Microorganism-assisted rare earth element purification method

Abstract

The invention discloses a method for microorganism-assisted purification of rare earth elements, and belongs to the technical field of rare earth extraction. The method comprises the following steps: activating and culturing acidithiobacillus acidophilus and aspergillus niger, and mixing to obtain a leached strain mixed solution; bacillus and Escherichia coli are activated and cultured and then mixed and dried to obtain adsorption strain powder, and the adsorption strain powder is subjected to immobilization treatment to obtain adsorption strain particles; the rare earth raw material and the leaching strain mixed solution are subjected to a leaching reaction under the action of an accelerant, and rare earth leaching liquid is obtained; carrying out adsorption treatment on the rare earth leachate through an adsorption column filled with adsorption strain particles, and desorbing to obtain an enriched rare earth solution; and carrying out precipitation reaction on the enriched rare earth solution and oxalic acid to obtain rare earth oxalate, and calcining to obtain the rare earth oxide. According to the method for purifying the rare earth elements under the assistance of microorganisms, the leaching efficiency, the adsorption selectivity and the cycling stability of the rare earth raw materials can be improved.

Description

Technical Field

[0001] This invention relates to the field of rare earth extraction technology, and in particular to a method for microbial-assisted purification of rare earth elements. Background Technology

[0002] Rare earth elements are considered "strategic key metals" of modern industry due to their irreplaceable role in low-carbon energy, defense technology, and the electronics industry. Traditional rare earth extraction methods mainly rely on chemical processes such as acid leaching and solvent extraction, which suffer from high energy consumption, heavy pollution, and large reagent consumption. To address these challenges, microbial-assisted purification technology has gradually emerged. It utilizes the metabolic activities of microorganisms (such as acid production and secretion of chelating agents) and cell surface adsorption characteristics to achieve green and low-cost extraction and separation of rare earth elements, becoming an important research direction in the field of rare earth metallurgy.

[0003] In microbial-assisted purification technologies, "bioleaching" is the primary method, utilizing microorganisms or their metabolites to convert solid rare earth minerals into soluble ions. Bioadsorption is secondary, using functional groups on the surface of microbial cells, such as carboxyl and phosphate groups, to selectively adsorb specific rare earth ions in the solution, thereby achieving separation and enrichment. In existing technologies, a typical approach uses *Thiobacillus acidophilus* for bioleaching and Bacillus and other microorganisms for adsorption separation. Although this method has achieved some success in extracting light rare earth elements, its leaching efficiency for light rare earth elements (such as La, Ce, Pr, Nd) and medium rare earth elements (such as Sm, Eu, Gd) is only 70%–80%, which is relatively low. Furthermore, the leaching process is easily inhibited by mineral toxicity, leading to significant fluctuations in recovery rates. In addition, the selective separation capability of the bioadsorption stage for different rare earth elements is limited, with adsorption capacity typically below 90 mg / g, and adsorption performance significantly degrades after repeated cycles, making it difficult to meet the demands of high-purity, high-efficiency industrial production. Therefore, there is an urgent need to develop a new microbial-assisted purification method that can significantly improve rare earth leaching efficiency and enhance adsorption selectivity. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for microbial-assisted purification of rare earth elements. This invention solves the problems of low leaching efficiency, poor adsorption selectivity, and insufficient cycle stability of rare earth elements by selecting leaching agents to leach rare earth raw materials under the action of accelerators and utilizing adsorption agents for adsorption and desorption.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for microbial-assisted purification of rare earth elements, comprising the following steps:

[0007] The first mixture of Thiobacillus acidophilus and Aspergillus niger is used to obtain the extractant;

[0008] Bacillus and Escherichia coli were mixed in a second process to obtain an adsorbent, and the adsorbent was then immobilized to obtain adsorbent particles.

[0009] Rare earth raw materials and leaching bacteria are subjected to a leaching reaction under the action of an accelerator to obtain a rare earth leachate; the accelerator includes citric acid, Tween 80 and FeSO4·7H2O.

[0010] The rare earth leachate is adsorbed through an adsorption column, and after desorption, a rare earth-enriched solution is obtained; the adsorption column is filled with the adsorption strain particles.

[0011] Rare earth oxides are obtained by reacting a rare earth enriched solution with oxalic acid to produce a precipitation reaction and then calcining the solution.

[0012] Preferably, the mass ratio of Thiobacillus acidophilus to Aspergillus niger in the leaching agent is 1:5 to 5:1.

[0013] Preferably, the mass ratio of Bacillus to Escherichia coli in the adsorbent is 5-7:3-5.

[0014] Preferably, the immobilization treatment includes: mixing the adsorbent agent with sodium alginate solution, adding it dropwise into CaCl2 solution to form immobilized particles, and solidifying the immobilized particles in phosphate buffer solution.

[0015] Preferably, the mass ratio of citric acid, Tween 80 and FeSO4·7H2O in the accelerator is 1-3:0.2-0.5:3-6.

[0016] Preferably, the leaching reaction is carried out under acidic conditions of pH 1.5 to 2.5, the leaching temperature is 28 to 32°C, and the leaching time is 48 to 72 hours.

[0017] Preferably, the leaching reaction is carried out under stirring conditions, the stirring speed is 50 to 150 rpm, and air is introduced into the leaching reaction at a flow rate of 0.5 to 1.0 vvm.

[0018] Preferably, in the adsorption treatment, the leachate passes through the adsorption column from bottom to top, and the flow rate of the leachate is 2-5 BV / h.

[0019] Preferably, the desorption solution is an ammonium citrate solution with a concentration of 0.2–0.5 mol / L.

[0020] Preferably, the precipitation reaction is carried out at a pH of 2 to 4, at a temperature of 20 to 60°C, and for a time of 0.5 to 2 hours.

[0021] Preferably, the calcination temperature is 800–1000°C, and the calcination time is 2–5 hours.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. This invention selects *Thiobacillus acidophilus* and *Aspergillus niger* as leaching agents, utilizing the two strains to form an "acid-complexation" dual-mechanism leaching system. The metabolites of the two strains complement each other. The low pH environment maintained by *Thiobacillus acidophilus* promotes the ionization of organic acids in *Aspergillus niger*, increasing the complexation efficiency. Meanwhile, the formation of organic acid complexes reduces the concentration of free rare earth ions in the solution, shifting the leaching reaction equilibrium to the right. Simultaneously, the protective layer formed by the organic acids on the mineral surface effectively alleviates the inhibitory effect of toxic mineral components on microorganisms. The purification method provided by this invention significantly improves the leaching efficiency of rare earth elements, increasing the leaching rate to 90%–95%, while reducing the recovery rate fluctuation range to ±3% during the 60-hour leaching process, thus improving the stability of the rare earth purification method.

[0024] 2. This invention selects Bacillus and Escherichia coli to form an adsorbent, and uses sodium alginate immobilization treatment to form adsorbent particles, which improves the adsorption selectivity and cycle stability of rare earth elements. In Examples 1 to 3, the adsorption capacity of rare earth elements reached 108 to 112 mg / g. After 10 adsorption-desorption cycles, the adsorption capacity retention rate exceeded 90%, which solved the problem of rapid decay of adsorption efficiency and significantly extended the cycle life of the adsorbent.

[0025] 3. This invention selects a combination of citric acid, Tween 80, and FeSO4·7H2O as the promoter system. Citric acid, as a highly efficient chelating agent, forms stable and soluble complexes with rare earth ions, effectively preventing rare earth precipitation and enhancing the leaching of medium rare earth elements. Tween 80 significantly improves the microbial-mineral contact efficiency by reducing the solid-liquid interfacial tension, accelerating the mass transfer process and alleviating toxicity inhibition. FeSO4·7H2O provides a substrate for Thiobacillus acidophilus, enhancing its acid production capacity to maintain the optimal leaching pH environment. The synergistic effect of the three provides a purer and more stable rare earth ion solution for the subsequent adsorption stage, thereby improving the leaching rate and adsorption capacity of rare earth elements. Detailed Implementation

[0026] This invention provides a method for microbial-assisted purification of rare earth elements, comprising the following steps:

[0027] The first mixture of Thiobacillus acidophilus and Aspergillus niger is used to obtain the extractant;

[0028] Bacillus and Escherichia coli were mixed in a second process to obtain an adsorbent, and the adsorbent was then immobilized to obtain adsorbent particles.

[0029] Rare earth raw materials and leaching bacteria are subjected to a leaching reaction under the action of an accelerator to obtain a rare earth leachate; the accelerator includes citric acid, Tween 80 and FeSO4·7H2O.

[0030] The rare earth leachate is adsorbed through an adsorption column, and after desorption, a rare earth-enriched solution is obtained; the adsorption column is filled with the adsorption strain particles.

[0031] Rare earth oxides are obtained by reacting a rare earth enriched solution with oxalic acid to produce a precipitation reaction and then calcining the solution.

[0032] This invention involves first mixing Thiobacillus acidophilus and Aspergillus niger to obtain an extractant;

[0033] In this invention, the *Thiobacillus acidophilus* is preferably activated and cultured in 9K medium, and the *Thiobacillus acidophilus* cells are obtained by centrifugation. In this invention, the activation culture is preferably performed at a pH of 2–4, at a temperature of 20–30°C, and for a duration of 24–48 hours. After activation culture, the *Thiobacillus acidophilus* cell concentration reaches 10⁻⁶. 8 ~10 9 CFU / mL; the centrifugation rate is preferably 1200–1500 r / min. In this invention, the preferred 9K culture medium formulation is: 0.5 g / L (NH4)2SO4, 0.05 g / L KCl, 0.2 g / L K2HPO4·3H2O, 0.5 g / L MgSO4·7H2O, 0.01 g / L Ca(NO3)2, 60 g / L FeSO4·7H2O, and an aqueous solution. In this invention, *Thiobacillus acidophilus* can dissolve rare earth elements in minerals through acid production in a strongly acidic environment, thereby improving the leaching efficiency of rare earth elements samarium, europium, and gadolinium.

[0034] In this invention, the *Aspergillus niger* is preferably activated and cultured in potato dextrose medium, and the mycelium is obtained by centrifugation; in this invention, the activation culture is preferably performed at a pH of 5-6, at a temperature of 20-30°C, and for a duration of 48-72 hours; the concentration of *Aspergillus niger* mycelium after activation culture reaches 10. 7 ~10 8 CFU / mL; the centrifugation rate is preferably 1200-1500 r / min. In this invention, the preferred formulation of the potato glucose culture medium is: 4 g / L potato extract powder, 20 g / L glucose, 15 g / L agar, and aqueous solution; the Aspergillus niger in this invention can secrete a variety of organic acids, enhance the complexation and dissolution ability of rare earth elements samarium and europium, and alleviate the inhibition of microorganisms by mineral toxicity.

[0035] In this invention, there are no special requirements for the first mixing order; in this invention, the preferred mass ratio of *Thiobacillus acidophilus* and *Aspergillus niger* in the leaching agent is 1:5 to 5:1. The leaching agent of this invention, by selecting a synergistic leaching combination of *Thiobacillus acidophilus* and *Aspergillus niger*, forms an "acid-complexation" dual-mechanism leaching system, significantly improving the leaching efficiency of rare earth elements, increasing the leaching rate to 90% to 95%, while maintaining the stability of a high leaching rate over a relatively long period of the leaching process.

[0036] In this invention, Bacillus and Escherichia coli are mixed in a second process to obtain an adsorbent, and the adsorbent is then immobilized to obtain adsorbent particles.

[0037] This invention does not have specific limitations on the sources of Bacillus and Escherichia coli; any commercially available product or strains purchased from a preservation center can be used. In this invention, the preferred mass ratio of Bacillus to Escherichia coli in the adsorbent is 5–7:3–5, more preferably 6:4; the second mixing order is not particularly required.

[0038] In this invention, the immobilization treatment preferably includes: mixing the adsorbent agent with a sodium alginate solution, adding it dropwise to a CaCl2 solution to form immobilized particles, and then solidifying the immobilized particles in a phosphate buffer solution; in this invention, the mixing volume ratio of the adsorbent agent and the sodium alginate solution is preferably 1-5:10-20, more preferably 1:10; the mixing is preferably done with magnetic stirring or slow stirring with a sterile glass rod to ensure that the bacteria and the sodium alginate solution are fully mixed to form a uniform suspension; the concentration of the sodium alginate solution is preferably 2-10%, more preferably 5%; in this invention, the concentration of the CaCl2 solution is preferably 2-10%, more preferably 5%; in this invention, the sodium alginate and CaCl2 solution are added dropwise to the CaCl2 solution, and the sodium alginate and CaCl2 solution are mixed... 2+ A cross-linking reaction occurs, forming gel particles. The CaCl2 solution needs to be continuously stirred during the dripping process to ensure particle uniformity; the particle size of the immobilized particles is preferably 2–5 mm; in this invention, the pH of the phosphate buffer is preferably 6–7, and the concentration of the phosphate buffer is preferably 10%–20%; the curing time is preferably 1–2 hours.

[0039] This invention involves leaching rare earth raw materials and leaching bacteria under the action of an accelerator to obtain a rare earth leachate.

[0040] In this invention, the particle size of the rare earth raw material is preferably below 150 mesh, and the rare earth raw material is prepared into a solution with a solid-liquid ratio w / v preferably of 1-5:15-30.

[0041] In this invention, the promoter comprises citric acid, Tween 80, and FeSO4·7H2O; the mass ratio of citric acid, Tween 80, and FeSO4·7H2O in the promoter is 1–3:0.2–0.5:3–6. In this invention, citric acid, as a chelation promoter, enhances the complexation and dissolution of rare earth ions; Tween 80, as a surfactant, improves the contact efficiency between minerals and microorganisms and reduces toxic inhibition; and FeSO4·7H2O, as a culture medium substrate, promotes the metabolism and activation of *Thiobacillus acidophilus*.

[0042] In this invention, the leaching reaction is preferably carried out under acidic conditions with a pH of 1.5 to 2.5, the leaching temperature is preferably 28 to 32°C, and the leaching time is preferably 48 to 72 hours.

[0043] In this invention, the leaching reaction is carried out under stirring conditions, the stirring speed is 50 to 150 rpm, and the leaching reaction preferably involves the introduction of air, the air flow rate is 0.5 to 1.0 vvm.

[0044] This invention involves adsorbing rare earth leachate through an adsorption column, and then desorbing it to obtain a rare earth-enriched solution.

[0045] In this invention, the adsorption column is filled with the adsorbed bacterial particles; in the adsorption treatment, the leachate passes through the adsorption column from bottom to top, and the flow rate of the leachate is preferably 2 to 5 BV / h.

[0046] In this invention, the desorption solution is an ammonium citrate solution, the concentration of which is preferably 0.2-0.5 mol / L; the desorption rate is preferably 2-5 BV / h; the adsorption column after desorption is washed and regenerated with phosphate buffer, and can be reused.

[0047] This invention involves reacting a rare earth enrichment solution with oxalic acid to induce a precipitation reaction, followed by calcination to obtain rare earth oxides.

[0048] In this invention, the precipitation reaction is preferably carried out under conditions of pH 2-4, the precipitation reaction temperature is preferably 20-60℃, and the precipitation reaction time is preferably 0.5-2 hours. In this invention, the volume ratio of the enriched rare earth solution to oxalic acid is preferably 1-5:5-1; the oxalic acid concentration is preferably 10%-30%, more preferably 20%. In this invention, rare earth elements in the enriched rare earth solution react with oxalic acid to form rare earth oxalates, which are then calcined to obtain rare earth oxides. In this invention, the calcination temperature is 800-1000℃, and the calcination time is 2-5 hours.

[0049] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] The rare earth raw material provided in this embodiment is an ion-adsorption rare earth ore. The rare earth element content in the raw material is 0.14% to 0.30%, of which light rare earth elements (La, Ce, Pr, Nd, etc.) account for about 80%, medium rare earth elements (Sm, Eu, Gd, etc.) account for about 15%, and heavy rare earth elements (Y, Dy) account for about 5%.

[0051] Example 1

[0052] A method for microbial-assisted purification of rare earth elements includes the following steps:

[0053] 1) Preparation of microbial inoculants

[0054] Thiobacillus acidophilus was cultured in 9K medium (pH 2.0, temperature 30℃) for 48 h to achieve a bacterial concentration of 10. 8 ~10 9 CFU / mL, and then the bacterial supernatant was collected by centrifugation at 1400 r / min; the 9K medium formula was: 0.5 g / L (NH4)2SO4, 0.05 g / L KCl, 0.2 g / L K2HPO4·3H2O, 0.5 g / L MgSO4 4· 7H2O, 0.01g / L Ca(NO3)2, 60g / L FeSO4·7H2O and water.

[0055] Aspergillus niger was cultured in potato dextrose medium (pH 5.0, temperature 28℃) for 72 h to achieve a bacterial concentration of 10. 7 ~10 7 CFU / mL, and then separated and collected Aspergillus niger cells under centrifugation at 1400 r / min; the potato glucose medium formula is: potato extract powder 4 g / L, glucose 20 g / L, agar 15 g / L, water.

[0056] 2) Mix Thiobacillus acidophilus and Aspergillus niger at a mass ratio of 1:1 to obtain the extracting agent;

[0057] Ion-adsorption rare earth ore was crushed to 150 mesh and added to a 500L stirred bioreactor at a solid-liquid ratio of 1:15. Leaching agents were added, along with 2 g / L citric acid, 0.3 g / L Tween 80, and 5 g / L FeSO4·7H2O as promoters. The leaching conditions were controlled as follows: pH 2.0, temperature 30℃, stirring speed 100 rpm, aeration rate 0.8 vvm, and leaching time 60 hours. After leaching, the solution was filtered through a 0.45 μm filter membrane to obtain a rare earth leachate with a rare earth ion concentration of 0.12 g / L.

[0058] 3) Mix Bacillus and Escherichia coli at a mass ratio of 6:4, add 4% sodium alginate and 2% CaCl2, and solidify in phosphate buffer (pH 6.8) for 2 hours. Allow to stand and dry to obtain immobilized adsorption particles.

[0059] The pH of the 500L rare earth leachate obtained in step 2) was adjusted to 6.8, and the solution was passed through a fixed-bed adsorption column at a flow rate of 3 BV / h. The fixed-bed adsorption column was filled with immobilized adsorption particles. After saturation adsorption, a 0.3mol / L ammonium citrate solution was introduced for desorption, and the enriched rare earth solution was collected. After desorption, the adsorption column was regenerated by rinsing with phosphate buffer (pH 6.8).

[0060] 4) Product purification:

[0061] The enriched rare earth solution obtained in step 3) was mixed with oxalic acid (concentration 20%) and a precipitation reaction was carried out at pH=3 and temperature 30℃ to obtain rare earth oxalate. The precipitate was then collected by centrifugation at 700 r / min and the precipitated rare earth oxalate was calcined at 800℃ for 2 h to obtain rare earth oxide powder.

[0062] Example 2

[0063] A method for microbial-assisted purification of rare earth elements includes the following steps:

[0064] 1) Preparation of microbial inoculants

[0065] Thiobacillus acidophilus was cultured in 9K medium (pH 2.5, temperature 28℃) for 48 h to achieve a bacterial concentration of 10. 8 ~10 9 CFU / mL, and then the bacterial supernatant was collected by centrifugation at 1200 r / min; the 9K medium formula was: 0.5 g / L (NH4)2SO4, 0.05 g / L KCl, 0.2 g / L K2HPO4·3H2O, 0.5 g / L MgSO4 4· 7H2O, 0.01g / L Ca(NO3)2, 60g / L FeSO4·7H2O and water.

[0066] Aspergillus niger was cultured in potato dextrose medium (pH 5.5, temperature 30℃) for 60 h to achieve a bacterial concentration of 10. 7 ~10 8 CFU / mL, and then separated and collected Aspergillus niger cells under centrifugation at 1200 r / min; the potato glucose medium formula is: potato extract powder 4 g / L, glucose 20 g / L, agar 15 g / L, water.

[0067] 2) Mix Thiobacillus acidophilus and Aspergillus niger at a mass ratio of 2:1 to obtain the extracting agent;

[0068] Ion-adsorption rare earth ore was crushed to 150 mesh and added to a 500L stirred bioreactor at a solid-liquid ratio of 1:20. Leaching agents were added, along with 1 g / L citric acid, 0.2 g / L Tween 80, and 3 g / L FeSO4·7H2O as promoters. The leaching conditions were controlled as follows: pH 1.8, temperature 28℃, stirring speed 80 rpm, aeration rate 0.6 vvm, and leaching time 54 hours. After leaching, the solution was filtered through a 0.45 μm filter membrane to obtain a rare earth leachate with a rare earth ion concentration of 0.11 g / L.

[0069] 3) Mix Bacillus and Escherichia coli at a mass ratio of 7:3, add 5% sodium alginate solution and 3% CaCl2 solution, mix, solidify in phosphate buffer (pH 6.5) for 1.5 h, let stand and dry to obtain immobilized adsorption particles;

[0070] The pH of the 500 L rare earth leachate obtained in step 2) was adjusted to 6.5, and the solution was passed through a fixed-bed adsorption column at a flow rate of 2 BV / h. The fixed-bed adsorption column was filled with immobilized adsorption particles. After saturation adsorption, a 0.2 mol / L ammonium citrate solution was introduced for desorption, and the enriched rare earth solution was collected. After desorption, the adsorption column was regenerated by rinsing with phosphate buffer (pH 6.5).

[0071] 4) Product purification:

[0072] The enriched rare earth solution obtained in step 3) was mixed with oxalic acid (concentration 15%) and a precipitation reaction was carried out at pH=3 and temperature 25℃ to obtain rare earth oxalate. The precipitate was then collected by centrifugation at 600 r / min and the precipitated rare earth oxalate was calcined at 900℃ for 3 h to obtain rare earth oxide powder.

[0073] Example 3

[0074] A method for microbial-assisted purification of rare earth elements includes the following steps:

[0075] 1) Preparation of microbial inoculants

[0076] Thiobacillus acidophilus was cultured in 9K medium (pH 1.8, temperature 32℃) for 42 h to achieve a bacterial concentration of 10. 8 ~10 9 CFU / mL, and then the bacterial supernatant was collected by centrifugation at 1500 r / min; the 9K medium formula was: 0.5 g / L (NH4)2SO4, 0.05 g / L KCl, 0.2 g / L K2HPO4·3H2O, 0.5 g / L MgSO4·7H2O, 0.01 g / L Ca(NO3)2, 60 g / L FeSO4·7H2O and water;

[0077] Aspergillus niger was cultured in potato dextrose medium (pH 6.0, temperature 25℃) for 65 h to achieve a bacterial concentration of 10. 7 ~10 8 CFU / mL, and then separated and collected Aspergillus niger cells under centrifugation at 1500 r / min; the potato glucose medium formula is: potato extract powder 4 g / L, glucose 20 g / L, agar 15 g / L, water.

[0078] 2) Mix Thiobacillus acidophilus and Aspergillus niger at a mass ratio of 1:2 to obtain the extracting agent;

[0079] Ion-adsorption rare earth ore was crushed to 150 mesh and added to a 500L stirred bioreactor at a solid-liquid ratio of 1:10. Leaching agents were added, along with citric acid (3 g / L), Tween 80 (0.5 g / L), and FeSO4·7H2O (6 g / L) as promoters. The leaching conditions were controlled as follows: pH 2.2, temperature 32℃, stirring speed 120 rpm, aeration rate 1.0 vvm, and leaching time 66 hours. After leaching, the solution was filtered through a 0.45 μm filter membrane to obtain a rare earth leachate with a rare earth ion concentration of 0.13 g / L.

[0080] 3) Mix Bacillus and Escherichia coli at a mass ratio of 5:5, add 3% sodium alginate solution and 4% CaCl2 solution, mix, solidify in phosphate buffer (pH 7.0) for 2 hours, let stand and dry to obtain immobilized adsorption particles;

[0081] The pH of the 500 L rare earth leachate obtained in step 2) was adjusted to 7.0, and the solution was passed through a fixed-bed adsorption column at a flow rate of 4 BV / h. The fixed-bed adsorption column was filled with immobilized adsorption particles. After saturation adsorption, 0.5 mol / L ammonium citrate solution was introduced for desorption, and the enriched rare earth solution was collected. After desorption, the adsorption column was regenerated by rinsing with phosphate buffer (pH 7.0).

[0082] 4) Product purification:

[0083] The enriched rare earth solution obtained in step 3) was mixed with oxalic acid (concentration 20%) and a precipitation reaction was carried out at pH=4 and temperature 40℃ to obtain rare earth oxalate. The precipitate was then collected by centrifugation at 800 r / min and the precipitated rare earth oxalate was calcined at 1000℃ for 4 h to obtain rare earth oxide powder.

[0084] Comparative Example 1

[0085] The difference between Comparative Example 1 and Example 1 is that only Thiobacillus acidophilus is added as an leaching agent for the leaching reaction, and Aspergillus niger is not added. The remaining steps are the same as in Example 1.

[0086] Comparative Example 2

[0087] The difference between Comparative Example 2 and Example 1 is that only Bacillus was added as an adsorbent, without adding Escherichia coli. The remaining steps are the same as in Example 1.

[0088] Comparative Example 3

[0089] Compared with Example 3, Comparative Example 3 did not add any accelerators (citric acid, Tween 80, FeSO4·7H2O) during the leaching reaction stage, and the remaining steps were the same as in Example 1.

[0090] Testing methods for each performance indicator:

[0091] Leaching rate: The rare earth element content in the leachate was determined by ICP-MS (inductively coupled plasma mass spectrometry), and the leaching rate was calculated.

[0092] Leaching rate: calculated by the amount of rare earth dissolved per unit time (g / L·h), based on the slope of the leaching curve;

[0093] Adsorption capacity: The equilibrium adsorption capacity (mg / g) was calculated through adsorption experiments and fitted using the Langmuir model;

[0094] Cyclic stability: After 10 adsorption-desorption cycles, the adsorption capacity retention rate in the 10th cycle was calculated.

[0095] Total recovery rate: The proportion of rare earth recovered from raw materials to the final product, verified by gravimetric method and ICP-MS;

[0096] Product purity: The purity of rare earth oxides was analyzed using XRF (X-ray fluorescence spectroscopy).

[0097] The following table shows a comparison of the experimental performance of Examples 1-3 and Comparative Examples 1-3:

[0098]

[0099] 1. Comparison of effects between Example 1 and Comparative Example 1

[0100] The leaching rate of rare earth elements in Comparative Example 1 (78.2%) and the leaching rate (0.12 g / L·h) were significantly lower than those in Example 1 (94.5%) and Example 1 (0.18 g / L·h).

[0101] In Comparative Example 1, thiobacillus acidophilus was used for leaching alone, but it lacked the synergistic effect of Aspergillus niger. The single strain could not effectively complex rare earth elements, resulting in incomplete leaching and susceptibility to mineral toxicity inhibition, leading to a slow leaching rate. However, in Example 1 of this invention, the polybasic organic acids secreted by thiobacillus acidophilus and Aspergillus niger can enhance the complexation and dissolution of rare earth elements, forming an "acid-complexation" dual-mechanism leaching, thereby improving leaching efficiency and resistance to mineral toxicity.

[0102] 2. Comparison of effects between Example 1 and Comparative Example 2

[0103] The adsorption capacity of Comparative Example 2, 86.5 mg / g, was significantly lower than that of Example 1, 110.3 mg / g. Furthermore, Comparative Example 2 exhibited poor cycling stability, with performance degradation exceeding 15% after 5 cycles.

[0104] In Comparative Example 2, a single adsorption strain cannot achieve both high capacity and high selectivity, resulting in low adsorption efficiency. Furthermore, the surface functional groups are prone to failure after repeated use, leading to rapid performance degradation. In contrast, in Example 1 of this invention, Escherichia coli provides high adsorption capacity and selectivity by displaying rare earth binding proteins on its surface, while Bacillus provides even better adsorption selectivity.

[0105] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for the microbial assisted purification of rare earth elements, characterized in that, The method comprises the following steps: mixing Thiobacillus acidophilus and Aspergillus niger to obtain leaching bacteria; mixing Bacillus and Escherichia coli to obtain adsorption bacteria, and performing immobilization treatment on the adsorption bacteria to obtain adsorption bacteria particles; performing leaching reaction on rare earth raw materials and the leaching bacteria under the action of a promoting agent to obtain a rare earth leaching solution; the promoting agent comprises citric acid, Tween 80 and FeSO4·7H2O; performing adsorption treatment on the rare earth leaching solution through an adsorption column to obtain a rare earth-enriched solution after desorption; the adsorption column is filled with the adsorption bacteria particles; performing precipitation reaction on the rare earth-enriched solution and oxalic acid, and obtaining rare earth oxide after calcination.

2. The method of claim 1, wherein the method is characterized by, The mass ratio of the Thiobacillus acidophilus and the Aspergillus niger in the leaching bacteria is 1:5-5:

1.

3. The method of claim 1, wherein the method is characterized by, The mass ratio of the Bacillus and the Escherichia coli in the adsorption bacteria is 5-7:3-5.

4. The method of claim 1, wherein the method is characterized by, The immobilization treatment comprises: mixing the adsorption bacteria and a sodium alginate solution, dropping the mixture into a CaCl2 solution drop by drop to form immobilized particles, and solidifying the immobilized particles in a phosphate buffer.

5. The method of claim 1, wherein the method further comprises: The mass ratio of the citric acid, the Tween 80 and the FeSO4·7H2O in the promoting agent is 1-3:0.2-0.5:3-6.

6. The method of claim 1, wherein the method is characterized by, The leaching reaction is performed under an acid condition with a pH of 1.5-2.5, the leaching temperature is 28-32℃, and the leaching time is 48-72h.

7. The method of claim 1, wherein the method further comprises: The leaching reaction is performed under stirring, the stirring speed is 50-150rpm, air is introduced into the leaching reaction, and the air flow is 0.5-1.0vvm.

8. The method of claim 1, wherein the method is characterized by, In the adsorption treatment, the leaching solution passes through the adsorption column from bottom to top, and the flow rate of the leaching solution is 2-5BV / h.

9. The method of claim 1, wherein the method is characterized by, The solution selected for the desorption is an ammonium citrate solution, and the concentration of the ammonium citrate solution is 0.2-0.5mol / L.

10. The method of claim 1, wherein the method is characterized by, The precipitation reaction is performed under a condition with a pH of 2-4, the precipitation reaction temperature is 20-60℃, and the precipitation reaction time is 0.5-2h. The calcination temperature is 800-1000℃, and the calcination time is 2-5h.

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