Preparation method and application of rod-like nanometer calcium carbonate

Abstract

The application belongs to the field of calcium carbonate materials, and particularly relates to a preparation method and application of rod-shaped nanometer calcium carbonate, the preparation method comprising: pretreatment, precursor treatment, carbonization reaction, separation and purification, and post-treatment. The application greatly reduces the preparation cost by optimizing the preparation process, and the obtained rod-shaped nanometer calcium carbonate has stable structure, a stable length-diameter ratio of 15-20:1, and good dispersibility, can greatly reduce the thermal conductivity, is applied to thermal insulation waterproof materials, and has remarkable economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of calcium carbonate materials, specifically relating to a method for preparing and applying rod-shaped nano-calcium carbonate, and more specifically to a method for preparing and applying rod-shaped nano-calcium carbonate that can meet the requirements of thermal insulation materials. Background Technology

[0002] Calcium carbonate is a tasteless, odorless, white solid inorganic compound that has seen rapid development in recent years. It comes in a wide variety of specifications and types and is widely used in rubber, plastics, papermaking, inks, cosmetics, and many other fields. Calcium carbonate exists in various morphologies, including cubic, spherical, needle-shaped, and rod-shaped forms, each with its unique properties. Different industries have different requirements for the morphology, particle size, and surface properties of calcium carbonate. For example, rod-shaped nano-calcium carbonate, due to its unique structure, possesses a variety of excellent properties, such as reinforcement and toughening, high oil absorption, adsorption, desorption, grinding, aroma retention, and slow-release properties, and is attracting increasing attention in many fields.

[0003] Currently, the preparation process of rod-shaped nano-calcium carbonate is becoming increasingly mature. The most commonly used method is to obtain it by calcining limestone into calcium oxide, then making calcium hydroxide emulsion, and finally reacting it with carbon dioxide. This process requires high-temperature calcination, which is energy-intensive. If the emitted carbon dioxide is not recovered and utilized, it can easily cause the greenhouse effect, which is not environmentally friendly. At the same time, because the reaction conditions are relatively complex, if not properly controlled, it can easily result in a wide particle size distribution and poor dispersibility. In addition, ordinary rod-shaped calcium carbonate has poor hydrophobicity, which makes it difficult to meet the performance requirements of some thermal insulation and waterproof materials for dispersing fillers. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method for preparing rod-shaped nano-calcium carbonate and its application. The rod-shaped nano-calcium carbonate obtained by the preparation method has an aspect ratio between 15 and 20:1, good dispersibility, and can be applied to thermal insulation and waterproof materials, exhibiting excellent low thermal conductivity and waterproof performance.

[0005] To achieve the above objectives, the present invention provides a method for preparing rod-shaped nano-calcium carbonate, comprising the following steps:

[0006] S1. Pretreatment: The desulfurization gypsum from the power plant is mixed with deionized water at a solid-liquid volume ratio of 1:3-5 kg / L. After ball milling, a pH adjuster is added to adjust the pH to 6.5-7.5, and then the mixture is centrifuged to obtain calcium slurry. The filtrate is treated to meet the standards before being discharged.

[0007] S2. Precursor treatment: Mix the calcium slurry obtained in S1 with deionized water at a volume ratio of 1:6-8, add a composite dispersant, and sonicate for 15-20 minutes to obtain the precursor colloid.

[0008] S3. Carbonation reaction: Adjust the pH of the precursor colloid to 9-11 with a pH adjuster, introduce CO2 gas into the precursor colloid, heat to 40-60℃, start ultrasonication and stir for 20-30 minutes, then continue to introduce CO2 gas until the pH is 6-7, add crystallization regulator, and use microwave intermittent heating treatment for 2-3 hours to form rod-shaped calcium carbonate slurry;

[0009] S4. Separation and purification: Centrifuge the rod-shaped calcium carbonate slurry, add sodium carboxymethyl cellulose and mix evenly, wash with ethanol 2-3 times, and vacuum dry at 50-60℃ for 5-8 hours to obtain rod-shaped calcium carbonate powder.

[0010] S5. Post-processing: The rod-shaped calcium carbonate powder obtained in S4 is ball-milled and mixed with silane coupling agent, and dried at 70-80℃ for 2-3 hours to obtain the final product.

[0011] This invention uses desulfurization gypsum from power plants as a calcium source, eliminating the need for calcination, thus reducing energy consumption. It also enables the resource utilization of solid waste, produces no carbon dioxide emissions, lowers production costs, and is more environmentally friendly. By mixing the calcium source with a composite dispersant to form a precursor colloid, calcium slurry agglomeration is prevented, providing a stable system for subsequent carbonization reactions. Through staged CO2 gas introduction and a combination of ultrasound and microwaves, the uniform distribution of crystal nuclei is first promoted at a higher pH through ultrasonic cavitation, and then accelerated at a lower pH through microwave directional heating. 2+ With CO3 2- Combined with the effect of crystallization regulator, longitudinal growth is promoted, achieving precise control of aspect ratio; by introducing sodium carboxymethyl cellulose into calcium carbonate during the purification process to improve its hydrophobicity, and then ball milling and mixing it with silane coupling agent, its hydrophobicity is further improved, and its dispersion performance in the matrix can also be improved.

[0012] Furthermore, in the above technical solution S1, after ball milling, the particle size of the power plant desulfurization gypsum is ≤40μm.

[0013] Further, in the above technical solution S2, the composite dispersant is a mixture of sodium citrate and sodium lignosulfonate in a 1-2:1 ratio, and the amount used is 1-5% of the total mass of the precursor colloid; the power of the ultrasonic treatment is 300-350W. Sodium lignosulfonate is an anionic surfactant containing a large number of sulfonic acid groups, hydroxyl groups, and other functional groups in its molecule. It can effectively disperse nanoparticles and prevent aggregation through electrostatic repulsion and steric hindrance effects, but its viscosity is relatively high. Sodium citrate is easily soluble in water, and mixing it with sodium lignosulfonate can play a certain dilution role, improving its fluidity. At the same time, it can effectively chelate Ca in the solution. 2+This reduces the interference of free ions on the crystallization process, helps form uniform crystal nuclei, and plays an auxiliary role in subsequent nucleation reactions. In this technical solution, sodium lignin sulfonate provides a strong negative charge through its sulfonic acid groups, while the carboxylic acid groups of sodium citrate further enhance charge repulsion. Simultaneously, the lignin macromolecular chains form a physical barrier, and the two work synergistically to improve dispersion efficiency. Furthermore, both play a role in crystallization and morphology regulation during the subsequent formation of rod-shaped calcium carbonate.

[0014] Furthermore, in the above technical solution S3, the power of the ultrasonic wave is 150-200W; the CO2 flow rate is 0.5-1.5L / min. In this invention, using higher ultrasonic power in the precursor colloidal stage is beneficial for system dispersion, while using lower ultrasonic power in the nucleation stage is beneficial for crystal nucleus formation and uniform distribution.

[0015] Furthermore, in the above technical solution S3, the crystallization regulator is polyvinylpyrrolidone, and the amount used is 0.1-0.3% of the total mass of the precursor colloid. In this technical solution, the use of a small amount of crystal form regulator can further interfere with the crystal face growth rate, thereby promoting the formation of rod-shaped calcium carbonate.

[0016] Furthermore, in the above technical solution S3, the microwave frequency of the intermittent microwave heating treatment is 915MHz, and the intermittent heating frequency is 2-5 minutes of heating followed by 2-5 minutes of intermittent heating. Microwaves are electromagnetic waves with wave characteristics such as reflection, transmission interference, diffraction, polarization, and energy transmission. The principle of intermittent microwave heating is to utilize the electromagnetic waves generated by a microwave generator to penetrate the interior of the material, interacting with the molecules to cause high-speed rotation and friction, achieving rapid and uniform heating, reducing agglomeration, and improving dispersibility. Simultaneously, intermittent treatment can prevent agglomeration or interference with crystal growth due to excessively high local temperatures caused by continuous heating. This invention uses 915MHz microwave intermittent heating treatment, which has a greater penetration depth, not only achieving rapid and uniform heating and promoting the reaction between calcium ions and carbonate ions, but also reducing agglomeration caused by local overheating. This provides conditions for the preferential growth of calcium carbonate crystals along a specific direction, which is beneficial for the formation of rod-shaped calcium carbonate.

[0017] Furthermore, in the above technical solution S4, the centrifugation speed is 4000-5000 rpm and the time is 10-20 min; the amount of sodium carboxymethyl cellulose added is 0.5-1% of the mass of the rod-shaped calcium carbonate slurry.

[0018] Furthermore, in the above technical solution S5, the mass ratio of the rod-shaped calcium carbonate powder to the silane coupling agent is 1:0.1-0.3; the silane coupling agent is KH-550. In this technical solution, the final surface coating of the rod-shaped nano-calcium carbonate with the silane coupling agent not only reduces interfacial defects between it and the insulation matrix when used in insulation materials, but also provides a moisture barrier effect to prevent moisture from damaging the insulation performance due to its high thermal conductivity. Simultaneously, it improves its uniform dispersion and reduces agglomeration.

[0019] Furthermore, in the above technical solution, the aspect ratio of the rod-shaped nano-calcium carbonate product is 15-20:1.

[0020] The present invention also provides an application of rod-shaped nano-calcium carbonate prepared by the above preparation method in thermal insulation and waterproof materials.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention uses desulfurized gypsum from power plants as a calcium source, eliminating the need for traditional limestone calcination, thus reducing energy consumption. It also enables the resource utilization of solid waste, with no carbon dioxide emissions, reducing production costs and being more environmentally friendly. It uses natural sodium lignosulfonate as a dispersant, resulting in low cost. It employs microwave interval heating, which has high heating efficiency and low energy consumption.

[0023] 2. This invention optimizes the preparation process by combining ultrasonic, microwave, and mechanical stirring multi-coupling technologies to effectively promote uniform distribution of crystal nuclei and accelerate the combination of calcium and carbonate ions, resulting in higher efficiency. Simultaneously, the phased introduction of carbon dioxide to control the pH of the system in a stepwise manner effectively induces the growth of rod-shaped crystals. Combined with a small amount of crystallization regulator, precise control of the aspect ratio is achieved. Adding a composite dispersant in the early stages to mix the calcium slurry into a precursor colloid prevents calcium slurry agglomeration, providing a stable system for subsequent carbonation reactions and also playing a role in crystallization and morphology regulation. Subsequently, the purification and post-treatment processes involve dual modification with sodium carboxymethyl cellulose and silane coupling agents, improving the hydrophobic properties of calcium carbonate and its dispersibility in the substrate.

[0024] 3. This invention significantly reduces the preparation cost by optimizing the preparation process. Moreover, the resulting rod-shaped nano-calcium carbonate has a stable structure with a length-to-diameter ratio of 15-20:1. When used in thermal insulation and waterproof material systems, it exhibits good dispersibility, which can greatly reduce the thermal conductivity and improve the thermal insulation and waterproof effect. Detailed Implementation

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the raw materials used in the following examples are all commercially available products and can be purchased from the market.

[0026] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions.

[0027] The desulfurization gypsum used in this invention has a calcium sulfate dihydrate content of over 90%. The pH adjuster used is hydrochloric acid for acidity and ammonia for alkalinity.

[0028] Example 1

[0029] A method for preparing rod-shaped nano-calcium carbonate includes the following steps:

[0030] S1. Pretreatment: Power plant desulfurization gypsum and deionized water are mixed at a solid-liquid volume ratio of 1:3 kg / L. After ball milling until the particle size is ≤40μm, pH adjuster is added to adjust the pH to 7, and then centrifuged to obtain calcium slurry.

[0031] S2. Precursor treatment: The calcium slurry obtained in S1 is mixed with deionized water at a volume ratio of 1:6, a composite dispersant is added, and the mixture is ultrasonically treated (power 300W) for 20 minutes to obtain the precursor colloid; wherein, the composite dispersant is a 1:1 mixture of sodium citrate and sodium lignosulfonate, and the amount used is 1% of the total mass of the precursor colloid;

[0032] S3. Carbonation reaction: Adjust the pH of the precursor colloid to 11 using a pH adjuster. Introduce CO2 gas into the precursor colloid at a rate of 0.5 L / min, raise the temperature to 40°C, start ultrasonication (150 W power), and stir for 30 min. Then continue introducing CO2 gas at a rate of 0.5 L / min until the pH reaches 7. Add a crystallization regulator, mix thoroughly, and then treat with microwave intermittent heating for 3 h (microwave frequency 915 MHz, 3 min heating intervals followed by 3 min intervals) to form rod-shaped calcium carbonate slurry. The crystallization regulator is polyvinylpyrrolidone, and the amount used is 0.3% of the total mass of the precursor colloid.

[0033] S4. Separation and purification: The rod-shaped calcium carbonate slurry was centrifuged at 4000 rpm for 20 min, and 0.5% sodium carboxymethyl cellulose by weight of the rod-shaped calcium carbonate slurry was added and mixed evenly. The mixture was then washed three times with ethanol and dried under vacuum at 50℃ for 8 h to obtain rod-shaped calcium carbonate powder.

[0034] S5. Post-processing: The rod-shaped calcium carbonate powder obtained in S4 is mixed with KH-550 at a mass ratio of 1:0.3, ball-milled, and dried at 70℃ for 3 hours to obtain the final product.

[0035] Example 2

[0036] A method for preparing rod-shaped nano-calcium carbonate includes the following steps:

[0037] S1. Pretreatment: Power plant desulfurization gypsum and deionized water are mixed at a solid-liquid volume ratio of 1:4 kg / L. After ball milling until the particle size is ≤40μm, pH adjuster is added to adjust the pH to 7, and then centrifuged to obtain calcium slurry.

[0038] S2. Precursor treatment: The calcium slurry obtained in S1 is mixed with deionized water at a volume ratio of 1:7, a composite dispersant is added, and the mixture is ultrasonically treated (power 350W) for 18 minutes to obtain the precursor colloid; wherein, the composite dispersant is a mixture of sodium citrate and sodium lignosulfonate at a ratio of 1.5:1, and the amount used is 3% of the total mass of the precursor colloid;

[0039] S3. Carbonation reaction: Adjust the pH of the precursor colloid to 10 using a pH adjuster. Introduce CO2 gas into the precursor colloid at a rate of 1.0 L / min, raise the temperature to 50°C, start ultrasonication (200 W power), and stir for 25 min. Then continue introducing CO2 gas at a rate of 1.0 L / min until the pH reaches 6. Add a crystallization regulator, mix thoroughly, and then treat with microwave intermittent heating for 2.5 h (microwave frequency 915 MHz, 5 min heating intervals followed by 5 min intervals) to form rod-shaped calcium carbonate slurry. The crystallization regulator is polyvinylpyrrolidone, and the amount used is 0.2% of the total mass of the precursor colloid.

[0040] S4. Separation and purification: The rod-shaped calcium carbonate slurry was centrifuged at 4500 rpm for 15 min, and 0.7% sodium carboxymethyl cellulose by weight of the rod-shaped calcium carbonate slurry was added and mixed evenly. The mixture was then washed three times with ethanol and dried under vacuum at 55℃ for 6 h to obtain rod-shaped calcium carbonate powder.

[0041] S5. Post-processing: The rod-shaped calcium carbonate powder obtained in S4 is mixed with KH-550 at a mass ratio of 1:0.2, ball-milled, and dried at 75℃ for 3 hours to obtain the final product.

[0042] Example 3

[0043] A method for preparing rod-shaped nano-calcium carbonate includes the following steps:

[0044] S1. Pretreatment: Power plant desulfurization gypsum and deionized water are mixed at a solid-liquid volume ratio of 1:5 kg / L. After ball milling until the particle size is ≤40μm, pH adjuster is added to adjust the pH to 7, and then centrifuged to obtain calcium slurry.

[0045] S2. Precursor treatment: The calcium slurry obtained in S1 is mixed with deionized water at a volume ratio of 1:8, a composite dispersant is added, and the mixture is ultrasonically treated (power 350W) for 15 minutes to obtain the precursor colloid; wherein, the composite dispersant is a mixture of sodium citrate and sodium lignosulfonate in a 2:1 ratio, and the amount used is 5% of the total mass of the precursor colloid;

[0046] S3. Carbonation reaction: Adjust the pH of the precursor colloid to 9 using a pH adjuster. Introduce CO2 gas into the precursor colloid at a rate of 1.5 L / min, raise the temperature to 60°C, start ultrasonication (power 200W), and stir for 20 min. Then continue introducing CO2 gas at a rate of 1.5 L / min until the pH reaches 6. Add a crystallization regulator, mix thoroughly, and then treat with microwave intermittent heating for 2 h (microwave frequency 915MHz, 2 min heating intervals followed by 2 min intervals) to form rod-shaped calcium carbonate slurry. The crystallization regulator is polyvinylpyrrolidone, and the amount used is 0.1% of the total mass of the precursor colloid.

[0047] S4. Separation and purification: Centrifuge the rod-shaped calcium carbonate slurry at 5000 rpm for 10 min, add 1% sodium carboxymethyl cellulose by weight of the rod-shaped calcium carbonate slurry and mix evenly, wash with ethanol 3 times, and vacuum dry at 60℃ for 5 h to obtain rod-shaped calcium carbonate powder.

[0048] S5. Post-processing: The rod-shaped calcium carbonate powder obtained in S4 is mixed with KH-550 at a mass ratio of 1:0.1, ball-milled, and dried at 80℃ for 2 hours to obtain the final product.

[0049] Comparative Example 1

[0050] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that no composite dispersant is added in step S2, while the rest is the same as in Example 1.

[0051] Comparative Example 2

[0052] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that the dispersant added in S2 is sodium citrate, while the rest is the same as in Example 1.

[0053] Comparative Example 3

[0054] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that the dispersant added in S2 is sodium lignosulfonate, while the rest is the same as in Example 1.

[0055] Comparative Example 4

[0056] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that no crystallization regulator is added in step S3, while the rest is the same as in Example 1.

[0057] Comparative Example 5

[0058] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that the microwave heating in S3 is a continuous microwave heating method, while the rest is the same as in Example 1.

[0059] Comparative Example 6

[0060] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that the microwave frequency for microwave heating in S3 is 2450MHz, while the rest is the same as in Example 1.

[0061] Comparative Example 7

[0062] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that CO2 is directly introduced into S3 until the pH reaches 7, followed by microwave intermittent heating for 3 hours. The rest is the same as in Example 1.

[0063] Comparative Example 8

[0064] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that sodium carboxymethyl cellulose is not added in step S4, while the rest is the same as in Example 1.

[0065] Comparative Example 9

[0066] A method for preparing rod-shaped nano-calcium carbonate differs from Example 1 in that KH-550 is not added in step S4, while the rest is the same as in Example 1.

[0067] Comparative Example 10

[0068] A method for preparing rod-shaped nano-calcium carbonate includes the following steps:

[0069] S1. After mixing calcium oxide obtained from limestone calcination with deionized water, the mixture is then sealed, stirred, sieved, and aged sequentially to prepare a calcium hydroxide suspension with a concentration of 1-5 wt%.

[0070] S2. The calcium hydroxide suspension obtained in S1 is transferred into a high-pressure reactor and carbon dioxide gas is introduced. Sodium hexametaphosphate is added, and the reaction is stirred at a system pressure of 2.5-15.0 MPa until the pH of the system is 4.0-6.0 to obtain a calcium carbonate reaction slurry.

[0071] S3. The calcium carbonate slurry obtained in S2 is subjected to pressurized rapid spray drying under a certain temperature and carbon dioxide atmosphere pressure to obtain rod-shaped nano calcium carbonate samples.

[0072] Test case

[0073] 1. The shape, aspect ratio, and surface Zeta potential of the final product rod-shaped calcium carbonate in Examples 1-3 and Comparative Examples 1-10 were detected, and the results are shown in Table 1.

[0074] Table 1. Shape, Aspect Ratio, and Surface Zeta Potential

[0075]

[0076] As can be seen from the results in Table 1, the final product rod-shaped nano-calcium carbonate obtained by the method of the present invention is all long rod-shaped with a particle size in the nanometer range and an aspect ratio between 15.8 and 19.3. The absolute value of the surface zeta potential is above 30mV, indicating that it has good dispersion performance. In Comparative Examples 1-3, the absence of a composite dispersant or the addition of only one dispersant in S2 significantly reduced the aspect ratio and the surface Zeta potential, indicating that pre-mixing the calcium source into a uniformly dispersed colloid is beneficial for the subsequent longitudinal crystallization of calcium carbonate and can improve the overall dispersion performance. In Comparative Example 4, the absence of a crystallization regulator in S3 also affected the aspect ratio, and the surface Zeta potential also decreased significantly, indicating that adding a small amount of crystallization regulator in this step is beneficial for longitudinal growth and surface charge enrichment. In Comparative Example 5, continuous microwave heating was used, but excessive or uneven heating easily caused the system to agglomerate, directly affecting the directional growth of crystals. Similarly, in Comparative Example 6, a higher microwave frequency was used, but its penetration ability was insufficient, resulting in excessively high local temperatures, which also affected the directional growth of crystals. In Comparative Example 7, the absence of a step-wise pH, the introduction of carbon dioxide in one step, and intermittent microwave heating without prior nucleation directly affected the subsequent directional growth of crystals. In Comparative Examples 8-9, the subsequent addition of calcium carbonate for modification did not significantly affect the aspect ratio, but it had a significant impact on the surface Zeta potential. Comparative Example 10 was prepared using the carbonation method described in the patent with publication number CN115028183A, resulting in rod-shaped calcium carbonate with a small aspect ratio and a low surface zeta potential.

[0077] 2. The rod-shaped nano-calcium carbonate prepared in Example 1 and Comparative Examples 1-10 were used to fill polyurethane foam insulation materials. Specifically, the following method was used: Component A (white component - composite polyol and foaming agent) and component B (black component - polymeric isocyanate - diphenylmethane diisocyanate) were added at a mass ratio of 1:1.7 using conventional methods. Then, 10% of the aforementioned rod-shaped nano-calcium carbonate was added, mixed thoroughly, and after the reaction was complete, injected into a mold for foaming and curing. The thermal conductivity, water resistance, and tensile strength of the material were then tested according to JG / T 314-2012, and the results are shown in Table 2.

[0078] Table 2 Thermal conductivity, water resistance and tensile strength

[0079]

[0080] As can be seen from the results in Table 2, the rod-shaped nano-calcium carbonate obtained by the preparation method of this invention can effectively reduce the thermal conductivity and water absorption rate of polyurethane foam insulation materials after being added to them, while also exhibiting good tensile strength. Compared to materials without the addition of rod-shaped nano-calcium carbonate, the performance of the materials is improved. However, due to differences in raw materials and steps during the preparation process, the rod-shaped nano-calcium carbonate obtained in Comparative Examples 1-10 does not perform as well as that in Example 1, and therefore its performance improvement in polyurethane foam insulation materials is relatively poor.

[0081] In summary, this invention optimizes the preparation process by adding a composite dispersant in the early stages to mix the calcium slurry into a precursor colloid, preventing calcium slurry agglomeration and providing a stable system for subsequent carbonation reactions. Simultaneously, the combination of ultrasonic, microwave, and mechanical stirring multi-coupling technologies effectively promotes uniform distribution of crystal nuclei and accelerates the combination of calcium and carbonate ions, achieving precise control over the aspect ratio. Subsequently, the purification and post-treatment processes involve dual modification with sodium carboxymethyl cellulose and silane coupling agents, improving the hydrophobic and dispersible properties of calcium carbonate. The resulting rod-shaped nano-calcium carbonate is long and rod-shaped with nanoscale particle sizes, aspect ratios between 15.8 and 19.3, and a surface zeta potential absolute value above 30 mV. It exhibits good dispersibility, is more environmentally friendly, and can be applied to thermal insulation and waterproofing materials, demonstrating significant economic and social benefits.

[0082] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. 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 preparing rod-shaped nano-calcium carbonate, characterized in that, Includes the following steps: S1. Pretreatment: Mix the power plant desulfurization gypsum with deionized water at a solid-liquid volume ratio of 1:3-5, ball mill the mixture, add a pH adjuster to adjust the pH to 6.5-7.5, centrifuge the mixture to obtain calcium slurry; S2. Precursor treatment: The calcium slurry obtained in S1 is mixed with deionized water at a volume ratio of 1:6-8, a composite dispersant is added, and the mixture is ultrasonically treated for 15-20 minutes to obtain a precursor colloid; the composite dispersant is a mixture of sodium citrate and sodium lignosulfonate in a 1-2:1 ratio, and the amount used is 1-5% of the total mass of the precursor colloid; S3. Carbonization reaction: Adjust the pH of the precursor colloid to 9-11 using a pH adjuster, introduce CO2 gas into the precursor colloid, heat to 40-60℃, start ultrasonication and stir for 20-30 minutes, then continue introducing CO2 gas until the pH is 6-7, add a crystallization regulator, and treat with microwave intermittent heating for 2-3 hours to form rod-shaped calcium carbonate slurry; the crystallization regulator is polyvinylpyrrolidone, and the amount used is 0.1-0.3% of the total mass of the precursor colloid; the microwave frequency of the microwave intermittent heating treatment is 915MHz, and the intermittent heating frequency is 2-5 minutes of heating followed by 2-5 minutes of rest. S4. Separation and purification: Centrifuge the rod-shaped calcium carbonate slurry, add sodium carboxymethyl cellulose and mix evenly, wash with ethanol 2-3 times, and vacuum dry at 50-60℃ for 5-8 hours to obtain rod-shaped calcium carbonate powder. S5. Post-processing: The rod-shaped calcium carbonate powder obtained in S4 is ball-milled and mixed with silane coupling agent, and dried at 70-80℃ for 2-3 hours to obtain the final product.

2. The method for preparing rod-shaped nano-calcium carbonate according to claim 1, characterized in that, In S1, after ball milling, the particle size of the power plant desulfurization gypsum is ≤40μm.

3. The method for preparing rod-shaped nano-calcium carbonate according to claim 1, characterized in that, In S2, the power of the ultrasonic treatment is 300-350W.

4. The method for preparing rod-shaped nano-calcium carbonate according to claim 1, characterized in that, In S3, the power of the ultrasonic wave is 150-200W; the flow rate of the CO2 is 0.5-1.5L / min.

5. The method for preparing rod-shaped nano-calcium carbonate according to claim 1, characterized in that, In S4, the centrifugation speed is 4000-5000 rpm and the time is 10-20 min; the amount of sodium carboxymethyl cellulose added is 0.5-1% of the mass of the rod-shaped calcium carbonate slurry.

6. The method for preparing rod-shaped nano-calcium carbonate according to claim 1, characterized in that, In S5, the mass ratio of the rod-shaped calcium carbonate powder to the silane coupling agent is 1:0.1-0.3; the silane coupling agent is KH-550.

7. The method for preparing rod-shaped nano-calcium carbonate according to claim 1, characterized in that, The aspect ratio of the rod-shaped nano-calcium carbonate product is 15-20:1.

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