JP6652454B2 - Metal recovery method and metal recovery device - Google Patents

Description

  An embodiment of the present invention relates to a metal recovery method and a metal recovery apparatus.

  A fuel cell is a clean power generation device that generates power by reacting hydrogen and oxygen and does not generate carbon dioxide during power generation. In particular, polymer electrolyte fuel cells (PEFCs) have advantages over other types of fuel cells, such as low-temperature operation and easy downsizing. Therefore, PEFC is commercially available as a distributed power source for home use. Furthermore, the mounting of PEFC on a fuel cell vehicle is being studied, and there is a high possibility that PEFC will become more widely used than before.

  The PEFC includes a membrane electrode assembly (MEA: Membrane Electrode Assembly) as an electrode material. The MEA contains a transition metal such as Pt (platinum) as a catalyst component. Generally, the transition metal used for the catalyst component of the MEA has a small amount of resources and is expensive.

  Therefore, it has been studied to recover and recycle transition metals such as Pt used in the MEA from the MEA. For example, a method of recovering a transition metal from an MEA by applying a voltage to the MEA immersed in an acidic solution containing halide ions has been studied.

JP 2015-161019 A

  In the above method, when a voltage is applied to the MEA, a transition metal such as Pt contained in the MEA is dissolved in the solution as a transition metal complex ion. Thus, the transition metal used for the MEA is recovered. On the other hand, when the concentration of the transition metal complex ion contained in the solution increases, a part of the transition metal recovered from the MEA may adhere to the MEA again, and the efficiency of recovering the transition metal from the MEA may decrease.

  An object of the present invention is to provide a metal recovery method and a metal recovery apparatus that can efficiently recover transition metals from a fuel cell.

In the method for recovering metal according to the embodiment, a step of immersing the membrane electrode assembly of the fuel cell in a solution in which anion exchange resin is dispersed and containing halide ions and is acidic and immersed in the solution Applying a voltage to the membrane electrode assembly to recover the transition metal from the membrane electrode assembly into the solution.

  According to the embodiment, it is possible to provide a metal recovery method and a metal recovery apparatus capable of efficiently recovering transition metals from a fuel cell.

5 is a graph showing a relationship between the pH of the solution, the standard electrode potential of Pt, and the form of Pt in the solution in the embodiment. It is a graph which shows the relationship of the pH of the solution which does not contain a chloride ion, the standard electrode potential of Pt, and the form of Pt in a solution. It is the schematic which shows the collection | recovery apparatus of the metal of embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

  The metal recovery method according to the embodiment includes a step of immersing the membrane electrode assembly (MEA) of the fuel cell in a solution containing halide ions and an anion exchange resin and being acidic (hereinafter, also referred to as an immersion step). Applying a voltage to the MEA immersed in the solution to recover the transition metal from the MEA into the solution (hereinafter, also referred to as a recovery step).

  The immersion step will be described.

  In the immersion step, the MEA constituting the fuel cell is immersed in the solution.

  The fuel cell is a polymer electrolyte fuel cell (PEFC). PEFC includes MEA as an electrode material. The MEA is formed by stacking a catalyst layer containing a catalyst component, an electrolyte membrane made of an electrolyte material such as a fluoropolymer such as perfluorosulfonic acid, and a diffusion layer made of a carbon material such as carbon paper and carbon cloth. Be composed.

  Here, an example in which the fuel cell is a PEFC will be described. However, the fuel cell may be a fuel cell including an MEA, such as a direct methanol fuel cell (DMFC).

  A catalyst component is attached to the catalyst layer constituting the MEA. The catalyst component is composed of a transition metal or the like. The form of such a catalyst component is not particularly limited, and examples thereof include a single transition metal, a compound containing a transition metal, and an alloy containing a transition metal. The transition metal constituting the catalyst component generally has a low resource content and is expensive. Such a transition metal includes at least one metal selected from the group consisting of Pt (platinum), Ru (ruthenium), and Co (cobalt).

  The solution in which the MEA is immersed contains a halide ion and an anion exchange resin. Also, the lysis solution is acidic. This solution is a solid-liquid mixture in which an anion exchange resin is dispersed.

  The halide ion contained in the solution is preferably at least one ion selected from the group consisting of chloride ion, iodide ion, and bromide ion. From the viewpoint that Pt generally used as a transition metal constituting a catalyst component of a fuel cell can be efficiently recovered from MEA, halide ions are more preferably chloride ions. Examples of the solution containing chloride ions include an aqueous hydrochloric acid solution and an aqueous sodium chloride solution. As the halide ions, only one of the above-mentioned ions may be used alone, or two or more of them may be used in combination.

  The concentration of the halide ion in the solution is appropriately adjusted according to the type of the halide ion. The concentration of chloride ions in the solution is preferably from 0.01 mol / L to 16.0 mol / L, and more preferably from 1.0 mol / L to 5.0 mol / L. The concentration of iodide ions in the solution is preferably from 0.01 mol / L to 16.0 mol / L, more preferably from 1.0 mol / L to 5.0 mol / L. The concentration of bromide ions in the solution is preferably from 0.01 mol / L to 16.0 mol / L, and more preferably from 1.0 mol / L to 5.0 mol / L. When the halide ion concentration is equal to or higher than the above lower limit, the transition metal can be efficiently recovered from the MEA into the solution. Further, when the concentration of the halide ions is equal to or lower than the above upper limit, the consumption of the halide ions consumed in the electrolysis by applying a voltage can be reduced. The fact that the upper limit of the concentration of chloride ions in the solution is 16.0 mol / L is a theoretical limit value at which chloride ions are dissolved.

  Here, as described later, in the recovery step, the concentration of the halide ions in the solution decreases as the transition metal reacts with the halide ions in the solution. Therefore, unless otherwise specified, the concentration of the halide ion in the solution indicates the concentration of the halide ion in the solution during the immersion step.

  The pH of the solution is preferably 5 or less, more preferably 3 or less. When the pH of the acidic solution is within the above range, the transition metal can be efficiently dissolved in the solution in the recovery step. On the other hand, if the pH of the solution is higher than 5, it is not easy to dissolve the transition metal in the solution in the recovery step.

  The method for producing the solution is not particularly limited as long as it can produce an acidic solution containing a halide ion and an anion exchange resin. For example, a solution is produced by mixing and stirring an anion exchange resin with an acidic solution containing halide ions.

  The method of immersing the MEA in the solution is not particularly limited, and a part of the MEA may be immersed in the solution, or the entire MEA may be immersed in the solution. However, in any case, the connection portion between the terminal to which voltage is applied and the MEA and the terminal to which voltage is applied in the recovery step are not immersed in the solution. The temperature of the solution when the MEA is immersed in the solution is not particularly limited, for example, 25 ° C. which is a normal temperature.

  Next, the collecting step will be described.

  In the recovery step, a voltage is applied to the MEA immersed in the solution in the immersion step. Here, for the MEA immersed in the solution in the immersion step, a terminal for applying a voltage is connected to a portion not immersed in the solution while the MEA is partially immersed in the solution. When a voltage is applied to the MEA, the transition metal is dissolved in the solution from the portion of the MEA immersed in the solution, and the transition metal in the MEA is recovered in the solution. After recovery, the form of the transition metal dissolved in the solution is a complex ion (hereinafter also referred to as a transition metal complex ion).

  FIG. 1 is a graph showing the relationship between the pH of the solution, the standard electrode potential of Pt, and the form of Pt in the solution in the embodiment. Here, the solution in FIG. 1 contains chloride ions as halide ions, and the concentration of chloride ions in the solution is 1.0 mol / L. The temperature of the solution in FIG. 1 is 25 ° C.

  As shown in FIG. 1, in the solution containing chloride ions, when the pH of the solution is 5 or less and the standard electrode potential of Pt is 0.70 V or more, the following formulas (1) and (2) are used. The reaction takes place and platinum complex ions are easily generated. The details are as follows.

  Equation (1) is a reversible reaction. Then, when an oxidation potential of 0.70 V or more and 0.75 V or less is applied to Pt, the reaction from left to right in equation (1) proceeds. That is, when an oxidation potential in the above range is applied to Pt, Pt as a transition metal reacts with chloride ion as a halide ion, and tetrachloroplatinate (II) ion as a platinum complex ion is formed. Generated.

  Equation (2) is also a reversible reaction. Then, when an oxidation potential of 0.75 V or more is applied to Pt, the reaction proceeds from left to right in equation (2). That is, when an oxidation potential equal to or higher than the above value is applied to Pt, Pt reacts with chloride ions to generate hexachloroplatinate (IV) ions, which are platinum complex ions.

  Thus, Pt is dissolved as a complex ion in a solution containing chloride ions and is recovered in the solution.

  In general, when an oxidation potential is applied to a transition metal, a transition metal oxide is formed as a by-product in addition to a transition metal complex ion generation reaction as shown in the above formulas (1) and (2). A reaction occurs. The transition metal oxide generated as a by-product precipitates on a portion of the transition metal immersed in the solution and forms a passive film on the surface of the transition metal. For this reason, a reaction for generating a transition metal complex ion from the transition metal is inhibited, and the efficiency of recovering the transition metal into the solution may be reduced.

  When a reduction potential is applied to a transition metal having such a passivation film, the transition metal oxide is reduced and the passivation film is removed. Therefore, when the polarity of the voltage applied to the transition metal is periodically inverted, the formation of the passive film is suppressed. When the passivation film is removed from the surface of the transition metal, the recovery efficiency of the transition metal, which has been reduced by the formation of the passivation film, is restored.

  In this manner, from the viewpoint of suppressing the formation of the passivation film due to the transition metal oxide and maintaining the efficiency of recovery of the transition metal into the solution, the polarity of the voltage applied to the MEA including the transition metal in the recovery step. Is preferably inverted periodically. The ratio (a / b) of the time a during which the oxidation potential is applied to the MEA to the time b during which the reduction potential is applied to the MEA depends on the size of the MEA, the amount of the transition metal attached to the MEA, and the amount of the solution. It is appropriately selected according to the conditions.

  Here, a solution containing no halide ion will be described for reference. FIG. 2 is a graph showing the relationship between the pH of a solution containing no chloride ion, the standard electrode potential of Pt, and the form of Pt in the solution.

  As shown in FIG. 2, in the solution containing no chloride ion, when the standard electrode potential of Pt becomes a predetermined value or more, an oxide of Pt is generated, and no platinum complex ion is generated. Therefore, Pt does not dissolve in a solution containing no chloride ions.

  Further, the anion exchange resin dispersed in the solution captures the transition metal recovered in the solution from the MEA in the recovery step. Here, as shown in the above formulas (1) and (2), the form of the transition metal recovered in the solution in the recovery step is a complex ion. That is, the form of the transition metal collected by the anion exchange resin is a complex ion.

  The anion exchange resin is not particularly limited, and is appropriately selected according to the type of the transition metal, the type of the halide ion, the pH of the solution, and the like.

  The concentration of the anion exchange resin in the solution is appropriately adjusted according to the amount of the transition metal contained in the MEA. The concentration of the anion exchange resin in the solution is preferably from 0.1 wt% to 10.0 wt%, more preferably from 1.0 wt% to 5.0 wt%.

  When the transition metal is Pt, the complex ions collected by the anion exchange resin are tetrachloroplatinate (II) ion and hexachloroplatinate (IV) ion as shown in the formulas (1) and (2). Is at least one platinum complex ion.

  Here, when the anion exchange resin is not contained in the solution, the transition metal complex ions recovered in the solution increase with the lapse of the voltage application time to the MEA in the recovery step. Increase the concentration of the transition metal complex ion. When a reduction potential is applied to the MEA, the transition metal complex ions present in the vicinity of the MEA may be reduced, and the transition metal may be reprecipitated on the MEA. In this way, the transition metal dissolved in the solution and recovered from the MEA is taken into the MEA again. Therefore, as the voltage application time to the MEA increases, the recovery efficiency of the transition metal from the MEA decreases.

  On the other hand, when the anion exchange resin is contained in the solution, the anion exchange resin captures the transition metal complex ions contained in the solution, so that the increasing rate of the concentration of the transition metal complex ions contained in the solution is increased. Is suppressed. As compared with the case where the anion exchange resin is not contained in the solution, the amount of the transition metal complex ions present in the vicinity of the MEA is reduced. Therefore, even if the reduction potential is applied to the MEA, the amount of the transition metal reprecipitated in the MEA is reduced. Few. Therefore, even if the time for applying the voltage to the MEA increases, the decrease in the recovery efficiency of the transition metal from the MEA is suppressed.

  As described above, when the anion exchange resin is contained in the solution together with the transition metal complex ions recovered from the MEA, the anion exchange resin suppresses an increase in the concentration of the transition metal complex ions contained in the solution. Therefore, an improvement in the recovery rate of the transition metal, a reduction in the recovery time of the transition metal, a reduction in the amount of the solution used, and the like can be achieved.

  The transition metal recovered in the solution by the recovery step can be reused by a known method. For example, by performing a separation treatment such as sedimentation separation or filtration separation on a solution containing the transition metal captured by the anion exchange resin, the anion exchange resin capturing the transition metal is recovered. You. Subsequently, the transition metal adsorbed on the anion exchange resin is desorbed from the anion exchange resin by washing the anion exchange resin. Thus, the anion exchange resin can be reused. The transition metal desorbed from the anion exchange resin can be reused by performing a known treatment depending on a desired use. The transition metal desorbed from the anion exchange resin can be sold to a recycler without any treatment.

  Further, since the solution obtained in the recovery step contains a large amount of expensive transition metal, it can be sold to a recycler or the like without performing the above treatment.

  Next, a metal recovery device according to an embodiment will be described. FIG. 3 is a schematic diagram showing the metal recovery apparatus 1 according to the embodiment. The metal recovery apparatus 1 is an apparatus that can perform the metal recovery method of the above-described embodiment. FIG. 3 shows a partial cross section for convenience of explanation.

  As shown in FIG. 3, the metal recovery apparatus 1 includes a storage unit 2 that stores an acidic solution 20 containing halide ions and an anion exchange resin and is immersed in the solution 20 in the storage unit 2. And a voltage application unit 3 for applying a voltage to the MEA 30 of the fuel cell.

  The storage unit 2 stores the solution 20. In addition, in addition to the MEA 30, an electrode 40, which is a counter electrode of the MEA 30, and a reference electrode 50 for measuring a voltage applied to the MEA 30 are immersed in the solution 20 in the storage unit 2. The MEA 30, the electrode 40, and the reference electrode 50 are connected to the voltage applying unit 3, respectively.

  The voltage application unit 3 applies a predetermined voltage to the MEA 30 including the transition metal and the electrode 40. It is preferable that the voltage application unit 3 periodically reverses the polarity of the voltage applied to the MEA 30 and the polarity of the voltage applied to the electrode 40.

  The electrode 40 is insoluble in the solution 20 and is made of a conductive material. The electrode 40 may be another MEA different from the MEA 30. The reference electrode 50 is an electrode for measuring the standard electrode potential of the MEA 30 applied to the MEA 30. Examples of the reference electrode 50 include a standard hydrogen electrode.

  Then, when a voltage is applied to the MEA 30 from the voltage application unit 3, the transition metal in the MEA 30 is dissolved in the solution 20 as transition metal complex ions. The transition metal complex ions are collected by the anion exchange resin in the solution 20. Thus, the transition metal contained in the MEA 30 constituting the fuel cell is recovered.

  After recovering the transition metal from the MEA 30, the MEA 30 from which the transition metal has been recovered and the MEA from which the transition metal has not been recovered are exchanged. Then, the unrecovered transition metal is recovered from the MEA by the metal recovery device 1. At this time, the used dissolving solution 20 from which the transition metal has been recovered may be exchanged for an unused dissolving solution from which the transition metal has not been recovered, or the used dissolving solution 20 from which the transition metal has been recovered may be used. You may continue.

  As shown in FIG. 3, the metal recovery device 1 includes a tank unit 4 connected to the storage unit 2, a gas-liquid separation unit 5 connected to the tank unit 4, and a tank unit connected to the gas-liquid separation unit 5. 6, a stirring member 6a provided in the tank section 6, a pump section 7 connected to the tank section 6, and a tank section 8 connected to the pump section 7 and the storage section 2.

  The tank section 4 connected to the storage section 2 and the gas-liquid separation section 5 discharges the dissolved liquid 20 flowing from the storage section 2 to the gas-liquid separation section 5. The gas-liquid separation unit 5 connected to the tank unit 4 and the tank unit 6 separates a liquid phase composed of the solution 20 and a gas phase composed of gases such as hydrogen, chlorine, and oxygen contained in the solution 20. The liquid and gas phases are stored. The gas phase part is stored in the upper part in the gas-liquid separation unit 5, and the liquid phase part is stored below the gas phase part. The tank section 6 connected to the liquid phase portion of the gas-liquid separation section 5 and the pump section 7 stores the dissolved liquid 20 flowing from the gas-liquid separation section 5. The stirring member 6 a provided in the tank 6 stirs the solution 20 stored in the tank 6 and disperses the anion exchange resin in the solution 20. The pump section 7 connected to the tank section 6 and the tank section 8 sucks the solution 20 in the tank section 6 and discharges the solution 20 to the tank section 8 to discharge the solution 20 in the metal recovery device 1. Circulate. The tank section 8 connected to the pump section 7 and the storage section 2 discharges the solution 20 supplied from the pump section 7 to the storage section 2.

  Further, as shown in FIG. 3, the metal recovery device 1 may include an exhaust unit 9 connected to the gas-liquid separation unit 5. The exhaust unit 9 exhausts the gas phase separated from the solution 20 in the gas-liquid separation unit 5 to the outside of the metal recovery device 1. For example, the exhaust unit 9 is connected to the upper side of the gas-liquid separator 5, and the gas phase stored on the upper side of the gas-liquid separator 5 is supplied to the exhaust unit 9.

  The flow of the solution 20 in the metal recovery device 1 will be described.

  The solution 20 accommodated in the tank 6 is stirred by the stirring member 6 a, and the anion exchange resin is uniformly dispersed in the solution 20. The solution 20 in the tank 6 is supplied from the tank 6 to the storage 2 via the tank 8 by the pump 7.

  In the storage unit 2, the transition metal in the MEA 30 is dissolved in the solution 20 as a transition metal complex ion by the voltage applied to the MEA 30 from the voltage application unit 3. The transition metal complex ions are collected by the anion exchange resin in the solution 20. Thus, the transition metal contained in the MEA 30 constituting the fuel cell is recovered.

  The solution 20 containing the anion exchange resin capturing the transition metal complex ions is discharged to the gas-liquid separation unit 5 via the tank unit 4. In the gas-liquid separation section 5, the gas phase contained in the solution 20 is separated from the solution 20. The gas phase separated from the solution 20 is discharged to the exhaust unit 9. The solution 20 from which the gas phase has been separated is discharged to the tank 6.

  After recovering the transition metal from the MEA 30, the pump unit 7 is stopped to stop the circulation of the solution 20. The MEA 30 from which the transition metal has been recovered is replaced with an MEA from which the transition metal has not been recovered. The anion exchange resin that has captured the transition metal complex ions is discharged from the tank unit 6 to the outside of the metal recovery device 1 through a drain port (not shown) provided in the tank unit 6. Thus, the anion exchange resin that has captured the transition metal complex ions is recovered.

  As described above, according to the metal recovery method and the metal recovery apparatus of the embodiment, the transition metal complex ions dissolved from the MEA of the fuel cell are collected by the anion exchange resin contained in the solution. The anion exchange resin suppresses an increase in the concentration of the transition metal complex ion contained in the solution and keeps the concentration of the transition metal complex ion low, so that the transition metal complex ion contained in the solution is reprecipitated on the MEA. Is suppressed. Therefore, transition metals constituting the catalyst component of the fuel cell can be efficiently recovered from the fuel cell.

  Although several embodiments of the present invention have been described, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

  DESCRIPTION OF SYMBOLS 1 ... Metal recovery apparatus, 2 ... Storage part, 3 ... Voltage application part, 4, 6, 8 ... Tank part, 5 ... Gas-liquid separation part, 6a ... Stirring member, 7 ... Pump part, 9 ... Exhaust part, 20 ... dissolution solution, 30 ... MEA, 40 ... electrode, 50 ... reference electrode.

Claims (7)

A step of immersing the membrane electrode assembly of the fuel cell in an acidic solution containing halide ions in which an anion exchange resin is dispersed ,
Applying a voltage to the membrane electrode assembly immersed in the solution to recover the transition metal from the membrane electrode assembly into the solution.   The metal recovery method according to claim 1, wherein the pH of the solution is 5 or less.   3. The method according to claim 1, wherein in the step of immersing the membrane electrode assembly, the concentration of the halide ion in the solution is 0.01 mol / L or more and 16.0 mol / L or less. 4.   4. The method according to claim 1, wherein in the step of recovering the transition metal, the polarity of a voltage applied to the membrane electrode assembly is periodically inverted. 5.   The method for recovering a metal according to claim 1, wherein the transition metal is at least one metal selected from the group consisting of Pt, Ru, and Co.   The method for recovering a metal according to any one of claims 1 to 5, wherein the halide ion is a chloride ion. A storage section in which an anion exchange resin is dispersed and stores an acidic solution containing halide ions ,
And a voltage application unit for applying a voltage to the membrane electrode assembly of the fuel cell immersed in the solution in the storage unit.

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