WO2025094831A1 - Method for recovering valuable substance - Google Patents

Abstract

The present invention provides a method for recovering a valuable substance, which is capable of reducing a lithium-containing transition metal compound at a heating temperature that is lower than ever before. This method for recovering a valuable substance is characterized by having: a reduction step in which a lithium-containing transition metal compound that is in contact with a formic acid solution is heated to reduce the lithium-containing transition metal compound; a water washing step in which a slurry that is obtained by mixing water and a reduction product obtained by reducing the lithium-containing transition metal compound is stirred; and a recovery step in which the slurry after the water washing step is subjected to solid-liquid separation to recover a valuable substance.

Description

How to collect valuable materials

This disclosure relates to a method for recovering valuable materials.

Lithium-ion batteries use lithium cobalt oxide, lithium cobalt nickel oxide, lithium cobalt nickel manganese oxide, etc. as their positive electrode materials, which contain valuable materials such as lithium, cobalt, nickel, and manganese. Therefore, it is desirable to recover valuable materials from the positive electrode materials removed from used lithium-ion batteries, for example.

For example, Patent Document 1 discloses a method of recovering valuable materials by carbonizing recycled raw materials that contain lithium-containing transition metal compounds. Also, for example, Patent Document 2 discloses a method of recovering valuable materials by reducing lithium-containing transition metal compounds with hydrogen.

JP 2022-164399 A JP 2021-521580 A

However, conventional technologies have a problem in that the heating temperatures during carbonization and hydrogen reduction are high. The heating temperatures for carbonization are 900°C to 1000°C, and for hydrogen reduction are 400°C to 700°C. If reduction must be carried out at high temperatures, it will consume a lot of energy and emit excess carbon dioxide, resulting in an undesirable carbon footprint (CFP).

The present disclosure therefore aims to provide a method for recovering valuable materials that enables reduction treatment of lithium-containing transition metal compounds at a lower heating temperature than conventional methods.

The method for recovering valuable materials according to one embodiment of the present disclosure is characterized by having a reduction step in which a lithium-containing transition metal compound that has been in contact with a formic acid solution is heated to reduce the lithium-containing transition metal compound, a water-washing step in which a slurry is obtained by mixing a reduction-treated product obtained by reducing the lithium-containing transition metal compound with water and stirring the resulting slurry, and a recovery step in which the slurry after the water-washing step is subjected to solid-liquid separation to recover valuable materials.

According to one aspect of the present disclosure, a method for recovering valuables can be provided that enables reduction treatment of lithium-containing transition metal compounds at a lower heating temperature than conventional methods.

1 shows a scanning electron microscope (SEM) photograph of the lithium-containing transition metal oxide used in Example 1. 1 shows a scanning electron microscope (SEM) photograph of the reduction treatment product of the lithium-containing transition metal oxide obtained in Example 1.

The method for recovering valuable materials according to this embodiment includes a reduction step in which the lithium-containing transition metal compound that has been in contact with a formic acid solution is heated to reduce the lithium-containing transition metal compound, a water-washing step in which a slurry is obtained by mixing the reduction product obtained by reducing the lithium-containing transition metal compound with water and stirring the resulting slurry, and a recovery step in which the slurry after the water-washing step is subjected to solid-liquid separation to recover valuable materials. Each of the above steps will be described in detail below.

(Reduction process)
The lithium-containing transition metal compound may be of any origin, and may be, for example, a positive electrode active material obtained from a used lithium ion secondary battery. The lithium-containing transition metal compound is, for example, an oxide containing transition metals such as nickel, cobalt, manganese, and lithium. The method of extracting the lithium-containing transition metal compound, which is a positive electrode active material, from the lithium ion secondary battery is not particularly limited, but for example, the lithium ion secondary battery is disassembled to remove the positive electrode, and the positive electrode is crushed or treated with a solvent to extract a raw material containing the lithium-containing transition metal compound from the positive electrode. The raw material containing the lithium-containing transition metal compound may be used in the reduction step, or the lithium-containing transition metal compound from which impurities (e.g., conductive material and binder) contained in the raw material have been separated and removed may be used in the reduction step.

Methods for contacting the lithium-containing transition metal compound with the formic acid solution include, for example, immersing the lithium-containing transition metal compound in the formic acid solution, applying the formic acid solution to the lithium-containing transition metal compound, and spraying the formic acid solution onto the lithium-containing transition metal compound. In the case of spraying the formic acid solution, it is preferable to spray the formic acid solution in the form of a mist of fine droplets with a diameter of 1 μm to 10 μm onto the lithium-containing transition metal compound, in order to increase the contact efficiency.

The formic acid concentration in the formic acid solution used is preferably 0.03 mol% or more, and more preferably 0.1 mol% or more, in order to increase the reduction efficiency of the lithium-containing transition metal compound. The upper limit of the formic acid concentration may be, for example, 5 mol% or less.

The lithium-containing transition metal compound in contact with the formic acid solution is heated using a heating furnace such as an electric furnace, rotary kiln, tubular furnace, or pusher furnace. Of these, a rotary kiln is preferable because the lithium-containing transition metal compound placed in the heating furnace can be reduced relatively uniformly. After the lithium-containing transition metal compound is placed in the heating furnace, it may be heated while supplying the formic acid solution, i.e., while contacting the lithium-containing transition metal compound with the formic acid solution, or the supply of the formic acid solution may be stopped and then the lithium-containing transition metal compound may be heated. The lithium-containing transition metal compound in contact with the formic acid solution may also be placed in a heating furnace and the lithium-containing transition metal compound heated.

The reduction step is preferably carried out in an inert gas atmosphere or a reduced pressure atmosphere in order to increase the reduction efficiency of the lithium-containing transition metal compound. The inert gas atmosphere is, for example, a nitrogen gas atmosphere or a rare gas atmosphere, with a nitrogen gas atmosphere being preferred. The oxygen concentration in the inert gas atmosphere or reduced pressure atmosphere is preferably 2% or less. The reduction step may also be carried out in an air atmosphere.

In the heating step of the reduction process, it is preferable that the maximum temperature reached is 130°C or higher and 300°C or lower, and the holding time at the maximum temperature is 3 minutes or longer, and it is even more preferable that the maximum temperature reached is 180°C or higher and 280°C or lower, and the holding time at the maximum temperature is 3 minutes or longer and 15 minutes or shorter.

By using formic acid as a reducing agent, it becomes possible to reduce a lithium-containing transition metal compound at a lower heating temperature than in the past. The reduction product obtained by reducing a lithium-containing transition metal compound contains a lithium compound and a transition metal compound. An example of the reduction reaction between a lithium-containing transition metal compound and formic acid is shown below. In the following, lithium nickel oxide is used as an example of the lithium-containing transition metal compound.
2LiNiO ₂ +2HCOOH → 2NiO+Li ₂ O+2H ₂ O+2CO ₂

(Water washing process)
The water washing step is carried out, for example, by putting the reduction product obtained by reducing the lithium-containing transition metal compound and water into a reaction tank equipped with a stirrer, and stirring the mixture (slurry). The time of the water washing step is, for example, 5 minutes to 1 hour. In the water washing step, for example, it is preferable to heat the slurry to 80° C. or higher, and more preferably to heat it to 80° C. or higher and 90° C. or lower. In addition, in the water washing step, it is preferable to stir the slurry at a stirring speed of 200 rpm or higher, and more preferably to stir it at 200 rpm or higher and 350 rpm or lower. In addition, in the water washing step, it is preferable to set the solid content concentration of the slurry to 500 g/L or higher, and more preferably to set it to 500 g/L or higher and 2000 g/L or lower. There is no particular limitation on the water used, but for example, ion-exchanged water, pure water, ultrapure water, etc. are preferable.

By the water washing step, the lithium compound in the reduction product is dissolved in the water in the slurry, and the transition metal compound in the reduction product remains as a solid content. For example, in the reduction product obtained by the above-mentioned reduction reaction formula, _Li2O is dissolved in the water in the slurry, and NiO remains as a solid content in the slurry.

(Recovery process)
In the recovery step, the slurry after the water washing step is subjected to solid-liquid separation to obtain a solid and a leachate. The leachate contains a lithium compound, and the solid contains a transition metal compound. The method of solid-liquid separation is not particularly limited, and for example, a suction filter, a centrifuge, a filter press, or the like is used. The lithium compound dissolved in the leachate may be recovered by precipitating it as a lithium salt, for example, by a crystallization process. In any case, the lithium compound and the transition metal compound can be separated and recovered as valuable materials.

The water washing step and the recovery step may be repeated multiple times. For example, the solid material obtained in the recovery step is subjected to the water washing step, and then the recovery step is performed on the slurry obtained in the water washing step. By performing the water washing step and the recovery step multiple times, the lithium compounds remaining in the solid material obtained in the recovery step can be recovered in the leachate, which may improve the recovery rate of the lithium compounds (in other words, improve the purity of the transition metal compounds in the solid material).

The present disclosure will be further explained below with reference to examples, but the present disclosure is not limited to the following examples.

Example 1
A rotary kiln having a rotating cylinder equipped with a heating function was used to reduce a lithium-containing transition metal oxide (composition formula: LiNi _0.90 Co _0.05 Mn _0.05 O ₂ ). Specifically, the reduction treatment was performed as follows. 10 g of lithium-containing transition metal oxide was charged from an inlet at one end of the rotating cylinder. Then, while rotating the rotating cylinder, nitrogen gas was supplied into the rotating cylinder to create a nitrogen gas atmosphere (oxygen concentration in the cylinder: 1.1%), and a formic acid solution having a formic acid concentration of 0.05 mol% was supplied at 55.5 mL/min. Then, while supplying nitrogen gas and formic acid solution, the inside of the rotating cylinder was heated at a temperature of 220° C. for 4 minutes, and then the reduced product of the lithium-containing transition metal oxide was taken out from an outlet at the other end of the rotating cylinder. FIG. 1 shows a scanning electron microscope (SEM) photograph of the lithium-containing transition metal oxide used in Example 1. FIG. 2 shows a scanning electron microscope (SEM) photograph of the reduction treatment product of the lithium-containing transition metal oxide obtained in Example 1.

Water was added to the reduction treatment product to prepare a slurry with a solid concentration of 10 g/L, and the slurry was stirred for 10 minutes. The slurry was filtered to separate a filtrate (leachate) and a solid. The amount of Li in the filtrate was measured by ICP emission spectrometry, and the lithium recovery rate was calculated by the following formula. As a result, the lithium recovery rate was 82%.
Lithium recovery rate=Li amount in filtrate/Li amount in lithium-containing transition metal oxide×100

Example 2
The same treatment as in Example 1 was carried out, except that the heating temperature inside the rotating cylinder was set to 150° C. The lithium recovery rate was 72%.

Example 3
The same treatment as in Example 1 was carried out, except that the heating temperature inside the rotating cylinder was set to 260° C. The lithium recovery rate was 86%.

Example 4
Except for changing the heating time in the rotating cylinder to 3 minutes, the same treatment as in Example 1 was carried out. The lithium recovery rate was 84%.

Comparative Example
The same treatment as in Example 1 was carried out, except that the nitrogen gas and the formic acid solution were not supplied into the rotating cylinder, and heating was carried out in an air atmosphere with an oxygen concentration of 20.8%. The lithium recovery rate was 5%.

Table 1 shows the reduction treatment conditions and the lithium recovery rate results.

In Examples 1 to 4, the heating temperature during reduction was 260°C or less, but it was still possible to reduce the lithium-containing transition metal oxide and recover the valuable lithium. The heating temperature in the Examples is lower than the heating temperatures used in conventional carbonization and hydrogen reduction processes. Therefore, it can be said that by using a formic acid solution as in the Examples, it was possible to reduce the lithium-containing transition metal compound at a lower heating temperature than in the past.

[Additional Notes]
(1)
a reduction step of heating the lithium-containing transition metal compound that has been contacted with a formic acid solution to reduce the lithium-containing transition metal compound;
a water washing step of mixing a reduction-treated product obtained by reducing the lithium-containing transition metal compound with water and stirring the resulting slurry;
and a recovery step of recovering valuable materials by solid-liquid separation of the slurry after the water-washing step.
(2)
The method for recovering valuable materials according to (1) above, wherein the formic acid concentration in the formic acid solution is 0.03 mol % or more.
(3)
The method for recovering valuable materials according to (1) or (2) above, wherein the heating in the reduction step is performed with a maximum temperature of 130° C. or higher and 300° C. or lower, and a holding time at the maximum temperature is 3 minutes or longer.
(4)
The method for recovering valuable materials according to any one of (1) to (3) above, wherein the reduction step is carried out under a nitrogen gas atmosphere.
(5)
The method for recovering valuable materials according to any one of (1) to (4), wherein the reduction step is carried out in an atmosphere having an oxygen concentration of 2% or less.
(6)
The method for recovering valuable materials according to any one of (1) to (5), wherein in the water washing step, the slurry is stirred at a temperature of 80° C. or higher and at a stirring speed of 200 rpm or higher.

Claims (6)

a reduction step of heating the lithium-containing transition metal compound that has been contacted with a formic acid solution to reduce the lithium-containing transition metal compound;
a water washing step of mixing a reduction-treated product obtained by reducing the lithium-containing transition metal compound with water and stirring the resulting slurry;
and a recovery step of recovering valuable materials by solid-liquid separation of the slurry after the water-washing step. The method for recovering valuable materials according to claim 1, wherein the formic acid concentration in the formic acid solution is 0.03 mol% or more. The method for recovering valuable materials according to claim 1 or 2, wherein the heating in the reduction step is performed with a maximum temperature of 130°C or higher and 300°C or lower, and the holding time at the maximum temperature is 3 minutes or longer. The method for recovering valuable materials according to claim 1 or 2, wherein the reduction step is carried out under a nitrogen gas atmosphere. The method for recovering valuable materials according to claim 1 or 2, wherein the reduction step is carried out in an atmosphere with an oxygen concentration of 2% or less. The method for recovering valuable materials according to claim 1 or 2, wherein in the water washing step, the slurry is stirred at a temperature of 80°C or higher and at a stirring speed of 200 rpm or higher.

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