A stable preparation method for unsteady spheroidal calcium carbonate crystals

Abstract

This invention discloses a stable preparation method for unsteady aragonite calcium carbonate crystals, belonging to the field of inorganic material preparation technology. The method uses γ-type dicalcium silicate (γ-C2S) as a slow-release calcium source and amino acids as crystal form regulators. CO2 is introduced into the system at room temperature and pressure to initiate a carbonization reaction. By constructing an unsteady reaction environment of "instantaneous supersaturation-kinetic passivation-heterogeneous adsorption," controllable nucleation of aragonite is achieved, and its transformation to calcite is significantly inhibited. Optionally, gypsum powder can be added as a crystal form stabilizer to further enhance the stability of aragonite through heterogeneous adsorption. This invention features a simple, green, and energy-saving process, yielding aragonite calcium carbonate crystals with high purity, regular morphology, and excellent long-term stability in water. It is suitable for applications such as carbon mineralization and carbon fixation, functional fillers, and low-carbon building materials.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material preparation technology, specifically relating to a method for controllable nucleation and crystal stabilization of calcium carbonate crystals, and more particularly to a method for the stable preparation of spherulite calcium carbonate crystals under unsteady-state reaction conditions. Background Technology

[0002] Calcium carbonate is an important inorganic compound widely used in building materials, papermaking, plastics, pharmaceuticals, and environmental remediation. Calcium carbonate has three common amorphous forms: calcite, aragonite, and aragonite. Among them, aragonite is a metastable phase with a unique spherical porous structure, large specific surface area, and good dispersibility, showing significant application potential in composite material reinforcement, drug carriers, optical coatings, and carbon mineralization and fixation.

[0003] However, aragonite is thermodynamically unstable at room temperature and pressure, and readily transforms spontaneously into stable calcite or aragonite crystals through a dissolution-recrystallization mechanism. This makes it difficult to maintain its morphology and properties over a long period, severely restricting its large-scale application. Existing preparation methods often suffer from problems such as low product purity, rapid crystal transformation, and poor process controllability.

[0004] Therefore, developing a novel preparation method that can control the nucleation, growth, and crystal transformation processes of aragonite in an unsteady environment, and achieving the controllable generation and stable maintenance of aragonite crystals, has become a technical challenge to be solved in this field. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art and provide a stable preparation method for unsteady spheroidal calcium carbonate crystals that is simple in process, mild in conditions, and has high product stability.

[0006] To achieve the above objectives, this invention provides a stable preparation method for unsteady aragonite calcium carbonate crystals. The core of this method lies in: introducing γ-C2S, a calcium source phase with low dissolution rate and negative surface charge, as a slow-release calcium source; combining this with an amino acid-based crystal form control agent and a dynamic gas-liquid reaction system to construct an unsteady (non-equilibrium) reaction environment; and utilizing a "transient supersaturation-kinetic passivation-heterogeneous adsorption" mechanism to achieve controllable generation and stable maintenance of aragonite crystals. Optionally, gypsum powder is introduced as a heterogeneous adsorbent material to further suppress phase transition by promoting the adsorption of aragonite on its surface.

[0007] The method includes the following steps:

[0008] (1) Mix Ca(OH)2 and SiO2 powders at a molar ratio of 2:1, calcine them in a muffle furnace at a heating rate of 8-12℃ / min to 1350-1400℃ (preferably 1380℃) and hold for 1-3 hours (preferably 2 hours), and obtain γ-C2S powder after natural cooling.

[0009] (2) Dissolve the amino acid crystal form regulator in deionized water to form a crystal form regulating solution with a concentration of 0.01~0.20mol / L and a pH of 8.5~10.5;

[0010] (3) Add the γ-C2S powder obtained in step (1) to the crystal form regulation solution obtained in step (2), wherein the mass ratio of the γ-C2S powder to water is (1.5~3.0):100, stir evenly to obtain a mixed solution;

[0011] (4) Optionally, gypsum powder is added to the mixed solution obtained in step (3) as a crystal stabilizer, and the amount of gypsum is 0.1% to 0.5% of the mass of the mixed solution;

[0012] (5) Introduce CO2 gas with a purity of ≥99% into the mixed system obtained in step (3) or (4) to carry out carbonization reaction. The CO2 gas flow rate is 0.2~1.0L / min, the introduce time is 5~30 minutes, the reaction temperature is 10~25℃, and the reaction pressure is atmospheric pressure.

[0013] (6) Separate, clean and dry the solid product after the reaction in step (5) to obtain aragonite calcium carbonate crystals.

[0014] Furthermore, in step (1), the purity of the γ-C2S powder is ≥90%, the remainder is calcium silicate mineral, and the particle size of the γ-C2S powder is 5~30μm.

[0015] Furthermore, in step (2), the amino acid crystal form regulator is one of glycine, aspartic acid, or glutamic acid.

[0016] Furthermore, in step (4), the particle size of the gypsum ranges from 3 to 50 μm.

[0017] Furthermore, in step (5), the preferred flow rate of the CO2 gas is 0.5 L / min, and the preferred inlet time is 10 minutes.

[0018] Furthermore, in step (6), the separation is carried out by one of static sedimentation, filtration or centrifugation; the washing is carried out by rinsing with deionized water and anhydrous ethanol in sequence; and the drying is carried out under vacuum or inert atmosphere at 40~80℃.

[0019] Furthermore, in step (6), the aragonite calcium carbonate crystal has aragonite phase as the main crystal phase and calcite phase content of less than 10%, preferably less than 5%.

[0020] Furthermore, the spheroidal calcium carbonate crystals are spherical or near-spherical with an average particle size of 1~20μm, preferably about 5μm.

[0021] The advantages of this invention compared to the prior art are as follows:

[0022] (1) High crystal stability: The obtained product has a high content of aragonite, and the conversion rate to calcite after long-term soaking in pure water is extremely low, thus achieving effective stabilization of the metastable crystal form.

[0023] (2) Innovative stabilization mechanism: The sustained-release properties of γ-C2S avoid competitive nucleation caused by excessively high instantaneous supersaturation, while utilizing its surface properties and interaction with aragonite to kinetically slow down the dissolution-recrystallization process of aragonite. The introduction of gypsum provides additional heterogeneous adsorption sites, further enhancing stability.

[0024] (3) Green and low-energy process: No high temperature and high pressure or complex organic additives are required. It can be prepared at room temperature and pressure. The process is simple and environmentally friendly.

[0025] (4) Strong controllability: By adjusting parameters such as γ-C2S dosage, amino acid type and concentration, solution pH, CO2 introduction conditions and whether or not gypsum is added, the purity of product crystal form, particle size and stability can be effectively controlled. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0027] Figure 1 This is the XRD pattern of γ-C2S prepared in Example 1 of this invention.

[0028] Figure 2 These are the XRD patterns of the samples prepared in Example 2, Comparative Example 1, and Comparative Example 2 of this invention (corresponding to Gv, Hv, and Lv, respectively).

[0029] Figure 3 This is a comparison chart of the crystal transformation rates of different samples after soaking in pure water for different times (Lv, Hv, and Gv in the chart represent aragonite samples prepared by different methods).

[0030] Figure 4It is a graph showing the crystal transformation rate of samples after being soaked in pure water for different times with gypsum powder added at different mass ratios. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0033] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0034] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0035] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0036] This invention provides a stable preparation method for unsteady spheroidal calcium carbonate crystals, comprising the following steps:

[0037] (1) Ca(OH)2 and SiO2 powders were mixed in a molar ratio of 2:1, heated to 1380℃ in a muffle furnace at a heating rate of 10℃ / min and held for 2 hours. After natural cooling, γ-C2S powder was obtained.

[0038] (2) Dissolve the amino acid crystal form regulator in deionized water to form a crystal form regulating solution with a concentration of 0.01~0.20mol / L and a pH of 8.5~10.5;

[0039] (3) Add the γ-C2S powder obtained in step (1) to the crystal form regulation solution obtained in step (2), wherein the mass ratio of the γ-C2S powder to water is (1.5~3.0):100, stir evenly to obtain a mixed solution;

[0040] (4) Add gypsum powder to the mixed solution obtained in step (3) as a crystal stabilizer. The added gypsum powder acts as an adsorption site, so that the calcium carbonate crystal product of aragonite generated during the carbonization process is adsorbed on the surface of the gypsum powder and its transformation into calcite and aragonite is inhibited, thereby improving the stability of aragonite. The amount of gypsum added is 0.2%-0.4% of the mass of the mixed solution.

[0041] (5) Introduce CO2 gas with a purity of ≥99% into the mixed system obtained in step (4) to carry out carbonization reaction. The CO2 gas flow rate is 0.2~1.0L / min, the introduction time is 5~20 minutes, the reaction temperature is 10~25℃, and the reaction pressure is atmospheric pressure.

[0042] (6) Separate, clean and dry the solid product after the reaction in step (5) to obtain aragonite calcium carbonate crystals.

[0043] In step (1), the purity of the γ-C2S powder is ≥95%, the remainder is calcium silicate mineral, and the particle size of the γ-C2S powder is 5-20 μm.

[0044] In step (2), the amino acid crystal form regulator is one of glycine, aspartic acid or glutamic acid.

[0045] In step (4), the particle size range of the gypsum is 3-30 μm.

[0046] In step (5), the CO2 gas is introduced at a flow rate of 0.5 L / min for 10 minutes.

[0047] In step (6), the solid-liquid separation is performed by one of the following methods: static sedimentation, vacuum filtration, or high-speed centrifugation.

[0048] In step (6), the cleaning is performed by rinsing with deionized water and anhydrous ethanol in sequence; the drying is performed under vacuum conditions at 40~60℃.

[0049] In step (6), the aragonite calcium carbonate crystal has an aragonite phase content of more than 80%, a calcite phase content of less than 3%, and a residual γ-C2S content of less than 20%.

[0050] The aragonite calcium carbonate crystals are spherical with an average particle size of 5 μm. After soaking in pure water with a liquid-to-solid ratio of 20 for 96 hours, the calcite content formed by the aragonite crystal transformation is less than 3%.

[0051] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0052] Example 1: Preparation of γ-C2S powder

[0053] Analytical grade Ca(OH)₂ and SiO₂ powders were weighed precisely at a molar ratio of 2:1 and mixed thoroughly. The mixture was placed in a corundum crucible and then placed in a muffle furnace. The temperature was increased to 1380℃ at a heating rate of 10℃ / min and held at this temperature for 2 hours. Heating was then stopped, and the material in the furnace was allowed to cool naturally to room temperature. The sintered block was removed, crushed, ground, and passed through a 200-mesh standard sieve to obtain γ-C₂S powder. X-ray diffraction (XRD) analysis confirmed that the main crystalline phase of the obtained powder was γ-C₂S, with a purity of approximately 94.5%, and the main impurity was β-C₂S. Its XRD pattern is shown below. Figure 1 As shown in the figure. The prepared γ-C2S powder was sealed and stored in a desiccator for later use.

[0054] Example 2: Preparation of spheroidal calcium carbonate (Gv sample)

[0055] Weigh 3.003 g of glycine and place it in a 500 mL beaker reactor. Add 150 mL of deionized water and stir magnetically until completely dissolved to obtain a glycine solution with a concentration of 0.20 mol / L. Adjust the pH of the solution to approximately 10.0 with a trace amount of ammonia. Add 3.445 g of γ-C2S powder prepared in Example 1 and 0.48 g of gypsum powder (gypsum content is 3% of the total mass) to the above solution. Maintain magnetic stirring (approximately 300 rpm) for 10 minutes to ensure uniform dispersion of γ-C2S and gypsum powder in the solution. Insert a microporous gas distributor into the bottom of the solution and introduce 99% pure CO2 gas at a flow rate controlled at 0.5 L / min. React for 10 minutes at room temperature and atmospheric pressure. After the reaction is complete, stop the gas flow and stirring, and allow to stand for 2 minutes. Then, vacuum filter the slurry to separate the solid precipitate. Wash the precipitate three times each with deionized water and anhydrous ethanol. The washed filter cake was placed in a vacuum drying oven and dried at 50°C for 4 hours to obtain a white powdery product (denoted as Gv).

[0056] Comparative Example 1: Preparation of high-purity spheroidal aragonite (Hv sample) by chemical precipitation

[0057] Measure 300 mL of deionized water into a 500 mL beaker, add 12.8 g of 25%-28% ammonia solution, and mix thoroughly. While stirring, slowly add 0.1 M CaCl2 solution. Subsequently, 99% CO2 gas is bubbled into the solution at a flow rate of 1 L / min, and the reaction is allowed to proceed for 10 minutes. After the reaction is complete, the resulting slurry is filtered and washed three times with anhydrous ethanol. The solid is then vacuum-dried at 50 °C for 4 hours to obtain a high-purity aragonite sample (denoted as Hv).

[0058] Comparative Example 2: Preparation of low-purity spheroidal aragonite (Lv sample) by metathesis method

[0059] 221g CaCl2 and 106g NH4Cl were dissolved in 1L of deionized water to prepare solution A. 552g K2CO3 was dissolved in 2L of deionized water to prepare solution B. Solution A and solution B were rapidly mixed under vigorous stirring and reacted for 10 minutes. After the reaction was complete, the precipitate was immediately filtered and washed thoroughly three times with anhydrous ethanol. The solid was vacuum dried at 50℃ for 4 hours to obtain a low-purity aragonite sample (denoted as Lv).

[0060] Product performance characterization and stability testing

[0061] 1. Phase Analysis: XRD phase analysis and quantification were performed on Gv, Hv, and Lv samples. Results showed (see...) Figure 2As shown): Hv contains 99% aragonite and 1% calcite; Lv contains 76.5% aragonite and 23.5% calcite; Gv contains 81.8% aragonite, 1% calcite, and 17.2% γ-C2S.

[0062] 2. Water stability test: Samples Gv, Hv, and Lv were dispersed in pure water at a liquid-to-solid ratio of 20, and immersed for 48, 72, and 96 hours respectively under static conditions. After the specified time, the samples were removed, filtered, washed with ethanol, and dried under low-temperature vacuum before XRD analysis to calculate the transformation rate from aragonite to calcite. The results are as follows: Figure 3 As shown: after soaking for 48 h, all the aragonite in Lv was transformed into calcite; the transformation rates of Hv at 48 h, 72 h, and 96 h were 18.69%, 47.68%, and 100%, respectively; while after soaking for 96 h, the calcite content of Gv was always less than 3%, and no significant transformation of aragonite occurred. The stability ranking was Gv>Hv>Lv.

[0063] 3. Effect of γ-C2S on the stability of aragonite: Hv and γ-C2S were uniformly mixed at a mass ratio of 0.625% and 6.25%, respectively, and soaked in pure water for 48h, 72h, 96h, 120h, and 144h. The results showed that when the γ-C2S content was 0.625%, the transformation rate after 96h of soaking was only 5.5%, and after 144h, all the aragonite was transformed into calcite; when the content was 6.25%, no significant transformation occurred after 216h of soaking.

[0064] 4. Stability under different solution conditions: The aragonite samples were immersed in solutions of different compositions for 1 hour. The results are as follows: Figure 4 As shown, aragonite completely transforms into calcite after immersion in 1M and 0.1M CaCl2 solutions for 1 hour; the transformation rates after 1 hour in 0.1M NaOH, 0.01M NaOH, and 0.005M Ca(OH)2 solutions are 88%, 88%, and 86%, respectively; the transformation rate in 0.02M Ca(OH)2 solution is only 30%; and the transformation rate after immersion in γ-C2S solution (γ-C2S was soaked in pure water for 1 day and then the supernatant was taken) is 79%. This indicates that the transformation of aragonite is significantly inhibited in low-concentration Ca(OH)2 solutions and γ-C2S leachates.

[0065] 5. The comparison results of stirring and standing conditions showed that: when the Lv sample was soaked for 1 hour without stirring, 25% of the aragonite remained unchanged, while under stirring conditions, all of it was transformed into calcite within 5 minutes; after the addition of γ-C2S, the sample did not undergo significant transformation under stirring conditions.

[0066] 6. Solid coexistence experiments showed that under the conditions of liquid-solid ratio of 10, stirring at 100 rpm and soaking for 5 min, the crystal transformation rates of aragonite mixed with different solid powders were as follows: γ-C2S 7.2%, gypsum 9.8%, and quartz sand 60%. However, the aragonite in the sample mixed with nano-SiO2 and limestone powder was completely transformed into calcite.

[0067] The experimental data above show that this method can form high-purity and stable aragonite crystals under normal temperature and pressure conditions. The presence of γ-C2S significantly delays the dissolution and crystal transformation of aragonite, realizing the long-term stable existence of metastable aragonite in the unstable carbonization system.

[0068] The above embodiments and test results fully demonstrate that the preparation method provided by the present invention can successfully obtain high-purity and high-stability aragonite calcium carbonate crystals under mild conditions, effectively solving the application bottleneck caused by its metastable characteristics.

[0069] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0070] Furthermore, it should be noted that the scope of the methods and systems in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0071] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A stable preparation method for unsteady spheroidal calcium carbonate crystals, characterized in that, Includes the following steps: (1) Mix Ca(OH)2 and SiO2 powders at a molar ratio of 2:1, calcine them in a muffle furnace at 1350-1400℃ and keep them warm, and then cool them naturally to obtain γ-C2S powder; (2) Dissolve the amino acid crystal form regulator in deionized water to form a crystal form regulating solution with a concentration of 0.01~0.20 mol / L and a pH of 8.5~10.5; the amino acid crystal form regulator is one of glycine, aspartic acid or glutamic acid; (3) Add the γ-C2S powder obtained in step (1) to the crystal form regulation solution obtained in step (2), wherein the mass ratio of the γ-C2S powder to water is (1.5~3.0):100, stir evenly to obtain a mixed solution; wherein the γ-C2S powder is a slow-release calcium source with a low dissolution rate; (4) Introduce CO2 gas with a purity of ≥99% into the mixed system obtained in step (3) to carry out carbonization reaction. The CO2 gas flow rate is 0.2~1.0 L / min, the reaction temperature is 10~25℃, and the reaction pressure is atmospheric pressure. (5) Separate, clean and dry the solid product after the reaction in step (4) to obtain aragonite calcium carbonate crystals.

2. The method according to claim 1, characterized in that, After step (3) and before step (4), gypsum powder is added to the mixed solution as a crystal stabilizer, with the amount of gypsum being 0.1% to 0.5% of the mass of the mixed solution.

3. The method according to claim 1, characterized in that, In step (1), the heating rate is 8-12℃ / min, the calcination temperature is 1380℃, and the holding time is 1-3 hours; the purity of the γ-C2S powder is ≥90%, and the particle size is 5~30μm.

4. The method according to claim 2, characterized in that, The particle size range of the gypsum powder is 3~50μm.

5. The method according to claim 1, characterized in that, In step (4), the CO2 gas is introduced for 5 to 30 minutes.

6. The method according to claim 1, characterized in that, In step (5), the separation is one of static sedimentation, filtration or centrifugation; the washing is rinsing with deionized water and anhydrous ethanol in sequence; and the drying is carried out under vacuum or inert atmosphere at 40~80℃.

7. The method according to claim 1, characterized in that, In step (5), the aragonite calcium carbonate crystal has aragonite phase as the main crystal form and calcite phase content of less than 10%.

8. The method according to claim 1, characterized in that, The spheroidal calcium carbonate crystals are spherical or near-spherical with an average particle size of 1~20μm.

9. The method according to claim 1 or 2, characterized in that, The aragonite calcium carbonate crystals obtained in step (5) have a transformation rate of less than 3% from the aragonite phase to the calcite phase after being soaked in pure water with a liquid-to-solid ratio of 20 for 96 hours.

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