A method for preparing α-hemihydrate gypsum using desulfurized gypsum

Abstract

This application provides a method for preparing α-hemihydrate gypsum using desulfurized gypsum. The method involves mixing desulfurized gypsum with salt production effluent, then introducing air to allow the calcium carbonate and calcium chloride in the desulfurized gypsum to react with the effluent to form calcium sulfate, while simultaneously oxidizing calcium sulfite to calcium sulfate. After a period of time, the mixture is placed in an autoclave with a certain amount of crystallizing agent added and stirred thoroughly. After the reaction is complete, the mixture is immediately filtered, dried, and ground to obtain α-hemihydrate gypsum. The method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in this application can improve the conversion rate of desulfurized gypsum to α-hemihydrate gypsum and meets the requirements of a green economy, thus possessing significant economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of hemihydrate gypsum production, and more particularly to a method for preparing α-hemihydrate gypsum using desulfurized gypsum. Background Technology

[0002] In industrial production processes, desulfurization gypsum, as a byproduct of flue gas desulfurization in industries such as coal-fired power plants and steel smelting, has a huge output that is increasing year by year. The main component of desulfurization gypsum is calcium sulfate dihydrate, and it also contains certain amounts of impurities such as calcium carbonate and calcium chloride. The presence of these impurities limits the high-value utilization of desulfurization gypsum. How to effectively treat and utilize this desulfurization gypsum has become an important issue in the fields of environmental protection and resource recycling.

[0003] Traditionally, desulfurized gypsum has been primarily treated by stockpiling or simple processing for use as building materials, such as cement retarders and gypsum board raw materials. However, these applications have low added value and fail to fully realize the potential value of desulfurized gypsum. With the increasing demand for high-quality gypsum in the building materials industry, especially α-hemihydrate gypsum which has attracted widespread attention due to its excellent physical properties, processing performance, and environmental characteristics, the conversion of desulfurized gypsum into α-hemihydrate gypsum has become a research hotspot.

[0004] On the other hand, the mother liquor discharged from the salt-making industry contains high concentrations of sulfate ions and sodium chloride. Direct discharge of this liquor would not only cause environmental pollution but also waste its valuable components. How to effectively utilize this mother liquor is also an urgent problem to be solved in the fields of environmental protection and resource recycling. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing α-hemihydrate gypsum using desulfurized gypsum, so as to solve the problem of treating desulfurized gypsum and salt production discharge mother liquor, and to realize the recycling of resources and the high value of products.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a method for preparing α-hemihydrate gypsum using desulfurized gypsum, wherein the method for preparing α-hemihydrate gypsum using desulfurized gypsum includes the following steps:

[0007] S1. After mixing the desulfurized gypsum and the mother liquor discharged from the salt production in the reaction vessel, air is introduced to cause the calcium carbonate and calcium chloride in the desulfurized gypsum to react with the mother liquor discharged from the salt production to generate calcium sulfate, and at the same time, calcium sulfite is oxidized to calcium sulfate.

[0008] S2. Add the liquid obtained in the above steps to the autoclave, add a certain amount of crystallizing agent to the autoclave, and stir evenly;

[0009] S3. After the reaction is complete, filter the material obtained in the autoclave.

[0010] S4. The filtered solid material is dried and then ground to obtain α-hemihydrate gypsum.

[0011] In one embodiment, in step S1, when the desulfurized gypsum is mixed with the salt production discharge mother liquor, the calcium ion content in the calcium carbonate and calcium chloride of the desulfurized gypsum and the sulfate content of the salt production mother liquor are used as the ratio of 1 t of desulfurized gypsum to 2.5 m³ of the mother liquor. 3 -5.0m 3 Mix the mother liquor discharged from the salt production process; simultaneously, introduce 0.1-0.5m... 3 / h of air oxidizes the calcium sulfite in the desulfurized gypsum, removing impurities from the desulfurized gypsum; the reaction time is 1-2h.

[0012] In one embodiment, the crystallization agent is a mixed solution of hydrochloric acid and citric acid, and the mass ratio of hydrochloric acid to citric acid is 7:3; wherein the amount of hydrochloric acid and citric acid added is 0.01-0.05 wt% of the dry weight of the desulfurized gypsum.

[0013] In one embodiment, the autoclave is operated under the following conditions: temperature 130-150℃, pressure 1.3-1.5 MPa, and autoclaving time 5-8 hours.

[0014] In one embodiment, step S4 uses a steam tube dryer for drying, and the drying temperature is greater than 110°C.

[0015] In one embodiment, a portion of the filtrate obtained in step S3 is returned to the reactor via a pipeline.

[0016] In one embodiment, steps S3 and S4 are completed using a continuous filtration, drying, and grinding integrated device, which includes: a shell, a belt filter section, a drying section, and a grinding section.

[0017] The outer shell has a chamber, the top of the outer shell has a feed pipe, and the bottom side of the outer shell has a liquid storage tank. The feed pipe is connected to the output end of the autoclave, and the material to be filtered is fed into the chamber of the outer shell through the feed pipe.

[0018] The belt filter section is disposed in the cavity of the outer shell. The belt filter section is used to filter the material entering the cavity of the outer shell and transport the filtered solid material to the drying section. The filtrate falls into the storage tank below.

[0019] A drying section is provided on one side of the belt filter section, and the drying section is used to dry solid materials.

[0020] The grinding section is located below the drying section and is used to grind the solid material after the drying process.

[0021] In one embodiment, the belt filter includes:

[0022] A drive roller and a tension roller are rotatably disposed within the housing.

[0023] A first rotating power unit is installed on the housing, and the power output end of the first rotating power unit is connected to the drive roller.

[0024] A filter conveyor belt, which is mounted on the drive roller and the tension roller, and has filter holes on it;

[0025] Baffles are provided on both sides of the filter conveyor belt.

[0026] In one embodiment, the drying section includes:

[0027] The first air blade is located above the downstream end of the belt filter section, and the air outlet direction of the first air blade is opposite to the conveying direction of the belt filter section.

[0028] The second air blade is located below the downstream end of the belt filter section;

[0029] A drying plate is inclinedly disposed below the second air blade. The drying plate is hollow and has a heat source inlet and a heat source outlet. An external heat source is input into the drying plate through the heat source inlet, and the heat source outlet is connected to the first air blade and the second air blade through a pipe.

[0030] Solid materials are transported through the belt filter section and fall onto the drying plate.

[0031] In one embodiment, the grinding section includes a second rotating power unit, a grinding blade shaft, a filter screen, and a collection shell; the collection shell is disposed at the bottom of the drying section; the filter screen is disposed inside the collection shell, and the grinding blade shaft is located inside the filter screen and rotatably disposed on the outer shell; the power output end of the second rotating power unit is connected to the grinding blade shaft.

[0032] The above-described technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0033] The method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in this invention achieves effective conversion and recycling of two industrial wastes by using desulfurized gypsum and salt production wastewater as raw materials, avoiding resource waste and improving resource utilization efficiency. This method avoids the direct discharge of desulfurized gypsum and salt production wastewater, reducing environmental pollution and aligning with green and environmentally friendly production concepts, thus helping to alleviate environmental pressure. Furthermore, converting desulfurized gypsum into high-quality α-hemihydrate gypsum significantly increases the added value of the product, broadens the application fields of desulfurized gypsum, and increases the economic benefits for enterprises.

[0034] Furthermore, this invention proposes a novel process for preparing α-hemihydrate gypsum from desulfurized gypsum. This process accelerates the reaction process and improves the conversion rate and conversion efficiency by introducing the mother liquor discharged from salt production and a phase transformation promoter, thus providing a new technical approach for the high-value utilization of desulfurized gypsum. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 A process flow diagram of the method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the structure of the continuous filtration, drying and grinding integrated device provided in an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the back of the continuous filtration, drying, and grinding integrated device provided in an embodiment of the present invention.

[0039] The labels for the various figures are as follows:

[0040] 1. Outer shell; 11. Feed pipe; 12. Liquid storage tank; 21. Drive roller; 22. Tensioning roller; 23. First rotating power unit; 24. Filter conveyor belt; 31. First air blade; 32. Second air blade; 33. Drying plate; 41. Second rotating power unit; 42. Grinding knife shaft; 43. Filter screen; 44. Collection shell; 241. Baffle. Detailed Implementation

[0041] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0042] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0044] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] Please see Figure 1 This application provides a method for preparing α-hemihydrate gypsum using desulfurized gypsum, specifically including the following steps:

[0046] S1. After mixing the desulfurized gypsum and the mother liquor discharged from the salt production in the reaction vessel, air is introduced to cause the calcium carbonate and calcium chloride in the desulfurized gypsum to react with the mother liquor discharged from the salt production to generate calcium sulfate, and at the same time, calcium sulfite is oxidized to calcium sulfate.

[0047] S2. Add the liquid obtained in the above steps to the autoclave, add a certain amount of crystallizing agent to the autoclave, and stir evenly;

[0048] S3. After the reaction is complete, filter the material obtained in the autoclave.

[0049] S4. The filtered solid material is dried and then ground to obtain α-hemihydrate gypsum.

[0050] The method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in this application has the following advantages:

[0051] (1) The process of this invention is simple and can be industrialized.

[0052] (2) By utilizing the salt-containing characteristics of the mother liquor, the solubility of desulfurized gypsum is increased, thereby increasing the conversion rate of desulfurized gypsum to α-hemihydrate gypsum.

[0053] (3) The sulfate ions in the mother liquor discharged from the salt production process are used to further react with the calcium carbonate and calcium chloride in the desulfurized gypsum, which not only removes impurities from the desulfurized gypsum, but also increases the yield of α-hemihydrate gypsum.

[0054] (4) It can not only make high-value use of industrial by-product desulfurization gypsum, but also reduce the amount of salt production mother liquor discharged, thus solving the two industrial wastes in one fell swoop, without generating new pollution, which is very much in line with the green economy.

[0055] In one embodiment, in step S1, when the desulfurized gypsum is mixed with the salt production discharge mother liquor, the calcium ion content in the calcium carbonate and calcium chloride of the desulfurized gypsum and the sulfate content of the salt production mother liquor are used as the ratio of 1 t of desulfurized gypsum to 2.5 m³ of the mother liquor. 3 -5.0m 3 Mix the mother liquor discharged from the salt production process; simultaneously, introduce 0.1-0.5m... 3 / h of air oxidizes the calcium sulfite in the desulfurized gypsum, removing impurities from the desulfurized gypsum; the reaction time is 1-2h.

[0056] In one embodiment, the crystallization agent is a mixed solution of hydrochloric acid and citric acid, and the mass ratio of hydrochloric acid to citric acid is 7:3; wherein the amount of hydrochloric acid and citric acid added is 0.01-0.05 wt% of the dry weight of the desulfurized gypsum.

[0057] In one embodiment, the autoclave is operated under the following conditions: temperature 130-150℃, pressure 1.3-1.5 MPa, and autoclaving time 5-8 hours.

[0058] In one embodiment, step S4 uses a steam tube dryer for drying, and the drying temperature is greater than 110°C.

[0059] In one embodiment, a portion of the filtrate obtained in step S3 is returned to the reactor via a pipeline. This partial return of filtrate from step S3 replenishes the water in the reactor, further dissolving the calcium sulfate produced in the reaction. Furthermore, by utilizing the water in the reactor from the filtered water, the filtered water is reused, conserving water resources.

[0060] The following are examples of the method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in this application, under different production conditions:

[0061] Example 1: 1 kg of desulfurized gypsum was mixed with 4 L of salt production wastewater, and air was introduced at a rate of 0.5 L / h. The mixture was stirred and reacted in a reactor for 1 h. After the reaction, the mixture was transferred to an autoclave, 0.02 wt% of a crystallizing agent was added, and the mixture was heated to 135 °C and reacted at 1.4 MPa for 6 h. After filtration, the solid was rapidly dried in a dryer to obtain 946 g of α-hemihydrate gypsum. Testing showed that its whiteness was 96%, its compressive strength reached 53 MPa, and its purity was 96%.

[0062] Example 2: 1 kg of desulfurized gypsum was mixed with 3.8 L of salt production wastewater, and air was introduced at a rate of 0.5 L / h. The mixture was stirred and reacted in a reactor for 1 h. After the reaction, the mixture was transferred to an autoclave, 0.02 wt% of a crystallizing agent was added, and the mixture was heated to 145 °C and reacted at 1.4 MPa for 6 h. After filtration, the solid was rapidly dried in a dryer to obtain 937 g of α-hemihydrate gypsum. Testing showed that its whiteness was 90%, its compressive strength reached 52 MPa, and its purity was 97%.

[0063] Example 3: 1 kg of desulfurized gypsum was mixed with 4 L of salt production wastewater, and air was introduced at a rate of 0.5 L / h. The mixture was stirred and reacted in a reactor for 1 h. After the reaction, the mixture was transferred to an autoclave, 0.03 wt% of a crystallizing agent was added, and the mixture was heated to 135 °C and reacted at 1.4 MPa for 6 h. After filtration, the solid was rapidly dried in a dryer to obtain 951 g of α-hemihydrate gypsum. Testing showed that its whiteness was 93%, its compressive strength reached 55 MPa, and its purity was 96%.

[0064] Example 4: 1 kg of desulfurized gypsum was mixed with 4 L of salt production wastewater, and air was introduced at a rate of 0.5 L / h. The mixture was stirred and reacted in a reactor for 1 h. After the reaction, the mixture was transferred to an autoclave, 0.02 wt% of a crystallizing agent was added, and the mixture was heated to 135 °C and reacted at 1.4 MPa for 7 h. After filtration, the solid was rapidly dried in a dryer to obtain 957 g of α-hemihydrate gypsum. Testing showed that its whiteness was 95%, its compressive strength reached 56 MPa, and its purity was 97%.

[0065] In summary, the method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in this application yields α-type calcium sulfate with high purity, fully developed crystal form, and superior performance, namely, a whiteness of 85%, a purity of ≥95%, and a compressive strength of ≥50 MPa.

[0066] Please see Figure 2-3In one embodiment, steps S3 and S4 are completed using a continuous filtration, drying, and grinding integrated device. This device includes: a housing 1, a belt filter section, a drying section, and a grinding section. The housing 1 contains a chamber, with an inlet pipe 11 at its top and a storage tank 12 on one side of its bottom. The inlet pipe 11 is connected to the output end of an autoclave, allowing the material to be filtered to enter the chamber of the housing 1 through the inlet pipe 11. The belt filter section is located within the chamber of the housing 1 and filters the material entering the chamber, transporting the filtered solid material to the drying section. The filtrate falls into the storage tank 12 below. The drying section is located to one side of the belt filter section and dries the solid material. The grinding section is located below the drying section and grinds the dried solid material.

[0067] A continuous filtration, drying, and grinding integrated device is used to filter, dry, and grind materials in the autoclave. Materials (including a mixture of solid calcium sulfate hemihydrate and liquid) are continuously fed into the outer shell 1 through the feed pipe 11. First, a belt filter filters the material. The filtered solid material (calcium sulfate hemihydrate) is automatically conveyed to a drying section on one side, while the filtrate flows downwards into a storage tank 12. After drying in the drying section, the solid material enters the grinding section for grinding, resulting in powdered α-hemihydrate gypsum. This continuous filtration, drying, and grinding integrated device enables continuous automatic processing of materials in the autoclave, eliminating the need for manual material handling and significantly improving efficiency, making it suitable for large-scale continuous production.

[0068] Optionally, an outlet can be provided at the bottom of the storage tank 12 in the drying section, and a reflux pipe can be provided at the outlet position. The other end of the reflux pipe is connected to the reaction vessel, and a reflux pump is installed on the reflux pipe to return the filtrate to the reaction vessel.

[0069] In one embodiment, the belt filter section includes a drive roller 21, a tension roller 22, and a filter conveyor belt 24. A first rotational power unit 23 is rotatably disposed within the housing 1, the drive roller 21 and the tension roller 22 are mounted on the housing 1, and the power output end of the first rotational power unit 23 is connected to the drive roller 21; the filter conveyor belt 24 is mounted on the drive roller 21 and the tension roller 22, and the filter conveyor belt 24 is provided with filter holes.

[0070] During filtration, the first rotating power unit 23 (specifically, a combination of a motor and a reducer) is activated, causing the drive roller 21 to rotate, which in turn drives the filter conveyor belt 24. Material enters the outer casing 1 from the feed pipe 11 and falls onto the filter conveyor belt 24 (specifically, the upstream end of the filter conveyor belt 24). Because the filter conveyor belt 24 has filter holes, it can filter out the hemihydrate gypsum solids. The filtrate flows downwards through the filter conveyor belt 24 into the storage tank 12 below, thus separating the hemihydrate gypsum solids from the filtrate. Simultaneously, the filter conveyor belt 24 transfers the hemihydrate gypsum solids to the downstream end, allowing them to enter the drying section, thus achieving the purpose of filtration. Since the filter conveyor belt 24 is always in operation, the hemihydrate gypsum solids on it are promptly delivered to the drying section, preventing accumulation and blockage that would affect the continuous filtration efficiency of the filter conveyor belt 24.

[0071] In addition, the uniformly operating filter conveyor belt 24 can feed the hemihydrate gypsum solids into the drying section in a relatively uniform and continuous manner. While ensuring the material supply for subsequent drying and grinding processes, it can also reduce the burden on the drying section, improve the uniformity and effect of drying, and avoid the phenomenon that the drying section cannot dry the hemihydrate gypsum solids uniformly and effectively due to the concentrated and clustered input of hemihydrate gypsum solids into the drying section.

[0072] Optionally, baffles 241 are provided on both sides of the filter conveyor belt 24. The baffles 241 prevent the hemihydrate gypsum solids from leaking from both sides of the filter conveyor belt 24, ensuring that the hemihydrate gypsum solids can smoothly enter the drying section under the conveying of the filter conveyor belt 24.

[0073] Optionally, the belt filter section is inclined, with the inclination direction from downstream (near the drying section end) to upstream (near the feed pipe 11 end) downward. This allows the residual filtrate on the filter conveyor belt 24 to move downward along the inclined surface of the filter conveyor belt 24 under its own gravity. At the same time, the linear speed of the filter conveyor belt 24 is controlled at 4-5 m / min, thereby preventing the filtrate from entering the drying section along the filter conveyor belt 24 and increasing the drying burden of the drying section.

[0074] In one embodiment, the drying section includes a first air blade 31, a second air blade 32, and a drying plate 33. The first air blade 31 is positioned above the downstream end of the belt filter section, and the air outlet direction of the first air blade 31 is opposite to the conveying direction of the belt filter section. The second air blade 32 is positioned below the downstream end of the belt filter section. The drying plate 33 is inclinedly positioned below the second air blade 32. The drying plate 33 is hollow and has a heat source inlet and a heat source outlet. An external heat source is input into the drying plate 33 through the heat source inlet, and the heat source outlet is connected to the first air blade 31 and the second air blade 32 through a pipe. Solid materials fall onto the drying plate 33 after being transported by the belt filter section.

[0075] Before drying, an external heating device (such as a boiler) generates a heat source (specifically, hot steam or hot air), which is introduced into the drying plate 33 through the heat source inlet, raising the temperature of the drying plate 33. The drying plate 33 is made of a metal material with good thermal conductivity, such as iron or aluminum. After the heat source fills the drying plate 33, it is output from the heat source outlet and introduced into the first air blade 31 and the second air blade 32 through pipes to supply the first air blade 31 and the second air blade 32, improving the utilization rate of the heat source. When the belt filter transports the hemihydrate calcium sulfate solid to below the first air blade 31, the hot air jet from the first air blade 31 dries the moisture (filtrate) on the surface of the hemihydrate calcium sulfate solid and the belt filter, preventing the moisture on the surface of the belt filter from falling onto the drying plate 33 below, and performing preliminary drying of the hemihydrate calcium sulfate solid. Then, after the belt filter transfers the hemihydrate calcium sulfate solid to above the drying plate 33, the hemihydrate calcium sulfate solid falls downward from the belt filter. Until it passes the location of the second air blade 32, the hot airflow emitted by the second air blade 32 can dry the hemihydrate calcium sulfate solid again. Furthermore, the lateral airflow causes the hemihydrate calcium sulfate solid to move downwards while simultaneously moving horizontally away from the second air blade 32 (e.g., Figure 2 (Moving from center to left), and the smaller volume of calcium sulfate hemihydrate solid is lighter than the larger volume of calcium sulfate hemihydrate solid, resulting in a greater horizontal movement of the smaller volume calcium sulfate solid. This separates the larger volume calcium sulfate solid from the smaller volume calcium sulfate solid, causing the smaller volume calcium sulfate solid to fall onto the drying plate 33 at a lower position than the larger volume calcium sulfate solid. Consequently, the larger volume calcium sulfate solid travels a longer distance on the drying plate 33, thus receiving a longer drying time, ensuring a better drying effect. Conversely, the smaller volume calcium sulfate solid travels a shorter distance on the drying plate 33, resulting in a shorter drying time, thus preventing over-drying and decomposition.

[0076] Therefore, the drying unit provided in this embodiment dries the calcium sulfate hemihydrate solid three times in succession to ensure the drying effect. Furthermore, it can match the appropriate drying time according to the different sizes of the calcium sulfate hemihydrate solid, thereby avoiding the phenomenon of over-drying and decomposition of the calcium sulfate hemihydrate solid.

[0077] Optionally, a temperature sensor can be installed on the drying surface of the drying plate 33 to monitor the temperature of the drying plate 33 in real time, and control the temperature and flow rate of the input heat source based on the temperature of the drying plate 33.

[0078] In one embodiment, the grinding section includes a second rotational power unit 41, a grinding blade shaft 42, a filter screen 43, and a collection shell 44; the collection shell 44 is disposed at the bottom of the drying section; the filter screen 43 is disposed inside the collection shell 44, and the grinding blade shaft 42 is located inside the filter screen 43 and is rotatably disposed on the outer shell 1; the power output end of the second rotational power unit 41 is connected to the grinding blade shaft 42.

[0079] After being dried in the drying section, the solid calcium sulfate hemihydrate enters the filter screen 43 (the filter screen 43 is cylindrical with an inlet on one side). The second rotating power unit 41 (specifically, a motor) drives the grinding blade shaft 42 to rotate. The rotating grinding blade shaft 42 breaks down and grinds the solid calcium sulfate hemihydrate into powder. Calcium sulfate hemihydrate that meets the particle size requirements can pass through the filter screen 43 and enter the space between the collection shell 44 and the filter screen 43. The calcium sulfate hemihydrate powder is collected by the collection shell 44 and output from the outlet, thus obtaining powdered calcium sulfate hemihydrate.

[0080] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing α-hemihydrate gypsum using desulfurized gypsum, characterized in that, The method for preparing α-hemihydrate gypsum using desulfurized gypsum includes the following steps: S1. Desulfurized gypsum is mixed with salt-making effluent containing high concentrations of sulfate ions and sodium chloride in a reaction vessel. Air is then introduced to cause the calcium carbonate and calcium chloride in the desulfurized gypsum to react with the effluent to form calcium sulfate, while simultaneously oxidizing calcium sulfite to calcium sulfate. Based on the calcium ion content in the calcium carbonate and calcium chloride of the desulfurized gypsum and the sulfate content in the salt-making effluent, the two are mixed at a ratio of 1 t of desulfurized gypsum to 2.5 m³-5.0 m³ of salt-making effluent. Simultaneously, air is introduced at a rate of 0.1-0.5 m³ / h to oxidize the calcium sulfite in the desulfurized gypsum and remove impurities. The reaction time is 1-2 hours. S2. Add the overall product obtained in the above steps into an autoclave, add a certain amount of crystallizing agent into the autoclave, and stir evenly; S3. After the reaction is complete, filter the material obtained in the autoclave. S4. Dry the filtered solid material and then grind it to obtain α-hemihydrate gypsum. The crystallization agent is a mixed solution of hydrochloric acid and citric acid, and the mass ratio of hydrochloric acid to citric acid is 7:3; wherein the amount of hydrochloric acid and citric acid added is 0.01-0.05 wt% of the dry weight of the desulfurized gypsum.

2. The method for preparing α-hemihydrate gypsum using desulfurized gypsum according to claim 1, characterized in that: The autoclave is operated under the following conditions: temperature 130-150℃, pressure 1.3-1.5 MPa, and autoclaving time 5-8 h.

3. The method for preparing α-hemihydrate gypsum using desulfurized gypsum according to claim 1, characterized in that: In step S4, a steam tube dryer is used for drying, and the drying temperature is greater than 110°C.

4. The method for preparing α-hemihydrate gypsum using desulfurized gypsum according to claim 1, characterized in that: Part of the filtrate obtained in step S3 is returned to the reactor through a pipeline.

5. The method for preparing α-hemihydrate gypsum using desulfurized gypsum according to claim 1, characterized in that, Steps S3 and S4 are completed using a continuous filtration, drying, and grinding integrated device, which includes: a shell, a belt filter section, a drying section, and a grinding section. The outer shell has a chamber, the top of the outer shell has a feed pipe, and the bottom side of the outer shell has a liquid storage tank. The feed pipe is connected to the output end of the autoclave, and the material to be filtered is fed into the chamber of the outer shell through the feed pipe. The belt filter section is disposed in the cavity of the outer shell. The belt filter section is used to filter the material entering the cavity of the outer shell and transport the filtered solid material to the drying section. The filtrate falls into the storage tank below. A drying section is provided on one side of the belt filter section, and the drying section is used to dry solid materials. The grinding section is located below the drying section and is used to grind the solid material after the drying process.

6. The method for preparing α-hemihydrate gypsum using desulfurized gypsum according to claim 5, characterized in that, The belt filter section includes: A drive roller and a tension roller are rotatably disposed within the housing. A first rotating power unit is installed on the housing, and the power output end of the first rotating power unit is connected to the drive roller. A filter conveyor belt, which is mounted on the drive roller and the tension roller, and has filter holes on it; Baffles are provided on both sides of the filter conveyor belt.

7. A method for preparing α-hemihydrate gypsum using desulfurized gypsum according to claim 5, characterized in that, The drying section includes: The first air blade is located above the downstream end of the belt filter section, and the air outlet direction of the first air blade is opposite to the conveying direction of the belt filter section. The second air blade is located below the downstream end of the belt filter section; A drying plate is inclinedly disposed below the second air blade. The drying plate is hollow and has a heat source inlet and a heat source outlet. An external heat source is input into the drying plate through the heat source inlet, and the heat source outlet is connected to the first air blade and the second air blade through a pipe. Solid materials are transported through the belt filter section and fall onto the drying plate.

8. A method for preparing α-hemihydrate gypsum using desulfurized gypsum according to claim 5, characterized in that: The grinding section includes a second rotating power unit, a grinding blade shaft, a filter screen, and a collection shell; the collection shell is disposed at the bottom of the drying section; the filter screen is disposed inside the collection shell, and the grinding blade shaft is located inside the filter screen and rotatably disposed on the outer shell; The power output end of the second rotating power unit is connected to the grinding blade shaft.

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