Method for preparing soil conditioner by treating phosphogypsum with lime nitrogen residues and soil conditioner

Abstract

The invention relates to the technical field of ardealite resource utilization, in particular to a method for preparing a soil conditioner by treating ardealite through lime nitrogen residues and the soil conditioner. After the lime nitrogen residues and the ardealite are naturally air-dried till the water content is smaller than or equal to 25%, the lime nitrogen residues and the ardealite are smashed and sieved to be prepared into powder; the lime nitrogen slag powder and the phosphogypsum powder are uniformly mixed according to a proper mass ratio, and nutritional ingredients in the lime nitrogen slag and the phosphogypsum are fully utilized, so that the lime nitrogen slag and the phosphogypsum are added into soil to supplement nutrients, reasonable matching of the nutrients in the conditioner is guaranteed, and the soil improvement and conditioning effects are achieved; activated slag is added, uniformly stirred and modified, the pH value is adjusted, then aging treatment and granulation are performed, free acid radicals (phosphate radicals, sulfate radicals and the like) in ardealite are promoted to be solidified, the content of heavy metal in the obtained soil conditioner is extremely low, and the requirement of ardealite soil conditioner (HG / T 4219) is met.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of phosphogypsum, and particularly to a method for treating phosphogypsum with lime nitrogen residue to prepare a soil conditioner and the soil conditioner. Background Art

[0002] Phosphogypsum is an acidic solid waste generated by the wet-process phosphoric acid process, mainly composed of calcium sulfate dihydrate, and also contains harmful elements such as arsenic, cadmium, lead, chromium, mercury, thallium, and F - etc., which easily cause secondary pollution to the environment during the stacking or resource utilization of phosphogypsum, hindering the development of the phosphorus chemical industry. Therefore, how to resourcefully utilize phosphogypsum has become a technical problem urgently to be solved in the development of the phosphorus chemical industry and has received extensive research, forming a large number of technical solutions for preparing fertilizers, soil conditioners, soil improvers, etc. with phosphogypsum as the raw material. For example: Patent No. 202110434000.2 discloses a phosphogypsum soil conditioner and its preparation method, which is prepared by mixing phosphogypsum treated with active microorganisms as a carrier, modified activated carbon, and an adsorbent, making full use of the plant nutrient elements such as phosphorus, calcium, sulfur, and silicon contained in phosphogypsum, improving the soil remediation ability, and enhancing the treatment effect on heavy metals.

[0003] For another example: Patent No. 202111294235.2 discloses a method for preparing a soil conditioner for passivating heavy metals in soil with phosphogypsum as the raw material. The phosphogypsum is ground with water and filtered to obtain a filtrate, and then a crystallizing agent and a modifier are added and stirred and mixed, followed by standing and filtering. The waste liquid is returned to grind phosphogypsum, and the solid is dried to constant weight to prepare a soil conditioner to achieve the purpose of passivating heavy metals in the soil and reducing the risk of heavy metal remigration.

[0004] For another example: Patent No. 202111294239.0 discloses a method for preparing a saline-alkali soil conditioner by fermenting and regulating phosphogypsum. The moisture content of phosphogypsum is adjusted and ground to expose several nutrients such as fluorine and phosphorus. Dry chicken manure is added to absorb the moisture content of the ground phosphogypsum to meet the requirements of fermentation treatment. It is bagged and sealed for fermentation. After being added to the soil, it can reduce the soil salt content, lower the pH, and promote the normal growth of crops.

[0005] Calcium cyanamide residue is a black solid waste generated during the production of carbendazim, thiourea, etc. It is alkaline with a faint pungent odor. Its main components are calcium hydroxide and calcium carbonate, and it also contains elements such as silicon, aluminum, iron, and magnesium. In addition, the calcium cyanamide residue contains nitrogen-containing substances such as cyanamide and dicyandiamide, and the total nitrogen content is relatively high. At present, calcium cyanamide residue has not been seen in the application in the field of soil conditioners, but calcium cyanamide has been widely used in the field of soil conditioner preparation. For example, the patent number 201510564109.2 discloses a calcium cyanamide multi-functional granular soil conditioner and its preparation method, which is prepared by mixing calcium cyanamide, auxiliary materials, lignite, fulvic acid potassium, zeolite powder, hot melt adhesive, urea, polyphosphoric acid, solid paraffin, etc. The hot melt adhesive is used as both a water-retaining agent and a chelating agent, and the auxiliary materials are used as neutralizing agents, activators, and synergists, and continuous granulation is carried out to make the product have a low moisture content and solve the problem of ammonia volatilization of calcium cyanamide.

[0006] For another example: The patent application number 201610651250.0 discloses a composite acidic tobacco field soil conditioner and its application method, which is prepared by separately pulverizing and sieving tobacco stalk biochar, calcium magnesium phosphate, magnesium hydroxide, potassium feldspar, and calcium cyanamide and then mixing them evenly. Calcium cyanamide, etc. are used to adjust soil acidity, relieve soil aluminum toxicity, and can also provide nutrient components such as nitrogen and phosphorus.

[0007] For another example: The patent number 201510501481.9 discloses a multi-functional acidic soil conditioner and its application method, which is prepared by mixing magnesium hydroxide, calcium carbonate, calcium hydroxide, calcium magnesium phosphate fertilizer, calcium cyanamide, lignite, weathered coal, peat, borax, and zinc sulfate evenly to solve problems such as serious soil acidification, structural degradation, and frequent occurrence of soil-borne diseases, promote the growth of crops, and improve the yield and quality of crops.

[0008] It can be seen that both phosphogypsum and calcium cyanamide have been applied in the field of soil conditioner and soil improver preparation, and a large number of technical literatures have been formed. However, the application of calcium cyanamide residue and phosphogypsum together in the field of soil conditioner preparation has not been reported, especially the relevant research on using calcium cyanamide residue to mix and treat phosphogypsum to prepare soil conditioner has not been seen. Summary of the Invention

[0009] Based on the above technical problems, the research team mixes calcium cyanamide residue and phosphogypsum in an appropriate ratio. After the mixture of calcium cyanamide residue and phosphogypsum materials is improved by mixing, it is prepared into a soil conditioner. On the basis of making full use of the beneficial nutrient elements for crop growth such as phosphorus, sulfur, calcium, and silicon contained in phosphogypsum, the contents of arsenic, cadmium, lead, chromium, and mercury in the soil conditioner are reduced.

[0010] The specific technical solution is as follows:

[0011] A method for preparing a soil conditioner by treating phosphogypsum with calcium cyanamide residue includes the following steps:

[0012] (1) Air-dry phosphogypsum and lime nitrogen residue naturally until the moisture content ≤ 25%, and crush and sieve them to obtain phosphogypsum powder and lime nitrogen residue powder; the crushing and sieving is through an 80 - 100 mesh sieve.

[0013] (2) Mix the phosphogypsum powder and lime nitrogen residue powder evenly according to a mass ratio of 10:0.1 - 2 to obtain a mixture.

[0014] (3) Add 1 - 20% of activated slag based on the phosphogypsum to the mixture, stir well for modification, adjust the pH value to 5 - 6.5, conduct aging treatment for at least 24 h, and granulate to obtain the product.

[0015] After air-drying lime nitrogen residue and phosphogypsum until the moisture content ≤ 25%, crush and sieve them respectively to prepare powders, and mix the lime nitrogen residue powder and phosphogypsum powder in an appropriate mass ratio. Make full use of the nutrient components in lime nitrogen residue and phosphogypsum, so that when added to the soil, it can supplement nutrients, ensure the reasonable nutrient combination in the conditioner, and realize the improvement and conditioning effect on the soil; use activated slag to add and stir well for modification treatment, adjust the pH value and then conduct aging treatment and granulation, so as to promote the solidification of free acid radicals (such as phosphate radicals, sulfate radicals, etc.) in phosphogypsum, and the heavy metal content in the obtained soil conditioner is extremely low, meeting the requirements of "Phosphogypsum Soil Conditioner" (HG / T 4219).

[0016] In order to improve the activation and modification effect of activated slag on the mixture, enhance the solidification effect on free acid radicals, and improve the synergistic effect of the mixture of lime nitrogen residue and phosphogypsum, preferably, the activated slag is obtained by crushing and sieving phosphate tailings, then roasting at 850 - 950 °C for 30 min and cooling to room temperature in a natural environment to obtain phosphate tailings powder; or the activated slag is obtained by crushing and sieving phosphate tailings, then acidifying with industrial waste acid and air-drying until the moisture content ≤ 25% to obtain phosphate tailings powder.

[0017] More preferably, the moisture content of the phosphate tailings powder ≤ 10%.

[0018] More preferably, the moisture content of the phosphate tailings powder is 0.67%.

[0019] In order to realize the recycling of waste acid, reduce the treatment difficulty and cost of raffinate acid produced by phosphoric acid purification process or waste acid produced by sulfuric acid production process, and turn waste into treasure, preferably, the pH value is adjusted using industrial waste acid. More preferably, the industrial waste acid is raffinate acid produced in the production of purified phosphoric acid; or the industrial waste acid is waste acid produced in the production process of sulfuric acid.

[0020] To ensure the promotion of the mixing effect of lime nitrogen slag and phosphogypsum after the addition of activated slag and enhance the conditioning performance of the conditioner, preferably, the aging treatment time is 24 - 72 h. More preferably, the aging treatment time is 48 h.

[0021] The second object of the present invention is to provide a soil conditioner prepared by the above method

[0022] Compared with the prior art, the technical effects of the present invention are reflected in:

[0023] The present invention mixes lime nitrogen slag and phosphogypsum in an appropriate ratio to form a mixture, uses activated slag to mix and modify, ages after adjusting the pH value, promotes the synergistic effect of lime nitrogen slag and phosphogypsum, improves the soil conditioning effect, helps to promote the growth of crops and increase the yield.

[0024] The heavy metal content of the soil conditioner obtained by the present invention is relatively low, and it can solidify the free acid radicals (phosphate, sulfate, F - etc.) in phosphogypsum, and improve the soil conditioning effect. At the same time, it can turn waste into treasure for phosphogypsum, lime nitrogen slag, phosphorus tailings, industrial waste acid, etc., make full use of elements such as phosphorus, nitrogen, calcium, sulfur, silicon, iron, magnesium in phosphogypsum, lime nitrogen slag, phosphorus tailings, ensure the soil conditioning effect, and balance the soil acidity and alkalinity. Moreover, it can also supplement medium and trace elements to the soil to ensure a reasonable combination of nutrient components.

[0025] The present invention can make great use of phosphogypsum, increase the consumption of phosphogypsum, reduce the stacking of phosphogypsum, and reduce the pressure on the environment caused by the landfill and stacking of phosphogypsum.

[0026] The process flow of the present invention is simple and easy to be industrialized and popularized. Brief Description of the Drawings

[0027] In order for those skilled in the art to fully understand the technical solution of the present invention, the technical solution content and the provided drawings are now combined.

[0028] Figure 1 It is a process flow chart of the present invention.

[0029] Figure 2 It is a process flow chart of another embodiment of the present invention.

[0030] Figure 3 It is a photo of the growth of strawberries in a potting strawberry experiment.

[0031] Figure 4 It is a photo of the growth of mint in a potting mint experiment.

[0032] Figure 5 It is a test report for supplying the sample prepared in Example 8 to a third party for testing. Detailed implementation manners

[0033] For the convenience of those skilled in the art to correctly understand the present invention, so that those skilled in the art can fully understand the technical content of the present invention, the technical solutions of the present invention will be further elaborated below in conjunction with the drawings and specific implementation manners. However, this elaboration does not limit the scope of protection required by the present invention. Those skilled in the art cannot limit the protection scope of the present invention only to the following elaboration content. Any equivalent replacement or change made by those skilled in the art or those familiar with the art in the art based on the technical solutions and inventive concepts of the present invention should be covered within the protection scope of the present invention.

[0034] As Figure 1 shown, in some embodiments, a method for treating phosphogypsum with lime nitrogen residue to prepare a soil conditioner includes the following steps:

[0035] (1) Naturally air-dry phosphogypsum and lime nitrogen residue to a moisture content ≤ 25%, and crush them through an 80-100 mesh sieve, such as: 80 mesh, 90 mesh, 100 mesh, etc., to obtain phosphogypsum powder and lime nitrogen residue powder;

[0036] (2) Mix the phosphogypsum powder and the lime nitrogen residue powder evenly according to a mass ratio of 10:0.1-2, such as: 10:0.1, 10:0.5, 10:0.8, 10:1, 10:1.2, 10:1.5, 10:1.7, 5:2, etc., to obtain a mixture;

[0037] (3) Add 1-20% of activated slag, such as: 1%, 5%, 7%, 14%, 17%, 20%, etc., based on phosphogypsum to the mixture, mix well for modification, adjust the pH value to be between 5-6.5, age for at least 24h, such as: 24h, 36h, 48h, 60h, 72h, etc., and granulate into particles of 1-4mm, such as: 1mm, 2mm, 3mm, 4mm, etc., then it is okay. The activated slag is obtained by crushing phosphorous tailings through an 80-100 mesh sieve, such as: 80 mesh, 90 mesh, 100 mesh, etc., then roasting at 850-950°C, such as: 850°C, 900°C, 950°C, etc., for 30min and cooling to room temperature in a natural environment to obtain phosphorous tailings powder.

[0038] By controlling the appropriate ratio of lime nitrogen residue and phosphogypsum, combining with the activation treatment of phosphorous tailings to prepare activated slag and adding it for mixing and modification, the synergistic effect of the mixture of lime nitrogen residue and phosphogypsum is enhanced, the heavy metal content is reduced, the free acid radicals in phosphogypsum are solidified, the soil conditioning effect is improved, which helps to promote the growth of crops and increase the yield.

[0039] As Figure 2As shown, in some embodiments, the activated slag is obtained by crushing phosphate tailings through an 80 - 100 mesh sieve, such as 80 mesh, 90 mesh, 100 mesh, etc., then acidifying with industrial waste acid and naturally air - drying to a moisture content ≤ 25%, such as 6%, 7.3%, 8%, 10%, 13%, 15%, 20%, 23%, 25%, etc., to obtain phosphate tailings powder. Activating phosphate tailings through acidification treatment enables the phosphate tailings that were previously discarded as solid waste to be added to the mixture of calcium cyanamide residue and phosphogypsum after activation, enhancing the synergistic effect of calcium cyanamide residue and phosphogypsum in conditioning soil. Moreover, it also realizes the recycling of industrial waste acid, turning waste into treasure and reducing the treatment cost of phosphate tailings.

[0040] In some embodiments, the pH value is adjusted using industrial waste acid. The industrial waste acid is the raffinate acid generated in the purification of phosphoric acid production; or the industrial waste acid is the waste acid generated during the production process of sulfuric acid. The recycling of industrial waste acid is realized.

[0041] In some embodiments of the present invention, for the industrial waste acid acidification treatment, industrial waste acid is directly added to the crushed and sieved phosphate tailings, and the mass ratio of the added industrial waste acid is controlled so that there is no obvious liquid seepage in the phosphate tailings, and then they are stirred and mixed after addition. In some embodiments, the stirring speed is 100 r / min for 10 min, and the mass ratio of industrial waste acid to phosphate tailings is 1:25.

[0042] In order to better verify the technical effects of the present invention, the research team carried out the following experimental studies, and the relevant experimental contents are described as follows:

[0043] The phosphogypsum is from a wet - process phosphoric acid production enterprise in Guizhou Province, and its physical and chemical properties are shown in Table 1 below:

[0044] Table 1

[0045]

[0046] The calcium cyanamide residue is from a thiourea production enterprise in Guizhou Province, and the composition of its elements is shown in Table 2 below:

[0047] Table 2

[0048]

[0049] The phosphate tailings slag is from a phosphate ore dressing enterprise in Guizhou Province, and its composition is shown in Table 3 below:

[0050] Table 3

[0051]

[0052] The residual acid is from a wet-process phosphoric acid purification production enterprise in Guizhou Province, and its composition is shown in Table 4 below:

[0053] Table 4

[0054]

[0055] The industrial waste sulfuric acid is from a sulfuric acid production enterprise in Guizhou Province, and its sulfate content is 165,199.27 ppm.

[0056] Experiment 1: Study on the effect of adding activated slag on the performance of soil conditioner.

[0057] 1. Preparation of test samples:

[0058] Example 1:

[0059] The phosphogypsum was naturally air-dried to a moisture content of 23.4%, crushed and sieved through a 100-mesh sieve to obtain phosphogypsum powder; the phosphorous tailings were crushed and sieved through a 100-mesh sieve, then calcined at 900 °C for 30 min and naturally cooled to room temperature to obtain activated slag; the phosphogypsum and activated slag were mixed at a mass ratio of 10:0.5, and industrial waste acid (residual acid produced by the phosphoric acid purification process) was added to adjust the pH value to be between 5 and 6.5, then aged for 48 h, and granulated into particles with a particle size between 1 and 4 mm, thus obtained.

[0060] Example 2:

[0061] The calcium cyanamide residue was naturally air-dried to a moisture content of 24.5%, crushed and sieved through a 100-mesh sieve to obtain calcium cyanamide residue powder; the activated slag was prepared according to the preparation method of Example 1, and the calcium cyanamide residue powder and activated slag were mixed at a mass ratio of 1:1, and industrial waste acid (residual acid produced by the phosphoric acid purification process) was added to adjust the pH value to be between 5 and 6.5, then aged for 48 h, and granulated into particles with a particle size between 1 and 4 mm, thus obtained.

[0062] Example 3:

[0063] The phosphogypsum powder and activated slag were prepared according to the preparation method of Example 1, the calcium cyanamide residue powder was prepared according to the preparation method of Example 2, the phosphogypsum powder and calcium cyanamide residue powder were mixed at a mass ratio of 10:1, then 5% of the activated slag based on the mass of the phosphogypsum powder was added, and industrial waste acid (residual acid produced by the phosphoric acid purification process) was added to adjust the pH value to be between 5 and 6.5, then aged for 48 h, and granulated into particles with a particle size between 1 and 4 mm, thus obtained.

[0064] Example 4:

[0065] Prepare phosphogypsum powder according to the preparation method of Example 1, prepare calcium cyanamide residue powder according to the preparation method of Example 2, mix the phosphogypsum powder and the calcium cyanamide residue powder in a mass ratio of 10:0.5, add industrial waste acid (the raffinate acid generated by the phosphoric acid purification process) to adjust the pH value to be between 5 and 6.5, then age for 48 h, and granulate into particles with a particle size between 1 and 4 mm to obtain the product.

[0066] 2. Detection

[0067] Perform detections on pH, F - (%), arsenic (mg / kg), cadmium (mg / kg), lead (mg / kg), chromium (mg / kg), mercury (mg / kg), thallium (mg / kg), etc. on the samples prepared in Examples 1 to 4, and record the detection results in Table 5 below:

[0068] Table 5

[0069]

[0070]

[0071] As can be seen from Tables 1 to 5: After the phosphogypsum, calcium cyanamide residue, and activated slag are mixed, the pH is adjusted, aged, and granulated with appropriate ratios to prepare a soil conditioner, it can synergistically solidify heavy metals, reduce the detectable amount of heavy metals, and improve the quality of the soil conditioner.

[0072] 3. Application test

[0073] 3.1 Strawberry pot experiment

[0074] Use the soil conditioner obtained in Example 3 for the pot experiment of strawberries. When potting strawberries, other treatment methods are the same. In the experimental group (2 pots), the soil conditioner prepared in Example 3 is added to the soil at 30% of the soil mass and mixed evenly; in the control group (1 pot), strawberries are directly cultivated in the soil without adding the soil conditioner. The total weight of the soil and the soil conditioner in the experimental group is equal to the weight of the soil in the control group.

[0075] The current situation indicators of the soil used are shown in Table 6 below:

[0076] A: Hydrolyzable nitrogen, mg / kg; B: Available phosphorus, mg / kg; C: Cation exchange capacity, cmol(+) / kg; D: Available sulfur, mg / kg.

[0077] Table 6

[0078]

[0079] Observe the growth of strawberries (such as Figure 3As shown in the figure: the strawberry plants in the experimental group grew robustly and evenly; the strawberry plants in the control group had small and thin roots, uneven growth, and accompanied by yellowing of leaves.

[0080] 3.2 Mint potted plant experiment

[0081] According to the operation method of the strawberry potted plant experiment, the soil conditioner prepared in Example 3 was used for the potted mint experiment. The soil conditioner was added to the soil at 30% of the soil mass and mixed evenly. Observe the growth of mint (as Figure 4 shown in the figure): the mint plants in the experimental group (3 pots) were tall, robust, and grew evenly; the mint plants in the control group (1 pot) had small and thin rhizomes and uneven growth.

[0082] 3.3 Detection of potted soil indicators

[0083] The soil indicators after conditioning in the experimental group were detected, and the results are shown in Table 7 below:

[0084] Table 7

[0085]

[0086] It can be seen that the soil conditioner of the present invention can improve the soil performance and promote the growth of strawberry plants.

[0087] Experiment 2. Research on the influence of different preparation methods on the performance of soil conditioner

[0088] 1. Preparation of test samples

[0089] Example 5

[0090] Prepare phosphogypsum powder and activated slag according to the preparation method of Example 1, prepare calcium cyanamide residue powder according to the preparation method of Example 2, mix the phosphogypsum powder and calcium cyanamide residue powder at a mass ratio of 10:1.3 to form a mixture, then add the activated slag at 5% of the mass of the phosphogypsum powder, and add industrial waste acid (the raffinate acid produced by the phosphoric acid purification process) to adjust the pH value between 5 - 6.5, and then age for 48h, and granulate into particles with a particle size between 1 - 4mm, thus obtaining.

[0091] Example 6

[0092] Prepare phosphogypsum powder and activated slag according to the preparation method of Example 1, prepare calcium cyanamide residue powder according to the preparation method of Example 2, mix the phosphogypsum powder and calcium cyanamide residue powder at a mass ratio of 10:1 to form a mixture, then add the activated slag at 1% of the mass of the phosphogypsum powder, and add industrial waste acid (the raffinate acid produced by the phosphoric acid purification process) to adjust the pH value between 5 - 6.5, and then age for 48h, and granulate into particles with a particle size between 1 - 4mm, thus obtaining.

[0093] Example 7

[0094] Prepare phosphogypsum powder and activated slag according to the preparation method of Example 1, prepare calcium cyanamide residue powder according to the preparation method of Example 2, mix the phosphogypsum powder and calcium cyanamide residue powder in a mass ratio of 10:0.8 to form a mixture, then add the activated slag according to 12% of the mass of the phosphogypsum powder, and add industrial waste acid (the raffinate acid produced by the phosphoric acid purification process) to adjust the pH value to be between 5 and 6.5, then age for 72 h, and granulate into particles with a particle size between 1 and 4 mm, thus obtaining.

[0095] Example 8

[0096] On the basis of Example 5, the phosphogypsum powder and calcium cyanamide residue powder are mixed in a mass ratio of 5:1 to form a mixture, and the others are the same as in Example 5.

[0097] Example 9

[0098] On the basis of Example 5, the activated slag is added according to 20% of the mass of the phosphogypsum powder, and the others are the same as in Example 5.

[0099] Example 10

[0100] On the basis of Example 5, the others are the same as in Example 5. The activated slag is the phosphotailings powder obtained by crushing the phosphotailings through a 100-mesh sieve, and then acidifying and treating with industrial waste acid (the raffinate acid produced by the phosphoric acid purification process) (stirring speed is 100 r / min for 10 min, and the mass ratio of industrial waste acid to phosphotailings is 1:25), and then naturally air-drying to a moisture content of 0.67%.

[0101] 2. Detection

[0102] Perform detections on pH, F - (%), arsenic (mg / kg), cadmium (mg / kg), lead (mg / kg), chromium (mg / kg), mercury (mg / kg), thallium (mg / kg), etc. on the samples prepared in Examples 5 to 10, and record the detection results in Table 8 below:

[0103] Table 8

[0104]

[0105] Note: The samples obtained in Example 8 were entrusted to a third party for detections of cadmium (mg / kg), lead (mg / kg), chromium (mg / kg), mercury (mg / kg), thallium (mg / kg).

[0106] As can be seen from Table 5 and Table 8, for the changes in the raw material dosage ratio and the preparation process, it will affect the quality of the soil conditioner, resulting in changes in the detectable heavy metal content in the soil conditioner.

[0107] For other matters not covered by the present invention, reference may be made to the prior art or the common general knowledge well-known to those skilled in the art, and they can be implemented by conventional technical means. For example, the industrial waste acid used in the present invention may be the waste acid generated in the sulfuric acid production process or the raffinate acid generated in the phosphoric acid purification process.

Claims

1. A method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag, characterized in that: The following steps are involved: (1) respectively drying the phosphogypsum and the lime nitrogen slag naturally to a moisture content of ≤25%, and crushing and sieving them to obtain phosphogypsum powder and lime nitrogen slag powder; (2) mixing phosphogypsum powder and lime nitrogen slag powder in a mass ratio of 10:0.1-2 to obtain a mixture; (3) The mixture is modified by adding activated slag accounting for 1-20% of phosphogypsum, adjusting the pH value to 5-6.5, aging for at least 24 hours, and granulating.

2. The method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag as claimed in claim 1, characterized in that: The crushing and screening is through a 80-100 mesh sieve.

3. The method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag as claimed in claim 1, characterized in that: The activated slag is obtained by crushing and screening the phosphorus tailings, roasting at 850-950°C for 30 minutes, and cooling to room temperature under natural environment to obtain phosphorus tailings powder; or the activated slag is obtained by crushing and screening the phosphorus tailings, acidifying with industrial waste acid, and naturally air-drying to a moisture content of ≤25% to obtain phosphorus tailings powder.

4. The method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag as claimed in claim 3, characterized in that: The water content of the phosphate tailings powder is ≤10%.

5. The method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag as claimed in claim 3 or 4, characterized in that: The water content of the phosphate tailings powder is 0.67%.

6. The method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag as claimed in claim 1, characterized in that: The pH value is adjusted by using industrial waste acid; the industrial waste acid is the raffinate acid produced in the purification of phosphoric acid production; or the industrial waste acid is the waste acid produced in the sulfuric acid production process.

7. The method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag as claimed in claim 1, characterized in that: The aging treatment time is 24-72h.

8. The method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag as claimed in claim 1 or 7, characterized in that: The aging time is 48 hours.

9. The method for preparing a soil conditioner by treating phosphogypsum with lime nitrogen slag as claimed in claim 1, characterized in that: The granulation is to form particles with a particle size of 1-4 mm.

10. A soil conditioner prepared according to the method of any one of claims 1 to 9.

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