Chemical Fact Sheet
Chromium
| Chemical Abstract Number (CAS #) | 7440-47-3 |
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| Synonyms | CHROM- (GERMAN); CHROME; CHROME- (FRENCH) |
| Analytical Methods | 200.7 - 200.8 - 6010 - 6020 |
| Molecular Formula | Cr |
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Synopsis
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Chromium - (Gr. chroma, color), Cr; at. wt. 51.9961(6); at. no. 24; m.p. 1907 deg C; b.p. 2671 deg C; sp. gr. 7.18 to 7.20 (20 deg C); valence chiefly 2, 3, or 6. Discovered in 1797 by Vauquelin, who prepared the metal the next year, chromium is a steel-gray, lustrous, hard metal that takes a high polish. The principal ore is chromate (FeCr2O4), which is found in Zimbabwe, Russia, Transvaal, Turkey, Iran, Albania, Finland, Democratic Republic of Madagascar, and the Philippines. The metal is usually produced by reducing the oxide with aluminum. Chromium is used to harden steel, to manufacture stainless steel, and to form many useful alloys. Much is used in plating to produce a hard, beautiful surface and to prevent corrosion. Chromium is used to give glass an emerald green color. It finds wide use as a catalyst. All compounds of chromium are colored; the most important are the chromates of sodium and potassium (K2CrO4) and the dichromates (K2Cr207) and the potassium and ammonium chrome alums, as KCr(SO4)2 - 12H20. The dichromates are used as oxidizing agents in quantitative analysis, also in tanning leather. Other compounds are of industrial value; lead chromate is chrome yellow, a valued pigment. Chromium compounds are used in the textile industry as mordants, and by the aircraft and other industries for anodizing aluminum. The refractory industry has found chromite useful for forming bricks and shapes, as it has a high melting point, moderate thermal expansion, and stability of crystalline structure. Many chromium compounds are toxic and should be handled with proper safeguards. Natural chromium contains four isotopes. Sixteen other isotopes are known. Chromium metal (99.991%) costs about $200/kg. Commercial grade chromium (99%) costs about $75/kg. |
| Use | INCR RESISTANCE & DURABILITY OF METALS; CHROMEPLATING OTHER METALS NUCLEAR & HIGH TEMPERATURE RESEARCH Pigments for floor covering products, paper, cement, and asphalt roofing. Used in coloring glass an emerald color. COMPONENT OF STAINLESS & HEAT RESISTING STEELS COMPONENT OF STAINLESS & HEAT RESISTING STEELS COMPONENT OF FULL ALLOY STEEL COMPONENT OF HIGH STRENGTH, LOW ALLOY, & ELECTRIC STEELS COMPONENT OF SUPERALLOYS, CAST IRONS, & CARBON STEEL COMPONENT OF OTHER ALLOYS-EG, NONFERROUS & MAGNETIC COMPONENT OF TOOL STEEL & WELDING MATERIALS 1) Use in fabrication of alloys; 2) use in preparation of alloy steels to enhance corrosion and heat resistance; 3) use in fabrication of plated products for decoration or increased wear resistance; 4) use in production of non-ferrous alloys to impart special qualities to the alloys; 5) use in production and processing of insoluble salts; 6) use as chemical intermediates; use in textile industry in dyeing, silk treating, printing, and moth proofing wool; 7) use in leather industry in tanning; use in photographic fixing baths; 8) use as catalysts for halogenation, alkylation, and catalytic cracking of hydrocarbons; and 9) use as fuel additives and propellant additives; in ceramics. Chromium and its compounds are used in metal alloys such as stainless steel; protective coatings on metal; magnetic tapes; and pigments for paints, cement, paper, rubber, composition floor covering and other materials. Other uses include organic chemical synthesis, photochemical processing and industrial water treatment. In medicine, chromium compounds are used in astringents and antiseptics. Chromium encounters many industrial applications, including its uses in steel and nonferrous alloys, metal-plating, refractory materials, chromate pigments and chromate preservatives. CONSTITUENT OF INORG PIGMENTS. SENSITIZER IN PHOTOGRAPHIC INDUSTRY; PREPARATION OF CHROMATES. (51)Chromium is used as a radioisotopic tracer. |
| Consumption Patterns | A recent study has projected a 3.4% growth in USA chromium (Cr) consumption leading to a total USA chromium (Cr) demand in the yr 2000 of 10X10+6 metric tons. (1976) Total consumption in USA= 3.27X10+5 metric tons. STAINLESS & HEAT RESISTING STEELS, 71.4%; FULL ALLOY STEEL, 15.2%; HIGH STRENGTH, LOW ALLOY & ELECTRIC STEELS, 3.1%; SUPERALLOYS, 2.8%; CAST IRONS, 2.6%; CARBON STEEL, 2.4%; OTHER, 2.5% (1982, CHROMIUM & CHROMIUM ALLOY USE) Stainless and heat resisting steel, 76%; full alloy steel, 11%; super alloys, 4% and other alloys, 9% (1986) Consumption of chromium ferroalloys, metal, and other chromium containing materials by end use. |
| Apparent Color | STEEL-GRAY, LUSTROUS METAL; BODY-CENTERED CUBIC STRUCTURE; GRAY CRYSTALS; BLUE-WHITE HARD METAL |
| Odor | Odorless |
| Boiling Point | 2642 DEG C |
| Melting Point | 1900 DEG C |
| Molecular Weight | 51.996 |
| Density | 7.14 |
| Sensitivity Data | Chromium aerosols caused irritation to the upper respiratory tract. Chromium causes severe nasal irritation. |
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Chemical and Physical Properties |
HEAT OF FUSION: 3660 CAL/G MOLE; 62.1 CAL/G LATENT HEAT OF FUSION: APPROX 3.5 KCAL/G-ATOM; HEAT CAPACITY (25 DEG C): 5.58 CAL/G-ATOM DEG TAKES A HIGH POLISH; HARD AS CORUNDUM & LESS FUSIBLE THAN PLATINUM ATOMIC NUMBER 24; VALENCES 1-6 THE ELEMENT CR IS AMPHOTERIC & CAN EXIST IN WATER IN SEVERAL DIFFERENT STATES UNDER STRONGLY OXIDIZING CONDITIONS, MAY BE CONVERTED TO HEXAVALENT STATE & OCCUR AS CHROMATE ANIONS IONIC (CRYSTAL) RADII (FOR COORDINATION NUMBER 6): 0.69(+3) ANGSTROM, 0.52(+6) ANGSTROM ELECTRONEGATIVITY (PAULING SCALE): 1.6; ORBITAL ELECTRONS: (AR)3D5-4S1; ABUNDANCE (% OF EARTH'S CRUST): 2X10-2 Chromium is a mixture of four stable isotopes with mass numbers 50 (4.31%), 52 (83.76%), 53 (9.55%) and 54 (2.38%). Thermal neutron capture cross sections are 17, 0.8, 18 and 0.38, respectively. Five radioistopes are known, two others (mass numbers 46 & 47) have been reported. Magnetic moments are slightly below the spin-only value of 3.88 boro magneton. Linear coefficient of thermal expansion at 20 deg C= 6.2X10-6 Thermal conductivity at 20 deg C, W(mK)= 91 Total emissivity at 100 deg C, nonoxidizing atm= 0.08 Elastic modulus, GPa= 250. Compressibility at 10-60 TPa= 70X10-3. BRITTLE METAL Chromium forms a number of cmpd in various oxidation states. Those of 2+ (chromous), 3+ (chromic) and 6+ (chromates) are the most important. Soluble in acids (except nitric) and strong alkalies. |
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Environmental Impact |
EXPOSURE TO CHROMIUM METAL DOES NOT GIVE RISE TO PULMONARY FIBROSIS OR PNEUMOCONIOSIS. Stainless steel use in mixing containers in the baking industries may be the source of extraneous chromium in food. Common operations in which exposure to chromium metal or insoluble chromium salts may occur includes the following: 1) use in fabrication of alloys; 2) use in preparation of alloy steels to enhance corrosion and heat resistance; 3) use in fabrication of plated products for decoration or increased wear resistance; 4) use in production of non ferrous alloys to impart special qualities to the alloys; 5) use in production and processing of insoluble salts; 6) use as chemical intermediates; use in textile industry in dyeing, silk treating, printing, and moth proofing wool; 7) use in leather industry in tanning; use in photographic fixing baths; 8) use as catalysts for halogenation, alkylation, and catalytic cracking of hydrocarbons; and 9) use as fuel additives and propellant additives; in photographic fixing baths and in ceramics. Common operations in which exposure to soluble chromic and chromous salts may occur include the following: 1) use in textile treatment in dyeing, printing, moth proofing, and water proofing; use in tanning of leather in gloves, garments, and shoe uppers; 2) use in manufacture of pigments of green varnishes, inks, paints, and glazes; 3) use in metal treatment and polishing; 4) use in photographic fixing baths for hardening of emulsions; use as catalysts and in manufacture of catalysts; and 5) use in chemical synthesis; use as corrosion inhibitors. Sol chromic & chromous salts (as Cr) OCCUPATIONAL EXPOSURE: CHROMIUM & ITS CMPD ARE FOUND IN 3 MAIN TYPES OF INDUST ACTIVITY: (I) MOST CR DERIV ARE USED IN METALLURGICAL INDUST (II) CHROMIUM CMPD ARE COMPONENT OF REFRACTORY MATERIALS & (III) MANY OF HIGHLY COLORED CHROMATE SALTS ARE USED IN PIGMENT, PAINT, TANNING & DYEING INDUSTRIES. In decreasing order, the est levels of exposure are: 1) occupational; 2) food; 3) water; and 4) air. Inhalation of the dust and fumes released during the manufacture of dichromate from chromite ore; inhalation of chromic acid mist during the electroplating and surface treatment of metals; and skin contact in various manufacturing processes. |
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Environmental Fate |
CHROMIUM IS FOUND IN NATURE ONLY IN THE COMBINED STATE & NOT AS THE ELEMENT. Chromium is widely distributed; avg concn 125 mg/kg in the continental crust, but rare in natural waters. PRESENT IN SMALL QUANTITIES IN ALL SOILS & PLANTS & CONSIDERED AGRICULTURALLY AS A DELETERIOUS ELEMENT. CERTAIN SOILS WITH A RELATIVELY HIGH CONTENT (0.2-0.4%) ARE SAID TO BE INFERTILE; CITRUS TREES GROWN ON THEM SHOW YELLOWING OF FOLIAGE. IRON CHROMITE (FEO.CR2O3), WHICH IS FOUND IN NATURE ONLY IN THE COMBINED STATE & NOT AS THE ELEMENT. DERIVED MAINLY FROM CHROMITE (FEO.CR2O3) FOUND IN CONSIDERABLE QUANTITIES IN RHODESIA, RUSSIA, SOUTH AFRICA, NEW CALEDONIA & THE PHILIPPINES & CONTAINS 40-50% CHROMIUM. CHROMIUM OCCURS IN NATURE MOSTLY AS CHROME IRON ORE (FEO.CR2O3). CHROMIUM IS PRESENT IN SMALL QUANTITIES IN ALL SOILS & PLANTS, @ 1-2.5 PPB IN SEA WATER, & @ ABOUT 200 PPM IN THE EARTH'S CRUST. THE NORMAL HUMAN ADULT BODY CONTAINS ABOUT 6 MG CR, WITH TISSUE CONCN OF 0.02-0.04 PPM CR ON DRY WT BASIS. IT IS PRESENT IN MINOR AMT IN IGNEOUS ROCKS & IS MUCH MORE ABUNDANT IN BASIC & ULTRABASIC TYPES THAN IN THE MORE SILICIC TYPES OF ROCKS. The most common meteorites, ie chondrites, contain 3,000 ug/g (ppm) chromium. Chromium in air associated with large particles (> 5 um diam) originates from wind blown soil and soil forming processes. /Total chromium/ The abundance of chromium in various materials is as follows: 80-200 ppm in the continental crust, 125 ppm avg; 1,000-3,400 ppm in ultramafic igneous rocks, 1,800 ppm avg; 40-600 ppm in basaltic igneous rocks, 220 ppm avg; 2-90 ppm in granitic igneous rocks, 20 ppm avg; 30-590 ppm in shales and clays, 120 ppm avg; and 10-1,000 ppm in coals, 20 ppm avg. Drinking water generally contains the same chromium levels as the surface and groundwaters, which serve as its source. Although some piping materials contain significant levels of chromium (corrosion resistant steel, 8-14%; cement, 5-120 ppm chromium), little is leached into the water. However, it should be noted that Cr(III) may be oxidized to Cr(VI) during the chlorination process. IT COULD OCCUR AS WATER POLLUTANT FROM CHROME CHEMICAL PLANTS OR IN LOSSES DURING PIGMENT PRODN OR LEATHER TANNING OPERATIONS. The two largest sources of chromium emission in the atmosphere are from the chemical manufacturing industry and combustion of natural gas, oil, and coal. Other sources include wind transport from road dust, cement producing plants because cement contains chromium, the wearing down of asbestos brake linings from automobiles or similar sources of wind carried asbestos since asbestos contains chromium, incineration of municipal refuse and sewage sludge, exhaust emission from automotive catalytic converters, emissions from cooling towers that use chromium compounds as rust inhibitors, waste waters from electroplating, leather tanning, and textile industries when discharge into surface waters, and solid wastes from chemical manufacture of chromium compounds or from municipal incineration when disposed of improperly in landfill sites. Particles emitted from coal fired power plants contained 2.3-31 ppm, chromium emitted gases contained 0.22-2.2 mg/cu m. Concn were reduced by fly ash collection to 0.19-6.6 ppm and 0.018-0.5 mg/cu m, respectively. The burning of wood in fireplaces, campfires, leaf burning, and rubbish incineration contribute chromium to the air. Air emissions containing chromium result from the following major industries: paper mills, organic & inorganic petro-chemicals, fertilizers, steel and metal foundries, motor vehicles, glass, cement, asbestos manufacture, textile mills and seam generation power plants. Wastewater treatment sludge from the production of chrome yellow, orange, and green pigments, chrome oxide green pigments, molybdate orange, zinc yellow, and iron blue pigments, and oven residue from chrome oxide green pigments contain toxic metals including hexavalent chromium. An est 4300 metric tons of sludge are generated per yr (50-60% of this in 1980 or 2100-2600 lb). These wastes are frequently disposed of in unlined lagoons and landfills or dumped in the open creating a potential for toxic environmental contamination. New York City emits 4.4x10+8 g/yr Cr. 43% of the daily Cr in New York City sewer burden and 24% of chromium emmission from New York City to vapor are from electroplating wastes, while residential waste and rain water runoff contribute 28% and 9%, respectively. The sources of chromium in waste streams are from its use as a corrosion inhibitor and from dyeing and tanning industries.In order to decide on a suitable sampling depth for grassland soil treated with sewage sludge and to assess implications for grazing animals, a field trial on two soils was designed to estimate the distribution of metals in grassland soil profiles following surface applications of sludge. Soil cores were taken using specialized equipment to 30 cm depth and divided into seven sections. Movement from the soil surface to a depth of 10 cm was observed for all of the seven metals; cadmium, chromium, copper, molybdenum, nickel, lead and zinc, but most of the metal (60%-100%, mean 87%) remained in the upper 5 cm of soil. Sampling to a depth of 5 or 7.5 cm would be most suitable for monitoring long-term grassland treated with surface applications of sludge. Aquatic Fate:Most of the chromium in surface waters may be present in particulate form as sediment. Some of the particulate chromium would remain as suspended matter and ultimately be deposited in sediments. The exact chemical forms of chromium in surface waters are not well defined. Although most of the soluble chromium in surface waters may be present as Cr(VI), a small amount may be present as Cr(III) organic complexes. Hexavalent chromium is the major stable form of chromium in seawater; however, Cr(VI) may be reduced to Cr(III) by organic matter present in water, and may eventually deposit in sediments. Atmospheric Fate: Under normal conditions, chromium(III) and Cr(0) are relatively unreactive in the atmosphere. Cr(VI) in air may react with particulate matter or gaseous pollutants to form Cr(III). However, these atmospheric reactions have not been extensively studied. Chromium is removed from air through wet and dry depositions. The total yearly deposition of chromium in urban areas may vary from 0.12 ug/sq m to 3 ug/sq m. In general, urban areas have higher total deposition than rural areas. Chromium concentration in a wet deposition may vary from 0.004 to 0.060 ug/ml and 0.0006 to 0.034 ug/l for urban and rural areas, respectively. The precipitated chromium from the air enters surface water or soil. TERRESTRIAL FATE: Uptake is greater from ultrabasic soils by a factor of 5-40 than on calcarious or silica-based soils. Snails showed an accumulation factor of 1x10+6. Leptospermum scoparum, a shrub, showed an accumulation factor of 1x10+3 compared to normal plants. Seaweed showed an accumulation factor of 1x10+2. The toxicologically important routes of entry are inhalation and ingestion. Exposure to the metal and its insoluble and soluble salts is generally via inhalation of dusts or fumes; the current threshold limit values for these compounds range from 0.05-0.5 mg/cu m. AVDI: The mean daily dietary intake of chromium from air, water, and food has been estimated to be 0.3, 4.0, and 280 ug, respectively. A recent study estimated a median value of 240 ug as the daily dietary intake of chromium from foods in Belgium; however, inhalation intake in occupationally exposed people and cigarette smokers may far exceed the inhalation intake in the general population. The US Food and Nutrition Board has recommended a safe and adequate dietary intake of 50-200 ug chromium/day total chromium Estimated safe and adequate daily dietary intakes of chromium: infants: 0-0.5 yr: 0.01-0.04 mg; 0.5-1 yr: 0.02-0.06 mg; children and adolescents: 1-3 yr: 0.02-0.08 mg; 4-6 yr: 0.03-0.12 mg; 7-10 yr: 0.05-0.2 mg; 11+ yr: 0.05-0.2 mg; adults: 0.05-0.2 mg /From table/ In the range of 0.03-0.1 mg. 280, 4, and 0.28 ug from food, water, and air IN USA VARIES WIDELY DUE TO DIET AND GEOGRAPHY. EST RANGE FROM 5 TO 115 UG/DAY WITH AN AVG OF 60-65 UG/DAY TO 5-500 UG/DAY, WITH AN AVG OF 280 UG/DAY. |
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Disposal |
At the time of review, criteria for land treatment or burial (sanitary landfill) disposal practices are subject to significant revision. Prior to implementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices. Precipitation is the preferred treatment process for removing toxic heavy metals from electroplating waters. Precipitation processes include hydroxide, lime and/or sulfide treatment. Chemical reduction is used to treat complex metals such as nickel, copper, hexavalent chromium waste, soluble lead, silver, metal containing cyanide, and mercury. Adsorption has shown potential for treating and polishing aqueous metal bearing wastes. Activated carbon, activated alumina, and iron filings are all applicable adsorbents. Alkaline chlorination and incineration are effective cyanide destruction treatments. Evaporation, ion-exchange, reverse osmosis, electrodialysis, and electrolytic recovery are waste reduction and recovery techniques applicable to metal bearing hazardous streams. |
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Atmosphere |
Chromium is associated with particulate matter in the air, and is not expected to exist in gaseous form.Chromium (Cr) is most highly concn in the smallest particles collected from ambient air. Bulk analysis does not allow adequate characterization of these particles. |
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