The main component of limestone is calcium carbonate (CaCO3). Lime and limestone are widely used as building materials and are also important raw materials for many industries. Calcium carbonate can be directly processed into stone and burned into quicklime, but it is also dangerous in the production process. Quicklime becomes slaked lime by absorbing moisture or adding water, and slaked lime is also called hydrated lime.
Lime includes quicklime and slaked lime. The main component of quicklime is CaO, which is generally lumpy, pure white, and light gray or light yellow when it contains impurities. The main component of slaked lime is Ca(OH)2. The slaked lime can be formulated into lime slurry, lime paste, lime mortar, etc., which are used as coating materials and brick adhesives.
Limestone is mainly formed in a shallow sea environment. Limestone generally contains some dolomite and clay minerals. When the content of clay minerals reaches 25% to 50%, it is called argillaceous rock. When the dolomite content reaches 25%~50%, it is called dolomitic limestone. Limestone is widely distributed, uniform in lithology, easy to be mined and processed, and is a kind of very versatile building material.
It has abundant limestone reserves in China, but the mining and utilization situation is uneven. The current problems are:
1. Low resource utilization
At present, the utilization rate of limestone mines that are officially mined has reached more than 90%, while the utilization rate of civilian mining resources is only 40%. Because the amount of civilian mining is greater than that of mechanized mining, it is estimated that the utilization rate of the entire limestone is about 60%.
2. The scale of the mine is small and the mining technology is backward
There are several or even more than a dozen small mining mines around a mountain. This backward mining method not only has low labor efficiency, great safety risks and serious waste of resources, but also causes large-scale destruction of mountain and vegetation, causing serious harm to the ecological environment around the mining area.
How to incorporate the technological progress of the mine into the overall plan of the technological progress of the enterprise, carry out the overall plan for the development of the mine, and deal with the relationship between recent mining and transportation mining, high-grade and low-grade, high-quality and inferior quality, reasonable mining, comprehensive utilization, reducing the stripping ratio, and expanding the utilization rate of mine resources are very worthy of study.
Applications of limestone particles ≥10mm:
Used as aggregate for highways, railways, concrete mixing plants, etc.
Used for burning lime, used in iron and steel metallurgy industry.
Equipment recommended: jaw crusher, impact crusher and hammer crusher
Applications of limestone particles and tailings ≤10mm:
Processed to less than 5mm, used as machine-made sand (equipment recommended: sand making machine, hammer crusher, roller crusher)
High mud content, processed to 100 mesh, used as stone powder for plastering walls;
Low mud content, processed to 200 mesh, used as additive for asphalt mixing station;
Low mud content, processed to 325 mesh, used as commercial concrete additive; High calcium content, processed to 250 mesh or 325 mesh as desulfurizer;
Equipment recommended: Raymond mill, vertical roller mill, ball mill
The output of common limestone crushing sand making production line is 100-200t/h, 200-400t/h, 200-500t/h, but with the large-scale production, 800t/h, 1000t/h or even higher capacity sand making lines will become a trend. Here are the configurations of limestone crushing and sand making plants with different production capacities.
200t/h crushing and sand making plant
Specifications of products: 0-5mm, 5-16mm, 16-31.5mm
Equipment configuration: PE750*1060 jaw crusher, PFW1315III impact crusher, 3Y2160 vibrating screen
400t/h sand making plant
Equipment configuration: PE1000*1200 jaw crusher, PFW1315III impact crusher (2 pcs), VSI1140 sand making machine
500t/h sand making plant
Specifications of products: 0-5mm high quality machine-made sand
Equipment configuration: PE jaw crusher, HST single-cylinder hydraulic cone crusher, HPT multi-cylinder hydraulic cone crusher, VSI6X sand making machine
800t/h sand making plant
Feeding size: ≤1000mm
Specifications of products: 0-5mm, 5-10mm, 10-20mm, 20-30mm, 20-40mm, 40-80mm
Production process:
Equipment configuration: PE1200*1500 jaw crusher, PF1820 impact crusher, PF1520 impact crusher,VSI1150sand making machine, XS2900 sand washing machine(2 pcs), ZSW600*150 vibrating feeder, 2YK3072vibrating screen(3 pcs), 3YK3072vibrating screen(2 pcs), belt conveyor(several pcs)
800-1000t/h high quality sand and gravel production plant
Specifications of products: 0-5mm, 10-20mm, 16-31.5mm
Equipment configuration: C6X1660 jaw crusher, PFW1318III impact crusher
The flow chart of the comprehensive utilization of limestone ore (aggregate, sand making, powder making) is shown in the figure as below.
Advantages
1. The utilization of ore is maximized: the products include aggregate, machine-made sand, stone powder, and fine stone powder. If there is grinding equipment, it is recommended to mine the surface rock first and apply its dust to wall coating before normal production, which can fully reduce the mud content of machine-made sand.
2. The system adopts dry production process. The produced aggregate and machine-made sand have low moisture content (generally less than 2%). It does not need to be equipped with a dehydration device like the wet production process, which can reduce the storage capacity of finished sand, will not freeze in cold seasons, and can continuously produce throughout the year.
3. The content of stone powder in the machine-made sand can be steplessly adjusted by a special classifier, the sand yield rate is high, the fineness modulus meets the standard of medium sand, and the content of stone powder can meet the requirements of hydropower engineering standards and urban construction standards, and the strength of the finished concrete is high. The fine powder can be recovered by dust removal and powder concentrator, and can be used as a subgrade cushion or as a raw material for slag bricks.
4. There is little or no water needed in the production process, which reduces the installation of water extraction and sewage treatment in the wet production process. The production site is small, the investment is small, and the operation and management personnel are less. It is easy to centralized operation and control, realizing automatic management, and has low operating costs. The low moisture content in the raw materials is good for screening, and the sand production rate is high (usually around 50%).
5. Since water resources are not used or used in a small amount, it is not affected by drought and cold seasons, and can be produced continuously throughout the year.
6. Save a lot of precious water resources.
7. According to actual experience, in specific areas, as long as the content of the source soil and organic matter is controlled, even if no powder classifying equipment is used, the produced machine-made sand can meet the requirements of hydraulic engineering and urban construction standards.
Disadvantages
1. The surface of the aggregate and machine-made sand produced is not as clean as that produced by the wet production process.
2. The vertical sand making machine is high-speed rotating equipment, which generates a lot of dust during the working process. In addition, dust will also be produced in the working process of vibrating screen and belt conveyor. This system has high requirements about the sealing and dust removing of the equipment, especially in dry and windy seasons or areas.
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