Method for preparing lanthanum hydroxycarbonate of hexagonal crystal system by hydrothermal synthesis

Abstract

The application discloses a method for preparing hexagonal hydroxyl carbonate lanthanum by hydrothermal synthesis, which comprises the following steps: diluting lanthanum chloride solution as a bottom liquid with deionized water and adding lanthanum carbonate as a crystal seed in a precipitation reactor; adding a feed liquid and a precipitator into the precipitation reactor by using a parallel flow precipitation mode, generating lanthanum carbonate after precipitation reaction, controlling the input speed of the feed liquid and the precipitator to control the precipitation reaction time and adjust the pH value; taking out the precipitate lanthanum carbonate in the precipitation reactor, drying after filtration to obtain lanthanum carbonate as a precursor; adding the lanthanum carbonate and deionized water into a reactor to perform a hydrothermal synthesis reaction, washing the obtained final product with deionized water, and performing suction filtration or centrifugation to obtain a white solid; and placing the white solid in an oven, drying to obtain hexagonal hydroxyl carbonate lanthanum. The production process is simple, and the method is suitable for industrialized batch production of hexagonal hydroxyl carbonate lanthanum.

Description

[0001] The present application is a divisional application of application No. 202110525397.6, filed on May 12, 2021, entitled "Method for preparing hexagonal hydroxyl carbonate of lanthanum by hydrothermal synthesis". TECHNICAL FIELD

[0002] The present application belongs to the field of hydrometallurgy, and particularly relates to a method for preparing hexagonal hydroxyl carbonate of lanthanum by hydrothermal synthesis. BACKGROUND

[0003] Rare earth luminescent materials are mainly applied to rare earth energy-saving lamps, white light LED lighting devices. The rare earth energy-saving lamp is a high-quality, efficient green lighting product, which has the advantages of high light efficiency, energy saving, low light decay, long service life, etc. compared with incandescent lamps, halogen powder made of fluorescent powder, etc. At present, the export volume of three primary color energy-saving lamps produced in China reaches about 80%, which is the largest manufacturing base of global energy-saving light sources. With the gradual popularization of green lighting, the market demand for three primary color fluorescent powder for energy-saving lamps will be greater in the future.

[0004] There are many factors that affect the luminescent efficiency of fluorescent powder, among which the selection of a good luminescent substrate is particularly important. The hexagonal hydroxyl carbonate of lanthanum has a relatively optimal crystal structure and is often used as a luminescent substrate for the production of fluorescent powder.

[0005] The document "Photocatalyst lanthanum hydroxycarbonate and its preparation method and application" is to add an aqueous solution of a carbon source (a mixture of urea or sodium hydroxide, sodium carbonate) into an aqueous solution of a lanthanum source (lanthanum oxide, lanthanum nitrate, lanthanum acetate), stir for 30-180 min, then put the mixed solution into a high-pressure reaction kettle at 90-180℃ for constant temperature for 12-24 hours, wash the obtained precipitate with water and ethanol by centrifugation, dry at 40-120℃ for 6-24 hours, and grind to obtain lanthanum hydroxycarbonate powder. The precipitant in this document uses a mixture of urea or sodium hydroxide, sodium carbonate, the solution uses an aqueous solution of lanthanum oxide, lanthanum nitrate, lanthanum acetate, and the high-temperature hydrothermal reaction is carried out in a high-pressure reaction, and the hydroxyl carbonate of lanthanum prepared under this condition is not a hexagonal structure.

[0006] Chinese Patent No. CN101279757A discloses that lanthanum oxide and ammonium bicarbonate or glycine are used as precursors, deionized water is used as a solvent, and they are placed in a sealed hydrothermal reaction kettle in proportion, the molar ratio of lanthanum oxide to ammonium bicarbonate or glycine is 1:20-1:45, the hydrothermal reaction kettle with the mixture is placed in a box-type resistance furnace and heated to 150-220℃, and heated at this temperature for 8-48h, and then naturally cooled to room temperature to obtain hydroxyl carbonate of lanthanum. However, the precursor for preparing the hydroxyl carbonate of lanthanum in this process is lanthanum oxide, which increases the process reaction steps and the consumption of materials and energy, and the product hydroxyl carbonate of lanthanum is not a hexagonal structure.

[0007] Chinese publication No. CN1369578A discloses that a water solution of rare earth nitrate and thiourea, or a water solution of rare earth oxide dissolved by nitric acid and thiourea, is injected into a closed pressure-resistant reactor in which a substrate is previously placed, and reacted at 150-200 DEG C for not less than 3 hours; the substrate is taken out, washed by water, dried, and a rare earth basic carbonate crystal film deposited on the substrate is obtained. However, the equipment and process require special auxiliary materials, increasing the difficulty and cost of preparation.

[0008] At present, there is no relevant description about the preparation of hexagonal hydroxyl carbonate lanthanum by atmospheric hydrothermal synthesis in the rare earth hydrometallurgy industry. SUMMARY

[0009] The present application aims to provide a method for preparing hexagonal hydroxyl carbonate lanthanum by hydrothermal synthesis, which is low in cost and easy to control, and suitable for industrial production of hexagonal hydroxyl carbonate lanthanum.

[0010] To achieve the above-mentioned purpose, the technical solution used by the present application is as follows:

[0011] The method for preparing hexagonal hydroxyl carbonate lanthanum by hydrothermal synthesis comprises the following steps:

[0012] In a precipitation reactor, a lanthanum chloride solution is diluted by deionized water as a bottom liquid, the concentration of the bottom liquid is 0.177-0.89 mol / L, and 10-50wt% of the bottom liquid is added as a seed crystal of lanthanum carbonate, and the temperature is raised to a set temperature of 30-55 DEG C, and the temperature is kept at the set temperature and stirred uniformly;

[0013] The parallel flow precipitation method is adopted, and a feed liquid and a precipitant are added to the precipitation reactor, and the temperature is kept at a set temperature, and lanthanum carbonate is generated after precipitation reaction; the feed liquid is a lanthanum chloride solution with a concentration of 1.42-1.84 mol / L, and the precipitant is a solution of ammonium bicarbonate with a concentration of 1.0-5.72 mol / L or a mixed solution of ammonium bicarbonate and ammonia water; the time of the precipitation reaction and the pH value are controlled by controlling the input speed of the feed liquid and the precipitant, the time of the precipitation reaction is 4-18 hours, and the pH value at the end of the precipitation is 6.5-7;

[0014] The precipitate lanthanum carbonate in the precipitation reactor is taken out, filtered and dried to obtain lanthanum carbonate as a precursor; the lanthanum carbonate and deionized water are added to a reactor in a mass ratio of 1:2-1:6, and the temperature is controlled at 110-160 DEG C for stirring, and hydrothermal synthesis reaction is carried out, and the temperature is kept for 6-20 hours;

[0015] The final product is washed by deionized water, and then filtered or centrifuged to obtain a white solid, and the white solid is placed in an oven and dried at 150-200 DEG C for 3-12 hours to obtain hexagonal hydroxyl carbonate lanthanum with a rare earth oxide content of 66-73wt%.

[0016] Further, the lanthanum chloride solution with a concentration of 1.42-1.84 mol / L is used as the original solution, and the original solution is diluted with deionized water to form a bottom solution, and the supernatant of the previous batch is used to dilute the bottom solution to form the bottom solution of the subsequent batch.

[0017] Further, the precipitant is ammonium bicarbonate solution or a mixed solution prepared by mixing ammonium bicarbonate and ammonia water, and the concentration of the solution is 1.0-5.72 mol / L, and the molar ratio of ammonium bicarbonate to ammonia water is 7:3.

[0018] Further, when the co-current precipitation is performed, the precipitant is added to the precipitation reactor at the same time as the feed liquid is added; the lanthanum chloride solution with a concentration of 1.42-1.84 mol / L is input to the feed liquid input port of the precipitation reactor, and the precipitant with a concentration of 1.0-5.72 mol / L is input to the precipitant input port of the precipitation reactor.

[0019] Further, the precipitation reactor and the reactor work in a normal pressure state.

[0020] Further, the precipitate lanthanum carbonate in the precipitation reactor is taken out, filtered, and then the filter cake is rinsed with deionized water and vacuum dried to obtain the lanthanum carbonate as a precursor.

[0021] The technical effects of the present application include:

[0022] 1. In the preparation method provided by the present application, the raw materials and auxiliary materials are common materials in the industrial production of hydrometallurgy industry, which are low in price and easy to obtain; the raw material used in the precipitation process is the lanthanum chloride solution obtained by the extraction separation process, which can be directly precipitated to prepare the precursor lanthanum carbonate of hexagonal system lanthanum hydroxide carbonate, without the need of further processing into oxides or nitrates to prepare the lanthanum hydroxide carbonate, thereby greatly shortening the process steps, reducing the energy consumption in the preparation process, and avoiding the use of other additives to increase the cost of auxiliary materials.

[0023] 2. The hydrothermal synthesis reaction in the present application is performed in a normal pressure state, and the process flow can be realized without the use of special pressurizing equipment.

[0024] 3. The process of the present application is simple in operation, good in repeatability, stable in product quality, and easy to realize industrialization and automatic continuous operation. DETAILED DESCRIPTION

[0025] Figure 1 is the XRD (X-ray diffraction analysis) spectrum of the hexagonal system lanthanum hydroxide carbonate prepared in the present application;

[0026] Figure 2 is the scanning electron microscope image of the hexagonal system lanthanum hydroxide carbonate prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0027] The following description fully illustrates specific embodiments of the application to enable one of ordinary skill in the art to practice and reproduce the application.

[0028] The method for preparing the hexagonal hydroxyl lanthanum carbonate by hydrothermal synthesis is specifically as follows:

[0029] Step 1: In the precipitation reactor, dilute the lanthanum chloride solution with deionized water as the bottom liquid, the bottom liquid concentration is 0.177-0.89 mol / L, add 10-50wt% of the lanthanum carbonate as the seed crystal to the bottom liquid, heat to the set temperature of 30-55℃, and keep the temperature and stir uniformly at the set temperature;

[0030] The solubility of rare earth carbonate in water is very small, but the solubility in alkali metal or ammonium carbonate solution is significantly increased.

[0031] In the process of precipitating rare earth carbonate, a stable crystal growth environment provided by the bottom liquid is needed to obtain a good crystal form, and a moderate pH buffer environment is a key factor to determine the difficulty of crystallization during the crystallization induction period. If the instantaneous pH value is too high, a mixture of several salts instead of one salt is formed, and the crystal is amorphous structure.

[0032] In the application, the lanthanum chloride solution with a concentration of 1.42-1.84 mol / L is used as the original solution, the original solution is diluted with deionized water to form the bottom liquid, and the supernatant of the previous batch is used to dilute the second batch and subsequent batches to form the reaction bottom liquid.

[0033] Step 2: Adopt the parallel flow precipitation method, add the feed liquid and the precipitant to the precipitation reactor, keep the temperature at the set temperature, and generate lanthanum carbonate after the precipitation reaction; the feed liquid is the lanthanum chloride solution with a concentration of 1.42-1.84 mol / L;

[0034] In the application, the raw material used in the precipitation process is the lanthanum chloride solution, which is obtained by the extraction separation process, and can be directly precipitated to prepare, avoiding the increase of the cost of auxiliary materials and energy consumption caused by the use of thiourea, glycine or the preparation of oxides and nitrates in other processes, and realizing the preparation from the front-end raw material.

[0035] In the application, the precipitant is the ammonium bicarbonate solution with a concentration of 1.0-5.72 mol / L; or the precipitant is a mixed solution prepared by mixing ammonium bicarbonate and ammonia water, and the concentration of the mixed solution is 1.0-5.72 mol / L, and the molar ratio of ammonium bicarbonate to ammonia water is 7:3. In the application, the precipitant is ammonium bicarbonate or a mixture of ammonium bicarbonate and ammonia water, and the raw materials are widely supplied and low in cost.

[0036] In the present application, the co-current precipitation method is that the precipitator is added into the precipitation reactor while the feed liquid is added. The feed liquid input port of the precipitation reactor inputs the lanthanum chloride solution with the concentration of 1.42-1.84 mol / L, and the precipitator input port inputs the precipitator with the concentration of 1.0-5.72 mol / L.

[0037] During the whole process of the co-current precipitation, the concentration of each ion in the bottom liquid solution is maintained in a stable range, the pH value favorable for the crystal growth can be well controlled, and the precipitation environment is relatively stable. In the present application, the precipitation reaction time and the pH value are controlled by controlling the input speed of the lanthanum chloride solution and the precipitator. The input speed of the input port is controlled, and the precipitator is slowly added into the reactor during the co-current precipitation. The precipitation reaction time is controlled to be 4-18 hours, and the pH value at the end of the precipitation is 6.5-7. The pH value is a key factor for the carbonated rare earth precipitation crystallization process and the crystal morphology. The accurate pH value is controlled during the reaction process to avoid the phenomenon that the addition amount is too large, the precipitation environment is unstable, the crystal nucleus production speed is affected, and the amorphous flocculent precipitate and the non-rare earth impurities are mixed in the product. In order to consider the rare earth yield, the crystal growth and the product purity, the precipitation is preferably controlled at the pH value of 6.5-7.

[0038] Step 3: The precipitate lanthanum carbonate in the precipitation reactor is taken out, filtered, and then the filter cake is rinsed with deionized water and vacuum dried to obtain the lanthanum carbonate as a precursor;

[0039] Step 4: The lanthanum carbonate and deionized water are added into the reactor at the mass ratio of 1:2-1:6, and the hydrothermal synthesis reaction is carried out under the condition that the temperature is controlled to be 110-160 ℃ and stirring is performed; the holding time is 6-20 hours;

[0040] The principle of the hydrothermal synthesis is that the chemical reaction of substances in an aqueous solution is utilized under the conditions of the temperature of 100-1000 ℃ and the pressure of 1 MPa-1 GPa. The hydrothermal method has the tendency to develop to low temperature and low pressure, i.e. the temperature is lower than 100 ℃, and the pressure is close to 1 standard atmosphere. Under the subcritical and supercritical hydrothermal conditions, the reactivity is improved because the reaction is at the molecular level, and therefore the hydrothermal reaction can replace some high-temperature solid-phase reactions. The utilization of the hydrothermal technology makes the insoluble or hardly soluble substances dissolve, which is an effective method for recrystallization, inorganic synthesis and material processing.

[0041] In the present application, the holding time is preferably 8-16 hours. The precipitation reactor and the reactor work under the normal pressure condition. Under the normal pressure condition, the hydrothermal synthesis process can be used to obtain the lanthanum oxyhydroxide carbonate, the total amount of rare earth of the product is high, the purity is high, the product is in the hexagonal crystal system, the whole process operation is simple, no new equipment is added, and the product can be prepared by using the existing equipment and raw and auxiliary materials; no labor cost and labor intensity are increased, and the method is suitable for realizing the industrialization and automatic continuous operation.

[0042] Step 5: The obtained final product is washed with deionized water, and then is filtered or centrifuged to obtain a white solid. The white solid is placed in an oven and dried at 150-200℃ for 3-12 hours to obtain hexagonal lanthanum hydroxycarbonate with REO accounting for 66-73wt%.

[0043] The lanthanum hydroxycarbonate is also called basic lanthanum carbonate, and has a general chemical formula of La(OH)CO3, belongs to a hexagonal system, and has a P-6 space group with a cell parameter of a=12.616, b=12.616, and c=10.022.

[0044] As shown in FIG. 1, it is an XRD (X-ray diffraction analysis) spectrum of the hexagonal lanthanum hydroxycarbonate prepared in the present application. Figure 1

[0045] The spectrum of the lanthanum hydroxycarbonate characterized in the spectrum is completely consistent with the peak value numbered 26-0815 in the diffraction spectrum, has high diffraction intensity, complete peak type, and clear peak position, and indicates that the product has good crystallinity. The cell parameter of 26-0815 is a structure parameter of a hexagonal system.

[0046] Example 1

[0047] In a precipitation reactor, a lanthanum chloride solution is prepared into a bottom solution with a concentration of 0.7mol / L by using deionized water, 30% lanthanum carbonate is added as a crystal seed, and after being uniformly stirred, a parallel flow precipitation mode is adopted to simultaneously control the flow rates of the lanthanum chloride solution and a precipitant (ammonium bicarbonate solution). The concentration of the solution is 1.5mol / L, the concentration of the precipitant is 3mol / L, the reaction temperature is controlled at 32℃, the reaction time is 6h, and the pH of the precipitation end point is 6.7.

[0048] After filtration, the filter cake is rinsed with deionized water and vacuum dried to obtain lanthanum carbonate. The lanthanum carbonate and deionized water are added into a reactor in a mass ratio of 1:4, the reaction temperature is controlled at 110℃, and the obtained product is washed with deionized water and then placed in an oven for drying at 150℃ for 12 hours to obtain hexagonal basic lanthanum carbonate with a total amount of REO=65%.

[0049] As shown in FIG. 2, it is a scanning electron microscope (SEM) image of the hexagonal lanthanum hydroxycarbonate prepared in Example 1 of the present application. Figure 2

[0050] The crystal structure of the obtained product, hexagonal lanthanum hydroxycarbonate, is clear, and is composed of regular flaky crystal plates to form spherical crystals with uniform sizes.

[0051] Example 2

[0052] ​​The lanthanum chloride solution is prepared into a base solution with a concentration of 0.5 mol / L by using deionized water, 20% lanthanum carbonate is added as a crystal seed, after uniform stirring, a concurrent precipitation method is adopted to simultaneously control the flow rates of the lanthanum chloride solution and a precipitating agent (a mixed solution of ammonium bicarbonate and ammonia water), the concentration of the precipitating agent is 2 mol / L, the reaction temperature is controlled at 48℃, the reaction time is 8h, and the pH value at the end of precipitation is 6.5.

[0053] After filtration, the filter cake is rinsed with deionized water and vacuum dried to obtain lanthanum carbonate. The lanthanum carbonate and deionized water are added into a reactor in a mass / volume ratio of 1:3, the reaction temperature is controlled at 150℃, and the obtained product is washed with deionized water and then dried in an oven at 180℃ for 8h to obtain hexagonal basic lanthanum carbonate with a total amount of REO of 68%.

[0054] Example 3

[0055] The lanthanum chloride solution is prepared into a base solution with a concentration of 0.5 mol / L by using deionized water, 20% lanthanum carbonate is added as a crystal seed, after uniform stirring, a concurrent precipitation method is adopted to simultaneously control the flow rates of the lanthanum chloride solution and a precipitating agent (a mixed solution of ammonium bicarbonate and ammonia water), the concentration of the precipitating agent is 2 mol / L, the reaction temperature is controlled at 48℃, the reaction time is 8h, and the pH value at the end of precipitation is 6.5.

[0056] After filtration, the filter cake is rinsed with deionized water and vacuum dried to obtain lanthanum carbonate. The lanthanum carbonate and deionized water are added into a reactor in a mass / volume ratio of 1:3, the reaction temperature is controlled at 150℃, and the obtained product is washed with deionized water and then dried in an oven at 180℃ for 8h to obtain hexagonal basic lanthanum carbonate with a total amount of REO of 68%.

[0057] The terms used in the present application are illustrative and exemplary, but not restrictive. Since the present application can be embodied in various forms without departing from the spirit or essential characteristics thereof, it should be understood that the above-described embodiments are not limited to any of the aforementioned details, but are to be construed broadly within the spirit and scope of the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are intended to be embraced by the claims.

Claims

1. A method for preparing hexagonal hydroxyl carbonate of lanthanum by hydrothermal synthesis, characterized in that, Comprise: In the precipitation reactor, dilute the lanthanum chloride solution with deionized water as the bottom liquid, the bottom liquid concentration is 0.177-0.89mol / L, add the lanthanum carbonate as the seed crystal which accounts for 10-50wt% of the bottom liquid, heat to the set temperature of 30-55℃, and keep the temperature and stir uniformly at the set temperature; Use the parallel flow precipitation method, add the feed liquid and the precipitant to the precipitation reactor, keep at the set temperature, the precipitation reactor works at normal pressure, after the precipitation reaction, the precursor lanthanum carbonate for preparing the hexagonal hydroxyl carbonate lanthanum is generated; the feed liquid is the lanthanum chloride solution with the concentration of 1.42-1.84mol / L, the precipitant is the ammonium bicarbonate solution or the mixed solution of ammonium bicarbonate and ammonia water with the concentration of 1.0-5.72mol / L; control the input speed of the feed liquid and the precipitant to control the precipitation reaction time and adjust the pH value, the precipitation reaction time is 4-18 hours, the pH value at the end of the precipitation is 6.5-7; Take out the precipitate lanthanum carbonate in the precipitation reactor, filter and dry to obtain the lanthanum carbonate as the precursor; add the lanthanum carbonate and deionized water in the reactor according to the mass ratio of 1:2-1:6, control the temperature at 110-160℃ and stir, the reactor works at normal pressure, carry out the hydrothermal synthesis reaction, and keep the temperature for 8-16 hours; Wash the obtained final product with deionized water, then use the suction filtration or centrifugation to obtain the white solid, place the white solid in the oven, dry at 150-200℃ for 3-12 hours, obtain the hexagonal hydroxyl carbonate lanthanum with the rare earth oxide accounting for 66-73wt%, the hexagonal hydroxyl carbonate lanthanum belongs to the hexagonal system, the space group is P-6, the cell parameters are a=12.616, b=12.616, c=10.

022.

2. The method for preparing lanthanum hydroxycarbonate with a hexagonal crystal system by hydrothermal synthesis according to claim 1, characterized in that, Use the lanthanum chloride solution with the concentration of 1.42-1.84mol / L as the original solution, dilute the original solution with deionized water to form the bottom liquid, and dilute the supernatant of the previous batch to form the bottom liquid for the subsequent batch.

3. The method for preparing lanthanum hydroxycarbonate with a hexagonal crystal system by hydrothermal synthesis according to claim 1, characterized in that, The precipitant is the ammonium bicarbonate solution or the mixed solution of ammonium bicarbonate and ammonia water, the solution concentration is 1.0-5.72mol / L, and the molar ratio of ammonium bicarbonate to ammonia water is 7:

3.

4. The method for preparing lanthanum hydroxycarbonate with a hexagonal crystal system by hydrothermal synthesis according to claim 1, characterized in that, When the parallel flow precipitation is carried out, the precipitant is added to the precipitation reactor at the same time as the feed liquid is added; the feed liquid with the concentration of 1.42-1.84mol / L is input to the feed liquid input port of the precipitation reactor, and the precipitant with the concentration of 1.0-5.72mol / L is input to the precipitant input port of the precipitation reactor.

5. The method for preparing lanthanum hydroxycarbonate with a hexagonal crystal system by hydrothermal synthesis according to claim 1, characterized in that, Take out the precipitate lanthanum carbonate in the precipitation reactor, filter, then use deionized water to leach the filter cake and vacuum dry to obtain the lanthanum carbonate as the precursor.

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