Preparation method of high-purity calcium carbonate taking oyster shell as raw material

Abstract

A method for preparing high-purity calcium carbonate from oyster shells, comprising the following steps: 1) oyster shell treatment; 2) preparation of calcium butyrate solution; 3) preparation of high-purity calcium carbonate. The raw material is oyster shell, which belongs to renewable resources, solving the environmental pollution problem of oyster shells, reducing the exploitation of lime mines, and protecting natural resources and the ecological environment; low-temperature reaction is adopted, and the ratio of oyster shell powder to butyric acid is controlled, the oyster shell powder is in excess, and the alkalinity of the solution is controlled, so that other metal ions exist in the form of precipitation, and a relatively pure calcium butyrate solution can be obtained; the molar ratio of calcium butyrate to sodium carbonate is controlled to be 1:0.8, and the precipitation is precipitated in stages, and the solution is controlled to be slightly acidic, so that other metal ions exist in the form of solution, and high-purity calcium carbonate can be obtained.

Description

Technical Field

[0001] This invention relates to the field of inorganic salt industry technology, and in particular to a method for preparing high-purity calcium carbonate using oyster shells as raw material. Background Technology

[0002] Oyster shells account for approximately 70%–90% of the total weight of oysters, with a calcium carbonate content as high as 88.59%–99.20%, and also contain trace elements and organic matter, making them a valuable inorganic salt resource. However, most oyster shells are discarded as part of marine waste, occupying valuable land and tidal flat resources. Furthermore, the organic matter in discarded oyster shells oxidizes and decomposes in the air, breeding large numbers of pathogenic microorganisms, causing significant environmental pollution and wasting solid waste resources. Therefore, the resource utilization of solid waste has become a hot research topic in current society.

[0003] Calcium carbonate is a valuable resource with a wide range of uses, while limestone is the commercial name for a mineral raw material. Throughout human history, limestone has been widely used due to its abundant distribution and easy accessibility in nature. It has a long history of mining as an important building material. In modern industry, limestone is a major raw material for manufacturing cement, lime, and calcium carbide. It is an indispensable fluxing agent in the metallurgical industry. High-quality limestone, after ultrafine grinding, is widely used in the manufacture of products such as paper, rubber, paint, coatings, pharmaceuticals, cosmetics, animal feed, sealants, adhesives, and polishing agents.

[0004] Chinese patent CN202211009977 improves upon the problems existing in other patents by proposing a method for preparing high-purity calcium carbonate. This method uses magnesium-containing carbonate minerals as raw materials, leaches out high-purity calcium chloride, uses the magnesium element in the magnesium-containing carbonate minerals to synthesize high-purity magnesium carbonate trihydrate crystals, and then uses an elemental substitution reaction to synthesize the high-purity calcium carbonate product. This method uses non-renewable minerals and involves multiple steps, making the operation relatively complex.

[0005] Limestone is a non-renewable resource. With the continuous progress of science and technology and the development of nanotechnology, it is of great significance to seek a method to prepare high-purity calcium carbonate from a renewable resource that can replace limestone as a raw material. This would allow the high-purity calcium carbonate produced to be widely used in industries such as electronics, special ceramics, electrolytic capacitor materials, and optical glass. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems in the prior art and to provide a method for preparing high-purity calcium carbonate using oyster shells as raw material.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing high-purity calcium carbonate from oyster shells includes the following steps:

[0009] 1) Oyster shell processing: air drying, aging, cleaning, alkali treatment, baking, crushing, and high-temperature calcination;

[0010] 2) Preparation of calcium butyrate solution: Mix the calcined oyster shell powder obtained after step 1) with pure water, keep the temperature at 0-5℃, add butyrate dropwise while stirring, and after the addition is completed, ensure that the final pH of the solution is >11, continue to keep warm and stir for a period of time, and finally filter to obtain calcium butyrate solution.

[0011] 3) Preparation of high-purity calcium carbonate: Stir the calcium butyrate solution obtained in step 2), control the temperature at 0-5℃, adjust the pH to 5-7 with butyric acid, add sodium carbonate solution dropwise in portions, keep warm for a period of time after each addition, then filter, and repeat the above reaction of adding sodium carbonate solution. Wash the filter cake with pure water until neutral, dry it, and obtain high-purity calcium carbonate with a calcium carbonate content of 99.8%-99.9%.

[0012] In step 1), the oyster shells are treated as follows: air-dried naturally, aged for 4 to 9 months, washed with clean water or seawater to remove surface impurities, soaked in sodium hydroxide solution for 10 to 20 hours, then washed with pure water, dried, crushed, and finally calcined at 800 to 1100°C for 6 to 8 hours; the mass concentration of the sodium hydroxide solution is 10% to 15%.

[0013] In step 2), the heat preservation and stirring time is 1 to 3 hours.

[0014] In step 2), the mass ratio of the calcined oyster shell powder to pure water is 1:10.

[0015] In step 2), the mass ratio of oyster shell powder to butyric acid is 1:1.9.

[0016] In step 3), the mass concentration of the sodium carbonate solution is 25%.

[0017] In step 3), the heat preservation period is 30 to 60 minutes.

[0018] In step 3), the number of times is 3 to 5.

[0019] In step 3), the molar ratio of calcium butyrate to sodium carbonate is 1:0.8.

[0020] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0021] (1) The raw material of this invention is oyster shell, which is a renewable resource. This not only solves the environmental pollution problem of oyster shell, but also reduces the mining of limestone, thus protecting natural resources and the ecological environment.

[0022] (2) The calcium carbonate content in oyster shells is as high as 88.59% to 99.20%, and after aging and alkali treatment, the content can reach 96.30% to 99.46%, which provides a good foundation for subsequent purification;

[0023] (3) The present invention uses a low-temperature reaction and controls the mass ratio of oyster shell powder to butyric acid to be 1:1.9, with excess oyster shell powder and control the alkalinity of the solution so that other metal ions exist in the form of precipitate, which can obtain a relatively pure calcium butyrate solution; controls the molar ratio of calcium butyrate to sodium carbonate to be 1:0.8 and uses segmented precipitation, and controls the solution to be slightly acidic so that other metal ions exist in the form of solution, which can obtain high-purity calcium carbonate; high-speed stirring can make the obtained calcium carbonate particles smaller.

[0024] (4) The process and equipment of this invention are simple, easy to operate, and easy to industrialize. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not only all of the embodiments.

[0026] A method for preparing high-purity calcium carbonate from oyster shells includes the following steps:

[0027] 1) Oyster shell processing: air drying, aging, cleaning, alkali treatment, baking, crushing, and high-temperature calcination;

[0028] 2) Preparation of calcium butyrate solution: The calcined oyster shell powder obtained after step 1) is mixed with pure water at a mass ratio of 1:10. The temperature is maintained at 0-5℃. Butyric acid (mass ratio of oyster shell powder to butyric acid is 1:1.9) is added dropwise while stirring for 6-8 hours. After the addition is completed, the final pH of the solution is ensured to be >11. The temperature is maintained and stirred for 1-3 hours. Finally, the solution is filtered using precision filter paper to obtain calcium butyrate solution.

[0029] 3) Preparation of high-purity calcium carbonate: Stir the calcium butyrate solution obtained in step 2), control the temperature at 0-5℃, adjust the pH to 5-7 with butyric acid, and add a 25% sodium carbonate solution dropwise in 3-5 portions. After each addition, keep warm for 30-60 minutes, then filter. Repeat the above reaction of adding sodium carbonate solution to the filtrate. Wash the filter cake with pure water until neutral, and dry it to obtain high-purity calcium carbonate with a calcium carbonate content of 99.8%-99.9%. The molar ratio of calcium butyrate to sodium carbonate is 1:0.8.

[0030] In step 1), the oyster shells are treated as follows: They are air-dried naturally and aged for 4–9 months. Afterward, they are washed with clean water or seawater to remove surface impurities, soaked in sodium hydroxide solution for 10–20 hours, rinsed with pure water, and dried in a forced-air oven at 150°C for 2–3 hours. Then, they are crushed using a crusher and finally calcined at 800–1100°C for 6–8 hours, followed by natural cooling to room temperature. The sodium hydroxide solution has a mass concentration of 10%–15%. This aging and alkali treatment effectively removes impurities from the oyster shells, achieving a content of 96.30%–99.46%, providing a good foundation for subsequent purification.

[0031] Specifically, a sodium carbonate solution with a mass concentration of 25% needs to be precisely filtered to remove impurities.

[0032] In this invention, the raw material used in step 1) is only oyster shells.

[0033] Example 1

[0034] 1) The oyster shell processing method is as follows: the oyster shells are naturally air-dried and aged for 6 months. After that, they are cleaned with water or seawater to remove surface impurities. They are then soaked in a 10% sodium hydroxide solution for 20 hours, cleaned with pure water, crushed with a crusher, and then calcined in an electrically heated muffle furnace at 1100℃ for 6 hours. After that, they are naturally cooled to room temperature.

[0035] 2) The preparation method of calcium butyrate is as follows: Weigh 100g of calcined oyster shell powder and 1000g of pure water into a three-necked flask equipped with a stirrer, place it in a water bath at 0-5℃, and add 190g of butyric acid dropwise while stirring for 6 hours. During the process, monitor the pH value of the solution to ensure that the pH value of the solution is >11. After the dropwise addition is completed, keep it warm and stir for another 2 hours. Then filter it with precision filter paper to obtain calcium butyrate solution.

[0036] 3) The preparation method of high-purity calcium carbonate is as follows: The calcium butyrate solution obtained in step 2) is placed in a reactor equipped with a high-speed stirring emulsifier. The stirring speed is 6000 rpm, the reaction temperature is controlled at 0-5℃, butyric acid is added dropwise to adjust the pH value, and the pH value of the solution is kept in the range of 5-7 during the reaction process. 366g of sodium carbonate solution with a mass concentration of 25% is added dropwise in five equal parts. After each addition, the solution is kept warm for 30 minutes, then filtered. The filtrate is then reacted again. The filter cake is washed with pure water until neutral. The five filter cakes are collected separately and dried at 150℃ to obtain high-purity calcium carbonate.

[0037] Example 2

[0038] 1) The oyster shell processing method is as follows: the oyster shells are naturally air-dried and aged for 9 months. They are then cleaned with clean water or seawater to remove surface impurities, soaked in 10% sodium hydroxide solution for 10 hours, cleaned with pure water, crushed with a crusher, and then continuously calcined at 1100℃ in a rotary kiln heated by electromagnetic induction. After discharge, the material is naturally cooled to room temperature.

[0039] 2) The preparation method of calcium butyrate is as follows: Weigh 100 kg of calcined oyster shell powder and 1000 kg of pure water and place them in a glass-lined reactor equipped with a stirrer. The material temperature is reduced to 0-5℃. Under stirring, add 190 kg of butyric acid dropwise for 6 hours. During the process, monitor the pH value of the solution to ensure that the pH value of the solution is >11. After the dropwise addition is completed, keep the temperature and stir for another 2 hours. Then filter the solution using a carbon rod filter to obtain calcium butyrate solution.

[0040] 3) The preparation method of high-purity calcium carbonate is as follows: The calcium butyrate solution obtained in step 2) is placed in a stainless steel emulsification kettle equipped with a high-speed stirring emulsifier. The stirring speed is 2800 rpm, and the reaction temperature is controlled at 0-5℃. Butyric acid is added dropwise to adjust the pH to 5-7 in three batches: 60 kg for the first batch, 246 kg for the second batch, and 60 kg for the third batch. A sodium carbonate solution with a mass concentration of 25% is added dropwise. After each addition, the solution is kept warm for 30 min. Then, the solution is centrifuged and filtered. The filtrate is then reacted again. The filter cake is washed with pure water until neutral. The three filter cakes are collected separately and dried at 150℃ to obtain high-purity calcium carbonate.

[0041] Comparative Example 1

[0042] Referring to the method of Example 1, steps 1) and 3) remain unchanged. The preparation method of calcium butyrate in step 2) is as follows: Weigh 100g of calcined oyster shell powder and 1000g of pure water into a three-necked flask equipped with a stirrer, place it in a water bath at 0-5℃, and add 238g of butyric acid dropwise while stirring for 6 hours until neutral. After the addition is completed, keep warm and stir for another 2 hours, and then filter with precision filter paper to obtain calcium butyrate solution; detect the calcium carbonate content of the sample.

[0043] Comparative Example 2

[0044] Referring to the method of Example 1, steps 1) and 3) remain unchanged. The preparation method of calcium butyrate in step 2) is as follows: Weigh 100g of calcined oyster shell powder and 1000g of pure water into a three-necked flask equipped with a stirrer, place it in a water bath at 50-60℃, and add 190g of butyric acid dropwise while stirring for 6 hours. During the process, monitor the pH value of the solution to ensure that the pH value of the solution is >11. After the dropwise addition is completed, keep the solution warm and stir for another 2 hours. Then filter the solution using precision filter paper to obtain calcium butyrate solution; detect the calcium carbonate content of the sample.

[0045] Comparative Example 3

[0046] Referring to the method of Example 1, steps 1) and 2) remain unchanged. The preparation method of high-purity calcium carbonate in step 3) is as follows: The calcium butyrate solution obtained in step 2) is placed in a reactor equipped with a high-speed stirring emulsifier. The stirring speed is 6000 rpm, and the reaction temperature is controlled at 0-5℃. 457g of sodium carbonate solution with a mass concentration of 25% is added dropwise in five equal parts. After each addition, the solution is kept warm for 30 minutes. Then, the solution is filtered, and the filtrate is reacted again. The filter cake is washed with pure water until neutral. The five filter cakes are collected separately, dried at 150℃, and the calcium carbonate content of the sample is detected.

[0047] Comparative Example 4

[0048] Referring to the method of Example 1, steps 1) and 2) remain unchanged. The preparation method of high-purity calcium carbonate in step 3) is as follows: The calcium butyrate solution obtained in step 2) is placed in a reactor equipped with a high-speed stirring emulsifier. The stirring speed is 6000 rpm, and the reaction temperature is controlled at 50-60℃. 366g of sodium carbonate solution with a mass concentration of 25% is added dropwise in five equal parts. After each addition, the solution is kept warm for 30 minutes. Then, the solution is filtered, and the filtrate is reacted again. The filter cake is washed with pure water until neutral. The five filter cakes are collected separately, dried at 150℃, and the calcium carbonate content of the sample is detected.

[0049] Comparative Example 5

[0050] Referring to the method of Example 1, steps 1) and 3) remain unchanged, but in step 2), butyric acid is replaced with one of formic acid, acetic acid, hydrochloric acid, or nitric acid, and other conditions remain unchanged. The calcium carbonate obtained is sampled and the calcium carbonate content of the sample is detected.

[0051] Table 1. Calcium carbonate content of samples

[0052] Content of Sample No. 1 Content of Sample No. 2 Content of sample No. 3 Content of sample No. 4 Content of sample No. 5 Example 1 99.82％ 99.94％ 99.97％ 99.96％ 99.91％ Example 2 99.80％ 99.95％ 99.90％ - - Comparative Example 1 98.72％ 99.01％ 99.26％ 99.83％ 99.13％ Comparative Example 2 98.82％ 99.31％ 99.91％ 99.87％ 99.80％ Comparative Example 3 98.58％ 98.97％ 99.14％ 99.60％ 99.07％ Comparative Example 4 98.88％ 99.42％ 99.93％ 99.88％ 99.54％ Comparative Example 5 97.62～98.41％ 98.13～98.78％ 98.40～99.37％ 98.62～99.55％ 98.48～98.89％

[0053] As shown in Table 1, the calcium carbonate prepared by the method of the present invention can meet the quality standard of high-purity calcium carbonate (99.90%), and a high yield can be obtained.

[0054] The raw material used in this invention is oyster shells, a renewable resource. This not only solves the environmental pollution problem caused by oyster shells but also reduces limestone mining, protecting natural resources and the ecological environment. The invention employs a low-temperature reaction and controls the ratio of oyster shell powder to butyric acid, with an excess of oyster shell powder and controlled alkalinity of the solution. This allows other metal ions to exist in precipitated form, resulting in a relatively pure calcium butyrate solution. Furthermore, by controlling the molar ratio of calcium butyrate to sodium carbonate to 1:0.8 and using segmented precipitation, while maintaining a slightly acidic solution, other metal ions remain in solution form, yielding high-purity calcium carbonate.

[0055] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing high-purity calcium carbonate from oyster shells, characterized in that, The method comprises the following steps: 1) oyster shell treatment: air-drying, aging, cleaning, alkali treatment, drying, crushing, high-temperature calcination; 2) preparation of calcium butyrate solution: the calcined oyster shell powder obtained after step 1) is mixed with pure water, the temperature is kept at 0-5 DEG C, butyric acid is added dropwise under stirring, after the dropwise addition is completed, the final pH of the solution is ensured to be greater than 11, and the solution is continuously stirred for a period of time, and finally, the calcium butyrate solution is obtained by filtration; wherein the mass ratio of oyster shell powder to butyric acid is 1:1.9; 3) preparation of high-purity calcium carbonate: the calcium butyrate solution obtained in step 2) is stirred, the temperature is controlled at 0-5 DEG C, the pH is adjusted to 5-7 with butyric acid, sodium carbonate solution is added dropwise in several portions, after each dropwise addition is completed, the solution is kept for a period of time, then filtered, the obtained filtrate is subjected to the above-mentioned dropwise addition of sodium carbonate solution reaction, the filter cake is washed with pure water until neutral, dried, and high-purity calcium carbonate is obtained, the content of calcium carbonate is 99.8%-99.9%; wherein the molar ratio of calcium butyrate to sodium carbonate is 1:0.

8.

2. The method for preparing high-purity calcium carbonate using oyster shells as raw material according to claim 1, characterized in that, In step 1), the oyster shell treatment is: naturally air-dried, after aging for 4-9 months, cleaned with clean water or seawater to remove surface impurities, soaked in sodium hydroxide solution for 10-20 h, then cleaned with pure water, dried, then crushed, and finally high-temperature calcined at 800-1100 DEG C for 6-8 h; the mass concentration of the sodium hydroxide solution is 10%-15%.

3. The method for preparing high-purity calcium carbonate using oyster shell as raw material according to claim 1, characterized in that: In step 2), the stirring for a period of time is 1-3 h.

4. The method for preparing high-purity calcium carbonate using oyster shell as raw material according to claim 1, characterized in that: In step 2), the mass ratio of the calcined oyster shell powder to pure water is 1:

10.

5. The method for preparing high-purity calcium carbonate using oyster shell as raw material according to claim 1, characterized in that: In step 3), the mass concentration of the sodium carbonate solution is 25%.

6. The method for preparing high-purity calcium carbonate using oyster shell as raw material according to claim 1, characterized in that: In step 3), the keeping for a period of time is 30-60 min.

7. The method of claim 1, wherein the method comprises: In step 3), the number of portions is 3-5. ​