WO2012070193A1

WO2012070193A1 - Leaching solution and metal collection method

Info

Publication number: WO2012070193A1
Application number: PCT/JP2011/006308
Authority: WO
Inventors: 泰子山田; 山口　欣秀; 岡本　正英
Original assignee: 株式会社日立製作所
Priority date: 2010-11-25
Filing date: 2011-11-11
Publication date: 2012-05-31
Also published as: US20130287654A1; JP5618913B2; JP2012126988A

Abstract

The purpose of the present invention is to provide a valuable metal collection method for collecting a metal from a lithium ion battery using a relatively simple facility without employing any complicated process. In the present invention, for achieving the purpose, lithium is selectively leached out from a positive electrode active material comprising a composite oxide of lithium and a transition metal element using a weakly acidic solution having a pH value of 4-7 in such a manner that the Li/Co selection ratio is increased and a high Li collection ratio can be achieved, and lithium is then collected from a leaching solution. With respect to the acidic solution obtained after the leaching out of lithium, any neutralization step for the acidic solution can be eliminated and the amount of the waste of the acidic solution can be reduced by using a solute which can generate a gas or the like to allow acidity of the acidic solution to disappear naturally.

Description

Exudate and metal recovery method

The present invention relates to a metal recovery technique for easily recovering metal from a lithium ion battery.

In recent years, the usage of secondary batteries has increased rapidly as electronic devices have become more portable. Rechargeable batteries are widely used not only for devices with relatively low power, such as mobile phones and portable music players, but also for devices that require high power, such as electric tools, electric bicycles, and electric vehicles, resulting in high energy density. Attention has been focused on the resulting lithium ion battery. Due to the increase in application to high-power devices, the necessity of recovering valuable materials from used batteries is increasing, and various techniques for recovering valuable metals from lithium ion batteries have been proposed.

For example, Non-Patent Document 1 features a recycling technology of a lithium ion battery, and systematically describes a method for recovering valuable metals constituting the lithium ion battery. According to a typical recycling method published in Non-Patent Document 1, for example, a used lithium ion battery is charged with all positive electrode active materials containing valuable metals by acid leaching after mechanical processing such as opening, dismantling, and grinding. Dissolve and use the difference in dissolution characteristics of each desired component to separate and collect each component by precipitation, or separate and collect the desired component by a process such as preferential solvent extraction. .

Patent Document 1 discloses a technique for recovering copper and cobalt using a diaphragm electrolysis method in which a solution in which a valuable metal obtained by acid leaching is dissolved is used as a catholyte and a cation exchange membrane is used as a diaphragm. . In this document, the liquid before the valuable metal treatment is defined as the exudate, and the liquid after the valuable metal treatment is defined as the solution.

Japanese Patent No. 3675392 Public number CN101673859A

Non-Patent Document 1 aims at improving both the recovery rate of valuable materials and increasing the purity of recovered materials by various devices, but the process is complicated and it is enormous for processing a large amount of waste batteries. There is much room for improvement in terms of capital investment.

Further, Patent Document 1 specifically uses the anion selectivity of the anion-selective membrane and the equipment (diaphragm electrolytic cell shown in FIG. 2 of Patent Document 1) using the ion-selective characteristics of the cation exchange membrane. Use the diffusion dialysis equipment (not shown). More specifically, Cu electrodeposition recovery by diaphragm electrolysis → pH adjustment → cobalt electrodeposition recovery by diaphragm electrolysis → pH adjustment → precipitation recovery of Fe (OH) 3 and Al (OH) 3 → by carbonate addition The main valuable metals can be recovered by a series of processes called Li2CO3 recovery. According to this technology, copper (divalent ions) and cobalt (trivalent ions) are electrochemically reduced and recovered, so that a high-purity metal can be obtained. However, when processing a large amount of waste batteries, There is room for improvement in that a huge amount of electricity needs to be applied.

For example, in order to recover about 100 kg of cobalt, it is necessary to continue a current of 1 ampere for about 100 hours, but before that, almost the same amount of electricity is applied even in the electrodeposition of copper. Collecting all the metal by itself alone is an unexpected process. Furthermore, since the amount of liquid increases each time multi-stage pH adjustment is performed, the concentration of lithium decreases when Li2CO3 is recovered at the final stage of a series of treatments. The rate is not necessarily high. This is because the saturated solubility of lithium carbonate is 1.3 wt% at 20 ° C., so that the unrecovered components increase as the liquid amount increases. In order to avoid this, processing such as adding a concentration step is necessary. Further, since Fe (OH) 3 and Al (OH) 3 tend to be gelled in a weakly acidic to neutral aqueous solution, Fe (OH) 3 and Al (OH) are based on the technique of Patent Document 1. ) The operation of the step of collecting 3 by filtration is not easy. On the other hand, when the liquid is diluted to facilitate the filtration operation, the lithium recovery rate is lowered. Further, since the surface of the gel-like precipitate of Fe (OH) 3 or Al (OH) 3 also has a property of adsorbing lithium ions, it is difficult to significantly improve the lithium recovery rate from this viewpoint.

The following is a brief description of an outline of typical inventions disclosed in the present application.

Lithium is selectively leached from a positive electrode active material containing lithium and a transition metal element using a weakly acidic (pH 4 to 7) exudate, and the transition metal element component that is a non-exudable solid content and the exudate To separate the lithium component. This is a waste-free process because a solution that spontaneously disappears and the solute concentration decreases is used as the acidic solution.

According to the present invention, it is possible to provide a valuable metal recovery method for easily recovering a valuable metal from a lithium ion battery with high efficiency.

It is the Li / Co ratio of the analysis result of the solution obtained by processing with the composition of the exudate and the exudate according to the example of the present invention. It is the process flow outline for collect | recovering valuable metals of the Example which concerns on this invention. It is a plot of the correlation of pH and oxidation-reduction potential according to the hydrogen peroxide concentration according to the example of the present invention. It is the Li / Co ratio of the analysis result of the solution obtained by processing with the composition of the exudate and the exudate according to the example of the present invention. It is a plot of the relationship between the exudation time and dissolved ozone concentration which concern on the Example of this invention.

Hereinafter, modes for carrying out the present invention will be described.

The outline of the valuable metal recovery method of the present embodiment will be described with reference to FIG. FIG. 2 is a schematic process flow for recovering valuable metals from the waste lithium battery (hereinafter, waste battery) of this example. First, each constituent member obtained by disassembling a waste battery (S101) is sorted for each member (S102), and only an electrode active material containing a valuable metal in a high concentration is taken out. The electrode active material thus taken out is treated with a selective lithium exudate (selective lithium exudation; S103) to obtain a lithium exuded solution. This lithium selective exudate and non-exudate are subjected to solid-liquid separation (S104). Li carbonate can be recovered as lithium carbonate Li2CO3 by mixing carbonate or carbon dioxide with the liquid A containing lithium (S105) (S106). The solid component B (S107) is recovered by the solid-liquid separation. In the case where a plurality of transition metals are contained, the solid component B is dissolved and separated by filtration by depositing and sedimenting in turn as a hydroxide by a simple operation of adjusting the pH after dissolving the solid component B (S108). Through this series of operations, valuable metals from the waste battery can be recovered.

Hereinafter, the valuable metal recovery flow will be described in more detail in accordance with the steps shown in FIG. In order to recover valuable metals from the waste battery, it is necessary to first disassemble the battery, but before the disassembly, there is a possibility that electric charge remains in the battery, and thus the battery is discharged. In this embodiment, the charge remaining in the battery is discharged by immersing the battery in a conductive liquid containing an electrolyte.

This discharge operation allows the lithium ions dispersed in the battery to be concentrated inside the positive electrode active material, thereby maximizing the amount of lithium recovered. In addition, the lithium selectivity in the leaching process is maximized by ensuring that lithium is incorporated in a specific crystal structure. When the positive electrode active material is LiCoO2, it is said that Li0.4CoO2 in the fully charged state and LiCoO2 in the fully discharged state, so there is a risk of lithium recovery loss of about 60% at maximum if the discharge treatment is omitted. Of course, there is also an advantage that the safety of the battery disassembly process and the pulverization process can be secured by discharging.

In this example, a sulfuric acid / γ-butyrolactone mixed solution was used as the conductive liquid containing the electrolyte. In this mixed solution, since sulfuric acid acts as an electrolyte, the conductivity (reciprocal of the resistance value) can be adjusted by adjusting the sulfuric acid concentration. In this example, the electrical resistance of the solution from the right end to the left end of the discharge vessel was measured and found to be 100 kΩ. If the resistance value of the solution is too small, the discharge proceeds too rapidly, which is dangerous. On the other hand, if the resistance value is too large, it takes too much time to reduce the practicality. In this embodiment, the solution resistance is preferably in the range of about 1 k to 1000 kΩ, and the electrolyte concentration may be adjusted so as to fall within this resistance value range.

Here, as the waste battery of the present embodiment, in addition to the so-called used battery whose charge capacity has been reduced due to reaching the limit of the predetermined number of times of charge and discharge, half of the battery generated due to problems in the battery manufacturing process, etc. Including old-fashioned inventory items that occur when products and product specifications change.

In S101, disassemble the waste battery after the discharge treatment. Using appropriate methods, disassemble the battery components of the waste battery after discharge, such as casing, packing / safety valves, circuit elements, spacers, current collectors, separators, and positive electrode and negative electrode active materials. Sort.

Of course, waste lithium ion batteries are often filled with gas and are in a pressurized state, and needless to say, work safety considerations are necessary. In this example, wet pulverization was performed while cooling in the state of being immersed in a conductive liquid containing the above electrolyte. By adopting wet pulverization under cooling, the gas filled in the battery could be safely crushed without being scattered in the atmosphere.

In addition, the composition of the conductive liquid containing the electrolyte is adjusted in order to promote separation of the positive electrode active material and the negative electrode active material coated and molded on the current collector surface from the current collector surfaces. Is fine. In the conductive liquid used in the discharge process, the conductivity should be noted. In the conductive liquid used in the wet grinding process, the viscosity and the dielectric constant should be noted. Since the required specifications differ between the discharge process and the wet pulverization process, the composition of the conductive liquid used for each process may be changed. In that case, it is necessary to prepare two or more kinds of conductive liquids. In this example, the same composition was used from the viewpoint of simplification and reduction of labor and cost.

The wet pulverization method that can be used in this embodiment includes, for example, a ball mill method, but is not necessarily limited thereto. Among constituent members such as housings, packing / safety valves, circuit elements, spacers, current collectors, separators, and electrode active materials, a positive electrode active material (hereinafter referred to as positive electrode active material) and a negative electrode active material (negative electrode active material) ) Is preferentially crushed and then sieved. Thereby, the positive electrode active material and the negative electrode active material are separated and recovered on the sieve under the sieve (S102).

In this example, sieving is used, but since it is originally pulverized in a wet manner, the slurry obtained by the wet pulverization is separated as it is by a filtering process using a relatively coarse filter. You can also. The recovery rate may be improved by introducing a continuous treatment from wet pulverization to filtration. The casing, packing / safety valve, current collector (aluminum foil, copper foil), etc. have a larger extensibility than the positive electrode active material (typically LiCoO2) or the negative electrode active material (typically graphite), Therefore, the breaking strength is also large. Because of this characteristic, the crushed material of the electrode active material has a smaller size than the crushed material obtained from other members, and as a result, it can be easily separated and collected by sieving or filtering.

The sieving material obtained by the above treatment is leached with a weakly acidic effluent (S103).

In this example, a used lithium-ion battery for a digital camera was disassembled. The positive electrode active material of the waste battery used in this example is a lithium compound mainly composed of LiCoO2, but may include a positive electrode active material of another composition such as iron phosphate, nickel, or manganese. The positive electrode active material was mixed with a weakly acidic leachate and stirred at room temperature for 1 hour to exude lithium. In this example, the reaction temperature and reaction time of the lithium selective leaching step are controlled, and before the positive electrode active material is completely dissolved, the leaching process is specifically stopped when the reaction rate becomes 80% or less. From a practical viewpoint, the reaction rate is most preferably about 70 to 75%. If it exceeds 80%, there is an increased risk that the selectivity in the lithium selective leaching reaction will deteriorate, and if it is less than 70%, the recovery rate will decrease and the economy will be impaired.

In this embodiment, in order to end the above exudation process, the exudate and the residue are separated (S104). As a separation method, centrifugation, filtration, or the like can be employed. In this example, the separation and recovery were performed by centrifugation at room temperature and 15000 rpm for 15 minutes. However, the higher the number of revolutions, the easier the separation of the exudate and the residue.

The Li / Co molar ratio of the obtained solution is shown in FIG. As shown in FIG. 1, the Li / Co molar ratio of the solution before dialysis when the positive electrode active material is completely leached using a strongly acidic exudate using the method described in Non-Patent Document 1. Was about 1. When exuded under a strongly acidic condition of pH ≦ 1, the Li / Co molar ratio is approximately 1.0. This is because the entire composition of lithium cobaltate is dissolved, and even if the dissolution is stopped halfway, the Li / Co molar ratio hardly changes. In contrast, in this example, when a weakly acidic exudate with 4 ≦ pH ≦ 7 is used, the Li / Co molar ratio is improved to 4 or more. This is because Li preferentially dissolves over Co (the detailed reaction mechanism is unknown). The weakly acidic exudate may be a buffer solution obtained by adding a substance having a buffering action to pure water. The Li / Co molar ratio in the case of a phthalic acid buffer solution (mixture of phthalic acid and potassium phthalate) prepared at pH = 4 is 4. In addition, when a redox potential adjusting agent is added to the weakly acidic solution, the Li / Co selection ratio is further increased. When a treatment liquid prepared by adjusting the hydrogen peroxide solution to a weakly acidic pH = 4 is used as the exudate, the Li / Co molar ratio is greatly improved to 335. Similarly, when carbon dioxide is added to ozone water, the Li / Co molar ratio is as high as 121.

For the lithium selective exudate of this example, an aqueous solution in which ozone, hydrogen peroxide, peracetic acid or the like is dissolved can be used. These solutes act as oxidants. In general, when recovering valuable metals from batteries, lithium cobaltate is completely dissolved using a high concentration of mineral acid to exude lithium cobaltate. In this example, high concentration mineral acid is not used, and the upper limit of the leaching temperature is 30 ° C. If it greatly exceeds 30 ° C., natural decomposition of ozone and hydrogen peroxide is accelerated, and a solute that does not contribute to the dissolution of the positive electrode active material is generated, so that the solute is wasted.

When an exudate having a pH of 4 to 7 and a redox potential of 0.3 to 0.4 volts is used, a high Li / Co molar ratio tends to be obtained. When the pH value is smaller than pH = 4, the dissolution rate of the positive electrode active material is increased, and the dissolution rate of Li is increased and the recovery rate is likely to be increased, but the dissolution rate of Co is also increased. The Li / Co molar ratio tends to decrease. In the range of the hydrogen peroxide concentration of the present embodiment shown in FIG. 3, cobalt exudation begins to increase when the hydrogen peroxide concentration is higher than 15%. The Li / Co molar ratio was high in the region where the hydrogen peroxide concentration was lower than 20%. In this example, the oxidation-reduction potential was 0.3 volts when the hydrogen peroxide solution concentration was 15%, and the oxidation-reduction potential was 0.4 volts when the hydrogen peroxide solution concentration was 20%. It was found that a high Li / Co molar ratio can be obtained in the range of 0.3 to 0.4 volts.

In the recovery liquid (A) obtained by the above selective leaching, lithium is selectively leached, and the solute (specifically hydrogen peroxide and ozone) used in the exudate spontaneously disappears. Natural extinction means that the concentration of a specific active ingredient is about half or less of the initial concentration without adding chemicals to promote neutralization and decomposition. For example, hydrogen peroxide spontaneously decomposes into water and oxygen molecules, and ozone naturally decomposes into oxygen molecules. Most of the generated oxygen molecules are discharged out of the solution. Carbon dioxide is vaporized and discharged out of the solution. Accordingly, since the solution becomes neutral due to spontaneous disappearance, the neutralization treatment performed after the conventional acid leaching is not required (S105).

In the subsequent operation, in the method proposed in Non-Patent Document 1, since the valuable metal solution obtained after the leaching treatment is a high-concentration solution of strong acid, a large amount of alkali is recovered prior to recovering lithium as lithium carbonate. So-called pH adjustment to mix the inevitably becomes inevitable. However, the ozone water and the hydrogen peroxide solution used in this example are naturally extinguisher solutions, and the liquidity of the recovered liquid (A) after the lithium cobaltate exudation treatment is weakly alkaline with a pH of 9 to 11. If the recovered liquid (A) thus obtained is treated as it is, such as mixing with an alkali metal-free carbonate such as calcium carbonate or carbon dioxide gas without neutralization such as pH adjustment, the alkali-free The precipitate can be recovered as lithium carbonate (S106).

Not only is neutralization not necessary, but ozone, hydrogen peroxide, carbon dioxide, etc. will naturally disappear, so the remaining liquid after lithium recovery will be water, so it can be used again for hydrogen peroxide water and ozone water. As a result, a waste-free metal recovery method can be constructed.

The transition metal component is recovered from the residue (B) obtained in the Li / transition metal separation in S104 (S107). In this example, since the positive electrode active material mainly composed of lithium cobaltate was treated, the residue (B) obtained by the treatment so far contains a small amount of unexuded lithium and cobalt. In order to separate and collect these by metal type, such as when separating them with high purity or when containing transition metals other than cobalt, after dissolving this residue (B), Separation and recovery can be carried out for each type of transition metal element by treatment using the difference in solubility characteristics of hydroxide, basically pH adjustment → precipitation recovery (S108). When the positive electrode active material contains a lithium compound other than LiCoO2, for example, in the case of an olivine-based positive electrode active material such as LiNiO2, LiMnO2, Li (Ni1 / 3Co1 / 3Mn1 / 3) O2, LiCoPO4, LiFePO4, LiCoPO4F, LiFePO4F, etc. By adjusting the pH of the liquid, Co, Ni, Mn, and Fe can be separated as hydroxides and recovered by precipitation.

The outline of the valuable metal recovery method of this example will be described. The valuable metal recovery method of this example is basically the same as that of Example 1. In the present embodiment, the difference from the first embodiment is that, in the leaching process in S103 of FIG. 2, an oxidant that spontaneously disappears and a buffer solution that suppresses the rate at which the oxidant spontaneously disappears are used as the weakly acidic exudate. Is a point. This makes it possible to achieve both a high Li / Co molar ratio and a high Li recovery rate in the lithium leaching reaction.

The exudate of this example is, for example, an acetic acid buffer solution (0.1 M, pH 4.7) or a phthalate buffer as a buffer solution composed of ozone water having a dissolved ozone concentration of 150 ppm as an oxidizing agent that spontaneously disappears, carboxylic acid, and salts thereof. A mixed solution (0.1 M, pH 4.0) can be used, but the type of oxidizing agent, the type of carboxylic acid, and the concentration thereof are not limited thereto. A positive electrode active material is added to the mixed solution of ozone water and a buffer solution, and the mixture is stirred for about 20 minutes to exude lithium (S103).

In this embodiment, in order to end the above exudation process, the exudate and the residue are separated (S104). As a separation method, centrifugation, filtration, and the like can be adopted. For example, in centrifugation, separation and recovery can be performed by treating at 10,000 rpm for 30 seconds at room temperature.

The recovered liquid (A) obtained by the above selective leaching is obtained as a lithium concentrate (S105), and the oxidizing agent (ozone) used in the leaching liquid is naturally extinguished. The Li / Co molar ratio of the recovered liquid (A) obtained in this example was 4243 in the case of the acetate buffer solution, and a high Li / Co molar ratio was obtained as in Example 1. Furthermore, as shown in FIG. 4, the lithium recovery rate is 18% when only ozone water is used as the exudate, whereas it is 28% when ozone water and a phthalate buffer solution are used. In addition, when a mixture of ozone water and an acetate buffer solution was used, a high value of 98% was obtained. Thus, by using ozone water and a buffer solution, a lithium recovery method with a high lithium recovery rate and a high Li / Co molar ratio could be established.

In the recovery of lithium, it is desirable that both the lithium recovery rate and the Li / Co molar ratio in the recovered components are higher, and the former is preferably close to 100%. The reason why the high lithium recovery rate can be realized by the oxidant and the buffer solution that disappear spontaneously will be described in detail below.

Phthalic acid is dissociated in aqueous solution according to the following

chemical formulas

1 and 2. The acid dissociation index (logarithm of the reciprocal of the dissociation constant) pKa of Chemical Formula 1 is 2.94, and the pKa of Chemical Formula 2 is 5.41. In the preferred pH range of 4 <pH <7 described in Example 1, the equilibrium of chemical formula 1 is almost completely biased to the right side, and chemical formula 2 is biased to the left side or to the right side depending on the pH. Alternatively, there are significant amounts of components on both sides. When a phthalate buffer solution is used, this pH-dependent equilibrium reaction keeps the pH within a suitable range and suppresses the decomposition of ozone, improving the lithium recovery rate from 18% to 28%. did.

(Chemical formula 1) C6H4 (COOH) 2 ⇔ C6H4 (COOH) COO ⁻ + H ⁺
(Chemical Formula 2) C6H4 (COOH) COO ⁻ ⇔ C6H4 (COO ⁻ ) 2 + H ⁺
Here, when an acetate buffer solution is used as the buffer solution, the lithium recovery rate is dramatically improved. The reason is described below.

In the preferable pH range, phthalic acid has many dissociated components. When phthalic acid is dissociated into C6H4 (COOH) COO 2 ⁻ , the electron density on the carboxyl group increases. Since the carboxy ion is an electron donating group, the electron density of the aromatic ring is increased as a result. In addition, since phthalic acid has an aromatic ring which is a weak electron-withdrawing group in the molecular structure, it tends to increase the electron density. When the electron density on the aromatic ring is high, electrons are easily taken away by the oxidizing agent. For this reason, when dissociated phthalate ions coexist with ozone as an oxidizing agent, ozone may oxidize part of the phthalate ions. At this time, ozone obtained by oxidizing phthalic acid is consumed without reacting with LiCoO2. In addition, oxidized phthalic acid becomes a neutral radical, but since this radical cannot contribute to the reaction of Chemical Formula 1 and Chemical Formula 2, the effective ion concentration constituting the buffer solution decreases, and the solution The buffering action is reduced. When the leaching reaction of LiCoO2 proceeds in a state where the buffering action is lowered, OH- is generated and the liquidity of the reaction solution is shifted to the alkali side. Since the reaction solution becomes alkaline, a part of ozone is decomposed without reacting with LiCoO2.

As a result of the above, the leaching reaction of LiCoO2 does not proceed. An example of a buffer solution that provides the same effect is benzoic acid.

On the other hand, since acetic acid has no site in the molecular structure where electron density such as an aromatic ring can be locally increased in comparison with phthalic acid, electrons are not easily taken away by the oxidizing agent. Acetic acid is more difficult to oxidize even if coexists. That is, since acetic acid is hardly decomposed, the buffering action in the reaction solution can be maintained for a long time.

In addition, since the acetate buffer solution can maintain the buffering action in the reaction solution, even if a dissolution reaction of the positive electrode active material occurs, the liquidity of the reaction solution does not become alkaline. Natural extinction can be suppressed, and as a result, ozone is effectively used for the leaching reaction of LiCoO 2 and a high lithium recovery rate can be realized.

Actually, the result of measuring the change in the dissolved ozone concentration during the leaching reaction of LiCoO 2 is shown in FIG. From FIG. 5, when the positive electrode active material is dissolved only with ozone water, the dissolved ozone concentration rapidly decreases in the first few minutes, and when the leaching time is 10 minutes, the dissolved ozone concentration decreases to about 5 ppm. On the other hand, when the acetic acid buffer solution is added to the ozone water, the dissolved ozone concentration at the same time is 50 ppm, which indicates that the decrease in the dissolved ozone concentration is suppressed. That is, when the positive electrode active material is leached, the concentration can be maintained by suppressing the decrease in the dissolved ozone concentration by adding an acetic acid buffer solution to the ozone water. And it is possible to perform the leaching reaction of lithium from a positive electrode active material efficiently by maintaining the dissolved ozone concentration high over a long period of time.

As is apparent from the above discussion, it is understood that the action of acetic acid is not limited to acetic acid, and any carboxylic acid having a carboxyl group that does not contain an aromatic ring may be used.

In this example, the results with an acetic acid buffer solution were shown. However, as a result of investigations by the inventors, aliphatic monocarboxylic acids such as propionic acid, butanoic acid and pentanoic acid can be used. If the number of carbon atoms constituting the carbon chain is larger than this, the solubility in water will be low, which is not suitable for practical use. The buffer concentration is generally about 0.1 mol / L, and is preferably at least 0.001 mol / L. The solubility of the substance having a small carbon number (value at 20 ° C .; the solute mass soluble in 100 g of water and the molar concentration at that time) is 37 g / 100 g water (0.005 mol / L) for propionic acid and 0.005 mol / L for butanoic acid, respectively. 5.6 g / 100 g water (0.032 mol / L) and pentanoic acid are 2.4 g / 100 g water (0.075 mol / L). The oxidative decomposition rate of the aliphatic monocarboxylic acid is butanoic acid> propionic acid> acetic acid. The smaller the number of hydrocarbons, the lower the oxidative decomposition rate, and both high Li / transition metal separation and high lithium recovery are achieved. The smaller the carbon number, the better. However, it is not suitable when the number of carbon atoms other than the carboxyl group is 0. For example, formic acid has an aldehyde group. Since the aldehyde group is oxidized by the oxidizing agent, the oxidizing agent is consumed in the oxidation reaction of the buffer solution, which is not suitable. Oxalic acid is not suitable because it has a low pKa of 1.25 and is classified as a strong acid. As for the aliphatic polyvalent carboxylic acid, oxalic acid, succinic acid, tartaric acid, citric acid, malic acid, and malonic acid can be used in consideration of pKa and solubility. Moreover, general glycine can also be used as a buffer solution.

From the above, a preferable buffer solution is preferably a buffer solution made of a substance having a carbon number of 1 to 4 (excluding carboxyl group carbon) and an acid dissociation index of 4 <pH <7 from the viewpoint of solubility.

If the above buffer solution is used, it is possible to achieve both high Li / transition metal separation and high Li recovery rate.

Note that Patent Document 2 discloses a method for recovering lithium and cobalt using an organic acid such as citric acid, succinic acid, malic acid or the like as an exudate of the positive electrode active material. However, since no buffer solution is used, the pH is low. For example, the pH of a solution having a concentration of 1.25 mol / L of citric acid described in Example 1 of Patent Document 2 is 1 or less. For this reason, all LiCoO2 dissolves, and the recovered lithium and cobalt are of low purity, and a separation operation is required to recover only lithium. On the other hand, in the present example, as a result of examination by the inventors, the exudate is suitable for weak acidity, and by exuding with weak acidity, only lithium is selectively exuded from the positive electrode active material, and the exudation residue By leaving only cobalt therein, the resulting metal can be highly purified.

As the buffer solution, other buffer solutions can be used as long as they are not only carboxylic acids but also buffer solutions exhibiting acidity (4 <pH <7). As a buffer solution other than carboxylic acid, for example, a buffer solution of phosphoric acid and its salt can be used. For example, there is a buffer solution composed of sodium dihydrogen phosphate and disodium hydrogen phosphate. However, the composition is not limited to this salt, and other compositions can be used. In this case, if phosphorus is recovered after recovering Li from the acidic solution in which Li is selectively dissolved, phosphorus can be reused as the solute of the buffer solution. As a method for separating and recovering phosphorus, there are separation operations such as dialysis membrane separation, acid retardation and ion exchange resin.

In this embodiment, ozone is used as an oxidant that spontaneously disappears, but hydrogen peroxide can be used instead.

In this example, LiCoO2 was used as the positive electrode active material. However, when a lithium compound other than LiCoO2 is contained, for example, olivine-based positive electrode actives such as LiNiO2, LiMnO2, Li (NiCoMn) O2, LiCoPO4, LiFePO4, LiCoPO4F, and LiFePO4F are used. Even in the case of substances, precipitation can be recovered by separating Co, Ni, Mn, and Fe as hydroxides by adjusting the pH of the liquid. The transition metal recovery operation is performed in the same manner as S107 and S108 in the first embodiment, and the method is the same as in the first embodiment.

As described above, a metal that achieves both high Li / transition metal separation and high lithium recovery rate by using a combination of a buffer solution having a selective leaching effect of lithium by suppressing the rate at which the oxidant and the oxidant spontaneously disappear. A recovery method could be provided.

Claims

In a metal recovery method for recovering a metal from a positive electrode active material of a lithium ion battery containing lithium and a transition metal element,
Leaching the valuable metal contained in the positive electrode active material into an acidic solution;
Recovering lithium from the acidic solution from which the valuable metal has leached,
The acid recovery method according to claim 1, wherein the acidic solution has a pH of 4 to 7.
In claim 1,
The said acid solution has a redox potential regulator, The metal recovery method characterized by the above-mentioned.
In claim 2,
The acid solution further comprises a pH adjuster, and the metal recovery method.
In claim 2 or claim 3,
The metal recovery method, wherein the redox potential regulator is hydrogen peroxide.
In claim 2 or claim 3,
The metal recovery method, wherein the redox potential regulator is ozone.
In claim 3,
The metal recovery method, wherein the pH adjuster is carbon dioxide.
In any one of Claims 1 thru | or 6.
Any one of the solute of the acidic solution, the oxidation-reduction potential adjusting agent, or the pH adjusting agent is a substance that spontaneously disappears from the solution.
In a metal exudate that exudes metal from the positive electrode active material of a lithium ion battery containing lithium and a transition metal element,
A metal exudate having a pH of 4 to 7 and a solute that spontaneously disappears.
In a metal recovery method for recovering a metal from a positive electrode active material of a lithium ion battery containing lithium and a transition metal element,
Leaching lithium contained in the positive electrode active material into an acidic solution containing an oxidant and a buffer solution that spontaneously disappear;
A step of recovering lithium from the acidic solution from which the lithium has exuded.
In claim 9,
The said buffer solution contains carboxylic acid and its salt as a solute, The metal recovery method characterized by the above-mentioned.
In claim 10,
The metal recovery method, wherein the carboxylic acid is an aliphatic carboxylic acid having a carboxyl group not containing an aromatic ring.
In claim 11,
The metal recovery method, wherein the carboxylic acid has 1 to 4 carbon atoms (excluding carboxyl groups).
In claim 10,
The metal recovery method, wherein the carboxylic acid is an organic acid or glycine.
In claim 9,
The said buffer solution contains phosphoric acid and its salt as a solute, The metal recovery method characterized by the above-mentioned.
In any of claims 9 to 14,
The metal recovery method according to claim 1, wherein the oxidant that spontaneously disappears is ozone or hydrogen peroxide solution.
In any of claims 9 to 15,
The acidic solution in the leaching step has a pH of 4 to 7, wherein the metal is recovered.
In a metal exudate that exudes metal from the positive electrode active material of a lithium ion battery containing lithium and a transition metal element,
A metal exudate having an oxidizing agent that spontaneously disappears and a buffer solution, and having a pH of 4 to 7.