WO2025234069A1 - Method for producing valuable metal - Google Patents

Abstract

Provided is a method by which it is possible to safely and efficiently recover a valuable metal from a starting material that contains waste lithium ion batteries or the like.　The present invention provides a method for producing a valuable metal from a starting material that contains the valuable metal, the method comprising: a step for preparing a starting material that contains lithium, aluminum, and a valuable metal; a step for subjecting the starting material to a reduction melting treatment so as to obtain a reduction product which contains slag and an alloy that contains the valuable metal; and a step for separating the slag from the reduction product so as to recover the alloy. In the step for performing the reduction melting treatment by adding a calcium-containing flux to the starting material, the reduction melting treatment is performed so that, in the slag to be generated, the mass ratio (calcium oxide)/(aluminum oxide + calcium oxide) is 0.20 or more and 0.25 or less and the mass ratio (lithium oxide)/(lithium oxide + aluminum oxide) is 0.27 or more and 0.32 or less, and the slag heating temperature is 1500°C or more and 1600°C or less.

Description

Valuable metal production methods

The present invention relates to a method for producing valuable metals from raw materials such as waste lithium-ion batteries.

In recent years, lithium-ion batteries have become popular as lightweight, high-power secondary batteries. Well-known lithium-ion batteries have a structure in which negative electrode material, positive electrode material, a separator, and electrolyte are sealed inside an outer can.

For example, the outer can is made of a metal such as aluminum (Al) or iron (Fe). The negative electrode material is made of a negative electrode active material (graphite, etc.) adhered to a negative electrode current collector (copper foil, etc.). The positive electrode material is made of a positive electrode active material (lithium nickel oxide, lithium cobalt oxide, etc.) adhered to a positive electrode current collector (aluminum foil, etc.). The separator is made of a porous polypropylene resin film, etc. The electrolyte contains an electrolyte such as lithium hexafluorophosphate (LiPF ₆ ).

One of the main uses of lithium-ion batteries is in hybrid and electric vehicles. As a result, it is expected that a large number of lithium-ion batteries installed in these vehicles will be discarded in the future as they reach the end of their lifecycle. In addition, some lithium-ion batteries are discarded as defective products during manufacturing. There is a demand for these used batteries and batteries that are defective during manufacturing (hereinafter referred to as "waste lithium-ion batteries") to be reused as resources.

A pyrometallurgical process has been proposed as a recycling method, in which all used lithium-ion batteries are melted in a high-temperature furnace. In this process, crushed used lithium-ion batteries are melted and the valuable metals to be recovered, such as cobalt (Co), nickel (Ni), and copper (Cu), are separated and recovered from low-value-added metals, such as iron (Fe) and aluminum (Al), by utilizing the difference in oxygen affinity between them. With this method, low-value-added metals are oxidized as much as possible to produce slag, while valuable metals are recovered as alloys by minimizing oxidation.

Patent Document 1 discloses a method for recovering valuable metals, including nickel and cobalt, from used lithium-ion batteries containing nickel and cobalt. Specifically, the method includes a melting step in which the used batteries are melted to obtain a molten material, an oxidation step in which the molten material or the used batteries before the melting step are subjected to an oxidation treatment of the used batteries, and a slag separation step in which slag is separated from the molten material to recover an alloy containing the valuable metals. The proposed process involves adding calcium oxide to the melting step to lower the liquidus temperature of the slag, thereby recovering the valuable metals.

Patent No. 6819827

However, the technology disclosed in Patent Document 1 still has issues. For example, with the method disclosed in Patent Document 1, if the slag liquidus temperature (hereinafter also referred to as the "slag melting point") is lowered too much by adding flux, the refractory material in the furnace walls of the treatment furnace can be corroded. If such erosion occurs, there is a risk of the treated material leaking outside the furnace, which is a safety issue. In addition, the cost of maintaining the refractory material in the furnace walls is enormous, making it impossible to recover valuable metals cheaply.

In response to these issues, the present applicant has proposed a processing method in which magnesia (MgO) is added in addition to flux when the raw materials are subjected to reduction melting (Patent Application No. 2022-155194). This method effectively forms a slag coating layer on the walls of the processing furnace, suppressing furnace wear and enabling safe and efficient processing. However, while magnesia facilitates the production of slag coating, it is a relatively expensive material, so it is desirable to reduce its usage. Furthermore, adding magnesia can increase the amount of slag produced, which may reduce processing efficiency.

The present invention was proposed in light of these circumstances, and aims to provide a method for safely and efficiently recovering valuable metals from raw materials, including discarded lithium-ion batteries.

The inventors conducted extensive research. As a result, they discovered that by adjusting the mass ratios of calcium oxide/(calcium oxide + aluminum oxide) and lithium oxide/(lithium oxide + aluminum oxide) in the slag produced by reducing and melting the raw materials to fall within a specific range, and then controlling the slag heating temperature within a specific range during the reducing and melting process, they could solve the above-mentioned problems without adding materials such as magnesia, which led to the completion of the present invention.

(1) The first aspect of the present invention is a method for producing valuable metals from raw materials containing the valuable metals, comprising: a preparation step of preparing raw materials containing at least lithium (Li), aluminum (Al), and the valuable metals; a reduction and melting step of subjecting the raw materials to a reducing and melting process to obtain a reduced product containing slag and an alloy containing the valuable metals; and a slag separation step of separating the slag from the reduced product to recover the alloy. In either or both of the preparation step and the reducing and melting step, a flux containing calcium (Ca) is added to the raw materials, and in the reducing and melting step, the mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the slag produced is set to between 0.20 and 0.25, and the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) is set to between 0.27 and 0.32. The reduction and melting process is performed at a slag heating temperature of between 1500°C and 1600°C.

(2) The second aspect of the present invention is a method for producing valuable metals according to the first aspect, wherein the raw materials include waste lithium-ion batteries.

(3) The third invention of the present invention is a method for producing valuable metals according to the first or second invention, wherein the melting furnace used in the reduction melting process is provided with a means for cooling the furnace walls from the outside.

(4) A fourth aspect of the present invention is a method for producing valuable metals according to any one of the first to third aspects, further comprising an oxidizing roasting step of oxidizing roasting the raw material to produce an oxidized roasted product prior to the reducing melting treatment, and the resulting oxidized roasted product is subjected to the reducing melting treatment.

The present invention provides a method for safely and efficiently recovering valuable metals from raw materials, including waste lithium-ion batteries.

FIG. 1 is a process diagram showing an example of the flow of a method for recovering valuable metals from waste lithium-ion batteries. FIG. 1 is a diagram showing a phase diagram of the Al ₂ O ₃ —CaO—Li ₂ O system calculated by thermodynamic calculation software (FactSage), and is a diagram plotting the results of melting tests in the examples.

The following describes a specific embodiment of the present invention (hereinafter referred to as the "present embodiment"). Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the gist of the present invention.

≪1. Methods for recovering valuable metals≫
The method for producing valuable metals according to this embodiment is a method for separating and recovering valuable metals from raw materials containing at least lithium (Li), aluminum (Al), and valuable metals. Therefore, it can also be described as a method for recovering valuable metals. The method according to this embodiment is primarily a method using a pyrometallurgical process, but may also be comprised of a pyrometallurgical process and a hydrometallurgical process.

Specifically, the method according to this embodiment includes the steps of: preparing raw materials containing at least lithium, aluminum, and valuable metals (preparation step); subjecting the prepared raw materials to a reduction melting process to obtain a reduced product (melt) containing an alloy containing the valuable metals and slag (reduction melting step); and separating the slag from the reduced product to recover the alloy (slag separation step).

In this method, a flux containing calcium (Ca) is added to the raw materials in either or both of the preparation process and the reduction and melting process to lower the slag melting point. Then, in the reduction and melting process, the mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the resulting slag is adjusted to between 0.20 and 0.25, and the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) is adjusted to between 0.27 and 0.32. The reduction and melting process is characterized by carrying out a slag heating temperature of between 1500°C and 1600°C to operate at the melting point of slag with these mass ratios.

In this method, materials such as magnesia (MgO), which facilitate the formation of a slag coating on the refractory material of the furnace walls, are not added.

Here, valuable metals are those to be recovered, and are, for example, copper (Cu), nickel (Ni), cobalt (Co), and combinations thereof, and are at least one metal or alloy selected from the group consisting of copper, nickel, cobalt, and combinations thereof. In the following, copper, nickel, and cobalt will be used as examples of valuable metals.

[Preparation process]
In the preparation step, a raw material to be treated is prepared. The raw material is the target of treatment for recovering valuable metals, and as described above, contains lithium and aluminum as well as at least one valuable metal selected from the group consisting of copper, nickel, and cobalt. The raw material may contain these components (Li, Al, Cu, Ni, Co) in the form of metals or in the form of compounds such as oxides. The raw material may also contain inorganic or organic components other than these components.

The raw materials are not particularly limited, and examples include waste lithium-ion batteries, dielectric materials (capacitors), and magnetic materials. Furthermore, there are no limitations on their form, so long as they are suitable for processing in the reduction melting process described below. Furthermore, in the preparation process, the raw materials may be subjected to a crushing process or other process to create a suitable form. Furthermore, in the preparation process, the raw materials may be subjected to a heat treatment or separation process to remove unnecessary components such as moisture and organic matter.

Furthermore, in the preparation process, a flux containing calcium (Ca) can be added to the raw materials. The flux to be added will be described in detail later. In the method according to this embodiment, the flux is added in either or both of the preparation process and the reduction melting process.

[Reduction melting process]
In the reduction melting process, the prepared raw materials are charged into a melting furnace, and the raw materials are heated and subjected to a reduction melting process to obtain a reduced product, which contains the alloy and slag separately.

Reducing melting is a process in which raw materials are heated and reduced and melted in a melting furnace to produce a reduced product. The purpose of this process is to convert low-value-added metals (such as Al) contained in the raw materials into oxides, while reducing and melting valuable metals (Cu, Ni, Co) to recover them as an integrated alloy. After reducing melting, a molten alloy is obtained. If the oxidizing roasting process described below is performed prior to reducing melting, the resulting oxidizing roasted material is loaded into a melting furnace and heated for reducing and melting. This keeps low-value-added metals (such as Al) oxidized by the oxidizing roasting process as oxides, while reducing and melting valuable metals (Cu, Ni, Co) to recover them as an integrated alloy.

In the reduction melting process, it is preferable to introduce a reducing agent. Furthermore, it is preferable to use carbon and/or carbon monoxide as the reducing agent. Carbon has the ability to easily reduce the valuable metals (Cu, Ni, Co) that are the target of recovery. For example, one mole of carbon can reduce two moles of valuable metal oxides (copper oxide, nickel oxide, etc.). Furthermore, reduction methods that use carbon or carbon monoxide are significantly safer than methods that use metal reducing agents (for example, the thermite reaction method using aluminum).

As carbon, artificial graphite and/or natural graphite can be used. Coal or coke can also be used if there is no risk of impurity contamination.

Alloys produced by reduction melting contain valuable metals. Therefore, it is possible to separate components containing valuable metals (alloys) from other components in the reduction product. This is because low-value-added metals (such as Al) have a high oxygen affinity, while valuable metals have a low oxygen affinity. For example, aluminum (Al), lithium (Li), carbon (C), manganese (Mn), phosphorus (P), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu) generally oxidize in the following order: Al > Li > C > Mn > P > Fe > Co > Ni > Cu. In other words, aluminum (Al) is most easily oxidized, and copper (Cu) is least oxidized. Therefore, low-value-added metals (such as Al) are easily oxidized and become slag, while valuable metals (Cu, Ni, Co) are reduced to metals (alloys). In this way, low-value-added metals and valuable metals can be efficiently separated into slag and alloys.

In the method according to the present embodiment, a flux containing calcium (Ca) can be added to the raw material during the reducing melting process. Specifically, the flux is added in either or both of the preparation process and the reducing melting process. The flux is primarily composed of calcium (Ca), and examples of such flux include calcium oxide (CaO) and calcium carbonate (CaCO ₃ ). However, if the raw material to be treated contains a required amount of calcium, the addition of a flux is not necessary.

Furthermore, in this method, no materials such as magnesia (MgO) are added to facilitate the production of slag coating.

The method according to this embodiment is characterized by minimizing the amount of calcium-containing flux added and blending the raw materials, and then performing a reduction melting process so that the mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the resulting slag is 0.20 or more and 0.25 or less, and the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) is 0.27 or more and 0.32 or less.

Here, since the alloy containing copper, nickel, and cobalt contains at least copper, the melting point of the alloy is 1300°C to 1400°C. In order to smoothly obtain an alloy (hereinafter also referred to as "metal") with such a melting point, the metal heating temperature (hereinafter also simply referred to as "metal heating temperature") must be 1350°C to 1450°C. In order to maintain this metal heating temperature, the heating temperature of the slag located in contact with the metal layer (hereinafter also simply referred to as "slag heating temperature") must be 1500°C to 1600°C. In order to obtain such a slag heating temperature, the slag melting point must be 1400°C to 1500°C.

For example, if the slag melting point is below 1400°C, the temperature difference with the slag heating temperature becomes large, making it difficult to form a slag coating on the refractory of the furnace walls of the processing furnace used in the reduction melting process, which may result in erosion of the refractory of the furnace walls. Furthermore, if the slag melting point exceeds 1500°C, the temperature difference with the slag heating temperature becomes small, increasing the viscosity of the slag produced and making it difficult to obtain metal smoothly, i.e., at a high recovery rate.

In the method according to this embodiment, the minimum amount of calcium-containing flux is added, and the mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the slag produced by the reduction melting process is set to 0.20 or more and 0.25 or less, and the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) is set to 0.27 or more and 0.32 or less. This minimizes the melting point of the slag, to the point where a slag coating can be produced.

Furthermore, because the reduction melting process is performed so that the resulting slag has the above mass composition, and a slag coating layer is formed on the furnace walls of the melting furnace, there is no need to add materials such as magnesia, which lower the viscosity of the slag and facilitate the formation of the slag coating, and the amount of such materials used can be reduced. Furthermore, by eliminating the use of materials such as magnesia and minimizing the amount of flux added to lower the slag melting point, the amount of slag produced can be reduced, significantly improving metal productivity.

Lithium (Li) and calcium (Ca) contribute to lowering the melting temperature of the slag. Therefore, by controlling the composition of the resulting slag so that it falls within the above mass ratio range, the melting temperature of the slag can be reduced to, for example, 1600°C or below. Furthermore, if there is a high amount of calcium in the slag, it becomes easier to remove phosphorus if it is contained in the raw materials. This is because phosphorus becomes an acidic oxide when oxidized, whereas calcium becomes a basic oxide when oxidized. Therefore, the more calcium there is in the slag, the more basic the slag composition becomes, and as a result, it becomes easier to incorporate phosphorus into the slag and remove it.

Regarding the chemical composition of the resulting slag, if the mass ratio (calcium oxide/(aluminum oxide + calcium oxide) (for convenience, referred to as "mass ratio A") or the mass ratio (lithium oxide/(lithium oxide + aluminum oxide)) (for convenience, referred to as "mass ratio B") is excessively high, specifically, if mass ratio A exceeds 0.25 or mass ratio B exceeds 0.32, the liquidus temperature of the slag will drop too much, and the melting point will be below 1400°C, for example, making it difficult to form a slag coating layer even when the furnace walls are cooled. Here, since the melting point of the resulting alloy composed of copper, nickel, and cobalt is approximately 1300°C to 1400°C, for example, in order to operate so that the metal heating temperature is 1350°C to 1450°C, i.e., to transfer heat from the slag to the metal, the slag temperature must be 1500°C to 1600°C. However, if the melting point of the slag is below 1,400°C, the coating cannot be formed effectively and the refractory material of the furnace wall may be eroded.

Furthermore, if mass ratio A or mass ratio B is excessively low, specifically if mass ratio A is less than 0.20 or mass ratio B is less than 0.27, the liquidus temperature of the slag will be high, and the raw material to be melted will not be able to be sufficiently melted, which may prevent efficient recovery of valuable metals.

For this reason, as mentioned above, during the reduction melting process, the mass ratio of calcium oxide to (aluminum oxide + calcium oxide) (mass ratio A) in the slag produced is set to between 0.20 and 0.25, and the mass ratio of lithium oxide to (lithium oxide + aluminum oxide) (mass ratio B) is set to between 0.27 and 0.32. This ensures a high level of safety during the reduction melting process, while suppressing erosion of the refractory material that makes up the side walls of the melting furnace, and also enables a high recovery rate of valuable metals.

The amounts of slag components (e.g., Al, Li, Ca) can be easily controlled by adjusting the composition of the raw materials and the amount of flux added to the raw materials. Specifically, for example, the amount of calcium (Ca) in the slag can be controlled by adding a calcium-containing flux to the material to be processed and adjusting the amount of the flux added. As mentioned above, examples of calcium-containing fluxes include calcium oxide (CaO) and calcium carbonate (CaCO ₃ ). Furthermore, the amounts of lithium (Li) and aluminum (Al) in the slag can be controlled by adjusting the composition of the raw materials in the preparation process.

Furthermore, in the reduction melting process, the heating temperature (slag heating temperature) is set to 1500°C or higher and 1600°C or lower. Slag heating temperatures above 1600°C result in unnecessary thermal energy consumption and accelerated wear of refractories, such as the crucible that makes up the melting furnace, potentially reducing productivity. In particular, reduction melting of lithium-containing raw materials results in the inclusion of lithium in the slag, resulting in significant wear of the refractories. For example, operation at slag heating temperatures above 1600°C is difficult from the perspective of refractory wear and the life of the melting furnace (furnace wall). Considering the upper limit of the slag heating temperature, a metal heating temperature in the range of 1350°C to 1450°C and a metal melting point in the range of 1300°C to 1400°C are preferred for smooth operation, i.e., for the separation of the metal and slag and the formation of a slag coating on the refractory. Furthermore, to achieve such a metal melting point, it is preferable for the metal to contain copper (Cu).

On the other hand, if the slag heating temperature is below 1500°C, the separation of the resulting slag from the alloy may be impaired, potentially reducing the recovery rate of valuable metals.

It is desirable for the melting furnace to be equipped with a mechanism for cooling the furnace walls from the outside, such as by water cooling. By cooling the furnace walls from the outside, the temperature of the slag in contact with the inner refractory surface can be lowered below the liquidus temperature of the slag, effectively forming a solidified slag layer (slag coating layer) on the refractory surface. When a slag coating layer is formed in this way, the refractory is protected and erosion of the refractory can be more effectively prevented.

The melting furnace is preferably a submerged arc furnace. As mentioned above, in order to transfer heat from the slag to the metal, the temperature of the upper slag layer must be higher than that of the lower metal layer. With a submerged arc furnace, the slag layer itself generates heat as the electrodes are immersed in the slag, making it possible to maintain the highest operating temperature for the slag layer, making it preferable.

If an oxidizing roasting treatment (oxidizing roasting step) is performed prior to the reducing melting treatment, there is no need to perform an oxidation treatment during the reducing melting treatment. However, if the oxidation in the oxidizing roasting treatment is insufficient or if the goal is to further adjust the degree of oxidation, an additional oxidation treatment may be performed during or after the reducing melting treatment. By performing an additional oxidation treatment, it becomes possible to more precisely adjust the degree of oxidation.

One example of a method for performing additional oxidation treatment is to blow an oxidizing agent into the molten material produced by the reduction melting treatment. Specifically, a metal tube (lance) is inserted into the molten material produced by the reduction melting treatment, and the oxidizing agent is blown in by bubbling to perform the oxidation treatment. In this case, oxygen-containing gases such as air, pure oxygen, and oxygen-enriched gases can be used as the oxidizing agent.

Furthermore, the reduction melting process can generate harmful substances such as dust and exhaust gases, but these can be neutralized by applying known exhaust gas treatment methods.

[Oxidation roasting process]
In the method according to the present embodiment, a step of oxidizing roasting the raw material to obtain an oxidized roasted product (oxidizing roasting step) can be further provided, as necessary, prior to the reducing melting treatment.

Oxidizing roasting (oxidation treatment) is a process in which raw materials are oxidized and roasted to produce oxidized roasted material. Even if the raw materials contain carbon, this carbon is oxidized and removed, making it possible to promote the alloying and integration of valuable metals during the reduction melting process. Specifically, during the reduction melting process, valuable metals are reduced to localized molten fine particles. At this time, the carbon contained in the charge acts as a physical obstacle to the aggregation of the molten fine particles (valuable metals), preventing the aggregation and integration of the molten fine particles and the resulting separation of the metal (alloy) from the slag, which can reduce the recovery rate of valuable metals. In this regard, by subjecting the raw materials to oxidizing roasting prior to the reduction melting process, carbon in the raw materials can be effectively removed, which promotes the aggregation and integration of the molten fine particles (valuable metals) produced during the reduction melting process, further increasing the recovery rate of valuable metals.

In the oxidizing roasting process, the degree of oxidation can be adjusted as follows. That is, as mentioned above, aluminum (Al), lithium (Li), carbon (C), manganese (Mn), phosphorus (P), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu) are generally oxidized in the following order: Al > Li > C > Mn > P > Fe > Co > Ni > Cu. In the oxidizing roasting process, the process is continued until all of the aluminum is oxidized. The process may be continued until some of the iron is oxidized, but it is preferable to minimize the oxidation of cobalt and maintain the degree of oxidation to a level that prevents the cobalt from being oxidized and recovered as slag.

When adjusting the degree of oxidation in the oxidizing roasting process, it is preferable to introduce an appropriate amount of oxidizing agent. In particular, when using raw materials containing waste lithium-ion batteries, it is preferable to introduce an oxidizing agent before treatment. Lithium-ion batteries contain metals such as aluminum and iron as exterior materials. They also contain aluminum foil and carbon materials as positive and negative electrode materials. Furthermore, in the case of battery modules, plastic is used for the external packaging. As all of these materials act as reducing agents, the degree of oxidation can be adjusted within an appropriate range by introducing an oxidizing agent.

The oxidizing agent is not particularly limited as long as it can oxidize carbon and low-value-added metals (such as Al), but oxygen-containing gases such as air, pure oxygen, and oxygen-enriched gases are preferred, as they are easy to handle. The amount of oxidizing agent introduced should be approximately 1.2 times (e.g., 1.15 to 1.25 times) the amount (chemical equivalent) required to oxidize each substance to be subjected to the oxidizing roasting treatment.

The heating temperature for the oxidizing roasting process is preferably 700°C or higher and 1100°C or lower, and more preferably 800°C or higher and 1000°C or lower. By setting the heating temperature to 700°C or higher, the efficiency of carbon oxidation can be further increased and the oxidation time can be shortened. Furthermore, by setting the heating temperature to 1100°C or lower, thermal energy costs can be reduced and the efficiency of oxidizing roasting can be increased.

Oxidation roasting can be carried out using a known roasting furnace. It is also preferable to use a furnace (backup furnace) different from the melting furnace used in the reduction melting process, and to carry out the process in that furnace. Any type of roasting furnace can be used, as long as it is possible to roast the pulverized material while supplying an oxidizing agent (oxygen, etc.) and carry out the process inside. Examples include conventionally known rotary kilns and tunnel kilns (hearth furnaces).

[Slag separation process]
In the slag separation process, slag is separated from the reduced product obtained by the reduction melting process, and alloys containing valuable metals are recovered. Slag and alloys have different specific gravities, and slag, which has a lower specific gravity than alloys, tends to collect on top of the alloys, allowing for efficient separation and recovery by gravity separation.

Furthermore, after the slag is separated from the reduced material in the slag separation process and the alloy is recovered, a sulfurization process may be performed to sulfurize the resulting alloy, or a crushing process may be performed to crush the mixture of sulfide and alloy obtained in the sulfurization process. Furthermore, the valuable metal alloy obtained through such a dry smelting process may be subjected to a hydrometallurgical process. The hydrometallurgical process removes impurities, and the valuable metals (Cu, Ni, Co) can be separated and refined and recovered individually. Examples of treatments used in hydrometallurgical processes include well-known techniques such as neutralization and solvent extraction.

As described above, in the method according to this embodiment, the mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the resulting slag during the reduction melting process is set to 0.20 or more and 0.25 or less, and the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) is set to 0.27 or more and 0.32 or less. This ensures that the melting temperature of the slag is at least 1600°C or less, for example 1500°C or less, making the slag less viscous. The reduction melting process is then carried out with the slag heating temperature set to 1500°C or more and 1600°C or less.

By doing this, for example, when the melting temperature (melting point) of the slag is 1500°C, by setting the slag heating temperature to 1600°C, it is possible to obtain slag with sufficiently low viscosity, and the slag and metal can be separated efficiently.

Furthermore, by not lowering the melting point of the slag too much, a coating (slag coating) can be applied between the slag and the furnace wall refractory, which protects the refractory on the side walls of the melting furnace and enables stable operation with a high level of safety.

In this case, the slag heating temperature is preferably 1500°C or higher, so the metal temperature is approximately 1400°C or higher, ensuring that the operating temperature of the metal is above its melting point and maintaining the fluidity of the metal. It is preferable that the resulting alloy has a melting point of 1400°C or lower, i.e., contains at least copper (Cu).

≪2. Method for producing valuable metals from waste lithium-ion batteries≫
In the method according to the present embodiment, the raw material to be treated is not limited as long as it contains at least lithium (Li), aluminum (Al), and valuable metals. Among them, the raw material preferably contains waste lithium-ion batteries.

Waste lithium-ion batteries contain lithium (Li) and valuable metals (Cu, Ni, Co), as well as low-value-added metals (Al, Fe) and carbon components. Therefore, by using waste lithium-ion batteries as a raw material, valuable metals can be efficiently separated and recovered. Note that the concept of waste lithium-ion batteries includes not only used lithium-ion batteries, but also defective products generated during the manufacturing process of lithium-ion batteries, such as cathode materials that make up the batteries, residues from the manufacturing process, and scrap generated during the lithium-ion battery manufacturing process. Therefore, waste lithium-ion batteries can also be referred to as lithium-ion battery waste.

Figure 1 is a process diagram showing an example of the flow of a method for producing valuable metals from waste lithium-ion batteries. As shown in Figure 1, this method comprises a waste battery pretreatment process (S1) in which the electrolyte and outer cans of waste lithium-ion batteries are removed; a crushing process (S2) in which the contents of the waste batteries are crushed to produce a crushed material; an oxidizing roasting process (S3) in which the crushed material is oxidizing-roasted; a reducing-melting process (S4) in which the oxidizing-melted material is reduced and melted to form an alloy; and a slag separation process (S5) in which slag is separated from the reduced material obtained in the reducing-melting process to recover the alloy.

Furthermore, although not shown, after the slag separation process (S5), a sulfurization process may be performed to sulfurize the obtained alloy, and a crushing process may be performed to crush the mixture of sulfide and alloy obtained in the sulfurization process. Details of each process are described below.

(Waste battery pretreatment process)
The waste battery pretreatment step S1 is performed to prevent explosion and render harmless the raw material waste lithium-ion batteries, and to remove the outer cans. Because lithium-ion batteries are sealed systems, they contain electrolytes and other substances. Crushing them in their original state is dangerous because of the risk of explosion. Therefore, it is preferable to discharge the batteries or remove the electrolyte by some method. Furthermore, outer cans are often made of metals such as aluminum (Al) and iron (Fe), and these metal outer cans are relatively easy to recover intact. Thus, removing the electrolyte and outer cans in the waste battery pretreatment step (S1) enhances safety and increases the recovery rate of valuable metals (Cu, Ni, Co).

The specific treatment method used in the waste battery pretreatment step S1 is not particularly limited, but examples include physically opening holes in the waste batteries with a needle-like blade to remove the electrolyte. Another example is burning the waste batteries to render them harmless.

(Crushing process)
In the pulverization step S2, the contents of the waste lithium-ion batteries are pulverized to obtain pulverized material. The pulverization treatment in the pulverization step S2 aims to increase the reaction efficiency in the pyrometallurgical process. By increasing the reaction efficiency, the recovery rate of valuable metals (Cu, Ni, Co) can be increased.

The specific grinding method is not particularly limited. Grinding can be carried out using a conventional grinder such as a cutter mixer.

In addition, when recovering aluminum (Al) or iron (Fe) contained in the outer can, the crushed material can be sieved using a sieve shaker. Aluminum (Al) can be easily powdered with light crushing, so it can be recovered efficiently. Iron (Fe) contained in the outer can can also be recovered by magnetic separation.

The waste battery pretreatment process S1 and the pulverization process S2 together correspond to the "preparation process" described above.

(Oxidation roasting process)
In the oxidizing roasting step S3, the pulverized material obtained in the pulverizing step S2 is oxidizing roasted to obtain an oxidizing roasted material. This step corresponds to the above-mentioned "oxidizing roasting step," and the details are as described therein.

(Reduction melting process)
In the reducing-melting step S4, the oxidizing roasted product obtained in the oxidizing roasting step S3 is subjected to a reducing-melting treatment to obtain a reduced product. This step corresponds to the above-mentioned "reducing-melting step," and the details are as described therein.

In particular, in the method according to this embodiment, a flux containing calcium (Ca) is added to the raw materials in one or more of the waste battery pretreatment process, the pulverization process, and the reduction melting process. The reduction melting process is characterized by ensuring that the mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the resulting slag is 0.20 or more and 0.25 or less, and the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) is 0.27 or more and 0.32 or less, and the slag heating temperature is 1500°C or more and 1600°C or less.

This allows for safe processing while suppressing erosion of the refractory material that makes up the side walls of the melting furnace, and also enables valuable metals to be recovered at a high rate.

(Slag separation process)
In the slag separation step S5, the slag is separated from the reduced product obtained in the reduction melting step S4 to recover the alloy. This step corresponds to the "slag separation step" described above, and the details are as explained therein.

Furthermore, after the slag separation process, a sulfurization process and a pulverization process may be carried out. Furthermore, the obtained valuable metal alloy may be subjected to a hydrometallurgical process. Details of the sulfurization process, pulverization process, and hydrometallurgical process are as described above.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples in any way.

[Flow of valuable metal recovery processing (operations in each process)]
A process for recovering valuable metals was carried out using waste lithium ion batteries containing lithium (Li), aluminum (Al), and valuable metals (Cu, Ni, Co) as raw materials.

(Waste battery pretreatment process and crushing process)
First, the waste lithium-ion batteries were prepared as follows: 18650-type cylindrical batteries, used automotive prismatic batteries, and defective batteries collected during the battery manufacturing process. The waste lithium-ion batteries were then immersed in salt water to discharge, after which the water was removed and the batteries were roasted in the air at a temperature of 260°C to decompose and remove the electrolyte, thereby obtaining the battery contents.

Next, the battery contents were pulverized using a pulverizer (product name: Good Cutter, manufactured by Ujiie Seisakusho Co., Ltd.) to obtain a pulverized product.

(Oxidation roasting process)
Next, the obtained pulverized material was subjected to oxidizing roasting in a rotary kiln in the atmosphere at a heating temperature of 900° C. for 180 minutes.

(Reduction melting process)
Next, the obtained oxidized roasted product was mixed so that the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) in the resulting slag would be the value shown in Table 1 below, and graphite powder was added as a reducing agent in an amount 0.6 times the total moles of valuable metals (Cu, Ni, Co) (i.e., 1.2 times the moles of graphite powder required to reduce the valuable metals), and calcium oxide (CaO) was also added as a flux. The flux was added and mixed in an amount such that the mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the slag resulting from the reducing melting treatment would be the value shown in Table 1 below.

In addition, a submerged arc furnace was used as the melting furnace for the reduction melting process, with the furnace walls cooled from the outside by a water-cooled jacket. Each test sample was heated to the specified reduction melting temperature (slag heating temperature) shown in Table 1 below to undergo the reduction melting process, alloying the valuable metals and obtaining alloys and slag.

(Slag separation process)
The slag was separated from the resulting reduced product, and the alloy was recovered as a recovered alloy.

[Slag component analysis]
The components of the slag separated from the reduced product were analyzed as follows: The obtained slag was cooled, pulverized, and analyzed by fluorescent X-rays.

(Valuable metal recovery rate)
The recovery rate of valuable metal (Co) was calculated based on the following formula 1. The components in the recovered alloy were analyzed by fluorescent X-rays.
Valuable metal recovery rate (%) =
(Weight of Co in recovered alloy) ÷ (Weight of Co in recovered alloy + Weight of Co in slag) × 100
...(Formula 1)

[Evaluation results]
Table 1 below shows the cobalt recovery rate and the results of checking whether or not the furnace wall refractory was worn when the slag obtained was heated at 1500° C. and 1600° C. while varying the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) and the mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the slag. The presence or absence of refractory wear was checked visually after the submerged arc furnace was turned off after the tests were completed, along with checking whether or not a slag coating layer had formed.

Figure 2 is a phase diagram of Al ₂ O ₃ -CaO-Li ₂ O slag, on which the results of the test on whether or not a slag coating layer was formed are plotted. The dashed line in Figure 2 indicates the liquidus calculated using thermodynamic calculation software (FactSage). This phase diagram does not include magnesia (MgO).

As can be seen from the results in Table 1, in Examples 1 and 2, a slag coating layer was formed on the furnace walls of the melting furnace, protecting the refractory, and no wear of the refractory was observed, allowing for highly safe processing. Furthermore, the slag and metal were easily separated, and good results were obtained with a cobalt recovery rate of 95% or more in all samples.

Furthermore, in Examples 1 and 2, a good slag coating layer was formed and the refractory material was protected without the need to add magnesia (MgO) or other additives. Furthermore, by minimizing the amount of calcium-containing flux added to lower the slag melting point, metal productivity was significantly improved.

On the other hand, in Comparative Examples 1 and 2, although a slag coating layer was formed, the cobalt recovery rate was lower than in the Examples. This is because the estimated slag melting point of the obtained slag composition was around 1550°C, so it is presumed that the slag was not completely melted and the high viscosity of the slag made it difficult to separate the slag and metal, and the presence of many small metal particles in the slag is thought to have resulted in a low cobalt recovery rate.

Furthermore, in Comparative Example 3, no slag coating layer was formed, leaving the refractory unprotected and significantly worn. This is thought to be because the liquidus temperature of the resulting slag composition was too low, with an estimated slag melting point of 1,370°C, so the slag hardly solidified even when the furnace wall was cooled, and as a result, almost no slag coating layer was formed.

In Reference Example 1, magnesia (MgO) was added along with the flux, and a reduction melting process was carried out to produce slag with the composition shown in Table 1 above. In Reference Example 1, the addition of magnesia allowed the easy formation of a slag coating layer, protecting the refractory material; however, the addition of expensive magnesia reduced the processing efficiency and increased the amount of slag.

Claims (4)

A method for producing valuable metals from raw materials containing the valuable metals, comprising:
A preparation step of preparing a raw material containing at least lithium (Li), aluminum (Al), and valuable metals;
a reducing and melting step of subjecting the raw material to a reducing and melting treatment to obtain a reduced product containing an alloy containing the valuable metal and slag;
a slag separation step of separating slag from the reduced product to recover an alloy,
In either one or both of the preparation step and the reduction melting step, a flux containing calcium (Ca) is added to the raw material,
In the reduction melting step,
The mass ratio of calcium oxide/(aluminum oxide + calcium oxide) in the resulting slag is 0.20 or more and 0.25 or less, and the mass ratio of lithium oxide/(lithium oxide + aluminum oxide) is 0.27 or more and 0.32 or less, and the slag heating temperature is 1500°C or more and 1600°C or less, and a reducing melting treatment is performed.
Methods for producing valuable metals. The raw material includes waste lithium-ion batteries.
The method for producing valuable metals according to claim 1. The melting furnace used in the reduction melting step is provided with a means for cooling the furnace wall from the outside.
The method for producing valuable metals according to claim 1. The method further includes an oxidizing roasting step of oxidizing roasting the raw material to form an oxidized roasted product prior to the reducing melting treatment, and the resulting oxidized roasted product is subjected to the reducing melting treatment.
The method for producing valuable metals according to claim 1.