Method for producing calcium-magnesium composite crystal whiskers by using two-alkali salty mud

Abstract

The invention discloses a method for producing calcium-magnesium composite whiskers by using two-alkali-process salty mud, which comprises the following steps: drying and roasting the two-alkali-process salty mud to obtain a mixture of calcium oxide and magnesium oxide; adding water into the mixture, and pulping and digesting at room temperature to obtain calcium-magnesium digested slurry; adding a magnesium sulfate solution into the calcium magnesium digestion slurry, and uniformly mixing to obtain a precursor; and transferring the precursor to a high-pressure reaction kettle, carrying out hydrothermal crystallization reaction, cooling, filtering, and drying to obtain the calcium-magnesium composite whisker. When the two-alkali method salty mud is used as a raw material, the salty mud does not need to be cleaned in advance, and trace soluble NaCl in the salty mud is fully utilized to serve as a whisker regulator; meanwhile, the two element components of calcium and magnesium in the two-alkali-process salty mud are effectively utilized, the calcium-magnesium composite whisker product with economic value is obtained, and an economic and effective way is provided for comprehensive utilization of the two-alkali-process salty mud; the method has the advantages of short process, simplicity in operation, low equipment requirement, low treatment cost, easiness in industrialization and the like.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection and solid waste resource utilization, and in particular to a method for producing calcium-magnesium composite whiskers by utilizing salt mud in a two-alkali process. Background Art

[0002] The purpose of brine purification is to remove the Ca 2+ Mg 2+ The ions are separated before entering the heating chamber. Brine is generally purified by the "two-alkali method" and other methods. After the reaction, flocculants are added to accelerate the separation of sediments. The supernatant is product-grade brine, and the sediment in the reaction barrel is salt mud. The two-alkali brine purification method uses caustic soda (NaOH) to remove Mg in the brine. 2+ , remove it with Mg(OH)2 precipitation, and use soda ash (NaCO3) to remove the Ca in the brine 2+ It is removed as CaCO3 precipitation. Salt sludge from the two-alkali process is primarily composed of calcium carbonate and magnesium hydroxide, with a small amount of NaCl. Currently, simple landfilling and stockpiling fail to effectively utilize the calcium and magnesium resources in salt sludge. Researching and developing appropriate industrially applicable salt sludge treatment technologies is a common technical challenge faced by all domestic salt production companies.

[0003] Anhydrous calcium sulfate whiskers possess excellent properties, including high strength, high modulus, high toughness, wear resistance, high temperature resistance, and excellent 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 directly used as filter materials, thermal insulation materials, fire-resistant insulation materials, infrared reflective materials, and high-insulation materials for wire coating. Basic magnesium sulfate whiskers are a powder with a chemical composition of xMg(OH)2·yMgSO4·nH2O (xyz type), with common types such as 513 type 5Mg(OH)2·MgSO4·3H2O. Basic magnesium sulfate whiskers not only exhibit excellent flame retardancy, but also possess high toughness, wear resistance, heat resistance, high strength, low density, and a high elastic modulus. They can improve the flame retardancy of products while also enhancing mechanical properties such as wear resistance, strength, and elasticity. They have broad application prospects in heat-resistant and wear-resistant parts in automobiles and machinery, as well as plastics, rubber, friction materials, and cement.

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

[0005] Composite whiskers composed of anhydrous calcium sulfate whiskers and 513-type 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 deformation temperature) through complementary performance (anhydrous calcium sulfate whiskers provide low cost, high toughness and fluidity, 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, and the composite reduces material costs by more than 20%, and is non-toxic and biodegradable). Development prospects focus on three major areas: lightweighting of automobiles (replacing glass fiber reinforced plastic components to improve impact resistance); biomedicine (using osteoconductivity and biocompatibility to develop degradable implants); and green building materials (improving fire resistance and reducing cement usage by 30% to reduce carbon emissions). Currently, it is necessary to overcome the bottlenecks of co-modification technology and large-scale production, relying on regional resources (such as Shandong gypsum mines) and technology clusters to seize the high-end market, with a potential scale exceeding 5 billion yuan (2027).

[0006] The preparation method of the composite whisker that existing anhydrous calcium sulfate whisker and 513 type basic magnesium sulfate whiskers are composed is based on low-cost raw materials (concentrated seawater, gypsum), solves twin whisker-matrix compatibility problem by surface collaborative modification and step-by-step composite process (melt blending / in-situ polymerization), and introduces directional dispersion technology to promote enhanced efficiency. That is, complicated steps cause energy consumption high, long cycle, whisker fracture, modifier (such as silane) residual possible environmental pollution, and recycling technology is immature. Therefore, the composite whisker that anhydrous calcium sulfate whisker and 513 type basic magnesium sulfate whiskers are composed has merged the advantage of two kinds of whiskers, can be widely used in the fields such as resin, plastics, rubber, friction, cement, and has broad market prospects.

[0007] Two-alkali salt mud primarily contains calcium carbonate and magnesium hydroxide, providing the calcium and magnesium chemical components needed to produce calcium sulfate whiskers and basic magnesium sulfate whiskers. Using two-alkali salt mud as raw material to produce calcium magnesium whiskers not only significantly reduces solid waste from the two-alkali process, reducing storage costs and improving the environment, but also enables high-value-added utilization of the two-alkali salt mud, turning waste into treasure, in line with a green, circular, and sustainable development strategy.

[0008] At present, some research on the preparation of whiskers using salt mud has been carried out at home and abroad. For example, "Chlor-alkali Salt Mud Whiskers Production" (Chlor-Alkali Industry, 2013, 49 (11): 41-42) reported a method for producing whiskers from chlor-alkali salt mud. The process is as follows: in the first step, industrial hydrochloric acid dissolves the salt mud to obtain a clear solution of CaCl2, MgCl2, and sodium salt; in the second step, sulfuric acid is added to make CaCl2, MgCl2, and sodium salt. 2+A CaSO4 precipitate is formed, and limestone milk is added to the clear solution obtained by separating the precipitate to obtain a Mg(OH)2 precipitate. In the third step, the obtained CaSO4 precipitate is hydrothermally synthesized into calcium sulfate whiskers by adding a crystallizing agent. In the fourth step, the magnesium sulfate and magnesium hydroxide precipitates are reacted in an autoclave to obtain basic magnesium sulfate whiskers. Patent No. CN 115074815 B discloses a method for preparing calcium sulfate dihydrate whiskers at room temperature using brine salt production byproducts as raw materials. The method utilizes salt mud and high nitrate water generated during the sodium sulfate brine salt production process as raw materials. The solution obtained by acidifying the salt mud and high nitrate water is reacted at room temperature to produce calcium sulfate dihydrate whiskers. The filtrate after the reaction is returned to the brine for salt production. Patent number CN 113668060 B discloses a process for continuously preparing hemihydrate and dihydrate calcium sulfate whiskers using salt mud. The process involves using salt mud as the raw material, adding dilute hydrochloric acid to dissolve and filter the resulting salt mud acid extract, which is then diluted and heated with an equal volume of sodium sulfate. After whisker growth is complete, the extract is filtered, washed, and dried to obtain hemihydrate calcium sulfate whiskers. The filtrate is then placed in an insulated container for aging, cooled, filtered, washed, and dried to obtain dihydrate calcium sulfate whiskers. Patent number CN113089076B discloses a method for preparing calcium sulfate whiskers based on chlor-alkali salt mud. The mud is dried, crushed, and washed to obtain a salt mud suspension. The calcium ions in the mud are then dissolved by acid washing. Pretreatment to remove impurities, and the addition of calcium sulfate seeds and sulfuric acid converts the calcium ions into high-purity calcium sulfate whiskers. Patent No. CN113186591 B discloses a method for preparing calcium sulfate hemihydrate whiskers using lime flue gas process salt mud. The method comprises the following steps: first, waste hydrochloric acid and lime flue gas process salt mud are stirred and reacted at room temperature; then, the reaction system is filtered; and then, the filtrate is reacted with equimolar and equal-volume dilute sulfuric acid under normal pressure to prepare calcium sulfate hemihydrate whiskers. In summary, the common process scheme for preparing whiskers using salt mud is to first dissolve the salt mud with acid to obtain calcium and magnesium ion solutions, and then obtain calcium sulfate whiskers and magnesium whiskers respectively. The disadvantage of this process scheme is that it requires the consumption of a large amount of hydrochloric acid or sulfuric acid to acidify the salt mud, which greatly increases production costs. In addition, the process flow is long, which is not conducive to industrial application.

[0009] Therefore, the technical problem to be solved by the present invention is how to fully utilize the two elemental components of calcium and magnesium in the two-alkali process salt mud without adding acid dissolution and whisker regulators, and realize a short process to prepare 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 salt mud from a two-alkali process. When the salt mud from the two-alkali process is used as a raw material, the method does not require pre-cleaning, and fully utilizes the trace soluble NaCl in the salt mud to act as a whisker regulator. At the same time, the two elemental components of calcium and magnesium in the salt mud from the two-alkali process are effectively utilized to obtain a calcium-magnesium composite whisker product with economic value, providing an economical and effective way for the comprehensive utilization of salt mud from the two-alkali process. The method of the present invention can achieve a short production process flow, simple operation, low equipment requirements, low processing cost, and easy industrialization.

[0011] In order to achieve the above object, the present invention provides a method for producing calcium-magnesium composite whiskers using salt mud of a two-alkali process, comprising the following steps:

[0012] S1. Drying and roasting the two-alkali process salt mud to obtain a mixture of calcium oxide and magnesium oxide; wherein the main components of the two-alkali process salt mud are calcium carbonate and magnesium hydroxide;

[0013] S2. adding water to the mixture and beating and digesting at room temperature to obtain calcium and magnesium digestion slurry;

[0014] S3, adding magnesium sulfate solution to the calcium-magnesium digestion slurry and mixing them to obtain a precursor;

[0015] S4. Transferring the precursor to a high-pressure reactor to perform a hydrothermal crystallization reaction, and then cooling, filtering, 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.

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

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

[0018] According to one aspect of the present invention, in step S1, the calcination is specifically: heating from room temperature to 750-1000°C at a heating rate of 5-15°C / min and keeping the 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 pulping and digesting at room temperature is 30-120 min.

[0020] According to one aspect of the present invention, in step S3, the concentration of the magnesium sulfate solution is 0.4-0.8 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 digestion 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 hours.

[0023] According to one aspect of the present invention, in step S4, the drying temperature is 80° C. and the drying 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] Beneficial effects of the present invention:

[0026] (1) The present invention proposes for the first time to utilize the two-alkali salt mud generated during the brine purification process to prepare composite whiskers consisting of anhydrous calcium sulfate whiskers and 513 type basic magnesium sulfate 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 policies on energy conservation, emission reduction, and green environmental protection.

[0027] (2) The present invention directly utilizes the two-alkali salt mud produced during the brine purification process as the raw material for the reaction. There is no need to perform additional water washing or acid treatment on the salt mud, and there is no need to add additives such as a crystal conversion agent and a crystal form promoter. Instead, a small amount of NaCl present in the salt mud itself can be used as a calcium sulfate whisker growth promoter, and the salt mud is subjected to a one-step method of roasting and hydrothermal crystallization reaction with a magnesium sulfate solution to obtain mixed whiskers, thereby reducing the content of impurities in the solution and facilitating the subsequent washing treatment of the whiskers.

[0028] (3) The method of the present invention has the advantages of simple process, green environmental protection, no need for complex and expensive equipment, simple structure, low energy consumption, energy saving and emission reduction, protection of natural resources, and the 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, and are free of impurities; and the calcium-magnesium composite whiskers have a regular morphology, are fibrous, and are not broken. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the XRD pattern of the composite whisker prepared in Example 1 of the present invention;

[0031] Figure 2 This is an SEM image of the composite whisker prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] To make the present invention easier to understand, the present invention is further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professional and technical personnel in this field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0033] In order to solve the problems in the prior art such as the need for acid dissolution and the lack of addition of whisker regulators, as well as the long preparation process and low product quality due to added impurities, the present inventors provide a method for producing calcium-magnesium composite whiskers using salt mud using a two-alkali process, comprising the following steps:

[0034] S1. Drying and roasting the two-alkali process salt mud to obtain a mixture of calcium oxide and magnesium oxide; wherein the main components of the two-alkali process salt mud are calcium carbonate and magnesium hydroxide;

[0035] S2. adding water to the mixture and beating and digesting at room temperature to obtain calcium and magnesium digestion slurry;

[0036] S3, adding magnesium sulfate solution to the calcium-magnesium digestion slurry and mixing them to obtain a precursor;

[0037] S4. Transferring the precursor to a high-pressure reactor to perform a hydrothermal crystallization reaction, and then cooling, filtering, 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.

[0038] In a specific embodiment, in step S1, the two-alkali process salt mud is well salt mud.

[0039] In a specific embodiment, the main components of the above-mentioned well salt mud are as follows by weight percentage (calculated on a dry basis): 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 a specific embodiment, in step S1, the drying is specifically: drying at 100-110° C. for 5-10 h.

[0041] In a specific embodiment, in step S1, the calcination is specifically: heating from room temperature to 750-1000°C at a heating rate of 5-15°C / min and keeping the temperature for 1-8 hours.

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

[0043] In a specific embodiment, in step S3, the concentration of the magnesium sulfate solution is 0.4-0.8 mol / L.

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

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

[0046] In a specific embodiment, in step S4, the drying temperature is 80° C. and the drying 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 is further described with reference to specific embodiments and comparative examples.

[0049] Example 1

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

[0051] (1) The salt mud obtained by the two-alkali process is dried at 105°C for 8 hours, and then placed in a muffle furnace at room temperature, heated at a rate of 10°C / min, and kept at 800°C for 2 hours to obtain a mixture (solid) of calcium oxide and magnesium oxide; wherein the salt mud obtained by the two-alkali process is well salt mud, and the main components are as follows by weight percentage (calculated on a dry basis): CaCO3 58.3%, Mg(OH)2 40.0%, Fe(OH)30.01%, Al(OH)30.02%, NaCl 1.0%, and CaSO4 0.67%.

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

[0053] (3) The calcium-magnesium digestion slurry in (2) was mixed and stirred evenly with 500 ml of a 0.6 M magnesium sulfate aqueous solution to obtain a precursor;

[0054] (4) The precursor in (3) was transferred to a high-pressure reactor for hydrothermal crystallization reaction at a temperature of 190°C for 24 hours, and then cooled to room temperature, filtered, and the filter cake was 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). Figure 1-2 As shown. Figure 1 It can be seen that the calcium magnesium composite whiskers prepared in Example 1 of the present invention are composed of anhydrous calcium sulfate and 513 type basic magnesium sulfate, and are free of impurities. Figure 2 It can be seen that the calcium-magnesium composite whiskers prepared in Example 1 of the present invention have regular morphology, are fibrous, have no breaks, are about 300 μm in length, about 3 μm in diameter, and have 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 h. The other steps and parameters are the same as those 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°C / min, the temperature is raised to 1000°C, and the temperature is kept at this temperature for 2 hours. The other steps and parameters are the same as those in embodiment 1.

[0060] Example 4

[0061] The differences between this example and Example 1 are as follows: (2) 20 g of the mixture of calcium oxide and magnesium oxide in (1) was added to 200 ml of water and slurried and digested at room temperature for 120 min to obtain a calcium-magnesium digestion slurry; (3) the calcium-magnesium digestion slurry in (2) was mixed and stirred evenly with 800 ml of a 0.5 M magnesium sulfate aqueous solution to obtain a precursor. The other steps and parameters were 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. The other steps and parameters are the same as those in Example 1.

[0064] In this comparative example, step (1) obtains a mixture of calcium oxide, magnesium oxide and undecomposed calcium carbonate; and the final product obtained in step (4) is 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 0.3 M. The other steps and parameters are the same as those in Example 1.

[0067] The final products obtained in step (4) of this comparative example are 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. The 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 changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for producing calcium magnesium composite whiskers using salt mud using a two-alkali process, characterized in that: The following steps are involved: S1. Drying and roasting the two-alkali process salt mud to obtain a mixture of calcium oxide and magnesium oxide; wherein the main components of the two-alkali process salt mud are calcium carbonate and magnesium hydroxide; S2. adding water to the mixture and beating and digesting at room temperature to obtain calcium and magnesium digestion slurry; S3, adding magnesium sulfate solution to the calcium-magnesium digestion slurry and mixing them to obtain a precursor; S4. Transferring the precursor to a high-pressure reactor to perform a hydrothermal crystallization reaction, and then cooling, filtering, 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.

2. The method for producing calcium-magnesium composite whiskers using two-alkali salt mud according to claim 1, wherein: In step S1, the two-alkali method salt mud is well salt mud.

3. The method for producing calcium-magnesium composite whiskers using two-alkali salt mud according to claim 1, characterized in that: In step S1, the drying is specifically: drying at 100-110° C. for 5-10 hours.

4. The method for producing calcium-magnesium composite whiskers using two-alkali salt mud according to claim 1, characterized in that: In step S1, the calcination is specifically as follows: heating from room temperature to 750-1000°C at a heating rate of 5-15°C / min and keeping the temperature for 1-8 hours.

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

6. The method for producing calcium-magnesium composite whiskers using two-alkali salt mud according to claim 1, characterized in that: In step S3, the concentration of the magnesium sulfate solution is 0.4-0.8 mol / L.

7. The method for producing calcium-magnesium composite whiskers using two-alkali salt mud 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 digestion slurry to the amount of magnesium sulfate in the magnesium sulfate solution is 1:0.6-1.

5.

8. The method for producing calcium-magnesium composite whiskers using two-alkali salt mud according to claim 1, characterized in that: In step S4, the temperature of the hydrothermal crystallization reaction is 180-220° C., and the time is 6-48 hours.

9. The method for producing calcium-magnesium composite whiskers using two-alkali salt mud according to claim 1, characterized in that: In step S4, the drying temperature is 80° C. and the drying time is 6-12 hours.

10. A calcium-magnesium composite whisker prepared by the method according to any one of claims 1 to 9.

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