Process for preparing nano calcium carbonate by wet method

Abstract

The invention relates to the technical field of calcium carbonate preparation, in particular to a process for preparing nano calcium carbonate by a wet method. The preparation process comprises the following steps: preparing the compound crystallization auxiliary agent; preparing a bacterial liquid; and preparing nano calcium carbonate. According to the invention, phthalic anhydride and glycine are combined to prepare a compound crystallization auxiliary agent, a glycine derivative and lauryl sodium sulfate are compounded to prepare the crystallization auxiliary agent, the molecular structure of the glycine derivative contains carboxylic acid groups and amide groups, and the functional groups enable the glycine derivative to form strong interaction with calcium carbonate; in addition, compared with a traditional stearic acid or silane coupling agent, the bifunctional structure of the glycine derivative can provide a stronger surface anchoring effect, reduce the use amount of auxiliaries, prevent agglomeration of nanoparticles and promote uniform nucleation, so that the yield of the nano calcium carbonate is improved.

Description

Technical Field

[0001] The invention relates to the technical field of calcium carbonate preparation, and in particular to a process for preparing nano calcium carbonate by a wet method. Background Art

[0002] Nano calcium carbonate is widely used in many 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, while giving the products better surface finish; in rubber products, adding nano calcium carbonate can improve tensile strength, tear strength and wear resistance, and reduce production costs; in coatings, nano calcium carbonate can improve hiding power, scrub resistance and weather resistance, and its steric hindrance effect can effectively prevent pigment sedimentation; in inks, nano calcium carbonate can improve printability, improve ink quick-drying and adhesion; as a high-grade paper filler, nano calcium carbonate can improve paper whiteness, opacity and smoothness, and significantly improve paper printability; in wastewater treatment, nano calcium carbonate can be used as an efficient adsorbent to remove heavy metal ions; adding it to building materials can improve the early strength and durability of cement.

[0003] Nano calcium carbonate has shown broad application prospects in many fields due to its unique physical and chemical properties. It can not only improve the performance and quality of the product, but also reduce production costs and promote the sustainable development of the industry. The existing technology for preparing nano calcium carbonate includes two methods: dry preparation and wet preparation. The wet preparation method is as follows: the calcium oxide formed after calcining the raw materials for producing calcium carbonate is dissolved in water and digested to generate a calcium hydroxide suspension; then high-purity carbon dioxide gas is introduced into the suspension of a certain concentration and purity for carbonization reaction; by controlling the temperature, pH value, flow rate of carbon dioxide gas and other parameters of the suspension, the nucleation rate of calcium carbonate crystal nuclei is adjusted to obtain nano calcium carbonate; finally, the prepared nano calcium carbonate is filtered, washed, dried and other steps to obtain the final product. The process of wet carbonization is relatively mature, simple to operate, and easy to realize industrial large-scale production. Furthermore, by optimizing the reaction conditions and the equipment design, high-efficiency and low-cost production can be achieved to meet the large market demand for nano calcium carbonate. However, nano calcium carbonate particles are prone to agglomeration during the preparation process, resulting in a wider particle size distribution. Therefore, it is necessary to suppress agglomeration through surface treatment and the use of a dispersant, but this will lead to a decrease in the yield of nano calcium carbonate. Therefore, the present invention provides a process for preparing nano calcium carbonate by a wet method, wherein an auxiliary agent is added to improve crystallization, prevent nano particles from agglomerating, and simultaneously improve the yield of nano calcium carbonate. Summary of the invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a process for preparing nano calcium carbonate by a wet process.

[0005] A process for preparing nano calcium carbonate by a wet method, comprising the following steps: S1: Prepare a compound crystallization aid Mix phthalic anhydride and glycine and stir, heat up for reaction, add glacial acetic acid, then cool and crystallize, filter and recrystallize with an ethanol aqueous solution to obtain a glycine derivative, and stir and mix the glycine derivative and sodium dodecyl sulfate to obtain a compound crystallization aid; S2: Prepare a bacterial solution Add peptone, beef extract and agar powder to deionized water, stir and then sterilize to obtain solution A. Mix 3-cyclohexylaminopropanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid and deionized water and sterilize to obtain solution B. Mix solution A and solution B and pour them into a petri dish, add alkalophilic bacillus and urea, and incubate at a constant temperature to obtain a bacterial solution; S3: Prepare nano calcium carbonate Clean and dry the spiral shell, calcine, grind, and sieve to obtain spiral shell powder. Mix the spiral shell powder with hydrochloric acid solution, then adjust the pH to 8-10, then add the compound crystallization aid, connect the carbon dioxide device and the carbonization device, start carbonization, stop passing carbon dioxide when the pH of the reaction system drops to 7.5, then add the bacterial solution, sodium bicarbonate and urea, and continue to pass carbon dioxide to obtain nano calcium carbonate.

[0006] Further, the preparation of the compound crystallization aid in step S1 includes the following steps: S1.1: Mix phthalic anhydride and glycine in a mass ratio of 1:(1-3), place them on a magnetic stirrer and stir at a speed of 200-250 r / min, and heat up to 80-100 °C, and react under these conditions for 20-30 min; S1.2: Then add an equal mass of glacial acetic acid to the system, then 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 dodecyl sulfate in a volume ratio of 1:(1-2) to obtain a compound crystallization aid.

[0007] Further, the preparation of the bacterial solution in step S2 includes the following steps: S2.1: Add 3-4 parts by mass of peptone, 10-12 parts by mass of beef extract and 20-30 parts by mass of agar powder to 800-850 parts by mass of deionized water, stir at 350-400 r / min for 20-25 min and then sterilize to obtain solution A; S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic 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 liquid A and liquid B in a mass ratio of 1:1, pour the mixture into a petri dish, and sequentially add Bacillus alkalophilus with a volume fraction of 2% and urea with a concentration of 2 mol / L. After culturing at a constant temperature of 35 - 36 °C for 48 - 49 h, a bacterial solution is obtained.

[0008] Further, step S3 for preparing nano calcium carbonate includes the following steps: S3.1: Clean and dry the spiral shell, calcine it in a muffle furnace at 700 - 800 °C for 4 - 5 h, grind it, and pass it through a 200 - mesh sieve to obtain spiral shell powder; S3.2: Mix the spiral shell powder with a hydrochloric acid solution at a liquid - solid ratio of 6:1 mL / g and react for 24 - 25 h. Then add a NaOH solution to adjust the pH to 8 - 10. Subsequently, add a compound crystallization aid accounting for 20 - 40% of the system mass. Adjust the solution temperature to 20 °C, connect the carbon dioxide device and the carbonization device, and start carbonization; S3.3: Real - time detect the pH value of the reaction system. When the pH of the reaction system drops to 7.5, stop passing carbon dioxide. Then add 20 - 25 mg / L of the bacterial solution, 1 mol / L of sodium bicarbonate, and 2 mol / L of urea, and continue to pass carbon dioxide for carbonization reaction for 24 - 25 h. Subsequently, take out the product, ultrasonicate it, centrifuge and wash it, dry it, grind it, and pass it through a sieve to obtain nano calcium carbonate.

[0009] Further, the Bacillus alkalophilus is specifically Bacillus alkalophilus H4.

[0010] Further, the concentration of the hydrochloric acid solution is 1 mol / L.

[0011] Further, 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: 1. The present invention combines phthalic anhydride and glycine to prepare a compound crystallization aid, and combines a glycine derivative with sodium dodecyl sulfate to prepare a crystallization aid. The molecular structure of the glycine derivative contains a carboxylic acid group and an amide group. These functional groups enable it to form a strong interaction with calcium carbonate. The oxygen atom in the carboxylic acid group has a lone pair of electrons, which can form a coordination bond with calcium carbonate, enhancing the interfacial binding force between the organic molecule and the inorganic particle. The amide group can form a hydrogen bond with the hydroxyl group or water molecule on the surface of calcium carbonate, further enhancing the binding force of the organic - inorganic interface. Moreover, compared with traditional stearic acid or silane coupling agents, the bifunctional group structure of the glycine derivative can provide a stronger surface anchoring effect, reducing the amount of the aid used. Sodium dodecyl sulfate, as an anionic surfactant, can reduce the surface tension of the solution, prevent nanoparticle aggregation, and promote uniform nucleation, thereby improving the yield of nano calcium carbonate.

[0012] 2. The present invention combines 3-cyclohexylaminopropanesulfonic acid and 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid to prepare a culture solution for the growth and development of Bacillus alkalophilus. Both 3-cyclohexylaminopropanesulfonic acid and 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid are biological buffers, which can stabilize the pH, adapt to the alkaline growth environment of Bacillus alkalophilus. Moreover, the combination of the two can also broaden the pH buffer range, avoid the pH fluctuation caused by urea hydrolysis, and ensure the yield of nano calcium carbonate.

[0013] 3. The present invention adds the bacterial liquid of Bacillus alkalophilus and the compound crystallization aid into the liquid prepared from calcium ion-containing spiral shell powder, and prepares calcium carbonate by wet method by adding carbon dioxide. The extracellular polymer and urease secreted by the cells of Bacillus alkalophilus can guide the directional crystallization of calcium carbonate to form nano-particles with uniform particle size. The extracellular polymer of Bacillus alkalophilus and glycine derivatives synergistically regulate the crystallization of calcium carbonate through bio-template effect and molecular interface modification, showing significant advantages in crystal form selection, dispersion stability and functional application, and improving the yield and purity of nano calcium carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings incorporated herein and constituting a part of the specification illustrate embodiments of the present disclosure, and together with the specification are further used to explain the principles of the present disclosure and enable those skilled in the relevant art to implement and use the present disclosure.

[0015] Figure 1 It is a process flow chart of a wet method for preparing nano calcium carbonate adopted in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The following describes in detail a process for preparing nano calcium carbonate by a wet method provided by the present invention with reference to the drawings and specific embodiments. At the same time, it should be noted here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments. For some well-known technologies, those skilled in the art can also adopt other alternative methods for implementation; moreover, the drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention. Example 1

[0017] A process for preparing nano calcium carbonate by a wet method, as Figure 1 shown, includes the following steps: S1: Prepare the compound crystallization aid S1.1: Mix phthalic anhydride and glycine in a mass ratio of 1:1, place it on a magnetic stirrer and stir at a speed of 200 r / min, and heat up to 80 °C, and react for 20 min under this condition; S1.2: Add acetic acid of the same mass as the system, then cool and crystallize. After filtration, recrystallize with 50wt% ethanol aqueous solution to obtain glycine derivatives. Stir and mix the glycine derivatives and sodium dodecyl sulfate in a volume ratio of 1:1 to obtain a compound crystallization aid.

[0018] S2: Prepare bacterial solution 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 r / min for 20 min and then perform sterilization treatment to obtain solution A. S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, and deionized water in a mass ratio of 1:0.5:4 and perform sterilization treatment to obtain solution B. S2.3: Mix solution A and solution B in a mass ratio of 1:1, pour them into a culture dish, add 2% volume fraction of Bacillus alkalophilus H4 and 2 mol / L urea in sequence, and incubate at a constant temperature of 35 °C for 48 h to obtain bacterial solution.

[0019] S3: Prepare nano calcium carbonate S3.1: Wash and dry the spiral shell, calcine it in a muffle furnace at 700 °C for 4 h, grind it, and pass through a 200-mesh sieve to obtain spiral shell powder. S3.2: Mix the spiral shell powder with 1 mol / L hydrochloric acid solution in a liquid-solid ratio of 6:1 mL / g and react for 24 h. Then add 1.5 mol / L NaOH solution to adjust the pH to 8. Subsequently, add 20% of the compound crystallization aid based on the mass of the solution. Adjust the solution temperature to 20 °C, connect the carbon dioxide device and the carbonization device, and start carbonization. S3.3: Detect the pH value of the reaction system in real time. Stop passing carbon dioxide when the pH of the reaction system drops to 7.5. Then add 20 mg / L of bacterial solution, 1 mol / L of sodium bicarbonate, and 2 mol / L of urea, and continue to pass carbon dioxide for carbonization reaction for 24 h. Subsequently, take out the product, perform ultrasonic treatment, centrifugal washing, drying, grinding, and sieving to obtain nano calcium carbonate. Example 2

[0020] A process for wet preparation of nano calcium carbonate, as Figure 1 shown, includes the following steps: S1: Prepare compound crystallization aid S1.1: Mix phthalic anhydride and glycine in a mass ratio of 1:3, place them on a magnetic stirrer and stir at a speed of 200 r / min, and heat up to 80 °C. React under this condition for 20 min. S1.2: Add acetic acid of the same mass as the system, then cool and crystallize. After filtration, recrystallize with 50wt% ethanol aqueous solution to obtain glycine derivatives. Stir and mix the glycine derivatives and sodium dodecyl sulfate at a volume ratio of 1:2 to obtain a compound crystallization aid.

[0021] S2: Prepare the bacterial solution 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. Stir at 350 r / min for 20 min and then perform sterilization treatment to obtain solution A. S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, and deionized water in a mass ratio of 1:0.8:8 and perform sterilization treatment to obtain solution B. S2.3: Mix solution A and solution B in a mass ratio of 1:1, pour them into a petri dish, add 2% by volume of Bacillus alkalophilus H4 and 2 mol / L of urea in sequence, and incubate at a constant temperature of 35 °C for 48 h to obtain the bacterial solution.

[0022] S3: Prepare nano calcium carbonate S3.1: Wash and dry the spiral shell, calcine it in a muffle furnace at 700 °C for 4 h, grind it, and pass it through a 200-mesh sieve to obtain spiral shell powder. S3.2: Mix the spiral shell powder and 1 mol / L hydrochloric acid solution at a liquid-solid ratio of 6:1 mL / g and react for 24 h. Then add 1.5 mol / L NaOH solution to adjust the pH to 8. Subsequently, add 40% of the compound crystallization aid based on the mass of the system, adjust the solution temperature to 20 °C, connect the carbon dioxide device and the carbonization device, and start carbonization. S3.3: Real-time detect the pH value of the reaction system. Stop passing carbon dioxide when the pH of the reaction system drops to 7.5. Then add 25 mg / L of the bacterial solution, 1 mol / L of sodium bicarbonate, and 2 mol / L of urea, and continue to pass carbon dioxide for carbonization reaction for 24 h. Subsequently, take out the product, ultrasonicate, centrifuge and wash, dry, grind, and sieve to obtain nano calcium carbonate. Example 3

[0023] A process for wet preparation of nano calcium carbonate, as Figure 1 shown, includes the following steps: S1: Prepare the compound crystallization aid S1.1: Mix phthalic anhydride and glycine in a mass ratio of 1:1, place them on a magnetic stirrer and stir at a speed of 250 r / min, and heat up to 100 °C. React under this condition for 30 min. S1.2: Add acetic acid of the same mass as the system, then cool and crystallize. After filtration, recrystallize with 50wt% ethanol aqueous solution to obtain glycine derivatives. Stir and mix the glycine derivatives and sodium dodecyl sulfate at a volume ratio of 1:1 to obtain a compound crystallization aid.

[0024] S2: Prepare the bacterial solution 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 r / min for 25 min and then perform sterilization treatment to obtain solution A. S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, and deionized water in a mass ratio of 1:0.5:4 and perform sterilization treatment to obtain solution B. S2.3: Mix solution A and solution B in a mass ratio of 1:1, pour them into a petri dish, add 2% volume fraction of Bacillus alkalophilus H4 and 2 mol / L urea in sequence, and incubate at a constant temperature of 36 °C for 49 h to obtain the bacterial solution.

[0025] S3: Prepare nano calcium carbonate S3.1: Clean and dry the spiral shell, calcine it in a muffle furnace at 750 °C for 5 h, grind it, and pass through a 200-mesh sieve to obtain spiral shell powder. S3.2: Mix the spiral shell powder and 1 mol / L hydrochloric acid solution at a liquid-solid ratio of 6:1 mL / g and react for 25 h. Then add 1.5 mol / L NaOH solution to adjust the pH to 10. Subsequently, add 20% of the compound crystallization aid based on the mass of the system, adjust the solution temperature to 20 °C, connect the carbon dioxide device and the carbonization device, and start carbonization. S3.3: Real-time detect the pH value of the reaction system. Stop passing carbon dioxide when the pH of the reaction system drops to 7.5. Then add 20 mg / L of the bacterial solution, 1 mol / L of sodium bicarbonate, and 2 mol / L of urea, continue to pass carbon dioxide for carbonization reaction for 25 h. Subsequently, take out the product, ultrasonicate, centrifuge and wash, dry, grind, and sieve to obtain nano calcium carbonate. Example 4

[0026] A process for wet preparation of nano calcium carbonate, as Figure 1 shown, includes the following steps: S1: Prepare the compound crystallization aid S1.1: Mix phthalic anhydride and glycine in a mass ratio of 1:1, place them on a magnetic stirrer and stir at a speed of 250 r / min, and heat up to 100 °C. React under this condition for 30 min. S1.2: Add acetic acid of the same mass as the system, then cool and crystallize. After filtration, recrystallize with 50wt% ethanol aqueous solution to obtain glycine derivatives. Stir and mix the glycine derivatives and sodium dodecyl sulfate in a volume ratio of 1:1 to obtain a compound crystallization aid.

[0027] S2: Prepare the bacterial solution 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 r / min for 25 min and then perform sterilization treatment to obtain solution A; S2.2: Mix 3-cyclohexylaminopropanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid and deionized water in a mass ratio of 1:0.5:4 and perform sterilization treatment to obtain solution B; S2.3: Mix solution A and solution B in a mass ratio of 1:1, pour them into a culture dish, sequentially add 2% volume fraction of Bacillus alkalophilus H4 and 2 mol / L urea, and incubate at a constant temperature of 36 °C for 49 h to obtain the bacterial solution.

[0028] S3: Prepare nano calcium carbonate S3.1: Wash and dry the spiral shell, calcine it in a muffle furnace at 800 °C for 5 h, grind it, and pass through a 200-mesh sieve to obtain spiral shell powder; S3.2: Mix the spiral shell powder with 1 mol / L hydrochloric acid solution in a liquid-solid ratio of 6:1 mL / g and react for 25 h. Then add 1.5 mol / L NaOH solution to adjust the pH to 10. Subsequently, add 20% of the compound crystallization aid based on the mass of the system, adjust the solution temperature to 20 °C, connect the carbon dioxide device and the carbonization device, and start carbonization; S3.3: Real-time detect the pH value of the reaction system. When the pH of the reaction system drops to 7.5, stop passing carbon dioxide. Then add 20 mg / L of the bacterial solution, 1 mol / L of sodium bicarbonate and 2 mol / L of urea, continue to pass carbon dioxide for carbonization reaction for 25 h. Subsequently, take out the product, ultrasonicate, centrifuge and wash, dry, grind, and sieve to obtain nano calcium carbonate.

[0029] Comparative example 1: The nano calcium carbonate commercially available in Comparative example 1.

[0030] Comparative example 2: Compared with Example 1, the difference in Comparative Example 2 is that step S1 is not carried out, and the compound crystallization aid is not added in step S3.2. Specifically, "S3.2: Mix the spiral shell powder with 1 mol / L hydrochloric acid solution at a liquid-solid ratio of 6:1 mL / g and react for 24 h, then add 1.5 mol / L NaOH solution to adjust the pH to 8, adjust the solution temperature to 20 °C, connect the carbon dioxide device and the carbonization device, and start carbonization", and the rest of the steps remain unchanged. The prepared nano-calcium carbonate is denoted as Comparative Example 2.

[0031] Comparative Example 3: Compared with Example 1, the difference in Comparative Example 3 is that step S2 is not carried out, and the bacterial solution is not added in step S3.3. Instead, the lubricating hydrogel is replaced with the lubricant prepared in step S2.1. Specifically, "S3.3: Real-time detect 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 to pass carbon dioxide for carbonization reaction for 24 h, then take out the product, ultrasonicate, centrifuge and wash, dry, grind, and sieve to obtain nano-calcium carbonate", and the rest of the steps remain unchanged. The prepared nano-calcium carbonate is denoted as Comparative Example 3.

[0032] Comparative Example 4: Compared with Example 1, the difference in Comparative Example 4 is that steps S1 and S2 are not carried out, and carbon dioxide is directly introduced in step S3 to prepare nano-calcium carbonate. Specifically, "S3: Prepare nano-calcium carbonate S3.1: Clean and dry the spiral shell, calcine it in a muffle furnace at 700 °C for 4 h, grind it, and sieve it through a 200-mesh sieve to obtain spiral shell powder; S3.2: Mix the spiral shell powder with 1 mol / L hydrochloric acid solution at a liquid-solid ratio of 6:1 mL / g and react for 24 h, then add 1.5 mol / L NaOH solution to adjust the pH to 8, adjust the solution temperature to 20 °C, connect the carbon dioxide device and the carbonization device, and start carbonization; S3.3: Real-time detect 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 to pass carbon dioxide for carbonization reaction for 24 h, then take out the product, ultrasonicate, centrifuge and wash, dry, grind, and sieve to obtain nano-calcium carbonate", and the rest of the steps remain unchanged. The prepared nano-calcium carbonate is denoted as Comparative Example 4.

[0033] Calculate the yields of the nano-calcium carbonates added in Examples 1-4 and Comparative Examples 2-3 of the present invention respectively, as shown in Table 1.

[0034] Table 1 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 The purity of the nano-calcium carbonate added with Examples 1-4 and Comparative Examples 1-3 of the present invention was tested separately, as shown in Table 2.

[0035] Table 2 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 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 yield of the conventional wet method for preparing nano-calcium carbonate without adding additives, that is, the method described in Comparative Example 4, is not as good as that of the examples 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 increase in yield is achieved by adding additives prepared by the present invention.

[0036] As can be seen from Table 2, the purity of Examples 1-4 is 99%, and the purity of Comparative Example 1 of the commercially available product is 98%. It can be seen that the nano-calcium carbonate prepared by the present invention has a higher purity, and the increase in purity can be achieved only through the raw material combination and additive combination of the present invention.

[0037] The above examples are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above examples without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A process for preparing nano calcium carbonate by wet method, characterized in that, The steps include: S1: Preparation of compound crystallization aid Phthalic anhydride and glycine are mixed and stirred, and heated to react, and then glacial acetic acid is added, and then cooled and crystallized, filtered and then recrystallized with ethanol aqueous solution to obtain a glycine derivative, and the glycine derivative and sodium dodecyl sulfate are mixed and stirred to obtain a composite crystallization aid; S2: Preparation of bacterial suspension Peptone, beef extract and agar powder are added to deionized water, and the mixture is stirred and sterilized to obtain liquid A. 3-cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid and deionized water are mixed and sterilized to obtain liquid B. Liquid A and liquid B are mixed and poured into a culture dish, and alkaliphilic Bacillus and urea are added, and the mixture is cultured at a constant temperature to obtain a bacterial liquid. S3: Preparation of Nano-Calcium Carbonate The snail shells are cleaned and dried, calcined, ground, and sieved to obtain snail shell powder, which is then mixed with a hydrochloric acid solution, and the pH is adjusted to 8-10. A compound crystallization aid is then added, a carbon dioxide device and a carbonization device are connected, and carbonization begins. When the pH of the reaction system drops to 7.5, the carbon dioxide is stopped, and bacterial liquid, sodium bicarbonate, and urea are added, and the carbon dioxide is continued to be passed 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: Phthalic anhydride and glycine are mixed in a mass ratio of 1:(1-3), stirred on a magnetic stirrer at a speed of 200-250 r / min, and heated to 80-100°C, and reacted under this condition for 20-30 min; S1.2: Add an equal amount of glacial acetic acid to the system, cool and crystallize, filter and recrystallize with 50-60wt% ethanol aqueous solution to obtain a glycine derivative, stir and mix the glycine derivative and sodium dodecyl sulfate in a volume ratio of 1: (1-2) to obtain a composite crystallization aid.

3. A process for preparing nano calcium carbonate by wet method according to claim 2, characterized in that, Step S2 is preparing 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 r / min for 20-25 min, and then sterilize to obtain liquid A; S2.2: 3-cyclohexylaminopropanesulfonic acid, 4-hydroxyethylpiperazineethanesulfonic acid and deionized water are mixed in a mass ratio of 1:(0.5-0.8):(4-8) and sterilized to obtain solution B; S2.3: Mix solution A and solution B in a mass ratio of 1:1 and pour into a culture dish. Add 2% volume fraction of alkaliphilic Bacillus and 2 mol / L urea in sequence. Culture 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: Wash and dry the snail shell, calcine it in a muffle furnace at 700-800°C for 4-5h, grind it, and pass it through a 200-mesh sieve to obtain snail shell powder; S3.2: Mix the snail shell powder and hydrochloric acid solution at a liquid-solid ratio of 6:1 mL / g and react for 24-25 hours, then add NaOH solution to adjust the pH to 8-10, then add 20-40% of the system mass of the compound crystallization aid, adjust the solution temperature to 20°C, connect the carbon dioxide device and the carbonization device, and start carbonization; S3.3: Real-time detection of the pH value of the reaction system. When the pH value of the reaction system drops to 7.5, stop passing carbon dioxide. Then add 20-25 mg / L of bacterial solution, 1 mol / L of sodium bicarbonate and 2 mol / L of urea. Continue passing carbon dioxide for carbonization reaction for 24-25 hours. Then take out the product, ultrasonicate it, wash it by centrifugation, 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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