Preparation method of gypsum-based self-leveling mortar with synergy of red mud-excited II-type anhydrous phosphogypsum and semi-hydrated phosphogypsum

Abstract

The invention discloses a preparation method of gypsum-based self-leveling mortar with synergy of red mud excited type II anhydrous phosphogypsum and semi-hydrated phosphogypsum. The gypsum-based self-leveling mortar is prepared from the following components in parts by weight: 60 to 70 parts of semi-hydrated phosphogypsum, 10 to 15 parts of type II anhydrous phosphogypsum, 15 to 25 parts of machine-made sand, 0.01 to 0.03 part of cellulose ether, 0.001 to 0.003 part of a de-foaming agent and 45 to 55 parts of a red mud exciting agent. The method comprises the following steps: (1) uniformly mixing semi-hydrated phosphogypsum, type II anhydrous phosphogypsum and machine-made sand; and (2) sequentially adding cellulose ether, a defoaming agent and a red mud exciting agent, and preparing and curing slurry to obtain the gypsum-based self-leveling mortar. According to the gypsum-based self-leveling mortar and the preparation method thereof, the resource utilization rate of the solid wastes such as the red mud and the phosphogypsum is greatly increased, and meanwhile, the prepared gypsum-based self-leveling mortar can meet the requirements on physical and mechanical properties in the national standard 'Gypsum-based self-leveling mortar' JC / T1023-2021.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly relates to a preparation method of a gypsum-based self-leveling mortar for activating type II anhydrous phosphogypsum and synergistically using hemihydrate phosphogypsum with red mud. Background Art

[0002] In recent years, with the continuous increase in the demand for efficient construction technologies and green building materials in the construction industry, gypsum-based self-leveling mortar has gradually become the mainstream material in fields such as indoor floor leveling and decorative base treatment due to its excellent fluidity, rapid hardening characteristics, environmental friendliness (such as humidity adjustment, fire prevention, light weight), and low shrinkage rate. However, traditional gypsum-based self-leveling mortar mostly uses natural gypsum or industrial by-product gypsum as raw materials, which has problems such as high resource consumption, high cost, and insufficient performance stability. Especially when it comes to comprehensive performance requirements such as high strength and water resistance, the existing technologies still face challenges.

[0003] Phosphogypsum is a large amount of industrial solid waste generated during the production of wet-process phosphoric acid. Its long-term open-air stacking not only occupies land but also causes soil and water pollution due to the leakage of acidic substances and heavy metals. At present, the resource utilization of phosphogypsum mainly focuses on the preparation of building materials (such as gypsum boards, blocks, etc.), but its application is limited by problems such as high impurity (such as phosphorus, fluorine, organic matter) content, high pretreatment cost, and poor performance stability. In recent years, researchers have tried to convert phosphogypsum into hemihydrate phosphogypsum (β-CaSO4·0.5H2O) or type II anhydrous phosphogypsum (β-CaSO4) through calcination modification to improve its resource utilization rate. Hemihydrate phosphogypsum has a fast hydration rate and high early strength, but has problems such as short setting time and large shrinkage rate; while type II anhydrous phosphogypsum has good stability and low shrinkage rate, but its hydration activity is poor and it needs to be activated by chemical activators (such as sulfates, alkaline activators), resulting in increased costs and possible introduction of harmful components.

[0004] Red mud is a strongly alkaline solid waste generated during the alumina smelting process, with a global annual emissions of about 150 million tons and a utilization rate of less than 10%. Its characteristics of high alkalinity (pH 10 - 12), rich in silicate, aluminate, and iron oxide make it have the potential to be used as a cementitious material activator. Existing research has shown that the alkaline environment of red mud can promote the dissolution of silicate and aluminate phases in the gypsum system, participate in the hydration reaction to generate enhanced phases such as ettringite (AFt), thereby improving the mechanical properties of the material. However, in the existing technologies, red mud is mostly used in cement or geopolymer systems, and its application in gypsum-based materials is still in the exploratory stage, especially the synergistic activation mechanism for the phosphogypsum composite system has not been clarified.

[0005] Currently, the research on self-leveling mortar based on phosphogypsum mostly focuses on the modification of single-form gypsum (such as hemihydrate gypsum or type II anhydrous gypsum), and has the following problems:

[0006] Semi-hydrated phosphogypsum system: The setting time is too short (usually <20 minutes), and the construction window period is insufficient; the hardened body is prone to microcracks and long-term strength reduction. Type II anhydrous phosphogypsum system: It needs to rely on high-cost chemical activators (such as NaOH, Na2SO4) to increase activity, and the activation efficiency is limited, making it difficult to meet the high-strength requirements of self-leveling mortar. Lack of composite system: There is a lack of systematic research on the synergistic effect of semi-hydrated gypsum and type II anhydrous gypsum, and the rapid hydration of semi-hydrated gypsum and the stability advantages of type II anhydrous gypsum have not been fully utilized. Insufficient synergistic utilization of solid waste: Existing technologies have not effectively combined the alkaline activation properties of red mud with the gelling potential of phosphogypsum, and have failed to achieve the environmental protection goal of "treating waste with waste". Summary of the invention

[0007] The object of the present invention is to provide a method for preparing a gypsum-based self-leveling mortar of red mud-activated type II anhydrous phosphogypsum and hemihydrate phosphogypsum, which has the advantages of full solid waste disposal, low preparation cost, simple technical route, excellent mechanical properties, low amount of admixtures, and high water resistance.

[0008] In one aspect of the present invention, the present invention provides a method for preparing a red mud activator. According to an embodiment of the present invention, the method comprises the following steps:

[0009] (1) drying the original red mud, and then grinding and sieving to obtain red mud powder;

[0010] (2) preparing a red mud solution by mixing red mud powder in a solid-liquid ratio of 1:3;

[0011] (3) Sodium hexametaphosphate is added to the red mud solution, and the solution is stirred and aged to obtain a red mud activator.

[0012] Red mud is a byproduct of the alumina production process. Its pH value is 10-12, which is alkaline. It contains a high content of alumina and is a Class II solid waste. It is generally red, moist, and lumpy. Sodium hexametaphosphate is a colorless, transparent crystalline powder with a chemical formula of Na4P6O 18 It can be used as a dispersant to maximize the pH value of red mud leaching, and it also has the function of improving the early strength and durability of cementitious materials.

[0013] In addition, the method for preparing a red mud activator according to the above embodiment of the present invention may also have the following additional technical features:

[0014] In some embodiments of the present invention, in step (1), the drying temperature is 105-115° C., and the drying time is 8-10 h; the grinding is performed by ball milling, and the time is 15-30 min; the sieving is performed by a square hole sieve, and the mesh number of the square hole sieve is 300 mesh;

[0015] In some embodiments of the present invention, in step (2), the mass ratio of sodium hexametaphosphate to red mud is 1-1.5:1;

[0016] In some embodiments of the present invention, in step (3), the stirring time is 5-10 min and the aging time is 24-48 h.

[0017] On the other hand, the present invention provides a gypsum-based self-leveling mortar in which red mud is used to activate type II anhydrous phosphogypsum and cooperate with hemihydrate phosphogypsum. According to the embodiments of the present invention, it comprises the following components in parts by weight: 60-70 parts of hemihydrate phosphogypsum, 10-15 parts of type II anhydrous phosphogypsum, 15-25 parts of manufactured sand, 0.01-0.03 parts of cellulose ether, 0.001-0.003 parts of defoamer, and 45-55 parts of red mud activator, and the red mud activator is prepared by the preparation method of the red mud activator.

[0018] On the other hand, the present invention provides a preparation method of a gypsum-based self-leveling mortar in which red mud is used to activate type II anhydrous phosphogypsum and cooperate with hemihydrate phosphogypsum. According to the embodiments of the present invention, it comprises the following steps:

[0019] (1) Mix the hemihydrate phosphogypsum, type II anhydrous phosphogypsum, and manufactured sand evenly;

[0020] (2) Add cellulose ether, defoamer, and red mud activator in sequence to prepare and cure the slurry, and the gypsum-based self-leveling mortar is obtained. Among them, the preparation of the slurry is carried out according to the standard of JC / T1023-2021.

[0021] The hydration rate of type II anhydrous phosphogypsum in the natural state is extremely slow and needs to be activated with an activator. The final strength is relatively high. At the same time, it can delay the hydration process of hemihydrate phosphogypsum and replace the use of retarders. The type II anhydrous phosphogypsum is prepared by calcining phosphogypsum at 800-1300 °C for 3 h, and its hydration activity is low. Hemihydrate phosphogypsum is a by-product in the process of industrial wet-process phosphoric acid preparation and is prepared after being heated at 140-160 °C for a while. Its pH value is about 2-5, showing acidity, gray, and odorless. Cellulose ether can effectively control the solution viscosity, improve the workability, and at the same time delay the evaporation of water to ensure the full hydration of gypsum-based materials.

[0022] When preparing the self-leveling mortar, it can react chemically with Ca 2+ , SO4 2- in the gypsum to generate ettringite (AFt). The specific chemical reaction process is as follows:

[0023] Al2O3 + 3H2O + 2OH - →2Al(OH)4 -

[0024] CaSO4 → Ca 2+ + SO4 2-

[0025] 6Ca 2+ + 2Al(OH)4 - + 3SO4 2- + 4OH- + 26H2O → Ca6Al2(SO4)3(OH) 12 ·26H2O

[0026] In addition, according to the preparation method of a gypsum-based self-leveling mortar according to the above embodiments of the present invention, the following additional technical features may also be included:

[0027] In some embodiments of the present invention, the preparation method of the hemihydrate phosphogypsum includes the following steps: drying the as-received hemihydrate phosphogypsum powder, and then grinding and sieving it to obtain the hemihydrate phosphogypsum.

[0028] In some embodiments of the present invention, the drying temperature is 180 - 200 °C, and the drying time is 8 - 10 h; the grinding is carried out by ball milling for 15 - 30 min; the sieving is carried out using a square-hole sieve with a mesh size of 200 meshes.

[0029] In some embodiments of the present invention, the mass percentage of β-CaSO4·0.5H2O in the hemihydrate phosphogypsum is greater than 70%, and the physical and mechanical properties should be able to meet the requirements for grades 3.0 - 4.0 in GB / T9776.

[0030] In some embodiments of the present invention, the defoaming agent is polyethylene glycol. The polyethylene glycol defoaming agent can effectively eliminate the bubbles during the stirring process, and has the characteristics of inhibiting the generation of new bubbles, and also has the advantage of being suitable for complex construction environments.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1) In the present invention, the pH value of the red mud activator is high because the lattice of the red mud is destroyed by ball milling, making it easier for alkaline substances to be released. After aging under the action of a dispersant, the pH value (11 - 12) reaches the highest, which has the effect of activating type II anhydrous phosphogypsum. This red mud activator can replace the traditional alkali activator to effectively reduce the modification cost and carbon emissions during the production process.

[0033] 2) SO4 in the hemihydrate phosphogypsum 2-It has an activating effect on Al-containing minerals in red mud, can generate ettringite (AFt), improve the late strength and water resistance, achieve the purposes of "treating waste with waste", "two-way activation", and "secondary strength improvement", and can effectively realize the high-efficient resource utilization of red mud and phosphogypsum, which conforms to the development concept of a "low-carbon" society. In addition, the introduction of red mud-activated type II anhydrous phosphogypsum delays the hydration process of hemihydrate phosphogypsum, replaces the retarder, and promotes the 30-minute fluidity of gypsum-based self-leveling mortar.

[0034] 3) The present invention provides a formula for gypsum-based self-leveling mortar, which realizes the full solid waste of the cementitious material, and the strength can meet the requirements of the physical and mechanical properties of G25 strength for gypsum-based self-leveling mortar in JC / T1023-2021, effectively reducing the raw material cost. At the same time, compared with the situation that traditional phosphogypsum self-leveling mortar requires a large amount of admixtures, it eliminates the complexity of admixture compounding and further reduces the production cost, providing a solution with both economy and practicability for the high-value utilization of industrial solid waste. Brief Description of the Drawings

[0035] Figure 1 It is a process diagram for the preparation of a red mud activator in Example 1 of the present invention;

[0036] Figure 2 It is a process diagram for the preparation of hemihydrate phosphogypsum powder in Example 2 of the present invention;

[0037] Figure 3 It is a process diagram for the preparation of gypsum-based self-leveling mortar in Example 2 of the present invention. Detailed Embodiments

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] Example 1

[0040] A preparation method of a red mud activator is as Figure 1 shown. Specifically, the relevant parameters and steps selected in this embodiment are as follows:

[0041] (1) Weigh 5 kg of original red mud and put it into a drying oven at 110 °C for drying for 10 h;

[0042] (2) Grind the dried red mud in a small cement test mill for 30 min and then pass it through a 300-mesh square-hole sieve;

[0043] (3) Prepare a red mud solution by mixing the sieved thick red mud according to a solid-liquid ratio of 1:3;

[0044] (4) Weigh 0.8 wt% of sodium hexametaphosphate, put it into the prepared red mud solution, and stir for 8 minutes to form a red mud turbid liquid, which is used after aging for 48 hours;

[0045] (5) The preparation of the red mud activator is completed.

[0046] Example 2

[0047] A gypsum-based self-leveling mortar with red mud-activated type II anhydrous phosphogypsum synergistically combined with hemihydrate phosphogypsum, comprising the following components in parts by weight: 60 parts of hemihydrate phosphogypsum, 15 parts of type II anhydrous phosphogypsum, 25 parts of manufactured sand, 0.02 part of cellulose ether, 0.002 part of polyethylene glycol defoamer, and 55 parts of the red mud activator prepared in Example 1.

[0048] A preparation method of a gypsum-based self-leveling mortar with red mud-activated type II anhydrous phosphogypsum synergistically combined with hemihydrate phosphogypsum, the steps are as follows:

[0049] (1) Prepare hemihydrate phosphogypsum powder, the hemihydrate phosphogypsum powder mainly uses phosphogypsum as raw material, and the relevant parameters and steps selected in this example are as follows:

[0050] a. Weigh 5 kg of as-received hemihydrate phosphogypsum powder;

[0051] b. Dry the hemihydrate phosphogypsum in a drying oven at 180 °C for 10 h;

[0052] c. Ball mill the dried hemihydrate phosphogypsum in a small cement test mill for 30 minutes and then pass through a 200-mesh square hole sieve;

[0053] d. The preparation of the hemihydrate phosphogypsum powder is completed and sealed for storage.

[0054] (2) Weigh 60 parts of hemihydrate phosphogypsum, 15 parts of type II anhydrous phosphogypsum, and 25 parts of manufactured sand, and then mix them evenly for standby;

[0055] (3) Weigh 0.02 part of cellulose ether and 0.002 part of defoamer, and put them into the powder prepared in step (2);

[0056] (4) Weigh 55 parts of the red mud activator and add it to the powder, and prepare the slurry according to the JC / T1023-2021 standard;

[0057] (5) Cure according to the laboratory standard test conditions;

[0058] (6) The preparation of the phosphogypsum-based self-leveling mortar is completed.

[0059] The gypsum-based self-leveling mortar prepared in this example realizes full solid waste utilization, and its basic properties can meet the requirements of the national standard "Gypsum-based Self-leveling Mortar" (JC / T 1023-2021). Its specific properties are shown in Table 1.

[0060] Table 1 Performance requirements of a kind of phosphogypsum-based self-leveling mortar

[0061]

[0062] Example 3

[0063] A gypsum-based self-leveling mortar with red mud-activated type II anhydrous phosphogypsum and hemihydrate phosphogypsum in synergy, comprising the following components in parts by weight: 50 parts of hemihydrate phosphogypsum, 30 parts of type II anhydrous phosphogypsum, 25 parts of manufactured sand, 0.02 part of cellulose ether, 0.002 part of polyethylene glycol defoamer, and 50 parts of the red mud activator prepared in Example 1.

[0064] A preparation method of a gypsum-based self-leveling mortar with red mud-activated type II anhydrous phosphogypsum and hemihydrate phosphogypsum in synergy, the steps are as follows:

[0065] (1) Prepare hemihydrate phosphogypsum powder. The hemihydrate phosphogypsum powder mainly uses phosphogypsum as the raw material. The relevant parameters and steps selected in this example are as follows:

[0066] a. Weigh 5 kg of raw hemihydrate phosphogypsum powder;

[0067] b. Dry the hemihydrate phosphogypsum in a drying oven at 180 °C for 10 h;

[0068] c. Ball mill the dried hemihydrate phosphogypsum in a small cement test mill for 30 min and then pass through a 200-mesh square hole sieve;

[0069] d. The hemihydrate phosphogypsum powder is prepared and sealed for storage.

[0070] (2) Weigh 50 parts of hemihydrate phosphogypsum, 20 parts of type II anhydrous phosphogypsum, and 25 parts of manufactured sand, and then mix them evenly for standby;

[0071] (3) Weigh 0.02 part of cellulose ether and 0.002 part of defoamer, and put them into the powder prepared in step (2);

[0072] (4) Weigh 50 parts of red mud activator and add it to the powder, and prepare the slurry according to the JC / T 1023-2021 standard;

[0073] (5) Cure according to the laboratory standard test conditions;

[0074] (6) The phosphogypsum-based self-leveling mortar is prepared.

[0075] The gypsum-based self-leveling mortar prepared in this example realizes full solid waste utilization, and its basic properties can meet the requirements of the national standard "Gypsum-based Self-leveling Mortar" (JC / T 1023-2021). Its specific properties are shown in Table 2.

[0076] Table 2 Performance Requirements of a Phosphogypsum-based Self-leveling Mortar

[0077]

[0078]

[0079] Example 4

[0080] A gypsum-based self-leveling mortar with red mud-activated type II anhydrous phosphogypsum and hemihydrate phosphogypsum as synergists, comprising the following components in parts by weight: 70 parts of hemihydrate phosphogypsum, 15 parts of type II anhydrous phosphogypsum, 25 parts of manufactured sand, 0.03 part of cellulose ether, 0.003 part of polyethylene glycol defoamer, and 50 parts of the red mud activator prepared in Example 1.

[0081] A preparation method of a gypsum-based self-leveling mortar with red mud-activated type II anhydrous phosphogypsum and hemihydrate phosphogypsum as synergists is as Figure 3 shown. Specifically, the relevant parameters and steps selected in this example are as follows:

[0082] (1) As Figure 2 shown, prepare hemihydrate phosphogypsum powder. The hemihydrate phosphogypsum powder mainly uses raw phosphogypsum as the raw material. The relevant parameters and steps selected in this example are as follows:

[0083] a. Weigh 5 kg of raw hemihydrate phosphogypsum powder;

[0084] b. Dry the hemihydrate phosphogypsum in a drying oven at 180 °C for 10 h;

[0085] c. Grind the dried hemihydrate phosphogypsum in a small cement mill for 30 min and then pass through a 200-mesh square-hole sieve;

[0086] d. The hemihydrate phosphogypsum powder is prepared and stored in a sealed manner.

[0087] (2) Weigh 70 parts of hemihydrate phosphogypsum, 15 parts of type II anhydrous phosphogypsum, and 25 parts of manufactured sand, and then mix them evenly for standby;

[0088] (3) Weigh 0.03 part of cellulose ether and 0.003 part of defoamer, and put them into the powder prepared in step (2);

[0089] (4) Weigh 50 parts of red mud activator and add it to the powder, and prepare the slurry according to the JC / T 1023-2021 standard;

[0090] (5) Cure according to the standard test conditions of the laboratory;

[0091] (6) The preparation of the phosphogypsum-based self-leveling mortar is completed.

[0092] The gypsum-based self-leveling mortar prepared in this example realizes full solid waste utilization, and its basic performance can meet the requirements of the national standard "Gypsum-based Self-leveling Mortar" (JC / T 1023-2021). Its specific performance is shown in Table 3.

[0093] Table 3 Performance Requirements of a Phosphogypsum-based Self-leveling Mortar

[0094]

[0095] Comparative Example 1

[0096] A gypsum-based self-leveling mortar of red mud-activated hemihydrate phosphogypsum, comprising the following components in parts by weight: 85 parts of hemihydrate phosphogypsum, 0 part of type II anhydrous phosphogypsum, 25 parts of manufactured sand, 0.03 part of cellulose ether, 0.003 part of polyethylene glycol defoamer, and 50 parts of the red mud activator prepared in Example 1.

[0097] A preparation method of a gypsum-based self-leveling mortar of red mud-activated hemihydrate phosphogypsum, as Figure 3 shown. Specifically, the relevant parameters and steps selected in this example are as follows:

[0098] (1) As Figure 2 shown, prepare hemihydrate phosphogypsum powder. The hemihydrate phosphogypsum powder mainly uses the original phosphogypsum as raw material. The relevant parameters and steps selected in this example are as follows:

[0099] a. Weigh 5 kg of the original hemihydrate phosphogypsum powder;

[0100] b. Dry the hemihydrate phosphogypsum in a drying oven at 180 °C for 10 h;

[0101] c. Grind the dried hemihydrate phosphogypsum in a small cement mill for 30 min and then pass through a 200-mesh square-hole sieve;

[0102] d. The preparation of the hemihydrate phosphogypsum powder is completed and sealed for storage.

[0103] (2) Weigh 75 parts of hemihydrate phosphogypsum, 0 part of type II anhydrous phosphogypsum, and 25 parts of manufactured sand, and then mix them evenly for standby;

[0104] (3) Weigh 0.03 part of cellulose ether and 0.003 part of defoamer, and put them into the powder prepared in step (2);

[0105] (4) Weigh 50 parts of red mud activator and add it to the powder, and prepare the slurry according to the JC / T 1023-2021 standard;

[0106] (5) Cure according to the standard test conditions in the laboratory;

[0107] (6) The preparation of the phosphogypsum-based self-leveling mortar is completed.

[0108] The gypsum-based self-leveling mortar prepared in this example realizes full solid waste utilization, and its basic performance can meet the requirements of the national standard "Gypsum-based Self-leveling Mortar" (JC / T 1023-2021). Its specific performance is shown in Table 4.

[0109] Table 4 Performance requirements of a kind of phosphogypsum-based self-leveling mortar

[0110]

[0111] Comparative Example 2

[0112] A gypsum-based self-leveling mortar for activating type II anhydrous phosphogypsum with red mud, comprising the following components in parts by weight: 0 parts of hemihydrate phosphogypsum, 85 parts of type II anhydrous phosphogypsum, 25 parts of manufactured sand, 0.03 part of cellulose ether, 0.003 part of polyethylene glycol defoamer, and 50 parts of the red mud activator prepared in Example 1.

[0113] A preparation method of a gypsum-based self-leveling mortar for activating type II anhydrous phosphogypsum with red mud, the steps are as follows:

[0114] (1) Weigh 0 parts of hemihydrate phosphogypsum, 75 parts of type II anhydrous phosphogypsum, and 25 parts of manufactured sand, and mix them evenly for standby;

[0115] (2) Weigh 0.03 part of cellulose ether and 0.003 part of defoamer, and put them into the powder prepared in step (2);

[0116] (3) Weigh 50 parts of red mud activator and add it to the powder, and prepare the slurry according to the JC / T 1023-2021 standard;

[0117] (4) Cure according to the standard test conditions in the laboratory;

[0118] (5) The preparation of the phosphogypsum-based self-leveling mortar is completed.

[0119] The gypsum-based self-leveling mortar prepared in this example realizes full solid waste utilization, and its basic performance can meet the requirements of the national standard "Gypsum-based Self-leveling Mortar" (JC / T 1023-2021). Its specific performance is shown in Table 5.

[0120] Table 5 Performance requirements of a kind of phosphogypsum-based self-leveling mortar

[0121]

[0122] By comparing the results of Example 4, Comparative Examples 1 and 2, it was found that there is a synergistic effect between the red mud activator and type II anhydrous phosphogypsum and hemihydrate phosphogypsum. Specifically, when using hemihydrate phosphogypsum and red mud activator alone, the flexural strength and compressive strength at 24 d were 5.4 MPa and 8.1 MPa respectively, and the dry flexural strength and compressive strength at 28 d were 9.6 MPa and 25.5 MPa respectively. Its early strength (1 d) was relatively high, while the dry compressive strength at 28 d just met the strength requirements of JC / T 1023, which was due to the relatively fast hydration rate of hemihydrate phosphogypsum in the early stage and the slow strength growth in the later stage. When using type II anhydrous phosphogypsum and red mud activator alone, the early strength was low and the growth was slow, while the later strength was relatively high, which was due to the low hydration activity of type II anhydrous phosphogypsum and the need for continuous activation by the red mud activator. When using hemihydrate phosphogypsum, type II anhydrous phosphogypsum and red mud activator, the flexural strength and compressive strength at 1 d were 6.8 MPa and 17.4 MPa respectively, and the flexural strength and compressive strength at 28 d were 15.3 MPa and 35.6 MPa respectively. The strength was significantly improved compared with that of single hemihydrate phosphogypsum / type II anhydrous phosphogypsum and red mud activator. There is a specific synergistic effect among red mud solution, hemihydrate phosphogypsum and type II anhydrous phosphogypsum, and its mechanism is as follows: due to the dense structure and low hydration activity of type II anhydrous gypsum, in the alkaline solution provided by red mud, OH - ions will destroy the passivation layer on the surface of type II anhydrous gypsum and accelerate the dissolution of Ca 2+ and SO4 2- , improving the hydration rate; hemihydrate phosphogypsum is more easily hydrolyzed into dihydrate phosphogypsum in an alkaline solution environment, promoting the crystallization and nucleation of dihydrate gypsum and the improvement of early strength; active Al2O3 in red mud reacts with Ca 2 + released by the hydration of gypsum under alkaline conditions to form ettringite (AFt), improving the later strength of the cementitious material. Therefore, it is comprehensively judged that hemihydrate phosphogypsum, type II anhydrous phosphogypsum and red mud activator have a composite synergistic effect.

[0123] The above content is only an example and explanation of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar methods to replace them. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims of the present invention, they should fall within the protection scope of the present invention.

Claims

1. A preparation method of a red mud activator, characterized in that, It includes the following steps: (1) Dry the as-received red mud, then grind and sieve it to obtain red mud powder; (2) Prepare a red mud solution with a solid-liquid ratio of 1:3 based on the red mud powder; (3) Add sodium hexametaphosphate to the red mud solution, stir and age it to obtain a red mud activator.

2. The preparation method of a red mud activator according to claim 1, characterized in that: In step (1), the drying temperature is 105 - 115 °C, and the drying time is 8 - 10 h; the grinding is carried out by ball milling for 15 - 30 min; the sieving is carried out using a square-hole sieve with a mesh number of 300 meshes.

3. The preparation method of a red mud activator according to claim 1, characterized in that: In step (2), the mass ratio of sodium hexametaphosphate to red mud is 1 - 1.5:

1.

4. The preparation method of a red mud activator according to claim 1, characterized in that: In step (3), the stirring time is 5 - 10 min, and the aging time is 24 - 48 h.

5. A gypsum-based self-leveling mortar for activating type II anhydrous phosphogypsum and synergistically using hemihydrate phosphogypsum with red mud, characterized in that, It includes the following components by weight: 60 - 70 parts of hemihydrate phosphogypsum, 10 - 15 parts of type II anhydrous phosphogypsum, 15 - 25 parts of manufactured sand, 0.01 - 0.03 parts of cellulose ether, 0.001 - 0.003 parts of defoamer, 45 - 55 parts of red mud activator, and the red mud activator is prepared by the preparation method of the red mud activator described in any one of claims 1 - 4.

6. A method for preparing the gypsum-based self-leveling mortar according to claim 5, characterized in that, It includes the following steps: (1) Mix the hemihydrate phosphogypsum, type II anhydrous phosphogypsum, and manufactured sand evenly; (2) Add cellulose ether, defoamer, and red mud activator in sequence, and carry out the preparation and curing of the slurry to obtain the gypsum-based self-leveling mortar.

7. A gypsum-based self-leveling mortar for activating II-type anhydrous phosphogypsum and synergistically using hemihydrate phosphogypsum according to claim 6, characterized in that, The preparation method of the hemihydrate phosphogypsum includes the following steps: Dry the as-received hemihydrate phosphogypsum powder, then grind and sieve it to obtain the hemihydrate phosphogypsum.

8. A gypsum-based self-leveling mortar for activating II-type anhydrous phosphogypsum and synergistically using hemihydrate phosphogypsum according to claim 7, characterized in that: The drying temperature is 180 - 200 °C, and the drying time is 8 - 10 h; the grinding is carried out by ball milling for 15 - 30 min; the sieving is carried out using a square-hole sieve with a mesh number of 200 meshes.

9. A gypsum-based self-leveling mortar for activating II-type anhydrous phosphogypsum and synergistically using hemihydrate phosphogypsum according to claim 6, characterized in that: The mass percentage of β-CaSO4·0.5H2O in the hemihydrate phosphogypsum is greater than 70%, and its physical and mechanical properties should be able to meet the requirements for grades 3.0 - 4.0 in GB / T9776.

10. A gypsum-based self-leveling mortar for activating II-type anhydrous phosphogypsum and synergistically using hemihydrate phosphogypsum according to claim 6, characterized in that: The defoamer is polyethylene glycol.

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