A method of recovering calcium sulfate

Abstract

The application provides a calcium sulfate recovery method, which comprises the following steps: an ammoniation carbonation step; a solid-liquid separation step; and a post-treatment step. Calcium sulfate suspension is ammoniated and carbonated to generate calcium carbonate and ammonium sulfate, so that calcium ions and sulfate ions are fully recovered, and the problem that calcium ions easily cause fouling and blockage of equipment, pipelines and pumps and bring difficulties to sewage treatment in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the field of calcium sulfate recycling technology, specifically relating to a method for recovering calcium sulfate. Background Technology

[0002] Acesulfame K, also known as AK sugar, is a food additive and a fourth-generation artificial sweetener. It is 200 times sweeter than sucrose. Acesulfame K can enhance the sweetness of food, has a good taste, and is calorie-free. It is not metabolized or absorbed in the human body, making it an ideal sweetener for middle-aged and elderly people, obese patients, and diabetic patients.

[0003] Triethylamine is used in the production of acesulfame potassium. In the subsequent recovery stage, calcium oxide is used to neutralize the acid solution, and triethylamine is recovered under alkaline conditions. After recovery, the calcium oxide is converted into a calcium sulfate solution, which is then separated into solid calcium sulfate using a centrifuge. Because the calcium sulfate solution contains trace amounts of residual triethylamine, a pungent triethylamine odor is emitted during centrifugation.

[0004] Chinese patent CN214087867U discloses a calcium sulfate recovery system for acesulfame potassium production, comprising a triethylamine recovery tank, a sulfuric acid high-level tank, and a centrifuge. The sulfuric acid high-level tank is located above the triethylamine recovery tank and connected to it via a sulfuric acid inlet pipe. The centrifuge is located below the triethylamine recovery tank and connected to it via a calcium sulfate outlet pipe. The triethylamine recovery tank is also connected to a calcium oxide inlet pipe and a wastewater inlet pipe. This utility model proposes a calcium sulfate recovery system for acesulfame potassium production that neutralizes the pH of the calcium sulfate solution to 4-5 with sulfuric acid before centrifugation, reducing triethylamine to triethylamine salt in the calcium sulfate solution. Triethylamine volatilizes less in a lower pH environment, thereby reducing the odor during calcium sulfate centrifugation and minimizing environmental pollution.

[0005] The technical solution for recovering calcium sulfate is to directly centrifuge the calcium sulfate solution. However, the calcium sulfate solution has a high viscosity, making it extremely difficult to separate calcium sulfate crystals even with direct centrifugation. Furthermore, direct centrifugation yields crude calcium sulfate, which cannot be used directly and has high disposal costs.

[0006] If the calcium sulfate suspension is not treated, the large amount of calcium ions it contains will cause scaling and clogging of equipment, pipes, and pumps, making wastewater treatment very difficult. Therefore, to address the shortcomings of existing technologies, it is necessary to design a calcium sulfate recovery method to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a method for recovering calcium sulfate from a calcium sulfate suspension generated during the acesulfame potassium production process. The calcium sulfate suspension has a high calcium sulfate content, and the calcium ions easily cause scaling and blockage of equipment, pipelines, and pumps, posing a significant challenge to wastewater treatment. Therefore, developing a method for recovering calcium sulfate from the calcium sulfate suspension is of great importance.

[0008] The technical solution of this invention is as follows: A method for recovering calcium sulfate includes the following steps: Ammonia carbonization step: Gas is introduced into the calcium sulfate suspension to ammonia carbonize the calcium sulfate, resulting in a gas-liquid suspension system; Solid-liquid separation step: Separate the gas-liquid suspension system into solid and liquid phases to obtain a solid phase and a liquid phase; Post-processing steps: Wash and dry the solid phase; evaporate and crystallize the liquid phase obtained in the solid-liquid separation step.

[0009] in: The gas used in the ammonia carbonization step is a gas containing ammonia and carbon dioxide.

[0010] Furthermore, the molar ratio of calcium sulfate in the ammonia, carbon dioxide, and calcium sulfate suspension is 2.0-2.3:1-1.3:1; Preferably, the molar ratio of calcium sulfate in the ammonia, carbon dioxide and calcium sulfate suspension is 2.1-2.3:1.1-1.3:1; More preferably, the molar ratio of calcium sulfate in the ammonia, carbon dioxide and calcium sulfate suspension is 2.3:1.3:1, 2:1:1 or 2.2:1.2:1; Furthermore, the gas in the ammonia carbonization step can be introduced simultaneously or in batches.

[0011] When a gas containing ammonia and carbon dioxide is introduced simultaneously, the final pH value of the gas-liquid suspension system is 6.5-7.5; further, the final pH value is preferably 6.6-7.4, 6.7-7.3, 6.8-7.2, 6.9-7.1 or 6.9-7.0; even further, the final pH value is preferably 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4 or 7.5.

[0012] When a gas containing ammonia is first introduced, the pH of the calcium sulfate suspension is adjusted to 8.5-10. Then, a gas containing carbon dioxide is introduced, which adjusts the final pH of the calcium sulfate suspension to 6.5-7.5. Furthermore, when a gas containing ammonia is introduced, the pH value of the calcium sulfate suspension is preferably 8.5-10, 8.6-9.9, 8.7-9.8, 8.8-9.7, 8.9-9.6, 9.0-9.5, 9.1-9.4, or 9.2-9.3; most preferably 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, or 10. Furthermore, when a gas containing carbon dioxide is introduced, the final pH value of the calcium sulfate suspension is 6.5-7.5; further, the final pH value is preferably 6.6-7.4, 6.7-7.3, 6.8-7.2, 6.9-7.1, or 6.9-7.0; even further, the final pH value is preferably 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, or 7.5.

[0013] Further, the reaction temperature of the ammonia carbonization step is 25℃-35℃; further, the temperature is preferably 26℃-34℃, 27℃-33℃, 28℃-32℃ or 29℃-31℃; even further, the temperature is preferably 26℃, 27℃, 28℃, 29℃, 30℃, 31℃, 32℃, 33℃, 34℃ or 35℃.

[0014] Furthermore, a centrifuge is used to centrifuge the gas-liquid suspension system obtained in the ammonia carbonization step to achieve solid-liquid separation, obtaining a solid phase and a liquid phase. Furthermore, a horizontal screw discharge sedimentation centrifuge can be used, suitable for continuous production with large production volumes.

[0015] Furthermore, the centrifuge speed is 3000-3800 r / min; preferably 3100-3700 r / min, 3200-3600 r / min, 3300-3500 r / min or 3400-3500 r / min; even more preferably 3400 r / min, 3450 r / min or 3500 r / min.

[0016] Furthermore, the solid and liquid phases obtained from the centrifuge need to be filtered using filter cloth. Filter cloths made of polyester or nylon materials are used, balancing permeability and retention rate.

[0017] Furthermore, the filter cloth has a mesh size of 200-300 mesh; the preferred mesh size is 210-290 mesh, 220-280 mesh, 230-270 mesh or 240-260 mesh; and even more preferably 240 mesh, 250 mesh or 260 mesh.

[0018] Furthermore, deionized water is used to wash the solid phase in the post-treatment step; room temperature deionized water is preferred.

[0019] Furthermore, the post-processing steps also include drying the solid phase using a fluidized bed at a temperature of 80℃-120℃; the preferred drying temperature is 85℃-115℃, 90℃-110℃, or 95℃-105℃; more preferably 100℃, 115℃, or 120℃.

[0020] Furthermore, in the post-processing step, an evaporation method is used to crystallize the liquid phase, with an evaporation temperature of 90℃-100℃; preferably, the evaporation temperature is 91℃-99℃, 92℃-98℃, 93℃-97℃ or 94℃-96℃; more preferably, it is 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃ or 100℃.

[0021] Compared with existing technologies, the beneficial effects are: 1. In view of the technical problems in the existing technology, a calcium sulfate recovery method is provided. By ammonia carbonization of calcium sulfate suspension, calcium carbonate and ammonium sulfate are generated, thereby fully recovering calcium ions and sulfate ions. This solves the problem that calcium ions can easily cause scaling and blockage of equipment, pipelines and pumps in the existing technology, which brings difficulties to sewage treatment. 2. Based on the calcium sulfate recovery method, and comparing Examples 1-3 with Comparative Examples 1-6, the present invention uses the following parameters to achieve a better conversion rate of calcium carbonate and ammonium sulfate: the molar ratio of ammonia, carbon dioxide, and calcium sulfate content in the calcium sulfate suspension; the final pH value of the calcium sulfate suspension; and the reaction temperature of the ammonia carbonation step. Furthermore, the final pH value of the calcium sulfate suspension and the reaction temperature of the ammonia carbonation step are adjusted in combination to ensure the conversion rate of calcium carbonate and ammonium sulfate. Detailed Implementation

[0022] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0023] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0024] Before introducing ammonia and carbon dioxide gases, the calcium sulfate content in the calcium sulfate suspension is determined, specifically including the following steps: A method for recovering calcium sulfate includes the following steps: Ammonia carbonization step: Ammonia and carbon dioxide gases are introduced into the calcium sulfate suspension to ammonia-carbonize the calcium sulfate. The calcium sulfate suspension reacts with the ammonia and carbon dioxide gases to form a gas-liquid suspension system. The molar ratio of ammonia, carbon dioxide, and calcium sulfate in the calcium sulfate suspension is 2-2.3:1-1.3:1. After introducing the gases, the final pH value of the calcium sulfate suspension is maintained at 6.5-7.5. The reaction takes place at atmospheric pressure and a temperature of 25℃-35℃ in the reactor.

[0025] Solid-liquid separation step: The gas-liquid suspension system obtained in the ammonia carbonization step is separated into solid and liquid phases, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution.

[0026] The solid-liquid separation is achieved using a horizontal screw discharge sedimentation centrifuge with a centrifuge speed of 3000-3800 r / min. The filter cloth is made of 200-300 mesh polyester or nylon material, taking into account both permeability and retention rate.

[0027] Post-processing steps: Wash and dry the solid phase obtained in the solid-liquid separation step; evaporate and crystallize the liquid phase obtained in the solid-liquid separation step to obtain ammonium sulfate crystals.

[0028] In this process, deionized water is used to wash the solid phase to obtain calcium carbonate solid.

[0029] Ammonium sulfate is crystallized by evaporating the liquid phase at a temperature of 90℃-100℃.

[0030] Example 1: A method for recovering calcium sulfate Includes the following steps: The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0031] (1) A gas containing ammonia and carbon dioxide is simultaneously introduced into the calcium sulfate suspension to carbonize the calcium sulfate suspension, forming a gas-liquid suspension system; wherein, the molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 2.3:1.3:1, and after the gas is introduced, the final pH value of the calcium sulfate suspension is 6.5; the reaction is carried out at atmospheric pressure at a temperature of 30°C in the reactor. (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3800 r / min, and filter it with a 200-mesh polyester material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution. (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 90°C to obtain 215g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 90°C to crystallize and obtain 289g of ammonium sulfate crystals.

[0032] In this example, the conversion rates of calcium carbonate and ammonium sulfate were 88.62% and 90.23%, respectively.

[0033] Example 2: A method for recovering calcium sulfate Includes the following steps: The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0034] (1) A gas containing ammonia is introduced into the calcium sulfate suspension to ammoniaate the calcium sulfate suspension. Then, a gas containing carbon dioxide is introduced to carbonize the calcium sulfate suspension, and finally a gas-liquid suspension system is formed. The molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 2:1:1, and the final pH value of the calcium sulfate suspension is 6.9. The reaction is carried out at atmospheric pressure at a temperature of 25°C in the reactor.

[0035] (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3000 r / min, and filter it with a 300-mesh nylon material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution. (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 100°C (temperature range) to obtain 206g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 100°C to crystallize and obtain 271g of ammonium sulfate crystals.

[0036] In this example, the conversion rates of calcium carbonate and ammonium sulfate were 84.91% and 84.61%, respectively.

[0037] Example 3: A method for recovering calcium sulfate Includes the following steps: The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0038] (1) A gas containing ammonia and carbon dioxide is simultaneously introduced into the calcium sulfate suspension to carbonize the calcium sulfate suspension, forming a gas-liquid suspension system; wherein, the molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 2.2:1.2:1, and the final pH value of the calcium sulfate suspension is 7.5; the reaction is carried out at atmospheric pressure at a temperature of 35℃ in the reactor. (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3500 r / min, and filter it with a 260-mesh polyester material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution. (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 120°C (temperature range) to obtain 215 g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 96°C to crystallize and obtain 291 g of ammonium sulfate crystals.

[0039] In this example, the conversion rates of calcium carbonate and ammonium sulfate were 88.62% and 90.85%, respectively.

[0040] Comparative Example 1: The difference from Example 1 is that the molar ratio of calcium sulfate in the ammonia, carbon dioxide, and calcium sulfate suspension is 1.5:0.8:1 (the proportions of ammonia and carbon dioxide are much lower). The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0041] (1) A gas containing ammonia and carbon dioxide is simultaneously introduced into the calcium sulfate suspension to carbonize the calcium sulfate suspension, forming a gas-liquid suspension system; wherein, the molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 1.5:0.8:1, and after the gas is introduced, the final pH value of the calcium sulfate suspension is 6.5; the reaction is carried out at atmospheric pressure at a temperature of 30°C in the reactor. (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3800 r / min, and filter it with a 200-mesh polyester material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution. (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 90°C to obtain 168g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 90°C to crystallize and obtain 226g of ammonium sulfate crystals.

[0042] In this example, the conversion rates of calcium carbonate and ammonium sulfate are 69.25% and 70.56%, respectively.

[0043] Comparative Example 2 The difference from Example 1 is that the molar ratio of ammonia, carbon dioxide, and calcium sulfate in the calcium sulfate suspension is 2.1:1.3:1, ensuring that the final pH value of the calcium sulfate suspension is 6 (the pH value is relatively low). The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0044] (1) A gas containing ammonia and carbon dioxide is simultaneously introduced into the calcium sulfate suspension to carbonize the calcium sulfate suspension, forming a gas-liquid suspension system; wherein, the molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 2.1:1.3:1, and after the gas is introduced, the final pH value of the calcium sulfate suspension is 6; the reaction is carried out at atmospheric pressure at a temperature of 30°C in the reactor. (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3800 r / min, and filter it with a 200-mesh polyester material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution. (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 90°C to obtain 192g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 90°C to crystallize and obtain 263g of ammonium sulfate crystals.

[0045] In this example, the conversion rates of calcium carbonate and ammonium sulfate were 79.14% and 82.11%, respectively.

[0046] Comparative Example 3 The difference from Example 1 is that the final pH value of the calcium sulfate suspension is maintained at 8.6 (the pH value is slightly high). The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0047] (1) A gas containing ammonia and carbon dioxide is simultaneously introduced into the calcium sulfate suspension to carbonize the calcium sulfate suspension, forming a gas-liquid suspension system; wherein, the molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 2.5:1.1:1, and after the gas is introduced, the final pH value of the calcium sulfate suspension is 8.6; the reaction is carried out at atmospheric pressure at a temperature of 30°C in the reactor. (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3800 r / min, and filter it with a 200-mesh polyester material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution. (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 90°C to obtain 212g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 90°C to crystallize and obtain 284g of ammonium sulfate crystals.

[0048] In this example, the conversion rates of calcium carbonate and ammonium sulfate were 87.38% and 88.67%, respectively.

[0049] Comparative Example 4 The difference from Example 2 is that the reaction temperature of the ammonia carbonization step is 20°C (the reaction temperature of the ammonia carbonization step is relatively low).

[0050] The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0051] (1) A gas containing ammonia is introduced into the calcium sulfate suspension to ammonia the calcium sulfate suspension, and then a gas containing carbon dioxide is introduced to carbonize the calcium sulfate suspension, thus forming a gas-liquid suspension system; wherein, the molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 2:1:1, and the final pH value of the calcium sulfate suspension is 6.9; the reaction is carried out at atmospheric pressure at a temperature of 20℃ in the reactor; (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3000 r / min, and filter it with a 300-mesh nylon material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution. (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 100°C (temperature range) to obtain 198 g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 100°C to crystallize and obtain 259 g of ammonium sulfate crystals.

[0052] In this example, the conversion rates of calcium carbonate and ammonium sulfate are 81.61% and 80.86%, respectively.

[0053] Comparative Example 5 The difference from Example 2 is that the reaction temperature of the ammonia carbonization step is 39°C (the reaction temperature of the ammonia carbonization step is relatively high).

[0054] The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0055] (1) A gas containing ammonia is introduced into the calcium sulfate suspension to ammonia the calcium sulfate suspension, and then a gas containing carbon dioxide is introduced to carbonize the calcium sulfate suspension, thus forming a gas-liquid suspension system; wherein, the molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 2:1:1, and the final pH value of the calcium sulfate suspension is 6.9; the reaction is carried out at atmospheric pressure at a temperature of 39°C in the reactor; (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3000 r / min, and filter it with a 300-mesh nylon material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution.

[0056] (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 100°C (temperature range) to obtain 192 g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 100°C to crystallize and obtain 251 g of ammonium sulfate crystals.

[0057] In this example, the conversion rates of calcium carbonate and ammonium sulfate were 79.14% and 78.36%, respectively. Comparative Example 6 The only difference from Example 1 is that the final pH of the calcium sulfate suspension is 5.7, and the temperature inside the reactor is 40°C (low pH, but high temperature).

[0058] The mass of calcium sulfate in the calcium sulfate suspension was determined to be 330 g.

[0059] (1) A gas containing ammonia and carbon dioxide is simultaneously introduced into the calcium sulfate suspension to carbonize the calcium sulfate suspension, forming a gas-liquid suspension system; wherein, the molar ratio of ammonia, carbon dioxide and calcium sulfate in the calcium sulfate suspension is 2.3:1.3:1, and after the gas is introduced, the final pH value of the calcium sulfate suspension is 5.7; the reaction is carried out at atmospheric pressure at a temperature of 40℃ in the reactor. (2) Centrifuge the gas-liquid suspension system obtained in step (1) using a horizontal screw discharge sedimentation centrifuge at a speed of 3800 r / min, and filter it with a 200-mesh polyester material filter cloth to obtain a solid phase and a liquid phase, wherein the solid phase includes calcium carbonate solid and the liquid phase includes ammonium sulfate solution. (3) Wash the solid phase obtained in step (2) with deionized water and dry it at 90°C to obtain 201g of calcium carbonate solid; evaporate the liquid phase obtained in step (2) at 90°C to crystallize and obtain 264g of ammonium sulfate crystals.

[0060] In this example, the conversion rates of calcium carbonate and ammonium sulfate were 82.85% and 82.42%, respectively. Results data: The mass of calcium carbonate and ammonium sulfate was measured by weighing, and the test results are shown in Table 1 below.

[0061] Table 1

[0062] Conclusion: In the system of reacting calcium sulfate suspension with ammonia and carbon dioxide to produce the target product calcium carbonate and the byproduct ammonium sulfate, pH value and reaction temperature have a significant impact on the conversion rate of calcium carbonate and ammonium sulfate. As long as the above factors are well controlled, a satisfactory conversion rate can be obtained.

[0063] It should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the given examples, those skilled in the art can modify or make equivalent substitutions to the technical solutions of the present invention as needed, without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for recovering calcium sulfate, characterized in that: Includes the following steps: Ammonia carbonization step: Gas is introduced into the calcium sulfate suspension to ammonia carbonize the calcium sulfate, resulting in a gas-liquid suspension system; Solid-liquid separation step: Separate the gas-liquid suspension system into solid and liquid phases to obtain a solid phase and a liquid phase; Post-processing steps: Wash and dry the solid phase; The liquid phase obtained in the solid-liquid separation step is evaporated and crystallized; The gas used in the ammonia carbonization step is a gas containing ammonia and carbon dioxide.

2. The method for recovering calcium sulfate according to claim 1, characterized in that: The molar ratio of calcium sulfate in the ammonia, carbon dioxide and calcium sulfate suspension is 2.0-2.3:1-1.3:

1.

3. The method for recovering calcium sulfate according to claim 2, characterized in that: The molar ratio of calcium sulfate in the ammonia, carbon dioxide and calcium sulfate suspension is 2.3:1.3:1, 2:1:1 or 2.2:1.2:

1.

4. The method for recovering calcium sulfate according to claim 1, characterized in that: The gas in the ammonia carbonization step can be introduced simultaneously or in batches.

5. The method for recovering calcium sulfate according to claim 4, characterized in that: When a gas containing ammonia and carbon dioxide is introduced simultaneously, the final pH value of the gas-liquid suspension system is 6.5-7.

5.

6. The method for recovering calcium sulfate according to claim 4, characterized in that: When a gas containing ammonia is first introduced, the pH of the calcium sulfate suspension is adjusted to 8.5-10. Then, a gas containing carbon dioxide is introduced, which adjusts the final pH of the calcium sulfate suspension to 6.5-7.

5.

7. The method for recovering calcium sulfate according to claim 1, characterized in that: The reaction temperature for the ammonia carbonization step is 25℃-35℃.

8. The method for recovering calcium sulfate according to claim 1, characterized in that: The gas-liquid suspension system obtained in the ammonia carbonization step is centrifuged to achieve solid-liquid separation, resulting in a solid phase and a liquid phase; the speed of the centrifuge is 3000-3800 r / min.

9. The method for recovering calcium sulfate according to claim 1, characterized in that: The solid and liquid phases obtained by centrifugation are filtered using a filter cloth; the filter cloth has a mesh size of 200-300.

10. The method for recovering calcium sulfate according to claim 1, characterized in that: The post-processing steps also include drying the solid phase using a fluidized bed at a temperature of 80℃-120℃.

11. The method for recovering calcium sulfate according to claim 1, characterized in that: In the post-processing step, evaporation is used to crystallize the liquid phase at a temperature of 90℃-100℃.

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