Method for circularly leaching rare earth metal from rare earth leaching tail liquid

Abstract

The method comprises the steps that the total ion concentration of rare earth metal in rare earth leaching tail liquid is adjusted to 0.5-20 mmol / L, then biomass is added, and low-molecular-weight organic acid, namely the rare earth leaching agent, is generated through anaerobic high-temperature and high-pressure treatment and catalysis. The invention further discloses application of the rare earth leaching agent in rare earth leaching. According to the method, the leaching tail liquid is used as a catalyst, low-molecular-weight organic acid such as lactic acid is prepared from biomass through catalysis and recycled for rare earth leaching, closed-loop operation of the leaching process is achieved, the whole leaching process is environmentally friendly, safe, efficient and easy to operate, the problem that in the prior art, the production cost of organic acid is high is solved, and the method is suitable for industrial production. And the production cost of rare earth metal leaching is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgy, and particularly relates to a method for leaching rare earth metals by circulating the tail liquid of rare earth leaching. Background Technology

[0002] Rare earth elements (REEs) are closely related to modern lifestyles. They hold an important position in the scientific community due to their unique magnetic and catalytic properties. The rare earth elements comprise 17 elements, including 15 lanthanides and two closely related elements, scandium (Sc) and yttrium (Y). Rare earth elements have important applications in clean energy, electronics, and defense.

[0003] Currently, hydrometallurgical processes remain the primary method for obtaining medium and heavy rare earth resources. However, these processes present two significant problems: First, the leaching process cannot completely extract all rare earth ions, leaving some residues in the solution. Second, unused leaching agents and unprecipitated rare earth ions remain in the mother liquor, forming what is known as "rare earth leaching tailings." These tailings typically still contain a certain concentration of rare earth metal ions and ammonium salts.

[0004] Traditionally, the treatment of rare earth leaching tailings has faced severe challenges and environmental pressures. Conventional treatment methods mainly include: Direct discharge or diluted discharge: This method not only causes a serious waste of valuable rare earth resources and leaching agents (such as ammonium sulfate), but also causes serious pollution to the aquatic ecological environment by the ammonia nitrogen and heavy metals that may be contained in the tail liquid.

[0005] Neutralization precipitation treatment: The pH value is adjusted by adding alkali solution, causing the residual rare earth to precipitate as hydroxides. Although this method can recover some rare earth, the precipitation process is cumbersome, produces a large amount of sludge, and cannot recover the valuable leaching agent, making it uneconomical.

[0006] Membrane separation technologies (such as reverse osmosis and electrodialysis) attempt to concentrate and recover rare earth elements and ammonium salts using membrane technology. However, this method suffers from problems such as high equipment investment, high operating costs, easy membrane fouling and scaling, and stringent pretreatment requirements, making it difficult to promote and apply on a large scale in the cost-sensitive rare earth hydrometallurgical industry.

[0007] Therefore, large quantities of rare earth leaching tailings are usually simply stored temporarily in tailings ponds, which not only occupy land resources but also pose a huge environmental risk of dam failure and leakage. How to efficiently, economically, and environmentally treat and recycle rare earth leaching tailings to achieve the full utilization of rare earth resources and a closed-loop cycle of the leaching process has become a common technical problem that urgently needs to be solved in the smelting and separation industry of ion-adsorption rare earth minerals. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above and to provide a method for leaching rare earth metals by circulating rare earth leaching tail liquid.

[0009] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for leaching rare earth metals from rare earth leaching tail liquid includes the following steps: The total concentration of rare earth metal ions in the rare earth leaching tail liquid is adjusted to 0.5-20 mmol / L, then biomass is added, and the mixture is subjected to anaerobic high temperature and high pressure treatment. The reaction product obtained after anaerobic high temperature and high pressure treatment is then added to the rare earth leaching system to be treated for leaching.

[0010] In the above-mentioned method for recycling rare earth leaching tail liquid to leach rare earth metals, preferably, the biomass includes L-xylose, D-xylose, arabinose, D-arabinose, D-fructose, D-aldosterone, L-sorbose, D-mannose, cellobiose, D-maltose, sucrose, inulin, soluble starch, α-cellulose, and M... At least one of the following: cellulose, xylan, dextran, corn stalks, corn starch, mulberry branches, furfural residue, and moso bamboo; The rare earth metals include at least one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium, and scandium.

[0011] In the above-mentioned method for leaching rare earth metals by circulating the leaching tail liquid, preferably, the amount of biomass added is 0.1-50 g / L; the temperature in the anaerobic high temperature and high pressure treatment process is 180-280℃, the pressure is not less than 0.8 MPa, and the treatment time is 15-60 min.

[0012] The above-mentioned method for leaching rare earth metals by circulating the rare earth leaching tail liquid preferably involves removing impurities from the rare earth tail liquid before adding biomass for anaerobic high-temperature and high-pressure treatment.

[0013] In the above-mentioned method of leaching rare earth metals by circulating the tail liquid of rare earth leaching, preferably, the reaction product is purified and then added to the rare earth leaching system to be treated for leaching. The purification involves passing the rare earth leaching agent through a cation exchange column to remove most of the rare earth ions, Fe, Al and other cations, and / or through a 2 nm nanofiltration membrane to remove most of the remaining organic matter, residual sugars and other macromolecular substances.

[0014] The preferred method for leaching rare earth metals by circulating the leaching tail liquid described above is characterized in that the purified reaction product is mixed with a leaching agent and added to the rare earth leaching system to be treated for leaching, wherein the leaching agent includes an ammonium salt leaching agent and / or a magnesium salt leaching agent.

[0015] In the above-mentioned method for leaching rare earth metals by circulating the leaching tail liquid, preferably, the concentration of functional organic matter in the reaction product is 0.005-2 mol / L, and the concentration of the leaching agent is 0.005-2 mol / L; the functional organic matter in the reaction product includes at least one of small molecule organic acids, small molecule aldehydes, small molecule alcohols, acetates, and formates.

[0016] In the above-mentioned method of leaching rare earth metals by circulating the tail liquid of rare earth leaching, preferably, the concentration ratio of functional organic matter to leaching agent in the reaction product is 3:1 to 1:3.

[0017] In the above-mentioned method for leaching rare earth metals by circulating the tailings of rare earth leaching, preferably, the ammonium salt leaching agent includes at least one of ammonium sulfate and ammonium chloride, and the magnesium salt leaching agent includes at least one of magnesium sulfate and magnesium chloride.

[0018] In the above-mentioned method of leaching rare earth metals by circulating the leaching tail liquid, preferably, the rare earth leaching tail liquid obtained after leaching is recycled to achieve a closed-loop circulation of the leaching tail liquid.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention creatively uses biomass to treat rare earth leaching tail liquid under anaerobic high temperature and high pressure conditions, realizing closed-loop operation of rare earth tail liquid leaching process. The whole leaching process is green, safe, efficient and easy to operate. This method maximizes the recovery and utilization of rare earth resources and high-value leaching agents (such as ammonium sulfate) in rare earth leaching tail liquid, fundamentally eliminating the external discharge of high ammonia nitrogen wastewater, solving the core problems of resource waste and environmental pollution in traditional processes, and conforming to the important direction of green metallurgy and sustainable development.

[0020] (2) No harmful waste is generated in the entire process of this invention. The use and conversion of biomass is environmentally friendly, and the source reduction and resource utilization of wastewater are ultimately achieved, which greatly reduces the environmental pressure on enterprises and the environmental risks of tail liquid storage.

[0021] In summary, this invention not only successfully transforms rare earth leaching tailings from an environmental burden into a valuable resource, but also improves the efficiency of the main process through innovative treatment methods, achieving economic, environmental, and social benefits. It provides a brand-new solution for the green and efficient mining of ion-adsorption type rare earth ores. Attached Figure Description

[0022] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This refers to the rare earth leaching efficiency of rare earth mineral samples after different rare earth elements catalyze different biomass in Example 1 of the present invention. Figure 2 This refers to the proportion of functional organic compounds in the catalytic product of Example 2 of this invention; Figure 3 This refers to the rare earth leaching efficiency of different leaching agents on rare earth mineral samples in Example 2 of the present invention. Figure 4 This refers to the rare earth leaching efficiency of rare earth mineral samples under different treatment methods in Embodiment 3 of the present invention. Figure 5 This refers to the leaching efficiency of the leachate in Embodiment 4 of the present invention when used to leach different rare earth resources. Detailed Implementation

[0024] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0027] Example 1: This embodiment is a research experiment, and the specific steps are as follows: (1) Chlorides of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y), and scandium (Sc) were added to 50 mL of deionized water to prepare single-ion solutions with a rare earth ion concentration of 5 mmol / L. A control experiment was conducted using 50 mL of deionized water without any rare earth metals. Subsequently, 5 g / L of glucose, xylan, and starch were added to the rare earth ion solution, and after thorough mixing, the solution was transferred to a PTFE-lined (100 mL) stainless steel high-pressure reactor. Nitrogen gas was continuously purged into the reactor for 3 min to remove oxygen from the reaction system. The reactor was then assembled. The reaction vessel was then transferred to a high-temperature oven and kept at 200°C with a pressure not lower than 0.8 MPa for 35 minutes. After the reaction vessel cooled naturally, the solution was removed, filtered through a 0.22 μm organic filter membrane, and then passed through a 2 nm tubular nanofiltration membrane to remove most of the remaining organic matter, residual sugars, and other macromolecular substances. Next, it was passed through a cation exchange column to remove most of the cationic impurities (the cation exchange column can be reused). The purified reaction product can be sterilized under high temperature and high pressure and then stored for a long time.

[0028] (2) After removing impurities in step (1), the reaction product was diluted to a total functional organic matter concentration of 0.1 mol / L, and then dissolved in 1.0 mol / L dilute hydrochloric acid to adjust its pH to 4.5 as a leaching agent solution for later use. A transparent plexiglass tube with an inner diameter of 74 mm was selected as the leaching column, and the bottom end was sealed with PVC with holes. Before filling the ore, permeable stones, filter paper and quartz sand were placed at the bottom of the plexiglass column for sealing and filtration. A 250 g sample of ion-adsorption type rare earth ore was weighed. In order to make the density of each part in the ore column the same, the ore sample was divided into 4 equal parts and evenly filled into the plexiglass tube column. The sample was manually compacted to the designed height. After filling the ore sample, a filter paper was placed on the top surface of the ore sample. Under the condition of a liquid-solid volume-to-mass ratio of 2.5:1, the leaching agent solution was injected through a peristaltic pump. Leachate was collected at the bottom of the leaching column, and the total rare earth ion concentration in the leaching solution was measured. The rare earth leaching rate was calculated based on the rare earth content in the rare earth ore sample. Figure 1 As shown.

[0029] Example 2: 1. Pretreatment of rare earth leaching tailings The leaching tailings of ion-adsorption rare earth ores were used as catalysts in the experiments. Although the leaching efficiency of each rare earth ion differed, they all showed significant catalytic effects overall. For ease of experimental operation, we focused on the total concentration of rare earth ions in the tailings to conduct experiments on the conversion of functional organic compounds. First, ammonium bicarbonate was used to remove impurities such as iron, aluminum, and silicon from the leaching tailings. Specifically, ammonium bicarbonate was added to the tailings, and after magnetic stirring for 30 minutes, the pH was controlled at 5-5.2. After standing for 8 hours, the supernatant was collected, and the pH of the supernatant was adjusted to 3.0 using dilute hydrochloric acid. The types and concentrations of ions in the leaching tailings at this point are shown in Table 1. Subsequently, the supernatant was concentrated using rotary evaporation until the total concentration of rare earth ions was 3 mmol / L.

[0030] Table 1. Ion types and concentrations (mg / L) in leachate tailings

[0031] 2. Construction of an experimental system for catalytically generating functional organic compounds from leaching tail liquid Glucose was added to the rare earth ion solution at a concentration of 5 g / L. After thorough mixing, the solution was transferred to a PTFE-lined stainless steel high-pressure reactor (100 mL model), and nitrogen gas was continuously purged into the reactor for 10 min to remove oxygen from the reaction system. The reactor was then assembled. Subsequently, the reactor was transferred to a high-temperature oven and kept at 230°C with a pressure not lower than 0.8 MPa for 35 min. After the reactor cooled naturally, the solution was removed, filtered, and prepared for analysis.

[0032] The total organic composition of glucose after conversion catalyzed by a total rare earth ion concentration of 3 mmol / L was determined using high performance liquid chromatography-mass spectrometry (HPLC-MS / MS). The data acquisition system mainly consisted of ultra-high performance liquid chromatography (Vanquish, UPLC, Thermo, USA) and high resolution mass spectrometry (Q Exactive HFX, Thermo, USA). Chromatographic column: Waters HSS T3 (100*2.1 mm, 1.8 μm); mobile phase: Phase A was 0.1% formic acid-water solution, Phase B was 0.1% formic acid-acetonitrile; flow rate: 0.3 mL / min; column temperature: 40 °C; injection volume: 2 μL; elution gradient: 0.0–1.0 min, Phase B maintained at 0%; 1.0–12.0 min, Phase B linearly changed from 0% to 95%; 12.0–13.0 min, Phase B maintained at 95%; 13.0–13.1 min, Phase B linearly changed from 95% to 0%; 13.1–17.0 min, Phase B maintained at 0%; throughout the analysis, the sample was placed in an autosampler at 4 °C. Primary and secondary spectra were acquired using a Thermo Q Exactive HFX high-resolution mass spectrometry system (USA). The raw data were processed using the metabolomics software ProgenesisQI (Waters Corporation, Milford, USA) for baseline filtering, peak identification, integration, retention time correction, and peak alignment, ultimately yielding a data matrix of retention time, mass-to-charge ratio, and peak intensity. The main databases used were public databases such as http: / / www.hmdb.ca / and https: / / metlin.scripps.edu / , as well as a self-built database. Results are as follows: Figure 2 As shown, the total organic acid content in the catalytic products is relatively high, mainly including lactic acid, gluconic acid, butyric acid, succinic acid, pyruvic acid, enoic acid, valeric acid, oxaloacetic acid and other organic acids, while the content of small molecule aldehydes, small molecule alcohols and small molecule esters is relatively low.

[0033] 3. Rare earth leaching experiment to catalyze the generation of functional organic compounds from leaching tail liquid The catalytic product was filtered through a 0.22 μm organic filter membrane, followed by a 2 nm tubular nanofiltration process to remove most of the remaining organic matter, residual sugars, and other macromolecular substances. Then, it was passed through a cation exchange column to remove most of the cationic impurities. The catalytic product was diluted to a total organic acid functional organic matter concentration of 0.1 mol / L, and then dissolved in 1.0 mol / L dilute hydrochloric acid to adjust the pH to 4.5 as the leaching agent. Similarly, 0.1 mol / L analytical grade lactic acid, gluconic acid, formic acid, and butyric acid were used as control leaching agents. A transparent acrylic tube with an inner diameter of 74 mm was used as the leaching column, with the bottom sealed with perforated PVC. Before filling with ore, permeable stones, filter paper, and quartz sand were placed at the bottom of the acrylic column for sealing and filtration. A 250 g sample of ion-adsorption rare earth ore (composition shown in Table 2) was weighed. To ensure uniform density within the column, the sample was divided into 5 equal portions, uniformly filled into the acrylic tube column, and manually compacted to the designed height. After loading the ore sample, a filter paper was placed on top of the sample. The leaching agent solution was injected using a peristaltic pump at a liquid-to-solid volume ratio of 2.5:1. The leachate was collected at the bottom of the leaching column, and the total rare earth ion concentration was measured. The rare earth leaching rate was calculated based on the rare earth content in the ore sample. Results Figure 3 As shown, the rich organic composition has a strong synergistic promoting effect on the leaching of rare earth elements, and the leaching effect on rare earth minerals is far higher than that of leaching agents composed of single organic acids.

[0034] Example 3: (1) Removal of impurities from the tailings: First, ammonium bicarbonate was used to remove impurities such as iron, aluminum, and silicon from the leaching tailings of ion-adsorption rare earth ores. The specific steps were as follows: ammonium bicarbonate was added to the tailings, and after magnetic stirring for 30 minutes, the pH was controlled at 5-5.2. After standing for 8 hours, the supernatant was collected, and the pH of the supernatant was adjusted to 3.0 using dilute hydrochloric acid. The types and concentrations of ions in the leaching tailings at this time are shown in Table 1. Subsequently, the supernatant was concentrated using rotary evaporation until the total concentration of rare earth ions was 5 mmol / L.

[0035] (2) Add glucose to the rare earth ion solution after purification in step (1), with a glucose addition amount of 5 g / L. After thorough mixing, transfer the solution to a PTFE-lined stainless steel high-pressure reactor (100 mL model), and continuously purge it with nitrogen gas for 10 min to remove oxygen from the reaction system. Assemble the reactor. Then transfer the reactor to a high-temperature oven and maintain a pressure of not less than 0.8 MPa at 230℃ for 35 min. Perform a leaching process on the catalytic reaction filtrate to remove impurities, while using no leaching process and only leaching (without removing impurities from the tail liquid) as controls. The leaching process includes: after the reactor cools naturally, remove the solution and filter it. Then, pass the solution through a 2 nm tubular nanofiltration membrane to remove most of the remaining organic matter, residual sugars, and other macromolecular substances, and then pass it through a cation exchange column to remove most of the cationic impurities (the cation exchange column can be reused later). The purified reaction product can be sterilized at high temperature and high pressure and then stored for a long time.

[0036] Three parallel experiments were conducted using three types of leaching agents: tailings liquid impurity removal + leaching agent impurity removal, tailings liquid impurity removal only, and leaching agent impurity removal only. The reaction product was diluted to a total functional organic matter concentration of 0.1 mol / L and then dissolved in 1.0 mol / L dilute hydrochloric acid to adjust the pH to 4.5 for later use as the leaching agent. A transparent acrylic tube with an inner diameter of 74 mm was used as the leaching column, with the bottom sealed with perforated PVC. Before filling with ore, permeable stone, filter paper, and quartz sand were placed at the bottom of the acrylic column for sealing and filtration. A 250 g sample of ion-adsorption rare earth ore (composition shown in Table 2) was weighed. To ensure uniform density within the column, the sample was divided into three equal parts and evenly filled into the acrylic tube column, then manually compacted to the designed height. After filling the sample, a filter paper was placed on top of the sample. The leaching agent solution was injected using a peristaltic pump at a total leaching agent volume-to-solid ratio of 2.5:1. The leachate was collected at the bottom of the leaching column, the concentration of rare earth ions in the leachate was measured, and the rare earth leaching rate was calculated. The results are shown in [Figure number missing]. Figure 4 As shown, the leaching agent that undergoes two-step impurity removal has a higher leaching efficiency for rare earth elements, indicating that these two impurity removal processes are one of the keys to improving leaching efficiency.

[0037] Example 4: The rare earth leaching tail liquid was pretreated according to the method described in Example 2, with the final concentration of the rare earth leaching tail liquid fixed at 5 mmol / L. Glucose was added to the rare earth leaching tail liquid at a concentration of 5 g / L. After thorough mixing, the solution was transferred to a PTFE-lined stainless steel high-pressure reactor (100 mL model), and nitrogen gas was continuously purged into it for 3 min to remove oxygen from the reaction system. The reactor was then assembled. The pressure was maintained at 230°C for 35 min at a constant temperature of not less than 0.8 MPa. After the reactor cooled naturally, the solution was removed. The reaction product was purified according to the method described in Example 2. The total organic matter concentrations in the diluted reaction products were 0.01, 0.025, 0.05, 0.075, and 0.1 mol / L, respectively. The pH of the reaction product was adjusted to 4.5 using 1.0 mol / L dilute hydrochloric acid and used as a leaching agent.

[0038] The leaching agent for ion-adsorption type rare earth ores adopts a compounding scheme, that is, 0.025 mol / L of the traditional leaching agent ammonium sulfate is compounded with the aforementioned organic acid leaching agents of different concentrations. The leaching agents for monazite and phosphogypsum are the aforementioned prepared leaching agents.

[0039] The ion-adsorption rare earth ore used in the experiment came from a rare earth mining area in Ganzhou City. The ore sample was dried at 35℃ and mixed using the quartering method before use. The ion-phase rare earth grade of the ore sample was 1.31‰. The ion-phase rare earth distribution of the ore sample was determined by ICP-single-channel scanning analysis, and the results are shown in Table 2. A transparent plexiglass tube with an inner diameter of 74 mm was selected as the leaching column, and the bottom end was sealed with perforated PVC. Before filling the ore, permeable stone, filter paper, and quartz sand were placed at the bottom of the plexiglass column for sealing and filtration. A rare earth ore sample of 250 g was weighed. To ensure uniform density in all parts of the column, the ore sample was evenly filled into the plexiglass tube column and manually compacted to the designed height. After filling the ore sample, a filter paper was placed on top of the ore sample. Under the condition that the total amount of leaching agent was 2.5:1 (liquid-to-solid volume ratio), the leaching agent solution was injected through a peristaltic pump. The leachate is collected at the bottom of the leaching column, the concentration of rare earth ions in the leachate is measured, and the rare earth leaching rate is calculated.

[0040] Table 2. Composition of ion-adsorbed rare earth minerals (μg / g)

[0041] Monazite powder and phosphogypsum powder were filled in the same manner. The monazite powder contained 33.62% rare earth elements, and the content of each rare earth element as a percentage of the total rare earth element content is shown in Table 3. The phosphogypsum ore contained 48.25% rare earth elements, and the content of each rare earth element as a percentage of the total rare earth element content is shown in Table 4.

[0042] Table 3. Percentage of each rare earth element in monazite (%)

[0043] Table 4. The percentage of each rare earth element in the total rare earth element content of phosphogypsum ore (%)

[0044] The experimental results are shown in Figure 5 As shown, from Figure 5 It can be seen that, in general, the combination of ammonium sulfate and the reaction product as a leaching agent has a strong leaching capacity for rare earth elements in ion-adsorption type rare earth ores, and can reach more than 90% of the whole-phase rare earth concentration; the prepared reaction product alone also has certain application potential in leaching monazite and phosphogypsum ores.

Claims

1. A method for leaching rare earth metals using a recycled rare earth leaching tail liquid, characterized in that, Includes the following steps: The total concentration of rare earth metal ions in the rare earth leaching tail liquid is adjusted to 0.5-20 mmol / L, then biomass is added, and the mixture is subjected to anaerobic high temperature and high pressure treatment. The reaction product obtained after anaerobic high temperature and high pressure treatment is then added to the rare earth leaching system to be treated for leaching.

2. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 1, characterized in that, The biomass includes L-xylose, D-xylose, arabinose, D-arabinose, D-fructose, D-aldosterone, L-sorbose, D-mannose, cellobiose, D-maltose, sucrose, inulin, soluble starch, α-cellulose, and M... At least one of the following: cellulose, xylan, dextran, corn stalks, corn starch, mulberry branches, furfural residue, and moso bamboo; The rare earth metals include at least one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium, and scandium.

3. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 1, characterized in that, The amount of biomass added is 0.1-50 g / L; the temperature in the anaerobic high temperature and high pressure treatment process is 180-280℃, the pressure is not less than 0.8 MPa, and the treatment time is 15-60 min.

4. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 1, characterized in that, The rare earth tailings are purified before being added to biomass for anaerobic high-temperature and high-pressure treatment.

5. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 1, characterized in that, The reaction product was purified and then added to the rare earth leaching system to be treated for leaching.

6. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 5, characterized in that, The purified reaction product is mixed with a leaching agent and added to the rare earth leaching system to be treated for leaching. The leaching agent includes an ammonium salt leaching agent and / or a magnesium salt leaching agent.

7. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 6, characterized in that, The concentration of the functional organic compound in the reaction product is 0.005-2 mol / L, and the concentration of the leaching agent is 0.005-2 mol / L; the functional organic compound in the reaction product includes at least one of small molecule organic acids, small molecule aldehydes, small molecule alcohols, acetates, and formates.

8. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 7, characterized in that, The concentration ratio of functional organic matter to leaching agent in the reaction product is 3:1 to 1:

3.

9. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 6, characterized in that, The ammonium salt leaching agent includes at least one of ammonium sulfate and ammonium chloride, and the magnesium salt leaching agent includes at least one of magnesium sulfate and magnesium chloride.

10. The method for leaching rare earth metals by circulating the rare earth leaching tail liquid as described in claim 1, characterized in that, The rare earth leaching tail liquid obtained after leaching is recycled.

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