Calcite type calcium carbonate whisker and preparation method thereof

Abstract

The invention discloses a preparation method of calcite type calcium carbonate whiskers, which comprises the following steps: (1) preparing a calcium hydroxide suspension, and heating the calcium hydroxide suspension to obtain a hot calcium hydroxide suspension for later use; (2) adding a seed crystal and a crystal form control agent into the hot calcium hydroxide suspension, and uniformly stirring to obtain a hot mixed suspension; (3) continuously introducing carbon dioxide into the hot mixed suspension liquid for reaction until the reaction is finished, stopping introducing the carbon dioxide to obtain a calcium carbonate suspension liquid, filtering and drying to obtain calcium carbonate powder; and (4) calcining the calcium carbonate powder in a furnace, and crushing to obtain the calcite type calcium carbonate whisker. The calcium carbonate whisker prepared by the method is calcite type, and a new research thought is provided for preparation of the calcite type calcium carbonate whisker; the calcite calcium carbonate whisker prepared by the method is the most stable phase of calcium carbonate, and the application field of the calcium carbonate whisker is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of calcium carbonate preparation, in particular to a calcite calcium carbonate whisker and a preparation method thereof. Technical Background

[0002] Whiskers are an inorganic material with a needle-like or fibrous shape. Common inorganic whiskers such as silicon carbide, potassium titanate, magnesium sulfate, etc. are used as needle-shaped single crystal reinforcement materials. They have the advantages of 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 low-cost green and environmentally friendly material with excellent properties such as high strength, high modulus, good heat resistance and thermal insulation. They have been widely used in the filling and modification of polymer materials, such as polypropylene, natural rubber, polyetheretherketone, etc. At present, the calcium carbonate whiskers reported publicly are mainly aragonite type (Guo Qiu, Preparation and wet surface modification of calcium carbonate whiskers for epoxy resin 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, adding crystal type control and other processes, it is currently the commonly used method for industrial preparation of calcium carbonate whiskers. (2) Double decomposition method: This method uses soluble calcium salt and carbonate as raw materials, and produces calcium carbonate whiskers by double decomposition reaction under certain solution concentration, reaction system temperature, and mechanical stirring rate. The yield of calcium carbonate whiskers prepared by this method is low, but the reaction process is simple. It is currently a commonly used method for studying calcium carbonate whiskers. (3) Urea hydrolysis method: Urea is reacted with soluble calcium salt. No crystal form control agent is required during the reaction process, 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. In addition, the use of urea as a raw material does not meet economic requirements and has a low cost-effectiveness, so it is difficult to industrialize. (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 and its preparation method and application. First, a compound of a crystal form control agent magnesium acetate, magnesium nitrate and sodium acetate is added to a calcium hydroxide suspension to form a mixed solution, the mixed solution is kept at a constant temperature of 80-100°C, and then carbon dioxide is introduced to react until the pH value of the mixed solution decreases, and then filtered and the precipitate is taken to obtain calcium carbonate whiskers. The whiskers prepared by this method are aragonite calcium carbonate.

[0004] Patent CN114959895B discloses an ultra-long calcium carbonate whisker and a preparation method thereof. The length of the ultra-long calcium carbonate whisker is more than 90um. First, prepare a calcium hydroxide suspension; mix a crystal form control agent with water to form a crystal form control solution; wherein the crystal form control agent contains at least magnesium ions and nitrate ions; then mix the crystal form control solution with the calcium hydroxide suspension to form a mixed solution, and increase the temperature of the mixed solution to 90-110°C; finally, keep the temperature of the mixed solution constant, and introduce carbon dioxide gas into the mixed solution for reaction. When the pH value of the reaction system decreases, filter and take the precipitate to obtain calcium carbonate whiskers. The obtained ultra-long calcium carbonate whiskers are of aragonite type and can be used in mortar to improve the flexural and tensile strength of the mortar and reduce cracks.

[0005] Patent CN114921851B discloses a method for preparing calcium carbonate whiskers by carbonization of carbide slag, and the preparation method is as follows: step one, preparing a magnesium salt solution, heating the magnesium salt solution to obtain a hot magnesium salt solution for standby use; step two, adding carbide slag to the hot magnesium salt solution, stirring evenly to obtain a mixed solution; step three, continuously introducing CO2-containing gas into the mixed solution, carbonizing for a period of time, filtering the slurry after the carbonization reaction is completed, and drying the filter residue to obtain calcium carbonate aragonite whiskers.

[0006] Patent CN113564688B discloses a method for preparing calcium carbonate whiskers, which firstly calcines and decomposes raw calcite ore or calcite tailings or limestone industrial waste into calcium oxide, then adds calcium oxide and magnesium chloride into deionized water and digests at a certain temperature, filters the filter cake, beats it and introduces it into excess CO2 for carbonation reaction to obtain heavy magnesium water, finally uniformly drops the filtrate after digestion conversion filtration into the filtrate after carbonation reaction filtration, and reacts at a certain temperature and stirring rate until no precipitation is produced and the reaction is terminated to obtain calcium carbonate whiskers. The method prepares aragonite calcium carbonate whiskers through multiple carbonization reactions.

[0007] Patent CN112723403B discloses a method for preparing calcium carbonate whiskers, and the specific method is as follows: 1) adding water to calcium oxide to carry out a digestion reaction, sieving, and obtaining a calcium hydroxide suspension; 2) passing carbon dioxide into a potassium hydroxide solution until the pH of the solution drops below 7 to obtain a crystal form controller I; 3) adding the crystal form controller I of step 2) to the calcium hydroxide suspension of step 1), stirring, aging, and then adding a crystal form controller II, which is at least one of strontium chloride, sodium phosphate and sodium citrate, stirring, and then passing lime kiln gas into the reaction solution to carry out a carbonation reaction until the pH of the reaction solution drops below 7, and then dehydrating, drying, crushing and sieving to obtain calcium carbonate whiskers.

[0008] Patent CN111926386B discloses a method for preparing calcium carbonate whiskers, which comprises dissolving silk fibroin and gum arabic in deionized water and stirring them thoroughly to obtain a crystal form control agent, then stirring and mixing high-purity nano calcium oxide with deionized water to obtain slurry A, filtering slurry A through a 100-mesh sieve to remove slag, then adding deionized water to dilute the slurry to obtain slurry B, then adding a crystal form control agent to slurry B, heating to 50-60°C and stirring at a constant temperature for 1-2h to obtain slurry C, then adding ammonia water to slurry C to adjust the pH value, and then putting it into a supergravity carbonization reactor for carbonization reaction, centrifuging the slurry obtained after the carbonization to obtain a precipitate, and then crushing the precipitate to obtain calcium carbonate aragonite whiskers.

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

[0010] Patent CN110029396B discloses a method for preparing functional calcium carbonate whiskers, which comprises the following steps: (1) preparing a Ca(OH)2 suspension; (2) adding the Ca(OH)2 suspension into a supergravity reactor, adding phosphoric acid as a crystal form controller and sodium stearate as a surface modifier, and then introducing CO2 to perform a carbonization reaction, using a digital pH meter to track the entire carbonization reaction process, and when the pH of the reaction slurry is 6.5-7.0, stopping the ventilation and the carbonization reaction ends; (3) centrifuging, drying, and crushing the product slurry in turn to obtain the desired product. The present invention has a simple production process, a short production cycle, and high production efficiency.

[0011] Patent CN108893775B discloses a method for preparing high-purity calcium carbonate whiskers, which comprises the following steps: firstly calcining a calcium carbonate raw material to decompose it into calcium oxide, then adding the calcium oxide into deionized water to digest it at a certain temperature, using a magnesium chloride solution as a crystal shape control agent, spraying the digested calcium hydroxide suspension into the magnesium chloride solution, introducing carbon dioxide at a certain rate using an aeration device with a certain pore diameter, thereby controlling the bubble volume and dispersion of the introduced gas and thereby making carbonate ions evenly distributed in the solution, and performing a carbonization reaction under stirring at a certain rate until the pH of the solution drops to 7 and the reaction is terminated, thereby obtaining high-purity aragonite 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 shape control agent is added and stirred evenly, carbon dioxide gas is introduced at a certain flow rate through a double-tube ventilation device to cause a carbonation reaction, and finally the obtained 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 uniformly mixed by ultrasound to obtain a triethanolamine-water solution mixed system; then anhydrous calcium chloride and urea are added to a polytetrafluoroethylene-lined reactor containing a triethanolamine-water mixed solution and heated for reaction; cooled and filtered, 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 method. The method is characterized in that sucrose is used as an auxiliary agent for the first time to obtain calcium carbonate whiskers with a high aspect ratio by hydrolyzing urea. Sucrose of different mass concentrations is added to a mixed solution of urea and calcium chloride at a certain temperature. After a period of reaction, the obtained product is washed with deionized water until the pH is neutral, and then dried to obtain calcium carbonate whiskers.

[0015] Patent CN101935865B discloses a method for preparing calcium carbonate whiskers with a high aspect ratio. The method uses quicklime as a raw material and bischofite as a crystal form control agent to prepare calcium carbonate whiskers through a carbonation reaction of carbon dioxide, and then recycles the mother liquor to prepare calcium carbonate whiskers, thereby completing multi-stage growth of a calcium carbonate whisker product with a high aspect ratio.

[0016] Patent CN1303264C discloses a method for producing high-purity aragonite calcium carbonate whiskers. The method uses quicklime or slaked lime as raw materials and magnesium salt as a crystal form control agent to produce aragonite calcium carbonate whiskers through a carbonation method using carbon dioxide. The method is characterized in that the magnesium salt solution is reused during the preparation of the calcium carbonate whiskers and slaked lime slurry is uniformly added during the carbonation reaction. By combining these two technologies, high-purity, high aspect ratio calcium carbonate whiskers can be produced.

[0017] In summary, it can be found that the mainstream method for synthesizing calcium carbonate whiskers is the carbonation method of calcium hydroxide and carbon dioxide, magnesium salt is the most commonly used crystal control agent, and the synthesized calcium carbonate whiskers are mainly aragonite structures. However, it can be found from published reports that calcite calcium carbonate has excellent stability compared to aragonite calcium carbonate. Summary of the invention

[0018] The purpose of the present invention is to provide a calcite calcium carbonate whisker and a preparation method thereof, so as to solve the stability problem of aragonite calcium carbonate whisker and fill the blank of calcite calcium carbonate whisker preparation.

[0019] In order to achieve the above object, the present invention provides the following technical solutions:

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

[0021] Step 1: preparing a calcium hydroxide suspension, heating the calcium hydroxide suspension to obtain a hot calcium hydroxide suspension for standby use;

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

[0023] Step 3: continuously introducing carbon dioxide into the hot mixed suspension to react until the reaction is completed, stopping the introduction of carbon dioxide to obtain a calcium carbonate suspension, filtering, and drying to obtain calcium carbonate powder;

[0024] Step 4: calcining and crushing the calcium carbonate powder in a furnace to obtain calcite calcium carbonate whiskers.

[0025] Preferably, the solid content of the calcium hydroxide suspension in step 1 is 12-15%.

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

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

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

[0029] Preferably, the crystal form controlling agent in step 2 is magnesium citrate, and the added amount is 0.5-2.0% of the mass of calcium hydroxide.

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

[0031] Preferably, in step 3, carbon dioxide is continuously introduced into the hot mixed suspension for reaction until the pH of the reaction system is ≤7.50, and the introduction of carbon dioxide is stopped to obtain a calcium carbonate suspension.

[0032] Preferably, in step 4, the calcium carbonate powder is calcined at a temperature of 430-450° C. for a time of 0.5-1.0 h.

[0033] Technical principle of the present invention:

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

[0035] (1) Raw material effects and synergistic mechanisms

[0036] 1) Calcium hydroxide suspension: As the starting material, the calcium hydroxide suspension provides the necessary calcium source for the entire reaction. By heating to 40-45°C, the fluctuation range of the solubility of calcium hydroxide is controlled, which also ensures the smooth progress of the reaction in the subsequent steps. The solid content is controlled between 12-15%. This precise range helps to balance the reaction rate and the uniformity of the product, and avoids uneven crystallization or low reaction efficiency caused by too high or too low solid content.

[0037] 2) Seeds (compound of magnesium borate and aluminum borate): The introduction of seed crystals is the key to controlling the morphology and structure of whiskers. Magnesium borate and aluminum borate are compounded in a mass ratio of (2-15): (3-15), which not only promotes the growth of specific crystal faces, but also guides calcium carbonate molecules to arrange in a predetermined direction through synergistic action to form a slender and uniform whisker structure. The addition amount is controlled at 0.5-3.0% of the mass of calcium hydroxide. This ratio just stimulates the directional growth of whiskers and avoids the impurity problem that may be caused by excessive addition.

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

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

[0040] Precise control of the amount of raw materials is the prerequisite for ensuring stable product quality and excellent performance. Too much or too little seed crystals and crystal form controllers will affect the growth rate, morphological distribution and final performance of the whiskers. For example, too little seed crystals may cause the whiskers to grow in different directions, while too much may cause excessive nucleation, affecting the length and diameter of the whiskers. Similarly, the amount of magnesium citrate must also be accurate to avoid adverse effects on the whisker morphology.

[0041] In the selection of process parameters, the concentration and flow rate of carbon dioxide, the stirring speed of the reaction system, and the pH control at the end point of the reaction are all crucial. High concentrations of carbon dioxide accelerate the carbonization reaction, but too high a concentration may cause the reaction to be too violent, affecting the morphology of the whiskers. The appropriate stirring speed ensures the uniformity of the reaction system, promotes effective contact between gas and liquid, and is conducive to the uniform growth of whiskers. Controlling the reaction to pH ≤ 7.50 and stopping the flow of carbon dioxide is to ensure the complete precipitation of calcium carbonate, while avoiding excessive carbonization to form calcium bicarbonate, which affects the morphology of calcium carbonate.

[0042] (3) Technical effects and optimization necessity

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

[0044] Compared with the prior art, the innovation of the present invention lies not only in its unique material selection and process design, but also in that it realizes the fine control of the growth process of calcium carbonate crystals, thereby significantly improving the quality and performance of the product. The specific advantages are reflected in the following aspects:

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

[0046] The present invention cleverly introduces magnesium borate and aluminum borate whiskers as crystal seeds. These two materials, with their excellent crystal structure and stability, provide an ideal template for the growth of calcium carbonate. At the same time, magnesium citrate is innovatively used as a crystal form controller. This move is like a "navigator" in a chemical reaction system, accurately guiding and controlling the growth path and rate of calcium carbonate molecules in a specific direction. Through this unprecedented fine control mechanism, the present invention can accurately shape calcium carbonate whiskers of uniform size and regular shape. The subsequent heat treatment process further stabilizes the structure of the whiskers, allowing them to be perfectly transformed into calcite, the most common form of calcium carbonate in nature, which gives the whiskers more stable physical and chemical properties.

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

[0048] For a long time, the preparation of calcite calcium carbonate whiskers has been a hot topic and difficulty in the field of materials science. The present invention not only successfully prepared high-quality calcite calcium carbonate whiskers, but also opened up new ideas and directions for research in this field. It breaks through the limitations of the preparation methods of the prior art in terms of material selection, process control, etc., demonstrates the possibility of optimizing the crystal structure through fine regulation, and provides valuable experience and inspiration for subsequent scientific research exploration.

[0049] (3) Stabilize phase and expand application areas

[0050] Calcite calcium carbonate is the most stable phase of calcium carbonate, and its unique physical and chemical properties make it have wide application potential in many fields. The calcite calcium carbonate whiskers prepared by the present invention not only retain the stability and durability of calcite itself, but also have excellent properties such as reinforcement and toughening due to its unique whisker morphology. This makes its application prospects in the fields of plastics, epoxy resins, coatings, friction materials, etc. become particularly broad. The emergence of the present invention has undoubtedly injected new vitality into the development of these fields, promoted the leap of calcium carbonate whiskers from theoretical research to practical application, and realized the effective transformation of technological achievements into economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The following are the scanning electron microscope images and X-ray diffraction patterns of the calcite calcium carbonate whiskers prepared in Example 1.

[0052] Figure 2 The following are the scanning electron microscope images and X-ray diffraction patterns of the calcite calcium carbonate whiskers prepared in Example 2.

[0053] Figure 3 The following are the scanning electron microscope images and X-ray diffraction patterns of the calcite calcium carbonate whiskers prepared in Example 3.

[0054] Figure 4 The following are the scanning electron microscope images and X-ray diffraction patterns of the calcite calcium carbonate whiskers prepared in Example 4.

[0055] Figure 5 The following are the scanning electron microscope images and X-ray diffraction patterns of the calcium carbonate prepared in Comparative Example 1.

[0056] Figure 6 The scanning electron microscope image and X-ray diffraction pattern of the calcium carbonate prepared in Comparative Example 2 are shown.

[0057] Figure 7 The following are the scanning electron microscope images and X-ray diffraction patterns of the calcium carbonate prepared in Comparative Example 3. DETAILED DESCRIPTION

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

[0059] Example 1

[0060] A method for preparing calcite type calcium carbonate whiskers comprises 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 standby use;

[0062] Step 2: adding 0.5% magnesium borate, 0.5% aluminum borate and 2.0% magnesium citrate based on the mass of calcium hydroxide into the hot calcium hydroxide suspension, stirring evenly to obtain a hot mixed suspension;

[0063] Step 3: Continuously introduce a 15.0% concentration and a flow rate of 2.0 m 3 / h carbon dioxide, the stirring speed during the reaction process is 1000r / min, until the pH of the reaction system reaches 7.50, the carbon dioxide is stopped, and a calcium carbonate suspension is obtained, which is filtered and dried to obtain calcium carbonate powder;

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

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

[0066] Example 2

[0067] A method for preparing calcite type calcium carbonate whiskers comprises 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 standby use;

[0069] Step 2: adding 0.2% magnesium borate, 0.3% aluminum borate and 0.5% magnesium citrate based on the mass of calcium hydroxide into the hot calcium hydroxide suspension, stirring evenly to obtain a hot mixed suspension;

[0070] Step 3: Continuously introduce a 20.0% concentration and a flow rate of 1.8 m 3 / h carbon dioxide, the stirring speed during the reaction is 900r / min, until the pH of the reaction system reaches 7.50, the carbon dioxide is stopped, and a calcium carbonate suspension is obtained, which is filtered and dried to obtain calcium carbonate powder;

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

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

[0073] Example 3

[0074] A method for preparing calcite type calcium carbonate whiskers comprises 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 standby use;

[0076] Step 2: adding 1.5% magnesium borate, 1.5% aluminum borate and 1.0% magnesium citrate based on the mass of calcium hydroxide into the hot calcium hydroxide suspension, stirring evenly to obtain a hot mixed suspension;

[0077] Step 3: Continuously introduce a 20.0% concentration and a flow rate of 1.8 m 3 / h carbon dioxide, the stirring speed during the reaction is 1200r / min, until the pH of the reaction system reaches 7.50, the carbon dioxide is stopped, and a calcium carbonate suspension is obtained, which is filtered and dried to obtain calcium carbonate powder;

[0078] Step 4: calcining the calcium carbonate powder in a furnace at 450° C. for 0.5 h, and crushing the calcined calcium carbonate to obtain calcite calcium carbonate whiskers.

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

[0080] Example 4

[0081] A method for preparing calcite type calcium carbonate whiskers comprises 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 standby use;

[0083] Step 2: adding 1.5% magnesium borate, 0.5% aluminum borate and 1.5% magnesium citrate based on the mass of calcium hydroxide to the hot calcium hydroxide suspension, stirring evenly to obtain a hot mixed suspension;

[0084] Step 3: Continuously introduce a 18.0% concentration and a flow rate of 1.9 m 3 / h carbon dioxide, the stirring speed during the reaction process is 1100r / min, until the pH of the reaction system reaches 7.50, the carbon dioxide is stopped, and a calcium carbonate suspension is obtained, which is filtered and dried to obtain calcium carbonate powder;

[0085] Step 4: calcining the calcium carbonate powder in a furnace at 450° C. for 0.8 h, and crushing the calcined calcium carbonate to obtain calcite calcium carbonate whiskers.

[0086] The calcium carbonate whiskers prepared in the example were subjected to SEM testing to observe their morphology. The results are as follows: Figure 4 As shown in (a), the calcium carbonate whiskers obtained in this embodiment have a relatively large aspect ratio; the XRD test 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 2, and the other method steps are the same as those in Example 1, which will not be repeated here.

[0089] The calcium carbonate prepared in the comparative example was subjected to SEM test 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 cubic calcium carbonate, which means that pure whisker-like calcium carbonate cannot be prepared without adding magnesium borate and aluminum borate. 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 2, and the other method steps are the same as those in Example 1, which will not be repeated here.

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

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that there is no operation process of step 4, and the other method steps are the same as those of Example 1, which will not be repeated here.

[0095] The calcium carbonate prepared in the example was subjected to SEM test to observe its morphology. The results are as follows Figure 7 As shown in (a), the calcium carbonate whiskers obtained in this embodiment; the XRD test 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 whisker has not been subjected to the later temperature treatment of 430-450°C, and its crystal form is mainly aragonite phase, rather than the most stable calcite phase.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing calcite type calcium carbonate whiskers, characterized in that, The following steps are involved: Step 1: preparing a calcium hydroxide suspension, heating the calcium hydroxide suspension to obtain a hot calcium hydroxide suspension for standby use; Step 2: adding seed crystals and a crystal form control agent to the hot calcium hydroxide suspension, stirring evenly to obtain a hot mixed suspension; Step 3: continuously introducing carbon dioxide into the hot mixed suspension to react until the reaction is completed, stopping the introduction of carbon dioxide to obtain a calcium carbonate suspension, filtering, and drying to obtain calcium carbonate powder; Step 4: calcining and crushing the calcium carbonate powder in a furnace to obtain calcite calcium carbonate whiskers.

2. the preparation method of calcite type calcium carbonate whisker according to claim 1, is characterized in that, The solid content of the calcium hydroxide suspension described in step 1 is 12-15%.

3. the preparation method of calcite type calcium carbonate whisker according to claim 2 is characterized in that, The calcium hydroxide suspension is heated to 40-45°C.

4. The preparation method of calcite type calcium carbonate whisker according to claim 1, wherein The seed crystals described in step 2 are a compound of magnesium borate and aluminum borate in a mass ratio of (2-15):(3-15).

5. The preparation method of calcite type calcium carbonate whisker according to claim 4, wherein The added amount of the seed crystal is 0.5-3.0% of the mass of calcium hydroxide.

6. The preparation method of calcite type calcium carbonate whisker according to claim 1, wherein The crystal form control agent described in step 2 is magnesium citrate, and the added amount is 0.5-2.0% of the mass of calcium hydroxide.

7. The preparation method of calcite type calcium carbonate whisker according to claim 1, wherein The concentration of carbon dioxide introduced in step 3 is 15.0-20.0% and the flow rate is 1.8-2.0m 3 / h; the stirring speed during the reaction process is 900-1200r / min.

8. The preparation method of calcite type calcium carbonate whisker according to claim 1, wherein In step 3, carbon dioxide is continuously introduced into the hot mixed suspension for reaction until the pH of the reaction system is ≤7.50, and the introduction of carbon dioxide is stopped to obtain a calcium carbonate suspension.

9. The preparation method of calcite type calcium carbonate whisker according to claim 1, wherein In step 4, the calcium carbonate powder is calcined at a temperature of 430-450° C. for a time of 0.5-1.0 h.

10. A calcite calcium carbonate whisker prepared according to the method according to any one of claims 1 to 9.

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