Continuous reaction system and method for low-cost preparation of high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum

Abstract

The invention belongs to the technical field of ardealite solid waste resource utilization, and particularly relates to a continuous reaction system and method for low-cost preparation of high-value calcium carbonate and ammonium sulfate from CO2 mineralized ardealite. According to the continuous reaction system provided by the invention, fluids in six functional areas, namely the ardealite dissolution ascending pipe, the ardealite dissolution downcomer, the impurity separation device, the product synthesis ascending pipe, the product synthesis downcomer and the product separation device, generate directional circulating flow due to fluid density difference; fluid in the whole continuous reaction system integrally forms closed circulation, continuous feeding of ardealite raw materials and continuous discharging of calcium carbonate and ammonium sulfate products can be achieved, compared with intermittent operation and continuous production processes, the auxiliary operation time can be shortened, the automatic control degree is higher, the product quality is more stable, the usage amount of ammonia water can be reduced, and the production cost is reduced. And the equipment investment is saved, so that the production cost is greatly reduced, and the method is suitable for industrial production and has important industrial application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource utilization of phosphogypsum solid waste, and specifically relates to a continuous reaction system and method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost. Background Art

[0002] Phosphogypsum is a solid waste produced by wet process phosphoric acid production, slightly soluble in water (solubility 2.2~2.6kg / m 3 ), the pH value is generally 2 to 4.5, and the main component is CaSO4·2H2O. Every ton of phosphate fertilizer produced (calculated as P2O5) produces about 4.5 to 5.0 tons of phosphogypsum. At present, phosphogypsum is usually stored in open spaces or released into rivers. More than 200 million tons of this waste are produced each year worldwide, and the huge stockpile occupies a large amount of land; in addition, because phosphogypsum is acidic, long-term storage will destroy the acid-base balance of the land and pollute groundwater. With the increase in my country's phosphate fertilizer production, the environmental pollution problem caused by the storage of phosphogypsum has become more prominent, causing many environmental risks. These problems have forced people to start looking for ways to deal with phosphogypsum.

[0003] At the same time, the environmental problems caused by CO2 have attracted the attention of countries around the world, and countries around the world are facing huge pressure to reduce CO2 emissions. Based on the concept of "waste treatment", many researchers have begun to study the use of phosphogypsum as a CO2 fixative.

[0004] The existing methods of fixing carbon dioxide by mineralization of phosphogypsum are mostly intermittent operations. For example, the invention patent with application number 201910457646.5 proposes a method for preparing micro-nanostructured calcium carbonate and ammonium sulfate using waste phosphogypsum. The phosphogypsum is ground into powder and dispersed in water to form a phosphogypsum dispersion; then, cationic surfactants and ammonium bicarbonate are added to the phosphogypsum dispersion in sequence at a temperature of 25 to 50°C and under stirring conditions. After mixing, the stirring reaction is continued until no bubbles are generated in the resulting mixed solution. The mixed solution is then filtered, and after the filtration is completed, the obtained upper solid is dried to obtain calcium carbonate; finally, the filtrate is concentrated and crystallized to obtain ammonium sulfate. In the above invention, CO2 and ammonia water need to be converted into ammonium bicarbonate before reacting with phosphogypsum. The process flow is relatively long and cannot be produced continuously.

[0005] The invention patent with application number 202310300598.5 proposes a device for continuously producing ammonium sulfate and calcium carbonate by mineralizing phosphogypsum with carbon dioxide, including a spray tower reaction device and a multi-stage kettle device. The injection of flue gas and the addition of raw materials such as ammonia water and solid waste gypsum are all carried out in the spray tower reaction device. The spray tower reaction device transports the reaction slurry in the reaction pool to the multi-stage kettle reaction device through a conveying pipeline equipped with a pressure pump. The multi-stage kettle reaction device includes several kettle reactors arranged in series. Since the volume of mixed slurry input from the reaction pool and transferred between different kettle reactors is relatively small each time, the raw materials can be transferred and reacted at a shorter time interval, and finally a fully reacted product can be obtained. However, the device needs to be equipped with a multi-stage reactor to obtain a completely reacted product, with many equipment, long process and high energy consumption, which greatly increases the equipment investment and production costs.

[0006] Based on the above problems, it is urgent to develop a new process and equipment for the low-cost preparation of high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum, in order to realize the resource utilization of phosphogypsum waste and CO2, and achieve carbon emission reduction effects at the same time. Summary of the invention

[0007] The purpose of the present invention is to provide a new process and new equipment for continuous CO2 mineralization of phosphogypsum to solve the problems mentioned in the above background technology, such as the large number of existing equipment, long and complex process flow, high energy consumption, difficult control and inability to operate continuously. To achieve the above purpose, the present invention proposes a continuous reaction system and method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost, wherein:

[0008] The present application provides a continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost, including a phosphogypsum dissolving device, an impurity separation device, a product synthesis device and a product separation device;

[0009] The phosphogypsum dissolving device comprises a phosphogypsum dissolving riser, a phosphogypsum dissolving downcomer, an air distributor, a raw material inlet and an air degassing zone, wherein the phosphogypsum dissolving riser is a columnar structure, the top of which is connected to the bottom of the air degassing zone, and the bottom of which is connected to the air distributor;

[0010] The product synthesis device comprises a product synthesis riser, a product synthesis downcomer, a CO2 distributor, an ammonia water inlet and a CO2 degassing zone, wherein the product synthesis riser is a columnar structure, the top of which is connected to the bottom of the CO2 degassing zone, and the bottom of which is connected to the CO2 distributor;

[0011] The impurity separation device and the product separation device are both separation tanks, and the separation tank comprises a tank inlet, a tank outlet, an exhaust port and a discharge port;

[0012] The top end of the phosphogypsum dissolution downcomer is connected to the air degassing zone, and the bottom end is connected to the tank inlet of the impurity separation device, and the tank outlet of the impurity separation device is connected to the product synthesis riser;

[0013] The top end of the product synthesis downcomer is connected to the CO2 degassing zone, and the bottom end is connected to the tank inlet of the product separation device, while the tank outlet of the product separation device is connected to the phosphogypsum dissolution riser.

[0014] Optionally, the separation tank is a tank body with a conical bottom structure.

[0015] Optionally, the raw material inlet is arranged at the lower side of the phosphogypsum dissolution riser, and the ammonia water inlet is arranged at the lower side of the product synthesis riser;

[0016] Preferably, a pH measuring port is also provided on the side of the product synthesis riser.

[0017] Optionally, for the separation tank structure of the impurity separation device and the product separation device, the tank inlet and / or tank outlet in the separation tank are arranged at the top or side wall of the separation tank, the exhaust port is arranged at the top of the separation tank, and the discharge port is arranged at the bottom of the separation tank.

[0018] Optionally, the air degassing zone is a combined structure of a cylindrical section and a frustum section, the large diameter end of the frustum section is connected to the cylindrical section, and the small diameter end of the frustum section is connected to the phosphogypsum dissolution riser; and / or,

[0019] The CO2 degassing zone is a combined structure of a cylindrical section and a frustum section, the large diameter end of the frustum section is connected to the cylindrical section, and the small diameter end of the frustum section is connected to the product synthesis riser.

[0020] Optionally, an auxiliary solid-liquid separation device is also provided in the air degassing zone and / or the impurity separation device and / or the product separation device.

[0021] Optionally, the auxiliary solid-liquid separation device is selected from a filter, a baffle or a hydrocyclone.

[0022] According to another aspect of the present application, there is provided the use of any of the above-mentioned continuous reaction systems for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost in preparing calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum.

[0023] According to the last aspect of the present application, a method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost is provided, using any of the above-mentioned continuous reaction systems for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost, the method comprising the following steps:

[0024] 1) injecting water into the continuous reaction system and exhausting excess gas through the exhaust port, so that the water in the continuous reaction system is interconnected;

[0025] 2) introducing air and CO2, the air enters the phosphogypsum dissolution riser through the air distributor, and the CO2 enters the product synthesis riser through the CO2 distributor, driving the water in the entire continuous reaction system to form a closed loop;

[0026] 3) adding phosphogypsum raw materials, the phosphogypsum raw materials enter the phosphogypsum dissolving riser from the raw material inlet and dissolve, the undissolved phosphogypsum raw materials are driven to the impurity separation device and settle to the bottom, the undissolved phosphogypsum continues to dissolve, and the undissolved impurities are regularly discharged from the discharge port of the impurity separation device;

[0027] 4) introducing ammonia water, which enters the product synthesis riser through the ammonia water inlet to react and generate calcium carbonate and ammonium sulfate, which are driven to the product separation device and then discharged continuously or regularly through the discharge port of the product separation device;

[0028] 5) The slurry mixture discharged from step 4) is subjected to solid-liquid separation outside the continuous reaction system, the mother liquor is returned to the continuous reaction system along with the phosphogypsum raw material, and the solid mixed product is dissolved, filtered, recrystallized and filtered to obtain a calcium carbonate product and an ammonium sulfate product respectively;

[0029] Preferably, the method further comprises the step of adding a phosphogypsum solvent; more preferably, the phosphogypsum solvent is selected from one or more of ammonium salts, organic alcohols, citric acid or citrates.

[0030] Optionally, in step (4), the pH value of the solution is controlled to be 8-10 by controlling the amount of ammonia water introduced.

[0031] Optionally, the method adopts normal temperature and pressure conditions. It is known to those skilled in the art that the method can also appropriately change the temperature and pressure conditions to promote the dissolution of phosphogypsum and the mass transfer of CO2.

[0032] The beneficial effects of this application include but are not limited to:

[0033] 1. The continuous reaction system and method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost proposed in the present invention couples and integrates the four steps of phosphogypsum dissolution, impurity separation, product synthesis and product separation into one reactor, and realizes the direct synthesis of calcium carbonate and ammonium sulfate by introducing CO2 and ammonia water into the phosphogypsum solution under normal temperature and pressure conditions by a "one-step method". Compared with the "two-step method" of first introducing CO2 into a strong alkali (NH4OH or NaOH, etc.) solution to obtain a carbonate [(NH4)2CO3 or Na2CO3] solution, and then adding phosphogypsum to the carbonate solution to prepare calcium carbonate, the amount of ammonia water used can be reduced, equipment investment can be saved, thereby significantly reducing production costs and facilitating industrial production.

[0034] 2. The continuous reaction system and method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost proposed in the present invention can realize the continuous feeding of phosphogypsum raw materials and the continuous discharging of calcium carbonate and ammonium sulfate products. Compared with intermittent operation, the continuous production process can reduce auxiliary operation time, have a higher degree of automatic control, and more stable product quality.

[0035] 3. The continuous reaction system and method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost proposed in the present invention can improve the separation effect of undissolved small particles of phosphogypsum and aqueous solution by adding auxiliary solid-liquid separation devices, including but not limited to filters, baffles and hydrocyclones, etc., in locations such as air degassing zones and impurity separation devices, thereby preventing phosphogypsum raw materials and insoluble impurities from entering the product synthesis riser and affecting the purity of the calcium carbonate product. Adding auxiliary solid-liquid separation devices, including but not limited to filters, baffles and hydrocyclones, etc., to the product separation device is beneficial to the separation of calcium carbonate and ammonium sulfate crystal products from mother liquor, preventing the crystal products from entering the phosphogypsum dissolution riser, thereby reducing side reactions and increasing product yields.

[0036] 4. The continuous reaction system and method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost proposed in the present invention can continuously prepare high-quality calcium carbonate and ammonium sulfate products, wherein the purity of the calcium carbonate product is 89.0-99.5%, and the purity of the ammonium sulfate product is 94.6-99.5%. By further adding an auxiliary solid-liquid separation device, the purity of the calcium carbonate product is 94.5-99.5%, and the purity of the ammonium sulfate product is 96.0-99.5%.

[0037] 5. The continuous reaction system and method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost proposed in the present invention can realize the continuous production of calcium carbonate and ammonium sulfate using CO2 mineralized phosphogypsum under normal temperature and pressure conditions, while the production schemes in the prior art mostly require additional control of the temperature and pressure of the reaction. For example, the temperature is controlled at 60-80°C in the embodiment of patent CN116177584A. The temperature condition of the one-step method is 20-180°C and the temperature condition of the indirect method is 50-60°C in the paper "Research Status of Preparation of Calcium Carbonate by Carbonization of Industrial By-product Gypsum" (Gui Jingneng, Gao Peiwei, Geng Fei, Ji Tianyi, Bao Liyi, Qin Qingdong, Inorganic Salt Industry, Vol. 50, No. 8, August 2018). The present scheme can carry out continuous production at normal temperature and pressure, can reduce production processes, significantly reduce costs, and has important industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0039] Figure 1 is a schematic diagram of a front view of a system device disclosed in an embodiment of the present invention;

[0040] Figure 2 is a schematic diagram of a left view of a system device disclosed in an embodiment of the present invention;

[0041] Figure 3 is a schematic diagram of a top view of a system device disclosed in an embodiment of the present invention;

[0042] Figure 4 is a schematic diagram of the baffles added to the air degassing zone in Example 1;

[0043] Figure 5 This is a schematic diagram of a combined device for adding baffles to the air degassing zone in Example 1;

[0044] Figure 6 is a schematic diagram of a baffle added to the impurity separation device in Example 1;

[0045] Figure 7 This is a schematic diagram of a baffle assembly device added to the product separation device in Example 1;

[0046] Figure 8 Schematic diagram of the impurity separation device and the product separation device in Example 2 with the addition of a filter assembly device;

[0047] Fig. 9 Schematic diagram of the combined device of the impurity separation device and the product separation device in Example 3 with the addition of a hydrocyclone;

[0048] Fig.10 is a schematic diagram of an impurity separation device and a product separation device in Example 4;

[0049] Fig.11 This is a SEM image of the calcium carbonate product of Example 1;

[0050] Fig.12 This is a SEM image of the calcium carbonate product of Example 5;

[0051] Fig.13 This is the SEM image of the calcium carbonate product of Example 6.

[0052] List of parts and reference numerals:

[0053] 1-phosphogypsum dissolving device, 11-phosphogypsum dissolving riser, 111-raw material inlet, 12-phosphogypsum dissolving downcomer, 13-air distributor, 14-air degassing zone, 141-cylindrical section, 142-cone section;

[0054] 2-impurity separation device, 21-tank inlet, 22-tank outlet, 23-exhaust port, 24-discharging port;

[0055] 3-product synthesis device, 31-product synthesis riser, 311-ammonia feed port, 312-pH measurement port, 32-product synthesis downcomer, 33-CO2 distributor, 34-CO2 degassing zone, 341-cylindrical section, 342-cone section;

[0056] 4-product separation device, 41-tank inlet, 42-tank outlet, 43-exhaust port, 44-discharge port;

[0057] 5-pH automatic control system; 6-air degassing zone baffle; 7-product separation device baffle;

[0058] 8-filter; 9-hydrocyclone. DETAILED DESCRIPTION

[0059] In order to more clearly illustrate the overall concept of the present application, a detailed description is given below in an illustrative manner in conjunction with the accompanying drawings.

[0060] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0061] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present application is not limited to the specific embodiments disclosed below.

[0062] In addition, in the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0063] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0064] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0065] In the present application, unless otherwise clearly specified and limited, a first feature "above" or "below" a second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples.

[0066] One of the purposes of the present invention is to provide a continuous reaction system device for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost, so as to solve the problem in the prior art that it is impossible to realize the continuous production of high-purity calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost.

[0067] Another object of the present invention is to provide a method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost based on the above-mentioned system device, so as to solve the problems of large amount of ammonia water used and high production cost caused by the "two-step method" process of the prior art, which requires first passing CO2 into a strong alkali or ammonia solution to prepare a carbonate solution, and then adding phosphogypsum to the carbonate solution to prepare calcium carbonate.

[0068] According to the continuous reaction system of the present application for preparing high-value calcium carbonate and ammonium sulfate with low cost from CO2 mineralized phosphogypsum, the system comprises a phosphogypsum dissolving device, an impurity separation device, a product synthesis device and a product separation device which are interconnected, wherein the phosphogypsum dissolving device comprises a phosphogypsum dissolving riser, a phosphogypsum dissolving downcomer, an air distributor and an air degassing zone, the product synthesis device comprises a product synthesis riser, a product synthesis downcomer, a CO2 distributor and a CO2 degassing zone, the impurity separation device and the product separation device are tank bodies with a conical bottom structure; the impurity separation device and the product separation device comprise a tank body inlet, a tank body outlet, an exhaust port and a discharge port; the phosphogypsum dissolving riser is a columnar structure, the top of which is connected to the bottom of the air degassing zone. The end is connected, and the bottom end is connected to the air distributor. The top end of the phosphogypsum dissolution downcomer is connected to the side wall of the air degassing zone, the bottom end of the phosphogypsum dissolution downcomer is connected to the tank inlet of the impurity separation device, and the tank outlet of the impurity separation device is connected to the lower side of the product synthesis riser; the product synthesis riser is also a column structure, the top end of which is connected to the bottom end of the CO2 degassing zone, and the bottom end is connected to the CO2 distributor. The top end of the product synthesis downcomer is connected to the side wall of the CO2 degassing zone, the bottom end of the product synthesis downcomer is connected to the tank inlet of the product separation device, and the tank outlet of the product separation device is connected to the lower side of the phosphogypsum dissolution riser.

[0069] As an embodiment, a raw material inlet is provided at the lower side of the phosphogypsum dissolution riser, and an ammonia water inlet and a pH measurement port are provided at the side of the product synthesis riser.

[0070] As an implementation mode, a pH automatic control system is arranged outside the product synthesis device, and is connected to the ammonia water inlet and the pH measurement port;

[0071] As an embodiment, the air degassing zone is a combined structure of a cylindrical section and a frustum section, the large diameter end of the frustum section is connected to the cylindrical section, and the small diameter end of the frustum section is connected to the phosphogypsum dissolution riser.

[0072] As an embodiment, the CO2 degassing zone is a combined structure of a cylindrical section and a frustum section, the large diameter end of the frustum section is connected to the cylindrical section, and the small diameter end of the frustum section is connected to the product synthesis riser.

[0073] As an embodiment, the tank inlet and the tank outlet of the impurity separation device and the product separation device may be at the top or side wall of the tank, the exhaust port is at the top of the tank, and the discharge port is at the bottom of the tank.

[0074] As an implementation mode, auxiliary solid-liquid separation devices may be added to the air degassing zone, the impurity separation device and the product separation device, including but not limited to filter screens, baffles and hydrocyclones.

[0075] According to the method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost provided in the present application, a continuous reaction system device for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost is used, comprising the following steps:

[0076] (1) introducing an aqueous solution into the device, and after the aqueous solution fills the impurity separation device and the product separation device and maintains a certain height, opening the exhaust ports of the impurity separation device and the product separation device, closing the exhaust ports after exhausting the gas, and continuing to add the aqueous solution until the water level exceeds a certain height of the top of the phosphogypsum dissolution downcomer and the top of the product synthesis downcomer, so that the liquids in the device are interconnected;

[0077] (2) air and CO2 enter the phosphogypsum dissolution riser and the product synthesis riser through the air distributor and the CO2 distributor, respectively, and are dispersed into small bubbles;

[0078] (3) Since the gas content in the phosphogypsum dissolution riser and the product synthesis riser is relatively high, the fluid density therein is relatively low, while the gas content in the phosphogypsum dissolution downcomer and the product synthesis downcomer is relatively low or even free of bubbles, so the fluid density therein is relatively high. Therefore, the fluids in the six functional areas, namely, the phosphogypsum dissolution riser, the phosphogypsum dissolution downcomer, the impurity separation device, the product synthesis riser, the product synthesis downcomer and the product separation device, generate directional circulation flow due to the difference in fluid density, that is, the fluid in the phosphogypsum dissolution riser flows upward, the fluid in the phosphogypsum dissolution downcomer flows downward, the fluid in the impurity separation device flows downward first and then upward, the fluid in the product synthesis riser flows upward, the fluid in the product synthesis downcomer flows downward, and the fluid in the product separation device flows downward first and then upward, thereby driving the fluid in the entire device to form a closed circulation as a whole;

[0079] (4) The phosphogypsum raw material enters the phosphogypsum dissolution riser from the raw material inlet, and phosphogypsum is slightly soluble in water, thereby ionizing Ca 2+ and SO4 2- The undissolved phosphogypsum flows upward with the fluid to the air degassing zone, and then moves to the impurity separation device through the phosphogypsum dissolving downcomer. The undissolved phosphogypsum raw material and insoluble impurities settle to the bottom in the impurity separation device. The undissolved phosphogypsum continues to dissolve, and the undissolved impurities are regularly discharged from the discharge port of the impurity separation device. The Ca in the solution 2+ and SO4 2- As the fluid flows directional to the product synthesis riser, ammonia water enters the product synthesis riser through the ammonia water inlet, wherein Ca 2+ 、SO4 2- It reacts with CO2 and aqueous ammonia to generate CaCO3 and ammonium sulfate. The products CaCO3 and (NH4)2SO4 move to the CO2 degassing zone along with the upwardly flowing fluid in the product synthesis riser, and move to the product separation device through the product synthesis downcomer for separation and collection, and then are continuously or periodically discharged from the system through the discharge port of the product separation device. The slurry mixture is separated into solid and liquid outside the reaction system, and the mother liquor returns to the reaction system with the phosphogypsum, while the solid mixed product is dissolved, filtered, recrystallized and filtered to obtain calcium carbonate product and ammonium sulfate product respectively.

[0080] As an implementation method, in order to control the particle size distribution and crystal form of the calcium carbonate product, necessary phosphogypsum solvents (including but not limited to various ammonium salts, organic alcohols, citric acid and its salts, etc.) may be used.

[0081] As an implementation mode, in steps (1) to (4), normal temperature and pressure conditions may be adopted, or certain temperature and pressure conditions may be adopted to promote the dissolution of phosphogypsum and the mass transfer of CO2.

[0082] As an implementation mode, in step (4), the amount of ammonia water introduced is automatically controlled by the pH automatic control system to ensure that the pH range of the solution is between 8-10.

[0083] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the following is a brief description of the present invention in conjunction with the attached drawings. Figures 1 to 13 The present invention is further described in detail with reference to the accompanying drawings and specific embodiments.

[0084] Example 1

[0085] like Figure 1-3As shown, this embodiment provides a continuous reaction system device for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost, comprising a phosphogypsum dissolving device 1, an impurity separation device 2, a product synthesis device 3 and a product separation device 4 which are interconnected, wherein the phosphogypsum dissolving device 1 and the product synthesis device 3 are two sets of interconnected external circulation slurry bed reactors, the phosphogypsum dissolving device 1 comprises a phosphogypsum dissolving riser 11, a phosphogypsum dissolving downcomer 12, an air distributor 13 and an air degassing zone 14, the product synthesis device 3 comprises a product synthesis upper and lower parts, and the product synthesis device 3 comprises a product synthesis lower and upper parts. The riser 31, the product synthesis downcomer 32, the CO2 distributor 33 and the CO2 degassing zone 34, the impurity separation device 2 and the product separation device 4 are tanks with conical bottom structures. The impurity separation device 2 adopts a conical bottom structure design to more conveniently collect undissolved phosphogypsum particles and insoluble impurities, which is conducive to the continued dissolution of undissolved phosphogypsum and the rapid discharge of undissolved impurity particles from the impurity separation device 2. The product separation device 4 adopts a conical bottom structure design to more conveniently collect crystallized products, which is conducive to the rapid discharge of products from the product separation device 4 to prevent side reactions.

[0086] The tank body of the impurity separation device 2 includes a tank body inlet 21, a tank body outlet 22, an exhaust port 23 and a discharge port 24;

[0087] The tank body of the product separation device 4 includes a tank body inlet 41, a tank body outlet 42, an exhaust port 43 and a discharge port 44;

[0088] The phosphogypsum dissolving riser 11 is a columnar structure, the top of which is connected to the bottom of the air degassing zone 14, and the bottom of which is connected to the air distributor 13. The top of the phosphogypsum dissolving downcomer 12 is connected to the side wall of the air degassing zone 14, the bottom of the phosphogypsum dissolving downcomer 12 is connected to the tank inlet 21 of the impurity separation device 2, and the tank outlet 22 of the impurity separation device 2 is connected to the lower side of the product synthesis riser 31.

[0089] The product synthesis riser 31 is also a column-type structure, with its top connected to the bottom of the CO2 degassing zone 34, and its bottom connected to the CO2 distributor 33. The top of the product synthesis downcomer 32 is connected to the side wall of the CO2 degassing zone 34, the bottom of the product synthesis downcomer 32 is connected to the tank inlet 41 of the product separation device 4, and the tank outlet 42 of the product separation device 4 is connected to the lower side of the phosphogypsum dissolution riser 11.

[0090] In this embodiment, a raw material inlet 111 is provided at the lower side of the phosphogypsum dissolution riser 11, and phosphogypsum solid powder or slurry is injected into the phosphogypsum dissolution riser 11 through the raw material inlet 111. An ammonia water inlet 311 and a pH measuring port 312 are provided on the side of the product synthesis riser 31.

[0091] In this embodiment, a pH automatic control system 5 is arranged outside the product synthesis device 3 and connected to the ammonia water inlet 311 and the pH measurement port 312 .

[0092] In this embodiment, the air degassing zone 14 is a combined structure of a cylindrical section 141 and a frustum section 142. The large diameter end of the frustum section 142 is connected to the cylindrical section 141, and the small diameter end of the frustum section 142 is connected to the phosphogypsum dissolution riser 11. The larger cross-sectional area of ​​the air degassing zone 14 can make the separation of air and slurry more complete.

[0093] In this embodiment, the CO2 degassing zone 34 is a combined structure of a cylindrical section 341 and a frustum section 342. The large diameter end of the frustum section 342 is connected to the cylindrical section 341, and the small diameter end of the frustum section 342 is connected to the product synthesis riser 31. The larger cross-sectional area of ​​the CO2 degassing zone 34 can make the separation of CO2 and the slurry more complete.

[0094] In this embodiment, the tank inlet 21 and the tank inlet 41 of the impurity separation device 2 and the product separation device 4 are both at the top of the tank, the tank outlet 22 and the tank outlet 42 are both at the side wall of the tank, the exhaust port 23 and the exhaust port 43 are at the top of the tank, and the discharge port 24 and the discharge port 44 are at the bottom of the tank.

[0095] In this embodiment, the air degassing zone 14 is added with Figure 4 The air degassing zone baffle 6 shown in the figure has a combined device structure as shown in the figure Figure 5 As shown, the slurry flow rate inside the baffle 6 in the air degassing zone is relatively low, and the phosphogypsum particles are accelerated to settle multiple times under the blocking and guiding effects of the baffle, thereby greatly reducing the phosphogypsum particles that enter the phosphogypsum dissolution downcomer 12 along with the slurry. A product separation device baffle 7 is added to the product separation device 4, and its structure is as shown in FIG. Figure 6 As shown, the structure of the combined device is as follows Figure 7 As shown, adding a baffle 7 of the product separation device can increase the sedimentation area of ​​the product, allowing the crystallized product to settle more fully, preventing the crystallized product from entering the phosphogypsum dissolution riser 11 along with the slurry, thereby avoiding side reactions and increasing the calcium carbonate yield.

[0096] The present embodiment implements a method for preparing high-value calcium carbonate and ammonium sulfate at low cost by mineralizing phosphogypsum with CO2, which adopts the above-mentioned continuous reaction system device for preparing high-value calcium carbonate and ammonium sulfate at low cost by mineralizing and fixing CO2 with phosphogypsum, including the following steps:

[0097] (1) introducing aqueous solution into the device, and after the water fills up the impurity separation device 2 and the product separation device 4 and maintains a certain height, opening the exhaust port 23 and the exhaust port 43 of the impurity separation device 2 and the product separation device 4, closing the exhaust port 23 and the exhaust port 43 after exhausting the gas, and continuing to add aqueous solution until the water level exceeds a certain height of the top of the phosphogypsum dissolution downcomer 12 and the top of the product synthesis downcomer 32, so that the liquids in the device are interconnected;

[0098] (2) Air and CO2 enter the phosphogypsum dissolution riser 11 and the product synthesis riser 31 through the air distributor 13 and the CO2 distributor 33, respectively, and are dispersed into small bubbles;

[0099] (3) Since the gas content in the phosphogypsum dissolution riser 11 and the product synthesis riser 31 is relatively high, the fluid density therein is relatively low, while the gas content in the phosphogypsum dissolution downcomer 12 and the product synthesis downcomer 32 is relatively low or even free of bubbles, so the fluid density therein is relatively high. Therefore, the fluid in the six connected functional areas, namely, the phosphogypsum dissolution riser 11, the phosphogypsum dissolution downcomer 12, the impurity separation device 2, the product synthesis riser 31, the product synthesis downcomer 32 and the product separation device 4, generates a directional circulation flow due to the density difference, that is, the fluid in the phosphogypsum dissolution riser 11 flows upward, the fluid in the phosphogypsum dissolution downcomer 12 flows downward, the fluid in the impurity separation device 2 flows downward first and then upward, the fluid in the product synthesis riser 31 flows upward, the fluid in the product synthesis downcomer 32 flows downward, and the fluid in the product separation device 4 flows downward first and then upward, thereby driving the fluid in the entire device to form a closed circulation as a whole;

[0100] (4) The phosphogypsum raw material enters the phosphogypsum dissolution riser 11 from the raw material inlet 111. Since phosphogypsum is slightly soluble in water, Ca is ionized. 2+ and SO4 2- The undissolved phosphogypsum flows upward with the fluid to the air degassing zone 14, and then moves to the impurity separation device 2 through the phosphogypsum dissolving downcomer 12. The undissolved phosphogypsum raw material and insoluble impurities settle to the bottom in the impurity separation device 2. The undissolved phosphogypsum continues to dissolve, and the undissolved impurities are regularly discharged from the discharge port 22. The Ca in the solution 2+ and SO4 2- As the fluid flows directional to the product synthesis riser 31, ammonia water enters the product synthesis riser 31 through the ammonia water inlet 311, wherein Ca 2+ 、SO4 2-It reacts with CO2 and aqueous ammonia to generate CaCO3 and ammonium sulfate. The products CaCO3 and (NH4)2SO4 move to the CO2 degassing zone 34 along with the upwardly flowing fluid in the product synthesis riser 31, and move to the product separation device 4 through the product synthesis downcomer 32 for separation and collection, and then are continuously or periodically discharged from the system device through the discharge port 44. The slurry mixture is separated into solid and liquid outside the reaction system, and the mother liquor returns to the reaction system with the phosphogypsum, while the solid mixed product is dissolved, filtered, recrystallized and filtered to obtain calcium carbonate product and ammonium sulfate product respectively.

[0101] In this embodiment, ammonium chloride is added to promote the dissolution of phosphogypsum.

[0102] In this embodiment, the experiment was carried out under normal temperature and pressure conditions.

[0103] In this embodiment, the solution pH is controlled to be 8 during the reaction.

[0104] Specifically, the phosphogypsum raw material used in this embodiment comes from Hubei Xingfa Chemical Group Co., Ltd., and its composition is shown in Table 1. The phosphogypsum slurry with a feed concentration of 13% is pumped into the phosphogypsum dissolving riser 11 through the raw material inlet 111, and the feed rate is 16 mL / min. The phosphogypsum is slightly dissolved in the phosphogypsum dissolving riser 11 to release Ca 2+ and SO4 2- , the undissolved phosphogypsum particles flow into the air degassing zone 14 with the fluid flow, and the cross-sectional area of ​​the cylindrical section 141 and the frustum section 142 in the air degassing zone increases, and the fluid flow rate decreases, making the phosphogypsum particles easier to settle. In addition, the baffle 6 in the air degassing zone forms a relatively closed flow field environment, which makes the undissolved phosphogypsum further settle, wherein large particles fall into the phosphogypsum dissolution riser 11 to continue to dissolve, and fine particles follow the fluid through the phosphogypsum dissolution downcomer 12 into the impurity separation device 2 to continue to settle to avoid entering the product synthesis riser 31. Ammonia water is introduced into the product synthesis riser 31 through the ammonia water inlet 311, and the solution pH is monitored in real time at the pH measurement port. The ammonia water flow rate is automatically adjusted through the pH control system to accurately control the optimal product synthesis environment in the device, thereby reducing side reactions and ammonia water consumption. At the same time, the morphology and particle size distribution of the calcium carbonate crystal product can be regulated. In this embodiment, the pH in the device is maintained at 8. Ca in the solution 2+ and SO4 2-Enter the product synthesis riser 31 and react with CO2 and ammonia water to generate calcium carbonate and ammonium sulfate. Calcium carbonate and ammonium sulfate flow with the fluid through the product synthesis downcomer 32 and enter the product separation device 4. With the assistance of the baffle 7 of the product separation device, they are continuously precipitated, separated, concentrated, collected and discharged from the system device. The slurry mixture is separated into solid and liquid outside the reaction system. The mother liquor continues to enter the reaction system with the phosphogypsum, and the solid mixed product is dissolved, filtered, recrystallized and filtered to obtain calcium carbonate products and ammonium sulfate products respectively. The parameters of the calcium carbonate and ammonium sulfate products synthesized in this embodiment are shown in Table 2. The SEM of the calcium carbonate product is as follows: Fig.11 As shown by Fig.11 It can be seen that the calcium carbonate product synthesized under the conditions of this embodiment is a calcite-type nano-calcium carbonate of about 100 nm.

[0105] Example 2

[0106] The difference between the continuous reaction system device for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost and Example 1 is that in this embodiment, not only is the air degassing zone 14 added as in Example 1, Figure 4 The degassing zone baffle 6 is shown, and a filter screen 8 is added to the impurity separation device 2 and the product separation device 4. The structure is as follows Figure 8 As shown, adding a filter 8 in the impurity separation device 2 can effectively prevent undissolved phosphogypsum particles and insoluble impurity particles from entering the product synthesis riser 31, affecting the product purity; adding a filter 8 in the product separation device 4 can prevent the product from entering the phosphogypsum dissolution riser 11 with the solution, thereby avoiding side reactions and increasing the yield of the crystallized product. In addition, the pore size of the filter 8 can be adjusted according to the particle size distribution of the phosphogypsum raw material. In this embodiment, the D 10 =2μm, and the pore size of the filter 14 used is 1μm.

[0107] In this embodiment, organic alcohol is added to the solution to promote the dissolution of phosphogypsum.

[0108] In this embodiment, the solution pH is controlled to be 9 during the reaction.

[0109] The method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost implemented in this embodiment is the same as the experimental conditions of Example 1, except that the undissolved phosphogypsum fine particles and insoluble impurities are blocked by the filter screen 8 and remain in the impurity separation device 5 after passing through the phosphogypsum dissolution downcomer 12 with the fluid into the impurity separation device 2, and the undissolved phosphogypsum continues to dissolve and the insoluble impurities are continuously or regularly discharged, and the solution carries Ca 2+ and SO4 2-Enter the product synthesis riser 31. Ammonia water is introduced into the product synthesis riser 31 to maintain the pH in the device at 9. 2+ and SO4 2- The product synthesis riser 31 reacts with CO2 and ammonia water to generate calcium carbonate and ammonium sulfate. The generated calcium carbonate and ammonium sulfate flow with the fluid through the product synthesis downcomer 32 into the product separation device 4. Under the blocking effect of the filter screen 8 in the product separation device 4, the calcium carbonate and ammonium sulfate are continuously precipitated, separated, concentrated, and collected to the cone bottom of the product separation device 4 on one side of the filter screen 8, and are discharged from the system device through the discharge port 44 of the product separation device 4. The slurry mixture is separated into solid and liquid outside the reaction system, and the mother liquor continues to enter the reaction system with the phosphogypsum, and the solid mixed product is dissolved, filtered, recrystallized and filtered to obtain calcium carbonate products and ammonium sulfate products respectively. The parameters of the calcium carbonate and ammonium sulfate products synthesized in this embodiment are shown in Table 2.

[0110] Example 3

[0111] The difference between the continuous reaction system device for preparing high-value calcium carbonate and ammonium sulfate from phosphogypsum with low cost from CO2 mineralization in this embodiment and that in embodiment 1 is that in this embodiment, the tank inlet 21 and the tank inlet 41 of the impurity separation device 2 and the product separation device 4 are both on the side wall of the tank, and the tank outlet 22 and the tank outlet 42 are both on the top of the tank. Moreover, in this embodiment, as in embodiment 1, the air degassing zone 14 is added with Figure 4 The air degassing zone baffle 6 is shown, and a hydrocyclone 9 is added to the impurity separation device 2 and the product separation device 4. The structure is as follows Fig. 9 As shown, adding a hydrocyclone 9 to the impurity separation device 2 can accelerate the solid-liquid separation process of the solid particles and the solution entering the impurity separation device 2, and prevent the undissolved phosphogypsum particles and the undissolved impurity particles from affecting the product purity; adding a hydrocyclone 9 to the product separation device 4 accelerates the separation of the crystallized product and the mother liquor, and prevents the crystallized product from entering the phosphogypsum dissolution riser 11 with the solution, thereby avoiding side reactions and increasing the yield of the crystallized product.

[0112] In this example, citric acid is added to promote the dissolution of phosphogypsum.

[0113] In this embodiment, the solution pH is controlled to be 10 during the reaction.

[0114] The method for preparing high-value calcium carbonate and ammonium sulfate from phosphogypsum with CO2 mineralization at low cost implemented in this embodiment is the same as the experimental conditions of Example 1, except that the undissolved phosphogypsum fine particles and insoluble impurities enter the impurity separation device 2 along the tank inlet 21 after passing through the phosphogypsum dissolution downcomer 12 with the fluid, and then enter the hydrocyclone 9 tangentially. Under the action of centrifugal force, the solid particles move downward in a spiral along the wall of the hydrocyclone 9 and are discharged from the discharge port 24, and the clear liquid carries the Ca 2+ and SO4 2- The product synthesis riser 31 is entered from the tank outlet 22. Ammonia water is introduced into the product synthesis riser 31 to maintain the pH in the device at 10. The Ca in the solution 2+ and SO4 2- In the product synthesis riser 31, it reacts with CO2 and ammonia water to generate calcium carbonate and ammonium sulfate. The generated calcium carbonate flows with the fluid through the product synthesis downcomer 32 into the product separation device 4 and then enters the hydrocyclone 9 tangentially along the tank inlet 41. Under the action of centrifugal force, the calcium carbonate and ammonium sulfate slurry mixture is discharged from the system device at the discharge port 44 of the product separation device 4 and undergoes solid-liquid separation outside the reaction system. The clear liquid continues to enter the reaction system with the phosphogypsum through the tank outlet 42, and the solid mixed product is dissolved, filtered, recrystallized and filtered to obtain calcium carbonate products and ammonium sulfate products, respectively. The parameters of the calcium carbonate and ammonium sulfate products synthesized in this embodiment are shown in Table 2.

[0115] Example 4

[0116] The difference between this embodiment and embodiment 3 is that in this embodiment, the tanks of the impurity separation device 2 and the product separation device 4 are used as hydrocyclones, and no auxiliary solid-liquid separation device is added inside. Fig.10 The product parameters of calcium carbonate and ammonium sulfate synthesized in this example are shown in Table 2.

[0117] Example 5

[0118] The difference between this embodiment and embodiment 1 is that the experimental raw material of this embodiment is phosphogypsum after flotation from Hubei Xingfa Chemical Group Co., Ltd., and its composition is shown in Table 3. Other conditions are the same as those of embodiment 1. The parameters of calcium carbonate and ammonium sulfate products synthesized in this embodiment are shown in Table 4. The SEM image of calcium carbonate product is shown in Fig.12 As shown by Fig.12 It can be seen that the calcium carbonate product synthesized under the conditions of this embodiment has a spindle structure, with a long axis of about 10 μm and a short axis of about 2 μm.

[0119] Example 6

[0120] The difference between this embodiment and embodiment 1 is that the liquid phase used in this embodiment is clean water, no additives for promoting the dissolution of phosphogypsum are added, and no crystal form control agent is added. The experiment is carried out at 80°C and 2 bar, and the other conditions are the same as those in embodiment 1. The parameters of the calcium carbonate and ammonium sulfate products synthesized in this embodiment are shown in Table 4, and the SEM image of the calcium carbonate product is shown in Fig.13 As shown by Fig.13 It can be seen that the calcium carbonate product synthesized under the conditions of this embodiment is aragonite calcium carbonate whiskers, whose major axis is about 20 μm and minor axis is about 1 μm.

[0121] Table 1

[0122] Element <![CDATA[SO3]]> CaO <![CDATA[SiO2]]> F <![CDATA[K2O]]> <![CDATA[P2O5]]> <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> BaO <![CDATA[TiO2]]> <![CDATA[Na2O]]> MgO content / % 47.7 41.2 7.13 1.87 0.549 0.399 0.326 0.275 0.193 0.149 0.121 0.0243

[0123] Table 2

[0124]

[0125] Table 3

[0126] Element CaO <![CDATA[SO3]]> <![CDATA[SiO2]]> <![CDATA[P2O5]]> <![CDATA[Al2O3]]> <![CDATA[K2O]]> <![CDATA[TiO2]]> <![CDATA[Fe2O3]]> <![CDATA[Na2O]]> MgO SrO NiO content / % 45.0 47.9 4.60 0.840 0.771 0.440 0.171 0.117 0.106 0.0434 0.0185 0.0196

[0127] Table 4

[0128] Serial number Special experimental conditions Calcium carbonate product purity / % Calcium carbonate product crystal form Ammonium sulfate product purity / % Example 1 Normal temperature and pressure 94.5％ Calcite 96.0％ Example 5 Normal temperature and pressure 97.0％ Spindle 99.5％ Example 6 80℃,2bar 99.5％ Aragonite 95.4％

[0129] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0130] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost, characterized in that: It includes a phosphogypsum dissolving device, an impurity separation device, a product synthesis device and a product separation device; The phosphogypsum dissolving device comprises a phosphogypsum dissolving riser, a phosphogypsum dissolving downcomer, an air distributor, a raw material inlet and an air degassing zone, wherein the phosphogypsum dissolving riser is a columnar structure, the top of which is connected to the bottom of the air degassing zone, and the bottom of which is connected to the air distributor; The product synthesis device comprises a product synthesis riser, a product synthesis downcomer, a CO2 distributor, an ammonia water inlet and a CO2 degassing zone, wherein the product synthesis riser is a columnar structure, the top of which is connected to the bottom of the CO2 degassing zone, and the bottom of which is connected to the CO2 distributor; The impurity separation device and the product separation device are both separation tanks, and the separation tank comprises a tank inlet, a tank outlet, an exhaust port and a discharge port; The top end of the phosphogypsum dissolution downcomer is connected to the air degassing zone, and the bottom end is connected to the tank inlet of the impurity separation device, and the tank outlet of the impurity separation device is connected to the product synthesis riser; The top end of the product synthesis downcomer is connected to the CO2 degassing zone, and the bottom end is connected to the tank inlet of the product separation device, while the tank outlet of the product separation device is connected to the phosphogypsum dissolution riser.

2. The continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost according to claim 1, characterized in that: The separation tank is a tank body with a conical bottom structure.

3. The continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost according to claim 1, characterized in that: The raw material inlet is arranged at the lower side of the phosphogypsum dissolution riser, and the ammonia water inlet is arranged at the lower side of the product synthesis riser; Preferably, a pH measuring port is also provided on the side of the product synthesis riser.

4. The continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost according to claim 1, characterized in that: For the separation tank structure of the impurity separation device and the product separation device, the tank inlet and / or tank outlet in the separation tank are arranged at the top or side wall of the separation tank, the exhaust port is arranged at the top of the separation tank, and the discharge port is arranged at the bottom of the separation tank.

5. The continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost according to claim 1, characterized in that: The air degassing zone is a combined structure of a cylindrical section and a frustum section, the large diameter end of the frustum section is connected to the cylindrical section, and the small diameter end of the frustum section is connected to the phosphogypsum dissolution riser; and / or, The CO2 degassing zone is a combined structure of a cylindrical section and a frustum section, the large diameter end of the frustum section is connected to the cylindrical section, and the small diameter end of the frustum section is connected to the product synthesis riser.

6. The continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost according to claim 1, characterized in that: An auxiliary solid-liquid separation device is also provided in the air degassing zone and / or the impurity separation device and / or the product separation device.

7. The continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost according to claim 6, characterized in that: The auxiliary solid-liquid separation device is selected from a filter screen, a baffle or a hydrocyclone.

8. Use of the continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost as described in any one of claims 1 to 7 in preparing calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum.

9. A method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost, characterized in that: A continuous reaction system for preparing high-value calcium carbonate and ammonium sulfate at low cost by using CO2 mineralized phosphogypsum as claimed in any one of claims 1 to 7, the method comprising the following steps: 1) injecting water into the continuous reaction system and exhausting excess gas through the exhaust port, so that the water in the continuous reaction system is interconnected; 2) introducing air and CO2, the air enters the phosphogypsum dissolution riser through the air distributor, and the CO2 enters the product synthesis riser through the CO2 distributor, driving the water in the entire continuous reaction system to form a closed loop; 3) adding phosphogypsum raw materials, the phosphogypsum raw materials enter the phosphogypsum dissolving riser from the raw material inlet and dissolve, the undissolved phosphogypsum raw materials are driven to the impurity separation device and settle to the bottom, the undissolved phosphogypsum continues to dissolve, and the undissolved impurities are regularly discharged from the discharge port of the impurity separation device; 4) introducing ammonia water, which enters the product synthesis riser through the ammonia water inlet to react and generate calcium carbonate and ammonium sulfate, which are driven to the product separation device and then discharged continuously or regularly through the discharge port of the product separation device; 5) The slurry mixture discharged from step 4) is subjected to solid-liquid separation outside the continuous reaction system, the mother liquor is returned to the continuous reaction system along with the phosphogypsum raw material, and the solid mixed product is dissolved, filtered, recrystallized and filtered to obtain a calcium carbonate product and an ammonium sulfate product respectively; Preferably, the method further comprises the step of adding a phosphogypsum solvent; more preferably, the phosphogypsum solvent is selected from one or more of ammonium salts, organic alcohols, citric acid or citrates.

10. The method for preparing high-value calcium carbonate and ammonium sulfate from CO2 mineralized phosphogypsum at low cost according to claim 9, characterized in that: In step (4), the pH value of the solution is controlled to be 8-10 by controlling the amount of ammonia water introduced.

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