A method and system for obtaining rare earth chloride crystals from a rare earth chloride solution

Abstract

The application provides a method and system for obtaining rare earth chloride crystals from a rare earth chloride solution, and relates to the technical field of rare earth chlorides. The method comprises the following steps: adjusting the pH value of the rare earth chloride solution and removing impurities by filtering after clarification; naturally evaporating and concentrating the rare earth chloride solution after impurity removal at the pH value to obtain a saturated rare earth chloride solution; wherein the pH value is 5.0-7.5; the saturated rare earth chloride solution is evaporated and concentrated to crystallize and precipitate rare earth chloride crystals; during the crystallization and precipitation process, a sunlight greenhouse is used, the solution temperature of a crystallization pool body is controlled to be 10-45 DEG C, and the relative humidity at the upper part of the crystallization pool is controlled to be 15-90%, so that the speed and process of the rare earth chloride crystals are controlled. By using the method provided by the application, high-quality rare earth chloride crystals can be prepared under relatively environmentally friendly conditions on the premise of greatly reducing the evaporation energy consumption.

Description

Technical Field

[0001] This invention relates to the field of rare earth chloride technology, and in particular to a method and system for obtaining rare earth chloride crystals from a rare earth chloride solution. Background Technology

[0002] Rare earth elements are widely used in the military and high-tech industries, holding significant strategic importance for national defense. Rare earth chlorides, as important rare earth compounds, are widely used in rare earth metals, petrochemicals, agriculture, medicine, electronic equipment and communications, optoelectronics, energy, and environmental protection. In agriculture, rare earth chlorides can improve plant resistance to stress; in medicine, lanthanum chloride can inhibit the growth of tumor cells; in functional materials, lanthanum chloride hydrate is an antiferromagnetic material that can be used as a storage medium for data storage and in the manufacture of magnetic sensors and other devices; in light industry, rare earth chlorides are used in leather tanning and textile dyeing; and in environmental protection, rare earth chlorides can be used to treat fluoride- and phosphorus-containing wastewater. Furthermore, rare earth chlorides are raw materials for the chloride electrolysis process to produce rare earth metals, and can also be used to prepare high-temperature ceramic materials and piezoelectric ceramics and other electronic components; cerium chloride is an indispensable raw material for petroleum catalytic cracking (FCC).

[0003] my country ranks first in the world in terms of rare earth reserves, production, exports, and consumption. Industrially, rare earth ore or rare earth-containing raw materials are usually decomposed by acid or alkali methods. After impurity removal or transformation, a mixed rare earth chloride solution is obtained, which is then extracted and separated to obtain a single rare earth chloride solution or a rare earth-enriched chloride solution.

[0004] During the preparation of rare earth chloride solutions, impurities are introduced by the rare earth concentrate raw materials and the chemical raw materials used, such as various saponifying agents such as ammonia water, liquid alkali, and lime used in the extraction. This results in a certain concentration of impurities such as ammonium ions, Na, Ca, Al, Th, or Fe in the rare earth chloride solution. Furthermore, the residual organic extraction phase will cause the total phosphorus or TOC (total organic carbon, which is the total amount of organic matter in water expressed by carbon content and is an important way to monitor organic pollutants) in the rare earth chloride to exceed the standard, thus seriously affecting the quality of rare earth chloride products.

[0005] In the prior art, there are two common methods for obtaining rare earth chloride crystals from rare earth chloride solutions: (1) Evaporation and concentration of the solution system for overall crystallization. The rare earth chloride solution is concentrated to a certain concentration by stirring and heating under positive or slightly negative pressure. The concentrated solution is then placed directly on a flat plate and cooled naturally by air or water to obtain plate-shaped rare earth chloride (i.e., rare earth chloride flakes). These flakes are then cut and packaged. This method has the following problems: Since it is an overall crystallization, the non-rare earth metal impurities (NH4+) present in the rare earth chloride solution are easily lost. 4+All of the rare earth chlorides (Na, Ca, Al, Th or Fe, etc.) and organic extractants are added to the rare earth chloride product. The product purity is not high and the product is in a lumpy state. Due to the high temperature evaporation operation, there is uneven heating in the evaporation and concentration process. Some solutions are heated quickly and some solutions are heated slowly. Due to the rapid heating, the temperature is too high. Some rare earth chloride solutions release acidic gases more quickly, which leads to a local decrease in the acidity of the solution system and the formation of rare earth hydroxides. The plate-shaped rare earth chloride product has poor water solubility and will produce turbidity after dissolution. This method is suitable for low-end rare earth chloride production. (2) High temperature evaporation and concentration - cooling method cooling crystallization method: Usually in Under normal or slightly negative pressure, single or multi-effect high-temperature heating is used to evaporate and concentrate the liquid, and the water evaporates. After the liquid reaches a certain concentration, it is passed to a cooling kettle with a jacket and coil. Heat exchange is carried out by natural water circulation cooling or a combination of low-temperature freezing water. Crystals are precipitated by utilizing the difference in solubility of rare earth chloride solution at different temperatures. During the cooling crystallization process, some non-rare earth metal impurities can be removed. This method has the following problems: due to the high-temperature evaporation operation, the local acidity of the solution decreases, resulting in the precipitation of rare earth hydroxide, which is manifested as visible turbidity in the rare earth chloride crystal product during dissolution. The energy consumption of this method is higher than that of method (1).

[0006] To further reduce the energy consumption of method (2), the prior art provides a method and apparatus for cooling and crystallizing rare earth chlorides. This method utilizes the principle of reduced boiling temperature under negative pressure to cool and crystallize the high-temperature rare earth chloride liquid flowing into a vacuum reactor. Boiling steam is extracted by a jet vacuum pump to maintain a negative pressure environment within the vacuum reactor. The liquid continuously evaporates and cools to crystallize, and the latent heat released during the crystallization process continuously provides a heat source for the evaporation of newly added liquid. Although this method employs multi-effect evaporation and utilizes waste heat or latent heat, it still requires external energy for evaporation and concentration. Specifically, producing 1 ton of rare earth chloride crystals requires 0.2 to 0.7 tons of steam.

[0007] According to the literature "Study on Production Conditions of Rare Earth Chlorides", when the pH value reaches 6.9-7.8, rare earth chlorides will precipitate rare earth hydroxides due to neutralization, resulting in dissolution turbidity. Therefore, in order to prevent the dissolution turbidity of rare earth chlorides caused by local pH increases, methods (1) and (2) usually control the solution to be evaporated and concentrated under high acid conditions (pH value of 1-3.5). However, this leads to the release of acidic gases during the evaporation and concentration process, resulting in environmental deterioration and equipment corrosion.

[0008] Therefore, in the field of rare earth chloride crystal preparation technology, safely and environmentally reducing the content of non-rare earth metal impurities, total phosphorus or TOC, and inhibiting the generation of rare earth hydroxides to obtain high-quality rare earth chlorides has become a technical problem to be solved. Summary of the Invention

[0009] To address the aforementioned problems, in a first aspect, the present invention provides a method for obtaining rare earth chloride crystals from a rare earth chloride solution, the method comprising:

[0010] Step 1: Adjust the pH of the rare earth chloride solution to 5.0-7.5, clarify it, and then filter to remove impurities;

[0011] Step 2: The purified rare earth chloride solution is naturally evaporated and concentrated at the specified pH value to obtain a saturated rare earth chloride solution;

[0012] Step 3: The saturated rare earth chloride solution is subjected to controlled crystallization to obtain rare earth chloride crystals with a particle size of 0.1 cm to 1.0 cm, and the proportion of particles with a particle size in the range of 0.2 cm to 0.6 cm is 55% to 80%. During the controlled crystallization process, the temperature of the saturated rare earth chloride solution is 10℃ to 45℃, and the relative humidity of the surface of the saturated rare earth chloride solution is 15% to 90%.

[0013] Preferably, the rare earth chloride solution comprises a single rare earth chloride or a rare earth enriched chloride obtained by separating a mixed rare earth chloride obtained from processing rare earth concentrate by ion exchange or solvent extraction.

[0014] Preferably, the rare earth concentration of the rare earth chloride solution is 0.5 mol / L to 2.0 mol / L.

[0015] Preferably, during the controlled crystallization process, the temperature of the saturated rare earth chloride solution is 25°C to 30°C, and the relative humidity of the surface layer of the saturated rare earth chloride solution is 35% to 65%.

[0016] Preferably, step 3 includes: the saturated rare earth chloride solution undergoes controlled crystallization to obtain the rare earth chloride crystals and brine; the brine and the rare earth chloride solution from step 1 are combined to return the brine to the natural evaporation concentration and controlled crystallization process.

[0017] In a second aspect, the present invention provides a system for obtaining rare earth chloride crystals from a rare earth chloride solution, the system being used to perform the method described in the first aspect above, the system comprising:

[0018] At least one evaporation concentration tank is used to naturally evaporate and concentrate the purified rare earth chloride solution in the pH range of 5.0 to 7.5 to obtain a saturated rare earth chloride solution.

[0019] At least one crystallization tank is used for controlled crystallization of the saturated rare earth chloride solution to obtain rare earth chloride crystals with a particle size of 0.2 cm to 0.6 cm accounting for 55% to 80%; the temperature of the saturated rare earth chloride solution in the crystallization tank is controlled at 10°C to 45°C, and the surface relative humidity is controlled at 15% to 90%.

[0020] Preferably, a sunroom is built above the evaporation and concentration tank; the sunroom is equipped with an exhaust pipe; and a circulating fan is installed above each of the evaporation and concentration tanks.

[0021] Preferably, a solar greenhouse is built above the crystallization precipitation pool; the solar greenhouse includes an electric telescopic support installed on the roof of the solar greenhouse and doors set on both sides of the solar greenhouse; wherein, the electric telescopic support is used to open or close the roof of the solar greenhouse;

[0022] The solar greenhouse is used to control the temperature of the saturated rare earth chloride solution to 10℃~45℃ and the surface humidity of the saturated rare earth chloride solution to 15%~90%.

[0023] Preferably, the multiple evaporation and concentration tanks are connected in a stepped manner, and the depth of the evaporation and concentration tanks is 30cm to 200cm.

[0024] Preferably, the multiple crystallization precipitation cells are connected in parallel, and the depth of the crystallization precipitation cells is 30cm to 100cm.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] This invention provides a method and system for obtaining rare earth chloride crystals from a rare earth chloride solution, relating to the field of rare earth chloride technology. The method includes: Step 1: Adjusting the pH of the rare earth chloride solution to 5.0–7.5, clarifying it, and then filtering to remove impurities; Step 2: Concentrating the purified rare earth chloride solution by natural evaporation using solar and wind power at the stated pH value to obtain a saturated rare earth chloride solution; Step 3: Controlling the crystallization of the saturated rare earth chloride solution to obtain rare earth chloride crystals with a particle size of 0.1 cm–1.0 cm, and a particle size range of 0.2 cm–0.6 cm comprising 55%–80% of the crystals; during the controlled crystallization process, the temperature of the saturated rare earth chloride solution is 10°C–45°C, and the relative humidity of the surface layer of the saturated rare earth chloride solution is 15%–90%. Using the method provided by this invention, high-quality rare earth chloride crystals can be prepared in a controllable manner while significantly reducing evaporation energy consumption, in a relatively environmentally friendly way.

[0027] This invention utilizes solar radiation or wind power to achieve natural evaporation concentration. On one hand, it eliminates the need for external heating and requires minimal power equipment, reducing energy consumption by 90%. On the other hand, the natural evaporation concentration proposed in this invention is a slow concentration process. Furthermore, by controlling the temperature and relative humidity of the saturated rare earth chloride solution during crystallization, the crystallization process is controlled, effectively preventing impurities from entering the crystals, thus obtaining a high-purity rare earth chloride crystal product.

[0028] (1) Natural evaporation concentration is adopted, which is a slow evaporation and concentration and slow crystallization process. On the one hand, since the slow natural evaporation concentration is carried out under the condition of pH value of 5.0 to 7.5, it is not easy to produce local excessive acidity, and the acidic gas in the solution is difficult to escape, which is conducive to improving the environment and reducing equipment corrosion. As the water content gradually decreases during the evaporation concentration process, the acidity shows an overall slow upward trend, and no rare earth hydroxide precipitation will be produced, thus effectively avoiding the generation of dissolution turbidity. The prepared rare earth chloride crystals have good water solubility and can meet the purity requirements of the product. On the other hand, by controlling the temperature of the saturated rare earth chloride solution within the range of 10℃ to 45℃ and controlling the surface humidity of the solution within the range of 15% to 90% during the slow controlled crystallization process, the obtained rare earth chloride crystals are large and complete with uniform particle size distribution and have high purity. The content of non-rare earth metal impurities in the precipitated rare earth chloride crystal products is less. Therefore, the method provided by this invention can ensure the relatively safe and environmentally friendly preparation of high-quality rare earth chloride crystals.

[0029] (2) Through natural evaporation and concentration, the oil-water separation of the extract phase introduced during the extraction and separation process can be achieved to the greatest extent, thereby reducing the total phosphorus and TOC of rare earth chloride crystals. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart illustrating a method for obtaining rare earth chloride crystals from a rare earth chloride solution according to an embodiment of the present invention.

[0032] Figure 2 This is a flowchart illustrating a specific process for obtaining rare earth chloride crystals from a rare earth chloride solution according to an embodiment of the present invention.

[0033] Figure 3This is a schematic diagram of the evaporation concentration tank and the crystallization precipitation tank in an embodiment of the present invention. Detailed Implementation

[0034] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0035] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0036] In a first aspect, the present invention provides a method for obtaining rare earth chloride crystals from a rare earth chloride solution, such as... Figure 1 As shown, the method includes:

[0037] S1, adjust the pH of the rare earth chloride solution to 5.0-7.5, clarify and filter to remove impurities;

[0038] Impurities in the process of obtaining rare earth chloride crystals from rare earth chloride solutions can be categorized into three types: non-rare earth metal impurities, excessive total phosphorus or TOC content due to extractant residues, and rare earth hydroxides generated during evaporation that cause the rare earth chloride crystals to dissolve and become turbid. Total phosphorus or TOC is introduced by chemical raw materials used in acid or alkali processes, such as residual organic extractive phases from ammonia, liquid alkali, lime, and other saponifying agents. These organic extractive phases cause excessive total phosphorus or TOC in the rare earth chloride crystals, severely affecting their quality. Non-rare earth metal impurities are introduced by rare earth concentrate raw materials and various saponifying agents, resulting in a certain concentration of ammonium ions, Na, Ca, Al, Fe, or Th impurities in the rare earth chloride solution. Al impurities completely form aluminum hydroxide precipitate at a pH of approximately 5, while Fe impurities completely form ferric hydroxide precipitate at a pH of approximately 3.5. Rare earth hydroxides are generated during high-temperature evaporation due to localized low acidity, causing the rare earth chloride crystals to dissolve and become turbid, with poor water solubility, rendering them unusable.

[0039] In this embodiment, the pH value is adjusted to 5.0-7.5 by adding ammonia or alkali before filtration to remove impurities. Some non-rare earth metal impurities such as iron, thorium, aluminum, and thorium are precipitated as hydroxides, which are then removed by clarification and filtration. The rare earth chloride solution after impurity removal is then allowed to evaporate naturally.

[0040] S2, the purified rare earth chloride solution is naturally evaporated and concentrated at the pH value to obtain a saturated rare earth chloride solution;

[0041] Among these methods, multi-stage evaporation concentration can progressively increase the concentration of rare earth chlorides, which is beneficial for improving evaporation concentration efficiency. For example, such as... Figure 2 As shown, the rare earth chloride solution is subjected to evaporation and concentration in sequence: first evaporation and concentration, second evaporation and concentration, third evaporation and concentration, ... N times.

[0042] In this embodiment, the pH value can be set slightly lower than the critical pH value at which rare earth hydroxide precipitation begins, in order to inhibit the formation of rare earth hydroxides. In specific operation, the pH value can be adjusted for rare earth chloride solutions with different rare earth contents and compositions.

[0043] In this embodiment, due to the slow concentration, the content of non-rare earth metal impurities in the rare earth chloride crystal product is low, which can also avoid dissolution and turbidity, and is more conducive to crystallization and purification. In addition, natural evaporation is a slow evaporation and concentration under static conditions, which can maximize the separation of oil and water from the organic extraction phase and reduce the total phosphorus and TOC of rare earth chloride crystals.

[0044] In existing technologies, during the process of obtaining rare earth chloride crystals through high-temperature evaporation and concentration for overall crystallization, to prevent the loss of rare earth elements and the resulting dissolution turbidity caused by localized pH increases, the solution is typically controlled under high-acid conditions (pH 1–3.5) for evaporation and concentration. However, this process leads to the release of acidic hydrogen chloride gas due to heating, resulting in a deterioration of the operating environment and equipment corrosion. Because the temperature is locally too high, hydrogen chloride in the solution overflows more rapidly, causing a rapid decrease in local acidity and a localized pH increase to above 7.5. This precipitates rare earth hydroxides, resulting in visible turbidity when the rare earth chloride crystals dissolve.

[0045] In this embodiment, natural evaporation concentration is adopted. The solution system is not stirred or is stirred with large flow. The evaporation process is slow, and the acidic gas in the solution is not easily passively released. As the solution gradually concentrates during the evaporation and concentration process, the water content decreases, and the acidity of the solution shows an overall upward trend. Rare earth hydroxide precipitation is not easily generated, and the generation of rare earth chloride crystal dissolution and turbidity is effectively avoided.

[0046] During natural evaporation concentration, slow evaporation prevents acidic gases from passively escaping from the solution. Therefore, a higher pH value can be controlled before natural evaporation concentration to remove most non-rare earth metal impurities while minimizing the fugitive emission of acidic gases and preventing corrosion of facilities. Slow natural evaporation concentration at a higher pH value allows the solution to be concentrated naturally using solar radiation or wind power, eliminating the need for external heating and reducing energy consumption by over 90%. Furthermore, the slow evaporation rate slows the crystallization process, reducing the amount of non-rare earth metal impurities entering the rare earth chloride crystals. Since natural evaporation concentration is carried out at a pH of 5.0–7.5, localized excessive acidity is less likely to occur, making it harder for acidic gases to escape, thus improving the environment and suppressing excessive fugitive emissions of hydrogen chloride. As the water content gradually decreases during evaporation concentration, the overall acidity of the solution increases, preventing the formation of rare earth hydroxides.

[0047] In the natural evaporation and concentration process, solar radiation is used for natural evaporation and concentration. To accelerate the evaporation rate of the solution, a circulating fan can be turned on during the evaporation and concentration process to achieve evaporation and concentration using the airflow of the circulating fan.

[0048] S3, the saturated rare earth chloride solution is subjected to controlled crystallization to obtain rare earth chloride crystals with a particle size of 0.1 cm to 1.0 cm, and the proportion of particles with a particle size in the range of 0.2 cm to 0.6 cm is 55% to 80%; during the controlled crystallization process, the temperature of the saturated rare earth chloride solution is 10℃ to 45℃, and the relative humidity of the surface of the saturated rare earth chloride solution is 15% to 90%.

[0049] In this embodiment, the temperature and surface humidity of the saturated rare earth chloride solution during the crystallization process are controlled within a certain range (the temperature of the saturated rare earth chloride solution is 10℃~45℃, and the surface humidity of the saturated rare earth chloride solution is 15%~90%) to achieve slow crystallization, so as to obtain rare earth chloride crystals with large crystal size (particle size of 0.1cm~1.0cm) and uniform distribution (of which 0.2cm~0.6cm particle size accounts for 55%-80%).

[0050] By utilizing and controlling solar radiation and wind power, the crystallization of rare earth chloride solutions is controlled, resulting in the precipitation of rare earth chloride crystals. Solid-liquid separation is then performed on the saturated rare earth chloride solution after the crystals have precipitated and the water has evaporated. Figure 2As shown, rare earth chloride crystals and brine are obtained. The brine consists of residual unevaporated and unconcentrated rare earth chlorides and residual impurities (non-rare earth impurities such as calcium, sodium, iron, magnesium, and thorium, as well as total phosphorus and TOC). The brine is returned to the system and combined with a low-concentration rare earth chloride solution. After pH adjustment, neutralization, impurity removal, and filtration, it is returned to the natural evaporation system. This process helps to improve the rare earth crystallization yield and also makes full use of the previous evaporation and concentration process, thereby increasing the concentration of the rare earth chloride solution returned for evaporation and crystallization.

[0051] Specifically, the temperature and relative humidity of the saturated chloride solution are controlled by opening and closing the roof and doors of the greenhouse. The temperature of the saturated rare earth chloride solution is controlled at 10℃~45℃ and the relative humidity of the surface of the saturated rare earth chloride solution is controlled at 15%~90%. Therefore, the crystallization process does not simply utilize solar and wind energy, but also achieves control of the crystallization conditions within a certain parameter range.

[0052] Since the cooling rate significantly affects the crystal particle size distribution and average particle size, excessively rapid cooling can lead to explosive nucleation, resulting in defects in the grown crystals. The final crystals will have smaller particle sizes, poorer distribution, and are more prone to encapsulating or adsorbing impurities. The slow crystallization process in this embodiment is more conducive to crystallization purification, resulting in a very low content of non-rare earth metal impurities in the precipitated product. The crystallization is a slow process. By controlling the temperature and surface humidity of the saturated rare earth chloride solution within a certain range (temperature of 10℃~45℃, surface relative humidity of 15%~90%), the temperature reduction is controlled, achieving slow crystallization. This controls the crystallization rate and process of rare earth chloride crystals, ensuring the crystallization effect. A small cooling gradient provides sufficient time for crystal growth, and the slow cooling rate ensures that the crystal growth rate exceeds the nucleation rate, avoiding explosive nucleation. Therefore, the resulting rare earth chloride crystals are large, intact, and have a uniform particle size distribution. Because of its large crystal size and therefore small specific surface area, non-rare earth metal impurities can be prevented from entering the crystal lattice and precipitating together with rare earth chlorides, thereby improving the purity of the product.

[0053] In addition, the concentration and crystallization of saturated rare earth chloride solution is a slow crystallization process that can produce large-particle crystals. This can further reduce the amount of residual organic extract phase adsorbed by the rare earth chloride crystals and also reduce the total phosphorus and TOC of the rare earth chloride crystals.

[0054] The embodiments of the present invention utilize solar radiation or wind power to achieve natural evaporation concentration and crystallization. On the one hand, no external energy is required for heating, and the power facilities are few, which can reduce energy consumption by 90%. On the other hand, the natural evaporation concentration proposed in the present invention is a slow concentration, and the crystallization process is controlled by regulating the temperature of the saturated rare earth chloride solution and the relative humidity of its surface, which can effectively prevent impurities from entering the crystal, thereby obtaining a high-purity rare earth chloride crystal product: (1) Since the process is a slow evaporation concentration and slow crystallization process under relatively low temperature conditions, on the one hand, since the slow natural evaporation concentration is carried out under the condition of pH value of 5.0 to 7.5, it is not easy to produce local acidity too high. The acidic gas in the solution is difficult to escape, which is beneficial to the environment and reduces equipment corrosion. As the water content gradually decreases during the evaporation and concentration process, the acidity tends to increase overall. Rare earth hydroxide precipitates will not be produced, thus effectively avoiding the generation of dissolution turbidity. The prepared rare earth chloride crystals have good water solubility and can meet the purity requirements of the product. On the other hand, by controlling the temperature of the saturated rare earth chloride solution within the range of 10℃ to 45℃ and controlling the surface humidity of the solution within the range of 15% to 90% during the slow controlled crystallization process, the obtained rare earth chloride crystals have large and complete particle size and uniform particle size distribution, and have the characteristics of high purity. The precipitated rare earth chloride crystal products contain less non-rare earth metal impurities. Therefore, the method provided by this invention can ensure the relatively safe and environmentally friendly preparation of high-quality rare earth chloride crystals; (2) Through natural evaporation and concentration, the oil and water can be separated to the greatest extent, reducing the total phosphorus and TOC of rare earth chloride crystals.

[0055] In some embodiments, the rare earth chloride solution comprises a single rare earth chloride or a rare earth enriched chloride obtained by separating a mixed rare earth chloride obtained from processing rare earth concentrate by ion exchange or solvent extraction.

[0056] In this embodiment, the processing of rare earth concentrate includes acid or alkaline decomposition of rare earth concentrate.

[0057] In some embodiments, the rare earth concentration of the rare earth chloride solution is 0.5 mol / L to 2.0 mol / L.

[0058] In this embodiment, the yield can be easily controlled by adjusting the rare earth concentration in the rare earth chloride solution.

[0059] In some embodiments, during the controlled crystallization process, the temperature of the saturated rare earth chloride solution is 25°C to 30°C, and the surface humidity of the saturated rare earth chloride solution is 35% to 65%.

[0060] In this embodiment, by further controlling the temperature and surface humidity of the saturated rare earth chloride solution within a certain range during the crystallization process (the temperature of the saturated rare earth chloride solution is 25℃~30℃, and the surface humidity of the saturated rare earth chloride solution is 35%~65%), the rate of temperature reduction is controlled, slow crystallization is achieved, and the crystallization rate and process of rare earth chloride crystal precipitation are controlled to ensure the crystallization effect, allowing the rare earth chloride crystals sufficient time to grow, resulting in larger and higher purity rare earth chloride crystals.

[0061] Specifically, slow crystallization involves a small cooling gradient range and a slow cooling rate, resulting in a crystal growth rate greater than the nucleation rate. This avoids explosive nucleation and minimizes the entry of non-rare earth metal impurities into the crystal lattice to co-precipitate with rare earth chlorides, thereby improving product purity. The resulting rare earth chloride crystals are large, intact, and have a uniform particle size distribution, exhibiting high purity.

[0062] In some implementations, step 3 includes:

[0063] The saturated rare earth chloride solution is subjected to controlled crystallization to obtain the rare earth chloride crystals and brine;

[0064] The brine and the rare earth chloride solution from step 1 are combined to return the brine to the natural evaporation concentration and controlled crystallization process.

[0065] The brine is a saturated rare earth chloride solution containing non-rare earth impurities.

[0066] like Figure 2 As shown, by combining the brine (a saturated rare earth chloride solution containing non-rare earth impurities) and the rare earth chloride solution to remove impurities, and then returning them for natural evaporation, concentration, and crystallization, it is beneficial to ensure the overall yield of rare earth chloride crystals.

[0067] In a second aspect, the present invention provides a system for obtaining rare earth chloride crystals from a rare earth chloride solution, the system being used to perform the method described in the first aspect above, the system comprising:

[0068] At least one evaporation and concentration tank 2 is used to naturally evaporate and concentrate the purified rare earth chloride solution in the pH range of 5.0 to 7.5 to obtain a saturated rare earth chloride solution.

[0069] At least one crystallization tank 6 is used for controlled crystallization of the saturated rare earth chloride solution to obtain rare earth chloride crystals with a particle size of 0.2 cm to 0.6 cm accounting for 55% to 80%; the temperature of the saturated rare earth chloride solution in the crystallization tank is controlled at 10°C to 45°C, and the surface relative humidity is controlled at 15% to 90%.

[0070] like Figure 3 As shown, Figure 3 This is a schematic diagram of the structure of the evaporation concentration tank and the crystallization precipitation tank in an embodiment of the present invention; wherein, Figure 3 (1) Main sectional view of evaporation and concentration tank 2. Figure 3 (3) Side sectional view of evaporation and concentration tank 2 Figure 3 (2) Main sectional view of crystallization precipitation tank 6. Figure 3 (4) Side sectional view of crystallization precipitation tank 6.

[0071] In this invention, the rare earth chloride solution after filtration and impurity removal is introduced into the evaporation and concentration tank 2. In the evaporation and concentration tank 2, the solution is gradually evaporated and concentrated using solar radiation and wind power until it reaches saturation. Then, it is transferred to the crystallization and precipitation tank 6.

[0072] Rare earth chloride crystals are crystallized and precipitated in crystallization tank 6 by utilizing and controlling solar radiation and wind power. This includes: naturally precipitating rare earth chloride crystals by utilizing solar radiation and wind power; performing solid-liquid separation on the saturated rare earth chloride solution after the rare earth chloride crystals have been precipitated and the water has been evaporated to obtain rare earth chloride crystal products and brine; returning the brine to merge with the low-concentration rare earth chloride solution in S1, and after pH adjustment and filtration to remove impurities, returning it to evaporation concentration tank 2 and crystallization tank 6 for evaporation and crystallization.

[0073] To ensure the evaporation effect, multiple evaporation concentration tanks 2 can be set up during the production process. The more evaporation concentration tanks 2 there are, the higher the concentration of rare earth chlorides can be, which is beneficial to improving the evaporation concentration efficiency. The saturated rare earth chloride solution obtained from the evaporation concentration tank 2 is transferred to multiple parallel crystallization precipitation tanks 6 in multiple ways.

[0074] For example, such as Figure 3 As shown, the rare earth chloride solution is sequentially introduced into the first evaporation concentration tank 2 (for one-time evaporation concentration), the second evaporation concentration tank (for two-time evaporation concentration), and the third evaporation concentration tank (for three-time evaporation concentration) to obtain a saturated rare earth chloride solution; the obtained saturated rare earth chloride solution is divided into three streams and enters three crystallization precipitation tanks 6 to obtain rare earth chloride crystals.

[0075] In this embodiment of the invention, the natural evaporation facility mainly consists of an evaporation concentration tank 2 and a crystallization precipitation tank 6. The entire system is simple, the solution in the tank is in a stable and static state, there is no high-temperature heating, the power facilities are few, and the production process is safe.

[0076] In some embodiments, a sunroom 1 is built above the evaporation and concentration tank 2; the sunroom is equipped with an exhaust pipe 4; and a circulating fan 3 is installed above each of the evaporation and concentration tanks.

[0077] The sunroom built above the evaporation and concentration tank 2 is used in conjunction with the exhaust pipe 4 to discharge the water vapor and a small amount of acidic gas generated during the natural evaporation and concentration process.

[0078] Specifically, an openable and closable sunshade 1 is built above multiple evaporation and concentration tanks 2; a circulating fan 3 is installed above each evaporation and concentration tank, and two adjacent evaporation and concentration tanks 2 share a circulating fan 3 to further provide wind power for natural evaporation and concentration, and accelerate the evaporation rate of the solution; the circulating fan 3 is also used to regulate the water vapor and a small amount of acidic gas generated during the evaporation and concentration process, and the exhaust pipe 4 collects and discharges the water vapor and a small amount of acidic gas generated during the evaporation and concentration process regulated by the circulating fan 3.

[0079] In the natural evaporation concentration process, slow natural evaporation concentration is achieved by introducing a solar greenhouse 1 and a circulating fan 3, which eliminates the need for external energy heating and reduces energy consumption by more than 90%. This not only controls the evaporation concentration rate of rare earth chloride solution, but also solves the problem of natural evaporation being completely dependent on the climate, as well as the dilution side effects of rain on the evaporation concentration process and the problem of continuous production operation during non-evaporation seasons such as winter.

[0080] In order to achieve controllable production within a certain parameter range, in some embodiments, a solar greenhouse 1 is built above the crystallization precipitation tank 6; the solar greenhouse 1 includes an electric telescopic support 7 installed on the roof of the solar greenhouse and doors 5 set on both sides of the solar greenhouse; wherein, the electric telescopic support 7 is used to open or close the roof of the solar greenhouse.

[0081] The solar greenhouse 1 is used to control the temperature of the saturated rare earth chloride solution to 10℃~45℃ and the surface humidity of the saturated rare earth chloride solution to 15%~90%.

[0082] Specifically, a closable solar greenhouse 1 is built above multiple crystallization pools 6. The convection of the solar greenhouse 1 through the door 5 and the opening or closing of the roof of the solar greenhouse 1 by the electric telescopic support 7 provide solar radiation and wind power for crystallization, so as to control the surface humidity and temperature of the rare earth chloride solution.

[0083] During the crystallization process, the introduction of a solar greenhouse (1) to control temperature and humidity facilitates slow crystallization. By controlling the temperature and surface humidity of the saturated rare earth chloride solution within a specific range during the concentration and crystallization process—10℃–45℃ and 15%–90%—the crystallization rate and process of the rare earth chloride solution system are controlled. This limits the temperature drop, ensuring slow crystallization, guaranteeing the crystallization effect, and allowing sufficient time for the rare earth chloride crystals to grow, resulting in high-purity crystals. Higher temperatures in the crystallization tank (6) and higher overall humidity in greenhouse (1) are detrimental to the crystallization of the rare earth chloride solution system; conversely, lower temperatures are beneficial for crystallization and growth. Furthermore, the solar greenhouse solves the problem of complete dependence on climate for evaporation concentration and crystallization, as well as the issues of rainwater dilution side effects and continuous production during non-evaporation seasons such as winter.

[0084] In some embodiments, the plurality of evaporation concentration tanks are connected in a stepped manner, and the depth of the evaporation concentration tanks is 30cm to 200cm.

[0085] In this embodiment, multiple evaporation concentration tanks 2 are connected in a multi-stage series to achieve step-by-step evaporation concentration; the rare earth chloride solution is introduced by gravity from one evaporation concentration tank 2 (the depth of the evaporation concentration tank is the same as that of the other evaporation concentration tank 2, but the height of the position is less than that of the other evaporation concentration tank 2) into another adjacent evaporation concentration tank 2; furthermore, the depth of the evaporation concentration tank 2 is preferably 50-80cm.

[0086] In some embodiments, the plurality of crystallization precipitation cells are connected in parallel, and the depth of the crystallization precipitation cells is 30cm to 100cm.

[0087] In this embodiment, the height difference between the last-stage evaporation and concentration tank 2 and the crystallization precipitation tank 6 (the height of the last-stage evaporation and concentration tank 2 is higher than the height of the crystallization precipitation tank 6) is used to achieve gravity flow from the last-stage evaporation and concentration tank 2 to the crystallization precipitation tank 6. The crystallization precipitation tanks 6 are connected in parallel, that is, they are divided into multiple paths and flow to multiple crystallization precipitation tanks 6 respectively to achieve transfer. The depth of the multiple crystallization precipitation tanks 6 is the same. Further, the depth of the crystallization precipitation tank 6 is preferably 50cm to 80cm.

[0088] To enable those skilled in the art to better understand the present invention, the preparation method provided by the present invention will be described below through several specific embodiments.

[0089] Example 1

[0090] This embodiment uses natural evaporation, concentration, and crystallization to obtain rare earth chloride crystals. The specific steps are as follows:

[0091] Lanthanum chloride was obtained by extraction and separation, and then neutralized, clarified, and filtered to remove impurities to obtain a lanthanum chloride solution with a REO (total rare earth oxides) of 212 g / L, a pH of 7.2, a TOC of 132 mg / L, and a Ca content of 0.20% (CaO / REO).

[0092] The obtained lanthanum chloride solution is pumped into an evaporation concentration tank. The three evaporation concentration tanks are connected in a stepped manner, each with a depth of 40 cm and a height difference of 50 cm between adjacent evaporation concentration tanks. The height difference between the last stage evaporation concentration tank and the crystallization precipitation tank is 30 cm. The lanthanum chloride solution flows to the next stage evaporation concentration tank through the height difference to continue evaporation and concentration. The saturated lanthanum chloride solution flows by gravity from the last stage evaporation concentration tank through the height difference into the crystallization precipitation tank to precipitate lanthanum chloride crystals.

[0093] The system includes an openable and closable sunroom above the evaporation and concentration tank. A circulating fan is installed along the tank's edge; when the fan is turned on, the airflow sweeps across the surface of the lanthanum chloride and cerium chloride solution, accelerating the evaporation process. An exhaust pipe is installed on the roof of the sunroom, with its bottom close to the solution surface, to collect and discharge the water vapor generated during the evaporation and concentration process.

[0094] A closable sunshade is constructed above the crystallization tank. An electrically operated telescopic bracket on the roof controls the degree of closure of the sunshade. When the sunshade is open, airflow sweeps across the surface of the saturated lanthanum chloride solution. By controlling the degree of closure and the airflow speed of the sunshade, the temperature of the solution in the crystallization tank and the relative humidity at the tank surface are adjusted to control the speed and process of lanthanum chloride crystal precipitation. During the crystallization process, the temperature of the saturated lanthanum chloride solution in the crystallization tank is controlled at 27℃-32℃, and the relative humidity above the crystallization tank is controlled at 35%-45%.

[0095] Lanthanum chloride crystals were tested, and the particle size range was found to be 0.14-0.88 cm. Particles with a size of 0.2 cm to 0.6 cm accounted for 69.91%, with an average particle size of 0.38 cm. The lanthanum chloride crystals contained 45.8% REO, 0.01% Ca (CaO / ∑REO), and 5 ppm TOC ( / ∑REO). Dissolving 10 g of lanthanum chloride crystals in 100 ml of water at pH 5.0 resulted in no visible turbidity, and the suspended solids concentration was 4 mg / L.

[0096] Throughout the evaporation and crystallization production process, the area around the evaporation and crystallization precipitation tank was monitored in accordance with HJ / T55-2000 "Technical Guidelines for Monitoring Unorganized Emissions of Air Pollutants". The concentration of hydrogen chloride emissions was lower than the atmospheric pollutant concentration limits at the boundaries of existing and newly built enterprises as specified in Table 6 of "Emissions of Pollutants from Rare Earth Industry".

[0097] Comparative Example 1 (Comparative Example of Example 1)

[0098] This comparative example uses a total evaporation and concentration method, and adjusts the pH value during the evaporation and concentration process. The specific steps are as follows:

[0099] The extracted solution was neutralized, clarified, and filtered to remove impurities, resulting in a lanthanum chloride solution with a REO of 212 g / L, a pH of 7.2, a TOC of 132 mg / L, and a Ca content of 0.20% (CaO / REO).

[0100] The resulting lanthanum chloride solution was adjusted to pH 2.5 and concentrated at high temperature under initial high acid conditions in an enamel-lined reactor. After concentration to a boiling point of 155°C, the solution was placed in a cooling pan and cooled by air to obtain blocky lanthanum chloride crystals. The production process generates hydrochloric acid gas, which requires centralized treatment.

[0101] Tests showed that lanthanum chloride crystals contained 46.9% REO, 0.20% Ca (CaO / ∑REO), and 330ppm TOC ( / ∑REO). When 10g of lanthanum chloride crystals were dissolved in 100ml of water with a pH of 5.0, there was no visible turbidity, and the concentration of suspended solids was 6mg / L.

[0102] Comparative Example 2 (Comparative Example of Example 1)

[0103] Since Comparative Example 1 involved evaporation and concentration under high acid conditions, and the hydrochloric acid gas was subsequently centrally processed after the experiment, this embodiment does not use high acid conditions during the high-temperature evaporation and concentration process. The specific steps of this embodiment are as follows:

[0104] The extracted solution was neutralized, clarified, and filtered to remove impurities, resulting in a lanthanum chloride solution with a REO of 212 g / L, a pH of 7.2, a TOC of 132 mg / L, and a Ca content of 0.20% (CaO / REO).

[0105] The lanthanum chloride solution was concentrated by high-temperature evaporation in an enamel-lined reactor. After concentration to a boiling point of 155°C, the solution was placed in a cooling pan and cooled by air to obtain blocky lanthanum chloride crystals. A small amount of acidic gas was generated during the evaporation process, which needed to be centrally treated.

[0106] Tests showed that lanthanum chloride crystals contained 46.6% REO, 0.21% Ca (CaO / ∑REO), and 357ppm TOC ( / ∑REO). When 10g of lanthanum chloride crystals were dissolved in 100ml of water with a pH of 5.0, visible turbidity was observed, and the concentration of suspended solids was 135mg / L.

[0107] Comparative Examples 1 and 2 show that during high-temperature evaporation and concentration, the acidity of the system needs to be controlled within a relatively high range to prevent the formation of localized rare earth hydroxides and to ensure that the resulting rare earth chlorides do not dissolve and become turbid. However, the acidic gases generated during the evaporation process need to be centrally treated.

[0108] Comparative Example 3 (Comparative Example of Example 1)

[0109] This comparative example uses a high-temperature evaporation and concentration followed by cooling and crystallization. The specific steps are as follows:

[0110] The extracted solution was neutralized, clarified, and filtered to remove impurities, resulting in a lanthanum chloride solution with a REO of 212 g / L, a pH of 7.2, a TOC of 132 mg / L, and a Ca content of 0.20% (CaO / REO).

[0111] The lanthanum chloride solution was heated and evaporated at 90℃ to concentrate it to 500g REO / L. Under the conditions of cooling rate of 1.5K / min, stirring rate of 150r / min, seed crystal addition of 2%, and crystal growth for 120min, the solution was cooled and crystallized at 45℃, and solid-liquid separation was performed to obtain lanthanum chloride crystal product.

[0112] The lanthanum chloride crystals were tested and found to have 45.8% REO, 0.05% Ca (CaO / REO), and 34 ppm TOC ( / ∑REO). When 10 g of lanthanum chloride crystals were dissolved in 100 ml of water at pH 5.0, visible turbidity was observed, and the concentration of suspended solids was 110 mg / L. The proportion of particles with a size of 0.2 cm to 0.6 cm was 45.81%, and the particle size ranged from 0.09 cm to 0.89 cm.

[0113] As can be seen from Comparative Example 3, the crystal size is still relatively small when using the cooling crystallization method because the entire crystallization process is fast.

[0114] From Examples 1 and Comparative Examples 1, 2, and 3, it can be seen that, compared with the current conventional methods, natural evaporation concentration crystallization can effectively control the crystal nucleation process during the concentration and cooling process, inhibit explosive nucleation, ensure larger lanthanum chloride crystal particle size, better avoid crystals carrying more mother liquor, reduce the calcium content of impurities in the crystals, and improve the purity of the product. The static operation of natural evaporation concentration is also conducive to reducing the total TOC of the crystals. At the same time, natural evaporation concentration is carried out under conditions close to the pH value of rare earth chloride neutralization precipitation, which can avoid the local generation of rare earth hydroxides while reducing hydrochloric acid overflow, improve the solubility of lanthanum chloride crystals, and reduce the generation of dissolved insoluble matter (visible turbidity).

[0115] Example 2

[0116] The difference from Example 1 is that a different raw material was used, namely a solution of monazite decomposition mixed with rare earth chloride. The specific steps are as follows:

[0117] The clarified mixed rare earth chloride solution produced by the monazite decomposition process has an REO content of 150 g / L, a TOC content of 220 ppm, a thorium content of 0.03% (ThO2 / ΣREO), an iron content of 0.04% (Fe2O3 / ΣREO), a Na content of less than 0.6% (Na2O / ΣREO), a Ca content of 0.4% (CaO / ΣREO), and a pH value of 5.5.

[0118] The natural evaporation concentration and crystallization system consists of two evaporation concentration tanks and one crystallization precipitation tank, connected in a stepped manner, with an effective depth of 60 cm for each tank. An openable and closable sunshade is built above the crystallization precipitation tank, with an electric telescopic bracket installed on the roof to control the degree of closure of the sunshade. When the sunshade is open, the airflow sweeps across the surface of the saturated chloride solution.

[0119] The obtained mixed rare earth chloride solution is pumped into a natural evaporation concentration tank. The solution then flows through a high-pressure flow to a lower-level evaporation concentration tank for further evaporation and concentration until saturation. Finally, it flows through a high-pressure flow to a crystallization precipitation tank, precipitating mixed rare earth chloride crystals. By controlling the degree of closure and wind speed of the solar greenhouse, the temperature of the solution in the crystallization precipitation tank and the relative humidity at the tank surface are adjusted. The temperature of the saturated lanthanum chloride solution is controlled at 30℃-35℃, and the relative humidity at the top of the crystallization precipitation tank is maintained at 45%-55%.

[0120] The obtained mixed rare earth chloride crystals were tested. The particle size of the mixed rare earth chloride crystals ranged from 0.13 cm to 0.78 cm, with 64.8% of the crystals being between 0.2 cm and 0.6 cm. The REO content was 46.7%, the thorium content was 0.006% (ThO2 / ΣREO), the iron content was 0.006% (Fe2O3 / ΣREO), the Na content was 0.20% (Na2O / ΣREO), and the calcium content was 0.09% (CaO / ΣREO). When 10 g of the mixed rare earth chloride tablets were dissolved in 100 ml of water at pH 5.0, there was no visible turbidity, and the concentration of suspended solids was 4 mg / L.

[0121] Throughout the evaporation and crystallization production process, the area around the evaporation and crystallization precipitation tank was monitored in accordance with HJ / T55-2000 "Technical Guidelines for Monitoring Unorganized Emissions of Air Pollutants". The concentration of hydrogen chloride emissions was lower than the atmospheric pollutant concentration limits at the boundaries of existing and newly built enterprises as specified in Table 6 of "Emissions of Pollutants from Rare Earth Industry".

[0122] Comparative Example 4 (Comparative Example of Example 2)

[0123] The clarified mixed rare earth chloride solution produced by the monazite decomposition process has an REO content of 150 g / L, a TOC content of 220 ppm, a thorium content of 0.03% (ThO2 / ΣREO), an iron content of 0.04% (Fe2O3 / ΣREO), a Na content of less than 0.6% (Na2O / ΣREO), a Ca content of 0.4% (CaO / ΣREO), and a pH value of 5.5.

[0124] The obtained mixed rare earth chloride solution was concentrated by high-temperature evaporation in an enamel-lined reactor. After the temperature reached 155°C, it was placed in a cooling pan and cooled by air to obtain mixed rare earth chloride flakes (i.e., mixed rare earth chloride flakes).

[0125] Tests showed that the mixed rare earth chloride tablets contained 0.027% thorium (ThO2 / ΣREO), 0.04% iron (Fe2O3 / ΣREO), 0.8% Na (Na2O / ΣREO), and 0.34% calcium (CaO / ΣREO). When 10 grams of rare earth chloride crystals were dissolved in 100 ml of water with a pH of 5.0, turbidity was observed, and the concentration of suspended solids was 403 mg / L.

[0126] Example 3

[0127] Raw materials: A lanthanum and cerium chloride concentrate solution was obtained by extraction and separation of mixed rare earth chlorides. The pH was adjusted to 6.5, clarified, filtered, and impurities were removed to obtain a lanthanum and cerium chloride solution. The concentrate contained: REO 100 g / L, TOC 125 ppm, Mg 0.021% (MgO / ΣREO), and Ca 0.035% (CaO / ΣREO).

[0128] Lanthanum chloride and cerium chloride solution were pumped into a 5-stage natural evaporation concentration tank (effective depth 120 cm). The solution was gradually concentrated by natural evaporation to obtain a saturated solution, which was then introduced into a crystallization precipitation tank (effective depth 60 cm) by means of elevation difference. The crystallization precipitation tank was covered by a sunshade. By controlling the degree of closure of the sunshade and the amount of ventilation, the temperature of the crystallization precipitation tank and the humidity at the top 20 cm of the crystallization precipitation tank were regulated, and lanthanum chloride and cerium chloride crystals were crystallized out.

[0129] The temperature of the crystallization precipitation tank solution was controlled at 25℃~30℃, and the relative humidity at the top of the crystallization precipitation tank was 30~35%. After 25 days of operation, the precipitated lanthanum chloride crystals were analyzed as follows: the particle size distribution was 0.16cm~0.88cm, with 57.2% of the particles being 0.3cm~0.6cm; the REO content was 45.7%, the Ca content was 88ppm (CaO / ΣREO), the Mg content was 82ppm (MgO / ΣREO), and the TOC was 8ppm ( / ΣREO); when 10g of mixed rare earth chloride crystals were dissolved in 100ml of water with a pH of 5.0, there was no visible turbidity, and the concentration of suspended solids was 5ppm.

[0130] Example 4

[0131] Raw materials: A lanthanum and cerium chloride concentrate solution was obtained by extraction and separation of mixed rare earth chlorides. The pH was adjusted to 6.5, clarified, and purified to obtain a lanthanum and cerium chloride solution. The concentrate contained: REO 100 g / L, TOC 125 ppm, Mg 0.021% (MgO / ΣREO), and Ca 0.035% (CaO / ΣREO).

[0132] Lanthanum chloride and cerium chloride solution is pumped into a 5-stage natural evaporation concentration tank (effective depth 80 cm). The solution is gradually concentrated by natural evaporation to obtain a saturated solution, which is then introduced into a crystallization precipitation tank (effective depth 60 cm) by elevation difference. The crystallization precipitation tank is covered by a sunshade. By controlling the degree of closure of the sunshade and the amount of ventilation, the temperature of the crystallization precipitation tank and the humidity at the top 20 cm of the crystallization precipitation tank are regulated, and lanthanum chloride and cerium chloride crystals are crystallized out.

[0133] The temperature of the crystallization precipitation tank solution was controlled at 30℃~35℃, and the relative humidity at the top of the crystallization precipitation tank was 40%~50%. After 25 days of operation, the precipitated lanthanum chloride crystals were analyzed as follows: the particle size distribution was 0.17cm~0.88cm, with 0.2cm~0.6cm accounting for 55.3%; the REO content was 45.5%, the Ca content was 76ppm (CaO / ΣREO), the Mg content was 66ppm (MgO / ΣREO), and the TOC was 6ppm ( / ΣREO); when 10g of mixed lanthanum chloride was dissolved in 100ml of water with a pH of 5.0, there was no visible turbidity, and the concentration of suspended solids was 5ppm.

[0134] Example 5

[0135] Raw materials: A lanthanum and cerium chloride concentrate solution was obtained by extraction and separation of mixed rare earth chlorides. The pH was adjusted to 6.5, clarified, and filtered to remove impurities, yielding a lanthanum and cerium chloride solution. The concentrate contained: REO 100 g / L, TOC 125 ppm, Mg 0.021% (MgO / ΣREO), and Ca 0.035% (CaO / ΣREO).

[0136] Lanthanum chloride and cerium chloride solution is pumped into a 5-stage natural evaporation concentration tank (effective depth 80 cm). The solution is gradually concentrated by natural evaporation to obtain a saturated solution, which is then introduced into a crystallization precipitation tank (effective depth 60 cm) by means of elevation difference. The crystallization precipitation tank is covered by a sunshade. By controlling the degree of closure of the sunshade and the amount of ventilation, the temperature of the crystallization precipitation tank and the humidity at the top 20 cm of the tank are regulated, and lanthanum chloride and cerium chloride crystals are crystallized out.

[0137] The temperature of the saturated solution in the crystallization precipitation tank was controlled at 25℃~30℃, and the relative humidity at the top of the crystallization precipitation tank was 55~65%. After 25 days of operation, the precipitated lanthanum cerium chloride crystals were analyzed as follows: the particle size distribution was 0.18cm~0.86cm, with 0.2cm~0.6cm accounting for 72.5%; the REO content was 46.1%, the Ca content was 61ppm (CaO / ΣREO), the Mg content was 54ppm (MgO / ΣREO), and the TOC was 4ppm ( / ΣREO); when 10g of mixed rare earth lanthanum cerium chloride was dissolved in 100ml of water with a pH of 5.0, there was no visible turbidity, and the concentration of suspended solids was 4ppm.

[0138] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0139] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0140] The above provides a detailed description of the method and system for obtaining rare earth chloride crystals from a rare earth chloride solution provided by the present invention. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for obtaining a rare earth chloride crystal from a rare earth chloride solution, characterized by, The method includes: Step 1: Adjust the pH of the rare earth chloride solution to 5.0~7.5, clarify it, and then filter to remove impurities; Step 2: The purified rare earth chloride solution is naturally evaporated and concentrated at the specified pH value to obtain a saturated rare earth chloride solution; Step 3: The saturated rare earth chloride solution is subjected to controlled crystallization to obtain rare earth chloride crystals with a particle size of 0.1 cm to 1.0 cm, and the proportion of particles with a particle size in the range of 0.2 cm to 0.6 cm is 55% to 80%. During the controlled crystallization process, the temperature of the saturated rare earth chloride solution is 10 ℃ to 45 ℃, and the relative humidity of the surface layer of the saturated rare earth chloride solution is 15% to 90%.

2. The method of claim 1, wherein, The rare earth chloride solution includes a single rare earth chloride or a rare earth enriched chloride obtained by separating a mixed rare earth chloride obtained from processing rare earth concentrate by ion exchange or solvent extraction.

3. The method according to claim 1, characterized in that, The rare earth concentration of the rare earth chloride solution is 0.5 mol / L to 2.0 mol / L.

4. The method of claim 1, wherein, Step 3 includes: The saturated rare earth chloride solution is subjected to controlled crystallization to obtain the rare earth chloride crystals and brine; The brine and the rare earth chloride solution from step 1 are combined to return the brine to the natural evaporation concentration and controlled crystallization process.

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