Chemical Fact Sheet
Cadmium
| Chemical Abstract Number (CAS #) | 7440-43-9 |
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| Synonyms | KADMIUM- (GERMAN); C-I-77180; Colloidal-cadmium |
| Analytical Methods | 200.7 - 200.8 - 6010 - 60201 |
| Molecular Formula | Cd |
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Synopsis
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Cadmium-(L.cadmia;Gr.kadmeia-ancient name for calamine, zinc carbonate), Cd; at.wt.112.411(8); at. no. 48; m.p. 321.07 deg C;b.p.767 deg C; sp. gr. 8.65 (20 degC); valence 2. Discovered by Stromeyer in 1817 from an impurity in zinc carbonate. Cadmium most often occurs in small quantities associated with zinc ores, such as sphalerite (ZnS). Greenockite (CdS) is the only mineral of any consequence bearing cadmium. Almost all cadmium is obtained as a by-product in the treatment of zinc, copper, and lead ores. It is a soft, bluish-white metal which is easily cut with a knife. It is simililar in many respects to zinc. It is a component of some of the lowest melting alloys; it is used in bearing alloys with low coefficients of friction and great resistance to fatigue; it is used extensively in electroplating, which accounts for about 60% of its use. It is also used in many types of solder, for standard E.M.F. cells, for Ni-Cd batteries, and as a barrier to control atomic fission. Cadmium compounds are used in black and white television phosphors and in blue and green phosphors for color TV tubes. It forms a number of salts, of which the sulfate is most common; the sulfide is used as a yellow pigment. Cadmium and solutions of its compounds are toxic. Failure to appreciate the toxic properties of cadmium may cause workers to be unwittingly exposed to dangerous fumes. Some silver solders, for example, contain cadmium and should be handled with care. Serious toxicity problems have been found from long-term exposure and work with cadmium plating baths. In 1927 the International Conference on Weights and Measures redefined the meter in terms of the wavelength of the red cadmium spectral line (i.e. 1 in = 1,553,164.13 wavelengths). This definition has been changed (see under Krypton). The current price of cadmium is about $100/kg (99.5%). It is available in high purity form for about $300/kg. Natural cadmium is made of eight isotopes. Thirty four other isotopes and isomers are now known and recognized. |
| Use | USE: IN ELECTROPLATING OF AUTOMOTIVE, AIRCRAFT & ELECTRONIC PARTS; MARINE EQUIPMENT & INDUSTRIAL MACHINERY; IN PREPN OF CADMIUM SULFIDES, CADMIUM SELENIDES & MIXT CONTAINING THESE SALTS FOR USE AS PIGMENTS (INCL PHOSPHORS) AS SOFT SOLDER & SOLDER FOR ALUMINUM; DEOXIDIZER IN NICKEL PLATING; PROCESS ENGRAVING; PHOTOMETRY OF UV SUN-RAYS; IN ELECTRODES FOR CADMIUM VAPOR LAMPS, PHOTOELECTRIC CELLS IN FIRE PROTECTION SYSTEMS, MACHINERY ENAMELS, BAKING ENAMELS; WESTON STANDARD CELL; PHOTOGRAPHY & LITHOGRAPHY; MFR FUNGICIDE PLATING & COATING AGENT-EG, FOR TRANSPORTATION EQUIPMENT COMPONENT OF BATTERIES-EG, NICKEL-CADMIUM BATTERIES CHEM INT FOR PLASTIC STABILIZERS-EG, CADMIUM STEARATE COMPONENT OF ALLOYS-EG, FOR BEARINGS & CONTROL RODS ANALYTICAL REAGENT-EG, FOR DETERMINATION OF NITRATE CHEM INT FOR OTHER CADMIUM CMPDS-EG, CADMIUM CHLORIDE A CONSTITUENT OF EASILY FUSIBLE ALLOYS, EG, LICHTENBERG'S, ABEL'S, LIPOWITZ', NEWTON'S, AND WOOD'S METAL. In low-melting alloys. In brazing alloys. In solar batteries. In television phosphors. Neutron absorber in nuclear reactors. Stabilizer for polyvinyl chloride. Amalgam in dentistry. Charging Jones reactors. |
| Consumption Patterns | PLATING & COATING, 51%; BATTERIES, 22%; CHEM INT FOR PIGMENTS, 13%; FOR STABILIZERS, 11%; OTHER USES, 3% (1979) 49% IN METAL PLATING, 18% IN PLASTICS STABILIZERS, 14% IN PIGMENTS & 19% IN MISC USES (NICKEL-CADMIUM BATTERIES, ALLOYS) (BUREAU OF NATIONAL AFFAIRS, INC, 1975) Coating and plating, 35%; batteries, 25%; pigments, 20%; plastics and synthetic products, 15%; and alloys and other uses, 5% (1986) |
| Apparent Color | SILVER-WHITE, BLUE-TINGED, LUSTROUS METAL; DISTORTED HEXAGONAL CLOSED-PACKED STRUCTURE |
| Odor | Odorless |
| Boiling Point | 765 DEG C |
| Melting Point | 321 DEG C |
| Molecular Weight | 112.41 |
| Density | 8.65 AT 25 DEG C |
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Chemical and Physical Properties |
MALLEABLE HEAT CAPACITY: 6.22 CAL/MOLE-DEG AT 25 DEG C & CONSTANT PRESSURE; READILY CUT WITH KNIFE Tarnishes in moist air. Cadmium becomes brittle at 80 deg C. Eight stable isotopes of cadmium (Cd) are known in nature with conventional abundances as follows: (106)Cd: 1.21%; (108)Cd: 0.88%; (110)Cd: 12.39%; (111)Cd: 12.75%; (112)Cd: 24.07%, (113)Cd: 12.26%; (114)Cd: 28.86%; (116)Cd: 7.58%. The electrical conductivity of cadmium is less than that of silver or copper, but greater than that of iron. Cadmium (Cd) has two radioisotopes: (109)Cd and (115)Cd. SOL IN ACID, AMMONIUM NITRATE & HOT SULFURIC ACID |
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Environmental Impact |
EXPOSURE HAS BEEN HIGH IN PAST CONCN OF SEVERAL MG/CU M OF AIR WERE REPORTED IN 1976 ACCUMULATOR FACTORY SHOWED AIR CONCN OF CADMIUM AS APPROX 0.04 MG/CU M. Workers in smelters and other metal-processing plants may be exposed to high concentrations of cadmium in the air. Cadmium appears in the workplace in solder, a neutron absorbent in the nuclear industry, alkaline storage batteries, an amalgam in dentistry, a stabilizer for polyvinyl chloride, engravings and pigments. Some occupations at risk include alloy makers, battery makers, engravers, textile workers, welders, solder workers and zinc and lead refiners. OCCUPATIONAL EXPOSURE: EXPOSURE OCCURS PRIMARILY IN SMELTING & REFINING ZINC, LEAD & COPPER ORES CONTAINING CADMIUM, SPRAYING CADMIUM CONTAINING PIGMENTS, PROCESSING SCRAP CONTAINING CADMIUM, ETC. |
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Environmental Fate |
Coal and other fossil fuels contain cadmium and their combustion releases the element into the environment. Occurs in a greenockite (cadmium sulfide) ore containing zinc sulfide also with lead and copper ores containing zinc. /Found/ in Canada, central and western USA, Peru, Australia, Mexico and Zaire. The principal cadmium-bearing mineral in primary deposits is sphalerite which also contains zinc. Among sedimentry rock types, the carbonaceous shales, formed under the reducing conditions, contain the most cadmium. Cadmium content: Peat: <1-3 ppm based on 10 samples; Coal: <1-20 ppm based on 12 samples; bitumens, solid hydrocarbons, asphalts <1-3 ppm based on 6 samples. Cadmium concentrations in: phosphatic rock: up to 100 mg/kg; igneous rock: 0.001 mg/kg. Volcanic action is considered to be the major natural source of cadmium. This is related to the very large quantities of particulate matter emitted, together with high enrichment of cadmium in volcanic aerosols. An investigation into trace element emissions from Mount Etna in Sicily estimated that 2.8 x 10-2 tons/day, or about 10 tons/year of cadmium was discharged into the atmosphere. Cadmium content in: sphalerite: 0.0001-2%; greenockite: 77.8%; hawleyite: 77.8%; chalcopyrite: < 0.4-110 ppm; marcasite: <0.3-<50 ppm; arsenopyrite: < 5 ppm; galena: < 10-3000 ppm; pyrite: < 0.06-42 ppm; pyrrhotite: trace; tetrahedrite: 80-2000 ppm; magnetite: 0-0.31 ppm; cadmium oxide: 87.5%; limonite: <5-1000 ppm; wad and manganese oxides: <10-1000 ppm; anglesite: 120- >1000 ppm; barite: < 0.2 ppm; anhydrite and gypsum: < 0.2 ppm; calcite: < 1-23 ppm; smithsonite: 0.1-2.35%; otavite: 65.18%; pyromorphite: < 1-8 ppm; scorodite: <1-5.8 ppm; beudantite: 100-1000 ppm; apatite: 0.14-0.15 ppm; bindheimite: 100-1000 ppm; silicates: 0.03-2.8 ppm. Liberation during smelting and refining of ores where it is a by-product of zinc, lead and copper-bearing ores. Liberation during recovery of metal by processing scrap; during melting and pouring of cadmium metal; during casting of alloys for cadmium-copper, cadmium-lead, cadmium-bismuth, cadmium-silver, cadmium-nickel, cadmium-lead-silver, cadmium-lead-silver-nickel, cadmium-lead-bismuth-tin, and cadmium-gold products used for coating telephone cables, trolley wires, welding, electrodes, automatic sprinkling systems, steam boilers, fire alarms, high pressure/temperature bearings, starting switches, aircraft relays, light duty circuit breakers, low temperature solder, and jewlery. Liberation during fabrication of metal, alloys, or plated steel. Liberation during casting and use of solders; during melting of cadmium ingots for paint and pigment manufacture used for coloring of plastics and ceramic glazes, electroplating, and in chemical synthesis. Liberation during coating on metals by hot dipping or spraying. Liberation during manufacture of nickel-cadmium batteries for use in radio-portable telephones, convenience appliances, and vented cells used in airplanes, helicopters, and stand-by power and lighting. ALL OF THE CADMIUM AND OR ITS SALTS USED AS STABILIZERS AND PIGMENTS IN PLASTICS COULD ENTER THE ENVIRONMENT, A PROCESS PARTICULARLY FACILITATED BY INCINERATION. THUS, DISPOSAL OF PLASTICS COULD CONTRIBUTE TO POLLUTION BY CADMIUM. Ceramic artists can be exposed to many hazardous materials, generally related to dry clays, glazes and kiln use. Glazes can contain lead, antimony, arsenic, barium, beryllium, boron, chromium, cobalt, cadmium, copper, vanadium and other materials which all have potential toxic effects. FORMS READILY FROM CONTACT OF CADMIUM VAPOR WITH AIR FOUND WHERE CADMIUM IS PRESENT IN EMISSIONS FROM THERMAL PROCESSES. Cadmium absorption, in humans may include: cutaneous absorption and transplacental absorption. Inhalation of cadmium in the form of aerosols or fumes. Cadmium constitutes a significant environmental pollutant and humans are exposed through food, water, air and especially, heavy smoking. To assess the pathophysiologic significance of increased body burdens of cadmium (Cd), cross-sectional evaluation of renal function and calcium, phosphorus and vitamin D metabolism was carried out in 38 industrial workers exposed to Cd for 11-37 yr. Average airborne concentrations of Cd ranged from 5 - 229 ug/cu m. Mean kidney Cd burden was 7.4 +/- 4.4 mg in nonsmokers and 12.3 +/- 7.2 mg for smokers. Mean liver Cd in nonsmokers was 4.5 +/-2.6 ug/g and 7.9 +/-4.9 ug/g in smokers. Liver or kidney Cd burden was considered elevated in 31% of the workers. Creatinine clearance was normal in all workers. Maximal urinary concentrating ability was abnormal in a significant fraction (52%) of the men. IN MAN ABOUT HALF OF TOTAL BODY BURDEN IS FOUND IN LIVER & KIDNEYS CADMIUM IN THESE ORGANS IS MAINLY BOUND TO A LOW MOLECULAR WEIGHT PROTEIN, IN FORM OF A METALLOTHIONEIN. |
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Drinking Water Impact |
Cadmium can enter surface waters from the natural sources and from a variety of manufacturing operations that involve either cadmium itself or zinc that contains a cadmium impurity. Cadmium can enter the water environment from the plating operations when spent plating solutions are discarded. The production of refined cadmium metal is a potential source of cadmium in nearby surface waters (from ore tailings and washings). ENVIRONMENTAL ACCUMULATION: GROUNDWATER CONTAMINATION FROM ELECTROPLATING OPERATIONS HAS BEEN REPORTED TO CAUSE CONCN OF UP TO 3.2 MG/L. |
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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 impementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices. Recycling: Sort, classify and put in a box properly labeled. Salvage profitably for reuse by local shop or sell as a scrap metal. Recommendable method: Landfill. Not recommendable method: Thermal destruction. |
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Atmosphere |
In the atmosphere of the working environment cadmium concentrations of 1-3 mg/cu m and 0.17-0.46 mg/cu m have been reported. Analysis indicates that retention levels resulting from present and predicted future concentrations of cadmium in the ambient air are well below kidney dysfunction level. Compared with 10 ug critical level, average urban air results in a daily cadmium retention of less than 0.1 ug. Estimates of maximum anticipated annual average ambient cadmium concentrations around the primary sources indicate that very low concentrations should result if the sources, both existing and new, comply with current ambient air standards for particulate matter. These annual average concentrations were estimated to range from a high of about 0.13 ug/cu m, for sewage sludge incinerators, to as little as 0.002 ug/cu m for municipal incinerators. Cadmium can enter the air from natural sources. |
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