Phosphogypsum-based curing agent for high-water-content river dredged sludge and method for curing sludge and making bricks by using phosphogypsum-based curing agent

Abstract

The invention provides an ardealite-based curing agent for high-water-content river dredged sludge and a method for curing sludge and making bricks by using the ardealite-based curing agent, and belongs to the technical field of solid waste recycling and environmental engineering. The ardealite-based curing agent for the high-water-content river dredged sludge comprises the following components in percentage by mass: 60%-70% of semi-hydrated ardealite, 5%-10% of particle size graded ardealite-based aggregates, 5%-10% of montmorillonite powder, 0.75%-3% of nano silicon dioxide and 7.5%-15% of an alkali activator, and the sum of the mass fractions of all the components is 100%. The ardealite aggregates are prepared from industrial ardealite, slag powder and cement according to the mass ratio of (75 to 85) to (5 to 15) to 10. The ardealite is used for treating the sludge, efficient solidification and resource utilization of the sludge are achieved through a composite cementing material synergistic excitation technology, a dynamic aging reaction process regulation and control technology and a heavy metal stabilization integration technology, and the purposes of improving the resource reutilization rate of the ardealite, reducing the cost of solidifying the sludge and achieving resource reutilization of the sludge are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource utilization and environmental engineering, and particularly relates to a phosphogypsum-based curing agent for river dredging sludge with high water content and a method for making bricks from the cured sludge. Background Art

[0002] Phosphogypsum is a by-product of the wet process for producing phosphoric acid. For every 1 ton of phosphoric acid produced, 4 - 5 tons of phosphogypsum will be generated. Its main component is calcium sulfate dihydrate, containing impurities such as soluble phosphorus (fluorine) and some heavy metal elements. Currently, the main method for treating phosphogypsum is stacking, which poses a risk of polluting the surrounding ecological environment; moreover, it will also occupy a large amount of land resources. Therefore, stacking is not a solution, and utilization is the way out. How to resourcefully utilize phosphogypsum and make it acceptable to the public is worthy of in-depth study.

[0003] In addition, a large amount of sludge is generated in the dredging and sediment removal projects of reservoirs, waterways, and ports. The sludge has a high water content, is in a soft and dilute state, is difficult to form, and is not easy to transport. If stacked in place, it will occupy a large amount of land and seriously affect the surrounding environment. Therefore, it has also become an inevitable trend to utilize the sludge after curing. However, due to the high water content of the sludge and the difficulty in reducing the water content through natural drying, a large amount of curing agent needs to be added to achieve the expected strength, resulting in a relatively high cost of sludge curing and thus affecting the popularization and application of sludge treatment technologies.

[0004] Chinese Patent Application No. 202310697739.1 discloses a method for preparing phosphogypsum-cured sludge for road materials, including the following steps: Step 1, weigh phosphogypsum solid waste, sludge, and silicon slag, and stir and mix them evenly. The phosphogypsum with a low water content is used to cure the sludge, and at the same time, the sludge also plays a role in wrapping and agglomerating the loose phosphogypsum particles; Step 2, weigh the mixture obtained in Step 1 and cement, and then stir and mix them evenly; Step 3, weigh the mixture obtained in Step 2, add a solid waste curing agent, and add an appropriate amount of water, and stir and mix them evenly to obtain a road base phosphogypsum-sludge material. This method for preparing phosphogypsum-cured sludge for road materials uses industrial waste phosphogypsum and sludge as the main raw materials, resourcefully utilizes solid waste, uses it as a subgrade material, has a large consumption, and improves its comprehensive utilization rate. However, the cost of the added curing agent is high, which limits the popularization of this method.

[0005] The Chinese invention patent with the application number 200910026859.9 discloses a method for the combined solidification treatment of phosphogypsum and sludge. This method can be used for the combined solidification treatment of sludge generated in civil engineering and water conservancy projects and industrial waste phosphogypsum. The specific implementation steps are as follows: a. Measure the water content of phosphogypsum, the water content and clay particle content of sludge; b. Crush phosphogypsum: To prevent incomplete reaction from affecting the solidification effect, crush the massive aggregates in phosphogypsum and screen them through a 5 mm sieve; c. Mix phosphogypsum and sludge: Mix the powdered phosphogypsum (after crushing) and sludge in a certain mass ratio and stir evenly. It is required that the water content of the phosphogypsum-sludge mixture is between 30% and 75%; d. Add solidifying agents: Then add quicklime and fly ash to the phosphogypsum-sludge mixture and stir mechanically for 2 - 5 minutes. The addition ratio is controlled at a mass ratio of quicklime to the phosphogypsum-sludge mixture of 4 - 8% and a mass ratio of fly ash to the phosphogypsum-sludge mixture of 2 - 7%; e. Stack and age: Stack the mixture and age it for 3 - 14 days. The solidified phosphogypsum-sludge mixed aggregates can be used as geotechnical fillers for paving roads, filling dams, etc., or can be stacked or directly landfilled as solid waste. However, a large amount of solidifying agents are incorporated, resulting in high treatment costs.

[0006] The treatment of high water content river dredging sludge (water content ≥ 60%) is a difficult problem in water environment treatment. Traditional methods have problems such as low solidification efficiency, slow strength development, and insufficient durability. In the existing technology, although phosphogypsum-based solidifying agents have been tried for sludge treatment, they have the following defects: poor adaptability to high water content: free water dilutes the concentration of the solidifying agent, resulting in incomplete gelation reaction; insufficient early strength: the hydration reaction of phosphogypsum is slow, and the 3-day compressive strength is often lower than 2 MPa; limited heavy metal stabilization effect: residual heavy metals are easily leached out, posing a high environmental risk; complex process: multi-stage pretreatment or high dosage of cement is required, resulting in high costs. Therefore, it is necessary to develop a method that can not only reduce the water content of dredging sludge, improve the solidification effect, but also consume a large amount of phosphogypsum. Summary of the Invention

[0007] The present invention provides a phosphogypsum-based solidifying agent for high water content river dredging sludge and a method for making bricks from solidified sludge. By using phosphogypsum to treat sludge, through the synergistic activation of composite cementitious materials, dynamic aging to control the reaction process, and integrated heavy metal stabilization technology, the high-efficiency solidification and resource utilization of sludge are realized, aiming to improve the resource recycling rate of phosphogypsum, reduce the cost of solidified sludge, and achieve the resource recycling of sludge.

[0008] The phosphogypsum-based solidifying agent for high water content river dredging sludge includes the following components: hemihydrate phosphogypsum, phosphogypsum group particles with particle size gradation, montmorillonite, nano-silica, sodium thiosulfate, and alkali activator.

[0009] Preferably, the phosphogypsum-based solidifying agent for highly water-containing river dredged sludge comprises the following components by mass fraction: 60%-70% of hemihydrate phosphogypsum, 5%-10% of phosphogypsum group particles with particle size gradation, 5%-10% of montmorillonite powder, 0.75%-3% of nano-silica, and 7.5%-15% of alkali activator; the sum of the mass fractions of each component is 100%; the phosphogypsum group particles are composed of industrial phosphogypsum, slag powder and cement with a mass ratio of (7.5-8.5):(0.5-1.5):1.

[0010] Preferably, the phosphogypsum-based solidifying agent for highly water-containing river dredged sludge further comprises sodium thiosulfate. When used in combination with montmorillonite, montmorillonite first adsorbs heavy metal ions, and then sodium thiosulfate conducts chemical chelation to form a "physical adsorption-chemical fixation" double barrier, greatly improving the fixation efficiency.

[0011] More preferably, the addition amount of the sodium thiosulfate is 1.5%-4.5%, and the sum of the mass fractions of each component is 100%.

[0012] Preferably, the hemihydrate phosphogypsum is obtained by calcining industrial phosphogypsum at 150-300 °C for 1-2 h, with the hemihydrate phosphogypsum content ≥90%, and grinding it to a specific surface area ≥400 m² / kg.

[0013] Preferably, the montmorillonite is organically modified montmorillonite.

[0014] Preferably, the organic modifiers of the organically modified montmorillonite include quaternary ammonium salts, organic phosphoric acids, β-cyclodextrin, β-cyclodextrin derivatives or mercapto compounds. The selection of the organic modifier depends on the types of heavy metals in the sludge. It can be montmorillonite modified by a single organic modifier or montmorillonite modified by different organic modifiers.

[0015] Preferably, the phosphogypsum group particles are prepared by the following steps: S1. Dry the industrial phosphogypsum powder, cement and slag powder, stir the dried powders evenly to obtain a mixture, put the mixture into a mold, and compact the mixture into a block using a press; S2. Crush the block obtained in step S1 using a crusher to obtain coarse aggregates; S3. Polish the coarse aggregates obtained in step S2 using a roller to remove the surface edges and corners of the coarse aggregates, and sieve the polished coarse aggregates using a screening device to obtain phosphogypsum group particles with different particle sizes.

[0016] Further preferably, the compaction process is divided into two stages of pressurization, and the pressurization method adopts the stress-unit increase. The first stage compaction pressure is 170 kN, the loading speed is 0.41 MPa / s, and the pressure is maintained for 5 minutes after the pressure reaches 170 kN; the pressure is applied at a speed of 0.33 MPa / s to make the second stage compaction pressure reach 270 kN, and the pressure is maintained for 20 minutes.

[0017] Preferably, the particle size gradation of the phosphogypsum group particles is as follows: the mass ratio of the phosphogypsum group particles with a particle size of 1-5 mm: 5-15 mm: 15-25 mm is 2-4: 4-6: 1-3.

[0018] The application of the phosphogypsum-based curing agent for high-water-content river channel dredged sludge in the curing of high-water-content river channel dredged sludge, wherein the water content of the high-water-content river channel dredged sludge is 65wt%~85wt%. The water content is the mass of water in the soil / total weight of the soil.

[0019] The method for curing and making bricks from dredged sludge from a river with high water content adopts the phosphogypsum-based curing agent for dredged sludge from a river with high water content, and the curing method comprises the following steps: adding the phosphogypsum-based curing agent for dredged sludge from a river with high water content into the sludge, fully and evenly mixing, pouring into a mold and vibrating to compact, using a hydraulic press to pressurize and form in two stages, and then demolding to form brick blanks after curing for 24 hours, wherein the brick blanks are first cured in an environment with a CO2 concentration of 20% to 30% for 24 to 48 hours, and then transferred to a 60 to 80°C steam curing box for treatment for 6 to 12 hours to obtain bricks.

[0020] Preferably, the phosphogypsum-based curing agent for the high-water content river dredged sludge is added in an amount of 20% to 40% of the sludge mass.

[0021] Preferably, the hydraulic press is divided into two stages of pressure molding, the first stage pressure is 5-8 MPa, and the pressure is maintained for 30-60 seconds, and the second stage pressure is 12-20 MPa, and the pressure is maintained for 60-300 seconds.

[0022] Compared with the existing technology, the advantages and technical effects of the present invention are: 1. In the phosphogypsum-based curing agent system for highly water-saturated river dredged sludge provided by the present invention, each component realizes the efficient solidification of sludge through physical-chemical multi-level synergistic effects. Hemihydrate phosphogypsum serves as the main gelling phase, providing initial hydration activity, reacting with the alkali activator to generate ettringite (AFt) and C-S-H gel, and forming a strength skeleton; at the same time, heavy metals are fixed through Ca²⁺ ion exchange and sulfate precipitation. The phosphogypsum group particles with particle size gradation reduce the porosity through the close packing of multi-level particles. The slag and cement inside continuously hydrate to compensate for the later strength, and the surface hydration products form a core-shell reinforcement structure with the matrix. The organically modified montmorillonite is selectively functionalized according to the types of heavy metals, forming a "physical adsorption-chemical chelation" double barrier with the metal thiosulfate complex of sodium thiosulfate, greatly improving the heavy metal fixation rate. Nano-silica fills the gel micropores and jointly promotes the pozzolanic reaction with the alkali activator. The generated C-S-H gel interweaves AFt crystals into a three-dimensional network, enhancing the 28-day compressive strength. Through multiple synergies such as the gelling effect of hemihydrate phosphogypsum, the skeleton effect of the aggregates, the adsorption-chelating function of montmorillonite, the densification filling of nanoparticles, and the reaction activation of alkali activation, this system achieves the balance of strength development (compressive strength ≥ 15 MPa), environmental safety (Pb leaching < 0.5 mg / L), and durability (freeze-thaw loss rate < 3%), and the comprehensive cost is reduced by 48.6% compared with traditional cement solidification.

[0023] 2. The method provided by the present invention makes the brick blank more dense through two-stage pressure forming; then through carbonization-steam co-curing, it realizes the cross-scale strengthening purpose of surface carbonation plugging and deep hydrothermal gelling, and at the same time solves the three major problems of insufficient early strength, poor durability, and heavy metal leaching risk of phosphogypsum sludge bricks. Through the synergistic excitation of composite cementitious materials, dynamic aging to control the reaction process, and heavy metal stabilization integration technology, the efficient solidification and resource utilization of sludge are realized, aiming to improve the resource recycling rate of phosphogypsum.

[0024] 3. The present invention realizes the resource utilization of phosphogypsum. If it cannot be resourcefully applied, it will occupy a large amount of land for storage and there is a potential risk of polluting the surrounding environment; the resource utilization of phosphogypsum and sludge realizes "treating waste with waste" and achieves the goal of turning waste into treasure.

[0025] 4. The present invention realizes the resource utilization of sludge. After the sludge is solidified, solidified soil that meets the engineering requirements is formed, made into bricks or blocks, or crushed and used for filling subgrades or river embankments, replacing increasingly scarce materials such as sand and gravel, thereby reducing the construction cost of the project. Specific Embodiments

[0026] The technical solutions of the present invention will be further described and illustrated below through examples. All raw materials used in the examples are commercially available or can be prepared by conventional methods.

[0027] Example 1 In the river channel dredging project in the middle reaches of the Yangtze River, the water content of the dredged silt is 80%, the Pb content is 150 mg / kg, and the Cd content is 12 mg / kg.

[0028] For the above-mentioned silt, a phosphogypsum-based solidifying agent for river dredging silt with high water content is provided. By mass fraction, it includes the following components: 68% hemihydrate phosphogypsum, 9% phosphogypsum group particles with particle size gradation, 9% cetyltrimethylammonium bromide modified montmorillonite powder, 2.5% nano-silica with a particle size of 15 - 25 nm, 2.8% sodium thiosulfate, and 8.7% alkali activator prepared by mixing carbide slag and sodium silicate in a mass ratio of 3:1.

[0029] The hemihydrate phosphogypsum is prepared by calcining industrial phosphogypsum at 250 °C for 1.5 h and grinding it to a specific surface area of 450 m² / kg.

[0030] The phosphogypsum group particles are composed of industrial phosphogypsum, slag powder, and cement with a mass ratio of 8:1:1. The particle size gradation of the phosphogypsum group particles is as follows: the mass ratio of phosphogypsum group particles with a particle size of 1 - 5 mm: 5 - 15 mm: 15 - 25 mm is 3.5:5:1.5. The phosphogypsum group particles are prepared by the following steps: S1. Dry the industrial phosphogypsum powder, cement, and slag powder, stir the dried powders evenly to obtain a mixture, put the mixture into a mold, and use a press to compact the mixture into a block. The compaction process is divided into two-stage pressurization, and the pressurization method is to increase by stress. The first-stage compaction pressure is 170 kN, the loading speed is 0.41 MPa / s, and after the pressure reaches 170 kN, keep the pressure for 5 min; apply pressure at a speed of 0.33 MPa / s to make the second-stage compaction pressure reach 270 kN, and keep the pressure for 20 min; S2. Use a crusher to crush the block obtained in step S1 to obtain coarse aggregates; S3. Use a roller to polish the coarse aggregates obtained in step S2 to remove the surface edges and corners of the coarse aggregates, and use a screening device to screen the polished coarse aggregates to obtain phosphogypsum group particles with different particle sizes.

[0031] The cetyltrimethylammonium bromide modified montmorillonite is prepared by intercalating and modifying sodium-based montmorillonite with cetyltrimethylammonium bromide, and the loading amount is 1.35 mmoL / g.

[0032] The method for making bricks by curing the above-mentioned sludge with the above-mentioned curing agent includes the following steps: Incorporate the phosphogypsum-based curing agent of the high-moisture-content river dredging sludge into the sludge, with the incorporation amount being 30% of the mass of the sludge. Mix thoroughly, pour it into a mold and vibrate it densely. Use a hydraulic press to press and form in two stages. The pressure in the first stage of the two-stage pressure forming of the hydraulic press is 6.5 MPa, with a pressure holding time of 45 s. The pressure in the second stage is 17 MPa, with a pressure holding time of 5 min. After curing for 24 h, demold to make brick blanks. The brick blanks are first cured in an environment with a CO2 concentration of 28% for 40 h, and then transferred to a steam curing box at 75 °C for treatment for 10 h to obtain bricks.

[0033] Refer to GB / T 50123-2019 "Standard for Geotechnical Test Methods" to determine the unconfined compressive strength of the solidified soil (specimen size Φ50 mm×H100 mm, loading rate 1 mm / min). The 28-day compressive strength of the specimen is 18.1 MPa.

[0034] Refer to GB 5085.3-2007 "Identification Standard for Hazardous Wastes - Identification for Leaching Toxicity" to determine that the leaching amount of lead in the solidified soil is 0.38 mg / L and the leaching amount of cadmium is 0.05 mg / L.

[0035] Refer to JC / T 422-2007 "Non-fired Waste Tailings Bricks" to determine that the water absorption rate of the solidified soil is 8.7%.

[0036] Refer to GB / T 50082-2024 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" to determine that the freeze-thaw loss rate of the solidified soil is 1.9% after 50 freeze-thaw cycles (-20 °C~25 °C).

[0037] It should be understood that the above embodiments are only used to illustrate the content of the present invention and are not used to limit the protection scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A phosphogypsum-based solidifying agent for river dredging sludge with high water content, characterized in that, By mass fraction, it includes the following components: 60% - 70% hemihydrate phosphogypsum, 5% - 10% phosphogypsum group particles with particle size gradation, 5% - 10% montmorillonite powder, 0.75% - 3% nano-silica, and 7.5% - 15% alkali activator, and the sum of the mass fractions of each component is 100%; the phosphogypsum group particles are composed of industrial phosphogypsum, slag powder and cement with a mass ratio of (7.5 - 8.5):(0.5 - 1.5):

1.

2. The phosphogypsum-based solidifying agent for highly water-containing river dredging sludge according to claim 1, characterized in that, The phosphogypsum-based solidifying agent for highly water-containing river dredging sludge described above also includes sodium thiosulfate.

3. The phosphogypsum-based solidifying agent for highly water-containing river dredging sludge according to claim 2, characterized in that, The addition amount of the sodium thiosulfate is 1.5% - 4.5%, and the sum of the mass fractions of each component is 100%.

4. The phosphogypsum-based solidifying agent for highly water-containing river dredging sludge according to claim 1, wherein, The hemihydrate phosphogypsum is obtained by calcining industrial phosphogypsum at 150 - 300 °C for 1 - 2 h, with the hemihydrate phosphogypsum content ≥ 90%, and grinding to a specific surface area ≥ 400 m² / kg.

5. The phosphogypsum-based solidifying agent for highly water-containing river dredging sludge according to claim 1, characterized in that, The montmorillonite described above is organically modified montmorillonite; the organic modifiers of the organically modified montmorillonite include quaternary ammonium salts, organic phosphonic acids, β-cyclodextrin, β-cyclodextrin derivatives or mercapto compounds.

6. The phosphogypsum-based solidifying agent for highly water-containing river dredging sludge according to claim 1, wherein The phosphogypsum group particles are prepared by the following steps: S1. Dry the industrial phosphogypsum powder, cement and slag powder, stir the dried powders evenly to obtain a mixture, put the mixture into a mold, and use a press to compact the mixture into blocks; S2. Use a crusher to crush the blocks obtained in step S1 to obtain coarse aggregates; S3. Use a roller to polish the coarse aggregates obtained in step S2 to remove the surface edges and corners of the coarse aggregates, and use a screening device to screen the polished coarse aggregates to obtain phosphogypsum group particles with different particle sizes; In step S1, the compaction process is divided into two-stage pressurization, and the pressurization method is to increase by stress. The first-stage compaction pressure is 170 kN, the loading speed is 0.41 MPa / s, and after the pressure reaches 170 kN, keep the pressure for 5 min; apply pressure at a speed of 0.33 MPa / s to make the second-stage compaction pressure reach 270 kN, and keep the pressure for 20 min.

7. The phosphogypsum-based solidifying agent for highly water-containing river dredging sludge according to claim 1, wherein The particle size gradation of the phosphogypsum group particles is as follows: the mass ratio of phosphogypsum group particles with particle sizes of 1 - 5 mm: 5 - 15 mm: 15 - 25 mm is 2 - 4:4 - 6:1 - 3.

8. Use of a phosphogypsum-based solidifying agent for highly water-containing river dredged sludge according to any one of claims 1 to 7 in solidifying highly water-containing river dredged sludge, characterized in that, The water content of the highly water-containing river dredging sludge is 65wt% - 85wt%.

9. A method for solidifying and brick-making of river dredging silt with high water content, characterized in that, Using the phosphogypsum-based solidifying agent for highly water-containing river dredging sludge according to any one of claims 1 - 7, the solidifying method includes the following steps: Incorporate the phosphogypsum-based solidifying agent for highly water-containing river dredging sludge into the sludge, stir evenly, pour it into a mold and vibrate it densely, use a hydraulic press to press it into shape in two stages, demold after curing for 24 h to make a brick blank, and first cure the brick blank in an environment with a CO2 concentration of 20% - 30% for 24 - 48 h, and then transfer it to a steam curing box at 60 - 80 °C for 6 - 12 h to obtain bricks.

10. The solidification brick-making method for highly water-containing river dredging sludge according to claim 9, characterized in that, The incorporation amount of the phosphogypsum-based solidifying agent for highly water-containing river dredged sludge is 20% - 40% of the mass of the sludge; the pressure in the first stage of the two-stage pressure forming by the hydraulic press is 5 - 8 MPa, with a pressure holding time of 30 - 60 s, and the pressure in the second stage is 12 - 20 MPa, with a pressure holding time of 60 - 300 s.