A hexagonal basic lanthanum carbonate and a method for preparing the same

Abstract

This invention relates to a hexagonal basic lanthanum carbonate and its preparation method, belonging to the field of rare earth compound technology. It addresses at least one of the problems of existing methods for synthesizing hexagonal basic lanthanum carbonate, including the presence of impurity phases in the product, dependence on high-temperature and high-pressure synthesis conditions, high cost and energy consumption, long reaction cycles, and low production efficiency, which are unfavorable for large-scale continuous production. This invention uses a lanthanum salt solution and a mixed precipitant, controlling the molar ratio of NH3·H2O and ammonium bicarbonate in the mixed precipitant, as well as the ratio of the total amount of NH3·H2O and ammonium bicarbonate added to water to the amount of lanthanum ions, to carry out the precipitation reaction and aging. Under normal pressure and mild conditions, a single-phase hexagonal basic lanthanum carbonate is prepared, avoiding the high energy consumption and safety hazards caused by high-temperature and high-pressure conditions. The process is simple and suitable for large-scale production.

Description

Technical Field

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

[0002] Lanthanum hydroxide carbonate (usually with the chemical formula LaCO3OH or La2(CO3)2(OH)2·H2O) is an important rare-earth functional material with broad application prospects in catalysis, optical materials, electronic ceramics, and biomedicine. Among them, hexagonal lanthanum hydroxide carbonate (with a chemical formula closer to LaCO3OH, corresponding to PDF card 26-0815) exhibits unique advantages in catalysis and functional materials applications due to its specific crystal structure and surface properties. Therefore, achieving its precise and controllable synthesis has significant research value and commercial significance.

[0003] In the existing technology, the synthesis method of hexagonal basic lanthanum carbonate produces products with impurity phases and depends on high temperature (e.g., >100℃) and high pressure synthesis conditions. It requires the use of special pressure vessels such as high pressure reactors or hydrothermal synthesis reactors, and requires supporting auxiliary systems such as pressure monitoring and safety protection, resulting in high equipment costs. Maintaining high temperature for a long time leads to high energy consumption and high operating costs. After the reaction, it is necessary to depressurize and cool down, resulting in long reaction cycles and low production efficiency, which is not conducive to large-scale continuous production. Summary of the Invention

[0004] In view of the above analysis, the present invention aims to provide a hexagonal basic lanthanum carbonate and its preparation method, so as to solve at least one of the problems of the existing synthesis methods of hexagonal basic lanthanum carbonate, such as the presence of impurity phases in the products, dependence on high temperature and high pressure synthesis conditions, high equipment and operating costs, high energy consumption, long reaction cycle, low production efficiency, and unfavorable for large-scale continuous production.

[0005] On one hand, the present invention provides a method for preparing hexagonal basic lanthanum carbonate, comprising the following steps: S1. Prepare a lanthanum salt solution and a mixed precipitant, wherein the mixed precipitant comprises NH3·H2O and ammonium bicarbonate, and the molar ratio of NH3·H2O to ammonium bicarbonate is 0.6~1.2:1; S2. The lanthanum salt solution and the mixed precipitant are added to water in a parallel flow to carry out a precipitation reaction. The ratio of the total amount of NH3·H2O and ammonium bicarbonate added to the water to the amount of lanthanum ions is always maintained at 3.5~4.0:1 to obtain the first reaction slurry. S3. The first reaction slurry is aged at 75~95℃ to obtain the second reaction slurry; S4. The second reaction slurry is filtered, washed, and dried to obtain hexagonal basic lanthanum carbonate.

[0006] Furthermore, in step S3, the first reaction slurry is aged at 75-95°C for 60-180 minutes.

[0007] Furthermore, the pH value of the first reaction slurry is greater than or equal to 7.5.

[0008] Further, in S1, the total molar concentration of NH3·H2O and ammonium bicarbonate in the mixed precipitant is 2~6 mol / L.

[0009] Furthermore, the precipitation reaction temperature in S2 is 25~35℃, and the precipitation reaction time is 20-60min.

[0010] Furthermore, the molar concentration of lanthanum ions in the lanthanum salt solution in S1 is 0.25~1.2 mol / L.

[0011] Furthermore, the lanthanum salt solution in S1 includes one or more of lanthanum chloride solution, lanthanum sulfate solution, lanthanum nitrate solution, and lanthanum acetate solution.

[0012] On the other hand, the present invention also provides a hexagonal basic lanthanum carbonate, which is prepared according to the above-described method for preparing hexagonal basic lanthanum carbonate.

[0013] Furthermore, in the XRD pattern of the hexagonal basic lanthanum carbonate, the ratio of the peak intensities of the characteristic peaks corresponding to the (300) crystal plane and the (302) crystal plane is 1.1~1.3, and the ratio of the peak intensities of the characteristic peaks corresponding to the (330) crystal plane and the (304) crystal plane is 1.3~1.6.

[0014] Furthermore, the particle size D of the hexagonal basic lanthanum carbonate is... v 50 represents 10~20µm.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. The XRD pattern of the hexagonal basic lanthanum carbonate of the present invention contains only the characteristic diffraction peak of hexagonal basic lanthanum carbonate (26-0815), without other impurity peaks, and the product has high crystallinity and a single crystal phase.

[0016] 2. Compared with existing technologies that use high temperature and high pressure to overcome the reaction energy barrier to obtain hexagonal basic lanthanum carbonate, this invention successfully synthesizes a single hexagonal basic lanthanum carbonate under normal pressure and mild liquid phase reaction conditions by precisely controlling the ratio of the mixed precipitant and the total amount of NH3·H2O and ammonium bicarbonate added to the water during the precipitation reaction to the amount of lanthanum ions. This represents a technological leap from "high temperature and high pressure" to "normal pressure and mild temperature".

[0017] 3. The preparation method of the present invention avoids the problems of high energy consumption and safety hazards caused by high temperature and high pressure conditions, and does not use any organic reagents. The process is simple and suitable for large-scale production.

[0018] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0019] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0020] Figure 1 The XRD pattern of hexagonal basic lanthanum carbonate in Example 1 of this invention; Figure 2 The XRD pattern of cubic basic lanthanum carbonate in Comparative Example 1 of this invention; Figure 3 The XRD pattern of lanthanum carbonate in Comparative Example 2 of this invention; Figure 4 The XRD pattern of lanthanum carbonate in Comparative Example 3 of this invention; Figure 5 This is a particle size distribution diagram of hexagonal basic lanthanum carbonate in Example 1 of the present invention; Figure 6 This is a scanning electron microscope image of hexagonal basic lanthanum carbonate in Example 1 of the present invention; Figure 7 This is a scanning electron microscope image of cubic basic lanthanum carbonate in Comparative Example 1 of this invention. Figure 8 This is a scanning electron microscope image of lanthanum carbonate in Comparative Example 2 of the present invention; Figure 9 This is a scanning electron microscope image of lanthanum carbonate in Comparative Example 3 of the present invention. Detailed Implementation

[0021] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0022] An embodiment of the present invention discloses a method for preparing hexagonal basic lanthanum carbonate, comprising the following steps: S1. Prepare a lanthanum salt solution and a mixed precipitant, wherein the mixed precipitant contains NH3·H2O and ammonium bicarbonate, and the molar ratio of NH3·H2O to ammonium bicarbonate is 0.6~1.2:1; S2. The lanthanum salt solution and the mixed precipitant are added to water in a co-current flow to carry out the precipitation reaction. The ratio of the total amount of NH3·H2O and ammonium bicarbonate added to the water to the amount of lanthanum ions is always maintained at 3.5~4.0:1 to obtain the first reaction slurry. S3. The first reaction slurry is aged at 75~95℃ to obtain the second reaction slurry; S4. The second reaction slurry is filtered, washed, and dried to obtain hexagonal basic lanthanum carbonate.

[0023] Compared to existing technologies, this invention utilizes the aging reaction of a lanthanum salt solution and a mixed precipitant under normal pressure and mild (75~95℃) conditions. It controls the molar ratio of NH3·H2O to ammonium bicarbonate in the mixed precipitant to be 0.6~1.2:1, while precisely controlling the total amount of NH3·H2O and ammonium bicarbonate added to the water to the molar ratio of lanthanum ions to remain at 3.5~4.0:1. This achieves the preparation of plate-like hexagonal basic lanthanum carbonate (corresponding to PDF card 26-0815), representing a technological leap from "high temperature and high pressure" to "normal pressure and mild conditions." It avoids the high energy consumption and safety hazards associated with high temperature and high pressure conditions, and does not use any organic reagents. The process is simple and suitable for large-scale production.

[0024] Specifically, the ratio of the total amount of NH3·H2O and ammonium bicarbonate added to the water to the amount of lanthanum ions is 3.5~4.0:1, for example, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.8:1, 4.0:1, or any combination thereof. When the ratio of the total amount of NH3·H2O and ammonium bicarbonate added to the water to the amount of lanthanum ions is less than 3.5, the product obtained is lanthanum carbonate; when the ratio of the total amount of NH3·H2O and ammonium bicarbonate added to the water to the amount of lanthanum ions is greater than 4.0, the product has poor crystallinity, which affects the filtration performance.

[0025] Specifically, the molar ratio of NH3·H2O to ammonium bicarbonate is 0.6 to 1.2:1, for example, 0.6:1, 0.8:1, 1.0:1, 1.2:1, or any combination thereof. These conditions are key to the synthesis of hexagonal basic lanthanum carbonate, avoiding the formation of cubic basic lanthanum carbonate or lanthanum carbonate impurities. When the molar ratio of NH3·H2O to ammonium bicarbonate is less than 0.6, the product obtained is lanthanum carbonate; when the molar ratio of NH3·H2O to ammonium bicarbonate is greater than 1.2, cubic basic lanthanum carbonate is finally generated (corresponding to PDF card 49-0981).

[0026] In practice, a lanthanum salt solution and a mixed precipitant are added to water in a parallel flow to carry out a precipitation reaction. The ratio of the total addition rate of NH3·H2O and ammonium bicarbonate (i.e., the total amount of NH3·H2O and ammonium bicarbonate added per unit time) to the addition rate of lanthanum ions (i.e., the amount of lanthanum ions added per unit time) is controlled to be 3.5~4.0:1. This ensures that the ratio of the total amount of NH3·H2O and ammonium bicarbonate in the mixed precipitant added to the water to the amount of lanthanum ions remains at 3.5~4.0:1 throughout the parallel flow process, resulting in the first reaction slurry. The precipitation reaction begins when the lanthanum salt solution and the mixed precipitant are first added to the water in a parallel flow and ends when the addition of the lanthanum salt solution and the mixed precipitant is stopped. The precipitation reaction time is the time during which the lanthanum salt solution and the mixed precipitant are added in a parallel flow.

[0027] Furthermore, the lanthanum salt solution in S1 includes one or more of the following: lanthanum chloride solution, lanthanum sulfate solution, lanthanum nitrate solution, and lanthanum acetate solution.

[0028] Furthermore, the molar concentration of lanthanum ions in the lanthanum salt solution in S1 is 0.25~1.2 mol / L, for example, 0.25 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, or any combination thereof. If the molar concentration of lanthanum ions in the lanthanum salt solution is too low, the amount of wastewater generated after the precipitation reaction will be large. If the molar concentration of lanthanum ions in the lanthanum salt solution is too high, the reaction system will have high supersaturation, the product particle size will be small, and it will be difficult to filter.

[0029] Furthermore, in S1, the total molar concentration of NH3·H2O and ammonium bicarbonate in the mixed precipitant is 2~6 mol / L, for example, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, or any combination thereof. When the above concentration is too low, the concentration of ammonium chloride obtained from the precipitation reaction is low, increasing the cost of wastewater recycling and treatment. When the above concentration is too high, the dissolution of ammonium bicarbonate during the preparation of the mixed precipitant becomes more difficult, and the volatilization of excessively high concentrations of NH3·H2O will also affect the operating environment. At the same time, the generated products may agglomerate, affecting the particle size distribution and filtration performance of the product.

[0030] Furthermore, the precipitation reaction temperature in S2 is 25-35℃ (e.g., 25℃, 28℃, 30℃, 33℃, 35℃, or any combination thereof), and the precipitation reaction time is 20-60 min (e.g., 20 min, 30 min, 40 min, 50 min, 60 min, or any combination thereof). If the precipitation reaction temperature is lower than the above conditions, the reaction will be incomplete; if the precipitation reaction temperature is higher than the above conditions, the bicarbonate ions in the mixed precipitant will decompose, and NH3·H2O will volatilize, damaging the environment and reducing the product yield. If the precipitation reaction time is less than the above range, it will affect the sufficiency of the reaction; if the precipitation reaction time is too long, it will reduce the reaction efficiency. The reactions involved in S2 (taking lanthanum chloride solution as an example) are shown in reaction formulas 1 and 2.

[0031] Reaction 1: 2LaCl3+2NH3·H2O+4NH4HCO3=La2(CO3)3↓+CO2↑+6NH4Cl+3H2O Reaction 2: LaCl3+2NH3·H2O+NH4HCO3=LaOHCO3↓+3NH4Cl+H2O Furthermore, during the precipitation reaction, when the lanthanum salt solution and the mixed precipitant are added to water in a co-current flow, the lanthanum ion addition rate is 0.001~0.003 mol / min, for example, 0.001 mol / min, 0.0015 mol / min, 0.002 mol / min, 0.0025 mol / min, 0.003 mol / min, or any combination thereof.

[0032] Furthermore, S2 is carried out under stirring at a speed of 200-400 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, or any combination thereof. If the stirring speed is lower than these conditions, the stirring is insufficient, resulting in high supersaturation of the reaction system and uneven product particle size distribution. If the stirring speed is higher than these conditions, the stirring shear force is large, leading to smaller product particle size and affecting filtration performance.

[0033] Specifically, in S2, a lanthanum salt solution and a mixed precipitant are added concurrently to water in a reaction vessel of a certain volume to carry out a precipitation reaction. The ratio of the volume of water to the volume of the reaction vessel is 5% to 20%, for example, 5%, 10%, 15%, 20%, or any combination thereof. If the water volume is too small, it cannot be stirred sufficiently; if the water volume is too large, the reaction system is diluted, increasing the amount of wastewater to be treated after the precipitation reaction.

[0034] Furthermore, the pH value of the first reaction slurry is greater than or equal to 7.5, for example, greater than or equal to 7.5, greater than or equal to 7.8, greater than or equal to 8.0, greater than or equal to 8.3, greater than or equal to 8.5, or any combination thereof. If the pH value of the first reaction slurry is too low, it cannot provide the alkaline conditions required for the next aging step, thereby affecting the purity of the product.

[0035] Further, in S3, the first reaction slurry is aged at 75~95℃ (e.g., 75℃, 80℃, 85℃, 90℃, 95℃ or any combination thereof) for 60~180 min (e.g., 60 min, 80 min, 100 min, 120 min, 150 min, 180 min or any combination thereof). When the aging temperature is below 75℃, cubic basic lanthanum carbonate is generated (corresponding to PDF card 49-0981). When the aging temperature is above 95℃, energy consumption increases, and special equipment or special heating media are required. If the aging time is less than the above conditions, the crystal form conversion rate is affected, which in turn affects the product purity. If the aging time is more than the above conditions, the production efficiency decreases. The lanthanum carbonate generated in S2 is further reacted in S3 to generate basic lanthanum carbonate, and the reaction process is shown in reaction formula 3 (taking lanthanum chloride as an example).

[0036] La2(CO3)3+2OH - =2LaOHCO3↓+CO3 2- Reaction 3 Furthermore, aging in S3 is carried out under stirring at a speed of 100-150 rpm, such as 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, or any combination thereof. This promotes complete crystal transformation and allows the crystals to grow further. If the stirring speed is lower than the above conditions, the crystal transformation rate will be affected, which in turn will affect the purity of the product. If the stirring speed is higher than the above conditions, the resulting hexagonal basic lanthanum carbonate crystals will have small particle size, affecting filtration performance and making them unsuitable for industrial application.

[0037] Furthermore, washing in S4 includes washing with water until the pH of the filtrate is 6.8 to 7.2 (e.g., a range of 6.8, 6.9, 7.0, 7.1, 7.2 or any combination thereof) to remove excess precipitant and other impurity ions.

[0038] Furthermore, the drying in S4 is carried out in an oven at a temperature of 50-80°C (e.g., a range of 50°C, 60°C, 70°C, 80°C or any combination thereof) for a drying time of 6-8 hours (e.g., a range of 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours or any combination thereof) to further remove adsorbed water from the product.

[0039] This invention also provides a hexagonal basic lanthanum carbonate, prepared according to the above-described method for preparing hexagonal basic lanthanum carbonate.

[0040] Furthermore, the XRD pattern of hexagonal basic lanthanum carbonate matches that of the standard card with JCPDS No. 26-0815.

[0041] Furthermore, in the XRD pattern of hexagonal basic lanthanum carbonate, the ratio of the peak intensities of the characteristic peaks corresponding to the (300) crystal plane and the (302) crystal plane is 1.1~1.3 (e.g., 1.1, 1.15, 1.2, 1.25, 1.3 or any combination thereof), and the ratio of the peak intensities of the characteristic peaks corresponding to the (330) crystal plane and the (304) crystal plane is 1.3~1.6 (e.g., 1.3, 1.4, 1.5, 1.6 or any combination thereof). This indicates that during the preparation of hexagonal basic lanthanum carbonate, there is a preferred orientation growth along the normal direction of the (300) and (330) crystal planes, thereby generating plate-like hexagonal basic lanthanum carbonate, such as... Figure 6 As shown.

[0042] Furthermore, the particle size D of hexagonal basic lanthanum carbonate v50 is 10~20µm, for example, 10µm, 12µm, 15µm, 18µm, 20µm or any combination thereof. The hexagonal basic lanthanum carbonate particles in the embodiments of the present invention are uniform in size, easy to clarify and filter, easy to wash, and suitable for large-scale industrial production.

[0043] Furthermore, the hexagonal basic lanthanum carbonate has a thin, lamellar structure with low agglomeration, which is beneficial for downstream applications. For example, in the field of catalysis, the thin, lamellar, and low-agglomeration structure gives hexagonal basic lanthanum carbonate a high specific surface area and more active sites, which can improve its efficiency and selectivity in catalytic reactions. In the field of environmental remediation, the low-agglomeration lamellar structure can efficiently treat fluoride- and phosphorus-containing wastewater.

[0044] Furthermore, the average thickness of the hexagonal basic lanthanum carbonate is 1.6 to 1.8 µm, for example, 1.6 µm, 1.65 µm, 1.7 µm, 1.75 µm, 1.8 µm or any combination thereof.

[0045] The present invention will be further described below through specific embodiments.

[0046] Example 1 S1. Prepare a mixed precipitant using 25% ammonia water and ammonium bicarbonate at a molar ratio of NH3·H2O to ammonium bicarbonate of 0.6:1. Add a certain amount of water to make the total molar concentration of NH3·H2O and ammonium bicarbonate in the mixed precipitant 2 mol / L. Prepare an aqueous solution of lanthanum chloride with a molar concentration of 0.5 mol / L.

[0047] S2. In a 500 mL reaction vessel, under a stirring speed of 280 rpm, a lanthanum chloride aqueous solution and a mixed precipitant are continuously and dropwise added to 100 mL of water at 25 °C to carry out a precipitation reaction. During the dropwise addition, the addition rate of lanthanum ions is controlled at 0.0015 mol / min, and the ratio of the total addition rate of NH3·H2O and ammonium bicarbonate (i.e., the total amount of NH3·H2O and ammonium bicarbonate added per unit time) to the addition rate of lanthanum ions is controlled at 3.5, so that the total amount of NH3·H2O and ammonium bicarbonate added to the water is equal to the lanthanum ion addition rate. 3+ The molar ratio of the substances was always 3.5:1. After reacting for 30 minutes, the addition of lanthanum chloride aqueous solution and mixed precipitant was stopped, resulting in the first reaction slurry with pH=7.5.

[0048] S3. Heat the first reaction slurry to 90°C, while adjusting the stirring speed to 100 rpm, and age for 120 minutes to obtain the second reaction slurry.

[0049] S4. The second reaction slurry was vacuum filtered, washed with pure water until the pH of the filtrate was 7.0, and dried at 60°C for 6 hours to obtain hexagonal basic lanthanum carbonate.

[0050] like Figure 1 As shown, the XRD pattern of hexagonal basic lanthanum carbonate in Example 1 is compared with the standard card (JCPDS). The sample (No. 26-0815) matches the standard and has no other impurity peaks. These peaks include the diffraction peak corresponding to the (002) crystal plane at 2θ=17.6°, the diffraction peak corresponding to the (300) crystal plane at 2θ=24.4°, the diffraction peak corresponding to the (302) crystal plane at 2θ=30.3°, the diffraction peak corresponding to the (330) crystal plane at 2θ=43.0°, the diffraction peak corresponding to the (304) crystal plane at 2θ=43.8°, and the diffraction peak corresponding to the (332) crystal plane at 2θ=46.8°. The lattice constants are a=b=1.262nm, c=1.002nm, α=β=90°, and γ=120°. This demonstrates the successful synthesis of impurity-free hexagonal basic lanthanum carbonate in this embodiment. Furthermore, the high intensity and sharp peak shape of the characteristic diffraction peaks in the XRD pattern indicate good crystallinity of the hexagonal basic lanthanum carbonate. Figure 5 , Figure 6 As shown, the hexagonal basic lanthanum carbonate in this embodiment has a thin plate-like structure with a uniform particle size distribution.

[0051] Example 2 S1. Prepare a mixed precipitant by mixing 25% ammonia water and ammonium bicarbonate in a 1:1 molar ratio of NH3·H2O to ammonium bicarbonate. Add a certain amount of water to make the total molar concentration of NH3·H2O and ammonium bicarbonate in the mixed precipitant 3 mol / L. Prepare an aqueous solution of lanthanum chloride with a molar concentration of 0.6 mol / L.

[0052] S2. In a 500 mL reaction vessel, under a stirring speed of 300 rpm, a lanthanum chloride aqueous solution and a mixed precipitant are continuously and dropwise added to 100 mL of water at 30 °C to carry out a precipitation reaction. During the dropwise addition, the addition rate of lanthanum ions is controlled at 0.0015 mol / min, and the ratio of the total addition rate of NH3·H2O and ammonium bicarbonate (i.e., the total amount of NH3·H2O and ammonium bicarbonate added per unit time) to the addition rate of lanthanum ions is controlled at 3.8, so that the total amount of NH3·H2O and ammonium bicarbonate added to the water is equal to the lanthanum ion addition rate. 3+ The molar ratio of the substances was always 3.8:1. After 40 minutes of reaction, the addition of lanthanum chloride aqueous solution and mixed precipitant was stopped, and the first reaction slurry with pH=8.0 was obtained.

[0053] S3. Heat the first reaction slurry to 85°C, while adjusting the stirring speed to 120 rpm, and age for 120 min to obtain the second reaction slurry.

[0054] S4. The second reaction slurry was vacuum filtered, washed with pure water until the pH of the filtrate was 7.0, and dried at 60°C for 6 hours to obtain hexagonal basic lanthanum carbonate.

[0055] The XRD pattern of hexagonal basic lanthanum carbonate in this embodiment is basically the same as that in Example 1, and will not be described again here.

[0056] Example 3 S1. Prepare a mixed precipitant by mixing 25% ammonia water and ammonium bicarbonate in a molar ratio of NH3·H2O to ammonium bicarbonate of 1.2:1. Add a certain amount of water to make the total molar concentration of NH3·H2O and ammonium bicarbonate in the mixed precipitant 4 mol / L. Prepare an aqueous solution of lanthanum chloride with a molar concentration of 0.9 mol / L.

[0057] S2. In a 500 mL reaction vessel, under a stirring speed of 360 rpm, a lanthanum chloride aqueous solution and a mixed precipitant aqueous solution are continuously and dropwise added to 100 mL of water at 35 °C (as the base solution) to carry out the precipitation reaction. During the dropwise addition, the addition rate of lanthanum ions is controlled at 0.00225 mol / min, and the ratio of the total addition rate of NH3·H2O and ammonium bicarbonate (i.e., the total amount of NH3·H2O and ammonium bicarbonate added per unit time) to the addition rate of lanthanum ions is controlled at 4.0, so that the total amount of NH3·H2O and ammonium bicarbonate added to the water is equal to the lanthanum ion addition rate. 3+ The molar ratio of the substances was always 4.0:1. After 40 minutes of reaction, the addition of lanthanum chloride aqueous solution and mixed precipitant aqueous solution was stopped, resulting in the first reaction slurry with pH=8.5.

[0058] S3. Heat the first reaction slurry to 80°C, while adjusting the stirring speed to 150 rpm, and age for 180 min to obtain the second reaction slurry.

[0059] S4. The second reaction slurry was vacuum filtered, washed with pure water until the pH of the filtrate was 7.0, and dried at 60°C for 6 hours to obtain hexagonal basic lanthanum carbonate.

[0060] The XRD pattern of hexagonal basic lanthanum carbonate in this embodiment is basically the same as that in Example 1, and will not be described again here.

[0061] Example 4 The difference from Example 1 is that in S3, the first reaction slurry is heated to 75°C and the stirring speed is adjusted to 100 rpm, and aged for 180 min to obtain the second reaction slurry. The remaining steps and conditions are the same as in Example 1.

[0062] The XRD pattern of hexagonal basic lanthanum carbonate in this embodiment is basically the same as that in Example 1, and will not be described again here.

[0063] Example 5 The difference from Example 1 is that in S3, the first reaction slurry is heated to 95°C, and the stirring speed is adjusted to 100 rpm. After aging for 60 minutes, the second reaction slurry is obtained. The remaining steps and conditions are the same as in Example 1.

[0064] The XRD pattern of hexagonal basic lanthanum carbonate in this embodiment is basically the same as that in Example 1, and will not be described again here.

[0065] Example 6 The difference from Example 1 is that an aqueous solution of lanthanum sulfate is used instead of an aqueous solution of lanthanum chloride, and the molar concentration of lanthanum ions in the aqueous solution of lanthanum sulfate is 0.25 mol / L. The remaining steps and conditions are the same as in Example 1.

[0066] The XRD pattern of hexagonal basic lanthanum carbonate in this embodiment is basically the same as that in Example 1, and will not be described again here.

[0067] Example 7 The difference from Example 1 is that an aqueous solution of lanthanum nitrate is used instead of an aqueous solution of lanthanum chloride, while the remaining steps and conditions are the same as in Example 1.

[0068] The XRD pattern of hexagonal basic lanthanum carbonate in this embodiment is basically the same as that in Example 1, and will not be described again here.

[0069] Example 8 The difference from Example 1 is that an aqueous solution of lanthanum acetate is used instead of an aqueous solution of lanthanum chloride, while the remaining steps and conditions are the same as in Example 1.

[0070] The XRD pattern of hexagonal basic lanthanum carbonate in this embodiment is basically the same as that in Example 1, and will not be described again here.

[0071] Comparative Example 1 The difference from Example 1 is that a mixed precipitant was prepared using 25% ammonia water and ammonium bicarbonate at a molar ratio of NH3·H2O to ammonium bicarbonate of 1.5:1. The remaining steps and conditions were consistent with Example 1, yielding spherical cubic basic lanthanum carbonate. Figure 7 As shown. And by Figure 2It can be seen that the XRD pattern of cubic basic lanthanum carbonate in Comparative Example 1 matches the standard card (JCPDS No. 49-0981).

[0072] Comparative Example 2 The difference from Example 1 is that a mixed precipitant was prepared using 25% ammonia water and ammonium bicarbonate at a molar ratio of NH3·H2O to ammonium bicarbonate of 0.5:1. The remaining steps and conditions were consistent with Example 1, yielding lanthanum carbonate, the microstructure of which is as follows. Figure 8 As shown. By Figure 3 It can be seen that the XRD pattern of lanthanum carbonate in Comparative Example 2 matches the standard card (JCPDS No. 25-1400).

[0073] Comparative Example 3 The difference from Example 1 is that the ratio of the total addition rate of NH3·H2O and ammonium bicarbonate (i.e., the total amount of NH3·H2O and ammonium bicarbonate added per unit time) to the addition rate of lanthanum ions is controlled to be 3.0, so that the total amount of NH3·H2O and ammonium bicarbonate added to the water is equal to the ratio of the lanthanum ion addition rate to the total amount of lanthanum ions. 3+ The molar ratio of the substances was always 3.0:1. After reacting for 30 minutes, a first reaction slurry with pH=6.5 was obtained. The remaining steps and conditions were consistent with those in Example 1, yielding lanthanum carbonate, the microstructure of which is as follows. Figure 9 As shown. By Figure 4 It can be seen that the XRD pattern of lanthanum carbonate in Comparative Example 3 matches the standard card (JCPDS No. 73-0439).

[0074] Comparative Example 4 The difference from Example 1 is that the ratio of the total addition rate of NH3·H2O and ammonium bicarbonate (i.e., the total amount of NH3·H2O and ammonium bicarbonate added per unit time) to the addition rate of lanthanum ions is controlled at 4.5, so that the total amount of NH3·H2O and ammonium bicarbonate added to the water is equal to the ratio of the lanthanum ion addition rate to the total amount of lanthanum ions. 3+ The molar ratio of the substances was always 4.5:1, the pH of the first reaction slurry was 9, and the remaining steps and conditions were consistent with those in Example 1. The resulting product had a small particle size and could not be effectively filtered and collected.

[0075] Comparative Example 5 The difference from Example 1 is that the first reaction slurry is heated to 70°C, while the remaining steps and conditions are the same as in Example 1. The resulting product is a mixed crystal of cubic basic lanthanum carbonate and hexagonal basic lanthanum carbonate.

[0076] The hexagonal basic lanthanum carbonate, cubic basic lanthanum carbonate, and lanthanum carbonate in each embodiment and comparative example were tested using the following procedure, and the results are shown in Table 1. Figures 1-9 .

[0077] (1) Particle size determination: Using water as the dispersion medium, a laser particle size analyzer (model: Bettersize 2600) from Dandong Bettersize was used to measure the particle size D. v 50.

[0078] (2) X-ray diffraction: X-ray powder diffractometer (model: X Pert PRO) from Panaco, Netherlands was used for testing. The test conditions were: Cu target (λ=1.5406Å), Kα rays, and test range of 10°. The XRD pattern and the intensity of each diffraction peak were obtained by scanning at 80°, a scanning speed of 5° / min, a tube current of 40 mA, and a tube voltage of 40 kV.

[0079] (3) Morphology and average thickness: The test was conducted using a German Zeiss field emission scanning electron microscope (model: ZEISS Sigma500). Under a magnification of 500x, the micromorphology of the sample was observed. Different areas were selected, and vertical or inclined lamellae were found and observed for thickness measurement. The thickness of no less than 5 lamellae structures was measured and the arithmetic mean was taken.

[0080] Table 1

[0081] From Table 1, Figures 1-4 , Figures 6-9 As can be seen, compared with Comparative Examples 1-5, Examples 1-8 of this application use a mixed precipitant containing NH3·H2O and ammonium bicarbonate, and control the molar ratio of NH3·H2O to ammonium bicarbonate to be 0.6-1.2:1. The lanthanum salt solution and the mixed precipitant are added to water in a co-current flow to carry out the precipitation reaction, so that the molar ratio of the total amount of NH3·H2O and ammonium bicarbonate added to the water to the molar amount of lanthanum ions in the lanthanum salt solution is always maintained at 3.5-4.0:1. Under normal pressure and mild temperature (75-95℃), plate-like hexagonal basic lanthanum carbonate (corresponding to PDF card 26-0815) was successfully synthesized.

[0082] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing hexagonal basic lanthanum carbonate, characterized in that, Includes the following steps: S1. Prepare a lanthanum salt solution and a mixed precipitant, wherein the mixed precipitant comprises NH3·H2O and ammonium bicarbonate, and the molar ratio of NH3·H2O to ammonium bicarbonate is 0.6~1.2:1; S2. The lanthanum salt solution and the mixed precipitant are added to water in a parallel flow to carry out a precipitation reaction. The ratio of the total amount of NH3·H2O and ammonium bicarbonate added to the water to the amount of lanthanum ions is always maintained at 3.5~4.0:1 to obtain the first reaction slurry. S3. The first reaction slurry is aged at 75~95℃ to obtain the second reaction slurry; S4. The second reaction slurry is filtered, washed, and dried to obtain hexagonal basic lanthanum carbonate.

2. The method for preparing hexagonal basic lanthanum carbonate according to claim 1, characterized in that, In step S3, the first reaction slurry is aged at 75-95°C for 60-180 minutes.

3. The method for preparing hexagonal basic lanthanum carbonate according to claim 1, characterized in that, The pH value of the first reaction slurry is greater than or equal to 7.

5.

4. The method for preparing hexagonal basic lanthanum carbonate according to claim 1, characterized in that, In S1, the total molar concentration of NH3·H2O and ammonium bicarbonate in the mixed precipitant is 2~6 mol / L.

5. The method for preparing hexagonal basic lanthanum carbonate according to claim 1, characterized in that, The precipitation reaction temperature in S2 is 25~35℃, and the precipitation reaction time is 20-60min.

6. The method for preparing hexagonal basic lanthanum carbonate according to claim 1, characterized in that, The molar concentration of lanthanum ions in the lanthanum salt solution in S1 is 0.25~1.2 mol / L.

7. The method for preparing hexagonal basic lanthanum carbonate according to claim 1, characterized in that, The lanthanum salt solution in S1 includes one or more of the following: lanthanum chloride solution, lanthanum sulfate solution, lanthanum nitrate solution, and lanthanum acetate solution.

8. A hexagonal basic lanthanum carbonate, characterized in that, It was prepared according to the method for preparing hexagonal basic lanthanum carbonate according to any one of claims 1-7.

9. The hexagonal basic lanthanum carbonate according to claim 8, characterized in that, In the XRD pattern of the hexagonal basic lanthanum carbonate, the ratio of the peak intensity of the characteristic peaks corresponding to the (300) crystal plane and the (302) crystal plane is 1.1~1.3, and the ratio of the peak intensity of the characteristic peaks corresponding to the (330) crystal plane and the (304) crystal plane is 1.3~1.

6.

10. The hexagonal basic lanthanum carbonate according to claim 8, characterized in that, The particle size D of the hexagonal basic lanthanum carbonate v 50 represents 10~20µm.

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