In-situ modification method for high dispersion and low oil absorption value nano calcium carbonate

Abstract

The application relates to the field of surface modification of functional materials, in particular to an in-situ modification preparation method of high-dispersion low-oil-absorption-value nano calcium carbonate, which comprises the following steps: step three, carbonization and in-situ modification: pumping the suspension slurry obtained in step two into a carbonization reactor, cooling to a carbonization starting temperature, and introducing CO2-containing gas to perform carbonization reaction; when the carbonization rate reaches 5% to 15%, a composite modifier is added to the reaction system, and the CO2-containing gas is continuously introduced to perform carbonization reaction until the end point, so that the nano calcium carbonate slurry modified in-situ is obtained. The composite modifier composed of a fatty acid or a salt thereof as a main modifier and a non-ionic surfactant as an auxiliary dispersant is introduced at the critical stage when the carbonization rate reaches 5% to 15%, so that instant in-situ chemical anchoring and surface hydrophobization treatment of the just-generated calcium carbonate nano particles are realized.

Description

Technical Field

[0001] This invention relates to the field of functional material surface modification technology, and in particular to an in-situ modification preparation method for highly dispersed, low oil absorption value nano-calcium carbonate. Background Technology

[0002] Nano-calcium carbonate is an important inorganic non-metallic functional filler, widely used in plastics, rubber, coatings, inks, sealants, and adhesives. Its small particle size and large specific surface area make it an optimal reinforcing filler, significantly improving the thixotropy, tensile strength, and elongation at break of finished products. However, its hydrophilic and oleophobic surface results in poor compatibility with organic matrices, leading to easy agglomeration and hindering the realization of the nano-effect. Furthermore, its high oil absorption value leads to the absorption of large amounts of plasticizers, severely degrading processing performance.

[0003] To address the aforementioned issues, existing technologies primarily employ post-processing modification techniques, i.e., surface modification of the slurry or dry powder after carbonization synthesis. However, this approach suffers from two significant technical bottlenecks: Firstly, post-processing modification suffers from an inherent defect of "pre-agglomeration - incomplete coating". During the period between synthesis and modification, nano-calcium carbonate undergoes irreversible hard agglomeration driven by its high surface energy. Subsequent modification can only coat the surface of the agglomerates, failing to reach the internal particles, resulting in persistently high oil absorption values. Even with increased modifier dosage, the oil absorption value generally remains above 20gDOP / 100gCaCO3.

[0004] Secondly, a single modifier cannot simultaneously achieve high dispersion and low oil absorption value. To obtain high dispersibility, the amount of modifier needs to be increased, but excessive modifier residue can actually lead to an increase in oil absorption value; conversely, reducing the amount results in insufficient surface coating and decreased dispersibility. Although fatty acid modifiers are inexpensive and widely used, they are difficult to disperse in aqueous phases and easily form micelles, leading to uneven coating. Simply increasing the amount cannot overcome the performance bottleneck. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide an in-situ modification preparation method for highly dispersed, low oil absorption value nano-calcium carbonate. Specifically, as follows: An in-situ modification method for preparing highly dispersed, low-oil-absorption nano-calcium carbonate includes the following steps: Step 1: Preparation of refined slurry: The CaO obtained from calcining limestone is digested and slag removed to obtain Ca(OH)2 refined slurry; Step 2, Premixing crystal form control agent: Add crystal form control agent to the Ca(OH)2 slurry obtained in Step 1, stir and disperse evenly to obtain Ca(OH)2 suspension slurry containing crystal form control agent; Step 3, Carbonization and In-situ Modification: The suspension slurry obtained in Step 2 is pumped into the carbonization reactor, cooled to the carbonization initiation temperature, and CO2 gas is introduced to carry out the carbonization reaction; when the carbonization rate reaches 5% to 15%, a composite modifier is added to the reaction system, and CO2 gas is continued to be introduced to carry out the carbonization reaction to the endpoint, and in-situ modified nano-calcium carbonate slurry is obtained. The composite modifier consists of a primary modifier and an auxiliary dispersant, wherein the primary modifier is a fatty acid or its salt, and the auxiliary dispersant is a nonionic surfactant. Step 4, Post-processing: The nano-calcium carbonate slurry obtained in Step 3 is heated and aged, then dehydrated, dried and crushed to depolymerize, thus obtaining the high-dispersion, low-oil-absorption nano-calcium carbonate finished product.

[0006] As a further technical solution of the present invention, in step one, the mass percentage concentration of the Ca(OH)2 slurry is 8% to 12%, and after preparation, it is aged at 15°C to 25°C for 12 to 36 hours.

[0007] As a further technical solution of the present invention, in step two, the crystal form control agent is selected from any one or a combination of two or more of citric acid, sodium citrate, sorbitol, sucrose, glucose, polyethylene glycol, and trisodium phosphate; the mass ratio of the crystal form control agent to Ca(OH)2 is (0.5~3.0)∶1000.

[0008] As a further technical solution of the present invention, the crystal form control agent is a composite crystal form control agent composed of citric acid and sorbitol in a mass ratio of 1:(0.5-2.0).

[0009] As a further technical solution of the present invention, in step three, the carbonization starting temperature is 10℃~25℃; the carbonization reaction is stopped when the pH value drops to 6.8~7.2, and the stirring speed of the carbonization reaction is 300rpm~800rpm.

[0010] As a further technical solution of the present invention, the carbonization reaction in step three adopts segmented temperature control: the temperature is controlled at 10℃ to 18℃ for the carbonization rate of 0 to 40%, and the temperature is controlled at 18℃ to 25℃ for the carbonization rate of 40% to 100%.

[0011] As a further technical solution of the present invention, in step three, the main modifier is one or a combination of two or more of the following: C12-C18 saturated fatty acids, C12-C18 unsaturated fatty acids, or alkali metal salts of the above fatty acids.

[0012] As a further technical solution of the present invention, in step three, the auxiliary dispersant is selected from one or more combinations of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, and polyethylene glycol.

[0013] As a further technical solution of the present invention, in step three, the mass ratio of the main modifier to the auxiliary dispersant in the composite modifier is 100:(5-30); the total amount of the composite modifier added is 2.0% to 6.0% of the theoretical mass of calcium carbonate produced.

[0014] As a further technical solution of the present invention, in step four, the temperature for heating and aging is 70℃~85℃, the aging time is 20min~40min; the drying temperature is 105℃~120℃, and the drying is carried out until the moisture content is ≤0.5%.

[0015] The beneficial effects of this invention are as follows: In this invention, a composite modifier consisting of a fatty acid or its salt as the main modifier and a nonionic surfactant as an auxiliary dispersant is introduced at the critical stage when the carbonation rate reaches 5% to 15%. At this time, the calcium carbonate crystal nuclei have just formed, and there are a large number of unsaturated calcium ions and hydroxyl groups on the surface, resulting in the highest activity. The added fatty acid can quickly form a chemical bond with the surface calcium ions to form calcium carboxylate salts, while the nonionic surfactant inhibits particle aggregation by intertwining the hydrophobic chain with the alkyl chain of the fatty acid and extending the hydrophilic chain into the water to generate steric hindrance. This maintains the uniform dispersion of the modifier in the slurry, achieving immediate in-situ chemical anchoring and surface hydrophobic treatment of the newly formed calcium carbonate nanoparticles. This solves the problem of incomplete coating and high oil absorption value caused by particle pre-agglomeration in the post-treatment modification process. The oil absorption value of the product is as low as 12 to 18 g DOP / 100 g CaCO3, which is about 40% to 55% lower than the existing post-treatment process.

[0016] In this invention, the chemical anchoring effect of the fatty acid main modifier and the steric hindrance effect of the nonionic auxiliary dispersant are combined to achieve a balance between high coating rate and excellent dispersion stability of the modified layer. This solves the problems of uneven coating caused by the easy formation of micelles in the aqueous phase by a single fatty acid modifier, and the difficulty in achieving both high dispersion and low oil absorption value. The product has an activation degree of ≥99.5%, and TEM observation shows that the particles are monodisperse and there are no visible agglomerates.

[0017] In this invention, a low-temperature segmented temperature control strategy is adopted, namely, low temperature in the early stage of carbonization to promote the rapid generation of a large number of nanocrystal nuclei, and moderate temperature increase in the later stage to promote the uniform adsorption of modifier. This achieves synergistic control of calcium carbonate particle size and modification effect, and solves the problems of wide particle size distribution and poor modification uniformity in traditional processes. The product has an average particle size of 30-80 nm, a particle size distribution PDI≤0.2, and a regular cubic morphology.

[0018] In this invention, carbonization synthesis and surface modification are combined into one step, eliminating the need for separate heating and modification after synthesis in traditional processes. This simplifies the process and reduces production costs. Furthermore, the modifier is a bulk chemical product that can be directly implemented on existing carbonization production lines. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0020] In the following examples and comparative examples, the oil absorption value was determined as follows: referring to the oil absorption determination method in GB / T19281-2014 "Analytical Methods for Calcium Carbonate", DOP (dioctyl phthalate) was used as the titration medium, and the result was expressed as the mass of DOP absorbed per 100g of calcium carbonate sample. The activation degree was determined as follows: a certain amount of modified nano-calcium carbonate sample was placed in water, stirred thoroughly, and allowed to stand. The percentage of the sample mass floating on the water surface relative to the total sample mass was measured. Particle size and morphology were observed and determined using transmission electron microscopy and scanning electron microscopy. Specific surface area was determined using the BET nitrogen adsorption method. Crystal form was determined using X-ray diffraction.

[0021] Example 1

[0022] This embodiment provides an in-situ modification method for preparing highly dispersed, low-oil-absorption nano-calcium carbonate, comprising the following steps: Step 1: Prepare the seminal fluid; Limestone is calcined at 1050℃ to obtain CaO and kiln gas. CaO is mixed with water at 90℃ in a mass ratio of 1:6 for digestion reaction to obtain a crude Ca(OH)2 slurry. The crude slurry is then sieved through 100-mesh, 200-mesh, and 325-mesh vibrating screens to remove slag. Water is added to adjust the mass percentage concentration of Ca(OH)2 to 10%, and the slurry is aged at 20℃ for 24 hours to obtain a refined Ca(OH)2 slurry. Step 2: Premixing crystal form control agent; Weigh out citric acid and sorbitol, with the amount of citric acid calculated as a Ca(OH)2 to citric acid mass ratio of 1000:1.2 and the amount of sorbitol calculated as a Ca(OH)2 to sorbitol mass ratio of 1000:1.0; dissolve both in deionized water to prepare a 3% (w / w) aqueous solution of the composite crystal form control agent; add this solution to the Ca(OH)2 slurry obtained in step one, and stir and disperse at 400 rpm for 20 min to obtain a Ca(OH)2 suspension containing the crystal form control agent; Step 3: Carbonization and in-situ modification; The suspension slurry obtained in step two is pumped into the carbonation reactor. The slurry temperature is reduced to 15°C through a heat exchanger. Under continuous stirring at 500 rpm, the kiln gas collected in step one is introduced at a flow rate of 1.0 L / min to carry out the carbonation reaction. When the carbonation rate reaches 10%, that is, about 10% of Ca(OH)2 in the system has been converted into CaCO3, a pre-prepared composite modifier is added to the reaction system. The composite modifier consists of: a main modifier, stearic acid and oleic acid mixed in a mass ratio of 3:1; and an auxiliary dispersant, fatty alcohol polyoxyethylene ether AEO-7, which accounts for 15% of the mass of the main modifier; and the total amount of composite modifier added is 3.5% of the theoretical mass of calcium carbonate produced. The carbonization reaction was carried out in stages with temperature control: the temperature was maintained at 15℃ during the carbonization rate of 0-40%; the temperature was slowly increased to 20℃ during the carbonization rate of 40%-100% and the pH value of the reaction system was continuously monitored. When the pH value dropped to 7.0, the carbonization reaction reached its endpoint, and the aeration and stirring were stopped to obtain the in-situ modified nano-calcium carbonate slurry.

[0023] Step 4: Post-processing; The slurry obtained in step three is heated to 80°C and aged for 30 minutes with continuous stirring to ensure that the modifier is fully chemically adsorbed and physically coated on the surface of the calcium carbonate particles. Then, it is dehydrated by a plate and frame filter press, and the filter cake is dried at 110°C to a moisture content of 0.3%. The dried product is then depolymerized by air jet milling to obtain the highly dispersed, low-oil-absorption nano-calcium carbonate product.

[0024] In this embodiment, the preparation method of the composite modifier is as follows: the fatty acid main modifier is heated to 70-80℃ to melt, an auxiliary dispersant is added, and the mixture is stirred evenly. Then, it is slowly added to hot water at 60-70℃, and emulsified and dispersed at 3000-5000 rpm for 10-15 minutes to form a uniform milky white aqueous dispersion, which is immediately used for in-situ modification. Alternatively, the fatty acid is saponified with an equimolar amount of sodium hydroxide or potassium hydroxide at 80℃ for 30 minutes to generate a fatty acid soap solution. After cooling to 40℃, an auxiliary dispersant is added, and the solution is diluted to a suitable concentration before use.

[0025] In this embodiment, the carbonization rate during the carbonization reaction is calculated by online monitoring of the conductivity value of the reaction slurry: the conductivity curves of the slurry at different carbonization rates are pre-calibrated, and conductivity data is collected in real time during the carbonization process. When the calculation shows that the carbonization rate reaches 10% (corresponding to the conductivity value dropping to approximately 85%-90% of the initial value), a pre-prepared composite modifier is added to the reaction system. As another optional real-time monitoring method, the carbonization rate can also be determined by measuring the ratio of the cumulative CO2 gas flow rate released by the reaction system to the theoretical total amount.

[0026] Example 2

[0027] The only difference between this embodiment and Embodiment 1 is that: In step two, the crystal form control agent uses sucrose as a single component, with a Ca(OH)2 to sucrose mass ratio of 1000:1.5, replacing the composite crystal form control agent of citric acid and sorbitol; In step three, the total amount of composite modifier added is 4.0% of the theoretical mass of calcium carbonate produced.

[0028] Example 3

[0029] The only difference between this embodiment and Embodiment 1 is that: In step three, the main modifier is stearic acid, and the total amount of composite modifier added is 3.0% of the theoretical mass of calcium carbonate produced; the carbonation reaction is maintained at 20°C throughout without segmented temperature control.

[0030] Example 4

[0031] The only difference between this embodiment and Embodiment 1 is that: In step three: the initial carbonization temperature is reduced to 10℃; the segmented temperature control is adjusted as follows: maintain 10℃ during the carbonization rate of 0-40%, and slowly increase the temperature to 18℃ during the carbonization rate of 40%-100%.

[0032] Example 5

[0033] The only difference between this embodiment and Embodiment 1 is that: In step three: the timing of adding the composite modifier is adjusted to when the carbonization rate reaches 15%; the auxiliary dispersant is alkylphenol polyoxyethylene ether OP-10, and the amount used accounts for 20% of the mass of the main modifier.

[0034] Comparative Example 1 (Post-treatment wet modification process) Step 1: Prepare the seminal fluid; Limestone was calcined at 1050℃ to obtain CaO and kiln gas. The CaO was then mixed with water at a mass ratio of 1:6 at 90℃ for a digestion reaction, yielding a crude Ca(OH)₂ slurry. The crude slurry was sequentially sieved through 100-mesh, 200-mesh, and 325-mesh vibrating screens to remove slag. Water was added to adjust the Ca(OH)₂ mass percentage concentration to 10%, and the mixture was aged at 20℃ for 24 hours to obtain a refined Ca(OH)₂ slurry.

[0035] Step 2: Premixing crystal form control agent; Weigh out citric acid and sorbitol, with the amount of citric acid used based on a Ca(OH)₂ to citric acid mass ratio of 1000:1.2 and the amount of sorbitol used based on a Ca(OH)₂ to sorbitol mass ratio of 1000:1.0. Dissolve both in deionized water to prepare a 3% (w / w) aqueous solution of the composite crystal form control agent. Add this solution to the Ca(OH)₂ slurry obtained in step one and stir at 400 rpm for 20 min to obtain a Ca(OH)₂ suspension containing the crystal form control agent.

[0036] Step 3: Carbonization synthesis (without in-situ modification); The suspension slurry obtained in step two was pumped into the carbonation reactor, and the slurry temperature was adjusted to 25°C. Under continuous stirring at 500 rpm, kiln gas was introduced at a flow rate of 1.0 L / min to carry out the carbonation reaction, without adding any modifiers. The pH value was continuously monitored, and aeration was stopped when the pH value dropped to 7.0, yielding unmodified nano-calcium carbonate slurry.

[0037] Step 4: Post-processing modification; The unmodified nano-calcium carbonate slurry obtained in step three was heated to 70°C, and stearic acid was added at a rate of 4% of the calcium carbonate mass. The mixture was kept at this temperature and stirred for 50 minutes for modification. Then, it was dehydrated by a plate and frame filter press, and the filter cake was dried at 110°C until the moisture content was 0.3%. The dried product was then depolymerized by air jet milling to obtain the finished nano-calcium carbonate product.

[0038] Comparative Example 2 (Integrated carbonization-modification process, modifier added before carbonization, no segmented temperature control or auxiliary dispersant) Step 1: Prepare the seminal fluid; Limestone was calcined at 1050℃ to obtain CaO and kiln gas. The CaO was then mixed with water at a mass ratio of 1:6 at 90℃ for a digestion reaction, yielding a crude Ca(OH)₂ slurry. The crude slurry was sequentially sieved through 100-mesh, 200-mesh, and 325-mesh vibrating screens to remove slag. Water was added to adjust the Ca(OH)₂ mass percentage concentration to 10%, and the mixture was aged at 20℃ for 24 hours to obtain a refined Ca(OH)₂ slurry.

[0039] Step 2: Premixing crystal form control agent; Weigh out citric acid and sorbitol, with the amount of citric acid used based on a Ca(OH)₂ to citric acid mass ratio of 1000:1.2 and the amount of sorbitol used based on a Ca(OH)₂ to sorbitol mass ratio of 1000:1.0. Dissolve both in deionized water to prepare a 3% (w / w) aqueous solution of the composite crystal form control agent. Add this solution to the Ca(OH)₂ slurry obtained in step one and stir at 400 rpm for 20 min to obtain a Ca(OH)₂ suspension containing the crystal form control agent.

[0040] Step 3: Integrated carbonization-modification treatment; The suspension slurry obtained in step two was pumped into the carbonation reactor, and the slurry temperature was adjusted to 25°C and maintained throughout the process. Before introducing kiln gas for the carbonation reaction, sodium stearate was added to the slurry in one go, at a rate of 4% of the theoretically produced calcium carbonate mass, and stirred thoroughly. Then, kiln gas was introduced at a flow rate of 1.0 L / min with stirring at 500 rpm to carry out the carbonation reaction. The pH value was continuously monitored, and the gas supply was stopped when the pH value dropped to 7.0, yielding the modified nano-calcium carbonate slurry.

[0041] Step 4: Post-processing; The slurry obtained in step three is heated to 80°C and kept at this temperature while stirring and aging for 30 minutes. It is then dehydrated using a plate and frame filter press, and the filter cake is dried at 110°C until the moisture content is 0.3%. The dried product is then deagglomerated by air jet milling to obtain the final product.

[0042] The products prepared in Examples 1-5, Comparative Examples 1 and 2 were subjected to performance testing, and the test results are shown in Table 1.

[0043] Table 1 The data in the table above shows that: (1) The oil absorption value of Comparative Example 1 is as high as 28g / 100g, the activation degree is only 95.2%, and the PDI is 0.35, indicating that the particles have undergone serious pre-agglomeration before modification in the post-processing process. The modifier cannot effectively encapsulate the interior of the agglomerates, resulting in the worst overall performance.

[0044] (2) The oil absorption value of Comparative Example 2 was 22g / 100g and the activation degree was 97.1%, which was better than Comparative Example 1, but the particle size was the largest. This indicates that the premature addition of the modifier interfered with the crystal nucleus generation process, and the single sodium stearate lacked the synergistic effect of the auxiliary dispersant, thus limiting the coating efficiency.

[0045] (3) The oil absorption value and activation degree of each embodiment of the present invention are significantly better than those of the two comparative examples, which verifies the effectiveness of the core technical feature of "introducing composite modifier in the carbonization critical stage".

[0046] (4) A comparison between Example 1 and Example 3 shows that segmented temperature control, compared with constant temperature of 20℃ throughout, resulted in smaller particle size and lower oil absorption value, proving that the low temperature in the early stage is beneficial to obtaining finer nanoparticles. Example 1 and Example 3 also compared the effects of compound fatty acids and single stearic acid, and compound fatty acids had advantages in both activation degree and oil absorption value.

[0047] (5) Example 4 uses a lower carbonization initiation temperature and segmented temperature control to obtain the finest particle size, the highest specific surface area and the lowest oil absorption value, indicating that further reducing the carbonization pre-stage temperature is beneficial to the explosive generation of crystal nuclei, which is the optimal implementation of the present invention.

[0048] (6) Example 2 uses a single crystal form control agent of sucrose. In Example 5, the timing of adding the modifier was adjusted to a carbonization rate of 15% and the auxiliary dispersant was replaced with OP-10. Although the indicators of both are slightly inferior to those of Example 1, the oil absorption value and activation degree are still significantly better than the comparative example, indicating that the technical solution of the present invention has significant performance advantages in a wide range of parameters.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A method for in-situ modification and preparation of highly dispersed, low-oil-absorption nano-calcium carbonate, characterized in that, Includes the following steps: Step 1: Preparation of refined slurry: The CaO obtained from calcining limestone is digested and slag removed to obtain Ca(OH)2 refined slurry; Step 2, Premixing crystal form control agent: Add crystal form control agent to the Ca(OH)2 slurry obtained in Step 1, stir and disperse evenly to obtain Ca(OH)2 suspension slurry containing crystal form control agent; Step 3, Carbonization and In-situ Modification: The suspension slurry obtained in Step 2 is pumped into the carbonization reactor, cooled to the carbonization initiation temperature, and CO2 gas is introduced to carry out the carbonization reaction; when the carbonization rate reaches 5% to 15%, a composite modifier is added to the reaction system, and CO2 gas is continued to be introduced to carry out the carbonization reaction to the endpoint, and in-situ modified nano-calcium carbonate slurry is obtained. The composite modifier consists of a primary modifier and an auxiliary dispersant, wherein the primary modifier is a fatty acid or its salt, and the auxiliary dispersant is a nonionic surfactant. Step 4, Post-processing: The nano-calcium carbonate slurry obtained in Step 3 is heated and aged, then dehydrated, dried and crushed to depolymerize, thus obtaining the high-dispersion, low-oil-absorption nano-calcium carbonate finished product.

2. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 1, characterized in that, In step one, the mass percentage concentration of the Ca(OH)2 slurry is 8% to 12%, and after preparation, it is aged at 15℃ to 25℃ for 12 to 36 hours.

3. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 1, characterized in that, In step two, the crystal form control agent is selected from any one or a combination of two or more of citric acid, sodium citrate, sorbitol, sucrose, glucose, polyethylene glycol, and trisodium phosphate; the mass ratio of the crystal form control agent to Ca(OH)2 is (0.5-3.0):1000.

4. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 3, characterized in that, The crystal form control agent is a composite crystal form control agent composed of citric acid and sorbitol in a mass ratio of 1:(0.5-2.0).

5. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 1, characterized in that, In step three, the initial carbonization temperature is 10℃~25℃; the carbonization reaction is stopped when the pH value drops to 6.8~7.2, and the stirring speed of the carbonization reaction is 300rpm~800rpm.

6. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 1, characterized in that, In step three, the carbonization reaction is carried out in stages with temperature control: the temperature is controlled at 10℃ to 18℃ for the carbonization rate of 0% to 40%, and at 18℃ to 25℃ for the carbonization rate of 40% to 100%.

7. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 1, characterized in that, In step three, the main modifier is one or a combination of two or more of the following: C12-C18 saturated fatty acids, C12-C18 unsaturated fatty acids, or alkali metal salts of the above fatty acids.

8. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 1, characterized in that, In step three, the auxiliary dispersant is selected from one or more combinations of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, and polyethylene glycol.

9. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 1, characterized in that, In step three, the mass ratio of the main modifier to the auxiliary dispersant in the composite modifier is 100:(5-30); the total amount of the composite modifier added is 2.0% to 6.0% of the theoretical mass of calcium carbonate produced.

10. The in-situ modification preparation method of highly dispersed, low oil absorption value nano-calcium carbonate according to claim 1, characterized in that, In step four, the temperature for heating and aging is 70℃~85℃, and the aging time is 20min~40min; the drying temperature is 105℃~120℃, and the drying is carried out until the moisture content is ≤0.5%.

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