Method for producing calcium-magnesium composite whisker by using two-alkali method salt mud

Abstract

The application discloses a method for producing calcium-magnesium composite whiskers by using two-alkali method salt mud, and comprises the following steps: drying and calcining two-alkali method salt mud to obtain a mixture of calcium oxide and magnesium oxide; adding water to the mixture and performing pulp digestion at room temperature to obtain calcium-magnesium digestion slurry; adding magnesium sulfate solution to the calcium-magnesium digestion slurry and uniformly mixing to obtain a precursor; transferring the precursor to a high-pressure reaction kettle to perform hydrothermal crystallization reaction, and then performing cooling, filtering and drying to obtain calcium-magnesium composite whiskers. When the two-alkali method salt mud is used as raw material, the method does not need to be pre-washed, and the trace soluble NaCl in the salt mud is fully utilized to play a role of whisker regulator; meanwhile, the two elements of calcium and magnesium in the two-alkali method salt mud are effectively utilized, and the calcium-magnesium composite whisker product with economic value is obtained, thereby providing an economic and effective way for comprehensive utilization of the two-alkali method salt mud; and the method has the advantages of short process, simple operation, low equipment requirement, low processing cost and easy industrialization.

Description

Technical Field

[0001] This invention relates to the field of environmental protection and solid waste resource utilization technology, specifically to a method for producing calcium-magnesium composite whiskers using alkali-alkali process salt mud. Background Technology

[0002] The purpose of brine purification is to remove the calcium from the original brine. 2+ Mg 2+ Ions are separated before entering the heating chamber. Brine is generally purified using methods such as the "two-alkali method," where a flocculant is added after the reaction to accelerate precipitate separation. The supernatant is the product-grade brine, and the precipitate in the reaction tank is salt mud. The two-alkali method for brine purification uses caustic soda (NaOH) to remove Mg from the brine. 2+ The calcium in the brine is removed by precipitation with Mg(OH)2, and by using sodium carbonate (NaCO3) to remove the calcium. 2+ The calcium and magnesium in the salt mud are removed by precipitation with CaCO3. The main components of the salt mud produced by the two-alkali process are calcium carbonate and magnesium hydroxide, with a small amount of NaCl. Currently, simple landfilling and stockpiling cannot effectively utilize the calcium and magnesium resources in the salt mud. Researching and developing reasonable industrial application technologies for salt mud treatment is a common technical challenge faced by all salt-producing enterprises in China.

[0003] Anhydrous calcium sulfate whiskers possess excellent properties such as high strength, high modulus, high toughness, wear resistance, high temperature resistance, and good infrared reflectivity. They can be used as reinforcing and toughening agents or functional fillers in resins, plastics, rubber, coatings, paints, papermaking, asphalt, friction and sealing materials; they can also be used directly as filter materials, thermal insulation materials, fire-resistant and heat-insulating materials, infrared reflective materials, and high-insulation materials for wires. Basic magnesium sulfate whiskers are a powder with the chemical composition xMg(OH)₂·yMgSO₄·nH₂O (xyz type), among which the 513 type 5Mg(OH)₂·MgSO₄·3H₂O is common. Basic magnesium sulfate whiskers not only have good flame retardant properties but also high toughness, wear resistance, heat resistance, high strength, low density, and high elastic modulus. They can not only improve the flame retardancy of products but also enhance the wear resistance, strength, elasticity, and other mechanical properties of materials, showing broad application prospects in automotive, machinery, heat-resistant and wear-resistant parts, plastics, rubber, friction materials, cement, and other fields.

[0004] The core advantages and development prospects of composite materials made from anhydrous calcium sulfate whiskers and type 513 basic magnesium sulfate whiskers:

[0005] Composite whiskers composed of anhydrous calcium sulfate whiskers and type 513 basic magnesium sulfate whiskers achieve synergistic optimization of mechanical properties (such as a 98.3% increase in flexural strength and a 45°C increase in heat distortion temperature) through complementary performance (anhydrous calcium sulfate whiskers provide low cost, high toughness, and flowability, while basic magnesium sulfate whiskers contribute high modulus, heat resistance, and biocompatibility). They are also environmentally friendly and economical (the raw materials are derived from abundant natural gypsum, reducing material costs by more than 20% and being non-toxic and biodegradable). Development prospects focus on three major areas: automotive lightweighting (replacing glass fiber reinforced plastic parts to improve impact resistance); biomedicine (developing biodegradable implants using osteoconductive and biocompatibility); and green building materials (improving fire resistance and reducing cement usage by 30% to lower carbon emissions). Currently, breakthroughs are needed in co-modification technology and large-scale production bottlenecks, leveraging regional resources (such as Shandong gypsum mines) and technology clusters to seize the high-end market, with a potential market size exceeding 5 billion yuan (by 2027).

[0006] Existing methods for preparing composite whiskers composed of anhydrous calcium sulfate whiskers and 513-type basic magnesium sulfate whiskers are based on low-cost raw materials (concentrated seawater, gypsum). They address the compatibility issue between the whiskers and the matrix through surface synergistic modification and stepwise composite processes (melt blending / in-situ polymerization), and introduce directional dispersion technology to improve reinforcement efficiency. However, these methods are cumbersome, resulting in high energy consumption, long production cycles, whisker breakage, and potential environmental pollution from residual modifiers (such as silanes), and recycling technologies are not yet mature. Therefore, composite whiskers composed of anhydrous calcium sulfate whiskers and 513-type basic magnesium sulfate whiskers combine the advantages of both types and can be widely used in resins, plastics, rubber, friction, cement, and other fields, with a promising market prospect.

[0007] The salt mud produced by the two-alkali process mainly contains calcium carbonate and magnesium hydroxide, which can provide the calcium and magnesium chemical components required for the production of calcium sulfate whiskers and basic magnesium sulfate whiskers. If calcium and magnesium whiskers are produced using the salt mud from the two-alkali process as raw material, it can not only dispose of a large amount of solid waste from the salt mud from the two-alkali process, reduce storage costs, and improve the environment, but also realize the high-value-added utilization of the salt mud from the two-alkali process, turning waste into treasure, which is in line with the green circular and sustainable development strategy.

[0008] Currently, some research has been conducted both domestically and internationally on the preparation of whiskers using salt mud. For example, the paper "Production of Whiskers from Chlor-Alkali Salt Mud" (Chlor-Alkali Industry, 2013, 49(11): 41-42) reports a method for producing whiskers from chlor-alkali salt mud. The process is as follows: First, industrial hydrochloric acid is used to dissolve the salt mud to obtain a clear solution of CaCl2, MgCl2, and sodium salt; Second, sulfuric acid is added to make CaCl2... 2+The process involves four steps: First, CaSO4 precipitate is formed. Limestone slurry is added to the clear liquid obtained after separating the precipitate to obtain Mg(OH)2 precipitate. Second, the CaSO4 precipitate is hydrothermally synthesized into calcium sulfate whiskers using a crystallizing agent. Third, basic magnesium sulfate whiskers are obtained by reacting magnesium sulfate and magnesium hydroxide precipitates in a high-pressure reactor. Patent CN 115074815 B discloses a method for preparing dihydrate calcium sulfate whiskers at room temperature using brine salt production byproducts as raw materials. This method utilizes salt mud and high-nitrate water generated during sodium sulfate brine salt production as raw materials. The solution after acid hydrolysis of the salt mud and the high-nitrate water are reacted at room temperature to prepare dihydrate calcium sulfate whiskers, and the filtrate after the reaction is returned to the brine for salt production. Patent CN 113668060 B discloses a process for continuously preparing hemihydrate and dihydrate calcium sulfate whiskers using salt mud. Salt mud is used as raw material; it is dissolved in dilute hydrochloric acid and filtered to obtain a salt mud acid leachate. This leachate is diluted and heated with an equimolar volume of sodium sulfate. After whisker growth, it is filtered, washed, and dried to obtain hemihydrate calcium sulfate whiskers. The filtrate is then placed in an insulated box for aging, cooled, filtered, washed, and dried to obtain dihydrate calcium sulfate whiskers. Patent CN113089076B discloses a method for preparing calcium sulfate whiskers based on chlor-alkali salt mud. The salt mud is sequentially dried, crushed, and washed to obtain a salt mud suspension. Calcium ions are then dissolved from the salt mud through acid washing. Pretreatment is used to remove impurities, and calcium sulfate seeds and sulfuric acid are added to convert the calcium ions into high-purity calcium sulfate whiskers. Patent CN113186591 B discloses a method for preparing hemihydrate calcium sulfate whiskers using lime flue gas method salt mud. First, waste hydrochloric acid is reacted with lime flue gas method salt mud at room temperature. Then, the reaction system is filtered, and the filtrate is reacted with an equimolar volume of dilute sulfuric acid under normal pressure to prepare hemihydrate calcium sulfate whiskers. In summary, the common process for preparing whiskers using salt mud currently involves first dissolving the salt mud with acid to obtain calcium and magnesium ion solutions, and then obtaining calcium sulfate whiskers and magnesium whiskers respectively. The disadvantages of this process are that it requires a large amount of hydrochloric acid or sulfuric acid to acidify the salt mud, significantly increasing production costs, and the process is lengthy, making it unsuitable for industrial application.

[0009] Therefore, the technical problem to be solved by this invention is how to fully utilize the calcium and magnesium elements in the salt mud of the two-alkali process without adding acid for dissolution or whisker modifiers to achieve a short-process preparation of high-quality anhydrous calcium sulfate whiskers and 513-type basic magnesium sulfate whiskers. Summary of the Invention

[0010] In view of the above-mentioned shortcomings, the present invention provides a method for producing calcium-magnesium composite whiskers using alkali-process salt mud. When using alkali-process salt mud as raw material, the present invention eliminates the need for pre-washing, fully utilizing the trace amounts of soluble NaCl in the salt mud as a whisker regulator. Simultaneously, it effectively utilizes the calcium and magnesium elements in the alkali-process salt mud to obtain economically valuable calcium-magnesium composite whisker products. This provides an economical and effective way to comprehensively utilize alkali-process salt mud. Using the method of the present invention, the production process is short, simple to operate, requires low equipment, has low processing costs, and is easily industrialized.

[0011] To achieve the above objectives, the present invention provides a method for producing calcium-magnesium composite whiskers using alkali-alkali process salt mud, comprising the following steps:

[0012] S1. The salt mud produced by the two-alkali method is dried and calcined to obtain a mixture of calcium oxide and magnesium oxide; wherein the main components of the salt mud produced by the two-alkali method are calcium carbonate and magnesium hydroxide.

[0013] S2. Add water to the mixture and digest it at room temperature to obtain a calcium-magnesium digest slurry;

[0014] S3. Add magnesium sulfate solution to the calcium-magnesium digest slurry and mix well to obtain the precursor;

[0015] S4. The precursor is transferred to a high-pressure reactor for hydrothermal crystallization reaction, and then cooled, filtered and dried to obtain calcium-magnesium composite whiskers; wherein the calcium-magnesium composite whiskers are composite whiskers composed of anhydrous calcium sulfate whiskers and 513 type basic magnesium sulfate whiskers.

[0016] According to one aspect of the present invention, in step S1, the salt mud obtained by the two-alkali method is well salt mud.

[0017] According to one aspect of the present invention, in step S1, the drying specifically involves drying at 100-110°C for 5-10 hours.

[0018] According to one aspect of the present invention, in step S1, the calcination specifically involves heating from room temperature to 750-1000°C at a heating rate of 5-15°C / min and holding at that temperature for 1-8 hours.

[0019] According to one aspect of the present invention, in step S2, the mass ratio of the mixture to water is 1:10-50; and the time for room temperature pulping and digestion is 30-120 min.

[0020] According to one aspect of the present invention, in step S3, the concentration of the magnesium sulfate solution is 0.4 to 0.8 mol / L.

[0021] According to one aspect of the present invention, in step S3, the ratio of the total amount of calcium oxide and magnesium oxide in the calcium-magnesium digest slurry to the amount of magnesium sulfate in the magnesium sulfate solution is 1:0.6-1.5.

[0022] According to one aspect of the present invention, in step S4, the temperature of the hydrothermal crystallization reaction is 180–220°C, and the time is 6–48 h.

[0023] According to one aspect of the present invention, in step S4, the drying temperature is 80°C and the time is 6-12 hours.

[0024] Based on the same inventive concept, the present invention also provides calcium-magnesium composite whiskers prepared by any of the above methods.

[0025] The beneficial effects of this invention are:

[0026] (1) This invention proposes for the first time to use the salt mud produced during the brine purification process to prepare anhydrous calcium sulfate whiskers and 513 type basic magnesium sulfate whiskers to make composite whiskers, which greatly reduces the production cost of whisker products, saves energy and reduces emissions, and realizes "turning waste into treasure", which is in line with the national policy of energy conservation, emission reduction and green environmental protection.

[0027] (2) This invention directly uses the salt mud produced during the brine purification process as the raw material for the reaction. There is no need to wash or acid the salt mud with water, and no need to add additives such as crystallization agents or crystal form promoters. Instead, the small amount of NaCl present in the salt mud itself can be used as a growth promoter for calcium sulfate whiskers. The salt mud is roasted and hydrothermally crystallized with magnesium sulfate solution in one step to obtain mixed whiskers, thereby reducing the content of impurities in the solution and facilitating the subsequent washing treatment of whiskers.

[0028] (3) The method of the present invention is simple in process, green and environmentally friendly, does not require complex and expensive equipment, and has a simple structure, low energy consumption, energy saving and emission reduction, and protects natural resources, achieving a unity of social and environmental benefits and economic benefits, and has good promotion and application value.

[0029] (4) The calcium-magnesium composite whiskers prepared by the present invention are composed of anhydrous calcium sulfate and 513 type basic magnesium sulfate, without impurities; and the calcium-magnesium composite whiskers have a regular morphology, are fibrous, and are not broken. Attached Figure Description

[0030] Figure 1 The image shows the XRD pattern of the composite whiskers prepared in Example 1 of this invention.

[0031] Figure 2 This is a SEM image of the composite whiskers prepared in Example 1 of the present invention. Detailed Implementation

[0032] To make the present invention easier to understand, specific embodiments are described below to further illustrate the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved herein can be purchased commercially or obtained by known methods.

[0033] To address the problems of existing technologies, such as the need for acid dissolution, lack of whisker modifiers, long preparation processes, and low product quality due to added impurities, the inventors provide a method for producing calcium-magnesium composite whiskers using the two-alkali process of salt mud, comprising the following steps:

[0034] S1. The salt mud produced by the two-alkali method is dried and calcined to obtain a mixture of calcium oxide and magnesium oxide; wherein the main components of the salt mud produced by the two-alkali method are calcium carbonate and magnesium hydroxide.

[0035] S2. Add water to the mixture and digest it at room temperature to obtain a calcium-magnesium digest slurry;

[0036] S3. Add magnesium sulfate solution to the calcium-magnesium digest slurry and mix well to obtain the precursor;

[0037] S4. The precursor is transferred to a high-pressure reactor for hydrothermal crystallization reaction, and then cooled, filtered and dried to obtain calcium-magnesium composite whiskers; wherein the calcium-magnesium composite whiskers are composite whiskers composed of anhydrous calcium sulfate whiskers and 513 type basic magnesium sulfate whiskers.

[0038] In one specific implementation, in step S1, the salt mud obtained through the two-alkali method is well-mining salt mud.

[0039] In one specific implementation scheme, the main components of the above-mentioned well salt mud, by weight percentage (dry basis), are: CaCO3 51.0-59.0%, Mg(OH)2 39-47%, Fe(OH)3 0.01-0.02%, Al(OH)3 0.02-0.03%, NaCl 1.0-1.2%, and CaSO4 0.65-0.95%.

[0040] In one specific implementation, in step S1, the drying process specifically involves drying at 100-110°C for 5-10 hours.

[0041] In one specific implementation, step S1, the calcination specifically involves heating from room temperature to 750-1000℃ at a heating rate of 5-15℃ / min and holding at that temperature for 1-8 hours.

[0042] In one specific implementation, in step S2, the mass ratio of the mixture to water is 1:10-50; the time for room temperature pulping and digestion is 30-120 min.

[0043] In one specific implementation, in step S3, the concentration of the magnesium sulfate solution is 0.4–0.8 mol / L.

[0044] In one specific implementation, in step S3, the ratio of the total amount of calcium oxide and magnesium oxide in the calcium-magnesium digest slurry to the amount of magnesium sulfate in the magnesium sulfate solution is 1:0.6-1.5.

[0045] In one specific implementation, in step S4, the temperature of the hydrothermal crystallization reaction is 180–220°C, and the time is 6–48 hours.

[0046] In one specific implementation, in step S4, the drying temperature is 80°C and the time is 6-12 hours.

[0047] The present invention also provides calcium-magnesium composite whiskers prepared by any of the above methods.

[0048] The following examples and comparative models further illustrate this point.

[0049] Example 1

[0050] A method for producing calcium-magnesium composite whiskers using alkali-alkali process salt mud includes the following steps:

[0051] (1) The salt mud from the two-alkali process was dried at 105℃ for 8 hours, and then placed in a muffle furnace at room temperature. The heating rate was 10℃ / min, and the temperature was held at 800℃ for 2 hours to obtain a mixture of calcium oxide and magnesium oxide (solid). The salt mud from the two-alkali process was well salt mud, and the main components by weight percentage (dry basis) were: CaCO3 58.3%, Mg(OH)2 40.0%, Fe(OH)3 0.01%, Al(OH)3 0.02%, NaCl 1.0%, and CaSO4 0.67%.

[0052] (2) Take 15 grams of the mixture of calcium oxide and magnesium oxide from (1), add 500 ml of water, and digest at room temperature for 60 minutes to obtain calcium and magnesium digestion slurry;

[0053] (3) Mix the calcium and magnesium digest slurry from (2) with 500 ml of magnesium sulfate aqueous solution (0.6 M) and stir until homogeneous to obtain the precursor;

[0054] (4) The precursor in (3) is transferred to a high-pressure reactor for hydrothermal crystallization reaction at a temperature of 190°C for 24 hours. Then it is cooled to room temperature, filtered, and the filter cake is dried at a temperature of 80°C for 12 hours to obtain calcium-magnesium composite whiskers.

[0055] The calcium-magnesium whiskers prepared above were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the results are as follows: Figure 1-2 As shown. By Figure 1 It can be seen that the calcium-magnesium composite whiskers prepared in Example 1 of this invention are composed of anhydrous calcium sulfate and type 513 basic magnesium sulfate, and contain no impurities. Figure 2 As can be seen, the calcium-magnesium composite whiskers prepared in Example 1 of the present invention have a regular morphology, are fibrous, without fractures, with a length of about 300 μm, a diameter of about 3 μm, and an aspect ratio of about 100.

[0056] Example 2

[0057] The difference between this embodiment and Embodiment 1 is that the temperature of the hydrothermal crystallization reaction in step (4) is 210°C and the time is 12 hours. Other steps and parameters are the same as in Embodiment 1.

[0058] Example 3

[0059] The difference between this embodiment and Embodiment 1 is that the heating rate in step (1) is 10℃ / min, the temperature is raised to 1000℃, and held for 2 hours. Other steps and parameters are the same as in Embodiment 1.

[0060] Example 4

[0061] The difference between this embodiment and Example 1 is as follows: (2) Take 20 grams of the mixture of calcium oxide and magnesium oxide from (1), add 200 ml of water, and digest at room temperature for 120 min to obtain a calcium-magnesium digestion slurry; (3) Mix the calcium-magnesium digestion slurry from (2) with 800 ml of magnesium sulfate aqueous solution (0.5 M) and stir evenly to obtain the precursor. Other steps and parameters are the same as in Example 1.

[0062] Comparative Example 1

[0063] The difference between this comparative example and Example 1 is that the calcination temperature in step (1) is 700°C. Other steps and parameters are the same as in Example 1.

[0064] In this comparative example, step (1) yields a mixture of calcium oxide, magnesium oxide, and undecomposed calcium carbonate; step (4) yields anhydrous calcium sulfate whiskers, 513 type basic magnesium sulfate whiskers, and undecomposed calcium carbonate particles.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that the concentration of magnesium sulfate in step (3) is 0.3M. Other steps and parameters are the same as in Example 1.

[0067] The final product obtained in step (4) of this comparative example is anhydrous calcium sulfate whiskers and magnesium hydroxide particles.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 1 is that the hydrothermal crystallization reaction temperature in step (4) is 160°C. Other steps and parameters are the same as in Example 1.

[0070] The final product obtained in step (4) of this comparative example is calcium sulfate hemihydrate whiskers, magnesium hydroxide particles, and a small amount of 513 type basic magnesium sulfate whiskers.

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for producing calcium-magnesium composite whiskers using salt mud produced by the two-alkali process, characterized in that, Includes the following steps: S1. The salt mud produced by the two-alkali method is dried and calcined to obtain a mixture of calcium oxide and magnesium oxide; wherein the main components of the salt mud produced by the two-alkali method are calcium carbonate and magnesium hydroxide; wherein the calcination is specifically carried out by heating from room temperature to 750-1000 ℃ at a heating rate of 5-15 ℃ / min and holding at that temperature for 1-8 hours. S2. Add water to the mixture and digest it at room temperature to obtain a calcium-magnesium digest slurry; S3. Add magnesium sulfate solution to the calcium-magnesium digest slurry and mix well to obtain the precursor; wherein the concentration of the magnesium sulfate solution is 0.4~0.8 mol / L; S4. The precursor is transferred to a high-pressure reactor for hydrothermal crystallization reaction, followed by cooling, filtration, and drying to obtain calcium-magnesium composite whiskers; wherein the calcium-magnesium composite whiskers are composite whiskers composed of anhydrous calcium sulfate whiskers and 513 type basic magnesium sulfate whiskers; wherein the temperature of the hydrothermal crystallization reaction is 180~220 ℃ and the time is 6~48 h.

2. The method for producing calcium-magnesium composite whiskers using salt mud produced by the two-alkali process according to claim 1, characterized in that, In step S1, the salt mud obtained through the two-alkali method is well-mining salt mud.

3. The method for producing calcium-magnesium composite whiskers using salt mud produced by the two-alkali process according to claim 1, characterized in that, In step S1, the drying process specifically involves drying at 100-110 ℃ for 5-10 h.

4. The method for producing calcium-magnesium composite whiskers using salt mud produced by the two-alkali process according to claim 1, characterized in that, In step S2, the mass ratio of the mixture to water is 1:10-50; the time for room temperature pulping and digestion is 30-120 min.

5. The method for producing calcium-magnesium composite whiskers using salt mud produced by the two-alkali process according to claim 1, characterized in that, In step S3, the ratio of the total amount of calcium oxide and magnesium oxide in the calcium-magnesium digest slurry to the amount of magnesium sulfate in the magnesium sulfate solution is 1:0.6-1.

5.

6. The method for producing calcium-magnesium composite whiskers using salt mud produced by the two-alkali process according to claim 1, characterized in that, In step S4, the drying temperature is 80 ℃ and the time is 6-12 h.

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