A semi-hydrated phosphogypsum gel material, and a preparation method and application thereof

Abstract

This disclosure pertains to the field of phosphogypsum technology, specifically relating to a hemihydrate phosphogypsum gel material, its preparation method, and its applications. The gel material is prepared using hemihydrate phosphogypsum, an alkaline activator, and a water-reducing agent. This reduces water consumption while achieving a good retarding effect. By introducing silicate compounds and crystal form regulators with succinic acid groups and silane groups, the synergistic effect of these compounds and regulators provides a cementing network for the dihydrate phosphogypsum crystals, increasing bonding strength and thus improving the strength of gypsum products. Therefore, the hemihydrate phosphogypsum gel material provided by this disclosure maintains the mechanical properties of the gel material while reducing water consumption and extending setting time.

Description

Technical Field

[0001] This disclosure belongs to the field of phosphogypsum technology, specifically relating to a hemihydrate phosphogypsum gel material, its preparation method and application. Background Technology

[0002] Phosphogypsum is a solid waste residue produced during the wet process of phosphoric acid production. Its utilization rate is extremely low, and it is mostly disposed of by stockpiling. Long-term stockpiling not only occupies a large amount of land resources, but also causes great harm to the environment. Therefore, the comprehensive development and utilization of phosphogypsum has become an urgent safety and environmental protection issue to be addressed. The hemihydrate phosphoric acid process has the advantages of low energy consumption and high phosphoric acid concentration. The shift from the dihydrate process to the hemihydrate process is the future development trend of the phosphoric acid chemical industry. Hemihydrate phosphogypsum is a by-product of the hemihydrate phosphoric acid process. Its main component is CaSO4·1 / 2H2O. It has potential gelling activity. The gelation reaction of hemihydrate phosphogypsum is as follows: 4CaSO4·1 / 2H2O + 2H2O → 3CaSO4·2H2O. However, hemihydrate phosphogypsum as a gelling material has the following disadvantages: (1) the water requirement is much greater than the actual water consumption for hydration; (2) the setting time is short.

[0003] Modifying hemihydrate phosphogypsum with admixtures such as water-reducing agents and retarders can effectively solve the aforementioned problems of hemihydrate phosphogypsum gel materials. 2+ By adsorbing onto the surface of gypsum particles, the properties of the solid-liquid interface of the gypsum particles are altered, thereby improving the dispersibility of the gypsum particles, releasing adsorbed water from phosphogypsum, reducing water demand, and increasing hydration rate; retarders are usually small-molecule organic acids such as citric acid and phosphates, which tend to react with free Ca2+. 2+ They combine to form insoluble substances, thereby reducing the supersaturation of the gypsum liquid phase, especially the early supersaturation, thus reducing the dissolution of hemihydrate gypsum and the formation of crystal nuclei, and thus slowing down the hydration process. Although such retarders have a good retarding effect, the reduction of supersaturation in the early stage of the reaction system restricts the formation of crystal nuclei and crystal growth, resulting in reduced overlap between crystals in the final set product, loose structure, and a significant decrease in the mechanical strength of the material.

[0004] Therefore, there is an urgent need to develop methods for utilizing hemihydrate phosphogypsum in order to prepare gel materials with good mechanical properties while reducing water consumption and extending setting time.

[0005] In view of this, this disclosure is hereby made. Summary of the Invention

[0006] The purpose of this disclosure is to provide a hemihydrate phosphogypsum gel material, its preparation method and application, which aims to reduce water consumption and prolong setting time while ensuring the mechanical properties of the gel material.

[0007] To achieve the above-mentioned objectives of this disclosure, the following technical solutions may be adopted:

[0008] The disclosed solution includes a hemihydrate phosphogypsum gel material, the raw materials of which, by mass parts, include: 100 parts hemihydrate phosphogypsum, 1-8 parts alkaline activator, 0.1-1.0 parts water-reducing agent, 0.05-0.30 parts crystal form regulator, 0.1-0.8 parts silicate compound and 40-60 parts water;

[0009] The crystal form regulator contains succinic acid groups and silane groups.

[0010] In some embodiments of this disclosure, the raw materials, by mass parts, include: 100 parts hemihydrate phosphogypsum, 2-5 parts alkaline activator, 0.1-0.5 parts water-reducing agent, 0.1-0.2 parts crystal form regulator, 0.2-0.5 parts silicate compound, and 40-60 parts water.

[0011] In some embodiments of this disclosure, the crystal form modifier is obtained by reacting epoxysiloxane with aspartic acid.

[0012] In some embodiments of this disclosure, when preparing the crystal form regulator, the molar ratio of the epoxy group in the epoxysiloxane to the amino group in the aspartic acid is controlled to be (1.0-1.2):1.

[0013] In some embodiments of this disclosure, the epoxysiloxane is selected from at least one of 3-glycidyl etheroxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, and 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0014] In some embodiments of this disclosure, the general chemical formula of the silicate compound is:

[0015]

[0016] In this configuration, R1, R2, and R3 are all C1-C8 alkyl groups, R4 is O-R4' or R4', R4' is a C1-C8 alkyl group or a substituted alkyl group, and the substituents on the substituted alkyl group are selected from OH or COOH.

[0017] In some embodiments of this disclosure, the silica compound is tetraethyl orthosilicate.

[0018] In some embodiments of this disclosure, the adsorbed water content of hemihydrate phosphogypsum is 15%-20%.

[0019] In some embodiments of this disclosure, the type of hemihydrate phosphogypsum is selected from at least one of α-type and β-type.

[0020] In some embodiments of this disclosure, the soluble phosphorus content of hemihydrate phosphogypsum is ≤0.1%, and the soluble fluorine content is ≤0.03%.

[0021] In some embodiments of this disclosure, the alkaline activator is selected from at least one of cement, quicklime, and blast furnace slag.

[0022] In some embodiments of this disclosure, the water-reducing agent is a polymeric water-reducing agent.

[0023] In some embodiments of this disclosure, the polymeric water-reducing agent is selected from at least one of polycarboxylate water-reducing agents, lignin sulfonate water-reducing agents, and starch water-reducing agents.

[0024] The solution provided in this disclosure also includes a method for preparing a hemihydrate phosphogypsum gel material, comprising: preparing the material according to the raw material composition of the hemihydrate phosphogypsum gel material.

[0025] In some embodiments of this disclosure, the method includes: first premixing and drying a portion of hemihydrate phosphogypsum with a water-reducing agent, and then mixing it with the remaining raw materials.

[0026] In some embodiments of this disclosure, a portion of hemihydrate phosphogypsum is first mixed with a water-reducing agent and dried to obtain a first material. The first material is then mixed with an alkaline activator to obtain a second material. The second material is then mixed with a crystal form regulator, tetraethyl orthosilicate, and the remaining hemihydrate phosphogypsum to obtain a third material. Finally, the third material is mixed with water.

[0027] In some embodiments of this disclosure, the hemihydrate phosphogypsum added during the preparation of the first material accounts for 50%-70% of the total mass of the hemihydrate phosphogypsum.

[0028] In some embodiments of this disclosure, the preparation process of the first material includes: ball milling a portion of hemihydrate phosphogypsum with a water-reducing agent, followed by drying and sieving.

[0029] In some embodiments of this disclosure, the ball milling speed is controlled to be 200 rpm-300 rpm and the ball milling time is 20 min-60 min.

[0030] In some embodiments of this disclosure, the sieve mesh size is 350-450 mesh.

[0031] In some embodiments of this disclosure, when preparing the first material, the drying temperature is controlled at 50°C-100°C and the drying time is 30 min-120 min.

[0032] Thirdly, this disclosure also provides the application of the hemihydrate phosphogypsum gel material in any of the above embodiments in building construction.

[0033] This disclosure utilizes hemihydrate phosphogypsum, an alkaline activator, and a water-reducing agent to prepare a gel material. While reducing water consumption, it achieves a good retarding effect. By introducing silica compounds and crystal form regulators containing succinic acid groups and silane groups, the succinic acid groups in the crystal form regulator can adsorb onto the {111} crystal faces of the phosphogypsum dihydrate through electrostatic interactions, thereby inhibiting crystal growth and forming plate-like crystals, which is beneficial for tight crystal bonding. During the hydration reaction, the silica compounds and the silane groups in the crystal form regulator undergo hydrolysis to form silica gel. These gels fill the voids caused by water evaporation and provide a cementing network for the phosphogypsum dihydrate crystals, increasing bonding strength and thus improving the strength of gypsum products. Therefore, the hemihydrate phosphogypsum gel material provided by this disclosure can maintain the mechanical properties of the gel material while reducing water consumption and extending setting time. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 SEM image of the gel material prepared in Example 1;

[0036] Figure 2 SEM image of the gel material prepared in Example 11;

[0037] Figure 3 SEM image of the gel material prepared in Example 12;

[0038] Figure 4 SEM image of the gel material prepared in Comparative Example 1;

[0039] Figure 5 The graph shows the results of calcium ion concentration determination in the hydrated liquid phase of the gel material in the examples and comparative examples. Detailed Implementation

[0040] The embodiments of this disclosure will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this disclosure. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0041] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein.

[0042] This disclosure provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0043] S1, Ingredients

[0044] The raw materials for the hemihydrate phosphogypsum gel material are prepared according to the formula. By mass, the raw materials for the hemihydrate phosphogypsum gel material include: 100 parts hemihydrate phosphogypsum, 1-8 parts alkaline activator, 0.1-1.0 parts water-reducing agent, 0.05-0.30 parts crystal form regulator, 0.1-0.8 parts silicate compound, and 40-60 parts water.

[0045] The crystal form regulator contains succinic acid groups and silane groups. The succinic acid groups in the crystal form regulator can be adsorbed onto the {111} crystal face of phosphogypsum dihydrate through electrostatic interaction, thereby inhibiting the growth of the crystal face and forming plate-like crystals, which is conducive to the tight bonding of crystals. During the hydration reaction, silica compounds hydrolyze with the silane groups in the crystal form regulator to form silica gel. These gels fill the gaps caused by water evaporation and provide a cementing network for the gypsum dihydrate crystals, increasing the bonding force and thus improving the strength of gypsum products.

[0046] It should be noted that the dosage of each component in the raw material formulation of hemihydrate phosphogypsum gel material must be within the above range. If it exceeds the above range, it will lead to a decrease in strength.

[0047] Specifically, when the dosage of hemihydrate phosphogypsum is 100 parts, the dosage of alkaline activator can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, etc.; the dosage of water-reducing agent can be 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1.0 parts, etc.; and the dosage of crystal form regulator can be 0.05 parts, 0.08 parts, 0.10 parts, 0.12 parts, 0.15 parts, etc. The dosages are 0.18 parts, 0.20 parts, 0.22 parts, 0.25 parts, 0.28 parts, 0.30 parts, etc. The dosages of silicate compounds are 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, etc., and the dosages of water are 40 parts, 43 parts, 45 parts, 48 ​​parts, 50 parts, 53 parts, 55 parts, 58 parts, 60 parts, etc.

[0048] The inventors optimized the dosage of each component. By mass, the raw materials include: 100 parts hemihydrate phosphogypsum, 2-5 parts alkaline activator, 0.1-0.5 parts water-reducing agent, 0.1-0.2 parts crystal form regulator, 0.2-0.5 parts silicate compound, and 40-60 parts water. Optimizing the dosage of each component further improves the mechanical properties of the gel material without affecting the water-reducing and retarding effects.

[0049] Furthermore, hemihydrate phosphogypsum can be a byproduct of the hemihydrate phosphoric acid process and can be a commercially available material. Its adsorbed water content can be 15%-20% (e.g., 15%, 16%, 17%, 18%, 19%, 20%, etc.). Within this range, it can be used in conjunction with the premixing process during preparation to act as a solubilizing agent for water-reducing agents, thus more fully utilizing the water-reducing and retarding effects of the water-reducing agent. The type of hemihydrate phosphogypsum is selected from at least one of α-type and β-type, and can be any one or both. The impurity content of hemihydrate phosphogypsum should not be too high, with soluble phosphorus content ≤0.1% and soluble fluorine content ≤0.03%.

[0050] Furthermore, the alkaline activator is selected from at least one of cement, quicklime, and blast furnace slag, and can be any one or more of the above.

[0051] Furthermore, the water-reducing agent can be a polymeric water-reducing agent. This polymeric agent is flexibly adsorbed on the surface of hemihydrate phosphogypsum, utilizing steric hindrance combined with electrostatic repulsion to disperse the particles, thereby improving the dispersibility and reducing water content of the gypsum. Since the steric hindrance effect is less affected by the hydration process, it also has a certain retarding effect. The retarding mechanism lies in the fact that the water-reducing agent molecules adsorbed on the surface of hemihydrate phosphogypsum slows down its dissolution rate in water, thus preventing excessive supersaturation in the reaction system and excessively rapid setting.

[0052] In some embodiments, the polymeric water-reducing agent is selected from at least one of polycarboxylate water-reducing agents, lignin sulfonate water-reducing agents, and starch water-reducing agents, and may be any one or more of the above.

[0053] Furthermore, the crystal form regulator can be obtained by reacting epoxysiloxane with aspartic acid, utilizing the reaction between the epoxy group and the amino group in aspartic acid to prepare the crystal form regulator. During the preparation of the crystal form regulator, the molar ratio of the epoxy group in the epoxysiloxane to the amino group in the aspartic acid is controlled to be (1.0-1.2):1, such as 1.0:1, 1.1:1, 1.2:1, etc.

[0054] Furthermore, the epoxysiloxane is selected from at least one of 3-glycidyl etheroxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, and 3-(2,3-epoxypropoxy)propyltrimethoxysilane. All of the above epoxysiloxanes are commercially available materials, and the epoxysiloxane used in preparing the crystal form regulator can be any one or more of the above.

[0055] In some embodiments, the general chemical formula of silicate compounds is:

[0056]

[0057] In the general formula, R1, R2, and R3 are all C1-C8 alkyl groups, R4 is O-R4' or R4', and R4' is a C1-C8 alkyl group or a substituted alkyl group. The substituents on the substituted alkyl group are selected from OH or COOH. C1-C8 alkyl refers to alkyl groups with 1-8 carbon atoms. Silicate compounds can hydrolyze with the silane portion of the crystal form regulator during the hydration reaction to form silica gel, which is beneficial for improving the strength of gypsum products.

[0058] In some embodiments, the silica compound may be tetraethyl orthosilicate, but is not limited thereto. Common silica compounds that satisfy the above general formula are all suitable for the formulations provided in the embodiments of this disclosure and can react with the silane portion of the crystal form regulator to improve the strength of gypsum products.

[0059] S2, premixed with water-reducing agent

[0060] First, a portion of hemihydrate phosphogypsum is premixed with a water-reducing agent and dried to obtain the first material. The premixed hemihydrate phosphogypsum with a certain adsorbed water content and the water-reducing agent yields a hemihydrate phosphogypsum / water-reducing agent composite with small particle size. After the adsorbed water is removed, it can, to some extent, aid in the solubility of the water-reducing agent. Compared to the traditional one-pot blending method, this method can fully utilize the water-reducing and retarding effects of the water-reducing agent. Drying is performed after premixing to prevent rapid reaction of the alkaline activator when mixed with it.

[0061] It should be added that, in the existing technology, the hemihydrate gypsum is usually dried during mixing to reduce its moisture content before being mixed with additives, alkaline activators, and water in a one-pot method, or the solid components are mixed and stirred first before being mixed with water. Neither of these methods is conducive to fully utilizing the role of the additives.

[0062] In some embodiments, premixing can be performed by ball milling. Under the action of ball milling and water-reducing agent, adsorbed water is discharged, further aiding in the solubility of the water-reducing agent. In actual operation, the preparation process of the first material includes: ball milling a portion of hemihydrate phosphogypsum with the water-reducing agent, followed by drying and sieving to obtain the first material with the required particle size.

[0063] In some embodiments, the hemihydrate phosphogypsum added during the preparation of the first material accounts for 50%-70% of the total mass of the hemihydrate phosphogypsum, and the proportion of hemihydrate phosphogypsum added during premixing is preferably more than half, so as to better solubilize the water-reducing agent. Specifically, the proportion of hemihydrate phosphogypsum added during premixing to the total mass of the hemihydrate phosphogypsum can be 50%, 55%, 60%, 65%, 70%, etc.

[0064] In some embodiments, when premixing by ball milling, the ball milling speed is controlled at 200 rpm-300 rpm, and the ball milling time is 20 min-60 min, to obtain a hemihydrate gypsum / water-reducing agent composite with smaller particle size. Under the action of ball milling and the water-reducing agent, adsorbed water is discharged, further aiding in the dissolution of the water-reducing agent. Specifically, the ball milling speed can be 200 rpm, 230 rpm, 250 rpm, 280 rpm, 300 rpm, etc., and the ball milling time can be 20 min, 30 min, 40 min, 50 min, 60 min, etc.

[0065] In some embodiments, when preparing the first material, the drying temperature is controlled at 50℃-100℃ and the drying time is 30min-120min to better remove adsorbed water. Specifically, the drying temperature can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc., and the drying time can be 30min, 50min, 80min, 100min, 120min, etc.

[0066] In some embodiments, the material is sieved after drying. The sieve mesh size can be 350-450 mesh. Within this range, the sieved material can meet the preparation requirements of the gel material. If there is any material that is not sieved, it can be returned to the ball mill for mixing.

[0067] S3. Preparation of gel materials

[0068] The first material is mixed with the remaining raw materials to obtain a gel material with good mechanical strength.

[0069] In some embodiments, the inventors optimized the order of adding each raw material. First, the first material was mixed with an alkaline activator to obtain the second material. The second material was then mixed with a crystal form regulator, tetraethyl orthosilicate, and the remaining hemihydrate phosphogypsum to obtain the third material. Finally, the third material was mixed with water to obtain a gel material of standard consistency.

[0070] Specifically, the amount of water used is determined based on the standard consistency of the gel material.

[0071] The hemihydrate phosphogypsum gel material provided in this disclosure can be used in building construction and has the advantages of low water consumption, good retarding effect, and high mechanical strength.

[0072] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0073] It should be noted that the sources of the hemihydrate gypsum and alkaline activating materials used in the following examples and comparative examples are as follows:

[0074] (1) Hemihydrate gypsum

[0075] β-Hemihydrate gypsum comes from Hubei Yihua Group Co., Ltd., and is a gray powdery solid prepared by low-temperature calcination of dihydrate phosphogypsum in a rotary kiln; α-hemihydrate gypsum is self-produced and is prepared by autoclaving microcrystallization of dihydrate phosphogypsum; the physical properties of hemihydrate gypsum are shown in Table 1.

[0076] Table 1. Test results of physical properties of hemihydrate phosphogypsum

[0077]

[0078] Hemihydrate gypsum with different adsorbed water contents was prepared by low-temperature drying, with a drying temperature of 50-80℃.

[0079] (2) Alkaline activating materials

[0080] The chemical compositions of P·O32.5 cement and blast furnace slag are as follows:

[0081] Table 2 Composition of alkaline activating materials

[0082]

[0083] Example 1

[0084] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0085] (1) Ingredients

[0086] The raw materials of the hemihydrate phosphogypsum gel material, calculated by mass parts, include the following components: 100 parts α-hemihydrate phosphogypsum, 2 parts quicklime, 0.5 parts PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), 0.1 parts crystal form regulator, 0.3 parts tetraethyl orthosilicate, and standard consistency water.

[0087] The crystal form regulator was prepared as follows: 3-(2,3-epoxypropoxy)propyltrimethoxysilane was dissolved in chloroform, and then aspartic acid was added and stirred until completely dissolved. The mixture was then heated to 80°C and refluxed for 10 hours. After the reaction was completed, the mixture was cooled to room temperature and extracted three times with water. The organic phase was then rotary evaporated to obtain an oily crystal form regulator. The ratio of epoxy groups in 3-(2,3-epoxypropoxy)propyltrimethoxysilane to amino groups in aspartic acid was 1.1:1.

[0088] (2) Premixing and preparing gel materials

[0089] 50% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 min; then it was placed in a hot dryer at 60℃ for 90 min, and then passed through a 400-mesh sieve to obtain the first material;

[0090] The first material is mixed with quicklime and stirred evenly to obtain the second material.

[0091] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0092] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0093] Example 2

[0094] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0095] (1) Ingredients

[0096] The raw materials of the hemihydrate phosphogypsum gel material, calculated by mass parts, include the following components: 100 parts α-hemihydrate phosphogypsum, 2 parts quicklime, 0.5 parts PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), 0.1 parts crystal form regulator, 0.3 parts tetraethyl orthosilicate, and standard consistency water.

[0097] The crystal form regulator was prepared as follows: 3-glycidyl etheroxypropyltriethoxysilane was dissolved in chloroform, and then aspartic acid was added and stirred until completely dissolved. The mixture was then heated to 80°C and refluxed for 10 hours. After the reaction was completed, the mixture was cooled to room temperature and extracted three times with water. The organic phase was then rotary evaporated to obtain an oily crystal form regulator. The ratio of epoxy groups in 3-glycidyl etheroxypropyltriethoxysilane to amino groups in aspartic acid was 1.1:1.

[0098] (2) Premixing and preparing gel materials

[0099] Mix 50% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 15%) with PC900 polycarboxylate superplasticizer, stir evenly, and then put it into a ball mill for ball milling at a speed of 300 rpm for 20 min; then put it into a hot dryer at 60℃ for 90 min, and then pass it through a 400-mesh sieve to obtain the first material.

[0100] The first material is mixed with quicklime and stirred evenly to obtain the second material.

[0101] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0102] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0103] Example 3

[0104] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0105] (1) Ingredients

[0106] The raw materials of the hemihydrate phosphogypsum gel material, calculated by mass parts, include the following components: 100 parts α-hemihydrate phosphogypsum, 2 parts quicklime, 0.5 parts PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), 0.1 parts crystal form regulator, 0.3 parts tetraethyl orthosilicate, and standard consistency water.

[0107] The crystal form regulator was prepared as follows: Epioxybutyltrimethoxysilane was dissolved in chloroform, and then aspartic acid was added and stirred until completely dissolved. The mixture was then heated to 80°C and refluxed for 10 hours. After the reaction was completed, the mixture was cooled to room temperature and extracted three times with water. The organic phase was then rotary evaporated to obtain an oily crystal form regulator. The ratio of epoxy groups in epioxybutyltrimethoxysilane to amino groups in aspartic acid was 1.1:1.

[0108] (2) Premixing and preparing gel materials

[0109] 60% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 15%) was mixed with PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 min; then it was placed in a hot dryer at 60℃ for 90 min, and then passed through a 400-mesh sieve to obtain the first material.

[0110] The first material is mixed with quicklime and stirred evenly to obtain the second material.

[0111] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0112] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0113] Example 4

[0114] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0115] (1) Ingredients

[0116] The raw materials of the hemihydrate phosphogypsum gel material, calculated by mass parts, include the following components: 100 parts α-hemihydrate phosphogypsum, 2 parts quicklime, 0.5 parts PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), 0.1 parts crystal form regulator, 0.3 parts tetraethyl orthosilicate, and standard consistency water.

[0117] The crystal form regulator was prepared as follows: 3-glycidyl etheroxypropylmethyldiethoxysilane was dissolved in chloroform, then aspartic acid was added and stirred until completely dissolved. The mixture was then heated to 80°C and refluxed for 10 hours. After the reaction was completed, the mixture was cooled to room temperature and extracted three times with water. The organic phase was then rotary evaporated to obtain an oily crystal form regulator. The ratio of epoxy groups in 3-glycidyl etheroxypropylmethyldiethoxysilane to amino groups in aspartic acid was 1.1:1.

[0118] (2) Premixing and preparing gel materials

[0119] 70% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 min; then it was placed in a hot dryer at 60℃ for 90 min, and then passed through a 400-mesh sieve to obtain the first material.

[0120] The first material is mixed with quicklime and stirred evenly to obtain the second material.

[0121] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0122] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0123] Example 5

[0124] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0125] (1) Ingredients

[0126] The raw materials of the hemihydrate phosphogypsum gel material, calculated by mass parts, include the following components: 100 parts α-hemihydrate phosphogypsum, 2 parts quicklime, 0.12 parts lignin calcium carbonate water-reducing agent (Shanghai Aladdin Biochemical Technology Co., Ltd.), 0.2 parts crystal form regulator, 0.5 parts tetraethyl orthosilicate, and standard consistency water.

[0127] The crystal form regulator was prepared as follows: 3-(2,3-epoxypropoxy)propyltrimethoxysilane was dissolved in chloroform, and then aspartic acid was added and stirred until completely dissolved. The mixture was then heated to 80°C and refluxed for 10 hours. After the reaction was completed, the mixture was cooled to room temperature and extracted three times with water. The organic phase was then rotary evaporated to obtain an oily crystal form regulator. The ratio of epoxy groups in 3-(2,3-epoxypropoxy)propyltrimethoxysilane to amino groups in aspartic acid was 1.1:1.

[0128] (2) Premixing and preparing gel materials

[0129] Mix 50% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) with a water-reducing agent, stir evenly, and then put it into a ball mill for ball milling at a speed of 300 rpm for 20 min; then put it into a hot dryer at 60℃ for 90 min, and then pass it through a 400-mesh sieve to obtain the first material.

[0130] The first material is mixed with quicklime and stirred evenly to obtain the second material.

[0131] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0132] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0133] Example 6

[0134] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0135] (1) Ingredients

[0136] The raw materials of the hemihydrate phosphogypsum gel material, calculated by mass parts, include the following components: 100 parts α-hemihydrate phosphogypsum, 2 parts quicklime, 0.3 parts starch sulfate water-reducing agent (weight average molecular weight of 107 g / mol), 0.1 parts crystal form regulator, 0.5 parts tetraethyl orthosilicate, and standard consistency water.

[0137] The crystal form regulator was prepared as follows: 3-(2,3-epoxypropoxy)propyltrimethoxysilane was dissolved in chloroform, and then aspartic acid was added and stirred until completely dissolved. The mixture was then heated to 80°C and refluxed for 10 hours. After the reaction was completed, the mixture was cooled to room temperature and extracted three times with water. The organic phase was then rotary evaporated to obtain an oily crystal form regulator. The ratio of amino groups in 3-(2,3-epoxypropoxy)propyltrimethoxysilane to aspartic acid was 1.1:1.

[0138] (2) Premixing and preparing gel materials

[0139] Mix 50% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) with a water-reducing agent, stir evenly, and then put it into a ball mill for ball milling at a speed of 300 rpm for 20 min; then put it into a hot dryer at 60℃ for 90 min, and then pass it through a 400-mesh sieve to obtain the first material.

[0140] The first material is mixed with quicklime and stirred evenly to obtain the second material.

[0141] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0142] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0143] Example 7

[0144] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0145] (1) Ingredients

[0146] The raw materials of the hemihydrate phosphogypsum gel material, calculated by mass parts, include the following components: 100 parts α-hemihydrate phosphogypsum, 5 parts cement (P·O32.5 ordinary silicate cement, Yichang Huaxin Cement Co., Ltd.), 0.5 parts PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), 0.1 parts crystal form regulator, 0.3 parts tetraethyl orthosilicate, and standard consistency water.

[0147] The crystal form regulator is the same as in Example 1.

[0148] (2) Premixing and preparing gel materials

[0149] 70% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with a water-reducing agent, stirred evenly, and then placed in a ball mill for ball milling at a speed of 200 rpm for 40 min. Then it was placed in a hot dryer at 70℃ for 30 min and then passed through a 400-mesh sieve to obtain the first material.

[0150] The first material is mixed with cement and stirred evenly to obtain the second material.

[0151] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0152] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0153] Example 8

[0154] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0155] (1) Ingredients

[0156] The raw materials of the hemihydrate phosphogypsum gel material, calculated by mass parts, include the following components: 100 parts α-hemihydrate phosphogypsum, 3 parts cement (P·O32.5 ordinary silicate cement, Yichang Huaxin Cement Co., Ltd.), 1.8 parts slag, 0.3 parts PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), 0.1 parts crystal form regulator, 0.3 parts tetraethyl orthosilicate, and standard consistency water.

[0157] The crystal form regulator is the same as in Example 1.

[0158] (2) Premixing and preparing gel materials

[0159] 60% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with starch sulfate water-reducing agent, stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 min. Then it was placed in a hot dryer at 60℃ for 90 min and then passed through a 400-mesh sieve to obtain the first material.

[0160] The first material is mixed with P·O32.5 cement and blast furnace slag, and the mixture is stirred evenly to obtain the second material.

[0161] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0162] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0163] Example 9

[0164] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, including the following steps:

[0165] (1) Ingredients

[0166] The raw materials for hemihydrate phosphogypsum gel material, calculated by weight, include the following components: 100 parts β-hemihydrate phosphogypsum, 2 parts quicklime, 0.5 parts PC900 polycarboxylate superplasticizer (Jiangsu Nigo Technology Co., Ltd.), 0.1 parts crystal form regulator, 0.3 parts tetraethyl orthosilicate, and water for standard consistency. Specifically, the amount of superplasticizer is 0.5% of the mass of hemihydrate phosphogypsum, the amount of quicklime is 2% of the mass of hemihydrate phosphogypsum, and the amount of water is determined according to the standard consistency.

[0167] The crystal form regulator is the same as in Example 1.

[0168] (2) Premixing and preparing gel materials

[0169] Mix 50% of the total mass of β-hemihydrate phosphogypsum (with an adsorbed water content of 15%) with a water-reducing agent, stir evenly, and then put it into a ball mill for ball milling at a speed of 200 rpm for 60 min. Then, heat dry it at 50℃ for 120 min, and then pass it through a 400-mesh sieve to obtain the first material.

[0170] The first material is mixed with quicklime and stirred evenly to obtain the second material.

[0171] The second material is mixed with the remaining hemihydrate phosphogypsum, and after being mixed evenly, the third material is obtained.

[0172] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0173] Example 10

[0174] The only difference from Example 1 is that the hemihydrate phosphogypsum is dried at 80°C until the adsorbed water content is 11%.

[0175] Example 11

[0176] The only difference from Example 1 is that after all components are mixed and stirred evenly, water is added to mix according to the standard consistency.

[0177] Comparative Example 1

[0178] The only difference from Example 1 is that no crystal form modifier and tetraethyl orthosilicate are added, and the amount of water is determined according to the standard consistency.

[0179] Comparative Example 2

[0180] The only difference from Example 1 is that no crystal form regulator is added, and the amount of water used is determined according to the standard consistency.

[0181] Comparative Example 3

[0182] The only difference from Example 1 is that: no tetraethyl orthosilicate is added, and the amount of water is determined according to the standard consistency.

[0183] Experimental Example 1

[0184] SEM analysis was performed on the gel materials prepared in Examples 1, 11, 12, and Comparative Example 1 to obtain... Figure 1 , Figure 2 , Figure 3 and Figure 4 .

[0185] Scanning electron microscopy (SEM): The gel materials prepared in Examples 1, 11, 12 and Comparative Example 1 were observed by scanning electron microscopy. The specific measurement method was as follows: A JEOL JSM-6490LV scanning electron microscope was used. The specimen size was 2×2×2cm. After demolding and curing for one day, the specimens were dried in an oven to constant weight. The original cross-section in the middle was taken for sample preparation and measurement.

[0186] from Figures 1-4 As can be seen from the data, compared with Examples 11, 12 and Comparative Example 1, Example 1 shows that there is more overlap between crystals in the gel material and the pore size of the hardened body is reduced.

[0187] Experimental Example 2

[0188] The retarding properties and strength of the gel materials prepared in the test examples and comparative examples are shown in Table 3.

[0189] Performance testing: (1) The standard consistency water requirement and initial and final setting times were determined according to GB / T17669.4-1999. (2) The 2-hour and oven-dry strength of the specimens were determined according to GB / T17669.3-1999. (3) Water content analysis: The content of gypsum adhering water and crystal water was determined using a Computrac MAX5000XL moisture analyzer.

[0190] Table 3. Test results of physical properties of gel materials

[0191]

[0192] The results of Examples 13 and 14 show that adding water-reducing agents can effectively reduce water consumption and has a certain coagulation effect. Due to the reduction in water consumption, the mechanical properties of the material also increase due to the reduction in the porosity of the internal structure.

[0193] The results of Examples 11 and 13 show that when hemihydrate gypsum is added in stages, the various properties or characteristics of the material remain almost unchanged. This is because, when the adsorbed water is low, it is impossible to achieve good encapsulation of the hemihydrate gypsum by the water-reducing agent during premixing. Ions can only be dissolved in free water, which enhances the contact between the two and then binds them through electrostatic attraction.

[0194] The results from Examples 1, 2, 10, and 11 show that the adsorbed water content of hemihydrate gypsum has a significant impact on various properties of the material. With increasing adsorbed water content, the water reduction rate increases, the setting time of the material is prolonged, and the mechanical properties increase. Higher adsorbed water content results in better encapsulation and dispersibility of the water-reducing agent on the gypsum during premixing, leading to better water reduction and slower dissolution of the encapsulated gypsum, thus extending the setting time. Typically, in traditional systems using water-reducing agents in conjunction with retarders, the use of retarders reduces the mechanical properties of the material because they inhibit the formation and growth of dihydrate gypsum crystal nuclei. However, the solution provided in this disclosure achieves both retarding and improved mechanical properties simultaneously. This is because the method of this disclosure involves partially unmixed hemihydrate gypsum, while partially premixed hemihydrate gypsum with the water-reducing agent. The former provides the supersaturation required for crystal nucleus formation, while the latter provides the ions required for crystal growth. This effectively slows down crystal growth through premixing without reducing the number of crystal nuclei, resulting in more complete crystal growth and a gel material with high mechanical properties. However, the adsorbed water content must be sufficient for the water-reducing agent to fully contact with the hemihydrate gypsum in order to achieve the desired technical effect. Therefore, there is no significant difference between Examples 10 and 11 at lower adsorbed water contents.

[0195] The results from Examples 1, 3, 4, and 12 show that the performance of Example 12 is inferior to that of the Examples. This is because, in the one-pot mixing process, all components are mixed simultaneously, preventing the water-reducing agent from effectively combining with the hemihydrate gypsum. This results in insufficient dispersion and encapsulation of the gypsum, leading to a low water reduction rate. Furthermore, the rapid dissolution of the gypsum creates a high degree of supersaturation. While this promotes crystal nucleus formation (a large number of nuclei facilitates direct and tight crystal bonding, improving mechanical properties), the higher water content compared to the Examples results in more pores. Therefore, these two factors combined contribute to the inferior mechanical properties compared to the Examples. The results from the three Examples also indicate that with increasing premix content, the water reduction rate increases, and the setting time prolongs. However, the material strength initially increases and then decreases, a consequence of the aforementioned two factors.

[0196] Experimental Example 3

[0197] To investigate the effect of the preparation method provided in this disclosure on the calcium ion concentration in the hydrated liquid phase, the calcium ion concentration was measured in liquid phases hydrated for different times, such as... Figure 5 As shown.

[0198] Aqueous phase ion concentration analysis: The sample was prepared at a water-to-solid-powder ratio of 10:1 and hydrated at 25°C. After hydration for a certain time, the sample was centrifuged to obtain supernatants from different hydration times. Lanthanum trichloride and anhydrous ethanol were added for protection, and deionized water was added to the volumetric flask for final volume adjustment. The calcium ion concentration was then determined using a photoelectron spectrometer (ESCACAB250).

[0199] Blank group (blank sample): prepared by mixing dried α-hemihydrate phosphogypsum (adsorbed water ≤ 5%) with water;

[0200] Example group (implementation sample): that is, the first material prepared in Example 1 is mixed with the remaining hemihydrate phosphogypsum and then water is added;

[0201] Comparative example (control sample): The dried α-hemihydrate phosphogypsum (adsorbed water ≤5%) was mixed with water and PC900 water-reducing agent at the same time.

[0202] Retarder group (retarder sample): The first material prepared in Example 1 was mixed with the remaining hemihydrate phosphogypsum and then an aqueous solution containing citric acid (0.25% of the hemihydrate phosphogypsum) was added.

[0203] from Figure 5 As can be seen, due to the rapid hydration rate of hemihydrate phosphogypsum, the blank sample solidified after 20 minutes, causing the calcium ion concentration in the hydrated liquid to remain unchanged. However, the sample with added water-reducing agent experienced a retarding effect, resulting in changes in calcium ion concentration within the test time range. The difference between the method provided in this disclosure (implementation sample) and the one-pot method (comparative sample) lies in the fact that after 10 minutes, the rate of calcium ion decrease in the improved sample slowed down, while the rate of decrease in the comparative sample remained similar to that within 10 minutes. This is because before 10 minutes, some gypsum that was not premixed with the water-reducing agent dissolved first in the preparation method provided in this disclosure. Therefore, the concentration of calcium ions dissolved in the early stage was comparable to that in the blank and comparative groups. Furthermore, as calcium sulfate dihydrate crystals rapidly formed, the liquid phase had a high saturation level, enabling the formation of a large number of crystal nuclei. The growth of these crystals facilitated subsequent contact and overlap between crystals, resulting in a denser gypsum crystal structure. As the reaction proceeds, the dissolution of hemihydrate phosphogypsum in the example group is slower than that in the comparative group due to the better encapsulation effect of the water-reducing agent. This results in a slower reduction of calcium ions in the liquid phase, thereby slowing down the growth of crystals.

[0204] Therefore, the preparation method provided in this disclosure, compared to the traditional one-pot method, can fully utilize the retarding effect of the water-reducing agent. It does not inhibit the formation of calcium sulfate dihydrate crystals, but it does inhibit subsequent crystal growth. This method differs from the retarding mechanism of commonly used retarders such as citric acid and phosphates. Common retarders capture calcium ions in the liquid phase and form insoluble substances with them, thus permanently consuming calcium ions and reducing the supersaturation of the liquid phase in the early stages, thereby inhibiting crystal nucleus growth and hindering the formation of high-strength, dense gypsum crystals.

[0205] Industrial applicability

[0206] This disclosure introduces silicate compounds and crystal form modifiers with succinic acid groups and silane groups during the preparation of hemihydrate phosphogypsum gel materials. Through formulation optimization, the gel materials can possess water-reducing and retarding properties while also exhibiting good mechanical properties. The method provided in this disclosure is simple and easy to implement, suitable for industrial applications, and the prepared gel materials have excellent comprehensive properties and promising market prospects.

Claims

1. A hemihydrate phosphogypsum gel material, characterized in that, By mass fraction, its raw materials include: 100 parts hemihydrate phosphogypsum, 1-8 parts alkaline activator, 0.1-1.0 parts water-reducing agent, 0.05-0.30 parts crystal form regulator, 0.1-0.8 parts silicate compound, and 40-60 parts water; The crystal form regulator contains succinic acid groups and silane groups.

2. The hemihydrate phosphogypsum gel material according to claim 1, characterized in that, By mass fraction, its raw materials include: 100 parts hemihydrate phosphogypsum, 2-5 parts alkaline activator, 0.1-0.5 parts water-reducing agent, 0.1-0.2 parts crystal form regulator, 0.2-0.5 parts silicate compound, and 40-60 parts water.

3. The hemihydrate phosphogypsum gel material according to claim 1 or 2, characterized in that, The crystal form regulator is obtained by reacting epoxysiloxane with aspartic acid.

4. The hemihydrate phosphogypsum gel material according to claim 3, characterized in that, When preparing the crystal form regulator, the molar ratio of the epoxy group in the epoxysiloxane to the amino group in the aspartic acid is controlled to be (1.0-1.2):

1.

5. The hemihydrate phosphogypsum gel material according to claim 3, characterized in that, The epoxysiloxane is selected from at least one of 3-glycidyl etheroxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, and 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

6. The hemihydrate phosphogypsum gel material according to claim 1, characterized in that, The general chemical formula of the silicate compounds is: ； In this configuration, R1, R2, and R3 are all C1-C8 alkyl groups, R4 is O-R4' or R4', R4' is a C1-C8 alkyl group or a substituted alkyl group, and the substituents on the substituted alkyl group are selected from OH or COOH.

7. The hemihydrate phosphogypsum gel material according to claim 6, characterized in that, The silica compound is tetraethyl orthosilicate.

8. The hemihydrate phosphogypsum gel material according to claim 1, characterized in that, The adsorbed water content of the hemihydrate phosphogypsum is 15%-20%.

9. The hemihydrate phosphogypsum gel material according to claim 1, characterized in that, The type of hemihydrate phosphogypsum is selected from at least one of the α type and β type.

10. The hemihydrate phosphogypsum gel material according to claim 1, characterized in that, The hemihydrate phosphogypsum has a soluble phosphorus content of ≤0.1% and a soluble fluorine content of ≤0.03%.

11. The hemihydrate phosphogypsum gel material according to claim 1, characterized in that, The alkaline activator is selected from at least one of cement, quicklime, and blast furnace slag.

12. The hemihydrate phosphogypsum gel material according to claim 1, characterized in that, The water-reducing agent is a polymeric water-reducing agent.

13. The hemihydrate phosphogypsum gel material according to claim 12, characterized in that, The polymeric water-reducing agent is selected from at least one of polycarboxylate water-reducing agents, lignin sulfonate water-reducing agents, and starch water-reducing agents.

14. A method for preparing the hemihydrate phosphogypsum gel material according to any one of claims 1-13, characterized in that, include: The hemihydrate phosphogypsum gel material is prepared according to its raw material composition.

15. The preparation method according to claim 14, characterized in that, include: First, a portion of the hemihydrate phosphogypsum is premixed with a water-reducing agent and dried, and then mixed with the remaining raw materials.

16. The preparation method according to claim 15, characterized in that, First, a portion of hemihydrate phosphogypsum is mixed with the water-reducing agent and dried to obtain a first material. The first material is then mixed with the alkaline activator to obtain a second material. The second material is then mixed with the crystal form regulator, silicate compound, and the remaining hemihydrate phosphogypsum to obtain a third material. Finally, the third material is mixed with water.

17. The preparation method according to claim 16, characterized in that, The hemihydrate phosphogypsum added during the preparation of the first material accounts for 50%-70% of the total mass of the hemihydrate phosphogypsum.

18. The preparation method according to claim 16 or 17, characterized in that, The preparation process of the first material includes: ball milling a portion of hemihydrate phosphogypsum with the water-reducing agent, followed by drying and sieving.

19. The preparation method according to claim 18, characterized in that, Control the ball mill speed to 200rpm-300rpm and the ball milling time to 20min-60min.

20. The preparation method according to claim 18, characterized in that, The sieve mesh size is 350-450 mesh.

21. The preparation method according to claim 16, characterized in that, When preparing the first material, the drying temperature is controlled at 50℃-100℃ and the drying time is 30min-120min.

22. The application of the hemihydrate phosphogypsum gel material according to any one of claims 1-13 or the hemihydrate phosphogypsum gel material prepared by the preparation method according to any one of claims 14-21 in building construction.

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