Aluminum is a metal coated with a matte silver oxide film, the properties of which determine its popularity: softness, lightness, ductility, high strength, corrosion resistance, electrical conductivity and lack of toxicity. In modern high technology The use of aluminum is given a leading place as a structural, multifunctional material.
The greatest value for industry as a source of aluminum is natural raw materials - bauxite, a rock component in the form of bauxite, alunite and nepheline.
Varieties of alumina-containing ores
More than 200 minerals are known that contain aluminum.
Only rock that can meet the following requirements is considered a raw material source:
- Natural raw materials must have a high content of aluminum oxides;
- The deposit must correspond to the economic feasibility of its industrial development.
- The rock must contain aluminum raw materials in a form that can be extracted in its pure form by known methods.
Feature of the natural rock bauxite
Natural deposits of bauxite, nepheline, alunite, clay, and kaolin can serve as a source of raw materials. Bauxite is the most saturated with aluminum compounds. Clays and kaolins are the most common rocks with a significant alumina content. Deposits of these minerals are found on the surface of the earth.
Bauxite in nature exists only in the form of a binary compound of metal with oxygen. This compound is extracted from natural mountain ore in the form of bauxite, consisting of oxides of several chemical elements: aluminum, potassium, sodium, magnesium, iron, titanium, silicon, phosphorus.
Depending on the deposit, bauxite contains from 28 to 80% alumina. This is the main raw material for obtaining a unique metal. The quality of bauxite as an aluminum raw material depends on its alumina content. This determines the physical properties bauxite:
- The mineral has a hidden crystalline structure or is in an amorphous state. Many minerals have hardened forms of hydrogels of simple or complex composition.
- The color of bauxite at different mining sites ranges from almost white to dark red. There are deposits with a black color of the mineral.
- The density of aluminum containing minerals depends on their chemical composition and is about 3,500 kg/m3.
- The chemical composition and structure of bauxite determines solid properties mineral. The strongest minerals have a hardness of 6 units on the scale accepted in mineralogy.
- As a natural mineral, bauxite has a number of impurities, most often these are oxides of iron, calcium, magnesium, manganese, and impurities of titanium and phosphorus compounds.
Bauxites, kaolins, and clays contain impurities of other compounds, which are separated into separate industries during the processing of raw materials.
Only in Russia do they use deposits with rock deposits that contain lower concentrations of alumina.
Recently, alumina began to be obtained from nephelines, which, in addition to alumina, contain oxides of metals such as potassium, sodium, silicon and, no less valuable, alum stone, alunite.
Methods for processing aluminum containing minerals
The technology for producing pure alumina from aluminum ore has not changed since the discovery of this metal. Its production equipment is being improved, allowing it to produce pure aluminum. The main production stages of obtaining pure metal:
- Extraction of ore from developed deposits.
- Primary processing of waste rocks in order to increase the concentration of alumina is an enrichment process.
- Preparation of pure alumina, electrolytic reduction of aluminum from its oxides.
The production process ends with metal with a concentration of 99.99%.
Alumina mining and beneficiation
Alumina or aluminum oxides do not exist in nature in their pure form. It is extracted from aluminum ores using hydrochemical methods.
Aluminum ore deposits in deposits usually explode, providing a site for its extraction at a depth of approximately 20 meters, from where it is selected and launched into the process of further processing;
- Using special equipment (screens, classifiers), the ore is crushed and sorted, discarding waste rock (tailings). At this stage of alumina enrichment, washing and screening methods are used as the most economically advantageous.
- The purified ore settled at the bottom of the concentration plant is mixed with a heated mass of caustic soda in an autoclave.
- The mixture is passed through a system of high-strength steel vessels. The vessels are equipped with a steam jacket that maintains the required temperature. The steam pressure is maintained at 1.5-3.5 MPa until the aluminum compounds are completely transferred from the enriched rock to sodium aluminate in a superheated sodium hydroxide solution.
- After cooling, the liquid undergoes a filtration stage, as a result of which solid sediment is separated and a supersaturated pure aluminate solution is obtained. By adding aluminum hydroxide residues from the previous cycle to the resulting solution, decomposition is accelerated.
- For final drying of aluminum oxide hydrate, a calcination procedure is used.
Electrolytic production of pure aluminum
Pure aluminum is produced using a continuous process that produces calcined aluminum enters the electrolytic reduction stage.
Modern electrolysers are a device consisting of the following parts:
- Made of steel casing lined with coal blocks and slabs. During operation, a dense film of frozen electrolyte is formed on the surface of the bath body, protecting the lining from destruction by the electrolyte melt.
- A layer of molten aluminum at the bottom of the bath, 10–20 cm thick, serves as the cathode in this installation.
- Current is supplied to the aluminum melt through carbon blocks and embedded steel rods.
- The anodes, suspended on an iron frame using steel pins, are provided with rods connected to a lifting mechanism. As combustion proceeds, the anode moves down, and the rods are used as an element for supplying current.
- In workshops, electrolyzers are installed sequentially in several rows (two or four rows).
Additional purification of aluminum by refining
If the aluminum extracted from the electrolysers does not meet the final requirements, it is subjected to additional purification by refining.
In industry, this process is carried out in a special electrolyzer, which contains three liquid layers:
- Bottom – refined aluminum with the addition of approximately 35% copper, serves as an anode. Copper is present to make the aluminum layer heavier; copper does not dissolve in the anode alloy; its density must exceed 3000 kg/m3.
- The middle layer is a mixture of fluorides and chlorides of barium, calcium, and aluminum with a melting point of about 730 ° C.
- Top layer - pure refined aluminum a melt that dissolves in the anode layer and rises upward. It serves as the cathode in this circuit. The current is supplied by a graphite electrode.
During the electrolysis process, impurities remain in the anode layer and electrolyte. The yield of pure aluminum is 95–98%. The development of aluminum-containing deposits has a leading place in the national economy, thanks to the properties of aluminum, which currently ranks second after iron in modern industry.
In modern industry, aluminum ore is the most popular raw material. The rapid development of science and technology has made it possible to expand the scope of its application. What aluminum ore is and where it is mined is described in this article.
Industrial importance of aluminum
Aluminum is considered the most common metal. It ranks third in terms of the number of deposits in the earth's crust. Aluminum is also known to everyone as an element in the periodic table, which belongs to light metals.
Aluminum ore is the natural raw material from which this metal is obtained. It is mainly mined from bauxite, which contains aluminum oxides (alumina) in the largest quantities - from 28 to 80%. Other rocks - alunite, nepheline and nepheline-apatite are also used as raw materials for the production of aluminum, but they are of poorer quality and contain significantly less alumina.
Aluminum ranks first in non-ferrous metallurgy. The fact is that due to its characteristics it is used in many industries. Thus, this metal is used in transport engineering, packaging production, construction, and for the manufacture of various consumer goods. Aluminum is also widely used in electrical engineering.
To understand the importance of aluminum for humanity, it is enough to take a closer look at the household things that we use every day. Many household items are made of aluminum: these are parts for electrical appliances (refrigerator, washing machine etc.), dishes, sports equipment, souvenirs, interior elements. Aluminum is often used for production different types containers and packaging. For example, cans or disposable foil containers.
Types of aluminum ores
Aluminum is found in more than 250 minerals. Of these, the most valuable for industry are bauxite, nepheline and alunite. Let's look at them in more detail.
Bauxite ore
Aluminum does not occur in nature in its pure form. It is mainly obtained from aluminum ore - bauxite. It is a mineral that mostly consists of aluminum hydroxides, as well as iron and silicon oxides. Due to the high alumina content (40 to 60%), bauxite is used as a raw material for the production of aluminum.
Physical properties of aluminum ore:
- opaque mineral of red and gray colors of various shades;
- the hardness of the strongest samples is 6 on the mineralogical scale;
- The density of bauxite, depending on the chemical composition, ranges from 2900-3500 kg/m³.
Bauxite ore deposits are concentrated in the equatorial and tropical zone land. More ancient deposits are located in Russia.
How is bauxite aluminum ore formed?
Bauxite is formed from alumina monohydrate, boehmite and diaspore, trihydrate hydrargillite and associated minerals hydroxide and iron oxide.
Depending on the composition of nature-forming elements, three groups of bauxite ores are distinguished:
- Monohydrate bauxite – contains alumina in monohydrate form.
- Trihydrate - such minerals consist of alumina in trihydrate form.
- Mixed - this group includes the previous aluminum ores in combination.
Deposits of raw materials are formed due to the weathering of acidic, alkaline, and sometimes basic rocks or as a result of the gradual deposition of large quantities of alumina on the sea and lake beds.
Alunite ores
This type of deposit contains up to 40% aluminum oxide. Alunite ore is formed in water basins and coastal zones under conditions of intense hydrothermal and volcanic activity. An example of such deposits is Lake Zaglinskoye in the Lesser Caucasus.
The rock is porous. Mainly consists of kaolinites and hydromicas. Ore with an alunite content of more than 50% is of industrial interest.
Nepheline
This is an aluminum ore of igneous origin. It is a fully crystalline alkaline rock. Depending on the composition and technological features of processing, several grades of nepheline ore are distinguished:
- first grade – 60–90% nepheline; it contains more than 25% alumina; processing is carried out by sintering;
- second grade – 40–60% nepheline, the amount of alumina is slightly lower – 22–25%; enrichment is required during processing;
- the third grade is nepheline minerals, which are of no industrial value.
World production of aluminum ores
Aluminum ore was first mined in the first half of the 19th century in the southeast of France, near the town of Box. This is where the name bauxite comes from. At first, this industry developed at a slow pace. But when humanity appreciated which aluminum ore was useful for production, the scope of aluminum application expanded significantly. Many countries have begun searching for deposits on their territories. Thus, the world production of aluminum ores began to gradually increase. The numbers confirm this fact. Thus, if in 1913 the global volume of ore mined was 540 thousand tons, then in 2014 it was more than 180 million tons.
The number of countries mining aluminum ore also gradually increased. Today there are about 30 of them. But over the past 100 years, leading countries and regions have constantly changed. Thus, at the beginning of the 20th century, the world leaders in the extraction of aluminum ore and its production were North America and Western Europe. These two regions accounted for about 98% of global production. After several decades, the countries became leaders in terms of quantitative indicators of the aluminum industry. Eastern Europe, Latin America And Soviet Union. And already in the 1950s–1960s, Latin America became the leader in terms of production. And in the 1980–1990s. There was a rapid breakthrough in the aluminum industry in Australia and Africa. In the current global trend, the main leading countries in aluminum production are Australia, Brazil, China, Guinea, Jamaica, India, Russia, Suriname, Venezuela and Greece.
Ore deposits in Russia
In terms of aluminum ore production, Russia ranks seventh in the world ranking. Although aluminum ore deposits in Russia provide the country with large quantities of metal, it is not enough to fully supply the industry. Therefore, the state is forced to buy bauxite from other countries.
In total, there are 50 ore deposits in Russia. This number includes both places where the mineral is being mined and deposits that have not yet been developed.
Most of the ore reserves are located in the European part of the country. Here they are located in Sverdlovsk, Arkhangelsk, Belgorod region, in the Komi Republic. All these regions contain 70% of the country's total proven ore reserves.
Aluminum ores in Russia are still mined from old bauxite deposits. Such areas include the Radynskoye field in the Leningrad region. Also, due to a shortage of raw materials, Russia uses other aluminum ores, the deposits of which are of poorer quality mineral deposits. But they are still suitable for industrial purposes. Thus, in Russia, nepheline ores are mined in large quantities, which also make it possible to obtain aluminum.
The French city of Les Baux de Provence, located in the south of the country, became famous for giving its name to the mineral bauxite. It was there in 1821 that mining engineer Pierre Berthier discovered deposits of unknown ore. It took another 40 years of research and testing to discover the possibilities of the new rock and recognize it as promising for the industrial production of aluminum, which in those years exceeded the price of gold.
Characteristics and origin
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, characterized by 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 most common impurities:
- silicon (represented by quartz, kaolinite and opal);
- titanium (in the form of rutile);
- calcium and magnesium compounds;
- rare earth elements;
- mica;
- in small quantities gallium, chromium, vanadium, zirconium, niobium, phosphorus, potassium, sodium and pyrite.
By origin, bauxites are lateritic and karst (sedimentary). The first, high-quality ones, were formed in the climate of the humid tropics as a result of deep chemical transformation of silicate rocks (the so-called laterization). The latter are of lower quality; they are a product of weathering, transfer and deposition of clay layers in new places.
Bauxites vary in:
- Physical condition (rocky, earthy, porous, loose, clay-like).
- Structure (in the form of fragments and peas).
- Textural 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 determined primarily by the ratio of alumina and silica content. The greater the amount of the first and the less of the second, the greater the industrial value. Important chemical feature mining engineers consider the so-called “breakability”, that is, how easily aluminum oxides can be extracted from the ore material.
Despite the fact that bauxite does not have a constant composition, its physical properties boil down to the following indicators:
| 1 | Color | 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, a diamond has a 10). Because of this softness, bauxite resembles clay. But unlike the latter, when adding water they do not form a homogeneous plastic mass |
Interestingly, physical status has nothing to do with the usefulness and value of bauxite. This is explained by 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, reserves of its primary ore are sufficient to satisfy this need for several more centuries, but not less than 100 years of production.
The US Geological Survey has released data according to which the world's bauxite resources amount to 55-75 billion tons. Moreover, most of them are concentrated in Africa (32%). Oceania accounts for 23%, the Caribbean and South America 21%, Asian continent 18%, other regions 6%.
The introduction of an aluminum recycling process also inspires optimism, which will slow down the depletion of natural reserves of primary aluminum ore (and at the same time save energy consumption).
The top ten countries in bauxite mining, represented by the same US Geological Survey, looked like this in 2016.
| 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 |
Vietnam is showing itself to be very promising, ending 2016 with a figure of 1,500 thousand. metric tons. But Malaysia, which was third in 2015, has sharply reduced bauxite development due to expectations of strict environmental laws and today ranks 15th in the world ranking.
Bauxite is usually mined in open pits. To obtain a working platform, a layer of ore is blasted at a depth of 20 centimeters and then removed. Pieces of the mineral are crushed and sorted: waste rock (the so-called “tailings”) is washed away with a stream of washing water, and fragments of dense ore remain at the bottom of the processing plant.
The most ancient bauxite deposits in Russia date back to the Precambrian era. They are located in the Eastern Sayan Mountains (Boksonskoye field). Younger aluminum ore, dating back to the Middle and Upper Devonian, is found in the Northern and Southern Urals, in the Arkhangelsk, Leningrad and Belgorod regions.
Industrial Application
Mined bauxites are divided according to their subsequent commercial use into metallurgical, abrasive, chemical, cement, refractory, etc.
Their main use, which accounts for 85% of world production, is to serve as a raw material for the production of alumina (aluminum oxide).
The technological chain looks like this: bauxite is heated with caustic soda, then filtered, the solid residue is precipitated and calcined. This product is anhydrous alumina, the penultimate transformation in the aluminum production cycle.
After that, all that remains is to immerse it in a bath of molten natural or synthetic cryolite and, through electrolytic reduction, isolate the metal itself.
The first to discover this technology in 1860 was the French chemist Henri Saint-Clair Deville. It replaced an expensive process in which aluminum was produced in a vacuum from potassium and sodium.
Next important area use of bauxite - use as abrasives.
When alumina is calcined, the result is synthetic corundum, a very hard material with a rating of 9 on the Mohs scale. It is crushed, separated and then added to the composition sandpaper and a variety of polishing powders and suspensions.
Sintered, powdered and fused into round granules, bauxite is also an excellent sandblasting abrasive. It is ideal for surface treatment, and due to its spherical shape it reduces wear on sandblasting equipment.
Another important purpose of bauxite is to participate as a proppant (a material that prevents specially created faults from closing) in the process of oil production using hydraulic fracturing. In this case, the treated bauxite rock particles resist hydraulic pressure and allow the cracks to remain open for as long as necessary for oil to escape.
Bauxite is also indispensable for creating fire-resistant products. Burnt 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 that would not be inferior in their properties. Research has revealed that clay materials, power plant ash and oil shale can be used to produce alumina.
However, the cost of the entire technological chain is many times higher. Silicon carbide has performed well as an abrasive and synthetic mullite as a refractory. Scientists hope that before the time of complete exhaustion natural resources bauxite an equivalent replacement will be found.
In modern industry, aluminum ore is the most popular raw material. The rapid development of science and technology has made it possible to expand the scope of its application. What aluminum ore is and where it is mined is described in this article.
Industrial importance of aluminum
Aluminum is considered the most common metal. It ranks third in terms of the number of deposits in the earth's crust. Aluminum is also known to everyone as an element in the periodic table, which belongs to light metals.
Aluminum ore is a natural raw material from which it is mainly mined from bauxite, which contains aluminum oxides (alumina) in the largest amount - from 28 to 80%. Other rocks - alunite, nepheline and nepheline-apatite are also used as raw materials for the production of aluminum, but they are of poorer quality and contain significantly less alumina.
Aluminum ranks first in non-ferrous metallurgy. The fact is that due to its characteristics it is used in many industries. Thus, this metal is used in transport engineering, packaging production, construction, and for the manufacture of various consumer goods. Aluminum is also widely used in electrical engineering.
To understand the importance of aluminum for humanity, it is enough to take a closer look at the household things that we use every day. Many household items are made of aluminum: these are parts for electrical appliances (refrigerator, washing machine, etc.), dishes, sports equipment, souvenirs, interior elements. Aluminum is often used to produce various types of containers and packaging. For example, cans or disposable foil containers.
Types of aluminum ores
Aluminum is found in more than 250 minerals. Of these, the most valuable for industry are bauxite, nepheline and alunite. Let's look at them in more detail.
Bauxite ore
Aluminum does not occur in nature in its pure form. It is mainly obtained from aluminum ore - bauxite. It is a mineral that mostly consists of aluminum hydroxides, as well as iron and silicon oxides. Due to the high alumina content (40 to 60%), bauxite is used as a raw material for the production of aluminum.
Physical properties of aluminum ore:
- opaque mineral of red and gray colors of various shades;
- the hardness of the strongest samples is 6 on the mineralogical scale;
- The density of bauxite, depending on the chemical composition, ranges from 2900-3500 kg/m³.
Bauxite ore deposits are concentrated in the equatorial and tropical zones of the earth. More ancient deposits are located in Russia.
How is bauxite aluminum ore formed?
Bauxite is formed from alumina monohydrate, boehmite and diaspore, trihydrate hydrargillite and associated minerals hydroxide and iron oxide.
Depending on the composition of nature-forming elements, three groups of bauxite ores are distinguished:
- Monohydrate bauxite - contains alumina in monohydrate form.
- Trihydrate - such minerals consist of alumina in trihydrate form.
- Mixed - this group includes the previous aluminum ores in combination.
Deposits of raw materials are formed due to the weathering of acidic, alkaline, and sometimes basic rocks or as a result of the gradual deposition of large quantities of alumina on the sea and lake beds.
Alunite ores
This type of deposit contains up to 40% aluminum oxide. Alunite ore is formed in water basins and coastal zones under conditions of intense hydrothermal and volcanic activity. An example of such deposits is Lake Zaglinskoye in the Lesser Caucasus.
The rock is porous. Mainly consists of kaolinites and hydromicas. Ore with an alunite content of more than 50% is of industrial interest.
Nepheline
This is an aluminum ore of igneous origin. It is a fully crystalline alkaline rock. Depending on the composition and technological features of processing, several grades of nepheline ore are distinguished:
- first grade - 60-90% nepheline; it contains more than 25% alumina; processing is carried out by sintering;
- second grade - 40-60% nepheline, the amount of alumina is slightly lower - 22-25%; enrichment is required during processing;
- the third grade is nepheline minerals, which are of no industrial value.
World production of aluminum ores
Aluminum ore was first mined in the first half of the 19th century in the southeast of France, near the town of Box. This is where the name bauxite comes from. At first it developed at a slow pace. But when humanity appreciated which aluminum ore was useful for production, the scope of aluminum application expanded significantly. Many countries have begun searching for deposits on their territories. Thus, the world production of aluminum ores began to gradually increase. The numbers confirm this fact. Thus, if in 1913 the global volume of ore mined was 540 thousand tons, then in 2014 it was more than 180 million tons.
The number of countries mining aluminum ore also gradually increased. Today there are about 30 of them. But over the past 100 years, leading countries and regions have constantly changed. Thus, at the beginning of the 20th century, the world leaders in the extraction of aluminum ore and its production were North America and Western Europe. These two regions accounted for about 98% of global production. A few decades later, in terms of quantitative indicators of the aluminum industry, Latin America and the Soviet Union became the leaders. And already in the 1950-1960s, Latin America became the leader in terms of production. And in the 1980-1990s. there was a rapid breakthrough in aluminum and Africa. In the current global trend, the main leading countries in aluminum production are Australia, Brazil, China, Guinea, Jamaica, India, Russia, Suriname, Venezuela and Greece.
Ore deposits in Russia
In terms of aluminum ore production, Russia ranks seventh in the world ranking. Although aluminum ore deposits in Russia provide the country with large quantities of metal, it is not enough to fully supply the industry. Therefore, the state is forced to buy bauxite from other countries.
In total, there are 50 ore deposits in Russia. This number includes both places where the mineral is being mined and deposits that have not yet been developed.
Most of the ore reserves are located in the European part of the country. Here they are located in the Sverdlovsk, Arkhangelsk, Belgorod regions, in the Komi Republic. All these regions contain 70% of the country's total proven ore reserves.
Aluminum ores in Russia are still mined from old bauxite deposits. Such areas include the Radynskoye field in the Leningrad region. Also, due to a shortage of raw materials, Russia uses other aluminum ores, the deposits of which are of poorer quality mineral deposits. But they are still suitable for industrial purposes. Thus, in Russia, nepheline ores are mined in large quantities, which also make it possible to obtain aluminum.
Aluminum is a metal coated with a matte silver oxide film, the properties of which determine its popularity: softness, lightness, ductility, high strength, corrosion resistance, electrical conductivity and lack of toxicity. In modern high technologies, the use of aluminum is given a leading place as a structural, multifunctional material.
The greatest value for industry as a source of aluminum is natural raw materials - bauxite, a rock component in the form of bauxite, alunite and nepheline.
Varieties of alumina-containing ores
More than 200 minerals are known that contain aluminum.
Only rock that can meet the following requirements is considered a raw material source:
Feature of the natural rock bauxite
Natural deposits of bauxite, nepheline, alunite, clay, and kaolin can serve as a source of raw materials. Bauxite is the most saturated with aluminum compounds. Clays and kaolins are the most common rocks with a significant alumina content. Deposits of these minerals are found on the surface of the earth.
Bauxite in nature exists only in the form of a binary compound of metal with oxygen. This compound is extracted from natural mountain ore in the form of bauxite, consisting of oxides of several chemical elements: aluminum, potassium, sodium, magnesium, iron, titanium, silicon, phosphorus.
Depending on the deposit, bauxite contains from 28 to 80% alumina. This is the main raw material for obtaining a unique metal. The quality of bauxite as an aluminum raw material depends on its alumina content. This determines the physical properties bauxite:
Bauxites, kaolins, and clays contain impurities of other compounds, which are separated into separate industries during the processing of raw materials.
Only in Russia do they use deposits with rock deposits that contain lower concentrations of alumina.
Recently, alumina began to be obtained from nephelines, which, in addition to alumina, contain oxides of metals such as potassium, sodium, silicon and, no less valuable, alum stone, alunite.
Methods for processing aluminum containing minerals
The technology for producing pure alumina from aluminum ore has not changed since the discovery of this metal. Its production equipment is being improved, allowing it to produce pure aluminum. The main production stages of obtaining pure metal:
- Extraction of ore from developed deposits.
- Primary processing of waste rocks in order to increase the concentration of alumina is an enrichment process.
- Preparation of pure alumina, electrolytic reduction of aluminum from its oxides.
The production process ends with metal with a concentration of 99.99%.
Alumina mining and beneficiation
Alumina or aluminum oxides do not exist in nature in their pure form. It is extracted from aluminum ores using hydrochemical methods.
Aluminum ore deposits in deposits usually explode, providing a site for its extraction at a depth of approximately 20 meters, from where it is selected and launched into the process of further processing;
- Using special equipment (screens, classifiers), the ore is crushed and sorted, discarding waste rock (tailings). At this stage of alumina enrichment, washing and screening methods are used as the most economically advantageous.
- The purified ore settled at the bottom of the concentration plant is mixed with a heated mass of caustic soda in an autoclave.
- The mixture is passed through a system of high-strength steel vessels. The vessels are equipped with a steam jacket that maintains the required temperature. The steam pressure is maintained at 1.5-3.5 MPa until the aluminum compounds are completely transferred from the enriched rock to sodium aluminate in a superheated sodium hydroxide solution.
- After cooling, the liquid undergoes a filtration stage, as a result of which solid sediment is separated and a supersaturated pure aluminate solution is obtained. By adding aluminum hydroxide residues from the previous cycle to the resulting solution, decomposition is accelerated.
- For final drying of aluminum oxide hydrate, a calcination procedure is used.
Electrolytic production of pure aluminum
Pure aluminum is produced using a continuous process that produces calcined aluminum enters the electrolytic reduction stage.
Modern electrolysers are a device consisting of the following parts:
Additional purification of aluminum by refining
If the aluminum extracted from the electrolysers does not meet the final requirements, it is subjected to additional purification by refining.
In industry, this process is carried out in a special electrolyzer, which contains three liquid layers:
During the electrolysis process, impurities remain in the anode layer and electrolyte. The yield of pure aluminum is 95–98%. The development of aluminum-containing deposits has a leading place in the national economy, thanks to the properties of aluminum, which currently ranks second after iron in modern industry.
Aluminum is one of the most popular and sought-after metals. In every industry it is not added to the composition of certain items. From instrument making to aviation. The properties of this lightweight, flexible and corrosion-resistant metal have appealed to many industries.
Aluminum itself (a fairly active metal) is practically never found in nature in its pure form and is extracted from alumina, the chemical formula of which is Al 2 O 3. But the direct route to obtaining alumina is, in turn, aluminum ore.
Differences in saturation
Basically, there are only three types of ores worth mentioning that you need to work with if you are mining aluminum. Yes, given chemical element very, very common, and can also be found in other compounds (there are about two and a half hundred of them). However, due to the very high concentration, the most profitable extraction will be from bauxite, alunite and nepheline.
Nephelines are an alkaline formation that appeared due to the high temperature of magma. One unit of this ore will yield up to 25% alumina as the main raw material. However, this aluminum ore is considered the poorest for miners. All compounds containing alumina in even smaller quantities than nephelines are obviously recognized as unprofitable.
Alunites were formed during volcanic as well as hydrothermal activities. They contain up to 40% of the essential alumina, being the “golden mean” in our trinity of ores.
And the first place, with a record aluminum oxide content of fifty percent or more, goes to bauxite! They are rightfully considered the main source of alumina. However, regarding their origin, scientists still cannot come to the only correct decision.
Either they migrated from their original place of origin and were deposited after the ancient rocks weathered, or they turned out to be sediment after some limestones dissolved, or they generally became the result of the decomposition of iron, aluminum and titanium salts, falling out as sediment. In general, the origin is still unknown. But the fact that bauxite is the most profitable is already certain.
Aluminum mining methods
The necessary ores are mined in two ways.
In terms of the open method of mining the treasured Al 2 O 3 in aluminum deposits, the three main ores are divided into two groups.
Bauxite and nepheline, as higher density structures, are cut by milling using a surface miner. Of course, it all depends on the manufacturer and model of the machine, but, on average, it is capable of removing up to 60 centimeters of rock at a time. After a complete passage of one layer, a so-called shelf is created. This method ensures that the combine operator remains safe in his position. In the event of a collapse, both the chassis and the operator's cab will be safe.
The second group contains alunites, which, due to their friability, are mined by quarry excavators and then unloaded onto dump trucks.
A radically different method is to punch a shaft. Here the mining principle is the same as in coal mining. By the way, the deepest aluminum mine in Russia is the one located in the Urals. The depth of the mine is 1550m!
Processing the resulting ore
Next, regardless of the chosen extraction method, the resulting minerals are sent to processing workshops, where special crushing devices break the minerals into fractions approximately 110 millimeters in size.
The next step is to obtain additional chemicals. additives and transportation to the further stage, which is sintering the rock in furnaces.
Having undergone decomposition and receiving aluminate pulp at the exit, we will send the pulp to be separated and drained from the liquid.
At the final stage, what is obtained is cleaned from alkalis and sent back to the oven. This time - for calcination. The finale of all actions will be the same dry alumina that is needed to obtain aluminum through hydrolysis.
Even though breaking through a shaft is considered a more difficult method, it causes less harm environment, how open method. If you are for the environment, you know what to choose.
Aluminum mining in the world
At this point we can say that indicators for interactions with aluminum around the world are divided into two lists. The first list will include countries that own the largest natural reserves of aluminum, but perhaps not all of these resources have time to be processed. And the second list contains the world leaders in the direct extraction of aluminum ore.
So, in terms of natural (although not realized everywhere, yet) wealth, the situation is like this:
- Guinea
- Brazil
- Jamaica
- Australia
- India
These countries can be said to possess the vast majority of Al 2 O 3 in the world. They account for 73 percent in total. The remaining supplies are scattered throughout to the globe not in such generous quantities. Guinea, which is located in Africa, in a global sense - largest deposit aluminum ores in the world. It “grabbed” 28%, which is even more than a quarter of the global deposits of this mineral.
And this is how things stand with the processes of mining aluminum ore:
- China is in first place and produces 86.5 million tons;
- Australia is a country of strange animals with its 81.7 million. tons in second place;
- Brazil - 30.7 million tons;
- Guinea, being the leader in reserves, is only in fourth place in terms of production - 19.7 million tons;
- India – 14.9 million tons.
You can also add to this list Jamaica, capable of producing 9.7 million tons, and Russia, with its figure of 6.6 million tons.
Aluminum in Russia
Regarding aluminum production in Russia, only Leningrad region and, of course, the Urals, as a true storehouse of minerals. The main method of extraction is mining. They mine four-fifths of all ore in the country. In total, on the territory of the Federation there are more than four dozen deposits of nepheline and bauxite, the resources of which will definitely be enough even for our great-great-grandchildren.
However, Russia also imports alumina from other countries. This is because local substances (for example, the Red Cap deposit in Sverdlovsk region) contain only half of alumina. Whereas Chinese or Italian rocks are saturated with Al 2 O 3 by sixty percent or more.
Looking at some of the difficulties with aluminum mining in Russia, it makes sense to think about the production of secondary aluminum, as the UK, Germany, USA, France and Japan have done.
Application of aluminum
As we already stated at the beginning of the article, the range of applications of aluminum and its compounds is extremely wide. Even at the stages of extraction from the rock, it is extremely useful. The ore itself, for example, contains small quantities of other metals, such as vanadium, titanium and chromium, useful for steel alloying processes. There is also a benefit at the alumina stage, because alumina is used in ferrous metallurgy as a flux.
The metal itself is used in the production of thermal equipment, cryogenic technology, participates in the creation of a number of alloys in metallurgy, and is present in the glass industry, rocketry, aviation, and even in the food industry as an E173 additive.
So, only one thing is certain. For many more years, humanity's need for aluminum, as well as its compounds, will not fade away. Which, accordingly, speaks exclusively of an increase in its production volumes.
