Coal gangue is a carbon-containing rock discharged from coal mines in the production process of development, mining, and coal washing. It is also one of the largest industrial solid wastes in my country. Containing carbon and other organic matter and inorganic silicate minerals, direct discharge or filling back into wells will waste resources, occupy land, and cause air, water and soil pollution. Therefore, exploring the utilization methods of coal gangue according to local conditions, high value-added utilization is an important way to increase the added value of coal gangue products and increase the profits of resource utilization enterprises.
Coal gangue is a solid waste discharged from the coal mining process and coal washing process. Including the excavation gangue in the process of tunnel excavation, the gangue extracted from the roof, the bottom plate and the interlayer during the excavation process, and the washing gangue picked out during the coal washing process. Its main components are Al2O3, SiO2, and also contain varying amounts of Fe2O3, CaO, MgO, Na2O, K2O, P2O5, SO3 and trace rare elements (gallium, vanadium, titanium, cobalt).
Coal gangue is not used, occupying a large area of land. The escape or leaching of sulfides in coal gangue will pollute the atmosphere, farmland and water bodies. Gangue mountains will also spontaneously combust and cause fires, or collapse in the rainy season, silting up rivers and causing disasters. The gangue is piled up in the open air. After leaching by rainfall, the soluble elements migrate into the soil and water with the rain, which may have a certain impact on the soil and water environment. The degree of impact depends on the discharge of pollutants in the leaching solution and the environmental properties of the location.
1. Coal gangue production of calcined kaolin
Kaolin is an important component of coal gangue. Coal gangue can produce ultra-fine calcined kaolin through fine processing technologies such as purification, ultra-fine pulverization, calcination and surface modification. It can be used not only as coating pigment and filler in papermaking, but also as filler and extender in plastics, rubber, aerospace, wire and cable, coatings, inks, food additives, cosmetics, pesticides and other fields. At the same time, it can also be used as a raw material for the production of ceramic industry and heat-resistant high-temperature pottery.
For example, Shuozhou in China is a major coal-producing city, and the annual coal output accounts for 1/4 of the province’s total. However, the poor coal quality and the high amount of coal gangue have always plagued enterprises. With an annual output of 200 million tons of coal, more than 40 million tons of coal gangue need to be stacked in the open air. That is, the coal gangue is subjected to grinding, pulping, and classification, and then enters the calcining rotary kiln for high-temperature heating, and the coal gangue crystals are heated to produce physical changes. The structure rearranges and eventually becomes ultrafine calcined kaolin.
2. Coal gangue power generation
Coal gangue contains a certain amount of carbon, which can be used for combustion to generate electricity. It is generally believed that coal gangue with a calorific value greater than 1500kcal/kg can be directly used as fuel for boilers, and coal gangue with a calorific value of 1000~1500kcal/kg needs to be mixed with a certain proportion of coal slime and medium coal with a higher calorific value to enter the boiler . The crushed coal gangue particles undergo multiple reciprocating cyclic combustion and reactions in the furnace, which can achieve full combustion, and the generated heat can be used for power generation. Statistics show that the calorific value of coal gangue in various parts of my country is generally low and varies greatly, and the calorific value of more than 1000kcal/kg is less than 30% of the total.
Coal gangue power plants are conducive to saving energy, improving environmental quality, turning harm into profit and turning waste into treasure; saving high-quality coal resources, alleviating the power shortage situation of coal mining enterprises; at the same time promoting industrial transfer and labor reemployment, as well as saving arable land.
3. Coal gangue used for paving
Among various industrial waste residues, coal gangue has a large output and high bearing capacity, which meets the requirements of highway roadbed fillers, so it has been widely used. Coal gangue, especially coal gangue with certain activity after spontaneous combustion, is a high-quality engineering filling material. It can be used alone or mixed with cohesive soil, fly ash, slaked lime, etc. as roadbed filler.
The gangue mixture replaces the lime soil to fill the base of the road pavement, which can consume a large amount of coal gangue, fly ash and other coal mine solid waste, reduce the harm to the environment such as coal gangue and fly ash, and the ecological benefits are very obvious.
4. Coal gangue production of lightweight concrete aggregate
The process of producing light aggregates from coal gangue can be roughly divided into two categories: the production of sintered coal gangue porous alkane aggregates with sintering agents and the production of expanded coal gangue ceramsites with rotary kilns. The lightweight aggregate produced with coal gangue has good performance, and high performance concrete can be prepared with this lightweight aggregate. The lightweight concrete prepared from the lightweight aggregate produced from coal gangue has the characteristics of low density, high strength and low water absorption, and is suitable for making prefabricated parts of various buildings.
5. Coal gangue recovery coal and pyrite
In addition to the above-mentioned utilization of coal gangue, a simple process is used to wash out good coal from coal gangue, select inferior coal from it by screening, and simultaneously select pyrite. Or recover pyrite, washed and mixed coal and medium coal from the jig separator used for coal preparation – the plane shaking table process. The recovered coal can be used as fuel for power boilers, the gangue can be used as building materials, and the pyrite can be used as chemical raw materials.
As an inevitable product in the process of coal production and coal washing, coal gangue contains harmful elements that seriously damage the surrounding environment, and long-term storage causes waste of energy. Therefore, it is necessary to strengthen the reuse of coal gangue or to treat the coal gangue to ensure that the harmful elements in it are reduced to the standard range, and finally realize the high value-added utilization of coal gangue – turning waste into treasure.