A solid waste filling method

Abstract

The present application relates to a kind of full solid waste paste slow-release mineralization filling method, comprising: the gaseous carbon dioxide captured in industrial emission source is stored in the storage tank in the filling station industrial site, while polyvinyl alcohol film coiled material is stored in filling station warehouse, gaseous carbon dioxide is encapsulated with polyvinyl alcohol film coiled material to obtain soluble carbon dioxide capsule;Mine solid waste aggregate is mixed with solid waste base cementitious material to prepare full solid waste paste slurry, and soluble carbon dioxide capsule is mixed into full solid waste paste slurry;Full solid waste paste slurry mixed with soluble carbon dioxide capsule is transported from surface filling station pipeline into underground stope;The carbon dioxide capsule in it is dissolved and releases carbon dioxide after filling into stope, so that the purpose of mineralization carbon fixation is realized.The present application makes carbon dioxide controllable slow-release, makes it and cementitious material hydration product occur persistent and thorough mineralization reaction, and reaches excellent carbon fixation effect.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide capture, utilization and storage technology, and specifically relates to a method for slow-release mineralization backfilling of solid waste paste. Background Technology

[0002] Carbon dioxide emissions are exacerbating global warming, leading to extreme weather events, ecosystem imbalances, and resource competition. Large-scale solid waste storage poses risks such as significant land occupation and dam collapses. Metal ore paste backfilling technology offers a new technological pathway for the co-processing of carbon dioxide and mine solid waste. Existing technologies typically involve using underground spaces formed by backfill or surrounding rock as reservoirs to introduce carbon dioxide for storage and isolation, or introducing carbon dioxide to mineralize and mix the backfill slurry. However, the former method carries leakage risks, while the latter has low storage efficiency. Therefore, existing technologies do not fully utilize the chemical carbon sequestration potential of backfill slurries. Although some mines are exploring carbon sequestration, these are mostly large-space open-type storage methods, which not only fail to meet the basic requirement of backfill supporting the surrounding rock but also pose a significant leakage risk. Summary of the Invention

[0003] In order to overcome the above-mentioned problems in the prior art, the present invention provides a method for slow-release mineralization backfilling of solid waste paste, which is used to solve the above-mentioned problems in the prior art.

[0004] A method for slow-release mineralization backfilling of solid waste paste, the method comprising:

[0005] H1. Gaseous carbon dioxide captured from industrial emission sources is stored in storage tanks located at the industrial site of the filling station, while polyvinyl alcohol membrane rolls are stored in the filling station warehouse. The gaseous carbon dioxide and polyvinyl alcohol membrane rolls are encapsulated to obtain soluble carbon dioxide capsules.

[0006] H2. Prepare a solid waste paste slurry by mixing mine solid waste aggregate with solid waste-based cementitious materials, and simultaneously mix soluble carbon dioxide capsules into the solid waste paste slurry;

[0007] H3. The solid waste paste slurry mixed with soluble carbon dioxide capsules is transported from the surface backfilling station pipeline into the underground mining area;

[0008] H4. After the carbon dioxide capsules mixed into the solid waste paste slurry are filled into the mining area, the polyvinyl alcohol film of the carbon dioxide capsules dissolves and releases carbon dioxide, thus achieving the purpose of mineralization and carbon fixation.

[0009] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the industrial emission source in step H1 is a power plant, smelter, or cement plant, and the storage tank is a double-walled steel carbon dioxide storage tank, with a vacuum drawn between the inner and outer tanks and filled with insulating material.

[0010] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the storage tank in step H1 converts low-temperature, high-pressure liquid carbon dioxide into room-temperature, low-pressure gaseous carbon dioxide, wherein the room temperature is approximately 25°C and the low pressure is 0.05 MPa.

[0011] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the polyvinyl alcohol is an NT-type polyvinyl alcohol.

[0012] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the soluble carbon dioxide capsule is rectangular in shape, with a side length and thickness of less than or equal to 2 cm, and the internal pressure of carbon dioxide inside the capsule is approximately 0.005-0.001 MPa.

[0013] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the solid waste-based cementitious material is a silicate cementitious material made from slag or fly ash solid waste with added pozzolanic activity or hydraulic properties.

[0014] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein step H2 specifically includes: H21. feeding the mine solid waste aggregate and solid waste-based cementitious material together into a first-stage paddle mixer, and achieving forced mixing of the materials in the paddle mixer to prepare a whole solid waste paste slurry;

[0015] H22. The solid waste paste slurry is discharged from the first stage paddle mixer and then enters the second stage ribbon mixer. At the same time, soluble carbon dioxide capsules are added into the second stage ribbon mixer via a conveyor belt. The solid waste paste slurry mixed with carbon dioxide capsules is discharged in an overflow manner.

[0016] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the paddle mixer is a single-shaft or twin-shaft horizontal paddle mixer with a rotational speed of 40-50 rpm.

[0017] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the two-stage ribbon mixer is a twin-shaft horizontal ribbon mixer with a rotation speed of 20-30 rpm.

[0018] In addition to the aspects and any possible implementations described above, a further implementation is provided in which a sealing layer and an isolation layer are provided at the stope height in H3, the sealing layer is filled with a paste slurry mixed with soluble carbon dioxide capsules, and the isolation layer is filled with a paste slurry without soluble carbon dioxide capsules.

[0019] Beneficial effects of the present invention

[0020] The present invention provides a method for slow-release mineralization backfilling of solid waste paste, comprising: storing gaseous carbon dioxide captured from industrial emission sources in storage tanks located at the industrial site of the backfilling station, while storing polyvinyl alcohol membrane rolls in the backfilling station warehouse; encapsulating the gaseous carbon dioxide and polyvinyl alcohol membrane rolls to obtain soluble carbon dioxide capsules; preparing a solid waste paste slurry by mixing mining solid waste aggregates and solid waste-based cementitious materials, while simultaneously mixing the soluble carbon dioxide capsules into the solid waste paste slurry; and preparing the solid waste paste slurry containing the soluble carbon dioxide capsules. The carbon dioxide capsules, mixed with the solid waste paste slurry, are transported from the surface backfilling station into the underground mining area. Upon entering the mining area, the polyvinyl alcohol film of the capsules dissolves, releasing carbon dioxide. This released carbon dioxide is temporarily sealed in the cavity formed after the capsules rupture, and comes into direct contact with the surrounding solid waste slurry. The calcium and magnesium ions leached from the solid waste particles of the paste backfill material, as well as the hydration products of the cementitious materials, can undergo a mineralization reaction with the carbonate ions produced after the carbon dioxide dissolves in water, generating stable... Carbonate precipitation permanently seals carbon dioxide. Therefore, this invention, through the controlled and slow release of carbon dioxide, allows it to undergo a sustained and thorough mineralization reaction with the solid waste paste slurry within the cavity formed after capsule rupture, achieving excellent carbon fixation. Furthermore, the solid waste paste slurry has high yield stress and viscosity, and its coarse and fine aggregate skeleton is tightly connected, ensuring uniform distribution of carbon dioxide capsules within the filling body's sealing layer. The added filling sealing layer further guarantees that even if carbon dioxide mineralization is insufficient in individual capsules, the risk of carbon dioxide leakage is limited and controllable. In addition, the carbon dioxide capsule mixing process is highly adaptable. Without altering the existing solid waste paste filling system, only the addition of gas storage, packaging, and transportation equipment is needed to upgrade the traditional filling process to a mineralization filling process. Ultimately, this achieves "waste synergy" between carbon dioxide and mine solid waste, "facility synergy" between the existing filling system and carbon dioxide capsule preparation equipment, and "process synergy" between the slow release of carbon dioxide and the continuous hydration reaction, providing a safe, stable, and economical solution for underground mine negative carbon filling mining. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process flow for slow-release mineralization backfilling of solid waste paste;

[0022] Figure 2 This is a schematic diagram of the key processes in the preparation and transportation of solid waste paste mixed with carbon dioxide capsules.

[0023] Among them: (A) the process of mixing carbon dioxide capsules; (B) the process of pumping slurry plungers; (C) the process of pipeline transportation of solid waste paste mixed with carbon dioxide capsules;

[0024] Figure 3 This is a schematic diagram illustrating the principle of carbon dioxide capsule sustained-release mineralization filling.

[0025] Among them: (A) the reaction system before carbon dioxide capsule dissolution and mineralization; (B) the reaction system after carbon dioxide capsule dissolution and mineralization. Detailed Implementation

[0026] To better understand the technical solution of this invention, the content of this invention includes, but is not limited to, the specific embodiments described below. Similar technologies and methods should be considered within the scope of protection of this invention. To make the technical problems to be solved, the technical solutions, and advantages of this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments.

[0027] It should be understood that the embodiments described in this invention are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0028] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0029] This invention discloses a method for slow-release mineralization backfilling of solid waste paste, the method comprising:

[0030] H1. Gaseous carbon dioxide captured from industrial emission sources is stored in storage tanks located at the industrial site of the filling station, while polyvinyl alcohol membrane rolls are stored in the filling station warehouse. The gaseous carbon dioxide and polyvinyl alcohol membrane rolls are encapsulated to obtain soluble carbon dioxide capsules.

[0031] H2. Prepare a solid waste paste slurry by mixing mine solid waste aggregate with solid waste-based cementitious materials, and simultaneously mix soluble carbon dioxide capsules into the solid waste paste slurry;

[0032] H3. The solid waste paste slurry mixed with soluble carbon dioxide capsules is transported from the surface backfilling station pipeline into the underground mining area;

[0033] H4. After the carbon dioxide capsules mixed into the solid waste paste slurry are filled into the mining area, the polyvinyl alcohol film of the carbon dioxide capsules dissolves and releases carbon dioxide, thus achieving the purpose of mineralization and carbon fixation.

[0034] Specifically, such as Figure 1 As shown, the process of the present invention is as follows:

[0035] S1, Soluble carbon dioxide capsule packaging:

[0036] Carbon dioxide captured from industrial emission sources such as power plants, smelters, and cement plants using chemical absorption methods is temporarily stored in tanks located at the filling station industrial site via tank truck transportation. The tanks are equipped with vaporizers, multi-stage pressure reducing valves, and pressure stabilizing devices to convert low-temperature, high-pressure liquid carbon dioxide into room-temperature, low-pressure gaseous carbon dioxide. Simultaneously, cold-melting polyvinyl alcohol film rolls produced by chemical enterprises using methods such as solution casting are temporarily stored in the filling station warehouse via truck transportation. During the sealing operation, gaseous carbon dioxide and the film rolls are fed into an integrated gas filling and sealing machine. After the film rolls are cut and shaped, gas is injected and injected, and then heated and sealed, soluble carbon dioxide capsules are finally produced. The vaporizers, multi-stage pressure reducing valves, and pressure stabilizing devices used in the above process are all existing equipment, and the specific usage process will not be described in detail in this invention.

[0037] In step S1, the room temperature and low pressure refer to the gaseous carbon dioxide meeting the temperature and pressure requirements when using polyvinyl alcohol film material for encapsulation. In actual operation, the temperature should be adjusted to around 25°C and the pressure to around 0.05MPa depending on the on-site effect.

[0038] The cold-soluble polyvinyl alcohol film in step S1 is an NT-type polyvinyl alcohol that can dissolve in the filling slurry at room temperature. In addition, in order to avoid it dissolving too quickly in the filling slurry and losing its carbon dioxide slow-release ability, the degree of alcoholysis of the polyvinyl alcohol film should not be too high. It should be adjusted to below 70% based on the field effect. At the same time, the thickness of the polyvinyl alcohol film should not be too low. It should be adjusted to 150 micrometers or more based on the field effect.

[0039] The soluble carbon dioxide capsules in step S1 refer to the finished capsule particles before being mixed into the solid waste paste slurry. In order to maximize the efficiency of carbon dioxide sealing while ensuring the safety and stability of the filling system, the capsules are made into rectangular shapes, and their side length and thickness should not exceed 2 cm. At the same time, in order to avoid capsule rupture, the internal pressure of the carbon dioxide should not be too high. It is adjusted in the range of 0.0005-0.001 MPa according to the test results. In this invention, it is preferred to adjust it to around 0.001 MPa.

[0040] Preferably, the carbon dioxide capsules of the present invention are mixed into the solid waste paste slurry with the following requirements: the carbon dioxide capsule addition ratio is 5%-15% of the total volume of the solid waste slurry. When the content of calcium and magnesium compounds in the filling slurry raw materials is low, the mixing ratio of carbon dioxide capsules is also reduced accordingly. Conversely, when the content of calcium and magnesium compounds in the filling slurry raw materials is high, the mixing ratio of carbon dioxide capsules is also increased accordingly.

[0041] S2, Preparation of solid waste paste slurry and capsule mixing, such as Figure 1 , Figure 2As shown in (A), a feeding belt or screw feeder is installed, which is the pre-feeding stage of the mixing section. Coarse aggregate or large particles are transported into the mixer via belt, while fine particles are fed to the screw feeder. Through the quantitative feeding belt or screw feeder, the solid waste aggregates such as tailings thickened underflow, smelting slag, and tunneling waste rock, along with solid waste-based cementitious materials, enter the first-stage paddle mixer. The paddles beat and shear to achieve forced mixing of the materials, preparing a solid waste paste slurry. The high-concentration slurry itself has yield strength. The high strength and viscosity of the slurry allow the carbon dioxide capsules to be evenly distributed within the material without agglomeration. The solid waste paste slurry is discharged from the first-stage paddle mixer and then enters the second-stage ribbon mixer. At the same time, soluble carbon dioxide capsules are added to the second-stage ribbon mixer via a conveyor belt. The ribbon pushes and shears the capsules to achieve uniform mixing. To ensure the mixing effect, the solid waste paste slurry containing carbon dioxide capsules is finally discharged by overflow. Due to the high concentration of the slurry, the carbon dioxide capsules are suspended in the solid waste paste slurry.

[0042] S3, steady-state pumping and pipeline transportation of paste slurry, such as Figure 2 (B) and Figure 2 As shown in (C), the solid waste paste slurry mixed with carbon dioxide capsules enters the S-shaped plunger pump. The plunger pump hydraulically drives the pistons in the two cylinders to reciprocate alternately to realize the inlet and outlet of the paste slurry. One end of the S-shaped valve is connected to the outlet pipe, and the other end swings left and right to connect to the outlet cylinder, realizing the continuous delivery of slurry under different stroke states of the pump body. The paste slurry under the action of pump pressure is transported in the composite metal filling pipe at a certain flow rate. The carbon dioxide capsules mixed in the paste slurry are stably suspended in the skeleton structure composed of coarse and fine aggregates such as waste rock and smelting slag. At the same time, the shear slip layer of the paste slurry avoids the contact friction between the carbon dioxide capsules and the pipe wall. The friction force formed by the contact between the inner wall of the rigid metal filling pipe and the slurry containing free water is equivalent to the shear force. The shear force is the largest in the area near the inner wall of the pipe, which causes the solid particles to move towards the center of the pipe and form a slip layer on the inner side of the pipe wall. The existence of the slip layer reduces the direct contact between the solid particles and capsules in the slurry and the pipe, and the slip layer plays a barrier role.

[0043] S4. Underground mining area backfilling and sealing:

[0044] The solid waste paste slurry mixed with carbon dioxide capsules is transported from the surface backfilling station pipeline into the underground mining area. The vertical backfilling pipeline is laid in the backfilling borehole, the horizontal backfilling pipeline is laid in the horizontal roadway, and near the mining area, it is laid in the backfilling return air shaft. Backfilling operations can only be carried out after the mining area has undergone rock drilling, blasting, and shoveling. Except for the first mining area, subsequent mining is carried out under the protection of artificial pillars in the backfill body. In order to reduce the risk of carbon dioxide leakage from the solid waste paste slurry, a two-part backfill body is set up in the vertical height of the mining area, with an upper isolation layer and a lower sealing layer. The sealing layer accounts for 80% of the total height of the mining area. The solid waste paste slurry mixed with carbon dioxide capsules is used for backfilling at this 80% height, and the remaining 20% ​​height is filled with paste slurry without capsules. This 20% part serves as a capping layer, which can better seal carbon dioxide and prevent its leakage.

[0045] S5. Slow-release carbon dioxide mineralization reaction: As mentioned earlier, the paste slurry is made of cementing materials; therefore, calcium hydroxide and hydrated calcium silicate are present in the paste slurry. Simultaneously, calcium and magnesium ions are leached from the solid waste in the paste slurry, and the paste slurry also contains a large amount of water. Therefore, as... Figure 3As shown, in the sealing layer formed in S4, after the carbon dioxide capsules mixed with the paste slurry are filled into the stope, a long-term (e.g., 28 days or longer) hydration and consolidation reaction process occurs. The polyvinyl alcohol film of the carbon dioxide capsules gradually dissolves and slowly releases carbon dioxide. The released carbon dioxide is temporarily sealed in the cavity formed after the capsule ruptures, and comes into direct contact with the surrounding solid waste slurry. Subsequently, the carbon dioxide hydrolyzes in the alkaline aqueous solution system of the paste slurry to form carbonate ions, which react with calcium hydroxide, hydrated calcium silicate, etc., in the paste slurry to produce calcium carbonate and silica gel products. Simultaneously, the carbonate ions also react with calcium and magnesium ions leached from the paste slurry. This slow-release reaction process ensures that the release of carbon dioxide matches the hydration process of the paste slurry, achieving continuous and thorough mineralization and carbon fixation. In the storage layer, carbonate ions react with magnesium and aluminum ions to form carbonate precipitates, thus fixing carbon dioxide in the form of carbonates, i.e., sealing it. The sealing layer above the storage layer ensures that the storage layer does not come into contact with the atmosphere, thereby ensuring that over a long period of time, the polyvinyl alcohol film of the carbon dioxide capsules in the storage layer continuously dissolves and the carbon dioxide is continuously solidified. The carbon dioxide inside the undissolved carbon dioxide capsules still exists in gaseous form. The filling and sealing layer further ensures that even if the carbon dioxide in individual carbon dioxide capsules is not fully mineralized, the risk of carbon dioxide leakage is limited and controllable. Since these undissolved carbon dioxide capsules are placed in the paste slurry, compared with the existing filling method that uses large volumes of carbon dioxide, these undissolved carbon dioxide capsules contain carbon dioxide gas in relatively independent and unconnected capsules. Therefore, even if individual carbon dioxide capsules leak, there is no risk of large-scale carbon dioxide gas leakage.

[0046] This invention utilizes a solid waste paste-like filling slurry prepared from mineral processing tailings, smelting slag, tunneling waste rock, and solid waste-based cementitious materials. This effectively disposes of mine solid waste while controlling mining-induced ground pressure and improving mining efficiency. Furthermore, polyvinyl alcohol (PVA) exhibits excellent carbon dioxide barrier properties. By adjusting its degree of hydrolysis and thickness, its dissolution rate in water can be controlled, allowing carbon dioxide gas to be injected into the membrane material and slowly released into the filling slurry. This process ensures that carbon dioxide release matches the hydration process of the cementitious material, achieving a superior mineralization and carbon fixation effect. This method offers technical advantages such as sustained and thorough mineralization reaction, limited and controllable leakage risk, and excellent process adaptability. Through waste synergy, facility synergy, and process synergy, it provides a safe, stable, and economical solution for underground mine negative carbon filling mining.

[0047] The volume of the storage tank in step S1 is 50-100m³. 3 A large, cylindrical, double-walled steel carbon dioxide storage tank is erected, with a vacuum drawn between the inner and outer tanks and filled with insulating materials such as perlite.

[0048] The low temperature and high pressure in step S1 refers to the storage environment of liquid carbon dioxide, namely a storage temperature of -40°C and a storage pressure of 2.2 MPa. The subsequent capsule production requires a suitable temperature and pressure for the encapsulation operation. The temperature and pressure here are for reference only.

[0049] The room temperature and low pressure in step S1 refers to the requirements for the use of gaseous carbon dioxide, that is, to meet the temperature and pressure requirements when using polyvinyl alcohol film material for encapsulation. In actual operation, the temperature should be adjusted to around 25°C and the pressure to around 0.05MPa depending on the on-site effect.

[0050] The vaporizer, multi-stage pressure reducing valve, and pressure stabilizing device in step S1 refer to the devices required to convert low-temperature, high-pressure liquid carbon dioxide into room-temperature, low-pressure gaseous carbon dioxide. The core function of the vaporizer is to complete the phase change process of carbon dioxide by absorbing heat from the environment or external heat sources. Depending on the ambient temperature of the filling station, an air-cooled vaporizer or an electrically heated vaporizer can be selected. The function of the multi-stage pressure reducing valve is to reduce the pressure of the high-pressure gas step by step to the required pressure. The function of the pressure stabilizing device is to ensure that the outlet pressure is stable and is not affected by fluctuations in the upstream pressure or flow rate.

[0051] The cold-soluble polyvinyl alcohol (PVA) membrane in step S1 is an NT-type PVA that can dissolve in the filling slurry at room temperature. Furthermore, to avoid its rapid dissolution in the filling slurry and loss of its carbon dioxide slow-release capability, the degree of hydrolysis of the PVA membrane should not be too high. Adjustments are made based on field results, keeping the degree of hydrolysis below 70%. Here, "field results" refers to the membrane material needing a suitable dissolution rate in the slurry. The rate should not be too fast, leading to premature carbon dioxide release, nor too slow, releasing carbon dioxide only after the hydration reaction is complete. It must match the purpose of slow-release mineralization. Therefore, research in this invention has found that a degree of hydrolysis below 70% meets the requirements. Simultaneously, the thickness of the PVA membrane should not be too small; adjustments are made based on field results, keeping the thickness above 150 micrometers.

[0052] The soluble carbon dioxide capsules in step S1 refer to the finished capsule particles before being mixed into the solid waste paste slurry. In order to maximize the efficiency of carbon dioxide sealing while ensuring the safety and stability of the filling system, and to facilitate the cutting and heat sealing of the roll material, they are made into rectangular capsule particles with a side length and thickness not exceeding 2 cm. At the same time, in order to avoid capsule rupture, the internal pressure of the carbon dioxide should not be too high. According to the test results, it is within [0.0005, 0.001] MPa, preferably adjusted to around 0.001 MPa.

[0053] The thickened tailings underflow in step S2 is a high-concentration tailings slurry obtained by the mineral processing plant after the ore is finely ground and processed, and then thickened and dewatered by deep cone gravity. Its solid mass fraction is 60%-70%. Under normal circumstances, all the water in the solid waste paste slurry is provided by it.

[0054] The smelting waste slag in step S2 is water-quenched slag and other waste slag after ore smelting and processing in a smelter. After coarse grinding or fine grinding and secondary refining, the particle size of the smelting waste slag is about -5mm, that is, the particle size is less than or equal to 5mm.

[0055] The waste rock in step S2 refers to the product of jaw crushing and gyratory crushing of the outer rock of the vein during mining, with a particle size of about -16mm.

[0056] The solid waste-based cementitious material in step S2 is a silicate cementitious material containing slag, fly ash, or other solid wastes with added pozzolanic activity or hydraulic properties. Preferably, an alkaline activating material is also added. To achieve sufficient strength to support the surrounding rock, the backfill needs to contain cement, but cement is more expensive than slag and fly ash, and cement production generates a large amount of carbon dioxide. Therefore, for economic and carbon reduction purposes, slag and fly ash are used to replace part of the cement as an alkaline activating material.

[0057] The paddle mixer in step S2 refers to the horizontal paddle mixer used for the first mixing of solid waste paste slurry. Its purpose is to achieve forced mixing of dry and wet materials. The blades are arranged in an alternating pattern on the mixing shaft. Single shaft or double shaft can be selected according to site requirements. The mixing intensity of 40-50 rpm can be selected according to site requirements.

[0058] The two-stage ribbon mixer in step S2 is a horizontal ribbon mixer used for the second mixing of solid waste paste slurry and the incorporation of carbon dioxide for gelation. The purpose is to further achieve uniform mixing of the various materials. The ribbon is spirally arranged on the mixing shaft. This invention prefers to use dual-shaft mixing, with the shearing directions of the two shafts being opposite and the speed being 20-30 rpm, so that the slurry is pushed back in the feeding direction.

[0059] The S-shaped plunger pump in step S3 is a pumping device designed to meet the requirements of larger particle size solid waste aggregates and carbon dioxide capsules. The plunger pumping and the S-shaped valve swing switching method can minimize the number of ruptured carbon dioxide capsules and ensure continuous and stable process.

[0060] The skeleton structure in step S3 refers to the dynamic stable structure formed by the mutual contact and combination of coarse and fine aggregates. Under the influence of this structure, the low-density carbon dioxide capsules can exist uniformly in the filling pipe without floating, ensuring flow stability.

[0061] In step S3, the high-concentration slurry flows naturally within the pipeline, forming a shear slip layer that is very thin and close to the inner pipe wall. This is a shear-thinning rheological phenomenon that occurs when the paste slurry is subjected to high shear rates at the pipe wall. The shear slip layer has low viscosity and induces fine particles to aggregate here, reducing pipeline resistance while preventing the carbon dioxide capsule from rupturing due to contact friction with the pipe wall.

[0062] The backfilling operation in step S4 refers to a green and efficient mining process where, after the ore mining is completed and a goaf is created, a paste-like slurry prepared on the surface is transported into the goaf and allowed to solidify and harden to support the ore and control ground pressure. Before the slurry is filled, backfilling retaining walls need to be constructed and backfilling pipes need to be suspended in the stope. The area where the backfilling slurry is filled is only a part of the underground space, and this part needs to be separated from other spaces by retaining walls. The backfilling pipes are not placed on the ground, but are suspended at the top or side wall of the roadway. After the slurry is filled, compressed air flushing is required to prevent backfilling slurry residue from remaining in the pipes, which could cause blockages during subsequent backfilling.

[0063] The sealing layer and isolation layer in step S4 are a safety measure to prevent severe floating of carbon dioxide capsules. Under normal circumstances, the carbon dioxide capsules in the sealing layer need to overcome the yield stress of the slurry and the frictional resistance of the skeleton structure before floating, and then slowly float under the viscous resistance of the slurry. For solid waste paste slurry, the risk of severe floating and leakage of carbon dioxide capsules is relatively small, but an isolation layer is still needed to prevent such risks.

[0064] The polyvinyl alcohol film dissolution in step S5 refers to the physical swelling process that occurs when the hydrophobic acetate ions on the molecular chains of the polyvinyl alcohol film material disrupt the regularity of hydrogen bonds, making it easier for water molecules to permeate. In order to control the dissolution rate of the polyvinyl alcohol film and give full play to its function of slow-release carbon dioxide, it needs to be chemically treated so that hydroxyl groups replace part of the acetate ions.

[0065] The solid waste paste slurry of this invention has high yield stress, high viscosity, and tight aggregate bonding, which is beneficial for the stable incorporation of carbon dioxide capsules—this is a major feature. Simultaneously, the slow dissolution and release of carbon dioxide through the polyvinyl alcohol film for complete mineralization is another major feature of this invention. This invention utilizes these two features to achieve the mineralization and sequestration of carbon dioxide.

[0066] For deep well filling mining, if the filling pipeline system has high requirements for the slurry, the preparation of the solid waste paste slurry can be completed on the surface and pumped to the well for carbon dioxide capsule mixing, horizontal ribbon mixing and S-shaped plunger pumping.

[0067] The following description, in conjunction with specific embodiments, illustrates this point.

[0068] A metal mining company has an annual production capacity of 3 million tons and adopts the upward segmented backfill mining method. The stope is 10 meters high, 6 meters wide, and 50 meters long. It uses a full solid waste paste backfill technology to achieve resource utilization of tailings, waste rock, and smelting slag. Fly ash cementing material is used as the binder, the backfill slurry concentration is 80%, and the slurry pump flow rate is 100 m³ / h. 3 / h, after the slurry is filled into the goaf, it solidifies to form a filling body with a strength of 3MPa, which can be used as an artificial pillar and artificial floor for mining adjacent mining areas. The coal-fired power plant under the mining enterprise group is equipped with two 630 MW coal-fired generator units, with an annual carbon emission of 6.5 million tons. The carbon emission pressure is relatively large, and it is planned to use the amine method to capture and store carbon dioxide for filling and mineralization. The carbon dioxide will be temporarily stored in storage tanks located in the industrial site of the filling station by tank truck transportation. The vaporizer, multi-stage pressure reducing valve and pressure stabilizing device attached to the storage tank realizes the conversion of low temperature and high pressure (-40℃, 2.2MPa) liquid carbon dioxide to normal temperature and low pressure (25℃, 0.05MPa) gaseous carbon dioxide. At the same time, the chemical enterprise uses cold-soluble polyvinyl alcohol film rolls (NT type polyvinyl alcohol, degree of alcoholysis) produced by solution casting method. 65% (200 micrometers thick) is temporarily stored in the filling station warehouse by truck. During the sealing operation, gaseous carbon dioxide and the roll material enter the gas-filling sealing machine together. After the roll material is cut and shaped, gas is injected and heated to seal, a soluble carbon dioxide capsule with a length, width and height of 2 cm, 1.5 cm and 1.5 cm respectively is finally produced, with an internal pressure of 0.001 MPa. The 15% low-concentration tailings slurry from the ore dressing plant is flocculated and gravity settled to a 65% concentration underflow by a deep cone thickener. It is then pumped to the feeding port of a first-stage paddle mixer by a slurry pump. At the same time, the metallurgical... Slag and fly ash cementitious materials are conveyed to the feed inlet of a first-stage paddle mixer via a screw feeder. Excavated waste rock is conveyed to the feed inlet of the first-stage paddle mixer via a quantitative feeding belt. The first-stage paddle mixer is a twin-shaft horizontal mixer with a mixing speed of 45 rpm. Forced mixing of the materials is achieved through the impact and shearing action of the paddles, preparing a solid waste paste slurry. The solid waste paste slurry exits from the first-stage paddle mixer and enters the second-stage ribbon mixer. Simultaneously, soluble carbon dioxide capsules are added to the second-stage ribbon mixer via a conveyor belt. The second-stage ribbon mixer is also a twin-shaft horizontal mixer with a mixing speed of 25 rpm. The capsules are uniformly mixed through a spiral shearing process. To ensure effective mixing, the solid waste paste slurry containing the carbon dioxide capsules is finally discharged via overflow. The prepared and mixed paste slurry enters an S-shaped plunger pump. The plunger pump hydraulically drives the pistons in two cylinders to alternately reciprocate, achieving the inflow and outflow of the paste slurry. One end of the S-shaped valve is connected to the discharge pipe, and the other end swings left and right to connect to the discharge cylinder, enabling continuous slurry delivery under different pump stroke conditions. Under pump pressure, the paste slurry is transported at a certain flow rate in a double-layer welded steel filling pipe. The pumping pressure is 2MPa, and the flow rate is 100m³.3 / h, the carbon dioxide capsules mixed in the paste slurry are stably suspended in the skeleton structure composed of coarse and fine aggregates such as waste rock and smelting slag. At the same time, the shear slip layer of the paste slurry avoids contact friction between the carbon dioxide capsules and the pipe wall. The paste slurry is transported from the surface filling station pipeline into the underground mining area. The vertical section of the filling pipeline is laid in the filling borehole, the horizontal section of the filling pipeline is laid in the horizontal roadway, and when it is close to the mining area, it is laid in the filling return air shaft. The overall filling ratio is 4. The mining area is excavated. Backfilling operations can only be carried out after drilling, blasting, and shoveling out the ore. Except for the first mining area, subsequent mining operations are conducted under the protection of artificial pillars in the backfill body. Before backfilling, hollow brick retaining walls are constructed and reinforced with shotcrete. To reduce the risk of carbon dioxide leakage from the solid waste paste slurry, a two-part backfill body is set up at the mining height: a sealing layer and an isolation layer. The first 8 meters of the mining height are filled with paste slurry mixed with capsules, and the last 2 meters of the mining height are filled with paste slurry without capsules. After filling, the flushing water is discharged outside the stope. The carbon dioxide capsules mixed in the paste slurry, after being filled into the stope, undergo a long-term hydration and consolidation reaction of the cementitious material. The polyvinyl alcohol film gradually dissolves and slowly releases carbon dioxide. The carbon dioxide hydrolyzes in the alkaline aqueous solution system to form carbonate ions, which react with the main hydration products of the cementitious material, such as calcium hydroxide and calcium silicate, to produce calcium carbonate and silica gel. This process ensures that the release of carbon dioxide matches the hydration process of the cementitious material, achieving the purpose of continuous and thorough mineralization and carbon fixation. In addition, carbonate ions can also undergo slow mineralization reactions with some magnesium and aluminum compounds. The carbon dioxide mineralization reaction is complete after 28 days of consolidation of the filling body. After the filling body is exposed during mining in the adjacent stope, no carbon dioxide leakage is detected. The measured strength of the mineralized filling body is 2 MPa, which meets the safety requirements of upward segmented mining. The scanning electron microscope and X-ray diffraction results of the mineralized filling body show that the mineralization reaction is uniform and thorough.

[0069] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for slow-release mineralization backfilling of solid waste paste, characterized in that, The method includes: H1. Gaseous carbon dioxide captured from industrial emission sources is stored in storage tanks located at the industrial site of the filling station, while polyvinyl alcohol membrane rolls are stored in the filling station warehouse. The gaseous carbon dioxide and polyvinyl alcohol membrane rolls are encapsulated to obtain soluble carbon dioxide capsules. H2. Prepare a solid waste paste slurry by mixing mine solid waste aggregate with solid waste-based cementitious materials, and simultaneously mix soluble carbon dioxide capsules into the solid waste paste slurry; H3. The solid waste paste slurry mixed with soluble carbon dioxide capsules is transported from the surface backfilling station pipeline into the underground mining area; H4. After the carbon dioxide capsules mixed into the solid waste paste slurry are filled into the mining area, the polyvinyl alcohol film of the carbon dioxide capsules dissolves and releases carbon dioxide, thus achieving the purpose of mineralization and carbon fixation.

2. The method according to claim 1, characterized in that, The industrial emission sources in step H1 are power plants, smelters, or cement plants. The storage tank is a double-walled steel carbon dioxide storage tank with a vacuum between the inner and outer tanks and filled with heat-insulating material.

3. The method according to claim 1, characterized in that, In step H1, the storage tank converts low-temperature, high-pressure liquid carbon dioxide into room-temperature, low-pressure gaseous carbon dioxide, where the room temperature is 25°C and the low pressure is 0.05 MPa.

4. The method according to claim 1, characterized in that, The polyvinyl alcohol is NT-type polyvinyl alcohol.

5. The method according to claim 1, characterized in that, The soluble carbon dioxide capsule is rectangular in shape, with a side length and thickness of less than or equal to 2 cm, and the internal pressure of carbon dioxide inside the capsule is between 0.0005 and 0.001 MPa.

6. The method according to claim 1, characterized in that, The solid waste-based cementitious material is a silicate cementitious material made from slag or fly ash solid waste with added pozzolanic activity or hydraulic properties.

7. The method according to claim 1, characterized in that, Step H2 specifically includes: H21. The solid waste aggregate from the mine and the solid waste-based cementitious material are fed together into a paddle mixer to achieve forced mixing of the materials and prepare a solid waste paste slurry; H22. The solid waste paste slurry is discharged from the first stage paddle mixer and then enters the second stage ribbon mixer. At the same time, soluble carbon dioxide capsules are added into the second stage ribbon mixer via a conveyor belt and discharged in an overflow manner into the solid waste paste slurry mixed with carbon dioxide capsules.

8. The method according to claim 7, characterized in that, The aforementioned paddle mixer is a single-shaft or twin-shaft horizontal paddle mixer with a rotation speed of 40-50 rpm.

9. The method according to claim 7, characterized in that, The two-stage ribbon mixer is a twin-shaft horizontal ribbon mixer with a rotation speed of 20-30 rpm.

10. The method according to claim 1, characterized in that, In the H3, a sealing layer and an isolation layer are set at the stope height. The sealing layer is filled with a paste slurry mixed with soluble carbon dioxide capsules, and the isolation layer is filled with a paste slurry without soluble carbon dioxide capsules.

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