Method and system for natural evaporation crystallization of rare earth chlorides

Abstract

The application provides a method and system for natural evaporation crystallization of rare earth chlorides, and relates to the technical field of rare earth chlorides, which comprises the following steps: adjusting the pH value of a rare earth chloride solution to 5.0-7.5, and filtering and removing impurities after clarification; performing natural evaporation concentration on the rare earth chloride solution after impurity removal at the pH value to obtain a saturated rare earth chloride solution; and performing natural crystallization on the saturated rare earth chloride solution to precipitate rare earth chloride crystals. By using the method provided by the application, high-quality rare earth chloride crystals can be prepared in a relatively safe and environmentally friendly manner under the premise of greatly reducing evaporation energy consumption.

Description

Technical Field

[0001] This invention relates to the field of rare earth chloride technology, specifically a method and system for the natural evaporation and crystallization of rare earth chlorides. 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 (abbreviated as 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 above problems, in a first aspect, the present invention provides a method for the natural evaporation and crystallization of rare earth chlorides, the method comprising:

[0010] Adjust the pH of the rare earth chloride solution to 5.0–7.5, clarify it, and then filter it to remove impurities.

[0011] The purified rare earth chloride solution was naturally evaporated and concentrated at the specified pH value to obtain a saturated rare earth chloride solution.

[0012] The saturated rare earth chloride solution crystallizes naturally to precipitate rare earth chloride crystals.

[0013] Preferably, the particle size of the rare earth chloride crystals is 0.1 cm to 1.0 cm; wherein, the proportion of rare earth chloride crystals with a particle size in the range of 0.2 cm to 0.6 cm is 55% to 80%.

[0014] Preferably, the rare earth chloride solution includes mixed rare earth chlorides obtained by processing rare earth concentrates, or single rare earth chlorides or rare earth enriched chlorides obtained by separating mixed rare earth chlorides by ion exchange or solvent extraction.

[0015] Preferably, the rare earth concentration of the rare earth chloride solution is 0.5 mol / L to 2.0 mol / L.

[0016] In a second aspect, the present invention provides a system for the natural evaporation and crystallization of rare earth chlorides, the system being used to perform the method described in the first aspect above, the system comprising:

[0017] At least one evaporation concentration tank is used to naturally evaporate and concentrate the filtered and impurity-removed rare earth chloride solution to obtain a saturated rare earth chloride solution.

[0018] At least one crystallization pool is provided for the natural crystallization of the saturated rare earth chloride solution to precipitate rare earth chloride crystals.

[0019] Preferably, the plurality of evaporation and concentration tanks are connected in a stepped series configuration, and the plurality of crystallization and precipitation tanks are connected in parallel configuration.

[0020] Preferably, the evaporation and concentration tank of the last stage is positioned at a different height from the crystallization and precipitation tank; the height of the evaporation and concentration tank of the last stage is higher than that of the crystallization and precipitation tank, so that the saturated rare earth chloride solution in the evaporation and concentration tank of the last stage flows by gravity to the crystallization and precipitation tank.

[0021] The depth of the evaporation and concentration tank is 30cm to 200cm.

[0022] Preferably, the depth of the crystallization precipitation pool is 30cm to 100cm.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] This invention provides a method and system for the natural evaporation crystallization of rare earth chlorides, relating to the field of rare earth chloride technology. The method includes: adjusting the pH of a rare earth chloride solution to 5.0–7.5, clarifying it, and then filtering to remove impurities; naturally evaporating and concentrating the purified rare earth chloride solution at the stated pH value to obtain a saturated rare earth chloride solution; and naturally crystallizing the saturated rare earth chloride solution to precipitate rare earth chloride crystals. Using the method provided by this invention, high-quality rare earth chloride crystals can be prepared in a relatively safe and environmentally friendly manner while significantly reducing evaporation energy consumption.

[0025] This invention utilizes solar radiation or wind power to achieve natural evaporation concentration and natural crystallization. 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 and crystallization process proposed in this invention is a slow concentration and crystallization process, effectively preventing impurities from entering the crystals and yielding high-purity rare earth chloride crystal products.

[0026] (1) Through natural evaporation concentration and natural crystallization, since this process is a slow evaporation concentration and slow crystallization process, on the one hand, because 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 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 quality requirements of the product. On the other hand, due to the slow natural crystallization, the obtained rare earth chloride crystals have the characteristics of high purity, large and complete crystal size, and relatively uniform crystal size distribution. The content of non-rare earth metal impurities in the precipitated rare earth chloride crystal products is less. Therefore, the method provided by the present invention can ensure the relatively safe and environmentally friendly preparation of high-quality rare earth chloride crystals.

[0027] (2) Through natural evaporation concentration and natural crystallization, the oil-water separation can be achieved to the greatest extent by introducing the extract phase during the extraction and separation process, thereby reducing the total phosphorus and TOC of rare earth chloride crystals. Attached Figure Description

[0028] 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.

[0029] Figure 1 This is a flowchart of a method for natural evaporation crystallization of rare earth chlorides according to an embodiment of the present invention;

[0030] Figure 2 This is a flowchart illustrating the natural evaporation and crystallization process of rare earth chlorides according to an embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram of the evaporation concentration tank and the crystallization precipitation tank in an embodiment of the present invention. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] In a first aspect, the present invention provides a method for the natural evaporation and crystallization of rare earth chlorides, such as... Figure 1 As shown, the method includes:

[0035] S1, adjust the pH of the rare earth chloride solution to 5.0-7.5, clarify it, and then filter to remove impurities;

[0036] 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 turbidity in the dissolution of rare earth chloride crystals. Among these, total phosphorus or TOC is introduced by chemical raw materials used in acid or alkaline processes, such as residual organic extractants from ammonia, liquid alkali, lime, and other saponifying agents. These organic extractants cause excessive total phosphorus or TOC in the rare earth chloride crystals, severely affecting their quality. Non-rare earth metal impurities... Metallic impurities are introduced from 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. Among them, the pH value at which Al impurities completely form aluminum hydroxide precipitate is around 5, and the pH value at which Fe impurities completely form iron hydroxide precipitate is around 3.5. Rare earth hydroxides are generated during high-temperature evaporation due to the decrease in acidity. These rare earth hydroxides cause the rare earth chloride crystals to dissolve and become turbid. The prepared rare earth chlorides cannot be used due to their poor water solubility.

[0037] In this embodiment, the pH value is adjusted to 5.0-7.5 by adding ammonia or alkali for filtration and impurity removal. Most of the non-rare earth metal impurities such as iron, thorium, aluminum, and thorium are precipitated in the form of hydroxides to remove most of the non-rare earth metal impurities. Then, the rare earth chloride solution is naturally evaporated.

[0038] S2, the purified rare earth chloride solution is naturally evaporated and concentrated at the pH value to obtain a saturated rare earth chloride solution;

[0039] 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.

[0040] 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 suppress the formation of rare earth hydroxides during the natural evaporation and concentration process. In specific operation, this critical pH value can be adjusted for rare earth chloride solutions with different rare earth contents and compositions.

[0041] In this embodiment, since the crystallization is slow and concentrated, 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, the rare earth chloride solution is slowly evaporated and concentrated 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 the rare earth chloride crystal.

[0042] 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 above 7.5. This precipitates rare earth hydroxides, resulting in visible turbidity when the rare earth chloride crystals dissolve.

[0043] 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.

[0044] 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.

[0045] In the natural evaporation and concentration process, solar radiation is used for natural evaporation and concentration. In order 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 by utilizing the wind power of the circulating fan. The circulating fan is located above the evaporation and concentration tank.

[0046] S3, the saturated rare earth chloride solution crystallizes naturally to precipitate rare earth chloride crystals.

[0047] A saturated rare earth chloride solution undergoes natural crystallization, with rare earth chloride crystals naturally precipitating through solar radiation and natural wind. After the rare earth chloride crystals have precipitated and the water has been evaporated, the saturated rare earth chloride solution undergoes solid-liquid separation to obtain rare earth chloride crystal products and rare earth chloride brine. The rare earth chloride 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). Figure 2 As shown, the old rare earth chloride brine is returned and combined with a low-concentration rare earth chloride solution. After pH adjustment and impurity removal, it is returned to the natural evaporation system for evaporation and crystallization. For example, as... Figure 2 As shown, the obtained saturated rare earth chloride solution was transferred in multiple ways to three parallel crystallization precipitation tanks to precipitate rare earth chloride crystals.

[0048] Since the cooling rate significantly affects the crystal grain 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 grain 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 product with minimal non-rare earth metal impurities. Natural crystallization is a slow process, ensuring optimal crystallization. The small cooling gradient provides sufficient time for crystal growth, and the slow cooling rate ensures that the crystal growth rate exceeds the nucleation rate, preventing explosive nucleation. This results in rare earth chloride crystals with high purity, larger and more complete crystal grains, and a more uniform grain size distribution. The larger crystal grain size also results in a smaller specific surface area, minimizing the possibility of non-rare earth metal impurities entering the crystal lattice and co-precipitating with the rare earth chloride, thus improving product purity. During the slow natural crystallization process, the temperature of the saturated rare earth chloride solution is within the range of 20℃ to 35℃, and the surface humidity of the solution is within the range of 35% to 65%.

[0049] In addition, natural crystallization of saturated rare earth chloride solution can produce crystals with larger particle size through a slow natural crystallization process. This can further reduce the amount of residual organic extract phase adsorbed by the rare earth chloride crystals, thereby maximizing the separation of oil and water by static settling and reducing the total phosphorus and TOC of the rare earth chloride crystals.

[0050] The embodiments of the present invention utilize solar radiation or wind power to achieve natural evaporation concentration and natural 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 and natural crystallization proposed in the present invention is a slow concentration and crystallization process, which effectively avoids impurities from entering the crystal and obtains a high-purity rare earth chloride crystal product: (1) Through natural evaporation concentration and natural crystallization, since the process is a slow evaporation 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 generate local acid. If the acidity is 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 quality requirements of the product. On the other hand, due to the slow natural crystallization, the slow process makes the obtained rare earth chloride crystals have the characteristics of high purity, large and complete crystal size, and relatively uniform crystal size distribution. The content of non-rare earth metal impurities in the precipitated rare earth chloride crystal products is less. Therefore, the method provided by the present invention can ensure the relatively safe and environmentally friendly preparation of high-quality rare earth chloride crystals; (2) By using natural evaporation and concentration and natural crystallization, the oil-water separation of the extract phase introduced during the extraction and separation process can be achieved to the greatest extent, reducing the total phosphorus and TOC of rare earth chloride crystals.

[0051] In some embodiments, the particle size of the rare earth chloride crystals is 0.1 cm to 1.0 cm; wherein, the proportion of rare earth chloride crystals with a particle size in the range of 0.2 cm to 0.6 cm is 55% to 80%.

[0052] In this embodiment, by controlling the temperature and surface humidity of the saturated rare earth chloride solution during the natural crystallization process within a certain range (the temperature of the saturated rare earth chloride solution is 20℃~35℃, and the surface humidity of the saturated rare earth chloride solution is 35%~65%), relatively slow crystallization is achieved, so as to obtain rare earth chloride crystals with larger crystal size (0.1cm~1.0cm) and more uniform distribution (of which 0.2cm~0.6cm particle size accounts for 55%-80%).

[0053] In some embodiments, the rare earth chloride solution includes mixed rare earth chlorides obtained by processing rare earth concentrates, or single rare earth chlorides or rare earth enriched chlorides obtained by separating mixed rare earth chlorides by ion exchange or solvent extraction.

[0054] In this embodiment, the processing of rare earth concentrate includes acid or alkaline decomposition of rare earth concentrate.

[0055] In some embodiments, the rare earth concentration of the rare earth chloride solution is 0.5 mol / L to 2.0 mol / L.

[0056] In this embodiment, the yield can be easily controlled by adjusting the rare earth concentration in the rare earth chloride solution.

[0057] In a second aspect, the present invention provides a system for obtaining rare earth chloride crystals from a rare earth chloride solution, the system comprising:

[0058] At least one evaporation and concentration tank 2 is used to naturally evaporate and concentrate the filtered and impurity-removed rare earth chloride solution to obtain a saturated rare earth chloride solution.

[0059] At least one crystallization pool 5 is provided for the natural crystallization of the saturated rare earth chloride solution to precipitate rare earth chloride crystals.

[0060] 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; Figure 3 (1) Main sectional view of the evaporation and concentration tank. Figure 3 (2) Main sectional view of the crystallization precipitation cell.

[0061] Rare earth chloride crystals are naturally crystallized in a crystallization and precipitation tank using solar radiation and wind power. This process includes: naturally crystallizing rare earth chloride crystals using solar radiation and wind power; performing solid-liquid separation on the saturated rare earth chloride solution after the rare earth chloride crystals have precipitated and the water has been evaporated to obtain rare earth chloride crystal products and rare earth chloride brine; returning the rare earth chloride brine to be combined with a low-concentration rare earth chloride solution, neutralizing and removing impurities by adjusting the pH value, and then returning it to the evaporation and concentration tank and the crystallization and precipitation tank for evaporation and crystallization.

[0062] Multiple evaporation and concentration tanks are used for step-by-step evaporation and concentration. To ensure the evaporation effect, multiple evaporation and concentration tanks can be set up during the production process. The more evaporation and concentration tanks there are, the higher the concentration of rare earth chloride can be, which is beneficial to improving the evaporation and concentration efficiency. The saturated rare earth chloride solution obtained from the evaporation and concentration tanks is transferred to multiple parallel crystallization and precipitation tanks.

[0063] For example, such as Figure 2 As shown, the rare earth chloride solution is subjected to a series of evaporation and concentration processes: one evaporation and concentration (introduced into the first evaporation and concentration tank), a second evaporation and concentration (introduced into the second evaporation and concentration tank), a third evaporation and concentration (introduced into the third evaporation and concentration tank), and so on, N times (introduced into the Nth evaporation and concentration tank) to obtain a saturated rare earth chloride solution. The obtained saturated rare earth chloride solution is divided into three streams and introduced into three crystallization precipitation tanks to obtain rare earth chloride crystals.

[0064] In this embodiment of the invention, the natural evaporation facility mainly consists of an evaporation concentration tank and a crystallization precipitation tank. 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.

[0065] In this invention, the rare earth chloride solution after filtration and impurity removal is introduced into an evaporation and concentration tank 2. In the evaporation and concentration tank 2, the solution is gradually concentrated using solar radiation and wind power until it reaches saturation. Then, it is transferred to a crystallization and precipitation tank 5. In the crystallization and precipitation tank 5, rare earth chloride crystals are naturally precipitated using solar radiation and wind power. This includes: naturally precipitating rare earth chloride crystals using solar radiation and natural wind power; performing solid-liquid separation on the saturated rare earth chloride solution after the crystals have precipitated and water has been evaporated to obtain rare earth chloride crystal products and rare earth chloride brine; returning the rare earth chloride brine to be combined with a low-concentration rare earth chloride solution, neutralizing it with pH and removing impurities, and then returning it to the evaporation and concentration tank 2 and the crystallization and precipitation tank for further evaporation and crystallization.

[0066] 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 5 through multiple channels.

[0067] 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 5 to obtain rare earth chloride crystals.

[0068] In this embodiment of the invention, the natural evaporation facility mainly consists of an evaporation concentration tank 2 and a crystallization precipitation tank 5. 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.

[0069] In some embodiments, the plurality of evaporation and concentration tanks are connected in a stepped series configuration, and the plurality of crystallization and precipitation tanks are connected in parallel configuration.

[0070] In this embodiment, as Figure 3As shown, 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 this evaporation concentration tank is the same as that of another evaporation concentration tank 2, but the height of its position is less than that of another evaporation concentration tank 2) into another adjacent evaporation concentration tank 2; the crystallization precipitation tanks 5 are connected in parallel, that is, they are divided into multiple paths that flow by gravity to multiple crystallization precipitation tanks 5 to achieve transfer.

[0071] In some embodiments, the final stage of the evaporation and concentration tank and the crystallization and precipitation tank are positioned at different heights; the final stage of the evaporation and concentration tank is positioned at a higher height than the crystallization and precipitation tank, so that the saturated rare earth chloride solution in the final stage of the evaporation and concentration tank flows by gravity to the crystallization and precipitation tank.

[0072] In this embodiment, the height difference between the last-stage evaporation and concentration tank 2 and the crystallization precipitation tank 5 (the height of the last-stage evaporation and concentration tank 2 is higher than the height of the crystallization precipitation tank 5) is used to achieve gravity flow from the last-stage evaporation and concentration tank 2 to the crystallization precipitation tank 5; the depth of the multiple crystallization precipitation tanks 5 is the same.

[0073] In some embodiments, the depth of the evaporation and concentration tank is 30cm to 200cm.

[0074] Furthermore, the depth of the evaporation and concentration tank is preferably 50cm to 80cm.

[0075] In some embodiments, the depth of the crystallization precipitation cell is 30cm to 100cm.

[0076] Furthermore, the depth of the crystallization precipitation pool is preferably 50cm to 80cm.

[0077] 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.

[0078] Example 1

[0079] This embodiment uses natural evaporation, concentration, and crystallization to obtain rare earth chloride crystals. The specific steps are as follows:

[0080] The extracted solution was neutralized, clarified, and filtered to remove impurities, resulting in 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).

[0081] The obtained lanthanum chloride solution was pumped into three evaporation concentration tanks connected in a stepped manner, each 40 cm deep, with a height difference of 50 cm between adjacent tanks. The height difference between the final evaporation concentration tank and the crystallization precipitation tank was 30 cm. The lanthanum chloride solution flowed through the height difference to the next evaporation concentration tank for further evaporation and concentration. Once saturated, the lanthanum chloride solution flowed by gravity from the final evaporation concentration tank through the height difference into the crystallization precipitation tank, precipitating lanthanum chloride crystals. Natural evaporation crystallization was affected by the local climate; the temperature of the lanthanum chloride solution was 25℃-32℃, and the relative humidity at the surface of the crystallization precipitation tank was 35%-55%.

[0082] Lanthanum chloride crystals were tested: the particle size range was 0.13-0.78 cm, with 65.81% of the particles being 0.2-0.6 cm, and the average particle size was 0.35 cm; lanthanum chloride crystals had REO content of 45.8%, Ca content of 0.018% (CaO / ∑REO), and TOC of 5 ppm ( / ∑REO); when 10 g of lanthanum chloride crystals were dissolved in 100 ml of water with a pH of 5.0, there was no visible turbidity, and the concentration of suspended solids was 4 mg / L.

[0083] Throughout the entire evaporation and crystallization production process, monitoring was conducted around the pool in accordance with the "Technical Guidelines for Monitoring Unorganized Emissions of Air Pollutants" (HJ / T 55-2000). 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 the "Rare Earth Industry Pollutant Emissions" standard.

[0084] Comparative Example 1 (Comparative Example of Example 1)

[0085] 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:

[0086] 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).

[0087] 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.

[0088] 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.

[0089] Comparative Example 2 (Comparative Example of Example 1)

[0090] 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:

[0091] 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).

[0092] 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.

[0093] 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.

[0094] 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.

[0095] Comparative Example 3 (Comparative Example of Example 1)

[0096] This comparative example uses a high-temperature evaporation and concentration followed by cooling and crystallization. The specific steps are as follows:

[0097] 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).

[0098] The lanthanum chloride solution was heated and evaporated at 90℃ to concentrate it to 500gREO / 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.

[0099] The lanthanum chloride crystals were tested and found to have a REO content of 45.8%, a Ca content of 0.05% (CaO / REO), and a TOC of 34 ppm ( / ∑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 suspended solids concentration was 110 mg / L. The particle size range was 0.09 cm to 0.89 cm, with particles ranging from 0.2 cm to 0.6 cm accounting for 45.81%.

[0100] As can be seen from Comparative Example 3, the cooling crystallization method, because the entire crystallization process is fast, still results in a relatively small crystal size despite the introduction of seed crystals.

[0101] 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).

[0102] Example 2

[0103] 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:

[0104] 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.

[0105] The natural evaporation concentration and crystallization system consists of two evaporation concentration tanks and one crystallization precipitation tank, which are connected in a stepped manner, with an effective depth of 60 cm for each tank.

[0106] The obtained mixed rare earth chloride solution is pumped into a natural evaporation concentration tank. The solution then flows through a high-pressure differential to a lower-level evaporation concentration tank for further evaporation and concentration until saturation. Finally, it flows through a high-pressure differential into a crystallization precipitation tank, where mixed rare earth chloride crystals precipitate out. Natural evaporation crystallization is affected by the local climate; the temperature of the mixed rare earth chloride solution in the tank is 28℃–35℃, and the relative humidity at the surface of the crystallization precipitation tank is 35%–55%.

[0107] The obtained mixed rare earth chloride crystals were tested. The mixed rare earth chloride crystals had a 0.2cm–0.6cm particle size distribution of 62.6%, indicating a narrow particle size distribution; the REO content was 46.5%, thorium content was 0.007% (ThO2 / ΣREO), iron content was 0.008% (Fe2O3 / ΣREO), Na content was 0.25% (Na2O / ΣREO), and calcium content was 0.09% (CaO / ΣREO); when 10g of the mixed rare earth chloride tablets were dissolved in 100ml of water at pH 5.0, no visible turbidity was observed, and the suspended solids concentration was 4mg / L.

[0108] Throughout the entire evaporation and crystallization production process, monitoring was conducted around the pool in accordance with the "Technical Guidelines for Monitoring Unorganized Emissions of Air Pollutants" (HJ / T 55-2000). 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 the "Rare Earth Industry Pollutant Emissions" standard.

[0109] Comparative Example 4 (Comparative Example of Example 2)

[0110] 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.

[0111] 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).

[0112] 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.

[0113] Example 3

[0114] 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).

[0115] Lanthanum and cerium chloride solution was pumped into a five-stage natural evaporation concentration tank (effective depth 120 cm), where it was gradually concentrated to obtain a saturated solution. This saturated solution was then introduced into a crystallization precipitation tank (effective depth 60 cm) via a height difference. Natural evaporation crystallization was influenced by the local climate; the temperature of the rare earth chloride solution was 22℃–32℃, and the relative humidity at the surface of the crystallization precipitation tank was 38%–48%. Lanthanum and cerium chloride crystals precipitated naturally.

[0116] Throughout the entire evaporation and crystallization production process, monitoring was conducted around the pool in accordance with the "Technical Guidelines for Monitoring Unorganized Emissions of Air Pollutants" (HJ / T 55-2000). 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 the "Rare Earth Industry Pollutant Emissions" standard.

[0117] Analysis of the precipitated lanthanum chloride crystals: the particle size distribution is 0.14 cm to 0.94 cm, of which the particle size distribution of 0.2 cm to 0.6 cm accounts for 53.2%; the REO content is 45.5%, the Ca content is 102 ppm (CaO / ΣREO), the Mg content is 102 ppm (MgO / ΣREO), and the TOC is 4 ppm ( / ΣREO); when 10 g of mixed rare earth chloride crystals are dissolved in 100 ml of water with a pH of 5.0, there is no visible turbidity, and the concentration of suspended solids is 5 ppm.

[0118] 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.

[0119] 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.

[0120] The above provides a detailed description of a method and system for the natural evaporation crystallization of rare earth chlorides provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas 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 natural evaporation crystallization of rare earth chlorides, characterized in that, The method comprises: The rare earth chloride solution is adjusted to a pH value of 5.0-7.5, and after clarification, impurities are removed by filtration; The rare earth chloride solution after removing impurities is naturally evaporated and concentrated at the pH value to obtain a saturated rare earth chloride solution; The saturated rare earth chloride solution is naturally crystallized to precipitate rare earth chloride crystals; The natural crystallization refers to a process of precipitating rare earth chloride crystals from the saturated rare earth chloride solution after removing impurities by using solar radiation and natural wind power.

2. The method of claim 1, wherein, The particle size of the rare earth chloride crystals is 0.1 cm-1.0 cm; wherein the proportion of the particle size of the rare earth chloride crystals in the range of 0.2 cm-0.6 cm is 55%-80%; In the process of natural crystallization, the temperature of the saturated rare earth chloride solution is 20℃-35℃, and the relative humidity of the surface layer of the saturated rare earth chloride solution is 35%-65%.

3. The method of claim 1, wherein, The rare earth chloride solution comprises mixed rare earth chlorides obtained by treating rare earth concentrates, or single rare earth chlorides or rare earth enriched chlorides obtained after separating mixed rare earth chlorides by ion exchange method or solvent extraction method.

4. The method of claim 1, wherein, The rare earth concentration of the rare earth chloride solution is 0.5 mol / L-2.0 mol / L.

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