Germanium recovery method

Abstract

To provide a germanium recovery method capable of recovering germanium efficiently at a low cost when manufacturing an optical fiber.SOLUTION: A germanium recovery method recovers germanium from an exhaust gas in a manufacturing process of an optical fiber preform. The method includes a first step of causing the exhaust gas to pass through a separation unit to separate the germanium from the exhaust gas. The exhaust gas is a gas emitted at a dewatering-sintering step when manufacturing the optical fiber preform.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Germanium is used as a raw material for various industrial products, such as semiconductor materials for diodes and additives for cores in glass optical fibers. The price of germanium has been rising in recent years. Therefore, for example, Patent Documents 1 to 3 disclose techniques for recovering germanium. Patent Document 1 discloses a technique for recovering germanium oxide, which is volatilized in the dehydration and sintering process during transparent vitrification, as metallic germanium using a reducing agent. Patent Document 2 discloses a technique for recovering germanium-containing particles with a bag filter in the deposition process of a porous base material and reusing them in the optical fiber manufacturing process. Patent Document 3 discloses a technique for removing and recovering germanium in a waste liquid treatment process by contacting a chelating fiber with a germanium-containing aqueous solution adjusted to a pH of 3 to 12 in a waste liquid treatment process. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 58-213838 [Patent Document 2] JP 2004-2088 A [Patent Document 3] JP 2017-140571 A Summary of the Invention [Problem to be solved by the invention]

[0004] During the manufacture of optical fiber, a 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 treated in the subsequent exhaust gas treatment and wastewater treatment processes, and is finally discharged together with silicon oxide as sludge. Although techniques for recovering germanium at each process of optical fiber manufacturing have been disclosed, it has not been easy to recover germanium efficiently and inexpensively. In Patent Document 1, carbon is used as a reducing agent, which generates toxic carbon monoxide. In Patent Document 2, a large amount of gas is treated, and the equipment becomes large. In the method using chelating fiber shown in Patent Document 3, the equipment is expensive.

[0005] An object of the present disclosure is to provide a germanium recovery method capable of recovering germanium efficiently and inexpensively during the manufacture of optical fibers. [Means for solving the problem]

[0006] The method for recovering germanium according to the present disclosure comprises the steps of: A method for recovering germanium from exhaust gas in a manufacturing process of an optical fiber preform, comprising the steps of: a first step of passing the exhaust gas through a separator to separate germanium from the exhaust gas; The exhaust gas is a gas that is exhausted during a dehydration and sintering process in the manufacture of an optical fiber preform. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a germanium recovery method that can efficiently and inexpensively recover germanium during the manufacture of optical fibers. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a flow of a method for recovering germanium according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram illustrating a first step according to a first aspect of an embodiment of the present disclosure. [Diagram 3]FIG. 3 is a diagram illustrating a first step and a second step according to a second aspect of an embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram showing a schematic diagram of an example of a process for treating a germanium extract. [Diagram 5] FIG. 5 is a diagram showing a schematic diagram of another example of the process for treating a germanium extract. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. A method for recovering germanium according to one embodiment of the present disclosure includes the steps of: (1) A method for recovering germanium from exhaust gas in a manufacturing process of an optical fiber preform, comprising the steps of: a first step of passing the exhaust gas through a separator to separate germanium from the exhaust gas; The exhaust gas is a gas that is exhausted during a dehydration and sintering process in the manufacture of an optical fiber preform.

[0010] According to the above-described germanium recovery method, germanium can be recovered using small-sized, inexpensive recovery equipment.

[0011] (2) In the above (1) method for recovering germanium, the separation device is a wet-type collection device, In the first step, the exhaust gas may be passed through the wet collector to extract germanium into a liquid.

[0012] By using a wet collector as the separation device, germanium can be recovered even if the exhaust gas contains dehydrated gases such as chlorine gas.

[0013] (3) In the method for recovering germanium described above in (2), the temperature of the liquid used for extracting germanium may be 30°C or higher and 80°C or lower.

[0014] By adjusting the temperature of the liquid, the concentration of germanium in the liquid can be increased, which can reduce costs such as transportation costs and regeneration costs when recycling recovered germanium.

[0015] (4) In the method for recovering germanium according to (1) above, The separation device is a dry adsorption device including an adsorbent; In the first step, germanium is adsorbed onto the adsorbent, The method for recovering germanium may further include, after the first step, a second step of extracting the germanium adsorbed to the adsorbent into a liquid.

[0016] By adopting a dry adsorption device as the separation device, the flexibility of the equipment is increased and operation becomes easier.

[0017] (5) In the method for recovering germanium according to (4) above, In the second step, germanium may be extracted into the liquid by adjusting at least one of the pH and the temperature of the liquid.

[0018] By adjusting the pH or temperature of the liquid, germanium can be extracted into the liquid efficiently and at low cost.

[0019] (6) In the method for recovering germanium according to (5) above, In the second step, the pH of the liquid may be adjusted to 0 or more and 6 or less.

[0020] By making the liquid acidic, germanium can be extracted efficiently.

[0021] (7) In the method for recovering germanium according to (5) or (6) above, In the second step, the liquid used for extracting germanium may have a temperature of 30°C or higher and 80°C or lower.

[0022] By adjusting the temperature of the liquid, the concentration of germanium in the liquid can be increased, which can reduce costs such as transportation costs and regeneration costs when recycling recovered germanium.

[0023] [Details of the embodiment of the present disclosure] Hereinafter, specific examples of the germanium recovery method of the present disclosure will be described with reference to the drawings. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0024] 1 is a diagram showing the flow of the optical fiber manufacturing process and the germanium recovery method according to the present embodiment. The optical fiber manufacturing process includes a porous preform manufacturing process AS1, a dehydration and sintering process AS2, and a fiber drawing process AS3. The germanium recovery method according to the present embodiment includes a first step S11 of separating germanium from the exhaust gas discharged from the furnace tube in the dehydration and sintering process AS2.

[0025] The porous preform manufacturing process AS1 is a process for manufacturing a porous glass preform for optical fiber by the OVD method, the VAD method, etc. The main component of the porous preform is silica, and germanium is added to the core.

[0026] The porous preform obtained in the porous preform manufacturing process AS1 is then dehydrated and made transparent in the dehydration and sintering process AS2. In the dehydration and sintering process AS2, the porous preform is first dehydrated using a gas having a dehydrating effect such as chlorine gas, and then sintered using helium gas or the like to make it transparent, thereby obtaining an optical fiber preform.

[0027] The optical fiber preform obtained by the transparentization in the dehydration and sintering step AS2 is then drawn in the drawing step AS3. By drawing the optical fiber preform, an optical fiber is obtained as a product.

[0028] As mentioned above, germanium is added to the porous base material as an additive. However, some of the germanium supplied in the porous base material manufacturing process AS1 is discharged with the exhaust gas without being added to the porous glass base material. In the subsequent dehydration and sintering process AS2, some of the germanium in the porous base material volatilizes due to high temperature heating and is discharged with the exhaust gas.

[0029] Since germanium is expensive, it is desirable to recover germanium contained in exhaust gas. Here, recovery of germanium from exhaust gas discharged in the porous base material manufacturing process AS1 can be considered. However, the flow rate of exhaust gas in the porous base material manufacturing process AS1 is very large, and the exhaust gas contains a large amount of solid matter other than germanium, such as silica. Therefore, there is a concern that the equipment for recovering germanium will become large and the recovery efficiency will decrease.

[0030] Therefore, the germanium recovery method according to the present embodiment recovers germanium from the exhaust gas discharged in the dehydration and sintering step AS2 of the optical fiber preform manufacturing. More specifically, the germanium recovery method according to the present embodiment includes a first step of passing the exhaust gas discharged in the dehydration and sintering step AS2 through a separator to separate germanium from the exhaust gas. Since the exhaust gas in the dehydration and sintering step AS2 has a smaller gas flow rate than the porous preform manufacturing step AS1, germanium can be recovered by a small and inexpensive recovery facility. Furthermore, since the exhaust gas from the dehydration and sintering step AS2 contains a small amount of solids, it is possible to avoid a decrease in recovery efficiency due to accumulation of solids in the separator.

[0031] (First embodiment: Separation by wet collector) In the first aspect of this embodiment, the separation device may be a wet collector 10. FIG. 2 is a diagram showing a first step using the wet collector 10. As the wet collector 10, various scrubbers and the like can be adopted. The wet collector 10 shown in FIG. 2 includes a scrubber 11, washing water 12, and a nozzle 13 for spraying the washing water 12. In the first step of this embodiment, the exhaust gas discharged from the furnace tube in which the dehydration and sintering step AS2 is performed is first introduced into the washing tower 11 of the wet collector 10. Next, the washing water 12 is sprayed from the nozzle 13 provided at the top of the washing tower 11, and germanium contained in the exhaust gas in the gas phase is transferred to the washing water 12 in the liquid phase. This allows germanium to be separated from the exhaust gas and extracted into the washing water 12. The washing water 12 containing germanium is sent to the recovery tank 40 when it reaches a predetermined standard determined based on the operation time, concentration, and the like. The exhaust gas from which germanium has been separated is sent from the top of the scrubbing tower 11 to an exhaust gas treatment device, where it is treated by a predetermined method (exhaust gas treatment step BS1).

[0032] This embodiment using the wet collector 10 as a separation device can be suitably adopted when the exhaust gas contains dehydrated gas, for example, during the dehydration process or immediately after the dehydration process. In the dehydration process, a dehydrated gas such as chlorine gas is supplied into the furnace tube. Therefore, if germanium is to be separated from the exhaust gas in the dehydration process using an adsorbent, the dehydrated gas contained in the exhaust gas will cause the adsorbent to deteriorate, shortening its lifespan. Therefore, when the exhaust gas contains dehydrated gas, germanium can be recovered while avoiding deterioration of the equipment by using the wet collector as a separation device.

[0033] In this embodiment, the temperature of the cleaning water 12 is preferably 30° C. or more and 80° C. or less. When the temperature of the cleaning water 12 is in this range, germanium can be contained in the cleaning water 12 at a high concentration, and costs such as transportation costs and regeneration costs when recycling the recovered germanium can be reduced.

[0034] (Second embodiment: Separation by dry adsorption device) In a second embodiment, which is another aspect of this embodiment, the separation device can be a dry adsorption device 20. Fig. 3 is a schematic diagram showing a first step using the dry adsorption device 20 and a second step, which will be described later. The dry adsorption device 20 includes an adsorbent 21.

[0035] The adsorbent 21 is not particularly limited as long as it can adsorb germanium, and for example, a zeolite-based adsorbent or activated carbon can be used. The shape of the adsorbent 21 is not particularly limited, and pellets or beads can be used, but the adsorbent 21 is preferably in pellet form.

[0036] In the first step of this embodiment, first, exhaust gas discharged from a furnace tube performing the dehydration and sintering step AS2 is introduced into a dry adsorption device 20. The introduced exhaust gas passes through an adsorbent 21, and germanium contained in the exhaust gas is adsorbed by the adsorbent 21. This makes it possible to separate germanium from the exhaust gas. The exhaust gas from which germanium has been separated is sent from the dry adsorption device to an exhaust gas treatment device and treated by a predetermined method (exhaust gas treatment step BS1).

[0037] The method for recovering germanium according to this embodiment using the dry adsorption device 20 further includes a second step of extracting the germanium adsorbed in the adsorbent 21 into the liquid 31 in the mixing tank 30 after the first step. When extracting germanium into the liquid 31 in the second step, the adsorbent 21 may be directly charged into the mixing tank 30 containing the liquid 31, or the adsorbent 21 may be placed in a mesh container made of resin and then the mesh container may be charged into the mixing tank 30. After the adsorbent 21 is charged, the adsorbent 21 is stirred using a stirring blade 32 or the like to sufficiently extract the germanium into the liquid 31. For example, water is used as the liquid 31. After the germanium is extracted, the adsorbent 21 is removed from the mixing tank 30 by settling or removing the mesh container. The liquid 31 from which the germanium has been extracted is sent to the recovery tank 40.

[0038] In the second step of this embodiment, it is preferable 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 preferable to adjust the pH of the liquid 31 to 0 or more and 6 or less. By making the liquid acidic, germanium can be extracted efficiently. It is also preferable to adjust the temperature of the liquid 31 to 30°C or more and 80°C or less. By adjusting the temperature of the liquid, the concentration of germanium in the liquid can be increased, and costs such as transportation costs and regeneration costs when recycling the recovered germanium can be reduced.

[0039] Dry adsorption devices are easy to install, and have a higher degree of freedom in terms of equipment compared to wet collection devices, such as the ability to select the adsorption capacity. Therefore, by using a dry adsorption device as a separation device, it is possible to reduce the size of the device and reduce costs. However, as described above, it is preferable to use a wet collection device when separating exhaust gas in the dehydration process. It is also possible to configure the exhaust gas introduction destination to be switched during the dehydration and sintering process, so that the wet collection device is used as the separation device during the dehydration process and the dry adsorption device is used during the sintering process.

[0040] (Treatment of germanium extract) A liquid in which germanium is extracted (hereinafter referred to as germanium extract) is obtained by the first step in the embodiment using a wet collector, or the second step in the embodiment using a dry adsorption device. The germanium extract is appropriately subjected to an extract treatment S2, and germanium is recovered. In the germanium recovery method of the present disclosure, the specific method of the extract treatment S2 is not particularly limited, but an example of the extract treatment S2 will be described below.

[0041] When solid residue is generated in the germanium extract, a process for separating the germanium extract from the solid residue may be performed in the extract treatment S2. As a method for separating the germanium extract from the solid residue, methods such as sedimentation, reduced pressure filtration, and pressure filtration can be used.

[0042] In the extraction solution treatment S2, a treatment for precipitating a germanium-containing compound from the germanium extraction solution (hereinafter, referred to as a precipitation treatment) may be performed. In the precipitation treatment, the germanium extraction solution may be concentrated or a metal salt may be added to the germanium extraction solution to precipitate the germanium-containing compound from the germanium extraction solution. In the precipitation treatment, the germanium extraction solution may be concentrated or a metal salt may be added to the germanium extraction solution to cause coprecipitation, thereby efficiently precipitating the germanium-containing compound by inexpensive means.

[0043] When a metal salt is added in the precipitation treatment, a soluble metal salt that forms a composite oxide with germanium or a sparingly soluble metal salt that adsorbs germanium may be added. When a soluble metal salt is added, germanium dissolved in the germanium extract can be recovered in high yield as a composite oxide with the added metal. When a sparingly soluble metal salt is added, germanium can be collected on the surface of the sparingly soluble metal salt to precipitate a germanium-containing compound, and germanium dissolved in the germanium extract can be recovered in high yield.

[0044] When a metal salt is added in the precipitation treatment, an alkaline earth metal salt may be added. By adding an alkaline earth metal salt, the germanium-containing compound can be favorably precipitated, and the germanium dissolved in the germanium extract can be recovered with a high yield. Examples of alkaline earth metal salts include magnesium chloride, magnesium sulfate, and calcium chloride. The amount of alkaline earth metal added may be 0.8 equivalents or more and 3.0 equivalents or less relative to the germanium equivalent in the liquid. By adding an alkaline earth metal salt in the above amount, not only the composite oxide containing germanium and alkaline earth metal in an equivalent ratio of 1:1 can be produced, but also the composite oxide containing a large amount of alkaline earth metal in the equivalent ratio can be produced, and the germanium dissolved in the germanium extract can be recovered with a high yield.

[0045] After the above-mentioned precipitation treatment, a treatment for separating the precipitated germanium-containing compound from the liquid (hereinafter referred to as solid-liquid separation treatment) may be performed. As a method for separation, a method such as sedimentation, reduced pressure filtration, or pressure filtration can be adopted. The separated germanium-containing compound is collected, and the separated liquid is treated as waste liquid as necessary.

[0046] The germanium-containing compound may be subjected to a classification process to separate the germanium-containing compound into a coarse particle fraction and a fine particle fraction. As the classification process, a thickener, a liquid cyclone, a centrifuge, etc. may be used. After the coarse particle fraction and the fine particle fraction are separated, the coarse particle fraction may be solid-liquid separated by a method such as settling, reduced pressure filtration, or pressure filtration to recover the coarse particle fraction of the germanium-containing compound. The liquid containing the fine particle fraction of the germanium-containing compound may be returned to the above-mentioned precipitation process and mixed with the germanium extract for recycling. By returning the classified fine particle fraction of the germanium-containing compound to the precipitation process and using it, the fine particle fraction functions as a seed crystal when precipitating the germanium-containing compound. This can induce the precipitation of the germanium compound, and the germanium dissolved in the germanium extract can be recovered at a high yield.

[0047] Here, one embodiment of the precipitation treatment and the solid-liquid separation treatment will be described with reference to FIG. 4. FIG. 4 is a diagram showing the precipitation treatment and the solid-liquid separation treatment. In FIG. 4, a precipitation tank 50 for carrying out the precipitation treatment, a filter press 60 for carrying out the solid-liquid separation treatment, a fine particle-containing liquid stock tank 70 for storing a fine particle-containing liquid 72 which is a liquid containing fine particles of the classified germanium-containing compound, and a waste liquid treatment facility 80 for carrying out the waste liquid treatment at the latter stage are shown. The fine particle-containing liquid stock tank 70, the precipitation tank 50, the filter press 60 and the waste liquid treatment facility 80 are connected by a liquid delivery pipe as shown in FIG. 4.

[0048] The precipitation tank 50 is equipped with an agitator blade 52, a germanium extracting solution inlet (not shown), and a reagent inlet 56. In the precipitation process, the germanium extracting solution is introduced into the precipitation tank 50 from the germanium extracting solution inlet. Then, a metal salt such as magnesium chloride is introduced into the germanium extracting solution through the reagent inlet 56, whereby a germanium-containing compound 62 is precipitated, and a slurry 58 containing the germanium-containing compound 62 is prepared.

[0049] In the solid-liquid separation process, the slurry 58 prepared in the precipitation tank 50 is filtered under pressure by the filter press 60, so that the germanium-containing compound 62 and the liquid are separated, and the germanium-containing compound 62 can be recovered. The separated liquid is transported to a waste liquid treatment facility 80 as necessary. Note that before the slurry 58 is transported from the precipitation tank 50 to the filter press 60, a classification process may be performed to separate the germanium-containing compound into coarse particles and fine particles. The liquid containing the coarse particles of the germanium-containing compound 62 may be transported to the filter press 60 and filtered under pressure, and the liquid containing the fine particles of the germanium-containing compound 62 (fine particle-containing liquid 72) may be stored in a fine particle-containing liquid stock tank 70. In the precipitation process, the fine particle-containing liquid 72 may be supplied from the fine particle-containing liquid stock tank 70 to the precipitation tank 50, and the fine particles may be used as seed crystals of the germanium-containing compound.

[0050] Next, another embodiment of the precipitation treatment and the solid-liquid separation treatment will be described with reference to FIG. 5. FIG. 5 is a diagram showing the precipitation treatment and the solid-liquid separation treatment. In FIG. 5, a germanium extract stock tank 140 for storing a germanium extract 142, an evaporator 150 for carrying out the precipitation treatment, and a filter press 160 for carrying out the solid-liquid separation treatment are shown. The germanium extract stock tank 140, the evaporator 150, and the filter press 160 are connected by a liquid delivery pipe as shown in FIG. 5.

[0051] The evaporator 150 receives the germanium extract 142 from the germanium extract stock tank 140, evaporates the liquid to prepare a concentrated liquid 152, and precipitates the germanium-containing compound 162 (precipitation process). The liquid containing the precipitated germanium-containing compound 162 is transported to a filter press 160, and the germanium-containing compound 162 is separated from the liquid, so that the germanium-containing compound 162 can be recovered (solid-liquid separation process). The liquid separated in the solid-liquid separation process may be returned to the germanium extract stock tank 140. EXAMPLES

[0052] Hereinafter, examples of the germanium recovery method according to the present disclosure will be described. Note that the present disclosure is not limited to these examples.

[0053] (Example 1: Separation using a wet collector) A wet collector was used to recover germanium in the exhaust gas during the dehydration and sintering process of the porous preform. A bubbling-type scrubber was used as the wet collector. The piping for the exhaust gas discharged from the furnace tube for manufacturing the optical fiber preform was connected to the scrubber, and the optical fiber preform was manufactured. In order to selectively treat the exhaust gas containing germanium from the exhaust gas discharged during the manufacturing process, a valve was controlled so that the exhaust gas was introduced into the scrubber only when the porous preform was being heated at a high temperature during the dehydration and sintering process.

[0054] A total of 1,000 liters of exhaust gas generated in the dehydration and sintering process was passed through a scrubber, and the washing water in the scrubber was taken out. 180 mg (elemental equivalent) of germanium was recovered from the washing water.

[0055] (Example 2: Separation using a dry adsorption device) A dry adsorption device equipped with an adsorbent was used to separate germanium from the exhaust gas during the sintering process. 60 kg of a zeolite-based adsorbent was used as the adsorbent. The exhaust gas piping from the furnace tube used to manufacture the optical fiber preform was connected to the dry adsorption device, and the optical fiber preform was manufactured. In order to selectively treat the exhaust gas containing germanium and prevent deterioration of the adsorbent, a valve was controlled so that the exhaust gas was introduced into the dry adsorption device only during the sintering process.

[0056] After one month of manufacturing the optical fiber preform, the adsorbent was removed from the dry adsorption device and its components were analyzed, revealing that 200 g (in elemental terms) of germanium had been separated.

[0057] As shown by the results of the above examples, the method for recovering germanium according to the present disclosure makes it possible to efficiently and inexpensively recover germanium from the exhaust gas in the dehydration and sintering step of manufacturing an optical fiber preform. [Explanation of symbols]

[0058] 10 Wet collection device 11 Washing tower 12 Washing water 13 Nozzle 20 Dry adsorption device 21 Adsorbents 30 Mixing tank 31 liquid 32,52 Stirring blade 40 Recovery Tank 50 Precipitation tank 56 Reagent inlet 58 Slurry 60,160 Filter Press 62,162 Germanium-containing compounds 70 Storage tank for liquid containing fine particles 72 Liquid containing fine particles 80 Waste liquid treatment equipment 140 Germanium Extraction Solution Stock Tank 142 Germanium Extract 150 Evaporator 152 Concentrate

Claims

1. A method for recovering germanium from exhaust gas in a manufacturing process of an optical fiber preform, comprising the steps of: a first step of passing the exhaust gas through a separator to separate germanium from the exhaust gas; The exhaust gas is a gas exhausted in a dehydration and sintering process of manufacturing an optical fiber preform. How to recover germanium.

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

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

4. The separation device is a dry adsorption device including an adsorbent; In the first step, germanium is adsorbed onto the adsorbent, After the first step, the method further includes a second step of extracting the germanium adsorbed on the adsorbent into a liquid. The method for recovering germanium according to claim 1.

5. The method for recovering germanium according to claim 4, wherein in the second step, germanium is extracted into the liquid by adjusting at least one of the pH and the temperature of 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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