Phosphogypsum and harmless and resourceful treatment method and application thereof

Abstract

The present application relates to a kind of phosphogypsum and its harmless and resourceful processing method and application, comprising the following steps: taking phosphogypsum raw material and carrying out ball milling screening, obtain phosphogypsum A;Phosphogypsum A is calcined at 200~240 ℃ for the first time, obtain phosphogypsum B;Phosphogypsum B is calcined at 120~140 ℃ for the second time, obtain phosphogypsum C;Phosphogypsum C is mixed into neutralizing agent, obtain phosphogypsum D.The present application effectively reduces the content of soluble phosphorus and soluble fluorine by first calcination, then increases the content of calcium sulfate hemihydrate in phosphogypsum by second calcination, realizes the harmless treatment of phosphogypsum and stimulates the cementitious properties of phosphogypsum, neutralizes with neutralizing agent, reduces the corrosivity of phosphogypsum, realizes the resource of phosphogypsum.

Description

Technical Field

[0001] This invention belongs to the field of road engineering and relates to a phosphogypsum and its harmless and resource-based treatment methods and applications. Background Technology

[0002] Phosphogypsum is a byproduct of the wet process for producing phosphoric acid. Its main component is calcium sulfate dihydrate, with a content ranging from 70% to 90%, and it contains pollutants primarily composed of soluble phosphorus and fluorine. Statistics show that in 2021, the annual production of phosphogypsum was approximately 80 million tons, but its utilization rate was only 45.6%, with stockpiling remaining the primary disposal method. The high content of soluble pollutants and poor gelling properties of phosphogypsum are the main reasons for its low utilization rate. Adopting appropriate methods to render phosphogypsum harmless and stimulating its gelling properties to achieve resource recovery is beneficial for improving its utilization rate, protecting the ecological environment, and achieving sustainable development.

[0003] Currently, the main methods for the harmless treatment of phosphogypsum include heat treatment, neutralization, and washing. Heat treatment, through calcination at 800℃, can remove soluble phosphorus and fluorine from phosphogypsum, but the high temperature and energy consumption, along with the production of anhydrous calcium sulfate, cause the phosphogypsum to lose its gelling properties, hindering its resource utilization. From the perspective of activating the gelling activity of phosphogypsum, the calcination temperature needs to be controlled between 150℃ and 160℃ to convert the dihydrate calcium sulfate in the phosphogypsum into hemihydrate calcium phosphate. However, under this temperature condition, soluble pollutants cannot be effectively removed, leaving the phosphogypsum still strongly acidic. Therefore, neither of the two heat treatment methods can simultaneously remove pollutants and activate the gelling properties of phosphogypsum. Neutralization, by adding reagents that can chemically react with impurities, converts soluble impurities into insoluble impurities, effectively reducing soluble impurities, but it also cannot activate the gelling properties of phosphogypsum.

[0004] In the utilization of phosphogypsum, the performance of phosphogypsum building materials is affected by their preparation process. The performance of phosphogypsum building materials and the determination of production processes are often studied by molding specimens using the vibration method. However, this method requires a water-cement ratio greater than 50% to ensure sufficient hydration between phosphogypsum and water. During the curing process, excess water molecules that do not participate in the reaction will "escape" into the external environment, increasing the porosity of the phosphogypsum building material and reducing its mechanical properties. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a method and application for the harmless and resource-based treatment of phosphogypsum, solving the technical problem in the prior art that the treatment of phosphogypsum is difficult to simultaneously remove soluble pollutants and activate the gelling activity of phosphogypsum.

[0006] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0007] In a first aspect, the present invention provides a method for the harmless and resource-based treatment of phosphogypsum based on a physicochemical approach, comprising the following steps:

[0008] The phosphogypsum raw material was ball-milled and sieved to obtain phosphogypsum A;

[0009] Phosphogypsum A was calcined for the first time at 200–240°C to obtain phosphogypsum B.

[0010] Phosphogypsum B was calcined a second time at 120–140°C to obtain phosphogypsum C.

[0011] A neutralizing agent is added to phosphogypsum C to obtain phosphogypsum D.

[0012] Preferably, ball milling and sieving involves first ball milling the phosphogypsum raw material using a ball mill, then passing it through a 0.075mm sieve to collect the sieved material.

[0013] Preferably, the first calcination time is 12 to 20 minutes.

[0014] In a further preferred embodiment, the first calcination is carried out at 220°C for 20 minutes.

[0015] Preferably, the second calcination time is 1 to 4 hours.

[0016] In a further preferred embodiment, the second calcination is carried out at 140°C for 2 hours.

[0017] Preferably, the neutralizing agent is calcium oxide.

[0018] Preferably, the amount of neutralizing agent is 0.4 to 0.6% of the mass of phosphogypsum C.

[0019] Secondly, the present invention provides a phosphogypsum prepared by the above-mentioned harmless and resource-based treatment method, wherein the phosphogypsum contains 80-94% hemihydrate calcium sulfate, 1-17% dihydrate calcium sulfate, and 0-10% anhydrous calcium sulfate.

[0020] Thirdly, the present invention provides an application of the above-mentioned phosphogypsum in the preparation of phosphogypsum blocks, wherein the phosphogypsum blocks are prepared by adding water to the phosphogypsum and stirring evenly to obtain a blank, and the blank is then pressed, shaped and cured.

[0021] Preferably, the water content in the billet is 17-20%; during pressing, the compaction density is 1.9-2.2 g / cm³. 3 Maintenance for 7 days or more.

[0022] Compared with the prior art, the beneficial effects of the present invention include:

[0023] (1) In view of the shortcomings in the harmless treatment, the present invention provides a harmless and resource-based treatment method for phosphogypsum based on physical-chemical methods. First, the content of soluble phosphorus and soluble fluorine is effectively reduced by the first calcination. Then, the content of calcium sulfate hemihydrate in phosphogypsum is increased by the second calcination, which stimulates the gelling properties of phosphogypsum. Furthermore, a more economical neutralizing agent is used to neutralize the phosphogypsum, thereby reducing its corrosiveness and realizing the resource utilization of phosphogypsum.

[0024] (2) In view of the defects of specimens formed by vibration method, the present invention adopts static pressure molding in the preparation of phosphogypsum blocks, which not only ensures that the hydration reaction of phosphogypsum is fully completed, but also avoids the formation of pores due to excessive water consumption, thus significantly improving the mechanical properties of phosphogypsum blocks.

[0025] In summary, this invention addresses the problem of contaminants in phosphogypsum using a physicochemical method, neutralizes its acidity, achieves harmless treatment of phosphogypsum, and stimulates its gelling properties. A static pressure molding method is designed to prepare phosphogypsum into blocks with good mechanical properties. These blocks and molding method can be applied to prefabricated road base courses, curbs, and sidewalk paving stones, thereby expanding the utilization of phosphogypsum. Attached Figure Description

[0026] Figure 1 A diagram showing the chemical composition of phosphogypsum raw materials;

[0027] Figure 2 The graph shows the change of the three-phase content in phosphogypsum obtained under calcination at 220℃ over time.

[0028] Figure 3 The differential thermal analysis (DTA) curves for phosphogypsum are shown, where (a) is the TG curve and (b) is the DTG curve.

[0029] Figure 4 A schematic diagram of the molding process for phosphogypsum block specimens;

[0030] Figure 5 The mechanical strength diagrams of phosphogypsum blocks under different water usage conditions are shown, where (a) is the compressive strength and (b) is the flexural strength.

[0031] Figure 6 The softening coefficient and water absorption rate of phosphogypsum block specimens under different compaction densities;

[0032] Figure 7 The mechanical strength diagrams are shown for phosphogypsum block specimens with different calcium oxide content and different curing times, where (a) is the compressive strength and (b) is the flexural strength. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] This invention relates to a physicochemical method for the harmless and resource-based treatment of phosphogypsum. It removes soluble phosphorus, fluorine, heavy metals, and other pollutants from phosphogypsum through two calcinations and lime neutralization, neutralizing the acidity of the phosphogypsum and addressing environmental pollution issues during its utilization. The method also increases the content of hemihydrate calcium sulfate in the phosphogypsum, activating its gelling properties. Furthermore, the method prevents water molecules from escaping during compaction, thus addressing the reduction in mechanical properties during the molding of phosphogypsum blocks. The phosphogypsum blocks prepared using this method exhibit a high softening coefficient and low water absorption, solving the problem of poor water resistance in phosphogypsum-based building materials.

[0035] The present invention will be further described in detail below through specific embodiments. To avoid redundancy, the raw materials used in the present invention will be described here:

[0036] Phosphogypsum from a certain region in Hubei Province was selected as the raw material. The particle diameter ranged from 150 μm to 300 μm, and the composition was as follows: Figure 1 As shown, the main components are SO3 and CaO, with a P2O5 content of 0.752% and a F content of 0.709%. It also contains metal oxides such as Fe2O3, Al2O3, and K2O, and has a pH value of 1.8.

[0037] The pH value of experimental grade calcium oxide produced in Shanghai was neutralized by phosphogypsum, and its main components are shown in Table 1.

[0038] Table 1. Main components of calcium oxide

[0039]

[0040] Example 1

[0041] A method for the harmless treatment and resource utilization of phosphogypsum based on physicochemical methods includes the following steps:

[0042] (1) Before the phosphogypsum is rendered harmless by physical calcination, the large diameter of the raw material particles makes it difficult to be fully heated during the calcination process. Therefore, a ball mill is used to grind the phosphogypsum to about 200 mesh. Powder with a particle size of less than 0.075 mm is separated by a 0.075 mm sieve. The sieve material is then taken to obtain phosphogypsum A.

[0043] (2) Phosphogypsum A was calcined at 220℃ for 20 minutes to obtain phosphogypsum B;

[0044] (3) Phosphogypsum B was calcined for a second time at 140℃ for 2 hours to obtain phosphogypsum C;

[0045] (4) Add 0.6% calcium oxide to phosphogypsum C to obtain phosphogypsum D.

[0046] Example 2

[0047] The only difference from Example 1 is the adjustment of the first calcination time in step (2); all other steps and conditions are the same as in Example 1. Step (2) specifically involves:

[0048] The phosphogypsum A powder, after ball milling and sieving, is calcined in a rotary kiln. To ensure effective initial impurity removal, the first calcination is preferably performed at 220°C. To ensure the production of anhydrous calcium sulfate during calcination, the calcination time needs to be controlled. The changes in the three-phase content of the calcined gypsum over time (0-21 minutes) are recorded. Figure 2 As shown.

[0049] from Figure 2 As can be seen, with the increase of calcination time, the content of calcium sulfate dihydrate in phosphogypsum gradually decreases, while the content of calcium sulfate hemihydrate gradually increases. After 20 minutes, the content of calcium sulfate hemihydrate actually decreases, and a small amount of anhydrous calcium sulfate is produced around 21 minutes. Therefore, a calcination time of 20 minutes is optimal.

[0050] The first calcination removes organic matter and attached water from phosphogypsum, increases the content of hemihydrate calcium sulfate, and reduces the content of soluble pollutants phosphorus and fluorine.

[0051] Example 3

[0052] The only difference from Example 1 is that the temperature and time of the second calcination in step (3) are adjusted, while the other steps and conditions are the same as in Example 1.

[0053] After the first calcination, phosphogypsum requires a second calcination. Thermogravimetric analysis (TGA) was performed on the raw phosphogypsum to preliminarily determine the temperature range for the conversion of calcium sulfate dihydrate to calcium sulfate hemihydrate. Before TGA, the phosphogypsum was dried in a 40℃ oven to remove any adhering water. Nitrogen was used as the protective gas, and a STA449F3 synchronous thermal analyzer was employed for testing. Differential thermal analysis was performed on the ball-milled phosphogypsum at a heating rate of 10℃ / min from 50℃ to 500℃. The test results are as follows: Figure 3 As shown.

[0054] Depend on Figure 3It can be seen that an endothermic peak appeared at 142.8℃, and the calcium sulfate dihydrate in phosphogypsum was undergoing a dehydration reaction to transform into calcium sulfate hemihydrate. When the temperature was 151.7℃, the peak began to flatten out. It can be seen that if the temperature is too high, the calcium sulfate hemihydrate will dehydrate and transform into anhydrous calcium sulfate. Therefore, it is preliminarily determined that the optimal transformation temperature of calcium sulfate hemihydrate in phosphogypsum is between 120℃ and 160℃.

[0055] Based on the results of thermogravimetric analysis, three temperature ranges (120℃, 140℃, and 160℃) were set, and the ball-milled phosphogypsum was heated for 1 to 4 hours respectively. The content of the three phases (calcium sulfate dihydrate, calcium sulfate hemihydrate, and anhydrous calcium sulfate) of the phosphogypsum after heating was tested to determine the optimal temperature and time for secondary heating. The content of the three phases of phosphogypsum at different temperatures and times is shown in Table 2.

[0056] Table 2. Three-phase content of phosphogypsum after heating at different temperatures and times.

[0057]

[0058]

[0059] Note: The three-phase content of phosphogypsum after secondary heating was determined using a Lechter LXT-310 gypsum phase composition analyzer in Table 2. This instrument was used according to the national standard GB / T36141-2018, "Analysis Method for Phase Composition of Building Gypsum." The data shows that the sum of the three-phase percentages for some groups is slightly greater than 100%, which should be attributed to instrument measurement error.

[0060] As shown in Table 2, the content of calcium sulfate hemihydrate in phosphogypsum is the highest when the heating temperature is 140℃ and the heating time is 2h. Therefore, the second calcination of this invention is preferably carried out at 120-140℃ for 1-4h, and more preferably at 140℃ for 2h.

[0061] After determining the temperature for the secondary calcination, the phosphogypsum was placed in an oven for secondary heating. The heating temperature was controlled at around 140℃ and the heating time was around 2 hours, resulting in modified phosphogypsum C with a high content of calcium sulfate hemihydrate.

[0062] Example 4

[0063] The only difference from Example 1 is that the amount of calcium oxide in step (4) is adjusted, while the other steps and conditions are the same as in Example 1.

[0064] After two calcinations, the phosphogypsum C is further neutralized by lime through a chemical process. Calcium oxide reacts with water to form calcium hydroxide, which can solidify soluble impurities in the phosphogypsum and neutralize acidic impurities. In this embodiment, the optimal dosage of calcium oxide in phosphogypsum (the percentage of calcium oxide mass to phosphogypsum mass) will be determined experimentally.

[0065] Add phosphogypsum C powder and different amounts of lime to 90 ml of water, stir for 1 min and let stand for 15 min. Filter out the remaining solid powder using neutral filter paper. Use a pH meter to test the pH value of the liquid. The test results are shown in Table 3.

[0066] Table 3 pH values ​​of phosphogypsum with different calcium oxide contents

[0067]

[0068] As shown in Table 3, when the calcium oxide content is 0.6%, all acidic impurities are neutralized. In order to save costs, the preferred calcium oxide content in this invention is 0.6%.

[0069] The contents of soluble phosphorus and soluble fluorine in phosphogypsum materials before and after secondary calcination and lime neutralization are shown in Table 4, and the contents of heavy metal elements in phosphogypsum before and after treatment are shown in Table 5.

[0070] Table 4. Water-soluble phosphorus and fluorine content before and after harmless treatment

[0071]

[0072]

[0073] Table 5. Heavy metal content of phosphogypsum before and after harmless treatment.

[0074]

[0075] As shown in Tables 4 and 5, the phosphogypsum obtained by the treatment method of this invention has effectively reduced soluble phosphorus, soluble fluorine, and heavy metals, meeting the relevant standard requirements.

[0076] Application Example 1

[0077] Water was added to the phosphogypsum C obtained in Example 1 and stirred evenly to obtain a blank. The blank was then pressed, molded, and cured to obtain phosphogypsum blocks. The water content in the blank was 17%. During the pressing process, the compacted density was 2.0 g / cm³. 3 Curing for 7 days. In this invention, molding is controlled by apparent density (i.e., the mass / volume of the added sample) until the specified apparent density is reached; apparent density is also known as compaction density.

[0078] The process of resource-based molding of phosphogypsum blocks is as follows: Figure 4As shown, the phosphogypsum building blocks used for mechanical property testing in this invention are 50mm × 50mm × 200mm in size. The molds are assembled according to these dimensions, and a waterproof polyethylene plastic wrap is evenly placed over the inner wall of the mold to ensure smooth removal of the mold without squeezing out moisture from the phosphogypsum. The specific steps for forming the blocks include:

[0079] (1) First, use a mixer to dry mix the phosphogypsum and calcium oxide (i.e., phosphogypsum D) after two calcinations. After that, add water into the mixer in the form of water mist within 1 minute to ensure that the water, phosphogypsum and calcium oxide react fully during the mixing process. After adding the specified amount of water, stir for 30 seconds. Then, use a stirring rod to stir the phosphogypsum that has not been mixed at the bottom of the mixer. Then, use the mixer to stir for another 30 seconds.

[0080] (2) After mixing, the mixture is evenly poured into the prepared mold. After filling, it is placed in the appropriate position of the compaction machine. The machine is controlled to apply the load at a speed of 0.5 mm / s. The molding is controlled by the compaction density. The mixture is pressed to the experimental density. After pressing and molding, the static pressure is released for 5 seconds to form a 50 mm × 50 mm × 200 mm block.

[0081] Application Example 2

[0082] The only difference from Application Example 1 is that the amount of water used in the billet is adjusted.

[0083] The optimal water content (the percentage of water added to the phosphogypsum by mass) and optimal compaction density (the ratio of the mass of the added material to the volume of the mold) for static pressing were determined by measuring the flexural and compressive strength of phosphogypsum block specimens.

[0084] First, based on the three-phase content of calcined phosphogypsum C, the theoretical water consumption of phosphogypsum C is calculated using chemical equation (1). It is calculated that phosphogypsum with 93% hemihydrate calcium sulfate content requires about 17% water for complete hydration. However, considering that water will be added in the form of spray, some loss will occur. In order to ensure the full progress of the hydration reaction, the amount of water can be appropriately increased on this basis during actual construction (generally 1% to 3% more than 17%, from 17% to 20%) to determine the optimal water consumption.

[0085] 2CaSO4·0.5H2O+3H2O=2CaSO4·2H2O (1)

[0086] Phosphogypsum blocks with different water contents were prepared according to the molding method in Application Example 1, and their compressive and flexural strengths were tested as follows: Figure 5 As shown in Table 6, the quality changes of phosphogypsum blocks cured for 3 days and 7 days are shown in Table 6.

[0087] Table 6. Quality changes of phosphogypsum blocks prepared with different water volumes after 3 and 7 days of curing.

[0088]

[0089] Depend on Figure 5 According to the results in Table 6, the flexural and compressive strength of the blocks is highest when the water content is 17%. As the water content increases, the excess water molecules escape, increasing the porosity of the blocks and thus causing a loss of mechanical properties. Therefore, the optimal water content is 17%.

[0090] Application Example 3

[0091] The only difference from Application Example 1 is that the compaction density in the billet is adjusted.

[0092] After determining the optimal water content, the compaction density of the billet was adjusted as shown in Table 7 below, and the performance of the obtained specimens was tested to determine the optimal compaction density.

[0093] Table 7 shows the strength of blocks with a water consumption of 17% made from different densities.

[0094] Table 7 Strength of specimens molded at different densities

[0095]

[0096] As shown in Table 7, within a suitable range, the strength of the blocks continuously increases with increasing density, and the coefficient of variation of the specimens decreases with increasing density. The density increases to 2.0 g / cm³. 3 At that point, the strength had already reached over 30 MPa with a small coefficient of variation. Further increasing the density required would drastically increase the pressure, leading to higher economic costs and energy consumption for the process. Furthermore, the performance of the blocks was already sufficient for applications such as building construction, curb stones, and road base courses.

[0097] Application Example 4

[0098] The only difference from Application Example 3 is that calcium oxide (i.e., phosphogypsum D) is added as a raw material to prepare phosphogypsum blocks.

[0099] Phosphogypsum blocks of different densities were prepared using 17% water and 0.6% calcium oxide as admixture. Their softening coefficient and water absorption rate were tested, and the results are as follows: Figure 6 As shown, with the compaction density increasing from 1.5 g / cm³... 3 Increased to 2.0 g / cm³ 3 Subsequently, the softening coefficient of the specimen increased from 0.75 to 0.92, and the water absorption rate decreased from 10.1% to 2.9%, indicating better water resistance of the material. Therefore, the optimal compaction density was determined to be 2.0 g / cm³. 3 .

[0100] Application Example 5

[0101] The only difference from application example 4 is that the amount of calcium oxide added and the curing time are adjusted.

[0102] To ensure the complete hydration reaction of phosphogypsum, the phosphogypsum blocks need to be cured. Curing times of 1 day, 3 days, 5 days, 7 days, and 14 days are required. Figure 7 The compressive and flexural strengths of phosphogypsum blocks with different calcium oxide content and curing days were determined.

[0103] Depend on Figure 7 It can be seen that the compressive and flexural strengths of the specimens increase with the increase of curing days. The strength after 14 days of curing is almost identical to that after 7 days of curing, therefore it can be concluded that the phosphogypsum is basically fully hydrated after 7 days of curing. The highest compressive and flexural strengths are achieved when the calcium oxide content is 0.6%, further verifying that the optimal calcium oxide content is 0.6%.

[0104] Compared with existing technologies, this invention uses a physicochemical method of secondary calcination and lime neutralization to render phosphogypsum harmless, removing major pollutants such as soluble phosphorus and fluorine, neutralizing the acidity of the phosphogypsum, increasing the content of hemihydrate calcium sulfate in the phosphogypsum, and activating the cementing properties of the phosphogypsum; a phosphogypsum molding method is designed, and various parameters of the mechanical static pressing method for molding blocks are determined, resulting in phosphogypsum blocks with strong water resistance and mechanical properties. Details are as follows:

[0105] (1) It removes the main pollutants such as soluble phosphorus and fluorine from phosphogypsum.

[0106] The phosphogypsum was first calcined at 220℃ for 20 minutes, effectively reducing the content of soluble phosphorus and fluorine. Using low-cost quicklime as a raw material for calcium hydroxide neutralizing agent further solidified the soluble contaminants in the phosphogypsum, reduced the heavy metal content, and eliminated the corrosiveness of the phosphogypsum. Adding 0.6% calcium oxide by mass to the phosphogypsum neutralized the acidic impurities, changing the pH value to 10.1. Contaminant analysis showed that the soluble phosphorus content decreased from 0.52% to 0.175%, and the soluble fluorine content decreased from 0.196% to 0.03%, both meeting the requirements of GB / T 23456. The content of heavy metals As in phosphogypsum decreased from 3.79 mg / kg to 0.63 mg / kg, Cr from 7.65 mg / kg to 0.99 mg / kg, and Cu from 6.36 mg / kg to 0.923 mg / kg. The content of other heavy metals also decreased significantly, meeting the requirements of the standard.

[0107] (2) It stimulated the gelling properties of phosphogypsum

[0108] After the first calcination, the calcium hemihydrate phosphate content in the phosphogypsum was 40%. A second calcination at 140℃ for 2 hours increased the calcium hemihydrate phosphate content to 93.83%. Under these conditions, the conversion efficiency of calcium hemihydrate phosphate was highest, giving the phosphogypsum material gelling properties. This was achieved with 17% water and 2.0 g / cm³... 3 The compacted blocks, after 7 days of curing, achieved a flexural strength of 6.22 MPa and a compressive strength of 32.57 MPa.

[0109] (3) Phosphogypsum blocks with strong water resistance and mechanical properties were prepared.

[0110] This invention determines the optimal formulation parameters for mechanically statically pressed blocks, with the optimal density of the compacted blocks being 2.0 g / cm³. 3 The optimal water content is 17%, and the optimal calcium oxide content is 0.6%, with curing for at least 7 days. Mechanical static pressing ensures the phosphogypsum blocks have strong water stability, increasing the softening coefficient to 0.94 and reducing water absorption by 70%, resulting in good water resistance. Blocks with a 17% water content exhibit higher compressive and flexural strengths, preventing water molecule escape from damaging the block's mechanical properties. After 14 days of curing, the compressive and flexural strengths of the blocks reached 38.99 MPa and 8.34 MPa respectively, exceeding the strength of C30 concrete.

[0111] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for the harmless and resource-based treatment of phosphogypsum based on a physicochemical approach, characterized in that, Includes the following steps: The phosphogypsum raw material was ball-milled and sieved to obtain phosphogypsum A; Phosphogypsum A was calcined for the first time at 200–240°C to obtain phosphogypsum B. Phosphogypsum B was calcined a second time at 120–140°C to obtain phosphogypsum C. A neutralizing agent is added to phosphogypsum C to obtain phosphogypsum D; The ball milling and sieving process involves first ball milling the phosphogypsum raw material using a ball mill, then passing it through a 0.075 mm sieve to collect the undersize material. The first calcination time is 12-20 minutes; The second calcination time is 1 to 4 hours.

2. The method for harmless and resource-based treatment of phosphogypsum based on physicochemical methods according to claim 1, characterized in that, The first calcination was carried out at 220℃ for 20 minutes.

3. The method for harmless and resource-based treatment of phosphogypsum based on physicochemical methods according to claim 1, characterized in that, The second calcination was carried out at 140℃ for 2 hours.

4. The method for harmless and resource-based treatment of phosphogypsum based on physicochemical methods according to claim 1, characterized in that, The neutralizing agent is calcium oxide, and the dosage is 0.4 to 0.6% of the mass of phosphogypsum C.

5. Phosphogypsum C or phosphogypsum D prepared by the harmless and resource-based treatment method as described in any one of claims 1-4.

6. The application of phosphogypsum C or phosphogypsum D as described in claim 5 in the preparation of phosphogypsum blocks, characterized in that, The phosphogypsum blocks are prepared by adding water to phosphogypsum C or phosphogypsum D and stirring evenly to obtain a blank, which is then pressed, shaped and cured.

7. The application according to claim 6, characterized in that, The water content in the blank is 17-20% of the phosphogypsum mass; during pressing, the compacted density is 1.9-2.2 g / cm³. 3 Maintenance for 7 days or more.

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