A method for extracting rare earths from monazite concentrate

Abstract

The application discloses a method for extracting rare earth from monazite concentrate, which comprises the following steps: step 1, mixing monazite concentrate with a preset amount of phosphorus-rare earth co-precipitation slag, adding sodium hydroxide solution and CaO powder, controlling the temperature to be 120-180 DEG C under sealed stirring and keeping the reaction for 9-12 h, so that the monazite concentrate and the phosphorus-rare earth co-precipitation slag are fully decomposed under alkaline conditions, and a mixed slurry is obtained; step 2, filtering and separating the mixed slurry in step 1, washing the filter residue with hot water at 80 DEG C for multiple times, and collecting the decomposition liquid and the decomposition residue respectively; and step 3, adding a preset amount of hydrochloric acid and hydrogen peroxide mixed solution into the decomposition residue in step 2, stirring and reacting at 80 DEG C for 2 h, and obtaining acid-insoluble residue and rare earth chloride solution after filtration treatment, so that the rare earth is extracted from the monazite. The application aims to reduce the concentration of sodium hydroxide in the monazite alkaline decomposition process.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a method for extracting rare earth elements from monazite concentrate. Background Technology

[0002] Rare earth elements are hailed as "vitamins of industry," possessing irreplaceable superior magnetic, optical, and electrical properties, playing a significant role in improving product performance, increasing product variety, and enhancing production efficiency. Due to their unique physicochemical properties, rare earth elements are widely used in metallurgy, military applications, and new materials. Monazite is one of the main rare earth minerals in my country, and the current mainstream process for processing single high-grade monazite concentrate is sodium hydroxide decomposition followed by hydrochloric acid leaching. To ensure complete rare earth leaching, it is usually necessary to ensure the complete transformation of stable rare earth phosphates in monazite into easily leached rare earth hydroxides. Therefore, the alkaline decomposition process must be sufficiently thorough, typically achieved by increasing the alkali concentration and extending the reaction time. Existing patent publication number CN112961995A discloses a method for improving the alkali decomposition rate of monazite concentrate. This method involves feeding a slurry obtained after grinding monazite concentrate and a concentrated alkali solution into a fully enclosed alkali decomposition tank. The alkali decomposition reaction temperature is controlled at an alkalinity of 50%-60%, 80℃-160℃, and a pressure of 0.01MPa-0.5MPa, with a reaction time of 4-12 hours. This method can achieve a decomposition rate of over 99.5% for monazite. Although using NaOH to decompose monazite can achieve good results, the high price of sodium hydroxide and the high alkali consumption make this method uneconomical. Summary of the Invention

[0003] The main objective of this invention is to provide a method for extracting rare earth elements from monazite concentrate, aiming to solve the technical problems of high alkalinity and high cost in the existing monazite alkaline decomposition process.

[0004] To achieve the above objectives, the present invention provides a method for extracting rare earth elements from monazite concentrate, the method comprising the following steps:

[0005] Step 1: Mix monazite concentrate with a predetermined amount of phosphorus-rare earth coprecipitate residue, add sodium hydroxide solution and CaO powder, and stir and heat to 120-180℃ under sealed conditions and keep the temperature for 9-12 hours to allow monazite concentrate and phosphorus-rare earth coprecipitate residue to fully decompose under alkaline conditions.

[0006] Step 2: Filter and separate the mixed slurry from Step 1 to obtain decomposition liquid and decomposition residue;

[0007] Step 3: Add a predetermined amount of hydrochloric acid and hydrogen peroxide mixed solution to the decomposition residue from Step 2, and then stir and react at 80°C for 2 hours. After filtration, acid-insoluble residue and rare earth chloride solution are obtained.

[0008] Optionally, the method further includes:

[0009] Step 4: Add the decomposition residue with a preset liquid-to-solid ratio to the rare earth chloride solution obtained in step 3 under water bath conditions, and keep it warm for 2 hours. After solid-liquid separation, the purified rare earth chloride solution after phosphorus removal and the phosphorus-rare earth co-precipitate residue are obtained.

[0010] Optionally, the liquid-solid ratio of the rare earth chloride solution to the decomposition residue in step 4 is (7-10) mL:1 g.

[0011] Optionally, in step 1, the mass ratio of monazite concentrate to phosphorus-rare earth co-precipitated residue is 100g:(0-10)g.

[0012] Optionally, in step 1, the mass ratio of CaO to monazite concentrate is (2-25) g: 100 g.

[0013] Optionally, in step 1, the concentration of the sodium hydroxide solution is 30%-50%.

[0014] Optionally, in step 3, the hydrochloric acid solution has a concentration of 4 mol / L, the hydrogen peroxide solution has a volume fraction of 3%, and the liquid-to-solid ratio of the hydrochloric acid and hydrogen peroxide mixture to the decomposition residue is 10 mL: 1 g.

[0015] Optionally, in step 1, monazite concentrate and phosphorus-rare earth co-precipitate residue are mixed and placed in a reactor.

[0016] Optionally, in step 2, the mixed slurry from step 1 is separated into solid and liquid components, and the filter residue is washed and filtered multiple times with deionized water at 80°C to obtain decomposition liquid and decomposition residue.

[0017] Optionally, in step 1, the volume ratio of sodium hydroxide solution to monazite concentrate is (300-600) mL: 100 g.

[0018] Beneficial effects:

[0019] (1) This invention employs a double-alkali decomposition process using calcium oxide and sodium hydroxide, followed by leaching with hydrochloric acid and hydrogen peroxide to treat monazite. Building upon existing technologies, the introduction of calcium oxide provides a certain amount of alkali to the reaction system, thereby reducing NaOH consumption. Furthermore, the formation of calcium phosphate reduces phosphorus activity in the reaction system, enhancing the forward trend of the monazite rare earth phosphate decomposition reaction and promoting the transformation of rare earth phosphate phases into easily extractable rare earth hydroxides, thus improving the monazite decomposition efficiency. The rare earth recovery rate in the monazite concentrate of this invention can reach over 93.3%.

[0020] (2) The rare earth in the alkali cake is dissolved by the acidity of the rare earth solution itself. As the amount of decomposition residue (alkali cake) added increases, the pH of the solution increases, and phosphorus in the solution adsorbs and precipitates with rare earth hydroxide, ultimately achieving the leaching of rare earth in the decomposition residue (alkali cake) and the deep purification of phosphorus in the solution. The precipitation product is mainly phosphorus-rare earth co-precipitate residue, which is returned to the alkali conversion process for regeneration. Attached Figure Description

[0021] Figure 1 This is a flowchart of an embodiment of a method for extracting rare earth elements from monazite concentrate according to the present invention;

[0022] Figure 2 for Figure 1 Based on the flowchart of rare earth solution preferential dissolution and purification treatment;

[0023] Figure 3 for Figure 1-2 The corresponding flowchart. Detailed Implementation

[0024] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0025] 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.

[0026] Reference Figure 1 The following is a process flow diagram of an embodiment of a method for extracting rare earth elements from monazite concentrate according to the present invention. The detailed process steps are as follows.

[0027] S1. Monazite concentrate is mixed with a predetermined amount of phosphorus-rare earth coprecipitate residue, and sodium hydroxide solution and CaO powder are added. The mixture is stirred and heated to 120-180℃ under sealed conditions and kept at this temperature for 9-12 hours to allow the monazite concentrate and phosphorus-rare earth coprecipitate residue to fully decompose under alkaline conditions, so that the phases of the monazite concentrate and phosphorus-rare earth coprecipitate residue are completely transformed, and finally a mixed slurry is obtained. Specifically, monazite concentrate and phosphorus-rare earth co-precipitate residue are placed in a reactor for reaction, and the mass ratio of monazite concentrate to phosphorus-rare earth co-precipitate residue is controlled at 100g:(0-10)g, and the concentration of sodium hydroxide solution added is 30%-50%, the volume of sodium hydroxide solution to the mass of monazite concentrate is (300-600)mL:100g; the mass ratio of CaO to monazite concentrate is (2-25)g:100g. The introduction of CaO provides a certain amount of alkali to the reaction system, thereby reducing the consumption of NaOH; and the formation of calcium phosphate reduces the activity of phosphorus in the reaction system, promoting the phase conversion of rare earth phosphate into easily extractable rare earth hydroxide.

[0028] S2 involves filtering the mixed slurry from S1 to obtain a decomposition liquid and a decomposition residue. Specifically, the filter residue after solid-liquid separation is washed multiple times with 80°C hot water, and the filtrate and filter residue are collected separately. In practical applications, the decomposition residue obtained in this step is called alkali cake.

[0029] In step S3, a predetermined amount of a mixed solution of hydrochloric acid and hydrogen peroxide is added to the decomposition residue from step S2. The mixture is then stirred and reacted at 80°C for 2 hours. After filtration, acid-insoluble residue and a rare earth chloride solution are obtained. The hydrochloric acid concentration is controlled at 4 mol / L, the hydrogen peroxide solution fraction is 3%, and the liquid-to-solid ratio of the hydrochloric acid / hydrogen peroxide solution to the decomposition residue is controlled at 10 mL:1 g. In practical applications, the leaching residue obtained in this step is called acid-insoluble residue. The final calculated rare earth leaching rate in monazite concentrate is 91.8%-93.3%.

[0030] The specific calculation steps for the leaching rate determination are as follows: Add the decomposition residue from step 2 to a 4 mol / L hydrochloric acid and hydrogen peroxide mixed solution with a liquid-to-solid ratio of 10. Then, stir the reaction at 80℃ for 2 hours. After the reaction, perform liquid-solid separation and collect the acid-insoluble residue and rare earth chloride solution separately. After washing and drying, take a sample to determine the phase and composition of the acid-insoluble residue, and titrate the total rare earth concentration of the rare earth chloride solution. Formula for calculating the leaching rate of monazite concentrate (1):

[0031] X1=(c×v×m2) / (m1×m3×a)(1); where c is the concentration of total rare earth elements in the leachate (g / L), v is the volume of the leachate (L), m1 is the mass of monazite used in the experiment (g), m2 is the mass of the decomposition residue of monazite after alkaline decomposition (g), m3 is the mass of the decomposition residue used in the acid leaching experiment (g), and a is the mass fraction of total rare earth elements in monazite.

[0032] Furthermore, in order to remove phosphorus from the rare earth chloride solution, such as Figure 2-3 As shown, Figure 3 The alkali cake shown is a decomposition residue. The method further includes:

[0033] Step 4: The rare earth chloride solution obtained in Step 3 is added to the decomposition residue with a preset liquid-to-solid ratio under water bath conditions, and the reaction is maintained at this temperature for 2 hours. After solid-liquid separation, a rare earth chloride purification solution and a phosphorus-rare earth coprecipitate residue are obtained. The phosphorus-rare earth coprecipitate residue can be decomposed under certain alkalinity and temperature conditions to obtain rare earth hydroxide and sodium phosphate-sodium hydroxide solution. Furthermore, in this step, the liquid-to-solid ratio of the rare earth chloride solution to the decomposition residue is controlled at (7-10) mL:1g. The P removal efficiency can then be determined by the concentration of P in the reaction solution before and after the addition of the decomposition residue and the total volume of the reaction solution. In this embodiment, the P removal efficiency is controlled to be above 99%. The formula for determining the removal rate is:

[0034] X2=1-(V p2 C p2 / (V p1 C p1 ))(2);

[0035] Where C p2 The concentration (g / L) of P in the reaction solution after adding the decomposition residue, V p2 The volume (mL) of the decomposition residue added after the reaction is C. p1 The concentration (g / L) of P in the solution before the reaction is added to the decomposition residue, V p2 Add the volume (mL) of the solution before the reaction to the decomposition residue.

[0036] Furthermore, by measuring and analyzing the rare earth leaching rate of the decomposition slag, the rare earth leaching rate of the decomposition slag in this embodiment is within the range of 73%-80%, and the formula for the measurement rate is as follows:

[0037] X3=((V RE2 C RE2 )-(V RE1 C RE1 )) / (C RE m) (3);

[0038] Where X3 is the rare earth leaching rate in the decomposition residue; V RE2 The volume (mL) of liquid after adding the decomposition residue during the reaction; C RE2 V represents the total rare earth concentration (g / L) in the liquid after adding the decomposition residue during the reaction; RE1 The volume of the rare earth solution used (mL); C RE1 denoted as , where is the total rare earth concentration in the rare earth solution (g / L); m is the total rare earth content in the decomposition residue (alkali cake).

[0039] In this embodiment, a monazite treatment process employing a dual-alkali decomposition method using calcium oxide and sodium hydroxide, followed by leaching with hydrochloric acid and hydrogen peroxide, is utilized. Building upon existing technologies, the introduction of CaO provides a certain amount of alkali to the reaction system, thereby reducing NaOH consumption. Furthermore, the formation of calcium phosphate reduces phosphorus activity in the reaction system, promoting the conversion of rare earth phosphate phases into easily extractable rare earth hydroxides, thus increasing the rare earth leaching rate in the monazite concentrate. The rare earth leaching rate in the monazite concentrate of this invention can reach over 93.3%. Additionally, the acidity of the rare earth solution itself readily dissolves the rare earth in the alkali cake. With the addition of the decomposition residue (alkali cake), the pH of the solution increases, causing phosphorus and rare earth hydroxides in the solution to adsorb and precipitate, ultimately achieving the leaching of rare earth hydroxides from the alkali cake and deep purification of phosphorus in the solution. The precipitated products are mainly active rare earth phosphates, which are returned to the alkali decomposition process to regenerate the decomposition residue (alkali cake).

[0040] Furthermore, to better illustrate the specific process of the present invention, the method of the present invention will be further described below with reference to specific embodiments.

[0041] Example 1

[0042] 100g of monazite concentrate was placed in a reaction vessel, and then 500mL of 30% sodium hydroxide solution and 18g of CaO were added. The autoclave was then sealed, stirring was started, and the temperature was raised to the target temperature of 160℃. After reaching the target temperature, the reaction was maintained for 9 hours. After the reaction was completed, the mixture was cooled, depressurized, and the reaction slurry was removed. Liquid-solid separation was performed, and the mixture was washed with 500mL of 80℃ deionized water. The filtrate and decomposition residue were collected separately. The decomposition residue was leached with a hydrochloric acid solution (4mol / L hydrochloric acid + 3% H2O2) at a liquid-to-solid ratio of 10mL / 1g to extract rare earth elements. The rare earth leaching rate from the monazite was 93.3%.

[0043] Take an appropriate amount of rare earth chloride solution and heat it in a water bath to the target temperature of 80℃. Add a decomposition residue with a liquid-to-solid ratio of 7. The decomposition residue is obtained from the alkaline decomposition, washing, and filtration in the previous step. Keep the mixture at the target temperature for 2 hours. After the reaction, separate the solid and liquid phases and collect the filtrate and the phosphorus-rare earth coprecipitate residue separately. The phosphorus removal rate in the rare earth chloride solution is 99.4%, and the rare earth leaching rate in the alkali cake is 73.1%. The precipitate product is returned to the monazite alkali decomposition process and reacted for 9 hours at a sodium hydroxide concentration of 30% and a temperature of 140℃. 98.8% of the phosphorus in the precipitate product dissolves into the liquid phase, thus achieving the decomposition of the phosphorus-rare earth coprecipitate residue.

[0044] Example 2

[0045] 100g of monazite concentrate was placed in a reaction vessel, and then 500mL of 50% sodium hydroxide solution and 16g of CaO were added. The autoclave was then sealed, stirring was started, and the temperature was raised to the target temperature of 180℃. After reaching the target temperature, the reaction was maintained for 12 hours. After the reaction was completed, the mixture was cooled, depressurized, and the reaction slurry was removed. Liquid-solid separation was performed, and the mixture was washed with 500mL of 80℃ deionized water. The filtrate and decomposition residue were collected separately. The decomposition residue was leached with a mixed solution of hydrochloric acid and hydrogen peroxide (4mol / L hydrochloric acid + 3% H2O2) at a liquid-to-solid ratio of 10mL / 1g to leach the rare earth elements. The rare earth leaching rate in monazite was 91.8%.

[0046] Take an appropriate amount of rare earth chloride solution and heat it in a water bath to the target temperature of 80℃. Add a decomposition residue with a liquid-to-solid ratio of 10. The decomposition residue is obtained from the alkaline decomposition, washing, and filtration in the previous step. Keep the mixture at the target temperature for 2 hours. After the reaction, separate the solid and liquid phases and collect the filtrate and the phosphorus-rare earth coprecipitate residue separately. The phosphorus removal rate in the rare earth chloride solution is 99.6%, and the rare earth leaching rate in the alkali cake is 79.6%. The precipitate product is returned to the monazite alkali decomposition process and reacted for 9 hours at a sodium hydroxide concentration of 30% and a temperature of 120℃. 98.4% of the phosphorus in the precipitate product dissolves into the liquid phase, thus achieving the decomposition of the phosphorus-rare earth coprecipitate residue.

[0047] Example 3

[0048] 100g of monazite concentrate was placed in a reactor, along with 5g of phosphorus-rare earth co-precipitate residue. Then, 500mL of 50% sodium hydroxide solution and 16g of CaO were added. The reactor was then sealed, stirring was initiated, and the temperature was raised to the target temperature of 180℃. After reaching the target temperature, the reaction was maintained for 12 hours. After the reaction, the mixture was cooled, depressurized, and the reaction slurry was removed. Liquid-solid separation was performed, and the slurry was washed with 500mL of 80℃ deionized water. The filtrate and decomposition residue were collected separately. The decomposition residue was leached with a mixed solution of hydrochloric acid and hydrogen peroxide (4mol / L hydrochloric acid + 3% H2O2) at a liquid-to-solid ratio of 10mL / 1g to leach the rare earth elements. The rare earth leaching rate in monazite was 92.6%.

[0049] Take an appropriate amount of rare earth chloride solution and heat it in a water bath to the target temperature of 80℃. Add a decomposition residue with a liquid-to-solid ratio of 10. The decomposition residue is obtained from the alkaline decomposition, washing, and filtration steps mentioned above. Maintain the temperature at the target for 2 hours. After the reaction, separate the solid and liquid phases and collect the filtrate and the phosphorus-rare earth coprecipitate residue separately. The phosphorus removal rate in the rare earth chloride solution is 99.3%, and the rare earth leaching rate in the alkali cake is 78.6%. The precipitate product is returned to the monazite alkali decomposition process and reacted for 9 hours at a sodium hydroxide concentration of 30% and a temperature of 120℃. 99.1% of the phosphorus in the precipitate product dissolves into the liquid phase, thus achieving the decomposition of the phosphorus-rare earth coprecipitate residue.

[0050] Comparative Example 1

[0051] 100g of monazite concentrate was placed in a reactor, and then 500mL of 30% sodium hydroxide solution and 0g of CaO were added. The reactor was then sealed, stirring was started, and the temperature was raised to the target temperature of 160℃. After the temperature was reached, the reaction was maintained for 9 hours. After the reaction was completed, the mixture was cooled, depressurized, and the reaction slurry was removed. Liquid-solid separation was performed, and 500mL of 80℃ deionized water was added for washing. Filtrate 1 and decomposition residue 1 were collected separately. Decomposition residue 1 was leached with a mixed solution of hydrochloric acid and hydrogen peroxide (4mol / L hydrochloric acid + 3% H2O2) at a liquid-to-solid ratio of 10mL / 1g to leach the rare earth elements. The rare earth leaching rate in monazite was 69.7%. It can be seen that the absence of CaO powder resulted in a lower rare earth leaching rate in monazite compared to that in Examples 1-2.

[0052] Further, an appropriate amount of rare earth chloride solution was taken and heated to the target temperature of 30°C in a water bath. Decomposition residue 1 with a liquid-to-solid ratio of 20 was added, and the mixture was kept at the target temperature for 2 hours. After the reaction was completed, the liquid and solid components were separated, and filtrate 2 and decomposition residue 2 were collected separately. The phosphorus removal efficiency in the rare earth chloride solution was 98.5%, and the rare earth leaching rate in decomposition residue 1 was 46.6%. Although the phosphorus removal efficiency was relatively high, the rare earth leaching rate in the alkali cake was relatively low.

[0053] Comparative Example 2

[0054] 100g of monazite concentrate was placed in a reactor, and then 500mL of 10% sodium hydroxide solution and 18g of CaO were added. The reactor was then sealed, stirring was started, and the temperature was raised to the target temperature of 160℃. After reaching the target temperature, the reaction was maintained for 9 hours. After the reaction was completed, the mixture was cooled, depressurized, and the reaction slurry was removed. Liquid-solid separation was performed, and 500mL of 80℃ deionized water was added for washing. Filtrate 1 and decomposition residue 1 were collected separately. Decomposition residue 1 was leached with a mixed solution of hydrochloric acid and hydrogen peroxide (4mol / L hydrochloric acid + 3% H2O2) at a liquid-to-solid ratio of 10mL / 1g to leach the rare earth elements. The rare earth leaching rate in monazite was 13.8%. It can be seen that reducing the sodium hydroxide solution in Comparative Example 2 also resulted in a lower rare earth leaching rate in monazite compared to Examples 1-2.

[0055] Further, an appropriate amount of rare earth chloride solution was taken and heated in a water bath to the target temperature of 80°C. Decomposition residue 1 with a liquid-to-solid ratio of 10 was added, and the mixture was kept at the target temperature for 0.5 hours. After the reaction, the liquid and solid phases were separated, and filtrate 2 and decomposition residue 2 were collected separately. The phosphorus removal efficiency in the rare earth chloride solution was 53.5%, and the rare earth leaching rate in the alkali cake was 47.6%. Both were lower than the corresponding data in Examples 1-2.

[0056] Comparative Example 3

[0057] 100g of monazite concentrate was placed in a reactor, and 10g of phosphorus-rare earth co-precipitate residue was added. Then, 500mL of 10% sodium hydroxide solution and 18g of CaO were added. The reactor was then sealed, stirring was started, and the temperature was raised to the target temperature of 160℃. After the temperature was reached, the reaction was maintained for 9 hours. After the reaction was completed, the mixture was cooled, depressurized, and the reaction slurry was removed. Liquid-solid separation was performed, and 500mL of 80℃ deionized water was added for washing. Filtrate 1 and decomposition residue 1 were collected separately. Decomposition residue 1 was leached with a hydrochloric acid solution (4mol / L hydrochloric acid + 3% H2O2) at a liquid-to-solid ratio of 10mL / 1g to leach the rare earth elements. The rare earth leaching rate in monazite was 16.2%. It can be seen that reducing the sodium hydroxide solution in Comparative Example 3 also resulted in a lower rare earth leaching rate in monazite compared to Example 3.

[0058] Further, an appropriate amount of rare earth chloride solution was taken and heated in a water bath to the target temperature of 80°C. Decomposition residue 1 with a liquid-to-solid ratio of 10 was added, and the mixture was kept at the target temperature for 0.5 hours. After the reaction, the liquid and solid phases were separated, and filtrate 2 and decomposition residue 2 were collected separately. The phosphorus removal efficiency in the rare earth chloride solution was 48.1%, and the rare earth leaching rate in the alkali cake was 53.9%. Both were lower than the corresponding data in Examples 1-2.

[0059] 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.

[0060] 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.

[0061] 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 extracting rare earth elements from monazite concentrate, characterized in that, The method includes the following steps: Step 1: Mix monazite concentrate with a predetermined amount of phosphorus-rare earth coprecipitate residue, add sodium hydroxide solution and CaO powder, and stir and heat to 120~180℃ under sealed conditions and keep the temperature for 9-12 hours to allow monazite concentrate and phosphorus-rare earth coprecipitate residue to fully decompose under alkaline conditions to obtain a mixed slurry. The mass ratio of monazite concentrate to phosphorus-rare earth coprecipitate residue is 100g:(5-10)g. Step 2: Filter and separate the mixed slurry from Step 1 to obtain decomposition liquid and decomposition residue; Step 3: Add a predetermined amount of hydrochloric acid and hydrogen peroxide mixed solution to the decomposition residue from Step 2, and then stir and react at 80°C for 2 hours. After filtration, acid-insoluble residue and rare earth chloride solution are obtained. Step 4: Add the decomposition residue with a preset liquid-to-solid ratio to the rare earth chloride solution obtained in Step 3 under water bath conditions, and keep it at the temperature for 2 hours. After solid-liquid separation, a rare earth chloride purification solution and a phosphorus-rare earth coprecipitate residue are obtained, and the phosphorus-rare earth coprecipitate residue is returned to Step 1.

2. The method for extracting rare earth elements from monazite concentrate according to claim 1, characterized in that, In step 4, the rare earth chloride solution can achieve synergistic leaching of rare earth and removal of phosphorus impurities with the decomposition residue. The liquid-solid ratio of the rare earth chloride solution to the decomposition residue is (7-10) mL:1g.

3. The method for extracting rare earth elements from monazite concentrate according to claim 1, characterized in that, In step 1, the mass ratio of CaO to monazite concentrate is (2-25)g:100g.

4. The method for extracting rare earth elements from monazite concentrate according to claim 1, characterized in that, In step 1, the concentration of the sodium hydroxide solution is 30%-50%.

5. The method for extracting rare earth elements from monazite concentrate according to claim 1, characterized in that, In step 3, the hydrochloric acid solution has a concentration of 4 mol / L, the hydrogen peroxide mixture has a volume fraction of 3%, and the liquid-solid ratio of the hydrochloric acid and hydrogen peroxide mixture to the decomposition residue is 5 mL-10 mL:1 g.

6. The method for extracting rare earth elements from monazite concentrate according to claim 1, characterized in that, In step 1, monazite concentrate and phosphorus-rare earth co-precipitate residue are mixed and placed in a reaction vessel.

7. The method for extracting rare earth elements from monazite concentrate according to claim 1, characterized in that, In step 2, the mixed slurry from step 1 is separated into solid and liquid components. The filter residue is washed and filtered multiple times with deionized water at 80°C to obtain decomposition liquid and decomposition residue.

8. The method for extracting rare earth elements from monazite concentrate according to any one of claims 1 to 7, characterized in that, In step 1, the volume ratio of sodium hydroxide solution to monazite concentrate is (300-600) mL: 100 g.

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