Boiling slag modified phosphogypsum-based cement retarder and preparation method thereof

Abstract

The present application relates to solid waste resource utilization field, disclose a kind of boiling furnace slag modified phosphogypsum-based cement retarder and its preparation method, retarder is prepared by 10-15 parts of base material and 0.5-3 parts of auxiliary material, by weight parts, base material is made of the following components: phosphogypsum 65-71 parts, boiling furnace slag 16-28 parts, calcium hydroxide 10-100 parts;By weight parts, auxiliary material is made of the following components: 0.1-5 parts sodium dodecyl benzene sulfonate, 2-10 parts citric acid, 0.2-2 parts lignin sulfonate, 1-18 parts anhydrous sodium sulfate, 0.1-10 parts fly ash.The scheme uses boiling furnace slag cooperates with calcium hydroxide to do exciter and is incorporated into phosphogypsum to excite phosphogypsum, to help improve the strength of water condensate;With boiling furnace slag instead of conventional lime to do exciter, not only save cost, also effectively comprehensive utilization of boiling furnace slag and phosphogypsum, solve the problem of phosphogypsum and boiling furnace slag resource utilization difficulty, while improving the performance of phosphogypsum-based water condensate.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, specifically to a fluidized bed slag modified phosphogypsum-based cement retarder and its preparation method. Background Technology

[0002] Phosphogypsum is a solid waste generated during the wet-process phosphoric acid production process, and its main component is calcium sulfate dihydrate. The composition of phosphogypsum is complex, containing not only calcium sulfate but also incompletely decomposed phosphate rock, residual phosphoric acid, fluorides, acid-insoluble substances, and organic matter. The presence of fluorine and organic matter has the greatest impact on the resource utilization of phosphogypsum. The indiscriminate dumping and accumulation of phosphogypsum severely damages the ecological environment, polluting groundwater resources and wasting land resources.

[0003] Currently, phosphogypsum is mainly used in gypsum building materials, cement retarder, ammonium sulfate fertilizer, and soil conditioner. Silicate cement is a widely used and important building cementitious material; therefore, using PG as a cement retarder is considered one of the most promising ways to utilize PG resources. Cement retarder can delay the cement hydration reaction, thereby extending the setting time of concrete, allowing fresh concrete to maintain its plasticity for a longer period, facilitating pouring, and improving construction efficiency. C3A and C4AF in cement clinker react with gypsum to form hydrated calcium sulfoaluminate and hydrated calcium sulfoferrate. These hydration products adhere to the surface of clinker particles, forming a thin film that seals the surface of the hydrated components, hindering the diffusion of water molecules and ions, thus delaying the continued hydration of cement particles, especially C3A, until the crystallization pressure reaches a certain value, causing the ettringite film to partially crack, allowing hydration to continue. Gypsum has a particularly significant effect on the early hydration of cement, resulting in better strength development and less shrinkage and creep.

[0004] Phosphogypsum is widely accepted as a cement retarder, but due to the harmful impurities affecting its performance and the difficulty in controlling the use of powdered phosphogypsum, it needs to be pretreated before being used in cement processing. Pretreatment of phosphogypsum generally involves processes such as water washing and neutralization with lime or alkaline calcium materials, and pelletizing the phosphogypsum powder improves its ease of use during cement processing. However, existing production and disposal methods cannot effectively reduce the content of water-soluble phosphorus and other harmful impurities in phosphogypsum, which has a certain impact on cement performance, preventing its widespread and large-scale use in cement production compared to natural gypsum. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a fluidized bed slag modified phosphogypsum-based cement retarder and its preparation method, so as to solve the problem of the difficulty in resource utilization of phosphogypsum and fluidized bed slag, and at the same time improve the performance of phosphogypsum-based hydrogelling agents.

[0006] To achieve the above objectives, the present invention provides a fluidized bed slag modified phosphogypsum-based cement retarder, prepared from 10-15 parts of base material and 0.5-3 parts of auxiliary materials.

[0007] By weight, the base material consists of the following components: 65-71 parts phosphogypsum, 16-28 parts fluidized bed slag, and 10-100 parts calcium hydroxide.

[0008] By weight, the auxiliary materials consist of the following components: 0.1-5 parts sodium dodecylbenzenesulfonate, 2-10 parts citric acid, 0.2-2 parts lignin sulfonate, 1-18 parts anhydrous sodium sulfate, and 0.1-10 parts fly ash.

[0009] In a second aspect, this invention provides a method for preparing a fluidized bed slag modified phosphogypsum-based cement retarder, comprising the following steps:

[0010] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and ball mill to obtain a mixture;

[0011] S2. Add sodium dodecylbenzenesulfonate, citric acid, lignin sulfonate and water to the mixture, stir and carry out hydrothermal reaction to recrystallize phosphogypsum and at the same time complete the reaction and elimination of harmful impurities; the solid-liquid ratio of water to phosphogypsum is 0.2-2.

[0012] S3. Calcium hydroxide and fluidized bed slag are added to the mixture from step S2 as activators and stirred at 20-60°C to obtain a slurry, thereby enhancing the strength of phosphogypsum.

[0013] S4. After the slurry solidifies, it is piled up and aged for a predetermined time to obtain the retarder.

[0014] Preferably, in step S1, the ball-to-material ratio of the ball mill is 2-10:1, the ball milling speed is 100-1000 r / min, and the ball milling time is 1-14 h.

[0015] Preferably, in step S2, the stirring time is 0.5-5 days.

[0016] Preferably, in step S3, calcium hydroxide is first added and stirred for 2-10 minutes to make the mixture alkaline, and then boiling slag is added and stirred for 2-200 minutes.

[0017] Preferably, in step S3, stirring is carried out under normal pressure, and calcium hydroxide is added to make the pH of the mixture ≥ 10.

[0018] Preferably, in step S4, the stacking and aging is carried out at a temperature of 15-30°C for 2-20 days.

[0019] Preferably, in step S4, granulation is performed before stacking and aging, and water is sprayed 3-5 times during stacking and aging to make the moisture content of the solid particles 5-20%. After stacking and aging, the particles are self-heated and air-dried.

[0020] Preferably, the granulation is performed using a disc granulator, and the particle size of the granules is controlled to be 15-30 mm.

[0021] Preferably, the fluidized bed slag has a particle size of 1-6 mm and a density of 800-900 kg / m³. 3 The main chemical components of the fluidized bed slag are SiO2 and Al2O3, with SiO2 and Al2O3 accounting for 51-80 wt%.

[0022] The technical solution of this invention has the following beneficial effects:

[0023] (1) Physical ball milling of phosphogypsum exposes soluble phosphorus, soluble fluorine and harmful impurities, but cannot eliminate them. A chemical method is used: sodium dodecylbenzene sulfonate is used as a surfactant, and citric acid and lignin sulfonate work together to convert phosphorus, fluorine and other impurities in phosphogypsum into citrate, removing most of the organic matter and some phosphorus, fluorine and other impurities. At the same time, it is beneficial to the subsequent reaction of fluidized bed slag and calcium hydroxide doping.

[0024] (2) Using calcium hydroxide as an activator, the fluidized bed slag reacts in an alkaline environment to generate gelling hydration products, which can fill the pores of phosphogypsum-based materials, thereby improving density and mechanical strength. At the same time, the gelling hydration products can both encapsulate calcium phosphate precipitates to form a dense structure and prevent phosphorus dissolution, and utilize their nanoporous structure to physically trap CaF2 particles or free F. - This reduces its migration, thereby solidifying the phosphorus and fluorine in phosphogypsum and further improving the performance of phosphogypsum-based cement retarder.

[0025] (3) Under alkaline conditions, the fluidized bed slag partially dissolves to generate active silica and alumina, releasing more adsorption sites. Through ion exchange and surface complexation / coprecipitation, it adsorbs harmful metals in phosphogypsum, effectively reducing the content of harmful impurities and thus improving the performance of phosphogypsum-based cement retarder.

[0026] (4) It effectively integrates fluidized bed slag and phosphogypsum, solving the problem of the difficulty in resource utilization of phosphogypsum and fluidized bed slag. It is environmentally friendly and low-cost, and suitable for large-scale solid waste treatment. Detailed Implementation

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] The present invention will be described in detail below through examples. All reagents used in the following examples are commercially available products.

[0029] Example 1:

[0030] A fluidized bed slag modified phosphogypsum-based cement retarder is prepared from 15 parts of base material and 3 parts of auxiliary materials. By weight, the base material consists of 71 parts phosphogypsum, 28 parts fluidized bed slag, and 100 parts calcium hydroxide. By weight, the auxiliary materials consist of 5 parts sodium dodecylbenzenesulfonate, 10 parts citric acid, 0.2 parts lignin sulfonate, 18 parts anhydrous sodium sulfate, and 0.1 parts fly ash. The fluidized bed slag has a particle size of 1-6 mm and a density of 800-900 kg / m³. 3 The main chemical components of the fluidized bed slag are SiO2 and Al2O3, with SiO2 and Al2O3 accounting for 51-80 wt%; the preparation method includes the following steps:

[0031] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and ball mill to obtain a mixture; the ball-to-material ratio of the ball mill is 10:1, the ball milling speed is 1000 r / min, and the ball milling time is 1 h;

[0032] S2. Add sodium dodecylbenzenesulfonate, citric acid, lignin sulfonate and water to the mixture, stir and carry out hydrothermal reaction to recrystallize phosphogypsum and simultaneously react with and eliminate harmful impurities; the solid-liquid ratio of water to phosphogypsum is 2, and the stirring time is 0.5 days.

[0033] S3. Calcium hydroxide and fluidized bed slag are added as activators to the mixture in step S2. The mixture is stirred at 20°C to obtain a slurry. Specifically, calcium hydroxide is added first and stirred for 10 minutes to make the mixture alkaline. Then, fluidized bed slag is added and stirred for another 200 minutes to enhance the strength of phosphogypsum. Calcium hydroxide is added to make the pH of the mixture 12.

[0034] S4. After the slurry solidifies, it is first granulated using a disc granulator to control the particle size to 15-30mm. It is then piled and aged at 30℃ for 20 days. During the aging period, water is sprayed 5 times to make the moisture content of the solid particles 20%. After the aging period, it is self-heated and air-dried to obtain the retarder.

[0035] Example 2:

[0036] A fluidized bed slag modified phosphogypsum-based cement retarder is prepared from 10 parts of base material and 0.5 parts of auxiliary materials. By weight, the base material consists of 65 parts phosphogypsum, 16 parts fluidized bed slag, and 10 parts calcium hydroxide. By weight, the auxiliary materials consist of 0.1 parts sodium dodecylbenzene sulfonate, 2 parts citric acid, 0.2 parts lignin sulfonate, 1 part anhydrous sodium sulfate, and 10 parts fly ash. The fluidized bed slag has a particle size of 1-6 mm and a density of 800-900 kg / m³. 3 The main chemical components of the fluidized bed slag are SiO2 and Al2O3, with SiO2 and Al2O3 accounting for 51-80 wt%; the preparation method includes the following steps:

[0037] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and ball mill to obtain a mixture; the ball-to-material ratio of the ball mill is 2:1, the ball milling speed is 100 r / min, and the ball milling time is 14 h;

[0038] S2. Add sodium dodecylbenzenesulfonate, citric acid, lignin sulfonate and water to the mixture, stir and carry out hydrothermal reaction to recrystallize phosphogypsum and simultaneously react with and eliminate harmful impurities; the solid-liquid ratio of water to phosphogypsum is 0.2, and the stirring time is 5 days.

[0039] S3. Calcium hydroxide and fluidized bed slag are added as activators to the mixture in step S2. The mixture is stirred at 60°C to obtain a slurry. Specifically, calcium hydroxide is added first and stirred for 2 minutes to make the mixture alkaline. Then, fluidized bed slag is added and stirred for another 2 minutes to enhance the strength of phosphogypsum. Calcium hydroxide is added to make the pH of the mixture 10.

[0040] S4. After the slurry solidifies, it is first granulated using a disc granulator to control the particle size to 15-30mm. It is then piled and aged at 15℃ for 2 days. During the aging process, water is sprayed 3 times to reduce the moisture content of the solid particles to 5%. After the aging process is completed, it is air-dried by self-heating to obtain the retarder.

[0041] Example 3:

[0042] A fluidized bed slag modified phosphogypsum-based cement retarder is prepared from 12 parts of base material and 1.5 parts of auxiliary materials. By weight, the base material consists of 68 parts phosphogypsum, 21 parts fluidized bed slag, and 30 parts calcium hydroxide. By weight, the auxiliary materials consist of 2.6 parts sodium dodecylbenzene sulfonate, 6 parts citric acid, 1.2 parts lignin sulfonate, 9 parts anhydrous sodium sulfate, and 5 parts fly ash. The fluidized bed slag has a particle size of 1-6 mm and a density of 800-900 kg / m³. 3The main chemical components of the fluidized bed slag are SiO2 and Al2O3, with SiO2 and Al2O3 accounting for 51-80 wt%; the preparation method includes the following steps:

[0043] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and ball mill to obtain a mixture; the ball-to-material ratio of the ball mill is 6:1, the ball milling speed is 550 r / min, and the ball milling time is 7 h;

[0044] S2. Add sodium dodecylbenzenesulfonate, citric acid, lignin sulfonate and water to the mixture, stir and carry out hydrothermal reaction to recrystallize phosphogypsum and at the same time complete the reaction and elimination of harmful impurities; the solid-liquid ratio of water to phosphogypsum is 1.1, and the stirring time is 2 days.

[0045] S3. Calcium hydroxide and fluidized bed slag are added as activators to the mixture in step S2. The mixture is stirred at 30°C to obtain a slurry. Specifically, calcium hydroxide is added first and stirred for 6 minutes to make the mixture alkaline. Then, fluidized bed slag is added and stirred for another 100 minutes to enhance the strength of the phosphogypsum. Calcium hydroxide is added to make the pH of the mixture 12.5.

[0046] S4. After the slurry solidifies, it is first granulated using a disc granulator to control the particle size to 15-30mm. It is then piled and aged at 18℃ for 11 days. During the aging process, water is sprayed 4 times to make the moisture content of the solid particles 12%. After the aging process is completed, it is self-heated and air-dried to obtain the retarder.

[0047] Example 4:

[0048] A fluidized bed slag modified phosphogypsum-based cement retarder is prepared from 10 parts of base material and 2 parts of auxiliary materials. By weight, the base material consists of 70 parts phosphogypsum, 19 parts fluidized bed slag, and 60 parts calcium hydroxide. By weight, the auxiliary materials consist of 3 parts sodium dodecylbenzene sulfonate, 4 parts citric acid, 1.5 parts lignin sulfonate, 10 parts anhydrous sodium sulfate, and 2 parts fly ash. The fluidized bed slag has a particle size of 1-6 mm and a density of 800-900 kg / m³. 3 The main chemical components of the fluidized bed slag are SiO2 and Al2O3, with SiO2 and Al2O3 accounting for 51-80 wt%; the preparation method includes the following steps:

[0049] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and ball mill to obtain a mixture; the ball-to-material ratio of the ball mill is 4:1, the ball milling speed is 750 r / min, and the ball milling time is 5 h;

[0050] S2. Add sodium dodecylbenzenesulfonate, citric acid, lignin sulfonate and water to the mixture, stir and carry out hydrothermal reaction to recrystallize phosphogypsum and simultaneously react with and eliminate harmful impurities; the solid-liquid ratio of water to phosphogypsum is 1.8, and the stirring time is 1.5 days.

[0051] S3. Calcium hydroxide and fluidized bed slag are added as activators to the mixture in step S2. The mixture is stirred at 45°C to obtain a slurry. Specifically, calcium hydroxide is added first and stirred for 4 minutes to make the mixture alkaline. Then, fluidized bed slag is added and stirred for another 120 minutes to enhance the strength of the phosphogypsum. Calcium hydroxide is added to make the pH of the mixture 11.5.

[0052] S4. After the slurry solidifies, it is first granulated using a disc granulator to control the particle size to 15-30mm. It is then piled and aged at 20℃ for 7 days. During the aging period, water is sprayed 4 times to make the moisture content of the solid particles 10%. After the aging period, it is self-heated and air-dried to obtain the retarder.

[0053] Comparative Example 1:

[0054] A phosphogypsum-based cement retarder is prepared from 12 parts of a base material and 1.5 parts of auxiliary materials. By weight, the base material consists of 68 parts phosphogypsum and 30 parts calcium hydroxide. By weight, the auxiliary materials consist of 2.6 parts sodium dodecylbenzene sulfonate, 6 parts citric acid, 1.2 parts lignin sulfonate, 9 parts anhydrous sodium sulfate, and 1 part fly ash. The fluidized bed slag has a particle size of 1-6 mm and a density of 800-900 kg / m³. 3 The main chemical components of the fluidized bed slag are SiO2 and Al2O3, with SiO2 and Al2O3 accounting for 51-80 wt%; the preparation method includes the following steps:

[0055] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and ball mill to obtain a mixture; the ball-to-material ratio of the ball mill is 6:1, the ball milling speed is 550 r / min, and the ball milling time is 7 h;

[0056] S2. Add sodium dodecylbenzenesulfonate, citric acid, lignin sulfonate and water to the mixture, stir and carry out hydrothermal reaction to recrystallize phosphogypsum and at the same time complete the reaction and elimination of harmful impurities; the solid-liquid ratio of water to phosphogypsum is 1.1, and the stirring time is 2 days.

[0057] S3. After the slurry solidifies, it is first granulated using a disc granulator to control the particle size to 15-30mm. It is then piled and aged at 18℃ for 11 days. During the aging period, water is sprayed 4 times to make the moisture content of the solid particles 12%. After the aging period, it is self-heated and air-dried to obtain the retarder.

[0058] Comparative Example 1 and Example 3 followed the same steps and experimental conditions, except that Comparative Example 1 did not include fluidized bed slag and calcium hydroxide.

[0059] Comparative Example 2:

[0060] A phosphogypsum-based cement retarder is prepared from 12 parts of a base material and 1.5 parts of auxiliary materials. By weight, the base material consists of the following components: 68 parts phosphogypsum, 21 parts fluidized bed slag, and 30 parts calcium hydroxide; the fluidized bed slag has a particle size of 1-6 mm and a density of 800-900 kg / m³. 3 The main chemical components of the fluidized bed slag are SiO2 and Al2O3, with SiO2 and Al2O3 accounting for 51-80 wt%; the preparation method includes the following steps:

[0061] S1. Ball mill the phosphogypsum to obtain a mixture; the ball-to-material ratio is 6:1, the ball milling speed is 550 r / min, and the ball milling time is 7 h;

[0062] S2. Add water to the mixture, mix and stir, and then carry out a hydrothermal reaction. The solid-liquid ratio of water to phosphogypsum is 1.1, and the stirring time is 2 days.

[0063] S3. Calcium hydroxide and fluidized bed slag are added as activators to the mixture in step S2 and stirred to obtain a slurry. Specifically, calcium hydroxide is added first and stirred for 6 minutes to make the mixture alkaline. Then, fluidized bed slag is added and stirred for another 100 minutes to enhance the strength of phosphogypsum. Calcium hydroxide is added to make the pH of the mixture 12.5.

[0064] S4. After the slurry solidifies, it is first granulated using a disc granulator to control the particle size to 15-30mm. It is then piled and aged at 18℃ for 11 days. During the aging process, water is sprayed 4 times to make the moisture content of the solid particles 12%. After the aging process is completed, it is self-heated and air-dried to obtain the retarder.

[0065] Comparative Example 2 and Example 3 followed the same steps and experimental conditions, the only difference being that Comparative Example 2 did not include fly ash and anhydrous sodium sulfate.

[0066] Comparative Example 3:

[0067] Comparative Example 1 and Example 3 followed the same steps and experimental conditions, the only difference being that no fluidized bed slag was added in Comparative Example 1.

[0068] The performance of the phosphogypsum-based cement retarder in Examples 1-4 of this invention was tested, and the phosphogypsum-based cement retarder prepared in Comparative Examples 1-3 was compared with that in GB / T21371-2008 "Industrial By-product Gypsum for Cement Production". The comparative data of modified phosphogypsum cement retarder produced by different technical solutions are shown in Table 1.

[0069] Table 1

[0070]

[0071]

[0072] Physical ball milling of phosphogypsum exposes soluble phosphorus, soluble fluorine, and harmful impurities, but these cannot be eliminated. A chemical method is used: sodium dodecylbenzene sulfonate is used as a surfactant, and citric acid and lignin sulfonate work together to convert impurities such as phosphorus and fluorine in phosphogypsum into citrates, removing most of the organic matter and some of the phosphorus and fluorine impurities. At the same time, it is beneficial to the subsequent reaction of fluidized bed slag and calcium hydroxide doping.

[0073] Fluidized bed slag, also known as boiling slag, is the waste residue produced during combustion in fluidized bed boilers. It has a stable chemical composition, is reactive, and is relatively easy to grind. The main components of fluidized bed slag are SiO2 and Al2O3. Physical ball milling of phosphogypsum exposes soluble phosphorus, soluble fluorine, and harmful impurities, and the alkaline environment provided by calcium hydroxide further enhances its properties. - Ca 2+ Water-soluble PO4 exposed with phosphogypsum 3- and F - Formation of sparingly soluble compounds such as calcium phosphate and CaF2, OH - Attacking the silica-alumina framework of fluidized bed slag: On one hand, it causes the breakage of Si-O-Si and Al-O-Si bonds, releasing active SiO2 and Al2O3. At 20-60℃, the active SiO2 and Al2O3 further react with Ca(OH)2 to generate gelling hydration products, including hydrated calcium silicate and hydrated calcium aluminate. These gelling hydration products can fill the pores of phosphogypsum-based materials, thereby improving density and mechanical strength. Simultaneously, the gelling hydration products can both encapsulate calcium phosphate precipitates, forming a dense structure to prevent phosphorus dissolution, and utilize their nanoporous structure to physically trap CaF2 particles or free phosphorus. - This reduces its migration, thereby solidifying the phosphorus and fluorine in phosphogypsum and further improving the performance of phosphogypsum-based cement retarder; on the other hand, it partially dissolves to generate active silica (H4SiO4) and aluminic acid (Al(OH)4). - This releases more adsorption sites and facilitates ion exchange (for cationic metals, such as Pb). 2+ Cd 2+ ) and surface complexation / coprecipitation (for anionic metals, such as AsO4) 3- The synergistic effect adsorbs harmful metals in phosphogypsum, effectively reducing the content of harmful impurities, thereby improving the performance of phosphogypsum-based cement retarder.

[0074] The phosphogypsum-based cement retarder obtained from the component configurations and corresponding preparation methods of Examples 1-4 exhibits significantly superior performance compared to the phosphogypsum-based cement retarder of Comparative Examples 1-3. Its setting performance and strength are markedly improved. When phosphogypsum modified using the components and corresponding experimental conditions of this invention is applied to cement production, its material properties are fundamentally altered. The process of changing the phosphogypsum crystal structure effectively removes and eliminates harmful impurities contained in the phosphogypsum, thereby changing the material properties of the phosphogypsum. Excessive phosphorus impurities in the retarder will reduce the retarding effect and increase the retarding time. As shown in Table 1, comparing Example 3 and Comparative Example 2, the use of anhydrous sodium sulfate and fly ash in conjunction with fluidized bed slag and calcium hydroxide can promote the solidification of phosphorus in the phosphogypsum, reduce the phosphorus content, thereby shortening the setting time of the cement retarder and improving its compressive and flexural strength. As can be seen from the comparison of Example 3 with Comparative Examples 1 and 3 in Table 1, calcium hydroxide as an activator significantly improves the setting performance and strength of the fluidized bed slag modified phosphogypsum-based cement retarder.

[0075] In summary, the technical solution of this invention uses fluidized bed slag and calcium hydroxide as an activator incorporated into phosphogypsum to modify phosphogypsum-based cement retarder, which has the following beneficial effects:

[0076] (1) Physical ball milling of phosphogypsum exposes soluble phosphorus, soluble fluorine and harmful impurities, but cannot eliminate them. A chemical method is used: sodium dodecylbenzene sulfonate is used as a surfactant, and citric acid and lignin sulfonate work together to convert phosphorus, fluorine and other impurities in phosphogypsum into citrate, removing most of the organic matter and some phosphorus, fluorine and other impurities. At the same time, it is beneficial to the subsequent reaction of fluidized bed slag and calcium hydroxide doping.

[0077] (2) Using calcium hydroxide as an activator, the fluidized bed slag reacts in an alkaline environment to generate gelling hydration products, which can fill the pores of phosphogypsum-based materials, thereby improving density and mechanical strength. At the same time, the gelling hydration products can both encapsulate calcium phosphate precipitates to form a dense structure and prevent phosphorus dissolution, and utilize their nanoporous structure to physically trap CaF2 particles or free F. - This reduces its migration, thereby solidifying the phosphorus and fluorine in phosphogypsum and further improving the performance of phosphogypsum-based cement retarder.

[0078] (3) Under alkaline conditions, the fluidized bed slag partially dissolves to generate active silica and alumina, releasing more adsorption sites. Through ion exchange and surface complexation / coprecipitation, it adsorbs harmful metals in phosphogypsum, effectively reducing the content of harmful impurities and thus improving the performance of phosphogypsum-based cement retarder.

[0079] (4) It effectively integrates fluidized bed slag and phosphogypsum, solving the problem of the difficulty in resource utilization of phosphogypsum and fluidized bed slag. It is environmentally friendly and low-cost, and suitable for large-scale solid waste treatment.

[0080] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A fluidized bed slag modified phosphogypsum-based cement retarder, characterized in that, It is prepared from 10-15 parts of base material and 0.5-3 parts of auxiliary materials. By weight, the base material consists of the following components: 65-71 parts phosphogypsum, 16-28 parts fluidized bed slag, and 10-100 parts calcium hydroxide. By weight, the auxiliary materials consist of the following components: 0.1-5 parts sodium dodecylbenzene sulfonate, 2-10 parts citric acid, 0.2-2 parts lignin sulfonate, 1-18 parts anhydrous sodium sulfate, and 0.1-10 parts fly ash. The preparation method of the fluidized bed slag modified phosphogypsum-based cement retarder includes the following steps: S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and ball mill to obtain a mixture; S2. Add sodium dodecylbenzenesulfonate, citric acid, lignin sulfonate and water to the mixture, stir and carry out hydrothermal reaction to recrystallize phosphogypsum and at the same time complete the reaction and elimination of harmful impurities; the solid-liquid ratio of water to phosphogypsum is 0.2-2. S3. Calcium hydroxide and fluidized bed slag are added to the mixture from step S2 as activators and stirred at 20-60°C to obtain a slurry, thereby enhancing the strength of phosphogypsum. S4. After the slurry solidifies, it is piled up and aged for a predetermined time to obtain the retarder.

2. The fluidized bed slag modified phosphogypsum-based cement retarder according to claim 1, characterized in that, In step S1, the ball-to-material ratio of the ball mill is 2-10:1, the ball mill speed is 100-1000 r / min, and the ball milling time is 1-14 h.

3. The fluidized bed slag modified phosphogypsum-based cement retarder according to claim 1, characterized in that, In step S2, the stirring time is 0.5-5 days.

4. The fluidized bed slag modified phosphogypsum-based cement retarder according to claim 1, characterized in that, In step S3, calcium hydroxide is first added and stirred for 2-10 minutes to make the mixture alkaline, and then boiling slag is added and stirred for 2-200 minutes.

5. The fluidized bed slag modified phosphogypsum-based cement retarder according to claim 4, characterized in that, In step S3, stirring is carried out under normal pressure, and calcium hydroxide is added to make the pH of the mixture ≥ 10.

6. The fluidized bed slag modified phosphogypsum-based cement retarder according to claim 1, characterized in that, In step S4, the stacking and aging process is carried out at a temperature of 15-30℃ for 2-20 days.

7. The fluidized bed slag modified phosphogypsum-based cement retarder according to claim 1, characterized in that, In step S4, granulation is carried out before stacking and aging. During the stacking and aging period, water is sprayed 3-5 times to make the moisture content of the solid particles 5-20%. After the stacking and aging is completed, the particles are self-heated and air-dried.

8. The fluidized bed slag modified phosphogypsum-based cement retarder according to claim 7, characterized in that, The granulation process uses a disc granulator to control the particle size to 15-30mm.

9. The fluidized bed slag modified phosphogypsum-based cement retarder according to any one of claims 1-8, characterized in that, The fluidized bed slag has a particle size of 1-6 mm and a density of 800-900 kg / m³. 3 The main chemical components of the fluidized bed slag are SiO2 and Al2O3, with the content of SiO2 and Al2O3 accounting for 51-80 wt%.

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