Process for the wet preparation of nanometric calcium carbonate

Abstract

The present application relates to the technical field of calcium carbonate preparation, in particular to a process for preparing nano calcium carbonate by wet method. The preparation process comprises the following steps: preparing a compound crystallization aid; preparing a bacteria solution; and preparing nano calcium carbonate. The compound crystallization aid is prepared by combining phthalic anhydride and glycine, and the crystallization aid is prepared by compounding a glycine derivative and sodium dodecyl sulfate. The molecular structure of the glycine derivative contains carboxylic acid groups and amide groups, which enable the glycine derivative to form a strong interaction with calcium carbonate, further enhancing the binding force of the organic-inorganic interface. Compared with traditional stearic acid or silane coupling agent, the double functional group structure of the glycine derivative can provide stronger surface anchoring effect, reduce the amount of the aid, prevent nano-particle agglomeration, promote uniform nucleation, and thus improve the yield of nano calcium carbonate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of calcium carbonate preparation, in particular to a process for preparing nano calcium carbonate by wet method. BACKGROUND

[0002] Nano calcium carbonate has a wide range of applications in various fields due to its unique physical and chemical properties. In plastics, nano calcium carbonate can significantly improve the mechanical properties and thermal stability of materials such as PP and PVC, and also impart better surface finish to the products. In rubber products, the addition of nano calcium carbonate can improve tensile strength, tear strength, and wear resistance, while reducing production costs. In coatings, nano calcium carbonate can improve hiding power, washability, and weather resistance, and its steric hindrance effect can effectively prevent pigment sedimentation. In inks, nano calcium carbonate can improve printing suitability, increase ink drying speed, and improve adhesion. As a high-grade paper filler, nano calcium carbonate can improve paper whiteness, opacity, and smoothness, and significantly improve printing suitability. In wastewater treatment, nano calcium carbonate can be used as a high-efficiency adsorbent to remove heavy metal ions. In building materials, the addition of nano calcium carbonate can improve the early strength and durability of cement.

[0003] Nano calcium carbonate has a wide range of applications in various fields due to its unique physical and chemical properties. It not only improves the performance and quality of products, but also reduces production costs and promotes the sustainable development of the industry. The existing technology for preparing nano calcium carbonate includes dry method and wet method. The wet method specifically involves dissolving calcined calcium oxide, which is the raw material for producing calcium carbonate, in water and performing digestion reaction to generate calcium hydroxide suspension. Then, high-purity carbon dioxide gas is introduced into the suspension of a certain concentration and purity to perform carbonation reaction. By controlling the temperature, pH value, and flow rate of carbon dioxide gas, the nucleation rate of calcium carbonate crystal nucleus is adjusted. Nano calcium carbonate is obtained. Finally, the prepared nano calcium carbonate is filtered, washed, and dried to obtain the final product. The wet carbonation method is relatively mature, simple to operate, and easy to realize industrial large-scale production. By optimizing the reaction conditions and equipment design, high efficiency and low cost production can be achieved to meet the market demand for nano calcium carbonate. However, nano calcium carbonate particles are prone to agglomeration during preparation, resulting in a wide particle size distribution. Therefore, surface treatment and the use of dispersants are needed to inhibit agglomeration, but this will result in a decrease in the yield of nano calcium carbonate. Therefore, the present application provides a process for preparing nano calcium carbonate by wet method, which adds additives to improve crystallization, prevent nano particle agglomeration, and increase the yield of nano calcium carbonate. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide a process for preparing nano calcium carbonate by wet method.

[0005] A process for preparing nano calcium carbonate by a wet method comprises the following steps:

[0006] S1: Preparation of compound crystallization aid

[0007] Phthalic anhydride and glycine are mixed and stirred, heated to react, and then glacial acetic acid is added, followed by cooling and crystallization, filtering and then recrystallizing with ethanol aqueous solution to obtain a glycine derivative, and the glycine derivative is mixed and stirred with sodium lauryl sulfate to obtain a composite crystallization aid;

[0008] S2: Preparation of bacterial suspension

[0009] Peptone, beef extract, and agar powder are added to deionized water, stirred, and sterilized to obtain solution A. 3-Cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid, and deionized water are mixed and sterilized to obtain solution B. Solution A and solution B are mixed and poured into a culture dish. Alkaliphilic Bacillus and urea are added, and cultured at a constant temperature to obtain a bacterial solution.

[0010] S3: Preparation of nano calcium carbonate

[0011] The snail shells are cleaned and dried, calcined, ground, and sieved to obtain snail shell powder. The snail shell powder is mixed with a hydrochloric acid solution, and then the pH is adjusted to 8-10. Subsequently, a compound crystallization aid is added, and a carbon dioxide device and a carbonization device are connected to start carbonization. When the pH of the reaction system drops to 7.5, the carbon dioxide flow is stopped, and then a bacterial solution, sodium bicarbonate, and urea are added, and the carbon dioxide flow is continued to obtain nano calcium carbonate.

[0012] Furthermore, step S1 of preparing a compound crystallization aid comprises the following steps:

[0013] S1.1: Mix phthalic anhydride and glycine in a mass ratio of 1:(1-3), stir on a magnetic stirrer at 200-250 rpm, and heat to 80-100°C. React under these conditions for 20-30 min.

[0014] S1.2: Add an equal amount of glacial acetic acid to the system, cool and crystallize, filter and recrystallize with a 50-60 wt% ethanol aqueous solution to obtain a glycine derivative, and stir and mix the glycine derivative and sodium lauryl sulfate in a volume ratio of 1:(1-2) to obtain a compound crystallization aid.

[0015] Furthermore, step S2 of preparing bacterial liquid includes the following steps:

[0016] S2.1: Add 3-4 parts by weight of peptone, 10-12 parts by weight of beef extract, and 20-30 parts by weight of agar powder to 800-850 parts by weight of deionized water. Stir at 350-400 rpm for 20-25 minutes, then sterilize to obtain Solution A.

[0017] S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid, and deionized water in a mass ratio of 1:(0.5-0.8):(4-8) and sterilize to obtain Solution B;

[0018] S2.3: Mix solution A and solution B in a 1:1 mass ratio and pour into a culture dish. Add 2% volume fraction of alkaliphilic Bacillus and 2 mol / L urea in that order. Incubate at a constant temperature of 35-36°C for 48-49 hours to obtain a bacterial solution.

[0019] Furthermore, step S3 of preparing nano calcium carbonate comprises the following steps:

[0020] S3.1: Clean and dry the snail shells, calcine them in a muffle furnace at 700-800°C for 4-5 hours, grind them, and pass them through a 200-mesh sieve to obtain snail shell powder;

[0021] S3.2: Mix the shell powder with hydrochloric acid solution at a liquid-to-solid ratio of 6:1 mL / g and allow to react for 24-25 hours. Then, add NaOH solution to adjust the pH to 8-10. Then, add 20-40% of the system weight of a compound crystallization aid. Adjust the solution temperature to 20°C, connect the carbon dioxide apparatus and carbonization apparatus, and begin carbonization.

[0022] S3.3: Detect the pH value of the reaction system in real time. When the pH of the reaction system drops to 7.5, stop adding carbon dioxide. Then add 20-25 mg / L bacterial liquid, 1 mol / L sodium bicarbonate and 2 mol / L urea. Continue the carbonization reaction with carbon dioxide for 24-25 hours. Then remove the product, sonicate it, centrifuge it for washing, dry it, grind it, and sieve it to obtain nano calcium carbonate.

[0023] Furthermore, the alkaliphilic Bacillus is specifically alkaliphilic Bacillus H4.

[0024] Furthermore, the concentration of the hydrochloric acid solution is 1 mol / L.

[0025] Furthermore, the concentration of the NaOH solution is 1.5 mol / L. Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] 1. The application combines phthalic anhydride and glycine to prepare a complex crystallization aid, and combines glycine derivatives with sodium dodecyl sulfate to prepare a crystallization aid, the molecular structure of the glycine derivative contains carboxylic acid groups and amide groups, these functional groups enable it to form a strong interaction with calcium carbonate, the oxygen atoms in the carboxylic acid group have lone pair electrons, which can form a coordination bond with calcium carbonate, enhancing the interfacial bonding force between organic molecules and inorganic particles, the amide group can form hydrogen bonds with the hydroxyl groups on the surface of calcium carbonate or water molecules, further enhancing the bonding force of the organic-inorganic interface, and compared with traditional stearic acid or silane coupling agent, the double functional group structure of glycine derivative can provide stronger surface anchoring effect, reducing the amount of aid used, sodium dodecyl sulfate as an anionic surfactant can reduce the surface tension of the solution, prevent nanoparticle agglomeration, promote uniform nucleation, thereby improving the yield of nano calcium carbonate.

[0027] 2. The application combines 3-cyclohexylamine propyl sulfonic acid and 4-hydroxyethyl piperazine ethanesulfonic acid to provide a culture solution for the growth and development of alkaliphilic Bacillus, both 3-cyclohexylamine propyl sulfonic acid and 4-hydroxyethyl piperazine ethanesulfonic acid are biological buffers that can stabilize pH, adapt to the alkaline growth environment of alkaliphilic Bacillus, and the combination of the two can also widen the pH buffering range, avoid pH fluctuations caused by urea hydrolysis, and ensure the yield of nano calcium carbonate.

[0028] 3. The application adds the bacterial solution of alkaliphilic Bacillus and the complex crystallization aid to the liquid prepared from calcium ion-containing conch powder, and prepares calcium carbonate by adding carbon dioxide, the exopolysaccharide and urease secreted by the bacterial body of alkaliphilic Bacillus can guide the directional crystallization of calcium carbonate, forming uniform nanoparticles, the exopolysaccharide of alkaliphilic Bacillus and glycine derivatives synergistically regulate calcium carbonate crystallization through biological template effect and molecular interface modification, showing significant advantages in crystal type selection, dispersion stability and functional application, improving the yield and purity of nano calcium carbonate. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings, which are incorporated herein and constitute part of the specification, illustrate embodiments of the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable a person skilled in the relevant art to implement and use the present disclosure.

[0030] Figure 1 A process flow chart for wet preparation of nano calcium carbonate is used in an embodiment of the application. DETAILED DESCRIPTION

[0031] Below, in conjunction with the accompanying drawings and specific examples, a process for preparing nano-calcium carbonate by a wet process provided by the present invention is described in detail. At the same time, it is noted that, in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art may also adopt other alternatives to implement some known technologies; and the accompanying drawings are only for more specific description of the embodiments, and are not intended to specifically limit the present invention. Example 1

[0032] A process for preparing nano calcium carbonate by wet method, such as Figure 1 As shown, the following steps are included:

[0033] S1: Preparation of compound crystallization aid

[0034] S1.1: Mix phthalic anhydride and glycine in a 1:1 mass ratio, stir on a magnetic stirrer at 200 rpm, and heat to 80°C for 20 min.

[0035] S1.2: Add an equal amount of glacial acetic acid to the system, cool and crystallize, filter and recrystallize with a 50 wt% ethanol aqueous solution to obtain a glycine derivative, and stir and mix the glycine derivative and sodium lauryl sulfate in a volume ratio of 1:1 to obtain a compound crystallization aid.

[0036] S2: Preparation of bacterial suspension

[0037] S2.1: Add 3 parts by mass of peptone, 10 parts by mass of beef extract, and 20 parts by mass of agar powder to 800 parts by mass of deionized water. Stir at 350 rpm for 20 min and then sterilize to obtain Solution A.

[0038] S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid, and deionized water in a mass ratio of 1:0.5:4 and sterilize to obtain Solution B.

[0039] S2.3: Mix solution A and solution B in a 1:1 mass ratio and pour into a culture dish. Add 2% volume fraction of alkaliphilic Bacillus H4 and 2 mol / L urea in sequence. Incubate at a constant temperature of 35°C for 48 h to obtain a bacterial solution.

[0040] S3: Preparation of nano calcium carbonate

[0041] S3.1: The shells were cleaned and dried, calcined in a muffle furnace at 700°C for 4 h, ground, and passed through a 200-mesh sieve to obtain shell powder;

[0042] S3.2: Mix the shell powder with a 1 mol / L hydrochloric acid solution at a liquid-to-solid ratio of 6:1 mL / g and allow to react for 24 h. Then, add a 1.5 mol / L NaOH solution to adjust the pH to 8. Then, add 20% of the system weight of a compound crystallization aid. Adjust the solution temperature to 20°C, connect the carbon dioxide apparatus and carbonization apparatus, and begin carbonization.

[0043] S3.3: Detect the pH value of the reaction system in real time. When the pH of the reaction system drops to 7.5, stop the carbon dioxide flow. Then add 20 mg / L of bacterial liquid, 1 mol / L of sodium bicarbonate and 2 mol / L of urea. Continue the carbonization reaction with carbon dioxide for 24 hours. Then remove the product, sonicate it, centrifuge it for washing, dry it, grind it, and sieve it to obtain nano calcium carbonate. Example 2

[0044] A process for preparing nano calcium carbonate by wet method, such as Figure 1 As shown, the following steps are included:

[0045] S1: Preparation of compound crystallization aid

[0046] S1.1: Mix phthalic anhydride and glycine in a mass ratio of 1:3, stir on a magnetic stirrer at 200 rpm, and heat to 80°C for 20 min.

[0047] S1.2: Add an equal amount of glacial acetic acid to the system, cool and crystallize, filter and recrystallize with a 50 wt% ethanol aqueous solution to obtain a glycine derivative, and stir and mix the glycine derivative and sodium lauryl sulfate in a volume ratio of 1:2 to obtain a compound crystallization aid.

[0048] S2: Preparation of bacterial suspension

[0049] S2.1: Add 4 parts by mass of peptone, 12 parts by mass of beef extract, and 30 parts by mass of agar powder to 850 parts by mass of deionized water. Sterilize at 350 rpm for 20 minutes and obtain Solution A.

[0050] S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid, and deionized water in a mass ratio of 1:0.8:8 and sterilize to obtain Solution B;

[0051] S2.3: Mix solution A and solution B in a 1:1 mass ratio and pour into a culture dish. Add 2% volume fraction of alkaliphilic Bacillus H4 and 2 mol / L urea in sequence. Incubate at a constant temperature of 35°C for 48 h to obtain a bacterial solution.

[0052] S3: Preparation of nano calcium carbonate

[0053] S3.1: The shells were cleaned and dried, calcined in a muffle furnace at 700°C for 4 h, ground, and passed through a 200-mesh sieve to obtain shell powder;

[0054] S3.2: Mix the shell powder with a 1 mol / L hydrochloric acid solution at a liquid-to-solid ratio of 6:1 mL / g and allow to react for 24 h. Then, add a 1.5 mol / L NaOH solution to adjust the pH to 8. Then, add 40% of the system weight of a compound crystallization aid. Adjust the solution temperature to 20°C, connect the carbon dioxide apparatus and carbonization apparatus, and begin carbonization.

[0055] S3.3: Detect the pH value of the reaction system in real time. When the pH of the reaction system drops to 7.5, stop passing carbon dioxide. Then add 25 mg / L bacterial liquid, 1 mol / L sodium bicarbonate and 2 mol / L urea. Continue the carbonization reaction with carbon dioxide for 24 hours. Then remove the product, sonicate it, centrifuge it, wash it, dry it, grind it, and sieve it to obtain nano calcium carbonate. Example 3

[0056] A process for preparing nano calcium carbonate by wet method, such as Figure 1 As shown, the following steps are included:

[0057] S1: Preparation of compound crystallization aid

[0058] S1.1: Mix phthalic anhydride and glycine in a 1:1 mass ratio, stir on a magnetic stirrer at 250 rpm, and heat to 100°C for 30 min.

[0059] S1.2: Add an equal amount of glacial acetic acid to the system, cool and crystallize, filter and recrystallize with a 50 wt% ethanol aqueous solution to obtain a glycine derivative, and stir and mix the glycine derivative and sodium lauryl sulfate in a volume ratio of 1:1 to obtain a compound crystallization aid.

[0060] S2: Preparation of bacterial suspension

[0061] S2.1: Add 3 parts by mass of peptone, 10 parts by mass of beef extract, and 20 parts by mass of agar powder to 800 parts by mass of deionized water. Stir at 400 rpm for 25 minutes and then sterilize to obtain Solution A.

[0062] S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid, and deionized water in a mass ratio of 1:0.5:4 and sterilize to obtain Solution B.

[0063] S2.3: Mix solution A and solution B in a 1:1 mass ratio and pour into a culture dish. Add 2% volume fraction of alkaliphilic Bacillus H4 and 2 mol / L urea in sequence. Incubate at a constant temperature of 36°C for 49 h to obtain a bacterial solution.

[0064] S3: Preparation of nano calcium carbonate

[0065] S3.1: The shells were cleaned and dried, calcined in a muffle furnace at 750°C for 5 h, ground, and passed through a 200-mesh sieve to obtain shell powder;

[0066] S3.2: Mix the shell powder with a 1 mol / L hydrochloric acid solution at a liquid-to-solid ratio of 6:1 mL / g and allow to react for 25 h. Then, add a 1.5 mol / L NaOH solution to adjust the pH to 10. Then, add 20% of the system weight of a compound crystallization aid. Adjust the solution temperature to 20°C, connect the carbon dioxide apparatus and carbonization apparatus, and begin carbonization.

[0067] S3.3: Detect the pH value of the reaction system in real time. When the pH of the reaction system drops to 7.5, stop adding carbon dioxide. Then add 20 mg / L bacterial liquid, 1 mol / L sodium bicarbonate and 2 mol / L urea. Continue the carbonization reaction with carbon dioxide for 25 hours. Then remove the product, sonicate it, centrifuge it, wash it, dry it, grind it, and sieve it to obtain nano calcium carbonate. Example 4

[0068] A process for preparing nano calcium carbonate by wet method, such as Figure 1 As shown, the following steps are included:

[0069] S1: Preparation of compound crystallization aid

[0070] S1.1: Mix phthalic anhydride and glycine in a 1:1 mass ratio, stir on a magnetic stirrer at 250 rpm, and heat to 100°C for 30 min.

[0071] S1.2: Add an equal amount of glacial acetic acid to the system, cool and crystallize, filter and recrystallize with a 50 wt% ethanol aqueous solution to obtain a glycine derivative, and stir and mix the glycine derivative and sodium lauryl sulfate in a volume ratio of 1:1 to obtain a compound crystallization aid.

[0072] S2: Preparation of bacterial suspension

[0073] S2.1: Add 3 parts by mass of peptone, 10 parts by mass of beef extract, and 20 parts by mass of agar powder to 800 parts by mass of deionized water. Stir at 400 rpm for 25 minutes and then sterilize to obtain Solution A.

[0074] S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid, and deionized water in a mass ratio of 1:0.5:4 and sterilize to obtain Solution B.

[0075] S2.3: Mix solution A and solution B in a 1:1 mass ratio and pour into a culture dish. Add 2% volume fraction of alkaliphilic Bacillus H4 and 2 mol / L urea in sequence. Incubate at a constant temperature of 36°C for 49 h to obtain a bacterial solution.

[0076] S3: Preparation of nano calcium carbonate

[0077] S3.1: The shells are cleaned and dried, calcined in a muffle furnace at 800°C for 5 h, ground, and passed through a 200-mesh sieve to obtain shell powder;

[0078] S3.2: Mix the shell powder with a 1 mol / L hydrochloric acid solution at a liquid-to-solid ratio of 6:1 mL / g and allow to react for 25 h. Then, add a 1.5 mol / L NaOH solution to adjust the pH to 10. Then, add 20% of the system weight of a compound crystallization aid. Adjust the solution temperature to 20°C, connect the carbon dioxide apparatus and carbonization apparatus, and begin carbonization.

[0079] S3.3: Detect the pH value of the reaction system in real time. When the pH of the reaction system drops to 7.5, stop adding carbon dioxide. Then add 20 mg / L bacterial liquid, 1 mol / L sodium bicarbonate and 2 mol / L urea. Continue the carbonization reaction with carbon dioxide for 25 hours. Then remove the product, sonicate it, centrifuge it, wash it, dry it, grind it, and sieve it to obtain nano calcium carbonate.

[0080] Comparative Example 1:

[0081] Comparative Example 1: Commercially available nano calcium carbonate.

[0082] Comparative Example 2:

[0083] Compared with Example 1, the difference of Comparative Example 2 is that step S1 is not performed, and no compound crystallization aid is added in step S3.2. Specifically, "S3.2: the snail shell powder is mixed with 1 mol / L hydrochloric acid solution at a liquid-solid ratio of 6:1 mL / g for 24 hours, and then 1.5 mol / L NaOH solution is added to adjust the pH to 8, the solution temperature is adjusted to 20°C, the carbon dioxide device and the carbonization device are connected, and carbonization is started". The remaining steps remain unchanged, and the prepared nano calcium carbonate is recorded as Comparative Example 2.

[0084] Comparative Example 3:

[0085] Compared with Example 1, the difference of Comparative Example 3 is that step S2 is not performed, and no bacterial liquid is added in step S3.3. Instead, the lubricating hydrogel is replaced with the lubricant prepared in step S2.1, specifically "S3.3: real-time detection of the pH value of the reaction system, stop passing carbon dioxide when the pH of the reaction system drops to 7.5, then add 1 mol / L sodium bicarbonate and 2 mol / L urea, continue the carbonization reaction with carbon dioxide for 24 hours, then take out the product, ultrasonicate, centrifuge and wash, dry, grind, and sieve to obtain nano calcium carbonate", the other steps remain unchanged, and the prepared nano calcium carbonate is recorded as Comparative Example 3.

[0086] Comparative Example 4:

[0087] Compared with Example 1, the difference of Comparative Example 4 is that step S1 and step S2 are not performed, and carbon dioxide is directly introduced into step S3 to prepare nano-calcium carbonate, specifically "S3: Preparation of nano-calcium carbonate

[0088] S3.1: The shells were cleaned and dried, calcined in a muffle furnace at 700°C for 4 h, ground, and passed through a 200-mesh sieve to obtain shell powder;

[0089] S3.2: Mix the shell powder with a 1 mol / L hydrochloric acid solution at a liquid-to-solid ratio of 6:1 mL / g and allow to react for 24 h. Then, add a 1.5 mol / L NaOH solution to adjust the pH to 8. Adjust the solution temperature to 20°C, connect the carbon dioxide apparatus and carbonization apparatus, and begin carbonization.

[0090] S3.3: Real-time monitoring of the pH value of the reaction system. When the pH of the reaction system drops to 7.5, the carbon dioxide gas flow is stopped, and 1 mol / L sodium bicarbonate and 2 mol / L urea are added. The carbonization reaction is continued for 24 hours. The product is then removed, ultrasonicated, centrifuged, washed, dried, ground, and sieved to obtain nano-calcium carbonate. The remaining steps remain unchanged, and the prepared nano-calcium carbonate is recorded as Comparative Example 4.

[0091] The yields of nano-calcium carbonate added to Examples 1-4 of the present invention and Comparative Examples 2-3 were calculated, as shown in Table 1.

[0092] Table 1

[0093] Yield (%) Example 1 72.35 Example 2 72.64 Example 3 72.14 Example 4 72.89 Comparative Example 2 62.96 Comparative Example 3 67.48 Comparative Example 4 60.78

[0094] The purity of the nano-calcium carbonate added to Examples 1-4 of the present invention and Comparative Examples 1-3 was tested, as shown in Table 2.

[0095] Table 2

[0096] purity(%) Example 1 99 Example 2 99 Example 3 99 Example 4 99 Comparative Example 1 98 Comparative Example 2 96 Comparative Example 3 94

[0097] As can be seen from Table 1, the yields of Examples 1-4 are above 72.14%, while the yield of Comparative Example 2 is 62.96%, the yield of Comparative Example 3 is 67.48%, and the yield of Comparative Example 4 is only 60.78%. It can be seen that the conventional wet method for preparing nano-calcium carbonate without adding an auxiliary agent, that is, the method described in Comparative Example 4, has a yield that is not as good as that of the embodiments of the present invention. It can be seen that the preparation method of the present invention has a better yield of nano-calcium carbonate, and the improvement in yield is achieved by adding an auxiliary agent prepared by the present invention.

[0098] It can be seen from Table 2 that the purity of Examples 1-4 is 99%, and the purity of Comparative Example 1 of a commercially available product is 98%. It can be seen that the nano-calcium carbonate prepared by the present invention has higher purity, and the improvement in purity can be achieved by the combination of raw materials and additives of the present invention.

[0099] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A process for preparing nano calcium carbonate by a wet process, characterized in that, The steps include: S1: Preparation of compound crystallization aid Phthalic anhydride and glycine are mixed and stirred, heated to react, and then glacial acetic acid is added, followed by cooling and crystallization, filtering and then recrystallizing with ethanol aqueous solution to obtain a glycine derivative, and the glycine derivative is mixed and stirred with sodium lauryl sulfate to obtain a composite crystallization aid; S2: Preparation of bacterial suspension Peptone, beef extract, and agar powder are added to deionized water, stirred, and sterilized to obtain solution A. 3-Cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid, and deionized water are mixed and sterilized to obtain solution B. Solution A and solution B are mixed and poured into a culture dish. Alkaliphilic Bacillus and urea are added, and cultured at a constant temperature to obtain a bacterial solution. S3: Preparation of nano calcium carbonate The snail shells are cleaned and dried, calcined, ground, and sieved to obtain snail shell powder. The snail shell powder is mixed with a hydrochloric acid solution, and then the pH is adjusted to 8-10. Subsequently, a compound crystallization aid is added, and a carbon dioxide device and a carbonization device are connected to start carbonization. When the pH of the reaction system drops to 7.5, the carbon dioxide flow is stopped, and then a bacterial solution, sodium bicarbonate, and urea are added, and the carbon dioxide flow is continued to obtain nano calcium carbonate.

2. A process for preparing nano-calcium carbonate by wet method according to claim 1, characterized in that, Step S1: preparing a compound crystallization aid, comprising the following steps: S1.1: Mix phthalic anhydride and glycine in a mass ratio of 1:(1-3), stir on a magnetic stirrer at 200-250 rpm, and heat to 80-100°C. React under these conditions for 20-30 min. S1.2: Add an equal amount of glacial acetic acid to the system, cool and crystallize, filter and recrystallize with a 50-60 wt% ethanol aqueous solution to obtain a glycine derivative, and stir and mix the glycine derivative and sodium lauryl sulfate in a volume ratio of 1:(1-2) to obtain a compound crystallization aid.

3. A process for preparing nano-calcium carbonate by wet method according to claim 2, characterized in that, Step S2 is to prepare a bacterial solution, comprising the following steps: S2.1: Add 3-4 parts by weight of peptone, 10-12 parts by weight of beef extract, and 20-30 parts by weight of agar powder to 800-850 parts by weight of deionized water. Stir at 350-400 rpm for 20-25 minutes, then sterilize to obtain Solution A. S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid, and deionized water in a mass ratio of 1:(0.5-0.8):(4-8) and sterilize to obtain Solution B; S2.3: Mix solution A and solution B in a 1:1 mass ratio and pour into a culture dish. Add 2% volume fraction of alkaliphilic Bacillus and 2 mol / L urea in that order. Incubate at a constant temperature of 35-36°C for 48-49 hours to obtain a bacterial solution.

4. A process for preparing nano-calcium carbonate by wet method according to claim 3, characterized in that, Step S3 prepares nano calcium carbonate, comprising the following steps: S3.1: Clean and dry the snail shells, calcine them in a muffle furnace at 700-800°C for 4-5 hours, grind them, and pass them through a 200-mesh sieve to obtain snail shell powder; S3.2: Mix the shell powder with hydrochloric acid solution at a liquid-to-solid ratio of 6:1 mL / g and allow to react for 24-25 hours. Then, add NaOH solution to adjust the pH to 8-10. Then, add 20-40% of the system weight of a compound crystallization aid. Adjust the solution temperature to 20°C, connect the carbon dioxide apparatus and carbonization apparatus, and begin carbonization. S3.3: Detect the pH value of the reaction system in real time. When the pH of the reaction system drops to 7.5, stop adding carbon dioxide. Then add 20-25 mg / L bacterial liquid, 1 mol / L sodium bicarbonate and 2 mol / L urea. Continue the carbonization reaction with carbon dioxide for 24-25 hours. Then remove the product, sonicate it, centrifuge it for washing, dry it, grind it, and sieve it to obtain nano calcium carbonate.

5. A process for preparing nano-calcium carbonate by wet method according to claim 3, characterized in that, The alkaliphilic Bacillus is specifically alkaliphilic Bacillus H4.

6. A process for preparing nano-calcium carbonate by wet method according to claim 4, characterized in that, The concentration of hydrochloric acid solution is 1 mol / L.

7. A process for preparing nano-calcium carbonate by wet method according to claim 4, characterized in that, The concentration of NaOH solution is 1.5 mol / L.

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