Preparation process of inactive sub-nano light calcium carbonate

Abstract

The invention discloses a preparation process of inactive sub-nano light calcium carbonate, which comprises the following steps: 1, mixing limestone with anthracite, putting into a lime kiln, and calcining to obtain quick lime; 2, sieving the quick lime, and removing powder ash and coal slag in the quick lime to obtain finished product lime; 3, adding water into the finished product lime, and digesting in a digesting machine to obtain slaked lime slurry; 4, aging the slaked lime slurry, and further digesting undigested calcium oxide in the slaked lime slurry to obtain aged slaked lime slurry; 5, diluting the aged slaked lime slurry, sending the slaked lime slurry to a carbonizer, introducing carbon dioxide, carrying out a carbonization reaction, continuously stirring in the carbonization process, adding a crystal form control agent and a dispersing agent, and starting a terahertz wave generator for scattering to control the crystal form and the agglomeration degree of calcium carbonate particles, so as to obtain cooked slurry after the reaction endpoint is reached; and 6, dehydrating, drying, scattering and depolymerizing the cooked pulp to obtain a finished product. The method has the advantage that the inactive sub-nano light calcium carbonate with very small agglomeration amount can be prepared.

Description

Technical Field

[0001] This invention belongs to the field of calcium carbonate preparation technology, and particularly relates to a process for preparing non-reactive sub-nanometer lightweight calcium carbonate. Background Technology

[0002] Non-reactive sub-nanometer light calcium carbonate refers to a hydrophilic light calcium carbonate product with a particle size between that of nano-light calcium carbonate and ordinary light calcium carbonate, without surface modification treatment. It has an average particle size of 100-500 nm and exhibits excellent performance in the manufacture of specialty paper (such as carbon paper, invoice paper, and art paper), rubber sealing strips, low-abrasion rubber products, and latex gloves. Its main characteristics are: uniform particle size, narrow secondary particle size distribution (80% distributed in the 0.1-4µm region), and D... 90 Less than 4µm, D max With a particle size of less than 8µm and a settling volume between 5.0 and 8.0, the product exhibits uniform particle size distribution, low agglomeration, good dispersibility, and relatively low oil absorption value, making it an excellent filler for specialty papers, high-grade rubber products, high-strength plastic products, and latex products.

[0003] However, inactive nano-calcium carbonate products are almost non-existent in the domestic market; only nano / sub-nanometer activated calcium carbonate products are available. This is mainly because nano / sub-nanometer calcium carbonate particles are very prone to agglomeration, and breaking up these agglomerates is extremely difficult. Laser particle size analyzer results show that the secondary particle size of inactive nano / sub-nanometer light calcium carbonate without surface modification is even larger than that of ordinary light calcium carbonate. Its application performance is inferior to ordinary light calcium carbonate, while its manufacturing cost is far higher, making it unacceptable to the market. Therefore, virtually no companies are willing to produce inactive nano / sub-nanometer light calcium carbonate. Nano / sub-nanometer calcium carbonate particles only exhibit relatively low agglomeration in solution. Therefore, in industrial production, surface modification treatment is typically performed on the carbonized slurry, coating the nano / sub-nanometer calcium carbonate particles with organic substances to reduce agglomeration. Furthermore, activated nano-calcium carbonate possesses nanomaterial characteristics; hence, only nano / sub-nanometer activated light calcium carbonate is available on the market, with no inactive nano / sub-nanometer light calcium carbonate.

[0004] Compared to nano-light calcium carbonate, non-reactive sub-nanometer light calcium carbonate has a larger native particle size ratio. Generally, nano-calcium carbonate has a particle size of less than 100 nanometers, with the mainstream particle size being 40-80 nanometers. During the industrial production of nano / sub-nanometer calcium carbonate, surface modification treatment is performed to prevent agglomeration during dehydration and drying. However, after surface treatment with organic compounds, sub-nanometer calcium carbonate changes from hydrophilic to oleophilic, making it unsuitable for the production of some hydrophilic products, such as paper coating, specialty paper fillers, and latex products.

[0005] Compared to ordinary light calcium carbonate, sub-nanometer light calcium carbonate has a much smaller primary particle size. The primary particle size of ordinary light calcium carbonate is generally around 1.0 micrometer (1000 nanometers), while the secondary average particle size of the product is 4.0-5.0 micrometers. max In the 10-15µm range, due to the coarse particle size, the surface smoothness, strength, and whiteness of the paper cannot meet the quality requirements in paper coating processes. In the production of low-abrasion rubber products, as a filler, its large particle size results in high abrasion, failing to meet the low-abrasion quality requirements. In the application of high-strength plastic products, the large particle size of ordinary light calcium carbonate also makes it impossible to meet the quality requirements for strength, folding resistance, and surface smoothness when used as a filler.

[0006] Compared to nano-calcium carbonate and ordinary light calcium carbonate, research on inactive sub-nanometer light calcium carbonate in China is very limited. Currently, there are no related production enterprises or production lines in China. On the one hand, although sub-nanometer light calcium carbonate has a larger particle size than nano-calcium carbonate, it still suffers from the problem of easy particle agglomeration. On the other hand, foreign countries impose technological blockades on my country, making it impossible to import technology. Due to fierce competition, domestic calcium carbonate companies have historically had low profitability, preventing them from investing heavily in research and development. Furthermore, the recent surge in nanotechnology has led universities and research institutions to focus their efforts on nano-calcium carbonate research, resulting in a severe lag in the production technology of inactive sub-nanometer light calcium carbonate. Currently, China relies entirely on imports for inactive sub-nanometer light calcium carbonate, with prices reaching 2000-2500 yuan per ton. Summary of the Invention

[0007] The purpose of this invention is to provide a process for preparing inactive sub-nanometer lightweight calcium carbonate. This invention has the advantage of producing inactive sub-nanometer lightweight calcium carbonate with very low agglomeration.

[0008] The technical solution of this invention: a process for preparing non-active sub-nanometer lightweight calcium carbonate, comprising the following steps: 1. Limestone is mixed with anthracite and fed into a lime kiln for calcination to obtain quicklime; 2. Sift the quicklime to remove the powder and slag, and obtain the finished lime; 3. The finished lime is added with water and put into a digester for digestion to obtain slaked lime slurry; Fourth, the quicklime slurry is aged to further digest the undigested calcium oxide, resulting in aged quicklime slurry. 5. Dilute the aged quicklime slurry and send it to the carbonation tower. Carbon dioxide is introduced to carry out the carbonation reaction. The carbonation process is continuously stirred, and crystal control agent and dispersant are added. The terahertz wave generator is turned on to disperse the particles in order to control the crystal form and agglomeration of calcium carbonate particles. After reaching the reaction endpoint, the slurry is obtained. 6. Dehydrate, dry, and break up the cooked pulp to obtain the finished product.

[0009] In the aforementioned non-reactive sub-nanometer lightweight calcium carbonate preparation process, in step four, the mass concentration of the aged quicklime slurry is 20-30%; in step five, the aged quicklime slurry is diluted to 8-12%.

[0010] In the aforementioned non-reactive sub-nanometer lightweight calcium carbonate preparation process, in step four, the mass concentration of the aged quicklime slurry is 25%; in step five, the aged quicklime slurry is diluted to 10%.

[0011] In the aforementioned non-reactive sub-nanometer lightweight calcium carbonate preparation process, in step five, the terahertz wave generator is always on throughout the carbonization process. Carboxylate dispersant is added 5-7 minutes after carbon dioxide is introduced, and carboxylate crystal form control agent is added 10-12 minutes after carbon dioxide is introduced.

[0012] In the aforementioned non-active sub-nanometer lightweight calcium carbonate preparation process, in step five, the aged quicklime slurry is diluted with warm or cold water to a concentration of 10% and a temperature of 20-25°C before being sent to the carbonation tower.

[0013] In the aforementioned non-reactive sub-nanometer lightweight calcium carbonate preparation process, in step five, the carbonization process is completed within 20 minutes by controlling the input rate of carbon dioxide and the temperature of the carbonization reaction.

[0014] In the aforementioned non-reactive sub-nanometer lightweight calcium carbonate preparation process, in step five, the carbonization reaction temperature is controlled between 20-25°C by adding crushed ice.

[0015] In the aforementioned non-active sub-nanometer lightweight calcium carbonate preparation process, in step five, the stirring speed is 270-310 r / min.

[0016] In the aforementioned non-reactive sub-nanometer lightweight calcium carbonate preparation process, the terahertz wave generator operates at a frequency of 3.2-3.32 THz and has a radiation power of 24-30 mW / cm².

[0017] In the aforementioned process for preparing non-active sub-nanometer lightweight calcium carbonate, in step six, the slurry is dehydrated by vacuum filtration to obtain a filter cake, and the filter cake is then freeze-dried under vacuum and dispersed and deagglomerated using an air jet mill.

[0018] Compared with existing technologies, the advantages of this invention are that it can prepare non-reactive sub-nanometer lightweight calcium carbonate with very low agglomeration, retaining its hydrophilicity, and can be used in the production of hydrophilic products. This is mainly achieved through the comprehensive use of the following technical means: First, by diluting the quicklime slurry to 10% and controlling the carbon dioxide input rate, the slurry temperature before and during the reaction, the carbonation reaction rate is greatly improved. This results in the formation of a large number of calcium carbonate crystal nuclei in the early stage of the carbonation reaction and compresses the growth time of the calcium carbonate crystal nuclei, thus reducing agglomeration.

[0019] Second, during the reaction process, terahertz waves with matching lattice vibration frequencies are used to disrupt hydrogen bonds and van der Waals forces between particles, thereby inhibiting aggregation.

[0020] Third, the slurry was stirred during the reaction process, and the stirring speed was limited to promote the dissolution of calcium hydroxide, break up carbon dioxide bubbles, increase the reaction rate, compress the growth time of calcium carbonate crystal nuclei, and prevent particle sedimentation and agglomeration.

[0021] Fourth, by using a dispersant first, the dispersion effect is improved, agglomeration is reduced, and the particles are dispersed more evenly. The crystal form control agent used afterward can be more accurately adsorbed onto the surface of each particle, avoiding excessively high / low concentrations of local additives, inhibiting the growth of calcium carbonate along certain directions and different nucleation rates on different crystal faces, ensuring good consistency of all crystal morphology, and reducing the total amount of additives used, thus lowering costs.

[0022] Add a dispersant 5-7 minutes after introducing carbon dioxide to allow the large number of particles generated in the early stage of the reaction to grow to a certain extent, forming sub-nano calcium carbonate instead of nano calcium carbonate. Then, the particles break up agglomeration under the action of the dispersant. After a certain period of time, add a crystal form control agent of the same system to avoid mutual interference between the additives and to avoid precipitation caused by ionic reactions that promotes agglomeration.

[0023] Fifth, there are various ways to dewater cooked pulp. This invention prefers vacuum filtration for dewatering. Compared with pressure filtration, it can reduce the compression and agglomeration of particles in the filter cake. The moisture content of the filter cake after dewatering is controlled at 15%~20%, avoiding excessive compression that leads to hard agglomeration.

[0024] Sixth, there are various ways to dry the filter cake. This invention prefers vacuum freeze drying, which directly sublimates and removes moisture, completely avoiding liquid bridge agglomeration and resulting in better product dispersibility.

[0025] Seventh, the dried filter cake can be dispersed and deagglomerated in various ways. The present invention prefers air jet milling to disperse and deagglomerate the powder. Compared with spray drying and oven static drying, the powder is more fully dispersed in the airflow. The airflow impact breaks up the small amount of soft agglomerates formed during the drying process, which has the best effect. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention.

[0027] Example: Preparation process of non-active sub-nanometer light calcium carbonate, including the following steps: First, limestone is mixed with anthracite and fed into a lime kiln for calcination to obtain quicklime. Step one is a standard procedure.

[0028] 2. Sift the quicklime to remove the dust and slag, obtaining the finished lime. Step 2 is a standard procedure.

[0029] 3. The finished lime is added to water and put into a digester for digestion to obtain slaked lime slurry.

[0030] Fourth, the quicklime slurry is aged to further digest the undigested calcium oxide, resulting in aged quicklime slurry with a mass concentration of 20-30%.

[0031] 5. Dilute the aged quicklime slurry with warm or cold water to a concentration of 10% and a temperature of 20-25℃, and then send it to the carbonization tower.

[0032] Start the terahertz wave generator. The operating frequency of the terahertz wave generator is 3.2-3.32 THz and the radiation power is 24-30mW / cm². In this example, 28mW / cm² is used. Start the stirring mechanism (anchor stirring head) of the carbonization tower and the stirring speed is 290r / min.

[0033] Carbon dioxide is introduced into the carbonization tower. 5-7 minutes after the introduction of carbon dioxide, a carboxylate dispersant, such as sodium polycarboxylate, is added, retaining the hydrophilic groups, to a concentration of about 0.12%. 10-12 minutes after the introduction of carbon dioxide, a carboxylate crystal form control agent, such as sodium citrate, is added, retaining the hydrophilic groups, to a concentration of about 0.1%.

[0034] By controlling the input rate of carbon dioxide, the input rate is made to be basically equal to the consumption rate. Overall, as the amount of calcium hydroxide in the slurry decreases, the input rate of carbon dioxide decreases until the reaction endpoint is reached, at which point the input of carbon dioxide is stopped, and a cooked slurry is obtained.

[0035] With sufficient carbon dioxide provided, the carbonization process can be completed within 20 minutes by controlling the reaction temperature. Since the reaction is exothermic, adding crushed ice maintains the carbonization reaction temperature between 20-25°C, resulting in a higher reaction rate and shorter reaction time.

[0036] 6. The cooked pulp is dehydrated by vacuum filtration. The moisture content of the dehydrated filter cake is controlled at 15%~20% to avoid excessive compression that leads to hard agglomeration. Preferably, the obtained filter cake is washed with anhydrous alcohol 1-2 times to reduce the moisture content of the filter cake, reduce hydrogen bond formation, and reduce agglomeration.

[0037] The filter cake is dried by vacuum freeze-drying, freezing to below -40℃, with a vacuum degree ≤10 Pa, and a drying time of 12~24 hours. The moisture is removed by direct sublimation, completely avoiding liquid bridge agglomeration and resulting in optimal product dispersibility.

[0038] The dried filter cake is broken up and deagglomerated using an air jet mill at a speed of 20-30 m / s. It is then passed through a 300-400 mesh sieve. The product that passes through the sieve is the finished product, while the agglomerates on the sieve can be returned to the air jet mill for reprocessing.

[0039] According to statistics, the production cost of the finished product is approximately RMB 1,380 per ton. The finished product was tested, and the following indicators were obtained (Table 1 below). These indicators are similar to those of imported products from abroad.

[0040] Table 1 Experimental Example 1: Based on the example, step five was adjusted by diluting the quicklime slurry to 5%, 15% and 18% respectively to obtain finished products one, two and three. The concentration of the quicklime slurry was kept unchanged and no dilution was performed to obtain finished product four.

[0041] The finished products 1, 2, 3 and 4 were tested, and the results are shown in Table 2.

[0042] Table 2 As shown in Table 2, further dilution of the quicklime slurry reduces its impact on the finished product's performance indicators and significantly increases subsequent drying energy consumption. Conversely, increasing the concentration leads to a significant decrease in the finished product's performance indicators. Therefore, diluting to 10% is the optimal solution, primarily for the following reasons: First, higher calcium hydroxide concentration leads to higher viscosity. Since the carbonization reaction occurs at a multiphase liquid interface, the reaction rate is closely related to the diffusion of reactants to the interface and the removal of products from the interface. The resistances during the reaction include gas film resistance, liquid film resistance at the gas-liquid interface, and liquid film resistance at the solid-liquid interface. The controlling steps of the entire reaction are either the dissolution of calcium hydroxide in the liquid film or the absorption of carbon dioxide in the liquid film, with liquid film resistance constraining the overall rate. The location of the reaction interface varies depending on the rate of calcium hydroxide dissolution and the rate of carbon dioxide absorption. If the former is faster, the reaction interface occurs within the liquid film at the gas-liquid interface; if the latter is faster, the reaction occurs within the liquid film at the solid-liquid interface, and crystallization occurs at the reaction interface. Higher slurry concentration and viscosity result in greater liquid film resistance, slower carbon dioxide mass transfer, slower reactant diffusion to the interface, and greater difficulty for products formed at the interface to leave, thus slowing down the overall carbonization reaction rate.

[0043] Secondly, due to the thermal instability of calcium carbonate crystals, they easily form barite and twins, and agglomerate into large particles (agglomeration). Under high concentrations of calcium hydroxide, the space between crystal nuclei is narrow, making it extremely easy to form barite and twins, i.e., agglomeration. At the same time, the higher the concentration of calcium hydroxide, the longer the entire carbonation reaction takes, meaning the later stages of the carbonation reaction are longer, resulting in more large crystals forming in the later stages, thus widening the particle size distribution of the product.

[0044] Third, when the concentration of calcium hydroxide is too low, the spacing between Ca(OH)2 particles is large. After CO2 dissolves, it needs to diffuse a longer distance to come into contact with the reactants. The diffusion rate becomes the rate-limiting step of the reaction, making it impossible to complete the reaction within 20 minutes. The time of the entire carbonization reaction increases, and more large crystals are formed in the later stage of the reaction. The particle growth time becomes longer, and agglomeration occurs, resulting in a wider particle size distribution of the product.

[0045] Fourth, a strongly alkaline environment enhances the repulsive force of negative charges on the particle surface. When the concentration of calcium hydroxide is too low, the repulsive force of charges decreases, and the probability of agglomeration increases.

[0046] Experimental Example 2: In this example, the input rate of carbon dioxide was matched with the reaction consumption rate. Assuming the input rate was V L / h, V dynamically decreased as the reaction time progressed. In Example 2, the input rate was adjusted to 0.8 V and 1.2 V respectively, yielding products five and six.

[0047] Testing of finished products five and six revealed an increased agglomeration phenomenon, primarily due to the following reasons: The concentration of carbon dioxide determines the overall carbonation reaction time; the higher the concentration, the shorter the carbonation reaction time, and vice versa. In the initial stage of the carbonation reaction, because the calcium hydroxide slurry contains a large number of free calcium ions, a high concentration of carbon dioxide, compared to a low concentration, effectively increases the amount of reactants fed, resulting in the formation of numerous calcium carbonate crystal nuclei. In the later stage of the carbonation reaction, the dissolution rate of calcium hydroxide controls the overall carbonation reaction rate. Therefore, the concentration of carbon dioxide has little effect on the carbonation reaction in the later stages, but the shortened overall carbonation reaction time reduces the growth time of crystal nuclei, resulting in fewer large crystals and a more uniform particle size distribution in the product. In the later stage of the carbonation reaction, the number of free calcium ions in the slurry decreases. Appropriately reducing the kiln gas flow rate will not affect the carbonation time. Maintaining a constant carbon dioxide input rate will result in excessive supply, leading to an excessively low pH in localized areas of the slurry, reduced charge repulsion, and the formation of large bubbles in the slurry, causing uneven gas-liquid contact and increasing the probability of agglomeration.

[0048] Experimental Example 3: Based on the previous example, slaked lime slurry at room temperature was diluted with room temperature water. The temperature of the diluted slaked lime slurry was measured to be 31°C. No ice was added for cooling during the carbonization reaction, resulting in product seven. Alternatively, slaked lime slurry was diluted with cold water to 15°C, and no ice was added for cooling during the carbonization reaction, resulting in product eight.

[0049] Testing revealed that the performance indicators of finished products seven and eight showed a significant decrease compared to the example. The main reasons are as follows: First, carbonization is an exothermic reaction. As the carbonization reaction proceeds, the temperature of the material inside the carbonization tower continuously increases. Since the solubility of calcium hydroxide is inversely proportional to temperature, that is, the higher the temperature, the lower the solubility of calcium hydroxide. In the later stage of the carbonization reaction, the rate at which calcium hydroxide dissolves and ionizes into Ca2+ controls the rate of the entire later stage of the carbonization reaction. Because the solubility of calcium hydroxide decreases with increasing temperature, the later stage of the carbonization reaction is prolonged, and the crystals grow more easily. This results in the formation of more large-particle crystals in the later stage of the carbonization reaction, thus widening the particle size distribution of the product.

[0050] Secondly, excessively high temperatures accelerate the growth rate of crystal nuclei, easily resulting in more large crystal particles.

[0051] Third, excessively high temperatures reduce the solubility of carbon dioxide in the liquid phase, decrease the rate of the early stage of the carbonization reaction, reduce the number of crystal nuclei, and increase the particle size of the product.

[0052] Fourth, when the temperature is too low, the ion diffusion rate is too low, and the reaction time increases, giving the initially formed crystals a longer growth time, resulting in a wider particle size distribution and increased agglomeration.

[0053] Experimental Example 4: Based on the example, the stirring speed was decreased or increased to obtain product nine. The performance indicators of product nine were lower than those of the example. The main reasons are as follows: At a stirring speed of 270-310 r / min, moderate turbulence is formed in the slurry, breaking up carbon dioxide bubbles, increasing the gas-liquid contact area, promoting the dissolution of Ca(OH)2, and preventing particle sedimentation and agglomeration. When the speed decreases, the CO2 bubbles become too large, the gas-liquid contact area is small, and the reaction rate is low, leaving more time for crystal growth. However, when the speed increases, mechanical energy is converted into heat energy, which will lead to an abnormal temperature rise in the reaction system. The strong shear and impact forces generated will cause the dispersant and crystal form control agent on the particle surface to be lost, and van der Waals forces between particles will dominate, forming agglomeration. In addition, high-speed stirring may generate static electricity through friction, resulting in uneven charge distribution on the particle surface, disrupting the electrostatic repulsion balance between particles, and forming a "chain-floc-block" agglomerated structure.

[0054] Experimental Example 5: Based on the previous example, the terahertz wave generator was omitted, resulting in product ten. Product ten had a GSD of 2.2 and a sedimentation volume < 5.0 ml / g, showing a significant decrease in performance. The main reasons are as follows: The embodiment employs a terahertz wave generator with specific power and frequency, which can match the lattice vibration frequency, disrupting interparticle hydrogen bonds and van der Waals forces, and inhibiting agglomeration. When the power is too high, it will cause the slurry temperature to rise, which will actually promote particle agglomeration; when the power is too low, the dispersing force is insufficient, and the agglomeration is not effectively suppressed.

Claims

1. A process for preparing non-active sub-nanometer lightweight calcium carbonate, characterized in that: Includes the following steps, 1. Limestone is mixed with anthracite and fed into a lime kiln for calcination to obtain quicklime; 2. Sift the quicklime to remove the powder and slag, and obtain the finished lime; 3. The finished lime is added with water and put into a digester for digestion to obtain slaked lime slurry; Fourth, the quicklime slurry is aged to further digest the undigested calcium oxide, resulting in aged quicklime slurry.

5. Dilute the aged quicklime slurry and send it to the carbonation tower. Carbon dioxide is introduced to carry out the carbonation reaction. The carbonation process is continuously stirred, and crystal control agent and dispersant are added. The terahertz wave generator is turned on to disperse the particles in order to control the crystal form and agglomeration of calcium carbonate particles. After reaching the reaction endpoint, the slurry is obtained.

6. Dehydrate, dry, and break up the cooked pulp to obtain the finished product.

2. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 1, characterized in that: In step four, the mass concentration of the aged quicklime slurry is 20-30%; in step five, the aged quicklime slurry is diluted to 8-12%.

3. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 2, characterized in that: In step four, the mass concentration of the aged quicklime slurry is 25%; in step five, the aged quicklime slurry is diluted to 10%.

4. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 1, characterized in that: In step five, the terahertz wave generator is always on throughout the carbonization process. Carboxylate dispersant is added 5-7 minutes after carbon dioxide is introduced, and carboxylate crystal form control agent is added 10-12 minutes after carbon dioxide is introduced.

5. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 4, characterized in that: In step five, the aged quicklime slurry is diluted with warm or cold water to a concentration of 10% and a temperature of 20-25°C before being sent to the carbonization tower.

6. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 1, characterized in that: In step five, the carbonization process is completed within 20 minutes by controlling the input rate of carbon dioxide and the temperature of the carbonization reaction.

7. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 6, characterized in that: In step five, the carbonization reaction temperature is controlled between 20-25°C by adding crushed ice.

8. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 1, characterized in that: In step five, the stirring speed is 270-310 r / min.

9. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 1, characterized in that: The terahertz wave generator operates at a frequency of 3.2-3.32 THz and has a radiated power of 24-30 mW / cm².

10. The preparation process of non-reactive sub-nanometer lightweight calcium carbonate according to claim 1, characterized in that: In step six, the cooked pulp is dehydrated by vacuum filtration to obtain filter cake, and the filter cake is then vacuum freeze-dried and broken up and deagglomerated by an air jet mill.

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