Method for purifying phosphogypsum based on phase reconstruction

Abstract

The invention discloses a method for purifying phosphogypsum based on phase reconstruction. The method comprises the following specific steps: (1) carrying out acid leaching and washing on phosphogypsum, and removing soluble phosphorus to obtain pretreated phosphogypsum; (2) adding an agent into the pretreated ardealite, uniformly mixing and roasting to obtain roasted ardealite; the medicament is at least one of solid organic acids; (3) leaching doped phosphorus from the roasted phosphogypsum, and carrying out solid-liquid separation; and (4) washing and drying filter residues to obtain purified gypsum. The removal rate of phosphorus reaches up to 90-100%, the purity of gypsum can reach 85-90%, and the requirements of first-grade natural dihydrate gypsum are met. The agent in the method has a double-effect synergistic effect, can promote phase change to reduce the phase change temperature, can change the existence form of phosphorus in the leachate, and is beneficial to phosphorus leaching, so that the eutectic phosphorus in the phosphogypsum can be mildly and efficiently removed, the purity of the gypsum is improved, and the comprehensive utilization of the phosphogypsum is facilitated.

Description

Technical Field

[0001] The invention relates to a method for efficiently purifying phosphogypsum based on phase reconstruction, and belongs to the field of phosphogypsum purification. Background Art

[0002] Phosphogypsum, a byproduct of phosphoric acid production, is produced in significant quantities, accounting for 70% of the total annual industrial gypsum output. Phosphogypsum is primarily stockpiled, occupying significant land resources. Its presence of impurities not only reduces its purity and limits its application, but also causes environmental pollution and even harms human health through the release of impurities. Therefore, removing impurities and improving its purity are crucial prerequisites for its comprehensive utilization.

[0003] Impurities in phosphogypsum can be mainly divided into adsorbed state, mixed state and doped state. Among them, the adsorbed state and mixed state are soluble phosphorus, which can be removed by simple acid washing and water washing. However, the eutectic phosphorus existing in the doped state replaces SO4 through isomorphous substitution. 2- However, eutectic phosphorus, which is present in the gypsum crystal structure, is difficult to remove through simple acid and water washing. Therefore, removing eutectic phosphorus is crucial for improving impurity separation efficiency. Currently, eutectic phosphorus removal is primarily achieved through hydrothermal reactions or high-temperature calcination. This process involves phase reconfiguration, with gypsum transforming between dihydrate, semi-hydrated, and anhydrous phases. Due to differences in binding energies between ions, phosphogypsum preferentially combines to form a pure calcium sulfate phase when transitioning from the dihydrate to the semi-hydrated or anhydrous phases, thereby allowing the eutectic phosphorus to be expelled. However, dehydration and hydration occur simultaneously in the hydrothermal reaction, and the phase transition requires a complete dissolution and recrystallization process, requiring relatively high temperatures. However, due to the small difference in binding energies between ions, the higher the temperature, the more energy is generated, making it highly susceptible to back-incorporation of impurities. Strong acids are typically required to enhance the binding energy difference. Calcination, on the other hand, expel impurities through atomic rearrangement triggered by the removal of water molecules. Furthermore, dehydration and hydration occur separately in this process, allowing the phase transition of phosphogypsum to be controlled by energy input, achieving eutectic phosphorus expulsion. Therefore, this process avoids back-incorporation of impurities. However, the temperature or time required to achieve phase change through roasting is high, resulting in high energy consumption. For example, Zheng et al. roasted at 200°C and 400°C for 2h to achieve the phase change of industrial by-product gypsum into semi-hydrated and anhydrous phases; and the phosphorus discharged is mostly in the form of insoluble phosphorus, resulting in poor direct water leaching effect. For example, Lv et al. roasted at 165°C for 2h and leached with water and acid respectively. They found that the phase after roasting was semi-hydrated gypsum, and the water leaching phosphorus removal rate was only 5.5%. The phosphorus removal rate was only over 90% when leaching with 1wt% H2SO4.

[0004] In view of this, providing a mild and efficient method for removing eutectic phosphorus in phosphogypsum is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The primary objective of the present invention is to provide a method for efficiently purifying phosphogypsum based on phase reconstruction. This method achieves gentle and efficient removal of soluble phosphorus and eutectic phosphorus (doped phosphorus) from phosphogypsum by adding a reagent to assist in calcination during the leaching process, promoting phase transformation, lowering the phase transition temperature, and regulating the phosphorus form in the leachate.

[0006] In order to achieve the above object, a method for purifying phosphogypsum based on phase reconstruction specifically comprises the following steps:

[0007] (1) acid leaching and washing the phosphogypsum to remove soluble phosphorus to obtain pretreated phosphogypsum;

[0008] (2) adding a reagent to the pretreated phosphogypsum, mixing them uniformly and calcining them to obtain calcined phosphogypsum; the reagent being at least one of solid organic acids;

[0009] (3) leaching the doped phosphorus from the calcined phosphogypsum and performing solid-liquid separation;

[0010] (4) Wash the filter residue and dry it to obtain purified gypsum.

[0011] In step (1), acid is added to the phosphogypsum according to a solid-liquid ratio of 1:2 to 1:20 g / mL; the acid includes an inorganic acid: at least one of sulfuric acid, hydrochloric acid, and nitric acid, and the acid concentration is 0.0001 to 0.01 mol / L.

[0012] After acid leaching in step (1), the product is washed with pure water several times, dried after solid-liquid separation, and ground through a 100-mesh sieve to obtain pretreated phosphogypsum.

[0013] During the acid leaching in step (1), the stirring rate is 150-400 rpm, and the stirring time does not exceed 2 hours; the solid-liquid ratio of pure water added for washing is 1:2-1:50 g / mL, and the number of washing times is 1-5 times.

[0014] In the present invention, the acid leaching and washing in step (1) can be carried out at room temperature. After filtration, the product can be placed in a blast drying oven for drying and grinding. The temperature of the blast drying oven is 40-60° C., and the grinding time is 2-24 hours. The grinding tool is an agate mortar or a ceramic mortar, and the grinding method is manual grinding.

[0015] The gypsum: agent ratio in step (2) is 1:1 to 20:1 g / g, and the agent includes at least one of p-toluenesulfonic acid, benzenesulfonic acid, aminosulfonic acid, and ascorbic acid.

[0016] Unlike conventional liquid acid-water reactions, this method uses a solid organic acid and phosphogypsum for solid-phase roasting in an anhydrous state. This reduces the temperature and time required for the phosphogypsum to reach the anhydrous phase, significantly saving time and energy. Furthermore, adding the solid organic acid during roasting is significantly more effective than adding it after roasting.

[0017] The phosphogypsum pretreated in step (2) is added with a reagent, mixed and ground evenly, the grinding tool is an agate mortar or a ceramic mortar, and the grinding method is manual grinding.

[0018] The roasting temperature in step (2) is 90-120° C., and the roasting time is 0.5-2 h.

[0019] In step (2) of the present invention, the reagent is added, and after being ground and mixed evenly, the mixture can be placed in an oven at a set temperature for roasting.

[0020] In step (3), pure water is added for leaching, and the solid-liquid ratio is 1:10 to 1:50 g / mL.

[0021] The stirring rate of step (3) leaching is 150-400 rpm, the stirring time is no more than 24 hours, and the standing time is no more than 4 hours. In step (3) of the present invention, pure water is added, and the solid-liquid separation can be carried out after magnetic stirring at room temperature and standing for a certain period of time.

[0022] Step (4) washing the filter residue with pure water for 3-5 times and drying at 60° C. for 12 h to obtain purified gypsum.

[0023] The present invention performs acid-addition microwave digestion on the phosphogypsum pretreated in step (1), and measures the phosphorus content in the digestion solution by ammonium molybdate spectrophotometry. The leachate from step (3) is then subjected to pH measurement, and the pH is between 2 and 6. The phosphate concentration is also measured by ammonium molybdate spectrophotometry. Calculations show that the phosphorus removal rate is as high as 90-100%.

[0024] The filtration residue dried in step (4) is tested for crystal water according to GB / T 5484-2024 "Chemical Analysis Methods for Gypsum", and the purity of gypsum is calculated to be 85-90% according to GB / T 5483-2024 "Natural Gypsum", which meets the requirements of first-grade natural dihydrate gypsum.

[0025] Compared with the prior art, the technical solution of the present invention has at least the following advantages:

[0026] 1. The present invention requires only a few types of additives and is simple to operate. The present invention only requires adding solid organic acid to the pretreated phosphogypsum, grinding it evenly, and then roasting it, followed by leaching with pure water to remove phosphorus impurities.

[0027] 2. The added agent of the present invention has a dual synergistic effect. The added agent of the present invention can promote the transformation of phosphogypsum into semi-hydrated or anhydrous gypsum, reduce the temperature required for the phase change of phosphogypsum, and achieve mild phosphorus removal; at the same time, during the leaching process, the addition of the agent can promote the dissolution of phosphorus and regulate the existence form of phosphorus by changing the pH, so that HPO4 2- →H3PO4 or H2PO4 - , achieving efficient phosphorus removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0029] Figure 1 This is a bar graph showing the gypsum phase composition and impurity removal rules after phosphogypsum was calcined at different temperatures for 2 hours;

[0030] Experimental results show that the best impurity removal effect is achieved when phosphogypsum is roasted into an anhydrous phase, and the present invention can greatly reduce the temperature at which phosphogypsum becomes an anhydrous phase after adding solid organic acid.

[0031] Figure 2 The XRD patterns of the phosphogypsum after calcination and the histograms of the contents of different gypsum phases in Examples 1, 2, 3, 4 and Comparative Examples 1 and 2 are shown;

[0032] The experimental results show that the addition of p-toluenesulfonic acid and benzenesulfonic acid can significantly accelerate the phase change process, so that phosphogypsum can be converted into anhydrous gypsum after roasting at 100°C for only 1 hour.

[0033] Figure 3 The pH diagrams of the leachates in Examples 1, 2, 3, 4 and Comparative Examples 1 and 2, as well as a schematic diagram of how to change the pH to promote phosphorus dissolution and regulate the existence form of phosphorus;

[0034] The experimental results show that adding the agent can significantly reduce the pH, which is conducive to the dissolution of the phosphorus removed, and can change the form of phosphorus, making HPO4 2- →H3PO4 or H2PO4 - , inhibiting the reverse doping of phosphorus.

[0035] Figure 4 The figure is a bar graph showing the phosphorus removal rate of phosphogypsum in Examples 1, 2, 3, 4 and Comparative Example 1;

[0036] The experimental results show that the phosphorus removal rate is significantly improved after adding the agent treatment.

[0037] Figure 5 1 is a bar graph showing the phosphorus removal rate of phosphogypsum in Example 1 and Comparative Example 2;

[0038] The experimental results show that the effect of adding the agent before roasting is significantly better than adding it after roasting, because adding it before roasting can promote the phase transformation into anhydrous gypsum, which is beneficial to the removal of phosphorus.

[0039] Figure 6 The figure is a bar graph showing the purity of gypsum in Examples 1, 2, 3, and 4, Comparative Examples 1 and 2, and the original slag;

[0040] The experimental results show that the purity of gypsum is improved after adding the agent. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] Moreover, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0043] When numerical ranges are given in the examples, it should be understood that unless otherwise specified herein, both endpoints of each numerical range and any value between the two endpoints may be used. Unless otherwise defined, all technical and scientific terms used herein are consistent with the prior art as understood by those skilled in the art and the description of the present invention. Any prior art methods, devices, and materials similar or equivalent to those described in the examples of the present invention may also be used to implement the present invention.

[0044] The technical solutions provided by the present invention are described in detail below with reference to specific examples, but they should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] A method for efficiently purifying phosphogypsum based on phase reconstruction comprises the following steps:

[0047] Step 1: Weigh 15 g of phosphogypsum using an electronic balance, add dilute hydrochloric acid with a pH of 4 and a solid-liquid ratio of 1:10 g / mL; use a room temperature magnetic stirrer for magnetic stirring, set the stirring speed to 300 rpm, stir for 30 minutes, and then filter; add pure water at a solid-liquid ratio of 1:30 g / mL and wash and filter 3 to 4 times, place in a 60°C forced air drying oven for 12 hours, and manually grind with an agate mortar and pass through a 100 mesh sieve to obtain pretreated phosphogypsum;

[0048] Step 2: Using an electronic balance, 0.1 g of the pretreated phosphogypsum was weighed, and p-toluenesulfonic acid was added according to the ratio of gypsum to reagent = 3:1 g / g. The mixture was manually ground using an agate mortar and pestle, and then placed in a 100° C. forced air drying oven, and calcined for 1 hour to obtain the calcined phosphogypsum.

[0049] Step 3: Using an electronic balance, 0.05 g of the calcined phosphogypsum was weighed and added to pure water at a solid-liquid ratio of 1:30 g / mL. The mixture was magnetically stirred using a room temperature magnetic stirrer at a speed of 300 rpm. After stirring for 12 h, the rotor was removed and allowed to stand at room temperature for 1 h. The leachate and the residue were then filtered and separated;

[0050] Step 4: Using a PHS-3E pH meter, the pH of the leachate was measured to be 3.12, and the phosphate concentration was measured by ammonium molybdate spectrophotometry. The filter residue was washed and filtered 3 to 5 times with pure water, and then dried at 60° C. for 12 hours to obtain purified gypsum.

[0051] Step 5: Using an electronic balance, weigh 0.1 g of the phosphogypsum pretreated in step 1 and perform acid-addition microwave digestion. The phosphorus content in the digestion solution is measured by ammonium molybdate spectrophotometry, and the phosphorus removal rate is calculated based on the phosphorus concentration in the leachate measured above.

[0052] Step 6: Determine the crystal water of the dried filter residue according to GB / T 5484-2024 "Chemical Analysis Methods for Gypsum" and calculate the gypsum purity according to GB / T5483-2024 "Natural Gypsum".

[0053] In this embodiment, the phosphorus content in the phosphogypsum after pretreatment in step 1 is 4126 mg / kg, and the phosphorus content in the supernatant after the above treatment (the supernatant obtained by leaching the phosphogypsum after roasting) is 123.8 mg / L. The calculated phosphorus extraction rate is 90% and the gypsum purity is 88%, which meets the first-class natural dihydrate gypsum standard.

[0054] Example 2

[0055] A method for efficiently purifying phosphogypsum based on phase reconstruction comprises the following steps:

[0056] Step 1: Weigh 15 g of phosphogypsum using an electronic balance, add dilute hydrochloric acid with a pH of 4 and a solid-liquid ratio of 1:10 g / mL; use a room temperature magnetic stirrer for magnetic stirring, set the stirring speed to 300 rpm, stir for 30 minutes, and then filter; add pure water at a solid-liquid ratio of 1:30 g / mL and wash and filter 3 to 4 times, place in a 60°C forced air drying oven for 12 hours, and manually grind with an agate mortar and pass through a 100 mesh sieve to obtain pretreated phosphogypsum;

[0057] Step 2: Using an electronic balance, 0.1 g of the pretreated phosphogypsum was weighed, and benzenesulfonic acid was added according to the ratio of gypsum to reagent = 3:1 g / g. The mixture was manually ground using an agate mortar and pestle, and then placed in a 100° C. forced air drying oven, and calcined for 1 hour to obtain the calcined phosphogypsum.

[0058] Step 3: Using an electronic balance, 0.05 g of the calcined phosphogypsum was weighed and added to pure water at a solid-liquid ratio of 1:30 g / mL. The mixture was magnetically stirred using a room temperature magnetic stirrer at a speed of 300 rpm. After stirring for 12 h, the rotor was removed and allowed to stand at room temperature for 1 h. The leachate and the residue were then filtered and separated;

[0059] Step 4: Using a PHS-3E pH meter, the pH of the leachate was measured to be 3.01, and the phosphate concentration was measured by ammonium molybdate spectrophotometry. The filter residue was washed and filtered 3 to 5 times with pure water, and then dried at 60° C. for 12 hours to obtain purified gypsum.

[0060] Step 5: Using an electronic balance, weigh 0.1 g of the phosphogypsum pretreated in step 1 and perform acid-addition microwave digestion. The phosphorus content in the digestion solution is measured by ammonium molybdate spectrophotometry, and the phosphorus removal rate is calculated based on the phosphorus concentration in the leachate measured above.

[0061] Step 6: Determine the crystal water of the dried filter residue according to GB / T 5484-2024 "Chemical Analysis Methods for Gypsum" and calculate the gypsum purity according to GB / T5483-2024 "Natural Gypsum".

[0062] In this embodiment, the phosphorus content in the phosphogypsum after pretreatment in step 1 is 4126 mg / kg, and the phosphorus content in the supernatant after the above treatment is 106.3 mg / L. The calculated phosphorus extraction rate is 77.3%, and the gypsum purity is 86%, which meets the first-class natural dihydrate gypsum standard.

[0063] Example 3

[0064] A method for efficiently purifying phosphogypsum based on phase reconstruction comprises the following steps:

[0065] Step 1: Weigh 15 g of phosphogypsum using an electronic balance, add dilute hydrochloric acid with a pH of 4 and a solid-liquid ratio of 1:10 g / mL; use a room temperature magnetic stirrer for magnetic stirring, set the stirring speed to 300 rpm, stir for 30 minutes, and then filter; add pure water at a solid-liquid ratio of 1:30 g / mL and wash and filter 3 to 4 times, place in a 60°C forced air drying oven for 12 hours, and manually grind with an agate mortar and pass through a 100 mesh sieve to obtain pretreated phosphogypsum;

[0066] Step 2: Using an electronic balance, 0.1 g of the pretreated phosphogypsum was weighed and added with aminosulfonic acid according to the ratio of gypsum to reagent = 3:1 g / g. The mixture was manually ground using an agate mortar and pestle, and then placed in a forced air drying oven at 100° C. and calcined for 1 hour to obtain the calcined phosphogypsum.

[0067] Step 3: Using an electronic balance, 0.05 g of the calcined phosphogypsum was weighed and added to pure water at a solid-liquid ratio of 1:30 g / mL. The mixture was magnetically stirred using a room temperature magnetic stirrer at a speed of 300 rpm. After stirring for 12 h, the rotor was removed and allowed to stand at room temperature for 1 h. The leachate and the residue were then filtered and separated;

[0068] Step 4: Using a PHS-3E pH meter, the pH of the leachate was measured to be 2.98, and the phosphate concentration was measured by ammonium molybdate spectrophotometry. The filter residue was washed and filtered 3 to 5 times with pure water, and then dried at 60° C. for 12 hours to obtain purified gypsum.

[0069] Step 5: Using an electronic balance, weigh 0.1 g of the phosphogypsum pretreated in step 1 and perform acid-addition microwave digestion. The phosphorus content in the digestion solution is measured by ammonium molybdate spectrophotometry, and the phosphorus removal rate is calculated based on the phosphorus concentration in the leachate measured above.

[0070] Step 6: Determine the crystal water of the dried filter residue according to GB / T 5484-2024 "Chemical Analysis Methods for Gypsum" and calculate the gypsum purity according to GB / T5483-2024 "Natural Gypsum".

[0071] In this embodiment, the phosphorus content in the phosphogypsum after pretreatment in step 1 is 4126 mg / kg, and the phosphorus content in the supernatant after the above treatment is 99.7 mg / L. The calculated phosphorus extraction rate is 71.9%, and the gypsum purity is 85%, which meets the first-class natural dihydrate gypsum standard.

[0072] Example 4

[0073] A method for efficiently purifying phosphogypsum based on phase reconstruction comprises the following steps:

[0074] Step 1: Weigh 15 g of phosphogypsum using an electronic balance, add dilute hydrochloric acid with a pH of 4 and a solid-liquid ratio of 1:10 g / mL; use a room temperature magnetic stirrer for magnetic stirring, set the stirring speed to 300 rpm, stir for 30 minutes, and then filter; add pure water at a solid-liquid ratio of 1:30 g / mL and wash and filter 3 to 4 times, place in a 60°C forced air drying oven for 12 hours, and manually grind with an agate mortar and pass through a 100 mesh sieve to obtain pretreated phosphogypsum;

[0075] Step 2: Using an electronic balance, 0.1 g of the pretreated phosphogypsum was weighed and ascorbic acid was added according to the ratio of gypsum to reagent = 3:1 g / g. The mixture was manually ground using an agate mortar and pestle, and then placed in a 100° C. forced air drying oven and calcined for 1 hour to obtain the calcined phosphogypsum.

[0076] Step 3: Using an electronic balance, 0.05 g of the calcined phosphogypsum was weighed and added to pure water at a solid-liquid ratio of 1:30 g / mL. The mixture was magnetically stirred using a room temperature magnetic stirrer at a speed of 300 rpm. After stirring for 12 h, the rotor was removed and allowed to stand at room temperature for 1 h. The leachate and the residue were then filtered and separated;

[0077] Step 4: Using a PHS-3E pH meter, the pH of the leachate was measured to be 3.44, and the phosphate concentration was measured by ammonium molybdate spectrophotometry. The filter residue was washed and filtered 3 to 5 times with pure water, and then dried at 60° C. for 12 hours to obtain purified gypsum.

[0078] Step 5: Using an electronic balance, weigh 0.1 g of the phosphogypsum pretreated in step 1 and perform acid-addition microwave digestion. The phosphorus content in the digestion solution is measured by ammonium molybdate spectrophotometry, and the phosphorus removal rate is calculated based on the phosphorus concentration in the leachate measured above.

[0079] Step 6: Determine the crystal water of the dried filter residue according to GB / T 5484-2024 "Chemical Analysis Methods for Gypsum" and calculate the gypsum purity according to GB / T5483-2024 "Natural Gypsum".

[0080] In this embodiment, the phosphorus content in the phosphogypsum after pretreatment in step 1 is 4126 mg / kg, and the phosphorus content in the supernatant after the above treatment is 46.6 mg / L. The calculated phosphorus extraction rate is 33.9%, and the gypsum purity is 85%, which meets the first-class natural dihydrate gypsum standard.

[0081] Comparative Example 1 (the difference from Example 1 is that no agent is added)

[0082] Step 1: Weigh 15 g of phosphogypsum using an electronic balance, add dilute hydrochloric acid with a pH of 4 and a solid-liquid ratio of 1:10 g / mL; use a room temperature magnetic stirrer for magnetic stirring, set the stirring speed to 300 rpm, stir for 30 minutes, and then filter; add pure water at a solid-liquid ratio of 1:30 g / mL and wash and filter 3 to 4 times, place in a 60°C forced air drying oven for 12 hours, and manually grind with an agate mortar and pass through a 100 mesh sieve to obtain pretreated phosphogypsum;

[0083] Step 2: Using an electronic balance, 0.1 g of the pretreated phosphogypsum was weighed and placed in a 100° C. forced air drying oven, and then taken out after roasting for 1 hour to obtain roasted phosphogypsum;

[0084] Step 3: Using an electronic balance, 0.05 g of the calcined phosphogypsum was weighed and added to pure water at a solid-liquid ratio of 1:30 g / mL. The mixture was magnetically stirred using a room temperature magnetic stirrer at a speed of 300 rpm. After stirring for 12 h, the rotor was removed and allowed to stand at room temperature for 1 h. The leachate and the residue were then filtered and separated;

[0085] Step 4: Using a PHS-3E pH meter, the pH of the leachate was measured to be 7.32, and the phosphate concentration was measured by ammonium molybdate spectrophotometry. The filter residue was washed and filtered 3 to 5 times with pure water, and dried at 60° C. for 12 hours to obtain purified gypsum.

[0086] Step 5: Using an electronic balance, weigh 0.1 g of the phosphogypsum pretreated in step 1 and perform acid-addition microwave digestion. The phosphorus content in the digestion solution is measured by ammonium molybdate spectrophotometry, and the phosphorus removal rate is calculated based on the phosphorus concentration in the leachate measured above.

[0087] Step 6: Determine the crystal water of the dried filter residue according to GB / T 5484-2024 "Chemical Analysis Methods for Gypsum" and calculate the gypsum purity according to GB / T5483-2024 "Natural Gypsum".

[0088] In this embodiment, the phosphorus content in the phosphogypsum after pretreatment in step 1 is 4126 mg / kg, and the phosphorus content in the supernatant after the above treatment is 2.1 mg / L. The calculated phosphorus extraction rate is 1.5%, and the gypsum purity is 83%, which meets the secondary standard of natural dihydrate gypsum.

[0089] Comparative Example 2 (the difference from Example 2 is that the reagent is added after roasting)

[0090] Step 1: Weigh 15 g of phosphogypsum using an electronic balance, add dilute hydrochloric acid with a pH of 4 and a solid-liquid ratio of 1:10 g / mL; use a room temperature magnetic stirrer for magnetic stirring, set the stirring speed to 300 rpm, stir for 30 minutes, and then filter; add pure water at a solid-liquid ratio of 1:30 g / mL and wash and filter 3 to 4 times, place in a 60°C forced air drying oven for 12 hours, and manually grind with an agate mortar and pass through a 100 mesh sieve to obtain pretreated phosphogypsum;

[0091] Step 2: Using an electronic balance, 0.1 g of the pretreated phosphogypsum was weighed and placed in a 100° C. forced air drying oven, and then taken out after roasting for 1 hour to obtain roasted phosphogypsum;

[0092] Step 3: Use an electronic balance to weigh 0.05g of the calcined phosphogypsum, add p-toluenesulfonic acid according to the ratio of gypsum to reagent = 3:1g / g, and then add pure water at a solid-liquid ratio of 1:30g / mL. Use a room temperature magnetic stirrer for magnetic stirring, set the stirring speed to 300rpm, stir for 12h, remove the rotor, and let it stand at room temperature for 1h, then filter and separate the leachate and the filter residue;

[0093] Step 4: Using a PHS-3E pH meter, the pH of the leachate was measured to be 2.89, and the phosphate concentration was measured by ammonium molybdate spectrophotometry. The filter residue was washed and filtered 3 to 5 times with pure water, and dried at 60° C. for 12 hours to obtain purified gypsum.

[0094] Step 5: Using an electronic balance, weigh 0.1 g of the phosphogypsum pretreated in step 1 and perform acid-addition microwave digestion. The phosphorus content in the digestion solution is measured by ammonium molybdate spectrophotometry, and the phosphorus removal rate is calculated based on the phosphorus concentration in the leachate measured above.

[0095] Step 6: Determine the crystal water of the dried filter residue according to GB / T 5484-2024 "Chemical Analysis Methods for Gypsum" and calculate the gypsum purity according to GB / T5483-2024 "Natural Gypsum".

[0096] In this embodiment, the phosphorus content in the phosphogypsum after pretreatment in step 1 is 4126 mg / kg, and the phosphorus content in the supernatant after the above treatment is 68.4 mg / L. The calculated phosphorus extraction rate is 49.7%, and the gypsum purity is 85%, which meets the first-class natural dihydrate gypsum standard.

Claims

1. A method for purifying phosphogypsum based on phase reconstruction, characterized in that: The specific steps include: (1) acid leaching and washing the phosphogypsum to remove soluble phosphorus to obtain pretreated phosphogypsum; (2) adding a reagent to the pretreated phosphogypsum, mixing them uniformly and calcining them to obtain calcined phosphogypsum; the reagent being at least one of solid organic acids; (3) leaching the doped phosphorus from the calcined phosphogypsum and performing solid-liquid separation; (4) Wash the filter residue and dry it to obtain purified gypsum.

2. The method according to claim 1, characterized in that In step (1), acid is added to the phosphogypsum according to a solid-liquid ratio of 1:2 to 1:20 g / mL; the acid includes an inorganic acid: at least one of sulfuric acid, hydrochloric acid, and nitric acid, and the acid concentration is 0.0001 to 0.01 mol / L.

3. The method according to claim 1, characterized in that After acid leaching in step (1), the product is washed with pure water several times, dried after solid-liquid separation, and ground through a 100-mesh sieve to obtain pretreated phosphogypsum.

4. The method according to claim 1, 2 or 3, characterized in that: During the acid leaching in step (1), the stirring rate is 150-400 rpm, and the stirring time does not exceed 2 hours; the solid-liquid ratio of pure water added for washing is 1:2-1:50 g / mL, and the number of washing times is 1-5 times.

5. The method according to claim 1, wherein The gypsum: agent ratio in step (2) is 1:1 to 20:1 g / g, and the agent includes at least one of p-toluenesulfonic acid, benzenesulfonic acid, aminosulfonic acid, and ascorbic acid.

6. The method according to claim 1, wherein: The phosphogypsum pretreated in step (2) is added with a reagent, mixed and ground evenly, the grinding tool is an agate mortar or a ceramic mortar, and the grinding method is manual grinding.

7. The method according to claim 1, 5 or 6, characterized in that: The roasting temperature in step (2) is 90-120° C., and the roasting time is 0.5-2 h.

8. The method according to claim 1, wherein: In step (3), pure water is added for leaching, and the solid-liquid ratio is 1:10 to 1:50 g / mL.

9. The method according to claim 1 or 8, characterized in that: In step (3), the leaching stirring rate is 150-400 rpm, the stirring time is no more than 24 hours, and the standing time is no more than 4 hours.

10. The method according to claim 1, wherein: Step (4) washing the filter residue with pure water for 3-5 times and drying to obtain purified gypsum.

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