Method for hydrothermal synthesis of hydrohonessite from phosphogypsum
By using phosphate-modified polycarboxylate superplasticizer and a high-salt system in the hydrothermal synthesis of phosphogypsum, the problems of high water consumption and uneven particle size in the hydrothermal synthesis of sodium calcite from phosphogypsum were solved, achieving low-energy consumption and high-efficiency preparation of sodium calcite, and the generated sodium calcite has fine particle size and good dispersibility.
Patent Information
- Application Number
- CN202610556775.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-24
- Publication Date
- 2026-06-19
AI Technical Summary
The existing process for the hydrothermal synthesis of sodium calcite from phosphogypsum has several problems, including high water consumption leading to increased reaction equipment volume and energy consumption, insufficient hydrothermal reaction driving force, and easy agglomeration and adhesion of products with uneven particle size.
By using phosphate-modified polycarboxylate superplasticizer and a high-salt system, the dispersion of phosphogypsum particles is achieved at a low liquid-to-solid ratio. Combined with sodium polycarboxylate salt to regulate crystal morphology, the uniform nucleation and refinement of sodium hydrate alum is promoted, thereby reducing water consumption and improving crystal transformation efficiency.
Highly efficient crystallization of sodium hydrate aluminate was achieved under low energy consumption conditions. The resulting sodium hydrate aluminate has small and uniform particle size and good dispersibility, which improves its activity as a functional filler or intermediate.
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Figure CN122233414A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of resource utilization of phosphogypsum and high-value preparation of solid waste, specifically to a method for hydrothermal synthesis of sodium calcite from phosphogypsum. Background Technology
[0002] Phosphogypsum is a major by-product solid waste generated during the wet-process phosphoric acid production. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), and it also contains impurities such as soluble phosphorus, fluorine, and organic matter. With the development of the phosphate fertilizer industry, the annual emissions of phosphogypsum have continued to increase. Large-scale stockpiling not only occupies land resources but may also cause groundwater and soil pollution. Therefore, the resource utilization of phosphogypsum has become an important research direction for current environmental governance and sustainable industrial development.
[0003] Currently, the main ways to utilize phosphogypsum resources include the preparation of building gypsum, cement retarders, cementitious materials, and mineral functional materials. Among these, converting phosphogypsum into sodium hydrate calcite (Na2Ca5(SO4)6·3H2O) through hydrothermal reaction is a utilization method with high added value. Sodium hydrate calcite has good early strength, micro-expansion properties, and ion exchange capacity, and has broad application prospects in cement modification, soil solidification, and heavy metal wastewater treatment.
[0004] In existing technologies, the hydrothermal synthesis of sodium hydrate alum from phosphogypsum typically employs a low-solids suspension system, meaning the liquid-to-solid ratio is usually high, generally greater than 3:1. While this process ensures good fluidity of the slurry, it has significant drawbacks: 1) The use of large amounts of water significantly increases the volume of the reaction system, leading to a substantial increase in the size of the reaction equipment and heating energy consumption. Furthermore, a large amount of wastewater needs to be treated after the reaction, increasing the cost of subsequent solid-liquid separation and wastewater treatment; 2) The driving force of the hydrothermal reaction is insufficient, often requiring the addition of more salt media and hydrothermal reaction promoters to improve conversion efficiency, thereby increasing production costs; 3) The prepared sodium hydrate alum is prone to agglomeration and adhesion, resulting in large and uneven particle sizes.
[0005] Therefore, developing a process that can efficiently and with low energy consumption transform phosphogypsum into sodium hydrate calcite and improve the dispersibility and uniformity of the generated sodium hydrate calcite is the key to breaking through the technological bottleneck of phosphogypsum's added value resource utilization. Summary of the Invention
[0006] To address the problems existing in the background art, the present invention provides a method for hydrothermal synthesis of sodium hydrate calcite from phosphogypsum, which can improve the crystal transformation efficiency of sodium hydrate calcite and produce sodium hydrate calcite crystals with fine and uniform particle size.
[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for the hydrothermal synthesis of sodium calcite from phosphogypsum includes the following steps: S1. Mix the raw phosphogypsum with water at a mass ratio of 100:(10-60), add phosphate ester modified polycarboxylate superplasticizer, stir evenly to obtain a high-flow phosphogypsum slurry; S2. Add a sodium ion-containing salt medium to the high-fluidity phosphogypsum slurry obtained in step S1, and carry out a hydrothermal crystallization reaction under normal pressure to obtain a sodium hydrate calcite slurry. S3. The sodium hydrate aluminate slurry obtained in step S2 is subjected to solid-liquid separation and dried to obtain sodium hydrate aluminate.
[0008] The phosphate-modified polycarboxylate superplasticizer is a polymer with phosphate groups grafted onto the side chains of a polycarboxylate molecule. The phosphate groups are any one or more of the following: -PO(OH)2, -PO(OR)(OH) or their salt forms.
[0009] According to the above scheme, the free water content of the undisturbed phosphogypsum is 8%-25%, of which calcium sulfate dihydrate accounts for more than 90% of the dry weight of the undisturbed phosphogypsum.
[0010] According to the above scheme, in step S1, the amount of phosphate ester modified polycarboxylate superplasticizer added is 0.1%-1% of the dry basis mass of the original phosphogypsum.
[0011] According to the above scheme, the amount of sodium ion-containing salt medium added in step S2 is 10%-30% of the dry basis mass of the original phosphogypsum, preferably 15%-25%.
[0012] According to the above scheme, the sodium-containing salt medium is one or more of sodium chloride, sodium sulfate, sodium carbonate, sodium phosphate, sodium formate, and sodium acetate.
[0013] According to the above scheme, in step S2, the temperature of the hydrothermal crystallization reaction is 70-120℃ and the time is 1-4h; further, the temperature of the hydrothermal crystallization reaction is 80-120℃ and the time is 1-3h.
[0014] According to the above scheme, in step S3, after solid-liquid separation, the separated liquid is recovered and recycled.
[0015] According to the above scheme, sodium polycarboxylate salt is also added in step S1.
[0016] According to the above scheme, the amount of sodium polycarboxylate added is 1-10% of the dry basis weight of the undisturbed phosphogypsum; more preferably, it is 3%-6%.
[0017] According to the above scheme, the sodium polycarboxylate salt is one or more of sodium tartrate, sodium malate, sodium polyacrylate, sodium citrate, and tetrasodium butanetetracarboxylate.
[0018] Phosphate groups on calcium ions (Ca 2+ It possesses extremely strong chelating and coordination capabilities, effectively competing for and adsorbing onto the surface of phosphogypsum particles even in high sulfate environments, maintaining adsorption stability. This results in electrostatic repulsion and steric hindrance between phosphogypsum particles, achieving full dispersion of phosphogypsum particles even at ultra-low liquid-to-solid ratios (high solid content), preventing particle agglomeration. Simultaneously, it constructs a high-solids-oversaturated environment at the micro-interface, achieving good fluidity of the high-solids-content slurry and providing a micro-reaction environment for the uniform nucleation of sodium hydrate calcite. Furthermore, this anchoring effect alters the Zeta potential of the gypsum surface, lowering the interfacial energy for sodium hydrate calcite nucleation. Under high sodium ion concentration conditions, it promotes the formation of a stable sodium-doped complex salt structure in the reaction system, achieving crystal refinement and homogenization control from a reaction kinetics perspective.
[0019] The beneficial effects of this invention are: This invention introduces a phosphate-modified polycarboxylate superplasticizer into the sodium hydrate calcite reaction system. Through the synergistic regulation of the phosphate-modified polycarboxylate superplasticizer and the high-salt system, the water consumption of the system is significantly reduced, achieving more effective dispersion of phosphogypsum under low water consumption conditions. This not only reduces the volume of the reaction system and heating energy consumption, but also enhances the chemical driving force of the hydrothermal crystallization reaction, shortens the reaction time, and improves the crystallization efficiency. At the same time, the high solubility supersaturated environment promotes the uniform nucleation of sodium hydrate calcite and shortens the ion diffusion distance of the reaction system. Combined with the impurity suppression effect of the phosphate-modified polycarboxylate superplasticizer, the crystallization reaction is more thorough, the product purity is higher, the dispersion effect is better, and the particle size is smaller. The prepared sodium hydrate calcite is highly regular, uniform in size, and has an extremely narrow distribution, with a finer and more uniform morphology.
[0020] Furthermore, by adding sodium polycarboxylate as a crystal morphology modifier, the morphology of the final crystal was controlled, resulting in short columnar sodium calcite with a particle size of approximately 3 μm, which significantly improved its activity as a functional filler or intermediate. Attached Figure Description
[0021] Figure 1 An optical microscope image of sodium calcite prepared in Example 1 of this invention; Figure 2 The images are photographs of the reaction process of preparing sodium hydrate calcite from undisturbed phosphogypsum as raw material in Example 2 of the present invention, where a is a photograph of undisturbed phosphogypsum, b is a photograph of the fluidity of high-fluidity phosphogypsum slurry, c is an optical microscope photograph of high-fluidity phosphogypsum slurry, and d is an optical microscope photograph of sodium hydrate calcite slurry. Figure 3 An optical microscope image of sodium calcite prepared in Example 2 of this invention; Figure 4An optical microscope image of sodium calcite prepared in Example 3 of this invention; Figure 5 An optical microscope image of sodium calcite prepared in Example 4 of this invention; Figure 6 An optical microscope image of sodium calcite prepared in Comparative Example 1 of this invention; Figure 7 An optical microscope image of sodium calcite prepared in Comparative Example 2 of this invention; Figure 8 An optical microscope image of sodium calcite prepared in Comparative Example 3 of this invention; Figure 9 An optical microscope image of sodium calcite prepared in Comparative Example 4 of this invention. Figure 10 An optical microscope photograph of sodium calcite prepared in Comparative Example 5 of this invention; Figure 11 This is an optical microscope image of sodium calcite prepared in Comparative Example 6 of this invention. Detailed Implementation
[0022] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.
[0023] The free water content of the undisturbed phosphogypsum in the examples is 12%-18%, of which calcium sulfate dihydrate accounts for more than 90% of the dry basis content of the undisturbed phosphogypsum.
[0024] The main chain of the phosphate-modified polycarboxylate superplasticizer is composed of acrylic acid and phosphate monomer HEMAP, and the side chain is polyoxyethylene ether (TPEG).
[0025] Common polycarboxylate superplasticizers (PCE), naphthalene-based superplasticizers (FDN), and melamine-based superplasticizers (SMF) are all commercially available industrial products.
[0026] Example 1 This embodiment provides a method for the hydrothermal synthesis of sodium calcite from phosphogypsum, the specific steps of which are as follows: 1) Mix raw phosphogypsum and water at a mass ratio of 100:40, add 0.4% of phosphate ester modified polycarboxylate superplasticizer by dry weight of raw phosphogypsum, stir evenly to obtain a high-flowability phosphogypsum slurry with a flowability of 190 mm. 2) Add 20% sodium sulfate by dry weight of undisturbed phosphogypsum to the slurry from step 1), heat to 98°C, and carry out hydrothermal crystallization reaction at 150 rpm. After 1 hour of reaction, a sodium calcite slurry with high solid content is obtained. 3) After the reaction is complete, the sodium hydrate calcite slurry is filtered and separated. The separated liquid is recycled and reused. The solid part is washed and dried to obtain needle-shaped sodium hydrate calcite solid product.
[0027] The optical photograph of the sodium calcite obtained in this embodiment is as follows: Figure 1 As shown in the figure, the obtained product has good dispersibility and no obvious agglomeration. The obtained sodium calcite is a needle-shaped crystal with a crystal length of about 10-20 μm.
[0028] Example 2 This embodiment provides a method for synthesizing sodium hydrate ettringite via a hydrothermal process using phosphogypsum. The specific steps are as follows: 1) Mix raw phosphogypsum and water at a mass ratio of 100:40, add 0.4% of phosphate ester modified polycarboxylate superplasticizer by dry weight of raw phosphogypsum, stir evenly to obtain a high-flowability phosphogypsum slurry with a flowability of 190 mm. 2) Add 20% sodium sulfate by dry weight of undisturbed phosphogypsum and 5% tetrasodium butanetetracarboxylate by dry weight of undisturbed phosphogypsum to the slurry from step 1), and heat to 98°C. Perform hydrothermal crystallization reaction at 150 rpm. After reacting for 1 hour, a sodium calcite slurry with high solid content is obtained. 3) After the reaction is complete, the sodium calcite slurry is filtered and separated. The separated liquid is recycled and reused, and the solid part is washed and dried to obtain the sodium calcite solid product.
[0029] Figure 2 These are photographs illustrating the reaction process of preparing sodium hydrate calcite from undisturbed phosphogypsum in this embodiment. Photograph a shows undisturbed phosphogypsum, photograph b shows the fluidity of the high-fluidity phosphogypsum slurry, photograph c shows an optical microscope image of the high-fluidity phosphogypsum slurry, and optical micrograph d shows an optical microscope image of the sodium hydrate calcite slurry. In this embodiment, by adding a phosphate-modified polycarboxylate superplasticizer, only a small amount of water is needed to obtain a liquid high-fluidity phosphogypsum slurry. After the crystallization reaction, the flaky calcium sulfate dihydrate in the gypsum slurry is completely converted into short columnar sodium hydrate calcite.
[0030] Figure 3 The optical micrographs of the sodium calcite prepared in this embodiment show that the obtained product has a uniform particle size and good dispersion effect. The obtained sodium calcite is a short columnar crystal with a particle size of about 3 μm.
[0031] Example 3 This embodiment provides a method for synthesizing sodium hydrate ettringite via a hydrothermal process using phosphogypsum. The specific steps are as follows: 1) Mix undisturbed phosphogypsum and water at a mass ratio of 100:60, add 0.4% of phosphate ester modified polycarboxylate superplasticizer by dry weight of undisturbed phosphogypsum, stir evenly to obtain a high-flowability phosphogypsum slurry with a flowability greater than 200 mm. 2) Add 20% sodium sulfate by dry weight of undisturbed phosphogypsum and 5% tetrasodium butanetetracarboxylate by dry weight of undisturbed phosphogypsum to the slurry from step 1), and heat to 98°C. Perform hydrothermal crystallization reaction at 150 rpm. After 2 hours of reaction, a slurry with high solid content of sodium calcite is obtained. 3) After the reaction is complete, the sodium hydrate calcite slurry is filtered and separated. The separated liquid is recycled and reused. The solid part is washed and dried to obtain short columnar sodium hydrate calcite solid product.
[0032] Figure 4 The image shows an optical micrograph of the sodium hydrate calcite prepared in this embodiment. As can be seen from the image, the obtained product has good dispersibility, no obvious agglomeration, and a relatively uniform particle size distribution. The obtained sodium hydrate calcite is a short columnar crystal with a particle size of approximately 5 μm.
[0033] Example 4 This embodiment provides a method for synthesizing sodium hydrate ettringite via a hydrothermal process using phosphogypsum. The specific steps are as follows: 1) Mix raw phosphogypsum and water at a mass ratio of 100:40, add 1% of phosphate ester modified polycarboxylate superplasticizer by dry weight of raw phosphogypsum, stir evenly to obtain a high-flowability phosphogypsum slurry with a flowability greater than 200 mm. 2) Add 20% sodium sulfate by dry weight of undisturbed phosphogypsum and 5% tetrasodium butanetetracarboxylate by dry weight of undisturbed phosphogypsum to the slurry from step 1), and heat to 98°C. Perform hydrothermal crystallization reaction at 150 rpm. After reacting for 1 hour, a sodium calcite slurry with high solid content is obtained. 3) After the reaction is complete, the sodium hydrate calcite slurry is filtered and separated. The separated liquid is recycled and reused. The solid part is washed and dried to obtain short columnar sodium hydrate calcite solid product.
[0034] Figure 5 The image shows an optical micrograph of the sodium hydrate calcite prepared in this embodiment. As can be seen from the image, the obtained product has good dispersibility and a uniform particle size distribution. The obtained sodium hydrate calcite is a short columnar crystal with a particle size of approximately 2 μm.
[0035] Comparative Example 1 The difference between this comparative example and Example 2 is that: 1) the mass ratio of undisturbed phosphogypsum to water is 100:70; 2) the phosphate ester modified polycarboxylate superplasticizer is replaced with an equal amount of ordinary polycarboxylate superplasticizer (the amount of polycarboxylate superplasticizer added is 0.4% of the dry basis mass of undisturbed phosphogypsum).
[0036] Optical microscope images of the sodium calcite prepared in this comparative example are shown below. Figure 6 As shown in the figure, the product was not completely converted; some of the product was in the form of flakes, while others were in the form of short columns and showed obvious aggregation.
[0037] Comparative Example 2 The difference between this comparative example and Example 2 is that: 1) the mass ratio of undisturbed phosphogypsum to water is 100:80; 2) the phosphate ester modified polycarboxylate superplasticizer is replaced with an equal amount of naphthalene-based superplasticizer.
[0038] Optical microscope images of the sodium calcite prepared in this comparative example are shown below. Figure 7 As shown in the figure, the obtained product is a short columnar crystal with obvious agglomeration, poor particle dispersibility, and a relatively large particle size of approximately 30 μm.
[0039] Comparative Example 3 The difference between this comparative example and Example 2 is that: 1) the mass ratio of undisturbed phosphogypsum to water is 100:80; 2) the phosphate ester modified polycarboxylate superplasticizer is replaced with an equal amount of melamine-based superplasticizer.
[0040] Optical microscope images of the sodium calcite prepared in this comparative example are shown below. Figure 8 As shown in the figure, the obtained product is a short columnar crystal with obvious agglomeration, poor dispersibility, uniform particle size, and a particle size of approximately 10 μm.
[0041] Comparative Example 4 The difference between this comparative example and Example 2 is that: 1) the mass ratio of undisturbed phosphogypsum to water is 100:300; 2) no water-reducing agent is added.
[0042] Optical microscope images of the sodium calcite prepared in this comparative example are shown below. Figure 9 As shown in the figure, the product was not completely converted, and most of it was in the form of flakes.
[0043] Comparative Example 5 The difference between this comparative example and Example 2 is that: 1) the mass ratio of undisturbed phosphogypsum to water is 100:100; 2) the phosphate-modified polycarboxylate superplasticizer is replaced with an equal amount of ordinary polycarboxylate superplasticizer.
[0044] Optical micrographs of the sodium hydroxide aluminate prepared in this comparative example are shown below. Figure 10 As shown in the figure, the product was not completely converted, and the particle size was unevenly distributed, with some particles appearing as plates and others as short columns.
[0045] Comparative Example 6 The differences between this comparative example and Example 2 are: 1) the mass ratio of undisturbed phosphogypsum to water is 100:300; 2) no water-reducing agent is added; and 3) the amount of salt medium added is up to 30% of the dry weight of the undisturbed phosphogypsum. Optical microscope images of the sodium calcite prepared in this comparative example are shown below. Figure 11 As shown in the figure, the obtained product has an unbalanced aspect ratio, uneven particle size, large-area agglomeration and adhesion, with only a small number of particles dispersed. The crystal regularity is extremely poor, and the crystal transformation reaction is incomplete.
[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for the hydrothermal synthesis of sodium calcite from phosphogypsum, characterized in that, Includes the following steps: S1. Mix the raw phosphogypsum with water at a mass ratio of 100:(10-60), add phosphate ester modified polycarboxylate superplasticizer, stir evenly to obtain a high-flow phosphogypsum slurry; S2. Add a sodium ion-containing salt medium to the high-flowability gypsum slurry obtained in step S1, and carry out a hydrothermal crystallization reaction under normal pressure to obtain a sodium hydrate calcite slurry; S3. The sodium hydrate aluminate slurry obtained in step S2 is subjected to solid-liquid separation and dried to obtain sodium hydrate aluminate.
2. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to claim 1, characterized in that, The free water content of unprocessed phosphogypsum is 8%-25%, of which calcium sulfate dihydrate accounts for more than 90% of the dry weight of unprocessed phosphogypsum.
3. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to claim 1, characterized in that, In step S1, the amount of phosphate-modified polycarboxylate superplasticizer added is 0.1%-1% of the dry basis mass of the original phosphogypsum.
4. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to claim 2, characterized in that, In step S2, the amount of sodium ion-containing salt medium added is 10%-30% of the dry weight of the undisturbed phosphogypsum.
5. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to claim 4, characterized in that, The sodium-containing salt medium is one or more of sodium chloride, sodium sulfate, sodium carbonate, sodium phosphate, sodium formate, and sodium acetate.
6. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to claim 1, characterized in that, In step S2, the hydrothermal crystallization reaction is carried out at a temperature of 70-120℃ for 1-4 hours.
7. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to claim 1, characterized in that, In step S3, after solid-liquid separation, the separated liquid is recovered and recycled.
8. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to any one of claims 1-7, characterized in that, Sodium polycarboxylate salt is also added in step S1.
9. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to claim 8, characterized in that, The amount of the sodium polycarboxylate added is 1%-10% of the dry weight of the undisturbed phosphogypsum.
10. The method for hydrothermal synthesis of sodium calcite from phosphogypsum according to claim 7, characterized in that, The sodium polycarboxylate salt is one or more of sodium tartrate, sodium malate, sodium polyacrylate, sodium citrate, and tetrasodium butanetetracarboxylate.