Valuable metal recovery method

Abstract

Provided is a method for efficiently recovering a valuable metal from a waste lithium ion battery. The present invention is a method for recovering a valuable metal from a waste lithium ion battery, the method being characterized by comprising: an oxidizing roasting step (S3) in which a raw material including a waste lithium ion battery is subjected to an oxidizing roasting treatment; and a reduction step (S4) in which the obtained oxidized roasted product is reduced in the presence of carbon. The dust in the exhaust gas generated in the oxidizing roasting step (S3) is recovered by heat treatment at 600 DEG C or more and less than 1000 DEG C, and at least a portion of the recovered heat-treated dust is added to the object to be treated in the reduction step (S4). It is preferable that the temperature at which the dust is heat-treated is 900 DEG C or more and less than 1000 DEG C.

Description

Technical Field

[0001] The invention relates to a method for recovering valuable metals contained in waste lithium-ion batteries. Background Art

[0002] In recent years, lithium-ion batteries have become popular as secondary batteries with light weight and high output. As lithium-ion batteries, it is known that a negative electrode material in which a negative electrode active material such as graphite is fixed to a negative electrode collector composed of copper foil, a positive electrode material in which a positive electrode active material such as lithium nickelate or lithium cobaltate is fixed to a positive electrode collector composed of aluminum foil, a separator composed of a porous resin film of polypropylene, and an electrolyte solution containing an electrolyte such as lithium hexafluorophosphate (LiPF6) are enclosed in a metal outer can such as aluminum or iron.

[0003] One of the main uses of lithium-ion batteries is hybrid vehicles or electric vehicles. It is foreseeable that as the life cycle of the vehicle ends, the lithium-ion batteries carried by the vehicle will be discarded in large quantities. Many proposals have been made to recycle such used batteries or defective products generated during manufacturing (hereinafter referred to as "wasted lithium-ion batteries") as resources. As a method for recycling waste lithium-ion batteries, a dry smelting process in which waste batteries are completely melted in a high-temperature furnace has been proposed (for example, refer to Patent Document 1).

[0004] The method disclosed in Patent Document 1 is to add waste lithium-ion batteries containing any one or more of metallic iron, metallic aluminum and carbon to replace at least a part of the exothermic agent and / or the reducing agent in the reduction process after the charge (copper concentrate) and the slag forming agent are put into a copper smelting furnace for roasting.

[0005] In the electrolyte of commercially available lithium ion batteries, lithium hexafluoride phosphate is used as described above. Lithium hexafluoride phosphate is widely used for reasons such as high solubility in carbonates commonly used as electrolytes, high lithium ion dissociation, and low cost. In the waste lithium ion batteries formed by roasting the so-called 18650 type batteries as common cylindrical lithium ion batteries, phosphorus (P) is contained at a ratio of about 0.2 mass %, and in the waste lithium ion batteries formed by roasting the square type batteries for vehicles, phosphorus (P) is contained at a ratio of about 0.1 mass %. Moreover, the phosphorus content in the battery contents when the iron outer can is removed in the case of the 18650 type, and the phosphorus content in the battery contents when the aluminum outer can is removed in the case of the square type batteries is higher.

[0006] When waste lithium-ion batteries containing phosphorus are put into a high-temperature environment where alloys are always present, such as in a copper refining furnace, the phosphorus is distributed into the alloy, and eventually almost all of the phosphorus is mixed into the crude copper as an impurity. In the electrolytic treatment of crude copper based on a wet smelting process, about 70% of the phosphorus is distributed into the electrolyte. Therefore, when the electrolysis is carried out, there is a problem of an increase in the phosphorus concentration in the electrolyte. In order to reduce the phosphorus concentration in the electrolyte, it is necessary to newly set up a clean liquid process for removing phosphorus in the wet smelting process. However, in the wet smelting process, it is not enough to just collect copper. It is not easy to add a process in a way that does not affect the recovery rate of other recovery target elements, both technically and cost-wise. Therefore, it is required to effectively remove phosphorus in the dry smelting process, which is the front process of the wet smelting process.

[0007] For example, according to the method disclosed in Patent Document 2, the alloy obtained by melting the contents of the waste lithium-ion battery through oxidative roasting and reduction is partially sulfided, thereby, even if the contents contain a high concentration of phosphorus, phosphorus can be distributed to the residual alloy, and valuable metals such as copper, nickel, and cobalt can be recovered as sulfides with a low phosphorus content. However, in the case of oxidative roasting treatment near the lower limit of the temperature range specified by the method, the oxidation removal of carbon (C) in the oxidative roasting treatment is insufficient due to the grade of the waste lithium-ion battery to be treated. As a result, the separation of metal and slag in the reduction melting treatment is hindered, and the recovery rate of valuable metals sometimes decreases. Furthermore, since impurities such as iron and phosphorus are also reduced, the cost for removing impurities through subsequent processes increases.

[0008] In order to avoid such a problem, it is effective to perform oxidation roasting near the upper limit of the temperature range specified by the method described in Patent Document 2, but this not only consumes thermal energy costs, but also sometimes makes temperature control difficult. As a result, the oxidation roasted product is sintered, so that sometimes an effective roasting process cannot be performed.

[0009] As described above, in the prior art, it is difficult to achieve both the quality of the oxidative roasting product and the processing efficiency of the oxidative roasting process.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent document 1: Japanese Patent No. 5818798.

[0013] Patent document 2: Japanese Patent Application Publication No. 2018-197385. Summary of the invention

[0014] Problems to be solved by the invention

[0015] In the above-mentioned valuable metal recovery method, for example, the dust generated during the oxidation roasting process contains valuable metals to be recovered. In the past, such dust was discharged outside the furnace and discarded. The inventors believe that if the valuable metals in the dust that was previously discarded are recovered, the valuable metals can be recovered more cheaply.

[0016] The present invention has been accomplished based on such knowledge, and an object of the present invention is to provide a method capable of efficiently recovering valuable metals from waste lithium-ion batteries.

[0017] Means for solving problems

[0018] As described above, based on the knowledge that valuable metals can be recovered more cheaply by effectively utilizing dust containing valuable metals, thereby reducing recovery losses, the inventors discovered that, particularly when recovering dust, by heating the dust at a specific temperature, the carbon content of the dust is effectively reduced, thereby completing the present invention.

[0019] (1) The first invention of the present invention is a method for recovering valuable metals, which is a method for recovering valuable metals from waste lithium-ion batteries, wherein the method comprises: an oxidative roasting step, in which a raw material containing the waste lithium-ion batteries is subjected to an oxidative roasting treatment; and a reduction step, in which the obtained oxidative roasted product is reduced in the presence of carbon, dust in the exhaust gas generated in the oxidative roasting step is subjected to a heat treatment at a temperature of not less than 600° C. and less than 1000° C. for recovery, and at least a portion of the recovered heat-treated dust is added to the treated material in the reduction step.

[0020] (2) A second aspect of the present invention is a method for recovering valuable metals, wherein in the first aspect, the dust is heated at a temperature of 900°C or higher and lower than 1000°C.

[0021] (3) The third invention of the present invention is a method for recovering valuable metals, wherein in the first invention or the second invention, in the oxidizing roasting step, an oxidant of 1.5 times or more of the chemical equivalent of carbon in the raw material to be treated is introduced, and the oxidizing roasting treatment is carried out under a treatment temperature condition selected within the range of not less than 600°C and not more than 900°C, and the carbon grade of the obtained oxidizing roasted product is set to less than 1.0% by mass.

[0022] Effects of the Invention

[0023] According to the present invention, a method for efficiently recovering valuable metals from waste lithium-ion batteries can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is a process diagram showing an example of the flow of a valuable metal recovery method.

[0025] Figure 2 This is a diagram showing the results of subjecting dust discharged in an oxidation roasting process to heat treatment to verify the extent to which the carbon grade in the dust is reduced depending on the temperature of the heat treatment.

[0026] Figure 3 This is a graph showing how the temperature of the dust heating process affects the rate of removal of carbon in the dust. DETAILED DESCRIPTION

[0027] Hereinafter, a specific embodiment of the present invention (hereinafter referred to as "this embodiment") will be described in detail. It should be noted that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the present invention.

[0028] 《1. Overview of methods for recovering valuable metals》

[0029] The method for recovering valuable metals of the present embodiment is a method for recovering valuable metals contained in waste lithium-ion batteries containing phosphorus (P). When recovering valuable metals from waste lithium-ion batteries, a dry smelting process and a wet smelting process are performed. The method for recovering valuable metals of the present embodiment mainly involves a dry smelting process.

[0030] Waste lithium-ion batteries (hereinafter also referred to as "waste batteries") are a concept of waste materials in the manufacturing process of lithium-ion batteries, including used lithium-ion batteries, defective products generated in the manufacturing process of positive electrode materials constituting secondary batteries, residues within the manufacturing process, and scraps. In addition, waste lithium-ion batteries contain valuable metals such as copper (Cu), nickel (Ni), and cobalt (Co).

[0031] Figure 1 This is a process diagram showing an example of the flow of a valuable metal recovery method. Figure 1 As shown, the method for recovering valuable metals of this embodiment comprises: a waste battery pretreatment step S1, which removes the electrolyte and outer can of the waste lithium-ion battery; a crushing step S2, which crushes the contents of the battery to make a crushed material; an oxidizing roasting step S3, which oxidizes and roasts the crushed material; and a reducing step S4, which reduces the oxidized roasted material and alloys the valuable metals.

[0032] In particular, the method of this embodiment is characterized in that dust in the exhaust gas generated in the oxidizing roasting step S3 is heat-treated at a specific temperature for recovery, and at least a portion of the recovered dust after the heat treatment is added to the treated object in the reduction step S4 for treatment.

[0033] By using such a method, it is possible to reduce the recovery loss of valuable metals contained in waste lithium-ion batteries, and to recover valuable metals by a more inexpensive and efficient operation.

[0034] It should be noted that by performing a wet smelting process on an alloy containing valuable metals obtained by a dry smelting process, impurity components can be removed, and valuable metals such as copper, nickel, and cobalt can be separated and purified, and each can be recovered. As a treatment in a wet smelting process, it can be carried out by known methods such as neutralization treatment and solvent extraction treatment. For example, in the case of an alloy composed of copper, nickel, and cobalt, after leaching the valuable metals with an acid such as sulfuric acid (leaching process), copper, for example, is extracted by solvent extraction (extraction process), and the solution containing the residual nickel and cobalt is supplied to the positive electrode active material manufacturing process in the battery manufacturing process.

[0035] 《2. About each process of recycling method》

[0036] Hereinafter, each step of the valuable metal recovery method according to the present embodiment will be described in detail.

[0037] [Waste battery pre-treatment process]

[0038] The waste battery pre-treatment step S1 is carried out for the purpose of preventing the explosion of waste lithium-ion batteries or making them harmless, removing the outer can, etc. That is, the waste lithium-ion battery is a closed system with an electrolyte, etc. inside. Therefore, if it is crushed in this state, it is possible to explode and there is a danger. Therefore, it is necessary to implement a discharge treatment or an electrolyte removal treatment by any method. In addition, the outer can is mostly made of metal aluminum (Al) and iron (Fe), and this metal outer can can be relatively easily directly recovered as a valuable metal. In this way, by removing the electrolyte and the outer can in the waste battery pre-treatment step S1, safety can be improved, and the recovery productivity of valuable metals such as copper, nickel, and cobalt can be improved.

[0039] The specific method of the treatment in the waste battery pretreatment step S1 is not particularly limited. For example, the waste battery can be physically perforated with a needle-shaped knife tip to allow the electrolyte inside to flow out and be removed. Alternatively, the waste battery can be directly heated to burn the electrolyte for harmlessness.

[0040] When recycling aluminum and iron contained in the outer cans constituting waste batteries, the outer cans can be crushed and then sieved using a vibrating screen. In the case of aluminum, even light crushing can easily turn it into powder and can be effectively recycled. In addition, the iron contained in the outer can can be recovered by magnetic separation.

[0041] [Crushing process]

[0042] In the pulverizing step S2, the contents of the waste battery are pulverized to obtain a pulverized product. The treatment in the pulverizing step S2 is performed for the purpose of improving the reaction efficiency in the dry smelting process. By improving the reaction efficiency, the recovery rate of valuable metals such as copper, nickel, and cobalt can be increased.

[0043] The specific pulverization method in the pulverization step S2 is not particularly limited, and the pulverization can be performed using a conventionally known pulverizer such as a cutter mixer.

[0044] [Oxidation roasting process]

[0045] (About oxidation roasting treatment)

[0046] In the oxidation roasting step S3, the crushed material is subjected to oxidation roasting to obtain an oxidation roasted material. In the oxidation roasting step S3, carbon (C) contained in the contents of the waste battery is oxidized and removed, and the crushed material is treated at an oxidation degree that can oxidize at least aluminum contained in the crushed material. It should be noted that the main elements constituting the waste lithium-ion battery are generally easily oxidized in the order of aluminum (Al)>lithium (Li)>carbon (C)>manganese (Mn)>phosphorus (P)>iron (Fe)>cobalt (Co)>nickel (Ni)>copper (Cu) according to the difference in their affinity with oxygen.

[0047] In this way, in the oxidation roasting step S3, the carbon contained in the contents of the waste battery can be removed by oxidizing and roasting the crushed material. As a result, the molten particles of the reduced valuable metals locally generated in the subsequent reduction step S4 can be agglomerated without physical obstacles caused by carbon, and can be recovered as an integrated alloy. In addition, in the reduction step S4, the phosphorus contained in the contents of the waste battery can be suppressed from being reduced by carbon, and the phosphorus can be effectively oxidized and removed, and the distribution into the alloy of the valuable metal can be suppressed.

[0048] That is, in the oxidation roasting step S3, the carbon content contained in the obtained oxidation roasted product is set to less than 1.0 mass%. In this way, by removing carbon in a manner that makes the carbon content almost 0 mass%, phosphorus can be effectively oxidized and removed, and the amount of carbon used for effectively reducing and alloying the valuable metals in the subsequent reduction step S4 can be easily adjusted.

[0049] Assuming that no oxidative roasting treatment is performed, that is, when the crushed material of the waste battery content is directly put into the furnace for reduction melting treatment, the carbon contained in the waste battery will hinder the separation of the metal and slag generated by the reduction melting treatment, resulting in a decrease in the recovery rate of valuable metals (or the slag cannot be fully removed). In addition, even if oxidation is performed together with the reduction melting treatment, it is difficult to make a more rigorous adjustment of the degree of oxidation, based on this point, the recovery rate of valuable metals will also decrease. In addition, when the removal of carbon in the oxidative roasting treatment is insufficient, and carbon more than the chemical equivalent of nickel, cobalt, and copper remains, even impurities such as iron and phosphorus contained in the crushed material are reduced, which will lead to a deterioration in the cost of impurity removal in the wet smelting process.

[0050] Here, in the method of this embodiment, in the oxidation roasting treatment, it is preferred to introduce an oxidant of 1.5 times or more of the chemical equivalent of carbon in the raw material containing the waste lithium ion battery (the amount required to oxidize the carbon). In addition, the amount of the oxidant introduced is more preferably 2.0 times or more and 3.0 times or less of the chemical equivalent of carbon in the raw material. The oxidant is not particularly limited, and air is preferably used from the perspective of easy operation and the purpose of cooling the remaining oxidation heat.

[0051] By introducing the oxidizing agent under the above-mentioned conditions, the oxidizing roasting treatment can be completed in a short time, and the carbon contained in the spent lithium-ion battery to be oxidized can be easily oxidatively removed.

[0052] Furthermore, in the oxidation roasting treatment, it is preferred that an oxidant is introduced under the above-mentioned conditions, and the oxidation roasting treatment is performed under the treatment temperature condition of 600° C. or higher and 900° C. or lower. Thus, compared with the past, the oxidation roasting treatment can be completed efficiently and effectively in a short time, and even if the treatment temperature is not set to a high temperature as in the past, the carbon in the raw material can be easily oxidized and removed.

[0053] That is, by introducing an oxidant under the above conditions and setting the temperature condition of the oxidation roasting treatment to 600°C or more, the carbon contained in the waste lithium-ion battery can be effectively oxidized and removed by a treatment time shorter than before. Furthermore, by setting the temperature condition of the oxidation roasting temperature to 900°C or less, the thermal energy cost can be suppressed and the temperature control can be easily performed. In this way, by performing the oxidation roasting treatment at a treatment temperature of 600°C or more and 900°C or less, the efficiency of the oxidation roasting treatment can be improved compared with the past.

[0054] Furthermore, when the oxidation roasting treatment is performed using a known rotary kiln or the like, by controlling the oxidation roasting temperature to 900° C. or less, it is possible to suppress the adhesion of furnace agglomerates to the inner wall of the kiln, and to perform the oxidation roasting treatment stably and uniformly.

[0055] In addition, in the method of the present embodiment, it is preferred to set the processing time of the oxidation roasting treatment so that the carbon grade (carbon content) of the obtained oxidation roasting product is less than 1.0 mass%. Here, for the specific processing time, an experiment is performed to find the relationship between the processing time, processing temperature and the amount of introduction of the oxidant in the oxidation roasting treatment and the carbon content contained in the obtained oxidation roasting product, and it is set based on the test results. For example, by setting the processing time of the oxidation roasting treatment to more than 2 hours, the carbon grade in the obtained oxidation roasting product is easily less than 1.0 mass%. Further, by setting the processing time to less than 3 hours, it is prevented from taking more than necessary processing time for oxidation roasting treatment, so the processing efficiency can be further improved.

[0056] Here, regarding the treatment temperature of the oxidation roasting treatment, when the treatment temperature is less than 600°C, even if the oxidant is introduced under the above conditions, the carbon will not decompose and will easily remain, and the oxidation of aluminum will only stay on the surface. In the subsequent reduction step S4, aluminum is easy to diffuse in the alloy. In addition, the residual carbon probably contains phosphorus. Therefore, when the residual carbon becomes more, the phosphorus that is more easily reduced will be reduced by carbon to a degree that cannot be ignored. In the subsequent reduction step S4, the phosphorus may be distributed to the alloy, which is not preferred. Moreover, in this series of processes, phosphorus cannot be effectively removed. Therefore, after the alloy is recovered, it is necessary to remove phosphorus from the alloy through a dephosphorization process. In addition, when the temperature condition of the oxidation roasting treatment is less than 600°C, the oxidation removal of carbon takes a long time, so the processing time becomes too long, which may cause obstacles to the operation.

[0057] On the other hand, when the treatment temperature of the oxidation roasting treatment is greater than 900°C, the oxidation roasted product is easily sintered, which sometimes hinders the operability of the treatment in the subsequent reduction step S4. In addition, when a known rotary kiln is used in the oxidation roasting treatment, the roasted product adheres to the refractory in the furnace and grows, sometimes causing clogging in the furnace, and the treatment efficiency in the reduction step S4 becomes easy to decrease. Furthermore, the furnace manufacturing cost and thermal energy cost for maintaining the temperature become extremely high, and effective treatment cannot be performed.

[0058] In addition, the oxidation roasting treatment can be carried out using, for example, a known roasting furnace. In addition, it is preferred that a furnace (preparatory furnace) different from the melting furnace used in the reduction melting treatment in the reduction step S4 is set, and the treatment is carried out in the preparatory furnace. As a roasting furnace, all forms of furnaces and kilns that can roast the crushed material while supplying oxygen so as to carry out oxidation treatment inside it can be used. As an example, it is preferred to use a rotary kiln, a tunnel kiln (open hearth: Hearthfurnace) and the like that are known in the past.

[0059] In this way, by preferably performing an oxidative roasting treatment under the above conditions, the carbon contained in the waste lithium-ion battery can be efficiently and effectively oxidized and removed. As a result, phosphorus as an impurity can be removed, and valuable metals can be recovered cheaply and effectively. It should be noted that since phosphorus can be effectively removed, the wet smelting process after the dry smelting process in the recovery of valuable metals can be simplified. Specifically, compared with the amount of waste lithium-ion batteries put into the dry smelting process, the amount of treatment in the wet smelting process can be reduced to about 1 / 4 to 1 / 3 in terms of mass ratio, and the wet smelting process can be simplified. Therefore, by setting the dry smelting process (waste battery pretreatment process S1 to reduction process S4) as a pretreatment in a broad sense, an alloy with less impurities (phosphorus) is obtained, and the amount of treatment is greatly reduced, thereby, the dry smelting process and the wet smelting process can be combined industrially.

[0060] (Recovery of dust in exhaust gas)

[0061] In the method of this embodiment, the dust in the exhaust gas generated by the treatment in the oxidation roasting step S3 is subjected to heat treatment at a temperature of 600°C or more and less than 1000°C, and the dust after the heat treatment is recovered. In addition, as described in detail later, it is characterized in that at least a part or all of the recovered dust after the heat treatment is added to the treated object (oxidation roasted object) in the reduction step S4 for reduction treatment.

[0062] The exhaust gas discharged during the oxidation roasting process contains dust, which has been discarded in the past. However, although the dust in the exhaust gas is rare, it contains valuable metals, and the recovery loss of valuable metals occurs through discarding. Therefore, the dust in the exhaust gas is recovered and added to the treated object in the reduction process of the subsequent process, and the reduction process is carried out together with the treated object, thereby suppressing the recovery loss of valuable metals.

[0063] At this time, in addition to valuable metals, the dust in the exhaust gas also contains a large amount of carbon. Therefore, when the recovered dust is directly added to the treated object for reduction treatment, a large amount of carbon is contained in the treated object, which is not preferred. Therefore, in the method of this embodiment, it is set to heat the dust in the exhaust gas generated by the oxidative roasting treatment, recover the dust after the heat treatment, and add it to the treated object in the reduction step S4. By setting it to heat the dust in the exhaust gas at a specific temperature and adding the dust after the heat treatment to the treated object for reduction treatment, the carbon in the dust can be oxidized and removed to reduce it, and it can prevent the treated object from containing carbon as the added object.

[0064] Here, Figure 2This is a graph showing the results of applying heat treatment to dust in exhaust gas discharged during oxidation roasting treatment and verifying to what extent the carbon grade in the dust is reduced according to the temperature of the heat treatment. Figure 3 This is a graph showing how the temperature of the dust heating process affects the rate of removal of carbon in the dust.

[0065] It should be noted that the oxidation roasting treatment is carried out by crushing the contents of the waste lithium-ion battery using a rotary kiln set in the atmosphere at a treatment temperature of 900°C and a treatment time of 2 hours. In addition, the dust in the exhaust gas discharged during the oxidation roasting treatment (supply to Figure 2 , Figure 3 The composition of the verified dust).

[0066] Table 1

[0067] (quality%) Ni Cu Al C dust 17 1.8 2.8 32

[0068] Reference Figure 2 It can be seen that the carbon grade in the dust begins to decrease in the region where the temperature of the dust heating treatment is 600°C or higher and lower than 1000°C. Figure 3 It is known that the removal rate of carbon in dust increases in the same temperature range as above. That is, the carbon grade in dust discharged in the oxidation roasting process can be effectively reduced by heating the dust at a temperature of 600°C or more and less than 1000°C.

[0069] It is also found that the effect of reducing the carbon grade in the dust and the effect of increasing the rate of reduction of the carbon grade are maximized when the heat treatment temperature is 900° C. or higher.

[0070] Thus, by heating the dust in the exhaust gas discharged in the oxidation roasting treatment at a temperature of 600° C. or higher and lower than 100° C., preferably 900° C. or higher and lower than 1000° C., the carbon in the dust can be oxidized and reduced effectively.

[0071] The specific method of heating the dust is not particularly limited. For example, a burner can be provided in the exhaust flue of the oxidation roasting treatment equipment. In addition, a conventionally known combustion tower can also be used.

[0072] [Reduction process]

[0073] In the reduction step S4, the oxidized roasted product obtained by the oxidizing roasting step S3 is reduced to obtain a reduced product. The purpose of the reduction step S4 is to keep the unnecessary oxides such as aluminum oxidized in the oxidizing roasting process as oxides, reduce and melt the oxides of valuable metals such as copper oxidized in the oxidizing roasting process, and recover the reduced product as an integrated alloy.

[0074] Here, in the reduction step S4, a reduction melting treatment is performed at least in the presence of carbon. By such a reduction melting treatment, a melt containing slag and an alloy containing valuable metals is obtained.

[0075] Carbon is a reducing agent that has the ability to easily reduce valuable metals such as copper, nickel, and cobalt that are the objects of recovery. For example, graphite that can reduce 2 moles of oxides of valuable metals such as copper oxides and nickel oxides with 1 mole of carbon can be cited. In addition, hydrocarbons that can reduce 2 to 4 moles with 1 mole of carbon can be used as a carbon supply source. In this way, by performing a reduction melting treatment in the presence of carbon as a reducing agent, the valuable metals can be efficiently reduced, and alloys containing valuable metals can be obtained more effectively. In addition, in the reduction using carbon, compared with the case of using aluminothermic reaction in which metal powder such as aluminum is used as a reducing agent for reduction, it has the advantage of extremely high safety.

[0076] In addition, as for carbon as a reducing agent, besides artificial graphite and natural graphite, coal, coke, etc. can also be used as long as the impurity level is acceptable in the product and subsequent processes. It should be noted that ammonia and carbon monoxide can be added in the reduction melting treatment.

[0077] At this time, it is preferred to moderately adjust the amount of carbon. When the amount of carbon is too much, in the case of containing phosphorus in the oxidation roasted product, most of the phosphorus is reduced by the carbon, and is distributed in the alloy containing the valuable metals such as copper, nickel, cobalt, and can not be effectively removed, becoming an alloy with a high phosphorus grade. On the other hand, when the amount of carbon is too little, although phosphorus is effectively removed and an alloy with a low phosphorus grade is obtained, the valuable metals are not effectively reduced, and the recovery rate of the valuable metals decreases. It should be noted that for the amount of carbon, in addition to considering the content of phosphorus remaining in the oxidation roasted product, it is also possible to consider that the price of the carbon (carbon supply source) used as a reducing agent and the difference (price difference) of the price of the valuable metals recovered are increased or decreased.

[0078] Specifically, in the reduction melting treatment in the reduction step S4, it is preferred to treat in the presence of carbon in an amount greater than 7.5% by mass and less than 10% by mass, more preferably in an amount greater than 8.0% by mass and less than 9.0% by mass, relative to 100% by mass of the oxidized roasted product to be treated. By controlling the amount of carbon in this way, the valuable metals can be effectively reduced to improve the recovery rate, and on the other hand, the reduction of phosphorus can be suppressed and phosphorus can be effectively separated to obtain an alloy with a low phosphorus grade.

[0079] The amount of carbon present can be adjusted by adding graphite etc. in the reduction melting treatment as described above. Here, preferably, the amount of carbon not oxidized and removed by the oxidation roasting treatment in the oxidation roasting process S3 is also included for adjustment. That is, the amount of carbon present is not only included in the amount of carbon added in the reduction melting treatment, but also included in the amount of carbon remaining in the oxidation roasted product. However, as described above, in the oxidation roasting process S3, a specific amount of oxidant is introduced, and the oxidation roasting treatment is carried out under the conditions of a specific temperature range, so the carbon contained in the raw material is effectively removed, and carbon is hardly included in the oxidation roasted product obtained. Therefore, about the amount of carbon in the reduction melting treatment, the amount of carbon added is a substantial amount, which can be freely adjusted by the added carbon.

[0080] In the method of this embodiment, as described above, the dust in the exhaust gas generated by the treatment in the oxidation roasting step S3 is subjected to heat treatment at a temperature of 600°C or more and less than 1000°C, and the dust after the heat treatment is recovered. In addition, it is characterized in that at least a part or all of the recovered dust after the heat treatment is added to the treated object (oxidation roasted object) in the reduction step S4 for reduction treatment.

[0081] In this way, by recovering the dust in the exhaust gas generated in the oxidizing roasting step S3 and adding it to the treated object of the reduction melting treatment for treatment, the recovery loss of the valuable metals can be reduced, and a more efficient recovery treatment can be performed.

[0082] As described above, the dust recovered from the exhaust gas and added to the treated object of the reduction melting treatment is preheated at a temperature of 600°C or more and less than 1000°C, preferably 900°C or more and less than 1000°C. Therefore, carbon is effectively reduced in the dust. However, in the dust after the heat treatment, a part of carbon sometimes remains, and the carbon acts as a reducing agent in the reduction treatment. Therefore, the amount of carbon present in the reduction melting treatment is adjusted in consideration of the amount of carbon remaining in the dust subjected to the heat treatment.

[0083] Here, try to consider the example that the dust in the exhaust gas discharged in the oxidation roasting process S3 is directly added to the oxidation roasting material as the processed object in this state, that is, the example that is added to the oxidation roasting material as the processed object without performing heat treatment. In this example, carbon is contained in high concentration in the dust that is not subjected to heat treatment, so even if the carbon in the dust is used as a reducing agent first, the use of the dust also has a limit. That is, for the use amount of the reducing agent in the reduction melting treatment, it is necessary to adjust to the use amount that can be alloyed by melting reduction of the valuable metals (Ni, Co, Cu, etc.) contained in the processed object and impurities (P, Fe, Mn, Al, etc.), so that the use limit is naturally set for the dust that contains high concentration of carbon without performing heat treatment.

[0084] In contrast, in the example where the dust obtained by heat-treating the dust is added to the mixture (oxidative roasting product), the carbon in the dust is reduced due to the heat treatment, so more dust can be added to the mixture compared to the above example (the example where the dust that has not been heat-treated is added to the mixture).

[0085] That is, in the method of this embodiment, it goes without saying that compared with the previous method of discarding dust, compared with the case of only introducing dust into reduction melting treatment (directly introducing dust without heating treatment), more dust containing valuable metals can be introduced into the reduction melting treatment, which can more effectively reduce the recovery loss of valuable metals and achieve efficient recovery of valuable metals.

[0086] As the temperature condition (melting temperature) in the reduction melting treatment, it is not particularly limited, and it is preferably set to a range of 1320°C or more and 1600°C or less, and more preferably set to a range of 1450°C or more and 1550°C or less. For example, if it is a copper alloy containing more than 50% by mass of cobalt, the melting point is about 1380°C or more, and if it is a copper alloy containing more than 50% by mass of nickel, the melting point is about 1320°C or more. Therefore, by reducing and melting at a temperature above 1320°C, it is easy to recover valuable metals such as copper, nickel, and cobalt as alloys. In addition, if the reduction melting is carried out under conditions above 1450°C, the fluidity of the obtained alloy becomes very good, and the separation efficiency of impurity components and valuable metals is improved, which is more preferred. On the other hand, when the melting temperature is greater than 1600°C, the heat energy is consumed in vain, the consumption of refractory materials such as crucibles and furnace walls becomes intense, and the productivity may decrease. Therefore, as the melting temperature, it is preferably set to 1600°C or less.

[0087] In the reduction melting treatment, it is preferable to use a flux. By performing the reduction melting using a flux, slag containing oxides such as aluminum can be dissolved in the flux and removed.

[0088] As a flux, a flux containing calcium (Ca) as a main component is preferred. For example, calcium oxide and calcium carbonate can be used. When phosphorus is oxidized, it becomes an acidic oxide. Therefore, the more alkaline the composition of the slag is, the easier it is to distribute phosphorus to the slag for removal. Therefore, it is better when there is more calcium that becomes an alkaline oxide in the slag, and it is better when there is less silicon (Si) that becomes an acidic oxide. In particular, it is preferred to add a flux for treatment in a manner that the mass ratio of silicon dioxide (SiO2) / calcium oxide (CaO) in the generated slag becomes 0.5 or less. In addition, when the proportion of aluminum oxide (Al2O3) is large, the melting point of the slag rises. Therefore, in order to melt the aluminum oxide, a sufficient amount of calcium is required. In particular, it is preferred to add a flux for treatment in a manner that the mass ratio of calcium oxide (CaO) / aluminum oxide (Al2O3) in the slag becomes 0.3 or more and 2.0 or less. As a result, the slag becomes alkaline, and phosphorus that generates acidic oxides can be effectively removed.

[0089] During the reduction melting treatment, dust, exhaust gas, etc. may be generated. However, these can be rendered harmless by performing conventionally known exhaust gas treatment.

[0090] In addition, sulfur can be added to the alloy obtained by the reduction melting treatment in the reduction step S4 before recovery, thereby making the alloy brittle and easy to crush. By crushing the alloy, the specific surface area can be increased, thereby improving the leaching property in the wet smelting process.

[0091] It should be noted that the above describes a method of reducing and melting the oxidized calcined product obtained in the oxidizing calcining step S3 to recover the reduced product as an integrated alloy. However, the reduction and melting do not necessarily have to be performed simultaneously, and each step may be performed independently.

[0092] Specifically, first, as a reduction step, the oxidized roasted product obtained by the oxidizing roasting step S3 is reduced to obtain a reduced product. The reduction step is to keep the unnecessary oxides such as aluminum oxidized in the oxidizing roasting process as oxides, reduce the oxides of valuable metals such as copper oxidized in the oxidizing roasting process, and recover the reduced product as an integrated alloy in the subsequent melting step.

[0093] In the reduction process, for example, the oxidized calcined product is heated and reduced at a temperature of 500°C to 1000°C (reduction temperature) and in the presence of carbon. The reduction temperature is not particularly limited, but by setting it in the range of 500°C to 1000°C, the reduction time can be shortened, the thermal energy cost can be suppressed, and the reduction treatment efficiency can be improved. It should be noted that when the reduction temperature is less than 500°C, the reduction reaction efficiency becomes low and the treatment requires a long time. On the other hand, when the reduction temperature is greater than 1000°C, sintering is likely to occur before the oxidized calcined product is reduced.

[0094] The reduction treatment can be performed using a reduction furnace, and the interior of the reduction furnace is heated to a desired temperature using a burner or the like, and the oxidized roasted product placed in the furnace is heated and reduced.

[0095] Then, in the melting step, the reduction product obtained in the reduction step is melted to be alloyed. By melting the reduction product in this way, a molten material is obtained, which includes slag containing oxides such as aluminum and an alloy containing copper, nickel, cobalt, etc. as valuable metals.

[0096] In the melting process, the temperature condition (melting temperature) in the melting process is not particularly limited, but is preferably set to a temperature of 1320° C. or more and 1600° C. or less. In addition, in the melting process, a flux such as calcium oxide and calcium carbonate is preferably used. It should be noted that dust, exhaust gas, etc. may sometimes be generated in the melting process, but they can be rendered harmless by implementing conventionally known exhaust gas treatment.

Claims

1. A method for recovering valuable metals, which is a method for recovering valuable metals from waste lithium-ion batteries, wherein: The method for recovering valuable metals comprises: an oxidative roasting step, in which the raw material containing the waste lithium-ion battery is subjected to an oxidative roasting treatment; and a reduction step of reducing the obtained oxidized roasted product in the presence of carbon, The dust in the exhaust gas generated in the oxidation roasting step is subjected to a heat treatment at 600° C. or higher and lower than 1000° C. for recovery, and at least a portion of the recovered heat-treated dust is added to the treated object in the reduction step.

2. The method for recovering valuable metals according to claim 1, wherein: The dust is heated at a temperature of 900°C or higher and lower than 1000°C.

3. The method for recovering valuable metals according to claim 1 or 2, wherein: In the oxidative roasting step, an oxidant of 1.5 times or more the chemical equivalent of carbon in the raw material to be treated is introduced, and the oxidative roasting treatment is carried out under treatment temperature conditions selected within the range of 600° C. to 900° C., so that the carbon grade of the obtained oxidative roasted product is set to less than 1.0 mass %.

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