A method for preparing hemihydrate gypsum powder from phosphogypsum by atmospheric salt solution method and hemihydrate gypsum powder
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG BRUNP RECYCLING TECH CO LTD
- Filing Date
- 2023-12-01
- Publication Date
- 2026-07-10
AI Technical Summary
Existing methods for treating phosphogypsum result in low resource utilization and environmental pollution. Furthermore, the atmospheric pressure salt solution method is not effective in regulating the crystal morphology of gypsum and lacks a consistent approach.
Betaine compounds were used as crystallizing agents. The pH value of the slurry was adjusted to carry out a constant-temperature dynamic reaction, thereby controlling the aspect ratio of hemihydrate gypsum crystals and utilizing the pH responsiveness of betaine to regulate the crystal morphology.
It has achieved controllability of the crystal morphology of hemihydrate gypsum and improved production efficiency, with obvious control effects and certain regularity.
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Figure CN117897365B_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of waste recycling technology, and more specifically, to a method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum and the hemihydrate gypsum powder. Background Technology
[0002] Phosphogypsum is a byproduct of phosphate fertilizer production, with its main component being CaSO4·2H2O, accounting for more than 80% by mass. Because phosphogypsum contains impurities such as SiO2, F, P, and organic matter, its comprehensive utilization is affected. The rapid development of the phosphate fertilizer industry has resulted in the production and discharge of large quantities of phosphogypsum, while its resource utilization rate is low. Currently, the main method for treating phosphogypsum is stockpiling, which occupies a large amount of land and causes environmental pollution.
[0003] The properties of hemihydrate gypsum are closely related to its morphology; particle size, shape, and particle size distribution significantly influence its performance and applications. Spherical or low aspect ratio hemihydrate gypsum crystals possess high strength and strong injectability, making them well-suited for use in building materials or as bone binders. High aspect ratio hemihydrate gypsum crystals (such as whisker-like and linear crystals) exhibit good thermal stability, strong chemical resistance, and good compatibility with polymers, ceramics, and other materials, making them suitable as reinforcing agents in composite materials.
[0004] The main methods for preparing hemihydrate gypsum using phosphogypsum include: calcination method, autoclaving method, pressurized aqueous solution method, and atmospheric pressure salt (alcohol) solution method.
[0005] The calcination method dehydrates dihydrate gypsum in a dry environment to produce hemihydrate (anhydrous) gypsum, but the product has low purity and its quality is difficult to control and unstable. The autoclaving method uses saturated steam as a solvent, and dihydrate gypsum is pressurized and heated in an autoclave to convert it into hemihydrate gypsum. This preparation process is simple and has a large output, but it has high energy consumption, the reaction process is difficult to control, and the high content of β-type hemihydrate gypsum leads to unstable product quality. The pressurized aqueous solution method has relatively complex process conditions, low production efficiency, and long preparation time, resulting in high production energy consumption and cost. The atmospheric pressure salt (alcohol) solution method is a new process developed in recent years. It is currently in the laboratory research to semi-industrial trial stage. Compared with the autoclaving method and the pressurized aqueous solution method, the atmospheric pressure salt (alcohol) solution method does not require a pressure vessel and has the advantages of low pressure, low synthesis temperature and energy consumption, and high production efficiency, and has good application prospects.
[0006] Among these methods, the preparation of hemihydrate gypsum using the atmospheric pressure salt (alcohol) solution method allows for convenient control of the crystal morphology and strength of gypsum crystals by adjusting the type and amount of salt (alcohol) medium and crystal-transforming agent, reaction temperature, liquid-solid ratio, pH, and other factors. Existing techniques employ different crystal-transforming agents to control the gypsum crystal morphology, but the control effect is not significant and lacks regularity.
[0007] In view of this, this disclosure is hereby made. Summary of the Invention
[0008] The purpose of this disclosure is to provide a method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution of phosphogypsum. This method can use the same crystallizing agent to adjust the pH value of the slurry to control the final crystal morphology, and the control effect is obvious and shows a certain regularity.
[0009] The purpose of this disclosure is to provide a hemihydrate gypsum powder with controllable morphology and high production efficiency.
[0010] This disclosure is implemented as follows:
[0011] In a first aspect, this disclosure provides a method for preparing hemihydrate gypsum powder using a phosphogypsum atmospheric pressure salt solution method, comprising:
[0012] A mixture of salt and crystallizing agent is mixed with purified phosphogypsum to form a slurry, wherein the crystallizing agent is a betaine compound with pH responsiveness.
[0013] Based on the isoelectric point of the crystallizing agent and the required aspect ratio of the hemihydrate gypsum crystals, the pH of the slurry is adjusted using an alkali or acid agent, and the slurry is subjected to a constant-temperature dynamic reaction and then filtered to obtain the final product. Specifically, when the pH value of the slurry is greater than the isoelectric point of the crystallizing agent, the aspect ratio of the hemihydrate gypsum crystals increases; when the pH value of the slurry is less than the isoelectric point of the crystallizing agent, the aspect ratio of the hemihydrate gypsum crystals decreases.
[0014] In an optional embodiment, the isoelectric point of the crystallizing agent is 5-8.
[0015] In an optional embodiment, the pH of the slurry is adjusted in the range of 2-10.
[0016] In an optional embodiment, the betaine compound is selected from one or more combinations of carboxylic acid betaine and sulfonic acid betaine, and the betaine compound has the following general formula: R1N + (CH3)2R2X - ;
[0017] Wherein, R1 is a substituted or unsubstituted C1-C12 alkyl straight chain, R2 is a substituted or unsubstituted C2-C12 alkyl straight chain, and X- is a carboxylate or sulfate group.
[0018] In an optional embodiment, the substituent in R1 includes an amino group, a hydroxyl group, or a thiol group; the substituent in R2 includes an amino group, a hydroxyl group, or a thiol group.
[0019] In an optional embodiment, the carboxylic acid-type betaine comprises CH3(CH2). 11 N +(CH3)2(CH2)2COO - N + (CH3)3(CH2) 12 COO - Or CH3(CH2)5N + (CH3)2(CH2)5COO - .
[0020] In an optional embodiment, the sulfonic acid-based betaine comprises CH3(CH2). 11 N + (CH3)2(CH2)3SO3 - .
[0021] In an optional embodiment, the amount of the crystallization agent added is 0.3 to 1% of the dry basis mass of calcium sulfate dihydrate in the purified phosphogypsum.
[0022] In an optional embodiment, the purified phosphogypsum contains 80-98% calcium sulfate dihydrate, ≤0.1% soluble phosphorus, and ≤0.03% soluble fluorine.
[0023] In an optional embodiment, the concentration of the salt in the mixture is 0.3 to 1.5 mol / L.
[0024] In an optional embodiment, the salt comprises any one or a combination of sodium sulfate, calcium nitrate, magnesium sulfate, and calcium chloride.
[0025] In an optional embodiment, the solid content of the slurry is 60-80%.
[0026] In an optional embodiment, the stirring speed of the isothermal dynamic reaction is 180–250 r / min.
[0027] In an optional embodiment, the alkaline agent includes any one or more combinations of sodium hydroxide, potassium hydroxide, calcium hydroxide, and calcium oxide.
[0028] In an optional embodiment, the acid agent includes any one or more combinations of hydrochloric acid and sulfuric acid.
[0029] In an optional embodiment, the solids are further subjected to washing, drying, and grinding after filtration.
[0030] In an optional embodiment, the washing includes washing with boiling water.
[0031] In an optional embodiment, the temperature for drying the solid is 110–120°C.
[0032] In an optional embodiment, the method for preparing the purified phosphogypsum 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 phosphogypsum.
[0033] In an optional embodiment, the mass ratio of the gypsum powder, the quicklime, and the water is 100:0.5-2:10-20.
[0034] 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.
[0035] In an optional embodiment, the temperature for drying the slurry is 40–50°C.
[0036] Secondly, this disclosure provides a hemihydrate gypsum powder, which is prepared by the method of preparing hemihydrate gypsum powder by the atmospheric pressure salt solution method of phosphogypsum as described in any of the foregoing embodiments.
[0037] This disclosure has the following beneficial effects: In the embodiments of this disclosure, the hemihydrate gypsum crystals prepared using only one crystallizing agent (betaine compound) can have their crystal morphology controlled by adjusting the pH value of the slurry to obtain hemihydrate gypsum crystals with different aspect ratios. The control principle is as follows: when the pH value of the liquid slurry is lower than the isoelectric point of the crystallizing agent, the positively charged crystallizing agent acts as a cationic surfactant, tending to adsorb onto the {010} crystal planes on the side of the hemihydrate gypsum crystal, making it easier for the hemihydrate gypsum to grow along the c-axis into a one-dimensional whisker shape; when the pH value of the slurry is higher than the isoelectric point of the crystallizing agent, the negatively charged crystallizing agent acts as an anionic surfactant, tending to adsorb onto the {111} crystal planes of the hemihydrate gypsum crystal, restricting the growth of the hemihydrate gypsum along the c-axis, resulting in a decrease in the aspect ratio of the crystal and a cylindrical shape. The method for preparing hemihydrate gypsum powder using the atmospheric pressure salt solution method for phosphogypsum disclosed in this disclosure exhibits significant control over crystal morphology, showing a trend that the higher the pH of the slurry, the smaller the aspect ratio of the obtained hemihydrate gypsum crystals. Therefore, the pH value of the slurry can be adaptively adjusted according to the desired aspect ratio of the hemihydrate gypsum crystals. Compared to amino acid-based crystal-transforming agents, the amphiphilic betaine molecule provided in this disclosure has higher proton acceptance and donation capabilities and charge stability, thus exhibiting higher sensitivity in crystal form control. Attached Figure Description
[0038] 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.
[0039] Figure 1 The image shows a SEM image of hemihydrate gypsum crystals obtained at pH = 2.1 in Example 5.
[0040] Figure 2 The image shows a SEM image of hemihydrate gypsum crystals obtained at pH 5.2 in Example 5.
[0041] Figure 3 This is a SEM image of the hemihydrate gypsum crystals obtained at pH = 8.3 in Example 5. Detailed Implementation
[0042] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.
[0043] This disclosure provides a method for preparing hemihydrate gypsum powder using a phosphogypsum atmospheric pressure salt solution method, comprising:
[0044] A mixture of salt and a crystal-changing agent is mixed with purified phosphogypsum to form a slurry. The crystal-changing agent is a pH-responsive betaine compound. The pH of the slurry is adjusted according to the isoelectric point of the crystal-changing agent and the desired aspect ratio of the hemihydrate gypsum crystals. The slurry undergoes a constant-temperature dynamic reaction and is then filtered to obtain the final product. Specifically, when the pH of the slurry is higher than the isoelectric point of the crystal-changing agent, the aspect ratio of the hemihydrate gypsum crystals increases; conversely, when the pH of the slurry is lower than the isoelectric point of the crystal-changing agent, the aspect ratio of the hemihydrate gypsum crystals decreases. In this disclosure, a pH-responsive betaine compound is used as the crystal-changing agent. Only one crystal-changing agent is needed to control the crystal morphology by adjusting the pH of the slurry. Furthermore, the control effect is significant, exhibiting a pattern where the higher the pH of the slurry, the smaller the aspect ratio of the obtained hemihydrate gypsum crystals.
[0045] Specifically, the method disclosed herein includes the following steps:
[0046] S1. Pretreatment of phosphogypsum.
[0047] First, the phosphogypsum is washed with water until the pH reaches 6.5–7.0, then dried and sieved to obtain gypsum powder. The gypsum powder, quicklime, and water are mixed to form a slurry and mixed for 24–48 hours, then dried to obtain purified phosphogypsum.
[0048] The mass ratio of gypsum powder, quicklime, and water is 100:0.5-2:10-20. Sieving involves passing the dried phosphogypsum through a square-hole sieve with a aperture of 0.2-0.4 mm. The slurry is dried at a temperature of 40-50℃.
[0049] The purified phosphogypsum contains 80-98% calcium sulfate dihydrate, ≤0.1% soluble phosphorus, and ≤0.03% soluble fluorine.
[0050] In some typical embodiments, the mass ratio of gypsum powder, quicklime, and water can be, for example, any one or a range between any two of 100:0.5:10, 100:1:15, 100:1.5:20, 100:2:15, 100:0.8:17, or 100:0.5:20. The mixing time can be, for example, any one or a range between any two of 24h, 30h, 36h, 42h, or 48h. The drying temperature can be, for example, any one or a range between any two of 40℃, 42℃, 45℃, 46℃, 48℃, or 50℃.
[0051] S2. Prepare the slurry.
[0052] The mixture of salt and crystallizing agent is heated to a preset temperature (95-100℃), and then purified phosphogypsum is added to prepare a slurry.
[0053] The salts include, but are not limited to, any one or a combination of sodium sulfate, calcium nitrate, magnesium sulfate, and calcium chloride.
[0054] Betaine compounds are selected from one or more combinations of carboxylic acid betaine and sulfonic acid betaine, and have the following general formula: R1N + (CH2)2R2X - Wherein, R1 is a substituted or unsubstituted C1-C12 alkyl straight chain, and R2 is a substituted or unsubstituted C2-C12 alkyl straight chain; X- is a carboxylate or sulfate group. The substituents in R1 include amino, hydroxyl, or mercapto groups; the substituents in R2 include amino, hydroxyl, or mercapto groups.
[0055] Specifically, carboxylic acid-type betaines include CH3(CH2). 11 N + (CH3)2(CH2)2COO - N + (CH3)3(CH2) 12 COO - Or CH3(CH2)5N + (CH3)2(CH2)5COO -Sulfonic acid-based betaines include CH3(CH2). 11 N + (CH3)2(CH2)3SO3 - .
[0056] In this disclosure, the mixture of salt and crystallizing agent is preheated to improve the mixing effect of the two, and then purified phosphogypsum is added, which makes it easier to disperse into a slurry.
[0057] In this disclosure, the amount of crystallizing agent added is 0.3-1% of the dry weight of calcium sulfate dihydrate in the purified phosphogypsum. The salt concentration in the mixture is 0.3-1.5 mol / L. The solid content of the final prepared slurry is 60-80%.
[0058] In some typical embodiments, the amount of crystallizing agent added is any one or a combination of 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1% of the dry weight of calcium sulfate dihydrate in the purified phosphogypsum. The salt concentration in the mixture is any one or a combination of 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.3 mol / L, or 1.5 mol / L. The solid content of the final slurry is any one or a combination of 60%, 65%, 68%, 70%, 72%, 75%, 78%, or 80%.
[0059] S3. Adjust the pH value to obtain the product.
[0060] Based on the isoelectric point of the crystallizing agent and the required aspect ratio of the hemihydrate gypsum crystals, the pH of the slurry is adjusted, and the slurry is subjected to a constant temperature dynamic reaction at a stirring speed of 180-250 r / min. The solid is then filtered, washed with boiling water, dried at a temperature of 110-120℃, and subsequently ground to obtain the final product.
[0061] The isoelectric point of the crystallization agent is 5-8.
[0062] Alkali agents include, but are not limited to, any one or more combinations of sodium hydroxide, potassium hydroxide, calcium hydroxide, and calcium oxide. Acid agents include, but are not limited to, any one or more combinations of hydrochloric acid and sulfuric acid.
[0063] In some typical embodiments, the pH of the slurry is adjusted to a range of 2-10, specifically a value between 2, 3, 4, 5, 6, 7, 8, 9, or 10. The stirring speed can be, for example, any one of 180 r / min, 200 r / min, 220 r / min, or 250 r / min. The drying temperature can be, for example, any one of 110°C, 115°C, or 120°C.
[0064] The features and performance of this disclosure will be further described in detail below with reference to embodiments.
[0065] Example 1
[0066] This embodiment provides a betaine crystallization agent with the molecular structural formula CH3(CH2). 11 N + (CH3)2(CH2)3SO3 - .
[0067] The preparation method includes: weighing N,N-dimethyldodecylamine and dissolving it in anhydrous tetrahydrofuran, heating it at 50°C to dissolve it. Then, 1,3-propanesulfonyl lactone is added dropwise, wherein the feed ratio of N,N-dimethyldodecylamine to 1,3-propanesulfonyl lactone is 1:1.2. After the addition is complete, the temperature is raised to 60°C and reacted for 12 hours. After centrifugation, a white precipitate is obtained, which is washed three times with diethyl ether and dried in a vacuum drying oven to obtain the product. The yield is 81%, and the optical purity is 99.2%.
[0068] 1 H-NMR(d-DMSO): δ0.82~0.84(t,3H),1.24~1.29(m,18H),1.74~1.77(m,2H) ),,2.26~2.28(m,2H),2.71~2.73(t,2H),3.30(s,6H),3.38~3.41(t,4H),.
[0069] Example 2
[0070] This embodiment provides a betaine crystallization agent with the molecular structural formula CH3(CH2). 11 N + (CH3)2(CH2)2COO - .
[0071] The preparation method includes: weighing N,N-dimethyldodecylamine and dissolving it in anhydrous tetrahydrofuran, heating to 50°C to dissolve, and then starting to add β-propiolactone dropwise, wherein the molar ratio of N,N-dimethyldodecylamine to β-propiolactone is 1:1.1. After the addition is complete, the mixture is stirred at 50°C for 12 hours, centrifuged to obtain a white precipitate, washed three times with diethyl ether, and dried in a vacuum drying oven to obtain the product, with a yield of 81% and an optical purity of 99.2%.
[0072] 1 H-NMR (d-DMSO): δ0.82~0.84(t,3H),1.24~1.29(m,18H),1.74~1.77(m,2H),2.86~2.88(t,2H),3.22(t,2H),3.32(s,6H),3.67(t,2H),.
[0073] Example 3
[0074] This embodiment provides a betaine crystallization agent with the molecular structural formula CH3(CH2)5N. + (CH3)2(CH2)5COO - .
[0075] The preparation method includes: weighing N,N-dimethylhexylamine and 6-bromohexanoic acid and dissolving them in anhydrous ethanol, adding potassium iodide as a catalyst, purging with nitrogen gas, reacting at a constant temperature of 35°C for 72 hours, filtering the reaction solution, drying the filter residue and dissolving it in water, and extracting it three times with diethyl ether. After drying the aqueous phase, the product is obtained with a yield of 68% and an optical purity of 99.6%.
[0076] The molar ratio of N,N-dimethylhexylamine to 6-bromohexanoic acid is 1:1.2, and the amount of potassium iodide added is 10% of the mass of N,N-dimethylhexylamine.
[0077] 1 H-NMR(d-DMSO): δ0.82~0.84(t,3H),1.28~1.32(m,8H),1.72~1.75(m,4H) ), 3.30 (s, 6H), 3.48~3.51 (t, 4H), 1.52~1.55 (m, 2H), 2.87~2.91 (t, 2H).
[0078] Example 4
[0079] This embodiment provides a betaine crystallization agent with the molecular structural formula N. + (CH3)3(CH2) 11 COO - .
[0080] The preparation method includes: slowly adding a mixed aqueous solution of sodium hydroxide and trimethylamine dropwise to an aqueous solution of methyl bromododecanoate at 0-5°C, completing the addition in about 3 hours; continuing the reaction with stirring at this temperature for 24 hours, after which the reaction is stopped. Hydrochloric acid (36% concentration) is added to neutralize to pH 5, and the product is purified by centrifugation, ultrafiltration, and resin purification to obtain a pure product with a yield of 79% and an optical purity of 99.5%.
[0081] The molar ratio of trimethylamine to methyl bromododecanoate is 1.2:1; in the mixed solution, the concentration of trimethylamine is 15 wt%, the concentration of sodium hydroxide is 28 wt%, and the concentration of the aqueous solution of methyl bromododecanoate is 1 wt%.
[0082] 1 H-NMR (d-DMSO): δ1.26~1.30(m,14H), 1.52~1.55(t,2H), 1.68~1.71(t,2H), 2.41~2.43(t,2H), 3.28~3.30(t,2H), 3.35(9H,s).
[0083] The isoelectric points of the betaine crystallizing agents prepared in Examples 1-4 were tested. The testing method included: adjusting the pH of the crystallizing agent solution with NaOH aqueous solution or HCl aqueous solution, measuring the conductivity (λ) of the solution at different pH values using a Zeta potentiometer, and plotting the pH-λ relationship curve. When the curve has a minimum point, it indicates that the number of positive and negative ions in the solution is equal, which is the isoelectric point.
[0084] Please refer to Table 1 for the test results:
[0085] Table 1. Isoelectric points of the crystal transformation agents prepared in Examples 1-4
[0086] Example 1 Example 2 Example 3 Example 4 isoelectric point 5.3 5.5 6.4 7.1
[0087] Example 5
[0088] A method for preparing hemihydrate gypsum powder using a phosphogypsum atmospheric pressure salt solution method includes the following steps:
[0089] (1) Pretreatment of phosphogypsum
[0090] The phosphogypsum was repeatedly washed with tap water until its pH value reached 6.8. After pretreatment, the phosphogypsum was dried and passed through a 0.3 mm square-hole sieve. Then, 0.5 wt% quicklime and 10% water were added to prepare a slurry for pretreatment for 48 hours, followed by drying at 45°C to obtain purified gypsum. The phosphogypsum source and physicochemical properties were as follows: It was sourced from a phosphate fertilizer plant in Hubei Province. The phosphogypsum was 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 was 0.08%, and an organic matter content of 0.05%. The pH of the leachate was between 1 and 2. The phosphogypsum used in subsequent examples had the same source and physicochemical properties as in this example.
[0091] The soluble phosphorus, soluble fluoride, and calcium sulfate dihydrate content in phosphogypsum were 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.
[0092] (2) Preparation of slurry
[0093] Prepare an aqueous solution with a sodium sulfate concentration of 0.7 mol / L and an amount of the crystallization agent prepared in Example 1 of 1% of the dry weight of calcium sulfate dihydrate in the purified gypsum. Pour the solution into a reaction vessel and heat it to 97°C. Add the purified gypsum to prepare a slurry with a solid content of 60%.
[0094] (3) Adjust the pH value to obtain the product from the reaction.
[0095] Add 3 mol / L KOH solution or concentrated sulfuric acid to adjust the pH of the slurry to 2-10, then carry out a constant temperature dynamic reaction with a stirring speed of about 200 r / min; finally, the product after the reaction is completed is quickly filtered, washed with boiling water, dried at 120℃, and ground to obtain α-hemihydrate gypsum powder.
[0096] By adjusting the pH of the slurry, hemihydrate gypsum crystals with different aspect ratios (the ratio of length to cross-sectional diameter) can be obtained.
[0097] The method for determining the pH of the slurry includes: extracting the slurry and filtering it with medium-speed qualitative filter paper, placing it into the filtered solution using a precision pH meter, letting it stand at room temperature for 15 minutes, and then taking the pH meter reading.
[0098] The method for testing the aspect ratio includes: observing the crystal morphology and size of hemihydrate gypsum using a JEOL JSM-6490LV scanning electron microscope, measuring the length and diameter of the crystals using Image-Pro Plus image analysis software, and calculating the average aspect ratio.
[0099] The above methods were used in subsequent embodiments when measuring the pH of the slurry and testing the aspect ratio.
[0100] Please refer to the length-to-diameter ratio test results of this embodiment. Figure 1 , Figure 2 , Figure 3 And Table 2:
[0101] Table 2: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Example 5
[0102] pH value 2.1 3.5 5.2 6.7 8.3 10.0 Aspect Ratio 19.0 6.2 1.7 1 0.3 0.3
[0103] Example 6
[0104] A method for preparing hemihydrate gypsum powder using a phosphogypsum atmospheric pressure salt solution method includes the following steps:
[0105] (1) Pretreatment of phosphogypsum
[0106] 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. Then, 2 wt% quicklime and 20% water were added to prepare a slurry. After pretreatment for 24 hours, it was dried at 45°C to obtain purified gypsum.
[0107] The obtained purified gypsum contained 93% calcium sulfate dihydrate, 0.038% soluble phosphorus, and 0.013% soluble fluorine.
[0108] (2) Preparation of slurry
[0109] Prepare an aqueous solution with a sodium sulfate concentration of 0.3 mol / L, a calcium chloride concentration of 0.5 mol / L, and the dosage of the crystallization agent prepared in Example 2 being 1% of the dry basis mass of calcium sulfate dihydrate in the purified gypsum. Pour the solution into a reaction vessel and heat it to 97°C. Add the purified gypsum to prepare a slurry with a solid content of 60%.
[0110] (3) Adjust the pH value to obtain the product from the reaction.
[0111] The pH of the slurry was adjusted to 2–10 by adding 3 mol / L KOH solution or concentrated sulfuric acid, followed by a constant-temperature dynamic reaction with a stirring speed of approximately 200 r / min. The final product was rapidly filtered, washed with boiling water, dried at 120℃, and ground to obtain α-hemihydrate gypsum powder. By adjusting the pH of the slurry, hemihydrate gypsum crystals with different aspect ratios can be obtained; please refer to Table 3 for details.
[0112] Table 3: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Example 6
[0113] pH value 2 3.1 5.5 7.2 9.6 Aspect Ratio 17.5 8.6 1.2 0.7 0.4
[0114] Example 7
[0115] A method for preparing hemihydrate gypsum powder using a phosphogypsum atmospheric pressure salt solution method includes the following steps:
[0116] (1) Pretreatment of phosphogypsum
[0117] 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 mesh sieve. Then, 1 wt% quicklime and 20% water were added to prepare a slurry. After pretreatment for 24 hours, the slurry was dried at 45°C to obtain purified gypsum.
[0118] The obtained purified gypsum contained 93% calcium sulfate dihydrate, 0.045% soluble phosphorus, and 0.011% soluble fluorine.
[0119] (2) Preparation of slurry
[0120] Prepare an aqueous solution with a calcium nitrate concentration of 1 mol / L and the amount of the crystallizing agent prepared in Example 3 is 1% of the dry weight of calcium sulfate dihydrate in the purified gypsum. Pour the solution into a reaction vessel and heat it to 95°C. Add the purified gypsum to prepare a slurry with a solid content of 80%.
[0121] (3) Adjust the pH value to obtain the product from the reaction.
[0122] The pH of the slurry was adjusted to 2–10 by adding 3 mol / L KOH solution or concentrated sulfuric acid, followed by a constant-temperature dynamic reaction with a stirring speed of approximately 200 r / min. The final product was rapidly filtered, washed with boiling water, dried at 120℃, and ground to obtain α-hemihydrate gypsum powder. By adjusting the pH of the slurry, hemihydrate gypsum crystals with different aspect ratios can be obtained; please refer to Table 4 for details.
[0123] Table 4: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Example 7
[0124] pH value 2.1 3.8 6.4 8.2 10 Aspect Ratio 22.3 7.5 0.8 0.4 0.2
[0125] Example 8
[0126] The difference from Example 7 is that step (2) uses the crystallization agent prepared in Example 4, and the solid content of the slurry is 70%; the drying temperature in step (3) is 110°C. By adjusting the pH of the slurry, hemihydrate gypsum crystals with different aspect ratios can be obtained, as detailed in Table 5:
[0127] Table 5: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Example 8
[0128] pH value 2.2 4.7 7.3 9.5 Aspect Ratio 25.7 5.7 1.3 0.2
[0129] Example 9
[0130] A method for preparing hemihydrate gypsum powder using a phosphogypsum atmospheric pressure salt solution method includes the following steps:
[0131] (1) Pretreatment of phosphogypsum
[0132] 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. Then, 1 wt% quicklime and 15% water were added to prepare a slurry. After pretreatment for 48 hours, it was dried at 45°C to obtain purified gypsum.
[0133] The obtained purified gypsum contained 93% calcium sulfate dihydrate, 0.052% soluble phosphorus, and 0.015% soluble fluorine.
[0134] (2) Preparation of slurry
[0135] Prepare an aqueous solution with a magnesium sulfate concentration of 1.3 mol / L and the amount of the crystallization agent prepared in Example 1 is 0.5% of the dry weight of calcium sulfate dihydrate in the purified gypsum. Pour the solution into a reaction vessel and heat it to 100°C. Add the purified gypsum to prepare a slurry with a solid content of 60%.
[0136] (3) Adjust the pH value to obtain the product from the reaction.
[0137] The pH of the slurry was adjusted to 2–10 by adding 3 mol / L KOH solution or concentrated sulfuric acid, followed by a constant-temperature dynamic reaction with a stirring speed of approximately 200 r / min. The final product was rapidly filtered, washed with boiling water, dried at 120℃, and ground to obtain α-hemihydrate gypsum powder. By adjusting the pH of the slurry, hemihydrate gypsum crystals with different aspect ratios can be obtained; please refer to Table 6 for details.
[0138] Table 6: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Example 9
[0139] pH value 2 3.4 5.3 7.2 9.5 Aspect Ratio 17.2 7.8 2.2 1.5 0.8
[0140] Example 10
[0141] The difference from Example 9 is that step (2) uses calcium nitrate at a concentration of 2 mol / L, and the crystallizing agent is the same as that in Example 4, with a doping amount of 0.3%. By adjusting the pH of the slurry, hemihydrate gypsum crystals with different aspect ratios can be obtained, as detailed in Table 7.
[0142] Table 7: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Example 10
[0143] pH value 2.1 4.5 7.2 9.5 Aspect Ratio 18.3 8.2 3.5 1.5
[0144] Comparative Example 1
[0145] The difference from Example 5 is that no crystallization agent was added. The aspect ratio of hemihydrate gypsum crystals grown at different pH levels was measured by adjusting the pH of the slurry; please refer to Table 8 for details.
[0146] Table 8: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Comparative Example 1
[0147] pH value 2 3.6 5.5 6.5 9.2 Aspect Ratio 14.5 15.3 15.8 16.2 18.2
[0148] Comparative Example 2
[0149] The difference from Example 5 is that the crystallization agent used was L-aspartic acid (isoelectric point 2.98). The aspect ratio of hemihydrate gypsum crystals grown at different pH levels was measured by adjusting the pH of the slurry; please refer to Table 9 for details.
[0150] Table 9: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Comparative Example 2
[0151] pH value 2.1 3.5 5.4 6.6 9.5 Aspect Ratio 10.5 7.8 7.5 7 6.2
[0152] Comparative Example 3
[0153] The difference from Example 5 is that the crystallization agent used was 12-aminododecanoic acid (isoelectric point 4.2). The aspect ratio of hemihydrate gypsum crystals grown at different pH levels was measured by adjusting the pH of the slurry; please refer to Table 10 for details.
[0154] Table 10: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Comparative Example 3
[0155] pH value 2.2 4 5.8 7.2 10 Aspect Ratio 13.2 13.5 14.1 13.8 13.5
[0156] Comparative Example 4
[0157] The difference from Example 5 is that the crystallization agent used was succinic acid. The aspect ratio of hemihydrate gypsum crystals grown at different pH levels was measured by adjusting the pH of the slurry; please refer to Table 11 for details.
[0158] Table 11: Aspect Ratio of Hemihydrate Gypsum Crystals Grown at Different pH Levels in Comparative Example 4
[0159] pH value 2.1 4.2 6.0 7.1 9.5 Aspect Ratio 8.5 8.1 7.7 3.5 flakes
[0160] As can be seen from Tables 1-11 above, the hemihydrate gypsum crystals prepared in this embodiment of the present disclosure, using only one crystallizing agent (betaine compound), can achieve control over the crystallization morphology of hemihydrate gypsum by adjusting the pH value of the slurry to obtain hemihydrate gypsum crystals with different aspect ratios. The control principle is as follows: when the pH value of the liquid slurry is lower than the isoelectric point of the crystallizing agent, the positively charged crystallizing agent acts as a cationic surfactant, tending to adsorb onto the {010} crystal planes on the side of the hemihydrate gypsum crystals, making it easier for the hemihydrate gypsum to grow along the c-axis into a one-dimensional whisker shape; when the pH value of the slurry is higher than the isoelectric point of the crystallizing agent, the negatively charged crystallizing agent acts as an anionic surfactant, tending to adsorb onto the {111} crystal planes of the hemihydrate gypsum crystals, restricting the growth of the hemihydrate gypsum along the c-axis, resulting in a decrease in the aspect ratio of the crystals and a cylindrical shape. The method for preparing hemihydrate gypsum powder using the atmospheric pressure salt solution method for phosphogypsum disclosed in this disclosure exhibits significant control over crystal morphology, showing a trend that the higher the pH of the slurry, the smaller the aspect ratio of the obtained hemihydrate gypsum crystals. Therefore, the pH value of the slurry can be adaptively adjusted according to the desired aspect ratio of the hemihydrate gypsum crystals. Compared to amino acid-based crystal-transforming agents, the amphiphilic betaine molecule provided in this disclosure has higher proton acceptance and donation capabilities and charge stability, thus exhibiting higher sensitivity in crystal form control.
[0161] The optional embodiments of this disclosure have been described in detail above; however, this disclosure is not limited thereto. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this disclosure and are all within the protection scope of this disclosure.
[0162] Industrial applicability
[0163] The hemihydrate gypsum crystals prepared in this disclosure, using only one crystallizing agent (betaine compound), can achieve control over the crystallization morphology of hemihydrate gypsum by adjusting the pH value of the slurry to obtain hemihydrate gypsum crystals with different aspect ratios. The control principle is as follows: when the pH value of the liquid slurry is lower than the isoelectric point of the crystallizing agent, the positively charged crystallizing agent acts as a cationic surfactant, tending to adsorb onto the {010} crystal planes on the sides of the hemihydrate gypsum crystals, making it easier for the hemihydrate gypsum to grow along the c-axis into a one-dimensional whisker shape; when the pH value of the slurry is higher than the isoelectric point of the crystallizing agent, the negatively charged crystallizing agent acts as an anionic surfactant, tending to adsorb onto the {111} crystal planes of the hemihydrate gypsum crystals, restricting the growth of the hemihydrate gypsum along the c-axis, resulting in a decrease in the aspect ratio of the crystals and a cylindrical shape. The method for preparing hemihydrate gypsum powder using the phosphogypsum atmospheric pressure salt solution method provided in this disclosure has a significant effect on controlling the crystallization morphology, and exhibits a pattern where the higher the pH of the slurry, the smaller the aspect ratio of the obtained hemihydrate gypsum crystals. Therefore, the pH of the slurry can be adjusted adaptively according to the desired aspect ratio of the hemihydrate gypsum crystals. Compared to amino acid-based crystallizers, the amphiphilic betaine molecule provided in this disclosure has higher proton accepting and donating capacity and charge stability, thus exhibiting higher sensitivity in crystal form regulation.
Claims
1. A method for preparing hemihydrate gypsum powder using a phosphogypsum atmospheric pressure salt solution, characterized in that, It includes: A mixture of salt and crystallizing agent is mixed with purified phosphogypsum to form a slurry, wherein the crystallizing agent is a betaine compound with pH responsiveness. Based on the isoelectric point of the crystallizing agent and the required aspect ratio of the hemihydrate gypsum crystals, the pH of the slurry is adjusted using an alkali or acid agent, and the slurry is subjected to a constant-temperature dynamic reaction and then filtered to obtain the final product. Specifically, when the pH value of the slurry is greater than the isoelectric point of the crystallizing agent, the aspect ratio of the hemihydrate gypsum crystals increases; when the pH value of the slurry is less than the isoelectric point of the crystallizing agent, the aspect ratio of the hemihydrate gypsum crystals decreases.
2. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The isoelectric point of the crystallizing agent is 5-8.
3. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The pH of the slurry can be adjusted within the range of 2-10.
4. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The betaine compound is selected from one or more combinations of carboxylic acid betaine and sulfonic acid betaine, and the betaine compound has the following general formula: R1N + (CH3)2R2X - ; Wherein, R1 is a substituted or unsubstituted C1~C12 alkyl straight chain, and R2 is a substituted or unsubstituted C2~C12 alkyl straight chain; X - It is a carboxylate or sulfonate group.
5. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 4, characterized in that, The substituents in R1 include amino, hydroxyl, or thiol groups; the substituents in R2 include amino, hydroxyl, or thiol groups.
6. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 4, characterized in that, The carboxylic acid-type betaine includes CH3(CH2). 11 N + (CH3)2(CH2)2COO - N + (CH3)3(CH2) 12 COO - Or CH3(CH2)5N + (CH3)2(CH2)5COO - .
7. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 4, characterized in that, The sulfonic acid-based betaine includes CH3(CH2). 11 N + (CH3)2(CH2)3SO3 - .
8. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The amount of the crystallizing agent added is 0.3-1% of the dry weight of calcium sulfate dihydrate in the purified phosphogypsum.
9. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The purified phosphogypsum contains 80-98% calcium sulfate dihydrate, ≤0.1% soluble phosphorus, and ≤0.03% soluble fluorine.
10. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The concentration of the salt in the mixture is 0.3~1.5 mol / L.
11. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The salt includes any one or a combination of sodium sulfate, calcium nitrate, magnesium sulfate, and calcium chloride.
12. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The solid content of the slurry is 60-80%.
13. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The stirring speed for the isothermal dynamic reaction is 180~250 r / min.
14. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The alkaline agent includes any one or a combination of sodium hydroxide, potassium hydroxide, calcium hydroxide, and calcium oxide.
15. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The acid includes any one or a combination of hydrochloric acid and sulfuric acid.
16. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The process after filtration also includes washing, drying, and grinding the solids.
17. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 16, characterized in that, The washing process includes washing with boiling water.
18. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 16, characterized in that, The temperature for drying the solid is 110~120℃.
19. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 1, characterized in that, The method for preparing the purified phosphogypsum includes: first washing the phosphogypsum with water until the pH is 6.5-7.0, then drying and sieving to obtain gypsum powder, mixing the gypsum powder, quicklime and water into a slurry for 24-48 hours, and then drying to obtain the purified phosphogypsum.
20. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 19, characterized in that, The mass ratio of the gypsum powder, the quicklime, and the water is 100:0.5~2:10~20.
21. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 19, 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.
22. The method for preparing hemihydrate gypsum powder by atmospheric pressure salt solution method of phosphogypsum according to claim 19, characterized in that, The temperature for drying the slurry is 40~50℃.
23. A hemihydrate gypsum powder, characterized in that, It is prepared by the method of preparing hemihydrate gypsum powder by the atmospheric pressure salt solution method of phosphogypsum as described in any one of claims 1-22.