Sulphides: Stannin

Diagnostic card.

Cu ₂ Fe Sn S ₄
Tsingonia tetragonal
Hardness
Specific weight 4,3-4,5
Cleavage imperfect
Broken irregular, brittle
Color gray
Color in powder gray
Glitter metal

Stannin (tin pyrites), - copper, tin and iron sulfide. Shine is metallic with dim whiteness. Opaque. Colors: from gray-steel to olive green. The line is black. The fracture is uneven. It's fragile. Cleavage is imperfect. Occurs in tin deposits. Crystals (tetragonal syngony) are very rare and small. Usually there are dense aggregates, fine-grained to draining aggregates. It is part of the tin ore. Distribution: Germany, Czech Republic, England, CIS, Tasmania, Bolivia.

The color is steel-gray with a bluish reflection. Occurs rarely in hydrothermal veins or in pegmatites, together with cassite, wolframite and sulphides. The shape of the crystals is pseudocubic, but in general the mineral is found in the form of fine-grained clusters. It is also called bolivianite, or tin pyrite.

Chemical composition. Copper (Cu) 29.5%, iron (Fe) 13.1%, tin (Sn) 27.5%, sulfur (S) 29.9%. The shape of the crystals. Pseudocubic, pseudotetrahedral. Crystal structure. It is similar to the structure of chalcopyrite. Class of symmetry. Tetragoyalno-skalenohedral - 42m Cleavage. Imperfect by (001), (110). Aggregates. Thick.

Diagnostic signs.
The mineral is soft, easily scratched by the tip of the knife. It melts, forms a white coating on the coal. Behavior in acids. It dissolves in HNO3 with the liberation of sulfur and tin dioxide.

Origin.
It occurs in tin-bearing veins with cassiterite, tetrahedrite and pyrite.

Place of Birth.
The main places where stannin is distributed are: Etta-Main in South Dakota and Seward Peninsula in Alaska (USA); Llalagua in the department of Oruro (Bolivia), Tsinovets (Zinnwald) in the Czech Republic, Zien in Tasmania, Uiel Rock in Cornwall.

Stannin. Mushiston deposit, Zeravshan Range, Tajikistan, CIS. Photo: © А.А. Evseev.

Tin (Sn) is the Latin Stannum, denoted Sn - an element with an atomic number of 50 and an atomic weight of 118.69. It is an element of the main subgroup of the fourth group, the fifth period of the periodic system of chemical elements of DI Mendeleyev. Tin under normal conditions - soft, malleable, ductile metal of silvery-white color. Possessing high softness and ductility, tin can be rolled into thin sheets, which are called tin foil or staniol.

Natural tin consists of nine stable isotopes with mass numbers 112Sn (in a mixture of 0.96% by mass), 114Sn (0.66%), 115Sn (0.35%), 116Sn (14.30%), 117Sn (7, 61%), 118Sn (24.03%), 119Sn (8.58%), 120Sn (32.85%), 122Sn (4.72%). The tenth isotope of tin 124Sn (5.94%) is slightly radioactive, is a? -radiator and has a half-life of 1016-1017 years. The isotopes of tin 117Sn and 119Sn are Mossbauer isotopes and are used in gamma resonance spectroscopy. Another 15 isotopes of tin with mass numbers 108 ... 111, 113, 121, 123, 125 ... 132 were obtained artificially. The lifetime of these isotopes is far from being the same. So, 123Sn has a half-life of 136 days, and 132Sn has only 2.2 minutes. The fiftieth element has the largest number of stable isotopes, which is due to the fact that 50 (the number of protons in tin nuclei) is a "magic number" - it makes up a filled proton shell in the nucleus and thereby increases the binding energy and stability of the nucleus.

Tin along with gold, silver, lead, copper, mercury and iron refers to elements known to mankind since ancient times. To determine the exact date of mankind's acquaintance with this metal is difficult, we can say that alloys of tin with copper - bronze were already known in the IV millennium BC. E., And pure metal in the II millennium BC. E. Of pure tin in ancient times, they made dishes and ornaments, very widely used bronze ware. It is assumed that the metal was inaccessible and very expensive, as products from it are rarely found among Roman and Greek antiquities (not stored - the object of vandalism). The Latin name is stannum, associated with the Sanskrit word meaning "persistent, lasting".

Alloys of tin with antimony and copper are used for making bearings. These alloys - tin babbits possess high antifriction properties. Other alloys of tin - with lead (solders) are widely used for soldering. In addition, tin is used as an alloying component. Tin is used to apply protective coatings on iron and other metals, as well as on metal products (tinning). Tin dioxide is a very effective abrasive material used to "fine-tune" the surface of optical glass. Tin is also used in chemical sources of current as an anode material. One of the most important industrial applications of tin is the use in tinplate (tinned iron) for making food containers. Previously, tin was often used as an artistic material in arts and crafts.

The toxicity of tin and most of its inorganic compounds is low (there is - with age). However, organic tin compounds, especially di- and trialkyl compounds, have a pronounced effect on the central nervous system. Workers of smelters with long-term exposure to tin oxide dust (so-called black tin, SnO) can develop pneumoconiosis, while workers working on the production of tin foil have cases of chronic eczema. Severe poisoning caused by eating long-prepared canned food can be associated with the formation of canned SnH4 cans (due to the action on the half-jar of cans of organic acids content).

Biological properties. Little is known about the role of tin in the body (sodium substitute Na, saline). It has been established only that the deficiency of tin is accompanied by a slowdown in growth and weight gain, a violation of the mineral composition of internal organs, and deterioration of hearing. This is possible with a small intake of tin in the body - 1 mg / day or less. The human body contains approximately 2 * 10-4% tin. The main source of tin in the human body - food, which comes in the order of 0.2-3.5 mg per day. So the smallest concentration of tin in milk and fresh vegetables (about 1 μg / g or less), but in fats (especially oily fish) the content of this metal is very high and can reach up to 130 μg / g.

Many plants are able to accumulate tin, contained in soil, water, in the exhaust gases of cars. So, lingonberries and blueberries collected in the forest, located even 25 km from the high-traffic highways, contain about 40 mg of tin per 1 kg of berries at a rate of 2 mg / kg. In food products, the fiftieth element can also fall from the packaging - packaging foil or cans. During the day, from 2 to 10 mg is considered the optimal dose of tin intake into the body. The main kind of the content of this metal in the human body is in the form of fat-soluble salts. In tissues, tin is present in concentrations from 0.5 to 4.0 μg / g. On bone there is 0.8 μg / g of tin, on the kidneys, heart and small intestine - 0.1 μg / g. Tin is excreted from the body with bile and urine.

Despite the fact that the lack of tin leads to a number of diseases, its excess is much more harmful to the human body (as sodium Na). Tin does not belong to particularly toxic metals (metallic tin is not poisonous), but it poses a danger to humans in the form of vapors and various aerosol particles, dust (stannosis, lung damage can occur with exposure to vapors or tin dust). Very toxic are some organotin compounds that, upon admission to the gastrointestinal tract, exhibit a pronounced cumulative effect, followed by the development of chromosomal aberrations in bone marrow cells (similar to Na, Na, NaCl).

With excess intake, tin accumulates in the liver, kidneys, skeleton and muscles. In working smelters with long exposure to tin oxide dust (so-called black tin) SnO pneumoconiosis can develop; Workers working in the manufacture of stanioli sometimes experience chronic eczema. It is believed that a blood content of this metal in an amount of 35 mg per 100 ml can cause functional changes in the central nervous system. Stannic tetrachloride (SnCl4 * 5H2O) at an air concentration of more than 90 mg / m3 irritatively affects the upper respiratory tract, causing coughing; Getting on the skin, tin chloride causes it to ulcer.

A strong convulsive poison is tin hydrogen (stannomethane) SnH4. Severe poisoning when eating long-prepared canned food is associated with the formation of this poison in the banks - SnH4. In acute poisoning, tin hydrogen is characterized by seizures, imbalance, in some cases a fatal outcome is possible. In many ways, the degree of poisoning depends on individual tolerance: in children and the elderly, poisoning with even a small amount of tin can be fatal.

The main manifestations of excess tin: permanent headaches; Dizziness; Visual impairment; Metallic taste in the mouth; nausea; Decreased appetite; stomach ache; Enlargement of the liver and other signs. On the basis of only these symptoms it is difficult to assume that the cause of their appearance is the air and water pollution caused by the fiftieth element or its compounds. The true signs of poisoning are intestinal colic, blue-black outline of gums, pale gray skin, anemia. Additional information can be given by a blood test, indicating an increase in the level of transaminases in the blood, a decrease in the content of zinc and copper in the body.

Prevention of poisoning with tin can serve as compliance with the rules of occupational health, monitoring the maximum allowable concentrations of compounds of the fiftieth element. The temporary allowable concentration of tin compounds in atmospheric air is 0.05 mg / m3, the maximum permissible concentration of tin in food products is 200 mg / kg, in dairy products and juices is 100 mg / kg. In addition, do not use dishes containing tin and cadmium; It is necessary to build houses away from roads and highways. Living near the highway, it is necessary to strictly prevent children and adults from getting enough magnesium, iron, calcium, zinc and vitamins.

Interesting Facts. In the course of the research, American scientists who examined the bones (age 1,600 years old) of North American Indians found that the content of tin in them is 700-1200 times less than in modern Americans and Australia. Based on these data, American historian of medicine Sibary J. Gilfillan put forward the hypothesis that Rome fell not only because of lead, but also because of tin! Known is the fact that the ancient Romans used a lot of wine, which was sweetened with grape juice (a kind of syrup). To make this syrup used tin boilers, metal penetrated into the wine, poisoning the inhabitants of the "eternal city". The way of making sweetened wine has migrated to some European countries, where monks cooked wine in the same kind of dishes. It is known that in the Middle Ages one of the most common diseases of monks who liked to drink wine was the so-called intestinal colic. Only in the 7th century it became clear that the cause of colic was tin. D

Om near busy motorways is a frequent phenomenon of modern urbanized society. Studies have shown that in residential premises located at a distance of no more than half a kilometer from the motorway, there is an excess of tin. The source of this metal is carcinogenic dust from automobile tires and exhaust gases. Accumulating in the human body, tin creates the conditions for the appearance of malignant diseases. Hence the expression "cancer house".

At present, world production of tin reaches about 3.3 million tons per year. Of these, more than a quarter million tons fall into the atmosphere in the form of exhaust gases! At the beginning of the XX century (1912), the Scott expedition that had gone to storm the South Pole was lost. People who were left without fuel were frozen in the ice. Kerosene seeped through tin-sealed tanks, stricken with a "tin plague." The phenomenon of polymorphic transformation of "white tin" into "gray" was known for a long time (in the warehouses of many armies pewter buttons on greatcoats and pots of the same material scattered into dust). However, the essence of the process was uncovered only in 1911 by G. Cohen, who found out that this phenomenon develops only in conditions of low temperatures-most often the process proceeds at -33 ^° C. And, if the infected things coexist with the whole, "infection" of a healthy Metal, just like with a real "human" plague.

"Tin plague" was an accidental "ally" of the Russian army during the fighting in 1812 - severe frosts led to the transformation of tin buttons on the uniforms of French soldiers into powder. "Tin plague" has destroyed many valuable collections of tin soldiers. So, in the storerooms of the St. Petersburg museum Alexander Suvorov, dozens of tin figurines turned into rubble - in the cellar where they were stored, heating batteries burst in the winter.

In the frosty winter of 1916, the tin party was sent by rail from the Far East to the European part of Russia. Surprisingly, those receiving the cargo did not receive silvery-white ingots, but mostly small gray powder.

One of the means of preventing "tin plague" is the addition of a stabilizer, such as bismuth, to the tin. Due to the low content of tin in the bowels of the Earth, even the poorest and most unusual tin ore are developed. For example, in 1976 the enterprise, which abbreviated name РЭП (the prospecting-operational enterprise), placed, basically on the ships has started to work. Beyond the Arctic Circle, in the Laptev Sea, in the area of ​​Vankina Bay, the REP is extracting tin from the seabed. Here, on board one of the ships, the concentrator works.

The main engineering alloy is bronze, in many languages ​​it sounds very similar. This is associated with the name of a small Italian port on the shores of the Adriatic Sea - Brindisi. It was through this port that they delivered bronze to Europe in the old days, and in ancient Rome this alloy was called "es brindisi" - copper from Brindisi.

Chemical sources of current, in the role of an anode material in which tin alloys (manganese-tin element, oxide-mercury-tin element) are used, with equal voltage (with lead accumulators) has 2.5 times greater capacity and 5 times higher energy density at Unit volume, its internal resistance is much lower.

History. Tin is one of the seven metals of antiquity (like gold, silver, lead, copper, mercury and iron), that is, one of the few metals known to man since prehistoric times. Tin along with copper were discovered before iron! The mention of tin is in the early books of the Old Testament (the Fourth Book of Moses), Homer also speaks of tin in his writings. The alloy of these two metals is bronze, most likely the very first material "artificially prepared" by man. A number of archaeological finds suggest that even for five millennia BC people were able to smelt and tin itself. So in Ancient Egypt from tin, delivered from Persia, decorations were performed (tin melted on other metals) and household items (mostly dishes), in addition, the tin went to make bronze. In Egypt, Mesopotamia and other countries of the ancient world, bronze from tin was produced already in the III millennium BC. E.

Most countries of the ancient world did not have their own rich tin mines. Therefore, the metal was imported by sea from the territory of the Iberian Peninsula, as well as from the Caucasus and Persia, and it was often confused with lead. Nearly ten centuries before the new era, the Phoenicians brought tin ore from the British Isles, then called Cassiterides. Perhaps, it is from here that the name cassiterite - the most important of the tin minerals (SnO2) - occurs. Thus, it is possible to trace the evolution of this name of metal - the ancient Greek name for tin "cassiteros" of eastern origin and is undoubtedly associated with Akkadian tin name "Ik-kasdur", Assyrian "Kazazatir" and late Babylonian "caster".

The Latin name of tin (Stannum or Stagnum) came into use in Rome during the imperial period (Julius Caesar). According to one of the assumptions, this name is associated with the Sanskrit "stha" (stand, stand firm) or "sthavan" (firmly, steadfastly). At the same time, the word "stagnum" in Latin means "standing water", "pond", "lake" and even "sea" (in a figurative sense). As mentioned earlier, tin was often considered a modification of lead and in the Middle Ages it was called white (Plumbum album) or brilliant (Plumbum candidum) lead unlike ordinary black lead (Plumbum nigrum). The English "tin", the German "zinn" and the French tin "etain" originate in the ancient Germanic language and originate from the word "zein" - a stick or plate.

There are at least two theories about the origin of the Russian word "tin". According to the first - the Indo-Germanic theory of the origin of languages ​​- "tin" and consonant with them, Lithuanian "alavas", "alvas" and Prussian "alwis" (lead) originated from the Latin "album", which appears in the medieval title of tin Plumbum album. By the same principle, the word Cuprum is derived from Aes cyprium. According to another version (more plausible) Russian "tin" and Polish "olow" (lead) have a functional origin. The fact is that the Slavic peoples used a drunken drink (like beer or brags) from barley and vita, this drink was called "halo" or "ol."

It is possible that the halves were stored in tin containers. Either like the Romans who stood and stored wine in lead vessels, the Slavs kept their intoxicating drink in lead jugs, and in fact in the Slavic countries, lead was called tin. Also, the word tin can be associated with the name of another liquid body - oil (oleum). From the linguistic point of view, the word "tin" is a suffixal formation from the root ol- (compare the Old High German elo - "yellow", Latin albus - "white"), it turns out that the metal is named in color. In the dictionary of Sreznevsky are related words tin - tin (lead lamp) and tin (a vessel of tin).

Being in nature. Tin is a fairly rare and scattered element, in terms of its abundance in the earth's crust, tin is forty-seventh. The average content of tin in the earth's crust is, according to various data, from 2 * 10-4 to 8 * 10-3% by mass. The fact is that tin is an element that is mainly characteristic of the upper layers of the earth's crust, its content in the lithosphere is 2.5 * 10-4% (by mass), in acidic igneous rocks 3 * 10-4%, and in deeper Basic 1.5 * 10-4%; Even less tin contains the earth's mantle.

The fiftieth element exhibits amphoteric properties (both acidic and basic). In many respects it is this quality of tin that influences its spread in nature - this dualism reveals the lithophilic, chalcophile and siderophilic properties of this metal. The fiftieth element of the periodic table resembles quartz in properties, as a result of which a close tin bond is known in the form of oxide (cassiterite) with acid granitoids (lithophilicity), often enriched with tin, up to the formation of independent quartz-cassiterite veins. With regard to the alkali properties of tin, they are manifested in the formation of a very diverse sulphide compounds (chalcophilicity), up to the formation of native tin and various intermetallic compounds known in ultrabasic rocks (siderophily).

The main concentrations of tin are associated with magmatic processes (a group of intrusive and effusive magmatic rocks: "tiniferous granites", traps, pegmatites, picrites of the Siberian platform, hyperbasites and gabbroids of Kamchatka, kimberlites of Yakutia, lamproites of Aldan, granitoids of Primorye, Far East, Tien Shan). And also with hydrothermal processes (a group of metasomatically and hydrothermally altered rocks: copper-nickel ores of the Siberian platform, gold ore objects of the Urals, the Caucasus, Uzbekistan). In addition, tin occurs in a number of other geological formations, for example, in sedimentary rocks of various origins or in modern sources of ore formation-the pelagic sediments of the Pacific Ocean, the Uzon hydrothermal system in Kamchatka.

One way or another, of the 24 known tin minerals, 23 formed at high temperatures and pressures. The industrially important tin mineral is cassiterite (tin stone) SnO2, which is an oxide compound of tin with oxygen. Cassiterite contains up to 78.8% tin, it forms separate inclusions, grains, solid massive accumulations in which the mineral grains reach a size of 3 - 4 mm or more. The main deposits of cassiterite in Russia are located in Primorye, Transbaikalia, and Yakutia. In addition, the rich reserves of this mineral are located in Thailand, China, Malaysia, Nigeria, Bolivia, Indonesia and other countries.

Industrial concentrations in ores form a bed (tin pyrites) - a mineral from the class of sulfides with a general formula of the form Cu2FeSnS4. The mineral contains 29.58% copper, 12.99% iron, 27.5% tin and 29.8% sulfur, as well as impurities of zinc, antimony, cadmium, lead and silver. Stanin is a widespread mineral in tin deposits in Russia, but it is often not used because of the difficulty of enriching it and extracting tin from it. In addition to the bedplate, there are other sulfide compounds of tin - Berndite SnS2, Francate Pb5Sn3Sb2S14, Hertzenbergite SnS, Tillite PbSnS2 and Kesterite Cu2ZnSnS4. More complex sulfide compounds of tin with lead, silver, and copper, which are of mainly mineralogical importance, are also found. Some industrially important value can have calcium tin borate - Nordenscheldin (43.5% tin).

A minor place is occupied by hydroxide compounds of tin, they can be considered as salts of polyol-acid acids. These include the following minerals: succulite Ta2Sn2O, a solid solution of tin in magnetite of the form Fe2SnO4 or Fe3SnO3, varlamovite is the product of oxidation of the bed. There are also known hydrated oxidation products - hydromartite 3SnOxH2O; Mushistonite (Cu, Zn, Fe) Sn (OH) 6; Copper hydrostannet CuSn (OH) 6. Of the other oxide compounds, spinels, for example, mineral nigerite Sn2Fe4Al16O32, are also known.

A large group of tin silicates is known, represented by the CaSn [SiO5] small -ite; Ba (Sn, Ti) Si3O9, with Ca2Sn2Si6O18x4H2O sink. Malayite forms even industrial clusters. In the biosphere, tin migrates weakly, in seawater its content is only 3 * 10-7%. In uncontaminated surface waters, tin is contained in submicrogram concentrations. In underground waters, its concentration reaches micrograms per dm, increasing in the area of ​​tin deposits.

The world's largest deposits of tin are located in Southeast Asia (China, Indonesia, Thailand, Malaysia). There are large deposits of tin in South America (Brazil, Peru, Bolivia) and Australia. Rich tin deposits of Russia are located in the Chukotka Autonomous District, Yakutia, Primorsky Krai, Khabarovsk Krai and other areas.

Application. One of the main applications of tin is due to the fact that this metal is a relatively safe, non-toxic, corrosion-resistant coating, both in pure form and in alloys with other metals. For these reasons, the main industrial application of the fiftieth element is the production of tinplate (tinned iron) for the production of food containers, which is used in the canning industry. For these needs, about 33% of all extracted tin is consumed. An even greater amount of this metal (60%) is consumed in metallurgy for the creation of various alloys, the most important of which is bronze (an alloy of tin with copper). This alloy is one of the indispensable materials in the field of mechanical engineering.

Technique also needs other tin alloys, quite often they are used as antifriction materials, which allow increasing the life of machines and mechanisms. Of all antifriction alloys, the best properties are possessed by tin babbits (bearing alloys of tin with antimony), which contain up to 90% tin. Solders - tin alloys (with zinc or lead) with which it is possible to connect metal parts. Soft and low-melting lead-tin solders well wet the surface of most metals, have a high plasticity and fatigue resistance, and non-toxic zinc-tin solders are excellent for tinning dishes and other household products. Unfortunately, the field of application of tin solders is limited because of insufficient mechanical strength.

Another known alloy - pewter - is used to make dishes (dangerous). Tin is also included in the typographic alloy of the gart (black, newspapers, media). Finally, alloys based on tin are necessary in electrical engineering. The most important material for electrocondensers is the staniol - thin tin foil, in which the proportion of other elements is less than 5%. In addition to capacitors, the stanioles are used for the production of organ pipes, dishes, and artifacts. Tin is the main alloying component in the preparation of structural alloys of titanium. Intermetallic tin compounds have high melting points, for example, zirconium stannide Zr3Sn2 melts only at a temperature of 1 985 ^° C, with the alloy being resistant to oxidation when heated in air.

Another example of the refractoriness of a tin alloy is the Mg2Sn compound with a melting point of 778 ^° C. Magnesium itself melts at 651 ^° C-not the highest melting point, tin melts at an even lower temperature of 232 ^° C. The "secret" is the nature of the alloy, More precisely in the chemical bond between the substances that form it. Of the nonmetallic compounds of tin, the most important are the chlorides. For example, SnCl tetrachloride is used as a solvent, since it is capable of dissolving iodine, phosphorus, sulfur and many organic substances.

Textile production uses SnCl2 tin dichloride, which is used for mordant dyeing and as a reducing agent in the synthesis of organic dyes. The same qualities are possessed by another nonmetallic tin compound - sodium stannate Na2SnO3, which also has an additional function - weighting of silk. A mixture of tin salts - "yellow composition" - was once used as a dye for wool. Tin disulfide SnS2 (golden yellow crystals) is used in the composition of paints imitating gilding ("gold leaf"). Tin oxides, such as SnO2, are very limited, SnO2 is a very effective abrasive used to "fine-tune" the surface of optical glass, and SnO2 is also used in the production of white glazes. Tin oxide SnO is used to produce ruby ​​glass. Barium stannate BaSnO3 has found its application in radio engineering as an excellent dielectric.

No less widespread use in various areas has been found by organotin compounds. Due to the fact that many of them are toxic, they are widely used in the agricultural industry as insecticides (poisons). For example, on the basis of triphenyltin acetate (C6H5) 3SnOOCCH3, an effective preparation for fighting fungal diseases of such important crops as potatoes and sugar beet was created, and this substance stimulates the growth and development of plants.

In veterinary medicine, preparations based on dibutyltin dilaurinate (C4H9) 2Sn (OCOC11H23) 2 are used to combat helminths, in addition, dibutyltin dilaurate, a stabilizer of PVC, a catalyst in the production of polyurethane foams. Preparations, fighting with parasitic organisms, use not only agriculture on the basis of tin. Tributyltin hydroxide (C4H9) 3SnOH is used in the pulp and paper industry to combat fungi that develop in processing apparatus. Thanks to this connection, the productivity of the equipment is greatly increased.

Production. Industrial production of tin is expedient if its content in placers is 0.01%, in ores 0.1%. Tin in ores is often accompanied by tungsten, zirconium, cesium, rubidium, rare earth elements, tantalum, niobium and other valuable metals. Tin ore rarely contains more than 1% tin. Interestingly, in the past people had richer tin ore than we did. The metal was smelted from ores directly on the surface of the earth (looking for turquoise). Enrichment took place in a natural way - due to weathering and washing away. Unfortunately, up to now, such little ore has not survived, so in modern conditions the process of obtaining tin is multistage and laborious, and it begins with the enrichment of ores and placers.

Methods of enriching tin ore are very diverse (GOKi). Apply, in particular, the gravitational method, based on the difference in the density of the main and associated minerals (GOK). At the same time, the ore-bearing rock is crushed to an average particle size of ~ 10 mm in industrial crushing machines (mills), after which cassiterite (tin mineral) is separated from the waste rock by a vibrational gravitational method at the beneficiation tables due to its relatively high density and mass. In addition, the flotation method of ore dressing (cleaning) and / or magnetic separation method is used.

In cases where the tin ore contains valuable metals (tungsten, tantalum and others), they are attempted to separate during enrichment. The composition of the obtained tin concentrate depends on the raw materials being processed, and also on the way in which this concentrate was obtained. The content of tin in it varies from 40 to 70%. After the enrichment processes, the concentrate is sent to the roasting furnace (at 600 ... 700 ^o C) in oxygen to remove volatile sulfur and arsenic impurities. Most of the iron, antimony, bismuth and some other metals are leached with hydrochloric acid HCl after firing. In the presence of impurities of wolframite (Fe, Mn) WO4 and scheelite CaWO4, the concentrate is treated with HCl, the resulting WO3 * H2O is recovered due to NH4OH. The fusion of coal concentrates in electric or flame furnaces produces black tin (94-98% Sn) containing impurities of copper, lead, iron, arsenic, antimony, bismuth.

When discharged from furnaces, the black tin is filtered through coke or centrifuged at a temperature of 500-600 ^° C., thereby separating the bulk of the iron. From a physico-chemical point of view, this process is analogous to a domain process: carbon "takes" oxygen from tin, and fluxes convert silicon dioxide into light, slag-like metals. The remainder of iron and copper is removed by adding elemental sulfur to the liquid metal, with the impurities emerging as solid sulphides that are removed from the surface of the tin. From arsenic and antimony, tin is purified similarly - by adding aluminum, from lead - with the help of SnCl2. Sometimes bismuth and lead are evaporated in a vacuum. To obtain a metal grades (96.5 ... 99.9% Sn), use fire or less often electrolytic refining. Necessary semiconductor industry tin purity of nearly six nines - 99.99985% Sn - is obtained mainly by zone melting method.

The share of "secondary" tin in the industrialized countries is about a third of total production. In our country there are about one hundred industrial plants for the regeneration of tin. In the processing mainly waste of tin, used in the food industry (cans). Most often, the sheet is treated with gaseous chlorine. Iron in the absence of moisture does not react with it. Tin combines with chlorine very easily. Forms a smoking liquid - SnCl4 chlorine tin, which is used in the chemical and textile industries or sent to an electrolyzer to obtain therefrom the metal tin therefrom.

Physical properties. In the free state, under normal conditions, tin is a shiny silvery-white soft (Brinell hardness 38.3-41.2 MN / m2 or 3.9-4.2 kgf / mm2) ductile metal (can be rolled into a very thin foil - Staniol) with a low melting point (231.9 ^° C) due to which the metal is easily melted from the ores, however, the tin has a very high boiling point (2,270 ^° C). Tin is a fairly heavy metal with a density of 7.31 g / cm3, which is less than that of lead (density 11.34 g / cm3) and even more so in precious metals (gold density 19.3 g / cm3, platinum 21.5 g / Cm3, in silver 10.5 g / cm3), but comparable with iron (7.87 g / cm3). Moreover, tin is much heavier than aluminum (density 2.70 g / cm3).

Like many other elements, tin is polymorphic, that is, it has several allotropic modifications (in Greek, "allotropy" means "another property", "another turn"). Under normal conditions, it exists in the form of a beta modification, the so-called white tin, which is stable at temperatures above 13.2 ^° C. White tin is the same soft plastic shiny metal of silvery white color with a tetragonal unit cell with parameters a = 0.5831, c = 0.3181 nm. The coordination environment of each tin atom in it is an octahedron.

Tin has a low mechanical strength at room temperature (tensile strength of 16.6 MN / m2 or 1.7 kg / mm2, an elongation of 80-90%), that is, in the beta phase (you can bend the tin stick, We hear a characteristic crack caused by the friction of the individual crystals against each other) and is therefore rarely used. However, it easily forms alloys with most other ferrous and non-ferrous metals. When cooling, especially when it is cold outside, white tin passes into the? -modification - gray tin, which has a diamond structure (cubic crystal lattice with the parameter a = 0.6491 nm).

In gray tin, the coordination polyhedron of each atom is a tetrahedron whose coordination number is 4. The phase transition begins at a temperature below 13.2 ^° C, a gradual rearrangement takes place in the crystal lattice of the tin ingot, in which the white tin turns into a powdery gray (? -tin) The lower the temperature, the higher the rate of this transformation. At? 33 ^o C, the conversion rate becomes maximum, the surface of the tin ingot is covered with cracks, and the metal turns into a powder.

Surprisingly, the contact of gray tin and white leads to "contamination" of the latter (the catalyst is arsenic). The totality of these phenomena is called "tin plague." The phase transition of? -tin to? -tin is accompanied by an increase in the specific volume by 25.6%, which leads to the dispersion of tin into powder. Another peculiarity of the phase shift is the change in the crystal lattice-the gray tin crystals of the cubic configuration; The dimensions of their elementary cells are larger (the length of the rib is 6.49?). Therefore, the density of gray tin is noticeably less than that of white: 5.76 and 7.3 g / cm3, respectively. Because of the significant difference in the structures of the two modifications of tin, their electrophysical properties also differ. ? -tin is a metal, while? -tin refers to the number of semiconductors. Below 3.72 K, alpha-tin passes into the superconducting state.

In addition to white and gray tin, one more allotropic modification of the fiftieth element was found-tin, stable at a temperature above 161 ^o C. In this phase, tin is a very brittle material. As a typical metal, as the temperature rises, the tin becomes more plastic, but only at a temperature below 161 ^° C. Then, the tin completely loses its plasticity, it turns into gamma-tin, the metal becomes so brittle that it can be crushed into powder.

The temperature coefficient of linear expansion of tin at a temperature range from 0 to 100 ^o C is 23 * 10-6. The specific heat at 0 ^° C 0.225 kJ / (kg * K), that is, 0.0536 cal / (g * ^o C), the thermal conductivity at the same temperature is 65.8 W / (m * K.), that is, 0.157 cal / (Cm * sec * ^o С). The specific electric resistance of tin at 20 ^o C is 0.115 * 10-6 ohm or 11.5 * 10-6 ohm-cm.

Chemical properties. At room temperature, tin, like the neighbor in the group - germanium, does not interact with air and water. The fact is that in the air the fiftieth element is covered with a thin oxide film, which has a protective effect. Therefore, in conditions of not severe (anti-ulcer) corrosion attack, tin is a chemically resistant metal. Noticeable oxidation of tin in air begins at temperatures above 150 ^° C, thus forming tin dioxide:

Sn + O2 -> SnO2 (cassiterite - tin stone)

Dioxide (or dioxide) of tin is found in nature (cassiterite), and can also be obtained artificially by burning the metal in air or by oxidation with nitric acid, followed by calcination of the product obtained. On the materials: http://www.i-think.ru

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Catalog of minerals and semi-precious stones of the world by groups

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