A light high-strength thermal insulation material prepared from phosphogypsum and a preparation method and application thereof

Abstract

The present application relates to the technical field of industrial solid waste resource utilization and multi-scene thermal protection, and particularly relates to a light high-strength thermal insulation material prepared from phosphogypsum as well as a preparation method and application thereof.The raw materials of the light high-strength thermal insulation material include, in parts by mass, 60-90 parts of phosphogypsum, 10-30 parts of cementitious solidification material, 1-5 parts of alkaline activator, 2-6 parts of calcium sulfate whisker with a length-diameter ratio of 5-30, 0.5-1.5 parts of reinforcing fiber, 0.5-2.5 parts of chemical foaming agent, 0.05-0.2 parts of hydroxypropyl methyl cellulose, 0.1-3 parts of auxiliary additive, and 30-80 parts of water; wherein the auxiliary additive includes water reducing agent and retarder.The raw materials in the thermal insulation material are interwoven to form a continuous three-dimensional cementitious framework, which not only improves the overall structural stability of the system, but also can wrap and passivate the residual phosphorus, fluorine and other impurities in the phosphogypsum, thereby reducing the adverse effects of the impurities on the hydration process.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization and multi-scenario thermal protection technology, and in particular to a lightweight, high-strength thermal insulation material prepared using phosphogypsum, its preparation method, and its application. Background Technology

[0002] Phosphogypsum is a major industrial byproduct generated during the wet-process phosphoric acid production. Its main component is calcium sulfate dihydrate, accompanied by impurities such as phosphorus, fluorine, organic matter, and heavy metals. With the rapid development of the phosphorus chemical industry, phosphogypsum emissions have continued to increase, with global annual production reaching hundreds of millions of tons and historical stockpiles exceeding billions of tons, while the comprehensive utilization rate remains below 60%. The long-term stockpiling of large quantities of phosphogypsum not only occupies significant land resources but also poses a significant ecological risk due to potential pollution of soil, water, and air through rainwater leaching and wind erosion. Currently, the main methods of phosphogypsum disposal are stockpiling and low-value utilization, such as its use as a cement retarder and building filler. However, its high impurity content and unstable performance limit its resource utilization. Developing efficient and low-carbon phosphogypsum resource utilization technologies, especially its high-value applications in cementitious materials and environmental remediation, is of great significance for promoting the reduction and resource utilization of bulk solid waste and achieving the "dual carbon" goal.

[0003] In recent years, the technology for the resource utilization of phosphogypsum has been continuously developing, with related research and patents mainly focusing on pretreatment purification and building material utilization. For example, CN1215011C proposes to remove soluble impurities from phosphogypsum through washing and grading to improve its utilization performance. However, this method only targets impurity removal and does not involve subsequent high-value utilization, so the overall resource utilization efficiency remains limited. Another example is CN1161943A, which discloses a process route for producing cement and sulfuric acid from phosphogypsum. Although it achieves large-scale consumption, it relies on high-temperature calcination, resulting in high energy consumption and large carbon emissions, which does not meet the current requirements for green and low-carbon development. In terms of building material applications, CN112079614A introduces modifiers to prepare high-strength phosphogypsum products, which improves the mechanical properties of the material to some extent. However, its system has high requirements for raw material purity and proportion control, and its adaptability to complex solid waste systems is insufficient. International patent WO2019210729A1 proposes a passivation treatment of harmful components in phosphogypsum through solidification / stabilization methods, and its application in the preparation of caulking materials. However, its application scenarios are relatively limited, making large-scale disposal difficult. In addition, recent studies have also attempted to co-utilize phosphogypsum with other solid wastes. For example, US20260028274 proposes co-preparing building materials with phosphogypsum and sludge, but such methods often rely on high-temperature treatment or complex processes, resulting in high energy consumption, high costs, and difficulties in industrialization.

[0004] Although existing technologies for the resource utilization of phosphogypsum have made some progress, they still generally suffer from the following shortcomings: First, impurities in phosphogypsum (such as phosphorus, fluorine, and organic matter) affect the cementation reaction process, leading to unstable setting time and limited strength development; second, some technologies rely on high-temperature calcination or complex modification processes, resulting in high energy consumption and costs, which are not conducive to green and low-carbon development; third, the overall mechanical properties and durability of the resulting materials still need to be improved; and fourth, in terms of environmental functions, such as insufficient ability to solidify / stabilize harmful substances like heavy metals. Therefore, it is necessary to develop a low-carbon cementitious material system with phosphogypsum as the main raw material, which can achieve efficient resource utilization while improving the mechanical properties and stability of the material, and endowing it with certain pollutant solidification functions to meet the needs of engineering applications. Summary of the Invention

[0005] This invention provides a method for preparing lightweight, high-strength, flame-retardant, and heat-insulating materials using phosphogypsum, solving the technical problems of phosphogypsum impurities interfering with hydration, low strength of foamed materials, easy fiber agglomeration, and high collapse rate. It realizes the high-value utilization of industrial solid waste and meets the stringent requirements of multiple scenarios such as thermal protection of lithium battery compartments, fireproofing and heat insulation of buildings, and thermal insulation of industrial equipment.

[0006] To achieve the above objectives, the present invention provides a lightweight, high-strength thermal insulation material prepared using phosphogypsum, wherein the raw materials of the lightweight, high-strength thermal insulation material, by weight, comprise: 60-90 parts of phosphogypsum; 10-30 parts of gelling and curing material; 1-5 parts of alkaline activator; 2-6 parts of calcium sulfate whiskers; 0.5 to 1.5 parts of reinforcing fiber; 0.5-2.5 parts of chemical foaming agent; Hydroxypropyl methylcellulose 0.05%~0.2 parts; Additives: 0.1-3 parts; 50 parts water; The auxiliary admixtures include water-reducing agents and retarder.

[0007] Preferably, the gelling and curing material includes cement; The alkaline activator includes quicklime; The reinforcing fiber includes one or more of basalt, rock wool, or polyester fiber; The chemical foaming agent includes one or more of sodium bicarbonate, hydrogen peroxide, aluminum powder, or zinc powder. The water-reducing agent includes one or a mixture of two of polycarboxylate water-reducing agents or naphthalene-based water-reducing agents, and the amount added is 0.5 to 1.0 parts by weight. The retarder is citric acid, and its addition amount is 0.02~0.08 parts by weight.

[0008] Under the same technical concept, the present invention also provides a method for preparing the lightweight, high-strength thermal insulation material prepared using phosphogypsum, comprising the following steps: S1. Pretreatment of phosphogypsum, adjusting the pH value to be controlled within the range of 6.0 to 8.0; S2. Dry mix the pretreated phosphogypsum, gelling and curing materials and alkaline activator from S1 to form a basic gelling system; S3. Add calcium sulfate whiskers to the basic gelling system in S2 and dry mix to make the calcium sulfate whiskers evenly dispersed in the gelling system. S4. Add hydroxypropyl methylcellulose to the gelling system in S3 and dry mix to make the hydroxypropyl methylcellulose uniformly coat the surface of the powder particles. S5. Dissolve the water-reducing agent and retarder in water beforehand to form a modified mixture; add the modified mixture to the gelling system in S4, and stir at a low speed of 200-300 r / min for 30-45 s to fully wet the powder; then increase the speed to 800-1000 r / min and stir at a high speed for 90-120 s to obtain a uniform and stable base slurry; S6. Add reinforcing fibers to the base slurry in S5, stir and mix to obtain the reinforced slurry; S7. Add a chemical foaming agent to the reinforced slurry in S6, stir and mix to obtain a foamed slurry; S8. Inject the foamed slurry from S7 into the mold to remove air bubbles, press and shape, and let stand at room temperature to obtain the initial set molded part. S9. Trim the surface of the initial solidified part in S8, demold it, and demold it for 12-24 hours. After curing, obtain a lightweight and high-strength heat insulation material prepared by phosphogypsum.

[0009] In this invention, phosphogypsum and gelling materials undergo a synergistic hydration reaction under alkaline activation conditions to generate hydration products such as ettringite (AFt) and calcium silicate hydrate (CSH) gel, forming a continuous gelling skeleton. Calcium sulfate whiskers, utilizing their high aspect ratio structure and homologous crystal characteristics, play a role in heterogeneous nucleation, bridging, filling, and microcrack inhibition within the system, inducing the directional growth of hydration products and improving interfacial bonding stability. Reinforcing fibers and hydroxypropyl methylcellulose together form a spatial support network, providing constraint and support for bubbles formed during foaming, reducing the probability of bubble merging and collapse. The gas released by the chemical foaming agent forms a uniform and stable closed-cell-semi-closed-cell composite structure under the constraint of the above multi-scale skeleton, thereby achieving a synergistic unity between lightweight, high strength, and low thermal conductivity of the material.

[0010] Preferably, the pretreatment in step S1 specifically includes: detecting the pH value of phosphogypsum; when the pH value is lower than 6.0, adding quicklime for neutralization and adjustment, so that the pH value is controlled within the range of 6.0 to 8.0.

[0011] Preferably, the mixing conditions for dry mixing in step S2 are: dry mixing at a speed of 300-400 r / min for 60-90 s; The mixing conditions for dry mixing in step S3 are: continue dry mixing at a speed of 400-500 r / min for 60-90 s; The mixing conditions for dry mixing in step S4 are: stirring at a speed of 300-400 r / min for 30-60 s; The mixing conditions described in step S6 are: continue stirring at a speed of 300-400 r / min for 30-60 s; The mixing conditions described in step S7 are: continue stirring at a speed of 1000-1200 r / min for 10-20 s; The molding and pressing conditions described in step S8 are as follows: the molding pressure is controlled at 0.2 to 0.6 MPa, and the holding time is 60 to 120 s.

[0012] Preferably, the method for removing air bubbles in step S8 is as follows: the slurry is injected into a mold for molding, and large air bubbles are removed by vibration pressing or mechanical pressing.

[0013] Preferably, the curing treatment method in step S9 specifically includes standard curing or low-temperature drying. The standard curing is curing for 28 days at a temperature of 20±2℃ and a humidity of ≥90%, and the low-temperature drying is drying at a temperature of 50~70℃ for 24~48 hours until constant weight.

[0014] Under the same technical concept, the present invention also provides a lightweight high-strength thermal insulation material prepared using phosphogypsum or a lightweight high-strength thermal insulation material prepared using phosphogypsum prepared by the same method, wherein the lightweight high-strength thermal insulation material prepared using phosphogypsum is used for one or more of the following: thermal protection of lithium batteries for new energy vehicles, fireproofing and thermal insulation of buildings, and thermal insulation of industrial equipment or pipelines.

[0015] The above-described solution of the present invention has the following beneficial effects: (1) A multi-component synergistic cementitious system based on phosphogypsum was constructed to achieve efficient structural reconstruction and stable curing under room temperature conditions. This invention uses phosphogypsum as the main raw material, which undergoes a synergistic hydration reaction with the cementitious curing material under alkaline activation conditions to generate a large amount of hydration products such as ettringite (AFt), hydrated calcium silicate (CSH) gel, and secondary calcium sulfate crystals. These products intertwine to form a continuous three-dimensional cementitious skeleton, which not only improves the overall structural stability of the system but also encapsulates and passivates residual phosphorus, fluorine, and other impurities in the phosphogypsum, reducing the adverse effects of impurities on the hydration process.

[0016] (2) A multi-scale reinforcement network of "calcium sulfate whiskers-basalt fiber" was constructed to achieve high strength and toughness under lightweight conditions. This invention introduces calcium sulfate whiskers and basalt fiber to form a multi-scale reinforcement system that combines microscopic whisker reinforcement with macroscopic fiber toughening. Among them, calcium sulfate whiskers and phosphogypsum belong to the calcium sulfate system and have good lattice compatibility and interfacial bonding ability. They can serve as heterogeneous nucleation sites for hydration products, induce uniform growth of ettringite and gel products, and improve the density of the matrix through bridging and filling. Basalt fiber forms a spatial support skeleton at the macroscopic scale, which can effectively disperse external stress and inhibit crack propagation. SEM results show that a large amount of hydration products can be induced to deposit on the surface of calcium sulfate whiskers and form a multi-scale synergistic reinforcement skeleton together with basalt fiber, which verifies the structural mechanism of lightweight and high strength synergistically achieved in the system of this invention from the microscopic level.

[0017] (3) A foaming-stabilizing-skeleton support synergistic mechanism was constructed to achieve uniform and stable multi-level pore structure control. In this invention, after the chemical foaming agent releases gas, the viscoelasticity of the slurry is improved under the thickening effect of hydroxypropyl methylcellulose. The increased slurry viscosity can prevent skeleton sinking and stratification, and assist in preventing micro-cracking. At the same time, the micro-rigid skeleton formed by calcium sulfate whiskers and the spatial support network constructed by basalt fibers form multiple stabilizing effects on the bubble interface, which can effectively reduce bubble merging, migration and collapse. Under the above synergistic effect, a closed-cell-semi-closed-cell composite structure with uniform pore size distribution is formed inside the material. Among them, the closed-cell structure can effectively block the heat conduction path and reduce the thermal conductivity; the semi-closed-cell structure is conducive to relieving thermal stress concentration and improving structural stability. Compared with the problems of large pore structure, pore wall cracking and mold collapse that are common in traditional phosphogypsum foaming materials, this invention can maintain high structural integrity while reducing material density, thereby achieving a synergistic improvement in thermal insulation performance and mechanical properties.

[0018] (4) A multi-level interfacial synergistic effect is formed, improving the material's durability and environmental safety. The CSH gel, ettringite, and secondary crystallization products formed in this invention have a large specific surface area and strong ion exchange capacity. They can stabilize and solidify heavy metal ions that may exist in phosphogypsum through multiple mechanisms such as physical encapsulation, surface adsorption, lattice solid solution, and chemical precipitation, reducing their migration and leaching risks. At the same time, the multi-scale reinforced structure can effectively reduce the internal shrinkage stress and the probability of microcrack propagation in the material, thereby improving the material's freeze-thaw resistance, water resistance, and long-term service stability. Compared with traditional phosphogypsum-based materials, which are prone to cracking, pulverization, and later strength decay, this invention still has good structural durability and environmental safety under lightweight conditions.

[0019] (5) This invention achieves a multi-functional integration of "lightweight, high-strength, flame-retardant, and heat-insulating" properties, broadening the application scenarios for high-value utilization of solid wastes such as phosphogypsum. The invention utilizes phosphogypsum, a cementitious material hydration system, and inorganic fibers to synergistically construct a stable inorganic framework. The material as a whole belongs to an inorganic non-combustible system, which is less likely to release toxic fumes under high temperatures and can effectively delay heat transfer through its internal porous structure, exhibiting excellent flame-retardant and thermal protection properties. Furthermore, by adjusting the cementitious system, hydration rate, and pore structure parameters, this invention achieves a balanced optimization of material density, thermal conductivity, and mechanical properties, making it suitable not only for building fire protection and insulation but also for thermal runaway insulation of lithium batteries in new energy vehicles, and insulation of industrial equipment and high-temperature pipelines, significantly improving the added value and application scope of phosphogypsum resource utilization. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a process flow diagram of the preparation method of the lightweight, high-strength thermal insulation material prepared by phosphogypsum according to the present invention. Figure 2 This is a photograph of the lightweight, high-strength thermal insulation material prepared using phosphogypsum in Example 1 of this invention. Figure 3 This is a cross-sectional view of the lightweight, high-strength thermal insulation material prepared using phosphogypsum in Example 1 of the present invention. Figure 4 This is a SEM image of the hydration crosslinking structure of the phosphogypsum-based composite cementitious system in Example 1 of the present invention; Figure 5This is a SEM image of the hierarchical porous structure formed by the foaming system in Embodiment 1 of the present invention; Figure 6 This is a SEM image of the interface between basalt fiber and cement matrix in Example 1 of the present invention; Figure 7 , 8 This is a SEM image of basalt fibers crossing the pore area and forming a connection structure with the pore wall in Embodiment 1 of the present invention; Figure 9 This is a SEM image of the lightweight, high-strength thermal insulation material lacking calcium sulfate whiskers in Comparative Example 1 of the present invention. Detailed Implementation

[0022] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Example 1 A phosphogypsum-based fire-retardant and heat-insulating cementitious material comprises, by weight, the following raw materials: 700g phosphogypsum, 300g cement, 500g water, 5g chemical foaming agent, 10g basalt fiber, 60g calcium sulfate whiskers, 1.5g hydroxypropyl methylcellulose (HPMC), 20g alkaline activator quicklime, 5g polycarboxylate superplasticizer, and 0.5g retarder (citric acid). The phosphogypsum is β-type phosphogypsum with a moisture content of less than 5%; the basalt fiber has a length of 9 mm; the calcium sulfate whiskers have an aspect ratio of 40; and the chemical foaming agent is a 30% hydrogen peroxide solution.

[0027] Figure 1 This is a process flow diagram of the preparation method of the lightweight, high-strength thermal insulation material prepared using phosphogypsum according to the present invention; According to Figure 1 The preparation method of the above-mentioned phosphogypsum-based fireproof and heat-insulating cementitious material includes the following steps: (1) Pretreatment of phosphogypsum was carried out, and the pH value was adjusted to control it at 7; (2) The phosphogypsum, cement and quicklime treated in step (1) are dry-mixed at 350 r / min for 75 s to form a basic cementitious system; (3) Add calcium sulfate whiskers to the basic gelling system and continue to dry mix at 450 r / min for 75 s to make the calcium sulfate whiskers evenly dispersed in the gelling system; (4) Add hydroxypropyl methylcellulose (HPMC) to the gelling system and continue stirring at 350 r / min for 45 s; (5) Dissolve 5g of polycarboxylate superplasticizer and 0.5g of retarder (citric acid) in 500g of water to form a modified mixture; add the modified mixture to the gelation system, stir at a low speed of 250 r / min for 40 s to fully wet the powder; then increase the speed to 900 r / min and stir at a high speed for 100 s to obtain a uniform and stable base slurry; (6) Add basalt reinforcing fibers to the base slurry and continue stirring at 350 r / min for 45 s to obtain the reinforced slurry; Figure 6 This is a SEM image of the interface between basalt fiber and cement matrix in Example 1 of the present invention.

[0028] (7) Add chemical foaming agent to the reinforced slurry and continue stirring at 1100 r / min for 15 s to obtain foamed slurry; Figure 5 This is a SEM image of the hierarchical porous structure formed by the foaming system in Embodiment 1 of the present invention; (8) Inject the foamed slurry into the mold and remove large air bubbles by vibration or mechanical pressing. Press the mold and control the molding pressure to 0.4 MPa. Hold the pressure for 90 s and let it stand at room temperature to obtain the initial solidified molded part. (9) The surface of the initial solidified molded part is trimmed and demolded. The demolding time is 24h. After curing for 28 days at a temperature of 20±2℃ and a humidity of ≥90%, a lightweight and high-strength heat insulation material prepared by phosphogypsum is obtained.

[0029] Figure 2 This is a photograph of the lightweight, high-strength thermal insulation material prepared using phosphogypsum in Example 1 of this invention. Figure 3 This is a cross-sectional view of the lightweight, high-strength thermal insulation material prepared using phosphogypsum in Example 1 of the present invention. The performance of the obtained material was tested. A cured specimen with dimensions of 40mm × 40mm × 160mm was dried at 105℃ ± 5℃ to constant weight. The mass and geometric dimensions were measured, and the density was calculated. The average of three specimens was taken, yielding a density of 896 kg / m³. The thermal conductivity was determined to be 0.156 W / (m·K) according to GB / T 10295-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Heat Flow Meter Method". The compressive strength was determined according to the principle of combined flexural and compressive strength testing in GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)". First, a three-point bending flexural strength test was performed on the specimen (40mm × 40mm × 160mm). Then, two halves of the specimen obtained after flexural fracture were used for compressive strength testing. The arithmetic mean of the two compressive strength results was taken, yielding a 28-day compressive strength of 2.3 MPa. This embodiment significantly improves the mechanical strength of the material by increasing the amount of cement and combining it with the synergistic reinforcement effect of calcium sulfate whiskers and basalt fibers, making it suitable for fireproof and heat-insulating boards with certain load-bearing requirements.

[0030] Microstructure analysis To further analyze the formation mechanism of the internal structure of the material of the present invention, the sample obtained in Example 1 was characterized by scanning electron microscopy (SEM), and the results are as follows: Figures 4-8 As shown.

[0031] Depend on Figure 4 As can be seen, a large number of needle-like and lamellar interwoven structures are formed inside the material, with calcium sulfate whiskers uniformly distributed in the cementitious matrix and a large number of hydration products attached to their surfaces. Analysis suggests that calcium sulfate whiskers can serve as heterogeneous nucleation sites during the formation of ettringite (AFt) and CSH gels, promoting the preferential precipitation and directional growth of hydration products on their surfaces. Simultaneously, the whiskers form obvious bridging and overlapping structures, which can construct a microscale rigid support network within the matrix, thereby improving the structural stability of the pore wall region.

[0032] Depend on Figure 5It is evident that the material exhibits a large number of uniformly distributed hierarchical porous structures, including both smaller closed-cell structures and some semi-closed-cell structures. The pore walls are generally intact, and no significant large-area through-hole collapse was observed. Analysis suggests that during the gas release process of the chemical foaming agent, hydroxypropyl methylcellulose enhances the viscoelasticity of the slurry. Simultaneously, the micro-rigid framework formed by calcium sulfate whiskers and the spatial support network constructed by basalt fibers stabilize the bubble interface, effectively inhibiting bubble coalescence and collapse.

[0033] Depend on Figure 6 and Figure 7 , Figure 8 As can be seen, basalt fibers are interwoven within the cementitious matrix, with a large amount of hydration products adhering to their surface, and no obvious debonding phenomenon is observed in the interface area. Some basalt fibers cross the pore area and form a connection structure with the pore wall, which can provide effective support for the pore wall area. Analysis suggests that basalt fibers not only play a role in crack bridging and toughening, but also participate in the foaming structure stabilization process. During the foaming stage, they can limit bubble migration and local collapse of the pore wall, thereby improving the overall structural stability of the material.

[0034] The above SEM results show that the system of the present invention forms a multi-scale synergistic reinforcement structure composed of hydration products, calcium sulfate whiskers and basalt fibers. The components are not simply superimposed, but form a clear coupling and synergistic mechanism in the gelation, hydration, foaming and reinforcement processes, thereby achieving a synergistic unity between lightweight, high strength and thermal insulation performance.

[0035] Example 2 A phosphogypsum-based fire-retardant and heat-insulating cementitious material comprises, by weight, 700g phosphogypsum, 300g cement, 500g water, 10g hydrogen peroxide, 15g basalt fiber, 40g calcium sulfate whiskers, 1.5g hydroxypropyl methylcellulose (HPMC), 20g alkaline activator quicklime, 5g polycarboxylate superplasticizer, and 0.5g retarder (citric acid). Its preparation method is basically the same as in Example 1, except for the adjustment of the proportions of each component.

[0036] The resulting material underwent performance testing, with the following results: density of 858 kg / m³, thermal conductivity of 0.172 W / (m·K), and 28-day flexural strength of 8.1 MPa. This embodiment, by increasing the content of foaming agent and basalt fiber while appropriately reducing the amount of calcium sulfate whiskers, creates a more uniform pore structure within the material and enhances fiber bridging, thereby significantly improving the material's flexural and impact resistance. It is suitable for lightweight thermal insulation components requiring high toughness.

[0037] Example 3 A phosphogypsum-based fire-retardant and heat-insulating cementitious material comprises, by weight, the following raw materials: 800g phosphogypsum, 200g cement, 500g water, 10g hydrogen peroxide, 5g basalt fiber, 60g calcium sulfate whiskers, 2.5g hydroxypropyl methylcellulose (HPMC), 20g quicklime, 20g alkaline activator quicklime, 5g polycarboxylate superplasticizer, and 0.5g retarder (citric acid). Its preparation method is basically the same as in Example 1, except for the adjustment of the proportions of each component.

[0038] The resulting material underwent performance testing, with the following results: density of 924 kg / m³, thermal conductivity of 0.097 W / (m·K), and 28-day compressive strength of 2.1 MPa. This embodiment, by increasing the phosphogypsum content and reducing the cement content, while optimizing the foaming and thickening systems, enables the material to form a microporous structure with higher porosity and uniform distribution, thereby significantly reducing the thermal conductivity. This makes it suitable for fireproof and thermal insulation materials with high requirements for thermal insulation performance.

[0039] Comparative Example 1 In the same formulation system as in Example 1, only the calcium sulfate whiskers were removed, while the remaining components and process conditions remained the same. Test results showed that the material had an apparent density of 905 kg / m³, a thermal conductivity of 0.168 W / (m·K), and a 28-day compressive strength of 1.4 MPa.

[0040] Compared to Example 1, the compressive strength of the material decreased significantly even with minimal density change, and the uniformity of the pore structure after foaming deteriorated considerably. Observations revealed thinning of the pore walls and interconnected pores in localized areas within the material, indicating that calcium sulfate whiskers not only act as traditional reinforcing fillers but also participate in the synergistic construction of the hydration structure and pore structure. Analysis suggests that calcium sulfate whiskers, due to their high aspect ratio and calcium sulfate crystal structure homologous to phosphogypsum, can serve as heterogeneous nucleation sites during the formation of ettringite and CSH gel, inducing uniform deposition of hydration products and forming a microscale bridging framework within the slurry. This framework enhances the local stiffness of the pore wall region during the foaming stage, thereby reducing the probability of bubble coalescence and pore wall collapse. When calcium sulfate whiskers are absent, the system lacks an effective microscopic support structure, leading to decreased stability of the foamed pore structure and uneven distribution of hydration products, ultimately resulting in a significant reduction in material strength and structural integrity. Relevant SEM images are shown below. Figure 9 As shown in the figure. This result indicates that there is a significant synergistic effect between calcium sulfate whiskers and the cementation and foaming systems, rather than a simple filling and reinforcing effect.

[0041] Comparative Example 2 Under the same conditions as in Example 1, only the basalt fiber was removed, while the remaining components and process parameters remained the same. Test results showed that the material density was 910 kg / m³, the thermal conductivity was 0.162 W / (m·K), and the 28-day compressive strength was 1.2 MPa.

[0042] Compared to Example 1, the overall brittleness of the material increased significantly, and the sample was more prone to through-cracks during compression. Simultaneously, the foamed slurry exhibited localized collapse during the settling stage, with some areas showing bubble aggregation and pore size coarsening. Analysis suggests that basalt fibers in this invention not only act as traditional crack inhibitors but also, together with hydroxypropyl methylcellulose, construct an internal spatial support network for the slurry. During the foaming stage, this network constrains the rising, migration, and merging of bubbles, improving the slurry's capacity to support bubbles and thus stabilizing the cell structure. Furthermore, basalt fibers can also bear some of the stress generated by crack propagation during hardening, delaying crack propagation through fiber pull-out and interfacial energy dissipation mechanisms. Without basalt fibers, the system lacks an effective spatial support structure, leading to decreased bubble stability and easier crack propagation, resulting in a simultaneous decline in both the material's mechanical properties and structural stability.

[0043] The above results indicate that basalt fiber not only plays a role as a reinforcing material, but also participates in the process of foam structure regulation and pore structure stabilization, and has a significant synergistic relationship with the foaming system and the cementing system.

[0044] Comparative Example 3 Under the same formulation conditions as in Example 1, without the addition of hydrogen peroxide foaming agent, and with the remaining components and process conditions maintained, the test results are as follows: the material density increased to 1320 kg / m³, the thermal conductivity increased to 0.32 W / (m·K), and the 28-day compressive strength increased to 4.2 MPa.

[0045] Compared to Example 1, the unfoamed system formed a typical dense structure, lacking a uniform porous structure inside the material. Heat could be rapidly conducted through the continuous solid-phase skeleton, thus significantly increasing the thermal conductivity. Although the dense structure improved the compressive strength of the material, the overall mass of the material increased significantly, and the thermal insulation performance decreased substantially, failing to meet the requirements of lightweight thermal insulation applications. Further analysis showed that the bubbles formed by the foaming agent in this invention were not randomly distributed, but formed a stable closed-cell-semi-closed-cell composite structure under the combined action of the cementing system, calcium sulfate whiskers, and basalt fibers. Among them, the early skeleton formed by the cementation reaction can improve the pore wall strength; calcium sulfate whiskers can enhance the local rigidity of the pore wall; and basalt fibers provide spatial support for the slurry during the foaming stage. The above-mentioned multi-component synergistic effect can effectively inhibit bubble merging and pore structure collapse, thereby maintaining high structural integrity while reducing density.

[0046] Therefore, this invention does not simply achieve lightweighting through foaming, but rather achieves a balance and unity between lightweight, high strength and thermal insulation performance through a synergistic mechanism of "foaming-foam stabilization-skeleton reinforcement".

Claims

1. A lightweight, high-strength thermal insulation material prepared using phosphogypsum, characterized in that, The raw materials of the lightweight, high-strength thermal insulation material, by weight, include: 60-90 parts of phosphogypsum; 10-30 parts of gelling and curing material; 1-5 parts of alkaline activator; 2-6 parts of calcium sulfate whiskers with an aspect ratio of 5-30; 0.5 to 1.5 parts of reinforcing fiber; 0.5-2.5 parts of chemical foaming agent; Hydroxypropyl methylcellulose 0.05~0.2 parts; Additives: 0.1-3 parts; 30-80 parts water; The auxiliary admixtures include water-reducing agents and retarder.

2. The lightweight, high-strength thermal insulation material prepared using phosphogypsum as described in claim 1, characterized in that, The gelling and curing material includes cement; The alkaline activator includes quicklime; The reinforcing fiber includes one or more of basalt, rock wool, or polyester fiber; The chemical foaming agent includes one or more of sodium bicarbonate, hydrogen peroxide, aluminum powder, or zinc powder. The water-reducing agent includes one or a mixture of two of polycarboxylate water-reducing agents or naphthalene-based water-reducing agents, and the amount added is 0.5 to 1.0 parts by weight. The retarder is citric acid, and its addition amount is 0.02~0.08 parts by weight.

3. A method for preparing a lightweight, high-strength thermal insulation material using phosphogypsum as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Pretreatment of phosphogypsum, adjusting the pH value to be controlled within the range of 6.0 to 8.0; S2. Dry mix the pretreated phosphogypsum, gelling and curing materials and alkaline activator from S1 to form a basic gelling system; S3. Add calcium sulfate whiskers to the basic gelling system in S2 and dry mix to make the calcium sulfate whiskers evenly dispersed in the gelling system. S4. Add hydroxypropyl methylcellulose to the gelling system in S3 and dry mix to make the hydroxypropyl methylcellulose uniformly coat the surface of the powder particles. S5. Dissolve the water-reducing agent and retarder in water beforehand to form a modified mixture; add the modified mixture to the gelling system in S4, and stir at a low speed of 200-300 r / min for 30-45 s to fully wet the powder. The speed was further increased to 800-1000 r / min and stirred at high speed for 90-120 s to obtain a uniform and stable base slurry. S6. Add reinforcing fibers to the base slurry in S5, stir and mix to obtain the reinforced slurry; S7. Add a chemical foaming agent to the reinforced slurry in S6, stir and mix to obtain a foamed slurry; S8. Inject the foamed slurry from S7 into the mold to remove air bubbles, press and shape, and let stand at room temperature to obtain the initial set molded part. S9. Trim the surface of the initial solidified part in S8, demold it, and demold it for 12-24 hours. After curing, obtain a lightweight and high-strength heat insulation material prepared by phosphogypsum.

4. The preparation method according to claim 3, characterized in that, The pretreatment described in step S1 specifically includes: detecting the pH value of phosphogypsum; when the pH value is lower than 6.0, adding quicklime for neutralization and adjustment to control the pH value within the range of 6.0 to 8.

0.

5. The preparation method according to claim 3, characterized in that, The mixing conditions for dry mixing in step S2 are: dry mixing at a speed of 300-400 r / min for 60-90 s; The mixing conditions for dry mixing in step S3 are: continue dry mixing at a speed of 400-500 r / min for 60-90 s; The mixing conditions for dry mixing in step S4 are: stirring at a speed of 300-400 r / min for 30-60 s; The mixing conditions described in step S6 are: continue stirring at a speed of 300-400 r / min for 30-60 s; The mixing conditions described in step S7 are: continue stirring at a speed of 1000-1200 r / min for 10-20 s; The molding and pressing conditions described in step S8 are as follows: the molding pressure is controlled at 0.2 to 0.6 MPa, and the holding time is 60 to 120 seconds.

6. The preparation method according to claim 3, characterized in that, The method for removing air bubbles in step S8 is as follows: the slurry is injected into the mold for molding, and large air bubbles are removed by vibration pressing or mechanical pressing.

7. The preparation method according to claim 3, characterized in that, The curing treatment method described in step S9 specifically includes standard curing or low-temperature drying. The standard curing is curing for 28 days at a temperature of 20±2℃ and a humidity of ≥90%. The low-temperature drying is drying at a temperature of 50~70℃ for 24~48 hours until constant weight.

8. A lightweight, high-strength thermal insulation material prepared using phosphogypsum as described in any one of claims 1-2, or a lightweight, high-strength thermal insulation material prepared using phosphogypsum as described in any one of claims 3-7, characterized in that... The lightweight, high-strength thermal insulation material prepared using phosphogypsum is used in one or more applications, including thermal protection of lithium batteries for new energy vehicles, fireproofing and insulation of buildings, and insulation of industrial equipment or pipelines.

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