A method for preparing low-cost synthetic pyrophyllite-based mica

Abstract

The application relates to the technical field of mica, and particularly discloses a preparation method of low-cost artificially-synthesized leaf-talc-based mica. The preparation method of the leaf-talc-based mica comprises the following steps: mixing leaf-talc tailings and a sulfuric acid solution in an autoclave, sealing and stirring, cooling, filtering, and obtaining impurity-removed leaf talc; adding urea and aluminum nitrate into dimethyl sulfoxide, stirring, adding the impurity-removed leaf talc, sealing and constant-temperature water-bath stirring, cooling, calcining and heat preservation, cooling, and obtaining modified leaf talc; mixing the modified leaf talc, fused magnesite, potassium fluosilicate and potassium carbonate, ball milling, calcining and heat preservation, cooling at a cooling rate of 2-4 DEG C / min and calcining, heat preservation, and grinding, and obtaining the leaf-talc-based mica. The leaf-talc-based mica prepared by the application has high strength and low cost, and is suitable for large-scale popularization and use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mica, and particularly relates to a preparation method of low-cost artificial synthetic phlogopite-based mica. BACKGROUND

[0002] As a unique mineral material, mica occupies an indispensable position in many fields such as electronics, aerospace, construction, and chemical industry. Its good insulation, high temperature resistance, chemical stability, and unique mechanical properties of the crystal structure make it a key raw material for the manufacture of many high-tech products and traditional industrial products. However, the acquisition and application of mica materials currently face many severe challenges.

[0003] Traditionally, natural mica is the main source of mica materials. However, natural mica has great limitations in strength. During the long and complex geological formation process, it is affected by various geological factors, such as pressure differences of different strata, temperature fluctuations, and uneven distribution of mineral composition, etc. This leads to a large number of defects in the internal crystal structure of natural mica, as well as high impurity content. This makes the strength of natural mica uneven, which is difficult to meet the requirements of some high-strength applications in modern industry. For example, in the field of aerospace, the parts of aircraft need to maintain structural integrity in extreme mechanical environments. The insufficient strength of natural mica makes it prone to damage when subjected to large external forces, vibrations, or complex stress conditions, which seriously threatens the safe operation of aircraft. In the field of electronic precision manufacturing, the requirements for material strength and stability are also strict. The performance shortcomings of natural mica limit the miniaturization and high performance development of electronic products, and cannot meet the high precision and high reliability requirements of precision instruments for parts.

[0004] The crystallization rate of natural mica also shows great instability. The crystallization process of mica has extremely strict requirements on the geological environment. The slight differences in factors such as mineral concentration, temperature gradient, and pressure change rate in the stratum will have a significant impact on the crystallization of mica. This leads to the extreme scarcity of high-quality, high-crystallinity mica veins. In the actual mined mica raw materials, a large amount of low-crystallinity mica is mixed in. Low crystallinity not only means that the mica crystal is not fully developed, and its physical properties are greatly reduced, but also requires more manpower, material resources and time cost for screening and purification in the subsequent processing process, which greatly reduces the resource utilization efficiency.

[0005] From the perspective of sustainable development, the environmental problems caused by excessive dependence on natural mica mining are becoming increasingly prominent. Large-scale open-pit mining and underground mining activities have seriously damaged the vegetation and surface structure of the mountain, leading to ecological problems such as soil erosion and land desertification. At the same time, a large amount of tailings and waste generated during the mining process will cause serious pollution to the soil, water sources and other ecological imbalances if not properly treated. In addition, with the rapid development of global industry, the market demand for mica continues to rise, but the natural mica resources are limited and increasingly scarce, which makes the price continue to rise. This not only brings heavy cost pressure to the downstream industry of mica, but also to some extent restricts the healthy development of related industries.

[0006] Although the existing method of synthesizing mica with quartz sand and aluminum oxide as raw materials has alleviated the dependence on natural mica to some extent, there are still many drawbacks. First of all, the procurement cost of quartz sand and aluminum oxide is high, and the price fluctuates greatly with the change of market supply and demand, which makes it difficult to effectively control the production cost of mica. Secondly, the production process of this synthesis method is complex, involving multiple reaction steps and strict reaction condition control, which requires high-precision production equipment and professional technical personnel, which undoubtedly further increases the production cost and technical threshold. In addition, a large amount of waste and pollutants will be generated during the production process, causing secondary pollution to the environment, and also failing to solve the long-standing environmental problems such as tailings disposal. In summary, it has become a key problem in the industry to develop a mica preparation technology that can overcome the performance limitations of natural mica, reduce costs and achieve sustainable development. SUMMARY

[0007] The purpose of the present application is to solve the problems existing in the prior art and to provide a preparation method of waterproof coating.

[0008] A low-cost artificial synthesis of pyrophyllite-based mica preparation method, comprising the following steps:

[0009] S1, mix pyrophyllite tailings and sulfuric acid solution in an autoclave, seal and stir, cool, filter, and obtain impurity-removed pyrophyllite;

[0010] S2, add urea and aluminum nitrate to dimethyl sulfoxide, stir, add impurity-removed pyrophyllite, seal and constant temperature water bath stirring, cool, calcine and keep warm, cool, and obtain modified pyrophyllite;

[0011] S3, mix modified pyrophyllite, fused magnesite, potassium fluosilicate and potassium carbonate, ball mill, calcine and keep warm, then cool at a cooling rate of 2-4 ℃ / min and calcine, keep warm, and grind to obtain pyrophyllite-based mica.

[0012] Preferably, in the step S1, the weight ratio of the pyrophyllite tailings and the sulfuric acid solution is 100-120:600-700.

[0013] Preferably, in the step S1, the concentration of the sulfuric acid solution is 0.9-1 mol / L.

[0014] Preferably, in the step S1, after sealing, stirring is performed at a temperature of 165-175℃ for 3-4h at a speed of 300-400rpm, and the pressure of the autoclave is 5-8MPa.

[0015] Preferably, in the step S2, the weight ratio of the urea, aluminum nitrate, dimethyl sulfoxide, and the impurity-removed pyrophyllite is 25-35, 5-15, 190-210:90-110.

[0016] Preferably, in the step S2, after adding the urea and the aluminum nitrate to the dimethyl sulfoxide, stirring is performed for 0.5-1h at a speed of 300-400rpm.

[0017] Preferably, in the step S2, the impurity-removed pyrophyllite is added, and constant-temperature water bath stirring is performed at a temperature of 80-90℃ for 22-26h at a speed of 100-200rpm.

[0018] Preferably, in the step S2, calcination and heat preservation are performed, the temperature is increased to 400-500℃ at a rate of 5-15℃ / min for calcination, and heat preservation is performed for 2-3h.

[0019] Preferably, in the step S3, the weight ratio of the modified pyrophyllite, the fused magnesite, the potassium fluosilicate, and the potassium carbonate is 250-350:150-250:100-200:40-60.

[0020] Preferably, in the step S3, the ball milling time is 2-3h, and the rotation speed is 250-350rpm.

[0021] Preferably, in the step S3, after ball milling, the temperature is first increased to 1400-1500℃ at a rate of 4-6℃ / min for calcination, heat preservation is performed for 2-3h, then the temperature is decreased to 1200-1300℃ at a rate of 2-4℃ / min for calcination, and heat preservation is performed for 2-3h.

[0022] Preferably, in the step S3, grinding is performed to 40-80 mesh.

[0023] Beneficial effects:

[0024] The application opens up a new way of preparing mica with low cost and sustainability by using pyrophyllite tailings as raw materials, replacing traditional quartz sand and aluminum oxide with pyrophyllite, which not only significantly reduces production cost, but also provides a practical comprehensive utilization scheme for pyrophyllite tailings processing, reducing resource waste and environmental burden.

[0025] The application greatly promotes the formation and growth of mica crystals by modifying pyrophyllite and expanding the interlayer structure of pyrophyllite, significantly improves the strength and hardness of pyrophyllite, and further enhances the mechanical properties of the final product pyrophyllite-based mica, so that it can withstand greater external force without being easily damaged in actual application. The intercalation reaction of urea and aluminum nitrate effectively supplements the aluminum element in pyrophyllite, accurately controls the silicon-aluminum ratio of pyrophyllite to the ideal value, and ensures the high-quality synthesis of pyrophyllite-based mica. At the same time, the in-situ generated aluminum oxide in the interlayer of pyrophyllite reduces the crystallization activation energy of phlogopite, accelerates the crystal growth rate, helps to form mica products with higher crystallinity and better quality, and broadens its application prospects in harsh material performance requirements such as electronics, aerospace, etc. DETAILED DESCRIPTION

[0026] The application will be further described below in conjunction with specific embodiments.

[0027] The pyrophyllite tailings used below are all purchased from Shaoxing Shangyu Pyrophyllite Mining Co., Ltd., containing impurities such as iron;

[0028] Example 1

[0029] A preparation method of low-cost artificial synthesis of pyrophyllite-based mica, comprising the following steps:

[0030] S1, mix 100g pyrophyllite tailings and 600g sulfuric acid solution with a concentration of 0.9mol / L in an autoclave, seal and stir at 165℃ for 3h, the stirring speed is 300rpm, the pressure is 5MPa, cool, filter, and obtain the impurity-removed pyrophyllite;

[0031] S2, add 25g urea and 5g aluminum nitrate to 190g dimethyl sulfoxide, stir for 0.5h, the stirring speed is 300rpm, add 90g impurity-removed pyrophyllite, seal and stir in a constant temperature water bath at 80℃ for 22h, the stirring speed is 100rpm, cool, heat to 400℃ at a heating rate of 5℃ / min, heat for 2h, cool, and obtain the modified pyrophyllite;

[0032] S3, 250g modified phlogopite, 150g fused magnesite, 100g potassium fluosilicate, 40g potassium carbonate were mixed, ball-milled for 2h at a rotating speed of 250rpm, heated to 1400℃ at a heating rate of 4℃ / min and calcined, kept for 2h, then cooled to 1200℃ at a cooling rate of 2℃ / min and calcined, kept for 2h, ground, to obtain phlogopite-based mica.

[0033] Example 2

[0034] A preparation method of low-cost artificially synthesized phlogopite-based mica, comprising the following steps:

[0035] S1, 120g phlogopite tailings, 700g sulfuric acid solution with a concentration of 1mol / L were mixed in an autoclave, sealed and stirred at 175℃ for 4h at a stirring speed of 400rpm and a pressure of 8MPa, cooled, filtered, to obtain impurity-removed phlogopite;

[0036] S2, 35g urea, 15g aluminum nitrate were added to 210g dimethyl sulfoxide, stirred for 1h at a stirring speed of 400rpm, 110g impurity-removed phlogopite was added, sealed and stirred in a constant-temperature water bath at 90℃ for 26h at a stirring speed of 200rpm, cooled, calcined at a heating rate of 15℃ / min to 500℃, kept for 3h, cooled, to obtain modified phlogopite;

[0037] S3, 350g modified phlogopite, 250g fused magnesite, 200g potassium fluosilicate, 60g potassium carbonate were mixed, ball-milled for 3h at a rotating speed of 350rpm, heated to 1500℃ at a heating rate of 6℃ / min and calcined, kept for 3h, then cooled to 1300℃ at a cooling rate of 4℃ / min and calcined, kept for 3h, ground, to obtain phlogopite-based mica.

[0038] Example 3

[0039] A preparation method of low-cost artificially synthesized phlogopite-based mica, comprising the following steps:

[0040] S1, 110g phlogopite tailings, 650g sulfuric acid solution with a concentration of 0.95mol / L were mixed in an autoclave, sealed and stirred at 170℃ for 3.5h at a stirring speed of 350rpm and a pressure of 6.5MPa, cooled, filtered, to obtain impurity-removed phlogopite;

[0041] S2, 30g urea, 10g aluminum nitrate were added to 200g dimethyl sulfoxide, stirred for 0.7h at a stirring speed of 350rpm, 100g impurity-removed phlogopite was added, sealed and stirred in a constant-temperature water bath at 85℃ for 24h at a stirring speed of 150rpm, cooled, calcined at a heating rate of 10℃ / min to 450℃, kept for 2.5h, cooled, to obtain modified phlogopite;

[0042] S3, 300 g of modified leaf talc, 200 g of fused magnesite, 150 g of potassium fluosilicate, and 50 g of potassium carbonate were mixed, ball-milled for 2.5 h at a rotation speed of 300 rpm, heated to 1450℃ at a heating rate of 5℃ / min and calcined, kept for 2.5 h, then cooled to 1250℃ at a cooling rate of 3℃ / min and calcined, kept for 2.5 h, and ground to obtain a leaf-talc-based mica.

[0043] Comparative Example 1

[0044] The difference between Comparative Example 1 and Example 3 is that the leaf talc is not modified.

[0045] A preparation method of a low-cost artificially synthesized leaf-talc-based mica, comprising the following steps:

[0046] S1, 110 g of leaf talc tailings and 650 g of a sulfuric acid solution with a concentration of 0.95 mol / L were mixed in an autoclave, sealed and stirred at 170℃ for 3.5 h at a stirring speed of 350 rpm and a pressure of 6.5 MPa, cooled, filtered, and a leaf-talc-based mica was obtained.

[0047] S2, 300 g of the leaf-talc-based mica, 200 g of fused magnesite, 150 g of potassium fluosilicate, and 50 g of potassium carbonate were mixed, ball-milled for 2.5 h at a rotation speed of 300 rpm, heated to 1450℃ at a heating rate of 5℃ / min and calcined, kept for 2.5 h, then cooled to 1250℃ at a cooling rate of 3℃ / min and calcined, kept for 2.5 h, and ground to obtain a leaf-talc-based mica.

[0048] Comparative Example 2

[0049] The difference between Comparative Example 2 and Example 3 is that aluminum nitrate is directly added to the leaf-talc-based mica for calcination, instead of first preparing an intercalation solution by mixing urea and aluminum nitrate, and then reacting with the leaf-talc-based mica for calcination.

[0050] A preparation method of a low-cost artificially synthesized leaf-talc-based mica, comprising the following steps:

[0051] S1, 110 g of leaf talc tailings and 650 g of a sulfuric acid solution with a concentration of 0.95 mol / L were mixed in an autoclave, sealed and stirred at 170℃ for 3.5 h at a stirring speed of 350 rpm and a pressure of 6.5 MPa, cooled, filtered, and a leaf-talc-based mica was obtained.

[0052] S2, 10 g of aluminum nitrate was added to 200 g of dimethyl sulfoxide, stirred for 0.7 h at a stirring speed of 350 rpm, 100 g of impurity-removed leaf spar was added, sealed and stirred in a constant temperature water bath at 85℃ for 24 h at a stirring speed of 150 rpm, cooled, calcined at a temperature rising rate of 10℃ / min to 450℃, kept for 2.5 h, cooled, and modified leaf spar was obtained;

[0053] S3, 300 g of modified leaf spar, 200 g of fused magnesite, 150 g of potassium fluosilicate and 50 g of potassium carbonate were mixed, ball-milled for 2.5 h at a rotating speed of 300 rpm, calcined at a temperature rising rate of 5℃ / min to 1450℃, kept for 2.5 h, then calcined at a temperature dropping rate of 3℃ / min to 1250℃, kept for 2.5 h, and grinded to obtain leaf spar-based mica.

[0054] Comparative Example 3

[0055] The difference between Comparative Example 3 and Example 3 is that step S2 does not perform calcination, and directly performs the subsequent preparation step of fluorophlogopite;

[0056] A preparation method of low-cost artificially synthesized leaf spar-based mica, comprising the following steps:

[0057] S1, 110 g of leaf spar tailings and 650 g of a sulfuric acid solution with a concentration of 0.95 mol / L were mixed in an autoclave, sealed and stirred at 170℃ for 3.5 h at a stirring speed of 350 rpm and a pressure of 6.5 MPa, cooled, filtered, and impurity-removed leaf spar was obtained;

[0058] S2, 30 g of urea and 10 g of aluminum nitrate were added to 200 g of dimethyl sulfoxide, stirred for 0.7 h at a stirring speed of 350 rpm, 100 g of impurity-removed leaf spar was added, sealed and stirred in a constant temperature water bath at 85℃ for 24 h at a stirring speed of 150 rpm, and cooled to obtain modified leaf spar;

[0059] S3, 300 g of modified leaf spar, 200 g of fused magnesite, 150 g of potassium fluosilicate and 50 g of potassium carbonate were mixed, ball-milled for 2.5 h at a rotating speed of 300 rpm, calcined at a temperature rising rate of 5℃ / min to 1450℃, kept for 2.5 h, then calcined at a temperature dropping rate of 3℃ / min to 1250℃, kept for 2.5 h, and grinded to obtain leaf spar-based mica.

[0060] Comparative Example 4

[0061] The difference between Comparative Example 4 and Example 3 is that in step S3, the system is not cooled, and is calcined at 1450℃ throughout the process;

[0062] A preparation method of low-cost artificially synthesized leaf spar-based mica, comprising the following steps:

[0063] S1, 110 g of pyrophyllite tailings, 650 g of a sulfuric acid solution with a concentration of 0.95 mol / L were mixed in an autoclave, sealed and stirred at 170℃ for 3.5 h, the stirring speed was 350 rpm, the pressure was 6.5 MPa, cooled, filtered, and 30 g of urea, 10 g of aluminum nitrate was added to 200 g of dimethyl sulfoxide, stirred for 0.7 h, the stirring speed was 350 rpm, 100 g of the impurity-removed pyrophyllite was added, sealed and stirred in a constant temperature water bath at 85℃ for 24 h, the stirring speed was 150 rpm, and calcined at a temperature rising rate of 10℃ / min to 450℃, the holding time was 2.5 h, and cooled to obtain a modified pyrophyllite;

[0064] S2, 10 g of aluminum nitrate was added to 200 g of dimethyl sulfoxide, stirred for 0.7 h, the stirring speed was 350 rpm, 100 g of the impurity-removed pyrophyllite was added, sealed and stirred in a constant temperature water bath at 85℃ for 24 h, the stirring speed was 150 rpm, and calcined at a temperature rising rate of 10℃ / min to 450℃, the holding time was 2.5 h, and cooled to obtain a modified pyrophyllite;

[0065] S3, 300 g of the modified pyrophyllite, 200 g of fused magnesia, 150 g of potassium fluosilicate, and 50 g of potassium carbonate were mixed, ball milled for 2.5 h at a speed of 300 rpm, heated to 1450℃ at a temperature rising rate of 5℃ / min and calcined for 5 h, and ground to obtain a pyrophyllite-based mica.

[0066] Performance test

[0067] Mechanical strength: The pyrophyllite-based mica prepared in Examples 1-3 and Comparative Examples 1-5 was tested for compressive strength and bending strength according to the standard JC / T 813-2024, and the results are shown in Table 1.

[0068] Crystallization rate: The pyrophyllite-based mica was prepared by the method of Examples 1-3 and Comparative Examples 1-5, respectively, under the same raw material specifications and reaction conditions, screened, and the weight of the mica was recorded as M1; then, according to the molar mass and stoichiometric relationship, the yield of the mica under ideal reaction conditions was calculated as M2.

[0069] The calculation formula is:

[0070] Table 1 Performance test results

[0071]

[0072] Data analysis:

[0073] From the data of Examples 1-3 in Table 1, it can be seen that the pyrophyllite-based mica prepared by the present application has obvious advantages in mechanical strength and crystallization rate. On the one hand, the average compressive strength is about 1173.9 MPa, and the highest can reach 1175.8 MPa, the average bending strength is about 169.7 MPa, and the highest can reach 171.2 MPa, indicating that the mechanical strength of the mica is extremely superior and stable; on the other hand, the average crystallization rate is about 87%, and the highest can reach 87.3%, indicating that the efficiency of the prepared mica is very high.

[0074] As can be seen from the data of Example 3 and Comparative Example 1 in Table 1, intercalation modification plays an important role in improving the flexural strength, compressive strength and crystallization efficiency of the muscovite based on the lepidolite. This is because the intercalation complex of urea and aluminum nitrate expands the interlayer structure of lepidolite, providing more favorable space for muscovite crystallization, so that the crystal growth is more sufficient, thereby improving the crystallization efficiency; at the same time, the modified structure enhances the internal binding force of the muscovite, so that the flexural strength and tensile strength are significantly improved.

[0075] As can be seen from the data of Example 3 and Comparative Example 2 in Table 1, the intercalation solution of urea and aluminum nitrate is prepared first and then reacted with the impurity-removed lepidolite, which is crucial to improving the flexural strength, compressive strength and crystallization efficiency of the muscovite based on the lepidolite. This is because the coordination of the amino group in the urea molecule and the aluminum ion in the aluminum nitrate can make the aluminum ion uniformly dispersed in the interlayer of the lepidolite, promoting the uniform generation of aluminum oxide during subsequent calcination, providing more and more uniform crystal nucleus for muscovite crystallization, and greatly improving the crystallization efficiency; at the same time, this uniform distribution of the structure enhances the overall performance of the muscovite, improving the flexural strength and tensile strength.

[0076] As can be seen from the data of Example 3 and Comparative Example 3 in Table 1, the calcination at 450℃ in step S2 is crucial to improving the flexural strength, compressive strength and crystallization efficiency of the muscovite based on the lepidolite. This is because at this temperature, the gas produced by the decomposition of urea expands the interlayer structure of lepidolite, and the decomposition of aluminum nitrate generates aluminum oxide, the expanded interlayer structure provides sufficient space for muscovite crystallization, promotes crystal growth, and improves the crystallization efficiency; and this structure optimization enhances the bonding effect in the muscovite, thereby improving the flexural strength and tensile strength.

[0077] As can be seen from the data of Example 3 and Comparative Example 4 in Table 1, reasonable cooling in step S3 has a positive effect on improving the flexural strength, compressive strength and crystallization efficiency of the muscovite based on the lepidolite. This is because during the cooling process, the atoms and molecules in the system have enough time to arrange in order, which helps to form more complete and regular muscovite crystal structure, thereby improving the crystallization efficiency; at the same time, slow cooling can reduce the internal stress of the crystal and enhance the bonding force between the crystals, significantly improving the flexural strength and tensile strength, while the whole high-temperature calcination in Comparative Example 4 is not conducive to the ordered growth of the crystal and the optimization of the structure.

[0078] It should be understood by those of ordinary skill in the art that the above discussion of any of the embodiments is merely exemplary and is not intended to suggest that the scope of the present application is limited to these examples; the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in detail for the sake of brevity.

Claims

1. A process for the preparation of low cost synthetic pyrophyllite based mica, characterized by, The method comprises the following steps: S1, mixing the pyrophyllite tailings and the sulfuric acid solution in an autoclave, sealing and stirring, cooling, filtering, and obtaining the impurity-removed pyrophyllite; S2, adding urea and aluminum nitrate to dimethyl sulfoxide, stirring, adding the impurity-removed pyrophyllite, sealing and constant-temperature water bath stirring, cooling, calcining at a temperature rising rate of 5-15 ℃ / min to 400-500 ℃, keeping for 2-3 h, cooling, and obtaining the modified pyrophyllite; in S2, the weight ratio of urea, aluminum nitrate, dimethyl sulfoxide, and impurity-removed pyrophyllite is 25-35:5-15:190-210:90-110; S3, mixing the modified pyrophyllite, fused magnesia, potassium fluosilicate, and potassium carbonate, ball milling, first calcining at a temperature rising rate of 4-6 ℃ / min to 1400-1500 ℃, keeping for 2-3 h, then calcining at a temperature falling rate of 2-4 ℃ / min to 1200-1300 ℃, keeping for 2-3 h, then calcining at a temperature falling rate of 2-4 ℃ / min, keeping, and grinding, and obtaining the pyrophyllite-based mica.

2. The process for the preparation of low cost synthetic mica based talc of claim 1, wherein, In S1, the weight ratio of pyrophyllite tailings and sulfuric acid solution is 100-120:600-700.

3. The process for the preparation of low cost synthetic mica based talc of claim 1, wherein, In S1, the concentration of the sulfuric acid solution is 0.9-1 mol / L.

4. The process for the preparation of low cost synthetic mica based talc of claim 1, wherein, In S1, after sealing, stirring is performed at a temperature of 165-175 ℃ for 3-4 h at a speed of 300-400 rpm, and the pressure of the autoclave is 5-8 MPa.

5. The process for the preparation of low cost synthetic mica based talc of claim 1, wherein, In S3, the weight ratio of modified pyrophyllite, fused magnesia, potassium fluosilicate, and potassium carbonate is 250-350:150-250:100-200:40-60.

6. The process for the preparation of low cost synthetic mica based talc of claim 1, wherein, In S3, the ball milling time is 2-3 h at a speed of 250-350 rpm.

7. The process for the preparation of low cost synthetic mica based talc of claim 1, wherein, In S3, grinding is performed to 40-80 mesh.

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