A method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag

Abstract

This invention discloses a method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag in the field of industrial solid waste resource utilization technology. The method includes: reacting dried carbide slag with hydrochloric acid, adjusting the pH to alkaline, and filtering to obtain calcium chloride filtrate; reacting the filtrate with ammonia water under closed pressurized conditions, while simultaneously adding a calcium-titanium base-level structural composite modifier for crystal form regulation, generating calcium hydroxide precipitate and ammonium chloride; after solid-liquid separation, the calcium hydroxide filter cake is washed with hot water, slurryed, air-dried, and graded and sieved to obtain a high specific surface area, high-purity calcium hydroxide product; the ammonium chloride-containing filtrate is evaporated and crystallized to recover industrial-grade ammonium chloride. This invention achieves high-value utilization of carbide slag, with an environmentally friendly process and excellent product performance.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization technology, specifically to a method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag. Background Technology

[0002] Calcium carbide slag is an industrial waste residue generated during the acetylene production process using the calcium carbide method, and its main component is calcium hydroxide. With the rapid development of my country's polyvinyl chloride (PVC), vinyl acetate, and other chemical products, the annual production of calcium carbide slag has reached tens of millions of tons. Because calcium carbide slag is highly alkaline and has a high water content, long-term open-air stockpiling not only occupies a large amount of land resources but also pollutes the soil and groundwater through leaching, causing serious environmental problems. Therefore, achieving efficient resource utilization of calcium carbide slag has become a key issue urgently needing to be addressed in the field of industrial solid waste treatment. Currently, the comprehensive utilization pathways of calcium carbide slag mainly include: using it as a building material raw material for cement production, preparing light calcium carbonate and calcium oxide, and using it for flue gas desulfurization and acidic wastewater treatment. Among these, converting calcium carbide slag into high-value-added calcium hydroxide products is one of the most economically valuable utilization directions.

[0003] Calcium hydroxide, also known as slaked lime, is widely used in petrochemicals, environmental protection, building materials, and pharmaceuticals and food. Particularly in dry flue gas desulfurization processes, calcium hydroxide acts as an absorbent, reacting with sulfur dioxide to form calcium sulfite. Its desulfurization efficiency is closely related to its specific surface area. Calcium hydroxide prepared by traditional methods typically has a low specific surface area, severely limiting its reactivity and desulfurization performance. Studies have shown that increasing the specific surface area of ​​calcium hydroxide can significantly enhance its mass transfer efficiency and conversion rate in gas-solid reactions. Therefore, researchers have explored various modification methods, such as adding surfactants, controlling crystallization conditions, and using centrifugal reactors, in order to obtain nanoscale or high specific surface area calcium hydroxide products. However, existing technologies still have the following shortcomings: First, the extraction efficiency of calcium ions from carbide slag is limited, and it is difficult to simultaneously achieve efficient calcium extraction and precise control of calcium hydroxide crystal form; second, during the ammoniation precipitation reaction, although increasing the temperature is beneficial for the precipitation of calcium hydroxide, it also causes a large amount of ammonia to escape, shifting the reversible reaction equilibrium to the left and reducing the calcium conversion rate and product purity; third, there is a lack of efficient inorganic modifiers that can simultaneously improve the specific surface area, dispersibility, and thermal stability of calcium hydroxide. Existing crystal form control agents are mostly organic surfactants, which have problems such as large dosage, easy introduction of impurities, and difficulty in recycling. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag. This method solves the technical problems of low specific surface area, easy ammonia escape leading to reaction equilibrium reversal, difficulty in removing impurities, and ineffective recovery of ammonium chloride when preparing calcium hydroxide from carbide slag.

[0005] The present invention achieves the above objectives through the following technical solutions: A method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag includes the following steps: S1, by weight, 100.0-120.0 parts of industrial calcium carbide slag raw material are dried, crushed, and sieved to obtain dried calcium carbide slag powder; the dried calcium carbide slag powder is put into a reaction vessel, 250.0-350.0 parts of hydrochloric acid are added, and the mixture is stirred; the temperature is raised to 70-90℃ for reaction; after the reaction is completed, ammonia water is added to adjust the pH value to 8.5-9.5 to obtain a reaction slurry; the reaction slurry is filtered to obtain calcium chloride filtrate and filter cake; S2, pump 300.0-450.0 parts of calcium chloride filtrate into a closed reactor, add 0.05-0.25 parts of calcium-titanium base-level structural composite modifier; stir, add 60.0-100.0 parts of ammonia water at room temperature; introduce nitrogen gas, heat to 40-80℃ to react, and obtain a mixed slurry; S3, centrifuge 350.0-550.0 parts of the mixed slurry to obtain calcium hydroxide filter cake and ammonium chloride-containing filtrate; wash the calcium hydroxide filter cake with hot deionized water at 50-70℃, and then wash it with hot deionized water at 70-80℃; obtain the washed filter cake; evaporate and crystallize the ammonium chloride-containing filtrate to obtain ammonium chloride; S4. Add 100.0-150.0 parts of washed filter cake to the slurry preparation tank, add 15.0-45.0 parts of deionized water and 0.05-0.1 parts of sodium hexametaphosphate, and prepare the slurry to obtain the slurry; dry the slurry and sieve it.

[0006] In this invention, the overall reaction mechanism of the method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag embodies the organic combination of chemical equilibrium shift and interface growth restriction. First, the carbide slag, as a raw material, undergoes an acid-base neutralization reaction with a strong inorganic acid. The calcium oxide and calcium hydroxide components in the solid phase are completely dissociated by the acid, transforming into highly solvated calcium ions, while releasing heat of reaction. During this leaching process, impurities such as aluminum, iron, and magnesium in the slag also enter the liquid phase. To achieve the goal of high-purity production, the difference in solubility product of different metal ions under specific pH conditions is utilized. By introducing an alkaline regulator, the proton concentration of the system is precisely controlled, causing impurity ions to preferentially transform into hydroxide precipitates and be removed, thereby obtaining a pure calcium salt raw material solution. The core conversion step occurs in a closed and pressurized reaction environment, where the calcium salt undergoes a metathesis reaction with an ammonia source. This reaction is thermodynamically a typical reversible equilibrium significantly affected by concentration and pressure. By introducing an inert gas and maintaining a specific system pressure, the apparent solubility of ammonia in the aqueous phase was artificially increased, thereby forcing the reaction towards the formation of solid products and byproduct salts according to the principle of equilibrium shift. During this process, the introduction of a calcium-titanium base-level composite modifier altered the crystallization pathway of calcium hydroxide. The active sites on the surface of the calcium-titanium base-level composite modifier preferentially occupied the highly polar crystal faces of calcium hydroxide nuclei through electrostatic attraction and chemical coordination. This interfacial barrier effect greatly limited the possibility of large-size crystal development, forcing the crystals to grow unsteadily in extremely thin lamellar or fine needle-like forms. The separated mixed slurry, utilizing the drastically different solubility characteristics of the target product and byproduct salts in hot water, was washed with deionized water at gradient temperatures, achieving deep removal of residual chloride ions while ensuring extremely low calcium source loss. Ultimately, during the high-speed slurry preparation and flash drying process after adding surfactants, the instantaneous and intense airflow impact force and heat energy are used to quickly remove moisture between particles, completing the dry powdering process before the particles physically agglomerate, thus achieving the mass production of high specific surface area calcium hydroxide and the co-production of industrial-grade by-product salt.

[0007] According to a preferred embodiment of the present invention, in step S1, the reaction time at 70-90°C is 30-60 minutes.

[0008] According to a preferred embodiment of the present invention, in step S2, the reaction time is 30-90 minutes after heating to 40-80°C.

[0009] According to a preferred embodiment of the present invention, in step S3, the washing time with hot deionized water at 70-80°C is 1-2 hours.

[0010] According to a preferred embodiment of the present invention, in step S4, the time for preparing the slurry is 15-30 minutes.

[0011] According to a preferred embodiment of the present invention, the preparation steps of the perovskite-based composite modifier include: A1, by weight, 10.0-15.0 parts of tetrabutyl titanate were added dropwise to 40.0-60.0 parts of anhydrous ethanol and stirred to obtain solution A; 25.0-40.0 parts of deionized water were added to 0.5-1.0 parts of concentrated hydrochloric acid and 0.1-0.3 parts of polyethylene glycol solution and stirred to obtain solution B; solution B was added dropwise to solution A to obtain titanium sol; the titanium sol was transferred to a reaction vessel and reacted at 120-150℃ to obtain titanium dioxide precursor; the titanium dioxide precursor was added to 80.0-120.0 parts of sodium hydroxide solution and hydrothermally treated at 110-150℃ to obtain crude product; the crude product was subjected to ion exchange with hydrochloric acid, centrifuged to obtain precipitate; the precipitate was washed with deionized water, dried, and calcined at 300-400℃ to obtain hydrotitanic acid / titanium dioxide nanotubes; A2, 5.0-8.0 parts of hydrotitanic acid / titanium dioxide nanotube powder were ultrasonically dispersed in 300.0-500.0 parts of deionized water, and 4.0-10.0 parts of magnesium nitrate hexahydrate and 2.0-5.0 parts of aluminum nitrate hexahydrate were added; while stirring, sodium hydroxide solution was added dropwise to adjust the pH to 9.5-10.5; the mixture was transferred to an autoclave and hydrothermally reacted at 100-120℃ to obtain a reaction mixture; the reaction mixture was centrifuged to obtain a precipitate; the precipitate was washed and dried to obtain the composite precursor; A3. Disperse 5.0-10.0 parts of the composite precursor in a mixed solvent of 200.0-400.0 parts of anhydrous ethanol and deionized water, add 0.5-1.5 parts of 3-aminopropyltriethoxysilane, and reflux at 60-80℃ under nitrogen protection to obtain a mixture; centrifuge the mixture to obtain a precipitate; disperse the precipitate in 150.0-300.0 parts of N,N-dimethylformamide, add 1.0-2.5 parts of 1,3,5-benzenetricarboxylic acid and 1.5-3.0 parts of cerium nitrate hexahydrate, and thermally react at 100-120℃, centrifuge to obtain a precipitate; wash and dry the precipitate to obtain an organic-inorganic hybrid intermediate; A4. Place 5.0-10.0 parts of the organic-inorganic hybrid intermediate in a tube furnace, hold at 200-250℃ under a nitrogen atmosphere, then raise the temperature to 300-400℃ and hold; cool to obtain the product; disperse the product in 100.0-200.0 parts of a 0.1-0.5 diammonium hydrogen phosphate solution and stir; centrifuge, wash with deionized water, and dry.

[0012] In this invention, the formation mechanism of the perovskite-based composite modifier lies in the multi-step synergistic transformation and heterogeneous interface construction at the micro- and nanoscale. In the initial preparation stage, titanate precursors undergo precise hydrolysis and condensation reactions in anhydrous alcohol solvent to construct a gel framework with three-dimensional cross-linking characteristics. Subsequently, under the induction of an acidic medium, titanium oxide segments rearrange to form chemically active sol particles. Entering the hydrothermal conversion stage, these particles undergo a vigorous dissolution and recrystallization process in a strongly alkaline environment. Alkali metal ions enter the interlayer of the titanium oxide framework, inducing layer peeling and spontaneous curling based on the principle of surface energy minimization, thus evolving into a hollow nanotube morphology. This tubular framework then undergoes deep exchange of interlayer metal ions and hydrogen ions through ion diffusion in an acidic solution, and the hydroxyl groups in the structure are removed by high-temperature calcination, achieving a transition from a hydrated state to a stable semiconductor oxide structure. To construct a hierarchical structure, magnesium and aluminum ions were introduced onto the nanotube surface using heterogeneous nucleation theory. By adjusting the alkalinity of the reaction system, layered double hydroxides were epitaxially grown on the tube wall with a specific orientation, forming a dendritic-like hierarchical composite that significantly increased the geometrical exposed area of ​​the material. Building upon this, nucleophilic amino groups were introduced through silanization modification. These groups act as anchoring sites to capture rare-earth metal centers and coordinate with polycarboxylated organic ligands to construct a highly ordered metal-organic framework coating in situ on the inorganic carrier surface. Finally, during a staged temperature-programmed process under inert gas protection, the organic ligands underwent controlled molecular breakage and in-situ carbonization, generating a carbon-based network with a high charge transfer rate. The rare-earth components were transformed into oxide clusters with abundant oxygen vacancies. The resulting composite material, after surface modification with phosphate, microscopically exhibits a hierarchical structure modifier with extremely high specific surface area and multifunctional active sites.

[0013] According to a preferred embodiment of the present invention, in step A1, the calcination time at 300-400°C is 2-4 hours.

[0014] According to a preferred embodiment of the present invention, in step A2, the hydrothermal reaction at 100-120°C takes 12-24 hours.

[0015] According to a preferred embodiment of the present invention, in step A3, the thermal reaction time at 100-120°C is 24-48 hours.

[0016] According to a preferred embodiment of the present invention, in step A4, the time for holding the temperature at 300-400°C is 2-3 hours.

[0017] The beneficial effects of this invention are as follows: This invention proposes a perovskite-based composite modifier with a multi-layered structure. This modifier has a core of hydrotitanic acid or titanium dioxide nanotubes, an intermediate shell of layered bimetallic hydroxide nanosheets, and an outer shell of defect-state cerium oxide nanoclusters derived from the pyrolysis of cerium-based metal-organic frameworks. After staged calcination under an inert atmosphere and surface modification with diammonium hydrogen phosphate, it exhibits an extremely high specific surface area, large pore volume, and a surface rich in active sites such as phosphate and hydroxyl groups. Introducing this modifier into the ammoniation precipitation reaction allows it to play multiple roles in situ during the nucleation and growth stages of calcium hydroxide crystals: firstly, its ultra-high specific surface area and mesoporous structure provide ample confined space and active sites for heterogeneous nucleation of calcium hydroxide, effectively inhibiting excessive crystal growth; secondly, the active groups on the modifier surface coordinate with calcium ions, regulating the preferred growth direction of calcium hydroxide crystals, promoting the formation of nanosheet or needle-like morphologies, controlling the primary particle size to the nanometer scale, and resulting in extremely thin crystals. After final drying by impact airflow and grading and sieving, the calcium hydroxide product has an extremely high specific surface area, high purity, good dispersibility and excellent reactivity.

[0018] The main process route of this invention is extremely simple and efficient, comprising only four main steps: acid leaching reaction, ammoniation precipitation reaction, solid-liquid separation and washing, and slurry preparation and drying classification. The process is short, requires low equipment investment, and is easy to operate, facilitating large-scale industrial production. All raw materials involved in the reaction are commercially available bulk chemical products, widely available and inexpensive. Crucially, this invention fully utilizes the "anomalous solubility" characteristic of calcium hydroxide, where its solubility decreases with increasing temperature, thus promoting precipitation. Simultaneously, the use of a closed, pressurized reactor effectively suppresses the escape of ammonia due to temperature rise, ensuring a high concentration of dissolved ammonia in the liquid phase and driving the reversible precipitation reaction towards the formation of calcium hydroxide. In the washing process, hot deionized water is used for multiple washes. Utilizing the characteristic that ammonium chloride solubility increases sharply with increasing temperature, chloride ions in the filter cake are efficiently removed. Simultaneously, because the solubility of calcium hydroxide decreases with increasing temperature, product dissolution and loss during the washing process are greatly reduced. The application of impact airflow drying technology results in a very short residence time of materials in the dryer, effectively avoiding the hard agglomeration of nanoparticles during the drying process and ensuring the nanoscale and high dispersibility of the product.

[0019] This invention realizes the high-value resource utilization and closed-loop recycling of industrial solid waste, calcium carbide slag. Using calcium carbide slag as raw material, calcium ions are extracted through acid leaching, and then converted into high-value-added calcium hydroxide product through ammoniation precipitation. Simultaneously, high-purity industrial-grade ammonium chloride crystals are produced as a byproduct, which can be sold as agricultural fertilizer or industrial raw material, achieving complete conversion and resource utilization of calcium in the calcium carbide slag. The ammonium chloride-containing filtrate generated during the process is concentrated, and the evaporation condensate is recycled for washing and slurry preparation. The crystallization mother liquor is returned to the system for recycling and concentration, achieving closed-loop recycling of water resources and efficient recovery of ammonium chloride. The entire process produces no wastewater or waste residue discharge, conforming to the development concepts of green chemical engineering and circular economy. Compared with traditional methods of landfilling or utilizing calcium carbide slag as low-value building materials, this invention significantly increases the added value of calcium carbide slag, resulting in significant economic and environmental benefits. Furthermore, the calcium-titanium base-level structural composite modifier of this invention, after completing its crystal form regulation function, is mostly retained in the calcium hydroxide product, preventing secondary pollution and possessing potential for value-added applications. In summary, this invention has achieved groundbreaking progress in terms of technical economy, environmental protection, and product performance. Detailed Implementation

[0020] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0021] Example 1 This embodiment provides a method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag, including the following steps: S1: 110.0g of industrial calcium carbide slag raw material was dried to constant weight in an oven at 110℃. It was then crushed sequentially using a jaw crusher and a ball mill, and passed through a 100-mesh standard sieve to obtain dried calcium carbide slag powder. The dried calcium carbide slag powder was added to a corrosion-resistant reactor equipped with a stirrer and a temperature control system. 300.0g of industrial hydrochloric acid (31% by mass) was slowly added at a rate of 7.5g / min, based on a molar ratio of effective calcium content in the calcium carbide slag to HCl of 1:2.1, while maintaining a stirring speed of 400rpm and controlling the reaction system temperature to not exceed 60℃. After the acid addition was complete, the temperature was raised to 80℃, and the reaction was continued with stirring for 45min. After the reaction was completed, ammonia water (5% by mass) was added to adjust the pH of the system to 9.0, causing impurity ions to precipitate. The reaction slurry was pumped into a plate and frame filter press for pressure filtration separation, obtaining calcium chloride filtrate and filter cake. The filtrate was stored in a storage tank for later use.

[0022] S2: Pump 375.0g of calcium chloride filtrate into a sealed reactor equipped with a stirrer, temperature control system, and pressure control system. Add 0.15g of calcium-titanium base-level structural composite modifier. Start stirring at 500rpm and slowly add 80.0g of industrial ammonia (28% by mass) at room temperature. After the ammonia is added, seal the reactor and purge with nitrogen to maintain the pressure inside the reactor at 0.2MPa (gauge pressure). Raise the temperature to 60℃ and maintain the temperature while stirring for 60min to obtain a mixed slurry containing calcium hydroxide precipitate, ammonium chloride, and CTHCM.

[0023] S3: 450.0g of the mixed slurry was pumped into a plate and frame filter press for solid-liquid separation, yielding a calcium hydroxide filter cake and a filtrate containing ammonium chloride. The calcium hydroxide filter cake was first washed with 60℃ hot deionized water (4 times the filter cake volume) for 30 minutes. After pressing and filtration, it was washed a second time with 75℃ hot deionized water (4 times the filter cake volume) for 30 minutes. After dehydration by pressing and filtration, the filter cake was sampled and the chloride ion content was determined by silver nitrate titration to be 0.06wt%, which is below 0.1wt% and qualified. The filtrate containing ammonium chloride was collected and then evaporated and crystallized to recover industrial-grade ammonium chloride.

[0024] S4: Add 125.0g of washed and qualified calcium hydroxide filter cake (wet weight, moisture content approximately 45wt%) to the slurry mixing tank, add 30.0g of deionized water and 0.075g of sodium hexametaphosphate, start high-speed stirring at 1000rpm, and mix for 22.5min to obtain a uniform slurry with a solid content of approximately 78wt%. The prepared slurry is then pumped into an impact airflow dryer for drying. The dryer inlet hot air temperature is 250℃, the outlet temperature is 100℃, the pulverizing blade circumferential speed is 65m / s, and the material residence time in the dryer is approximately 2s. After drying, the powder is collected by a two-stage gas-solid separation system consisting of a cyclone separator and a bag filter, and then sent to an air classifier for classification and sieving via a pneumatic conveying system. The classifier frequency is 45Hz, and the classifying wheel speed is 3000rpm. Powder with a particle size of less than 325 mesh (44 μm) is collected as the finished calcium hydroxide product, while coarse particles with a particle size of more than 325 mesh are returned to the slurry mixing tank for reprocessing.

[0025] Preparation of perovskite-based structural composite modifier: A1: 12.5g of tetrabutyl titanate was slowly added dropwise to 50.0g of anhydrous ethanol at a rate of 2mL / min. The mixture was stirred for 30min to form a homogeneous, transparent, pale yellow solution, denoted as solution A. Separately, 32.5g of deionized water was added to 0.75g of concentrated hydrochloric acid (37% by mass) and 0.2g of polyethylene glycol (PEG-4000), and stirred thoroughly until completely dissolved; this solution is denoted as solution B. Under vigorous stirring (800rpm), solution B was slowly added dropwise to solution A at a rate of 4mL / min. After the addition was complete, stirring was continued for 60min to obtain a homogeneous and stable titanium sol. This titanium sol was transferred to a polytetrafluoroethylene-lined high-pressure reactor, sealed, and placed in a forced-air drying oven. The temperature was increased from room temperature to 135℃ at a rate of 2℃ / min, and the reaction was carried out at this constant temperature for 36h via hydrothermal reaction. After the hydrothermal reaction was completed, the mixture was allowed to cool naturally to room temperature. The reaction product was then centrifuged (9000 rpm, 12 min) and washed three times each with deionized water and anhydrous ethanol, with each wash volume being 8 times the volume of the precipitate. The washed precipitate was placed in a vacuum drying oven and dried at 70℃ and a vacuum of -0.092 MPa for 18 h to obtain a white powdery titanium dioxide precursor. This white powder was added to 100.0 g of sodium hydroxide solution (10 mol / L), transferred to a high-pressure reactor, and hydrothermally treated at 130℃ for 24 h to obtain a crude product. The crude product was washed with 0.1 mol / L hydrochloric acid for ion exchange until neutral (pH≈7), and then centrifuged (9000 rpm, 12 min) to obtain a precipitate. The precipitate was washed with deionized water until Cl... - The test was negative (no white precipitate was detected using 0.1 mol / L AgNO3 solution), and then the nanotubes were vacuum dried at 70℃ for 18 h. Finally, they were placed in a muffle furnace and heated to 350℃ at a heating rate of 1℃ / min. They were calcined in air for 3 h and then naturally cooled to obtain hydrogen titanate / titanium dioxide nanotubes.

[0026] A2: 6.5 g of hydrotitanic acid / titanium dioxide nanotube powder was ultrasonically dispersed in 400.0 g of deionized water at a solid-liquid ratio of 1:60 (g / mL). The ultrasonic power was 400 W, the frequency was 40 kHz, and the ultrasonic time was 45 min to obtain a uniform nanotube suspension. 7.0 g of magnesium nitrate hexahydrate and 3.5 g of aluminum nitrate hexahydrate were added sequentially to this suspension, controlling the molar ratio of Mg²⁺ to Al³⁺ to be 3:1. After dissolving by stirring at room temperature, 30.0 g of sodium hydroxide solution (1.0 mol / L) was added dropwise at a rate of 0.8 mL / min to adjust the pH of the system to 10.0, while maintaining vigorous stirring (stirring speed 1000 rpm) during the addition. After pH adjustment, the mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to a hydrothermal reaction at 110 °C for 18 h. After the reaction was completed, the product was allowed to cool naturally to room temperature. The product was then centrifuged (7000 rpm, 10 min), washed with deionized water until the pH of the washing solution reached 7.0-7.5, and then washed once with anhydrous ethanol. The precipitate was dried under vacuum at 70 °C for 12 h to obtain the composite precursor (TNTs@MgAl-LDH).

[0027] A3: 7.5 g of TNTs@MgAl-LDH powder was dispersed in a mixed solvent of 300.0 g anhydrous ethanol and deionized water at a solid-liquid ratio of 1:40 (g / mL) (volume ratio of anhydrous ethanol to deionized water was 2:1). After ultrasonic dispersion for 30 min, the mixture was transferred to a three-necked flask and heated to 70 °C in a constant temperature water bath. 1.0 g of 3-aminopropyltriethoxysilane (APTES) was added to the system, the amount of APTES added being 13.3% of the mass of TNTs@MgAl-LDH. The mixture was refluxed and stirred under nitrogen protection for 9 h. After the reaction was completed, the product was centrifuged (7000 rpm, 10 min) and washed three times each with anhydrous ethanol and deionized water, with each wash volume being 6 times the volume of the precipitate. The washed solid product was vacuum dried at 60 °C for 12 h to obtain the APTES-functionalized composite precursor (TNTs@MgAl-LDH-APTES). The functionalized product was redispersed in 225.0 g of N,N-dimethylformamide at a solid-liquid ratio of 1:30 (g / mL), along with 1.75 g of 1,3,5-benzenetricarboxylic acid and 2.25 g of cerium nitrate hexahydrate. The mixture was transferred to a high-pressure reactor and reacted solvothermically at 110 °C for 36 h. After the reaction, the mixture was allowed to cool naturally to room temperature and centrifuged (8000 rpm, 10 min). The product was washed three times each with DMF, anhydrous ethanol, and deionized water. The washed product was then vacuum dried at 70 °C for 24 h to obtain the organic-inorganic hybrid intermediate.

[0028] A4: 7.5 g of organic-inorganic hybrid intermediate powder was placed in a tube furnace and calcined in stages under a nitrogen atmosphere (nitrogen flow rate 150 mL / min). The calcination program was set as follows: In the first stage, the temperature was increased from room temperature to 225 °C at a rate of 1 °C / min and held at this temperature for 1.5 h; in the second stage, the temperature was increased to 350 °C at a rate of 1 °C / min and held at this temperature for 2.5 h. After calcination, the product was naturally cooled to room temperature to obtain a black calcined product. The calcined product was dispersed in 150.0 g of 0.3 mol / L diammonium hydrogen phosphate aqueous solution at a solid-liquid ratio of 1:20 (g / mL) and stirred and impregnated at room temperature for 3 h. After impregnation, the product was centrifuged (7000 rpm, 10 min), washed with deionized water until the conductivity of the washing solution was below 50 μS / cm, and vacuum dried at 90 °C for 18 h to finally obtain the perovskite-based structural composite modifier (CTHCM).

[0029] Example 2 This embodiment provides a method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag, including the following steps: S1: 100.0g of industrial calcium carbide slag raw material was dried to constant weight in an oven at 110℃. It was then crushed sequentially using a jaw crusher and a ball mill, and passed through a 100-mesh standard sieve to obtain dried calcium carbide slag powder. The dried calcium carbide slag powder was added to a corrosion-resistant reactor equipped with a stirrer and temperature control system. 250.0g of industrial hydrochloric acid (31% by mass) was slowly added at a rate of 5.0g / min, based on a molar ratio of effective calcium content in the calcium carbide slag to HCl of 1:2.0, while maintaining a stirring speed of 300rpm and controlling the reaction system temperature to not exceed 60℃. After the acid addition was complete, the temperature was raised to 70℃, and the reaction was continued with stirring for 30min. After the reaction was completed, ammonia water (5% by mass) was added to adjust the pH of the system to 8.5, causing impurity ions to precipitate. The reaction slurry was pumped into a plate and frame filter press for filtration separation, obtaining calcium chloride filtrate and filter cake. The filtrate was stored in a storage tank for later use.

[0030] S2: Pump 300.0g of calcium chloride filtrate into a sealed reactor equipped with a stirrer, temperature control system, and pressure control system. Add 0.05g of calcium-titanium base-level structural composite modifier. Start stirring at 400rpm and slowly add 60.0g of industrial ammonia (28% by mass) at room temperature. After the ammonia is added, seal the reactor and purge with nitrogen to maintain the pressure inside the reactor at 0.1MPa (gauge pressure). Raise the temperature to 40℃ and maintain the temperature while stirring for 30min to obtain a mixed slurry containing calcium hydroxide precipitate, ammonium chloride, and CTHCM.

[0031] S3: 350.0g of the mixed slurry was pumped into a plate and frame filter press for solid-liquid separation, yielding a calcium hydroxide filter cake and a filtrate containing ammonium chloride. The calcium hydroxide filter cake was first washed with 50℃ hot deionized water (3 times the filter cake volume) for 20 minutes. After pressing and filtration, it was washed a second time with 70℃ hot deionized water (3 times the filter cake volume) for 20 minutes. After dehydration by pressing and filtration, the filter cake was sampled and the chloride ion content was determined to be 0.08wt% by silver nitrate titration. The filtrate containing ammonium chloride was collected and then evaporated and crystallized to recover industrial-grade ammonium chloride.

[0032] S4: Add 100.0g of washed and qualified calcium hydroxide filter cake (wet weight, moisture content approximately 50wt%) to the slurry mixing tank, add 15.0g of deionized water and 0.05g of sodium hexametaphosphate, start high-speed stirring at 800rpm, and mix for 15min to obtain a uniform slurry with a solid content of approximately 70wt%. The prepared slurry is then pumped into an impact airflow dryer for drying. The dryer inlet hot air temperature is 200℃, the outlet temperature is 80℃, the pulverizing blade circumferential speed is 50m / s, and the material residence time in the dryer is approximately 3s. The dried powder is collected by a two-stage gas-solid separation system consisting of a cyclone separator and a bag filter, and then sent to an air classifier for classification and sieving via a pneumatic conveying system. The classifier frequency is 30Hz, and the classifying wheel speed is 2000rpm. Powder with a particle size smaller than 325 mesh is collected as the finished calcium hydroxide product, while coarse particles larger than 325 mesh are returned to the slurry mixing tank for reprocessing.

[0033] Preparation of perovskite-based structural composite modifier: A1: 10.0 g of tetrabutyl titanate was slowly added dropwise to 40.0 g of anhydrous ethanol at a rate of 2 mL / min. The mixture was stirred for 30 min to form a homogeneous, transparent, pale yellow solution, denoted as solution A. Separately, 25.0 g of deionized water was added to 0.5 g of concentrated hydrochloric acid (37% by mass) and 0.1 g of polyethylene glycol (PEG-4000), and stirred thoroughly until completely dissolved; this solution is denoted as solution B. Under vigorous stirring (800 rpm), solution B was slowly added dropwise to solution A at a rate of 3 mL / min. After the addition was complete, stirring was continued for 60 min to obtain a homogeneous and stable titanium sol. This titanium sol was transferred to a polytetrafluoroethylene-lined high-pressure reactor, sealed, and placed in a forced-air drying oven. The temperature was increased from room temperature to 120 °C at a rate of 2 °C / min, and the mixture was kept at this temperature for 24 h for hydrothermal reaction. After the hydrothermal reaction was completed, the mixture was allowed to cool naturally to room temperature. The reaction product was centrifuged (8000 rpm, 15 min) and washed three times each with deionized water and anhydrous ethanol, with each wash volume being 5 times the volume of the precipitate. The washed precipitate was placed in a vacuum drying oven and dried at 60℃ and a vacuum of -0.09 MPa for 24 h to obtain a white powdery titanium dioxide precursor. This white powder was added to 80.0 g of sodium hydroxide solution (10 mol / L), transferred to a high-pressure reactor, and hydrothermally treated at 110℃ for 24 h to obtain a crude product. The crude product was washed with 0.1 mol / L hydrochloric acid for ion exchange until neutral (pH≈7), and centrifuged (8000 rpm, 15 min) to obtain a precipitate. The precipitate was washed with deionized water until Cl... - The test was negative (no white precipitate was detected using 0.1 mol / L AgNO3 solution), and then the nanotubes were vacuum dried at 60℃ for 24 h. Finally, they were placed in a muffle furnace and heated to 300℃ at a heating rate of 1℃ / min. They were calcined in air for 2 h and then naturally cooled to obtain hydrogen titanate / titanium dioxide nanotubes.

[0034] A2: 5.0 g of titanate / titanium dioxide nanotube powder was ultrasonically dispersed in 300.0 g of deionized water at a solid-liquid ratio of 1:60 (g / mL). The ultrasonic power was 300 W, the frequency was 40 kHz, and the ultrasonic time was 30 min to obtain a uniform nanotube suspension. 4.0 g of magnesium nitrate hexahydrate and 2.0 g of aluminum nitrate hexahydrate were added sequentially to this suspension. After dissolving by stirring at room temperature, 20.0 g of sodium hydroxide solution (0.5 mol / L) was added dropwise at a rate of 0.5 mL / min to adjust the pH of the system to 9.5. Vigorous stirring (800 rpm) was maintained during the dropwise addition. After pH adjustment, the mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to a hydrothermal reaction at 100 °C for 12 h. After the reaction, the mixture was naturally cooled to room temperature, and the product was centrifuged (6000 rpm, 10 min). It was washed with deionized water until the pH of the washing solution reached 7.0-7.5, and then washed once with anhydrous ethanol. The washed precipitate was vacuum dried at 60℃ for 12 h to obtain the composite precursor (TNTs@MgAl-LDH).

[0035] A3: 5.0 g of TNTs@MgAl-LDH powder was dispersed in a mixed solvent of 200.0 g of anhydrous ethanol and deionized water at a solid-liquid ratio of 1:40 (g / mL) (volume ratio of anhydrous ethanol to deionized water was 1:1). After ultrasonic dispersion for 30 min, the mixture was transferred to a three-necked flask and heated to 60 °C in a constant temperature water bath. 0.5 g of 3-aminopropyltriethoxysilane (APTES) was added to the system, the amount of APTES added being 10% of the mass of TNTs@MgAl-LDH. The mixture was refluxed and stirred under nitrogen protection for 6 h. After the reaction was completed, the product was centrifuged (6000 rpm, 10 min) and washed three times each with anhydrous ethanol and deionized water, with each wash volume being 5 times the volume of the precipitate. The washed solid product was vacuum dried at 50 °C for 12 h to obtain the APTES-functionalized composite precursor (TNTs@MgAl-LDH-APTES). The functionalized product was redispersed in 150.0 g of N,N-dimethylformamide at a solid-liquid ratio of 1:30 (g / mL), along with 1.0 g of 1,3,5-benzenetricarboxylic acid and 1.5 g of cerium nitrate hexahydrate. The mixture was transferred to a high-pressure reactor and reacted solvothermically at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature and centrifuged (8000 rpm, 10 min). The product was washed three times each with N,N-dimethylformamide, anhydrous ethanol, and deionized water. The washed product was then vacuum-dried at 60 °C for 24 h to obtain an organic-inorganic hybrid intermediate.

[0036] A4: 5.0 g of organic-inorganic hybrid intermediate powder was placed in a tube furnace and calcined in stages under a nitrogen atmosphere (nitrogen flow rate 100 mL / min). The calcination program was set as follows: In the first stage, the temperature was increased from room temperature to 200℃ at a rate of 1℃ / min and held at that temperature for 1 h; in the second stage, the temperature was increased to 300℃ at a rate of 1℃ / min and held at that temperature for 2 h. After calcination, the product was naturally cooled to room temperature to obtain a black calcined product. The calcined product was dispersed in 100.0 g of 0.1 mol / L diammonium hydrogen phosphate aqueous solution at a solid-liquid ratio of 1:20 (g / mL) and stirred and impregnated at room temperature for 2 h. After impregnation, the product was centrifuged (6000 rpm, 10 min), washed with deionized water until the conductivity of the washing solution was below 50 μS / cm, and vacuum dried at 80℃ for 24 h to finally obtain the perovskite-based structural composite modifier (CTHCM).

[0037] Example 3 This embodiment provides a method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag, including the following steps: S1: 120.0g of industrial calcium carbide slag raw material was dried to constant weight in an oven at 120℃. It was then crushed sequentially using a jaw crusher and a ball mill, and passed through a 100-mesh standard sieve to obtain dried calcium carbide slag powder. The dried calcium carbide slag powder was added to a corrosion-resistant reactor equipped with a stirrer and a temperature control system. 350.0g of industrial hydrochloric acid (32% by mass) was slowly added at a rate of 10.0g / min, based on a molar ratio of effective calcium content in the calcium carbide slag to HCl of 1:2.2, while maintaining a stirring speed of 500rpm and controlling the reaction system temperature to not exceed 60℃. After the acid addition was complete, the temperature was raised to 90℃, and the reaction was continued with stirring for 60min. After the reaction was completed, ammonia water (5% by mass) was added to adjust the pH of the system to 9.5, causing impurity ions to precipitate. The reaction slurry was pumped into a plate and frame filter press for filtration separation, obtaining calcium chloride filtrate and filter cake. The filtrate was stored in a storage tank for later use.

[0038] S2: Pump 450.0g of calcium chloride filtrate into a sealed reactor equipped with a stirrer, temperature control system, and pressure control system. Add 0.25g of calcium-titanium base-level structural composite modifier. Start stirring at 600rpm and slowly add 100.0g of industrial ammonia (28% by mass) at room temperature. After the ammonia is added, seal the reactor and purge with nitrogen to maintain the pressure inside the reactor at 0.3MPa (gauge pressure). Raise the temperature to 80℃ and maintain the temperature with stirring for 90min to obtain a mixed slurry containing calcium hydroxide precipitate, ammonium chloride, and CTHCM.

[0039] S3: 550.0 g of the mixed slurry was pumped into a ceramic membrane filtration system for solid-liquid separation (membrane pore size 0.1 μm), yielding a calcium hydroxide filter cake and a filtrate containing ammonium chloride. The calcium hydroxide filter cake was first washed with 70°C hot deionized water (wash volume 5 times the filter cake volume, washing time 30 min), and then washed a second time with 80°C hot deionized water (wash volume 5 times the filter cake volume, washing time 30 min). After two washings, the filter cake was dehydrated by pressure filtration, and a sample was taken for silver nitrate titration to determine the chloride ion content, which was 0.04 wt%. The filtrate containing ammonium chloride was collected and then evaporated and crystallized to recover industrial-grade ammonium chloride.

[0040] S4: Add 150.0g of washed and qualified calcium hydroxide filter cake (wet weight, moisture content approximately 40wt%) to the slurry mixing tank, along with 45.0g of deionized water and 0.10g of sodium hexametaphosphate. Start high-speed stirring at 1200rpm and mix for 30min to obtain a uniform slurry with a solid content of approximately 85wt%. Pump the prepared slurry into an impact airflow dryer for drying. The dryer inlet hot air temperature is 300℃, the outlet temperature is 120℃, the pulverizing blade circumferential speed is 80m / s, and the material residence time in the dryer is approximately 1s. After drying, the powder is collected by a two-stage gas-solid separation system consisting of a cyclone separator and a bag filter. Then, it is sent to an air classifier for grading and screening via a pneumatic conveying system. The classifier frequency is 60Hz, and the classifying wheel speed is 4000rpm. Powder with a particle size smaller than 325 mesh is collected as the finished calcium hydroxide product, while coarse particles larger than 325 mesh are returned to the slurry mixing tank for reprocessing.

[0041] Preparation of perovskite-based structural composite modifier: A1: 15.0 g of tetrabutyl titanate was slowly added dropwise to 60.0 g of anhydrous ethanol at a rate of 3 mL / min. The mixture was stirred for 30 min to form a homogeneous, transparent, pale yellow solution, denoted as solution A. Separately, 40.0 g of deionized water was added to 1.0 g of concentrated hydrochloric acid (37% by mass) and 0.3 g of polyethylene glycol (PEG-4000), and stirred thoroughly until completely dissolved; this solution is denoted as solution B. Under vigorous stirring (1000 rpm), solution B was slowly added dropwise to solution A at a rate of 5 mL / min. After the addition was complete, stirring was continued for 60 min to obtain a homogeneous and stable titanium sol. This titanium sol was transferred to a polytetrafluoroethylene-lined high-pressure reactor, sealed, and placed in a forced-air drying oven. The temperature was increased from room temperature to 150 °C at a rate of 2 °C / min, and the mixture was kept at this temperature for 48 h for hydrothermal reaction. After the hydrothermal reaction was completed, the mixture was allowed to cool naturally to room temperature. The reaction product was centrifuged (10,000 rpm, 10 min) and washed three times each with deionized water and anhydrous ethanol, with each wash volume being 10 times the volume of the precipitate. The washed precipitate was placed in a vacuum drying oven and dried at 80℃ and a vacuum of -0.095 MPa for 12 h to obtain a white powdery titanium dioxide precursor. This white powder was added to 120.0 g of sodium hydroxide solution (10 mol / L), transferred to a high-pressure reactor, and hydrothermally treated at 150℃ for 24 h to obtain a crude product. The crude product was washed with 0.1 mol / L hydrochloric acid for ion exchange until neutral (pH≈7), and centrifuged (10,000 rpm, 10 min) to obtain a precipitate. The precipitate was washed with deionized water until Cl... - The test was negative (no white precipitate was detected using 0.1 mol / L AgNO3 solution), and then the nanotubes were vacuum dried at 80℃ for 12 h. Finally, they were placed in a muffle furnace and heated to 400℃ at a heating rate of 1℃ / min. They were calcined in air for 4 h and then naturally cooled to obtain hydrogen titanate / titanium dioxide nanotubes.

[0042] A2: 8.0 g of titanate / titanium dioxide nanotube powder was ultrasonically dispersed in 500.0 g of deionized water at a solid-liquid ratio of 1:60 (g / mL). The ultrasonic power was 500 W, the frequency was 40 kHz, and the ultrasonic time was 60 min to obtain a uniform nanotube suspension. 10.0 g of magnesium nitrate hexahydrate (purity ≥98%) and 5.0 g of aluminum nitrate hexahydrate (purity ≥98%) were added sequentially to this suspension. After dissolving by stirring at room temperature, 40.0 g of sodium hydroxide solution (1.0 mol / L) was added dropwise at a rate of 1.0 mL / min to adjust the pH of the system to 10.5, while maintaining vigorous stirring (stirring speed 1200 rpm) during the addition. After pH adjustment, the mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to a hydrothermal reaction at 120 °C for 24 h. After the reaction was completed, the product was allowed to cool naturally to room temperature. The product was then centrifuged (8000 rpm, 10 min), washed with deionized water until the pH of the washing solution reached 7.0-7.5, and then washed once with anhydrous ethanol. The washed precipitate was vacuum dried at 80 °C for 12 h to obtain the composite precursor (TNTs@MgAl-LDH).

[0043] A3: 10.0 g of TNTs@MgAl-LDH powder was dispersed in a mixed solvent of 400.0 g anhydrous ethanol and deionized water at a solid-liquid ratio of 1:40 (g / mL) (volume ratio of anhydrous ethanol to deionized water was 3:1). After ultrasonic dispersion for 30 min, the mixture was transferred to a three-necked flask and heated to 80 °C in a constant temperature water bath. 1.5 g of 3-aminopropyltriethoxysilane (APTES) was added to the system, the amount of APTES added being 15% of the mass of TNTs@MgAl-LDH. The mixture was refluxed and stirred for 12 h under nitrogen protection. After the reaction was completed, the product was centrifuged (8000 rpm, 10 min) and washed three times each with anhydrous ethanol and deionized water, with each wash volume being 8 times the volume of the precipitate. The washed solid product was vacuum dried at 60 °C for 12 h to obtain the APTES-functionalized composite precursor (TNTs@MgAl-LDH-APTES). The functionalized product was redispersed in 300.0 g of N,N-dimethylformamide (DMF) at a solid-liquid ratio of 1:30 (g / mL), along with 2.5 g of 1,3,5-benzenetricarboxylic acid and 3.0 g of cerium nitrate hexahydrate. The mixture was transferred to a high-pressure reactor and reacted solvothermically at 120 °C for 48 h. After the reaction, the mixture was allowed to cool naturally to room temperature and centrifuged (8000 rpm, 10 min). The product was washed three times each with DMF, anhydrous ethanol, and deionized water. The washed product was then vacuum-dried at 80 °C for 24 h to obtain an organic-inorganic hybrid intermediate.

[0044] A4: 10.0 g of organic-inorganic hybrid intermediate powder was placed in a tube furnace and calcined in stages under nitrogen atmosphere (nitrogen flow rate 200 mL / min). The calcination program was set as follows: In the first stage, the temperature was increased from room temperature to 250℃ at a rate of 1℃ / min and held at that temperature for 2 h; in the second stage, the temperature was increased to 400℃ at a rate of 1℃ / min and held at that temperature for 3 h. After calcination, the product was naturally cooled to room temperature to obtain a black calcined product. The calcined product was dispersed in 200.0 g of 0.5 mol / L diammonium hydrogen phosphate aqueous solution at a solid-liquid ratio of 1:20 (g / mL) and stirred and impregnated at room temperature for 4 h. After impregnation, the product was centrifuged (8000 rpm, 10 min), washed with deionized water until the conductivity of the washing solution was below 50 μS / cm, and vacuum dried at 100℃ for 12 h to finally obtain the perovskite-based structural composite modifier (CTHCM).

[0045] Comparative Example 1 The specific implementation method is the same as in Example 1, except that no calcium-titanium base layer structural composite modifier is added. The remaining steps and parameters are exactly the same as in Example 1.

[0046] Comparative Example 2 The specific implementation method is the same as in Example 1, except that the calcium-titanium base layer structural composite modifier is replaced with an equal mass of polyethylene glycol (PEG-4000). The remaining steps and parameters are exactly the same as in Example 1.

[0047] Comparative Example 3 The specific implementation method is the same as in Example 1, except that the perovskite-based composite modifier used is not modified with diammonium hydrogen phosphate solution in step A4. That is, after the A4 step, only the product is obtained by staged calcination (200-250℃ and 300-400℃) without stirring with diammonium hydrogen phosphate solution. The remaining preparation steps, main process steps, and parameters are exactly the same as in Example 1.

[0048] Performance testing The methods for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste calcium carbide slag described in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing according to the following steps: The BET specific surface area of ​​calcium hydroxide products was determined by nitrogen adsorption-desorption method: 0.20-0.30 g of sample was placed in a quartz sample tube and pretreated under vacuum at 200℃ for 3 h. Then, high-purity nitrogen was used as the adsorbate at liquid nitrogen temperature (-196℃) and the nitrogen adsorption was measured within the relative pressure range of 0.05-0.30. The equilibrium time for each relative pressure point was set to 30 s. The specific surface area of ​​the sample was calculated using the multi-point BET equation (5 points were selected within the range of P / P0=0.05-0.30), and the unit was m² / g.

[0049] The calcium hydroxide content was determined by sucrose complexation-hydrochloric acid titration: 0.5000g of sample was accurately weighed and placed in a 250mL Erlenmeyer flask. 30.0g of sucrose and 150.0mL of deionized water were added. The flask was tightly sealed and magnetically stirred for 30min to fully dissolve the calcium hydroxide. 3 drops of phenolphthalein indicator (1% by mass) were added, and titrated with 0.5000mol / L hydrochloric acid standard solution until the solution changed from red to colorless and did not fade within 30s. The volume of hydrochloric acid standard solution consumed was recorded. A blank test was also performed. The calcium hydroxide content was calculated using the following formula: Ca(OH)2 content (wt%) = [C×(V-V0)×0.03708]÷m×100%, where C is the concentration of hydrochloric acid standard solution (mol / L), V is the volume of hydrochloric acid consumed by the sample (mL), V0 is the volume of hydrochloric acid consumed by the blank (mL), 0.03708 is the millimolecular mass of calcium hydroxide (g / mmol), and m is the sample mass (g).

[0050] The chloride ion content was determined by silver nitrate titration: 5.000 g of sample was accurately weighed and placed in a 150 mL beaker. 50.0 mL of deionized water was added, and the sample was magnetically stirred and extracted for 30 min. After filtration, 20.0 mL of the filtrate was transferred to an Erlenmeyer flask, and 2 drops of potassium chromate indicator (5% by mass) were added. Titration with 0.01000 mol / L silver nitrate standard solution continued until the solution changed from yellow to brick red. The volume of silver nitrate standard solution consumed was recorded. The chloride ion content was calculated using the following formula: Cl - Content (wt%) = [(C×V×0.03545×50.0)÷20.0]÷m×100%, where C is the concentration of silver nitrate standard solution (mol / L), V is the volume of silver nitrate standard solution consumed (mL), 0.03545 is the millimolecular mass of chloride ions (g / mmol), and m is the sample mass (g).

[0051] The 325-mesh sieve residue rate was determined by the dry sieving method: 100.0g of sample was weighed and placed in a 325-mesh (44μm aperture) standard test sieve, the sieve cover was closed, and the sieve was placed on a mechanical vibrating sieve separator. The vibration frequency was set to 300 times / minute, and the sieving time was 15 minutes. After the sieving was completed, the mass of the material on the sieve was weighed. The sieve residue rate was calculated by the following formula: Sieving residue rate (wt%) = (mass of material on the sieve ÷ mass of sample) × 100%.

[0052] The crystal morphology of calcium hydroxide products was observed using a scanning electron microscope: a small amount of sample was uniformly dispersed on a conductive carbon tape, and any loose particles were blown away with a rubber bulb. The sample was then placed in an ion sputtering instrument for gold sputtering treatment (sputtering current 20mA, time 60s), and then placed in the sample chamber of a scanning electron microscope. The sample was observed and images were taken under the conditions of accelerating voltage 5kV and working distance 8-10mm, with magnification of 20,000 to 50,000 times.

[0053] Test results: Table 1: Test results of each embodiment and comparative example

[0054] As can be seen from Table 1, Examples 1-3 effectively solved the technical problems of low specific surface area, easy ammonia escape leading to reaction equilibrium reversal, difficulty in removing impurities, and ineffective recovery of ammonium chloride in the preparation of calcium hydroxide from carbide slag in the prior art compared with Comparative Examples 1-3.

[0055] Firstly, regarding specific surface area, the specific surface area of ​​Comparative Example 1 without any modifier was only 12.3 m² / g. The specific surface area of ​​Comparative Example 2 increased to 28.6 m² / g after adding the organic modifier PEG-4000. The specific surface area of ​​Comparative Example 3 reached 41.2 m² / g when using a modifier without diammonium hydrogen phosphate modification. However, after using the perovskite-based multi-level structured composite modifier (CTHCM) of the present invention in Examples 1-3, the specific surface areas reached 68.7 m² / g, 55.2 m² / g, and 79.5 m² / g, respectively, which were significantly higher than all comparative examples. This indicates that the modifier with a nanotube-layered bimetallic hydroxide-defect state cerium oxide multi-level structure prepared by the present invention through a four-step method provides a large number of heterogeneous nucleation sites during the ammoniation precipitation process and effectively inhibits the excessive growth of calcium hydroxide crystals. At the same time, the inert atmosphere staged calcination and diammonium hydrogen phosphate surface modification further enhance the dispersion and regulation ability of the modifier, thereby solving the problem of low specific surface area.

[0056] Secondly, regarding the issue of ammonia easily escaping and causing a reversal of the reaction equilibrium, although the test results did not directly measure the amount of ammonia escaped, it can be indirectly proven from the product purity and chloride ion content: Comparative Example 1 had a chloride ion content as high as 0.15wt%, indicating that there was still a lot of ammonium chloride residue after washing. This may be due to incomplete precipitation reaction caused by ammonia escape, resulting in calcium hydroxide crystals that partially encapsulated ammonium chloride or had a loose crystal structure. In contrast, the chloride ion contents of Comparative Examples 2 and 3 were 0.11wt% and 0.07wt%, respectively, which were still higher than the 0.06wt%, 0.08wt%, and 0.04wt% of Examples 1-3. The chloride ion content of Example 3 was only 0.04wt%, indicating that ammonia escape was effectively suppressed under closed and pressurized conditions, the reaction equilibrium shifted to the right, the generated calcium hydroxide precipitate was purer and the crystals were more complete, and ammonium chloride was more easily removed during washing, thus solving the problem of equilibrium reversal caused by ammonia escape.

[0057] Secondly, regarding the difficulty in removing impurities, the Ca(OH)2 content of Comparative Example 1 was only 94.2 wt%, indicating that a large amount of impurities (such as unprecipitated magnesium, aluminum, iron, or unreacted ammonium chloride) remained in the product. The Ca(OH)2 contents of Comparative Examples 2 and 3 were 95.5 wt% and 96.0 wt%, respectively, while the Ca(OH)2 contents of Examples 1-3 reached 96.8 wt%, 96.1 wt%, and 97.2 wt%, respectively, especially Example 3, which reached as high as 97.2 wt%. This was due to the precise control of the pH value between 8.5 and 9.5 in step S1, which ensured that the Fe... 3+ And Al 3+ The effective precipitation prevents the amphoteric dissolution of Al(OH)3. At the same time, the CTHCM modifier in the ammoniation precipitation process selectively adsorbs calcium ions, promoting the formation of high-purity calcium hydroxide crystals, thus solving the problem of difficult removal of impurities.

[0058] Finally, regarding the issue of ineffective ammonium chloride recovery, although the test results did not directly provide the ammonium chloride recovery rate, it can be inferred from the filtrate treatment and product chloride ion content that: the chloride ion content in the filter cakes of Examples 1-3 was all below 0.1 wt%, with the lowest being only 0.04 wt%, indicating that most of the ammonium chloride entered the filtrate through washing and was recovered by evaporation and crystallization; while the chloride ion content in Comparative Example 1 was as high as 0.15 wt%, meaning that the washing was insufficient or that the ammonium chloride was encapsulated during the precipitation reaction, leading to difficulties in recovery; in addition, Examples 1-3 used hot deionized water at 50-80℃ for multiple washes, taking advantage of the characteristic that the solubility of ammonium chloride increases sharply with increasing temperature, to efficiently wash away the ammonium chloride in the filter cake, while utilizing the anomalous solubility characteristic of calcium hydroxide to reduce product loss, ensuring a high concentration of ammonium chloride in the filtrate and high efficiency of subsequent evaporation and crystallization, thus solving the problem of ineffective ammonium chloride recovery.

[0059] In summary, Examples 1-3 are significantly superior to Comparative Examples 1-3 in terms of specific surface area, product purity, chloride ion removal, and crystal morphology control. This fully demonstrates that the present invention has successfully solved the four core problems of the prior art by introducing CTHCM modifier, closed pressurized ammoniation precipitation, precise pH control, and hot water washing as synergistic technical solutions.

[0060] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag, characterized in that, Includes the following steps: S1, by weight, 100.0-120.0 parts of industrial carbide slag raw material are dried, crushed, and sieved to obtain dried carbide slag powder; the dried carbide slag powder is put into a reaction vessel, 250.0-350.0 parts of hydrochloric acid are added, and the mixture is stirred; The temperature is raised to 70-90℃ for reaction; after the reaction is completed, ammonia water is added to adjust the pH value to 8.5-9.5 to obtain a reaction slurry; the reaction slurry is filtered to obtain calcium chloride filtrate and filter cake; S2, pump 300.0-450.0 parts of calcium chloride filtrate into a closed reactor, add 0.05-0.25 parts of calcium-titanium base-level structural composite modifier; stir, add 60.0-100.0 parts of ammonia water at room temperature; introduce nitrogen gas, heat to 40-80℃ to react, and obtain a mixed slurry; S3, centrifuge 350.0-550.0 parts of the mixed slurry to obtain calcium hydroxide filter cake and ammonium chloride-containing filtrate; wash the calcium hydroxide filter cake with hot deionized water at 50-70℃, and then wash it with hot deionized water at 70-80℃. The washed filter cake was obtained; the filtrate containing ammonium chloride was evaporated and crystallized to obtain ammonium chloride; S4. Add 100.0-150.0 parts of washed filter cake to the slurry preparation tank, add 15.0-45.0 parts of deionized water and 0.05-0.1 parts of sodium hexametaphosphate, and prepare the slurry to obtain the slurry; dry the slurry and sieve it.

2. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to claim 1, characterized in that, In step S1, the reaction time is 30-60 minutes after heating to 70-90℃.

3. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to claim 1, characterized in that, In step S2, the reaction time is 30-90 minutes after heating to 40-80℃.

4. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to claim 1, characterized in that, In step S3, the washing time with hot deionized water at 70-80℃ is 1-2 hours.

5. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to claim 1, characterized in that, In step S4, the mixing time is 15-30 minutes.

6. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to any one of claims 1-5, characterized in that, The preparation steps of the perovskite-based composite modifier include: A1, by weight, 10.0-15.0 parts of tetrabutyl titanate were added dropwise to 40.0-60.0 parts of anhydrous ethanol and stirred to obtain solution A; 25.0-40.0 parts of deionized water were added to 0.5-1.0 parts of concentrated hydrochloric acid and 0.1-0.3 parts of polyethylene glycol solution and stirred to obtain solution B; solution B was added dropwise to solution A to obtain titanium sol; the titanium sol was transferred to a reaction vessel and reacted at 120-150℃ to obtain titanium dioxide precursor; the titanium dioxide precursor was added to 80.0-120.0 parts of sodium hydroxide solution and hydrothermally treated at 110-150℃ to obtain crude product; the crude product was subjected to ion exchange with hydrochloric acid, centrifuged to obtain precipitate; the precipitate was washed with deionized water, dried, and calcined at 300-400℃ to obtain hydrotitanic acid / titanium dioxide nanotubes; A2, 5.0-8.0 parts of hydrotitanic acid / titanium dioxide nanotube powder were ultrasonically dispersed in 300.0-500.0 parts of deionized water, and 4.0-10.0 parts of magnesium nitrate hexahydrate and 2.0-5.0 parts of aluminum nitrate hexahydrate were added; while stirring, sodium hydroxide solution was added dropwise to adjust the pH to 9.5-10.5; the mixture was transferred to an autoclave and hydrothermally reacted at 100-120℃ to obtain a reaction mixture; the reaction mixture was centrifuged to obtain a precipitate; the precipitate was washed and dried to obtain the composite precursor; A3. Disperse 5.0-10.0 parts of the composite precursor in a mixed solvent of 200.0-400.0 parts of anhydrous ethanol and deionized water, add 0.5-1.5 parts of 3-aminopropyltriethoxysilane, and reflux at 60-80℃ under nitrogen protection to obtain a mixture; centrifuge the mixture to obtain a precipitate; disperse the precipitate in 150.0-300.0 parts of N,N-dimethylformamide, add 1.0-2.5 parts of 1,3,5-benzenetricarboxylic acid and 1.5-3.0 parts of cerium nitrate hexahydrate, and thermally react at 100-120℃, centrifuge to obtain a precipitate; wash and dry the precipitate to obtain an organic-inorganic hybrid intermediate; A4. Place 5.0-10.0 parts of the organic-inorganic hybrid intermediate in a tube furnace, hold at 200-250℃ under a nitrogen atmosphere, then raise the temperature to 300-400℃ and hold; cool to obtain the product; disperse the product in 100.0-200.0 parts of a 0.1-0.5 diammonium hydrogen phosphate solution and stir; centrifuge, wash with deionized water, and dry.

7. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to claim 6, characterized in that, In step A1, the calcination time at 300-400℃ is 2-4 hours.

8. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to claim 6, characterized in that, In step A2, the hydrothermal reaction at 100-120℃ takes 12-24 hours.

9. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to claim 6, characterized in that, In step A3, the thermal reaction time at 100-120℃ is 24-48 hours.

10. The method for preparing high specific surface area calcium hydroxide and ammonium chloride from industrial solid waste carbide slag according to claim 6, characterized in that, In step A4, the temperature is raised to 300-400℃ and held for 2-3 hours.

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