Recovery method of precious metal and method for producing metal

Abstract

To provide a recovery method of precious elements capable of removing impurity elements and selectively recovering Ni and Co.SOLUTION: An oxide containing at least one valuable element selected from the group consisting of Ni and Co, as well as Mn, and impurity elements such as Cu and Fe, is mixed with a reducing agent to obtain a mixed oxide. By heating the mixed oxide, the oxide is reduced to obtain the metal. The metal is contacted with an acid solution to obtain a leach solution containing valuable elements and impurity elements. A sulfidizing agent is added to the leach solution to precipitate copper as copper sulfide, thereby obtaining a copper-depleted leach solution as a copper removal solution. An oxidizing agent is added to the copper removal solution to precipitate iron as iron hydroxide, thereby obtaining a copper removal solution depleted of iron as a valuable element solution containing valuable elements. The reducing agent contains at least one selected from the group consisting of C-based reducing agents, Si-based reducing agents, and Al-based reducing agents, and the amount of reducing agent added, R, satisfies a specific formula (1).SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, the demand for lithium-ion batteries has been increasing rapidly due to the widespread use of electric vehicles. In particular, given the current trend toward reducing CO2 emissions, demand for electric vehicles that do not use fossil fuels is expected to continue to expand in the future, and the resulting demand for lithium-ion batteries is also expected to increase further.

[0003] Generally, the cathode 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 even on a global scale. Therefore, recovering these metal elements (valuable elements) from the positive electrode material of waste 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 also contains an electrolyte solution. Therefore, when recovering valuable elements from the positive electrode material of used lithium-ion batteries, preliminary treatment such as removal of the electrolyte, crushing, and crushing is carried out prior to 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 dry processing, the reduction of complex oxides (LiNiO2, LiCoO2, LiMnO2) produces slag as well as metals containing valuable elements (Ni, Co, Mn). 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 metal for recovery.

[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 metals obtained by dry processing are reused as cathode materials for lithium-ion batteries, impurity elements (Cu and Fe) contained in the metals can deteriorate battery performance, so it is desirable to remove as many impurity elements as possible.

[0008] The present invention has been made in view 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 research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to

[11] . [1] A method for recovering valuable elements, comprising: adding a reducing agent 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, 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 elements and the impurity elements; adding a sulfiding agent to the leachate to precipitate copper as copper sulfide, thereby obtaining a copper-removed leachate; adding an oxidizing agent to the copper-removed solution to precipitate iron as iron hydroxide, thereby obtaining a valuable element solution containing the valuable elements; (0.30a-0.15b+0.60)×[Ni]≦R≦(0.33a-0.17b+0.67)×[Ni]+(0.33a-0.17b+0.67)×[Co]+(0.23a-0.12b+0.47)×[Mn]...(1) However, in the above formula (1), R: Amount of the reducing agent added (unit: parts by mole) [Ni]: Nickel content of the above oxide (unit: parts by mole) [Co]: Cobalt content of the above oxide (unit: parts by mole) [Mn]: Manganese content of the above oxide (unit: parts by mole) a: The molar ratio of the content (unit: molar parts) of the C-based reducing agent in the reducing agent to the total amount (unit: molar parts) of the reducing agent added b: The molar ratio of the content (unit: molar parts) of the Si-based reducing agent in the reducing agent to the total amount (unit: molar parts) of the reducing agent added is. [2] The method for recovering valuable elements according to [1] above, 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 mixed oxide is heated to a temperature of 1400°C or higher. [4] The method for recovering a valuable element according to any one of [1] to [3] above, wherein the metal obtained by heating the mixed oxide contains the valuable element and the impurity element. [5] The method for recovering a valuable element according to any one of [1] to [4] above, wherein the metal is powdered and then brought into contact with the acid solution. [6] The method for recovering valuable elements according to any one of [1] to [5] 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% by volume or more relative to the acid. [7] The method for recovering valuable elements according to [6] above, wherein the oxidizing agent for the acid solution is hydrogen peroxide. [8] The method for recovering valuable elements according to any one of [1] to [7] 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. [9] The method for recovering a valuable element according to any one of [1] to [8] above, wherein 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 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.

[10] The method for recovering valuable elements according to [9] above, wherein the temperature of the copper removal solution to which the oxidizing agent has been added is 10°C or higher.

[11] A method for producing a metal, comprising using the method for recovering valuable elements according to any one of [1] to

[10] above to produce a metal containing at least one element selected from the group consisting of nickel and cobalt. [Effects of the Invention]

[0010] 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 explanation of the drawings]

[0011] [Figure 1] 1 is a flowchart showing an example of a method for recovering valuable elements. [Figure 2] Potential-pH diagrams of Cu and Ni (S-H2O system). [Figure 3] Potential-pH diagrams of Fe and Ni (O2-H2O system). DETAILED DESCRIPTION OF THE INVENTION

[0012] [Method for recovering valuable elements] In the method for recovering valuable elements of this embodiment (also referred to as "the present recovery method" for convenience), the positive electrode material (oxide) of waste lithium ion batteries is subjected to dry treatment and wet treatment.

[0013] FIG. 1 is a flowchart showing an example of a method for recovering valuable elements. The recovery method will be explained briefly with reference to FIG. In the dry treatment, first, a reducing agent (described later) is added to oxides (Ni, Co, Mn, Cu, Fe) in an amount described later to obtain a mixed oxide. The resulting mixed oxide is then heated to reduce the oxides, yielding metals (Ni, Co, Cu, Fe) and slag (Mn), which are then separated as appropriate. Before the wet treatment, the metals obtained are preferably powdered to obtain metal powders (Ni, Co, Cu, Fe). In the hydroprocessing process, metals (metal powders) are first brought into contact with an acid solution to obtain a leachate (Ni, Co, Cu, Fe) and a leach residue, which are then separated as appropriate. Next, a sulfiding agent is added to the resulting leachate to precipitate copper sulfide (Cu), yielding a copper-removed solution (Ni, Co, Fe). If necessary, the two are separated. An oxidizing agent is then added to the copper removal solution to precipitate iron hydroxide (Fe) and obtain a solution of valuable elements (Ni, Co).

[0014] In this way, impurity elements (Cu, Fe) can be removed from the oxide, while the valuable elements Ni and Co can be selectively recovered, distinguished from the valuable element Mn. According to this recovery method, valuable elements can be easily recovered from the cathode material (oxide) of waste lithium ion batteries with a purity high enough to be reused as raw materials for lithium ion batteries.

[0015] Next, the recovery method will be described in more detail.

[0016] <Reducing target (oxide)> The object to be reduced 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) and manganese (Mn), and impurity elements, which are copper (Cu) and iron (Fe). Specifically, the object to be reduced in this recovery method is, for example, a positive electrode material for waste lithium-ion batteries. The cathode material (oxide) is obtained from waste lithium-ion batteries by undergoing pre-processing such as removing the electrolyte, crushing, pulverizing, and sorting.

[0017] Addition of reducing agent (obtaining mixed oxides) 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.

[0018] Reducing Agent As the reducing agent in the dry treatment, at least one selected from the group consisting of a C-based reducing agent containing carbon, a Si-based reducing agent containing silicon, and an Al-based reducing agent containing aluminum is used. Examples of carbon-based reducing agents include graphite, coal, and coke. Examples of the Si-based reducing agent include ferrosilicon, metallic silicon, and silicon sludge. Examples of Al-based reducing agents include metallic aluminum, aluminum sludge, and aluminum dross.

[0019] <<Amount of reducing agent added R>> As will be described later, by heating a mixed oxide, which is a mixture of an oxide and a reducing agent, the oxide is reduced to obtain a metal (product metal) and slag (product slag). In this case, the amount of reducing agent added is an amount R that satisfies the following formula (1). This suppresses the reduction of Mn, resulting in a metal with a low Mn content. Furthermore, a high reduction rate is achieved for Ni and Co (especially Ni). For details, see Test A below.

[0020] (0.30a-0.15b+0.60)×[Ni]≦R≦(0.33a-0.17b+0.67)×[Ni]+(0.33a-0.17b+0.67)×[Co]+(0.23a-0.12b+0.47)×[Mn]...(1) However, in the above formula (1), R: Amount of reducing agent added (unit: parts by mole) [Ni]: Nickel content of the oxide (unit: parts by mole) [Co]: Cobalt content of the oxide (unit: parts by mole) [Mn]: Manganese content of the oxide (unit: parts by mole) a: The molar ratio of the content of C-based reducing agent in the reducing agent (unit: molar parts) to the total amount of reducing agent added (unit: molar parts) b: Molar ratio of the content (unit: molar parts) of the Si-based reducing agent in the reducing agent to the total amount of reducing agents added (unit: molar parts)

[0021] 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 determined. 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). X-ray fluorescence (XRF) analysis may also be used.

[0022] Heating mixed oxides (obtaining metals) Next, the mixed oxide (a mixture of oxide and reducing agent) is heated, which reduces the oxide. During 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 to heat 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 shaft furnace, and a steelmaking furnace.

[0023] 《Heating temperature》 The temperature (heating temperature) at which the mixed oxide is heated is preferably equal to or higher than the melting point of the oxide (cathode material) containing nickel oxide, cobalt oxide, and manganese oxide. Considering the heating efficiency of the electric furnace, the heating temperature is preferably 1400°C or higher, more preferably 1450°C or higher, and even more preferably 1450°C or higher.

[0024] The cathode material of waste lithium-ion batteries may contain lithium. For example, lithium carbonate, when heated within the above temperature range, exceeds its melting point and becomes liquefied, making it difficult to handle. However, the lithium contained in the cathode material is an oxide, and its melting point is more than 500°C higher than that of lithium carbonate, so it transfers to the resulting slag while maintaining its form. Therefore, in this embodiment, the handling problems caused by liquefaction described above do not occur.

[0025] The higher the heating temperature, the faster the reduction reaction rate, so by increasing the heating temperature, the time required to reduce the oxide can be shortened. However, if the heating temperature is too high, it may result in the volatilization of Ni and Co. Therefore, the heating temperature is preferably 1600°C or lower, and more preferably 1550°C or lower.

[0026] <Heated 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.

[0027] <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 prevent poor reduction (insufficient reduction reaction). Although there is no particular upper limit, the heating time is preferably 6 hours or less, and more preferably 5 hours or less.

[0028] <Products (metal and slag)> 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. Note that a portion of the Mn contained in the oxide may also be recovered as this metal.

[0029] The metal obtained by reducing the oxide (also referred to as the "product metal") is an alloy containing at least valuable elements (Ni, Co) and impurity elements (Cu, Fe). The resulting metal may contain only one of the valuable elements (Ni, Co).

[0030] By reducing the oxide (cathode material), slag is produced in addition to the metal. For example, when an Al-based reducing agent is used as the reducing agent, the slag (also called "produced slag") contains oxides such as Al2O3. In addition, the produced slag contains Mn, a valuable element that was not contained in the produced metal, in the form of an oxide (for example, MnO). However, separating Mn from the produced metal by hydrometallurgy 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.

[0031] <Separation of metal and slag> As for the product metal and the product slag obtained by the reduction of the oxide, it is preferable to separate them before powdering the product metal, as will be described later. The method of separation is not particularly limited, and known methods can be used.

[0032] <Metal powderization (obtaining metal powder)> Next, it is preferable to powder the resulting metal to obtain a metal powder. In the wet treatment, as described below, the produced metal is first subjected to leaching using an acid solution. At this time, if the produced metal remains in the state obtained by oxide reduction, the leaching efficiency may be insufficient. Therefore, it is preferable to powder the produced metal before performing leaching using an acid solution.

[0033] 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 may increase the risk of an explosive reaction. Therefore, 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 (the same applies hereinafter).

[0034] 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 include methods using a grinding device such as a jaw crusher or a vibration mill; atomization; and the like.

[0035] <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), thereby obtaining a leachate containing the valuable elements and impurity elements. The metal from which the valuable elements and impurity elements have been leached becomes a residue (leaching residue). The method for bringing the metal into contact 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.

[0036] 《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 large compared to the amount of acid solution), some of the metal elements, such as valuable elements, that have dissolved in the acid solution may reach saturated solubility and precipitate, resulting in an insufficient leaching rate. Therefore, 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.

[0037] 《Acid liquid》 The acid solution to be brought into contact with the metal contains at least an acid.

[0038] (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 perspective of realizing the "battery-to-battery" concept of recycling used 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 allows valuable elements to be obtained in the form of sulfates, which are easily usable as cathode materials for lithium-ion batteries. Sulfuric acid containing chloride may also be used as the acid.

[0039] ((acid concentration)) The concentration (acid concentration) of the acid (e.g., 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. There is no particular upper limit, but the acid concentration is preferably 8.0 mol / L or less, more preferably 6.0 mol / L or less, even more preferably 4.0 mol / L or less, and particularly preferably 3.0 mol / L or less.

[0040] (Oxidizing agent for acid solutions) The inventors have found through their investigations that even when the solid-liquid ratio (metal / acid solution) and 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 accelerator. Examples of oxidizing agents for acid solutions include hydrogen peroxide, hypochlorous acid, potassium permanganate, and ozone. Among these, hydrogen peroxide and ozone are preferred because the use of hypochlorous acid and potassium permanganate may require complicated post-treatment for chlorine, potassium, manganese, etc.

[0041] ((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% by volume or more, more preferably 1.0% by volume or more, even more preferably 3.0% by volume or more, even more preferably 5.0% by volume or more, particularly preferably 6.0% by volume or more, and most preferably 6.9% by volume or more, relative to the acid (e.g., sulfuric acid). On the other hand, the content of the oxidizing agent for the acid solution (for example, hydrogen peroxide) in the acid solution is preferably 15.0% by volume or less, more preferably 13.0% by volume or less, and even more preferably 10.0% by volume or less, relative to the acid (for example, sulfuric acid).

[0042] Contact Time The time for which the metal is brought into 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 ensure sufficient 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.

[0043] <Separation of leachate and leach residue> As described below, it is preferable to separate the leachate and the leach residue before adding the sulfiding agent to the leachate. The separation method is not particularly limited, and any known solid-liquid separation method can be used.

[0044] Adding sulfurizing agent (obtaining copper removal solution) Next, a sulfiding 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. In this way, the leachate from which copper (Cu) has been selectively removed is obtained as a copper-removed solution.

[0045] Figure 2 shows the potential-pH diagram for copper (Cu) and nickel (Ni) (S-H2O system). Figure 2 shows the region on the potential-pH diagram for the copper (Cu)-sulfur (S)-water (H2O) system where precipitation of copper (Cu) and nickel (Ni) oxides (hydroxides) or sulfides occurs, taking into account their solubility. Cobalt precipitates in the same manner as nickel, so cobalt is not shown in Figure 2. As shown in Figure 2, copper (Cu) is selectively precipitated in the region where the pH is 3.0 or less and the oxidation-reduction potential is low. Although not shown in Figure 2, in this region, copper precipitates as copper (II) sulfide (CuS). Utilizing this, by making the leachate low pH and reducing, 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.

[0046] Sulfurizing agents Examples of sulfurizing agents to be added to the leaching solution include sulfur (S), hydrogen sulfide (HS), sodium hydrogen sulfide (NaSH), and sodium sulfide (NaS). 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 either case, hydrogen sulfide gas may be generated by the sulfurization reaction, so care must be taken when carrying out this procedure.

[0047] 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.

[0048] (Amount of sulfurizing agent added) From the viewpoint of sufficiently removing copper contained in the leachate, the amount of sulfiding agent added is preferably 1.0 equivalent or more, more preferably 1.5 equivalents or more, and even more preferably 2.0 equivalents or more, relative to the copper (Cu) contained in the leachate. On the other hand, adding an excessive amount of sulfiding agent may result in an increase in the amount of sulfides (precipitates) of valuable elements (Ni, Co, etc.), potentially reducing the amount of the valuable elements desired to remain in the resulting copper removal solution. From this perspective, the amount of sulfiding 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.

[0049] For example, when using 1.0 equivalent of sodium hydrogen sulfide (NaSH) as the sulfiding agent to produce copper(II) sulfide (CuS), 1 mole of sodium hydrogen sulfide (NaSH) is used for every mole of copper (Cu) contained in the leachate.

[0050] 《Sulfide pH》 When a sulfiding agent is added to the leachate to precipitate copper sulfides, if the pH of the leachate to which the sulfiding agent has been added (sulfiding pH) is high, the amount of sulfides (precipitates) of valuable elements that are to be left in the copper removal solution may increase. Therefore, the sulfiding 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 leaching solution. The pH adjuster is not particularly limited, and examples thereof include sulfuric acid and sodium hydroxide.

[0051] Sulfurization Time The time (sulfurization time) for sulfurizing the copper contained in the leachate by reacting it with the sulfurizing agent 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.

[0052] Separation of copper sulfide and copper removal solution As described below, it is preferable to separate the copper sulfide from the copper removal solution before adding the oxidizing agent to the copper removal solution. The separation method is not particularly limited, and any known solid-liquid separation method can be used.

[0053] <Addition of oxidizing agent (obtaining valuable element solution)> 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).

[0054] Figure 3 shows the potential-pH diagram for iron (Fe) and nickel (Ni) (O2-H2O system). Figure 3 shows the region where precipitates of oxides (hydroxides) of iron (Fe) and nickel (Ni) form on the potential-pH diagram for the iron (Fe)-oxygen (O2)-water (H2O) system, taking into account their solubility. Cobalt precipitates in the same manner as nickel, so cobalt is not shown in Figure 3. As shown in Figure 3, iron (Fe) is selectively precipitated in the region where the pH is between 3.0 and 7.0 and where the redox potential is high. Although not shown in Figure 3, in this region, iron precipitates as iron (III) oxide hydroxide (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 (III) oxide hydroxide and selectively removed. In other words, a valuable element solution is obtained, which is a copper-removal solution from which iron (Fe) has been removed.

[0055] Oxidizing agent Examples of oxidizing agents to be 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. Of these, air, hydrogen peroxide and ozone are preferred because the use of hypochlorous acid and potassium permanganate may require complicated post-treatment for chlorine, potassium, manganese, etc.

[0056] (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) added as a gas 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.

[0057] The unit "vvm" is a unit that expresses the volume ratio of gas blown into the liquid per minute. For example, if the amount of oxidant A added is 2 vvm, then 2 L of oxidant A is blown into 1 L of copper removal solution per minute.

[0058] For the same reason, the amount of oxidizing agent B (hydrogen peroxide, hypochlorous acid, potassium permanganate) added is preferably 0.005% by volume or more, more preferably 0.015% by volume or more, even more preferably 0.050% by volume or more, and particularly preferably 0.100% by volume or more, relative to the copper removal solution. On the other hand, the amount of oxidizing agent B added is preferably 1.500% by volume or less, more preferably 1.000% by volume or less, even more preferably 0.500% by volume or less, and particularly preferably 0.300% by volume or less, relative to the copper removal solution.

[0059] Oxidation temperature The inventors have conducted research and found that the use of the above-mentioned oxidizing agents alone may not be sufficient to oxidize the iron contained in the copper removal solution. 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.

[0060] Oxidative 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, precipitation may be difficult to form. Therefore, the oxidizing pH is preferably 3.0 or higher, more preferably 3.7 or higher, even more preferably 4.0 or higher, and particularly preferably 4.5 or higher. On the other hand, if the oxidation pH is too high, there is a concern that the coprecipitation of valuable elements (Ni, Co, etc.) will increase, and the amount of the valuable elements desired to remain in the obtained valuable element solution will decrease. 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 includes sulfuric acid, sodium hydroxide, etc.

[0061] 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.

[0062] <<oxidation promoter>> In order to increase the reaction rate 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 powder. The principle behind the increase in reaction rate due to the oxidation aid is catalytic action. Specifically, the oxidation aid tends to be negatively charged in the aqueous solution (copper removal solution), so Fe 2+ It adsorbs ions and Fe 2+ Internal e - This weakens the bond with Fe 2+ →Fe 3+ +e - It is thought that the activation energy of this reaction (Fe oxidation reaction) decreases, accelerating the reaction.

[0063] (Amount of auxiliary oxidation agent added) It is believed that the larger the amount of oxidation aid added, the larger the reaction surface area and the faster the rate of the Fe oxidation reaction. Therefore, the amount of 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 aid is too large, there is a concern that the coprecipitation of valuable elements (such as Ni and Co) will increase. Therefore, the amount of the oxidation aid 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.

[0064] (particle size of oxidation aid) If the particle size of the oxidation promoter is too small, the reaction surface area becomes too large, which may increase the coprecipitation of valuable elements (Ni, Co, etc.). Therefore, the particle size of the oxidation promoter 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 promoter 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 promoter is preferably 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.0 μm or less.

[0065] <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 separation method is not particularly limited, and known solid-liquid separation methods 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. [Example]

[0066] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0067] [Test A] In Test A, the amount R of the reducing agent (C-based reducing agent, Si-based reducing agent, and Al-based reducing agent) added was investigated.

[0068] <Test A1: C-based reducing agent> NiO, CoO, and MnO were mixed to prepare an oxide. The contents of Ni, Co, and Mn (unit: parts by mole) in the prepared oxide are shown in Table 1 below. As the reducing agent, a C-based reducing agent, which is coke, was prepared.

[0069] A mixed oxide was obtained by adding a C-based reducing agent to the prepared oxide in the amount (unit: parts by mole) shown in Table 1 below. The mixed oxide obtained was filled into a molding die, and pressure was applied to the molding die from the outside to obtain a molded body of the mixed oxide. The compact was then heated for 3 hours in an Ar atmosphere using a heater (electric resistance furnace) maintained at a temperature of 1450°C to reduce the oxides, yielding metal (product metal) and slag (product slag), which were then separated.

[0070] The content (unit: mol %) of each element in the produced metal was determined by X-ray fluorescence (XRF) analysis, and the results are shown in Table 1 below. The Ni reduction rate (unit: %) was calculated from the Ni content of the oxide and the Ni content of the produced metal. The results are shown in Table 1 below.

[0071] [Table 1]

[0072] As shown in Table 1 above, in Nos. 1 to 6, the Mn content of the produced metal was 9.0 mol % or less, and the Ni reduction rate was 85% or more. In contrast, No. 7 had a Ni reduction rate of 70%. In addition, in Nos. 8 and 9, the Mn content of the produced metal was 28.5 mol % or more.

[0073] From the viewpoint of keeping the Mn content of the produced metal low, an upper limit of 2.70 molar parts can be derived for the amount of reducing agent added, R. This upper limit can be expressed by the formula [Ni] + [Co] + α(C) × [Mn], where α(C) = 0.70.

[0074] If the amount of reducing agent added, R, is too low, NiO is not reduced, Ni is contained in the produced slag, and the Ni reduction rate is reduced. Specifically, when the amount of reducing agent added, R, is 0.70 parts by mole, the Ni reduction rate is 70% (No. 7). Here, when the amount of reducing agent added, R, is 0.90 parts by mole or more, the Ni reduction rate is 85% or more (Nos. 1 to 6). From this, 0.90 parts by mole can be derived as the lower limit of the amount of reducing agent added, R. This lower limit can be expressed by the formula β(C) × [Ni], and β(C) = 0.90 is obtained.

[0075] In order to efficiently recover not only Ni but also Co, the amount of reducing agent added, R, is preferably 2.00 molar parts or more. In this case, the lower limit of the amount of reducing agent added, R, corresponds to [Ni] + [Co].

[0076] <Test A2: Si-based reducing agent> Oxides were prepared in the same manner as in Test A1 described above. The contents of Ni, Co, and Mn (unit: parts by mole) in the prepared oxides are shown in Table 2 below. As the reducing agent, a Si-based reducing agent, which is metallic silicon, was prepared. To the prepared oxide, a Si-based reducing agent was added in the amount (unit: parts by mole) shown in Table 2 below to obtain a mixed oxide. The resulting mixed oxide was molded and heated in the same manner as in the above-mentioned test A1 to obtain a product metal and a product slag. Next, in the same manner as in Test A1 described above, the content (unit: mol %) of each element in the produced metal and the Ni reduction rate (unit: %) were determined. The results are shown in Table 2 below.

[0077] [Table 2]

[0078] As shown in Table 2 above, in Nos. 10 to 15, the Mn content of the produced metal was 8.9 mol % or less, and the Ni reduction rate was 86% or more. In contrast, No. 16 had a Ni reduction rate of 70%. In addition, in Nos. 17 and 18, the Mn content of the produced metal was 27.6 mol % or more.

[0079] From the viewpoint of keeping the Mn content of the produced metal low, an upper limit of 1.35 molar parts can be derived for the amount of reducing agent added, R. This upper limit can be expressed by the formula 0.50 × [Ni] + 0.50 × [Co] + α(Si) × [Mn], which gives α(Si) = 0.35.

[0080] If the amount of reducing agent R is too low, NiO is not reduced, and Ni is contained in the resulting slag, resulting in a low Ni reduction rate. Specifically, when the amount of reducing agent R is 0.35 parts by mole, the reduction rate of Ni is 70% (No. 16). Here, when the amount of reducing agent added, R, is 0.45 parts by mole or more, the Ni reduction rate is 86% or more (Nos. 10 to 15). From this, 0.45 parts by mole can be derived as the lower limit of the amount of reducing agent added, R. This lower limit can be expressed by the formula β(Si) × [Ni], and β(Si) = 0.45 is obtained.

[0081] When the amount R of the reducing agent added is 1.25 parts by mole or more, Si is mixed into the produced metal, but this does not interfere with the recovery of Ni and Co when they are separated and recovered in the subsequent wet treatment.

[0082] In order to efficiently recover not only Ni but also Co, the amount of reducing agent added, R, is preferably 1.00 molar parts or more. In this case, the lower limit of the amount of reducing agent added, R, corresponds to 0.50 × [Ni] + 0.50 × [Co].

[0083] <Test A3: Al-based reducing agent> Oxides were prepared in the same manner as in Test A1 described above. The contents of Ni, Co, and Mn (unit: parts by mole) in the prepared oxides are shown in Table 3 below. As the reducing agent, an Al-based reducing agent, which is metallic aluminum, was prepared.

[0084] To the prepared oxide, an Al-based reducing agent was added in the amount (unit: parts by mole) shown in Table 3 below to obtain a mixed oxide. The resulting mixed oxide was molded and heated in the same manner as in the above-mentioned test A1 to obtain a product metal and a product slag. Next, in the same manner as in Test A1 described above, the content (unit: mol %) of each element in the produced metal and the Ni reduction rate (unit: %) were determined. The results are shown in Table 3 below.

[0085] [Table 3]

[0086] As shown in Table 3 above, in Nos. 19 to 24, the Mn content of the produced metal was 8.8 mol % or less, and the Ni reduction rate was 85% or more. In contrast, No. 25 had a Ni reduction rate of 70%. In addition, Nos. 26 and 27 had a Mn content of 27.1 mol % or more in the produced metal.

[0087] From the viewpoint of keeping the Mn content of the produced metal low, an upper limit of 1.80 molar parts can be derived for the amount of reducing agent added, R. This upper limit can be expressed by the formula 0.67 × [Ni] + 0.67 × [Co] + α(Al) × [Mn], which gives α(Al) = 0.47.

[0088] If the amount of reducing agent added, R, is too low, NiO is not reduced, Ni is contained in the produced slag, and the Ni reduction rate is reduced. Specifically, when the amount of reducing agent added, R, is 0.47 parts by mole, the Ni reduction rate is 70% (No. 25). Here, when the amount of reducing agent added, R, is 0.60 parts by mole or more, the Ni reduction rate is 85% or more (Nos. 19 to 24). From this, 0.60 parts by mole can be derived as the lower limit of the amount of reducing agent added, R. This lower limit can be expressed by the formula β(Al) × [Ni], which gives β(Al) = 0.60.

[0089] To efficiently recover not only Ni but also Co, the amount of reducing agent added, R, should be 1.34 molar parts or more. In this case, the lower limit of the amount of reducing agent added, R, corresponds to 0.67 × [Ni] + 0.67 × [Co].

[0090] When the amount R of the reducing agent added is 1.67 parts by mole or more, Al is mixed into the produced metal, but this does not interfere with the recovery of Ni and Co when they are separated and recovered in the subsequent hydroprocessing.

[0091] The above-described appropriate range for the amount R of reducing agent added also applies when the reducing agent is a mixture of a C-based reducing agent, a Si-based reducing agent, and an Al-based reducing agent. That is, the amount of reducing agent added is set to an amount R that satisfies the following formula (1). (0.30a-0.15b+0.60)×[Ni]≦R≦(0.33a-0.17b+0.67)×[Ni]+(0.33a-0.17b+0.67)×[Co]+(0.23a-0.12b+0.47)×[Mn]...(1)

[0092] In the above formula (1), a is the molar ratio (C-based reducing agent / total reducing agent) of the content (unit: molar parts) of the C-based reducing agent in the reducing agent to the total amount of reducing agent added (unit: molar parts). Furthermore, b is the molar ratio (Si-based reducing agent / total reducing agent) of the content (unit: molar parts) of the Si-based reducing agent in the reducing agent to the total amount of reducing agent added (unit: molar parts).

[0093] By adopting such an addition amount R, it is possible to obtain a produced metal with a low Mn content, and also to reduce the amount of Ni contained in the produced slag, thereby achieving a high Ni reduction rate.

[0094] <Test A4: C-based reducing agent, Si-based reducing agent, and Al-based reducing agent> Oxides were prepared in the same manner as in Test A1 described above. The contents of Ni, Co, and Mn (unit: parts by mole) in the prepared oxides are shown in Table 4 below. At least one of a C-based reducing agent, a Si-based reducing agent, and an Al-based reducing agent was added as a reducing agent to the prepared oxide in the amount (unit: parts by mole) shown in Table 4 below to obtain a mixed oxide. Graphite was used as the C-based reducing agent, metallic silicon was used as the Si-based reducing agent, and metallic aluminum was used as the Al-based reducing agent.

[0095] The resulting mixed oxide was molded and heated in the same manner as in the above-mentioned test A1, thereby reducing the cathode material (oxide) and obtaining a produced metal and a produced slag. Next, in the same manner as in Test A1 described above, the content (unit: mol %) of each element in the produced metal and the reduction rate (unit: %) of each element were determined. The results are shown in Table 4 below.

[0096] [Table 4] TIFF2025155136000006.tif241136

[0097] As described above, when a carbon-based reducing agent is used as the reducing agent, the amount of reducing agent added (unit: parts by mole) is set to R, which satisfies 0.90 × [Ni] ≦ R ≦ [Ni] + [Co] + 0.70 × [Mn]. Specifically, the amount of reducing agent added is set to R, which satisfies 0.216 ≦ R ≦ 0.376. As shown in Table 4 above, Nos. 28 to 33, in which the additive amount R fell within the above range, had a Ni reduction rate of 79% or more and a Mn content of the produced metal of 4.6 mol % or less. In contrast, No. 34, in which the additive amount R was below the above range, had a Ni reduction rate of 69%, which was lower than Nos. 28 to 33. In addition, in Nos. 35 to 36, in which the additive amount R exceeded the above range, the Mn content of the resulting metal was 17.0% or more, which was higher than that of Nos. 28 to 33.

[0098] As described above, when a Si-based reducing agent is used as the reducing agent, the amount of reducing agent added (unit: molar parts) R is set to satisfy 0.45 × [Ni] ≦ R ≦ 0.5 × [Ni] + 0.5 × [Co] + 0.35 × [Mn]. Specifically, the amount of reducing agent added R is set to satisfy 0.108 ≦ R ≦ 0.188. As shown in Table 4 above, Nos. 37 to 42, in which the additive amount R fell within the above range, had a Ni reduction rate of 76% or more and a Mn content of the produced metal of 4.6 mol % or less. In contrast, No. 43, in which the additive amount R was below the above range, had a Ni reduction rate of 70%, which was lower than Nos. 37 to 42. In addition, Nos. 44 to 45, in which the additive amount R exceeded the above range, had a Mn content of 16.2 mol % or more in the resulting metal, which was higher than Nos. 37 to 42.

[0099] As described above, when an Al-based reducing agent is used as the reducing agent, the amount of reducing agent added (unit: molar parts) R is set to satisfy 0.60 × [Ni] ≦ R ≦ 0.67 × [Ni] + 0.67 × [Co] + 0.47 × [Mn]. Specifically, the amount of reducing agent added R is set to satisfy 0.144 ≦ R ≦ 0.252. As shown in Table 4 above, Nos. 46 to 51, in which the additive amount R fell within the above range, had a Ni reduction rate of 77% or more and a Mn content of the produced metal of 4.4 mol % or less. In contrast, No. 52, in which the additive amount R was below the above range, had a Ni reduction rate of 60%, which was lower than Nos. 46 to 51. In addition, Nos. 53 to 54, in which the amount of addition R exceeded the above range, had a Mn content of 12.0 moles or more in the produced metal, which was higher than Nos. 46 to 51.

[0100] Furthermore, as shown in Table 4 above, in Nos. 55 to 58, in which the reducing agent was a mixture of a C-based reducing agent, a Si-based reducing agent, and an Al-based reducing agent and the amount R of the reducing agent added satisfied the above formula (1), the Mn content of the produced metal was low and a high Ni reduction rate was obtained. In contrast, Nos. 59 to 60, in which the additive amount R did not satisfy the above formula (1), had a higher Mn content in the produced metal than Nos. 55 to 58, or a lower Ni reduction rate than Nos. 55 to 58. Similar trends were observed in the comparisons between Nos. 61-64 and Nos. 65-66, between Nos. 67-70 and Nos. 71-72, and between Nos. 73-76 and Nos. 77-78.

[0101] [Test B] <Preparing the cathode material> A cathode material (oxide) 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, and the cathode material was separated. The cathode material was crushed and pulverized into powder form. The contents (unit: parts by mol) of Ni, Co, and Mn in the positive electrode material (oxide) were 0.24 parts by mol, 0.08 parts by mol, and 0.08 parts by mol, respectively, similar to the oxide used in the above-mentioned test A4. The positive electrode material contained Cu and Fe as impurity elements in addition to Ni, Co, and Mn.

[0102] Addition of reducing agent To the prepared cathode material (oxide), at least one reducing agent selected from the group consisting of a C-based reducing agent, a Si-based reducing agent, and an Al-based reducing agent was added in the same amount R (unit: parts by mole) as in Nos. 28-30, 37-39, 46-48, 55-56, 61-62, 67-68, and 73-74 of Test A4 described above, to obtain mixed oxides. Graphite was used as the C-based reducing agent, metallic silicon was used as the Si-based reducing agent, and metallic aluminum was used as the Al-based reducing agent.

[0103] <Heating mixed oxides> The resulting mixed oxide was molded and heated in the same manner as in the above-mentioned test A1, thereby reducing the cathode material (oxide) and obtaining a produced metal and a produced slag. Next, the content (unit: mol%) of each element in the produced metal and the reduction rate (unit: %) of each element were determined in the same manner as in Test A1 described above. The results were all similar to those of Nos. 28-30, 37-39, 46-48, 55-56, 61-62, 67-68, and 73-74 in Test A4 described above.

[0104] <Metal powdering> Of the metals (product metals) obtained by reduction of the positive electrode material, metals having the compositions shown in Table 5 below were pulverized using a vibration mill to obtain metal powders. The particle size of the resulting metal powder was 1100 μm.

[0105] <Contact between metal and acidic solution> 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 5 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. In this way, 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 5 below. As shown in Table 5 below, the leaching rate for each element was 100 mass %, and all of the elements were leached from the metal into the leachate.

[0106] [Table 5]

[0107] <Addition of sulfurizing agent> The content (unit: g / L) of each element in the obtained leachate is shown in Table 6 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 sulfided by reacting with the sulfiding agent (sulfiding time: 20 minutes) and precipitated as copper sulfide (copper (II) sulfide).The copper sulfide was then separated from the copper-removed leachate, which was the copper-removed solution. The content (unit: g / L) of each element in the copper removal solution was determined by ICP-AES (inductively coupled plasma atomic emission spectroscopy), and the results are shown in Table 6 below. Furthermore, for each element, the ratio of the content in the copper removal solution to the content in the leaching solution was calculated as the residual rate a (unit: mass %). The results are shown in Table 6 below. As shown in Table 6 below, the Cu content in the copper removal solution was very low, which indicates that Cu was removed from the leachate with very high efficiency.

[0108] <Addition of oxidizing agent> Next, the copper removal solution was first diluted with water. The contents of each element (unit: g / L) in the diluted copper removal solution are shown in Table 6 below. The reason for dilution was that in a preliminary experiment, when an oxidizing agent was added to a model solution having a composition similar to that of the copper removal solution shown in Table 6 below, excessive precipitation occurred, making stirring impossible in some cases. Hydrogen peroxide was added as an oxidizing agent to the diluted copper removal solution, and the mixture was stirred. The amount of the oxidizing agent (hydrogen peroxide) added was 0.020% by volume relative to the diluted copper removal solution. 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-removed solution was oxidized by reacting with the oxidizing agent (oxidation time: 1.0 hour) and precipitated as iron hydroxide (iron (III) oxide hydroxide).The iron hydroxide was then separated from the valuable element solution, which was the copper-removed 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 6 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 6 below. As shown in Table 6 below, the content of Fe in the valuable element solution is very low, which indicates that Fe was removed from the copper removal solution with very high efficiency.

[0109] Furthermore, for each element, the final residual rate in the valuable element solution was calculated as the total residual rate (unit: mass%) from residual rate a and residual rate b. The results are shown in Table 6 below. The results shown in Table 6 below show that by performing dry processing, then powdering the metal obtained by the dry processing, and then performing wet processing, valuable elements (Ni, Co) could be recovered with very high purity.

[0110] [Table 6]

[0111] [Test C] <Preparing the cathode material ~ Powdering the metal> The steps from preparation of the positive electrode material to powdering of the metal were the same as those in Test B, and therefore the explanation will be omitted.

[0112] <Contact between metal and acidic solution> 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 7 below. A metal (metal powder) was brought into contact with an acid solution to obtain a leachate in the same manner as in Test B 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 into the leachate was calculated in the same manner as in the above-mentioned Test B. The results are shown in Table 7 below. As shown in Table 7 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% by volume or more in order to sufficiently leach valuable metals (Ni, Co). However, when the amount exceeds 6.9% by volume, the leaching rate reaches a plateau. Therefore, from the viewpoint of cost, it was found that the amount of oxidizing agent (hydrogen peroxide) for the acid solution in this example is preferably 6.9% by volume.

[0113] [Table 7]

[0114] <Addition of sulfurizing agent> Sodium hydrogen sulfide (NaSH) was added as a sulfiding agent to the leachate shown in Table 6 in the amount (unit: equivalent) shown in Table 8 below, and the mixture was stirred. At this time, the sulfiding pH was adjusted to the value shown in Table 8 below. The copper contained in the leachate was precipitated as copper sulfide in the same manner as in Test B described above, except that the amount of sulfiding agent added and the sulfiding pH were changed, 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 B. The results are shown in Table 8 below. As shown in Table 8 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 8 below, as the sulfurization pH increased, there was a tendency for copper removal to become insufficient and for the Ni and Co residual rates 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).

[0115] [Table 8]

[0116] <Addition of oxidizing agent> First, the copper removal solution obtained in Test Example 8-4 in Table 8 above was diluted five times. Next, hydrogen peroxide was added as an oxidizing agent to the diluted copper removal solution in the amount (unit: vol %) shown in Table 9 below, followed by stirring. At this time, the oxidation pH and oxidation temperature (unit: °C) were adjusted to the values ​​shown in Table 9 below. The iron contained in the copper removal solution was precipitated as iron hydroxide to obtain a valuable element solution in the same manner as in Test B described above, except that the amount of oxidizing agent added, the oxidation pH, and the oxidation temperature were changed. 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 B. The results are shown in Table 9 below. As shown in Table 9 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 9 below, as the oxidation pH increased, iron was more efficiently removed, but the Ni and Co residual rates tended to decrease. From the above, it was found that within the scope of this example, the amount of oxidizing agent (hydrogen peroxide) added was preferably 0.030% by volume, and the oxidation pH was preferably in the range of 4.5 to 5.0.

[0117] [Table 9]

Claims

1. A reducing agent is added to an oxide containing at least one valuable element selected from the group consisting of nickel and cobalt, and manganese, and impurity elements, 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-removed solution; adding an oxidizing agent to the copper-removing solution to precipitate iron as iron hydroxide, thereby obtaining the copper-removing solution from which iron has been removed as a valuable element solution containing the valuable element; the reducing agent contains at least one selected from the group consisting of a carbon-containing C-based reducing agent, a silicon-containing Si-based reducing agent, and an aluminum-containing Al-based reducing agent; The method for recovering valuable elements, wherein the amount R of the reducing agent added satisfies the following formula (1): (0.30a-0.15b+0.60)×[Ni]≦R≦(0.33a-0.17b+0.67)×[Ni]+(0.33a-0.17b+0.67)×[Co]+(0.23a-0.12b+0.47)×[Mn]...(1) However, in the formula (1), R: Amount of the reducing agent added (unit: parts by mole) [Ni]: Nickel content of the oxide (unit: molar parts) [Co]: Cobalt content of the oxide (unit: molar parts) [Mn]: manganese content of the oxide (unit: molar parts) a: the molar ratio of the content (unit: molar parts) of the C-based reducing agent in the reducing agent to the total amount (unit: molar parts) of the reducing agent added b: the molar ratio of the content (unit: molar parts) of the Si-based reducing agent in the reducing agent to the total amount (unit: molar parts) of the reducing agent added is.

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

3. 2. The method for recovering valuable elements according to claim 1, wherein the mixed oxide is heated to a temperature of 1400°C or higher.

4. 2. The method for recovering valuable elements according to claim 1, wherein the metal obtained by heating the mixed oxide contains the valuable element and the impurity element.

5. The method for recovering valuable elements according to any one of claims 1 to 4, wherein the metal is powdered and then brought into contact with the acid solution.

6. The acid solution contains an acid and an oxidizing agent for the acid solution, 5. 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.

7. 7. The method for recovering valuable elements according to claim 6, wherein the oxidizing agent for the acid solution is hydrogen peroxide.

8. the amount of the sulfiding agent added is 1.0 equivalent or more relative to the copper contained in the leaching solution; 5. 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 precipitating the copper sulfide.

9. 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; 5. The method for recovering a valuable element 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.

10. 10. The method for recovering valuable elements according to claim 9, wherein the temperature of the copper removal solution to which the oxidizing agent has been added is 10°C or higher.

11. A method for producing a metal, comprising producing a metal containing at least one element selected from the group consisting of nickel and cobalt, using the method for recovering valuable elements according to any one of claims 1 to 4.

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