Services Ltd, ).

Chromic hydroxide is produced by adding a solution of ammonium hydroxide to the solution of a chromium salt ( Sax & Lewis, ). It is produced by one company each in Argentina, Brazil, France, Japan and Turkey, two each in Austria, Spain, the UK and the USA and four in India ( Chemical Information Services Ltd, ).

Chromic chloride is also produced by three companies in the UK, two in the Federal Republic of Germany and one each in Australia and the German Democratic Republic ( Chemical Information Services Ltd, ).

In Japan, chromic chloride has been produced from chromic sulfate by converting it to purified chromic carbonate, which is treated with hydrochloric acid. About 100 tonnes of chromic chloride were produced by one Japanese company in ; there were no reported imports or exports. Four companies currently produce chromic chloride in Japan ( Chemical Information Services Ltd, ).

Chromic chloride hexahydrate is prepared by dissolving freshly prepared chromium hydroxide in hydrochloric acid. Anhydrous chromic chloride can be produced by passing chlorine over a mixture of chromic oxide and carbon ( Sax & Lewis, ). Chromic chloride has been produced by two companies in the USA, but no data on volumes were available.

Chromic acetate was produced by five companies in the USA, but no data on volumes were available ( IARC, a ); it is now produced by one company ( Chemical Information Services Ltd, ). Annual production in Japan has been about 30 tonnes ( IARC, a ). Chromic acetate is currently produced by two companies each in Japan and the UK and one each in Australia, Canada and Italy ( Chemical Information Services Ltd, ).

Solutions of chromic acetate are produced by dissolving freshly prepared hydrous chromic oxide in acetic acid ( IARC, a ). Commercial mixtures of chromic acetate with sodium acetate have been prepared by reduction of sodium dichromate with glucose or corn sugar in the presence of acetic acid ( Copson, ).

(d) Chromium[VI] compounds

Hexavalent chromium compounds that are commonly manufactured include sodium chromate, potassium chromate, potassium dichromate, ammonium dichromate and chromium trioxide. Other materials that contain chromium[VI] are paint and primer pigments, graphic art supplies, fungicides, wood preservatives and corrosion inhibitors (National Institute for Occupational Safety and Health, ). Each chromate-producing process involves the roasting of chromite ore with soda and lime at about °C in a furnace or rotary kiln (Gafafer, ). Water-soluble hexavalent chromium compounds do not occur in the ore but comprise part of roast, residue and product materials (Kuschner & Laskin, ). The presence of lime ensures that aluminium and silicon oxides in the ore are converted to insoluble compounds, the soluble sodium chromate being recovered by a leaching and crystallization process (National Institute for Occupational Safety and Health, ). Chromium trioxide is produced by acidifying the leachate solution with sulfuric acid (Gafafer, ). In the manufacture of pigments, chromium trioxide or alkali chromates are reacted with soluble compounds of zinc, lead, iron, molybdenum, strontium and other metals (Stern, ). The insoluble precipitates are washed, filtered and dried in the wet department of the processing plant and then ground, blended and packed in the dry departments, where conditions are often dustiest (Gafafer, ).

Ammonium dichromate is produced by a crystallization process involving equivalent amounts of sodium dichromate and ammonium sulfate. When low alkali salt content is required, it can be prepared by the reaction of ammonia with chromium trioxide (Hartford, ).

Ammonium dichromate is produced by one company each in Argentina, Australia, Brazil, France, Japan, Spain and Switzerland, by two each in the Federal Republic of Germany and India, by four in the USA, and by five in the UK (Chemical Information Services Ltd, ).

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Calcium chromate is produced commercially by the reaction of calcium chloride with sodium chromate. Hydrated forms can be made, but the anhydrous salt is the only product of commercial significance (IARC, a).

Calcium chromate is currently produced by three companies in the USA, but no data on volumes were available (Chemical Information Services Ltd, ). Calcium chromate was formerly produced in Japan at an annual rate of about 100 tonnes, but it has been produced recently in only small amounts for reagent use (IARC, a). It is also produced by one company each in Australia and the UK and two in France (Chemical Information Services Ltd, ).

Chromium trioxide is produced commercially by the reaction of sodium dichromate with concentrated sulfuric acid (Hartford, ). In , there were two US producers of chromium trioxide, each with a capacity to produce 18 thousand tonnes per year (Anon., ). Annual US production in was in the range of 26 thousand tonnes (Hartford, ). In , there were six US producers (Chemical Information Services Ltd, ) with a combined capacity of 52 thousand tonnes per year (Anon., a).

Commercial production in Japan was started before . In , three companies produced a total of tonnes, of which tonnes were exported; there were no reported imports (IARC, a). Four companies currently produce chromium trioxide in Japan (Chemical Information Services Ltd, ).

Chromium trioxide is also produced by four companies each in the Federal Republic of Germany, India and the UK, three in China, two each in Argentina, Brazil and Mexico and one each in France, Italy, Pakistan, Poland and the USSR (Chemical Information Services Ltd, ).

Potassium chromate is produced by the reaction of potassium dichromate with potassium hydroxide or potassium carbonate (Hartford, ).

There was one US producer in , but no data on volumes were available; combined US imports of potassium chromate and potassium dichromate in that year were 2.7 tonnes (US Department of Commerce, ). There are currently two US producers, but no data on volumes were available (Chemical Information Services Ltd, ). Combined US imports of the two compounds in , and , respectively, were 580, 750 and tonnes from the UK (52%), the USSR (22%), the Federal Republic of Germany (13%) and Canada (11%); combined US exports for the same years were 64, 19 and 9 tonnes to the Philippines (40%), the Republic of Korea (30%) and Panama (30%) (Papp, ).

The two Japanese producers made about one tonne in for reagent uses; there were no reported imports or exports (IARC, a). One company currently produces potassium chromate in Japan (Chemical Information Services Ltd, ). It is also produced by five companies in the UK, four in Brazil, three each in India and Italy, and one each in Argentina, Canada, the Federal Republic of Germany, Spain and Switzerland (Chemical Information Services Ltd, ).

Potassium dichromate is produced industrially by roasting chrome ore with potassium carbonate (IARC, a), or, preferably, by reacting sodium dichromate with potassium chloride (Hartford, ). Combined US production of potassium dichromate and potassium chromate in was estimated to be ' tonnes, the potassium dichromate believed to be the more important industrially (IARC, a).

Three companies in the USA produce potassium dichromate (Chemical Information Services Ltd, ). Current information on imports/exports is given above. Potassium dichromate was first produced commercially in Japan before . Production by two companies in amounted to about tonnes, well below the tonnes level of and below the level of tonnes. Exports are believed to be minor (IARC, a).

Potassium dichromate is also produced by six companies in India, five in the UK, four in Brazil, two each in the Federal Republic of Germany and Italy, and one each in Argentina, Romania, Spain, Switzerland, Turkey, Yugoslavia and the USSR (Chemical Information Services Ltd, ).

Sodium chromate is produced commercially by roasting chromite ore with sodium carbonate, or with sodium carbonate and calcium oxide, and leaching to dissolve the sodium chromate. After treatment to remove hydrated alumina, the sodium chromate solution is either marketed directly or evaporated to produce hydrated or anhydrous crystals (Hartford & Copson, ). Sodium chromate may also be produced from sodium dichromate by treatment with sodium hydroxide.

Two companies produced sodium chromate in the USA in . The combined US production of sodium chromate and sodium dichromate increased from 123 thousand tonnes in to 144 thousand tonnes in (Hartford, ), and was 159 thousand tonnes in . Currently, three companies in the USA have been reported to produce sodium chromate, but data on production volumes were not available (Chemical Information Services Ltd, ).

Commercial production in Japan started before . Production in by the two producing companies was less than 10 tonnes (IARC, a); two companies currently produce this compound (Chemical Information Services Ltd, ). It is also produced by five companies in India, four in Brazil, three in the UK, two in the Federal Republic of Germany and one in Spain (Chemical Information Services Ltd, ).

Sodium dichromate is produced commercially by the reaction of sulfuric acid with sodium chromate (Hartford, ). Three companies in the USA produced this compound in . In , two of five companies that produced it (Chemical Information Sciences Ltd, ) had a combined capacity of 144 thousand tonnes per year (Anon., b).

Sodium dichromate was first produced commercially in Japan in about . In , the combined production of two companies was estimated to be 20.7 thousand tonnes, slightly below the level of 21 thousand tonnes (IARC, a). Three companies currently produce it in that country (Chemical Information Services Ltd, ).

Sodium dichromate is also produced by five companies in India, four each in Brazil and the UK, three in China, two each in the Federal Republic of Germany and Turkey, and one each in Argentina, Czechoslovakia, Italy, Mexico, Pakistan, Poland, Romania, Spain, Switzerland and the USSR (Chemical Information Services Ltd, ).

Barium chromate is produced commercially by the reaction of barium chloride with sodium chromate (Copson, ). Five companies in the USA produced this chemical in (IARC, a), and now there are four (Chemical Information Services Ltd, ), but no data on volumes were available. Barium chromate is produced by one company in Japan (Chemical Information Services Ltd, ). Production in was estimated to have been less than 50 tonnes; there were no reported imports or exports (IARC, a). It is also produced by four companies in France, two in the UK, and one each in Australia, Austria, Belgium, the Federal Republic of Germany, India, Italy and Spain (Chemical Information Services Ltd, ).

Basic lead chromate (Chrome Orange) is produced by the reaction of lead oxide with sodium dichromate in the presence of acetic acid or by the reaction of lead nitrate with sodium chromate in the presence of sodium carbonate (Chalupski, ). No information on production of this compound in the USA was available, but combined production of Chrome Yellow and Chrome Orange, containing various proportions of basic lead chromate, amounted to 32.1 thousand tonnes in and 28.2 thousand tonnes in (Hartford, ). Basic lead chromate is also produced by one company each in Argentina, Colombia, the Federal Republic of Germany, Italy, Japan, Poland and Spain (Chemical Information Services Ltd, ).

Lead chromate (Chrome Yellow) can be produced by reacting sodium chromate with lead nitrate, or by reacting lead monoxide with chromic acid solution. By varying the proportion of reactants, either lead chromate (PbCrO4) or lead chromate oxide (basic lead chromate; PbO.PbCrO4) can be produced. High lead chromate content is associated with yellow pigments; increasing the lead chromate oxide content gives orange colours; and mixing with lead molybdate gives red pigments (Chalupski, ).

No information on production of this compound in the USA was available, but combined production of Chrome Yellow and Chrome Orange pigments was 32.1 thousand tonnes in and 28.2 thousand tonnes in (Hartford, ). Assuming an average of 70% lead chromate in these pigments, about 20 thousand tonnes of lead chromate were produced in the USA or imported for use in these pigments in that year. Lead chromate is currently produced by five companies in the USA (Chemical Information Services Ltd, ).

Commercial production in Japan was started in about , and there were three major producers and one minor producer in . Production in was 10.8 thousand tonnes and exports were tonnes. Six companies currently produce lead chromate in Japan (Chemical Information Services Ltd, ). Production of Chrome Yellow in , and , respectively, was , and tonnes (Sasaki, , , ).

Lead chromate is also produced by six companies in Spain, five in Italy, three in Belgium, two each in Argentina, Austria, Canada, China, the Federal Republic of Germany, France, the Netherlands and Turkey, and one each in Australia, Colombia, Mexico, Poland, Taiwan and the UK (Chemical Information Services Ltd, ).

Molybdenum orange pigments are variable complexes of lead sulfate, lead chromate and lead molybdate, made by pouring sodium dichromate, sulfuric acid and sodium molybdate into excess lead nitrate, preferably cold, at pH3. An ageing step is required in precipitation to permit development of the orange tetragonal form (Hartford, ).

Molybdenum orange is currently produced by four companies in the USA (Chemical Information Services Ltd, ). US imports for , and , respectively, were 980, 750 and tonnes from Canada (78%), the Federal Republic of Germany (16%) and Japan (6%) (Papp, ). Four companies currently produce molybdenum orange and molybdenum red in Japan (Chemical Information Services Ltd, ), and production of molybdenum red in , and , respectively, was , and tonnes (Sasaki, , , ).

Molybdenum orange (including molybdenum red) is also produced by one company each in Australia, Austria, Canada, Colombia, India, Italy, Mexico and Taiwan, two each in Belgium, the Federal Republic of Germany, France and the Netherlands and four in Spain (Chemical Information Services Ltd, ).

Strontium chromate is prepared by adding a solution of a strontium salt to a solution of sodium chromate (Lalor, ).

Production of strontium chromate by three companies in the USA in was estimated to be 680 tonnes (Lalor, ). US imports in were 242 tonnes, mostly from Canada (US Department of Commerce, ). It is currently produced by five companies in the USA, but no data on volumes are available (Chemical Information Services Ltd, ). US imports for , and , respectively, were 390, 120 and 120 tonnes from France (61%), the Federal Republic of Germany (15%) and Canada (11%) (Papp, ).

Production in Japan began after . The combined production of three companies in was about 600 tonnes, comparable with that of the previous seven years; there were no reported imports or exports (IARC, a). Two companies currently produce strontium chromate in that country (Chemical Information Services Ltd, ).

Strontium chromate is also produced by four companies in France, two each in Australia, Italy, Spain and the UK and one each in Austria, Belgium, Brazil and the Federal Republic of Germany (Chemical Information Services Ltd, ).

Zinc chromates have been produced commercially since about . Basic zinc chromates (including 'zinc chromates') are prepared by reaction between a solution of chromium trioxide and a slurry of zinc oxide. Zinc potassium chromates are prepared by a reaction between a solution of sodium dichromate, a slurry of zinc oxide and a solution of potassium chloride (Lalor, ).

Zinc chromate (zinc tetroxychromate) is currently produced by three companies each in Belgium, France, Italy, Japan, Spain and the USA, two each in Argentina and Austria, and one each in Australia, Canada, Colombia, India, the Netherlands, Norway, Poland, Taiwan, Turkey and the UK. Zinc potassium chromate is produced by two companies in Austria, one each in Belgium, France, Italy, Norway, Turkey and the USA (Chemical Information Services Ltd, ), and probably elsewhere. Production of 'zinc chromate' in Japan in , and was , and tonnes, respectively (Sasaki, , , ).

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