Bauxite texture. The amazing mineral bauxite

Bauxite is a widespread rock, consisting mainly of aluminum hydroxide minerals. Named after the village of Les Baux in southern France, where the specimen was discovered and described in 1821. The world learned about the properties of bauxite after the Paris exhibition of 1855, which demonstrated aluminum obtained from it, presented as “clay silver”. Indeed, outwardly bauxite is similar to clay, but in its physical and chemical properties has nothing to do with her.

Bauxite is a widespread rock, consisting mainly of aluminum hydroxide minerals.

By color, they are most often red, brown, less often - white, gray, black, green, or with impurities of various colors. Bauxites do not dissolve in water. Outwardly, they may look clayey or stony, in structure - dense or porous, finely crystalline or amorphous. The density depends on the iron content. Quite often, rounded grains formed by alumina or iron oxide can be included in the groundmass. With a content of 50-60% iron oxide, the rock becomes important iron ore. The hardness of bauxite on the Mohs scale ranges from 2 to 7. Its chemical formula, in addition to aluminum oxide hydrates, which make up the main ore mass, includes iron, silicon, titanium, magnesium and calcium carbonate, phosphorus, sodium, potassium, zirconium, and vanadium in the form of various compounds. Sometimes - an admixture of pyrite.

Bauxites do not dissolve in water

Depending on the nature of the rock-forming mineral, bauxites can be divided into 3 main groups:

monohydrate, in which alumina is present in only one form (diaspore, boehmite);
trihydrate containing alumina in three-water form (gibbsite);
mixed, combining the first 2 groups.

The quality and grade of bauxite as aluminum ore depends on the content of aluminum oxide in terms of dry matter. In the highest grade, it is contained in an amount of 52%, in the lowest it is at least 28%. Even in the same field, the amount of alumina can vary significantly. The quality of the rock decreases with an increase in the content of silicon oxide.

Bauxite ore is valued, from which alumina is easily extracted. Its various varieties and brands are used in industry in their own way.

How bauxite is mined (video)

Place of Birth

About 90% of the world's bauxite reserves are located in 18 tropical countries. Typically, the quality of lateritic bauxites formed as a result of deep chemical processing of aluminosilicate rocks in a tropical climate is high. Sedimentary bauxite, formed as a result of the transfer of lateritic weathering products and their redeposition, can be both high-grade and substandard. Deposits are located in the form of layers, lenses or nests, often on the surface of the earth or in its uppermost layers. Therefore, ore is mainly mined open way using powerful career technology. World reserves are characterized by uneven territorial distribution. More than 50 countries have ore deposits, with 93% of these reserves located in 12 of them. Large deposits are found in Australia, Africa, South and Central America, Asia, Oceania, and Europe. The highest content of alumina in ore mined in Italy (64%) and China (61%).

Gallery: bauxite stone (50 photos)

The largest bauxite deposits in Russia are located in Severouralsk, 70% of the total amount of ore in the country is mined there. These are the oldest deposits on earth, they are over 350 million years old. The recently commissioned Cheremukhovskaya-Glubokaya mine is located 1,500 meters underground. Its uniqueness lies in the extraction and transportation of ore: there are 3 lifting machines on 1 pile driver. The proven reserves are 42 million tons, and the aluminum content in the ore is almost 60%. The Cheremukhovskaya mine is the deepest mine in the Russian Federation. It should meet the country's demand for aluminum within 30-40 years.

The cost of 1 ton of ore without transportation costs in Russia is 20-26 dollars, for comparison, in Australia -10. Due to unprofitability, bauxite mining was stopped in Leningradskaya, Chelyabinsk region. In Arkhangelsk, rock is mined with an open pit high level alumina, however, the increased content of chromium and gypsum reduces its value.

The quality of ores from Russian deposits is inferior to foreign ones, and their processing is more complicated. In terms of bauxite mining, Russia ranks 7th in the world.

Use of bauxite

The use of bauxite in 60% falls on the production of aluminum. Its production and consumption ranks first in the world among non-ferrous metals. It is necessary in shipbuilding, aviation and food industries. Using aluminum profiles in the sea, their strength, lightness and resistance to corrosion are of great importance. The consumption of bauxite in construction is developing dynamically, more than 1/5 of the produced aluminum is spent on these needs. When ore is smelted, electrocorundum is obtained - an industrial abrasive. Allocated impurity residues of non-ferrous metals are raw materials for the production of pigments, paints . Alumina obtained from the ore is used as a molding material in metallurgy. Concrete made with the addition of aluminous cement hardens quickly, is resistant to high temperatures and liquid acidic environments. The absorbent properties of bauxite make it suitable for use in the manufacture of oil spill cleanup products. Low-iron rocks are used to manufacture refractories that can withstand temperatures up to 1900°C.

The demand for aluminum and other ore processing products is growing, so developed countries are investing in the development of deposits even with a low threshold of profitability.

The use of bauxite in jewelry is found only in author's works. Unusual color samples are used to make souvenirs, in particular polished balls. The mineral bauxite folk medicine is not used, since its therapeutic possibilities have not been found to date. Also, its magical properties have not been revealed, so it does not attract the attention of psychics.

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Bauxite refers to sedimentary, aluminous rocks. Its name comes from the French "Vaux" - a village in Provence (France) at the place of the original finds.

bauxite has characteristics: texture legume or oolitic, in rare cases - aphanitic (i.e. very dense with barely visible minerals) or collomorphic. The texture is massive, resembling conglomerates or brecciated in appearance.

Bauxite is made up of several minerals:

Alumina hydrates (hydrargillite, boehmite, diaspore);

Clay minerals: chlorite, siderite, oxides and hydroxides of iron, pyrite, quartz, chalcedony, etc.

Also, bauxites differ in the quantitative proportions of the minerals contained in it - alumina hydrates. Classify: boehmite-diaspore, hydrargillite and mixed bauxites. The content of Al2O3 in bauxites ranges from 28 to 45%; Fe2O3 - from 2 to 50-60%. Sometimes there are increased contents of Ga, Zr, Zn, Co, Ni, Cr, Cu, Ba, etc.

Most often, the bauxite mineral is a stony rock of medium or high hardness. But sometimes there are also earthy representatives, loosely connected, who get their hands dirty. If bauxite is moistened, it becomes non-ductile. Density - 2.7 g/cm3; the specific gravity varies around 3. The main colors are red, brown, gray to white, the shades will depend on the percentage of iron.

Bauxites occur in the form of lenses, nests, sheet-like deposits. By origin, several types of bauxite are distinguished: residual or lateritic, which are products of modern weathering of various igneous rocks. Most often, such specimens have a reddish tint.

The next species is colloid-sedimentary, which "ripen" on continental or neglected - maritime zones. Coastal-marine, they are also called lagoonal bauxites, most often located on an uneven karst surface of limestones and overlapped with layered marls or bituminous limestones.

CALCITE ON BOXITE

Continental developments are divided into four groups:

1) slope (deluvial), which, respectively, originate and lie on the slopes;

2) valleys, lining ancient ravines, they form lenses among fossil remains, mainly kaolinite clays;

3) lacustrine, or hollow, which grow in the central and coastal parts of lake pits. Such bauxites are also accompanied by kaolinite clays;

4) karst, which respectively fill karst funnels and depressions in the relief. Most often they are underlain by kaolinite clays, under which there are carbonate rocks.

There are several main deposits of bauxite: residual or lateritic bauxites are mined in the Yenisei Ridge; coastal marine come from the Urals, the same representatives are found in the Sayan Mountains, in Central Asia. The main deposits of continental bauxites are located in the area of Kamensk Uralsky (slope), in Northern Kazakhstan (karst), Tikhvin (valley). Large bauxite deposits are known in Australia, Brazil, Guinea, India, Indonesia, and Vietnam.

Bauxite is the main source of aluminum production. The main use of the mineral is in ferrous metallurgy in the form of a flux, as well as for the creation of artificial paints, abrasives, sorbents for cleaning oil products from impurities.

Since ancient times, jewelers have used bauxite to produce synthetic stones. Aluminum crystals, after cleaning in electric furnaces, turned into synthetic white s. Chromium oxides were added to sapphire and red was obtained. Ruby was used to make stones for watches.

Currently, aluminum is used in the jewelry industry for the manufacture of bracelets, chains, brooches, etc. Aluminum goes well with precious stones.

According to the mineralogical composition, bauxites are divided into: 1) monohydrate - boehmite and diaspore, 2) trihydrate - gibbsite, and 3) mixed. Both monohydrates and trihydrates of alumina can be present in these types of ores. In some deposits, anhydrous alumina (corundum) is present along with trihydrate.

Bauxites from deposits in Eastern Siberia belong to two completely different types in terms of age, genesis, appearance, and mineralogical composition. The first is a kind of argillite-like metamorphosed rocks with an indistinctly pronounced bean microstructure, and the second has a typical bean structure.

The main components of bauxites are oxides of aluminium, iron, titanium and silicon; oxides of magnesium, calcium, phosphorus, chromium and sulfur are contained in amounts from tenths of a percent to 2%. The content of oxides of gallium, vanadium and zirconium is thousandths of a percent.

In addition to Al 2 O 3, the boehmite-diaspore bauxites of Eastern Siberia are characterized by a high content of SiO 2 and Fe 2 O 3 , and sometimes also titanium dioxide (gibbsite type).

Technical requirements for bauxite are regulated by GOST, which regulates the content of alumina and its ratio to silica (silica module). In addition, GOST provides for the content of harmful impurities in bauxite, such as sulfur, calcium oxide, phosphorus. These requirements, depending on the method of processing, the type of deposit and its technical and economic conditions for each deposit, may vary.

In the diaspore-boehmite bauxites of Eastern Siberia, the characteristic bean structure is observed mainly only under a microscope, and the cementing material predominates over the bean. There are two main types of bauxites of this type: diaspore-chlorite and diaspore-boehmite-hematite.

In deposits of the gibbsite type, bauxites with a typical bean structure predominate, among which are distinguished: dense, stony and weathered, destroyed, called loose. In addition to stony and loose bauxites, clayey bauxites and clays make up a significant part. The bean part of stony and loose bauxites is mainly composed of hematite and magnetite. The sizes of the bobbins are from fractions of a millimeter to a centimeter. The cementing part of stony bauxites, as well as varieties of bauxites, are composed of fine-grained and finely dispersed clay minerals and gibbsite, usually colored reddish-brown by iron hydroxides.

The main rock-forming minerals of bauxites of the diaspore-boehmite type are chlorite-daphnite, hematite, diaspore, boehmite, pyrophyllite, illite, and kaolinite; impurities - sericite, pyrite, calcite, gypsum, magnetite, zircon and tourmaline. The presence of chlorite, as well as high-silica aluminosilicates - illite and pyrophyllite, determines the high content of silica in bauxites. Mineral grain sizes from fractions of a micron to 0.01 mm. Minerals in bauxites are in close association, forming finely dispersed mixtures, and only in some areas and thin layers do some minerals form segregations (chlorite) or beans. In addition, various replacements and changes in minerals are often observed due to the processes of weathering and metamorphism.

The rock-forming minerals of gibbsite-type bauxites are aluminum trihydrate - gibbsite, hematite (hydrohematite), goethite (hydrogoethite), maghemite, kaolinite, halloysite, hydromicas, quartz, rutile, ilmenite, and anhydrous alumina (corundum). Impurities are represented by magnetite, tourmaline, apatite, zircon, etc.

The main alumina mineral, gibbsite, is observed in the form of a finely dispersed, weakly crystallized mass and, more rarely, relatively large (0.1–0.3 mm) crystals and grains. Finely dispersed gibbsite is usually colored by iron hydroxides in yellowish and brown colors and almost does not polarize under a microscope. Large grains of gibbsite are characteristic of stony bauxites, where they form crustification rims around the beans. Gibbsite is closely associated with clay minerals.

Titanium minerals are represented by ilmenite and rutile. Ilmenite is present both in the cementing part of bauxite and in the legume in the form of grains ranging in size from 0.003–0.01 to 0.1–0.3 mm. Rutile in bauxites, finely dispersed in size from fractions to 3–8 mk and

2. Study of the material composition

When studying the material composition of bauxites, as follows from the above, we are dealing with amorphous, finely dispersed and fine-grained minerals that are in close paragenetic intergrowths and are almost always colored by iron oxides and hydroxides. Therefore, in order to make a qualitative and quantitative mineralogical analysis of bauxites, it is necessary to use various research methods.

From the original ore sample, ground to -0.5 or -1.0 mm, take hinges: one -10 G for mineralogical, the second -10 g for chemical and the third -5 G for thermal analyses. Diaspore-boehmite bauxite samples are crushed to 0.01–0.07 mm and gibbsite - up to 0.1–0.2 mm.

The mineralogical analysis of the crushed sample is carried out after its preliminary discoloration, i.e., the dissolution of iron oxides and hydroxides in oxalic and hydrochloric

acids or alcohol saturated with hydrogen chloride. If carbonates are present, the samples are first treated with acetic acid. In the obtained solutions, the content of oxides of iron, aluminum, silicon and titanium is determined chemically.

The mineralogical composition of the insoluble residue can be investigated by separation in heavy liquids after preliminary disintegration and elutriation, and by separation in heavy liquids without preliminary elutriation.

For a more complete study of clay minerals, elutriation is used (variant I), while clay fractions can be studied by other methods of analysis (thermal, X-ray diffraction) and without separation in heavy liquids. Option II of the analysis is the fastest, but less accurate.

The main operations and methods of analysis used in the study of the material composition of bauxites are described below.

Examining under a microscope produced in transparent and polished sections and in immersion preparations. In a laboratory study, the entire complex of analyzes should be preceded by the study of bauxites in thin sections. The mineralogical composition, the degree of dispersion of minerals, the relationship of minerals with each other, the degree of weathering, structure, etc., are determined from sections prepared from various bauxite samples. Minerals of iron oxides and hydroxides, ilmenite, rutile and other ore minerals are studied in polished sections. At the same time, it should be taken into account that the minerals of iron oxides and hydroxides are almost always in close connection with clay and alumina minerals, therefore, as our studies have shown, their optical properties do not always coincide with the data of reference samples.

When studying the mineralogical composition of bauxites, especially their loose varieties, the immersion method is widely used. In immersion preparations, the mineralogical composition is studied mainly by the optical properties of minerals, and the quantitative ratio of minerals in the sample is also determined.

The study of bauxite rocks under a microscope in transparent and polished sections and immersion preparations should be carried out at maximum magnifications. Even so, it is not always possible to elucidate the necessary morphological and optical properties of minerals, the nature of their fine intergrowths. These tasks are solved only with the simultaneous use of electron microscopic and electron diffraction methods of investigation.

elutriation is used to separate relatively coarse-grained fractions from fine-grained ones, requiring other methods of study. For colored bauxites (brown, greenish), this analysis is carried out only after bleaching. The most fine-grained bauxites, densely cemented, are elutriated after preliminary disintegration.

Disintegration of the discolored sample is carried out by boiling with a peptizer in Erlenmeyer flasks under reflux. A number of reagents (ammonia, liquid glass, soda, sodium pyrophosphate, etc.) can be used as a peptizer. The ratios of liquid and solid are taken the same as for clays. In some cases, as, for example, in diaspore-boehmite bauxite, disintegration does not completely occur even with the help of a peptizer. Therefore, the non-disaggregated part is additionally rubbed in a mortar with light pressure with a rubber pestle.

There are various elutriation methods. For clay rocks, they are most fully described by M. F. Vikulova. Elutriation of bauxite samples was carried out by us in liter glasses, as described by I. I. Gorbunov. Marks are made on the walls: the top one is for 1 l, below it by 7 cm - for draining particles<1 mk and 10 "g below the liter mark - to drain particles > 1 mk. The elutriated liquid is drained using a siphon: the upper 7-cm layer after 24 h(particles less than 1 mk), 10 cm layer in 1 h 22 min(particles 1–5 mk) and after 17 min 10 sec(particles 5–10 m.k.). Fractions larger than 10 mk scattered on sieves. To prevent the suspension from being sucked in from a depth below the design level, a tip designed by V. A. Novikov is put on the lower end of the siphon lowered into the suspension.

From a fraction smaller than 1 mk or 5 mk in some cases with the help of a supercentrifuge (with a rotation speed of 18-20 thousand rpm). rpm) it is possible to isolate fractions enriched in particles with a size of hundredths of a micron. This is achieved by changing the feed rate of the suspension into the centrifuge. The principle of operation and the use of a supercentrifuge for granulometric analysis are described by K. K. Nikitin.

Gravity analysis for bauxite rocks produced on electric centrifuges at 2000–3000 rpm in liquids of specific gravity 3.2; 3.0; 2.8; 2.7; 2.5.

Separation into monomineral fractions of samples by centrifugation in heavy liquids without preliminary elutriation is almost not achieved. Thin classes (1–5 mk) even after elutriation, they are poorly separated in heavy liquids. This is apparently due to high degree dispersion, as well as the finest intergrowths of minerals. Thus, before gravitational analysis, it is necessary to separate the samples into classes by elutriation. Thin classes (1–5 mk and sometimes 10 mk are studied by thermal, X-ray diffraction, microscopic and other methods without separation in heavy liquids. From larger fractions in heavy liquids, it is possible to separate diaspore from boehmite (liquid with a specific gravity of 3.0), pyrite, ilmenite, rutile, tourmaline, zircon, epidote, etc. (in a liquid with a specific gravity of 3.2), boehmite to gibbsite and kaolinite (fluid specific gravity 2.8), gibbsite from kaolinite (fluid specific gravity 2.5).

It should be noted that for better separation in heavy liquids, discolored samples or fractions after elutriation are not dried to dryness, but are filled with a heavy liquid in a wet state, since a dried sample may lose its ability to disperse. The use of gravity analysis in the study of the mineralogical composition of bauxites is described in detail by E. V. Rozhkova et al.

Thermal analysis is one of the main methods for studying bauxite samples. As you know, bauxites are composed of minerals containing water. Depending on the change in temperature, various phase transformations occur in the sample, accompanied by the release or absorption of heat. The use of thermal analysis is based on this property of bauxites. The essence of the method and methods of work are described in special literature.

Thermal analysis is carried out by various methods, most often using the method of heating curves and the method of dehydration. Recently, installations have been constructed on which heating and dehydration curves (loss in weight) are simultaneously recorded. Thermal curves are recorded both for initial samples and for fractions isolated from them separately. As an example, the thermal curves of a greenish-gray chlorite variety of diaspore bauxite and its individual fractions are given. Here, on the thermal curve of the diaspore fraction II, the

endothermic effect at a temperature of 560°, which corresponds to the endothermic effects on curves I and III at temperatures of 573 and 556°. On the heating curve of the clay fraction IV, the endothermic stops at 140, 652, and 1020° correspond to illite. The endothermic stop at 532° and weak exothermic effects at 816 and 1226° can be explained by the presence of a small amount of kaolinite. Thus, the endothermic effect at 573° on the original sample (curve I) corresponds to both diaspore and kaolinite, and at 630° to illite (652° on curve IV) and chlorite. With the polymineral composition of the sample, thermal effects are superimposed; as a result, it is impossible to get a clear idea of the composition of the original rock without analyzing the constituent parts or fractions.

In gibbsite bauxites, the mineralogical composition is determined much more easily from thermal curves. All thermograms show an endothermic effect in the range from 204 to 588° with a maximum at 288–304°, indicating the presence of gibbsite. In the same temperature range, iron hydroxides goethite and hydrogoethite lose water, but since the amount of water in them is approximately 2 times less than in gibbsite, the amount of gibbsite will affect the depth of effect corresponding to iron hydroxides. The second endothermic effect in the range 500–752° with a maximum at 560–592° and the corresponding exothermic effect at 980–1020° characterize kaolinite.

Halloysite and muscovite, which are present in small amounts in the studied bauxites, are not reflected in the thermograms, except for a small endothermic effect at 116–180°, which apparently belongs to halloysite. The reason for this is the low content of these minerals and the imposition of a number of effects. In addition, if kaolinite and micas are present in the samples, then, as is known, even a slight admixture of kaolinite in mica is expressed on thermograms by the kaolinite effect.

The amount of gibbsite can be determined from the areas of the first endothermic effect. The area is measured with a planimeter. The most enriched in gibbsite sample with the maximum content of alumina and water, the lowest content of silica and iron oxides can be taken as a standard. The value of A1 2 O 3 gibbsite in other samples is determined from the calculation

where X- the value of the determined gibbsite A1 2 O 3 ;

S is the area of the endothermic gibbsite effect of the test sample on the thermogram, cm 2,

BUT- A1 2 O 3 content of the gibbsite reference sample;

K is the area of the reference sample on the thermogram, cm 2.

The dependence of the areas of the endothermic effect on the content of gibbsite can be expressed graphically. To do this, the A1 2 O 3 content is plotted along the abscissa axis as a percentage, and the corresponding areas in square centimeters are plotted along the ordinate axis. By measuring the area of the endothermic effect corresponding to gibbsite on the curve, one can calculate the content of A1 2 O 3 in the test sample from the graph.

The dehydration method is based on the fact that minerals containing water, at certain temperatures, lose weight. Weight loss determines the amount of mineral in the sample. In some cases, especially when the temperature intervals for mineral dehydration overlap, this method is unreliable. Therefore, it should be used simultaneously with the recording of heating curves, although such a combined method is not always available due to the lack of special installations.

The simplest method for determining weight loss was developed in SIMS. To do this, you need to have a drying cabinet, a muffle, a thermocouple, torsion balances, etc. The method of work, the course of analysis and the results of its application for clays and bauxites are described in detail by V.P. Astafiev.

The recalculation of weight loss during heating in each temperature range can be carried out not by the amount of the mineral, as V.P. Astafiev recommends, but by the amount of Al 2 O 3. contained in this mineral. The results obtained can be compared with the data chemical analysis. The recommended 2-hour hold at 300° for samples enriched in gibbsite is insufficient. The sample reaches a constant weight within 3-4 hours of heating, i.e., when all the gibbsite water is released. In clay varieties poor in gibbsite, its dehydration at 300° occurs completely within 2 h. Losses in the weight of samples at different temperatures can be expressed graphically if the temperature values (from 100 to 800°) are plotted along the abscissa axis, and the corresponding weight losses (H 2 O) as a percentage along the ordinate axis. The results of the quantitative determination of minerals by the method of V.P. Astafiev usually agree well with the results of thermal analysis in terms of areas of effects and with recalculation for the mineral composition of the chemical analysis of samples.

Chemical analysis gives the first idea of the quality of bauxites in the study of their material composition.

The weight ratio of alumina to silica determines the flint modulus, which is a criterion for the quality of bauxites. The larger this modulus, the better the quality of the bauxites. The module value for bauxite ranges from 1.5 to 12.0. The ratio of alumina content to weight loss on ignition (p.p.p.) gives some indication of the type of bauxite. Thus, in gibbsite bauxites, the loss on ignition is much higher than in diaspore-boehmite. In the first, it ranges from 15 to 25%, and in the second, from 7 to 15%. Loss on ignition in bauxite is usually taken as the amount of H 2 O, since SO 3 , CO 2 and organic matter are only rarely found in large quantities. Calcite and pyrite are present as admixtures in diaspore-boehmite bauxites. The sum of SO3 and CO2 in them is 1–2%. Gibbsite-type bauxites sometimes contain organic matter, but its amount does not exceed 1%. This type of bauxite is characterized by high contents of iron oxide (10–46%) and titanium dioxide (2–9%). Iron is presented mainly in the form of an oxide and is included in the composition of hematite, goethite, magnetite and their hydrated forms. The diaspore-boehmite bauxites contain ferrous iron, the content of which varies from 1 to 17%. Its high content is due to the presence of chlorite and small amounts of pyrite. In bauxites of the gibbsite type, ferrous iron is included in the composition of ilmenite.

The presence of alkalis may indicate the presence of micas in the bauxite rock. Thus, in diaspore-boehmite bauxites, a relatively high content of alkalis (K 2 O + Na 2 O = 0.5–2.0%) is explained by the presence of hydromicas of the illite type. Oxides of calcium and magnesium can be part of carbonates, clay minerals and chlorite. Their content usually does not exceed 1–1.5%. Chromium and phosphorus are also minor impurities in bauxites. Other impurity elements Cr, Mn, Cu, Pb, Ni, Zn, As, Co, Ba, Ga, Zr, V are present in bauxites in negligible amounts (thousandths and ten thousandths of a percent).

When studying the material composition of bauxites, a chemical analysis of individual monomineral fractions is also carried out. For example, in boehmite-diaspore and gibbsite fractions, the content of alumina, losses on ignition and impurities - silica, oxides of iron, magnesium, vanadium, gallium and titanium dioxide are determined. Fractions enriched in clay minerals are analyzed for silica content, total alkali, alumina, oxides of calcium, magnesium, iron and loss on ignition. High silica content in the presence of alkalis in clay fractions from diaspore-boehmite bauxites indicates the presence of illite-type hydromicas. In clay fractions of kaolinite-gibbsite bauxites, if there are no alkalis and minerals of free silica, a high content of SiO 2 may indicate a high silica content of kaolinite.

According to the chemical analysis, it is possible to recalculate the mineral composition. The chemical analysis of monomineral fractions is converted into molecular quantities, according to which the chemical formulas of the studied minerals are calculated. The recalculation of the chemical composition of bauxites for minerals is carried out to control other methods or as an addition to them. For example, if the main silica-containing minerals in the sample are quartz and kaolinite, then, knowing the amount of quartz, the remaining part of the silica bound in kaolinite is determined. Based on the amount of silica per kaolinite, one can calculate the amount of alumina required to link it into the kaolinite formula. The total content of kaolinite can be used to determine the amount of Al 2 O 3 in the form of alumina hydrates (gibbsite or others). For example, the chemical composition of bauxite: 51.6% A1 2 O 3 ; 5.5% SiO 2 ; 13.2% Fe 2 O 3 ; 4.3% TiO 2 ; 24.7% p.p.p.; amount 99.3%. The amount of quartz in the sample is 0.5%. Then the amount of SiO 2 in kaolinite will be equal to the difference between its total content in the sample (5.5%) and SiO 2 quartz (0.5%), i.e. 5.0%.

and the amount of A1 2 O 3 attributable to 5.0% SiO 2 kaolinite will be

The difference between the total content of A1 2 O 3 in the rock (51.6) and A1 2 O 3 attributable to kaolinite (4.2) is Ai 2 O 3 alumina hydrates, i.e. 47.4%. Knowing that gibbsite is the mineral of alumina hydrate in the studied bauxites, we calculate the amount of gibbsite from the amount of A1 2 O 3 (47.4%) obtained for alumina hydrates, based on its theoretical composition (65.4% A1 2 O 3 ; 34.6 % H 2 O). In this case, by the amount of alumina, it will be equal to

The data obtained can be controlled by weight loss on ignition, which is taken here as the amount of H 2 O. Thus, for linking A1 2 O 3 \u003d 47.4% into gibbsite,

According to chemical analysis, the total content of H 2 0 in the sample is 24.7 (p. p. p.), i.e., approximately coincides with the content of H 2 0 in gibbsite. In this case, no water remains on other minerals (kaolinite, iron hydroxides). Therefore, the amount of alumina equal to 47.4%, in addition to the trihydrate, includes some more monohydrate or anhydrous alumina. The above example shows only the principle of recalculation. In reality, most bauxites are more complex in terms of mineralogical composition. Therefore, when converting chemical analysis to mineralogical, data from other analyzes are also used. For example, in gibbsite bauxites, the amount of gibbsite and clay minerals should be calculated from dehydration or thermal analysis data, taking into account their chemical composition.

However, despite the complexity of the mineralogical composition, for some bauxites it is possible to recalculate the chemical composition to the mineralogical one.

Phase chemical analysis. The basic principles of the chemical phase analysis of bauxites are set out in the book by V. V. Dolivo-Dobrovolsky and Yu. V. Klimenko. When studying bauxites in Eastern Siberia, it turned out that this method in each specific case requires some changes and improvements. This is explained by the fact that rock-forming bauxite minerals, especially clay minerals, have wide limits of solubility in mineral acids.

Chemical phase analysis for the study of bauxites is carried out mainly in two versions: a) incomplete chemical phase analysis (selective dissolution of one or a group of minerals) and b) complete chemical phase analysis.

Incomplete chemical phase analysis is performed, on the one hand, for the purpose of pre-treatment of samples for subsequent examination of insoluble residues under a microscope, thermal, X-ray diffraction and other analyzes, on the other hand, for the quantitative determination of one or two components. The amount of minerals is determined by the difference in weights before and after dissolution or by recalculation of the chemical composition of the dissolved part of the sample.

With the help of selective dissolution, the amount of oxides and hydroxides of iron (sometimes chlorite) is determined. The issue of deferrization of bauxites is covered in detail in the works of VIMS. In bauxites of the diaspore-boehmite type, iron oxides and chlorites are dissolved in 6N. Hcl. In gibbsite bauxites, iron hydroxides and oxides are maximally (90–95%) extracted into solution upon dissolution in alcohol saturated with hydrogen chloride (3 N) at W: T = 50. In this case, 5–10% of alumina of the total its amount in bauxite, and titanium dioxide up to 40%. Bauxite bleaching can be carried out in 10% oxalic acid by heating on a water bath for 3–4 h at W: T = 100. Under these conditions, titanium-containing minerals dissolve less (about 10-15% TiO 2), but more is extracted into the alumina solution (25-40%), with the extraction of iron oxides by 80-90%. Thus, for maximum preservation of titanium minerals during bauxite discoloration, 10% oxalic acid should be used, and for the preservation of alumina minerals, an alcohol solution saturated with hydrogen chloride should be used.

The carbonates (calcite) present in some bauxites dissolve in 10% acetic acid when heated for 1 h at W: T=100 (see chapter "Copper sandstones"). Their dissolution must precede the bleaching of the bauxites.

Incomplete chemical phase analysis is also used for the quantitative determination of alumina minerals. There are several methods for their determination based on selective dissolution. In some bauxites, the amount of gibbsite can be determined fairly quickly by dissolving samples in 1N. KOH or NaOH according to the method described by V. V. Dolivo-Dobrovolsky and Yu. V. Klimenko. Low-water and anhydrous minerals of alumina - diaspore and corundum in bauxites can be determined by dissolving samples in hydrofluoric acid without heating, similar to the method for determining sillimanite and andalusite, which we describe below. A. A. Glagolev and P. V. Kulkin indicate that corundum and diaspore from secondary quartzites of Kazakhstan in hydrofluoric acid in the cold for 20 h practically insoluble.

A complete chemical phase analysis, due to the peculiarity of the material composition of bauxites and different behavior during the dissolution of the same minerals from different deposits, has its own specifics for each type of bauxites. After the dissolution of kaolinite in the residue, A1 2 O 3 and SiO 2 are determined. The amount of pyrophyllite is calculated from the content of the latter, while it should be borne in mind that silica is almost constantly present in the diaspora itself (up to 11%).

For gibbsite bauxites, in which monohydrate alumina minerals are absent or constitute an insignificant part, chemical phase analysis can be reduced to two or three stages. According to this scheme, gibbsite is dissolved by double treatment with alkali. According to the content of A1 2 O 3 in the solution, the amount of gibbsite in the sample is calculated. But on the example of gibbsite bauxites of Eastern Siberia, it turned out that in some samples more alumina is leached than it is contained in the form of gibbsite. In these bauxites, free alumina, which is formed during the physicochemical decomposition of kaolinite, apparently passes into alkaline extracts. Taking into account the peculiarities of gibbsite bauxites, when performing chemical phase analysis, it is necessary to carry out the analysis in parallel without treatment of samples with alkali. First, the sample is dissolved in HCl of specific gravity 1.19 by heating for 2 h. Under these conditions, gibbsite, iron oxides and hydroxides are completely dissolved.

Spectral, X-ray diffraction and other analyzes are very effective in studying bauxite. As is known, spectral analysis gives a complete picture of the elemental composition of the ore. It is produced both for initial samples and for individual fractions isolated from them. Spectral analysis in bauxite determines the content of the main components (Al, Fe, Ti, Si), as well as impurity elements Ga, Cr, V, Mn, P, Zr, etc.

X-ray diffraction analysis is widely used, which makes it possible to determine the phase composition of various fractions. For the same purpose, electron diffraction and electron microscopy studies are used. The essence of these analyses, preparation methods, methods for interpreting the results are described in special literature. It should be noted here that in the study by these methods, the method of sample preparation is of great importance. For X-ray diffraction and electron diffraction methods of analysis, it is necessary to obtain more or less monomineral fractions, as well as to separate particles by size. For example, in diaspore-boehmite bauxites, fractions less than 1 mk X-ray diffraction analysis reveals only illite, and electron diffraction analysis reveals only kaolinite. This is due to the fact that illite is in the form of large particles that cannot be studied by an electron diffraction (particles larger than 0.05 mk), and kaolinite, on the contrary, due to the high degree of dispersion, is detected only by electron diffraction. Thermal analysis confirmed that this fraction is a mixture of illite and kaolinite.

The electron microscopic method does not give a definite answer, since in bauxites, especially densely cemented ones, the natural shape of particles after grinding and dissolving samples in acids is not preserved. Therefore, viewing under an electron microscope is of auxiliary or control value for electron diffraction and X-ray diffraction analyses. It makes it possible to judge the degree of homogeneity and dispersity of a particular fraction, the presence of impurities that can be reflected by the above analyzes.

Of the other research methods, magnetic separation should be noted. Maghemite-hematite beans are isolated with a permanent magnet.

Sometimes in the news you can hear such a term as "bauxite". What are bauxites, why are they needed? The purpose for which they are used, where they are mined and what features they have, will be discussed in the article.

General concept

Bauxite got its name from the area in the south of France, which is called Les Baux. What bauxites are, it becomes clear when you get acquainted with their description. This is an ore of aluminum, which consists of a hydrate of oxides of iron, silicon, aluminum. Bauxite is also used as a raw material for the production of alumina-containing refractories. In industrial substance, the content of alumina ranges from 39 to 70%. In addition, the mineral is used as a flux in the manufacture of ferrous metals.

To date, the extraction of bauxite is the most important source of learning aluminum ore. It is on this that almost the entire world metallurgical industry is based, with minor exceptions.

Compound

Considering in more detail what bauxite is, it can be noted that this is a rock that has a rather complex composition. It includes substances such as aluminum hydroxide, silicates and iron oxides, as well as silicon in the form of opal, quartz and kaolinite.

In addition, the composition contains titanium in the form of an oxide mineral (rutile and other compounds), magnesium carbonate, calcium, sodium, zirconium, chromium, phosphorus, potassium, gallium, vanadium compounds and other elements. Sometimes pyrite impurities are found in bauxite alumina.

Value

The chemical component of the mineral varies quite widely. First of all, the difference in indicators is influenced by the mineralogical form of aluminum hydroxide, as well as the amount of various impurities. A bauxite deposit is considered valuable if the ore mined contains sufficient amounts of silica and alumina. Also important role plays the so-called opening of bauxites. In other words, it is the ease and simplicity of its extraction.

Bauxites have various physical properties. They have a rather unstable appearance, in connection with which it is difficult to determine their quality by visual signs. This is what causes great difficulties in the search for the mineral. Therefore, rock samples are examined under a microscope before a decision is made to start mining.

Appearance

Continuing to consider what bauxite is, you should pay attention to their appearance. They are clay-like, and often stony. There are bauxites quite dense, porous, with earthy or cellular fracture. Quite often, in the groundmass one can meet the inclusion of rounded bodies, which create an oolitic (sedimentary) structure of the ore.

Bauxites come in a variety of colors ranging from dark red to white. Basically they are painted in red brick or brown color. There is also a mineralogical difference between bauxites. It lies in the fact that in their composition there is a high content of aluminum in the form of hydroxide or kaolinite (aluminum silicate). In this regard, several types of bauxite are distinguished: diaspore, boehmite, mixed, and hydrargillite.

Mining

More than 90% of bauxite reserves in the world are concentrated in 18 countries. Impressive deposits are found in regions with a hot climate. Russian Federation has small deposits of bauxite and mainly imports raw materials. The largest deposits are in the following countries:

Guinea - about 20 billion tons;
Australia - more than 7 billion tons;
Brazil - about 6 billion tons;
Vietnam - 3 billion tons;
India and Indonesia - about 2.5 billion tons.

In Russia, bauxites are the most High Quality mined in the North Ural region. There are also deposits in the Leningrad region, in the Boksitogorsk region. The most promising source of raw materials are the Sredne-Timan deposits, which are located in the Komi Republic. Explored reserves are presumably estimated at more than 250 million tons.

Application of bauxite

After melting the rock, alumina cement is also obtained. As can be seen, the range of applications of bauxites is quite wide, which makes them a particularly valuable raw material.

Kinds

One of the rare types of bauxite is alunite, which is mined only in Azerbaijan, in the Zaglik deposit. According to the proven proven reserves, it is more than 200 thousand tons.

However, on the territory of Uzbekistan, presumably, there are also reserves of alunite ores. Their deposits were explored in the Gushsai field. Perhaps there is about 130 million tons. However, the development and extraction of these ores is currently not carried out, which allows Azerbaijan to be the only country where alunite is mined.

Features of mining and processing

Bauxite is mined mainly by open pit mining, but in some cases underground. The method of developing a deposit depends on how the mineral rocks are deposited. Technology system different processing is used, it is influenced by the composition of the rock. Aluminum production is carried out in two stages. The first is the production of alumina using various chemical methods, and the second is the isolation of pure metal through the electrolysis of aluminum fluoride salts.

To obtain alumina, the Bayer hydrochemical method (sintering) is used, as well as a combination: serial and parallel methods. The main feature of the Bayer method is that during the leaching (treatment) of bauxite, concentrated sodium is obtained, after which the alumina passes into the form of a sodium aluminate solution. The solution is then cleaned of red mud and alumina (aluminum hydroxide) is precipitated. After that, leaching is carried out, and aluminum is obtained.

Low-quality bauxites are processed in the most difficult way. This is a method of sintering a mixture of crushed bauxite with soda and limestone (three-component charge) at a temperature of 1250 degrees Celsius in special furnaces, which during production process revolve. After that, the resulting material (speck) is leached with a weakly concentrated solution. The precipitated hydroxide is then filtered off.

The above methods for producing aluminum are very complex processes, but they allow you to get the maximum amount of metal from the rock.

Bauxite is the most important source of aluminum, and the metal itself is very valuable, as it is used in the automotive, aircraft and ship industries. It is also widely used in the military-industrial complex, which makes this metal strategically important.

The first appeal to the unusual properties of the mineral was given after an exhibition in Paris in 1855. It presented an amazing silver-colored metal, light in weight and strong in chemical resistance. The metal was designated "clay silver". It's about aluminum. And the raw materials for its production are bauxites. Such a funny name was given by the area from Provence, France, in which the first large deposit was discovered.

For the 19th century, obtaining aluminum was something difficult and very expensive. Then the metal was used only for jewelry. I remembered the Soviet period, in tablespoons and forks made of aluminum in bulk.

The main raw material for the production of AL metal was and remains bauxite.

Bauxite in its original form. Curious about chemical and physical properties

Bauxite in geology:
Complex rock. Consists of aluminum hydroxides, iron oxides and impurities of other elements.
For the production of aluminum, bauxite is used with a high percentage of Al-alumina from 40%. Quality determination is carried out by the ratio of the concentration of alumina and silica.
Bauxite having a slight "opening" is valued. This is a term for the quality and speed of extraction of alumina.
Visually detecting bauxite in a deposit is not easy. The search for this rock is very difficult due to the dispersion of the components. For example, only brightly crystallized impurities can be distinguished under a microscope.

Variety of types of bauxite alumina:
The appearance of the rock is a clay-like or stony mass.
There are dense, flint-like minerals, and there are pumice-like minerals. With the same porous rough cellular fracture. Sometimes in the mass you can find unusual rounded inclusions. Then the structure is called oolitic, and the bodies let you know that the found rock contains raw materials for the production of iron.
The wide range of colors is amazing. Bauxite can be found in gray-whitish, pale cream or dark cherry hues. These are rare cases. More common bauxite is red-brown or brick-red.
The rock is also interesting in that it does not have a clearly defined value of specific gravity, as is the case with sulfur or silicon. Light rocks with a porous structure have a specific gravity of about 1.2 kg/m3. The densest are ferruginous bauxites with a specific gravity of 2.8 kg/m3.
Bauxite outwardly similar to clay, but in other characteristics it is strikingly different from it. So, for example, bauxite cannot be diluted in water and make a plastic mass, as is done with clay. This is due to the shape and mineralogical difference.
According to the mineral composition, bauxites are divided into boehmite, diaspore, hydroargillite and mixed, depending on the chemical form of the aluminum contained.
The richest deposits of bauxite:
Almost 90% of all valuable mineral deposits are located on the territory of 18 countries. This is due to the occurrence of lateritic crusts formed by the weathering of aluminosilicates over millennia in a hot and humid climate.
There are 6 huge deposits. In Guinea - almost 20 billion tons. In Australia, more than 7 billion tons. In Brazil, up to 6 billion tons. In Vietnam, 3 billion tons. In India, 2.5 billion tons. In Indonesia, 2 billion tons. On the territory of these countries 2/3 of the earth's bauxite reserves are concentrated.
On the territory of the Russian Federation, the found deposits are not classified as large, but are of great value for the production of aluminum in the country. Large deposits were found in the Boksitogorsk region near St. Petersburg. And the most pure and valuable deposit in Russia is the North Urals.

The magical and healing properties of bauxite

Bauxite little used for making amulets. Unless a very unusual shape catches your eye, your hands will reach out to make crafts out of it.

Earlier, in the 18th and 19th century, bauxite was used in precious metal settings, mostly silver, only because of the unusual red hue. There are few such decorations, they were not popular.

According to the therapeutic effect, no value was also revealed. The aluminum contained in the rock is present in the human body in scanty concentrations. In plants, it is present at the micron level.

The main value of bauxite is a raw material for aluminum production.

The very first large bauxite deposit in the Urals was named "Red Riding Hood".
The breed got its name from France. The first deposit was found in the province of Provence near the town of Bo or Boaks (Beaux).
There are 10 main industrial grades of the mineral, differing in alumina concentration and composition.
The oldest of the bauxites can be found in tropical countries. These "pebbles" were formed in the Cenozoic or Proterozoic.
The greatest contribution to the development of technologies for the production of aluminum from bauxite was made by Russian scientists: Bayer, Manoilov, Strokov, Lileev and Kuznetsov. According to the Bayer method, discovered at the end of the 19th century, alumina is still being produced.