A kind of purification method of calcium citrate

Abstract

The invention relates to the field of preparation and treatment of citrate, and provides a method for purifying calcium citrate. The method comprises the following steps: dehydrating a calcium citrate suspension and then dissolving it in a citric acid solution, filtering it and then neutralizing it with a food-grade calcium carbonate slurry, and then dehydrating and drying it, so that silicate, sulfate and hydrochloric acid insoluble matter in the calcium citrate can be effectively removed, thereby solving the problems of high-end product blank, unstable quality, low conversion rate, low equipment utilization rate and the like in the current calcium citrate production.

Description

Technical Field

[0001] The invention relates to the field of preparation and treatment of high-quality citrate, and in particular to a method for purifying calcium citrate. Background Art

[0002] Calcium citrate, scientific name 2-hydroxypropane-1,2,3-tricarboxylic acid calcium tetrahydrate, molecular formula C 12 H 10 Ca3O 14 , is widely used in the field of food additives and pharmaceutical raw materials, and the optimization of its production process is the focus of industry attention. The traditional preparation method involves neutralizing calcium carbonate and citric acid solution. This process requires multiple steps such as filtration, washing and drying. However, since the calcium carbonate used is derived from calcium carbonate ore, the calcium carbonate ore is limited by geological conditions and has unstable quality. It is easy to contain silicates, sulfates, hydrochloric acid insolubles, etc., causing the quality of calcium citrate to fluctuate. The calcium citrate produced by the traditional preparation method is limited by the quality of calcium carbonate ore, and the quality fluctuates greatly. The silicates and hydrochloric acid insolubles contained therein are non-toxic and harmless, but they not only affect the taste, but also affect gastrointestinal motility, increase the burden on the liver, and hinder the absorption of calcium; sulfate intake will irritate the human stomach and intestines, affect gastrointestinal function, corrode the stomach and intestines in severe cases, and cause damage to the nervous system, which may cause dizziness, headache, blurred vision, mental distraction, limb fatigue and other symptoms. In severe cases, it may cause insomnia, difficulty swallowing, difficulty breathing, etc., causing poisoning and other events, especially for vulnerable groups such as infants and the elderly. In the traditional preparation method, the above impurities fluctuate, sometimes silicate can reach 100ppm, sulfate 50ppm, and hydrochloric acid insoluble matter 0.05%. The content of the above impurities exceeds the explicit requirements of some high-end markets and high-end customers, and cannot meet the needs of the high-end market. The calcium carbonate raw materials are unstable. Usually one batch meets the production needs, and the next batch cannot meet the production needs. Even the same batch of calcium carbonate has a large fluctuation, the product supply is not smooth, affecting market development, and the price of high-quality calcium carbonate is expensive, and the profit margin of the produced calcium citrate is low.

[0003] In the production of high-quality calcium citrate, in addition to efficiency and cost control, product quality and safety supervision is crucial, which involves strict control of every link from raw material selection to production control, and finally to the packaging and transportation of the final product. Therefore, it is urgent to develop a production and processing method for calcium citrate with good product quality, high safety, and both efficiency and cost control. Summary of the invention

[0004] In order to overcome the problems of low quality of calcium citrate in the prior art and high impurity contents of silicate, sulfate, hydrochloric acid insoluble matter and the like, the present invention provides a method for purifying calcium citrate, wherein a calcium citrate suspension is dehydrated and then dissolved in a citric acid solution, filtered and then neutralized with a food-grade calcium carbonate slurry, and then dehydrated and dried, so that silicate, sulfate and hydrochloric acid insoluble matter in the calcium citrate can be effectively removed, thereby solving the problems of a lack of high-end products, unstable quality, low conversion rate, low equipment utilization rate and the like in the current production of calcium citrate.

[0005] The method for purifying calcium citrate provided by the invention comprises the following steps: dehydrating a calcium citrate suspension, then completely dissolving it in a citric acid solution, adding calcium carbonate slurry to the filtrate after precise filtration, neutralizing it to a pH of 4-5, and finally dehydrating and drying it to obtain the calcium citrate.

[0006] More specifically, the above-mentioned method for purifying calcium citrate comprises the following steps: 1) Dehydration: Dehydrating the calcium citrate suspension by centrifuge to obtain the first calcium citrate wet material; Preferably, the rotation speed of the centrifuge dehydration in step 1) is 700-800 rpm, the time is 10-12 min, and the moisture content of the first calcium citrate wet material obtained is 35-45%.

[0007] 2) Redissolving: completely dissolving the first calcium citrate wet material in the citric acid solution to obtain a clear calcium hydrogen citrate solution; Preferably, the mass concentration of the citric acid solution in step 2) is 14-16%, and the ratio of the mass of citric acid in the citric acid solution to the mass of the calcium citrate wet material is (4-5):1.

[0008] 3) Precision filtration: The calcium hydrogen citrate solution is subjected to 0.22-0.8 μm precision filtration to obtain a filtrate.

[0009] 4) Re-neutralization: adding food-grade calcium carbonate slurry evenly to the filtrate obtained in step 4) for neutralization, maintaining the neutralization temperature at 70-90° C., controlling the pH to 4.0-5.0 and then stopping the addition to complete the neutralization, thereby obtaining calcium citrate slurry; Preferably, the food-grade calcium carbonate slurry in step 4) is prepared by mixing food-grade calcium carbonate and water in a mass ratio of 1:(1-1.5), and stirring is maintained at 100-150 rpm during the neutralization process.

[0010] 5) Re-dehydration: adding the calcium citrate slurry obtained in step 4) to a centrifuge for dehydration to obtain a second calcium citrate wet material; Preferably, in step 5), the rotation speed of the centrifuge for dehydration is 700-800 rpm, and the dehydration time is 10-12 min; and the moisture content of the second calcium citrate wet material is 35-45%.

[0011] 6) Drying: drying the second calcium citrate wet material obtained in step 5) to obtain a second calcium citrate dry material; Preferably, the drying temperature in step 6) is 80-100° C. and the drying time is 4-5 h.

[0012] In the above step 1), the calcium citrate suspension is prepared by neutralizing citric acid and calcium carbonate. The specific method is: after filtering the citric acid solution through a filter, inject it into a reactor, heat it and uniformly add calcium carbonate slurry to the reactor, continue stirring during the addition process, stop adding when the pH is 5.0-7.0, and obtain an initial calcium citrate suspension without impurities removal.

[0013] In the preparation method of the calcium citrate suspension, the mass concentration of the citric acid solution is 0.3-0.35 g / mL, the concentration of the calcium carbonate slurry is 0.3-0.4 g / mL, the mesh number of the filter is 200-250 mesh, the citric acid solution is heated to 80-90°C before adding the calcium carbonate slurry, the neutralization temperature of the reactor is maintained at 70-90°C when the calcium carbonate slurry is added, and the flow rate of the calcium carbonate slurry is 13-17m 3 / h, the stirring speed is 100-150 rpm; Controlling the reaction at 70-90°C can greatly reduce the amount of carbon dioxide generated by the reaction that dissolves in water, promote the forward reaction, and make the reaction complete.

[0014] Preferably, in step 3), a 0.22 μm ceramic membrane is used for precision filtration. The use of a ceramic membrane for precision filtration is convenient for pressurization, easy to clean, and has corrosion resistance. The pressure of the precision filtration in step 3) is 0.6-1.5 MPa. As a further preference, the ceramic membrane is disassembled and cleaned after each treatment.

[0015] By purifying calcium citrate through the above method, the yield of citric acid can reach 97-99%, and the yield of calcium carbonate can reach 98-99%, thereby achieving good yield while greatly reducing the impurity content.

[0016] The neutralization reaction of the present invention adopts the above optimized ratio, and the solution concentration and stirring speed can be reasonably controlled according to the production requirements, etc., to ensure that the yield of the calcium citrate produced is guaranteed on the basis of improving the purity. On the other hand, purified water, as a large consumable material of this reaction, can be recycled as acid dissolving water during the dehydration process, as a reaction raw material for a neutralization, reducing the water and electricity costs used in the reaction. The use and maintenance parameters of 0.22 μm ceramic membrane filtration in industrial production are consistent with those used in conventional industrial production, and will not be repeated in this article.

[0017] The present invention uses citric acid as a dissolving medium, precision filtration as a key control point, and ensuring the yield as a prerequisite, which can reduce the silicate contained in the calcium citrate produced by most domestic production lines by 45%-65%, the sulfate by 45%-70%, and the hydrochloric acid insoluble matter by 75%-80%, effectively improving the product quality and far exceeding the national standard requirements, meeting the needs of the high-end market and high-end customers, and can increase the profits of the enterprise and further enhance the competitiveness of the enterprise in the industry. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the implementation cases described are only some implementation cases of the present invention, not all implementation cases. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Example 1 A method for purifying calcium citrate, the specific steps are as follows: 1) Preparation of calcium citrate suspension: First, anhydrous citric acid was dissolved in deionized water to prepare a citric acid solution with a concentration of 0.3 g / mL. The citric acid solution was filtered through a 200-mesh filter and then entered into a reactor. The temperature was raised to 80°C for insulation. 0.3 g / mL of calcium carbonate slurry was added into the reactor. The stirring was maintained at 100 rpm for 17 min. During this period, the flow rate of the calcium carbonate slurry was 15 m / s. 3 / h, the pH end point was 5.12, and a calcium citrate suspension was obtained.

[0020] 2) The calcium citrate suspension obtained in step 1) was dehydrated by centrifuge at a speed of 700 rpm for 10 minutes to obtain a first calcium citrate wet material with a moisture content of 37.5%.

[0021] 3) The first calcium citrate wet material obtained in step 2) is completely dissolved in a citric acid solution with a mass concentration of 14%, and the dissolution ratio of the mass of citric acid in the citric acid solution to the mass of the calcium citrate wet material is 4.2:1, to obtain a calcium hydrogen citrate solution, and the calcium hydrogen citrate solution is filtered through a 0.22 μm ceramic membrane with a membrane inlet pressure of 0.62 MPa to ensure that the dissolved acid solution is free of precipitation and impurities, to obtain a filtrate.

[0022] 4) Add food-grade calcium carbonate to water of the same mass as food-grade calcium carbonate to obtain food-grade calcium carbonate slurry. Add the filtrate obtained in step 3) to another reactor, heat it to 80°C, pump the food-grade calcium carbonate slurry into the reactor, and keep stirring at 100 rpm for 10 min. During this time, the flow rate of the calcium carbonate slurry is 15 m / s. 3 / h, the pH end point was 4.82, and calcium citrate slurry was obtained.

[0023] 5) The calcium citrate slurry obtained in step 4) is dehydrated again by the same method as in step 2) to obtain a second calcium citrate wet material, wherein the moisture content of the second calcium citrate wet material is 39.8%.

[0024] 6) The second calcium citrate wet material obtained in step 5) is put into a dryer and dried at 85° C. for 4 hours to obtain the second calcium citrate dry material.

[0025] By the method of this embodiment, 4705.7 kg of calcium citrate is actually obtained, of which 3200 kg of citric acid is used in total, and 4754.2 kg of calcium citrate can be obtained theoretically. Calculated based on citric acid, the final yield of calcium citrate is 98.98%; a total of 2525 kg of food-grade calcium carbonate is used, and 4801.7 kg of calcium citrate is obtained theoretically. Calculated based on food-grade calcium carbonate, the final yield of calcium citrate is 98%.

[0026] Example 2 A method for purifying calcium citrate, the specific steps are as follows: 1) Preparation of calcium citrate suspension: First, anhydrous citric acid was dissolved in deionized water to prepare a citric acid solution with a concentration of 0.32 g / ml. The citric acid solution was filtered through a 200-mesh filter and then entered into a reactor. The temperature was raised to 80°C for insulation. 0.34 g / mL of calcium carbonate slurry was added into the reactor. The stirring was maintained at 100 rpm for 18 min. During this period, the flow rate of the calcium carbonate slurry was 15 m / s. 3 / h, the pH end point was 5.22, and a calcium citrate suspension was obtained.

[0027] 2) The calcium citrate suspension obtained in step 1) was dehydrated by centrifuge at a speed of 700 rpm for 10 minutes to obtain a first calcium citrate wet material with a moisture content of 38.9%.

[0028] 3) The first calcium citrate wet material obtained in step 2) is completely dissolved in a citric acid solution with a mass concentration of 14%, and the dissolution ratio of the mass of citric acid in the citric acid solution to the mass of the calcium citrate wet material is 4.2:1, to obtain a calcium hydrogen citrate solution, and the calcium hydrogen citrate solution is filtered through a 0.8 μm ceramic membrane with a membrane inlet pressure of 1.43 MPa to ensure that the acid solution after the dissolution is free of precipitation and impurities, to obtain a filtrate.

[0029] 4) Add food-grade calcium carbonate into water with a mass 1.2 times that of food-grade calcium carbonate to prepare a slurry to obtain a food-grade calcium carbonate slurry. Add the filtrate obtained in step 3) into another reactor, heat it to 80°C, pump the food-grade calcium carbonate slurry into the reactor, and keep stirring at 100 rpm for 10 min. During this time, the flow rate of the calcium carbonate slurry is 15 m / s. 3 / h, the pH end point was 4.78, and calcium citrate slurry was obtained.

[0030] 5) The calcium citrate slurry obtained in step 4) is dehydrated again by the same method as in step 2) to obtain a second calcium citrate wet material, wherein the moisture content of the second calcium citrate wet material is 38.4%.

[0031] 6) The second calcium citrate wet material obtained in step 5) is put into a dryer and dried at 85° C. for 4 hours to obtain the second calcium citrate dry material.

[0032] By the method of this embodiment, 4979.3 kg of calcium citrate is actually obtained, of which 3400 kg of citric acid is used in total, and 5051.3 kg of calcium citrate can be obtained theoretically. Calculated based on citric acid, the final yield of calcium citrate is 98.57%; a total of 2666.4 kg of food-grade calcium carbonate is used, and 5070.6 kg of calcium citrate is obtained theoretically. Calculated based on food-grade calcium carbonate, the final yield of calcium citrate is 98.2%.

[0033] Example 3 A method for purifying calcium citrate, the specific steps are as follows: 1) Preparation of calcium citrate suspension: First, anhydrous citric acid was dissolved in deionized water to prepare a citric acid solution with a concentration of 0.35 g / ml. The citric acid solution was filtered through a 200-mesh filter and then entered into a reactor. The temperature was raised to 80°C for insulation. 0.38 g / mL of calcium carbonate slurry was added into the reactor. The stirring was maintained at 100 rpm for a total of 19 min. During this period, the flow rate of the calcium carbonate slurry was 15 m / s. 3 / h, the pH end point was 5.42, and a calcium citrate suspension was obtained.

[0034] 2) The calcium citrate suspension obtained in step 1) was dehydrated by centrifuge at a speed of 700 rpm for 10 minutes to obtain a first calcium citrate wet material with a moisture content of 40.5%.

[0035] 3) The first calcium citrate wet material obtained in step 2) is completely dissolved in a citric acid solution with a mass concentration of 14%, and the dissolution ratio of the mass of citric acid in the citric acid solution to the mass of the calcium citrate wet material is 4.8:1, to obtain a calcium hydrogen citrate solution, and the calcium hydrogen citrate solution is filtered through a 0.22 μm ceramic membrane with a membrane inlet pressure of 0.65 MPa to ensure that the acid solution after the dissolution is free of precipitation and impurities, to obtain a filtrate.

[0036] 4) Add food-grade calcium carbonate into water with a mass 1.5 times that of food-grade calcium carbonate to prepare a slurry to obtain a food-grade calcium carbonate slurry. Add the filtrate obtained in step 3) into another reactor, heat it to 80°C, pump the food-grade calcium carbonate slurry into the reactor, and keep stirring at 120 rpm for 10 min. During this time, the flow rate of the calcium carbonate slurry is 15 m / s. 3 / h, the pH end point was 4.68, and calcium citrate slurry was obtained.

[0037] 5) The calcium citrate slurry obtained in step 4) is dehydrated again by the same method as in step 2) to obtain a second calcium citrate wet material, wherein the moisture content of the second calcium citrate wet material is 40.2%.

[0038] 6) The second calcium citrate wet material obtained in step 5) is put into a dryer and dried at 85° C. for 4 hours to obtain the second calcium citrate dry material.

[0039] By the method of this embodiment, 5264.8 kg of calcium citrate is actually obtained, wherein a total of 3600 kg of citric acid is used, and 5348.4 kg of calcium citrate can be obtained theoretically. Calculated based on citric acid, the final yield of calcium citrate is 98.44%; a total of 2805 kg of food-grade calcium carbonate is used, and 5334.2 kg of calcium citrate is obtained theoretically. Calculated based on food-grade calcium carbonate, the final yield of calcium citrate is 98.7%.

[0040] Example 4 A method for purifying calcium citrate, the specific steps are as follows: 1) Preparation of calcium citrate suspension: First, anhydrous citric acid was dissolved in deionized water to prepare a citric acid solution with a concentration of 0.32 g / ml. The citric acid solution was filtered through a 200-mesh filter and then entered into a reactor. The temperature was raised to 80°C for insulation. 0.33 g / ml of calcium carbonate slurry was added into the reactor. The stirring was maintained at 100 rpm for a total of 19 minutes. During this period, the flow rate of the calcium carbonate slurry was 15 m / s. 3 / h, the pH end point was 6.07, and a calcium citrate suspension was obtained.

[0041] 2) The calcium citrate suspension obtained in step 1) was dehydrated by centrifuge at a speed of 700 rpm for 10 minutes to obtain a first calcium citrate wet material with a moisture content of 39.2%.

[0042] 3) The first calcium citrate wet material obtained in step 2) is completely dissolved in a citric acid solution with a mass concentration of 14%, and the dissolution ratio of the mass of citric acid in the citric acid solution to the mass of the calcium citrate wet material is 4.8:1, to obtain a calcium hydrogen citrate solution, and the calcium hydrogen citrate solution is filtered through a 0.8 μm ceramic membrane with a membrane inlet pressure of 1.47 MPa to ensure that the acid solution after the solution is free of precipitation and impurities, to obtain a filtrate.

[0043] 4) Add food-grade calcium carbonate into water with a mass 1.2 times that of food-grade calcium carbonate to prepare a slurry to obtain a food-grade calcium carbonate slurry. Add the filtrate obtained in step 3) into another reactor, heat it to 80°C, pump the food-grade calcium carbonate slurry into the reactor, and keep stirring at 120 rpm for 10 min. During this time, the flow rate of the calcium carbonate slurry is 15 m / s. 3 / h, the pH end point was 4.76, and calcium citrate slurry was obtained.

[0044] 5) The calcium citrate slurry obtained in step 4) is dehydrated again by the same method as in step 2) to obtain a second calcium citrate wet material, wherein the moisture content of the second calcium citrate wet material is 41.3%.

[0045] 6) The second calcium citrate wet material obtained in step 5) is put into a dryer and dried at 85° C. for 4 hours to obtain the second calcium citrate dry material.

[0046] 7) In this embodiment, 5054.5 kg of calcium citrate is actually obtained, of which 3500 kg of citric acid is used in total, and 5199.9 kg of calcium citrate can be obtained theoretically. Calculated based on citric acid, the final yield of calcium citrate is 97.2%; a total of 2703.9 kg of food-grade calcium carbonate is used, and 5141.9 kg of calcium citrate is obtained theoretically. Calculated based on food-grade calcium carbonate, the final yield of calcium citrate is 98.3%.

[0047] Comparative Examples 1-4 A first calcium citrate wet material was prepared in the same manner as step 1) and step 2) of Examples 1-4, and the first calcium citrate wet material was directly dried at 85° C. for 4 h to obtain first citric acid dry materials of Comparative Examples 1-4, respectively.

[0048] Results comparison The first calcium citrate dry material and the second calcium citrate dry material in Examples 1-4 were sent to a nationally recognized laboratory, and sulfate and hydrochloric acid insoluble matter were tested according to the Japanese Food Additives Standard, and silicate was tested according to GB / T 9742-2008. The results are shown in the following table: As can be seen from the above table, the comparative example is not treated by the present method compared with the embodiment, so the contents of silicate, sulfate and hydrochloric acid insolubles in the comparative example are significantly higher than those in the embodiment. After being treated by the present method, the silicate in Examples 1-4 can be reduced by 58.6%, 40.6%, 64.1% and 43.3%, respectively, the sulfate content can be reduced by 70.3%, 49.7%, 66.1%, 46.9%, respectively, and the hydrochloric acid insolubles can be reduced by 75%, 75%, 75% and 80%, respectively, indicating that the impurities of silicate, sulfate and hydrochloric acid insolubles in calcium citrate can be significantly reduced by the present method.

[0049] The invention uses citric acid as a dissolving medium, ceramic membrane filtration as a key control point, and ensuring the yield as a prerequisite. After multiple tests, factors such as concentration ratio and filtration pore size are tested one by one, and finally a solution ratio, production process and production equipment with high conversion rate and less impurities of calcium citrate are obtained. The invention can reduce silicate contained in calcium citrate produced by most production lines in the industry by 45%-65%, sulfate by 45%-70%, and hydrochloric acid insoluble matter by 75%-80%, thereby effectively improving product quality, meeting the needs of special customers, expanding the market scale, and enhancing product competitiveness.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any equivalent substitutions, modifications, etc. made by technicians in this field without any creative work within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for purifying calcium citrate, characterized in that: The specific steps include: 1) Dehydration: Dehydrating the calcium citrate suspension by centrifuge to obtain the first calcium citrate wet material; 2) Redissolving: completely dissolving the first calcium citrate wet material in the citric acid solution to obtain a clear calcium hydrogen citrate solution; 3) Precision filtration: The calcium hydrogen citrate solution is subjected to 0.22-0.8 μm precision filtration to obtain a filtrate; 4) Re-neutralization: adding food-grade calcium carbonate slurry evenly to the filtrate obtained in step 4) for neutralization, and stopping the addition after controlling the pH to 4.0-5.0, and neutralization is completed to obtain calcium citrate slurry; 5) Re-dehydration: adding the calcium citrate slurry obtained in step 4) to a centrifuge for dehydration to obtain a second calcium citrate wet material; 6) Drying: Drying the second calcium citrate wet material obtained in step 5) to obtain a second calcium citrate dry material.

2. The method for purifying calcium citrate according to claim 1, wherein The calcium citrate suspension in step 1) is prepared by neutralizing citric acid and calcium carbonate. The specific method is: after filtering the citric acid solution through a filter, inject it into a reactor, heat it and uniformly add calcium carbonate slurry to the reactor, continue stirring during the addition process, stop adding when the pH is 5.0-7.0, and obtain an initial calcium citrate suspension without impurities removal.

3. The method for purifying calcium citrate according to claim 2, wherein In the preparation method of the calcium citrate suspension, the mass concentration of the citric acid solution is 0.3-0.35 g / mL, the concentration of the calcium carbonate slurry is 0.3-0.4 g / mL, the mesh number of the filter is 200-250 meshes, the citric acid solution is heated to 80-90° C. before adding the calcium carbonate slurry, the neutralization temperature of the reactor is maintained at 70-90° C. when the calcium carbonate slurry is added, and the flow rate of the calcium carbonate slurry is 13-17 m / s. 3 / h, and the stirring speed is 100-150 rpm.

4. The method for purifying calcium citrate according to claim 1 or 2, characterized in that: In step 1), the rotation speed of the centrifuge for dehydration is 700-800 rpm, the time is 10-12 min, and the moisture content of the first calcium citrate wet material obtained is 35-45%.

5. The method for purifying calcium citrate according to claim 1 or 2, characterized in that: The mass concentration of the citric acid solution in step 2) is 14-16%, and the mass ratio of the citric acid in the citric acid solution to the mass of the calcium citrate wet material is (4-5):

1.

6. The method for purifying calcium citrate according to claim 1 or 2, characterized in that: The pressure of the precision filtration in step 3) is 0.6-1.5 MPa.

7. The method for purifying calcium citrate according to claim 1 or 2, characterized in that: The food-grade calcium carbonate slurry in step 4) is prepared by mixing food-grade calcium carbonate and water in a mass ratio of 1:(1-1.5), and the stirring is maintained at 100-150 rpm during the neutralization process, and the neutralization temperature is maintained at 70-90°C.

8. The method for purifying calcium citrate according to claim 1 or 2, characterized in that: The speed of the centrifuge dehydration in step 5) is 700-800 rpm, and the time is 10-12 min; the moisture content of the second calcium citrate wet material is 35-45%; the temperature of the drying in step 6) is 80-100°C, and the time is 4-5 h.

9. The method for purifying calcium citrate according to claim 1 or 2, characterized in that: In step 3), a 0.22 μm ceramic membrane is used for precision filtration.

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