Industrial alumina is prepared from bauxite (Al2O3 3H2O) and diaspore. For Al2O3 with high purity, it is generally prepared by chemical method. There are many isomorphic crystals of Al2O3, including 10, and there are mainly three crystal forms, namely α-Al2O3, β-Al2O3 and γ-Al2O3. Among them, the structure and properties are different, and it almost completely transforms into α-Al2O3 at the high temperature above 1300℃.
Chinese name
Alumina [6]
Foreign name
Alumina [6]
chemical formula
Alumina [6]
molecular weight
10 1.96
Chemical abstracts service registration number
1344-28- 1[6]
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Basic information, main components, chemical properties, physical properties, variants, development, safety and quality inspection indicators, industry overview, main functions, applicability, enterprise development, TA theory.
Basic information
Alumina is a stable oxide of aluminum, and its chemical formula is Al2O3. It is also called bauxite in mining, ceramics and materials science.
Properties: white solid, insoluble in water, odorless, tasteless, extremely hard, easy to absorb moisture but not deliquescent (burning does not absorb moisture). Alumina is a typical amphoteric oxide (corundum is α-shaped, belongs to the most densely packed hexagonal, is an inert compound, slightly soluble in acid and alkali [1]), soluble in inorganic acids and alkaline solutions, and almost insoluble in water and nonpolar organic solvents; Relative density (d204)4.0；; ; The melting point is 2050℃.
Molecular structure diagram
Storage: sealed, dried and preserved.
Uses: Used as analytical reagent, organic solvent dehydrating agent, adsorbent, organic reaction catalyst, abrasive, polishing agent, aluminum smelting raw material and refractory. [2]
major constituent
Alumina contains aluminum and oxygen. If the bauxite raw material is chemically treated to remove the oxides of silicon, iron and titanium, the product is high-purity alumina raw material, and the Al2O3 content is generally above 99%. The mineral phase consists of 40% ~ 76% γ- Al2O3 and 24% ~ 60% α- Al2O3. γ-al2o 3 can be transformed into α-al2o 3 at 950 ~ 1200℃, and its volume shrinks obviously. [3]
chemical property
Reaction with acid:
Al2O3 + 6HCl = 2AlCl3 + 3H2O
Al2O3 + 6H+ = 2Al3+ + 3H2O
Reacting with molten alkali;
Al2O3+2NaOH= 2NaAlO2 (sodium metaaluminate) +H2O
React with alkali solution:
Al2O3+ 2NaOH +3H2O = 2Na[Al(OH)4] (sodium tetrahydroxyaluminate)
It can also be abbreviated as: Al2O3+2OH-=2AlO2- (metaaluminate ion) +H2O.
physical features
InChI = 1/al2o/ralo 2/C2- 1-3
Molecular weight: 10 1.96
Melting point: 2054℃
Boiling point: 2980℃
True density: 3.97 g/cm3.
Bulk density: 0.85g/ml (325 mesh to 0 mesh) 0.9g/ml (120 mesh to 325 mesh).
Crystal structure: Trilateral system (hexadecimal)
Solubility: Insoluble in water at room temperature.
Conductivity: it is not conductive at room temperature.
Al2O3 is an ionic crystal.
Thermochemical characteristics:
δFHθ(l)= 1620.57 kJ/mol
δFHθ(s)= 1675.69 kJ/mol
Sθ(l)= 67.24 Joule/mol K( 1 bar)
Sθ(s)=50.9 Joule/mol k
different
There are many varieties of Al2O3, among which α and γ are common, all of which are white crystals.
In nature, corundum is α-type and belongs to the densest hexagonal filler, with high melting point, high hardness, insolubility in acid and alkali, corrosion resistance and good insulation.
At 723K***, aluminum hydroxide can be mixed with aluminum hydroxide or aluminum ammonium alum to obtain γ type, which is insoluble in water, but has strong water absorption and adsorption capacity and catalytic activity.
The β-shape has ionic conductivity and allows Na+ to pass through.
develop
According to the data, China is the largest alumina producer in the world. In 20 10, the global alumina output was 56.355 million tons, and that of China reached 28.955 million tons, up 20. 14% year-on-year, accounting for 5 1.38% of the global total. In 20 10 year, the apparent consumption of alumina in China reached 3.32110,000 tons, with an annual growth rate of 14.05%, net import of 4.26 million tons, bauxite import of 3010.9 million tons, external dependence of 39.7 1%, and alumina export.
aluminium oxide
With the rapid development of electrolytic aluminum, ceramics, medicine, electronics, machinery and other industries in China, the market demand for alumina still has a large room for growth, and the output of alumina will continue to increase. According to the data of China's alumina output in 2005-20 10, it is predicted that China's alumina output in 2014% will reach 33 million tons, and will continue to grow on the basis of 20 1 12.
In addition, in view of the continuous and substantial increase in the area of projects under construction in China and the continuous urbanization process, the prospect of aluminum industry in the future is very optimistic. It is predicted that China's alumina demand will increase by 15% to 38190,000 tons in 20 18, and will reach 42 million tons in 20 12, with a year-on-year increase of 10%.
safe
Intake: low risk, easy to cause Alzheimer's disease, and harmful to children's intelligence.
Inhalation: May cause irritation or lung injury.
Skin: low risk
Eyes: low risk
Unless otherwise specified, SI units and standard air temperature and pressure are used.
Quality inspection index
Dissolved substances in water,% ≤0.5
Silicate qualified
Alkali metals and alkaline earth metals,% ≤0.50
Heavy metal (calculated by lead),% ≤0.005
Chloride,% ≤0.0 1
Sulfate,% ≤0.05
Loss on ignition,% ≤5.0
Iron,% ≤0.0 1
General situation of industry
China is rich in bauxite resources, with proven conservative reserves of 2.3 billion tons, ranking fourth in the world, and has the resource conditions for developing alumina industry. According to incomplete statistics since 2004, there are 27 announced alumina investment projects in China, with an estimated total scale of 1 604. 1 000 tons. Even if foreign bauxite resources are not considered, the total scale will reach 28 14438+00000 tons. At the end of 2006, China Aluminum Company produced 9.52 million tons of alumina. Together with the published alumina scale under construction, the total alumina scale in China is19.92 million tons, which is close to the sum of all proposed (expanded) alumina projects abroad. The rapid development of alumina industry is different from the previous low-level repeated construction, but it is a large-scale, high-level and optimized structure, which greatly improves the overall level and competitiveness of alumina industry in China. However, if this investment fever continues to expand in disorder, it will inevitably lead to a relative surplus of products.
There are more than 40 alumina enterprises in China, and the built and under construction production capacity exceeds 43.5 million tons/year, of which the domestic bauxite processing capacity is 32.5 million tons/year. In 20 10, the national alumina output was 28.96 million tons, making it the largest alumina producer in the world.
The risk of investing in alumina industry is different from other industries such as electrolytic aluminum, which is manifested in the following aspects:
The technology is relatively complicated.
Under normal circumstances, it takes about 2 ~ 3 years for a project to reach production from design and start-up, which is characterized by large investment and high risk.
Market price fluctuates.
The information asymmetry between supply and demand further aggravates the fluctuation of alumina price, which will further affect the investment income of alumina projects.
Need a lot of skilled workers
In the project commissioning, commissioning and future production organization and management, a large number of old experts and skilled workers who are proficient in alumina technology and have practical experience are needed.
Dependence on resources and energy
With the increasingly fierce competition for resources at home and abroad, high-quality resources suitable for the development of alumina industry are becoming scarcer and scarcer, so the economic service life of the project must be considered when investing in alumina industry.
suggestion
In view of the rapid development of alumina industry and avoiding the disorderly expansion of electrolytic aluminum industry, there are five suggestions as follows:
Control the total scale of alumina construction
Alumina industry is a resource, capital and technology-intensive raw material industry. Because a large number of tailings and red mud will be produced in the production process (there is no good treatment method to add them to cement raw materials so far, and the products can only be used in industry), which has a great impact on the environment. Bauxite, as a non-renewable resource, directly restricts the total amount and life cycle of alumina industry in a region. Therefore, governments at all levels and relevant departments must accurately grasp the development situation, resource and environmental constraints and basic laws of alumina industry, strictly control new alumina projects in accordance with the requirements of total control, resolutely stop blind development and low-level redundant construction, and strive to achieve the unity of alumina industry development, full utilization of resources and optimization of ecological environment.
Optimize the layout of alumina industry
The competent department of mineral resources should comprehensively verify the bauxite stock resources and promote the exploration of bauxite resources. When the resource reserves are greatly improved, the development planning department will increase the distribution or agree to expand the production capacity of the enterprises in distribution as appropriate. Without the consent of the proposed alumina project outside the planning layout, the provincial environmental protection department shall not arrange environmental impact assessment, and the unauthorized construction must be stopped. Punitive electricity prices shall be imposed on alumina projects and self-owned power plants that are not built within the planning layout without consent.
Strictly developed economic scale
New alumina projects must adopt domestic research and development of mineral processing? Bayer process and concentrator construction simultaneously. It is strictly forbidden to launch alumina projects with backward technology such as sintering method and mixed method. The single-line scale of new alumina projects should reach more than 300,000 tons, and it is not allowed to build alumina projects with a reasonable economic scale of less than 300,000 tons. For small alumina plants with backward technology and serious pollution, it is necessary to switch production or close down within a time limit.
optimize the allocation of resources
According to the Mineral Resources Law, bauxite resources are managed by the mineral resources management department. Without the approval of the mineral resources management department, all localities may not approve the exploitation of bauxite by themselves. The illegal examination and approval and unauthorized exploitation of bauxite, once verified, should be held responsible for the relevant personnel. Strengthen the setting of mining rights and balanced management of resources, and optimize the allocation of resources. The competent department of mineral resources shall, on the basis of comprehensive verification and systematic analysis of bauxite resources, make reasonable planning and comprehensive balance of bauxite resources and mining rights. According to the construction scale and reasonable production cycle, the distribution enterprises must ensure the bauxite resources that meet the production demand of 5 ~ 10 years before the project is completed and put into production, and simultaneously build a concentrator using d Bayer process.
Production of alumina by Bayer process
Compared with the main domestic production methods, Bayer process saves 15% ~ 20% of construction investment, 10% of production cost and 50% of energy consumption. Compared with the conventional Bayer process, Bayer process (A/S= 10) for treating high-grade bauxite has similar technological process and basically the same main production energy consumption indicators. Therefore, it is an important way to solve the development of alumina industry in China to produce alumina by Bayer process and treat medium-grade diaspore bauxite in China, which has remarkable economic and social benefits.
Generally speaking, there are many problems in the development of aluminum and aluminum compounds industry in China in 2005. In 2004, the investment and construction of electrolytic aluminum industry was restrained by macro-control, but the investment focus of aluminum industry shifted to D alumina and aluminum processing industry in the upstream and downstream of the industrial chain. [4]
major function
General introduction
Ruby and sapphire are mainly composed of alumina, which will show different colors because of other impurities, while sapphire is blue because of iron oxide and titanium oxide.
2. Among the main components of bauxite, alumina has the highest content. In industry, bauxite is purified into alumina by Bayer process, and then converted into metallic aluminum by Hall-Herout process.
3. Aluminum reacts with oxygen in the air to form a dense alumina film, covering the aluminum surface exposed to the air.
Aluminum is a good conductor of electricity and heat. The crystal morphology of alumina is suitable for grinding materials and cutting tools because of its high hardness.
5. Alumina powder is often used as a carrier for chromatographic analysis.
In August, 2004, scientists working in 3M company in the United States developed an alloy made of aluminum and rare earth elements, which was used to make strengthened glass called transparent alumina.
Data: The hardness of corundum powder can be used as abrasive, polishing powder and alumina sintered at high temperature, which is called artificial corundum or artificial gem, and can be used to manufacture diamonds in mechanical bearings or watches. Alumina is also used as a high-temperature refractory to make refractory bricks, crucibles, porcelain and artificial gem. Alumina is also the raw material for aluminum smelting. Calcining aluminum hydroxide can produce γ-. γ-Al2O3 has strong adsorption and catalytic activity, and can be used as adsorbent and catalyst. The main component of corundum is α-Al2O3. Bucket or conical triangular crystal. Have glass luster or diamond luster. The density is 3.9 ~ 4. 1g/cm3, the hardness is 9 and the melting point is 2000 15℃. Insoluble in water, acid and alkali. High temperature resistance. Colorless and transparent is called white jade, reddish and containing trace trivalent chromium is called ruby; Blue containing ferrous iron, ferric iron or tetravalent titanium is called sapphire; Dark gray and dark black containing a small amount of ferroferric oxide are called corundum powder. It can be used as bearings for precision instruments, diamonds for clocks and watches, grinding wheels, polishing agents, refractories and electrical insulators. Colored gems that can be used for decoration. Artificial ruby single crystal can be used as laser material. In addition to natural minerals, it can also be made by melting aluminum hydroxide with hydrogen-oxygen flame.
vector
Alumina powder is often used as a medium for chromatographic analysis.
Making tempered glass
Data: The hardness of corundum powder can be used as abrasive, polishing powder and alumina sintered at high temperature, which is called artificial corundum or artificial gem, and can be used to manufacture diamonds in mechanical bearings or watches. Alumina is also used as a high-temperature refractory to make refractory bricks, crucibles, porcelain and artificial gem. Alumina is also the raw material for aluminum smelting. γ-Al2O3 can be prepared by calcining aluminum hydroxide. γ-Al2O3 has strong adsorption and catalytic activity, and can be used as adsorbent and catalyst. The main component of corundum is α-Al2O3. Bucket or conical triangular crystal. Have glass luster or diamond luster. The density is 3.9 ~ 4. 1g/cm3, the hardness is 9 and the melting point is 2000 15℃. Insoluble in water, acid and alkali. High temperature resistance. Colorless and transparent is called white jade, reddish and containing trace trivalent chromium is called ruby; Blue containing ferrous iron, ferric iron or tetravalent titanium is called sapphire; Dark gray and dark black containing a small amount of ferroferric oxide are called corundum powder. It can be used as bearings for precision instruments, diamonds for clocks and watches, grinding wheels, polishing agents, refractories and electrical insulators. Colored gems that can be used for decoration. Artificial ruby single crystal can be used as laser material. In addition to natural minerals, it can also be made by melting aluminum hydroxide with hydrogen-oxygen flame.
Alumina is the reason why metallic aluminum is not easily corroded in air. Pure aluminum easily reacts with oxygen in the air to form a thin aluminum oxide film covering the aluminum surface exposed to the air. This alumina film can prevent aluminum from being further oxidized. The thickness and performance of oxide film can be improved by anodic treatment (anodic corrosion protection).
bauxite
(Al2O3 3H2O and Al2O3 3H2O) are the main minerals of aluminum in nature. After crushing, it was impregnated with high-temperature sodium hydroxide solution to obtain sodium metaaluminate solution. Filtering to remove residues, cooling the filtrate, adding aluminum hydroxide crystals, and after stirring for a long time, decomposing the sodium aluminate solution to separate out aluminum hydroxide; After separation and washing, the precipitate was calcined at 950- 1200℃ to obtain α -alumina powder, and the mother liquor could be recycled. This method was invented by Austrian scientist K.J.Bayer in 1888, and it is still the main method for industrial production of alumina, which is called "Bayer method".
α alumina
In the lattice of α-alumina, oxygen ions are packed in hexagonal shape, and Al3+ is symmetrically distributed in the octahedral coordination center surrounded by oxygen ions, so the lattice energy is very large, so the melting point and boiling point are very high. Alpha alumina is insoluble in water and acid, also known as alumina in industry, and is the basic raw material for manufacturing metallic aluminum. It is also used to make various refractory bricks, refractory crucibles, refractory pipes and high temperature resistant experimental instruments; It can also be used as abrasive, flame retardant, filler, etc. High purity α -alumina is also the raw material for producing artificial corundum, artificial ruby and sapphire. It is also used to produce substrates for modern large-scale integrated circuits.
γ alumina
Aluminum hydroxide was dehydrated at 140- 150℃ to prepare γ-alumina. It is also called activated alumina and aluminum glue in industry. In its structure, oxygen ions are closely packed with the cubic center, while Al3+ is irregularly distributed in octahedral and tetrahedral spaces surrounded by oxygen ions. γ -alumina is insoluble in water, but soluble in strong acid or alkali solution. When heated to 1200℃, it will be completely converted into α -alumina γ-alumina is a porous substance with an internal surface area of hundreds of square meters/gram, which has high activity and adsorption capacity. Industrial products are usually colorless or pinkish cylindrical particles with good pressure resistance. They are usually used as adsorbents, catalysts and catalyst carriers in petroleum refining and petrochemical industries. In industry, it is a deacidifying agent for transformer oil and turbine oil, and also used for chromatographic analysis; It is a neutral and strong desiccant in the laboratory, and its drying capacity is no less than that of phosphorus pentoxide. Heating at 175℃ for 6-8 hours after use can be recycled.
In the world, the alumina produced by Bayer process accounts for more than 90% of the total output, most of which is used to make metallic aluminum, and less than 10% is used for other purposes.
Electrolytic alumina
The main process of industrial large-scale production of electrolytic aluminum is molten salt electrochemical process, which can be expressed by simple chemical formula as follows:
Molten salt electrolysis
Main reaction: Al2O3+2C → 2Al+CO2↑+CO↑.
Anode 960 ~ 990℃ cathode
Side effects: AlF3+C→Al+CF3.
3NaFAlF3+C →Al+NaF+CF4+F2
NaF+C → Na+CF4
β alumina
Another is β-Al2O3, which has ionic conductivity (allows Na to pass through), and uses β-bauxite as electrolyte to make sodium-sulfur battery. Because of its large storage capacity per unit weight and large current discharge, this battery has broad application prospects. The negative electrode of this battery is molten sodium, the positive electrode is sodium polysulfide (Na2Sx), and the electrolyte is β -bauxite (sodium ion conductor).
The temperature range of this battery can reach 620 ~ 680 K, and its storage capacity is 3 ~ 5 times that of lead battery. Using β-Al2O3 ceramics as the diaphragm of electrolytic salt solution to produce caustic soda has the characteristics of high product purity and little pollution.
Grinding alumina
Alumina is suitable for various dry and wet treatment processes, and can finely polish the rough surface of any workpiece. It is one of the most economical abrasives. This sharp water chestnut synthetic abrasive is second only to diamond in hardness, and it is especially suitable for use in the case of strict requirements on iron pollution. It can be used for the roughest cutting, or it can be made into pebble shape, and the workpiece can be machined with precise size to achieve extremely low roughness. Because of its high density, sharp and diamond-shaped structure, it is one of the fastest cutting abrasives.
Alumina is made of high-quality bauxite ore fused by brown corundum, while high-quality aluminate is used to produce powdered corundum and white corundum. Their natural crystal structure makes them have high hardness and fast cutting performance. At the same time, they are often used as raw materials for bonding abrasives and coating abrasives.
Alumina can be recycled for many times, and the number of cycles is related to the material grade and specific process, and most standard abrasive sand blasting equipment can be used.
Applicable industries: aerospace industry, automobile industry, consumer goods processing, casting/die casting, OEM dealers, semiconductor industry and other different fields.
Scope of application: surface electroplating, painting, glazing and pretreatment before coating PTFE; Deburring aluminum and alloy products and removing pot scale; Mold cleaning; Pretreatment before metal sandblasting; Dry grinding and wet grinding; Precision optical refraction; Grinding of minerals, metals, glass and crystals; Glass carving and paint additives.
Activated alumina
Technical indicators
Appearance of activated alumina: Activated alumina is a white spherical porous particle with uniform particle size, smooth surface, high mechanical strength, strong hygroscopicity, no swelling, no cracking after water absorption, non-toxic, tasteless, insoluble in water and ethanol, and has a strong adsorption effect on fluorine, which is mainly used for defluoridation of drinking water in high fluorine areas.
Activated alumina can selectively adsorb gas, water vapor and moisture in some liquids. After the adsorption is saturated, it can be heated and dehydrated at about 175-3 15℃ to revive. Adsorption resurrection can be carried out many times. Besides being used as a desiccant, it can also absorb the lubricating oil vapor in polluted oxygen, hydrogen, carbon dioxide and natural gas. Can be used as catalyst, catalyst carrier and chromatographic analysis carrier.
Under some operating conditions and regeneration conditions, the drying depth of activated alumina is as high as -70 degrees below the dew point temperature.
Alumina is nontoxic. Many pots we use for cooking are made of aluminum. Aluminum is more active, and it will become alumina when it reacts with oxygen in the air. This alumina film is very dense and adheres to the surface to prevent the aluminum inside from continuing to react with oxygen.
However, eating too much aluminum is harmful. It is generally believed that aluminum will affect people's intelligence. It has been reported that the elderly are prone to get Alzheimer's disease if they eat too much aluminum, and children eating too much aluminum will affect their intellectual development.
Usually, there is only one way for us to ingest aluminum: food, aluminum pot, and food containing aluminum (such as fried fritters, when fried, alum is used as an expansion agent, and alum contains aluminum).
Ordinary contact with aluminum products is no problem. There is no danger of poisoning.
Activated alumina filter element for faucet water purification is harmless to people. Activated carbon particles are harmless to human body. Activated carbon is safe, harmless and non-toxic to human body and is made of carbon-containing materials. Black in appearance and well-developed in internal pore structure, it is a microcrystalline carbon material with strong adsorption capacity. There are a lot of invisible micropores in activated carbon, which is attractive and can effectively absorb impurities and heavier molecules, such as chlorine, benzene and ammonia.
Alumina itself is non-toxic, and ordinary contact in life will generally not affect the health of the body, but entering the human body from the respiratory tract or esophagus may have an impact on the health, such as decreased immunity, mental retardation, slow response and other adverse effects.
Alumina is a compound with high hardness, which is often used to make refractories. At present, there are more than 10 kinds of alumina known, with different structures and properties. Alumina itself is harmless, but long-term contact is generally not recommended, otherwise it will affect the human nervous system. For example, children or middle-aged and elderly people are often exposed to alumina, which may lead to decreased immunity. Children, in particular, are often exposed to alumina, which may cause mental retardation and slow response. In addition, if more alumina is ingested through the esophagus, it may affect the development of the brain and the growth and development between bones, such as osteoporosis. When the human body comes into contact with the dust or gas of alumina, alumina can accumulate in the human body, which will affect various organs of the human body and even affect the reproductive system of the human body, seriously endangering health.