Low-carbon preparation method of coal mine underground filling material

Abstract

The invention discloses a low-carbon preparation method of an underground coal mine filling material, which comprises the following steps: firstly preparing carbon sequestration precursor mineralized water, premixing the carbon sequestration precursor mineralized water with cement and fly ash, and compounding coal gangue aggregate; cO2 reacts with calcium and magnesium active components to generate calcium carbonate, a compact mineralized coating is formed on the surfaces of particles, and the structural compactness is improved; and the cement mixing amount is dynamically adjusted based on strength increase, and low-carbon replacement is achieved. Through structural strengthening of the calcium carbonate coating and dynamic cement parameter adjustment, under the extreme condition that the cement consumption is reduced by 70%, it can still be guaranteed that the uniaxial compressive strength of the filling body within 7 days reaches 3.10 MPa (exceeding the underground safety standard 55%), meanwhile, 50-100 kg of CO2 is stored in each cubic meter of material in a solid mode, and the coal-based solid waste mixing amount is increased to 95.38%. The low-carbon preparation process provided by the invention provides an integrated innovation scheme of negative carbon, low cost and high solid waste utilization for the field of mine filling.

Description

Technical Field

[0001] The present invention belongs to the technical field of underground filling in mines, and particularly relates to a low-carbon preparation method for filling materials in coal mines. Background Art

[0002] In the field of mine exploitation, underground filling technology is the core means to ensure mining safety and control surface subsidence. However, the traditional filling material system has long relied on cement-based cementitious materials, resulting in high filling costs and serious environmental burdens. According to statistics, the average price of ordinary Portland cement in a certain mining area reached 500 yuan / ton in 2024, and the cement consumption in a single filling operation could reach the scale of thousands of tons, and the cost of cementitious materials alone exceeded 500,000 yuan. More seriously, as a key area of global carbon emissions in cement production, the decomposition of raw material carbonate and fuel combustion in the cement production process contribute 0.44 tons of CO2 / ton of CaCO3 decomposition and emission intensities of 2.66 - 2.72 tons of CO2 / ton of standard coal respectively. The global cement-related CO2 emissions in 2023 have accounted for 8% of the total emissions from human activities. It is estimated that when the global cement production increases to 5 billion tons in 2030, the annual emissions will exceed 3.8 billion tons.

[0003] On the other hand, there are significant imbalances in the field of industrial solid waste resource utilization. Taking fly ash as an example, China's output reached 899 million tons in 2023, accounting for more than 55% of the global total. However, the existing technology still limits its application to low-value-added scenarios. Although the upgrading of dust removal and desulfurization technologies in thermal power plants has improved the collection efficiency of fly ash, it has not simultaneously promoted its in-depth utilization in the high-value building materials field. At the same time, traditional filling materials generally adopt a simple compound system of sand and gravel aggregates and cement, and their early strength development is slow (the 3-day compressive strength is only 0.5 - 1.0 MPa), and the 7-day strength is also less than 2.0 MPa, which is difficult to meet the strict requirements of rapid load-bearing of the filling body in deep mining. To make up for the strength defect, the cement dosage is often forced to be increased in engineering practice, forming a vicious cycle of "high cost - high emission - low performance".

[0004] There are three major structural contradictions in the existing technology: First, the filling materials rely too much on the cementitious system, which not only pushes up the mining cost (the comprehensive filling cost reaches 300 - 500 yuan / m 3 ) but also increases the pressure of carbon emission reduction; second, although bulk solid wastes such as fly ash have pozzolanic activity, they have not been effectively activated, and there are key blockages in the resource recycling chain; third, it is difficult to synergistically optimize the mechanical properties of materials and construction efficiency, and the insufficient early strength directly threatens the safety of mines. These problems seriously restrict the process of green mine construction, and it is urgent to develop a new type of low-carbon filling material system to achieve a breakthrough balance between cost reduction, efficiency improvement and environmental friendliness. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a low-carbon preparation method for filling materials in coal mines, aiming to solve the technical problems such as high proportion of cement, high cost, low strength of underground filling materials, and low utilization rate of fly ash in the prior art.

[0006] The present invention is realized through the following technical solutions:

[0007] A low-carbon preparation method for filling materials in coal mines includes the following steps:

[0008] Step 1) In a closed and vacuum mineralization test device, put water into the mineralization reaction kettle, introduce CO2 for mineralization stirring, set the rotation speed of the mineralization reaction kettle, and obtain carbon sequestration precursor mineralized water after stirring.

[0009] Step 2) Put the carbon sequestration precursor mineralized water prepared in Step 1), cement, and fly ash into a stirring reaction kettle for stirring, and then add coal gangue for mixing and stirring to obtain a filling material sample.

[0010] Step 3) Use the filling material without CO2 introduced as the original control group, test the 7-day uniaxial compressive strength of the filling material sample prepared in Step 2), and compare it with the strength of the original control group; when the strength of the filling material sample is greater than that of the original control group, gradually reduce the cement dosage in Step 2) to reduce the strength of the filling material sample; when the strength of the filling material sample is less than that of the original control group, gradually reduce the CO2 introduction amount of the mineralization parameter in Step 1), gradually reduce the mineralization reaction stirring time in Step 1), and gradually extend the stirring time in Step 2) to improve the strength of the filling material sample.

[0011] Step 4) When the cement dosage is gradually reduced to a certain specific ratio, if the strength of the filling material sample is consistent with that of the original control group at this time, then this specific ratio of cement dosage ratio is the low-carbon preparation ratio. Repeat Step 1) and Step 2 according to this ratio to obtain the filling materials for coal mines.

[0012] Preferably, the amount of CO2 introduced in Step 1) is 1 - 3L, and the stirring time is 1 - 30min.

[0013] Preferably, the pH value of the carbon sequestration precursor mineralized water in Step 1) is 5.0 - 5.6.

[0014] Preferably, the stirring time in Step 2) is adjusted according to the pH value of the carbon sequestration precursor mineralized water. When the pH value of the carbon sequestration precursor mineralized water ≥ 5.4, the stirring time is 20 - 30min; when the pH value ≤ 5.2, the stirring time is 10 - 20min; when the pH value is between 5.2 - 5.4, the stirring time is 0 - 10min.

[0015] Preferably, the rotation speeds of the stirring in steps 1) and 2) are both 300 - 500 r / min.

[0016] Preferably, in step 3), gradually reducing the cement dosage in step 2) specifically means: reducing the cement dosage by 2% each time.

[0017] Preferably, in step 3), gradually reducing the CO2 input amount of the mineralization parameter in step 1) specifically means: reducing the input amount by 0.5 - 1 L each time; gradually reducing the stirring time of the mineralization reaction in step 1) specifically means: reducing the stirring time by 5 - 10 min each time; gradually extending the stirring time in step 2) specifically means: extending the stirring time by 5 - 10 min each time.

[0018] Preferably, the cement dosage ratio of the specific ratio in step 4) is a mass ratio, totaling 100 wt%, specifically as follows:

[0019] Mineralized water for carbon sequestration precursor: Cement: Fly ash: Coal gangue = 19:(4 - 12.5):(37.5 - 46):31.

[0020] The beneficial effects of the present invention are as follows:

[0021] (1) Compared with traditional filling materials, through the structural strengthening of the calcium carbonate coating and dynamic cement parameter adjustment in the present invention, the strength can be made equal to that of the control group while reducing the cementitious materials. On the premise of meeting the underground filling strength requirements, the consumption of cementitious materials is reduced by more than 70% (the mass ratio in the cementitious materials is at least 7.5%). At the same time, coal-based solid wastes such as fly ash and coal gangue are introduced as core components (the mass ratio of coal-based solid wastes in solid materials reaches 95.38%, and the mass ratio of fly ash in cementitious materials reaches 92.5%), significantly reducing the cost of cementitious materials by more than 50%. Combining with the CO2 mineralization and sequestration technology, for every 1 L of CO2 injected to prepare filling materials, carbon emission reduction and cement substitution can be achieved simultaneously (the cement consumption is reduced by 14%). The comprehensive cost of a single filling operation is reduced by 30% - 40% compared with the traditional scheme, and the carbon emission intensity in the whole life cycle is reduced by more than 50%, significantly reducing the material cost and the carbon emission in the whole life cycle.

[0022] (2) By activating the pozzolanic activity of fly ash and coupling with the CO2 co-mineralization reaction, the present invention realizes the high-value utilization of coal-based solid wastes (fly ash + coal gangue) in filling materials (the admixture exceeds 90%). Taking a coal mine with an annual output of tens of millions of tons as an example, adopting the technical scheme of the present invention can annually consume 300,000 to 500,000 tons of coal-based solid wastes, promoting the comprehensive utilization rate of mine solid wastes to more than 95%, completely solving the industry pain points of difficult stacking and slow consumption of coal-based solid wastes, and providing a technical closed-loop for building a "zero-emission" green mine.

[0023] (3) During the preparation of the filling material, through the CO2-directed mineralization reaction, the present invention permanently sequesters the industrially captured CO2 inside the filling body, forming a "negative carbon" effect. Combining with the indirect emission reduction brought about by a 70% reduction in cement consumption (0.89 - 1.22 tons of CO2 emissions reduced per ton of cement), the carbon footprint per unit filling volume is reduced by 60% - 80% compared with the traditional process under the dual paths, providing a quantifiable low-carbon transformation path for the mining industry.

[0024] (4) Compared with traditional solid filling and paste filling, while maintaining the 7-day compressive strength of the filling body at 1.5 - 2.0 MPa (meeting the underground safety standards), the present invention significantly improves the growth rate of the early strength of the material, significantly shortens the mining and filling connection cycle, and has the characteristics of high fluidity and short setting time. It can reach the required strength for filling in an extremely short time, thus flexibly adapting to various scenarios such as overburden isolation grouting and paste filling, breaking through the limitation of poor spatial adaptability of traditional solid filling.

[0025] (5) The present invention transforms coal-based solid waste from low-end landfill resources into high-value-added filling base materials, drives cross-industry collaboration among thermal power, coal, and building materials, forms an integrated industrial chain of "solid waste recycling - carbon capture and utilization - green mining", creates emerging growth points for the regional economy, and has significant economic and environmental benefits, being suitable for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a diagram of the uniaxial compressive strength results of the filling material sample prepared in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0028] Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art. The experimental methods without specific conditions indicated are all conventional methods in the art.

[0029] The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0030] A low-carbon preparation method for a coal mine underground filling material, the specific steps are as follows:

[0031] (1) In a closed and vacuum mineralization test device, take an appropriate amount of water and put it into the mineralization reaction kettle, introduce 1 - 3 L of CO2 for mineralization stirring for 1 - 30 min, set the rotation speed of the mineralization reaction kettle to 300 - 500 r / min, and obtain carbon sequestration precursor mineralized water (pH = 5.0 - 5.6) after stirring.

[0032] (2) Mix the carbon sequestration precursor mineralized water prepared above with cement and fly ash in a reaction kettle and stir. Then add coal gangue and mix and stir for 10 - 30 min. Set the rotation speed of the stirring reaction kettle at 300 - 500 r / min to obtain a filling material sample.

[0033] Adjust the stirring time according to the pH value of the carbon sequestration precursor mineralized water. When the pH value of the carbon sequestration precursor mineralized water ≥ 5.4, the stirring time is 20 - 30 min; when the pH value ≤ 5.2, the stirring time is 10 - 20 min; when the pH value is between 5.2 - 5.4, the stirring time is 0 - 10 min.

[0034] (3) Use the filling material without CO2 injection as the original control group. Test the 7-day uniaxial compressive strength of the filling material sample prepared above, compare it with the strength of the original control group, and adjust the parameters in the following way:

[0035] When the strength of the filling material sample is greater than that of the original control group, gradually reduce the cement dosage in step (2) (the reduction amplitude each time is 2%) to reduce the strength of the filling material sample.

[0036] When the strength of the filling material sample is less than that of the original control group, increase the strength of the filling material sample by gradually reducing the CO2 injection amount of the mineralization parameter in step (1) (the reduction amplitude each time is 0.5 - 1 L), gradually reducing the mineralization reaction stirring time in step (1) (the reduction amplitude each time is 5 - 10 min), and gradually extending the stirring time in step (2) (the increase amplitude each time is 5 - 10 min).

[0037] (4) When the cement dosage is gradually reduced to a certain specific ratio, if the strength of the filling material sample is consistent with that of the original control group at this time, then this specific ratio of cement dosage is the low-carbon preparation ratio. Repeat steps (1) - (2) according to this ratio to prepare the coal mine underground filling material.

[0038] Example 1

[0039] A low-carbon preparation method for a coal mine underground filling material, the specific steps are as follows:

[0040] (1) Weigh 19 parts of water by weight and pour it into a reaction kettle. Assemble the mineralization reaction kettle to make it airtight, and then place the reaction kettle in a vacuum state. Keep the ambient temperature at 15 - 25 °C, and respectively introduce 1 L, 2 L, and 3 L of CO2, and start stirring and mineralizing at a rate of 500 r / min for 10 min. Respectively obtain carbon sequestration precursor mineralized water (both are 19 parts) with pH values of 5.4, 5.1, and 5.0.

[0041] (2) Weigh 12.5 parts of cement and 37.5 parts of fly ash dry materials by weight, mix them evenly and put them into a stirring reaction kettle. Then, add the carbon sequestration precursor mineralized water with pH values of 5.4, 5.1, and 5.0 prepared in step (1) (all 19 parts) respectively, and mix and stir at a rate of 500 r / min for 10 min. Then, weigh 31 parts of coal gangue by weight, mix it evenly with the above slurry, put it into a stirring reaction kettle, and mix and stir at a rate of 500 r / min for 10 min to obtain the product.

[0042] Using the filling material prepared by the traditional preparation method (i.e., using water to replace the carbon sequestration precursor mineralized water, with the same dosages of other raw materials and preparation parameters) as the original control group, its uniaxial compressive strength at 7 days is only 5.80 MPa, while the uniaxial compressive strengths of the filling materials prepared in this example at 7 days are 8.21 MPa (pH = 5.4), 8.13 MPa (pH = 5.1), and 7.82 MPa (pH = 5.0) respectively, which is increased by 34.8% - 41.6% compared with the original control group.

[0043] Comparative Example 1

[0044] Adopt the traditional preparation method to directly prepare the filling material by wet mineralization. The specific steps are as follows:

[0045] Weigh 9.5 parts of cement, 28.6 parts of fly ash, and 14.3 parts of water by weight, pour them into the reaction kettle. Assemble the mineralization reaction kettle to make it airtight, then put the reaction kettle in a vacuum state, keep the environmental temperature at 15 - 25 °C, introduce 1 L and 2 L of CO2 respectively, start stirring and mineralizing at a rate of 500 r / min for 10 min; then weigh 47.6 parts of coal gangue by weight, mix it evenly with the above slurry, put it into a stirring reaction kettle, and mix and stir at a rate of 500 r / min for 10 min to obtain the product.

[0046] Using the filling material prepared by the traditional non - mineralization preparation method (i.e., directly mixing water, cement, fly ash, and coal gangue and then stirring) as the original control group, its uniaxial compressive strength at 7 days is 4.75 MPa. The uniaxial compressive strengths of the filling materials prepared by the above direct wet mineralization at 7 days are 5.45 MPa and 4.27 MPa respectively. Compared with the original control group, the strength of the filling material only increases by 14.7% under the injection amount of 1 L of CO2, while the strength of the filling material even decreases by 10.1% under the injection amount of 2 L of CO2.

[0047] Comparative Example 2

[0048] Adopt the traditional preparation method to directly prepare the filling material by wet mineralization. The specific steps are as follows:

[0049] Weigh 19.2 parts of cement, 57.8 parts of fly ash and 23 parts of water by weight, and pour them into the reaction kettle. Assemble the mineralization reaction kettle to make it airtight, and then put the reaction kettle in a vacuum state. Keep the ambient temperature at 15 - 25 °C, and introduce 1L and 2L of CO₂ respectively. Start stirring for mineralization at a rate of 500 r / min for 10 min to obtain the product.

[0050] Take the filling material prepared by the traditional non - mineralization preparation method (i.e., directly mixing water, cement and fly ash and then stirring) as the original control group. Its uniaxial compressive strength at 7 days is 8.98 MPa. The uniaxial compressive strengths of the filling materials prepared by the above direct wet - method mineralization at 7 days are 6.86 MPa and 6.44 MPa respectively. Compared with the original control group, the strength of the filling material decreases by 23.6% under the injection amount of 1L of CO₂, and the strength of the filling material decreases by 28.3% under the injection amount of 2L of CO₂.

[0051] Example 2

[0052] A low - carbon preparation method for a coal mine underground filling material, the specific steps are as follows:

[0053] (1) Weigh 19 parts of water by weight and pour it into the reaction kettle. Assemble the mineralization reaction kettle to make it airtight, and then put the reaction kettle in a vacuum state. Keep the ambient temperature at 15 - 25 °C, introduce 1L of CO₂, and start stirring for mineralization at a rate of 500 r / min for 10 min. Obtain the carbon sequestration precursor mineralized water (19 parts) with a pH value of 5.4.

[0054] (2) Weigh 4 - 12.5 parts of cement and 37.5 - 46 parts of fly ash by weight respectively. Mix the dry materials evenly and put them into the stirring reaction kettle. Then add the carbon sequestration precursor mineralized water (19 parts) with a pH value of 5.4 prepared in step (1) and mix and stir at a rate of 500 r / min for 10 min. Then weigh 31 parts of coal gangue by weight, mix it evenly with the above slurry and put it into the stirring reaction kettle, and mix and stir at a rate of 500 r / min for 10 min to prepare the filling material samples S1 - S5. At the same time, take the filling material without CO₂ injection as the original control group. The specific dosage and parameters are shown in Table 1 below.

[0055] Table 1 Low - carbon preparation experimental parameters

[0056]

[0057]

[0058] The statistical situation of the uniaxial compressive strength of the finally prepared filling material samples under the conditions of curing for 3 days and 7 days is as Figure 1 and Table 2 show.

[0059] Table 2 Uniaxial Compressive Strength after 3-day and 7-day Curing

[0060]

[0061] From Figure 1 and Table 2, it can be seen that the low-carbon preparation process of the present invention has significant advantages compared with the prior art (original control group). At the same time, referring to the experimental data of Comparative Examples 1 and 2, the specific analysis is as follows:

[0062] 1. The cement dosage is significantly reduced, and the cost and carbon emissions are reduced synchronously

[0063] (1) The breakthrough improvement of the cement replacement rate

[0064] The prior art (original control group) needs to use 0.6 kg of cement per unit material (accounting for 25% of the mass of the cementitious material). Under the premise of ensuring the 7-day strength meets the standard, the cement dosage of the present invention is significantly reduced. For example, in Group S1 (cement dosage 0.54 kg), the cement dosage is reduced by 10%, and the 7-day strength is 7.70 MPa, which is 6.9% higher than that of the original control group; in Group S4 (cement dosage 0.3 kg), the cement dosage is reduced by 50%, and the 7-day strength still reaches 4.10 MPa, which is more than twice the underground safety standard (1.5 - 2.0 MPa); in Group S5 (cement dosage 0.18 kg), the cement dosage is reduced by 70% (only accounting for 7.5% of the mass of the cementitious material), and the 7-day strength is 3.10 MPa, still meeting the underground requirements.

[0065] (2) The synergistic improvement of CO2 mineralization efficiency and strength

[0066] The 7-day strength of Group S1 (1L of CO2 injection) reaches 7.70 MPa, while that of Comparative Example 1 (traditional wet mineralization) only increases by 14.7%. It shows that the present invention optimizes the interfacial reaction between CO2 and fly ash / coal gangue through directional activation (10 min) in the mineralization reactor, avoiding the increase in porosity caused by excessive CO2 in traditional wet mineralization (for example, the strength decreased by 10.1% after 2L of CO2 injection in Comparative Example 1).

[0067] (3) Comprehensive benefits

[0068] Adopting the low-carbon preparation process of the present invention, the cement dosage can be reduced to a minimum of 30% of the original level, and the cost of the single-fill cementitious material is reduced by 40% - 60%.

[0069] 2. The dual synergistic effect of CO2 sequestration and solid waste consumption

[0070] (1) Innovation in the carbon emission reduction path

[0071] 1 L of CO2 was injected into all experimental groups (S1 - S5), and through the mineralization reaction, CO2 was permanently stored in the filling body, forming a "negative carbon" effect. Taking group S5 as an example, about 50 - 100 kg of CO2 was stored per cubic meter of material (converted based on the injection volume), and with the indirect emission reduction of 70% in cement reduction (0.89 - 1.22 tons of CO2 emissions per ton of cement production), the carbon footprint of the whole life cycle was reduced by more than 60%.

[0072] (2) High - volume resource utilization of coal - based solid waste (fly ash + coal gangue)

[0073] The dosage of coal - based solid waste in the original control group was 3.3 kg (coal - based solid waste accounted for 84.62% of the mass of solid materials, and fly ash accounted for 75% of the mass of cementitious materials). Through optimizing the ratio in the present invention, the dosage of coal - based solid waste in group S5 was increased to 3.72 kg (coal - based solid waste accounted for 95.38% of the mass of solid materials, and fly ash accounted for 92.5% of the mass of cementitious materials). The single - filling could consume 8.75% more coal - based solid waste. Calculated based on a coal mine with an annual output of ten million tons, the annual consumption of coal - based solid waste could be increased by 100,000 - 150,000 tons, and the comprehensive utilization rate was increased to more than 95%.

[0074] 3. Strength performance meets the requirements of underground engineering

[0075] (1) Improvement of 7 - day strength safety redundancy

[0076] The 7 - day uniaxial compressive strength of the existing technology (original control group) was 7.20 MPa, far exceeding the underground requirement of 1.5 - 2.0 MPa, with the problem of "over - design". Through precise regulation in the present invention, the safety redundancy was improved. For example, the 7 - day uniaxial compressive strength of group S3 (cement dosage reduced by 30% compared with the original control group) reached 4.65 MPa, which was 2.3 times of the underground standard, having both safety and economy; the 7 - day uniaxial compressive strength of group S5 (cement dosage reduced by 70% compared with the original control group) was 3.10 MPa, still maintaining 55% safety redundancy.

[0077] (2) Potential for optimizing early strength

[0078] The 3 - day uniaxial compressive strength of group S1 (cement dosage reduced by 10% compared with the original control group) was 3.05 MPa, close to that of the original control group (3.60 MPa), proving that through process optimization, the balance between early strength and cement reduction requirements can be achieved.

[0079] 4. Enhanced process compatibility and engineering adaptability

[0080] (1) Optimization of fluidity and pipeline transportation

[0081] All experimental groups (S1 - S5) maintained a stirring time of 20 min. However, due to the increased mass ratio of coal-based solid waste in the cementitious material (92.5%) and the CO2 micropore regulation effect, the fluidity of the filling material was significantly improved, pipeline wear was reduced, and it was more suitable for long-distance transportation scenarios.

[0082] (2) Flexible adaptation to multiple scenarios

[0083] The strength gradients of groups S3 - S5 (from 4.65 MPa to 3.10 MPa) cover different burial depths and ground pressure conditions, and can match the process requirements of various technologies such as overburden isolation grouting and paste filling.

[0084] 5. Technical defects of traditional wet mineralization and the principle of the present invention

[0085] In Comparative Example 1, the injection of 2 L of CO2 led to a 10.1% decrease in strength. Because the traditional process could not control the CO2 diffusion path, excessive CO2 generated loose carbonate crystals, weakening the cementitious structure. In Comparative Example 2, when there was no coal gangue, the CO2 mineralization reaction intensified the dispersion of fly ash particles, resulting in a decrease in the density of the material (a 28.3% decrease in strength). The present invention utilizes the reaction of carbon dioxide with calcium and magnesium active components to generate calcium carbonate and form a dense mineralized coating on the particle surface to make up for the strength loss after the reduction of cement. Its action mechanism is as follows: During the mineralization process, mineral deposition can fill the micropores, cracks or defects in the matrix, thereby making the structure of the material more dense. Mineralized materials usually form a multi-level structure, such as from nanocrystals to microfibers, and then to macroscopic layered structures. Each level of structure contributes to the strength of the material, thus effectively improving the overall structural density of the material.

[0086] In summary, through the structural strengthening of the calcium carbonate coating and dynamic cement parameter adjustment, the present invention can ensure that the uniaxial compressive strength of the filling body reaches 3.10 MPa at 7 days (exceeding the underground safety standard by 55%) under the extreme condition of a 70% reduction in cement consumption. At the same time, 50 - 100 kg of CO2 can be sequestered per cubic meter of material, and the mass proportion of coal-based solid waste in solid materials is increased to 95.38%. Compared with the prior art, the core advantages of the present invention are as follows: (1) Technical breakthrough: Through CO2-directed mineralization + solid waste synergistic activation, the present invention still maintains a 7-day strength of 3.10 MPa (exceeding the underground standard by 55%) under the condition of a 70% reduction in cement consumption. However, due to the rough process of traditional wet mineralization, excessive CO2 or single solid waste will lead to a significant decrease in strength (the maximum decrease is 28.3%). (2) Low-carbon economy: 50 - 100 kg of CO2 is sequestered per cubic meter of material, and indirect emissions reduction due to cement reduction is superimposed, resulting in a 60% - 80% reduction in the carbon footprint throughout the life cycle; the cost of the cementitious material is reduced by 40% - 60%, and the comprehensive utilization rate of fly ash / coal gangue is over 95%. (3) Engineering universality: By adjusting the cement dosage (0.18 - 0.6 kg) and CO2 mineralization parameters, different geological conditions (strength range 3.10 - 7.70 MPa) can be adapted, and at the same time, the fluidity is significantly improved, thereby reducing the equipment wear degree. The low-carbon preparation process of the present invention provides an integrated solution of "negative carbon - low cost - high solid waste utilization" for the mine filling field, and can promote the green transformation of the thermal power - coal - building materials industrial chain.

[0087] The embodiments described above are only a part of the embodiments of the present invention, rather than all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the present invention claimed, but only represents the selected embodiments of the present invention. The protection scope of the present invention shall be subject to the scope claimed in the claims. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A low-carbon preparation method for a filling material in coal mines, characterized in that, It includes the following steps: Step 1) In a closed and vacuum mineralization test device, put water into the mineralization reactor, introduce CO2 for mineralization stirring, set the rotation speed of the mineralization reactor, and obtain carbon sequestration precursor mineralized water after stirring; Step 2) Put the carbon sequestration precursor mineralized water prepared in Step 1), cement, and fly ash into a stirring reactor for stirring, and then add coal gangue for mixing and stirring to obtain a filling material sample; Step 3) Take the filling material without CO2 introduction as the original control group, test the uniaxial compressive strength of the filling material sample prepared in Step 2), and compare it with the strength of the original control group; when the strength of the filling material sample is greater than that of the original control group, gradually reduce the cement dosage in Step 2) to reduce the strength of the filling material sample; when the strength of the filling material sample is less than that of the original control group, gradually reduce the CO2 introduction amount of the mineralization parameter in Step 1), gradually reduce the mineralization reaction stirring time in Step 1), and gradually extend the stirring time in Step 2) to improve the strength of the filling material sample; Step 4) When the cement dosage is gradually reduced to a certain specific ratio, if the strength of the filling material sample is consistent with that of the original control group at this time, then the cement dosage ratio of this specific ratio is the low-carbon preparation ratio. Repeat Step 1) and Step 2 according to this ratio to prepare the coal mine underground filling material.

2. The low-carbon preparation method of a coal mine underground filling material according to claim 1, characterized in that, In Step 1), the amount of CO2 introduced is 1 - 3 L, and the stirring time is 1 - 30 min.

3. A low-carbon preparation method of a filling material for underground coal mines according to claim 1, characterized in that, In Step 1), the pH value of the carbon sequestration precursor mineralized water is 5.0 - 5.

6.

4. A low-carbon preparation method of a filling material for coal mines underground according to claim 3, characterized in that, In Step 2), the stirring time is adjusted according to the pH value of the carbon sequestration precursor mineralized water. When the pH value of the carbon sequestration precursor mineralized water ≥ 5.4, the stirring time is 20 - 30 min; when the pH value ≤ 5.2, the stirring time is 10 - 20 min; when the pH value is between 5.2 - 5.4, the stirring time is 0 - 10 min.

5. A low-carbon preparation method of a filling material for underground coal mines according to claim 1, characterized in that, The stirring rotation speeds in Step 1) and Step 2) are both 300 - 500 r / min.

6. The low-carbon preparation method of a filling material for underground coal mines according to claim 1, characterized in that In Step 3), gradually reducing the cement dosage in Step 2) specifically means: reducing the cement dosage by 2% each time.

7. A low-carbon preparation method of a filling material for underground coal mines according to claim 1, characterized in that, In Step 3), gradually reducing the CO2 introduction amount of the mineralization parameter in Step 1) specifically means: reducing the introduction amount by 0.5 - 1 L each time; gradually reducing the mineralization reaction stirring time in Step 1) specifically means: reducing the stirring time by 5 - 10 min each time; gradually extending the stirring time in Step 2) specifically means: extending the stirring time by 5 - 10 min each time.

8. According to the low-carbon preparation method of a coal mine underground filling material described in claim 1, characterized in that In Step 4), the cement dosage ratio of the specific ratio is a mass ratio, totaling 100 wt%, specifically as follows: Carbon sequestration precursor mineralized water: Cement: Fly ash: Coal gangue = 19:(4 - 12.5):(37.5 - 46):31.

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