The structure of the tellurium atom. Structure of the tellurium atom Tellurium minerals

It is unlikely that anyone will believe the story about the sea captain, who, in addition, is a professional circus wrestler, a famous metallurgist and a consultant physician at a surgical clinic. In the world of chemical elements, such a variety of professions is a very common phenomenon, and Kozma Prutkov’s expression does not apply to them: “A specialist is like gumboil: his completeness is one-sided.” Let us remember (even before talking about the main object of our story) iron in cars and iron in blood, iron is a magnetic field concentrator and iron is an integral part of ocher... True, the “professional training” of elements sometimes took much more time than preparation intermediate yoga. So element No. 52, which we are about to talk about, was used for many years only to demonstrate what it really is, this element named after our planet: “tellurium” - from tellus, which in Latin means “Earth”. "

This element was discovered almost two centuries ago. In 1782, mining inspector Franz Joseph Müller (later Baron von Reichenstein) examined gold ore found in Semigorye, in what was then Austria-Hungary. It turned out to be so difficult to decipher the composition of the ore that it was called Aurum problematicum - “doubtful gold.” It was from this “gold” that Muller isolated a new metal, but there was no complete confidence that it was truly new. (It later turned out that Müller was wrong about something else: the element he discovered was new, but it can only be classified as a metal with great reserve.)

To dispel doubts, Müller turned for help to a prominent specialist, the Swedish mineralogist and analytical chemist Bergman.

Unfortunately, the scientist died before finishing the analysis of the sent substance - in those years, analytical methods were already quite accurate, but the analysis took a lot of time.

Other scientists also tried to study the element discovered by Müller, but only 16 years after its discovery, Martin Heinrich Klaproth, one of the leading chemists of that time, irrefutably proved that this element was actually new and proposed the name “tellurium” for it.

As always, after the discovery of the element, the search for its applications began. Apparently, based on the old principle dating back to the times of atrochemistry - the world is a pharmacy, the Frenchman Fournier tried to treat some serious diseases with tellurium, in particular leprosy. But without success - only many years later was tellurium able to provide doctors with some “minor services”. More precisely, not tellurium itself, but salts of telluric acid K 2 TeO 3 and Na 2 TeO 3, which began to be used in microbiology as dyes that give a certain color to the bacteria being studied. Thus, with the help of tellurium compounds, the diphtheria bacillus is reliably isolated from a mass of bacteria. If not in treatment, then at least in diagnosis, element No. 52 turned out to be useful to doctors.

But sometimes this element, and even more so some of its compounds, add trouble to doctors. Tellurium is quite toxic. In our country, the maximum permissible concentration of tellurium in the air is considered to be 0.01 mg/m3. Of the tellurium compounds, the most dangerous is hydrogen telluride H 2 Te, a colorless poisonous gas with an unpleasant odor. The latter is quite natural: tellurium is an analogue of sulfur, which means that H 2 Te should be similar to hydrogen sulfide. It irritates the bronchi and has a harmful effect on the nervous system.

These unpleasant properties did not prevent tellurium from entering technology and acquiring many “professions.”

Metallurgists are interested in tellurium because even small additions to lead greatly increase the strength and chemical resistance of this important metal. Lead doped with tellurium is used in the cable and chemical industries. Thus, the service life of sulfuric acid production devices coated on the inside with a lead-tellurium alloy (up to 0.5% Te) is twice as long as that of the same devices lined simply with lead. The addition of tellurium to copper and steel facilitates their machining.

In glass production, tellurium is used to give glass a brown color and a higher refractive index. In the rubber industry, it is sometimes used as an analogue of sulfur for the vulcanization of rubbers.

Tellurium is a semiconductor

However, these industries were not responsible for the jump in prices and demand for element No. 52. This leap occurred in the early 60s of our century. Tellurium is a typical semiconductor, and a technological semiconductor. Unlike germanium and silicon, it melts relatively easily (melting point 449.8°C) and evaporates (boils at just below 1000°C). Consequently, it is easy to obtain thin semiconductor films from it, which are of particular interest to modern microelectronics.

However, pure tellurium as a semiconductor is used to a limited extent - for the manufacture of field-effect transistors of some types and in devices that measure the intensity of gamma radiation. Moreover, a tellurium impurity is deliberately introduced into gallium arsenide (the third most important semiconductor after silicon and germanium) in order to create electronic-type conductivity in it*.

* The two types of conductivity inherent in semiconductors are described in detail in the article “Germanium”.

The scope of application of some tellurides - compounds of tellurium with metals - is much broader. Tellurides of bismuth Bi 2 Te 3 and antimony Sb 2 Te 3 have become the most important materials for thermoelectric generators. To explain why this happened, let's take a short digression into the field of physics and history.

A century and a half ago (in 1821), the German physicist Seebeck discovered that in a closed electrical circuit consisting of different materials, the contacts between which are at different temperatures, an electromotive force is created (it is called thermo-emf). After 12 years, the Swiss Peltier discovered an effect opposite to the Seebeck effect: when an electric current flows through a circuit composed of different materials, at the contact points, in addition to the usual Joule heat, a certain amount of heat is released or absorbed (depending on the direction of the current).

For approximately 100 years, these discoveries remained “things in themselves”, curious facts, nothing more. And it would not be an exaggeration to say that a new life for both of these effects began after the Hero of Socialist Labor, Academician A.F. Ioffe and his colleagues developed a theory of using semiconductor materials for the manufacture of thermoelements. And soon this theory was embodied in real thermoelectric generators and thermoelectric refrigerators for various purposes.

In particular, thermoelectric generators, which use tellurides of bismuth, lead and antimony, provide energy to artificial Earth satellites, navigation and meteorological installations, and cathodic protection devices for main pipelines. The same materials help maintain the desired temperature in many electronic and microelectronic devices.

In recent years, another tellurium chemical compound with semiconductor properties, cadmium telluride CdTe, has attracted great interest. This material is used for the manufacture of solar cells, lasers, photoresistors, and radiation counters. Cadmium telluride is also famous for the fact that it is one of the few semiconductors in which the Han effect is noticeably manifested.

The essence of the latter is that the very introduction of a small plate of the corresponding semiconductor into a sufficiently strong electric field leads to the generation of high-frequency radio emission. The Hahn effect has already found application in radar technology.

In conclusion, we can say that quantitatively the main “profession” of tellurium is alloying lead and other metals. Qualitatively, the main thing, of course, is the work of tellurium and tellurides as semiconductors.

Useful admixture

In the periodic table, tellurium is located in the main subgroup of group VI next to sulfur and selenium. These three elements are similar in chemical properties and often accompany each other in nature. But the share of sulfur in the earth’s crust is 0.03%, selenium is only 10–5%, and tellurium is even an order of magnitude less – 10–6%. Naturally, tellurium, like selenium, is most often found in natural sulfur compounds - as an impurity. It happens, however (remember the mineral in which tellurium was discovered) that it comes into contact with gold, silver, copper and other elements. More than 110 deposits of forty tellurium minerals have been discovered on our planet. But it is always mined together with either selenium, or gold, or other metals.

In the USSR, copper-nickel tellurium-containing ores of Pechenga and Monchegorsk, tellurium-containing lead-zinc ores of Altai and a number of other deposits are known.

Tellurium is isolated from copper ore at the stage of purifying blister copper by electrolysis. A sediment - sludge - falls at the bottom of the electrolyser. This is a very expensive intermediate product. To illustrate the composition of the sludge from one of the Canadian plants: 49.8% copper, 1.976% gold, 10.52% silver, 28.42% selenium and 3.83% tellurium. All these valuable components of the sludge must be separated, and there are several ways to do this. Here's one of them.

The sludge is melted in a furnace and air is passed through the melt. Metals, except gold and silver, oxidize and turn into slag. Selenium and tellurium are also oxidized, but into volatile oxides, which are captured in special devices (scrubbers), then dissolved and converted into acids - selenium H 2 SeO 3 and telluric H 2 TeO 3 . If sulfur dioxide SO2 is passed through this solution, the following reactions will occur:

H 2 SeO 3 + 2SO 2 + H 2 O → Se ↓ + 2H 2 SO 4,

H 2 TeO 3 + 2SO 2 + H 2 O → Te ↓ + 2H 2 SO 4.

Tellurium and selenium fall out at the same time, which is very undesirable - we need them separately. Therefore, the process conditions are selected in such a way that, in accordance with the laws of chemical thermodynamics, selenium is primarily reduced first. This is helped by selecting the optimal concentration of hydrochloric acid added to the solution.

Tellurium is then deposited. The resulting gray powder, of course, contains a certain amount of selenium and, in addition, sulfur, lead, copper, sodium, silicon, aluminum, iron, tin, antimony, bismuth, silver, magnesium, gold, arsenic, chlorine. Tellurium must first be purified from all these elements by chemical methods, then by distillation or zone melting. Naturally, tellurium is extracted from different ores in different ways.

Tellurium is harmful

Tellurium is being used more and more widely and, therefore, the number of people working with it is increasing. In the first part of the story about element No. 52, we already mentioned the toxicity of tellurium and its compounds. Let’s talk about this in more detail, precisely because more and more people have to work with tellurium. Here is a quote from a dissertation on tellurium as an industrial poison: white rats injected with tellurium aerosol “showed restlessness, sneezed, rubbed their faces, and became lethargic and drowsy.” Tellurium has a similar effect on people.

Tellurium itself and its compounds can bring troubles of different “calibers”. They, for example, cause baldness, affect blood composition, and can block various enzyme systems. Symptoms of chronic poisoning with elemental tellurium are nausea, drowsiness, emaciation; the exhaled air acquires a foul, garlicky odor of alkyl tellurides.

In case of acute tellurium poisoning, serum with glucose, and sometimes even morphine, is administered intravenously. Ascorbic acid is used as a prophylactic. But the main prevention is case sealing of devices, automation of processes in which tellurium and its compounds are involved.

Element No. 52 brings a lot of benefits and therefore deserves attention. But working with it requires caution, clarity and, again, concentrated attention.

Appearance of tellurium

Crystalline tellurium is most similar to antimony. Its color is silvery-white. Crystals are hexagonal, the atoms in them form helical chains and are connected by covalent bonds to their nearest neighbors. Therefore, elemental tellurium can be considered an inorganic polymer. Crystalline tellurium is characterized by a metallic luster, although due to its complex of chemical properties it can rather be classified as a non-metal. Tellurium is brittle and quite easy to turn into powder. The question of the existence of an amorphous modification of tellurium has not been clearly resolved. When tellurium is reduced from telluric or telluric acid, a precipitate forms, but it is still not clear whether these particles are truly amorphous or just very small crystals.

Bicolor anhydride

As befits a sulfur analogue, tellurium exhibits valences of 2–, 4+ and 6+, and much less often 2+. Tellurium monoxide TeO can only exist in gaseous form and is easily oxidized to TeO 2 . This is a white, non-hygroscopic, completely stable crystalline substance that melts without decomposition at 733°C; it has a polymer structure, the molecules of which are built like this:

Tellurium dioxide is almost insoluble in water - only one part of TeO 2 per 1.5 million parts of water passes into the solution and a solution of weak telluric acid H 2 TeO 3 of negligible concentration is formed. The acidic properties of telluric acid H 6 TeO 6 are also weakly expressed. This formula (and not H 2 TeO 4) was assigned to it after salts of the composition Ag 6 TeO 6 and Hg 3 TeO 6, which are highly soluble in water, were obtained. The anhydride TeO 3 that forms telluric acid is practically insoluble in water. This substance exists in two modifications - yellow and gray: α-TeO 3 and β-TeO 3. Gray tellurium anhydride is very stable: even when heated, it is not affected by acids and concentrated alkalis. It is purified from the yellow variety by boiling the mixture in concentrated caustic potassium.

Second exception

When creating the periodic table, Mendeleev placed tellurium and its neighboring iodine (as well as argon and potassium) in groups VI and VII not in accordance with, but contrary to their atomic weights. Indeed, the atomic mass of tellurium is 127.61, and that of iodine is 126.91. This means that iodine should not be behind tellurium, but in front of it. Mendeleev, however, did not doubt the correctness of his reasoning, since he believed that the atomic weights of these elements were not determined accurately enough. Mendeleev's close friend, the Czech chemist Boguslav Brauner, carefully checked the atomic weights of tellurium and iodine, but his data coincided with the previous ones. The validity of exceptions confirming the rule was established only when the periodic system was based not on atomic weights, but on nuclear charges, when the isotopic composition of both elements became known. Tellurium, unlike iodine, is dominated by heavy isotopes.

By the way, about isotopes. Currently, 22 isotopes of element No. 52 are known. Eight of them - with mass numbers 120, 122, 123, 124, 125, 126, 128 and 130 - are stable. The last two isotopes are the most common: 31.79 and 34.48%, respectively.

Tellurium minerals

Although tellurium is significantly less abundant on Earth than selenium, more minerals of element 52 are known than those of its counterpart. Tellurium minerals are of two types in composition: either tellurides or products of the oxidation of tellurides in the earth's crust. Among the first are calaverite AuTe 2 and krennerite (Au, Ag) Te 2, which are among the few natural gold compounds. Natural tellurides of bismuth, lead, and mercury are also known. Native tellurium is very rarely found in nature. Even before the discovery of this element, it was sometimes found in sulfide ores, but could not be correctly identified. Tellurium minerals have no practical significance - all industrial tellurium is a by-product of processing ores of other metals.

Those - chem. element VI of group of the periodic system of elements; at. n. 52, at. m. 127.60. A shiny silver-gray brittle substance with a metallic sheen. In compounds it exhibits oxidation states of -2, +4 and +6. Natural B consists of eight stable isotopes with mass numbers 120, 122-126, 128 and 130. 16 radioactive isotopes are known with half-lives from 2 to 154 days. The most common heavy isotopes are those with mass numbers 128 and 130. T. was discovered (1782) by the Hungarian. researcher F. Muller von Reichenstein. Tellurium is a trace element; its content in the earth's crust is 10-7%. Contained in many minerals with gold, silver, platinum, copper, iron, lead, bismuth, and sulfide minerals. The crystal lattice of T. is hexagonal with periods a - 4.4570 A and c = 5.9290 A. Density (t-pa 20p C) 6.22 g/cm3; /pl 449.5° C; boiling point 990±2° C.

An “amorphous” modification of Tellurium (dark brown powder) is known, which irreversibly turns crystalline when heated. Temperature coefficient linear expansion of polycrystalline T. (16-17) 10-6 deg-1, y coefficient. thermal conductivity (temperature 20° C) 0.014 cal/cm X X sec x deg; specific heat capacity (temperature 25° C) 0.048 cal/g x deg. T. is a semiconductor with a band gap of 0.34 eV. The electrical conductivity of crystal depends on the purity and degree of perfection of the crystal. In the purest samples it is equal to ~0.02 ohm-1 x cm-1. Electron mobility 1700, hole mobility 1200 cm2/v x sec. When melted, Tellurium transforms into a metallic state. Tellurium is diamagnetic, specific magnetic susceptibility is 0.3 10-6 cm3/g (at room temperature). Hardness on the Mohs scale 2.0-2.5; Wed microhardness 58 kgf/mm2, modulus of norms, elasticity 4200 kgf/mm2, coefficient. compressibility (temperature 30° C) 1.5-10 6 cm2/kgf. Tellurium single crystals with (0001) orientation break brittlely at a stress of 14 kgf/mm2.

According to chemistry Holy T. reminds you of sulfur. , but less active. At room temperature it does not oxidize in air; when heated, it burns to form Te02 dioxide - white crystalline, slightly soluble in water. TeO and Te03, which are less stable than Te02, are also known. Under normal conditions, Tellurium very slowly reacts with water with the release of hydrogen and the formation of sulfuric acid with the formation of a red TeS03 solution; when diluted with water, a reverse reaction occurs with the release of tellurium. T. dissolves in nitric acid to form telluric acid H2TeO3; in dilute hydrochloric acid it dissolves slightly.

Tellurium dissolves slowly in alkalis. With hydrogen it forms telluride H2Te - a colorless gas with an unpleasant odor, condensing at a temperature of -2°C and solidifying at a temperature of -51.2°C, an unstable compound that easily decomposes under the influence of even weak oxidizing agents. Tellurium does not form sulfides that are stable under normal conditions; the TeS2 compound is stable at temperatures down to -20° C. T forms continuous solid solutions with selenium. The known compositions are TeXb (fluoride only), TeX4 and TeX2, which are obtained by direct interaction of elements. At room temperature, everything is solid, partially decomposing with water; only TeFe is a colorless gas with an unpleasant odor. When heated, T. reacts with many metals, forming.

The raw materials for the production of Tellurium are sludge from copper-nickel and sulfuric acid production, as well as products obtained from lead refining. Anode sludge is processed using an acidic or alkaline method, converting sulfur into the tetravalent state and then reducing it with sulfur dioxide from solutions at the end of the solution. hydrochloric or electrolytic. In addition, materials containing T. can be processed using the chlorine method. High-purity tellurium is obtained by sublimation and zone recrystallization (the most effective method of deep purification, allowing to obtain a substance with a purity of 99.9999%).

Tellurium compounds are toxic, their effect on the human body is similar to the effect of selenium and arsenic compounds. The most powerful poison is telluride. The maximum permissible concentration of T in the air is 0.01 mg/mV. T is used in the vulcanization of rubber and in the production of lead cables (the addition of up to 0.1% Te improves the mechanical properties of lead). T. compounds are used in the glass industry (for coloring glass and porcelain) and in photography. Tellurium is widely used in the synthesis of semiconductor compounds. T. connections are the main material for the production of thermoelements.

Tellurium is a trace element (their content in the earth's crust is 1 ⋅ 10⁻ ⁷ %. Tellurium rarely forms independent . It is usually found in nature as impurities in sulfides, as well as in native sulfur. The main sources of tellurium and selenium are waste from sulfuric acid production, which accumulates in dust chambers, as well as sediments (sludge) formed during electrolytic purification of copper. The sludge, among other impurities, also contains silver selenide Ag 2 Se and some. When burning sludge, tellurium oxide TeO is formed 2 , as well as oxides of heavy metals. Tellurium is reduced from TeO oxides 2 when exposed to sulfur dioxide in an aquatic environment:

TeO 2 + H 2 O = H 2 TeO 3

H 2 SeO 3 + 2SO 2 + H 2 O = Se + 2H 2 SO 4

Tellurium, like , forms allotropic modifications - crystalline and amorphous. Crystalline tellurium is silver-gray in color, fragile, and easily ground into powder. Its electrical conductivity is insignificant, but increases when illuminated. Amorphous tellurium is brown in color and less stable than amorphous tellurium at 25 degrees. becomes crystalline.

In terms of chemical properties, tellurium has significant similarities with sulfur. It burns in air (greenish-blue), forming the corresponding oxides TeO 2. Unlike SO 2 Tellurium oxide is a crystalline substance and is poorly soluble in water.

Tellurium does not combine directly with hydrogen. When heated, it reacts with many metals, forming the corresponding salts (), for example K 2 Te. Tellurium reacts with water even under normal conditions:

Te + 2H 2 O = TeO 2 + 2H 2

Like selenium, tellurium is oxidized to the corresponding acids H 2 TeO 4 , but under more severe conditions and the action of other oxidizing agents:

Te + 3H 2 O 2 (30%) = H 6 TeO 6

In boiling aqueous solutions of alkalis, tellurium, like sulfur, slowly dissolves:

3Te + 6KOH = 6K 2 Te + K 2 TeO 3 + 3H 2 O

Tellurium is used primarily as a semiconductor material.

Properties of tellurium

Hydrogen telluride can be prepared by treating tellurides with dilute acids:

Na 2 Te + H 2 SO 4 = Na 2 SO 4 + H 2 Te

Hydrogen telluride under normal conditions is a colorless gas with characteristic unpleasant odors (more unpleasant than the smell of H 2 S, but more toxic, and hydrogen telluride is less toxic). Tellurium hydrides exhibit reducing properties to a greater extent than, and H 2 Te in water is approximately the same as that of hydrogen sulfide. Aqueous solutions of hydrides exhibit a pronounced acidic reaction due to their dissociation in aqueous solutions according to the following scheme:

H 2 Te ↔ H + HTe ⁺

↓

H+Te²⁺

In the series O - S - Se - Te, the radii of their ions are E² ⁺ hold a hydrogen ion. This is confirmed by experimental data, which confirmed that hydrotelluric acid is stronger than hydrosulfide acid.

In the series O - S - Se - Te, the ability for thermal dissociation of hydrides increases: it is most difficult to decompose water when heated, and tellurium hydrides are unstable and decompose even with low heating.

Salts of hydrotelluric acid (tellurides) are similar in properties to sulfides. They are obtained, like sulfides, by the action of tellurium hydrogen on soluble metal salts.

Tellurides are similar to sulfides in terms of solubility in water and acids. For example, when hydrogen tellurium is passed through an aqueous solution of Cu 2 SO 4 copper telluride is obtained:

H 2 Te + CuSO 4 = H 2 SO 4 + CuTe

Te forms TeO compounds with oxygen 2 and TeO 3 they are formed during the combustion of tellurium in air, during the firing of tellurides, and also during the combustion of tellurium hydrides:

Te + O 2 = TeO 2

2ZnTe + 3O 2 = 2ZnO + 2TeO 2

2H 2 Te + 3O 2 = 2H 2 O + 2TeO 2

TeO2 - acid oxides (anhydrides). When dissolved in water, they form, respectively, telluric acid:

TeO 2 + H 2 O = H 2 TeO 3

This acid dissociates in an aqueous solution somewhat less strongly than sulfurous acid. Telluric acid has not been obtained in free form and exists only in aqueous solutions.

While sulfur compounds with an oxidation state of 4+ in chemical reactions predominantly act as reducing agents, with an increase in the oxidation state of sulfur to 6+, TeO 2 and the corresponding acids exhibit mainly oxidizing properties, respectively being reduced to Te. In practice, tellurium is obtained in free form using these methods:

H 2 TeO 3 + 2SO 2 + H 2 O = 2H 2 SO 4 + Te

Telluric acid exhibits reducing properties only when interacting with strong oxidizing agents:

3H 2 TeO 3 + HClO 3 = 3H 2 TeO 4 + HCl

Free telluric acid H 2 TeO 4 - usually isolated as crystalline hydrate H 2 TeO 4 2H 2 O which is written as H 6 TeO 6 . In orthotelluric acid H 6 TeO 6 hydrogen atoms can be partially or completely replaced by metal atoms, forming Na6TeO6 salts.

Tellurium is a silvery-white, brittle substance with a characteristic metallic luster. In this case, a thin layer of tellurium has a red-brown tint when exposed to light, and the vapor has a golden-yellow color. Because tellurium is inert, quartz or graphite is used as container materials when melting it. Tellurium is a rare element, and the significant demand for it determines its high cost.

When producing tellurium, waste from the electrolytic refining of lead and copper is mainly used. After burning the sludge, tellurium precipitates in the cinder, after which it is washed in hydrochloric acid. The resulting hydrochloric acid solution is isolated by passing through sulfur dioxide. For further purification from sulfur, selenium and other impurities, tellurium is dissolved in an alkaline medium, where under the action of aluminum or zinc it turns into disodium ditelluride. It is then passed through oxygen or air, and to obtain high-purity tellurium, it is chlorinated, followed by purification by rectification, hydrolyzed with water and reduced with hydrogen.

The main producers of tellurium in the CIS are:

OJSC Almalyk Mining and Metallurgical Plant (Uzbekistan);
- OJSC “Ural Mining and Metallurgical Company” (Russian Federation);
- CJSC Kyshtym Copper Electrolyte Plant (Russian Federation).

Tellurium is used in the production of special lead, which has increased strength and ductility. This property is widely used in the production of wires and other cable products. The combination of tellurium and lead reduces the dissolution of lead under the influence of sulfuric acid by 10 times. This property is used in lead-acid batteries.

In special chemical equipment, tellurium glasses are used, which have exceptional transparency, electrical conductivity and fusibility. Some types of glasses with the addition of tellurium are semiconductors. They are widely used in electronics. And special glasses, with tellurium dioxide, doped with rare earth metals, are used in optical quantum generators as active bodies.

Tellurium alloys are used to create a reflective deformable layer of compact discs. Tellurium in the form of vapor is used for fluorescent lamps. The light emitted by such lamps has a spectrum comparable to natural sunlight.

Tellurium is a chemical element of group 16 (according to the outdated classification - the main subgroup of group VI, chalcogens), period 5 in the periodic table, has atomic number 52; denoted by the symbol Te (lat. Tellurium), belongs to the family of metalloids.
Content in the earth's crust is 1·10-6% by weight. About 100 tellurium minerals are known. The most common tellurides are copper, lead, zinc, silver and gold.
An isomorphic admixture of tellurium is observed in many sulfides, but the Te - S isomorphism is less pronounced than in the Se - S series, and sulfides contain a limited admixture of tellurium. Among tellurium minerals, altaite (PbTe), sylvanite (AgAuTe4), calaverite (AuTe2), hessite (Ag2Te), krennerite [(Au, Ag)Te], petzite (Ag3AuTe2), muthmannite [(Ag, Au)Te] are of particular importance , montbreuite (Au2Te3), nagiagite (4S5), tetradymite (Bi2Te2S). There are oxygen compounds of tellurium, for example TeO2 - tellurium ochre. Native tellurium also occurs together with selenium and sulfur (Japanese telluric sulfur contains 0.17% Te and 0.06% Se).

Reserves at tellurium deposits in 2012, tons *

* US Geological Survey data

The main source of tellurium is sludge produced during the electrolytic purification of blister (anodic) copper. For every 500 tons of copper ore, there is typically one pound (0.45 kg) of tellurium. Tellurium is produced primarily in the United States, China, Belgium, Russia, Japan and Canada.
Anode slurry contains selenides and tellurides of noble metals in compositions with the formula M2Se or M2Te (M = Cu, Ag, Au). At temperatures of 500 °C, the anode sludge is heated with sodium carbonate in the presence of air. Metal ions are reduced to metals while telluride is converted to sodium tellurite - M2Te + O2 + Na2CO3 > Na2TeO3 + 2M + CO2.
Tellurites leach from mixtures with water and are usually present as hydrotellurites HTeO3– in solution. Selenites are also formed during this process, but they can be separated by adding sulfuric acid. Hydrotellurites are transformed into insoluble tellurium dioxide, while selenites remain in solution - HTeO3- + ОH– + H2SO4 > TeO2 + SO42- + 2H2O.
Reduction to metal is done either by electrolysis or by the reaction of tellurium dioxide with sulfur dioxide in sulfuric acid - TeO2 + 2 SO2 + 2H2O > Te + SO42- + 4H+.
Commercial grade tellurium is usually sold as a powder and is also available in the form of slabs, ingots, or rods.
The largest consumer of tellurium is metallurgy, where it is used in iron, copper and lead alloys. Adding tellurium to stainless steel and copper makes these metals more workable. The addition of tellurium makes it possible to obtain malleable cast iron, which, when smelted, has the advantages of gray cast iron: liquid casting, casting properties, and machinability. In lead, tellurium improves strength and durability and reduces the corrosive effect of sulfuric acid.
Semiconductors and electronics. Cadmium telluride (CdTe) is used in solar cells. Tests by the Renewable Energy Laboratory in the United States have shown that this material provides many benefits for the operation of a new generation of solar cells. Massive commercial production of solar cells using CdTe in recent years has led to a significant increase in demand for tellurium. If some of the cadmium in CdTe is replaced by zinc, the ratio (Cd,Zn) is formed, which is used in solid state X-ray sensors.
CRT (cadmium-mercury-tellurium) alloys have received absolutely exceptional importance, which have fantastic characteristics for detecting radiation from rocket launches and observing the enemy from space through atmospheric windows (cloud cover does not matter). MCT is one of the most expensive materials in the modern electronics industry.
Organotelluride such as ethane telluride, diethyl telluride, diisopropyl telluride, diethyl and methyl telluride, allyl telluride are used as the basis for organometallic growth phase epitaxy to produce multilayer semiconductor compounds.
A number of systems containing tellurium have recently discovered the existence in them of three (possibly four) phases, in which superconductivity does not disappear at a temperature slightly above the boiling point of liquid nitrogen.
Tellurium as tellurium oxide is used to create layers of rewritable optical discs, including Compact Discs ReWritable (CD-RW), ReWritable Blu-ray Digital Video Discs and ReWritable (DVD-RW).
Tellurium is used in new phase change memory chips developed by Intel. Bismuth telluride (Bi2Te3) and lead telluride are used in elements of thermoelectric devices. Lead telluride is also used in infrared sensors.
Other uses. Tellurium is used to color ceramics. The phenomenon of a strong increase in optical refraction after adding selenides and tellurides to glass is used in the production of glass fibers for telecommunications. Mixtures of selenium and tellurium are used with barium peroxide as an oxidizing agent in delay powder for electric blasting caps.
Organic tellurides are used as initiators for radical polymerization; electron-rich mono- and ditellurides have antioxidant activity. Tellurium can be used instead of sulfur or selenium to vulcanize rubber. Rubber produced in this way exhibits improved thermal resistance. Tellurites are used to identify the pathogens responsible for diphtheria.
Tellurium consumption in countries around the world is distributed as follows: China - 80-100 tons, Russia - 10 tons, USA - 50-60 tons. In total, about 400 tons of tellurium are consumed annually in the world as a whole. The table below provides approximate data on tellurium production in the world (data from the USGS, various reviews and articles on the market).

Tellurium production in the world, tons*

* US Geological Survey data

Tellurium is a rare element, and significant demand with a small volume of production determines its high price (about $200-300 per kg, depending on purity), but despite this, the range of its applications is constantly expanding.
The price of tellurium in 2000 was about US$30 per kilogram. Between 2004 and 2011, tellurium prices increased continuously, with the exception of 2009. During these years, the price of tellurium was determined by a significant increase in demand and limited supply. In 2011, the price of tellurium reached US$350 per kilogram. However, in 2012, tellurium prices fell sharply to approximately US$150 per kilogram.

The tellurium market currently faces a number of challenges. As a by-product of copper production, the tellurium market is highly dependent on trends in the main (copper) market. A decrease in copper production along with the use of new alternative technologies for producing this metal, for example, will affect the supply volumes of tellurium.
As supply volumes are in doubt, the price of the material is skyrocketing. According to many market forecasts, the price of tellurium will rise again in the next 2-3 years. It is known that there is a range of different tellurium replacement products on the market, which are already beginning to be used amid supply shortages. However, as experts note, none of the replacements has the same properties as tellurium. In addition, a potential increase in demand for tellurium could result from developments in the solar thin film sector.

Tellurium(Latin tellurium), te, chemical element of group VI of the main subgroup of Mendeleev’s periodic system; atomic number 52, atomic mass 127.60, classified as rare scattered elements. It occurs in nature as eight stable isotopes with mass numbers 120, 122-126, 128, 130, of which the most common are 128 te (31.79%) and 130 te (34.48%). Of the artificially obtained radioactive isotopes, 127 te (T 1/2 = 105) are widely used as labeled atoms days) and 129 te (T 1/2 = 33,5 days) . T. open F. Muller in 1782. The German scientist M. G. Klaproth confirmed this discovery and gave the element the name “tellurium” (from the Latin tellus, genitive telluris - Earth). The first systematic studies of the chemistry of T. were carried out in the 30s. 19th century AND I. Berzelius.

Distribution in nature . T. is one of the rarest elements; average content in the earth's crust (clark) ~1 ? 10 -7% by weight. T. is scattered in magma and the biosphere; from some hot underground springs it is precipitated along with s, ag, au, pb and other elements. Hydrothermal deposits of au and non-ferrous metals enriched in T are known; About 40 minerals of this element are associated with them (the most important are altaite, tellurobismuthite, etc. natural tellurides) . Typical admixtures of T. are found in pyrite and other sulfides. T. is extracted from polymetallic ores.

Physical and chemical properties. T. is silvery-white in color with a metallic sheen, fragile, and becomes plastic when heated. Crystallizes in the hexagonal system: A= 4.4570 A; With= 5.9290 A; density 6.25 G/ cm 3 at 20°C; t pl 450°C; t kip 990 ± 1.0 °C; specific heat capacity at 20 °C 0.204 kJ/(kg? TO); thermal conductivity at 20 °C 5.999 Tue/(m? TO) ; temperature coefficient of linear expansion 1.68? 10 -5 (20°C). T. is diamagnetic, specific magnetic susceptibility at 18 °C is 0.31? 10 -6. Brinell hardness 184.3 Mn/m 2 (18,43 kgf/mm 2) . Atomic radius 1.7 A, ionic radii: Te 2- 2.22 A, te 4+ 0.89 A, te 6+ 0.56 A.

T. - semiconductor. Band gap 0.34 ev. Under normal conditions and up to the melting point, pure T. has conductivity R-type. With a decrease in temperature in the range (-100 ° C) - (-80 ° C), a transition occurs: the conductivity of T. becomes n-type. the temperature of this transition depends on the purity of the sample, and the purer the sample, the lower it is.

Configuration of the outer electron shell of the te 5 atom s 2 5 r 4. In compounds it exhibits oxidation states –2; +4; +6, less often +2. T. - chemical analogue sulfur And Selena with more pronounced metallic properties. With oxygen, T. forms teo oxide, teo 2 dioxide, and teo 3 trioxide. teo exists above 1000 °C in the gas phase. teo 2 is obtained by combustion of te in air, has amphoteric properties, is sparingly soluble in water, but easily soluble in acidic and alkaline solutions. teo 3 is unstable and can only be obtained by decomposition of telluric acid. When heated, hydrogen reacts with hydrogen to form hydrogen telluride h 2 te, a colorless poisonous gas with a pungent, unpleasant odor. Reacts easily with halogens; it is characterized by halides of the tex 2 and tex 4 types (where X-cl and Br); tef 4, tef 6 were also obtained; All of them are highly volatile and hydrolyze with water. T. directly interacts with nonmetals (s, P), as well as with metals; it reacts at room temperature with concentrated nitric and sulfuric acids, in the latter case teso 3 is formed, which oxidizes when heated to teoso 4. Relatively weak acids te are known: hydrotelluric acid (solution of h 2 te in water), telluric acid h 2 teo 3 and telluric acid h 6 teo 6 ; their salts (respectively tellurides, tellurites and tellurates) are slightly or completely insoluble in water (with the exception of alkali metal and ammonium salts). Some organic derivatives of T. are known, for example rteh, dialkyl tellurides r 2 te - low-boiling liquids with an unpleasant odor.

Receipt. T. is extracted as a by-product during the processing of sulfide ores from intermediate products of copper, lead and zinc production, as well as from some gold ores. The main source of raw materials for the production of copper is copper electrolysis sludge, containing from 0.5 to 2% te, as well as ag, au, se, cu and other elements. The sludge is first freed from cu, se, the residue containing noble metals, te, pb, sb and other components is melted down to obtain an alloy of gold and silver. T. in this case, in the form of na 2 teo 3, passes into soda-tellurium slag, where its content reaches 20-35%. The slag is crushed, ground and leached with water. From solution, T. is deposited by electrolysis on the cathode. The resulting tellurium concentrate is treated with alkali in the presence of aluminum powder, transferring the tellurium into solution in the form of tellurides. The solution is separated from the insoluble residue, which concentrates heavy metal impurities, and is blown with air. In this case, T. (99% pure) is deposited in the elemental state. T. of increased purity is obtained by repeating telluride processing. The purest T. is obtained by a combination of methods of chemical purification, distillation, and zone melting.

Application. T. is used in semiconductor technology ; as an alloying additive - in lead alloys, cast iron and steel to improve their workability and increase mechanical characteristics; bi 2 te 3 and sb 2 te 3 are used in thermogenerators, and cdte - in solar powered and as semiconductors laser materials. T. is also used for bleaching cast iron, vulcanizing latex mixtures, and producing brown and red glasses and enamels.

T. N. Graver.

Tellurium in the body . T. is constantly present in the tissues of plants and animals. In plants growing on soils rich in T., its concentration reaches 2? 10 -4 -2.5 ? 10 -3%, in terrestrial animals - about 2? 10 -6%. In humans, the daily intake of T. from food and water is about 0.6 mg. is excreted from the body mainly in urine (over 80%), as well as in feces. Moderately toxic to plants and highly toxic to mammals (causes growth retardation, hair loss, paralysis, etc.).

Occupational poisoning of T. is possible during its smelting and other production operations. Chills, headache, weakness, rapid pulse, lack of appetite, metallic taste in the mouth, garlicky smell of exhaled air, nausea, dark coloration of the tongue, irritation of the respiratory tract, sweating, hair loss are observed. Prevention: compliance with occupational hygiene requirements, individual skin protection measures, medical examinations of workers.

Lit.: Kudryavtsev A, A.. Chemistry and technology of selenium and tellurium, 2nd ed., M.. 1968; Fundamentals of Metallurgy, vol. 4, ch. viii, M.. 1967; Filyand M. A.. Semenova E. I.. Properties of rare elements, 2nd ed., M.. 1964; Buketov E. A., Malyshev V. P.. Extraction of selenium and tellurium from copper-electrolyte sludge, A.-A.. 1969; bowen h. i. M.. trace elements in biochemistry, l.-n. y.. 1966.