Method for recovering valuable element

Abstract

In this method, a reducing agent containing at least one member selected from the group consisting of iron metal and iron oxides is added to an oxide containing at least one valuable element selected from the group consisting of nickel, cobalt, and manganese and further containing copper and iron as impurity elements to obtain an oxide mixture. The oxide mixture is heated to reduce the oxide to thereby obtain metals. The metals are brought into contact with an acid liquid to obtain a leachate containing the valuable element and the impurity elements. A sulfurizing agent is added to the leachate to sediment the copper as copper sulfide, and the leachate from which the copper has been removed is obtained as a copper-free solution. An oxidizing agent is added to the copper-free solution to sediment the iron as iron hydroxide, and the copper-free solution from which the iron has been removed is obtained as a valuable-element solution containing the valuable element. Thus, the present invention can provide a method for recovering a valuable element, the method being capable of removing impurity elements.

Description

Method for recovering valuable elements

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

[0002] In recent years, the demand for lithium-ion batteries has been increasing rapidly due to the widespread use of smartphones, personal computers, and electric vehicles. ２ From the perspective of reducing emissions, demand for electric vehicles that do not use fossil fuels is expected to continue to expand in the future, and the demand for lithium-ion batteries is also expected to increase further in the future.

[0003] Generally, lithium-ion batteries are composed of a combination of components such as a cathode material, an anode material, and a separator, and also contain an electrolyte. The cathode material of a lithium-ion battery is composed of an oxide (composite oxide) containing nickel (Ni), cobalt (Co), manganese (Mn), etc. The supply of metal elements such as Ni, Co, and Mn that make up the cathode material is by no means abundant, even on a global scale. For this reason, recovering these metal elements (valuable elements) from the cathode material of used lithium-ion batteries is highly desirable from the perspective of effective resource utilization. Here, "used lithium-ion batteries" refers to used lithium-ion batteries; defective lithium-ion batteries (those generated during the manufacturing process of lithium-ion batteries); etc.

[0004] When recovering valuable elements from the cathode material of used lithium-ion batteries, prior to recovery, it is necessary to carry out pre-treatment such as removal of the electrolyte, crushing, pulverization, etc. After such pre-treatment, the cathode material is separated from the used lithium-ion batteries, and then the valuable elements are recovered from the separated cathode material.

[0005] Dry processing is one example of a process for recovering valuable elements. In dry processing (see, for example, Patent Document 1), for example, a reducing agent is added to oxide (cathode material) separated from waste lithium-ion batteries, followed by heating to obtain metal and slag. The two are then separated to recover metal containing valuable elements.

[0006] Japanese Patent Application Laid-Open No. 2021-95628

[0007] Metals obtained by dry processing may contain impurity elements in addition to valuable elements such as Ni and Co. Examples of 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, the presence of impurity elements (Cu and Fe) in the metals may deteriorate battery performance. For this reason, 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.

[0009] As a result of extensive research, the present inventors have found that the above object can be achieved by adopting the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to

[12] : [1] A method for recovering valuable elements, comprising: adding a reducing agent containing at least one element selected from the group consisting of metallic iron and iron oxide to an oxide containing at least one valuable element selected from the group consisting of nickel, cobalt, and manganese and copper and iron as impurity elements 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-removed solution to precipitate iron as iron hydroxide, and obtaining the copper-removed solution from which iron has been removed as a valuable element solution containing the valuable element. [2] The method for recovering a valuable element according to [1] above, wherein the oxide is obtained from waste lithium-ion batteries. [3] The method for recovering a valuable element according to [1] or [2] above, wherein the metal is powdered before being brought into contact with the acid solution. [4] The method for recovering a valuable element according to any of [1] to [3] above, wherein the iron oxide is ferrous oxide. [5] The method for recovering a valuable element according to any of [1] to [4] above, wherein the mixed oxide is heated to a temperature of 1,450°C or higher. [6] The method for recovering a valuable element according to any of [1] to [5] above, wherein the metal obtained by heating the mixed oxide contains the valuable element and the impurity element. [7] The method for recovering a valuable element according to any of [1] to [6] 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. [8] The method for recovering valuable elements according to [7] above, wherein the oxidizing agent for the acid solution is hydrogen peroxide. [9] The method for recovering valuable elements according to any one of [1] to [8] 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.

[10] The method for recovering a valuable element according to any one of [1] to [9] 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 oxidizing agent A added is 0.1 vvm or more relative to the copper-removing solution, the amount of oxidizing agent B added is 0.005 vol% or more relative to the copper-removing solution, and the pH of the copper-removing 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] The method for recovering a valuable element according to

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

[12] The method for recovering a valuable element according to any one of [1] to

[11] above, wherein the reducing agent is at least one selected from the group consisting of dust, scale, sludge, and scrap.

[0010] According to the present invention, a method for recovering valuable elements that can remove impurity elements can be provided.

[0011] A flowchart showing an example of a method for recovering valuable elements. An Ellingham diagram (standard free energy change vs. temperature diagram). A potential-pH diagram (S-H) of Cu and Ni. ２ The potential-pH diagram of Fe and Ni (O ２ -H ２ O system).

[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), a cathode material (oxide) of a waste lithium ion battery is subjected to dry treatment and wet treatment.

[0013] FIG. 1 is a flowchart illustrating an example of a method for recovering valuable elements. This method will be described briefly with reference to FIG. 1 . In the dry treatment, a reducing agent (described later) is added to oxides (Ni, Co, Mn, Cu, and Fe) to obtain a mixed oxide. The resulting mixed oxide is then heated to reduce the oxides, yielding metals (Ni, Co, Mn, Cu, and Fe) and slag. The two are separated as appropriate. Prior to the wet treatment, the resulting metals are preferably powdered to obtain metal powders (Ni, Co, Mn, Cu, and Fe). In the wet treatment, the metals (metal powders) are first contacted with an acid solution to obtain a leachate (Ni, Co, Mn, Cu, and Fe) and a leach residue. The two are separated as appropriate. A sulfiding agent is then added to the resulting leachate to precipitate copper sulfides (Cu), yielding a copper-removed solution (Ni, Co, Mn, and Fe). The two are separated as appropriate. An oxidizing agent is then added to the copper removal solution to precipitate iron hydroxide (Fe) to obtain a valuable element solution (Ni, Co, Mn).

[0014] In this way, valuable elements (Ni, Co, Mn) can be recovered from the oxide while removing impurity elements (Cu, Fe). This recovery method makes it possible to easily recover valuable elements from the cathode material (oxide) of used lithium-ion batteries with a purity high enough to be reused as a raw material for lithium-ion batteries.

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

[0016] <Subject to be reduced (oxide)> The subject to be reduced in this recovery method is an oxide containing at least one valuable element selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn) and impurity elements such as copper (Cu) and iron (Fe), specifically, for example, a cathode material for used lithium-ion batteries. The valuable element may be at least one element selected from the group consisting of Ni and Co. The cathode material (oxide) is obtained by subjecting the used lithium-ion batteries to pre-treatment such as removal of the electrolyte, crushing, pulverization, and sorting.

[0017] <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.

[0018] <<Findings Obtained by the Inventors>> The positive electrode material of a lithium ion battery is generally LiNiO ２ , LiCoO ２ , LiMnO ２ When dry processing is considered thermodynamically, for example, LiNiO ２ and LiCoO ２ At high temperatures, LiNiO decomposes as follows to produce NiO and CoO, respectively: ２ →Li ２ O+2NiO+1 / 2O ２ 2LiCoO ２ →Li ２ O+2CoO+1 / 2O ２

[0019] The standard free energy change (ΔG) in the decomposition reaction of NiO and CoO ０ ) are shown below: NiO → Ni + 1 / 2O ２ : ΔG ０ =234900-84.68T[J] CoO→Co+1 / 2O ２ : ΔG ０ =235480-71.55T [J]. Any substance having a free energy change value lower than these standard free energy change values ​​at any high temperature can be used as a reducing agent.

[0020] Conventionally, substances with strong reducing power, such as carbonaceous materials, Al-containing materials, and Si-containing materials, have been used as reducing agents. This is intended to avoid insufficient reduction. When the reducing power of the reducing agent is insufficient and insufficient reduction occurs, a portion 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, when a carbonaceous material is used as a reducing agent, the CO ２Furthermore, when an Al-containing or Si-containing substance is used as the reducing agent, the cost is high because the price of the reducing agent itself is relatively high. ２ From the viewpoints of reducing the amount of carbon generated and reducing costs, it is desirable to use a reducing agent other than these. Therefore, the present inventors investigated substances that are not carbonaceous, are relatively inexpensive, and are not rare, as potential new reducing agents. As a result, they found that metallic iron (Fe) or iron oxide is effective.

[0021] The standard free energy change (ΔG ０ ) is as follows: FeO = Fe + 1 / 2O ２ : ΔG ０ =264430-64.73T[J]Fe ３ O ４ =3FeO+1 / 2O ２ : ΔG ０ =302370-108.15T[J]

[0022] FIG. 2 is an Ellingham diagram (standard free energy change vs. temperature diagram). Referring to the standard free energy change and the Ellingham diagram (FIG. 2) described above, the Fe / FeO equilibrium is more noble than the Ni / NiO equilibrium and the Co / CoO equilibrium, suggesting the possibility of reduction by Fe. ３ O ４ The equilibrium is more noble than the Ni / NiO equilibrium but more noble than the Co / CoO equilibrium. Therefore, it is expected that Ni will be recovered as metal and Co will remain in the slag. Specifically, the following reaction is expected: NiO + Fe → Ni + FeO: ΔG ０ =-29530-19.95T[J] CoO+Fe→Co+FeO:ΔG ０ =-28950-6.82T[J]

[0023] In the Ellingham diagram (Figure 2), the higher the position, the easier it is to metallize. When Si or Al is used as a reducing agent, Mn also tends to metallize. Therefore, by using Fe (or FeO) as a reducing agent, it is expected that only Ni and Co will metallize without metallizing Mn.

[0024] For the reasons described above, the present recovery method uses a reducing agent containing at least one of metallic iron (Fe) and iron oxide. As the metallic iron (Fe), for example, scrap or granulated iron used in steel mills may be used.

[0025] Iron oxide is generally ferrous oxide (FeO), also known as wustite, and triiron tetroxide (FeO), also known as magnetite. ３ O ４ ) and ferric oxide (Fe), also known as hematite ２ O ３ ) Among these, magnetite and hematite have a higher standard free energy change than wüstite at the same temperature, and may be less likely to cause a reduction reaction. For this reason, ferrous oxide (wüstite) is preferred as the iron oxide because it is more likely to cause a reduction reaction. The iron oxide may be at least one of dust, scale, and sludge (hereinafter referred to as "dusts" for convenience) that are generated secondarily in the iron-making process. Using dusts as the iron oxide is preferred from the viewpoints of effectively utilizing by-products of the iron-making process and utilizing an inexpensive iron source.

[0026] <<Amount of Reducing Agent Added>> The amount 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), reduction using 1.0 equivalent of the reducing agent is expressed as follows: Fe + (NiO, CoO, MnO) → (Ni, Co, Mn) + FeO 3FeO + (NiO, CoO, MnO) → (Ni, Co, Mn) + Fe ３ O ４

[0027] 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 oxide to be reduced are measured and regarded as the contents of NiO, CoO, and MnO in the oxide to be reduced, respectively. The contents of Ni, Co, and Mn are measured using an energy dispersive X-ray analyzer (EDX).

[0028] The amount of reducing agent added is preferably 1.0 equivalent or more, more preferably 1.1 equivalent or more, even more preferably 1.2 equivalents or more, and particularly preferably 1.4 equivalents or more, because this makes it easier to prevent insufficient reduction.

[0029] However, if a large amount of reducing agent is added to the oxide to avoid insufficient reduction, the amount of iron (Fe) contained in the resulting metal (product metal) tends to be large. Conventionally, to suppress the Fe content in the product metal (for example, to 10 mass% or less), it is necessary to reduce the amount of reducing agent added (for example, less than 1.1 equivalents), which makes it difficult to suppress insufficient reduction. However, in the present recovery method, Fe can be removed by wet treatment, so the amount of reducing agent added can be increased (for example, 1.1 equivalents or more), making it easier to suppress insufficient reduction.

[0030] Therefore, there is no particular upper limit to the amount of reducing agent added. However, from the viewpoint of facilitating the removal of Fe by wet treatment, it is preferable that the amount of Fe contained in the produced metal is small. Furthermore, even if an excessive amount of reducing agent is added, the effect is saturated. Therefore, the amount of reducing agent added is preferably 2.0 equivalents or less, and more preferably 1.8 equivalents or less.

[0031] <Heating the mixed oxide (obtaining metal)> Next, the mixed oxide (a mixture of oxide and reducing agent) is heated. This reduces the oxide. During heating, CaO, SiO ２A flux such as a fluorine-containing compound may be added to the mixed oxide. 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.

[0032] <Heating Temperature> The temperature at which the mixed oxide is heated (heating temperature) is preferably 1300° C. or higher, more preferably 1350° C. or higher, even more preferably 1400° C. or higher, and particularly preferably 1450° C. or higher, because this makes it easier to suppress insufficient reduction. There is no particular upper limit, but the heating temperature is preferably 1800° C. or lower, more preferably 1700° C. or lower.

[0033] <Heating Atmosphere> The atmosphere (heating atmosphere) when heating the mixed oxide may be, for example, nitrogen gas (N ２ Suitable examples of the atmosphere include an inert atmosphere such as a nitrogen atmosphere, an argon gas (Ar) atmosphere, and a reducing atmosphere such as a carbon monoxide gas (CO) atmosphere.

[0034] <<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.

[0035] <<Products (Metals and Slag)>> Metals are produced by reducing the oxide (cathode material) to be reduced. That is, valuable elements (Ni, Co, Mn) contained in the oxide are recovered as metals.

[0036] The metal obtained by reducing the oxide (also referred to as the "product metal") is an alloy containing valuable elements (Ni, Co, Mn) and impurity elements (Cu, Fe). The product metal may contain only one of the valuable elements (Ni, Co, Mn).

[0037] By reducing an oxide (cathode material), slag may be produced in addition to metal. The slag (also called "produced slag") contains oxides such as FeO. In addition, the produced slag may also contain oxides of valuable elements (e.g., MnO) that were not included in the produced metal. When an oxide containing Mn is reduced, the Mn / MnO equilibrium becomes the Fe / FeO equilibrium and the FeO / Fe ３ O ４ Since the Mn content is lower than the equilibrium value, it is possible to prevent Mn from being mixed into the resulting metal obtained by reduction. However, separating Mn from the resulting metal by hydrometallurgy is a heavy burden. Preventing Mn from being mixed into the resulting metal and retaining Mn in the resulting slag is beneficial because it reduces this burden.

[0038] <Separation of Metal and Slag> As for the produced metal and slag obtained by reduction of the oxide, it is preferable to separate them before powdering the produced metal, as described below. The separation method is not particularly limited, and known methods can be used.

[0039] <Metal Powdering (Obtaining Metal Powder)> Next, it is preferable to powder the resulting metal to obtain metal powder. In the wet treatment, as described below, the resulting metal is first subjected to leaching using an acid solution. At this time, if the resulting metal remains in the state obtained by oxide reduction, the leaching efficiency may be insufficient. For this reason, it is preferable to powder the resulting metal before performing leaching using an acid solution.

[0040] 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 laser diffraction / scattering method (the same applies below).

[0041] 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.

[0042] <Contacting the Metal with Acid Solution (Obtaining Leaching Solution)> Next, the metal (metal powder) is brought into contact with the acid solution to leach out valuable elements (Ni, Co, Mn) and impurity elements (Cu, Fe). That is, a leachate containing the valuable elements and impurity elements is obtained. 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 include a method of immersing the metal in the acid solution; a method of spraying the acid solution on the metal; and the like.

[0043] <<Solid-Liquid Ratio (Metal / Acid Solution)>> If the amount of acid solution brought into contact with the metal is too small (the amount of metal is too large relative 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. Meanwhile, the solid-liquid ratio (metal / acid solution) is preferably 1 / 50 or more, more preferably 1 / 35 or more, and even more preferably 1 / 20 or more.

[0044] <<Acid Solution>> The acid solution to be brought into contact with the metal contains at least an acid.

[0045] (Acid) Examples of acids used in the acid solution include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid. These may be used alone or in combination of two or more. From the perspective of realizing a "battery-to-battery" system in which used lithium-ion batteries are recycled and reused as raw materials for lithium-ion batteries, it is preferable to use sulfuric acid as the acid. This is because valuable elements can be obtained in the form of sulfates, which are easily usable as cathode materials for lithium-ion batteries. Chlorides may be contained in sulfuric acid and used as the acid.

[0046] ((Acid Concentration)) The concentration of the acid (e.g., sulfuric acid) used in the acid solution (acid concentration) 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.

[0047] (Oxidizing Agent for Acid Solution) The inventors have found 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. Of these, hydrogen peroxide and ozone are preferred because the use of hypochlorous acid and potassium permanganate may require complicated post-treatment of chlorine, potassium, manganese, etc.

[0048] ((Content of oxidizing agent for acid solution)) From the viewpoint of carrying out sufficient leaching, the content of the oxidizing agent for 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 acid solution (e.g., 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 (e.g., sulfuric acid).

[0049] <<Contact Time>> The time for contacting the metal 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.

[0050] <Separation of Leachate and Leaching Residue> As described below, it is preferable to separate the leaching solution from the leaching residue before adding the sulfiding agent to the leaching solution. The separation method is not particularly limited, and known solid-liquid separation methods can be used.

[0051] <Addition of sulfurizing agent (obtaining copper-removed solution)> Next, a sulfurizing agent is added to the leachate containing valuable elements (Ni, Co, Mn) 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.

[0052] FIG. 3 shows the potential-pH diagram (SH) of copper (Cu) and nickel (Ni). ２ In Figure 3, copper (Cu)-sulfur (S)-water (H ２The potential-pH diagram for the ZnO (NiO) system shows the region where copper (Cu) and nickel (Ni) oxide (hydroxide) or sulfide precipitates, taking solubility into account. Note that cobalt precipitates in a similar manner to nickel, so cobalt is not shown in Figure 3 . As shown in Figure 3 , copper (Cu) selectively precipitates in the region where the pH is 3.0 or less and the redox potential is low. Although not shown in Figure 3 , copper precipitates as copper(II) sulfide (CuS) in this region. Taking advantage of this, the leachate is made low pH and reducing, so that copper (Cu) contained in the leachate precipitates as copper(II) sulfide and is selectively removed. In other words, a copper-removed solution is obtained, which is a leachate from which copper (Cu) has been removed.

[0053] Sulfurizing agent: Sulfur (S), hydrogen sulfide (H ２ S), sodium hydrogen sulfide (NaSH), sodium sulfide (Na ２ S), and the like, which may be used alone or in combination of two or more. Among 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 preferred over 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.

[0054] 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.

[0055] (Amount of sulfurizing agent added) From the viewpoint of sufficiently removing copper contained in the leaching solution, the amount of sulfurizing 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 leaching solution. 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 resulting 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 leaching solution.

[0056] For example, when 1.0 equivalent of sodium hydrogen sulfide (NaSH) is used as a sulfiding agent to generate copper (II) sulfide (CuS), 1 mol of sodium hydrogen sulfide (NaSH) is used for 1 mol of copper (Cu) contained in the leachate.

[0057] <<Sulfiding 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 to be left in the copper removal solution may increase. For this reason, 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 sulfiding 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.

[0058] <<Sulfurization Time>> The time (sulfurization time) for sulfiding the copper contained in the leachate by reacting it with the sulfiding 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 sulfidation time is preferably 3.0 hours or less, more preferably 2.0 hours or less, and even more preferably 1.0 hour or less.

[0059] <Separation of copper sulfide and copper removal solution> As described below, it is preferable to separate the copper sulfide and the copper removal solution before adding the oxidizing agent to the copper removal solution. The separation method is not particularly limited, and known solid-liquid separation methods can be used.

[0060] <Addition of Oxidizing Agent (Obtaining Valuable Element Solution)> Next, an oxidizing agent is added to the copper-removal solution containing valuable elements (Ni, Co, Mn) 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 valuable elements (Ni, Co, Mn).

[0061] FIG. 4 shows the potential-pH diagram of iron (Fe) and nickel (Ni) (O ２ -H ２ In FIG. 4, the iron (Fe)-oxygen (O ２ ) - Water (H ２The potential-pH diagram for the copper (Fe) system shows the region where precipitates of iron (Fe) and nickel (Ni) oxides (hydroxides) are formed, taking solubility into account. Note that cobalt precipitates in a similar manner to nickel, so cobalt is not shown in FIG. 4 . As shown in FIG. 4 , iron (Fe) selectively precipitates in the region where the pH is 3.0 or higher and 7.0 or lower and the redox potential is high. Although not shown in FIG. 4 , in this region, iron precipitates as iron (III) oxide hydroxide (FeO(OH)). Taking advantage of this, the copper removal solution is made acidic to neutral and oxidizing, whereby 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.

[0062] 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 because the use of hypochlorous acid and potassium permanganate may require complicated post-treatment for chlorine, potassium, manganese, and the like.

[0063] (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 to the copper removal solution 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 to the copper removal solution is preferably 5.0 vvm or less, more preferably 4.0 vvm or less, and even more preferably 3.0 vvm or less.

[0064] The unit "vvm" is a unit that expresses the volume ratio of the gas blown into the liquid per minute. For example, if the amount of oxidizing agent A added is 2 vvm, 2 L of oxidizing agent A is blown into 1 L of copper removal solution per minute.

[0065] 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.

[0066] <<Oxidation Temperature>> The inventors of the present invention have found that the oxidation of iron contained in the copper removal solution may be insufficient simply by using the oxidizing agent 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. Meanwhile, the oxidation temperature is preferably 90°C or lower, and more preferably 80°C or lower.

[0067] <<Oxidation pH>> When an oxidizing agent is added to a copper removal solution to precipitate iron hydroxides, if the pH (oxidation pH) of the copper removal solution to which the oxidizing agent has been added is too low, precipitation may be difficult to form. Therefore, the oxidation 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 coprecipitation of valuable elements (such as Ni and Co) will increase, reducing the amount of valuable elements desired to remain in the resulting valuable element solution. Therefore, the oxidation pH is preferably 7.0 or lower, more preferably 6.0 or lower, and even more preferably 5.0 or lower. The oxidation pH is adjusted, for example, by adding a pH adjuster to the copper removal solution. Examples of pH adjusters include, but are not limited to, sulfuric acid and sodium hydroxide.

[0068] 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. 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.

[0069] In order to increase the reaction rate for producing the precipitate of iron hydroxide, an oxidation aid may be used in combination with the above-mentioned oxidizing agent. Examples of the oxidation aid include ferric oxide (Fe ２ O ３ ) and iron (III) oxide hydroxide (FeO(OH)), and the oxidation aid is preferably in the form of powder. The oxidation aid increases the reaction rate due to catalytic action. Specifically, since the oxidation aid is likely to be negatively charged in the aqueous solution (copper removal solution), Fe ２＋ Adsorbs ions and Fe ２＋ Internal e － This weakens the bond with Fe ２＋ →Fe ３＋ +e － It is believed that the activation energy of the reaction (Fe oxidation reaction) is reduced, accelerating the reaction.

[0070] (Amount of Oxidizing Agent Added) It is believed that the greater the amount of oxidation aid added, the greater the reaction surface area and the higher the rate of the Fe oxidation reaction. Therefore, the amount of oxidation aid added relative to the copper removal solution 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. On the other hand, if the amount of oxidation aid added is too large, there is a concern that coprecipitation of valuable elements (such as Ni and Co) may increase. Therefore, the amount of oxidation aid added relative to the copper removal solution 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.

[0071] (Particle size of oxidation aid) If the particle size of the oxidation aid is too small, the reaction surface area becomes too large, which may increase the coprecipitation of valuable elements (such as Ni and Co). Therefore, the particle size of the oxidation aid 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 aid 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 aid is preferably 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.0 μm or less.

[0072] <Separation of iron hydroxide and valuable element solution> It is preferable to separate the iron hydroxide and the valuable element solution. The separation method is not particularly limited, and a 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.

[0073] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0074] [Test A] <Preparation of Cathode Material: Test A> A cathode material for a used lithium-ion battery was prepared. Specifically, the used lithium-ion battery was subjected to pre-treatments such as disassembly, discharge, and removal of the electrolyte, to separate the cathode material (oxide). The composition ratio (molar ratio) of nickel (Ni), cobalt (Co), and manganese (Mn) in the cathode material is shown in Table 1 below. The cathode material further contained copper (Cu) and iron (Fe) as impurity elements.

[0075]

[0076] <Preparation of Reducing Agent: Test A> Graphite (C) powder, metallic aluminum (Al) powder, and FeSi powder were prepared as reducing agents. Furthermore, metallic iron (Fe) powder obtained by atomization, ferrous oxide (FeO) powder, dust powder generated in the steelmaking process, and scale powder generated in the steelmaking process were prepared as other reducing agents. The compositions of the dust and scale are shown in Table 2 below. In Table 2 below, "M.Fe" indicates the amount of metallic Fe.

[0077]

[0078] <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 150 kg, and further, one of the reducing agents described above and a flux (CaO, SiO ２) was added to obtain a mixed oxide. The obtained mixed oxide was heated under an Ar atmosphere. In this way, the cathode material was reduced. The heating time was 3 hours in all cases. The type and amount of the reducing agent used (unit: equivalent) and the heating temperature (unit: °C) are shown in Table 3 below.

[0079] The reduction rates (unit: mass %) are shown in Table 3 below. The reduction rate is the ratio of the amount of metal actually obtained to the theoretical amount of metal produced by the reduction reaction. As shown in Table 3 below, a high reduction rate was obtained in all examples. A relatively high reduction rate was also obtained when dust or scale was used as the reducing agent.

[0080] CO per ton of cathode material ２ Amount generated (unit: kg-CO ２ / t) is shown in Table 3 below. As shown in Table 3 below, when metallic iron or iron oxide is used as a reducing agent, ２ The amounts of generated carbon dioxide were all lower than when graphite was used as the reducing agent.

[0081] The cost required for reduction per kg of cathode material was calculated relative to the cost when graphite was used as the reducing agent. The results are shown in Table 3. As shown in Table 3, the cost increased when Al or FeSi was used as the reducing agent, whereas the cost decreased when metallic iron or iron oxide was used.

[0082] Thus, by using metallic iron or iron oxide as a reducing agent, it is possible to reduce CO while maintaining a high reduction rate. ２ We were able to reduce the amount of waste generated and reduce costs.

[0083]

[0084] <Metal Powdering: Test A> The compositions of the metals and slag produced by the reduction of the cathode material were determined. Of the metals produced by the reduction of the cathode material, those having the compositions shown in Table 4 below were powdered using a vibration mill to obtain metal powders. The particle size of the obtained metal powder was 1100 μm.

[0085] Contact of Metal with Acid Solution: 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). A metal (metal powder) having the composition shown in Table 4 below was contacted with the prepared acid solution 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 concentrations of each element in the leachate were 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% by mass, meaning that all elements were leached from the metal into the leachate.

[0086]

[0087] <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 sulfurizing agent to the obtained leachate, and the mixture was stirred at room temperature (25°C). The amount of sulfurizing agent (sodium hydrogen sulfide) added was 2.0 equivalents relative to the Cu content of the leachate. The pH (sulfurization pH) of the leachate to which the sulfurizing agent had been added was adjusted to 0 (zero) using sulfuric acid and sodium hydroxide as pH adjusters. Thus, copper (Cu) contained in the leachate was sulfided by reaction with the sulfurizing agent (sulfidation time: 20 minutes), resulting in precipitation as copper sulfide (copper(II) sulfide). The copper sulfide was then separated from the copper-removed leachate, which was a copper-removed solution. The content (unit: g / L) of each element in the copper-removed solution was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). 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 leaching solution 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 was very low, and therefore it can be seen that Cu was removed from the leaching solution with very high efficiency.

[0088] <Addition of Oxidizing Agent: Test A> Next, the copper removal solution was first diluted with water. The content (unit: g / L) of each element in the diluted copper removal solution is 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 a composition similar to that of 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 the solution was stirred. The amount of oxidizing agent (hydrogen peroxide) added was 0.020% by volume relative to the diluted copper removal solution (diluted). The pH (oxidation pH) of the copper removal solution to which the oxidizing agent had been added was adjusted to 4.5 using sulfuric acid and sodium hydroxide as pH adjusters. The temperature (oxidation temperature) of the copper removal solution to which the oxidizing agent had been added was set to and maintained at 70°C. In this way, iron (Fe) contained in the copper removal solution was oxidized by reaction with the oxidizing agent (oxidation time: 1.0 hour) and precipitated as iron hydroxide (iron(III) oxide hydroxide). Thereafter, 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 determined as the residual rate b (unit: mass %). The results are shown in Table 5 below. As shown in Table 5 below, the content of Fe in the valuable element solution was very low, and therefore it can be seen that Fe was removed from the copper removal solution with very high efficiency.

[0089] Furthermore, for each element, the final residual rate in the valuable element solution was calculated as the overall 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 metal obtained by the dry processing, and then performing wet processing, valuable elements (Ni, Co, Mn) could be recovered with very high purity.

[0090]

[0091] [Test B] <Preparation of cathode material to powdering of metal: Test B> The steps from preparation of cathode material to powdering of metal were the same as those in Test A, and therefore a description thereof will be omitted.

[0092] <Contact between Metal and Acid Solution: Test B> An oxidizing agent for the acid solution (hydrogen peroxide) was added to sulfuric acid (concentration: 2.0 mol / L) in the amount (volume %) shown in Table 6 below to prepare multiple acid solutions. A metal (metal powder) was contacted with the acid solution to obtain a leachate in the same manner as in Test A described above, except that the amount of oxidizing agent added was changed. Furthermore, the leaching rate (mass %) of each element from the metal to the leachate was calculated in the same manner as in Test A described above. 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 was preferably 6.9 vol% or more to sufficiently leach valuable metals (Ni, Co, Mn). However, the leaching rate plateaued when the amount added exceeded 6.9 vol%. Therefore, from the viewpoint of cost, it was found that within the scope of this example, the amount of oxidizing agent (hydrogen peroxide) added for the acid solution was preferably 6.9% by volume.

[0093]

[0094] <Addition of Sulfiding Agent: Test B> Sodium hydrogen sulfide (NaSH) was added as a sulfiding agent to the leachate shown in Table 5 above in the amount (unit: equivalent) shown in Table 7 below, and the mixture was stirred. 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-removed solution were determined in the same manner as in Test A described above. The results are shown in Table 7 below. As shown in Table 7 below, to sufficiently remove copper, the amount of sulfiding agent added is preferably 2.0 equivalents or more relative to copper, but it was found that the Ni residual rate and Co residual rate decreased as the amount of sulfiding agent added increased. Furthermore, as shown in Table 7 below, as the sulfurization pH increased, copper removal became insufficient and the Ni and Co residual rates tended to decrease. From the above, it was found that within the range of this example, the preferred amount of sulfurizing agent added was 2.0 equivalents and the preferred sulfurization pH was 0 (zero).

[0095]

[0096] <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 diluted copper removal solution in the amount (volume %) shown in Table 8 below, and the mixture was stirred. The oxidation pH and oxidation temperature (°C) were adjusted to the values ​​shown in Table 8 below. Except for changing the amount of oxidizing agent, the oxidation pH, and the oxidation temperature, the procedure was the same as in Test A described above, whereby the iron contained in the copper removal solution was precipitated as iron hydroxide to obtain a valuable element solution. Note that no oxidation promoter was used in either Test A or Test B. Furthermore, the Fe content (mg / L), Ni residual rate (mass %), and Co residual rate (mass %) in the obtained valuable element solution were determined in the same manner as in Test A described above. 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, iron was more efficiently removed, while the Ni and Co residual rates tended to decrease. From the above, it was found that within the range 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.

[0097]

Claims

1. A reducing agent containing at least one element selected from the group consisting of metallic iron and iron oxide is added to an oxide containing at least one valuable element selected from the group consisting of nickel, cobalt, and manganese, and impurity elements of 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 removal solution; a copper-removing solution from which iron has been removed, the copper-removing solution being obtained as a valuable element solution containing the valuable element; and

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 iron oxide is ferrous oxide.

5. 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.

6. 3. The method for recovering a valuable element according to claim 1, wherein the metal obtained by heating the mixed oxide contains the valuable element and the impurity element.

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.

12. 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.