Fly ash slag carbon sequestration geopolymer and preparation method and application thereof

Abstract

The application discloses a fly ash and slag carbon fixation geopolymer as well as a preparation method and application thereof, and relates to the technical field of building materials. The preparation method of the fly ash and slag carbon fixation geopolymer comprises the following steps: S1, adding fly ash into a carbonate solution, uniformly mixing, and introducing carbon dioxide gas to perform a carbon fixation reaction to obtain carbon fixation fly ash; S2, adding carbon fixation slag into the carbonate solution, uniformly mixing, and introducing carbon dioxide gas to perform a carbon fixation reaction to obtain carbon fixation slag; S3, mixing the carbon fixation fly ash obtained in the step S1 and the carbon fixation slag obtained in the step S2, adding an activator, i.e., anhydrous sodium silicate, and uniformly stirring, then adding water and stirring to obtain the fly ash and slag carbon fixation geopolymer. The fly ash and slag carbon fixation geopolymer obtained by the application has a high carbon fixation rate, and the initial setting time can reach 65 min without adding a retarder, and the geopolymer matrix strength can reach 35.2 MPa after 7 days.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and more specifically, to a fly ash slag carbon sequestrant, its preparation method, and its application. Background Technology

[0002] Global warming is one of the major environmental challenges facing the world today. China has been actively taking measures to reduce greenhouse gas emissions in order to achieve green and low-carbon development. To achieve global carbon neutrality and carbon emission reduction goals, it is necessary not only to reduce carbon emissions from production but also to develop effective carbon capture technologies. Current research has explored the use of industrial waste slag and fly ash as supplementary cementitious materials in cement production, enabling waste recycling. Slag and fly ash contain a certain amount of calcium-containing phase, which can convert carbon dioxide into carbonate compounds, possessing significant carbon sequestration potential. The carbon sequestration rate of waste is affected by factors such as temperature, pressure, solvent, solid-liquid ratio, carbonization time, and material particle size, with solvent and particle size having the most significant impact on the carbonization rate. Existing waste carbon sequestration methods often use costly chemical agents or energy-intensive conditions to improve efficiency; however, introducing new substances often hinders the reuse of carbon-sequestrated waste. Therefore, it is necessary to develop a new carbon sequestration method that achieves low-cost, high-efficiency carbon sequestration under ambient temperature and pressure conditions and enables the reuse of carbon-sequestrated waste.

[0003] Existing technology discloses a method for carbonization modification of slag, a carbonization-modified slag cementitious material, and its preparation method. The carbon fixation method involves gas-solid reaction carbonization at ambient temperature and pressure. The slag is placed under conditions of 20–30℃, 50–70% relative humidity, and 30–100% carbon dioxide volume concentration for 3–168 hours to complete the carbonization modification. Then, the modified slag is used as a cementitious material to prepare geopolymers through a two-step method. Slag carbonization modification can not only capture and store some carbon dioxide but also effectively extend the setting time of the carbonized slag cementitious material. However, its carbon fixation efficiency is low, only 1.5%, which is not conducive to improving the strength of the geopolymer and makes it difficult to adapt to practical engineering applications. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects or deficiencies of existing waste carbon sequestration methods, which have low carbon sequestration efficiency, and to provide a method for preparing fly ash and slag carbon sequestration geopolymers.

[0005] Another object of the present invention is to provide a fly ash slag carbon sequestrant.

[0006] Another objective of this invention is to provide an application of fly ash slag carbon sequestrants in building materials.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a fly ash slag carbon sequestrant includes the following steps:

[0009] S1. Add fly ash to a carbonate solution, mix well, and pass carbon dioxide gas through to carry out a carbon fixation reaction to obtain carbon-fixed fly ash;

[0010] S2. Add the carbon-fixing slag to the carbonate solution, mix well, and then pass carbon dioxide gas through to carry out the carbon fixation reaction to obtain the carbon-fixing slag.

[0011] S3. Mix the carbon-fixed fly ash obtained in step S1 and the carbon-fixed slag obtained in step S2, add anhydrous sodium silicate as an activator and stir evenly, then add water and stir to obtain fly ash slag carbon-fixed geopolymer.

[0012] The preparation method of this invention involves adding fly ash and slag to a carbonate solution and then introducing carbon dioxide. On one hand, carbonate ions react with carbon dioxide and water to generate bicarbonate ions. These bicarbonate ions then react with the active calcium oxide in the fly ash or slag to form stable calcium carbonate, thus achieving carbon fixation. On the other hand, carbonate ions increase the solubility of carbon dioxide at room temperature and pressure, which is beneficial for promoting the carbon fixation reaction. Furthermore, the consumed carbonate ions can be regenerated through continuous injection of carbon dioxide, further improving the carbon fixation efficiency. The carbon-fixed slag and fly ash obtained after carbon fixation have lower active calcium oxide content and higher calcium carbonate content compared to the slag or fly ash before carbon fixation. This results in a longer setting time and higher strength for the resulting geopolymer. In the formed geopolymer, the active calcium oxide reacts with water to form calcium hydroxide, providing an alkaline environment for the geopolymer pore liquid and accelerating the reaction. Therefore, the geopolymer sets faster. When the active calcium oxide content decreases, the geopolymer setting time becomes longer.

[0013] Preferably, the carbonate in step S1 can be either sodium carbonate or potassium carbonate.

[0014] Preferably, the concentration of the carbonate solution in step S1 or step S2 is 0.2–1 mol / L. Specifically, it can be 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, or 1 mol / L. To improve the carbon fixation efficiency of fly ash or slag, it is necessary to select an appropriate carbonate concentration. If the carbonate concentration is too low, the carbon fixation reaction rate is slow and the carbon fixation time is long; if the carbonate concentration is too high, it will result in waste of raw materials.

[0015] Preferably, the ratio of the mass of fly ash in step S1 or the mass of slag in step S2 to the volume of carbonate solution is 0.1 to 0.5 (g / ml). Within this ratio range, all fly ash or slag can be well wetted in the carbonate solution, which is beneficial for a more complete carbon fixation reaction.

[0016] Preferably, the flow rate of the carbon dioxide gas introduced in step S1 or step S2 is 0.1 to 1 mL / (min·g). In a specific embodiment, the purity of the carbon dioxide gas introduced in step S1 or step S2 is 99%, and the flow rate of the carbon dioxide gas is 0.5 mL / (min·g).

[0017] Preferably, the carbon fixation reaction in step S1 or step S2 is carried out at a temperature of 25–65°C. In a specific embodiment, the carbon fixation reaction in step S1 or step S2 is carried out at a temperature of 45°C, and can be conducted under stirring in a water bath at a stirring speed of 1000 rpm / min. Generally, the carbon fixation reaction in step S1 can be carried out at room temperature with stirring, but the reaction temperature can be appropriately increased to accelerate the reaction rate.

[0018] Preferably, the carbon fixation reaction time in step S1 or step S2 is 0.5 to 6 hours. In specific embodiments, the stirring time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0019] It should be noted that the carbon-fixed fly ash and carbon-fixed slag obtained in steps S1 and S2 need to be dried. The carbon-fixed fly ash and carbon-fixed slag can be dried in a drying oven at 102℃ for 24 hours.

[0020] Preferably, the mass ratio of carbon-fixing fly ash and carbon-fixing slag, anhydrous sodium silicate and water in step S3 is 40-60:40-60:10-20:30-50. Under this ratio, the resulting geopolymer exhibits superior performance.

[0021] Preferably, the modulus (Si2O / Na2O) of the anhydrous sodium silicate in step S3 is 1 to 2.

[0022] A type of fly ash slag carbon sequestration geopolymer is also within the scope of protection of this invention.

[0023] Preferably, the initial setting time of the fly ash slag carbon-fixing geopolymer is greater than 60 minutes, and the carbon fixation rate is higher than 9.5%.

[0024] This invention also protects the application of a fly ash slag carbon-fixing geopolymer in building materials.

[0025] The present invention has the following beneficial effects:

[0026] (1) This invention employs a solid-liquid carbonization process to prepare carbon-fixed fly ash and carbon-fixed slag into fly ash and slag carbon-fixed geopolymers. Compared with the traditional gas-solid carbonization reaction, the preparation method of this invention has a faster carbon fixation rate and a deeper degree of carbonization, achieving complete carbonization within 3 hours. The fly ash and slag carbon-fixed geopolymers obtained by this invention have excellent properties. Without the addition of a retarder, the initial setting time can reach 65 minutes, and the geopolymer matrix strength can reach 35.2 MPa after 7 days.

[0027] (2) In the process of preparing fly ash slag carbon geopolymer, the present invention does not require the prior preparation of alkali solution, but can directly add water, which can avoid the safety hazards caused by alkali solution transportation. Attached Figure Description

[0028] Figure 1 The image shows a comparison of the XRD patterns of carbonized fly ash and non-carbonized fly ash in Example 1.

[0029] Figure 2 The image shows a comparison of XRD patterns of carbonized slag and non-carbonized slag in Example 1. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0031] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0032] Example 1

[0033] A method for preparing a fly ash slag carbon sequestrant includes the following steps:

[0034] S1. Add 500g of fly ash to 2L of sodium carbonate solution with a concentration of 0.5mol / L, mix well, then pass carbon dioxide gas with a volume fraction of 99% through the solution at a flow rate of 0.5mL / (min·g), heat in a water bath to 45℃, set the stirring speed to 1000rpm / min and stir for 3h, then let stand for 6h, filter, and place the filter residue in an oven to dry at 102℃ for 24h to obtain carbon-fixed fly ash;

[0035] S2. Add 500g of slag to 2L of sodium carbonate solution with a concentration of 0.5mol / L, mix well, and then pass in carbon dioxide gas with a volume fraction of 99% at a flow rate of 0.5mL / (min·g). Heat the mixture in a water bath to 45℃, set the stirring speed to 1000rpm / min and stir for 3h. Then let it stand for 6h, filter, and place the filter residue in an oven to dry at 102℃ for 24h to obtain carbon-fixed slag.

[0036] S3. Mix the carbon-fixed fly ash and carbon-fixed slag obtained in steps S1 and S2, add anhydrous sodium silicate as an activator and stir evenly, then add water and stir to obtain fly ash slag carbon-fixed geopolymer, wherein the mass ratio of carbon-fixed fly ash and carbon-fixed slag, anhydrous sodium silicate and water is 50:50:15:45, and the modulus of anhydrous sodium silicate (Si2O / Na2O) is 1.0.

[0037] Example 2

[0038] A method for preparing a fly ash slag carbon sequestrant is basically the same as that in Example 1, except that the concentration of sodium carbonate solution in steps S1 and S2 is 1 mol / L.

[0039] Example 3

[0040] A method for preparing a fly ash slag carbon sequestrant is basically the same as that in Example 1, except that the temperature of the water bath in steps S1 and S2 is 25°C.

[0041] Example 4

[0042] A method for preparing a fly ash slag carbon sequestrant is basically the same as that in Example 1, except that the volume of sodium carbonate in steps S1 and S2 is 1L, that is, the ratio of the mass of fly ash in step S1 or the mass of slag in step S2 to the volume of carbonate solution is 0.5 (g / ml).

[0043] Example 5

[0044] A method for preparing a fly ash slag carbon sequestrant is basically the same as that in Example 1, except that the water bath temperature in steps S1 and S2 is 65°C.

[0045] Example 6

[0046] A method for preparing a carbon-fixed geopolymer from fly ash and slag is basically the same as that in Example 1, except that the mass ratio of carbon-fixed fly ash and carbon-fixed slag, anhydrous sodium silicate and water in step S3 is 40:60:15:45.

[0047] Example 7

[0048] A method for preparing a carbon-fixed geopolymer from fly ash and slag is basically the same as that in Example 1, except that the mass ratio of carbon-fixed fly ash and carbon-fixed slag, anhydrous sodium silicate and water in step S3 is 60:40:15:45.

[0049] Example 8

[0050] A method for preparing a carbon-fixed geopolymer from fly ash and slag is basically the same as that in Example 1, except that the mass ratio of carbon-fixed fly ash and carbon-fixed slag, anhydrous sodium silicate and water in step S3 is 50:50:10:45.

[0051] Example 9

[0052] A method for preparing a carbon-fixed geopolymer from fly ash and slag is the same as in Example 1, except that in step S3, the mass ratio of carbon-fixed fly ash and carbon-fixed slag, anhydrous sodium silicate and water is 50:50:20:45.

[0053] Example 10

[0054] A method for preparing a carbon-fixed geopolymer from fly ash and slag is basically the same as that in Example 1, except that the mass ratio of carbon-fixed fly ash and carbon-fixed slag, anhydrous sodium silicate and water in step S3 is 50:50:15:35.

[0055] Example 11

[0056] A method for preparing a fly ash slag carbon sequestrant is basically the same as that in Example 1, except that the anhydrous sodium silicate modulus (Si2O / Na2O) in step S3 is 2.0.

[0057] Comparative Example 1

[0058] This comparative example provides a method for preparing fly ash and slag geopolymers. Fly ash and slag are mixed, an activator, anhydrous sodium silicate, is added and stirred evenly, and then water is added and stirred to obtain fly ash and slag geopolymers. The mass ratio of fly ash and slag, anhydrous sodium silicate and water is 50:50:15:45, and the modulus of anhydrous sodium silicate (Si2O / Na2O) is 1.0.

[0059] Comparative Example 2

[0060] This comparative example provides a method for preparing carbon-fixing geopolymers from fly ash and slag, including the following steps:

[0061] S1. Add 500g of fly ash to 2L of water, mix well, then introduce carbon dioxide gas with a volume fraction of 99% at a flow rate of 0.5mL / (min·g), heat in a water bath to 45℃, set the stirring speed to 1000rpm / min and stir for 3h, then let stand for 6h, filter, and place the filter residue in an oven to dry at 102℃ for 24h to obtain carbon-fixed fly ash;

[0062] S2. Add 500g of slag to 2L of water, mix well, and then introduce carbon dioxide gas with a volume fraction of 99% at a flow rate of 0.5mL / (min·g). Heat the water bath to 45℃, set the stirring speed to 1000rpm / min and stir for 3h. Then let it stand for 6h, filter, and place the filter residue in an oven to dry at 102℃ for 24h to obtain carbon-fixed slag.

[0063] S3. Mix the carbon-fixed fly ash and carbon-fixed slag obtained in steps S1 and S2, add anhydrous sodium silicate as an activator and stir evenly, then add water and stir to obtain fly ash slag carbon-fixed geopolymer, wherein the mass ratio of carbon-fixed fly ash and carbon-fixed slag, anhydrous sodium silicate and water is 50:50:15:45, and the modulus of anhydrous sodium silicate (Si2O / Na2O) is 1.0.

[0064] Performance testing

[0065] (1) XRD test: X-ray diffraction analysis was performed on the carbon-fixed fly ash obtained in Example 1 and the raw fly ash without carbon fixation treatment. The results are as follows: Figure 1 As shown, from Figure 1 The increased peak value of the calcium carbonate phase indicates the formation of more calcium carbonate, demonstrating successful carbon fixation of the fly ash. Similarly, X-ray diffraction analysis was performed on the carbon-fixed slag obtained in Example 1 and the raw material slag without carbon fixation treatment. The results are as follows... Figure 2 As shown, the enhancement of the calcium carbonate phase can also be seen, proving that the carbon fixation of the slag was successful.

[0066] (2) Geopolymer setting time test: The test was conducted using a Vicat apparatus in accordance with the national standard GB / T 1346-2011.

[0067] (3) Mechanical properties test of geopolymer: According to the standard JGJ / T 70-2009, a 70.7mm×70.7mm×70.7mm cube was used as the research object, and the test instrument was YNS-3000 material testing machine.

[0068] (4) Geopolymer carbon fixation rate = carbon dioxide absorption mass / (total mass of carbon-fixing fly ash and carbon-fixing slag), where the carbon dioxide absorption mass is calculated based on the mass loss caused by heating to 900℃.

[0069] The setting time, carbon fixation rate, and mechanical properties of all fly ash slag carbon-fixing geopolymers from the embodiments and the fly ash slag geopolymer from Comparative Example 1 were tested, and the results are as follows.

[0070] Table 1. Results of setting time tests for Example 1 and Comparative Example 1

[0071]

[0072]

[0073] Table 2 Comparison of geopolymer carbon sequestration rates in various examples and comparative examples.

[0074]

[0075] Table 3. Mechanical test results of geopolymers in each embodiment and comparative example.

[0076]

[0077] As shown in Table 1, the initial setting time of the fly ash and slag carbon-fixed geopolymer in Example 1 reached 65 min, and the final setting time was as long as 84 min. In Example 2, the initial setting time of the fly ash and slag carbon-fixed geopolymer reached 73 min, and the final setting time was as long as 95 min, significantly higher than the initial and final setting times of the geopolymers in Comparative Examples 1 and 2. This indicates that the carbon fixation modification treatment of fly ash and slag in this invention can effectively delay the setting time of the fly ash and slag carbon-fixed geopolymer, which is beneficial for the promotion and application of fly ash and slag carbon-fixed geopolymers in engineering. The initial and final setting times of the fly ash and slag carbon-fixed geopolymers in Examples 3-11 are basically equivalent to those in Example 1.

[0078] Table 2 shows that the carbon fixation of fly ash is affected by various factors. When the sodium carbonate solution concentration is 0.5 mol / L, the carbon fixation rate of the fly ash-slag carbon-fixing geopolymer can reach 12.5%. Further increasing the sodium carbonate solution concentration to 1 mol / L results in a slight decrease in the carbon fixation rate, possibly because the solubility of carbon dioxide decreases with increasing sodium carbonate concentration. Increasing the ratio of fly ash or slag mass to sodium carbonate solution volume (solid-liquid ratio) weakens the carbonization process. As the solid-liquid ratio increases, the carbon fixation rate decreases because when the proportion of fly ash or slag increases, the sodium carbonate solution cannot fully wet the solid powder, thus affecting the depth of carbon fixation. The preparation processes of the carbon-fixed fly ash and carbon-fixed slag in Examples 6-11 are exactly the same as in Example 1. Therefore, the carbon fixation rate of the fly ash-slag carbon-fixing geopolymers obtained in Examples 6-11 is comparable to that in Example 1.

[0079] The carbon fixation rate of the fly ash and slag carbon-fixing geopolymer in Comparative Example 2 was only 5.2%, indicating that the addition of carbonates has a promoting effect on the carbon fixation reaction of fly ash and slag. This is because, on the one hand, carbonate ions react with carbon dioxide and water to generate bicarbonate ions, and bicarbonate ions react with active calcium oxide in fly ash or slag to obtain stable calcium carbonate, thus achieving carbon fixation; on the other hand, carbonate ions can increase the solubility of carbon dioxide at room temperature and pressure, which is conducive to promoting the carbon fixation reaction. At the same time, the consumed carbonate ions can be regenerated by continuously injected carbon dioxide, thus further improving the carbon fixation efficiency.

[0080] As shown in Table 3, compared with Comparative Example 2, carbonization can improve the strength of fly ash-slag carbon-fixed geopolymers in Example 1. Compared with Example 1, Examples 6 and 7 show that fly ash exhibits lower activity than slag, and increasing the mass ratio of fly ash deteriorates the strength of fly ash-slag carbon-fixed geopolymers. Compared with Example 1, the strength of the carbon-fixed geopolymer in Example 8 is significantly reduced because the reduced amount of sodium silicate leads to insufficient reaction between carbon-fixed fly ash, carbon-fixed slag, sodium silicate, and water. In Example 9, the increased amount of sodium silicate results in increased geopolymer strength. Compared with Example 1, Example 10 reduces the amount of water, increasing the alkalinity of the geopolymer pore liquid environment. Under strongly alkaline activation conditions, the reaction to form the geopolymer is more vigorous, resulting in higher geopolymer strength. Compared with Example 1, Example 11 increases the modulus of sodium silicate, which hinders the dissolution of sodium silicate and affects the reaction of the geopolymer matrix, thus reducing its strength. The strength of the fly ash slag carbon sequestration geopolymers in Examples 2-5 is basically the same as that in Example 1.

[0081] The strength of the geopolymer in Comparative Example 2 was higher than that in Example 8 because the amount of anhydrous sodium silicate in Comparative Example 2 was higher than that in Example 8, and the amount of anhydrous sodium silicate has a significant impact on the strength of the geopolymer. The strength of the geopolymer in Comparative Example 2 was also slightly higher than that in Example 7 because the mass ratio of fly ash to slag in Example 7 (60:40) was higher than that in Comparative Example 2 (50:50), and an increase in the mass ratio of fly ash would deteriorate the strength of the fly ash and slag carbon-fixed geopolymer.

[0082] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A fly ash slag carbon sequestration geopolymer, characterized in that, Its preparation method includes the following steps: S1. Add fly ash to a carbonate solution, mix well, and pass carbon dioxide gas through to carry out a carbon fixation reaction to obtain carbon-fixed fly ash; S2. Add the carbon-fixing slag to the carbonate solution, mix well, and then pass carbon dioxide gas through to carry out the carbon fixation reaction to obtain the carbon-fixing slag. S3. Mix the carbon-fixed fly ash obtained in step S1 and the carbon-fixed slag obtained in step S2, add anhydrous sodium silicate as an activator and stir evenly, then add water and stir to obtain fly ash slag carbon-fixed geopolymer. In step S3, the mass ratio of carbon-fixing fly ash, carbon-fixing slag, anhydrous sodium silicate, and water is 40-60:40-60:15-20:30-50; the modulus of the anhydrous sodium silicate is 1-2.

2. The fly ash slag carbon sequestration geopolymer as described in claim 1, characterized in that, The concentration of the carbonate solution in step S1 or step S2 is 0.2~1 mol / L.

3. The fly ash slag carbon sequestration geopolymer as described in claim 1, characterized in that, The ratio of the mass of fly ash in step S1 or the mass of slag in step S2 to the volume of carbonate solution is 0.1~0.5 (g / ml).

4. The fly ash slag carbon sequestration geopolymer as described in claim 1, characterized in that, The flow rate of carbon dioxide gas introduced in step S1 or step S2 is 0.1~1 mL / (min•g).

5. The fly ash slag carbon sequestration geopolymer as described in claim 1, characterized in that, The temperature of the carbon fixation reaction in step S1 or step S2 is 25~65℃.

6. The fly ash slag carbon sequestration geopolymer as described in claim 1, characterized in that, The carbon fixation reaction in step S1 or step S2 takes 0.5 to 6 hours.

7. The fly ash slag carbon sequestration geopolymer as described in claim 1, characterized in that, The initial setting time is greater than 60 minutes, and the carbon fixation rate is higher than 9.5%.

8. The application of the fly ash slag carbon sequestrant as described in any one of claims 1 to 7 in building materials.

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