Environment-friendly method for selectively leaching heavy rare earth from weathering crust eluviation type rare earth ore

Abstract

The application discloses an environment-friendly method for selectively leaching heavy rare earth from weathered crust elution-deposited rare earth ore, and belongs to the technical field of bio-metallurgy and rare earth hydrometallurgy. The method comprises the following steps: activating a microbial strain to obtain activated bacterial solution; dissolving an organic nitrogen source and a carbon source in water to obtain a culture solution, and inoculating the activated bacterial solution to obtain inoculated culture solution; adding sterilized weathered crust elution-deposited rare earth ore into the inoculated culture solution to perform leaching experiment, and obtaining leaching solution rich in heavy rare earth; the concentration of the organic nitrogen source in the culture medium is 1-2 g / L, and the concentration of the carbon source is 2-10 g / L. Through accurate control of the concentration of the carbon source and the concentration of the nitrogen source in the culture system, the method realizes the synergistic effect of selective leaching of heavy rare earth and clean and low-ammonia-nitrogen emission, and has good industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of biometallurgy and rare earth hydrometallurgy technology, specifically relating to an environmentally friendly method for selectively leaching heavy rare earths from weathered crust leached rare earth ores. Background Technology

[0002] Rare earth elements, often referred to as "industrial vitamins," are widely used in permanent magnets, catalysis, hydrogen storage, precision optics, and defense industries, serving as core elements supporting green energy transformation and high-end manufacturing. Weathering crust leaching-type rare earth deposits in South my country are characterized by a complete distribution of light and heavy rare earth elements, particularly rich in heavy rare earth elements, supplying over 90% of the global heavy rare earth market and making them a core source of global heavy rare earth resources. In these deposits, rare earth elements are mainly adsorbed onto the surface of clay minerals in the form of hydrated ions or hydroxyl hydrated ions, and can be leached through exchange reactions in electrolyte solutions.

[0003] Currently, the commonly used industrial process is chemical in-situ leaching, which uses ammonium salts such as ammonium sulfate as leaching agents. The rare earth elements are displaced into the solution through ion exchange between ammonium ions and rare earth ions adsorbed on the surface of clay minerals. While this process is technically mature and has high leaching efficiency, it has gradually revealed several problems in long-term practice. Firstly, there is the serious problem of ammonia nitrogen pollution. Traditional processes typically use high-concentration ammonium sulfate (3%-5%) as a leaching agent, leaving a large amount of ammonium ions in the leachate after the reaction. After rare earth recovery, the ammonia nitrogen concentration in the effluent often reaches hundreds or even thousands of mg / L. Although subsequent wastewater treatment is required, the cost is high and it is difficult to fully meet the standards. According to the "Emission Standard of Pollutants for Rare Earth Industry" (GB 26451-2011), the direct emission limit for ammonia nitrogen is 15 mg / L. However, if the effluent from traditional processes is not deeply treated, it far exceeds this standard, leading to ecological and environmental problems such as eutrophication of water bodies around the mining area.

[0004] Secondly, the leaching selectivity is poor. Traditional ammonium sulfate chemical leaching lacks selectivity, exhibiting non-specific exchange for both light rare earth elements with larger ionic radii and heavy rare earth elements with smaller ionic radii. In actual production, to improve leaching efficiency, it is often necessary to increase the amount of ammonium sulfate used. This not only increases the cost of the reagents but also causes light and heavy rare earth elements in the leachate to mix together, which is detrimental to subsequent rare earth separation processes.

[0005] To address this, researchers have explored biometallurgical technology. Biometallurgical technology utilizes the biological, chemical, and physical processes of microorganisms and their metabolites to leach target metals from ores, offering advantages such as environmental friendliness, low energy consumption, and simple processes. Existing research indicates that certain microorganisms and their metabolites can interact with minerals. For example, invention patent CN113293287A discloses a method for leaching weathered crust eluting rare earth ores using microorganisms, demonstrating that bacteria such as *Pseudomonas aeruginosa* have a certain leaching effect on weathered crust eluting rare earth ores in both direct and indirect action systems. However, existing reports and studies largely remain at the level of phenomenological description. On the one hand, no publicly available methods have been found to achieve selective leaching of light and heavy rare earth elements by controlling the composition of the culture medium or leaching conditions. Considering the naturally enriched heavy rare earth elements in weathered crust eluting rare earth ores in South China, achieving selective separation of light and rare earth elements during the leaching stage would significantly reduce the purification costs of subsequent rare earth extraction and separation, possessing significant economic value. On the other hand, regarding the ammonia nitrogen pollution problem, although some studies have attempted to reduce the amount of ammonium salts by combining inorganic magnesium / calcium salts and organic ligands with ammonium salts, the concentration of ammonia nitrogen in the leachate remains high and has not yet met the national direct emission standards. Therefore, developing an environmentally friendly leaching method that can achieve selective leaching of heavy rare earth elements and control ammonia nitrogen pollution at its source has significant practical importance and application value. Summary of the Invention

[0006] This invention provides an environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores, in order to solve the technical problems of poor rare earth leaching selectivity and serious ammonia nitrogen pollution in existing ammonium sulfate chemical leaching processes, as well as the difficulty of existing bioleaching methods in simultaneously achieving heavy rare earth selectivity and meeting ammonia nitrogen emission standards.

[0007] Glucose and sucrose are common carbon sources for microbial culture, while tryptone and soybean peptone are common organic nitrogen sources. The organic acids and iron carriers produced by microbial metabolism can complex with rare earth ions, thereby promoting rare earth dissolution—a widely accepted understanding in the field of microbial-mineral interactions. However, current research largely focuses on obtaining rare earth leachates using microbial strains, and has not yet revealed how to achieve selective leaching of heavy rare earth elements and ensure that ammonia nitrogen in the leachate directly meets emission standards.

[0008] The key inventive point of this invention lies in achieving, through precise control of maintaining a low concentration of organic nitrogen source and a moderate concentration of carbon source in the leaching system, and utilizing specific microorganisms for leaching, the following two effects, which are difficult to achieve simultaneously by conventional methods, can be accomplished in the same process: (1) Selective preferential leaching of heavy rare earth relative to light rare earth: In ores with similar initial contents of light rare earth (La-Eu) and heavy rare earth (Gd-Lu, Y), the leaching amount of heavy rare earth is significantly higher than that of light rare earth, overcoming the defect of indiscriminate leaching in traditional ammonium sulfate chemical leaching agent, and also surpassing the limitation of existing bioleaching technology that only focuses on the total rare earth leaching rate. (2) The concentration of ammonia nitrogen in the leachate is reduced to below 15 mg / L in situ, which meets the direct emission standards of the rare earth industry: no additional denitrification treatment is required, which solves the long-standing problem of ammonia nitrogen pollution in rare earth mining from the source.

[0009] Based on a thorough understanding of the general mechanisms of microbial mineral leaching, this invention elevates carbon and nitrogen sources from existing culture medium components to process control parameters, focusing on the precise control of carbon and nitrogen source concentrations and ratios to achieve low-pollution selective leaching of rare earth elements. Regarding the selectivity of rare earth leaching, this invention provides bacteria with sufficient energy and a carbon skeleton by supplementing with an appropriate amount of carbon source, promoting the production of sufficient organic acids and iron carriers, which form soluble complexes with rare earth ions. Utilizing the larger complexation constants and stronger hydrated ion migration capabilities of heavy rare earth elements with these bio-organic molecules, selective leaching of heavy rare earth elements is achieved. Regarding ammonia nitrogen control, by supplementing with an appropriate amount of carbon source, bacteria are driven to efficiently assimilate organic nitrogen into their own proteins, nucleic acids, and other cellular substances, while simultaneously inhibiting the ammonia production process caused by amino acid decomposition due to carbon starvation, allowing ammonia nitrogen to naturally decrease below emission standards during the leaching process.

[0010] This invention achieves a synergistic effect of selective leaching of heavy rare earth elements and clean, low-ammonia emissions through precise control of carbon and nitrogen source concentrations, and has great industrial application value.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leached rare earth ores, characterized by comprising the following steps: The microbial strains were activated to obtain activated bacterial solutions. The activation method was as follows: after thawing, the microbial strains were inoculated into nutrient broth medium (NB medium) and cultured aerobically in a microbial incubator at a temperature of 20-35℃ and a rotation speed of 100-300 rpm for 12-48 hours. A culture medium containing an organic nitrogen source and a carbon source was prepared, wherein the concentration of the organic nitrogen source in the culture medium was 1-2 g / L and the concentration of the carbon source was 2-10 g / L. Sterilized weathered crust leaching rare earth ore was added to the culture medium, and then activated bacterial solution was inoculated into the culture medium. A leaching experiment was carried out in a microbial incubator at a temperature of 20-35℃ and a rotation speed of 100-300 rpm. The leaching experiment lasted for 5 to 7 days to obtain a leachate rich in heavy rare earth elements.

[0012] As a preferred technical solution, the organic nitrogen source is at least one of tryptone, soybean peptone, and acid-hydrolyzed casein; the carbon source is at least one of glucose, sucrose, maltose, and mannitol; the concentration of the organic nitrogen source in the culture medium is preferably 1 g / L; and the concentration of the carbon source is preferably 5 g / L.

[0013] As a preferred technical solution, the microbial species is the type strain of *Pseudomonas* genus, *Pseudomonas aeruginosa*. Pseudomonas aeruginosa ATCC 10145), the type strain of the genus *Bacillus*, *Bacillus deficientis* ( ). Brevundimonas diminuta ATCC 11568), the type strain of the genus Bacillus (Bacillus subtilis) Bacillus subtilis ATCC 6051), the type strain of the genus Bacillus brevis (Bacillus brevis). Brevibacillus brevis ATCC 8246), the type strain of the genus *Microbacterium*, is *Microbacterium aureum*. Exiguobacterium aurantiacum ATCC 35652), or the type strain of Citrobacter spp., Citrobacter freundii ( Citrobacter freundii These strains (ATCC8090) can be purchased commercially through the China Industrial Microbial Culture Collection Center, the China Center for Type Culture Collection, or the China General Microbial Culture Collection Center. These strains can utilize various carbon sources such as glucose, sucrose, maltose, or mannitol, as well as various nitrogen sources such as tryptone, soybean peptone, or acid-hydrolyzed casein.

[0014] Compared with existing ammonium sulfate chemical leaching processes and existing bioleaching technologies, the present invention has the following advantages and beneficial effects: (1) Selectivity of heavy rare earth leaching: Under the specific process conditions described in this invention, the leaching concentration of light rare earth elements is 1000-3000 μg / L, while the leaching concentration of heavy rare earth elements is 4000-9000 μg / L. The ratio of heavy rare earth to light rare earth leaching concentrations is approximately 3-4 times, exhibiting a significant selective leaching effect. This unique leaching selectivity means that: rare earth elements can be leached in groups, with priority given to extracting heavy rare earths of higher value or specific combinations. Subsequently, existing methods such as salt exchange can be used to leach the remaining light rare earths. The resulting leachate, which is relatively enriched in heavy rare earths and relatively depleted in light rare earths, simplifies the subsequent complex rare earth separation process and reduces production costs.

[0015] (2) Extremely low environmental pollution and excellent environmental benefits: The ammonia nitrogen content in the leachate can be controlled below 15 mg / L, which fully complies with the limit of 15 mg / L for direct discharge by existing enterprises as stipulated in the "Rare Earth Industry Pollutant Discharge Standard". This means that the leachate tailwater can be directly discharged or reused without expensive deep ammonia removal treatment, which subverts the traditional treatment model of polluting first and then treating, and realizes clean production from the source.

[0016] (3) Potential economic benefits: Reduce water treatment costs and eliminate the construction and operation costs of ammonia nitrogen wastewater treatment facilities in traditional processes; simplify the rare earth separation process, selective leaching of heavy rare earths reduces the number of stages and acid and alkali consumption in subsequent rare earth extraction and separation processes; low reagent costs, the main components of the culture medium are inexpensive peptone and glucose, and the required dosage is low, which has a certain cost advantage compared to consuming a large amount of ammonium sulfate.

[0017] In summary, this invention provides an environmentally friendly, highly selective, and economically efficient method for selective leaching of heavy rare earth elements, which helps to promote the advancement of green mining technology for rare earth elements. Attached Figure Description

[0018] Figure 1 The results of the measurement of the changes in the leaching concentrations of light rare earth elements and heavy rare earth elements with leaching time in Example 1; Figure 2 The results are the test results of the change of ammonia nitrogen concentration in the leachate with leaching time in Example 1; Figure 3 The results of the test on the changes in the leaching concentrations of light rare earth elements and heavy rare earth elements with the amount of glucose used in Example 2; Figure 4 The results of the test on the change of ammonia nitrogen concentration in the leachate as a function of tryptone dosage in Example 3; Figure 5 The results are the test results of the changes in the leaching concentrations of light rare earth elements and heavy rare earth elements with the amount of tryptone used in Example 3. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail.

[0020] In this invention, the light rare earth elements refer to the set of all elements including lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), and europium (Eu); the heavy rare earth elements refer to the set of all elements including gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y).

[0021] Example 1 An environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leached rare earth ores includes the following steps: (1) Bacterial activation: Pseudomonas aeruginosa strains stored in an ultra-low temperature freezer at -80℃ and preserved with glycerol were thawed in a freezer at 4℃ and inoculated into a culture flask containing 100 mL of NB medium. The composition of NB medium was 5 g / L tryptone, 3 g / L beef extract, and 5 g / L NaCl. The culture was carried out in an aerobic incubator at 30℃ and 200 rpm for 24 hours to obtain activated bacterial solution.

[0022] (2) In a sterile operating table, 1g of tryptone was added to 94mL of deionized water via sterile filtration through a sterile filter membrane. Then, it was added together with 5mL of 100g / L glucose solution to a 250mL culture flask that had been autoclaved. The initial concentrations of tryptone and glucose in this culture system were 1g / L and 5g / L, respectively. Then, 2g of weathered crust leaching rare earth ore, pre-sterilized at 170℃ for 2 hours, was added. This ore was taken from Maofeng Mountain, Guangdong Province. The mineral sample contained 1433ug / g of light rare earth (La-Eu) and 1373ug / g of heavy rare earth (Gd-Lu, Y). Finally, 1mL of bacterial solution activated in NB medium with a concentration of 1×10⁻⁶ was added. 8 CFU / mL of *Pseudomonas aeruginosa* culture was inoculated into the system. The culture flasks were then placed in a microbial incubator at 30°C and 200 rpm for leaching experiments. Samples were taken at different time points (1 day, 3 days, 5 days, and 7 days). The samples were centrifuged at 10,000 rpm for 15 minutes, and the supernatant was collected. The supernatant was then filtered through a 0.22 μm pore size cellulose acetate membrane. Finally, the rare earth element and ammonia nitrogen content of the supernatant was determined using ICP-MS and spectrophotometry, respectively.

[0023] Figure 1 The results of the measurement of the changes in the leaching concentrations of light rare earth elements and heavy rare earth elements with leaching time in Example 1 are as follows: Figure 1It can be seen that the leaching concentrations of both light and heavy rare earth elements (LREEs) initially increased rapidly with leaching time, then increased slowly and eventually stabilized. After seven days, the leaching reaction basically reached equilibrium, with the final leaching concentrations of LREEs and heavy rare earth elements being 2448 ug / L and 8876 ug / L, respectively. Compared to LREEs, heavy rare earth elements exhibit significant leaching selectivity.

[0024] Figure 2 The change in ammonia nitrogen concentration in the leachate as of leaching time in Example 1 is shown below. Figure 2 It can be seen that during the entire leaching process from 1 to 7 days, the ammonia nitrogen concentration in the leachate remained within the range of 3.3-7.1 mg / L. The final concentration of ammonia nitrogen in the leachate after 7 days was 3.3 mg / L, which met the direct emission standard of ammonia nitrogen concentration not exceeding 15 mg / L for rare earth industries.

[0025] Comparative Example 1 To verify the crucial roles of carbon and nitrogen sources in the culture medium for microbial leaching of rare earth elements and for controlling ammonia nitrogen in the leachate, comparative leaching experiments were conducted in media containing only tryptone as a nitrogen source or only glucose as a carbon source. The procedure for this comparative experiment was the same as in Example 1, except that the glucose solution or tryptone solution was replaced with sterile water.

[0026] Under the condition of adding only the carbon source glucose, the final concentration of ammonia nitrogen in the leachate was only 0.1 mg / L; the final leaching concentrations of light and heavy rare earth elements were only 486 ug / L and 1140 ug / L, respectively, which were far lower than 2448 ug / L and 8876 ug / L in Example 1. This indicates that when only a carbon source is added and no nitrogen source is available, bacterial growth is limited and the rare earth leaching efficiency is significantly reduced.

[0027] Under the condition of adding only nitrogen source tryptone, the final concentration of ammonia nitrogen in the leaching was 50.46 mg / L, which was not only significantly higher than 3.3 mg / L in Example 1, but also exceeded the direct emission standard of ammonia nitrogen ≤15 mg / L in the rare earth industry; the final leaching concentrations of light and heavy rare earth were 2196 ug / L and 4933 ug / L, respectively, showing obvious leaching effect and certain heavy rare earth leaching selectivity, but lower than 2448 ug / L and 8876 ug / L in Example 1.

[0028] Based on the results of Example 1 and Comparative Example 1, it can be confirmed that the selective leaching of heavy rare earth elements by bacteria can only be synergistically improved when both carbon and nitrogen sources are present. Furthermore, the carbon source plays a key role in reducing the ammonia nitrogen concentration in the system, while the nitrogen source contributes more to the selective leaching of heavy rare earth elements than the carbon source.

[0029] Example 2 To investigate the effective concentration of glucose as a carbon source, this embodiment conducted a series of leaching studies under gradient glucose concentrations. In a sterile operating room, 5 mL of glucose solutions at concentrations of 20 g / L, 40 g / L, 100 g / L, 200 g / L, or 300 g / L were added to a series of autoclaved 250 mL culture flasks containing 94 mL of 1 g of tryptone dissolved in each flask. The initial concentration of tryptone in the culture flasks was 1 g / L, and the initial concentrations of glucose were 1 g / L, 2 g / L, 5 g / L, 10 g / L, or 15 g / L, respectively. Then, 2 g of weathered crust leached rare earth ore, pre-sterilized at 170 °C for 2 hours, was added. Then, 1 mL of Pseudomonas aeruginosa activated in NB medium was inoculated into the system. Subsequently, the culture flask was placed in a microbial incubator at 30 ℃ and 200 rpm for leaching experiments. After 7 days, samples were taken and centrifuged at 10,000 rpm for 15 minutes. The supernatant was collected and filtered through a 0.22 μm pore size cellulose acetate membrane. Finally, the rare earth element and ammonia nitrogen content of the supernatant were determined by ICP-MS and spectrophotometer, respectively.

[0030] Figure 3 The results of the leaching concentration of light rare earth and heavy rare earth elements in Example 2 are as follows: the test results of this example also show the significant characteristics of selective leaching of heavy rare earth elements, and the ammonia nitrogen concentration is less than 15 mg / L. Under 1 g / L glucose conditions, the leaching concentrations of light and heavy rare earth elements were 3267 ug / L and 5502 ug / L, respectively, with an ammonia nitrogen concentration of 8.8 mg / L; under 2 g / L glucose conditions, the leaching concentrations of light and heavy rare earth elements were 2159 ug / L and 7336 ug / L, respectively, with an ammonia nitrogen concentration of 3.2 mg / L; under 5 g / L glucose conditions, the leaching concentrations of light and heavy rare earth elements were 2448 ug / L and 8876 ug / L, respectively, with an ammonia nitrogen concentration of 3.3 mg / L; under 10 g / L glucose conditions, the leaching concentrations of light and heavy rare earth elements were 2423 ug / L and 8941 ug / L, respectively, with an ammonia nitrogen concentration of 3.4 mg / L; and under 15 g / L glucose conditions, the leaching concentrations of light and heavy rare earth elements were 2559 ug / L and 8932 ug / L, respectively, with an ammonia nitrogen concentration of 3.3 mg / L.

[0031] The results of this embodiment show that adding 1 g / L glucose to 1 g / L tryptone medium can support bacterial metabolic consumption and reduce ammonia nitrogen to below 15 mg / L, while achieving selective leaching of heavy rare earth elements, confirming that the effective concentration of glucose as a carbon source is 1 g / L. Increasing the glucose concentration to 2 g / L and 5 g / L significantly increased both the total rare earth leaching amount and the selectivity of heavy rare earth leaching. Further increasing the glucose concentration to 10 g / L and 15 g / L resulted in rare earth leaching effects that were essentially the same as with 5 g / L glucose, confirming that the optimal concentration of glucose as a carbon source is 5 g / L.

[0032] Example 3 To investigate the effective concentration of tryptone as a nitrogen source, this embodiment conducted a series of leaching studies under gradient concentrations of tryptone. In a sterile operating room, 5 mL of 100 g / L glucose solution was added to a series of 250 mL culture flasks (94 mL each containing 1 g, 2 g, 3 g, 4 g, or 5 g of dissolved tryptone) that had been autoclaved. The initial glucose concentration in this system was 5 g / L, and the initial tryptone concentrations were 1 g / L, 2 g / L, 3 g / L, 4 g / L, or 5 g / L, respectively. Then, 2 g of weathered crust leaching rare earth ore, pre-sterilized at 170°C for 2 hours, was added. Finally, 1 mL of *Pseudomonas aeruginosa* culture activated in NB medium was inoculated into the system. Subsequently, the culture flasks were placed in a microbial incubator at 30 ℃ and 200 rpm for leaching experiments. Samples were taken after 7 days. The obtained samples were centrifuged at 10,000 rpm for 15 minutes, and the supernatant was collected. The supernatant was filtered through a 0.22 μm pore size cellulose acetate membrane. Finally, the rare earth element and ammonia nitrogen contents of the supernatant were determined by ICP-MS and spectrophotometer, respectively.

[0033] Figure 4 The results of the test on the change of ammonia nitrogen concentration in the leachate with the amount of tryptone used in Example 3 show that the ammonia nitrogen concentration in the leachate increases significantly with the increase of tryptone dosage. When the tryptone dosage is gradually increased from 1 g / L to 2 g / L, 3 g / L, 4 g / L, and 5 g / L, the ammonia nitrogen concentration increases from 3.3 mg / L to 11.2 mg / L, 106.4 mg / L, 153.1 mg / L, and 183.8 mg / L, respectively, far exceeding the direct emission standard of no more than 15 mg / L for ammonia nitrogen in the rare earth industry.

[0034] Figure 5The variation of light rare earth and heavy rare earth leaching concentrations with tryptone dosage in Example 3 shows that the leaching concentration of heavy rare earths decreased from 8876 μg / L with 1 g / L tryptone to approximately 5500 μg / L with 2-5 g / L tryptone, while the leaching concentration of light rare earths increased with increasing tryptone dosage. This example demonstrates that as the nitrogen source tryptone dosage increases, the ammonia nitrogen concentration increases significantly, and the leaching selectivity of heavy rare earths decreases significantly. The optimized concentration of nitrogen source tryptone is 1 g / L, which can control the ammonia nitrogen concentration within the direct emission limits of the rare earth industry while maintaining the leaching selectivity of heavy rare earths.

[0035] Example 4 To investigate whether the strains described in this invention are limited to Pseudomonas aeruginosa (ATCC 10145), this embodiment conducted a series of leaching studies using model strains of different genera as leaching microorganisms.

[0036] Compared with Example 1, the only difference in this example is that the bacterial strain is replaced with a defective shortwave monoclonal bacteria (…). B. diminuta ATCC 11568), Bacillus subtilis ( B. subtilis ATCC 6051), Bacillus shorthandis ( B. brevis ATCC 8246), Microbacterium aureum ( E. aurantiacum ATCC 35652) or Citrobacter freundii ( C. freundii (ATCC 8090), all other processes were the same as in Example 1. After 7 days of leaching, samples were taken and centrifuged at 10,000 rpm for 15 minutes. The supernatant was collected and filtered through a 0.22 μm pore size cellulose acetate membrane. Finally, the rare earth element and ammonia nitrogen content of the supernatant were determined by ICP-MS and spectrophotometer, respectively.

[0037] The results of this example show that all the strains exhibited significant heavy rare earth leaching selectivity, and the ammonia nitrogen concentrations were all below 15 mg / L. The light and heavy rare earth leaching concentrations of *Bacillus subtilis* were 1197 μg / L and 4374 μg / L, respectively, with an ammonia nitrogen concentration of 6.2 mg / L; the light and heavy rare earth leaching concentrations of *Bacillus subtilis* were 1901 μg / L and 6082 μg / L, respectively, with an ammonia nitrogen concentration of 1.8 mg / L; the light and heavy rare earth leaching concentrations of *Bacillus brevis* were 1893 μg / L and 6447 μg / L, respectively, with an ammonia nitrogen concentration of 1.9 mg / L; the light and heavy rare earth leaching concentrations of *Microbacterium aureum* were 2022 μg / L and 6149 μg / L, respectively, with an ammonia nitrogen concentration of 1.7 mg / L; and the light and heavy rare earth leaching concentrations of *Citrobacter freundii* were 1857 μg / L and 5953 μg / L, respectively, with an ammonia nitrogen concentration of 2.9 mg / L.

[0038] Example 5 To investigate that the carbon source described in this invention is not limited to glucose, this embodiment uses typical carbon sources such as sucrose, maltose, and mannitol as examples for leaching studies. Compared with Example 1, the only difference in this embodiment is that glucose is replaced with sucrose, maltose, or mannitol. All other processes are the same as in Example 1. After leaching for 7 days, samples were taken and centrifuged at 10,000 rpm for 15 minutes. The supernatant was collected and filtered through a 0.22 μm pore size cellulose acetate membrane. Finally, the rare earth element and ammonia nitrogen content of the supernatant were determined using ICP-MS and spectrophotometry, respectively.

[0039] The results of this example show that heavy rare earth elements exhibit significant leaching selectivity under different carbon source conditions, and the ammonia nitrogen concentration is below 15 mg / L for all conditions. When the carbon source is sucrose, the leaching concentrations of light and heavy rare earth elements are 2530 μg / L and 8952 μg / L, respectively, with an ammonia nitrogen concentration of 3.3 mg / L; when the carbon source is maltose, the leaching concentrations of light and heavy rare earth elements are 2446 μg / L and 8914 μg / L, respectively, with an ammonia nitrogen concentration of 3.4 mg / L; and when the carbon source is mannitol, the leaching concentrations of light and heavy rare earth elements are 2784 μg / L and 8923 μg / L, respectively, with an ammonia nitrogen concentration of 3.4 mg / L.

[0040] Example 6 To investigate that the nitrogen source described in this invention is not limited to tryptone, this embodiment uses typical nitrogen sources such as soybean peptone and acid-hydrolyzed casein as examples for leaching studies. Compared with Example 1, the only difference in this embodiment is that tryptone is replaced with soybean peptone or acid-hydrolyzed casein. All other processes are the same as in Example 1. After leaching for 7 days, samples were taken and centrifuged at 10,000 rpm for 15 minutes. The supernatant was collected and filtered through a 0.22 μm pore size cellulose acetate membrane. Finally, the rare earth element and ammonia nitrogen content of the supernatant were determined using ICP-MS and spectrophotometer, respectively.

[0041] The results of this example show that heavy rare earth elements exhibit significant leaching selectivity under different nitrogen source conditions, and the ammonia nitrogen concentration is below 15 mg / L in all cases. When the nitrogen source is soybean peptone, the leaching concentrations of light and heavy rare earth elements are 1959 μg / L and 7152 μg / L, respectively, with an ammonia nitrogen concentration of 2.2 mg / L. When the nitrogen source is acid-hydrolyzed casein, the leaching concentrations of light and heavy rare earth elements are 2010 μg / L and 6136 μg / L, respectively, with an ammonia nitrogen concentration of 1.1 mg / L.

[0042] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. An environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leached rare earth ores, characterized in that, Includes the following steps: Microbial strains are activated to obtain activated bacterial solutions; A culture medium containing an organic nitrogen source and a carbon source is prepared, wherein the concentration of the organic nitrogen source in the culture medium is 1-2 g / L and the concentration of the carbon source is 2-10 g / L; the weathered crust leaching rare earth ore after sterilization is added to the culture medium, and then activated bacterial solution is inoculated into the culture medium to carry out leaching experiments to obtain a leachate rich in heavy rare earth elements.

2. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores according to claim 1, characterized in that, The concentration of the organic nitrogen source in the culture medium is 1 g / L.

3. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leached rare earth ores according to claim 1, characterized in that, The concentration of carbon source in the culture medium is 5 g / L.

4. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores according to claim 1, characterized in that, The microbial species are at least one of Pseudomonas aeruginosa, Defective shortwave monoclonal bacteria, Bacillus subtilis, Bacillus brevis, Microbacterium aureum, and Citrobacter freundii.

5. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores according to claim 1, characterized in that, The activation treatment method is as follows: after the microbial strain is thawed, it is inoculated into a nutrient broth culture medium and cultured aerobically in a microbial incubator at a temperature of 20-35℃ and a rotation speed of 100-300 rpm for 12-48 hours.

6. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores according to claim 1, characterized in that, The organic nitrogen source is at least one of tryptone, soybean peptone, and acid-hydrolyzed casein.

7. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores according to claim 1, characterized in that, The carbon source is at least one of glucose, sucrose, maltose, and mannitol.

8. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores according to any one of claims 1 to 6, characterized in that, The leaching experiment was conducted in a microbial incubator.

9. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores according to claim 8, characterized in that, The temperature of the microbial incubator is 20-35℃, and the rotation speed is 100-300 rpm.

10. The environmentally friendly method for selectively leaching heavy rare earth elements from weathered crust leaching rare earth ores according to claim 1, characterized in that, The leaching experiment lasted for 5 to 7 days.

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