Chemistry

Gallium #31

subgroup of gallium. The content of each of the members of this subgroup in the earth's crust in the series gallium (4-10~4%) - indium (2-10~6) - thallium (8-10-7) is decreasing. All three "elements are extremely dispersed, and being in the form of certain minerals is not typical for them. On the contrary, minor impurities of their compounds contain ores of many metals. Ga, In and Ti are obtained from waste during the processing of such ores.
In the free state, gallium, indium and thallium are silver-white metals. Their most important constants are compared below:
Ga InTl

Physical properties of gallium

Density, g/cjH3 5.9 7.3 11.9
Melting point, °С. . . 30 157 304
Boiling point, °С... . 2200 2020 1475
Electrical conductivity (Hg = 1) . . 2 11 6

By hardness gallium close to lead, In and Ti - even softer 6-13.
Gallium and indium do not change in dry air, and thallium is covered with a gray film of oxide. When heated, all three elements combine vigorously with oxygen and sulfur. They interact with chlorine and bromine already at ordinary temperatures, with iodine only when heated. Located in a series of voltages near iron, Ga, In and Ti are soluble in acids.14 '15
The usual valency of gallium and indium is three. Thallium gives derivatives in which it is tri- and monovalent. eighteen
The oxides of gallium and its analogues - white Ga 2 O 3, yellow 1p203 and brown T1203 - are insoluble in water - the corresponding hydroxides E (OH) 3 (which can be obtained from salts) are gelatinous sediments, practically insoluble in water, but soluble in acids. White hydroxides of Ga and In are also soluble in solutions of strong alkalis with the formation of gallates and indates similar to aluminates. They therefore have an amphoteric character, and the acidic properties are less pronounced in 1p(OH) 3, and stronger in Ga(OH) 3 than in Al(OH) 3 . So, in addition to strong alkalis, Ga (OH) 3 is soluble in strong solutions of NH 4 OH. On the contrary, red-brown Ti(OH) 3 does not dissolve in alkalis.
The Ga"" and In" ions are colorless, the Ti" ion has a yellowish color. The salts of most acids produced from them are highly soluble in water, but highly hydrolyzed; Of the soluble salts of weak acids, many undergo almost complete hydrolysis. While derivatives of the lower valences Ga and In are not typical for them, for thallium the most characteristic are precisely those compounds in which it is monovalent. Therefore, T13+ salts have markedly pronounced oxidizing properties.

Thallium oxide (T120) is formed as a result of the interaction of elements at high temperatures. It is a black hygroscopic powder. With water, thallium oxide forms yellow nitrous oxide (T10H), which, when heated, easily splits off water and goes back to T120.
Thallium oxide hydrate is highly soluble in water and is a strong base. The salts it forms are mostly colorless and
crystallize without water. Chloride, bromide and iodide are almost insoluble, but some other salts are soluble in water. Arbitrary TiOH and weak acids due to hydrolysis give an alkaline reaction in solution. Under the action of strong oxidizing agents (for example, chlorine water), monovalent thallium is oxidized to trivalent.57-66
In terms of the chemical properties of the elements and their compounds, the gallium subgroup is in many ways similar to the germanium subgroup. So, for Ge and Ga, the higher valency is more stable, for Pb and T1 it is lower, the chemical nature of the hydroxides in the series Ge-Sn-Pb and Ga-In-Ti changes of the same type.Sometimes more subtle "features of similarity appear further, for example, the low solubility of halide (Cl, Br, I) salts of both Pbn and Ti. For all that, there are significant differences between the elements of both subgroups (partly due to their different valence): the acidic nature of the hydroxides of Ga and its analogues is much less pronounced than that of the corresponding elements of the germanium subgroup, in contrast to PbF 2, thallium fluoride is highly soluble, etc.

Gallium Supplement

1. All three members of the subgroup under consideration were discovered using a spectroscope: 1 thallium - in 1861, indium - in 1863 and gallium - in 1875. The last of these elements was predicted and described by D. I. Mendeleev 4 years before its discovery (VI § 1). Natural gallium is composed of isotopes with mass numbers 69 (60.2%) and 71 (39.8); indium-113 (4.3) and 115 (95.7); thallium - 203 (29.5) and 205 (70.5%).
2. In the ground state, the atoms of the elements of the gallium subgroup have the structure of outer electron shells 4s2 34p (Ga), 5s25p (In), 6s26p (Tl) and are univalent, i ) kcal/g-atom. Successive ionization energies are 6.00; 20.51; 30.70 for Ga; 5.785; 18.86; 28.03 for In: 6.106; 20.42; 29.8 eV for T1. The affinity of a thallium atom for an electron is estimated at 12 kcal/g-atom.
3. For gallium, the rare mineral gallite (CuGaS 2) is known. Traces of this element are constantly found in zinc ores. Significantly large amounts of it: E (up to 1.5%) were found in the ashes of some hard coals. However, the main raw material for the industrial production of gallium is bauxite, usually containing minor impurities (up to 0.1%). It is extracted by electrolysis from alkaline liquids, which are an intermediate product of the processing of natural bauxite into commercial alumina. The size of the annual world production of gallium is still estimated at a few tons, but can be significantly increased.
4. Indium is obtained mainly as a by-product in the complex processing of sulfur ores Zn, Pb and Cu. Its annual world production is several tens of tons.
5. Thallium is concentrated mainly in pyrite (FeS2). Therefore, sulfuric acid production sludge is a good raw material for obtaining this element. The annual world production of thallium is less than that of India, but is also in the tens of tons.
6. To isolate Ga, In, and T1 in the free state, either the electrolysis of solutions of their salts or the incandescence of oxides in a hydrogen flow is used. The heats of melting and evaporation of metals have the following values: 1.3 and 61 (Ga), 0.8 and 54 (In), 1.0 and 39 kcal/g-atom (T1). The heats of their sublimation (at 25°C) are 65 (Ga), 57 (In), and 43 kcal/g-atom (T1). In pairs, all three elements are composed almost exclusively of monatomic molecules.
7. The crystal lattice of gallium is formed not by individual atoms (as is usual for metals), but by diatomic molecules (rf = 2.48A). It is thus an interesting case of the coexistence of molecular and metallic structures (III § 8). Ga2 molecules are also preserved in liquid gallium, whose density (6.1 g/cm) is greater than that of a solid metal (an analogy with water and bismuth). An increase in pressure is accompanied by a decrease in the melting point of gallium. At high pressures, in addition to the usual modification (Gal), the existence of two other forms of it has been established. Triple points (with a liquid phase) lie for Gal - Gall at 12 thousand atm and 3 °C, and for Gall - Galll ​​- at 30 thousand atm and 45 °C.
8. Gallium is very prone to hypothermia, and it was possible to keep it in a liquid state down to -40 ° C. Repeated repetition of rapid crystallization of a supercooled melt can serve as a method for purifying gallium. In a very pure state (99.999%), it was also obtained by electrolytic refining, as well as by hydrogen reduction of carefully purified GaCl3. The high boiling point and fairly uniform expansion on heating make gallium a valuable material for filling high-temperature thermometers. Despite its outward resemblance to mercury, the mutual solubility of both metals is relatively low (in the range from 10 to 95 °C, it varies from 2.4 to 6.1 atomic percent for Ga in Hg and from 1.3 to 3.8 atomic percent for Hg to Ga). Unlike mercury, liquid gallium does not dissolve alkali metals and well wets many non-metallic surfaces. In particular, this applies to glass, by applying gallium to which mirrors can be obtained that strongly reflect light (however, there is an indication that very pure gallium, which does not contain indium impurities, does not wet glass). The deposition of gallium on a plastic base is sometimes used to quickly obtain radio circuits. An alloy of 88% Ga and 12% Sn melts at 15°C, and some other alloys containing gallium (eg 61.5% Bi, 37.2% Sn and 1.3% Ga) have been proposed for dental fillings. They do not change their volume with temperature and hold well. Gallium can also be used as a valve seal in vacuum technology. However, it should be borne in mind that at high temperatures it is aggressive towards both glass and many metals.
9. In connection with the possibility of expanding the production of gallium, the problem of assimilation (i.e., mastering by practice) of this element and its compounds becomes urgent, which requires research to find areas for their rational use. There is a review article and monographs on gallium.
10. The compressibility of indium is slightly higher than that of aluminum (at 10 thousand atm, the volume is 0.84 of the original). With increasing pressure, its electrical resistance decreases (up to 0.5 of the initial value at 70,000 atm) and the melting point increases (up to 400°C at 65,000 atm). Sticks of metallic indium crunch when bent, like pewter. On paper, it leaves a dark line. An important use of indium is associated with the manufacture of germanium AC rectifiers (X § 6 add. 15). Due to its fusibility, it can play the role of a lubricant in bearings.
11. The introduction of a small amount of indium into copper alloys greatly increases their resistance to sea water, and the addition of indium to silver enhances its brilliance and prevents tarnishing in air. The addition of indium gives alloys for dental fillings increased strength. The electrolytic indium coating of other metals well protects them from corrosion. An alloy of indium with tin (1:1 by mass) solders glass well with glass or metal, and an alloy of 24% In and 76% Ga melts at 16°C. An alloy melting at 47 ° C 18.1% In with 41.0 - Bi, 22.1 - Pb, 10.6 - Sn and 8.2 - Cd finds medical use in complex bone fractures (instead of gypsum). There is a monograph on the chemistry of indium
12. The compressibility of thallium is approximately the same as indium, but two allotropic modifications (hexagonal and cubic) are known for it, the transition point between which lies at 235 ° C. Under high pressure, another one arises. The triple point of all three forms lies at 37 thousand atm and 110°C. This pressure corresponds to an abrupt decrease by about 1.5 times in the electrical resistance of the metal (which at 70 thousand atm is about 0.3 of the usual one). Under a pressure of 90,000 atm, the third form of thallium melts at 650°C.
13. Thallium is used mainly for the manufacture of alloys with tin and lead, which have high acid resistance. In particular, the alloy composition of 70% Pb, 20% Sn and 10% T1 well withstands the action of mixtures of sulfuric, hydrochloric and nitric acids. There is a monograph on thallium.
14. With respect to water, gallium and compact indium are stable, while thallium in the presence of air is slowly destroyed by it from the surface. Gallium reacts with nitric acid only slowly, while thallium reacts very vigorously. On the contrary, sulfuric, and especially hydrochloric, acid easily dissolves Ga and In, while T1 interacts with them much more slowly (due to the formation of a protective film of sparingly soluble salts on the surface). Solutions of strong alkalis easily dissolve gallium, act only slowly on indium and do not react with thallium. Gallium also noticeably dissolves in NH4OH. Volatile compounds of all three elements color a colorless flame in characteristic colors: Ga - in dark purple (L. \u003d 4171 A), almost imperceptible to the eye, In - in dark blue (L, \u003d 4511 A), T1 - in emerald green (A, \u003d \u003d 5351 A).
15. Gallium and indium do not appear to be poisonous. On the contrary, thallium is highly toxic, and in the nature of the action it is similar to Pb and As. It affects the nervous system, digestive tract and kidneys. Symptoms of acute poisoning do not appear immediately, but after 12-20 hours. With slowly developing chronic poisoning (including through the skin), excitation and sleep disturbance are observed primarily. In medicine, thallium preparations are used to remove hair (for lichen, etc.). Thallium salts have found application in luminous compositions as substances that increase the duration of the glow. They also proved to be a good remedy for mice and rats.
16. In the voltage series, gallium is located between Zn and Fe, while indium and thallium are between Fe and Sn. The Ga and In transitions according to the E + 3 + Ze = E scheme correspond to normal potentials: -0.56 and -0.33 V (in an acidic environment) or -1.2 and -1.0 V (in an alkaline environment). Thallium is converted by acids into a monovalent state (normal potential -0.34 V). The transition T1 + 3 + 2e \u003d T1 + is characterized by a normal potential of + 1.28 V in an acidic environment or + 0.02 V - in an alkaline one.
17. The heats of formation of E203 oxides of gallium and its analogues decrease along the series 260 (Ga), 221 (In), and 93 kcal/mol (T1). When heated in air, gallium is practically oxidized only to GaO. Therefore, Ga203 is usually obtained by dehydration of Ga (OH) h. Indium, when heated in air, forms In2O3, and thallium forms a mixture of T12O3 and T120, with the higher the content of the higher oxide, the lower the temperature. Up to T1203, thallium can be oxidized by the action of ozone.
18. The solubility of E2O3 oxides in acids increases along the series Ga - In - Tl. In the same series, the strength of the bond between the element and oxygen decreases: Ga2O3 melts at 1795°C without decomposition, ln203 transforms into ln304 only above 850°C, and finely divided T1203 begins to split off oxygen already at about 90°C. However, much higher temperatures are required for complete conversion of T1203 to T120. Under an excess pressure of oxygen, In203 melts at 1910°C, while T1203 melts at 716°C.
19. The heats of hydration of oxides according to the scheme E2O3 + ZH20 = 2E(OH)3 are +22 kcal (Ga), +1 (In) and -45 (T1). In accordance with this, the ease of splitting off water by hydroxides increases from Ga to T1: if Ga(OH)3 is completely dehydrated only upon calcination, then T1(OH)3 passes into T1203 even when standing under the liquid from which it was isolated.
20. When acidic solutions of gallium salts are neutralized, its hydroxide precipitates approximately in the pH range = 3-4. Freshly precipitated Ga(OH)3 is highly soluble in strong ammonia solutions, but as it ages, the solubility decreases more and more. Its isoelectric point lies at pH = 6.8, and PR = 2 10~37. For lp(OH)3, PR = 1 10-31 was found, and for T1(OH)3 - 1 10~45.
21. The following values ​​were determined for the second and third dissociation constants of Ga(OH)3 according to the acidic and basic types:

H3Ga03 /C2 = 5-10_I K3 = 2-10-12
Ga(OH)3 K2“2. Yu-P / Nz \u003d 4 -10 12
Thus, gallium hydroxide is a case of an electrolyte very close to ideal amphotericity.

1. The difference in the acidic properties of gallium hydroxides and its analogues is clearly manifested when they interact with solutions of strong alkalis (NaOH, KOH). Gallium hydroxide readily dissolves to form type M gallates, which are stable both in solution and in the solid state. When heated, they easily lose water (Na salt - at 120, K salt - at 137 ° C) and pass into the corresponding anhydrous salts of the MGa02 type. Divalent metals (Ca, Sr) obtained from solutions of gallates are characterized by another type - M3 ■ 2H20, which are also almost insoluble. They are completely hydrolyzed by water.
   Thallium hydroxide is easily peptized by strong alkalis (with the formation of a negative sol), but is insoluble in them and does not give tallates. Dry way (by fusion of oxides with the corresponding carbonates) derivatives of the ME02 type were obtained for all three elements of the gallium subgroup. However, in the case of thallium, they turned out to be mixtures of oxides.
   1. The effective radii of the Ga3+, In3*, and T13* ions are 0.62, 0.92, and 1.05 A, respectively. In an aqueous medium, they are apparently directly surrounded by six water molecules. Such hydrated ions are somewhat dissociated according to the scheme E(OH2)a T * E (OH2)5 OH + H, and their dissociation constants are estimated at 3 ■ 10-3°(Ga) and 2 10-4 (In).
   2. The halide salts of Ga3+, In3* and T13*' are generally similar to the corresponding salts of A13*. In addition to fluorides, they are relatively fusible and readily soluble not only in water, but also in a number of organic solvents. Of these, only yellow Gal3 are painted

   The chemical element gallium is practically not found in nature in free form. It exists in impurities of minerals, from which it is difficult to separate it. Gallium is considered a rare substance, some of its properties are not fully understood. However, it is used in medicine and electronics. What is this element? What properties does it have?

   Gallium - metal or non-metal?

   The element belongs to the thirteenth group of the fourth period. It is named after the historical region - Gaul, of which France was a part - the birthplace of the discoverer of the element. The symbol Ga is used to denote it.

   Gallium is included in the group of light metals along with aluminum, indium, germanium, tin, antimony and other elements. As a simple substance, it is fragile and soft, has a silvery-white color with a slight bluish tint.

   Discovery history

   Mendeleev "predicted" gallium, leaving a place for it in the third group of the periodic table (according to the outdated system). He roughly named its atomic mass and even predicted that the element would be discovered spectroscopically.

   A few years later, the metal was discovered by the Frenchman Paul Emile Lecoq. In August 1875, a scientist was studying the spectrum from a deposit in the Pyrenees and noticed new purple lines. The element was named gallium. Its content in the mineral was extremely small and Lecoq managed to isolate only 0.1 grams. The discovery of the metal was one of the confirmations of the correctness of Mendeleev's prediction.

   

   Physical Properties

   Gallium metal is very ductile and fusible. At low temperatures, it is in a solid state. To turn it into a liquid, a temperature of 29.76 degrees Celsius or 302.93 Calvin is sufficient. You can melt it by holding it in your hand or dropping it into a hot liquid. Too high temperatures make it very aggressive: at 500 degrees Celsius and above, it is able to corrode other metals.

   The crystal lattice of gallium is formed by diatomic molecules. They are very stable, but weakly interconnected. It takes very little energy to break their bond, so gallium becomes liquid without difficulty. It is five times more fusible than indium.

   In the liquid state, the metal is denser and heavier than in the solid state. In addition, it conducts electricity better. Under normal conditions, its density is 5.91 g/cm³. The metal boils at -2230 degrees Celsius. When solidified, it expands by approximately 3.2%.

   

   Chemical properties

   In many chemical properties, gallium is similar to aluminum, but exhibits less activity and reactions with it are slower. It does not react with air, instantly forming an oxide film that prevents its oxidation. It does not react to hydrogen, boron, silicon, nitrogen and carbon.

   The metal interacts well with almost any halogen. It reacts with iodine only when heated; it reacts with chlorine and bromine even at room temperature. In hot water, it begins to displace hydrogen, forms salts with mineral acids, and also releases hydrogen.

   With other metals, gallium is able to form amalgams. If liquid gallium is dropped onto a solid piece of aluminum, it will begin to penetrate into it. Invading the crystal lattice of aluminum, the liquid substance will make it brittle. Within a few days, a solid metal bar can be crushed by hand, without much effort.

   Application

   In medicine, gallium metal is used to fight tumors and hypercalcemia, it is also suitable for radioisotope diagnosis of bone cancer. However, preparations containing the substance may cause side effects such as nausea and vomiting.

   Gallium metal is also used in microwave electronics. It is used for the manufacture of semiconductors and LEDs, as a piezo material. Metal adhesives are obtained from an alloy of gallium with scandium or nickel. In an alloy with plutonium, it plays the role of a stabilizer and is used in nuclear bombs.

   Glasses with this metal have a high refractive index, and its oxide Ga 2 O 3 allows the glass to transmit infrared rays. Pure gallium can be used to make simple mirrors, as it reflects light well.

   

   Distribution and deposits of gallium

   Where to get gallium? Metal can be easily ordered online. Its cost ranges from 115 to 360 dollars per kilogram. The metal is considered rare, it is very dispersed in the earth's crust and practically does not form its own minerals. Since 1956, all three have been found.

   Often gallium is found in the composition of zinc, iron, Its impurities are found in coal, beryl, garnet, magnetite, tourmaline, feldspar, chlorites and other minerals. On average, its content in nature is about 19 g/t.

   

   Most gallium is found in substances that are close to it in composition. Because of this, it is difficult and expensive to extract from them. The metal's own mineral is called gallite with the formula CuGaS 2 . It also contains copper and sulfur.

   Impact on a person

   Little is known about the biological role of the metal and its effects on the human body. In the periodic table, it is next to the elements that are vital to us (aluminum, iron, zinc, chromium). There is an opinion that, as an ultramicroelement, gallium is part of the blood, accelerating its flow and preventing the formation of blood clots.

   One way or another, a small amount of the substance is contained in the human body (10 -6 - 10 -5%). Gallium enters it together with water and agricultural food. It lingers in the bone tissue and liver.

   Gallium metal is considered low-toxic or conditionally toxic. Upon contact with the skin, small particles remain on it. It looks like a gray dirty spot that is easily removed with water. The substance does not leave burns, but in some cases it can cause dermatitis. It is known that a high content of gallium in the body causes disorders in the liver, kidneys and nervous system, but this requires a very large amount of metal.

   Gallium(lat. Gallium), Ga, a chemical element of group III of the periodic system of D. I. Mendeleev, serial number 31, atomic mass 69.72; silvery white soft metal. Consists of two stable isotopes with mass numbers 69 (60.5%) and 71 (39.5%).

   The existence of Gallium ("ekaaluminium") and its main properties were predicted in 1870 by D. I. Mendeleev. The element was discovered by spectral analysis in Pyrenean zinc blende and isolated in 1875 by the French chemist P. E. Lecoq de Boisbaudran; named after France (lat. Gallia). The exact coincidence of the properties of Gallium with those predicted was the first triumph of the periodic system.

   The average content of Gallium in the earth's crust is relatively high, 1.5·10 -3% by weight, which is equal to the content of lead and molybdenum. Gallium is a typical trace element. The only Gallium mineral, CuGaS 2 gallite, is very rare. The geochemistry of Gallium is closely related to the geochemistry of aluminum, which is due to the similarity of their physicochemical properties. The main part of Gallium in the lithosphere is enclosed in aluminum minerals. The gallium content in bauxite and nepheline ranges from 0.002 to 0.01%. Elevated concentrations of Gallium are also observed in sphalerites (0.01-0.02%), in hard coals (together with germanium), and also in some iron ores.

   Physical properties of Gallium. Gallium has a rhombic (pseudotetragonal) lattice with parameters a = 4.5197Å, b = 7.6601Å, c = 4.5257Å. Density (g / cm 3) of solid metal 5.904 (20 ° C), liquid 6.095 (29.8 ° C), that is, during solidification, the volume of Gallium increases; t pl 29.8°C, t bp 2230°C. A distinctive feature of Gallium is a large range of liquid state (2200°C) and low vapor pressure at temperatures up to 1100-1200°C. The specific heat capacity of solid Gallium is 376.7 J/(kg K), i.e. 0.09 cal/(g deg) in the range of 0-24°C, liquid, respectively, 410 j/(kg K), i.e. 0.098 cal /(g deg) in the range of 29-100°C. Electrical resistivity (ohm cm) of solid Gallium 53.4 10 -6 (0°C), liquid 27.2 10 -6 (30°C). Viscosity (poise \u003d 0.1 n sec / m 2): 1.612 (98 ° C), 0.578 (1100 ° C), surface tension 0.735 n / m (735 dyn / cm) (30 ° C in an atmosphere of H 2) . The reflection coefficients for the wavelengths of 4360Å and 5890Å are 75.6% and 71.3%, respectively. The thermal neutron capture cross section is 2.71 barns (2.7 10 -28 m 2).

   Chemical properties of Gallium. Gallium is stable in air at ordinary temperatures. Above 260°C in dry oxygen, slow oxidation is observed (the oxide film protects the metal). In sulfuric and hydrochloric acids, gallium dissolves slowly, in hydrofluoric acid - quickly, in nitric acid in the cold, gallium is stable. Gallium slowly dissolves in hot alkali solutions. Chlorine and bromine react with Gallium in the cold, iodine - when heated. Molten gallium at temperatures above 300 ° C interacts with all structural metals and alloys.

   The most stable trivalent compounds of Gallium, which are in many respects similar in properties to the chemical compounds of aluminum. In addition, mono- and divalent compounds are known. The highest oxide Ga 2 O 3 is a white substance, insoluble in water. The corresponding hydroxide precipitates from solutions of Gallium salts in the form of a white gelatinous precipitate. It has a pronounced amphoteric character. When dissolved in alkalis, gallates (for example, Na) are formed, when dissolved in acids, Gallium salts: Ga 2 (SO 4) 3, GaCl 3, etc. The acidic properties of Gallium hydroxide are more pronounced than that of aluminum hydroxide [Al( OH) 3 is in the range of pH = 10.6-4.1, and Ga(OH) 3 is in the range of pH = 9.7-3.4].

   Unlike Al(OH) 3 , Gallium hydroxide dissolves not only in strong alkalis, but also in ammonia solutions. When boiling, gallium hydroxide precipitates again from the ammonia solution.

   Of the gallium salts, GaCl 3 chloride (mp 78°C, bp 200°C) and Ga 2 sulfate (SO 4) 3 are of greatest importance. The latter with alkali metal and ammonium sulfates forms double salts of the alum type, for example (NH 4) Ga (SO 4) 2 12H 2 O. Gallium forms ferrocyanide Ga 4 3, which is poorly soluble in water and dilute acids, which can be used to separate it from Al and a number of other elements.

   Getting Gaul. The main source of Gallium is aluminum production. Gallium during the processing of bauxite by the Bayer method is concentrated in the circulating mother liquors after the allocation of Al(OH) 3 . Gallium is isolated from such solutions by electrolysis on a mercury cathode. From the alkaline solution obtained after treatment of the amalgam with water, Ga(OH) 3 is precipitated, which is dissolved in alkali and Gallium is isolated by electrolysis.

   With the soda-lime method of processing bauxite or nepheline ore, Gallium is concentrated in the last fractions of sediments released during carbonization. For additional enrichment, the precipitate of hydroxides is treated with milk of lime. In this case, most of the Al remains in the precipitate, and Gallium passes into solution, from which gallium concentrate (6-8% Ga 2 O 3) is isolated by passing CO 2; the latter is dissolved in alkali and gallium is isolated electrolytically.

   The residual anodic alloy of the Al refining process by the three-layer electrolysis method can also serve as a source of Gallium. In the production of zinc, the sources of Gallium are sublimates (Weltz oxides) formed during the processing of leaching tailings of zinc cinders.

   Liquid Gallium obtained by electrolysis of an alkaline solution, washed with water and acids (HCl, HNO 3), contains 99.9-99.95% Ga. A purer metal is obtained by vacuum melting, zone melting, or by drawing a single crystal from the melt.

   Application of Gallium. The most promising application of Gallium is in the form of chemical compounds such as GaAs, GaP, GaSb, which have semiconductor properties. They can be used in high-temperature rectifiers and transistors, solar cells and other devices where the photoelectric effect in the barrier layer can be used, as well as in infrared radiation receivers. Gallium can be used to make optical mirrors that are highly reflective. An alloy of aluminum with gallium has been proposed instead of mercury as a cathode for ultraviolet radiation lamps used in medicine. Liquid Gallium and its alloys are proposed to be used for the manufacture of high-temperature thermometers (600-1300°C) and manometers. Of interest is the use of Gallium and its alloys as a liquid coolant in power nuclear reactors (this is hindered by the active interaction of Gallium at operating temperatures with structural materials; the Ga-Zn-Sn eutectic alloy has a lesser corrosive effect than pure Gallium).

   Gallium is an element of the main subgroup of the third group of the fourth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 31. It is designated by the symbol Ga (lat. Gallium). Belongs to the group of light metals. The simple substance gallium is a soft, ductile metal of silver-white (according to other sources, light gray) color with a bluish tint.
   The average content of gallium in the earth's crust is 19 g/t. Gallium is a typical trace element with a dual geochemical nature. Due to the closeness of its crystal chemical properties with the main rock-forming elements (Al, Fe, etc.) and the wide possibility of isomorphism with them, gallium does not form large accumulations, despite the significant clarke value.
   

   The following minerals with a high content of gallium are distinguished: sphalerite (0 - 0.1%), magnetite (0 - 0.003%), cassiterite (0 - 0.005%), garnet (0 - 0.003%), beryl (0 - 0.003%), tourmaline (0 - 0.01%), spodumene (0.001 - 0.07%), phlogopite (0.001 - 0.005%), biotite (0 - 0.1%), muscovite (0 - 0.01%), sericite ( 0 - 0.005%), lepidolite (0.001 - 0.03%), chlorite (0 - 0.001%), feldspars (0 - 0.01%), nepheline (0 - 0.1%), heckmanite (0.01 - 0.07%), natrolite (0 - 0.1%). The concentration of gallium in sea water is 3 10-5 mg/l.
   Gallium deposits are known in Southwest Africa, Russia, and the CIS countries. The world resources of gallium in bauxite are estimated at over one billion kilograms. In addition, a significant amount of gallium is available in the world reserves of zinc ores. However, only a small fraction of the gallium in bauxite and zinc ore is economically recoverable.
   Gallium may not be enough, but it cannot be called rare. It is more abundant than many known metals such as antimony, molybdenum, silver and tungsten, but unlike these elements, gallium is rarely, if ever, found in economic concentrations in natural minerals. The two main sources of commercial gallium are its extraction from bauxite during the production of alumina and its extraction from residues resulting from zinc oxide leaching prior to electrolysis.
   Gallium does not exist in the earth's crust in elemental form, but occurs most often in the form of a gallium(III) salt. Proizvodstvoditsya primarily from bauxite. In 2010, with a global production capacity of 256-261 tons, 78 tons of metal were produced in this way. The production of gallium in the world as a whole in 2010 was estimated to be approximately 201-212 tons. This circumstance clearly demonstrates the high degree of secondary reduction of the metal, as well as the excess production / processing capacity at the present time. Consumption of gallium in 2010 was at the level of 280 tons, which indicated the presence of a shortage in the world market and partial consumption of metal from stocks. In 2011, gallium consumption dropped to 218 tons, resulting in a surplus of the metal on the market (the global production of primary gallium amounted to 292 tons).
   Secondary recovery (processing) of gallium. The shortage of gallium obtained from ore has led to significant volumes of its secondary production. In Japan, approximately 90 tons of metallic gallium in 2010 was produced by recycling from waste, and another 60 tons of gallium potentially contained within the liquid phase epitaxy production loop, not immediately available for consumption or in a form usable for other purposes.
   The secondary reduction of gallium in semiconductor manufacturing processes is also an important source. Due to the multi-step nature of semiconductor fabrication and the requirement for extremely high quality control at each step, much more gallium is required than is actually contained in semiconductors. The US Department of Energy reported that in 2010, global gallium recycling capacity accounted for approximately 42% (partly as a result of the aforementioned semiconductor manufacturing process) of global gallium production capacity.
   China is believed to be the leading producer of primary gallium, followed by Germany, Kazakhstan, Ukraine, South Korea and Russia. Gallium is also produced in Hungary and Japan. World production of refined gallium, including recovery from waste, is estimated at 378 tons (2011).
   China, Japan, the UK and the US were the main producers of refined gallium in 2010. Gallium is produced from recycling in Canada, Germany, Japan, the UK and the USA. Neo Material estimated that 50% of the gallium consumed worldwide in 2010 came from recycled sources.
   The main gallium producers in China are Aluminum Corporation China Ltd, Beijing Jia Semiconductor Material Co. Ltd, China Crystal Technologies Ltd, East Mianchi Gallium Hope Industry Co. and Zhuhai Fanyuan. China's total gallium production capacity in 2010 was estimated at 141 tons.
   Most of the primary gallium production capacity is now located in China, Germany and Kazakhstan, following a reduction in the number of companies refining gallium in Russia and the closure of a plant in France. China has increased its primary gallium production capacity from 141 tons/year in 2010 to 280 tons/year by the end of 2011.
   A significant proportion of gallium comes from secondary production, especially from the processing of GaAs and waste products resulting from liquid phase epitaxy. The main centers of secondary production are Japan and North America. At the same time, there is not enough data on the efficient processing of gallium-containing waste in China, despite the fact that the country is becoming one of the main consumers of this metal.
   Gallium is the basis of the electronics industry. Gallium is the basis of compounds such as gallium arsenide (GaAs) and gallium nitride (GaN), semiconductors used in the electronics industry. It is also used in the manufacture of memory cells.
   Optoelectronic devices such as LEDs, laser diodes, photosensors and solar cells made from GaAs continue to be the main area of ​​gallium consumption worldwide. In the near future, the use of GaAs is expected to increase, especially in the communications markets. The growth in the use of cellular communications and satellite navigation devices is expected to lead to an increase in demand for gallium.
   Gallium is used in the form of GaN in laser diodes and light-emitting diodes (LEDs). New GaN devices are being used to create high-density storage (CD players and digital video players), high-quality laser printing, communications, and lighting. GaN transistors operate at higher voltages and higher energy densities than GaAs devices. Gallium is used in some high temperature thermometers, and a eutectic alloy of gallium, indium and tin is widely used in such thermometers, replacing mercury. Gallium is also used as a component in low-melting alloys and in the creation of shiny mirrors. Gallium salts such as gallium citrate and gallium nitrate are used in medicine.
   Global demand for gallium in recent years has been strongest in the optoelectronics industry, especially in LEDs. Because of its superior properties, GaAs is increasingly being used in place of silicon in integrated circuits in many security applications. The mobile phone market has predominantly been responsible for the growth in gallium consumption over the past few years.
   The gallium market experienced growth: in 2010, the demand for the metal was strong in both the electronics and optoelectronic sectors. The increase in gallium consumption was driven by growing demand for smartphones and multi-band, multi-mode handsets, as well as an increase in the use of LEDs in lighting and display screens. In China, about half of the identified consumption is in NdFeB magnetic materials - a pattern not replicated elsewhere in the world, but which has potential for growth in Japan.
   Gallium can be replaced in semiconductor fabrication with indium, and in solar cell thin film technology by silicon-based technologies, some forms of thin film cadmium selenide or copper indium selenide based photovoltaic cells among others. The development of these various forms of solar cell technology means that the outlook for the global market for gallium remains unclear. The advantages of gallium as a component of solar cell technologies also do not seem to be the final advantage in comparison with competing materials and compositions.
   The main use for gallium is in the production of optoelectronics and semiconductors. Further demand for gallium comes from its use as a transparent anode in large area displays and solid state lighting, thin film transistors, neodymium iron boron magnets and batteries, lithium batteries and copper-indium gallium selenide photovoltaic cells. In general, the use of gallium in some electronics has been held back due to its limited supply. The metal is being replaced as less economically important, with total world production only about one-tenth that of indium.

   Gallium consumption in the world, tons*

   year	2008	2009	2010	2011	2012
   Japan	122.3	111.3	116.0	114.0	110.0
   USA	28.7	24.9	33.5	35.3	35.0
   Other countries	39.2	40.6	130.5	68.7	75.0
   Total	190.2	176.8	280.0	218.0	220.0

   * summary data

   Gallium prices (hereinafter the price of gallium imported into the US, USGS data) rose from 2004 to 2011, except for 2005, 2006 and 2009, driven by the growth of the smartphone market, increased use of LEDs in lighting and demand for optoelectronic devices (Blu-ray, DVD, etc.). In the period from 2003 to 2011, gallium prices in the world market increased by more than 1.5 times from approximately $411/kg to $688/kg. In 2012, gallium prices dropped slightly - to an average of $556/kg, but remained at a very high level.
   

   With vast bauxite resources, India has the potential to increase alumina production from export-oriented smelters, which could boost supplies of the metal for domestic consumption and the global market. Demand for gallium is likely to increase due to the growth of the country's electronics industry. Of strategic importance is the development of local technology, as well as cooperation with foreign countries for the purification and production of metal. Zinc deposits, as an alternative source, will become economically viable when readily available sources of gallium are used up.
   Demand for gallium is projected to grow at around 15% per annum through 2015, and this increased demand will be fueled by both existing excess capacity, especially in secondary refining, and new mainstream capacity planned for China and possibly in North America. An unused stock of recycled material will pile up in China while recycling remains low.