JP7359062B2 - Method for recovering valuable metals from waste lithium-ion batteries - Google Patents

Description

The present invention relates to a method for recovering valuable metals from waste lithium ion batteries.

In recent years, lithium ion batteries have become popular as lightweight, high-output secondary batteries. BACKGROUND ART Lithium ion batteries are known in which a negative electrode material, a positive electrode material, a separator, an electrolytic solution, and the like are sealed in a metal exterior can made of aluminum, iron, or the like. The negative electrode material consists of a negative electrode active material (such as graphite) fixed to a negative electrode current collector (copper foil). The positive electrode material consists of a positive electrode active material (lithium nickelate, lithium cobaltate, etc.) fixed to a positive electrode current collector (aluminum foil). The separator is a porous resin film of polypropylene or the like. The electrolyte includes an electrolyte such as lithium hexafluorophosphate (LiPF ₆ ).

One of the major uses of lithium-ion batteries is hybrid cars and electric cars. Along with the life cycle of automobiles, the lithium-ion batteries installed in them are expected to be disposed of in large quantities in the future. It is desired to reuse these materials as resources. Against this background, a technology has been proposed for recovering and reusing valuable metals (Ni, Co, Cu, etc.) contained in waste batteries through a pyrometallurgical process in which the entire amount of waste batteries is melted in a high-temperature furnace.

In addition to valuable metals, waste lithium ion batteries contain impurity elements such as carbon (C), aluminum (Al), fluorine (F), and phosphorus (P). Therefore, when recovering valuable metals from waste batteries, it is necessary to remove these impurity elements. In the pyrometallurgy process, combustible components (C, etc.) in impurity elements are burned off, the remaining impurity elements are oxidized, and valuable metals are reduced and alloyed to separate them from the oxidized impurities that have turned into slag. It is being Patent Documents 1 and 2 are cited as documents disclosing a pyrometallurgical process for recovering valuable metals (Ni, Co, Cu, etc.) from waste lithium ion batteries.

Patent Document 1 describes a method for recovering cobalt from a lithium ion battery containing aluminum and carbon, which includes the steps of preparing a bath furnace equipped with means for injecting _O2 , and adding CaO and carbon as a slag forming agent. preparing a metallurgical charge comprising a lithium ion battery; feeding the metallurgical charge to a furnace with oxygen injection, whereby at least some cobalt is reduced and collected in the metal phase; A method including a step of separating slag from a metal phase by pouring is disclosed (Claim 1 of Patent Document 1). Further, Patent Document 2 describes a method for recovering valuable metals containing nickel and cobalt from waste lithium ion batteries, which includes a melting step of melting the waste battery to obtain a melt, and an oxidation treatment of the waste battery. A method is disclosed that includes an oxidation step, a slag separation step of separating slag from the melt to recover an alloy containing valuable metals, and a dephosphorization step of separating phosphorus contained in the alloy (Patent Document Claim 2).

By the way, in the pyrometallurgical process for recovering valuable metals, it is important to control the degree of redox in the process of reducing and alloying valuable metals (melting process). For example, if the degree of reduction is adjusted to be too weak (the degree of oxidation is high), valuable metals will be oxidized and incorporated into the slag, making it difficult to recover them as molten alloy. Therefore, in order to increase the recovery rate of valuable metals, it is necessary to adjust the degree of reduction to a certain degree.

On the other hand, it is not preferable to adjust the degree of reduction to be excessively high (to reduce the degree of oxidation) because it will actually reduce the recovery rate of valuable metals. For example, if the degree of reduction is too high, impurity carbon may remain without being oxidized and removed, which may impede separation of alloy (valuable metal) and slag (impurities other than carbon). In addition, if the degree of reduction is too high, impurities other than carbon may be incorporated into the valuable metal alloy, since this prevents impurities other than carbon from being oxidized and turned into slag. In particular, among impurities, phosphorus (P) has the property of being relatively easily reduced, so if the degree of reduction is adjusted to be high, phosphorus will be incorporated into the valuable metal alloy without being turned into slag. Therefore, in order to recover valuable metals stably and efficiently, it is desirable to appropriately control the degree of redox in the melting process.

In the conventional method of recovering valuable metals using the pyrometallurgical process, a reducing agent such as graphite was added to promote the reduction of valuable metals during the reduction and alloying process (melting process). . In addition, the dust generated during the oxidation roasting process that precedes the melting process was discharged outside the furnace and discarded.

Patent No. 5818798 Patent No. 5853585

However, upon investigation by the present inventors, it was found that the dust discharged in the oxidation roasting process mainly contains carbon, and that this can be effectively used as a reducing agent in the subsequent melting process. It was also found that dust contains a considerable amount of valuable metals, and by using dust as a reducing agent, it is possible to increase the recovery rate of the final valuable metals.

The present invention was completed based on such knowledge, and an object of the present invention is to provide a method that can effectively utilize the dust discharged in the oxidation roasting process to recover valuable metals at low cost and efficiently. do.

The present invention includes the following aspects (1) to (3). Note that in this specification, the expression "~" includes numerical values at both ends thereof. That is, "X to Y" is synonymous with "more than or equal to X and less than or equal to Y."

(1) A method for recovering valuable metals from waste lithium ion batteries, comprising:
an oxidative roasting step of oxidizing and roasting the waste lithium ion battery to obtain an oxidized roasted product;
a melting step of melting the oxidized roasted product to obtain a melt;
a slag separation step of separating slag from the melt and recovering an alloy containing valuable metals,
A method of collecting dust generated in the oxidation roasting step and adding at least a part of the collected dust to the object to be processed in the melting step.

(2) The method of (1) above, wherein the valuable metal is at least one selected from cobalt (Co), nickel (Ni), and copper (Cu).

(3) The method of (1) or (2) above, wherein the heating temperature in the melting step is 1300°C or more and 1500°C or less.

According to the present invention, a method is provided in which valuable metals can be recovered at low cost and efficiently by effectively utilizing the dust discharged in the oxidation roasting process.

FIG. 2 is a process diagram showing an example of the flow of a method for recovering valuable metals.

Hereinafter, a specific embodiment of the present invention (hereinafter referred to as "this embodiment") will be described in detail. Note that the present invention is not limited to the following embodiments, and various changes can be made without departing from the gist of the present invention.

≪1. Overview of valuable metal recovery methods≫
The valuable metal recovery method of this embodiment is a method for recovering valuable metals contained in waste lithium ion batteries. Methods for recovering valuable metals from waste batteries are broadly classified into pyrometallurgical smelting processes and hydrometallurgical smelting processes. The recovery method of this embodiment mainly relates to a pyrometallurgical smelting process.

Waste lithium-ion batteries include used lithium-ion batteries, defective products generated during the manufacturing process of positive electrode materials that make up batteries, residues from the manufacturing process, waste materials generated during the battery manufacturing process, and other waste materials such as these. Contains mixtures. Waste batteries contain valuable metals (Ni, Co, Cu, etc.). The amount of each valuable metal contained in the waste battery is not particularly limited, but for example, copper (Cu) may be contained in an amount of 10% by mass or more, and may be contained in an amount of 20% by mass or more.

FIG. 1 is a process diagram showing an example of the flow of a method for recovering valuable metals. As shown in FIG. 1, the recovery method of the present embodiment includes a pretreatment step S1 in which the electrolyte and outer can of the waste battery are removed as necessary, and the battery contents are pulverized as necessary to form a pulverized product. pulverizing step S2, oxidizing roasting step S3 of oxidizing and roasting the pulverized material to obtain an oxidized roasted material, melting step S4 of melting and alloying the oxidized roasted material, and separating slag from the melt to produce a valuable product. The method includes a slag separation step S5 of recovering an alloy containing metal.

≪2. About each step of the collection method≫
Each step of the valuable metal recovery method of this embodiment will be specifically explained below.

[Pre-treatment process]
In the recovery method of this embodiment, a pretreatment step S1 may be provided as necessary. The pretreatment step S1 is performed for the purpose of preventing the waste lithium ion battery from exploding or rendering it harmless, removing the outer can, and the like. A waste battery such as a used lithium ion battery is a closed system and contains an electrolyte and the like inside. If pulverization is performed in that state, there is a risk of explosion and it is dangerous, so it is desirable to perform discharge treatment or electrolyte removal treatment by some method. By removing the electrolytic solution and the outer can in the pretreatment step S1, safety can be improved and the recovery rate of valuable metals (Ni, Co, Cu, etc.) can be increased.

The specific method of the pretreatment step S1 is not particularly limited. For example, the electrolyte inside the battery may be removed by physically making a hole in the battery with a needle-like cutting edge to flush out the electrolyte inside the battery. Alternatively, the waste battery may be heated as it is, and the electrolyte may be burned to render it harmless.

The outer can is often made of metal such as aluminum (Al) or iron (Fe). By going through the pretreatment step S1, the outer can can be easily recovered as metal. For example, by pulverizing the removed outer can and then sieving it using a sieve shaker, the aluminum and iron contained in the outer can can be recovered. Aluminum easily becomes powder even if it is lightly crushed, so it can be efficiently recovered. In addition, the iron contained in the outer can can be recovered by magnetic sorting.

[Crushing process]
In the recovery method of this embodiment, a crushing step S2 may be provided as necessary. In the pulverization step S2, the battery contents obtained through the pretreatment step S1 are pulverized to obtain a pulverized product. By providing the crushing step S2, the reaction efficiency in the subsequent step can be increased, thereby increasing the recovery rate of valuable metals (Ni, Co, Cu, etc.). The specific pulverization method of the pulverization step S2 is not limited. For example, a method of pulverizing the battery contents using a known pulverizer such as a cutter mixer can be mentioned.

[Oxidation roasting process]
In the oxidative roasting step S3, the pulverized product is oxidized and roasted to obtain an oxidized roasted product. By oxidizing and roasting, thermally decomposed components such as carbon (C) contained in the battery contents can be burned and removed. Further, impurities other than carbon (P, Fe, Mn, Al, etc.) can be made into oxides, which can be separated and removed from valuable metals as slag in a subsequent process. If the pretreatment step S1 and/or the pulverization step S2 are provided, the waste lithium ion battery (battery contents, pulverized material) obtained through each of the above steps becomes the object of oxidative roasting.

Since dust is generated during the oxidation roasting process, this dust is collected and effectively used in the subsequent melting process. That is, waste lithium ion batteries contain a large amount of carbonaceous components such as carbon and organic components. For example, carbon is often used in negative electrodes. Furthermore, polypropylene is used for the separator, and plastic is used for part of the exterior material. These carbonaceous components (carbon, organic components) are burned and removed by oxidative roasting, but some of them are incompletely burned and soot (carbon) is generated. This soot is discharged outside the furnace and collected as dust. In addition, some of the metal components contained in the waste lithium-ion batteries are volatilized and discharged to the outside of the furnace together with soot. Therefore, the collected dust contains metal components such as valuable metals as well as soot. Dust may be collected by a known method. For example, the dust may be discharged out of the furnace along with the exhaust gas, and the dust may be separated and recovered from the exhaust gas using a dust collector.

In the oxidative roasting step S3, it is preferable to heat (oxidative roasting) at a temperature of 700° C. or higher. By setting the oxidation roasting temperature to 700° C. or higher, the efficiency of removing impurities contained in the battery can be further increased. On the other hand, the oxidative roasting temperature is preferably 900°C or lower. Thereby, thermal energy costs can be suppressed and processing efficiency can be increased.

The oxidative roasting step S3 is preferably performed in the presence of an oxidizing agent. As a result, carbon (C) among impurities contained in the battery contents can be efficiently burned and removed, and other impurities such as aluminum (Al) can be oxidized and turned into slag. In particular, when carbon is burned and removed, the molten fine particles of valuable metal generated in the subsequent melting step S4 are easily aggregated and integrated without physical hindrance. Therefore, the valuable metal obtained as a melt can be easily recovered as an integrated alloy. The main elements that make up waste batteries have different affinities with oxygen, and generally, aluminum (Al) > lithium (Li) > carbon (C) > manganese (Mn) > phosphorus (P) > iron. (Fe)>Cobalt (Co)>Nickel (Ni)>Copper (Cu) is more likely to be oxidized in this order.

The oxidizing agent is not particularly limited as long as it can burn off carbon and oxidize other impurities. However, oxygen-containing gases such as air, pure oxygen, oxygen-enriched gases, etc., which are easy to handle, are preferred. The amount of the oxidizing agent introduced can be, for example, about 1.2 times the chemical equivalent required for oxidizing each substance to be oxidized.

In the oxidation roasting step S3, a known roasting furnace can be used. However, it is preferable to use a furnace (preliminary furnace) different from the melting furnace used in the melting step S4, and to carry out the process in the preparatory furnace. As the roasting furnace, any type of kiln capable of carrying out oxidation treatment by supplying oxygen while roasting the pulverized material inside the kiln can be used. As an example, a conventionally known rotary kiln or tunnel kiln (hearth furnace) can be suitably used.

[Melting process]
In the melting step S4, the oxidized roasted material is melted to obtain a molten material consisting of an alloy and slag. Through the melting process, impurities other than carbon (P, Fe, Mn, Al, etc.) are incorporated into the slag as oxides. On the other hand, valuable metals (Ni, Co, Cu, etc.) that are difficult to form oxides are melted and integrated into a molten alloy, which is recovered in a subsequent process.

In the melting step S4, at least a portion of the dust collected in the oxidative roasting step S3 is added to the object to be treated (the oxidized roasted material or the molten material). By adding dust, the addition of reducing agents such as graphite can be eliminated or reduced, resulting in cost savings. That is, dust has soot (carbon) as its main component and functions as a reducing agent. By adding dust to the workpiece in the melting step S4, reduction melting is performed in the presence of carbon contained in the dust, and oxides of valuable metals (Ni, Co, Cu, etc.) contained in the workpiece are easily removed. And it is efficiently returned. Thermite method using metal powder such as aluminum is known as a reduction method, but reduction using carbon has the advantage of being extremely safe compared to the thermite method.

Furthermore, dust contains metal components such as valuable metals in addition to soot (carbon). In fact, according to the inventors' investigation, dust contains about 60% by mass of carbon and about 40% by mass of other components such as nickel (Ni) and cobalt (Co). It contained. Therefore, by adding dust in the melting step S4, the valuable metals (Ni, Co, Cu, etc.) discharged as dust can be returned to the valuable metal alloy, making it possible to improve the recovery rate of the valuable metals.

A part of the collected dust may be added to the object to be processed in the melting step S4, or all of it may be added. The amount of dust added should be adjusted to such an extent that valuable metals (Ni, Co, Cu, etc.) contained in the object to be treated can be melted and reduced, and impurities (P, Fe, Mn, Al, etc.) are not reduced. good. Specifically, the carbon content ratio in the dust may be analyzed in advance, and the amount of dust added may be determined based on the obtained carbon content and the required degree of reduction.

If necessary, a reducing agent other than dust may be added to the object to be processed in the melting step S4. That is, if the dust alone is insufficient to sufficiently reduce the valuable metals in the object to be treated, another reducing agent may be additionally added. Other reducing agents include, for example, graphite, which can reduce 2 moles of valuable metal oxide with 1 mole of carbon. Further, carbon sources such as hydrocarbons capable of reducing 2 to 4 moles of valuable metal oxides per mole of carbon and carbon monoxide capable of reducing 1 mole of valuable metal oxides per mole of carbon can be used.

In the melting step S4, flux may be added to the oxidized roasted product. The flux preferably contains an element that takes in impurity elements to form a basic oxide with a low melting point, and among these, one containing a calcium compound that is inexpensive and stable at room temperature is more preferred. Since phosphorus becomes an acidic oxide when oxidized, the more basic the slag formed by the treatment in the melting step S4, the more easily phosphorus is incorporated into the slag. Examples of calcium compounds include calcium oxide (CaO) and calcium carbonate (CaCO ₃ ).

Note that when adding flux, the above-mentioned reducing agent dust and/or carbon may be added in excess. In the absence of flux, excessive carbon addition may reduce the phosphorus compounds in the waste battery and contaminate the molten alloy with phosphorus. On the other hand, when a waste battery is melted in the presence of a flux, even if carbon is in excess, the flux takes in phosphorus compounds and prevents them from being mixed into the molten alloy.

In the melting step S4, flux components other than the calcium compound may be added. However, it is preferable to add the flux so that the ratio of the calcium component to the silicon component on an oxide basis (mass ratio SiO ₂ /CaO) in the slag after melting is 0.50 or less. Here, the ratio is the mass ratio of silicon dioxide to calcium oxide. Silicon components such as silicon dioxide are difficult to volatilize by heating in the melting step S4, and become acidic oxides when turned into slag. By reducing the silicon component relative to the calcium compound that forms the basic oxide, the slag becomes more basic, making it easier for the slag to take in phosphorus. That is, by adding flux so that the mass ratio of silicon dioxide to calcium oxide is small, it is possible to promote the incorporation of phosphorus into the slag and to suppress the mixing of phosphorus into the alloy.

Further, it is preferable to add the flux so that the ratio of calcium oxide to aluminum oxide in the slag after melting (mass ratio CaO/Al ₂ O ₃ ) on an oxide basis is 0.30 or more and 2.00 or less. The flux may be added so that the mass ratio CaO/Al ₂ O ₃ is 0.40 or more, or may be added so that the mass ratio CaO/Al ₂ O ₃ is 1.90 or less. Aluminum oxide is a component that increases the slag melting point. Therefore, if there is a large amount of aluminum oxide in the melting step S4, a sufficient amount of calcium component is required to melt the aluminum oxide. Moreover, aluminum oxide is a component that forms an amphoteric oxide, and can be an acidic oxide or a basic oxide. Therefore, by adjusting the ratio of the amount of aluminum oxide to the amount of calcium compounds that form the basic oxide within a predetermined range, it is possible to appropriately control the melting of aluminum oxide and the acidity during melting. can be easily incorporated into the slag.

When adding flux, each mass ratio in the slag after melting may be adjusted by adjusting the amount of flux added, or by adjusting the concentration of components contained in the flux. Further, flux may be added so that the calcium oxide contained in the slag after melting is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 21% by mass or more, based on the oxide. This makes it possible to increase the recovery rate of valuable metals, especially cobalt (Co). On the other hand, from the viewpoint of economy, flux may be added so that the calcium oxide content in the slag after melting is 80% by mass or less, or 60% by mass or less. Note that the mass of each component on the "oxide basis" is the mass of the oxide, assuming that each component contained in the slag after melting has all changed to an oxide.

The heating temperature (melting temperature) in the melting process is not particularly limited. However, the melting temperature is preferably 1300°C or higher, more preferably 1350°C or higher. By melting at 1300° C. or higher, valuable metals are sufficiently melted, and the fluidity of the molten alloy becomes sufficiently high. Therefore, the separation efficiency between the molten alloy (valuable metal) and the slag (impurities) is improved in the slag separation step S5, which will be described later. On the other hand, if the melting temperature exceeds 1500° C., thermal energy is wasted, and refractories such as the crucible and furnace walls are also severely worn out, which may reduce productivity. Therefore, it is preferable that the melting temperature is 1500°C or less.

Although dust, exhaust gas, etc. may be generated during the melting process, these can be made harmless by performing conventionally known exhaust gas treatment.

[Slag separation process]
In the slag separation step S5, slag is separated from the molten material obtained in the melting step S4, and a molten alloy containing valuable metals is recovered. Since the slag and alloy contained in the melt have different specific gravity, it is possible to recover each of the slag and alloy by utilizing the difference in specific gravity. The processing method for recovering valuable metals from the alloy is not particularly limited, and may be performed by known methods such as neutralization treatment and solvent extraction treatment. In the case of alloys consisting of cobalt (Co), nickel (Ni), and copper (Cu), valuable metals are leached out with an acid such as sulfuric acid (leaching process), and then copper is extracted by solvent extraction (extraction process). ), an example of a method in which the remaining nickel and cobalt solution is used to produce a positive electrode active material in a battery manufacturing process.

As explained above, in the method of this embodiment, the dust emitted in the oxidation roasting process is not disposed of, but is used as a reducing agent in the melting process, thereby effectively converting alloys containing valuable metals. can be obtained. Furthermore, since the addition of a reducing agent such as graphite can be eliminated or reduced, it also leads to cost reduction. Furthermore, valuable metals discharged as dust can be returned to the alloy, and the recovery rate of valuable metals can be improved. As a result, valuable metals can be recovered at low cost and efficiently.

EXAMPLES Hereinafter, the present invention will be explained in more detail using Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Pre-treatment process>
First, as waste lithium ion batteries, 18650 type cylindrical batteries, used prismatic batteries for automobiles, and defective products collected in the battery manufacturing process were prepared. Then, the waste lithium ion batteries are immersed in salt water and discharged, the moisture is removed, and the batteries are roasted in the air at a temperature of 260°C to decompose and remove the electrolyte and outer can. I got something. The main element composition of the battery contents was as shown in Table 1 below.

<Crushing process>
The obtained battery contents were pulverized using a pulverizer (trade name: Good Cutter, manufactured by Ujiie Seisakusho Co., Ltd.) to obtain a pulverized product.

<Oxidation roasting process>
The obtained pulverized product was put into a rotary kiln and oxidized and roasted in the atmosphere at 800° C. for 180 minutes to obtain an oxidized and roasted product.

This pulverized material was roasted by introducing air into a rotating rotary kiln, and the dust generated in the furnace was collected by a dust collection filter provided in the exhaust route. The main components in the dust were as shown in Table 2 below.

<Melting process>
Calcium oxide and silicon dioxide were added as a flux to the obtained oxidized roasted product, and a reducing agent was added to adjust the degree of redox, and these were mixed and charged into an alumina crucible. This was heated to 1400° C. by resistance heating and melted for 60 minutes to obtain a melt. Valuable metals were alloyed in the melt.

As the reducing agent, dust obtained from the oxidation roasting process was used in Example 1, and graphite fine powder was used in Comparative Example 1, and the carbonaceous components were added in the same amount. Further, the amount of the carbonaceous component was set to be the same molar amount as the total amount of each mole of copper, nickel, and cobalt contained in the oxidized roasted product.

<Slag separation process>
The slag was separated from the obtained melt by utilizing the difference in specific gravity, and the alloy was recovered.

The recovered alloy was also subjected to elemental analysis using an ICP analyzer (manufactured by Agilent Technologies, Inc., Agilent 5100SUDV) to determine the contents of copper, nickel, and cobalt. Next, the determined content was compared with the main element composition of the battery contents obtained in the pretreatment step, and the recovery rate of copper, nickel, and cobalt, which are to be recovered as valuable metals, was calculated. The results obtained are shown in Table 3 below.

As explained above, in Example 1, the dust discharged from the oxidation roasting process was used as a reducing agent in the melting process, so there was no need to use the fine graphite powder used as the reducing agent in Comparative Example 1. , resulting in cost reduction. Further, as can be seen from Table 3, in Example 1, the valuable metal discharged as dust could be returned to the alloy, so the recovery rate of the valuable metal could be improved.

Claims (3)

A method for recovering valuable metals from waste lithium ion batteries, the method comprising:
an oxidative roasting step of oxidizing and roasting the waste lithium ion battery to obtain an oxidized roasted product;
a melting step of melting the oxidized roasted product to obtain a melt;
a slag separation step of separating slag from the melt and recovering an alloy containing valuable metals,
A method of collecting dust generated in the oxidation roasting step and adding at least a part of the collected dust to the object to be processed in the melting step. The method according to claim 1, wherein the valuable metal is at least one selected from cobalt (Co), nickel (Ni), and copper (Cu). The method according to claim 1 or 2, wherein the heating temperature in the melting step is 1300°C or more and 1500°C or less.

Images