Phosphogypsum and its modification methods, high-strength water-resistant paper-faced gypsum board and its preparation methods

Abstract

This application provides a phosphogypsum and its modification method, as well as a high-strength, water-resistant paper-faced gypsum board and its preparation method. The phosphogypsum modification method includes: drying the phosphogypsum to be modified to constant weight; mixing aluminum sulfate with the dried phosphogypsum, followed by microwave calcination, grinding, and aging to obtain modified anhydrous phosphogypsum. This phosphogypsum modification method can effectively reduce the content of soluble impurities in phosphogypsum, and the process is simple.

Description

Technical Field

[0001] This application relates to, but is not limited to, the field of building materials, and particularly to a phosphogypsum and its modification method, a high-strength water-resistant paper-faced gypsum board and its preparation method. Background Technology

[0002] Desulfurized gypsum, with its main components similar to natural gypsum and a higher calcium sulfate content, can replace natural gypsum in the production of gypsum board and wall materials. However, current desulfurized gypsum products still suffer from low mechanical properties and poor water resistance, resulting in low utilization in the construction field and hindering their economic benefits. Some desulfurized gypsum is stockpiled and landfilled, which will have a long-term adverse impact on the ecological environment. Therefore, improving the overall performance of desulfurized gypsum to increase its utilization rate in the construction field is crucial. Phosphogypsum, similarly a solid waste with potential application value, contains impurities such as soluble phosphorus, fluorine, and eutectic phosphorus. These impurities delay hydration, affecting the performance of phosphogypsum products and thus limiting its application. Therefore, improving and researching the pretreatment process for phosphogypsum is currently a key focus.

[0003] Although there are numerous studies both domestically and internationally on improving the strength of gypsum board, the commonly used methods mainly include directly introducing additives such as fibers, reinforcing agents, and toughening agents to enhance the performance of gypsum board, or directly compounding it with other inorganic cementitious materials to improve the density of the matrix structure, thereby increasing the strength and toughness of the gypsum board. However, due to the large variety of components involved, the preparation process is relatively complex, and the finished product is also expensive. Summary of the Invention

[0004] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0005] This application provides a phosphogypsum and its modification method, a high-strength water-resistant paper-faced gypsum board and its preparation method. The phosphogypsum modification method can effectively reduce the content of soluble impurities in phosphogypsum, and the process is simple. The paper-faced gypsum board has high strength and good water resistance. The raw materials and processes for preparation are simple, and it can realize the resource utilization of desulfurized gypsum and phosphogypsum.

[0006] This application provides a method for modifying phosphogypsum, the modification method comprising:

[0007] The phosphogypsum to be modified was dried to constant weight;

[0008] Aluminum sulfate was mixed with phosphogypsum dried to constant weight, microwaved, ground, and aged to obtain modified anhydrous phosphogypsum.

[0009] In the embodiments of this application, the microwave calcination temperature can be 750°C to 850°C, the microwave calcination time can be 10 min to 15 min, the microwave calcination power can be 3.48 kW to 3.52 kW, and the microwave calcination frequency can be 2445 Hz to 2455 Hz.

[0010] In the embodiments of this application, the mass ratio of aluminum sulfate to phosphogypsum dried to constant weight can be from 0.1:99.9 to 0.5:99.5.

[0011] This application also provides a modified anhydrous phosphogypsum, which is prepared by the phosphogypsum modification method provided in the above application embodiment. The modified anhydrous phosphogypsum contains ≥90% type II anhydrous gypsum and has a pH value in the range of 6 to 8.

[0012] This application provides a high-strength, water-resistant paper-faced gypsum board, which comprises 100 parts by weight of gypsum clinker, 0.1 to 0.5 parts by weight of inorganic salt whiskers, 0.4 to 0.7 parts by weight of water-reducing agent, and 0.1 to 0.5 parts by weight of retarder;

[0013] The gypsum clinker, by mass percentage, comprises 80% to 90% desulfurized gypsum clinker and 10% to 20% of the modified anhydrous phosphogypsum provided in the above embodiments of this application.

[0014] In the embodiments of this application, the inorganic salt whiskers may be selected from any one or more of calcium carbonate whiskers and anhydrous calcium sulfate whiskers.

[0015] In the embodiments of this application, the aspect ratio of the inorganic salt whiskers can be from 30:1 to 80:1.

[0016] In the embodiments of this application, the water-reducing agent may be selected from any one or more of polycarboxylate superplasticizers, melamine-based water-reducing agents, and naphthalene-based water-reducing agents.

[0017] In the embodiments of this application, the retarder may be selected from any one or more of sodium citrate and protein-based retarders.

[0018] This application also provides a method for preparing the high-strength, water-resistant paper-faced gypsum board as described above, the method comprising:

[0019] Dissolve the water-reducing agent and retarder in part of the water, add inorganic salt whiskers and disperse to obtain an additive solution;

[0020] Desulfurized gypsum clinker, modified anhydrous phosphogypsum, the aforementioned additive solution, and water are mixed and ultrasonically vibrated to control the water-to-gypsum ratio at 0.4 to 0.5, thereby obtaining a slurry.

[0021] The slurry is guided onto the lower protective paper, and the upper protective paper is laid on top. The mixture is then shaped and dried to obtain the high-strength, water-resistant paper-faced gypsum board.

[0022] In the embodiments of this application, the preparation method may further include: preparing the modified anhydrous phosphogypsum using the phosphogypsum modification method provided in the above embodiments of this application before mixing the desulfurized gypsum clinker, the modified anhydrous phosphogypsum, the additive solution and water.

[0023] The technical solution of this application embodiment can achieve the following beneficial effects:

[0024] (1) Aluminum sulfate is used as a functional additive and mixed evenly with phosphogypsum in a certain proportion. Combined with microwave calcination and grinding processes, impurities such as soluble phosphorus, soluble fluorine and eutectic phosphorus in phosphogypsum are dissolved or transformed into insoluble precipitates, providing more channels for impurity dissolution and making the phosphogypsum calcined evenly. Among them, aluminum sulfate can transform soluble impurities into insoluble impurities, removing soluble impurities to a greater extent. In addition, the microwave calcination technology used has the following advantages compared with the traditional sintering technology: microwave heating has the characteristics of uniform heat transfer, fast heating speed, short sintering time and safety and no pollution, which has better efficiency.

[0025] (2) Microwave-calcined anhydrous phosphogypsum can act as a heterogeneous nucleus to promote the hydration of desulfurized gypsum. Some of the anhydrous phosphogypsum that does not participate in the reaction fills the pores of the matrix and optimizes the crystal structure of desulfurized gypsum. The modified anhydrous phosphogypsum contains fewer impurities and has hydration activity. Some of the anhydrous phosphogypsum can participate in the hydration reaction. Inorganic whiskers can be used to modify desulfurized gypsum to increase the effective bonding points between crystals in the matrix, bridge and fill pores, and disperse stress. The combined effect of whiskers and modified anhydrous phosphogypsum can synergistically modify and optimize the internal crystal structure of desulfurized gypsum.

[0026] (3) Desulfurized gypsum and phosphogypsum are both industrial by-products. Currently, their utilization rate is low, and it is impossible to effectively obtain their added value, which causes environmental pollution and increases space pressure. The paper-faced gypsum board of this application mainly includes components such as desulfurized gypsum and phosphogypsum. The microwave-calcined anhydrous phosphogypsum is used in combination with desulfurized gypsum, which can greatly reduce the cost of gypsum board while improving the performance of gypsum products. While increasing its resource utilization rate, it can reduce the pressure on the environment and has the economic benefits of energy saving, environmental protection and low cost.

[0027] (4) The high-strength water-resistant paper-faced gypsum board of this application has the characteristics of low cost and green environmental protection, and can be widely used in the field of interior decoration and renovation, or as gypsum board and gypsum block.

[0028] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application may be realized and obtained by means of the methods described in the description. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in detail below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other.

[0030] This application provides a method for modifying phosphogypsum, the modification method comprising:

[0031] The phosphogypsum to be modified was dried to constant weight;

[0032] Aluminum sulfate was mixed with phosphogypsum dried to constant weight, microwaved, ground, and aged to obtain modified anhydrous phosphogypsum.

[0033] In the embodiments of this application, the microwave calcination temperature can be from 750°C to 850°C, for example, it can be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C or 850°C.

[0034] In the embodiments of this application, the microwave calcination time can be 10 min to 15 min, for example, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min.

[0035] In the embodiments of this application, the power of the microwave calcination can be from 3.48kW to 3.52kW, for example, it can be 3.48kW, 3.5kW or 3.52kW.

[0036] In the embodiments of this application, the frequency of microwave calcination can be from 2445Hz to 2455Hz, for example, it can be 2445Hz, 2450Hz or 2455Hz.

[0037] In the embodiments of this application, the mass ratio of aluminum sulfate to phosphogypsum dried to constant weight can be from 0.1:99.9 to 0.5:99.5, for example, it can be 0.1:99.9, 0.2:99.8, 0.3:99.7, 0.4:99.6 or 0.5:99.5.

[0038] In the embodiments of this application, the temperature at which the phosphogypsum to be modified is dried to constant weight can be 40°C to 50°C, for example, 45°C.

[0039] In the embodiments of this application, the grinding time can be 3 to 8 minutes until the average particle size of the modified anhydrous phosphogypsum is 30 μm to 40 μm.

[0040] In the embodiments of this application, the aging time can be from 12h to 24h, for example, it can be 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0041] In embodiments of this application, the phosphogypsum modification method may include:

[0042] The phosphogypsum to be modified was dried at 40°C to 50°C to constant weight;

[0043] Aluminum sulfate and phosphogypsum dried to constant weight are mixed evenly at a mass ratio of 0.1:99.9 to 0.5:99.5. The mixture is spread evenly and microwaved in a microwave oven with a power of 3.48kW to 3.52kW and a frequency of 2445Hz to 2455Hz for 10 to 15 minutes. The temperature in the microwave oven is controlled within the range of 750℃ to 850℃ during the microwave calcination process.

[0044] The phosphogypsum is removed from the microwave heating furnace, ground for 3 to 8 minutes, and aged for 12 to 24 hours to obtain modified anhydrous phosphogypsum with an average particle size of 30 μm to 40 μm.

[0045] This application also provides a modified anhydrous phosphogypsum, which is prepared by the phosphogypsum modification method provided in the above application.

[0046] In the embodiments of this application, the content of type II anhydrous gypsum in the modified anhydrous phosphogypsum can be ≥90%, for example, it can be 90%, 91%, 92%, 93%, 94% or 95%.

[0047] In the embodiments of this application, the pH value of the modified anhydrous phosphogypsum is in the range of 6 to 8, for example, it can be 6, 6.5, 7, 7.5 or 8.

[0048] In the embodiments of this application, the average particle size of the modified anhydrous phosphogypsum can be 30 μm to 40 μm.

[0049] This application provides a high-strength, water-resistant paper-faced gypsum board, which comprises 100 parts by weight of gypsum clinker, 0.1 to 0.5 parts by weight of inorganic salt whiskers, 0.4 to 0.7 parts by weight of water-reducing agent, and 0.1 to 0.5 parts by weight of retarder;

[0050] The gypsum clinker, by mass percentage, comprises 80% to 90% desulfurized gypsum clinker and 10% to 20% of the modified anhydrous phosphogypsum provided in the above embodiments of this application.

[0051] In the embodiments of this application, the high-strength water-resistant paper-faced gypsum board may be composed of the following components: 100 parts by weight of gypsum clinker, 0.1 to 0.5 parts by weight of inorganic salt whiskers, 0.4 to 0.7 parts by weight of water-reducing agent, and 0.1 to 0.5 parts by weight of retarder;

[0052] The gypsum clinker, by mass percentage, consists of 80% to 90% desulfurized gypsum clinker and 5% to 20% modified anhydrous phosphogypsum, wherein the modified anhydrous phosphogypsum is the modified anhydrous phosphogypsum provided in the above embodiments of this application.

[0053] In embodiments of this application, the high-strength, water-resistant paper-faced gypsum board may include:

[0054] 100 parts by weight of gypsum clinker, wherein the gypsum clinker comprises 80 to 90 parts by weight of desulfurized gypsum clinker and 10 to 20 parts by weight of modified anhydrous phosphogypsum. For example, 100 parts by weight of the gypsum clinker may include 80, 82, 84, 86, 88, or 90 parts by weight of desulfurized gypsum clinker, and also include 20, 18, 16, 14, 12, or 10 parts by weight of the modified anhydrous phosphogypsum.

[0055] 0.1 to 0.5 parts by weight of inorganic salt whiskers, for example, may include 0.1, 0.2, 0.3, 0.4, or 0.5 parts by weight of inorganic salt whiskers;

[0056] 0.4 to 0.7 parts by weight of water-reducing agent, for example, may include 0.4, 0.5, 0.6 or 0.7 parts by weight of water-reducing agent;

[0057] 0.1 to 0.5 parts by weight of retarder, for example, may include 0.1, 0.2, 0.3, 0.4 or 0.5 parts by weight of retarder.

[0058] In the embodiments of this application, the average particle size of the desulfurized gypsum clinker can be from 20 μm to 60 μm, and the BET specific surface area can be 1.253 m². 2 / g to 1.582m 2 / g, with a purity of 95% to 98%.

[0059] In the embodiments of this application, the inorganic salt whiskers may be selected from any one or more of calcium carbonate whiskers and anhydrous calcium sulfate whiskers.

[0060] In the embodiments of this application, the aspect ratio of the inorganic salt whiskers can be from 30:1 to 80:1, for example, it can be 30:1, 40:1, 50:1, 60:1, 70:1 or 80:1.

[0061] In the embodiments of this application, the purity of the inorganic salt whiskers can be 95% to 98%.

[0062] In the embodiments of this application, the water-reducing agent may be selected from any one or more of polycarboxylate superplasticizers, melamine-based water-reducing agents, and naphthalene-based water-reducing agents.

[0063] In the embodiments of this application, the solid content of the water-reducing agent can be greater than 98%, and the water reduction rate can be greater than 14%.

[0064] In the embodiments of this application, the retarder may be selected from any one or more of sodium citrate and protein-based retarders.

[0065] This application also provides a method for preparing high-strength, water-resistant paper-faced gypsum board as described above, including:

[0066] Dissolve the water-reducing agent and retarder in part of the water, add inorganic salt whiskers and disperse to obtain an additive solution;

[0067] Desulfurized gypsum clinker, modified anhydrous phosphogypsum, the aforementioned additive solution, and water are mixed and ultrasonically vibrated to control the water-to-gypsum ratio at 0.4 to 0.5, thereby obtaining a slurry.

[0068] The slurry is guided onto the lower protective paper, and the upper protective paper is laid on top. The mixture is then shaped and dried to obtain the high-strength, water-resistant paper-faced gypsum board.

[0069] In the embodiments of this application, the inorganic salt whiskers can be dispersed by ultrasonic dispersion.

[0070] The method for preparing high-strength water-resistant paper-faced gypsum board according to the embodiments of this application can use ultrasonic vibration to uniformly disperse each component in the slurry, while breaking the desulfurized gypsum crystals to obtain finer, more irregular crystal forms, accelerating the dissolution rate of hemihydrate calcium sulfate, improving the hydration performance of desulfurized gypsum, and obtaining high-strength gypsum board products; moreover, the process is simple and the production cost is low.

[0071] In the embodiments of this application, the preparation method may further include: preparing the modified anhydrous phosphogypsum using the phosphogypsum modification method provided in the above embodiments of this application before mixing the desulfurized gypsum clinker, the modified anhydrous phosphogypsum, the additive solution and water.

[0072] In the embodiments of this application, the drying temperature of the paper-faced gypsum board can be from 150°C to 180°C. For example, the drying of the paper-faced gypsum board may include: a first drying stage: the drying temperature can be from 150°C to 200°C, and the drying time can be from 0.5h to 1h; a second drying stage: the drying temperature can be from 100°C to 130°C, and the drying time can be from 0.5h to 1.5h; a third drying stage: the drying temperature can be from 45°C to 60°C, and the drying time can be from 12h to 36h.

[0073] The technical solution of this application will be described in detail below with reference to the embodiments.

[0074] In the following examples, the average particle size of the desulfurized gypsum clinker is 30 μm, and the BET specific surface area is 1.264 m². 2 / g, purity 98%; the modified anhydrous phosphogypsum used contains approximately 95% type II anhydrous gypsum, has a pH of 7.5, and an average particle size of 30μm; the whiskers used are anhydrous calcium sulfate whiskers with an aspect ratio of 30:1 to 80:1 and a purity of 98%; the water-reducing agent used is ZY-HPWR-S type polycarboxylate high-efficiency water-reducing agent produced by Hunan Zhongyan Building Materials, with a solid content of 99% and a water reduction rate of 15%; the retarder used is HN-302 type protein retarder produced by Hebei Xietong Chemical Co., Ltd.; the drying temperature of the paper-faced gypsum board is 160℃, dried to constant weight.

[0075] Example 1

[0076] The high-strength water-resistant paper-faced gypsum board of this embodiment is prepared from the following raw materials: 90 parts by weight of desulfurized gypsum clinker, 10 parts by weight of modified anhydrous phosphogypsum, 0.3 parts by weight of whiskers (calcium carbonate whiskers with an aspect ratio of 30:1), 0.4 parts by weight of water-reducing agent, 0.15 parts by weight of retarder, and a water-to-gypsum ratio of 0.45.

[0077] The preparation process of the high-strength water-resistant paper-faced gypsum board in this embodiment includes:

[0078] (1) Dry the phosphogypsum to be modified at 45°C to constant weight; mix aluminum sulfate and the dried phosphogypsum at a mass ratio of 0.2:99.8 evenly, spread the mixture evenly, and microwave calcine it in a microwave heating furnace with a power of 3.5KW and a frequency of 2450Hz for 15 minutes. During the microwave calcine process, the temperature in the microwave heating furnace is controlled at 800°C; take out the phosphogypsum from the microwave heating furnace, grind it for 5 minutes, and age it for 12 hours to obtain modified anhydrous phosphogypsum. The average particle size of the modified anhydrous phosphogypsum is 30μm, the content of type II anhydrous gypsum is ≥90%, and the pH value is in the range of 6 to 8.

[0079] (2) Dissolve the water-reducing agent and the retarder in part of the water, add whiskers and ultrasonically disperse for 30 seconds to obtain the admixture solution;

[0080] (3) Mix the desulfurized gypsum clinker, the modified anhydrous phosphogypsum obtained in step (1), the additive solution and water, and oscillate with ultrasonic waves to control the water-to-gypsum ratio to 0.45 to obtain a slurry;

[0081] (4) The slurry obtained in step (3) is guided to the lower protective paper, and the upper protective paper is laid on it. The paper is then shaped and dried to obtain the high-strength water-resistant paper-faced gypsum board.

[0082] Example 2

[0083] The high-strength, water-resistant paper-faced gypsum board of this embodiment is prepared from the following raw materials: 85 parts by weight of desulfurized gypsum clinker, 15 parts by weight of modified anhydrous phosphogypsum, 0.3 parts by weight of whiskers (the mass ratio of calcium carbonate whiskers to anhydrous calcium sulfate whiskers is 1:1, and the aspect ratios of calcium carbonate whiskers to anhydrous calcium sulfate whiskers are 30:1 and 50:1, respectively), 0.38 parts by weight of water-reducing agent, and 0.15 parts by weight of retarder, with a water-to-gypsum ratio of 0.43.

[0084] The preparation process of the high-strength water-resistant paper-faced gypsum board in this embodiment includes:

[0085] (1) The phosphogypsum to be modified is dried at 45°C to constant weight; aluminum sulfate and the dried phosphogypsum are mixed evenly at a mass ratio of 0.25: 99.75, the mixture is spread evenly, and microwave calcined in a microwave heating furnace with a power of 3.5KW and a frequency of 2450Hz for 13 minutes. The temperature in the microwave heating furnace is controlled at 800°C during the microwave calcination process; the phosphogypsum in the microwave heating furnace is taken out, ground for 5 minutes, and aged for 12 hours to obtain modified anhydrous phosphogypsum. The average particle size of the modified anhydrous phosphogypsum is 30μm, the content of type II anhydrous gypsum is ≥90%, and the pH value is in the range of 6 to 8.

[0086] Steps (2) to (4) are the same as the preparation method in Example 1.

[0087] Example 3

[0088] The high-strength water-resistant paper-faced gypsum board of this embodiment is prepared from the following raw materials: 90 parts by weight of desulfurized gypsum clinker, 10 parts by weight of modified anhydrous phosphogypsum, 0.5 parts by weight of whiskers (calcium carbonate whiskers with an aspect ratio of 30:1), 0.5 parts by weight of water-reducing agent, and 0.15 parts by weight of retarder, with a water-to-gypsum ratio of 0.42.

[0089] (1) The phosphogypsum to be modified was dried at 45°C to constant weight; aluminum sulfate and the dried phosphogypsum were mixed evenly at a mass ratio of 0.3:99.7, the mixture was spread evenly, and microwaved in a microwave heating furnace with a power of 3.5KW and a frequency of 2450Hz for 15 minutes. The temperature in the microwave heating furnace was controlled at 800°C during the microwave calcination process; the phosphogypsum in the microwave heating furnace was taken out, ground for 5 minutes, and aged for 12 hours to obtain modified anhydrous phosphogypsum with an average particle size of 30μm.

[0090] Steps (2) to (4) are the same as the preparation method in Example 1.

[0091] Example 4

[0092] The high-strength water-resistant paper-faced gypsum board of this embodiment is prepared from the following raw materials: 85 parts by weight of desulfurized gypsum clinker, 15 parts by weight of modified anhydrous phosphogypsum, 0.5 parts by weight of whiskers (calcium carbonate whiskers with an aspect ratio of 80:1), 0.5 parts by weight of water-reducing agent, and 0.2 parts by weight of retarder, with a water-to-gypsum ratio of 0.42.

[0093] The preparation process of the high-strength water-resistant paper-faced gypsum board in this embodiment includes:

[0094] (1) Dry the phosphogypsum to be modified at 45°C to constant weight; mix aluminum sulfate and the dried phosphogypsum at a mass ratio of 0.5:99.5 evenly, spread the mixture evenly, and microwave calcine it in a microwave heating furnace with a power of 3.5KW and a frequency of 2450Hz for 15 minutes. During the microwave calcine process, the temperature in the microwave heating furnace is controlled at 800°C; take out the phosphogypsum from the microwave heating furnace, grind it for 5 minutes, and age it for 12 hours to obtain modified anhydrous phosphogypsum. The average particle size of the modified anhydrous phosphogypsum is 30μm, the content of type II anhydrous gypsum is ≥90%, and the pH value is in the range of 6 to 8.

[0095] Steps (2) to (4) are the same as the preparation method in Example 1.

[0096] Comparative Example 1

[0097] The paper-faced gypsum board of this comparative example was prepared using the following raw materials: 100 parts by weight of desulfurized gypsum clinker, 0.3 parts by weight of whiskers (calcium carbonate whiskers), 0.4 parts by weight of water-reducing agent, and 0.15 parts by weight of retarder, with a water-to-gypsum ratio of 0.45.

[0098] The preparation process of the high-strength, water-resistant paper-faced gypsum board in this comparative example includes:

[0099] (1) Dissolve the water-reducing agent and the retarder in part of the water, add whiskers and ultrasonically disperse for 30s to obtain an admixture solution;

[0100] (2) Mix the desulfurized gypsum clinker, the admixture solution and water, and oscillate with ultrasonic waves to control the water-to-gypsum ratio at 0.45 to obtain a slurry;

[0101] (3) The slurry obtained in step (2) is guided to the lower protective paper, and the upper protective paper is laid on it. The paper is then shaped and dried to obtain the high-strength water-resistant paper-faced gypsum board.

[0102] Comparative Example 2

[0103] The paper-faced gypsum board of this comparative example was prepared using the following raw materials: 90 parts by weight of desulfurized gypsum clinker, 10 parts by weight of modified anhydrous phosphogypsum, 0.4 parts by weight of water-reducing agent, and 0.15 parts by weight of retarder, with a water-to-gypsum ratio of 0.45.

[0104] The preparation process of the high-strength, water-resistant paper-faced gypsum board in this comparative example includes:

[0105] (1) The phosphogypsum to be modified was dried at 45°C to constant weight; aluminum sulfate and the dried phosphogypsum were mixed evenly at a mass ratio of 0.2:99.8, the mixture was spread out, and microwaved in a microwave heating furnace with a power of 3.5KW and a frequency of 2450Hz for 15 minutes. The temperature in the microwave heating furnace was controlled at 800°C during the microwave calcination process; the phosphogypsum in the microwave heating furnace was taken out, ground for 5 minutes, and aged for 12 hours to obtain modified anhydrous phosphogypsum with an average particle size of 30μm.

[0106] (2) Dissolve the water-reducing agent and the retarder in part of the water to obtain an admixture solution;

[0107] Steps (3) and (4) are the same as the preparation method in Example 1.

[0108] The mechanical properties and water absorption rate of the paper-faced gypsum board (15 mm thick) prepared in the above embodiments were tested according to the Chinese national standard GB / T 9775-2008 "Paper-faced Gypsum Board". The test results are shown in Table 1.

[0109] Table 1 Mechanical properties and water absorption rate of paper-faced gypsum board

[0110]

[0111] It can be seen that, compared with the paper-faced gypsum board without modified anhydrous phosphogypsum in Comparative Example 1 and the paper-faced gypsum board without whiskers in Comparative Example 2, the paper-faced gypsum board with both modified anhydrous phosphogypsum and inorganic salt whiskers added in the present application embodiment has significantly higher mechanical strength; moreover, the paper-faced gypsum board in the present application embodiment has better water resistance.

[0112] While the embodiments disclosed in this application are as described above, the content is merely for the purpose of facilitating understanding of this application and is not intended to limit this application. Any person skilled in the art to which this application pertains may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in this application; however, the scope of protection of this application shall still be determined by the scope defined in the appended claims.

Claims

1. A method for modifying phosphogypsum, characterized in that, include: The phosphogypsum to be modified was dried to constant weight; Aluminum sulfate was mixed with phosphogypsum dried to constant weight, microwave-calcined, ground, and aged to obtain modified anhydrous phosphogypsum. The microwave calcination temperature is 750℃ to 850℃; the microwave calcination time is 10min to 15min; the microwave calcination power is 3.48kW to 3.52kW; and the microwave calcination frequency is 2445MHz to 2455MHz. The mass ratio of the aluminum sulfate to the phosphogypsum dried to constant weight is from 0.1:99.9 to 0.5:99.

5.

2. A modified anhydrous phosphogypsum, characterized in that, The modified anhydrous phosphogypsum is prepared by the method described in claim 1, wherein the content of type II anhydrous gypsum in the modified anhydrous phosphogypsum is ≥90%, and the pH value is in the range of 6 to 8.

3. A high-strength, water-resistant paper-faced gypsum board, characterized in that, include: 100 parts by weight of gypsum clinker, 0.1 to 0.5 parts by weight of inorganic salt whiskers, 0.4 to 0.7 parts by weight of water-reducing agent and 0.1 to 0.5 parts by weight of retarder; The gypsum clinker, by mass percentage, comprises 80% to 90% desulfurized gypsum clinker and 10% to 20% modified anhydrous phosphogypsum according to claim 2.

4. The high-strength, water-resistant paper-faced gypsum board according to claim 3, wherein, The inorganic salt whiskers are selected from any one or more of calcium carbonate whiskers and anhydrous calcium sulfate whiskers.

5. The high-strength, water-resistant paper-faced gypsum board according to claim 4, wherein, The aspect ratio of the inorganic salt whiskers is from 30:1 to 80:

1.

6. The high-strength, water-resistant paper-faced gypsum board according to any one of claims 3 to 5, wherein, The water-reducing agent is selected from any one or more of polycarboxylate superplasticizers, melamine-based water-reducing agents, and naphthalene-based water-reducing agents.

7. The high-strength, water-resistant paper-faced gypsum board according to any one of claims 3 to 5, wherein, The retarder is selected from any one or more of sodium citrate and protein-based retarders.

8. A method for preparing high-strength, water-resistant paper-faced gypsum board according to any one of claims 3 to 7, characterized in that, include: Dissolve the water-reducing agent and retarder in part of the water, add inorganic salt whiskers and disperse to obtain an additive solution; Desulfurized gypsum clinker, modified anhydrous phosphogypsum, the aforementioned additive solution, and water are mixed and ultrasonically vibrated to control the water-to-gypsum ratio at 0.4 to 0.5, thereby obtaining a slurry. The slurry is guided onto the lower protective paper, and the upper protective paper is laid on top. The mixture is then shaped and dried to obtain the high-strength, water-resistant paper-faced gypsum board.

9. The method for preparing high-strength, water-resistant paper-faced gypsum board according to claim 8, characterized in that, Also includes: The modified anhydrous phosphogypsum is prepared by the phosphogypsum modification method according to claim 1 before mixing the desulfurized gypsum clinker, the modified anhydrous phosphogypsum, the additive solution and water.

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