Metal recovery method

Abstract

Metal deposited by electrolysis is integrated with a negative electrode so as to be able to be solidified from wastewater. However, for actual recovery, it is necessary to extract the negative electrode and, for example, scrape off the surface thereof so as to recover the metal.　A metal recovery method according to the present invention comprises: a treatment target solution injection step for injecting, into a container in which electrode plates are disposed, a solution containing metal which exists in an ionic state; a resting step for leaving the solution stationary with respect to the electrode plates; a sponge-like metal porous body formation step for supplying an electric current between the electrode plates and causing a sponge-like metal porous body to be formed on the electrode plate which has become a negative electrode; and a separation step for separating the sponge-like metal porous body from the electrode. The metal which has been deposited on the electrode is not fixed to the electrode plate, and can therefore be easily recovered.

Description

Metal recovery method

[0001] The present invention relates to a method for recovering metals present in an ionic state in waste liquid, particularly copper, from waste liquid containing a large amount of aqueous hydrogen peroxide.

[0002] In recent years, copper, which has high conductivity, has been used for the fine wiring used in ICs and other devices. When forming extremely fine wiring, a subtractive method is used in which a copper film is formed over the entire surface and unnecessary parts are removed by etching to form a circuit. This method generates waste liquid containing a large amount of copper.

[0003] Electrolysis is often used to recover metals from waste liquids containing metal ions. Patent Document 1 discloses a method for electrolytic extraction of powder metal from a solution in which a cylindrical electrolytic cell is formed with a cylindrical cathode on the inside, the inner surface of the electrolytic cell being used as the anode, and a treatment solution is passed through the solution to deposit the metal. Patent Document 1 also describes a method for removing the metal powder deposited on the cathode by passing a flushing solution in the opposite direction to the flow of the treatment solution during metal deposition.

[0004] Special Publication No. 2003-505598

[0005] Electrolysis is a suitable method for recovering metals from wastewater because it increases the recovery rate. However, although the metal precipitated by electrolysis becomes integrated with the cathode and can be solidified from the wastewater, actual recovery requires removing the cathode and scraping its surface to recover the metal. Patent Document 1 attempts to improve the ease of recovery by reducing the velocity and current density of the fluid passing through the electrolytic cell, which makes it easier to produce powdered metal rather than plate-like metal on the cathode.

[0006] However, even with this method, if wastewater is still being processed, metal will adhere to the cathode. If the adhered metal grows, it will be impossible to recover the deposited metal as a powder, even if a flushing solution is used. As a result, there was a problem in that the device had to be disassembled, the electrode removed, and the deposited metal scraped off.

[0007] The present invention was conceived in view of the above-mentioned problems, and was completed by discovering that when the waste liquid to be treated (hereinafter referred to as the "liquid to be treated") is left stationary rather than flowing relative to the electrodes, and a large current density is applied to the cathode, the precipitated metal fine particles form a structure that embraces hydrogen generated by electrolysis.

[0008] More specifically, the metal recovery method of the present invention is characterized by comprising a liquid to be treated injection step in which a solution containing metals existing in an ionic state is injected into a container in which electrode plates are placed; a standing step in which the solution is allowed to stand still relative to the electrode plates; a spongy metal porous body formation step in which an electric current is passed between the electrode plates to form a spongy metal porous body on the electrode plate that serves as the cathode; and a peeling step in which the spongy metal porous body is separated from the electrode.

[0009] In the metal recovery method of the present invention, when the liquid to be treated is electrolyzed, the liquid is not subjected to a flow, and only a slight upward flow of hydrogen bubbles generated from the electrode occurs. When a relatively large current is applied to the cathode in this state, the deposited metal becomes fine particles that grow to a certain size or larger. Then, before metallic bonding with the electrode occurs, they are pushed away from the electrode by the hydrogen bubbles generated at the cathode.

[0010] Meanwhile, the hydrogen bubbles that push out the metal particles are also surrounded by the surrounding deposited metal particles. As a result, an unstable deposit (hereinafter referred to as a "spongy metal porous body" or "spongy metal porous body") is formed, in which metal particles envelop the hydrogen bubbles. This deposit is not adhered to the cathode, and can be easily peeled off and recovered from the cathode with a slight physical or electrical stimulus. Therefore, there is no need to scrape off and recover the metal that has adhered to the electrode plate.

[0011] Furthermore, since particles are usually difficult to settle and filter, they tend to remain on the inner walls of the storage tank, the surfaces of the electrode plates, or the connection terminals. However, this sponge-like metal porous body maintains its shape in the liquid unless it is subjected to strong stimuli, and can be handled as a mass, which means that it can be recovered completely.

[0012] Furthermore, since almost no metal remains adhered to the electrodes, the electrodes can be used for long periods without polishing the surface, resulting in a dramatic increase in the lifespan of the device that implements the metal recovery method of the present invention.

[0013] Fig. 1 is a configuration diagram of a metal recovery device for carrying out a metal recovery method according to the present invention. Fig. 2 is an enlarged view of a portion of Fig. 1. Fig. 3 is a flow diagram showing the processing (main flow) of a controller. Fig. 4 is a flow diagram showing the processing of adding hydrogen peroxide performed during step S108. Fig. 5 is a conceptual diagram showing the progression of the formation of a spongy metal porous body. Fig. 6 is a conceptual diagram of a state in which a spongy metal porous body has grown on a cathode plate. Fig. 7 is a conceptual diagram showing how the spongy metal porous body on a cathode is peeled off by air bubbles. Fig. 8 is a diagram showing the configuration when an electrode vibrator that vibrates an electrode plate is provided.

[0014] The metal recovery method according to the present invention will be described below with reference to the drawings. Note that the following description exemplifies one embodiment of the present invention and one example, and the present invention is not limited to the following description. The following description can be modified within the scope of the present invention.

[0015] [Explanation of Components] Fig. 1 illustrates a configuration diagram of an apparatus (hereinafter also referred to as "metal recovery apparatus 1") for carrying out the metal recovery method according to the present invention. Fig. 2 shows a partially enlarged view. Referring to Figs. 1 and 2, the metal recovery apparatus 1 includes a storage tank 10 for storing the liquid to be treated, an electrode plate 12 serving as an electrode, a power supply 14 for supplying power to the electrode plate 12, a bubble generator 16, and a controller 18. It is also preferable that a concentration meter 20 and a water level meter 22 are also provided. A filter 26 may be provided below the storage tank 10 to separate the metal recovered after treatment from the liquid to be treated from which the metal has been recovered.

[0016] Furthermore, an injection pipe 40 for injecting the liquid to be treated into the storage tank 10 and an injection pipe opening / closing valve 40a for opening and closing the injection pipe 40 may be provided. Also, an addition tank 28 for adding hydrogen peroxide solution to the storage tank 10 and an addition opening / closing valve 28a for opening and closing the tank 28 may be provided.

[0017] <Storage Tank 10> The storage tank 10 is a container that stores the liquid to be treated and electrolyzes the treated liquid. It may be sealed, but since hydrogen is generated by electrolysis, an outlet (not shown in the drawing) is required for releasing the hydrogen. In addition, an inlet for injecting the liquid to be treated is also provided at the top of the storage tank 10. In the drawing, the top of the storage tank 10 is shown as open, so the inlet is the top opening of the storage tank 10. Note that the inlet may be provided somewhere other than at the top of the storage tank 10.

[0018] An outlet 10a is provided at the bottom of the storage tank 10 for recovering the electrolyzed liquid and the metals deposited by electrolysis. A funnel-shaped outlet 10a is more suitable for pushing out the spongy porous metal body in which the liquid has settled. The spongy porous metal body will be described in detail later.

[0019] The opening and closing of the outlet 10a is controlled by an instruction signal C from the controller 18, which will be described later. ＥＶ The opening and closing mechanism may be configured to open and close by

[0020] A through-hole 10b is provided on the side of the storage tank 10 to guide a power line 14c from the power source 14 into the storage tank 10. The power line 14c passes through the through-hole 10b in a liquid-tight manner. Therefore, even if the liquid to be treated enters the storage tank 10, there is no leakage from the through-hole 10b.

[0021] <Electrode Plate 12> The electrode plate 12 is a conductive material that serves as a cathode or an anode. It may be in the form of a plate, but other shapes are also acceptable. Titanium or stainless steel is suitable for the electrode plate 12, as the deposited metal is less likely to adhere to it. It is also preferable that the surface is smooth, as this makes it difficult for the sponge-like metal porous body to bond. It is even more preferable that the surface of the electrode plate 12 is mirror-finished.

[0022] The electrode plates 12 are connected so that opposing electrode plates 12 have opposite polarities. In other words, except for the electrode plates 12 at both ends, electrode plates 12 of the same polarity are arranged with electrode plates 12 of opposite polarity sandwiched between them. Figure 2 shows a state in which five electrode plates 12 are arranged. These are referred to as electrode plates 12a, 12b, 12c, 12d, and 12e. Of these electrode plates 12, opposing electrode plates 12 have opposite polarities.

[0023] More specifically, the set of electrode plates 12a, 12c, and 12e and the set of electrode plates 12b and 12d are electrode plates 12 of the same polarity. These are electrode plates that always have the same polarity. These sets may be referred to as identical electrode plates 12A and identical electrode plates 12B. In other words, one identical electrode plate 12A is made up of electrode plates 12a, 12c, and 12e, and the other identical electrode plate 12B is made up of electrode plates 12b and 12d. Of course, "one" and "the other" may be reversed.

[0024] <Power supply 14> The power supply 14 may be either a constant voltage power supply or a constant current power supply, but a constant current power supply is preferable. A bipolar power supply is more preferable. Here, a bipolar power supply is a power supply that can reverse the positive and negative polarities of the electrode terminals. The power supply 14 has at least two terminals 14a and 14b. A power line 14c is connected to each terminal. The power supply 14 also receives an instruction signal C from a controller 18, which will be described later. ＶＩ is controlled by.

[0025] One pole (terminal) of the power supply 14 is connected to one of the identical electrode plates 12, and the other pole (terminal) is connected to the other identical electrode plate 12. Fig. 2 shows a state in which terminal 14a of the power supply 14 is connected to one identical electrode plate 12A, and the other terminal 14b is connected to the other identical electrode plate 12B. The power line 14c is electrically connected to the electrode plate 12 via connection terminal 14d.

[0026] <Air Bubble Generator 16> The air bubble generator 16 is composed of an air pump 16a, an air pipe 16b, and an air diffusion nozzle 16c. When the air pump 16a is operated and air is sent to the air diffusion nozzle 16c through the air pipe 16b, air is ejected from the outlet 16d of the air diffusion nozzle 16c (see Figure 2). In the liquid, the ejected air becomes air bubbles and rises.

[0027] The air diffusion nozzle 16c is disposed below the electrode plate 12. The air bubble generator 16 serves to direct the generated air bubbles against the electrode plate 12, vibrating the electrode plate 12. Therefore, it is preferable that the air bubbles generated from the air diffusion nozzle 16c have a diameter large enough to vibrate the electrode plate 12 when they strike the electrode plate 12.

[0028] The diameter and speed of the bubbles sufficient to shake the electrode plate 12 cannot be determined in general depending on the position of the storage tank 10 and the aeration nozzle 16c. However, if the bubble diameter is less than 100 μm at the time of contact with the electrode plate 12, it is difficult to shake the electrode plate 12. On the other hand, bubbles that are too large will crush the sponge-like metal porous body and return it to fine particles, making it more difficult to recover the deposited metal. The operation of the bubble generator 16 is controlled by an instruction signal C from the controller 18, which will be described later. Ｂ is controlled by

[0029] <Controller 18> The controller 18 is composed of a CPU (Central Processor Unit), a memory, and an input / output device. The controller 18 controls the operation of at least the power supply 14 and the bubble generator 16. More specifically, the controller 18 receives an instruction signal C ＶＩ The ON / OFF of the power supply 14, the applied power (voltage or current), the polarity, etc. can be controlled by the signal S ＶＩ This allows the user to know the current operating status of the power supply 14. The operating status includes information such as the currently applied voltage and current as well as polarity.

[0030] The controller 18 also outputs an instruction signal C Ｂ This allows the ON / OFF of the bubble generator 16 and the amount of bubbles to be generated (directly, the amount of air blown by the air blower pump 16a) to be controlled.

[0031] The controller 18 also controls the opening and closing of the outlet 10a of the storage tank 10 by issuing an instruction signal C ＥＶ The injection pipe opening / closing valve 40a of the injection pipe 40 for injecting the liquid to be treated into the storage tank 10 is controlled by an instruction signal C ＭＶ Furthermore, the additional supply opening / closing valve 28a for supplying the hydrogen peroxide solution stored in the additional supply tank 28 to the storage tank 10 may be controlled by the instruction signal C.ＰＶ It may be controlled by.

[0032] In addition, when the concentration meter 20, the water level meter 22, and the hydrogen peroxide concentration meter 30 are provided, the received signals S Ｑ , S Ｌ , S Ｈ２Ｏ２ By receiving this signal, the metal ion concentration of the liquid to be treated in the storage tank 10, the liquid level of the liquid to be treated in the storage tank 10, and the concentration of hydrogen peroxide in the storage tank 10 can be known.

[0033] Furthermore, when the metal ion concentration in the liquid to be treated becomes equal to or lower than a predetermined value, the controller 18 can output a notification signal SF indicating that the recovery of the metals has been completed. The notification signal SF may be used by the controller 18 itself.

[0034] <Concentration meter 20> The concentration meter 20 measures the metal ion concentration of the liquid to be treated in the storage tank 10. The measurement result is output as a received signal S Ｑ The signal is transmitted to the controller 18 by the signal . The concentration meter 20 may be of any type as long as it can measure the metal ion concentration. FIG. 1 shows the concentration meter 20 configured with a concentration meter main body 20a, a first pipe 20b, a pump 20c, and a second pipe 20d. Alternatively, a concentration meter may be used in which a portion of the storage tank 10 main body is configured with a transparent material, and the metal ion concentration is measured by obtaining information on the light absorption of the liquid from the transparent material through image processing or the like. This is because, even if the metal ion concentration is not measured directly, if an indicator that can be converted to the metal ion concentration by measuring an indicator that can be used in place of the metal ion concentration, it can be said that the metal ion concentration is being measured.

[0035] First pipe 20b collects the liquid to be treated from the bottom of storage tank 10 and sends it to concentration meter main body 20a by pump 20c. After measurement, the liquid to be treated is returned to the top of storage tank 10 by second pipe 20d. Note that because the amount of liquid used in concentration meter 20 is extremely small, the circulation of the liquid to be treated within storage tank 10 brought about by pump 20c does not affect the production of the sponge-like metal porous body.

[0036] <Water level meter 22> The water level meter 22 detects the liquid level of the liquid to be treated in the storage tank 10 and sends a received signal S ＬThe water level meter 22 can be suitably used when disposing of the treated liquid from the storage tank 10 after treatment, and when filling the empty storage tank 10 with new treated liquid.

[0037] <Hydrogen peroxide concentration meter 30> The hydrogen peroxide concentration meter 30 measures the concentration of hydrogen peroxide in the liquid to be treated and outputs the measurement result as a reception signal S Ｈ２Ｏ２ The controller 18 is notified by a signal from the processing unit 14. The liquid to be treated contains a relatively high concentration of hydrogen peroxide, which contributes to the dissolution of copper. If copper remains as a solid on the inner wall of the storage tank 10 or on the surface of the electrode plate 12, the copper can be removed from the storage tank 10 by re-dissolving it with the liquid to be treated. Therefore, the hydrogen peroxide concentration meter 30 is provided to measure the hydrogen peroxide concentration in the liquid to be treated so that additional hydrogen peroxide can be added to the storage tank 10 when necessary.

[0038] <Flow Straightening Guide 24> The flow straightening guide 24 is provided between the electrode plate 12 and the inner wall of the storage tank 10. The lower end 24d has an opening that can capture all of the bubbles from the aeration nozzle 16c. Therefore, the flow straightening guide 24 is large enough to completely surround the outlet 16d of the aeration nozzle 16c, at least when viewed from above. The upper end 24u is positioned below the liquid surface of the liquid being treated. With this configuration, the bubbles generated from the aeration nozzle 16c rise from the bottom to the top of the storage tank 10. The upward flow generated at this time flows toward the inner wall surface of the storage tank 10 at the liquid surface and circulates between the flow straightening guide 24 and the inner wall surface of the storage tank 10 as a flow from top to bottom.

[0039] The flow rectifying guide 24 is a component whose purpose is to suppress the generation of an in-plane swirling flow, which will be described later. Therefore, as long as it can suppress the in-plane swirling flow, it does not have to be shaped to completely surround the electrode plate 12. For example, taking FIG. 2 as an example, flow rectifying guides 24 may be provided as flat plate-shaped components parallel to the electrode plates 12a and 12e between the electrode plate 12a and the storage tank 10, and between the electrode plate 12e and the storage tank 10. It is also preferable to position the electrode plate 12 parallel to the inner wall of the storage tank 10, and to position the flow rectifying guide 24 between the inner wall and the electrode plate 12.

[0040] <Filter 26> The filter 26 is attached below the discharge port 10a of the storage tank 10. It filters the fine powder precipitated by electrolysis. Note that, because the precipitated metal from the discharge port 10a is discharged as a sponge-like metal porous body, the filter 26 does not need to have meshes fine enough to filter fine particles of several microns or less. It is sufficient if the filter can capture fine particles of 10 μm or larger, for example.

[0041] [Explanation of Operational State] Figure 3 shows the processing flow (main flow) of the controller 18. See also Figures 1 and 2. The metal recovery method according to the present invention is implemented according to this processing flow. When the operation of the metal recovery device 1 starts (step S100), an end determination is made (step S102). If the processing is to continue (N branch in step S102), control proceeds to the next processing. Note that the end determination may be made by entering a standby state in response to a signal from another device.

[0042] If the process is to be terminated (Y branch in step S102), the process is stopped (step S104). The termination conditions include the user stopping the device itself, an emergency stop, or the end of the liquid to be treated. Of course, other conditions may also be used.

[0043] If the treatment is to be continued (N branch in step S102), first, the liquid to be treated is poured into the storage tank 10 (step S106). The liquid to be treated is poured until at least the electrode plate 12 and the connection terminal 14d portion between the electrode plate 12 and the power supply 14 are completely immersed in the liquid. This is because, if the connection terminal 14d is immersed in the liquid to be treated, even if a spark is generated at the connection terminal 14d, there is no risk of igniting hydrogen present on the surface of the liquid to be treated.

[0044] The injection of the liquid to be treated is initiated by an instruction signal C ＭＶ The process starts by opening the injection pipe opening / closing valve 40a, and the received signal S Ｌ The controller 18 determines that the injection is complete and issues an instruction signal C ＭＶ This treatment is a liquid-to-be-treated injection step in which a solution containing metals present in an ionic state is injected into a container in which an electrode plate is placed.

[0045] Next, the process waits for a certain period of time (step S108). The liquid to be treated here is assumed to be a copper etching solution. Copper etching solutions often contain a relatively large amount of hydrogen peroxide and are strong acids with a pH of approximately 1. The purpose of holding the liquid to be treated for a while in the storage tank 10 is to dissolve copper components remaining on the electrode plate 12, the inner wall surface of the storage tank 10, the electrode terminals, etc. Therefore, this step is not a main step in metal recovery, and may be skipped. Of course, this step may also be a static step in which the solution is allowed to stand still relative to the electrode plate.

[0046] FIG. 4 shows the process flow for adding hydrogen peroxide during step S108. Step S108 can be considered a waiting process for dissolving the remaining copper components. However, if the concentration of hydrogen peroxide in the solution to be treated is low, the expected effect cannot be obtained. Therefore, when step S108 is entered, the hydrogen peroxide concentration M ＨＯ In this step, the hydrogen peroxide concentration is measured by the hydrogen peroxide concentration meter 30, and the result is output as a received signal S Ｈ２Ｏ２ This is implemented by notifying the controller 18 by

[0047] Next, the measured hydrogen peroxide concentration M ＨＯ and the threshold M ＴＨＯ (Step S132). ＴＨＯ The hydrogen peroxide concentration M can be suitably set to 1 to 20 mass %. ＨＯ is the threshold M ＴＨＯ If the value is equal to or less than the threshold value M (Y branch of step S132), hydrogen peroxide is added at least ＴＨＯ The hydrogen peroxide is further added up to the amount above (step S134) because there is a risk that the copper remaining in the reservoir 10 may not be dissolved properly due to a shortage of hydrogen peroxide.

[0048] On the other hand, the hydrogen peroxide concentration M ＨＯ is the threshold M ＴＨＯ If it is higher (N branch in step S132), nothing is done and the process returns to the main routine (step S136).

[0049] Referring again to Fig. 3, after step S108, a current is passed between the electrode plates 12 (step S110). In Fig. 3, this is expressed as "power application." This is performed when the controller 18 sends an instruction signal C ＶＩ This is carried out by transmitting a current between the opposing identical electrode plates 12A and 12B. When a current flows between the opposing identical electrode plates 12, copper is deposited while hydrogen is generated from the identical electrode plate that serves as the cathode. In FIG. 2, for example, if the identical electrode plate 12A serves as the anode and the identical electrode plate 12B serves as the cathode, hydrogen is generated from the electrode plates 12b and 12d that are identical electrode plates 12B, and copper is deposited.

[0050] At this time, if there is a flow of the liquid to be treated between the electrode plates 12, the deposited copper will adhere to the electrode plates 12 as if plated. However, if the liquid to be treated between the electrode plates 12 is stationary, the electrolytic reaction will proceed as the deposited copper takes in minute hydrogen bubbles.

[0051] Figure 5 shows a conceptual diagram of this progression. Figure 5 shows a cross-section of a cathode plate. For the purposes of explanation, copper and hydrogen are generated on only one side. Copper is represented by black circles, and hydrogen by white circles. Referring to Figure 5(a), fine copper powder Cu1 is initially deposited on the surface of the cathode plate. After copper is deposited by electrolysis for a while, the solution remains stationary, as described above. Microscopically, the cathode surface becomes deficient in copper ions, making it easier for hydrogen to be generated. Hydrogen H1 generated from the surface of the cathode plate forms microbubbles, which prevent the deposited copper Cu1 from adhering to the electrode (Figure 5(b)). This can be said to push the copper Cu1 away from the electrode. Therefore, the deposited copper Cu1 cannot form large agglomerates and remains as fine powder, away from the cathode plate surface. At this time, the copper Cu1 fine powder is attracted toward the cathode.

[0052] Meanwhile, the hydrogen microbubbles H1 are pushed away from the cathode plate together with the copper Cu1 micropowder by the next generated copper micropowder Cu2 (Fig. 5(c)). The hydrogen microbubbles H1 maintain their shape without breaking due to surface tension, capturing the copper Cu1 micropowder on their surface. The copper Cu2 is then pushed away from the cathode plate surface by the next generated hydrogen microbubbles H2 (Fig. 5(d)).

[0053] In this way, the hydrogen microbubbles that are generated one after another push the metal micropowder that is attracted to the cathode plate away from the cathode plate, and the metal micropowder further pushes the hydrogen microbubbles away from the cathode plate. As this reaction continues, a mass of hydrogen microbubbles that looks as if they are embraced by copper micropowder is formed on the cathode plate. This formed mass is called a "sponge-like metal porous body." Since the metal used here is copper, it can also be called a "sponge-like copper porous body" or a "sponge-like copper porous body."

[0054] Figure 6 shows a conceptual diagram of a sponge-like porous metal body (reference numeral 60) grown on a cathode plate. The sponge-like porous metal body 60 is made up of fine metal powder particles that are simply held together by the surface tension of hydrogen microbubbles, so it maintains its shape in the liquid. However, the bond itself is very weak, and even slight vibrations can cause it to shake. Furthermore, because it is not firmly attached to the electrode plate 12, it can easily peel off and fall off when the electrode plate 12 is subjected to slight physical vibrations.

[0055] Furthermore, the sponge-like porous metal (copper) body 60 grows on the cathode plate because the deposited copper fine powder is attracted to the cathode plate, but when the polarity of the electrode plate 12 is reversed, the force attracting it toward the cathode plate disappears and it falls. If the sponge-like porous metal body 60 that has fallen into the liquid is poked with a stick or the like, tiny hydrogen bubbles separate and foam. Therefore, if bubbles appear when the sponge-like porous metal body 60 is pressed in the liquid, it can be determined that the sponge-like porous metal body 60 has been generated.

[0056] It is believed that the sponge-like metal porous body 60 is formed by the above mechanism, so when the current flowing between the electrode plates 12 increases, the amount of hydrogen microbubbles generated increases, and a more unstable sponge-like metal porous body 60 can be formed. This allows the metal to be easily separated from the electrode plate 12, that is, to be deposited in a state that makes it easy to recover. In current experiments, ２ ~200 A / dm ２It has been confirmed that a sponge-like metal porous body 60 suitable for recovery can be obtained within this range. If the current density is too low, the sponge-like metal porous body 60 is not formed, and the metal deposits and adheres to the cathode. If the current density is too high, the efficiency of copper production (deposition) may be reduced.

[0057] This reaction is a phenomenon that occurs depending on the current density of the cathode electrode plate 12. Therefore, if the area of ​​the cathode electrode plate 12 is smaller than the area of ​​the anode electrode plate 12, the generation of the sponge-like metal porous body 60 on the cathode plate can be promoted even if the same current is passed through them.

[0058] In the configuration shown in FIG. 2 , the identical electrode plate 12A is composed of three electrode plates 12, and the identical electrode plate 12B is composed of two electrode plates 12. If the identical electrode plate 12B is used as the cathode, the number of electrode plates 12 serving as cathodes will be fewer than the number of electrode plates 12 serving as anodes. This allows the current density of the identical electrode plate 12B to be higher than that of the identical electrode plate 12A, and allows the sponge-like porous metal body 60 to be formed more efficiently. Of course, the area of ​​the cathode electrode plate 12 may be reduced while maintaining the same number of electrodes. As described above, this process (step S110 in FIG. 3 ) can be considered a sponge-like porous metal body formation process in which a current is passed between the electrode plates to form a sponge-like porous metal body 60 on the cathode electrode plate.

[0059] 2, if the same electrode plate 12B is used as the cathode, then there will always be an anode plate on both sides of every cathode plate. This configuration is more preferable because it can reduce the flow of the solution on the surface of the cathode plate.

[0060] 3 again, after a current is passed between the electrode plates 12 for a certain period of time (step S110), the current is stopped and the bubble generator 16 is operated (step S112). Ｂ is sent to the air bubble generator 16 (more specifically, the air pump 16a).

[0061] A conceptual diagram of this process is shown in Figure 7. The bubble generator 16 generates bubbles from below the electrode plate 12. The generated bubbles collide with the electrode plate 12 or the sponge-like porous metal body 60, shaking the electrode plate 12. They also float upward on the surface of the electrode plate 12. The vibration of the electrode plate 12 at this time and the stimulation caused by the bubbles sweeping across the surface of the electrode plate 12 cause the sponge-like porous metal body 60 to detach from the electrode plate 12 and fall.

[0062] Therefore, this step (step S112 in FIG. 3) can be said to be a peeling step in which the spongy porous metal body 60 is peeled off from the electrode. In addition, since the spongy porous metal body 60 is peeled off from the electrode plate by the air bubbles, this is a peeling step in which the spongy porous metal body 60 is peeled off from the electrode, and is a step in which the air bubbles come into contact with the electrode plate.

[0063] At this time, a flow from bottom to top occurs within the storage tank 10. If a flow straightening guide 24 is provided between the electrode plate 12 and the inner wall of the storage tank 10, the flow from bottom to top passes between the electrode plate 12 and the inner wall of the storage tank 10 and flows from top to bottom. In this way, it is possible to suppress the occurrence of a swirling flow (called an "in-plane swirling flow") in which a flow from bottom to top and a flow from top to bottom simultaneously occur between the electrode plates 12.

[0064] The in-plane swirling flow breaks down the sponge-like metal porous body 60 into small pieces, breaking it down into tiny hydrogen bubbles and fine metal powder. The fine metal powder may float in the liquid being treated, making it difficult to recover, which is undesirable.

[0065] The process of generating these bubbles (step S112) is a process of peeling the sponge-like metal porous body 60 from the electrode plate 12. In the metal recovery device 1 according to the present invention, a sponge-like metal porous body 60 is generated in which fine metal powder is loosely bound together, and the bond to the electrode plate 12 is also loose, so that it can be peeled off from the electrode plate 12 by means other than the use of bubbles.

[0066] For example, by providing an electrode plate vibrator for directly vibrating the electrode plate 12, the sponge-like porous metal body 60 can be peeled off from the electrode plate 12. Fig. 8 shows a state in which an electrode plate vibrator 50A and an electrode plate vibrator 50B are provided, which can vibrate the same electrode plate 12A and the same electrode plate 12B, respectively. These electrode plate vibrators 50 can be controlled by instruction signals from the controller 18. The process using the electrode plate vibrator is a peeling process in which the sponge-like porous metal body 60 is pulled off from the electrode, and is a process in which vibration is applied to the electrode plate.

[0067] Furthermore, the sponge-like porous metal body 60 can also be peeled off from the electrode plate 12 by reversing the polarity of the identical electrode plate 12A and the identical electrode plate 12B. As already explained, the sponge-like porous metal body 60 is attracted to the cathode plate. Therefore, by reversing the polarity of the opposing electrode plate 12, the cathode to which the sponge-like porous metal body 60 was attracted changes to an anode, and a repulsive force acts on the sponge-like porous metal body 60. On the other hand, by changing the opposing electrode plate 12 to a cathode, an attractive force acts toward the opposing electrode plate 12. Therefore, the sponge-like porous metal body 60 can be peeled off from the electrode plate 12. Therefore, the process of reversing the polarity is a peeling process in which the sponge-like porous metal body 60 is pulled away from the electrode, and is a process in which the polarity of the electrode plate is reversed.

[0068] If the power supply 14 is a bipolar type, the polarity of the electrode plate 12 is reversed by an instruction signal C ＶＩ This can be done by

[0069] As described above, step S110 is a peeling process for separating the sponge-like metal porous body 60 from the electrode, and the peeling means may be replaced with a process of blowing air bubbles against the electrode plate 12, a process of vibrating the electrode plate 12, or a process of reversing the polarity of the electrode plate 12.

[0070] 3 again, after the bubble generator 16 has been operated for a certain period of time, the bubble generator 16 is stopped and the system waits for a certain period of time (step S114). This waiting period is intended to allow the flow of the liquid to be treated between the electrode plates 12 caused by the bubble generator 16 to settle.

[0071] Next, the metal ion concentration Mq in the liquid to be treated is measured and compared with the threshold value Mth (step S116). Ｑ If the metal ion concentration Mq is equal to or less than the threshold value Mth (Y branch in step S116), the recovery of metals from the current liquid to be treated is considered to be complete, and the process proceeds to the liquid discharge step (step S118). Note that the measurement of the metal ion concentration may be performed continuously.

[0072] At this time, the controller 18 may internally generate and transmit a notification signal SF indicating completion of treatment (see FIG. 1). If the metal ion concentration Mq is not equal to or less than the threshold value Mth (N branch in step S116), control returns to the process of again passing a current between the electrode plates 12 (step S110). In other words, the settling step, the sponge-like metal porous body formation step, and the peeling step are repeated until the metal ion concentration in the liquid to be treated falls below a predetermined value.

[0073] When the process proceeds to step S118, it can be determined that the process for the liquid to be treated has been completed, and the liquid to be treated is discarded. This is because the controller 18 issues an instruction signal C Ｖ This can be done by opening the outlet 10a of the storage tank 10.

[0074] The metal recovered as a sponge-like porous metal body 60 and the liquid to be treated are discharged from the outlet 10a. The precipitated metal can be recovered by filtering this with an appropriate filter 26. This process is a process in which the liquid to be treated is filtered and the sponge-like porous metal body 60 is recovered.

[0075] As described above, according to the metal recovery method of the present invention, metal ions in the liquid to be treated can be recovered as loosely bound clumps.

[0076] The present invention can be used not only to recover copper from etching waste liquid, but also to recover dissolved metals from waste liquid containing other metals.

[0077] 1 Metal recovery device 10 Storage tank 10a Discharge port 10b Through hole 12 Electrode plate 12a, 12b, 12c, 12d, 12e Electrode plate 12A Same electrode plate 12B Same electrode plate 14 Power supply 14a, 14b Terminal 14c Power line 14d Connection terminal 16 Bubble generator 16a Air blower pump 16b Air blower pipe 16c Air diffuser nozzle 16d Spout 18 Controller 20 Concentration meter 20a Concentration meter body 20b First piping 20c Pump 20d Second piping 22 Water level gauge 24 Rectification guide 24u Upper end (of rectification guide) 24d Lower end (of rectification guide) 26 Filter 28 Additional tank 28a Additional opening / closing valve 30 Hydrogen peroxide concentration meter 40 Injection pipe 40 Injection pipe opening / closing valve a 50 Electrode plate vibrator 60 Sponge-like metal porous body C ＥＶ Instruction signal C ＶＩ Instruction signal C Ｂ Indication signal C ＭＶ Instruction signal C ＰＶ Instruction signal S Ｑ , S Ｌ , S Ｈ２Ｏ２ Received signal S ＶＩ Received signal SF Notification signal M ＨＯ Hydrogen peroxide concentration M ＴＨＯ Threshold value Mq Metal ion concentration Mth Threshold value

Claims

1. a process of injecting a solution containing a metal present in an ionic state into a container in which an electrode plate is disposed; a step of allowing the solution to stand still relative to the electrode plate; a step of forming a sponge-like porous metal body on the electrode plate serving as a cathode by passing an electric current between the electrode plates; A peeling step of peeling off the sponge-like metal porous body from the electrode, A metal recovery method, wherein the peeling step is a step of bringing air bubbles into contact with the electrode plate or the sponge-like metal porous body.

2. A process for injecting a solution containing a metal present in an ionic state into a container in which an electrode plate is disposed; a step of allowing the solution to stand still relative to the electrode plate; a step of forming a sponge-like porous metal body on the electrode plate serving as a cathode by passing an electric current between the electrode plates; A peeling step of peeling off the sponge-like metal porous body from the electrode, The metal recovery method, wherein the peeling step is a step of applying vibration to the electrode plate.

3. A process for injecting a solution containing a metal present in an ionic state into a container in which an electrode plate is disposed; a step of allowing the solution to stand still relative to the electrode plate; a step of forming a sponge-like porous metal body on the electrode plate serving as a cathode by passing an electric current between the electrode plates; A peeling step of peeling off the sponge-like metal porous body from the electrode, A metal recovery method, wherein the peeling step is a step of reversing the polarity of the electrode plate.

4. A metal recovery method as described in claim 1, wherein the standing process, the sponge-like metal porous body formation process, and the peeling process are repeated until the metal ion concentration in the solution falls below a predetermined value.

5. A metal recovery method described in claim 2, wherein the standing process, the sponge-like metal porous body formation process, and the peeling process are repeated until the metal ion concentration in the solution falls below a predetermined value.

6. A metal recovery method described in claim 3, wherein the standing process, the sponge-like metal porous body formation process, and the peeling process are repeated until the metal ion concentration in the solution falls below a predetermined value.