JP7845576B2 - Aqueous solution recovery method - Google Patents

Description

This invention relates to an aqueous solution recovery method for recovering lithium contained in a composite oxide obtained by dissolving a lithium-ion battery, as an aqueous solution containing lithium.

Lithium-based batteries (hereinafter referred to as "lithium-ion batteries") are used in a range of devices, from relatively small devices such as personal computers and smartphones to large devices such as electric vehicles and solar energy storage systems.

Lithium-ion batteries are formed using metal casings such as iron or aluminum. Inside the casing, there is a positive electrode material, where a positive electrode active material such as lithium nickelate or lithium cobaltate is fixed to aluminum foil, and a negative electrode material, where a negative electrode active material such as graphite is fixed to the surface of copper foil. A separator made of a porous polypropylene resin film or the like is placed between the positive and negative electrode materials, and the inside of the casing is filled with an electrolyte such as lithium hexafluoride phosphate and sealed.

Lithium-ion batteries are disposed of as waste lithium-ion batteries due to performance degradation from repeated charging and discharging, as well as equipment disposal. They are also disposed of as waste lithium-ion batteries when defective products are produced during the manufacturing process. Therefore, with the recent increase in the number of electric vehicles manufactured, the number of lithium-ion batteries to be disposed of (the number of waste lithium-ion batteries) manufactured for electric vehicles is expected to increase.

Waste lithium-ion batteries contain valuable metals such as copper, nickel, cobalt, and lithium. Therefore, in relation to the disposal of waste lithium-ion batteries, technologies for recovering and recycling these valuable metals are being developed as a measure to protect resources and prevent environmental pollution.

As a method for recovering valuable metals from waste lithium-ion batteries, a dry smelting method has been proposed in which waste lithium-ion batteries are melted at high temperatures, and metals including copper, nickel, and cobalt are recovered from the molten metal obtained by the melting process. A key advantage of this dry smelting method is that metals with low resource value, such as aluminum, oxidize and become slag, making them easily separate from valuable metals like copper, nickel, and cobalt.

In the dry smelting process, lithium contained in waste lithium-ion batteries oxidizes to lithium oxide, which, along with aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, etc., forms slag. Because the lithium content in the formed slag is low, recovering and reusing the lithium is not easy.

Therefore, research and development are being conducted on methods for recovering lithium from slag with a low lithium content. For example, Patent Document 1 discloses a method for producing slag with a high lithium content by specifying the range of Al/Li and Si/Li values and the Al and Si content for Li-containing slag obtained by melting raw materials such as waste lithium-ion batteries. Patent Document 2 also discloses a method for recovering lithium chloride generated in molten metal as a metal fume by adding a chloride source to the molten metal obtained in a dry smelting method for waste lithium-ion batteries.

Japanese Patent Publication No. 2023-173717 Special Publication No. 2022-507413

However, the method disclosed in Patent Document 1 requires careful selection of the flux components added to the molten metal during the dry smelting process. Applying this flux as a recycled industrial by-product (reuse) is difficult, making its practical application in actual operations challenging. Furthermore, the method disclosed in Patent Document 2, when recovering the generated lithium chloride as metal fumes, can cause damage to surrounding equipment such as furnace walls due to the adhesion of metal fumes. Therefore, an increase in the costs required for equipment maintenance and repair is anticipated, making practical application in actual operations difficult.

The present invention has been made in view of the above circumstances, and its object is to provide an aqueous solution recovery method that can recover lithium contained in a composite oxide as an aqueous solution containing lithium.

[1] A method for recovering lithium contained in a composite oxide as an aqueous solution containing lithium, comprising: a contact step of contacting the composite oxide with chlorine or a chlorine compound, which has been adjusted so that the molar ratio of chlorine to lithium contained in the composite oxide is 1.0 or more and 5.5 or less, at a temperature of 500°C or more and 1350°C or less; and an aqueous solution recovery step of recovering the aqueous solution in which the lithium has permeated by contacting the chlorine or chlorine compound and the composite oxide that have undergone the contact step with an aqueous solution.
[2] The aqueous solution recovery method according to [1], wherein the chlorine compound comprises at least one of alkali metal chlorides and alkaline earth metal chlorides.
[3] The aqueous solution recovery method according to [1] or [2], wherein the composite oxide is the slag remaining after the metal is recovered by a process of recovering a metal containing one or two elements of cobalt and nickel from the molten metal obtained by dissolving a lithium-ion battery.
[4] The aqueous solution recovery method according to any one of [1] to [3], wherein the aqueous solution that is brought into contact with the chlorine or chlorine compound and the composite oxide after the contact step has a pH value of 5.0 or more and 10.0 or less.

According to the present invention, lithium contained in a complex oxide can be recovered as a lithium-containing aqueous solution.

The embodiments of the present invention will be described below. The aqueous solution recovery method of the present invention is a method for recovering lithium contained in a complex oxide as an aqueous solution containing lithium.

As a composite oxide, the slag remaining after the recovery of a metal containing one or two elements from cobalt and nickel from the molten metal obtained by dissolving lithium-ion batteries using a dry smelting method may be used.

The aqueous solution recovery method of the present invention comprises a contact step of bringing chlorine or a chlorine compound, which has been adjusted so that the molar ratio of chlorine to lithium contained in the composite oxide is 1.0 or more and 5.5 or less, into contact with the composite oxide at a temperature of 500°C or more and 1350°C or less.

By setting the molar ratio of chlorine to lithium in the composite oxide to 1.0 or higher, the chlorination reaction between lithium and chlorine or chlorine compounds is promoted.

Furthermore, if the molar ratio of chlorine to lithium contained in the composite oxide is less than 1.0, the chlorination reaction between lithium and chlorine or chlorine compounds will not be promoted, and lithium cannot be sufficiently recovered. Also, if the molar ratio of chlorine to lithium contained in the composite oxide is too high, the amount of chlorine added to the lithium will be excessive, and even if the supply of chlorine or chlorine compounds is further increased, there will be no change in the effect of lithium recovery, and processing costs will increase. Therefore, the molar ratio of chlorine to lithium contained in the composite oxide is preferably 5.5 or less, and more preferably 5.0 or less.

Here, the adjustment of chlorine or chlorine compounds may be performed by calculating the mass of lithium contained in the complex oxide before contact with the complex oxide, and adjusting the amount of chlorine to lithium based on the calculated mass of lithium so that the molar ratio of chlorine to lithium is between 1.0 and 5.5. More specifically, the amount of chlorine or chlorine compound to be contacted with the complex oxide may be adjusted so that the molar ratio of chlorine to lithium is between 1.0 and 5.5. The method for calculating the mass of lithium is not limited as long as it is a method that can calculate the mass of lithium contained in the complex oxide. For example, a portion of the complex oxide may be dissolved in acid, and the measurement and calculation may be performed using inductively coupled plasma atomic emission spectrometry (ICP-AES). Alternatively, in the process of producing the complex oxide, the calculation may be based on the mass concentration of lithium contained in each raw material and the weight ratio of each raw material to the total raw materials.

Contact between chlorine or chlorine compounds and complex oxides should be carried out at a temperature between 500°C and 1350°C. If contact occurs below 500°C, the chlorination reaction between lithium contained in the complex oxide and chlorine or chlorine compounds will not be promoted. Since the chlorination reaction between lithium and chlorine or chlorine compounds is promoted at higher temperatures, contact at 600°C or higher is preferable, and contact at 800°C or higher is more preferable. Furthermore, if the temperature exceeds 1350°C, although the chlorination reaction between lithium and chlorine or chlorine compounds is promoted and lithium chloride is produced, the volatilization of lithium chloride occurs, hindering subsequent penetration into the aqueous solution and reducing the lithium recovery rate.

Here, chlorine may be provided by chlorine gas. The chlorine compound may be a metal chloride. Specifically, the chlorine compound may include at least one of alkali metal chlorides or alkaline earth metal chlorides. Alkaline earth metals also include beryllium and magnesium. These chlorine compounds and chlorine have higher boiling points than compounds of heavy metals and chlorine. Therefore, by setting the temperature at which chlorine or a chlorine compound comes into contact with the composite oxide to between 500°C and 1350°C, the volatilization of the chlorine compound and chlorine can be suppressed, and the formation of lithium as lithium chloride from the lithium contained in the composite oxide can be promoted.

Furthermore, the temperature at the time of contact between chlorine or a chlorine compound and the complex oxide may be controlled more specifically as the temperature of the complex oxide. Alternatively, it may be controlled as the temperature of the atmosphere inside the reaction vessel into which the chlorine or chlorine compound and the complex oxide are charged.

The present invention provides an aqueous solution recovery method which includes an aqueous solution recovery step in which an aqueous solution is brought into contact with chlorine or a chlorine compound and a complex oxide that has undergone a contact step, thereby recovering an aqueous solution into which lithium has permeated.

Contact between chlorine or a chlorine compound and a complex oxide accelerates the chlorination reaction between the lithium contained in the complex oxide and the chlorine or chlorine compound, producing lithium chloride. Therefore, by bringing the chlorine or chlorine compound and the complex oxide, which have undergone the contact process, into contact with an aqueous solution, the generated lithium chloride is incorporated into the aqueous solution, resulting in a state where lithium permeates the aqueous solution. As a result, the lithium contained in the complex oxide is recovered as an aqueous solution permeated with lithium.

The contact time between chlorine or a chlorine compound and the complex oxide is preferably 20 minutes or more and 180 minutes or less. This is because setting the contact time within this range further promotes the chlorination reaction between lithium and chlorine or the chlorine compound, allowing for more reliable recovery of the lithium contained in the complex oxide as lithium permeating the aqueous solution. Furthermore, if the contact time exceeds 180 minutes, no improvement in lithium recovery efficiency is observed, even if the time is extended.

The aqueous solution used to contact chlorine or a chlorine compound with a complex oxide preferably has a pH value of 5.0 to 10.0. This is because setting the pH value of the aqueous solution within this range suppresses the dissolution of heavy metals (nickel, cobalt, manganese, etc.) into the aqueous solution, while promoting the penetration of lithium, which has few coexisting elements, into the aqueous solution. Pure water or the like may be used as the aqueous solution.

From the viewpoint of recovering an aqueous solution in which lithium has permeated using the aqueous solution recovery method of the present invention, the lithium-containing composite oxide preferably has a lithium content of 0.5% by mass or more, and more preferably 1.0% by mass or more, in terms of lithium element.

Next, the results of implementing the aqueous solution recovery method of the present invention will be described. In each example, one of four types of oxides (A to D) with different molar ratios of calcium oxide and silicon dioxide (CaO/ _SiO₂ ) and mass (mass%) of lithium was used as the lithium-containing composite oxide. Table 1 shows the component information of the oxides (A to D) used in the examples.

Then, chlorine compounds were brought into contact with the oxides (A to D) shown in Table 1, such that the molar ratio of chlorine to lithium contained in each oxide was a predetermined value, and the mixture was held at a predetermined temperature for 60 minutes. Next, an aqueous solution was prepared in a weight ratio of 30 times that of the chlorine compound and oxide. The chlorine compound and oxide were immersed in the aqueous solution and stirred for 120 minutes, then filtered to obtain an aqueous solution containing lithium. Calcium chloride ( _CaCl₂ ) was used as the chlorine compound. Pure water with a pH value of 5.0 to 10.0 was used as the aqueous solution.

Next, the lithium content (mass%) in the obtained aqueous solution was measured, and the lithium recovery rate was calculated as the percentage (%) of the lithium content (mass%) in the aqueous solution relative to the total mass (mass%) of lithium contained in the oxides (A to D). The results are shown in Tables 2 and 3.

Comparative Examples 1 to 19, shown in Table 3, were conducted with oxides A to D as composite oxides, using a molar ratio of chlorine to lithium (Cl/Li) of 0.5, or with a contact temperature of 1400°C between each oxide and the chlorine compound, or with a contact temperature of 400°C between each oxide and the chlorine compound. As a result, the recovery rate of lithium was limited to a maximum of 40% of the total lithium contained in each oxide.

Examples 1 to 31 of the present invention, shown in Table 2, were carried out with a molar ratio of chlorine to lithium (Cl/Li) contained in oxide A of 1.0 to 5.5, and a contact temperature of 500°C to 1350°C between oxide A and the chlorine compound. In these cases, more than 50% of the total lithium contained in oxide A was recovered as an aqueous solution.

Examples 32 to 46 of the present invention used oxides B, C, and D as composite oxides. The molar ratio of chlorine to lithium contained in oxides B, C, and D (Cl/Li) was set to 1.8 or more and 5.5 or less, and the contact temperature between oxides B, C, and D and the chlorine compound was set to 800°C or more and 1000°C or less. As a result, more than 70% of the total lithium contained in oxides B, C, and D could be recovered as an aqueous solution.

From the above, it has been confirmed that the aqueous solution recovery method of the present invention can recover lithium contained in a composite oxide as a lithium-containing aqueous solution. Furthermore, it has been confirmed that the aqueous solution recovery method of the present invention can be applied to composite oxides having various compositions while containing lithium, and that a lithium-containing aqueous solution can be recovered without the volatilization of chlorine or chlorine compounds.

Claims (5)

A method for recovering lithium contained in a complex oxide as an aqueous solution containing lithium,
A contact step in which the chlorine or chlorine compound, which has been adjusted so that the molar ratio of chlorine to lithium contained in the composite oxide is 2.7 or more and 5.5 or less, is brought into contact with the composite oxide at a temperature of 500°C or more and 1350°C or less,
A water solution recovery step involves contacting the chlorine or chlorine compound and the composite oxide that have undergone the contact step with an aqueous solution to recover the aqueous solution in which the lithium has permeated;
A method for recovering an aqueous solution, comprising the following characteristics. The aqueous solution recovery method according to claim 1, wherein the chlorine compound comprises at least one of alkali metal chlorides and alkaline earth metal chlorides. The aqueous solution recovery method according to claim 1, wherein the composite oxide is the slag remaining after the metal is recovered from the molten metal obtained by dissolving a lithium-ion battery, by a process that recovers a metal containing one or two elements from cobalt and nickel. The aqueous solution recovery method according to claim 2, wherein the composite oxide is the slag remaining after the metal is recovered from the molten metal obtained by dissolving a lithium-ion battery, by a process that recovers a metal containing one or two elements from cobalt and nickel. The aqueous solution recovery method according to any one of claims 1 to 4, wherein the aqueous solution that is brought into contact with the chlorine or chlorine compound and the composite oxide after the contact step has a pH value of 5.0 or more and 10.0 or less.