METHOD OF FILLING ABANDONED MINESHAFT AND CONCURRENTLY MINERALIZING AND SEQUESTERING CO2 USING SOLID WASTE SLURRIES

Description

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims the benefit and priority of Chinese Patent Application No. 202410957507X filed with the China National Intellectual Property Administration on Jul. 17, 2024, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.

TECHNICAL FIELD

The present disclosure belongs to the technical field of solid waste resource utilization for building materials in the field of resources and environment, and specifically relates to a method of filling an abandoned mineshaft and concurrently mineralizing and sequestering CO₂ using solid waste slurries.

BACKGROUND

Based on the data released by the Global Carbon Budget, global CO₂ emissions have reached 416×10⁸ tons (t) in 2024. Greenhouse gases such as CO₂ have caused a series of serious environmental problems such as global warming and glaciers melting. How to reduce the CO₂ emissions and reduce the impact of greenhouse effect has become a difficult problem that the world needs to face and solve together. The accumulation of industrial solid wastes such as fly ash produced by thermal power plants, desulfurized gypsum, and carbide slags produced by chemical plants in a large amount has caused serious pollution to the environment. There is an urgent need to solve the frequent accidents such as broken surrounding rock collapse, mining area collapse, and surrounding foundation subsidence in a process of coal mining. Grouting reinforcement materials are widely used in bridge subgrade reinforcement, waterproofing and plugging, and prevention of collapse in broken and loose surrounding rock areas, due to their advantages of high strength, excellent fluidity, and stable structure. Although the current materials such as a concrete could effectively absorb CO₂, since the concrete is used for building structures, it could not provide an enclosed space required for sequestering, and thus could not be used to sequester CO₂ gas.

“CO₂ sequestration grouting reinforcement material and construction method thereof” (Patent No.: CN109851309B), discloses subjecting a cement, a microsilica powder or a blast furnace slag powder or a fly ash, a water glass, alkyl phenyl polyoxyethylene ether, a water reducer, sodium dodecyl sulfate, and water to stirring and pulping, and then grouting quickly the grouting reinforcement material into surrounding rock to form a closed surrounding rock area; introducing CO₂ into divided surrounding rock areas and then plugging the divided surrounding rock areas. In this patent, a silica gel generated by a reaction of the water glass and high-concentration CO₂ is used to reinforce a bottom layer, and the silica gel is combined with a high-alumina activated cement material with rapid strength improvement in the later stage to reinforce the bottom layer. However, sequestering CO₂ underground has some safety problems such as gas leakage and secondary environmental pollution.

“Method of coal-based solid waste slurry filling synergistic mineralizing and sequestering CO₂” (Patent No.: CN115977724A) discloses a method of coal-based solid waste slurry filling synergistic mineralizing and sequestering CO₂. The method utilizes slurry filling technology to treat coal-based solid wastes in mining areas, while constructing a closed circle of the goaf area in a development area of overlying strata cracks in a goaf area. The method utilizes pump(s) to fill CO₂ into the goaf area of a mineshaft along the same slurry transport pipeline, and the CO₂ is subjected to mineralization reaction with the coal-based solid waste. This method obviously introduces the CO₂ into the goaf area under pressure through pipeline transportation based on traditional methods, which has problems such as gas leakage, while the mineralization reaction only occurs on the upper and lower surfaces of the coal-based solid waste slurry, so it is still impossible to realize the mineralization of CO₂ inside during the solidification.

The patent application “method of sequestering CO₂ and filling large areas of suspended roof goaf area by using industrial solid waste” (Patent No.: CN118065968A) discloses: transporting the industrial solid waste and a coal gangue to a crushing device and conducting crushing and grinding, then adding a cement and a fly ash to the crushing device to obtain a mixed solid waste mixture; transporting the mixed solid waste mixture to a carbon fixation reaction device, adding a certain proportion of water to the carbon fixation reaction device, and continuously stirring a resulting mixture to form a solid waste mixed slurry; transporting CO₂ from a carbon dioxide collection device to the carbon fixation reaction device and continuously stirring, and subjecting the CO₂ and the solid waste mixed slurry to full reaction to achieve CO₂ mineralisation to form a sequestering material; and drilling a sequestering borepore and connecting the sequestering borepore with a pump delivery device, and introducing the sequestering material after the full reaction to the suspended ceiling device until the suspended ceiling is full.

In the above methods, it is emphasized that CO₂ fully reacts with the solid waste mixed slurry to form the sequestering material. That is to say, CO₂ is sequestered by the mineralization reaction during the stirring process. Further, the above methods simply introduce the sequestering material to the suspended ceiling device until the suspended ceiling is full, which could not sequester the CO₂ stably and prevent the CO₂ from emitting into the atmosphere, and thus the above methods could not fundamentally solve the problem of environmental pollution caused by solid waste accumulation.

SUMMARY

In view of the above problems, the present disclosure provides a method of filling an abandoned mineshaft and concurrently stably mineralizing and sequestering CO₂ using solid waste slurries. The method could stably sequester CO₂ and prevent CO₂ from emitting into the atmosphere, while solving the environmental pollution problem caused by solid waste accumulation, preventing the problems of broken surrounding rock collapse, mining area collapse, and surrounding foundation subsidence in the abandoned mineshaft.

In order to solve the above technical problems, the present disclosure adopts the following technical solution.

A method of filling an abandoned mineshaft and concurrently mineralizing and sequestering CO₂ using solid waste slurries, including the following steps:

• • S1, pouring and spraying a solid waste-based plugging slurry to inner walls and a bottom portion of the abandoned mineshaft, and curing to form a plugging layer;
  • S2, grouting a solid waste-based CO₂ foam slurry into the abandoned mineshaft, and curing to form a porous stone body with CO₂-filled pores, wherein the porous stone body with CO₂-filled pores plays a supporting role for the abandoned mineshaft; and
  • S3, grouting a solid waste-based micro-expansion slurry into a top portion of the abandoned mineshaft, and curing to form a closed protective shell to prevent CO₂ from leaking out of the abandoned mineshaft.

In some embodiments, in step S1, the solid waste-based plugging slurry includes (or consists of) the following raw materials:

• • a solid powder material A: including (or consisting of) at least two solid wastes selected from the group consisting of a steel slag powder, a red mud, a magnesium slag, a fly ash, a carbide slag, and a desulfurized gypsum; and
  • a liquid raw material A: including (or consisting of) at least one selected from the group consisting of water, a water glass, and sodium hydroxide.

In some embodiments, the solid waste-based plugging slurry is prepared by a process including the steps of: putting the solid powder material A into a reactor, stirring to be uniform, and then adding the liquid raw material A thereto and fully stirring to obtain the solid waste-based plugging slurry.

In some embodiments, in step S2, the solid waste-based CO₂ foam slurry comprises the following raw materials:

• • the solid powder material B: including (or consisting of) at least two solid wastes selected from the group consisting of a steel slag powder, a red mud, a magnesium slag, a fly ash, a carbide slag, and a desulfurized gypsum; and
  • the liquid raw material B: including (or consisting of) at least one selected from the group consisting of water, a water glass, and sodium hydroxide.

In some embodiments, the solid waste-based CO₂ foam slurry is prepared by a process including the steps of: putting the solid powder material B into a reactor, stirring to be uniform, then adding the liquid raw material B and introducing CO₂, fully stirring, and then subjecting a resulting mixture to pulping mineralization to obtain the solid waste-based CO₂ foam slurry.

In some embodiments, the CO₂ is introduced at a mass flow of 1 litre/minute (L/min) to 2 L/min, and the stirring is conducted at a stirring speed of 400 rpm to 1000 rpm for 10 minutes to 30 minutes.

In some embodiments, a cover of the reactor has been subjected to porous treatment to facilitate multiple-site mineralization; the reactor is provided with a gas overflow collection device to recover an overflow gas; and the reactor is made of a steel or other pressure resistant materials, which can achieve pressurized ventilation, facilitating enhancing of carbonation reaction and gas entrainment.

In some embodiments, in step S3, the solid waste-based micro-expansion slurry includes (or consists of) the following raw materials: a fly ash, a carbide slag, coal gangue particles, an expansion agent, and water.

In some embodiments, the expansion agent is one selected from the group consisting of quicklime, magnesium oxide, a desulfurized gypsum, a gypsum, and an expansive soil.

In some embodiments, the solid waste-based micro-expansion slurry is prepared by a process including the steps of: putting a solid powder material C into a reactor; stirring to be uniform; and then adding the water thereto and fully stirring to obtain the solid waste-based micro-expansion slurry.

Compared with the prior art, some embodiments of the present disclosure have the following beneficial effects.

In the present disclosure, a solid waste is used as a main material to plug the bottom portion, a mineralized slurry is poured inside, and then the top is sealed. That is to say, the present disclosure adopts a method of sequestering the whole, which is a bottom +sequestered middle +a cover. By controlling a stirring speed (gas-liquid-solid three-phase), on one hand, carbon dioxide could be mineralized during the stirring process, on the other hand, carbon dioxide gas could be wrapped in a slurry, so that after grouting, carbon dioxide is sequestered in a stone body to form dense pores, and sequestered carbon dioxide does not overflow, and the carbon dioxide could continue to be mineralized subsequently.

Therefore, the method could stably sequester CO₂ and prevent CO₂ from emitting into the atmosphere, while solving a problem of environmental pollution caused by solid waste accumulation, preventing the occurrence of broken surrounding rock collapse, mining area collapse, and surrounding foundation subsidence in the abandoned mineshaft.

The solid waste-based plugging slurry of the present disclosure adopts a desulfurized gypsum as a main raw material. After the desulfurized gypsum is dried at 105° C., a dried desulfurized gypsum generates calcium sulfate whiskers when in contact with water, which is helpful to improve structure of system and improve strength. A cover of a reactor involved in the preparation of solid waste-based CO₂ foam slurry needs to be porous to facilitate multi-site mineralization of CO₂. Multi-site mineralization could make CO₂ evenly distributed in a slurry and form a stable slurry. Appropriate stirring conditions are conducive to the formation of stable CO₂ microbubbles, and compared with the prior art of introducing large amounts of CO₂ underground for sequestering, the method avoids secondary disasters caused by large amounts of gas leakage, and shows a high degree of safety. Further, sequestered CO₂ microbubbles could continue to undergo subsequent reactions, realizing efficient fixation of CO₂ and effective sequestration.

In the present disclosure, introduced CO₂ could be a CO₂-containing waste gas emitted from factories, thermal power plants, industrial equipment, etc. Main raw materials of the slurry are industrial solid wastes, and the raw materials could be combined according to the locally abundant solid wastes, tailored to local conditions, without the need for long-distance transportation of the raw materials, saving transportation costs and reducing raw material costs, reflecting ecological environmental protection and comprehensive utilization of solid waste resources.

In the present disclosure, carbon dioxide is introduced for pulping mineralization, a new method of fluid introducing of CO₂ and solid waste particles-containing slurries is established, and multi-element solid waste synergistic cementitious in-situ carbon fixation is innovatively proposed with improved efficiency, which achieves synchronous introducing and backfilling of CO₂ and solid waste micropowder, and meanwhile allows for improved compressive strength of the obtained material. The present disclosure has simple preparation methods and stable performance, and is suitable for large-scale production. The method of the present disclosure treats waste with waste and turns waste into treasure, which embodies the characteristics of synergistic coupling of social environmental protection benefits and economic benefits of solid waste utilization and CO₂ emission reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of the abandoned mineshaft after filling according to an embodiment of the present disclosure;

FIG. 2 shows a scanning electron microscope (SEM) image of the stone body of the solid waste-based plugging slurry according to an embodiment of the present disclosure;

FIG. 3 shows a preparation device diagram of the solid waste-based CO₂ foam slurry according to an embodiment of the present disclosure;

FIG. 4 shows a structural diagram of the reactor according to an embodiment of the present disclosure;

FIG. 5A shows a photograph of a mineralized grouting stone body prepared after curing at a stirring speed of 600 rpm according to an embodiment of the present disclosure;

FIG. 5B shows a photograph of a mineralized grouting stone body prepared after curing at a stirring speed of 800 rpm according to an embodiment of the present disclosure;

FIG. 5C shows a photograph of a cross-section of the mineralized grouting stone body in FIG. 5B;

FIG. 5D shows a microscopic analysis diagram of the mineralized grouting stone body in FIG. 5B; and

FIG. 6 shows a diagram of the solid waste-based micro-expansion slurry stone body according to an embodiment of the present disclosure and views of cross and longitudinal sections thereof.

In the drawings: 1 refers to a solid waste-based plugging slurry; 2 refers to a solid waste-based CO₂ foam slurry; 3 refers to a solid waste-based micro-expansion slurry; 4 refers to a reactor; 5 refers to a gas overflow collection tank; 6 refers to a gas overflow collection pipe; 7 refers to a communicating pipe; 8 refers to a mass flowmeter; 9 refers to a carbon dioxide pressure reducing valve; and 10 refers to a carbon dioxide cylinder.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following clearly and completely describes the technical solutions in examples of the present disclosure. Apparently, the described examples are merely a part rather than all of the embodiments of the present disclosure.

Example 1

This Example was intended to provide a method of filling an abandoned mineshaft and concurrently mineralizing and sequestering CO₂ using solid waste slurries, which was specifically performed according to the following three steps.

• • S1, A solid waste-based plugging slurry was poured and sprayed to inner walls and a bottom portion of the abandoned mineshaft, and cured to form a plugging layer.
  • S2, A solid waste-based CO₂ foam slurry was grouted into the abandoned mineshaft, and cured to form a porous stone body with CO₂-filled pores.
  • S3, A solid waste-based micro-expansion slurry was grouted into a top portion of the abandoned mineshaft, and cured to form a closed protective shell.

As shown in FIG. 1, the above steps could ensure that: no leakage occurs at the bottom of the abandoned mineshaft and an enclosure through the plugging layer; the abandoned mineshaft is supported by forming the porous stone body with CO₂-filled pores; and CO₂ is prevented from leaking out of the abandoned mineshaft through the closed protective shell.

That is to say, the method could stably sequester CO₂ and prevent CO₂ from emitting into the atmosphere, while solving the environmental pollution problem caused by solid waste accumulation, preventing the occurrence of problems such as broken surrounding rock collapse, mining area collapse, and surrounding foundation subsidence in the abandoned mineshaft.

Example 2

This Example provided a solid waste-based plugging slurry and preparation method thereof based on Example 1.

2.1 Solid Waste-Based Plugging Slurry

The solid waste-based plugging slurry consisted of the following raw materials: a solid powder: consisting of at least two solid wastes selected from the group consisting of a steel slag powder, a red mud, a magnesium slag, a fly ash, a carbide slag, and a desulfurized gypsum; and a liquid raw material: consisting of at least one selected from the group consisting of water, a water glass, and sodium hydroxide.

In some examples, 50 to 70 parts of the fly ash, 20 to 30 parts of the carbide slag, and 5 to 10 parts of the desulfurized gypsum were mixed to be uniform with 0 to 8 parts of the water glass, 0 to 2 parts of the sodium hydroxide, and 60 to 80 parts of the water.

2.2 Preparation Method

A method for preparing the solid waste-based plugging slurry was preformed as follows.

• • (1) The raw materials were accurately weighed: 64 parts of the fly ash, 27 parts of the carbide slag, 9 parts of the desulfurized gypsum, 7 parts of the water glass, 1.5 parts of the sodium hydroxide and 70 parts of the water. The water glass had a modulus of 3.3 and a Baume degree of 40.
  • (2) The solid powder material was put into a reactor according to the formula and stirred to be uniform for 5 minutes, then the liquid raw material was added thereto, and a resulting mixture was fully stirred at a stirring speed of about 600 rpm for 20 minutes to obtain the solid waste-based plugging slurry.

After curing, a stone body has a 28-day compressive strength of 18.5 Megapascals (MPa), a density of 1.57 g/cm³ and a consolidation time of 5.2 hours.

In the present disclosure, a fly ash from circulating fluidized bed, a carbide slag, a desulfurized gypsum, sodium hydroxide, a water glass, and water are used as raw materials, and pozzolanic reaction and hydration reaction are conducted among the raw materials during stirring, so that cementitious substances such as hydrated aluminosilicate are generated, and the desulfurized gypsum serves as whiskers, thereby enhancing structure of system.

FIG. 2 shows a scanning electron microscope (SEM) image of the stone body. Calcium sulfate whiskers in the desulfurized gypsum are reinforced, and rod-shaped substances are the calcium sulfate whiskers, which could effectively suppress system shrinkage and compact the structure, which is one of the main reasons leading to higher compressive strength of the system.

Example 3

This Example provides a solid waste-based CO₂ foam slurry and preparation method thereof based on Example 1.

3.1 Solid Waste-Based CO₂ Foam Slurry

The solid waste-based CO₂ foam slurry was prepared from the following raw materials: a solid powder material: consisting of at least two solid wastes selected from the group consisting of a steel slag powder, a red mud, a magnesium slag, a fly ash, a carbide slag, and a desulfurized gypsum; and a liquid raw material: consisting of at least one selected from the group consisting of water, a water glass, and sodium hydroxide.

In some examples, the solid waste-based CO₂ foam slurry was prepared from the following raw materials: 50 to 70 parts of the fly ash, 20 to 30 parts of the carbide slag, and 5 to 10 parts of the desulfurized gypsum, 60 to 80 parts of the water, and a certain amount of CO₂.

Introduced CO₂ could be a CO₂-containing waste gas emitted by factories, thermal power plants, industrial equipment, etc.

3.2 Preparation Method

A preparation device diagram of the solid waste-based CO₂ foam slurry is shown in FIG. 3, including a reactor, a mass flowmeter, a carbon dioxide pressure reducing valve, and a carbon dioxide cylinder.

A method for preparing the solid waste-based CO₂ foam slurry was preformed as follows.

• • (1) The raw materials were accurately weighed: 64 parts of the fly ash, 27 parts of the carbide slag, 9 parts of the desulfurized gypsum, 7 parts of the water glass, 1.5 parts of the sodium hydroxide, and 70 parts of the water. The water glass had a modulus of 3.3 and a Baume degree of 40.
  • (2) The solid powder material was put into the reactor (as shown in FIG. 4) according to the formula and stirred at a stirring speed of 600 rpm to be uniform for 5 minutes, then the liquid raw material was added thereto, and a resulting mixture was fully stirred at a stirring speed of 800 rpm, meanwhile CO₂ was introduced at a mass flow rate of 2 L/min into the reactor with stirring.
  • (3) The latter stirring is conducted for 20 minutes to obtain the solid waste-based CO₂ foam slurry.

FIG. 4 shows the reactor involved in the preparation process of the present disclosure, where a cover of the reactor is designed with multiple pores to facilitate multi-site mineralization of the CO₂. Multi-site mineralization could make CO₂ evenly distributed in a slurry, thereby forming a stable slurry. Introduced CO₂ reacts with calcium hydroxide to generate calcium carbonate, to compact structure of system, thereby improving the strength of grouting reinforcement materials and bringing CO₂ into the slurry through multiple pores. The reactor is made of a steel or other pressure resistant materials, which could achieve pressurized ventilation, facilitating enhancing of carbonation reaction and gas entrainment.

Specifically, CO₂ is introduced to each pore through branch tubes of a multi pass component, with each pore inserted into a CO₂ tube for uniform ventilation. Tubes are extended to a bottom of the reactor to control a gas flow rate and increase a contact time between carbon dioxide gas and the slurry as much as possible, ensuring mineralization reaction and gas being trapped in the slurry, and thereby minimizing the overflow of the carbon dioxide gas.

In some embodiments, a gas overflow collection device is further included, the gas overflow collection device including a gas overflow collection tank, a gas overflow collection pipe and a communicating pipe; the reactor is connected to the gas overflow collection tank through the gas overflow collection pipe and the communicating pipe. The CO₂ gas that is introduced into the reactor but not mineralized or entrained flows into the gas overflow collection tank through the gas overflow collection pipe and the communicating pipe for collection and reuse. Also, when a pressure in the gas overflow collection tank reaches a certain value, the CO₂ gas inside will also return to the reactor through the gas overflow collection pipe and the communicating pipe for mineralization reaction. Specifically, the gas overflow collection pipe and the communicating pipe are equipped with corresponding valves, and the valves could control the connection or closure of the gas overflow collection pipe and the communicating pipe.

As shown in FIG. 4, multiple pores are distributed on the cover of the reactor in the device for preparing the solid waste-based multi-site micro foaming carbon solidification grouting reinforcement material, which facilitates the introduction of CO₂ into multiple locations for multi-site mineralization, generating more nano-CaCO₃ and enhancing the structure of the system. During the mineralization process, the CO₂ is transformed from a gas phase to a liquid phase CO₃²⁻, and finally to a solid phase CaCO₃. During this multi-phase transformation process, the Gibbs free energy (ΔrG⁰_m, kJ/mol) is less than 0, and this reaction thus could be performed spontaneously. The specific reaction process is shown in schemes 5 to 9.

After curing at 600 rpm, a stone body has a 28-day compressive strength of 18.9 MPa, a density of 1.58 g/cm³ and a consolidation time of 4.8 hours.

After curing at 800 rpm, a stone body has a 28-day compressive strength of 17.9 MPa, a density of 1.51 g/cm³ and a consolidation time of 5 hours.

FIGS. 5A and 5B show that when placed in water, the stone body cured at 800 rpm produces more bubbles than the stone body cured at 600 rpm, and there are more uniform micropores at the interface of the stone body after cutting, indicating that a large amount of CO₂ could be plugged under a high-speed condition. FIG. 5C shows that after curing at 800 rpm, a cross-section of a stone body presents uniform fine pores; FIG. 5D shows the microstructure of the stone body after curing at 800 rpm. There is a large amount of nano-calcium carbonate in a test block, and cloud-like structure and rod-shaped structure of the mineralized cementitious system are interlaced, making internal structure of the stone body compact and dense. During the grouting process, CO₂ microbubbles sequestered in the pores could continue to undergo subsequent mineralization reaction, achieving efficient CO₂ fixation with an effective carbon fixation rate of 15%.

After curing for 28 days, due to the continuous mineralization, the 28-day compressive strength of the grouting material increased to 25.2 MPa.

Example 4

This Example provided a solid waste-based micro-expansion slurry and preparation method thereof based on Example 1.

4.1 Solid Waste-Based Micro-Expansion Slurry

The solid waste-based micro-expansion slurry consisted of the following raw materials: a fly ash, a carbide slag, coal gangue particles, an expansion agent (quicklime, magnesium oxide, a desulfurized gypsum, etc.) and water.

In some examples, a formula is as follows: 50 to 70 parts of the fly ash, 20 to 30 parts of the carbide slag, and 0 to 10 parts of the coal gangue particles, 5 to 10 parts of the expansion agent (dried desulfurized gypsum), and 60 to 80 parts of the water.

The expansion agent was desulfurized gypsum, gypsum, expansive soil, etc., after being dried at 105° C.

The coal gangue particles each had a particle size of less than 2 mm.

4.2 Preparation Method

A method for preparing the solid waste-based micro-expansion slurry was performed as follows.

• • (1) The raw materials were accurately weighed: 64 parts of the fly ash, 27 parts of the carbide slag, 10 parts of the coal gangue particles (having a particle size of less than 2 mm), 9 parts of the micro-expansion agent (desulfurized gypsum after being dried at 105° C.), and the water.
  • (2) The fly ash, the carbide slag, the coal gangue particles, and the micro-expansion agent material were put into a reactor according to the formula and stirred to be uniform for 5 minutes, then the water was added thereto, and a resulting mixture was fully stirred at a stirring speed of about 200 rpm for 20 minutes to obtain the solid waste-based micro-expansion slurry.

After curing, a stone body has a 28-day compressive strength of 17.9 Megapascals (MPa), a density of 1.58 g/cm³, and a consolidation time of 5.1 hours.

The stone body of the solid waste-based micro-expansion slurry and cross and longitudinal sections thereof are shown in FIG. 6, where black areas represent the coal gangue particles and white areas represent cementitious material. From the cross and longitudinal sections, it can be seen that the cementitious material tightly wraps around the coal gangue particles, indicating that the cementitious material has good diffusion and permeability, and could effectively consolidate the broken particles. In addition, due to an addition of the micro-expansion agent, there are no obvious cracks in the stone body, which could result in a sealing effect to prevent CO₂ from leaking out of the abandoned mineshaft.

The above “parts” refer to parts by weight.

The above are merely preferred embodiments of the present disclosure, but the present disclosure is not limited to the above embodiments.