Basic praseodymium carbonate and preparation method thereof

Abstract

The invention relates to basic praseodymium carbonate and a preparation method thereof, and the preparation method comprises the following steps: introducing carbon dioxide gas into a praseodymium salt solution, adding an alkali solution to carry out carbonization reaction, and aging to obtain the basic praseodymium carbonate. The preparation method of the basic praseodymium carbonate is simple to operate, mild in condition and controllable in crystal form by combining a bubble dispersion technology with a carbonization reaction, so that the basic praseodymium carbonate with a good crystal form can be obtained in a relatively short time under a low-temperature condition, and effective regulation and control of the crystal form are realized by utilizing the advantage that homogeneous precipitation can be realized by a carbonization method.

Description

Technical Field

[0001] This invention relates to the field of rare earth hydrometallurgy, and in particular to a basic praseodymium carbonate and its preparation method. Background Technology

[0002] Praseodymium-neodymium metal is an important raw material for NdFeB permanent magnet materials. Its production process mainly employs an oxide electrolysis method based on a fluoride system, with praseodymium-neodymium oxide (a mixture of praseodymium oxide and neodymium oxide) as the raw material. Praseodymium-neodymium carbonate is an intermediate in the preparation of praseodymium-neodymium oxide. Furthermore, with the development of advanced technologies, the demand for praseodymium-neodymium metal products is increasingly stringent in terms of purity, crystal form, and particle size. Therefore, seeking new technologies for preparing high-purity praseodymium-neodymium carbonate with controllable crystal form is imperative.

[0003] The existing ammonium bicarbonate precipitation method for preparing praseodymium-neodymium carbonates tends to generate large-volume flocculent precipitates. This not only increases the difficulty of filtration but also results in small particle sizes of the rare earth oxides, making them prone to agglomeration and difficult to control in terms of morphology. Furthermore, it may introduce impurities into the feed solution, leading to substandard product quality. Currently, the ammonium bicarbonate precipitation method is challenging in preparing praseodymium-neodymium carbonates with different morphologies, especially spherical praseodymium-neodymium carbonates. Therefore, compared to the ammonium bicarbonate precipitation method, the carbonation method for preparing rare earth carbonates has certain advantages.

[0004] CO2 / HCO3 by carbonization - / CO3 2- The buffer system can achieve low-saturation precipitation, thereby improving the crystal quality of rare earth carbonates. Therefore, the carbonation method is particularly suitable for high-end rare earth materials (such as phosphors and catalyst precursors) that have strict requirements on crystal morphology and particle size. It is a typical application of green chemistry in the rare earth field.

[0005] The existing ammonium bicarbonate precipitation method is a liquid-liquid precipitation reaction crystallization. However, the method of directly mixing two solutions often results in a relatively fast reaction rate and a relatively difficult-to-control precipitation process, making it difficult to regulate the crystal quality such as the purity, particle size distribution, and morphology of the rare earth carbonate produced.

[0006] Using CO2 gas as a carbon source transforms the traditional liquid-liquid precipitation process into a gas-liquid two-phase reaction crystallization process, increasing the controllable operational variables and making the crystallization process more controllable. This method can also be applied to the absorption and capture of CO2 waste gas. While gas-liquid reaction crystallization with carbon dioxide can avoid the introduction of impurity ions, compared to the liquid-liquid precipitation process, the complexity of the gas-liquid two-phase reaction crystallization process itself, the lack of basic data, and the unclear understanding of its fundamental principles increase the difficulty of studying this system, making the gas-liquid reaction crystallization process relatively complex and challenging to control.

[0007] The gas-liquid reaction crystallization process is complex, involving several processes such as carbon dioxide absorption and dissolution, chemical reactions, crystal nucleation and growth. These processes are coupled together, accompanied by the exchange of matter and energy. Furthermore, temperature has a significant impact on the gas-liquid reaction crystallization process; higher temperatures result in faster crystal growth rates and a greater likelihood of forming larger grains. At high temperatures, particle collisions are intense, and the mutual constraints between particles lead to varying degrees of deformation, thereby altering the crystal's morphology and size. The evolution of crystal shape during crystallization is a complex process controlled by multiple factors. Spherical morphologies are more difficult to prepare than plate-like basic praseodymium carbonate due to the relatively stable overall molecular radius and the restricted free movement of rare earth ions during crystallization.

[0008] Although the carbonation method has advantages such as simple operation, high product yield and high purity, the process conditions of the carbonation method are not easy to control, and the resulting products are prone to uneven particle size. Therefore, how to prepare monodisperse basic praseodymium carbonate with regular morphology and uniform particle size is still an urgent problem to be solved. Summary of the Invention

[0009] To solve the above-mentioned technical problems, the present invention aims to provide a basic praseodymium carbonate and its preparation method. The preparation method of basic praseodymium carbonate provided by the present invention effectively utilizes carbon dioxide carbonation to prepare a basic praseodymium carbonate precursor in an acidic system, prepares spherical praseodymium oxide with uniform particle distribution, uniform average particle size, and good dispersibility, and ultimately achieves precise control of the morphology and structure of praseodymium oxide.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing basic praseodymium carbonate, the method comprising the following steps:

[0012] Carbon dioxide gas is passed into a praseodymium salt solution, an alkaline solution is added to carry out a carbonation reaction, and after aging, basic praseodymium carbonate is obtained.

[0013] Carbonization is a typical gas-liquid or gas-liquid-solid multiphase reaction process, theoretically based on the two-film theory, which explains the absorption mechanism of gaseous absorbents by liquid absorbents. When CO2 dissolves in the liquid phase, it is converted into H2CO3 and HCO3-. - and CO3 2- It exists in three forms and reacts with metal ions in solution to form carbonates or bicarbonates.

[0014] The carbonization process mainly includes three stages: gaseous CO2 enters the solution and rapidly dissolves in water to generate H2CO3, and H2CO3 ionizes to generate CO3. 2- RE2(CO3)3 ions dissolve, resulting in the formation of RE2(CO3)3 particles. Among them, OH...- The addition of ions will neutralize the H+ released from the ionization of H2CO3. + To promote the precipitation of rare earth carbonates and advance the reaction, NaOH solution or NH3·H2O solution is added during the carbonation process. The OH groups in the solution will then be present. - The number of ions increases.

[0015] The carbonation synthesis mechanism mainly encompasses two aspects: the carbonation chemical reaction mechanism and the rare earth carbonate crystal form control mechanism. During the carbonation reaction, the dissolution of CO2 gas is considered a key control step. The CO2 gas dissolution rate (r...) A The relationship between r and the pH of the solution can be expressed by the following formula: A =Ak[OH - [CO2]-[CO2] eq In this formula, [OH] - ] represents OH in the solution - The concentration of CO2; [CO2] is the concentration of CO2 before chemical equilibrium is reached; [CO2] eq This represents the CO2 concentration under equilibrium conditions; k represents the rate constant; and A represents a parameter related to the contact area between the CO2 bubbles and the liquid, which can more accurately reflect the carbonation kinetics in actual operation. When the introduced CO2 gas forms smaller bubbles, the gas-liquid contact area increases accordingly, the value of A increases significantly, the CO2 dissolution rate accelerates, which is beneficial to the formation of rare earth carbonates. Therefore, by optimizing bubble dispersion technology, the formation efficiency of rare earth carbonates can be effectively improved, thereby achieving precise control of the rare earth carbonate crystal form.

[0016] This invention effectively controls the average particle size and uniformity. Its underlying mechanism lies in the fact that the carbonation reaction is a controllable, slow nucleation process involving gas-liquid-solid coupling. This process provides a uniform supply of carbonate ions and effectively controls the supersaturation of the reaction, resulting in a stable crystal nucleation rate and the formation of basic praseodymium carbonate particles with a narrow average particle size distribution. Supersaturation is crucial in the crystallization process; higher supersaturation leads to a rapid increase in the nucleation rate, resulting in faster crystal growth and the formation of particles with a large average particle size and uneven size distribution.

[0017] This invention provides a simple, mild, and controllable method for preparing basic praseodymium carbonate by utilizing bubble dispersion technology. This method enables the preparation of basic praseodymium carbonate with good crystal form under low temperature conditions and short aging time. Furthermore, it leverages the advantage of homogeneous precipitation through carbonation to achieve effective control of crystal form.

[0018] Furthermore, the method of the present invention can obtain basic praseodymium carbonate with high purity and small average particle size. Based on this, spherical praseodymium oxide with high purity and small average particle size can be obtained by calcination.

[0019] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0020] Preferably, the concentration of praseodymium ions in the praseodymium salt solution is 0.1 mol / L to 0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] This invention further controls the concentration of praseodymium ions in the praseodymium salt solution to be between 0.1 mol / L and 0.5 mol / L. The concentration of praseodymium ions has a significant impact on the particle size of the crystallized product. Within a specific concentration range, the higher the concentration, the larger the particle size of the crystallized product. If the concentration of praseodymium ions is too high, the stirring may not be sufficient, leading to the agglomeration of some crystal grains and the formation of amorphous aggregates. If the concentration of praseodymium ions is too low, the supersaturation is very low, the number of nuclei is small, and the resulting crystallized product will have a coexistence of large and small particles, with a wide particle size distribution and uneven size.

[0022] Preferably, the praseodymium salt includes any one or a combination of at least two of praseodymium chloride, praseodymium sulfate, or praseodymium nitrate. Typical but non-limiting combinations include combinations of praseodymium chloride and praseodymium sulfate, combinations of praseodymium sulfate and praseodymium nitrate, combinations of praseodymium chloride and praseodymium nitrate, and combinations of praseodymium chloride, praseodymium sulfate, and praseodymium nitrate.

[0023] Preferably, the praseodymium salt solution also includes a crystal form control agent.

[0024] Preferably, the crystal form control agent comprises any one or at least two combinations of polyethylene glycol, CTAB (hexadecyltrimethylammonium bromide), or urea. Typical but non-limiting combinations include combinations of polyethylene glycol and CTAB, combinations of CTAB and urea, combinations of polyethylene glycol and urea, and combinations of polyethylene glycol, CTAB, and urea.

[0025] Preferably, the molecular weight of the polyethylene glycol is 600-10000.

[0026] Simple carbonization reactions often fail to yield products with ideal crystal forms or morphologies. Adding appropriate crystal form control agents to the reaction solution can regulate the crystal growth of rare earth carbonates, altering the crystal morphology and controlling the crystal size. Crystal form control agents intervene in the crystal precipitation process by binding with ions, influencing induction time, interacting with soluble intermediate clusters, and inhibiting crystal growth. Neither direct liquid-liquid mixing nor gas-liquid reaction crystallization can directly produce small-sized crystals in a single step; however, adding crystal form control agents offers the potential to regulate crystal size, thereby obtaining even smaller crystals.

[0027] The crystal form control agent in this invention includes any one or at least two combinations of polyethylene glycol, CTAB (hexadecyltrimethylammonium bromide), or urea, wherein polyethylene glycol is a nonionic surfactant, CTAB is a cationic surfactant, and urea is a non-surfactant.

[0028] Preferably, the concentration of the crystal form control agent in the praseodymium salt solution is 1 g / L-10 g / L, for example, it can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] This invention further controls the concentration of the crystal form control agent in the praseodymium salt solution to 1 g / L-10 g / L. The amount of crystal form control agent added has a significant impact on the morphology of the crystallized product. Adding the crystal form control agent can effectively control the morphology of the crystallized product. Within a specific range, the crystallized product can tend to be spherical and have a more uniform particle size. If the concentration of the crystal form control agent is too high, the crystal form control agent will adhere to the surface of the crystallized product, hindering the normal growth of the crystallized product and thus affecting the carbon dioxide mass transfer process. If the concentration of the crystal form control agent is too low, the morphology improvement will be insignificant, and the crystal form control agent will have little effect.

[0030] Preferably, the flow rate of the carbon dioxide gas is 0.5 L / min to 1.5 L / min, for example, it can be 0.5 L / min, 0.6 L / min, 0.7 L / min, 0.8 L / min, 0.9 L / min, 1.0 L / min, 1.1 L / min, 1.2 L / min, 1.3 L / min, 1.4 L / min or 1.5 L / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the pressure of the carbon dioxide gas is 0.04 MPa-0.12 MPa, for example, it can be 0.04 MPa, 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.10 Pa, 0.11 MPa or 0.12 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the alkaline solution comprises any one or at least two combinations of ammonia, sodium hydroxide, or potassium hydroxide. Typical but non-limiting combinations include a combination of ammonia and sodium hydroxide, a combination of sodium hydroxide and potassium hydroxide, a combination of ammonia and potassium hydroxide, and a combination of ammonia, sodium hydroxide, and potassium hydroxide.

[0033] Preferably, the concentration of the alkaline solution is 1 mol / L to 5 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the pH of the carbonization reaction is 5.0-5.5, for example, it can be 5.0, 5.1, 5.2, 5.4, 5.3 or 5.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] This invention further controls the pH of the carbonation reaction to 5.0-5.5, as the pH of the carbonation reaction has a significant impact on the crystal form of the product. When the pH is too low (insufficient alkali solution), the average particle size of the product is the smallest, but the crystallization is incomplete and the crystals are severely stacked. When the pH is 5.0-5.5, the resulting crystals are smooth spherical particles with a uniform average particle size. When the pH is too high (excessive alkali solution), the average particle size of the product increases, and the size distribution is uneven. This is because at low ammonia content, the subsequent growth momentum of the crystals is insufficient, making it difficult to obtain products with suitable morphology and average particle size. Only when the ammonia content is within the appropriate range can the crystallization be more complete, resulting in basic praseodymium carbonate particles with a uniform average particle size.

[0036] Preferably, the carbonization reaction temperature is 60℃-80℃, for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0037] Preferably, the carbonization reaction time is 10 min to 30 min, for example, it can be 10 min, 12 min, 15 min, 18 min, 20 min, 25 min or 30 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the carbonization reaction is accompanied by stirring at a speed of 600 rpm to 1000 rpm, such as 600 rpm, 700 rpm, 800 rpm, 900 rpm, 950 rpm or 1000 rpm, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the aging time is 1-5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours or 5 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the aging temperature is 25℃-80℃, for example, it can be 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0041] This invention further controls the aging time to 1-5 hours. Studies have shown that the aging process is a typical Ostwald ripening process, characterized by the dissolution of small particles and the growth of large particles. Therefore, the average particle size distribution widens with the extension of aging time. This invention suppresses the Ostwald ripening process by aging at low temperatures, resulting in a uniform average particle size of the generated basic praseodymium carbonate particles. An appropriate aging time is beneficial for obtaining spherical or near-spherical particles with uniform particle size. If the aging time is too short, ripening is insufficient, the system surface energy remains high, the crystal nuclei fail to grow sufficiently, and the resulting product has low crystallinity and many internal defects. If the aging time is too long, over-ripening occurs, and the continued Ostwald ripening drives further grain growth, increasing the particle size and leading to agglomeration.

[0042] Preferably, after the aging process is completed, before obtaining basic praseodymium carbonate, the aging product is further subjected to solid-liquid separation, washing, and drying.

[0043] Preferably, the drying time is 24h-48h, for example, it can be 24h, 26h, 28h, 30h, 32h, 35h, 38h, 40h, 42h, 45h or 48h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] Preferably, the drying temperature is 80℃-120℃, for example, it can be 80℃, 85℃, 90℃, 100℃, 110℃ or 120℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0046] (1) Prepare a praseodymium chloride solution with a concentration of 0.1 mol / L to 0.5 mol / L and a crystal form control agent concentration of 1 g / L to 10 g / L;

[0047] (2) Introduce carbon dioxide gas at a pressure of 0.04MPa-0.12MPa and a flow rate of 0.5L / min-1.5L / min into the praseodymium chloride solution in step (1), add an alkaline solution with a concentration of 1mol / L-5mol / L to maintain the pH at 5.0-5.5, and stir at 600rpm-1000rpm during the process. Carbonize at 60℃-80℃ for 10min-30min, stop the gas introduction, and age at 25℃-80℃ for 1h-5h to obtain the product;

[0048] (3) The aged product obtained in step (2) is subjected to solid-liquid separation, washed until the washing liquid is neutral, and dried at 80℃-120℃ for 24h-48h to obtain basic praseodymium carbonate.

[0049] In a second aspect, the present invention provides a basic praseodymium carbonate, which is prepared according to the preparation method described in the first aspect; the basic praseodymium carbonate has a sphericity of 0.8-1 and a particle size of 5μm-15μm.

[0050] This invention defines a sphericity ψ ≥ 0.9 as quasi-spherical, a sphericity ψ between 0.7 and 0.9 as ellipsoidal or irregular, and a sphericity ψ < 0.7 as clearly not spherical. The formula for calculating sphericity is generally as follows: Where A is the projected area and P is the projected perimeter.

[0051] The basic praseodymium carbonate provided by this invention has uniform particle size, good crystal form, and spherical morphology. It also has high purity and small particle size, and is expected to be applied to the preparation of high-end rare earth materials. Based on this, spherical praseodymium oxide with high purity and small average particle size can be obtained by calcination.

[0052] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0053] Compared with the prior art, the present invention has at least the following beneficial effects:

[0054] (1) This invention provides a simple, mild and controllable method for preparing basic praseodymium carbonate by combining bubble dispersion technology with carbonation reaction, enabling the preparation of basic praseodymium carbonate with good crystal form in a short time under low temperature conditions, and utilizing the advantage of homogeneous precipitation by carbonation method to achieve effective control of crystal form.

[0055] (2) The basic praseodymium carbonate provided by the present invention has a uniform average particle size, good crystal form, controllable morphology, high purity and small average particle size, and is expected to be applied to the preparation of high-end rare earth materials. On this basis, spherical praseodymium oxide with high purity and small average particle size can be obtained by calcination. Attached Figure Description

[0056] Figure 1 This is a SEM image of the basic praseodymium carbonate particles prepared in Example 1 of this invention at a scale of 50 μm.

[0057] Figure 2 This is a SEM image of the basic praseodymium carbonate particles prepared in Example 1 of this invention at a scale of 10 μm.

[0058] Figure 3 This is a SEM image of the basic praseodymium carbonate particles prepared in Example 2 of this invention at a scale of 10 μm.

[0059] Figure 4 This is a SEM image of the disc-shaped basic praseodymium carbonate particles prepared in Example 3 of this invention at a scale of 1 μm.

[0060] Figure 5 This is a SEM image of the elliptic basic praseodymium carbonate particles prepared in Example 4 of this invention at a scale of 1 μm.

[0061] Figure 6 This is a SEM image of the elliptical, disc-shaped basic praseodymium carbonate particles prepared in Example 5 of the present invention at a scale of 0.5 μm.

[0062] Figure 7 This is a SEM image of the basic praseodymium carbonate particles prepared in Example 6 of the present invention at a scale of 1 μm.

[0063] Figure 8 This is a SEM image of the flake-shaped basic praseodymium carbonate particles prepared in Example 7 of the present invention at a scale of 5 μm.

[0064] Figure 9 This is a SEM image of the flake-shaped basic praseodymium carbonate particles prepared in Example 8 of the present invention at a scale of 10 μm.

[0065] Figure 10This is a SEM image of the blocky basic praseodymium carbonate particles prepared in Example 9 of the present invention at a scale of 1 μm.

[0066] Figure 11 This is a SEM image of the flake-shaped basic praseodymium carbonate particles prepared in Example 10 of the present invention at a scale of 5 μm.

[0067] Figure 12 This is a SEM image of the cake-shaped basic praseodymium carbonate particles prepared in Example 11 of the present invention at a scale of 1 μm.

[0068] Figure 13 This is a SEM image of the flake-shaped basic praseodymium carbonate particles prepared in Comparative Example 1 of the present invention at a scale of 5 μm. Detailed Implementation

[0069] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0070] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0071] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0072] Example 1

[0073] This embodiment provides a method for preparing basic praseodymium carbonate, the method comprising the following steps:

[0074] (1) Prepare a praseodymium chloride solution with a concentration of 0.1 mol / L;

[0075] (2) Introduce carbon dioxide gas at a pressure of 0.04 MPa and a flow rate of 1 L / min into the praseodymium chloride solution in step (1), add ammonia water with a concentration of 1 mol / L to maintain the pH at 5.0-5.5, and stir at 800 rpm during the process. Carbonize at 60°C for 20 min, stop the gas introduction, and age at 25°C for 2 h to obtain the product;

[0076] (3) The aged product obtained in step (2) is subjected to solid-liquid separation, washed until the washing liquid is neutral, and dried at 80°C for 24 hours to obtain basic praseodymium carbonate.

[0077] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 1 and Figure 2 As shown in the figure, the basic praseodymium carbonate is spherical with a sphericity of 0.998, and the particle size is uniform, ranging from 5 to 10 μm.

[0078] Example 2

[0079] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between the preparation method and that in Example 1 is that the concentration of the praseodymium chloride solution in step (1) is 0.2 mol / L.

[0080] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 3 As shown, from Figure 3 It can be seen that step (3) yields basic praseodymium carbonate with a sphericity of 0.988 and a particle size of 10-15 μm, and the particle size is uniform.

[0081] As can be seen from Examples 1 and 2, the desired praseodymium carbonate crystals with uniform average particle size and complete morphology can be obtained in a concentration range of 0.1 mol / L to 0.5 mol / L.

[0082] Example 3

[0083] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between the preparation method and that in Example 1 is that: step (1) prepares a praseodymium chloride solution with a concentration of 0.1 mol / L and a polyethylene glycol (molecular weight of 2000) concentration of 1 g / L.

[0084] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 4 As shown, from Figure 4 It can be seen that step (3) yields a disc-shaped basic praseodymium carbonate with a sphericity of 0.991 and an average particle size of about 1 μm, which has a central depression.

[0085] Compared to the product prepared without polyethylene glycol, the average particle size of the precipitate obtained after adding polyethylene glycol as a crystal form control agent was significantly reduced, and the morphology changed from spherical to disc-shaped. XRD analysis showed that both were basic praseodymium carbonate.

[0086] Example 4

[0087] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between the preparation method and that in Example 1 is that step (1) prepares a praseodymium chloride solution with a concentration of 0.1 mol / L and a CTAB concentration of 1 g / L.

[0088] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 5 As shown, from Figure 5 It can be seen that step (3) yields stacked ellipsoidal basic praseodymium carbonate.

[0089] Compared to the product prepared without CTAB, the precipitate obtained after adding the crystal form control agent CTAB was significantly smaller in size, with an average particle size of about 1 μm. The morphology changed from spherical to ellipsoidal, and the sphericity of the product was 0.880. XRD analysis showed that both were basic praseodymium carbonate.

[0090] Example 5

[0091] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between the preparation method and that in Example 1 is that: step (1) prepares a praseodymium chloride solution with a concentration of 0.1 mol / L and a urea concentration of 1 g / L.

[0092] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 6 As shown, from Figure 6 It can be seen that step (3) yields an elliptical, cake-shaped precipitate of basic praseodymium carbonate with an average particle size of about 1 μm.

[0093] Compared to the product prepared without urea, the precipitate obtained after adding urea, a crystal form control agent, was significantly smaller, with an average particle size of about 1 μm. The morphology changed from spherical to elliptical disc shape, and the sphericity of the product was 0.997. XRD analysis showed that both were basic praseodymium carbonate.

[0094] Example 6

[0095] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between this method and that in Example 1 is that the pH is maintained at 7-7.5 in step (2), while the rest of the preparation method remains unchanged.

[0096] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 7 As shown, from Figure 7 It can be seen that step (3) yields a composite product of 1-5 μm spherical basic praseodymium carbonate with a sphericity of 0.983 and needle-shaped basic praseodymium carbonate with a length of about 1 μm. Under these conditions, the crystal morphology is not uniform, and it is impossible to obtain a simple and uniform spherical basic praseodymium carbonate.

[0097] Example 7

[0098] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between this method and that in Example 1 is that the pH is maintained at 4.0-4.5 in step (2), while the rest of the preparation method remains unchanged.

[0099] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 8 As shown, from Figure 8 It can be seen that step (3) yields praseodymium carbonate flakes with a length of 5-10 μm and a width of about 1 μm.

[0100] Example 8

[0101] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between this method and that in Example 1 is that the carbonization reaction in step (2) is carried out at a temperature of 25°C.

[0102] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 9 As shown, from Figure 9 It can be seen that step (3) yields sheet-like basic praseodymium carbonate precipitates with a large difference in aspect ratio, a length of 5-10 μm and a width of 1-5 μm.

[0103] Example 9

[0104] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between this method and that in Example 1 is that the carbonization reaction in step (2) is carried out at a temperature of 100°C.

[0105] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 10 As shown, from Figure 10 It can be seen that step (3) yields irregular blocky basic praseodymium carbonate of about 1 μm.

[0106] Example 10

[0107] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between this method and Example 1 is that the mass concentration of polyethylene glycol in step (2) is 50 g / L.

[0108] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 11 As shown, from Figure 11 It can be seen that step (3) yields irregular flake-shaped basic praseodymium carbonate with a diameter of less than 1 μm.

[0109] Example 11

[0110] This embodiment provides a method for preparing basic praseodymium carbonate. The difference between this method and Example 1 is that the mass concentration of polyethylene glycol in step (2) is 0.5 g / L.

[0111] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 12 As shown, from Figure 12 It can be seen that step (3) yields irregular cake-shaped basic praseodymium carbonate with a diameter of 1-5 μm.

[0112] Comparative Example 1

[0113] This comparative example provides a method for preparing basic praseodymium carbonate. The difference between this method and Example 1 is that step (2) is replaced by: preparing a 1 mol / L ammonium bicarbonate solution and introducing it into the praseodymium chloride solution at a speed of 5 rpm using a peristaltic pump. The speed of the peristaltic pump is controlled to maintain the pH of the system at 5.0-5.5 during the carbonization process. The reaction is terminated after 20 min and aged at 25°C for 2 h to obtain the precipitated product. That is, carbon dioxide is not introduced in step (2), only an alkaline solution is introduced.

[0114] SEM images of the prepared basic praseodymium carbonate are shown below. Figure 13 As shown, from Figure 13 It can be seen that step (3) yields sheet-like basic praseodymium carbonate precipitates with similar aspect ratios, both around 1-5 μm.

[0115] test:

[0116] The basic praseodymium carbonate prepared in the examples and comparative examples was tested, and the test results are shown in Table 1 below.

[0117] Table 1

[0118]

[0119] The test results show that:

[0120] (1) As can be seen from Examples 1-2 and Examples 3-5, the present invention can obtain spherical basic praseodymium carbonate crystals by adding one or more of polyethylene glycol (molecular weight of 600-10000), CTAB or urea as crystal form control agents. Adding crystal form control agents can significantly reduce the size of the obtained basic praseodymium carbonate crystals, and the morphology of the obtained products will be different depending on the addition of different crystal form control agents. Therefore, crystal form control agents play an important role in the preparation of basic praseodymium carbonate precipitate. It is expected that by making good use of crystal form control agents, basic praseodymium carbonate with good crystallization, controllable morphology and small average particle size can be obtained.

[0121] (2) By comparing Example 1 with Examples 6-7, it can be seen that the present invention further controls the pH of the carbonization reaction to 5.0-5.5. The pH of the carbonization reaction has an important influence on the crystal form of the product. When the pH is too low (insufficient amount of alkaline solution added), the average particle size of the product is the smallest, but the crystallization is incomplete and the crystal stacking is serious. When the pH is 5.0-5.5, the crystal morphology is smooth spherical particles with uniform average particle size. When the pH is too high (excessive amount of alkaline solution added), the average particle size of the product increases and the size distribution is uneven. This is because under low ammonia content, the subsequent growth momentum of the crystal is insufficient, and it is difficult to obtain a product with a suitable morphology and average particle size. Only when the ammonia content is in a suitable range can the crystallization be more complete, and basic praseodymium carbonate particles with uniform average particle size are obtained.

[0122] (3) A comparison between Example 1 and Examples 8-9 shows that when the carbonization temperature is too low, the product obtained at 25°C also transforms into a plate-like morphology compared to the spherical product prepared at 60°C. XRD analysis shows that both are basic praseodymium carbonate. In the process of preparing basic praseodymium carbonate by carbonization, the product is elongated and thin at lower temperatures, while it exhibits a spherical structure with smooth edges at higher temperatures. It is evident that temperature is also a major factor affecting the morphology of the crystallized product, regulating the formation rate and growth speed of the crystal nucleus, thereby determining the morphology and structure of the product.

[0123] (4) By comparing Example 1 with Examples 10-11, it can be seen that the present invention further controls the concentration of the crystal form control agent in the praseodymium salt solution to 1g / L-10g / L. The amount of crystal form control agent added has a great influence on the crystal morphology. Adding crystal form control agent can effectively control the morphology of the crystal product. Within a certain range, the crystal product can tend to be spherical and the particle size is more uniform. If the concentration of crystal form control agent is too high, the crystal form control agent will adhere to the surface of the crystal product, hindering the normal growth of the crystal product and thus affecting the mass transfer process of carbon dioxide. If the concentration of crystal form control agent is too low, the morphology improvement will not be obvious and the crystal form control agent will not play a significant role.

[0124] (5) As can be seen from Example 1 and Comparative Example 1, when the precipitant is ammonium bicarbonate solution instead of carbon dioxide gas, the size of the precipitate obtained by ammonium bicarbonate is slightly smaller and the morphology changes to flake-like compared to the product prepared by the carbonation method. XRD analysis shows that both are basic praseodymium carbonate. Therefore, changing the type of precipitant will change the morphology of the crystals and the size of the precipitate will also change accordingly, but the type of product remains unchanged.

[0125] In summary, this invention provides a simple, mild, and controllable method for preparing basic praseodymium carbonate by combining bubble dispersion technology with carbonation reaction. This method enables the preparation of basic praseodymium carbonate with good crystal form at low temperature and in a short time. Furthermore, the carbonation method allows for homogeneous precipitation, thus achieving effective control over the crystal form.

[0126] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing basic praseodymium carbonate, characterized in that, The preparation method includes the following steps: Carbon dioxide gas is passed into a praseodymium salt solution, an alkaline solution is added to carry out a carbonation reaction, and after aging, basic praseodymium carbonate is obtained.

2. The preparation method according to claim 1, characterized in that, In the praseodymium salt solution, the concentration of praseodymium ions is 0.1 mol / L to 0.5 mol / L; Preferably, the praseodymium salt includes any one or a combination of at least two of praseodymium chloride, praseodymium sulfate, or praseodymium nitrate.

3. The preparation method according to claim 1 or 2, characterized in that, The praseodymium salt solution also includes a crystal form control agent; Preferably, the crystal form control agent includes any one or at least a combination of two of polyethylene glycol, CTAB, or urea; Preferably, the concentration of the crystal form control agent in the praseodymium salt solution is 1 g / L-10 g / L.

4. The preparation method according to any one of claims 1-3, characterized in that, The flow rate of the carbon dioxide gas is 0.5 L / min to 1.5 L / min; Preferably, the pressure of the carbon dioxide gas is 0.04 MPa-0.12 MPa.

5. The preparation method according to any one of claims 1-4, characterized in that, The alkaline solution includes any one or at least a combination of two of ammonia, sodium hydroxide, or potassium hydroxide. Preferably, the concentration of the alkaline solution is 1 mol / L to 5 mol / L.

6. The preparation method according to any one of claims 1-5, characterized in that, The pH of the carbonization reaction is 5.0-5.5; Preferably, the carbonization reaction temperature is 60℃-80℃; Preferably, the carbonization reaction takes 10-30 minutes; Preferably, the carbonization reaction is accompanied by stirring at a speed of 600 rpm to 1000 rpm.

7. The preparation method according to any one of claims 1-6, characterized in that, The aging time is 1-5 hours; Preferably, the aging temperature is 25℃-80℃.

8. The preparation method according to any one of claims 1-7, characterized in that, After the aging process is completed, before obtaining basic praseodymium carbonate, the aging product is further subjected to solid-liquid solid-liquid separation, washing, and drying. Preferably, the drying time is 24h-48h; Preferably, the drying temperature is 80℃-120℃.

9. The preparation method according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: (1) Prepare a praseodymium chloride solution with a concentration of 0.1 mol / L to 0.5 mol / L and a crystal form control agent concentration of 1 g / L to 10 g / L; (2) Introduce carbon dioxide gas at a pressure of 0.04MPa-0.12MPa and a flow rate of 0.5L / min-1.5L / min into the praseodymium chloride solution in step (1), add an alkaline solution with a concentration of 1mol / L-5mol / L to maintain the pH at 5.0-5.5, and stir at 600rpm-1000rpm during the process. Carbonize at 60℃-80℃ for 10min-30min, stop the gas introduction, and age at 25℃-80℃ for 1h-5h to obtain the product; (3) The aged product obtained in step (2) is subjected to solid-liquid separation, washed until the washing liquid is neutral, and dried at 80℃-120℃ for 24h-48h to obtain basic praseodymium carbonate.

10. A basic praseodymium carbonate, characterized in that, The basic praseodymium carbonate is prepared by the preparation method according to any one of claims 1-9; the basic praseodymium carbonate has a sphericity of 0.8-1 and a particle size of 5μm-15μm.

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