A method for bioleaching of rare earths combining surface functionalization modification and biosurfactant reinforcement

Abstract

The application discloses a kind of biological leaching rare earth methods combined with surface functionalization modification and biological surfactant intensification, belong to biological metallurgy and rare earth resources extraction technical field, comprising the following steps: mineral surface functionalization modification, interface wetting control, combined microbial population biological leaching, leaching liquid recovery and detection;The application is organically integrated by three-stage intensification strategy, forms the complete technical scheme different from the existing single ore leaching agent optimization, simple acid modification or surface active agent addition, aims at solving the key technical bottleneck that mineral-microorganism interface interaction is weak in the process of medium-lean oxidized ore biological leaching, provides new technical approach for efficient green extraction of Baiyunebo medium-lean oxidized ore rare earth resources.

Description

Technical Field

[0001] This invention belongs to the field of biometallurgy and rare earth resource extraction technology, specifically involving a bioleaching method for rare earths that combines surface functionalization modification and biosurfactant enhancement, which is particularly suitable for the green and efficient extraction of rare earth resources from lean oxide ore in Bayan Obo. Background Technology

[0002] Rare earth elements, as non-renewable key strategic resources, are indispensable core materials for strategic emerging industries such as new energy, high-end manufacturing, aerospace, and electronic information. Their efficient development and utilization are of paramount importance to ensuring national strategic resource security and promoting the high-quality development of high-end manufacturing. The Bayan Obo deposit is the core production area of ​​light rare earth resources in northern my country, with proven light rare earth reserves accounting for more than 80% of the country's total reserves, making it a core guarantee base for my country's rare earth resource supply. After decades of large-scale mining, the high-grade, easily beneficiated rare earth ore resources of this deposit are increasingly depleted, and a large amount of medium-lean oxide ore resources and iron ore tailings have accumulated. Among them, the medium-lean oxide ore of Bayan Obo specifically refers to low-grade, difficult-to-process ore with rare earth (REO) grades between 0.5% and 12% and iron grades between 25% and 35%. Its main rare earth minerals are bastnaesite and monazite, mostly in a fine-grained embedded state densely encapsulated by iron oxides and silicate gangue minerals. A dense iron-silicon oxide passivation film easily forms on the mineral surface. It also contains associated valuable components such as fluorite, niobium minerals, and phosphates. Conventional beneficiation processes are difficult to process, resulting in low rare earth recovery rates and insufficient resource utilization. Currently, rare earth extraction from the medium-lean oxide ore of Bayan Obo faces problems such as high energy consumption during roasting, significant waste gas pollution, high acid consumption during strong acid leaching, severe equipment corrosion, and significant ecological and environmental risks. Furthermore, the recovery rate of fine-grained, lattice-encapsulated rare earth minerals is low, failing to meet the development requirements of green metallurgy under the "dual carbon" target.

[0003] In recent years, biometallurgical technology has attracted widespread attention in the field of low-grade mineral resource processing due to its advantages such as ambient temperature and pressure operation, short process flow, green and low-carbon environmental protection, low reagent consumption, and strong adaptability to low-grade ores. Among them, fungi (such as Aspergillus niger and Penicillium) can dissolve rare earth minerals by producing organic acids through metabolism. However, it has drawbacks such as high mycelial viscosity, low mass transfer efficiency of the leaching system, long cultivation cycle, and insufficient leaching efficiency for rare earth minerals with stable crystal lattices. For example, Chinese patent application CN120555782A discloses a bioleaching method for extracting rare earth elements from fly ash using Aspergillus niger. This method relies on the acid production from Aspergillus niger metabolism to achieve rare earth dissolution, and does not include a targeted pretreatment process designed for the dense passivation film on the mineral surface, thus failing to solve the core problem of obstructed contact between microorganisms and minerals.

[0004] To address the issues of weak mineral interfacial interactions and low leaching efficiency, some existing technologies enhance rare earth leaching effects through the addition of modifying agents or surfactants. For example, Chinese patent CN119040629A discloses a method for bioleaching of ion-adsorption rare earth ores using modified biomass. This method modifies biomass with sulfuric acid solution, mixes the modified biomass with a culture medium, inoculates microorganisms to obtain a fermentation broth, and uses it for leaching. This approach increases the content of active functional groups on the surface of biomass through acid modification, thereby enhancing the biomass' ability to complex and adsorb rare earth ions to a certain extent. However, the use of concentrated sulfuric acid for modification results in severe equipment corrosion, high costs for acidic wastewater disposal, and significant environmental risks, making it unsuitable for large-scale industrial applications. For example, Chinese patent CN115505736A discloses a method for bioleaching ion-adsorption type rare earth minerals under neutral or near-neutral conditions. This method improves leaching efficiency by adding biosurfactants before leaching. Although this method verifies the enhancing effect of biosurfactants, it only uses a single surfactant addition method and does not form a synergistic enhancement system with targeted pretreatment of the mineral surface. It cannot simultaneously solve the three core problems of mineral surface passivation barrier, weak microbial-mineral interface binding force, and low mass transfer efficiency of the leaching system. At the same time, this method is aimed at easily leached ion-adsorption type rare earth minerals, and its leaching effect on lattice-distributed rare earth minerals is extremely limited.

[0005] In summary, while existing rare earth bioleaching technologies have made some progress, the following common technical bottlenecks remain insurmountable in their application to difficult-to-process lattice-type rare earth ores, such as the medium-lean oxide ore in Bayan Obo: First, for these difficult-to-leach ores, which are covered with a dense iron-silicon oxide passivation film and have rare earth elements embedded in a fine-grained lattice, there is a lack of mineral surface pretreatment and interface control methods, making it impossible to fundamentally solve the core problem of obstructed contact between microorganisms and minerals and low mass transfer efficiency of the leaching system; Second, a synergistic enhancement system is lacking, and existing technologies mostly employ single... First, the addition of modifying agents, surfactants, or strain optimization methods have not formed a multi-level synergistic enhancement system of "mild functionalization modification of mineral surfaces - biophilic regulation of interfaces - enhanced mass transfer by biosurfactants", and cannot simultaneously solve the problems of surface passivation and low dissolution efficiency. Second, some processes using strong acid modification have problems such as severe equipment corrosion, high waste liquid disposal costs, and high environmental risks, which cannot meet the requirements of green and low-carbon industrial applications. At the same time, existing strains mostly use single fungi or general mixed strains, which have problems such as long leaching cycles and high acid consumption. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a combined surface functionalization modification and biosurfactant-enhanced bioleaching method for rare earth minerals. This method introduces low-concentration citric acid pretreatment at low temperatures into the bioleaching process of rare earth oxide ores, selectively dissolving the iron oxide passivation film under mild conditions while simultaneously introducing hydroxyl (-OH) and carboxyl (-COOH) active functional groups onto the mineral surface. Subsequently, rhamnolipid biosurfactants are used to regulate interfacial wetting, reducing liquid-solid interfacial tension and enhancing the permeability of the leachate to mineral microfractures. Finally, a combined bacterial community of Bacillus subtilis and Bacillus megaterium is used for bioleaching. The organic integration of these three-stage enhancement strategies forms a complete technical solution distinct from existing methods involving single leaching agent optimization, simple acid modification, or surfactant addition. This approach aims to solve the key technical bottleneck of weak mineral-microorganism interfacial interaction during the bioleaching of medium-lean oxide ores, providing a new technical pathway for the efficient and green extraction of rare earth resources from the medium-lean oxide ores of Bayan Obo.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] This invention provides a method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement, comprising the following steps:

[0009] Mineral surface functionalization modification: The lean oxide ore in Bayan Obo is crushed and ground to a predetermined fineness to obtain mineral powder; the obtained mineral powder is mixed with a low-concentration citric acid solution at a predetermined solid-liquid ratio, and shaken under low temperature conditions to selectively dissolve the iron oxide passivation film on the surface of the mineral powder, while introducing hydroxyl (-OH) and carboxyl (-COOH) active functional groups on the mineral surface to obtain a surface-modified slurry;

[0010] Interface wetting regulation: Rhamnolipin biosurfactant was added to the surface-modified slurry, and the mixture was continued to be shaken at room temperature to reduce the contact angle of the mineral surface, improve the hydrophilicity and wettability of the mineral surface, enhance the penetration ability of the leachate into the micro-fractures of the mineral, and obtain the interface-regulated slurry.

[0011] Bioleaching of combined microbial communities: Bacillus subtilis and Bacillus megaterium were activated and cultured separately, and then inoculated into LB liquid medium for pre-culture in a certain proportion until the logarithmic growth phase to obtain an active bacterial suspension of the combined microbial community; the active bacterial suspension was inoculated into the interface-controlled slurry at an inoculation rate of 5%-15%, and the bioleaching reaction was carried out under the same conditions as the culture of the combined microbial community. During the process, the pH value of the leaching system was monitored at regular intervals to determine whether it was within a stable range, thereby determining the state of the microbial community;

[0012] Leachate recovery and testing: After leaching, the leaching slurry is subjected to solid-liquid separation, and the supernatant is collected to obtain rare earth leachate; the leaching residue is washed to remove residual bacterial metabolic acid, and the leachate is subjected to rare earth element analysis to calculate the rare earth leaching rate.

[0013] Furthermore, in the functional modification of mineral surfaces, medium-lean oxide ores are crushed and ground until the mineral powder particle size reaches the range of 0.038μm-0.074μm.

[0014] Furthermore, in the functional modification of mineral surfaces, the concentration of the low-concentration citric acid solution is 0.1 wt.%-1.0 wt.%.

[0015] Furthermore, in the functional modification of mineral surfaces, the solid-liquid ratio of mineral powder to citric acid solution is 50 g / L-100 g / L.

[0016] Furthermore, in the functional modification of mineral surfaces, the processing temperature under low-temperature conditions is 25℃-40℃.

[0017] Furthermore, in the functional modification of mineral surfaces, the oscillation treatment time is 2-8 hours, and the rotation speed is 100rpm-200rpm.

[0018] Furthermore, in the interface wetting control, the final concentration of the added rhamnolipin biosurfactant in the slurry is 0.1 wt.%-0.5 wt.%.

[0019] Furthermore, in the interface wetting control, the processing temperature under room temperature conditions is 20℃-30℃.

[0020] Furthermore, in the interface wetting control, the oscillation treatment time is 0.5-2 hours, and the rotation speed is 100rpm-200rpm.

[0021] Furthermore, in the interface wetting control, after treatment with rhamnolipin, the contact angle of the mineral surface was reduced to below 40°.

[0022] Furthermore, in the bioleaching of the combined microbial community, the inoculum amounts of Bacillus subtilis and Bacillus megaterium were both 5 vol.%-15 vol.%, the pre-culture time was 6-12 hours, the OD value of the active bacterial suspension of the combined microbial community was 2.0-3.0, the temperature during the construction and leaching of the combined microbial community was 28℃-40℃, and the shaking speed of the shaker under oscillation was 120 rpm-150 rpm.

[0023] Furthermore, in the combined microbial bioleaching, the composition of the LB liquid medium is: 8.0 g / L-12.0 g / L tryptone, 3.0 g / L-7.0 g / L yeast extract, and 8.0 g / L-12.0 g / L NaCl.

[0024] Furthermore, in the combined microbial bioleaching process, the leaching time is 6-8 days.

[0025] Furthermore, in the leachate recovery and detection, the leachate is obtained by centrifugation at a speed of 8000rpm-10000rpm for a time of 5min-10min.

[0026] The rare earth leaching rate in the leachate is ≥50.63%.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) This invention innovatively introduces low-concentration citric acid low-temperature pretreatment into the bioleaching process of rare earth oxide ores. Citric acid, as a weak organic acid, can complex and dissolve the iron oxide passivation film on the mineral surface under mild conditions (25℃-40℃), avoiding the corrosion of equipment by strong acids and the environmental pollution of acidic waste liquid, and has significant advantages in green environmental protection. At the same time, citric acid molecules can introduce -OH and -COOH active sites on the mineral surface through chemical bonding. These active functional groups can enhance the adhesion ability of subsequent microbial extracellular polymers (EPS) on the mineral surface, solving the problem of blocked contact between microorganisms and minerals, and creating favorable interface conditions for subsequent bioleaching.

[0029] (2) This invention uses rhamnolipin biosurfactant as the core medium for interface regulation. Its special amphiphilic molecular structure can effectively reduce the liquid-solid interfacial tension and significantly improve the penetration ability of the leachate into mineral microcracks, solving the problem of low mass transfer efficiency in the leaching system in the prior art. The penetration ability of the aqueous solution into mineral microcracks is greatly improved. At the same time, the carboxyl and hydroxyl functional groups in the rhamnolipin molecule have selective complexation ability for rare earth ions, and can play a dual function of "wetting-complexation" during the leaching process. Compared with the single addition of surfactant in the prior art, this invention gives rhamnolipin the dual effect of interface modification and rare earth capture, forming a new mechanism that is different from the prior art.

[0030] (3) This invention employs a combined bacterial community of Bacillus subtilis and Bacillus megaterium for bioleaching. Bacillus subtilis possesses strong acid-producing and bio-adsorption capabilities, and can metabolize to produce small-molecule organic acids such as acetic acid, lactic acid, and citric acid, which can effectively dissolve rare earth minerals; Bacillus megaterium has been proven to decompose Bayan Obo ore and release rare earth elements. The combination of the two creates a synergistic effect, and compared with single species, the combined bacterial community significantly improves the rare earth leaching efficiency of low-oxidation ore in Bayan Obo. Existing studies have shown that rhamnolipids have excellent biocompatibility with the two Bacillus species, which can promote the colonization of the bacterial community on the mineral surface, providing a biological basis for the synergistic leaching of the combined bacterial community.

[0031] (4) This invention constructs a three-level enhancement strategy of “surface functionalization modification – interface wetting regulation – combined microbial bioleaching”, forming a complete technology chain. The enhancement measures at each level have a synergistic effect: citric acid pretreatment not only removes the passivation film and introduces active functional groups, but the residual citric acid can also serve as a carbon source and complexing agent for the combined microbial community; the wetting regulation of rhamnolipids enhances the penetration ability of the leachate into the ore, and the carboxyl groups in its molecular structure can form a coordination synergy with citric acid, further enhancing the complexation and stabilization effect on rare earth ions; the combined microbial community is more likely to adhere and colonize on the surface of the functionalized mineral, and the organic acids produced by metabolism form a multi-organic acid-surfactant composite leaching system with the added citric acid and rhamnolipids. The organic integration of the three-level strategy produces a synergistic effect of “1+1+1>3”.

[0032] (5) The entire process of the present invention operates under mild conditions of normal temperature and pressure and near neutrality. It does not require high temperature and high pressure equipment or strong corrosive reagents such as strong acids and strong alkalis. The equipment investment is low, the operating energy consumption is small, and there is no risk of secondary pollution. It fully meets the industrial development direction of green metallurgy under the "dual carbon" target. At the same time, the present invention is designed for the Baiyun Obo medium-lean oxide ore, a typical difficult-to-process rare earth resource in my country. The process parameters are controllable, the process is simple, and it is easy to scale up. It has clear industrial application prospects and promotion value. Attached Figure Description

[0033] Figure 1 The process flow diagram of the combined surface functionalization modification and biosurfactant-enhanced bioleaching of rare earths according to the present invention. Detailed Implementation

[0034] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0035] A combined surface functionalization modification and biosurfactant-enhanced bioleaching method for rare earths, such as... Figure 1 As shown, it includes the following steps:

[0036] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and a citric acid solution with a mass fraction of 0.1 wt.%–1.0 wt.% was added, maintaining a solid-liquid ratio of 50 g / L–100 g / L. The mixture was treated in a constant-temperature water bath at 25℃–40℃ with shaking at a speed of 100 rpm–200 rpm for 2–8 hours. After treatment, the surface-modified slurry was obtained.

[0037] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to achieve a final concentration of 0.1 wt.%-0.5 wt.%, and the slurry was further treated with shaking at 20℃-30℃ and 100rpm-200rpm for 0.5-2 hours to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to below 40°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0038] Bioleaching with a combined microbial community: *Bacillus subtilis* and *Bacillus megaterium* were inoculated at 5 vol.%-15 vol.% into LB liquid medium and pre-cultured for 6-12 hours. The LB liquid medium consisted of 8.0 g / L-12.0 g / L tryptone, 3.0 g / L-7.0 g / L yeast extract, and 8.0 g / L-12.0 g / L NaCl. The culture was carried out at 28℃-40℃ and 120 rpm-150 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.0-3.0. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a rate of 5%-15%, and leached under the same conditions as the culture for 8 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5-2.5, thus determining the state of the microbial community.

[0039] Leachate recovery and detection: The leachate was obtained by centrifugation at 8000rpm-10000rpm for 5-10min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity.

[0040] The mineral used in the various embodiments of the present invention is the medium-lean oxide ore of Bayan Obo.

[0041] Example 1

[0042] A bioleaching method for rare earth elements, combining surface functionalization modification and biosurfactant enhancement, includes the following steps:

[0043] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and 0.5 wt.% citric acid solution was added, maintaining a solid-liquid ratio of 75 g / L. The mixture was treated in a 30℃ constant-temperature water bath shaker at 150 rpm for 4 hours. After treatment, the surface-modified slurry was obtained.

[0044] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to a final concentration of 0.2 wt.%, and the slurry was further treated with shaking at 25°C and 150 rpm for 1 hour to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to 35.8°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0045] Bioleaching with a combined microbial community: 15 vol.% inoculum of *Bacillus subtilis* and 5 vol.% inoculum of *Bacillus megaterium*, preserved in glycerol, were inoculated into LB liquid medium and pre-cultured for 6 hours. The LB liquid medium consisted of 10 g / L tryptone, 5 g / L yeast extract, and 10 g / L NaCl. The culture was carried out at 30°C and 150 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.71. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a 10 vol.% inoculum and leached under the same conditions as the culture for 6 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5–2.5, thus determining the state of the microbial community.

[0046] Leachate recovery and detection: The leachate was obtained by centrifugation at 10,000 rpm for 10 min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity. The rare earth leaching rate in the leachate was 59.22%.

[0047] Example 2

[0048] A bioleaching method for rare earth elements, combining surface functionalization modification and biosurfactant enhancement, includes the following steps:

[0049] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and 0.5 wt.% citric acid solution was added, maintaining a solid-liquid ratio of 50 g / L. The mixture was treated in a 30℃ constant-temperature water bath shaker at 150 rpm for 8 hours. After treatment, the surface-modified slurry was obtained.

[0050] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to a final concentration of 0.2 wt.%, and the slurry was further treated with shaking at 25°C and 150 rpm for 2 hours to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to below 36.3°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0051] Bioleaching with a combined microbial community: 15 vol.% inoculum of *Bacillus subtilis* and 5 vol.% inoculum of *Bacillus megaterium*, preserved in glycerol, were inoculated into LB liquid medium and pre-cultured for 6 hours. The LB liquid medium consisted of 8 g / L tryptone, 3 g / L yeast extract, and 8 g / L NaCl. The culture was carried out at 30°C and 135 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.59. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a 5 vol.% inoculum and leached under the same conditions as the culture for 6 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5–2.5, thus determining the state of the microbial community.

[0052] Leachate recovery and detection: The leachate was obtained by centrifugation at 9000 rpm for 10 min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity. The rare earth leaching rate in the leachate was 59.12%.

[0053] Example 3

[0054] A bioleaching method for rare earth elements, combining surface functionalization modification and biosurfactant enhancement, includes the following steps:

[0055] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and 0.5 wt.% citric acid solution was added, maintaining a solid-liquid ratio of 100 g / L. The mixture was treated in a 40℃ constant-temperature water bath shaker at 150 rpm for 2 hours. After treatment, the surface-modified slurry was obtained.

[0056] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to a final concentration of 0.5 wt.%, and the slurry was further treated with shaking at 25°C and 150 rpm for 0.5 hours to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to below 36.6°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0057] Bioleaching with a combined microbial community: 15 vol.% inoculum of Bacillus subtilis and 5 vol.% inoculum of Bacillus megaterium, preserved in glycerol, were inoculated into LB liquid medium and pre-cultured for 6 hours. The LB liquid medium consisted of 12 g / L tryptone, 7 g / L yeast extract, and 12 g / L NaCl. The culture was carried out at 30°C and 120 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.43. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a 15 vol.% inoculum and leached under the same conditions as the culture for 6 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5–2.5, thus determining the state of the microbial community.

[0058] Leachate recovery and detection: The leachate was obtained by centrifugation at 8000 rpm for 8 min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity. The rare earth leaching rate in the leachate was 58.64%.

[0059] Example 4

[0060] A bioleaching method for rare earth elements, combining surface functionalization modification and biosurfactant enhancement, includes the following steps:

[0061] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and 1.0 wt.% citric acid solution was added, maintaining a solid-liquid ratio of 75 g / L. The mixture was treated in a 40℃ constant-temperature water bath shaker at 100 rpm for 4 hours. After treatment, the surface-modified slurry was obtained.

[0062] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to a final concentration of 0.5 wt.%, and the slurry was further treated with shaking at 30°C and 100 rpm for 1 hour to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to below 37.5°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0063] Bioleaching with a combined microbial community: 10 vol.% inoculum of *Bacillus subtilis* and 10 vol.% inoculum of *Bacillus megaterium*, preserved in glycerol, was inoculated into LB liquid medium and pre-cultured for 10 hours. The LB liquid medium consisted of 10 g / L tryptone, 5 g / L yeast extract, and 10 g / L NaCl. The culture was carried out at 28°C and 150 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.58. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a 10 vol.% inoculum and leached under the same conditions as the culture for 7 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5–2.5, thus determining the state of the microbial community.

[0064] Leachate recovery and detection: The leachate was obtained by centrifugation at 10,000 rpm for 8 min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity. The rare earth leaching rate in the leachate was 57.93%.

[0065] Example 5

[0066] A bioleaching method for rare earth elements, combining surface functionalization modification and biosurfactant enhancement, includes the following steps:

[0067] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and 1.0 wt.% citric acid solution was added, maintaining a solid-liquid ratio of 100 g / L. The mixture was treated in a constant-temperature water bath shaker at 25℃ and 200 rpm for 8 hours. After treatment, the surface-modified slurry was obtained.

[0068] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to a final concentration of 0.5 wt.%, and the slurry was further treated with shaking at 30°C and 100 rpm for 2 hours to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to below 37.6°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0069] Bioleaching with a combined microbial community: 10 vol.% inoculum of Bacillus subtilis and 10 vol.% inoculum of Bacillus megaterium, preserved in glycerol, were inoculated into LB liquid medium and pre-cultured for 10 hours. The LB liquid medium consisted of 8 g / L tryptone, 3 g / L yeast extract, and 8 g / L NaCl. The culture was carried out at 28°C and 120 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.51. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a 5 vol.% inoculum and leached under the same conditions as the culture for 7 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5–2.5, thus determining the state of the microbial community.

[0070] Leachate recovery and detection: The leachate was obtained by centrifugation at 9000 rpm for 8 min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity. The rare earth leaching rate in the leachate was 58.84%.

[0071] Example 6

[0072] A bioleaching method for rare earth elements, combining surface functionalization modification and biosurfactant enhancement, includes the following steps:

[0073] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and 1.0 wt.% citric acid solution was added, maintaining a solid-liquid ratio of 100 g / L. The mixture was treated in a constant-temperature water bath shaker at 25℃ and 200 rpm for 2 hours. After treatment, the surface-modified slurry was obtained.

[0074] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to a final concentration of 0.1 wt.%, and the slurry was further treated with shaking at 30℃ and 100 rpm for 0.5 hours to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to below 37.1°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0075] Bioleaching with a combined microbial community: 10 vol.% inoculum of *Bacillus subtilis* and 10 vol.% inoculum of *Bacillus megaterium*, preserved in glycerol, was inoculated into LB liquid medium and pre-cultured for 10 hours. The LB liquid medium consisted of 12 g / L tryptone, 7 g / L yeast extract, and 12 g / L NaCl. The culture was carried out at 28°C and 120 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.49. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a 15 vol.% inoculum and leached under the same conditions as the culture for 6 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5–2.5, thus determining the state of the microbial community.

[0076] Leachate recovery and detection: The leachate was obtained by centrifugation at 8000 rpm for 5 min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity. The rare earth leaching rate in the leachate was 56.66%.

[0077] Example 7

[0078] A bioleaching method for rare earth elements, combining surface functionalization modification and biosurfactant enhancement, includes the following steps:

[0079] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and 0.1 wt.% citric acid solution was added, maintaining a solid-liquid ratio of 75 g / L. The mixture was treated in a constant-temperature water bath shaker at 25℃ and 200 rpm for 4 hours. After treatment, the surface-modified slurry was obtained.

[0080] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to a final concentration of 0.1 wt.%, and the slurry was further treated with shaking at 20℃ and 200 rpm for 1 hour to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to below 38.8°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0081] Bioleaching with a combined microbial community: 5 vol.% inoculum of *Bacillus subtilis* and 15 vol.% inoculum of *Bacillus megaterium*, preserved in glycerol, were inoculated into LB liquid medium and pre-cultured for 12 hours. The LB liquid medium consisted of 10 g / L tryptone, 5 g / L yeast extract, and 10 g / L NaCl. The culture was carried out at 40°C and 135 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.43. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a 10 vol.% inoculum and leached under the same conditions as the culture for 8 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5–2.5, thus determining the state of the microbial community.

[0082] Leachate recovery and detection: The leachate was obtained by centrifugation at 10,000 rpm for 5 min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity. The rare earth leaching rate in the leachate was 55.83%.

[0083] Example 8

[0084] A bioleaching method for rare earth elements, combining surface functionalization modification and biosurfactant enhancement, includes the following steps:

[0085] Mineral surface functionalization modification: Lean oxide mineral powder from Bayan Obo was placed in an Erlenmeyer flask, and 0.1 wt.% citric acid solution was added, maintaining a solid-liquid ratio of 50 g / L. The mixture was treated in a constant-temperature water bath shaker at 25℃ and 200 rpm for 8 hours. After treatment, the surface-modified slurry was obtained.

[0086] Interface wetting control: Rhamnolipin was added to the surface-modified slurry to a final concentration of 0.1 wt.%, and the slurry was further treated with shaking at 20℃ and 200 rpm for 2 hours to obtain an interface-controlled slurry. The contact angles of the mineral surfaces before and after treatment were measured using a contact angle meter. After rhamnolipin treatment, the contact angle further decreased to below 39.1°, indicating that the mineral surface had become hydrophilic, which is conducive to the penetration of aqueous solutions and the adhesion of microorganisms.

[0087] Bioleaching with a combined microbial community: 5 vol.% inoculum of *Bacillus subtilis* and 15 vol.% inoculum of *Bacillus megaterium*, preserved in glycerol, were inoculated into LB liquid medium and pre-cultured for 12 hours. The LB liquid medium consisted of 8 g / L tryptone, 3 g / L yeast extract, and 8 g / L NaCl. The culture was carried out at 40°C and 150 rpm on a shaker until the logarithmic growth phase, yielding an active bacterial suspension with an OD value of 2.38. This active bacterial suspension was then inoculated into an interface-controlled mineral slurry at a 5 vol.% inoculum and leached under the same conditions as the culture for 8 days with shaking. During leaching, the pH of the leaching system was monitored periodically to ensure it remained stable within the range of 1.5–2.5, thus determining the state of the microbial community.

[0088] Leachate recovery and detection: The leachate was obtained by centrifugation at 9000 rpm for 5 min. The leachate residue was washed to remove residual bacterial metabolic acids. The rare earth leaching rate was calculated to evaluate the leaching effect and selectivity. The rare earth leaching rate in the leachate was 55.68%.

[0089] Comparative Example 1

[0090] A bioleaching method for rare earth elements enhanced with biosurfactants differs from Example 1 in that it does not involve citric acid pretreatment; instead, the mineral powder is directly bioleached after interfacial wetting and regulation with rhamnolipids. Due to the absence of a pre-dissolved iron oxide passivation film on the mineral surface, the rare earth leaching rate is only 40.02%, indicating a low dephosphorization efficiency.

[0091] Comparative Example 2

[0092] A surface-functionalized modification method for enhancing the bioleaching of rare earth elements differs from Example 4 in that it omits rhamnolipid surfactant treatment and directly performs bioleaching after citric acid pretreatment. Due to the lack of interfacial wetting control of the rare earth oxide ore, the rare earth leaching rate is 45.63%.

[0093] Comparative Example 3

[0094] A bioleaching method for rare earths, combining surface functionalization modification and biosurfactant enhancement, differs from Example 1 in that the combined microbial community is replaced by using only Bacillus subtilis for bioleaching, without using Bacillus megaterium. The rare earth leaching rate is 47.33%, indicating that the combined microbial community can form a synergistic effect. Compared with the single microbial community, the combined microbial community significantly improves the rare earth leaching efficiency of the low-grade oxide ore in Bayan Obo.

[0095] In summary, this invention provides a method for the bio-dephosphorization of high-phosphorus hematite based on micro-electric field cascade domestication and nutrient slow-release regulation. It also provides a combined surface functionalization modification and biosurfactant-enhanced bioleaching method for rare earth elements. Through the synergistic effect of a three-tiered enhancement strategy—citric acid surface functionalization modification, rhamnolipin interface wetting regulation, and bioleaching by a combination of Bacillus subtilis and Bacillus megaterium—this method can significantly improve the bioleaching efficiency of rare earth elements in the low-grade oxide ore of Bayan Obo.

Claims

1. A method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement, characterized in that, Includes the following steps: Mineral surface functionalization modification: medium-lean oxide ore is crushed and ground to a predetermined fineness to obtain mineral powder; the mineral powder is mixed with a low-concentration citric acid solution and subjected to agitation treatment to obtain a surface-modified slurry; Interface wetting control: Rhamnolipin biosurfactant was added to the surface-modified slurry, and the mixture was shaken to obtain an interface-controlled slurry. Bioleaching of combined microbial communities: Bacillus subtilis and Bacillus megaterium were activated and cultured separately, inoculated in proportion, and cultured to the logarithmic growth phase to obtain an active bacterial suspension of the combined microbial community; the active bacterial suspension was inoculated into the interface-controlled slurry at an inoculation rate of 5%-15%, and the bioleaching reaction was carried out under the same conditions as the culture of the combined microbial community. Leachate recovery and testing: After leaching, the leaching slurry is subjected to solid-liquid separation, and the supernatant is collected to obtain rare earth leachate; the leaching residue is washed to remove residual bacterial metabolic acid, and the leachate is subjected to rare earth element analysis to calculate the rare earth leaching rate.

2. The method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement according to claim 1, characterized in that, In the functional modification of mineral surfaces, medium-lean oxide ores are crushed and ground until the mineral powder particle size reaches the range of 0.038μm-0.074μm.

3. The method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement according to claim 1, characterized in that, In the functional modification of mineral surfaces: the concentration of low-concentration citric acid solution is 0.1wt.%-1.0wt.%; the solid-liquid ratio of mineral powder to citric acid solution is 50g / L-100g / L.

4. The method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement according to claim 1, characterized in that, In the functional modification of mineral surfaces: the treatment temperature is 25℃-40℃; the vibration treatment time is 2-8 hours, and the rotation speed is 100rpm-200rpm.

5. The method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement according to claim 1, characterized in that, In the interface wetting control: the final concentration of the added rhamnolipin biosurfactant in the slurry is 0.1wt.%-0.5wt.%; the treatment temperature is 20℃-30℃; the shaking treatment time is 0.5-2 hours, and the rotation speed is 100rpm-200rpm.

6. The method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement according to claim 1, characterized in that, In interface wetting control, after treatment with rhamnolipin, the contact angle of the mineral surface was reduced to below 40°.

7. The method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement according to claim 1, characterized in that, In the bioleaching of the combined microbial community, the inoculum amounts of Bacillus subtilis and Bacillus megaterium were both 5 vol.%-15 vol.%, the pre-culture time was 6-12 hours, the OD value of the active bacterial suspension of the combined microbial community was 2.0-3.0, the temperature during the construction and leaching of the combined microbial community was 28℃-40℃, and the shaking speed of the shaker under oscillation was 120 rpm-150 rpm.

8. The method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement according to claim 1, characterized in that, In the combined microbial bioleaching process, the culture medium consisted of 8.0 g / L-12.0 g / L tryptone, 3.0 g / L-7.0 g / L yeast extract, and 8.0 g / L-12.0 g / L NaCl; the leaching time was 6-8 days.

9. The method for bioleaching rare earth elements by combining surface functionalization modification and biosurfactant enhancement according to claim 1, characterized in that, In the leachate recovery and testing, the leachate was obtained by centrifugation at a speed of 8000rpm-10000rpm for 5min-10min; the rare earth leaching rate in the leachate was ≥50.63%.

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