All-solid-waste carbon-sequestration cementing material and preparation method thereof

Abstract

The invention provides an all-solid waste carbon sequestration cementing material and a preparation method thereof, and belongs to the technical field of solid waste materials. The carbon sequestration cementing material is prepared from the following raw materials in parts by mass: 100 parts of steel slag powder, 2-30 parts of carbide slag and 1-3 parts of a modifier. The prepared carbon sequestration cementing material is excellent in performance, the compressive strength of the carbon sequestration cementing material ranges from 108 MPa to 131 MPa, and the carbon sequestration rate ranges from 16% to 25%. High-value utilization and negative carbon production of the solid waste can be realized, and the method is suitable for the technical fields of prefabricated buildings, concrete aggregate preparation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste materials, and in particular to an all-solid waste solid carbon cementitious material and a preparation method thereof. Background Art

[0003] As the mainstay of my country's economic development, the steel industry ranks first in the world in terms of scale and production line categories. Due to many problems such as the lack of valuable mineral phases and poor stability, the large-scale high-value consumption of steel slag has not made substantial breakthroughs, and the utilization of steel slag is worrying, with a comprehensive utilization rate of only 22%. The main component of stainless steel slag is γ-C2S minerals, which have low hydration activity and are more difficult to use than other steel slags (such as converter slag, etc.). The accumulation of steel slag not only occupies land resources and consumes a lot of financial resources, but also causes serious environmental pollution.

[0004] Carbon Capture Utilization and Storage (CCUS) technology is an effective means to achieve a significant reduction in CO2 emissions. Among them, mineral storage technology for CO2 has attracted widespread attention due to its good stability and economic potential. Steel slag can be used as a carrier for capturing CO2 because it is rich in calcium and alkaline substances. It can undergo carbonation reaction in a CO2 environment and convert into highly stable CaCO3, thereby promoting long-term carbonation. Stainless steel slag is rich in γ-dicalcium silicate (γ-C2S), has low hydration activity, but high carbonation activity, and is a good carbonation raw material. Using steel slag to capture and solidify CO2 and replace cement for various projects can achieve the goal of "using waste (CO2) to treat waste (stainless steel slag)" with steel slag.

[0005] At present, the carbon capture technology of steel slag has a certain theoretical and experimental basis, and the application of carbonized products of steel slag in building materials has been proven to have broad prospects. The patent application with publication number CN116573910A discloses a method for preparing a high-strength carbonized steel slag cementitious material, which proposes to use a liquid lifting agent mixed with steel slag to obtain a carbonized cementitious material by pressing and molding. Under a carbonization pressure of 0.1MPa, the compressive strength of the material reaches 107.58MPa, and the CO2 absorption is 16.95%. However, considering that the size of the cementitious material obtained by this method is large, there may be problems such as low pressure and difficulty in complete carbonization in a short time.

[0006] The patent application with publication number CN114538867A discloses a method for preparing cement-based materials from carbonized steel slag slurry, which firstly carbonizes the steel slag by passing CO2 into a slurry made of steel slag and water. The CO2 absorption rate in this process is 11.54wt.%, and then the carbonized steel slag slurry is mixed with cement and other materials to obtain cement-based materials. The 28d compressive strength of the prepared cementitious material reaches 64.3MPa, and the volume stability meets the standard. However, the cement substitution rate is only 0% to 30%, which cannot achieve large-scale utilization of steel slag and negative carbon production. The patent application with publication number CN117735877A discloses a method for preparing a high-activity mineral slurry from wet carbonized steel slag. The invention places biochar and steel slag in a high-pressure reactor with a stirring device, stirs at a low speed and introduces CO2 gas until the pressure in the reactor reaches 3MPa, then stirs at a high speed to obtain a slurry, and finally prepares the slurry into a cement specimen, whose 7d compressive strength reaches 47MPa and CO2 absorption is 14.89g. This technology has a high carbonization pressure and high requirements for equipment, and the prepared slurry needs to be used in combination with a cementitious material, which is complex in process and high in cost.

[0007] The existing forming process for steel slag samples is mostly focused on pressing, but the density of pressed samples is low and CO2 diffusion is hindered, resulting in low carbonization degree and low carbon fixation rate. At the same time, the temperature and pressure required by the existing carbonization process are relatively high, the carbonization reaction conditions are relatively harsh, the process is relatively complex, and the energy consumption is high. In addition, the existing carbonization process lacks coordinated research on the moisture content and pore structure of the sample before carbonization.

[0008] In the steel slag sample molding process, casting molding can produce higher initial porosity than pressing molding, thus more effectively promoting CO2 diffusion. This is because the initial porosity of the cast molded specimen can be significantly controlled by controlling the water-solid ratio, and the pore structure and porosity play a key role in promoting CO2 diffusion. Therefore, how to obtain a high carbon fixation gel material and its preparation method is a technical problem that needs to be solved at present. Summary of the invention

[0009] The purpose of the present invention is to provide a full-solid waste carbon-fixing cementitious material and a preparation method thereof, so as to solve the technical problem of low carbon fixation rate of current carbon-fixing materials.

[0010] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0011] The present invention provides a full-solid waste carbon-fixing cementitious material, which is prepared from raw materials containing the following parts by mass:

[0012] 100 parts of steel slag powder, 2-30 parts of carbide slag and 1-3 parts of modifier;

[0013] The modifier comprises one or more of sodium citrate, citric acid, sodium bicarbonate, sodium pyrophosphate and sodium tartrate.

[0014] The present invention also provides a method for preparing a solid waste carbon-fixing cementitious material, comprising the following steps:

[0015] 1) Weighing and mixing the raw materials according to their mass fractions to obtain a mixture, and mixing the mixture with water to obtain a slurry;

[0016] 2) pouring the slurry into a mold, drying it after natural curing, and controlling the moisture content to be 6-8% to obtain a sample;

[0017] 3) Carbonizing the sample in a CO2 atmosphere to obtain a fully solid waste carbon-fixing cementitious material.

[0018] Furthermore, in the step 1), the water-to-solid ratio of the slurry is 0.2 to 0.4.

[0019] Furthermore, in the step 2), the calculation formula of the moisture content is w%=(m1-m2) / m2×100%;

[0020] In the formula, m1 is the mass of the sample after drying for t time; m2 is the mass of the completely dried dry basis sample, and w% is the moisture content.

[0021] Furthermore, in the step 2), the natural curing time is 12 to 24 hours, and the drying temperature is 30 to 50°C.

[0022] Furthermore, in the step 3), the concentration of CO2 is 99.9vt.%, and the pressure of CO2 is 0.1-0.4MPa.

[0023] Furthermore, the carbonization temperature is 20-80° C., the carbonization time is 6-96 hours, and the carbonization is carried out under vacuum conditions, and the vacuum is evacuated to 0.7-0.8 MPa.

[0024] Beneficial effects of the present invention:

[0025] 1. Currently, the preparation methods of steel slag products are mainly divided into two types: pressing and casting. Products prepared by pressing have the characteristics of high production efficiency and high compressive strength, and are the method used by most of the current research on carbonized steel slag products. However, due to the low porosity, the migration of CO2 may be hindered during the carbonization reaction, resulting in a low degree of reaction. Casting has the characteristics of large porosity and uniform pore distribution. The carbon fixation rate may be improved by preparing steel slag test blocks in this way. However, steel slag and carbide slag cannot be cast normally during the casting process due to the extremely poor fluidity of the slurry. The present invention uses sodium bicarbonate and citric acid modifiers to solve the problem that the steel slag slurry has poor fluidity and is difficult to cast during the molding process. During the stirring process, citric acid combines with sodium bicarbonate to form sodium citrate and CO2. Sodium citrate reacts with Ca in the slurry. 2+ The chelation reaction generates calcium citrate complex, which not only improves the fluidity of the slurry and makes the matrix have more micropores, providing a large number of effective channels for CO2 migration during the carbonization process of steel slag; it can also promote the Ca 2+ At the same time, the generated CO2 can generate some tiny pores in the matrix, and some CO2 dissolves to form carbonic acid, which reacts with Ca in the slurry. 2+ The reaction forms small calcium carbonate crystals that act as nucleation sites. During the carbonation process, the Ca2+ chelated by calcium citrate 2+ Dissolves in acidic environment and reacts with Ca in the matrix 2+ The carbonation reaction takes place together to form calcium carbonate crystals. The multiple effects of the modifiers make the material prepared by the invention have high compressive strength, high carbon fixation rate and low porosity.

[0026] 2. The present invention uses carbide slag as an additive to improve the carbonization performance of steel slag. Carbide slag contains a large amount of Ca(OH)2, which can react with CO2 to generate calcium carbonate. After adding part of the carbide slag, on the one hand, it replaces part of the steel slag, thereby improving the carbon fixation rate of the material; on the other hand, the carbonization product generated by its carbonization can be bonded with the carbonization product of the steel slag to promote the improvement of strength.

[0027] 3. The present invention uses stainless steel slag and carbide slag as raw materials to prepare all-solid waste carbonization cementitious materials. Carbide slag has high carbonization activity, but its application in building materials is limited due to its poor cementitiousness. Stainless steel slag has few hydration active mineral phases and is difficult to be effectively utilized. The present invention treats solid waste with low utilization rate through carbonization and curing, while achieving the purpose of "reduction, harmlessness, and resource utilization" of industrial solid waste, achieving extremely low energy consumption and negative CO2 emissions, so as to accelerate the progress of carbon emission reduction tasks.

[0028] 4. The carbonization device used in the present invention is cheap and simple, and the carbonization system adopted is low pressure and low temperature, which can further reduce energy consumption and cost, and has great economic and social benefits.

[0029] Therefore, the carbon-fixing cementitious material prepared by the present invention has excellent performance, a compressive strength of 108MPa to 131MPa, and a carbon fixation rate of 16% to 25%. It can achieve high-value utilization of solid waste and negative carbon production, and is suitable for technical fields such as prefabricated buildings and concrete aggregate preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The carbon fixation efficiency diagram of the carbon fixation cementitious material prepared in the embodiment of the present invention and the comparative example;

[0031] Figure 2 The compressive strength diagram of the carbon-fixing cementitious material prepared in the embodiments of the present invention and the comparative examples;

[0032] Figure 3 These are microscopic morphology pictures of Examples 1 to 4, Comparative Example 1 and Comparative Example 4. DETAILED DESCRIPTION

[0033] The present invention provides a full-solid waste carbon-fixing cementitious material, which is prepared from raw materials containing the following parts by mass:

[0034] 100 parts of steel slag powder, 2-30 parts of carbide slag and 1-3 parts of modifier;

[0035] The modifier comprises one or more of sodium citrate, citric acid, sodium bicarbonate, sodium pyrophosphate and sodium tartrate.

[0036] In the present invention, the content of the carbide slag is preferably 10 to 30 parts by mass, and more preferably 20 to 30 parts by mass.

[0037] In the present invention, the content of the modifier is preferably 1 to 2.5 parts by mass, and more preferably 2 to 2.5 parts by mass.

[0038] In the present invention, the modifier is preferably citric acid and sodium bicarbonate, and the molar ratio of citric acid to sodium bicarbonate is preferably 1:3.

[0039] The present invention also provides a method for preparing a solid waste carbon-fixing cementitious material, comprising the following steps:

[0040] 1) Weighing and mixing the raw materials according to their mass fractions to obtain a mixture, and mixing the mixture with water to obtain a slurry;

[0041] 2) pouring the slurry into a mold, drying it after natural curing, and controlling the moisture content to be 6-8% to obtain a sample;

[0042] 3) Carbonizing the sample in a CO2 atmosphere to obtain a fully solid waste carbon-fixing cementitious material.

[0043] In the present invention, in step 1), the water-to-solid ratio of the slurry is 0.2-0.4, preferably 0.3.

[0044] In the present invention, in the step 2), the calculation formula of the moisture content is w%=(m1-m2) / m2×100%;

[0045] In the formula, m1 is the mass of the sample after drying for t time; m2 is the mass of the completely dried dry basis sample, and w% is the moisture content.

[0046] In the present invention, in the step 2), the natural curing time is 12 to 24 hours, preferably 14 to 22 hours, and more preferably 16 to 20 hours; the drying temperature is 30 to 50°C, preferably 35 to 45°C, and more preferably 40°C.

[0047] In the present invention, in the step 3), the concentration of CO2 is 99.9vt.%, and the pressure of CO2 is 0.1-0.4MPa, preferably 0.2-0.3MPa.

[0048] In the present invention, the carbonization temperature is 20-80°C, preferably 30-60°C, and more preferably 40-50°C; the carbonization time is 6-96h, preferably 10-90h, and more preferably 15-80h; the carbonization is carried out under vacuum conditions, and the vacuum is evacuated to 0.7-0.8MPa, preferably 0.7MPa.

[0049] In the present invention, the raw material types are:

[0050] The stainless steel slag comes from a factory in Beihai, Guangxi Zhuang Autonomous Region. Its CaO content is 56-65%, and the main mineral is γ-type Ca2SiO4 (γ-C2S), which has low hydration activity and high carbonization activity. The raw material used later is the stainless steel slag that is ball milled for 60 minutes and then sieved to a fine powder with a particle size of ≤150μm.

[0051] The calcium carbide slag comes from a factory in Yulin, Guangxi Zhuang Autonomous Region, and its CaO content is 90-92%. The raw material used later is the stainless steel slag that has been ball milled for 60 minutes and then sieved to a fine powder with a particle size of ≤150μm.

[0052] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0053] Example 1

[0054] 1) Weigh 100 parts by mass of steel slag powder and 10 parts by mass of carbide slag, weigh water at a water-to-solid ratio of 0.3, and stir for 4 minutes using a cement slurry mixer to prepare a slurry;

[0055] 2) Pour the slurry into a mold and shape it for 24 hours. Take out the molded sample and place it in an oven at 40℃±1℃ to dry it to control the moisture content to 7%;

[0056] 3) Place the sample in a carbonization kettle, evacuate to above 0.7 MPa, introduce CO2 with a concentration of 99.9 vt.%, maintain the carbonization pressure at 0.4 MPa, the carbonization temperature at 20°C, and control the carbonization time at 24 h to obtain a high-strength solid carbon cementitious material.

[0057] Example 2

[0058] The steps for preparing the high-strength carbon-fixing cementitious material in this embodiment are different from those in Embodiment 1 in that 2.5 parts by mass of a modifier are added to the raw materials in step 1), and the modifier consists of 1.08 parts of citric acid and 1.42 parts of sodium bicarbonate.

[0059] The fluidity of the slurries prepared in Example 1 and Example 2 was tested, and the results are shown in Table 1 below.

[0060] Table 1 Fluidity test results of Example 1 and Example 2

[0061]

[0062] Example 3

[0063] The steps for preparing the high-strength carbon-fixing cementitious material in this embodiment are different from those in Embodiment 2 in that 20 parts by mass of carbide slag are added to the raw materials in step 1).

[0064] Example 4

[0065] The steps for preparing the high-strength carbon-fixing cementitious material in this embodiment are different from those in Embodiment 2 in that 30 parts by mass of carbide slag are added to the raw materials in step 1).

[0066] Comparative Example 1

[0067] 1) Weigh 100 parts by mass of steel slag powder, weigh water at a water-to-solid ratio of 0.3, and stir for 4 minutes using a cement slurry mixer to prepare a slurry;

[0068] 2) Pour the slurry into a mold and shape it for 24 hours. Take out the molded sample and place it in an oven at 40℃±1℃ to dry it to control the moisture content to 7%;

[0069] 3) Place the sample in a carbonization kettle, evacuate to above 0.7 MPa, introduce CO2 with a concentration of 99.9 vt.%, maintain the carbonization pressure at 0.4 MPa, the carbonization temperature at 20°C, and control the carbonization time at 24 h to obtain a high-strength solid carbon cementitious material.

[0070] Comparative Example 2

[0071] The steps for preparing the high-strength carbon-fixing cementitious material in this comparative example are different from those in comparative example 1 in that the moisture content of the sample is controlled to be 6% in step 2).

[0072] Comparative Example 3

[0073] The steps for preparing the high-strength carbon-solidified cementitious material in this comparative example are different from those in comparative example 1 in that water is weighed at a water-to-solid ratio of 0.25 in step 1) and the water content of the sample is controlled to be 6% in step 2).

[0074] Comparative Example 4

[0075] The steps for preparing the high-strength carbon-fixing cementitious material in this comparative example are different from those in comparative example 1 in that the carbonization temperature in step 3) is 40°C.

[0076] Comparative Example 5

[0077] The steps of preparing the high-strength carbon-fixing cementitious material in this comparative example are different from those in comparative example 1 in that 2.5 parts by mass of a modifier are added to the raw materials in step 1), and the modifier consists of 1.08 parts of citric acid and 1.42 parts of sodium bicarbonate.

[0078] Comparative Example 6 (without controlling moisture content)

[0079] 1) Weigh 100 parts by mass of steel slag powder, weigh water at a water-to-solid ratio of 0.3, and stir for 4 minutes using a cement slurry mixer to prepare a slurry;

[0080] 2) Pour the slurry into a mold and form it for 24 hours. Take out the formed sample and place it directly in a carbonization kettle. Evacuate it to above 0.7 MPa, introduce CO2 with a concentration of 99.9 vt.%, maintain the carbonization pressure at 0.4 MPa, the carbonization temperature at 20°C, and control the carbonization time to 24 hours to obtain a fixed carbon cementitious material.

[0081] The sample will lose water during natural curing in the mold until it is demolded. The moisture content is about 16% after demolding. The compressive strength of the cementitious material prepared by this method is 5-7MPa. After carbonization, the cross-section of the test block all appears red under the phenolphthalein indicator, and the degree of carbonization is extremely low. Too high a moisture content will cause the diffusion of CO2 to be hindered during the carbonization process.

[0082] Comparative Example 7 (water content is too low)

[0083] 1) Weigh 100 parts by mass of steel slag powder, weigh water at a water-to-solid ratio of 0.3, and stir for 4 minutes using a cement slurry mixer to prepare a slurry;

[0084] 2) Pour the slurry into a mold and form it for 24 hours. Take out the formed sample and place it in an oven at 40℃±1℃ to dry it so as to control the moisture content to 0%; evacuate to above 0.7MPa, introduce CO2 with a concentration of 99.9vt.%, maintain the carbonization pressure at 0.4MPa, the carbonization temperature at 20℃, and control the carbonization time to 24h to obtain a carbon-fixing cementitious material.

[0085] Since there is a certain humidity in the carbonization chamber, samples with low moisture content can still undergo carbonization reaction, but the compressive strength of the cementitious material obtained by this method is only 30MPa.

[0086] Test Case

[0087] The carbon fixation rates of the high-strength carbon fixation cementitious materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 are calculated according to Formula (1) and Formula (2):

[0088]

[0089] Where, CO2 (wt.%) is the absorption rate / loss rate of CO2; Δm CO2 m is the mass loss of CO2 produced by the decomposition of calcium carbonate at high temperature; 105℃ is the weight of the sample after drying; CO 2carbonated(wt.％) is the loss rate of CO2 in the sample after carbonization; CO 2initial(wt.％) is the CO2 loss rate of the uncarbonized sample.

[0090] The test results are as follows Figure 1 As shown in the figure, it can be seen that the carbon fixation rate of the sample is significantly improved after the addition of the modifier, indicating that the modifier can improve the carbonization effect of the sample. With the increase of the amount of carbide slag, the carbon fixation rate also increases. This is because the high calcium component of carbide slag provides more calcium sources and increases the alkalinity of the sample.

[0091] Compressive strength test: The compressive strength of the high-strength carbon-fixing cementitious materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was measured according to GB / T 17671-2021 "Test method for strength of cement mortar". The results are as follows: Figure 2 As shown, it can be seen that the compressive strength of the sample is improved to a certain extent after the addition of the modifier. The compressive strength of Example 2 and Example 3 is relatively high, indicating that carbide slag has significantly improved the strength performance of the carbonized steel slag sample. The strength of Example 4 is reduced. This is because compared with steel slag, carbide slag has no cementing materials such as silica gel in the carbonized product. Therefore, when more carbide slag is added, the degree of cementation of the sample matrix decreases, resulting in reduced strength.

[0092] Figure 3The microscopic morphology diagrams of Examples 1 to 4, Comparative Example 1 and Comparative Example 4 show that after adding the modifier, the overall cementation of the sample is improved, the particles of the carbonized product are bonded to each other, and the modifier can provide nucleation sites for the formation of the carbonized product, so that calcium carbonate grows and accumulates around the nucleation sites, thereby forming a structure that is conducive to the development of strength. By comparing Examples 2 to 4 with Comparative Example 1, it can be seen that after adding carbide slag, the morphology of the carbonized product changes, the crystallinity of the carbonized product is higher, the morphology is more uniform, the sample has fewer pores, and the matrix is ​​denser. This is the result of the mutual cementation coupling of the carbide slag carbonized product and the steel slag carbonized product to form a dense structure. By comparing Examples 2 to 4, it can be seen that adding 20 parts by mass of carbide slag can make the sample form a denser structure, which is consistent with the result of compressive strength; adding 30 parts by mass of carbide slag reduces the degree of cementation of the sample.

[0093] It can be seen from the above embodiments that the present invention provides a full solid waste carbon-fixing cementitious material and a preparation method thereof. The carbon-fixing cementitious material prepared by the present invention has excellent performance, a compressive strength of 108MPa to 131MPa, and a carbon fixation rate of 16% to 25%. It can achieve high-value utilization of solid waste and negative carbon production, and is suitable for technical fields such as prefabricated buildings and concrete aggregate preparation.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A solid waste carbon-fixing cementitious material, characterized in that: Prepared from the following raw materials in parts by weight: 100 parts of steel slag powder, 2-30 parts of carbide slag and 1-3 parts of modifier; The modifier comprises one or more of sodium citrate, citric acid, sodium bicarbonate, sodium pyrophosphate and sodium tartrate.

2. The method for preparing the all-solid waste carbon-fixing cementitious material according to claim 1, characterized in that: The following steps are involved: 1) Weighing and mixing the raw materials according to their mass fractions to obtain a mixture, and mixing the mixture with water to obtain a slurry; 2) pouring the slurry into a mold, drying it after natural curing, and controlling the moisture content to be 6-8% to obtain a sample; 3) Carbonizing the sample in a CO2 atmosphere to obtain a fully solid waste carbon-fixing cementitious material.

3. The preparation method according to claim 2, characterized in that: In the step 1), the water-to-solid ratio of the slurry is 0.2 to 0.

4.

4. The preparation method according to claim 2 or 3, characterized in that: In the step 2), the calculation formula of moisture content is w%=(m1-m2) / m2×100%; In the formula, m1 is the mass of the sample after drying for t time; m2 is the mass of the completely dried dry basis sample, and w% is the moisture content.

5. The preparation method according to claim 4, characterized in that: In the step 2), the natural curing time is 12 to 24 hours, and the drying temperature is 30 to 50°C.

6. The preparation method according to claim 2, 3 or 5, characterized in that: In the step 3), the concentration of CO2 is 99.9vt.%, and the pressure of CO2 is 0.1-0.4MPa.

7. The preparation method according to claim 6, characterized in that: The carbonization temperature is 20-80° C., the carbonization time is 6-96 hours, and the carbonization is carried out under vacuum conditions, and the vacuum is evacuated to 0.7-0.8 MPa.

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