A phosphogypsum-based recessed brick and its preparation method and system

Abstract

This invention discloses a phosphogypsum-based sinking brick and its preparation method and system, relating to the field of phosphogypsum resource utilization technology. The preparation method includes: (1) adding phosphogypsum, water, and flotation agent into a flotation device with ultrasonic function, starting the flotation device to perform ultrasonic mineralization washing of the phosphogypsum, and then dewatering the washed phosphogypsum in a spiral dewatering machine to obtain impurity-removed phosphogypsum; (2) mixing raw materials including impurity-removed phosphogypsum, sand, stone, cement, mineral powder, rolled steel scale, and water, and conveying them to a high-frequency vibrating brick press for pressing and molding; (3) carbonizing and pressurizing the pressed sinking brick, and obtaining the finished sinking brick after the curing is completed. The sinking brick prepared by this invention has a compressive strength of up to 24.7 MPa and a softening coefficient of up to 0.95, making full use of phosphogypsum while ensuring that the sinking brick has good strength and water resistance.

Description

Technical Field

[0001] This invention relates to the field of phosphogypsum resource utilization technology, specifically to a phosphogypsum-based sinking brick and its preparation method. Background Technology

[0002] Phosphogypsum is a major solid waste generated during the wet-process phosphoric acid production process, and its main component is calcium sulfate dihydrate (CaSO4·2H2O). With the rapid development of the phosphate fertilizer industry, phosphogypsum emissions have increased year by year. Statistics show that approximately 4.5-5.5 tons of phosphogypsum are generated for every ton of phosphoric acid produced. However, due to the presence of small amounts of soluble phosphorus and fluorine impurities in phosphogypsum, its comprehensive utilization is limited. Currently, the global comprehensive utilization rate of phosphogypsum is less than 15%, and large quantities are disposed of through stockpiling, which not only occupies land resources but may also pollute soil, water, and air. Therefore, how to efficiently and environmentally utilize phosphogypsum has become an important issue in the fields of resource comprehensive utilization and environmental protection.

[0003] In the field of building materials, phosphogypsum, due to its main component being calcium sulfate, possesses certain cementing properties and can be used to prepare gypsum-based building materials such as gypsum boards and gypsum blocks. However, traditional gypsum-based building materials suffer from low strength and poor water resistance, limiting their application range. In recent years, researchers have attempted to use phosphogypsum to prepare building materials with higher strength and durability, such as recessed bricks, through modification and composite methods. Recessed bricks are a type of building material commonly used in riverbank protection and dam reinforcement projects, requiring high compressive strength, good water resistance, and frost resistance. Traditionally, recessed bricks are made from raw materials such as cement and sand, resulting in high costs and the consumption of large amounts of natural resources. Therefore, utilizing phosphogypsum to prepare recessed bricks not only enables the resource utilization of phosphogypsum but also reduces the production cost of recessed bricks, resulting in significant economic and environmental benefits.

[0004] Phosphogypsum, a major solid waste generated during the wet-process phosphoric acid production, has a complex composition, containing a large amount of organic matter and soluble phosphorus, fluorine, and other impurities. These impurities are distributed on the surface and between the crystal structures of phosphogypsum, causing a decrease in the strength of the hardened dihydrate gypsum body, weakening the crystal bonding of dihydrate gypsum, resulting in a decrease in the strength of gypsum cementitious materials and poor water resistance. The compressive strength of 28-day phosphogypsum-soaked bricks is only 12-17 MPa, and expansion cracks will appear in the bricks after soaking for 60 days, affecting the quality of phosphogypsum-soaked bricks.

[0005] Therefore, it is necessary to develop a phosphogypsum-based sinking brick and its preparation method. The resulting sinking brick has high strength and good water resistance, effectively solving the environmental problems caused by phosphogypsum stockpiling and promoting the resource utilization of phosphogypsum. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the aforementioned background technology and provide a phosphogypsum-based sinking brick and its preparation method. The resulting sinking brick has high strength and good water resistance, effectively solving the environmental problems caused by phosphogypsum stockpiling and promoting the resource utilization of phosphogypsum.

[0007] The technical solution of this invention is: a method for preparing recessed bricks based on phosphogypsum, comprising:

[0008] (1) Add phosphogypsum, water and flotation agent to a flotation device with ultrasonic function, start the flotation device to perform ultrasonic mineralization water washing of phosphogypsum, and then put the washed phosphogypsum into a spiral dewatering machine for dewatering to obtain impurity-removed phosphogypsum.

[0009] (2) The raw materials, including impurity-removed phosphogypsum, sand, stone, cement, mineral powder, rolled steel scale and water, are mixed and transported to a high-frequency vibrating brick press to be pressed into shape.

[0010] (3) The pressed and molded sinking bricks are carbonized and pressure cured. After curing, the finished sinking bricks are obtained.

[0011] Preferably, in step (1), the flotation agent includes terpineol, and the mass ratio of phosphogypsum to water and flotation agent is 1:2.3-2.7:0.02%-0.05%. Further, the mass ratio of phosphogypsum to water and flotation agent is 1:2.3-2.5:0.02%-0.03%.

[0012] Preferably, in step (1), the ultrasonic frequency during ultrasonic mineralization washing is 40-70 kHz, and the washing time is 20-25 min. Further, the ultrasonic frequency is 40-50 kHz.

[0013] Preferably, in step (1), the liquid washed by water in the flotation device and the liquid extracted by the spiral dewatering machine are both fed into the wastewater treatment tank for treatment. The pH is adjusted to 9-10 with hydrochloric acid and then circulated back to the flotation device for the next phosphogypsum washing.

[0014] Preferably, in step (2), the mass percentages of each raw material are as follows: sand 53.5-57.8%, stone 26.3-30.5%, phosphogypsum (removed impurities) 2.2-3.2%, cement 0.8-2.2%, mineral powder 10.2-12.2%, steel scale 0.5-0.8%, and water 1.2-1.5%. The phosphogypsum (removed impurities) is calculated based on the dry weight after dehydration, and the sum of the mass percentages of the above raw materials is 100%.

[0015] Furthermore, in step (2), the mass percentages of each raw material are as follows: sand 53.9-55.3%, stone 28.0-29.1%, impurity-removed phosphogypsum 2.2-2.7%, cement 0.8-1.0%, mineral powder 10.2-11.2%, rolled steel scale 0.6-0.8%, and water 1.4-1.5%. The impurity-removed phosphogypsum is calculated based on the dry weight after dehydration, and the sum of the mass percentages of the above raw materials is 100%.

[0016] Preferably, in step (2), the conditions for pressing include: vibration frequency of 50-60Hz, excitation force of 70-80kN, and molding pressure of 20-25MPa.

[0017] Preferably, in step (3), the conditions for carbonization and pressure curing include: curing temperature of 50-60℃, carbon dioxide concentration of 50-60%, curing pressure of 0.8-1.0MPa, ambient humidity of 50-60%, and curing time of 48-72h. The carbon dioxide concentration in this invention refers to volume percentage.

[0018] This invention also provides recessed bricks obtained by any of the above-mentioned methods for preparing phosphogypsum-based recessed bricks, comprising the following raw materials by mass percentage:

[0019]

[0020] The sum of the mass percentages of the above components is 100%. The impurity-removed phosphogypsum is obtained by adding phosphogypsum to a flotation device with ultrasonic function for ultrasonic mineralization and washing, followed by dehydration. The weight of the impurity-removed phosphogypsum is based on the dry weight after dehydration.

[0021] Preferred ingredients include the following raw materials by mass percentage: 53.9-55.27% sand, 28.0-29.1% stone, 2.62-3.0% purified phosphogypsum, 0.85-0.9% cement, 10.2-11.19% mineral powder, 0.6-0.77% rolled steel scale, and 1.40-1.48% water.

[0022] This invention also provides a preparation system for any of the above-mentioned methods for preparing phosphogypsum-based recessed bricks, including an ultrasonic mineralization washing component, a pressing and molding component, and a curing component.

[0023] The ultrasonic mineralization washing assembly includes a flotation device with ultrasonic function, a spiral dewatering machine, and a wastewater treatment tank. The outlet of the flotation device is connected to the inlet of the spiral dewatering machine. The outlet of the flotation device and the outlet of the spiral dewatering machine are both connected to the inlet of the wastewater treatment tank. The outlet of the wastewater treatment tank leads to the inlet of the flotation device.

[0024] The pressing and molding assembly includes a silo for storing various solid materials such as impurity-removed phosphogypsum, sand, stone, cement, mineral powder, and rolled steel scale separately, a weighing hopper connected to the silo, a mixing tank, a high-frequency vibrating brick press, and a brick collecting machine. The outlet of the weighing hopper is connected to the inlet of the mixing tank, the outlet of the mixing tank is connected to the inlet of the high-frequency vibrating brick press, and the outlet of the high-frequency vibrating brick press is connected to the inlet of the brick collecting machine. The mixing tank is also connected to a water inlet pipe for adding raw material water.

[0025] The maintenance components include a carbonization pressure maintenance device.

[0026] Preferably, the flotation device with ultrasonic function includes an ultrasonic generator and a flotation machine. The ultrasonic generator is equipped with a transmission probe connected to the flotation machine. The outlet of the flotation machine and the outlet of the spiral dewatering machine are both connected to the inlet of the wastewater treatment tank. The outlet of the wastewater treatment tank leads to the inlet of the flotation machine.

[0027] The beneficial effects of this invention are:

[0028] (1) To fully develop and utilize phosphogypsum, a solid waste, a new resource utilization approach for phosphogypsum was proposed, which was prepared into sinking bricks that can be used in waterway improvement projects, reducing the use of materials such as cement and having significant economic value.

[0029] (2) An ultrasonic mineralization water washing process for phosphogypsum was proposed, which effectively removes impurities such as organic matter, soluble phosphorus, and soluble fluorine from phosphogypsum, solves the problem of phosphogypsum products easily absorbing water and swelling, which leads to product damage, improves material strength and water resistance, and ensures the quality of phosphogypsum products.

[0030] (3) This invention uses ultrasonic flotation to wash phosphogypsum. Terpineol, as a flotation agent, can selectively adsorb impurity particles onto their surfaces. Combined with the ultrasonic cavitation effect, solid-liquid separation is enhanced. The ultrasonic frequency is 40-70 kHz, which generates a strong cavitation effect, effectively breaking down impurities encapsulated in the phosphogypsum and shortening the washing time to the optimal range. At the same time, excessive ultrasonication is avoided, which would lead to excessive refinement of phosphogypsum particles, maintaining the stability of the raw material gradation and ensuring the quality of subsequent molding. Precise control of the phosphogypsum-water-flotation agent ratio reduces water consumption while ensuring the impurity removal effect, thus reducing the energy consumption for subsequent dehydration.

[0031] (4) A material ratio for the settling bricks was proposed, which fully utilizes the resources of two solid wastes: phosphogypsum and rolled steel scale. Sand and stone form a skeleton system, which, combined with mineral powder and cement, forms a multi-graded dense structure, improving compressive strength. Rolled steel scale contains trivalent iron, which can combine with the soluble phosphorus remaining in phosphogypsum to produce insoluble products, improving the quality of the subsequent settling bricks. Impurity-removed phosphogypsum (2.2-3.2%) replaces part of the cement, reducing production costs.

[0032] (5) During the pressing process, the 50-60Hz vibration frequency and the 70-80kN excitation force work together to achieve uniform material distribution and eliminate molding defects; the 20-25MPa molding pressure ensures the initial density of the brick body, providing a good microstructure foundation for subsequent carbonization curing.

[0033] (6) A carbonization and pressure curing method for sinking bricks was proposed. The carbon mineralization process is realized by sinking bricks, which can both dispose of a large amount of solid waste and seal carbon dioxide, thus having certain carbon reduction benefits.

[0034] (7) In the preparation system of the present invention, the effluent from the flotation device and the effluent from the spiral dewatering machine are treated in the wastewater treatment pond and can be recycled, thereby realizing the resource utilization of wastewater, reducing production costs and reducing environmental pollution.

[0035] (8) The preparation system of the present invention can be fully automated (stirring-pressing-curing), which can improve production efficiency and reduce labor costs.

[0036] (9) The compressive strength of the recessed brick prepared by the present invention can reach up to 24.7 MPa and the softening coefficient can reach up to 0.95. It makes full use of phosphogypsum while ensuring that the recessed brick has good strength and water resistance. Attached Figure Description

[0037] Figure 1 This is a flow chart of a process for preparing recessed bricks based on phosphogypsum according to the present invention.

[0038] Figure 2 This is a schematic diagram of the system structure for preparing the present invention.

[0039] Among them: 1-flotation machine 2-ultrasonic generator 3-spiral dewatering machine 4-wastewater treatment pond 5-silo 6-weighing hopper 7-mixing tank 8-high frequency vibrating brick press 9-brick collecting machine 10-water inlet pipe 11-carbonization pressure curing device. Detailed Implementation

[0040] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0041] The present invention will be described in detail below through embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0042] This invention provides a process for preparing sinking bricks based on phosphogypsum solid waste. The process effectively treats the phosphogypsum to reduce the content of soluble phosphorus, thereby preparing sinking bricks with high strength and good water resistance.

[0043] A method for preparing settling bricks based on phosphogypsum solid waste mainly includes the following steps: (1) ultrasonic mineralization and washing; (2) high-frequency vibration pressing of settling bricks; and (3) carbonization and pressure curing of settling bricks. The specific operation steps of each process are as follows.

[0044] Step 1: Ultrasonic mineralization water washing

[0045] (1) Add phosphogypsum, water, and flotation agent to a flotation device with ultrasonic function at a mass ratio of 1:2.3-2.7:0.02%-0.05%. The flotation agent is terpineol. Start the flotation device to perform ultrasonic mineralization washing of phosphogypsum. After washing, an upper layer of floating matter, a lower layer of phosphogypsum, and a middle layer of washing liquid are formed in the flotation device. The upper layer of floating matter is transported off-site for disposal. The lower layer of phosphogypsum is put into a spiral dewatering machine for dehydration and drying to obtain impurity-free phosphogypsum. The liquid extracted by the spiral dewatering machine is sent to a wastewater treatment pond for treatment. The pH is adjusted to 9-10 with hydrochloric acid and recycled back to the flotation device to replace the addition of water for the next phosphogypsum washing.

[0046] Step 2: High-frequency vibration pressing of the bricks

[0047] The moisture content of the purified phosphogypsum was measured. Raw materials including purified phosphogypsum, sand, stone, cement, mineral powder, rolled steel scale, and water were mixed. The mass percentages of each raw material were as follows: sand 53.5-57.8%, stone 26.3-30.5%, purified phosphogypsum 2.2-3.2%, cement 0.8-2.2%, mineral powder 10.2-12.2%, rolled steel scale 0.5-0.8%, and water 1.2-1.5%. The purified phosphogypsum was calculated based on its dry weight after water removal. The sum of the mass percentages of the above raw materials was 100%. After the materials were completely mixed, the mixture was conveyed to a high-frequency vibrating brick press for molding. The vibration frequency was 50-60Hz, the excitation force was 70-80kN, and the molding pressure was 20-25MPa. Each brick weighed 21-23kg. After molding, the bricks were collected using a brick collecting machine.

[0048] Step 3: Carbonization and pressure curing of recessed bricks

[0049] After the recessed bricks are pressed into shape, they need to undergo carbonization and pressure curing. The main equipment used in this step is a carbonization and pressure curing device. The recessed bricks are placed in the carbonization and pressure curing device for curing. The curing temperature in the carbonization and pressure curing device is 50-60℃, the carbon dioxide concentration (volume percentage) is 50-60%, the curing pressure is 0.8-1.0MPa, the ambient humidity is 50-60%, and the curing time is 48-72 hours. After curing, the finished recessed bricks are obtained.

[0050] like Figure 2As shown, the present invention also provides a settling brick preparation system based on phosphogypsum solid waste, comprising an ultrasonic mineralization washing component, a pressing and molding component, and a curing component. The structure of each component is as follows.

[0051] The ultrasonic mineralization washing assembly includes an ultrasonic flotation device, a spiral dewatering machine 3, and a wastewater treatment tank 4. The ultrasonic flotation device includes an ultrasonic generator 2 and a flotation machine 1. The ultrasonic generator 2 is equipped with a transmission probe connected to the flotation machine for transmitting sound waves. The outlet of the flotation machine 1 and the outlet of the spiral dewatering machine 3 are both connected to the inlet of the wastewater treatment tank 4, and the outlet of the wastewater treatment tank 4 leads to the inlet of the flotation machine 1. Figure 2 In the ultrasonic mineralization water washing assembly, the dashed line indicates the direction of liquid flow.

[0052] The pressing and molding assembly includes a silo 5 for separately storing various solid materials such as impurity-removed phosphogypsum, sand, stone, cement, mineral powder, and rolled steel scale; a weighing hopper 6 connected to the silo 5; a mixing tank 7; a high-frequency vibrating brick press 8; and a brick collecting machine 9. The outlet of the weighing hopper 6 is connected to the inlet of the mixing tank 7, the outlet of the mixing tank 7 is connected to the inlet of the high-frequency vibrating brick press 8, and the outlet of the high-frequency vibrating brick press 8 is connected to the inlet of the brick collecting machine 9. A water inlet pipe 10 is also connected to the mixing tank 7 for adding raw material water. A moisture content detection device is installed between the outlet of the spiral dewatering machine 3 and the silo 5 to measure the moisture content of the impurity-removed phosphogypsum.

[0053] The curing components include a carbonization pressure curing device 11, which is connected to the outlet of the brick collecting machine 9.

[0054] In some preferred embodiments, a control system can be configured to be connected to the silo 5, weighing hopper 6, mixing tank 7, high-frequency vibrating brick press 8, and brick collecting machine 9 respectively. This control system controls the opening and closing of each discharge port of the silo 5, reads the weight of the material in the weighing hopper 6 to control the amount of each material added, and controls the start-up of the mixing tank 7, high-frequency vibrating brick press 8, and brick collecting machine 9 to achieve the pressing and forming of the bricks. The control system is also connected to a moisture content detection device, and the dosage of phosphogypsum and tap water is set in the control system based on the measurement results (the control system is connected to the water inlet pipe 10 to control the amount of water added).

[0055] The present invention will be further described in detail below with reference to various embodiments.

[0056] Unless otherwise specified, the methods described in the following embodiments are conventional methods; the materials described are commercially available unless otherwise specified. In the following embodiments, the phosphogypsum used is waste phosphogypsum from the phosphogypsum industrial park in Dawu County, Xiaogan City, Hubei Province. The chemical composition of the phosphogypsum is shown in Table 1. The cement used is 42.5 grade ordinary Portland cement, and the steel scale is waste iron oxide scale produced by a hot rolling mill in Wuhan.

[0057] Table 1. Chemical composition (mass fraction) of phosphogypsum

[0058]

[0059] Example 1

[0060] like Figure 1 As shown, this embodiment provides a method for preparing sedimentation bricks based on phosphogypsum solid waste, including the following steps:

[0061] Step 1: Ultrasonic mineralization water washing

[0062] Phosphogypsum, tap water, and flotation agent (terpineol) are added to flotation machine 1 at a mass ratio of 1:2.3:0.025%. Flotation machine 1 is turned on for stirring and washing. At the same time, ultrasonic generator 2 is started, and sound waves are transmitted to the phosphogypsum mixture through a transmission probe. The sound wave frequency is 45KHz, and the washing time is 20min. The characteristics of ultrasound are used to efficiently separate organic matter, soluble phosphorus, and soluble fluoride in phosphogypsum. After flotation washing, the upper floating matter, lower phosphogypsum, and middle washing liquid are obtained. The upper floating matter is transported for disposal. The lower phosphogypsum is sent to spiral dewatering machine 3 for dehydration and drying to obtain impurity-removed phosphogypsum. The middle washing liquid and the water dewatered by spiral dewatering machine 3 are sent to wastewater treatment tank 4 for treatment. Hydrochloric acid solution is added to adjust the pH to 9.5. The treated liquid is recycled back to flotation machine 1 to replace the addition of tap water for the next batch of phosphogypsum washing.

[0063] Step 2: High-frequency vibration pressing of the bricks

[0064] The moisture content of the dewatered phosphogypsum after dewatering by the spiral dewatering machine 3 is measured using a moisture content detection device. Based on the measurement results, the dosage of the dewatered phosphogypsum and tap water is set in the control system. The control system controls the sand, stone, dewatered phosphogypsum, cement, mineral powder and rolled steel scale to be discharged from the silo 5 in sequence and weighed in the weighing hopper 6. After weighing, they enter the mixing tank 7 for mixing. After mixing for 2 minutes, tap water is added through the water inlet pipe 10 and mixing continues for 1 minute.

[0065] The mass percentages of various materials added are as follows: sand 55.27%; stone 28.07%; phosphogypsum (with impurities removed) 2.62%; cement 0.85%; mineral powder 11.19%; rolled steel scale 0.60%; and water 1.4%, where the weight of the phosphogypsum (with impurities removed) is the weight after deducting the weight of water. After the materials are completely mixed, they are conveyed to a high-frequency vibrating brick press 8 for pressing and molding. The vibration frequency is 55Hz, the excitation force is 75kN, and the molding pressure is 23MPa. After pressing and molding, bricks are collected by a brick collecting machine 9.

[0066] Step 3: Carbonization and pressure curing of recessed bricks

[0067] After the recessed bricks are pressed into shape, they need to undergo carbonization and pressure curing. The main equipment used in this step is the carbonization and pressure curing device 11. The recessed bricks are placed in the carbonization and pressure curing device 11 for curing. The curing temperature in the carbonization and pressure curing device is 60℃, the carbon dioxide concentration is 58%, the curing pressure is 0.9MPa, the ambient humidity is 53%, and the curing time is 72 hours. After curing, the finished recessed bricks are obtained.

[0068] Example 2

[0069] like Figure 1 As shown, this embodiment provides a method for preparing sedimentation bricks based on phosphogypsum solid waste, including the following steps:

[0070] Step 1: Ultrasonic mineralization water washing

[0071] Phosphogypsum, tap water, and flotation agent (terpineol) are added to flotation machine 1 at a mass ratio of 1:2.3:0.025%. Flotation machine 1 is turned on for stirring and washing. At the same time, ultrasonic generator 2 is started, and sound waves are transmitted to the phosphogypsum mixture through a transmission probe. The sound wave frequency is 45KHz, and the washing time is 20min. The characteristics of ultrasound are used to efficiently separate organic matter, soluble phosphorus, and soluble fluoride in phosphogypsum. After flotation washing, the upper floating matter, lower phosphogypsum, and middle washing liquid are obtained. The upper floating matter is transported for disposal. The lower phosphogypsum is sent to spiral dewatering machine 3 for dehydration and drying to obtain impurity-removed phosphogypsum. The middle washing liquid and the water dewatered by spiral dewatering machine 3 are sent to wastewater treatment tank 4 for treatment. Hydrochloric acid solution is added to adjust the pH to 9.5. The treated liquid is recycled back to flotation machine 1 to replace the addition of tap water for the next batch of phosphogypsum washing.

[0072] Step 2: High-frequency vibration pressing of the bricks

[0073] The moisture content of the dewatered phosphogypsum after dewatering by the spiral dewatering machine 3 is measured using a moisture content detection device. Based on the measurement results, the dosage of the dewatered phosphogypsum and tap water is set in the control system. The control system controls the sand, stone, dewatered phosphogypsum, cement, mineral powder and rolled steel scale to be discharged from the silo 5 in sequence and weighed in the weighing hopper 6. After weighing, they enter the mixing tank 7 for mixing. After mixing for 2 minutes, tap water is added through the water inlet pipe 10 and mixing continues for 1 minute.

[0074] The mass percentages of various materials added are as follows: sand 53.98%; stone 29.08%; phosphogypsum (with impurities removed) 2.20%; cement 2.20%; mineral powder 10.29%; rolled steel scale 0.77%; and water 1.48%. The weight of the phosphogypsum (with impurities removed) is the weight after deducting the water content. After the materials are completely mixed, they are conveyed to a high-frequency vibrating brick press 8 for pressing and molding. The vibration frequency is 55Hz, the excitation force is 75kN, and the molding pressure is 23MPa. After pressing, bricks are collected using a brick collecting machine 9.

[0075] Step 3: Carbonization and pressure curing of recessed bricks

[0076] After the recessed bricks are pressed into shape, they need to undergo carbonization and pressure curing. The main equipment used in this step is the carbonization and pressure curing device 11. The recessed bricks are placed in the carbonization and pressure curing device 11 for curing. The curing temperature in the carbonization and pressure curing device is 60℃, the carbon dioxide concentration is 58%, the curing pressure is 0.9MPa, the ambient humidity is 53%, and the curing time is 72 hours. After curing, the finished recessed bricks are obtained.

[0077] Example 3

[0078] like Figure 1 As shown, this embodiment provides a method for preparing sedimentation bricks based on phosphogypsum solid waste, including the following steps:

[0079] Step 1: Ultrasonic mineralization water washing

[0080] Phosphogypsum, tap water, and flotation agent (terpineol) are added to flotation machine 1 at a mass ratio of 1:2.3:0.05%. Flotation machine 1 is turned on for stirring and washing. At the same time, ultrasonic generator 2 is started, and sound waves are transmitted to the phosphogypsum mixture through a transmission probe. The sound wave frequency is 70KHz, and the washing time is 20min. The characteristics of ultrasound are used to efficiently separate organic matter, soluble phosphorus, and soluble fluoride in phosphogypsum. After flotation washing, the upper floating matter, lower phosphogypsum, and middle washing liquid are obtained. The upper floating matter is transported for disposal. The lower phosphogypsum is sent to spiral dewatering machine 3 for dehydration and drying to obtain impurity-removed phosphogypsum. The middle washing liquid and the water dewatered by spiral dewatering machine 3 are sent to wastewater treatment tank 4 for treatment. Hydrochloric acid solution is added to adjust the pH to 9.5. The treated liquid is recycled back to flotation machine 1 to replace the addition of tap water for the next batch of phosphogypsum washing.

[0081] Step 2: High-frequency vibration pressing of the bricks

[0082] The moisture content of the dewatered phosphogypsum after dewatering by the spiral dewatering machine 3 is measured using a moisture content detection device. Based on the measurement results, the dosage of phosphogypsum and tap water is set in the control system. The control system controls the sand, stone, dewatered phosphogypsum, cement, mineral powder and rolled steel scale to be discharged from the silo 5 in sequence and weighed in the weighing hopper 6. After weighing, they enter the mixing tank 7 for mixing. After mixing for 2 minutes, tap water is added through the water inlet pipe 10 and mixing continues for 1 minute.

[0083] The mass percentages of various materials added are as follows: sand 55.27%; stone 28.07%; phosphogypsum (with impurities removed) 2.62%; cement 0.85%; mineral powder 11.19%; rolled steel scale 0.60%; and water 1.4%, where the weight of phosphogypsum is the weight after deducting the weight of water. After the materials are completely mixed, they are conveyed to a high-frequency vibrating brick press 8 for pressing and molding. The vibration frequency is 55Hz, the excitation force is 75kN, and the molding pressure is 23MPa. After pressing and molding, bricks are collected by a brick collecting machine 9.

[0084] Step 3: Carbonization and pressure curing of recessed bricks

[0085] After the recessed bricks are pressed into shape, they need to undergo carbonization and pressure curing. The main equipment used in this step is the carbonization and pressure curing device 11. The recessed bricks are placed in the carbonization and pressure curing device 11 for curing. The curing temperature in the carbonization and pressure curing device is 60℃, the carbon dioxide concentration is 58%, the curing pressure is 0.9MPa, the ambient humidity is 53%, and the curing time is 72 hours. After curing, the finished recessed bricks are obtained.

[0086] Comparative Example 1

[0087] This comparative example provides a method for preparing comparative recessed bricks, including the following steps:

[0088] Step 1: Ultrasonic mineralization water washing

[0089] Phosphogypsum, tap water, and flotation agent (terpineol) are added to flotation machine 1 at a mass ratio of 1:2.3:0.025%. Flotation machine 1 is turned on for stirring and washing. At the same time, ultrasonic generator 2 is started, and sound waves are transmitted to the phosphogypsum mixture through a transmission probe. The sound wave frequency is 45KHz, and the washing time is 20min. The characteristics of ultrasound are used to efficiently separate organic matter, soluble phosphorus, and soluble fluoride in phosphogypsum. After flotation washing, the upper floating matter, lower phosphogypsum, and middle washing liquid are obtained. The upper floating matter is transported for disposal. The lower phosphogypsum is sent to spiral dewatering machine 3 for dehydration and drying to obtain impurity-removed phosphogypsum. The middle washing liquid and the water dewatered by spiral dewatering machine 3 are sent to wastewater treatment tank 4 for treatment. Hydrochloric acid solution is added to adjust the pH to 9.5. The treated liquid is recycled back to flotation machine 1 to replace the addition of tap water for the next batch of phosphogypsum washing.

[0090] Step 2: High-frequency vibration pressing of the bricks

[0091] The moisture content of the dewatered phosphogypsum after dewatering by the spiral dewatering machine is measured using a moisture content detection device. Based on the measurement results, the dosage of phosphogypsum and tap water is set in the control system. The control system controls the sand, stone, dewatered phosphogypsum, cement, mineral powder and rolled steel scale to be discharged from the silo 5 in sequence and weighed in the weighing hopper 6. After weighing, they enter the mixing tank 7 for mixing. The mixing is carried out for 2 minutes. After the materials are evenly mixed, tap water is added through the water inlet pipe 10 and the mixing continues for 1 minute.

[0092] The mass percentages of various materials added are as follows: sand 54.18%; stone 29.19%; phosphogypsum (with impurities removed) 5.30%; cement 0.88%; mineral powder 7.66%; rolled steel scale 1.30%; and water 1.49%. The weight of the phosphogypsum (with impurities removed) is the weight after deducting the water content. After the materials are fully mixed, they are conveyed to a high-frequency vibrating brick press 8 for pressing and molding. The vibration frequency is 55Hz, the excitation force is 75kN, and the molding pressure is 23MPa. After pressing, bricks are collected using a brick collecting machine 9.

[0093] Step 3: Carbonization and pressure curing of recessed bricks

[0094] After the recessed bricks are pressed into shape, they need to undergo carbonization and pressure curing. The main equipment used in this step is the carbonization and pressure curing device 11. The recessed bricks are placed in the carbonization and pressure curing device 11 for curing. The curing temperature in the carbonization and pressure curing device is 60℃, the carbon dioxide concentration is 58%, the curing pressure is 0.9MPa, the ambient humidity is 53%, and the curing time is 72 hours. After curing, the finished recessed bricks are obtained.

[0095] Comparative Example 2

[0096] This comparative example provides a method for preparing comparative recessed bricks, including the following steps:

[0097] Step 1: Ultrasonic mineralization water washing

[0098] Phosphogypsum, tap water, and flotation agent (terpineol) are added to flotation machine 1 at a mass ratio of 1:2.3:0.01%. Flotation machine 1 is turned on for stirring and washing. At the same time, ultrasonic generator 2 is started, and sound waves are transmitted to the phosphogypsum mixture through a transmission probe. The sound wave frequency is 20KHz, and the washing time is 20min. The characteristics of ultrasound are used to efficiently separate organic matter, soluble phosphorus, and soluble fluoride in phosphogypsum. After flotation washing, the upper floating matter, lower phosphogypsum, and middle washing liquid are obtained. The upper floating matter is transported for disposal. The lower phosphogypsum is sent to spiral dewatering machine 3 for dehydration and drying to obtain impurity-removed phosphogypsum. The middle washing liquid and the water dewatered by spiral dewatering machine 3 are sent to wastewater treatment tank 4 for treatment. Hydrochloric acid solution is added to adjust the pH to 9.5. The treated liquid is recycled back to flotation machine 1 to replace the addition of tap water for the next batch of phosphogypsum washing.

[0099] Step 2: High-frequency vibration pressing of the bricks

[0100] The moisture content of the dewatered phosphogypsum after dewatering by the spiral dewatering machine is measured using a moisture content detection device. Based on the measurement results, the dosage of the dewatered phosphogypsum and tap water is set in the control system. The control system controls the sand, stone, dewatered phosphogypsum, cement, mineral powder and rolled steel scale to be discharged from the silo 5 in sequence and weighed in the weighing hopper 6. After weighing, they enter the mixing tank 7 for mixing. After mixing for 2 minutes, tap water is added through the water inlet pipe 10 and mixing continues for 1 minute.

[0101] The mass percentages of various materials added are as follows: sand 55.27%; stone 28.07%; phosphogypsum (with impurities removed) 2.62%; cement 0.85%; mineral powder 11.19%; rolled steel scale 0.60%; and water 1.4%, where the weight of the phosphogypsum (with impurities removed) is the weight after deducting the weight of water. After the materials are completely mixed, they are conveyed to a high-frequency vibrating brick press 8 for pressing and molding. The vibration frequency is 55Hz, the excitation force is 75kN, and the molding pressure is 23MPa. After pressing and molding, bricks are collected by a brick collecting machine 9.

[0102] Step 3: Carbonization and pressure curing of recessed bricks

[0103] After the recessed bricks are pressed into shape, they need to undergo carbonization and pressure curing. The main equipment used in this step is the carbonization and pressure curing device 11. The recessed bricks are placed in the carbonization and pressure curing device 11 for curing. The curing temperature in the carbonization and pressure curing device is 60℃, the carbon dioxide concentration is 58%, the curing pressure is 0.9MPa, the ambient humidity is 53%, and the curing time is 72 hours. After curing, the finished recessed bricks are obtained.

[0104] Comparative Example 3

[0105] This comparative example provides a method for preparing comparative recessed bricks, including the following steps:

[0106] Step 1: Ultrasonic mineralization water washing

[0107] Phosphogypsum, tap water, and flotation agent (terpineol) are added to flotation machine 1 at a mass ratio of 1:2.3:0.025%. Flotation machine 1 is turned on for stirring and washing. At the same time, ultrasonic generator 2 is started, and sound waves are transmitted to the phosphogypsum mixture through a transmission probe. The sound wave frequency is 45KHz, and the washing time is 20min. The characteristics of ultrasound are used to efficiently separate organic matter, soluble phosphorus, and soluble fluoride in phosphogypsum. After flotation washing, the upper floating matter, lower phosphogypsum, and middle washing liquid are obtained. The upper floating matter is transported for disposal. The lower phosphogypsum is sent to spiral dewatering machine 3 for dehydration and drying to obtain impurity-removed phosphogypsum. The middle washing liquid and the water dewatered by spiral dewatering machine 3 are sent to wastewater treatment tank 4 for treatment. Hydrochloric acid solution is added to adjust the pH to 9.5. The treated liquid is recycled back to flotation machine 1 to replace the addition of tap water for the next batch of phosphogypsum washing.

[0108] Step 2: High-frequency vibration pressing of the bricks

[0109] The moisture content of the dewatered phosphogypsum after dewatering by the spiral dewatering machine is measured using a moisture content detection device. Based on the measurement results, the dosage of phosphogypsum and tap water is set in the control system. The control system controls the sand, stone, dewatered phosphogypsum, cement, mineral powder and rolled steel scale to be discharged from the silo 5 in sequence and weighed in the weighing hopper 6. After weighing, they enter the mixing tank 7 for mixing. The mixing is carried out for 2 minutes. After the materials are evenly mixed, tap water is added through the water inlet pipe 10 and the mixing continues for 1 minute.

[0110] The mass percentages of various materials added are as follows: sand 55.27%; stone 28.07%; phosphogypsum (with impurities removed) 2.62%; cement 0.85%; mineral powder 11.19%; rolled steel scale 0.60%; and water 1.4%. The weight of the phosphogypsum (with impurities removed) is the weight after deducting the water content. After the materials are fully mixed, they are conveyed to a high-frequency vibrating brick press 8 for pressing and molding. The vibration frequency is 55Hz, the excitation force is 75kN, and the molding pressure is 23MPa. After pressing, bricks are collected using a brick collecting machine 9.

[0111] Step 3: Carbonization and pressure curing of recessed bricks

[0112] After the recessed bricks are pressed into shape, they need to undergo carbonization and pressure curing. The main equipment used in this step is the carbonization and pressure curing device 11. The recessed bricks are placed in the carbonization and pressure curing device 11 for curing. The curing temperature in the carbonization and pressure curing device is 30℃, the carbon dioxide concentration is 30%, the curing pressure is 0.5MPa, the ambient humidity is 50%, and the curing time is 72 hours. After curing, the finished recessed bricks are obtained.

[0113] Comparative Example 4

[0114] This comparative example provides a method for preparing comparative recessed bricks, including the following steps:

[0115] Step 1: Ultrasonic mineralization water washing

[0116] Phosphogypsum, tap water, and flotation agent (terpineol) are added to flotation machine 1 at a mass ratio of 1:2.3:0.025%. Flotation machine 1 is turned on for stirring and washing. At the same time, ultrasonic generator 2 is started, and sound waves are transmitted to the phosphogypsum mixture through a transmission probe. The sound wave frequency is 45KHz, and the washing time is 20min. The characteristics of ultrasound are used to efficiently separate organic matter, soluble phosphorus, and soluble fluoride in phosphogypsum. After flotation washing, the upper floating matter, lower phosphogypsum, and middle washing liquid are obtained. The upper floating matter is transported for disposal. The lower phosphogypsum is sent to spiral dewatering machine 3 for dehydration and drying to obtain impurity-removed phosphogypsum. The middle washing liquid and the water dewatered by spiral dewatering machine 3 are sent to wastewater treatment tank 4 for treatment. Hydrochloric acid solution is added to adjust the pH to 9.5. The treated liquid is recycled back to flotation machine 1 to replace the addition of tap water for the next batch of phosphogypsum washing.

[0117] Step 2: High-frequency vibration pressing of the bricks

[0118] The moisture content of the dewatered phosphogypsum after dewatering by the spiral dewatering machine is measured using a moisture content detection device. Based on the measurement results, the dosage of phosphogypsum and tap water is set in the control system. The control system controls the sand, stone, dewatered phosphogypsum, cement, mineral powder and rolled steel scale to be discharged from the silo 5 in sequence and weighed in the weighing hopper 6. After weighing, they enter the mixing tank 7 for mixing. The mixing is carried out for 2 minutes. After the materials are evenly mixed, tap water is added through the water inlet pipe 10 and the mixing continues for 1 minute.

[0119] The mass percentages of various materials added are as follows: sand 55.27%; stone 28.07%; phosphogypsum (with impurities removed) 2.62%; cement 0.85%; mineral powder 11.19%; rolled steel scale 0.60%; and water 1.4%, where the weight of the phosphogypsum (with impurities removed) is the weight after deducting the weight of water. After the materials are completely mixed, they are conveyed to a high-frequency vibrating brick press 8 for pressing and molding. The vibration frequency is 55Hz, the excitation force is 75kN, and the molding pressure is 23MPa. After pressing and molding, bricks are collected by a brick collecting machine 9.

[0120] Step 3: Carbonization and pressure curing of recessed bricks

[0121] After the recessed bricks are pressed into shape, they need to undergo carbonization and pressure curing. The main equipment used in this step is the carbonization and pressure curing device 11. The recessed bricks are placed in the carbonization and pressure curing device 11 for curing. The curing temperature in the carbonization and pressure curing device is 40℃, the carbon dioxide concentration is 40%, the curing pressure is 0.7MPa, the ambient humidity is 50%, and the curing time is 72 hours. After curing, the finished recessed bricks are obtained.

[0122] Performance testing

[0123] Samples were taken from the recessed bricks produced in the above embodiments and comparative examples, and their compressive strength and softening coefficient were determined using a compressive strength testing machine. The test results of the embodiments and comparative examples are shown in Table 2.

[0124] Table 2. Test results for the examples and comparative examples.

[0125]

[0126] As shown in Table 2 above, the compressive strength of the recessed bricks obtained in the embodiments of the present invention is above 24 MPa, and the softening coefficient is as high as 0.95. The only difference between Comparative Example 1 and Example 1 is the amount of raw materials used in the formula in step 2. According to Example 1 and Comparative Example 1, the amount of phosphogypsum used in Comparative Example 1 is too large, the amount of mineral powder is too small, and the amount of rolled steel scale is too large, which leads to the compressive strength of the recessed bricks not meeting the requirements.

[0127] The only difference between Example 1 and Comparative Example 2 is the amount of terpineol used and the ultrasonic frequency. As can be seen from Table 2, the softening coefficient of the submerged brick in Comparative Example 2 is significantly lower. This is because the ultrasonic mineralization water washing did not effectively remove impurities such as organic matter, soluble phosphorus, and soluble fluorine from the phosphogypsum, resulting in poor water resistance of the submerged brick.

[0128] Based on the comparison of Example 1, Comparative Example 3, and Comparative Example 4, it can be seen that the only difference between the three examples is the curing conditions in step 3. The compressive strength of the recessed bricks prepared in Comparative Example 3 and Comparative Example 4 does not meet the requirements. Therefore, the optimal conditions in step 3 are a curing temperature of 50-60℃, a carbon dioxide concentration of 50-60%, a curing pressure of 0.8-1.0MPa, an ambient humidity of 50-60%, and a curing time of 48-72h.

Claims

1. A method for preparing recessed bricks based on phosphogypsum, characterized in that, include: (1) Add phosphogypsum, water, and flotation agent to a flotation device with ultrasonic function. The flotation agent is terpineol. The mass ratio of phosphogypsum to water and flotation agent is 1:(2.3-2.7):(0.02%-0.05%). Start the flotation device to perform ultrasonic mineralization water washing on the phosphogypsum. The ultrasonic frequency during ultrasonic mineralization water washing is 40-70KHz, and the water washing time is 20-25min. After washing, the phosphogypsum is then put into a spiral dewatering machine for dewatering to obtain impurity-removed phosphogypsum. (2) Mix the raw materials including impurity-removed phosphogypsum, sand, stone, cement, mineral powder, rolled steel scale and water. The mass percentage of each raw material is as follows: sand 53.5-57.8%, stone 26.3-30.5%, impurity-removed phosphogypsum 2.2-3.2%, cement 0.8-2.2%, mineral powder 10.2-12.2%, rolled steel scale 0.5-0.8%, water 1.2-1.5%. The impurity-removed phosphogypsum is based on the dry weight after water removal. The sum of the mass percentages of the above raw materials is 100%. The mixture is then conveyed to a high-frequency vibrating brick press and pressed into shape. (3) The pressed and molded recessed bricks are subjected to carbonization and pressure curing. After curing, the finished recessed bricks are obtained. The conditions for carbonization and pressure curing include: curing temperature of 50-60℃, carbon dioxide concentration of 50-60%, curing pressure of 0.8-1.0 MPa, ambient humidity of 50-60%, and curing time of 48-72h.

2. The method for preparing recessed bricks based on phosphogypsum as described in claim 1, characterized in that, In step (1), the liquid washed by water in the flotation device and the liquid extracted by the spiral dewatering machine are both fed into the wastewater treatment tank for treatment. The pH is adjusted to 9-10 with hydrochloric acid and then circulated back to the flotation device for the next phosphogypsum washing.

3. The method for preparing recessed bricks based on phosphogypsum as described in claim 1, characterized in that, In step (2), the conditions for pressing and molding include: vibration frequency of 50-60Hz, excitation force of 70-80kN, and molding pressure of 20-25MPa.

4. A type of recessed brick prepared by any of the phosphogypsum-based methods as described in claims 1 to 3, characterized in that, Including the following raw materials by mass percentage: Sand 53.5-57.8%, Stone 26.3-30.5%, Impurities removed from phosphogypsum 2.2-3.2%, Cement 0.8-2.2%, Mineral powder 10.2-12.2%, Steel scale: 0.5-0.8% Water 1.2-1.5%, The sum of the mass percentages of the above components is 100%. The impurity-removed phosphogypsum is obtained by adding phosphogypsum to a flotation device with ultrasonic function for ultrasonic mineralization and washing, followed by dehydration. The weight of the impurity-removed phosphogypsum is based on the dry weight after dehydration.

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