Fly ash composition, what material is fly ash?

The country takes coal as the main energy source, 76 of the electricity is produced by coal, and the annual coal consumption reaches more than 400 million tons, accounting for the country's raw coal production for one year, the national emission of fly ash has exceeded 100 million tons, becoming the world's largest ash country, causing serious environmental pollution and occupying a large amount of land.

Chemical composition of fly ash. The silicon content is the highest, followed by aluminum, which exists in the form of complex double salts and has poor acid solubility. The iron content is relatively low, it is present in the form of oxides, and it has good acid solubility.

In addition, there are unburned carbon pellets, CAO, and small amounts of MGO, Na2O, K2O, SO3, etc. The harmful component in fly ash is unburned carbon particles, which have high water absorption, low strength, and easy weathering, which is not conducive to the resource utilization of fly ash. SiO2 and Al2O3 in fly ash contribute greatly to the volcanic properties of fly ash, and Al2O3 is beneficial to reduce the melting point of fly ash and make it easy to form glass beads, which are beneficial components for recycling.

When fly ash is applied to the construction industry, the higher the CAO content in the bound state, the higher its self-hardening, and its activity is much higher than that of low-calcium fly ash, which is very helpful to improve the early strength of concrete. More than 90% of the fly ash emitted by power plants in China is low-calcium fly ash, and the development of high-calcium fly ash is a way to improve the resource characteristics of fly ash.

Particle composition of fly ash. According to the morphology of fly ash particles, fly ash particles can be divided into: glass beads; spongy vitreous (including smaller, denser, less porous vitreous and larger, loose and porous vitreous); Charcoal pellets.

The content of microbeads in the fly ash discharged from power plants in China is not high, and most of them are spongy glass, and the particle distribution is extremely uneven. Through grinding treatment, the morphology and structure of the original fly ash are destroyed, making it a broken polyhedron with relatively uniform particle size, increasing its specific surface area, thereby improving its surface activity and improving the difference of its performance.

Fly ash can be used as an admixture of cement, mortar, concrete, and become a component of cement and concrete, fly ash is used as a raw material instead of clay to produce cement clinker, to manufacture sintered bricks, autoclaved aerated concrete, foam concrete, hollow bricklaying, sintered or non-sintered ceramsite, paving roads; construction of dams, construction of ports, backfilling of potholes and lowlands in farmland, coal mine subsidence areas and mines; It can also be used to sort useful substances such as drifting beads, microbeads, iron fine powder, carbon, aluminum, etc., among which drifting beads and microbeads can be used as thermal insulation materials, refractory materials, plastics, and rubber fillers respectively.

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Its chemical composition is mainly Al2O3 and SiO2, and the secondary components are CAO and Fe2O3 and a small amount of MGO and SO3.

Fly ash is a building material.

Fly ash, also known as fly ash, is the tiny ash particles discharged from the fuel during combustion, which can be used as building materials, and can be used to add certain cementitious materials, auxiliary raw materials and other substances to make fly ash dry mortar, fly ash ceramsite, fly ash aerated concrete, etc.

The chemical composition of fly ash is related to factors such as coal composition, boiler type, combustion, etc., and the emission is directly related to the ash content in coal combustion, and China burns 1t of coal, which can produce about 250-300kg of fly ash.

Hazards

The physical and chemical properties of eight kinds of waste incineration fly ash at home and abroad were systematically studied by means of energy spectroscopy, ash melting point furnace, XRD, mercury porosimeter and other instruments. Studies have shown that the composition of fly ash varies greatly depending on factors such as raw material, furnace type, sampling location, etc.

Due to the difference in the composition of fly ash, waste incineration fly ash is easier to melt than coal ash, which is beneficial to the melting treatment, which is mainly due to the difference of SiO2 content and SiO2 Al2O3 in fly ash, and there is a positive relationship between melting point and SiO2 content. There are conditions for the addition of CAO to achieve fluxing, and the crystalline phase composition of different fly ash is different due to different incineration conditions and fly ash composition. The internal pore size of fly ash is mainly distributed in the range, and the specific surface area of fly ash is g.

Fly ash: It is the fine ash collected from the flue gas after coal combustion, and fly ash is the main solid waste discharged from coal-fired power plants.

The main oxide composition of fly ash in thermal power plants in China is: SIO, alumina, FEO, ferric oxide, CAO, titanium dioxide, etc. With the development of the power industry, the emission of fly ash from coal-fired power plants has increased year by year, and it has become one of the industrial waste residues with large emissions in China.

If a large amount of fly ash is not treated, it will produce dust and pollute the atmosphere; If discharged into the water system, the river will be silted up, and the toxic chemicals in it can also cause harm to humans and organisms. However, fly ash can be recycled, such as as as admixture for concrete.

Fly ash resembles cement in appearance, and the color varies from creamy white to grayish-black. The color of fly ash is an important quality indicator that reflects the amount and difference of carbon content. To a certain extent, it can also reflect the fineness of fly ash, the darker the color, the finer the particle size of fly ash, and the higher the carbon content.

Fly ash is the fine ash that is captured from the flue gas after coal is burned, and is the main solid waste discharged from coal-fired power plants. The solid waste left over after coal combustion will enter the natural carbon cycle. With the development of the power industry, the emission of fly ash from coal-fired power plants has increased year by year, and it has become one of the industrial waste residues with large emissions in China.

Compared with the organic carbon produced by natural erosion of rocks, fly ash is less susceptible to oxidation and accounts for a larger proportion of fossil organic carbon emissions in rivers than when it is imported. Fly ash deposited in some areas, such as the Yangtze estuary, has significantly altered the properties of the sediments, allowing human changes to the carbon cycle to be preserved in the form of a geological record.

Comprehensive utilization of fly ash in China

Turning waste into treasure and harm into profit has become an important technical and economic policy in China's economic construction, an important means to solve the contradiction between environmental pollution and lack of resources in China's power production, and also one of the tasks faced by power production. After development, fly ash has been widely used in various departments such as construction, building materials, and water conservancy.

The processing and utilization process of material extraction from fly ash, and the production of building materials, chemical products, composite materials and other types of products with fly ash as raw materials. At present, the field of fly ash resource utilization in China mainly involves building materials, road engineering, filling materials, and agricultural applications, and the products mainly include cement, bricks, concrete, ceramsite and inorganic refractory fiber materials produced with fly ash as raw materials.

Fly ash is an auxiliary material used in concrete, in order to increase the slump of concrete and increase the construction speed.

Fly ash is a kind of pozzolana material, ** inorganic components in coal. The chemical composition is mainly silica and aluminum oxide (silicon oxide content is about 48%, alumina content is about 27%), and the other components are iron oxide, calcium oxide, magnesium oxide, potassium oxide, sodium oxide, sulfur trioxide and unburned organic matter (loss on ignition).

Characteristics of fly ash.

1) Fly ash has a chemical activity similar to volcanic ash, so it can be used as a reference when performing property analysis.

2) Presence of globular particles. When fly ash is formed, it will melt due to high temperature combustion to form glass beads, and there are a large number of spherical particles in the fly ash after cooling, which can effectively reduce the surface area of the wall when used in the construction industry.

3) Able to be matched with concrete. It is more effective to use fly ash when the gaps in the concrete need to be filled, and it can strengthen the cohesion of the concrete itself with the addition of a small amount of water.

China is a country with coal as the main energy source, and coal accounts for 90% of the total proven primary energy. At present, about 75% of China's coal resources are used for thermal power generation, and coal-fired power plants will produce a large amount of fly ash, of which only a small part is utilized, and most of it is piled up.

Fly ash is the main solid waste discharged from coal-fired power plants and coal gangue and slime comprehensive utilization power plants. In recent years, researchers have analyzed the fly ash of some power plants located in the central and western regions of China, and found that the alumina content in the fly ash is as high as more than 50%, which is a new type of fly ash - high-alumina fly ash. The content of Al2O3 in high-alumina fly ash is nearly twice as high as that of ordinary fly ash, and close to the content of traditional bauxite (generally 55% to 65%), which is a very important non-traditional aluminum resource.

Bauxite, also known as bauxite, is a general term for industrially available ores with gibbsite, diaspore or diaspore as the main mineral components. 92% of the world's bauxite production is used to produce metallurgical-grade alumina, and the remaining 8% is used in other industries, known as non-metallurgical alumina or multi-variety alumina. Aluminum is an important metal material second only to steel.

For every 1t of metal aluminum, about 2t of metallurgical grade alumina raw materials are required. According to China Customs, China imported a total of 10,000 tons of bauxite in 2019, and in 2018, China imported a total of 10,000 tons of bauxite, an increase year-on-year, and the annual import volume exceeded the level of 100 million tons for the first time. From a national point of view, Guinea, Australia and Indonesia still maintain a three-legged situation, which is the top three largest countries in China to import bauxite, accounting for more than 94% of the total imports.

In view of the shortage of bauxite resources in China, the production of alumina from high-alumina fly ash is not only expected to alleviate the shortage of aluminum resources, but also reduce the pollution of fly ash to the atmosphere and water bodies and the occupation of a large number of land resources. At present, fly ash is mainly used in construction (production of cement, bricklaying, glass-ceramic), agriculture (soil improvement, fertilizer production), environmental protection (wastewater treatment, flue gas desulfurization) and other aspects. In addition to the above traditional areas of fly ash utilization, China has vigorously and actively guided enterprises to carry out the comprehensive utilization of high-alumina fly ash since the "Eleventh Five-Year Plan" period.

According to the characteristics of high-alumina fly ash, scientific research workers have improved its resource utilization, and began to focus on the extraction of major elements such as aluminum-silicon and trace elements such as grain, germanium, nickel and vanadium in fly ash, so as to realize the comprehensive utilization of high-alumina fly ash resources.

Fly ash is the fine ash in the flue gas produced by the combustion of coal. Usually refers to the fine ash collected from the flue gas of coal-fired thermal power plants.

Fly ash is a small sphere formed by coal entering the furnace of 1300 1500, under the condition of suspension combustion, heated and then cooled, with a smooth surface and fine pores. Its main components are silicon dioxide, aluminum oxide, iron oxide, calcium oxide, magnesium oxide, sulfur trioxide, etc.

The emission of fly ash is related to the ash content of the coal burned, and the higher the ash content, the greater the emissions. A large amount of fly ash is not treated, which will produce dust and pollute the atmosphere. Direct discharge into the water system will silt up rivers and lakes, cause pollution to water bodies, damage aquatic ecosystems, affect the aquaculture industry, and the harmful components in it also have adverse effects on human health.

Fly ash is a solid residue produced when coal is burned, which is a powdery gray substance. The main components of fly ash are oxides such as silicon oxide, alumina, oxane iron, calcium oxide, magnesium oxide, potassium oxide and sodium oxide. Among them, silica has the highest content, usually accounting for more than 50% of the total fly ash.

At the same time, fly ash also contains a certain amount of amorphous silicate substances, which have high reactivity and activity, and are widely used in cement production and other fields. In addition, the composition of fly ash varies depending on the type of raw coal used and the conditions under which it is burned.

In addition, with the increasing requirements for environmental protection and resources, the research on the reuse of fly ash is also constantly being debated and deepened, which improves the value of its utilization. Fly ash can be processed and utilized in a variety of ways, such as the preparation of new concrete materials, ceramic materials and glass fiber products in the field of materials industry; In the cement industry, it is used as an admixture to replace some cement raw materials and enhance the durability of concrete; In the field of environmental protection, it is used as adsorbent, desulfurizer and denitrification agent.

In summary, the main components of fly ash are oxygen and tardination chemicals such as silicon oxide, alumina, iron oxide, calcium oxide, magnesium oxide, potassium oxide and sodium oxide. In addition, amorphous silicate substances are also one of the important components of fly ash. Through the utilization of fly ash, it can improve its comprehensive utilization benefits and make greater contributions to environmental protection.

First, the use of fly ash.

1. Fly ash can be used as an admixture of cement, mortar and concrete, and become a component of cement and concrete, and fly ash is used as a raw material instead of clay to produce cement clinker, manufacture sintered bricks, autoclaved aerated concrete, foam concrete, hollow bricklaying, sintered or non-sintered ceramite, and pave roads;

2. Construct dams, build ports, backfill of farmland potholes, lowlands, coal mine subsidence areas and mines;

3. Drift beads, microbeads, iron powder, carbon, aluminum and other useful substances can also be sorted from them, among which drifting beads and microbeads can be used as thermal insulation materials, refractory materials, plastics, and rubber fillers respectively.

Second, the composition of fly ash.

The particle composition of fly ash, according to the morphology of fly ash particles, can be divided into: glass beads; spongy vitreous (including smaller, denser, less porous vitreous and larger, loose and porous vitreous);

Carbon particles, the content of microbeads in the fly ash discharged from power plants in China is not high, most of them are sponge-like vitreous, and the particle distribution is extremely uneven.