Preparation method of superfine calcium hydrophosphate for milk powder

Abstract

The invention discloses a preparation method of superfine calcium hydrophosphate for milk powder, which comprises the following steps: S1, taking calcium carbonate, adding water to prepare slurry, and adding a small amount of phosphoric acid for pre-acidification treatment; s2, slowly adding the pre-acidified calcium carbonate slurry into a phosphoric acid solution, and reacting at 25-50 DEG C to obtain a semi-finished product of calcium hydrogen phosphate dihydrate; s3, a certain amount of fatty acid surface modifier is added into the obtained semi-finished calcium hydrogen phosphate dihydrate product and mixed uniformly, and the addition amount of the fatty acid surface modifier is 0.2-0.4% of the mass of the semi-finished calcium hydrogen phosphate dihydrate product; and S4, carrying out superfine grinding to obtain the superfine calcium hydrogen phosphate. The nano-like calcium hydrogen phosphate dihydrate which is moderate in particle size, low in cost and good in suspension property can be obtained, and the calcium hydrogen phosphate dihydrate is suitable for strengthening calcium in milk powder and is a food additive which is stable in property, excellent in taste and wide in application range.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and particularly relates to a preparation method of ultrafine calcium hydrogen phosphate for milk powder. Background Art

[0002] Calcium hydrogen phosphate is a new generation of calcium fortifier for milk powder. Calcium hydrogen phosphate can supplement two elements, calcium and phosphorus, with comprehensive nutrition and an acceptable cost, making it an ideal calcium fortifier. Food-grade calcium hydrogen phosphate is usually prepared by reacting food-grade phosphoric acid with calcium carbonate. The obtained calcium hydrogen phosphate cannot be directly used in milk powder and needs to be processed and pulverized before it can be applied to milk powder.

[0003] Moreover, the requirements for the whiteness, fineness, black dot impurities, taste, and stability of the calcium source in formulated milk powder are relatively high. Conventional calcium carbonate is mostly heavy calcium carbonate, and there are obvious differences in taste between batches of heavy calcium carbonate, with poor taste. Light calcium carbonate is accompanied by problems of black dot foreign matters, and there are differences in physical properties between different batches of calcium carbonate, and the screening process is complex.

[0004] Dicalcium phosphate dihydrate is a white, odorless, crystalline powder or granule. As a food additive, a nano-like product obtained after ultrafine pulverization is an excellent calcium fortifier used in formulated milk powder.

[0005] Due to the poor thermal stability of the crystal water of dicalcium phosphate dihydrate, it will slowly lose water above 35 degrees. Heat generation is inevitable during the pulverization process, which is not conducive to ultra-fine and refined pulverization, and the free water content will increase after long-term storage, resulting in a sticky phenomenon.

[0006] The patent (a production process of dicalcium phosphate dihydrate for a fluoride-containing toothpaste, patent number CN115072684A) discloses a process for synthesizing dicalcium phosphate dihydrate using phosphoric acid and calcium carbonate as raw materials, in which it is necessary to add stabilizers, magnesium hydrogen phosphate and sodium pyrophosphate, to improve the stability of the crystal water of dicalcium phosphate dihydrate. The process is complex and introduces new impurity ions, affecting the product content.

[0007] Therefore, the granular dicalcium phosphate dihydrate currently on the market generally has problems such as low purity, poor whiteness, poor crystal water stability, poor stability after pulverization, and cannot be used as a raw material for ultra-fine pulverization processing. Moreover, the nano-like dicalcium phosphate dihydrate has problems such as stickiness, agglomeration, adhesion, and poor mixing uniformity. Summary of the Invention

[0008] The purpose of the present invention is to provide a preparation method of ultrafine calcium hydrogen phosphate for milk powder to solve the deficiencies of the prior art.

[0009] The purpose of the present invention is achieved by the following technical solutions:

[0010] A preparation method of ultrafine calcium hydrogen phosphate for milk powder, comprising the following steps:

[0011] S1. Prepare calcium carbonate by adding water to form a slurry, and add a small amount of phosphoric acid for pre-acidification treatment;

[0012] S2. Slowly add the pre-acidified calcium carbonate slurry into the phosphoric acid solution, and react at 25°C to 50°C to obtain a semi-finished product of calcium hydrogen phosphate dihydrate;

[0013] S3. Add a certain amount of fatty acid-based surface modifier to the obtained semi-finished product of calcium hydrogen phosphate dihydrate and mix evenly. The addition amount of the fatty acid-based surface modifier is 0.2% to 0.4% of the mass of the semi-finished product of calcium hydrogen phosphate dihydrate;

[0014] S4. Perform ultrafine grinding to obtain ultrafine calcium hydrogen phosphate.

[0015] Preferably, the calcium carbonate in step S1 is heavy calcium carbonate obtained by crushing natural carbonate minerals.

[0016] Preferably, the dosage ratio of the calcium carbonate to the phosphoric acid in steps S1 and S2 is 1:(1 to 1.2) in terms of molar ratio.

[0017] Preferably, the dosage of the phosphoric acid in step S1 is 2% to 5% of the total mass of the phosphoric acid.

[0018] Preferably, the feeding amount of the calcium carbonate slurry per minute in step S2 is 1% to 5% of the total mass of the calcium carbonate slurry.

[0019] Preferably, step S1 further includes:

[0020] Take calcium carbonate and add it to 4 to 7 times its mass of water to obtain a calcium carbonate slurry; take a small amount of phosphoric acid and prepare an aqueous solution with a mass percentage concentration of 20% to 50%, and then slowly add it to the calcium carbonate slurry for pre-acidification treatment.

[0021] Preferably, step S2 further includes:

[0022] Take the remaining phosphoric acid and prepare an aqueous solution with a concentration of 30% to 60%, and then slowly add it to the pre-acidified calcium carbonate slurry. After adding, stir and react for 20 to 40 minutes, then stand for aging for 1 to 3 hours, filter and dry to obtain the semi-finished product of calcium hydrogen phosphate dihydrate.

[0023] Preferably, the drying temperature is 45°C to 60°C and the drying time is 2 to 6 hours.

[0024] Preferably, before adding the fatty acid-based surface modifier in step S3, first perform primary grinding on the semi-finished product of calcium hydrogen phosphate dihydrate and pass through a sieve of 80 to 120 meshes.

[0025] Preferably, in step S4, ultrafine grinding is performed to an average particle size of 5 to 20 μm.

[0026] In this application, through raw material pretreatment and controlling certain reaction conditions, a semi-finished product of high bulk density crystalline calcium hydrogen phosphate dihydrate suitable for ultrafine processing and pulverization is obtained. It has excellent thermal stability, can withstand high temperatures of 60 °C, and can meet the heat generation problems during the operation of the vast majority of ultrafine pulverization equipment. Then, by adding processing aids and mixing, it is further ultrafinely pulverized to obtain a kind of calcium hydrogen phosphate dihydrate with a moderate particle size, low cost, and good suspension property, which is suitable for calcium fortification in milk powder and is a food additive with stable properties, excellent taste, and a wide range of applications. Specific Embodiments

[0027] The present invention provides a preparation method of ultrafine calcium hydrogen phosphate for milk powder, comprising the following steps:

[0028] S1. Take calcium carbonate, add water to prepare a slurry, and add a small amount of phosphoric acid for pre-acidification treatment;

[0029] S2. Slowly add the pre-acidified calcium carbonate slurry into the phosphoric acid solution, and react at 25 °C to 50 °C to obtain a semi-finished product of calcium hydrogen phosphate dihydrate;

[0030] S3. Add a certain amount of fatty acid-based surface modifier to the obtained semi-finished product of calcium hydrogen phosphate dihydrate and mix evenly. The addition amount of the fatty acid-based surface modifier is 0.2 - 0.4% of the mass of the semi-finished product of calcium hydrogen phosphate dihydrate;

[0031] S4. Perform ultrafine pulverization to obtain ultrafine calcium hydrogen phosphate.

[0032] This application discloses a preparation method of ultrafine calcium hydrogen phosphate for milk powder using calcium carbonate and phosphoric acid as raw materials. First, prepare calcium carbonate into a slurry and perform pre-acidification treatment with a small amount of phosphoric acid. By pre-acidifying the calcium carbonate slurry with acid, a buffer salt system can be generated, reducing the pH value of the calcium carbonate slurry and making the neutralization reaction milder. Moreover, phosphoric acid can react with a small amount of impurities in calcium carbonate to form phosphates such as magnesium hydrogen phosphate, which can be used as a stabilizer to improve the stability of the crystal water of calcium hydrogen phosphate. Then, slowly add the pre-acidified calcium carbonate slurry into the phosphoric acid solution, enabling a small amount of calcium carbonate to contact and react with sufficient phosphoric acid in water. After the calcium carbonate reaction is complete, calcium hydrogen phosphate dihydrate slowly and evenly precipitates, obtaining a semi-finished product of calcium hydrogen phosphate dihydrate with high bulk density and suitable for ultrafine pulverization. Then, add a small amount of fatty acid-based surface modifier for modification and perform ultrafine pulverization. The prepared calcium hydrogen phosphate dihydrate with a nano-like structure has high stability and good suspension effect. Moreover, the fatty acid-based surface modifier is only composed of carbon, hydrogen, and oxygen elements, has good biocompatibility, high safety, stable properties, and does not introduce other impurity ions.

[0033] Conventional nano-hydroxyapatite-like calcium hydrogen phosphate needs to have a particle size of 5 to 10 microns to have good suspension. In this application, by adding a small amount of fatty acid surface modifiers, they are evenly adsorbed on the particle surface, significantly improving the suspension of nano-hydroxyapatite-like calcium hydrogen phosphate. Therefore, the particle size of nano-hydroxyapatite-like calcium hydrogen phosphate does not need to be controlled within this range to achieve the same suspension effect, which facilitates production and reduces the energy consumption of ultrafine grinding equipment.

[0034] Due to the unique calcium carbonate pretreatment method used in this application, the stability of the crystal water of the calcium dihydrogen phosphate product is significantly increased. After the particle size reaches the nano-level, the moisture has high stability, which can improve the agglomeration phenomenon and enhance the flowability. By pretreating calcium carbonate, it is possible to avoid obvious differences in the moisture of calcium dihydrogen phosphate before and after grinding due to differences in calcium carbonate raw materials, and improve the applicability of calcium carbonate raw materials between different batches.

[0035] In summary, in this application, through raw material pretreatment and control of certain reaction conditions, a high bulk density crystalline calcium dihydrogen phosphate semi-finished product suitable for ultrafine processing and grinding is obtained. It has excellent thermal stability, can withstand high temperatures of 60 degrees, and can meet the heat generation problems during the operation of most ultrafine grinding equipment. Then, through the addition of processing aids and mixing, it is further ultrafinely ground to obtain a nano-calcium dihydrogen phosphate with moderate particle size, low cost, and good suspension. It is suitable for calcium fortification in milk powder and is a food additive with stable properties, excellent taste, and wide application range.

[0036] The fatty acid surface modifiers can be oleic acid, stearic acid, or other food-grade fatty acid surface modifiers. Oleic acid is preferably used. Oleic acid is an unsaturated fatty acid. In addition to having a good modification effect, it also has certain benefits to the human body.

[0037] Preferably, the calcium carbonate in step S1 is heavy calcium carbonate prepared by grinding natural carbonate minerals, which has a wide source and low cost.

[0038] Preferably, the dosage of calcium carbonate and phosphoric acid in step S1 and step S2 is 1:(1 - 1.2) in terms of molar ratio. Using a slightly excessive amount of phosphoric acid can make calcium carbonate react fully, reduce the residue of calcium carbonate, and improve the purity of calcium hydrogen phosphate.

[0039] The dosage of phosphoric acid in step S1 is 2 - 5% of the total phosphoric acid mass.

[0040] Preferably, the feeding amount of calcium carbonate slurry per minute is 1 - 5% of the total calcium carbonate slurry mass.

[0041] Preferably, step S1 further includes:

[0042] Take calcium carbonate and add it to 4 to 7 times its mass of water to obtain a calcium carbonate slurry; take a small amount of phosphoric acid and prepare an aqueous solution with a mass percentage concentration of 20 to 50%, and then slowly add it to the calcium carbonate slurry for pre-acidification treatment.

[0043] Preferably, step S2 further includes:

[0044] Take the remaining phosphoric acid and prepare an aqueous solution with a concentration of 30 to 60%, then slowly add it to the calcium carbonate slurry after pre-acidification treatment. After adding, stir and react for 20 to 40 minutes, and the stirring rate is preferably controlled at 160 to 220 rpm. Then let it stand and age for 1 to 3 hours to fully precipitate calcium hydrogen phosphate dihydrate. After filtration, dry it to obtain a semi-finished product of calcium hydrogen phosphate dihydrate.

[0045] Preferably, the drying temperature is below 60°C, more preferably 45 to 60°C, and the time is 2 to 6 hours. Drying at this temperature will not remove the crystal water in the semi-finished product of calcium hydrogen phosphate dihydrate, and calcium hydrogen phosphate dihydrate with stable moisture can be obtained.

[0046] Preferably, before adding the fatty acid-based surface modifier in step S3, first perform primary crushing on the semi-finished product of calcium hydrogen phosphate dihydrate, and pass through a sieve with 80 to 120 meshes. Performing primary crushing can improve the uniformity of solid-liquid mixing.

[0047] Preferably, in step S4, it is superfine pulverized to an average particle size of 5 to 20 μm. As described above, using the method provided in the present application, superfine pulverization does not need to strictly control the product particle size to 5 to 10 μm, which can reduce the energy consumption of superfine pulverization, relax the process conditions, and facilitate processing and production.

[0048] Example 1

[0049] A preparation method of ultrafine calcium hydrogen phosphate for milk powder, comprising the following steps:

[0050] (1) Synthesis

[0051] Weigh phosphoric acid and calcium carbonate as raw materials according to a molar ratio of 1:1. Add calcium carbonate to 5 times its mass of water, stir and prepare a slurry. Take 5% of the total phosphoric acid dosage, dilute it with water to a concentration of 40% (mass percentage concentration), and slowly add it to the calcium carbonate slurry for pre-treatment of calcium carbonate. Dilute the remaining phosphoric acid with water to a concentration of 50% (mass percentage concentration). Slowly add the treated calcium carbonate slurry to the phosphoric acid solution, control the stirring rate at 160 rpm, and control the feeding speed per minute at 2% of the total mass of the calcium carbonate slurry. After adding, stir and react fully for 30 minutes, let it stand and age for 2 hours, filter, and dry at 60 degrees for 3 hours to obtain a solid-phase product with a bulk density of 0.72 g / cm 3 .

[0052] (2) Crushing

[0053] The product is primarily pulverized using a pulverizer and reserved after passing through a 120-mesh sieve; oleic acid is weighed according to 0.2% of the mass of calcium hydrogen phosphate dihydrate, and is uniformly mixed in batches multiple times using a high-efficiency solid-liquid mixer, and further pulverized to an average particle size of 12 μm using an impact mill of a superfine powder equipment to obtain calcium hydrogen phosphate dihydrate for milk powder.

[0054] Final finished product index data: bulk density 0.46 g / cm 3 , loss on ignition 26.09%, calcium hydrogen phosphate content 99.48%.

[0055] Suspensibility measurement: Take 10 g and mix it evenly with 100 mL of water, then let it stand. After 15 min, the solid phase height of sedimentation is 94 mL, and the sedimentation ratio is 0.94 (the larger the sedimentation volume ratio, the slower the particle sedimentation speed and the better the suspensibility).

[0056] Example 2

[0057] (1) Synthesis

[0058] Phosphoric acid and calcium carbonate are weighed as raw materials according to a molar ratio of 1:1. Calcium carbonate is added to 5 times its mass of water and stirred to form a slurry. Take 2% of phosphoric acid and dilute it with water to a concentration of 40%, and slowly add it to the calcium carbonate slurry for pre-treatment of calcium carbonate. Dilute the remaining phosphoric acid with water to a concentration of 50%, and slowly add the treated calcium carbonate slurry to the phosphoric acid solution. The stirring rate is controlled at 220 rpm, and the feeding speed per minute is controlled at 1% of the total slurry mass. After adding, stir and react fully for 30 min, let it stand for aging for 2 h, filter, and dry at 60 °C for 3 h to obtain a solid-phase product with a bulk density of 0.81 g / cm 3 .

[0059] (2) Superfine pulverization

[0060] The product is primarily pulverized using a pulverizer and reserved after passing through a 120-mesh sieve; oleic acid is weighed according to 0.2% of the mass of calcium hydrogen phosphate dihydrate, and is uniformly mixed in batches multiple times using a high-efficiency solid-liquid mixer, and further pulverized to an average particle size of 7 μm using an impact mill of a superfine powder equipment to obtain calcium hydrogen phosphate dihydrate for milk powder.

[0061] Final finished product index data: bulk density 0.49 g / cm 3 , loss on ignition 25.86%, calcium hydrogen phosphate content 99.76%.

[0062] Suspensibility measurement: Take 10 g and mix it evenly with 100 mL of water, then let it stand. After 15 min, the solid phase height of sedimentation is 97 mL, and the sedimentation ratio is 0.97.

[0063] Comparative Example 1 (without adding oleic acid)

[0064] (1) Synthesis

[0065] Weigh phosphoric acid and calcium carbonate as raw materials according to a molar ratio of 1:1. Add calcium carbonate to 5 times its mass of water and stir to form a slurry. Take 2% of phosphoric acid, dilute it with water to a concentration of 40%, and slowly add it to the calcium carbonate slurry for pre-treatment of calcium carbonate. Dilute the remaining phosphoric acid with water to a concentration of 50%. Slowly add the treated calcium carbonate slurry to the phosphoric acid solution, control the stirring rate at 220 rpm, control the feeding speed per minute at 1% of the total slurry mass. After adding, stir well for reaction for 30 min, stand for aging for 2 h, filter, and dry at 60 °C for 3 h to obtain a solid-phase product with a bulk density of 0.80 g / cm 3 .

[0066] (2) Ultrafine grinding

[0067] Primarily grind the product using a grinder, and reserve it after passing through a 120-mesh sieve; use an impact mill of ultrafine powder equipment to grind it to an average particle size of 7 - 8 μm to obtain dicalcium hydrogen phosphate.

[0068] Final finished product index data: bulk density 0.44 g / cm 3 , loss on ignition 26.16%, and dicalcium hydrogen phosphate content 99.35%.

[0069] Suspensibility determination: Take 10 g and mix it evenly with 100 mL of water, then let it stand. After 15 min, the solid-phase height of sedimentation is 87 mL, and the sedimentation ratio is 0.87, which is lower than that of Example 2 (the larger the sedimentation volume ratio, the slower the particle sedimentation speed and the better the suspensibility).

[0070] Comparative Example 2 (calcium carbonate pre-treatment is cancelled)

[0071] (1) Synthesis

[0072] Weigh phosphoric acid and calcium carbonate as raw materials according to a molar ratio of 1:1. Dilute phosphoric acid with water to a concentration of 50%. Slowly add the calcium carbonate slurry to the phosphoric acid solution, control the stirring rate at 220 rpm, control the feeding speed per minute at 1% of the total slurry mass. After adding, stir well for reaction for 30 min, stand for aging for 2 h, filter, and dry at 60 °C for 3 h to obtain a solid-phase product with a bulk density of 0.71 g / cm 3 .

[0073] (2) Ultrafine grinding

[0074] Primarily grind the product using a grinder, and reserve it after passing through a 120-mesh sieve; Weigh oleic acid according to 0.2% of the mass of dicalcium hydrogen phosphate, mix it evenly in batches using a high-efficiency solid-liquid mixer, and further use an impact mill of ultrafine powder equipment to grind it to an average particle size of 7 - 8 μm to obtain dicalcium hydrogen phosphate.

[0075] Final finished product index data: bulk density 0.48 g / cm 3, the loss on ignition is 24.65%, and the calcium hydrogen phosphate content is 102.21% (compared with Example 2, in Comparative Example 2, the stability of the loss on ignition and content indicators decreases. The national standard requirement range for the loss on ignition is 24.5% - 26.5%, and the detected value is close to the minimum requirement. The thermal stability of the crystal water in the product is poor, and there is a risk of non - compliance during storage and re - processing, resulting in limited application).

[0076] Suspensibility determination: Take 10 g and mix it evenly with 100 mL of water, then let it stand. After 15 min, the solid - phase height of sedimentation is 94 mL, and the sedimentation ratio is 0.94.

[0077] Comparative Example 3 (increasing the feeding speed of calcium carbonate)

[0078] (1) Synthesis

[0079] Weigh phosphoric acid and calcium carbonate as raw materials according to a molar ratio of 1:1. Add calcium carbonate to 5 times its mass of water, stir to form a slurry. Take 2% of phosphoric acid, dilute it with water to a concentration of 40%, and slowly add it to the calcium carbonate slurry for pre - treatment of calcium carbonate. Dilute the remaining phosphoric acid with water to a concentration of 50%. Slowly add the treated calcium carbonate slurry to the phosphoric acid solution, control the stirring rate at 220 rpm, and control the feeding speed per minute at 6% of the total slurry mass. After adding, stir and react fully for 30 min, let it stand for aging for 2 h, filter, and dry at 60 degrees for 3 h to obtain a solid - phase product.

[0080] (2) Ultrafine grinding

[0081] Primarily grind the product using a grinder, and reserve it after passing through a 120 - mesh sieve; Weigh oleic acid according to 0.2% of the mass of calcium hydrogen phosphate dihydrate, mix it evenly in batches using a high - efficiency solid - liquid mixer, and further grind it to an average particle size of 7 μm using an ultrafine powder equipment impact mill to obtain calcium hydrogen phosphate dihydrate for milk powder.

[0082] Final finished - product index data: Bulk density 0.32 g / cm 3 , the loss on ignition is 25.96%, and the calcium hydrogen phosphate content is 100.21%; compared with Example 2, the bulk density of Comparative Example 3 decreases.

[0083] Suspensibility determination: Take 10 g and mix it evenly with 100 mL of water, then let it stand. After 15 min, the solid - phase height of sedimentation is 95 mL, and the sedimentation ratio is 0.95.

[0084] Example 3

[0085] (1) Synthesis

[0086] Weigh calcium carbonate and phosphoric acid as raw materials according to a molar ratio of 1:1.1. Add calcium carbonate to 6 times its mass of water and stir to form a slurry. Take 3% phosphoric acid and dilute it with water to a concentration of 30%. Slowly add it to the calcium carbonate slurry for pre-treatment of calcium carbonate. Dilute the remaining phosphoric acid with water to a concentration of 50%. Slowly add the treated calcium carbonate slurry to the phosphoric acid solution, control the stirring rate at 180 rpm, and control the feeding speed per minute at 1% of the total slurry mass. After adding, stir well for reaction for 30 min, let it stand for aging for 2 h, filter, and dry at 50 °C for 5 h to obtain a solid-phase product with a bulk density of 0.78 g / cm 3 .

[0087] (2) Ultrafine grinding

[0088] Primarily grind the product using a grinder, and reserve it after passing through a 100-mesh sieve; weigh oleic acid according to 0.4% of the mass of calcium hydrogen phosphate dihydrate, mix it evenly in batches using a high-efficiency solid-liquid mixer, and further grind it to an average particle size of 7 μm using an impact mill of an ultrafine powder equipment to obtain calcium hydrogen phosphate dihydrate for milk powder.

[0089] Final finished product index data: bulk density 0.56 g / cm 3 , loss on ignition 26.08%, calcium hydrogen phosphate content 99.43%;

[0090] Suspensibility measurement: Take 10 g and mix it evenly with 100 mL of water, then let it stand. After 15 min, the sediment solid phase height is 98 mL, and the sedimentation ratio is 0.98.

[0091] Example 4

[0092] (1) Synthesis

[0093] Weigh phosphoric acid and calcium carbonate as raw materials according to a molar ratio of 1:1. Add calcium carbonate to 5 times its mass of water and stir to form a slurry. Take 2% phosphoric acid and dilute it with water to a concentration of 40%. Slowly add it to the calcium carbonate slurry for pre-treatment of calcium carbonate. Dilute the remaining phosphoric acid with water to a concentration of 40%. Slowly add the treated calcium carbonate slurry to the phosphoric acid solution, control the stirring rate at 220 rpm, and control the feeding speed per minute at 3% of the total slurry mass. After adding, stir well for reaction for 30 min, let it stand for aging for 2 h, filter, and dry at 45 °C for 6 h to obtain a solid-phase product with a bulk density of 0.75 g / cm 3 .

[0094] (2) Ultrafine grinding

[0095] Primarily grind the product using a grinder, and reserve it after passing through an 80-mesh sieve; weigh oleic acid according to 0.2% of the mass of calcium hydrogen phosphate dihydrate, mix it evenly in batches using a high-efficiency solid-liquid mixer, and further grind it to an average particle size of 12 μm using an impact mill of an ultrafine powder equipment to obtain calcium hydrogen phosphate dihydrate for milk powder.

[0096] Final product index data: bulk density 0.47 g / cm 3 , loss on ignition 25.74%, calcium hydrogen phosphate content 100.11%.

[0097] Suspensibility determination: Take 10 g and mix it evenly with 100 mL of water, then let it stand. After 15 min, the solid phase height of sedimentation is 96 mL, and the sedimentation ratio is 0.96.

[0098] Example 5

[0099] (3) Synthesis

[0100] Weigh calcium carbonate and phosphoric acid as raw materials according to the molar ratio of 1:1.2. Add calcium carbonate to 5 times its mass of water, stir to form a slurry. Take 2% of phosphoric acid and dilute it with water to a concentration of 40%, and slowly add it to the calcium carbonate slurry for pre-treatment of calcium carbonate. Dilute the remaining phosphoric acid with water to a concentration of 30%. Slowly add the treated calcium carbonate slurry to the phosphoric acid solution, control the stirring rate at 220 rpm, and control the feeding speed per minute at 2% of the total slurry mass. After adding, stir and react fully for 30 min, let it stand and age for 1.5 h, filter, and dry at 60 °C for 2 h to obtain a solid-phase product with a bulk density of 0.78 g / cm 3 .

[0101] (4) Ultrafine grinding

[0102] Primarily grind the product using a grinder, and reserve it after passing through an 80-mesh sieve; Weigh oleic acid according to 0.2% of the mass of calcium hydrogen phosphate dihydrate, and mix it evenly in batches using a high-efficiency solid-liquid mixer. Further grind it to an average particle size of 18 μm using an ultrafine powder equipment impact mill to obtain calcium hydrogen phosphate dihydrate for milk powder.

[0103] Final product index data: bulk density 0.50 g / cm 3 , loss on ignition 25.49%, calcium hydrogen phosphate content 99.12%.

[0104] Suspensibility determination: Take 10 g and mix it evenly with 100 mL of water, then let it stand. After 15 min, the solid phase height of sedimentation is 94 mL, and the sedimentation ratio is 0.94.

[0105] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A preparation method of ultrafine calcium hydrogen phosphate for milk powder, characterized in that, It includes the following steps: S1. Take calcium carbonate, add water to prepare a slurry, and add a small amount of phosphoric acid for pre-acidification treatment; S2. Slowly add the pre-acidified calcium carbonate slurry into the phosphoric acid solution, and react at 25°C to 50°C to obtain a semi-finished product of calcium hydrogen phosphate dihydrate; S3. Add a certain amount of fatty acid-based surface modifier to the obtained semi-finished product of calcium hydrogen phosphate dihydrate, and mix evenly. The addition amount of the fatty acid-based surface modifier is 0.2 to 0.4% of the mass of the semi-finished product of calcium hydrogen phosphate dihydrate; S4. Perform ultrafine grinding to obtain ultrafine calcium hydrogen phosphate.

2. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 1, characterized in that the calcium carbonate in step S1 is heavy calcium carbonate prepared by crushing natural carbonate minerals.

3. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 1, characterized in that the dosage ratio of the calcium carbonate to the phosphoric acid in steps S1 and S2 is 1:(1 to 1.2) in terms of molar ratio.

4. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 1, characterized in that the dosage of the phosphoric acid in step S1 is 2 to 5% of the total mass of the phosphoric acid.

5. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 1, characterized in that the feeding amount of the calcium carbonate slurry per minute in step S2 is 1 to 5% of the total mass of the calcium carbonate slurry.

6. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 1, characterized in that step S1 further includes: Take calcium carbonate, add it to 4 to 7 times its mass of water to obtain a calcium carbonate slurry; take a small amount of phosphoric acid and prepare an aqueous solution with a mass percentage concentration of 20 to 50%, and then slowly add it to the calcium carbonate slurry for pre-acidification treatment.

7. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 6, characterized in that step S2 further includes: Take the remaining phosphoric acid and prepare an aqueous solution with a concentration of 30 to 60%, and then slowly add it to the pre-acidified calcium carbonate slurry. After adding, stir and react for 20 to 40 min, then stand for aging for 1 to 3 h, filter and dry to obtain the semi-finished product of calcium hydrogen phosphate dihydrate.

8. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 7, characterized in that the drying temperature is 45 to 60°C, and the drying time is 2 to 6 h.

9. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 1, characterized in that before adding the fatty acid-based surface modifier in step S3, first perform primary grinding on the semi-finished product of calcium hydrogen phosphate dihydrate and pass through a sieve of 80 to 120 meshes.

10. The preparation method of ultrafine calcium hydrogen phosphate for milk powder according to claim 1, characterized in that in step S4, it is ultrafine ground to an average particle size of 5 to 20 μm.