Ardealite high-content harmless high-strength baking-free brick and preparation method thereof

Abstract

The invention provides an ardealite high-content harmless high-strength baking-free brick and a preparation method thereof.The preparation method comprises the steps that S1, ardealite pretreatment is conducted, specifically, ardealite is dried and dehydrated, and pretreated ardealite with the free water content being 10%-15% and the crystal water content being 12%-17% is obtained; s2, uniformly mixing 70-85% by mass of the pretreated phosphogypsum, 2-8% by mass of carbide slag, 3-18% by mass of cement and 6-15% by mass of a curing agent to obtain a mixed dry material; s3, the mixed dry material is poured into a mold for high-pressure forming; and S4, demolding and curing after high-pressure forming to obtain the phosphogypsum high-doping-amount harmless high-strength baking-free brick.

Description

Technical Field

[0001] This invention relates to the field of resource utilization of industrial solid waste, specifically to a method for preparing harmless, high-strength, non-fired bricks using phosphogypsum, carbide slag, cement, and curing agents. Background Technology

[0002] With the acceleration of industrialization, the output of industrial solid waste is constantly increasing, especially industrial by-products such as phosphogypsum, fly ash, and carbide slag. These solid wastes not only occupy a large amount of land resources but also easily pollute the environment during storage. Currently, the comprehensive utilization rate of phosphogypsum is low, with most being disposed of through stockpiling, which wastes resources and poses environmental risks. Although phosphogypsum has cementing properties and can be used to prepare various building materials, its impurities and high moisture content severely affect its utilization performance.

[0003] To address these issues, researchers began exploring the possibility of using phosphogypsum in the preparation of non-fired bricks. Compared to traditional sintered bricks, non-fired bricks offer advantages such as energy saving, emission reduction, and environmental friendliness. Their production process does not require high-temperature sintering and can be completed through physical pressing or chemical curing methods. However, existing technologies for producing non-fired bricks using phosphogypsum still have some shortcomings, mainly manifested in low admixture dosage, low resource utilization rate, and low product strength. Furthermore, some technologies involve pretreatment of phosphogypsum during the preparation process, such as washing and calcination, which not only increases investment costs but also raises issues related to wastewater treatment and energy consumption.

[0004] Therefore, developing a non-fired brick preparation process that achieves high phosphogypsum content, a simple preparation procedure, high product strength, and environmental friendliness is of great significance. This will not only improve the resource utilization efficiency of phosphogypsum and reduce environmental pollution, but also provide a new source for green and environmentally friendly building materials. Simultaneously, this process can also achieve the goal of treating waste with waste, solving the problem of industrial waste disposal, and promoting green industrial development.

[0005] Several invention patents have been developed to address the environmental hazards caused by phosphogypsum and carbide slag and to achieve the goal of waste treatment.

[0006] Patent CN106278103A discloses an autoclaved gypsum brick and its manufacturing method, comprising phosphogypsum, carbide slag, fly ash, slag powder, a modifier, and a saturated sulfate solution. This invention, by increasing the amount of phosphogypsum added and combining it with a new modifier and a saturated sulfate solution, produces autoclaved gypsum bricks with good performance, high quality, and high strength. Furthermore, the low steam curing temperature during the manufacturing process saves steam costs and energy. However, this patent still has issues regarding the need to further improve the utilization rate of phosphogypsum and reduce production costs.

[0007] Patent CN106365578A discloses a method for preparing building materials using phosphogypsum. The method first prepares a dry mixture from phosphogypsum, aluminosilicate industrial waste, calcareous cementitious materials, and aggregates. Then, water or water with a dissolved activator is added to prepare a wet mixture. This mixture is then subjected to static standing and static pressing molding, and finally cured naturally or with steam to produce an ultra-high-strength material. This invention solves the problems of phosphogypsum's high impurity content and difficulty in utilization, and simultaneously couples with a large amount of aluminosilicate industrial waste to prepare ultra-high-strength building materials with high compressive strength. However, this patent still faces the challenge of further improving the density and compliance of the molding process.

[0008] In view of this, the present invention provides a method for preparing harmless high-strength non-fired bricks with high phosphogypsum content, which yields environmentally friendly high-strength non-fired bricks and provides a new approach to alleviating the environmental pollution problem of phosphogypsum and the resource utilization of industrial solid waste. Summary of the Invention

[0009] This invention aims to provide a method for preparing harmless, high-strength, non-fired bricks with a high dosage of phosphogypsum. The main raw material is phosphogypsum, and the auxiliary materials are carbide slag, a curing agent, and ordinary 42.5 cement. The advantage of this method lies in its three-stage curing of harmful impurities in phosphogypsum: first, the alkalinity of the carbide slag is used to adjust the pH of the phosphogypsum and neutralize some soluble phosphorus and fluoride, causing them to form insoluble phosphides and fluorides; second, the chemical properties of the curing agent are used to react with most of the soluble phosphorus and fluoride to form inert substances; and third, a dense non-fired brick is prepared using cement and a high-pressure molding process, further curing the harmful impurities. This method not only achieves the harmless treatment of phosphogypsum, with the product leachate meeting national surface water environmental quality standards, but also produces high-strength non-fired bricks that can be applied in traditional construction fields, achieving the goal of treating waste with waste and utilizing waste resources. It is suitable for large-scale resource-based treatment of phosphogypsum.

[0010] This invention provides a high-strength, non-fired brick with high phosphogypsum content, comprising the following components by mass fraction: 70%-85% pretreated phosphogypsum, 2%-8% carbide slag, 3%-18% cement, and 6%-15% curing agent. The pretreated phosphogypsum has a free water content of 10-15% and a crystal water content of 12-17%.

[0011] Furthermore, the pretreated phosphogypsum is obtained by microwave or heating dehydration of phosphogypsum at 150℃-180℃.

[0012] This invention also provides a method for preparing high-content, harmless, high-strength, non-fired bricks with high phosphogypsum content, comprising the following steps: S1. Pretreatment of phosphogypsum: Phosphogypsum is dried and dehydrated to obtain pretreated phosphogypsum with a free water content of 10-15% and a crystal water content of 12-17%. S2. By mass fraction, mix 70%-85% pretreated phosphogypsum, 2%-8% carbide slag, 3%-18% cement and 6%-15% curing agent evenly to obtain a mixed dry material; S3. Pour the mixed dry materials into the mold and perform high-pressure molding; S4. After high-pressure molding, demolding and curing are performed to obtain high-strength, harmless, non-fired bricks with high phosphogypsum content.

[0013] Furthermore, the particle size of the phosphogypsum is ≤80 mesh.

[0014] Furthermore, the particle size of the carbide slag is ≤100 mesh.

[0015] Furthermore, the pretreated phosphogypsum has a free water content of 10-15% and a crystal water content of 12-15%.

[0016] Furthermore, the high-pressure molding conditions are as follows: the pressure is maintained at 40-110 MPa, and the pressure is held for 5-10 minutes.

[0017] Furthermore, the maintenance conditions are: maintenance in an environment with a temperature of 10℃-20℃ and an air humidity of ≥50%.

[0018] Furthermore, the cement is 42.5 silicate cement.

[0019] Furthermore, the unfired brick has a soluble phosphorus content of <0.4 mg / L, a soluble fluorine content of <8.0 mg / L, a pH of 6-8, and a compressive strength of >22 MPa.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. On the one hand, this invention utilizes the alkalinity of carbide slag and the properties of the curing agent to chemically neutralize most of the soluble phosphorus and fluoride in phosphogypsum, causing it to form insoluble phosphides and fluorides. On the other hand, it employs a high-pressure molding process to promote the mutual compression and overlapping of calcium sulfate dihydrate crystals into a dense structure. Simultaneously, the cementitious binding effect enhances the strength of the brick blank while physical methods further solidify the harmful substances in the phosphogypsum. This invention organically combines chemical and physical curing methods, efficiently achieving the harmless treatment of phosphogypsum.

[0021] 2. The non-fired bricks provided by this invention contain a high amount of phosphogypsum, which has the disadvantages of high soluble P and N content and poor mechanical strength. However, the phosphogypsum non-fired bricks prepared by the method provided by this invention have excellent properties such as qualified leachate, strong mechanical properties, and low water absorption. The leachate of the non-fired bricks, tested according to the method specified in GB 5086.1-1997, shows soluble phosphorus less than 0.4 mg / L, soluble fluoride less than 8.0 mg / L, and pH 6-8. The leachate meets the leachate standard for open-air filling materials in GB32124-2024 "Specifications for the Treatment and Disposal of Phosphogypsum". Furthermore, the compressive strength of the non-fired bricks meets the standard requirement of 25 MPa compressive strength in JC / T422-2007 "Non-sintered Waste Tailings Bricks" (Grade MU25).

[0022] 3. This invention controls the free water content of phosphogypsum to 10-15% and the crystal water content to 12-15% through microwave drying. During microwave treatment at 150℃, all molecules in the phosphogypsum begin to vibrate, and the material temperature rises. This not only causes a large-scale loss of free water but also, due to localized high temperatures and intensified crystal desorption, some dihydrate calcium sulfate crystals lose their crystal water and transform into hemihydrate gypsum, while the morphology of a small portion of the crystals changes. After microwave drying, the phosphogypsum raw material becomes fluffy and possesses some cementing properties, which facilitates the penetration of components such as curing agents. Simultaneously, the hemihydrate gypsum with cementing properties can rehydrate, contributing to the formation of a denser structure in the unfired bricks and improving product strength. Detailed Implementation

[0023] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0024] The phosphogypsum and curing agent used in the following examples and comparative examples were all provided by Yidu Xingfa Chemical Co., Ltd. The wet basis water content of the phosphogypsum was 30%, the dry basis water-soluble P2O5 content of the phosphogypsum was 0.6%, and the dry basis water-soluble F content of the phosphogypsum was 0.5%. The main components of the curing agent and their mass fraction percentages are as follows: Al2(SO4)3·nH2O 32%, [Al2(OH)3] ... n Cl 6-n ] m 28%, (C3H3O2Na) n 25%; The calcium carbide slag was purchased from Hubei Hongxinfa Trading Co., Ltd., with a free water content of <1%. Its main components and the mass percentage of each component are: CaO 80%, SiO2 6%, Al2O3 2%, Na2O 1%, Cl 1%. The cement was purchased from Huaxin Cement Co., Ltd., and was 42.5 silicate cement.

[0025] Example 1 A method for preparing a high-strength, non-fired brick with high phosphogypsum content includes the following steps: S1. Pretreatment of phosphogypsum: Phosphogypsum is passed through an 80-mesh sieve, and the sieve-filled material is dried under microwave at 150°C for 30 minutes to obtain phosphogypsum with a free water content of 13% and a crystal water content of 12%. The microwave power is 3.12kW and the microwave frequency is 2645Hz. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 72% of pretreated phosphogypsum, 4% of pretreated carbide slag, 15% of cement, and 9% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixed dry material obtained in step S1 into a steel mold for high-pressure molding. The pressure is maintained at 50MPa and the holding time is 5min to obtain a brick blank. S3. Demold the brick blanks obtained in S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity at no less than 50%. After curing for 10 days, you will get the finished product: harmless high-strength non-fired bricks.

[0026] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the compressive strength of the unfired bricks was 29.4 MPa, the soluble phosphorus content in the leachate was 0.21 mg / L, the soluble fluoride content was 7.1 mg / L, and the pH value was 7.2. Therefore, the phosphogypsum unfired bricks prepared by the method of this invention have good mechanical properties and are environmentally friendly (P≤0.5 ppm, F≤10 ppm).

[0027] Example 2 A method for preparing a high-strength, non-fired brick with high phosphogypsum content includes the following steps: S1. Pretreatment of phosphogypsum: Phosphogypsum is passed through an 80-mesh sieve, and the sieve material is dried under microwave at 150°C for 30 minutes to obtain phosphogypsum with a free water content of 13% and a crystal water content of 12%. The microwave power is 3.12kW and the microwave frequency is 2645Hz. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 75% of pretreated phosphogypsum, 4% of pretreated carbide slag, 11% of cement, and 10% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixture obtained in step S1 into a steel mold and pressurize it under high pressure. The pressure is maintained at 70MPa and the holding time is 6min. S3. Demold the brick blanks from S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity at no less than 50%. After curing for 15 days, you will get the finished harmless high-strength non-fired bricks.

[0028] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the compressive strength of the unfired bricks was 28.8 MPa, the soluble phosphorus content in the leachate was 0.25 mg / L, the soluble fluoride content was 7.6 mg / L, and the pH value was 7.2. Therefore, the phosphogypsum unfired bricks prepared by the method of this invention have good mechanical properties and are environmentally friendly (P≤0.5 ppm, F≤10 ppm).

[0029] Example 3 A method for preparing a high-strength, non-fired brick with high phosphogypsum content includes the following steps: S1. Pretreatment of phosphogypsum: Phosphogypsum is passed through an 80-mesh sieve, and the sieve material is dried under microwave at 150°C for 30 minutes to obtain phosphogypsum with a free water content of 13% and a crystal water content of 12%. The microwave power is 3.12kW and the microwave frequency is 2645Hz. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 80% of pretreated phosphogypsum, 5% of pretreated carbide slag, 3% of cement, and 12% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixture obtained in step S1 into a steel mold and pressurize it under high pressure. The pressure is maintained at 100MPa and the holding time is 8min. S3. Demold the brick blanks from S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity at no less than 50%. After curing for 15 days, you will get the finished harmless high-strength non-fired bricks.

[0030] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the compressive strength of the unfired bricks was 25.3 MPa, the soluble phosphorus content in the leachate was 0.32 mg / L, the soluble fluoride content was 7.8 mg / L, and the pH value was 6.2. Therefore, the phosphogypsum unfired bricks prepared by the method of this invention have good mechanical properties and are environmentally friendly (P≤0.5 ppm, F≤10 ppm).

[0031] Example 4 S1. Pretreatment of phosphogypsum: Pass the phosphogypsum through an 80-mesh sieve, and microwave the sieve material at 150℃ for 20 minutes to obtain phosphogypsum with a free water content of 15% and a crystal water content of 16%. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 72% of pretreated phosphogypsum, 4% of pretreated carbide slag, 15% of cement, and 9% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixed dry material obtained in step S1 into a steel mold for high-pressure molding. The pressure is maintained at 50MPa and the holding time is 5min to obtain a brick blank. S3. Demold the brick blanks obtained in S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity at no less than 50%. After curing for 10 days, you will get the finished product: harmless high-strength non-fired bricks.

[0032] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the compressive strength of the unfired bricks was 22.4 MPa, the soluble phosphorus content in the leachate was 0.25 mg / L, the soluble fluoride content was 7.9 mg / L, and the pH value was 6.9. Therefore, although the phosphogypsum unfired bricks prepared by drying phosphogypsum in this embodiment have basically qualified soluble phosphorus, fluoride content, and pH in the leachate, the phosphogypsum does not possess some of its cementing properties due to the ineffective removal of crystal water, resulting in a decrease in the final strength of the unfired bricks.

[0033] Comparative Example 1 S1. Pretreatment of phosphogypsum: Phosphogypsum is passed through an 80-mesh sieve, and the sieve material is dried under microwave at 150°C for 30 minutes to obtain phosphogypsum with a free water content of 13% and a crystal water content of 12%. The microwave power is 3.12kW and the microwave frequency is 2645Hz. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 72% of pretreated phosphogypsum, 0% of pretreated carbide slag, 18% of cement, and 10% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixture obtained in step S1 into a steel mold and pressurize it under high pressure. The pressure is maintained at 50MPa and the holding time is 5min. S3. Demold the brick blanks from S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity no less than 50%. After curing for 10 days, you will get the finished harmless high-strength non-fired bricks.

[0034] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the compressive strength of the unfired bricks was 30.5 MPa, the soluble phosphorus content in the leachate was 0.46 mg / L, the soluble fluoride content was 20.6 mg / L, and the pH value was 5.5. Therefore, although the phosphogypsum unfired bricks prepared according to the method of Comparative Example 1 have better mechanical properties, the pH and soluble fluoride content of the leachate are unqualified.

[0035] Comparative Example 2 S1. Pretreatment of phosphogypsum: Phosphogypsum is passed through an 80-mesh sieve, and the sieve material is dried under microwave at 150°C for 30 minutes to obtain phosphogypsum with a free water content of 13% and a crystal water content of 12%. The microwave power is 3.12kW and the microwave frequency is 2645Hz. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 72% of pretreated phosphogypsum, 10% of pretreated carbide slag, 18% of cement, and 0% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixture obtained in step S1 into a steel mold and pressurize it under high pressure. The pressure is maintained at 50MPa and the holding time is 5min. S3. Demold the brick blanks from S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity no less than 50%. After curing for 10 days, you will get the finished harmless high-strength non-fired bricks.

[0036] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the compressive strength of the unfired bricks was 29.5 MPa, the soluble phosphorus content in the leachate was 11.4 mg / L, the soluble fluoride content was 35.7 mg / L, and the pH value was 12.3. Therefore, although the phosphogypsum unfired bricks prepared according to the method of Comparative Example 2 have better mechanical properties, the pH, soluble phosphorus, and soluble fluoride in the leachate are all unqualified.

[0037] Comparative Example 3 S1. Pretreatment of phosphogypsum: Phosphogypsum is passed through an 80-mesh sieve, and the sieve-filled material is microwave-dried at 150°C for 10 minutes to obtain phosphogypsum with a free water content of 18% and a crystal water content of 18%. The microwave power is 3.12kW and the microwave frequency is 2645Hz. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 72% of pretreated phosphogypsum, 4% of pretreated carbide slag, 15% of cement, and 9% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixture obtained in step S1 into a steel mold and pressurize it under high pressure. The pressure is maintained at 50MPa and the holding time is 5min. S3. Demold the brick blanks from S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity no less than 50%. After curing for 10 days, you will get the finished harmless high-strength non-fired bricks.

[0038] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the unfired bricks could not be molded, the strength could not be measured, the soluble phosphorus content in the leachate was 0.38 mg / L, the soluble fluoride content was 7.9 mg / L, and the pH value was 7.0. Therefore, it can be seen that the unfired bricks prepared according to the method of Comparative Example 3, due to the excessively high content of free water and crystal water in the phosphogypsum, could not be molded under high pressure, losing the high-pressure curing effect, resulting in a significant decrease in the soluble phosphorus and soluble fluoride indicators of the product's leachate compared to Example 1.

[0039] Comparative Example 4 S1. Pretreatment of phosphogypsum: Phosphogypsum is passed through an 80-mesh sieve, and the sieve-filled material is microwave-dried at 150°C for 50 minutes to obtain phosphogypsum with 8% free water content and 10% crystal water content. The microwave power is 3.12kW and the microwave frequency is 2645Hz. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 72% of pretreated phosphogypsum, 4% of pretreated carbide slag, 15% of cement, and 9% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixture obtained in step S1 into a steel mold and pressurize it under high pressure. The pressure is maintained at 50MPa and the holding time is 5min. S3. Demold the brick blanks from S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity no less than 50%. After curing for 10 days, you will get the finished harmless high-strength non-fired bricks.

[0040] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the compressive strength of the unfired bricks was 18.3 MPa, the soluble phosphorus content in the leachate was 0.22 mg / L, the soluble fluoride content was 7.1 mg / L, and the pH value was 6.9. Therefore, although the pH, soluble phosphorus, and soluble fluoride in the leachate of the phosphogypsum unfired bricks prepared according to the method of Comparative Example 4 were qualified, the low free water and bound water content in the phosphogypsum prevented it from fully utilizing the cementitious properties of cement and residual hemihydrate gypsum, resulting in lower strength of the unfired bricks.

[0041] Comparative Example 5 S1. Pretreatment of phosphogypsum: Phosphogypsum is passed through an 80-mesh sieve, and the sieve-filled material is microwave-dried at 150°C for 30 minutes to obtain phosphogypsum with a free water content of 13% and a crystal water content of 12%. The microwave power is 3.12kW and the microwave frequency is 2645Hz. Pretreatment of carbide slag: Pass through a 100-mesh sieve to obtain carbide slag with a mesh size of ≤100. By weight percentage, 72% of pretreated phosphogypsum, 4% of pretreated carbide slag, 15% of cement, and 9% of curing agent are mixed evenly to obtain a mixed dry material. S2. Pour the mixed dry material obtained in step S1 into a steel mold for high-pressure molding. The pressure is maintained at 30MPa and the holding time is 5min to obtain a brick blank. S3. Demold the brick blanks obtained in S2 and place them indoors at 15℃ for curing, keeping the indoor air humidity at no less than 50%. After curing for 10 days, you will get the finished product: harmless high-strength non-fired bricks.

[0042] Unconfined compressive strength tests were conducted on samples of the unfired bricks, and the control indicators of important characteristic pollutants in the leachate were tested according to the methods specified in GB 5086.1-1997. The test results were as follows: the compressive strength of the unfired bricks was 16.8 MPa, the soluble phosphorus content in the leachate was 0.31 mg / L, the soluble fluoride content was 7.9 mg / L, and the pH value was 7.0. It can be seen that the phosphogypsum unfired bricks prepared according to the method of Comparative Example 5 had higher soluble phosphorus and fluoride contents in the leachate and lower strength than those of Example 1, indicating that high pressure helps to solidify pollutants and improves the strength of the unfired bricks.

[0043] The experimental data for the examples and comparative examples are shown in Table 1.

[0044] Table 1

[0045] As shown in Table 1, the leachate from the phosphogypsum-based non-fired bricks prepared by the method of this invention has significantly lower soluble phosphorus and soluble fluoride content than the original phosphogypsum. The soluble phosphorus content is less than 0.4 mg / L, the soluble fluoride content is less than 8.0 mg / L, and the pH is 6-8. The leachate meets the leachate standard for open-air filling materials in GB32124-2024, "Specifications for the Treatment and Disposal of Phosphogypsum". Furthermore, the compressive strength of the non-fired bricks also meets the standard requirement of 25 MPa compressive strength in JC / T422-2007, "Non-Sintered Waste Tailings Bricks" (Grade MU25). In contrast, the leachate from phosphogypsum-based non-fired bricks treated only with carbide slag or curing agents cannot meet the leachate standard for open-air filling materials in GB32124-2024, and therefore cannot be used as harmless non-fired bricks. In addition, the content of free water and water of crystallization in phosphogypsum is crucial to the performance of non-fired bricks. As can be seen from the above data, when the free water content is 10-15% and the water of crystallization content is 12-17%, the obtained non-fired bricks can effectively fix soluble P and F, and at the same time, the non-fired bricks have good mechanical strength.

Claims

1. A high-strength, non-fired brick with high phosphogypsum content, characterized in that... By mass fraction, it includes the following components: 70%-85% pretreated phosphogypsum, 2%-8% carbide slag, 3%-18% cement and 6%-15% curing agent; The pretreated phosphogypsum has a free water content of 10-15% and a crystal water content of 12-17%.

2. The high-content, harmless, high-strength, non-fired brick with high phosphogypsum content according to claim 1, characterized in that, The pretreated phosphogypsum is obtained by microwave or heating dehydration of phosphogypsum at 150℃-180℃.

3. A method for preparing a high-strength, non-fired brick with high phosphogypsum content, characterized in that, Includes the following steps: S1. Pretreatment of phosphogypsum: Phosphogypsum is dried and dehydrated to obtain pretreated phosphogypsum with a free water content of 10-15% and a crystal water content of 12-17%. S2. By mass fraction, mix 70%-85% pretreated phosphogypsum, 2%-8% carbide slag, 3%-18% cement and 6%-15% curing agent evenly to obtain a mixed dry material; S3. Pour the mixed dry materials into the mold and perform high-pressure molding; S4. After high-pressure molding, demolding and curing are performed to obtain high-strength, harmless, non-fired bricks with high phosphogypsum content.

4. The method for preparing a high-content, harmless, high-strength, non-fired brick with high phosphogypsum content according to claim 3, characterized in that, The phosphogypsum has a particle size ≤ 80 mesh.

5. The method for preparing a high-content, harmless, high-strength, non-fired brick with high phosphogypsum content according to claim 3, characterized in that, The particle size of the carbide slag is ≤100 mesh.

6. The method for preparing a high-content, harmless, high-strength, non-fired brick with high phosphogypsum content according to claim 3, characterized in that, The pretreated phosphogypsum has a free water content of 10-15% and a crystal water content of 12-15%.

7. The method for preparing a high-content, harmless, high-strength, non-fired brick with high phosphogypsum content according to claim 3, characterized in that, The high-pressure molding conditions are as follows: pressure is maintained at 40-110 MPa, and pressure is held for 5-10 minutes.

8. The method for preparing a high-content, harmless, high-strength, non-fired brick with high phosphogypsum content according to claim 3, characterized in that, The maintenance conditions are: maintenance in an environment with a temperature of 10℃-20℃ and an air humidity of ≥50%.

9. The method for preparing a high-content, harmless, high-strength, non-fired brick with high phosphogypsum content according to claim 3, characterized in that, The cement is 42.5 silicate cement.

10. The method for preparing a high-content, harmless, high-strength, non-fired brick with phosphogypsum as described in claim 3, characterized in that, The unfired bricks have a soluble phosphorus content of <0.4 mg / L, a soluble fluorine content of <8.0 mg / L, a pH of 6-8, and a compressive strength of >22 MPa.

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