A gypsum crystal modifier, alpha-type high-strength gypsum powder and a preparation method and application thereof

Abstract

The application discloses a gypsum crystal modifier, alpha-type high-strength gypsum powder and a preparation method and application thereof, and belongs to the technical field of building gypsum. The preparation method of the gypsum crystal modifier comprises the following steps: mixing and stirring a first sodium hydroxide solution and 2,6-diaminoheptanedioic acid, continuously adding maleic anhydride and a second sodium hydroxide solution in batches, and then stirring and reacting under the condition of 40 DEG C to 60 DEG C and pH value of 12 to 14 to obtain the crystal modifier. The application also proposes the application of the crystal modifier in the preparation of alpha-type high-strength gypsum. The application also proposes alpha-type high-strength gypsum powder which is prepared by using the above-mentioned crystal modifier to convert gypsum. The crystal modifier can improve the strength of the gypsum powder to more than 45.5 MPa, and when the crystal modifier is used as a cementing material in a gypsum-based self-leveling mortar system and the like, the mortar system can be ensured not to be affected by cement, lime, water reducing agent and the like, and the setting time can be controlled.

Description

Technical Field

[0001] This invention relates to the field of gypsum technology, specifically to a gypsum crystallization agent, α-type high-strength gypsum powder, its preparation method, and its application. Background Technology

[0002] Phosphogypsum is an industrial byproduct of the wet-process phosphoric acid production. Phosphogypsum contains many impurities and has a complex composition. These impurities (such as heavy metals and acidic substances) not only pollute soil and water bodies but also seriously affect the application performance of phosphogypsum. Even after washing, the mechanical properties of some solid waste phosphogypsum are still not ideal in applications.

[0003] There are three methods for preparing α-type high-strength gypsum: pressurized steam method (evaporization method), pressurized aqueous solution method (hydrothermal method), and atmospheric pressure salt solution method. Among them, the evaporation method and the hydrothermal method have been industrialized and applied to the conversion of different types of gypsum.

[0004] Industrial by-product gypsum varies in its trace impurities and properties due to differences in processing methods and raw material sources. Different sources of α-type high-strength gypsum require different crystal-changing agents for production; therefore, the types of crystal-changing agents and the difficulty of crystal-changing processes vary greatly depending on the source of the gypsum.

[0005] High-strength α-type phosphogypsum powder prepared by existing crystallization technology generally suffers from problems such as long setting time of the cement paste and strength that only meets the α25 standard of JC / T 2038—2010 "α-type High-strength Gypsum". When this gypsum powder is used as a cementitious material in practical applications, the addition of cement, lime, or water-reducing agents to the mortar results in phenomena such as prolonged non-setting, low strength, and surface powdering. In addition, phosphogypsum itself is heavily contaminated with oil, and conventional water washing cannot completely remove oil and impurities. The self-leveling mortar prepared from it will have a black oil film or spots on the surface after hardening, making it impossible to attach coverings, which greatly limits the utilization of industrial by-product phosphogypsum.

[0006] The main problems with existing technologies for α-type high-strength phosphogypsum powder are:

[0007] 1) Low strength. The α-type high-strength phosphogypsum powder prepared by existing technology generally has problems such as high water consumption for the standard consistency of the paste and low oven-dry strength of the gypsum, and only meets the α25 standard of JC / T 2038—2010 "α-type high-strength gypsum".

[0008] 2) Heavy oil stains. Phosphogypsum itself is very oily, and conventional water washing cannot completely remove the oil and impurities. After the gypsum-based self-leveling compound hardens, there is an oil film on the surface, making it impossible to attach coverings, and it is also very easy to mold, which greatly limits the use of phosphogypsum.

[0009] 3) No setting after adding alkali. Because the pH value of α-type high-strength phosphogypsum powder is usually around 5, the pH value needs to be adjusted to neutral or alkaline in actual application (the standard for gypsum-based self-leveling mortar clearly requires a pH value ≥ 7). However, after adding alkaline materials such as cement or lime, the gypsum-based self-leveling system cannot set, or the setting time cannot be controlled.

[0010] 4) No setting after adding polycarboxylate superplasticizers and other additives. Superplasticizers, as key additives for controlling fluidity, play an irreplaceable role in mortar systems. However, the crystallizing agent in α-type high-strength phosphogypsum powder and organic substances such as superplasticizers can easily produce synergistic effects during hydration, which can also lead to the gypsum-based self-leveling mortar system not setting or having an uncontrollable setting time.

[0011] Many α-type high-strength gypsum production lines already in operation in the construction industry have not yet resolved the technical difficulties in applying α-type high-strength phosphogypsum powder produced from industrial by-product phosphogypsum. This has led to the shutdown of most production lines and restrictions on the use of industrial by-product phosphogypsum. Therefore, the development of α-type high-strength phosphogypsum powder compatible with gypsum-based self-leveling mortars and other composite cementitious materials is urgently needed. Summary of the Invention

[0012] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a gypsum crystallization agent, α-type high-strength gypsum powder, its preparation method and application, thereby solving the technical problems of α-type high-strength gypsum powder not setting and lacking strength due to its inability to resist alkali or incompatibility with water-reducing agents in the prior art.

[0013] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing a gypsum crystallization agent, comprising the following steps:

[0014] The first sodium hydroxide solution and 2,6-diaminopimelic acid were mixed and stirred. Then, maleic anhydride and the second sodium hydroxide solution were added in batches. The reaction was then carried out under the conditions of 40℃~60℃ and pH value 12~14 to obtain the crystallization agent.

[0015] In any embodiment, the first sodium hydroxide solution and the 2,6-diaminopimelic acid are mixed and stirred at a molar ratio of (0.5–2.0):1; the mass concentration of the first sodium hydroxide solution is 15%–50%; and / or, the total amount of maleic anhydride added is in a molar ratio of (1.0–2.5):1 to the 2,6-diaminopimelic acid.

[0016] In any embodiment, the total amount of the first sodium hydroxide solution and the second sodium hydroxide solution added is in a molar ratio of (1.0 to 2.5):1 to the 2,6-diaminopimelic acid, and the mass concentration of the second sodium hydroxide is 15% to 50%.

[0017] In any embodiment, the maleic anhydride and the second sodium hydroxide solution are added in 2 to 3 batches.

[0018] In addition, the present invention also proposes a gypsum crystallization agent, which is prepared by the above preparation method.

[0019] Furthermore, the present invention also proposes the application of the gypsum crystallization agent prepared by the above preparation method or the above gypsum crystallization agent in the preparation of α-type high-strength gypsum powder.

[0020] Furthermore, this invention also proposes an α-type high-strength gypsum powder, prepared using the aforementioned gypsum crystallization agent; the mass ratio of the gypsum crystallization agent to the gypsum is (0.18–4):1000. The gypsum is one or more of industrial by-product gypsum such as desulfurized gypsum, lactic acid gypsum, titanium gypsum, and phosphogypsum, with phosphogypsum being preferred.

[0021] In addition, the present invention also proposes a method for preparing the above-mentioned α-type high-strength gypsum, comprising the following steps: spraying a gypsum crystallizing agent into the gypsum and mixing it, then placing it for 5 to 7 days, then pressing it into gypsum bricks, steam-pressing the gypsum bricks at 140°C to 160°C and 0.4 MPa to 0.6 MPa, and then drying and ball milling to obtain α-type high-strength gypsum powder.

[0022] In some embodiments, before spraying the crystallizing agent, the process further includes mixing graphite powder and ultrafine calcium oxide and then incorporating them into gypsum; the mass ratio of the graphite powder, the ultrafine calcium oxide and the gypsum is (0.2-5):(5-20):1000.

[0023] In addition, the present invention also proposes a gypsum-based self-leveling mortar, comprising the above-mentioned α-type high-strength gypsum powder.

[0024] In any embodiment, the above-mentioned gypsum-based self-leveling mortar, calculated by weight, includes 200 to 700 parts of α-type high-strength gypsum powder, 1 to 200 parts of ordinary Portland cement, 300 to 800 parts of 40-70 mesh medium sand, 0 to 4 parts of polycarboxylate superplasticizer, 0 to 1.5 parts of hydrophilic colloidal stabilizer, 0 to 2 parts of polyether defoamer, and 0 to 4 parts of amino acid retarder.

[0025] In any embodiment, the above-mentioned gypsum-based self-leveling mortar, calculated by weight, includes 450 to 550 parts of α-type high-strength gypsum powder, 25 to 75 parts of ordinary Portland cement, 400 to 500 parts of medium sand of 40 to 70 mesh, 2 to 3 parts of polycarboxylate superplasticizer, 0.5 to 1 part of xanthan gum stabilizer, 0.5 to 1 part of defoamer, and 0.3 to 0.6 parts of amino acid retarder.

[0026] Compared with the prior art, the beneficial effects of the present invention include: the preparation method of the gypsum crystallizing agent proposed in the present invention includes the following steps: mixing and stirring a first sodium hydroxide solution and 2,6-diaminopimelic acid, then adding maleic anhydride and a second sodium hydroxide solution in batches, and then stirring and reacting at 40℃~60℃ and pH value 12~14 to obtain the crystallizing agent. The crystallizing agent is used in the preparation of α-type high-strength gypsum, so that the gypsum eventually forms short columnar crystals, thereby increasing the strength of α-type high-strength gypsum powder produced by gypsum combined with autoclaving process to above 45.5MPa, and the setting time of self-leveling mortar can be controlled. Attached Figure Description

[0027] Figure 1 This is a photograph of the crystallization agent prepared in Example 1 of the present invention.

[0028] Figure 2 This is a SEM image of the α-type high-strength phosphogypsum powder prepared by steam pressure crystallization in Example 1 of this invention.

[0029] Figure 3 This is the XRD pattern of α-type high-strength phosphogypsum powder prepared by steam pressure crystallization in Example 1 of the present invention.

[0030] Figure 4 This is a crystal form diagram of the α-type high-strength phosphogypsum powder obtained in Example 1 of the present invention.

[0031] Figure 5 This is a photograph of a gypsum-based self-leveling mortar sample made from α-type high-strength phosphogypsum powder in Example 2 of the present invention; it can harden normally.

[0032] Figure 6 This is a crystal diagram of the α-type phosphogypsum powder prepared by crystallization in Comparative Example 1 of this invention.

[0033] Figure 7 This is a photograph of a triple mold used to pour gypsum-based self-leveling mortar made from α-type high-strength phosphogypsum powder, as described in Comparative Example 2 of this invention; it has not hardened after 24 hours.

[0034] Figure 8 This is a photograph of a sample block of gypsum-based self-leveling mortar made from α-type high-strength phosphogypsum powder, as described in Comparative Example 3 of this invention; it has not hardened after 24 hours.

[0035] Figure 9 This is a photograph of a triple mold used to pour gypsum-based self-leveling mortar made from α-type phosphogypsum powder, as described in Comparative Example 5 of this invention; it has not hardened after 24 hours. Detailed Implementation

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] This specific embodiment provides a method for preparing a gypsum crystallization agent, including the following steps:

[0040] The first sodium hydroxide solution and 2,6-diaminopimelic acid were mixed and stirred at a molar ratio of (0.5–2.0):1. Then, maleic anhydride and the second sodium hydroxide solution were added in batches. The mixture was then stirred and reacted at 40–60°C and pH 12–14 to obtain the gypsum crystallizing agent. The mass concentration of the first sodium hydroxide solution or the second sodium hydroxide solution was 15%–50%. The molar ratio of the total amount of the first sodium hydroxide solution and the second sodium hydroxide solution to the 2,6-diaminopimelic acid was (1.0–2.5):1. The molar ratio of the total amount of the maleic anhydride solution to the 2,6-diaminopimelic acid was (1.0–2.5):1.

[0041] In some embodiments, the maleic anhydride and the second sodium hydroxide solution are added in 2 to 3 batches.

[0042] This specific embodiment also proposes a gypsum crystallization agent, which is prepared by the above preparation method.

[0043] This specific embodiment also proposes the application of the gypsum crystallization agent prepared by the above preparation method or the above gypsum crystallization agent in the preparation of α-type high-strength gypsum.

[0044] This specific embodiment also proposes an α-type high-strength gypsum powder, prepared using the above-mentioned gypsum crystallization agent to transform gypsum; the mass ratio of the gypsum crystallization agent to the gypsum is (0.18-4):1000. The gypsum is one or more of industrial by-product gypsum such as desulfurized gypsum, lactic acid gypsum, titanium gypsum, and phosphogypsum, with phosphogypsum being preferred.

[0045] This specific embodiment also proposes a method for preparing the above-mentioned α-type high-strength gypsum powder, including the following steps: spraying a crystallizing agent into gypsum and mixing, then letting it stand for 5 to 7 days, then pressing it into gypsum bricks, steam-pressing the gypsum bricks at 140℃ to 160℃ and a pressure of 0.4MPa to 0.6MPa for 3 to 5 hours, and then drying and ball milling to obtain α-type high-strength gypsum powder.

[0046] During the crystallization process, under high-temperature and high-pressure conditions, the gypsum crystallization agent reacts rapidly on the gypsum surface, while graphite powder is evenly distributed around the gypsum crystals. As an excellent thermal conductor, graphite rapidly heats the gypsum crystals, ultimately causing the gypsum crystals to grow towards a short-axis shape. The gypsum blocks after crystallization are quickly transferred to a microwave drying workshop. During microwave drying, by controlling the microwave frequency, utilizing the low dielectric constant of gypsum and the microwave thermal effect of graphite, the drying temperature is controlled between 130℃ and 180℃, and the drying time between 10 min and 30 min, resulting in short-axis crystals. The dried gypsum blocks are then conveyed to a crusher and ball mill for crushing, ball milling, and sieving to 150 mesh to 325 mesh. The sieved α-high-strength gypsum powder is stored in an aging chamber for later use.

[0047] In some embodiments, industrial by-product phosphogypsum is pre-soaked in 40% sulfuric acid, stirred at low speed for 30 minutes, washed with water, and filtered. Sulfuric acid soaking is used to remove impurities such as oil, eutectic phosphorus, and fluorine from the phosphogypsum. At the same time, it can greatly increase the whiteness. After use, the sulfuric acid can be returned to the acidolysis tank in the initial stage of the phosphate fertilizer plant for secondary recycling.

[0048] In some embodiments, before spraying the crystallizing agent, the process further includes mixing graphite powder and ultrafine calcium oxide and then incorporating the mixture into the gypsum; the mass ratio of the graphite, the ultrafine calcium oxide, and the gypsum is (0.2-5):(5-20):1000. The gypsum is one or more of industrial by-product gypsum such as desulfurized gypsum, lactic acid gypsum, titanium gypsum, and phosphogypsum, and the gypsum is preferably phosphogypsum.

[0049] This specific embodiment also proposes a gypsum-based self-leveling mortar, comprising the above-mentioned α-type high-strength gypsum powder.

[0050] In some embodiments, the gypsum-based self-leveling mortar, by weight, comprises 200 to 700 parts of α-type high-strength gypsum powder, 1 to 200 parts of ordinary Portland cement, 300 to 800 parts of 40-70 mesh medium sand, 0 to 4 parts of polycarboxylate superplasticizer, 0 to 1.5 parts of hydrophilic colloidal stabilizer, 0 to 2 parts of polyether defoamer, and 0 to 4 parts of amino acid retarder.

[0051] In some embodiments, the above-mentioned gypsum-based self-leveling mortar, calculated by weight, includes 450 to 550 parts of α-type high-strength gypsum powder, 25 to 75 parts of ordinary Portland cement, 400 to 500 parts of 40-70 mesh medium sand, 2 to 3 parts of polycarboxylate superplasticizer, 0.5 to 1 part of hydrophilic adhesive stabilizer, 0.5 to 1 part of polyether defoamer, and 0.3 to 0.6 parts of amino acid retarder.

[0052] The α-type high-strength gypsum powder prepared by the crystallization agent obtained by this invention is compatible with cement, polycarboxylate superplasticizers and other additives in the cementitious material application system. The additives can act better on the gypsum itself without being interfered with.

[0053] In the preparation method of α-type high-strength gypsum of the present invention, the gypsum powder contains trace amounts of graphite powder during the autoclaving and microwave drying stages, which improves the autoclaving and drying efficiency, greatly shortens the production time, and thus optimizes the crystal form of α-type high-strength phosphogypsum powder.

[0054] It should be noted that the ultrafine calcium oxide in this invention has a fineness of 600 mesh to 2000 mesh and is used to neutralize the acid-treated phosphogypsum to make its pH value ≥ 7; the graphite is flake graphite with a fineness of 600 mesh to 4000 mesh.

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] In this invention, the terms "some embodiments," "this embodiment," and examples are used to describe a subset of all possible embodiments. However, it is understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0057] If the application documents contain similar descriptions such as "first / second", the following explanation shall be added: In the following description, the terms "first / second / third" are used only to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0058] In this embodiment, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, object A and / or object B can represent three situations: object A exists alone, object A and object B exist simultaneously, and object B exists alone.

[0059] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. The polycarboxylate-type water-reducing agents, xanthan gum-type suspension stabilizers, polyether-type defoamers, and amino acid-type retarders in the following embodiments or comparative examples are all from the prior art.

[0060] The industrial by-product phosphogypsum in the following examples is acid-washed phosphogypsum. The acid treatment method is as follows: the industrial by-product phosphogypsum is directly soaked in 40% sulfuric acid, stirred at low speed for 30 minutes, washed with water, and filtered by pressure. Sulfuric acid soaking is used to remove impurities such as oil, eutectic phosphorus, and fluorine compounds from the phosphogypsum. Simultaneously, it can significantly increase whiteness. After use, the sulfuric acid can be returned to the acidolysis tank in the initial stage of the phosphate fertilizer plant for secondary recycling. The properties of the phosphogypsum before and after acid washing are shown in Table 1.

[0061] Table 1. Acid-treated phosphogypsum

[0062] Example 1

[0063] This embodiment proposes a gypsum crystallization agent, which is prepared by the following steps:

[0064] S1. Add 1 mol of 20% sodium hydroxide to the reaction vessel in advance, then add 1 mol of 2,6-diaminopimelic acid and stir at 80 r / min for 5 min.

[0065] S2. Add a total of 2 mol of maleic anhydride and 1 mol of sodium hydroxide with a mass concentration of 20% in two batches, stirring for 2 minutes after each addition.

[0066] S3. Add 0.3 mol of maleic anhydride and 0.2 mol of 20% sodium hydroxide again, making them in excess in the reaction system;

[0067] S4. Heat the system in the reactor to 40°C, monitor the pH value of the system, and make the pH value 13-14; continue to stir the reaction at 80r / min for 30min to obtain brownish-yellow liquid gypsum crystallization agent.

[0068] Combination Figure 1 It can be seen that the prepared gypsum crystallization agent is brownish-yellow, and the effective component of the obtained brownish-yellow gypsum crystallization agent is about 45% to 60%.

[0069] This embodiment also proposes a method for preparing the above-mentioned α-type high-strength gypsum powder, including the following steps: Industrial by-product phosphogypsum is pre-soaked in 40% sulfuric acid, stirred at low speed for 30 minutes, and then washed and filtered. 0.2 kg of graphite powder and 10 kg of ultrafine calcium oxide are mixed and then incorporated into 1000 kg of phosphogypsum. Simultaneously, 1.42 kg of gypsum crystallizing agent prepared in this embodiment is sprayed onto the mixture, and it is left to stand for 6 days. Afterwards, it is pressed into phosphogypsum bricks. The molding pressure of the brick-making machine needs to be greater than 250 KN. The brick size is approximately 10 cm × 10 cm × 30 cm. The bricks are neatly stacked on a pallet. The phosphogypsum bricks are then steam-pressed and crystallized at 150°C and 0.5 MPa for 3 hours. The crystallized gypsum blocks are then quickly transferred to a microwave drying room for drying. The drying temperature is controlled at 150°C, and the drying time is 20 minutes, ultimately yielding short-axis crystals. The dried gypsum blocks are conveyed by a conveyor belt to a crusher and ball mill for crushing and ball milling, and then sieved to 150-325 mesh. The sieved α-high-strength phosphogypsum powder is stored in an aging silo for aging and future use.

[0070] Combination Figure 2 , Figure 3 and Figure 4 It can be seen that the α-type high-strength phosphogypsum powder produced by the above process has a eutectic phosphorus content of 0.0011%, a standard consistency water content of 31%, an initial setting time of 9 min, a final setting time of 11 min, a flexural strength of 5.3 MPa at 2 h, and a compressive strength of 45.5 MPa after drying.

[0071] Example 2

[0072] This embodiment proposes a gypsum crystallization agent, which is prepared by the following steps:

[0073] S1. Add 1 mol of 20% sodium hydroxide to the reaction vessel in advance, then add 1 mol of 2,6-diaminopimelic acid and stir at 80 r / min for 5 min.

[0074] S2. Add a total of 1 mol of maleic anhydride and 0.5 mol of 20% sodium hydroxide in two batches, stirring for 2 minutes after each addition.

[0075] S3. Add 0.1 mol of maleic anhydride and 0.1 mol of 20% sodium hydroxide again, making them in excess in the reaction system;

[0076] S4. Heat the system in the reactor to 50°C, monitor the pH value of the system, and make the pH value 12; continue to stir the reaction at 80 r / min for 30 min to obtain the brown gypsum crystallizing agent solution.

[0077] This embodiment also proposes a method for preparing the above-mentioned α-type high-strength gypsum powder, including the following steps: Industrial by-product phosphogypsum is pre-soaked in 40% sulfuric acid, stirred at low speed for 30 minutes, and then washed and filtered. 0.5 kg of graphite powder and 15 kg of ultrafine calcium oxide are mixed and added to 1000 kg of phosphogypsum. Simultaneously, 1.77 kg of the gypsum crystallization agent prepared in this embodiment is sprayed onto the mixture, and it is left to stand for 6 days. Then, it is pressed into phosphogypsum bricks. The molding pressure of the brick-making machine needs to be greater than 250 KN. The brick size is approximately 10 cm × 10 cm × 30 cm. The bricks are neatly stacked on a pallet. The phosphogypsum bricks are steam-pressed at 145°C and 0.5 MPa for 3 hours to achieve crystallization. The crystallized gypsum blocks are then quickly transferred to a microwave drying room for drying. The drying temperature is controlled at 145°C, and the drying time is 30 minutes, ultimately obtaining short-axis crystalline grains. The dried gypsum blocks are conveyed by a conveyor belt to a crusher and ball mill for crushing, ball milling and sieving to 150-325 mesh. The sieved α-high strength gypsum powder is stored in an aging silo for later use.

[0078] The α-type high-strength gypsum produced by the above process has a eutectic phosphorus content of 0, a standard viscosity water content of 33%, an initial setting time of 10 min, and a final setting time of 12 min; its 2-hour flexural strength is 4.7 MPa, and its dry compressive strength is 41.36 MPa.

[0079] Example 3

[0080] The gypsum crystallization agent in this embodiment is the same as that in Example 1.

[0081] This embodiment also proposes a method for preparing the above-mentioned α-type high-strength gypsum powder, including the following steps: industrial by-product phosphogypsum is pre-washed with water, stirred at low speed for 30 minutes, and then filtered. 3.54 kg of the gypsum crystallizing agent prepared in this embodiment is sprayed onto 1000 kg of phosphogypsum and mixed, then left to stand for 7 days. Afterwards, it is pressed into phosphogypsum bricks. The molding pressure of the brick-making machine needs to be greater than 250 KN. The brick size is approximately 5cm × 12cm × 25cm. The bricks are neatly stacked on a pallet. The phosphogypsum bricks are then steam-pressed at 145℃ and 0.5MPa for 5 hours to achieve crystallization. The crystallized gypsum blocks are quickly transferred to a microwave drying workshop for drying, controlling the drying temperature at 180℃ and the drying time at 60 minutes. The dried gypsum blocks are conveyed to a crusher and ball mill for crushing, ball milling, and sieving to 150-325 mesh. The sieved α-type high-strength gypsum powder is stored in an aging chamber for later use.

[0082] The α-type high-strength gypsum produced by the above process has a standard viscosity of approximately 38%, an initial setting time of 30 minutes, a final setting time of 38 minutes, a flexural strength of 4.1 MPa after 2 hours, and a compressive strength of 33.98 MPa after drying.

[0083] Comparative Example 1

[0084] The difference between this comparative example and Example 1 is that, in the preparation method of α-type high-strength gypsum powder, conventional gypsum crystallizing agent A is used instead of the gypsum crystallizing agent prepared in Example 1. All other process steps, raw materials, and dosages are the same as in Example 1. Gypsum crystallizing agent A is a gypsum crystallizing agent with a molar ratio of aluminum sulfate to potassium tartrate of 1:0.378, and the mass ratio of gypsum crystallizing agent A to phosphogypsum is 2:1000. The crystal structure diagram of the obtained α-type phosphogypsum powder is shown below. Figure 6 As shown.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that, in the preparation method of α-type high-strength gypsum powder, conventional gypsum crystallizer B is used to replace the gypsum crystallizer prepared in Example 1. Other process steps, raw materials and dosages are the same as in Example 1. Among them, gypsum crystallizer B is citric acid, and the mass ratio of gypsum crystallizer B to phosphogypsum is 1.8:1000.

[0087] Comparative Example 3

[0088] The difference between this comparative example and Example 1 is that, in the preparation method of α-type high-strength gypsum powder, conventional gypsum crystallizer C is used to replace the gypsum crystallizer prepared in Example 1. Other process steps, raw materials and dosages are the same as in Example 1. Among them, gypsum crystallizer C is a gypsum crystallizer with a molar ratio of disodium EDTA to potassium aluminum sulfate of 1:1, and the mass ratio of gypsum crystallizer C to phosphogypsum is 2.1:1000.

[0089] Comparative Example 4

[0090] This comparative example is α-type phosphogypsum powder produced in Hubei Province and sold in a certain market.

[0091] Comparative Example 5

[0092] This comparative example is α-type phosphogypsum powder produced in Sichuan and sold in a certain market.

[0093] The performance results of the α-type high-strength gypsum pastes in Examples 1-3 and Comparative Examples 1-5 are shown in Tables 2 and 3.

[0094] Table 2

[0095]

[0096] Table 3

[0097]

[0098] Application examples

[0099] This application example proposes a gypsum-based self-leveling mortar, which, according to the mass percentages, includes 500 parts of any α-type high-strength phosphogypsum powder or commercially available gypsum powder from Examples 1-3 and Comparative Examples 1-5, 50 parts of ordinary Portland cement, and 450 parts of 40-70 mesh medium sand, with the following additives: 2-3 parts of polycarboxylate-type water-reducing agent, 1 part of xanthan gum-type suspension stabilizer, 0.5 parts of polyether-type defoamer, and 0-1.2 parts of amino acid-type retarder. After mixing evenly, a self-leveling dry powder mortar is obtained. The specific dosage and performance test results of each component of the gypsum-based self-leveling mortar prepared by adding water and stirring are shown in Table 4.

[0100] The self-leveling mortar is prepared by the following steps: mixing α-type high-strength gypsum powder, ordinary Portland cement, 40-70 mesh medium sand, polycarboxylate-type water-reducing agent, xanthan gum-type suspension stabilizer, polyether-type defoamer, and amino acid-type retarder, and stirring evenly to obtain self-leveling dry powder mortar. After adding water and stirring, gypsum-based self-leveling mortar is obtained.

[0101] Table 4

[0102]

[0103] Combination Figure 5 , Figure 7 , Figure 8 and Figure 9It can be seen that the gypsum-based self-leveling mortar samples prepared from the α-type high-strength phosphogypsum powder in Examples 1-3 can harden normally, while the gypsum-based self-leveling mortars prepared from Comparative Examples 1-5 cannot set and harden normally. The α-type high-strength phosphogypsum powder produced by this invention, after formula adjustment, can set and harden normally within the expected time in gypsum-based self-leveling formulation systems with additives such as cement and polycarboxylate superplasticizers, while achieving a post-drying strength of 50MPa-70MPa. The α-type high-strength phosphogypsum powder produced by this invention solves the problems of industrial by-product phosphogypsum being unresistant to alkali, having low strength, and being unsuitable for practical application as a cementitious material after crystallization. The α-type high-strength phosphogypsum powder prepared by this invention has high strength, can be used in various proportions with superplasticizers, cement, lime, and other substances, is adaptable to various gypsum systems, and has high strength and controllable setting time, making it practically valuable.

[0104] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a gypsum crystallization modifier, characterized by, The method comprises the following steps: The first sodium hydroxide solution and 2, 6-diamino pimelic acid are mixed and stirred, then maleic anhydride and the second sodium hydroxide solution are added in batches, and then the reaction is carried out under the conditions of 40-60℃ and pH 12-14 to obtain the gypsum crystal modifier.

2. The method of claim 1, wherein the gypsum conversion agent is prepared by the steps of: The first sodium hydroxide solution and the 2, 6-diamino pimelic acid are mixed and stirred at a molar ratio of (0.5-2.0):1; the mass concentration of the first sodium hydroxide solution is 15%-50%; and / or the total addition amount of the maleic anhydride and the 2, 6-diamino pimelic acid are at a molar ratio of (1.0-2.5):1; and / or the total addition amount of the first sodium hydroxide solution and the second sodium hydroxide solution and the 2, 6-diamino pimelic acid are at a molar ratio of (1.0-2.5):1, and the mass concentration of the second sodium hydroxide is 15%-50%.

3. A gypsum crystallization modifier characterized by, The gypsum crystal modifier is prepared by the preparation method of any one of claims 1-2.

4. The gypsum crystal modifier prepared by the preparation method of any one of claims 1-2 or the gypsum crystal modifier of claim 3 is used in the preparation of α-type high-strength gypsum powder.

5. A high-strength alpha gypsum powder, characterized by, The gypsum crystal modifier of claim 3 is used to prepare the gypsum by recrystallization; the mass ratio of the gypsum crystal modifier to the gypsum is (0.18-4):1000.

6. A method of producing the α-type high-strength gypsum powder according to claim 5, characterized by, The method comprises the following steps: The gypsum crystal modifier is sprayed into the gypsum, and then the gypsum is placed for 5-7 days, and then the gypsum is pressed into a gypsum brick, and then the gypsum brick is subjected to autoclave recrystallization at 140-160℃ and a pressure of 0.4-0.6 MPa, and then the gypsum brick is dried and ground to obtain the α-type high-strength gypsum powder.

7. The method of claim 6, wherein the alpha-type high-strength gypsum powder is prepared by adding 0.1 to 0.5 parts by weight of the sodium polyphosphate to 100 parts by weight of the gypsum powder. Before the gypsum crystal modifier is sprayed, the graphite powder and the superfine calcium oxide are mixed and then added into the gypsum; the mass ratio of the graphite powder, the superfine calcium oxide and the gypsum is (0.2-5):(5-20):1000.

8. A gypsum-based self-leveling mortar, characterized in that, The α-type high-strength gypsum powder of claim 5 or the α-type high-strength gypsum powder prepared by the preparation method of claim 6 or 7.

9. The gypsum-based self-leveling mortar according to claim 8, characterized in that According to weight fraction, the α-type high-strength gypsum powder 200-700 parts, common Portland cement 1-200 parts, medium sand 300-800 parts, polycarboxylic acid water reducing agent 0-4 parts, hydrophilic colloidal stabilizer 0-1.5 parts, polyether defoaming agent 0-2 parts and amino acid retarder 0-4 parts are included.

10. The gypsum-based self-leveling mortar according to claim 9, characterized in that According to weight fraction, the α-type high-strength gypsum powder 450-550 parts, common Portland cement 25-75 parts, medium sand 400-600 parts, polycarboxylic acid water reducing agent 2-3 parts, hydrophilic colloidal stabilizer 0.5-1 parts, polyether defoaming agent 0.5-1 parts and amino acid retarder 0.3-0.6 parts are included.

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