JP2017226895A - Method for recovering metal, and metal recovery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering a metal(s) and a metal recovery device capable of efficiently recovering a transition metal(s) from a fuel battery.SOLUTION: Provided is a method for recovering a metal(s) comprising: a step where a membrane electrode joined body of a fuel battery is immersed into an acidic solution comprising halide ions and an anion exchange resin; and a step where voltage is applied to the membrane electrode joined body immersed into the solution, and a transition metal(s) is recovered from the membrane electrode joined body to the solution.SELECTED DRAWING: Figure 3

Description

  Embodiments described herein relate generally to a metal recovery method and a metal recovery apparatus.

  A fuel cell is a clean power generator that generates power by reacting hydrogen with oxygen and does not generate carbon dioxide during power generation. In particular, the polymer electrolyte fuel cell (PEFC) has advantages such as being operable at a low temperature and being easily miniaturized as compared with other types of fuel cells. Therefore, PEFC is commercially available as a home-use distributed power source. Furthermore, PEFC is also being considered for use in fuel cell vehicles, and is likely to be more widely used.

  The PEFC includes a membrane electrode assembly (MEA) as an electrode material. The MEA contains a transition metal such as Pt (platinum) as a catalyst component. In general, transition metals used for the catalyst component of MEA have a small amount of resources and are expensive.

  Therefore, recovery of transition metals such as Pt used for MEA from MEA is being studied. For example, a method for recovering a transition metal from an MEA by applying a voltage to an MEA immersed in an acidic solution containing halide ions has been studied.

Japanese Patent Laying-Open No. 2015-161019

  Regarding the above method, when a voltage is applied to the MEA, a transition metal such as Pt contained in the MEA is dissolved into the solution as a transition metal complex ion. Thus, the transition metal used for 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 recovery efficiency of the transition metal from the MEA may decrease.

  The problem to be solved by the present invention is to provide a metal recovery method and a metal recovery device capable of efficiently recovering a transition metal from a fuel cell.

  The metal recovery method according to the embodiment includes a step of immersing a membrane electrode assembly of a fuel cell in a solution that contains halide ions and an anion exchange resin and is acidic, and is immersed in the solution. Applying a voltage to the membrane electrode assembly, and recovering 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 a transition metal from a fuel cell.

It is a graph which shows the relationship between the pH of the solution in embodiment, the standard electrode potential of Pt, and the form of Pt in a solution. It is a graph which shows the relationship between 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 of the embodiment includes a step of immersing a membrane electrode assembly (MEA) of a fuel cell in an acidic solution containing halide ions and an anion exchange resin (hereinafter also referred to as an immersion step). And a step of applying a voltage to the MEA immersed in the solution and recovering the transition metal from the MEA into the solution (hereinafter also referred to as a recovery step).

  The dipping process will be described.

  In the dipping step, MEA constituting the fuel cell is dipped in the solution.

  The fuel cell is a polymer electrolyte fuel cell (PEFC). The PEFC includes MEA as an electrode material. MEA is made 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, a diffusion layer made of a carbon material such as carbon paper or carbon cloth, and the like. Composed.

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

  A catalyst component adheres 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 transition metal simple substance, a compound containing a transition metal, and an alloy containing a transition metal. The transition metal constituting the catalyst component generally has a small amount of resources and is expensive. Examples of such a transition metal include at least one metal selected from the group consisting of Pt (platinum), Ru (ruthenium), and Co (cobalt).

  The solution for immersing the MEA contains halide ions and an anion exchange resin. Moreover, the 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 that is generally used as a transition metal constituting the catalyst component of the fuel cell can be efficiently recovered from the MEA, the halide ion is more preferably a chloride ion. Examples of the solution containing chloride ions include a hydrochloric acid aqueous solution and a sodium chloride aqueous solution. As the halide ions, only one of the above-described ions may be used alone, or two or more may be used in combination.

  The concentration of halide ions in the solution is appropriately adjusted according to the type of halide ions. The concentration of chloride 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 iodide ions in the solution is preferably 0.01 mol / L or more and 16.0 mol / L or less, and more preferably 1.0 mol / L or more and 5.0 mol / L or less. The concentration of bromide 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. When the halide ion concentration is equal to or higher than the lower limit described above, the transition metal can be efficiently recovered from the MEA into the solution. In addition, when the concentration of halide ions is equal to or less than the above upper limit value, it is possible to reduce the consumption amount of halide ions consumed by electrolysis by applying a voltage. The upper limit value of the concentration of chloride ions in the solution is 16.0 mol / L is a theoretical limit value for dissolving chloride ions.

  Here, as will be described later, in the recovery step, the concentration of 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 halide ions in the solution indicates the concentration of halide ions in the solution in the dipping process.

  The pH of the solution is preferably 5 or less, and more preferably 3 or less. When the pH of the acidic solution is within the above-described 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 an acid-containing solution containing halide ions and anion exchange resin can be produced. For example, an anion exchange resin is mixed with an acidic solution containing halide ions and stirred to produce a solution.

  The method for 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 the voltage is applied and the MEA and the terminal to which the voltage is applied are not immersed in the solution in the recovery process. Further, the temperature of the solution when the MEA is immersed in the solution is not particularly limited, for example, 25 ° C. which is room temperature.

  Next, the recovery process will be described.

  In the recovery process, a voltage is applied to the MEA immersed in the solution in the immersion process. Here, with respect to the MEA immersed in the dissolving solution in the immersion step, a terminal for applying a voltage is connected to a portion not immersed in the dissolving solution while being partially immersed in the dissolving 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. Moreover, the temperature of the solution in FIG. 1 is 25 ° C.

  As shown in FIG. 1, in a 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 equations (1) and (2) are used. Reaction occurs and platinum complex ions are easily generated. Details are as follows.

  Formula (1) is a reversible reaction. 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 Formula (1) proceeds. That is, when an oxidation potential within the above-described range is applied to Pt, the transition metal Pt and the halide ion chloride ion react, and the platinum complex ion tetrachloroplatinum (II) ion Generated.

  Moreover, Formula (2) is also a reversible reaction. When an oxidation potential of 0.75 V or higher is applied to Pt, the reaction from left to right in Formula (2) proceeds. That is, when an oxidation potential higher than the above value is applied to Pt, Pt and chloride ions react to generate hexachloroplatinum (IV) ion, which is a platinum complex ion.

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

  In general, when an oxidation potential is applied to the transition metal, in addition to the transition metal complex ion formation reaction as shown in the above formulas (1) and (2), the transition metal oxide is a byproduct. The resulting reaction takes place. The transition metal oxide produced as a by-product is deposited on the transition metal immersed in the solution, and forms a passive film on the surface of the transition metal. For this reason, the reaction of generating a transition metal complex ion from the transition metal is inhibited, and the recovery efficiency of the transition metal into the solution may be lowered.

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

  Thus, from the viewpoint of suppressing the formation of a passive film by the transition metal oxide and maintaining the recovery efficiency of the transition metal in the solution, the polarity of the voltage applied to the MEA including the transition metal in the recovery process Is preferably reversed periodically. The ratio (a / b) between the time a for applying the oxidation potential to the MEA and the time b for applying the reduction potential to the MEA is the size of the MEA, the amount of transition metal adhering to the MEA, and the amount of the solution. It is appropriately selected depending on the above.

  Here, as a reference, a solution that does not contain halide ions will be described. FIG. 2 is a graph showing the relationship between the pH of a solution not containing chloride ions, the standard electrode potential of Pt, and the form of Pt in the solution.

  As shown in FIG. 2, in the solution not containing chloride ions, when the standard electrode potential of Pt becomes a predetermined value or more, an oxide of Pt is generated and platinum complex ions are not generated. Therefore, Pt does not dissolve in a solution that does not contain chloride ions.

  Further, the anion exchange resin dispersed in the solution collects the transition metal recovered from the MEA in the solution 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 transition metal, the type of 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 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%, and 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 tetrachloroplatinum (II) ion and hexachloroplatinum (IV) ion as shown in the formulas (1) and (2). At least one of the platinum complex ions.

  Here, when the anion exchange resin is not included in the solution, the transition metal complex ions recovered in the solution increase with the passage of voltage application time to the MEA in the recovery step. The concentration of the transition metal complex ion increases. When a reduction potential is applied to the MEA, transition metal complex ions existing 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, the recovery efficiency of the transition metal from MEA falls as the application time of the voltage to MEA increases.

  On the other hand, when the anion exchange resin is contained in the solution, the anion exchange resin collects the transition metal complex ions contained in the solution, so that the increase rate of the concentration of the transition metal complex ions contained in the solution is increased. It is suppressed. Compared to the case where an anion exchange resin is not included in the solution, transition metal complex ions present in the vicinity of the MEA are reduced. Therefore, even when a reduction potential is applied to the MEA, the amount of transition metal re-deposited on the MEA is Few. Therefore, even if the application time of the voltage to MEA increases, the fall of the recovery efficiency of the transition metal from 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, it is possible to improve the recovery rate of the transition metal, shorten the recovery time of the transition metal, reduce the amount of solution used, and the like.

  The transition metal recovered in the solution by the recovery process can be reused by a known method. For example, the anion exchange resin collecting the transition metal is recovered by subjecting the solution containing the transition metal collected in the anion exchange resin to a separation treatment such as sedimentation separation or filtration separation. The Subsequently, by washing the anion exchange resin, the transition metal adsorbed on the anion exchange resin is desorbed from 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 according to the desired application. Further, the transition metal desorbed from the anion exchange resin can be sold to a recycler or the like without being treated.

  In addition, 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 the above treatment.

  Next, the metal recovery apparatus according to the embodiment will be described. FIG. 3 is a schematic view showing a metal recovery apparatus 1 according to the embodiment. The metal recovery apparatus 1 is an apparatus that can implement the metal recovery method of the above-described embodiment. In FIG. 3, for convenience of explanation, a cross section is partially shown.

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

  The storage unit 2 stores the solution 20. Further, in addition to the MEA 30, an electrode 40 that 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 reservoir 2. The MEA 30, the electrode 40, and the reference electrode 50 are each connected to the voltage application unit 3.

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

  When a voltage is applied from the voltage application unit 3 to the MEA 30, the transition metal in the MEA 30 is dissolved in the solution 20 as a transition metal complex ion. 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 the transition metal is recovered from the MEA 30, the MEA 30 that has recovered the transition metal and the MEA that has not recovered the transition metal are exchanged. Then, the metal recovery device 1 recovers the unrecovered transition metal from this MEA. At this time, the used solution 20 in which the transition metal is recovered may be exchanged with an unused solution in which the transition metal is not recovered, or the used solution 20 in which the transition metal is recovered is used. You may continue.

  As shown in FIG. 3, the metal recovery apparatus 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 6 a provided in the tank unit 6, a pump unit 7 connected to the tank unit 6, and a tank unit 8 connected to the pump unit 7 and the storage unit 2.

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

  In addition, 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 apparatus 1. For example, the exhaust unit 9 is connected to the upper side of the gas-liquid separation unit 5, and the gas phase stored in the upper side of the gas-liquid separation unit 5 is supplied to the exhaust unit 9.

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

  The solution 20 accommodated in the tank unit 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 unit 6 is supplied from the tank unit 6 through the tank unit 8 to the storage unit 2 by the pump unit 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 from the voltage application unit 3 to the MEA 30. 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 that collects the transition metal complex ions is discharged to the gas-liquid separation unit 5 through the tank unit 4. In the gas-liquid separation unit 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 unit 6.

  And after collect | recovering transition metals from MEA30, the pump part 7 is stopped and the circulation of the solution 20 is stopped. The MEA 30 that has recovered the transition metal is replaced with an MEA that has not recovered the transition metal. The anion exchange resin that collects 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 collects the transition metal complex ions is recovered.

  As described above, according to the metal recovery method and 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 the increase in the concentration of the transition metal complex ions contained in the solution and keeps the concentration of the transition metal complex ions low, so that the reprecipitation of the transition metal complex ions contained in the solution onto the MEA is performed. Is suppressed. Therefore, the transition metal that constitutes 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 presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Metal collection | 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 ... solution, 30 ... MEA, 40 ... electrode, 50 ... reference electrode.

Claims (7)

Immersing the fuel cell membrane electrode assembly in an acidic solution containing halide ions and an anion exchange resin; and
And a step of 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 metal recovery method according to claim 1, wherein in the step of immersing the membrane electrode assembly, the concentration of the halide ions in the solution is 0.01 mol / L or more and 16.0 mol / L or less.   The metal recovery method according to claim 1, wherein in the step of recovering the transition metal, the polarity of the voltage applied to the membrane electrode assembly is periodically reversed.   5. The metal recovery method according to claim 1, wherein the transition metal is at least one metal selected from the group consisting of Pt, Ru, and Co. 6.   The metal recovery method according to claim 1, wherein the halide ions are chloride ions. A reservoir for storing a solution that contains halide ions and an anion exchange resin and is acidic;
A metal recovery apparatus comprising: a voltage application unit configured to apply a voltage to a membrane electrode assembly of a fuel cell immersed in the solution in the storage unit.

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