Method for preparing whitening type Ⅱ anhydrous gypsum by using phosphogypsum
By performing flotation whitening and liquid-phase crystallization on phosphogypsum, the problems of low whiteness and high energy consumption of anhydrous gypsum in the existing technology have been solved, and high-whiteness Type II anhydrous gypsum has been prepared, expanding its application in high-end building materials and decorative materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUIZHOU FANG MICROCRYSTAL TECH CO LTD
- Filing Date
- 2026-05-18
- Publication Date
- 2026-07-24
AI Technical Summary
Existing methods for preparing type II anhydrous gypsum suffer from problems such as low whiteness, high energy consumption, and difficulty in achieving water balance, which limit its application in high-end building materials and decorative materials.
Using phosphogypsum as raw material, type II anhydrous gypsum with a whiteness ≥90% is prepared by flotation whitening and liquid-phase crystallization in a dilute mixed acid system, combined with flotation reagents and microbubble technology to remove macromolecular organic matter and reorganize the crystal structure.
This technology enables the preparation of high-whiteness anhydrous gypsum, reduces production costs, decreases the need for grinding and processing, and enhances the application value of the product.
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Figure CN122444210A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of resource utilization technology of phosphogypsum, and more specifically, to a method for preparing whitening type II anhydrous gypsum using phosphogypsum. Background Technology
[0002] Type II anhydrous gypsum, chemically composed of anhydrous calcium sulfate (CaSO4), is an important inorganic chemical raw material with wide applications in fillers, building materials, and decorative materials. Currently, Type II anhydrous gypsum is prepared by dehydrating natural gypsum or phosphogypsum through high-temperature calcination. However, with the increasing depletion of natural gypsum resources and rising environmental protection requirements, developing a technical route for preparing anhydrous gypsum using phosphogypsum as a raw material has become an important direction for development in this field.
[0003] High-temperature calcination typically involves temperatures above 800℃, resulting in high energy consumption. Furthermore, the produced Type II anhydrous gypsum is often gray or grayish-white due to impurities in the raw materials, leading to low whiteness and severely limiting its application in high-end building materials, decorative materials, and polymer composites. To address these issues, researchers have developed various phosphogypsum purification and whitening technologies. Existing phosphogypsum whitening methods can be broadly categorized into physical, chemical, and thermal treatment methods. Physical methods primarily include washing and flotation. Washing removes some soluble impurities, while flotation separates organic matter and easily floatable mud components. Studies have shown that through desliming and flotation, the whiteness of phosphogypsum concentrate can reach 58%. Chemical methods mainly employ acid leaching or lime neutralization to transform or remove harmful impurities through chemical reactions. Thermal treatment, or high-temperature calcination, alters the microstructure of phosphogypsum, converting soluble phosphorus impurities into inert, insoluble substances while simultaneously removing most soluble fluorine and organic matter.
[0004] However, the aforementioned existing technologies still have several shortcomings. While physical methods are relatively simple to operate, their purification effect is limited, resulting in only a slight increase in the whiteness of the product. Furthermore, the washing process generates a large amount of wastewater, making water balance management difficult and leading to secondary pollution. Although lime neutralization in chemical methods can effectively remove soluble fluoride and phosphorus, it often requires subsequent heat treatment to achieve ideal product performance. Traditional high-temperature calcination methods can improve product whiteness to some extent, but they suffer from high calcination temperatures (typically above 800℃), high energy consumption, and high production costs. Studies have shown that anhydrous gypsum prepared by calcination at 900℃ can achieve a whiteness of 86.12%, but this requires significant energy. More importantly, the whiteness of anhydrous gypsum products prepared using existing technologies generally struggles to exceed the critical threshold of 90%, limiting their application in the high-end market.
[0005] Therefore, developing a method for preparing whitening anhydrous gypsum using wet-process phosphoric acid by-product phosphogypsum as raw material, with low production cost, high product whiteness, and good process stability, not only has significant economic benefits, but also has profound practical significance for promoting the resource utilization of industrial solid waste and protecting the ecological environment. Summary of the Invention
[0006] To address the problems of low whiteness, high energy consumption, and difficulty in achieving water balance in existing methods for preparing Type II anhydrous gypsum, this invention provides a method for preparing whitening Type II anhydrous gypsum using phosphogypsum, comprising: S1. Obtain phosphogypsum raw material; S2. Immerse the phosphogypsum raw material in a dilute mixed acid of sulfuric acid and phosphoric acid to obtain the slurry to be whitened; S3. Add the slurry to be whitened into the whitening equipment, add flotation reagent, and then introduce microbubbles for flotation whitening to obtain whitened phosphogypsum slurry; S4. Add concentrated sulfuric acid to the whitening phosphogypsum slurry to induce crystallization and obtain anhydrous gypsum slurry; S5. Post-process the anhydrous gypsum slurry to obtain Type II anhydrous gypsum with a whiteness ≥90%.
[0007] Optionally, in step S2, the flotation whitening process includes organic matter separation and large particle impurity separation to obtain the whitened phosphogypsum slurry.
[0008] Optionally, in step S5, the post-processing includes: filtering and separating the anhydrous gypsum slurry to obtain filtrate and filter cake, then using washing liquid to perform multi-stage countercurrent washing on the filter cake, and then drying it at 80℃-120℃.
[0009] Optionally, the multi-stage countercurrent washing includes at least two stages; The washing solution is obtained after the multi-stage countercurrent washing, and the washing solution is mixed with a portion of the filtrate to obtain the dilute mixed acid.
[0010] Optionally, the mass concentration of sulfuric acid in the dilute mixed acid is 5%-25%; and the mass concentration of P2O5 in the phosphoric acid is 2%-15%.
[0011] Optionally, the solid-liquid ratio of the phosphogypsum to the dilute mixed acid is 1:1.5~5.
[0012] Optionally, the flotation reagent is one or more combinations of dodecylamine, dodecyltrimethylammonium bromide, tetradecylamine, and octadecylamine.
[0013] Optionally, the amount of flotation reagent added is 0.05%-2% of the mass of phosphogypsum.
[0014] Optionally, in step S2, the mixing time is 10 min - 60 min; the flotation whitening time is 5 min - 30 min; the crystallization time is 1 h - 7 h; and the crystallization conditions are: sulfuric acid mass concentration of 20% - 45% and temperature of 65℃ - 100℃.
[0015] Optionally, the phosphogypsum includes dihydrate gypsum or hemihydrate gypsum.
[0016] To address the problems of low whiteness, high energy consumption, and difficulty in achieving water balance in existing methods for preparing Type II anhydrous gypsum, this invention offers the following advantages: 1. The phosphogypsum raw material is first whitened by flotation. The whitened gypsum slurry is then transformed into type II anhydrous gypsum through liquid phase crystallization. During the crystallization process, the crystal structure changes and the organic matter trapped inside the crystal is released. After being decomposed by sulfuric acid, the whiteness is improved again.
[0017] 2. When phosphogypsum raw materials are floated and whitened in a certain dilute mixed acid system, large organic molecules are decomposed into smaller organic molecules by the mixed acid, making them easier to capture by flotation reagents. Secondly, the dilute mixed acid obtained from flotation is a mixture of the filtrate and washing liquid of anhydrous gypsum, which can be recycled, reducing production costs and making water balance easy to control.
[0018] 3. The whitened phosphogypsum slurry is directly converted into Type II anhydrous gypsum through liquid-phase crystallization. During the crystallization process, the internal structure of the crystal is reorganized, resulting in fine and uniform Type II anhydrous gypsum crystals. This reduces grinding and further lowers production costs in subsequent applications. Attached Figure Description
[0019] Figure 1 A flowchart illustrating a method for preparing whitening type II anhydrous gypsum using phosphogypsum is shown. Figure 2 A process flow diagram of a method for preparing whitening type II anhydrous gypsum using phosphogypsum is shown. Detailed Implementation
[0020] The present disclosure will now be discussed with reference to several exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and thus implement the present disclosure, and are not intended to imply any limitation on the scope of the disclosure.
[0021] As used herein, the term "comprising" and its variations are to be interpreted as open-ended terms meaning "including but not limited to". The term "based on" is to be interpreted as "at least partially based on". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment". The term "another embodiment" is to be interpreted as "at least one other embodiment". The terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments and are not intended to limit the indicated devices, elements, or components to having a specific orientation or being constructed and operated in a specific orientation. Furthermore, some of the above terms may be used to indicate other meanings besides orientations or positional relationships; for example, the term "upper" may in some cases indicate a dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application according to the specific circumstances. In addition, the terms "installed", "set up", "equipped with", "connected", and "linked" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, elements, or components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, the terms "first," "second," etc., are mainly used to distinguish different devices, elements, or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance or quantity of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.
[0022] Example 1: A method for preparing whitening type II anhydrous gypsum using phosphogypsum, such as Figure 1 As shown, it includes the following steps: S1. Obtain phosphogypsum raw material; S2. Immerse the phosphogypsum raw material in a dilute mixed acid of sulfuric acid and phosphoric acid to obtain the slurry to be whitened; S3. Add the slurry to be whitened into the whitening equipment, add flotation reagent, and then introduce microbubbles for flotation whitening to obtain whitened phosphogypsum slurry; S4. Add concentrated sulfuric acid to the whitening phosphogypsum slurry to induce crystallization and obtain anhydrous gypsum slurry; S5. Post-process the anhydrous gypsum slurry to obtain Type II anhydrous gypsum with a whiteness ≥90%.
[0023] In this embodiment, phosphogypsum raw material with a solid-liquid ratio of 1 kg:5 kg is immersed in a dilute mixed acid system of sulfuric acid and phosphoric acid and stirred uniformly for 60 minutes to form a slurry to be whitened. The mass concentration of sulfuric acid in the dilute mixed acid system is 25%, and the mass concentration of P2O5 in the phosphoric acid is 15%. The slurry to be whitened is added to the flotation equipment, and flotation reagent is added at a rate of 0.08% of the mass of phosphogypsum. Simultaneously, microbubbles are introduced by compressed air supply for flotation whitening for 20 minutes. After flotation whitening, concentrated sulfuric acid is added to the slurry for crystallization for 7 hours. The crystallization conditions are that the mass concentration of sulfuric acid in the dilute mixed acid system is 45% and the temperature is 65°C, thereby obtaining anhydrous gypsum slurry. In this application, the flotation reagent can preferably be any one or a combination of dodecylamine, dodecyltrimethylammonium bromide, tetradecylamine, and octadecylamine.
[0024] Specifically, the post-treatment of anhydrous gypsum slurry involves: Anhydrous gypsum slurry is filtered to obtain filtrate and filter cake. The filter cake is then subjected to a three-stage countercurrent washing process using a washing liquid, ultimately yielding washing liquid and wet-based type II anhydrous gypsum. A portion of the obtained filtrate is returned to the phosphoric acid extraction system, while the remaining filtrate is mixed with all the washing liquid to prepare a dilute mixed acid. Next, the wet-based type II anhydrous gypsum filter cake is dried at 120°C to obtain type II anhydrous gypsum with a whiteness ≥90%. In this application, the phosphogypsum is dihydrate gypsum or hemihydrate gypsum.
[0025] Specifically, such as Figure 2 As shown, this invention involves flotation whitening of dihydrate or hemihydrate gypsum in a unique mixed acid system containing sulfuric acid and phosphoric acid. Large carbon-containing organic molecules in the gypsum are acidified in the mixed acid medium, forming smaller organic molecules. These smaller molecules are collected by flotation reagents and carried to the surface of the slurry by microbubbles, thus separating the organic matter. Undecomposed feldspar minerals or colored large particles such as FeS in the phosphogypsum are discharged from the bottom of the specialized whitening equipment by gravity, improving whiteness; this is the separation of large impurities. During the crystallization process of the whitened gypsum slurry, even smaller organic molecules encased within the crystal nuclei are released and decomposed under the action of concentrated sulfuric acid, producing Type II anhydrous gypsum with higher whiteness. This type of gypsum has a wider market application, suitable for high-end polymer filler applications or building materials requiring high whiteness, increasing added value. Example 2: A method for preparing whitening type II anhydrous gypsum using phosphogypsum includes the following steps: S1. Obtain phosphogypsum raw material; S2. Immerse the phosphogypsum raw material in a dilute mixed acid of sulfuric acid and phosphoric acid to obtain the slurry to be whitened; S3. Add the slurry to be whitened into the whitening equipment, add flotation reagent, and then introduce microbubbles for flotation whitening to obtain whitened phosphogypsum slurry; S4. Add concentrated sulfuric acid to the whitening phosphogypsum slurry to induce crystallization and obtain anhydrous gypsum slurry; S5. Post-process the anhydrous gypsum slurry to obtain Type II anhydrous gypsum with a whiteness ≥90%.
[0026] In this embodiment, phosphogypsum raw material with a solid-liquid ratio of 1 kg:1.5 kg is immersed in a dilute mixed acid system of sulfuric acid and phosphoric acid and stirred uniformly for 10 minutes to form a slurry to be whitened. The mass concentration of sulfuric acid in the dilute mixed acid system is 5%, and the mass concentration of P2O5 in the phosphoric acid is 2%. The slurry to be whitened is added to the flotation equipment, and flotation reagents are added at an amount of 1.0% of the mass of phosphogypsum. Simultaneously, microbubbles are introduced through a venturi jet for flotation whitening for 10 minutes. After flotation whitening, concentrated sulfuric acid is added to the slurry for crystallization for 1 hour. The crystallization conditions are that the mass concentration of sulfuric acid in the dilute mixed acid system is 20% and the temperature is 100°C, thereby obtaining anhydrous gypsum slurry. In this application, the flotation reagents can preferably be any one or a combination of dodecylamine, dodecyltrimethylammonium bromide, tetradecylamine, and octadecylamine.
[0027] Specifically, the post-treatment of anhydrous gypsum slurry involves: Anhydrous gypsum slurry is filtered to obtain filtrate and filter cake. The filter cake is then washed in a five-stage countercurrent process with a washing liquid to obtain washing liquid and wet-based type II anhydrous gypsum. Part of the filtrate is returned to the phosphoric acid extraction system, while the other part of the filtrate is mixed with all the washing liquid to prepare a dilute mixed acid. Next, the wet-based type II anhydrous gypsum filter cake is dried at 80°C to obtain type II anhydrous gypsum with a whiteness ≥90%.
[0028] Example 3: A method for preparing whitening type II anhydrous gypsum using phosphogypsum includes the following steps: S1. Obtain phosphogypsum raw material; S2. Immerse the phosphogypsum raw material in a dilute mixed acid of sulfuric acid and phosphoric acid to obtain the slurry to be whitened; S3. Add the slurry to be whitened into the whitening equipment, add flotation reagent, and then introduce microbubbles for flotation whitening to obtain whitened phosphogypsum slurry; S4. Add concentrated sulfuric acid to the whitening phosphogypsum slurry to induce crystallization and obtain anhydrous gypsum slurry; S5. Post-process the anhydrous gypsum slurry to obtain Type II anhydrous gypsum with a whiteness ≥90%.
[0029] In this embodiment, phosphogypsum raw material with a solid-liquid ratio of 1 kg:3 kg is immersed in a dilute mixed acid system of sulfuric acid and phosphoric acid and stirred uniformly for 30 minutes to form a slurry to be whitened. The mass concentration of sulfuric acid in the dilute mixed acid system is 18%, and the mass concentration of P2O5 in the phosphoric acid is 6%. The slurry to be whitened is added to the flotation equipment, and flotation reagents are added at an amount of 1.5% of the mass of phosphogypsum. Simultaneously, microbubbles are introduced through a Venturi jet for flotation whitening for 10 minutes. After flotation whitening, concentrated sulfuric acid is added to the slurry for crystallization for 4.5 hours. The crystallization conditions are that the mass concentration of sulfuric acid in the dilute mixed acid system is 30% and the temperature is 78°C, thereby obtaining anhydrous gypsum slurry. In this application, the flotation reagents can preferably be any one or a combination of dodecylamine, dodecyltrimethylammonium bromide, tetradecylamine, and octadecylamine.
[0030] Specifically, the post-treatment of anhydrous gypsum slurry involves: Anhydrous gypsum slurry is filtered to obtain filtrate and filter cake. The filter cake is then subjected to three-stage countercurrent washing with washing liquid to obtain washing liquid and wet-based type II anhydrous gypsum. Part of the filtrate is returned to the phosphoric acid extraction system, and the other part of the filtrate is mixed with all the washing liquid to prepare dilute mixed acid. Next, the wet-based type II anhydrous gypsum filter cake is dried at 80°C to obtain type II anhydrous gypsum with a whiteness ≥90%.
[0031] Those skilled in the art will understand that the above embodiments are specific examples of implementing this disclosure, and in practical applications, various changes can be made in form and detail without departing from the scope of this disclosure.
Claims
1. A method for preparing whitening type II anhydrous gypsum using phosphogypsum, characterized in that, The method includes the following steps: S1. Obtain phosphogypsum raw material; S2. Immerse the phosphogypsum raw material in a dilute mixed acid of sulfuric acid and phosphoric acid to obtain the slurry to be whitened; S3. Add the slurry to be whitened into the whitening equipment, add flotation reagent, and then introduce microbubbles for flotation whitening to obtain whitened phosphogypsum slurry; S4. Add concentrated sulfuric acid to the whitening phosphogypsum slurry to induce crystallization and obtain anhydrous gypsum slurry; S5. Post-process the anhydrous gypsum slurry to obtain Type II anhydrous gypsum with a whiteness ≥90%.
2. The method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 1, characterized in that, In step S3, the flotation whitening process includes organic matter separation and large particle impurity separation to obtain the whitened phosphogypsum slurry.
3. The method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 1, characterized in that, In step S5, the post-processing includes: filtering and separating the anhydrous gypsum slurry to obtain filtrate and filter cake, then washing the filter cake in a multi-stage countercurrent manner with washing liquid, and then drying it at 80℃-120℃.
4. The method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 3, characterized in that, The multi-stage countercurrent washing includes at least two stages; The washing solution is obtained after the multi-stage countercurrent washing, and the washing solution is mixed with a portion of the filtrate to obtain the dilute mixed acid.
5. A method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 1 or 4, characterized in that, The mass concentration of sulfuric acid in the dilute mixed acid is 5%-25%; the mass concentration of P2O5 in the phosphoric acid is 2%-15%.
6. The method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 1, characterized in that, The solid-liquid ratio of the phosphogypsum to the dilute mixed acid is 1:1.5~5.
7. The method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 1, characterized in that, The flotation reagent is one or more combinations of dodecylamine, dodecyltrimethylammonium bromide, tetradecylamine, and octadecylamine.
8. A method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 1 or 7, characterized in that, The amount of flotation reagent added is 0.05%-2% of the mass of phosphogypsum.
9. A method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 1, characterized in that, In step S2, the mixing time is 10 min - 60 min; the flotation whitening time is 5 min - 30 min; the crystallization time is 1 h - 7 h; and the crystallization conditions are: sulfuric acid mass concentration of 20% - 45% and temperature of 65℃ - 100℃.
10. A method for preparing whitening type II anhydrous gypsum using phosphogypsum according to claim 1, characterized in that, The phosphogypsum includes dihydrate gypsum or hemihydrate gypsum.