ТАЛЛИЙ

Описание

Thallium was discovered in 1861 by Sir William Crookes (and independently by Claude-Auguste Lamy a year later) and occurs in the lithosphere at 0.7 ppm. The name thallium is in reference to the particularly bright green spectral lines seen in the spectra resultant from a flame spectroscopy test (from Greek thallos, meaning a green shoot or twig), the one used in its discovery. Thallium is a heavy metallic element that exists in the environment mainly combined with other elements (primarily oxygen, sulfur, and the halogens) in inorganic compounds.

Химические свойства

Thallium is a soft, bluish-white, heavy, very soft metal insoluble in water and organic solvents. It turns gray on exposure to air.

Физические свойства

Thallium has much the same look (silvery) and feel as lead and is just as malleable. Unlikelead, which does not oxidize readily, thallium will oxidize in a short time, first appearing as adull gray, then turning brown, and in just a few years or less turning into blackish corrodedchunks of thallium hydroxide. This oxide coating does not protect the surface of thalliumbecause it merely flakes off exposing the next layer to oxidation.
Thallium is just to the left of lead in period 6, and both might be considered extensionsof the period 6 transition elements. Thallium’s high corrosion rate makes it unsuitable formost commercial applications. Its melting point is 304°C, its boiling point is 1,473°C, andits density is 11.85 g/cm³.

Изотопы

There are a total of 55 isotopes for thallium. All are radioactive with relativelyshort half-lives, and only two are stable. The stable ones are Tl-203, which constitutes29.524% of the element’s existence in the Earth’s crust, and Tl-205, which makes up70.476% of the element’s natural abundance found in the Earth’s crust.

Происхождение имени

From the Greek word thallos, meaning “young shoot” or “green twig.” Named for the green spectral line produced by the light from the element in a spectroscope.

Вхождение

Thallium is the 59th most abundant element found in the Earth’s crust. It is widely distributedover the Earth, but in very low concentrations. It is found in the mineral/ores ofcrooksite (a copper ore; CuThSe), lorandite (TlAsS₂), and hutchinsonite (lead ore, PbTl). Itis found mainly in the ores of copper, iron, sulfides, and selenium, but not in its elementalmetallic state. Significant amounts of thallium are recovered from the flue dust of industrialsmokestacks where zinc and lead ores are smelted.

Характеристики

Elemental thallium metal is rare in nature mainly because it oxidizes if exposed to air (oxygen)and water vapor, forming thallium oxide, a black powder. Although some compounds ofthallium are both toxic and carcinogenic, they have some uses in the field of medicine. Somecompounds have the ability to alter their electrical conductivity when exposed to infraredlight.

Использование

Thallium is used in photoelectric cells, insemiconductor studies, and in low-rangeglass thermometers. It is alloyed with manymetals. Many of its salts are used as rodent poisons. Radioactive thallium-201 is used fordiagnostic purposes in nuclear medicine inpatients with coronary artery disease.

Определение

A soft malleable grayish metallic element belonging to group 13 of the periodic table. It is found in lead and cadmium ores, and in pyrites (FeS₂). Thallium is highly toxic and was used previously as a rodent and insect poison. Various compounds are now used in photocells, infrared detectors, and lowmelting glasses. Symbol: Tl; m.p. 303.5°C; b.p. 1457°C; r.d. 11.85 (20°C); p.n. 81; r.a.m. 204.3833.

Методы производства

Thallium sulfide is insoluble in alkaline solution, but soluble in acid, allowing its separation from group I elements. Thallium chloride is only slightly soluble in cold water, which permits its separation from chlorides of cadmium, copper, tellurium, and zinc.
Thallium metal may be obtained from the compounds in several ways: by electrolysis of carbonates, sulfates, or perchlorates; by precipitation of metallic thallium with zinc; and by reduction of thallous oxalate or chloride. A number of industrial processes for the recovery of thallium have been described in the literature. Several of them depend on the extraction of thallium from flue dust by boiling it in acidified water.

Общее описание

Bluish-white soft malleable metal or gray granules. Density 11.85 g / cm3. Emits toxic fumes when heated. May be packaged under water.

Реакции воздуха и воды

Flammable in the form of powder or dust. Insoluble in water.

Профиль реактивности

THALLIUM is a reducing agent. Reacts so vigorously with fluorine that the metal becomes incandescent [Mellor 5:421 1946-47].

Опасность

In all forms, thallium is very toxic if inhaled, when in contact with the skin, and in particular,if ingested. Mild thallium poisoning causes loss of muscle coordination and burningof the skin, followed by weakness, tremor, mental aberration, and confusion.
Thallium disease (thallotoxicosis) results from the ingestion of relatively large doses (morethan a few micrograms). The severity may vary with the age and health of the patient. Nervesbecome inflamed, hair is lost, the patient experiences stomach pain, cramps, hemorrhage,rapid heartbeat, delirium, coma, and respiratory paralysis. The disease has the potential tocause death in about one week. In the past thallium was one of the poisons of choice used bymurderers because it acts slowly and makes victims suffer. In 1987 then Iraqi dictator SaddamHussein’s agents mixed thallium powder in orange juice or yogurt and fed it to people heperceived to be his enemies. There were at least 40 thallium poisonings, mostly of Kurdishleaders. (William Langewiesche, “The Accuser,” Atlantic, March 2005, 56.)

Угроза здоровью

Thallium and its soluble compounds arehighly toxic in experimental animals. Theacute toxic symptoms in humans are nausea,vomiting, diarrhea, polyneuritis, convulsion,and coma. Ingestion of 0.5 g can be fatalto humans. Severe chronic toxicity can leadto kidney and liver damage, deafness, andloss of vision. Other signs of toxicity fromchronic exposure include reddening of theskin, abdominal pain, polyneuritis, loss ofhair, pain in legs, and occasionally cataracts.Ingestion of thallium salts in children hascaused neurological abnormalities, mentalretardation, and psychoses.
Hoffman (2000) reviewed thallium poisoningin women during pregnancy and cited acase that began in the first trimester of pregnancyresulting in fetal demise. John Peter andViraraghavan (2005) have reviewed toxicityof thallium and public health risk and discussedenvironmental concerns and variousremoval technologies from aquatic system.
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Профиль безопасности

Human poison by unspecified route. Human systemic effects by ingestion: nerve or sheath structural changes, extra-ocular muscle changes, sweating, and other effects. Flammable in the form of dust when exposed to heat or flame. Violent reaction with F2. When heated to decomposition it emits toxic fumes of Tl. Used as a rodenticide and fungicide, and in lenses and prisms, in highdensity liquids. See also THALLIUM COMPOUNDS and POWDERED METALS.

Возможный контакт

Thallium is usually obtained as a byproduct from the flue dust generated during the roasting of pyrite ores in the smelting and refining of lead and zinc. Thallium has not been produced in the United States since 1984, but is imported for use in the manufacture of electronics, optical lenses, and imitation precious jewels. It also has use in some chemical reactions and medical procedures. Thallium and its compounds are used as a rodenticide and fungicide; in the manufacture of plates and prisms, high-density liquids; as insecticides, catalysts; in certain organic reactions, in phosphor activators; in bromoiodide crystals for lenses, plates, and prisms in infrared optical instruments; in photoelectric cells; in mineralogical analysis; alloyed with mercury in low-temperature thermometers, switches and closures; in high-density liquids; in dyes and pigments; in fire-works; and imitation precious jewelry. It forms a stainless alloy with silver and a corrosion-resistant alloy with lead. Its medicinal use for epilation has been almost discontinued. Highly persistent in the environment. Note: Thallium was used in the past as a rodenticide, it has been banned in the United States due to its toxicity from accidental exposure. In some countries, thallium(I)sulfate(2:1) is still used as a rat poison and ant bait.

Канцерогенность

Female mice treated orally or cutaneously with high doses of thallium showed a degenerative process in the genital tract similar to that found in castrated animals or after uterine denervation. The diagnoses were papilloma, precancerous lesions, and cancer. The control mice did not develop cancer.

Экологическая судьба

Metallic thallium (TI) is bluish white or gray; it is very soft and malleable. The element can exist in the environment mainly combined with other elements (primarily oxygen, sulfur, and the halogens) in inorganic compounds. Thallium exists in monovalent (thallous, thallium (I), Tl⁺¹) and trivalent (thallic, thallium (III), Tl⁺³) states. Monovalent thallium ions also are more stable in aqueous solution, but trivalent thallium (Tl⁺³) can be stabilized by complexing agents. Monovalent thallium is similar to potassium (K⁺) in ionic radius and electrical charge, which contribute to its toxic nature.
Compounds of thallium, however, are generally soluble in water and the element is found primarily as the monovalent ion (Tl⁺). Thallium tends to adsorb to soils and sediments, and to bioconcentrate in aquatic plants, invertebrates, and fish. Terrestrial plants can also absorb thallium from soil. Thallium is quite stable in the environment because it is neither transformed nor biodegraded. However, thallium may be bioconcentrated by organisms from water. The US Environmental Protection Agency has identified several National Priorities List sites polluted by thallium.

Перевозки

Thallium: UN3288 Toxic solids, inorganic, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required. UN1707 Thallium compounds, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required.

Несовместимости

Varies. Cold thallium ignites on contact with fluorine. Thallium metal reacts violently with strong acids (such as hydrochloric, sulfuric, and nitric) and strong oxidizers (such as chlorine, bromine, and fluorine). Cold thallium ignites on contact with fluorine. Reacts with other halogens at room temperature.

Утилизация отходов

Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal. Dilute thallium solutions may be disposed of in chemical waste landfills. When possible, thallium should be recovered and returned to the suppliers.