Method for purifying ardealite through graded coupling forced external circulation flotation column

Abstract

The invention discloses a method for purifying ardealite through a grading coupling forced external circulation flotation column, and belongs to the field of solid waste comprehensive utilization. The method comprises the following steps: 1) adding water into ardealite for size mixing to obtain ardealite slurry; 2) screening to remove high-silicon large-particle minerals and undecomposed phosphorite, and collecting undersize phosphogypsum slurry; (3) a reverse flotation collecting agent is added, and stirring and size mixing are conducted; wherein a reverse flotation collecting agent is distillate oil collected from coal tar at the temperature of 160-250 DEG C; (4) the ardealite ore pulp is sequentially fed into two sets of flotation columns with forced outer circulation to be subjected to roughing reverse flotation operation and concentration reverse flotation operation, concentrated ardealite ore pulp and middling are obtained through concentration, roughing reverse flotation operation is conducted on the middling again, and closed circulation is formed; 5, the selected ardealite pulp is subjected to washing, filter pressing and drying, and purified ardealite is obtained.The method is simple in technological process, the ardealite decoloring effect and the purity improving effect are remarkable, the purification cost is low, the purified ardealite yield is high, and good industrial application value is achieved.

Description

Technical Field

[0001] This invention belongs to the field of solid waste comprehensive utilization technology, specifically relating to a method for purifying phosphogypsum using a graded coupled forced external circulation flotation column. Background Technology

[0002] Phosphogypsum is the most significant solid waste product of the phosphate chemical industry, generating approximately 4.5-5 tons of phosphogypsum for every ton of wet-process phosphoric acid produced. As the world's largest producer of phosphate fertilizer, my country produces over 80 million tons of phosphogypsum annually, with accumulated stockpiles exceeding 800 million tons. The large-scale open-air stockpiling of phosphogypsum not only occupies land resources, but the harmful substances it contains, such as phosphorus, fluorine, and heavy metals, also pollute soil and groundwater through rainwater leaching, posing a serious threat to the ecological environment of the Yangtze and Yellow River basins.

[0003] Phosphogypsum, primarily composed of calcium sulfate dihydrate, can replace natural phosphogypsum in the building materials industry. However, as a byproduct of phosphoric acid production, phosphogypsum carries a large amount of mineral impurities associated with phosphate rock. These impurities significantly impact downstream applications. For example, quartz, silicates, and organic matter not only affect the purity and appearance of phosphogypsum but also increase the difficulty of grinding it, resulting in building materials with low strength and a tendency to crack. Therefore, most of the quartz and organic matter must be removed before phosphogypsum can be utilized as a resource.

[0004] Flotation purification technology, as an important means of pretreatment of phosphogypsum, selectively separates harmful impurities from phosphogypsum, effectively improving its quality. The purified phosphogypsum exhibits significantly improved purity and whiteness, meeting the raw material requirements for high-value-added products such as building materials and cement retarders.

[0005] However, flotation purification technology still faces many challenges in practical applications. Firstly, due to the presence of impurities, the particle size distribution of phosphogypsum is extremely uneven, especially containing large-sized undecomposed phosphate rock or gangue particles. These particles cannot be effectively separated during phosphogypsum back-flotation as they rise with the bubbles and enter the tailings, thus affecting the quality and whiteness of the concentrate. Secondly, the flotation reagents are complex. Phosphogypsum contains various mineral components, making the selection of suitable collectors and modifiers complicated. Commonly used collectors such as fatty acids, No. 2 oil, and coconut oil are not ideal in their selectivity and effectiveness against silicates and organic matter in flotation, thus usually requiring high reagent dosages, leading to high flotation costs and a high tailings volume, reaching 15%-25% of the original ore. Furthermore, traditional phosphogypsum flotation can only remove specific impurities in a single flotation operation and requires the addition of acid and alkali modifiers, resulting in a long flotation process and high costs. Furthermore, the flotation process is complex. The flotation process for phosphogypsum mainly involves reverse flotation and reverse flotation + forward flotation. Forward flotation can improve the quality and whiteness of phosphogypsum, but reverse flotation and forward flotation use different reagents and collectors, limiting water recycling. Moreover, forward flotation often results in a large amount of collector adhering to the surface of gypsum particles in the concentrate, affecting the downstream applications of phosphogypsum, such as the inability to effectively convert it into hemihydrate or anhydrous gypsum. In addition, traditional flotation machines with mechanical agitation used for flotation occupy a large area. When used to process phosphogypsum, due to its complex composition and fine particles, the flotation efficiency is low and the power consumption is high.

[0006] In conclusion, flotation purification technology is an important way to overcome the difficulties in the utilization of phosphogypsum. However, it is necessary to optimize the reagent system, develop more energy-efficient flotation equipment and simpler processes, and improve process stability in order to truly promote the phosphogypsum resource utilization industry towards large-scale, high-value and sustainable development. Summary of the Invention

[0007] The purpose of this invention is to provide a method for purifying phosphogypsum using a staged coupled forced external circulation flotation column, which has significant purification and whitening effects, high yield, simpler process flow, lower energy consumption and purification costs, and improves the utilization rate of phosphogypsum.

[0008] To solve the above problems, the present invention adopts the following solution: A method for purifying phosphogypsum using a staged coupled forced external circulation flotation column is provided, comprising the following steps: 1) Add water to phosphogypsum to make a slurry, thus obtaining phosphogypsum slurry; 2) Screen the phosphogypsum slurry obtained in step 1) to remove high-silica large-particle minerals and undecomposed phosphate rock, and collect the phosphogypsum slurry under the screen. 3) Add the reverse flotation collector to the phosphogypsum slurry obtained in step 2) and stir to adjust the slurry; wherein the reverse flotation collector is the distillate oil collected from coal tar at 160-250℃; 4) The phosphogypsum slurry obtained in step 3) is sequentially fed into two sets of flotation columns with forced external circulation for roughing and cleaning two-stage reverse flotation operations, wherein: the roughing process yields tailings and roughing phosphogypsum slurry. The roughing phosphogypsum slurry is then treated with the same reverse flotation collector as in step 3) and cleaned to obtain cleaning phosphogypsum slurry and middlings enriched with certain impurities. The middlings are then subjected to roughing and reverse flotation operations again to form a closed-loop circulation. 5) The selected phosphogypsum slurry obtained in step 4) is washed and filtered with water to further remove residual soluble impurities, and then dried to obtain purified phosphogypsum.

[0009] According to the above scheme, in step 1), the CaSO4·2H2O content in phosphogypsum is 75-85%, the whiteness of phosphogypsum is <30, the SiO2 content is 5-9%, and the organic matter content is 1-3%.

[0010] According to the above scheme, in step 1), the solid content of the phosphogypsum slurry is 30-40 wt%.

[0011] According to the above scheme, in step 2), the sieve aperture is 100-400μm, which is beneficial to obtain a particle size that matches the subsequent double reverse flotation.

[0012] According to the above scheme, in step 2), a high-frequency vibrating screen is used for screening, wherein the vibration frequency is 1500-2500 times / minute.

[0013] According to the above scheme, in step 3), the amount of reverse flotation collector added is 0.1-0.5 kg / t phosphogypsum; preferably 0.2-0.3 kg / t phosphogypsum.

[0014] According to the above scheme, in step 3), the reverse flotation collector is a distillate oil collected from coal tar at 160-250℃, which has strong hydrophobicity and surface activity. For example, phenolic oil, a distillate oil from coal tar collected at 170-180℃, mainly consists of phenol, cresol, xylenol, methylnaphthalene, dimethylnaphthalene, etc. The quartz surface in phosphogypsum contains silanol groups (Si-OH), and the hydroxyl groups (-OH) of phenolic compounds in phenolic oil readily form hydrogen bonds with it, causing phenolic molecules to be directionally adsorbed onto the quartz surface. The hydrophobic groups are arranged outwards, achieving highly selective collection of quartz. Simultaneously, the adsorbed phenolic molecules form a hydrophobic film on the quartz surface, reducing hydration and enhancing its adhesion to air bubbles. Furthermore, the aromatic compounds in phenolic oil have similar structures to organic matter, making them easily adsorbed. This affinity leads to the enrichment of phenolic oil on the surface of organic matter, covering the hydrophilic sites on the organic matter surface to form a uniform hydrophobic surface, improving the floatability of the organic matter. Phenolic oil is preferred as a reverse flotation collector.

[0015] According to the above scheme, in step 4), the flotation column with forced external circulation includes a column body, an external circulation pump, and a liquid level and flow control system; wherein a radial flow stabilizing tube plate is provided in the column body, which plays a role in dispersing bubbles and stabilizing the flow pattern without the need for a bubble scraping device. The external circulation pump extracts part of the slurry from the bottom of the column body and sends it into the column body in a swirling manner, which enhances the mixing of materials in the column while reducing the height of the column flotation.

[0016] Preferably, the flotation column is also equipped with a bubble generator at the inlet of the external circulation pump, which is connected to the circulating slurry feed pipe. This changes the traditional bubble introduction method of flotation columns. The generated microbubbles and the adhering particles are fed tangentially into the column, forming a swirling state inside the column. The bubbles and mineral particles play a good mixing role inside the column.

[0017] Preferably, the column is divided into a foam zone and a trapping zone from top to bottom. The phosphogypsum slurry is fed from the middle of the column and flows downward. In the trapping zone, bubbles are formed and collide with particles in a countercurrent. Hydrophobic solid particles are adhered to the surface of the bubbles, forming an aggregate of mineralized bubbles that rises to the foam zone and becomes foam, which is discharged from the top with the airflow to form tailings.

[0018] According to the above scheme, in step 4), during the fine selection process, the amount of reverse flotation collector added is 0.05-0.3 kg / t phosphogypsum; preferably 0.1-0.2 kg / t phosphogypsum.

[0019] According to the above scheme, in step 4), during roughing, organic matter and quartz are adsorbed on the surface of rising bubbles in the adsorption column and flow out from the top of the flotation column as tailings, while the bottom of the flotation column flows out as roughing phosphogypsum slurry.

[0020] According to the above scheme, in step 4), the rough phosphogypsum slurry is fed into the second flotation column and reverse flotation is performed again. The phosphogypsum slurry flowing out from the bottom of the flotation column is the refined phosphogypsum slurry, and the middlings flowing out from the top of the flotation column are enriched with certain impurities. The middlings are fed back into the inlet of the first flotation column to form a closed loop.

[0021] According to the above scheme, in step 4), the tailings yield is 10-20%. Here, the yield refers to the cumulative total tailings yield.

[0022] According to the above scheme, in step 5), the soluble impurities are soluble phosphorus and fluorine.

[0023] According to the above scheme, in step 5), the purified phosphogypsum has a SiO2 content of less than 1.5%, a purity of more than 10%, and a whiteness of more than 120% (relative value).

[0024] This invention provides a method for purifying phosphogypsum using a graded coupled forced external circulation flotation column. By coupling screening and grading with two-stage reverse flotation, only a single coal tar byproduct is needed as the reverse flotation collector to simultaneously remove organic matter and silicon from phosphogypsum. The purification and whitening effects are significant, with high yield, a simpler process flow, and lower energy consumption and purification costs. The specific mechanism is as follows: This invention first removes large particles of quartz and undecomposed phosphate rock from phosphogypsum through screening and grading, thus removing large mineral particles that are difficult to float in advance, and selecting phosphogypsum with a suitable particle size for subsequent reverse flotation. It also uses distillate oil collected from coal tar at 160-250℃ as a collector for both roughing and cleaning, which has strong hydrophobicity and surface activity, achieving high selective collection of quartz and improving the floatability of quartz and organic matter, maintaining high flotation efficiency and selectivity. Simultaneously, it cleverly applies the operational principle of fractional separation in chemical distillation to a two-stage flotation operation of "roughing and cleaning." During roughing, the impurity content is relatively high, and phenolic oil mainly adsorbs and dissolves organic matter, thus being preferentially removed in the roughing stage. Therefore, roughing mainly removes organic matter and some SiO2, while the cleaning process further removes the remaining organic matter and SiO2. The phosphogypsum slurry obtained from the roughing process is fed into the cleaning column for further enrichment of calcium sulfate. After secondary flotation, the impurity content and types of the middlings obtained from the top of the cleaning column are similar to those of the phosphogypsum raw material. It can be returned to the roughing column for further enrichment of impurities, reducing tailings and increasing the total concentrate yield. The synergistic forced external circulation design can enhance the countercurrent contact effect of the phosphogypsum slurry in the flotation column collecting zone, ensuring gas-liquid contact within the column. This greatly improves the enrichment efficiency of impurities such as organic matter and quartz in the tailings. Combined with a highly efficient phenolic oil collector, organic matter and quartz can be removed from phosphogypsum simultaneously without separate removal, significantly shortening the flotation process and reducing flotation costs.

[0025] The beneficial effects of this invention are as follows: 1. This invention provides a novel enhanced flotation purification process for phosphogypsum. It removes large particles of quartz and undecomposed phosphate rock from the phosphogypsum through screening and classification. Then, using distillate oil from coal tar (a byproduct of coal dry distillation) as a collector, two reverse flotation processes (one roughing and one cleaning) are performed in two sets of flotation columns with forced external circulation to remove quartz and organic impurities from the phosphogypsum. Finally, the concentrate is washed and filtered to obtain purified phosphogypsum powder. This method features a simple process flow, enhanced classification and reverse flotation in two stages, and a flotation column design with forced external circulation, achieving complementary functions and synergistic overall efficient removal of quartz and organic matter. This invention significantly shortens the flotation process, reduces flotation costs, and achieves remarkable phosphogypsum purification, reducing SiO2 content to below 1.5%, increasing phosphogypsum purity by more than 10 percentage points, reducing tailings yield to only 10%, and increasing whiteness by more than 120% (relative value). It has broad prospects for industrial application.

[0026] 2. The coal tar distillate oil collector used in this invention has high selectivity for impurity minerals and can be applied simultaneously to the roughing and cleaning processes to remove quartz and organic impurities from phosphogypsum without the need for adjusting agents such as acids and alkalis. In addition, the collector is inexpensive, widely available, and solves the problem of utilizing by-product resources in coal chemical industry, thus having significant environmental value and economic benefits. Furthermore, collectors with different flotation properties can be obtained through fine cutting of distillates in the coal tar distillation process to adapt to different changes in impurities and contents in phosphogypsum, exhibiting good performance adjustability and strong applicability.

[0027] 3. This invention uses a flotation column with forced external circulation to replace the traditional flotation machine for two-stage series reverse flotation operation. The forced external circulation design can enhance the countercurrent contact effect of phosphogypsum slurry in the flotation column collection zone, avoiding the fluid turbulence and bubble coalescence that are prone to occur in traditional flotation columns, and ensuring sufficient gas-liquid contact within the column. Compared with traditional flotation machines, the flotation column with forced external circulation does not require stirring and foam scraping devices, greatly reducing the footprint and reducing overall energy consumption by more than 20%. Compared with ordinary flotation columns, the forced circulation slurry swirl feed forms a better mixture within the column while significantly reducing the required flotation column height. Detailed Implementation

[0028] The specific technical implementation schemes of the present invention will be further explained and illustrated below through examples.

[0029] Example 1 A certain phosphogypsum from Hubei Province has a CaSO4·2H2O content of 80.5%, a whiteness of 24.3, a SiO2 content of 8.1%, an organic matter content of 2.4%, and a pH value of 4.13. A purification and impurity removal experiment was conducted, including the following steps: 1) Add water to phosphogypsum to adjust its solid content to 35%, then stir and disperse it thoroughly to form a uniform slurry; 2) The phosphogypsum slurry obtained in step 1) is fed into a high-frequency vibrating screen system for particle size classification. The vibrating screen frequency is 1500 times / min and the screen aperture is 200μm. The phosphogypsum slurry under the screen is collected.

[0030] 3) The phosphogypsum slurry obtained in step 2) is fed into a slurry mixing tank. Phenolic oil (boiling range 170-180℃) is added to the slurry in the tank as a collector at a rate of 0.20 kg / t. The mixture is then stirred and dispersed thoroughly. 4) The phosphogypsum slurry obtained in step 3) is fed into the first-stage flotation column with forced external circulation for reverse flotation. The flotation column with forced external circulation includes a column body (400mm in diameter and 1m in height), an external circulation pump, and a level and flow control system. A radial flow stabilizer plate is installed inside the column to disperse bubbles and stabilize the flow pattern, eliminating the need for a bubble scraper. The external circulation pump draws out a portion of the slurry from the bottom of the column and feeds it into the column in a swirling manner, enhancing material mixing within the column while reducing the height of the column flotation, thus avoiding phenomena such as fluid turbulence and bubble coalescence that are common in traditional flotation columns. A bubble generator is also installed at the inlet of the external circulation pump, connected to the circulating slurry feed pipe, to draw in bubbles using the Venturi effect. The column is divided into a foam zone and a trapping zone from top to bottom. The phosphogypsum slurry is fed in from the middle of the column, flowing downwards. In the trapping zone, bubbles form and collide with particles in a counter-current flow. Hydrophobic solid particles adhere to the surface of the bubbles, forming aggregates of mineralized bubbles that rise to the foam zone and become foam, exiting from the top with the airflow as tailings. Hydrophilic particles that are not adhered to the foam are discharged from the bottom of the column, becoming the roughing phosphogypsum slurry.

[0031] 5) The roughing tailings obtained in step 4) are sent to the tailings tank, and the roughing phosphogypsum slurry enters the cleaning slurry preparation tank. Phenolic oil is added to the slurry in the tank as a collector at a rate of 0.10 kg / t. The slurry is then sent to the second-stage flotation column with forced external circulation for cleaning. The operation method is exactly the same as that of roughing, and concentrate and middlings with certain impurities are obtained.

[0032] 6) The middlings obtained in step 5) are fed into the roughing slurry tank and mixed with the raw phosphogypsum slurry. The roughing reverse flotation operation is carried out again to form a closed loop; the concentrate enters the purified gypsum slurry tank.

[0033] 7) The purified phosphogypsum from the purified gypsum slurry tank is washed with water, filtered by pressure, and completely dried at 80℃ to obtain phosphogypsum powder, in which the CaSO4·2H2O content is 91.2%, the phosphogypsum concentrate yield is 93.79%, the whiteness of phosphogypsum is 58.02, the SiO2 content is 1.21%, the organic matter content is 0.30%, the water-soluble P2O5 content is 0.031%, and the water-soluble fluorine content is 0.023%.

[0034] Example 2 A certain phosphogypsum from Hubei Province has a CaSO4·2H2O content of 80.5%, a whiteness of 24.3, a SiO2 content of 8.1%, an organic matter content of 2.4%, and a pH value of 4.13. A purification and impurity removal experiment was conducted, including the following steps: Phosphogypsum was mixed with water to achieve a solid content of 35% and thoroughly stirred and dispersed. The phosphogypsum slurry was then fed into a high-frequency vibrating screen for sieving and classification. The screen aperture was 100 μm. The material on the screen was removed. Phenolic oil was added as a collector to the collected phosphogypsum slurry at a rate of 0.10 kg / t and thoroughly stirred and dispersed. The phosphogypsum slurry was then fed into two sets of flotation columns with forced external circulation for a "roughing and cleaning" reverse flotation operation. The flotation column structure and flotation process used were the same as in Example 1. The phosphogypsum purified by flotation was washed with water, filtered, and dried to obtain phosphogypsum powder with a CaSO4·2H2O content of 88.2%, a phosphogypsum concentrate yield of 84.3%, a phosphogypsum whiteness of 54.5, a SiO2 content of 0.96%, an organic matter content of 0.75%, a water-soluble P2O5 content of 0.041%, and a water-soluble fluorine content of 0.027%.

[0035] Example 3 A certain phosphogypsum from Hubei Province has a CaSO4·2H2O content of 80.5%, a whiteness of 24.3, a SiO2 content of 8.1%, an organic matter content of 2.4%, and a pH value of 4.13. A purification and impurity removal experiment was conducted, including the following steps: Phosphogypsum was mixed with water to achieve a solid content of 35% and thoroughly stirred and dispersed. The phosphogypsum slurry was then fed into a high-frequency vibrating screen for grading and screening. The screen aperture was 200 μm, and the material on the screen was removed. Phenolic oil was added as a collector to the collected undersize phosphogypsum slurry at a rate of 0.5 kg / t and thoroughly stirred and dispersed. The phosphogypsum slurry was then sequentially fed into two sets of flotation columns with forced external circulation for a "roughing and cleaning" reverse flotation operation. The flotation columns and flotation process used were the same as in Example 1. The flotation-purified phosphogypsum was washed with water, filtered, and dried to obtain the final product, high-grade phosphogypsum powder, with a CaSO4·2H2O content of 92.5%, a phosphogypsum concentrate yield of 90.2%, a phosphogypsum whiteness of 60.3, a SiO2 content of 1.01%, an organic matter content of 0.25%, a water-soluble P2O5 content of 0.019%, and a water-soluble fluorine content of 0.024%.

[0036] Example 4 A certain phosphogypsum from Hubei Province has a CaSO4·2H2O content of 80.5%, a whiteness of 24.3, a SiO2 content of 8.1%, an organic matter content of 2.4%, and a pH value of 4.13. A purification and impurity removal experiment was conducted, including the following steps: Phosphogypsum was mixed with water to achieve a solid content of 35% and thoroughly stirred and dispersed. The phosphogypsum slurry was then fed into a high-frequency vibrating screen for grading and screening. The screen aperture was 200 μm, and the material on the screen was removed. Phenolic oil was added as a collector to the collected undersize phosphogypsum slurry at a rate of 0.05 kg / t and thoroughly stirred and dispersed. The phosphogypsum slurry was then sequentially fed into two sets of flotation columns with forced external circulation for a "roughing and cleaning" reverse flotation operation. The flotation columns and flotation process used were the same as in Example 1. The phosphogypsum purified by flotation was washed with water, filtered, and dried to obtain the final product, high-grade phosphogypsum powder, with a CaSO4·2H2O content of 88.7%, a phosphogypsum concentrate yield of 89.1%, a phosphogypsum whiteness of 53.3, a SiO2 content of 1.41%, an organic matter content of 1.25%, a water-soluble P2O5 content of 0.037%, and a water-soluble fluorine content of 0.020%.

[0037] Industrial measurements show that the technology of this invention significantly reduces the floor space required for processing each ton of phosphogypsum compared to traditional flotation machines, reduces power consumption by 23%, and lowers reagent costs to only 4 yuan, resulting in a total operating cost of 23 yuan per ton. Currently, even companies using column flotation technology (which differs from our process in terms of reagents and column structure) generally face costs exceeding 30 yuan per ton.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Within the technical scope disclosed in the present invention, any equivalent substitutions or modifications made according to the technical solution and inventive concept of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for purifying phosphogypsum using a staged coupled forced external circulation flotation column, characterized in that, Includes the following steps: 1) Add water to phosphogypsum to make a slurry, thus obtaining phosphogypsum slurry; 2) Screen the phosphogypsum slurry obtained in step 1) to remove high-silica large-particle minerals and undecomposed phosphate rock, and collect the phosphogypsum slurry under the screen. 3) Add the reverse flotation collector to the phosphogypsum slurry obtained in step 2) and stir to adjust the slurry; wherein the reverse flotation collector is the distillate oil collected from coal tar at 160-250℃; 4) The phosphogypsum slurry obtained in step 3) is sequentially fed into two sets of flotation columns with forced external circulation for roughing and cleaning two-stage reverse flotation operations, wherein: the roughing process yields tailings and roughing phosphogypsum slurry, the roughing phosphogypsum slurry is added with a reverse flotation collector and then cleaned to obtain cleaning phosphogypsum slurry and middlings, the middlings are then subjected to roughing and reverse flotation operations again to form a closed loop; 5) The selected phosphogypsum slurry obtained in step 4) is washed with water, filtered by pressure, and dried to obtain purified phosphogypsum.

2. The method according to claim 1, characterized in that, In step 1), the CaSO4·2H2O content in phosphogypsum is 75-85%, the whiteness of phosphogypsum is <30, the SiO2 content is 5-9%, and the organic matter content is 1-3%; the solid content in phosphogypsum slurry is 30-40wt%.

3. The method according to claim 1, characterized in that, In step 2), the sieve mesh size is 100-400μm.

4. The method according to claim 1, characterized in that, In step 2), a high-frequency vibrating screen is used for screening, wherein the vibration frequency is 1500-2500 times / minute.

5. The method according to claim 1, characterized in that, In step 3), the amount of reverse flotation collector added is 0.1-0.5 kg / t phosphogypsum; in step 4), during the fine cleaning process, the amount of reverse flotation collector added is 0.05-0.3 kg / t phosphogypsum.

6. The method according to claim 1, characterized in that, In step 3), the reverse flotation collector is phenol oil.

7. The method according to claim 1, characterized in that, In step 4), the flotation column with forced external circulation includes a column body, an external circulation pump, and a level and flow control system; wherein a radial flow stabilizing tube plate is provided in the column body to disperse bubbles and stabilize the flow pattern; the external circulation pump draws out part of the slurry from the bottom of the column body and sends it into the column body in a swirling manner, which enhances the mixing of materials in the column and reduces the height of the column flotation.

8. The method according to claim 7, characterized in that, The flotation column is also equipped with a bubble generator at the inlet of the external circulation pump, which is connected to the circulating slurry feed pipe.

9. The method according to claim 1, characterized in that, In step 4), the tailings yield is 10-20%.

10. The method according to claim 1, characterized in that, In step 5), the purified phosphogypsum has a SiO2 content of less than 1.5%, a purity of more than 10%, and a whiteness of more than 120%.