Composite dispersion early strength agent suitable for phosphogypsum-red mud-based cementing material and preparation method of composite dispersion early strength agent

Abstract

The invention discloses a composite dispersion early strength agent suitable for a phosphogypsum-red mud-based cementing material and a preparation method thereof.The composite dispersion early strength agent comprises a water reducing agent serving as a dispersion component and an early strength agent serving as an early strength component, the dispersion component is an amphoteric water reducing agent synthesized through a water solution free radical copolymerization method, and the early strength agent is an amphoteric water reducing agent synthesized through a water solution free radical copolymerization method. The early strength component is obtained through a small molecule compound compounding method. The composite water reducer dispersing early-stage agent is suitable for phosphogypsum-red mud based cementing materials, and has the advantages of enhancing the dispersity of all components in a system, increasing the contact area between phosphogypsum and red mud particles and slag, promoting hydration of the cementing materials and improving the 3d strength, the 7d strength and the 28d strength of the cementing materials.

Description

Technical Field

[0001] This invention belongs to the field of admixture technology, and particularly relates to a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials and its preparation method. Background Technology

[0002] Numerous studies have explored the application of phosphogypsum and red mud in cementitious materials to improve the utilization rate of these two solid wastes. However, the effects of various commercially available admixtures on phosphogypsum-red mud-based cementitious materials are not significant. The problem with phosphogypsum lies in the low dissolution rate of calcium sulfate dihydrate in the system. Since phosphogypsum is the source of the vast majority of sulfate ions in the system, the sulfate ion concentration directly affects the formation of ettringite, thus impacting the strength of the cementitious material. The main problem with red mud is the low utilization rate of the iron and aluminum phases, resulting in fewer hydration products such as hydrated calcium ferrate and hydrated calcium aluminate, which also affect the strength of the cementitious material. Therefore, the current use of red mud as a cementitious material, especially in combination with phosphogypsum, suffers from low utilization, unsatisfactory strength, poor fluidity of the cementitious system, and long setting time. Using commercially available polycarboxylate superplasticizers leads to problems such as bleeding, long setting time, and poor early strength in the cementitious material. Therefore, a suitable admixture formulation for this solid waste system is needed to address these issues. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials and its preparation method.

[0004] The present invention is achieved through the following technical solutions.

[0005] This invention provides a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials. By weight, it comprises 10-15 parts of a water-reducing agent and 85-90 parts of an early strength agent. The water-reducing agent comprises the following components: 45-60 parts of acrylic acid, 450-500 parts of methyl allyl polyoxyethylene ether, 20-30 parts of N-(2-aminoethyl)acrylamide, 7-9 parts of 3-mercaptopropionic acid, 8-12 parts of ammonium persulfate, 57-92 parts of alkaline solution, and 810-924 parts of deionized water.

[0006] Preferably, the early strength agent comprises the following components in parts by weight: 25-30 parts calcium gluconate, 20-25 parts sodium citrate, 20-25 parts sodium aluminate, 20-25 parts aluminum borate, and 5-10 parts lithium sulfate.

[0007] A method for preparing a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials includes the steps of preparing a water-reducing agent and an early strength agent separately, and then mixing the water-reducing agent and the early strength agent to obtain a composite dispersing early strength agent; The method for preparing the water-reducing agent includes the following steps: A1: Take acrylic acid, methyl allyl polyoxyethylene ether, 3-mercaptopropionic acid, ammonium persulfate and N-(2-aminoethyl)acrylamide; A2: Mix methyl allyl polyoxyethylene ether and deionized water to obtain solution A; A3: Preparation of solution B: Dissolve acrylic acid, N-(2-aminoethyl)acrylamide and 3-mercaptopropionic acid in deionized water; A4: Solution C: Dissolve ammonium persulfate in deionized water; A5: After solution A is dissolved by stirring, add solutions B and C dropwise to solution A, and continue heating and stirring for at least 30 minutes after titration to obtain solution D; A6: After the reaction is complete, let solution D cool naturally to room temperature, then add alkaline solution dropwise until pH=7, then add deionized water and mix to obtain a water-reducing agent solution; A7: The water-reducing agent aqueous solution is made into a solid dry powder through freeze drying process.

[0008] Preferably, in A2, methyl allyl polyoxyethylene ether and deionized water are mixed in a mass ratio of 1:1 and stirred in a water bath at 55-65°C for 20-40 minutes. In A4, ammonium persulfate is dissolved in deionized water at a ratio of 1:20.

[0009] Preferably, in step A5, after solution A is stirred and dissolved for 15-30 minutes, solutions B and C are added dropwise to solution A at a uniform rate over a period of 210-270 minutes, and after titration, the solution is heated and stirred continuously for at least 30 minutes to obtain solution D.

[0010] Preferably, a 25-35% sodium hydroxide solution is added dropwise to A6.

[0011] Preferably, deionized water is added to A6 until the solid content is 30-50% to obtain a water-reducing agent solution.

[0012] Preferably, the method for preparing the early strength agent includes the following steps: B1: Calcium gluconate, sodium citrate, sodium aluminate, aluminum borate, and lithium sulfate are mixed evenly to obtain a mixture; B2: Screening the mixture; B3: The sieved mixture is dried to obtain an early strength agent.

[0013] Preferably, the mixture in B2 is sieved using an 80-100 mesh screen.

[0014] Preferably, B3 is dried in an oven at 40-60°C until the moisture content is less than 1%.

[0015] The beneficial effects of this invention are as follows: This invention addresses the problems of severe agglomeration, difficulty in dispersion, and poor early strength of phosphogypsum-red mud-based cementitious materials. It synthesizes an amphoteric polycarboxylate superplasticizer, freeze-dries it into a solid powder, and then combines it with several small molecule compounds that promote early strength to form a novel admixture that is convenient to use, has good compatibility, stable chemical properties, and is easy to store and transport.

[0016] The composite dispersing early strength agent described in this invention enhances the fluidity of phosphogypsum-red mud-based cementitious materials, improves workability, and shortens the system setting time and improves early strength by increasing the solubility of phosphogypsum and further stimulating the activity of aluminum components in red mud. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0018] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0019] Red mud particles exhibit a negative potential in cementitious material suspensions, and the key to the dispersibility of polycarboxylate superplasticizers lies in the negatively charged -COO groups. - The functional groups adsorb onto cement particles exhibiting a positive electrical potential, achieving dispersion through their long side-chain structure. However, when red mud is introduced into the cementitious system, the red mud particles exhibit a negative electrical potential, preventing ordinary polycarboxylate superplasticizers from effectively adsorbing onto the cementitious particles and thus hindering their dispersion performance. To properly disperse red mud components, a positively charged functional group needs to be introduced into the polycarboxylate superplasticizer to form an amphoteric superplasticizer, which can then readily adsorb onto the red mud particles.

[0020] This invention utilizes acrylic acid, methyl allyl polyoxyethylene ether, and N-(2-aminoethyl)acrylamide to open carbon-carbon double bonds and interconnect them under the action of initiators and chain transfer agents to form a polymer backbone structure, while simultaneously introducing -COO... - -N + The purpose of the long side chain structure.

[0021] The ratio of acrylic acid, N-(2-aminoethyl)acrylamide, and methyl allyl polyoxyethylene ether directly affects the magnitude of the anionic and cationic zeta potentials and the side chain density of the synthesized amphoteric water-reducing agent. Acrylic acid contains -COO... - N-(2-aminoethyl)acrylamide has -N +The amounts of the two small-molecule monomers directly determine the levels of anionic and cationic potentials; methyl allyl polyoxyethylene ether has a long side-chain structure, and the density of the side chains directly affects the dispersion effect of the water-reducing agent. Taking all the above factors into consideration, this invention controls n1(-COO) - ):n2(-N + =3.0~4.0, and [n1(-COO) - )+n2(-N + )]:n3 (polyether side chain)=4.5~5.5.

[0022] In this invention, 3-mercaptopropionic acid is a chain transfer agent. During synthesis, the chain transfer agent connects the unsaturated polyether side chains to the methacrylic acid backbone. The amount of chain transfer agent affects the molecular weight and polymerization rate of the polymer. Excessive or insufficient molecular weight of the water-reducing agent will adversely affect its dispersion performance. To ensure a suitable polymerization rate and appropriate molecular weight after synthesis, the amount of chain transfer agent in this invention is controlled at n1 (3-mercaptopropionic acid):n2 (polyether side chains) = 0.4~0.6.

[0023] In this invention, ammonium persulfate acts as an initiator. During the synthesis process, ammonium persulfate undergoes pyrolysis under heating, generating two active free radicals, SO4. - These two free radicals are crucial for initiating the polymerization reaction. Insufficient ammonium persulfate will decrease the reaction rate and prolong the reaction time, while excessive amounts will increase side reactions and affect product concentration. In this invention, the initiator dosage is controlled at n1 (ammonium persulfate):n2 (polyether side chain) = 0.15~0.3.

[0024] In preparing the amphoteric polycarboxylate superplasticizer, this invention uses water bath heating, which makes the reaction vessel more uniformly heated. The water bath temperature is controlled at 55-65℃. Maintaining a certain temperature is beneficial for better breaking of ionic bonds and accelerating the reaction rate. In order not to affect the molecular structure of the copolymer, the reaction temperature cannot be too high. Therefore, the reaction temperature is controlled at 55-65℃.

[0025] For early-strength agents: The main function of calcium gluconate is to accelerate the dissolution of phosphogypsum, providing more free Ca to the system. 2+ and SO4 2- It primarily accelerates the dissolution of phosphogypsum by adjusting the pH value, and also provides calcium. 2+It promotes the reaction of aluminum and calcium in red mud, forming early hydration products (such as ettringite), thereby improving early strength. When its content is below 20%, it cannot significantly accelerate the dissolution of phosphogypsum and the reaction of red mud, resulting in poor early strength effect and long setting time. When it is above 30%, excessive calcium gluconate may lead to excessively high ion concentration in the solution, inhibiting crystal growth and causing drying shrinkage cracks in the material. At the same time, it increases costs and its hygroscopic nature leads to a decrease in the stability of the early strength agent.

[0026] Sodium citrate's main function is to chelate calcium. 2+ And Al 3+ Optimizing the microstructure of the reaction products of phosphogypsum and red mud and adjusting the pH value of the system through buffering improves the uniformity and workability of the material. When its content is below 15%, insufficient complexation leads to premature reaction of metal ions in the system, generating uneven hydration products and resulting in reduced strength. When it is above 25%, excessive sodium citrate inhibits the dissolution and hydration reaction of phosphogypsum, resulting in prolonged setting time and decreased early strength.

[0027] Sodium aluminate's main function is to provide AlO2. - , with Ca in the system 2+ The reaction produces ettringite, which provides early strength and also creates a certain alkaline environment, enhancing the reactivity of iron and aluminum oxides in the red mud. When its content is below 15%, the early alkaline environment of the system is insufficient, hydration is slow, and it is difficult to form sufficient early hydration products, resulting in insufficient strength. When it is above 25%, excessive sodium aluminate will cause excessive alkalinity, which may lead to instability in the system and may cause the setting time to be shortened too much, affecting the workability.

[0028] The main function of aluminum borate is to provide Al. 3+ With SO4 in the system 2- The reaction produces ettringite, which provides the material with density and early strength. It also improves the crystal morphology of phosphogypsum in the system and increases the uniformity of hydration products. When its content is below 15%, Al... 3+ The drawback is that the amount of ettringite formed is low, resulting in limited early strength development. When the content exceeds 25%, excessive aluminum borate may cause uneven crystallization within the material, reducing its stability.

[0029] The main function of lithium sulfate is to regulate the crystallization process of phosphogypsum by releasing sulfate ions, preventing structural defects caused by premature crystallization. Additionally, lithium ions can enhance the activity of aluminum and iron oxides in red mud, further promoting the hydration reaction. When its content is below 5%, it is difficult to effectively control the crystal growth of phosphogypsum, which may lead to internal crystal defects in the material. Above 10%, it may inhibit the hydration reaction of red mud and phosphogypsum, and cause the deposition of byproducts, reducing the overall strength.

[0030] Example 1: like Figure 1 As shown, a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials includes a water-reducing agent. By mass parts, the water-reducing agent includes the following components: 57 parts of acrylic acid (AA), 480 parts of methyl allyl polyoxyethylene ether 2400 (HPEG-2400), 23 parts of N-(2-aminoethyl)acrylamide, 8 parts of 3-mercaptopropionic acid (MPA), 9 parts of ammonium persulfate (APS), 73 parts of 30% sodium hydroxide solution, and 860 parts of deionized water.

[0031] The method for preparing the water-reducing agent includes the following steps: A1: Prepare the raw materials. Weigh out acrylic acid, methyl allyl polyoxyethylene ether 2400 (HPEG-2400), 3-mercaptopropionic acid, ammonium persulfate and N-(2-aminoethyl)acrylamide according to the corresponding mass ratio using an electronic scale and a glass beaker. A2: Add the weighed methyl allyl polyoxyethylene ether 2400 (HPEG-2400) and deionized water to a four-necked flask, mix them in a 1:1 mass ratio, and then place the four-necked flask in a water bath and heat it at 60°C for 30 minutes while stirring with a mechanical stirrer to completely dissolve the methyl allyl polyoxyethylene ether 2400 (HPEG-2400) to obtain solution A; A3: Preparation of solution B: Dissolve the weighed acrylic acid, N-(2-aminoethyl)acrylamide and 3-mercaptopropionic acid in deionized water; A4: Solution preparation C: Dissolve the weighed ammonium persulfate in deionized water at a mass ratio of 1:20; A5: After solution A in the four-necked flask is dissolved by stirring in a water bath at the specified temperature and with a mechanical stirrer for 20 minutes, solutions B and C are added dropwise to solution A in the four-necked flask at a uniform rate over a period of 260 minutes to prevent incomplete reaction due to short reaction time, which would affect the dispersion performance of the water-reducing agent. After titration, the mixture is heated and stirred for 30 minutes to ensure complete copolymerization of the aqueous solutions of each component, resulting in solution D. A6: After the reaction is complete, let solution D cool naturally to room temperature, then add 30% sodium hydroxide solution until pH=7, then add deionized water until the solid content is 40%, to obtain amphoteric polycarboxylate superplasticizer solution; A7: The aqueous solution of amphoteric polycarboxylate superplasticizer is made into a solid dry powder using a freeze-drying oven.

[0032] Example 2: like Figure 1As shown, a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials comprises, by weight, 15 parts of water-reducing agent and 85 parts of early strength agent, wherein the water-reducing agent is based on Example 1.

[0033] The early strength agent, by weight, comprises the following components: 30 parts calcium gluconate, 20 parts sodium citrate, 20 parts sodium aluminate, 20 parts aluminum borate, and 10 parts lithium sulfate.

[0034] A method for preparing a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials includes the steps of preparing a water-reducing agent and an early strength agent separately, and then mixing the water-reducing agent and the early strength agent to obtain a composite dispersing early strength agent; The preparation method of the early strength agent includes the following steps: B1: Mix calcium gluconate, sodium citrate, sodium aluminate, aluminum borate, and lithium sulfate evenly to obtain 200g of mixture; B2: The mixture is sieved using a 90-mesh screen, mainly to remove large particles and reduce errors; B3: The sieved mixture is placed in an oven and dried at 50°C until the moisture content is less than 1% to obtain an early strength agent.

[0035] Example 3: like Figure 1 As shown, a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials comprises, by weight, 15 parts of water-reducing agent and 85 parts of early strength agent, wherein the water-reducing agent is based on Example 1.

[0036] The early strength agent, by weight, comprises the following components: 25 parts calcium gluconate, 25 parts sodium citrate, 20 parts sodium aluminate, 20 parts aluminum borate, and 10 parts lithium sulfate.

[0037] A method for preparing a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials includes the steps of preparing a water-reducing agent and an early strength agent separately, and then mixing the water-reducing agent and the early strength agent to obtain a composite dispersing early strength agent; The preparation method of the early strength agent includes the following steps: B1: Mix calcium gluconate, sodium citrate, sodium aluminate, aluminum borate, and lithium sulfate evenly to obtain 200g of mixture; B2: Sieve the mixture using an 80-mesh sieve; B3: The sieved mixture is placed in an oven and dried at 40°C until the moisture content is less than 1% to obtain an early strength agent.

[0038] Example 4: like Figure 1As shown, a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials comprises, by weight, 15 parts of water-reducing agent and 85 parts of early strength agent, wherein the water-reducing agent is based on Example 1.

[0039] The early strength agent, by weight, comprises the following components: 25 parts calcium gluconate, 20 parts sodium citrate, 25 parts sodium aluminate, 25 parts aluminum borate, and 5 parts lithium sulfate.

[0040] A method for preparing a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials includes the steps of preparing a water-reducing agent and an early strength agent separately, and then mixing the water-reducing agent and the early strength agent to obtain a composite dispersing early strength agent; The preparation method of the early strength agent includes the following steps: B1: Mix calcium gluconate, sodium citrate, sodium aluminate, aluminum borate, and lithium sulfate evenly to obtain 200g of mixture; B2: Sieve the mixture using a 100-mesh sieve; B3: The sieved mixture is placed in an oven and dried at 60°C until the moisture content is less than 1% to obtain an early strength agent.

[0041] Example 5: like Figure 1 As shown, a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials comprises, by weight, 10-15 parts of a water-reducing agent and 85 parts of an early strength agent. The water-reducing agent comprises the following components: 45 parts of acrylic acid (AA), 450 parts of methyl allyl polyoxyethylene ether 2400 (HPEG-2400), 20 parts of N-(2-aminoethyl)acrylamide, 7 parts of 3-mercaptopropionic acid (MPA), 8 parts of ammonium persulfate (APS), 57 parts of sodium hydroxide solution, and 810 parts of deionized water.

[0042] The early strength agent, by weight, comprises the following components: 25 parts calcium gluconate, 20 parts sodium citrate, 25 parts sodium aluminate, 20 parts aluminum borate, and 10 parts lithium sulfate.

[0043] A method for preparing a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials includes the steps of preparing a water-reducing agent and an early strength agent separately, and then mixing the water-reducing agent and the early strength agent to obtain a composite dispersing early strength agent; The method for preparing the water-reducing agent includes the following steps: A1: Prepare the raw materials. Weigh out acrylic acid, methyl allyl polyoxyethylene ether 2400 (HPEG-2400), 3-mercaptopropionic acid, ammonium persulfate and N-(2-aminoethyl)acrylamide according to the corresponding mass ratio using an electronic scale and a glass beaker. A2: Add the weighed methyl allyl polyoxyethylene ether 2400 (HPEG-2400) and deionized water to a four-necked flask, mix them in a 1:1 mass ratio, and then place the four-necked flask in a water bath and heat it at 55°C for 20 minutes while stirring with a mechanical stirrer to completely dissolve the methyl allyl polyoxyethylene ether 2400 (HPEG-2400) to obtain solution A; A3: Preparation of solution B: Dissolve the weighed acrylic acid, N-(2-aminoethyl)acrylamide and 3-mercaptopropionic acid in deionized water; A4: Solution preparation C: Dissolve the weighed ammonium persulfate in deionized water at a mass ratio of 1:20; A5: After solution A in the four-necked flask is dissolved by stirring in a water bath at the specified temperature and with a mechanical stirrer for 15 minutes, solutions B and C are added dropwise to solution A in the four-necked flask at a uniform rate over a period of 210 minutes. After titration, the solution is heated and stirred for 30 minutes to ensure that the copolymerization reaction of each component aqueous solution is complete, thus obtaining solution D. A6: After the reaction is complete, let solution D cool naturally to room temperature, then add 25% sodium hydroxide solution until pH=7, then add deionized water until the solid content is 30%, to obtain amphoteric polycarboxylate superplasticizer solution; A7: The aqueous solution of amphoteric polycarboxylate superplasticizer is made into a solid dry powder using a freeze-drying oven.

[0044] The preparation method of the early strength agent includes the following steps: B1: Mix calcium gluconate, sodium citrate, sodium aluminate, aluminum borate, and lithium sulfate evenly to obtain 200g of mixture; B2: Sieve the mixture using an 80-mesh sieve; B3: The sieved mixture is placed in an oven and dried at 40°C until the moisture content is less than 1% to obtain an early strength agent.

[0045] Example 6: like Figure 1 As shown, a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials comprises, by weight, 15 parts of water-reducing agent and 90 parts of early strength agent. The water-reducing agent comprises the following components: 60 parts of acrylic acid (AA), 500 parts of methyl allyl polyoxyethylene ether 2400 (HPEG-2400), 30 parts of N-(2-aminoethyl)acrylamide, 9 parts of 3-mercaptopropionic acid (MPA), 12 parts of ammonium persulfate (APS), 92 parts of sodium hydroxide solution, and 924 parts of deionized water.

[0046] The early strength agent, by weight, comprises the following components: 25 parts calcium gluconate, 25 parts sodium citrate, 25 parts sodium aluminate, 20 parts aluminum borate, and 5 parts lithium sulfate.

[0047] A method for preparing a composite dispersing early strength agent suitable for phosphogypsum-red mud-based cementitious materials includes the steps of preparing a water-reducing agent and an early strength agent separately, and then mixing the water-reducing agent and the early strength agent to obtain a composite dispersing early strength agent; The method for preparing the water-reducing agent includes the following steps: A1: Prepare the raw materials. Weigh out acrylic acid, methyl allyl polyoxyethylene ether 2400 (HPEG-2400), 3-mercaptopropionic acid, ammonium persulfate and N-(2-aminoethyl)acrylamide according to the corresponding mass ratio using an electronic scale and a glass beaker. A2: Add the weighed methyl allyl polyoxyethylene ether 2400 (HPEG-2400) and deionized water to a four-necked flask. Mix methyl allyl polyoxyethylene ether 2400 (HPEG-2400) and deionized water in a 1:1 mass ratio. Then place the four-necked flask in a water bath and heat it at 65°C for 40 minutes while stirring with a mechanical stirrer to completely dissolve methyl allyl polyoxyethylene ether 2400 (HPEG-2400) to obtain solution A. A3: Preparation of solution B: Dissolve the weighed acrylic acid, N-(2-aminoethyl)acrylamide and 3-mercaptopropionic acid in deionized water; A4: Solution preparation C: Dissolve the weighed ammonium persulfate in deionized water at a mass ratio of 1:20; A5: After solution A in the four-necked flask is dissolved by stirring in a water bath at a specified temperature and with a mechanical stirrer for 30 minutes, solutions B and C are added dropwise to solution A in the four-necked flask at a uniform rate over a period of 270 minutes. After titration is completed, the solution is heated and stirred for 30 minutes to ensure that the copolymerization reaction of each component aqueous solution is complete, thus obtaining solution D. A6: After the reaction is complete, let solution D cool naturally to room temperature, then add 35% sodium hydroxide solution until pH=7, then add deionized water until the solid content is 50%, to obtain amphoteric polycarboxylate superplasticizer solution; A7: The aqueous solution of amphoteric polycarboxylate superplasticizer is made into a solid dry powder using a freeze-drying oven.

[0048] The preparation method of the early strength agent includes the following steps: B1: Mix calcium gluconate, sodium citrate, sodium aluminate, aluminum borate, and lithium sulfate evenly to obtain 200g of mixture; B2: Sieve the mixture using a 100-mesh sieve; B3: The sieved mixture is placed in an oven and dried at 60°C until the moisture content is less than 1%, thus obtaining the early strength agent.

[0049] The water-reducing agent of Example 1 and the composite dispersing early-strength agent of Examples 2-6 were applied to the standard mix proportion of phosphogypsum-red mud-based all-solid-waste green cement. The cement includes cement phosphogypsum, slag, red mud, quicklime, and a water-cement ratio of 0.35. Among them, the phosphogypsum is dried undisturbed phosphogypsum, which needs to be crushed and dried, and the slag is S95 grade slag.

[0050] The specific mixing method is as follows: First, mix phosphogypsum, slag, red mud, and water according to the specified proportions. Then, add the composite dispersant according to the proportions in Table 1, and mix the composite dispersant early-strength agents of Examples 2-6 using a two-component method. First, stir the phosphogypsum, slag, red mud, and water. During the stirring process, gradually add the mixed water-reducing agent prepared in Example 1 or the composite dispersant early-strength agents prepared in Examples 2-6. Stir together at low speed for 120 seconds, stop stirring for 15 seconds, and then stir at high speed for 120 seconds before pouring into the mold. The experimental results of the paste performance are shown in Table 1.

[0051] Table 1. Early performance test results of Examples 1-6

[0052] In the above seven embodiments, the benchmark case is the test result without adding the composite dispersing early strength agent of the present invention. Example 1 is the synthesis experiment of the dispersing component of the present invention, namely the amphoteric water-reducing agent. Examples 2-6 are five examples in which the amphoteric water-reducing agent and the early strength component are compounded within the aforementioned range of the present invention to obtain the composite dispersing early strength agent proposed in the present invention, and its effect on the performance of phosphogypsum-red mud-based solid waste cementitious materials is tested.

[0053] The composite dispersing early-strength agent proposed in this invention significantly improves the fluidity of phosphogypsum-red mud-based cementitious materials, with an improvement of over 136%, meeting construction requirements. Furthermore, the setting time is significantly shortened, and the strength is substantially improved from 3 days to 28 days.

Claims

1. A composite dispersant for early strength in phosphogypsum-red mud-based cementitious materials, characterized in that: The product comprises, by weight, 10-15 parts of water-reducing agent and 85-90 parts of early-strength agent. The water-reducing agent includes the following components: 45-60 parts of acrylic acid, 450-500 parts of methyl allyl polyoxyethylene ether, 20-30 parts of N-(2-aminoethyl)acrylamide, 7-9 parts of 3-mercaptopropionic acid, 8-12 parts of ammonium persulfate, 57-92 parts of alkaline solution, and 810-924 parts of deionized water.

2. The composite dispersing early strength agent suitable for phosphogypsum-red mud based cementitious materials as described in claim 1, characterized in that: The early strength agent, by weight, comprises the following components: 25-30 parts calcium gluconate, 20-25 parts sodium citrate, 20-25 parts sodium aluminate, 20-25 parts aluminum borate, and 5-10 parts lithium sulfate.

3. A method for preparing a composite dispersing early-strength agent suitable for phosphogypsum-red mud-based cementitious materials as described in any one of claims 1-2, characterized in that: The process includes the steps of preparing water-reducing agent and early-strength agent separately, and then mixing the water-reducing agent and early-strength agent to obtain a composite dispersion early-strength agent; The method for preparing the water-reducing agent includes the following steps: A1: Take acrylic acid, methyl allyl polyoxyethylene ether, 3-mercaptopropionic acid, ammonium persulfate and N-(2-aminoethyl)acrylamide; A2: Mix methyl allyl polyoxyethylene ether and deionized water to obtain solution A; A3: Preparation of solution B: Dissolve acrylic acid, N-(2-aminoethyl)acrylamide and 3-mercaptopropionic acid in deionized water; A4: Solution C: Dissolve ammonium persulfate in deionized water; A5: After solution A is dissolved by stirring, add solutions B and C dropwise to solution A, and continue heating and stirring for at least 30 minutes after titration to obtain solution D; A6: After the reaction is complete, let solution D cool naturally to room temperature, then add alkaline solution dropwise until pH=7, then add deionized water and mix to obtain a water-reducing agent solution; A7: The water-reducing agent aqueous solution is made into a solid dry powder through freeze drying process.

4. The preparation method of the composite dispersing early strength agent suitable for phosphogypsum-red mud based cementitious materials as described in claim 3, characterized in that: The methyl allyl polyoxyethylene ether and deionized water in A2 are mixed in a mass ratio of 1:1 and stirred in a water bath at 55-65℃ for 20-40 minutes. In A4, ammonium persulfate is dissolved in deionized water at a ratio of 1:

20.

5. The preparation method of the composite dispersing early strength agent suitable for phosphogypsum-red mud based cementitious materials as described in claim 3, characterized in that: In step A5, after solution A is stirred and dissolved for 15-30 minutes, solutions B and C are added dropwise to solution A at a uniform rate over a period of 210-270 minutes. After titration, the solution is heated and stirred continuously for at least 30 minutes to obtain solution D.

6. The preparation method of the composite dispersing early strength agent suitable for phosphogypsum-red mud based cementitious materials as described in claim 3, characterized in that: A 25-35% sodium hydroxide solution is added dropwise to A6.

7. The preparation method of the composite dispersing early strength agent suitable for phosphogypsum-red mud based cementitious materials as described in claim 3, characterized in that: Deionized water is added to A6 until the solid content is 30-50% to obtain a water-reducing agent solution.

8. The preparation method of the composite dispersing early strength agent suitable for phosphogypsum-red mud based cementitious materials as described in claim 3, characterized in that: The preparation method of the early strength agent includes the following steps: B1: Calcium gluconate, sodium citrate, sodium aluminate, aluminum borate, and lithium sulfate are mixed evenly to obtain a mixture; B2: Screening the mixture; B3: The sieved mixture is dried to obtain an early strength agent.

9. The preparation method of the composite dispersing early strength agent suitable for phosphogypsum-red mud based cementitious materials as described in claim 8, characterized in that: The mixture in B2 is sieved using an 80-100 mesh screen.

10. The method for preparing a composite dispersing early strength agent suitable for phosphogypsum-red mud based cementitious materials as described in claim 8, characterized in that: B3 is dried in an oven at 40-60℃ until the moisture content is less than 1%.

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