Method for preparing nanosheet calcium sulfate from phosphogypsum, nanosheet calcium sulfate and application thereof

Abstract

The disclosure discloses a method for preparing nanosheet calcium sulfate from phosphogypsum, nanosheet calcium sulfate and application thereof, and relates to the technical field of waste recovery. The method comprises the following steps: obtaining purified gypsum by pretreating phosphogypsum; mixing inorganic salt and an alcohol solution containing a crystal form regulator, clarifying, aging, and obtaining a crystallization template liquid, wherein the crystal form regulator is a combination of coniferyl alcohol and 1,2-di(4-pyridyl)ethylene; beating and reacting the purified gypsum and the crystallization template liquid, and obtaining nanosheet calcium sulfate after post-treatment. The disclosure can control the crystal morphology of calcium sulfate, inhibit the growth of the {111} crystal face, realize the growth of the crystal in a two-dimensional plane, and further form a sheet-shaped crystal. The growth environment of the crystal is relatively stable and is not easily affected by impurities. The nanosheet calcium sulfate prepared has good dispersibility and is not easily agglomerated.

Description

Technical Field

[0001] This disclosure relates to the field of waste recycling technology, and more specifically, to a method for preparing nano-sheet calcium sulfate using phosphogypsum, the nano-sheet calcium sulfate and its applications. Background Technology

[0002] In existing technologies, there are many studies on the preparation of micron-sized calcium sulfate using industrial waste gypsum, and the crystal forms are mostly whiskers, short columnar, and spherical. There are few studies on nano-sized crystals or other specific shapes.

[0003] Nano-calcium sulfate is a functional inorganic powder material that possesses the excellent properties of ordinary powder materials, such as light weight, good cementation, sound insulation, heat insulation, and flame retardancy. It also has the characteristics of nanomaterials, such as good toughness, high strength, and strong affinity. It has advantages such as high temperature resistance and chemical corrosion resistance, and is widely used in many fields such as medicine, papermaking, environmental protection, and coatings.

[0004] As a special type of crystalline material, flaky calcium sulfate is increasingly used not only as a filler, reinforcing agent, and flame retardant in rubber and plastics, but also in the cosmetics industry, where it has attracted widespread attention for its role as a skin-smoothing and tactile improver for body pigments. Furthermore, its flaky structure amplifies the crystal surface effect, enhancing the reflection and refraction of light and heat, and holds promise for applications in thermal insulation materials, thereby increasing the comprehensive utilization value of gypsum byproducts.

[0005] It is evident that the preparation of nanosheet calcium sulfate materials has broad application prospects, but there is currently little research in this area, and there are no reports on the preparation of nanosheet calcium sulfate using phosphogypsum with many impurities.

[0006] In view of this, this disclosure is hereby made. Summary of the Invention

[0007] The purpose of this disclosure is to provide a method for preparing nano-sheet calcium sulfate using phosphogypsum, the nano-sheet calcium sulfate, and its applications.

[0008] This disclosure is implemented as follows:

[0009] In a first aspect, this disclosure provides a method for preparing nano-sheet calcium sulfate using phosphogypsum, comprising:

[0010] Purified gypsum is obtained by pretreatment of phosphogypsum;

[0011] After mixing and clarifying an inorganic salt and an alcohol solution containing a crystal form regulator, the mixture is aged to obtain a crystallization template solution. The crystal form regulator is a combination of leucopicrin and 1,2-di(4-pyridyl)ethylene.

[0012] The purified gypsum is pulped and reacted with the crystallization template liquid. After the reaction is completed, post-treatment yields nano-sheet calcium sulfate.

[0013] In an optional embodiment, the molar ratio of the taurine to the 1,2-bis(4-pyridyl)ethylene is 0.8-1.4:1.

[0014] In an optional embodiment, the amount of the crystal form regulator is 2 to 5% of the mass of the purified gypsum.

[0015] In an optional embodiment, the alcohol solution is a mixed solution of ethylene glycol and glycerol, wherein the mass ratio of glycerol in the alcohol solution is 30-50%.

[0016] In an optional embodiment, the solid-liquid ratio of the purified gypsum to the crystallizing template liquid during pulping is 0.02–0.25 g: 1 mL.

[0017] In an optional embodiment, the reaction between the purified gypsum and the crystallization template liquid after pulping is a isothermal reaction carried out under intermittent stirring conditions.

[0018] In an optional embodiment, the intermittent stirring conditions include stirring for 5 minutes every 15 to 30 minutes at a stirring speed of 200 to 300 rpm.

[0019] In an optional embodiment, the isothermal reaction is carried out at a temperature of 50-70°C for 5-10 hours.

[0020] In an optional embodiment, the inorganic salt includes one or more of calcium nitrate and sodium sulfate.

[0021] In an optional embodiment, the final concentration of the inorganic salt is 0.5 to 1 mol / L.

[0022] In an optional embodiment, the inorganic salt and the alcohol solution containing the crystal form regulator are mixed at a temperature of 60–80°C, and then aged at a constant temperature for 30 min–2 h.

[0023] In an optional embodiment, the pretreatment includes first washing the phosphogypsum with water until the pH is 6.5 to 7.0, then drying and sieving to obtain gypsum powder, mixing the gypsum powder, quicklime and water into a slurry for 24 to 48 hours, and then drying to obtain the purified gypsum.

[0024] In an optional embodiment, the mass ratio of the gypsum powder, the quicklime, and the water is 100:0.5 to 2:10 to 20.

[0025] In an optional embodiment, the sieving includes passing the dried phosphogypsum through a square-hole sieve with a aperture of 0.2-0.4 mm.

[0026] In an optional embodiment, the drying temperature is 40–50°C.

[0027] In an optional embodiment, the purified gypsum contains 80-98% calcium sulfate dihydrate, ≤0.1% soluble phosphorus, and ≤0.03% soluble fluorine.

[0028] In an optional embodiment, the post-processing includes: filtering the reaction solution to obtain a first filtrate and a first filter residue; washing the first filter residue with the alcohol solution and drying it to constant weight; then immersing it in an ether solution and stirring for 0.5-1 h; filtering to obtain a second filtrate and a second filter residue; and drying the second filter residue to constant weight to obtain the nano-sheet calcium sulfate.

[0029] In an optional embodiment, the method for preparing nano-sheet calcium sulfate using phosphogypsum further includes recovering alcohol waste liquid:

[0030] The washing liquid obtained after washing the first filtrate with the alcohol solution is combined and then subjected to a first vacuum distillation to recover the alcohol.

[0031] When the volume of the concentrate is 1 / 3 to 1 / 5 of the original volume, heating is stopped. After the concentrate is cooled to room temperature, diethyl ether is added to extract the organic matter, resulting in an alcohol solution containing inorganic salts and an ether solution containing crystal form regulators.

[0032] The alcohol solution containing inorganic salts was sealed and kept in the dark at room temperature for 3-4 days, and then filtered to obtain inorganic salt crystals.

[0033] The ether solution containing the crystal form regulator and the second filtrate were combined and subjected to a second vacuum distillation to ensure that the concentrations of 1,2-di(4-pyridyl)ethylene and leucopicrin were both ≥0.2 mol / L. The mixture was then sealed and allowed to stand at room temperature in the dark for 3-4 days before filtration to obtain supramolecular crystals, i.e., crystals formed by the non-covalent self-assembly of 1,2-di(4-pyridyl)ethylene and leucopicrin.

[0034] In an optional embodiment, the temperature of the first vacuum distillation is 120-200°C, and the vacuum degree is 0.1-1 mmHg.

[0035] In an optional embodiment, the temperature of the second vacuum distillation is 50-70°C, and the vacuum degree is 0.1-1 mmHg.

[0036] In an optional embodiment, the recovery rate of the inorganic salt is 75-85%, and the total recovery rate of the 1,2-di(4-pyridyl)ethylene and taurine is 55-60%.

[0037] In an optional embodiment, the concentrations of the 1,2-bis(4-pyridyl)ethylene and the paclitaxel are detected by ultraviolet absorption spectroscopy, liquid chromatography, or mass spectrometry.

[0038] Secondly, this disclosure provides a nano-sheet calcium sulfate, which is prepared by the method of preparing nano-sheet calcium sulfate using phosphogypsum as described in any of the foregoing embodiments.

[0039] Thirdly, this disclosure provides the use of the nano-sheet calcium sulfate as described in the foregoing embodiments in the preparation of fillers, reinforcing agents, flame retardants, skin smoothing agents, or thermal insulation materials.

[0040] This disclosure has the following beneficial effects:

[0041] The method for preparing nano-sheet calcium sulfate using phosphogypsum disclosed herein employs a composition of leucopicrin and 1,2-di(4-pyridyl)ethylene as a crystal form regulator. The complex formed by the self-assembly of leucopicrin and 1,2-di(4-pyridyl)ethylene in the liquid phase through coordination and π-π stacking interactions serves as a crystallization template for calcium sulfate, thereby controlling the crystal morphology of the calcium sulfate. Specifically, the o-phenolic hydroxyl groups of leucopicrin interact with the CaO on the surface of the calcium sulfate crystals. 2+ The crystals adsorb onto the {111} crystal plane, effectively inhibiting the growth of the {111} crystal plane and thus achieving crystal growth on a two-dimensional plane, forming plate-like crystals. Compared to using traditional crystal-changing agents or single crystal-changing agents, the template method for preparing calcium sulfate crystals provides a more stable crystal growth environment, less susceptible to impurities. Furthermore, the crystal template provided in this disclosure effectively prevents crystal aggregation, resulting in well-dispersed, non-adhesive plate-like nanocrystals. The prepared nano-plate-like calcium sulfate exhibits excellent dispersibility and is not prone to aggregation. It can be widely used in the preparation of fillers, reinforcing agents, flame retardants, skin smoothing agents, or thermal insulation materials. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a SEM image of the nano-sheet calcium sulfate obtained by the method of preparing nano-sheet calcium sulfate using phosphogypsum provided in Example 1 of this disclosure, at a scale of 1 μm.

[0044] Figure 2SEM image of the nano-sheet calcium sulfate obtained by the method of preparing nano-sheet calcium sulfate using phosphogypsum provided in Example 1 of this disclosure at a scale of 500 nm;

[0045] Figure 3 This is a schematic diagram illustrating the compositional analysis of the nano-sheet calcium sulfate obtained by the method of preparing nano-sheet calcium sulfate using phosphogypsum according to Embodiment 1 of this disclosure, and the phase composition of the first filter residue after drying.

[0046] Figure 4 This is a schematic diagram of the structure of the supramolecular crystal provided in Embodiment 4 of this disclosure. Detailed Implementation

[0047] The embodiments of this disclosure will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this disclosure. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0048] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein.

[0049] This disclosure provides a method for preparing nano-sheet calcium sulfate using phosphogypsum, which includes the following steps:

[0050] S1. Pretreatment of phosphogypsum.

[0051] Purified gypsum is obtained by pretreatment of phosphogypsum.

[0052] The pretreatment process includes washing the phosphogypsum with water until the pH reaches 6.5–7.0, then drying and sieving it (through a square-hole sieve with a aperture of 0.2–0.4 mm) to obtain gypsum powder. The gypsum powder, quicklime, and water are mixed in a mass ratio of 100:0.5–2:10–20 to form a slurry, which is then mixed for 24–48 hours and dried at 40–50°C to obtain purified gypsum.

[0053] In some typical embodiments, the mass ratio of gypsum powder, quicklime, and water can be, for example, any one or any two of the following: 100:0.5:10, 100:1:15, 100:1.5:20, 100:2:15, 100:0.8:17, and 100:0.5:20. The mixing time can be, for example, any one or any two of the following: 24h, 30h, 36h, 42h, and 48h. The drying temperature can be, for example, any one or any two of the following: 40℃, 42℃, 45℃, 46℃, 48℃, and 50℃.

[0054] The purified gypsum contains 80-98% calcium sulfate dihydrate, ≤0.1% soluble phosphorus, and ≤0.03% soluble fluorine.

[0055] S2. Prepare the crystallization template solution.

[0056] An inorganic salt and an alcohol solution containing a crystal form regulator are mixed and clarified at 60–80°C, and then aged for 30 min–2 h to obtain a crystallization template solution.

[0057] The inorganic salts include one or more of calcium nitrate and sodium sulfate. The final concentration of the inorganic salts is 0.5–1 mol / L. The inorganic salts in this disclosure are used to enhance the solubility of purified gypsum.

[0058] The crystal form regulator is a composition of leucopicrin and 1,2-di(4-pyridyl)ethylene; the molar ratio of leucopicrin to 1,2-di(4-pyridyl)ethylene is 0.8-1.4:1. The dosage of the crystal form regulator is 2-5% of the mass of the purified gypsum. In some typical embodiments, the molar ratio of leucopicrin to 1,2-di(4-pyridyl)ethylene can be, for example, any one or any two of the following: 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1. The dosage of the crystal form regulator is any one or any two of the following: 2%, 3%, 4%, 5% of the mass of the purified gypsum.

[0059] This disclosure uses a composition of leucopicrin and 1,2-di(4-pyridyl)ethylene as a crystal form regulator. The complex formed by the self-assembly of leucopicrin and 1,2-di(4-pyridyl)ethylene in the liquid phase through coordination and π-π stacking interactions serves as a crystallization template for calcium sulfate, thereby controlling the crystal morphology of calcium sulfate. The o-phenolic hydroxyl groups of leucopicrin interact with the CaO on the surface of calcium sulfate crystals. 2+ They combine and adsorb onto the {111} crystal face, inhibiting the growth of the crystal face and thus forming plate-like crystals.

[0060] The alcohol solution is a mixture of ethylene glycol and glycerol, with the glycerol content in the alcohol solution being 30-50% by mass. In some typical embodiments, the glycerol content in the alcohol solution is any one or any combination of 30%, 35%, 40%, 45%, and 50%, or a range between any two of these values.

[0061] In this disclosure, the alcohol solution is used as a solvent for the conditioning agent. This disclosure selects a specific mixed solution of ethylene glycol and glycerol as the alcohol solution, which can maintain the stability of the crystal growth environment and is conducive to the growth of sheet-like nanostructures.

[0062] S3. Preparation of nanosheet calcium sulfate.

[0063] Purified gypsum and crystallization template liquid were mixed at a solid-liquid ratio of 0.02-0.25 g: 1 mL and reacted at a constant temperature under intermittent stirring. After the reaction was completed, nano-sheet calcium sulfate was obtained through post-treatment.

[0064] The intermittent stirring conditions included stirring for 5 minutes every 15–30 minutes at a stirring speed of 200–300 rpm. The isothermal reaction temperature was 50–70℃, and the reaction time was 5–10 hours.

[0065] In some typical embodiments, the solid-liquid ratio of the purified gypsum to the crystallization template solution can be, for example, any one or any two of the following: 0.02 g: 1 mL, 0.05 g: 1 mL, 0.08 g: 1 mL, 0.1 g: 1 mL, 0.12 g: 1 mL, 0.15 g: 1 mL, 0.2 g: 1 mL, 0.22 g: 1 mL, 0.25 g: 1 mL. The stirring speed can be, for example, any one or any two of the following: 200 rpm, 250 rpm, 280 rpm, 300 rpm. The isothermal reaction temperature can be, for example, any one or any two of the following: 50°C, 55°C, 60°C, 65°C, 70°C. The reaction time can be, for example, any one or any two of the following: 5 h, 6 h, 7 h, 8 h, 9 h, 10 h.

[0066] The post-processing includes: filtering the reaction solution to obtain a first filtrate and a first filter residue; washing the first filter residue with an alcohol solution and drying it to constant weight; then immersing it in an ether solution and stirring for 0.5-1 h; filtering to obtain a second filtrate and a second filter residue; and drying the second filter residue to constant weight to obtain nano-sheet calcium sulfate.

[0067] In this process, the alcohol solution can wash away the residual crystal form regulator on the first filter residue, while the ether can extract the crystal form regulator. This disclosure achieves the removal and purification of impurities from the filter residue through washing and extraction steps, thereby obtaining nano-sheet calcium sulfate.

[0068] S4. Recycle alcohol waste liquid.

[0069] (1) The washing liquid produced after washing the first filtrate with the alcohol solution is combined and then subjected to a first vacuum distillation to recover the alcohol; the temperature of the first vacuum distillation is 120-200℃ and the vacuum degree is 0.1-1mmHg.

[0070] (2) When the volume of the concentrate is 1 / 3 to 1 / 5 of the original volume, stop heating. After the concentrate is cooled to room temperature, add diethyl ether to extract the organic matter, and obtain an alcohol solution containing inorganic salts and an ether solution containing crystal form regulator.

[0071] (3) The alcohol solution containing inorganic salts was sealed and kept in the dark at room temperature and left to stand for 3-4 days before being filtered to obtain inorganic salt crystals.

[0072] (4) Combine the ether solution containing the crystal form regulator and the second filtrate, and perform a second vacuum distillation. Detect the concentrations of 1,2-di(4-pyridyl)ethylene and leucopicrin using UV absorption spectroscopy, liquid chromatography, or mass spectrometry to ensure they are both ≥0.2 mol / L. Then, seal and allow to stand at room temperature in the dark for 3–4 days. Filter to obtain supramolecular crystals, i.e., crystals formed by the non-covalent self-assembly of 1,2-di(4-pyridyl)ethylene and leucopicrin. The temperature of the second vacuum distillation is 50–70 °C, and the vacuum degree is 0.1–1 mmHg.

[0073] The recovery rate of inorganic salts was 75-85%, and the total recovery rate of 1,2-bis(4-pyridyl)ethylene and leucovorin was 55-60%.

[0074] The nano-sheet calcium sulfate prepared by the above method exhibits excellent dispersibility and is not prone to agglomeration. It can be widely used in the preparation of fillers, reinforcing agents, flame retardants, skin smoothing agents, or thermal insulation materials.

[0075] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0076] The sources and physicochemical properties of the raw materials used in the embodiments and comparative examples in this disclosure are as follows:

[0077] Source and physicochemical properties of phosphogypsum: The phosphogypsum from a phosphate fertilizer plant in Hubei Province is grayish-black in color, with a whiteness of 22.71, a free water content of 25.71%, a total phosphorus content of 1.524%, a soluble phosphorus content of 0.4986%, a total fluorine content of 0.22%, of which the soluble fluorine content is 0.08%, an organic matter content of 0.05%, and a leachate pH between 1 and 2.

[0078] Example 1

[0079] This embodiment provides a method for preparing nano-sheet calcium sulfate using phosphogypsum, including the following steps:

[0080] S1, Phosphogypsum Pretreatment

[0081] The phosphogypsum was repeatedly washed with tap water until its pH value was 6.8. After pretreatment, the phosphogypsum was dried and passed through a 0.3 mm square hole sieve to obtain gypsum powder. Then, 0.5 wt% quicklime and 10% water were added according to the mass of the gypsum powder to prepare a slurry. After mixing for 48 hours, the slurry was dried at 45°C to obtain purified gypsum.

[0082] The mass content of soluble phosphorus, soluble fluoride, and calcium sulfate dihydrate in phosphogypsum was tested according to the standard GB / T 23456-2009 "Phosphogypsum". The obtained purified gypsum contained 92% calcium sulfate dihydrate, 0.051% soluble phosphorus, and 0.015% soluble fluoride.

[0083] S2. Prepare the crystallization template solution.

[0084] A mixed solution of glycerol and ethylene glycol in a mass ratio of 1:1 was prepared. Paclitaxel, 1,2-di(4-pyridyl)ethylene, and calcium nitrate were added. The solution was heated to 60°C and stirred until homogeneous and clear. Then, stirring was stopped, and the solution was aged at this constant temperature for 30 minutes. The total mass of paclitaxel and 1,2-di(4-pyridyl)ethylene was 3.8% of the mass of the purified gypsum; the molar ratio of paclitaxel to 1,2-di(4-pyridyl)ethylene was 1.1:1; and the final concentration of calcium nitrate was 0.5 mol / L.

[0085] S3. Preparation of plate-like crystals

[0086] The pretreated gypsum was added to the crystallization template solution to obtain a slurry with a solid-liquid ratio (g / mL) of 0.16. The slurry was reacted at a constant temperature of 60°C for 10 hours under intermittent stirring conditions (stirring for 5 minutes every 20 minutes at a stirring speed of 250 rpm). The slurry was filtered while hot to obtain a first filtrate and a first filter residue. The first filter residue was washed with the above mixed alcohol solution and dried at 50°C to constant weight. Then it was immersed in an ether solution and stirred for 0.5 hours. After filtration, a second filtrate and a second filter residue were obtained. The second filter residue was dried at 50°C to constant weight to obtain flaky calcium sulfate crystals.

[0087] The crystal morphology of gypsum was observed using a JEOL JSM-6490LV scanning electron microscope, and the phase composition of the sample was analyzed and determined using a TD-3500 X-ray diffractometer.

[0088] Test results as follows Figure 1 , Figure 2 and Figure 3 As shown, from Figure 1 and Figure 2 As can be seen, the product prepared in this embodiment is in sheet form, with good dispersion between crystals, and is not prone to agglomeration or adhesion. From Figure 3As can be seen, this embodiment successfully prepared flaky calcium sulfate crystals.

[0089] Example 2

[0090] This embodiment provides a method for preparing nano-sheet calcium sulfate using phosphogypsum, including the following steps:

[0091] S1, Phosphogypsum Pretreatment

[0092] The phosphogypsum was repeatedly washed with tap water until its pH value was 6.5. After pretreatment, the phosphogypsum was dried and passed through a 0.2 mm square hole sieve to obtain gypsum powder. Then, 1 wt% quicklime and 15% water were added according to the mass of the gypsum powder to prepare a slurry. After mixing for 24 hours, the slurry was dried at 40°C to obtain purified gypsum.

[0093] The obtained purified gypsum contained 91% calcium sulfate dihydrate, 0.048% soluble phosphorus, and 0.012% soluble fluorine.

[0094] S2. Prepare the crystallization template solution.

[0095] A mixed solution of glycerol and ethylene glycol in a mass ratio of 3:7 was prepared. Paclitaxel, 1,2-di(4-pyridyl)ethylene, and calcium nitrate were added. The solution was heated to 70°C and stirred until homogeneous and clear. Then, stirring was stopped, and the solution was aged at this constant temperature for 2 hours. The total mass of paclitaxel and 1,2-di(4-pyridyl)ethylene was 2% of the mass of the purified gypsum; the molar ratio of paclitaxel to 1,2-di(4-pyridyl)ethylene was 0.9:1; and the final concentration of calcium nitrate was 0.8 mol / L.

[0096] S3. Preparation of plate-like crystals

[0097] The pretreated gypsum was added to the crystallization template solution to obtain a slurry with a solid-liquid ratio (g / mL) of 0.06. The slurry was reacted at a constant temperature of 70°C for 5 hours under intermittent stirring conditions (stirring for 5 minutes every 30 minutes at a stirring speed of 300 rpm). The mixture was filtered while hot to obtain a first filtrate and a first filter residue. The first filter residue was washed with the above mixed alcohol solution and dried at 55°C to constant weight. Then it was immersed in an ether solution and stirred for 0.8 hours. After filtration, a second filtrate and a second filter residue were obtained. The second filter residue was dried at 55°C to constant weight to obtain flaky calcium sulfate crystals.

[0098] Example 3

[0099] This embodiment provides a method for preparing nano-sheet calcium sulfate using phosphogypsum, including the following steps:

[0100] S1 is the same as in Example 1.

[0101] S2. Prepare the crystallization template solution.

[0102] A mixed solution of glycerol and ethylene glycol in a mass ratio of 4:6 was prepared. Paclitaxel, 1,2-di(4-pyridyl)ethylene, and sodium sulfate were added. The solution was heated to 80°C and stirred until homogeneous and clear. Then, stirring was stopped, and the solution was aged at this constant temperature for 1 hour. The total mass of paclitaxel and 1,2-di(4-pyridyl)ethylene was 5% of the mass of the purified gypsum; the molar ratio of paclitaxel to 1,2-di(4-pyridyl)ethylene was 1.3:1; and the final concentration of sodium sulfate was 1 mol / L.

[0103] S3. Preparation of plate-like crystals

[0104] The pretreated gypsum was added to the crystallization template solution to obtain a slurry with a solid-liquid ratio (g / mL) of 0.25. The slurry was reacted at a constant temperature for 8 hours under intermittent stirring conditions (stirring for 5 minutes every 15 minutes at a stirring speed of 200 rpm). The mixture was filtered while hot to obtain a first filtrate and a first filter residue. The first filter residue was washed with the above mixed alcohol solution and dried at 60°C to constant weight. Then it was immersed in an ether solution and stirred for 1 hour. After filtration, a second filtrate and a second filter residue were obtained. The second filter residue was dried at 60°C to constant weight to obtain flaky calcium sulfate crystals.

[0105] Example 4

[0106] This embodiment is the same as Embodiment 1, except that after obtaining the flaky calcium sulfate crystals, this embodiment also includes S4, recovering the alcohol waste liquid from Embodiment 1.

[0107] (1) Combine the first filtrate and the washing liquid obtained after washing with alcohol solution, and perform vacuum distillation at 120°C with the vacuum degree controlled at 0.5 mmHg to recover ethylene glycol. After boiling at 120°C for 20 min, continue to heat to 200°C and boil for 20 min to recover most of the alcohol solvent.

[0108] (2) After the concentrate is cooled to room temperature, add 1 / 3 of the volume of diethyl ether to extract the organic matter. Repeat the extraction 3 times and combine the diethyl ether phases to obtain an alcohol solution containing inorganic salts and an ether solution containing crystal form regulator.

[0109] (3) The alcohol solution of inorganic salt is sealed and kept in the dark at room temperature. After 3 days, it is filtered to obtain inorganic salt crystals. The remaining alcohol solution is recovered by distillation in step (1).

[0110] (4) Combine the ether solution containing the crystal form regulator obtained in step (2) and the second filtrate, and concentrate them by vacuum distillation at 60℃ and 1 mmHg, so that the concentrations of 1,2-di(4-pyridyl)ethylene and leucopicrin are both ≥0.2 mol / L (determined by mass spectrometry). Then, seal and let stand at room temperature in the dark for 3 days, and filter to obtain supramolecular crystals (such as...). Figure 4As shown in the figure, the crystal is formed by the non-covalent self-assembly of 1,2-bis(4-pyridyl)ethylene and leucopicrin, and the remaining solution is recovered by vacuum distillation.

[0111] The recovery rate of inorganic salts was 78.2%, and the total recovery rate of 1,2-bis(4-pyridyl)ethylene and leucine was 55.3%.

[0112] Example 5

[0113] This embodiment is the same as Embodiment 1, except that after obtaining the flaky calcium sulfate crystals, this embodiment also includes S4, recovering the alcohol waste liquid from Embodiment 1.

[0114] (1) Combine the first filtrate and the washing liquid obtained after washing with alcohol solution, and perform vacuum distillation at 140°C with the vacuum degree controlled at 0.8 mmHg to recover ethylene glycol. After boiling at 140°C for 20 min, continue to heat to 180°C and boil for 20 min to recover most of the alcohol solvent.

[0115] (2) After the concentrate is cooled to room temperature, add 1 / 4 volume of diethyl ether to extract the organic matter. Repeat the extraction 3 times and combine the diethyl ether phases to obtain an alcohol solution containing inorganic salts and an ether solution containing crystal form regulator.

[0116] (3) The alcohol solution of inorganic salt is sealed and kept in the dark at room temperature. After 4 days, it is filtered to obtain inorganic salt crystals. The remaining alcohol solution is recovered by distillation in step (1).

[0117] (4) Combine the ether solution containing the crystal form regulator obtained in step (2) and the second filtrate, and concentrate them by vacuum distillation at a temperature of 70°C and a vacuum of 0.5 mmHg, so that the concentrations of 1,2-di(4-pyridyl)ethylene and leucopicrin are both ≥0.2 mol / L (measured by UV absorption spectroscopy). Then, seal and let stand at room temperature in the dark for 4 days, and filter to obtain supramolecular crystals, that is, crystals formed by the non-covalent self-assembly of 1,2-di(4-pyridyl)ethylene and leucopicrin. The remaining solution is recovered by vacuum distillation.

[0118] The recovery rate of inorganic salts was 81.5%, and the total recovery rate of 1,2-bis(4-pyridyl)ethylene and leucovorin was 58.3%.

[0119] Comparative Example 1

[0120] This comparative example is basically the same as Example 1, except that in this comparative example, the crystal form regulator only includes leucopicrin.

[0121] Comparative Example 2

[0122] This comparative example is basically the same as Example 1, except that in this comparative example, the crystal form regulator only includes 1,2-di(4-pyridyl)ethylene.

[0123] Experimental Example

[0124] The above Examples 1-5 and Comparative Examples 1-2 were subjected to the following tests: the particle size and particle size distribution of the powders prepared in the examples and comparative examples were tested using a Bettersize 2000 laser particle size analyzer. The test results are as follows:

[0125]

[0126] As can be seen from the table above, neither of the comparative examples yielded dispersed, flaky calcium sulfate crystals. Comparative Examples 1 and 2, containing only one crystal form regulator component, could not form supramolecular crystals as crystallization templates, and the crystal form regulation effect of a single component only resulted in short columnar crystals. Particle size distribution reflects the degree of crystal aggregation; a larger particle size distribution indicates more aggregated powder.

[0127] In summary, the method for preparing nano-sheet calcium sulfate using phosphogypsum disclosed herein employs a composition of leucopicrin and 1,2-di(4-pyridyl)ethylene as a crystal form regulator. The complex formed by the self-assembly of leucopicrin and 1,2-di(4-pyridyl)ethylene in the liquid phase through coordination and π-π stacking interactions serves as a crystallization template for calcium sulfate, thereby controlling its crystal morphology. Specifically, the o-phenolic hydroxyl groups of leucopicrin interact with the CaO on the surface of the calcium sulfate crystals. 2+ The crystals adsorb onto the {111} crystal plane, effectively inhibiting the growth of the {111} crystal plane and thus achieving crystal growth on a two-dimensional plane, forming plate-like crystals. Compared to using traditional crystal-changing agents or single crystal-changing agents, the template method for preparing calcium sulfate crystals provides a more stable crystal growth environment, less susceptible to impurities. Furthermore, the crystal template provided in this disclosure effectively prevents crystal aggregation, resulting in well-dispersed, non-adhesive plate-like nanocrystals. The prepared nano-plate-like calcium sulfate exhibits excellent dispersibility and is not prone to aggregation. It can be widely used in the preparation of fillers, reinforcing agents, flame retardants, skin smoothing agents, or thermal insulation materials.

[0128] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0129] Industrial applicability

[0130] The method for preparing nano-sheet calcium sulfate using phosphogypsum disclosed herein employs a composition of leucopicrin and 1,2-di(4-pyridyl)ethylene as a crystal form regulator. The complex formed by the self-assembly of leucopicrin and 1,2-di(4-pyridyl)ethylene in the liquid phase through coordination and π-π stacking interactions serves as a crystallization template for calcium sulfate, thereby controlling the crystal morphology of the calcium sulfate. Specifically, the o-phenolic hydroxyl groups of leucopicrin interact with the CaO on the surface of the calcium sulfate crystals. 2+ The crystals adsorb onto the {111} crystal plane, effectively inhibiting the growth of the {111} crystal plane and thus achieving crystal growth on a two-dimensional plane, forming plate-like crystals. Compared to using traditional crystal-changing agents or single crystal-changing agents, the template method for preparing calcium sulfate crystals provides a more stable crystal growth environment, less susceptible to impurities. Furthermore, the crystal template provided in this disclosure effectively prevents crystal aggregation, resulting in well-dispersed, non-adhesive plate-like nanocrystals. The prepared nano-plate-like calcium sulfate exhibits excellent dispersibility and is not prone to aggregation. It can be widely used in the preparation of fillers, reinforcing agents, flame retardants, skin smoothing agents, or thermal insulation materials.

Claims

1. A method for producing nanosheet-shaped calcium sulfate using phosphogypsum, characterized by, It includes: Purified gypsum is obtained by pretreatment of phosphogypsum; After mixing and clarifying an inorganic salt and an alcohol solution containing a crystal form regulator, the mixture is aged to obtain a crystallization template solution. The crystal form regulator is a combination of leucopicrin and 1,2-di(4-pyridyl)ethylene. The purified gypsum is pulped and reacted with the crystallization template liquid. After the reaction is completed, post-treatment yields nano-sheet calcium sulfate.

2. The method for manufacturing nanosheet-shaped calcium sulfate using phosphogypsum according to claim 1, characterized by, The molar ratio of the paclitaxel to the 1,2-bis(4-pyridyl)ethylene is 0.8-1.4:

1.

3. The method for producing nanosheet-shaped calcium sulfate using phosphogypsum according to any one of claims 1 to 2, characterized by, The amount of the crystal form regulator is 2-5% of the mass of the purified gypsum. 4.The method for preparing nanosheet-shaped calcium sulfate using phosphogypsum according to claim 1, wherein the phosphogypsum is phosphogypsum that is obtained by a method comprising: mixing phosphoric acid and gypsum; and precipitating calcium sulfate by adjusting the pH of the mixture. The alcohol solution is a mixture of ethylene glycol and glycerol, and the mass ratio of glycerol in the alcohol solution is 30-50%. 5.The method for preparing nanosheet-shaped calcium sulfate using phosphogypsum according to claim 1, wherein the phosphogypsum is phosphogypsum that is obtained by a method comprising: mixing phosphoric acid and gypsum; and precipitating calcium sulfate by adjusting the pH of the mixture. The solid-liquid ratio of the purified gypsum to the crystallization template liquid during pulping is 0.02~0.25 g:1 mL.

6. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 1, characterized in that, The reaction between the purified gypsum and the crystallization template liquid after pulping is a isothermal reaction carried out under intermittent stirring conditions.

7. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 6, characterized in that, The intermittent stirring conditions include stirring for 5 minutes every 15-30 minutes at a stirring speed of 200-300 rpm.

8. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 6, characterized in that, The isothermal reaction is carried out at a temperature of 50-70℃ for 5-10 hours.

9. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 1, characterized in that, The inorganic salts include one or more of calcium nitrate and sodium sulfate.

10. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 1, characterized in that, The final concentration of the inorganic salt is 0.5~1 mol / L.

11. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 1, characterized in that, The inorganic salt and the alcohol solution containing the crystal form regulator are mixed at a temperature of 60-80°C, and then aged at a constant temperature for 30 min-2 h.

12. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 1, characterized in that, The pretreatment includes washing the phosphogypsum with water until the pH is 6.5-7.0, then drying and sieving to obtain gypsum powder. The gypsum powder, quicklime and water are mixed into a slurry and mixed for 24-48 hours, and then dried to obtain the purified gypsum.

13. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 12, characterized in that, The mass ratio of the gypsum powder, the quicklime, and the water is 100:0.5~2:10~20.

14. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 12, characterized in that, The sieving process includes passing the dried phosphogypsum through a square-hole sieve with a aperture of 0.2-0.4 mm.

15. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 12, characterized in that, The drying temperature is 40~50℃.

16. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 1, characterized in that, The purified gypsum contains 80-98% calcium sulfate dihydrate, ≤0.1% soluble phosphorus, and ≤0.03% soluble fluorine.

17. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 1, characterized in that, The post-processing includes: filtering the reaction solution to obtain a first filtrate and a first filter residue; washing the first filter residue with the alcohol solution and drying it to constant weight; then immersing it in an ether solution and stirring for 0.5-1 h; filtering to obtain a second filtrate and a second filter residue; and drying the second filter residue to constant weight to obtain the nano-sheet calcium sulfate.

18. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 17, characterized in that, The method for producing nano-sheet calcium sulfate using phosphogypsum also includes the recovery of alcohol waste liquid: The washing liquid obtained after washing the first filtrate with the alcohol solution is combined and then subjected to a first vacuum distillation to recover the alcohol. When the volume of the concentrate is 1 / 3 to 1 / 5 of the original volume, heating is stopped. After the concentrate is cooled to room temperature, diethyl ether is added to extract the organic matter, resulting in an alcohol solution containing inorganic salts and an ether solution containing crystal form regulators. The alcohol solution containing inorganic salts was sealed and kept away from light at room temperature and left to stand for 3-4 days before being filtered to obtain inorganic salt crystals. The diethyl ether solution containing the crystal form regulator and the second filtrate were combined and subjected to a second vacuum distillation to ensure that the concentrations of 1,2-di(4-pyridyl)ethylene and leucopicrin were both ≥0.2 mol / L. The mixture was then sealed and allowed to stand at room temperature in the dark for 3-4 days before filtration to obtain supramolecular crystals, i.e., crystals formed by the non-covalent self-assembly of 1,2-di(4-pyridyl)ethylene and leucopicrin.

19. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 18, characterized in that, The temperature of the first vacuum distillation is 120~200℃, and the vacuum degree is 0.1-1 mmHg.

20. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 18-19, characterized in that, The temperature of the second vacuum distillation is 50-70℃, and the vacuum degree is 0.1-1 mmHg.

21. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 18, characterized in that, The recovery rate of the inorganic salt is 75-85%, and the total recovery rate of the 1,2-bis(4-pyridyl)ethylene and the paclitaxel is 55-60%.

22. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 18, characterized in that, The concentrations of the 1,2-bis(4-pyridyl)ethylene and the paclitaxel were detected by ultraviolet absorption spectroscopy, liquid chromatography or mass spectrometry.

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