Germanium recovery method

Abstract

Provided is a germanium recovery method whereby germanium can be recovered efficiently and inexpensively during the production of optical fibers. The germanium recovery method is a method for recovering germanium from an exhaust gas in a process for manufacturing an optical fiber preform, and includes a first step for separating germanium from the exhaust gas by passing the exhaust gas through a separation device. The exhaust gas is a gas exhausted in a dehydration sintering step for manufacturing the optical fiber base material.

Description

Technical Field

[0001] The present disclosure relates to a method for recovering germanium. Background Art

[0002] Germanium is used as a raw material for various industrial products such as semiconductor materials such as diodes and additives for the core of glass optical fibers. In recent years, the price of germanium has risen. Therefore, for example, patent documents 1 to 3 disclose technologies for recovering germanium. Patent document 1 discloses a technology for recovering germanium oxide volatilized in the dehydration and sintering process during transparent vitrification as metallic germanium using a reducing agent. Patent document 2 discloses a technology for recovering germanium-containing particles through a bag filter in the deposition process of a porous matrix and reusing them in the optical fiber manufacturing process. Patent document 3 discloses a technology for contacting chelate-forming fibers with a germanium-containing aqueous solution whose pH is adjusted to be greater than 3 and less than 12 in a waste liquid treatment process to remove and recover germanium in the aqueous solution.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 58-213838

[0006] Patent Document 2: Japanese Patent Application Publication No. 2004-2088

[0007] Patent Document 3: Japanese Patent Application Publication No. 2017-140571 Summary of the invention

[0008] Technical problem to be solved by the invention

[0009] When manufacturing optical fiber, part of germanium, which is an additive for the core of the optical fiber, is discharged together with the exhaust gas. The germanium contained in the exhaust gas is processed in the exhaust gas treatment / drainage treatment process in the later stage, and is finally discharged as sludge together with silicon oxide. Although the technology of recovering germanium in each process of manufacturing optical fiber has been disclosed, it is not easy to recover germanium efficiently and cheaply. In Patent Document 1, since carbon is used as a reducing agent, poisonous carbon monoxide is generated. In Patent Document 2, the amount of gas to be processed is large, and the equipment becomes large. In the method using chelated fiber shown in Patent Document 3, the equipment is expensive.

[0010] An object of the present disclosure is to provide a method for recovering germanium that can efficiently and inexpensively recover germanium when manufacturing optical fibers.

[0011] Technical solutions for solving technical problems

[0012] The germanium recovery method disclosed in the present invention is a method for recovering germanium from exhaust gas in the manufacturing process of optical fiber mother material, including a first step of separating germanium from the exhaust gas by passing the exhaust gas through a separation device, wherein the exhaust gas is the gas exhausted in the dehydration sintering process of manufacturing the optical fiber mother material.

[0013] Effects of the Invention

[0014] According to the present disclosure, it is possible to provide a germanium recovery method capable of efficiently and inexpensively recovering germanium when manufacturing optical fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram showing a flow of a germanium recovery method according to an embodiment of the present disclosure.

[0016] Figure 2 It is a diagram schematically showing a first step according to the first aspect of one embodiment of the present disclosure.

[0017] Figure 3 It is a diagram schematically showing a first step and a second step according to the second aspect of one embodiment of the present disclosure.

[0018] Figure 4 This is a diagram schematically showing an example of a treatment process of a germanium extract solution.

[0019] Figure 5 This is a diagram schematically showing another example of the treatment process of the germanium extract. DETAILED DESCRIPTION

[0020] [Description of Embodiments of the Present Disclosure]

[0021] First, embodiments of the present disclosure will be listed and described.

[0022] Germanium recovery method according to one embodiment of the present disclosure

[0023] (1) A method for recovering germanium from exhaust gas in the manufacturing process of optical fiber base material.

[0024] The method comprises the following steps: passing the exhaust gas through a separation device to separate germanium from the exhaust gas;

[0025] The exhaust gas is the gas exhausted in the dehydration sintering process of manufacturing the optical fiber base material.

[0026] According to the above-mentioned method for recovering germanium, germanium can be recovered by using a small and inexpensive recovery device.

[0027] (2) In the method for recovering germanium according to (1) above,

[0028] The separation device may be a wet capture device, and in the first step, the exhaust gas may be passed through the wet capture device to extract germanium into liquid.

[0029] By using a wet capture device as the separation device, germanium can be recovered even when the exhaust gas contains dehydrated gas such as chlorine gas.

[0030] (3) In the method for recovering germanium according to (2) above,

[0031] The temperature of the liquid used for extracting germanium may be 30° C. or higher and 80° C. or lower.

[0032] By adjusting the temperature of the liquid, the concentration of germanium in the liquid can be increased, and the costs such as transportation costs and recycling costs for recycling the recovered germanium can be reduced.

[0033] (4) In the method for recovering germanium according to (1) above,

[0034] Alternatively, the separation device may be a dry adsorption device having an adsorbent, and in the first step, germanium is adsorbed on the adsorbent. The germanium recovery method may further include a second step of extracting the germanium adsorbed on the adsorbent into a liquid after the first step.

[0035] By adopting a dry adsorption device as a separation device, the degree of freedom of the equipment is improved and the operation becomes easier.

[0036] (5) In the method for recovering germanium according to (4) above,

[0037] In the second step, at least one of the pH and the temperature of the liquid may be adjusted to extract germanium into the liquid.

[0038] By adjusting the pH or temperature of the liquid, germanium can be extracted into the liquid at low cost and high efficiency.

[0039] (6) In the method for recovering germanium according to (5) above,

[0040] In the second step, the pH of the liquid may be adjusted to 0 or more and 6 or less.

[0041] By making the liquid acidic, germanium can be extracted efficiently.

[0042] (7) In the method for recovering germanium according to (5) or (6),

[0043] In the second step, the temperature of the liquid for extracting germanium may be 30° C. or higher and 80° C. or lower.

[0044] By adjusting the temperature of the liquid, the concentration of germanium in the liquid can be increased, and the costs such as transportation costs and recycling costs for recycling the recovered germanium can be reduced.

[0045] [Details of the embodiments of the present disclosure]

[0046] Hereinafter, a specific example of the germanium recovery method disclosed in the present invention will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to these examples, but is shown by the claims, and is intended to include all changes within the meaning and scope equivalent to the claims.

[0047] Figure 1 1 is a diagram showing the process of manufacturing an optical fiber and the flow of the germanium recovery method according to the present embodiment. The optical fiber manufacturing process includes a porous base material manufacturing process AS1, a dehydration and sintering process AS2, and a drawing process AS3. The germanium recovery method according to the present embodiment includes a first step S11 of separating germanium from exhaust gas discharged from a furnace core tube in the dehydration and sintering process AS2.

[0048] The porous base material manufacturing step AS1 is a step of manufacturing a porous glass base material for optical fiber by the OVD method, VAD method, etc. The main component of the porous base material is silicon dioxide, and germanium is added to the core.

[0049] Next, the porous base material obtained in the porous base material manufacturing step AS1 is dehydrated and made transparent by the dehydration sintering step AS2. In the dehydration sintering step AS2, the porous base material is first dehydrated using a gas having a dehydrating effect such as chlorine, and then the porous base material is sintered using helium or the like to make it transparent and obtain an optical fiber base material.

[0050] Next, in the drawing step AS3, the optical fiber preform obtained by the transparency in the dehydration sintering step AS2 is drawn. By drawing the optical fiber preform, an optical fiber as a product is obtained.

[0051] As described above, germanium is added to the porous base material as an additive. However, part of the germanium supplied in the porous base material manufacturing process AS1 is not added to the porous glass base material, but is discharged together with the exhaust gas. In addition, in the subsequent dehydration sintering process AS2, part of the germanium in the porous base material is also volatilized by heating at high temperature and discharged together with the exhaust gas.

[0052] Since germanium is expensive, it is desirable to recover the germanium contained in the exhaust gas. Here, it is possible to study the recovery of germanium from the exhaust gas discharged in the porous base material manufacturing process AS1. However, in the porous base material manufacturing process AS1, the flow rate of the exhaust gas is very large, and the exhaust gas contains a large amount of solid components other than germanium such as silicon dioxide. For this reason, there is a concern that the equipment for recovering germanium will be enlarged and the recovery efficiency will be reduced.

[0053] Therefore, the germanium recovery method involved in the present embodiment recovers germanium from the exhaust gas discharged in the dehydration and sintering process AS2 of manufacturing the optical fiber base material. More specifically, the germanium recovery method involved in the present embodiment includes a first step of passing the exhaust gas discharged in the dehydration and sintering process AS2 through a separation device to separate germanium from the exhaust gas. Since the gas flow rate of the exhaust gas in the dehydration and sintering process AS2 is small compared with the porous base material manufacturing process AS1, germanium can be recovered by a small and inexpensive recovery device. In addition, since the exhaust gas of the dehydration and sintering process AS2 contains little solid components, it is avoided that the solid components accumulate in the separation device and reduce the recovery efficiency.

[0054] (First aspect: separation by wet capture device)

[0055] In the first aspect of the present embodiment, the separation device may be a wet capture device 10 . Figure 2 1 is a diagram schematically showing a first step using the wet collection device 10. As the wet collection device 10, various scrubbers and the like can be adopted. Figure 2 The wet capture device 10 shown is equipped with a cleaning tower 11, cleaning water 12, and a nozzle 13 for spraying the cleaning water 12. In the first step of the present invention, the exhaust gas discharged from the furnace core tube in the dehydration sintering step AS2 is first introduced into the cleaning tower 11 of the wet capture device 10. Next, the cleaning water 12 is sprayed from the nozzle 13 provided at the top of the cleaning tower 11 to transfer the germanium contained in the exhaust gas as a gas phase to the cleaning water 12 as a liquid phase. In this way, germanium can be separated from the exhaust gas and extracted into the cleaning water 12. The cleaning water 12 containing germanium is sent to the recovery tank 40 at a time point that reaches a predetermined reference determined based on the operation time, concentration, etc. The exhaust gas after the germanium is separated is sent to the exhaust gas treatment device from the upper part of the cleaning tower 11 and treated by a predetermined method (exhaust gas treatment step BS1).

[0056] For example, when the exhaust gas contains dehydrated gas during the dehydration process or immediately after the dehydration process, the present aspect using the wet capture device 10 as the separation device can be suitably adopted. In the dehydration process, dehydrated gas such as chlorine is supplied to the furnace core tube. For this reason, for example, when it is desired to use an adsorbent to separate germanium from the exhaust gas in the dehydration process, the dehydrated gas contained in the exhaust gas aggravates the deterioration of the adsorbent and shortens the life of the adsorbent. Therefore, when the exhaust gas contains dehydrated gas, by using a wet capture device as the separation device, germanium can be recovered while avoiding the deterioration of the equipment.

[0057] In this aspect, the temperature of the washing water 12 is preferably 30° C. to 80° C. If the temperature of the washing water 12 is within this range, the washing water 12 can contain germanium at a high concentration, and the transportation cost and recycling cost of recycling the recovered germanium can be reduced.

[0058] (Second aspect: separation by dry adsorption device)

[0059] In a second aspect as another aspect of the present embodiment, the separation device may be a dry adsorption device 20 . Figure 3 1 is a diagram schematically showing a first step and a second step to be described below using the dry adsorption device 20 . The dry adsorption device 20 includes an adsorbent 21 .

[0060] The adsorbent 21 is not particularly limited as long as it can adsorb germanium, and for example, zeolite-based adsorbents and activated carbon can be used. The shape of the adsorbent 21 is not particularly limited, and granular or beaded adsorbents can be used, but the adsorbent 21 is preferably granular.

[0061] In the first step of the present invention, exhaust gas discharged from the furnace core tube in the dehydration sintering step AS2 is first introduced into the dry adsorption device 20. The introduced exhaust gas passes through the adsorbent 21, and at this time, germanium contained in the exhaust gas is adsorbed by the adsorbent 21. In this way, germanium can be separated from the exhaust gas. The exhaust gas from which germanium is separated is sent from the dry adsorption device to the exhaust gas treatment device and treated by a predetermined method (exhaust gas treatment step BS1).

[0062] The method for recovering germanium according to the present aspect using the dry adsorption device 20 further includes a second step of extracting the germanium adsorbed on the adsorbent 21 into the liquid 31 in the mixing tank 30 after the first step. In the second step, when extracting germanium into the liquid 31, the adsorbent 21 may be directly put into the mixing tank 30 including the liquid 31, or the adsorbent 21 may be put into a mesh container made of resin and then the mesh container may be put into the mixing tank 30. After the adsorbent 21 is put into the liquid 31, stirring is performed using a stirring blade 32 or the like, so that the germanium is fully extracted into the liquid 31. As the liquid 31, water is used, for example. After the germanium is extracted, the adsorbent 21 is removed from the mixing tank 30 by sedimentation separation or by taking out the mesh container. The liquid 31 from which the germanium is extracted is sent to the recovery tank 40.

[0063] In the second step of the present aspect, it is preferred to adjust at least one of the pH and temperature of the liquid 31 to extract germanium into the liquid 31. More specifically, it is preferred to adjust the pH of the liquid 31 to be greater than 0 and less than 6. By making the liquid acidic, germanium can be efficiently extracted. In addition, it is preferred to adjust the temperature of the liquid 31 to be greater than 30°C and less than 80°C. By adjusting the temperature of the liquid, the concentration of germanium in the liquid can be increased, and the costs such as transportation costs and recycling costs for recycling the recovered germanium can be reduced.

[0064] The dry adsorption device is easy to set up, the adsorption capacity can be selected, etc., and the degree of freedom of the equipment is high compared with the wet capture device. Therefore, by using the dry adsorption device as the separation device, the device can be miniaturized and the cost can be reduced. However, as mentioned above, in the case of separating the exhaust gas in the dehydration process, it is preferred to use a wet capture device. It can also be configured so that the introduction destination of the exhaust gas is switched in the middle of the dehydration sintering process, so that the wet capture device is used as the separation device during the implementation of the dehydration process, and the dry adsorption device is used as the separation device during the implementation of the sintering process.

[0065] (Processing of Germanium Extract)

[0066] By using the first step in the aspect of using a wet capture device or the second step in the aspect of using a dry adsorption device, a liquid containing germanium (hereinafter referred to as a germanium extract) is obtained. The germanium extract is appropriately subjected to extract treatment S2 to recover germanium. In the germanium recovery method disclosed herein, the specific method of extract treatment S2 is not particularly limited, and an example of extract treatment S2 is described below.

[0067] When solid residue is generated in the germanium extract, the germanium extract and the solid residue may be separated in the extract treatment S2. Methods for separating the germanium extract and the solid residue include sedimentation separation, reduced pressure filtration, and pressure filtration.

[0068] In the extract treatment S2, a treatment for precipitating the germanium-containing compound from the germanium extract (hereinafter referred to as precipitation treatment) may also be performed. In the precipitation treatment, the germanium-containing compound may be precipitated from the germanium extract by concentrating the germanium extract or adding a metal salt to the germanium extract. In the precipitation treatment, the germanium-containing compound may be efficiently precipitated in a cheap manner by concentrating the germanium extract or adding a metal salt to the germanium extract for coprecipitation.

[0069] When adding a metal salt during the precipitation treatment, a soluble metal salt that forms a composite oxide with germanium or a sparingly soluble metal salt that adsorbs germanium may also be added. If a soluble metal salt is added, the germanium dissolved in the germanium extract can be recovered at a high yield as a composite oxide with the added metal. If a sparingly soluble metal salt is added, germanium can be concentrated on the surface of the sparingly soluble metal salt to precipitate a germanium-containing compound, and the germanium dissolved in the germanium extract can be recovered at a high yield.

[0070] In the case of adding a metal salt during the precipitation treatment, an alkaline earth metal salt may also be added. If an alkaline earth metal salt is added, it is suitable for precipitating a germanium-containing compound, and the germanium dissolved in the germanium extract can be recovered at a high yield. As alkaline earth metal salts, magnesium chloride, magnesium sulfate, calcium chloride, etc. may be cited. The amount of alkaline earth metal salt added may be more than 0.8 equivalents and less than 3.0 equivalents relative to the germanium equivalent in the liquid. By adding an alkaline earth metal salt in the above-mentioned amount, it is not limited to a composite oxide containing germanium and an alkaline earth metal in an equivalent ratio of 1:1, and it is also possible to induce the formation of a composite oxide with more alkaline earth metals at an equivalent ratio, and it is possible to recover the germanium dissolved in the germanium extract at a high yield.

[0071] After the above-mentioned precipitation treatment, the precipitated germanium-containing compound may be separated from the liquid (hereinafter referred to as solid-liquid separation treatment). As the separation method, methods such as precipitation separation, reduced pressure filtration, and pressure filtration may be adopted. The separated germanium-containing compound is recovered, and the separated liquid is treated as waste liquid as needed.

[0072] The germanium-containing compound can also be subjected to a classification process of being divided into a coarse-grained grade and a micro-particle grade. As a classification process, a concentrator, a hydrocyclone, a centrifuge, etc. can be used. After being divided into the coarse-grained grade and the micro-particle grade, the coarse-grained grade can also be separated by solid-liquid separation by precipitation separation, vacuum filtration, pressure filtration, etc. to recover the coarse-grained grade of the germanium-containing compound. The liquid containing the micro-particle grade of the germanium-containing compound can also be returned to the above-mentioned precipitation process and mixed with the germanium extract for recycling. By returning the micro-particle grade of the germanium-containing compound after classification to the precipitation process for use, the micro-particle grade functions as a seed crystal when the germanium-containing compound is precipitated. Thus, the precipitation of the germanium compound can be induced, and the germanium dissolved in the germanium extract can be recovered with a high yield.

[0073] Here, refer to Figure 4 One aspect of the precipitation treatment and the solid-liquid separation treatment will be described. Figure 4 Schematically shows the precipitation process and the solid-liquid separation process. Figure 4, a precipitation tank 50 for implementing precipitation treatment, a filter press 60 for implementing solid-liquid separation treatment, a particle-level liquid containing storage tank 70 for storing a particle-level liquid containing the classified germanium-containing compound, i.e., a particle-level liquid containing liquid 72, and a waste liquid treatment device 80 for implementing the waste liquid treatment in the later stage are shown. The particle-level liquid containing storage tank 70, the precipitation tank 50, the filter press 60 and the waste liquid treatment device 80 are connected by a pipe for liquid infusion such as Figure 4 Connections shown.

[0074] The precipitation tank 50 includes a stirring blade 52, a germanium extract inlet (not shown), and a reagent inlet 56. In the precipitation process, the germanium extract is introduced into the precipitation tank 50 from the germanium extract inlet. Then, a metal salt such as magnesium chloride is introduced into the germanium extract through the reagent inlet 56, thereby precipitating a germanium-containing compound 62, and preparing a slurry 58 containing the germanium-containing compound 62.

[0075] In the solid-liquid separation process, the slurry 58 prepared in the precipitation tank 50 is pressure-filtered by the filter press 60, so that the germanium-containing compound 62 is separated from the liquid, and the germanium-containing compound 62 can be recovered. The separated liquid is transported to the waste liquid treatment equipment 80 as needed. It should be noted that before the slurry 58 is transported from the precipitation tank 50 to the filter press 60, a classification process can also be implemented to divide the germanium-containing compound into a coarse particle grade and a fine particle grade. The coarse particle grade liquid containing the germanium-containing compound 62 can also be transported to the filter press 60 for pressure filtration, and the fine particle grade liquid (fine particle grade containing liquid 72) containing the germanium-containing compound 62 is stored in the fine particle grade containing liquid storage tank 70. Then, in the precipitation process, the fine particle grade containing liquid 72 can also be supplied from the fine particle grade containing liquid storage tank 70 to the precipitation tank 50, and the fine particle grade can be flexibly used as a seed of the germanium-containing compound.

[0076] Next, refer to Figure 5 Another aspect of the precipitation treatment and the solid-liquid separation treatment will be described. Figure 5 Schematically shows the precipitation process and the solid-liquid separation process. Figure 5 , a germanium extract storage tank 140 for storing a germanium extract 142, an evaporator 150 for performing a precipitation process, and a filter press 160 for performing a solid-liquid separation process are shown. The germanium extract storage tank 140, the evaporator 150, and the filter press 160 are connected to each other through a pipe for infusion such as Figure 5 Connections shown.

[0077] The evaporator 150 receives the germanium extract 142 from the germanium extract storage tank 140, evaporates the liquid to prepare a concentrated solution 152, and precipitates the germanium-containing compound 162 (precipitation treatment). The germanium-containing compound 162 is separated from the liquid by conveying the liquid containing the precipitated germanium-containing compound 162 to the filter press 160, and the germanium-containing compound 162 can be recovered (solid-liquid separation treatment). The liquid separated in the solid-liquid separation treatment can also be returned to the germanium extract storage tank 140.

[0078] [Example]

[0079] Hereinafter, examples of the germanium recovery method according to the present disclosure will be described. It should be noted that the present disclosure is not limited to these examples.

[0080] (Example 1: Separation by wet capture device)

[0081] Germanium in the exhaust gas during the dehydration sintering process of the porous base material was recovered using a wet collection device. A bubbling scrubber was used as the wet collection device. The exhaust gas pipe discharged from the furnace core tube for manufacturing the optical fiber base material was connected to the scrubber, and the optical fiber base material was manufactured. In order to selectively process the exhaust gas containing germanium in the exhaust gas discharged in the manufacturing process, the valve was controlled so that the exhaust gas was introduced into the scrubber only when the porous base material was heated at a high temperature in the dehydration sintering process.

[0082] After a total of 1000 liters of exhaust gas generated in the dehydration sintering step was passed through the scrubber, the washing water in the scrubber was taken out, and 180 mg (based on the element) of germanium was recovered from the taken out washing water.

[0083] (Example 2: Separation by dry adsorption device)

[0084] The germanium in the exhaust gas during the sintering process was separated using a dry adsorption device equipped with an adsorbent. As the adsorbent, 60 kg of a zeolite-based adsorbent was used. The exhaust gas pipe discharged from the furnace core tube used to manufacture the optical fiber mother material was connected to the dry adsorption device, and the optical fiber mother material was manufactured. In order to selectively process the exhaust gas containing germanium and prevent the deterioration of the adsorbent, the valve was controlled so that the exhaust gas was introduced into the dry adsorption device only during the sintering process.

[0085] After one month of manufacturing the optical fiber base material, the adsorbent of the dry adsorption device was taken out and analyzed for components. As a result, it was found that 200 g (based on element conversion) of germanium could be separated.

[0086] The results of the above-mentioned examples also show that according to the method for recovering germanium according to the present disclosure, germanium can be recovered efficiently and inexpensively from exhaust gas in the dehydration sintering step of manufacturing an optical fiber preform.

[0087] Description of Reference Numerals

[0088] 10 Wet capture device

[0089] 11. Cleaning tower

[0090] 12. Washing water

[0091] 13 Nozzle

[0092] 20 Dry adsorption device

[0093] 21 Adsorbent

[0094] 30 Mixing tank

[0095] 31 Liquid

[0096] 32, 52 stirring blade

[0097] 40 Recovery tank

[0098] 50 Sedimentation Tank

[0099] 56 Reagent input port

[0100] 58 Slurry

[0101] 60, 160 filter press

[0102] 62, 162 Germanium-containing compounds

[0103] 70 Micronized liquid storage tank

[0104] 72 micron-level liquid

[0105] 80 Waste liquid treatment equipment

[0106] 140 Germanium Extract Storage Tank

[0107] 142 Germanium Extract

[0108] 150 Evaporator

[0109] 152 Concentrate.

Claims

1. A method for recovering germanium from exhaust gas in the manufacturing process of optical fiber mother material. The germanium recovery method includes a first step of passing the exhaust gas through a separation device to separate germanium from the exhaust gas. The exhaust gas is the gas exhausted in the dehydration sintering process of manufacturing the optical fiber base material.

2. The method for recovering germanium according to claim 1, wherein: The separation device is a wet capture device, In the first step, the exhaust gas is passed through the wet capture device to extract germanium into the liquid.

3. The method for recovering germanium according to claim 2, wherein: In the first step, the temperature of the liquid used for extracting germanium is 30° C. or higher and 80° C. or lower.

4. The method for recovering germanium according to claim 1, wherein: The separation device is a dry adsorption device equipped with an adsorbent, In the first step, germanium is adsorbed on the adsorbent. The method for recovering germanium further includes a second step of extracting the germanium adsorbed on the adsorbent into a liquid after the first step.

5. The method for recovering germanium according to claim 4, wherein: In the second step, at least one of the pH and the temperature of the liquid is adjusted to extract germanium into the liquid.

6. The method for recovering germanium according to claim 5, wherein: In the second step, the pH of the liquid is adjusted to 0 or more and 6 or less.

7. The method for recovering germanium according to claim 5 or 6, wherein: In the second step, the temperature of the liquid used for extracting germanium is 30° C. or higher and 80° C. or lower.

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