Lithium recovery device and lithium recovery method

Abstract

This lithium recovery device 10C is provided with a processing tank 1 that is partitioned into a supply tank 11 and a recovery tank 13 by a lithium ion-conducting electrolyte membrane 2. In order to selectively move Li+ to an aqueous solution RS in the recovery tank 13 from an aqueous solution SW in the supply tank 11, the aqueous solution SW containing Li+ and other metal ions Mn+, this lithium recovery device 10C is also provided with: a first power supply 51 which is connected between a first electrode 31 that has a porous structure and is arranged so as to be in contact with a supply tank 11-side surface of the electrolyte membrane 2 and a second electrode 32A that is arranged within the recovery tank 13, in such a manner that the first electrode 31 functions as the positive electrode; and a sub power supply 53 which is connected in series to the positive electrode of the first power supply 51, while having the positive electrode thereof connected to a sub electrode 41 that is arranged within the supply tank 11 at a distance from the electrolyte membrane 2.

Description

[Technical Field]

[0001] The present invention relates to a lithium recovery apparatus and a lithium recovery method for selectively recovering lithium ions from an aqueous solution. [Background technology]

[0002] Lithium (Li) is a highly sought-after resource used as a raw material for lithium-ion batteries and fusion reactor fuel, and there is a need for stable and inexpensive extraction methods. One stable source of Li is cation Li. + Li exists dissolved in seawater and other materials in this form. Furthermore, since the positive electrode of lithium-ion secondary batteries mainly contains lithium as lithium cobalt oxide (LiCoO2), etc., there is a demand for inexpensive recovery technologies from batteries that have been discarded due to battery life, etc. Adsorption methods have been conventionally applied to recover Li from seawater and other materials, but a more selective method has been developed: recovery by electrodialysis using an electrolyte membrane with lithium ion conductivity (for example, Patent Document 1, Non-Patent Document 1).

[0003] A lithium recovery method by electrodialysis described in Patent Document 1, etc., will be explained with reference to Figure 11. The lithium recovery apparatus 100 is configured such that a lithium ion conductive electrolyte membrane (hereinafter referred to as an electrolyte membrane) 2 divides the processing tank 1 into a supply tank 11 and a recovery tank 13, and a power supply 151 is connected between an electrode 131 placed in the supply tank 11 and an electrode 132 placed in the recovery tank 13, with electrode 131 as the positive electrode. A lithium-containing aqueous solution SW, such as seawater, is introduced into the supply tank 11 as a lithium source, and a lithium recovery aqueous solution RS, such as pure water, is introduced into the recovery tank 13.

[0004] When a voltage is applied by the power supply 151, the Li-containing aqueous solution SW in the supply tank 11 undergoes the reaction shown in equation (1) below near the electrode 131, generating water (H2O) and oxygen (O2). Furthermore, the Li-containing aqueous solution SW generates chloride ions (Cl - If it contains hydroxide ions (OH), the reaction shown in equation (2) below occurs near electrode 131, generating chlorine (Cl2). - ), and furthermore, Cl- As the anions such as + decrease, in order to maintain the charge balance, the Li in the Li-containing aqueous solution SW + undergoes the electrochemical reaction of the following formula (3) on the surface of the electrolyte membrane 2 and moves into the electrolyte membrane 2. In each formula, Li + contained in the electrolyte membrane 2 (electrolyte) is represented as Li [Chemical formula]

[0005] On the other hand, in the Li recovery aqueous solution RS in the recovery tank 13, near the electrode 132, the reaction of the following formula (4) occurs to generate hydrogen (H2) and OH - . As OH - increases, in order to maintain the charge balance, the Li in the electrolyte membrane 2 + undergoes the electrochemical reaction of the following formula (5) on the surface of the electrolyte membrane 2 and moves in. As a result, due to the electrochemical potential difference of Li + contained in each of the Li-containing aqueous solution SW, the electrolyte membrane 2, and the Li recovery aqueous solution RS, Li + permeates through the electrolyte membrane 2 and moves into the Li recovery aqueous solution RS. Since the size of the lattice defect sites of the electrolyte membrane 2 is small, metal ions M + such as Na + , Ca 2+ and the like, which have a larger diameter than Li + and are contained in the Li-containing aqueous solution SW, are not permeated. Therefore, Li n+ selectively moves from the Li-containing aqueous solution SW into the Li recovery aqueous solution RS, and an aqueous solution of Li + (lithium hydroxide aqueous solution) is obtained in the recovery tank 13. + [Chemical formula]

[0006] In the recovery by electrodialysis, electrons e from the Li-containing aqueous solution SW to the Li recovery aqueous solution RS from the electrodes 131 and 132 -The greater the amount of Li transferred per unit time, the faster the reactions in equations (1), (4), etc., occur, and Li in electrolyte membrane 2. + The amount of movement per unit time (Li + The mobility will also increase. Furthermore, in order to form an electric field in the thickness direction within the electrolyte membrane 2, it is preferable that electrodes 131 and 132 are provided in contact with the electrolyte membrane 2 (Patent Document 1), and in this case, the aqueous solutions SW and RS have a porous structure such as a mesh so that they are in contact with the electrolyte membrane 2. However, electron e - If you increase the voltage of power supply 151 in an attempt to increase the amount of movement per unit time, in reality, above a certain voltage, Li + The mobility becomes difficult to increase beyond that point. This is because, when the electrolyte membrane 2 is given a potential difference greater than a certain amount on both sides, it reaches a potential at which some of the metal ions constituting the electrolyte are reduced, and electron e - This is thought to be due to the fact that it also becomes conductive. When such a voltage is applied, the electrolyte membrane 2 receives electrons e supplied from the negative electrode of the power supply 151 to the electrode 132. - A portion of it is moved to electrode 131. As a result, electrons e move from electrode 131 to electrode 132 via power supply 151 as the applied voltage increases. - Even if the amount of electrons transferred per unit time increases, the electrons e between aqueous solution SW and electrode 131, and between electrode 132 and aqueous solution RS remain constant. - Since the amount of movement per unit time does not increase significantly, Li + The mobility does not increase as much as the applied voltage increases. Furthermore, electrons e conduct through the electrolyte membrane 2. - This method of generating energy using Joule thermal energy results in reduced energy efficiency. Therefore, it can be said that there are limitations to improving productivity with this recovery method.

[0007] Therefore, the present inventors have developed a technique to suppress the potential difference between the two sides of the electrolyte membrane by forming a circuit with electrodes spaced apart from the electrolyte membrane, rather than directly applying the voltage for electrodialysis to both sides of the electrolyte membrane in order to prevent the electrolyte membrane from exhibiting electronic conductivity (Patent Document 2). Specifically, as shown in Figure 11, the lithium recovery device 100 places one of the electrodes 131 and 132, in this case electrode 132, in the recovery tank 13, spaced apart from the electrolyte membrane 2. With this configuration, even if the voltage of the power supply 151 is increased to a certain extent, the potential difference between the two sides of the electrolyte membrane 2 does not become so large, and therefore the electrolyte membrane 2 is less likely to exhibit electronic conductivity, Li + It can increase mobility. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6233877 [Patent Document 2] Japanese Patent Publication No. 2019-141807 [Non-patent literature]

[0009] [Non-Patent Document 1] Kunugi S., Inaguma Y., Itoh M., "Electrochemical recovery and isotope separation of lithium ion employing lithium ion conductive perovskite-type oxides", Solid State Ionics, Vol. 122, Issues 1-4, pp. 35-39, July 1999 [Overview of the project] [Problems that the invention aims to solve]

[0010] As mentioned above, in the electrodialysis recovery method, as the applied voltage increases, Li +Mobility increases. However, if the Li-containing aqueous solution SW is seawater or contains chloride ions, in reality, Li + The mobility does not increase easily with respect to voltage. Furthermore, while platinum (Pt), which has excellent catalytic activity for the reaction in equation (1), is preferable for the positive electrode 131, if the Li-containing aqueous solution SW contains chloride ions, it forms platinum chloride (PtCl2), impairing the inherently high catalytic activity of platinum, increasing the electrode reaction overpotential and decreasing the reaction rate in equation (1). Also, in the recovery method by electrodialysis, Li + Mobility is Li to the electrolyte membrane surface. + Since the rate-limiting factor is the diffusion of Li in the electrolyte membrane, + If the Li concentration of the aqueous solution in contact with the supply side surface is low, it will not increase easily with respect to the applied voltage. When seawater is used as the Li source, the Li concentration is low, so it is difficult to further increase the recovery speed even with the recovery method described in Patent Document 2. In addition, lithium recovery from used lithium-ion secondary batteries requires a recovery rate closer to 100%. However, as lithium recovery progresses, the Li of the dissolution solution of the waste battery used as the Li source... + Since the concentration decreases, Li + As mobility decreases and the amount of Li remaining in the dissolution approaches zero, energy efficiency becomes extremely low. Therefore, these recovery methods have room for improvement in terms of productivity.

[0011] This invention has been made in view of the above-mentioned problems, and aims to provide a lithium recovery method and lithium recovery apparatus that can recover lithium by electrodialysis with high productivity from a low-concentration Li source containing chloride ions, such as seawater. [Means for solving the problem]

[0012] Through diligent research, the inventors discovered that chloride ions adsorbed on the surface of the electrolyte membrane inhibit the dissolution of lithium ions into the electrolyte membrane. They then conceived that by providing an electrode with a higher potential and spaced further away from the electrolyte membrane in the Li-containing aqueous solution on the positive electrode side, chloride ions are attracted by electrostatic force to the vicinity of this electrode, reducing the concentration near the electrolyte membrane surface. Simultaneously, lithium ions are attracted by electrostatic force to the vicinity of the electrolyte membrane surface where the relative potential is lower.

[0013] In other words, the lithium recovery apparatus according to the present invention comprises a processing tank partitioned into a first tank and a second tank, and is a device for moving lithium ions from an aqueous solution containing lithium ions contained in the first tank to water or an aqueous solution contained in the second tank. The lithium recovery apparatus according to the present invention comprises a lithium-ion conductive electrolyte membrane partitioning the processing tank, a first electrode having a porous structure provided in contact with the surface of the lithium-ion conductive electrolyte membrane on the first tank side, a second electrode provided in the second tank spaced apart from the lithium-ion conductive electrolyte membrane, a secondary electrode provided in the first tank and spaced apart from the first electrode and the lithium-ion conductive electrolyte membrane, a first power supply connected between the first electrode and the second electrode with the first electrode as positive, and a secondary power supply connected in series with the positive electrode of the first power supply and with the positive electrode connected to the secondary electrode. Another lithium recovery apparatus according to the present invention further comprises the second electrode having a porous structure and provided in contact with the lithium-ion conductive electrolyte membrane, a third electrode provided in the second tank spaced apart from the second electrode and the lithium-ion conductive electrolyte membrane, and a second power supply connected in series with the negative electrode of the first power supply and also connecting the negative electrode to the third electrode.

[0014] The lithium recovery method according to the present invention is a method of moving lithium ions from an aqueous solution containing lithium ions contained in the first tank to water or an aqueous solution contained in the second tank in a processing tank partitioned into a first tank and a second tank. The lithium recovery method according to the present invention applies a voltage between a first electrode having a porous structure provided in contact with the surface of the lithium ion conductive electrolyte membrane partitioning the processing tank on the first tank side, and a second electrode provided in the second tank spaced apart from the lithium ion conductive electrolyte membrane, with the first electrode as the positive terminal and a secondary power supply connected in series with the positive terminal of the secondary electrode provided in the first tank spaced apart from the lithium ion conductive electrolyte membrane. Another lithium recovery method according to the present invention involves a second power supply, the second electrode having a porous structure and provided in contact with the lithium-ion conductive electrolyte membrane, connected in series with the negative electrode of the first power supply, and the negative electrode of a third electrode provided in the second tank spaced apart from the second electrode and the lithium-ion conductive electrolyte membrane, to which a voltage is further applied. [Effects of the Invention]

[0015] According to the lithium recovery apparatus and lithium recovery method of the present invention, lithium can be selectively and rapidly recovered from aqueous solutions such as seawater, which contain chloride ions and lithium at extremely low concentrations, and which coexist with other metal ions, thereby improving productivity, and furthermore, energy efficiency is less likely to decrease. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram illustrating the configuration of a lithium recovery device according to the first embodiment of the present invention. [Figure 2] Figure 1 is a schematic diagram of a lithium recovery apparatus illustrating a lithium recovery method according to the first embodiment of the present invention. [Figure 3] Figure 1 is a circuit diagram of a lithium recovery apparatus illustrating a lithium recovery method according to a modified example of the first embodiment of the present invention. [Figure 4]This is a schematic diagram illustrating the configuration of a lithium recovery device according to a modified example of the first embodiment of the present invention. [Figure 5] Figure 4 is a schematic diagram of a lithium recovery apparatus illustrating a lithium recovery method according to a modified example of the first embodiment of the present invention. [Figure 6] This is a schematic diagram illustrating the configuration of a lithium recovery device and a lithium recovery method according to a modified example of the first embodiment of the present invention. [Figure 7] This is a schematic diagram illustrating the configuration of a lithium recovery apparatus and a lithium recovery method according to a second embodiment of the present invention. [Figure 8] Figure 7 is a circuit diagram of a lithium recovery apparatus illustrating a lithium recovery method according to a second embodiment of the present invention. [Figure 9A] This graph shows the dependence of the amount of lithium transferred per unit time on the Li source LiOH concentration in the examples and comparative examples according to the first embodiment of the present invention. [Figure 9B] This graph shows the dependence of the amount of lithium transferred per unit time on the Li source LiOH concentration in examples and comparative examples according to the second embodiment of the present invention. [Figure 10] This graph shows the amount of lithium transferred per unit time from a 0.001 mol / L LiOH aqueous solution and a 1.0 mol / L LiCl aqueous solution in the examples and comparative examples of the present invention. [Figure 11] This is a schematic diagram of a lithium recovery apparatus illustrating a conventional lithium recovery method using electrodialysis. [Modes for carrying out the invention]

[0017] Embodiments for implementing the lithium recovery apparatus and lithium recovery method according to the present invention will be described with reference to the drawings. In the drawings, the size of certain elements may be exaggerated, and shapes may be simplified, in order to clarify the explanation. In addition, in the description of each embodiment, elements identical to those in the previous embodiment will be denoted by the same reference numerals, and their explanations will be omitted as appropriate.

[0018] [First Embodiment] (Lithium recovery device) As shown in Figure 1, the lithium recovery apparatus 10 according to the first embodiment of the present invention comprises a processing tank 1, an electrolyte membrane (lithium-ion conductive electrolyte membrane) 2 that partitions the processing tank 1, a first electrode 31, a second electrode 32, a third electrode 33, and a sub-electrode 41 coated on each surface of the electrolyte membrane 2, and three power supplies connected in series: a sub-power supply 53, a first power supply 51, and a second power supply 52. ​​The lithium recovery apparatus 10 may further include a stirrer 72. The processing tank 1 is partitioned by the electrolyte membrane 2 into a supply tank (first tank) 11 that contains a Li-containing aqueous solution SW such as seawater, and a recovery tank (second tank) 13 that contains a Li recovery aqueous solution RS. The first electrode 31 is located on the supply tank 11 side, and the second electrode 32 is located on the recovery tank 13 side. The sub-electrode 41 is located in the supply tank 11, and the third electrode 33 is located in the recovery tank 13, both spaced apart from the electrolyte membrane 2. The first power supply 51 has its positive (+) terminal connected to the first electrode 31 and its negative (-) terminal connected to the second electrode 32. The second power supply 52 is connected in series with the negative terminal of the first power supply 51, that is, its positive terminal is connected to the second electrode 32 and its negative terminal is connected to the third electrode 33. The auxiliary power supply 53 is connected in series with the positive terminal of the first power supply 51, that is, its negative terminal is connected to the first electrode 31 and its positive terminal is connected to the auxiliary electrode 41. Therefore, the lithium recovery apparatus 10 according to this embodiment is configured in a way that, compared to a conventional lithium recovery apparatus using the electrodialysis method (for example, the lithium recovery apparatus 100 shown in Figure 11), the first power supply 51 (power supply 151 in Figure 11) applies a voltage directly between both sides of the electrolyte membrane 2, with both electrodes 31 and 32 (electrodes 131 and 132 in Figure 11) in contact with the electrolyte membrane 2, and additionally includes a sub-power supply 53 and a second power supply 52 connected in series to both electrodes of the first power supply 51, a sub-electrode 41 connected to the positive electrode of the sub-power supply 53, and a third electrode 33 connected to the negative electrode of the second power supply 52. ​​The elements constituting the lithium recovery apparatus according to this embodiment of the present invention will be described below.

[0019] The treatment tank 1 is made of a material that does not corrode or otherwise deteriorate even when in contact with the Li-containing aqueous solution SW and the Li recovery aqueous solution RS (for example, lithium hydroxide (LiOH) aqueous solution) including the Li after recovery. Furthermore, the treatment tank 1 only needs to have a volume corresponding to the required processing capacity, and its shape and other characteristics are not particularly limited.

[0020] The electrolyte membrane 2 has lithium ion conductivity and contains Li contained in the Li-containing aqueous solution SW. + Other metal ions M n+ It is an electrolyte that does not conduct electricity, and furthermore, electrons e - It is preferable that Li does not conduct electricity. + Other metal ions M n+ For example, if the Li-containing aqueous solution SW is seawater, then K + Na + Mg 2+ Ca 2+ These are examples. More preferably, the electrolyte membrane 2 is an electrolyte made of ceramics having these properties. Specifically, lithium lanthanum titanium oxide (La 2 / 3-x Li 3x Examples include TiO3 (also known as LLTO). Such electrolyte membranes 2 have a certain proportion of lattice defects, and because the size of these lattice defect sites is small, Li + Larger metal ions do not conduct electricity.

[0021] The first electrode 31 and the second electrode 32 are electrodes that work together to apply a voltage between both sides of the electrolyte membrane 2. The first electrode 31 is in contact with the side of the electrolyte membrane 2 facing the supply tank 11, and the second electrode 32 is in contact with the side of the electrolyte membrane 2 facing the recovery tank 13. Furthermore, in the lithium recovery apparatus 10 according to this embodiment, the first electrode 31 also applies a voltage in conjunction with the third electrode 33 described later. It is preferable that the first electrode 31 and the second electrode 32 have a porous structure such as a mesh so that a voltage is applied to a wide area of ​​the electrolyte membrane 2, while the Li-containing aqueous solution SW or the Li recovery aqueous solution RS comes into contact with a sufficient area of ​​the surface of the electrolyte membrane 2.

[0022] The first electrode 31 is preferably made of an electrode material that has catalytic activity and electronic conductivity for the reaction of formula (1) and the reaction of formula (3) below, is stable even when a voltage is applied in a Li-containing aqueous solution SW, and is also preferably made of a material that is easy to process into the aforementioned shape. The second electrode 32 is preferably made of an electrode material that has catalytic activity and electronic conductivity for the reaction of formula (5) and the reaction of formula (1) below, is stable even when a voltage is applied in a Li recovery aqueous solution RS, including after Li recovery, and is also preferably made of a material that is easy to process into the aforementioned shape. The first electrode 31 and the second electrode 32 are preferably made of such electrode materials, for example, platinum (Pt). Alternatively, the first electrode 31 may be made of a Li-containing aqueous solution SW which is Cl - If it contains, carbon (C) may be used. Note that the following formula (3) is used for Li in an aqueous solution (Li-containing aqueous solution SW). + This shows the reaction in which Li moves into the electrolyte membrane 2. Equation (5) below shows Li in the electrolyte membrane 2. + This reaction shows the transfer of lithium to an aqueous solution (Li recovery aqueous solution RS). [ka]

[0023] The auxiliary electrode 41 is an electrode that forms a higher potential than the surface of the electrolyte membrane 2 in the Li-containing aqueous solution SW. Therefore, it is preferable that the auxiliary electrode 41 is placed in the supply tank 11 so as not to contact the electrolyte membrane 2 and the first electrode 31, and is placed parallel to the first electrode 31. Furthermore, in order to keep the voltage V3 of the auxiliary power supply 53 low, it is preferable that the auxiliary electrode 41 is placed close to the first electrode 31 without causing a short circuit, as described below. In addition, it is preferable that the auxiliary electrode 41 has a mesh-like shape or the like to increase the contact area with the Li-containing aqueous solution SW. The auxiliary electrode 41 is formed of an electrode material that has catalytic activity and electronic conductivity for the reaction shown in formula (1) below, and is stable even when a voltage is applied in the Li-containing aqueous solution SW. If the Li-containing aqueous solution SW contains halide ions, the auxiliary electrode 41 is further protected against their oxidation reaction, for example, chloride ions (Cl -If ), it has catalytic activity for the reaction shown in formula (2) below. The auxiliary electrode 41 is preferably made of carbon (C), platinum (Pt), or carbon supported with platinum nanoparticles as a catalyst. [ka]

[0024] The third electrode 33 is an electrode for forming a potential lower than the surface of the electrolyte membrane 2 in the Li recovery aqueous solution RS. Therefore, it is preferable that the third electrode 33 is positioned in the recovery tank 13 so as not to contact the electrolyte membrane 2 and the second electrode 32, and is positioned parallel to the second electrode 32. Furthermore, in order to keep the voltage V2 of the second power supply 52 low, it is preferable that the third electrode 33 is positioned close to the second electrode 32, as described later, but not so close that it shorts out. In addition, it is preferable that the third electrode 33 has a mesh-like shape or the like to increase the contact area with the Li recovery aqueous solution RS. The third electrode 33 is formed of an electrode material that has catalytic activity and electronic conductivity for the reaction shown in formula (4) below, and is stable even when a voltage is applied in the Li recovery aqueous solution RS, including after Li recovery, for example, platinum (Pt) is preferred. Alternatively, the third electrode 33 can be made of carbon (C), copper (Cu), or stainless steel, which are stable at a potential lower than the potential at which the reaction in equation (4) occurs, and it is more preferable to have fine particles of Pt, which function as a catalyst, supported on the surface of these materials. [ka]

[0025] The first power supply 51, the second power supply 52, and the auxiliary power supply 53 are DC power supply devices that apply predetermined voltages V1, V2, and V3, respectively, and are connected in series from the positive side in the order of auxiliary power supply 53, first power supply 51, and second power supply 52. ​​The first power supply 51 has its positive electrode connected to the first electrode 31 and its negative electrode connected to the second electrode 32. The second power supply 52 has its positive electrode connected to the second electrode 32 and its negative electrode connected to the third electrode 33. The auxiliary power supply 53 has its positive electrode connected to the auxiliary electrode 41 and its negative electrode connected to the first electrode 31. In other words, the connection node 5n1 between the first power supply 51 and the auxiliary power supply 53 is connected to the first electrode 31, and the connection node 5n2 between the first power supply 51 and the second power supply 52 is connected to the second electrode 32 (see Figure 2). The first power supply 51 applies a voltage V1 between both sides of the electrolyte membrane 2, supplying Li to the electrolyte membrane 2. + A potential gradient is created to conduct electrons. The second power supply 52 applies a voltage V2 to the Li recovery aqueous solution RS that forms a potential lower than the surface of the electrolyte membrane 2, thereby allowing electrons e to flow from the recovery tank 13 side to the supply tank 11 side of the electrolyte membrane 2. - This suppresses conduction. Furthermore, the first power supply 51 and the second power supply 52, connected in series, act as a single main power supply, applying a voltage (V1 + V2) greater than the voltage V1 applied between both sides of the electrolyte membrane 2 between the Li-containing aqueous solution SW and the Li recovery aqueous solution RS. The secondary power supply 53 applies a voltage V3 to the Li-containing aqueous solution SW that forms a potential higher than the surface of the electrolyte membrane 2, thereby reducing the Li potential near the surface of the electrolyte membrane 2, which has a relatively lower potential. + While Cl is localized by electrostatic attraction, - It repels anions such as these through electrostatic repulsion.

[0026] The agitator 72 is a device that circulates the Li-containing aqueous solution SW in the supply tank 11 so that the Li-containing aqueous solution SW in contact with the first electrode 31 is continuously replaced during operation, and is provided as needed. Similarly, the agitator 72 may circulate the Li-recovery aqueous solution RS in the recovery tank 13 so that the Li-recovery aqueous solution RS in contact with the second electrode 32 is continuously replaced. The agitator 72 can be a known device, for example, as shown in Figure 1, it can be a structure that stirs the aqueous solutions SW and RS by rotating a screw in the tanks 11 and 13. Alternatively, a circulation device 71 may be provided that circulates the aqueous solutions SW and RS by pump between the tanks 11 and 13 and circulation tanks provided outside the treatment tank 1, respectively (see the modified example shown in Figure 4).

[0027] Li-containing aqueous solution SW is a Li source, and lithium ions Li + In addition to K + Na + Ca 2+ Other metal ions such as M n+ This is an aqueous solution containing [a specific substance]. Examples of such aqueous solutions include seawater, waste brine after extracting salt from seawater, groundwater such as hot spring water, and aqueous solutions obtained by crushing and roasting used lithium-ion secondary batteries, dissolving them in acid, and then adjusting the pH as needed.

[0028] Li recovery aqueous solution RS is made from lithium ions recovered from Li-containing aqueous solution SW. + This is a solution for containing Li. In order to selectively obtain only Li from the metal, the Li recovery aqueous solution RS contains lithium ions Li + Other metal ions (Na + An aqueous solution that does not contain (etc.) is preferred, and furthermore, OH - A aqueous solution that does not contain any other anions, especially halide ions, is preferred, and pure water may also be used. However, Li + To ensure smooth movement, at the start of recovery (when power is applied), the Li recovery aqueous solution RS contains Li + It is preferable that the aqueous solution contains (a lithium hydroxide (LiOH) aqueous solution).

[0029] The lithium recovery device 10 may further include a heating device that heats the electrolyte membrane 2 via a Li-containing aqueous solution SW or a Li-recovery aqueous solution RS to bring the electrolyte membrane 2 to a predetermined temperature. The heating device can be a known heater for heating liquids, and preferably has a temperature control function. The heating device is, for example, an immersion type and is installed by being immersed in the Li-recovery aqueous solution RS in the recovery tank 13. For this reason, the heating part of the heating device that is immersed in the Li-recovery aqueous solution RS is made of a material that does not deteriorate such as corrosion even when in contact with the Li-recovery aqueous solution RS, similar to the treatment tank 1. The heating device only needs to be able to bring the electrolyte membrane 2 to a predetermined temperature, and it is not necessary to make the Li-containing aqueous solution SW or the Li-recovery aqueous solution RS have a uniform liquid temperature. However, depending on the volume of the treatment tank 1, a stirrer 72 may be provided. The temperature of the electrolyte membrane 2 should be above the freezing point and below the boiling point of the aqueous solutions SW and RS, and is preferably high, as described below.

[0030] The lithium recovery device 10 may also be equipped with a liquid level sensor or the like to sense fluctuations in the amounts of the Li-containing aqueous solution SW and the Li recovery aqueous solution RS during operation. Furthermore, if carbon dioxide (CO2) from the atmosphere unintentionally dissolves in the Li recovery aqueous solution RS during operation, and lithium carbonate (Li2CO3) precipitates, the conductivity of the Li recovery aqueous solution RS will decrease, which is undesirable. To prevent this, it is preferable that the lithium recovery device 10 is configured so that the Li recovery aqueous solution RS is not exposed to the atmosphere. In addition, for safety reasons, it is preferable that the lithium recovery device 10 is equipped with an exhaust means to exhaust gases such as O2, H2, and Cl2 generated during operation (by the reactions of formulas (1), (4), and (2)) so that they do not fill the inside. It is also possible to recover Cl2 etc. generated from the Li-containing aqueous solution SW as a by-product. For this purpose, it is preferable that the lithium recovery device 10 is equipped with check valves in the supply tank 11 and the recovery tank 13 of the processing tank 1, for example, to exhaust gases generated from the aqueous solutions SW and RS to the outside of the processing tank 1 and to prevent outside air from flowing in.

[0031] (Lithium recovery method) A lithium recovery method according to the first embodiment of the present invention will be described with reference to Figures 2 and 3. The lithium recovery method according to this embodiment is carried out as follows using the lithium recovery apparatus 10 according to the first embodiment shown in Figure 1. Note that the agitator 72 is omitted in Figure 2.

[0032] In the lithium recovery device 10, the auxiliary power supply 53, the first power supply 51, and the second power supply 52, which are connected in series, can be considered as a single power supply (referred to as power supply 50). Similarly, the first power supply 51 and the second power supply 52 can be considered as a single power supply (referred to as main power supply 51-52). Power supply 50 applies a positive voltage (V3 + V1 + V2) to the auxiliary electrode 41 and the third electrode 33. Simultaneously, the main power supply 51-52 applies a positive voltage (V1 + V2) to the first electrode 31 and the third electrode 33. Then, the following reaction occurs in the Li-containing aqueous solution SW in the supply tank 11. Near the auxiliary electrode 41 and the first electrode 31, hydroxide ions (OH) in the Li-containing aqueous solution SW are released. - ) produces the reaction shown in equation (1) below, and electron e - By releasing gases, water (H2O) and oxygen (O2) are generated, and electrons are supplied to the auxiliary electrode 41 and the first electrode 31. - It releases the following: Li-containing aqueous solution SW releases halide ions, such as chloride ions (Cl - If it contains ), the reaction shown in equation (2) below occurs, and electron e - The system generates gases depending on the type of anion contained in the Li-containing aqueous solution SW, such as releasing chlorine (Cl2). In the Li-containing aqueous solution SW, OH - As other anions decrease, Li in the Li-containing aqueous solution SW decreases in order to maintain the charge balance. + The reaction shown in equation (3) below, in which the substance moves into the electrolyte membrane 2, occurs on the surface of the electrolyte membrane 2, i.e., in the vicinity of the first electrode 31. [ka]

[0033] Here, in the Li-containing aqueous solution SW, the application of voltage V3 by the auxiliary power supply 53 creates a potential gradient where the auxiliary electrode 41 has a higher potential than the surface of the electrolyte membrane 2 (first electrode 31). Therefore, OH - and Cl - It is attracted to the auxiliary electrode 41 by electrostatic attraction. Also, since the potential of the auxiliary electrode 41 is sufficiently high, Cl is attracted in its vicinity. - It is easily oxidized, and the reaction of formula (2) tends to occur rapidly. Therefore, near the auxiliary electrode 41, Cl is produced by the reaction of formula (2). - The amount decreases. Then, the auxiliary electrode 41 is further attracted by electrostatic force and Cl - It is attracted. As a result, the area near the first electrode 31, which has a lower potential than the auxiliary electrode 41, is relatively Cl - As the concentration decreases, the reaction shown in equation (1) will primarily occur.

[0034] Meanwhile, in the Li recovery aqueous solution RS of the recovery tank 13, the following reaction occurs. Near the third electrode 33, when a voltage (V1 + V2) is applied by the main power supply 51-52, the H2O in the Li recovery aqueous solution RS is converted into electrons e - When supplied, the reaction shown in equation (4) below occurs, producing hydrogen (H2) and OH - This generates H in the vicinity of the third electrode 33. + As the amount decreases, Li in the electrolyte membrane 2 decreases near the surface of the electrolyte membrane 2, i.e., in the vicinity of the second electrode 32. + The reaction shown in equation (5) below occurs, in which the OH group moves to the Li recovery aqueous solution RS. At the same time, the second power supply 52 applies a positive voltage V2 of a predetermined magnitude based on voltages V1 and V3 to the second electrode 32 and the third electrode 33. Then, near the second electrode 32, the OH group in the Li recovery aqueous solution RS - This produces the reaction shown in equation (1) below, and electron e - The ions are released to the second electrode 32, generating H2O and O2. As a result, a charge imbalance occurs near the second electrode 32, resulting in an excess of cations due to the reactions in equation (1) and equation (5). However, to compensate for the cation deficiency near the third electrode 33 caused by the reaction in equation (4), Li is released from the second electrode 32 to the vicinity of the third electrode 33. +It moves rapidly, and as a result, the charge imbalance in the Li recovery aqueous solution RS is eliminated. The relative relationship between the magnitudes of the voltage V1 and the voltage V2 will be described later.

Chemical formula

[0035] From the reaction of formula (3) to the reaction of formula (5), that is, Li in the Li-containing aqueous solution SW + enters from the surface of the electrolyte membrane 2 into the interior, and Li in the electrolyte membrane 2 + moves, and the movement of Li in the electrolyte membrane 2 + to the Li recovery aqueous solution RS in the electrolyte membrane 2 proceeds as follows. By applying the voltage (V1 + V2) by the main power supply 51-52, as the reaction of formula (3), Li in the Li-containing aqueous solution SW + enters the lattice defect sites on the surface of the electrolyte membrane 2. Then, by applying the voltage V1 by the first power supply 51, since there is a potential gradient with a lower potential on the opposite side (recovery tank 13 side) surface of the electrolyte membrane 2, Li that has entered the lattice defect sites on the surface + jumps (hopping) to the lattice defect sites near the deep part side of the electrolyte membrane 2. In this way, Li + repeatedly moves from the lattice defect sites of the electrolyte membrane 2 to the nearby lattice defect sites, and finally, as the reaction of formula (5), it moves from the lattice defect sites on the surface of the recovery tank 13 side into the Li recovery aqueous solution RS. And due to the movement of Li at the lattice defect sites on the surface of the supply tank 11 side of the electrolyte membrane 2 into the deep part of the electrolyte membrane 2, another Li adsorbed nearby + or Li in the Li-containing aqueous solution SW + enters, and these Li + move in the electrolyte membrane 2 in the same way.

[0036] In the lithium recovery device 10 according to the present embodiment, as described above, by applying the voltage V3 by the sub-power supply 53, a potential gradient is formed in the Li-containing aqueous solution SW, so that even if the Li-containing aqueous solution SW contains Cl - relatively, Cl near the electrolyte membrane 2 - ​​The concentration is low. Therefore, Cl on the surface of electrolyte membrane 2 - Adsorption is reduced, and inhibition of the reaction in equation (3) is suppressed. Furthermore, in the Li-containing aqueous solution SW, due to the potential gradient, the cation Li + However, due to electrostatic attraction, it is drawn to the surface of the electrolyte membrane 2 (first electrode 31), and the concentration becomes relatively high in that vicinity. Therefore, the Li in the Li-containing aqueous solution SW + Even at low concentrations, Li + The Li can diffuse sufficiently onto the surface of the electrolyte membrane 2. Furthermore, the Li of the Li-containing aqueous solution SW is dispersed between the two surfaces of the electrolyte membrane 2. + Li has a large concentration relative to its value. + A concentration gradient is formed, such as Li + A large chemical potential difference arises due to the concentration gradient, so Li between lattice defect sites in the electrolyte membrane 2. + The movement of [the group] will be facilitated.

[0037] Furthermore, when the voltage V2 is applied by the second power supply 52, a potential gradient is formed in the Li recovery aqueous solution RS with the area near the surface of the electrolyte membrane 2 being positive and the area near the third electrode 33 being negative, so Li + The Li near the surface of the electrolyte membrane 2 is attracted by electrostatic force towards the vicinity of the third electrode 33. + The concentration decreases. As a result, Li + As the concentration gradient expands, an even larger chemical potential difference is generated, Li between lattice defect sites in electrolyte membrane 2. + This will further facilitate their movement.

[0038] Thus, Li in electrolyte membrane 2 + The movement of Li in electrolyte membrane 2 + The greater the concentration gradient, the faster the reaction. Therefore, the stronger the electric field generated in the Li-containing aqueous solution SW by the voltage V3 of the auxiliary power supply 53, and the stronger the electric field generated in the Li recovery aqueous solution RS by the voltage V2 of the second power supply 52, the faster the reactions of equation (3) and equation (5) will be, and the Li in the Li-containing aqueous solution SW will be recovered. +The Li can be rapidly transferred into the electrolyte membrane 2 and then into the Li recovery aqueous solution RS for recovery. Furthermore, the stronger the electric field generated in the Li-containing aqueous solution SW, the more Li can be recovered from the Li-containing aqueous solution SW. + Even at low concentrations, the reaction in equation (3) can be accelerated. Also, if the Li-containing aqueous solution SW is Cl - When it contains, the stronger the electric field generated in the Li-containing aqueous solution SW, the stronger the reaction of formula (3) becomes. - Li in electrolyte membrane 2 is less likely to be inhibited. + Furthermore, the movement of OH becomes faster as the potential gradient across the electrolyte membrane 2 increases, i.e., as the voltage V1 of the first power supply 51 increases. In addition, the larger the voltage V1, the greater the difference in reaction rates between the reaction of equation (4) and the reaction of equation (1) in the Li recovery aqueous solution RS. - As the rate of increase becomes faster, the reaction in equation (5) becomes faster, and Li in electrolyte membrane 2 + It can be transferred to the Li recovery aqueous solution RS.

[0039] As mentioned above, the larger the voltages V1 and V2, and the stronger the electric field due to voltage V3, the Li + The amount of electrons transported per unit time increases. However, when the voltage V3 is increased to strengthen the electric field and reaches the voltage at which electrolysis of water occurs, the reaction shown in equation (4) below occurs near the first electrode 31 in the Li-containing aqueous solution SW, generating H2. This reaction involves electrons e - Since it receives electrons, the reaction in the vicinity of the first electrode 31 is different from the reaction in the following equation (1) above, which is electron e - The movement of (see Figure 2) is reversed. When the vicinity of the first electrode 31, i.e., the side of the electrolyte membrane 2 on the supply tank 11 side, reaches the H2 generation potential, some of the metal ions constituting the electrolyte membrane 2 are reduced, regardless of the magnitude of the applied voltage V1 between the two sides of the electrolyte membrane 2 (for example, if the electrolyte membrane 2 is LLTO, Ti 4+ +e - →Ti 3+ The potential reaches ) and electron transfer occurs in the electrolyte membrane 2. Then, electrons e conduct through the electrolyte membrane 2. - Li generates Joule heat, +Energy efficiency during transport decreases sharply. Furthermore, the effect of suppressing the occurrence of electron conduction in the electrolyte membrane 2 by applying the voltage V2 described later decreases. Therefore, the voltage V3 should be less than the voltage at which electrolysis of water occurs, and preferably higher within this range. In reality, the voltage at which electrolysis of water occurs is several hundred mV higher than the theoretical voltage (1.229V, 25℃) due to the electrode performance that determines the electrode reaction overpotential of each electrode (for voltage V3, the first electrode 31 and the auxiliary electrode 41). Furthermore, in this embodiment, even if the voltage V3 is greater than or equal to the above value, if the voltage V2 is greater than or equal to a certain extent than the voltage V3, the potential of the side of the electrolyte membrane 2 on the supply tank 11 side will not drop below the potential at which H2 is generated, and electrolysis of water will not occur, so the voltage V3 can be set to an even larger value. [ka]

[0040] Here, the portion of the Li-containing aqueous solution SW sandwiched between the first electrode 31 and the auxiliary electrode 41 is denoted as "SW". E The portion of the Li recovery aqueous solution RS sandwiched between the second electrode 32 and the third electrode 33 is denoted as "RS". E This is represented as . The lithium recovery device 10 according to this embodiment includes a second power supply 52, a first power supply 51, a sub-power supply 53, and a Li-containing aqueous solution SW, as shown in Figure 3. E Electrolyte membrane 2, Li recovery aqueous solution RS E The circuit includes a closed circuit connected in a ring shape, followed by the second power supply 52. ​​Currents I3, I1, and I2 flow counterclockwise through this closed circuit (the first circuit) by power supplies 53, 51, and 52 (power supply 50) connected in series, as indicated by the dotted arrows. Note that in the electrolyte membrane 2, if electron transport properties are not exhibited, electrons e - Li + It moves in the opposite direction (in the same direction as current I1). Also, in the Li-containing aqueous solution SW, electron e - Instead of part of OH - It moves. Similarly, in the Li recovery aqueous solution RS, electrons e - Instead of part of OH - , and Li in the opposite direction+ and H + It moves.

[0041] The lithium recovery device 10 has the positive electrode of the first power supply 51 and the negative electrode of the auxiliary power supply 53 (connection node 5n1) connected to the electrolyte membrane 2 and the Li-containing aqueous solution SW via the first electrode 31. E They are connected to each other. In addition, the negative electrode of the first power supply 51 and the positive electrode of the second power supply 52 (connection node 5n2) are connected to the electrolyte membrane 2 and the Li recovery aqueous solution RS via the second electrode 32. E They are connected to each other. Therefore, the lithium recovery device 10 transmits from the connection node 5n1 to the electrolyte membrane 2, or to the Li-containing aqueous solution SW. E Alternatively, current can flow from the electrolyte membrane 2 to the connection node 5n1. Similarly, the lithium recovery device 10 can supply Li recovery aqueous solution RS from the connection node 5n2. E Current can flow in either direction, or from the electrolyte membrane 2 to the connection node 5n2. The resistance of the electrolyte membrane 2 (resistance between the first electrode 31 and the second electrode 32, Li + (The resistance of movement) is R EL , Li-containing aqueous solution SW E The resistance (the resistance between the first electrode 31 and the auxiliary electrode 41) is R SW Li recovery aqueous solution RS E The resistance (the resistance between the second electrode 32 and the third electrode 33) is R RS This is expressed as follows. Furthermore, the lithium recovery device 10 has a reaction resistance R due to the reaction of formula (1) (O2 generation) and the reaction of formula (2) (Cl2 generation) at the auxiliary electrode 41. c41 The reaction resistance R due to the reaction of equation (1) and the reaction of equation (2) at the first electrode 31. c31 It also includes.

[0042] In the lithium recovery device 10, as described above, in order to prevent the reaction of formula (4) from occurring at the first electrode 31, electrons e are transferred from the Li-containing aqueous solution SW to the first electrode 31. -As the element moves or does not move, current flows or does not flow from the connection node 5n1 connected to the positive electrode of the first power supply 51 to the first electrode 31. Therefore, the lithium recovery device 10 consists of a second power supply 52, a first power supply 51, an electrolyte membrane 2, and an aqueous solution RS for Li recovery as a second circuit. E The system includes a closed circuit connected in a ring shape, with the second power supply 52 connected in that order. As shown in Figure 3, currents I4, I1, and I2 flow through this closed circuit, as indicated by the gray arrows, due to the first power supply 51 and the second power supply 52 (main power supply 51-52) connected in series. The current that branches off from current I1 (from connection node 5n1) and flows through the first electrode 31 to the electrolyte membrane 2 is represented as I4. The lithium recovery device 10 should set the voltage V3 so that current I4 flows in this direction, or not (does not flow in the reverse direction), that is, so that I4≧0. For current I4, the relationship I3+I4=I1 holds, so it is sufficient that I1≧I3.

[0043] To achieve this, the lithium recovery device 10 can, for example, connect ammeters in series (not shown) to the first power supply 51 and the auxiliary power supply 53, respectively, and apply voltages V1 and V3 while measuring currents I1 and I3. Furthermore, the resistance R between the first electrode 31 and the auxiliary electrode 41... SW , reaction resistance R at auxiliary electrode 41 c41 The lower each of these values, the stronger the electric field generated in the Li-containing aqueous solution SW, even with a small voltage V3, resulting in a higher effect. Reaction resistance R c41 The resistance R is lower as the surface area of ​​the auxiliary electrode 41 immersed in the Li-containing aqueous solution SW increases, and as the catalytic activity of the reaction in equation (1) of the auxiliary electrode 41 increases. SW The resistance R is lower the larger the area of ​​the first electrode 31 and the auxiliary electrode 41 immersed in the Li-containing aqueous solution SW, and the shorter the distance between them. SW The higher the electronic conductivity of the Li-containing aqueous solution SW, the lower the coefficient of this coefficient.

[0044] As mentioned above, the stronger the electric field generated in the Li-containing aqueous solution SW by the voltage V3, the stronger the Li in the Li-containing aqueous solution SW. + Li + The movement speed of the Li-containing aqueous solution SW becomes high, and the Cl contained in it- The inhibition of Li + mobility is further suppressed. Also, the reaction of formula (1) or further the reaction of formula (2) at the first electrode 31 such that current I4 flows from the positive electrode (connection node 5n1) of the first power source 51 to the first electrode 31, and the total reaction amount of the reaction of formula (1) and the reaction of formula (2) at the auxiliary electrode 41 are related directly to the amount of Li + moving through the electrolyte membrane 2, and Li + corresponding to the amount of current (I3 + I4) moves through the electrolyte membrane 2. Therefore, in order to increase the Li recovery rate more rapidly, it is more preferable that the total current amount of (I3 + I4), that is, the current I1, is larger. Also, in terms of energy efficiency, it is preferable that I4 is smaller, and it is most preferable that I4 = 0 (I1 = I3). However, in operation, it is preferable that I1 > I3 including a margin so that I1 < I3 does not occur. Also, in order to increase the Li recovery rate, it is preferable that I1 > I3 (I4 > 0) and O2 is generated at the first electrode 31. Note that even if the voltage V3 is less than the voltage at which electrolysis of water occurs, if the voltage V1 is not a certain magnitude or more with respect to this voltage V3, the current I4 flows in the reverse direction (I4 < 0), and electron conductivity appears in the electrolyte membrane 2 (see the second embodiment described later). In the present embodiment, as will be described below, the voltage V1 can be set to a sufficient magnitude.

[0045] In the lithium recovery method according to the present invention, the larger the voltage V1, the more the amount of movement of Li + can be increased. However, if the voltage V1, that is, the potential difference between both surfaces of the electrolyte membrane 2, is equal to or higher than the voltage at which a part of the metal ions constituting the electrolyte membrane 2 is reduced (for example, if the electrolyte membrane 2 is LLTO, Ti 4+ + e - → Ti 3+ ), appropriately referred to as the electrolyte reduction voltage), the electrolyte membrane 2 may become capable of conducting electrons e - from the recovery tank 13 side to the supply tank 11 side (see Patent Document 2). Therefore, even if the voltage V1 is increased further, the amount of movement of Li + does not increase by the increased amount of the voltage V1, and the energy efficiency decreases.

[0046] However, in this embodiment, a second power supply 52 connected between the second electrode 32 and the third electrode 33 applies a voltage V2 to generate an appropriate potential difference with the second electrode 32 as positive. Then, electrons e supplied from the third electrode 33 to the Li recovery aqueous solution RS - However, electrons move from the second electrode 32 on the surface of the electrolyte membrane 2 to the positive electrode of the second power supply 52, and the potential of the second electrode 32 is maintained at approximately the O2 generation potential. Since the O2 generation potential is higher than the reduction potential of the metal ions constituting the electrolyte membrane 2, electrons e are generated in the electrolyte membrane 2 regardless of the potential difference between its two surfaces. - It does not conduct electrons. Therefore, the voltage V1 can be set to a voltage greater than or equal to the electrolyte reduction voltage of the electrolyte membrane 2. In other words, if such a large voltage V1 is applied without applying voltage V2, electrons e will not be conducted from the negative electrode side (recovery tank 13 side) of the electrolyte membrane 2. - The metal ions are reduced by incorporating electrons. This phenomenon is particularly likely to occur with transition metal ions. However, in this embodiment, as described above, when voltage V2 is applied, the electrolyte membrane 2 does not reach the reduction potential of the metal ions, and the electrolyte membrane 2 does not incorporate electrons e - Do not communicate.

[0047] Thus, in the lithium recovery method according to this embodiment, electrons e are transferred from the Li recovery aqueous solution RS to the second electrode 32. - Since it is released, the Li recovery aqueous solution RS is released from the positive electrode of the second power supply 52 through the second electrode 32. E Current flows through it. Therefore, the lithium recovery device 10 has a third circuit consisting of a second power supply 52 and a Li recovery aqueous solution RS E The closed circuit consists of the following components, and currents I5 and I2 flow through it as shown by the white arrows, powered by the second power supply 52. ​​The current that branches off from current I2 (from the connection node 5n2) and flows to the second electrode 32 is denoted as I5. The lithium recovery device 10 is configured as follows so that current I5 flows in this direction, or not (does not flow in the reverse direction), that is, so that I5 ≥ 0.

[0048] For current I5, the relationship I1 + I5 = I2 holds, so in order to make I5 ≥ 0, voltages V1 and V2 are set so that I1 ≤ I2. Resistance of electrolyte membrane 2 (resistance between first electrode 31 and second electrode 32, Li + (The resistance of movement) is R EL Li recovery aqueous solution RS E The resistance (the resistance between the second electrode 32 and the third electrode 33) is R RS This is expressed as follows. Furthermore, the lithium recovery device 10 has a reaction resistance R due to the reaction of formula (4) (H2 generation) at the third electrode 33. c33 , and the reaction resistance R due to the reaction of formula (1) (O2 generation) at the second electrode 32 c32 This further includes the following. Then, the first circuit is represented by equation (6) below, the second circuit by equation (7) below, and the third circuit by equation (8) below. Note that the resistance of electrodes 31, 32, 41, 33 and the wiring is ignored here.

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[0049] From equations (6) and (7), equation (9) is obtained, and from equations (7) and (8), equation (10) is obtained. Current I1 is given by equation (11) from equation (10). Current I2 is given by equation (12) from equation (8). Current I3 is given by equation (13) from equation (9). For I1 ≤ I2, equation (14) must hold. Solving equation (14) gives equation (15). Substituting equation (12) for I2 and equation (13) for I3 in equation (11) and solving for I1 gives equation (16). Substituting equation (16) into equation (15) gives equation (17).

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[0050] Thus, the larger the voltage V1 of the first power supply 51 and the voltage V3 of the auxiliary power supply 53, the larger the voltage V2 of the second power supply 52 should be set accordingly. To achieve this, the lithium recovery device 10 can, for example, connect an ammeter in series (not shown) to the first power supply 51 and the second power supply 52, and apply voltages V1 and V2 while measuring the currents I1 and I2. Also, the resistance R between the second electrode 32 and the third electrode 33... RS , the reaction resistance R at the third electrode 33 c33 The lower each of these values, the greater the effect that can be obtained even with a small voltage V2. Reaction resistance R c33 The resistance R is lower as the surface area of ​​the third electrode 33 immersed in the Li recovery aqueous solution RS increases, and as the catalytic activity of the reaction in equation (4) of the third electrode 33 increases. RS The resistance R is lower the larger the area of ​​the second electrode 32 and the third electrode 33 immersed in the Li recovery aqueous solution RS, and the shorter the distance between them. RS The higher the electronic conductivity of the lithium recovery aqueous solution RS, the lower the coefficient of this coefficient.

[0051] Furthermore, the reaction amount of the reaction in equation (1) that occurs at the second electrode 32, i.e., the magnitude of the current I5 (≧0), is Li + It is not directly related to the amount of displacement. On the other hand, if the voltage V2 is insufficient compared to the voltages V1 and V3, and equation (17) does not hold, then I5 < 0, and current flows from the second electrode 32 to the negative electrode of the auxiliary power supply 53, causing the reaction of equation (4) to occur at the second electrode 32 as well. At this time, the voltage V1 is expressed by the following equation (18). c32 ' is the reaction resistance due to the reaction (H2 generation) of equation (4) at the second electrode 32. However, even if I5 < 0, (|I5| × R c32 The potential of the side of the electrolyte membrane 2 facing the recovery tank 13, determined by '), is the reduction potential of the metal ions constituting the electrolyte membrane 2 (in the case of Ti, Ti 4+ →Ti 3+ |I5| should be small enough to be higher than -0.488V vs. SHE.

number

[0052] As described above, the larger the voltage V2 is, the larger the Li concentration gradient in the electrolyte membrane 2 becomes, and the faster the movement of Li in the electrolyte membrane 2 becomes. However, as the voltage V2 becomes larger with respect to the voltage V2 (the minimum value in Equation (17)) at which I1 = I2, the current I5 increases, and the generation of O2 near the second electrode 32 (the reaction in Equation (1)) and the generation of H2 near the third electrode 33 (the reaction in Equation (4)) increase more than the increase in the movement amount of Li, and the energy efficiency decreases. On the other hand, even for the voltage V2 where I1 > I2, as described above, if the difference |I5| between I1 and I2 is sufficiently small, the electron conductivity does not appear in the electrolyte membrane 2, so the voltage V2 can be set to at least such a value at a minimum. However, during the operation of the lithium recovery device 10, for example, due to the increase in the Li concentration of the Li recovery aqueous solution RS, it is not easy to maintain the currents I1 and I2 constant, such as the decrease in the resistance R. Therefore, it is preferable to set the voltage V2 so that I1 < I2 as a margin. For example, at the start of operation of the lithium recovery device 10, it is set to be larger by a difference of 0.5 V or more, preferably more than 0 V and 1 V or less or (V1 / 10) or less with respect to the voltage V2 at which I1 = I2. + The larger the Li concentration gradient becomes, the faster the movement of Li in the electrolyte membrane 2 becomes. + However, as the voltage V2 becomes larger with respect to the voltage V2 (the minimum value in Equation (17)) at which I1 = I2, the current I5 increases, and the generation of O2 near the second electrode 32 (the reaction in Equation (1)) and the generation of H2 near the third electrode 33 (the reaction in Equation (4)) increase more than the increase in the movement amount of Li, and the energy efficiency decreases. + On the other hand, even for the voltage V2 where I1 > I2, as described above, if the difference |I5| between I1 and I2 is sufficiently small, the electron conductivity does not appear in the electrolyte membrane 2, so the voltage V2 can be set to at least such a value at a minimum. + However, during the operation of the lithium recovery device 10, for example, due to the increase in the Li concentration of the Li recovery aqueous solution RS, it is not easy to maintain the currents I1 and I2 constant, such as the decrease in the resistance R. RS Therefore, it is preferable to set the voltage V2 so that I1 < I2 as a margin. For example, at the start of operation of the lithium recovery device 10, it is set to be larger by a difference of 0.5 V or more, preferably more than 0 V and 1 V or less or (V1 / 10) or less with respect to the voltage V2 at which I1 = I2.

[0053] In the lithium recovery method according to the present invention, as the operation time elapses, the liquid amounts of the Li-containing aqueous solution SW and the Li recovery aqueous solution RS decrease. Therefore, for the Li-containing aqueous solution SW, it is preferable to replenish the supply tank 11 regularly or constantly. Alternatively, as described later, it is more preferable to constantly circulate the Li-containing aqueous solution SW outside the treatment tank 1 during operation. For the Li recovery aqueous solution RS, it is preferable to add water (H2O) or the like to the recovery tank 13 regularly or constantly. In the lithium recovery device 10, it is preferable that the liquid levels of the supply tank 11 and the recovery tank 13 are aligned during operation.

[0054] For the lithium recovery aqueous solution RS after operation has finished, lithium can be recovered by, for example, evaporating the water as needed to concentrate the lithium, then generating lithium carbonate (Li2CO3) by carbon dioxide (CO2) bubbling or the like and precipitating it. Alternatively, after generating lithium carbonate, lithium hydroxide (LiOH) can be generated by further cooling or evaporating the water to create a supersaturated state and precipitating it, thereby recovering the lithium. Furthermore, if the lithium-containing aqueous solution SW is Cl - If it contains Cl2, Cl2 will be generated on the supply tank 11 side, and it can be recovered together with the O2 that is generated together, and separated and recovered by known methods such as utilizing the difference in boiling points (O2: -183.0°C, Cl2: -101.5°C).

[0055] In this invention, a secondary power supply 53 is connected in series with the positive electrode of a first power supply 51 that applies a voltage V1 between both sides of the electrolyte membrane 2, and a secondary electrode 41 with a potential higher than the surface of the electrolyte membrane 2 is provided in the Li-containing aqueous solution SW, + While Cl is localized near the electrolyte membrane 2, - This keeps the Cl away from the electrolyte membrane 2. As a result, the Cl on the surface of the electrolyte membrane 2 - Li in Li-containing aqueous solution SW due to adsorption + The inhibition of dissolution into electrolyte membrane 2 is suppressed. Therefore, Cl in seawater, etc. - A Li source containing a high concentration of Li is used as a Li-containing aqueous solution SW. + It can be efficiently recovered. Also, in the Li-containing aqueous solution SW, Li is relatively close to the electrolyte membrane 2. + Because the concentration is high, Li + A concentration gradient is efficiently formed, Li + This can accelerate the movement of Li in the electrolyte membrane 2. This effect is due to the Li in the Li-containing aqueous solution SW. + The effect becomes more pronounced at lower concentrations.

[0056] Furthermore, in this embodiment, in addition to the first power supply 51 that applies a voltage V1 between both sides of the electrolyte membrane 2, a second power supply 52 is provided in series with its negative electrode. A third electrode 33 with a potential lower than the surface of the electrolyte membrane 2 is provided in the Li recovery aqueous solution RS, and this potential difference, i.e., the voltage V2 of the second power supply 52, is set to correspond to the voltage V1. As a result, even if a large potential difference is generated between both sides of the electrolyte membrane 2 that causes it to reach the reduction potential of its metal ions, electrons e - It is difficult for it to conduct electricity. As a result, Li + The recovery rate of Li can be made high in accordance with the potential gradient in the electrolyte membrane 2. Furthermore, since the first electrode 31 and the second electrode 32 are provided in contact with both sides of the electrolyte membrane 2, a potential gradient is efficiently formed in the electrolyte membrane 2 by the first power supply 51, and Li in the electrolyte membrane 2 + The movement speed can be increased. Furthermore, if the voltage V2 of the second power supply 52 is increased in accordance with the increase in the voltage V1 of the first power supply 51, Li will be introduced into the electrolyte membrane 2. + The concentration gradient is formed more efficiently, Li + The movement of the substance within the electrolyte membrane 2 can be accelerated even further.

[0057] Li in the electrolyte membrane 2 + The movement of the electrolyte membrane is faster with higher temperatures, in addition to the voltage V1. Therefore, a higher temperature for the electrolyte membrane 2 is preferable. Also, the resistance R of the electrolyte membrane 2 and aqueous solutions SW and RS. EL ,R SW ,R RS Furthermore, the reaction resistances at electrodes 31, 32, 41, and 33 decrease with increasing temperature. The applicable temperature range is above the freezing point and below the boiling point of aqueous solutions SW and RS, preferably 20°C or higher.

[0058] (modified version) In the lithium recovery apparatus according to the above embodiment, since the Li source containing chloride ions is in direct contact with the supply tank side surface of the electrolyte membrane, even if the chloride ions are kept away from the first electrode provided on this surface of the electrolyte membrane by electrostatic repulsion due to voltage application from the auxiliary power supply, the catalytic activity will be impaired to some extent during long-term operation. Furthermore, in Li recovery by electrodialysis, the Li of the electrolyte membrane+ The higher the pH of the aqueous solution on the supply side compared to the aqueous solution on the recovery side, the higher the pH of Li + It has high mobility. For example, when seawater is used as the lithium source, seawater is weakly alkaline, while the aqueous solution on the recovery side increases in concentration as it progresses, changing from pure water to a LiOH aqueous solution, and its pH also rises, becoming higher than that of the supply side. + This would result in a decrease in mobility. Therefore, in order to prevent chloride ions from coming into contact with the electrolyte membrane and to increase the pH of the aqueous solution in contact with the supply side surface of the electrolyte membrane, the following configuration was adopted. A lithium recovery apparatus and lithium recovery method according to a modification of the first embodiment of the present invention will be described below with reference to Figures 4 and 5.

[0059] As shown in Figure 4, a lithium recovery device 10A according to a modification of the first embodiment of the present invention comprises a processing tank 1, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2 and an ion exchange membrane 62 that partition the processing tank 1, a first electrode 31, a second electrode 32, a third electrode 33, a sub-electrode 41 coated on each surface of the electrolyte membrane 2, and three power supplies 53, 51, and 52 connected in series. The lithium recovery device 10A may further include a circulation device (circulation means) 71 and a stirrer 72. The processing tank 1 is partitioned in one direction by the ion exchange membrane 62 and the electrolyte membrane 2 into three parts: a supply tank (first tank) 11 that contains a Li-containing aqueous solution SW such as seawater, an intermediate tank 12 that contains a Li-containing aqueous solution AS, and a recovery tank (second tank) 13 that contains a Li recovery aqueous solution RS. Specifically, the ion exchange membrane 62 partitions the supply tank 11 and the intermediate tank 12, and the electrolyte membrane 2 partitions the intermediate tank 12 and the recovery tank 13. The auxiliary electrode 41 is provided in the supply tank 11. The third electrode 33 is provided in the recovery tank 13, spaced apart from the electrolyte membrane 2. Therefore, the lithium recovery apparatus 10A according to this modified example has an additional ion exchange membrane 62 that partitions the processing tank 1 between the auxiliary electrode 41 and the first electrode 31 compared to the lithium recovery apparatus 10 according to the embodiment shown in Figure 1, and the supply tank 11 is further partitioned by the ion exchange membrane 62 into the supply tank 11 and the intermediate tank 12.

[0060] The ion exchange membrane 62 is Li +It conducts cations containing at least . The ion exchange membrane 62 allows Cl to enter the Li-containing aqueous solution AS in the intermediate tank 12. - It is possible to prevent the inclusion of halide ions such as Li. The ion exchange membrane 62 is a cation exchange membrane that allows cations to pass through and shields anions, Li + ,K + Na + A monovalent cation selective permeable ion exchange membrane that allows only monovalent cations to pass through, a bipolar monovalent ion selective permeable ion exchange membrane that allows monovalent ions to pass through, etc., can be applied. Known ion exchange membranes can be applied, for example, SELEMION® CMV (manufactured by AGC Engineering Co., Ltd.) or NEOSEPTA CSE (manufactured by Astrom Co., Ltd.) can be used as a cation exchange membrane, SELEMION® CSO (manufactured by AGC Engineering Co., Ltd.) can be used as a monovalent cation selective permeable ion exchange membrane, and NEOSEPTA CIMS (manufactured by Astrom Co., Ltd.) can be used as a bipolar monovalent ion selective permeable ion exchange membrane. In the lithium recovery device 10A, as in the above embodiment, it is preferable that the distance between the auxiliary electrode 41 and the first electrode 31 is short, so it is preferable that the ion exchange membrane 62 is arranged so that the distance between it and the electrolyte membrane 2 (first electrode 31) is short, and therefore it is preferable that the intermediate tank 12 is short in the partition direction of the processing tank 1.

[0061] The circulation device 71 includes, for example, a pump and a filter for removing dust and debris. In particular, when the Li-containing aqueous solution SW is seawater or hot spring water, it is preferable to apply voltage while circulating the Li-containing aqueous solution SW from these sources into the supply tank 11. With such a configuration, Li + Even if the recovery process progresses, the Li in the Li-containing aqueous solution SW + The concentration is maintained at a nearly constant level, and even with low-concentration Li aqueous solutions, the Li recovery rate does not easily decrease, allowing for long-term continuous operation. Alternatively, the Li-containing aqueous solution SW in the supply tank 11 may be replaced by the circulation device 71 at regular intervals. Furthermore, the lithium recovery device 10A may have a structure in which the supply tank 11 is open to the outside (for example, into the sea) via a filter or the like.

[0062] Li-containing aqueous solution AS is obtained from Li-containing aqueous solution SW contained in supply tank 11, and Cl - etc., OH - This is an aqueous solution from which anions other than Li have been removed. Li-containing aqueous solution AS can be treated with pure water at the start of recovery (when power is applied), similar to the Li recovery aqueous solution RS. + It is preferable that the aqueous solution contains (LiOH aqueous solution).

[0063] The auxiliary power supply 53, similar to the embodiment described above, applies a voltage V3 to the Li-containing aqueous solution AS in contact with the supply-side surface of the electrolyte membrane 2, thereby creating a potential higher than that of the surface of the electrolyte membrane 2, and bringing Li near the surface of the electrolyte membrane 2. + The Li is distributed unevenly by electrostatic attraction. In this modified example, a high potential difference is generated between the two sides of the ion exchange membrane 62, i.e., between the Li-containing aqueous solution SW and the Li-containing aqueous solution AS, on the supply tank 11 side of the Li-containing aqueous solution SW, and the Li in the Li-containing aqueous solution SW is distributed unevenly. + The cations containing are transferred to the Li-containing aqueous solution AS.

[0064] The lithium recovery device 10A may also be equipped with a circulation device 71 or a stirrer 72 in the intermediate tank 12. The circulation device 71 that circulates the Li-containing aqueous solution AS contains Li + The tank may also include a sedimentation tank for precipitating cations other than those mentioned above, and a filter to prevent the precipitate from returning to the intermediate tank 12.

[0065] A lithium recovery method according to a modified version of the first embodiment of the present invention will be described with reference to Figure 5. In Figure 5, the circulation device 71 and the agitator 72 are omitted. The lithium recovery method according to this modified version can be carried out in the same manner as the lithium recovery method according to the first embodiment using the lithium recovery device 10A according to a modified version of the first embodiment shown in Figure 4.

[0066] In the lithium recovery device 10A, the auxiliary power supply 53 applies a voltage V3 to the Li-containing aqueous solution SW. +Cations such as these permeate the ion exchange membrane 62 and move into the Li-containing aqueous solution AS. Furthermore, as described in the above embodiment, due to the potential gradient caused by the voltage V3, Li in the Li-containing aqueous solution AS + The ions are attracted to the surface of the electrolyte membrane 2 (first electrode 31) by electrostatic attraction. The reaction upon application of voltages V1, V2, and V3 is as described in the above embodiment. Note that if the ion exchange membrane 62 is a monovalent cation selective permeable ion exchange membrane or a bipolar monovalent ion selective permeable ion exchange membrane, Li-containing aqueous solution AS contains Li + ,K + Na + Only monovalent cations such as Ca move in, 2+ Divalent and trivalent cations such as ions do not move. Therefore, the amount of precipitate in the Li-containing aqueous solution AS that comes into contact with the supply side surface of the electrolyte membrane 2 can be reduced, and Li can be recovered from the Li-containing aqueous solution AS to the Li recovery aqueous solution RS. + Its movement is not hindered.

[0067] The settings for voltages V1, V2, and V3 are as described in the above embodiment. However, the Li-containing aqueous solution SW E Resistor R SW This is the sum of the resistances of the Li-containing aqueous solutions SW, AS and the ion exchange membrane 62 between the first electrode 31 and the auxiliary electrode 41. Also, at the start of recovery, the Li-containing aqueous solution AS is pure water (Li + If the LiOH aqueous solution does not contain or has a low concentration of LiOH, first operate only the auxiliary power supply 53 to supply Li to the Li-containing aqueous solution AS. + It is preferable to move the fluid until it reaches a predetermined concentration, and then further operate the first power supply 51 and the second power supply 52.

[0068] According to the lithium recovery apparatus of this modified example, anions such as chloride ions are shielded from the Li-containing aqueous solution in the supply tank, making it difficult for anions to be contained in the aqueous solution that comes into contact with the supply side surface of the electrolyte membrane, and further reducing the degradation of the first electrode provided on this surface of the electrolyte membrane. Furthermore, even if the Li-containing aqueous solution in the supply tank has a low pH ranging from acidic to weakly alkaline, the aqueous solution that comes into contact with the supply side surface of the electrolyte membrane can be made to have a high pH, ​​and Li-containing aqueous solution can be controlled in relation to the applied voltage.+ Increased mobility leads to improved energy efficiency.

[0069] The lithium recovery device relating to this modified example is li + The lithium recovery apparatus may be equipped with two or more ion exchange membranes that conduct cations containing lithium, and the processing tank may be divided into four or more sections, with two or more intermediate tanks provided between the supply tanks and recovery tanks at both ends. In such a lithium recovery apparatus, all ion exchange membranes are sandwiched between the first electrode and the auxiliary electrode in the supply tank. By providing multiple ion exchange membranes, anions such as chloride ions are better shielded from the Li-containing aqueous solution in the supply tank, so that anions are less likely to be contained in the aqueous solution in contact with the supply side surface of the electrolyte membrane, and the first electrode provided on this side of the electrolyte membrane is less likely to deteriorate. In addition, the pH of the aqueous solution in contact with the supply side surface of the electrolyte membrane can be made higher, further improving energy efficiency.

[0070] Furthermore, monovalent cation selective permeable ion exchange membranes and bipolar monovalent cation selective permeable ion exchange membranes (collectively referred to as monovalent cation selective permeable ion exchange membranes) often lack sufficient resistance to strong alkalinity. On the other hand, aqueous solutions from which anions have been removed from Li-containing aqueous solution SW tend to become strongly alkaline when the cation concentration is high. Therefore, in the lithium recovery apparatus 10A according to the above modification, when a monovalent cation selective permeable ion exchange membrane is applied to the ion exchange membrane 62 to move only monovalent cations to the Li-containing aqueous solution AS in the intermediate tank 12, before the cation concentration of the Li-containing aqueous solution AS becomes high, Li + Transferring Li to the Li recovery aqueous solution RS, +It is necessary to adjust the pH of the Li-containing aqueous solution AS to a predetermined value or lower by removing monovalent cations other than the primary cation from the Li-containing aqueous solution AS, for example, by precipitating them. The lithium recovery device according to this modified example can be equipped with a combination of a cation exchange membrane that conducts cations containing polyvalent ions and a monovalent ion selective permeable ion exchange membrane. On the other hand, if the number of ion exchange membranes is increased, the resistance between the first electrode and the auxiliary electrode increases, and it becomes difficult to generate a strong electric field when the applied voltage from the auxiliary power supply is less than the voltage at which electrolysis of water occurs. Therefore, it is preferable to place only a portion of the multiple ion exchange membranes between the first electrode connected to the auxiliary power supply and the auxiliary electrode, and to apply voltage to the other ion exchange membranes with another additional auxiliary power supply.

[0071] That is, the lithium recovery apparatus 10B according to another modification of the first embodiment of the present invention, as shown in Figure 6, comprises a processing tank 1, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2 and ion exchange membranes 61, 62 that partition the processing tank 1, a first electrode 31 and a second electrode 32, a third electrode 33, auxiliary electrodes 41, 42, 43 coated on each surface of the electrolyte membrane 2, three power supplies 53, 51, 52 connected in series, and an auxiliary power supply 54. The lithium recovery apparatus 10B may further include a circulation device 71 and a stirrer 72 as needed (see Figures 1 and 4). The processing tank 1 is divided in one direction by two ion exchange membranes 61, 62 and the electrolyte membrane 2 into four sections: a supply tank (first tank) 11 containing Li-containing aqueous solution SW, an intermediate tank 12a containing Li-containing aqueous solution AS', an intermediate tank 12b containing Li-containing aqueous solution AS, and a recovery tank (second tank) 13 containing Li-recovery aqueous solution RS. More specifically, the ion exchange membrane 61 separates the supply tank 11 from the intermediate tank 12a, the ion exchange membrane 62 separates the intermediate tank 12a from the intermediate tank 12b, and the electrolyte membrane 2 separates the intermediate tank 12b from the recovery tank 13. The third electrode 33 is provided in the recovery tank 13, spaced apart from the electrolyte membrane 2. The auxiliary electrodes 41 and 43 are provided in the intermediate tank 12a, spaced apart from each other, with auxiliary electrode 41 facing the ion exchange membrane 62 and auxiliary electrode 43 facing the ion exchange membrane 61. Auxiliary electrode 42 is provided in the supply tank 11. The auxiliary power supply 54 has its positive electrode connected to auxiliary electrode 42 and its negative electrode connected to auxiliary electrode 43. Therefore, the lithium recovery device 10B according to this modified example has the following configuration compared to the lithium recovery device 10A according to the modified example shown in Figure 4: an ion exchange membrane 61 that partitions the processing tank 1 on the supply side of the auxiliary electrode 41, an auxiliary power supply 54 for applying a voltage between both sides of the ion exchange membrane 61, and auxiliary electrodes 42 and 43 connected to the auxiliary power supply 54.

[0072] The ion exchange membrane 61, like the ion exchange membrane 62, has Li in relation to the electrolyte membrane 2. + It is provided on the supply side, Li +It conducts cations containing at least one of the specified ions. The ion exchange membrane 61 can be the same ion exchange membrane as the ion exchange membrane 62. Alternatively, one of the ion exchange membranes 61 and 62 may be a cation exchange membrane that conducts cations containing polyvalent ions, and the other may be a monovalent cation selective permeable ion exchange membrane or a bipolar monovalent ion selective permeable ion exchange membrane.

[0073] Auxiliary electrodes 42 and 43 are connected to the auxiliary power supply 54 and are electrodes for applying a voltage that creates a high potential difference on the supply tank 11 side between the two sides of the ion exchange membrane 61. For this purpose, auxiliary electrode 42 is placed in the supply tank 11 and auxiliary electrode 43 is placed in the intermediate tank 12a, both facing the ion exchange membrane 61. It is preferable that auxiliary electrodes 42 and 43 are placed parallel to each other. Furthermore, it is preferable that auxiliary electrodes 42 and 43 have a mesh-like shape or the like, through which aqueous solutions can pass, so that the aqueous solutions SW and AS' that come into contact with the surface of the ion exchange membrane 61 in the tanks 11 and 12a are continuously exchanged. In this modified example, auxiliary electrode 41 is formed of an electrode material that is stable even when voltage is applied in the Li-containing aqueous solution AS', including after Li recovery, and the same applies to auxiliary electrode 43. Auxiliary electrode 42 is formed of an electrode material that is stable even when voltage is applied in the Li-containing aqueous solution SW, similar to auxiliary electrode 41 in the first embodiment. Furthermore, the auxiliary electrode 43 is positioned at a distance from the auxiliary electrode 41, which is located within the same intermediate tank 12a. For this reason, the distance between the same intermediate tank 12a, i.e., between the ion exchange membrane 61 and the ion exchange membrane 62, is designed to be sufficiently long in the partition direction of the processing tank 1 (left-right direction in Figure 6).

[0074] The auxiliary power supply 54 applies a voltage V4 between both sides of the ion exchange membrane 61, i.e., between the Li-containing aqueous solution SW and the Li-containing aqueous solution AS', so that the Li-containing aqueous solution SW on the supply tank 11 side generates a high potential difference. + The cations containing are transferred to the Li-containing aqueous solution AS'. The auxiliary power supply 54 is a DC power supply, similar to the auxiliary power supply 53, with its positive electrode connected to the auxiliary electrode 42 in the supply tank 11 and its negative electrode connected to the auxiliary electrode 43 in the intermediate tank 12a.

[0075] Li-containing aqueous solution AS' is obtained from Li-containing aqueous solution SW contained in supply tank 11, and Cl - etc., OH - This is an aqueous solution from which anions other than Li have been removed. Li-containing aqueous solution AS' can be treated with pure water at the start of recovery (when power is applied), similar to Li-containing aqueous solution AS and Li recovery aqueous solution RS. + It is preferable that the aqueous solution contains (LiOH aqueous solution).

[0076] As mentioned above, many monovalent ion selective permeable ion exchange membranes do not have sufficient resistance to strong alkalis. In this modified example, Li is added to the Li-containing aqueous solution AS in the intermediate tank 12b. + When transferring only monovalent cations containing Li, it is preferable to apply a monovalent ion selective permeable ion exchange membrane to the ion exchange membrane 61 and to pre-add an acid to prevent the Li-containing aqueous solution AS' from becoming strongly alkaline due to cations transferred from the Li-containing aqueous solution SW. The acid added to the Li-containing aqueous solution AS' is Li + We selected a compound that does not precipitate, and also avoided Cl, which easily generates gas through oxidation reactions and impairs the catalytic activity of the platinum electrode. - Avoid using nitric acid or sulfuric acid, and sulfuric acid is preferable. Li-containing aqueous solution AS' is NO3 - Even if they contain anions such as OH, these anions are shielded by the ion exchange membrane 62, so the Li-containing aqueous solution AS in contact with the electrolyte membrane 2 does not contain these anions. - Since a Li-containing aqueous solution AS that does not contain any anions other than Li may be strongly alkaline, it is preferable to apply a cation exchange membrane with high alkali resistance to the ion exchange membrane 62. With this configuration, the Li-containing aqueous solution AS that comes into contact with the side of the electrolyte membrane 2 on the supply tank 11 side is Li + Make the concentration sufficiently high, high Li + Li can be efficiently recovered through mobility.

[0077] The lithium recovery method using the lithium recovery device 10B according to this modified example can be performed by applying voltage with power supplies 51, 52, and 53, and further applying voltage with a sub-power supply 54, similar to the lithium recovery method using the lithium recovery device 10A according to the modified example (see Figure 5). The settings of voltages V1, V2, and V3 are as described in the modified example. Furthermore, the larger the applied voltage V4 from the sub-power supply 54, the stronger the electric field generated in the aqueous solutions SW and AS' between the sub-electrode 42 and sub-electrode 43, and the stronger the Li contained in the Li-containing aqueous solution SW. + The amount of cations containing this Li that moves per unit time into the Li-containing aqueous solution AS' increases. + If the amount of Li transferred per unit time is small, the Li of the Li-containing aqueous solution AS' + The concentration decreases, and furthermore, the Li of the Li-containing aqueous solution AS + The concentration decreases, so Li + Mobility is the rate-limiting factor.

[0078] On the other hand, if the voltage V4 is greater than a certain value, the reaction shown in equation (1) below occurs near the auxiliary electrode 42, generating O2, and furthermore, the Li-containing aqueous solution SW becomes Cl - If it contains Li, the reaction shown in equation (2) below occurs, generating Cl2. At the same time, the reaction shown in equation (4) below occurs near the auxiliary electrode 43, generating H2. The more these reactions occur, the lower the energy efficiency becomes, so Li + It is preferable that the voltage V4 is small within the range where mobility is not rate-limiting. Furthermore, the electric field generated by the application of voltage V4 becomes stronger with respect to voltage V4 as the distance between the auxiliary electrodes 42 and 43 and the ion exchange membrane 61 is shorter, and as the electronic conductivity of the Li-containing aqueous solutions SW and AS' is higher. Therefore, by arranging the auxiliary electrodes 42 and 43 and by making the Li-containing aqueous solution AS' an aqueous solution containing ions at the start of operation, the Li-containing electric field becomes stronger with respect to voltage V4. + This can increase the amount of cations that move per unit time. [ka]

[0079] Furthermore, similar to the above modified example, if the Li-containing aqueous solution AS is pure water or a low-concentration LiOH aqueous solution at the start of recovery, first, the auxiliary power supplies 53 and 54 are activated to add Li to the Li-containing aqueous solution AS. + It is preferable to move the solution to reach a predetermined concentration before further operating the first power supply 51 and the second power supply 52. ​​With the lithium recovery device 10B, the voltage applied between both sides of the ion exchange membrane 61 and between both sides of the ion exchange membrane 62 can be set individually. Therefore, it is easy to individually manage the pH of the Li-containing aqueous solutions AS' and AS during operation.

[0080] In this modified lithium recovery apparatus 10B, a cation exchange membrane that conducts cations containing polyvalent ions can be applied to the ion exchange membrane 61, and a monovalent ion selective permeable ion exchange membrane can be applied to the ion exchange membrane 62. With this configuration, only the polyvalent ions among the cations contained in the Li-containing aqueous solution SW can be precipitated and recovered from the Li-containing aqueous solution AS' in the intermediate tank 12a. + Other monovalent ions can be recovered from the Li-containing aqueous solution AS in the intermediate tank 12b. However, in order to prevent the Li-containing aqueous solutions AS' and AS that are in contact with both sides of the ion exchange membrane 62 from becoming strongly alkaline, the power supplies 51, 52, 53, and 54 are driven to prevent high concentrations of cations, or Li is released from the Li-containing aqueous solutions AS' and AS. + It is preferable to recover cations other than those mentioned above in a timely manner. Alternatively, the lithium recovery apparatus 10B according to this modified example may be equipped with three ion exchange membranes arranged in the order of a cation exchange membrane, a monovalent ion selective permeable ion exchange membrane, and a cation exchange membrane, thereby providing three intermediate tanks. Acid is added to the aqueous solutions in the first and second intermediate tanks from the supply side to prevent them from becoming strongly alkaline. With this configuration, the Li of the aqueous solution in contact with the electrolyte membrane 2 of the third intermediate tank can be recovered. + The concentration can be increased, and polyvalent cations can be recovered from the intermediate tank in the first tank.

[0081] [Second Embodiment] In the lithium recovery apparatus according to the above embodiment, by providing a third electrode in the recovery tank spaced apart from the electrolyte membrane, the voltage applied between both sides of the electrolyte membrane is increased, thereby increasing the Li recovery rate. On the other hand, Li can also be recovered at a low speed by operating with a small voltage. Hereinafter, a lithium recovery apparatus and lithium recovery method according to the second embodiment of the present invention will be described with reference to Figure 7.

[0082] (Lithium recovery device) As shown in Figure 7, the lithium recovery apparatus 10C according to the second embodiment of the present invention comprises a processing tank 1, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2 that divides the processing tank 1 into a supply tank (first tank) 11 and a recovery tank (second tank) 13, a first electrode 31 covering the supply tank 11 side surface of the electrolyte membrane 2, a second electrode 32A provided in the recovery tank 13, a secondary electrode 41 provided in the supply tank 11, and a secondary power supply 53 and a first power supply 51 connected in series. The lithium recovery apparatus 10C may further include a circulation device 71 and a stirrer 72 as needed (see Figures 1 and 4). The lithium recovery apparatus 10C according to this embodiment is configured such that, compared to the lithium recovery apparatus 10 according to the first embodiment shown in Figure 1, the second power supply 52 and the third electrode 33 are removed, and the second electrode 32 is replaced with a second electrode 32A spaced apart from the electrolyte membrane 2. In the lithium recovery device 10C, the first power supply 51 acts as the main power supply and applies a voltage V1 between both sides of the electrolyte membrane 2 and between the Li-containing aqueous solution SW and the Li recovery aqueous solution RS.

[0083] The second electrode 32A, like the second electrode 32 in the first embodiment, is an electrode paired with the first electrode 31 to apply a voltage between both sides of the electrolyte membrane 2. The second electrode 32A is positioned in the recovery tank 13 so as not to contact the electrolyte membrane 2, preferably with a short distance between it and the electrolyte membrane 2, and preferably positioned parallel to the electrolyte membrane 2. The second electrode 32A is preferably shaped like a mesh or the like to increase the contact area with the Li recovery aqueous solution RS, similar to the third electrode 33 in the first embodiment. Alternatively, the second electrode 32A may have a porous structure and be in contact with the electrolyte membrane 2, similar to the second electrode 32 in the first embodiment. The second electrode 32A is formed of an electrode material that has catalytic activity and electronic conductivity for the reaction shown in formula (4) below, and is stable even when a voltage is applied in the Li recovery aqueous solution RS, including after Li recovery, for example, platinum (Pt) is preferred. [ka]

[0084] (Lithium recovery method) A lithium recovery method according to a second embodiment of the present invention will be described with reference to Figure 7. The lithium recovery method according to this embodiment is performed as follows using the lithium recovery apparatus 10C according to the second embodiment.

[0085] In the lithium recovery device 10C, the auxiliary power supply 53 and the first power supply 51, which are connected in series, can be considered as a single power supply (referred to as power supply 53-51). Power supply 53-51 applies a positive voltage (V3 + V1) to the auxiliary electrode 41 and the second electrode 32A. Simultaneously, the first power supply 51 applies a positive voltage V1 to the first electrode 31 and the second electrode 32A. Then, in the Li-containing aqueous solution SW of the supply tank 11, similar to the first embodiment, OH in the Li-containing aqueous solution SW is released near the auxiliary electrode 41 and the first electrode 31. - However, the reaction shown in equation (1) below occurs, and electron e - By releasing gases and generating H2O and O2, electrons are sent to the auxiliary electrode 41 and the first electrode 31. - It releases Li. Li-containing aqueous solution SW is Cl -If it contains, the reaction shown in equation (2) below occurs in the vicinity of the auxiliary electrode 41, and electron e - It releases OH to generate Cl2. In Li-containing aqueous solution SW, OH - As other anions decrease, Li in the Li-containing aqueous solution SW decreases in order to maintain the charge balance. + The reaction shown in equation (3) below, in which the substance moves into the electrolyte membrane 2, occurs on the surface of the electrolyte membrane 2, i.e., in the vicinity of the first electrode 31. [ka]

[0086] On the other hand, in the Li recovery aqueous solution RS of the recovery tank 13, near the second electrode 32A, H2O in the Li recovery aqueous solution RS is converted into electrons e - When supplied, the reaction shown in equation (4) below occurs, producing H2 and OH - This generates OH - As the amount increases, in order to maintain the charge balance, Li in electrolyte membrane 2 + The reaction described in equation (5) below, in which the material moves, occurs on the surface of the electrolyte membrane 2. [ka]

[0087] From the reaction in equation (3) to the reaction in equation (5), that is, Li in an aqueous solution SW containing Li + Penetration from the surface to the interior of electrolyte membrane 2, Li in electrolyte membrane 2 + The movement of Li in electrolyte membrane 2. +The transfer of ions to the Li recovery aqueous solution RS is as described in the first embodiment. In this embodiment, if the potential difference between both sides of the electrolyte membrane 2 due to the application of voltage V1 is greater than or equal to the electrolyte reduction voltage of the electrolyte membrane 2, the electrolyte membrane 2 exhibits electronic conductivity, and even if the voltage V1 is further increased, the Li recovery rate does not increase by as much as the increase in voltage V1, and the energy efficiency decreases sharply (see Patent Document 2). Specifically, although it depends on the electronic conductivity of the electrolyte membrane 2 and the electrode performance that determines the electrode reaction overpotential, the electrolyte membrane 2 can exhibit electronic conductivity when a voltage greater than 2.0V is applied between both sides. Therefore, in this embodiment, it is preferable to set the applied voltage V1 by the first power supply 51 so that the potential difference between both sides of the electrolyte membrane 2 is less than or equal to the electrolyte reduction voltage. In the lithium recovery device 10C according to this embodiment, since the second electrode 32A is provided spaced apart from the electrolyte membrane 2, the voltage V1 can be set to a certain extent relative to the electrolyte reduction voltage of the electrolyte membrane 2.

[0088] Furthermore, the voltage V3 is set to be less than the voltage at which electrolysis of water occurs, as in the first embodiment. In this embodiment, even if the voltage V3 is greater than or equal to the aforementioned value obtained by taking into account the electrode performance, etc., in addition to the theoretical voltage for electrolysis of water (1.229V), if the voltage V1 is greater than or equal to a certain extent than the voltage V3, electrolysis of water will not occur. However, even if the voltage V3 is less than the voltage at which electrolysis of water occurs, if it exceeds a certain magnitude relative to the voltage V1, electron transfer properties will be exhibited in the electrolyte membrane 2. Here, the aqueous solution in the portion of the Li-containing aqueous solution SW sandwiched between the first electrode 31 and the auxiliary electrode 41 is denoted as "SW". E The portion of the Li recovery aqueous solution RS sandwiched between the electrolyte membrane 2 and the second electrode 32A is denoted as "RS". E This is represented as . The lithium recovery device 10C according to this embodiment includes a first power supply 51, a sub-power supply 53, and a Li-containing aqueous solution SW, as shown in Figure 8. E Electrolyte membrane 2, Li recovery aqueous solution RS E (Not shown in the diagram) The circuit includes a closed circuit connected in a ring in the order of the first power supply 51. Currents I3 and I1 flow counterclockwise through this closed circuit (first circuit) as shown by the dotted arrows, through the first power supply 51 and the auxiliary power supply 53 (power supply 53-51) connected in series.

[0089] Furthermore, in the lithium recovery device 10C, the positive electrode of the first power supply 51 and the negative electrode of the auxiliary power supply 53 (connection node 5n1) are connected to the electrolyte membrane 2 and the Li-containing aqueous solution SW via the first electrode 31. E They are connected to each other. Therefore, the lithium recovery device 10C transmits from the connection node 5n1 to the electrolyte membrane 2, or from the Li-containing aqueous solution SW E Current can flow in either direction, or from the electrolyte membrane 2 to the connection node 5n1, but as described in the first embodiment, the system is configured such that current I4 flows from the connection node 5n1 to the electrolyte membrane 2, or does not flow. To this end, the lithium recovery device 10C is configured as a second circuit to include the first power supply 51, the electrolyte membrane 2, and the Li recovery aqueous solution RS E The circuit includes a closed circuit (not shown in the diagram), and currents I4 and I1 flow counterclockwise from the first power supply 51 as indicated by the gray arrows. The current that branches off from current I1 (from connection node 5n1) and flows towards the electrolyte membrane 2 via the first electrode 31 is represented as I4.

[0090] The lithium recovery device 10C should be configured such that the voltage V3 is set so that the current I4 flows in this direction, or not (not flows in the reverse direction), i.e., I4≧0. Since the relationship I3+I4=I1 holds for the current I4, it should be I1≧I3. The resistance of the electrolyte membrane 2 (resistance between the first electrode 31 and the second electrode 32A, Li + (The resistance of movement) is R EL , Li-containing aqueous solution SW E The resistance (the resistance between the first electrode 31 and the auxiliary electrode 41) is R SW This is expressed as follows. In this embodiment, the resistor R EL However, Li recovery aqueous solution RS E This also includes the resistance (resistance between electrolyte membrane 2 and second electrode 32A) (resistance of electrolyte membrane 2 and Li recovery aqueous solution RS). E (The sum of the resistances) is used. In addition, the lithium recovery device 10C has a reaction resistance R due to the reaction of equation (1) (O2 generation) and the reaction of equation (2) (Cl2 generation) at the auxiliary electrode 41. c41 The reaction resistance R due to the reaction of equation (1) and the reaction of equation (2) at the first electrode 31. c31, the reaction resistance R due to the reaction of equation (4) at the second electrode 32A c32 This further includes the following. Then, the first circuit is represented by equation (19) below, and the second circuit by equation (20) below. Note that the resistance of electrodes 31, 32A, 41 and the wiring is ignored here.

number

[0091] From equations (19) and (20), we obtain equation (9). The current I1 is given by equation (21) from equation (20). The current I3 is given by equation (13) from equation (9). For I1 ≥ I3, equation (22) must hold. Solving equation (22) gives equation (23). Substituting equation (13) for I3 in equation (21) and solving for I1 gives equation (24). Substituting equation (24) into equation (23) gives equation (25).

number

[0092] Thus, the voltage V3 of the auxiliary power supply 53 is set to be less than the voltage at which electrolysis of water occurs, and is set to be below a certain level corresponding to the voltage V1 of the first power supply 51 so that equation (25) holds, and preferably is greater within this range. To this end, the lithium recovery device 10C can, for example, apply voltages V1 and V3 while measuring currents I1 and I3 by connecting ammeters in series (not shown) to the first power supply 51 and the auxiliary power supply 53, respectively. Also, the resistance R between the first electrode 31 and the auxiliary electrode 41 SW , reaction resistance R at auxiliary electrode 41 c41 The lower each of these values, the stronger the electric field generated in the Li-containing aqueous solution SW, even with a small voltage V3, resulting in a higher effect. Reaction resistance R c41 The resistance R is lower as the surface area of ​​the auxiliary electrode 41 immersed in the Li-containing aqueous solution SW increases, and as the catalytic activity of the reaction in equation (1) of the auxiliary electrode 41 increases. SW The resistance R is lower the larger the area of ​​the first electrode 31 and the auxiliary electrode 41 immersed in the Li-containing aqueous solution SW, and the shorter the distance between them.SW The higher the electronic conductivity of the Li-containing aqueous solution SW, the lower the coefficient of this coefficient.

[0093] In this embodiment, similar to the first embodiment, a secondary power supply 53 is provided in series with the positive electrode of the first power supply 51 that applies a voltage between both sides of the electrolyte membrane 2, and a secondary electrode 41 with a potential higher than the surface of the electrolyte membrane 2 is provided in the Li-containing aqueous solution SW, thereby enabling the use of seawater and other Cl - Li sources containing high concentrations of Li + A low-concentration Li source is used as a Li-containing aqueous solution SW. + It can be recovered efficiently.

[0094] (modified version) The lithium recovery apparatus according to this embodiment may be configured to divide the processing tank 1 into three or more sections, similar to the lithium recovery apparatuses 10A and 10B according to the modified first embodiment shown in Figures 4 and 6, and may also be equipped with ion exchange membranes 61 and 62. [Examples]

[0095] The lithium recovery apparatus and lithium recovery method according to the present invention have been described above, along with embodiments for carrying out the present invention. Below, examples confirming the effects of the present invention will be described. It goes without saying that the present invention is not limited to these embodiments and the embodiments described above, and various modifications and alterations based on these descriptions are also included in the spirit of the present invention.

[0096] The amount of lithium transferred by applying a voltage for a certain period of time was measured for the lithium recovery apparatus according to the first embodiment of the present invention shown in Figure 1, and the lithium recovery apparatus according to the second embodiment of the present invention shown in Figure 7.

[0097] (Manufacturing of a lithium recovery device) The lithium recovery device uses a plate-shaped La as the electrolyte membrane, measuring 50mm x 50mm and 0.5mm thick. 0.57 Li 0.29TiO3 (lithium-ion conductive ceramic LLTO, manufactured by Toho Titanium Co., Ltd.) was used. On the center of each side of this electrolyte membrane, grid-like electrodes measuring 19.5 mm × 20.5 mm were formed as the first and second electrodes, with a thickness of 10 μm, a width of 0.5 mm, and a spacing of 0.5 mm. Lead wires for connecting to the power supply were also formed to connect to these electrodes. The first and second electrodes and lead wires were formed by screen printing Pt paste onto the surface of the electrolyte membrane and firing it in air at 900°C for 1 hour. In addition, a 20 mm × 20 mm Pt mesh electrode was used as a secondary electrode, and a 20 mm × 20 mm Ni mesh electrode was used as a third electrode. The electrolyte membrane with the electrodes formed was installed in a processing tank made of acrylic plate, and partitioned into a supply tank and a recovery tank. The secondary electrode was placed in the supply tank and the third electrode was placed in the recovery tank, both facing the electrodes on the surface of the electrolyte membrane (distance between secondary electrode and electrolyte membrane: 50 mm). Furthermore, the processing tank was housed in a constant temperature bath with a temperature control function. Then, a first power supply was connected between the first and second electrodes, with the first electrode as the positive electrode. A secondary power supply was connected in series to the positive electrode of the first power supply, and its positive electrode was connected to the secondary electrode. A second power supply was connected in series to the negative electrode of the first power supply, and its negative electrode was connected to the third electrode, thus forming a lithium recovery device. In addition, ammeters were inserted between the first power supply and the first electrode, between the second power supply and the first power supply and the third electrode (between the second power supply 52 and connection node 5n2 in Figure 2), and between the secondary power supply and the secondary electrode.

[0098] As lithium-containing aqueous solutions (Li sources), 1.0 mol / L, 0.1 mol / L, and 0.001 mol / L lithium hydroxide (LiOH) aqueous solutions were prepared, and 150 ml of each was added to the supply tank of the lithium recovery device so that the first electrode and the secondary electrode were completely immersed. In addition, as a lithium recovery aqueous solution, a 0.1 mol / L lithium hydroxide aqueous solution was prepared, and 150 ml of each was added to the recovery tank of the lithium recovery device so that the second electrode and the third electrode were completely immersed. Furthermore, for each of the lithium-containing aqueous solutions and the lithium recovery aqueous solutions, lithium hydroxide aqueous solutions of the same concentration were placed in replenishment tanks for the lithium-containing aqueous solutions and for the lithium recovery aqueous solutions, which were installed outside the processing tank of the lithium recovery device in the constant temperature bath, respectively, and adjusted to the same liquid temperature of 40°C (=313.15K) as the lithium hydroxide aqueous solutions in the supply tank and the recovery tank.

[0099] (Lithium recovery experiment) As Example 1 of the first embodiment of the present invention (see Figure 1), the DC voltages shown in Table 1 were applied for 1 hour using a first power supply (voltage V1), a second power supply (voltage V2), and a secondary power supply (voltage V3). To suppress changes in the concentration of the lithium hydroxide aqueous solution in the supply tank and recovery tank associated with electrodialysis, while applying the voltage, the aqueous solution was replenished from the replenishment tank to the supply tank and recovery tank respectively at a constant rate using a liquid transfer pump, and the lithium hydroxide aqueous solution was pumped out at the same rate. After the voltage was applied, the Li concentration in the aqueous solution in the recovery tank and the lithium hydroxide aqueous solution pumped out from the recovery tank was measured using an inductively coupled plasma atomic emission spectrometer (ICP-OES) (Optima7000DV, manufactured by PerkinElmer Corporation), and the amount of Li transferred due to the voltage application for 1 hour was calculated. Table 1 shows the amount of Li transferred per hour.

[0100] As Example 2 of the second embodiment of the present invention (see Figure 7), the DC voltages shown in Table 1 were applied for 1 hour using a first power supply (voltage V1) and a secondary power supply (voltage V3). As Comparative Example 1, the voltages were applied for 1 hour using a first power supply (voltage V1) and a second power supply (voltage V2). As Comparative Example 2, only the first power supply (voltage V1) was applied for 1 hour. In the same manner as in the above experiment, while applying the voltage, lithium hydroxide aqueous solution of the same concentration was replenished from the replenishment tank to the supply tank and the recovery tank, respectively, and lithium hydroxide aqueous solution was pumped out at the same rate. After the voltage was applied, the Li concentration of the aqueous solution in the recovery tank and the lithium hydroxide aqueous solution pumped out from the recovery tank was measured, and the amount of Li transferred per unit time was calculated and is shown in Table 1.

[0101] A 1.0 mol / L lithium chloride (LiCl) aqueous solution was prepared as the Li-containing aqueous solution (Li source), and a 1.0 mol / L lithium hydroxide aqueous solution was prepared as the Li recovery aqueous solution. Lithium recovery experiments were conducted for Example 1 and Comparative Example 1 in the same manner as with the lithium hydroxide aqueous solution. In addition, a 1.0 mol / L lithium chloride (LiCl) aqueous solution was prepared as the Li-containing aqueous solution (Li source), and a 0.1 mol / L lithium hydroxide aqueous solution was prepared as the Li recovery aqueous solution. Lithium recovery experiments were conducted for Example 2 and Comparative Example 2 in the same manner as with the lithium hydroxide aqueous solution. After voltage application, the Li concentration in the aqueous solution in the recovery tank and the lithium hydroxide aqueous solution pumped out from the recovery tank was measured, and the amount of Li transferred per unit time was calculated, which is shown in Table 1.

[0102] Figure 9A shows the graphs for Example 1 and Comparative Example 1 showing the dependence of the Li source LiOH concentration on the amount of Li transferred per unit time when the Li-containing aqueous solution (Li source) is a lithium hydroxide aqueous solution, and Figure 9B shows the graphs for Example 2 and Comparative Example 2. Furthermore, Figure 10 shows the graphs for the amount of Li transferred per unit time when the Li-containing aqueous solution is a 0.001 mol / L lithium hydroxide aqueous solution and a 1.0 mol / L lithium chloride aqueous solution, respectively, for the Examples and Comparative Examples.

[0103] [Table 1]

[0104] Comparing Example 1 with Comparative Example 1, and Example 2 with Comparative Example 2, as shown in Table 1, Figure 9A, and Figure 9B, the effects of Example 1 and Example 2 according to the present invention were greater when the concentration of the lithium hydroxide aqueous solution used as the Li source was low. Furthermore, as shown in Table 1 and Figure 10, the effects of Example 1 and Example 2 according to the present invention were also greater when lithium chloride aqueous solution was used as the Li source. In addition, comparing Example 1 with Example 2, by providing a third electrode with a low potential on the recovery tank side, the applied voltage V1 between both sides of the electrolyte membrane could be increased, thereby increasing the Li recovery rate.

[0105] Based on the above, the lithium recovery apparatus and lithium recovery method according to the embodiment of the present invention are suitable for Li sources and Cl sources with low Li concentration. - It was confirmed that this enables faster recovery from Li sources containing [the substance]. [Explanation of Symbols]

[0106] 10, 10A, 10B, 10C Lithium Recovery System 1. Processing tank 11 Supply tank (1st tank) 12 Intermediate tank 12a,12b Intermediate tank 13. Recovery tank (second tank) 2. Electrolyte membrane (lithium-ion conductive electrolyte membrane) 31 1st electrode 32,32A 2nd electrode 33 Third electrode 41 Sub-electrode 42,43 Sub-electrode 51 1st power supply 52 2nd power supply 53 Sub-power supply 54 Sub-power supply 61,62 Ion exchange membrane AS Li-containing aqueous solution RS Li recovery aqueous solution SW Li-containing aqueous solution

Claims

1. A lithium recovery apparatus comprising a processing tank divided into a first tank and a second tank, wherein lithium ions are transferred from an aqueous solution containing lithium ions contained in the first tank to water or an aqueous solution contained in the second tank, A lithium-ion conductive electrolyte membrane partitions the aforementioned processing tank, A first electrode having a porous structure is provided in contact with the first tank-side surface of the lithium-ion conductive electrolyte membrane, A second electrode is provided in the second tank, spaced apart from the lithium-ion conductive electrolyte membrane, A secondary electrode provided in the first tank and spaced apart from the first electrode and the lithium-ion conductive electrolyte membrane, A first power supply is connected between the first electrode and the second electrode, with the first electrode as the positive terminal. A lithium recovery apparatus characterized by comprising a secondary power supply connected in series with the positive electrode of the first power supply and having a positive electrode connected to the secondary electrode.

2. A lithium recovery apparatus comprising a processing tank divided into a first tank and a second tank, wherein lithium ions are transferred from an aqueous solution containing lithium ions contained in the first tank to water or an aqueous solution contained in the second tank, A lithium-ion conductive electrolyte membrane partitions the aforementioned processing tank, A first electrode having a porous structure is provided in contact with the first tank-side surface of the lithium-ion conductive electrolyte membrane, and a second electrode is provided in contact with the second tank-side surface, A secondary electrode provided in the first tank and spaced apart from the first electrode and the lithium-ion conductive electrolyte membrane, The second tank contains a third electrode spaced apart from the second electrode and the lithium-ion conductive electrolyte membrane, A first power supply is connected between the first electrode and the second electrode, with the first electrode as the positive terminal. A secondary power supply is connected in series with the positive electrode of the first power supply and has its positive electrode connected to the secondary electrode, A lithium recovery apparatus characterized by comprising a second power supply connected in series with the negative electrode of the first power supply and connected to the negative electrode of the third electrode.

3. The lithium recovery apparatus according to claim 2, characterized in that the voltage of the first power supply is greater than or equal to the voltage applied to the lithium-ion conductive electrolyte membrane that causes the lithium-ion conductive electrolyte membrane to reach the reduction potential of at least one metal element contained in the lithium-ion conductive electrolyte membrane.

4. The device further comprises one or more ion exchange membranes that conduct cations containing at least lithium ions, The processing tank is partitioned in one direction in the order of the first tank, one or more intermediate tanks, and the second tank. The lithium-ion conductive electrolyte membrane partitions the processing tank into the second tank and the adjacent intermediate tank. The ion exchange membrane partitions the processing tank into the intermediate tank and the adjacent intermediate tank or the first tank. A lithium recovery apparatus according to any one of claims 1 to 3, characterized in that lithium ions are moved from an aqueous solution containing lithium ions contained in the first tank, via the water or aqueous solution contained in the intermediate tank, to the water or aqueous solution contained in the second tank.

5. A lithium recovery apparatus according to any one of claims 1 to 3, characterized in that it comprises a circulation means for circulating an aqueous solution containing lithium ions between the outside and the inside of the first tank.

6. A lithium recovery method comprising transferring lithium ions from an aqueous solution containing lithium ions contained in the first tank to water or an aqueous solution contained in the second tank, in a treatment tank partitioned into a first tank and a second tank, A first power supply is connected with the first electrode as the positive terminal between a first electrode having a porous structure, which is provided in contact with the surface of the lithium-ion conductive electrolyte membrane that partitions the processing tank on the first tank side, and a second electrode provided in the second tank spaced apart from the lithium-ion conductive electrolyte membrane, A lithium recovery method characterized by applying a voltage to a secondary power supply, which is connected in series with the positive electrode of the first power supply and has its positive electrode connected to a secondary electrode provided in the first tank at a distance from the lithium-ion conductive electrolyte membrane.

7. A lithium recovery method comprising transferring lithium ions from an aqueous solution containing lithium ions contained in the first tank to water or an aqueous solution contained in the second tank, in a treatment tank partitioned into a first tank and a second tank, A first power supply is connected with the first electrode as the positive terminal between a first electrode having a porous structure, which is provided in contact with the first tank side surface of the lithium-ion conductive electrolyte membrane that partitions the processing tank, and a second electrode having a porous structure, which is provided in contact with the second tank side surface. A secondary power supply is connected in series with the positive electrode of the first power supply, and the positive electrode of the secondary electrode is connected to a secondary electrode provided in the first tank, spaced apart from the lithium-ion conductive electrolyte membrane. A lithium recovery method characterized by applying a voltage to a second power supply, which is connected in series with the negative electrode of the first power supply and has its negative electrode connected to a third electrode provided in the second tank, spaced apart from the second electrode and the lithium-ion conductive electrolyte membrane.

8. The lithium recovery method according to claim 7, characterized in that the first power supply applies a voltage to the lithium-ion conductive electrolyte membrane that is greater than or equal to the voltage applied to the lithium-ion conductive electrolyte membrane that causes the first power supply to reach the reduction potential of at least one metal element contained in the lithium-ion conductive electrolyte membrane.

9. The processing tank is partitioned in one direction in the order of the first tank, one or more intermediate tanks, and the second tank. The intermediate tank and the adjacent intermediate tank or the first tank are separated by an ion exchange membrane that conducts cations containing at least lithium ions. The second tank and the adjacent intermediate tank are separated by the lithium-ion conductive electrolyte membrane. A lithium recovery method according to any one of claims 6 to 8, characterized in that lithium ions are moved from an aqueous solution containing lithium ions contained in the first tank, via the water or aqueous solution contained in the intermediate tank, to the water or aqueous solution contained in the second tank.

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