Calcite type calcium carbonate whisker and its preparation method

Abstract

The application discloses a preparation method of calcite type calcium carbonate whisker, and comprises the following steps: (1) preparing calcium hydroxide suspension, heating and warming the calcium hydroxide suspension to obtain hot calcium hydroxide suspension, and waiting for use; (2) adding crystal seeds and crystal type control agent into the hot calcium hydroxide suspension, and stirring uniformly to obtain hot mixed suspension; (3) continuously feeding carbon dioxide into the hot mixed suspension until the reaction is completed, stopping the feeding of carbon dioxide, obtaining calcium carbonate suspension, filtering, drying, and obtaining calcium carbonate powder; and (4) calcining and pulverizing the calcium carbonate powder in a furnace to obtain the calcite type calcium carbonate whisker. The calcium carbonate whisker prepared by the application is of the calcite type, and the application provides a new research thought for the preparation of the calcite type calcium carbonate whisker. The calcite type calcium carbonate whisker prepared by the application is the most stable phase of calcium carbonate, and the application field of the calcium carbonate whisker is expanded.

Description

Technical Field

[0001] This invention belongs to the field of calcium carbonate preparation technology, specifically a calcite-type calcium carbonate whisker and its preparation method. Technical Background

[0002] Whiskers are an inorganic material, and their shape is needle-like or fibrous. Common inorganic whiskers such as silicon carbide, potassium titanate, and magnesium sulfate are used as needle-like single crystal reinforcing materials. They have advantages such as high strength, good heat resistance, wear resistance and flame retardancy, and are often used to reinforce polymer materials. Calcium carbonate whiskers are a high-quality and inexpensive green and environmentally friendly material with excellent properties such as high strength, high modulus, good heat resistance and heat insulation. They have been widely used for filling and modifying polymer materials, such as polypropylene, natural rubber, polyether ether ketone and other fields. At present, the calcium carbonate whiskers reported in the public are mainly aragonite type (Guo Qiu, Preparation of calcium carbonate whiskers for epoxy resin and wet surface modification and its influence on mechanical properties [C], Guangxi University, 2017). The main methods for preparing calcium carbonate whiskers are: (1) Carbonation method: mainly using natural limestone as raw material, through high temperature calcination, digestion reaction, carbonation reaction, addition of crystal form control and other processes, it is currently the commonly used method for industrial preparation of calcium carbonate whiskers. (2) Metathesis method: This method uses soluble calcium salts and carbonates as raw materials to produce calcium carbonate whiskers through a metathesis reaction under certain conditions of solution concentration, reaction system temperature, and mechanical stirring rate. This method has a low yield of calcium carbonate whiskers, but the reaction process is simple and it is currently a commonly used method for studying calcium carbonate whiskers. (3) Urea hydrolysis method: Urea reacts with soluble calcium salts. The reaction process does not require the addition of crystal form control agents, but the controllability of the reaction process is poor. The urea hydrolysis method for preparing calcium carbonate whiskers has high requirements for reaction conditions, which will inevitably increase the requirements for equipment and power. Furthermore, using urea as a raw material is not economical and has a low cost-performance ratio, thus making industrialization difficult. (4) Calcium bicarbonate heating hydrolysis method: First, a calcium bicarbonate solution is prepared, and then calcium carbonate whiskers are prepared by controlling the heating temperature, heating rate, stirring intensity, and other conditions of the solution. This method is relatively complex, difficult to operate, and has low production efficiency.

[0003] Patent CN114875494B discloses a hyperbranched three-dimensional calcium carbonate whisker, its preparation method, and its applications. First, a mixture of magnesium acetate (a crystal form control agent), magnesium nitrate, and sodium acetate is added to a calcium hydroxide suspension to form a mixture. The mixture is kept at a constant temperature of 80-100℃, and then carbon dioxide is introduced to carry out the reaction until the pH value of the mixture decreases. The mixture is then filtered, and the precipitate is collected to obtain calcium carbonate whiskers. The whiskers prepared by this method are aragonite-type calcium carbonate.

[0004] Patent CN114959895B discloses an ultra-long calcium carbonate whisker and its preparation method. The ultra-long calcium carbonate whiskers have a length of 90 μm or more. First, a calcium hydroxide suspension is prepared; a crystal form control agent is mixed with water to form a crystal form control solution; wherein the crystal form control agent contains at least magnesium ions and nitrate ions; then, the crystal form control solution and the calcium hydroxide suspension are mixed to form a mixed solution, and the temperature of the mixed solution is raised to 90-110℃; finally, the temperature of the mixed solution is kept constant, and carbon dioxide gas is introduced into the mixed solution to carry out the reaction. When the pH value of the reaction system decreases, the mixture is filtered, and the precipitate is collected to obtain the calcium carbonate whiskers. The obtained ultra-long calcium carbonate whiskers are aragonite-type and can be applied to mortar to improve the flexural and tensile strength of the mortar and reduce cracking.

[0005] Patent CN114921851B discloses a method for preparing calcium carbonate whiskers by carbonization of carbide slag. The preparation method is as follows: Step 1, prepare a magnesium salt solution, heat the magnesium salt solution to obtain a hot magnesium salt solution, and set it aside; Step 2, add carbide slag to the hot magnesium salt solution, stir evenly to obtain a mixed liquid; Step 3, continuously introduce CO2 gas into the mixed liquid, carbonize for a period of time, filter the slurry after the carbonization reaction is completed, and dry the filter residue to obtain calcium carbonate aragonite whiskers.

[0006] Patent CN113564688B discloses a method for preparing calcium carbonate whiskers. The method involves first calcining and decomposing calcite ore, calcite tailings, or limestone industrial waste into calcium oxide. Then, calcium oxide and magnesium chloride are added to deionized water and digested at a certain temperature. The resulting filter cake is slurried and then carbonated with excess CO2 to produce magnesium hydroxide solution. Finally, the filtrate from the digestion and conversion process is uniformly added dropwise to the filtrate from the carbonation reaction, and the reaction is carried out at a certain temperature and stirring rate until no precipitation occurs, thus obtaining calcium carbonate whiskers. This method prepares aragonite-type calcium carbonate whiskers through multiple carbonation reactions.

[0007] Patent CN112723403B discloses a method for preparing calcium carbonate whiskers. The specific method is as follows: 1) Calcium oxide is added to water for digestion reaction, and then sieved to obtain a calcium hydroxide suspension; 2) Carbon dioxide is passed into a potassium hydroxide solution until the pH of the solution drops below 7 to obtain crystal form control agent I; 3) Crystal form control agent I from step 2) is added to the calcium hydroxide suspension from step 1), stirred, aged, and then crystal form control agent II is added. Crystal form control agent II is at least one of strontium chloride, sodium phosphate, and sodium citrate. The mixture is stirred, and then lime kiln gas is passed into the reaction solution to carry out a carbonation reaction until the pH of the reaction solution drops below 7. The mixture is then dehydrated, dried, pulverized, and sieved to obtain calcium carbonate whiskers.

[0008] Patent CN111926386B discloses a method for preparing calcium carbonate whiskers. First, silk fibroin and gum arabic are dissolved in deionized water and stirred thoroughly to obtain a crystal form control agent. Then, high-purity nano-calcium oxide is mixed with deionized water to obtain slurry A. Slurry A is passed through a 100-mesh sieve and filtered to remove slag. Next, deionized water is added to the slurry to dilute it and obtain slurry B. Then, the crystal form control agent is added to slurry B, and the mixture is heated to 50-60℃ and stirred at a constant temperature for 1-2 hours to obtain slurry C. Next, ammonia water is added to slurry C to adjust the pH value, and then the mixture is placed in a high-gravity carbonation reactor for carbonation. After carbonation, the resulting slurry is centrifuged to obtain a precipitate. The precipitate is dried and pulverized to obtain calcium carbonate aragonite whiskers.

[0009] Patent CN111778547B discloses a method for preparing aragonite-type calcium carbonate whiskers, comprising the following steps: 1) taking a certain amount of calcium chloride-rich solution and adjusting the pH value of the solution to neutral by using ammonia or hydrochloric acid; 2) mixing the solution obtained in step 1) with ammonia and placing it in a reaction vessel with a stirrer for reaction, while simultaneously introducing CO2 gas at a certain rate during the reaction, and controlling the concentration of calcium ions in the solution, reaction temperature, stirring speed, and amount of ammonia during the reaction; after the reaction is completed, filtering the solution to obtain a solid reaction product and filtrate; 3) washing and drying the solid product obtained in step 2) to obtain aragonite-type calcium carbonate whisker material.

[0010] Patent CN110029396B discloses a method for preparing functional calcium carbonate whiskers, which includes the following steps: (1) preparing a Ca(OH)2 suspension; (2) adding the Ca(OH)2 suspension to a high-gravity reactor, adding phosphoric acid as a crystal form control agent and sodium stearate as a surface modifier, and then introducing CO2 to carry out a carbonization reaction. A digital pH meter is used to track the entire carbonization reaction process. When the pH of the reaction slurry is 6.5-7.0, the gas is stopped, and the carbonization reaction ends; (3) the product slurry is centrifuged, dried, and pulverized sequentially to obtain the desired product. The production process of this invention is simple, the production cycle is short, and the production efficiency is high.

[0011] Patent CN108893775B discloses a method for preparing high-purity calcium carbonate whiskers. The method is as follows: first, calcium carbonate raw material is calcined and decomposed into calcium oxide, then the calcium oxide is added to deionized water and digested at a certain temperature. Using magnesium chloride solution as a crystal shape control agent, the digested calcium hydroxide suspension is sprayed into the magnesium chloride solution. Carbon dioxide is introduced at a certain rate using an aeration device with a certain pore size to control the volume and dispersion of the introduced gas bubbles, thereby making the carbonate ions uniformly distributed in the solution. The carbonation reaction is carried out under stirring at a certain rate until the pH of the solution drops to 7 and the reaction ends, resulting in high-purity aragonite-type calcium carbonate whiskers.

[0012] Patent CN107916452B discloses a method for preparing calcium carbonate whiskers with continuously controllable morphology: first, calcium oxide is added to deionized water and digested at a certain temperature; then, a crystal morphology control agent is added and stirred evenly; carbon dioxide gas is introduced at a certain flow rate using a double-tube aeration device to carry out a carbonation reaction; finally, the resulting suspension is filtered, washed, and dried to obtain aragonite whiskers.

[0013] Patent CN103806088B discloses a method for preparing calcium carbonate whiskers using triethanolamine as an auxiliary agent. First, triethanolamine and distilled water are mixed at room temperature and then ultrasonically mixed to obtain a triethanolamine-water solution mixture. Next, anhydrous calcium chloride and urea are added to a reaction vessel lined with polytetrafluoroethylene containing the triethanolamine-water solution and heated to react. After cooling and filtration, the mixture is washed with distilled water to neutralize, filtered, and dried to obtain calcium carbonate whiskers.

[0014] Patent CN103834997B discloses a method for preparing calcium carbonate whiskers using a hydrothermal process. Its key feature is the first-time use of sucrose as an auxiliary agent, obtaining high aspect ratio calcium carbonate whiskers through urea hydrolysis. At a specific temperature, different mass concentrations of sucrose are added to a mixed solution of urea and calcium chloride. After a period of reaction, the resulting product is washed with deionized water until the pH is neutral, and then dried completely to obtain the calcium carbonate whiskers.

[0015] Patent CN101935865B discloses a method for preparing high aspect ratio calcium carbonate whiskers. This method uses quicklime as raw material and magnesium chloride as a crystal form control agent. Calcium carbonate whiskers are prepared through a carbonation reaction with carbon dioxide. The mother liquor is then recycled to produce more calcium carbonate whiskers, thus completing a multi-stage growth process for high aspect ratio calcium carbonate whisker products.

[0016] Patent CN1303264C discloses a method for manufacturing high-purity aragonite-type calcium carbonate whiskers. This method uses quicklime or hydrated lime as raw material and magnesium salts as crystal form control agents to produce aragonite-type calcium carbonate whiskers via carbon dioxide carbonation. The method is characterized by the reuse of the magnesium salt solution during the preparation of the calcium carbonate whiskers and the uniform addition of hydrated lime slurry during the carbonation reaction. This combination of techniques allows for the production of high-purity calcium carbonate whiskers with a high aspect ratio.

[0017] In summary, the mainstream method for synthesizing calcium carbonate whiskers is currently the carbonation method, which involves the reaction of calcium hydroxide with carbon dioxide. Magnesium salts are the most commonly used crystal form control agents, and the synthesized calcium carbonate whiskers mainly have an aragonite structure. However, published reports indicate that calcite calcium carbonate exhibits superior stability compared to aragonite calcium carbonate. Summary of the Invention

[0018] The purpose of this invention is to provide a calcite-type calcium carbonate whisker and its preparation method, so as to solve the stability problem of aragonite calcium carbonate whiskers and fill the gap in the preparation of calcite calcium carbonate whiskers.

[0019] To achieve the above objectives, the present invention provides the following technical solution:

[0020] A method for preparing calcite-type calcium carbonate whiskers includes the following steps:

[0021] Step 1: Prepare a calcium hydroxide suspension by heating the calcium hydroxide suspension to obtain a hot calcium hydroxide suspension for later use;

[0022] Step 2: Add the seed crystals and crystal form control agent to the hot calcium hydroxide suspension and stir evenly to obtain a hot mixed suspension;

[0023] Step 3: Continuously introduce carbon dioxide into the hot mixed suspension to react until the reaction is complete. Stop introducing carbon dioxide to obtain a calcium carbonate suspension. Filter and dry the suspension to obtain calcium carbonate powder.

[0024] Step 4: Calcine and pulverize the calcium carbonate powder in a furnace to obtain calcite-type calcium carbonate whiskers.

[0025] Preferably, the solid content of the calcium hydroxide suspension in step one is 12-15%.

[0026] Preferably, the calcium hydroxide suspension is heated to 40-45°C.

[0027] Preferably, the seed crystals mentioned in step two are a mixture of magnesium borate and aluminum borate in a mass ratio of (2-15):(3-15).

[0028] Preferably, the amount of seed crystals added is 0.5-3.0% of the mass of calcium hydroxide.

[0029] Preferably, the crystal form control agent mentioned in step two is magnesium citrate, and the amount added is 0.5-2.0% of the mass of calcium hydroxide.

[0030] Preferably, in step three, the concentration of carbon dioxide introduced is 15.0-20.0%, and the flow rate is 1.8-2.0 m³ / s. 3 / h; the stirring speed during the reaction process is 900-1200 r / min.

[0031] Preferably, in step three, carbon dioxide is continuously introduced into the hot mixed suspension for reaction until the pH of the reaction system is ≤7.50, at which point the carbon dioxide introduction is stopped, and a calcium carbonate suspension is obtained.

[0032] Preferably, the calcination temperature of the calcium carbonate powder in step four is 430-450℃, and the time is 0.5-1.0h.

[0033] Technical principle of the invention:

[0034] In exploring the technical principles of this invention, we not only need to elaborate on the specific operation of each step, but also deeply analyze the unique role of each raw material, the synergistic mechanism between them, and the importance of accurately controlling the amount of raw materials and process parameters, so as to reveal how this invention achieves unexpected technical effects.

[0035] (1) Role and Synergistic Mechanism of Raw Materials

[0036] 1) Calcium hydroxide suspension: As a starting material, the calcium hydroxide suspension provides the necessary calcium source for the entire reaction. Heating to 40-45℃ controls the fluctuation range of calcium hydroxide solubility, ensuring the smooth progress of subsequent reaction steps. Maintaining the solid content between 12-15% helps balance the reaction rate and product uniformity, avoiding uneven crystallization or low reaction efficiency caused by excessively high or low solid content.

[0037] 2) Seed crystals (a mixture of magnesium borate and aluminum borate): The introduction of seed crystals is key to controlling the morphology and structure of whiskers. Magnesium borate and aluminum borate are mixed in a mass ratio of (2-15):(3-15). Each not only promotes the growth of specific crystal faces but also, through synergistic effects, guides calcium carbonate molecules to align in a predetermined direction, forming a slender and uniform whisker structure. The addition amount is controlled at 0.5-3.0% of the calcium hydroxide mass. This ratio precisely stimulates the directional growth of whiskers while avoiding the impurities that may result from excessive addition.

[0038] 3) Crystal form control agent (magnesium citrate): Magnesium citrate, as a crystal form control agent, fine-tunes the nucleation and growth process of calcium carbonate crystals through its specific chemical action. Its addition amount is between 0.5% and 2.0% of the mass of calcium hydroxide. This precise control ensures the purity and morphological consistency of the whiskers, effectively preventing the formation of other undesirable crystal forms.

[0039] (2) Control of raw material usage and process parameters

[0040] Precise control of raw material dosage is a prerequisite for ensuring stable product quality and excellent performance. Too much or too little seed crystals and crystal form control agents will affect the growth rate, morphological distribution, and final properties of whiskers. For example, too few seed crystals may lead to inconsistent whisker growth directions, while too many may cause excessive nucleation, affecting the length and diameter of the whiskers. Similarly, the dosage of magnesium citrate must also be precise to avoid adverse effects on whisker morphology.

[0041] In selecting process parameters, the concentration and flow rate of carbon dioxide, the stirring speed of the reaction system, and the control of the pH value at the reaction endpoint are all crucial. High concentrations of carbon dioxide accelerate the carbonization reaction, but excessively high concentrations may lead to an overly vigorous reaction, affecting the morphology of the whiskers. A suitable stirring speed ensures the homogeneity of the reaction system, promotes effective contact between the gas and liquid, and is beneficial for the uniform growth of whiskers. Stopping the carbon dioxide flow when the pH reaches ≤ 7.50 ensures complete precipitation of calcium carbonate while avoiding excessive carbonization to form calcium bicarbonate, which would affect the morphology of calcium carbonate.

[0042] (3) Technical effects and the necessity of optimization

[0043] Through precise control of the method of this invention, high-quality and highly stable calcite-type calcium carbonate whiskers were successfully prepared. These whiskers show broad application prospects in toughening materials, fillers, and functional materials. Optimizing process parameters and raw material dosages not only improves production efficiency and product quality but also reduces production costs, providing strong support for industrial production. Therefore, in-depth research and meticulous control of each step of the preparation process are key to achieving unexpected technical effects and driving technological progress.

[0044] Compared with existing technologies, the innovation of this invention lies not only in its unique material selection and process design, but also in its ability to achieve precise control over the growth process of calcium carbonate crystals, thereby significantly improving the quality and performance of the product. Specific advantages are reflected in the following aspects:

[0045] (1) Precise control to reshape crystal morphology

[0046] This invention ingeniously introduces magnesium borate and aluminum borate whiskers as seed crystals. These two materials, with their excellent crystal structure and stability, provide ideal templates for the growth of calcium carbonate. Simultaneously, it innovatively employs magnesium citrate as a crystal form control agent. This act acts as a "navigator" in the chemical reaction system, precisely guiding and controlling the growth path and rate of calcium carbonate molecules in specific directions. Through this unprecedentedly precise control mechanism, this invention can accurately shape calcium carbonate whiskers of uniform size and regular shape. The subsequent heat treatment process further stabilizes the whisker structure, perfectly transforming it into the calcite form, the most common form of calcium carbonate in nature, endowing the whiskers with more stable physicochemical properties.

[0047] (2) Opening up new paths and leading the research trend

[0048] The preparation of calcite-type calcium carbonate whiskers has long been a hot topic and a challenge in materials science. This invention not only successfully prepared high-quality calcite-type calcium carbonate whiskers, but also opened up new avenues and directions for research in this field. It overcomes the limitations of existing preparation methods in terms of material selection and process control, demonstrating the possibility of optimizing crystal structure through precise control, and providing valuable experience and inspiration for subsequent scientific research.

[0049] (3) Stable phase state, broadening application fields

[0050] Calcite-type calcium carbonate, as the most stable phase of calcium carbonate, possesses unique physicochemical properties that give it broad application potential in multiple fields. The calcite-calcite whiskers prepared in this invention not only retain the stability and durability of calcite itself but also possess excellent reinforcing and toughening properties due to their unique whisker morphology. This makes its application prospects particularly broad in plastics, epoxy resins, coatings, and friction materials. The emergence of this invention undoubtedly injects new vitality into the development of these fields, promotes the leap from theoretical research to practical application of calcium carbonate whiskers, and effectively transforms technological achievements into economic benefits. Attached Figure Description

[0051] Figure 1 The images show scanning electron microscope (SEM) and X-ray diffraction (XRD) patterns of the calcite calcium carbonate whiskers prepared in Example 1.

[0052] Figure 2 The images show scanning electron microscope (SEM) and X-ray diffraction (XRD) patterns of the calcite calcium carbonate whiskers prepared in Example 2.

[0053] Figure 3 The images show scanning electron microscope (SEM) and X-ray diffraction (XRD) patterns of the calcite calcium carbonate whiskers prepared in Example 3.

[0054] Figure 4 The image shows a scanning electron microscope (SEM) image and an X-ray diffraction pattern of the calcite calcium carbonate whiskers prepared in Example 4.

[0055] Figure 5 The images show scanning electron microscope (SEM) and X-ray diffraction (XRD) patterns of the calcium carbonate prepared in Comparative Example 1.

[0056] Figure 6 The images show scanning electron microscope (SEM) and X-ray diffraction (XRD) patterns of the calcium carbonate prepared in Comparative Example 2.

[0057] Figure 7 The images show scanning electron microscope (SEM) and X-ray diffraction (XRD) patterns of the calcium carbonate prepared in Comparative Example 3. Detailed Implementation

[0058] The present invention will be further described in detail below with reference to specific embodiments. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope and application of the present invention.

[0059] Example 1

[0060] A method for preparing calcite-type calcium carbonate whiskers includes the following steps:

[0061] Step 1: Prepare a calcium hydroxide suspension with a solid content of 12%, and heat the calcium hydroxide suspension to 40°C to obtain a hot calcium hydroxide suspension for later use;

[0062] Step 2: Add 0.5% magnesium borate, 0.5% aluminum borate, and 2.0% magnesium citrate (by weight of calcium hydroxide) to the hot calcium hydroxide suspension and stir until homogeneous to obtain a hot mixed suspension;

[0063] Step 3: Continuously introduce a 15.0% concentration solution into the thermally mixed suspension at a flow rate of 2.0 m³ / s. 3 The carbon dioxide flow rate was 1000 r / min, and the stirring speed during the reaction process was 1000 r / min until the pH of the reaction system reached 7.50. The carbon dioxide flow was then stopped, and a calcium carbonate suspension was obtained. The suspension was filtered, dried, and calcium carbonate powder was obtained.

[0064] Step 4: Calcine the calcium carbonate powder in a furnace at 430°C for 1 hour, and then pulverize the calcined calcium carbonate to obtain calcite-type calcium carbonate whiskers.

[0065] The calcium carbonate whiskers prepared in the examples were subjected to SEM testing to observe their morphology, and the results are as follows: Figure 1 As shown in (a), the calcium carbonate whiskers obtained in this example have a large aspect ratio; the XRD detection results are as follows. Figure 1 (b) shows calcite calcium carbonate.

[0066] Example 2

[0067] A method for preparing calcite-type calcium carbonate whiskers includes the following steps:

[0068] Step 1: Prepare a calcium hydroxide suspension with a solid content of 15%, and heat the calcium hydroxide suspension to 45°C to obtain a hot calcium hydroxide suspension for later use;

[0069] Step 2: Add 0.2% magnesium borate, 0.3% aluminum borate, and 0.5% magnesium citrate (by weight of calcium hydroxide) to the hot calcium hydroxide suspension and stir until homogeneous to obtain a hot mixed suspension;

[0070] Step 3: Continuously introduce a 20.0% concentration solution at a flow rate of 1.8 m³ into the thermally mixed suspension. 3The carbon dioxide flow rate was 900 r / min, and the stirring speed during the reaction process was 900 r / min until the pH of the reaction system reached 7.50. The carbon dioxide flow was then stopped, and a calcium carbonate suspension was obtained. The suspension was filtered, dried, and calcium carbonate powder was obtained.

[0071] Step 4: Calcine the calcium carbonate powder in a furnace at 450°C for 1 hour, and then pulverize the calcined calcium carbonate to obtain calcite-type calcium carbonate whiskers.

[0072] The calcium carbonate whiskers prepared in the examples were subjected to SEM testing to observe their morphology, and the results are as follows: Figure 2 As shown in (a), the calcium carbonate whiskers obtained in this example have a large aspect ratio; the XRD detection results are as follows. Figure 2 (b) shows calcium carbonate calcium carbonate.

[0073] Example 3

[0074] A method for preparing calcite-type calcium carbonate whiskers includes the following steps:

[0075] Step 1: Prepare a calcium hydroxide suspension with a solid content of 15%, and heat the calcium hydroxide suspension to 40°C to obtain a hot calcium hydroxide suspension for later use;

[0076] Step 2: Add 1.5% magnesium borate, 1.5% aluminum borate, and 1.0% magnesium citrate (by weight of calcium hydroxide) to the hot calcium hydroxide suspension and stir until homogeneous to obtain a hot mixed suspension.

[0077] Step 3: Continuously introduce a 20.0% concentration solution at a flow rate of 1.8 m³ into the thermally mixed suspension. 3 The carbon dioxide flow rate was 1 / h, and the stirring speed during the reaction process was 1200 r / min until the pH of the reaction system reached 7.50. Then, the carbon dioxide flow was stopped, and a calcium carbonate suspension was obtained. The suspension was filtered, dried, and calcium carbonate powder was obtained.

[0078] Step 4: Calcine the calcium carbonate powder in a furnace at 450°C for 0.5 hours, and then pulverize the calcined calcium carbonate to obtain calcite-type calcium carbonate whiskers.

[0079] The calcium carbonate whiskers prepared in the examples were subjected to SEM testing to observe their morphology, and the results are as follows: Figure 3 As shown in (a), the calcium carbonate whiskers obtained in this example have a large aspect ratio; the XRD detection results are as follows. Figure 3 (b) shows calcite calcium carbonate.

[0080] Example 4

[0081] A method for preparing calcite-type calcium carbonate whiskers includes the following steps:

[0082] Step 1: Prepare a calcium hydroxide suspension with a solid content of 13%, and heat the calcium hydroxide suspension to 43°C to obtain a hot calcium hydroxide suspension for later use;

[0083] Step 2: Add 1.5% magnesium borate, 0.5% aluminum borate, and 1.5% magnesium citrate (by weight of calcium hydroxide) to the hot calcium hydroxide suspension and stir until homogeneous to obtain a hot mixed suspension.

[0084] Step 3: Continuously introduce a solution of 18.0% concentration and a flow rate of 1.9 m³ into the thermally mixed suspension. 3 The carbon dioxide flow rate was 1 / h, and the stirring speed during the reaction process was 1100 r / min until the pH of the reaction system reached 7.50. Then, the carbon dioxide flow was stopped, and a calcium carbonate suspension was obtained. The suspension was filtered, dried, and calcium carbonate powder was obtained.

[0085] Step 4: Calcine the calcium carbonate powder in a furnace at 450°C for 0.8 hours, and then pulverize the calcined calcium carbonate to obtain calcite-type calcium carbonate whiskers.

[0086] The calcium carbonate whiskers prepared in the examples were subjected to SEM testing to observe their morphology, and the results are as follows: Figure 4 As shown in (a), the calcium carbonate whiskers obtained in this example have a large aspect ratio; the XRD detection results are as follows. Figure 4 (b) shows calcite calcium carbonate.

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 1 is that magnesium borate and aluminum borate are not added in step two. The other methods and steps are the same as in Example 1, and will not be repeated here.

[0089] The calcium carbonate prepared in the comparative example was subjected to SEM testing to observe its morphology. The results are as follows: Figure 5 As shown in (a), the calcium carbonate whiskers obtained by this method contain a large amount of near-cubic calcium carbonate, which means that pure whisker-like calcium carbonate cannot be prepared without the addition of magnesium borate and aluminum borate. XRD results are as follows... Figure 5 (b) shows calcite calcium carbonate.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Example 1 is that magnesium citrate is not added in step two. The other methods and steps are the same as in Example 1, and will not be repeated here.

[0092] The calcium carbonate prepared in the examples was subjected to SEM testing to observe its morphology, and the results are as follows. Figure 6As shown in (a), the calcium carbonate obtained in this example has a mixed morphology of whiskers and cubic-like structures, which means that pure calcium carbonate whiskers cannot be prepared without the crystal form control agent magnesium citrate. XRD results are as follows... Figure 6 (b) shows calcite calcium carbonate.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that step four is omitted. The other methods and steps are the same as in Example 1, and will not be repeated here.

[0095] The calcium carbonate prepared in the examples was subjected to SEM testing to observe its morphology, and the results are as follows. Figure 7 As shown in (a), this embodiment yields calcium carbonate whiskers; the XRD results are as follows. Figure 7 As shown in (b), its main component is aragonite calcium carbonate, followed by calcite calcium carbonate. Comparative Example 3 shows that the prepared calcium carbonate whiskers were not subjected to subsequent temperature treatment at 430-450℃, and their crystal form is mainly aragonite phase, rather than the most stable calcite phase.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing calcite-type calcium carbonate whiskers, characterized in that, Includes the following steps: Step 1: Prepare a calcium hydroxide suspension by heating the calcium hydroxide suspension to obtain a hot calcium hydroxide suspension for later use; Step 2: Add the seed crystals and crystal form control agent to the hot calcium hydroxide suspension and stir evenly to obtain a hot mixed suspension. The seed crystals are a mixture of magnesium borate and aluminum borate in a mass ratio of (2-15):(3-15). The crystal form control agent is magnesium citrate, and the amount added is 0.5-2.0% of the mass of calcium hydroxide. Step 3: Continuously introduce carbon dioxide into the hot mixed suspension to react until the reaction is complete. Stop introducing carbon dioxide to obtain a calcium carbonate suspension. Filter and dry the suspension to obtain calcium carbonate powder. Step 4: Calcine and pulverize the calcium carbonate powder in a furnace to obtain calcite-type calcium carbonate whiskers.

2. The method for preparing calcite-type calcium carbonate whiskers according to claim 1, characterized in that, The solid content of the calcium hydroxide suspension mentioned in step one is 12-15%.

3. The method for preparing calcite-type calcium carbonate whiskers according to claim 2, characterized in that, The calcium hydroxide suspension is heated to 40-45°C.

4. The method for preparing calcite-type calcium carbonate whiskers according to claim 1, characterized in that, The amount of seed crystals added is 0.5-3.0% of the mass of calcium hydroxide.

5. The method for preparing calcite-type calcium carbonate whiskers according to claim 1, characterized in that, In step three, the concentration of carbon dioxide introduced is 15.0-20.0%, and the flow rate is 1.8-2.0 m³ / s. 3 / h; the stirring speed during the reaction process is 900-1200 r / min.

6. The method for preparing calcite-type calcium carbonate whiskers according to claim 1, characterized in that, In step three, carbon dioxide is continuously introduced into the hot mixed suspension for reaction until the pH of the reaction system is ≤7.50, at which point the carbon dioxide introduction is stopped, and a calcium carbonate suspension is obtained.

7. The method for preparing calcite-type calcium carbonate whiskers according to claim 1, characterized in that, In step four, the calcium carbonate powder is calcined at a temperature of 430-450℃ for 0.5-1.0h.

8. A calcite-type calcium carbonate whisker prepared by the method according to any one of claims 1-7.

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