WO2025192009A1 - Aqueous solution recovery method - Google Patents

Abstract

Provided is an aqueous solution recovery method with which it is possible to recover lithium contained in a composite oxide as a lithium-containing aqueous solution.　This aqueous solution recovery method for recovering lithium contained in a composite oxide as a lithium-containing aqueous solution includes: a contact step for bringing chlorine or a chlorine compound adjusted so that the substance amount ratio of chlorine to lithium contained in the composite oxide is 1.0-5.5 into contact with the composite oxide at a temperature of 500-1350°C; and an aqueous solution recovery step for bringing the aqueous solution into contact with the composite oxide and the chlorine or chlorine compound that underwent the contact step, thereby recovering the aqueous solution permeated with the lithium.

Description

Aqueous solution recovery method

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

Batteries that use lithium (hereinafter referred to as "lithium-ion batteries") are used in a wide range of devices, from relatively small devices such as personal computers and smartphones to large devices such as electric vehicles and solar power storage facilities.

Lithium-ion batteries are constructed using exterior materials made from metals such as iron or aluminum. Inside the exterior material are positive electrode materials, which consist of aluminum foil with a positive electrode active material such as lithium nickel oxide or lithium cobalt oxide adhered to it, and negative electrode materials, which consist of copper foil with a negative electrode active material such as graphite adhered to its surface. A separator made of a porous resin film such as polypropylene is placed between the positive and negative electrode materials, and the interior of the exterior material is filled with an electrolyte such as lithium hexafluorophosphate and sealed inside.

Lithium-ion batteries are disposed of as waste lithium-ion batteries due to performance degradation caused by repeated charging and discharging, or due to the disposal of the equipment. They are also disposed of as waste lithium-ion batteries when defective products are discovered during the manufacturing process. Therefore, with the increase in the number of electric vehicles manufactured in recent years, it is expected that the number of lithium-ion batteries manufactured for electric vehicles (the number of waste lithium-ion batteries) that are disposed of will also increase.

Waste lithium-ion batteries contain valuable metals such as copper, nickel, cobalt, and lithium. Therefore, with regard to the disposal of waste lithium-ion batteries, technologies are being developed to recover and recycle valuable metals as a measure to conserve resources and prevent environmental pollution.

As a method for recovering valuable metals from used lithium-ion batteries, a pyrometallurgical process has been proposed, in which the batteries are melted at high temperatures and metals including copper, nickel, and cobalt are recovered from the molten metal obtained by the melting. In the pyrometallurgical process, metals with low resource value, such as aluminum, are oxidized and turn into slag, which has the advantage that they can be easily separated from valuable metals such as copper, nickel, and cobalt.

In the pyrometallurgical process, the lithium contained in the waste lithium-ion batteries is oxidized to lithium oxide, which forms slag together with aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, etc. Because the lithium content in the slag that is formed is low, it is not easy to recover and reuse the lithium.

For this reason, research and development is being conducted into 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 ranges of Al/Li and Si/Li values and the Al and Si contents for Li-containing slag obtained by melting raw materials such as waste lithium-ion batteries. Furthermore, Patent Document 2 discloses a method for recovering lithium chloride produced in molten metal obtained by melting waste lithium-ion batteries using a pyrometallurgical process, by adding a chloride source to the molten metal, as metal fumes.

Japanese Patent Application Laid-Open No. 2023-173717 Special Publication No. 2022-507413

However, the method disclosed in Patent Document 1 requires careful selection of the components of the flux added to the molten metal during the pyrometallurgical refining process, making it difficult to recycle (reuse) industrial by-products when using this flux, and therefore not easy to apply to actual operations. Furthermore, the method disclosed in Patent Document 2, when recovering the produced lithium chloride as metal fumes, can cause damage to surrounding furnace walls and other equipment due to the adhesion of metal fumes. This is likely to increase the costs required for equipment maintenance and renovation, making it difficult to apply to actual operations.

The present invention was made in consideration of the above circumstances, and its purpose 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, the method comprising: a contacting step of contacting the composite oxide with chlorine or a chlorine compound, the chlorine or chlorine compound being adjusted so that the substance amount 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 recovering step of contacting the chlorine or chlorine compound and the composite oxide that have been subjected to the contacting step with an aqueous solution to recover the aqueous solution into which the lithium has permeated.
[2] The method for recovering an aqueous solution according to [1], wherein the chlorine compound contains at least one of an alkali metal chloride and an alkaline earth metal chloride.
[3] The aqueous solution recovery method according to [1] or [2], wherein the composite oxide is slag remaining after a metal containing one or two elements selected from cobalt and nickel is recovered from molten metal obtained by dissolving lithium-ion batteries in a process.
[4] The aqueous solution recovery method according to any one of [1] to [3], wherein the aqueous solution to be brought into contact with the chlorine or chlorine compound that has undergone the contacting step and the composite oxide has a pH value of 5.0 or more and 10.0 or less.

According to the present invention, lithium contained in the composite oxide can be recovered as an aqueous solution containing lithium.

The following describes an embodiment of the present invention. The aqueous solution recovery method of the present invention is a method for recovering lithium contained in a composite oxide as an aqueous solution containing lithium.

As a composite oxide, slag remaining after metals containing one or two of cobalt and nickel are recovered from molten metal obtained by dissolving lithium-ion batteries using a pyrometallurgical process may be used.

The aqueous solution recovery method of the present invention includes a contacting step in which chlorine or a chlorine compound, which has been adjusted so that the mass ratio of chlorine to lithium contained in the composite oxide is 1.0 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.

By ensuring that the mass ratio of chlorine to lithium contained in the composite oxide is 1.0 or greater, the chlorination reaction between lithium and chlorine or a chlorine compound is promoted.

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

Here, the chlorine or chlorine compound may be adjusted by calculating the mass of lithium contained in the composite oxide before contacting it with the composite oxide, and adjusting the mass ratio of chlorine to lithium based on the calculated mass of lithium so that the mass ratio of chlorine to lithium is 1.0 or more and 5.5 or less. More specifically, the amount of chlorine or chlorine compound to be contacted with the composite oxide may be adjusted so that the mass ratio of chlorine to lithium is 1.0 or more and 5.5 or less. 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 composite oxide. For example, a portion of the composite oxide may be dissolved in acid, and measurement and calculation may be performed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Alternatively, in the process of producing the composite oxide, the mass concentration of lithium may be calculated 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.

Chlorine or chlorine compounds are contacted with the composite oxide at a temperature of 500°C or higher and 1350°C or lower. This is because contact at temperatures below 500°C does not promote the chlorination reaction between the lithium contained in the composite oxide and chlorine or chlorine compounds. The higher the temperature, the more promoted the chlorination reaction between lithium and chlorine or chlorine compounds. Therefore, contact at 600°C or higher is preferred, and contact at 800°C or higher is even more preferred. Furthermore, at temperatures above 1350°C, although the chlorination reaction between lithium and chlorine or chlorine compounds is promoted to produce lithium chloride, volatilization of the lithium chloride occurs, preventing its subsequent penetration into an aqueous solution and reducing the lithium recovery rate.

Here, chlorine gas may be used as the chlorine. A metal chloride may be used as the chlorine compound. Specifically, the chlorine compound may include at least one of an alkali metal chloride and an alkaline earth metal chloride. Note that alkaline earth metals also include beryllium and magnesium. These chlorine compounds and chlorine have higher boiling points than compounds of heavy metals and chlorine. For this reason, by setting the temperature during contact between the chlorine or chlorine compound and the composite oxide to 500°C or higher and 1350°C or lower, the volatilization of the chlorine compound and chlorine is suppressed, and the production of lithium contained in the composite oxide as lithium chloride can be promoted.

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

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

Contacting the composite oxide with chlorine or a chlorine compound promotes the chlorination reaction between the lithium contained in the composite oxide and the chlorine or chlorine compound, producing lithium chloride. Therefore, by bringing an aqueous solution into contact with the chlorine or chlorine compound and composite oxide that have undergone the contacting step, the produced lithium chloride is incorporated into the aqueous solution, resulting in lithium permeating the aqueous solution. As a result, the lithium contained in the composite oxide is recovered as an aqueous solution permeated with lithium.

The time for contacting the composite oxide with chlorine or a chlorine compound is preferably 20 minutes or more and 180 minutes or less. By setting the time for the contact step within this range, the chlorination reaction between lithium and chlorine or a chlorine compound is further promoted, and the lithium contained in the composite oxide can be more reliably recovered as lithium that permeates into the aqueous solution. Note that if the contact time exceeds 180 minutes, no improvement in lithium recovery efficiency will be observed even if the time is extended.

The aqueous solution that is brought into contact with the chlorine or chlorine compound and the composite oxide preferably has a pH value of 5.0 or higher and 10.0 or lower. By setting the pH value of the aqueous solution within this range, the dissolution of heavy metals (nickel, cobalt, manganese, etc.) into the aqueous solution is suppressed, and the penetration of lithium, which contains few coexisting elements, into the aqueous solution is promoted. Pure water, etc. may be used as the aqueous solution.

From the perspective of recovering an aqueous solution permeated with lithium 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, calculated as elemental lithium.

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) was used as the lithium-containing composite oxide, which differed in the substance ratio of calcium oxide to silicon dioxide (CaO/SiO ₂ ) and the mass (mass %) of lithium contained. The component information of the oxides (A to D) used in the examples is shown in Table 1.

Then, a chlorine compound was contacted with the oxides (A to D) shown in Table 1 so that the mass ratio of chlorine to lithium contained in each oxide was a predetermined value, and the mixture was maintained at a predetermined temperature for 60 minutes. An aqueous solution with a weight ratio of 30 times the chlorine compound and oxide was then prepared, and the chlorine compound and oxide were immersed in the aqueous solution while stirring for 120 minutes and filtered to obtain an aqueous solution containing lithium. Calcium chloride (CaCl ₂ ) 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 resulting aqueous solution was measured, and the percentage (%) of the lithium content (mass%) in the aqueous solution relative to the mass (mass%) of lithium contained in the oxides (A-D) was calculated as the lithium recovery rate. The results are shown in Tables 2 and 3.

In Comparative Examples 1 to 19 shown in Table 3, the ratio of chlorine to lithium (Cl/Li) contained in each of oxides A to D as composite oxides was set to 0.5, or the temperature at which each oxide was brought into contact with the chlorine compound was set to 1400°C, or the temperature at which each oxide was brought into contact with the chlorine compound was set to 400°C. As a result, the maximum recovery rate of lithium was only 40% of the total lithium contained in each oxide.

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

Inventive Examples 32 to 46 used oxides B, C, and D as the composite oxides. The molar ratio of chlorine to lithium (Cl/Li) contained in oxides B, C, and D was set to 1.8 or more and 5.5 or less, and the temperature during contact 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 was recovered as an aqueous solution.

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

Claims (4)

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