Preparation method of low-cost high-dosage phosphogypsum-based aggregate

Abstract

The invention relates to a preparation method of a low-cost high-dosage phosphogypsum-based aggregate, and belongs to the technical field of artificial aggregate building materials. The invention aims to solve the problems of low mixing amount, high cost and low strength of the existing ardealite-based aggregate. The preparation method comprises the following steps: mixing ardealite powder, waste residue powder, namely S95 granulated blast-furnace slag powder and red mud, and inorganic cementing materials, namely PO42.5 cement and sulphoaluminate cement in proportion, granulating by a granulator, and curing to prepare ardealite-based aggregate with the particle size of 4.75-19 mm; the method is low in cost and large in phosphogypsum mixing amount, the prepared aggregate is high in strength, when the aggregate is used in concrete, consumption of natural aggregate and the concrete preparation cost are remarkably reduced, the environmental problem caused by accumulation of a large amount of phosphogypsum is effectively solved, and the method has important significance on environmental protection and economic development; the process flow is simple, industrial production is easy, a new thought is provided for high-value utilization of ardealite resources, and the method has a profound influence on promotion of circular economy and sustainable development.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a method for preparing a low-cost and high-dosage phosphogypsum-based aggregate. Background Art

[0002] Phosphogypsum is an important by-product in the wet process of preparing phosphoric acid. Its main chemical component is CaSO4·2H2O, accompanied by various impurities such as free water, organic matter, heavy metals, rare earth elements, and possible radioactive elements. The complexity of phosphogypsum production results in it containing a variety of soluble (such as residual sulfuric acid, nitric acid, soluble phosphates, potassium salts, sodium salts, fluorides, etc.) and insoluble impurities (such as , , and other metal ions, as well as insoluble phosphates Ca3(PO4)2 and fluorides CaF2, etc.).

[0003] According to statistics, the world produces nearly 300 million tons of phosphogypsum each year, and it continues to increase at a rate of about 200 million tons per year. Taking the United States and China as examples, the United States produces about 60 million tons each year, while China produces about 80 million tons each year. The global cumulative emissions of phosphogypsum have reached about 6 billion tons, and it is expected that its total stockpile will increase to twice the current level in the next 20 to 40 years. Therefore, the management and comprehensive utilization of phosphogypsum has become one of the most severe challenges facing the phosphate industry. The storage of phosphogypsum without any pretreatment not only occupies a large amount of land resources, but also may cause serious pollution to the soil, water and atmospheric environment.

[0004] In order to deal with the accumulation of phosphogypsum, countries around the world have explored a variety of ways to utilize it, such as using it as a cement retarder, road filling material, cementitious material, gypsum board, building gypsum, sulfuric acid preparation and gypsum bricks, etc. However, the existing comprehensive utilization of phosphogypsum generally has problems such as high impurity content, low product added value, and high impurity removal costs, resulting in unbalanced product benefits.

[0005] In the field of preparation of phosphogypsum-based aggregates, although there have been some successful attempts, there are still many deficiencies. For example, CN110451864A discloses a phosphogypsum unfired ceramsite light aggregate and a preparation method thereof, the phosphogypsum unfired ceramsite light aggregate comprising a mixture of phosphogypsum, mineral powder, cement and water, the weight percentages of each raw material in the mixture are: phosphogypsum 80-90%, mineral powder 3.3-10%, cement 6.5-10%, the weight of the water is 17% of the total weight of the mixture; the present invention also provides a method for preparing phosphogypsum unfired ceramsite light aggregate, with phosphogypsum as the main material, cement as the alkaline activator, and mineral powder as the active material. The material is prepared through modification, granulation, curing, crushing, screening and other processes. The phosphogypsum unfired ceramsite lightweight aggregate produced by the invention can be widely used in highway roadbed materials, C40 and below grade concrete, cement concrete blocks and other products, and can consume a large amount of phosphogypsum inventory, turning waste into treasure, which is of great significance for saving resources, achieving optimal resource allocation and sustainable development. Although the method realizes the reuse of phosphogypsum, it needs to carry out modification pretreatment and crushing treatment after granulation of the original phosphogypsum, which not only increases energy consumption, but also may cause secondary pollution to the environment.

[0006] Another example is CN113354376A, which discloses a phosphogypsum-based aggregate and a preparation method thereof, belonging to the technical field of road construction materials; the phosphogypsum-based aggregate is prepared by mixing A powder and B solution into balls; the A powder comprises: 50%-80% phosphogypsum, 15%-45% waste slag powder, and 3%-6% alkaline activator; the B solution comprises 1%-2% sodium hexametaphosphate, 0.1%-0.2% cellulose ether, and the rest is water; the preparation method comprises: 1) mixing phosphogypsum, slag powder, and alkaline activator to obtain A powder; 2) mixing sodium hexametaphosphate, cellulose ether, and cellulose ether; 1) adding phosphogypsum ether into water to dissolve to obtain solution B; 2) putting the powder A obtained in step 1) into a ball-forming machine, and continuously spraying solution B into the ball-forming machine to mix with the powder A to form balls to obtain aggregate; 3) curing the aggregate by immersing it in water to obtain the phosphogypsum-based aggregate; the present invention achieves a short curing period and high strength of the phosphogypsum-based aggregate; the method prepares the phosphogypsum-based aggregate by using phosphogypsum, slag powder and alkaline activator, and improves its stability by spraying water-soluble silicone on the surface of the aggregate; however, the method requires high cost, and the utilization rate of solid waste needs to be further improved.

[0007] Although the above research demonstrates the potential utilization value of phosphogypsum in the field of new building materials, the phosphogypsum-based aggregates prepared by existing technologies generally have problems such as low dosage, high cost, and low strength, making it difficult to promote and apply them on a large scale. Therefore, developing a method for preparing phosphogypsum-based aggregates with low cost, high dosage, and high strength is of great significance for solving the problem of phosphogypsum accumulation, reducing the consumption of natural aggregates, promoting resource recycling, and environmental protection and economic development. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for preparing a low-cost and high-dosage phosphogypsum-based aggregate, thereby solving the technical problems of low dosage, high cost and low strength that are common in the current field of phosphogypsum-based aggregate preparation.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is a method for preparing a low-cost and high-dosage phosphogypsum-based aggregate, comprising the following steps: Step 1: Put the phosphogypsum into a ball mill and grind it to obtain phosphogypsum powder; Step 2: weigh the three raw materials of phosphogypsum powder, waste slag powder and inorganic gelling material in proportion, and mix them evenly to obtain raw materials for preparing phosphogypsum-based aggregate; Step 3: Put the raw material into the granulator, adjust the angle and speed of the granulator and spray an appropriate amount of water, continue to sprinkle the raw material and spray water until the particle size of the agglomerated particles reaches more than 4.75 mm, and the primary phosphogypsum-based aggregate is obtained; Step 4: Place the primary phosphogypsum-based aggregate into a water-retaining bag for solidification; Step 5: Curing the solidified primary phosphogypsum-based aggregate to obtain a finished phosphogypsum-based aggregate.

[0010] In a preferred embodiment, the phosphogypsum in Step 1 is original phosphogypsum.

[0011] In a preferred embodiment, the raw materials of the phosphogypsum-based aggregate raw material in Step 2 include phosphogypsum powder, waste slag powder, and inorganic gelling materials, in which the phosphogypsum powder accounts for 80% to 90% by weight, the waste slag powder accounts for 0% to 15%, and the inorganic gelling materials accounts for 5% to 20%.

[0012] In a preferred embodiment, the waste slag powder in Step 2 is one of S95 granulated blast furnace slag powder and red mud, or a mixture of the two in a weight ratio.

[0013] In a preferred solution, the inorganic cementitious material in Step 2 is one of P•O42.5 cement and sulphoaluminate cement, or a mixture of the two in a weight ratio.

[0014] In a preferred embodiment, the granulator in Step 3 is a disc granulator with a diameter of 1 to 1.5 m. Before granulation, the angle of the granulator is adjusted to 45 to 55° and the rotation speed is 8 to 12 r / min.

[0015] In a preferred embodiment, the amount of water sprayed into the raw material in Step 3 is 10% to 20% of the weight ratio of the raw material.

[0016] In a preferred embodiment, the curing of the primary phosphogypsum-based aggregate in Step 4 is to place the primary phosphogypsum-based aggregate in a water-retaining bag and naturally stack it for 24 hours before solidifying.

[0017] In a preferred embodiment, the curing in Step 5 is water sprinkling curing or immersion curing for 28 days, and the particle size of the obtained phosphogypsum-based aggregate product is 4.75~19mm.

[0018] In the preferred embodiment, the phosphogypsum-based aggregate product obtained in Step 5 also has the following performance characteristics: cylinder pressure strength ≥6.47MPa, bulk density ≥933kg / m³, 1h water absorption ≤10%, and softening coefficient ≥0.80.

[0019] The present invention provides a method for preparing a low-cost and high-dosage phosphogypsum-based aggregate, which has the following beneficial effects: 1. The present invention effectively solves the problem of large-scale accumulation and difficulty in handling of phosphogypsum, and realizes the rational use of resources. Compared with the traditional method, the phosphogypsum-based aggregate prepared by this method has higher strength, lower cost, and higher dosage. In addition, by preparing aggregate from industrial waste, environmental pollution is reduced, and ecological protection is achieved; 2. The method of the present invention significantly increases the content of phosphogypsum in aggregate, up to 80% to 90%, reduces the consumption of natural aggregate and reduces costs; 3. The present invention realizes low-cost preparation of phosphogypsum-based aggregate by using waste slag powder and common inorganic gelling materials in combination with a reasonable preparation process; 4. The present invention utilizes industrial wastes such as phosphogypsum, slag and red mud, effectively solves the environmental problems caused by the large-scale accumulation of phosphogypsum, realizes the recycling of resources, and significantly reduces the pollution of these wastes to the environment; 5. The present invention improves the quality and performance of aggregate by optimizing the parameters and curing conditions of the granulator; 6. The phosphogypsum-based aggregate prepared by the present invention has low cost and can be used in concrete, thereby reducing the consumption of natural aggregate and the preparation cost of concrete; 7. The phosphogypsum used in the present invention is original phosphogypsum, which only needs to be ground and does not require other pretreatment, thereby reducing energy consumption and equipment corrosion; 8. The present invention uses 80% or more phosphogypsum as the main raw material through natural hydration and processing to produce a new type of aggregate with no burning, low energy consumption, low cost, and no pollution to the environment; 9. The present invention optimizes the preparation process and parameters to obtain phosphogypsum-based aggregates with high strength and good performance, which meet the requirements of national standards; 10. The aggregate prepared by the present invention has low cost and excellent performance, has broad prospects for promotion and application, and is of great significance to environmental protection and economic development. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and implementation examples: Figure 1 The phosphogypsum-based aggregate finished product prepared by the present invention; Figure 2 XRD patterns of phosphogypsum-based aggregates 7d and 28d prepared by the present invention; Figure 3 This is a SEM image of the phosphogypsum-based aggregate 7d prepared by the present invention at 50 times magnification; Figure 4 This is a SEM image of the phosphogypsum-based aggregate 28d prepared by the present invention at 50 times magnification; Figure 5 This is a SEM image of the phosphogypsum-based aggregate 7d prepared by the present invention, magnified 500 times; Figure 6 This is a SEM image of the phosphogypsum-based aggregate 28d prepared by the present invention, magnified 500 times; Figure 7 This is a SEM image of the phosphogypsum-based aggregate 7d prepared by the present invention, magnified 20,000 times; Figure 8 This is a SEM image of the phosphogypsum-based aggregate 28d prepared in the present invention, magnified 20,000 times. DETAILED DESCRIPTION

[0021] The embodiments of the present invention are further described below in conjunction with the accompanying drawings: Example 1 A method for preparing a low-cost, high-dosage phosphogypsum-based aggregate comprises the following steps: Step 1: Put the phosphogypsum into a ball mill and grind it to obtain phosphogypsum powder; Step 2: weigh the three raw materials of phosphogypsum powder, waste slag powder and inorganic gelling material in proportion, and mix them evenly to obtain raw materials for preparing phosphogypsum-based aggregate; Step 3: Put the raw material into the granulator, adjust the angle and speed of the granulator and spray an appropriate amount of water, continue to sprinkle the raw material and spray water until the particle size of the agglomerated particles reaches more than 4.75 mm, and the primary phosphogypsum-based aggregate is obtained; Step 4: Place the primary phosphogypsum-based aggregate into a water-retaining bag for solidification; Step 5: Curing the solidified primary phosphogypsum-based aggregate to obtain a finished phosphogypsum-based aggregate.

[0022] In this embodiment, the phosphogypsum in Step 1 is original phosphogypsum.

[0023] Furthermore, the raw materials of the phosphogypsum-based aggregate raw materials in Step 2 include phosphogypsum powder, waste slag powder, and inorganic gelling materials, in which the phosphogypsum powder accounts for 80% to 90% by weight, the waste slag powder accounts for 0% to 15%, and the inorganic gelling materials accounts for 5% to 20%.

[0024] Furthermore, the waste slag powder in Step 2 is one of S95 granulated blast furnace slag powder and red mud, or a mixture of the two in a weight ratio.

[0025] Furthermore, the inorganic cementitious material in Step 2 is one of P•O42.5 cement and sulphoaluminate cement, or a mixture of the two in a weight ratio.

[0026] Furthermore, the granulator in Step 3 is a disc granulator with a diameter of 1-1.5 m. Before granulation, the angle of the granulator is adjusted to 45-55° and the rotation speed is 8-12 r / min.

[0027] Furthermore, the amount of water sprayed into the raw material in Step 3 is 10% to 20% of the weight ratio of the raw material.

[0028] Furthermore, the curing of the primary phosphogypsum-based aggregate in Step 4 is to place the primary phosphogypsum-based aggregate in a water-retaining bag and naturally stack it for 24 hours before solidifying.

[0029] Furthermore, the curing in Step 5 is water sprinkling curing or immersion curing for 28 days, and the particle size of the obtained phosphogypsum-based aggregate product is 4.75~19mm.

[0030] Furthermore, the phosphogypsum-based aggregate product prepared in Step 5 also has the following performance characteristics: cylinder pressure strength ≥6.47MPa, bulk density ≥933kg / m³, 1h water absorption ≤10%, and softening coefficient ≥0.80.

[0031] Example 2 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 10% P•O42.5 cement, 10% sulphoaluminate cement, and 20% water; the curing method is watering curing.

[0032] Example 3 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 15% P•O42.5 cement, 5% sulphoaluminate cement, and 20% water; the curing method is watering curing.

[0033] The raw material ingredients of the phosphogypsum-based aggregates of Examples 1 to 3 are shown in Table 1: Table 1 Ingredients of Examples 1 to 3

[0034] Example 4 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 5% P•O42.5 cement, 15% S95 granulated blast furnace slag powder, and 20% water; the curing method is water sprinkling curing.

[0035] Example 5 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 10% P•O42.5 cement, 10% S95 granulated blast furnace slag powder, and 20% water; the curing method is water sprinkling curing.

[0036] Example 6 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 15% P•O42.5 cement, 5% S95 granulated blast furnace slag powder, and 20% water; the curing method is water sprinkling curing.

[0037] The raw material ingredients of the phosphogypsum-based aggregates of Examples 4 to 6 are shown in Table 2: Table 2 Ingredients of Examples 4 to 6

[0038] Example 7 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, the raw material includes, by weight: 80% phosphogypsum, 5% sulphoaluminate cement, 15% S95 granulated blast furnace slag powder, and 20% water; the curing method is water sprinkling curing.

[0039] Example 8 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 10% sulphoaluminate cement, 10% S95 granulated blast furnace slag powder, and 20% water; the curing method is water sprinkling curing.

[0040] Example 9 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, the raw material includes, by weight: 80% phosphogypsum, 15% sulphoaluminate cement, 5% S95 granulated blast furnace slag powder, and 20% water; the curing method is water sprinkling curing.

[0041] The raw material ingredients of the phosphogypsum-based aggregates of Examples 7 to 9 are shown in Table 3: Table 3 Ingredients of Examples 7 to 9

[0042] Example 10 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 85% phosphogypsum, 5% P•O42.5 cement, 10% S95 granulated blast furnace slag powder, and 20% water; the curing method is water sprinkling curing.

[0043] Embodiment 11 In another preferred embodiment, on the basis of the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, the raw material includes, by weight: 80% phosphogypsum, 5% P•O42.5 cement, 10% S95 granulated blast furnace slag powder, 5% red mud, and 20% water; and the curing method is watering curing.

[0044] Example 12 In another preferred embodiment, on the basis of the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 5% P•O42.5 cement, 5% S95 granulated blast furnace slag powder, 10% red mud, and 20% water; the curing method is water sprinkling curing.

[0045] The raw material ingredients of the phosphogypsum-based aggregates of Examples 10 to 12 are shown in Table 4: Table 4 Ingredients of Examples 10 to 12

[0046] Example 13 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 20% P•O42.5 cement, and 20% water; the curing method is watering curing.

[0047] Embodiment 14 In another preferred embodiment, based on the above-mentioned embodiment 1, when preparing the raw material of phosphogypsum-based aggregate, it includes, by weight: 80% phosphogypsum, 20% sulphoaluminate cement, and 20% water; the curing method is watering curing.

[0048] The raw material ingredients of the phosphogypsum-based aggregate of Examples 13-14 are shown in Table 5: Table 5 Ingredients of Examples 13-14

[0049] The performance of the phosphogypsum-based aggregates obtained in Examples 1 to 14 above was tested, and the results are shown in Table 6. The performance of the aggregates was tested in accordance with the requirements of the national standard GB17431.2-2010-T "Lightweight aggregates and their test methods Part 2: Lightweight aggregate test methods".

[0050] Table 6 Aggregate performance test results obtained in Examples 1 to 14

[0051] By comparing Examples 1-3, 4-6, 7-9, 10-12, and 13-14, it can be seen that when the phosphogypsum content (80%) remains unchanged, the aggregate strength first increases and then decreases with the increase of P•O42.5 cement content and the decrease of sulphoaluminate cement. When the P•O42.5 cement content is 10% and the sulphoaluminate cement content is 10%, the maximum aggregate strength is 7.73 MPa. When the phosphogypsum content (80%) remains unchanged, the aggregate strength increases with the increase of P•O42.5 cement content. When the P•O4 When the 2.5 cement content is 15% and the S95 slag powder content is 5%, the maximum aggregate strength is 8.04MPa; and it is found that the mixture of sulphoaluminate cement and S95 slag powder alone cannot improve the aggregate strength very well; at the same time, when the P•O42.5 cement content remains unchanged, adding a small amount of red mud can improve the aggregate strength. When the P•O42.5 cement content is 5%, the S95 slag powder content is 10%, and the red mud content is 5%, the maximum aggregate strength is 6.77MPa; and the above results all meet the requirements of the national standard GB 17431.2-2010-T "Lightweight aggregate and its test methods Part 1: Lightweight aggregate" for grade 900 artificial aggregate, 1h water absorption rate and softening coefficient.

[0052] By comparing Examples 1-3, 4-6, 7-9, 10-12, and 13-14, it can be seen that with the increase in the amount of the two cements, the preparation cost of the phosphogypsum aggregate is also increasing. Although the preparation cost of the examples adding sulphoaluminate cement and red mud is slightly higher, the cost is less than 100 yuan, and it can be widely used in concrete, so that the waste phosphogypsum is recycled, the consumption of natural aggregates and the preparation cost of concrete are reduced, and the problem of large-scale accumulation of phosphogypsum is solved, which is of great significance to environmental protection and economic development.

[0053] By adopting the above method, after repeated tests and demonstrations, the phosphogypsum-based aggregate prepared in this embodiment has various performance indicators that meet the national standard GB / T17431.2-2010 "Light Aggregate Performance Standard"; the cylinder compressive strength of the phosphogypsum-based aggregate is 8.04MPa, and the bulk density is 960kg / m 3 The water absorption rate in 1h is 8.1% and the softening coefficient is 0.88. Figure 1 ,from Figure 1It can be seen that the surface of the phosphogypsum-based aggregate is smooth and the particles are uniform.

[0054] Figure 2 Figure 3 is the XRD spectrum of phosphogypsum-based aggregate at 7d and 28d. The characteristic peaks of ettringite and CaSO4·2H2O can be observed from the spectrum, respectively. The spectrum at 7 days and 28 days does not change much, and calcium sulfate dihydrate and ettringite (AFt) are detected in both, which is consistent with the guessed volcanic ash reaction products of slag, indicating that the slag contained in the aggregate has participated in the reaction after 7 days of water curing. The type of hydration product at 28 days is the same as that at 7 days. The reason for the increase in aggregate strength at 28 days may be that the ettringite generated in the early stage wrapped the cement particles and hindered the cement hydration. With the growth of ettringite crystals, the ettringite on the surface of cement particles expanded and cracked, and the cement and slag continued to react. The ettringite and hydrated calcium silicate gel increased, tightly wrapped the unreacted gypsum, reduced the internal pores, and improved the density of the aggregate. It is worth noting that no characteristic peak of Ca(OH)2 was found in the spectrum. Ca(OH)2 is a product of hydration of cementitious materials and also a reactant for the formation of calcium sulfonate. Excess phosphogypsum can provide sufficient calcium sulfate for the system reaction, and Ca(OH)2 is further consumed during the hydration reaction.

[0055] The above analysis focuses on the products of aggregate formation. The following analysis will focus on the microscopic morphology of aggregate. Figure 3 , Figure 4 The SEM images of the phosphogypsum-based aggregate at 7d and 28d. The microstructure of the aggregate detected by SEM can be seen when magnified 50 times. The microstructure of the aggregate is mostly dense and integral. Figure 3 Compared with 28-day aggregate Figure 4 There are many holes, which can be seen under 500 times magnification. Figure 5 Some areas are already somewhat dense, but have not yet developed into a dense whole. There are many attachments on the surface. Figure 6 The dense entity has obvious development and growth, and the surface attachments are reduced; continue to magnify to 20,000 times, you can see that at high magnification Figure 7 , Figure 8As shown in the figure, the hydrated part of the aggregate is arranged tightly and very dense, without defects such as microcracks. The edge may be part of the morphology of calcium sulfonate. The formed product is also relatively thick and dense, with certain microcracks and pores, and the number of needle-shaped hydrated calcium silicate gel is small. Its reaction mechanism is similar to the hydration process of concrete. Cement and mineral powder are used as cementitious materials in the aggregate. Under the action of water, hydration produces hydration products such as Ca(OH)2, and the alkaline environment produced stimulates the hydration of slag under the action of calcium sulfate provided by phosphogypsum, forming more calcium sulfonate and CSH gel. Phosphogypsum not only acts as a filler in the aggregate, but also can participate in the hydration reaction as a reactant. With the generation of hydration products such as CSH gel and calcium sulfonate, the aggregate becomes increasingly dense, the strength and density increase, and the water absorption rate decreases.

[0056] In the preferred solution, the phosphogypsum in Step 1 is original phosphogypsum; the above settings ensure the purity and consistency of the raw materials, reduce the pretreatment steps, and improve production efficiency. In Step 2, the conversion of phosphogypsum is effectively promoted through precisely controlled chemical reaction conditions, laying a solid foundation for subsequent purification and utilization.

[0057] In the preferred scheme, the raw materials of the phosphogypsum-based aggregate raw material in Step 2 include phosphogypsum powder, waste slag powder, and inorganic cementitious materials, of which phosphogypsum powder accounts for 80% to 90% by weight, waste slag powder accounts for 0% to 15%, and inorganic cementitious materials account for 5% to 20%; the above settings ensure the efficient utilization of phosphogypsum and the resource utilization of waste. At the same time, the appropriate addition of inorganic cementitious materials enhances the strength and durability of the aggregate, laying a solid foundation for the subsequent preparation of building materials.

[0058] In a preferred embodiment, the waste slag powder in Step 2 is one of S95 granulated blast furnace slag powder and red mud, or a mixture of the two in a weight ratio; the above arrangement can significantly improve the strength and durability of the material; wherein, S95 granulated blast furnace slag powder strengthens the concrete matrix with its excellent activity and filling properties; red mud improves the material's impermeability and durability through its unique chemical composition, and the two work synergistically to achieve a better effect.

[0059] In a preferred embodiment, the inorganic cementitious material in Step 2 is one of P•O42.5 cement and sulphoaluminate cement, or a mixture of the two in a weight ratio; the above configuration, It can not only improve the early strength and durability of the material, but also effectively adjust the setting time to meet different construction needs; at the same time, reasonable control of the mixing ratio can further optimize the material performance and ensure the quality of the project.

[0060] In the preferred embodiment, the granulator in Step 3 is a disc granulator with a diameter of 1 to 1.5 m. Before granulation, the angle of the granulator is adjusted to 45 to 55° and the rotation speed is 8 to 12 r / min. The above settings can ensure that the material is evenly distributed in the disc, effectively promote the formation and growth of particles, reduce material adhesion and breakage, and improve granulation efficiency and finished product quality.

[0061] In the preferred solution, the amount of water sprayed into the raw material in Step 3 is 10% to 20% of the weight ratio of the raw material; the above setting can effectively adjust the humidity of the raw material, promote mixing uniformity, and improve the quality of particle forming in the subsequent processing; at the same time, the addition of water within this range can also effectively suppress dust flying and improve the production environment.

[0062] In the preferred scheme, the curing of the primary phosphogypsum-based aggregate in Step 4 is to place the primary phosphogypsum-based aggregate in a water-retaining bag and naturally stack it for 24 hours before solidifying; the above setting can ensure that the phosphogypsum-based aggregate fully absorbs moisture, promotes internal chemical reactions, and effectively enhances its structural stability and strength; then, the cured aggregate is taken out and necessary screening and crushing are carried out to meet the specific requirements of subsequent building materials applications.

[0063] In the preferred scheme, the curing in Step 5 is water sprinkling curing or immersion curing for 28 days, and the particle size of the finished phosphogypsum-based aggregate is 4.75~19mm; the above settings ensure that the structure of the phosphogypsum-based aggregate is stable during the full hydration process and achieves ideal strength and durability; at the same time, the precise control of the particle size of the finished product is conducive to the subsequent uniform distribution and performance of the building materials.

[0064] In summary, the present invention proposes a method for preparing phosphogypsum-based aggregate with low cost and high dosage, which solves the technical problems of low dosage, high cost and low strength that are common in the current field of phosphogypsum-based aggregate preparation. Compared with the traditional method, the present method adopts 80% to 90% of phosphogypsum powder as the main raw material, which greatly increases the dosage of phosphogypsum and effectively solves the problem of large-scale accumulation of phosphogypsum and environmental pollution. In terms of raw material selection, in addition to phosphogypsum powder, waste slag powder (such as S95 granulated blast furnace slag powder and red mud) and inorganic cementitious materials (such as P•O42.5 cement and sulphoaluminate cement) are also added. This diversified raw material combination not only reduces the cost, but also improves the performance of the aggregate. It uses a disc granulator to granulate, and strictly controls the angle, rotation speed of the granulator and the amount of water added to the raw material to ensure the particle size and quality of the aggregate particles. This is a fine control process that is rarely involved in traditional methods. The method of natural stacking and curing with water-retaining bags and sprinkling or immersion curing simplifies the process flow, reduces energy consumption, and ensures the strength of the aggregate. The invention realizes the preparation of low-cost and high-performance phosphogypsum-based aggregate by utilizing high-dosage phosphogypsum and combining the composite effect of waste slag powder and inorganic cementitious materials, which is a major innovation in the traditional phosphogypsum treatment method; in the granulation process, by finely adjusting the angle, rotation speed and water addition amount of the granulator, aggregate particles with uniform particle size and stable quality are obtained, and this process optimization significantly improves the quality and consistency of the product; the method not only solves the problems of accumulation and environmental pollution of phosphogypsum, but also improves economic benefits through the secondary utilization of solid waste, achieving a win-win situation of environmental protection and economy; through scientific solidification and maintenance methods, the strength and stability of phosphogypsum-based aggregate are guaranteed, so that it can be applied to fields such as concrete, broadens the application scope of phosphogypsum, and provides new ideas and directions for the resource utilization of phosphogypsum; in the future, with the continuous advancement of technology and continuous optimization of technology, the production cost of phosphogypsum-based aggregate is expected to be further reduced, and the performance will be more superior, injecting more green power into the building materials industry and promoting the sustainable development of the industry.

Claims

1. A method for preparing a low-cost and high-dosage phosphogypsum-based aggregate, characterized in that: The preparation method comprises the following steps: Step 1: Put the phosphogypsum into a ball mill and grind it to obtain phosphogypsum powder; Step 2: weigh the three raw materials of phosphogypsum powder, waste slag powder and inorganic gelling material in proportion, and mix them evenly to obtain raw materials for preparing phosphogypsum-based aggregate; Step 3: Put the raw material into the granulator, adjust the angle and speed of the granulator and spray an appropriate amount of water, continue to sprinkle the raw material and spray water until the particle size of the agglomerated particles reaches more than 4.75 mm, and the primary phosphogypsum-based aggregate is obtained; Step 4: Place the primary phosphogypsum-based aggregate into a water-retaining bag for solidification; Step 5: Curing the solidified primary phosphogypsum-based aggregate to obtain a finished phosphogypsum-based aggregate.

2. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 1, characterized in that: The phosphogypsum in Step 1 is original phosphogypsum.

3. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 1, characterized in that: The raw materials of the phosphogypsum-based aggregate raw materials in Step 2 include phosphogypsum powder, waste slag powder, and inorganic cementitious materials, of which the phosphogypsum powder accounts for 80% to 90% by weight, the waste slag powder accounts for 0% to 15%, and the inorganic cementitious materials accounts for 5% to 20%.

4. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 3, characterized in that: The waste slag powder in Step 2 is one of S95 granulated blast furnace slag powder and red mud, or a mixture of the two in a weight ratio.

5. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 4, characterized in that: The inorganic cementitious material in Step 2 is one of P·O42.5 cement and sulphoaluminate cement, or a mixture of the two in a weight ratio.

6. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 1, characterized in that: The granulator in Step 3 is a disc granulator with a diameter of 1-1.5 m. Before granulation, the angle of the granulator is adjusted to 45-55° and the rotation speed is 8-12 r / min.

7. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 6, characterized in that: The amount of water sprayed into the raw material in Step 3 is 10% to 20% of the weight ratio of the raw material.

8. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 1, characterized in that: The curing of the primary phosphogypsum-based aggregate in the Step 4 is to place the primary phosphogypsum-based aggregate in a water-retaining bag and naturally stack it for 24 hours before solidifying.

9. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 1, characterized in that: The curing in Step 5 is water sprinkling curing or immersion curing for 28 days, and the particle size of the finished phosphogypsum-based aggregate is 4.75-19 mm.

10. The method for preparing a low-cost and high-dosage phosphogypsum-based aggregate according to claim 9, characterized in that: The phosphogypsum-based aggregate product prepared in Step 5 also has the following performance characteristics: cylinder pressure strength ≥6.47MPa, bulk density ≥933kg / m³, 1h water absorption ≤10%, and softening coefficient ≥0.80.

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