Method for preparing machine-made sand from high-mica granite

Abstract

The invention discloses a method for preparing machine-made sand from high-mica granite, which comprises the following steps: coarsely crushing and intermediately crushing granite, screening the intermediately crushed product by using a strip-shaped sieve, and finely crushing the oversize product to the required particle size to obtain a finely crushed product; undersize products obtained after screening of the intermediate crushed products are screened are screened into large-sheet-diameter free mica and fine sand through a square hole screen, the fine sand and the fine crushed products are further screened into materials of + 2.5 mm and-2.5 mm, the materials of + 2.5 mm are further screened through a strip-shaped screen, and gravel containing no free mica and sheet-shaped free mica are obtained; the-2.5 mm materials are sorted through a strong magnetic sorting machine, and magnetic material free mica and non-magnetic material free mica-free machine-made sand are obtained; and uniformly mixing the machine-made sand without the free mica with the sandstone without the free mica according to a ratio to obtain a machine-made sand product. The high-mica-content granite can be processed and prepared into the artificial sand with the free mica content smaller than 2%, and the requirements of high-standard building materials are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-metallic mineral materials and building materials processing. More specifically, the present invention relates to a method for preparing machine-made sand from high-mica granite. Background Art

[0002] With the rapid development of infrastructure construction, the demand for machine-made sand is increasing day by day. On the one hand, natural sand resources are becoming increasingly exhausted, and on the other hand, there is no natural sand available near major construction projects. Therefore, the development of machine-made sand materials has become an important choice for construction sand. Granite, as an igneous rock with a wide distribution and rich reserves, is an excellent raw material for preparing machine-made sand. However, the mica content in some granites is relatively high, and mica is a layered silicate mineral with characteristics such as low hardness, easy breakage, and well-developed cleavage. During the crushing process of granite, mica is easily broken into flaky particles along the cleavage plane and remains in the machine-made sand. These flaky mica particles will seriously affect the quality of the machine-made sand and further affect the performance of concrete. First, the flaky mica particles will reduce the bulk density and compactness of the machine-made sand, resulting in poor workability and reduced strength of the concrete. Second, the adhesion between the flaky mica particles and the cement paste is weak, which is likely to form weak links in the concrete and reduce the durability of the concrete. In addition, the flaky mica particles will also affect the impermeability, frost resistance and other properties of the concrete. Generally speaking, it is traditionally considered that granite with a high mica content is difficult to be used to prepare high-quality machine-made sand, and its application range is limited.

[0003] To solve the problem of preparing machine-made sand from high-mica granite, scholars at home and abroad have conducted a large number of studies. Traditional treatment methods mainly include gravity separation, flotation, etc. Among them, gravity separation mainly includes water washing method with water as the medium and air separation method with air as the medium. According to the mineral composition of granite, the density difference between mica and its associated minerals is not large, but mica is in an obvious flaky form, while other minerals are basically granular. When the raw ore is ground to a certain particle size and placed in a gravity separation device, mica can be enriched and stratified in the light mineral zone due to its thin sheet diameter, while other minerals are enriched in the heavy mineral zone, thus realizing the separation and enrichment of mica. In the mica removal test of machine-made sand for the Three Gorges Project using the gravity separation method, various separation tests of mica were carried out using gravity separation equipment including spiral classifiers, shaking tables, jigs, etc. Under various test conditions, there was no obvious separation effect. In addition, China's Sinohydro Bureau 8 also adopted the method of water washing with a spiral classifier to separate mica in machine-made sand in the Karuma project in Uganda. The mica content in the machine-made sand was 4%. The water consumption for mica separation was large, the speed was slow, the production efficiency was low, and the mica separation effect was not obvious. The flotation method for mica separation has relatively low separation intensity and large water consumption, and most of it is currently carried out under acidic or alkaline conditions, which puts forward high requirements for wastewater treatment and equipment. At the same time, chemical agents are added in flotation, which may affect the performance of concrete. Therefore, considering the problems in terms of comprehensive economy, environmental protection, etc., the scheme of removing mica from machine-made sand by the flotation method is not very practical. Based on this, therefore, it is of great significance to develop a method for preparing machine-made sand from high-mica granite that is efficient, environmentally friendly, and low-cost. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and / or defects and provide at least the advantages described hereinafter.

[0005] To achieve these objects and other advantages of the present invention, a method for preparing machine-made sand from high-mica granite is provided, including the following steps: Step 1: First, coarsely crush the granite, then medium-crush the coarsely crushed product, then screen the medium-crushed product using a bar screen, and then finely crush the oversize product after screening the medium-crushed product to obtain a finely crushed product. Screen the undersize product after screening the medium-crushed product using a square-hole screen to select large-diameter free mica and fine sand; Step 2: Mix the fine sand with the finely crushed product and screen them through a square-hole screen or a straight-line screen into +2.5 mm and -2.5 mm materials. Among them, the +2.5 mm material is further screened using a bar screen. The oversize is sand and gravel without free mica, and the undersize is flaky free mica; Step 3: Separate the -2.5 mm material screened in Step 2 using a high-intensity magnetic separator. The magnetic material obtained is mainly free mica, and the non-magnetic material is machine-made sand without free mica; Step 4: Uniformly mix the manufactured sand without free mica with the sand or +2.5 mm material without free mica obtained in Step 2 according to a ratio to obtain a manufactured sand product.

[0006] Preferably, in Step 1, jaw crushers or gyratory crushers are used for coarse crushing, and the particle size of the coarse crushing product is 100 - 300 mm. Cone crushers or impact crushers are used for medium crushing, and the particle size of the medium crushing product is 20 - 60 mm. Rod mills or roll crushers are used for fine crushing, and the particle size of the fine crushing product is less than 5 mm.

[0007] Preferably, in Step 1, the aperture size of the bar screen is 2 - 10 mm, and the aperture size of the square hole screen is 5 mm.

[0008] Preferably, in Step 1, when the granite does not contain mica with large diameters, the medium crushing product can be directly subjected to fine crushing without the step of screening with a bar screen.

[0009] Preferably, in Step 2, the aperture size of the square hole screen or the straight line screen is 2.5 mm, and the aperture size of the bar screen is 0.1 - 1 mm.

[0010] Preferably, in Step 3, during high-intensity magnetic separation, dry magnetic separation process or wet magnetic separation process is adopted. When the wet magnetic separation process is adopted, the manufactured sand without free mica obtained by magnetic separation needs to be precipitated and dehydrated.

[0011] Preferably, in Step 4, the mass ratio of the manufactured sand without free mica to the sand or +2.5 mm material without free mica obtained in Step 2 is 4 - 8:1.

[0012] Preferably, the content of free mica in the obtained manufactured sand product in Step 4 is less than 2%.

[0013] Preferably, the mixture of fine sand and fine crushing product in Step 2 is subjected to microwave heating treatment to further improve the mica separation efficiency. The specific method is as follows: S1: First, dry the mixture and control its water content to be less than 2%; S2: Then, subject the dried mixture to microwave heating treatment in an industrial microwave heating device. During heating, first preheat with low power, and then perform multi-stage microwave heating with high power after preheating; S3: After the microwave heating is completed, quickly introduce cold air to cool down.

[0014] Preferably, in S2, the preheating power of the microwave at low power is 5 - 10 kW, preheating for 10 - 20 min, heating at low power until the surface temperature of the mixture is 80 - 120 °C, the heating power at high power is 40 - 60 kW, with an interval of 20 s every 40 s during heating, and heating for a total of 120 - 360 s until the surface temperature of the mixture is 200 - 300 °C.

[0015] The present invention has at least the following beneficial effects: The core of the present invention lies in effectively separating free mica in manufactured sand through selective crushing, selective screening, and magnetic separation processes, thereby obtaining qualified manufactured sand products; using a bar screen to effectively remove large - diameter free mica in manufactured sand; using a rod mill or a pair - roll machine for fine crushing to protect mica flakes from being overly crushed; using a magnetic separation process to remove free mica in sand and gravel, further improving the quality of the finished manufactured sand; the present invention also provides two options of dry and wet magnetic separation processes, which can be selected according to actual situations, improving the flexibility of the process. Through a reasonable sand blending system, manufactured sand products with excellent particle size distribution can be stably obtained; the present invention can process high - mica - content granite to prepare artificial manufactured sand with a free mica content of less than 2%, meeting the requirements of high - standard building materials; secondly, all processes adopt physical processing methods, avoiding the use of chemical agents, reducing environmental pollution and ensuring that the quality of artificial sand is not affected by the agents. In addition, the separated free mica can be comprehensively utilized as a non - metallic mineral resource, further improving the resource utilization rate. The present invention also conducts microwave heating treatment on the fine - crushed product and then rapidly cools it with cold air. By utilizing the difference in thermal expansion coefficients between granite and mica, different thermal stresses are generated on the mineral surface, cracks are generated on the mineral surface, making it easier for mica to fall off from granite, and improving the subsequent screening and magnetic separation efficiency.

[0016] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart for preparing manufactured sand from high - mica granite of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS The following further describes the present invention in detail with reference to the drawings, so that those skilled in the art can implement it according to the description in the specification.

[0019] It should be understood that terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0020] Example 1 A method for preparing manufactured sand from high - mica granite, the process flow chart of which is as Figure 1As shown in the figure, it specifically includes the following steps: Step 1: Take 20 tons of granite with 18% mica content (including mica with a particle size greater than 2 mm). Use a jaw crusher to coarsely crush the granite to about 200 mm, and then use a cone crusher to medium-crush the granite of about 200 mm to about 50 mm. Since the granite sample contains mica with a particle size greater than 2 mm, screen the medium-crushed product with a 2-mm bar screen, and then use a rod mill to finely crush the oversize product after screening of the medium-crushed product to less than 5 mm to obtain a finely crushed product. After screening the undersize product of the medium-crushed product with a 5-mm square hole screen, 0.05 tons of large-size free mica and 0.63 tons of fine sand are obtained; Step 2: Mix the fine sand with the finely crushed product and screen it with a square hole screen with a screen hole size of 2.5 mm to obtain 3.0 tons of material A with a size of +2.5 mm and 16.9 tons of material B with a size of -2.5 mm. Among them, the +2.5 mm material A is further screened with a bar screen with a screen hole size of 0.2 mm to obtain 2.9 tons of sand and gravel C without free mica and 0.05 tons of large-size free mica D; Step 3: Wetly separate the -2.5 mm material B screened in Step 2 by a high-gradient magnetic separator (magnetic field intensity is 0.75 T, pulp concentration is 25%, and feed rate is 1 ton / hour) to obtain 5.0 tons of magnetic material E (mainly free mica, secondarily water and other substances) and 17.3 tons of non-magnetic material F (manufactured sand without free mica); Step 4: After precipitation and dehydration of the non-magnetic material F obtained by magnetic separation, take 13.1 tons of dry weight sample and mix it evenly with 2.7 tons of sand and gravel C without free mica to obtain a manufactured sand product.

[0021] The free mica content in the manufactured sand product is 1.5%, meeting the requirements for free mica content in the "Code for Construction of Hydraulic Concrete" (DL / T 5144-2015). In addition, the particle size distribution of the manufactured sand is reasonable, and the stone powder content is 12.7% (the allowable range in the code is 6% - 18%), all meeting the code requirements.

[0022] Example 2 A method for preparing manufactured sand from high-mica granite, including the following steps: Step 1: Take 20 tons of granite with 15% mica content (the particle size range of mica is 0 - 2 mm, without large-size mica). Use a gyratory crusher to coarsely crush the granite to about 250 mm, and then use a counterattack crusher to medium-crush the granite of about 250 mm to about 60 mm. Since the granite sample does not contain large-size mica, the medium-crushed product does not need to be screened and directly enters the fine crushing operation. Use a pair-roll crusher to finely crush the granite of about 60 mm to less than 5 mm to obtain a finely crushed product; Step 2: Sort the crushed products using a straight-line sieve with a screen hole size of 2.5 mm to obtain 2.9 tons of material A with a size of +2.5 mm and 17.0 tons of material B with a size of -2.5 mm. Since the particle size distribution of mica in granite is 0 - 2 mm, there are no large-diameter mica particles in the +2.5 mm particle size range. Based on this, the materials in this particle size range do not need to enter the bar screen for further sorting; Step 3: Sort the -2.5 mm material B obtained by screening in Step 2 using a dry roller high-intensity magnetic separator (magnetic field strength is 1.0 T, and the feeding speed is 0.6 tons per hour) to obtain 4.8 tons of magnetic material E (mainly free mica, secondarily other substances) and 12.2 tons of non-magnetic material F (manufactured sand without free mica); Step 4: Take 12.2 tons of the non-magnetic sample F obtained by magnetic separation and mix it evenly with 2.5 tons of material A to obtain the manufactured sand product.

[0023] The content of free mica in the manufactured sand product is 1.8%, which meets the requirements for the content of free mica in the "Code for Construction of Hydraulic Concrete" (DL / T 5144 - 2015). In addition, the particle size distribution of the manufactured sand is reasonable, and the stone powder content is 10.6% (the allowable range in the code is 6% - 18%), both meeting the code requirements.

[0024] Example 3 A method for preparing manufactured sand from high-mica granite includes the following steps: Step 1: Take 20 tons of granite with a mica content of 12% (the particle size range of mica is 0 - 2 mm, without large-diameter mica), use a jaw crusher to coarsely crush the granite to about 300 mm, and then use a cone crusher to medium-crush the granite of about 300 mm to about 80 mm. Since there is no large-diameter mica in the granite sample, the material obtained by medium-crushing directly enters the fine-crushing operation. Use a pair-roll crusher to finely crush the granite of about 80 mm to less than 5 mm to obtain the crushed product; Step 2: Sort the crushed product using a straight-line sieve with a screen hole size of 2.5 mm to obtain 3.2 tons of material A with a size of +2.5 mm and 16.8 tons of material B with a size of -2.5 mm. Since the particle size distribution of mica in granite is 0 - 2 mm, there are no large-diameter mica particles in the +2.5 mm particle size range. Based on this, the materials in this particle size range do not need to enter the bar screen for further sorting; Step 3: Sort the -2.5 mm material B obtained by screening in Step 2 using a high-gradient magnetic separator for wet separation (magnetic field strength is 0.75 T, pulp concentration is 25%, and feeding speed is 1 ton per hour) to obtain 1.6 tons of magnetic material E (mainly free mica, secondarily water and other substances) and 15.1 tons of non-magnetic material F (manufactured sand without free mica); Step 4: After subjecting the non-magnetic material F obtained by magnetic separation to precipitation and dehydration, 3.2 tons of material A is added to 12.9 tons of the dry-weight sample and mixed evenly to obtain manufactured sand products.

[0025] The content of free mica in the manufactured sand products is 0.9%, meeting the requirements for the content of free mica in the "Code for Construction of Hydraulic Concrete" (DL / T 5144-2015). In addition, the particle size distribution of the manufactured sand is reasonable, and the stone powder content is 11.8% (the allowable range in the code is 6% - 18%), both meeting the code requirements.

[0026] Example 4 A method for preparing manufactured sand from high-mica granite specifically includes the following steps: Step 1: Take 20 tons of granite with a mica content of 18%. The granite is coarsely crushed to about 200 mm by a jaw crusher, then medium-crushed to about 50 mm by a cone crusher, and then the medium-crushed product is screened by a 2-mm bar screen. The oversize product after screening of the medium-crushed product is finely crushed to less than 5 mm by a rod mill to obtain a finely crushed product. The undersize product after screening of the medium-crushed product is sorted by a 5-mm square-hole screen to obtain 0.05 tons of large-diameter free mica and 0.63 tons of fine sand; Step 2: After mixing the fine sand with the finely crushed product, the mixture is subjected to microwave heating treatment: S1: First, the mixture is dried to control its water content below 2%; S2: Then, the dried mixture is preheated in an industrial-grade microwave heating device at 5 kW for 20 min until the surface temperature of the mixture reaches 110 °C, and then heated intermittently at 50 kW, heating for 40 s and then interval for 20 s, with a total heating time of 240 s until the surface temperature of the mixture reaches 260 °C; S3: After microwave heating is completed, cold air is quickly introduced for cooling; The cooled mixture is screened by a square-hole screen with a screen hole size of 2.5 mm to obtain 3.1 tons of +2.5-mm material A and 16.8 tons of -2.5-mm material B. Among them, the +2.5-mm material A is further screened by a bar screen with a screen hole size of 0.2 mm to obtain 2.97 tons of sand and gravel C without free mica and 0.09 tons of large-diameter free mica D; Step 3: The -2.5-mm material B screened in Step 2 is wet-separated by a high-gradient magnetic separator (magnetic field intensity is 0.75 T, pulp concentration is 25%, and feed rate is 1 ton / hour) to obtain 6.5 tons of magnetic material E (mainly free mica, secondarily water and other substances) and 15.1 tons of non-magnetic material F (manufactured sand without free mica); Step 4: After the non-magnetic material F obtained by magnetic separation is precipitated and dehydrated, 13.1 tons of dry weight samples are taken and mixed evenly with 2.7 tons of sand and gravel C without free mica to obtain manufactured sand products.

[0027] In this embodiment, since microwave heating is used to treat the mixture of fine sand and finely crushed products, and then quickly cooled with cold air, due to the difference in the thermal expansion coefficients of granite and mica, different thermal stresses are generated on the mineral surface, cracks are generated on the mineral surface, making it easier for mica to fall off from granite. When screening at +2.5 mm, mica is more likely to fall off with the vibration during screening, and thus more mica is magnetically separated during magnetic separation. The content of free mica in the manufactured sand products prepared in this embodiment is 0.8%, which meets the requirements for the content of free mica in the "Code for Construction of Hydraulic Concrete" (DL / T 5144-2015). In addition, the particle size distribution of the manufactured sand is reasonably distributed, and the stone powder content is 12.7% (the specified allowable range is 6% - 18%), all meeting the specification requirements.

[0028] Example 5 A method for preparing manufactured sand from high-mica granite, comprising the following steps: Step 1: Take 20 tons of granite with a mica content of 15% (the particle size range of mica is 0 - 2 mm, without large particle size mica). The granite is coarsely crushed to about 250 mm by a gyratory crusher, and then the granite of about 250 mm is medium-crushed to about 60 mm by a counterattack crusher. Since there is no large particle size mica in the granite sample, the medium-crushed product does not need to be screened and directly enters the fine crushing operation. The granite of about 60 mm is finely crushed to less than 5 mm by a pair-roll crusher to obtain finely crushed products; Step 2: Perform microwave heating treatment on the finely crushed products: S1: First, dry the finely crushed products to control their water content below 2%; S2: Then, preheat the dried finely crushed products in an industrial-grade microwave heating device at 10 kW for 10 min until the surface temperature of the finely crushed products reaches 120 °C, and then perform intermittent heating at 60 kW, heating for 40 s and then spacing for 20 s, for a total of 360 s, until the surface temperature of the finely crushed products reaches 300 °C; S3: After microwave heating is completed, quickly introduce cold air to cool down; The cooled mixture is screened with a square-hole sieve with a screen hole size of 2.5 mm to obtain 3.4 tons of +2.5 mm material A and 16.6 tons of -2.5 mm material B. Since the particle size distribution of mica in granite is 0 - 2 mm, there are no large particle size mica particles in the +2.5 mm particle size range. Based on this, the materials in this particle size range do not need to enter a bar screen for further separation treatment; Step 3: Sort the -2.5 mm material B obtained by screening in Step 2 through a dry-roll high-intensity magnetic separator (magnetic field strength: 1.0 T, feed rate: 0.6 tons per hour) to obtain 5.4 tons of magnetic material E (mainly free mica, and other substances in minor amounts) and 11.2 tons of non-magnetic material F (manufactured sand without free mica). Step 4: Take 11.2 tons of the non-magnetic sample F obtained by magnetic separation and mix it evenly with 2.3 tons of the +2.5 mm material A to obtain the manufactured sand product.

[0029] In this embodiment, since microwave heating is used to treat the mixture of fine sand and finely crushed product, and then rapid cooling is carried out with cold air, taking advantage of the difference in the thermal expansion coefficients of granite and mica, different thermal stresses are generated on the mineral surface, cracks are generated on the mineral surface, making it easier for mica to peel off from granite. During the +2.5 mm screening, mica is more likely to peel off with the vibration during screening, and thus more mica is magnetically separated during magnetic separation. The content of free mica in the manufactured sand product obtained in this embodiment is 0.7%, meeting the requirements for the content of free mica in the "Code for Construction of Hydraulic Concrete" (DL / T 5144-2015). In addition, the particle size distribution of the manufactured sand is reasonably distributed, and the stone powder content is 12.5% (the allowable range in the specification is 6% - 18%), all meeting the specification requirements.

[0030] Comparative Example 1 When treating a granite raw material with a mica content of 18%, air separation is used to separate free mica in the -2.5 mm manufactured sand. The specific steps are as follows: Step 1: Take 20 tons of granite with a mica content of 18%. Use a jaw crusher to coarsely crush the granite to about 200 mm, then use a cone crusher to medium-crush the granite of about 200 mm to about 50 mm. Then, screen the medium-crushed product with a 2 mm bar screen, and use a rod mill to finely crush the oversize product after screening of the medium-crushed product to less than 5 mm to obtain the finely crushed product. After screening the undersize product after screening of the medium-crushed product with a 5 mm square hole screen, obtain 0.05 tons of large-diameter free mica and 0.63 tons of fine sand. Step 2: Mix the finely crushed product and the fine sand and screen them with a square hole screen with a screen hole size of 2.5 mm to obtain 3.8 tons of +2.5 mm material A and 16.15 tons of -2.5 mm material B. Among them, the +2.5 mm material A is screened with a bar screen with a screen hole size of 0.2 mm to obtain 3.6 tons of sand and gravel C without free mica and 0.12 tons of large-diameter free mica D. Step 3: Feed the -2.5 mm material B obtained by screening in Step 2 into a drying device for dehydration and drying treatment to obtain 15.75 tons of sand and gravel E. Step 4: Pass the -2.5 mm sand and gravel E obtained by screening in Step 3 through a ZXF-600 type vibrating air separator (wind speed 10 m / s, processing capacity 50 t / h) to obtain 4.55 tons of mica flakes G and 11.2 tons of product sand F (free of free mica); Step 5: Take 11.2 tons of product sand F obtained by air separation and mix it evenly with 3.6 tons of sand and gravel C without free mica obtained by screening with a bar screen to obtain a manufactured sand product. After testing, the content of free mica in the manufactured sand is 2.8%, which does not meet the requirements for the content of free mica in the "Code for Construction of Hydraulic Concrete" (DL / T 5144-2015). In addition, the gradation of the manufactured sand is inappropriate, and the stone powder content is 6.8%. Compared with Example 1, the quality of the manufactured sand obtained by air separation has significantly declined.

[0031] Comparative Example 2 When processing a granite raw material with a mica content of 18%, the crushed fine product is not subjected to -2.5 mm classification screening using a straight screen. The specific steps are as follows: Step 1: Take 20 tons of granite with a mica content of 18%. Coarsely crush the granite to about 200 mm using a jaw crusher, then medium-crush the granite of about 200 mm to about 50 mm using a cone crusher. Then, screen the medium-crushed product using a 2 mm bar screen, and further finely crush the oversize product after screening of the medium-crushed product to less than 5 mm using a rod mill to obtain a fine crushed product. After screening the undersize product after screening of the medium-crushed product using a 5 mm square hole screen, obtain 0.05 tons of large-diameter free mica and 0.63 tons of fine sand; Step 2: Mix the fine crushed product and the fine sand to obtain manufactured sand A. Subject the manufactured sand A to wet magnetic separation using a high-gradient magnetic separator (magnetic field intensity 0.8 T, pulp concentration 18%, feed rate 0.7 tons per hour) to obtain 6.15 tons of magnetic material B (mainly free mica) and 13.8 tons of non-magnetic material C (manufactured sand without free mica); After precipitation and dehydration of the non-magnetic material C obtained by magnetic separation, a manufactured sand product is obtained. After testing, the content of free mica in the manufactured sand product is 4.3%, which does not meet the requirements for the content of free mica in the "Code for Construction of Hydraulic Concrete" (DL / T 5144-2015). At the same time, the stone powder content of this manufactured sand is 7.1%, the particle size distribution is biased towards the fine particle size grade, and the continuity is poor.

[0032] Comparative Example 3 When processing a granite raw material with a mica content of 18%, a water washing process is used to separate free mica in the -2.5 mm manufactured sand. The specific steps are as follows: Step 1: Take 20 tons of granite with a mica content of 18%. Use a jaw crusher to coarsely crush the granite to about 200 mm, then use a cone crusher to medium-crush the granite of about 200 mm to about 50 mm. Then, screen the medium-crushed product with a 2-mm bar screen, and use a rod mill to finely crush the oversize product to less than 5 mm to obtain a finely crushed product. After screening the undersize product with a 5-mm square-hole screen, 0.05 tons of large-diameter free mica and 0.63 tons of fine sand are obtained. Step 2: Mix the finely crushed product and the fine sand and screen them with a 2.5-mm square-hole screen to obtain 3.2 tons of +2.5-mm material A and 16.75 tons of -2.5-mm material B. Among them, the +2.5-mm material A is screened with a 0.2-mm bar screen machine to obtain 3.08 tons of free-mica-free sand and gravel C and 0.12 tons of large-diameter free mica D. Step 3: Feed the -2.5-mm material B (16.75 tons) obtained in Step 2 into a drum washer for water washing. The water washing process uses a high-pressure spraying method (nozzle pressure 0.4 MPa) and combines with the rotation and stirring of the drum to make the attached fine mud, floating ash, and some free mica sheets desorb and peel off from the surface of the aggregate. About 56 tons of clean water are consumed in this process (about 2.8 tons per ton of raw material B). The washed material is preliminarily dehydrated by a vibrating dewatering screen to obtain a mortar slurry. Step 4: After the washed mortar slurry is precipitated and dehydrated, 13.2 tons of sand sediment material E and 3.55 tons of peeled sediment F are obtained. Subsequently, the 13.2 tons of sand sediment material E is evenly mixed with the 3.08 tons of +2.5-mm free-mica-free sand and gravel A obtained in Step 2 to obtain a manufactured sand product. After testing, the free mica content in the manufactured sand product is 2.6%, which does not meet the requirements for the free mica content in the "Code for Construction of Hydraulic Concrete" (DL / T 5144-2015). The particle gradation of the manufactured sand is reasonable, and the stone powder content is 13.7%, and the stone powder content is qualified.

[0033] Although the embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, other modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrations shown and described here.

Claims

1. A method for preparing machine-made sand from high mica granite, characterized in that, It includes the following steps: Step 1: First, coarsely crush the granite, then medium-crush the coarsely crushed product, then screen the medium-crushed product with a bar screen, and then finely crush the oversize product after screening the medium-crushed product to obtain a finely crushed product. The undersize product after screening the medium-crushed product is screened and separated into large-diameter free mica and fine sand by a square-hole screen; Step 2: Mix the fine sand and the finely crushed product and screen them through a square-hole screen or a straight-line screen into materials of +2.5 mm and -2.5 mm. Among them, the +2.5 mm material is further screened with a bar screen. The oversize is sand and gravel without free mica, and the undersize is flaky free mica; Step 3: Separate the -2.5 mm material screened in Step 2 by a high-intensity magnetic separator. The obtained magnetic material is mainly free mica, and the non-magnetic material is manufactured sand without free mica; Step 4: Mix the manufactured sand without free mica with the sand and gravel without free mica or the +2.5 mm material obtained in Step 2 in proportion and mix them evenly to obtain a manufactured sand product.

2. The method for preparing machine-made sand from high-mica granite as described in claim 1, characterized in that, In the said Step 1, the coarse crushing is carried out by a jaw crusher or a gyratory crusher, the particle size of the coarsely crushed product is 100 - 300 mm, the medium crushing is carried out by a cone crusher or a counterattack crusher, the particle size of the medium-crushed product is 20 - 60 mm, and the fine crushing is carried out by a rod mill or a pair of roll crushers. The particle size of the finely crushed product is less than 5 mm.

3. The method for preparing machine-made sand from high-mica granite according to claim 1, characterized in that, In the said Step 1, the aperture size of the bar screen is 2 - 10 mm, and the aperture size of the square-hole screen is 5 mm.

4. The method for preparing machine-made sand from high-mica granite according to claim 1, characterized in that, In the said Step 1, when the granite does not contain large-diameter mica, the medium-crushed product can directly go through the fine crushing step without screening with a bar screen.

5. The method for preparing machine-made sand from high-mica granite as claimed in claim 1, wherein In the said Step 2, the aperture size of the square-hole screen or the straight-line screen is 2.5 mm, and the aperture size of the bar screen is 0.1 - 1 mm.

6. The method for preparing machine-made sand from high mica granite as claimed in claim 1, wherein, In the said Step 3, during high-intensity magnetic separation, a dry magnetic separation process or a wet magnetic separation process is adopted. When the wet magnetic separation process is adopted, the manufactured sand without free mica obtained by magnetic separation needs to be precipitated and dehydrated.

7. The method for preparing machine-made sand from high-mica granite as claimed in claim 1, characterized in that, In the said Step 4, the mass ratio of the manufactured sand without free mica to the sand and gravel without free mica or the +2.5 mm material obtained in Step 2 is 4 - 8:

1.

8. The method for preparing machine-made sand from high mica granite according to claim 1, characterized in that, Perform microwave heating treatment on the mixture of the fine sand and the finely crushed product in Step 2 to further improve the mica separation efficiency. The specific method is as follows: S1: First, dry the mixture and control its water content to be less than 2%; S2: Then, perform microwave heating treatment on the dried mixture in an industrial-grade microwave heating device. During heating, first preheat with a low power, and then perform multi-stage microwave heating with a high power after preheating; S3: After the microwave heating is completed, quickly introduce cold air to cool down.

9. The method for preparing machine-made sand from high-mica granite as claimed in claim 8, wherein, In the said S2, the microwave low-power preheating power is 5 - 10 kW, preheat for 10 - 20 min, heat with low power until the surface temperature of the mixture is 80 - 120 °C, the high-power heating power is 40 - 60 kW, heat for 40 s each time with an interval of 20 s, and heat for a total of 120 - 360 s until the surface temperature of the mixture is 200 - 300 °C.

10. The method for preparing machine-made sand from high-mica granite according to claim 1, characterized in that, In the said Step 4, the free mica content of the obtained manufactured sand product is less than 2%.

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