Mechanically-activated coal slime-coal particle grouting filling material for remining of residual coal and application of mechanically-activated coal slime-coal particle grouting filling material

Abstract

The invention belongs to the field of mining and utilization of mine resources, and particularly relates to a mechanically activated coal slime-coal particle grouting filling material for remining of residual coal and application, the coal slime-coal particle grouting filling material comprises a cementing material and water, the concentration of the cementing material is 65-70%, and the balance is water; the cementing material comprises the following components in percentage by mass: 10%-50% of high-ash coal slime, 25%-40% of high-ash coal slime, 15%-20% of cement and 25%-30% of coal particles; and mechanically activating. The activated coal slime is high-ash-content coal slime which is dried, milled by a ball mill and mechanically activated, and the mechanical activation time is 2-8 hours. The coal particles are raw coal cut by a coal mining machine, and the diameter of the coal particles is 2.5 mm-10 mm. And grouting materials are pumped into gaps of the residual coal pillars along the grouting holes, maintenance is conducted after grouting is completed, the mold is dismantled till the filling body is completely solidified, the filling body and the coal pillars form a whole at the moment, and a coal mining machine is adopted for cutting according to the conventional raw coal mining technology. The method is simple, and the use effect is good.

Description

Technical Field

[0001] This invention belongs to the field of mining and utilization of mineral resources, and specifically relates to a mechanically activated coal slime-coal particle grouting filling material for residual coal mining and its application. Background Technology

[0002] Currently, common methods for residual coal remining include hydraulic remining, fully mechanized long-arm remining, and backfilling remining. Backfilling remining of room-and-pillar goafs can address the safety hazards of large-scale collapse and spontaneous combustion in room-and-pillar goafs, and is therefore attracting considerable attention. In research on backfill materials for remining residual coal, coal gangue is used as aggregate and cement as a binder to form the backfill. However, this process presents two problems: 1) the backfill material mixes with the raw coal, increasing the ash content of the raw coal per unit mass of remined coal, increasing the workload of washing and beneficiation, and reducing resource extraction efficiency; 2) the high cost of cement and transportation materials increases the unit cost of remined raw coal. Therefore, developing backfill materials with low ash content, low cost, and wide availability that are easy to wash and beneficiate is of great significance for promoting the application of residual coal remining technology.

[0003] Coal slime contains minerals such as coal powder, clay, quartz, and calcite. Direct combustion of coal slime easily leads to environmental pollution and low efficiency. Therefore, the resource utilization of coal slime is a major issue concerning the clean utilization of resources and energy and environmental pollution control. Research and applications of coal slime mainly focus on enhancing the stability and suspension of coal-water slurry, as well as the influencing factors and mechanisms of coal slime-water sedimentation separation to obtain coal slime and industrial circulating water. In-depth and systematic research is still lacking on using coal slime as a grouting material for re-mining residual coal. Mechanical modification involves using high-energy ball milling to convert mechanical energy into the internal energy of the material, thereby altering its physicochemical properties. However, the clay content in coal slime, along with its cementing and expansion properties, negatively impacts the mechanical properties of the backing material. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this paper provides a mechanically activated coal slime-coal particle grouting filling material for residual coal re-mining and its application. Based on the chemical composition characteristics of coal slime, a mechanical activation method is introduced to enhance the cementing properties while reducing the water absorption properties of coal slime, thereby enhancing the flow properties and compressive strength of the grouting material and providing conditions for residual coal re-mining.

[0005] A mechanically activated coal slime-coal particle grouting filling material for residual coal re-mining is characterized in that: the coal slime-coal particle grouting filling material includes a cementing material and water, the cementing material concentration is 65%-70%, and the balance is water; the cementing material includes, by mass ratio: 10%-50% high-ash coal slime, 25%-40% high-ash coal slime, 15%-20% cement, and 25%-30% coal particles; through mechanical activation, the mechanically activated high-ash coal slime acquires cementing properties to assist in filling the gaps between coal particles as fine material, thereby reducing the amount of cement used.

[0006] Furthermore, the mechanical activation process of high-ash coal slime is as follows: the high-ash coal slime is vacuum dried, then milled using a ball mill to control the particle size to 3 micrometers to 6 micrometers, and finally mechanically activated for 2 to 8 hours to destroy the crystal lattice in the high-ash coal slime and generate cementing properties.

[0007] Furthermore, the coal particles are obtained by cutting raw coal with a coal mining machine, crushing it with a jaw crusher, and screening it with a 10mm aperture vibrating screen. The particle size of the coal particles is 2.5mm~10mm; the particle size distribution is 40% for 2.5-5mm and 60% for 5-10mm, which are used as aggregates to improve the compactness and mechanical strength of the filling body.

[0008] Furthermore, the cement type is PO42.5.

[0009] A method for preparing mechanically activated coal slime-coal particle grouting and backfilling material for residual coal re-mining, comprising the following steps: A crusher and a screening machine are used to crush and screen the washed raw coal to obtain coal particles that can be used as aggregate for grouting materials, and the diameter of the coal particles is controlled to be 2.5mm~10mm. High-ash coal slime is vacuum dried to a moisture content of 3% to 5%, and then mechanically activated. A cementing material is obtained by thoroughly mixing 10%-50% high-ash coal slime, 5%-40% mechanically activated high-ash coal slime, 10%-20% cement, and 20%-30% coal particles by mass ratio. The cementing material is mixed with water at a concentration of 65%-74% to obtain a mechanically activated coal slime-coal particle grouting filling material for residual coal remining.

[0010] Furthermore, the mechanical activation process involves: vacuum drying the high-ash coal slime for 6 hours to control its moisture content at 3%-5%; using a planetary ball mill to achieve a particle size of 3-6 micrometers in the high-ash coal slime, thereby disrupting the clay lattice and activating its cementing properties; and filling the gaps between coal particles and assisting in cementation through mechanical activation of the high-ash coal slime. Compared with traditional coal gangue-cement filling materials, this reduces cement usage by 30%-40%, and the bonding strength between the filling material and the residual coal is ≥2.5MPa.

[0011] Furthermore, the mechanical activation process is as follows: the planetary ball mill rotates at 400 r / min, using zirconia grinding balls with a particle size of 7 mm:5 mm:3 mm = 3:3:4 and a ball-to-material ratio of 3:1, and grinding for 2-8 hours.

[0012] An application of a mechanically activated coal slime-coal particle grouting filling material for residual coal mining, targeting the residual coal pillars in room-and-pillar goaf, includes the following steps: Grouting holes are constructed around the coal pillar, with the hole diameter and depth extending to the center of the coal pillar. Molds are custom-made to match the cross-section of the coal pillar. The grout is pumped into the gap of the coal pillar along the grouting hole. At the same time, the mold is placed around the coal pillar and fixed to ensure that the grout fills the gap. During the grouting process, the grouting pressure is checked at intervals to avoid the coal pillar from cracking due to a sudden increase in pressure. After grouting is completed, the filling material is cured and the mold is removed until the filling material is completely solidified. At this point, the filling material and the coal pillar form a whole, and the coal can be cut using a coal mining machine according to the conventional raw coal mining process.

[0013] An application of a mechanically activated coal slime-coal particle grouting filling material for residual coal re-mining, targeting residual coal in fractured zones, includes the following steps: Brick isolation walls were constructed on both sides of the fracture zone, and cement mortar was used to seal the surface. Grouting ports were reserved on the isolation walls. Add 0.5% glass fiber by mass to the grouting material and stir it with a high-speed disperser to make the glass fiber evenly dispersed; use a grouting pump to pump the modified grouting material into the crushing zone along the grouting port until the grout flows out from the overflow hole, and then stop grouting. Curing is carried out until the compressive strength of the filling body is ≥3MPa, the fractured zone forms a stable structure, and mining is carried out using a fully mechanized mining support in conjunction with a coal mining machine.

[0014] An application of a mechanically activated coal slime-coal particle grouting filling material for residual coal re-mining, targeting residual coal at edges and corners, includes the following steps: Small, mobile grouting equipment is selected to suit narrow working spaces in corner areas; Along the edge of the residual coal, divide the grouting area into 2m sections. Construct two grouting holes in each section. First, pump in the grouting material until the current section is filled. After curing, proceed with the grouting of the next section to gradually form a protective layer of the filling body. After all the grouting in the sections is completed and cured, the residual coal areas at the edges and corners will form a continuous mineable face, which will then be mined along the strike using a small coal mining machine.

[0015] Beneficial Effects: This invention proposes a research method for activating coal slime with high-energy mechanical force, enhancing its cementitious properties, reducing slurry concentration, and meeting transportation characteristics and mechanical strength requirements. This invention proposes using coal slime to replace part of the cement as a grouting material and coal particles as coarse aggregate supporting the structure to prepare grouting filling material for remined residual coal. Using this grouting material as a filling material for remined residual coal has advantages such as wide availability, short-distance transportation, improved recyclability of remined residual coal, and reduced raw coal washing costs.

[0016] The filling material of this invention has the following advantages: by mechanically activating coal slime to replace 30%-40% of cement, the cement usage is reduced from the traditional 200kg / ton slurry to 120kg / ton, reducing material costs by 40%; at the same time, the coal slime is utilized as a resource, eliminating coal slime storage costs (saving 50,000 yuan per mu per year), reducing the washing and beneficiation process by two steps, saving 2 million yuan in washing and beneficiation costs annually (based on a 100,000-ton / year remining project); the 28-day uniaxial compressive strength of the filling body is ≥4MPa, which is more than 68% higher than that of traditional coal gangue-cement materials (2.5MPa); and it bonds well with residual coal. With a strength ≥2.5MPa, stripping is avoided during mining, and the cutting efficiency of coal mining machines is increased by 50%; the composition of coal particles and residual coal is consistent, and the impurity rate after washing and screening after remining is reduced to 4%-5%, which is more than 72% lower than that of traditional materials (18%), and the raw coal recovery rate is increased to 88%; the grouting slurry concentration is 65%-70%, the slump expansion is ≥210mm, and the pipeline transportation distance can reach 340-350m, which is suitable for long-distance underground grouting needs; it realizes the full utilization of high ash coal slime, reduces the land occupation and environmental pollution caused by coal slime stockpiling, and meets the requirements of green mine construction. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the preparation process of the mechanically activated coal slime-coal particle grouting and filling material for residual coal mining according to the present invention.

[0018] Figure 2 This is a graph showing the change in slurry viscosity with the amount of activated coal slime added in an embodiment of the present invention.

[0019] Figure 3 This is a graph showing the change in slurry slump expansion with the amount of activated coal slime added in an embodiment of the present invention. Detailed Implementation

[0020] The embodiments of the present invention will be further described below with reference to the accompanying drawings: This invention discloses a mechanically activated coal slime-coal particle grouting and filling material for residual coal re-mining, composed of a cementing material and water. The cementing material concentration is 65%-70% (the balance being water), and the cementing material comprises the following components by mass ratio: High ash coal slime: 25%-35%, moisture content controlled at 3%-5% (achieved through vacuum drying), its main function is to assist in filling; Mechanically activated high-ash coal slime: 25%-40%, prepared by planetary ball mill activation. Activation parameters are: rotation speed 400 r / min, zirconia grinding balls (ball-to-material ratio 3:1, grinding ball particle size 7mm:5mm:3mm=3:3:4), activation time 2-8h (optimal is 6h). After activation, the coal slime particle size is 3-6 micrometers, and the metakaolin content is ≥35%. It can activate cementitious properties and replace part of the cement. Cement: 15%-20%, using PO42.5 ordinary Portland cement as the main binder; Coal particles: 25%-30%, obtained from raw coal cut by a coal mining machine through jaw crushing and screening by a 10mm aperture vibrating screen, with a particle size distribution of 40% for 2.5-5mm and 60% for 5-10mm, used as aggregate to improve the density and mechanical strength of the filling body; the effect of activated coal slime addition on slurry properties is as follows. Figure 2 As shown, the slurry viscosity varies with the amount of activated coal slime added. The horizontal axis represents the amount of activated coal slime added (5%-40%), and the vertical axis represents the viscosity (mPa·s). It shows that when 40% activated coal slime is added, the viscosity increases by 30% compared to when 5% is added, but it still meets the conveying requirements. like Figure 3 The bar chart shown illustrates the change in slurry slump spread with the amount of activated coal slime added, labeled "Adding 5% activated coal slime for 2 hours (slump spread 205mm)", "Adding 25% activated coal slime for 2 hours (slump spread 160.75mm)", "Adding 40% activated coal slime for 2 hours (slump spread 127.5mm)" and "65% concentration of raw coal slime (slump spread 212.5mm)", visually demonstrating the optimizing effect of activated coal slime on conveying performance.

[0021] like Figure 2 As shown, this invention discloses a method for preparing mechanically activated coal slime-coal particle grouting and backfilling material for residual coal re-mining, the steps of which are as follows: Step 1: Raw coal pretreatment uses a jaw crusher to crush the raw coal. After crushing, the material is screened through a 10mm aperture vibrating screen to collect coal particles in the range of 2.5-10mm in size. The particles are then sealed and stored for later use to prevent moisture and clumping.

[0022] Step 2: Coal slime activation treatment. Take high-ash coal slime (ash content ≥ 60%) and put it into a vacuum drying oven. Dry it for 6 hours at 80℃ and -0.08MPa vacuum to reduce the moisture content to 3%-5%. Put the dried coal slime into the grinding jar (500mL) of the Beijing Greedman BM6Pro planetary ball mill. Add zirconia grinding balls (7mm:5mm:3mm=3:3:4) at a ball-to-material ratio of 3:1. Set the speed to 400r / min and the activation time to 2-8 hours (stop the machine for 20 minutes after every 1 hour of activation to avoid the temperature from affecting the activation effect). After activation, transfer the coal slime into a sealed bag (humidity ≤ 30%) for storage to obtain mechanically activated high-ash coal slime.

[0023] Step 3: Mixing the cementing material. Weigh out 25%-35% high-ash coal slime, 25%-40% mechanically activated high-ash coal slime, 15%-20% cement, and 25%-30% coal particles by mass ratio, and put them into a twin-shaft mixer (300 r / min). Mix for 8-10 minutes until the materials are evenly mixed to form a cementing material.

[0024] Step 4: When preparing the grout, add deionized water to the cementing material and adjust the cementing material concentration to 65%-70%. Put the mixture into a high-speed disperser (speed 1500r / min) and stir for 5 minutes to ensure that the grout is free of lumps and has the required uniformity. After testing the slump expansion to be ≥210mm, it can be used for grouting.

[0025] 3. Application methods of backfill materials in residual coal mining Different grouting processes are adopted for different types of residual coal areas: (1) Coal pillars remaining in room-and-pillar goaf Preliminary preparation: Construct grouting holes within a 1.5m radius around the coal pillar, with a diameter of 50mm and a depth to the center of the coal pillar, and a hole spacing of 1.5m; Customize steel molds (5m×3m×2m) that match the cross-section of the coal pillar, and apply a release agent (vegetable oil) to the inner wall of the mold. Grouting operation: Use a grouting pump (working pressure 1.2-1.5MPa) to pump the grouting material into the coal pillar gap along the grouting hole. At the same time, put a steel mold around the coal pillar and fix it to ensure that the grout fills the gap. During the grouting process, check the grouting pressure every 30 minutes to avoid the coal pillar from cracking due to sudden pressure rise. Curing and Mining: After grouting, remove the mold after 72 hours of curing and continue curing for 3 months until the filling material is completely solidified (compressive strength ≥ 3.5 MPa). At this time, the filling material and the coal pillar form an integral whole, and the coal mining machine can be used to cut it according to the conventional raw coal mining process.

[0026] (2) Residual coal in the broken zone Isolation and protection: Construct brick isolation walls (300mm thick) on both sides of the fracture zone, seal them with cement mortar, and reserve grouting ports with a diameter of 80mm (spaced 2m apart). Modified grouting: Add 0.5% glass fiber (6mm in length) to the grouting material and stir for 3 minutes using a high-speed disperser (1200r / min) to ensure uniform fiber dispersion; use a low-pressure grouting pump (working pressure 0.8-1.0MPa) to pump the modified grouting material into the crushing zone through the grouting port until the grout flows out from the overflow hole, then stop grouting; Curing and Mining: Curing for 28 days until the compressive strength of the filling body is ≥3MPa, and the broken zone forms a stable structure, then using a fully mechanized mining support in conjunction with a coal mining machine for mining.

[0027] (3) Residual coal at the edges Equipment selection: Select small mobile grouting equipment (grouting pressure 0.8-1.0MPa, grout tank capacity 1m³), suitable for narrow working spaces in corner areas; Segmented grouting: Along the edge of the residual coal, divide the grouting area into 2m segments. Construct 2 grouting holes (40mm diameter, 1.5m depth) for each segment. First, pump in the grouting material until the current segment is filled. After curing for 24 hours, proceed with the grouting of the next segment, gradually forming a protective layer of 1-1.5m thickness. Mining operations: After all grouting in sections is completed and cured for 1 month (compressive strength ≥ 2.5 MPa), a continuous mineable face will be formed in the corner residual coal area, and a small coal mining machine will be used to mine along the strike.

[0028] 4. Test methods for the performance of filling materials Step 1: Sample preparation Select a 50mm×100mm standard cylindrical mold, evenly coat the inner wall with vegetable oil (0.1mm thickness), and seal the longitudinal gaps of the mold with high-temperature resistant tape; slowly pour the grout into the mold, and at the same time place it on a vibration table (frequency 50Hz) to vibrate for 3 minutes to remove air bubbles in the grout until the grout is flush with the top of the mold.

[0029] Step 2: Standard curing After the slurry has solidified for 24 hours, remove the mold and take out the sample. Place the sample in a curing chamber (temperature 20℃±2℃, humidity 95%±3%) and cure for 28 days. During the curing period, avoid collision and moisture to the sample.

[0030] Step 3: Mechanical property testing was conducted using a WAW-1000D universal testing machine. The loading rate was set to 0.03 mm / s and the data acquisition frequency to 15 Hz. Uniaxial compressive strength tests were performed on the cured specimens. The maximum pressure value when the specimen broke was recorded, and the compressive strength was calculated. Five parallel specimens were prepared for each group, and the average value was taken as the final result.

[0031] Step 4: Conveying performance test. Refer to GB / T50080-2016 "Standard for Test Method of Performance of Ordinary Concrete Mixture". Use a slump spread meter (upper diameter 100mm, lower diameter 200mm, height 300mm). After filling the instrument with grout, lift the instrument vertically. After 30 seconds, measure the slump spread diameter of the grout. A value ≥210mm is considered to meet the pipeline conveying requirements. Example

[0032] The grouting material was prepared with a cementing material concentration of 70%, and the mass ratio of the cementing material was: 30% high-ash coal slime, 30% activated coal slime (activated for 6 hours), 15% cement, and 25% coal particles. Preparation process: Raw coal is crushed and screened to obtain 2.5-10mm coal particles. After the coal slime is vacuum dried, it is activated by a planetary ball mill for 6 hours. After mixing and stirring the components, water is added to adjust the concentration, and the mixture is dispersed at high speed for 5 minutes. Performance tests: slump spread 215mm, 28-day compressive strength 4.2MPa; Application scenario: coal pillars remaining in room-and-pillar goaf, grouting pressure 1.5MPa, after 3 months of curing, they form an integral whole with the coal pillar, and the impurity rate of re-mining and washing is 5%. Example

[0033] The grout was prepared with a cementitious material concentration of 65%, and the mass ratio of the cementitious material was: 25% high-ash coal slime, 40% activated coal slime (activated for 6 hours), 15% cement, and 20% coal particles. Preparation process: Same as in Example 1, except the amount of activated coal slime added is adjusted to 40%; Performance tests: slump spread 212mm, 28-day compressive strength 4.8MPa; Application scenario: Crushed coal with residual coal, modified with 0.5% glass fiber, grouting pressure 1.0MPa, compressive strength 3.2MPa after 28 days of curing, impurity rate of re-mining and washing 4%. Example

[0034] The grout was prepared with a cementitious material concentration of 67%, and the mass ratio of the cementitious material was: 35% high-ash coal slime, 25% activated coal slime (activated for 8 hours), 20% cement, and 20% coal particles. Preparation process: The activation time was extended to 8 hours, and the rest was the same as in Example 1; Performance tests: slump spread 210mm, 28-day compressive strength 4.5MPa; Application scenario: residual coal at the edge and corner, using mobile grouting equipment, grouting in sections, curing for 1 month, and then re-mining and washing impurity rate of 4.5%.

[0035] Comparative Example (Traditional Coal Gangue-Cement Material) Prepared with a cementitious material concentration of 74%, the component mass ratio is 50% coal gangue, 20% cement, and 30% water; Performance testing: slump spread 180mm, 28-day compressive strength 2.5MPa; Application results: The impurity rate of re-mining and washing is 18%, the cement consumption is 200 kg / ton of slurry, and the stripping rate of the filling body during coal cutting by the coal mining machine is 30%.

[0036] As can be seen from the comparison between the embodiments and the comparative embodiments, the material of the present invention is significantly superior to traditional materials in terms of mechanical properties, washing efficiency and cost control, and fully meets the technical requirements for residual coal mining.

[0037] This invention is particularly applicable to coal slime washed and processed underground and coal slime stored in water tanks, but it is not limited to underground coal slime and can be adapted to coal slime in the mining industry.

[0038] The implementation steps for the invention of activated coal slime slurry are as follows: (1) A crusher and a screening machine are used to obtain coal particles with a diameter of 2.5 mm-10 mm as aggregate for grouting material; (2) Weigh grinding balls of different sizes, wash them with clean water, and dry them in a drying oven for later use; (3) Weigh 5%-40% of coal slime into a beaker and dry it in a vacuum drying oven for 4 hours for later use; (4) Measure 5%-40% of coal slime into the grinding cylinder, add the corresponding mass of grinding balls, close the grinding chamber door, set the grinding time and speed, and start mechanically activating the coal slime; (5) Turn off the ball mill and remove the activated coal slime and store it in a sealed bag; (6) Weigh out 10%-50% raw coal slime, 5%-40% activated coal slime, 10%-20% cement, and 20%-30% coal particles by mass ratio to prepare a slurry with a cementing material concentration of 65%-74%, and stir for 5 minutes; (7) The slurry is quickly transferred to the expansion slump test mold and slowly poured out to the expansion test plate at a uniform speed; (8) Apply a layer of vegetable oil to the inner wall of the mold and use tape to seal the mold to prevent water leakage from the longitudinal gaps. Transfer the slurry into the mold and demold after molding. After the specimen has reached a certain strength, remove the mold tape and the upper and lower fixing covers, place it in a curing chamber for 28 days, and test its compressive strength. During the compressive strength test, the loading method is axial constant rate loading, with a loading rate of 0.2 mm / min, until the filling material breaks.

[0039] In this invention, coal slime is mechanically ground to activate it and improve its cementitious properties, thereby reducing the amount of cement used. The coal slime-coal particle grouting material, used as a backfill material for residual coal re-mining, solves the problem of difficult utilization of coal slime, and is particularly suitable for high-ash coal slime deposited in deep mines. Furthermore, in this patent, the backfill material is extracted together with the raw coal, reducing ash content and washing costs.

[0040] Implementation content Example 1: Weigh out the corresponding mass of coal slime, cement, and coal particles according to a slurry concentration of 74%. Mix the coal slime, coal particles, and cement evenly with water. After mixing for 5 minutes, test the slump spread. Quickly transfer the mixture to a standard mold. After molding and demolding, transfer it to a standard curing chamber (20 degrees Celsius, 95% humidity) for 28 days. Finally, conduct a uniaxial compressive strength test on a universal testing machine.

[0041] Example 2; Following the operating steps of Example 1. The difference is that activated coal slime is used as the grouting material, and the activation time of the coal slime is 2 hours. The slurry concentration is changed to 70%. Calculated with solid mass as 100%, the activated coal slime mass ratio is 5%, the coal slime mass is 45%, the cement mass is 20%, and the coal particle mass is 30%.

[0042] Example 3: Following the operating steps of Example 2. The difference is that activated coal slime is used as the grouting material, and the activation time of the coal slime is 2 hours. The slurry concentration is changed to 65%. Calculated with solid mass as 100%, the activated coal slime mass ratio is 5%, the coal slime mass is 45%, the cement mass is 20%, and the coal particle mass is 30%.

[0043] Example 4: Following the operating steps of Example 2. The difference is that activated coal slime is used as the grouting material, and the activation time of the coal slime is 6 hours. The slurry concentration is changed to 65%. Calculated with solid mass as 100%, the activated coal slime mass ratio is 5%, the coal slime mass is 45%, the cement mass is 20%, and the coal particle mass is 30%.

[0044] Example 5: Following the operating steps of Example 2. The difference is that activated coal slime is used as the grouting material, and the activation time of the coal slime is 8 hours. The slurry concentration is changed to 65%. Calculated with solid mass as 100%, the activated coal slime mass ratio is 5%, the coal slime mass is 45%, the cement mass is 20%, and the coal particle mass is 30%.

[0045] Example 6: Following the operating steps of Example 2. The difference is that when using activated coal slime as the grouting material, the grout concentration is changed to 65%. Calculated with solid mass as 100%, the activated coal slime mass ratio is 25%, the coal slime mass is 25%, the cement mass is 20%, and the coal particle mass is 30%.

[0046] Example 7; Following the operating steps of Example 6. The difference is that when activated coal slime is used as the grouting material, the activation time of the coal slime is 2 hours. The slurry concentration is changed to 65%. Calculated with solid mass as 100%, the activated coal slime mass ratio is 40%, coal slime mass is 10%, cement mass is 20%, and coal particle mass is 30%.

[0047] A comparison of different methods revealed that activation time significantly affects the cementing activity of coal slime. A higher proportion of activated coal slime is beneficial for enhancing the mechanical properties of the grouting material, but it reduces its flow characteristics, including viscosity and slump spread. The typical effect of activated coal slime addition on slurry viscosity (a) and slump spread (b) is shown below. Figure 2 As shown.

Claims

1. A mechanically activated coal slime-coal particle grouting and filling material for residual coal re-mining, characterized in that: The coal slime-coal particle grouting filling material includes a binder and water. The binder concentration is 65%-70%, with the balance being water. The binder consists of 10%-50% high-ash coal slime, 25%-40% high-ash coal slime, 15%-20% cement, and 25%-30% coal particles by mass. Through mechanical activation, the mechanically activated high-ash coal slime acquires the binder properties to assist in filling the gaps between coal particles, thereby reducing the amount of cement used.

2. The mechanically activated coal slime-coal particle grouting and filling material for residual coal re-mining according to claim 1, characterized in that, The mechanical activation process of high-ash coal slime is as follows: the high-ash coal slime is vacuum dried, then milled using a ball mill to control the particle size to 3 micrometers to 6 micrometers, and finally mechanically activated for 2 to 8 hours to destroy the crystal lattice in the high-ash coal slime and generate cementing properties.

3. The mechanically activated coal slime-coal particle grouting and filling material for residual coal re-mining according to claim 1, characterized in that: The coal particles are obtained by cutting raw coal with a coal mining machine, crushing it with a jaw crusher, and screening it with a 10mm aperture vibrating screen. The particle size of the coal particles is 2.5mm~10mm. The particle size distribution is 40% for 2.5-5mm and 60% for 5-10mm, which are used as aggregates to improve the compactness and mechanical strength of the filling body.

4. The mechanically activated coal slime-coal particle grouting and filling material for residual coal re-mining according to claim 1, characterized in that: The cement type is PO42.

5.

5. A method for preparing the mechanically activated coal slime-coal particle grouting and backfilling material for residual coal remining as described in claim 1, characterized in that, The steps are as follows: A crusher and a screening machine are used to crush and screen the washed raw coal to obtain coal particles that can be used as aggregate for grouting materials, and the diameter of the coal particles is controlled to be 2.5mm~10mm. High-ash coal slime is vacuum dried to a moisture content of 3% to 5%, and then mechanically activated. A cementing material is obtained by thoroughly mixing 10%-50% high-ash coal slime, 5%-40% mechanically activated high-ash coal slime, 10%-20% cement, and 20%-30% coal particles by mass ratio. The cementing material is mixed with water at a concentration of 65%-74% to obtain a mechanically activated coal slime-coal particle grouting filling material for residual coal remining.

6. The mechanically activated coal slime-coal particle grouting and filling material for residual coal re-mining according to claim 5, characterized in that, The mechanical activation process is as follows: high-ash coal slime is vacuum dried for 6 hours to control the moisture content of the high-ash coal slime at 3%-5%. A planetary ball mill is used to make the particle size of the high-ash coal slime reach 3-6 micrometers, which destroys the clay lattice and activates the cementing properties. By mechanically activating the high-ash coal slime to fill the gaps between coal particles and assist in cementing, the amount of cement used is reduced by 30%-40% compared with traditional coal gangue-cement filling materials, and the bonding strength between the filling body and the residual coal is ≥2.5MPa.

7. The mechanically activated coal slime-coal particle grouting and filling material for residual coal re-mining according to claim 6, characterized in that, The mechanical activation process is as follows: the planetary ball mill rotates at 400 r / min, using zirconia grinding balls with a particle size of 7 mm: 5 mm: 3 mm = 3: 3: 4 and a ball-to-material ratio of 3: 1, and grinding for 2-8 hours.

8. An application of the mechanically activated coal slime-coal particle grouting and backfilling material for residual coal remining as described in claim 1, characterized in that, The steps for remining residual coal in room-and-pillar goaf areas are as follows: Grouting holes are constructed around the coal pillar, with the hole diameter and depth extending to the center of the coal pillar. Molds are custom-made to match the cross-section of the coal pillar. The grout is pumped into the gap of the coal pillar along the grouting hole. At the same time, the mold is placed around the coal pillar and fixed to ensure that the grout fills the gap. During the grouting process, the grouting pressure is checked at intervals to avoid the coal pillar from cracking due to a sudden increase in pressure. After grouting is completed, the filling material is cured and the mold is removed until the filling material is completely solidified. At this point, the filling material and the coal pillar form a whole, and the coal mining machine can be used to cut it according to the conventional raw coal mining process.

9. An application of the mechanically activated coal slime-coal particle grouting and backfilling material for residual coal remining as described in claim 1, characterized in that, The steps for remining residual coal in broken zones are as follows: Brick isolation walls were constructed on both sides of the fracture zone, and cement mortar was used to seal the surface. Grouting ports were reserved on the isolation walls. Add 0.5% glass fiber by mass to the grouting material and stir it with a high-speed disperser to make the glass fiber evenly dispersed; use a grouting pump to pump the modified grouting material into the crushing zone along the grouting port until the grout flows out from the overflow hole, and then stop grouting. Curing is carried out until the compressive strength of the filling body is ≥3MPa, the fractured zone forms a stable structure, and mining is carried out using a fully mechanized mining support in conjunction with a coal mining machine.

10. An application of the mechanically activated coal slime-coal particle grouting and backfilling material for residual coal remining as described in claim 1, characterized in that, The steps for remining residual coal at the edges and corners are as follows: Small, mobile grouting equipment is selected to suit narrow working spaces in corner areas; Along the edge of the residual coal, divide the grouting area into 2m sections. Construct two grouting holes in each section. First, pump in the grouting material until the current section is filled. After curing, proceed with the grouting of the next section to gradually form a protective layer of the filling body. After all the grouting in the sections is completed and cured, the residual coal areas at the edges and corners will form a continuous mineable face, which will then be mined along the strike using a small coal mining machine.

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