Method and system for synergistically preparing vaterite from waste stone powder, waste hydrochloric acid and carbide slag

Abstract

The invention belongs to the technical field of industrial solid waste recycling and inorganic functional material preparation, and relates to a method and system for preparing vaterite through waste stone powder, waste hydrochloric acid and carbide slag in a synergistic manner. The method comprises the following steps: dissolving waste stone powder with waste hydrochloric acid, and adding carbide slag to supplement a calcium source in a dissolved solution; dissolving to generate carbon dioxide, and carrying out solid-liquid separation after dissolving to obtain a calcium chloride solution; adding ammonia water into the obtained calcium chloride solution to adjust the pH to be alkaline, then adding an ammonium bicarbonate solution, introducing carbon dioxide generated by dissolution, adding an acrylic polymer as a modifier, and carrying out carbonization reaction to prepare vaterite calcium carbonate. According to the method, the vaterite type calcium carbonate product with high purity and stable crystal form can be prepared through the waste stone powder, waste hydrochloric acid and carbide slag synergistically, and high-value conversion of waste is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial solid waste resource utilization and inorganic functional material preparation, and relates to a method and system for collaboratively preparing vaterite from waste stone powder, waste hydrochloric acid and carbide slag. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] At present, the treatment of waste is relatively scattered. Waste rock powder is usually only used as concrete admixture or directly landfilled. Industrial waste hydrochloric acid is simply neutralized, and carbide slag is treated with a single acid washing method, which fails to form an effective closed-loop utilization. This scattered treatment results in the inability to fully extract the effective components in each waste, low resource utilization, and high overall production costs.

[0004] Vaterite is a metastable crystal form of calcium carbonate. Compared with common calcite and aragonite, its unique physical and chemical properties make it have significant advantages in the fields of biomedicine, environmental engineering, materials science, etc. Since waste stone powder, industrial waste hydrochloric acid and carbide slag contain raw materials for preparing vaterite, they can be used as raw materials to prepare vaterite. However, the inventors found in their research that waste hydrochloric acid itself contains certain soluble impurities (such as sodium, potassium salt, etc.), which are easy to produce high concentrations of interfering ions in the reaction system during the process of dissolving waste stone powder, which will destroy Ca 2+ With CO 3 2- The ion balance between the two is affected, thus affecting the nucleation and crystal growth of vaterite, resulting in reduced product purity and unstable crystal form. At the same time, most of the current vaterite preparation processes rely on conventional CaCl 2 –NH 4 Cl–NH 3 ·H 2 O system often requires a large amount of organic solvent or excess ammonia, which not only wastes resources but also generates a large amount of by-products, increasing the difficulty of waste liquid treatment and environmental governance. 2 The failure to effectively capture and reuse by-products has further aggravated the problems of environmental pollution and waste of resources. Summary of the invention

[0005] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a method and system for the coordinated preparation of vaterite from waste stone powder, waste hydrochloric acid carbide slag, and the present invention can coordinately prepare a high-purity, crystal-stable vaterite-type calcium carbonate product from waste stone powder, waste hydrochloric acid carbide slag, thereby achieving high-value conversion of waste.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] In a first aspect, a method for preparing vaterite by synergistically using waste stone powder, waste hydrochloric acid and carbide slag, comprises the following steps: using waste hydrochloric acid to dissolve waste stone powder, and adding carbide slag to supplement the calcium source in the solution after dissolution; dissolution generates carbon dioxide, and solid-liquid separation is performed after dissolution to obtain a calcium chloride solution; adding ammonia water to the obtained calcium chloride solution to adjust the pH to alkaline, then adding ammonium carbonate solution, introducing the carbon dioxide generated by the dissolution, and adding an acrylic acid polymer as a modifier to perform a carbonization reaction to obtain vaterite calcium carbonate.

[0008] First of all, the main components of waste rock powder are calcium carbonate, silicate minerals and other carbonates, while calcium hydroxide is the main component of carbide slag. Compared with carbide slag, waste rock powder has a larger processing capacity, carbide slag has stronger alkalinity, and waste hydrochloric acid has weaker acidity. Therefore, waste hydrochloric acid is mainly used to dissolve waste rock powder, which can not only process waste rock powder and waste hydrochloric acid on a large scale, but also the carbon dioxide produced by dissolving carbonate can be used as a raw material for the subsequent preparation of vaterite. At the same time, although the calcium content in waste rock powder is lower than that in carbide slag, its high silicon dioxide content itself can provide auxiliary effects for the reaction system. The present invention adds carbide slag, which has a higher calcium content and can significantly supplement the calcium element in the system, thereby increasing the purification efficiency of calcium in waste rock powder, and at the same time can improve the Ca content in the system by supplementing the source. 2+ It can improve the stability of concentration and effectively dilute the influence of interfering impurities in waste hydrochloric acid; in addition, the strong alkalinity of carbide slag can also pre-adjust the concentration of calcium chloride solution after dissolution.

[0009] Secondly, by adding ammonia water, the pH of the system can be further adjusted while the interfering impurities in the diluted waste hydrochloric acid can be further adjusted to avoid the impurities affecting the formation of vaterite calcium carbonate. On this basis, ammonium carbonate is further added to further supplement the carbon source, and an acrylic acid polymer is added as a modifier, so that vaterite calcium carbonate can be prepared.

[0010] In some embodiments, saturated sodium bicarbonate solution is used to capture and recover the dissolved carbon dioxide, which can more efficiently capture and recover the generated carbon dioxide.

[0011] The carbonization reaction described in the present invention refers to a reaction in which calcium ions are carbonated. In some embodiments, the waste liquid after the carbonization reaction is pyrolyzed to form ammonia and HCl; ammonia is used to prepare ammonia water, which can be used to adjust the pH of calcium chloride solution; and / or, ammonia is used to prepare ammonium carbonate solution, which can be used for carbonization reaction; and / or, HCl is used for waste hydrochloric acid to dissolve waste rock powder. Through by-product recovery and closed-loop reuse, a full-process closed-loop system of "acid leaching-neutralization-carbonization-regeneration" can be built to achieve the organic integration and coordinated utilization of waste rock powder, waste hydrochloric acid and carbide slag, ensure the complementarity of effective components in each waste, increase resource utilization to more than 90%, and significantly reduce processing costs.

[0012] In addition, compared with the single carbide slag and waste hydrochloric acid treatment method, the method of the present invention using waste rock powder, carbide slag and waste hydrochloric acid to treat the waste rock powder not only "dilutes" the interfering impurities in the waste acid, but also regulates the ion balance and suppresses impurities, thereby avoiding Na + , K + Impurities such as these are difficult to remove effectively and affect Ca 2+ With CO 3 2- reaction balance, thereby preventing crystal mixing and low product purity; and the silicon component in the waste stone powder can assist the reaction of the dissolution system to a certain extent, forming a more ideal reaction environment for the dissolution system, thereby greatly improving the utilization rate of calcium ions in the entire system; it can also produce carbon dioxide for the preparation of vaterite, avoiding the introduction of new carbon dioxide and reducing energy consumption.

[0013] In a second aspect, a system for preparing vaterite in a coordinated manner using waste rock powder, waste hydrochloric acid carbide slag, is provided for implementing the above method, comprising:

[0014] a calcium chloride solution preparation unit for preparing calcium chloride solution and carbon dioxide from waste hydrochloric acid, waste rock powder and waste rock powder;

[0015] The vaterite preparation unit is used for carbonizing the calcium chloride solution from the calcium chloride solution preparation unit and carbon dioxide to prepare vaterite.

[0016] In some embodiments, a two-stage alkali washing tower is further included to capture and recover the dissolved carbon dioxide through a saturated sodium bicarbonate solution. The recovery rate of the two-stage alkali washing tower can reach more than 95%.

[0017] In some embodiments, an ammonium chloride pyrolysis unit is further included, which is used to pyrolyze the waste liquid after the carbonization reaction to form ammonia and HCl.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention utilizes waste acid to “treat waste with waste”, adopts industrial waste hydrochloric acid directly as acid solution, and utilizes waste stone powder as the main calcium source raw material, which not only reduces the cost of raw materials, but also utilizes the acidic resources in the waste acid to realize the recycling of waste materials and the treatment of waste stone powder, thus avoiding the waste of pure acid resources and realizing the resource utilization of waste stone powder. At the same time, during the leaching process, the interfering ions in the waste acid are “diluted” through the synergistic effect of calcium carbide slag, maintaining the Ca in the reaction system. 2+ With CO 3 2- balance.

[0020] 2. The present invention uses the high calcium supplementation effect of carbide slag, which is used as high calcium waste (containing highly active Ca(OH) 2 ), adding a small amount of calcium carbide slag can significantly supplement the problem of insufficient calcium content in the waste rock powder, making the Ca content in the overall system 2+ The concentration is stable and the calcium dissolution rate in the waste rock powder is increased from about 50% to 75%, ensuring reaction stability and product purity.

[0021] 3. The present invention uses multiple wastes in a coordinated closed-loop manner to construct a full-process closed-loop system of "acid leaching - neutralization - carbonization - regeneration". 2 By capturing and recycling, pyrolyzing ammonium chloride waste liquid to regenerate reagents, and utilizing silicon slag as building materials, we can increase resource utilization to over 90% and significantly reduce the processing costs of waste liquid and purchased reagents.

[0022] 4. The method provided by the present invention has a high degree of process integration and is simple to operate. The entire process realizes the continuous connection of pretreatment, dissolution, regulation, carbonization, product separation and solution integration. The equipment structure is relatively simple, which is convenient for industrial promotion and large-scale application. Through the method of the present invention, by optimizing the conditions, the purity of the vaterite-type calcium carbonate product finally obtained is increased to ≥96%, and the mineralization yield reaches 99.95%. At the same time, the process energy consumption and carbon emissions are significantly reduced (carbon emissions are reduced by 70%, and energy consumption is reduced to about 400kWh / ton), realizing green and low-energy production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 is a flowchart of an embodiment of the present invention;

[0025] Figure 2 This is the XRD pattern of vaterite prepared in the embodiment of the present invention. DETAILED DESCRIPTION

[0026] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0028] The main technical problem of the present invention is how to synergistically utilize three industrial wastes, namely, waste stone powder, waste hydrochloric acid and carbide slag, to achieve closed-loop high-value conversion and prepare a high-purity, crystal-stable vaterite-type calcium carbonate product, thereby reducing production costs. The secondary technical problem is how to overcome the problem of high-concentration interfering ions caused by soluble impurities (such as sodium, potassium salt, etc.) in the waste acid when dissolving the waste stone powder, and ensure that the Ca 2+ With CO 3 2- The balance between the two should be achieved to promote the uniform nucleation and crystal growth of vaterite; at the same time, CO 2 Byproducts such as calcium sulfate and calcium sulfate can be produced, thereby optimizing the entire solution environment and reducing the risk of environmental pollution. Again, the present invention is also committed to giving full play to the advantages of high calcium content in carbide slag, complementing with waste stone powder, improving the utilization efficiency of calcium in the system, ensuring the stability of calcium ion concentration during the entire reaction process, and thus ensuring the quality of the product and the continuous and stable operation of the process. Therefore, the present invention proposes a method and system for the coordinated preparation of vaterite from three wastes: waste stone powder, waste hydrochloric acid carbide slag.

[0029] A typical embodiment of the present invention provides a method for preparing vaterite by synergistically using waste stone powder, waste hydrochloric acid and carbide slag, wherein waste stone powder is dissolved by waste hydrochloric acid, and carbide slag is added to supplement the calcium source in the solution after dissolution; carbon dioxide is generated by dissolution, and solid-liquid separation is performed after dissolution to obtain a calcium chloride solution; ammonia water is added to the obtained calcium chloride solution to adjust the pH to alkaline, and then ammonium carbonate solution is added, the carbon dioxide generated by the dissolution is introduced, and an acrylic acid polymer is added as a modifier to perform a carbonization reaction to prepare vaterite calcium carbonate.

[0030] Among them, carbide slag can be added to waste hydrochloric acid for dissolution after mixing with waste rock powder, or carbide slag can be added during the process of dissolving waste rock powder with waste hydrochloric acid; or carbide slag can be added after the waste hydrochloric acid dissolves the waste rock powder.

[0031] In some embodiments, the temperature for dissolving the waste rock powder with waste hydrochloric acid is 40-60° C. This condition is conducive to improving the dissolution rate of calcium in the waste rock powder.

[0032] In some embodiments, the time for dissolving the waste rock powder with waste hydrochloric acid is 30 to 60 minutes. This condition is conducive to improving the dissolution rate of calcium in the waste rock powder.

[0033] In some embodiments, the solid-liquid ratio of waste rock powder to waste hydrochloric acid is 1:4-6 g / mL. This condition is conducive to improving the dissolution rate of calcium in the waste rock powder.

[0034] In some embodiments, the mass ratio of waste rock powder to carbide slag is 3 to 5: 1. This condition is conducive to improving the dissolution rate of calcium in the waste rock powder.

[0035] When two or more of the above conditions of temperature, time, solid-liquid ratio of waste rock powder to waste hydrochloric acid, and mass ratio of waste rock powder to calcium carbide slag are met at the same time, it is more conducive to improving the dissolution rate of calcium in waste rock powder. When all conditions are fully met, the dissolution rate of calcium in waste rock powder is increased from the original 50% to about 75%.

[0036] In some embodiments, saturated sodium bicarbonate solution is used to capture and recover dissolved carbon dioxide.

[0037] In some embodiments, ammonia water is added to the obtained calcium chloride solution to adjust the pH to 8.5-9.0. + , K + The content of Ca 2+ The concentration remains stable.

[0038] In some embodiments, a bicarbonate solution is added so that Ca 2+ With HCO 3 - The molar ratio is 1:1.1~1.3.

[0039] In some embodiments, the amount of acrylic acid polymer added is 0.8-1.2% of the mass of calcium ions in the solution.

[0040] In some embodiments, the temperature of the carbonization reaction is 15-20°C.

[0041] In some embodiments, the waste liquid after the carbonization reaction is pyrolyzed to form ammonia and HCl; ammonia is used to prepare ammonia water, which can be used to adjust the pH of calcium chloride solution; and / or, ammonia is used to prepare ammonium carbonate solution, which can be used for carbonization reaction; and / or, HCl is used as waste hydrochloric acid to dissolve waste rock powder.

[0042] Specifically, the pyrolysis temperature is 300-350°C.

[0043] Another embodiment of the present invention provides a system for preparing vaterite in a coordinated manner using waste rock powder, waste hydrochloric acid carbide slag, which is used to implement the above method, including:

[0044] a calcium chloride solution preparation unit for preparing calcium chloride solution and carbon dioxide from waste hydrochloric acid, waste rock powder and waste rock powder;

[0045] The vaterite preparation unit is used for carbonizing the calcium chloride solution from the calcium chloride solution preparation unit and carbon dioxide to prepare vaterite.

[0046] In some embodiments, a two-stage alkali washing tower is further included for capturing and recovering the dissolved carbon dioxide through a saturated sodium bicarbonate solution.

[0047] In some embodiments, an ammonium chloride pyrolysis unit is also included, which is used to pyrolyze the waste liquid after the carbonization reaction to form ammonia and HCl.

[0048] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0049] Example

[0050] A method for preparing vaterite by synergistically using waste stone powder, waste hydrochloric acid carbide slag, such as Figure 1 As shown, the steps are as follows:

[0051] 1. Raw material mixing and acid leaching reaction

[0052] In this step, the raw material is directly selected from the waste stone powder that has been basically dried (CaO content 35% to 50%, SiO 2 Content 8% to 17%) and carbide slag (active Ca(OH) 2 Content ≥ 60%), the waste hydrochloric acid is pre-treated (filtered to remove suspended matter, Fe 3+ The concentration is controlled at 1.2~1.5mol / L, Na + / K + ≤0.1mol / L), no further grinding of waste rock powder is required. The raw materials are prepared in a mass ratio of waste rock powder: carbide slag = 8:2. The solid-liquid ratio of the entire mixture to waste hydrochloric acid is set to 1:4, that is, 40L of waste hydrochloric acid is used for every 10kg of solid (including waste rock powder and carbide slag). First, add the waste rock powder to the waste hydrochloric acid and dissolve it at 50°C. Use a mechanical stirrer with a speed of 600rad / min and continue the reaction for 30 minutes; add carbide slag after 15 minutes of reaction. The purpose of this stage is to use waste hydrochloric acid to leach the waste rock powder. At the same time, carbide slag acts as a high calcium supplement to increase the Ca in the system. 2+According to the determination, under this process condition, the dissolution rate of calcium in waste rock powder increased from the original 50% to about 75%, making the Ca content in the whole system 2+ The concentration is stable at about 80 mg / L (fluctuation is controlled within ±3%). At the same time, part of the carbonate reacts to generate CO 2 , the released CO 2 The amount is about 0.6 kg CO per 10 kg solid 2 .

[0053] 2.CO 2 Capture and recovery

[0054] In order to make full use of the CO generated in the acid leaching reaction 2 A two-stage caustic washing tower system is used to remove the released CO 2 The specific operation is: CO emitted during the reaction 2 Pre-prepared saturated sodium bicarbonate (NaHCO 3 ) solution to wash the CO 2 After passing through the two-stage scrubbing system, the CO in the scrubbing liquid 2 The recovery purity can reach 99%, and the recovery rate is above 95%. 2 After simple purification, it is stored for later use as a carbon source for subsequent carbonization reactions. This step not only effectively avoids CO 2 It not only reduces direct emissions, but also realizes the resource utilization of by-products.

[0055] 3. Solution separation and pH control

[0056] After the acid leaching reaction is completed, the mixed solution is separated by continuous filtration or filter pressing to obtain two parts:

[0057] Residue: Mainly undissolved waste stone powder, rich in SiO 2 (≥60%), which can be used as concrete admixture later;

[0058] Calcium Chloride Solution: Contains CaCl 2 , initial Ca 2+ The concentration is about 2.5 mol / L, and it also contains some interfering ions (Na + , K + ).

[0059] In order to optimize the subsequent carbonization reaction, the pH of the clear solution needs to be adjusted to 9.0. To this end, ammonia water is slowly added for neutralization and regulation. Under the guidance of the online pH monitor, the regulation time is completed within about 5 minutes. + , K + The content of Ca2+ The concentration remains stable. The stable ionic environment of the regulated solution provides ideal conditions for subsequent carbonization.

[0060] 4. Low temperature carbonization and crystal orientation control

[0061] CaCl after pH adjustment 2 The clear liquid enters the carbonization reaction stage. The operating conditions are:

[0062] Reaction temperature: 18°C; reaction pressure: 0.1MPa; CO 2 Flow rate: 300 mL / min; reaction time: 60 minutes. In the carbonization reaction, 1M ammonium carbonate solution was added in sequence (the dosage was calculated based on theory to make Ca 2+ :HCO 3 - The molar ratio is 1:1.2) and the high-purity CO recovered previously 2 . In order to achieve the crystal orientation of vaterite, an acrylic polymer modifier is added in this process, and its addition amount is calculated as 1% of the mass of calcium ions in the solution. This modifier helps to regulate crystal nucleation and growth and inhibit the interference of impurity ions on the crystal form. After 60 minutes of reaction, the product showed characteristic peaks 2θ at 24.9°, 27.1° and 32.8° respectively through X-ray diffraction (XRD) detection, indicating that the vaterite crystal form is stable, such as Figure 2 The product purity test results show that the purity of vaterite is ≥96%, the mineralization yield reaches 99.95%, and the final output ratio is about 53.5%.

[0063] 5. Byproduct recovery and closed-loop reuse

[0064] After the carbonization reaction is completed, the vaterite calcium carbonate product is separated by centrifugation or filtration, and the ammonium chloride waste liquid contained in the residual liquid is pyrolyzed. The operation is:

[0065] About NH 4 Cl solution (concentration ≥ 15%) is pyrolyzed at 300-350°C to generate ammonia and HCl.

[0066] The recovered ammonia gas is condensed and mixed with water to prepare ammonia water with a concentration of 10-15%, which is reused for pH control and preparation of ammonium carbonate solution.

[0067] HCl is condensed and then recycled into the waste hydrochloric acid system, ensuring that the reagent recycling rate reaches more than 85%.

[0068] In addition, the acid leaching residue is rich in SiO 2 After drying, it can be directly used as a concrete admixture (≥60%), achieving 100% conversion of solid waste. Through this closed-loop system, the production of each ton of vaterite products can reduce CO 2The emissions are about 0.5 tons, and the overall process carbon emissions are reduced by 70% compared with the traditional process. At the same time, the cost of purchased reagents is reduced by about 60%, and the process energy consumption is reduced from the traditional 800kWh / ton to about 400kWh / ton.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing vaterite by synergistically using waste rock powder, waste hydrochloric acid carbide slag, characterized in that: The waste stone powder is dissolved by using waste hydrochloric acid, and carbide slag is added to supplement the calcium source in the solution after the dissolution; the dissolution generates carbon dioxide, and solid-liquid separation is performed after the dissolution to obtain a calcium chloride solution; Ammonia water is added to the obtained calcium chloride solution to adjust the pH to alkaline, and then ammonium carbonate solution is added, carbon dioxide generated by the solution is introduced, and an acrylic acid polymer is added as a modifier to perform a carbonization reaction to prepare vaterite calcium carbonate.

2. The method according to claim 1, characterized in that: The temperature for dissolving waste stone powder with waste hydrochloric acid is 40-60°C; Or, the time for dissolving the waste stone powder with waste hydrochloric acid is 30 to 60 minutes; Or, the solid-liquid ratio of waste rock powder to waste hydrochloric acid is 1:4-6, g / mL; Or, the mass ratio of waste rock powder to carbide slag is 3 to 5:

1.

3. The method according to claim 1, characterized in that: Saturated sodium bicarbonate solution is used to capture and recycle dissolved carbon dioxide.

4. The method according to claim 1, characterized in that: Ammonia water was added to the obtained calcium chloride solution to adjust the pH to 8.5 to 9.

0.

5. The method according to claim 1, characterized in that: Add ammonium carbonate solution to make Ca 2+ With HCO3 - The molar ratio is 1:1.1-1.3; Or, the amount of acrylic acid polymer added is 0.8 to 1.2% of the mass of calcium ions in the solution; Alternatively, the temperature of the carbonization reaction is 15-20°C.

6. The method according to claim 1, characterized in that: The waste liquid after the carbonization reaction is pyrolyzed to form ammonia and HCl; ammonia is used to prepare ammonia water, which can be used to adjust the pH of calcium chloride solution; and / or, ammonia is used to prepare ammonium carbonate solution, which can be used for carbonization reaction; and / or, HCl is used as waste hydrochloric acid to dissolve waste rock powder.

7. The method according to claim 6, characterized in that: The pyrolysis temperature is 300-350°C.

8. A system for preparing vaterite by synergistically using waste rock powder, waste hydrochloric acid carbide slag, characterized in that: The method for implementing claim 1 comprises: a calcium chloride solution preparation unit for preparing calcium chloride solution and carbon dioxide from waste hydrochloric acid, waste rock powder and waste rock powder; The vaterite preparation unit is used for carbonizing the calcium chloride solution from the calcium chloride solution preparation unit and carbon dioxide to prepare vaterite.

9. The system according to claim 8, characterized in that: It also includes two-stage caustic wash towers for capturing and recovering dissolved carbon dioxide using a saturated sodium bicarbonate solution.

10. The system according to claim 8, characterized in that: The invention also comprises an ammonium chloride pyrolysis unit, which is used for pyrolyzing the waste liquid after the carbonization reaction to form ammonia and HCl.

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