Bauxites and alumina. Bauxite - Formula, Chemical Properties and Applications. Characteristics and origins
Have you ever come across an unusual "clay" that for some reason did not form a mass with water suitable for modeling? If so, then you were not holding clay in your hands, but bauxite rock. Its formula cannot reflect the exact composition, because a variety of substances can enter into it. But first things first. Consider this rock from all angles, having studied in detail the composition, properties and significance for humans.
The history of the discovery and why it is called so
The name of the ore is the same as the place of its discovery. The composition is very diverse, but the main components are various hydrates of aluminum oxides, iron-containing and silicon-containing substances. The chemical formula of bauxite does not reflect the entire composition, but it is used mainly in the aluminum industry as the main source of raw materials. The content of aluminum-containing substances can be 40-60% or more.
The dense mineral comes in a wide variety of shades, from red to green to gray. But you will never come across transparent bauxite. More often it is dense and hard, sometimes it occurs in the form of an earthy and loose substance. In this case, when touched, traces will remain on the hands.
Perhaps we would now call this mineral berthite, if in 1821 a French geologist named Pierre Berthier did not become modest, having found during summer vacation an unusual find. The rock he discovered was made of stone with unusual properties.
Berthier did not know that several decades would pass, and bauxite, the formula of which is Al 2 O 3 xnH 2 O, would become a raw material, without which aluminum industry did not develop at such a fast pace. But what happened happened. And the mineral is called the Provencal village of Les Baux de Provence (spelled in French Les Baux).
It took 30 years for the composition of the rock to be assessed by the mineralogists of the time, but in the 50s bauxite took its place in the Paris exhibition center, originally called "clay silver". It looks very much like clay.
Composition
In order for the formula of bauxite in chemistry to accurately reflect the composition of the mineral, it is necessary to take into account all the substances that it contains. There are many of them, let's call those that are most common:
- hydrates of aluminum oxides, you are already familiar with it - Al 2 O 3 xnH 2 O;
- iron hydroxides, oxides and silicates forming the ore mass;
- silicon (quartz (SiO 2), opal (SiO 2 x nH 2 O), kaolinite (Al 4 (OH) 8));
- titanium (rutile (TiO 2) and others);
- carbonates (CaCO 3, MgCO 3, etc.);
- compounds of chromium, zirconium, phosphorus, sodium, potassium, vanadium, gallium and other elements;
- pyrite (FeS 2).
Ore is valued, primarily containing alumina, and the less silica, the better. To characterize the quality, the so-called silicon module of bauxite was introduced, the formula for its finding: μ Si \u003d Al 2 O 3 / SiO 2. The resulting value shows which of the methods is better for processing the ore.
Properties
As already mentioned, the composition of the mineral is very diverse, which greatly affects its properties. But some physical properties you can highlight:
- colors - you can find all shades of red (from light pink to dark red), green (from gray-green to grassy) and gray (from light tones, including white to dark gray almost black);
- the state can also be different: they distinguish stony, porous, loose, earthy and clay-like;
- density directly depends on the amount of iron-containing substances and varies from 1.8 to 3.2 g / cm 3;
- hardness is maximum 6 on the Mohs scale;
- opaque.
For the industry, there is one chemical trait that is most important - "breakup", which means whether it is easy enough to extract the aluminum oxides from this ore.
Places where there are deposits
Bauxite is mined either by open pit or underground. The main ore reserves are concentrated where it is humid and warm - these are the tropics and subtropics. Here are the best bauxite deposits and 2/3 of the world's reserves.
If we are talking about the Russian Federation, then its deposits are not enough even to meet their own needs. But developments are underway. Bauxite ore is mined in Arkhangelsk, Leningrad and Belgorod regions, Sverdlovsk and Chelyabinsk.
The constant growth in demand for aluminum leads to an increase in production. The United States carried out calculations according to which the world reserves of bauxite range from 55 to 75 billion tons. This will be enough for another hundred years or so. What's next? Scientists are trying to find other ways of extracting aluminum that are equally efficient and cheap.
Processing
Aluminum is the main reason for the extraction of this ore. The process of its extraction consists of the following stages: obtaining alumina, then pure metal (by electrolysis). In turn, alumina (alumina formula) can be obtained by the Bayer method, by sintering or by a combined method.
The scheme of the Bayer process is as follows: highly crushed bauxite is treated with sodium hydroxide and sodium aluminate is obtained, from which alumina is then precipitated. Then it only remains to carry out electrolysis - and the aluminum is ready.
Low quality ore is sintered. This process is as follows: the crushed rock is mixed with calcium carbonate and soda, placed in an oven and sintered at 1250 ° C. Then the cake is treated with sodium alkali of low concentration, aluminum hydroxide is filtered and electrolysis is carried out.
The combined method consists of primary processing of alumina from bauxite by the Bayer method and subsequent processing of the remaining helmet by sintering.
Application
Having studied bauxite, its properties and applications in metallurgy, now you can find out where else the ore is used. IN chemical industry in the production of paints, as a filler in varnishes. The oil refining industry uses it as a sorbent.
Ferrous metallurgy uses fluxes obtained by smelting rocks. Electrocorundum obtained in an electric furnace from bauxite, having a hardness of 9, is used as an abrasive material.
Another component of bauxite is also used - alumina. Alumina cement is produced from it - a composition that has high binding properties even at low temperatures, which is especially important for housing construction in the Far North.
If bauxite, the formula and application of which we are now considering, contains a small amount of iron, then the rock is used in the production of refractories.
But for lithotherapists and magicians, bauxite is not of interest, since the rock does not have either medicinal or magical properties.
Occasionally, only jewelers can have fun by creating some kind of trinket or souvenir from ore, for example, polishing it in the shape of a ball - and on a stand.
It looks impressive and original.
Bauxite is a widespread rock consisting mainly of the minerals aluminum hydroxide. It is named after the settlement of Les Baux in the south of France, where the sample was discovered and described in 1821. The world learned about the properties of bauxite after the Paris exhibition of 1855, which demonstrated the aluminum obtained from it, presented as “clay silver”. Indeed, outwardly bauxite is similar to clay, but in its physical and chemical properties it has nothing to do with it.
Bauxite is a widespread rock composed mainly of the minerals aluminum hydroxide
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, fine-crystalline or amorphous. The density depends on the iron content. Rounded grains formed by alumina or iron oxide can often be included in the groundmass. With a content of 50-60% iron oxide, the rock takes on the value of iron ore. The hardness of bauxite on the Mohs scale ranges from 2 to 7. Its chemical formula, in addition to hydrates of aluminum oxides, which make up the main ore mass, includes in the form of various compounds iron, silicon, titanium, magnesium and calcium carbonate, phosphorus, sodium, potassium, zirconium, vanadium. Sometimes - an admixture of pyrite.
Bauxite does not dissolve in water
Depending on the nature of the rock-forming mineral, bauxite can be divided into 3 main groups:
- monohydrate, in which alumina is presented in only one form (diaspora, boehmite);
- trihydrate containing alumina in trihydrate form (gibbsite);
- mixed, combining the first 2 groups.
The quality and grade of bauxite as an aluminum ore depends on the content of alumina on a dry basis. In the highest brand it is contained in the amount of 52%, in the lowest it is not less than 28%. Even in one deposit, the amount of alumina can vary significantly. The quality of the rock decreases with increasing silicon oxide content.
Bauxite ore is prized, 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 found in 18 tropical countries. Usually, the quality of laterite 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 laterite weathering products and their redeposition, can be either high-grade or substandard. Deposits are located in the form of layers, lenses or nests, often on the surface of the earth or in the uppermost layers. Therefore, the ore is mainly mined in an open pit using powerful mining equipment. World reserves are characterized by uneven territorial distribution. More than 50 countries have ore deposits, and 93% of these reserves are located in 12 of them. Large deposits have been found in Australia, Africa, South and Central America, Asia, Oceania, and Europe. The highest alumina content 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% is mined there total ore in the country. These are the oldest deposits on earth, over 350 million years old. The recently commissioned Cheremukhovskaya-Glubokaya mine is located 1,500 meters underground. Its uniqueness in the extraction and transportation of ore: there are 3 lifting machines on 1 head. The proven reserves are 42 million tons, and the aluminum content in the ore is almost 60%. The Cheremukhovskaya mine is the deepest in the Russian Federation. It should meet the country's demand for aluminum for 30-40 years.
The cost of 1 ton of ore without transportation costs in Russia is $ 20-26, for comparison, in Australia -10. Due to unprofitability, the production of bauxite in the Leningradskaya, Chelyabinsk region... In Arkhangelsk, open-cut rock is mined from 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 the process of processing them is more complicated. Russia ranks 7th in the world for the production of bauxite.
Use of bauxite
The use of bauxite in 60% falls on the production of aluminum. Its production and consumption ranks 1st in the world among non-ferrous metals. It is required in shipbuilding, aviation and food industries. When using aluminum profiles at sea, their strength, lightness and resistance to corrosion are of great importance. The consumption of bauxite in construction is dynamically developing; more than 1/5 of the produced aluminum is used for these needs. When smelting ore, 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 ore is used as a molding material in metallurgy. Concrete made with the addition of alumina cement hardens quickly, is resistant to high temperatures and liquid acidic environments. The absorbent properties of bauxite allow it to be used in the manufacture of oil spill cleaners. Low-iron rocks are used to make refractories that can withstand temperatures up to 1,900 ° C.
The demand for aluminum and other ore processing products is growing, therefore the developed countries invest in the development of fields even with a low threshold of profitability.
The use of bauxite in jewelry is found only in original works. Samples of unusual color are used to make souvenirs, in particular, polished balls. The mineral bauxite is not used in folk medicine, since its medicinal potential has not yet been discovered. Also, its magical properties have not been revealed, so it does not attract the attention of psychics.
How to make an amulet with your own hands (video)
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The French city of Les Baux-de-Provence, located in the south of the country, became famous for giving the name to the mineral bauxite. It was there in 1821 that mining engineer Pierre Berthier discovered deposits of an unknown ore. It took another 40 years of research and testing to discover the possibilities of a new breed and to recognize it as promising for industrial production aluminum, which in those years exceeded gold in price.
Characteristics and origins
Bauxite is the primary aluminum ore. Almost all the aluminum that has ever been produced in the world is converted from them. This rock is a composite raw material with a complex and heterogeneous structure.
It includes aluminum oxides and hydroxides as its main components. Iron oxides also serve as ore-forming minerals. And among the impurities, the most common are:
- silicon (represented by quartz, kaolinite and opal);
- titanium (as rutile);
- calcium and magnesium compounds;
- rare earth elements;
- mica;
- small amounts of gallium, chromium, vanadium, zirconium, niobium, phosphorus, potassium, sodium and pyrite.
Bauxites differ in:
- Physical condition (stony, earthy, porous, loose, clay-like).
- Structure (in the form of debris and peas).
- Texture features (with a homogeneous or layered composition).
- Density (varies from 1800 to 3200 kg / m³).
Chemical and physical properties
The chemical properties of bauxite have a wide range associated with the variable composition of the material. However, the quality of the mined minerals is primarily determined by the ratio of the content of alumina and silica. The greater the amount of the former and less of the latter, the more significant the industrial value. Mining engineers consider an important chemical feature to be the so-called "opening", that is, how easily it is possible to extract aluminum oxides from ore material.
Despite the fact that bauxite does not have a constant composition, their physical properties are reduced to the following indicators:
| № | Name | Characteristic |
|---|---|---|
| 1 | Colour | brown, orange, brick, pink, red; less often gray, yellow, white and black |
| 2 | Veins | usually white, but sometimes they can be colored by iron impurities |
| 3 | Shine | Dull and earthy |
| 4 | Transparency | Opaque |
| 5 | Specific gravity | 2-2.5 kg / cm³ |
| 6 | Hardness | 1-3 on the Mohs mineralogical scale (for comparison - for diamond 10). Because of this softness, bauxite resembles clay. But unlike the latter, when water is added, they do not form a homogeneous plastic mass |
Interestingly, physical status has nothing to do with the usefulness and value of bauxite. This is due to the fact that they are processed into another material, the properties of which differ significantly from the original rock.
World reserves and production
Despite the fact that the demand for aluminum is constantly increasing, the reserves of its primary ore are sufficient to meet this need for several more centuries, but not less than 100 years of production.
The US Geological Survey released data according to which the world's bauxite resources are 55-75 billion tons. Moreover, most of them are concentrated in Africa (32%). Oceania accounts for 23%, the Caribbean and South America 21%, the Asian continent 18%, other regions 6%.
The introduction of the aluminum utilization process also inspires optimism, which will slow down the depletion of natural reserves of primary aluminum ore (and at the same time save electricity consumption).
The top ten countries in the extraction of bauxite, represented by the same US Geological Survey, looked like this in 2016.
| № | Country | Thousand metric tons |
|---|---|---|
| 1 | Australia | 82 000 |
| 2 | China | 65 000 |
| 3 | Brazil | 34 500 |
| 4 | India | 25 000 |
| 5 | Guinea | 19 700 |
| 6 | Jamaica | 8 500 |
| 7 | Russia | 5 400 |
| 8 | Kazakhstan | 4 600 |
| 9 | Saudi Arabia | 4 000 |
| 10 | Greece | 1 800 |
Bauxites are usually mined in open pit mines. To obtain a working site, the ore layer is blasted to a depth of 20 cm and then removed. The pieces of the mineral are crushed and sorted: the waste rock (the so-called "tailings") is washed away by the flow of washing water, and the fragments of dense ore remain at the bottom of the processing plant.
The oldest bauxite deposits in Russia date back to the Precambrian era. They are located in the Eastern Sayan Mountains (Boksonskoye field). Younger aluminum ore, from the Middle and Upper Devonian times, is found in the Northern and Southern Urals, in the Arkhangelsk, Leningrad and Belgorod regions.
Industrial application
The mined bauxite is classified according to their subsequent commercial use into metallurgical, abrasive, chemical, cement, refractory, etc.
Their main application, which accounts for 85% of the world's development, is to serve as a raw material for the production of alumina (aluminum oxide).
The technological chain looks like this: bauxite is heated with sodium hydroxide, then filtered, a solid residue is precipitated and calcined. This product - anhydrous alumina, the penultimate transformation in the aluminum production cycle.
Then it remains to immerse it in a bath of molten natural or synthetic cryolite and select the metal itself by electrolytic reduction.
The first to discover this technology in 1860 was the French chemist Henri Saint-Clair Deville. It replaced the costly process that produced aluminum in a vacuum from potassium and sodium. The next important area of \u200b\u200bbauxite use is as abrasives.
If alumina is calcined, the result is synthetic corundum - a very hard material with a factor of 9 on the Mohs scale. It is crushed, separated, and then added to the composition of sandpaper and various polishing powders and suspensions.
Sintered, pulverized and fused into round granules bauxite is also an excellent sandblasting abrasive. It is ideal for surface treatment and, due to its spherical shape, reduces wear on sandblasting equipment.
Another important purpose of bauxite is to participate as a proppant (a material that does not allow specially created faults to close) in the process of oil production by hydraulic fracturing. In this case, the treated bauxite particles are resistant to hydraulic pressure and allow fractures to remain open as long as necessary for oil to escape.
Bauxite is also irreplaceable for creating refractory products. Fired alumina can withstand temperatures up to 1780 C. This property is used both for the production of bricks and concrete, and for the creation of equipment for the metallurgical industry, special glass and even fire-resistant clothing.
Conclusion
Chemists and technologists are constantly looking for adequate substitutes for bauxite, which would not be inferior in their properties. Studies have shown that clay materials, power plant ash and oil shale can be used to produce alumina.
However, the cost of the entire technological chain is several times higher. Silicon carbide has proven itself well as an abrasive and synthetic mullite as a refractory. Scientists hope that by the time the natural resources of bauxite are completely depleted, an equivalent replacement will be found.
History claims that bauxite was found by French geologist Pierre Berthier in 1821. The scientist was in the village of Le Bo on vacation. While walking, he broke off a piece of unknown rock in a nearby canyon and named it after the village.
The bauxite formula allows you to get a different color range of this breed: from snow-white to almost black. Less commonly, it is red, gray, or brown.
If you look at bauxite, then outwardly this rock strongly resembles clay. But clay dissolves in water, but bauxite ore does not. Bauxite also differs from clay in that in the first ore, aluminum is hydroxide, and in the second, kaolinite. The mineral is not transparent, but its density may differ - everything will depend on the iron content in it, the indicator of which ranges from 2900 to 3500 kg / m3. Its structure can be different - from porous to homogeneous, with all kinds of inclusions (iron oxide, alumina).
In nature, there are very beautiful specimens that can be a full-fledged souvenir.
Chemical composition
The value of bauxite depends on the elements concentrated in it, such as aluminum hydroxide or compounds of silicon and iron. Also in the ore you can find such components as carbonates, calcites and titanites. Besides them, there are many chemical elements: Na, K, Mg, Cr, V, Ga. Bauxite contains the following components:
Scientists say that bauxite is valuable when it has a high aluminum content, but silicon oxide, on the contrary, degrades this composition.
Main groups
Geologists distinguish between three main groups of bauxite depending on their chemical composition:
- Monohydroxide. This group is represented by bauxite ores that contain rock-forming components such as diaspora and boehmite.
- Trihydroxide. The second group is represented by ores containing rock-forming minerals, for example, gibbsite.
- Mixed. The third group combines the features of groups 1 and 2, where rock-forming minerals are organically mixed with each other.
How are bauxite ores created in natural conditions? Residual species are formed in tropical climates.
In order for the ore to "mature", complex chemical processes are required under the influence of a unique combination of high humidity and positive temperature.
Sedimentary bauxite is formed in drier and cooler regions under the influence of weathering products (transport and redeposition). Most often, such a rock occurs in layers.
Mineral application
Bauxite is the planet's primary source of aluminum. It is also used for making alumina cement, which hardens quickly at low temperatures and has high binding properties. This breed is used in the following areas:
- Ferrous metallurgy (as a flux).
- During the production of paints.
- In the abrasive industry.
The mineral is almost never used in jewelry production, only souvenirs are made. Quite beautiful and unique specimens are found in nature. As for the healing and magical qualities, this ore does not have such. For bauxite to form, complex chemical processes must occur. They are mainly created by weathering feldspars. The world's bauxite reserves are concentrated in countries with hot and humid climates. Therefore, there are two ways to create bauxite: a chemogenic residual sample and a chemogenic sedimentary sample.
In the vastness of Russia
The first deposits of bauxite ore were discovered in the North Ural region. The ore vein is very deep (up to 1 km deep). Extraction is carried out by the mine method. A deposit was also found in the Arkhangelsk region, but these bauxites contain too many impurities (chromium, gypsum).
Promising deposits have been found in the Komi region. Everything is complicated by the fact that the infrastructure here is poorly developed, which greatly interferes with the work on production. There are also known mining sites in the Angara region
Extraction and processing
How bauxite is mined depends on its quality. Most often, the open method is used, but sometimes the mine method is also used. The main process consists of two parts: the extraction of alumina and the extraction of aluminum (electrolysis). In order to extract alumina from ore, they resort to the Bayer method. Bauxite is finely ground and treated with sodium hydroxide. As a result, an aluminum solution is formed. Then the red scar is cleaned and aluminum hydroxide is deposited from it.
Lower grade bauxite ore is processed using a sophisticated method... First, it is crushed, then mixed with limestone and soda. Further, this mixture is baked in special ovens that rotate. When the rock has cooled down, it is treated with an alkaline substance. The hydroxide precipitates, it is separated and filtered.
In factories, both methods are usually used, resulting in a large amount of aluminum. All manipulations lead to waste-free production.
Bauxite belongs to sedimentary, aluminous rocks. Its name comes from the French "Baux" - a village in Provence (France) at the place of the original finds.
Bauxitis has characteristic signs: the structure is leguminous or oolitic, in rare cases - aphanitic (that is, very dense with subtle minerals) or collomorphic. The texture is massive, resembling conglomerates or brecciated in appearance.
Bauxite is composed of several minerals:
Alumina hydrates (hydrargillite, boehmite, diaspora);
Clay minerals: chlorite, siderite, oxides and hydroxides of iron, pyrite, quartz, chalcedony, etc.
Bauxites also differ in the quantitative proportions of the minerals it contains - alumina hydrates. They are classified as: boehmite - diaspore, hydrargillic and mixed bauxites. Al2O3 content in bauxite ranges from 28 to 45%; Fe2O3 - from 2 to 50-60%. Sometimes, there is an increased content of Ga, Zr, Zn, Co, Ni, Cr, Cu, Ba, etc.
Most often, the mineral bauxite is a rocky rock of medium to high hardness. But sometimes there are also earthy representatives, loosely connected, which get their hands dirty. If bauxite is moistened, then it becomes not plastic. Density - 2.7 g / cm3; specific gravity varies about 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, and sheet-like deposits. By origin, several types of bauxite are distinguished: residual or lateritic, which are products of the modern weathering of various igneous rocks. Most often, such specimens have a reddish tint.
The next type is colloidal-sedimentary, which “mature” in continental or coastal - marine zones. Coastal-marine, also called lagoon bauxites, are most often located on the uneven karst surface of limestones and overlain by layered marls or bituminous limestones.
CALCITE ON BOXITE
Continental developments are divided into four groups:
1) slope (deluvial), which, respectively, originate and occur on the slopes;
2) valley, lined with ancient ravines, they form lenses among the remains of fossils, 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 sinkholes 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-sea ones come from the Urals, the same representatives are found in the Sayan Mountains, in Central Asia. The main deposits of continental bauxite are located in the Kamensk Uralsky area (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 application 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 the purification of oil products from impurities.
Since ancient times, jewelers have used bauxite for the production of synthetic stones. Aluminum crystals after cleaning in electric ovens turned into synthetic white c. Chromium oxides were added to the sapphire and red was obtained. Stones for watches were made from ruby.
Currently, aluminum is used in the jewelry industry for the manufacture of bracelets, chains, brooches, etc. Aluminum goes well with precious stones.