A lithium slag composite admixture, low-carbon lithium slag concrete and its preparation method

Abstract

This invention discloses a lithium slag composite admixture, low-carbon lithium slag concrete, and their preparation method, belonging to the field of concrete technology. The method includes the following steps: preparing calcium-type lithium slag synthetic zeolite using lithium slag; preparing lithium slag-based negatively charged mesoporous silica using the waste liquid generated during the preparation of the calcium-type lithium slag synthetic zeolite; and finally mixing the calcium-type lithium slag synthetic zeolite, the lithium slag-based negatively charged mesoporous silica, and the undisturbed lithium slag to obtain the composite admixture. This invention solves the problem of excessively high SO3 content in lithium slag concrete under high admixture dosage, and also addresses the technical defects of insufficient lithium slag activity and low concrete strength, effectively reducing the cracking risk of lithium slag concrete, comprehensively improving the density and workability of lithium slag concrete, and realizing the high-value-added resource utilization of lithium slag solid waste.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to a lithium slag composite admixture, low-carbon lithium slag concrete, and its preparation method. Background Technology

[0002] With the rapid development of electronic products and new energy vehicles, the demand for lithium has increased significantly. Statistics show that my country's annual demand for lithium carbonate exceeds 30,000 tons. Lithium carbonate is mainly obtained through the smelting of mineral-based lithium ores, and the smelting process generates lithium slag as a byproduct. Lithium smelting is divided into two processes: the lithium-alkali process and the lithium-acid process, with the lithium-acid process being the primary source of lithium slag. The lithium-acid process involves calcining spodumene ore at 1100-1300℃ in a rotary kiln and then producing lithium salts using the sulfuric acid process, discharging lithium slag in the process. Statistics show that the annual production and stockpiling of lithium slag already exceed ten million tons, with low utilization rates. This not only occupies a large amount of land but also causes serious pollution to water sources and the environment. Therefore, exploring high-value-added utilization of lithium slag has become a crucial technical issue that needs to be addressed for the sustainable development of the lithium salt industry.

[0003] The chemical composition of lithium slag is mainly amorphous silica (approximately 40-60%) and alumina (approximately 15-25%), along with small amounts of iron and calcium oxide. It has good grindability and certain pozzolanic activity. Using lithium slag as a cementitious admixture or mineral additive in concrete can lead to a secondary hydration reaction with Ca(OH)₂, a product of cement hydration, thereby improving the compressive strength of concrete and refining the microstructure of hydration products. However, the application of lithium slag in concrete also has several drawbacks. Its dosage should not be too high, generally not exceeding 30%, mainly for the following reasons: First, lithium slag has a high SO₃ content (generally >6%), and high dosages can easily lead to poor stability and a high risk of cracking in concrete. Second, the activity of lithium slag mainly relies on the secondary hydration reaction. When the dosage is high, the alkalinity and pH value of the hydration environment decrease, preventing the lithium slag from fully exerting its activity, resulting in lower early and later strength of the concrete. Third, the microscopic morphology of lithium slag particles is a "rod-shaped" porous structure, which leads to a high water absorption rate (>15%) and no lubrication effect on cement paste, affecting the workability of concrete.

[0004] In existing technologies, the dosage of lithium slag in concrete is usually relatively small. Most technological improvements focus on addressing the problem of lithium slag's easy water absorption, without fully considering the cracking risk caused by the high SO3 content of lithium slag. Chinese patent CN111646773A discloses a method for preparing lithium slag concrete, which uses the combined action of an activator and a coupling agent to form substances such as CSH on the surface of the lithium slag to fill the pore structure and reduce water absorption, but it does not consider the problem of high SO3 content in the lithium slag. Chinese patent CN115872695B discloses a lithium mica slag concrete, which modifies lithium extraction tailings by "coating" it and uses a series of air-entraining agents and admixtures to avoid the influence of free sodium, potassium, and sulfate ions on the concrete's performance. However, this technical solution only adds 1.5-2.5% lithium slag by weight, essentially not as an admixture, requiring not only modification of the lithium slag powder but also special formulation of the air-entraining agents and admixtures, making the technical solution complex.

[0005] Therefore, to achieve the large-scale consumption of lithium slag solid waste and its high-volume application in concrete, it is necessary to fully consider and effectively solve a series of key technical problems in the application of lithium slag, such as the high risk of concrete cracking due to high SO3 content and poor concrete density due to insufficient activity. This will improve the overall performance of lithium slag admixture concrete, enhance the safety of engineering structures, extend their service life, and reduce solid waste environmental pollution. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, one objective of this invention is to provide a method for preparing a low-carbon lithium slag composite admixture. This invention utilizes lithium slag to prepare synthetic zeolite, further utilizes the waste liquid generated during the preparation of calcium-type lithium slag synthetic zeolite to prepare lithium slag-based negative calcium mesoporous silica, and mixes it with undisturbed lithium slag to form a multi-element composite admixture. This not only solves the problem of excessive SO3 content in lithium slag concrete under high admixture dosage, but also addresses the technical defects of insufficient lithium slag activity and low concrete strength, effectively reducing the cracking risk of lithium slag concrete, comprehensively improving the density and workability of lithium slag concrete, realizing high-value-added resource utilization of lithium slag solid waste, and conforming to the national low-carbon strategic goal.

[0007] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0008] A method for preparing a low-carbon lithium slag composite admixture includes the following steps:

[0009] S1. Lithium slag and calcium hydroxide are mixed, ball-milled, calcined, and then ground into powder;

[0010] S2. Mix the powder obtained in step S1 with water, add calcium aluminate and EDTA to adjust the molar ratio of Si / Al to obtain a mixture, then add silane coupling agent solution, mix evenly, age and then crystallize, filter to obtain solid product and waste liquid, and after washing and drying, obtain calcium-type lithium slag synthetic zeolite.

[0011] S3. Adjust the pH of the waste liquid obtained in step S2 to 6-7, filter it, take the filtrate, and then adjust the pH of the filtrate to 3-5 to obtain silica sol; add the silica sol to a hexadecyltrimethylammonium bromide solution, adjust the pH of the mixed solution to 9-10, and then carry out a polycondensation reaction. After separation and washing, a solid product is obtained, and then the solid product is reacted at high temperature to obtain mesoporous silica.

[0012] S4. The mesoporous silica obtained in step S3 is added to an aqueous solution of Ca(NO3)2, ultrasonically dispersed, and then filtered. The solid product is washed and dried to obtain lithium slag-based negative calcium mesoporous silica.

[0013] S5. The composite admixture is obtained by mixing the calcium-type lithium slag synthetic zeolite, lithium slag-based negative calcium mesoporous silica and undisturbed lithium slag at a mass ratio of 1:(2~6):(30~80).

[0014] Lithium slag contains abundant silicon, aluminum, and other elements, making it a valuable raw material for synthesizing zeolites. Compared to conventional synthetic zeolites, the alkali metal oxides (Li₂O) in lithium slag act as fluxes during crystallization, lowering the reaction temperature. Simultaneously, trace active components (lithium and sodium ions) in the slag act as crystallization promoters, improving the structural integrity of the synthesized zeolite. Furthermore, the inherent alkali metal ions occupy zeolite framework sites, resulting in more active sites and higher ion exchange capacity. In the preparation process of calcium-type lithium slag-synthesized zeolite, lithium slag and calcium hydroxide are first subjected to high-energy ball milling to remove large impurities, break chemical bonds in the lithium slag, and increase the physical reaction surface area, promoting full contact between the lithium slag and calcium hydroxide. Simultaneous high-temperature calcination and stirring in a reactor fully melt the amorphous SiO₂ and Al₂O₃ in the lithium slag, forming aluminate and silicate ions, which then react with calcium ions in the calcium hydroxide to form soluble calcium silicates and calcium aluminates. During hydrothermal crystallization, EDTA improves the dissolution efficiency of calcium aluminate, and additional calcium aluminate is added to adjust the Si / Al ratio. Silane coupling agents achieve cross-linking effects; silane hydrolysis generates active hydroxyl (Si-OH) groups, which can form Si-O-Si and Al-O-Si cross-linking bridges with Si-O bonds and aluminum-oxygen (Al-O) bonds in the zeolite framework, enhancing the stability of the zeolite framework. This bridging effect effectively prevents the zeolite from deconstructing or dissolving in alkaline environments, improving the alkali resistance of the synthesized zeolite. Furthermore, a large number of calcium ions are introduced into the synthesized zeolite structure during both the alkali fusion and hydrothermal crystallization stages. The addition of synthesized zeolite to concrete also generates a large number of free calcium ions. The dual-charge characteristic of calcium ions, compared to monovalent cations, enhances the oxygen bond strength of zeolite and reduces the bond relaxation effect in the crystal framework. These two aspects combined enhance the stability and strength of the synthesized zeolite framework in alkaline environments, improving the adsorption and fixation capacity of the synthesized zeolite for sulfate ions in concrete. This method was used to prepare calcium-type lithium slag synthetic zeolite with higher selectivity and adsorption capacity for sulfate polyvalent anions.

[0015] The lithium slag composite admixture in this invention contains a large amount of undisturbed lithium slag. When lithium slag is added to concrete, it will generate a large amount of free SO4. 2- Ions cause concrete to easily expand and crack. The calcium-type lithium slag synthetic zeolite prepared by this invention has a high ion exchange capacity and is particularly effective against polyvalent anions such as SO42-. 2- It has higher selectivity and can effectively remove SO4 2- Adsorbed within the porous structure of the calcium-type lithium slag synthetic zeolite, the free calcium ions surrounding the synthetic zeolite can react with sulfate ions to form calcium sulfate precipitate, solidifying the sulfate ions and reducing SO42- in the concrete pore solution. 2- The concentration is significantly reduced, thus mitigating the technical problem of high SO3 content in lithium slag concrete, which leads to easy expansion and cracking of the concrete when using large amounts of lithium slag concrete.

[0016] The waste liquid generated during the preparation of calcium-type lithium slag zeolite contains abundant soluble silicates (SiO3). 2- ) and aluminates (AlO2) - Its silicates can be used as silicon source precursors for mesoporous silica, and the preparation of mesoporous silica from waste liquid can achieve further efficient utilization of lithium slag solid waste. In the preparation process of lithium slag-based mesoporous silica, dissolved aluminates (AlO2) under weakly acidic conditions... - CTAB will be converted into Al(OH)3 precipitate, and other impurities can also precipitate, while silicates remain dissolved. This step effectively reduces impurities in mesoporous silica. Under acidic conditions, silicates can polymerize to form silica sol. CTAB dissolved in water will combine to form spherical or rod-shaped microstructures, forming channels. When the mixed solution is adjusted with dilute ammonia, under alkaline conditions, silicic acid (Si(OH)4) will undergo hydrolysis and condensation reactions to form an ordered silicon-oxygen framework. Finally, after calcination, the bubbles formed by CTAB are removed, retaining a uniform and stable mesoporous silica structure. When mesoporous silica is mixed with calcium nitrate aqueous solution, calcium ions coordinate with the silanol groups (Si-OH) on the surface of mesoporous silica, achieving calcium ion loading on mesoporous silica, while nitrate ions are not directly adsorbed on the surface of the mesoporous material.

[0017] Mesoporous silica possesses a regular mesoporous structure with longitudinal channels. Its high specific surface area provides more active sites, allowing it to react rapidly with Ca(OH)₂ in concrete to generate more and denser CSH gel, accelerating the hydration process. Furthermore, the mesoporous structure can regulate the migration and distribution of moisture within the concrete, prolonging hydration time and achieving an internal curing effect, thus improving the mechanical and durability properties of concrete. Negative calcium mesoporous silica has a surface loaded with a large number of calcium ions. Under alkaline conditions, these abundant calcium ions can react with silicate ions bound to the surface or pores of the mesoporous silica, as well as OH⁻ in the solution. - The reaction generates calcium hydroxide, which increases the alkalinity of the solution and achieves the alkali activation effect, accelerates the depolymerization of O-Si-O and Al-O-Si-O bonds in lithium slag, promotes the volcanic ash reaction of lithium slag, and at the same time, the free calcium ions in mesoporous silica and synthetic zeolite can effectively increase the nucleation sites of CSH in concrete, thus comprehensively improving the reactivity of lithium slag and the density of concrete.

[0018] Preferably, in step S1, the mass ratio of analytical grade calcium hydroxide to lithium slag is 1:(0.5~1); the ball milling uses a planetary ball mill with a rotation speed of 400-500 rpm;

[0019] Preferably, the calcination temperature is 550-600℃ and the time is 100-120 min.

[0020] Preferably, in step S2, the molar ratio of Si / Al is (2~3):1, and the mass of EDTA is 5%~10% of the mass of calcium aluminate.

[0021] Preferably, the concentration of the silane coupling agent solution is 10wt%~12wt%, and the mass ratio of the mixture to the silane coupling agent solution is (4~6):1.

[0022] Preferably, the silane coupling agent includes at least one of trichlorohexylsilane, KH550, and KH570.

[0023] Preferably, in step S3, the temperature of the polycondensation reaction is 40~50℃, and the mixture is stirred for 10~14h and then allowed to stand for 10~14h.

[0024] Preferably, in step S3, the high-temperature reaction is carried out at a temperature of 500-600°C for 5-6 hours.

[0025] Preferably, in step S4, the mass ratio of the mesoporous silica to the Ca(NO3)2 aqueous solution is 1:(2~3), and the concentration of the Ca(NO3)2 aqueous solution is 0.7~1.0 mol / L.

[0026] Preferably, the specific surface area of ​​the undisturbed lithium slag is 400~600m². 2 / kg, the specific surface area of ​​the calcium-type lithium slag synthesized zeolite is 3000~4000 m² / kg. 2 / kg, the specific surface area of ​​the lithium slag-based negative calcium mesoporous silica is 11000~13000 m² / kg. 2 / kg. The resulting lithium slag composite admixture achieves a layered particle filling system, with nano-sized mesoporous silica particles filling the micron-sized harmful pores in the cement matrix, effectively enhancing density and comprehensively improving the early and later strength of concrete.

[0027] Another object of the present invention is to provide a low-carbon lithium slag composite admixture prepared by the preparation method described above, wherein the composite admixture comprises calcium-type lithium slag synthetic zeolite, lithium slag-based negative calcium mesoporous silica, and undisturbed lithium slag.

[0028] Another object of the present invention is to provide a lithium slag concrete made using the aforementioned low-carbon lithium slag composite admixture, comprising the following components in parts by weight: 100-150 parts cement, 325-440 parts low-carbon lithium slag composite admixture, 10-15 parts corn gluten solution, 950-1100 parts crushed stone, 700-780 parts sand, 140-155 parts water, and 6-9 parts water-reducing agent.

[0029] The corn gluten solution is prepared by mixing analytical grade corn gluten with (80~90) wt% ethanol solution at a mass ratio of (0.5~1.0):9.5.

[0030] The method for preparing lithium slag concrete of the present invention includes the following steps:

[0031] M1. Weigh each component according to the parts by weight;

[0032] M2. Mix the low-carbon lithium slag composite admixture with 1 / 3 water-reducing agent and 1 / 3 water, ultrasonically mix for 1-2 minutes, then add corn gluten solution and mix evenly, then add cement, crushed stone, sand, 2 / 3 water-reducing agent and 2 / 3 water, mix evenly to obtain concrete paste.

[0033] This invention first ultrasonically mixes a low-carbon lithium slag composite admixture with a portion of a water-reducing agent and water to improve the dispersibility of the lithium slag composite admixture. Then, it is mixed with a corn gluten solution. Corn gluten can form a coating film, is almost insoluble in water, but soluble in alkaline aqueous solutions with a pH value above 11.5. The corn gluten solution is mixed with the lithium slag composite admixture and water, so that the lithium slag composite admixture absorbs some water and is sealed, so that it does not absorb too much water during the concrete mixing process and does not affect the flowability of the lithium slag concrete. In the later setting and hardening process, as the internal alkalinity of the concrete continues to rise during hydration, the internal alkalinity of the concrete rises to above 12, and the corn gluten dissolves, without affecting the participation of the lithium slag-rich composite admixture in the cement-based secondary hydration.

[0034] Compared with the prior art, the advantages of the present invention are:

[0035] (1) The present invention uses calcium-type lithium slag synthetic zeolite prepared from lithium slag, lithium slag-based negative calcium mesoporous silica prepared from waste liquid generated during the synthetic zeolite preparation process, and original lithium slag to form a multi-component composite admixture. Under the synergistic effect of each component, it not only solves the problem of excessive SO3 content and easy cracking of concrete in large-volume lithium slag admixture concrete, but also solves the technical defects of insufficient lithium slag activity and low concrete strength, thus realizing the high added value resource utilization of lithium slag solid waste.

[0036] (2) The calcium-type lithium slag synthetic zeolite prepared by this invention has high structural integrity, more active sites, and higher ion exchange capacity. The cross-linking effect of the silane coupling agent and the alkali melting and hydrothermal crystallization stages both introduce a large number of calcium ions, comprehensively enhancing the stability and strength of the synthetic zeolite framework in an alkaline environment, and improving the adsorption and fixation capacity of the synthetic zeolite for sulfate ions in concrete. This results in the preparation of a calcium-type lithium slag synthetic zeolite with higher selectivity and adsorption capacity for polyvalent sulfate anions. The calcium-type lithium slag synthetic zeolite carries SO4 from the original lithium slag into the concrete. 2- Fixed within its porous structure, while free Ca adhering to the zeolite surface 2+ With SO4 2- The formation of CaSO4 precipitate effectively reduces SO4 in concrete. 2-concentration.

[0037] (3) The waste liquid generated during the preparation of calcium-type lithium slag synthetic zeolite contains abundant soluble silicates, which can be used as a silicon source for mesoporous silica, realizing the efficient utilization of waste. Calcium nitrate mixed with mesoporous silica enables calcium ions to be loaded onto the mesoporous silica. The regular mesoporous structure and high specific surface area of ​​mesoporous silica provide more active sites, which react rapidly with Ca(OH)2 in concrete to generate more and denser CSH gel, accelerating the hydration process. The original lithium slag, calcium-type lithium slag synthetic zeolite, and lithium slag-based negative calcium mesoporous silica work together to achieve a hierarchical particle filling system, further enhancing the density. The mesoporous structure can regulate the migration and distribution of water inside the concrete, playing an internal curing role. The negative calcium mesoporous silica surface is loaded with a large number of calcium ions. Under alkaline conditions, the abundant calcium ions can react with silicate ions bound to the surface or inside the pores and OH in the solution. - The reaction produces calcium hydroxide, which increases the alkalinity of the solution and achieves the alkali activation effect, thus promoting the reaction of lithium slag pozzolanic. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] In the following examples and comparative examples, lithium slag is a byproduct generated during the production of lithium sulfate using the sulfuric acid process after calcination of spodumene; the density of the lithium slag is 2.3~2.4 g / m³. 3 Its specific surface area is 400~600m² 2 / kg.

[0040] The lithium slag concrete of the present invention comprises the following components in parts by weight: 100-150 parts of cement, 325-440 parts of low-carbon lithium slag composite admixture, 10-15 parts of corn gluten solution, 950-1100 parts of crushed stone, 700-780 parts of sand, 140-155 parts of water, and 6-9 parts of water-reducing agent.

[0041] The cement is ordinary Portland cement P•O 42.5; the sand can be natural river sand and / or manufactured sand. When it is a mixture of natural river sand and manufactured sand, the mass ratio of manufactured sand to natural river sand is (2~3):(7~8), the fineness modulus of natural sand is 2.8~3.2, the fineness modulus of manufactured sand is 2.7~3.0, and the stone powder content is less than 10%; the crushed stone is 5~25mm continuously graded crushed stone; the water-reducing agent is polycarboxylate water-reducing agent with a water reduction rate of 35% and a solid content of 37%.

[0042] Example 1

[0043] This embodiment provides a low-carbon lithium slag composite admixture, the preparation method of which includes the following steps:

[0044] S1. Add lithium slag and analytical grade calcium hydroxide in a ball mill at a mass ratio of 1:1 and ball mill for 20 min. Then add the mixture to a high-temperature reactor and calcine at 550℃ for 120 min while stirring. After cooling, grind the molten mixture and pass it through a 200-mesh sieve to obtain powder.

[0045] S2. Add deionized water at a solid-liquid ratio of 1:8 and stir until homogeneous. Then add calcium aluminate to adjust the Si / Al molar ratio to 2:1, and add 10% EDTA (by weight of calcium aluminate). Stir for 20 minutes to obtain a mixture. Then add a 10wt% trichlorotrihexylsilane solution (mass ratio of the mixture to the trichlorotrihexylsilane solution is 5:1). Mix thoroughly and allow to stand for 10 hours. Then crystallize in a crystallization kettle at 100℃ for 8 hours. After filtration, obtain a solid product and waste liquid. Wash the solid product until the pH value is 6.5~7.5 and then dry to obtain calcium-type lithium slag synthetic zeolite. The specific surface area of ​​the calcium-type lithium slag synthetic zeolite is 3000~4000 m². 2 / kg, micropores with a pore size distribution of 0.5~1nm;

[0046] S3. Adjust the pH of the waste liquid obtained in step S2 to 6-7 to precipitate the aluminate. After filtration, a relatively pure silicate solution is obtained. Then, dilute hydrochloric acid is added to adjust the pH of the silicate solution to 4 to obtain silica sol. The silica sol is washed with deionized water and dried to constant weight for later use. Then, the above silica sol is added to a 0.1 mol / L hexadecyltrimethylammonium bromide solution. The mass ratio of silica sol to CTAB analytical grade is 10:1. The pH of the mixed solution is adjusted to 10 with dilute ammonia. After stirring at 40°C for 12 h, it is allowed to stand for 12 h. After the polycondensation reaction, the solid product is obtained by separation, washing with deionized water and ethanol. Then, the solid product is calcined at 550°C for 6 h. After cooling to room temperature, mesoporous silica is obtained.

[0047] S4. The mesoporous silica obtained in step S3 was added to a 0.7 mol / L Ca(NO3)2 aqueous solution, with a mass ratio of mesoporous silica to Ca(NO3)2 aqueous solution of 1:2. The mixture was ultrasonically dispersed for 20 min and stirred for 4 h. The solid product was filtered out, washed, and dried to obtain lithium slag-based negative calcium mesoporous silica. The specific surface area of ​​the lithium slag-based negative calcium mesoporous silica was 11000~13000 m². 2 / g.

[0048] S5. The composite admixture is obtained by mixing calcium-type lithium slag synthetic zeolite, lithium slag-based negative calcium mesoporous silica and undisturbed lithium slag at a mass ratio of 5:20:300.

[0049] Example 2

[0050] This embodiment provides a low-carbon lithium slag composite admixture, the preparation method of which includes the following steps:

[0051] S1. Add lithium slag and analytical grade calcium hydroxide at a mass ratio of 1:0.5 to a ball mill and ball mill for 30 min. Then add the mixture to a high-temperature reactor and calcine at 600℃ for 100 min while stirring. After cooling, grind the molten mixture and pass it through a 200-mesh sieve to obtain powder.

[0052] S2. Add deionized water at a solid-liquid ratio of 1:6 and stir until homogeneous. Then add calcium aluminate to adjust the Si / Al molar ratio to 3:1, and add 5% (by weight) EDTA from the calcium aluminate. Stir for 30 minutes to obtain a mixture. Then add a 12wt% KH550 solution, with a mass ratio of the mixture to the KH550 solution of 6:1. Mix thoroughly and allow to stand for 10 hours. Then place in a crystallization kettle at 90℃ for 10 hours. After filtration, obtain a solid product and waste liquid. Wash the solid product until the pH value is 6.5~7.5 and then dry to obtain calcium-type lithium slag synthetic zeolite. The specific surface area of ​​the calcium-type lithium slag synthetic zeolite is 3000~4000 m². 2 / kg, micropores with a pore size distribution of 0.5~1nm;

[0053] S3. Adjust the pH of the waste liquid obtained in step S2 to 6-7 to precipitate the aluminate. After filtration, a relatively pure silicate solution is obtained. Then, dilute hydrochloric acid is added to adjust the pH of the silicate solution to 5 to obtain silica sol. The silica sol is washed with deionized water and dried to constant weight for later use. Then, the silica sol is added to a 0.2 mol / L hexadecyltrimethylammonium bromide solution. The mass ratio of silica sol to CTAB analytical grade is 10:1. The pH of the mixed solution is adjusted to 9 with dilute ammonia. After stirring at 50°C for 12 h, it is allowed to stand for 12 h. After the polycondensation reaction, the solid product is obtained by separation, washing with deionized water and ethanol. Then, the solid product is calcined at 600°C for 5 h, taken out and cooled to room temperature to obtain mesoporous silica.

[0054] S4. The mesoporous silica obtained in step S3 was added to a 1.0 mol / L Ca(NO3)2 aqueous solution, with a mass ratio of mesoporous silica to Ca(NO3)2 aqueous solution of 1:3. The mixture was ultrasonically dispersed for 30 min and stirred for 3 h. The solid product was filtered out, washed, and dried to obtain lithium slag-based negative calcium mesoporous silica. The specific surface area of ​​the lithium slag-based negative calcium mesoporous silica was 11000~13000 m². 2 / g;

[0055] S5. The composite admixture is obtained by mixing calcium-type lithium slag synthetic zeolite, lithium slag-based negative calcium mesoporous silica and undisturbed lithium slag at a mass ratio of 5:20:300.

[0056] Example 3

[0057] The low-carbon lithium slag composite admixture in this embodiment is basically the same as that in Example 1, except that the mass ratio of calcium-type lithium slag synthetic zeolite, lithium slag-based negative calcium mesoporous silica and undisturbed lithium slag is 10:30:400.

[0058] Comparative Example 1

[0059] The lithium slag composite admixture in this comparative example was obtained by mixing synthetic zeolite, mesoporous silica and undisturbed lithium slag in a mass ratio of 5:20:300.

[0060] The synthetic zeolite used in this comparative example is a Y-type synthetic zeolite produced by Shandong Hefeng Environmental Protection Technology Co., Ltd., with an effective component content of 99%, a relative crystallinity of 80-88%, and a total specific surface area of ​​350-400 m². 2 / g; Mesoporous silica is mesoporous silica micro powder produced by Beijing Zhongke Keyou Technology Co., Ltd., with a specific surface area of ​​11000-12000 m². 2 / kg.

[0061] Comparative Example 2

[0062] The low-carbon lithium slag composite admixture in this comparative example is basically the same as that in Example 1, except that sodium hydroxide is used instead of calcium hydroxide and sodium aluminate is used instead of calcium aluminate.

[0063] Comparative Example 3

[0064] The low-carbon lithium slag composite admixture in this comparative example is basically the same as that in Example 1, except that chlorotrihexylsilane solution is not added.

[0065] Comparative Example 4

[0066] The low-carbon lithium slag composite admixture in this comparative example is basically the same as that in Example 1, except that step S4 is omitted.

[0067] Example 4

[0068] This embodiment provides a lithium slag concrete, comprising the following components in parts by weight: 150 parts cement, 325 parts low-carbon lithium slag composite admixture of Example 1, 10 parts corn gluten solution, 1100 parts crushed stone, 700 parts sand, 140 parts water, and 9 parts water-reducing agent.

[0069] The corn gluten solution is prepared by mixing analytical grade corn gluten with 80 wt% ethanol solution at a mass ratio of 0.5:9.5.

[0070] The method for preparing lithium slag concrete in this embodiment includes the following steps:

[0071] M1. Weigh each component according to the parts by weight;

[0072] M2. Mix low-carbon lithium slag composite admixture, 1 / 3 water-reducing agent and 1 / 3 water, and mix with an ultrasonic mixer at an ultrasonic frequency of 24 kHz for 1-2 minutes to improve the dispersibility of low-carbon lithium slag composite admixture. Then add corn gluten solution and mix evenly. Then add cement, crushed stone, sand, 2 / 3 water-reducing agent and 2 / 3 water, and mix evenly to obtain concrete paste.

[0073] Example 5

[0074] This embodiment is basically the same as embodiment 4, except that the low-carbon lithium slag composite admixture of embodiment 2 is used instead of the low-carbon lithium slag composite admixture of embodiment 1.

[0075] Example 6

[0076] This embodiment is basically the same as embodiment 4, except that the lithium slag concrete in this embodiment includes the following components in parts by weight: 100 parts cement, 440 parts low-carbon lithium slag composite admixture of embodiment 3, 15 parts corn gluten solution, 950 parts crushed stone, 780 parts sand, 155 parts water, and 6 parts water-reducing agent.

[0077] Comparative Example 5

[0078] The difference between Comparative Example 5 and Example 4 is that the low-carbon lithium slag composite admixture of Comparative Example 1 is used instead of the low-carbon lithium slag composite admixture of Example 1.

[0079] Comparative Example 6

[0080] The difference between Comparative Example 6 and Example 4 is that the low-carbon lithium slag composite admixture of Comparative Example 2 is used instead of the low-carbon lithium slag composite admixture of Example 1.

[0081] Comparative Example 7

[0082] The difference between Comparative Example 7 and Example 4 is that the low-carbon lithium slag composite admixture of Comparative Example 3 is used instead of the low-carbon lithium slag composite admixture of Example 1.

[0083] Comparative Example 8

[0084] The difference between Comparative Example 8 and Example 4 is that the low-carbon lithium slag composite admixture of Comparative Example 4 is used instead of the low-carbon lithium slag composite admixture of Example 1.

[0085] The workability, mechanical properties, and crack resistance of the lithium slag concrete from Examples 4-6 and Comparative Examples 4-8 were tested. The sulfate ion content of the fresh concrete was also determined. The sulfate ion content was mainly determined by ion chromatography. The specific test method is as follows: cement paste was ultrasonically extracted with ultrapure water and centrifuged. The supernatant was purified by solid-phase extraction column and filtered through a 0.22 μm aqueous PES filter membrane. The sulfate ion content in the filtrate was determined by ion chromatography and quantified by external standard method.

[0086] According to the provisions of GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the workability of the fresh concrete in the examples and comparative examples was tested; according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete" and GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", the mechanical properties and early crack resistance of the concrete were tested. The test results are shown in Table 1.

[0087] Table 1. Results of tests on working performance, mechanical properties, and durability.

[0088]

[0089] As shown in Table 1, the test results indicate that, in terms of workability, the slump of Examples 4-6 is ≥200mm, demonstrating high workability and ensuring excellent pumpability of the concrete. Regarding mechanical properties, the 28-day compressive strength of Examples 4-6 ranges from 52.6 to 54.8 MPa. In contrast, the 28-day compressive strengths of Comparative Examples 5 and 7 are 51.5 MPa and 52.3 MPa, respectively, which are lower than those of Example 4. This suggests that the calcium-type lithium slag-based synthetic zeolite framework exhibits better stability and strength under alkaline conditions. As an admixture, it is widely distributed in concrete and can, to some extent, improve the strength of concrete. Furthermore, the lithium slag-based negative calcium mesoporous silica of this invention has a better effect on improving concrete strength. The 28-day strength of Comparative Example 6 was 52.0 MPa, indicating that the series of calcium-type solutions used in the preparation of synthetic zeolite can not only improve the stability of synthetic zeolite in the alkaline environment of concrete, but also increase the overall calcium ion concentration of the concrete by adding the calcium-rich synthetic zeolite to the cementitious base, thereby accelerating the hydration reaction of the concrete and improving its strength. The experimental results of Comparative Example 8 show that the negative calcium mesoporous silica surface is loaded with a large number of calcium ions, which can effectively increase the alkalinity of concrete and achieve alkali activation under alkaline conditions, promote the lithium slag pozzolanic reaction, and improve the density of concrete.

[0090] Regarding sulfate ion content and crack resistance, the sulfate ion content and total crack area per unit area in Examples 4-6 were 0.25%-0.28% and 34-38 mm, respectively. 2 / m 2 The experimental results of Comparative Example 5 demonstrate that using commercially available synthetic zeolite and mesoporous silica to form a composite admixture with undisturbed lithium slag can only adsorb sulfate ions to a certain extent, and its overall effect on improving the resistance of concrete to sulfur trioxide damage is relatively unsatisfactory. The experimental results of Comparative Example 6 demonstrate that during the alkali fusion and hydrothermal crystallization stages, a large number of calcium ions are introduced into the synthetic zeolite structure, which can enhance the oxygen bond strength of the zeolite and reduce the bond relaxation effect in the crystal framework. The experimental results of Comparative Example 7 demonstrate that trichlorohexylsilane can form Si-O-Si and Al-O-Si crosslinking bridges with the Si-O and Al-O bonds in the zeolite framework, enhancing the stability of the zeolite framework and improving the alkali resistance of the synthetic zeolite. Both of these can enhance the stability and strength of the synthetic zeolite framework in alkaline environments and improve the adsorption and fixation capacity of synthetic zeolite for sulfate ions in concrete.

[0091] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a low-carbon lithium slag composite admixture, characterized in that, Includes the following steps: S1. Lithium slag and calcium hydroxide are mixed, ball-milled, calcined, and then ground into powder; S2. Mix the powder obtained in step S1 with water, add calcium aluminate and EDTA to adjust the molar ratio of Si / Al to obtain a mixture, then add silane coupling agent solution, mix evenly, age and then crystallize, filter to obtain solid product and waste liquid, and after washing and drying, obtain calcium-type lithium slag synthetic zeolite. S3. Adjust the pH of the waste liquid from step S2 to 6-7, filter and collect the filtrate, then adjust the pH of the filtrate to 3-5 to obtain silica sol; add the silica sol to a hexadecyltrimethylammonium bromide solution, adjust the pH of the mixed solution to 9-10 and carry out a polycondensation reaction, after separation and washing to obtain a solid product, and then carry out a high-temperature reaction to obtain mesoporous silica; S4. The mesoporous silica obtained in step S3 is added to an aqueous solution of Ca(NO3)2, ultrasonically dispersed, and then filtered. The solid product is washed and dried to obtain lithium slag-based negative calcium mesoporous silica. S5. The composite admixture is obtained by mixing the calcium-type lithium slag synthetic zeolite, lithium slag-based negative calcium mesoporous silica and undisturbed lithium slag at a mass ratio of 1:(2~6):(30~80).

2. The method for preparing a low-carbon lithium slag composite admixture according to claim 1, characterized in that, In step S1, the roasting temperature is 550~600℃ and the time is 100~120min.

3. The method for preparing a low-carbon lithium slag composite admixture according to claim 1, characterized in that, In step S2, the molar ratio of Si / Al is (2~3):1, and the mass of EDTA is 5%~10% of the mass of calcium aluminate.

4. The method for preparing a low-carbon lithium slag composite admixture according to claim 1, characterized in that, The concentration of the silane coupling agent solution is 10wt%~12wt%, and the mass ratio of the mixture to the silane coupling agent solution is (4~6):

1.

5. The method for preparing a low-carbon lithium slag composite admixture according to claim 1, characterized in that, In step S3, the temperature of the polycondensation reaction is 40~50℃, and the mixture is stirred for 10~14h and then allowed to stand for 10~14h.

6. The method for preparing a low-carbon lithium slag composite admixture according to claim 1, characterized in that, In step S3, the high-temperature reaction is carried out at a temperature of 500~600℃ for 5~6 hours.

7. The method for preparing a low-carbon lithium slag composite admixture according to claim 1, characterized in that, In step S4, the mass ratio of the mesoporous silica to the Ca(NO3)2 aqueous solution is 1:(2~3), and the concentration of the Ca(NO3)2 aqueous solution is 0.7~1.0 mol / L.

8. The method for preparing a low-carbon lithium slag composite admixture according to claim 1, characterized in that, The specific surface area of ​​the undisturbed lithium slag is 400~600 m². 2 / kg, the specific surface area of ​​the calcium-type lithium slag synthesized zeolite is 3000~4000 m² / kg. 2 / kg, the specific surface area of ​​the lithium slag-based negative calcium mesoporous silica is 11000~13000 m² / kg. 2 / kg.

9. The low-carbon lithium slag composite admixture prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The composite admixture includes calcium-type lithium slag synthetic zeolite, lithium slag-based negative calcium mesoporous silica, and undisturbed lithium slag.

10. A lithium slag concrete made using the low-carbon lithium slag composite admixture as described in claim 9, characterized in that, The following components are included in parts by weight: 100-150 parts cement, 325-440 parts low-carbon lithium slag composite admixture, 10-15 parts corn praseodymium solution, 950-1100 parts crushed stone, 700-780 parts sand, 140-155 parts water, and 6-9 parts water-reducing agent.

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