JP7103626B2 - Lithium recovery device and lithium recovery method - Google Patents

Description

The present invention relates to a lithium recovery device and a lithium recovery method for selectively recovering lithium ions from an aqueous solution.

Lithium (Li) is a resource that is in high demand as a raw material for lithium ion secondary batteries, fuels for fusion reactors, and the like, and there is a demand for a stable supply and cheaper sampling method. As a stable source of Li, there is seawater dissolved in the form of cation Li ⁺ . Further, since the positive electrode of the lithium ion secondary battery mainly contains Li as lithium cobalt oxide (LiCoO ₂ ) or the like, an inexpensive recovery technique from a battery discarded due to battery life or the like is expected.

As a technique for recovering Li from seawater or the like, an adsorption method using a lithium adsorbent such as lithium manganese oxide has been widely applied. However, in the adsorption method, since the selectivity of the adsorbent is incomplete, a large amount of sodium, magnesium, calcium, potassium, etc. dissolved in seawater are also recovered with respect to Li at a low concentration (170 ppb). .. In addition, there are problems such as rapid deactivation of the surface of the adsorbent due to adhesion of suspensions and microorganisms, and limitation of the number of times of reuse due to insufficient mechanical strength of the adsorbent.

Therefore, recovery by an electrodialysis method using an electrolyte membrane having lithium ion conductivity has been developed (for example, Patent Document 1 and Non-Patent Document 1). The Li recovery method by the electrodialysis method will be described with reference to FIG. In the lithium recovery device 100, the treatment tank 1 is divided into a supply tank 11 and a recovery tank 12 by an electrolyte membrane 2 to which electrodes 131 and 132 made of porous membranes are attached on both sides, and a power supply 105 is connected between the electrodes 131 and 132. The positive (+) electrode is connected to the electrode 131 on the supply tank 11 side, and the negative (−) electrode is connected to the electrode 132 on the recovery tank 12 side. A Li-containing aqueous solution SW such as seawater is charged into the supply tank 11 as a Li source, and a Li recovery aqueous solution AS such as pure water is charged into the recovery tank 12. Then, when a voltage is applied, the electricity of the following formula (1) on the surface of the electrode 131 in contact with the aqueous solution SW of the supply tank 11 and the following formula (2) on the surface of the electrode 132 in contact with the aqueous solution AS of the recovery tank 12 A chemical reaction occurs. Then, due to the electrochemical potential difference of Li ⁺ (Li ⁺ (SW), Li ⁺ (electrolyte), Li ⁺ (AS)) contained in each of the aqueous solution SW, the electrolyte membrane 2 (electrolyte), and the aqueous solution AS, the aqueous solution SW From the inside, Li ⁺ permeates the electrolyte membrane 2 and moves to the aqueous solution AS. Since the size of the lattice defect site is small, the electrolyte membrane 2 does not allow metal ions M ^{n +} other than Li ⁺ contained in the aqueous solution SW, such as Na ⁺ and Ca ²⁺ , which have a diameter larger than Li ⁺ , to permeate. Therefore, Li ⁺ selectively moves from the aqueous solution SW to the aqueous solution AS, and an aqueous solution of Li ⁺ (lithium hydroxide (LiOH) aqueous solution) is obtained in the recovery tank 12.

Japanese Patent No. 6233877

Kunugi S., Inaguma Y., Itoh M., "Electrochemical recovery and isotope separation of lithium ion epitaxial lithium ion conductive perovskite-type oxides", Solid State Ionics, Vol. 122, Issues 1-4, pp. 35-39, July 1999

In the recovery method described in Patent Document 1 and the like, the larger the amount of each electron e ⁻ transferred from the aqueous solution SW to the electrode 131 and from the electrode 132 to the aqueous solution AS per hour, the more the equations (1) and (2). The reaction of Li + becomes faster, and the amount of movement of Li ⁺ per hour also increases. However, when the voltage of the power supply 105 is increased in an attempt to increase the amount of movement of electrons e- per hour ^, in reality, at a voltage above a certain level, the amount of movement of Li ⁺ per hour is unlikely to increase further. Become. It is considered that this is because the electrolyte membrane 2 also conducts the electron e ^- when the potential difference on both sides reaches the potential at which a part of the metal ions constituting the electrolyte is reduced. When such a voltage is applied, as shown by the thick broken line arrow in FIG. 7, the electrolyte membrane 2 moves a part of the electrons e ⁻ supplied from the negative electrode of the power supply 105 to the electrode 132 to the electrode 131. It ends up. As a result, even if the amount of movement of electrons e-moving from the electrode 131 to the electrode 132 via the power supply 105 increases due to the increase in the applied voltage, the amount of electrons e ^- moving between the aqueous solution SW and the electrode 131 and between the electrode 132 and the aqueous solution AS increases. Since the amount of movement of electrons e ^- in time does not increase so much, the amount of movement of Li ⁺ per hour does not increase. Moreover, energy efficiency will be reduced. Therefore, it can be said that this recovery method has a limit in improving productivity.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a lithium recovery method and a lithium recovery device by an electrodialysis method, which have high selectivity and productivity.

According to diligent research, the present inventors did not apply a voltage for electrodialysis from both sides of the electrolyte membrane and separated it from the electrolyte membrane in order to suppress the potential difference between the two sides so that electron conductivity was not exhibited in the electrolyte membrane. I came up with the idea of forming a circuit with the electrodes.

That is, the lithium recovery device according to the present invention includes a treatment tank partitioned into a first tank and a second tank, and the water or aqueous solution contained in the second tank contains lithium ions contained in the first tank. It is a device for moving lithium ions from the aqueous solution, and is provided in the lithium ion conductive electrolyte membrane that partitions the treatment tank, the first electrode provided in the first tank, and the second tank. A second electrode, a power supply for connecting a positive electrode to the first electrode and a negative electrode to the second electrode are provided. Then, in the lithium recovery device according to the present invention, the first electrode has a porous structure and is provided in contact with one surface of the lithium ion conductive electrolyte membrane, and the second electrode is the lithium ion conduction device. The configuration is provided so as to be separated from the sex electrolyte membrane. Alternatively , in the lithium recovery device according to the present invention, one of the first electrode and the second electrode has a porous structure and is provided in contact with one surface of the lithium ion conductive electrolyte membrane, and the other is provided. A third electrode having a porous structure provided apart from the lithium ion conductive electrolyte membrane and provided in contact with the surface opposite to the one surface of the lithium ion conductive electrolyte membrane is further provided , and the power supply is provided. As a configuration including a first power supply and a second power supply connected in series, the third electrode is connected between the first power supply and the second power supply.

With this configuration, in the lithium recovery device according to the present invention, by providing the electrode connected to one electrode of the power supply at a distance from the electrolyte membrane, the electrolyte membrane has a large potential difference on both sides even if the applied voltage is large. Since the electron conductivity is not exhibited, the electrons supplied from the second electrode do not conduct the electrolyte film to the first electrode side. Therefore, as the applied voltage increases, the amount of lithium transferred per hour increases.

Further, in the lithium recovery method according to the present invention, in a treatment tank divided into a first tank and a second tank by a lithium ion conductive electrolyte membrane, the water or aqueous solution contained in the second tank is added to the first tank. This is a method of moving lithium ions from the contained aqueous solution containing lithium ions. The lithium recovery method according to the present invention comprises an electrode having a porous structure provided in contact with the surface of the lithium ion conductive electrolyte membrane on the side of the first tank, and the lithium ion in the second tank. A power source connected to a second electrode provided so as to face the opposite surface of one surface of the conductive electrolyte film so as to be separated from the surface and the side of the first tank as a positive electrode applies a voltage. .. Alternatively, in the lithium recovery method according to the present invention, the side of the first tank is connected as a positive electrode between electrodes having a porous structure provided in contact with both sides of the lithium ion conductive electrolyte membrane. An electrode having a porous structure connected to one power source in series with the first power source and provided on the side of one of the first tank or the second tank, and the porous structure in the one tank. A voltage is applied by a second power source connected between an electrode having a quality structure and a second electrode provided apart from the lithium ion conductive electrolyte membrane.

By such a method, by connecting a power source between an electrode provided in contact with one side of the electrolyte membrane and an electrode separated from the electrolyte membrane and applying a voltage, the electrolyte membrane can be formed on both sides even if the voltage increases. Since the potential difference between the two is not large and the electron conductivity is not exhibited, the electrons supplied from the electrodes in the second tank connected to the negative electrode of the power supply do not conduct the electrolyte membrane to the first tank side. Therefore, by increasing the applied voltage, the amount of lithium transferred per hour can be increased.

According to the lithium recovery device and the lithium recovery method according to the present invention, lithium can be selectively and quickly recovered from an aqueous solution such as seawater in which lithium coexists with other metal ions at an extremely low concentration to achieve productivity. Can be improved, and energy efficiency is unlikely to decrease.

It is the schematic explaining the structure of the lithium recovery apparatus which concerns on 1st Embodiment of this invention. It is the schematic of the lithium recovery apparatus shown in FIG. 1 explaining the lithium recovery method which concerns on 1st Embodiment of this invention. It is the schematic explaining the structure of the lithium recovery apparatus and the lithium recovery method which concerns on 2nd Embodiment of this invention. It is a graph which shows the voltage dependence of the movement amount of lithium per time in an Example and a comparative example. It is a graph which shows the voltage dependence of the energy consumption per lithium transfer amount in an Example and a comparative example. It is a graph which shows the voltage dependence of the potential difference between both sides of the lithium ion conductive electrolyte membrane in the Example which concerns on 1st Embodiment of this invention. It is the schematic of the lithium recovery apparatus explaining the conventional lithium recovery method by the electrodialysis method.

A mode for carrying out the lithium recovery device and the lithium recovery method according to the present invention will be described with reference to the drawings.

[First Embodiment]
(Lithium recovery device)
As shown in FIG. 1, the lithium recovery device 10 according to the first embodiment of the present invention has a first electrode coated on each surface of a treatment tank 1, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2, and an electrolyte membrane 2. It includes a 31 and a third electrode 32, a second electrode 4, and a power supply 5. The treatment tank 1 is composed of an electrolyte membrane 2 and a supply tank (first tank) 11 for accommodating a Li-containing aqueous solution SW such as seawater and a recovery tank (second tank) 12 for accommodating an aqueous solution AS for Li recovery. It is divided into two. The second electrode 4 is provided in the recovery tank 12 at a distance from the electrolyte membrane 2. In the power supply 5, the positive (+) electrode is connected to the first electrode 31, and the negative (−) electrode is connected to the second electrode 4. That is, the lithium recovery device 10 according to the present embodiment newly adds a connection destination of the negative electrode of the power supply 5 to the conventional lithium recovery device by the electrodialysis method (for example, the lithium recovery device 100 shown in FIG. 7). The configuration is changed to the second electrode 4. Hereinafter, each element constituting the lithium recovery device according to the embodiment of the present invention will be described.

The treatment tank 1 is made of a material that does not deteriorate even if it comes into contact with the Li-containing aqueous solution SW and the Li recovery aqueous solution AS (for example, lithium hydroxide (LiOH) aqueous solution) including after Li recovery. The processing tank 1 may have a volume corresponding to the required processing capacity, and the shape and the like are not particularly limited.

It is preferable that the electrolyte membrane 2 is an electrolyte that has lithium ion conductivity and does not conduct metal ions M ^{n +} other than Li ⁺ contained in the Li-containing aqueous solution SW, and further does not conduct electrons e ⁻ . The metal ions M ⁿ + other than Li ⁺ are, for example, Na ⁺ , Mg ²⁺ , Ca ²⁺ , etc. when the Li-containing aqueous solution SW is seawater. More preferably, it is a ceramic electrolyte having these properties. Specific examples thereof include lithium lanthanum titanium oxide (La _{2 / 3-x} Li _3x TiO ₃ , also referred to as LLTO).

The first electrode 31 is an electrode provided for contacting the surface of the electrolyte membrane 2 on the supply tank 11 side and pairing with the second electrode 4 described later to apply a voltage. The first electrode 31 has a porous structure such as a network so that the Li-containing aqueous solution SW comes into contact with a sufficient area on the surface of the electrolyte membrane 2 while applying a voltage over a wide range of the electrolyte membrane 2. The first electrode 31 is made of an electrode material that has catalytic activity and electron conductivity for the reaction of the following formula (3) and the reaction of the following formula (4) and is stable even when a voltage is applied in a Li-containing aqueous solution SW. Further, it is preferable that the material is easily processed into the above-mentioned shape, and for example, platinum (Pt) is preferable.

The third electrode 32 is provided in contact with the surface of the electrolyte membrane 2 on the recovery tank 12 side, if necessary, so that the Li recovery aqueous solution AS comes into contact with a sufficient area on the surface of the electrolyte membrane 2. Like the one electrode 31, it has a porous structure such as a net. The third electrode 32 has catalytic activity and electron conductivity for the reaction of the following formula (5) in which Li ⁺ in the electrolyte membrane 2 is eluted into the Li recovery aqueous solution AS, and the Li recovery aqueous solution including after Li recovery. It is preferably a material that is formed of an electrode material that is stable even when a voltage is applied in AS and that can be easily processed into the shape, and for example, platinum (Pt) is preferable.

The second electrode 4 is an electrode provided in the recovery tank 12 in pair with the first electrode 31 to apply a voltage, and is arranged so as not to come into contact with the electrolyte membrane 2 and the third electrode 32. Further, the second electrode 4 is preferably arranged in parallel with the first electrode 31, and is preferably in a mesh shape or the like so as to increase the contact area with the Li recovery aqueous solution AS. The second electrode 4 has catalytic activity and electron conductivity for the reaction of the following formula (6), and is formed of an electrode material that is stable even when a voltage is applied in the Li recovery aqueous solution AS including after Li recovery. Platinum (Pt) and nickel (Ni) are preferable.

The power supply 5 is a DC power supply device, in which the positive electrode is connected to the first electrode 31 and the negative electrode is connected to the second electrode 4, and a predetermined voltage is applied.

The Li-containing aqueous solution SW is a Li source and is an aqueous solution containing other metal ions M ^{n +} such as Na ⁺ and Ca ²⁺ in addition to the lithium ion Li ⁺ . Examples of such an aqueous solution include an aqueous solution in which seawater, hot spring water, a used lithium ion secondary battery and the like are crushed and dissolved in an acid, and then the pH is adjusted.

The Li recovery aqueous solution AS is a solution for containing the lithium ion Li ⁺ recovered from the Li-containing aqueous solution SW. In order to selectively obtain only Li from the metals, the Li recovery aqueous solution AS is preferably an aqueous solution that does not contain metal ions (Na ⁺ or the like) other than lithium ion Li ⁺ , and may be pure water. However, in order to allow the movement of Li ⁺ to proceed smoothly at the start of recovery (at the start of power application), the Li recovery aqueous solution AS is an aqueous solution containing a small amount of Li ⁺ (lithium hydroxide (LiOH) aqueous solution). Is preferable.

(Lithium recovery method)
The lithium recovery method according to the first embodiment of the present invention will be described with reference to FIG. The lithium recovery method according to the present embodiment is carried out as follows by the lithium recovery device 10 according to the first embodiment shown in FIG.

In the lithium recovery device 10, when the power source 5 applies a positive voltage V to the first electrode 31 with respect to the second electrode 4, in the vicinity of the first electrode 31, hydroxide ions (hydroxide ions) in the Li-containing aqueous solution SW ( OH ⁻ ) causes the reaction of the following equation (3) to release the electron e ⁻ to the first electrode 31 to generate water (H ₂ O) and oxygen (O ₂ ). In the Li-containing aqueous solution SW, the reaction of the following formula (4) in which Li ⁺ in the Li-containing aqueous solution SW moves into the electrolyte membrane 2 in order to maintain the charge balance as the OH ⁻ decreases is carried out by the electrolyte. It occurs in the vicinity of the film 2, that is, in the vicinity of the first electrode 31. When the reactions of the following equation (3) and the following equation (4) are combined, the reaction of the following equation (1) occurs in the vicinity of the first electrode 31. On the other hand, in the vicinity of the second electrode 4, H ₂ O in the Li recovery aqueous solution AS is supplied with electrons e ⁻ to cause the reaction of the following equation (6), and hydrogen (H ₂ ) and OH ⁻ are generated. To generate. In the Li recovery aqueous solution AS, the reaction of the following formula (5) in which Li ⁺ in the electrolyte membrane 2 moves in order to maintain the charge balance as OH ⁻ increases is carried out by the electrolyte membrane 2. Occurs in the vicinity. When the reactions of the following formula (6) and the following formula (5) are combined, the reaction of the following formula (2) occurs in the Li recovery aqueous solution AS.

In this way, even if the second electrode 4, which is one of the pair of electrodes connected to the power source 5, is arranged apart from the electrolyte membrane 2, the formula is the same as in the conventional lithium recovery method (see FIG. 7). The reactions of (1) and (2) can be generated, and Li ⁺ in the Li-containing aqueous solution SW can be selectively conducted in the electrolyte membrane 2 and moved into the Li recovery aqueous solution AS for recovery. Since the second electrode 4 is separated from the electrolyte membrane 2 by being separated by the Li recovery aqueous solution AS, the potential difference between both sides of the electrolyte membrane 2 is small with respect to the voltage V of the power supply 5. Therefore, even if the applied voltage V is large, it is difficult for the electrolyte membrane 2 to conduct electrons e ⁻ . On the other hand, since the first electrode 31 is provided in contact with the electrolyte membrane 2, the equations (1) and (2) do not require a significant increase in the voltage V as compared with the conventional lithium recovery method. Reaction is likely to occur. Further, since the third electrode 32 is provided in contact with the surface of the electrolyte membrane 2 in contact with the Li recovery aqueous solution AS, the reaction in which Li ⁺ in the electrolyte membrane 2 is eluted into the Li recovery aqueous solution AS is active. Even if the second electrode 4 is separated from the electrolyte membrane 2, the reaction of the formula (2) is likely to occur. The longer the distance between the second electrode 4 and the electrolyte membrane 2, the higher the effect of the present invention, and even if the voltage V is large, it is difficult for the electrolyte membrane 2 to conduct electrons e- ^, while the voltage V is sufficiently applied. If it is not increased, there will be no electrochemical potential difference for Li ⁺ to move.

(Modification example)
The lithium recovery device 10 according to the first embodiment may have a structure in which the third electrode 32 is not provided, that is, the first electrode 31 is formed on only one side of the electrolyte membrane 2. Alternatively, the lithium recovery device 10 is provided with an electrode (not shown) separated from the electrolyte membrane 2 and the first electrode 31 in the supply tank 11 instead of the second electrode 4, and the positive electrode of the power supply 5 is attached to this electrode. It is also possible to connect and connect the negative electrode to the third electrode 32. In such a configuration, in the Li-containing aqueous solution SW, the reaction of the formula (3) occurs in the vicinity of the electrode separated from the electrolyte membrane 2, and the reaction of the formula (4) occurs in the vicinity of the electrolyte membrane 2. The reaction of the formula (1) occurs by integrating the reactions. Therefore, as in the embodiment shown in FIG. 2, Li ⁺ can be selectively conducted in the electrolyte membrane 2, and the movement of Li ⁺ per time is performed by increasing the voltage V of the power supply 5. The amount can be increased. However, when the negative electrode of the power source 5 is in contact with the electrolyte membrane 2, the constituent elements of the electrolyte membrane 2 tend to be reduced, so that the applied voltage V is preferably not very large. Further, since the Li-containing aqueous solution SW has high electron conductivity depending on the concentration of metal ions M ^{n +} and the like, the potential of the surface of the electrolyte membrane 2 on the supply tank 11 side becomes close to the positive electrode of the power supply 5, and the electrolyte membrane 2 The potential difference on both sides tends to be large.

[Second Embodiment]
In the first embodiment, the potential difference between both sides of the electrolyte membrane is suppressed by not directly connecting the power supply to one side of the electrolyte membrane. However, as the recovery of lithium progresses, the potential of the surface of the electrolyte membrane on the recovery tank side approaches the negative electrode of the power supply through the aqueous solution on the recovery tank side where the electron conductivity is increased. Therefore, when the applied voltage V is large, the potential difference on both sides of the electrolyte membrane reaches the potential at which some of the metal ions constituting the electrolyte membrane are reduced (for example, Ti ⁴⁺ + e-→ Ti ³⁺ ), ^and the electrolyte There is a risk that the film will conduct electrons ^e- . Therefore, in order to further suppress the potential difference on both sides of the electrolyte membrane with respect to the applied voltage, the following configuration is used. Hereinafter, the lithium recovery device and the lithium recovery method according to the second embodiment of the present invention will be described with reference to FIG. The same elements as those in the first embodiment (see FIGS. 1 and 2) are designated by the same reference numerals, and the description thereof will be omitted.

(Lithium recovery device)
The lithium recovery device 10A according to the second embodiment of the present invention includes a treatment tank 1, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2, and a first electrode 31 and a third electrode 32 coated on each surface of the electrolyte membrane 2. The second electrode 4 and the power source 5A in which the first power source 51 and the second power source 52 are connected in series are provided. That is, the lithium recovery device 10A according to the present embodiment includes a power supply 5A instead of the power supply 5 with respect to the lithium recovery device 10 according to the first embodiment, and further, a third electrode 32 between the power supplies 51 and 52 of the power supply 5A. It is a configuration in which is connected.

The first power supply 51 and the second power supply 52 are DC power supply devices, respectively, and the first power supply 51 is connected in series on the positive electrode side and the second power supply 52 is connected in series on the negative electrode side to form a power supply 5A. In the first power source 51, the positive electrode is connected to the first electrode 31, the negative electrode is connected to the second power source 52, and the negative electrode is connected to the third electrode 32. That is, the first power supply 51 is connected between the first electrode 31 and the third electrode 32 provided in contact with both surfaces of the electrolyte membrane 2. The first power supply 51 connected in this way is provided to keep the potential difference on both sides of the electrolyte membrane 2 constant. On the other hand, in the second power supply 52, the negative electrode is connected to the second electrode 4. That is, in the entire power supply 5A, the positive electrode is connected to the first electrode 31 and the negative electrode is connected to the second electrode 4 as in the power supply 5. The second power supply 52 connected in this way is provided to set the voltage V applied by the power supply 5A.

(Lithium recovery method)
In the lithium recovery method according to the second embodiment of the present invention, when the power source 5A applies a voltage V, the reaction of the following formula (1) is carried out in the Li-containing aqueous solution SW in the supply tank 11 as in the first embodiment. In the Li recovery aqueous solution AS in the recovery tank 12, the reaction of the following formula (2) occurs, and Li ⁺ in the Li-containing aqueous solution SW is conducted in the electrolyte membrane 2 and moved into the Li recovery aqueous solution AS. .. In the present embodiment, the first power source 51 keeps the potential difference between the first electrode 31 and the third electrode 32 sandwiching the electrolyte membrane 2 from both sides constant. That is, even if the voltage V of the entire power source 5A is increased by the second power source 52, or the electron conductivity of the Li recovery aqueous solution AS increases due to an increase in Li ⁺ concentration or the like, the recovery tank 12 of the electrolyte film 2 Since the potential on the side surface is fixed by the third electrode 32 connected to the negative electrode of the first power supply 51, it does not approach the potential of the second electrode 4. Therefore, by setting the voltage V1 of the first power supply 51 to be less than the potential difference at which the electrolyte membrane 2 has electron conductivity, the electrolyte membrane 2 can conduct electrons e ^- even if the voltage V of the power supply 5A is large. However, the recovery rate of Li ⁺ can be increased.

The lithium recovery method according to the present embodiment is particularly effective when the applied voltage V is large, and therefore it is preferable that the voltage V2 of the second power supply 52 is larger than the voltage V1 of the first power supply 51 (V1 + V2 = V). .. The voltage V1 of the first power supply 51 may be set according to the electron conductivity of the electrolyte membrane 2 as described above, while the lower limit is not particularly specified, but is preferably more than 0 V. Due to the potential gradient between both sides of the electrolyte membrane 2, Li ⁺ , which is a cation adsorbed on the surface of the electrolyte membrane 2 on the supply tank 11 side, causes the electrolyte membrane 2 to move to the surface of the low potential recovery tank 12 side. Easy to conduct and move.

(Modification example)
The lithium recovery device 10A according to the second embodiment has an electrode (FIG.) separated from the electrolyte membrane 2 and the first electrode 31 in the supply tank 11 instead of the second electrode 4, as in the modified example of the first embodiment. (Not shown) may be provided, and the second power supply 52 may be further connected to the positive electrode side of the first power supply 51 to connect the positive electrode of the second power supply 52 to the electrode in the supply tank 11. Even in such a configuration, the voltage V2 of the second power supply 52 can be increased to increase the amount of movement of Li ⁺ per hour.

The lithium recovery devices 10 and 10A according to the first and second embodiments may include a circulation device that circulates the Li-containing aqueous solution SW between the outside and the supply tank 11. The circulation device includes, for example, a pump, a filter for removing dust and the like, and the like. In particular, when the Li-containing aqueous solution SW is seawater, hot spring water, or the like, it is preferable to apply a voltage while circulating the Li-containing aqueous solution SW from these supply sources into the supply tank 11. By such a method, the Li ⁺ concentration of the Li-containing aqueous solution SW is maintained almost constant even if the recovery of Li ⁺ progresses, and the Li recovery rate is unlikely to decrease even with a low-concentration Li aqueous solution for a long time. Continuous operation is possible. Alternatively, the Li-containing aqueous solution SW in the supply tank 11 may be replaced by the circulation device every fixed time of operation. Further, the lithium recovery devices 10 and 10A may have a structure in which the supply tank 11 is opened to the outside (for example, in the sea) via a filter or the like.

The lithium recovery device and the lithium recovery method according to the present invention have been described above in terms of embodiments of the present invention, but examples of confirmed effects of the present invention will be described below. It should be noted that the present invention is not limited to this example and the above-described embodiment, and it goes without saying that various modifications, modifications, etc. based on these descriptions are also included in the gist of the present invention.

For the lithium recovery device according to the first and second embodiments of the present invention shown in FIGS. 1 to 3, and the conventional lithium recovery device shown in FIG. 7 as a comparative example, the amount of lithium movement due to voltage application for a certain period of time is measured. It was measured.

(Manufacturing of lithium recovery device)
As the lithium recovery device, a plate-shaped La _0.57 Li _0.29 TiO ₃ (lithium ion conductive ceramics LLTO, manufactured by Toho Titanium Co., Ltd.) having a thickness of 50 mm × 50 mm and a thickness of 0.5 mm was used as the electrolyte film. At the center of each of the two sides of the electrolyte membrane, grid-like electrodes having a thickness of 10 μm, a width of 0.5 mm, and an interval of 0.5 mm are provided as the first electrode and the third electrode in a size of 19.5 mm × 20.5 mm. A lead wire for connecting to a power source was formed, which was formed in the above and further connected to this electrode. The first electrode, the third electrode, and the lead wire were formed by screen-printing Pt paste on the surface of the electrolyte membrane and firing at 900 ° C. for 1 h in the air. Further, as the second electrode, a 20 mm × 20 mm Ni mesh electrode was used. The electrolyte membrane on which the electrodes and the like are formed is mounted in a processing tank made of an acrylic plate and partitioned into a supply tank and a recovery tank, and the second electrode is arranged in the recovery tank so as to face the third electrode on the surface of the electrolyte membrane. Then (distance between the second electrode and the electrolyte membrane: 50 mm), a lithium recovery device was used.

A 1 mol / l lithium hydroxide aqueous solution as a Li-containing aqueous solution was placed in the supply tank of the lithium recovery device, and a 0.001 mol / l lithium hydroxide aqueous solution as a Li recovery aqueous solution was placed in the recovery tank in an amount of 150 ml each at the first electrode and the second. It was charged so that the electrode and the third electrode were completely immersed.

(Example 1)
As shown in FIG. 2, the positive electrode of the power supply was connected to the first electrode, the negative electrode was connected to the second electrode, and a DC voltage was applied without connecting anything to the third electrode. When the voltage was applied, the current value was measured with an ammeter (not shown) connected in series with the power supply. Then, after applying the voltage for 1 hour, the Li concentration of the aqueous solution in the recovery tank was measured by an inductively coupled plasma emission spectrometry (ICP-OES) apparatus (Optima 7000DV, manufactured by PerkinElmer Co., Ltd.), and the amount of movement of Li was calculated. did. A similar experiment was performed with the applied voltage varied from 1V to 10V in 1V increments. The experiment was carried out at room temperature (24 ° C.) including Examples 2-1 and 2-2 and Comparative Examples.

(Example 2-1)
As shown in FIG. 3, the positive electrode of the first power supply is connected to the first electrode, the negative electrode is connected to the third electrode and the positive electrode of the second power supply, and the negative electrode of the second power supply is connected to the second electrode. A DC voltage was applied from the power source and the second power source. Further, an ammeter was inserted and connected between the second power supply and the second electrode (not shown). Similar to Example 1, the current value was measured when the voltage was applied, and the Li concentration of the aqueous solution in the recovery tank was measured after the application was stopped. In Example 2-1 the voltage of the first power supply is fixed to 2V, the sum of the voltages of the first power supply and the second power supply is used as the applied voltage, and the voltage of the second power supply is set in 1V increments from 3V to 8V. Was changed and the experiment was conducted.

(Example 2-2)
In FIG. 3, simulating the case where the first power supply is 0 V, the first power supply is removed from Example 2-1 and the first electrode and the third electrode are short-circuited and connected to the positive electrode of the second power supply. , A DC voltage was applied from the second power source. Similar to Example 1, the current value was measured when the voltage was applied, and the Li concentration of the aqueous solution in the recovery tank was measured after the application was stopped. In Example 2-2, the experiment was performed by setting the applied voltage to 3V, 4V, and 10V.

(Comparison example)
The second electrode is removed from the lithium recovery device, and as shown in FIG. 7, the positive electrode of the power supply is connected to the first electrode and the negative electrode is connected to the third electrode, and the current value is measured in the same manner as in Example 1. A DC voltage was applied, and after the application was stopped, the Li concentration of the aqueous solution in the recovery tank was measured. In the comparative example, the experiment was performed by setting the applied voltage to 2V, 3V, and 4V.

For each of Example 1, Example 2-1 and Example 2-2, and Comparative Example, the amount of Li movement due to voltage application for 1 hour was calculated for each applied voltage. In addition, the energy consumption per 1 mg of Li transfer amount was calculated from the applied voltage, the measured current value, and the Li transfer amount. The amount of movement of Li per time and the amount of energy consumed per amount of Li movement are shown in FIGS. 4 and 5 in a voltage-dependent graph.

In the comparative example in which the power supply was connected between the first electrode and the third electrode connected to both sides of the electrolyte membrane, the amount of movement of Li per hour increased when the applied voltage was increased from 2V to 3V, but further. Even if it was increased to 4V, there was almost no change from the time when 3V was applied. Further, when 2V was applied, almost no current flowed, that is, the electrolyte membrane did not show electron conductivity, but when 3V was applied, a large amount of current flowed, and even if the amount of movement of Li per hour increased. The energy consumption increased significantly beyond that. It was confirmed that when 4 V was applied, the current value increased about twice as much as when 3 V was applied, and the amount of movement of Li per hour hardly changed, and it was difficult to further increase the amount of movement. ..

In Example 1 in which a power source was connected between the first electrode connected to one side of the electrolyte membrane and the second electrode separated from the electrolyte membrane, Li ⁺ hardly moved when the applied voltage was 3 V or less. This is because not only the electrolyte membrane but also an extremely low concentration lithium hydroxide aqueous solution having low electron conductivity exists between the first electrode and the second electrode, so that the potential difference near both sides of the electrolyte membrane is small, and Li ⁺ It is presumed that this was because it did not conduct the electrolyte film. However, when the applied voltage becomes 4 V or more, the amount of movement of Li ⁺ becomes sufficiently large, and the amount of movement of Li per hour increases in proportion to the voltage. Further, as the voltage increased, the current value increased and the energy consumption for moving a certain amount of Li gradually increased, but the amount of change was small and there was no problem in terms of energy efficiency. The increase in energy consumption is mainly due to the overvoltage generated in the first and second electrodes connected to both electrodes of the power supply and the energy loss due to heat generation (Joule heat) generated by the electron conduction of the lithium hydroxide aqueous solution in the recovery tank. Conceivable. In Example 1, a voltage of about 6.3 V is required to obtain the amount of movement of Li corresponding to the applied voltage of 3 V in the comparative example. However, in Example 1, since electron conduction hardly occurs in the electrolyte membrane even when a voltage of such a magnitude is applied, unnecessary current that is not involved in the movement of Li ⁺ does not flow and is consumed as compared with Comparative Example. Energy is significantly reduced. Therefore, in the first embodiment, by increasing the applied voltage, the amount of movement of Li per hour can be increased to speed up the recovery of Li, and the energy efficiency is hardly lowered.

In Example 2-1 in which the power supply in which the first power supply and the second power supply are connected in series is connected between the first electrode and the second electrode, and the third electrode is connected between the first power supply and the second power supply. Since the voltage between the first electrode and the third electrode connected to both sides of the electrolyte membrane was secured at 2V by the first power supply, the amount of movement of Li was sufficiently large even when the total applied voltage was 3V. Further, unlike the case of applying 3V in the comparative example, the current due to the electron conduction of the electrolyte membrane hardly flows, so that the energy efficiency is good. Then, as in Example 1, the amount of movement of Li per hour increased in proportion to the applied voltage. Further, the energy consumption for moving a certain amount of Li was sufficiently small, although the amount of change with increasing voltage was larger than that of Example 1, and was within a range where there was no problem from the viewpoint of energy efficiency.

In Example 2-2 in which the first electrode and the third electrode connected to both sides of the electrolyte membrane were short-circuited, Li ⁺ hardly moved when the applied voltage was 3 V, as in Example 1, and the voltage was increased to 4 V or more. The amount of movement of Li per hour increased in proportion to. In addition, the energy consumption for moving a certain amount of Li is sufficiently small, and as in Example 2-1 there is an effect of suppressing electron conduction in the electrolyte membrane and speeding up Li recovery by applying a large voltage. It can be said that. However, in Example 2-2, the amount of movement of Li per hour was smaller than that in Example 2-1 and Example 1. It is presumed that this is because the electrolyte membrane is fixed at the same potential on both sides and there is no potential gradient. That is, in Example 2-1 it can be said that the movement of Li ⁺ in the electrolyte membrane was promoted because the first power source provided a potential gradient of 2 V between both sides of the electrolyte membrane. Further, in Example 1, when the applied voltage becomes 4 V or more, electron conduction occurs in the lithium hydroxide aqueous solution in the recovery tank, and the potential of the surface of the electrolyte film on the recovery tank side (third electrode side) by the second electrode. However, it is presumed that the potential gradient was generated below the surface on the first electrode side connected to the positive electrode of the power supply.

As described above, in Example 1, the surface of the electrolyte membrane on the recovery tank side was not directly applied with a voltage, but it was presumed to have a low potential with respect to the surface on the supply tank side. Therefore, in Example 1, a voltmeter was connected between the first electrode and the third electrode, and the potential difference between both sides of the electrolyte membrane was measured. As shown in FIG. 6, the potential difference between both sides of the electrolyte membrane of Example 1 gradually increases as the applied voltage increases, and when the applied voltage is 7 V or more, the potential difference becomes 2 V, which is the fixed potential difference of Example 2-1. Almost reached. As described above, in Example 1, the movement of Li ⁺ in the electrolyte membrane was promoted by generating a potential difference between both sides of the electrolyte membrane as in Example 2-1. On the other hand, in Example 1, the applied voltage did not reach 10 V or less, but when a larger voltage was applied, the potential difference on both sides was reached so that the electrolyte membrane had electron conductivity, and as in the comparative example, It is presumed that the amount of movement of Li per hour is unlikely to increase any more. According to the comparative example, the electrolyte membrane has electron conductivity when the potential difference between the two surfaces is at least 3 V or more. On the other hand, in Examples 2-1 and 2-2, even if the applied voltage is further increased, the electrolyte membrane is unlikely to have electron conductivity, and the amount of Li transferred per hour can be further increased. It is presumed that it can be done. Further, in Example 1, the potential difference between both sides of the electrolyte membrane when 4 V was applied when the amount of Li movement was sufficiently large was 1.1 V. Therefore, in Example 2-1 on both sides of the electrolyte membrane. It is presumed that the potential difference between them, that is, the voltage of the first power source is preferably about 1 V or more.

From the above, it was confirmed that both the lithium recovery device and the lithium recovery method according to the first and second embodiments of the present invention realize high-speed recovery of Li and suppression of increase in energy consumption. Further, if the applied voltage does not allow the electrolyte membrane to have electron conductivity, the lithium recovery device according to the first embodiment of the present invention having a relatively simple structure is suitable, while Li recovery is faster. It can be said that the lithium recovery device according to the second embodiment of the present invention is suitable for this purpose.

10,10A Lithium recovery device 1 Treatment tank 11 Supply tank (1st tank)
12 Recovery tank (2nd tank)
2 Electrolyte membrane (lithium ion conductive electrolyte membrane)
31 First electrode (electrode with porous structure)
32 Third electrode (electrode with a porous structure)
4 Second electrode (second electrode)
5,5A power supply 51 1st power supply 52 2nd power supply AS Li recovery aqueous solution SW Li-containing aqueous solution

Claims (8)

A treatment tank divided into a first tank and a second tank is provided, and lithium ions are transferred from the lithium ion-containing aqueous solution contained in the first tank to the water or aqueous solution contained in the second tank. It ’s a device,
The lithium ion conductive electrolyte membrane that partitions the treatment tank, the first electrode that is provided in contact with the surface of the lithium ion conductive electrolyte membrane on the first tank side and has a porous structure, and the inside of the second tank. A lithium recovery device comprising a second electrode provided separately from the lithium ion conductive electrolyte membrane , a positive electrode connected to the first electrode, and a power source connecting the negative electrode to the second electrode. .. A treatment tank divided into a first tank and a second tank is provided, and lithium ions are transferred from the lithium ion-containing aqueous solution contained in the first tank to the water or aqueous solution contained in the second tank. It ’s a device,
A lithium ion conductive electrolyte film that partitions the treatment tank, a first electrode provided in the first tank, a second electrode provided in the second tank, and a third electrode having a porous structure. A power source for connecting a positive electrode to the first electrode and a negative electrode to the second electrode is provided.
The power supply consists of a first power supply and a second power supply connected in series.
One of the first electrode and the second electrode has a porous structure and is provided in contact with one surface of the lithium ion conductive electrolyte membrane, and the other is provided apart from the lithium ion conductive electrolyte membrane. Be,
The third electrode is provided in contact with the surface opposite to the one surface of the lithium ion conductive electrolyte membrane, and is connected between the first power source and the second power source. Lithium recovery device. The first electrode is provided in contact with the surface of the lithium ion conductive electrolyte membrane on the first tank side and has a porous structure.
The lithium recovery device according to claim 2 , wherein the second electrode is provided apart from the lithium ion conductive electrolyte membrane. The lithium recovery device according to any one of claims 1 to 3 , further comprising a circulation means for circulating an aqueous solution containing lithium ions between the outside and the inside of the first tank. In a treatment tank divided into a first tank and a second tank by a lithium ion conductive electrolyte membrane, lithium is added to the water or aqueous solution contained in the second tank from the lithium ion-containing aqueous solution contained in the first tank. It is a lithium recovery method that moves ions.
An electrode having a porous structure provided in contact with the surface of the lithium ion conductive electrolyte membrane on the side of the first tank is opposed to the lithium ion conductive electrolyte membrane in the second tank so as to be separated from each other. A lithium recovery method, characterized in that a voltage is applied to a power source connected to a second electrode provided in the above with the side of the first tank as a positive electrode. In a treatment tank divided into a first tank and a second tank by a lithium ion conductive electrolyte membrane, lithium is added to the water or aqueous solution contained in the second tank from the lithium ion-containing aqueous solution contained in the first tank. It is a lithium recovery method that moves ions.
A first power source in which the side of the first tank is connected as a positive electrode between electrodes having a porous structure provided in contact with both sides of the lithium ion conductive electrolyte membrane.
An electrode having a porous structure, which is connected in series to the first power source and provided on the side of one of the first tank or the second tank, and an electrode having the porous structure in the one tank. A method for recovering lithium , which comprises applying a voltage to a second power source connected to the second electrode provided apart from the lithium ion conductive electrolyte membrane. The lithium recovery method according to claim 6 , wherein the second electrode is provided in the second tank. The lithium recovery according to any one of claims 5 to 7 , wherein the voltage is applied while circulating the aqueous solution containing lithium ions between the outside and the inside of the first tank. Method.

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