Method for recovering lithium used for lithium ion secondary battery positive electrode material, and method for producing lithium adsorbent

Abstract

To provide a lithium recovering method, which is high in lithium recovery rate and excellent in stability.SOLUTION: A method for recovering lithium from a lithium-ion secondary battery positive electrode material (A) represented by the formula (A): LiaMnbFecMxPO4, comprises the steps (I) to (III-1) as follows: (I) adding an oxidizing agent and water to the lithium-ion secondary battery positive electrode material (A) to obtain a mixed solution i; (II) adjusting the pH of the obtained mixed solution i to 4-9 and mixing to obtain a mixed solution ii; (III-1) filtering the obtained mixed solution ii to obtain a lithium-containing filtrate iii; and thereafter, using the obtained filtrate iii to undergo predetermined steps (I)' to (III-1)' to obtain the filtrate iii' as a lithium-rich solution, or by using the obtained filtrate iii' again as filtrate iii in step (I)' to repeat steps (I)' to (III-1)' multiple times to finally obtain the filtrate iii' as a lithium-rich solution, thereby recovering lithium.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering lithium using a positive electrode material for a lithium ion secondary battery composed of olivine-type lithium phosphate, and a method for producing a lithium adsorbent. [Background technology]

[0002] Positive electrode materials made of compounds such as Li(Fe,Mn)PO4 with an olivine structure are highly useful as positive electrode materials for lithium-ion secondary batteries and are widely used. However, because the raw material lithium is expensive, there is a strong demand for the recovery and reuse of such lithium.

[0003] In this context, for example, Patent Document 1 discloses a Li 1.6 Mn 1.6 Granules for lithium adsorption obtained from lithium manganese oxides such as O4, so-called LMO-type materials, have been disclosed, and attempts have been made to adsorb Li contained in salt lake brine. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-90401 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the case of recovering lithium using the lithium adsorption granules described in the above patent documents, there is a concern about elution of manganese, and there is also a risk that the recovery rate of lithium may decrease due to repeated recovery, and therefore there is still room for improvement.

[0006] Therefore, the present invention relates to a method for recovering lithium with a high lithium recovery rate and excellent stability. [Means for solving the problem]

[0007] Therefore, as a result of intensive studies to solve the above problems, the present inventors have found a method for efficiently recovering lithium from a positive electrode material for a lithium-ion secondary battery composed of a specific olivine-type lithium phosphate.

[0008] That is, the present invention provides the following formula (A): Li a Mn b Fe c M x PO4···(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3. ) A method for recovering lithium from a positive electrode material (A) for a lithium-ion secondary battery represented by the following steps (I) to (III-1): (I) A step of adding an oxidizing agent and water to the positive electrode material (A) for a lithium-ion secondary battery to obtain a mixed solution i (II) A step of adjusting the pH of the obtained mixed solution i to 4 to 9 and mixing to obtain a mixed solution ii (III-1) A step of filtering the obtained mixed solution ii to obtain a lithium-containing filtrate iii After passing through the above steps, then the following steps (I)' to (III-1)' are carried out using the obtained filtrate iii: (I)' A step of adding the positive electrode material (A) for a lithium-ion secondary battery and an oxidizing agent to the obtained filtrate iii to obtain a mixed solution i' (II)' A step of adjusting the pH of the obtained mixed solution i' to 4 to 9 and mixing to obtain a mixed solution ii' (III-1)' A step of filtering the obtained mixed solution ii' to obtain a lithium-containing filtrate iii' Through this process, the obtained filtrate iii' is obtained as a lithium-rich solution, or by using the obtained filtrate iii' again as the filtrate iii in step (I)', the above steps (I)' to (III-1)' are repeated multiple times, and finally the obtained filtrate iii' is obtained as a lithium-rich solution. It provides a method for recovering lithium.

[0009] In addition, the present invention relates to the following formula (A): Li a Mn b Fe c M x PO4···(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3. ) A method for producing a lithium adsorbent from a positive electrode material (A) for a lithium ion secondary battery represented by the following steps (I) to (III-2): (I) A step of adding an oxidizing agent and water to the positive electrode material (A) for a lithium ion secondary battery to obtain a mixed solution i (II) A step of adjusting the pH of the obtained mixed solution i to 4 to 9 and mixing to obtain a mixed solution ii (III-2) A step of obtaining a residue iii after filtering the obtained mixed solution ii It also provides a method for producing a lithium adsorbent comprising the above steps.

Advantages of the Invention

[0010] In the lithium recovery method of the present invention, since the positive electrode material (A) for a lithium ion secondary battery is the target, excellent stability can be ensured while effectively improving the recovery rate, and a highly versatile lithium-rich solution can be obtained. In addition, a lithium adsorbent with excellent lithium adsorption properties can also be obtained, so it is highly useful as a method for producing a lithium adsorbent.

Best Mode for Carrying Out the Invention

[0011] The following is a detailed description of the present invention. The method for recovering lithium of the present invention is represented by the following formula (A): Li a Mn b Fe c M x PO4···(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3. ) Lithium is recovered from the positive electrode material (A) for a lithium-ion secondary battery represented by the following formula (A) (hereinafter also referred to as "positive electrode material (A)"). Generally, the positive electrode material, which is olivine-type lithium phosphate as represented by the above formula (A), has a very stable crystal structure compared to so-called LTO-type positive electrode materials such as lithium titanate and lithium manganate, and LMO-type positive electrode materials. Therefore, it is difficult to directly extract lithium from such materials, and there has been a situation where it is difficult to recover a sufficient amount. However, with the method of the present invention, lithium can be effectively recovered even from such a positive electrode material (A).

[0012] In the above formula (A), for a, 0.6 ≤ a ≤ 1.2 is preferable, 0.65 ≤ a ≤ 1.15 is more preferable, and 0.7 ≤ a ≤ 1.1 is even more preferable. For b, 0.4 ≤ b ≤ 0.8 is preferable. For c, 0.2 ≤ c ≤ 0.6 is preferable. For x, 0 ≤ x ≤ 0.2 may be acceptable, further 0 ≤ x ≤ 0.15 may be acceptable, and 0 ≤ x ≤ 0.1 may be acceptable. Also, M may further be Mg, Al, Ti, Zn, Nb, Co, Zr, or Gd.

[0013] Specifically, for example, LiMnPO4, LiFePO4, LiMn 0.3 Fe0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.9 Fe 0.1 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.75 Fe 0.15 Mg 0.1 PO4, LiMn 0.75 Fe 0.19 Zr 0.03 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4, Li 0.6 Mn 0.84 Fe 0.36 PO4, etc. Among them, LiMn 0.8 Fe 0.2 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4 is preferred.

[0014] The BET specific surface area of ​​the positive electrode material (A) is preferably 5 m 2 / g~30m 2 / g, more preferably 10m 2 / g~25m 2 / g. In order to ensure such a suitable BET specific surface area, the positive electrode material (A) is preferably in the form of granules. The BET specific surface area of ​​the positive electrode material (A) refers to a value determined from an adsorption isotherm by a nitrogen adsorption method, and can be measured using, for example, a flow-type automatic specific surface area measuring device (FlowSorbIII2305, manufactured by Shimadzu Corporation) under conditions of a nitrogen-helium mixed gas containing 30% nitrogen.

[0015] From the viewpoint of increasing the efficiency of recovering lithium, the average particle size of the positive electrode material (A) is preferably 1 μm to 40 μm, more preferably 5 μm to 35 μm. As the positive electrode material (A) having such an average particle size, for example, a positive electrode material obtained by hydrothermal synthesis is preferably used. The average particle size of the positive electrode material (A) is the D obtained from the volume-based particle size distribution based on the laser diffraction / scattering method. 50 The values ​​are the particle diameters (median diameters) at 50% of the cumulative particle size.

[0016] There are no particular limitations on whether the positive electrode material (A) is supported on carbon, but from the viewpoint of increasing the versatility of the high-lithium content liquid obtained by the present invention, it is preferable that the positive electrode material (A) is supported on carbon.

[0017] In the method for recovering lithium of the present invention, step (I) is a step of adding an oxidizing agent and water to a positive electrode material (A) for a lithium ion secondary battery (positive electrode material (A)) to obtain a mixed solution I. Following this step, by going through the subsequent step (II), lithium can be effectively extracted from the positive electrode material (A).

[0018] Specific examples of the oxidizing agent that can be used include one or more selected from peroxo acid salts, permanganates, and hydrogen peroxide salts. More specific examples of peroxoacid salts include sodium peroxodisulfate, potassium peroxodisulfate, ammonium peroxodisulfate, peroxochromate, peroxotitanate, etc. More specific examples of permanganates include hydrogen permanganate, potassium permanganate, sodium permanganate, etc. More specific examples of hydrogen peroxide salts include sodium hydrogen peroxide, potassium hydrogen peroxide, magnesium hydrogen peroxide, etc. Among these, from the viewpoint of effectively increasing the recovery efficiency of lithium, peroxo acid salts are preferred, and sodium peroxodisulfate (Na2S2O8) is more preferred.

[0019] The amount of oxidizing agent added may vary depending on the composition of the positive electrode material (A), but is preferably 0.1 to 0.9 parts by mass, more preferably 0.15 to 0.85 parts by mass, and even more preferably 0.2 to 0.8 parts by mass, per part by mass of the positive electrode material (A).

[0020] From the viewpoint of efficiently recovering lithium, the solid content concentration of the mixed liquid i obtained in step (I) is preferably 0.1 mass % to 40 mass %, more preferably 0.5 mass % to 35 mass %, and even more preferably 1 mass % to 30 mass %, based on 100 mass % of the mixed liquid i. The amount of water to be added may be adjusted as appropriate depending on the amount of the positive electrode material (A) and the amount of the oxidizing agent to be added, and also so that the resulting mixed solution i has an appropriate solid concentration.

[0021] Step (II) is a step of adjusting the pH of the mixed solution i obtained in step (I) to 4 to 9 and mixing the resultant mixture to obtain mixed solution ii, which allows the reaction for extracting lithium from the positive electrode material (A) to proceed efficiently. The pH of the mixed solution i is 4 to 9, preferably 4.5 to 8.5, and more preferably 5 to 8. To adjust the pH, a pH adjuster such as sodium hydroxide or potassium hydroxide may be used as appropriate. The pH is measured at 25°C. The temperature of the mixed liquid i is preferably adjusted to 5°C to 60°C, and may be 15°C to 45°C. If the pH of the mixed solution i obtained in step (I) is already within the above range, there is no need to adjust the pH again here. Furthermore, the temperature of the mixture ii obtained in step (II) is preferably 5°C to 60°C, more preferably 15°C to 45°C.

[0022] Furthermore, from the viewpoint of efficiently proceeding the reaction for extracting lithium from the positive electrode material (A), it is preferable to stir the mixed solution i. The stirring time is preferably 1 hour to 72 hours, more preferably 2 hours to 48 hours, and even more preferably 3 hours to 24 hours.

[0023] Step (III-1) is a step of filtering the mixed solution ii obtained in step (II) and obtaining a lithium-containing filtrate iii, which contains the lithium extracted from the positive electrode material (A) in the form of ions. When filtering the mixed solution ii, it is preferable to use a method using centrifugation from the viewpoint of efficiently increasing the recovery efficiency of lithium. When performing filtration by such a method using centrifugation, a normal centrifuge may be used, and the rotor speed is preferably 1000 rpm to 5000 rpm, more preferably 1500 rpm to 4500 rpm.

[0024] In the method for recovering lithium of the present invention, after the above steps (I) to (III-1), the filtrate iii obtained in step (III-1) is used to undergo the following steps (I)' to (III-1)'. The filtrate iii obtained through only the above steps (I) to (III-1) can also be used as a high-lithium-containing liquid.

[0025] Step (I)' is a step of adding the positive electrode material for a lithium ion secondary battery (A) and an oxidizing agent to the filtrate iii obtained in step (III-1) and mixing them to obtain a mixed solution i'. The oxidizing agent that can be used and the amount thereof to be added are the same as the oxidizing agent that can be used in step (I) and the amount thereof to be added. The solids concentration of the mixed solution i' obtained in step (I)' is the same as the solids concentration of the mixed solution i obtained in step (I), and may be adjusted to such a solids concentration by adding water as appropriate.

[0026] Step (II)' is a step of adjusting the pH of the mixed solution i' obtained in step (I)' to 4 to 9 to obtain a mixed solution ii'. The pH, temperature, and stirring conditions for the mixed solution i' and the resulting mixed solution ii' in step (II)', as well as the stirring conditions for mixing, are the same as those for the mixed solution i and the resulting mixed solution ii in step (I).

[0027] Step (III-1)' is a step of filtering the mixed solution ii' obtained in step (II)' and then obtaining a lithium-containing filtrate iii'. The filtration in step (III-1)' is the same as the filtration in step (III-1).

[0028] In the method for recovering lithium of the present invention, after the steps (I)' to (III-1)', a filtrate iii' obtained in step (III-1)' is obtained as a lithium-rich liquid, or the steps (I)' to (III-1)' are repeated multiple times by using the obtained filtrate iii' again as the filtrate iii in step (I)', and finally a filtrate iii' obtained in step (III-1)' is obtained as a lithium-rich liquid.

[0029] That is, one aspect of the present invention is a method of performing the above steps (I) to (III-1), and then performing the above steps (I)' to (III-1)' once using the filtrate iii obtained, to obtain filtrate iii' obtained in step (III-1)' as a high-lithium liquid. Another aspect of the present invention is a method of performing the above steps (I) to (III-1), and then performing the above steps (I)' to (III-1)' multiple times using the filtrate iii obtained, to obtain filtrate iii' finally obtained in step (III-1)' as a high-lithium liquid.

[0030] As described above, the method for recovering lithium of the present invention is a method in which, after passing through the above steps (I) to (III-1), the above steps (I)' to (III-1)' are repeated once or multiple times, thereby effectively recovering lithium from the positive electrode material (A) and obtaining a high-lithium content solution containing the recovered lithium as ions at an extremely high concentration. Therefore, from the viewpoint of obtaining a high-lithium content solution containing lithium at a higher concentration, it is preferable to repeat the steps (I)' to (III-1)' multiple times rather than performing the steps (I)' to (III-1)' once.

[0031] The amount of lithium contained in the high-lithium solution, i.e., the amount of lithium contained in the filtrate iii' as the high-lithium solution finally obtained in step (III-1)', is preferably 0.7 mol to 1 mol, more preferably 0.8 mol to 1 mol, and even more preferably 0.9 mol to 1 mol relative to 1 mol of lithium constituting the positive electrode material (A) used in step (I), i.e., the initially used positive electrode material (A). The lithium concentration in the high-lithium solution may be controlled by adjusting the water content of the filtrate iii' as appropriate, and may be, for example, 0.1 mol / L to 3000 mol / L, 1 mol / L to 3000 mol / L, 10 mol / L to 3000 mol / L, 100 mol / L to 3000 mol / L, 1000 mol / L to 3000 mol / L, or 1500 mol / L to 2500 mol / L.

[0032] Thus, according to the method for recovering lithium of the present invention, lithium can be efficiently recovered from the positive electrode material (A) composed of olivine-type lithium phosphate, and a highly versatile high-lithium solution can be obtained. For example, if the high-lithium solution is applied to olivine-type lithium phosphate that has deteriorated due to use as a positive electrode material, and lithium has been released from it, it can be effectively and efficiently restored to the pre-deteriorated olivine-type lithium phosphate by applying the high-lithium solution obtained by the method of the present invention.

[0033] The present invention is also highly useful as a method for producing a lithium adsorbent. That is, the method for producing a lithium adsorbent of the present invention is a method for producing a lithium adsorbent from a positive electrode material (A) for a lithium ion secondary battery represented by the above formula (A), which comprises the following steps (I) to (III-2): (I) A step of adding an oxidizing agent and water to a positive electrode material (A) for a lithium ion secondary battery to obtain a mixed solution i. (II) A step of adjusting the pH of the obtained mixed solution i to 4 to 9 and mixing the mixture to obtain a mixed solution ii. (III-2) A step of filtering the obtained mixed liquid ii and then obtaining filter cake iii Equipped with. As described above, the method for producing a lithium adsorbent of the present invention comprises steps (I) and (II) in the method for recovering lithium of the present invention, and includes step (III-2) instead of step (III-1) in the method for recovering lithium of the present invention. Therefore, steps (I) and (II) in the method for producing a lithium adsorbent of the present invention are the same as steps (I) and (II) in the method for recovering lithium of the present invention. The lithium adsorbent obtained by the present invention has extremely high lithium adsorption capacity, and even if a low-quality lithium-containing resource is used, the material represented by the above formula (A) can be obtained.

[0034] Step (III-2) in the method for producing a lithium adsorbent of the present invention is a step of filtering the mixed solution ii obtained in step (II) and then obtaining filter cake iii. After filtering the mixed solution ii obtained in step (II), both the filtrate iii and the filter cake iii are obtained. In the method for recovering lithium of the present invention, one of the filtrate iii is used, whereas in the method for producing a lithium adsorbent of the present invention, the other filter cake iii is used. As described above, the filtrate iii obtained by the method for recovering lithium of the present invention is a liquid containing lithium at a high concentration, whereas the filter cake iii has an effectively reduced amount of lithium. Therefore, the filter cake iii can be used as a lithium adsorbent having excellent lithium adsorption properties.

[0035] The filtration of the mixed solution ii in the step (III-2) is performed in the same manner as the filtration of the mixed solution ii in the above step (III-1). The obtained filter cake iii is preferably dried.

[0036] The amount of lithium contained in the filter cake iii is preferably 0 mol to 0.3 mol, more preferably 0 mol to 0.2 mol, and even more preferably 0 mol to 0.1 mol, relative to 1 mol of lithium constituting the positive electrode material for lithium ion secondary batteries (A) used in step (I).

[0037] The resulting filter cake iii is an adsorbent derived from the positive electrode material (A) and can be used as a lithium adsorbent. Therefore, it has very high lithium adsorption ability. Therefore, even if a low-quality resource with a low lithium concentration (specifically, a resource with a lithium concentration of about 0.01 ppm to 1000 ppm), such as wastewater discharged in the manufacturing process of the positive electrode material or seawater, can be used, lithium can be efficiently and effectively adsorbed.

[0038] In this case, for example, the lithium adsorbent obtained by the present invention is first added to the resource to be treated for lithium adsorption, and the mixture is stirred at 1°C to 99°C, preferably 20°C to 60°C, for 1 hour to 72 hours, preferably 1 hour to 48 hours. Next, the mixture is filtered, and the resulting filter cake is dried and then recovered. The recovered material can be obtained as a material represented by the above formula (A) in the same way as the positive electrode material (A), and can be fully utilized as a positive electrode material. It can also be effectively used as the positive electrode material (A) in step (I)' of the method for recovering lithium. [Example]

[0039] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. The measurements and preparations were carried out according to the following methods.

[0040] <Component analysis of cathode material (A), filtrate, and filter cake> The positive electrode material (A), the filtrate, and the filter cake were subjected to component analysis by ICP optical emission spectroscopy (ICP-OES) using a calibration curve method, and the lithium content was confirmed.

[0041] <pH Measurement> Measurement was performed using a pH meter (F-52, manufactured by HORIBA).

[0042] <Preparation of cathode material (A)> LiMn produced by hydrothermal method and then granulated 0.7 Fe 0.3 PO4(BET specific surface area: 20m 2 / g, average particle size: 10 μm) was prepared and used as a positive electrode material (A).

[0043] <<Preparation of simulated liquid to be treated for lithium adsorption>> A single-element standard solution for lithium ICP atomic emission spectrometry was dissolved in 1 g of water in 1 L to prepare an aqueous solution with a lithium concentration of 1000 ppm, which was used as a simulant solution to be treated by lithium adsorption.

[0044] [Example 1] The following treatments 1) to 4) were carried out to carry out a method for recovering lithium and a method for producing a lithium adsorbent. That is, in the treatment 1), the method of recovering lithium (the above steps (I) to (III-1)) was carried out, and at the same time, a lithium adsorbent was produced, and then, in the treatment 2), the method of recovering lithium (the above steps (I)' to (III-1)') was repeated multiple times using the lithium adsorbent obtained in the treatment 1).

[0045] 1) 100 g of the positive electrode material (A) was mixed with 30 g of NaSO and 1 L of water and stirred to obtain a mixed solution i. The resulting mixed solution i had a pH of 6 and a temperature of 25°C, and it was confirmed that it could be used as is without any additional pH adjustment. Next, mixed solution i was mixed and stirred at 25°C for 1 hour to obtain mixed solution ii. The resulting mixed liquid ii was filtered using a centrifuge (Tabletop Centrifuge 2010, manufactured by Kubota Shoji Co., Ltd., rotor speed 3000 rpm) to recover filtrate iii, and at the same time, filter cake iii was collected separately, which was dried and then recovered. The amount of lithium contained in the recovered filter cake iii was 0.1 mole per mole of lithium constituting the positive electrode material (A) used, and it was confirmed that a useful lithium adsorbent was obtained.

[0046] 2) Next, the collected filter cake iii was added to 1 L of the simulated liquid and stirred at 25°C for 1 hour. This was subjected to the same filtration as in 1) above, and separated into 100 g of filter cake iii-A and wastewater, and only filter cake iii-A was collected. The collected filter cake iii-A was LiMn 0.7 Fe 0.3 It was confirmed that it was expressed as PO4 (the same as the positive electrode material (A) used), and it was found that it can also be used as the positive electrode material (A) in step (I)' in the method for recovering lithium.

[0047] 3) 100 g of the filter cake iii-A obtained in the process 2) above was used as the positive electrode material (A), and this was mixed with 30 g of NaSO and the filtrate iii obtained in the process 1) above. The mixture was stirred at 25°C for 1 hour, and then filtered using a centrifuge (2010, manufactured by Kubota Shoji Co., Ltd., rotor speed 3000 rpm) to recover filtrate iii', which was simultaneously dried.

[0048] 4) The procedure of subjecting the solution to the treatment in 3) above and then subjecting it to the treatment in 2) above was repeated 300 times to finally obtain filtrate x as a high-lithium solution. The obtained filtrate x had a lithium concentration of 1700 mol / L, and it was confirmed that a high-lithium solution was obtained.

Claims

1. The following formula (A): Li ａ Mn ｂ Fe ｃ M ｘ 2O ４ ・・・(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x represent numbers that satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0, and that satisfy a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.) A method for recovering lithium from a positive electrode material (A) for a lithium ion secondary battery represented by the following steps (I) to (III-1): (I) A step of adding an oxidizing agent and water to the positive electrode material for a lithium ion secondary battery (A) to obtain a mixed solution i. (II) A step of adjusting the pH of the obtained mixed solution i to 4 to 9 and mixing the mixture to obtain a mixed solution ii. (III-1) A step of filtering the obtained mixed solution (ii) and obtaining a lithium-containing filtrate (iii) Then, the obtained filtrate iii is used to carry out the following steps (I)' to (III-1)': (I)' A step of adding and mixing the positive electrode material for a lithium ion secondary battery (A) and an oxidizing agent to the obtained filtrate iii to obtain a mixed solution i'. (II) 'A step of adjusting the pH of the obtained mixed solution i' to 4 to 9 to obtain mixed solution ii' (III-1) A step of filtering the resulting mixed solution (ii) to obtain a lithium-containing filtrate (iii). and obtaining a filtrate iii' as a lithium-rich liquid, or by repeating the above steps (I)' to (III-1)' multiple times by using the obtained filtrate iii' again as the filtrate iii in step (I)', a method for recovering lithium in which a filtrate iii' is finally obtained as a lithium-rich liquid.

2. 2. The method for recovering lithium according to claim 1, wherein the oxidizing agent used in step (I) and step (I)' is one or more selected from the group consisting of peroxo acid salts, permanganates, and hydrogen peroxide salts.

3. 3. The method for recovering lithium according to claim 1, wherein the temperature of the mixed solution ii or mixed solution ii' obtained in step (II) or step (II)' is 5°C to 60°C.

4. 3. The method for recovering lithium according to claim 1, wherein the oxidizing agent added in step (I) is 0.1 to 0.9 parts by mass per 1 part by mass of the positive electrode material for a lithium ion secondary battery (A).

5. 3. The method for recovering lithium according to claim 1 or 2, wherein the amount of lithium contained in the filtrate iii' as the lithium-rich solution finally obtained in the step (III-1)' is 0.7 mol to 1 mol per 1 mol of lithium constituting the positive electrode material (A) for a lithium ion secondary battery used in the step (I).

6. The following formula (A): Li ａ Mn ｂ Fe ｃ M ｘ 2O ４ ・・・(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x represent numbers that satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0, and that satisfy a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.) A method for producing a lithium adsorbent from a positive electrode material (A) for a lithium ion secondary battery represented by the following steps (I) to (III-2): (I) A step of adding an oxidizing agent and water to the positive electrode material for a lithium ion secondary battery (A) to obtain a mixed solution i. (II) A step of adjusting the pH of the obtained mixed solution i to 4 to 9 and mixing the mixture to obtain a mixed solution ii. (III-2) A step of filtering the obtained mixed liquid ii and then obtaining filter cake iii A method for producing a lithium adsorbent, comprising:

7. 7. The method for producing a lithium adsorbent according to claim 6, wherein the oxidizing agent used in the step (I) is one or more selected from the group consisting of peroxo acid salts, permanganates, and hydrogen peroxide salts.