A method for phosphogypsum sequestration based on concrete 3D printing

Abstract

The application discloses a phosphogypsum sealing method based on concrete 3D printing and belongs to the technical field of industrial solid waste resource utilization and building 3D printing. The application aims at the problems of low resource utilization rate of phosphogypsum, high risk of fluorine ion leaching and mechanical property deterioration of mixed application, adopts a composite structure of a phosphogypsum composite core and a 3D printing concrete shell, realizes double sealing through core chemical solidification and shell physical blocking, pours core material into the cavity while printing the shell, and prepares a complete component through capping and sealing and standard curing. The volume proportion of the phosphogypsum core reaches 55% to 65%, the fluorine ion sealing rate is greater than or equal to 90%, the mechanical property of the component meets the requirements of water conservancy projects, the application has the advantages of low carbon and environmental protection and low construction cost, and is suitable for engineering scenes such as dikes and revetments.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization and building 3D printing materials technology, specifically involving a method for sealing phosphogypsum based on concrete 3D printing, which is particularly suitable for the preparation of low-carbon and environmentally friendly components in water conservancy projects such as dikes, canals, and slope protection. Background Technology

[0002] Phosphogypsum is a typical solid waste produced in the wet-process phosphoric acid industry, with approximately 4-5 tons of phosphogypsum generated as a byproduct for every ton of phosphoric acid produced. Currently, the global cumulative stockpile of phosphogypsum exceeds 6 billion tons, and my country's annual emissions exceed 80 million tons, but the comprehensive utilization rate is less than 40%. - Pollutants such as fluoride (containing 0.5-2.5% of fluoride) not only occupy large amounts of land when stored for a long time, but also leach into the soil and groundwater system through rainwater, causing regional fluoride pollution and seriously threatening the ecological environment and human health.

[0003] Existing technologies for the resource utilization of phosphogypsum mainly fall into four categories: agricultural improvement, building material preparation, chemical extraction, and mine backfilling. Among these, using phosphogypsum as a concrete admixture is an important approach to achieving large-scale disposal. However, conventional admixture processes generally achieve a utilization rate of less than 30% for phosphogypsum, and soluble impurities in phosphogypsum significantly degrade the mechanical properties and durability of concrete. While pretreatment processes such as water washing and lime neutralization can reduce the impact of impurities, they suffer from high energy consumption, secondary pollution, and increased costs. Furthermore, existing technologies struggle to simultaneously resolve the contradiction between high utilization rates of phosphogypsum and the control of environmental risks associated with fluoride ions, limiting its widespread application in large-scale scenarios such as water conservancy projects.

[0004] 3D printing technology, as an emerging intelligent construction technology, boasts advantages such as no need for templates, fast construction speed, high material utilization, and strong design flexibility, providing a new technological path for the high-value utilization of industrial solid waste. However, existing 3D printing technology for adding phosphogypsum to concrete still uses a monolithic mixing method, which cannot effectively block the migration and diffusion of fluoride ions and suffers from problems such as unstable mechanical properties and poor printability. Therefore, developing a new phosphogypsum treatment technology with high utilization rate, high fluoride sequestration rate, excellent mechanical properties, and low carbon emissions is of great significance for promoting the green transformation of the phosphate chemical industry and the sustainable development of water conservancy projects. Summary of the Invention

[0005] This invention addresses the problems of low utilization rate, high environmental risk, and deterioration of mechanical properties in existing phosphogypsum resource utilization technologies. It provides a phosphogypsum storage method based on concrete 3D printing. Through the design of a composite component consisting of a core and an outer shell, it achieves large-scale disposal of phosphogypsum and efficient storage of fluoride ions, while ensuring that the mechanical properties of the component meet engineering requirements. This provides technical support for the safe application of phosphogypsum in water conservancy projects.

[0006] To achieve the above objectives, this invention provides a method for sealing phosphogypsum based on 3D concrete printing. The method uses a composite component formed by a phosphogypsum composite material core structure and a 3D-printed concrete shell to seal the phosphogypsum. The method includes the following steps: S1: Prepare phosphogypsum composite material and concrete shell material respectively. The phosphogypsum composite material, based on 100 parts of total cementitious material mass, includes 70 parts of phosphogypsum, 12-24 parts of fly ash, 3-11 parts of slag, and 3-11 parts of silica fume, with a water-cement ratio of 0.6. S2: A screw extrusion 3D printer is used to print a concrete shell with cavities from the concrete shell material; S3: While printing the concrete shell, pour the well-mixed phosphogypsum composite material into the cavity to form the core structure, and continue printing and pouring until the design height is reached. S4: After the cavity is filled, the concrete capping structure is printed so that the 3D printed concrete shell seals and wraps the phosphogypsum composite material core structure, forming a complete composite component. S5: Place the composite components in an environment with a temperature of 20±2℃ and a relative humidity of ≥95% and cure them until the specified age.

[0007] Preferably, the concrete shell material comprises 80-100 parts cement, 1000-1500 parts fine aggregate, 2-5 parts polycarboxylate high-performance water-reducing agent, and 0.1-0.3 parts concrete lubricant, with a water-cement ratio of 0.4-0.45.

[0008] Preferably, the total amount of slag and silica fume in the phosphogypsum composite material is 14 parts, and the specific ratio is 70 parts phosphogypsum, 16 parts fly ash, 7 parts slag, and 7 parts silica fume.

[0009] Preferably, the phosphogypsum is raw phosphogypsum, a byproduct of wet-process phosphoric acid production, dried at 60℃~65℃ to constant weight, with a specific surface area of ​​192m² / kg~200m² / kg, and F - The content is 0.5-2.5%; the slag is S95 grade blast furnace slag powder with a specific surface area of ​​621m² / kg~650m² / kg; the fly ash is Grade I fly ash with a specific surface area of ​​962m² / kg; the silica fume has a SiO2 content ≥90% and an average particle size of 0.1-0.3μm.

[0010] Preferably, the cement in the concrete shell material is P·O42.5 ordinary Portland cement; the fine aggregate is natural sand or granite waste sand with a particle size of 0.5-1mm, and the granite waste sand replacement rate is 0%-100%.

[0011] Preferably, the 3D printing parameters are set as follows: sealing thickness 10-40mm, printing time interval 0-60s, and extrusion speed 30-70mm / s; The ratio of feed rate to extrusion rate during 3D printing is 0.8-1.33.

[0012] Preferably, the 3D printing parameters are set as follows: sealing thickness 15mm, printing time interval 0s, extrusion speed 50mm / s, feed speed 40mm / s, printing layer height 10mm, and printing bandwidth 10mm.

[0013] Preferably, in step S3, a vibrator is used to assist in the tamping of the phosphogypsum composite material during the injection process. The tamping frequency is 50Hz~60Hz, and the tamping time is 10-15s / layer, so that the phosphogypsum composite material is dense and tightly bonded to the inner wall of the outer shell.

[0014] Preferably, the core structure of the phosphogypsum composite material accounts for 55%-65% of the volume of the composite component.

[0015] Preferably, the curing period in step S5 is not less than 28 days, and during the curing period, moisture evaporation and external disturbance to the component surface should be avoided. The concrete shell material also includes 0.2-0.5 parts of triethanolamine.

[0016] The present invention has the following beneficial effects: 1. This invention adopts a composite component design with a core structure of phosphogypsum composite material and a 3D printed concrete shell. Phosphogypsum is used as the core material, and the core structure accounts for up to 61% of the volume, which is far higher than the utilization rate limit of 30% of the traditional admixture method, and can realize the large-scale consumption of phosphogypsum.

[0017] 2. This invention utilizes the dual effects of chemical curing of the core cementitious material and physical barrier properties of the outer concrete to achieve soluble F - With a sequestration rate of ≥90% and a leaching concentration far below the 10 mg / L limit specified in the Integrated Wastewater Discharge Standard GB8978-1996, the environmental risks associated with the resource utilization of phosphogypsum have been effectively addressed.

[0018] 3. The composite component prepared by the optimized parameters of this invention has a 28-day compressive strength of ≥24.5MPa, which meets the strength requirements of general slope protection blocks in the "Technical Specification for Precast Concrete Block Slope Protection Engineering" DB34 / T2233-2021, and can be directly applied to water conservancy projects such as dikes, canals, and slope protection.

[0019] 4. This invention can dispose of a large amount of industrial solid waste such as phosphogypsum, fly ash, and slag. Carbon emissions during the material production stage are reduced by more than 40% compared to traditional concrete. No complicated pretreatment process is required, and 3D printing technology eliminates the need for templates, reducing construction costs by 20%-30%.

[0020] 5. The preparation process of this invention is simple, the printing parameters are easy to control, and the size and shape of the components can be flexibly designed according to engineering needs. It is compatible with existing mainstream screw extrusion 3D printing equipment, which is convenient for industrial and large-scale production applications. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 This is a process flow diagram of the 3D printing of phosphogypsum in concrete.

[0023] Figure 2 (a), (b), (c), and (d) are schematic diagrams of the 3D printing process of phosphogypsum concrete structures.

[0024] Figure 3 (a), (b), and (c) are model diagrams of the 3D printing process of phosphogypsum concrete. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0026] Example 1 This embodiment provides a composite component prepared using the aforementioned phosphogypsum encapsulation method based on concrete 3D printing, employing optimal mix proportions and printing parameters, as detailed below: 1. Raw material ratio Core materials (phosphogypsum composite material): 700g phosphogypsum, 160g fly ash, 70g S95 grade slag, 70g silica fume, 600g water (water-binder ratio 0.6).

[0027] Shell material (concrete shell material): P 1000g of O42.5 ordinary Portland cement, 10000g of natural sand, 33g of polycarboxylate high-performance water-reducing agent, 2g of concrete lubricant, 3.3g of triethanolamine, and 4000g of water (water-cement ratio 0.4).

[0028] 2. Printing parameters The sealing thickness is 15mm, the printing time interval is 0s, the extrusion speed is 50mm / s, the feed speed is 40mm / s, the printing layer height is 10mm, and the printing bandwidth is 10mm.

[0029] 3. Preparation steps S1, Preparation of materials: Dry the undisturbed phosphogypsum in an oven at 60℃ to constant weight, and after pulverization, control the specific surface area to be 192~200m² / kg; weigh all raw materials according to the ratio, put the solid components of the phosphogypsum composite material and the concrete shell material into the mixer respectively, dry mix at 20rpm for 2 minutes, mix evenly, and obtain dry mixtures of the two materials respectively.

[0030] S2, Printing a Concrete Shell: A screw extrusion 3D printer is used to print a concrete shell with cavities. The printing layer height is 10mm, the printing bandwidth is 10mm, the shell infill density is 100%, and the infill path is a concentric circle. The printing parameters are set as follows: seal thickness 15mm, printing time interval 0s, extrusion speed 50mm / s, and the ratio of feed speed to extrusion speed is 0.8.

[0031] S3, Synchronous Injection of Core Structure: While printing the concrete shell, metered water is added to the dry mix of phosphogypsum composite material and stirred for 3-5 minutes to form a uniform slurry. The uniformly stirred phosphogypsum composite material is then synchronously injected into the cavity through an injection device to form the core structure. Injection is carried out while printing until the designed height is reached. After each layer is injected, a vibrator is used to assist in compaction. The vibration frequency is 50Hz~60Hz and the vibration time is 10-15s / layer to ensure that the core material is dense and tightly bonded to the inner wall of the shell.

[0032] S4, Printing the capping structure: When printing reaches the designed height of 150mm, stop pouring and print the concrete capping structure, so that the 3D printed concrete shell seals and wraps the phosphogypsum composite material core structure, forming a complete composite component.

[0033] S5, Standard Curing: After printing, immediately cover the surface of the component with plastic film and place it in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days. During the curing period, avoid moisture evaporation and external disturbance to the surface of the component.

[0034] 4. Performance Test Results soluble F - Sequestration rate: 90.68%, F in leachate after 63 days - The concentration was 2.1 mg / L, which is far below the limit specified in the Integrated Wastewater Discharge Standard GB8978-1996.

[0035] 28-day compressive strength: 24.5 MPa in the X direction, 16.2 MPa in the Y direction, and 12.3 MPa in the Z direction, which meets the strength requirements of the slope protection block.

[0036] Core-shell interface bonding strength: 1.3MPa, good interface bonding, no obvious cracks or voids.

[0037] The core structure of the phosphogypsum composite material accounts for approximately 60% of the volume of the composite component, which is within the design scope.

[0038] Example 2 The difference between this embodiment and Embodiment 1 lies in the printing parameters; the sealing thickness is 20mm, while all other conditions remain the same. Performance test results: soluble F - Sequestration rate: 92.18%, F in leachate after 63 days - The concentration is 1.7 mg / L.

[0039] 28-day compressive strength: 26.8 MPa in the X direction, 17.5 MPa in the Y direction, and 13.1 MPa in the Z direction.

[0040] Example 3 The difference between this embodiment and Embodiment 1 lies in the printing parameters; the extrusion speed is 40 mm / s, while all other conditions remain the same. Performance test results: soluble F - Sequestration rate: 87.21%, F in leachate after 63 days - The concentration is 2.8 mg / L.

[0041] 28-day compressive strength: 21.8 MPa in the X direction, 14.7 MPa in the Y direction, and 11.2 MPa in the Z direction.

[0042] Example 4 The difference between this embodiment and Embodiment 1 is that the outer shell material uses 100% granite waste sand instead of natural sand; all other conditions are the same. Performance test results: soluble F - Sequestration rate: 90.23%, F in leachate after 63 days - The concentration is 2.2 mg / L.

[0043] 28-day compressive strength: 23.7 MPa in the X direction, 15.8 MPa in the Y direction, and 11.9 MPa in the Z direction.

[0044] Carbon emissions during the material production stage: 8.5% lower than in Example 1.

[0045] Comparative Example 1 This comparative example uses a traditional monolithic blending method to prepare 3D-printed phosphogypsum concrete. The phosphogypsum content is 30%, and the remaining cementitious materials are cement, fly ash, and slag, with a water-cement ratio of 0.45. Performance test results: soluble F - Sequestration rate: 52.3%, F in leachate after 63 days - The concentration was 18.7 mg / L, exceeding the national standard limit.

[0046] 28-day compressive strength: 16.5 MPa, lower than the strength requirement for slope protection blocks.

[0047] Comparative Example 2 This comparative example uses cement curing to treat phosphogypsum, with phosphogypsum content of 50%, cement content of 50%, and a water-cement ratio of 0.5. Performance test results: soluble F - Sequestration rate: 68.7%, F in leachate after 63 days - The concentration was 12.3 mg / L, exceeding the national standard limit.

[0048] 28-day compressive strength: 19.2 MPa, lower than the strength requirement for slope protection blocks.

[0049] As can be seen from the above embodiments and comparative examples, this invention achieves a balance between high utilization rate, high fluoride sequestration rate, and excellent mechanical properties of phosphogypsum through the design of a composite component of the core structure and the outer shell, and optimization of 3D printing parameters, which is significantly superior to existing traditional technologies. The composite component prepared by this invention can be directly applied to engineering projects such as water conservancy slope protection and embankments, providing a safe, efficient, and low-carbon new approach for the large-scale resource utilization of phosphogypsum.

[0050] Table 1 Performance comparison of Examples 1-4 and Comparative Examples 1-2

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for sealing phosphogypsum based on concrete 3D printing, characterized in that, A composite component formed by a phosphogypsum composite material core structure and a 3D-printed concrete shell is used to seal phosphogypsum. The method includes the following steps: S1: Prepare phosphogypsum composite material and concrete shell material respectively. The phosphogypsum composite material, based on 100 parts of total cementitious material mass, includes 70 parts of phosphogypsum, 12-24 parts of fly ash, 3-11 parts of slag, and 3-11 parts of silica fume, with a water-cement ratio of 0.

6. S2: A screw extrusion 3D printer is used to print a concrete shell with cavities from the concrete shell material; S3: While printing the concrete shell, pour the well-mixed phosphogypsum composite material into the cavity to form the core structure, and continue printing and pouring until the design height is reached. S4: After the cavity is filled, the concrete capping structure is printed so that the 3D printed concrete shell seals and wraps the phosphogypsum composite material core structure, forming a complete composite component. S5: Place the composite components in an environment with a temperature of 20±2℃ and a relative humidity of ≥95% and cure them until the specified age.

2. The method for sealing phosphogypsum based on concrete 3D printing according to claim 1, characterized in that, The concrete shell material comprises 80-100 parts cement, 1000-1500 parts fine aggregate, 2-5 parts polycarboxylate high-performance water-reducing agent, and 0.1-0.3 parts concrete lubricant, with a water-cement ratio of 0.4-0.

45.

3. The method for sealing phosphogypsum based on concrete 3D printing according to claim 1, characterized in that, The total amount of slag and silica fume in the phosphogypsum composite material is 14 parts, and the specific ratio is 70 parts phosphogypsum, 16 parts fly ash, 7 parts slag, and 7 parts silica fume.

4. The method for sealing phosphogypsum based on concrete 3D printing according to claim 1, characterized in that, The phosphogypsum is a raw phosphogypsum byproduct of the wet-process phosphoric acid industry, dried to constant weight at 60℃~65℃, with a specific surface area of ​​192m² / kg~200m² / kg, and F... - The content is 0.5-2.5%; the slag is S95 grade blast furnace slag powder with a specific surface area of ​​621m² / kg~650m² / kg; the fly ash is Grade I fly ash with a specific surface area of ​​962m² / kg; the silica fume has a SiO2 content ≥90% and an average particle size of 0.1-0.3μm.

5. The method for sealing phosphogypsum based on concrete 3D printing according to claim 1, characterized in that, The cement in the concrete shell material is P·O42.5 ordinary Portland cement; the fine aggregate is natural sand or granite waste sand with a particle size of 0.5-1mm, and the replacement rate of granite waste sand is 0%-100%.

6. The method for sealing phosphogypsum based on concrete 3D printing according to claim 1, characterized in that, The 3D printing parameters are set as follows: sealing thickness 10-40mm, printing time interval 0-60s, and extrusion speed 30-70mm / s. The ratio of feed rate to extrusion rate during 3D printing is 0.8-1.

33.

7. The method for sealing phosphogypsum based on concrete 3D printing according to claim 6, characterized in that, The 3D printing parameters are set as follows: sealing thickness 15mm, printing time interval 0s, extrusion speed 50mm / s, feed speed 40mm / s, printing layer height 10mm, and printing bandwidth 10mm.

8. The method for sealing phosphogypsum based on concrete 3D printing according to claim 1, characterized in that, In step S3, a vibrator is used to assist in the tamping of the phosphogypsum composite material during the injection process. The tamping frequency is 50Hz~60Hz and the tamping time is 10-15s / layer, which makes the phosphogypsum composite material dense and tightly bonded to the inner wall of the outer shell.

9. A method for sealing phosphogypsum based on concrete 3D printing according to claim 1, characterized in that, The core structure of the phosphogypsum composite material accounts for 55%-65% of the volume of the composite component.

10. A method for sealing phosphogypsum based on concrete 3D printing according to claim 2, characterized in that, In step S5, the curing period shall not be less than 28 days, and during the curing period, moisture evaporation and external disturbance to the component surface shall be avoided. The concrete shell material also includes 0.2-0.5 parts of triethanolamine.

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