Method for regulating morphology of alpha-semi-hydrated gypsum prepared from desulfurized gypsum in ethylene glycol-water system

Abstract

The invention discloses a morphology control method for preparing alpha-semi-hydrated gypsum by using desulfurized gypsum in an ethylene glycol-water system, which comprises the following steps: (1) mother liquor preparation: mixing inorganic salt, a crystal modifier and an ethylene glycol water solution to prepare a mother liquor; (2) feeding and crystal transformation: feeding the desulfurized gypsum into the mother liquor, mixing to form turbid liquid with specific solid content, and carrying out crystal transformation reaction under the normal-pressure hydrothermal condition of 80-100 DEG C; and (3) product collection: carrying out solid-liquid separation on the turbid liquid after the crystal transformation reaction, and washing and drying the solid phase to obtain the alpha-semi-hydrated gypsum. The invention provides a morphology regulation method of alpha-semi-hydrated gypsum prepared from desulfurized gypsum in an ethylene glycol water system, which can be used for preparing alpha-semi-hydrated gypsum with four different morphologies of nickel coin shape, short column shape, long rod shape and whisker shape at a relatively high conversion rate, and realizing large-range flexible regulation of average length-diameter ratio from 0.1-80.

Description

Technical Field

[0001] The invention relates to the field of alpha-hemihydrate gypsum preparation, and in particular to a method for controlling the morphology of alpha-hemihydrate gypsum prepared by utilizing desulfurized gypsum in an ethylene glycol-water system. Technical Background

[0002] Desulfurized gypsum is a byproduct of the calcium-based wet desulfurization process in thermal power plants. With the improvement of national environmental protection requirements, the coverage of desulfurization equipment in power plants has also increased, and the amount of desulfurized gypsum produced has increased sharply. In addition to occupying too much land resources, a large amount of desulfurized gypsum is also prone to secondary pollution. The main utilization of desulfurized gypsum in China is as a cement additive, roadbed material, soil modifier and building material, etc., and its application range is limited. α-Hemihydrate gypsum is a type of gypsum with excellent performance, which has the characteristics of high hardness, high strength and good wear resistance; α-Hemihydrate gypsum has a variety of morphologies, and α-Hemihydrate gypsum with different morphologies has different properties and different application fields. α-Hemihydrate gypsum whiskers refer to micro-nano single crystals with needle-like crystal morphology and a large aspect ratio. Since the atomic structure orientation of α-hemihydrate gypsum whiskers is highly consistent, its strength is almost equivalent to the theoretical strength of the valence bond between atoms. Due to its excellent compressive strength, flexural strength, toughness and chemical stability, α-hemihydrate gypsum whiskers are mostly added to composite materials as a modifier to compensate for or enhance the toughness, strength or viscosity of the matrix material. The aspect ratio of short columnar α-hemihydrate gypsum crystals is significantly lower than that of α-hemihydrate gypsum whiskers, its anisotropy is reduced, and the crystal packing density is high. This structure gives it higher compressive strength. Short columnar α-hemihydrate gypsum is usually used in high-performance building materials, biomedical materials, precision casting and other fields.

[0003] At present, the main preparation methods of α-hemihydrate gypsum are autoclave and normal pressure hydrothermal method. Invention patent CN118184191A adopts autoclave to prepare short columnar α-hemihydrate gypsum using desulfurized gypsum, and the desulfurized gypsum is washed and pretreated for 3 times and then dried. During the third pretreatment, 1% of the mass of desulfurized gypsum is additionally added with lime; a solution containing a crystallization agent is added to the pretreated desulfurized gypsum and mixed evenly, wherein the mass of the crystallization agent aluminum sulfate and water is 0.08-0.12wt% and 10-15wt% of the dry weight of the desulfurized gypsum, respectively; the obtained mixture is pressed on both sides by a press at a pressure of 20Mpa, and then put into an autoclave, autoclaved at 150°C and 1.4Mpa for 8-10 hours, and then immediately dried at 100°C to obtain the product. Invention patent CN114956624A adopts autoclave method to prepare ultra-high strength α-hemihydrate gypsum from phosphogypsum, using phosphogypsum after washing and purification with defluorination slag as raw material, stirring the phosphogypsum raw material and the crystal conversion agent solution in a mixer and then transporting them to the autoclave, setting the reaction temperature and stirring rate, reaching the set reaction temperature, and reacting at constant temperature for 20 to 120 minutes, releasing the pressure from the autoclave, drying at 80 to 130 ° C and grinding to obtain α ultra-high strength gypsum products. The autoclave method requires high-pressure equipment, high reaction temperature, high pressure and harsh reaction conditions, and the product is a mixture of α-hemihydrate gypsum and β-hemihydrate gypsum, the product quality is not guaranteed, and it will also generate large energy consumption. The reaction conditions of the normal pressure hydrothermal method are relatively mild, and the reaction medium mainly includes acid solution, salt solution system and alcohol aqueous solution system. The driving force for the mutual transformation of dihydrate gypsum and hemihydrate gypsum is the difference in the degree of reaction between the two. During the hydrothermal reaction, the activity of the aqueous solution can be reduced through a specific solution system, thereby reducing the phase transition temperature, increasing the solubility of dihydrate gypsum while reducing the solubility of α-hemihydrate gypsum. Therefore, dihydrate gypsum can be converted into α-hemihydrate gypsum at a lower temperature.

[0004] Invention patent CN109280979A uses desulfurized gypsum and hydrochloric acid to react under normal pressure in a normal pressure acid solution system to obtain semi-hydrated gypsum whiskers: first, the dried desulfurized gypsum is ground into fine powder; the ground desulfurized gypsum is screened to remove large particles of impurities; the screened desulfurized gypsum is added to a certain concentration of hydrochloric acid, stirred and mixed into a slurry, and the slurry is reacted at a certain temperature; after the normal pressure hydrothermal reaction is completed, the slurry is filtered; the filter cake obtained after the filtration is washed with an organic solvent; the washed filter cake is dried to obtain semi-hydrated gypsum whiskers. However, acidic solutions are usually highly corrosive, and are highly corrosive to reaction equipment and pipelines during the preparation process, increasing maintenance costs; the crystal morphology is difficult to control, and the crystal growth of α-semi-hydrated gypsum may be affected by the acidic substances in the solution, resulting in unstable crystal morphology. During the normal pressure acid solution method, acidic gases may be released into the air, causing air pollution and affecting the surrounding environment. Invention patent CN118359221A uses phosphogypsum to prepare high-strength gypsum in a normal pressure salt solution system: nitrate, crystal conversion agent and deionized water are poured into a container in sequence and stirred until completely dissolved to obtain a salt solution system; after the salt solution system is heated to the hydrothermal reaction temperature, phosphogypsum is added for hydrothermal reaction; after the hydrothermal reaction is completed, the hydrothermal reaction system is immediately filtered; the filter cake after the mixed solution is filtered is washed and dried; the filtrate after filtration is collected and recycled. However, a relatively high concentration of Cl is usually introduced into the normal pressure salt solution system. - Ions will accelerate the corrosion of the inner wall of the metal reactor and the metal structure in the building in actual production and application. In view of the above limitations, the invention patent CN114349039B prepares α-hemihydrate gypsum in a glycerol-water system, and the steps are: adding the gypsum raw material to the acidic solution system, mixing to form a gypsum suspension slurry; heating the gypsum suspension slurry to above 80°C, adding seed crystals, and stirring the reaction at this temperature; after a period of reaction, the suspension is separated from the liquid while hot, and the separated solid phase is washed with boiling water and dried to obtain an α-hemihydrate gypsum product. However, due to the high viscosity of glycerol, the material transfer efficiency is low, the crystals are not uniform, and the shape is irregular, resulting in poor product quality.

[0005] The ethylene glycol water system has the characteristics of mild reaction conditions, environmental protection and low viscosity. These advantages enable it to produce high-quality products at a lower cost and higher efficiency in the preparation process of α-hemihydrate gypsum, and has less impact on the environment and equipment. It is an ideal solvent system. The current technology for preparing α-hemihydrate gypsum with different morphologies has the disadvantages of complex preparation process and harsh reaction conditions. In addition, α-hemihydrate gypsum with different morphologies requires different preparation processes or needs to add different types of crystallization agents or regulators. Summary of the invention

[0006] The present invention provides a method for controlling the morphology of α-hemihydrate gypsum prepared by using desulfurized gypsum in an ethylene glycol-water system. α-hemihydrate gypsum with different morphologies is obtained by controlling the inorganic salt, the crystal inverting agent and the solid content, thereby realizing flexible morphology control in a wide range from nickel coin shape to whisker shape (aspect ratio 0.1-80).

[0007] The specific technical solutions are as follows:

[0008] (1) Preparation of mother solution: Mixing inorganic salt, crystal-changing agent and ethylene glycol aqueous solution to prepare mother solution, wherein the volume fraction of ethylene glycol is controlled to be 30-60 vol%;

[0009] (2) Adding materials to crystallize: adding desulfurized gypsum to the mother liquor to obtain a suspension, wherein the mass percentage of desulfurized gypsum in the suspension is controlled to be 2-20 wt%, and then performing a crystallization reaction under normal pressure hydrothermal conditions at 80-100°C;

[0010] (3) Product collection: The suspension after the crystallization reaction is separated into solid and liquid, and the solid phase is washed and dried to obtain the α-hemihydrate gypsum product.

[0011] The key to the preparation method of α-hemihydrate gypsum with different morphologies proposed by the present invention is: using desulfurized gypsum as a raw material, in an ethylene glycol-water system, by adjusting the concentration ratio of inorganic salts, crystallization agents and solid content, using crystallization dynamics and steric hindrance to coordinately control the morphology of α-hemihydrate gypsum, and realizing a wide range of flexible control from nickel coin-shaped to whisker-shaped morphology (aspect ratio of 0.1-80). Inorganic salts can increase the reaction driving force and promote transformation, causing the crystal aspect ratio to increase; the steric hindrance effect of the crystallization agent causes the α-hemihydrate gypsum nucleation site to be covered, which inhibits the transformation process, and at the same time compresses the growth in the c-axis direction, resulting in a decrease in the aspect ratio; within a certain range, the aspect ratio control effect of the crystallization agent is inversely proportional to the solid content, the higher the solid content, the larger the aspect ratio, and vice versa. In addition, the present invention reacts under a normal pressure alcohol-water system, the reaction conditions are mild, the energy consumption and equipment corrosion are reduced, and it has strong environmental friendliness and economy.

[0012] The effect of the carboxylic acid compound as a crystallization agent on the morphology of α-hemihydrate gypsum in step (1) mainly comes from the effect of the carboxyl group on the free Ca in the solution. 2+ Under the action of the crystallization agent, the Ca 2+ It chelates with the carboxyl group and forms a stable 1:1 complex through coordination bonds, adsorbs on the specific surface of the crystal, hinders the growth of the crystal along the C-axis direction, and thus affects the morphology.

[0013] In step (1), the crystal-changing agent is ethylene glycol bis (2-aminoethyl ether) tetraacetic acid (EGTA), disodium ethylenediaminetetraacetate (Na 2One or more of EDTA, 1,3-propylenediaminetetraacetic acid (PDTA), and 1,6-propylenediaminetetraacetic acid (HDTA);

[0014] Furthermore, in step (1), the concentration of the crystal-changing agent is 1.0×10 -4 ~7.5×10 -3 mol / L.

[0015] In step (1), the alcohol in the alcohol aqueous solution is selected from ethylene glycol. Ethylene glycol has good fluidity and strong hydrogen bonding with water molecules, which can effectively reduce the water activity of the solution and provide thermodynamic conditions for preparing α-hemihydrate gypsum from desulfurized gypsum.

[0016] In the ethylene glycol aqueous solution, the greater the proportion of alcohol is, the lower the water activity of the system is, the greater the driving force for conversion is, and the faster the conversion rate is.

[0017] Furthermore, the monovalent inorganic salt described in step (1) is NaCl, KCl, LiCl, NH 4 One of the Cl, with a concentration of 0.10~1mol / L.

[0018] Furthermore, in the ethylene glycol aqueous solution, the volume fraction of ethylene glycol is 30 to 60 vol%.

[0019] In step (2), the desulfurized gypsum refers to the byproduct of calcium-based wet desulfurization in coal-fired power plants. The process of preparing α-hemihydrate gypsum from desulfurized gypsum is a dissolution-crystallization process. Desulfurized gypsum of different particle sizes has different surface characteristics. Desulfurized gypsum raw materials with small particle sizes can provide more nucleation sites and promote the crystallization process.

[0020] Furthermore, the desulfurized gypsum is in powder or fine granular form, with a particle size of 2 to 50 μm. In step (2), the amount of desulfurized gypsum added is the solid content in the suspension. Increasing the solid content can increase the nucleation sites of α-hemihydrate gypsum and improve the conversion rate; while too large a solid content will cause insufficient development of α-hemihydrate gypsum and affect its quality.

[0021] Furthermore, the mass percentage of desulfurized gypsum in the suspension is 2-20wt%.

[0022] Furthermore, in step (2), the crystallization reaction temperature is 80-100° C. and the time is 0.5-22 h.

[0023] In step (3), the product collection includes washing and drying; washing with anhydrous ethanol and drying at a temperature of 45 to 70°C

[0024] The research found that under the above process conditions, four different morphologies of α-hemihydrate gypsum, namely whisker, long rod, short column and nickel coin, were prepared.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The present invention adopts alcohol-water medium to carry out hydrothermal reaction under normal pressure, does not require high-pressure equipment, has mild reaction conditions, has low corrosion to equipment, is simple to operate and easy to control, and is conducive to reducing costs and saving energy consumption.

[0027] (2) The present invention effectively controls the aspect ratio of α-hemihydrate gypsum by controlling the concentration ratio of inorganic salt, crystal inversion agent and solid content, thereby obtaining α-hemihydrate gypsum with different morphologies to ensure that a high-quality product is obtained at a high conversion rate.

[0028] (3) The present invention uses desulfurized gypsum as a raw material to prepare α-hemihydrate gypsum of different morphologies, which not only solves the occupation of land resources and pollution and damage to the ecological environment caused by desulfurized gypsum, but also realizes the high added value resource utilization of desulfurized gypsum. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a process flow chart for preparing α-hemihydrate gypsum by using desulfurized gypsum in an alcohol-water system.

[0030] Figure 2 This is a scanning electron microscope image of the whisker-like α-hemihydrate gypsum obtained in Example 1.

[0031] Figure 3 This is a scanning electron microscope image of the long rod-shaped α-hemihydrate gypsum prepared in Example 2.

[0032] Figure 4 This is a scanning electron microscope image of the short columnar α-hemihydrate gypsum obtained in Example 3.

[0033] Figure 5 This is a scanning electron microscope image of the nickel coin-shaped (aspect ratio of 0.1) α-hemihydrate gypsum prepared in Example 4. DETAILED DESCRIPTION

[0034] Example 1 Prepare an aqueous solution with a volume percentage of 50 vol% of ethylene glycol water, add sodium chloride, and control the concentration to 0.15 mol / L. Add desulfurized gypsum to the mother liquor, and control the solid content to 3 wt%. React for 1 hour at 95°C, normal pressure, and a stirring rate of 350 rpm. After the conversion is completed, separate the slurry from the solid and liquid, wash with anhydrous ethanol, and dry the solid at 60°C for 2 hours to obtain whisker-like α-hemihydrate gypsum with a product aspect ratio of 80.

[0035] Example 2 Prepare a 50 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 1.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 95°C, normal pressure, and a stirring rate of 350rpm for 2h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain long rod-shaped α-hemihydrate gypsum with an aspect ratio of 2.89.

[0036] Example 3 Prepare a 50 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 2.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 95°C, normal pressure, and a stirring rate of 350rpm for 11 hours. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2 hours to obtain short columnar α-hemihydrate gypsum with an aspect ratio of 1.01.

[0037] Example 4 Prepare a 50 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 4.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 95°C, normal pressure, and a stirring rate of 350rpm for 20h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain nickel coin-shaped α-hemihydrate gypsum with an aspect ratio of 0.1.

[0038] Example 5 Prepare an aqueous solution with a volume percentage of 60 vol% of ethylene glycol water, add sodium chloride to obtain a mother liquor, and control the concentration at 0.15 mol / L. Add desulfurized gypsum to the mother liquor, and control the solid content to be 3 wt%. React for 1.5 hours at 90°C, normal pressure, and a stirring rate of 350 rpm. After the conversion is completed, separate the slurry from the solid and liquid, wash with anhydrous ethanol, and dry the solid at 60°C for 2 hours to obtain whisker-like α-hemihydrate gypsum with an aspect ratio of 27.64.

[0039] Example 6 Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 1.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 90°C, normal pressure, and a stirring rate of 350rpm for 3h. After the conversion was completed, the slurry was separated into solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain long rod-shaped α-hemihydrate gypsum with an aspect ratio of 2.71.

[0040] Example 7 Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 2.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 90°C, normal pressure, and a stirring rate of 350rpm for 9h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain short columnar α-hemihydrate gypsum with an aspect ratio of 0.82. Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and ethylenediaminetetraacetic acid

[0041] Example 8 The mother solution was obtained by disodium (Na2EDTA), and the concentration was controlled at 0.15 mol / L and 4.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 90°C, normal pressure, and a stirring rate of 350rpm for 20h. After the conversion was completed, the slurry was separated into solid and liquid, washed with anhydrous ethanol, and dried at 60°C for 2h to obtain nickel coin-shaped α-hemihydrate gypsum with an aspect ratio of 0.17.

[0042] Example 9 Prepare an aqueous solution with a volume percentage of 60 vol% of ethylene glycol water, add sodium chloride to obtain a mother liquor, and control the concentration at 0.15 mol / L. Add desulfurized gypsum to the mother liquor, and control the solid content to be 3 wt%. React for 1 hour at 100°C, normal pressure, and a stirring rate of 350 rpm. After the conversion is completed, separate the slurry from the solid and liquid, wash with anhydrous ethanol, and dry the solid at 60°C for 2 hours to obtain whisker-like α-hemihydrate gypsum with a product aspect ratio of 23.83.

[0043] Example 10 Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 1.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 100°C, normal pressure, and a stirring rate of 350rpm for 3h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain long rod-shaped α-hemihydrate gypsum with an aspect ratio of 3.01.

[0044] Embodiment 11 Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 2.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 100°C, normal pressure, and a stirring rate of 350rpm for 1h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 8h to obtain short columnar α-hemihydrate gypsum with an aspect ratio of 1.1.

[0045] Example 12 Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 4.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 100°C, normal pressure, and a stirring rate of 350rpm for 1h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain nickel coin-shaped α-hemihydrate gypsum with an aspect ratio of 0.24.

[0046] Example 13 Prepare an aqueous solution with a volume percentage of 60 vol% of ethylene glycol water, add sodium chloride and ethylene glycol bis (2-aminoethyl ether) tetraacetic acid (EGTA) to obtain a mother solution, and control the concentrations at 0.15 mol / L and 1.0×10 -4mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 95°C, normal pressure, and a stirring rate of 350rpm for 3h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain long rod-shaped α-hemihydrate gypsum with an aspect ratio of 2.97.

[0047] Embodiment 14 Prepare an aqueous solution with a volume percentage of 60 vol% of ethylene glycol water, add sodium chloride to obtain a mother liquor, and control the concentration at 0.15 mol / L. Add desulfurized gypsum to the mother liquor, and control the solid content to be 3 wt%. React for 1 hour at 95°C, normal pressure, and a stirring rate of 350 rpm. After the conversion is completed, separate the slurry from the solid and liquid, wash with anhydrous ethanol, and dry the solid at 60°C for 2 hours to obtain whisker-like α-hemihydrate gypsum with an aspect ratio of 23.91.

[0048] Embodiment 15 Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 1.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 95°C, normal pressure, and a stirring rate of 350rpm for 3h. After the conversion was completed, the slurry was separated into solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain long rod-shaped α-hemihydrate gypsum with an aspect ratio of 3.15.

[0049] Example 16 Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 2.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 95°C, normal pressure, and a stirring rate of 350rpm for 7h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain short columnar α-hemihydrate gypsum with an aspect ratio of 1.13.

[0050] Embodiment 17 Prepare an aqueous solution with a volume percentage of 30 vol% of ethylene glycol water, add sodium chloride and ethylene glycol bis (2-aminoethyl ether) tetraacetic acid (EGTA) to obtain a mother liquor, and control the concentrations at 0.15 mol / L and 1.5×10-3 mol / L, respectively. Add desulfurized gypsum to the mother liquor and control the solid content to be 3 wt%. React for 8 hours at 90°C, normal pressure, and a stirring rate of 350 rpm. After the conversion is completed, separate the slurry solid from the liquid, wash with anhydrous ethanol, and dry the solid at 60°C for 2 hours to obtain short columnar α-hemihydrate gypsum.

[0051] Embodiment 18 Prepare a 60 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 7.5×10 -3 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 90°C, normal pressure, and a stirring rate of 350rpm for 22h. After the conversion was completed, the slurry was separated into solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain nickel coin-shaped α-hemihydrate gypsum with an aspect ratio of 0.18.

[0052] Embodiment 19 Prepare a 50 vol% aqueous solution of ethylene glycol water, add sodium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 2×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 20wt%. The reaction was carried out at 95°C, normal pressure, and a stirring rate of 350rpm for 22h. After the conversion was completed, the slurry was separated from the solid and liquid, washed with anhydrous ethanol, and dried at 60°C for 2h to obtain whisker-like α-hemihydrate gypsum with an aspect ratio of 21.4, which was not short columnar α-hemihydrate gypsum.

[0053] Embodiment 20 Prepare a 50 vol% aqueous solution of ethylene glycol water, add lithium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.1 mol / L and 1.5×10 -3 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 80°C, normal pressure, and a stirring rate of 350rpm for 22h, and the slurry was separated into solid and liquid. After washing with anhydrous ethanol, the solid was dried at 60°C for 2h to obtain irregular α-hemihydrate gypsum.

[0054] Embodiment 21 Prepare an aqueous solution with a volume percentage of 50 vol% of ethylene glycol water, add sodium chloride and 1,3-propylenediaminetetraacetic acid (PDTA) to obtain a mother solution, and control the concentrations at 1 mol / L and 1.5×10 -3 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 90°C, normal pressure, and a stirring rate of 350rpm for 20h. After the conversion was completed, the slurry was separated from the solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain α-hemihydrate gypsum with an aspect ratio of 3.4.

[0055] Embodiment 22 Prepare an aqueous solution with a volume percentage of 50 vol% of ethylene glycol water, add sodium chloride and 1,6-propylenediaminetetraacetic acid (HDTA) to obtain a mother solution, and control the concentrations at 1 mol / L and 1.5×10 -3 mol / L. Desulfurized gypsum was added to the mother liquor to control the solid content to 3wt%. The reaction was carried out at 90°C, normal pressure and a stirring rate of 350rpm for 19h. After the conversion was completed, the slurry was separated from the solid and liquid, and washed with anhydrous ethanol to obtain α-hemihydrate gypsum.

[0056] Embodiment 23 Prepare a 60 vol% aqueous solution of ethylene glycol water, add potassium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 2.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor, and the solid content was controlled to be 3wt%. The reaction was carried out at 95°C, normal pressure, and a stirring rate of 350rpm for 6h. After the conversion was completed, the slurry was separated into solid and liquid, and the solid was washed with anhydrous ethanol and dried at 60°C for 2h to obtain polymorphic potassium gypsum.

[0057] Embodiment 24 Prepare a 60 vol% aqueous solution of ethylene glycol water, add ammonium chloride and disodium ethylenediaminetetraacetate (Na 2 EDTA) to obtain the mother solution, and the concentration was controlled at 0.15 mol / L and 2.0×10 -4 mol / L. Desulfurized gypsum was added to the mother liquor to control the solid content to 3wt%. The reaction was carried out at 95°C, normal pressure and a stirring rate of 350rpm for 20h to convert it into α-hemihydrate gypsum with irregular morphology.

Claims

1. A method for controlling the morphology of α-hemihydrate gypsum prepared by using desulfurized gypsum in an ethylene glycol-water system, characterized in that: Here are the steps: (1) Preparation of mother solution: Mix different concentrations of inorganic salts, crystal-changing agents and ethylene glycol aqueous solution to prepare mother solution and heat to a certain temperature; (2) Adding materials and crystallization: adding desulfurized gypsum to the mother liquor and mixing to form a suspension with a specific solid content, and performing a crystallization reaction under normal pressure hydrothermal conditions; (3) Product collection: The suspension after the crystallization reaction is separated into solid and liquid, and α-hemihydrate gypsum is obtained after washing with anhydrous ethanol and drying.

2. The method according to claim 1, characterized in that In step (1), the inorganic salt is a monovalent inorganic salt such as LiCl, NaCl, KCl, NH4Cl, etc.

3. The method according to claim 1, characterized in that In step (1), the concentration of the inorganic salt is 0.10 mol / L to 1 mol / L.

4. The method according to claim 1, characterized in that: In step (1), the crystal-transforming agent is one of ethylene glycol bis(2-aminoethyl ether)tetraacetic acid (EGTA), disodium ethylenediaminetetraacetic acid (Na2EDTA), 1,3-propylenediaminetetraacetic acid (PDTA), and 1,6-propylenediaminetetraacetic acid (HDTA).

5. The method according to claim 1, characterized in that In step (1), the concentration of the crystal-changing agent is 1.0×10 -4 ~7.5×10 -3 mol / L.

6. The method according to claim 1, characterized in that In step (1), the volume fraction of ethylene glycol is 30 to 60 vol%.

7. The method according to claim 1, characterized in that In step (2), the mass percentage of desulfurized gypsum in the suspension is 2% to 20wt%.

8. The method according to claim 1, characterized in that In step (2), the crystallization reaction temperature is 80°C to 100°C, and the time is 0.5 to 22 hours.

9. The method according to claim 1, characterized in that: In step (3), the solid-liquid separation is carried out, and the solid phase is washed with anhydrous ethanol and dried at 45-70° C. to obtain α-hemihydrate gypsum with an aspect ratio of 0.1-80.

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