Semi-hydrated phosphogypsum gel material, and preparation method therefor and use thereof

Abstract

A semi-hydrated phosphogypsum gel material, and a preparation method therefor and the use thereof. By preparing the gel material from semi-hydrated phosphogypsum, an alkaline activator and a water-reducing agent, a good retarding effect can be achieved while water consumption is reduced; and by introducing a silicic acid compound and a crystal form regulator that has a succinic acid group and a silane group, a cementitious network can be provided for dihydrate gypsum crystals by means of the cooperation between the silicic acid compound and the crystal form regulator, resulting in an increase in binding strength, and therefore the strength of a gypsum product is improved. Therefore, the semi-hydrated phosphogypsum gel material can ensure the mechanical properties of the gel material on the premise of reducing water consumption and prolonging setting time.

Description

A semihydrated phosphogypsum gel material, and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of phosphogypsum, and in particular relates to a semi-hydrated phosphogypsum gel material, and a preparation method and application thereof. Background Art

[0002] Phosphogypsum is a solid waste residue produced during the wet production of phosphoric acid. It has an extremely low utilization rate and is mostly treated 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 a safety and environmental protection issue that needs to be urgently addressed. The semi-hydrated phosphoric acid process has the advantages of low energy consumption and high phosphoric acid concentration. The shift from the dihydrate process to the semi-hydrated process is the future development trend of phosphorus chemical industry. Semi-hydrated phosphogypsum is a by-product of the semi-hydrated phosphoric acid process. Its main component is CaSO4·1 / 2H2O, which has potential gelling activity. The gelling reaction of semi-hydrated phosphogypsum is as follows: 4CaSO4·1 / 2H2O+2H2O→3CaSO4·2H2O. However, semi-hydrated phosphogypsum has the following disadvantages as a gelling material: (1) the water requirement is much greater than the actual hydration water consumption; (2) the setting time is short.

[0003] Modification of hemihydrate phosphogypsum by adding admixtures such as water reducing agent and retarder can effectively solve the above problems of hemihydrate phosphogypsum gel material. 2+ It is adsorbed on the surface of gypsum particles, changing the properties of the solid-liquid interface of gypsum particles, thereby improving the dispersibility of gypsum particles, releasing the adsorbed water in phosphogypsum, reducing water demand, and increasing the hydration rate; retarders are usually small molecular organic acids such as citric acid and phosphates, which tend to react with free Ca 2+ Combined into insoluble matter, thereby reducing the supersaturation of the gypsum liquid phase, especially the early supersaturation, thereby reducing the dissolution of hemihydrate gypsum and the formation of crystal nuclei, and then slowing down the hydration process; although this type of retarder has a good retarding effect, due to the early reduction of the supersaturation of the reaction system, the formation of crystal nuclei and crystal growth are restricted, which reduces the overlap between the crystals of the final setting product, loosens the structure, and significantly reduces the mechanical strength of the material.

[0004] Therefore, there is an urgent need to develop a method for utilizing hemihydrate phosphogypsum so as to prepare gel materials with good mechanical properties while reducing water consumption and prolonging setting time.

[0005] In view of this, the present disclosure is proposed.

[0006] Summary of the Invention

[0007] The purpose of the present disclosure includes providing a hemihydrate phosphogypsum gel material, and a preparation method and application thereof, aiming to reduce water consumption, prolong setting time while ensuring the mechanical properties of the gel material.

[0008] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions can be adopted:

[0009] The solution provided by the present disclosure includes a hemihydrate phosphogypsum gel material, the raw materials of which include, by weight: 100 parts of hemihydrate phosphogypsum, 1-8 parts of alkaline activator, 0.1-1.0 parts of water reducer, 0.05-0.30 parts of crystal form regulator, 0.1-0.8 parts of silicic acid compound and 40-60 parts of water;

[0010] The crystal form regulator contains a succinic acid group and a silane group.

[0011] In some embodiments of the present disclosure, the raw materials include, by mass, 100 parts of hemihydrate phosphogypsum, 2-5 parts of alkaline activator, 0.1-0.5 parts of water reducer, 0.1-0.2 parts of crystal form regulator, 0.2-0.5 parts of silicic acid compound and 40-60 parts of water.

[0012] In some embodiments of the present disclosure, the crystal form modifier is obtained by reacting epoxysiloxane with aspartic acid.

[0013] In some embodiments of the present disclosure, when preparing the crystal form modifier, the molar ratio of the epoxy group in the epoxysilicone to the amine group in the aspartic acid is controlled to be (1.0-1.2):1.

[0014] In some embodiments of the present disclosure, the epoxysiloxane is selected from at least one of 3-glycidoxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0015] In some embodiments of the present disclosure, the general chemical formula of the silicic acid compound is:

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

[0017] In some embodiments of the present disclosure, the silicic acid compound is ethyl orthosilicate.

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

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

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

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

[0022] In some embodiments of the present disclosure, the water reducer is a polymer water reducer.

[0023] In some embodiments of the present disclosure, the polymer water reducer is selected from at least one of a polycarboxylic acid water reducer, a lignin sulfonate water reducer, and a starch water reducer.

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

[0025] In some embodiments of the present disclosure, the process includes premixing a portion of the hemihydrate phosphogypsum with a water reducer, drying the mixture, and then mixing the mixture with the remaining raw materials.

[0026] In some embodiments of the present disclosure, part of the hemihydrate phosphogypsum is first mixed with a water reducer and dried to obtain a first material, the first material is mixed with an alkaline activator to obtain a second material, the second material is mixed with a crystal form regulator, ethyl orthosilicate and the remaining hemihydrate phosphogypsum to obtain a third material, and the third material is mixed with water.

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

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

[0029] In some embodiments of the present 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 the present disclosure, the sieve mesh number is 350-450 mesh.

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

[0032] In a third aspect, the present disclosure further provides an application of the hemihydrate phosphogypsum gel material in any of the above embodiments in building construction.

[0033] The present invention utilizes hemihydrate phosphogypsum, an alkaline activator, and a water reducer to prepare a gel material, which reduces water consumption while achieving a good retarding effect. By introducing a silicic acid compound and a crystal form modifier having succinic acid and silane groups, the succinic acid groups in the crystal form modifier can electrostatically adsorb onto {111} crystal faces of the dihydrate phosphogypsum, thereby inhibiting crystal face growth and forming plate-like crystals that facilitate close crystal overlap. During the hydration reaction, the silicic acid compound and the silane groups in the crystal form modifier hydrolyze to form a silica gel. This gel fills voids created by water evaporation and provides a bonding network for the dihydrate gypsum crystals, increasing bonding strength and thereby improving the strength of the gypsum product. Therefore, the hemihydrate phosphogypsum gel material provided by the present invention can maintain the mechanical properties of the gel material while reducing water consumption and extending setting time. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0035] FIG1 is a SEM image of the gel material prepared in Example 1;

[0036] FIG2 is a SEM image of the gel material prepared in Example 11;

[0037] FIG3 is a SEM image of the gel material prepared in Example 12;

[0038] FIG4 is a SEM image of the gel material prepared in Comparative Example 1;

[0039] FIG5 is a graph showing the results of measuring the calcium ion concentration in the hydration liquid phase of the gel materials in Examples and Comparative Examples. DETAILED DESCRIPTION

[0040] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

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

[0042] The present disclosure provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0043] S1. Ingredients

[0044] The ingredients are prepared according to the raw material formula of the hemihydrate phosphogypsum gel material. The raw materials of the hemihydrate phosphogypsum gel material include, by mass, 100 parts of hemihydrate phosphogypsum, 1-8 parts of an alkaline activator, 0.1-1.0 parts of a water reducer, 0.05-0.30 parts of a crystal form regulator, 0.1-0.8 parts of a silicic acid compound and 40-60 parts of water.

[0045] Among them, the crystal form regulator contains succinic acid groups and silane groups. The succinic acid groups in the crystal form regulator can be adsorbed on the {111} crystal plane with dihydrate phosphogypsum through electrostatic interaction, thereby inhibiting the growth of the crystal plane and forming plate-like crystals, which is conducive to tight crystal overlap. During the hydration reaction, silicic acid compounds and the silane groups in the crystal form regulator are hydrolyzed to form silica gel. On the one hand, these gels fill the gaps caused by water evaporation, and on the other hand, they can provide a bonding network for dihydrate gypsum crystals, increase the bonding force, and thus improve the strength of gypsum products.

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

[0047] Specifically, in the case of 100 parts of hemihydrate phosphogypsum, the amount of alkaline activator can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, etc., the amount of water reducer can be 0.1 part, 0.3 part, 0.5 part, 0.8 part, 1.0 part, etc., the amount of crystal form regulator can be 0.05 part, 0.08 part, 0.10 part, 0.12 part, 0.15 part, The amount of silicic acid compound can be 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, etc., and the amount of water can be 40 parts, 43 parts, 45 parts, 48 ​​parts, 50 parts, 53 parts, 55 parts, 58 parts, 60 parts, etc.

[0048] The inventors optimized the amounts of each component. The raw materials, calculated by weight, include: 100 parts hemihydrate phosphogypsum, 2-5 parts alkaline activator, 0.1-0.5 parts water reducer, 0.1-0.2 parts crystal form modifier, 0.2-0.5 parts silicic acid compound, and 40-60 parts water. By optimizing the amounts of each component, the mechanical properties of the gel material were further improved while maintaining the water-reducing and retarding effects.

[0049] Furthermore, the 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 in the preparation process to serve the purpose of dissolving the water reducer, and more fully exert the water-reducing and retarding effects of the water reducer. The type of hemihydrate phosphogypsum is selected from at least one of α-type and β-type, and can be any one or both of the above. The impurity content of the hemihydrate phosphogypsum should not be too high, with a soluble phosphorus content of ≤0.1% and a soluble fluorine content of ≤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 reducer can be a polymeric water reducer. Polymer water reducers flexibly adsorb onto the surface of hemihydrate phosphogypsum, utilizing steric hindrance in conjunction with electrostatic repulsion to disperse the particles, thereby improving gypsum dispersibility and reducing water content. Because the steric hindrance effect is less affected by the hydration process, it also has a certain retarding effect. The retarding mechanism is that the water reducer molecules adsorb onto the surface of hemihydrate phosphogypsum, slowing its dissolution in water, thereby preventing excessive supersaturation in the reaction system and premature coagulation.

[0052] In some embodiments, the polymer water reducer is selected from at least one of a polycarboxylic acid water reducer, a lignin sulfonate water reducer, and a starch water reducer, and can be any one or more of the above.

[0053] Furthermore, the crystal form modifier can be obtained by reacting epoxysiloxane with aspartic acid, wherein the epoxy groups react with the amine groups in the aspartic acid to prepare the crystal form modifier. When preparing the crystal form modifier, the molar ratio of the epoxy groups in the epoxysiloxane to the amine groups 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-glycidyloxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane. The above epoxysiloxanes are all commercially available materials. The epoxysiloxane used in the preparation of the crystal form regulator can be any one or more of the above.

[0055] In some embodiments, the silicic acid compound has the general chemical formula:

[0056] In the general formula, 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 substituent on the substituted alkyl group is selected from OH or COOH. C1-C8 alkyl refers to an alkyl group with 1-8 carbon atoms. During the hydration reaction, the silicic acid compound can hydrolyze with the silane portion of the crystal form modifier to form a silica gel, which helps improve the strength of gypsum products.

[0057] In some embodiments, the silicate compound can be ethyl orthosilicate, but is not limited thereto. Common silicate compounds that meet the above general formula are suitable for the formula provided in the embodiments of the present disclosure, and can react with the silane part of the crystal form regulator to improve the strength of gypsum products.

[0058] S2, premixed with water reducer

[0059] First, a portion of the hemihydrate phosphogypsum and the water reducer are premixed and dried to obtain a first material. The hemihydrate phosphogypsum with a certain amount of adsorbed water is premixed with the water reducer to produce a hemihydrate gypsum / water reducer composite with a small particle size. After the adsorbed water is removed, it can help dissolve the water reducer to a certain extent. Compared to traditional one-pot blending, this can fully utilize the water-reducing and retarding effects of the water reducer. Drying after premixing prevents rapid reaction of the alkaline activator when mixed with the alkaline activator.

[0060] It should be added that in the prior art, hemihydrate gypsum is usually dried during mixing to reduce its water content before being mixed with admixtures, alkaline activator, and water in a one-pot method, or the solid components are first mixed and then mixed with water. Both of the above methods are not conducive to fully exerting the effect of the admixture.

[0061] In some embodiments, premixing can be performed by ball milling. During ball milling and with the aid of a water reducer, adsorbed water is expelled, further aiding in the dissolution of the water reducer. In practice, the preparation of the first material includes ball milling a portion of the hemihydrate phosphogypsum with the water reducer, followed by drying and sieving to obtain a first material having a desired particle size.

[0062] In some embodiments, the hemihydrate gypsum added during the preparation of the first material accounts for 50%-70% of the total mass of the hemihydrate gypsum. The hemihydrate gypsum added during premixing preferably accounts for more than half of the total mass to better dissolve the water reducer. Specifically, the hemihydrate gypsum added during premixing can account for 50%, 55%, 60%, 65%, 70%, etc.

[0063] In some embodiments, when premixing is performed by ball milling, the ball milling speed is controlled to be 200-300 rpm and the ball milling time is 20-60 minutes to obtain a hemihydrate gypsum / water reducer composite with smaller particle size. During ball milling and with the water reducer, adsorbed water is expelled, further aiding in the dissolution of the water reducer. 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 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, etc.

[0064] In some embodiments, when preparing the first material, the drying temperature is controlled to be 50° C.-100° C., and the drying time is controlled to be 30 min-120 min to better remove adsorbed water. Specifically, the drying temperature can be 50° C., 60° C., 70° C., 80° C., 90° C., 100° C., etc., and the drying time can be 30 min., 50 min., 80 min., 100 min., 120 min., etc.

[0065] In some embodiments, the material is sieved after drying, and the mesh size can be 350-450 mesh. The sieve within this range can make the sieved material meet the preparation requirements of the gel material. If there is material that is not sieved, it can be returned to the ball mill for mixing.

[0066] S3. Preparation of gel material

[0067] The first material is mixed with the remaining raw materials to obtain a gel material with good mechanical strength.

[0068] In some embodiments, the inventors optimized the order of adding each raw material, first mixing the first material with an alkaline activator to obtain a second material, then mixing the second material with a crystal form regulator, ethyl orthosilicate, and the remaining hemihydrate phosphogypsum to obtain a third material, and then mixing the third material with water to obtain a gel material of standard consistency.

[0069] Specifically, the amount of water used is determined according to the standard consistency of the gel material.

[0070] The hemihydrate phosphogypsum gel material provided by the embodiments of the present disclosure can be used in building construction and has the advantages of low water consumption, good retarding effect, and high mechanical strength.

[0071] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0072] It should be noted that the sources of the hemihydrate gypsum and alkaline activating materials used in the following examples and comparative examples are:

[0073] (1) Hemihydrate gypsum

[0074] 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 from dihydrate phosphogypsum using the autoclaved microcrystallization method. The physical properties of hemihydrate gypsum are shown in Table 1.

[0075] Table 1 Physical properties test results of hemihydrate phosphogypsum

[0076] Hemihydrate gypsum with different adsorbed water contents is prepared by low-temperature drying at a drying temperature of 50 to 80°C.

[0077] (2) Alkaline excited materials

[0078] The chemical composition of P·O32.5 cement and blast furnace slag is as follows:

[0079] Table 2 Composition of alkaline excited materials

[0080] Example 1

[0081] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0082] (1) Ingredients

[0083] Calculated by mass, the raw materials of hemihydrate phosphogypsum gel material include the following components: 100 parts of α-hemihydrate phosphogypsum, 2 parts of quicklime, 0.5 parts of PC900 polycarboxylic acid water reducer (Jiangsu Nigao Technology Co., Ltd.), 0.1 parts of crystal form regulator, 0.3 parts of tetraethyl orthosilicate, and water of standard consistency.

[0084] The crystal form modifier is prepared as follows: 3-(2,3-epoxypropyloxy)propyltrimethoxysilane is dissolved in chloroform, then aspartic acid is added and stirred until completely dissolved. The mixture is then heated to 80°C and refluxed with stirring for 10 hours. After the reaction is complete, the mixture is cooled to room temperature and extracted three times with water. The organic phase is then rotary evaporated to obtain an oily crystal form modifier. The ratio of epoxy groups in 3-(2,3-epoxypropyloxy)propyltrimethoxysilane to amino groups in aspartic acid is 1.1:1.

[0085] (2) Premixing and preparing gel material

[0086] 50% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with PC900 polycarboxylate water reducer (from Jiangsu Nigao Technology Co., Ltd.), stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 minutes; then placed in a heat drying oven at 60° C. for 90 minutes, and then passed through a 400-mesh sieve to obtain a first material;

[0087] The first material is mixed with quicklime, and stirred evenly to obtain the second material.

[0088] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0089] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0090] Example 2

[0091] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0092] (1) Ingredients

[0093] Calculated by mass, the raw materials of hemihydrate phosphogypsum gel material include the following components: 100 parts of α-hemihydrate phosphogypsum, 2 parts of quicklime, 0.5 parts of PC900 polycarboxylic acid water reducer (Jiangsu Nigao Technology Co., Ltd.), 0.1 parts of crystal form regulator, 0.3 parts of tetraethyl orthosilicate, and water of standard consistency.

[0094] The crystal form modifier is prepared as follows: 3-glycidoxypropyltriethoxysilane is dissolved in chloroform, then aspartic acid is added and stirred until completely dissolved. The mixture is then heated to 80°C and refluxed with stirring for 10 hours. After the reaction is complete, the mixture is cooled to room temperature and extracted three times with water. The organic phase is then rotary evaporated to obtain an oily crystal form modifier. The ratio of epoxy groups in 3-glycidoxypropyltriethoxysilane to amino groups in aspartic acid is 1.1:1.

[0095] (2) Premixing and preparing gel material

[0096] 50% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 15%) was mixed with PC900 polycarboxylate water reducer, stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 minutes; then placed in a heat drying at 60° C. for 90 minutes, and then passed through a 400-mesh sieve to obtain a first material.

[0097] The first material is mixed with quicklime, and stirred evenly to obtain the second material.

[0098] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0099] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0100] Example 3

[0101] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0102] (1) Ingredients

[0103] Calculated by mass, the raw materials of hemihydrate phosphogypsum gel material include the following components: 100 parts of α-hemihydrate phosphogypsum, 2 parts of quicklime, 0.5 parts of PC900 polycarboxylic acid water reducer (Jiangsu Nigao Technology Co., Ltd.), 0.1 parts of crystal form regulator, 0.3 parts of tetraethyl orthosilicate, and water of standard consistency.

[0104] The crystal form modifier is prepared as follows: epoxybutyltrimethoxysilane is dissolved in chloroform, then aspartic acid is added and stirred until completely dissolved. The mixture is then heated to 80°C and refluxed with stirring for 10 hours. After the reaction is complete, the mixture is cooled to room temperature and extracted three times with water. The organic phase is then rotary evaporated to obtain an oily crystal form modifier. The ratio of epoxy groups in epoxybutyltrimethoxysilane to amino groups in aspartic acid is 1.1:1.

[0105] (2) Premixing and preparing gel material

[0106] 60% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 15%) was mixed with PC900 polycarboxylate water reducer (Jiangsu Nigao Technology Co., Ltd.), stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 minutes; then placed in a heat drying at 60°C for 90 minutes, and then passed through a 400-mesh sieve to obtain a first material.

[0107] The first material is mixed with quicklime, and stirred evenly to obtain the second material.

[0108] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0109] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0110] Example 4

[0111] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0112] (1) Ingredients

[0113] Calculated by mass, the raw materials of hemihydrate phosphogypsum gel material include the following components: 100 parts of α-hemihydrate phosphogypsum, 2 parts of quicklime, 0.5 parts of PC900 polycarboxylic acid water reducer (Jiangsu Nigao Technology Co., Ltd.), 0.1 parts of crystal form regulator, 0.3 parts of tetraethyl orthosilicate, and water of standard consistency.

[0114] The crystal form modifier is prepared as follows: 3-glycidoxypropylmethyldiethoxysilane is dissolved in chloroform, then aspartic acid is added and stirred until completely dissolved. The mixture is then heated to 80°C and refluxed with stirring for 10 hours. After the reaction is complete, the mixture is cooled to room temperature and extracted three times with water. The organic phase is then rotary evaporated to obtain an oily crystal form modifier. The ratio of epoxy groups in 3-glycidoxypropylmethyldiethoxysilane to amino groups in aspartic acid is 1.1:1.

[0115] (2) Premixing and preparing gel material

[0116] 70% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with PC900 polycarboxylate water reducer (Jiangsu Nigao Technology Co., Ltd.), stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 minutes; then placed in a heat drying at 60°C for 90 minutes, and then passed through a 400-mesh sieve to obtain a first material.

[0117] The first material is mixed with quicklime, and stirred evenly to obtain the second material.

[0118] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0119] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0120] Example 5

[0121] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0122] (1) Ingredients

[0123] Calculated by mass, the raw materials of hemihydrate phosphogypsum gel material include the following components: 100 parts of α-hemihydrate phosphogypsum, 2 parts of quicklime, 0.12 parts of lignin calcium carbonate water reducer (Shanghai Aladdin Biochemical Technology Co., Ltd.), 0.2 parts of crystal form regulator, 0.5 parts of tetraethyl orthosilicate, and water of standard consistency.

[0124] The crystal form modifier is prepared as follows: 3-(2,3-epoxypropyloxy)propyltrimethoxysilane is dissolved in chloroform, then aspartic acid is added and stirred until completely dissolved. The mixture is then heated to 80°C and refluxed with stirring for 10 hours. After the reaction is complete, the mixture is cooled to room temperature and extracted three times with water. The organic phase is then rotary evaporated to obtain an oily crystal form modifier. The ratio of epoxy groups in 3-(2,3-epoxypropyloxy)propyltrimethoxysilane to amino groups in aspartic acid is 1.1:1.

[0125] (2) Premixing and preparing gel material

[0126] 50% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with a water reducer, stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 minutes; then placed in a heat drying oven at 60° C. for 90 minutes, and then passed through a 400-mesh sieve to obtain a first material.

[0127] The first material is mixed with quicklime, and stirred evenly to obtain the second material.

[0128] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0129] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0130] Example 6

[0131] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0132] (1) Ingredients

[0133] Calculated by mass, the raw materials of the hemihydrate phosphogypsum gel material include the following components: 100 parts of α-hemihydrate phosphogypsum, 2 parts of quicklime, 0.3 parts of starch sulfate water reducer (weight average molecular weight is 107 g / mol), 0.1 parts of crystal form regulator, 0.5 parts of tetraethyl orthosilicate, and water of standard consistency.

[0134] The crystal form modifier is prepared as follows: 3-(2,3-epoxypropyloxy)propyltrimethoxysilane is dissolved in chloroform, then aspartic acid is added and stirred until completely dissolved. The mixture is then heated to 80°C and refluxed with stirring for 10 hours. After the reaction is complete, the mixture is cooled to room temperature and extracted three times with water. The organic phase is then rotary evaporated to obtain an oily crystal form modifier. The ratio of 3-(2,3-epoxypropyloxy)propyltrimethoxysilane to the amino group in aspartic acid is 1.1:1.

[0135] (2) Premixing and preparing gel material

[0136] 50% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with a water reducer, stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 minutes; then placed in a heat drying oven at 60° C. for 90 minutes, and then passed through a 400-mesh sieve to obtain a first material.

[0137] The first material is mixed with quicklime, and stirred evenly to obtain the second material.

[0138] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0139] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0140] Example 7

[0141] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0142] (1) Ingredients

[0143] The raw materials of the hemihydrate phosphogypsum gel material include the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 5 parts of cement (P·O32.5 ordinary Portland cement, Yichang Huaxin Cement Co., Ltd.), 0.5 parts of PC900 polycarboxylate water reducer (Jiangsu Nigao Technology Co., Ltd.), 0.1 parts of crystal form regulator, 0.3 parts of tetraethyl orthosilicate, and water of standard consistency.

[0144] The crystal form regulator is the same as that in Example 1.

[0145] (2) Premixing and preparing gel material

[0146] 70% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with a water reducer, stirred evenly, and then placed in a ball mill for ball milling at a speed of 200 rpm for 40 minutes; then placed in a heat drying at 70° C. for 30 minutes, and then passed through a 400-mesh sieve to obtain a first material.

[0147] The first material is mixed with cement, and stirred evenly to obtain the second material.

[0148] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0149] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0150] Example 8

[0151] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0152] (1) Ingredients

[0153] The raw materials of the hemihydrate phosphogypsum gel material include the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of cement (P·O32.5 ordinary Portland cement, Yichang Huaxin Cement Co., Ltd.), 1.8 parts of slag, 0.3 parts of PC900 polycarboxylate water reducer (Jiangsu Nigao Technology Co., Ltd.), 0.1 parts of crystal form regulator, 0.3 parts of tetraethyl orthosilicate, and water of standard consistency.

[0154] The crystal form regulator is the same as that in Example 1.

[0155] (2) Premixing and preparing gel material

[0156] 60% of the total mass of α-hemihydrate phosphogypsum (with an adsorbed water content of 20%) was mixed with a starch sulfate water reducer, stirred evenly, and then placed in a ball mill for ball milling at a speed of 300 rpm for 20 minutes; then placed in a heat drying oven at 60° C. for 90 minutes, and then passed through a 400-mesh sieve to obtain a first material.

[0157] The first material is mixed with P·O32.5 cement and blast furnace slag, and stirred evenly to obtain the second material.

[0158] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0159] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0160] Example 9

[0161] This embodiment provides a method for preparing a hemihydrate phosphogypsum gel material, comprising the following steps:

[0162] (1) Ingredients

[0163] The raw materials for the hemihydrate phosphogypsum gel material, calculated by weight, include the following: 100 parts β-hemihydrate phosphogypsum, 2 parts quicklime, 0.5 parts PC900 polycarboxylate superplasticizer (from Jiangsu Nigao Technology Co., Ltd.), 0.1 parts crystal form modifier, 0.3 parts tetraethyl orthosilicate, and water for standard consistency. Specifically, the superplasticizer is used at 0.5% of the weight of the hemihydrate phosphogypsum, the quicklime at 2% of the weight of the hemihydrate phosphogypsum, and the water dosage is determined based on the standard consistency.

[0164] The crystal form regulator is the same as that in Example 1.

[0165] (2) Premixing and preparing gel material

[0166] 50% of the total mass of β-hemihydrate phosphogypsum (with an adsorbed water content of 15%) was mixed with a water reducer, stirred evenly, and then placed in a ball mill for ball milling at a speed of 200 rpm for 60 minutes; then placed in a heat drying at 50° C. for 120 minutes, and then passed through a 400-mesh sieve to obtain a first material.

[0167] The first material is mixed with quicklime, and stirred evenly to obtain the second material.

[0168] The second material is mixed with the remaining hemihydrate phosphogypsum, and the mixture is evenly mixed to obtain the third material.

[0169] The third material is mixed with water and stirred to obtain a hemihydrate phosphogypsum gel material.

[0170] Example 10

[0171] The only difference from Example 1 is that the hemihydrate phosphogypsum is dried at 80° C. to an adsorbed water content of 11%.

[0172] Example 11

[0173] The only difference from Example 1 is that after all components are mixed and stirred evenly, water is added and mixed according to standard consistency.

[0174] Comparative Example 1

[0175] The only difference from Example 1 is that no crystal form regulator and ethyl orthosilicate are added, and the amount of water used is determined according to the standard consistency.

[0176] Comparative Example 2

[0177] 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.

[0178] Comparative Example 3

[0179] The only difference from Example 1 is that no ethyl orthosilicate is added and the amount of water used is determined according to the standard consistency.

[0180] Test Example 1

[0181] The gel materials prepared in Test Example 1, Example 11, Example 12 and Comparative Example 1 were subjected to SEM analysis to obtain Figures 1, 2, 3 and 4.

[0182] Scanning electron microscopy (SEM): The gel materials prepared in Example 1, Example 11, Example 12 and Comparative Example 1 were observed by scanning electron microscopy. Specific measurement method: A JEOL JSM-6490LV scanning electron microscope was used, and the specimen size was 2×2×2 cm. After demolding and curing for one day, the specimen was baked in an oven to constant weight. The middle original cross-section was taken and sampled for measurement.

[0183] As can be seen from Figures 1 to 4, compared with Example 11, Example 12 and Comparative Example 1, in Example 1, there are more overlaps between crystals in the gel material, and the pore size of the hardened body is reduced.

[0184] Test Example 2

[0185] The retarding properties and strength of the gel materials prepared in the examples and comparative examples were tested, and the results are shown in Table 3.

[0186] Performance testing: (1) Determine the water consumption for standard consistency and the initial and final setting times according to GB / T17669.4-1999. (2) Determine the 2h and absolute dry strength of the specimens according to GB / T17669.3-1999. (3) Water content analysis: Use a Computrac MAX5000XL moisture analyzer to determine the adhering water and crystallization water content of the gypsum.

[0187] Table 3 Physical properties test results of gel materials

[0188] From the results of Example 13 and Example 14, it can be seen that the addition of a water reducer can effectively reduce water consumption and has a certain coagulation effect. Due to the reduction in water consumption, the mechanical properties of the material are also increased due to the reduction in porosity of the internal structure.

[0189] From the results of Example 11 and Example 13, it can be seen that the performance or properties of the material are almost unchanged when the hemihydrate gypsum is added step by step. This is because: when the adsorbed water is low, it is impossible to achieve good wrapping of the hemihydrate gypsum by the water reducer during premixing, because ions can only be dissolved in free water, which enhances the contact between the two and then combines them through electrostatic attraction.

[0190] The results of Examples 1, 2, 10, and 11 show that the adsorbed water content of hemihydrate gypsum has a significant impact on various material properties. With increasing adsorbed water content, the water reduction rate increases, the setting time of the material is prolonged, and the mechanical properties are enhanced. The higher the adsorbed water content, the better the encapsulation and dispersion of the water-reducing agent on the gypsum during premixing, resulting in a more effective water-reducing effect, a slower dissolution rate of the encapsulated gypsum, and, in turn, a longer setting time. Typically, in conventional systems where a water-reducing agent is used in conjunction with a retarder, the use of the retarder reduces the mechanical properties of the material because it inhibits the formation and growth of dihydrate gypsum crystal nuclei. However, the solution provided by the present disclosure achieves both retarded setting and improved mechanical properties. This is because, in the present method, some hemihydrate gypsum is not premixed, while some is premixed with the water-reducing agent. The former provides the supersaturation required for crystal nucleation, while the latter provides the ions required for crystal growth. This premixing method effectively slows crystal growth without reducing the number of crystal nuclei, resulting in more complete crystal growth and a gel material with high mechanical properties. However, the technical effect can only be achieved when the adsorbed water content is sufficient for the water reducer to fully contact with the hemihydrate gypsum. Therefore, there is no obvious difference between Example 10 and Example 11 at a lower adsorbed water content.

[0191] From the results of Examples 1, 3, 4, and 12, it can be seen that the various properties of Example 12 are inferior to those of the Examples. This is because all components are mixed simultaneously in the one-pot method, and the water reducer cannot combine well with the hemihydrate gypsum, so its dispersion and encapsulation effect on the gypsum is not very fully exerted, resulting in a low water reduction rate and rapid dissolution of the gypsum to form a high supersaturation. Although this is conducive to the formation of crystal nuclei (the formation of a large number of crystal nuclei is conducive to direct crystallization and close overlap, improving mechanical properties), due to the higher water consumption than the Examples, more pores are formed. Therefore, under the influence of these two factors, its mechanical properties are still inferior to those of the Examples. The results of the three Examples show that with the increase of the premix amount, the water reduction rate increases and the setting time is prolonged, but the material strength shows a trend of first increasing and then decreasing. This is the result of the influence of the above two factors.

[0192] Test Example 3

[0193] In order to study the effect of the preparation method provided by the present disclosure on the calcium ion concentration in the hydrated liquid phase, the calcium ion concentration of the liquid phase hydrated for different times was measured, as shown in FIG5 .

[0194] Analysis of aqueous phase ion concentration: The sample was prepared at a water-paste ratio of 10:1 and hydrated at 25°C. After a certain period of hydration, the sample was centrifuged to obtain the supernatant liquid with different hydration times. Lanthanum trichloride and anhydrous ethanol were added for protection, and deionized water was added to the volumetric flask to make up the volume. The calcium ion concentration was then determined using a photoelectron spectrometer (ESCACAB250).

[0195] Blank group (blank sample): dried α-hemihydrate phosphogypsum (absorbed water ≤ 5%) mixed with water;

[0196] Example group (implementation sample): the first material prepared in Example 1 was mixed with the remaining hemihydrate phosphogypsum and then water was added;

[0197] Comparative Example Group (comparative sample): dried α-hemihydrate phosphogypsum (absorbed water ≤ 5%) was mixed with water and PC900 water reducer at the same time;

[0198] Retarder group (retarder sample): The first material prepared in Example 1 was mixed with the remaining hemihydrate phosphogypsum, and then an aqueous solution of citric acid (0.25% of the hemihydrate gypsum) was added.

[0199] As can be seen from Figure 5, due to the rapid hydration rate of hemihydrate phosphogypsum, the blank sample condenses after 20 minutes, thereby causing the calcium ions in the hydration liquid to no longer change, while the sample with the addition of a water reducer has a retarding effect, causing the calcium ion concentration of the sample to still change within the test time range. The difference between the method prepared by the present disclosure (implementation sample) and the one-pot method (comparative example group) is that after 10 minutes, the rate of decrease of calcium ions in the improved group sample slows down, while the rate of decrease of the comparative example sample remains similar to that within 10 minutes; the reason is that before 10 minutes, some of the gypsum that is not premixed with the water reducer in the preparation method provided by the present disclosure is first dissolved, so the concentration of calcium ions dissolved in the early stage is comparable to that of the blank group and the comparative example group, and as the formation of calcium sulfate dihydrate crystals is rapidly consumed, the liquid phase has a higher saturation at this stage, and a large number of crystal nuclei can be formed, which is conducive to contact and overlap between subsequent crystals as the crystals grow, thereby forming a more dense gypsum crystal. As the reaction proceeds, the dissolution of hemihydrate phosphogypsum in the example group is slower than that in the comparative example group due to the better wrapping effect of the water reducer, and the decrease of calcium ions in the liquid phase slows down, thereby achieving the effect of slowing down the growth of crystals.

[0200] Thus, the preparation method provided by the present disclosure can fully utilize the retarding effect of the water reducer, compared to the traditional one-pot method, and does not inhibit the formation of calcium sulfate dihydrate crystals, but does inhibit subsequent crystal growth. This method differs from the retarding mechanism of commonly used retarders such as citric acid and phosphates. Commonly used retarders capture calcium ions in the liquid phase and form insolubles with them, thereby permanently consuming calcium ions and reducing the liquid phase supersaturation in the early stage, thereby inhibiting the growth of crystal nuclei, which is not conducive to the formation of high-strength, dense gypsum crystals. Industrial Applicability

[0201] The present disclosure introduces a silicic acid compound and a crystal form modifier having succinic acid and silane groups during the preparation of a hemihydrate phosphogypsum gel material. Through formulation optimization, the gel material exhibits both water-reducing and retarding properties while also possessing good mechanical properties. The method provided by the present disclosure is simple and easy to implement, suitable for industrial applications, and the resulting gel material exhibits excellent overall performance and promising market prospects.

Claims

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

2. The hemihydrate phosphogypsum gel material according to claim 1, wherein By mass parts, its raw materials include: 100 parts of hemihydrate phosphogypsum, 2 - 5 parts of alkaline activator, 0.1 - 0.5 part of water reducer, 0.1 - 0.2 part of crystal form regulator, 0.2 - 0.5 part of silicate compound, and 40 - 60 parts of water.

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

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

1.

5. The hemihydrate phosphogypsum gel material according to claim 3 or 4, characterized in that, The epoxy siloxane is selected from at least one of 3 - glycidoxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6 - epoxyhexyltriethoxysilane, 3 - glycidoxypropylmethyldiethoxysilane, and 3 - (2,3 - epoxypropoxy)propyltrimethoxysilane.

6. The hemihydrate phosphogypsum gel material according to any one of claims 1-5, characterized in that, The general chemical formula of the silicate compound is as follows: Among them, 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, and the substituents on the substituted alkyl group are selected from OH or COOH.

7. The hemihydrate phosphogypsum gel material according to claim 6, wherein, The silicate compound is tetraethyl orthosilicate.

8. The hemihydrate phosphogypsum gel material according to any one of claims 1-7, characterized in that The adsorbed water content of the hemihydrate phosphogypsum is 15% - 20%.

9. The hemihydrate phosphogypsum gel material according to any one of claims 1-8, characterized in that, The type of the hemihydrate phosphogypsum is selected from at least one of α - type and β - type.

10. The hemihydrate phosphogypsum gel material according to any one of claims 1-9, characterized in that, The soluble phosphorus content of the hemihydrate phosphogypsum ≤ 0.1%, and the soluble fluorine content ≤ 0.03%.

11. The hemihydrate phosphogypsum gel material according to any one of claims 1-10, 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 any one of claims 1-11, characterized in that, The water reducer is a high - molecular water reducer.

13. The hemihydrate phosphogypsum gel material according to claim 12, characterized in that, The high - molecular water reducer is selected from at least one of polycarboxylate water reducers, lignosulfonate water reducers, and starch water reducers.

14. A method for preparing the hemihydrate phosphogypsum gel material according to any one of claims 1-13, characterized in that, Include: Prepare according to the raw material composition of the hemihydrate phosphogypsum gel material.

15. The preparation method according to claim 14, characterized in that, Include: First, premix and dry part of the hemihydrate phosphogypsum with the water reducer, and then mix with the remaining raw materials.

16. The preparation method according to claim 15, wherein, First, mix and dry part of the hemihydrate phosphogypsum with the water reducer to obtain the first material, mix the first material with the alkaline activator to obtain the second material, mix the second material with the crystal form regulator, silicate compound, and the remaining hemihydrate phosphogypsum to obtain the third material, and mix the third material with water.

17. The preparation method according to claim 16, wherein, The hemihydrate phosphogypsum added when preparing 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 part of the hemihydrate phosphogypsum with the water reducer, and then drying and sieving.

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

20. The preparation method according to claim 18 or 19, characterized in that, The sieve mesh number is 350 mesh - 450 mesh.

21. The preparation method according to any one of claims 16-20, characterized in that, When preparing the first material, control the drying temperature to be 50°C - 100°C, and the drying time to be 30 min - 120 min.

22. Use of the hemihydrate phosphogypsum gel material according to any one of claims 1-13 or the hemihydrate phosphogypsum gel material according to any one of claims 14-21 in construction.

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