Thallium

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{ syn. }

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29.524 %

{ syn. }

70.476 %

In traces

In traces

In traces

In traces

Attention

Thallium is a chemical element with the element symbol Tl and atomic number 81 in the periodic table it is on the third main group of the boron group. The soft, gray and lead very similar metal is highly toxic.

History

Thallium ( from Ancient Greek θαλλός Thallos, green branch ', because of its green spectral line at 535 nm) was detected by its characteristic green spectral line in 1861 in England by Sir William Crookes spectroscopy in lead chamber sulfuric acid sludge from a factory. At the same time the Frenchman Auguste Lamy succeeded in preparing the metal electrolytically.

Occurrence limits

Thallium is not a rare element, but there are very few minerals with high thallium content: as the Crookesit (Sweden and Russia), the Lorandite (USA) and the Hutchinsonit. The vast amount is included as an accompanying element in potassium-containing clays, soils, and granites. The natural content here is 0.4 to 6.5 milligrams per kilogram. To meet demand, the resulting from the smelting of copper, lead, zinc, and other sulfide ores amount is sufficient.

For drinking water, the Federal Institute for Risk Assessment is based on a tolerance value up to five micrograms per liter.

The isotope 205Tl is the Endnuklid the radioactive decay of neptunium series. Because standing in front of him last radioactive isotope 209Bi has an extremely long half-life of about 19 trillion years, the amount of thallium takes only very slowly towards the earth.

Production and representation

Metallic thallium is usually obtained by precipitation with zinc. The world production is low with five tons of thallium per year.

Properties

Fresh cut surfaces of the soft and malleable metal are high gloss, after a short time they become covered with a blue-gray oxide film. In humid air, and water to form thallium (I ) hydroxide, which is a very strong base. In alkaline solutions it is insoluble.

In contrast to the lighter group members thallium occurs mainly in the oxidation state I, and II and III are possible. Therefore, thallium may occur as a companion in many different minerals.

In many properties similar to thallium in oxidation state I strongly the much lighter potassium, which is not least due to very similar ionic radii. Thus, thallium carbonate is the only slightly water-soluble Schwermetallcarbonat. On the other hand, there are also parallels to the corresponding oxidation state of the silver ( thallium halides are poorly soluble and sensitive to light ).

Thallium compounds exhibit intense green flame coloration, in the spectroscope is a sharp emission line at 535 nm characteristic (important in forensics ).

With halogens thallium already reacted at room temperature. The forming thallium halides (except fluorides) are capable of fluorescence by absorption of small traces of water at -180 ° C.

Use

• Low melting glasses ( between 125 to 150 ° C)
• Infrared transmitting glasses
• Glasses with high refractive index optics of photocopiers and fax machines
• High IR refractive media for ATR spectroscopy ( from Thalliumbromoiodid, known as KRS -5)
• Thallium (I ) sulfate as rat poison ( Zeliokörner ) ( now banned because of toxicity in many countries)
• Lead- thallium alloys for power rollers for continuous electrolytic galvanizing of steel sheet
• Thallium sulfide for the production of photocells
• Detectors for gamma radiation
• In myocardial scintigraphy
• Thallium nitrate as a green phosphor in distress signals ( problematic due to toxicity)
• As mercury alloy ( amalgam) in thermometers for low temperatures ( down to -58 ° C)
• As high-temperature superconductors in Hg0, 8Tl0, 2Ba2Ca2Cu2O8
• In addition lead tellurides to increase efficiency of thermoelectric materials

Physiology

Thallium is well absorbed by the body, especially through the gastrointestinal tract or the lungs. Trivalent thallium ( Tl3 ) in the body is quickly reduced to monovalent thallium (Tl ) and oxidized elemental to (Tl ), which is spread very quickly and the Na / K pump is transported from the bloodstream into the tissues and organs. Due to the ionic radius of Tl is as potassium ions K viewed and transported by the body. High concentrations of Tl can be found in kidney and liver, and the colon tissue and in certain bones. After recovering from poisoning Tl is still long to be found in nails and hair. Furthermore, Tl is questionable in the excretion from the body. Similar to the amatoxins at a Amanita mushroom poisoning is also subject to Tl the so-called enterohepatic circulation. The attempted detoxification via the liver, and finally with the bile secretion is prevented by the reabsorption of Tl in the intestine. Although this route of excretion is quantitatively smaller than the via the kidneys, but this is particularly affected by the damage caused by Tl . Therefore sets in the excretion via the bile and the intestine ( biliary system ) medically induced detoxification with iron ( III) hexacyanoferrate (II ) ( commonly known as Prussian blue known). The secretions of the bile excreted Tl are chemically bound of " Prussian Blue " and eventually excreted in the feces.

No biological function has been confirmed to thallium.

Safety

Toxicity

Thallium and thallium -containing compounds are highly toxic and must be handled with great caution.

The lethal dose for adults is about 800 mg. Acute poisoning occurs in four phases, the first of which is relatively general symptomatic with alternating diarrhea and constipation. In this phase, changes in the hair roots can already be seen, which then usually goes to the 13th day in the typical for thallium poisoning hair loss in certain parts of the body in varying degrees. In the second phase, provide a neurological and psychological changes that manifest themselves as excessive pain perception in peripheral parts of the body. The poisoning culminates in the third phase after the 10th day of incorporation. There are, indeed severe visual disorders that are caused by the paralysis of the corresponding cranial nerves. The increased activity of the heart (tachycardia ) may be explained by the action of thallium on the impulse formation of the sinus node and on the excitation transfer, which leads through the resulting cardiac arrhythmia in the lethal Tl poisoning. By the third week of poisoning the probability of a lethal output decreases and the late phase is adjusted. Here usually show irreversible damage to nerve processes lines of the lower parts of the body, impaired reflexes and muscle wasting. It may remain a permanently reduced mental performance. The Body develops after a few months again. Reduced levels lead to chronic poisoning, the longer time may remain undetected (possibly are Mees Nail bands to watch ), this then has, however, mostly on an intentional poisoning through, as a natural absorption of toxic quantities is hardly given.

Enrichments

In cement production located thallium can accumulate in the exhaust gas cleaning system in the form of its volatile halides.

Animal and plant foods usually contain no more than 0.1 mg Tl / kg. However, for example, fungi and some cabbage thallium accumulate up to 1 mg / kg.