Process for preparing high-purity calcium sulfate whisker from desulfurized gypsum and calcium sulfate whisker

Abstract

The invention relates to the technical field of desulfurization gypsum treatment, in particular to a process for preparing high-purity calcium sulfate whiskers from desulfurization gypsum. The invention discloses a process for preparing high-purity calcium sulfate whiskers from desulfurized gypsum, which comprises the following steps: adding water to prepare the desulfurized gypsum into slurry, and adding a dispersing agent for dispersing; an oxidizing agent is added into the slurry for an oxidation reaction, solid-liquid separation is performed after the oxidation reaction is completed, and oxidized gypsum and oxidized liquid are obtained; dissolving the oxidized gypsum by using an acid solution to obtain acid-soluble slurry; adding an additive and a regulator into the acid-soluble slurry, and carrying out hydrothermal reaction to obtain regulated slurry after the reaction is finished; and carrying out solid-liquid separation on the adjusted slurry, and then rinsing and drying to obtain the calcium sulfate whiskers. According to the process disclosed by the invention, the high-purity calcium sulfate whisker can be obtained, and the problems of difficulty in impurity removal, difficulty in morphology control and possibility of secondary pollution in a traditional method are solved.

Description

Technical Field

[0001] The invention relates to the technical field of desulfurized gypsum treatment, in particular to a process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum and the calcium sulfate whiskers. Background Art

[0002] In recent years, with growing awareness of environmental protection and demand for resource recycling, the efficient conversion of industrial solid waste into high-value-added products has become a research hotspot. Desulfurized gypsum, a typical industrial byproduct, primarily originates from lime slurry used by steel mills and other enterprises to absorb SO₂ pollutants from sintering flue gases. This gypsum contains over 90% calcium sulfate dihydrate (CaSO₄·2H₂O), along with small amounts of impurities such as SiO₂, Al₂O₃, and MgO. Despite its enormous production, desulfurized gypsum is currently mostly used as a cement retarder or in the production of gypsum board due to its complex composition and difficulty in direct utilization. The remainder is disposed of as solid waste in landfills, a significant waste of precious resources, significant land occupation, and potential environmental threats.

[0003] To address these challenges, researchers are committed to exploring effective resource utilization pathways for desulfurized gypsum, specifically converting it into high-purity calcium sulfate whiskers, which have broad industrial application prospects. Calcium sulfate whiskers are a fibrous single-crystalline material favored for its excellent wear resistance, high-temperature resistance, and thickening properties. They have broad application prospects in various fields, including plastics, rubber, and coatings.

[0004] However, the following technical difficulties were encountered in the process of preparing calcium sulfate whiskers using desulfurized gypsum: (1) Difficulty in removing impurities Since there are various impurity elements in desulfurization gypsum, these impurities may affect the purity and performance of the final product, so effective pretreatment methods are required to ensure the quality of the raw materials.

[0005] (2) Difficulty in morphology control Obtaining calcium sulfate whiskers with uniform morphology and a moderate aspect ratio is crucial to enhancing their application value. However, existing methods often struggle to precisely control crystal growth conditions, resulting in irregular product morphology and limiting their commercial applications.

[0006] (3) Secondary pollution risk Certain processing steps may generate new environmental pollution problems, such as wastewater discharge, which violates the principles of green manufacturing.

[0007] To address the above issues, existing solutions mainly include the following technical routes: (1) Dissolution crystallization method By adjusting the supersaturation of the solution to induce crystal precipitation, this method can produce calcium sulfate whiskers with relatively uniform morphology, but the process is greatly affected by multiple factors such as temperature, pressure, and pH value, making it difficult to control and resulting in low yields, making it unsuitable for large-scale industrial production.

[0008] (2) Mechanical activation method Mechanical energy is used to break up desulfurized gypsum particles, increasing the active surface area. Acid dissolution is then used to remove impurities, and accelerators and crystal form control agents are added to guide whisker formation. While this method can produce products with longer diameters and uniform morphology, the addition of a large number of auxiliary reagents increases costs and introduces more control variables, making the process more complex.

[0009] (3) Chemical conversion method The method disclosed in patent CN 104451856 A involves removing impurities with sulfuric acid before preparing calcium sulfate hemihydrate whiskers. However, the whiskers obtained by this method have less than ideal morphology, a low aspect ratio, and low economic value.

[0010] In summary, the aforementioned technical approaches rarely consider the economic and environmental requirements of actual industrial production, and generally face the problems of complex operation, high costs, and difficulty in achieving efficient resource utilization. Therefore, it is particularly urgent to develop a new process that can effectively solve the resource utilization problem of desulfurized gypsum while being economical and environmentally friendly.

[0011] To this end, the present application provides a process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum. Summary of the Invention

[0012] In order to overcome the shortcomings of the existing technology, the present invention provides a process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum. First, the desulfurized gypsum is added with water to form a slurry and a dispersant is added to ensure uniform dispersion. Then, an oxidizing agent is added for oxidation treatment to completely convert calcium sulfite into calcium sulfate and remove some impurities. After solid-liquid separation, the obtained oxidized gypsum is dissolved in an acid solution, and additives and regulators are added. A hydrothermal reaction is carried out under specific conditions to control crystal growth. Finally, high-purity calcium sulfate whiskers are obtained through the steps of solid-liquid separation, rinsing and drying. The problems of difficult impurity removal, difficult morphology control and possible secondary pollution in traditional methods are solved.

[0013] The technical solution adopted by this application to solve its technical problems is: In a first aspect, the present application provides a process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum, comprising the following steps: (1) Add water to prepare desulfurized gypsum into slurry, and add dispersant to disperse it; Then, an oxidant is added to the slurry to carry out an oxidation reaction. After the oxidation reaction is completed, solid-liquid separation is carried out to obtain oxidized gypsum and oxidized liquid; (2) using an acid solution to dissolve the oxidized gypsum in step (1) to obtain an acid-soluble slurry; adding additives and a regulator to the acid-soluble slurry to carry out a hydrothermal reaction, and obtaining an adjusted slurry after the reaction is completed; (3) The adjusted slurry in step (2) is subjected to solid-liquid separation, and then rinsed and dried to obtain calcium sulfate whiskers.

[0014] In one or more technical solutions, in step (1), water is added to prepare the desulfurized gypsum into a slurry having a desulfurized gypsum content of 5-30% by mass.

[0015] In one or more technical solutions, in step (1), the oxidant is any one or more of chlorine, calcium hypochlorite, hydrogen peroxide, chlorine dioxide, and sodium hypochlorite; the amount of the oxidant added is 1-2% of the mass of the desulfurized gypsum, the oxidation reaction temperature is room temperature, and the oxidation reaction time is 0.5-1.5 h.

[0016] In one or more technical solutions, in step (1), the dispersant is composed of sodium polyacrylate and sodium lauryl sulfate in a mass ratio of 2:1; the feeding amount of the dispersant is 0.05-0.1% of the mass of the desulfurized gypsum.

[0017] In one or more technical solutions, in step (2), the acid solution is one or more of sulfuric acid solution, hydrochloric acid solution, nitric acid solution, and citric acid solution, the concentration of the acid solution is 1-5 mol / L, the liquid-solid ratio is maintained at 2-5:1 during dissolution, the dissolution time is 1-3 h, and the dissolution temperature is 50-80°C.

[0018] In one or more technical solutions, in step (2), the additive is any one or more of calcium hydroxide, sodium hydroxide, and potassium hydroxide; Additives were added to the acid-soluble slurry to adjust the pH of the acid-soluble slurry to 6.5, and then a regulator was added to carry out a hydrothermal reaction. The temperature of the hydrothermal reaction was 120° C., and the time of the hydrothermal reaction was 2 h.

[0019] In one or more technical solutions, in step (2), the adjusting agent is composed of calcium hydrogen sulfate and sodium oleate in a mass ratio of 3:1, and the amount of the adjusting agent is 0.1-0.2% of the mass of the oxidized gypsum.

[0020] In one or more technical solutions, in step (3), the drying temperature is 100-120°C.

[0021] In a second aspect, the present application provides calcium sulfate whiskers, including calcium sulfate whiskers prepared by the process described in the first aspect.

[0022] In one or more technical solutions, the calcium sulfate whiskers have an average aspect ratio of ≥40 and an average length of greater than 150 microns.

[0023] Compared with the prior art, the present invention has the following beneficial effects: The process of the present invention first uses water and a dispersant to mix and prepare a slurry, then adds an oxidant to oxidize the calcium sulfite into calcium sulfate, fully utilizing the calcium and sulfur elements therein, then uses an acid solution to dissolve the calcium sulfate, and then adds additives and regulators. The prepared calcium sulfate has uniform composition, high output rate, easy process control, low cost, high economic value, no secondary pollution, and is easy to realize industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings and examples.

[0025] Figure 1 This is a scanning electron microscope image of the calcium sulfate whiskers prepared in Example 1 of the present application; Figure 2 This is a scanning electron microscope image of the calcium sulfate whiskers prepared in Comparative Example 1 of the present application; Figure 3 This is a scanning electron microscope image of the calcium sulfate whiskers prepared in Comparative Example 2 described in this application. DETAILED DESCRIPTION

[0026] In order to facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the embodiments. The contents mentioned in the embodiments are not intended to limit the present invention.

[0027] As used herein, the term "and / or" includes all combinations of any one or more of the associated listed items. The terms used herein are only used to describe specific embodiments and are not intended to limit the present invention. As used herein, the singular forms "a", "an", "an" and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. It is further understood that "including", when used in this specification, specifies the stated features, integers, steps, operations, elements and / or components, but does not preclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0028] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It is further understood that terms, such as those defined in commonly used dictionaries, are interpreted in accordance with their meanings in the context of the relevant art and are not idealized or overly formalized unless expressly defined otherwise herein.

[0029] The exemplary inventions described herein may suitably lack any one or more element limitations not specifically disclosed herein. Therefore, terms such as "comprises," "includes," "contains," and the like should be understood broadly and non-restrictively. In addition, the terminology used herein is used as a description, not a limitation, and it is unintentional to use these terminology expressions that do not include any equivalent characteristics, but only describe a portion of their characteristics, but various modifications are possible within the scope of the invention according to the rights. Therefore, although the present invention has been specifically disclosed through preferred embodiments and optional features, the modifications disclosed herein to embody the changes of the invention may be recorded by those skilled in the art, and such modifications and changes will be considered to be within the scope of the invention.

[0030] A process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum comprises the following steps: (1) Add water to prepare desulfurized gypsum into slurry, and add dispersant to disperse it; Then, an oxidant is added to the slurry to carry out an oxidation reaction. After the oxidation reaction is completed, solid-liquid separation is carried out to obtain oxidized gypsum and oxidized liquid; (2) using an acid solution to dissolve the oxidized gypsum in step (1) to obtain an acid-soluble slurry; adding additives and a regulator to the acid-soluble slurry to carry out a hydrothermal reaction, and obtaining an adjusted slurry after the reaction is completed; (3) The adjusted slurry in step (2) is subjected to solid-liquid separation, and then rinsed and dried to obtain calcium sulfate whiskers.

[0031] Specifically, in step (1), water is added to prepare a slurry having a desulfurized gypsum content of 5-30% by weight. Therefore, preparing the desulfurized gypsum into a slurry of appropriate concentration (5-30% slurry) can ensure the fluidity of the material during subsequent processing, facilitate operation, and ensure uniform reaction.

[0032] In step (1), the dispersant is composed of sodium polyacrylate and sodium lauryl sulfate in a mass ratio of 2:1; the feeding amount of the dispersant is 0.05-0.1% of the mass of the desulfurized gypsum.

[0033] In this application, the dispersant combination can provide good dispersing performance, prevent particle agglomeration, and ensure that subsequent reactions are more uniform.

[0034] In step (1), the oxidant is any one or more of chlorine, calcium hypochlorite, hydrogen peroxide, chlorine dioxide, and sodium hypochlorite; the amount of the oxidant added is 1-2% of the mass of the desulfurized gypsum, the oxidation reaction temperature is room temperature, and the oxidation reaction time is 0.5-1.5h.

[0035] In this application, the oxidant completely oxidizes the calcium sulfite in the desulfurized gypsum into more stable calcium sulfate, thereby improving the purity of the raw material. The oxidation reaction is carried out at room temperature in order to reduce energy consumption and simplify the process.

[0036] Specifically, in step (2), the acid solution is one or more of sulfuric acid solution, hydrochloric acid solution, nitric acid solution, and citric acid solution, the concentration of the acid solution is 1-5 mol / L, the liquid-solid ratio is maintained at 2-5:1 during dissolution, the dissolution time is 1-3 hours, and the dissolution temperature is 50-80°C.

[0037] Therefore, the above-mentioned acid solution can dissolve the oxidized gypsum (mainly composed of calcium sulfate) while avoiding the introduction of excessive impurities or the generation of harmful by-products.

[0038] In step (2), the additive is any one or more of calcium hydroxide, sodium hydroxide, and potassium hydroxide; Additives were added to the acid-soluble slurry to adjust the pH of the acid-soluble slurry to 6.5. A conditioning agent was then added and a hydrothermal reaction was carried out at a temperature of 120°C for 2 hours. The conditioning agent consisted of calcium hydrogen sulfate and sodium oleate in a mass ratio of 3:1, and the amount of the conditioning agent was 0.1-0.2% of the mass of the oxidized gypsum.

[0039] In this application, the pH value of the acid-soluble slurry is adjusted to about 6.5. An appropriate pH value is important for controlling crystal growth. It not only helps remove impurities but also promotes the formation of calcium sulfate whiskers with a specific morphology. The role of the regulator is to further regulate the growth process of the crystals, especially their shape and size. Specifically, calcium bisulfate has a high solubility in water, making it easier to dissolve and participate in the hydrothermal reaction. Calcium bisulfate can serve as a seed crystal or template to promote crystal growth. The seed crystal provides an initial crystal core, enabling more orderly crystal growth, resulting in calcium sulfate whiskers with uniform morphology and a moderate aspect ratio.

[0040] Sodium oleate, as a surfactant, can control the surface energy of the crystals, affecting the aspect ratio and morphology of the whiskers. Surfactants can reduce the surface tension of the liquid, promote crystal growth in a specific direction, and reduce crystal agglomeration, resulting in well-dispersed and well-formed calcium sulfate whiskers.

[0041] Specifically, in step (3), the rinsing liquid is typically distilled water, which is used to rinse the calcium sulfate whiskers obtained after solid-liquid separation to remove impurities and reaction residues attached to the whiskers and improve the purity of the product. The temperature set during the drying process is 100-120°C to remove moisture from the calcium sulfate whiskers and obtain a dried product.

[0042] The following examples and comparative examples further illustrate the process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum described in this application.

[0043] 1. Experimental equipment and parameter settings: Reaction: A glass reactor (50 L volume, adjustable speed 0-2000 rpm, equipped with a constant temperature jacket) was used to carry out step (1).

[0044] Solid-liquid separation equipment: Plate and frame filter press (filtration area 0.5m 2 , working pressure 0.6MPa).

[0045] Hydrothermal reaction equipment: high-pressure reactor (made of 316L stainless steel, volume 10L, pressure resistance 2.5MPa, temperature control accuracy ±2°C), used for step (2).

[0046] Drying equipment: vacuum drying oven (temperature range 50-200℃, vacuum degree 0.09MPa).

[0047] 2. Chemical Principle Steps (1) Slurry preparation and oxidation treatment, the chemical principles involved are as follows: Oxidation: Hydrogen peroxide oxidizes calcium sulfite (CaSO3) in desulfurized gypsum into calcium sulfate (CaSO4), while some metal impurities (such as Fe 2+ ) are oxidized to a high valence state, facilitating subsequent separation.

[0048] For solid-liquid separation, the slurry was filtered through a plate and frame filter press (pressure 0.4 MPa, filter cloth pore size 10 μm) to separate the oxidized gypsum (water content 15%) and the oxidized liquid.

[0049] The chemical principles involved in step (2) are as follows: Acid dissolution removes residual metal oxide impurities (such as Al2O3, MgO).

[0050] Under hydrothermal conditions, calcium bisulfate provides seeds to guide the directional growth of crystals, and sodium oleate is adsorbed on the crystal surface to inhibit lateral growth, thereby forming whiskers with a high aspect ratio.

[0051] 3. Detection method (1) Element content detection Detection items: Ca, Al, Mg, K, Na, sulfate (SO4 2- )content Detection method: ①X-ray fluorescence spectrometry (XRF): Equipment: XRF spectrometer (model: PANalytical Axios MAX, excitation source: Rh target, detection limit: 0.01%).

[0052] Sample preparation: Grind the dried calcium sulfate whiskers to 200 mesh, press into tablets and test directly.

[0053] Applicable elements: Ca, Al, Mg, K, Na (detection of major elements in solid samples).

[0054] (2) Ion chromatography (IC): Equipment: Ion chromatograph (model: Thermo Scientific Dionex ICS-5000+, chromatographic column: AS11-HC).

[0055] Sample preparation: dissolve the whiskers in deionized water, filter and inject.

[0056] Applicable items: Sulfate content (detection limit: 0.1 mg / L).

[0057] (3) Whisker morphology and size characterization Test items: average aspect ratio, average length, surface morphology Detection method: Scanning Electron Microscopy (SEM): Equipment: Field emission scanning electron microscope (model: Hitachi SU8010, accelerating voltage: 5 kV, working distance: 8 mm).

[0058] Sample preparation: The whiskers were dispersed in ethanol, ultrasonicated for 10 min, and then added dropwise to a silicon wafer, which was then gold-sprayed (thickness 5 nm).

[0059] Data analysis: 50 whiskers were randomly selected, and their length and diameter were measured using ImageJ software to calculate the average aspect ratio.

[0060] (4) Laser particle size analyzer (LSA) (assisted verification of length distribution): Equipment: Malvern Mastersizer 3000 (measuring range: 0.1-1000 μm) Example 1: A process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum, comprising the following steps: The composition of desulfurization gypsum in a steel plant is shown in Table 1 below: Table 1 Composition of desulfurization gypsum from a steel plant

[0061] (1) Slurry preparation and oxidation treatment Take the desulfurization gypsum shown in the table above, add water to make it into a slurry with a mass concentration of 5%, add a dispersant with a mass concentration of 0.05% of the desulfurization gypsum and disperse it for 2 hours; the dispersant is composed of sodium polyacrylate and sodium lauryl sulfate in a mass ratio of 2:1.

[0062] Then add hydrogen peroxide with a content of 1% by mass of desulfurized gypsum, stir and oxidize at room temperature for 0.5h. After the reaction is completed, solid-liquid separation is performed to obtain oxidized gypsum and oxidized liquid. The oxidized gypsum enters the next step, and the oxidized liquid is mixed with desulfurized gypsum to form a slurry.

[0063] The composition of oxidized gypsum is shown in Table 2 below: Table 2 Composition of oxidized gypsum

[0064] (2) Acid dissolution and hydrothermal reaction Use hydrochloric acid solution to dissolve the gypsum shown in the table above. The concentration of the hydrochloric acid solution used is 1 mol / L. During the dissolution, maintain a liquid-to-solid ratio of 2:1. After stirring and reacting at 50°C for 1 hour, obtain an acid-soluble slurry. Pump the acid-soluble slurry into the reactor. Sodium hydroxide was added as an additive to adjust the pH of the acid-soluble slurry to 6.5, and then an adjusting agent of 0.1% by mass of the oxidized gypsum was added; a hydrothermal reaction was carried out at a temperature of 120° C. and a time of 2 h to obtain an adjusted slurry; the adjusting agent was composed of calcium hydrogen sulfate and sodium oleate in a mass ratio of 3:1.

[0065] (3) Post-processing and drying The adjusted slurry of step (2) is cooled to room temperature; solid-liquid separation is performed, and the solid is rinsed twice with distilled water with a rinsing liquid-solid ratio of 2:1. After rinsing, it is placed in a vacuum drying oven and dried at 100°C for 3 hours. After drying, the solid is calcium sulfate whiskers.

[0066] The composition of calcium sulfate whiskers is shown in Table 3 below: Table 3 Calcium sulfate whisker composition

[0067] Example 2: A process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum, comprising the following steps: The composition of desulfurization gypsum in a steel plant is shown in Table 4 below: Table 4 Composition of desulfurization gypsum from a steel plant

[0068] (1) Slurry preparation and oxidation treatment Take the desulfurized gypsum shown in the table above, add water to make a slurry with a mass concentration of 15%, add a dispersant with a mass concentration of 0.1% of the desulfurized gypsum, and disperse for 2 hours; the dispersant is composed of sodium polyacrylate and sodium lauryl sulfate in a mass ratio of 2:1; Then add hydrogen peroxide with a concentration of 2% by weight of desulfurized gypsum, stir and oxidize at room temperature for 1 hour. After the reaction is completed, solid-liquid separation is performed to obtain oxidized gypsum and oxidized liquid. The oxidized gypsum enters the next step, and the oxidized liquid is mixed with desulfurized gypsum to prepare a slurry. The composition of the oxidized gypsum is shown in Table 5 below: Table 5 Composition of oxidized gypsum

[0069] (2) Acid dissolution and hydrothermal reaction Use hydrochloric acid solution to dissolve the gypsum shown in the table above. The concentration of the hydrochloric acid solution used is 3 mol / L. During the dissolution, maintain a liquid-to-solid ratio of 4:1. Stir the reaction at 60°C for 2 hours and then pump the slurry into the reactor. Sodium hydroxide was added as an additive to adjust the pH of the acid-soluble slurry to 6.5, and then an adjusting agent of 0.2% by mass of the oxidized gypsum was added; a hydrothermal reaction was carried out at a temperature of 120° C. and a time of 2 h to obtain an adjusted slurry; the adjusting agent was composed of calcium hydrogen sulfate and sodium oleate in a mass ratio of 3:1.

[0070] (3) Post-processing and drying The adjusted slurry from step (2) was cooled to room temperature; solid-liquid separation was performed, and the solid was rinsed twice with distilled water at a rinsing liquid-solid ratio of 2:1. After rinsing, the solid was placed in a vacuum drying oven and dried at 110°C for 4 hours. The dried solid was calcium sulfate whiskers. The composition of the calcium sulfate whiskers is shown in Table 6 below: Table 6 Calcium sulfate whisker composition

[0071] Example 3: A process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum, comprising the following steps: The composition of desulfurization gypsum in a steel plant is shown in Table 7 below: Table 7 Composition of desulfurization gypsum from a steel plant

[0072] (1) Slurry preparation and oxidation treatment Take the desulfurized gypsum shown in the table above, add water to make a slurry with a mass concentration of 30%, add a dispersant with a mass concentration of 0.08% of the desulfurized gypsum, and disperse for 2 hours; the dispersant is composed of sodium polyacrylate and sodium lauryl sulfate in a mass ratio of 2:1; Then add hydrogen peroxide with a concentration of 1.5% by weight of the desulfurized gypsum, stir and oxidize at room temperature for 1.5 hours. After the reaction is completed, solid-liquid separation is performed to obtain oxidized gypsum and oxidized liquid. The oxidized gypsum enters the next step, and the oxidized liquid is mixed with the desulfurized gypsum to prepare a slurry. The composition of the oxidized gypsum is shown in Table 8 below: Table 8 Composition of oxidized gypsum

[0073] (2) Acid dissolution and hydrothermal reaction Use hydrochloric acid solution to dissolve the gypsum shown in the table above. The concentration of the hydrochloric acid solution used is 5 mol / L. During the dissolution, maintain a liquid-to-solid ratio of 5:1. Stir the reaction at 80°C for 3 hours and then pump the slurry into the reactor. Sodium hydroxide was added as an additive to adjust the pH of the acid-soluble slurry to 6.5, and then an adjusting agent of 0.15% by mass of the oxidized gypsum was added; a hydrothermal reaction was carried out at a temperature of 120° C. and a time of 2 h to obtain an adjusted slurry; the adjusting agent was composed of calcium hydrogen sulfate and sodium oleate in a mass ratio of 3:1.

[0074] (3) Post-processing and drying The adjusted slurry from step (2) was cooled to room temperature; solid-liquid separation was performed, and the solid was rinsed three times with distilled water at a rinsing liquid-solid ratio of 3:1. After rinsing, the solid was placed in a vacuum drying oven and dried at 120°C for 5 hours. The dried solid was calcium sulfate whiskers. The composition of the calcium sulfate whiskers is shown in Table 9 below: Table 9 Calcium sulfate whisker composition

[0075] Comparative Example 1: A process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum, with only sodium oleate added as a regulator, and the remaining conditions being the same as in Example 1. Table 10 shows the composition of the calcium sulfate whiskers prepared in Comparative Example 1.

[0076] Table 10 Calcium sulfate whisker composition

[0077] Comparative Example 2: A process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum, without adding a regulator, and with the remaining conditions being the same as in Example 1. Table 11 shows the composition of the calcium sulfate whiskers prepared in Comparative Example 2.

[0078] Table 11 Calcium sulfate whisker composition

[0079] The average aspect ratio and average length of the calcium sulfate whiskers prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were simultaneously tested, and the results are summarized in Table 12.

[0080] Table 12

[0081] At the same time, from Figure 1 It can be seen that the calcium sulfate whiskers prepared in Example 1 have good dispersibility and a large aspect ratio.

[0082] from Figure 2 It can be seen that the calcium sulfate whiskers of Comparative Example 2 are relatively regular, and the hexagonal prism shape that calcium sulfate whiskers should have is more obvious, but the major diameter is relatively small; from Figure 3 It can be seen that in Comparative Example 3, no regulator was added, and calcium sulfate crystals showed agglomeration and aggregation during the crystallization process. The crystals adhered to each other, had different appearances, and were uneven in length and thickness.

[0083] It can be seen from the data in Tables 3, 6 and 9 that the calcium sulfate whiskers prepared by the process of the present invention contain almost no impurity elements (such as Al, Mg, K, Na, etc.), and the contents of these elements are all below the detection limit (<0.01%); this indicates that the process can effectively remove impurities in the original desulfurization gypsum, thereby preparing a high-purity product.

[0084] Although the products prepared in Comparative Examples 1 and 2 were also analyzed for composition (see Tables 10 and 11), their control of certain impurity elements was less effective than that in the Examples. For example, the Mg content in Comparative Example 2 was 0.08%.

[0085] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious replacement without departing from the concept of the present invention is within the scope of protection of the present invention.

Claims

1. A process for preparing high-purity calcium sulfate whiskers using desulfurized gypsum, characterized in that: The following steps are involved: (1) Add water to prepare desulfurized gypsum into slurry, and add dispersant to disperse it; Then, an oxidant is added to the slurry to carry out an oxidation reaction. After the oxidation reaction is completed, solid-liquid separation is carried out to obtain oxidized gypsum and oxidized liquid; (2) using an acid solution to dissolve the oxidized gypsum in step (1) to obtain an acid-soluble slurry; adding additives and a regulator to the acid-soluble slurry to carry out a hydrothermal reaction, and obtaining an adjusted slurry after the reaction is completed; (3) The adjusted slurry in step (2) is subjected to solid-liquid separation, and then rinsed and dried to obtain calcium sulfate whiskers.

2. The process according to claim 1, characterized in that In step (1), water is added to prepare the desulfurized gypsum into a slurry having a desulfurized gypsum content of 5-30% by mass.

3. The process according to claim 1, characterized in that In step (1), the oxidant is any one or more of chlorine, calcium hypochlorite, hydrogen peroxide, chlorine dioxide, and sodium hypochlorite; the amount of the oxidant added is 1-2% of the mass of the desulfurized gypsum, the oxidation reaction temperature is room temperature, and the oxidation reaction time is 0.5-1.5h.

4. The process according to claim 1, characterized in that In step (1), the dispersant is composed of sodium polyacrylate and sodium lauryl sulfate in a mass ratio of 2:1; the feeding amount of the dispersant is 0.05-0.1% of the mass of the desulfurized gypsum.

5. The process according to claim 1, characterized in that In step (2), the acid solution is one or more of sulfuric acid solution, hydrochloric acid solution, nitric acid solution, and citric acid solution, the concentration of the acid solution is 1-5 mol / L, the liquid-solid ratio is maintained at 2-5:1 during dissolution, the dissolution time is 1-3 hours, and the dissolution temperature is 50-80°C.

6. The process according to claim 1, characterized in that In step (2), the additive is any one or more of calcium hydroxide, sodium hydroxide, and potassium hydroxide; Additives were added to the acid-soluble slurry to adjust the pH of the acid-soluble slurry to 6.5, and then a regulator was added to carry out a hydrothermal reaction. The temperature of the hydrothermal reaction was 120° C., and the time of the hydrothermal reaction was 2 h.

7. The process according to claim 1, characterized in that In step (2), the adjusting agent is composed of calcium hydrogen sulfate and sodium oleate in a mass ratio of 3:1, and the feeding amount of the adjusting agent is 0.1-0.2% of the mass of the oxidized gypsum.

8. The process according to claim 1, characterized in that In step (3), the drying temperature is 100-120°C.

9. A calcium sulfate whisker, characterized in that The invention comprises calcium sulfate whiskers prepared by the process according to any one of claims 1 to 8.

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