A method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste

Abstract

This invention provides a method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste. The method comprises the following steps: S1: mixing calcium-containing solid waste and an ammonium salt solution, reacting the mixture, and filtering to obtain a calcium-containing filtrate; S2: mixing the calcium-containing filtrate, CO2 gas, and a crystal form control agent, reacting the mixture, and filtering to obtain nano-calcium carbonate; S3: mixing the nano-calcium carbonate with an aqueous solution containing a surfactant, reacting the mixture, centrifuging, washing, and drying to obtain monodisperse nano-calcium carbonate. This method improves the calcium leaching rate from calcium-containing solid waste, achieves explosive nucleation and rapid growth of calcium carbonate, enhances the reactivity and reaction time between the surfactant and the nano-calcium carbonate particles, and improves the dispersion and surface modification degree of the calcium carbonate nanoparticles.

Description

Technical Field

[0001] This invention relates to the field of nano-calcium carbonate preparation technology, and in particular to a method for preparing monodisperse nano-calcium carbonate using calcium-containing industrial solid waste. Background Technology

[0002] Alkaline solid wastes containing calcium, such as steel slag, red mud, and carbide slag, are difficult to utilize directly and have low value due to their complex composition, high alkalinity, and high content of heavy metals. They are mostly used in low-end fields such as cement and building materials, resulting in the waste of valuable resources.

[0003] Calcium carbonate is an important chemical raw material with advantages such as low price, non-toxicity, non-irritation, good color, high whiteness, and excellent mechanical properties. It is widely used in industries such as rubber, plastics, inks, papermaking, pharmaceuticals, food, and cosmetics. Nano-calcium carbonate is a new industry that has been continuously upgraded and developed from light calcium carbonate products. It has advantages that ordinary calcium carbonate does not possess, such as fine particle size, large specific surface area, and high activity. The particle size, dispersibility, structural morphology, and surface properties of nano-calcium carbonate products affect and determine their functionality and application areas.

[0004] Currently, the main methods for producing calcium carbonate include the carbonation method (Ca(OH)2-H2O-CO2), ammonium chloride (CaCl2-NH4Cl), calcium chloride method (CaCl2-Na2CO3), and Solvay method (CaCl2-NaHCO3). All of these methods involve complex processes such as mass transfer, heat transfer, crystal nucleation, crystal growth, and agglomeration in a gas-liquid-solid multiphase system. These methods also have problems such as large calcium carbonate particle size, uneven particle size distribution, poor dispersion, and difficulty in separation.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste. This method improves the leaching rate of calcium in calcium-containing solid waste, realizes the explosive nucleation and rapid growth of calcium carbonate, enhances the reactivity and reaction time between surfactants and nano-calcium carbonate particles, and improves the dispersion and surface modification degree of calcium carbonate nanoparticles.

[0007] This invention provides a method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste, comprising the following steps:

[0008] S1: Mix calcium-containing solid waste and ammonium salt solution and react them. After filtration, obtain calcium-containing filtrate.

[0009] S2: After mixing calcium-containing filtrate, CO2 gas and crystal form control agent, the mixture is reacted and filtered to obtain nano-calcium carbonate;

[0010] S3: Nano-calcium carbonate is mixed with an aqueous solution containing a surfactant and reacted. After centrifugation, washing, and drying, monodisperse nano-calcium carbonate is obtained.

[0011] In step S1, the calcium-containing solid waste is selected from at least one of red mud, carbide slag, steel slag, and yellow phosphorus slag; the ammonium salt in the ammonium salt solution has a mass content of 9-20%, and the ammonium salt is selected from at least one of ammonium nitrate, ammonium chloride, and ammonium acetate, preferably ammonium chloride; the mass ratio of calcium-containing solid waste to ammonium salt solution is (0.05-0.2):1, for example (0.086-0.170):1; the mixing temperature is 20-50℃, for example 25℃, and the time is 5-10min, for example 10min; the reaction temperature is 60-120℃, for example 120℃, and the time is 1-6h, for example 1-3h; the calcium chloride mass content in the calcium-containing filtrate is 5-14%, for example 7.18-13.3%.

[0012] In step S2, the crystal form control agent is selected from at least one of glucose, sodium polyphosphate, dodecylbenzenesulfonic acid, sodium dodecyl sulfate, polyethylene glycol, sodium sulfate, citric acid, and oxalic acid; the mass ratio of the crystal form control agent to nano-calcium carbonate is (0.002-0.005):1, preferably (0.003-0.005):1; the CO2-containing gas is a mixture of N2 and CO2, and the mass content of CO2 in the CO2-containing gas is 2-100%, for example, 10-80%; the CO2-containing gas can be introduced by self-absorption, for example, by using a Venturi tube; the reaction temperature is 20-50℃, for example, 25℃, and the time is 1-10 min, for example, 3-10 min.

[0013] In step S3, the surfactant is selected from at least one of stearic acid, dodecylbenzene sulfonic acid, silane coupling agent, aluminate coupling agent and titanate coupling agent; the mass ratio of surfactant to nano-calcium carbonate is (0.03-0.05):1; the reaction temperature is 20-50℃, for example 50℃, and the time is 5-10min, for example 10min; the drying temperature is 60-100℃ and the time is 6-12h.

[0014] In steps S1-S3 above, a mixing and reversing device can be used for mixing. The mixing and reversing device includes a housing, with a feeding chamber located at the top inside the housing and connected to the feeding port. A stator is fixedly located at the bottom inside the housing, and the stator has a hollow cavity. A rotor is located in the hollow cavity, and there is an adjustable gap between the rotor and the stator. The top of the gap is connected to the feeding chamber. Multiple guide grooves are provided circumferentially on the inner wall of the stator and the outer wall of the rotor. The rotor is connected to the drive shaft of the drive mechanism through a rotating shaft. A return port is located at the top of the housing, and the two ends of the return port are connected to the feeding chamber and the return pipe, respectively. An outlet is located at the bottom of the housing and connected to the bottom of the gap. The outlet is connected to the lower part of the return pipe through a three-way valve. A venturi tube is located in the middle of the return pipe, and the throat of the venturi tube is connected to the air inlet. An air inlet valve is located on the air inlet.

[0015] Furthermore, the feed chamber is shaped like an inverted frustum, with its bottom flush with the top of the stator. Both the hollow cavity of the stator and the rotor are frustum-shaped. The rotor is connected to a lifting mechanism, which allows the rotor to move up and down relative to the stator to adjust the gap size. The gap size is adjustable within the range of 20-500 μm, for example, 50-200 μm. The rotor speed is adjustable within the range of 1000-6000 r / min, and the intake volume of CO2-containing gas is adjusted via an intake valve.

[0016] In step S1, the mixing speed is 1000-5000 r / min and the time is 5-10 min; in step S2, the mixing speed is 2000-6000 r / min and the time is 1-10 min; in step S3, the mixing speed is 1000-3000 r / min and the time is 5-10 min.

[0017] The monodisperse nano-calcium carbonate obtained above has a regular morphology, a purity >98.2%, a chlorine content <0.006%, an alkalinity of 7.5-7.8, a sedimentation volume of 2.8-3.8 mL / g, a particle size of 10-100 nm, a narrow particle size distribution, and is white in color with no visible impurities.

[0018] This invention provides a method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste. In the ammonium salt leaching stage of the calcium-containing solid waste, the high-pressure liquid film shearing and high-frequency oscillation effect formed by the high-speed rotation of the stator and rotor of the mixing and reaction device enhances the crushing and reaction capabilities of the calcium-containing solid waste particles, improving the contactability and reactivity between the calcium-containing solid waste and the ammonium salt solution. CO2 gas is precisely and controllably introduced into the reaction system through the inlet and inlet valve at the venturi tube throat, forming nano-microbubbles to accelerate the escape of ammonia during the reaction, thus improving the leaching rate and leaching time of calcium from the calcium-containing solid waste. In the carbonization stage of the calcium-containing filtrate, the Bernoulli principle is used to pre-mix the CO2 gas with the calcium-containing filtrate to obtain a first gas-liquid mixture containing large bubbles. This mixture enters the inverted conical reaction chamber through the inlet at the top of the shell, and then enters the micron-scale dynamically confined micro-reaction space formed by the stator and rotor. The squeezing and shearing action during the high-speed rotation of the particles breaks down large bubbles into extremely small bubbles, forming a second gas-liquid mixture at the micrometer scale. This increases the gas-liquid contact area between CO2 and the calcium-containing filtrate, improves the gas-liquid mass transfer process and micro-mixing efficiency, and suppresses the inhomogeneity of mass, temperature, and concentration within the system. This allows the reaction time between CO2 and the calcium-containing filtrate to match the mixing time between the gas and liquid materials, precisely controlling the CO2 absorption rate and the supersaturation of the reaction system during the reaction. This enables the explosive nucleation and rapid growth of calcium carbonate, resulting in nano-calcium carbonate with small particle size and narrow particle size distribution. In the surface functionalization stage, the shearing, breaking, and deagglomeration capabilities of the high-speed rotating liquid film at the micrometer scale can break up soft agglomerates during the preparation and storage of nano-calcium carbonate, enhancing the reactivity and reaction time between the surfactant and the nano-calcium carbonate particles, thus obtaining monodisperse nano-calcium carbonate. Compared with existing autoclave / tank reactors and related processes, this invention is simple to operate, has a short process flow, is easy to stabilize in batches, and has low cost and low energy consumption in preparing monodisperse nano-calcium carbonate, with good industrialization prospects. It provides an important way for the large-scale, low-cost, and resource-based utilization of industrial solid waste, the improvement of the quality and efficiency of nano-calcium carbonate products, and the technological advancement of calcium carbonate and its related application industries. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 Scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) surface scans of steel slag;

[0021] Figure 2Scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) surface scans of red mud;

[0022] Figure 3 Here are scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) images of steel slag after calcium leaching with ammonium salts, as shown in Example 1.

[0023] Figure 4 The image shows the XRD pattern of the monodisperse nano-calcium carbonate prepared in Example 1.

[0024] Figure 5 Scanning electron microscope image of monodisperse nano-calcium carbonate prepared in Example 1;

[0025] Figure 6 Here are scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) images of red mud after calcium leaching with ammonium salts, as shown in Example 2.

[0026] Figure 7 Scanning electron microscope image of monodisperse nano-calcium carbonate prepared in Example 2;

[0027] Figure 8 Scanning electron microscope image of monodisperse nano-calcium carbonate prepared in Example 3;

[0028] Figure 9 The particle size distribution curve of the monodisperse nano-calcium carbonate prepared in Example 4;

[0029] Figure 10 The particle size distribution curve of the monodisperse nano-calcium carbonate prepared in Example 5;

[0030] Figure 11 This is a schematic diagram of the mixing and reaction device in Example 6;

[0031] Figure 12 This is a schematic diagram of the rotor structure of the mixing and reversing device in Example 6;

[0032] Figure 13 A scanning electron microscope image of the calcium carbonate prepared in Example 7;

[0033] Figure 14 The particle size distribution curve of calcium carbonate prepared in Example 7;

[0034] Figure 15 This is a scanning electron microscope image of the calcium carbonate prepared in Comparative Example 1.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1: Housing; 2: Feed chamber; 3: Feed inlet; 4: Stator; 5: Rotor; 6: Guide groove; 7: Guide groove; 8: Shaft; 9: Return port; 10: Return pipe; 11: Outlet; 12: Three-way valve; 13: Venturi tube; 14: Air inlet; 15: Air inlet valve; 16: Exhaust port; 17: Discharge port. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The calcium-containing solid waste used in each embodiment is as follows:

[0041] Steel slag: This is an irregular mass at the micrometer scale, mainly containing calcium, silicon, iron, aluminum, magnesium, and phosphorus. Calcium, silicon, and phosphorus are evenly distributed, as are iron, magnesium, and manganese. The calcium content (calculated as CaO) in steel slag is 47.95%, silicon (calculated as SiO2) is 10.92%, iron (calculated as Fe2O3) is 27.45%, manganese (calculated as MnO) is 4.23%, and phosphorus (calculated as P2O5) is 2.33%. Morphology and elemental distribution are as follows: Figure 1 As shown.

[0042] Red mud: Consists of micron-sized irregular masses, primarily containing calcium, silicon, iron, titanium, and aluminum. The calcium content (calculated as CaO) is 48.21%, silicon as SiO2 is 15.51%, iron as Fe2O3 is 16.75%, titanium as TiO2 is 6.52%, and aluminum as Al2O3 is 5.76%. Morphology and elemental distribution are as follows: Figure 2 As shown.

[0043] Example 1

[0044] The method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste in this embodiment includes the following steps:

[0045] (I) Calcium leaching of calcium-containing solid waste ammonium salt

[0046] Dissolve 50g of ammonium chloride in 200mL of water to form a clear ammonium chloride solution. The mass content of ammonium chloride in the solution is 20%.

[0047] Weigh 40g of steel slag and disperse it in the above ammonium chloride solution to form a stable suspension, controlling the mass ratio of steel slag to ammonium chloride solution to be 0.160:1.

[0048] The above suspension was added to the mixing and reaction apparatus of Example 6. The rotor speed of the mixing and reaction apparatus was 5000 r / min, and the stator and rotor gap was set to 100 μm. The mixture was rotated and reacted at 25°C for 10 min, and then transferred to a reaction vessel. The mixture was reacted at 120°C for 3 h, and the insoluble residue phase and calcium-containing filtrate were obtained by filtration.

[0049] (ii) Carbonization of calcium-containing filtrate

[0050] The calcium-containing filtrate obtained in step (I) was simultaneously introduced into the mixed gas of N2 and CO2 into the mixed reaction apparatus of Example 6 for carbonation reaction. The mass content of CO2 in the mixed gas was 80%. Sodium polyphosphate was added simultaneously as a crystal form control agent. The inlet flow rate of CO2 gas was 500 mL / min. The mass ratio of ammonium polyphosphate to calcium carbonate was 0.005:1. The rotor speed of the mixed reaction apparatus was 6000 r / min. The reaction was carried out at 25°C for 3 min. After centrifugation and washing, the mixture was dried at 60°C for 12 h to obtain nano-calcium carbonate.

[0051] (III) Surface Functionalization Treatment

[0052] The nano-calcium carbonate obtained in step (II) was dispersed in an aqueous solution containing dodecylbenzenesulfonic acid and subjected to rapid surface functionalization modification in the mixing and reaction apparatus of Example 6. The mass ratio of dodecylbenzenesulfonic acid to calcium carbonate was 0.05:1, the rotor speed of the mixing and reaction apparatus was 3000 r / min, and the reaction was carried out at 50°C for 10 min. After centrifugation and washing, it was dried at 60°C for 12 h to obtain monodisperse nano-calcium carbonate.

[0053] The mass ratio of calcium oxide leached from the steel slag to the total calcium oxide in the steel slag was calculated, yielding a calcium extraction rate of 81.2%. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) images of the slag phase after ammonium salt calcium leaching of the steel slag were obtained. Figure 3 As shown, the calcium content decreased significantly, while the iron content increased significantly. The calcium chloride content in the obtained calcium-containing filtrate was 13.3%, and the yield of monodisperse nano-calcium carbonate was 93.8%.

[0054] The monodisperse nano-calcium carbonate prepared in this embodiment has a regular morphology, a calcium carbonate purity of 98.4%, a chlorine content of 0.004%, an alkalinity of 7.5, and a sedimentation volume of 3.4 mL / g. The measured average particle size is 50 nm, with a narrow particle size distribution. The product is white and has no visible impurities. Figure 4 The XRD pattern shows that the monodisperse nano-calcium carbonate has a spherulite-type crystal structure, as shown in the scanning electron microscope image. Figure 5 As shown, from Figure 5 As can be seen, monodisperse nano-calcium carbonate consists of near-spherical particles with a narrow particle size distribution and a particle size of approximately 55 nm.

[0055] Example 2

[0056] The method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste in this embodiment includes the following steps:

[0057] (I) Calcium leaching of calcium-containing solid waste ammonium salt

[0058] 35g of ammonium chloride was dissolved in 200mL of water to form a clear ammonium chloride solution with a mass content of 14.9%.

[0059] Weigh 40g of red mud and disperse it in the above ammonium chloride solution to form a stable suspension, and control the mass ratio of red mud to ammonium chloride solution to be 0.170:1.

[0060] The above suspension was added to the mixing and reaction apparatus of Example 6. The rotor speed of the mixing and reaction apparatus was 3000 r / min, and the stator and rotor gap was set to 100 μm. The mixture was rotated and reacted at 25°C for 10 min, and then transferred to a reaction vessel. The mixture was reacted at 120°C for 1 h, and then filtered to obtain an insoluble residue phase and a calcium-containing filtrate.

[0061] (ii) Carbonization of calcium-containing filtrate

[0062] The calcium-containing filtrate obtained in step (I) was simultaneously introduced into the mixed gas of N2 and CO2 into the mixed reaction apparatus of Example 6 for carbonation reaction. The mass content of CO2 in the mixed gas was 60%. Sodium sulfate was added simultaneously as a crystal form control agent. The mass ratio of sodium sulfate to calcium carbonate was 0.005:1. The rotor speed of the mixed reaction apparatus was 3000 r / min. The reaction was carried out at 25°C for 3 min. After centrifugation and washing, the mixture was dried at 60°C for 12 h to obtain nano-calcium carbonate.

[0063] (III) Surface Functionalization Treatment

[0064] The nano-calcium carbonate obtained in step (II) was dispersed in an aqueous solution containing stearic acid and subjected to rapid surface functionalization modification in the mixing and reaction apparatus of Example 6. The mass ratio of stearic acid to calcium carbonate was 0.03:1, the rotor speed of the mixing and reaction apparatus was 2000 r / min, and the reaction was carried out at 50°C for 10 min. After centrifugation and washing, it was dried at 60°C for 12 h to obtain monodisperse nano-calcium carbonate.

[0065] The mass ratio of calcium oxide dissolved from red mud to total calcium oxide in the red mud was calculated, yielding a calcium extraction rate of 72.1%. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) images of the slag phase after ammonium salt leaching of red mud were obtained. Figure 6 As shown, the calcium content decreased significantly, while the iron content increased significantly. The percentage of calcium chloride in the obtained calcium-containing filtrate was 12.1%, and the yield of monodisperse nano-calcium carbonate was 95.2%.

[0066] The monodisperse nano-calcium carbonate prepared in this embodiment has a regular morphology, a calcium carbonate purity of 98.6%, a chlorine content of 0.005%, an alkalinity of 7.6, a sedimentation volume of 3.6 mL / g, and a particle size distribution with an average particle size of 80 nm. The particle size distribution is narrow, the product is white, and no visible impurities are observed. Scanning electron micrographs are shown below. Figure 7 As shown, from Figure 7 As can be seen, monodisperse nano-calcium carbonate consists of nanoparticles with an aspect ratio of approximately 1.2, a narrow particle size distribution, and an average particle size of approximately 90 nm.

[0067] Example 3

[0068] The method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste in this embodiment includes the following steps:

[0069] (I) Calcium leaching of calcium-containing solid waste ammonium salt

[0070] 25g of ammonium chloride was dissolved in 250mL of water to form a clear ammonium chloride solution, the mass content of which was 9%.

[0071] Weigh 40g of red mud and disperse it in the above ammonium chloride solution to form a stable suspension, controlling the mass ratio of red mud to ammonium chloride solution to be 0.145:1.

[0072] The above suspension was added to the mixing and reaction apparatus of Example 6. The rotor speed of the mixing and reaction apparatus was 6000 r / min, and the stator and rotor gap was set to 50 μm. The mixture was rotated and reacted at 25°C for 10 min, and then transferred to a reaction vessel. The mixture was reacted at 120°C for 3 h, and the insoluble residue phase and calcium-containing filtrate were obtained by filtration.

[0073] (ii) Carbonization of calcium-containing filtrate

[0074] The calcium-containing filtrate obtained in step (I) was simultaneously introduced into the mixed gas of N2 and CO2 into the mixed reaction apparatus of Example 6 for carbonation reaction. The mass content of CO2 in the mixed gas was 20%. Citric acid was added simultaneously as a crystal form control agent. The inlet flow rate of CO2 gas was 1000 mL / min. The mass ratio of citric acid to calcium carbonate was 0.003:1. The rotor speed of the mixed reaction apparatus was 4000 r / min. The reaction was carried out at 25°C for 3 min. After centrifugation and washing, the mixture was dried at 60°C for 12 h to obtain nano-calcium carbonate.

[0075] (III) Surface Functionalization Treatment

[0076] The nano-calcium carbonate obtained in step (II) was dispersed in an aqueous solution containing stearic acid and subjected to rapid surface functionalization modification in the mixing and reaction apparatus of Example 6. The mass ratio of stearic acid to calcium carbonate was 0.05:1, the rotor speed of the mixing and reaction apparatus was 2000 r / min, and the reaction was carried out at 50°C for 10 min. After centrifugation and washing, it was dried at 60°C for 12 h to obtain monodisperse nano-calcium carbonate.

[0077] The mass ratio of calcium oxide dissolved from red mud to total calcium oxide in red mud was calculated, yielding a calcium extraction rate of 52.6%; the percentage of calcium chloride in the obtained calcium-containing filtrate was 9.7%; and the yield of monodisperse nano-calcium carbonate was 96.4%.

[0078] The monodisperse nano-calcium carbonate prepared in this embodiment has a regular morphology, a calcium carbonate purity of 98.3%, a chlorine content of 0.005%, an alkalinity of 7.6, a sedimentation volume of 3.8 mL / g, and a particle size distribution with an average particle size of 40 nm. The particle size distribution is narrow, the product is white, and no visible impurities are observed. Scanning electron micrographs are shown below. Figure 8 As shown, from Figure 8 As can be seen, monodisperse nano-calcium carbonate consists of spherical nanoparticles with a narrow particle size distribution and a particle size of approximately 40 nm.

[0079] Example 4

[0080] The method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste in this embodiment includes the following steps:

[0081] (I) Calcium leaching of calcium-containing solid waste ammonium salt

[0082] Dissolve 30g of ammonium chloride in 200mL of water to form a clear ammonium chloride solution. The mass content of ammonium chloride in the solution is 13%.

[0083] Weigh 20g of steel slag and disperse it in the above ammonium chloride solution to form a stable suspension, controlling the mass ratio of steel slag to ammonium chloride solution to be 0.086:1.

[0084] The above suspension was added to the mixing and reaction apparatus of Example 6. The rotor speed of the mixing and reaction apparatus was 4000 r / min, and the stator and rotor gap was set to 200 μm. The mixture was rotated and reacted at 25°C for 10 min, and then transferred to a reaction vessel. The mixture was reacted at 120°C for 3 h. After filtration, insoluble residue phase and calcium-containing filtrate were obtained.

[0085] (ii) Carbonization of calcium-containing filtrate

[0086] The calcium-containing filtrate obtained in step (I) was simultaneously introduced into the mixed gas of N2 and CO2 into the mixed reaction apparatus of Example 6 for carbonation reaction. The mass content of CO2 in the mixed gas was 20%. Polyethylene glycol was added simultaneously as a crystal form control agent. The inlet flow rate of CO2 gas was 500 mL / min. The mass ratio of polyethylene glycol to calcium carbonate was 0.003:1. The rotor speed of the mixed reaction apparatus was 6000 r / min. The reaction was carried out at 25°C for 3 min. After centrifugation and washing, the mixture was dried at 60°C for 12 h to obtain nano-calcium carbonate.

[0087] (III) Surface Functionalization Treatment

[0088] The nano-calcium carbonate obtained in step (II) was dispersed in an aqueous solution containing stearic acid and subjected to rapid surface functionalization modification in the mixing and reaction apparatus of Example 6. The mass ratio of stearic acid to calcium carbonate was 0.05:1, the rotor speed of the mixing and reaction apparatus was 3000 r / min, and the reaction was carried out at 50°C for 10 min. After centrifugation and washing, it was dried at 60°C for 12 h to obtain monodisperse nano-calcium carbonate.

[0089] The mass ratio of calcium oxide dissolved from the steel slag to the total calcium oxide in the steel slag was calculated, and the calcium extraction rate of the steel slag was found to be 79.5%; the percentage content of calcium chloride in the obtained calcium-containing filtrate was 7.18%; and the yield of monodisperse nano calcium carbonate was 95.8%.

[0090] The monodisperse nano-calcium carbonate prepared in this embodiment has a regular morphology, a calcium carbonate purity of 98.7%, a chlorine content of 0.005%, an alkalinity of 7.8, a sedimentation volume of 2.8 mL / g, and a particle size distribution curve as shown in the figure. Figure 9 As shown, the average particle size is 98 nm, the particle size distribution is narrow, the product is white, and no visible impurities are observed. Scanning electron microscopy reveals an average particle size of 90 nm.

[0091] Example 5

[0092] The method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste in this embodiment includes the following steps:

[0093] (I) Calcium leaching of calcium-containing solid waste ammonium salt

[0094] 40g of ammonium chloride was dissolved in 200mL of water to form a clear ammonium chloride solution, the mass content of which was 20%.

[0095] Weigh 40g of steel slag and disperse it in the above ammonium chloride solution to form a stable suspension, controlling the mass ratio of steel slag to ammonium chloride solution to be 0.167:1.

[0096] The above suspension was added to the mixing and reaction apparatus of Example 6. The rotor speed of the mixing and reaction apparatus was 6000 r / min, and the stator and rotor gap was set to 200 μm. The mixture was rotated and reacted at 25°C for 10 min, and then transferred to a reaction vessel. The mixture was reacted at 120°C for 3 h, and the insoluble residue phase and calcium-containing filtrate were obtained by filtration.

[0097] (ii) Carbonization of calcium-containing filtrate

[0098] The calcium-containing filtrate obtained in step (I) was simultaneously introduced into the mixed gas of N2 and CO2 into the mixed reaction apparatus of Example 6 for carbonation reaction. The mass content of CO2 in the mixed gas was 10%. Glucose was added simultaneously as a crystal form control agent. The mass ratio of glucose to calcium carbonate was 0.003:1. The rotor speed of the mixed reaction apparatus was 5000 r / min. The reaction was carried out at 25°C for 10 min. After centrifugation and washing, the mixture was dried at 60°C for 12 h to obtain nano-calcium carbonate.

[0099] (III) Surface Functionalization Treatment

[0100] The nano-calcium carbonate obtained in step (II) was dispersed in an aqueous solution containing stearic acid and subjected to rapid surface functionalization modification in the mixing and reaction apparatus of Example 6. The mass ratio of stearic acid to calcium carbonate was 0.05:1, the rotor speed of the mixing and reaction apparatus was 3000 r / min, and the reaction was carried out at 50°C for 10 min. After centrifugation and washing, it was dried at 60°C for 12 h to obtain monodisperse nano-calcium carbonate.

[0101] The mass ratio of calcium oxide dissolved from the steel slag to the total calcium oxide in the steel slag was calculated, and the calcium extraction rate of the steel slag was found to be 68.7%; the percentage content of calcium chloride in the obtained calcium-containing filtrate was 11.5%; and the yield of monodisperse nano calcium carbonate was 95.8%.

[0102] The monodisperse nano-calcium carbonate prepared in this embodiment has a regular morphology, a calcium carbonate purity of 98.8%, a chlorine content of 0.004%, an alkalinity of 7.7, a sedimentation volume of 3.1 mL / g, and a particle size distribution curve as shown in the figure. Figure 10 As shown, the average particle size is 94 nm, the particle size distribution is narrow, the product is white, and no visible impurities are observed. Scanning electron microscopy reveals an average particle size of 89 nm.

[0103] Example 6

[0104] Combination Figure 11 , Figure 12As shown, this embodiment provides a mixing and reversing device for embodiments 1-5. The mixing and reversing device includes a housing 1, with a feeding chamber 2 located at the upper part of the housing 1, which communicates with a feeding port 3. A stator 4 is fixedly located at the lower part of the housing 1, and the stator 4 has a hollow cavity. A rotor 5 is located in the hollow cavity, and there is an adjustable gap between the rotor 5 and the stator 4. The top of the gap communicates with the feeding chamber 2. Multiple guide grooves 6 are provided circumferentially at intervals on the inner wall of the stator 4 and the outer wall of the rotor 5. The rotor 5 is connected to the drive shaft of the drive mechanism via a rotating shaft 8 and multiple guide grooves 7. A return port 9 is provided at the top of the housing 1. The two ends of the return port 9 are connected to the feed chamber 2 and the return pipe 10, respectively. An outlet 11 is provided at the bottom of the housing 1, which is connected to the bottom of the gap. The outlet 11 is connected to the lower part of the return pipe 10 via a three-way valve 12. A venturi tube 13 is provided in the middle of the return pipe 10. The throat of the venturi tube 13 is connected to the air inlet 14. An air inlet valve 15 is provided on the air inlet 14.

[0105] The shell 1 can be a cylindrical closed shell with an independent feed inlet 3, a return outlet 9 and an vent 16 at its top. The feed inlet 3, the return outlet 9 and the vent 16 are respectively connected to the feed chamber 2. The feed inlet 3 is used to send the material to the feed chamber 2, the return outlet 9 is used to return the material in the gap to the feed chamber 2, and the vent 16 is used to exhaust the air.

[0106] A feeding chamber 2 is located at the upper part of the housing 1. The feeding chamber 2 is shaped like an inverted frustum, and its bottom is flush with the top of the stator 4, facilitating the material in the feeding chamber 2 to enter the gap between the stator 4 and the rotor 5 for mixing and reaction. The stator 4 and rotor 5 are located at the lower part of the housing 1. The stator 4 is housed within the hollow cavity of the rotor 5, and a gap exists between the stator 4 and the rotor 5. This gap forms a micron-scale dynamically confined micro-reaction space, which is beneficial for generating high-pressure liquid film shearing and high-frequency oscillation during high-speed rotation. This enhances the crushing and reaction capabilities of calcium-containing solid waste particles and improves the contactability and reactivity between calcium-containing solid waste and ammonium salt solution.

[0107] The method of adjusting the gap size is not strictly limited, as long as it can be adjusted within the range of 20-500μm. Specifically, the hollow cavity of the stator 4 and the rotor 5 are matched frustum shapes, with the hollow cavity and the frustum sides of the rotor 5 having the same inclination angle. Furthermore, the upper and lower base dimensions of the hollow cavity frustum are larger than those of the rotor 5 frustum. The stator 4 and rotor 5 are coaxially arranged. When the stator 4 and rotor 5 are relatively fixed, there is a fixed gap between them.

[0108] Furthermore, the rotor 5 can be connected to a lifting mechanism, which can drive the rotor 5 to move up and down relative to the stator 4 to adjust the gap size. The gap size can be adjusted within the range of 20-500μm according to actual process requirements. It can be understood that when the rotor 5 moves upward relative to the stator 4, the gap between the stator 4 and the rotor 5 decreases; when the rotor 5 moves downward relative to the stator 4, the gap between the stator 4 and the rotor 5 increases.

[0109] In addition, multiple guide grooves 6 are provided circumferentially at intervals on the inner wall of the stator 4, with a depth of 1-2 mm; multiple guide grooves 7 are provided circumferentially at intervals on the outer wall of the rotor 5, with a depth of 1-2 mm. The guide grooves 6 and 7 can be arranged from top to bottom along the inner wall of the stator 4 and the outer wall of the rotor 5; at the same time, the guide grooves 6 and 7 can be inclined at an angle of 45-75 degrees, with a spacing of 1-2 mm between adjacent guide grooves 6 and adjacent guide grooves 7.

[0110] Rotor 5 is connected to the drive shaft of the drive mechanism via shaft 8. The drive mechanism drives rotor 5 to rotate via the drive shaft and shaft 8. The rotational speed of rotor 5 is adjustable within the range of 1000-6000 r / min. During high-speed rotation, stator 4 and rotor 5 generate high-pressure liquid film shearing and high-frequency oscillation, thereby enhancing the crushing and reaction capabilities of calcium-containing solid waste particles and improving the contactability and reactivity between calcium-containing solid waste and ammonium salt solution. Simultaneously, the gap between stator 4 and rotor 5 forms a micron-scale dynamically confined micro-reaction space. Utilizing the squeezing and shearing action during the high-speed rotation of rotor 5, large CO2 bubbles are sheared into extremely small bubbles, forming a micron-scale second gas-liquid mixture. This increases the gas-liquid contact area between CO2 and the calcium-containing filtrate, improves the gas-liquid mass transfer process and micro-mixing efficiency, and suppresses internal mass transfer within the system. The non-uniformity of quantity, temperature, and concentration allows the reaction time of CO2 with calcium-containing filtrate to be matched with the mixing time between gas and liquid materials. This precisely controls the absorption rate of CO2 and the supersaturation of the reaction system during the reaction, enabling explosive nucleation and rapid growth of calcium carbonate, resulting in nano-calcium carbonate with small particle size and narrow particle size distribution. In addition, the shearing, breaking, and deagglomeration capabilities of the high-speed rotating liquid film within the micron scale can break up soft agglomerates during the preparation and storage of nano-calcium carbonate, enhancing the reactivity and reaction time between surfactants and nano-calcium carbonate particles, thus obtaining monodisperse nano-calcium carbonate.

[0111] One end of the reflux pipe 10 is connected to the reflux port 9, and the other end of the reflux pipe 10 forms the discharge port 17. When the mixing effect of the mixing and reaction device does not meet the preset requirements, the material can be returned to the mixing and reaction device through the reflux pipe 10 via the outlet 11 to continue the mixing and reaction. When the mixing effect of the mixing and reaction device meets the preset requirements, the material can be discharged through the discharge port 17.

[0112] A venturi tube 13 is provided in the middle of the return pipe 10, through which CO2-containing gas can be self-drawn into the mixing and reaction device. The outlet 11 is connected to the venturi tube 13, through which CO2-containing gas is introduced to obtain a preliminary gas-liquid mixed flow. Subsequently, a second gas-liquid mixed flow is obtained in the micron-scale dynamic confined microenvironment formed by the gap between the stator 4 and the rotor 5, which enhances the mixing and reaction capability between gas and liquid. CO2 gas is precisely and controllably introduced into the reaction system through the inlet 14 and inlet valve 15 at the throat of the venturi tube 13, forming nano-micro bubbles to accelerate the escape of ammonia during the reaction process, thereby improving the leaching rate and leaching time of calcium in calcium-containing solid waste. In addition, by utilizing Bernoulli's principle, CO2 gas and calcium-containing filtrate are pre-mixed through pressure difference to obtain a first gas-liquid mixture containing large bubbles. This mixture enters the inverted frustum-shaped feed chamber 2 through the feed inlet 3 at the top of the shell 1, and then enters the micron-scale dynamic confined micro-reaction space formed by the stator 4 and rotor 5, where the large bubbles are sheared into extremely small bubbles to form a micron-scale second gas-liquid mixture, thereby improving the gas-liquid mass transfer process and micro-mixing efficiency.

[0113] Example 7

[0114] Except for replacing the mixing and reaction device in Example 1 with an existing mixing and reaction device (ZJRIII-4 type three-stage emulsifying pump from Anhui Zhongjinghuasheng Technology Co., Ltd.), everything else is the same as in Example 1.

[0115] The mass ratio of calcium oxide dissolved from the steel slag to the total calcium oxide in the steel slag was calculated, and the calcium extraction rate of the steel slag was found to be 68.3%. The percentage content of calcium chloride in the obtained calcium-containing filtrate was 10.56%, and the yield of monodisperse nano calcium carbonate was 89.2%.

[0116] Combination Figure 13 , Figure 14 The nano-calcium carbonate prepared in this embodiment has the morphology of a spherical secondary agglomerate composed of 50nm primary particles. The average particle size of the agglomerate measured by the particle size distribution curve is 3μm. The purity of calcium carbonate is 97.3%, the chlorine content is 0.083%, the alkalinity is 7.9, the sedimentation volume is 2.6mL / g, and the average particle size is 2.7μm.

[0117] Compare with Example 1

[0118] Except for replacing the mixing and reaction device with a conventional mechanical stirring device in the carbonization step of the calcium-containing filtrate, the rest is the same as in Example 1; that is, in this comparative example, the rotation reaction in the carbonization step of the calcium-containing filtrate is carried out under mechanical stirring conditions, followed by centrifugation, washing, and drying to obtain nano-calcium carbonate.

[0119] The calcium carbonate prepared in this embodiment has an irregular morphology, consisting of spherical aggregates of primary particles around 10 nm in size, accompanied by irregular blocks around 300 nm in size. The average particle size measured by the particle size distribution curve is 1.8 μm. The purity of the calcium carbonate is 97.4%, the chlorine content is 0.065%, the alkalinity is 7.6, and the sedimentation volume is 2.3 mL / g. Scanning electron microscopy images are shown below. Figure 15 As shown, from Figure 15 As can be seen, spherical particles and irregular masses appear simultaneously, with the spherical aggregates having a particle size of approximately 1.5 μm.

[0120] Compare with Example 2

[0121] Except for replacing the mixing and reaction device with a conventional mechanical stirring device in the calcium leaching step of calcium-containing solid waste ammonium salt, the rest is the same as in Example 1; that is, in this comparative example, the rotational mixing in the calcium leaching step of calcium-containing solid waste ammonium salt is carried out under mechanical stirring conditions, and then transferred to the reaction vessel for reaction.

[0122] The mass ratio of calcium oxide dissolved from the steel slag to the total calcium oxide in the steel slag was calculated, and the calcium extraction rate of the steel slag was found to be 56.3%. The percentage content of calcium chloride in the resulting calcium-containing filtrate was 8.5%.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing monodisperse nano-calcium carbonate from calcium-containing industrial solid waste, characterized in that, Includes the following steps: S1: Mix calcium-containing solid waste and ammonium salt solution and react them. After filtration, obtain calcium-containing filtrate. S2: The calcium-containing filtrate, CO2 gas, and crystal form control agent are mixed and reacted. After filtration, nano-calcium carbonate is obtained. The crystal form control agent is selected from sodium polyphosphate, sodium sulfate, citric acid, polyethylene glycol, or glucose. The mass ratio of crystal form control agent to nano-calcium carbonate is (0.002-0.005):

1. S3: Nano-calcium carbonate is mixed with an aqueous solution containing a surfactant and reacted. After centrifugation, washing, and drying, monodisperse nano-calcium carbonate is obtained. The reaction temperature is 20-50 ℃ and the reaction time is 5-10 min. Mixing is performed using a mixing and reaction device; The mixing and reversing device includes a housing, with a feed chamber located at the top inside the housing and connected to a feed inlet. A stator is fixedly located at the bottom inside the housing, and the stator has a hollow cavity. A rotor is located in the hollow cavity, and there is an adjustable gap between the rotor and the stator. The top of the gap is connected to the feed chamber. Multiple guide grooves are spaced circumferentially on the inner wall of the stator and the outer wall of the rotor. The rotor is connected to the drive shaft of the drive mechanism via a rotating shaft. A return port is located at the top of the housing, and its two ends are connected to the feed chamber and the return pipe, respectively. An outlet is located at the bottom of the housing and connected to the bottom of the gap. The outlet is connected to the lower part of the return pipe via a three-way valve. A venturi tube is located in the middle of the return pipe, and the throat of the venturi tube is connected to the air inlet. An air inlet valve is located on the air inlet. In step S1, the mixing speed is 1000-5000 r / min and the time is 5-10 min; in step S2, the mixing speed is 2000-6000 r / min and the time is 1-10 min; in step S3, the mixing speed is 1000-3000 r / min and the time is 5-10 min.

2. The method according to claim 1, characterized in that, In step S1, the calcium-containing solid waste is selected from at least one of red mud, carbide slag, steel slag and yellow phosphorus slag; the ammonium salt in the ammonium salt solution has a mass content of 9-20%, and the ammonium salt is selected from at least one of ammonium nitrate, ammonium chloride and ammonium acetate.

3. The method according to claim 1, characterized in that, In step S1, the mass ratio of calcium-containing solid waste to ammonium salt solution is (0.05-0.2):1; the reaction temperature is 60-120 ℃ and the reaction time is 1-6 h.

4. The method according to claim 1, characterized in that, In step S2, the mass content of CO2 in the CO2-containing gas is 2-100%; the reaction temperature is 20-50 ℃, and the reaction time is 1-10 min.

5. The method according to claim 1, characterized in that, In step S3, the surfactant is selected from at least one of stearic acid, dodecylbenzene sulfonic acid, silane coupling agent, aluminate coupling agent and titanate coupling agent; the mass ratio of surfactant to nano-calcium carbonate is (0.03-0.05):

1.

6. The method according to claim 1, characterized in that, The particle size of monodisperse nano-calcium carbonate is 10-100 nm.

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