A method for preparing solid calcium bicarbonate using calcium-rich solid waste

Abstract

This application relates to the interdisciplinary field of inorganic compound synthesis and building materials technology, specifically to a method for preparing solid calcium bicarbonate using calcium-rich solid waste. The method includes: grinding: crushing and grinding the calcium-rich solid waste to obtain solid waste powder; preparing a leaching solution; leaching: adding the solid waste powder to the leaching solution for leaching, filtering to obtain a filtrate; and generating: adjusting the relative permittivity of the filtrate to <50, adjusting the pH range to 9-11, mixing thoroughly, introducing carbon dioxide gas to generate a white precipitate, centrifuging or filtering to obtain solid calcium bicarbonate. This application fully utilizes the alkalinity and calcium-rich properties of solid waste, meeting the requirements for calcium bicarbonate preparation. It not only solves the land occupation and pollution problems associated with solid waste but also produces a high-value-added material, opening up a new path for the resource utilization of solid waste in the interdisciplinary field of inorganic compound synthesis and building materials technology.

Description

Technical Field

[0001] This application relates to the interdisciplinary field of inorganic compound synthesis and building materials technology, specifically to a method for preparing solid calcium bicarbonate using calcium-rich solid waste. Background Technology

[0002] Calcium bicarbonate (Ca(HCO3)2) is a key substance in the natural carbon cycle and biochemical processes. In the Earth's largest carbon reservoir—the ocean and groundwater systems—bicarbonates are the primary chemical form of carbon dioxide (CO2). It not only determines the alkalinity and hardness of natural water but is also a core intermediate in natural geological evolution such as limestone dissolution, stalactite formation, and coral reef construction. Its unique phase transition capability makes it an important precursor for the synthesis of biomimetic bone repair materials and novel low-carbon cementitious materials. Furthermore, compared to calcium carbonate, calcium bicarbonate immobilizes twice the amount of CO2 in its molecular structure (Ca:C ratio of 1:2), making it a highly promising solid carbon storage material with broad and diverse application prospects.

[0003] Although the concept of calcium bicarbonate was proposed two centuries ago, pure solid calcium bicarbonate has not been successfully isolated in nature or in the laboratory under normal conditions (such as room temperature and atmospheric pressure). The core reason for its unstable existence lies in its strong ionic polarization effect. In aqueous solutions or under conventional solid-phase conditions, divalent calcium ions (Ca... 2+ It has a strong electric field, which will induce the formation of bicarbonate ions (HCO3-) that bond with it. - The OH group undergoes strong polarization, causing the OH bond to break and lose a proton (deprotonation), thus rapidly transforming into the more stable calcium carbonate (CaCO3) precipitate. Therefore, traditional theory holds that calcium bicarbonate can only exist in aqueous solution, and it will immediately decompose if an attempt is made to obtain a solid through evaporation, heating, or other means.

[0004] The conventional method for producing calcium bicarbonate is to directly use soluble calcium salts (such as calcium chloride and calcium nitrate) and alkaline substances. This production method requires large-scale procurement of soluble calcium salts to maintain production, resulting in a relatively limited source of raw materials and high production costs. Summary of the Invention

[0005] To address the issue of high production costs associated with the direct use of soluble calcium salts in existing calcium bicarbonate production methods, this application provides a method for preparing solid calcium bicarbonate using calcium-rich solid waste. my country's industrial production generates a large amount of calcium-rich alkaline solid waste (such as carbide slag, steel slag, waste concrete, and magnesium slag). These wastes not only contain abundant calcium but also provide the necessary alkalinity for calcium bicarbonate precipitation. Therefore, utilizing these solid wastes as a calcium source to produce high-value-added solid calcium bicarbonate not only meets the needs of calcium bicarbonate production but also solves the land occupation and pollution problems associated with solid waste, opening up a new path for the resource utilization of solid waste.

[0006] This application provides a method for preparing solid calcium bicarbonate using calcium-rich solid waste, employing the following technical solution: A method for preparing solid calcium bicarbonate using calcium-rich solid waste includes the following steps: Grinding: The calcium-rich solid waste is crushed and ground to obtain solid waste powder; the calcium content (calculated as calcium oxide) of the calcium-rich solid waste accounts for ≥20% of the total mass of the calcium-rich solid waste; Preparation of the extract: The extractant is dissolved in water to obtain an aqueous extract; then the aqueous extract or acetic acid is added to a low-polarity solvent and mixed evenly to obtain the extract; the extractant includes at least one of ammonium chloride, ammonium nitrate, acetic acid, citric acid, and tetrasodium glutamate diacetate; the low-polarity solvent includes at least one of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, acetone, and butanone; Leaching: The solid waste powder is added to the leaching solution for leaching, and the filtrate is obtained after filtration; Formation: Adjust the relative permittivity of the filtrate to <50, adjust the pH range to 9-11, mix thoroughly, introduce carbon dioxide gas, generate a white precipitate, centrifuge or filter to obtain solid calcium bicarbonate.

[0007] By employing the above technical solution, the extractant or acetic acid extracts calcium ions from solid waste powder through an ion exchange reaction, forming soluble calcium salts. Adding a low-polarity solvent to the leachate lowers the relative permittivity of the system, weakens the solvation effect of water molecules on ions, and promotes the ion exchange rate between calcium ions and the extractant. Adding a low-polarity solvent also improves the flowability of the mixture of leachate and solid waste powder, ensuring leaching efficiency. Acetic acid can be added alone when preparing the leachate because it has good solubility in low-polarity solvents. Other extractants, such as ammonium chloride or ammonium nitrate, have very low solubility in low-polarity solvents, resulting in low leaching efficiency in the absence of water. Therefore, ammonium chloride or ammonium nitrate should be dissolved in an aqueous solution before preparing the leachate. Similarly, citric acid or tetrasodium glutamate diacetate has poor solubility in some low-polarity solvents; it is best to dissolve these substances in an aqueous solution before preparing the leachate.

[0008] Compared to other low-polarity solvents, water is more easily retained in the pore structure of the residual solid powder through hydrogen bonding during the leaching process and is removed from the filtrate system during filtration. Meanwhile, because calcium ions have high solubility in both water and low-polarity solvents, they are retained in the filtrate. This fully utilizes the leaching effect of water on calcium ions while appropriately reducing the water content in the filtrate through residual solid waste and filtration, thus lowering the relative permittivity of the solution and promoting the stability of bicarbonate ions.

[0009] After obtaining the filtrate, the relative permittivity of the filtrate is controlled to be less than 50 to ensure low system polarity, reduce carbon dioxide dissolution resistance, improve carbonation efficiency, and maintain bicarbonate ion stability. Maintaining the pH of the filtrate between 9 and 11 effectively induces the formation of calcium bicarbonate precipitate.

[0010] This application makes full use of the alkaline and calcium-rich properties of solid waste, which meets the needs of calcium bicarbonate preparation. It not only solves the land occupation and pollution problems of solid waste, but also prepares high-value-added materials, opening up a new path for the resource utilization of solid waste in the cross-disciplinary field of inorganic compound synthesis and building materials technology.

[0011] Preferably, in the leaching step, the molar ratio of water molecules in the leachate to calcium in the solid waste powder is less than 5.

[0012] By adopting the above technical solution, if the ratio is ≥5, the excessive water content will lead to the deprotonation of bicarbonate ions, which is not conducive to the formation of calcium bicarbonate.

[0013] Preferably, in the leaching step, the mass ratio of the solid waste powder to the leaching solution is 1:1-50.

[0014] By adopting the above technical solution, the leaching solution is within the above range in order to ensure the fluidity of the mixed system, thereby improving the leaching efficiency and the production efficiency of calcium bicarbonate.

[0015] Preferably, in the step of preparing the extract, the extractant is tetrasodium diglutamate.

[0016] By employing the above technical solution, the tetrasodium glutamate diacetate molecule contains four carboxylic acid groups and one amino group, forming a three-dimensional spatial structure similar to a "molecular clamp," resulting in a significantly higher complexation constant for calcium ions compared to citric acid and acetic acid. This structure can firmly bind calcium ions, achieving a high leaching rate of calcium ions in the solid waste micronized powder leaching step, while reducing the co-solubility of impurity ions. The tetrasodium glutamate diacetate molecule contains hydrophilic carboxyl groups and hydrophobic alkyl chains, exhibiting good dispersibility in low-polarity solvents such as methanol / ethanol, forming a homogeneous microemulsion system that promotes the migration of calcium ions from the solid phase to the liquid phase.

[0017] Preferably, in the step of preparing the extract, the extractant is a first extraction mixture of tetrasodium glutamate diacetate and ammonium chloride.

[0018] By employing the above technical solution, ammonium chloride directly disrupts the crystal structure of calcium ions in solid waste powder, exposing deep-seated calcium ions to the liquid phase, thus overcoming the limitation of tetrasodium glutamate diacetate (TCGA) primarily chelating surface calcium ions. The calcium ions generated by ammonium chloride readily combine with carbonate and sulfate ions in an alkaline environment to form secondary precipitates. TGA, through strong chelation, locks in calcium ions, forming stable water-soluble complexes and blocking the precipitation pathway. The combination of TGA and ammonium chloride is more effective than adding TGA alone.

[0019] Preferably, the molar ratio of tetrasodium glutamate diacetate and ammonium chloride in the first extraction mixture is 1:1-1.5.

[0020] By adopting the above technical solution, when the molar ratio of ammonium chloride is too low, the effect of destroying the calcium ion crystal structure in the solid waste powder is weakened, less deep calcium ions are exposed, and tetrasodium glutamate diacetate is difficult to chelate; when the molar ratio of ammonium chloride is too high, the overall chelating ability of tetrasodium glutamate diacetate decreases, and relatively less calcium ions are captured. Therefore, after extensive research and experimental verification, the applicant finally determined that the molar ratio of tetrasodium glutamate diacetate and ammonium chloride in the first extraction mixture of this application is preferably as described above.

[0021] Preferably, in the step of preparing the extract, the extractant is a second extraction mixture of citric acid and acetic acid.

[0022] By employing the above technical solution, citric acid, containing three carboxyl groups, can simultaneously form stable eight-membered ring chelates with calcium ions, significantly reducing the concentration of free metal ions. Acetic acid, with its small molecular weight and strong permeability, can rapidly disrupt the surface structure of solid waste powder, releasing internal calcium ions. Simultaneously, its weak acidity provides adequate hydrogen ions, promoting the dissociation of citric acid and enhancing the number of chelating active groups. The formation of a broad-range buffer pair between citric acid and acetic acid avoids both damage to the chelating agent structure and prevents the recrystallization of calcium ions under alkaline conditions.

[0023] Preferably, the molar ratio of citric acid to acetic acid in the second extraction mixture is 1:2-3.5.

[0024] By adopting the above technical solution, when the molar ratio of acetic acid is too low, the effect of acetic acid on destroying the surface structure of solid waste powder is weakened, and less calcium ions are released from the interior; when the molar ratio of acetic acid is too high, the chelating ability of citric acid decreases, and relatively less calcium ions are captured. Therefore, after extensive research and experimental verification, the applicant finally determined that the molar ratio of citric acid to acetic acid in the second extraction mixture of this application is preferably as described above.

[0025] Preferably, the extractant is at least one of ammonium chloride or ammonium nitrate.

[0026] By employing the above technical solution, ammonium chloride / ammonium nitrate reacts with the calcium-containing components in the solid waste powder, releasing soluble calcium salts and generating ammonia gas. The ammonia gas generated can be absorbed by water or acidic solutions, converting into ammonia water, which is used for pH adjustment of the subsequent filtrate.

[0027] Preferably, the concentration of the extractant in the aqueous solution is 0.5-12 mol / L.

[0028] By adopting the above technical solution, the polarity of water is not conducive to the stability of bicarbonate ions. Therefore, the solute concentration should be increased to reduce the use of water. Thus, the extractant concentration should be maintained at 0.5-12 mol / L.

[0029] In summary, this application has the following beneficial effects: 1. Because this application makes full use of the alkaline and calcium-rich properties of solid waste, it meets the preparation requirements of calcium bicarbonate, which not only solves the land occupation and pollution problems of solid waste, but also prepares high-value-added materials, opening up a new path for the resource utilization of solid waste in the cross-disciplinary field of inorganic compound synthesis and building materials technology. 2. This application uses a first extraction mixture of tetrasodium glutamate diacetate and ammonium chloride, which can compensate for the limitation of tetrasodium glutamate diacetate in mainly chelating surface calcium ions by ammonium chloride, and tetrasodium glutamate diacetate blocks the secondary precipitation formation pathway. 3. This application uses a second extraction mixture of citric acid and acetic acid, which can release internal calcium ions through acetic acid and exert the chelating effect of citric acid; citric acid and acetic acid form a wide-range buffer pair to prevent calcium ions from regenerating and precipitating under alkaline conditions. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope image of calcium bicarbonate in the product prepared in Example 2 of this application.

[0031] Figure 2 This is the X-ray diffraction pattern of calcium bicarbonate in the product prepared in Example 2 of this application. Detailed Implementation

[0032] The raw materials in this application include the following: Calcium-rich solid waste: refers to substances containing calcium components (calculated as calcium oxide) accounting for ≥20% of the total mass of calcium-rich solid waste; preferably at least one of waste cement, carbide slag, steel slag and magnesium slag; Tetrasodium glutamate diacetate: Uses a commercially available product with CAS number 51981-21-6; Low polarity solvents include at least one of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, acetone, and butanone. This application only uses ethanol and ethylene glycol as examples.

[0033] Polarity adjuster: used to adjust the relative permittivity of the filtrate to less than 50, including at least one of methanol, ethanol, ethylene glycol, glycerol, isopropanol, acetone, and butanone; pH adjuster: used to adjust the pH range of the filtrate to 9-11, including at least one of acetic acid, citric acid, ammonia, and small organic molecule amines; small organic molecule amines include at least one of methylamine, ethylamine, diethylamine, triethylamine, butylamine, monoethanolamine, diethanolamine, triethanolamine, and isopropanolamine; The present application will be further described in detail below with reference to embodiments and comparative examples.

[0034] Example 1 A method for preparing solid calcium bicarbonate using calcium-rich solid waste includes the following steps: Grinding: Waste cement is crushed and ground to obtain solid waste powder; the average particle size of the solid waste powder is less than 150 μm, and the calcium oxide component accounts for 50 wt% of the total mass of the solid waste powder; Preparation of the extract: Dissolve tetrasodium glutamate diacetate in water to prepare 500 mL of 1 mol / L tetrasodium glutamate diacetate aqueous solution; then add the tetrasodium glutamate diacetate aqueous solution to 4500 mL of anhydrous ethanol and mix evenly to obtain the extract; Leaching: Add 1000g of waste cement solid waste powder to the leaching solution and leach for 4 hours. After filtration, obtain the filtrate. Formation: The relative permittivity of the filtrate is 30. If it is less than 50, no adjustment is needed. Add methylamine to adjust the pH to 10 (adjustment to 9-11 is also acceptable). After mixing evenly, purge with carbon dioxide gas for 1 hour to form a white precipitate. Filter to obtain the product.

[0035] Example 2 A method for preparing solid calcium bicarbonate using calcium-rich solid waste includes the following steps: Grinding: Waste cement is crushed and ground to obtain waste cement solid waste powder; the average particle size of the waste cement solid waste powder is less than 150μm, and the calcium oxide component accounts for 50wt% of the total mass of the waste cement solid waste powder; Preparation of the leaching solution: Dissolve ammonium nitrate in water to prepare 500 mL of a 10 mol / L ammonium nitrate aqueous solution; then add the ammonium nitrate aqueous solution to 4500 mL of anhydrous ethanol and mix thoroughly to obtain the leaching solution; Leaching: Add 1000g of waste cement solid waste powder to the leaching solution and leach for 4 hours. After filtration, obtain the filtrate. Ammonia gas is generated during the leaching process and can be collected. Formation: The relative permittivity of the filtrate is 18, less than 50, so no adjustment is needed. Ammonia gas generated in the leaching step is introduced to adjust the pH to 10. After thorough mixing, carbon dioxide gas is introduced for 0.5 hours, resulting in a white precipitate. The precipitate is then filtered to obtain the product. Electron microscopy and X-ray diffraction of the product are performed (see [reference needed]). Figure 1 and Figure 2 .

[0036] Example 3 A method for preparing solid calcium bicarbonate using calcium-rich solid waste includes the following steps: Grinding: Waste cement is crushed and ground to obtain waste cement solid waste powder; the average particle size of the waste cement solid waste powder is less than 150μm, and the calcium oxide component accounts for 50wt% of the total mass of the waste cement solid waste powder; Preparation of leaching solution: Dissolve ammonium nitrate in water to prepare 800 mL of 10 mol / L ammonium nitrate aqueous solution; then add the ammonium nitrate aqueous solution to 4200 mL of anhydrous ethanol and mix evenly to obtain the leaching solution; Leaching: Add 1000g of waste cement solid waste powder to the leaching solution and leach for 4 hours. After filtration, obtain the filtrate. Ammonia gas is generated during the leaching process and can be collected. Formation: The relative permittivity of the filtrate is 33, which is less than 50 and does not require adjustment. Ammonia gas generated in the leaching step is introduced to adjust the pH to 10. After mixing evenly, carbon dioxide gas is introduced for 0.5 hours to form a white precipitate. The precipitate is then filtered to obtain the product.

[0037] Example 4 A method for preparing solid calcium bicarbonate using calcium-rich solid waste includes the following steps: Grinding: The steel slag is crushed and ground to obtain steel slag solid waste powder; the average particle size of the steel slag solid waste powder is less than 150μm, and the calcium oxide component accounts for 32wt% of the total mass of the steel slag solid waste powder; Preparation of the leaching solution: Add 500 mL of acetic acid to 4500 mL of ethylene glycol and mix thoroughly to obtain the leaching solution; Leaching: Add 1000g of steel slag solid waste powder to the leaching solution and leach for 4 hours. After filtration, obtain the filtrate. Formation: The relative permittivity of the filtrate is 34, which is less than 50 and does not require adjustment. Add methylamine to adjust the pH to 10, mix well, and then pass carbon dioxide gas through for 1 hour to form a white precipitate. Filter to obtain the product.

[0038] Comparative Example 1 A method for preparing solid calcium bicarbonate using calcium-rich solid waste includes the following steps: Grinding: Waste cement is crushed and ground to obtain waste cement solid waste powder; the average particle size of the waste cement solid waste powder is less than 150μm, and the calcium oxide component accounts for 50wt% of the total mass of the waste cement solid waste powder; Preparation of the leaching solution: Dissolve ammonium nitrate in water to prepare 2000 mL of 3 mol / L ammonium nitrate aqueous solution; then add the ammonium nitrate aqueous solution to 3000 mL of anhydrous ethanol and mix evenly to obtain the leaching solution; Leaching: Add 1000g of waste cement solid waste powder to the leaching solution and leach for 4 hours. After filtration, obtain the filtrate. Ammonia gas is generated during the leaching process and can be collected. Formation: The relative permittivity of the filtrate is 44, which is less than 50 and does not require adjustment. Ammonia gas generated in the leaching step is introduced to adjust the pH to 10. After mixing evenly, carbon dioxide gas is introduced for 0.5 hours to form a white precipitate. The precipitate is then filtered to obtain the product.

[0039] Performance testing The products of Examples 1-4 and Comparative Example 1 were subjected to the following performance tests, and the test results are shown in Table 1.

[0040] Yield and purity The yield of the product from the examples or comparative examples was determined by weighing, and the purity of calcium bicarbonate in the product was determined by high performance liquid chromatography.

[0041] Table 1 Performance test results of Examples 1-4 and Comparative Example 1

[0042] Referring to Table 1, comparing Examples 1-4 and Comparative Example 1, it can be seen that the above method can effectively prepare calcium bicarbonate from calcium-rich solid waste. This is because tetrasodium diacetate, ammonium nitrate, or acetic acid extracts calcium ions from the solid waste powder through an ion exchange reaction, forming a soluble calcium salt. Adding a low-polarity solvent to the leachate lowers the relative permittivity of the system, weakens the solvation effect of water molecules on ions, and promotes the ion exchange rate between calcium ions and the leachate agent. Adding a low-polarity solvent also improves the fluidity of the mixture of leachate and solid waste powder, ensuring leaching efficiency.

[0043] For high-purity calcium bicarbonate to be produced, the molar ratio of water molecules in the leachate to calcium in the solid waste powder must be less than 5. As in Examples 3 and 1 (Comparative Example 1), when the molar ratio of water molecules in the leachate to calcium in the solid waste powder is ≥5, the excessively high water content in the subsequent filtrate leads to deprotonation of bicarbonate ions, which is detrimental to calcium bicarbonate formation. In particular, in Comparative Example 1, the formed calcium bicarbonate rapidly transforms into calcium carbonate precipitate under the influence of water, with no solid calcium bicarbonate forming.

[0044] Examples 5-7 Example 5 is based on the preparation method of Example 4, but with adjustments: Leaching: Add 1000g of waste cement solid waste powder to 1000g of leachate and leach for 4 hours. After filtration, obtain the filtrate.

[0045] Example 6 is based on the preparation method of Example 4, but with adjustments: Leaching: Add 1000g of waste cement solid waste powder to 10000g of leachate and leach for 4 hours. After filtration, obtain the filtrate.

[0046] Example 7 is based on the preparation method of Example 4, but with adjustments: Leaching: Add 1000g of waste cement solid waste powder to 50000g of leachate and leach for 4 hours. After filtration, obtain the filtrate.

[0047] The products from Examples 5-7 were subjected to the performance tests described above, and the test results are shown in Table 2.

[0048] Table 2 Performance Test Tables for Examples 4-7

[0049] Referring to Table 2, and comparing Examples 4-7, it can be seen that as the content of the leachate increases, the product yield and the purity of calcium bicarbonate show a trend of continuous increase followed by stabilization. This is because the leachate content within the aforementioned range is intended to ensure the fluidity of the mixed system, thereby improving leaching efficiency and calcium bicarbonate production efficiency. However, from a production cost perspective, there is no need to increase the amount of leachate added indefinitely.

[0050] Examples 8-10 Example 8 is based on the preparation method of Example 1, but with adjustments: Preparation of leaching solution: Dissolve ammonium chloride in water to prepare 500 mL of 5 mol / L ammonium chloride aqueous solution; then add the ammonium chloride aqueous solution to 4500 mL of anhydrous ethanol and mix evenly to obtain the leaching solution.

[0051] Example 9 is based on the preparation method of Example 1, but with adjustments: Preparation of the extract: Dissolve citric acid in water to prepare 500 mL of 2 mol / L citric acid aqueous solution; then add the citric acid aqueous solution to 4500 mL of anhydrous ethanol and mix evenly to obtain the extract.

[0052] Example 10 is based on the preparation method of Example 1, but with adjustments made to the preparation method: Preparation of the leaching solution: Dissolve acetic acid in water to prepare 500 mL of 12 mol / L acetic acid aqueous solution; then add the acetic acid aqueous solution to 4500 mL of anhydrous ethanol and mix evenly to obtain the leaching solution.

[0053] The products from Examples 8-10 were subjected to the performance tests described above, and the test results are shown in Table 3.

[0054] Table 3 Performance test results for Examples 1, 2 and 8-10

[0055] Referring to Table 3, a comparison of Examples 1, 2, and 8-10 shows that tetrasodium glutamate diacetate (TCDD) is the most effective extractant. This is because the TCDDD molecule contains four carboxylic acid groups and one amino group, forming a three-dimensional structure similar to a "molecular clamp," resulting in a significantly higher complexation constant for calcium ions compared to citric acid and acetic acid. This structure can firmly bind calcium ions, achieving a high leaching rate in the solid waste micronized powder extraction step and reducing the co-dissolution of impurity ions. Furthermore, the TCDDD molecule contains hydrophilic carboxyl groups and hydrophobic alkyl chains, exhibiting good dispersibility in low-polarity solvents such as methanol / ethanol, forming a homogeneous microemulsion system that promotes the migration of calcium ions from the solid phase to the liquid phase.

[0056] Examples 11-15 Example 11 is based on the preparation method of Example 1, but with adjustments: Preparation of the extract: Tetrasodium glutamate diacetate and ammonium chloride, as the first extraction mixture, were added together to 1000 mL of water and dissolved to obtain an aqueous solution of the first extraction mixture, wherein the molar sum of tetrasodium glutamate diacetate and ammonium chloride was 1 mol, and the molar ratio of tetrasodium glutamate diacetate and ammonium chloride was 1:1.3; then 500 mL of the aqueous solution of the first extraction mixture was added to 4500 mL of anhydrous ethanol and mixed evenly to obtain the extract.

[0057] Examples 12-15 are based on the preparation method of Example 11, but the molar ratio of tetrasodium diacetate of glutamic acid and ammonium chloride is adjusted. The specific adjustments are shown in Table 4.

[0058] The products of Examples 11-15 were subjected to the above performance tests, and the test results are shown in Table 4.

[0059] Table 4. Molar ratio of tetrasodium glutamate diacetate and ammonium chloride in Examples 1 and 11-15, and performance test results.

[0060] Referring to Table 4, a comparison of Examples 1 and 11-15 shows that replacing the extractant with a first extraction mixture of tetrasodium glutamate diacetate and ammonium chloride yields better results. This is because ammonium chloride directly disrupts the crystal structure of calcium ions in the solid waste powder, exposing deep-seated calcium ions to the liquid phase, thus compensating for the limitation of tetrasodium glutamate diacetate primarily chelating surface calcium ions. Calcium ions generated from the dissolution of ammonium chloride readily combine with carbonate and sulfate ions in an alkaline environment to form secondary precipitates. Tetrasodium glutamate diacetate, through strong chelation, locks in calcium ions, forming stable water-soluble complexes and blocking the precipitation pathway. The combination of tetrasodium glutamate diacetate and ammonium chloride is more effective than adding tetrasodium glutamate diacetate alone.

[0061] As the molar percentage of ammonium chloride increases, the product yield and calcium bicarbonate purity initially rise and then fall. This is because as the molar percentage of ammonium chloride increases, its destructive effect on the calcium ion crystal structure in the solid waste powder intensifies, exposing more deep-seated calcium ions. This allows tetrasodium glutamate diacetate to chelate more calcium ions, leading to a continuous increase in product yield and calcium bicarbonate purity. However, once a certain range is exceeded, the overall chelating capacity of tetrasodium glutamate diacetate decreases, resulting in fewer captured calcium ions and a decline in both product yield and calcium bicarbonate purity.

[0062] Examples 16-20 Example 16 adjusts the preparation method based on the preparation method of Example 1: Preparation of the extract: Citric acid and acetic acid, as the second extraction mixture, are added together to 1000 mL of water and dissolved to obtain an aqueous solution of the second extraction mixture, wherein the molar sum of citric acid and acetic acid is 2 mol and the molar ratio of citric acid and acetic acid is 1:3; then 500 mL of the aqueous solution of the second extraction mixture is added to 4500 mL of anhydrous ethanol and mixed evenly to obtain the extract.

[0063] Examples 17-20 are based on the preparation method of Example 16, but the molar ratio of citric acid and acetic acid is adjusted. The specific adjustments are shown in Table 5.

[0064] The products of Examples 16-20 were subjected to the above performance tests, and the test results are shown in Table 5.

[0065] Table 5. Molar ratio of citric acid and acetic acid in Examples 1 and 16-20, and performance test results.

[0066] Referring to Table 5, a comparison of Examples 1 and 16-20 shows that replacing the extractant with a second extraction mixture of citric acid and acetic acid yields better results than adding tetrasodium glutamate diacetate alone. This is because citric acid contains three carboxyl groups, which can simultaneously form stable eight-membered ring chelates with calcium ions, significantly reducing the concentration of free metal ions. Acetic acid has a small molecular weight and strong permeability, which can quickly destroy the surface structure of solid waste powder, releasing internal calcium ions. Simultaneously, its weak acidity provides appropriate hydrogen ions, promoting the dissociation of citric acid and increasing the number of chelating active groups. The formation of a broad-range buffer pair between citric acid and acetic acid avoids both damage to the chelating agent structure and prevents the recrystallization of calcium ions under alkaline conditions.

[0067] As the molar percentage of acetic acid increases, the product yield and calcium bicarbonate purity initially rise and then fall. This is because as the molar percentage of acetic acid increases, its destructive effect on the calcium ion crystal structure in the solid waste powder intensifies, exposing more deep-seated calcium ions. Citric acid then chelates more calcium ions, leading to a continuous increase in product yield and calcium bicarbonate purity. However, once a certain range is exceeded, the overall chelating capacity of citric acid decreases, resulting in fewer captured calcium ions and a decline in both product yield and calcium bicarbonate purity.

[0068] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing solid calcium bicarbonate using calcium-rich solid waste, characterized by, Includes the following steps: Grinding: The calcium-rich solid waste is crushed and ground to obtain solid waste powder; the calcium content (calculated as calcium oxide) of the calcium-rich solid waste accounts for ≥20% of the total mass of the calcium-rich solid waste; Preparation of the extract: The extractant is dissolved in water to obtain an aqueous extract; then the aqueous extract or acetic acid is added to a low-polarity solvent and mixed evenly to obtain the extract; the extractant includes at least one of ammonium chloride, ammonium nitrate, acetic acid, citric acid, and tetrasodium glutamate diacetate; the low-polarity solvent includes at least one of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, acetone, and butanone; Leaching: The solid waste powder is added to the leaching solution for leaching, and the filtrate is obtained after filtration; Formation: Adjust the relative permittivity of the filtrate to <50, adjust the pH range to 9-11, mix thoroughly, introduce carbon dioxide gas, generate a white precipitate, centrifuge or filter to obtain solid calcium bicarbonate.

2. The method of claim 1, wherein the calcium-rich solid waste is used to produce solid calcium bicarbonate. In the leaching step, the molar ratio of water molecules in the leachate to calcium in the solid waste powder is less than 5.

3. The method for preparing solid calcium bicarbonate using calcium-rich solid waste according to claim 1, characterized in that: In the leaching step, the mass ratio of the solid waste powder to the leaching solution is 1:1-50.

4. The method for preparing solid calcium bicarbonate using calcium-rich solid waste according to claim 1, characterized in that: In the step of preparing the extract, the extractant is tetrasodium diacetate of glutamate.

5. The method for preparing solid calcium bicarbonate using calcium-rich solid waste according to claim 1, characterized in that: In the step of preparing the extract, the extractant is a first extraction mixture of tetrasodium glutamate diacetate and ammonium chloride.

6. The method for preparing solid calcium bicarbonate using calcium-rich solid waste according to claim 5, characterized in that: The molar ratio of tetrasodium glutamate diacetate and ammonium chloride in the first extraction mixture is 1:1-1.

5.

7. The method for preparing solid calcium bicarbonate using calcium-rich solid waste according to claim 1, characterized in that: In the step of preparing the extract, the extractant is a second extraction mixture of citric acid and acetic acid.

8. The method for preparing solid calcium bicarbonate using calcium-rich solid waste according to claim 7, characterized in that: The molar ratio of citric acid to acetic acid in the second extraction mixture is 1:2-3.

5.

9. The method for preparing solid calcium bicarbonate using calcium-rich solid waste according to claim 1, characterized in that: The extractant is at least one of ammonium chloride or ammonium nitrate.

10. The method for preparing solid calcium bicarbonate from calcium-rich solid waste according to claim 1, characterized in that: The concentration of the extractant in the aqueous solution is 0.5-12 mol / L.

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