Method for recovering valuable substance

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 valuables

[0001] The present disclosure relates to a method for recovering valuable materials.

[0002] Lithium-ion battery positive electrode materials include lithium cobalt oxide, lithium cobalt nickel oxide, and lithium cobalt nickel manganese oxide, which contain valuable materials such as lithium, cobalt, nickel, and manganese. Therefore, it is desirable to recover valuable materials from positive electrode materials removed from used lithium-ion batteries, for example.

[0003] For example, Patent Document 1 discloses a method for recovering valuable materials by carbonizing a recycled raw material containing a lithium-containing transition metal compound. Also, for example, Patent Document 2 discloses a method for recovering valuable materials by hydrogen reduction of a lithium-containing transition metal compound.

[0004] JP 2022-164399 A JP 2021-521580 A

[0005] However, conventional techniques 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 the heating temperatures for hydrogen reduction are 400°C to 700°C. The high temperature reduction temperatures result in high energy consumption and excessive carbon dioxide emissions, resulting in an undesirable carbon footprint (CFP).

[0006] Therefore, an object of the present disclosure is to provide a method for recovering valuable materials that enables reduction treatment of a lithium-containing transition metal compound at a heating temperature lower than conventional methods.

[0007] A method for recovering valuable materials according to one embodiment of the present disclosure is characterized by comprising: a reduction step of heating a lithium-containing transition metal compound that has been brought into contact 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 to obtain a slurry; and a recovery step of performing solid-liquid separation of the slurry after the water-washing step to recover valuable materials.

[0008] According to one aspect of the present disclosure, it is possible to provide a method for recovering valuable materials that enables reduction treatment of a lithium-containing transition metal compound at a heating temperature that is lower than conventional methods.

[0009] 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-treated product of the lithium-containing transition metal oxide obtained in Example 1.

[0010] The method for recovering valuable materials according to this embodiment includes a reduction step of heating a lithium-containing transition metal compound that has been brought into contact 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 to obtain a slurry, and a recovery step of performing solid-liquid separation of the slurry after the water-washing step to recover valuable materials. Each of the above steps will be described in detail below.

[0011] (Reduction Step) The lithium-containing transition metal compound may be of any origin, and examples thereof include 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 a transition metal such as nickel, cobalt, or manganese, and lithium. The method for extracting the lithium-containing transition metal compound serving as the positive electrode active material from a lithium-ion secondary battery is not particularly limited. For example, the lithium-ion secondary battery is disassembled, the positive electrode is removed, and the positive electrode is pulverized or treated with a solvent to extract a raw material containing the lithium-containing transition metal compound from the positive electrode. This raw material containing the lithium-containing transition metal compound may be used in the reduction step, or a lithium-containing transition metal compound from which impurities (e.g., conductive materials and binders) contained in the raw material have been separated and removed may be used in the reduction step.

[0012] Examples of methods for contacting a lithium-containing transition metal compound with a formic acid solution include a method of immersing a lithium-containing transition metal compound in a formic acid solution, a method of applying a formic acid solution to a lithium-containing transition metal compound, a method of spraying a formic acid solution onto a lithium-containing transition metal compound, etc. In the case of the method of spraying a formic acid solution, for example, in terms of increasing contact efficiency, it is preferable to spray the formic acid solution in the form of a mist of fine particle droplets having a diameter of 1 μm to 10 μm onto the lithium-containing transition metal compound.

[0013] The formic acid concentration in the formic acid solution used is preferably 0.03 mol% or more, more preferably 0.1 mol% or more, from the viewpoint of increasing 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.

[0014] The lithium-containing transition metal compound in contact with the formic acid solution is heated using a heating furnace such as an electric furnace, a rotary kiln, a tubular furnace, or a pusher furnace. Among these, a rotary kiln is preferred because it can relatively uniformly reduce the lithium-containing transition metal compound charged into the heating furnace. After charging the lithium-containing transition metal compound into the heating furnace, the compound 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 before heating the lithium-containing transition metal compound. Alternatively, the lithium-containing transition metal compound in contact with the formic acid solution may be charged into the heating furnace and heated.

[0015] The reduction step is preferably carried out under 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, and a nitrogen gas atmosphere is preferred. The oxygen concentration in the inert gas atmosphere or the reduced pressure atmosphere is preferably 2% or less. The reduction step may also be carried out under an air atmosphere.

[0016] In the heating in the reduction step, it is preferable that the maximum temperature be 130°C or higher and 300°C or lower, and that the holding time at the maximum temperature be 3 minutes or longer, and it is more preferable that the maximum temperature be 180°C or higher and 280°C or lower, and that the holding time at the maximum temperature be 3 minutes or higher and 15 minutes or shorter.

[0017] 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 conventional methods. 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

[0018] (Water-Washing Step) The water-washing step is carried out, for example, by adding a reduction-treated product obtained by reducing a lithium-containing transition metal compound and water to a reaction tank equipped with a stirrer, and stirring the mixture (slurry). The time for the water-washing step is, for example, 5 minutes to 1 hour. In the water-washing step, for example, the slurry is preferably heated to 80°C or higher, more preferably 80°C to 90°C. Furthermore, in the water-washing step, the slurry is preferably stirred at a stirring speed of 200 rpm or higher, more preferably 200 rpm to 350 rpm. Furthermore, in the water-washing step, the solids concentration of the slurry is preferably 500 g / L or higher, more preferably 500 g / L to 2000 g / L. The water used is not particularly limited, but is preferably, for example, ion-exchanged water, pure water, ultrapure water, etc.

[0019] By the water washing step, the lithium compound in the reduction treatment product is dissolved in the water in the slurry, and the transition metal compound in the reduction treatment product remains as a solid. For example, the reduction treatment product obtained by the reduction reaction formula described above is ２ O dissolves in the water in the slurry, and NiO remains as a solid in the slurry.

[0020] (Recovery Step) In the recovery step, the slurry after the water washing step is subjected to solid-liquid separation to obtain a solid material and a leachate. The leachate contains a lithium compound, and the solid material 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 may be 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 either case, the lithium compound and the transition metal compound can be separated and recovered as valuable resources.

[0021] The water-washing step and the recovery step may be repeated multiple times. For example, the solid obtained in the recovery step is subjected to the water-washing step, and then the slurry obtained in the water-washing step is subjected to the recovery step. By performing the water-washing step and the recovery step multiple times, the lithium compounds remaining in the solid 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).

[0022] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples.

[0023] Example 1 A rotary kiln having a rotating cylinder equipped with a heating function was used to produce a lithium-containing transition metal oxide (composition formula: LiNi ０．９０ Co ０．０５ Mn ０．０５ O ２) was subjected to a reduction treatment. Specifically, the reduction treatment was carried out as follows. 10 g of lithium-containing transition metal oxide was introduced into the rotating shell through an inlet at one end. Then, while the rotating shell was rotating, nitrogen gas was supplied into the rotating shell to create a nitrogen gas atmosphere (oxygen concentration in the shell: 1.1%), and a formic acid solution with a formic acid concentration of 0.05 mol% was supplied at 55.5 mL / min. Then, while supplying nitrogen gas and the formic acid solution, the rotating shell was heated at 220°C for 4 minutes, and the reduced lithium-containing transition metal oxide was removed from the outlet at the other end of the rotating shell. 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 reduced lithium-containing transition metal oxide obtained in Example 1.

[0024] 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 into 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 using 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

[0025] Example 2 The same treatment as in Example 1 was carried out, except that the heating temperature inside the rotating drum was set to 150° C. The lithium recovery rate was 72%.

[0026] Example 3 The same treatment as in Example 1 was carried out, except that the heating temperature inside the rotating drum was set to 260° C. The lithium recovery rate was 86%.

[0027] Example 4 The same treatment as in Example 1 was carried out except that the heating time in the rotating drum was set to 3 minutes. The lithium recovery rate was 84%.

[0028] Comparative Example The same treatment as in Example 1 was carried out except that nitrogen gas and formic acid solution were not supplied into the rotating drum and heating was carried out in an air atmosphere with an oxygen concentration of 20.8%. The lithium recovery rate was 5%.

[0029] Table 1 shows the reduction treatment conditions and the lithium recovery rate results.

[0030]

[0031] In Examples 1 to 4, the heating temperature during reduction was 260°C or lower, but it was still possible to reduce the lithium-containing transition metal oxide and recover lithium, a valuable resource. The heating temperatures in the Examples were lower than the heating temperatures used in conventional carbonization treatments and hydrogen reduction treatments. 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 conventional treatments.

[0032] [Notes] (1) A method for recovering valuable materials, comprising: a reduction step of heating a lithium-containing transition metal compound that has been brought into contact with a formic acid solution to reduce the lithium-containing transition metal compound; a water-washing step of mixing a reduced product obtained by reducing the lithium-containing transition metal compound with water to produce a 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), wherein the formic acid solution has a formic acid concentration of 0.03 mol% or more. (3) The method for recovering valuable materials according to (1) or (2), wherein the heating in the reduction step is performed to a maximum temperature of 130°C or more and 300°C or less, and wherein the maximum temperature is maintained for 3 minutes or more. (4) The method for recovering valuable materials according to any one of (1) to (3), wherein the reduction step is performed in 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 the water-washing step involves stirring the slurry at a temperature of 80° C. or higher and at a stirring speed of 200 rpm or higher.

Claims

1. A method for recovering valuable materials, comprising: a reduction step of heating a lithium-containing transition metal compound that has been brought into contact 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 to obtain a slurry, and a recovery step of performing solid-liquid separation of the slurry after the water-washing step to recover valuable materials.

2. 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.

3. A method for recovering valuable materials as described in 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.

4. The method for recovering valuable materials according to claim 1 or 2, wherein the reduction step is carried out under a nitrogen gas atmosphere.

5. A method for recovering valuable materials according to claim 1 or 2, 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 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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