Analysis of Comprehensive Utilization of Coal Gangue

2026年2月7日 | admin | B2
"Source: National Energy Information Platform"
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Polaris solid waste network news: Coal gangue is a black-gray rock with a low carbon content and harder than coal, which is produced in the process of well construction, excavation, coal mining and coal washing. Coal gangue is solid waste produced in the process of coal production and processing, and its annual emission is equivalent to about 10% of the coal output in that year.
1. The production of coal gangue
In the coal mining industry, for every 100 million tons of coal produced in China, about 14 million tons of gangue are discharged. In the coal washing industry, for every 100 million tons of coking coal washed, 20 million tons of gangue are discharged, and for every 100 million tons of power coal washed, the amount of gangue discharged is 15 million tons. In recent three years, the output of new coal gangue is about 650 million tons.
As the largest coal-producing country in the world, China has a large number of coal gangue, which can be utilized as resources and improve the ecological environment of mining areas to ensure the green and sustainable development of modern coal mining enterprises.[1].
2. Relevant laws and regulations of coal gangue
In 1998, the State Economic and Trade Commission and other eight departments jointly issued the Management Measures for Comprehensive Utilization of Coal Gangue, which was revised in 2014. In order to guide and standardize the comprehensive utilization of coal gangue, reduce its impact on land resources occupation and environment, promote the development of circular economy and promote the construction of ecological civilization, detailed guidance was given to its comprehensive management and encouragement measures. Technical Policy Essentials of Comprehensive Utilization of Coal Gangue in 1999 took power generation, building materials production, backfilling and harmless treatment of coal gangue as the main direction of comprehensive utilization technology, and developed high-tech and high-value-added coal gangue comprehensive utilization technology and products. In 2012, the Technical Guidelines for the Utilization of Coal Gangue made detailed requirements for the use of coal gangue in different fields. In 2021, Guiding Opinions on Comprehensive Utilization of Bulk Solid Wastes in the Tenth Five-Year Plan pointed out the direction for the comprehensive utilization of bulk solid wastes such as coal gangue.
3. The characteristics of coal gangue
3.1 Physical characteristics
When coal gangue is piled up for a long time, it will spontaneously ignite when the internal temperature reaches a certain value, so coal gangue is often divided into undisturbed coal gangue and spontaneous combustion coal gangue. Among them, the appearance of undisturbed coal gangue is mostly black or gray-black, and the surface is mostly adhered with slime and fine coal gangue. Spontaneous combustion coal gangue has low carbon content, relatively high porosity, and the bulk density is between 0.9 and 1.3 g/cm3. The surface layer is mostly pottery red or pottery yellow, and there will be black centers due to insufficient internal carbon combustion.[2].
Fig. 1 undisturbed coal gangue (a) and spontaneous combustion coal gangue (b)[2]
The water absorption characteristics of coal gangue have great influence on its comprehensive utilization. Its porosity determines the water absorption characteristics of coal gangue, with water absorption of about 2.0-6.0% and plasticity index of about 3.0-15. The water absorption of spontaneous combustion coal gangue is about 3.0-11.6%, and the plasticity index is about 1.03-0.8.
3.2 chemical characteristics
The main chemical compositions of coal gangue are Al2O3, SiO2 and C, followed by CaO, Fe2O3 and MgO. The mineral components are mainly kaolin, hydromica, bauxite and carbon.[3]. The composition of coal gangue is influenced by different regions, and the composition of coal gangue varies greatly in different regions of China, so I won’t repeat it here.
3.3 Hazards of Coal Gangue
Coal gangue is a solid waste produced with coal mining. Except for partial filling and comprehensive utilization, most coal gangue is piled up for a long time to form a gangue hill, which occupies land resources. The harm of coal gangue to the natural environment is mainly reflected in the following aspects: 1. Coal gangue will form fine dust in the process of stacking and transportation, which will be suspended in the atmosphere under the action of wind, causing harm to human health. On the other hand, due to its own characteristics, coal gangue is prone to spontaneous combustion, releasing a variety of harmful gases and producing a large number of explosive smoke, so it will have different degrees of impact on the surrounding atmospheric environment and the growth of animals and plants. 2. In the process of coal gangue storage, the harmful elements in it will dissolve and enter the water body or soil environment under the action of rainfall, which will cause certain damage to the nutrients in the soil, and even lead to acidification of the land around the coal gangue hill, which will affect human health and vegetation growth.
4. Application of coal gangue
China began to use coal gangue as early as the middle of last century, and its comprehensive utilization began gradually in the middle and late 1970s. The comprehensive utilization of coal gangue is influenced by factors such as the ratio of aluminum to silicon and the content of carbon and sulfur, and it is mainly used for producing alumina, fuel, chemical raw materials, ceramic raw materials, building materials and road engineering filling.
Fig. 2 keyword co-occurrence analysis of comprehensive utilization of coal gangue in HowNet.
4.1 Production of Al2O3
There are many useful substances such as SiO2 _ 2 and Al _ 2O _ 3 in coal gangue. If it is extracted and utilized as bauxite, it can not only reduce the negative impact of coal gangue on the ecological environment, but Al2O3 alleviate the shortage of bauxite resources in China. At present, the methods of extracting alumina from coal gangue are similar to fly ash. The essence is to leach Al2O3 from coal gangue, mainly by acid leaching.[3]Alkali leaching method[4]Wait a few kinds. At present, the alkali method has been widely used in the actual production process. Acid leaching method is to use acidic solution to transform soluble components into salts and leach them into the solution, remove impurities from metal salts by adding reagents, and finally transform aluminum salts to form Al2O3. The main reactions are shown in (1)~(4). In order to improve its leaching effect, pre-activation is needed to improve the reactivity of coal gangue. Most of the extractant used in this process is strong acid, which requires high materials for industrial operation equipment and pipelines, and at the same time, there are many impurities accompanying leaching, which is difficult to meet the requirements of metallurgical grade Al2O3, limiting its industrial application in Al2O3 recovery.
Al2O3 + H2SO4 → Al2(SO4)3 + H2O (1)
Al2(SO4)3 + NH3·H2O → Al(OH)3 + (NH4) 2SO4 (2)
Al(OH)3 → γ-Al2O3 + 3H2O (3)
γ-Al2O3 → α-Al2O3 (4)
The alkaline leaching method is mainly Bayer method. The basic principle is to extract the crushed coal gangue with NaOH solution to obtain leaching solution of sodium aluminate and solid red mud containing silicon. After filtering and adding NaOH for seed decomposition, Al(OH)3 product can be obtained, and Al2O3 product can be obtained after calcination. The main reaction is shown in (5):
Al2O3·H2O + NaOHNaAl(OH)4 (5)
4.2 Production of building materials
Using coal gangue to prepare building materials mainly includes brick making, cement raw materials, ceramic materials and so on. Brick making. Brick making from coal gangue usually uses the calorific value of coal gangue itself to provide the required energy for drying and baking. The calorific value of coal gangue in China is 3300~6300 kJ/kg.[5]When the calorific value is low, some coal can be added for production, so making bricks with coal gangue can significantly reduce energy consumption. At present, the technology of making bricks from gangue in China is relatively mature, and solid gangue bricks, porous load-bearing gangue bricks and hollow gangue bricks have been developed and produced. Produce cement. The main components of coal gangue are SiO2 _ 2 and Al _ 2O _ 3, which are similar to the chemical composition of clay and can replace part of clay to produce cement. The crushed coal gangue is mixed with lime according to a certain proportion, and the clinker with calcium silicate as the main component is obtained after calcination, and then it is ground with gypsum and other materials to obtain cement with high compressive strength. Concrete aggregate. When coal gangue is used in aggregate, it usually needs a certain heat treatment to remove carbon and organic matter in coal gangue, so as to reduce weak components in coal gangue aggregate, at the same time, make the minerals in it edge, generate active substances and improve the surface activity of its aggregate. Wang Aiguo et al.[2]This paper studies the present situation of using coal gangue to prepare concrete aggregate in China, discusses the technical means to improve the performance of coal gangue aggregate concrete for a long time, and analyzes the existing problems.
4.3 Backfill and subgrade materials
Backfill. Because coal gangue is produced in the process of well construction, excavation, coal mining and coal washing, if the pollutant content is low, it can be used to fill the valleys, coal mining subsidence areas and low-lying areas for construction projects.[6]. Subgrade materials. As a road base material, coal gangue can be used for surface decoration of public squares, paving roads or parking lots, which can reduce the cost of subgrade, foundation or dam foundation construction and reduce the occupied land area. Backfilling and subgrade materials can realize the mass consumption of coal gangue, but these utilization methods fail to fully reflect the resource value of coal gangue, and valuable metals or other elements in it are not effectively utilized.
4.4 Other applications
Coal gangue can also be used to prepare building materials such as molding sand, ceramsite and ceramics, and multifunctional materials such as thermal insulation materials, refractory materials and cementitious materials, which are not described in detail here.
5. Insufficient utilization of coal gangue
Although the comprehensive utilization of coal gangue has made great progress, there are still some problems as follows. 1. The overall utilization level is not high. 2. The basic research on comprehensive utilization technology of coal gangue needs to be strengthened. 3. The research on comprehensive utilization technology of coal gangue is not deep enough. According to the "Guiding Opinions on Comprehensive Utilization of Bulk Solid Waste in the Tenth Five-Year Plan", it is necessary to strengthen the comprehensive utilization capacity of coal gangue, expand its utilization scale and orderly reduce its stock in the follow-up work. And make breakthroughs in key bottleneck technologies and establish its comprehensive utilization innovation system. We will continue to promote the application of coal gangue in engineering construction, subsidence area treatment, mine filling and other fields, guide the use of coal gangue to produce new wall materials, decoration materials, etc., and further promote its application in agriculture and the extraction of valuable components under the premise of controllable risks, and strengthen the application and promotion of high-yield and high value-added products.
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