A method for preparing a paste for filling and solidifying co2

Abstract

The application discloses a preparation method of a paste for filling and solidifying CO2, which comprises the following steps: taking raw materials by weight parts: 5-25 parts of cement, 5-25 parts of carbide slag, 25-45 parts of fly ash, 25-45 parts of coal gangue, pre-pulverized coal gangue, mixing the raw materials, adding water with a solid-water mass ratio of 7:3, stirring, a stirring speed is 80-100 r / min, high-purity CO2 is introduced into the stirred paste, and the paste is stirred through a stirrer, a CO2 gas pressure is 0.1 MPa, a stirring speed is 120-160 r / min, and a stirring time is 1-2.5 hours. The paste prepared by the method has good flow performance, solidification performance and mechanical performance, the prepared paste can be filled into a goaf in a mine, and the paste can realize the purposes of supporting the goaf, preventing surface subsidence, protecting an ecological environment, rationally utilizing solid waste and reducing carbon emission.

Description

Technical Field

[0001] This invention relates to the field of ecological restoration technology, specifically to a method for preparing a paste for filling and solidifying CO2. Background Technology

[0002] Achieving greenhouse gas emission reduction has become a hot topic in the international community. Among these technologies, mineral sequestration of CO2 can effectively reduce CO2 emissions and mitigate global warming. It mimics the natural weathering process of silicate minerals, where CO2 reacts with metal oxide-containing materials to form stable, water-insoluble carbonates, thus permanently sequestering CO2. Coal gangue is a solid waste generated during coal mining and washing; it is a low-carbon, hard rock that is associated with coal seams during coal formation. Fly ash is a product of coal combustion, composed of fine particles (small particles of burning fuel) emitted with flue gas from coal-fired boilers, and has potential cementing properties. In the presence of water, fly ash (especially Class C fly ash) hardens and becomes more solid over time. Calcium carbide slag is the waste residue produced after the hydrolysis of calcium carbide to obtain acetylene gas; it is highly alkaline. These solid waste materials contain a large amount of metal oxides and have high alkalinity and activity. Therefore, they can be mixed with water in a certain ratio to form a paste. After fully reacting with CO2, it can be used as a filling material for mining goaf or other geological cavities. On the one hand, this achieves comprehensive utilization of solid waste, reduces environmental load and pollution, and at the same time achieves the purpose of solidifying CO2. On the other hand, the prepared paste is inexpensive and has value for promotion and utilization. Summary of the Invention

[0003] This invention proposes a method for preparing a paste containing solid wastes such as coal gangue, fly ash, and carbide slag, which can be used for filling and CO2 solidification. This significantly improves the utilization rate of solid wastes such as coal gangue, while simultaneously achieving the goal of solidifying CO2 and reducing carbon emissions. The invention prepares a paste with good flow properties, solidification properties, and mechanical properties. Filling the paste into mined-out areas achieves the goals of supporting the mined-out areas, preventing surface subsidence, protecting the ecological environment, rationally utilizing solid waste, and reducing carbon emissions.

[0004] The technical solution of the present invention is as follows: a method for preparing a paste for filling and solidifying CO2, comprising the following steps: taking raw materials by weight: 5-25 parts cement, 5-25 parts carbide slag, 25-45 parts fly ash, 25-45 parts coal gangue, pretreated coal gangue, mixing the raw materials, adding water and stirring at a solid-to-water mass ratio of 7:3, stirring at a speed of 80-100 r / min, introducing high-purity CO2 into the stirred paste, and stirring with a stirrer at a CO2 pressure of 0.1 MPa, a stirring speed of 120-160 r / min, and a stirring time of 1-2.5 hours.

[0005] Preferably, the cement is 42.5 type ordinary Portland cement, and the particle size of the coal gangue is less than or equal to 10 mm, wherein the coal gangue particles with a particle size of less than 5 mm are controlled to be more than 50%.

[0006] Preferably, the raw materials are weighed in the following proportions by weight: 25 parts cement, 25 parts carbide slag, 25 parts fly ash, and 22.5 parts coal gangue.

[0007] Preferably, the raw materials are weighed in the following proportions by weight: 20 parts cement, 20 parts carbide slag, 30 parts fly ash, and 30 parts coal gangue. Compared with conventional fly ash and coal gangue solid backfilling technology, the main raw materials for paste preparation in this invention are solid wastes such as coal gangue, fly ash, and carbide slag, as well as CO2 captured from industrial emission sources such as power plants. The emissions are large and the price is low, and the preparation process is simple. Using fly ash to partially replace cement results in low investment costs but high economic benefits. By adjusting the raw material ratio, the paste can achieve different strength requirements, making the material ratio flexible and applicable to various scenarios. Detailed Implementation

[0008] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0009] Example 1

[0010] A method for preparing a composite cementitious filling paste is as follows:

[0011] The following ingredients were mixed by mass fraction: 15 wt% cement, 15 wt% carbide slag, 35 wt% fly ash, and 35 wt% coal gangue. The coal gangue was pretreated. The raw materials were first mixed using a dry-mix mortar mixer. The solid mixing time was 2 minutes. Water was added and stirred for 4 minutes at a solid-to-water mass ratio of 7:3. The stirring speed was 100 r / min. After stirring, a paste was obtained and solidified. The strength on day 28 after solidification was 6.52 MPa.

[0012] The cement used is 42.5 type ordinary Portland cement, and the coal gangue particles with a diameter of less than 5mm account for 65.97wt% of the total coal gangue mass.

[0013] The mechanical strength test of the paste on day 28 after solidification was a uniaxial compressive strength test, conducted using an electro-hydraulic digital display pressure testing machine. During the test, a continuous and uniform load was applied at a rate of 0.3 MPa / s to 0.5 MPa / s. The loading rate of the testing machine was manually controlled. When the paste approached failure and began to deform rapidly, the machine's throttle was stopped and adjusted until failure occurred. The failure load was then recorded. The compressive strength calculation formula is as follows:

[0014]

[0015] P—uniaxial compressive strength (MPa), F—destructive load of specimen (N), A—bearing area of ​​specimen (mm²) 2 )

[0016] Example 2

[0017] A method for preparing a composite cementitious filling paste is as follows:

[0018] The following materials were prepared by mass fraction: 15 wt% cement, 15 wt% carbide slag, 35 wt% fly ash, and 35 wt% coal gangue. The coal gangue was pretreated. The raw materials were first mixed in a dry mortar mixer for 2 minutes. Water was added and stirred for 4 minutes at a solid-to-water mass ratio of 7:3. High-purity CO2 (0.1 MPa) was then introduced into the paste and stirred at a speed of 150 r / min for 2 hours. The CO2 solidification amount per kilogram of paste was measured to be 15.9 g. After sufficient reaction with CO2, the 28-day strength of the paste was 8.61 MPa, showing a significant increase in strength.

[0019] The cement used is 42.5 type ordinary Portland cement, and the coal gangue particles with a diameter of less than 5mm account for 65.97wt% of the total coal gangue mass.

[0020] In the composite cemented filling paste of Example 2, cement, carbide slag, and fly ash were used as binders, coal gangue was added as aggregate, and CO2 was introduced in the form of gas. Cement was purchased from the market, fly ash was collected from a thermal power plant, carbide slag was collected from a chemical plant, coal gangue was obtained from a gangue stockpile site, and CO2 used in the experiment was purchased from the market.

[0021] Pre-treatment of coal gangue involves crushing large pieces of coal gangue and then screening them to obtain corresponding particles. The particle size of the coal gangue is less than or equal to 10 mm, with particles smaller than 5 mm accounting for more than 50%. Particles larger than 10 mm after screening need to be further crushed mechanically or manually until the particle size requirement is met. Composite cemented filling paste is prepared according to the above method. Cement, carbide slag, fly ash, and coal gangue are proportioned according to Table 1 to obtain pastes with different ratios. The pastes with different ratios are divided into two equal portions. One portion is not introduced with CO2, and its strength is tested after curing (as shown in Table 3). The other portion is introduced with CO2, and its strength is tested after curing (as shown in Table 4). The results in Tables 3 and 4 show that introducing CO2 into the paste significantly improves the strength after curing.

[0022] Table 1 Material Proportions

[0023]

[0024] Table 2. Amount of paste solidified by CO2 after 2 hours of CO2 introduction.

[0025] Table 3 Compressive strength of the paste before reaction with CO2 and after curing

[0026]

[0027] Table 4 Compressive strength of the paste after CO2 reaction and curing

[0028] In the above embodiments, the cement is 42.5 grade ordinary Portland cement with a mass fraction of 5%~25%, the calcium carbide slag has a mass fraction of 5%~25%, the fly ash has a mass fraction of 25%~45%, and the coal gangue has a mass fraction of 25%~45%. All the above mass fractions refer to the total mass percentage of the solids in the prepared paste, and the mass ratio of solids to water in the paste is 7:3. The solid raw materials are first mixed evenly using a dry-mix mortar mixer for 1~3 minutes. Then, the mixed solid raw materials are placed in a mixer with water added and stirred for 2~5 minutes at a speed of 80~100 r / min. The stirred paste is placed in a clean container, and high-purity CO2 is introduced into the paste and stirred using a stirrer at a pressure of 0.1 MPa, a stirring speed of 120~160 r / min, and a stirring time of 1~2.5 hours. After stirring, the paste proposed in this invention is obtained.

[0029] Therefore, the paste prepared by this invention can not only effectively solidify CO2, providing an effective solution for CO2 emission reduction, but also significantly improve the strength of the paste after solidification, making it applicable in mining goaf areas with more severe geological conditions, and exhibiting superior overall performance.

Claims

1. A method for preparing a paste for filling and solidifying CO2, characterized in that, Includes the following steps: Raw materials are prepared in parts by weight: 25 parts cement, 25 parts carbide slag, 25 parts fly ash, 22.5 parts coal gangue, and pre-crushed coal gangue. The raw materials are mixed and stirred with water at a solid-to-water mass ratio of 7:

3. The stirring speed is 80-100 r / min. High-purity CO2 is introduced into the stirred paste, and the mixture is stirred using a stirrer at a pressure of 0.1 MPa and a stirring speed of 120-160 r / min for 1-2.5 hours. The solid is a mixture of cement, carbide slag, fly ash, and coal gangue. The cement used is 42.5 type ordinary Portland cement. The coal gangue particles are all less than or equal to 10 mm in diameter, with coal gangue particles less than 5 mm accounting for more than 50% of the total coal gangue mass.

2. The method for preparing a paste for filling and solidifying CO2 according to claim 1, characterized in that, The raw materials are weighed in the following proportions by weight: 20 parts cement, 20 parts carbide slag, 30 parts fly ash, and 30 parts coal gangue.

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