Preparation method and application of rod-like nano calcium carbonate

Abstract

The invention belongs to the field of calcium carbonate materials, and particularly relates to a preparation method and application of rodlike nano calcium carbonate, and the preparation method comprises the steps of pretreatment, precursor treatment, carbonization reaction, separation and purification and post-treatment. By optimizing the preparation process, the preparation cost is greatly reduced, and the obtained rod-like nano calcium carbonate is stable in structure, has the length-diameter ratio stabilized at (15-20): 1, is good in dispersity, can greatly reduce the heat conductivity coefficient, is applied to a thermal insulation waterproof material, and has remarkable economic benefits and social benefits.

Description

Technical Field

[0001] The present invention belongs to the field of calcium carbonate materials, and specifically relates to a preparation method and application of rod-shaped nano calcium carbonate, and more specifically to a preparation method and application of rod-shaped nano calcium carbonate that can meet the requirements of thermal insulation materials. Background Art

[0002] Calcium carbonate is an odorless, tasteless white solid inorganic compound that has developed rapidly in recent years. It has a wide variety of specifications and varieties and is widely used in many fields such as rubber, plastics, papermaking, printing ink, cosmetics, etc. Calcium carbonate has various morphologies, including cube-shaped, spherical, needle-shaped, and rod-shaped, etc. Each morphology has its unique properties, and different industries have different requirements for the morphology, particle size, surface properties, etc. of calcium carbonate. For example, due to its unique structure, rod-shaped nano calcium carbonate has a variety of excellent properties, such as reinforcement and toughening, large oil absorption, adsorption, desorption, grinding, fragrance retention, and slow release properties, etc., and has received more and more attention in many fields.

[0003] At present, the preparation process of rod-shaped nano calcium carbonate is becoming increasingly mature. Among them, the more commonly used method is to calcine limestone into calcium oxide, then make it into calcium hydroxide emulsion and react with carbon dioxide. This process requires high-temperature calcination, which consumes a lot of energy. If the emitted carbon dioxide is not recycled and utilized, it is easy to cause the greenhouse effect and is not environmentally friendly; at the same time, due to the relatively complex reaction conditions, if not well controlled, it is easy to result in a wide particle size distribution and poor dispersibility; in addition, ordinary rod-shaped calcium carbonate has poor hydrophobicity, so it is difficult to meet the performance requirements of some thermal insulation and waterproof materials for dispersible fillers. Summary of the Invention

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

[0005] To achieve the above object, the present invention provides a preparation method of rod-shaped nano calcium carbonate, including the following steps: S1. Pretreatment: Mix power plant desulfurized gypsum and deionized water according to a solid-liquid volume ratio of kg / L of 1:3 - 5. After ball milling, add a pH regulator to adjust the pH to 6.5 - 7.5, and then centrifuge to obtain calcium slurry; wherein, the filtrate is discharged after being treated to meet the standards; S2. Precursor treatment: Mix the calcium slurry obtained in S1 and deionized water according to a volume ratio of 1:6 - 8, add a composite dispersant, and perform ultrasonic treatment for 15 - 20 min to obtain a precursor colloid; S3. Carbonization reaction: Use a pH regulator to adjust the pH of the precursor colloid to 9 - 11. Introduce CO2 gas into the precursor colloid, heat it to 40 - 60 °C, start ultrasonic waves, and stir for 20 - 30 min. Then continue to introduce CO2 gas until the pH reaches 6 - 7. Add a crystallization regulator and perform microwave intermittent heating treatment for 2 - 3 h to form a rod-shaped calcium carbonate slurry. S4. Separation and purification: Centrifuge the rod-shaped calcium carbonate slurry, add sodium carboxymethylcellulose and mix evenly, wash it with ethanol 2 - 3 times, and vacuum dry it at 50 - 60 °C for 5 - 8 h to obtain rod-shaped calcium carbonate powder. S5. Post-treatment: Ball mill and mix the rod-shaped calcium carbonate powder obtained in S4 with a silane coupling agent, and dry it at 70 - 80 °C for 2 - 3 h to obtain the final product.

[0006] The present invention uses power plant desulfurization gypsum as the calcium source, without the need for calcination, reducing energy consumption. At the same time, it can also realize the resource utilization of solid waste, without carbon dioxide emissions, reducing production costs and being more environmentally friendly. By mixing the calcium source with a composite dispersant to form a precursor colloid, it can prevent the agglomeration of calcium slurry and provide a stable system for the subsequent carbonization reaction. By introducing CO2 gas in segments and combining ultrasonic waves and microwaves, first, the ultrasonic cavitation effect promotes the uniform distribution of crystal nuclei at a higher pH, and then the microwave directional heating accelerates the combination of Ca 2+ and CO3 2- at a lower pH. At the same time, under the action of the crystallization regulator, it promotes longitudinal growth to achieve precise control of the aspect ratio. By introducing sodium carboxymethylcellulose into calcium carbonate during the purification process to improve its hydrophobic performance, and then ball milling and mixing it with a silane coupling agent, it can further improve its hydrophobicity and also improve its dispersion performance in the use matrix.

[0007] Further, in the above technical solution S1, after ball milling, the particle size of the power plant desulfurization gypsum is ≤ 40 μm.

[0008] Further, in the above technical solution S2, the composite dispersant is a mixture of sodium citrate and sodium lignosulfonate at a ratio of 1 - 2:1, and the usage amount is 1 - 5% of the total mass of the precursor colloid; the power of the ultrasonic treatment is 300 - 350 W. Sodium lignosulfonate is an anionic surfactant, containing a large number of functional groups such as sulfonic acid groups and hydroxyl groups in the molecule. It can effectively disperse nanoparticles through electrostatic repulsion and steric hindrance effects to prevent agglomeration, but its viscosity is relatively high; sodium citrate is easily soluble in water. Mixing with sodium lignosulfonate can play a certain dilution role to improve its fluidity. At the same time, it can effectively chelate Ca in the solution. 2+, reducing the interference of free ions on the crystallization process, helps to form uniform crystal nuclei and can play an auxiliary role in the subsequent nucleation reaction. In this technical solution, sodium lignosulfonate provides strong negative charges through sulfonic acid groups, and the carboxyl groups of sodium citrate further strengthen charge repulsion. At the same time, the lignin macromolecular chains form a physical barrier, and the two work together to improve the dispersion efficiency. In addition, the two also play a certain role in crystal formation and morphology regulation during the subsequent formation of rod-shaped calcium carbonate.

[0009] Further, in the above technical solution S3, the power of the ultrasonic wave is 150 - 200 W; the flow rate of CO2 introduced is 0.5 - 1.5 L / min. In the present invention, using a higher ultrasonic power in the precursor colloid stage is beneficial to the dispersion of the system, while using a lower ultrasonic power in the nucleation stage is beneficial to the formation and uniform distribution of crystal nuclei.

[0010] Further, in the above technical solution S3, the crystallization regulator is polyvinylpyrrolidone, and the usage amount is 0.1 - 0.3% of the total mass of the precursor colloid. In this technical solution, the combined use of a small amount of crystal form regulator can further interfere with the crystal plane growth rate, thus promoting the formation of rod-shaped calcium carbonate.

[0011] Further, in the above technical solution S3, the microwave frequency of the microwave intermittent heating treatment is 915 MHz, and the intermittent heating frequency is heating for 2 - 5 min and then intermittent for 2 - 5 min. Microwave is an electromagnetic wave and has wave characteristics such as reflection, transmission, interference, diffraction, polarization, and the accompanying energy transmission of electromagnetic waves. The principle of microwave intermittent heating is to use the electromagnetic waves generated by the microwave generator to penetrate the interior of the material, interact with the intermolecular substances, cause high-speed rotation and friction, achieve rapid and uniform heating, reduce agglomeration, and improve dispersion. At the same time, the intermittent treatment can prevent agglomeration or affect crystal growth due to excessive local temperature caused by continuous heating. The present invention adopts 915 MHz microwave intermittent heating treatment, which has a greater penetration depth. It can not only achieve rapid and uniform heating, promote the reaction between calcium ions and carbonate ions, but also reduce phenomena such as agglomeration caused by local overheating, providing conditions for the preferential growth of calcium carbonate crystals along a specific direction and being beneficial to the formation of rod-shaped calcium carbonate.

[0012] Further, in the above technical solution S4, the centrifugation speed is 4000 - 5000 rpm, and the time is 10 - 20 min; the amount of sodium carboxymethylcellulose added is 0.5 - 1% of the mass of the rod-shaped calcium carbonate slurry.

[0013] Further, 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, finally coating the surface of the rod-shaped nano calcium carbonate with the silane coupling agent can not only reduce the interfacial defects between it and the thermal insulation matrix in the thermal insulation material, but also play a moisture shielding effect to avoid the destruction of the heat insulation performance due to the high thermal conductivity of water. At the same time, it can also improve its uniform dispersion and reduce agglomeration.

[0014] Further, in the above technical solution, the aspect ratio of the rod-shaped nano calcium carbonate product is 15 - 20:1.

[0015] The present invention also provides an application of the rod-shaped nano calcium carbonate prepared by the above preparation method in thermal insulation and waterproof materials.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention uses the desulfurized gypsum from power plants as the calcium source, without using traditional limestone calcination, reducing energy consumption. At the same time, it can also realize the resource utilization of solid waste, without carbon dioxide emissions, reducing production costs and being more environmentally friendly; using natural lignin sulfonate as the dispersant has a low cost; using microwave intermittent heating treatment has a high heating efficiency and low energy consumption.

[0017] 2. By optimizing the preparation process, the present invention combines multiple coupling technologies of ultrasonic, microwave and mechanical stirring, which can effectively promote the uniform distribution of crystal nuclei and accelerate the combination of calcium ions and carbonate ions, with higher efficiency. At the same time, by introducing carbon dioxide in a segmented manner to control the pH of the system in a stepwise manner, it can effectively induce the growth of rod-shaped crystals. Combined with the action of a small amount of crystal regulators, precise control of the aspect ratio can be achieved; adding a composite dispersant in the early stage to mix the calcium slurry into a precursor colloid can prevent the agglomeration of the calcium slurry, provide a stable system for the subsequent carbonization reaction, and at the same time play a role in crystal and morphology regulation; after purification and double modification with sodium carboxymethylcellulose and silane coupling agent in the post-treatment process, the hydrophobic performance of calcium carbonate can be improved, and at the same time its dispersion performance in the use matrix can also be improved.

[0018] 3. By optimizing the preparation process, the present invention greatly reduces the preparation cost, and the obtained rod-shaped nano calcium carbonate has a stable structure, and the aspect ratio is stably maintained at 15 - 20:1. When used in the thermal insulation and waterproof material system, it has good dispersion, can greatly reduce the thermal conductivity, and improve the thermal insulation and waterproof effect. Specific Embodiments

[0019] The experimental methods in the following examples are all conventional methods unless otherwise specified. The raw materials involved in the following examples are all ordinary commercially available products and can be obtained through the market unless otherwise specified.

[0020] All the above technical features of the present invention can be combined with the technical features specifically described below (such as in the embodiments) to form new or preferred technical solutions.

[0021] The content of calcium sulfate dihydrate in the desulfurized gypsum from the power plant used in the present invention is above 90%. Among the pH regulators used, the acidic regulator is hydrochloric acid and the alkaline regulator is ammonia water.

[0022] Example 1 A preparation method of rod-shaped nano calcium carbonate, comprising the following steps: S1. Pretreatment: Mix the desulfurized gypsum from the power plant with deionized water at a solid-liquid volume ratio of kg / L of 1:3, grind it to a particle size of ≤40 μm by ball milling, then add a pH regulator to adjust the pH to 7, and centrifuge to obtain calcium slurry. S2. Precursor treatment: Mix the calcium slurry obtained in S1 with deionized water at a volume ratio of 1:6, add a composite dispersant, and treat it by ultrasonic wave (power 300W) for 20 min to obtain a precursor colloid; wherein, the composite dispersant is a 1:1 mixture of sodium citrate and sodium lignosulfonate, and the usage amount is 1% of the total mass of the precursor colloid. S3. Carbonization reaction: Adjust the pH of the precursor colloid to 11 with a pH regulator, introduce CO2 gas into the precursor colloid at a rate of 0.5 L / min, heat up to 40 °C, start ultrasonic wave (power 150W), and stir for 30 min, then continue to introduce CO2 gas at a rate of 0.5 L / min until the pH is 7, add a crystallization regulator, mix evenly, and then perform microwave intermittent heating treatment for 3 h (wherein, the microwave frequency is 915 MHz, each heating is 3 min and the interval is 3 min) to form rod-shaped calcium carbonate slurry; wherein, the crystallization regulator is polyvinylpyrrolidone, and the usage amount is 0.3% of the total mass of the precursor colloid. S4. Separation and purification: Centrifuge the rod-shaped calcium carbonate slurry at a speed of 4000 rpm for 20 min, add sodium carboxymethylcellulose accounting for 0.5% of the mass of the rod-shaped calcium carbonate slurry, mix evenly, wash it with ethanol 3 times, and dry it in vacuum at 50 °C for 8 h to obtain rod-shaped calcium carbonate powder. S5. Post-treatment: Mix the rod-shaped calcium carbonate powder obtained in S4 with KH-550 at a mass ratio of 1:0.3, ball mill it, and dry it at 70 °C for 3 h to obtain the final product.

[0023] Example 2 A preparation method of rod-shaped nano calcium carbonate, comprising the following steps: S1. Pretreatment: Mix the desulfurized gypsum from the power plant with deionized water at a solid-liquid volume ratio of kg / L of 1:4, grind it to a particle size of ≤40 μm by ball milling, then add a pH regulator to adjust the pH to 7, and centrifuge to obtain calcium slurry. S2. Precursor treatment: Mix the calcium slurry obtained in S1 with deionized water at a volume ratio of 1:7, add a composite dispersant, and treat it by ultrasonic wave (power 350 W) for 18 min to obtain a precursor colloid; wherein, the composite dispersant is a mixture of sodium citrate and sodium lignosulfonate at a ratio of 1.5:1, and the dosage is 3% of the total mass of the precursor colloid; S3. Carbonization reaction: Adjust the pH of the precursor colloid to 10 with a pH regulator, introduce CO2 gas into the precursor colloid at a rate of 1.0 L / min, heat up to 50 °C, start ultrasonic wave (power 200 W), and stir for 25 min, then continue to introduce CO2 gas at a rate of 1.0 L / min until the pH is 6, add a crystallization regulator, mix evenly, and then perform microwave intermittent heating treatment for 2.5 h (wherein, the microwave frequency is 915 MHz, heat for 5 min each time and intermittent for 5 min) to form a rod-shaped calcium carbonate slurry; wherein, the crystallization regulator is polyvinylpyrrolidone, and the dosage is 0.2% of the total mass of the precursor colloid; S4. Separation and purification: Centrifuge the rod-shaped calcium carbonate slurry at a speed of 4500 rpm for 15 min, add sodium carboxymethylcellulose accounting for 0.7% of the mass of the rod-shaped calcium carbonate slurry, mix evenly, wash it with ethanol 3 times, and vacuum dry it at 55 °C for 6 h to obtain rod-shaped calcium carbonate powder; S5. Post-treatment: Mix the rod-shaped calcium carbonate powder obtained in S4 with KH-550 at a mass ratio of 1:0.2, ball mill it, and dry it at 75 °C for 3 h to obtain the final product.

[0024] Example 3 A preparation method of rod-shaped nano calcium carbonate, comprising the following steps: S1. Pretreatment: Mix the power plant desulfurization gypsum with deionized water at a solid-liquid volume ratio of kg / L of 1:5, ball mill it until the particle size ≤ 40 μm, then add a pH regulator to adjust the pH to 7, and centrifuge to obtain a calcium slurry; S2. Precursor treatment: Mix the calcium slurry obtained in S1 with deionized water at a volume ratio of 1:8, add a composite dispersant, and treat it by ultrasonic wave (power 350 W) for 15 min to obtain a precursor colloid; wherein, the composite dispersant is a mixture of sodium citrate and sodium lignosulfonate at a ratio of 2:1, and the dosage is 5% of the total mass of the precursor colloid; S3. Carbonization reaction: Adjust the pH of the precursor colloid to 9 with a pH regulator, introduce CO2 gas into the precursor colloid at a rate of 1.5 L / min, raise the temperature to 60 °C, start the ultrasonic wave (power 200 W), and stir for 20 min. Then continue to introduce CO2 gas at a rate of 1.5 L / min until the pH reaches 6. Add a crystallization regulator, mix evenly, and then perform microwave intermittent heating treatment for 2 h (where the microwave frequency is 915 MHz, heating for 2 min each time and intermittent for 2 min) to form rod-shaped calcium carbonate slurry; among them, the crystallization regulator is polyvinylpyrrolidone, and the dosage is 0.1% of the total mass of the precursor colloid; S4. Separation and purification: Centrifuge the rod-shaped calcium carbonate slurry at 5000 rpm for 10 min, add sodium carboxymethylcellulose accounting for 1% of the mass of the rod-shaped calcium carbonate slurry and mix evenly, wash it 3 times with ethanol, and dry it in vacuum at 60 °C for 5 h to obtain rod-shaped calcium carbonate powder; S5. Post-treatment: Mix the rod-shaped calcium carbonate powder obtained in S4 with KH-550 at a mass ratio of 1:0.1, ball mill it, and dry it at 80 °C for 2 h to obtain the final product.

[0025] Comparative Example 1 A preparation method of rod-shaped nano calcium carbonate, different from Example 1 in that no composite dispersant is added in S2, and the others are the same as Example 1.

[0026] Comparative Example 2 A preparation method of rod-shaped nano calcium carbonate, different from Example 1 in that the dispersant added in S2 is sodium citrate, and the others are the same as Example 1.

[0027] Comparative Example 3 A preparation method of rod-shaped nano calcium carbonate, different from Example 1 in that the dispersant added in S2 is sodium lignosulfonate, and the others are the same as Example 1.

[0028] Comparative Example 4 A preparation method of rod-shaped nano calcium carbonate, different from Example 1 in that no crystallization regulator is added in S3, and the others are the same as Example 1.

[0029] Comparative Example 5 A preparation method of rod-shaped nano calcium carbonate, different from Example 1 in that continuous microwave heating is used for microwave heating in S3, and the others are the same as Example 1.

[0030] Comparative Example 6 A preparation method of rod-shaped nano calcium carbonate, different from Example 1 in that the microwave frequency of microwave heating in S3 is 2450 MHz, and the others are the same as Example 1.

[0031] Comparative Example 7 A preparation method of rod-shaped nano calcium carbonate, which is different from Example 1 in that in S3, CO2 is directly introduced at one time until the pH reaches 7, and then microwave intermittent heating treatment is carried out for 3 h, and the others are the same as in Example 1.

[0032] Comparative Example 8 A preparation method of rod-shaped nano calcium carbonate, which is different from Example 1 in that in S4, sodium carboxymethylcellulose is not added, and the others are the same as in Example 1.

[0033] Comparative Example 9 A preparation method of rod-shaped nano calcium carbonate, which is different from Example 1 in that in S4, KH-550 is not added, and the others are the same as in Example 1.

[0034] Comparative Example 10 A preparation method of rod-shaped nano calcium carbonate comprises the following steps: S1. After mixing calcium oxide obtained by calcining limestone with deionized water, through successive sealed stirring, sieving and aging, a calcium hydroxide suspension with a concentration of 1-5 wt% is prepared; S2. Transfer the calcium hydroxide suspension obtained in S1 into a high-pressure reactor, introduce carbon dioxide gas, add sodium hexametaphosphate, and under the system pressure of 2.5-15.0 MPa, stir and react until the system pH is 4.0-6.0 to obtain a calcium carbonate reaction slurry; S3. Under a certain temperature and carbon dioxide atmosphere pressure, carry out pressure-assisted rapid spray drying on the calcium carbonate slurry obtained in S2 to obtain a rod-shaped nano calcium carbonate sample.

[0035] Test Example 1. Detect 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, and the results are shown in Table 1.

[0036] Table 1 Shape, aspect ratio and surface Zeta potential

[0037] As can be seen from the results in Table 1, the final product of rod-shaped nano calcium carbonate obtained by the method of the present invention is all long rod-shaped, and the particle size is in the nanometer range. The aspect ratio is between 15.8 and 19.3, and the absolute value of the surface Zeta potential is above 30 mV, indicating good dispersion performance. In Comparative Examples 1-3, no composite dispersant or only one dispersant was added in S2, and the aspect ratio decreased significantly, and the surface Zeta potential decreased significantly, indicating that premixing the calcium source into a uniformly dispersed colloid is beneficial to the longitudinal crystallization of subsequent calcium carbonate and can improve the overall dispersion performance; in Comparative Example 4, no crystallization regulator was added in S3, which 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 to longitudinal growth and surface charge enrichment; in Comparative Example 5, microwave continuous heating was used. Since the heating was too high or uneven, it was easy to cause agglomeration of the system, directly affecting the oriented growth of crystallization; similarly, in Comparative Example 6, a higher microwave frequency was used, and its penetration ability was insufficient, resulting in too high local temperature, which also affected the oriented growth of crystallization; in Comparative Example 7, the stepped pH was not used, carbon dioxide was introduced at one time and microwave intermittent heating was carried out, and the nucleation reaction was not carried out first, directly affecting the subsequent oriented growth of crystals; in Comparative Examples 8-9, modification of calcium carbonate was carried out in the subsequent step, which had little effect on the aspect ratio, but had a greater impact on its surface Zeta potential. In Comparative Example 10, the carbonization method in the patent with the publication number CN115028183A was used for preparation, and the obtained rod-shaped calcium carbonate had a small aspect ratio and a low surface Zeta potential.

[0038] 2. Fill the rod-shaped nano calcium carbonate prepared in Example 1 and Comparative Examples 1-10 into polyurethane foam thermal insulation materials. The specific method is as follows: After adding component A (white material - composite polyol and foaming agent) and component B (black material - polymeric isocyanate - diphenylmethane diisocyanate) with a mass ratio of 1:1.7 according to the conventional method, then add 10% of the total amount of the above rod-shaped nano calcium carbonate, mix evenly, and after the reaction is completed, inject it into the mold for foaming and curing. Then, according to JG / T 314-2012, the thermal conductivity, waterproofness and tensile strength of the material are detected, and the results are shown in Table 2.

[0039] Table 2 Thermal conductivity, waterproofness and tensile strength

[0040] As can be seen from the results in Table 2, the final product, rod-shaped nano calcium carbonate obtained by the preparation method of the present invention can effectively reduce the thermal conductivity and water absorption rate of the material after being added to the polyurethane foam thermal insulation material, and at the same time has good tensile strength, and the material properties are improved compared with the materials without adding rod-shaped nano calcium carbonate. In Comparative Examples 1-10, due to the differences in raw materials and steps during the preparation process, the properties of the obtained rod-shaped nano calcium carbonate are inferior to those of Example 1, so the improvement of the material properties after being used in the polyurethane foam thermal insulation material is relatively poor.

[0041] In summary, by optimizing the preparation process, the present invention adds a composite dispersant in the early stage to mix the calcium slurry to form a precursor colloid, which can prevent the calcium slurry from agglomerating and provide a stable system for the subsequent carbonization reaction. At the same time, the combination of ultrasonic, microwave and mechanical stirring multi-coupling technologies can effectively promote the uniform distribution of crystal nuclei and accelerate the combination of calcium ions and carbonate ions, effectively realizing the precise control of the aspect ratio; after that, through the purification process and the double modification of sodium carboxymethyl cellulose and silane coupling agent in the post-treatment process, the hydrophobic and dispersive properties of calcium carbonate are improved. The obtained final product, rod-shaped nano calcium carbonate, is all long rod-shaped, and the particle size is in the nanometer range, the aspect ratio is between 15.8 and 19.3, the absolute value of the surface Zeta potential is above 30 mV, with good dispersibility and more environmental protection, and can be applied to thermal insulation and waterproof materials, with significant economic and social benefits.

[0042] Finally, it should be emphasized that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing rod-shaped nano calcium carbonate, characterized in that: The following steps are involved: S1. Pretreatment: The desulfurized gypsum from the power plant is mixed with deionized water at a solid-liquid volume ratio of 1:3-5, ball-milled, and a pH regulator is added to adjust the pH to 6.5-7.5, and then centrifuged to obtain a calcium slurry; S2. Precursor treatment: The calcium slurry obtained in S1 is mixed with deionized water in a volume ratio of 1:6-8, a composite dispersant is added, and ultrasonic treatment is performed for 15-20 minutes to obtain a precursor colloid; S3. Carbonization reaction: adjust the pH value of the precursor colloid to 9-11 with a pH regulator, introduce CO2 gas into the precursor colloid, raise the temperature to 40-60°C, start ultrasonic wave, and stir for 20-30min, then continue to introduce CO2 gas until the pH value is 6-7, add a crystallization regulator, and use microwave intermittent heating for 2-3h to form a rod-shaped calcium carbonate slurry; S4. Separation and purification: The rod-shaped calcium carbonate slurry was centrifuged, sodium carboxymethyl cellulose was added and mixed evenly, then washed with ethanol 2-3 times, and vacuum dried at 50-60°C for 5-8h to obtain a rod-shaped calcium carbonate powder; S5. Post-processing: The rod-shaped calcium carbonate powder obtained in S4 is mixed with the silane coupling agent by ball milling, and then dried at 70-80°C for 2-3h to obtain the final product.

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

3. The method for preparing a rod-shaped nano calcium carbonate according to claim 1, wherein: In S2, the composite dispersant is a mixture of sodium citrate and sodium lignin sulfonate in a ratio of 1-2:1, and the amount used is 1-5% of the total mass of the precursor colloid; the power of the ultrasonic treatment is 300-350W.

4. The method for preparing a rod-shaped nano calcium carbonate according to claim 1, wherein: 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 a rod-shaped nano calcium carbonate according to claim 1, wherein: In S3, the crystallization regulator is polyvinyl pyrrolidone, and the usage amount is 0.1-0.3% of the total mass of the precursor colloid.

6. The method for preparing a rod-shaped nano calcium carbonate according to claim 1, wherein: In S3, the microwave frequency of the microwave intermittent heating treatment is 915 MHz, and the frequency of the intermittent heating is heating for 2-5 minutes and intermittent for 2-5 minutes.

7. The method for preparing a rod-shaped nano calcium carbonate according to claim 1, wherein: In S4, the centrifugal 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.

8. The method for preparing a 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; and the silane coupling agent is KH-550.

9. The method for preparing a rod-shaped nano calcium carbonate according to claim 1, wherein: The aspect ratio of the rod-shaped nano calcium carbonate product is 15-20:

1.

10. Use of rod-shaped nano calcium carbonate prepared by the preparation method according to any one of claims 1 to 9 in thermal insulation and waterproof materials.

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