Method for recovering valuable elements

Abstract

A reducing agent containing metallic iron and / or iron oxide is added to an oxide containing valuable elements which are Ni and / or Co and Mn and impurity elements which are copper and iron in an amount of 1.5 equivalent or less to obtain a mixed oxide. By heating the mixed oxide, the oxide is reduced to obtain metals. The metals are brought into contact with an acid solution to obtain a leachate. A sulfurizing agent is added to the leachate to precipitate the copper, and a leachate from which the copper has been removed is obtained as a copper removal solution. An oxidizing agent is added to the copper removal solution to precipitate the iron, and the copper removal solution from which the iron has been removed is obtained as a valuable element solution containing the valuable elements. Thus, a valuable element recovery method capable of removing impurity elements and selectively recovering Ni and Co can be provided.

Description

[Technical field]

[0001] The present invention relates to a method for recovering valuable elements. [Background technology]

[0002] In recent years, the demand for lithium-ion batteries has been rapidly increasing due to the popularity of electric vehicles. In particular, from the perspective of the recent need to reduce CO2 emissions, demand for electric vehicles that do not use fossil fuels is expected to continue to expand in the future, and the associated demand for lithium-ion batteries is also expected to increase further in the future.

[0003] In general, the positive electrode material of a lithium-ion battery is made of an oxide (composite oxide) containing nickel (Ni), cobalt (Co), manganese (Mn), etc. Specific examples of this composite oxide include LiNiO2, LiCoO2, and LiMnO2. Metal elements such as Ni, Co, and Mn cannot be said to be abundant worldwide. For this reason, recovering these metal elements (valuable elements) from the positive electrode materials of discarded lithium-ion batteries is extremely beneficial from the perspective of effective resource utilization. Here, "waste lithium ion batteries" refers to waste lithium ion batteries (used products); defective lithium ion batteries (those generated during the manufacturing process of lithium ion batteries); etc.

[0004] A lithium ion battery is composed of a combination of components such as a positive electrode material, a negative electrode material, and a separator, and further contains an electrolyte solution and the like. For this reason, when recovering valuable elements from the positive electrode material of used lithium-ion batteries, preliminary treatment such as removal of the electrolyte, pulverization, and crushing is carried out prior to the recovery. After such pre-treatment, the positive electrode material is separated from the waste lithium-ion batteries, and then valuable elements are recovered from the separated positive electrode material. As a treatment for recovering valuable elements, there is a dry treatment (for example, Patent Document 1) in which the positive electrode material is heated together with a reducing agent to reduce and generate valuable elements. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-95628 Summary of the Invention [Problem to be solved by the invention]

[0006] In the dry process, the reduction of complex oxides (LiNiO2, LiCoO2, LiMnO2) produces metals containing valuable elements (Ni, Co, Mn) as well as slag. At this time, it may be required to minimize the reduction of Mn (to leave Mn in the slag without transferring it to the metal) and to selectively transfer Ni and Co to the metals and recover them.

[0007] Furthermore, metals obtained by dry processing may contain impurity elements in addition to valuable elements such as Ni and Co. Impurity elements include copper (Cu) and iron (Fe) derived from waste lithium-ion batteries. When the metal obtained by dry processing is reused as a positive electrode material for lithium-ion batteries, if the metal contains impurity elements (Cu and Fe), it may deteriorate the battery performance. Therefore, it is desirable to remove the impurity elements as much as possible.

[0008] The present invention has been made in consideration of the above points, and an object of the present invention is to provide a method for recovering valuable elements that can remove impurity elements and selectively recover Ni and Co. [Means for solving the problem]

[0009] As a result of extensive investigations, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention.

[0010] That is, the present invention provides the following [1] to

[12] . [1] A method for recovering a valuable element, comprising the steps of: adding 1.5 equivalents or less of a reducing agent containing at least one selected from the group consisting of metallic iron and iron oxide to an oxide containing valuable elements which are at least one selected from the group consisting of nickel and cobalt, and manganese, and impurity elements which are copper and iron, to obtain a mixed oxide; heating the mixed oxide to reduce the oxide to obtain a metal; contacting the metal with an acid solution to obtain a leachate containing the valuable element and the impurity element; adding a sulfiding agent to the leachate to precipitate copper as copper sulfide, thereby obtaining the leachate from which copper has been removed as a copper-removing solution; adding an oxidizing agent to the copper-removing solution to precipitate iron as iron hydroxide, and obtaining the copper-removing solution from which iron has been removed as a valuable element solution containing the valuable element. [2] The method for recovering valuable elements according to the above [1], wherein the oxide is obtained from waste lithium-ion batteries. [3] The method for recovering valuable elements according to [1] or [2] above, wherein the metal is powdered and then contacted with the acid solution. [4] The method for recovering valuable elements according to any one of the above [1] to [3], wherein the mixed oxide is heated to a temperature of 1450° C. or higher. [5] The method for recovering valuable elements according to any one of the above [1] to [4], wherein the iron oxide is ferrous oxide. [6] The method for recovering valuable elements according to any one of the above [1] to [5], wherein the reducing agent is at least one selected from the group consisting of dust, scale, sludge and scrap. [7] The method for recovering a valuable element according to any one of the above [1] to [6], wherein the metal obtained by heating the mixed oxide contains the valuable element and the impurity element. [8] The method for recovering a valuable element according to any one of [1] to [7] above, wherein the acid solution contains an acid and an oxidizing agent for the acid solution, and the content of the oxidizing agent for the acid solution is 0.5 volume % or more relative to the acid. [9] The method for recovering valuable elements according to the above [8], wherein the oxidizing agent for the acid solution is hydrogen peroxide.

[10] A method for recovering a valuable element according to any one of [1] to [9] above, wherein the amount of the sulfurizing agent added is 1.0 equivalent or more relative to the copper contained in the leachate, and the pH of the leachate to which the sulfurizing agent has been added is adjusted to 3.0 or less when precipitating the copper sulfide.

[11] The method for recovering a valuable element according to any one of the above [1] to

[10] , wherein the oxidizing agent is at least one kind of oxidizing agent A selected from the group consisting of air and ozone, or at least one kind of oxidizing agent B selected from the group consisting of hydrogen peroxide, hypochlorous acid, and potassium permanganate, the amount of the oxidizing agent A added is 0.1 vvm or more relative to the copper removal solution, the amount of the oxidizing agent B added is 0.005 vol% or more relative to the copper removal solution, and the pH of the copper removal solution to which the oxidizing agent has been added is adjusted to 3.0 or more and 7.0 or less when precipitating the iron hydroxide.

[12] The method for recovering valuable elements according to

[11] above, wherein the temperature of the copper removal solution to which the oxidizing agent has been added is 10°C or higher. Effect of the Invention

[0011] According to the present invention, it is possible to provide a method for recovering valuable elements that can remove impurity elements and selectively recover Ni and Co. [Brief description of the drawings]

[0012] [Figure 1] 1 is a flowchart showing an example of a method for recovering valuable elements. [Diagram 2] This is an Ellingham diagram (standard free energy change-temperature diagram). [Diagram 3] This is a potential-pH diagram (S-H2O system) for Cu and Ni. [Figure 4] This is a potential-pH diagram of Fe and Ni (O2-H2O system). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] [Method of recovering valuable elements] In the method for recovering valuable elements according to the present embodiment (also referred to as "the present recovery method" for convenience), a positive electrode material (oxide) of a waste lithium ion battery is subjected to dry treatment and wet treatment.

[0014] FIG. 1 is a flow chart showing an example of a method for recovering valuable elements. The present recovery method will be explained briefly with reference to FIG. In the dry treatment, a reducing agent (described later) is first added to the oxides (Ni, Co, Mn, Cu, Fe) to obtain a mixed oxide. At this time, a slag former (described later) may also be added. The resulting mixed oxide is then reduced by heating to obtain the metals (Ni, Co, Cu, Fe) and slag (Mn), which can then be separated if necessary. Prior to the wet treatment, the metals obtained are preferably powdered to obtain metal powders (Ni, Co, Cu, Fe). In wet processing, metals (metal powders) are first contacted with an acid solution to obtain a leachate (Ni, Co, Cu, Fe) and a leach residue, which are then separated as appropriate. A sulfiding agent is then added to the resulting leachate to precipitate copper sulfides (Cu) to obtain a copper-removed solution (Ni, Co, Fe). If appropriate, the two are separated. An oxidizing agent is then added to the copper removal solution to precipitate iron hydroxide (Fe) to obtain a valuable element solution (Ni, Co).

[0015] In this way, impurity elements (Cu, Fe) can be removed from the oxide, while the valuable elements Ni and Co can be selectively recovered, separate from Mn, which is also a valuable element. According to this recovery method, valuable elements can be easily recovered from the positive electrode material (oxide) of discarded lithium ion batteries with a purity high enough to be reused as a raw material for lithium ion batteries.

[0016] Next, the recovery method will be described in more detail.

[0017] <Reduced object (oxide)> The object of reduction in this recovery method is an oxide containing valuable elements, which are at least one selected from the group consisting of nickel (Ni) and cobalt (Co), manganese (Mn), and impurity elements, which are copper (Cu) and iron (Fe), and specifically, for example, a cathode material for a waste lithium-ion battery. This cathode material (oxide) may further contain a quasi-valuable element, which is lithium (Li). The cathode material (oxide) is obtained from waste lithium-ion batteries by carrying out pre-processing such as removing the electrolyte, crushing, pulverizing, and sorting.

[0018] Addition of reducing agent (obtaining mixed oxide) First, a reducing agent is added to an oxide to be reduced to obtain a mixed oxide which is a mixture of the oxide and the reducing agent.

[0019] Findings Obtained by the Inventors The positive electrode material of a lithium-ion battery is generally made of an oxide (composite oxide) such as LiNiO2, LiCoO2, or LiMnO2. Considering the thermodynamics of dry processing, for example, LiNiO2 and LiCoO2 decompose at high temperatures as follows, producing NiO and CoO, respectively. 2LiNiO2 → Li2O+2NiO+1 / 2O2 2LiCoO2 → Li2O+2CoO+1 / 2O2

[0020] The standard free energy change (ΔG 0 ) are shown below, respectively. NiO→Ni+1 / 2O2:ΔG 0 =234900-84.68T[J] CoO→Co+1 / 2O2:ΔG 0 =235480-71.55T[J] Materials that have free energy change values ​​lower than these standard free energy change values ​​at any elevated temperature can be used as reducing agents.

[0021] When valuable elements are recovered as metals from composite oxides by dry processing, Mn is generally inevitably reduced and converted to the metal. However, since it is difficult to separate Mn that has been converted into metal by subsequent wet processing, it is desirable to avoid reducing Mn as much as possible (to leave Mn in the slag).

[0022] Conventionally, materials with strong reducing power, such as Al-containing and Si-containing materials, are used as reducing agents. This is to avoid poor reduction. If the reducing power of the reducing agent is insufficient and poor reduction occurs, a part of the cathode material is separated as slag in the form of oxide, and the content of valuable elements in the metal obtained by reducing the cathode material is reduced. However, since elements higher up in the Ellingham diagram (Figure 2), which will be described later, are more likely to metallize, when Si or Al is used as a reducing agent, Mn is also likely to metallize, and this makes it impossible to meet the need to minimize the reduction of Mn. Therefore, the present inventors investigated substances that have a lower reducing power than Al-containing and Si-containing substances as potential new reducing agents, and found that metallic iron (Fe) or iron oxide is effective.

[0023] The standard free energy change (ΔG 0 ) is as follows: FeO→Fe+1 / 2O2:ΔG 0 =264430-64.73T[J] Fe3O4→3FeO+1 / 2O2:ΔG 0 =302370-108.15T[J]

[0024] Figure 2 is an Ellingham diagram (standard free energy change-temperature diagram). Referring to the above-mentioned standard free energy change and the Ellingham diagram (FIG. 2), the Fe / FeO equilibrium is less noble than the Ni / NiO equilibrium and the Co / CoO equilibrium, and reduction by Fe is considered possible. In addition, the FeO / Fe3O4 equilibrium is less noble than the Ni / NiO equilibrium, but more noble than the Co / CoO equilibrium. Therefore, it is expected that Ni can be recovered as metal and Co can remain in the slag. Specifically, the following reactions are expected: NiO+Fe→Ni+FeO:ΔG 0 =-29530-19.95T[J] CoO+Fe→Co+FeO:ΔG 0 =-28950-6.82T[J]

[0025] As mentioned above, the higher an element is on the Ellingham diagram (Figure 2), the easier it is to metallize. Therefore, by using Fe (or FeO) as a reducing agent, it is expected that only Ni and Co will be metallized, without metallizing Mn.

[0026] Reducing Agent For the reasons mentioned above, in the present recovery method, a reducing agent containing at least one selected from the group consisting of metallic iron (Fe) and iron oxide is used. As metallic iron (Fe), for example, scrap or nuggets of iron used in steel mills may be used.

[0027] Iron oxide is generally divided into three types: ferrous oxide (FeO), also known as wustite; triiron tetroxide (Fe3O4), also known as magnetite; and ferric oxide (Fe2O3), also known as hematite. Of these, magnetite and hematite have a higher standard free energy change than that of wustite at the same temperature, and may be less likely to cause a reduction reaction. For this reason, ferrous oxide (wustite) is preferred as the iron oxide because it easily induces a reduction reaction. The iron oxide may be at least one of dust, scale, and sludge (hereinafter, for convenience, referred to as "dusts") that are generated as by-products in the iron-making process. The use of dust as iron oxide is preferable from the viewpoint of effectively utilizing by-products of the iron-making process and from the viewpoint of utilizing an inexpensive iron source.

[0028] Amount of reducing agent added The amount of reducing agent required to reduce the oxide to be reduced is called 1.0 equivalent. For example, when the reducing agent is metallic iron (Fe) or ferrous oxide (FeO), the reduction with one equivalent of the reducing agent is shown as follows, respectively: Fe+(NiO,CoO,MnO)→(Ni,Co,Mn)+FeO 3FeO+(NiO,CoO,MnO)→(Ni,Co,Mn)+Fe3O4

[0029] When determining the amount of reducing agent to be added, first, the contents of NiO, CoO and MnO in the oxide to be reduced are obtained. Specifically, the contents of Ni, Co, and Mn in the object to be reduced (oxide) are measured and regarded as the contents of NiO, CoO, and MnO in the object to be reduced (oxide), respectively. The contents of Ni, Co and Mn are measured using an energy dispersive X-ray analyzer (EDX).

[0030] The smaller the amount of reducing agent added, the higher the proportion of valuable elements (the lower the proportion of Fe) in the resulting metal, which prevents excess Fe from remaining in the metal without being used as a reducing agent. Furthermore, the smaller the amount of reducing agent added, the more Ni and Co metals are obtained, with a higher proportion of Ni in particular. This is presumably because, as Ni is higher than Co in the Ellingham diagram (Figure 2), Ni is easier to metallize than Co, and Ni is reduced first by Fe (or iron oxide). For these reasons, the amount of reducing agent added is 1.5 equivalents or less, preferably 1.4 equivalents or less, more preferably 1.3 equivalents or less, even more preferably 1.2 equivalents or less, particularly preferably 1.1 equivalents or less, and most preferably 1.0 equivalent or less.

[0031] The lower limit of the amount of the reducing agent to be added is not particularly limited, so long as the proportion of Fe is reduced. However, from the viewpoint of suppressing insufficient reduction, the amount of the reducing agent added is preferably 0.1 equivalent or more, more preferably 0.3 equivalent or more, and even more preferably 0.5 equivalent or more.

[0032] If a large amount of reducing agent is added to the oxide in order to avoid insufficient reduction, the amount of elements other than valuable elements (for example, Fe) contained in the produced metal tends to increase. However, in the present recovery method, Fe can be removed by wet treatment, so the amount of reducing agent added can be increased, making it easier to suppress insufficient reduction.

[0033] Heating mixed oxides (obtaining metals) Next, the mixed oxide (a mixture of oxide and reducing agent) is heated, whereby the oxide is reduced. In addition, when heating, a flux such as CaO or SiO2 may be added in addition to the reducing agent. That is, the mixed oxide may further contain a flux. The equipment used for heating the mixed oxide is not particularly limited, and examples thereof include conventionally known equipment such as an electric furnace, a resistance furnace, a high-frequency melting furnace, a low-frequency melting furnace, a rotary kiln, a vertical furnace, and a steelmaking furnace.

[0034] 《Heating temperature》 The temperature when the mixed oxide is heated (heating temperature) is preferably 1300° C. or higher, more preferably 1350° C. or higher, further preferably 1400° C. or higher, and particularly preferably 1450° C. or higher, because this makes it easier to suppress insufficient reduction. Although there is no particular upper limit, the heating temperature is preferably 1800° C. or lower, and more preferably 1700° C. or lower.

[0035] <Heating atmosphere> Suitable atmospheres for heating the mixed oxide (heating atmosphere) include, for example, inert atmospheres such as nitrogen gas (N2) atmosphere and argon gas (Ar) atmosphere; reducing atmospheres such as carbon monoxide gas (CO) atmosphere; and the like.

[0036] Heating time: The time for heating the mixed oxide (heating time) is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 3 hours or more, because this makes it easier to suppress insufficient reduction. Although there is no particular upper limit, the heating time is preferably 6 hours or less, and more preferably 5 hours or less.

[0037] 《Product (metal)》 Metals are produced by reducing the oxide (cathode material) to be reduced. In other words, the valuable elements Ni and Co contained in the oxide are recovered as metals.

[0038] The metal obtained by reduction of the oxide (also called the "product metal") is an alloy containing valuable elements (Ni, Co) and impurity elements (Cu, Fe). The product metal may contain only one of the valuable elements (Ni, Co). The product metal may be a metal having a greater proportion of one valuable element than another valuable element.

[0039] Product (Slag) By reducing the oxide (cathode material), in addition to the metal, slag (also called "produced slag") is obtained. The produced slag contains FeO and the like. In addition, the produced slag contains Mn, a valuable element that was not contained in the produced metal, in the form of an oxide (MnO). When reducing an oxide (cathode material) containing Mn, the Mn / MnO equilibrium is less noble than the Fe / FeO equilibrium and the FeO / Fe3O4 equilibrium, so that it is possible to prevent Mn from being mixed into the product metal obtained by reduction. In addition, separating Mn from the produced metal by wet processing is a heavy burden, so it is beneficial to prevent Mn from being mixed into the produced metal and keep Mn in the produced slag, as this burden can be reduced.

[0040] Separation of metal and slag It is preferable to separate the product metal and the product slag obtained by the reduction of the oxide before powdering the product metal (described later). The method of separation is not particularly limited, and any known method can be used.

[0041] <Metal powderization (obtaining metal powder)> Next, the resulting metal is preferably pulverized to obtain a metal powder. In the wet treatment, as described below, the generated metal is first subjected to leaching using an acid solution. At this time, if the generated metal is in a state obtained by reduction of the oxide, the leaching efficiency may be insufficient. Therefore, it is preferable to powder the generated metal before performing leaching using an acid solution.

[0042] The smaller the particle size of the metal powder, the better the leaching efficiency. However, if the particle size of the metal powder is too small, it may become difficult to handle or the risk of an explosive reaction may increase. Taking these points into consideration, the particle size of the metal powder is kept within an appropriate range. Specifically, for example, the particle size of the metal powder is preferably 250 to 6000 μm, and more preferably 300 to 5000 μm. The particle size is the volume-based median diameter (particle size at 50% cumulative value) in the particle size distribution determined by a laser diffraction / scattering method (hereinafter the same).

[0043] The method for powdering the produced metal is not particularly limited as long as it can keep the particle size of the resulting metal powder within an appropriate range, and examples of the method include methods using a grinding device such as a jaw crusher or a vibration mill; atomization methods; and the like.

[0044] Contact of metal with acid solution (obtaining leachate) Next, the metal (metal powder) is brought into contact with an acid solution to leach out the valuable elements (Ni, Co) and impurity elements (Cu, Fe), that is, to obtain a leachate containing the valuable elements and the impurity elements. The metal from which valuable elements and impurity elements have been leached becomes a residue (leaching residue). The method for contacting the metal with the acid solution is not particularly limited, but examples thereof include a method of immersing the metal in the acid solution, and a method of spraying the acid solution onto the metal.

[0045] 《Solid-liquid ratio (metal / acid liquid)》 If the amount of acid solution brought into contact with the metal is too small (the amount of metal is too great compared to the amount of acid solution), some of the metal elements, such as valuable elements, that have dissolved in the acid solution will reach saturation solubility and precipitate, which may result in an insufficient leaching rate. For this reason, the ratio of the mass (unit: g) of the solid metal to the volume (unit: mL) of the liquid acid solution (also referred to as the "solid-liquid ratio (metal / acid solution)") is preferably 1 / 5 or less, more preferably 1 / 7 or less, and even more preferably 1 / 10 or less. When the solid-liquid ratio (metal / acid solution) is 1 / 10, for example, 1 g of metal is immersed in 10 mL of acid solution. On the other hand, the solid-liquid ratio (metal / acid liquid) is preferably 1 / 50 or more, more preferably 1 / 35 or more, and even more preferably 1 / 20 or more.

[0046] 《Acid liquid》 The acid solution to be brought into contact with the metal contains at least an acid.

[0047] (acid) The acid used in the acid solution includes inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and these may be used alone or in combination of two or more kinds. From the viewpoint of realizing the "battery-to-battery" concept of recycling waste lithium-ion batteries and using them again as raw materials for lithium-ion batteries, it is preferable to use sulfuric acid as the acid, because it is possible to obtain valuable elements in the form of sulfates, which are easy to use as cathode materials for lithium-ion batteries. A chloride may be contained in sulfuric acid and used as the acid.

[0048] ((acid concentration)) The concentration (acid concentration) of the acid (eg, sulfuric acid) used in the acid solution is preferably 0.1 mol / L or more, more preferably 0.5 mol / L or more, and even more preferably 1.0 mol / L or more, because this can increase the leaching rate. Although there is no particular upper limit, the acid concentration is preferably 8.0 mol / L or less, more preferably 6.0 mol / L or less, further preferably 4.0 mol / L or less, and particularly preferably 3.0 mol / L or less.

[0049] (Oxidizing agent for acid solutions) As a result of investigations conducted by the present inventors, it was found that even when the solid-liquid ratio (metal / acid solution) and the acid concentration are within the above-mentioned ranges, leaching may be insufficient. For this reason, it is preferable to add an oxidizing agent (oxidizing agent for acid solution) to the acid solution as a leaching promoter. Examples of the oxidizing agent for acid solution include hydrogen peroxide, hypochlorous acid, potassium permanganate, ozone, etc. Among these, hydrogen peroxide and ozone are preferable because the use of hypochlorous acid and potassium permanganate may require complicated post-treatment for chlorine, potassium, manganese, etc.

[0050] ((Oxidizing agent content for acid solution)) From the viewpoint of carrying out sufficient leaching, the content of the oxidizing agent for the acid solution (e.g., hydrogen peroxide) in the acid solution is preferably 0.5 vol. % or more, more preferably 1.0 vol. % or more, even more preferably 3.0 vol. % or more, even more preferably 5.0 vol. % or more, particularly preferably 6.0 vol. % or more, and most preferably 6.9 vol. % or more, relative to the acid (e.g., sulfuric acid). On the other hand, the content of the oxidizing agent for the acid solution (eg, hydrogen peroxide) in the acid solution is preferably 15.0 vol % or less, more preferably 13.0 vol % or less, and even more preferably 10.0 vol % or less, relative to the acid (eg, sulfuric acid).

[0051] Contact Time The time for which the metal is in contact with the acid solution (contact time) is preferably 0.5 hours or more, more preferably 0.8 hours or more, and even more preferably 1.0 hour or more, in order to sufficiently carry out leaching. On the other hand, from the viewpoint of productivity, the contact time is preferably 3.0 hours or less, more preferably 1.5 hours or less.

[0052] Separation of leachate and leach residue It is preferable to separate the leachate and the leach residue before adding the sulfurizing agent (described later). The method of separation is not particularly limited, and a known solid-liquid separation method can be used.

[0053] Adding sulfurizing agent (obtaining copper removal solution) Next, a sulfurizing agent is added to the leachate containing valuable elements (Ni, Co) and impurity elements (Cu, Fe) to precipitate the impurity element copper (Cu) as copper sulfide. Thus, the leachate from which copper (Cu) has been selectively removed is obtained as a copper removal solution.

[0054] Figure 3 shows the potential-pH diagram of copper (Cu) and nickel (Ni) (S-H2O system). Figure 3 shows the area where oxide (hydroxide) or sulfide precipitates of copper (Cu) and nickel (Ni) form, taking into account their solubility, on the potential-pH diagram of the copper (Cu)-sulfur (S)-water (H2O) system. Incidentally, since cobalt precipitates in a manner similar to that of nickel, cobalt is not shown in FIG. As shown in Fig. 3, in the region where the pH is 3.0 or less and the oxidation-reduction potential is low, copper (Cu) is selectively precipitated. Although not shown in Fig. 3, in this region, copper precipitates as copper (II) sulfide (CuS). By utilizing this, the leachate is made to have a low pH and be reducing, so that the copper (Cu) contained in the leachate is precipitated as copper (II) sulfide and selectively removed. In other words, a copper-removed solution is obtained, which is the leachate from which copper (Cu) has been removed.

[0055] Sulfurizing agents Examples of sulfurizing agents to be added to the leaching solution include sulfur (S), hydrogen sulfide (H2S), sodium hydrogen sulfide (NaSH), sodium sulfide (Na2S), etc., and these may be used alone or in combination of two or more. Of these, from the viewpoint of ease of handling, sulfur, sodium hydrogen sulfide, and sodium sulfide, which can be handled as a solid or solution, are preferable to hydrogen sulfide, which is a toxic gas. However, in any case, hydrogen sulfide gas may be generated by the sulfurization reaction, so care must be taken when carrying out the process.

[0056] The temperature of the leachate to which the sulfurizing agent has been added (sulfurization temperature) is not particularly limited, and may be, for example, room temperature.

[0057] (Amount of sulfurizing agent added) From the viewpoint of sufficiently removing copper contained in the leachate, the amount of the sulfiding agent added is preferably 1.0 equivalent or more relative to the copper (Cu) contained in the leachate, more preferably 1.5 equivalents or more, and even more preferably 2.0 equivalents or more. On the other hand, if an excessive amount of sulfurizing agent is added, the amount of sulfides (precipitates) of valuable elements (Ni, Co, etc.) increases, and the amount of valuable elements desired to remain in the obtained copper removal solution may decrease. From this viewpoint, the amount of sulfurizing agent added is preferably 3.0 equivalents or less, more preferably 2.5 equivalents or less, and even more preferably 2.0 equivalents or less, relative to the copper (Cu) contained in the leachate.

[0058] For example, when using 1.0 equivalent of sodium hydrosulfide (NaSH) as the sulfiding agent to produce copper(II) sulfide (CuS), 1 mol of sodium hydrosulfide (NaSH) is used for every 1 mol of copper (Cu) in the leachate.

[0059] 《Sulfide pH》 When a sulfurizing agent is added to the leachate to precipitate copper sulfides, if the pH of the leachate to which the sulfurizing agent has been added (sulfurization pH) is high, the amount of sulfides (precipitates) of valuable elements to be left in the copper removal solution may increase. For this reason, the sulfurization pH is preferably 3.0 or less, more preferably 2.0 or less, even more preferably 1.0 or less, and particularly preferably 0 (zero). The sulfurization pH is adjusted, for example, by adding a pH adjuster to the leachate. The pH adjuster is not particularly limited, and examples thereof include sulfuric acid and sodium hydroxide.

[0060] Sulfurization Time The time for sulfurizing the copper contained in the leachate by reacting it with the sulfurizing agent (sulfurization time) is preferably 0.1 hours or more, more preferably 0.2 hours or more, and even more preferably 0.3 hours or more. On the other hand, from the viewpoint of productivity, the sulfurization time is preferably 3.0 hours or less, more preferably 2.0 hours or less, and even more preferably 1.0 hour or less.

[0061] Separation of copper sulfide and copper removal solution It is preferable to separate the copper sulfide from the copper removal solution before adding the oxidizing agent (described later). The method of separation is not particularly limited, and a known solid-liquid separation method can be used.

[0062] Addition of oxidizing agent (obtaining a solution of valuable elements) Next, an oxidizing agent is added to the copper removal solution containing the valuable elements (Ni, Co) and iron (Fe) to precipitate the impurity element iron (Fe) as iron hydroxide. In this way, the copper removal solution from which iron (Fe) has been selectively removed is obtained as a valuable element solution containing the valuable elements (Ni, Co).

[0063] Figure 4 shows the potential-pH diagram for iron (Fe) and nickel (Ni) (O2-H2O system). Figure 4 shows the area where the oxide (hydroxide) precipitates of iron (Fe) and nickel (Ni) form, taking into account their solubility, on the potential-pH diagram for the iron (Fe)-oxygen (O2)-water (H2O) system. Incidentally, since cobalt precipitates in a manner similar to that of nickel, cobalt is not shown in FIG. As shown in Fig. 4, in the region where the pH is 3.0 or more and 7.0 or less and the oxidation-reduction potential is high, iron (Fe) is selectively precipitated. Although not shown in Fig. 4, in this region, iron precipitates as iron hydroxide (III) oxide (FeO(OH)). By utilizing this, the copper-removal solution is made acidic to neutral and oxidizing, so that the iron (Fe) contained in the copper-removal solution is precipitated as iron hydroxide (III) oxide and is selectively removed. In other words, a valuable element solution is obtained, which is a copper-removal solution from which iron (Fe) has been removed.

[0064] Oxidizing Agent Examples of the oxidizing agent added to the copper removal solution include at least one oxidizing agent A selected from the group consisting of air and ozone; and at least one oxidizing agent B selected from the group consisting of hydrogen peroxide, hypochlorous acid, and potassium permanganate. Among these, air, hydrogen peroxide and ozone are preferred, since the use of hypochlorous acid and potassium permanganate may require complicated post-treatment of chlorine, potassium, manganese, etc.

[0065] (Amount of oxidizing agent added) From the viewpoint of sufficiently oxidizing the iron contained in the copper removal solution, the amount of oxidizing agent A (air, ozone) which is a gas added is preferably 0.1 vvm or more, more preferably 0.3 vvm or more, and even more preferably 0.5 vvm or more, relative to the copper removal solution. On the other hand, the amount of oxidizing agent A added is preferably 5.0 vvm or less, more preferably 4.0 vvm or less, and even more preferably 3.0 vvm or less, relative to the copper removal solution.

[0066] The unit "vvm" is a unit that expresses the volume ratio of gas injected into the liquid per minute. For example, if the amount of oxidant A added is 2 vvm, then 2 L of oxidant A is injected per minute into 1 L of copper removal solution.

[0067] For the same reason, the amount of oxidizing agent B (hydrogen peroxide, hypochlorous acid, potassium permanganate) added is preferably 0.005 vol.% or more, more preferably 0.015 vol.% or more, even more preferably 0.050 vol.% or more, and particularly preferably 0.100 vol.% or more, relative to the copper removal solution. On the other hand, the amount of oxidizing agent B added is preferably 1.500 vol % or less, more preferably 1.000 vol % or less, further preferably 0.500 vol % or less, and particularly preferably 0.300 vol % or less, relative to the copper removal solution.

[0068] Oxidation temperature As a result of investigations conducted by the present inventors, it was found that there are cases where the oxidation of iron contained in the copper removal solution is insufficient simply by using the oxidizing agents described above. Therefore, from the viewpoint of promoting oxidation, it is preferable to increase the temperature (oxidation temperature) of the copper removal solution to which the oxidizing agent has been added. Specifically, the oxidation temperature is preferably 10° C. or higher, more preferably 30° C. or higher, and even more preferably 50° C. or higher. On the other hand, the oxidation temperature is preferably 90° C. or lower, more preferably 80° C. or lower.

[0069] Oxidation pH When an oxidizing agent is added to a copper removal solution to precipitate iron hydroxide, if the pH of the copper removal solution to which the oxidizing agent has been added (oxidizing pH) is too low, it may be difficult to form a precipitate. Therefore, the oxidizing pH is preferably 3.0 or more, more preferably 3.7 or more, even more preferably 4.0 or more, and particularly preferably 4.5 or more. On the other hand, if the oxidation pH is too high, there is a concern that the coprecipitation of valuable elements (Ni, Co, etc.) increases, and the amount of valuable elements desired to remain in the obtained valuable element solution decreases. Therefore, the oxidation pH is preferably 7.0 or less, more preferably 6.0 or less, and even more preferably 5.0 or less. The oxidation pH is adjusted, for example, by adding a pH adjuster to the copper removal solution, which is not particularly limited and may include sulfuric acid, sodium hydroxide, etc.

[0070] Oxidation Time The time (oxidation time) for reacting the iron contained in the copper removal solution with the oxidizing agent is preferably 0.3 hours or more, more preferably 0.5 hours or more, and even more preferably 1.0 hour or more. On the other hand, from the viewpoint of productivity, the oxidation time is preferably 3.0 hours or less, more preferably 2.0 hours or less, and even more preferably 1.5 hours or less.

[0071] 《Oxidation promoter》 In order to increase the rate of the reaction for producing the precipitate of iron hydroxide, an oxidizing agent may be used in combination with the above-mentioned oxidizing agent. The oxidation aid may be, for example, at least one selected from the group consisting of ferric oxide (Fe2O3) and iron(III) oxide hydroxide (FeO(OH)), and the oxidation aid is preferably in the form of a powder. The principle by which the oxidation promoter increases the reaction rate is catalytic action. Specifically, the oxidation promoter tends to become negatively charged in the aqueous solution (copper removal solution), so Fe 2+ It adsorbs ions and Fe 2+ Inside e - This weakens the bond with Fe 2+ →Fe 3+ +e - It is believed that the activation energy of this reaction (Fe oxidation reaction) decreases, accelerating the reaction.

[0072] (Amount of auxiliary oxidation agent added) It is believed that the more the amount of the oxidation aid is added, the larger the reaction surface area becomes, and the faster the rate of the Fe oxidation reaction becomes. Therefore, the amount of the oxidation aid added is preferably 0.1 g / L or more, more preferably 0.5 g / L or more, and even more preferably 1.0 g / L or more, relative to the copper removal solution. On the other hand, if the amount of the oxidation promoter added is too large, there is a concern that the coprecipitation of valuable elements (such as Ni and Co) may increase. Therefore, the amount of the oxidation promoter added is preferably 40.0 g / L or less, more preferably 10.0 g / L or less, and even more preferably 5.0 g / L or less, relative to the copper removal solution.

[0073] (Particle size of oxidation promoter) If the particle size of the oxidation assistant is too small, the reaction surface area becomes too large, and there is a concern that the coprecipitation of valuable elements (Ni, Co, etc.) increases. Therefore, the particle size of the oxidation assistant is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. On the other hand, if the particle size of the oxidation assistant is too large, the reaction surface area becomes too small and the desired effect may not be obtained. Therefore, the particle size of the oxidation assistant is preferably 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.0 μm or less.

[0074] Separation of iron hydroxide and valuable element solution It is preferable to separate the iron hydroxide and the valuable element solution from each other. The method for separation is not particularly limited, and any known solid-liquid separation method can be used. The valuable elements in the valuable element solution thus obtained can be used, for example, as a positive electrode material for lithium ion batteries. EXAMPLES

[0075] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples described below.

[0076] [Test A] <Preparation of cathode material: Test A> A cathode material for a used lithium-ion battery was prepared. Specifically, the used lithium-ion batteries were subjected to pre-treatment such as disassembly, discharge, and removal of the electrolyte to separate the positive electrode material. The composition ratio (molar ratio) of nickel (Ni), cobalt (Co), and manganese (Mn) in the positive electrode material is shown in Table 1 below. The positive electrode material further contained copper (Cu) and iron (Fe) as impurity elements.

[0077] [Table 1]

[0078] Preparation of reducing agent: Test A As reducing agents, graphite (C) powder, metallic aluminum (Al) powder, and metallic silicon (Si) powder were prepared. As another reducing agent, powder of metallic iron (Fe) obtained by atomization processing and powder of ferrous oxide (FeO) were prepared. As further reducing agents, powders of dust, scale and scrap generated in the steelmaking process were prepared. The compositions of the dust, scale and scrap are shown in Table 2 below. In Table 2 below, "M.Fe" indicates the amount of metallic Fe.

[0079] [Table 2]

[0080] Addition of reducing agent and heating of mixed oxide: Test A The prepared cathode material was placed in an electric furnace with a heat capacity of 50 to 80 kg, and then any of the reducing agents described above and flux (CaO, SiO2) were added and heated. The heating time was 3 hours in each case. In this manner, the positive electrode material was reduced to obtain a product metal and a product slag, which were then separated from each other. The type and amount of the reducing agent used (unit: equivalent), the heating temperature (unit: °C) and the heating atmosphere (Ar, N2 or CO) are shown in Table 3 below.

[0081] The reduction ratio (unit: mass %) was determined for each of the metallic elements Ni, Co, and Mn. The reduction rate is the ratio of the amount of metal actually obtained to the theoretical amount of metal produced by the reduction reaction. For example, if the reduction rate of Co is 20 mol%, it means that 20 mol% of the Co contained in the cathode material is reduced to the product metal, and the rest remains as oxide in the product slag. The results are shown in Table 3 below.

[0082] As shown in Table 3 below, the generated metals in Test Examples 3-1 to 3-23 were higher in reduction rates of Ni and Co while suppressing the reduction rate of Mn compared to Reference Test Examples 3-1 to 3-6, which used C, Al, or Si as the reducing agent. In other words, Ni and Co could be selectively recovered.

[0083] Comparing the test examples (for example, test examples 3-1 to 3-3) that differ only in the amount of reducing agent added, there was a tendency that the smaller the amount of reducing agent added, the smaller the proportion of Fe in the generated metal was, and the larger the total proportion of Ni and Co. There was also a tendency that the smaller the amount of reducing agent added, the larger the proportion of Ni in the generated metal was (the smaller the proportion of Co was). The same was true for Test Examples 3-4 to 3-6, Test Examples 3-7 to 3-9, Test Examples 3-10 to 3-12, Test Examples 3-13 to 3-15, Test Examples 3-16 to 3-17, Test Examples 3-18 to 3-19, Test Examples 3-20 to 3-21, and Test Examples 3-22 to 3-23.

[0084] [Table 3] TIFF0007670248000004.tif80142

[0085] Metal Powdering: Test A The compositions of the metals and slag produced by the reduction of the positive electrode material were determined. Among the metals produced by the reduction of the positive electrode material, metals having the compositions shown in Table 4 below were pulverized using a vibration mill to obtain metal powders. The particle size of the resulting metal powder was 1100 μm.

[0086] Contact between metal and acid: Test A An acid solution was prepared by adding 7.0% by volume of hydrogen peroxide as an oxidizing agent to sulfuric acid (concentration: 2.0 mol / L). The prepared acid solution was contacted with a metal (metal powder) having the composition shown in Table 4 below at a solid-liquid ratio (metal / acid solution) of 1 / 10 (contact time: 1.0 hour). Specifically, the metal powder was immersed in the acid solution. Thus, a leachate and a leach residue were obtained, and the two were separated. The concentration of each element in the leachate was determined using XRF (X-ray fluorescence) analysis, and the leaching rate (unit: mass%) of each element from the metal to the leachate was calculated. The results are shown in Table 4 below. As shown in Table 4 below, the leaching rate for each element was 100 mass %, meaning that all of the elements were leached from the metal into the leachate.

[0087] [Table 4]

[0088] <Addition of sulfurizing agent: Test A> The content (unit: g / L) of each element in the obtained leachate is shown in Table 5 below. Sodium hydrogen sulfide (NaSH) was added as a sulfiding agent to the obtained leachate and stirred at room temperature (25° C.). The amount of sulfiding agent (sodium hydrogen sulfide) added was 2.0 equivalents relative to the Cu contained in the leachate. The pH of the leachate to which the sulfurizing agent was added (sulfurization pH) was adjusted to 0 (zero) using sulfuric acid and sodium hydroxide as pH adjusters. In this way, the copper (Cu) contained in the leachate was sulfurized by reacting with the sulfurizing agent (sulfurization time: 20 minutes) and precipitated as copper sulfide (copper (II) sulfide). After that, the copper sulfide was separated from the copper-removed solution, which is the leachate from which the copper had been removed. The content (unit: g / L) of each element in the copper removal solution was determined by ICP-AES (inductively coupled plasma atomic emission spectrometry), and the results are shown in Table 5 below. Furthermore, for each element, the ratio of the content in the copper removal solution to the content in the leachate was calculated as the residual rate a (unit: mass %). The results are shown in Table 5 below. As shown in Table 5 below, the Cu content in the copper removal solution is very low, which shows that Cu was removed from the leachate with very high efficiency.

[0089] Addition of oxidizing agent: Test A Next, the copper removal solution was first diluted with water. The contents of each element in the diluted copper removal solution (unit: g / L) are shown in Table 5 below. The reason for dilution was that in a preliminary experiment, when an oxidizing agent was added to a model solution having the same composition as the copper removal solution shown in Table 5 below, excessive precipitation occurred, making stirring impossible in some cases. Hydrogen peroxide was added as an oxidizing agent to the copper removal solution (diluted) and stirred. The amount of the oxidizing agent (hydrogen peroxide) added was 0.020% by volume relative to the copper removal solution (diluted). The pH of the copper removal solution to which the oxidizing agent had been added (oxidation pH) was adjusted to 4.5 using sulfuric acid and sodium hydroxide as pH adjusters, and the temperature of the copper removal solution to which the oxidizing agent had been added (oxidation temperature) was set to and maintained at 70°C. In this way, the iron (Fe) contained in the copper removal solution was oxidized by reacting with the oxidizing agent (oxidation time: 1.0 hour) and precipitated as iron hydroxide (iron (III) oxide hydroxide). After that, the iron hydroxide was separated from the valuable element solution, which was the copper removal solution from which iron had been removed. The content (unit: g / L) of each element in the valuable element solution was determined by ICP-AES. The results are shown in Table 5 below. Furthermore, for each element, the ratio of the content in the valuable element solution to the content in the copper removal solution (diluted) was calculated as the residual rate b (unit: mass %). The results are shown in Table 5 below. As shown in Table 5 below, the Fe content in the valuable element solution is very low, so it can be seen that Fe was removed from the copper removal solution with very high efficiency.

[0090] Furthermore, for each element, the final residual rate in the valuable element solution was calculated as the total residual rate (unit: mass%) from the residual rate a and the residual rate b. The results are shown in Table 5 below. The results shown in Table 5 below show that by performing dry processing, then powdering the metals obtained by the dry processing, and then performing wet processing, valuable elements (Ni, Co) could be recovered with very high purity.

[0091] [Table 5]

[0092] [Test B] <Preparation of cathode material ~ Metal powder: Test B> The steps from preparation of the positive electrode material to powdering of the metal were the same as those in Test A, and therefore the explanation will be omitted.

[0093] Contact between metal and acid: Test B A plurality of acid solutions were prepared by adding an oxidizing agent for the acid solution (hydrogen peroxide) to sulfuric acid (concentration: 2.0 mol / L) in the amount (unit: volume %) shown in Table 6 below. A metal (metal powder) was brought into contact with an acid solution to obtain a leachate in the same manner as in Test A described above, except that the amount of oxidizing agent for the acid solution was changed. Furthermore, the leaching rate (unit: mass%) of each element from the metal to the leachate was calculated in the same manner as in the above-mentioned Test A. The results are shown in Table 6 below. As shown in Table 6 below, the leaching rate increased as the amount of oxidizing agent for the acid solution increased. It was found that the amount of oxidizing agent for the acid solution (hydrogen peroxide) added should be 6.9 volume % or more in order to sufficiently leach valuable metals (Ni, Co). However, when the amount of addition exceeds 6.9% by volume, the leaching rate reaches a plateau. Therefore, from the viewpoint of cost, it was found that within the scope of this example, 6.9% by volume is the most suitable amount of the oxidizing agent (hydrogen peroxide) for the acid solution.

[0094] [Table 6]

[0095] <Addition of sulfurizing agent: Test B> Sodium hydrogen sulfide (NaSH) was added as a sulfiding agent to the leachate shown in Table 5 in the amount (unit: equivalent) shown in Table 7 below, and the mixture was stirred. At this time, the sulfiding pH was adjusted to the value shown in Table 7 below. Except for changing the amount of sulfiding agent added and the sulfiding pH, the copper contained in the leachate was precipitated as copper sulfide in the same manner as in Test A described above, to obtain a copper-removed solution. Furthermore, the Cu content (unit: mg / L), Ni residual rate (unit: mass %) and Co residual rate (unit: mass %) in the obtained copper removal solution were determined in the same manner as in the above-mentioned Test A. The results are shown in Table 7 below. As shown in Table 7 below, in order to sufficiently remove copper, the amount of sulfurizing agent added is preferably 2.0 equivalents or more relative to copper, but it was found that the Ni retention rate and Co retention rate decrease as the amount of sulfurizing agent added increases. Furthermore, as shown in Table 7 below, as the sulfurization pH increased, there was a tendency for copper removal to become insufficient, and for the Ni residual rate and Co residual rate to decrease. From the above, it was found that within the range of this example, the amount of sulfurizing agent added was preferably 2.0 equivalents and the sulfurization pH was preferably 0 (zero).

[0096] [Table 7]

[0097] <Addition of oxidizing agent: Test B> First, the copper removal solution obtained in Test Example 7-4 in Table 7 above was diluted 5 times. Next, hydrogen peroxide was added as an oxidizing agent to the copper removal solution (diluted) in the amount (unit: volume %) shown in Table 8 below, and the mixture was stirred. At this time, the oxidation pH and oxidation temperature (unit: °C) were adjusted to the values ​​shown in Table 8 below. Except for changing the amount of oxidizing agent added, the oxidation pH, and the oxidation temperature, the same procedure as in Test A described above was followed to precipitate the iron contained in the copper removal solution as iron hydroxide, thereby obtaining a valuable element solution. In both Test A and Test B, no auxiliary oxidation agent was used. Furthermore, the Fe content (unit: mg / L), Ni residual rate (unit: mass%) and Co residual rate (unit: mass%) in the obtained valuable element solution were determined in the same manner as in the above-mentioned Test A. The results are shown in Table 8 below. As shown in Table 8 below, it was found that in order to sufficiently remove iron, it is preferable to set the oxidation pH to 6.0, or to set the oxidation pH to 4.5 or higher and add an oxidizing agent. Furthermore, as shown in Table 8 below, as the oxidation pH increased, while iron was more efficiently removed, there was a tendency for the Ni residual rate and Co residual rate to decrease. From the above, it was found that within the scope of this example, the amount of oxidizing agent (hydrogen peroxide) added is preferably 0.030% by volume, and the oxidation pH is preferably in the range of 4.5 to 5.0.

[0098] [Table 8]

[0099] [Test C] A valuable element solution was obtained by carrying out dry and wet treatments (i.e., from preparation of the positive electrode material to addition of the oxidizing agent) in accordance with Test A. For convenience, the mass of the positive electrode material (oxide) used is set to 100 kg, as shown in Table 9 below. In Comparative Test Example 9-1, only dry treatment was carried out. Comparative Test Example 9-2 and Test Examples 9-1 to 9-2 differ in the amount of FeO added as a reducing agent.

[0100] The Ni+Co recovery rate (unit: mass%) was calculated from the Ni+Co reduction rate (unit: mass%) of the product metal obtained by the dry treatment and the Ni+Co residual rate (unit: mass%) of the valuable element solution obtained by the wet treatment. The results are shown in Table 9 below. When only the dry treatment was carried out, the Ni+Co reduction rate of the produced metals was shown in Table 9 below as the Ni+Co recovery rate.

[0101] In addition, the proportion of Ni+Co in the metal elements of the valuable element solution obtained by the wet treatment was calculated as the final Ni+Co purity (unit: mass%). The results are shown in Table 9 below. However, in Comparative Test Example 9-1 in which only the dry treatment was carried out, the Ni+Co purity of the product metal obtained by the dry treatment is shown in Table 9 below as the final Ni+Co purity.

[0102] Comparing Comparative Test Example 9-1 and Test Example 9-1, the dry treatment conditions were the same for both, but in Test Example 9-1, in which wet treatment was performed, valuable elements (Ni + Co) were ultimately obtained with a higher purity than in Comparative Test Example 9-1, in which wet treatment was not performed.

[0103] Comparing Comparative Test Example 9-2 with Test Examples 9-1 to 9-2, Test Examples 9-1 to 9-2, in which the amount of FeO added as a reducing agent was 1.5 equivalents or less, had a smaller Fe mass in the generated metal and a smaller total mass of the reducing agent, sulfurizing agent, and oxidizing agent than Comparative Test Example 9-2, in which the amount of FeO added as a reducing agent was 2.0 equivalents.

[0104] [Table 9]

Claims

1. A reducing agent containing at least one element selected from the group consisting of metallic iron and iron oxide is added in an amount of 1.5 equivalents or less to an oxide containing at least one element selected from the group consisting of nickel and cobalt, valuable elements being manganese, and impurity elements being copper and iron, to obtain a mixed oxide; The mixed oxide is heated to reduce the oxide, thereby obtaining a metal containing at least one selected from the group consisting of nickel and cobalt, copper and iron; contacting the metal with an acid solution to obtain a leachate containing at least one selected from the group consisting of nickel and cobalt, copper and iron; adding a sulfiding agent to the leachate to precipitate copper as copper sulfide, obtaining the leachate from which copper has been removed as a copper-removed solution containing at least one selected from the group consisting of nickel and cobalt and iron; a step of adding an oxidizing agent to the copper-removing solution to precipitate iron as iron hydroxide, and obtaining the copper-removing solution from which iron has been removed as a valuable element solution containing at least one element selected from the group consisting of nickel and cobalt.

2. The method for recovering valuable elements according to claim 1 , wherein the oxide is obtained from waste lithium ion batteries.

3. 3. The method for recovering valuable elements according to claim 1, wherein the metal is powdered before being contacted with the acid solution.

4. 3. The method for recovering valuable elements according to claim 1, wherein the mixed oxide is heated to a temperature of 1450° C. or higher.

5. 3. The method for recovering valuable elements according to claim 1, wherein the iron oxide is ferrous oxide.

6. 3. The method for recovering valuable elements according to claim 1, wherein the reducing agent is at least one selected from the group consisting of dust, scale, sludge and scrap.

7. The acid solution contains an acid and an oxidizing agent for the acid solution, 3. The method for recovering valuable elements according to claim 1, wherein the content of the oxidizing agent for the acid solution is 0.5% by volume or more relative to the acid.

8. 8. The method for recovering valuable elements according to claim 7, wherein the oxidizing agent for the acid solution is hydrogen peroxide.

9. The amount of the sulfurizing agent added is 1.0 equivalent or more relative to the copper contained in the leachate, 3. The method for recovering valuable elements according to claim 1, wherein the pH of the leachate to which the sulfiding agent has been added is adjusted to 3.0 or less when the copper sulfide is precipitated.

10. The oxidizing agent is at least one oxidizing agent A selected from the group consisting of air and ozone, or at least one oxidizing agent B selected from the group consisting of hydrogen peroxide, hypochlorous acid, and potassium permanganate; The amount of the oxidizing agent A added is 0.1 vvm or more relative to the copper removal solution, the amount of the oxidizing agent B added is 0.005% by volume or more relative to the copper removal solution; 3. The method for recovering valuable elements according to claim 1, wherein the pH of the copper removal solution to which the oxidizing agent has been added is adjusted to 3.0 or more and 7.0 or less when precipitating the iron hydroxide.

11. 11. The method for recovering valuable elements according to claim 10, wherein the temperature of the copper removal solution to which the oxidizing agent has been added is 10°C or higher.

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