Bauxite origin. Aluminum ore: deposits, mining

14.10.2019

Bauxite: , boehmite, hydrogoethite, hydrohematite, aluminogethite, aluminohematite, . By appearance bauxites are very diverse. Their color is usually red, brownish-brown, less often gray, white, yellow, black. By state of aggregation distinguish bauxites that are dense (stony), porous, earthy, friable and clay-like; according to structural characteristics - clastic (pelite, sandstone, gravelite, conglomerate) and concretionary (oolitic, pisolite, leguminous); by texture - collomorphic (homogeneous, layered, etc.). Due to different porosity, the density of bauxite varies from 1800 (loose bauxite) to 3200 kg/m 3 (stony bauxite).

According to the predominant mineral composition, bauxites are distinguished: monohydroxide, composed of diaspore, boehmite, trihydroxide -; mixed composition - diaspore-boehmite, boehmite-gibbsite. There are also more detailed divisions of bauxites depending on the mineral composition: chamosite-boehmite, chamosite-gibbsite, gibbsite-kaolinite, goethite-chamosite-boehmite, kaolinite-boehmite, etc. According to the conditions of formation, bauxites are divided mainly into lateritic (residual) and redeposited (sedimentary). Bauxites were formed either as a result of deep chemical processing (lateralization) of aluminosilicate rocks in a humid tropical climate (lateritic bauxites) or as a result of the transfer of lateritic weathering products and their redeposition (sedimentary bauxites). Depending on the tectonic position, bauxites of platform and geosynclinal areas, as well as bauxites of oceanic islands, are distinguished. Bauxites form sheet-like and lens-shaped bodies of variable thickness, and in terms of deposits they are linear, isometric and irregular in shape. Often deposits consist of several (in vertical section) lenses. The quality of lateritic bauxites is usually high, while sedimentary bauxites can range from high-grade (for example, the North Ural deposits) to substandard (Boksonskoye deposit in Buryatia).

Bauxite is the main ore for the extraction of alumina (AL 2 O 3) and aluminum; used in the abrasive industry (electrocorundum), in ferrous metallurgy (flux when smelting open-hearth steel), low-iron bauxites are used to produce high-alumina mullitized refractories, fast-hardening aluminous cements, etc. Bauxites are a complex raw material; they contain Ga, as well as Fe, Ti, Cr, Zr, Nb, and rare earth elements. The quality requirements for mined (commercial) bauxite are determined by GOST, as well as contractual terms between suppliers and consumers. According to the classification of the current GOST 972-74, bauxite is divided into 8 grades depending on the weight ratio of the contents of alumina and silica (the so-called silicon module). For the lowest grade (B-6, grade II), the silicon module must be at least 2 with an alumina content of at least 37%; for high-grade bauxites (B-0, B-00) the silicon module must be more than 10 with an alumina content of 50% and above . The selected varieties and grades of bauxite have their own areas of industrial use.

Bauxite is mined by open-pit or, less commonly, underground methods. The choice of technological scheme for processing bauxite depends on its composition. The production of aluminum from bauxite is carried out in 2 stages: in the first, alumina is obtained by chemical methods, in the second, pure metal is isolated from alumina by electrolysis in a melt of aluminum fluoride salts. When producing alumina, they mainly use the hydrochemical Bayer method, the sintering method, as well as the combined Bayer-sintering method (parallel and sequential options). The principle of the Bayer process consists of treating (leaching) finely ground bauxite with a concentrated solution of caustic soda, as a result of which the alumina goes into solution in the form of sodium aluminate (NaAl 3 O 2). Aluminum hydroxide (alumina) is precipitated from an aluminate solution purified from red mud. Low-quality bauxite is processed more in a complicated way— the sintering method, in which a three-component charge (a mixture of crushed bauxite with limestone and soda) is sintered at 1250°C in rotary kilns. The resulting cake was sintered with a circulating alkaline solution of weak concentrations. The precipitated hydroxide is separated and filtered. The parallel combined Bayer-sintering scheme provides for the simultaneous processing of high-quality and low-grade (high-silicon) bauxite at one plant. The sequential combined scheme of this method includes the processing of bauxite into alumina, first by the Bayer method and then the additional extraction of alumina from red helmets by sintering them with limestone and soda. The main bauxite-bearing areas (see map) are located in the European part of the USSR, in the Urals, and in Kazakhstan.

In the European part, they are known in the Arkhangelsk region (Iksinskoye, etc.), in the Middle (Vezhayu-Vorykvinskoye, etc.) and Southern Timan (Timsherskoye, Puzlinskoye, etc.), in the Leningrad region (Tikhvinskoye) and Belgorod region (Vislovskoye, etc.) regions of the RSFSR. In the Urals, bauxite deposits are developed in the Sverdlovsk (North Ural bauxite-bearing region) and Chelyabinsk (South Ural deposits) regions of the RSFSR. Within Northern Kazakhstan, bauxite deposits are concentrated in the Kustanay (Krasnooktyabrskoye deposit, Belinskoye, Ayatskoye, East Ayatskoye and other deposits) and Turgay (East Turgay group of deposits) regions of the Kazakh SSR. IN eastern Siberia bauxites are found in the area of the Chadobetsky uplift of the Angara region and in the eastern (Boksonsky) region.

The most ancient bauxites in the USSR are known from the Bokson deposit (Precambrian, Vendian). The bauxites of the North Ural group are associated with Middle Devonian deposits, while the Middle Timan bauxites are associated with Middle and Upper Devonian deposits. Bauxites of the Iksinsky and Vislovsky deposits occur in Lower Carboniferous deposits; the deposits of Northern Kazakhstan were formed in the Cretaceous and Paleogene times and are the youngest.

It has large reserves of bauxite (deposits in the provinces of Shandong, Henan, Gansu, Yunnan, Liaoning, Shaanxi, etc.), (deposits of Halimba, Nyirad, Iskaszentgyorgy, Gant, etc.), (deposits of Vlasenica, Drniš, Lika Plateau, Bijela Lipa , Obrovac, Niksic, Bijela Polana), bauxite deposits are also known in the DPRK.

In industrialized capitalist and developing countries, bauxite reserves at the beginning of 1982 amounted to about 22 billion tons, incl. proven 13.5 billion tons. The main reserves of bauxite are located in developing countries - about 75% (16.7 billion tons), incl. proven about 75% (10.1 billion tons). IN developed countries deposits of high-quality bauxite are known in the form of laterite covers in Australia; Their share in total reserves is approximately 20%. The bulk of bauxite deposits are located in little-explored areas of tropical countries, so it is expected that the trend of reserves growing faster than production will continue.

In 1974, the International Association of Bauxite Mining Countries was created. It initially included:

See also Aluminum industry.

BOXITES [called area of Les Baux in the south of France, where bauxite deposits were first discovered], bauxite, consisting mainly of aluminum hydroxides (aluminum gel, gibbsite, boehmite, diaspores, etc.), oxides and hydroxides of iron and clay minerals. The color is red in various shades, brownish-brown, less often white, yellow, gray (to black). They are found in the form of dense (rocky) or porous formations, as well as in the form of loose earthy and clay-like masses. Based on their structure, they are classified as clastic (pelite, sandstone, gravelite, conglomerate) and concretionary (oolitic, pisolite, leguminous); by texture - homogeneous, layered and other bauxites. Density varies from 1800 kg/m 3 (loose) to 3200 kg/m 3 (rocky). According to the predominant mineral composition, bauxites are distinguished: monohydroxide (diaspore, boehmite), trihydroxide (gibbsite) and mixed composition (diaspore-boehmite, boehmite-gibbsite, chamosite-boehmite, chamosite-gibbsite, gibbsite-kaolinite, goethite-chamosite-boehmite, etc.). ).

Bauxites are formed during deep chemical transformations (lateritization) of aluminosilicate rocks in a humid tropical climate (lateritic or residual bauxites) or during the transfer of lateritic weathering products and their redeposition (sedimentary bauxites). As a result of the superposition of these processes, bauxites of a mixed (polygenic) type are formed. The deposits are sheet-like, lens-shaped or irregularly shaped (karst pockets). The quality of lateritic bauxites is usually high (50% $\ce(Al_2O_3)$ and higher), sedimentary bauxites can range from high-grade (55–75% $\ce(Al_2O_3)$) to substandard (less than 37% $\ce (Al_2O_3)$ ). In Russia, the quality requirements for mined (commercial) bauxite are determined by GOST, as well as contractual terms between suppliers and consumers. Depending on the ratio (by weight) of alumina and silica content (the so-called silicon module), bauxite is divided into 8 grades. For the lowest grade (B-6, 2nd grade), the silicon module should be over 2 with an alumina content of at least 37%; for high-grade bauxites (B-0, B-00) the silicon module should be over 10 with an alumina content of 50% and more. In foreign classifications, bauxite with a silicon modulus of over 7 is classified as high-quality.

Bauxite deposits according to reserves are divided into large (over 50 million tons), medium (5–50 million tons) and small (up to 5 million tons). The reserves of the world's largest deposit, Boke (Guinea), are estimated at 2.5 billion tons. 83.7% of reserves are concentrated in lateritic deposits, 9.5% in polygenic deposits and 6.8% in sedimentary deposits.

Bauxite deposits have been explored in more than 50 countries around the world. Total bauxite reserves are estimated at 29.3 billion tons, confirmed reserves at 18.5 billion tons (2nd half of the 2000s). The largest confirmed reserves are in: Guinea (7.4 billion tons; over 40% of world reserves), Jamaica (2 billion tons; 10.8%), Brazil (1.9 billion tons; 10.3%) , Australia (1.8 billion tons; 9.7%), India (0.77 billion tons; 4.2%), Guyana (0.7 billion tons; 3.8%), Greece (0. 6 billion tons; 3.2%), Suriname (0.58 billion tons; 3.1%), China (0.53 billion tons; 2.8%). The largest bauxite province in the world is the West African bauxite province (or Guinea).

In Russia, the total reserves of bauxite are over 1.4 billion tons, proven reserves are over 1.1 billion tons (beginning of 2013). There are 57 deposits (including 4 large and 7 medium). The main bauxite reserves are concentrated in the Sverdlovsk region (about 1/3 of the reserves of the Russian Federation; sedimentary deposits of the North-Ural bauxite-bearing region - large Cheremukhovskoye, medium - Krasnaya Shapochka, Kalinskoye, Novokalinskoye), the Komi Republic (26% of the reserves of the Russian Federation; polygenic deposits of the Vorykvinsky group of the Timan bauxite-bearing zones - large Vezhayu-Vorykvinskoye, medium - Verkhneshugorskoye, Vostochnoye), Arkhangelsk region (18% of reserves of the Russian Federation; large Iksinsky sedimentary deposit), Belgorod region (about 16% of reserves of the Russian Federation; large Vislovskoye laterite deposit, medium - Melikhovo-Shebekinskoye). Bauxite reserves have also been identified in the Krasnoyarsk and Altai territories, the Kemerovo region, the Republic of Bashkortostan, Leningrad region. Ores from Russian deposits, compared to foreign analogues, are of lower quality and more difficult development conditions. The richest ores ($\ce(Al_2O_3)$ 56%) in the deposits Northern Urals; The largest (approx. 18% of Russian reserves) Iksinsky deposit is composed of low-quality bauxites.

World bauxite production exceeded 196 million tons/year (2nd half of the 2000s). Main producing countries: Australia (62.6 million tons/year), China (27 million tons/year), Brazil (22.8 million tons/year), Guinea (18.2 million tons/year), Jamaica (14.9 million tons/year), India (13.9 million tons/year). In Russia, the extraction of bauxite from the subsoil in 2012 amounted to 5.14 million tons; 9 deposits were developed, 6 of them in the Sverdlovsk region.

Alumina and aluminum are extracted from bauxite. Bauxite is also used in the production of paints, artificial abrasives (electrocorundum), as fluxes in ferrous metallurgy, and sorbents for purifying petroleum products from various impurities; low-iron bauxites - for producing high-alumina refractories, quick-hardening cements, etc. Bauxites are complex raw materials; in addition to aluminum and iron, they contain gallium, as well as titanium, chromium, zirconium, niobium, and rare earth elements.

As noted earlier, bauxite contains various combinations up to 100 elements of the periodic table. The number of minerals is also close to 100. From a technological point of view, all bauxite minerals can be divided into three groups. The first includes aluminum-containing minerals - gibbsite, boehmite, diaspore. The second includes minerals that complicate or disrupt the technology for producing alumina. These are silica-containing minerals, various silicates and aluminosilicates, carbonates, sulfides, and organic substances. The third group is ballast compounds, which do not undergo changes during technological processing and are removed from the technological cycle in the form of sludge. These include iron oxides and titanium-containing compounds. It should be noted that this division is arbitrary, since it does not take into account all the qualities of minerals, as well as the fact that under different production conditions the behavior of minerals can be exactly the opposite. For example, the mineral calcite (CaCO3), which is a harmful impurity in the Bayer process, is converted into a useful component in the sintering method, etc.
Silicon-containing bauxite minerals and their leaching behavior. The silica content (SiO2) in bauxite varies widely (2-20%) and is characterized by the silicon module. Silica in bauxite is found in free and bound forms. Silicon-containing bauxite minerals include opal SiO2*H2O, chalcedony SiO2, α-quartz SiO2, as well as various aluminosilicates and silicates (kaolinite Al2O3*2SiO2*2H2O, chamosite (Mg, Al, Fe)12 [(Si, Al)8O20]( OH)16 and other minerals). According to the reactivity of dissolution in alkaline aluminate solutions, silica-containing minerals can be arranged as follows: silica hydrogel - opal mineral - kaolin minerals - quartz.
Kaolinite- the main silica-containing mineral of bauxite. Its group also includes dikkit and nacrite.
The heating curves of this mineral have 2 endothermic effects in the range from 400 to 600 °C and one exothermic effect at 900 °C. In minerals with a disordered structure, another endothermic effect appears at 100-200 °C.
When heated, the following transformations occur:

When heated, kaolinite transforms into metakaolinite, then into silicon spinel, and the final product is mullite with crystalline stone.
Kaolinite and minerals of its group interact with alkali-aluminate solutions to form sodium hydroalumina silicate (see formula (4.9)). The intensity of its dissolution depends on the concentration of the alkali-aluminate solution and its temperature. Thus, when the Na2O content increases from 120 to 220 g/l at a process temperature of 105 °C, kaolinite completely dissolves. Reducing the temperature of the aluminate solution to 70 °C, compared to 105 °C, leads to a sharp decrease in the solubility of the mineral. Under the conditions of the Bayer hydrochemical method, kaolin minerals are completely decomposed first.
Quartz usually included in bauxite in the form of α-modification: α-SiO2. Its content in bauxite is variable and ranges from 3 to 11%. There is conflicting information about the behavior of quartz in alkaline solutions. In particular, the authors F.F. Wolf and O.I. Pudovkin believe that α-SiO2 does not dissolve in strong alkali-aluminate solutions with a Na2O concentration of 300 g/l and a caustic modulus of the solution of 4-7 units. According to other researchers, with sufficiently fine grinding, the solubility of quartz is not inferior to the solubility of silicic acid gel. Subsequently, using electron microscopy, the authors S.I. Kuznetsov and others showed that individual α-SiO2 crystals dissolve in alkaline solutions already at 100 °C. Thus, quartz under the conditions of the Bayer hydrochemical method is an active component. At elevated temperatures (220-230 °C) during autoclave leaching of bauxite, quartz dissolves completely.
Chamosite(Fe2+, Mg)23 * (Fe3+, Al)0.7 * (Si1.4*Al0.6)O5 * (OH)4 - this mineral belongs to the group of layered aluminosilicates. The term “chamosite” often refers to ferruginous chlorite. In alumina-containing raw materials, bauxite is also the main silica-containing mineral. It is most often found in the bauxite deposits of SUBR, Timan and YuUBR. The chemical composition of chamosites is very variable. There are chamosites with a predominance of di- and trivalent iron.
The content of the main components in them varies within the following limits: SiO2 = 18-33%, Al2O3 = 20-30%, Fe2O3 = 1-18%, FeO = 2-39%, MgO = 0.6-6.5%, H2O = 7-11%.
It was experimentally established that in aluminate solutions in the Bayer process, the solubility of chamosite depends on its chemical and mineralogical composition. In particular, deeply oxidized chamosite containing FeO ≤ 1% dissolves by 96% in 4 hours already at 95 °C. Low-oxidized chamosite with a FeO content of about 11.5% under the same conditions dissolves by 25-35%.
The interaction of chamosite with NaOH can be described by the following reaction:

This reaction may be one of the reasons for the increase in pressure in autoclaves and the appearance of divalent iron in solutions. It was found that during the processing of a new type of raw material - Timan bauxite at the Ural aluminum smelters, the number of blow-offs in autoclave batteries sharply increased, which also confirms the version of the decomposition of chamosites and chlorites during leaching.
It should be noted that the release of hydrogen during this reaction can be dangerous.
The process of converting bauxite silica into GASN occurs in 2 stages (Fig. 4.12):
1) dissolution of silica in an alkaline aluminate solution (see formula (4.6));
2) crystallization of GASN from solution (see formulas (4.7), (4.8)). The solubility of GASN decreases with increasing temperature; for this reason, aluminosilicate solutions are better and more deeply desiliconized when the process is carried out at temperatures of 150-170 °C.

Most researchers believe that chemical composition The released HASN is not constant, depends on the temperature, composition and concentration of the aluminate solution and corresponds to the conventional formula nNа2O*Al2O3*(1.4-2)SiO2*xH2O. This aluminosilicate, in its composition and form, belongs to a natural mineral called “sodalite”: 7(Na2O*Al2O3*SiO2)*2NaAlO2*nH2O.
The formation of insoluble compounds with silica causes the main losses of aluminum oxide and alkali with red mud in the form of HASN (see formula (3.4) - losses of Na2O and Al2O3 in the form nNa2O*Al2O3*(1.4-2)SiO2*xH2O).
Silica (SiO2) is one of the most harmful impurities when processing bauxite using the Bayer method. Hence the restriction on the use of bauxite with a low silicon module, less than 7-8 units.
In the presence of lime, part of the bauxite silica binds into a new compound called “aluminum hydrogarnet” (3CaO*Al2O3*0.55SiO2*5.5H2O), which leads to a decrease in alkali losses with red mud. In this case, the following chemical reaction occurs:

For example, when leaching North Ural bauxite without adding lime, red mud is formed with a Na2O content of 6 to 8%. When adding 3 wt.% CaO to this bauxite pulp, the alkali content in the red mud is reduced to 3-4%.
The rate and completeness of dissolution of free quartz depends on the particle size, the concentration of the aluminate solution and the temperature of the process (see Fig. 4.13, 4.14). Amorphous silica and its gel dissolve faster in caustic alkalis than quartz. Coarse-grained quartz dissolves more slowly than highly dispersed quartz.
The dissolution of silicon minerals and the release of insoluble GASN compounds from aluminate solutions during the leaching process leads to overgrowth of heat exchange equipment when heating bauxite with a circulating solution in heat exchangers, as well as to losses of useful components. Therefore, to weaken this harmful effect, it is recommended to keep bauxite pulp in wet mixers at a temperature of 100 ° C for 4-6 hours before heating. This leads to the creation of conditions for the transfer of the soluble part of bauxite silica into sodium hydroaluminosilicate even before leaching of the main aluminum-containing bauxite minerals.

Interesting curves were obtained by I.S. Lileev when he studied the behavior of dissolved silica in low-modulus aluminate solutions with αk = 1.7 at t = 70 °C. Three regions of the silica state were clearly identified (see Fig. 4.15). Region I is the region of the equilibrium state of the solution. Region II, bounded on the state diagram by the equilibrium line (OS), is the region of the equilibrium state of silica, and the limiting supersaturation line (OA), called the metastable region. A solution in the metastable region can remain in a state of unstable equilibrium for any length of time, retaining silica. Region III belongs to the labile region and is absolutely unstable. Being in this area leads to spontaneous (spontaneous) crystallization of GASN. Subsequently, the behavior of silica was studied under the same conditions, but only in the region of increased alumina concentrations in solution. Thanks to the averaging and approximation of the obtained experimental data, it was possible to derive equations for the limitation of these regions.

By extrapolating experimental data on the behavior of silica in concentrated aluminate solutions, mathematically processed results of the behavior of silica in solution were obtained and the region of the metastable state of silica was clearly identified.
The pattern of silica retention in the metastable region was also confirmed in solutions with high alumina concentrations. It was also shown that diluting these concentrated solutions to generally accepted concentrations allows silica to remain in the metastable region (RH curve), which allows for the subsequent separation of red mud from the aluminosilicate solution.
Region I: region of the equilibrium state of silica.
Region II: region of the metastable state of silica.
Region III: the region of the labile state of silica, in which silica is practically not retained in solution and is intensively released from it in the form of HASN.
Extremely high concentrations of silica in aluminate solutions have to be dealt with when leaching ore and cake. Desiliconization of aluminate solutions through GASN is possible due to the extremely low silica content (OS curve) in the equilibrium state region. The region above the OA curve is the region of the labile state of silica, where it practically cannot be retained by the solution and is released from it.
Iron-containing bauxite minerals and their leaching behavior. Constant companions of the main rock-forming minerals of bauxite - aluminum oxide and hydroxide and kaolinite - are iron compounds. Iron-containing bauxite minerals are represented by four classes of compounds: oxides, sulfides and sulfates, carbonates and silicates. From the first, most common class of minerals, hematite and hydrohematite, goethite and hydrogoethite, limonite and hematogel, as well as magnetite and maghemite should be distinguished. It has been established that diaspore bauxites are richer in sulfides compared to boehmite-gibbsite and gibbsite bauxites. Iron carbonates are present predominantly in gibbsite bauxites.
Goethite(α-FeOOH) is a constant companion of bauxites and is the main mineral of gibbsite bauxites in tropical countries and Mediterranean deposits. The crystal lattice of goethite is similar to diaspore, and γ-FeOOH in its structure corresponds to boehmite.
Under the conditions of the Bayer process, goethite in alkaline solutions, being dehydrated, transforms into hematite α-Fe2O3. Without affecting the chemistry of the Bayer process, goethite can disrupt the thickening process of red mud. This is due to its ability to reversibly dehydrogenate and hydrogenate. If bauxite is fired until the mineral goethite is completely dehydrated, the thickening process occurs without complications.
Lepidocrocite(γ-FeOOH) is a rare mineral in bauxites; its structure corresponds to boehmite. This mineral is an unstable compound, and in alkaline aluminate solutions it recrystallizes into maghemite - γ-, α-Fe2O3, Fe2O3. This connection is magnetic.
Hematite(α-Fe2O3) is the main iron-containing mineral of SUBR bauxite. The amount of hematite from the total Fe2O3 content in bauxite is often 80-90%. Hematite is part of the beans and the cementing mass. Often finely dispersed and found in close association with other minerals. In bauxite, hematite is so finely dispersed that it can be separated into pure form fails. Artificial hematite can be obtained by dehydrating goethite by heating or treating it with an alkaline solution. Hematite is practically insoluble in alkaline aluminate solutions and is a ballast impurity in the Bayer process. Hematite is weakly magnetic, and this is explained by the presence in it of a small amount of magnetite Fe3O4 and maghemite γ-Fe2O3.
Maghemite(γ-Fe2O3) - highly magnetic. IN natural conditions found in sedimentary rocks rich in organic matter. It can also be obtained by dehydrating lepidocrocite or goethite. When heated, it irreversibly transforms into hematite.
Magnetite((FeIIFeIII2)O4) is an inert component of bauxite and does not interact with alkali-aluminate solutions.
Iron carbonates. The most common mineral is siderite FeСO3.
Found in monohydrate and gibbsite bauxites. Its amount in these bauxites is variable. The average content in Red October bauxites is 6%. In some batches - up to 30%. Siderite is rarely a pure mineral. It contains manganese and magnesium in noticeable quantities (from 5 to 30%). The replacement of iron with calcium occurs in more limited quantities (up to 10%). This mineral is a very harmful impurity, because it intensively and irreversibly interacts with alkaline solutions, which leads to their decausticization.
In particular: FeCO3+ 2NaOH + H2O = NaCO3+ Fe(OH)3 + 1/2 H2.
The formation of hydrogen can lead to increased pressure in autoclaves. Fe(OH)3 is a finely dispersed colloidal component of red mud; its presence in red mud increases the consumption of rye flour during thickening. In addition, alkaline solutions are contaminated with divalent iron, the content of which ranges from 0.008 to 0.725 g/l. During decomposition, iron is released together with aluminum hydroxide and reduces the quality of the resulting product.
Iron sulfide minerals. Almost all sulfur (92-95%) in bauxite is represented by iron sulfide minerals: pyrite, melnikovite-pyrite, pyrrhotite, marcasite, chalcopyrite.
According to the reactivity of dissolution in alkaline solutions, they are arranged in the following series: melnikovite-pyrite → pyrrhotite → marcasite → pyrite → chalcopyrite. The most common mineral is pyrite (FeS2), a typical representative of sulfide iron in bauxite. There is a colloidal variety: melnikovite. In alkaline aluminate solutions in the Bayer method, pyrite dissolves by 10-20%, and melnikovite by 100%. Isomorphic substitutions of iron with nickel and cobalt up to 14-20% are possible. Iron sulfide minerals have a negative effect on Bayer and sintering processes. Therefore, there are restrictions on the sulfur content in bauxite raw materials. It has been experimentally established that it is cost-effective to process bauxite using both the Bayer method and the sintering method with a sulfur content of no more than 1%. The presence of sulfides leads to irreversible losses of alkali in the form of sulfides, polysulfides and sodium sulfates. At the moment, methods have been developed for purifying alkali-aluminate solutions from sulfur and iron impurities by adding copper or zinc oxide to solutions.
The chemical reaction of pyrite decomposition in alkaline aluminate solutions is presented below:

The extraction of sulfur into solution depends on the mineralogical form and structure of the sulfide. Melnikovite has the most reactivity. The decomposition of sulfide minerals mainly occurs at temperatures above 180 °C, and increases with heating. An increase in the concentration of alkali in the solution has a similar effect. This problem occurs acutely when bauxite with a sulfur content of more than 1% is received for processing. With such a sulfur content, the contamination of solutions with iron sharply increases, and the quality of the resulting alumina decreases. Iron goes into solution in the form of the compound Na2*2H2O - sodium hydroxothioferrate. In addition, it was noticed that equipment corrosion is increasing (the service life of heat exchange equipment using evaporation is reduced from 4.5 years to 9 months). Pipelines are also being rapidly destroyed.
V.V. Grachev established a direct dependence of the contamination of solutions with iron on the content of sulfide sulfur in the solution (see Table 4.2).

Thus, it was shown that the higher the content of sulfide sulfur in the solution, the more dissolved iron it contains. Subsequently, the presence of four forms of sulfur in alkaline aluminate solutions was established: S2- - sulfide, S2O3b2- - thiosulfate, SO3b2- - sulfite, SO4b2- - sulfate.
During oxidation during the leaching process, the following changes occur in the transition forms of sulfur:

S2- → S2О3в2- → SO3в2- → SO4в2-

The behavior of these forms of sulfur oxidation during the leaching of sulfide minerals is presented in Fig. 4.16.

The activation energy for the transition of sulfide sulfur to various forms has been calculated and has following values: I. Еа = 2100 kJ/mol to S2О3в2-; II. Еа = 4396 kJ/mol to SO3в2-; III. Еа = 6007 kJ/mol to SO4в2-.
From the data presented it is clear that the first stage is the least energy-intensive; it occurs at temperatures below 100 °C. It has been experimentally proven that complete oxidation of sulfide sulfur to sulfate sulfur requires a certain time (see Table 4.3).

The rate of interaction depends on the contact surface and the solubility of oxygen in the aluminate solution, i.e., very highly dispersed oxygen must be supplied.
Iron is an integral companion of sulfur; it is also found in aluminate solutions in various forms and undergoes the following changes during the oxidation of sulfur:
2- - iron hydroxysulfate (red);
3- - gives the solution green at 25 °C;
3-n - hydroxoaqua complex.
During the decomposition process, this hydroxoaqua complex of iron coprecipitates with aluminum hydroxide, introducing itself into its crystal lattice, and contaminates the resulting hydroxide with iron impurities, further reducing the quality of the resulting alumina.
Ways to combat sulfide minerals:
1) roasting above 600 °C allows you to destroy sulfide minerals and remove most of the sulfur in the form of gases, but complete removal of sulfur cannot be achieved;
2) flotation of pyrite of bauxite raw materials (water flotation of pyrite and its flotation in alkali-aluminate solutions were experimentally tested at the Department of Metallurgy of Light Metals UPI by F.F. Fedyaev, V.S. Shemyakin, V.V. Saltanov, etc.) . Subsequently, industrial tests of this technology were carried out at the concentrating plant in the city of V. Pyshma and at the Bogoslovsky aluminum smelter. However, this technology has not received industrial implementation;
3) radiometric and photometric enrichment during ore preparation of bauxite raw materials are currently the most promising areas;
4) addition of ZnO to aluminate solutions. As a result, ZnS is formed, which removes sulfide sulfur with red mud. The content of ferrous iron in the solution is sharply reduced. For the first time this technology, developed at the Department of Metallurgy of Light Metals UPI V.V. Grachev, T.A. Uncoated and others, was successfully used at the Ural Aluminum Smelter in the mid-70s-80s. last century.
Titanium-containing bauxite minerals and their leaching behavior. Titanium oxide TiO2 is contained in all bauxites, both in free form and in the form of various chemical compounds. The total amount of TiO2 in bauxite is variable and ranges from 1 to 10%. In particular, in bauxites of the Altai deposit - 2-4% TiO2, Krasnooktyabrsky - 1.5-2.5% TiO2, Tatar - 2-10% TiO2, Gayansky - 1-2% TiO2.
The main titanium minerals: anatase, rutile, occasionally brookite, ilmenite; less commonly sphene, titanomagnetite, perovskite.
Rutile(TiO2) is a common mineral in bauxite. In some cases, up to 8-10% Fe(II) and Fe(III) are present. Rutile is the carrier of uranium and thorium in bauxite. In alkaline solutions, rutile can form a number of compounds such as sodium titanates and silicates. In the presence of lime, a perovskite compound is formed - CaO*TiO2. Chemically, rutile is less active than anatase.
Anataz(TiO2) is the most common titanium mineral in bauxite. Contains up to 1% iron and tin. The structure of anatase is similar to rutile, and the differences lie in the different arrangement of the [TiO6] octahedra. In technological processes of alumina production, it serves as a source of alkali losses due to the formation of sodium titanates. In the presence of calcium oxide, perovskite crystallizes. With increasing temperature, anatase activity increases sharply.
Ilmenite(FeO*TiO2) - is part of the cemented mass of bauxite. Ilmenite is inert in the Bayer process.
Sphene(CaO*TiO2*SiO2) - in bauxites, SUBR is present in the form of large isolated grains or accumulations of small grains with undeveloped edges. The color is yellow-green or brownish-gray. Sphene is also found in the cementing mass of bauxite, less commonly in beans. In the technological process, sphene is also inert.
Titanomagnetite(TiO2*Fe3O4) - more often found in diaspore-boehmite bauxites in the form of inclusions on large black crystals with a metallic luster. The mineral is inert in the technological process.
The behavior of titanium minerals during bauxite leaching was studied for the first time at VAMI. The data obtained showed that when artificially obtained rutile was treated with an alkaline or aluminate solution, the TiO2 content in the solution turned out to be insignificant - from 12 to 100 mg/l (see Fig. 4.17).
In the presence of lime additive, the TiO2 content in the solution is not detected.
It was later found that the addition of TiO2 during leaching of North Ural bauxite, as well as pure diaspore and boehmite, reduces the extraction of alumina into the solution (Fig. 4.17, 4.18). In the presence of lime, introduced based on the ratio CaO:TiO2≥1, the addition of TiO2 does not reduce the yield of alumina into the solution. The role of lime in this case is reduced to the formation of calcium titanate: 2CaO*TiO2*nH2O.

During the experiment, it was noticed that when the diaspore is dissolved in an alkaline aluminate solution in the presence of TiO2, the walls of the autoclaves become covered with a solid white coating, which is not washed off with water. Chemical and X-ray analysis of this plaque showed that it is insoluble sodium metatitanate - NaНТiO3.
TiO2 + NaOH = NaНТiO3
TiO2 + 2NaOH = Na2TiO3 + H2O
Na2ТiO3 + Н2О = NaНТiO3 + NaOH
Based on this, it was assumed that the same film could cover diaspore or boehmite crystals. Its thickness was established to be 18 angstroms. Sharp negative impact titanium on diaspore dissolution is shown in Fig. 4.19.

Thus, the negative effect of titanium oxide on the dissolution of diaspore and boehmite is shown. This is explained by the fact that a protective film of sodium metatitanate has time to form on the crystal already during the heating of the pulp at a lower temperature than the leaching temperature of diaspore bauxite, i.e., before noticeable dissolution of the diaspore mineral and boehmite. With prolonged stirring, the particles that make up the film aggregate into larger flakes, the film is destroyed and the rate of dissolution of diaspore and boehmite increases. Two forms of sodium titanate have been established:
1) Na2O*3TiO2*2.5H2O - needle-shaped crystals obtained in solutions with Na20R concentrations up to 400 g/l;
2) 3Na2O*5TiO2*3H2O - small equiaxed crystals obtained in solutions with a Na2O concentration of more than 400 g/l.
Later, titanium compounds 5Fe2O3*TiO2*Al2O3 and 8Fe2O3*6Al2O3*TiO2*SiO2 were discovered in the red mud of Hungarian factories, which were called “Dorr sands”.
Below is a series of dissolution activities of the main titanium minerals in alkaline aluminate solutions:

TiO2 gel → anatase → rutile

At the moment, bauxite with the following content of titanium oxide in the raw material is supplied to the Ural aluminum smelters: SUBR - 1.5-2% TiO2, Middle Timan bauxite - 3-4% TiO2. Moreover, in the Subrovsky bauxite, the titanium mineral is presented in the form of anatase, and in the Middle Timan bauxite - in the form of rutile.
Carbonate-containing bauxite minerals and their leaching behavior. Among the minerals containing calcium carbonate, the following minerals are found: calcite CaCO3, dolomite MgCO3*CaCO3, hydromagnesite 4MgCO3*Mg(OH)2*4H2O and siderite FeCO3. All these minerals are easily decomposed under autoclave leaching conditions:
MeCO3 + 2NaOH = Na2CO3 + Me (OH)2
Carbonates are very harmful impurities in raw materials, because they convert the expensive caustic alkali NaOH into carbonate Na2CO3.
Calcite(CaCO3) is the most common carbonate in bauxite. The heating curve has one endo-effect in the region of 800-950 °C, which is explained by the dissociation reaction: CaCO3 → CaO + CO2. Calcite is actively decomposed by alkalis and the more strongly, the higher the temperature of the solution and the concentration of alkali in it. This mineral is one of the harmful impurities in bauxite due to the decausticization of active alkali in solution according to the reaction CaCO3 + 2NaOH = Na2CO3 + Ca(OH)2.
The most high content Calcite content was noted in North Ural bauxites - up to 7% CO2, so SUBR currently uses various mechanical methods for bauxite enrichment. In North Ural bauxites, calcite is disseminated into beans and cementing mass. It also fills cracks and voids, forming brushes and coarsely crystallized ores in them. When wet grinding and leaching bauxite, calcium carbonate reacts with alkali, turning it into soda. The equilibrium constant of this reaction at a temperature of 25 °C is calculated using the following formula:

where αCO3в2-, α(ОН)- - ion activity; LpCaCO3, LpCa(OH)2 - the product of the solubility of CaCO3 and Ca(OH)2.
With heating, the equilibrium constant of the reaction increases, since the solubility product of calcite increases and the solubility product of lime decreases; at 200 °C it is equal to unity. It was found that in a weakly heated aluminosilicate solution, namely during wet grinding of bauxite (t = 95 ° C), calcite decomposes to form soda and 3-calcium aluminate, which under these conditions is less soluble than lime. In particular:

3CaCO3 + 2NaAl(OH)4 + 4NaOH = 3CaO*Al2O3*6H2O + 3Na2CO3.

In Fig. Figure 4.20 shows the solubility isotherms of solid phases formed in the Na2O-CaO-Al2O3-CO2-H2O system at various temperatures, obtained by M.G. Leitezen and T.A. Potapova. This diagram shows the stability regions of 3CaO*Al2O3*6H2O.

All aluminate solutions with a composition above curve I are enriched in soda and do not interact with calcite. Solutions located below curve I decompose calcite with the formation of 3-calcium aluminate, and the region of its stability increases with increasing concentration of caustic alkali in the solution. It was later found that at elevated temperatures, 3-calcium hydroaluminate becomes unstable and decomposes with alkali according to the reaction

3CaO * Al2O3 * 6H2O + 2NaOH = 2NaAl(OH)4 + Ca(OH)2

Thus, the data presented show that during wet grinding of diaspore bauxites containing calcite impurities, this mineral completely decomposes with the formation of 3-calcium hydroaluminate and soda, and this hydroaluminate, when leached, further decomposes into lime and sodium aluminate. It has been established that calcium carbonates accelerate the leaching of diaspore bauxites, but they should be considered as harmful impurities, since during the decomposition of carbonates, decausticization of the alkali occurs and the accumulation of soda in aluminate solutions. Subsequently, during evaporation, sodium carbonate is released from the solution in the form of “red soda” and sent to the sintering stage for its causticization. In addition, great difficulties are created when evaporating alkaline aluminate solutions, since the heating tubes of evaporators quickly become overgrown with soda, causing the productivity of the devices to sharply decrease. For these reasons, diaspore bauxite containing more than 3-4% CO2 is not recommended for processing into alumina using the Bayer method. An increase in CO2 content above the recommended norm leads to the need to increase the power of the sintering stage.
Phosphorus and small traces of bauxite. The phosphorus content in bauxite in the form of P2O5 varies from traces to 8.0% and on average ranges from 0.4-0.6%.
Phosphorus concentrations are not determined by the mineral or genetic type of bauxite, nor by the age of the deposits.
The phosphorus content (P2O5) in bauxites from various deposits is as follows: in SUBR bauxites - 0.67%; in bauxites of the YuUBR - 0.20%; in STBR bauxite - 0.27%.
The most probable phosphorus minerals in bauxite are apatite 3 [Ca3PO4] * [Ca F, Cl)2]; vivianite Fe3(PO4)2 * 8H2O; francolite Ca10(PO4)6 * [A], AF2, (OH)2, CO3, O; evansite Al3(PO4)2 * 3Al(OH)3 * 12H2O.
The maximum P2O5 content in SUBR bauxite is 0.8%. Phosphorus is considered a very harmful impurity. When processing bauxite using the Bayer method, phosphorus is almost completely transferred into an alkaline aluminate solution, forming the compound Na3FO4. Subsequently, with a slight decrease in the temperature of the solution, sodium phosphate crystallizes, encrusting heat pipes, heating surfaces of heat exchangers and evaporators, reducing the duration of their operation. The presence of phosphorus affects the grain size of aluminum hydroxide (crushes it), this causes a decrease in the quality of the commercial product.
The pattern of distribution of small impurities in bauxites of various geological or lithologic-mineralogical types has been poorly studied. However, elements such as zirconium, vanadium, chromium, nickel and cobalt are present in all bauxite. Currently, 43 chemical elements have been identified in bauxite, 27 of which are classified as minor impurities (their content in bauxite is less than 0.1%). The mineralogical forms of minor impurities in bauxite have not been sufficiently studied. Most impurities, such as gallium and scandium, do not form independent minerals, but due to the proximity of the radii of their ions to the radii of aluminum ions, they enter the lattices of diaspora, boehmite and gibbsite minerals. When processing bauxite using the Bayer method, scandium and other rare earth elements are completely converted into red mud, in which their content increases by 1.5-2 times from the initial content in bauxite. Red mud currently belongs to man-made waste and is a raw material base for the production of these elements.
The content of small impurities in bauxite is presented in table. 6.5. Of greatest interest are those impurities that tend to accumulate in solutions during cyclic production - V, Ga, Cr.
Vanadium and its behavior during leaching. Vanadium may be associated with ferric oxide. A relationship has been noted between its content and the amount of iron oxide in bauxite.
The dependence is expressed by the following formula, %: V2O5 = 4.8*Fe2O3 *10v-3, where Fe2O3 is the percentage content in bauxite. In addition, a connection between vanadium and aluminum minerals was noticed due to the proximity of their ionic radii. There is an increase in the V2O5 content with an increase in the silicon module of bauxite, which may be a consequence of the inclusion of vanadium in aluminum hydroxide minerals. The highest vanadium content is observed in such alumina raw materials as high-iron blast furnace slag. In the hydrochemical processing of alumina production, vanadium is distributed approximately equally between the alkali-aluminate solution and the solid phase (red mud).
Accumulating in the aluminate solution during decomposition, it falls out of the solution along with aluminum hydroxide, reducing its quality. The V2O5 content in factory circulating solutions ranges from 1.1 to 1.5 g/l, so these solutions can serve as a source for obtaining vanadium from them. The main method for isolating vanadium from alkaline aluminate solutions is the crystallization method, based on reducing the solubility of vanadium compounds depending on the concentration of the solution and a decrease in temperature. Currently, this product is extracted only at the Pavlodar aluminum smelter.
Gallium and its behavior during leaching. Gallium: tmelt = 30 °C, t = 2000 °C; has a high heat capacity. This element does not form independent minerals, but can isomorphically replace aluminum in its hydroxides. It has been noted that there is more of it in diaspore bauxites, since crystalline GaOOH is isomorphic to the AlOOH diaspore and can be incorporated into its crystal lattice. In the technological stages of alumina production, gallium oxide interacts with alkali and goes into solution in the form of dissolved sodium gallate:

Some gallium leaves technological process with red mud as a result of coprecipitation and chemical interaction of gallate anion with metal cations. The gallium content in the main products obtained in the Bayer process is given in table. 4.4.

A significant amount of commercial gallium entering the world market is produced by the aluminum industry as a by-product of bauxite processing. Research and industrial practice have shown that about 2/3 of gallium oxide from bauxite goes into solution, and 1/3 remains in red mud. By sintering red mud with limestone and soda, and then treating it with an alkaline aluminate solution, the remaining gallium can be extracted from bauxite. In the same way, gallium can be extracted from bauxite processed using the sintering method. The source of gallium in alumina production is aluminate solutions, previously purified from impurities. At foreign alumina refineries, gallium is extracted from Bayer process solutions by electrolysis on a mercury anode. We have developed methods for electrochemical deposition on a gallium cathode, as well as cementation of gallium from solutions with aluminum gallamide. A large amount of work was carried out at the Institute of Chemical Technology of the Ural Branch of the Russian Academy of Sciences under the leadership of S.P. Yatsenko on obtaining ultra-pure metal corresponding to the TU 48-4-350-84 grade. They also showed that the optimal scale of gallium production at an alumina plant with an average productivity of 0.5-1.0 million tons of alumina is a workshop producing 5-10 tons of gallium per year. In this case, the gallium concentration established in circulating solutions depends little on the scale of gallium production.
Gallium has a number of valuable properties and is used in LEDs, lasers, and solar batteries. It has found wide application as a component of low-melting alloys, solders, diffusion-hardening compounds, as well as in dental materials.
Chromium and its behavior during leaching. Chromium compounds are usually found in bauxites in small quantities (0.02-0.04%), but some bauxites contain up to 3.0% Cr2O3. In addition to its supposed connection with iron hydroxide, chromium is associated in bauxite with boehmite; Trivalent chromium is soluble in alkaline solutions to form sodium hexahydrooxochromate. If there is an excess of alkali, these compounds can accumulate in aluminate solutions, turning them greenish. If chromium and bauxite enter the sintering stage, then after its oxidation with oxygen during the sintering process, sodium chromates are formed, which are highly soluble in water and alkaline solutions; in them, chromium is in the 6-valent form. In these reactions this compound is very toxic. The color of 6-valent chromium in alkaline solutions is red. To remove 6-valent chromium, you can use various reducing agents, in particular Ns2S, FeSO4*10H2O. Chromium passes into the 3-valent state and is released from alkaline solutions in the form of Cr(OH)3, and a certain amount of aluminum coprecipitates with it, i.e., the loss of aluminum with red mud increases slightly.
Organic substances in bauxite and their behavior in alkali-aluminate solutions. Bauxite deposits of all types contain organic substances of different origins. These are mainly products of decomposition of plant residues that have migrated into deposits; mineralized plant residues are less commonly observed. The average content of organic substances in bauxite is as follows: in the form of bitumen - up to 0.052%, humins - up to 0.036%.
Humic compounds include high molecular weight compounds. According to the accepted classification, humic substances are divided into 3 groups:
1) water-soluble - fulvic acids;
2) soluble in alcohol - hematamilanic acids and their derivatives;
3) insoluble in either water or alcohol - humic acids.
The permissible organic content in alumina production solutions should be less than 3% oxygen. Organic matter is very harmful to the technological process, since its presence affects the speed and completeness of bauxite leaching. Humins slow down the decomposition of aluminate solutions, reduce the surface tension of solutions, which leads to foaming, as well as slowing down the thickening of red mud. Roasting, and in some cases washing, of bauxite can reduce the maximum concentration of organic substances in aluminate solutions. At the moment, the fight against organics in alkaline aluminate solutions comes down to the use of antifoaming agents in the form of various organic surfactants that allow them to extinguish foam, as well as the oxidation of organics with oxygen or ozone. The material balance of the distribution of organic substances is presented in Table. 4.5.

The numerator of the fraction is the percentage of the total amount of organic substances, and the denominator is the percentage of the amount of dissolved organic substances.
Thus, from this material balance it is clear that the bulk of organic matter - 83% - was released from the cycle with waste red mud. Organic substances are removed from solution mainly with soda (co-precipitated with red soda) and Al(OH)3. Aluminum hydroxide obtained by decomposition in the Bayer branch is colored by organic substances in pink in contrast to the snow-white hydroxide obtained by sintering. The more organic substances there are, the more of them leave the cycle in these ways. It has been established that organic substances are capable of accumulating in aluminate solutions to a certain limit, when an equilibrium occurs between their intake and removal from the solution. At this equilibrium, the content of these substances must remain below the limit, otherwise additional measures are needed to purify the solutions.
Studies have shown that humic substances are almost completely leached from bauxite in the form of highly soluble alkaline humates. Bitumen is leached by no more than 10%, and when the autoclaved pulp is diluted and thickened, they completely precipitate. Humins are oxidized during leaching and partially at other stages to form sodium oxalate and resinous substances. These resinous substances, consisting mainly of carboxylic acids, color aluminate solutions in brown, and at high contents their solutions turn black.
Studying the effect of organic substances on the leaching process, M.N. Smirnov showed that organic substances containing alcohol groups accelerate the leaching of diaspore bauxites. Moreover, it was found that they increase the activity of lime, increasing its solubility in aluminate solutions. Resinous substances (sodium oxalate and acetate) do not affect the extraction of alumina from diaspore bauxite. Organic substances representing bitumen reduce the rate of dissolution of diaspores in bauxite. According to M.N. Smirnov, such substances, when leached, envelop particles of aluminum minerals in bauxite and make it difficult for the aluminate solution to access them. Organic substances slow down the decomposition of aluminate solutions, the crystallization of recycled soda and the thickening of red mud, and also complicate the evaporation of the mother liquor. Resinous organic substances reduce the surface tension of aluminate solutions and thereby contribute to their foaming during transportation and mixing. Particularly strong foaming is observed in mixers after grinding bauxite, in red mud washers, as well as in decomposers.
From bauxite, from 3.8 to 11.9% of organic impurities, which are various shapes organics (see Fig. 4.21). During long-term circulation in the Bayer cycle, the content of organic matter in the circulating solution is almost 30 times higher than its supply with bauxite. The main carriers of this impurity are the circulating solution, the first industrial water and the seed hydroxide. Organic substances complicate the process of thickening red mud, decomposition of aluminate solutions, crystallization of vanadium and cementation of gallium. There are three main groups of organic substances in alkaline aluminate solutions: humins and primary products of their decomposition with a molecular weight greater than 500, intermediate (phenolic acids and benzene carbonates) and low molecular weight products. Alcohols, phenols, ketones, and aliphatic carboxylic acids have the ability to form foam (Table 4.6).

The combined Bayer-sintering scheme ensures the maintenance of the optimal amount of organic substances in circulating solutions by removing them with red mud, aluminum hydroxide and, especially, circulating soda. When processing bauxite only using the Bayer method, it is necessary to specially separate organic impurities from solutions in order to reduce their content in the recycled materials.
In the history of the development of the aluminum industry, there is a well-known example when a newly built alumina plant, operating according to the Bayer method, had to be closed after several months of operation due to severe contamination of the circulating solutions with organic substances.

What is bauxite?

Bauxite is a natural stone native to France. It was in the south of this country that this aluminum ore was first discovered. The name "bauxite" also comes from French word"bauxite".

The name is associated with an area called Lebo, where this stone was discovered. In this article we will consider both physical and chemical properties of bauxite, but first, let’s look at the composition and determine what components are included in it.

Description and properties of bauxite

So what is this breed? Bauxite is the name given to aluminum ore. It contains aluminum hydroxide, as well as oxides of such chemicals like silicon and iron.

In addition to these components, bauxite contains alumina. Its percentage can range from forty to sixty percent and even higher. Bauxite is considered a truly unique and amazing natural stone.

Let's turn to history. For the first time about amazing properties of bauxite was said in one thousand eight hundred and fifty-five at an exhibition in the French capital of Paris. There was an interesting stone there. It looked like a beautiful silver color.

Its weight was very small, but it was quite strong from a chemical point of view. This metal was labeled "clay silver" at the exhibition. This description describes the properties and type of aluminum. But the raw material from which this interesting metal is obtained is called bauxite.

It is worth noting that aluminum is obtained only from those bauxites in which the percentage of aluminum alumina is at least forty percent. Very great value have bauxites, from which it is not difficult to obtain alumina.

In its appearance kind of bauxite very similar to clay, but in terms of characteristics it has nothing in common with it. Bauxite, unlike clay, is completely insoluble in water.

The first location of bauxite deposits on the territory of our country, which were found in the Urals, was called “Little Red Riding Hood”. Bauxite is the most important stone from which aluminum is obtained.

Bauxite deposits and mining

Bauxite- This is a very complex rock in its composition. The main part of them consists of alumina hydrates. But besides it, bauxite also contains other components. The most harmful component is silicon oxide.

As for other substances, it is quite possible to find in bauxite such components as magnesium, manganese and calcium oxide, titanium dioxide and others. Let's take a closer look physical properties bauxite.

In appearance, bauxite can be red or other shades. Bauxite is found in both pink and dark red colors. The stone can also have a gray tint from lighter to charcoal black. If we evaluate bauxite hardness, then this value is equal to 6 on the Mohs scale.

The density of the stone can vary from 2900 to 3500 kilograms per cubic meter. In terms of transparency, bauxite is opaque. Stones can be formed from different minerals. Based on this, the breed can be divided into three main groups.

The first group includes bauxite, for which the rock-forming mineral is diaspore or boehmite. Such bauxites are called monohydrate. In them, alumina is presented in only one form.

The next group includes those bauxites for which the so-called gibbsites are the basis. Such stones contain alumina in trihydrate form. And the last, third group includes those bauxites that combine the forms of the first groups.

Bauxite deposit depends on the degree of weathering in a particular zone of acidic, alkaline, and sometimes basic rocks. Bauxite deposits can also form in areas where alumina is deposited in lake and sea basins.

Thus, two main reasons for the location of bauxite can be identified. The first reason is called platform reason. It is associated with continental sediments that lie horizontally. The second reason is related to the area where coastal-marine type deposits are located.

Almost the entire reserve of bauxite on the globe - 90% - is concentrated mainly in those countries where the climate is tropical or subtropical.

This is due to the fact that the stone is formed mainly where active weathering of aluminum rocks occurs and this process continues for a significantly long period. The reason for weathering is climate.

Guinea ranks first in the world in terms of bauxite reserves. Its territory contains about twenty billion tons of bauxite. Australia is in second place in terms of the quantity of this stone. There are approximately seven billion tons of bauxite.

As for Russia, the reserves of this stone in our country are so small that there is no such amount of ore that would be enough for consumption within the state. The share of world reserves of this type of raw material is only one percent of the global supply of stone.

The highest quality bauxite deposits in our country are considered to be bauxites located in the North Ural bauxite region. A new area of this raw material is the Middle Timan group, which is located in the northwestern region of the Komi Republic. Bauxite mining is carried out here and this area is considered more promising than the one mentioned at the beginning.

Russia is only in seventh place in the world in the production of aluminum ores. Due to the fact that the country itself cannot provide itself with the metal in the required quantity, it has to purchase bauxite from foreign countries.

There are fifty deposits of this ore on the territory of the Russian Federation. This figure includes both territories in which bauxite mining is being actively carried out, as well as those where deposits have not yet been fully developed.

Largest part bauxite reserves located in the European part of Russia. This includes the previously mentioned Komi Republic, as well as the Arkhangelsk, Sverdlovsk and Belgorod regions. All of these areas contain about seventy percent of all bauxite reserves in our country.

To the old ones bauxite deposit in Russia it can be called Radynskoye, which is located on the territory of the Leningrad region. Bauxite mining continues there today.

Locations bauxite deposits can be roughly divided into four groups. The first group is called a unique deposit. In such areas, the amount of ore exceeds five hundred million tons. The second group is large and medium-sized deposits. Here the bauxite deposits range from fifty to five hundred tons.

The last group is small deposits. In such territories presence of bauxite in figures it is less than fifty million tons.

Applications of bauxite

Main bauxite use lies in the ability to extract aluminum from it. But this stone is also used in other areas. In the ferrous metallurgy industry, alumina is also commonly used as a flux.

In addition, bauxite can be used in the production of paints. By melting this stone, alumina cement can also be produced. What if melt bauxite in an electric furnace, then the final product can be electrocorundum.

Bauxite price

Bauxite price depends primarily on the quality of the stone. Also, the total cost will depend on how much material is ordered. For example, if you purchase bauxite wholesale, then the price will decrease significantly.

BOXITES (from the name of the area of Les Baux, Lex Baux, in the south of France, where their deposits were first discovered * a. bauxite; n. Bauxite; f. bauxites; i. bauxitas) - aluminum ore, consisting mainly of aluminum hydroxides, oxides and hydroxides of iron and clay minerals.

The main ore-forming minerals of bauxite: diaspore, boehmite, gibbsite, goethite, hydrogoethite, hydrohematite, kaolinite, chamosite, chlorites, rutile, anatase, ilmenite, aluminogethite, aluminohematite, siderite, calcite, micas. Bauxite is very diverse in appearance. Their color is usually red, brownish-brown, less often gray, white, yellow, black. According to their state of aggregation, bauxites are distinguished as dense (stony), porous, earthy, friable and clay-like; according to structural characteristics - clastic (pelite, sandstone, gravelite, conglomerate) and concretionary (oolitic, pisolite, leguminous); by texture - collomorphic (uniform, layered, etc.). Due to different porosity, the density of bauxite varies from 1800 (loose bauxite) to 3200 kg/m3 (stony bauxite).

According to the predominant mineral composition, bauxites are distinguished: monohydroxide, composed of diaspore, boehmite, trihydroxide - gibbsite; mixed composition - diaspores-boehmite, boehmite-gibbsite. There are also more detailed divisions of bauxites depending on the mineral composition: chamosite-boehmite, chamosite-gibbsite, gibbsite-kaolinite, goethite-chamosite-boehmite, kaolinite-boehmite, etc. According to the conditions of formation, bauxites are divided mainly into lateritic (residual) and redeposited (sedimentary). Bauxites were formed either as a result of deep chemical processing (lateralization) of aluminosilicate rocks in a humid tropical climate (lateritic bauxites) or as a result of the transfer of lateritic weathering products and their redeposition (sedimentary bauxites). Depending on the tectonic position, bauxites of platform and geosynclinal areas, as well as bauxites of oceanic islands, are distinguished. Bauxites form sheet-like and lens-shaped bodies of variable thickness, and in terms of deposits they are linear, isometric and irregular in shape. Often deposits consist of several (in vertical section) lenses. The quality of lateritic bauxites is usually high, while sedimentary bauxites can range from high-grade (for example, the North Ural deposits) to substandard (Boksonskoye deposit in Buryatia).

Bauxite is the main ore for the extraction of alumina (AL2O3) and aluminum; used in the abrasive industry (electrocorundum), in ferrous metallurgy (flux when smelting open-hearth steel), low-iron bauxites - for the production of high-alumina mullitized refractories, fast-hardening aluminous cements, etc. Bauxites are complex raw materials; they contain Ga, as well as Fe, Ti, Cr, Zr, Nb, and rare earth elements. In the USSR, the quality requirements for mined (commercial) bauxite are determined by GOST, as well as contractual terms between suppliers and consumers. According to the classification of the current GOST 972-74, bauxite is divided into 8 grades depending on the weight ratio of the contents of alumina and silica (the so-called silicon module). For the lowest grade (B-6, grade II), the silicon module must be at least 2 with an alumina content of at least 37%; for high-grade bauxites (B-0, B-00) the silicon module must be more than 10 with an alumina content of 50% and above . The selected varieties and grades of bauxite have their own areas of industrial use.

Bauxite is mined by open-pit or, less commonly, underground methods. The choice of technological scheme for processing bauxite depends on its composition. The production of aluminum from bauxite is carried out in 2 stages: in the first, alumina is obtained by chemical methods, in the second, pure metal is isolated from alumina by electrolysis in a melt of aluminum fluoride salts. When producing alumina, they mainly use the hydrochemical Bayer method, the sintering method, as well as the combined Bayer-sintering method (parallel and sequential options). The principle of the Bayer process involves treating (leaching) finely ground bauxite with a concentrated solution of sodium hydroxide, resulting in the alumina going into solution in the form of sodium aluminate (NaAl3O2). Aluminum hydroxide (alumina) is precipitated from an aluminate solution purified from red mud. Low-quality bauxite is processed in a more complex way - the sintering method, in which a three-component charge (a mixture of crushed bauxite with limestone and soda) is sintered at 1250°C in rotary kilns. The resulting cake is leached with a circulating alkaline solution of weak concentrations. The precipitated hydroxide is separated and filtered. The parallel combined Bayer-sintering scheme provides for the simultaneous processing of high-quality and low-grade (high-silicon) bauxite at one plant. The sequential combined scheme of this method includes the processing of bauxite into alumina, first by the Bayer method and then the additional extraction of alumina from red helmets by sintering them with limestone and soda. The main bauxite-bearing areas (see map) are located in the European part of the USSR, in the Urals, and in Kazakhstan.

In the European part, they are known in the Arkhangelsk region of the RSFSR (Iksinskoye, etc.), in the Middle (Vezhayu-Vorykvinskoye, etc.) and Southern Timan (Timsherskoye, Puzlinskoye, etc.), in the Leningrad (Tikhvinskoye) and Belgorod (Vislovskoye, etc. ) regions of the RSFSR. In the Urals, bauxite deposits are developed in the Sverdlovsk (North Ural bauxite-bearing region) and Chelyabinsk (South Ural deposits) regions of the RSFSR. Within Northern Kazakhstan, bauxite deposits are concentrated in the Kustanay (Krasnooktyabrskoye deposit, Belinskoye, Ayatskoye, East Ayatskoye and other deposits) and Turgay (East Turgay group of deposits) regions of the Kazakh SSR. In eastern Siberia, bauxites are found in the area of the Chadobetsky uplift of the Angara region and in the eastern Sayan Mountains (Boksonskoe).

The most ancient bauxites in the USSR are known from the Bokson deposit (Precambrian, Vendian). Bauxites of the North Ural group are associated with Middle Devonian deposits, and Middle Timan bauxites are associated with Middle and Upper Devonian deposits. Bauxites of the Iksinsky and Vislovsky deposits occur in Lower Carboniferous deposits; the deposits of Northern Kazakhstan were formed in the Cretaceous and Paleogene times and are the youngest.

The People's Republic of China (deposits in the provinces of Shandong, Henan, Gansu, Yunnan, Liaoning, Shaanxi, etc.), the People's Republic of China (the deposits of Halimba, Nyirád, Iskaszentgyörgy, Gant, etc.), the SFRY (the deposits of Vlasenica, Drniš, the Lika Plateau, etc.) have large reserves of bauxite. Bijela Lipa, Obrovac, Niksic, Bijela Polana), bauxite deposits are also known in the Socialist Republic of Vietnam, Vietnam, and the DPRK.

In industrialized capitalist and developing countries, bauxite reserves at the beginning of 1982 amounted to about 22 billion tons, incl. proven 13.5 billion tons. The main reserves of bauxite are located in developing countries - about 75% (16.7 billion tons), incl. proven about 75% (10.1 billion tons). In developed countries, deposits of high-quality bauxite are known in the form of lateritic nappes in Australia; Their share in total reserves is approximately 20%. The bulk of bauxite deposits are located in little-explored areas of tropical countries, so it is expected that the trend of reserves growing faster than production will continue.

In 1974, the International Association of Bauxite Mining Countries was created. It initially included Australia, Guinea, Jamaica, Guyana, Suriname and the SFRY, then Ghana, Haiti and the Dominican Republic. Brazil, Greece, India, Türkiye, the USA, and France also have significant reserves of bauxite.

Bauxite production in industrialized capitalist and developing countries in 1981 amounted to 73.0 million tons, incl. in developing countries 40.9, in industrialized countries 32.12. Australia ranks first in bauxite production, followed by Guinea, Jamaica, Suriname, Brazil, and Guyana. In the future, the largest increase in bauxite mining capacity is expected in Australia, Guinea and Brazil. According to forecasts (80-90s), the vast majority of alumina refineries will be built in bauxite-mining countries, and the volume foreign trade bauxite production, which amounted to about 35 million tons in the early 80s, will increase at a relatively slow pace.