Lightweight environment-friendly phosphogypsum aerated brick and preparation method thereof

Abstract

The invention discloses a light environment-friendly ardealite aerated brick and a preparation method thereof, and belongs to the technical field of aerated bricks, the raw materials of the aerated brick comprise modified ardealite, silt, fly ash, cement, quicklime, a foaming agent and a special excitant, and the method comprises the following steps: carrying out alkaline wet grinding and aging modification on undisturbed ardealite to prepare modified slurry; the preparation method comprises the following steps: mixing the raw materials, and adding a special exciting agent compounded by metal salt, crystal nucleus and a surface active component according to a specific proportion to prepare matrix slurry; a finished product is prepared through chemical excitation, pouring gas forming, standing hardening and high-temperature autoclaved curing. Through the synergistic effect of physical and chemical modification and a ternary excitation system, the problems of ardealite delayed coagulation and difficult silt dispersion are effectively solved, large-dosage utilization of multi-source solid waste is realized, the obtained product has the advantages of low density, high strength, uniform pore structure and the like, the production process is stable, the hardening speed is high, the mold collapse and suffocation phenomena are completely eradicated, and the production cost is reduced. The economic and environment-friendly benefits are obvious.

Description

Technical Field

[0001] This invention relates to the field of aerated concrete block technology, specifically to a lightweight and environmentally friendly phosphogypsum aerated concrete block and its preparation method. Background Technology

[0002] Autoclaved aerated concrete (AAC) blocks have become the dominant wall material in modern construction, replacing solid clay bricks, due to their lightweight, heat insulation, fire resistance, and ease of construction. Traditional AAC block production mainly relies on siliceous materials (such as quartz sand) and calcareous materials (such as cement and lime).

[0003] Introducing bulk solid waste into the aerated concrete block production system is considered one of the most effective ways to achieve its resource utilization.

[0004] However, in actual production, there are many technical bottlenecks in directly using phosphogypsum and silt to prepare aerated bricks. Phosphogypsum usually contains acidic impurities such as phosphates and fluorides, which seriously interfere with the cement hydration process, leading to unstable gas generation in the aerated brick slurry, slow setting and hardening of the brick body, and even phenomena such as mold collapse and failure to set, which greatly affect production efficiency and yield. Silt, due to its fine particles, high mud content, and low activity, often results in poor slurry rheology, making it difficult to form a uniform pore structure, thus affecting the strength and thermal insulation performance of the bricks.

[0005] Existing technologies often attempt to address these issues by reducing the amount of solid waste or increasing the amount of cement. However, this not only fails to fundamentally solve the solid waste disposal problem but also increases production costs. Therefore, the industry urgently needs a manufacturing technology that can adapt to the complex characteristics of solid waste and produce high-performance aerated concrete blocks while maintaining high admixture levels. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a lightweight and environmentally friendly phosphogypsum aerated concrete block and its preparation method. This invention employs a synergistic "modification pretreatment-ternary activation" technology, overcoming the technical bottlenecks of phosphogypsum retarding and silt dispersion. It achieves high-value utilization of multi-source solid waste through large-scale admixture, resulting in a lightweight and high-strength finished product with a short production cycle and eliminating mold collapse and air trapping, significantly improving the resource utilization level of solid waste and possessing both excellent environmental and economic benefits.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A lightweight and environmentally friendly phosphogypsum aerated brick is made from the following raw materials in parts by weight: 60-120 parts of modified phosphogypsum slurry (on a dry basis); 50-110 parts of silt slurry (on a dry basis); 150-300 parts of fly ash; 50-80 parts of cement; 40-70 parts of quicklime; 0.4-1.0 parts of a foaming agent; and 1-10 parts of a special activator.

[0009] The weight percentages are calculated based on a dry basis. This invention employs a "dry basis" metering method to precisely control the chemical reaction ratios between solid materials, avoiding fluctuations in slurry moisture content that could affect formula stability. In actual production, modified phosphogypsum and silt are added in slurry form, and their moisture content is included in the total water consumption for production.

[0010] The modified phosphogypsum slurry is a product of undisturbed phosphogypsum after neutralization with alkaline substances and physical modification. Unisturbed phosphogypsum contains a large amount of soluble phosphorus and fluorine impurities. Neutralization modification can eliminate most of the acidic impurities, while physical modification (grinding) can improve its particle size distribution and increase its reactivity.

[0011] The specialized activator is the core component of this invention, comprising a metal salt component capable of reacting with phosphate ions to form a sparingly soluble precipitate, a nucleation component that promotes hydration, and a surface-active component that regulates the rheological properties of the slurry. This activator solves the problems of slow setting and mold collapse in high-dosage phosphogypsum and silt systems through the synergistic effect of chemical chelation, lattice induction, and surface modification.

[0012] The special activator is composed of a metal salt component, a crystal nucleus component and a surface active component; the mass ratio of the three components is: 3.0~5.0 parts of metal salt component: 0.5~1.5 parts of crystal nucleus component: 0.5~1.5 parts of surface active component.

[0013] Preferably, the raw materials for preparing the silt slurry include at least one of river dredging sediment, lake silt, or construction pit waste sand, and the silt slurry undergoes impurity removal and grinding treatment. Impurity removal removes large stones and organic floating matter, and grinding treatment exposes more fresh surfaces for the silt particles, which is beneficial for bonding with cementing materials.

[0014] Preferably, the specific components of the dedicated activator are selected as follows:

[0015] The metal salt component is selected from at least one of soluble aluminum salts or soluble iron salts. These two salts dissociate into metal cations (Al2O3, Al ... 3+ or Fe 3+ It can rapidly combine with the difficult-to-treat phosphate ions remaining in phosphogypsum to form aluminum phosphate or iron phosphate precipitates that are extremely difficult to dissolve in an alkaline environment, thereby eliminating the toxic effect of phosphorus on ettringite crystals.

[0016] The nucleus component is selected from at least one of lithium salt, nano-hydrated calcium silicate, nano-silica, or ultrafine calcium carbonate. These nano or submicron-sized powders have extremely high specific surface areas, which can serve as a substrate for heterogeneous nucleation, reduce the nucleation barrier of hydration products, and significantly accelerate the early hardening of the green body.

[0017] The surface-active component is selected from at least one of lignin sulfonate, polycarboxylate superplasticizer, or naphthalene superplasticizer. This component is mainly used to adsorb onto the surface of silt and phosphogypsum particles, disperse the particles through electrostatic repulsion or steric hindrance, release encapsulated water, reduce the viscosity of high-mud content slurry, and improve the uniformity of bubble structure.

[0018] This invention also provides a method for preparing the above-mentioned lightweight and environmentally friendly phosphogypsum aerated brick, comprising the following steps:

[0019] S1. Raw material pretreatment: Modified phosphogypsum slurry and silt slurry are prepared separately. To ensure accurate measurement and slurry fluidity, the dry basis content of modified phosphogypsum in the modified phosphogypsum slurry is controlled at 50-65%, and the dry basis content of silt in the silt slurry is controlled at 50-65%.

[0020] As a preferred embodiment, the preparation process of the modified phosphogypsum slurry includes: mixing 100 parts by weight of undisturbed phosphogypsum, 1.0-5.0 parts by weight of an alkaline modifier, and 55-85 parts by weight, followed by wet grinding and aging treatment; the alkaline modifier is selected from at least one of quicklime, carbide slag, red mud, and white mud; the pH value of the modified phosphogypsum slurry is adjusted to 6.0-9.0. Adjusting the pH value to neutral or weakly alkaline is to prevent the acidic environment from damaging the gas-generating stability of the aluminum powder added later.

[0021] More preferably, the grinding fineness of the modified phosphogypsum slurry is controlled to have a residue of ≤15% on a 0.08mm square-hole sieve, and the aging time is at least 12 hours. The aging process helps the modifier to fully react with the phosphogypsum, allowing the generated insoluble impurities to crystallize and grow, reducing interference with subsequent hydration.

[0022] S2. Mixing and preparing the slurry: Modified phosphogypsum slurry, silt slurry, fly ash, cement, special activator and water are pumped into a mixer and mixed to prepare the matrix slurry.

[0023] In this step, the key process control point is that the special activator is added at the same time as or before the addition of fly ash, and the matrix slurry is kept in a stirring state for at least 60 seconds before the addition of quicklime in step S3. This sequence is crucial, as it allows the metal salt component (such as aluminum salt) in the special activator to preferentially contact and react with the soluble phosphorus remaining in the modified phosphogypsum slurry to generate chemically stable insoluble phosphates, thereby completing a "secondary sealing" of impurities and preventing a sharp increase in pH value after the subsequent addition of quicklime, which could lead to the re-dissolution of some impurities.

[0024] Add an appropriate amount of water to control the water-to-material ratio of the prepared matrix slurry at 0.58~0.65, and control the slurry diffusion at 240~260mm.

[0025] S3. Activation and casting: Add quicklime to the matrix slurry, stir and react, then add the gas-generating agent, mix evenly, and then cast into the mold.

[0026] To ensure the smooth progress of the gas-generating reaction, the slurry temperature is controlled to rise to 40-50℃ before adding the gas-generating agent. This temperature range is conducive to the reaction between aluminum powder and alkaline solution to produce hydrogen gas, and it matches the thickening rate of the slurry, preventing mold collapse or gas trapping.

[0027] S4. Static Curing and Hardening: The mold after casting is sent into the static curing chamber and statically cured at a controlled temperature until the green body hardens.

[0028] Preferably, the ambient temperature for static curing is 50~65℃, and the static curing time is 2~4 hours. A higher static curing temperature, combined with the effect of the nucleation component, can significantly shorten the hardening time of the high-dosage phosphogypsum system and improve production efficiency.

[0029] S5. Cutting and autoclaving: The hardened blank that has reached the cutting strength is demolded and cut, and then sent into an autoclave for autoclaving and curing under high temperature and high pressure to obtain the finished product.

[0030] Preferably, the autoclaving pressure is 1.1~1.4 MPa, and the constant pressure curing time is 7~10 h. Under these conditions, the active calcium oxide, silicon dioxide, alumina, and calcium sulfate in the raw materials undergo a full hydrothermal reaction to generate high-strength hydrated minerals such as tobermorite, giving the aerated concrete blocks excellent mechanical properties.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The lightweight and environmentally friendly phosphogypsum aerated concrete blocks provided by this invention significantly break through the dependence of traditional aerated concrete production on high-quality siliceous and calcareous natural resources, achieving significant economic and environmental benefits. Its technological advantages stem primarily from the organic combination of its components: using modified phosphogypsum to replace natural gypsum not only solves the problem of stockpiling large quantities of industrial solid waste, but also utilizes its abundant sulfate ions to activate fly ash and promote the formation of ettringite skeletons; using silt (such as river dredging sediment or construction waste sand) to replace finely ground quartz sand fully leverages its fine particle filling effect; combined with a cementing system composed of fly ash, cement, and quicklime, it significantly reduces raw material costs while ensuring the blocks possess excellent lightweight and high-strength properties, successfully achieving a high comprehensive utilization rate of solid waste.

[0033] The core innovation of this invention lies in the deep synergistic effect of modified phosphogypsum slurry and a special activator, which completely solves the common technical bottlenecks such as "non-setting, mold collapse, and low strength" in high-dosage phosphogypsum systems. The modified phosphogypsum slurry undergoes pre-neutralization and physical modification, eliminating most acidic impurities and optimizing particle size distribution. The special activator, on this basis, constructs a triple synergistic mechanism of "chemical impurity removal + lattice induction + rheological optimization": its metal salt component "secondarily blocks" residual soluble phosphorus and fluorine during the slurry mixing stage; the nucleation component compensates for the setting lag caused by phosphogypsum by lowering the nucleation barrier; and the surface-active component improves the rheological properties of high-mud-content silt slurry by releasing encapsulated water. This synergistic mode of "physical pretreatment + chemical activation regulation" ensures rapid hardening of the slurry and uniform pore structure during the static settling stage, endowing the finished product with excellent mechanical properties and volume stability. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0035] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0036] A method for preparing lightweight and environmentally friendly phosphogypsum aerated bricks includes the following steps:

[0037] S1. Raw material pretreatment and slurry preparation

[0038] Preparation of modified phosphogypsum slurry: 100 parts by weight of unprocessed phosphogypsum, 1.0-5.0 parts by weight of alkaline modifier, and 55-85 parts by weight of water are mixed. The alkaline modifier is selected from at least one of quicklime, carbide slag, red mud, and white mud. The mixture is wet-milled in a ball mill, controlling the grinding fineness to ≤15% residue on a 0.08mm square-hole sieve. The pH of the ground slurry is adjusted to 6.0-9.0 and pumped into a storage tank for aging treatment, with an aging time of at least 12 hours. Finally, the slurry concentration is adjusted so that the dry basis content of modified phosphogypsum in the modified phosphogypsum slurry is controlled within the range of 50-65%.

[0039] Preparation of silt slurry: Select at least one of the following raw materials: river dredging sediment, lake silt, or construction pit waste sand. After removing large particles and organic floating matter using a cleaning device, grind the mixture finely. Adjust the slurry concentration to control the dry basis content of silt in the slurry within the range of 50-65%.

[0040] S2. Mixed pulping

[0041] According to the formula ratio of the present invention, the following raw materials (parts by weight, all on a dry basis) are weighed respectively: 60-120 parts of modified phosphogypsum; 50-110 parts of silt; 150-300 parts of fly ash; 50-80 parts of cement; and 1-10 parts of special activator.

[0042] The weighed modified phosphogypsum slurry, silt slurry, fly ash, cement, special activator, and appropriate amount of water are put into a mixer and mixed to prepare a matrix slurry. The water-to-material ratio of the prepared matrix slurry is controlled at 0.58~0.65, and the slurry diffusion is controlled at 240~260mm.

[0043] The special activator is composed of a metal salt component, a crystal nucleus component, and a surface-active component; the mass ratio of the three components is: 3.0~5.0 parts of metal salt component: 0.5~1.5 parts of crystal nucleus component: 0.5~1.5 parts of surface-active component; the activator includes a metal salt component (selected from soluble aluminum salt or soluble iron salt) that can react with phosphate ions to form insoluble precipitates, a crystal nucleus component (selected from lithium salt, nano-hydrated calcium silicate, nano-silica or ultrafine calcium carbonate) that promotes hydration reaction, and a surface-active component (selected from lignin sulfonate, polycarboxylate superplasticizer or naphthalene superplasticizer) that regulates the rheology of the slurry.

[0044] Key process control: In terms of the feeding sequence, the special activator is added simultaneously with or before the addition of fly ash. Before adding quicklime, the matrix slurry is kept agitated for at least 60 seconds to ensure that the metal salt components fully contact and react with the soluble phosphorus in the slurry.

[0045] S3. Activation and Casting

[0046] Add 40-70 parts (dry basis) of weighed quicklime to the well-stirred matrix slurry. After adding the quicklime, stir at high speed to cause a slaking reaction, and the temperature of the slurry will begin to rise.

[0047] When the slurry temperature rises to the range of 40~50℃, add 0.4~1.0 parts of the weighed gas-generating agent (usually aluminum powder paste or aluminum powder suspension). Continue to stir quickly and evenly (stirring time is usually controlled at 30~50s), and then immediately pour the slurry into the preheated mold.

[0048] S4. Static Rest and Hardening

[0049] After casting, the mold is placed in a static curing chamber. Static curing is carried out at an ambient temperature of 50-65℃. During this period, the slurry expands and gradually solidifies. The static curing time is controlled at 2-4 hours, until the green body reaches sufficient strength for cutting.

[0050] S5. Cutting and Steaming

[0051] After hardening, the green body is demolded and cut horizontally and vertically to predetermined specifications using a cutting machine to remove waste. The cut green bodies are then grouped and fed into an autoclave for high-temperature and high-pressure curing. The pressure inside the autoclave is controlled at 1.1~1.4MPa, and the constant pressure curing time is 7~10 hours. After curing, the green body is cooled and depressurized before being removed from the autoclave, thus obtaining the finished lightweight and environmentally friendly phosphogypsum aerated brick.

[0052] The present invention will be further described below through specific embodiments.

[0053] Example 1

[0054] This embodiment provides a lightweight and environmentally friendly phosphogypsum aerated brick, which is made from raw materials comprising the following parts by weight (based on dry weight):

[0055] 85 parts modified phosphogypsum; 80 parts silt; 220 parts fly ash; 60 parts cement; 55 parts quicklime; 0.6 parts gas-generating agent (aluminum powder paste); 4 parts special activator.

[0056] The special activator is composed of aluminum sulfate (metal salt component), nano silica (crystal nucleus component), and polycarboxylate superplasticizer (surface active component) in a mass ratio of 4:1:1.

[0057] Its preparation method includes the following steps:

[0058] S1. Raw material pretreatment:

[0059] Preparation of modified phosphogypsum slurry: 100 parts by weight of unprocessed phosphogypsum, 2.0 parts by weight of quicklime (alkaline modifier), and 65 parts by weight of water are mixed. Wet grinding is performed in a ball mill, controlling the grinding fineness to 12% residue on a 0.08mm square-hole sieve. The pH of the ground slurry is 7.0, and it is pumped into a storage tank for aging for 16 hours. Finally, the moisture content is finely adjusted as needed to achieve a dry basis (solid content) of 60% for the modified phosphogypsum slurry.

[0060] Preparation of silt slurry: The riverbed dredged mud is treated by removing impurities and grinding, and the dry basis content of the silt slurry is adjusted to 55%.

[0061] S2. Mixing and Pulping: Add the measured amounts of modified phosphogypsum slurry, silt slurry, fly ash, cement, special activator, and water to the mixer. Adjust the total water volume (including water contained in the slurry itself) to control the water-to-material ratio (water / total dry weight) of the matrix slurry at 0.60, and the slurry diffusion at 250 mm. The special activator is added simultaneously with the fly ash, and before adding quicklime in step S3, maintain the matrix slurry in a stirring state for 90 seconds to allow the activator to fully disperse and pre-react.

[0062] S3. Activation and casting: Add quicklime to the matrix slurry, stir to react and raise the slurry temperature to 45°C, then add the gas-generating agent, stir for 40 seconds to mix evenly, and then pour into the mold.

[0063] S4. Static Curing and Hardening: After casting, the mold is placed in a static curing chamber. The ambient temperature for static curing is controlled at 60℃, and the static curing time is 2.5 hours, until the green body hardens.

[0064] S5. Cutting and Autoclaving: The hardened green body is cut and fed into an autoclave. The autoclaving pressure is controlled at 1.2 MPa, and the constant pressure curing time is 8 hours to obtain the finished product.

[0065] Example 2

[0066] This embodiment provides a lightweight, environmentally friendly phosphogypsum aerated brick with a high solid waste content, which is made from raw materials comprising the following parts by weight (based on dry weight):

[0067] 110 parts modified phosphogypsum; 110 parts silt; 150 parts fly ash; 50 parts cement; 40 parts quicklime; 0.5 parts gas-generating agent (aluminum powder paste); 8 parts special activator.

[0068] The special activator is composed of aluminum sulfate (metal salt component), nano silica (crystal nucleus component), and polycarboxylate superplasticizer (surface active component) in a mass ratio of 4:1:1.

[0069] Its preparation method includes the following steps:

[0070] S1. Raw material pretreatment:

[0071] Preparation of modified phosphogypsum slurry: By weight, mix 100 parts of unprocessed phosphogypsum, 3.5 parts of carbide slag (alkaline modifier), and 80 parts of water. Wet grind until 10% residue remains on a 0.08mm square-hole sieve. Set the slurry pH to 8.0 and age for 24 hours. Adjust the dry basis content of the modified phosphogypsum slurry to 55%.

[0072] Preparation of silt slurry: The waste sand from the construction foundation pit is treated by removing impurities and grinding, and the dry basis content of the silt slurry is adjusted to 60%.

[0073] S2. Mixing and Slurry Preparation: Add the measured amounts of modified phosphogypsum slurry, silt slurry, fly ash, cement, special activator, and water to the mixer. Adjust the total water volume to control the water-to-material ratio of the matrix slurry at 0.58 and the slurry diffusion at 245 mm. The special activator is added before adding the fly ash, and the matrix slurry is kept stirred for 120 seconds before adding quicklime in step S3.

[0074] S3. Activation and casting: Add quicklime to the matrix slurry, stir to react and raise the slurry temperature to 42°C, then add the gas-generating agent, stir for 50 seconds to mix evenly and then pour into the mold.

[0075] S4. Static Curing and Hardening: The mold after casting is sent into the static curing chamber, and the ambient temperature for static curing is controlled at 65℃. The static curing time is 3.0 hours until the green body hardens.

[0076] S5. Cutting and Autoclaving: The hardened green body is cut and fed into an autoclave. The autoclaving pressure is controlled at 1.3 MPa, and the constant pressure curing time is 9 hours to obtain the finished product.

[0077] Example 3

[0078] This embodiment provides a lightweight and environmentally friendly phosphogypsum aerated brick, which is made from raw materials comprising the following parts by weight (based on dry weight):

[0079] 60 parts modified phosphogypsum; 50 parts silt; 300 parts fly ash; 80 parts cement; 70 parts quicklime; 0.8 parts gas-generating agent (aluminum powder paste); 2 parts special activator.

[0080] The special activator is composed of aluminum sulfate (metal salt component), nano silica (crystal nucleus component), and polycarboxylate superplasticizer (surface active component) in a mass ratio of 4:0.8:1.2.

[0081] Its preparation method includes the following steps:

[0082] S1. Raw material pretreatment:

[0083] Preparation of modified phosphogypsum slurry: Mix 100 parts by weight of undiluted phosphogypsum, 1.5 parts by weight of quicklime (alkaline modifier), and 60 parts by weight. Wet grind until 14% residue remains on a 0.08mm square-hole sieve. Set the slurry pH to 6.5 and age for 12 hours. Adjust the dry basis content of the modified phosphogypsum slurry to 62%.

[0084] Preparation of silt slurry: The lake silt is treated by removing impurities and grinding, and the dry basis content of the silt slurry is adjusted to 52%.

[0085] S2. Mixing and Slurry Preparation: Add the measured amounts of modified phosphogypsum slurry, silt slurry, fly ash, cement, special activator, and water to the mixer. Adjust the total water volume to control the water-to-material ratio of the matrix slurry at 0.62 and the slurry diffusion at 260 mm. The special activator is added simultaneously with the fly ash, and the matrix slurry is kept stirred for 60 seconds before adding quicklime in step S3.

[0086] S3. Activation and casting: Add quicklime to the matrix slurry, stir to raise the slurry temperature to 48°C, then add the gas-generating agent, stir for 30 seconds to mix evenly, and then pour into the mold.

[0087] S4. Static Curing and Hardening: The mold after casting is sent into the static curing chamber, and the ambient temperature for static curing is controlled at 55℃. The static curing time is 2.0 hours until the green body hardens.

[0088] S5. Cutting and Autoclaving: The hardened green body is cut and fed into an autoclave. The autoclaving pressure is controlled at 1.1 MPa, and the constant pressure curing time is 7 hours to obtain the finished product.

[0089] Example 4

[0090] This embodiment provides a lightweight, environmentally friendly phosphogypsum aerated concrete block using different types of activators. The aerated concrete block is made from raw materials comprising the following parts by weight (based on dry weight):

[0091] 90 parts modified phosphogypsum; 70 parts silt; 200 parts fly ash; 70 parts cement; 60 parts quicklime; 0.6 parts gas-generating agent (aluminum powder paste); 5 parts special activator.

[0092] The special activator is composed of ferric chloride (metal salt component), nano-hydrated calcium silicate (crystal nucleus component), and naphthalene-based water-reducing agent (surface active component) in a mass ratio of 3:1:1.

[0093] Its preparation method includes the following steps:

[0094] S1. Raw material pretreatment:

[0095] Preparation of modified phosphogypsum slurry: By weight, mix 100 parts of unprocessed phosphogypsum, 2.5 parts of white mud (alkaline modifier), and 65 parts of water. Wet grind until 12% residue remains on a 0.08mm square-hole sieve. The slurry pH is 7.5, and it is aged for 18 hours. Adjust the dry basis content of the modified phosphogypsum slurry to 60%.

[0096] Preparation of silt slurry: Same as in Example 1, but with a dry basis content of 55%.

[0097] S2. Mixing and Pulping: Add the measured raw materials to the mixer. Adjust the total water volume to control the water-to-material ratio of the matrix slurry at 0.60 and the slurry diffusion at 250 mm. The special activator is added simultaneously with the fly ash, and the matrix slurry is kept stirred for 90 seconds before adding quicklime in step S3.

[0098] S3. Activation and casting: Add quicklime to the matrix slurry, stir to react and raise the slurry temperature to 45°C, then add the gas-generating agent, stir for 40 seconds to mix evenly, and then pour into the mold.

[0099] S4. Static Curing and Hardening: The cast mold is placed in a static curing chamber, and the ambient temperature for static curing is controlled at 60℃ for 2.6 hours.

[0100] S5. Cutting and Autoclaving: The hardened green body is cut and fed into an autoclave. The autoclaving pressure is controlled at 1.2 MPa, and the constant pressure curing time is 8 hours to obtain the finished product.

[0101] Comparative Example 1

[0102] This comparative example is used to verify the necessity of the metal salt component. Its raw material formulation and preparation process are basically the same as those in Example 1, with the only difference being the composition of the special activator.

[0103] Raw material formulation (based on dry weight):

[0104] 85 parts modified phosphogypsum; 80 parts silt; 220 parts fly ash; 60 parts cement; 55 parts quicklime; 0.6 parts gas-generating agent (aluminum powder paste); 4 parts special activator.

[0105] The special activator does not contain metal salt components and is composed of nano-silica (crystal nucleus component) and polycarboxylate superplasticizer (surface active component) in a mass ratio of 1:1.

[0106] Its preparation methods include:

[0107] S1. Raw material pretreatment: Same as in Example 1 (the modified phosphogypsum slurry preparation ratio is: 100 parts of raw phosphogypsum, 2.0 parts of quicklime, and 65 parts of water).

[0108] S2. Mixing and Pulping: Add the raw materials to the mixer, adjust the water-to-material ratio to 0.60, and the diffusion degree to 250mm. Add the special activator and maintain stirring for 90 seconds.

[0109] Steps S3-S5: The process parameters are the same as in Example 1. However, in actual operation, due to the lack of metal salt components, the slurry experienced severe mold collapse in the mold, and a qualified finished product could not be successfully produced.

[0110] Comparative Example 2

[0111] This comparative example is used to verify the necessity of the crystal nucleus component. Its raw material formulation and preparation process are basically the same as those in Example 1, with the only difference being the composition of the special activator.

[0112] Raw material formulation (calculated based on dry weight): Same as Example 1.

[0113] The special activator does not contain a crystal nucleus component and is composed of aluminum sulfate (metal salt component) and polycarboxylate superplasticizer (surface active component) in a mass ratio of 4:1.

[0114] Its preparation methods include:

[0115] S1. Raw material pretreatment: Same as in Example 1.

[0116] S2. Mixing and Pulping: Add the raw materials to the mixer, adjust the water-to-material ratio to 0.60, and the diffusion degree to 250mm. Add the special activator and maintain stirring for 90 seconds.

[0117] Steps S3-S5: Process parameters are the same as in Example 1. In step S4, even at 60°C, the hardening of the billet is extremely slow due to the lack of nucleation induction, and the static resting time is extended to 6.5 hours before the cutting strength is barely reached.

[0118] Comparative Example 3

[0119] This comparative example is used to verify the necessity of the surface-active component. Its raw material formulation and preparation process are basically the same as those in Example 1, with the only difference being the composition of the special activator.

[0120] Raw material formulation (calculated based on dry weight): Same as Example 1.

[0121] The special activator does not contain surface-active components and is composed of aluminum sulfate (metal salt component) and nano-silica (crystal nucleus component) in a mass ratio of 4:1.

[0122] Its preparation methods include:

[0123] S1. Raw material pretreatment: Same as in Example 1.

[0124] S2. Mixing and Pulping: The raw materials are put into the mixer and a special activator is added. Under the same water volume (water-to-material ratio 0.60), due to the lack of dispersion effect of surface-active components, the slurry viscosity is extremely high and the diffusion is only 180mm.

[0125] Steps S3-S5: Process parameters are the same as in Example 1. Due to the excessive thickness of the slurry, the bubbles generated by the gas-generating agent are difficult to diffuse evenly, resulting in a "stuck air" phenomenon in the green body, and the final product has a large and uneven pore structure.

[0126] Comparative Example 4

[0127] This comparative example is used to verify the necessity of pretreatment of modified phosphogypsum slurry. Its formulation is the same as that of Example 1, except for the raw material pretreatment step.

[0128] Raw material formulation (calculated based on dry weight): Same as Example 1.

[0129] Its preparation methods include:

[0130] S1. Raw material pretreatment: No neutralization, modification, or aging treatment is performed. 100 parts of undisturbed phosphogypsum are directly mixed with 65 parts of water to prepare a slurry, and the dry basis content is adjusted to 60%; the preparation of the silt slurry is the same as in Example 1.

[0131] S2. Mixing and Pulping: Add the undisturbed phosphogypsum slurry, silt slurry, and other raw materials (including the full-component special activator described in Example 1, i.e., a mass ratio of 4:1:1) to the mixer. Adjust the water-to-material ratio to 0.60 and the diffusion degree to 250 mm. Maintain stirring for 90 seconds.

[0132] Steps S3-S5: Process parameters are the same as in Example 1. Although a special activator was added, the slurry failed to coagulate (did not coagulate) during the static resting stage because the concentration of acidic impurities in the undisturbed phosphogypsum was too high and it had not been adjusted by aging crystals.

[0133] To further verify the technical effect of the lightweight and environmentally friendly phosphogypsum aerated bricks of the present invention, we conducted systematic performance tests on the aerated bricks prepared in Examples 1-4 and Comparative Examples 1-4.

[0134] All tests were conducted in strict accordance with the Chinese national standard GB / T 11968-2020 "Autoclaved Aerated Concrete Blocks".

[0135] Dry density: Calculated by measuring the volume and mass of the specimen after drying it to constant weight (unit: kg / m³).

[0136] Compressive strength: The test block of the specified size is subjected to pressure test using a pressure testing machine (unit: MPa).

[0137] Static hardening time: Record the time required from the completion of pouring until the hardness of the billet reaches a level that allows the cutting machine to cut it without causing collapse (unit: h).

[0138] Appearance and pore structure evaluation: The uniformity of pores, pore size and the presence of macroscopic defects such as cracks, mold collapse and air blockage are evaluated by visual observation and microscopic observation.

[0139] The specific test results are shown in Table 1.

[0140] Table 1 Performance test results of aerated concrete blocks

[0141]

[0142] By comparing and analyzing the above experimental data, the following conclusions can be drawn:

[0143] (1) Significant synergistic effect (Examples 1-4 vs Comparative Examples 1-4)

[0144] Examples 1-4, under different solid waste dosages and formulation adjustments, all produced qualified products conforming to the GB / T 11968-2020 standard. In particular, Examples 1 and 3, while maintaining a low dry density (approximately 600 kg / m³), achieved compressive strengths of 5.2 MPa and 6.4 MPa, respectively, realizing the goal of lightweight and high strength. This demonstrates that the technical route of this invention, "modified pretreatment + special activator," possesses extremely high stability and universality.

[0145] (2) The “chemical phosphorus-locking” effect of metal salt components is indispensable (Example 1 vs Comparative Example 1)

[0146] Comparative Example 1, after removing the metal salt components from the special activator, directly led to mold collapse failure. This strongly demonstrates that the residual soluble phosphates in phosphogypsum have a serious retarding and destructive effect on cement hydration. The metal salt components, through chemical reactions, form insoluble precipitates, effectively sealing off harmful impurities, which is the basis for the system's normal setting and molding.

[0147] (3) The key impact of crystal nucleus composition on production efficiency (Example 1 vs Comparative Example 2)

[0148] In Comparative Example 2, although hardening eventually occurred in the absence of nucleation components, the settling time was extended from 2.5 hours in Example 1 to 6.5 hours. This indicates that in a high-content phosphogypsum system, the hydration of cement itself alone is insufficient to overcome the setting lag problem. Adding nano-silica or CSH as nuclei significantly lowers the nucleation barrier and drastically shortens the production cycle.

[0149] (4) Regulation of pore structure and density by surface-active components (Example 1 vs Comparative Example 3)

[0150] Comparative Example 3 lacked surfactants, resulting in poor slurry diffusion and hindered aluminum powder gas generation (gas trapping). The final product had a dry density as high as 685 kg / m³ (far exceeding the 605 kg / m³ of Example 1), and due to the deteriorated pore structure, its compressive strength actually decreased to 3.1 MPa. This confirms that surfactants play a crucial role in improving the rheological properties of high-mud-content silt slurries and optimizing their pore structure.

[0151] (5) Necessity of pretreatment process (Example 1 vs Comparative Example 4)

[0152] Comparative Example 4, using undisturbed phosphogypsum directly, failed to form (do not solidify) even with the addition of a full-component activator. This clearly demonstrates that physicochemical modification pretreatment is a prerequisite for this technical solution. It reduces the total amount of impurities and optimizes the crystal morphology, creating the necessary environment for the subsequent activator to function. Only by combining "pre-modification" with "post-activation" can the large-scale resource utilization of phosphogypsum be truly realized.

[0153] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A lightweight, environmentally friendly phosphogypsum aerated brick, characterized in that, The aerated concrete block is made from the following raw materials in parts by weight: 60-120 parts modified phosphogypsum slurry; 50-110 parts silt slurry; 150-300 parts fly ash; 50-80 parts cement; and 40-70 parts quicklime. 0.4-1.0 parts of vaporizing agent; 1-10 parts of special activator; The weight percentages are calculated based on a dry basis; the modified phosphogypsum slurry is a product of undisturbed phosphogypsum after neutralization with alkaline substances and physical modification; the special activator includes a metal salt component that can react with phosphate ions to form an insoluble precipitate, a nucleation component that promotes hydration reaction, and a surface-active component that regulates the rheological properties of the slurry.

2. The lightweight and environmentally friendly phosphogypsum aerated brick according to claim 1, characterized in that, The metal salt component is selected from at least one of soluble aluminum salt or soluble iron salt; the crystal nucleus component is selected from at least one of lithium salt, nano-hydrated calcium silicate, nano-silica or ultrafine calcium carbonate; the surface-active component is selected from at least one of lignin sulfonate, polycarboxylate superplasticizer or naphthalene superplasticizer.

3. The lightweight and environmentally friendly phosphogypsum aerated brick according to claim 1, characterized in that, The special activator is composed of a metal salt component, a crystal nucleus component and a surface active component; the mass ratio of the three components is: 3.0~5.0 parts of metal salt component: 0.5~1.5 parts of crystal nucleus component: 0.5~1.5 parts of surface active component.

4. A method for preparing lightweight environmentally friendly phosphogypsum aerated bricks as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Raw material pretreatment: Modified phosphogypsum slurry and silt slurry are prepared separately, wherein the dry basis content of modified phosphogypsum in the modified phosphogypsum slurry is 50-65%, and the dry basis content of silt in the silt slurry is 50-65%; S2. Mixing and preparing the slurry: Mix and stir the modified phosphogypsum slurry, silt slurry, fly ash, cement, special activator and water to prepare the matrix slurry; S3. Activation and casting: Add quicklime to the matrix slurry, stir and react, then add the gas-generating agent, mix evenly, and then pour into the mold; S4. Static curing and hardening: The mold after casting is statically cured at a controlled temperature until the green body hardens; S5. Cutting and autoclaving: The hardened blank is cut and then autoclaved under high temperature and high pressure to obtain the finished product.

5. The preparation method according to claim 4, characterized in that, In step S1, the preparation process of the modified phosphogypsum slurry includes: taking 100 parts by weight of undisturbed phosphogypsum, 1.0 to 5.0 parts by weight of alkaline modifier, and 55 to 85 parts by weight of water, mixing them, and performing wet grinding and aging treatment; the alkaline modifier is selected from at least one of quicklime, carbide slag, red mud, and white mud; the pH value of the modified phosphogypsum slurry is adjusted to 6.0 to 9.

0.

6. The preparation method according to claim 4, characterized in that, In step S1, the grinding fineness of the modified phosphogypsum slurry is controlled to have a residue of ≤15% on a 0.08mm square hole sieve, and the aging time is at least 12 hours.

7. The preparation method according to claim 4, characterized in that, In step S2, an appropriate amount of water is added so that the water-to-material ratio of the matrix slurry is controlled at 0.58~0.65 and the slurry diffusion is controlled at 240~260mm.

8. The preparation method according to claim 4, characterized in that, In step S3, before adding the gas-generating agent, the slurry temperature is controlled to rise to 40~50℃.

9. The preparation method according to claim 4, characterized in that, In step S4, the ambient temperature for static curing is 50~65℃, and the static curing time is 2~4h.

10. The preparation method according to claim 4, characterized in that, In step S5, the pressure of autoclaving is 1.1~1.4MPa, and the constant pressure curing time is 7~10h.

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