A preparation method of low-viscosity calcium carbonate

Abstract

The invention belongs to the technical field of calcium carbonate preparation, and specifically provides a method for preparing low-viscosity calcium carbonate, comprising S1 carbonization and crystal surface control, wherein alkylphenol polyoxyethylene ether and dimethylformamide are added to calcium hydroxide slurry as composite crystal form control agents, the pH value is controlled in a weak alkaline environment, a primary carbonization is performed, and then aging-secondary carbonization is performed until the pH value is stabilized at 7.0-7.5; S2 wet graft modification, wherein a multifunctional group monomer is added to the slurry after the secondary carbonization, and the mixture is reacted at 60-65°C for 1.5-2.5 hours. A modified slurry is obtained, and itaconic acid and an initiator are added. The temperature is maintained at 70-85°C under an inert gas atmosphere, and the reaction time is 3.5 hours to 4.5 hours. S3 microwave-ultrasonic synergistic drying is performed, and the modified slurry is dehydrated to a solid content of 40%-50% by a centrifuge, and then dried using a microwave frequency of 2.45 GHz and an ultrasonic frequency of 20 kHz to obtain a dried product. S4 The dried product is crushed and classified, and a secondary surface modification is performed. The obtained calcium carbonate product has very low viscosity and oil absorption.

Description

Technical Field

[0001] The invention relates to the technical field of calcium carbonate preparation, and in particular to a method for preparing low-viscosity calcium carbonate. Background Art

[0002] Calcium carbonate, a key inorganic chemical product, is widely used in industries such as rubber, plastics, papermaking, coatings, and inks. It can significantly improve the heat resistance, wear resistance, dimensional stability, and rigidity of finished products, while also effectively reducing production costs. However, traditionally produced calcium carbonate often suffers from high viscosity, making processing more difficult and reducing product performance. Furthermore, high-viscosity slurries are prone to sedimentation and agglomeration, requiring frequent stirring or the addition of anti-settling agents, increasing inventory management costs. Summary of the Invention

[0003] In view of the defect of high viscosity of calcium carbonate in the prior art, the present invention provides a method for preparing low-viscosity calcium carbonate, which achieves a dual reduction in oil absorption value and viscosity through multi-step coordinated regulation.

[0004] To achieve the above object, the present invention provides the following technical solution: a method for preparing low-viscosity calcium carbonate, comprising the following steps:

[0005] S1: Carbonization and crystal surface control: Alkylphenol polyoxyethylene ether and dimethylformamide are added to the calcium hydroxide slurry as composite crystal form control agents, and the pH is adjusted to a weak alkaline environment of 8.5±0.2. Then, CO2 is introduced for a primary carbonization, and the reaction is terminated when the conductivity of the calcium hydroxide slurry drops to 10%-15% of the initial value. Then, aging-secondary carbonization is carried out, and the slurry is allowed to stand at a certain temperature for a period of time, and then CO2 is introduced a second time until the pH stabilizes at 7.0-7.5;

[0006] S2: Wet grafting modification: add multifunctional group monomer to the secondary carbonized slurry and react at 60-65°C for 1.5-2.5 hours to obtain modified slurry, then add itaconic acid and initiator, maintain the temperature at 70-85°C under argon or nitrogen atmosphere, and the reaction time is 3.5h-4.5h;

[0007] S3: Microwave-ultrasonic synergistic drying: After the modified slurry is dehydrated to a solid content of 40%-50% by a centrifuge, it is dried using a microwave frequency of 2.45 GHz and an ultrasonic frequency of 20 kHz to obtain a dry product;

[0008] S4: The dried product is crushed and classified, and the surface is modified for a second time to obtain the final low-viscosity calcium carbonate product.

[0009] As a further improvement of the present invention, the alkylphenol polyoxyethylene ether in S1 is octylphenyl polyoxyethylene ether, and its addition amount is 0.03%-0.08% of the dry basis mass of calcium hydroxide, and the addition amount of dimethylformamide in S1 is 0.1%-0.5% of the dry basis mass of calcium hydroxide.

[0010] As a further improvement of the present invention, the rate of the first CO2 introduction in S1 is 0.5-1.0 L / min, and the rate of the second CO2 introduction in S1 is 0.2-0.5 L / min.

[0011] As a further improvement of the present invention, in the aging-secondary carbonization in S1, the temperature is maintained at 40-50° C. and the standing time is 30-60 minutes.

[0012] As a further improvement of the present invention, the multifunctional monomer added in step S2 is acryloxypropyltrimethoxysilane, and its addition amount is 1.5%-2.5% of the dry basis mass of calcium hydroxide; the addition amount of itaconic acid in S2 is 2%-4% of the dry basis mass of calcium hydroxide, and the addition amount of the initiator is 0.02%~0.08% of the dry basis mass of calcium hydroxide, and the initiator is ammonium persulfate or potassium persulfate.

[0013] As a further improvement of the present invention, before the acryloxypropyltrimethoxysilane is added to the carbonized slurry, it is pre-hydrolyzed for 30 minutes in a mixture of water and ethanol in a mass ratio of 1:1 using acetic acid as a catalyst.

[0014] As a further improvement of the present invention, the microwave power density in step S3 is 3-5 W / m 2 , the ultrasonic power density is 0.5-1.2 W / cm², and the energy input ratio of microwave to ultrasonic is 2.5-3.5:1.

[0015] As a further improvement of the present invention, the drying process in step S3 adopts dynamic coupling control, specifically:

[0016] Stage 1: microwave power 4-5 W / g, ultrasonic power density 1.0-1.2 W / cm², lasting 10-15 minutes;

[0017] Second stage: microwave power 3-4W / g, ultrasonic power density 0.5-0.8 W / cm², lasting 20-25 minutes.

[0018] As a further improvement of the present invention, the pulverization in S4 adopts a jet mill, the rotation speed of the classifying wheel is 2000-3000 rpm, and the particle size of the low-viscosity calcium carbonate product obtained is controlled to be 1.8-5.5 μm.

[0019] As a further improvement of the present invention, the secondary surface modification in step S4 is specifically as follows: the product obtained by classification is placed in a mixer and sprayed with a cyclodextrin grafted modified polymalic acid ethanol solution with a mass concentration of 10% for rolling mixing, the mixing temperature is 70-80°C, the mixing time is 25-35 minutes, and the spraying amount of the cyclodextrin grafted modified polymalic acid ethanol solution is 0.1%-0.6% of the mass of the product obtained by classification.

[0020] Beneficial effects of the present invention:

[0021] 1. Alkylphenol polyoxyethylene ether promotes the formation of high-energy crystal planes, while acryloxypropyltrimethoxysilane enables the grafting of itaconic acid. The grafted itaconic acid has a certain chain length and volume, weakening the interaction between particles, reducing friction and cohesion between particles, allowing particles to move freely and achieving overall viscosity reduction. Furthermore, by synergizing microwave heating with ultrasonic oscillation during the drying stage, microwaves selectively heat the moisture within the particles, while ultrasonic waves break up the surface crust, improving the coating effect, reducing oil absorption, and thus reducing viscosity.

[0022] 2. The cyclodextrin cavity can include solvent molecules to form a hydration layer, reducing the internal friction resistance of the particles in the solvent; in addition, the carboxylic acid group of polymalic acid disperses the particles through electrostatic repulsion and steric hindrance. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] The present invention provides a method for preparing low-viscosity calcium carbonate, comprising the following steps:

[0025] S1: Carbonization and Crystal Surface Control: Alkylphenol polyoxyethylene ether (preferably octylphenyl polyoxyethylene ether, added at a rate of 0.03%-0.08% based on the dry weight of the calcium hydroxide) and dimethylformamide (added at a rate of 0.1%-0.5% based on the dry weight of the calcium hydroxide) are added to the calcium hydroxide slurry as composite crystal form control agents, and the pH is controlled at 8.3-8.7. A primary carbonization is performed by introducing CO2 (at a rate of 0.5-1.0 L / min). The reaction endpoint is determined when the conductivity drops to 10%-15% of the initial value. This is followed by aging and secondary carbonization. During the aging stage, the slurry is allowed to stand for 30-60 minutes at a temperature of 40-50°C to promote directional crystal nucleation growth. During the secondary carbonization, CO2 is again introduced (at a rate of 0.2-0.5 L / min) until the pH stabilizes at 7.0-7.5, forming a uniform crystal form.

[0026] As a further explanation of this embodiment, by using alkylphenol polyoxyethylene ether and dimethylformamide to synergistically inhibit the growth of calcium hydroxide crystals on the 0001 crystal plane and the 1010 crystal plane, the formation and exposure of other crystal planes are promoted, so that the proportion of high-energy crystal planes reaches more than 60%. By regulating the surface energy of calcium carbonate with alkylphenol polyoxyethylene ether, by selectively adsorbing specific crystal planes, changing the charge distribution of the crystal planes, disordered growth is suppressed, and a regular structure and morphology with low oil absorption is formed. Secondary carbonization can promote directional growth of crystal planes and optimize particle density.

[0027] S2: Wet grafting modification

[0028] A multifunctional monomer is added to the carbonized slurry for grafting modification. The multifunctional monomer is preferably acryloxypropyltrimethoxysilane, and the amount added is 1.5%-2.5% by weight of the dry calcium hydroxide. Before addition, the multifunctional monomer must be pretreated by dissolving it in a mixture of water and ethanol (1:1 by mass). A small amount of acetic acid (0.5% by mass of the acryloxypropyltrimethoxysilane) is added as a catalyst to fully hydrolyze it. Impurities are then filtered to obtain a clear solution. The modification reaction is carried out at 60-65°C for 1.5-2.5 hours to obtain a modified slurry. The mass ratio of the mixture to the multifunctional monomer is 6:1.

[0029] Then, add itaconic acid (monomer) and an initiator (such as ammonium persulfate or potassium persulfate). Maintain the temperature at 70-85°C under an argon or nitrogen atmosphere for 3.5-4.5 hours. The amount of itaconic acid added is 2%-4% of the dry weight of the calcium hydroxide, and the amount of initiator added is 0.02%-0.08% of the dry weight of the calcium hydroxide.

[0030] As a further explanation of this example, the high-energy crystal planes generated in S1, promoted by alkylphenol polyoxyethylene ether, were then grafted with itaconic acid via acryloxypropyltrimethoxysilane. The grafted itaconic acid forms a long-chain structure with its unique spatial dimensions, weakening interactions between the particles, such as van der Waals and electrostatic forces. This reduces frictional resistance and cohesive effects generated when the particles contact each other, allowing the particles to slide freely and decompose, effectively lowering the overall viscosity of the system.

[0031] S3: Microwave-ultrasonic synergistic drying

[0032] After the modified slurry is centrifuged to a solids content of 40%-50%, it is dried using a synergistic effect of microwaves and ultrasound. The microwave frequency is 2.45 GHz, the ultrasound frequency is 20 kHz, the microwave power density is 3-5 W / g, the ultrasound power density is 0.5-1.2 W / cm², and the energy input ratio of microwave to ultrasound is (2.5-3.5):1. The drying process is dynamically coupled and is divided into two stages:

[0033] Stage 1: microwave power 4-5 W / g, ultrasonic power density 0.8-1.2 W / cm², lasting 10-15 minutes;

[0034] Second stage: microwave power 3-4W / g, ultrasonic power density 0.5-0.8 W / cm², lasting 20-25 minutes.

[0035] As a further explanation of this embodiment, by using microwave heating and ultrasonic oscillation in synergy during the drying stage, microwaves selectively heat the moisture inside the particles, and ultrasonic waves break the surface hard shell, thereby improving the coating effect, reducing the oil absorption value, and thus reducing the viscosity.

[0036] S4: Crushing, classification and secondary surface modification

[0037] The dried product is crushed and classified using a jet mill, with a classifying wheel speed of 2000-3000 rpm, to control the finished product particle size to 1.8-5.5 μm. A secondary surface modification is then performed: the classified product is placed in a mixer and sprayed with a 10% cyclodextrin-grafted polymalic acid ethanol solution (the spray volume is 0.1%-0.6% of the dried product mass). The mixture is then rolled and mixed at 70°C-80°C for 25-35 minutes to obtain the final low-viscosity calcium carbonate product.

[0038] As a further explanation of this embodiment, the cyclodextrin cavity can include solvent molecules to form a hydration layer, reducing the internal friction resistance of the particles in the solvent; in addition, the carboxylic acid group of polymalic acid disperses the particles through electrostatic repulsion and steric hindrance.

[0039] Example 1

[0040] S1: Take a calcium hydroxide slurry with a concentration of 15% (w / w), add 0.03% octylphenyl polyoxyethylene ether based on the dry mass of calcium hydroxide and 0.1% dimethylformamide based on the dry mass of calcium hydroxide, control the pH to be maintained at 8.3, and introduce CO2 at a rate of 0.5 L / min for primary carbonization. When the conductivity drops to 10% of the initial value, stop introducing CO2 and pH control.

[0041] The slurry was then allowed to stand for 30 min with the temperature maintained at 40°C, and then CO2 was introduced again at a rate of 0.2 L / min until the pH stabilized at 7.5.

[0042] S2: Add 1.5% acryloxypropyltrimethoxysilane (1.5% by weight, dry weight, of calcium hydroxide) to the secondary carbonized slurry of S1. Prior to addition, the acryloxypropyltrimethoxysilane was hydrolyzed in a 1:1 mixture of water and ethanol using acetic acid as a catalyst for 30 minutes. The ratio of the mixture to acryloxypropyltrimethoxysilane was 6:1. After addition, the reaction was continued at 60°C for 1.5 hours to obtain a modified slurry.

[0043] Itaconic acid (monomer) and ammonium persulfate were then added, and the reaction was carried out under a nitrogen atmosphere at 70°C for 3.5 hours. The amount of itaconic acid added was 2% of the dry weight of the calcium hydroxide, and the amount of initiator added was 0.02% of the dry weight of the calcium hydroxide.

[0044] S3: The modified slurry was centrifugally dehydrated to a solids content of 50%. It was then dried using microwaves at a frequency of 2.45 GHz and ultrasound at a frequency of 20 kHz. The first stage was conducted at a microwave power of 4 W / g and an ultrasound power density of 0.8 W / cm² for 10 minutes. The second stage was conducted at a microwave power of 3 W / g and an ultrasound power of 0.5 W / cm² for 20 minutes. A dried product was obtained.

[0045] S4: The dried product is crushed and classified using a jet mill with a classifying impeller speed of 2000 rpm, controlling the finished product particle size to 1.8-5.5 μm. A secondary surface modification is then performed: the classified product is placed in a mixer and sprayed with a 10% cyclodextrin-grafted modified polymalic acid ethanol solution at a concentration of 0.1% (based on the mass of the dried product). The mixture is then rolled and mixed at 70°C for 25 minutes to obtain the final low-viscosity calcium carbonate product.

[0046] Example 2

[0047] S1: Take a calcium hydroxide slurry with a concentration of 15% (w / w), add 0.05% octylphenyl polyoxyethylene ether based on the dry mass of calcium hydroxide and 0.3% dimethylformamide based on the dry mass of calcium hydroxide, control the pH to be maintained at 8.5, and introduce CO2 at a rate of 0.7 L / min for primary carbonization. When the conductivity drops to 13% of the initial value, stop introducing CO2 and pH control.

[0048] The slurry was then allowed to stand for 45 minutes with the temperature maintained at 45°C, and then CO2 was introduced again at a rate of 0.3 L / min until the pH stabilized at 7.3.

[0049] S2: Add 2.0% acryloxypropyltrimethoxysilane (2.0% by weight, dry weight, of calcium hydroxide) to the secondary carbonized slurry of S1. Prior to addition, the acryloxypropyltrimethoxysilane was hydrolyzed in a 1:1 mixture of water and ethanol using acetic acid as a catalyst for 30 minutes. The ratio of the mixture to acryloxypropyltrimethoxysilane was 6:1. After addition, the temperature was maintained at 60°C for 2 hours to obtain a modified slurry.

[0050] Itaconic acid (monomer) and ammonium persulfate were then added, and the temperature was maintained at 78°C under a nitrogen atmosphere for 4 hours. The amount of itaconic acid added was 3% of the dry weight of the calcium hydroxide, and the amount of initiator added was 0.05% of the dry weight of the calcium hydroxide.

[0051] S3: The modified slurry was centrifugally dehydrated to a solids content of 45%. It was then dried using microwaves at a frequency of 2.45 GHz and ultrasonic waves at a frequency of 20 kHz. The first stage was conducted at a microwave power of 4 W / g and an ultrasonic power density of 1.0 W / cm² for 13 minutes. The second stage was conducted at a microwave power of 4 W / g and an ultrasonic power of 0.7 W / cm² for 23 minutes. A dried product was obtained.

[0052] S4: The dried product is crushed and classified using a jet mill with a classifying impeller speed of 2500 rpm, controlling the finished product particle size to 1.8-5.5 μm. A secondary surface modification is then performed: the classified product is placed in a mixer and sprayed with a 10% cyclodextrin-grafted modified polymalic acid ethanol solution at a concentration of 0.4% (based on the mass of the dried product). The mixture is then rolled and mixed at 75°C for 30 minutes to obtain the final low-viscosity calcium carbonate product.

[0053] Example 3

[0054] S1: Take a calcium hydroxide slurry with a concentration of 15% (w / w), add 0.08% octylphenyl polyoxyethylene ether based on the dry mass of calcium hydroxide and 0.5% dimethylformamide based on the dry mass of calcium hydroxide, control the pH to be maintained at 8.7, and introduce CO2 at a rate of 1.0 L / min for primary carbonization. When the conductivity drops to 15% of the initial value, stop introducing CO2 and pH control.

[0055] The slurry was then allowed to stand for 60 minutes with the temperature maintained at 50°C, and then CO2 was introduced again at a rate of 0.5 L / min until the pH stabilized at 7.0.

[0056] S2: Add 2.5% acryloxypropyltrimethoxysilane (2.5% by weight, dry weight, of calcium hydroxide) to the secondary carbonized slurry of S1. Prior to addition, the acryloxypropyltrimethoxysilane was hydrolyzed in a 1:1 mixture of water and ethanol using acetic acid as a catalyst for 30 minutes. The ratio of the mixture to acryloxypropyltrimethoxysilane was 6:1. After addition, the reaction was continued at 65°C for 2.5 hours to obtain a modified slurry.

[0057] Itaconic acid (monomer) and ammonium persulfate were then added, and the temperature was maintained at 85°C under a nitrogen atmosphere for 4.5 hours. The amount of itaconic acid added was 4% of the dry weight of the calcium hydroxide, and the amount of initiator added was 0.08% of the dry weight of the calcium hydroxide.

[0058] S3: The modified slurry was centrifugally dehydrated to a solids content of 40%. It was then dried using microwaves at a frequency of 2.45 GHz and ultrasound at a frequency of 20 kHz. The first stage was conducted at a microwave power of 5 W / g and an ultrasound power density of 1.2 W / cm² for 10 minutes. The second stage was conducted at a microwave power of 4 W / g and an ultrasound power of 0.8 W / cm² for 20 minutes. A dried product was obtained.

[0059] S4: The dried product is crushed and classified using a jet mill with a classifying impeller speed of 3000 rpm, controlling the finished product particle size to 1.8-5.5 μm. A secondary surface modification is then performed: the classified product is placed in a mixer and sprayed with a 10% cyclodextrin-grafted modified polymalic acid ethanol solution at a concentration of 0.6% (based on the mass of the dried product). The mixture is then rolled and mixed at 80°C for 35 minutes to obtain the final low-viscosity calcium carbonate product.

[0060] Comparative Example 1:

[0061] This comparative example is based on Example 2, except that in step S1, the addition of octylphenyl polyoxyethylene ether is omitted.

[0062] Comparative Example 2:

[0063] This comparative example is based on Example 2, except that in step S1, the addition of dimethylformamide is omitted.

[0064] Comparative Example 3:

[0065] This comparative example is based on Example 2, except that in step S1, the aging-secondary carbonization process is omitted.

[0066] Comparative Example 4:

[0067] This comparative example is based on Example 2, except that the grafting modification process in step S2 is omitted.

[0068] Comparative Example 5:

[0069] This comparative example is based on Example 2, except that hot air drying (80° C., 6 hours) is used in step S3 instead of microwave-ultrasonic synergistic drying.

[0070] Comparative Example 6:

[0071] This comparative example is based on Example 2, except that in step S4, the step of grafting and modifying the polymalic acid ethanol solution with cyclodextrin is omitted.

[0072] The finished calcium carbonate products obtained in Examples 1-3 and Comparative Examples 1-6 were subjected to experimental determination:

[0073] Oil absorption determination: DOP titration method according to GB / T 19281-2014;

[0074] Viscosity measurement: According to GB / T 10247-2008, a rotational viscometer (Brookfield DV2T) was used at a shear rate of 250 s⁻¹ and a temperature of 25±0.5°C. The measurement results of each embodiment and comparative example are shown in the following comparison table:

[0075]

[0076] As can be seen from the above table, the present application achieves dual optimization of oil absorption and viscosity of calcium carbonate through the synergistic effect of composite crystal form control agent octylphenyl polyoxyethylene ether, dimethylformamide and aging-secondary carbonization, grafting modification, microwave-ultrasonic drying and surface modification, which is significantly better than calcium carbonate prepared by traditional process.

[0077] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above-mentioned implementation measures. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing low-viscosity calcium carbonate, characterized in that: The following steps are involved: S1: Carbonization and crystal plane control: alkylphenol polyoxyethylene ether and dimethylformamide are added to the calcium hydroxide slurry as composite crystal form control agents. The pH value is controlled in a weak alkaline environment of 8.5±0.2, and CO2 is introduced for primary carbonization. The reaction endpoint is determined by the decrease of the conductivity of the calcium hydroxide slurry to 10%-15% of the initial value. Then, aging-secondary carbonization is carried out. The slurry is allowed to stand at a certain temperature for a period of time, and then CO2 is introduced for a second time until the pH stabilizes at 7.0-7.

5. S2: Wet grafting modification: add multifunctional group monomer to the secondary carbonized slurry and react at 60-65°C for 1.5-2.5 hours to obtain modified slurry, then add itaconic acid and initiator, maintain the temperature at 70-85°C under argon or nitrogen atmosphere, and the reaction time is 3.5h-4.5h; The multifunctional monomer added in step S2 is acryloxypropyltrimethoxysilane, and its addition amount is 1.5%-2.5% of the dry weight of calcium hydroxide; the addition amount of itaconic acid in step S2 is 2%-4% of the dry weight of calcium hydroxide, and the addition amount of initiator is 0.02%-0.08% of the dry weight of calcium hydroxide, and the initiator is ammonium persulfate or potassium persulfate; Before adding the acryloxypropyltrimethoxysilane to the carbonized slurry, it was pre-hydrolyzed in a mixture of water and ethanol with a mass ratio of 1:1 for 30 minutes using acetic acid as a catalyst; S3: Microwave-ultrasonic synergistic drying: the modified slurry is dehydrated to a solid content of 40%-50% by a centrifuge, and then dried using a microwave frequency of 2.45 GHz and an ultrasonic frequency of 20 kHz to obtain a dry product; S4: crushing and classifying the dried product, and performing secondary surface modification to obtain the final low-viscosity calcium carbonate product; The secondary surface modification in step S4 is specifically as follows: placing the classified product in a mixer and spraying a 10% mass concentration of cyclodextrin grafted modified polymalic acid ethanol solution for rolling mixing, the mixing temperature is 70-80°C, the mixing time is 25-35 minutes, and the spraying amount of the cyclodextrin grafted modified polymalic acid ethanol solution is 0.1%-0.6% of the mass of the classified product.

2. The preparation method of low-viscosity calcium carbonate according to claim 1, wherein The alkylphenol polyoxyethylene ether in S1 is octylphenyl polyoxyethylene ether, and its addition amount is 0.03%-0.08% of the dry basis mass of calcium hydroxide. The addition amount of dimethylformamide in S1 is 0.1%-0.5% of the dry basis mass of calcium hydroxide.

3. The preparation method of low-viscosity calcium carbonate according to claim 1, wherein The rate of the first CO2 injection in S1 is 0.5-1.0 L / min, and the rate of the second CO2 injection in S1 is 0.2-0.5 L / min.

4. The preparation method of low-viscosity calcium carbonate according to claim 1, wherein In the aging-secondary carbonization in S1, the standing time is 30-60 minutes and the temperature is maintained at 40-50°C.

5. The preparation method of low-viscosity calcium carbonate according to claim 1, wherein In step S3, the microwave power density is 3-5 W / g, the ultrasonic power density is 0.5-1.2 W / cm², and the energy input ratio of microwave to ultrasonic is 2.5-3.5:

1.

6. The method for preparing low-viscosity calcium carbonate according to claim 5, wherein The drying process in step S3 adopts dynamic coupling control, specifically: Stage 1: microwave power 4-5 W / g, ultrasonic power density 1.0-1.2 W / cm², lasting 10-15 minutes; Second stage: microwave power 3-4 W / g, ultrasonic power density 0.5-0.8 W / cm², lasting 20-25 minutes.

7. The method for preparing low-viscosity calcium carbonate according to claim 1, wherein The pulverization in S4 is performed using a jet mill with a classifying wheel speed of 2000-3000 rpm. The particle size of the obtained low-viscosity calcium carbonate product is controlled to be 1.8-5.5 μm.

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