JP7540199B2 - Method for preparing molten raw material and method for recovering valuable metals - Google Patents

Description

The present invention relates to a method for preparing molten raw materials and a method for recovering valuable metals.

There are two main methods for recycling used or in-process defective batteries, such as lithium-ion batteries (hereafter referred to as waste batteries), and recovering the valuable metals they contain: dry and wet methods.

In the dry process, crushed waste batteries are melted and the valuable metals to be recovered are separated and recovered from other metals with low added value by utilizing the difference in oxygen affinity between them. In other words, low added value elements such as iron are oxidized as much as possible to produce slag, and valuable materials such as cobalt are recovered as alloys by minimizing oxidation.

For example, Patent Document 1 discloses a valuable metal recovery method that includes a dry method. According to Patent Document 1, this technology reduces the slag viscosity during dry processing of waste batteries such as lithium-ion batteries, enabling operation at low temperatures, and ensures separation of the slag and alloys to efficiently recover valuable metals.

JP 2012-224876 A

Now, the reduction melting process in the valuable metal recovery method can be carried out, for example, using a melting furnace. However, for example, metal composites such as waste batteries have a large overall volume relative to the valuable metals, and simply charging them into the melting furnace as is may not be enough to increase the weight of molten raw material that can be charged per unit capacity of the melting furnace (hereinafter also referred to as the furnace loading bulk density).

In addition, if the bulk density of the material packed in the furnace is low, the heat transfer of the molten raw material in the reduction furnace will deteriorate, and it will take a long time to raise the temperature to the specified temperature required for reduction melting, which may make it impossible to carry out an efficient reduction melting process.

The present invention has been proposed in light of these circumstances, and aims to provide a method for preparing molten raw material that can perform efficient reduction melting treatment even for molten raw material in which the overall volume of the metal complex is large relative to the valuable metal.

The inventors of the present invention have conducted extensive research to solve the above-mentioned problems. As a result, they discovered that the above problems could be solved by mixing the molten raw material with a flux containing calcium oxide to form a granulated product, which led to the completion of the present invention.

(1) The first aspect of the present invention is a method for preparing a molten raw material to be used in a reduction melting process in which a roasted product of a metal composite containing a valuable metal is reduced and melted as the molten raw material to obtain slag and an alloy containing the valuable metal. The method for preparing the molten raw material includes mixing the roasted product with a flux containing calcium oxide, and granulating the resulting mixture to obtain a granulated product.

(2) The second aspect of the present invention is a method for preparing a molten raw material according to the first invention, in which a granulated material is obtained by applying a pressure of 2 t/cm or more to the mixture.

(3) The third aspect of the present invention is a method for preparing a molten raw material according to the first or second invention, in which the metal composite contains waste lithium-ion batteries.

(4) A fourth aspect of the present invention is a method for recovering valuable metals, which comprises the steps of: roasting the metal composite to obtain a roasted product as a molten raw material; mixing the roasted product with a flux containing calcium oxide and granulating the resulting mixture to obtain a granulated product; and reducing and melting the granulated product as a molten raw material to obtain slag and an alloy containing the valuable metal. The method comprises the steps of: roasting the metal composite to obtain a roasted product; mixing the roasted product with a flux containing calcium oxide and granulating the resulting mixture to obtain a granulated product; and reducing and melting the granulated product as a molten raw material to obtain slag and an alloy containing the valuable metal.
It is.

According to the present invention, efficient reduction melting treatment can be performed.

FIG. 1 is a process diagram showing an example of the flow of a valuable metal recovery method.

A specific embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described in detail below. Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

≪1. Overview of the method for preparing molten raw materials≫
The method for preparing a molten raw material according to the present embodiment is a method for preparing a raw material before melting (molten raw material) to be subjected to a melting treatment, which is a target of a reduction melting treatment in a valuable metal recovery method for recovering mainly valuable metals. Here, in the valuable metal recovery method, a metal composite containing a valuable metal is roasted to obtain a roasted product, and the roasted product is reduced and melted as a molten raw material to be subjected to the melting treatment to obtain slag and an alloy containing the valuable metal.

Specifically, the method for preparing the molten raw material according to this embodiment is characterized in that the roasted metal composite used as the molten raw material is mixed in advance with a flux containing calcium oxide to obtain a mixture (mixing step S41), and the mixture is granulated to obtain a granulated product (granulation step S42).

In this way, by mixing the molten raw material with flux and granulating it to form granules, and then charging these granules into a melting furnace, it is possible to increase the amount of material loaded into the melting furnace and increase the bulk density loaded into the furnace. In addition, by mixing the roasted material with flux to form granules, the adhesion between the roasted material and the flux in the granules is increased, and the thermal conductivity to the roasted material during the reduction melting process is also improved. This increases the speed at which the temperature is raised to the specified temperature required for reduction melting (heating rate), allowing for an efficient reduction melting process.

In this specification, the term "granulated material" refers to a material that has been granulated by bonding together roasted metal composites, and has at least enough hardness to maintain its shape.

These granulated materials are obtained by mixing the roasted material and flux and granulating them, and have a degree of hardness that allows them to maintain their shape. Therefore, for example, they can be transported on a conveyor or the like while maintaining their shape and not collapsing. In this way, the molten raw material processed by the method for preparing molten raw material according to this embodiment is easy to handle.

Furthermore, this embodiment is characterized in that the roasted material is mixed with a flux containing calcium oxide. By adding a flux containing calcium as a main component to the molten raw material, the flux containing calcium as a main component functions as a binder, and the hardness of the granulated material can be increased. However, if a flux containing calcium carbonate as a main component is added to the molten raw material, it will thermally decompose in a short time during the reduction melting process and generate carbon dioxide gas. If the molten material is in a foamed state like this, the amount of raw material charged must be controlled taking into account the amount of swelling of the upper surface of the molten material due to foaming. For example, if the amount of raw material charged is reduced, production efficiency will decrease. Also, if the molten material is in a foamed state, there is a risk that the molten material will overflow from the opening on the upper surface of the melting furnace.

Therefore, by mixing the roasted material with a flux containing calcium oxide, it is possible to effectively prevent the molten material from becoming foamy, thereby preventing a decrease in production efficiency due to the molten material becoming foamy.

The molten raw materials to be treated include, for example, waste materials resulting from the deterioration of automobiles or electronic devices, scrap lithium-ion batteries generated as the lithium-ion batteries reach the end of their lifespan, or metal composites containing waste batteries such as defective products produced during the battery manufacturing process.

Below, we will explain the method for preparing the molten raw material, along with each step of the valuable metal recovery method, using as an example the case in which the molten raw material obtained from waste lithium-ion batteries is the target of processing.

In the present invention, the molten raw material to be treated is not limited to the roasted product of a metal composite containing waste batteries. However, waste batteries contain many non-valuable metals derived from battery packs and the like in addition to valuable metals derived from electrodes, so the volume of the entire metal composite is large compared to the valuable metals. This can easily lead to a problem that the bulk density of the material packed in the furnace cannot be increased and efficient reduction melting treatment cannot be performed. Therefore, the benefits of the present invention can be preferably enjoyed by treating roasted products of a metal composite containing waste batteries.

≪2. Each step of the valuable metal recovery method≫
The method for preparing the molten raw material will be described below together with the valuable metal recovery method that is the premise of the method.

Specifically, the valuable metal recovery method includes a waste battery pretreatment process S1 in which the electrolyte and outer cans are removed from the waste batteries as shown in FIG. 1, a crushing process S2 in which the waste batteries subjected to the waste battery pretreatment process S1 are crushed to obtain a crushed product, a roasting process S3 in which the crushed product is roasted to obtain a roasted product, a molten raw material preparation process S4 in which the roasted product is mixed with a flux containing calcium oxide, the resulting mixture is granulated to obtain a granulated product, and a reduction melting process S5 in which the granulated product is reduced and melted as the molten raw material to obtain slag and an alloy containing valuable metals.

[Waste battery pretreatment process]
In the waste battery pretreatment process S1, the electrolyte and the outer can are removed from the waste battery. Since the waste battery contains the electrolyte and the like, there is a risk of explosion if the waste battery is crushed in its current state. Furthermore, the outer can contained in the waste battery often contains gold, aluminum, iron, etc., and such aluminum, iron, etc. can be relatively easily recovered as valuable metals as they are. By removing the electrolyte and the outer can from the battery through this process, safety can be improved and the recovery productivity of valuable metals such as copper, nickel, and cobalt can be increased.

The specific method for the waste battery pretreatment process S1 is not particularly limited, but examples include a method in which the waste battery is physically opened with a needle-shaped blade and the electrolyte and outer can are removed. In addition, the waste battery may be heated to burn the electrolyte and render it harmless.

In addition, in the waste battery pretreatment process S1, when recovering aluminum or iron contained in the outer can, for example, the removed outer can can be crushed and then sieved using a sieve shaker. Aluminum can be efficiently recovered from the outer can because it easily becomes powder even with light crushing. In addition, iron can be recovered from the outer can by sorting using magnetic force.

[Crushing process]
In the pulverization step S2, the waste batteries (metal composite) subjected to the waste battery pretreatment step S1 are pulverized to obtain a pulverized material, which can increase the reaction efficiency in the reduction melting step S5 described later and increase the recovery rate of valuable metals such as copper, nickel, and cobalt.

The crushing device used in the crushing process is not particularly limited, and crushing can be performed using a conventionally known crusher such as a cutter mixer.

[Roasting process]
In the roasting step S3, the crushed waste battery material is roasted to obtain a roasted material. If the melting raw material contains carbon, the aggregation of metal is hindered in the reducing and melting step S5 described later, and the separability of metal and slag is reduced, resulting in a reduction in the recovery rate of valuable metals. Therefore, the crushed material is roasted to oxidize and remove the carbon contained in the crushed material, thereby effectively separating the metal and slag in the reducing and melting step S5 described later, thereby improving the recovery rate of valuable metals.

In addition, in the roasting process S3, at least the aluminum of the metals contained in the pulverized material is oxidized. In the reduction melting process S5 described below, the aluminum contained in the pulverized material can be separated from the metal as slag.

The conditions for the roasting process are not particularly limited, but it is preferable to carry out the roasting process at a degree of oxidation that can oxidize at least the carbon and aluminum contained in the pulverized material. Specifically, the roasting temperature is preferably 700°C or higher. The upper limit of the roasting temperature is not particularly limited, but is preferably 900°C or lower. If the roasting temperature is too high, some of the iron and other materials used mainly in the outer shells of the waste batteries will adhere to the inner walls of the roasting furnace body of a kiln, etc., which may hinder smooth operation or lead to deterioration of the kiln itself, and is therefore undesirable.

In addition, during the roasting process, it is preferable to introduce an appropriate amount of oxidizing agent into the furnace to adjust the degree of oxidation. There are no particular limitations on the oxidizing agent, but it is preferable to use an oxygen-containing gas such as air, pure oxygen, or oxygen-enriched gas, because of ease of handling. The amount of oxidizing agent introduced can be, for example, about 1.2 times the chemical equivalent required for oxidation of each substance to be subjected to the oxidation process.

[Melted raw material preparation process]
The molten raw material preparation step S4 is a step of preparing a raw material (molten raw material) to be subjected to a reduction melting treatment in the next reduction melting step S5. The mixture is mixed with the flux containing the powder to obtain a mixture (mixing step S41), and the mixture is granulated to obtain a granulated material (granulation step S42).

In this way, prior to the reduction melting process, the roasted material to be melted and the flux are mixed and granulated to obtain a granulated material containing the roasted material and flux. Then, by charging the melting raw material in the form of such a granulated material into a melting furnace and subjecting it to the reduction melting process, it is possible to increase the amount of material filled into the furnace and the bulk density of the material, and also to improve the thermal conductivity to the roasted material, enabling an efficient reduction melting process.

The mixing process S41 and the granulation process S42 included in the molten raw material preparation process S4 are described below.

(Mixing process)
In the mixing step S41, the roasted product obtained in the roasting step S3 is mixed with a flux containing calcium oxide to obtain a mixture. Conventionally, flux is generally added to a melting furnace during a reducing and melting process in order to dissolve and remove slag. In the method for preparing a molten raw material according to the present embodiment, the roasted product is mixed with calcium oxide flux to obtain a mixture prior to the reducing and melting process, and the mixture is granulated in a granulation step S42 to be described later to produce granules.

In addition, by including a flux containing calcium oxide in the granules, it is possible to effectively prevent the molten material from becoming foamy, thereby preventing a decrease in production efficiency due to the molten material becoming foamy. Furthermore, the strength characteristics of the resulting granules are improved, and the amount of material filled into the furnace and the filling bulk density can be more effectively increased.

The lower limit of the mixing ratio of flux containing calcium oxide to the roasted product is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, per 100 parts by mass of roasted product in the mixture. The upper limit of the flux content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, per 100 parts by mass of roasted product in the mixture.

In addition, the flux itself functions as a binder. Therefore, by mixing the roasted material with the flux and granulating the resulting mixture, it is possible to effectively obtain a granulated material that is bound together.

When mixing the roasted material and the flux, various mixers such as a Henschel mixer can be used. As mentioned above, the flux itself functions as a binder, so water or a binder is not required. In addition, granules obtained without mixing water or a binder do not require a process for drying the granules, which is advantageous in terms of operating costs.

When carbon is used as a reducing agent in the reduction melting step S5 described below, carbon may be included in the mixture together with the flux.

(Granulation process)
In the granulation step S42, the mixture obtained in the mixing step S41 is granulated to obtain a granulated product. Specifically, for example, a granulator is used to granulate the mixture obtained by applying a predetermined pressure (linear pressure) capable of binding the mixture together, thereby obtaining a granulated product having a hardness sufficient to maintain its shape.

The pressure (linear pressure) applied when granulating the mixture is not particularly limited, but the lower limit is preferably 1.0 t/cm or more, more preferably 1.5 t/cm or more, and even more preferably 2.0 t/cm or more. There is no particular upper limit, but if it exceeds 4.0 t/cm, it will not be possible to increase the bulk density packed in the furnace, so it is preferably 4.0 t/cm or less.

In the granulated material obtained in this manner, the flux functions as a binder, and the pressure (linear pressure) applied during granulation results in a granulated material that is bound together. In addition, because the granulated material is in the form of a granule, the adhesion between the roasted material and the flux in the granulated material is increased, improving the thermal conductivity of the roasted material.

[Reduction melting process]
In the reduction melting step S5, the granulated material is reduced and melted as a melting raw material to obtain slag and an alloy containing valuable metals. The reduction melting step S5 aims to recover the reduced material as an integrated alloy by leaving unnecessary oxides such as aluminum oxidized in the roasting step S3 as oxides, while reducing and melting oxides of valuable metals such as copper oxidized in the roasting step S3. The alloy obtained as a molten material is also called "molten alloy".

In this embodiment, in the melting raw material preparation step S4, prior to reducing and melting the melting raw material, the mixture obtained by mixing the melting raw material and the flux is granulated to obtain a granulated material. Therefore, by charging this granulated material into the melting furnace as the melting raw material, the amount of material filled into the melting furnace can be increased and the bulk density of the material filled in the furnace can be increased, and the amount of melting can be increased to perform an efficient reducing and melting process. In addition, since the granulated material is in the form of a granulated material, the adhesion between the roasted material and the flux in the granulated material is increased, and the thermal conductivity to the roasted material during the reducing and melting process can be improved. As a result, the speed at which the temperature is raised to a predetermined temperature required for reducing and melting (heating rate) is increased, the melting process time is shortened, and a more efficient reducing and melting process can be performed.

The reduction melting step S5 is preferably carried out in the presence of, for example, carbon or carbon monoxide. Carbon has the ability to easily reduce valuable metals such as copper, nickel, and cobalt, which are the targets of recovery, and is a reducing agent that can reduce, for example, two moles of valuable metal oxides, such as copper oxide and nickel oxide, with one mole of carbon. Reduction using carbon or carbon monoxide is also extremely safer than, for example, the thermite reaction, which uses metal powder, such as aluminum, as a reducing agent.

As carbon, in addition to artificial graphite and natural graphite, coal, coke, etc. can be used as long as there is no risk of contamination with impurities.

The temperature conditions (melting temperature) in the melting process are not particularly limited, but a temperature of 1300°C or higher and 1500°C or lower is preferable. If the melting temperature is lower than 1300°C, the fluidity of the molten alloy may deteriorate, and the efficiency of separating impurities and valuable metals may deteriorate. On the other hand, if the melting temperature is higher than 1500°C, thermal energy will be wasted and refractories such as crucibles will be rapidly worn out, which may reduce productivity. Therefore, it is preferable to set the melting temperature at 1500°C or lower.

The melting furnace may be a burner furnace having a burner or an electric furnace having a heating means using electricity, etc., but an electric furnace is preferable.

In the melting process, it is preferable to use a flux. By melting the reduced material using a flux, the slag containing oxides such as aluminum can be dissolved in the flux and removed. In this embodiment, since the granular material that is the melting raw material contains a predetermined amount of flux, it is not necessary to use a flux in the melting process.

When a flux is used in the melting process, it is preferable that the flux contains calcium as a main component, and for example, calcium oxide or calcium carbonate can be used. Furthermore, if calcium carbonate is used as the flux, the melt may become foamy, so it is preferable to use a flux containing calcium oxide. The flux used in the melting process may be the same as the flux contained in the granular material, or it may be different.

Sulfur may also be added to the alloy obtained in the reduction melting process before the alloy is recovered, making it brittle and easier to crush. Crushing the alloy increases its specific surface area, which improves its leachability in the hydrometallurgical process.

When phosphorus is contained in the melting raw material, phosphorus becomes an acidic oxide when oxidized, so the more basic the slag composition, the easier it is to remove phosphorus into the slag. The more calcium that becomes a basic oxide in the slag, the better, and the less silicon that becomes an acidic oxide, and it is particularly preferable that the mass ratio of silicon dioxide/calcium oxide in the slag is 0.5 or less. In addition, since the melting point of the slag increases when the proportion of aluminum oxide is large, a sufficient amount of calcium is required to melt the aluminum oxide, and it is particularly preferable that the mass ratio of calcium oxide/aluminum oxide in the slag is 0.3 to 2. This makes the slag basic, and phosphorus that forms an acidic oxide can be effectively removed. In addition, dust and exhaust gases may be generated in the melting process, but these can be rendered harmless by applying conventional exhaust gas treatment.

In this way, since phosphorus can be removed by the above-mentioned dry treatment process, when the recovered molten alloy is subjected to a hydrometallurgical process, the process can be simplified. At this time, it is also advantageous that the amount of material processed in this hydrometallurgical process is reduced by about 1/4 to 1/3 in mass ratio compared to the amount of waste batteries input. Therefore, by treating the dry process (waste battery pretreatment process S1 to reduction melting process S5) as a pretreatment in a broad sense, it is possible to obtain an alloy with fewer impurities (phosphorus) and significantly reduce the amount of material processed, making it industrially possible to combine the dry smelting process and the hydrometallurgical process.

The treatment in the hydrometallurgical process can be performed by known methods such as neutralization and solvent extraction, and is not particularly limited. For example, in the case of an alloy consisting of cobalt, nickel, and copper, valuable metals are leached with an acid such as sulfuric acid (leaching process), and then copper is extracted by solvent extraction or the like (extraction process), and the remaining solution containing nickel and cobalt is discharged to the positive electrode active material production process in the battery production process.

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

[Example 1]
The electrolyte and the outer can were removed from the waste lithium-ion batteries, which were mainly composed of copper, aluminum, and carbon, and further contained nickel, cobalt, iron, and lithium (waste battery pretreatment process), and the batteries were pulverized to obtain a pulverized product (pulverization process). The pulverized product was then roasted (roasting process), and 0.60 t of the roasted product obtained by oxidation treatment was added with 0.10 t of CaO (calcium oxide) as a flux, and mixed in a Henschel mixer to obtain a mixture of 0.70 t (mixing process). This mixture was pressed using a briquette machine having a roll with a diameter of 650 mm and a width of 100 mm under conditions of a linear pressure of 2.0 t/cm and a rotation speed of 3 rpm to obtain a granulated product (30 mm x 25 mm x 7.5 mm) (granulation process).

The granulated material was then transported by conveyor to a melting furnace (electric furnace) so that the charge volume was 60 L. From the weight and volume of the raw material charged at this time, the packing bulk density of the raw material charged into the furnace (hereinafter also referred to as the furnace packing bulk density) was calculated.

Next, electricity was applied to the melting furnace (electric furnace) with an average output of 130 kW to heat the charged raw materials to 1,400°C. The time required for this temperature increase was measured to determine the temperature increase rate.

The temperature was then raised to 1400°C and held at this state for 30 minutes while observing the condition of the top surface of the melt.

[Example 2]
The same procedure as in Example 1 was carried out except that the pressure conditions of the briquetting machine in the granulation step were set to a linear pressure of 3.0 t/cm.

[Comparative Example 1]
The same procedure as in Example 1 was carried out except that 0.16 t of CaCO ₃ (calcium carbonate) was added as a flux to 0.54 t of the sintered product obtained by the oxidation treatment, and the pressing conditions of the briquette machine were set to a linear pressure of 3.0 t/cm.

[Comparative Example 2]
The same procedure as in Example 1 was repeated except that 0.16 t of _CaCO3 (calcium carbonate) was added as a flux to 0.54 t of the sintered product obtained by the oxidation treatment, 1.0 wt% of water and 1.0 wt% of a binder (α-starch) were added to the mixed raw material in a weight ratio relative to the mixed raw material, and the briquetting machine was set to a linear pressure of 3 t/cm to pressurize the mixture, and the obtained granules were dried.

[Comparative Example 3]
The same procedure as in Example 1 was repeated, except that the mixture was not granulated and was charged directly into the melting furnace (electric furnace).

The amount of sintered material, amount of flux, amount of granulated material, and granulation line pressure for each example and comparative example are shown in Table 1. The furnace filling bulk density, heating rate, and presence or absence of foaming for each example and comparative example are shown in Table 2.

As can be seen from Tables 1 and 2, in Examples 1 and 2, in which the molten raw material was prepared from a granulated mixture of calcium oxide and flux and the granulated material was subjected to the reduction melting process, it was possible to increase the bulk density filled in the furnace, the heating rate was also high, and it was possible to effectively prevent the molten material from becoming foamy.

In addition, in Example 2, in which granulation was performed with a granulation line pressure of 3.0 t/cm, it was found that the bulk density packed in the furnace could be increased and the time required to raise the temperature to the specified temperature required for reduction melting could be further shortened.

On the other hand, in Comparative Examples 1 and 2 in which CaCO ₃ (calcium carbonate) was added as a flux to the sintered material obtained by oxidation treatment, the bulk density packed in the furnace and the heating rate were high like those in the Examples, but bubbles were observed in the molten material.

Furthermore, in Comparative Example 3, in which the mixture with flux containing calcium oxide was not granulated, the bulk density packed in the furnace could not be increased and the heating rate was also low, so the objective of the present invention, which is to perform an efficient reduction melting process, could not be achieved.

Claims (3)

A method for preparing a molten raw material to be subjected to a reduction and melting step in which a roasted product of a metal composite containing a valuable metal is reduced and melted as a molten raw material to obtain slag and an alloy containing the valuable metal, comprising:
The metal composite includes a waste lithium ion battery,
A granulation step of mixing the roasted product with a flux containing calcium oxide and granulating the resulting mixture by applying a pressure of 2 t/cm or more to obtain a granulated product.
Method for preparing molten raw materials. 2. The method for preparing a molten raw material according to claim 1, wherein in the granulation step, the roasted product and the flux are mixed to obtain a granulated product such that a content ratio of the flux is 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the roasted product in the mixture. A method for recovering valuable metals, comprising the steps of: reducing and melting a roasted product of a metal composite containing valuable metals as a melting raw material to recover the valuable metals;
The metal composite includes a waste lithium ion battery,
A roasting step of roasting the metal composite to obtain a roasted product;
a molten raw material preparation step of mixing the roasted product with a flux containing calcium oxide, and granulating the resulting mixture by applying a pressure of 2 t/cm or more to obtain a granulated product;
a reduction and melting step of reducing and melting the granulated material as a melting raw material to obtain slag and an alloy containing the valuable metal;
A valuable metal recovery method comprising the steps of:

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