Method for preparing nano-flake calcium sulfate from phosphogypsum, nano-flake calcium sulfate and use thereof

Abstract

A method for preparing nano-flake calcium sulfate from phosphogypsum, nano-flake calcium sulfate and a use thereof, relating to the technical field of waste recovery. The method comprises: pretreating phosphogypsum to obtain purified gypsum; mixing an inorganic salt with an alcohol solution containing a crystal form regulator and clarifying same, and then carrying out aging to obtain a crystallization template solution, wherein the crystal form regulator is a composition of piceatannol and 1,2-bis(4-pyridyl)ethylene; and slurrying and reacting the purified gypsum and the crystallization template solution, and after the reaction is completed, carrying out post-treatment to obtain the nano-flake calcium sulfate. The crystal morphology of calcium sulfate can be regulated and controlled; and the growth of crystal plane {111} is inhibited, such that crystal growth on a two-dimensional plane is achieved, thereby forming flaky crystals. The crystal growth environment is relatively stable and is not prone to being affected by impurities; and the prepared nano-flake calcium sulfate has good dispersibility and is not prone to agglomeration.

Description

Method for preparing nano-flaky calcium sulfate using phosphogypsum, nano-flaky calcium sulfate and application thereof Technical Field

[0001] The present disclosure relates to the technical field of waste recycling, and in particular to a method for preparing nano-flaky calcium sulfate by utilizing phosphogypsum, the nano-flaky calcium sulfate and applications thereof. Background Art

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

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

[0004] Flake calcium sulfate, a special type of crystalline material, is finding increasing applications not only as a filler, reinforcement, and flame retardant in rubber and plastics, but also in cosmetics, where it is widely used as a body pigment to improve the smoothness and feel of the skin. Furthermore, its flake structure amplifies the crystal facet effect, enhancing the reflection and refraction of light and heat, promising applications in thermal insulation materials and increasing the overall utilization value of gypsum byproducts.

[0005] It can be seen that the preparation of nano-flaky calcium sulfate materials has broad application prospects, but there are currently few studies in this area, and there are no reports on the preparation of nano-flaky calcium sulfate using phosphogypsum with more impurities.

[0006] In view of this, the present disclosure is proposed.

[0007] Summary of the Invention

[0008] The purpose of the present disclosure is to provide a method for preparing nano-flaky calcium sulfate using phosphogypsum, nano-flaky calcium sulfate and applications thereof.

[0009] The present disclosure is achieved as follows:

[0010] In a first aspect, the present disclosure provides a method for preparing nano-flaky calcium sulfate using phosphogypsum, comprising:

[0011] Pre-treating phosphogypsum to obtain purified gypsum;

[0012] The inorganic salt and the alcohol solution containing the crystal form modifier are mixed and clarified, and then aged to obtain a crystallization template solution, wherein the crystal form modifier is a combination of piceatannol and 1,2-di(4-pyridyl)ethylene;

[0013] The purified gypsum and the crystallization template liquid are slurried and reacted, and after the reaction is completed, nano-flaky calcium sulfate is obtained through post-processing.

[0014] In an optional embodiment, the molar ratio of the piceatannol to the 1,2-di(4-pyridyl)ethylene is 0.8-1.4:1.

[0015] In an optional embodiment, the amount of the crystal form regulator is 2-5% of the mass of the purified gypsum.

[0016] In an optional embodiment, the alcohol solution is a mixed solution of ethylene glycol and glycerol, and the mass ratio of the glycerol in the alcohol solution is 30-50%.

[0017] In an optional embodiment, the solid-to-liquid ratio of the purified gypsum and the crystallization template liquid during slurrying is 0.02-0.25 g:1 mL.

[0018] In an optional embodiment, the reaction between the purified gypsum and the crystallization template liquid after slurrying is a constant temperature reaction carried out under intermittent stirring conditions.

[0019] In an optional embodiment, the intermittent stirring condition includes stirring for 5 minutes every 15 to 30 minutes, and the stirring speed is 200 to 300 rpm.

[0020] In an optional embodiment, the temperature of the isothermal reaction is 50-70° C., and the reaction time is 5 to 10 hours.

[0021] In an optional embodiment, the inorganic salt includes one or more of calcium nitrate and sodium sulfate.

[0022] In an optional embodiment, the final concentration of the inorganic salt is 0.5 to 1 mol / L.

[0023] In an optional embodiment, the temperature for mixing the inorganic salt and the alcohol solution containing the crystal form regulator is 60-80° C., and then the aging is carried out at a constant temperature for 30 minutes to 2 hours.

[0024] In an optional embodiment, the pretreatment includes first washing the phosphogypsum with water to a pH of 6.5 to 7.0, then drying and sieving to obtain gypsum powder, preparing the gypsum powder, quicklime and water into a slurry and mixing it for 24 to 48 hours, and drying to obtain the purified gypsum.

[0025] In an optional embodiment, the mass ratio of the gypsum powder, the quicklime and the water is 100:0.5-2:10-20.

[0026] In an optional embodiment, the screening includes passing the dried phosphogypsum through a square hole sieve with a pore size of 0.2-0.4 mm.

[0027] In an optional embodiment, the drying temperature is 40-50°C.

[0028] In an optional embodiment, the mass content of calcium sulfate dihydrate in the purified gypsum is 80-98%, the mass content of soluble phosphorus is ≤0.1%, and the mass content of soluble fluorine is ≤0.03%.

[0029] In an optional embodiment, the post-treatment 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 it for 0.5-1h, filtering it to obtain a second filtrate and a second filter residue, and drying the second filter residue to constant weight to obtain the nano-flaky calcium sulfate.

[0030] In an optional embodiment, the method for preparing nano-flaky calcium sulfate using phosphogypsum further comprises recovering alcohol waste liquid:

[0031] combining the first filtrate with the washing liquid produced after washing with the alcohol solution, and performing a first reduced-pressure distillation to recover the alcohol;

[0032] When the volume of the concentrated solution is 1 / 3 to 1 / 5 of the original volume, heating is stopped, and after the concentrated solution is cooled to room temperature, ether is added to extract the organic matter to obtain an alcohol solution containing inorganic salts and an ether solution containing a crystal form modifier;

[0033] The alcohol solution containing the inorganic salt is sealed and kept in the dark at room temperature, and filtered for 3 to 4 days to obtain inorganic salt crystals;

[0034] The ether solution containing the crystal form modifier and the second filtrate are combined, and subjected to a second reduced-pressure distillation to ensure that the measured concentrations of 1,2-di(4-pyridyl)ethylene and piceatannol are both ≥0.2 mol / L. The mixture is then sealed and kept in the dark at room temperature, and filtered for 3 to 4 days to obtain supramolecular crystals, i.e., crystals self-assembled by 1,2-di(4-pyridyl)ethylene and piceatannol through non-covalent bonds.

[0035] In an optional embodiment, the temperature of the first reduced pressure distillation is 120-200° C., and the vacuum degree is 0.1-1 mmHg.

[0036] In an optional embodiment, the temperature of the second reduced-pressure distillation is 50-70° C., and the vacuum degree is 0.1-1 mmHg.

[0037] 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 piceatannol is 55-60%.

[0038] In an optional embodiment, the concentrations of the 1,2-di(4-pyridyl)ethylene and the piceatannol are detected by ultraviolet absorption spectroscopy, liquid chromatography or mass spectrometry.

[0039] In a second aspect, the present disclosure provides a nano-flaky calcium sulfate, which is prepared by the method for preparing nano-flaky calcium sulfate using phosphogypsum as described in any of the aforementioned embodiments.

[0040] In a third aspect, the present disclosure provides use of the nano-platelet calcium sulfate as described in the aforementioned embodiment in the preparation of a filler, a reinforcing agent, a flame retardant, a skin smoothing agent or a thermal insulation material.

[0041] The present disclosure has the following beneficial effects:

[0042] The present invention provides a method for preparing nano-flaky calcium sulfate using phosphogypsum, which uses a combination of piceatannol and 1,2-di(4-pyridyl)ethylene as a crystal modifier. The complex formed by self-assembly of piceatannol and 1,2-di(4-pyridyl)ethylene in the liquid phase through coordination and π-π stacking can serve as a crystal template for calcium sulfate, thereby regulating the crystal morphology of calcium sulfate. The o-phenolic hydroxyl group of piceatannol reacts with the CaCl2-containing hydroxyl group on the surface of the calcium sulfate crystal. 2+ The calcium sulfate binds to and adsorbs on the {111} crystal plane, effectively inhibiting its growth, thereby achieving two-dimensional crystal growth and forming flaky crystals. Compared to using traditional crystal-transforming agents or a single crystal-transforming agent, the template method for preparing calcium sulfate crystals disclosed herein can provide a more stable growth environment for the crystals, making them less susceptible to impurities. Furthermore, the crystallization template provided by the present disclosure can effectively prevent crystal agglomeration, forming well-dispersed, non-sticky flaky nanocrystals. The prepared nano-flaky calcium sulfate has 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0044] FIG1 is a SEM image of nano-flaky calcium sulfate obtained by the method for preparing nano-flaky calcium sulfate using phosphogypsum provided in Example 1 of the present disclosure at a scale of 1 μm;

[0045] FIG2 is a SEM image of nano-flaky calcium sulfate obtained by the method for preparing nano-flaky calcium sulfate using phosphogypsum provided in Example 1 of the present disclosure at a scale of 500 nm;

[0046] FIG3 is a schematic diagram of the composition analysis of the nano-flaky calcium sulfate obtained by the method for preparing nano-flaky calcium sulfate using phosphogypsum provided in Example 1 of the present disclosure and the physical phase after drying the first filter residue;

[0047] FIG4 is a schematic diagram of the structure of the supramolecular crystal provided in Example 4 of the present disclosure. DETAILED DESCRIPTION

[0048] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0049] The endpoints of the ranges and any values ​​disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0050] The present disclosure provides a method for preparing nano-flaky calcium sulfate using phosphogypsum, which comprises the following steps:

[0051] S1. Phosphogypsum pretreatment.

[0052] The phosphogypsum is pretreated to obtain purified gypsum.

[0053] Among them, the pretreatment includes first washing the phosphogypsum with water to a pH of 6.5-7.0, then drying and sieving (through a square hole sieve with a pore size of 0.2-0.4 mm) to obtain gypsum powder, and preparing gypsum powder, quicklime and water in a mass ratio of 100:0.5-2:10-20 into a slurry, mixing for 24-48 hours, and drying at 40-50°C to obtain purified gypsum.

[0054] In some typical embodiments, the mass ratio of gypsum powder, quicklime, and water can be, for example, any one of 100:0.5:10, 100:1:15, 100:1.5:20, 100:2:15, 100:0.8:17, or 100:0.5:20, or a range between any two thereof. The mixing time can be, for example, any one of 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours, or a range between any two thereof. The drying temperature can be, for example, any one of 40° C., 42° C., 45° C., 46° C., 48° C., or 50° C., or a range between any two thereof.

[0055] The mass content of calcium sulfate dihydrate in the purified gypsum is 80-98%, the mass content of soluble phosphorus is ≤0.1%, and the mass content of soluble fluorine is ≤0.03%.

[0056] S2. Prepare crystallization template solution.

[0057] The inorganic salt and the alcohol solution containing the crystal form regulator are mixed and clarified at 60-80° C., and then aged for 30 minutes to 2 hours to obtain a crystallization template solution.

[0058] The inorganic salt includes one or more of calcium nitrate and sodium sulfate. The final concentration of the inorganic salt is 0.5 to 1 mol / L. The inorganic salt in the present disclosure is used to enhance the dissolution rate of the purified gypsum.

[0059] The crystal form modifier is a combination of piceatannol and 1,2-di(4-pyridyl)ethylene; the molar ratio of piceatannol to 1,2-di(4-pyridyl)ethylene is 0.8-1.4:1. The amount of the crystal form modifier is 2-5% by weight of the purified gypsum. In some typical embodiments, the molar ratio of piceatannol to 1,2-di(4-pyridyl)ethylene can be, for example, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or any range between any two of them. The amount of the crystal form modifier is 2%, 3%, 4%, or 5% by weight of the purified gypsum, or any range between any two of them.

[0060] The present invention adopts a composition of piceatannol and 1,2-di(4-pyridyl)ethylene as a crystal modifier. The complex formed by self-assembly of piceatannol and 1,2-di(4-pyridyl)ethylene in the liquid phase through coordination and π-π stacking is used as a crystal template for calcium sulfate to regulate the crystal morphology of calcium sulfate. The o-phenolic hydroxyl group of piceatannol reacts with the CaCl2-containing hydroxyl group on the surface of the calcium sulfate crystal. 2+ It combines and adsorbs on the {111} crystal plane, inhibiting the growth of the crystal plane and forming a lamellar crystal.

[0061] The alcohol solution is a mixed solution of ethylene glycol and glycerol, wherein the mass proportion of glycerol in the alcohol solution is 30% to 50%. In some typical embodiments, the mass proportion of glycerol in the alcohol solution is any one of 30%, 35%, 40%, 45%, and 50%, or a range between any two of the above.

[0062] In the present disclosure, the alcohol solution is used as a solvent for the regulator. The present disclosure selects a specific mixed solution of ethylene glycol and propylene glycol as the alcohol solution, which can maintain the stability of the crystal growth environment and is conducive to the growth of sheet-like nanostructures.

[0063] S3. Prepare nano-flaky calcium sulfate.

[0064] The purified gypsum and the crystallization template liquid are slurried according to a solid-liquid ratio of 0.02-0.25 g:1 mL and reacted at a constant temperature under intermittent stirring conditions. After the reaction is completed, nano-flaky calcium sulfate is obtained through post-treatment.

[0065] The intermittent stirring conditions include stirring for 5 minutes every 15 to 30 minutes at a stirring speed of 200 to 300 rpm. The constant temperature reaction temperature is 50-70° C. and the reaction time is 5 to 10 hours.

[0066] In some typical embodiments, the solid-liquid ratio of the purified gypsum to the crystallization template liquid can be, for example, any one of 0.02g:1mL, 0.05g:1mL, 0.08g:1mL, 0.1g:1mL, 0.12g:1mL, 0.15g:1mL, 0.2g:1mL, 0.22g:1mL, 0.25g:1mL, or a range between any two of them. The stirring speed can be, for example, any one of 200rpm, 250rpm, 280rpm, or 300rpm, or a range between any two of them. The temperature of the isothermal reaction can be, for example, any one of 50°C, 55°C, 60°C, 65°C, or 70°C, or a range between any two of them. The reaction time can be, for example, any one of 5h, 6h, 7h, 8h, 9h, or 10h, or a range between any two of them.

[0067] The post-processing includes: filtering the reaction liquid 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 it for 0.5-1 hour, filtering it to obtain a second filtrate and a second filter residue, and drying the second filter residue to constant weight to obtain nano-flaky calcium sulfate.

[0068] 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. The present invention can remove impurities and purify the filter residue through the washing and extraction steps, thereby obtaining nano-flaky calcium sulfate.

[0069] S4. Recovering alcohol waste liquid.

[0070] (1) The first filtrate and the washing liquid produced after washing with the alcohol solution are combined, and the alcohol is recovered by a first reduced pressure distillation; the temperature of the first reduced pressure distillation is 120-200° C., and the vacuum degree is 0.1-1 mmHg.

[0071] (2) When the volume of the concentrated solution is 1 / 3 to 1 / 5 of the original volume, heating is stopped, and after the concentrated solution is cooled to room temperature, ether is added to extract the organic matter to obtain an alcohol solution containing an inorganic salt and an ether solution containing a crystal form modifier;

[0072] (3) The alcohol solution containing the inorganic salt is sealed and kept in the dark at room temperature, and filtered for 3 to 4 days to obtain inorganic salt crystals;

[0073] (4) The ether solution containing the crystal form modifier and the second filtrate are combined, subjected to a second reduced pressure distillation, and the concentrations of 1,2-di(4-pyridyl)ethylene and piceatannol are determined to be ≥0.2 mol / L by ultraviolet absorption spectroscopy, liquid chromatography, or mass spectrometry. The mixture is then sealed and placed in the dark at room temperature, and filtered for 3-4 days to obtain supramolecular crystals, i.e., crystals self-assembled by non-covalent bonds between 1,2-di(4-pyridyl)ethylene and piceatannol. The temperature of the second reduced pressure distillation is 50-70° C., and the vacuum degree is 0.1-1 mmHg.

[0074] The recovery rate of the inorganic salt is 75-85%, and the total recovery rate of 1,2-di(4-pyridyl)ethylene and piceatannol is 55-60%.

[0075] The nano-scale calcium sulfate flakes prepared by the above method have good dispersibility and are not easy to agglomerate. They can be widely used in the preparation of fillers, reinforcing agents, flame retardants, skin smoothing agents or thermal insulation materials.

[0076] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0077] The sources and physicochemical properties of the raw materials used in the examples and comparative examples of this disclosure are as follows:

[0078] Source and physical and chemical properties of phosphogypsum: The phosphogypsum from a phosphate fertilizer plant in Hubei Province is gray-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 an extract pH between 1 and 2.

[0079] Example 1

[0080] This embodiment provides a method for preparing nano-flaky calcium sulfate using phosphogypsum, comprising the following steps:

[0081] S1. Phosphogypsum pretreatment

[0082] The phosphogypsum was repeatedly washed with tap water until its pH value reached 6.8. The pretreated 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.

[0083] The soluble phosphorus, soluble fluoride, and calcium sulfate dihydrate content of the phosphogypsum were tested according to the GB / T 23456-2009 standard for "Phosphogypsum." The purified gypsum obtained contained 92% calcium sulfate dihydrate, 0.051% soluble phosphorus, and 0.015% soluble fluoride.

[0084] S2. Prepare crystallization template solution.

[0085] A mixed solution of glycerol and ethylene glycol in a 1:1 mass ratio was prepared, and piceatannol, 1,2-di(4-pyridyl)ethylene, and calcium nitrate were added. The solution was heated to 60°C and stirred until homogeneous and clear. Stirring was then stopped and the solution was aged at this temperature for 30 minutes. The total mass of piceatannol and 1,2-di(4-pyridyl)ethylene was 3.8% of the mass of the purified gypsum. The molar ratio of piceatannol to 1,2-di(4-pyridyl)ethylene was 1.1:1. The final calcium nitrate concentration was 0.5 mol / L.

[0086] S3. Preparation of flake crystals

[0087] The pretreated gypsum was added to the crystallization template liquid to obtain a slurry having 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), and filtered while hot to obtain a first filtrate and a first filter residue. The first filter residue was washed with the mixed alcohol solution and dried at 50°C to a constant weight, then immersed in an ether solution and stirred for 0.5 hours, filtered to obtain a second filtrate and a second filter residue, and the second filter residue was dried at 50°C to a constant weight to obtain flaky calcium sulfate crystals.

[0088] The crystal morphology of the gypsum was observed using a JEOL JSM-6490LV scanning electron microscope, and the phase composition of the samples was determined using a TD-3500 X-ray diffractometer.

[0089] The test results are shown in Figures 1, 2, and 3. As can be seen from Figures 1 and 2, the product prepared in this example is flaky, with good dispersion between crystals, and is not prone to agglomeration or adhesion. As can be seen from Figure 3, this example successfully prepared flaky calcium sulfate crystals.

[0090] Example 2

[0091] This embodiment provides a method for preparing nano-flaky calcium sulfate using phosphogypsum, comprising the following steps:

[0092] S1. Phosphogypsum pretreatment

[0093] The phosphogypsum was repeatedly washed with tap water until its pH value reached 6.5. The pretreated 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.

[0094] The mass content of calcium sulfate dihydrate in the obtained purified gypsum is 91%, the mass content of soluble phosphorus is 0.048%, and the mass content of soluble fluorine is 0.012%.

[0095] S2. Prepare crystallization template solution.

[0096] A mixed solution of glycerol and ethylene glycol (3:7 by mass) was prepared, to which piceatannol, 1,2-di(4-pyridyl)ethylene, and calcium nitrate were added. The solution was heated to 70°C and stirred until homogeneous and clear. Stirring was then stopped and the solution was aged at this temperature for 2 hours. The total mass of piceatannol and 1,2-di(4-pyridyl)ethylene was 2% of the mass of the purified gypsum. The molar ratio of piceatannol to 1,2-di(4-pyridyl)ethylene was 0.9:1. The final calcium nitrate concentration was 0.8 mol / L.

[0097] S3. Preparation of flake crystals

[0098] The pretreated gypsum was added to the crystallization template liquid to obtain a slurry having 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), and filtered while hot to obtain a first filtrate and a first filter residue. The first filter residue was washed with the mixed alcohol solution and dried at 55°C to a constant weight, then immersed in an ether solution and stirred for 0.8 hours, filtered to obtain a second filtrate and a second filter residue, and the second filter residue was dried at 55°C to a constant weight to obtain flaky calcium sulfate crystals.

[0099] Example 3

[0100] This embodiment provides a method for preparing nano-flaky calcium sulfate using phosphogypsum, comprising the following steps:

[0101] S1 is the same as Example 1.

[0102] S2. Prepare crystallization template solution.

[0103] A mixed solution of glycerol and ethylene glycol (4:6 by mass) was prepared, and piceatannol, 1,2-di(4-pyridyl)ethylene, and sodium sulfate were added. The solution was heated to 80°C and stirred until homogeneous and clear. Stirring was then stopped and the solution was aged at this temperature for 1 hour. The total mass of piceatannol and 1,2-di(4-pyridyl)ethylene was 5% of the mass of the purified gypsum. The molar ratio of piceatannol to 1,2-di(4-pyridyl)ethylene was 1.3:1. The final sodium sulfate concentration was 1 mol / L.

[0104] S3. Preparation of flake crystals

[0105] The pretreated gypsum was added to the crystallization template liquid to obtain a slurry having a solid-liquid ratio (g / mL) of 0.25. The slurry was reacted at a constant temperature for 8 h under intermittent stirring conditions (stirring for 5 min every 15 min at a stirring speed of 200 rpm), and filtered while hot to obtain a first filtrate and a first filter residue. The first filter residue was washed with the mixed alcohol solution and dried at 60° C. to constant weight, then immersed in an ether solution and stirred for 1 h, filtered to obtain a second filtrate and a second filter residue, and the second filter residue was dried at 60° C. to constant weight to obtain flaky calcium sulfate crystals.

[0106] Example 4

[0107] This embodiment is the same as Example 1, except that, after obtaining the flaky calcium sulfate crystals, this embodiment further comprises S4, recovering the alcohol waste liquid in Example 1.

[0108] (1) The first filtrate and the washing liquid produced after washing with the alcohol solution were combined, and vacuum distillation was performed at 120°C with the vacuum degree controlled at 0.5 mmHg to recover ethylene glycol. After boiling at 120°C for 20 minutes, the temperature was further raised to 200°C and boiled for 20 minutes to recover most of the alcohol solvent.

[0109] (2) After the concentrate is cooled to room temperature, ether (1 / 3 of the volume of the concentrate) is added to extract the organic matter. The extraction is repeated three times and the ether phases are combined to obtain an alcohol solution containing an inorganic salt and an ether solution containing a crystal form modifier.

[0110] (3) The alcohol solution of the inorganic salt is sealed and kept away from light at room temperature, and filtered to obtain inorganic salt crystals after 3 days. The remaining alcohol solution is recovered according to the distillation step of step (1).

[0111] (4) The ether solution containing the crystal form modifier obtained in step (2) and the second filtrate were combined and concentrated by vacuum distillation at a distillation temperature of 60° C. and a vacuum degree of 1 mmHg, so that the measured concentrations of 1,2-di(4-pyridyl)ethylene and piceatannol were both ≥0.2 mol / L (determined by mass spectrometry). The mixture was then sealed and kept in the dark at room temperature for 3 days, and filtered to obtain supramolecular crystals (as shown in FIG4 ), i.e., crystals formed by self-assembly of 1,2-di(4-pyridyl)ethylene and piceatannol through non-covalent bonds. The remaining solution was recovered by vacuum distillation.

[0112] The recovery rate of inorganic salts was 78.2%, and the total recovery rate of 1,2-di(4-pyridyl)ethylene and piceatannol was 55.3%.

[0113] Example 5

[0114] This embodiment is the same as Example 1, except that, after obtaining the flaky calcium sulfate crystals, this embodiment further comprises S4, recovering the alcohol waste liquid in Example 1.

[0115] (1) The first filtrate and the washing liquid produced after washing with the alcohol solution were combined, and vacuum distillation was performed at 140° C. with the vacuum degree controlled at 0.8 mmHg to recover ethylene glycol. After boiling at 140° C. for 20 minutes, the temperature was further raised to 180° C. and boiled for 20 minutes to recover most of the alcohol solvent.

[0116] (2) After the concentrate is cooled to room temperature, ether (1 / 4 of the volume of the concentrate) is added to extract the organic matter. The extraction is repeated three times and the ether phases are combined to obtain an alcohol solution containing an inorganic salt and an ether solution containing a crystal form modifier.

[0117] (3) The alcohol solution of the inorganic salt is sealed and kept away from light at room temperature, and filtered for 4 days to obtain inorganic salt crystals. The remaining alcohol solution is recovered according to the distillation step of step (1).

[0118] (4) The ether solution containing the crystal form modifier obtained in step (2) and the second filtrate are combined and concentrated by vacuum distillation at a distillation temperature of 70° C. and a vacuum degree of 0.5 mmHg, so that the measured concentrations of 1,2-di(4-pyridyl)ethylene and piceatannol are both ≥0.2 mol / L (determined by ultraviolet absorption spectroscopy), and then sealed and kept in the dark at room temperature for 4 days to obtain supramolecular crystals, i.e., crystals self-assembled by 1,2-di(4-pyridyl)ethylene and piceatannol through non-covalent bonds, and the remaining solution is recovered by vacuum distillation.

[0119] The recovery rate of inorganic salts was 81.5%, and the total recovery rate of 1,2-di(4-pyridyl)ethylene and piceatannol was 58.3%.

[0120] Comparative Example 1

[0121] This comparative example is substantially the same as Example 1, except that, in this comparative example, the crystal form modifier only includes piceatannol.

[0122] Comparative Example 2

[0123] This comparative example is substantially the same as Example 1, except that, in this comparative example, the crystal form modifier only includes 1,2-di(4-pyridyl)ethylene.

[0124] Experimental example

[0125] The above Examples 1-5 and Comparative Examples 1-2 were tested as follows. The testing method included using a laser particle size analyzer, Bettersize 2000, to test the particle size and particle size distribution of the powders prepared in the Examples and Comparative Examples. The test results are as follows:

[0126] As can be seen from the table above, none of the comparative examples produced dispersed flaky calcium sulfate crystals. Comparative Examples 1 and 2, containing only one crystal form modifier component, failed to form supramolecular crystals as a crystallization template, and the crystal form adjustment effect of a single component only produced short columnar crystals. Particle size distribution can reflect the degree of crystal agglomeration; larger particle size distributions indicate more agglomerated powder.

[0127] In summary, the present disclosure provides a method for preparing nano-flaky calcium sulfate using phosphogypsum, which uses a combination of piceatannol and 1,2-di(4-pyridyl)ethylene as a crystal modifier. The complex formed by self-assembly of piceatannol and 1,2-di(4-pyridyl)ethylene in the liquid phase through coordination and π-π stacking can serve as a crystal template for calcium sulfate, thereby regulating the crystal morphology of calcium sulfate. The o-phenolic hydroxyl group of piceatannol reacts with the CaCl2-containing cations on the surface of the calcium sulfate crystal. 2+ The calcium sulfate binds to and adsorbs on the {111} crystal plane, effectively inhibiting its growth, thereby achieving two-dimensional crystal growth and forming flaky crystals. Compared to using traditional crystal-transforming agents or a single crystal-transforming agent, the template method for preparing calcium sulfate crystals disclosed herein can provide a more stable growth environment for the crystals, making them less susceptible to impurities. Furthermore, the crystallization template provided by the present disclosure can effectively prevent crystal agglomeration, forming well-dispersed, non-sticky flaky nanocrystals. The prepared nano-flaky calcium sulfate has 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.

[0128] The foregoing description is merely a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present disclosure shall be included within the scope of protection of the present disclosure. Industrial Applicability

[0129] The present invention provides a method for preparing nano-flaky calcium sulfate using phosphogypsum, which uses a combination of piceatannol and 1,2-di(4-pyridyl)ethylene as a crystal modifier. The complex formed by self-assembly of piceatannol and 1,2-di(4-pyridyl)ethylene in the liquid phase through coordination and π-π stacking can serve as a crystal template for calcium sulfate, thereby regulating the crystal morphology of calcium sulfate. The o-phenolic hydroxyl group of piceatannol reacts with the CaCl2-containing hydroxyl group on the surface of the calcium sulfate crystal. 2+ The calcium sulfate binds to and adsorbs on the {111} crystal plane, effectively inhibiting its growth, thereby achieving two-dimensional crystal growth and forming flaky crystals. Compared to using traditional crystal-transforming agents or a single crystal-transforming agent, the template method for preparing calcium sulfate crystals disclosed herein can provide a more stable growth environment for the crystals, making them less susceptible to impurities. Furthermore, the crystallization template provided by the present disclosure can effectively prevent crystal agglomeration, forming well-dispersed, non-sticky flaky nanocrystals. The prepared nano-flaky calcium sulfate has 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.

Claims

1. A method for preparing nano-sheet calcium sulfate using phosphogypsum, characterized in that, it includes: obtaining purified gypsum by pre-treating phosphogypsum; mixing an inorganic salt and an alcohol solution containing a crystal form regulator until clarified, and then aging to obtain a crystallization template solution, wherein the crystal form regulator is a composition of piceatannol and 1,2-bis(4-pyridyl)ethylene; pulping and reacting the purified gypsum with the crystallization template solution, and after the reaction ends, nano-sheet calcium sulfate is obtained through post-treatment.

2. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to claim 1, characterized in that, the molar ratio of piceatannol to 1,2-bis(4-pyridyl)ethylene is 0.8 - 1.4:

1.

3. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 2, characterized in that, the dosage of the crystal form regulator is 2 - 5% of the mass of the purified gypsum.

4. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 3, characterized in that, the alcohol solution is a mixed solution of ethylene glycol and glycerol, and the mass ratio of glycerol in the alcohol solution is 30 - 50%.

5. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 4, characterized in that, the solid-liquid ratio during pulping of the purified gypsum and the crystallization template solution is 0.02 - 0.25 g:1 mL.

6. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 5, characterized in that, the reaction after pulping the purified gypsum and the crystallization template solution is a constant temperature 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 min every 15 - 30 min, and the stirring speed is 200 - 300 rpm.

8. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 6 - 7, characterized in that, the temperature of the constant temperature reaction is 50 - 70 °C, and the reaction time is 5 - 10 h.

9. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 8, characterized in that, the inorganic salt includes one or more of calcium nitrate and sodium sulfate.

10. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 9, 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 any one of claims 1 - 10, characterized in that, the temperature for mixing the inorganic salt and the alcohol solution containing the crystal form regulator is 60 - 80 °C, and then aging is carried out at a constant temperature for 30 min - 2 h.

12. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 11, characterized in that, The pretreatment includes first washing the phosphogypsum with water until the pH is 6.5 - 7.0, then drying and sieving it to obtain gypsum powder. The gypsum powder, quicklime, and water are formulated into a slurry and mixed for 24 - 48 h, 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 any one of claims 12 - 13, characterized in that, the sieving includes sieving the dried phosphogypsum through a square - hole sieve with a pore diameter of 0.2 - 0.4 mm.

15. The method for preparing nano - sheet calcium sulfate using phosphogypsum according to any one of claims 12 - 14, characterized in that, the drying temperature is 40 - 50 °C.

16. The method for preparing nano - sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 15, characterized in that, the mass content of calcium sulfate dihydrate in the purified gypsum is 80 - 98%, the mass content of soluble phosphorus is ≤0.1%, and the mass content of soluble fluorine is ≤0.03%.

17. The method for preparing nano - sheet calcium sulfate using phosphogypsum according to any one of claims 1 - 16, characterized in that, the post - treatment 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 then 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 preparing nano - sheet calcium sulfate using phosphogypsum further includes recovering alcohol waste liquid: combining the first filtrate and the washing liquid produced after washing with the alcohol solution, and performing first - stage vacuum distillation to recover alcohol; when the volume of the concentrated liquid is 1 / 3 - 1 / 5 of the original volume, stop heating. After the concentrated liquid is cooled to room temperature, add ether to extract organic matter to obtain an alcohol solution containing inorganic salts and an ether solution containing a crystal - form regulator; the alcohol solution containing inorganic salts is sealed and left to stand at room temperature in the dark for 3 - 4 days, and then filtered to obtain inorganic salt crystals; combining the ether solution containing the crystal - form regulator and the second filtrate, and performing second - stage vacuum distillation to make the measured concentrations of 1,2 - bis(4 - pyridyl)ethylene and piceatannol both ≥0.2 mol / L, then sealing and leaving to stand at room temperature in the dark for 3 - 4 days, and filtering to obtain supramolecular crystals, that is, crystals formed by the self - assembly of 1,2 - bis(4 - pyridyl)ethylene and piceatannol through non - covalent bonds.

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

21. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 18-20, 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 piceatannol is 55-60%.

22. The method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 18-21, characterized in that, the concentrations of the 1,2-bis(4-pyridyl)ethylene and the piceatannol are detected by ultraviolet absorption spectroscopy, liquid chromatography or mass spectrometry.

23. A nano-sheet calcium sulfate, characterized in that, it is prepared by the method for preparing nano-sheet calcium sulfate using phosphogypsum according to any one of claims 1-22.

24. Use of the nano-sheet calcium sulfate according to claim 23 in the preparation of a filler, a reinforcing agent, a flame retardant, a skin smoothing agent or a heat insulating material.

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