Modified polyurethane filler as well as preparation method and application thereof

Abstract

The invention relates to the technical field of biological hydrometallurgy, and particularly discloses a modified polyurethane filler as well as a preparation method and application thereof. According to the invention, a polyurethane filler is subjected to acid modification by means of chemical etching, organic-inorganic compounding and the like, and is coated with an oxidized alginate-chitosan composition-silicon dioxide composite coating liquid; and a three-section curing method is combined to prepare the modified polyurethane filler with obviously improved specific surface area, hydrophilicity, mechanical strength, stability of a coating layer and other properties. Bioleaching equipment is further provided by taking modified polyurethane as a filler, and is coupled with the performance of the modified filler through precise control of a pulse oxygen supply system and multi-parameter collaboration of equipment integration; the problems that in a traditional packed bed reactor, oxygen supply is uneven, mass transfer efficiency is low, hyphae are prone to being damaged, and packing of the packed bed reactor is prone to being blocked are systematically solved, and a fungus leaching system can stably operate for a long time.

Description

Technical Field

[0001] The invention relates to the technical field of biohydrometallurgy, and specifically discloses a modified polyurethane filler, a preparation method and application thereof. Background Art

[0002] Molybdenum is a rare and strategic metal, primarily found in various minerals as compounds, such as molybdenite (MoS2) and wolfenite (PbMoO4). In recent years, the global molybdenum industry has experienced rapid expansion, and with it, the accumulation of molybdenum tailings has continued to rise, posing an increasingly severe challenge to the ecological environment. Tailings accumulation not only consumes significant land resources but also can cause environmental problems such as soil and water pollution and dust dispersion. Notably, molybdenum tailings are generally rich in valuable metals such as molybdenum, tungsten, and iron, making them a secondary mineral resource with great development potential. Scientific and efficient comprehensive utilization of these elements can not only alleviate resource shortages but also achieve a win-win situation in terms of environmental and economic benefits. Compared with traditional hydrometallurgy and pyrometallurgy, bioleaching technology offers advantages such as zero secondary pollution, low energy consumption, mild reaction conditions, and low construction and operating costs, making it suitable for leaching valuable metals from molybdenum tailings.

[0003] In the field of bioleaching technology, packed-bed reactors using polyurethane fillers as carriers are widely used in valuable metal leaching and bioremediation processes due to their large specific surface area and high chemical stability. Currently, these bioleaching packed-bed reactors primarily use conventional polyurethane as a microbial carrier, loading strains such as Aspergillus niger onto the filler surface. The target metals are leached using the acidic substances and secretions produced by the microbial metabolic activities.

[0004] However, existing technologies still have significant shortcomings. On the one hand, the smooth surface and poor hydrophilicity of conventional polyurethane fillers lead to low microbial attachment efficiency and slow biofilm formation, significantly limiting the effective load of bacteria like Aspergillus niger and reducing the efficiency of bioleaching. On the other hand, polyurethane materials have limited mechanical strength. During long-term leaching, they are susceptible to breakage and deformation due to erosion by microbial metabolites and solution erosion, shortening the filler's service life and increasing operating costs. Furthermore, the mechanical strength of existing fillers needs to be improved, and the limited number of bacterial attachment sites further affects bioleaching effectiveness. Summary of the Invention

[0005] In view of the problems of low microbial attachment efficiency, poor mechanical properties, and inconvenience for fungal fixation in conventional polyurethane fillers in the prior art, the present invention modifies the polyurethane filler to improve its roughness, hydrophilicity, and mechanical strength, thereby increasing the filler's load capacity for Aspergillus niger, enhancing the bioleaching efficiency and filler service life to meet the needs of actual industrial applications. The present invention also applies the modified polyurethane filler prepared above to bioleaching equipment, and further uses it for leaching molybdenum tailings to achieve the recycling of elements such as Mo, W, Al, and Fe. In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing a modified polyurethane filler, the preparation method comprising the following steps: Step 1: immersing the polyurethane filler in an acid solution for acid modification to obtain an acid-modified polyurethane filler; Step 2: coating the composite coating liquid on the surface of the acid-modified polyurethane filler and curing the composite coating liquid to obtain a modified polyurethane filler; Wherein, the composite coating liquid is a mixed dispersion of oxidized alginate, chitosan composition and silicon dioxide; The chitosan composition comprises chitosan and carboxymethyl chitosan.

[0006] This method scientifically and rationally acid-modifies polyurethane fillers through chemical etching and organic-inorganic composite methods, followed by coating with an oxidized alginate-chitosan composition-silica composite coating solution to produce a modified polyurethane filler. Acid modification improves the roughness and hydrophilicity of the polyurethane filler at the microstructural and chemical group levels. The components of the composite coating solution work synergistically in specific mass ratios to further enhance specific surface area, hydrophilicity, and mechanical strength, systematically addressing the performance shortcomings of polyurethane fillers in bioleaching applications.

[0007] In this method, the polyurethane filler is first modified with an acid solution. The corrosive nature of the acid causes hydrolysis of some ester or urea bonds on the filler surface. The resulting microscopic grooves and pores increase the filler's surface roughness, providing physical support for subsequent microbial attachment. Furthermore, the introduction of polar groups, such as hydroxyl and carboxyl groups, significantly improves the filler's hydrophilicity, making it easier for microorganisms to adhere to the filler surface.

[0008] The present invention optimizes the components and amounts of the dip-coating composite coating solution, using an oxidized alginate-chitosan composition-silicon dioxide composite coating solution formulated in a specific mass ratio. The reasons for this design are as follows: (1) In terms of the design of raw material composition: the aldehyde groups on the oxidized alginate molecular chain can react with the amino groups of chitosan to form a Schiff base reaction, achieving covalent cross-linking between the two. At the same time, the hydroxyl groups of chitosan / carboxymethyl chitosan and the silanol groups of silica and the hydroxyl groups on the surface of polyurethane are physically cross-linked through hydrogen bonding, jointly constructing a "chemical-physical dual cross-linking network" to enhance the adhesion between the coating and the substrate, and improve the water resistance and long-term stability of the coating. In addition, the carboxyl groups of the oxidized alginate further enhance the hydrophilicity and have good biocompatibility. Silica is dispersed in the coating liquid and forms protrusions on the filler surface after curing. Together with the structure formed by acid modification, it constructs a hierarchical rough structure, greatly increasing the specific surface area. At the same time, the high hardness and chemical stability of silica enhance the mechanical properties and anti-scouring ability of the coating and inhibit structural damage during biodegradation.

[0009] (2) In terms of the ratio of raw materials, chitosan is mainly used in the chitosan composition to ensure the rigidity of the coating and sufficient cross-linking sites, and carboxymethyl chitosan is used as a supplement to balance the hydrophilicity and water solubility, avoiding the uneven coating caused by the poor water solubility of pure chitosan. At the same time, through the synergistic effect of the hydroxyl and amino groups of the two, a basis is provided for subsequent cross-linking and silica dispersion.

[0010] (3) In terms of the synergistic relationship between each step and raw materials, in terms of specific surface area, the rough structure formed by acid modification and the protrusions constructed by silica synergistically construct a hierarchical rough structure, further increasing the surface complexity and porosity, providing abundant attachment sites for microorganisms. In terms of hydrophilicity, the polar groups introduced by acid modification work together with the hydrophilic groups in the oxidized alginate and chitosan composition to make the filler surface easily wetted by aqueous solution, promoting the exchange of substances between microorganisms and the filler surface. The improvement in mechanical strength depends on the covalent cross-linking network of oxidized alginate and chitosan, the physical reinforcement of silica, and the buffering effect of the chitosan elastic network, which enhances the filler's resistance to scour and wear.

[0011] Preferably, the mass ratio of the oxidized alginate, the chitosan composition and the silicon dioxide is 4-6:20-24:2-4; and the mass ratio of the chitosan and the carboxymethyl chitosan is 8-9:1-2.

[0012] The oxidized alginate, chitosan composition, and silica complement each other in this ratio. A suitably high proportion of chitosan composition ensures the coating's flexibility and biocompatibility; an appropriate amount of oxidized alginate acts as a crosslinking agent, ensuring the formation of a crosslinked network; and silica, at the right ratio, enhances the coating's durability by increasing roughness and strength without compromising its flexibility, allowing it to adapt to the mechanical stresses and chemical environments experienced during leaching.

[0013] Preferably, the acid solution includes at least one of a hydrochloric acid solution or a sulfuric acid solution.

[0014] Preferably, the mass fraction of the acid solution is 5%-8%.

[0015] Preferably, the immersion time is 2 h-4 h and the temperature is 20° C.-30° C., and in the present invention, it is carried out at room temperature.

[0016] Preferably, the oxidized alginate comprises oxidized sodium alginate.

[0017] Preferably, the polyurethane filler has a void density of 10 ppi-30 ppi and a density of 0.22 g / cm 3 -0.5g / cm 3 ; In the present invention, a cubic polyurethane filler with a side length of 1.5 cm-2.5 cm is selected.

[0018] Preferably, the silicon dioxide is hydrophilic nano-scale silicon dioxide.

[0019] In the present invention, a 5%-8% by mass acid solution is used to acid-modify the polyurethane filler for 2-4 hours. This optimized concentration range and time ensure effective etching while avoiding damage to the polyurethane matrix structure caused by excessively high concentrations or prolonged treatment time, which can lead to reduced filler strength or pore collapse, affecting void density and mechanical properties. It also avoids slow reactions or low acid etching levels, resulting in insignificant roughening effects, caused by excessively low concentrations or short treatment times.

[0020] In the present invention, hydrophilic nano-scale silica is dispersed in the coating liquid, and after curing, nano-scale protrusions are formed on the surface of the filler, which together with the micron-scale structure formed by acid modification construct a "micron-nano" hierarchical rough structure, greatly increasing the specific surface area.

[0021] The void density of the polyurethane filler selected in the present invention is 10 ppi-30 ppi. The reason for this is that the void density is selected in consideration of the coating to be performed later. The void density of the coating is appropriate, which is conducive to the easy entry of microorganisms into the filler and provides sufficient space for the growth and metabolic activities of microorganisms, facilitating the exchange of nutrients and metabolic products. The density is selected to be 0.22 g / cm 3 -0.5g / cm 3 Within this range, it has certain strength and stability. After later coating, it can better withstand the mechanical stress in the bioleaching process, such as the scouring and stirring of the solution, and is not easy to break and deform, thereby ensuring the structural integrity and service life of the filler.

[0022] The size of 1.5 cm to 2.5 cm on a side is suitable. It will not lead to insufficient contact area with the molybdenum tailings due to the filler being too large, thereby affecting the leaching effect, nor will it increase the difficulty and cost of filling due to the filler being too small. At the same time, it is conducive to the uniform distribution of the solution among the fillers, thereby improving the uniformity and efficiency of the leaching reaction. In addition, cube fillers of this size are easy to operate and maintain during the bioleaching process, such as being convenient in adding and replacing fillers and cleaning reactors, which is conducive to industrial-scale application and promotion.

[0023] The use of polyurethane fillers of the above specifications can provide good conditions for the bioleaching process, is conducive to the loading and growth of microorganisms, and improves the leaching efficiency of molybdenum tailings. It also has many advantages in actual operation and engineering applications.

[0024] Preferably, the preparation method of the composite coating liquid comprises the following steps: preparing a chitosan composition solution according to a mass ratio of chitosan composition to water of 1:12 to 1:16, adding oxidized alginate and dissolving it, adding silicon dioxide and dispersing it evenly to obtain an oxidized alginate-chitosan composition-silicon dioxide composite coating liquid.

[0025] Preferably, the preparation method of oxidized alginate comprises the following steps: mixing a potassium periodate solution with an alginate solution, reacting at 34°C to 38°C for 4h to 7h under light-proof conditions to obtain an oxidized alginate solution, dialyzing, and freeze-drying to obtain oxidized alginate; wherein the mass ratio of alginate to potassium periodate is 1:0.65-0.75.

[0026] In the present invention, the degree of alginate oxidation significantly impacts the properties of the composite coating solution, the properties of the modified polyurethane filler, and the subsequent microbial loading and growth. Precisely controlling the degree of oxidation is a key factor in preparing high-performance modified polyurethane fillers. The degree of oxidation alters the molecular structure and properties of the alginate. Moderately oxidized alginate interacts better with the chitosan composition and silica, forming a uniform, continuous composite coating on the polyurethane filler surface with excellent performance, high stability, and suitable mechanical strength.

[0027] Preferably, the dipping temperature is 30° C.-35° C., and the dipping time is 20 min-30 min.

[0028] Preferably, the curing is a three-stage curing method, which includes an initial curing stage, an intermediate curing stage and a final curing stage; The temperature of the initial curing stage is 20°C-30°C, the humidity is 50%-60%, and the time is 1 h-2 h; the temperature of the intermediate curing stage is 31°C-35°C, the humidity is 40%-50%, and the time is 2 h-4 h; the temperature of the final curing stage is 40°C-50°C, the humidity is 30%-40%, and the time is 3 h-4 h.

[0029] The initial curing stage is the structural formation phase. During this stage, the oxidized alginate and chitosan composition undergo initial crosslinking, forming a preliminary structure. The silica particles are evenly dispersed during this stage, enhancing the filler's mechanical strength. Maintaining a humidity of 50%-60% during this stage prevents the chitosan composition from dehydrating too quickly and causing cracking. High temperatures should also be avoided, preventing premature curing of the alginate and affecting subsequent crosslinking reactions.

[0030] The intermediate curing stage is the crosslinking and strengthening phase, which accelerates the moisture-curing reaction of the polyurethane filler and increases the crosslink density. Simultaneously, the chitosan composition further shrinks, forming a stable network structure with the silica. During this stage, it is important to control the heating rate to 2°C / min-4°C / min to prevent sudden temperature rises that could cause cracking in the coating. At the same time, ventilation should be maintained to promote moisture diffusion and accelerate curing.

[0031] The final curing stage is the complete curing phase, ensuring the polyurethane filler is fully cured and achieves optimal mechanical properties. During this stage, the synergistic effect of the silica and chitosan combination further enhances mechanical strength. After curing, the filler is allowed to cool naturally to room temperature to avoid stress cracking caused by temperature fluctuations.

[0032] The three-stage curing method provided by the present invention can take into account the characteristics of each component, achieve coordinated curing through temperature gradient, humidity gradient and time control, and is beneficial to the stability of the coating layer.

[0033] In a second aspect, the present invention provides a modified polyurethane filler prepared by the preparation method of the modified polyurethane filler provided in the first aspect.

[0034] In a third aspect, the present invention also provides the use of the modified polyurethane filler in a bioleaching device.

[0035] Given that the modified polyurethane filler provided by the present invention has a large specific surface area and significantly improved hydrophilicity and mechanical strength, when applied to bioleaching equipment, the increased specific surface area provides more attachment sites for microorganisms, enhancing hydrophilicity and promoting microbial adsorption, creating favorable conditions for microbial loading and growth. The complex roughness structure allows microorganisms to better anchor to the filler surface, preventing them from being washed away by the solution. The excellent hydrophilicity facilitates the exchange of substances between microbial cells and the filler surface, thereby forming an efficient bioleaching system and improving the leaching efficiency of the target metal.

[0036] In a fourth aspect, the present invention further provides a bioleaching device comprising a packed bed reactor 1, a pressure relief valve 2, a thermal insulation jacket 3, two screens 4, a dissolved oxygen monitor 5, a pH monitor 6, an oxygen cylinder 7, a bacteria filter 8, an electromagnetic pulse valve 9, a pulse controller 10, a reactor discharge pipe 11, a temperature-controlled water tank 12, a flow pump 13, and a liquid storage tank 14; The two screens 4 are respectively arranged at the top and bottom of the packed bed reactor 1; In which, the liquid storage tank body 14 is connected to the packed bed reactor 1 through the flow pump 13, the pressure relief valve 2 is arranged at the top of the packed bed reactor 1 and is connected to its internal space, the insulation jacket 3 is arranged on the outer wall of the packed bed reactor 1, the reactor discharge pipe 11 is connected to the bottom of the packed bed reactor 1, the probe of the dissolved oxygen monitor 5 and the probe of the pH monitor 6 are both extended between the bottom screen 4 and the reactor discharge pipe 11, the electromagnetic pulse valve 9 and the pulse controller 10 are arranged between the bacteria filter 8 and the packed bed reactor 1; the oxygen cylinder 7 is connected to the packed bed reactor 1 through the bacteria filter 8; the temperature control water tank 12 is respectively connected to the top and bottom of the insulation jacket 3.

[0037] Wherein, the packed bed reactor 1 is filled with the modified polyurethane filler.

[0038] In addition, the molybdenum tailings are sieved through a 50-80 mesh sieve.

[0039] In the present invention, the top of the packed bed reactor 1 refers to the top wall of the packed bed reactor 1 and the spatial range of a preset distance near the top wall; the bottom of the packed bed reactor 1 refers to the lower wall of the packed bed reactor 1 and the spatial range of a preset distance near the lower wall.

[0040] This bioleaching equipment systematically solves problems such as uneven oxygen supply, low mass transfer efficiency, easy damage to mycelium, and easy clogging of packed bed reactor packing in traditional packed bed reactors through precise control of the pulse oxygen supply system, multi-parameter coordination of equipment integration, and performance coupling with modified fillers. It has four core advantages: high efficiency, energy saving, stability and environmental protection.

[0041] The bioleaching equipment provided by the present invention uses an oxygen cylinder 7, an electromagnetic pulse valve 9, and a pulse controller 10 to provide dissolved oxygen to the mycelial cells in the packed bed reactor 1 while simultaneously generating a pulsed airflow. The shear force of the pulsed airflow alters the mycelial surface morphology while simultaneously flushing the cells on the packing surface, achieving the dual goals of oxygenating the cells and unclogging the bed, enabling the long-term, stable operation of the fungal leaching system.

[0042] Even if the bed is blocked due to the formation of mycelium aggregates and the adsorption of molybdenum tailings particles after long-term operation, the gaps in the bed fillers can be cleared by increasing the gas and water flow rate to make the fillers form a fluidized state.

[0043] In a fifth aspect, the present invention further provides a method for fungal leaching of molybdenum tailings, which uses the above-mentioned bioleaching equipment for leaching, and specifically comprises the following steps: S1. The Aspergillus niger hyphae and the modified polyurethane filler were solidified and cultured in a fungal liquid culture medium to obtain a modified polyurethane filler loaded with Aspergillus niger; S2. The modified polyurethane filler loaded with Aspergillus niger is added to the packed bed reactor of the bioleaching device 1 between the two screens 4; S3. After the fungal liquid culture medium is mixed with the molybdenum tailings, it is placed in the reservoir 14 to obtain a molybdenum tailings slurry; S4. The molybdenum tailings slurry is pumped into the packed bed reactor 1 through the flow pump 13, and the molybdenum tailings are subjected to fungal leaching to obtain a leachate.

[0044] Preferably, the fungal liquid culture medium comprises a sucrose liquid culture medium. The specific composition of the sucrose liquid culture medium is as follows: per liter, 100 g sucrose, 0.5 g KNO3, 0.5 g KH2PO4, 2.0 g yeast extract, 2.0 g peptone, and the balance is water.

[0045] Aspergillus niger can be purchased or isolated and cultured by oneself. The Aspergillus niger used in the present invention was purchased from Beina Biotechnology, and the strain number is BNCC352250.

[0046] Preferably, the curing culture temperature is 30° C. to 34° C., the rotation speed is 100 rpm to 150 rpm, and the time is 30 h to 42 h.

[0047] Preferably, the total stacking area of ​​the modified polyurethane filler loaded with Aspergillus niger is 70%-80% of the effective volume of the packed bed reactor 1.

[0048] Preferably, during the fungal leaching, the molybdenum tailings slurry flow rate is 1.2 L / h-1.8 L / h, the electromagnetic pulse frequency is 0.4 Hz-0.6 Hz, the dissolved oxygen is 3.5 mg / L-6.0 mg / L, the temperature is 33°C-37°C, the leachate pH is 2.2-2.6, and the leaching time is 54 h-60 h.

[0049] The fungal leaching method for molybdenum tailings provided by the present invention systematically solves the problems of low microbial attachment efficiency, high mass transfer resistance, extensive metabolic regulation, and low mechanical strength of fillers in traditional fungal leaching through multiple synergies, such as modified fillers to enhance microbial load, precise equipment control of environmental parameters, and matching process parameters to metabolic needs. Compared with free mycelial pellet leaching reactors and fixed biofilm leaching reactors, this method has the advantages of less damage to mycelial cells, less clogging of the bed, good mass transfer performance, higher bioleaching efficiency, and lower operating costs. This solution provides an efficient, stable, and intelligent engineering solution for large-scale biotreatment of difficult-to-treat minerals such as molybdenum tailings, and has significant economic value and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 Schematic diagram of the bioleaching equipment in Example 4 of the present invention, including: 1. packed bed reactor 1, 2. pressure relief valve, 3. insulation jacket, 4. screen, 5. dissolved oxygen monitor, 6. pH monitor, 7. oxygen cylinder, 8. bacteria filter, 9. electromagnetic pulse valve, 10. pulse controller, 11. reactor discharge pipe, 12. temperature-controlled water tank, 13. flow pump, and 14. liquid storage tank. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0053] The polyurethane filler used in the present invention was purchased from Jiangsu Shuijingling Environmental Protection New Materials Co., Ltd. The carboxylation degree of the carboxymethyl chitosan used in the present invention is ≥80%, and the chitosan is a medium viscosity chitosan, both of which were purchased from Shanghai Yuanye Biotechnology Co., Ltd. The hydrophilic nano-silica in the embodiment of the present invention was purchased from Shanghai Yuanjiang Chemical Co., Ltd. with the product number of YJ958 and an average particle size of 50 nm.

[0054] Example 1 An embodiment of the present invention provides a method for preparing a modified polyurethane filler, the method comprising the following steps: Step 1: Preparation of acid-modified polyurethane filler First, soak the polyurethane filler in anhydrous ethanol for 15 minutes to remove the surface release agent or contaminants, and then dry it in a 40°C oven for 2 hours to ensure that the surface is clean and dry, thereby obtaining the pretreated polyurethane filler; The pretreated polyurethane filler was completely immersed in a 7% sulfuric acid solution for 3 hours to perform acid modification. After the acid modification, it was neutralized with a 5% sodium bicarbonate solution for 5 minutes, and then repeatedly rinsed with deionized water until neutral and dried in a 50°C oven for 2 hours to obtain an acid-modified polyurethane filler. Among them, the polyurethane filler has a void density of 30ppi, a density of 0.5 g / cm3, and a side length of 2cm.

[0055] Step 2: Preparation of modified polyurethane filler (1) Immerse the acid-modified polyurethane filler in a 5% NaOH solution and oscillate at room temperature for 30 min to convert the residual carboxyl groups (-COOH) on the surface into more active hydroxyl groups (-OH) and further remove surface impurities. Rinse with deionized water until neutral and dry at 50 °C for 2 h to obtain the secondary activated polyurethane filler for later use. (2) Take 125 g of sodium alginate, add it to 625 mL of ethanol, and stir thoroughly to obtain a sodium alginate-ethanol dispersion; 750 mL of a 0.5 mol / L potassium periodate solution prepared in the dark was slowly added to the sodium alginate-ethanol dispersion. The mixture was reacted at 36°C for 4 h in the dark. Ethylene glycol was then added to terminate the reaction for 15 min. The resulting reaction solution was placed in a dialysis bag and dialyzed with deionized water for three days, with the water changed four times a day. After dialysis, the solution was poured into a watch glass and pre-frozen in a -18°C refrigerator for 12 h. The pre-frozen sample was freeze-dried to obtain white oxidized sodium alginate.

[0056] The molecular weight of the sodium alginate selected in the present invention is 5 million Da to 6 million Da, and the dialysis bag is MD77-3500D.

[0057] (3) Take 400 g of chitosan and 100 g of carboxymethyl chitosan, add them to 7.5 L of deionized water, heat and stir in a 50 ° C water bath, and after complete dissolution, reduce the temperature to 37 ° C and add 125 g of oxidized sodium alginate. After stirring evenly, add 75 g of hydrophilic nano-silica and continue stirring until the silica is evenly dispersed to obtain an oxidized alginate-chitosan composition-silica composite coating liquid; (4) Immerse the secondary activated polyurethane filler completely in the above-mentioned oxidized alginate-chitosan composition-silica composite coating liquid, shake it at room temperature for 20 minutes to ensure that the pores and surface are evenly adsorbed with the coating liquid, remove the filler, and drain it until no liquid drops are left, thereby obtaining the dipped filler; The dipped filler is placed in a temperature-controlled curing box for three-stage curing. After the curing is completed, a modified polyurethane filler is obtained, which is recorded as modified polyurethane filler I.

[0058] The three-stage curing conditions are as follows: the initial curing stage is at a temperature of 25°C, a humidity of 55%, and a time of 1.5 h; the intermediate curing stage is at a temperature of 34°C, a humidity of 45%, and a time of 3 h; and the final curing stage is at a temperature of 45°C, a humidity of 35%, and a time of 3.5 h.

[0059] Example 2 An embodiment of the present invention provides a method for preparing a modified polyurethane filler, the method comprising the following steps: Step 1: Preparation of acid-modified polyurethane filler First, soak the polyurethane filler in anhydrous ethanol for 15 minutes to remove the surface release agent or contaminants, and then dry it in a 40°C oven for 2 hours to ensure that the surface is clean and dry, thereby obtaining the pretreated polyurethane filler; The pretreated polyurethane filler was completely immersed in a 5% sulfuric acid solution for 4 hours for acid modification. After the acid modification, it was neutralized with a 5% sodium bicarbonate solution for 5 minutes, and then repeatedly rinsed with deionized water until neutral and dried in a 50°C oven for 2 hours to obtain an acid-modified polyurethane filler. Among them, the void density of polyurethane filler is 10ppi and the density is 0.22 g / cm 3 , side length is 2cm.

[0060] Step 2: Preparation of modified polyurethane filler (1) Immerse the acid-modified polyurethane filler in a 5% NaOH solution at room temperature for 30 min with shaking, then rinse with deionized water until neutral, and dry at 50 °C for 2 h to obtain the secondary activated polyurethane filler for later use; (2) Take 100 g of sodium alginate, add it to 500 mL of ethanol, and stir thoroughly to obtain a sodium alginate-ethanol dispersion; 650 mL of a 0.5 mol / L potassium periodate solution prepared in the dark was slowly added to the sodium alginate-ethanol dispersion. The mixture was reacted at 38°C in the dark for 5 h. Ethylene glycol was added to terminate the reaction for 15 min. The resulting reaction solution was placed in a dialysis bag and dialyzed with deionized water for three days, with the water changed four times a day. After dialysis, the solution was poured into a watch glass and pre-frozen in a -18°C refrigerator for 12 h. The pre-frozen sample was freeze-dried to obtain white oxidized sodium alginate.

[0061] The molecular weight of the sodium alginate selected in the present invention is 5 million Da to 6 million Da, and the dialysis bag is MD77-3500D.

[0062] (3) Take 450 g of chitosan and 50 g of carboxymethyl chitosan, add them to 6 L of deionized water, heat and stir in a 50°C water bath, and after complete dissolution, reduce the temperature to 37°C and add 100 g of oxidized sodium alginate. After stirring evenly, add 50 g of hydrophilic nano-silica and continue stirring until the silica is evenly dispersed to obtain an oxidized alginate-chitosan composition-silica composite coating liquid; (4) Immerse the secondary activated polyurethane filler completely in the above-mentioned oxidized alginate-chitosan composition-silica composite coating liquid, shake it at room temperature for 20 minutes to ensure that the pores and surface are evenly adsorbed with the coating liquid, remove the filler, and drain it until no liquid drops are left, thereby obtaining the dipped filler; The dipped filler is placed in a temperature-controlled curing box for three-stage curing. After the curing is completed, a modified polyurethane filler is obtained, which is recorded as modified polyurethane filler II.

[0063] The three-stage curing conditions are as follows: the initial curing stage is at a temperature of 20°C, a humidity of 60%, and a time of 2 hours; the intermediate curing stage is at a temperature of 31°C, a humidity of 50%, and a time of 4 hours; and the final curing stage is at a temperature of 40°C, a humidity of 30%, and a time of 4 hours.

[0064] Example 3 An embodiment of the present invention provides a method for preparing a modified polyurethane filler, the method comprising the following steps: Step 1: Preparation of acid-modified polyurethane filler First, soak the polyurethane filler in anhydrous ethanol for 15 minutes to remove the surface release agent or contaminants, and then dry it in a 40°C oven for 2 hours to ensure that the surface is clean and dry, thereby obtaining the pretreated polyurethane filler; The pretreated polyurethane filler was completely immersed in a hydrochloric acid solution with a mass fraction of 8% for 2 hours to perform acid modification. After the acid modification, it was neutralized with a 5% sodium bicarbonate solution for 5 minutes, and then repeatedly rinsed with deionized water until neutral and dried in a 50°C oven for 2 hours to obtain an acid-modified polyurethane filler. Among them, the void density of polyurethane filler is 30 ppi and the density is 0.5 g / cm 3 , side length is 2cm.

[0065] Step 2: Preparation of modified polyurethane filler (1) Immerse the acid-modified polyurethane filler in a 5% NaOH solution at room temperature for 30 min with shaking, then rinse with deionized water until neutral, and dry at 50 °C for 2 h to obtain the secondary activated polyurethane filler for later use; (2) Take 125 g of sodium alginate, add it to 700 mL of ethanol, and stir thoroughly to obtain a sodium alginate-ethanol dispersion; 710 mL of a 0.5 mol / L potassium periodate solution prepared in the dark was slowly added to the sodium alginate-ethanol dispersion. The mixture was reacted at 34°C in the dark for 7 h. Ethylene glycol was then added to terminate the reaction for 15 min. The resulting reaction solution was placed in a dialysis bag and dialyzed with deionized water for three days, with the water changed four times a day. After dialysis, the solution was poured into a watch glass and pre-frozen in a -18°C refrigerator for 12 h. The pre-frozen sample was freeze-dried to obtain white oxidized sodium alginate.

[0066] The molecular weight of the sodium alginate selected in the present invention is 5 million Da to 6 million Da, and the dialysis bag is MD77-3500D.

[0067] (3) Take 400 g of chitosan and 100 g of carboxymethyl chitosan, add them to 8 L of deionized water, heat and stir in a water bath at 50 °C, and after complete dissolution, reduce the temperature to 37 °C and add 125 g of oxidized sodium alginate. After stirring evenly, add 83 g of hydrophilic nano-silica and continue stirring until the silica is evenly dispersed to obtain an oxidized alginate-chitosan composition-silica composite coating liquid; (4) Immerse the secondary activated polyurethane filler completely in the above-mentioned oxidized alginate-chitosan composition-silica composite coating liquid, shake it at room temperature for 20 minutes to ensure that the pores and surface are evenly adsorbed with the coating liquid, remove the filler, and drain it until no liquid drops are left, thereby obtaining the dipped filler; The dipped filler is placed in a temperature-controlled curing box for three-stage curing. After the curing is completed, a modified polyurethane filler is obtained, which is recorded as modified polyurethane filler III.

[0068] The three-stage curing conditions are as follows: the initial curing stage is at a temperature of 30°C, a humidity of 40%, and a time of 1 hour; the intermediate curing stage is at a temperature of 35°C, a humidity of 40%, and a time of 2 hours; and the final curing stage is at a temperature of 50°C, a humidity of 40%, and a time of 3 hours.

[0069] Example 4 The embodiment of the present invention provides a bioleaching device, the schematic diagram of which is shown as follows: Figure 1 As shown, the bioleaching equipment includes: a packed bed reactor 1, a pressure relief valve 2, an insulation jacket 3, two screens 4, a dissolved oxygen monitor 5, a pH monitor 6, an oxygen cylinder 7, a bacteria filter 8, an electromagnetic pulse valve 9, a pulse controller 10, a reactor discharge pipe 11, a temperature-controlled water tank 12, a flow pump 13 and a liquid storage tank 14.

[0070] The two screens 4 are respectively arranged at the top and bottom of the packed bed reactor 1 In which, the liquid storage tank body 14 is connected to the packed bed reactor 1 through the flow pump 13, the pressure relief valve 2 is arranged at the top of the packed bed reactor 1 and is connected to its internal space, the insulation jacket 3 is arranged on the outer wall of the packed bed reactor 1, the reactor discharge pipe 11 is connected to the bottom of the packed bed reactor 1, the probe of the dissolved oxygen monitor 5 and the probe of the pH monitor 6 are both extended between the bottom screen 4 and the reactor discharge pipe 11, the electromagnetic pulse valve 9 and the pulse controller 10 are arranged between the bacteria filter 8 and the packed bed reactor 1; the oxygen cylinder 7 is connected to the packed bed reactor 1 through the bacteria filter 8; the temperature control water tank 12 is respectively connected to the top and bottom of the insulation jacket 3.

[0071] The packed bed reactor is filled with the modified polyurethane filler provided in any one of Examples 1 to 3. The total volume of the filler added does not exceed 80% of the effective volume between the upper and lower screens, thereby reserving fluidized space for backwashing the filler.

[0072] The packed bed reactor 1 has a cylindrical body and a conical bottom, connecting the pulse airflow pipeline, the liquid storage tank pipeline, and the reactor discharge pipe. A pressure relief valve 2 and a reactor discharge pipe 11 are installed on the top of the packed bed reactor 1. The reactor discharge pipe 11 is used to discharge the leachate. A dissolved oxygen monitor 5 and a pH monitor 6 are installed in the leachate discharge pipe. A branch of the leachate discharge pipe is provided with a reflux pipe connected to the bottom of the packed bed reactor 1. The reactor is wrapped with an insulation jacket 3 that controls the system temperature. The water inlet and outlet pipes of the insulation jacket 3 are connected to a temperature-controlled water tank 12.

[0073] A fungal culture medium containing a certain concentration of molybdenum tailings is pumped into the bottom of the packed-bed reactor 1 via flow pump 13 from a reservoir 14. The molybdenum tailings must be of a particle size of at least 10 mesh before being added to the reservoir 14. The concentration of molybdenum tailings added to the reservoir 14 must not exceed a concentration that significantly inhibits the normal metabolism of the acid-producing fungal cells within the packing. Mycelial cells on and within the packing utilize the fungal culture medium for growth, reproduction, and acid production. Valuable metal elements in the molybdenum tailings are leached through acidolysis and chelation with organic acids, as well as the microenvironmental dissolution effect at the cell-mineral interface when the cells come into direct contact with the molybdenum tailings, forming a leachate rich in valuable metal ions.

[0074] Oxygen cylinder 7 provides dissolved oxygen for the mycelial cells in packed-bed reactor 1, which require metabolic processes. A bacteria filter 8 is installed in the oxygen pipeline to prevent contaminants from entering the reactor. The oxygen pipeline is also equipped with an electromagnetic pulse valve 9 and a pulse controller 10 (to control the pulse interval), which deliver high-pressure oxygen into the packed-bed reactor in the form of pulsed airflow. This pulsed airflow increases local turbulence intensity and corresponding fluid shear forces, thereby altering the mycelial morphology and flushing the mycelial cells and adsorbed molybdenum tailings particles from the packing surface. This effectively limits mycelial extension, controls excessive mycelial growth, promptly removes aging cells, prevents excessive adsorption of molybdenum tailings particles, and clears interstitial spaces in the packing, thereby preventing blockage in the packed-bed reactor.

[0075] Example 5 Based on the bioleaching equipment provided in Example 4 of the present invention, a method for fungal leaching of molybdenum tailings is provided. In this embodiment, a packed bed reactor is filled with the modified polyurethane filler I prepared in Example 1, and the method specifically includes the following steps: S1. Inoculate spores of Aspergillus niger (strain number BNCC352250) into sterilized liquid sucrose culture medium and culture at 32°C and 120 rpm for 3 days to form mycelial pellets. Place a motor-driven three-blade stirring paddle in the culture medium containing mycelial pellets and stir at 2000 rpm for 10 min. Cut the mycelial pellets into fragments, with a length of ≤1 mm.

[0076] The modified polyurethane filler I was sterilized by radiation sterilization and then placed in a liquid sucrose culture medium containing mycelial fragments. The modified polyurethane filler I and the liquid sucrose culture medium were mixed in a volume ratio of 2:1 and cultured at 32°C and 120 rpm for 36 hours to allow the mycelial cells to be immobilized inside and on the surface of the modified polyurethane filler I, thereby obtaining the modified polyurethane filler I loaded with Aspergillus niger. S2. Add modified polyurethane filler I loaded with Aspergillus niger, with a total bulk volume of 6.8 L, between two screens 4, each with a 4-mesh void density, in a packed-bed reactor 1 of a biofiltration apparatus. The fungus leaching packed-bed reactor 1 has a diameter of 10 cm, a height of 140 cm, and an effective volume of 9.0 L. S3. The sterilized sucrose liquid medium was added to the reservoir body 14, and the sterilized molybdenum tailings were passed through a 50-mesh sieve and added to the reservoir body 14, the molybdenum tailings particles were slurried in the sucrose liquid medium at a concentration of 2% molybdenum tailings slurry; In step S4, the molybdenum tailings slurry is introduced into the packed bed reactor 1 via flow pump 13, where it comes into contact with the Aspergillus niger on the surface and within the modified polyurethane filler I. The modified polyurethane filler I creates favorable conditions for microbial loading and growth. Aspergillus niger utilizes the sucrose liquid medium for growth and acid production. Simultaneously, through acidolysis and complexation with organic acids, and through the microenvironmental dissolution effects at the cell-mineral interface when the cells come into direct contact with the molybdenum tailings particles, the Aspergillus niger leaches valuable metal elements from the molybdenum tailings, forming a leachate containing metal ions.

[0077] Dissolved oxygen was supplied to the mycelial cells in the packed-bed reactor 1 through an oxygen cylinder 7, an electromagnetic pulse valve 9, and a pulse controller 10, while simultaneously generating a pulsed airflow. The operating parameters of the fungus leaching packed-bed reactor were: a flow rate of 1.5 L / h through the inlet pipe connected to the flow pump 13, a gas flow rate of 0.4 vvm, a pulse frequency of 0.5 Hz, a dissolved oxygen content of 4.0 mg / L in the leachate, and a temperature of 35°C. After 60 hours of leaching, the leachate pH was measured to be 2.3. The reactor discharge pipe 11 was opened to allow the molybdenum tailings leachate to flow out at a flow rate of 1.5 L / h. The average leaching rates of Mo, W, Al, and Fe in the molybdenum tailings leachate were determined to be 75.9%, 90.2%, 68.4%, and 54.9%, respectively.

[0078] Even if the bed becomes clogged after long-term operation due to the formation of mycelial aggregates and the adsorption of molybdenum tailings particles, increasing the air and water flow rate can fluidize the packing and clear the gaps between the packing in the bed. The leached packed bed reactor operated for 30 days without any packing blockage, and the coating maintained good integrity throughout the 30-day period.

[0079] Example 6 Based on the bioleaching equipment provided in Example 4 of the present invention, a method for fungal leaching of molybdenum tailings is provided. In this embodiment, a packed bed reactor is filled with the modified polyurethane filler II prepared in Example 2, and the method specifically includes the following steps: S1. Inoculate spores of Aspergillus niger (strain number BNCC352250) into sterilized liquid sucrose culture medium and culture at 32°C and 120 rpm for 3 days to form mycelial pellets. Place a motor-driven three-blade stirring paddle in the culture medium containing mycelial pellets and stir at 2000 rpm for 10 min. Cut the mycelial pellets into fragments, with a length of ≤1 mm.

[0080] The modified polyurethane filler I was sterilized by radiation sterilization and then placed in a liquid sucrose culture medium containing mycelial fragments. The volume ratio of the modified polyurethane filler I to the liquid sucrose culture medium was 2:1, and the culture was carried out at 32°C and 120 rpm for 36 hours to allow the mycelial cells to be immobilized inside and on the surface of the modified polyurethane filler I, thereby obtaining a modified polyurethane filler II loaded with Aspergillus niger. S2. Add modified polyurethane filler I loaded with Aspergillus niger, with a total bulk volume of 7.2 L, between two screens 4, each with a 4-mesh void density, in a packed-bed reactor 1 of a bioleaching apparatus. The fungus leaching packed-bed reactor 1 has a diameter of 10 cm, a height of 140 cm, and an effective volume of 9.0 L. S3. The sterilized sucrose liquid medium was added to the reservoir body 14, and the sterilized molybdenum tailings were passed through a 50-mesh sieve and added to the reservoir body 14, the molybdenum tailings particles were slurried in the sucrose liquid medium at a concentration of 2% molybdenum tailings slurry; In step S4, the molybdenum tailings slurry is introduced into the packed bed reactor 1 via flow pump 13, where it comes into contact with the Aspergillus niger on the surface and within the modified polyurethane filler I. The modified polyurethane filler I creates favorable conditions for microbial loading and growth. Aspergillus niger utilizes the sucrose liquid medium for growth and acid production. Simultaneously, through acidolysis and complexation with organic acids, and through the microenvironmental dissolution effects at the cell-mineral interface when the cells come into direct contact with the molybdenum tailings particles, the Aspergillus niger leaches valuable metal elements from the molybdenum tailings, forming a leachate containing metal ions.

[0081] The operating parameters of the fungal leaching packed bed reactor were: a flow rate of 1.7 L / h through the inlet pipe connected to flow pump 13, a gas flow rate of 0.6 vvm, a pulse frequency of 0.6 Hz, a dissolved oxygen content of 5.0 mg / L in the leachate, and a temperature of 36°C. After 64 hours of leaching, the leachate pH was measured to be 2.2. The reactor discharge pipe 11 was opened to allow the molybdenum tailings leachate to flow out at a flow rate of 1.7 L / h. The average leaching rates of Mo, W, Al, and Fe in the molybdenum tailings leachate were determined to be 76.4%, 89.6%, 65.6%, and 52.3%, respectively.

[0082] No packing blockage occurred during the 30-day operation of the leached packed bed reactor, and the coating integrity was good during the 30-day period.

[0083] Comparative Example 1 This comparative example provides a method for fungal leaching of molybdenum tailings, based on the bioleaching equipment provided in Example 4. This method is essentially the same as that in Example 5, differing only in that the packed-bed reactor 1 is filled with unmodified polyurethane filler, the type, void density, density, and side length of which are identical to those in Example 1. The operating parameters of the fungal leaching packed-bed reactor are essentially the same as those in Example 5, differing only in that the leachate pH was measured to be 2.2 after 68 hours of leaching; all other parameters remain the same. The average leaching rates of Mo, W, Al, and Fe in the molybdenum tailings leachate were determined to be 63.3%, 82.6%, 57.0%, and 46.5%, respectively.

[0084] Comparative Example 2 This comparative example provides a method for fungal leaching of molybdenum tailings based on the bioleaching equipment provided in Example 4. The method for fungal leaching of molybdenum tailings is basically the same as that in Example 5, except that the type of modified polyurethane filler filled in the packed bed reactor 1 is different, and the void density, density and side length of the polyurethane filler are the same as those in Example 1.

[0085] Among them, the preparation method of the modified polyurethane filler in this comparative example is basically the same as that in Example 1, except that the "chitosan composition" is replaced by an equal amount of "gelatin", and the "oxidized alginate-chitosan composition-silicon dioxide composite coating liquid" is further replaced by "oxidized alginate-gelatin-silicon dioxide composite coating liquid", and the other parameters are not changed.

[0086] However, it was found that the coating began to peel off significantly after about 15 days of use. The reason may be that the acidic conditions accelerated the hydrolysis of gelatin, destroyed the coating skeleton, and caused the cross-linked structure of the coating to disintegrate.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a modified polyurethane filler, characterized in that: The preparation method comprises the following steps: Step 1: immersing the polyurethane filler in an acid solution for acid modification to obtain an acid-modified polyurethane filler; Step 2: coating the composite coating liquid on the surface of the acid-modified polyurethane filler and curing the composite coating liquid to obtain a modified polyurethane filler; Wherein, the composite coating liquid is a mixed dispersion of oxidized alginate, chitosan composition and silicon dioxide; The chitosan composition comprises chitosan and carboxymethyl chitosan.

2. The method for preparing the modified polyurethane filler according to claim 1, wherein: The acid solution comprises at least one of a hydrochloric acid solution or a sulfuric acid solution; and / or The mass fraction of the acid solution is 5%-8%; and / or The immersion time is 2 h-4 h and the temperature is 20° C.-30° C.; and / or The oxidized alginate comprises oxidized sodium alginate; and / or The polyurethane filler has a void density of 10 ppi-30 ppi and a density of 0.22 g / cm 3 -0.5 g / cm 3 and / or The silicon dioxide is hydrophilic nano-scale silicon dioxide.

3. The method for preparing the modified polyurethane filler according to claim 1, wherein: The preparation method of the composite coating liquid comprises the following steps: dissolving a chitosan composition in water to obtain a chitosan composition solution, adding oxidized alginate and silicon dioxide to the chitosan composition solution, and dispersing them uniformly to obtain an oxidized alginate-chitosan composition-silicon dioxide composite coating liquid; and / or The preparation method of oxidized alginate comprises the following steps: mixing a potassium periodate solution with an alginate solution, reacting the mixture at 34° C. to 38° C. for 4 to 7 hours in a dark environment to obtain oxidized alginate; Wherein, the mass ratio of alginate to potassium periodate is 1:0.65-0.

75.

4. The method for preparing the modified polyurethane filler according to claim 1, wherein: The curing is a three-stage curing method, which includes an initial curing stage, an intermediate curing stage and a final curing stage; The temperature of the initial curing stage is 20°C-30°C, the humidity is 50%-60%, and the time is 1 h-2 h; the temperature of the intermediate curing stage is 31°C-35°C, the humidity is 40%-50%, and the time is 2 h-4 h; the temperature of the final curing stage is 40°C-50°C, the humidity is 30%-40%, and the time is 3 h-4 h.

5. A modified polyurethane filler, characterized in that: The modified polyurethane filler is prepared by the preparation method of any one of claims 1 to 4.

6. Use of the modified polyurethane filler according to claim 5 in bioleaching equipment.

7. A bioleaching device, characterized in that: It includes a packed bed reactor (1), a pressure relief valve (2), a heat-insulating jacket (3), two screens (4), a dissolved oxygen monitor (5), a pH monitor (6), an oxygen cylinder (7), a bacteria filter (8), an electromagnetic pulse valve (9), a pulse controller (10), a reactor discharge pipe (11), a temperature-controlled water tank (12), a flow pump (13) and a liquid storage tank (14); The two screens (4) are respectively arranged at the top and bottom of the packed bed reactor (1); The liquid storage tank (14) is connected to the packed bed reactor (1) via the flow pump (13); the pressure relief valve (2) is provided at the top of the packed bed reactor (1); the thermal insulation jacket (3) is provided on the outer wall of the packed bed reactor (1); the reactor discharge pipe (11) is connected to the bottom of the packed bed reactor (1); the probe of the dissolved oxygen monitor (5) and the probe of the pH monitor (6) are both inserted between the screen (4) at the bottom and the reactor discharge pipe (11); the electromagnetic pulse valve (9) and the pulse controller (10) are provided between the bacteria filter (8) and the packed bed reactor (1); the oxygen cylinder (7) is connected to the packed bed reactor (1) via the bacteria filter (8); and the temperature control water tank (12) is respectively connected to the top and bottom of the thermal insulation jacket (3). Wherein, the packed bed reactor 1 is filled with the modified polyurethane filler according to claim 5.

8. Use of the bioleaching equipment according to claim 7 in molybdenum tailings treatment.

9. A method for fungal leaching of molybdenum tailings, characterized in that: Leaching is performed using the bioleaching equipment according to claim 7, specifically comprising the following steps: S1. The Aspergillus niger hyphae and the modified polyurethane filler according to claim 5 are solidified and cultured in a fungal liquid culture medium to obtain a modified polyurethane filler loaded with Aspergillus niger; S2. adding the modified polyurethane filler loaded with Aspergillus niger between the two screens (4) of the packed bed reactor (1) of the bioleaching equipment according to claim 7; S3. After mixing the fungal liquid culture medium with the molybdenum tailings, the mixture is placed in a liquid storage tank (14) to obtain a molybdenum tailings slurry; S4. The molybdenum tailings slurry is pumped into the packed bed reactor (1) through a flow pump (13), and the molybdenum tailings are subjected to fungal leaching to obtain a leachate.

10. The method for fungal leaching of molybdenum tailings according to claim 9, wherein: The curing culture temperature is 30°C to 34°C, the rotation speed is 100 rpm to 150 rpm, and the time is 30 h to 42 h; and / or The total stacking area of ​​the modified polyurethane filler loaded with Aspergillus niger is 70%-80% of the effective volume of the packed bed reactor (1); and / or During the fungal leaching, the molybdenum tailings slurry flow rate is 1.2 L / h-1.8 L / h, the electromagnetic pulse frequency is 0.4 Hz-0.6 Hz, the dissolved oxygen is 3.5 mg / L-6.0 mg / L, the temperature is 33°C-37°C, the leachate pH is 2.2~2.6, and the leaching time is 54 h-60 h.

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