Chemical Fact Sheet
Thallium
| Chemical Abstract Number (CAS #) | 7440-05-3 |
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Synonyms |
RAMOR |
| Analytical Methods | 200.7 - 200.8 - 6010 - 6020 - 279.2 |
| Molecular Formula | Tl |
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Synopsis
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Thallium - (Gr. thallos, a green shoot or twig), Tl; at. wt. 204.3833(2); at. no. 81; m.p. 304 deg C; b.p. 1473 +/- 10 deg C; sp. gr. 11.85 (20 deg C); valence 1, or 3. Thallium was discovered spectroscopically in l861 by Crookes. The element was named after the beautiful green spectral line, which identified the element. The metal was isolated both by Crookes and Lamy in 1862 about the same time. Thallium occurs in crooksite, lorandite, and hutchinsonite. It is also present in pyrites and is recovered from the roasting of this ore in connection with the production of sulfuric acid. It is also obtained from the smelting of lead and zinc ores. Extraction is somewhat complex and depends on the source of the thallium. Manganese nodules, found on the ocean floor, contain thallium. When freshly exposed to air, thallium exhibits a metallic luster, but soon develops a bluish-gray tinge, resembling lead in appearance. A heavy oxide builds up on thallium, if left in air, and in the presence of water the hydroxide is formed. The metal is very soft and malleable. It can be cut with a knife. Forty seven isotopic forms of thallium, with atomic masses ranging from 179 to 210 are recognized. Natural thallium is a mixture of two isotopes. The element and its compounds are toxic and should be handled carefully. Contact of the metal with skin is dangerous, and when melting the metal adequate ventilation should be provided. Thallium is suspected of carcinogenic potential for man. Thallium sulfate has been widely employed as a rodenticide and ant killer. It is odorless and tasteless, giving no warning of its presence. Its use, however, has been prohibited in the U.S. since 1975 as a household insecticide and rodenticide. The electrical conductivity of thallium sulfide changes with exposure to infrared light, and this compound is used in photocells. Thallium bromide-iodide crystals have been used as infrared optical materials. Thallium has been used, with sulfur or selenium and arsenic, to produce low melting glasses which become fluid between 125 and 150 deg C. These glasses have properties at room temperatures similar to ordinary glasses and are said to be durable and insoluble in water. Thallium oxide has been used to produce glasses with a high index of refraction. Thallium has been used in treating ringworm and other skin infections; however, its use has been limited because of the narrow margin between toxicity and therapeutic benefits. A mercury-thallium alloy, which forms a eutectic at 8.5% thallium, is reported to freeze at -60 deg C, some 20 degrees below the freezing point of mercury. Thallium metal (99.999%) costs about $1/g. |
| Use | In semiconductor research. Alloyed with mercury for switches and closures which operate at subzero temperatures. MFR OF THALLIUM SALTS; MFR OF MERCURY ALLOYS; LOW-MELTING GLASSES; ELECTRODES IN DISSOLVED OXYGEN ANALYZERS. In photoelectric cells, lamps, and, in electronics, in scintillation counters. As catalyst in organic synthesis. Constituent of special alloy anode plates for use in magnesium seawater batteries. |
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Consumption Patterns |
60-70% ELECTRONICS INDUSTRY; BALANCE IN PHARMACEUTICALS, ALLOYS AND GLASS MANUFACTURING (1984). |
| Apparent Color | BLUISH-WHITE, VERY SOFT, INELASTIC, HEAVY METAL; Soft, malleable; THALLIUM METAL IS SOMEWHAT SOFTER THAN LEAD & WHEN FRESHLY MELTED RESEMBLES TIN IN WHITENESS |
| Boiling Point | 1457 DEG C |
| Melting Point | 303.5 DEG C |
| Molecular Weight | 204.38 |
| Density | 11.85 g/cu m |
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Chemical and Physical Properties |
Specific heat @ 20 deg C: 0.13 J/g First ionization energy: 590 kJ/mol Heat of fusion: 21.1 J/g Atomic volume: 5.15X10+30 W/(C.m) Thermal conductance: 0.39 W/(cm.k) Covalent radius: 0.148 nm Electronegativity, Pauling's scale: 1.8 Brinell hardness: 2 Linear coefficient of expansion: 28X10-6 Electrical resistivity: 18 micro ohms/cm Tensile strength: 9.0 MPa VALENCE 1, 3; NATURAL ISOTOPES: 203 (29.50%), 205 (70.50%); EASILY FUSIBLE, LEAVES A STREAK ON PAPER OXIDIZES SUPERFICIALLY IN AIR FORMING A COATING OF TL2O; FORMS ALLOYS WITH OTHER METALS & READILY AMALGAMATES WITH MERCURY MAY BE DISTILLED IN A STREAM OF HYDROGEN THALLIUM OXIDIZES RAPIDLY, TURNING FIRST GRAY, THEN BROWNISH-BLACK FROM AN OXIDE COATING Bond strength <22 kcal/mol Heat of formation (gaseous)= 43.55 kcal/mol Begins to volatilize at 174 deg C Exists in two oxidation states, thallous and thallic. Below 230 deg C: close-packed hexagonal; above 230 deg C: body-centered cubic Thallium(I), forms relatively few complexes with the exception of those with halogen, oxygen, and sulfur ligands. In this & several other respects, thallium(I) has chemical properties similar to those of the alkali metal cations. |
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Environmental Impact |
POISONING HAS OCCURRED FOLLOWING ABSORPTION AFTER INHALATION OF DUST OR FUME INGESTION FROM CONTAMINATED HANDS OR FOOD OR AS A RESULT OF SKIN CONTACT. GENERAL POPULATION EXPOSURE TO THALLIUM MAY OCCUR AS A RESULT OF ATMOSPHERIC POLLUTION FROM COAL BURNING POWER PLANTS & FROM COPPER, LEAD & ZINC SMELTERS. CONTAMINATION OF DRINKING WATER MAY OCCUR FROM SMELTING & REFINING THALLIUM INTAKE IN SUCH AREAS MAY EXCEED NORMAL DIETARY INTAKE ESTIMATED FOR ADULTS AT ABOUT 2 UG/DAY. Inhalation and consumption of vegetables and fruits are the major routes of thallium intakes.POISONING MOST OFTEN RESULTED FROM ACCIDENTAL INGESTION OF RODENT OR ANT BAIT WHICH CONSISTED OF THALLIUM ACETATE MIXED WITH GRAIN, BREAD CRUMBS, HONEY OR SYRUP. THALLIUM, UNFORTUNATELY, IS TASTELESS & ODORLESS, SO THAT ITS PRESENCE WAS ENTIRELY MASKED CHRONIC POISONING CAN COME FROM SKIN ABSORPTION. |
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Environmental Fate |
OCCURS IN CROOKSITE, (CU,TL,AG)2SE, FOUND IN SWEDEN; IN LORANDITE, TLAGS2, FOUND IN GREECE; IN HUTCHINSONITE, (TL,CU,AG)2S.-PBS.2AS2S3, FOUND IN SWITZERLAND. IS 0.3 PPM CONTENT OF THE EARTHS CRUST; HAS BEEN DETECTED IN VOLCANIC ROCKS, METEORITES & PLANTS. In nature it does not occur in the elemental state but is present as a trace compound in many minerals, mainly associated with potassium and rubidium. The mean abundance of thallium in the earth's crust is approximately 1 ppm. Thallium occurs in small amounts in almost all living organisms. Natural levels in plants are reported as being between 0.01 and 3800 ppm ash weight, with 0.5 ppm being typical for most species. OCCURS IN CROOKSITE, (CU,TL,AG)2SE, FOUND IN SWEDEN; IN LORANDITE, TLAGS2, FOUND IN GREECE; IN HUTCHINSONITE, (TL,CU,AG)2S.-PBS.2AS2S3, FOUND IN SWITZERLAND. IS 0.3 PPM CONTENT OF THE EARTHS CRUST; HAS BEEN DETECTED IN VOLCANIC ROCKS, METEORITES & PLANTS. In nature it does not occur in the elemental state but is present as a trace compound in many minerals, mainly associated with potassium and rubidium. The mean abundance of thallium in the earth's crust is approximately 1 ppm. Thallium occurs in small amounts in almost all living organisms. Natural levels in plants are reported as being between 0.01 and 3800 ppm ash weight, with 0.5 ppm being typical for most species. Information on dietary intakes of thallium in the United Kingdom is presented, current intakes are estimated to be about 0.005 mg/day. The dietary intake and published data on urinary excretion are consistent. It is considered that brassicae are likely to be the main source of dietary exposure to thallium in food produced on contaminated land. |
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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. Reuse: Return to the suppliers. Recommendable methods: Solidification, & landfill. Not recommendable method: Thermal destruction. Peer review: Convert sol cmpd to insol form, solidify and landfill. (Peer-review conclusions of an IRPTC expert consultation (May 1985)). |
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