Metal leaching agent and method for leaching and recovering metal from retired photovoltaic module step by step

Abstract

The invention relates to a metal leaching agent and a method for leaching and recovering metal from a retired photovoltaic module step by step. The metal leaching agent comprises an acidophilic thiobacillus ferrooxidans solution, a hidden acidophilic bacteria solution and a thiobacillus thiooxidans solution, the volume ratio of the acidophilic thiobacillus ferrooxidans liquid to the hidden acidophilic bacteria liquid to the thiobacillus thiooxidans liquid is (0.5-1.5): (0.5-1.5): (0.5-1.5); wherein the concentration of the acidophilic thiobacillus ferrooxidans, the acidophilic hidden bacteria and the thiobacillus thiooxidans is (1-9) * 10 < 8 > cells / mL. Furthermore, the invention provides a method for leaching and recovering metal from the retired photovoltaic module step by step. According to the method, the metal leaching agent is utilized, mild and green recovery of aluminum and silver in the decommissioned photovoltaic cell piece and full-process recovery of the decommissioned photovoltaic module can be achieved through step-by-step biological leaching, and the method has the excellent leaching effect on aluminum and silver.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization, and in particular to a metal leaching agent and a method for stepwise leaching and recycling metals from a decommissioned photovoltaic module. BACKGROUND

[0002] The decommissioned photovoltaic module, such as a crystalline silicon photovoltaic cell, contains high-value elements such as silver, aluminum, silicon, etc., and the economic value of these elements accounts for about 30% to 40% of the total cost of the module. With the rapid development of the global photovoltaic industry, the full-process large-scale processing of decommissioned photovoltaic modules has become an urgent problem to be solved. Traditional landfill disposal not only wastes valuable metal resources, but also poses a risk of soil pollution by heavy metals such as lead solder. Therefore, it is of great economic value and environmental significance to fully recycle and utilize the metal resources such as silver and aluminum in decommissioned photovoltaic modules.

[0003] In recent years, continuous breakthroughs have been made in the separation of metals and optimization of energy consumption using hydrometallurgy, pyrometallurgy, and bioleaching technologies, but there are also significant shortcomings. For example, traditional hydrometallurgy and pyrometallurgical recycling technologies have high energy consumption and high costs, and are prone to wastewater or waste gas pollution. Although bioleaching technology is environmentally friendly, simultaneous recovery often leads to increased separation costs.

[0004] Currently, bioleaching is still an important recycling technology in the field of metal recycling from decommissioned photovoltaic modules, which is characterized by reduction and harmlessness. The leaching of aluminum metal mainly relies on the metabolic activity of acidophilic bacteria, among which the most widely used acidophilic bacteria are Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. These bacteria can produce an acidic environment by oxidizing sulfur or ferrous iron to dissolve aluminum metal. This type of bacteria has the characteristics of high-efficiency metal dissolution and strong environmental adaptability, but the single-bacterium leaching method often has the problem of low leaching efficiency. SUMMARY

[0005] To overcome the problems in the prior art, the primary purpose of the present application is to provide a metal leaching agent, which is prepared by mixing three specific bacterial solutions, i.e., Acidithiobacillus ferrooxidans solution, Acidiphilium cryptum solution, and Acidithiobacillus thiooxidans solution, to achieve a synergistic effect and excellent aluminum leaching effect.

[0006] The second purpose of the present application is to provide a preparation method of the metal leaching agent.

[0007] The third purpose of the present application is to provide a metal leaching solution.

[0008] The fourth purpose of the present application is to provide the application of the above-mentioned metal leaching agent or metal leaching solution in leaching aluminum metal.

[0009] The fifth purpose of the present application is to provide a method for stepwise leaching and recycling metals from a decommissioned photovoltaic module.

[0010] The above object of the present application is achieved by the following technical solutions. The present application claims a metal leaching agent, which comprises Acidithiobacillus ferroxidans liquid, Acidiphilium cryptum liquid and Acidithiobacillus thiooxidans liquid. 8 The concentration of the Acidithiobacillus ferroxidans, Acidiphilium cryptum and Acidithiobacillus thiooxidans is (1-9)×10

[0011] The present application provides a metal leaching agent, which comprises Acidithiobacillus ferroxidans liquid, Acidiphilium cryptum liquid and Acidithiobacillus thiooxidans liquid.

[0012] Specifically, the volume ratio of the Acidithiobacillus ferroxidans liquid, Acidiphilium cryptum liquid and Acidithiobacillus thiooxidans liquid is 1.2-1.5:0.9-1.4:0.8-1.2.

[0013] Specifically, the concentration of the Acidithiobacillus ferroxidans, Acidiphilium cryptum and Acidithiobacillus thiooxidans is (2-5)×10 8 Specifically, the concentration of the Acidithiobacillus ferroxidans, Acidiphilium cryptum and Acidithiobacillus thiooxidans is (2.5-3.5)×10 8 cells / mL.

[0014] In the second aspect, the present application provides a preparation method of a metal leaching agent, which comprises uniformly mixing Acidithiobacillus ferroxidans liquid, Acidiphilium cryptum liquid and Acidithiobacillus thiooxidans liquid.

[0015] In the third aspect, the present application provides a metal leaching liquid, which is activated by the above metal leaching agent in a culture medium and is obtained by culturing to logarithmic growth phase.

[0016] Preferably, in the metal leaching liquid, the concentration of the Acidithiobacillus ferroxidans, Acidiphilium cryptum and Acidithiobacillus thiooxidans is (0.8-9)×10 9 Specifically, in the metal leaching liquid, the concentration of the Acidithiobacillus ferroxidans, Acidiphilium cryptum and Acidithiobacillus thiooxidans is (1-3)×10 9 cells / mL.

[0017] Preferably, the culture medium comprises the following components: ammonium sulfate 3~5 g / L, dipotassium hydrogen phosphate 0.5~1 g / L, magnesium sulfate 0.5 g / L, potassium chloride 0.1~0.2 g / L, ferrous sulfate 20~40 g / L, and sulfuric acid is used to adjust the pH to 1.5~2.5; more preferably, the culture medium comprises the following components: ammonium sulfate 4 g / L, dipotassium hydrogen phosphate 1 g / L, magnesium sulfate 0.5 g / L, potassium chloride 0.1 g / L, ferrous sulfate 30 g / L, and sulfuric acid is used to adjust the pH to 2.

[0018] Preferably, the time for the metal leaching agent to grow to the logarithmic phase in the culture medium is 16~20 h; more preferably, the growth time is 18 h.

[0019] Preferably, the volume ratio of the metal leaching agent to the culture medium is 1:45~55; more preferably, the volume ratio is 1:50.

[0020] Preferably, the activation conditions are: temperature 28~30℃, pH 1.5~2.5, rotation speed 150~200 rpm, and time 15~20 h.

[0021] In a fourth aspect, the present application provides the use of the above-mentioned metal leaching agent or metal leaching solution in leaching metal aluminum.

[0022] In a fifth aspect, the present application provides a method for stepwise leaching and recycling metals from a decommissioned photovoltaic module, comprising the following steps: S1. The decommissioned photovoltaic module is pretreated by pyrolysis to obtain a mixture comprising cell pieces, glass, and bus bars; S2. The mixture of step S1 is separated to obtain cell pieces; S3. The cell pieces of step S2 are immersed in the above-mentioned metal leaching solution, and leaching is carried out under an ultrasonic field to obtain an aluminum-rich solution; wherein the power density of the ultrasonic field is 40~100 W / L; S4. After washing the cell pieces after the primary leaching of step S3, the cell pieces are immersed in the cyanogen-producing bacterial metal leaching agent activated by the culture medium, and electrodeposition is carried out to obtain elemental silver; S5. The aluminum-rich solution of step S3 is subjected to a neutralization reaction to obtain aluminum hydroxide.

[0023] Based on the metal leaching agent or the activated metal leaching solution, the present application provides a method for stepwise leaching and recycling metals from a decommissioned photovoltaic module, which introduces an ultrasonic field in the aluminum leaching process, and the ultrasonic field can enhance mass transfer and microbial activity, and can better leach aluminum metal in the cell pieces in combination with the metal leaching solution; in addition, the ultrasonic field can also be used as pretreatment for subsequent silver leaching to remove the interference of impurities on the surface of the cell pieces on silver leaching; electrodeposition recovery is carried out simultaneously in the silver leaching process, thereby improving the leaching rate and recovery rate of the metals.

[0024] The method provided by the application is green and environmentally friendly, does not produce harmful gases, does not discharge any toxic and harmful substances into the environment, has the characteristics of high efficiency, environmental protection and high resource degree, is a resource recycling method integrating reduction, harmlessness and high value, can effectively solve the potential problem of environmental pollution caused by improper disposal of retired photovoltaic layer components, realize the recycling of high-value materials, and provide an environmentally and economically valuable solution for metal recycling in retired photovoltaic components.

[0025] Preferably, in the step S4, the cyanogen-producing bacterial metal leaching agent comprises at least one of Chromobacterium violaceum, Pseudomonas fluorescens and Pseudomonas aeruginosa; more preferably, the cyanogen-producing bacterial agent is Pseudomonas aeruginosa. In this preferred case, the metal silver leaching efficiency is higher.

[0026] Preferably, in the step S4, the strain in the cyanogen-producing bacterial metal leaching agent is activated to the logarithmic growth phase, and the culture medium used comprises the following components: peptone 8-12 g / L, yeast extract 4-6 g / L, sodium chloride 4-6 g / L, glucose 0.8-1.2 g / L; more preferably, the components of the culture medium comprise the following components: peptone 10 g / L, yeast extract 5 g / L, sodium chloride 5 g / L, glucose 1 g / L.

[0027] Preferably, the time for the strain in the cyanogen-producing bacterial metal leaching agent to grow to the logarithmic phase is 16-20 h; more preferably, the growth time is 18 h.

[0028] Preferably, in the step S4, the volume ratio of the cyanogen-producing bacteria to the culture medium is 1:45-55; more preferably, the volume ratio is 1:50.

[0029] Preferably, the culture conditions of the cyanogen-producing bacterial metal leaching agent in the culture medium are: temperature 25-30℃, rotation speed 150-200 rpm, time 15-20 h.

[0030] Preferably, in the step S3, the volume ratio of the battery piece to the metal leaching liquid is 1:1500-2500; further preferably, the volume ratio of the battery piece to the metal leaching liquid is 1:1800-2000.

[0031] Preferably, in the step S3, the ultrasonic conditions are: frequency 30-50 kHz, power density 70-90 W / L, intermittent operation of On 50-75 s / Off 225-250 s; more preferably, the frequency is 40 kHz, the power density is 80 W / L, and the intermittent operation is On 60 s / Off 240 s.

[0032] Preferably, in the step S1, the retired photovoltaic module is decomposed by pyrolysis. Preferably, the pyrolysis is carried out at a temperature of 450-550℃, a heating rate of 15-25℃ / min, and a vacuum degree of 0.05-1.05 Pa; more preferably, the pyrolysis is carried out at a temperature of 500℃, a heating rate of 10℃ / min, and a vacuum degree of 1 Pa.

[0033] Preferably, in the steps S3 and S4, the temperature during the leaching is 25-35℃.

[0034] Preferably, in the step S4, the leaching is carried out with stirring, and the stirring speed is 500-600 rpm; more preferably, the stirring speed is 500 rpm.

[0035] Preferably, in the step S4, the electrodeposition is carried out under the following conditions: the cathode is a graphite plate, the anode is a titanium mesh, the current density is 0.5-1.5 mA / cm 2 , and the reaction temperature is 25-35℃; more preferably, the current density is 1 mA / cm 2 , and the reaction temperature is 30℃.

[0036] Preferably, in the step S5, the aluminum-rich solution is subjected to a neutralization reaction with a sodium hydroxide solution to obtain aluminum hydroxide. The concentration of sodium hydroxide in the sodium hydroxide solution is 1-2 mol / L, and the neutralization reaction is carried out at a temperature of 25-35℃; more preferably, the concentration of sodium hydroxide in the sodium hydroxide solution is 1.5 mol / L, and the neutralization reaction is carried out at a temperature of 30℃.

[0037] Compared with the prior art, the present application has the following beneficial effects: (1) The present application provides a metal leaching agent, which comprises an acidophilic ferrous-oxidizing Thiobacillus liquid, a hidden acidophilic bacteria liquid, and an oxidizing sulfur Thiobacillus liquid. The combination of the above three kinds of bacteria liquids plays an excellent synergistic effect. The metal leaching liquid obtained by activating and culturing the same can achieve better aluminum leaching effect than the metal leaching agent composed of any two kinds of bacteria liquids.

[0038] (2) The present application provides a method for stepwise leaching and recycling metals from a retired photovoltaic module. The method introduces an ultrasonic field in the aluminum leaching process, which can enhance mass transfer and microbial activity. The combination with the metal leaching liquid can better leach the aluminum metal in the battery piece. In addition, the ultrasonic field can also be used as a pretreatment for subsequent silver leaching to remove the interference of impurities on the surface of the battery piece on silver leaching. The electrodeposition recovery is carried out simultaneously in the silver leaching process, thereby improving the leaching rate and recovery rate of the metal. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1A flowchart of a method for stepwise leaching and recycling metals from a decommissioned photovoltaic module. DETAILED DESCRIPTION

[0040] The present application is further illustrated by the following description with reference to the accompanying drawings and specific examples, which do not limit the present application in any form.

[0041] The reagents and raw materials used in the following examples are as follows: Acidophilic ferrous-oxidizing Thiobacillus (T.f) Acidithiobacillus ferrooxidans , manufactured by Shanghai Jiachu Biological Engineering Co., Ltd., with the brand SHMCC D24636; Concealed acidophilic bacteria (A.concretonis) Acidiphilium cryptum , manufactured by Beijing Baoerbo Biological Technology Co., Ltd., with the brand ATCC 33463; Sulfur-oxidizing Thiobacillus (T.s) Thiobacillus thiooxidans , manufactured by Shanghai Jiachu Biological Engineering Co., Ltd., with the brand SHMCC D24637; Purple Chromobacterium (C.violaceum) Chromobacterium violaceum , manufactured by Shanghai Jiachu Biological Engineering Co., Ltd., with the brand ATCC 31532; Pseudomonas aeruginosa (P.aeruginosa) Pseudomonas aeruginosa , manufactured by Shanghai Fuxiang Biological Technology Co., Ltd., with the brand ATCC 9027; Pseudomonas fluorescens (P.fluorescens) Pseudomonas fluorescens , manufactured by Shanghai Fuxiang Biological Technology Co., Ltd., with the brand ATCC 49642; Ferrous-oxidizing Thiobacillus (T.f) Acidithiobacillus ferrooxidans , manufactured by Shanghai Lianmai Biological Engineering Co., Ltd., with the brand ATCC 340112.

[0042] Unless otherwise specified, other materials, reagents, etc. employed by the present application can be obtained from commercial channels.

[0043] Example 1 1.2 mL of each of the acidophilic ferrous-oxidizing Thiobacillus liquid, the concealed acidophilic bacteria liquid and the sulfur-oxidizing Thiobacillus liquid (the concentration of acidophilic ferrous-oxidizing Thiobacillus in the acidophilic ferrous-oxidizing Thiobacillus liquid is 3×10 8 cells / mL; the concentration of concealed acidophilic bacteria in the concealed acidophilic bacteria liquid is 3×10 8 cells / mL; and the concentration of sulfur-oxidizing Thiobacillus in the sulfur-oxidizing Thiobacillus liquid is 3×10 8 cells / mL) were mixed to prepare a metal leaching agent.

[0044] Acidophilic bacteria culture medium was prepared using deionized water (ammonium sulfate 4 g / L, dipotassium hydrogen phosphate 1 g / L, magnesium sulfate 0.5 g / L, potassium chloride 0.1 g / L, ferrous sulfate 30 g / L, and sulfuric acid to adjust the pH to 2). The prepared culture medium was then sterilized at 121℃ for 15 min.

[0045] The metal leaching agent was added to the acidophilic bacteria culture medium to activate the bacterial strains, and cultured for 18 h until the logarithmic growth phase (the concentration of each bacterium was 1×10⁻⁶). 9 The metal leachate was obtained by culturing at 150 rpm and 30°C.

[0046] Example 2 The difference between this embodiment and Embodiment 1 is that: 1.5 mL of *Thiobacillus acidophilus* solution, 0.9 mL of *Hypericum septum* solution, and 1.2 mL of *Thiobacillus thiooxidans* solution are mixed to prepare a metal leaching agent.

[0047] Example 3 The difference between this embodiment and Embodiment 1 is that: 1.4 mL of *Thiobacillus acidophilus* solution, 1.4 mL of *Hypericum ferrooxidans* solution, and 0.8 mL of *Thiobacillus thiooxidans* solution are mixed to prepare a metal leaching agent.

[0048] Example 4 like Figure 1 As shown, a method for stepwise leaching and recovering metals from decommissioned photovoltaic modules includes the following steps: S1. The retired crystalline silicon photovoltaic modules are from Shenzhen Yujia Electronics Technology Co., Ltd. The retired crystalline silicon photovoltaic modules used as experimental samples have had their aluminum frames and junction boxes removed; they can also be referred to as retired crystalline silicon photovoltaic laminates. The retired photovoltaic modules were subjected to pyrolysis and desealing treatment at 500℃, a reaction time of 30 min, a heating rate of 10℃ / min, and a vacuum degree of 1 Pa, yielding a mixture of solar cells, glass, and busbars. S2. The mixture of battery cells, glass and busbar obtained in step S1 is sorted to obtain battery cells, glass and busbar respectively; the obtained glass can be recycled, the busbar can be used for corresponding metal recovery, and the battery cells can be further subjected to bioleaching. S3. The battery cell obtained in step S2 is cut into square pieces (1×1 cm, 0.2~0.3 g) and immersed in the metal leaching solution of Example 1 (the volume ratio of battery cell to leaching solution is 1:1800). An aluminum-rich solution is obtained by leaching under an ultrasonic field. The ultrasonic frequency is 40 kHz, the power density is 80 W / L, the operation is intermittent (On 60 s / Off 240 s), the leaching time is 5 days, and the temperature is set to 30℃. S4, preparation of cyanogen-producing bacterial metal leaching agent of silver: deionized water is used to prepare cyanogen-producing bacterial culture medium (10 g / L of proteose peptone, 5 g / L of yeast extract, 5 g / L of sodium chloride, and 1 g / L of glucose), and the prepared culture medium is sterilized at 121°C for 15 min; 1.2 mL of Pseudomonas aeruginosa bacterial liquid is put into the cyanogen-producing bacterial culture medium to activate the strain, and the culture is carried out for 18 h to the logarithmic growth phase, so as to obtain the cyanogen-producing bacterial metal leaching agent of silver. During the culture, the rotation speed is kept at 150 rpm, and the temperature is set to 25°C; S5, the battery piece after leaching in step S3 is washed with deionized water and dried, and is immersed in the cyanogen-producing bacterial metal leaching agent (the volume ratio of the battery piece to the leaching agent is 1:600), and the leaching process is synchronized with the electrodeposition to extract silver. The rotation speed is 500 rpm, the temperature is 30°C, and the stirring leaching time is 5 d; the electrodeposition process is as follows: a graphite plate is selected as the cathode, a titanium mesh is selected as the anode, the current density is 1 mA / cm 2 , and the reaction temperature is 30°C; S6, 1.5 mol / L of sodium hydroxide solution is added to the aluminum-rich solution obtained in S3 to obtain aluminum hydroxide through neutralization reaction. The temperature of the neutralization reaction is 30°C, and the reaction time is 75 min.

[0049] Example 5 Example 5 is different from example 4 in that, in step S4, the Pseudomonas aeruginosa is replaced by Chromobacterium violaceum.

[0050] Example 6 Example 6 is different from example 4 in that, in step S4, the Pseudomonas aeruginosa is replaced by Pseudomonas fluorescens.

[0051] Example 7 Example 7 is different from example 4 in that, in step S3, the power density of the ultrasonic field in the aluminum leaching process is adjusted to 70 W / L.

[0052] Example 8 Example 8 is different from example 4 in that, in step S3, the power density of the ultrasonic field in the aluminum leaching process is adjusted to 90 W / L.

[0053] Example 9 Example 9 is different from example 4 in that, in step S3, the metal leaching agent prepared in example 2 is used.

[0054] Example 10 Example 10 is different from example 4 in that, in step S3, the metal leaching agent prepared in example 3 is used.

[0055] Example 11 Example 11 differs from Example 4 in that both steps of bioleaching (i.e. steps S3 and S5) are carried out using the metal leaching solution in Example 1 to complete the leaching step.

[0056] Comparative Example 1 Comparative Example 1 differs from Example 4 in that both steps of bioleaching (i.e. steps S3 and S5) are carried out using the cyanide-generating metal leaching agent in step S4 to complete the leaching step.

[0057] Comparative Example 2 Comparative Example 2 differs from Example 4 in that the bacterial combination of the acidophilic bacterial metal leaching agent is changed to 1.8 mL of Acidithiobacillus ferroxidans liquid and 1.8 mL of Leptospirillum tenuo.

[0058] Comparative Example 3 Comparative Example 3 differs from Example 4 in that the bacterial combination of the acidophilic bacterial metal leaching agent is changed to 1.8 mL of Leptospirillum tenuo liquid and 1.8 mL of Acidithiobacillus thiooxidans liquid.

[0059] Comparative Example 4 Comparative Example 4 differs from Example 4 in that the bacterial combination of the acidophilic bacterial metal leaching agent is changed to 1.8 mL of Acidithiobacillus ferroxidans liquid and 1.8 mL of Acidithiobacillus thiooxidans liquid.

[0060] Comparative Example 5 Comparative Example 5 differs from Example 4 in that in step S3, the ultrasonic field is not added to the aluminum leaching process, but is changed to stirring leaching, wherein the stirring speed is 500 rpm, the temperature is 30°C, and the stirring leaching time is 5 days.

[0061] Comparative Example 6 Comparative Example 6 differs from Example 4 in that the Acidithiobacillus ferroxidans of the acidophilic bacterial metal leaching agent is changed to Acidithiobacillus ferrooxidans.

[0062] Comparative Example 7 Comparative Example 7 differs from Example 4 in that in step S3, the power density of the ultrasonic process is changed to 150 W / L.

[0063] During the bioleaching process, 5.0 mL samples were periodically extracted from the reactor, centrifuged at a speed of 8000 rpm for 5 min, and then the metal ion concentrations of aluminum (Al) and silver (Ag) in the supernatant were analyzed using ICP-OES. At the same time, the recovered aluminum and silver recovered by neutralization precipitation and electrodeposition were measured for recovery purity by ICP-OES, and then the metal recovery rates of aluminum and silver were calculated. The specific data are shown in Table 1.

[0064] Table 1 Metal leaching rate data of each group

[0065] From the above Table 1, in Examples 5-6, the leaching rate of silver is lower than that of Example 4, indicating that the cyanogen-producing bacterial metal leaching agent composed of Pseudomonas aeruginosa strains in Example 4 has better silver leaching effect than the cyanogen-producing bacteria in Examples 5-6, and is more suitable as a silver leaching strain for step-by-step bioleaching.

[0066] In Examples 7-8, the leaching rate of aluminum is lower than that of Example 4, indicating that when the power density of the ultrasonic field is set to 80 W / L in the process of aluminum leaching by acidophilic bacteria, the activity of the acidophilic bacteria and the mass transfer of the reactor are better, and the acidophilic bacteria have more beneficial effects on aluminum leaching.

[0067] In Examples 9-10, the leaching rate and recovery rate of aluminum are slightly lower than those of Example 4, indicating that when the bacterial proportion of Acidithiobacillus ferroxidans, Acidiphilium cryptum, and Acidithiobacillus thiooxidans in the acidophilic bacterial metal leaching agent is 1:1:1, better leaching rate and recovery rate can be achieved.

[0068] In Example 11, the leaching rate and recovery rate of aluminum are not much different from those of Example 4, but the leaching rate and recovery rate of silver are both 0, indicating that the acidophilic bacteria have good aluminum leaching effect, but cannot leach silver in the battery sheet.

[0069] The leaching rate and recovery rate of aluminum and silver in Comparative Example 1 are significantly lower than those of Example 4, indicating that the use of cyanogen-producing bacteria for simultaneous recovery of aluminum and silver is not good, and subsequent separation and recovery of the obtained leaching solution is needed, prolonging the recovery process and cost.

[0070] In Comparative Examples 2-4, the leaching rate of aluminum is significantly lower than that of Example 4, indicating that the composite acidophilic bacterial agent composed of Acidithiobacillus ferroxidans, Acidiphilium cryptum, and Acidithiobacillus thiooxidans is more suitable for step-by-step bioleaching than the commonly used combination of two acidophilic bacterial solutions, and has better aluminum leaching effect. The metal leaching agent provided by the present application can achieve efficient symbiosis through "iron-sulfur metabolism coupling", thereby synergistically promoting the leaching of aluminum; wherein the Acidiphilium cryptum maintains the dual effects of iron cycle and organic acid dissolution to synergize with Acidithiobacillus ferroxidans and Acidithiobacillus thiooxidans for leaching, thereby improving the recovery rate of aluminum.

[0071] In Comparative Example 5, the leaching rate and recovery rate of aluminum and silver are significantly lower than those of Example 4, indicating that the application of an ultrasonic field can enhance mass transfer and microbial activity, thereby improving the leaching rate and recovery rate of the aluminum leaching process; and as a pretreatment for subsequent silver leaching, removing impurities on the surface of the battery sheet makes silver more easily leached. It can be seen that the introduction of an ultrasonic field simultaneously improves the leaching effect and recovery rate of microbial aluminum leaching and silver leaching.

[0072] In the comparative example 6, the leaching rate and recovery rate of aluminum are both lower than those in the example 4, indicating that replacing the acidophilic iron-oxidizing Thiobacillus in the metal leaching agent with iron-oxidizing Thiobacillus cannot achieve the synergistic aluminum leaching effect of the original combination.

[0073] In the comparative example 7, the leaching rate and recovery rate of aluminum are both significantly lower than those in the example 4, indicating that increasing the power density of the ultrasonic field can damage the activity of acidophilic microorganisms in the aluminum leaching process, causing the leaching process to lose biological driving force, thereby greatly reducing the leaching rate of aluminum.

[0074] In summary, the present application uses the strategy of combining step-by-step biological leaching, acidophilic bacteria complex leaching, electrochemical deposition method and neutralization method, and uses the complex metal leaching agent containing acidophilic iron-oxidizing Thiobacillus liquid, hidden acidophilic bacteria liquid and sulfur-oxidizing Thiobacillus liquid, which is different from the growth environment and optimal growth conditions required by cyanide-producing bacteria. Through step-by-step leaching, better aluminum and silver leaching effects can be achieved, and efficient separation and recovery of aluminum and silver in retired photovoltaic cell sheets are realized. In a low pH environment, aluminum is preferentially dissociated under the action of the metal leaching agent, avoiding the masking effect of silver; silver is targeted leached in the metabolic process of cyanide-producing bacteria, significantly improving the leaching rate and recovery rate; the ultrasonic field enhances mass transfer and microbial activity, improving the leaching efficiency of aluminum and reducing the difficulty of subsequent silver leaching; the simultaneous electro-deposition in the silver leaching process shortens the recovery process and improves the recovery rate and economic benefits. This method can effectively solve the potential pollution problem to the environment, and has the characteristics of low energy consumption, high economic benefits and environmental protection and cleanliness.

[0075] Finally, it should be explained that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. For those skilled in the art, on the basis of the above description and ideas, other different forms of changes or variations can also be made, which do not need to be or cannot be exhaustively listed here. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A metal leaching agent, characterized in that, The metal leaching agent comprises *Thiobacillus ferrooxidans* solution, *Acinetobacter cryptana* solution, and *Thiobacillus thiooxidans* solution; the volume ratio of the *Thiobacillus ferrooxidans* solution, *Acinetobacter cryptana* solution, and *Thiobacillus thiooxidans* solution is 0.5~1.5:0.5~1.5:0.5~1.5; the concentration of the *Thiobacillus ferrooxidans*, *Acinetobacter cryptana*, and *Thiobacillus thiooxidans* solution is (1~9)×10⁻⁶. 8 cells / mL.

2. The metal leaching agent according to claim 1, characterized in that, The volume ratio of the *Thiobacillus ferrooxidans* solution, the *Acanthophyte* solution, and the *Thiobacillus thiooxidans* solution is 1.2~1.5:0.9~1.4:0.8~1.

2.

3. The method for preparing the metal leaching agent according to any one of claims 1 to 2, characterized in that, The solution of *Thiobacillus acidophilus*, *Thiobacillus ferrooxidans*, and *Thiobacillus thiooxidans* is obtained by mixing them evenly.

4. A metal leaching solution, characterized in that, The metal leaching agent described in any one of claims 1 to 2 is activated in a culture medium and cultured until the logarithmic growth phase is reached to obtain the product.

5. The metal leachate according to claim 4, characterized in that, The concentration of *Thiobacillus ferrooxidans*, *Acrylophilic acidophilus*, and *Thiobacillus thiooxidans* in the metal leachate is (0.8~9) × 10⁻⁶. 9 cells / mL.

6. The use of the metal leaching agent according to any one of claims 1 to 2 or the metal leaching solution according to any one of claims 4 to 5 in the leaching of metallic aluminum.

7. A method for stepwise leaching and recovering metals from decommissioned photovoltaic modules, characterized in that, Includes the following steps: S1. The retired photovoltaic modules are pretreated by pyrolysis to obtain a mixture containing solar cells, glass and busbars; S2. Separate the mixture described in step S1 to obtain battery cells; S3. Immerse the battery cell described in step S2 into the metal leaching solution described in any one of claims 4 to 5, and leach it under an ultrasonic field to obtain an aluminum-rich solution; wherein the power density of the ultrasound is 40 to 100 W / L; S4. After cleaning the battery cells after the initial leaching in step S3, immerse them in a metal leaching agent for cyanogenic bacteria activated by culture medium for electrodeposition to obtain elemental silver. S5. The aluminum-rich solution obtained in step S3 is neutralized to obtain aluminum hydroxide.

8. The method according to claim 7, characterized in that, In step S4, the cyanide-producing bacteria metal leaching agent includes at least one of Chromobacterium violaceum, Pseudomonas fluorescens, and Pseudomonas aeruginosa.

9. The method according to claim 7, characterized in that, In step S3, the ultrasound conditions are: frequency of 30~50 kHz, power density of 70~90 W / L, and intermittent operation with an on cycle of 50~75 s and an off cycle of 225~250 s.

10. The method according to claim 7, characterized in that, Selected from at least one of (a) to (c) below: (a) In step S4, the leaching temperature is 25~35℃; (b) In step S4, stirring is performed during leaching, and the stirring speed is 500~600 rpm; (c) In step S4, the electrodeposition conditions are as follows: a graphite plate is used as the cathode, a titanium mesh is used as the anode, and the current density is 0.5~1.5 mA / cm². 2 The reaction temperature is 25~35℃.

Images