A fly ash-based geopolymer carbon fixation and adsorption material and its preparation method

Abstract

The present invention discloses a fly ash-based geopolymer carbon sequestration and adsorption material and a preparation method thereof, belonging to the technical field of engineering materials. The material of the present invention is modified by adding 13X zeolite with a specific particle size, and its carbon sequestration and adsorption performance is significantly improved through an in-situ hydrothermal conversion process. The fly ash-based geopolymer material and the preparation method disclosed by the present invention are simple and easy to implement, and are easy to be implemented in industrial production, and can overcome the disadvantages of the current direct reaction of solid waste with CO2 to generate mineralized (carbonate) filling materials, low mineralization efficiency and unstable reaction products. The geopolymer carbon sequestration and adsorption material of the present invention has a wide application prospect, provides a new method for synergistically solving carbon sequestration, solid waste disposal, and reuse of abandoned underground spaces, and has important environmental protection, social and economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering materials, and discloses a fly ash-based geopolymer carbon sequestration and adsorption material and a preparation method thereof. Background Art

[0002] Mining activities will form huge underground spaces in abandoned mines. Disposing solid waste materials that can adsorb CO2 in the abandoned underground spaces will help to break through the technical bottleneck of carbon-waste co-disposal in the underground spaces of closed mines, realize the technical upgrade of the underground carbon storage industry from passive carbon sequestration to active carbon sequestration, and transform these abandoned spaces into large-scale underground spaces for carbon-waste co-sequestration. The guiding opinions on the comprehensive utilization of bulk solid waste point out that the utilization efficiency of bulk solid waste should be improved. At present, the carbon-waste co-disposal in underground spaces is mainly carried out by reacting solid waste with CO2 to form mineralized (carbonate) filling materials. The mineralized filling materials formed in this way have defects such as low mineralization efficiency (depending on high-temperature environment), unstable reaction products (some products at high temperature are prone to decomposition), and low strength (low cementation strength between particles). Therefore, it is urgent to break through the restriction of fly ash mineralization and storage of CO2.

[0003] As a porous material, geopolymer has the potential to adsorb CO2. At present, some scholars have incorporated rice husk ash (microporous material) into geopolymer. Although it can increase the micropores (<2 nm) in the system and improve the CO2 adsorption capacity to a certain extent, it only enhances the CO2 adsorption capacity by adding microporous materials and does not fully utilize the adsorption potential brought by the pores of different scales in geopolymer. Therefore, in the present invention, by introducing a microporous material with high adsorption performance, the proportion of micropores in geopolymer is first increased, and then the geopolymer is subjected to hydrothermal conversion to further convert the pores in the geopolymer into micropores (<2 nm) and mesopores (2-50 nm), comprehensively increasing the proportion of micropores and mesopores in the geopolymer and significantly enhancing the CO2 adsorption capacity of the modified carbon sequestration geopolymer. Summary of the Invention

[0004] In view of the high reactivity of aluminosilicate in fly ash, the excellent performance of 13X zeolite in adsorbing CO2, and the significant effect of the phase transformation from conventional geopolymer to zeolite on enhancing the specific surface area of the material, the present application provides a fly ash-based geopolymer carbon sequestration and adsorption material and a preparation method thereof. By adding 13X zeolite to the fly ash geopolymer and then performing hydrothermal conversion under alkaline conditions, the microporous and mesoporous pore structures of the material are comprehensively improved and the specific surface area of the material is increased, which will significantly enhance its carbon dioxide adsorption capacity.

[0005] Among them, fly ash is rich in highly reactive silica and alumina. After reacting with an alkaline solution, a series of chemical reactions such as depolymerization-condensation occur to synthesize a stable three-dimensional network material with a large number of pores, which can provide a large number of adsorption sites for the storage of carbon dioxide.

[0006] In addition, the proportion of micropores in conventional geopolymers is relatively small, and micropores are important factors affecting the specific surface area and adsorption performance of geopolymers. The effective pore diameter of 13X zeolite is about 1 nm, which can effectively adsorb CO2 gas molecules with a diameter of about 0.33 nm. Moreover, due to its large specific surface area and high metal cation content, it can interact with CO2 during the adsorption process, thereby effectively capturing CO2. If 13X zeolite can be introduced into geopolymers, the proportion of micropores and the CO2 adsorption potential of geopolymers will be significantly improved. In addition, the amorphous three-dimensional gel network structure of geopolymers is thermodynamically unstable, which means that they will very slowly transform into the zeolite crystal phase under normal temperature and pressure. The transformation into the zeolite crystal phase will significantly increase the proportion of micropores and mesopores, the specific surface area, and the CO2 adsorption potential of the material. This process may take a long time. Accelerating this phase transformation process and improving the efficiency and integrity of the phase transformation in a specific environment will bring hope for further enhancing the CO2 adsorption performance. Therefore, introducing 13X zeolite to increase the proportion of micropores in geopolymer materials and carrying out the phase transformation of geopolymers into zeolites under specific environments to increase the proportion of their micropores and mesopores will comprehensively improve the micropores and mesopores that affect the CO2 adsorption potential of geopolymers and synthesize new solid waste-based high-efficiency carbon fixation materials. It has broad prospects and significance for promoting carbon sequestration, solid waste disposal, and transforming the space of abandoned mines into carbon waste disposal spaces.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The first technical object of the present invention is to provide a fly ash-based geopolymer carbon fixation and adsorption material, which is mainly prepared from the following substances:

[0009] 100 parts of fly ash, 55 - 70 parts of water, 10 - 34 parts of 13X zeolite, and 15 - 38 parts of alkali activator.

[0010] Optionally, for the fly ash-based geopolymer carbon fixation and adsorption material, the solid-liquid mass ratio is 0.55 - 0.7, the silicon-aluminum molar ratio is 1.7 - 2.0, and the curing temperature is a constant 80 °C.

[0011] Optionally, the alkali activator is a mixed powder of sodium hydroxide and sodium silicate. By weight, the alkali activator includes 12 - 27 parts of sodium silicate and 3 - 11 parts of sodium hydroxide;

[0012] Moreover, the modulus of the alkali activator is 0.8 - 1.1, which is the molar ratio of SiO2 to Na2O; the sodium hydroxide is an analytical pure powder; the sodium silicate is an analytical pure powder with a modulus of 2.8.

[0013] Optionally, the 13X zeolite is a white powder with a pore size of about 1 nm, and CO2 molecules can be adsorbed in the pores; the particle size is 2 μm~4 μm, and the bulk density is ≥0.33 g / mL, so as to be better dispersed in the geopolymer slurry.

[0014] The second technical purpose of the present invention is to provide a method for preparing the fly ash-based polymer carbon fixation adsorption material, which specifically comprises the following steps:

[0015] S1: Dissolve sodium hydroxide in water at room temperature. After it is completely dissolved and restored to room temperature, heat it in a water bath to 50°C and maintain the temperature. Then, add sodium silicate in batches in a ratio of 1 to 2 parts while stirring until the sodium silicate is completely dissolved, thereby preparing an alkaline activator solution.

[0016] S2: After the alkaline activator solution described in S1 is cooled to room temperature, fly ash is gradually added thereto while being stirred with a glass rod to form a geopolymer slurry. The slurry is then stirred at a speed of 400 r / min on a disperser for 4 to 6 minutes to ensure uniform mixing.

[0017] S3: The geopolymer slurry obtained in step S2 is taken out from the disperser, and then 13X zeolite is added in batches, and the weight parts added in batches are 3.4 parts. After each addition of 13X zeolite, it is necessary to stir again on the disperser at a speed of 400 r / min for 1 to 2 minutes to ensure that the 13X zeolite and the slurry are fully mixed, so as to prepare a fly ash-13X zeolite composite geopolymer slurry.

[0018] S4: Pour the fly ash-13X zeolite composite geopolymer slurry described in S3 into a plastic mold, cure it in a constant temperature box at 80° C. for 24 h, then take it out and demould it.

[0019] S5: Place the demoulding geopolymer sample described in S4 into a polytetrafluoroethylene-lined reactor, add 2 mol / L sodium hydroxide solution into the reactor, and place the reactor in a 100°C constant temperature box for hydrothermal reaction for 48 hours; take out the geopolymer sample from the reactor, and wash it repeatedly with deionized water until the pH of the washed liquid is close to 8; place the sample in a constant temperature box and dry it at 60°C. After drying, a fly ash-based modified geopolymer carbon-fixing material is obtained.

[0020] It should be noted that the materials of the present invention are modified by adding 13X zeolite with a specific particle size, and their carbon fixation and adsorption performance is significantly improved through an in-situ hydrothermal conversion process. The fly ash-based geopolymer materials and preparation methods disclosed in the present invention are simple and easy to implement, and are easy to be implemented in industrial production. They can overcome the disadvantages of the current direct reaction of solid waste with CO2 to generate mineralized (carbonate) filling materials, low mineralization efficiency and unstable reaction products. By introducing 13X zeolite into fly ash-based geopolymers, the micropore porosity of the materials is increased; the mesopore porosity and micropore porosity are improved through in-situ hydrothermal conversion, comprehensively improving the micropores and mesopores of the materials, endowing the materials with extremely high porosity and specific surface area, and significantly enhancing their CO2 adsorption performance. The geopolymer carbon fixation and adsorption materials of the present invention have broad application prospects, providing a new method for synergistically solving carbon sequestration, solid waste disposal, and reuse of abandoned underground spaces, and having important environmental protection, social and economic benefits.

[0021] As can be seen from the above technical solutions, compared with the prior art, the present invention provides a fly ash-based geopolymer carbon fixation and adsorption material and a preparation method thereof, having the following excellent effects:

[0022] In the present invention, 13X zeolite is introduced into the geopolymer to select the optimal formula of the geopolymer with the most micropores and the largest specific surface area; then, the 13 zeolite-modified geopolymer with the largest specific surface area is subjected to hydrothermal conversion. By introducing 13X zeolite, nano-scale micropores are introduced into the fly ash-based geopolymer, and the micropore and mesopore pore structures of the geopolymer itself are improved through the hydrothermal conversion of the geopolymer material, significantly increasing the micropore and mesopore porosities of the carbon-fixing geopolymer and the specific surface area affecting the adsorption performance. The specific surface area reaches 359.98 m 2 / g, which is nearly 30 times higher than that before improvement, significantly enhancing the carbon dioxide adsorption capacity of this material. Under the conditions of 40 °C and 5 MPa, the carbon dioxide adsorption capacity of the geopolymer introduced with 13X zeolite and subjected to hydrothermal conversion reaches 70.6 cm 3 / g, the carbon dioxide adsorption capacity of the optimal geopolymer introduced with 13X zeolite without hydrothermal conversion is 36.7 cm 3 / g, and the carbon dioxide adsorption capacity of the geopolymer without introducing 13X zeolite and without hydrothermal conversion is 2.5 cm 3 / g. Therefore, the carbon dioxide adsorption capacity of the geopolymer introduced with 13X zeolite and subjected to hydrothermal conversion is nearly 28 times higher than that of the geopolymer without introducing 13X zeolite and without hydrothermal conversion, and 1.9 times higher than that of the geopolymer only introduced with 13X zeolite without hydrothermal conversion. In addition, according to the calculation of the actual gas state equation, the storage capacity of net space carbon dioxide is about 107.6 kg / m 3 , while the use of the geopolymer of the present invention for filling can achieve a carbon dioxide sequestration capacity of 137.3 kg / m 3, with a year-on-year increase of nearly 28%, and at the same time disposed of solid waste fly ash. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required in the description of the embodiments or the prior art will be briefly introduced below. It should be noted that the accompanying drawings in the description are only embodiments of the present invention, and for those skilled in the art or ordinary technicians, other drawings can be obtained based on the provided drawings without creative efforts.

[0024] Figure 1 Schematic diagram of the preparation method of fly ash-based geopolymer carbon fixation and adsorption material disclosed by the present invention.

[0025] Figure 2 XRD spectrum of geopolymer.

[0026] Figure 3 Low-temperature liquid nitrogen adsorption diagram of geopolymer.

[0027] Figure 4 Pore size distribution diagram of geopolymer (2 - 150 nm).

[0028] Figure 5 Field emission electron microscope (a is raw fly ash, b is geopolymer without any modification, c and d are geopolymers added with 13X zeolite, e and f are geopolymers modified by hydrothermal process).

[0029] Figure 6 Fourier transform infrared spectroscopy spectrum.

[0030] Figure 7 GEO-0 isothermal adsorption diagram.

[0031] Figure 8 GEO-6 isothermal adsorption diagram.

[0032] Figure 9 GEO-6HC isothermal adsorption diagram. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The technical solutions disclosed by the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings of the specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0034] The embodiments of the present invention disclose a preparation method of fly ash-based geopolymer carbon fixation and adsorption material.

[0035] For a better understanding of the present invention, the following specific embodiments are used to further elaborate the present invention. However, it should not be construed as a limitation of the present invention. For those skilled in the art, some non-essential improvements and adjustments made based on the above-mentioned invention content are also considered to fall within the protection scope of the present invention.

[0036] To simplify the number of experiments, the orthogonal experiment method was adopted in the implementation mode to design a total of 16 groups of experiments with four factors and four levels, including examples (GEO-1 to GEO-16) and a control group (GEO-0), to find the optimal formula with high specific surface area and porosity, and then perform hydrothermal conversion experiments. The experimental scheme is shown in Table 1. According to the data in Table 1, even when using fly ash from different sources (with different silica and alumina contents), samples with the same chemical composition can be prepared according to the parameters in the table.

[0037] Table 1 Experimental group settings

[0038]

[0039] It should be noted that the micropore specific surface area measured by carbon dioxide adsorption test shows that the GEO-6 group has the highest specific surface area. Therefore, the silica-alumina ratio, solid-liquid mass ratio, and modulus of the alkali activator of the control group GEO-0 are the same as those of the GEO-6 group, and the GEO-0 group does not add 13X zeolite.

[0040] In view of the fact that the GEO-6 group has the highest specific surface area, geopolymers were developed based on the chemical composition of the GEO-6 group, and hydrothermal conversion was performed on the generated geopolymers to finally form the GEO-6HC hydrothermal conversion group.

[0041] Since the production processes are similar, the production processes of some samples are listed below.

[0042] Control group (GEO-0):

[0043] (1) The fly ash geopolymer prepared by GEO-0 has the following physical properties: the solid-liquid mass ratio is 0.6; the silica-alumina molar ratio is 1.8.

[0044] The fly ash geopolymer prepared by GEO-0, according to the mass fraction ratio, includes the following components: 100 parts of fly ash, 70 parts of water, 0 parts of 13X zeolite, and 15 parts of alkali activator, including 12 parts of sodium silicate and 3 parts of sodium hydroxide.

[0045] (3) The alkali activator used in the control group is a mixed powder of sodium hydroxide and sodium silicate. Among them, sodium hydroxide is an analytical pure powder, sodium silicate is an analytical pure powder with a modulus of 2.8, and the modulus after mixing the two is 0.8.

[0046] (4) Dissolve sodium hydroxide in water at room temperature. After it is completely dissolved and restored to room temperature, heat it in a water bath to 50 °C and maintain this temperature. Then add sodium silicate in batches at a ratio of 1 - 2 parts, while stirring, until the sodium silicate is completely dissolved, thus preparing an alkali activator solution.

[0047] (5) After cooling the alkali activator solution described in (4) to room temperature, slowly add fly ash to it step by step, while stirring with a glass rod to make a geopolymer slurry. Then stir it on a disperser at a speed of 400 r / min for 6 minutes to ensure uniform mixing.

[0048] (6) Pour the geopolymer slurry described in (5) into a plastic mold and cure it in an incubator at 80 °C for 24 h, then take it out and demold.

[0049] (7) After preparation, characterize the samples. The specific characterization methods are: field emission electron microscopy (FSEM) and energy dispersive spectroscopy (EDS) determination, X-ray diffraction analysis (XRD), measuring the specific surface area and pore (2 - 500 nm) distribution by passing liquid nitrogen, and measuring the micropore (≤2 nm) pore distribution by passing carbon dioxide.

[0050] Example GEO - 6

[0051] (1) The fly ash geopolymer prepared in Example GEO - 6 has the following physical properties: the solid-liquid mass ratio is 0.6; the silicon-aluminum molar ratio is 1.8.

[0052] (2) The fly ash geopolymer prepared in Example GEO - 6, by mass fraction ratio, includes the following components: 100 parts of fly ash, 60 parts of water, 34 parts of 13X zeolite, 24 parts of alkali activator, including 17 parts of sodium silicate and 7 parts of sodium hydroxide.

[0053] (3) The alkali activator used in Example GEO - 6 is a mixed powder of sodium hydroxide and sodium silicate. Among them, sodium hydroxide is an analytical pure powder, sodium silicate is an analytical pure powder with a modulus of 2.8, and the modulus after mixing the two is 0.8.

[0054] (4) The 13X zeolite used in Example GEO - 6 is a white powder with a particle size of 2 μm - 4 μm and a bulk density ≥0.33 g / mL.

[0055] (5) Dissolve sodium hydroxide in water at room temperature. After it is completely dissolved and restored to room temperature, heat it in a water bath to 50 °C and maintain this temperature. Then add sodium silicate in batches at a ratio of 1 - 2 parts, while stirring, until the sodium silicate is completely dissolved, thus preparing an alkali activator solution.

[0056] After cooling the alkali activator solution described in (5) to room temperature, slowly add fly ash to it step by step, stirring with a glass rod while adding, to make a geopolymer slurry. Then stir on a disperser at a speed of 400 r / min for 6 minutes to ensure uniform mixing.

[0057] (7)Take out the geopolymer slurry obtained in (6) from the disperser, and then add 13X zeolite in batches, 3.4 parts each time, with a total addition amount of 34 parts; after adding 13X zeolite each time, it is necessary to stir again on the disperser at a speed of 400 r / min for 2 minutes to ensure full mixing of 13X zeolite and the slurry, and prepare a fly ash-13X zeolite composite geopolymer slurry.

[0058] (8)Pour the fly ash-13X zeolite composite geopolymer slurry described in (7) S3 into a plastic mold, cure it in an incubator at a temperature of 80 °C for 24 hours, and then take it out and demold it.

[0059] (9)After preparation, characterize the samples. The specific characterization methods are: field emission electron microscopy (FSEM) and energy spectrum determination, X-ray diffraction analysis (XRD), measuring the specific surface area and pore (2 - 500 nm) distribution by passing liquid nitrogen, and the micropore (≤2 nm) pore distribution by passing carbon dioxide.

[0060] Example GEO-6HC hydrothermal conversion group

[0061] (1)The fly ash geopolymer under the joint influence of the multiple foaming agents prepared in Example GEO-6HC has the following physical properties: the solid-liquid mass ratio is 0.6; the silicon-aluminum molar ratio is 1.8.

[0062] (2)The fly ash geopolymer prepared in Example GEO-6HC, according to the mass fraction ratio, includes the following components: 100 parts of fly ash, 60 parts of water, 34 parts of 13X zeolite, and 24 parts of alkali activator, including 17 parts of sodium silicate and 7 parts of sodium hydroxide.

[0063] (3)The alkali activator used in Example GEO-6HC is a mixed powder of sodium hydroxide and sodium silicate. Among them, sodium hydroxide is an analytical pure powder, and sodium silicate is an analytical pure powder with a modulus of 2.8. After mixing, the modulus is 0.8.

[0064] (4)The 13X zeolite used in Example GEO-6HC is a white powder with a particle size of 2 μm - 4 μm and a bulk density ≥ 0.33 g / mL.

[0065] (5) Dissolve sodium hydroxide in water at room temperature. After it is completely dissolved and restored to room temperature, heat it in a water bath to 50 °C and maintain this temperature. Then, add sodium silicate in batches at a ratio of 1 - 2 parts, stirring while adding until sodium silicate is completely dissolved, thereby preparing an alkali activator solution.

[0066] (6) After cooling the alkali activator solution described in (5) to room temperature, slowly add fly ash to it step by step, stirring with a glass rod while adding to make a geopolymer slurry. Then, stir it on a disperser at a speed of 400 r / min for 6 minutes to ensure uniform mixing.

[0067] (7) Take out the geopolymer slurry obtained in (6) from the disperser, and then add 13X zeolite in batches, 3.4 parts each time, with a total addition amount of 34 parts; after adding 13X zeolite each time, re-stir it on the disperser at a speed of 400 r / min for 2 minutes to ensure full mixing of 13X zeolite and the slurry, and prepare a fly ash - 13X zeolite composite geopolymer slurry.

[0068] (8) Pour the fly ash - 13X zeolite composite geopolymer slurry described in (7) into a plastic mold, cure it in an incubator at a temperature of 80 °C for 24 h, then take it out and demold.

[0069] (9) Put the demolded geopolymer sample described in (8) into a reaction kettle lined with polytetrafluoroethylene, add a 2 mol / L sodium hydroxide solution to the reaction kettle, and place the reaction kettle in an incubator at 100 °C for 48 h; take out the geopolymer sample from the reaction kettle, wash it repeatedly with deionized water until the pH of the washed liquid is close to 8; put the sample into an incubator to dry at 60 °C, and after drying is completed, the fly ash - based modified geopolymer carbon sequestration material is obtained.

[0070] (10) After preparation, characterize the sample. The specific characterization methods are: field emission electron microscopy (FSEM) and energy spectrum determination, X - ray diffraction analysis (XRD), measuring the specific surface area and pore size distribution (2 - 500 nm) by passing liquid nitrogen, and measuring the micropore (≤2 nm) pore size distribution of carbon dioxide.

[0071] Performance Testing

[0072] Conduct X - ray diffraction analysis (XRD), field emission electron microscopy analysis (FSEM), and specific surface area and pore analysis on the sample, and count its specific surface area, porosity, and porosity of different pore sizes for range analysis.

[0073] 1) XRD diffraction analysis is as Figure 2 shown:

[0074] The phase analysis of geopolymer samples was carried out by X-ray diffraction analysis. Curve 1 is the spectrum of fly ash, Curve 2 is the spectrum of fly ash-based geopolymer (GEO-0), Curve 3 is the spectrum of fly ash-based geopolymer added with 13X zeolite (GEO-6), and Curve 4 is the spectrum of fly ash-based geopolymer added with 13X zeolite and subjected to hydrothermal conversion (GEO-6HC).

[0075] It can be seen from Curve 1 that fly ash contains components such as quartz and mullite, and there is a bulge between 10° and 30°, representing the amorphous vitreous body of fly ash.

[0076] It can be seen from Curve 2 that after a series of reactions during the preparation of geopolymer, the bulge between 10° and 30° shifts to between 20° and 40°, presenting a diffuse, bun-shaped peak, proving that the vitreous body in fly ash dissolves and forms a new amorphous gel substance. Quartz crystal phase and mullite crystal phase still exist in GEO-0 after preparation, indicating that quartz and mullite do not participate in the reaction during the polymerization of geopolymer.

[0077] It can be seen from Curve 3 that GEO-6 is added with 13X zeolite, and the crystal phase of X-type zeolite is also detected in the spectrum, and the peak intensities of quartz and mullite in the spectrum are weakened compared with Curve 2, proving that the added 13X zeolite can coexist and be evenly mixed with the geopolymer.

[0078] It can be seen from Curve 4 that compared with the sample without hydrothermal conversion (Curve 3), a large number of new zeolite crystal phases are formed and some existing zeolite crystal phases are enhanced, proving that the pore structure of the geopolymer is optimized, providing more adsorption sites for CO2 adsorption. In fact, under this alkaline high-temperature condition, the alkaline environment provides favorable conditions for the nucleation and growth of zeolite crystals. The amorphous three-dimensional gel dissolves in the alkaline environment, rearranges and recombines to form nano-ordered structure zeolite crystals, and the high-temperature environment will accelerate this phase transition reaction process. The above phase transition process will increase the porosity and specific surface area of the material and enhance the CO2 adsorption performance.

[0079] 2) Specific surface area and pore analysis are as Figure 3 shown:[[]]END]]

[0080] When the relative pressure (P / P0) is relatively low, the adsorption capacity of GEO-6 rapidly reaches 30 cm 3 / g, while the adsorption capacity of GEO-6HC reaches 50 cm 3 / g. This part represents the microporous part of the material, and the adsorption capacities of both increase rapidly, verifying that the added 13X zeolite does not react and is relatively evenly present in the carbon fixation material. The initial adsorption capacity of GEO-6HC is higher than that of GEO-6. The analysis is that under the action of hydrothermal treatment, additional micropores are further formed inside the material.

[0081] At a relative pressure P / P0 = 0.5, the corresponding pore size is about 4 nm, and the adsorption amount at this time is approximately equal to the filling volume of the micropores. Hysteresis loops appear in all three samples. A relatively small hysteresis loop appears in GEO-6 at a relative pressure of about 0.8. According to the latest IUPAC classification, it is similar to the H4-type hysteresis loop. This type of hysteresis loop usually appears on adsorbents with a mixture of micropores and mesopores and in solids containing narrow slit pores. This verifies that the addition of 13X zeolite in GEO-6 forms such a hysteresis loop due to the combination of the micropores of the zeolite and the pores of the geopolymer itself. GEO-6HC also belongs to the H4-type hysteresis loop, but its hysteresis loop starts to appear at a relative partial pressure of about 0.1. This is because hydrothermal conversion will lead to the formation of a large number of mesopore pores in the sample, and the mesopore pores will cause capillary condensation, resulting in the phenomenon that the desorption pressure is always less than the adsorption pressure at the same adsorption amount. The hysteresis loop of GEO-0 belongs to the H3-type hysteresis loop.

[0082] At relatively high relative pressures, no saturated adsorption plateau appears in GEO-0, GEO-6, and GEO-6HC. Similar to the type II isothermal adsorption curve, as the relative pressure increases, the multilayer adsorption of the carbon fixation material gradually forms. When the saturated vapor pressure is reached, there are infinitely many adsorption layers, resulting in the absence of a saturated adsorption plateau.

[0083] 3) As Figure 4 shown, by comparing the pore size distribution diagrams of GEO-0, GEO-6, and GEO-6HC, it can be seen that the mesopore pore volume is GEO-0 < GEO-6 < GEO-6HC. This is because hydrothermal conversion causes the gel substances in the geopolymer sample to transform into the zeolite phase, increasing the mesopore pores in the sample, which will enhance its carbon dioxide adsorption capacity.

[0084] 4) The field emission electron microscope scan is as Figure 5 shown:

[0085] Regarding the difference between GEO-6 and GEO-0 with or without the addition of 13X zeolite, it can be clearly found in the picture that the added 13X zeolite (marked by the yellow circle in the figure) has a particle size of 2 - 5 μm, which is the same as the size of the added zeolite 13X. At the same time, point scanning is performed on the marked zeolite particles in Figure (d). It can be found that the hydrothermal product mainly contains 24.54 wt% of Si element, 14.4 wt% of Al element, and 7.44 wt% of Na element. After calculation, n(Na):n(Al):n(Si) = 1:3.29:1.94, which is very close to the theoretical molecular structural formula of 13X zeolite n(Na):n(Al):n(Si) = 1:3.35:2.02. Its composition is almost the same as that of 13X zeolite, which can prove that 13X zeolite did not participate in the reaction during the polymerization process of the geopolymer.

[0086] 5) Fourier transform infrared spectroscopy (FTIR) test is as Figure 6 shown below:

[0087] The FTIR spectra of each sample are as Figure 6 , and a broad absorption peak can be observed at 3450 cm -1 for all samples, which refers to the stretching vibration of the -OH group of water molecules on the sample surface. The bending vibration of the -OH group of free water molecules at 1645 cm -1 enhances the absorption peak, and the peak at 456 cm -1 is the bending vibration peak of the Si-O-Si bond.

[0088] The strong absorption peak of fly ash at 1100 cm -1 represents the asymmetric stretching vibration of the Si-O-Si bond in it, while GEO-0 has a broad absorption peak at 1020 cm -1 , which represents the asymmetric stretching vibration of the Si-O-T (T = Si or Al) bond in the geopolymer sample. This bond is the characteristic chemical bond for the successful polymerization of the geopolymer, and it reflects the process of Al substituting Si in fly ash: the active substances in fly ash react under the action of the alkali activator, alumina decomposes and releases Al 3+ , and during the geopolymerization reaction process, Al 3+ substitutes Si 4+ to form a silicon-aluminum long chain with Si-O-T bonds. In the FTIR spectrum, this is reflected as the strong absorption peak of fly ash at 1100 cm -1 shifts to around 1020 cm -1 , confirming that some Si-O-Si bonds are converted into Si-O-Al bonds. However, since the mass fractions of alumina and silica in fly ash are not equal, Al 3+ cannot completely substitute Si 4+ , and there is an inconspicuous symmetric stretching vibration peak of the Si-O-Si bond at 870 cm -1 , representing the unreacted fly ash particles in the system.

[0089] The relatively strong broad peak that appears at 990 cm -1 for 13X zeolite is due to the asymmetric stretching vibration of Si-O-T (T = Si or Al) inside 13X zeolite, which increases the vibration amplitude of the absorption peak at this location; the significant absorption peak at 755 cm -1 is caused by the symmetric stretching vibration of the tetrahedral Si-O-Si bond and Al-O-Al bond inside 13X zeolite; in addition, the peak at 562 cm -1 is the vibration absorption peak of the double six-membered ring of 13X zeolite, and this peak is the characteristic absorption peak of 13X zeolite.

[0090] Compared with GEO-0, 13X zeolite is added to GEO-6, resulting in the peak at 1020 cm -1 shifting to 990 cm -1 at this position. This is because there are more Si-O-T bonds in 13X zeolite, and the asymmetric stretching vibration of internal Si-O-T (T = Si or Al) makes the vibration amplitude of the absorption peak at this position increase. The absorption peak at 755 cm -1 is caused by the symmetric stretching vibration of internal tetrahedral Si-O-Si bonds and Al-O-Al bonds of the added 13X zeolite. In addition, the absorption peak at 562 cm -1 is the vibration absorption peak of the double six-membered ring of 13X zeolite. This peak is the characteristic absorption peak of 13X zeolite, which also proves that 13X zeolite is uniformly mixed and coexists with geopolymers.

[0091] The vibration absorption peaks of GEO-6HC at 755 cm -1 and 562 cm -1 are broader than those of GEO-6, indicating that more Si-O-T bonds are formed during the hydrothermal conversion process.

[0092] In the FTIR spectrum, the formation of chemical bonds such as Si-O-T indicates the degree of formation of amorphous gel substances in the geopolymerization reaction. Although it is still difficult to judge the degree of geopolymerization reaction only based on the positions of various chemical bonds in FTIR, it is of great significance for qualitative analysis of the geopolymerization reaction.

[0093] 6) Carbon dioxide isothermal adsorption test:

[0094] The CO2 isothermal adsorption test was carried out on samples GEO-0, GEO-6, and GEO-6HC using an isothermal adsorption instrument. The tests were carried out at 40 °C respectively, and the pressure range was set to 0~5 MPa. The test results are shown in Figure 7 , Figure 8 , Figure 9 .

[0095] At the temperature and pressure of 40 °C and 5 MPa, the CO2 adsorption capacity of GEO-0 is 2.5 cm 3 / g, and the adsorption capacity of GEO-6 is 36.7 cm 3 / g, as shown in Table 2. After adding 13X zeolite, the adsorption capacity increased significantly, which proves that adding 13X zeolite is effective in improving the micropore porosity of the sample. In the isothermal adsorption image of sample GEO-6, the adsorption capacity of the sample increases very rapidly at low pressure, indicating that this part is the added microporous material playing the adsorption role, because micropores are more likely to adsorb CO2 at low pressure, proving that the added microporous material 13X zeolite performs excellently.

[0096] At a temperature and pressure environment of 40 °C and 5 MPa, the adsorption capacity of GEO-6HC is 70.6 cm 3 / g, while the adsorption capacity of GEO-6 is only 36.7 cm 3 / g. After improving the pore structure through hydrothermal conversion, the adsorption capacity of the sample is significantly improved, which proves that the improvement of the pores of the sample by hydrothermal conversion is effective. The mesopore specific surface area and micropore specific surface area measured by nitrogen adsorption and carbon dioxide adsorption tests show that the hydrothermal conversion group GEO-6HC has increased the mesopore and micropore volume and specific surface area of the existing geopolymer GEO-6, as shown in Table 2. In the isothermal adsorption image of sample GEO-6HC compared with GEO-6, at lower pressures, the adsorption capacity of this part of sample GEO-6HC is larger than that of GEO-6, proving that hydrothermal conversion has an excellent improvement on the performance of geopolymer in adsorbing CO2. In this case, 13X zeolite is used to optimize the micropores of the geopolymer and perform CO2 adsorption tests. At a temperature and pressure environment of 40 °C and 5 MPa, the CO2 adsorption capacity reaches 36.7 cm 3 / g; while the product of this case treated by adding 13X zeolite and hydrothermal conversion innovation technology comprehensively improves and enhances the micropores and mesopores that affect the CO2 adsorption performance of the geopolymer, and the adsorption capacity reaches 70.6 cm 3 / g under the same working conditions.

[0097] Table 2 Comparison table of micropore and mesopore structure parameters and carbon dioxide adsorption capacity

[0098]

[0099] In summary, the fly ash-based modified geopolymer carbon fixation material prepared by the present invention through adding 13X zeolite and performing hydrothermal conversion process can not only introduce microporous materials to increase micropores, but also cause the phase change of the geopolymer amorphous three-dimensional gel to zeolite crystals, thereby increasing the micropores and mesopores. It comprehensively regulates and enhances the micropores and mesopore porosity that control the specific surface area of the material, so as to enhance the carbon dioxide adsorption capacity. This method not only improves the high-value utilization of fly ash, but also provides a new environmental protection solution for carbon capture and storage, with significant social and economic significance. This case opens up a new way for the coordinated disposal of carbon waste and the reuse of abandoned underground space.

[0100] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the amounts of materials defined herein can be adjusted accordingly in other embodiments without departing from the spirit or scope of the present invention. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a fly ash-based geopolymer carbon fixation and adsorption material, characterized in that, The method specifically comprises the following steps: S1: Weigh the raw materials respectively according to the proportion, then dissolve sodium hydroxide in water, heat in a water bath and add sodium silicate one by one, stir and dissolve to prepare an alkaline activator solution; S2: slowly adding fly ash to the alkaline activator solution prepared in S1, stirring to obtain a geopolymer slurry; S3: gradually adding 13X zeolite to the geopolymer slurry prepared in S2, stirring to obtain fly ash-13X zeolite composite geopolymer slurry; the 13X zeolite is a white powder with a particle size of 2 μm to 4 μm and a bulk density of ≥0.33 g / mL; S4: pouring the fly ash-13X zeolite composite geopolymer slurry prepared in S3 into a mold, and demoulding after constant temperature curing; S5: adding sodium hydroxide solution to the geopolymer sample after demoulding in S4, hydrothermal reaction, followed by washing and drying, to obtain the fly ash-based geopolymer carbon fixation adsorption material; The raw materials are mainly composed of the following substances in parts by weight: 100 parts of fly ash, 55-70 parts of water, 10-34 parts of 13X zeolite, 15-38 parts of alkali activator; The weight proportion of the sodium silicate in S1 added in batches is 1-2 parts, the weight proportion of the 13X zeolite in S3 added in batches is 3.4 parts, and the concentration of the sodium hydroxide solution in S5 is 2 mol / L, and the added amount is 54 parts.

2. The preparation method of the fly ash-based geopolymer carbon fixation and adsorption material according to claim 1, characterized in that, The alkaline activator is a mixed powder of sodium hydroxide and sodium silicate, and the alkaline activator includes 12 to 27 parts of sodium silicate and 3 to 11 parts of sodium hydroxide in parts by weight; Moreover, the modulus of the alkaline activator is 0.8-1.1; the sodium hydroxide is analytically pure powder; and the sodium silicate is analytically pure powder with a modulus of 2.

8.

3. The preparation method of the fly ash-based geopolymer carbon fixation and adsorption material according to claim 1, wherein, The stirring speed in S2 is 400 r / min, and the stirring time is 4-6 min; the stirring speed in S3 is 400 r / min, and the stirring time is 1-2 min; the constant temperature curing temperature in S4 is 80°C, and the curing time is 24 h; the hydrothermal reaction temperature in S5 is 100°C, and the reaction time is 48 h.

4. A fly ash-based polymer carbon fixation adsorption material prepared by the method as claimed in claim 1.

5. The fly ash-based geopolymer carbon fixation and adsorption material according to claim 4, characterized in that, The fly ash-based polymer carbon fixation adsorption material has a solid-liquid mass ratio of 0.55-0.7, a silicon-aluminum molar ratio of 1.7-2.0, and a constant curing temperature of 80°C.

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