Chemical Fact Sheet
Silver
| Chemical Abstract Number (CAS #) | 7440-22-4 |
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| Synonyms | Argentum; Silber (GERMAN); Silver-atom-; Silver-metal-; L-3-; Silflake-135-; SR-999-; TCG-7R-; V-9-; Algaedyn-; Silpowder-130-; CI-77820-; C-I-77820-; Caswell-No-735-; EPA-pesticide-chemical-code-072501-; Germany: C-Pigment 2; Silver,-colloidal-; Shell-silver-; Amalgum- |
| Analytical Methods | 200.7 - 200.8 - 6010 - 6020 |
| Molecular Formula | Ag |
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Synopsis
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Silver-(Anglo-Saxon,Seolforsiolfur), Ag (L. argentum), at. wt. 107.8682(2); at. no. 47; f.p. 961.78 deg C; b.p. 2162 deg C; sp.gr. 10.50(20 deg C); valence 1, 2. Silver has been known since ancient times. It is mentioned in Genesis. Slag dumps in Asia Minor and on islands in the Aegean Sea indicate that man learned to separate silver from lead as early as 3000 B.C. Silver occurs native and in ores such as argentite (Ag2S) and horn silver (AgCl); lead, lead-zinc, copper, gold, and copper-nickel ores are principal sources. Mexico, Canada, Peru, and the U.S. are the principal silver producers in the western hemisphere. Silver is also recovered during electrolytic refining of copper. Commercial fine silver contains at least 99.9% silver. Purities of 99.999+% are available commercially. Pure silver has a brilliant white metallic luster. It is a little harder than gold and is very ductile and malleable, being exceeded only by gold and perhaps palladium. Pure silver has the highest electrical and thermal conductivity of all metals, and possesses the lowest contact resistance. It is stable in pure air and water, but tarnishes when exposed to ozone, hydrogen sulfide, or air containing sulfur. The alloys of silver are important. Sterling silver is used for jewelry, silverware, etc. where appearance is paramount. This alloy contains 92.5% silver, the remainder being copper or some other metal. Silver is of utmost importance in photography, about 30% of the U.S. industrial consumption going into this application. It is used for dental alloys. Silver is used in making solder and brazing alloys, electrical contacts, and high capacity silver-zinc and silver-cadmium batteries. Silver paints are used for making printed circuits. It is used in mirror production and may be deposited on glass or metals by chemical deposition, electrodeposition, or by evaporation. When freshly deposited, it is the best reflector of visible light known, but is rapidly tarnishes and loses much of its reflectance. It is a poor reflector of ultraviolet. Silver fulminate (Ag2C2N202), a powerful explosive, is sometimes formed during the silvering process. Silver iodide is used in seeding clouds to produce rain. Silver chloride has interesting optical properties as it can be made transparent; it also is a cement for glass. Silvet nitrate, or lunar caustic, the most important silver compound, is used extensively in photography. While silver itself is not considered to be toxic, most of its salts are poisonous. Natural silver contains two stable isotopes. Forty nine other radioactive isotopes and isomers are known. Silver compounds can be absorbed in the circulatory system and reduced silver deposited in the various tissues of the body. A condition, known as argyria, results, with a greyish pigmentation of the skin and mucous membranes. Silver has germicidal effects and kills many lower organisms effectively without harm to higher animals. Silver for centuries has been used traditionally for coinage by many countries of the world. In recent times, however, consumption of silver has at times greatly exceeded the output. In 1939, the price of silver was fixed by the U.S. Treasury at 71 cents/troy oz., and at 90.5 cents/troy oz. in 1946. In November 1961 the U.S. Treasury suspended sales of nonmonetized silver, and the price stabilized for a time at about $1.29, the melt-down value of silver U.S. coins. The Coinage Act of 1965 authorized a change in the metallic composition of the three U.S. subsidiary denominations to clad or composite type coins. This was the first change in U.S. coinage since the monetary system was established in 1792. Clad dimes and quarters are made of an outer layer of 75% Cu and 25% Ni bonded to a central core of pure Cu. The composition of the one- and five-cent pieces remains unchanged. One-cent coins are 95% Cu and 5% Zn. Five-cent coins are 75% Cu and 25% Ni. Old silver dollars are 90% Ag and 1O% Cu. Earlier subsidiary coins of 90% Ag and 1O% Cu officially were to circulate alongside the clad coins; however, in practice they have largely disappeared (Gresham's Law), as the value of the silver is now greater than their exchange value. Silver coins of other countries have largely been replaced with coins made of other metals. On June 24, 1968, the U.S. Government ceased to redeem U.S. Silver Certificates with silver. Since that time, the price of silver has fluctuated widely. As of January 1996, the price of silver was about $5.30/troy oz. (17 cents/g); however the price has fluctuated considerably due to market instability. |
| Use | Mfr ornaments; for electroplating; ingredient in dental alloys; for making vessels & apparatus used in mfr medicinal chem, in processing foods & beverages, in handling org acids; as catalyst in hydrogenation & oxidn processes Electrical contacts; high capacity silver-zinc & silver-cadmium batteries bearing linings in air-cooled air craft engines component of photographic materials, eg, camera films, electric & electronic products, sterling ware, brazing alloys & solders, electroplated ware, commemorative medals, minted counage, jewelry, medical & dental supplies, mirrors, & ceramic paints; catalyst, eg, in oxidation of ethylene to ethylene oxide Medication: Antiinfective agent. |
| Consumption Patterns | Photographic materials, 43%; electric & electronic products, 26%; sterling ware, 6%; braxing alloys & solders, 6%; electroplated ware, 2%; catalysts, 2%; commemorative medals, 2%; minted coinage, 2%; other, 11% (1982) Photography, 45%; electrical and electronics products, 25%; sterlingware, electroplated ware, and jewelry, 11%; brazing alloys and solders, 5%; other, 14% (1986) |
| Apparent Color | White metal, face-centered cubic structure |
| Boiling Point | approx 2000 DEG C |
| Melting Point | 960.5 deg C |
| Molecular Weight | 107.868 |
| Density | 10.49 @ 15 deg C |
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Chemical and Physical Properties |
Poor reflector of UV; Pure silver has highest electrical & thermal conductivity & lowest contact resistance of all metals. Molten metal dissolves 20 times its vol of oxygen under 1 atm & gives it up on solidification. Soft, ductile, malleable, lustrous metal. Silver has the oxidation states +1, and less frequently +2; higher ones are rare. |
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Environmental Impact |
Where men work with metallic silver, small particles may accidentally penetrate the exposed skin. This may occur in occupations involving the filing, drilling, hammering, turning, engraving, polishing, forging, soldering & smelting of silver. Inhalation of metallic silver by silver finishers using "rouge" (an iron oxide) believed to be responsible for a fine granular pigmentation of elastic laminae of pulmonary arteries & elastic fibrils of alveolar walls. Metallic silver may be inhaled by silver finishers leading to abmormal chest X-Ray findings. Its importance lies in failure to recognize cause of such X-Ray changes resulting in unnecessary diagnostic studies or exclusion from employment. The following list incl some common operations in which exposure to silver metal cmpd may occur. 1. Liberation during mining and purification from ore; during refining from secondary sources 2. Use in manufacture of silver nitrate for use in photography, mirrors, plating, inks, dyes, and porcelain; and as germicides, antiseptics, caustics, and analytical reagents 3. Use in manufacture of silver salts as catalysts in oxidation-reduction and polymerization reactions; in chemical synthesis; in glass manufacture, in silver plating, as lab reagents, and in medicine 4. Liberation from manufacture and casting of alloys; during fabrication of silver metal, alloys, and bimetals for electrical uses; and during electroplating operations and fabrication of solders and brazing alloys; during manufacture and use of photographic chemicals and materials; during manufacture of mirrors, and during manufacture of silver powder pigments and paints. During radiographic film processing, workers may be exposed to a mixture of toxic fumes, especially in darkrooms without adequate ventilation. |
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Environmental Fate |
Occurrence in earth's crust: 0.1 ppm; also present in seawater: 0.01 ppm. Found native or assoc with copper, gold & lead. Principal ores are argentite, cerargyrite or horn silver (mixture of halides), proustite & pyrargyrite. Present in unpolluted freshwaters at concn up to 0.5 ug/l while sediments, soils, rocks, and minerals contain from 0.1 to 0.5 mg of silver/kg.Sources of silver in the atmosphere include emissions from smelting operations, cloud seeding operation (silver iodide), coal combustion, steel and iron production, cement manufacture, urban refuse incineration, and cigarette tobacco. Urban refuse incineration contributes about 1.7 ng/cu m to the ambient air as silver. Sorption and precipitation processes are effective in reducing the concn of dissolved silver and result in higher concn in the bed sediments than in the overlying waters. Sorption by manganese dioxide and precipitation with halides are probably the dominant controls on the mobility of silver in the aquatic environment. Algae, daphnia, fresh water mussels, and fathead minnows were all found capable of accumulating silver; but the food chain was not an important route of silver accumulation for animals at higher tropic levels, suggesting no food chain magnification. Sorbtion appears to be the dominant process leading to partitioning into sediments. It appears that magnesium dioxide, ferric compounds, and clay minerals all have some degree of adsorptive affinity for silver and are involved in its deposition into sediments. Sewage sludge amended soils may have 10 times or more silver than normal. Granite igneous rock in Nevada contains up to 50 mg/kg silver. Silver has also been reported at concn of 14-20 mg/kg in bottom sediments in California coastal basins. Beef: 0.004-0.024 mg/kg; Mutton and lamb: 0.006-0.011 mg/kg. Beef liver 0.005-0.194 mg/kg. Milk powder 0.010 + or - 0.04 mg/kg Ag; potato powder 0.015 + or - 0.005 mg/kg Ag. Brown sugar 0.3 mg/kg silver, demerara sugar 0.004 mg/kg Ag, granulated sugar 0.002 mg/kg. Wheat 0.5 mg/kg dry weight silver, bran 1.0 mg/kg dry weight silver, flour 0.4 mg/kg dry weight silver. Mollusks 0.1-10.0 mg/kg dry weight silver; crustaceans 2.0 mg/kg dry weight. Trout (Lake Cayuga NY) contained 0.48-0.68 mg/kg dry weight silver. Mollusks collected from coastal areas of the North Sea have been reported to contain silver concn of up to 2.0 mg/kg. 0.027-0.054 mg/kg of silver was detected in cow milk from market samples in various USA cities. Silver or soluble silver compounds can affect the body if they are inhaled or if they come in contact with the eyes or skin. They can also affect the body if they are swallowed. /Silver metal and soluble silver compounds Silver may be released from silver amalgam dental fillings when placed in unlined cavities.Estimates of silver in human diets have varied widely from an avg of 0.4 ug/day for three Italian populations to 27 + or - 17 ug/day in the United Kingdom. Two subjects had ingested between 10 and 20 ug/d from food during a 30-day period. The investigator, by NAA, found a daily intake from food of 1-16 ug. Silver is one of the most physically & physiologically cumulative of the elements, leading to a disturbing, permanent cosmetic effect when body burden has accumulated Ag in excess of 1 g. The highest concn of silver are usually found in the liver and spleen and to some extent in the muscle, skin, and brain. Normal values of silver in kidneys, liver, and spleen are reported to be about 0.4, 0.7, and 2.7 mg/kg dry wt, respectively, by emission spectrometry. By neutron activation analysis: up to 0.045 mg/kg wet wt (kidney); up to 0.032 mg/kg (liver); and up to 0.060 mg/kg (lung). Reported silver concn in the skin of persons with argyria are of the magnitude 50-70 mg/kg dry wt, ie, several thousand times higher than normal values (0.035 + or - 0.015 mg/kg dry wt). Normal concn in skin was reported as 0.035 + or - 0.015 mg/kg dry wt 0.006 + or - 0.002 mg/kg wet wt in liver, 0.001 + or - 0.002 in kidney and 0.002 + or - 0.0001 in lung. The silver concn in the skin of persons with argyria was 63 + or - 8 mg/kg dry wt. 72 mg/kg wet wt in one case. Silver content in 8 human kidney medulla in the United Kingdom= 0.002 + or - 0.0002 ug/g wet wt. Silver content in 11 human livers in the United Kingdom= 0.006 + or - 0.002 ug/g wet wt. Silver content in 6 human lymph nodes in the United Kingdom= 0.001 + or - 0.0002 ug/g wet wt. Silver content in 6 human muscles in the United Kingdom= 0.002 + or - 0.0005 ug/g wet wt. Silver content in 5 human testes in the United Kingdom= 0.002 + or - 0.0004 ug/g wet wt. Silver content in 6 human ovaries in the United Kingdom= 0.002 + or - 0.0005 ug/g wet wt. Silver content in 22 bones (ribs) from patients who lived in a hard water area in the United Kingdom= 1.1 + or - 0.2 ug/g wet wt. Silver content in 22 bones (ribs) from patients who lived in a soft water area in the United Kingdom= 1.1 + or - 0.2 ug/g wet wt. Silver content in 10 samples of the human whole brain in the United Kingdom= 0.004 + or - 0.002 ug/g wet wt. Silver content in 2 samples of the human frontal lobe in the United Kingdom= 0.003 + or - 0.001 ug/g wet wt. Silver content in 2 samples of the human basal ganglia in the United Kingdom= 0.004 + or - 0.002 ug/g wet wt. Silver content in 8 human kidneys in the United Kingdom= 0.002 + or - 0.0002 ug/g wet wt. Silver content in 8 human kidney cortex in the United Kingdom= 0.001 + or - 0.0002 ug/g wet wt. Urine samples collected from six males, aged 28 to 51 years, who had been employed in jewelry handicraft for 7 to 23 years, were analyzed for silver. Urinary silver ranged from 5 to 261 micrograms per 24 hours. A mean value of about 27 micrograms was found after shifts over 5 days in workers performing investment casting with oxyacetylene flame, while the mean urinary silver level in workers performing the electromagnetic induction process was about 5 micrograms after shifts. Silver content in 11 human lung in the United Kingdom= 0.002 + or - 0.0001 ug/g wet wt. |
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Drinking Water Impact |
Fresh water: avg 0.2 ug/l; sea water: avg 0.24 ug/l Public drinking water supplies and river waters have a median concn of silver between 0.09-0.23 ug/l. A range of nondetected to 5 ug/l was reported for 380 finished drinking waters from the USA. Seawater has been reported to contain silver concn of 0.055-1.5 ug/l. Silver was found in 6.6% of 1,577 surface water samples collected in the United States. Concentrations in samples containing silver varied from 0.1 to 38 ug/l with a mean of 2.6 ug/l. The highest silver concentration was in the Colorado River at Loma, Colorado. The Genesee River in New York has received photoprocessing effluents for approximately 70 years. In 1973, on most sampling dates from May 31 to October 17, it contained 20 ug/l silver. However, levels of 90 to 260 ug/l were detected in June. Sediments contained up to 150 mg/kg silver dry weight. Raw Lake Ontario water at the Eastman Kodak intake pipe contained 1 ug/l silver. The Susquehanna River in Pennsylvania, which contained the highest concentrations of silver, was estimated to be transporting 4.5 tons of silver per year to the ocean. |
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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. |
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Atmosphere |
Atmospheric concn of silver varied little from non-industrial to industrial cities with values ranging from 0.04 to 10.5 ng/cu m. Chadron, Nebraska (1973), which has a population of 6,000 in a sparsely inhabited region, and San Francisco (1970) had the same average ambient air concn of silver in 0.15 ng/cu m. Washington DC: Silver concn in air in 1974 was 1.1 ng/cu m; Chicago, IL: ambient Ag concn was 4.3 ng/cu m. Air concn of silver over southern California is of the magnitude 2 ng/cu m. Aerosol silver contamination in Heidelberg, Germany (April-June 1971)= 4.2 ng/cu m, 0.0032 ppb; Neles, MI (June 1969)= 1 ng/ cu m, 0.00077 ppb; East Chicago, IL (June 1969)= 2.4 ng/cu m, 0.0019 ppb. Aerosol silver concentration in Northwest, IN (1969)= 1.5 ng/cu m. Aerosol silver concentration in Kellogg, ID city hall= 10.5 (range 0.936 to 36.5) ng/cu m. Average concentrations of mercury, antimony, cadmium, zinc, and lead ranged from 113 to 10,800 ng/cu m. The nearby Bunker Hill smelter smelts silver rich lead concentrates and roaster zinc concentrates. Aerosol silver concentration in Chadron, NE (1973)= ave 0.15 (range 0.02 to 1.8) ng/cu m - (June -Sept 1973)= 0.14 ng/cu m - (June-Sept 1974)= 0.04 ng/cu m. Environmental exposure to various metals was determined through analysis of air samples collected from the breathing zones of the exposed workers during an 8 hour shift. Silver was the most prevalent contaminant detected in all samples. The environmental levels of silver ranged from 0.27 to to 0.60 mg/cu m when gold melting was performed using oxyacetylene flame. |
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