Method for removing impurities from rare earth ore

Abstract

The application discloses a method for removing impurities from rare earth ore, and comprises the following steps: step 1, grinding the rare earth ore to a preset particle size, adding an alkali solution with a certain concentration, stirring, heating to 90-180 DEG C and keeping the temperature for 3-9 hours to remove silicon impurities, and obtaining filtrate 1 and filter residue; step 2, continuously adding a high-concentration alkali solution to the filter residue, stirring, heating to 140-260 DEG C and keeping the temperature for 5-10 hours, and filtering and separating to obtain filtrate 2 and decomposition residue, wherein the filtrate 2 is a mixed solution of sodium hydroxide and sodium phosphate; and step 3, crystallizing and separating the filtrate 2 to obtain sodium phosphate solid and sodium hydroxide residual liquid, and respectively concentrating and processing the obtained sodium hydroxide residual liquid according to a preset proportion and returning to step 2 and step 1. The application aims to reduce the introduction of impurities in the process of treating rare earth ore, reduce the impurity content of circulating alkali solution, and finally realize efficient operation of the alkali conversion-acid leaching process of rare earth concentrate.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a method for removing impurities from rare earth ores. Background Technology

[0002] Monazite and xenotime are both important rare earth phosphate minerals in my country. Currently, the main method for decomposing rare earth phosphate minerals is liquid alkali decomposition. This method involves using a 50%–60% sodium hydroxide solution, stirring in a reactor at 140–160°C for 8–12 hours, to decompose monazite into rare earth hydroxide alkali cake and sodium phosphate-sodium hydroxide solution. The rare earth hydroxide alkali cake is then dissolved in hydrochloric acid to obtain rare earth chloride products. The sodium phosphate-sodium hydroxide solution is cooled and centrifuged to obtain crude sodium phosphate and recycled sodium hydroxide alkali solution. Xenotime requires more stringent reaction conditions, achieving phase transformation at 200–300°C. For example, patent CN117587274A discloses a method for high-pressure alkali leaching of xenotime, which achieves rare earth phosphate phase decomposition and acid leaching extraction of rare earth resources at 40%–80% sodium hydroxide and temperatures as high as 240–260°C. The presence of silicon inevitably complicates the filtration process in alkali-to-alkali conversion. High silicon content in the sodium phosphate-sodium hydroxide solution concentration and separation process can easily lead to sodium-silicon slag formation and pipe blockage. Furthermore, high silicon content in the rare earth solution is detrimental to subsequent rare earth separation. Existing patent CN111020242A discloses a process for separating uranium, thorium, and rare earth elements from monazite concentrate. However, the sodium hydroxide-sodium phosphate solution obtained from alkali decomposition, after evaporation, concentration, and centrifugation, has an excessive silicon content in the resulting circulating alkali solution, severely reducing its effective alkali concentration. This high silicon content also easily leads to pipe blockage and material caking, severely restricting material flow and reducing the operating efficiency of the rare earth smelting process. The patent addresses this by adding lime milk to the circulating alkali solution to precipitate silicates, thereby reducing the silicon content in the system. Therefore, eliminating the impact of silicon re-leaching to achieve high-value, sustainable production of valuable components is imperative. Summary of the Invention

[0003] The main objective of this invention is to provide a method for removing impurities from rare earth ores, aiming to solve the technical problem that the high silicon content in the existing rare earth ore alkali decomposition process affects the smelting efficiency of rare earth ores.

[0004] To achieve the above objectives, the present invention provides a method for removing impurities from rare earth ores, the method comprising the following steps:

[0005] Step 1: Grind the rare earth ore to the preset particle size, add low concentration alkaline solution, stir and heat to 120-180℃ and keep it at the temperature for 3-9 hours to remove silicon impurities, and obtain filtrate 1 and filter residue.

[0006] Step 2: Add high-concentration alkaline solution to the filter residue, stir and heat to 140-260℃ and keep it at this temperature for 5-10 hours. Filter and separate to obtain filtrate 2 and decomposition residue. Filtrate 2 is a mixed solution of sodium hydroxide and sodium phosphate.

[0007] Step 3: Separate filtrate 2 by crystallization to obtain sodium phosphate solid and sodium hydroxide residue. Then concentrate the sodium hydroxide residue according to a preset ratio and return it to steps 2 and 1.

[0008] Optionally, in step 2, the mass fraction of sodium hydroxide in filtrate 2 is 10% to 15%.

[0009] Optionally, in step 3, the remaining sodium hydroxide solution of a preset ratio is concentrated to a sodium hydroxide mass fraction of 15% to 25% and then returned to step 1.

[0010] Optionally, in step 3, the remaining sodium hydroxide solution of a preset ratio is concentrated to a sodium hydroxide mass fraction of 30% to 40% and then returned to step 2.

[0011] Optionally, in step 2, the high-concentration alkaline solution is obtained by mixing the concentrated sodium hydroxide residue with solid sodium hydroxide, and the mass fraction of sodium hydroxide in the high-concentration alkaline solution is 50% to 80%.

[0012] Optionally, in step 1, the rare earth ore is ground to 50-500 mesh.

[0013] Optionally, in step 1, the temperature is controlled to rise to 90℃-180℃, and the reaction time is maintained at this temperature for 5-9 hours.

[0014] Optionally, in step 1, the rare earth ore includes one or more of monazite and xenotime.

[0015] Optionally, in step 1, the rare earth ore is mixed with a low-concentration alkaline solution and placed in a reaction vessel.

[0016] Optionally, in step 3, the remaining sodium hydroxide solution is concentrated according to a volume ratio of 2:8 to 8:2 and returned to steps 2 and 1 respectively.

[0017] Beneficial effects:

[0018] This invention involves grinding rare earth ore to a predetermined particle size and placing it in a high-pressure reactor. A low-concentration alkaline solution of 10%-25% is then added to remove silicon impurities. After filtration, filtrate 1 and filter residue are obtained. The filter residue is then placed back into the high-pressure reactor, and a high-concentration alkaline solution of 50%-80% is added. After filtration and separation, filtrate 2 and decomposition residue are obtained. In this step, filtrate 2 is first crystallized to separate sodium phosphate solids. The remaining sodium hydroxide solution obtained from the solid-liquid separation is then concentrated and reused as a component of the low-concentration and high-concentration alkaline solutions. This achieves the recycling of alkaline solution under conditions of silicon impurity removal, eliminating the need for adding lime slurry to the recycled alkaline solution for desilication treatment. Simultaneously, it avoids problems such as clogging and caking of recrystallized alkaline solution and slow solid-liquid separation rates in subsequent processing. Furthermore, this invention proposes a method for removing impurities from rare earth ores. By reducing the introduction of impurities during the rare earth ores processing, it achieves source control of impurities in the rare earth ores alkali-to-acid leaching process and reduces the introduction of impurities in the circulating alkali solution, ultimately achieving efficient operation of the rare earth ores alkali-to-acid leaching process. Attached Figure Description

[0019] Figure 1 This is a flowchart of an embodiment of a method for removing impurities from rare earth minerals according to the present invention;

[0020] Figure 2 for Figure 1 The corresponding process flow diagram for rare earth ore processing. Detailed Implementation

[0021] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0022] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings.

[0023] Reference Figure 1 The following is a process flow diagram of an embodiment of a method for removing impurities from rare earth ores according to the present invention. The detailed process steps are as follows.

[0024] Step 1: Grind the rare earth ore to the preset particle size, add a low concentration of alkaline solution, stir and heat to 90-180℃ and keep it at that temperature for 3-9 hours to remove silicon impurities, and obtain filtrate 1 and filter residue.

[0025] Specifically, the added low-concentration alkaline solution (derived from the filtrate obtained in a subsequent filtration step and having undergone concentration and separation treatment) preferably contains 15%–25% sodium hydroxide by mass. The ground rare earth ore powder is mixed with the low-concentration alkaline solution and placed in a reaction vessel under sealed conditions. The reaction temperature is controlled at 90–180°C and maintained for 3–9 hours to selectively separate soluble impurities, such as silicon, from the rare earth ore, thereby reducing the silicon content in the alkaline solution after alkali conversion. Furthermore, the impurity removal rate can be determined by separately collecting samples of the above-mentioned filtrate 1 and filter residue.

[0026] Furthermore, the formula for determining the impurity removal rate is as follows:

[0027] X = (c × v) / (m × a);

[0028] Where X is the silicon removal rate, c is the silicon content in filtrate 1 (g / L), v is the volume of filtrate 1 (L), m is the mass of rare earth ore used (g), and a is the silicon content in rare earth ore (wt%). The value of c can be determined by conventional detection methods to measure the silicon content in filtrate 1 and rare earth ore. Thus, the content of each element in rare earth ore can be obtained and the impurity removal rate can be calculated through the above method.

[0029] Preferably, to improve the impurity removal efficiency of rare earth ore, the rare earth ore is generally ground to 50-500 mesh before impurity removal treatment. Step 2: Add high-concentration alkaline solution to the filter residue, stir and heat to 140-260℃ and keep the temperature for 5-10 hours. Filter and separate to obtain filtrate 2 and decomposition residue, wherein the filtrate 2 is a mixed solution of sodium hydroxide and sodium phosphate.

[0030] Specifically, in this step, the sodium hydroxide mass fraction in the high-concentration alkaline solution is 50% to 80%, and it is obtained by mixing the concentrated filtrate 2 with solid sodium hydroxide. The filter residue and sodium hydroxide solution are reacted in a reaction vessel under sealed conditions. Therefore, after the reaction is kept at a certain temperature for a certain period of time, it is necessary to wait for the reaction temperature to drop and the pressure to be released before adding water for dilution, filtration and separation. The filtration and separation will yield filtrate 2 and decomposition residue.

[0031] Further, filtrate 2 is subjected to crystallization separation to obtain sodium phosphate solid and sodium hydroxide residue. The obtained sodium hydroxide residue is then concentrated according to a preset ratio and returned to steps 2 and 1. Specifically, filtrate 2 is subjected to conventional crystallization separation to separate sodium phosphate solid and sodium hydroxide residue. The sodium hydroxide residue is then concentrated and returned to steps 2 and 1. The sodium hydroxide mass fraction in the alkaline solution returned to step 1 is 15%–25%, and the sodium hydroxide mass fraction in the alkaline solution returned to step 2 is 30%–40%. The specific concentration steps all adopt existing technology and are not detailed here. Preferably, the sodium hydroxide residue is concentrated and returned to steps 2 and 1 according to a volume ratio of 2:8 to 8:2.

[0032] Furthermore, the rare earth ore includes one or more of monazite and xenotime, that is, the rare earth ore can be monazite, xenotime, or a mixture of monazite and xenotime. The above process is carried out using rare earth ore. Figure 2 deal with.

[0033] In this embodiment, rare earth ore is ground to a preset particle size and placed in a high-pressure reactor. A low-concentration alkaline solution is added to remove silicon impurities. After filtration, filtrate 1 and filter residue are obtained. The filter residue is then placed in the high-pressure reactor, and a high-concentration alkaline solution is added. After filtration and separation, filtrate 2 and decomposition residue are obtained. The filtrate 2 obtained in this step can be used to first crystallize and separate sodium phosphate solids, and then concentrate the remaining sodium hydroxide solution obtained from the solid-liquid separation. This solution can be reused as a component of the low-concentration alkaline solution and the high-concentration alkaline solution. Thus, under the condition of removing silicon impurities, the alkaline solution can be recycled without the need to add lime milk to the recyclable alkaline solution for desilication treatment.

[0034] Furthermore, to better illustrate the specific process of the present invention, the method of the present invention will be further described below with specific examples of monazite and xenotime.

[0035] Example 1

[0036] Monazite concentrate was ground to 50 mesh. 100g of the ground powder was mixed with 700mL of 20% sodium hydroxide solution and added to a high-pressure reactor. Stirring was started, and the temperature was raised to 90℃. After reaching the reaction temperature, the mixture was kept at that temperature for 5 hours. After the reaction was completed, the solid and liquid phases were separated, and filtrate 1 and filter residue were collected separately. The silicon removal rate in the rare earth elements was determined to be 54.9%, with a monazite decomposition rate of 2.56%. The silicon content in monazite decreased by 54.9%.

[0037] The pretreated rare earth concentrate (filter residue) is then mixed with a 50% sodium hydroxide solution and added to a high-pressure alkaline reactor. The reactor is sealed and stirred and heated. After the reaction temperature is controlled to rise to 150°C and held for 9 hours, heating is stopped. Once the reaction temperature has decreased, the pressure is released and the material is discharged. Water is added to dilute the slurry, and the sodium hydroxide and sodium phosphate mixture is first crystallized to separate the sodium phosphate solid. The remaining sodium hydroxide solution after solid-liquid separation is then concentrated and returned to the pre-purification process. After concentration to approximately 40% sodium hydroxide by mass, solid sodium hydroxide is added proportionally to bring the sodium hydroxide content to 50%-80% by mass before returning to the rare earth alkaline conversion process. After multiple cycles, the circulating alkaline solution contains 4.25 g / L of silicon, eliminating the need for desiliconization treatment with lime slurry.

[0038] Example 2

[0039] Monazite concentrate was ground to 500 mesh. 100g of the ground powder was mixed with 700mL of 25% sodium hydroxide solution and added to a high-pressure reactor. Stirring was started, and the temperature was raised to 120℃. After the reaction temperature was reached, it was maintained at this temperature for 5 hours. After the reaction was completed, the solid and liquid phases were separated, and filtrate 1 and filter residue were collected separately. The silicon removal rate in the rare earth ore was determined to be 63.2%, with a monazite decomposition rate of 10.80%. The silicon content in the rare earth ore decreased by 63.2%.

[0040] The pretreated rare earth concentrate (filter residue) is mixed with a 50% sodium hydroxide solution and added to a high-pressure alkaline reactor. The reactor is sealed and stirred and heated. After the reaction temperature is raised to 150°C and maintained for 9 hours, heating is stopped. After the reaction temperature drops, the pressure is released and the material is discharged. Water is added to dilute the slurry, and the sodium hydroxide and sodium phosphate mixture is first crystallized to separate the sodium phosphate solid. The remaining sodium hydroxide solution after solid-liquid separation is then concentrated and returned to the pre-purification process. After concentration to approximately 40% sodium hydroxide by mass, solid sodium hydroxide is added proportionally to bring the sodium hydroxide content to 50%-80% by mass before returning to the rare earth ore alkali conversion process. After multiple cycles, the circulating alkaline solution contains 3.91 g / L of silicon, eliminating the need for desiliconization treatment by adding lime slurry.

[0041] Example 3

[0042] Yttrium phosphate ore was ground to 500 mesh. 100g of the ground powder was mixed with 300mL of 25% sodium hydroxide solution and added to a high-pressure reactor. Stirring was started, and the temperature was raised to 160℃. After the reaction temperature was reached, it was maintained at this temperature for 5 hours. After the reaction was completed, the solid and liquid phases were separated, and filtrate 1 and filter residue were collected separately. The silicon removal rate in the rare earth elements was determined to be 66.3%, with a rare earth decomposition rate of 2.70%. The silicon content in the rare earth elements decreased by 66.3%.

[0043] The pretreated rare earth concentrate (filter residue) is mixed with a 60% sodium hydroxide solution and added to a high-pressure alkaline reactor. The reactor is then sealed and stirred and heated. After the reaction temperature is raised to 260℃ and maintained for 5 hours, heating is stopped. Once the reaction temperature has decreased, the pressure is released and the material is discharged. The slurry is diluted with water, and the sodium hydroxide and sodium phosphate mixture is first crystallized to separate the sodium phosphate solid. The remaining sodium hydroxide solution after solid-liquid separation is then concentrated and returned to the rare earth pre-removal process. After multiple cycles of concentration, the circulating alkaline solution contains 3.68 g / L of silicon, eliminating the need for desiliconization treatment with lime slurry.

[0044] Example 4

[0045] Yttrium phosphate ore was ground to 100 mesh. 100g of the ground powder was mixed with 700mL of 25% sodium hydroxide solution and added to a high-pressure reactor. Stirring was started, and the temperature was raised to 140℃. After the reaction temperature was reached, it was maintained at this temperature for 5 hours. After the reaction was completed, the solid and liquid components were separated, and filtrate 1 and filter residue were collected separately. The silicon removal rate in the rare earth elements was determined to be 62.6%, with a total removal rate of 22.6%, and a rare earth decomposition rate of 2.18%. The silicon content in the rare earth elements decreased by 62.6%.

[0046] The pretreated rare earth concentrate (filter residue) was mixed with a 60% sodium hydroxide solution and added to a high-pressure alkaline reactor. The reactor was sealed and stirred and heated. After the reaction temperature was raised to 240℃ and maintained for 5 hours, heating was stopped. After the reaction temperature decreased, the pressure was released and the material was discharged. The slurry was diluted with water, and the sodium hydroxide and sodium phosphate mixture was first crystallized to separate the sodium phosphate solid. The remaining sodium hydroxide solution after solid-liquid separation was then concentrated and returned to the rare earth pre-removal process. After multiple cycles of concentration, the circulating alkaline solution contained 3.24 g / L of silicon, eliminating the need for desiliconization treatment by adding lime slurry to the circulating alkaline solution.

[0047] Comparative Example 1

[0048] Monazite concentrate was ground to 50 mesh. 100g of the ground powder was mixed with 700mL of 8% sodium hydroxide solution and added to a high-pressure reactor. Stirring was started, and the temperature was raised to 140℃. After the reaction temperature was reached, the mixture was kept at this temperature for 9 hours. After the reaction was completed, the solid and liquid phases were separated, and filtrate 1 and filter residue were collected separately. The silicon removal rate in the rare earth elements was determined to be 10.9%, with a rare earth decomposition rate of 1.29%. The silicon content in the rare earth elements decreased by only 10.9%.

[0049] The pretreated rare earth concentrate (filter residue) is mixed with a 50% sodium hydroxide solution and added to a high-pressure alkaline reactor. The reactor is sealed and stirred and heated. After the reaction temperature is controlled to rise to 150°C and held for 10 hours, heating is stopped. After the reaction temperature drops, the pressure is released and the material is discharged. Water is added to dilute the slurry, and the sodium hydroxide and sodium phosphate mixture is first crystallized to separate solid sodium phosphate. The remaining sodium hydroxide solution after solid-liquid separation is then concentrated and returned to the rare earth pre-removal process. After concentration to a sodium hydroxide mass fraction of approximately 30%, solid sodium hydroxide is added proportionally to bring the sodium hydroxide mass fraction to 50%-60%, and the solution is returned to the rare earth alkaline conversion process. After multiple cycles, the circulating alkaline solution contains 8.55 g / L of silicon, requiring the addition of lime slurry for desilication treatment.

[0050] Comparative Example 2

[0051] Monazite concentrate was ground to 300 mesh. 100g of the ground powder was mixed with 700mL of 8% sodium hydroxide solution and added to a high-pressure reactor. Stirring was started, and the temperature was raised to 50℃. After the reaction temperature was reached, the mixture was kept at that temperature for 5 hours. After the reaction was completed, the solid and liquid phases were separated, and filtrate 1 and filter residue were collected separately. The results showed that the silicon removal rate in the rare earth elements was less than 1%, and the rare earth decomposition rate was less than 1%.

[0052] The pretreated rare earth concentrate (filter residue) is mixed with a 50% sodium hydroxide solution and added to a high-pressure alkaline reactor. The reactor is sealed and stirred and heated. After the reaction temperature is controlled to rise to 150°C and held for 9 hours, heating is stopped. After the reaction temperature drops, the pressure is released and the material is discharged. Water is added to dilute the slurry, and the sodium hydroxide and sodium phosphate mixture is first crystallized to separate the sodium phosphate solid. The remaining sodium hydroxide solution after solid-liquid separation is then concentrated and returned to the rare earth pre-purification process. After concentration to a sodium hydroxide mass fraction of approximately 30%, solid sodium hydroxide is added proportionally to bring the sodium hydroxide mass fraction to 50%-60%, and the solution is returned to the rare earth alkaline conversion process. After multiple cycles, the circulating alkaline solution contains 9.61 g / L of silicon, requiring the addition of lime slurry for desiliconization.

[0053] Comparative Example 3

[0054] Monazite concentrate was ground to 500 mesh. 100g of the ground powder was mixed with 700mL of 50% sodium hydroxide solution and added to a high-pressure reactor. Stirring was started, and the temperature was raised to 140℃. After the reaction temperature was reached, the mixture was kept at this temperature for 9 hours. After the reaction was completed, the solid and liquid phases were separated, and filtrate 1 and filter residue were collected separately. The silicon removal rate in the rare earth elements was determined to be 75.3%, with a rare earth decomposition rate of 96.3%. The silicon content in the rare earth elements decreased by 75.3%, but at this point, monazite was also decomposed, and most of the impurities—silicon and rare earth hydroxide—remained in the alkali cake.

[0055] Comparative Example 4

[0056] Monazite concentrate was ground to 500 mesh. 100g of the ground powder was mixed with 700mL of 50% sodium hydroxide solution and added to a high-pressure reactor. Stirring was started, and the temperature was raised to 140℃. After the reaction temperature was reached, the mixture was kept at this temperature for 3 hours. After the reaction was completed, the solid and liquid phases were separated, and filtrate 1 and filter residue were collected separately. The silicon removal rate in the rare earth elements was determined to be 54.6%, with a rare earth decomposition rate of 58.9%. The silicon content in the rare earth elements decreased by 54.6%, but a large amount of rare earth phosphates were also decomposed, and impurity silicon remained in the alkali cake along with rare earth hydroxide.

[0057] Table 1 - Reaction parameters and measured data of the examples and comparative examples

[0058]

[0059]

[0060] As shown in Table 1 above, Examples 1-4 employ the specific process of this invention. Compared to the processes disclosed in Comparative Examples 1-4, this invention can efficiently remove silicon content from monazite and xenotime. While monazite was ground in Comparative Examples 1-4, 8% sodium hydroxide solution was added in Comparative Examples 1-2, and the reaction temperatures were 140°C and 50°C respectively. The resulting impurity removal efficiency was significantly lower than in Examples 1-2. Similarly, in Comparative Examples 3-4, by setting the reaction temperature to 140°C and adding 50% sodium hydroxide solution, the final impurity removal efficiency was slightly lower than in Examples 1-2, but the phosphorus decomposition rate was much higher than in Examples 1-4. Since the phosphorus decomposition rate corresponds to the decomposition of rare earth minerals, Comparative Examples 3-4 did not achieve selective separation of silicon and rare earth minerals. Meanwhile, in Examples 3-4, xenotime phosphate was used to remove silicon impurities. The final Si removal rate (%) and P decomposition rate (%) were basically not much different from the data in Examples 1-2. It can be seen that the specific process in this invention achieves the conditions for removing soluble silicon impurities, and further realizes the recycling of alkaline solution without the need to add lime milk to the recycled alkaline solution for desiliconization treatment.

[0061] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0062] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0063] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for removing impurities from rare earth minerals, characterized in that, The method includes the following steps: Step 1: Grind the rare earth ore to the preset particle size, add a low-concentration alkaline solution with a sodium hydroxide mass fraction of 15%~25%, stir and heat to 90~180℃ in a closed reaction vessel and keep it at the temperature for 3-9 hours to selectively remove silicon impurities, and obtain filtrate 1 and filter residue. Step 2: Add a high-concentration alkaline solution with a sodium hydroxide mass fraction of 50% to 80% to the filter residue, stir and heat to 140 to 260°C and keep the temperature for 5 to 10 hours, filter and separate to obtain filtrate 2 and decomposition residue, wherein the filtrate 2 is a mixed solution of sodium hydroxide and sodium phosphate. Step 3: Separate filtrate 2 by crystallization to obtain sodium phosphate solid and sodium hydroxide residue. Then concentrate the sodium hydroxide residue according to a preset ratio. One part is concentrated to a sodium hydroxide mass fraction of 30%~40% and returned to step 2 for use in preparing the high-concentration alkaline solution. The other part is concentrated to a sodium hydroxide mass fraction of 15%~25% and returned to step 1 for use in the low-concentration alkaline solution.

2. The method for removing impurities from rare earth ore according to claim 1, characterized in that, In step 2, the mass fraction of sodium hydroxide in filtrate 2 is 10% to 15%.

3. The method for removing impurities from rare earth ore according to claim 1, characterized in that, In step 2, the high-concentration alkaline solution is obtained by mixing the concentrated sodium hydroxide residue with solid sodium hydroxide. The mass fraction of sodium hydroxide in the high-concentration alkaline solution is 50% to 80%.

4. The method for removing impurities from rare earth ore according to claim 1, characterized in that, In step 1, the rare earth ore is ground to 50-500 mesh.

5. The method for removing impurities from rare earth ore according to claim 1, characterized in that, In step 1, the temperature is controlled to rise to 90℃-180℃, and the reaction time is maintained at this temperature for 5-9 hours.

6. The method for removing impurities from rare earth ore according to claim 1, characterized in that, In step 1, the rare earth ore includes one or more of monazite and xenotime.

7. The method for removing impurities from rare earth ore according to claim 1, characterized in that, In step 3, the remaining sodium hydroxide solution is concentrated according to a volume ratio of 2:8 to 8:2 and returned to steps 2 and 1 respectively.

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