Valuable element recovery method and metal production method

Abstract

Provided is a method for recovering valuable elements such as Ni and Co, said method being capable of selectively recovering. In the recovery method, a reducing agent and a slag former containing CaO and SiO2 are added to an oxide containing manganese and at least one element selected from nickel and cobalt, and heating is performed to reduce the oxide. The reducing agent contains a carbon-containing substance and an iron-containing substance, and the iron-containing substance is at least one substance selected from the group consisting of metallic iron and iron oxides. The total amount of the carbon-containing substance and the iron-containing substance added is 1.0-1.5 equivalents (inclusive).

Description

Technical Field

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

[0002] In recent years, due to the popularity of electric vehicles, the demand for lithium-ion batteries is increasing rapidly.

[0003] In particular, from the perspective of recent reductions in CO2 generation, it is expected that the demand for electric vehicles that do not use fossil fuels will further increase in the future, and the demand for lithium-ion batteries is expected to increase further in the future.

[0004] Generally, the positive electrode material of a lithium ion battery is formed of an oxide (composite oxide) containing nickel (Ni), cobalt (Co), manganese (Mn), etc. Specific examples of the composite oxide include LiNiO2, LiCoO2, LiMnO2, etc.

[0005] Even on a global scale, metal elements such as Ni, Co, and Mn are not abundant.

[0006] Therefore, from the viewpoint of effective utilization of resources, it is very beneficial to recover these metal elements (valuable elements) from the positive electrode material of lithium ion batteries.

[0007] Lithium-ion batteries are composed of a combination of components such as a positive electrode material, a negative electrode material, and a separator, and further contain an electrolyte solution and the like.

[0008] Therefore, when recovering valuable elements from the positive electrode material of a lithium ion battery, pretreatment such as removal of the electrolyte, pulverization, and crushing is performed before recovery.

[0009] After such pretreatment, the positive electrode material is separated from the lithium-ion battery, and valuable elements are recovered from the separated positive electrode material.

[0010] The treatment for recovering valuable elements is divided into two types: wet treatment in which the positive electrode material is dissolved in an acid and then subjected to solvent extraction and electrolytic refining, and dry treatment in which the positive electrode material is heated together with a reducing agent and a slag-forming agent to reduce and generate valuable elements (for example, Patent Document 1).

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: Japanese Patent Application Publication No. 2021-95628 Summary of the invention

[0014] Problems to be solved by the invention

[0015] In the dry treatment, by reducing the composite oxides (LiNiO2, LiCoO2, LiMnO2), slag is generated in addition to metals containing valuable elements (Ni, Co, Mn).

[0016] At this time, it is sometimes required to prevent Mn from being reduced as much as possible (to prevent Mn from being transferred to the metal and remaining in the slag), and to selectively transfer Ni and Co to the metal and recover them.

[0017] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for recovering valuable elements capable of selectively recovering Ni and Co.

[0018] Solutions to the problem

[0019] The present inventors have conducted intensive studies and, as a result, have found that the above-mentioned object can be achieved by adopting the following configuration, thereby completing the present invention.

[0020] That is, the present invention provides the following [1] to

[11] .

[0021] [1] A method for recovering valuable elements, the method comprising:

[0022] The oxide is reduced by adding a reducing agent and a slag-forming agent containing CaO and SiO2 to an oxide containing at least one element selected from nickel and cobalt and manganese and heating the mixture. The reducing agent contains a carbon-containing substance and an iron-containing substance, and the iron-containing substance is at least one selected from metallic iron and iron oxide. The total amount of the carbon-containing substance and the iron-containing substance added is greater than 1.0 equivalent and less than 1.5 equivalent.

[0023] [2] The method for recovering valuable elements according to [1] above, wherein:

[0024] The amount of the above carbon-containing material added is 1.0 equivalent.

[0025] [3] The method for recovering valuable elements according to [1] or [2] above, wherein:

[0026] The above oxide further contains lithium.

[0027] [4] The method for recovering valuable elements according to any one of [1] to [3] above, wherein:

[0028] The manganese content in the oxide is 3 mass % or more and 12 mass % or less.

[0029] [5] The method for recovering valuable elements according to any one of [1] to [4] above, wherein:

[0030] The mass ratio (CaO / SiO2) of CaO and SiO2 contained in the above-mentioned slag-forming agent is less than 0.50.

[0031] [6] The method for recovering valuable elements according to any one of [1] to [5] above, wherein:

[0032] The temperature at which the oxide is heated is 1450° C. or higher.

[0033] [7] The method for recovering valuable elements according to any one of [1] to [6] above, wherein:

[0034] The above-mentioned iron oxide is ferrous oxide.

[0035] [8] The method for recovering valuable elements according to any one of [1] to [7] above, wherein:

[0036] The iron-containing substance is at least one selected from dust, scale, sludge and scrap iron.

[0037] [9] The method for recovering valuable elements according to any one of [1] to [8] above, wherein:

[0038] By reducing the oxide, a metal containing iron and at least one element selected from nickel and cobalt is obtained.

[0039]

[10] The method for recovering valuable elements according to any one of [1] to [9] above, wherein:

[0040] The above oxides are obtained from lithium-ion batteries.

[0041]

[11] A method for manufacturing a metal, the method comprising:

[0042] A metal containing iron and at least one element selected from nickel and cobalt is produced using the method for recovering valuable elements described in any one of [1] to

[10] .

[0043] Effects of the Invention

[0044] According to the present invention, Ni and Co can be selectively recovered. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a graph showing the results of reduction experiment 1.

[0046] Figure 2 It is a graph showing the results of reduction experiment 2.

[0047] Figure 3 It is the Ellingham diagram (standard free energy change-temperature curve). DETAILED DESCRIPTION

[0048] [Methods for recovering valuable elements]

[0049] In the method for recovering valuable elements of the present invention (hereinafter, for convenience, also referred to as "the present recovery method"), a reducing agent and a slag-forming agent containing CaO and SiO2 are added to an oxide containing at least one element selected from nickel and cobalt and manganese and heated to reduce the above-mentioned oxide, wherein the above-mentioned reducing agent contains a carbon-containing substance and an iron-containing substance, and the above-mentioned iron-containing substance is at least one selected from metallic iron and iron oxide, and the total amount of the above-mentioned carbon-containing substance and the above-mentioned iron-containing substance added is greater than 1.0 equivalent and less than 1.5 equivalents.

[0050] In summary, the present recovery method is a method for selectively recovering at least one element selected from nickel (Ni) and cobalt (Co) (hereinafter also referred to as “valuable element”) from a positive electrode material (oxide) of a lithium-ion battery by dry treatment.

[0051] <Understandings Obtained by the Present Invention>

[0052] The positive electrode material of a lithium-ion battery is generally formed of oxides (complex oxides) such as LiNiO2, LiCoO2, and LiMnO2.

[0053] Considering dry processing from a thermodynamic point of view, for example, LiNiO2 and LiCoO2 decompose at high temperature as follows to produce NiO and CoO, respectively.

[0054] 2LiNiO2→Li2O+2NiO+1 / 2O2

[0055] 2LiCoO2→Li2O+2CoO+1 / 2O2

[0056] The standard free energy change (ΔG 0 ) are shown below respectively.

[0057] NiO→Ni+1 / 2O2:ΔG 0 =234900-84.68T[J]

[0058] CoO→Co+1 / 2O2:ΔG 0 =235480-71.55T[J]

[0059] Substances having free energy change values ​​lower than these standard free energy change values ​​may be used as reducing agents at any temperature within the elevated temperature.

[0060] When recovering valuable elements in the form of metals from a composite oxide by dry treatment, Mn is generally inevitably reduced and transferred into the metal.

[0061] However, Mn transferred to the metal is difficult to separate. Therefore, it is desirable not to reduce Mn as much as possible (to allow Mn to remain in the slag).

[0062] Therefore, the present inventors conducted the reduction experiments 1 and 2 described below. As a result, they found that Mn can be retained in the slag and Ni and Co can be selectively transferred to the metal by using a specific reducing agent in a specific addition amount.

[0063] In reduction experiments 1 and 2, the oxide to be reduced (positive electrode material of lithium ion battery) was heated in an argon atmosphere at 1650° C. in a state where a reducing agent and a slag-forming agent were added, thereby generating metal and slag.

[0064] The generated metal is referred to as “generated metal”, and the generated slag is referred to as “generated slag”.

[0065] As the reducing agent, a carbon-containing substance and an iron-containing substance were used in combination. Specifically, coke (C) was used as the carbon-containing substance, and metallic iron (Fe) was used as the iron-containing substance.

[0066] In the reduction experiment 1, the amount of Fe added was 1.0 equivalent, and the amount of C added was 0.5 equivalent.

[0067] In the reduction experiment 2, the amount of C added was 1.0 equivalent, and the amount of Fe added was 0.5 equivalent.

[0068] As described later, the amount of the reducing agent required to reduce NiO and CoO of the oxides is 1.0 equivalent.

[0069] It should be noted that a slag-making agent containing calcium oxide (CaO) and silicon dioxide (SiO2) was used in reduction experiments 1 and 2. 30 kg of the slag-making agent was used for 45 kg of the oxide (positive electrode material).

[0070] The reduction rate (unit: mass %) of each metal element was determined based on the following formula.

[0071] Reduction rate = 100 × (amount of metal element contained in the generated metal [kg]) / (amount of metal element contained in the oxide to be reduced [kg])

[0072] Furthermore, the residual rate (unit: mass %) of each metal element in the generated slag was determined based on the following formula.

[0073] Residual rate in generated slag = 100 × (amount of metal elements contained in generated slag [kg]) / (amount of metal elements contained in oxide to be reduced [kg])

[0074] Figure 1 is a graph showing the results of reduction experiment 1, Figure 2 It is a graph showing the results of reduction experiment 2.

[0075] like Figure 1-2 As shown, a high reduction rate of more than 70 mass % (particularly more than 80 mass % for Ni) can be achieved for Ni and Co. That is, Ni and Co can be transferred to the generated metal at a high reduction rate.

[0076] In addition, the reduction rate of Mn is at a very low level (5 mass % or less), and a large amount of Mn can be retained in the slag.

[0077] In addition, by comparing the results of reduction experiments 1 and 2, a higher reduction rate was obtained for Ni and Co when the addition amount of coke (C) was set to 1.0 equivalent (reduction experiment 2) compared with the case where the addition amount of metallic iron (Fe) was set to 1.0 equivalent (reduction experiment 1).

[0078] From the above results, by using a specific reducing agent in a specific addition amount, a product metal containing less Mn and more Ni and Co can be obtained. That is, Ni and Co can be selectively recovered.

[0079] Next, the present recovery method will be described in more detail.

[0080] It should be noted that the following description also serves as a description of the method for producing the metal of the present invention.

[0081] <Reduction target (oxide)>

[0082] The reduction target in the present recovery method is an oxide containing at least one element selected from nickel (Ni) and cobalt (Co) and manganese (Mn), specifically, for example, a positive electrode material of a lithium ion battery.

[0083] The oxide may further contain lithium (Li).

[0084] The positive electrode material (oxide) is obtained by subjecting the lithium ion battery to pretreatment such as removal of the electrolyte.

[0085] In general, depending on the composition range of an oxide (complex oxide) used as a positive electrode material for a lithium ion battery, the Mn content in the oxide is preferably 3% by mass or more, and more preferably 5% by mass or more.

[0086] Likewise, the content of Mn in the oxide is preferably 12% by mass or less, more preferably 10% by mass or less.

[0087] The Mn content in the oxide was determined using ICP (inductively coupled plasma) emission spectrometry, and can also be determined simply using fluorescent X-ray elemental analysis (XRF), after confirming that the same measurement results as those obtained using ICP emission spectrometry were obtained.

[0088] <Reducing Agent>

[0089] The reducing agent used in the present recovery method contains a carbon-containing substance and an iron-containing substance. That is, a carbon-containing substance and an iron-containing substance are used in combination as the reducing agent.

[0090] Thereby, as described above, the reduction rate of Mn can be suppressed, and a high reduction rate can be obtained for Ni and Co. That is, a product metal containing less Mn and a large amount of Ni and Co can be obtained.

[0091] The content (total content) of the carbon-containing substance and the iron-containing substance in the reducing agent is preferably 90 mass % or more, more preferably 95 mass % or more, further preferably 98 mass % or more, and particularly preferably 100 mass %.

[0092] Examples of the carbon-containing substance include solid carbon-containing substances such as graphite, coke, coal, and solid hydrocarbons; and gaseous carbon-containing substances such as carbon monoxide (CO) and hydrocarbon gas (for example, propane gas).

[0093] When a carbon-containing substance is used as a reducing agent, it is preferable from the viewpoint that gases such as CO, CO 2 , and H 2 O are generated after reduction and the amount of generated slag does not increase.

[0094] The iron-containing substance is at least one selected from metallic iron (Fe) and iron oxides. Hereinafter, the iron-containing substance as a reducing agent will be described.

[0095] Figure 3 It is the Ellingham diagram (standard free energy change-temperature curve).

[0096] Referring to the above standard free energy change and Ellingham diagram ( Figure 3 ), the Fe / FeO equilibrium is lower than the Ni / NiO equilibrium and the Co / CoO equilibrium, and it can be considered that reduction based on Fe is possible.

[0097] In addition, although the FeO / Fe3O4 balance is lower than the Ni / NiO balance, it is higher than the Co / CoO balance.

[0098] Therefore, selective reduction of Ni and Co (making the produced metal contain Ni and making the produced slag contain Co) can also be expected. Specifically, the following reaction can be expected.

[0099] NiO+Fe→Ni+FeO:ΔG 0 =-29530-19.95T[J]

[0100] CoO+Fe→Co+FeO:ΔG 0 =-28950-6.82T[J]

[0101] It should be noted that in Ellingham Figure 3 ), the higher it is, the easier it is to metalize.

[0102] If Si or Al is used as a reducing agent, Mn is also easily metallized.

[0103] Therefore, it is also possible to expect that only Ni and Co can be metallized without metallizing Mn by using Fe (or FeO) as a reducing agent.

[0104] As the metallic iron (Fe), for example, scrap iron or granular iron used in an ironworks or the like can be used.

[0105] Iron oxides are generally classified into three types: ferrous oxide (FeO) called wutrite, ferrosoferric oxide (Fe3O4) called magnetite, and ferric oxide (Fe2O3) called hematite.

[0106] Among them, the standard free energy change of magnetite and hematite is higher than the standard free energy change of wutite at the same temperature, and it is difficult to cause reduction reaction in some cases.

[0107] Therefore, from the reason that a reduction reaction is easily induced, ferrous oxide (wüstite) is preferable as the iron oxide.

[0108] The iron oxide may be at least any one of dust, scale, and sludge (hereinafter referred to as "dust" for convenience) generated as a by-product in an ironmaking process.

[0109] From the viewpoint of effectively utilizing by-products of the ironmaking process and utilizing an inexpensive iron source, it is preferred to use dust as the iron oxide.

[0110] 《Amount of reducing agent added》

[0111] The total amount of the carbon-containing substance and the iron-containing substance added as the reducing agent is 1.0 equivalent or more and 1.5 equivalent or less.

[0112] Thereby, as described above, the reduction rate of Mn can be suppressed, and a high reduction rate can be obtained for Ni and Co. That is, a product metal containing less Mn and a large amount of Ni and Co can be obtained.

[0113] The total amount of the carbon-containing substance and the iron-containing substance added is 1.0 equivalent or more, preferably 1.2 equivalent or more, and more preferably 1.3 equivalent or more, in accordance with the stoichiometric composition.

[0114] On the other hand, the total amount added is preferably 1.4 equivalents or less.

[0115] In addition, in the calculation of the equivalent of the carbon-containing substance, the fixed carbon component contained in the carbon-containing substance and the carbon component and the hydrogen component in the volatile component are taken into account as components contributing to reduction.

[0116] For example, when the carbon-containing substance is coke, the amount of coke added×the carbon content in the coke (unit: mass %) is calculated.

[0117] In addition, when the carbon-containing substance is propane gas, the amount of propane added (unit: Nm 3 ) / 22.4)×(12×3+8).

[0118] Among the carbon-containing substances and iron-containing substances used as the reducing agent, the addition amount of only the carbon-containing substance such as coke (C) is preferably 1.0 equivalent.

[0119] Thereby, as described above, a higher reduction rate can be obtained for Ni and Co.

[0120] The amount of the reducing agent required to reduce the oxides NiO and CoO to be reduced is referred to as 1.0 equivalent.

[0121] For example, when the reducing agent is metallic iron (Fe), ferrous oxide (FeO), and coke (C), the reduction using 1 equivalent of the reducing agent is as follows.

[0122] Fe+(NiO,CoO)→(Ni,Co)+FeO

[0123] 3FeO+(NiO,CoO)→(Ni,Co)+Fe3O4

[0124] C+2(NiO,CoO)→2(Ni,Co)+CO2

[0125] When determining the amount of reducing agent to be added, the contents of NiO and CoO in the oxide to be reduced are first determined.

[0126] Specifically, the contents of Ni and Co in the object to be reduced (oxide) are measured, and these contents are regarded as the contents of NiO and CoO in the object to be reduced (oxide), respectively.

[0127] The contents of Ni and Co were measured using an energy dispersive X-ray analyzer (EDX).

[0128] <Slag-forming agent>

[0129] In the present recovery method, a slag-forming agent containing calcium oxide (CaO) and silicon dioxide (SiO2) is used.

[0130] The content (total content) of CaO and SiO2 in the slag-forming agent is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 98% by mass or more, and particularly preferably 100% by mass.

[0131] 《Mass ratio (CaO / SiO2)》

[0132] Regarding slag-forming agents, the mass ratio of CaO to SiO2 (CaO / SiO2) is also called basicity.

[0133] The mass ratio (CaO / SiO2) of the slag-forming agent used in the present recovery method is not particularly limited, and is, for example, 2.00 or less, preferably 1.80 or less, and more preferably 1.60 or less.

[0134] However, from the reason that the reduction rate of Mn can be further suppressed, it is preferred that the slag-making agent has a low basicity. Specifically, the mass ratio (CaO / SiO2) of the slag-making agent is preferably 1.50 or less, more preferably 1.00 or less, further preferably 0.50 or less, and particularly preferably 0.35 or less.

[0135] Furthermore, by making the slag-making agent have a low basicity, a produced slag containing a large amount of Li can be obtained in addition to produced metals containing Ni and Co. This also makes it possible to recover lithium simply and efficiently.

[0136] In addition, the method of further recovering Li from the generated slag is not particularly limited, and various methods such as a method of recovering Li in the form of lithium carbonate by wet treatment may be mentioned.

[0137] The lower limit of the mass ratio (CaO / SiO2) of the slag-forming agent is not particularly limited, and is, for example, 0.15, preferably 0.20, more preferably 0.25, and further preferably 0.30.

[0138] 《Mass ratio {(CaO+Li2O) / SiO2}》

[0139] The slag-making agent may contain lithium oxide (Li2O) as a raw material in addition to CaO and SiO2.

[0140] The slag-forming agent is preferably prepared in consideration of the amount of lithium contained in the raw material.

[0141] Specifically, from the reasons of easy maintenance of reduction smelting ability (easy to suppress the decrease in reduction reaction rate) and easy fixation of Li2O to slag (high possibility of Li recovery in subsequent steps), {(CaO+Li2O) / SiO2} of the slag-making agent is preferably 0.05 or more, more preferably 0.10 or more, and further preferably 0.15 or more.

[0142] On the other hand, from the reasons of easily suppressing the increase of slag volume and easily fixing Li2O in the slag, {(CaO+Li2O) / SiO2} of the slag-forming agent is preferably less than 2.50, more preferably less than 2.00, and further preferably less than 1.50.

[0143] 《Amount of slag-forming agent added》

[0144] The amount of the slag-forming agent added is not particularly limited, but the mass ratio of the slag-forming agent to the oxide to be reduced (slag-forming agent / oxide) is preferably 0.40 to 1.00, more preferably 0.45 to 0.85, and even more preferably 0.50 to 0.80.

[0145] <Heating>

[0146] In the present recovery method, a reducing agent and a slag-forming agent are added to the oxide to be reduced and the oxide is heated, thereby reducing the oxide.

[0147] From the reason that poor reduction can be easily suppressed, the temperature when heating the oxide (heating temperature) is preferably 1300° C. or higher, more preferably 1350° C. or higher, further preferably 1400° C. or higher, and particularly preferably 1450° C. or higher.

[0148] The upper limit of the heating temperature is not particularly limited and can be appropriately set according to the performance of the equipment (furnace) used for heating, but if the heating temperature is too high, it may cost too much. Therefore, the heating temperature is preferably 1800°C or less, more preferably 1700°C or less.

[0149] As the gas atmosphere when heating the oxide (heating gas atmosphere), for example, an inert gas atmosphere such as a nitrogen (N 2 ) atmosphere and an argon (Ar) atmosphere; a reducing gas atmosphere such as a carbon monoxide (CO) atmosphere; etc. can be appropriately listed.

[0150] From the perspective of easily suppressing poor reduction, the time for heating the oxide (heating time) is preferably 1 hour or longer, more preferably 2 hours or longer, and even more preferably 3 hours or longer.

[0151] The upper limit of the heating time is not particularly limited. However, if the heating time is too long, it may sometimes cost too much. Therefore, the heating time is preferably less than 6 hours, more preferably less than 5 hours.

[0152] The equipment used for heating the oxide is not particularly limited, and examples thereof include conventionally known equipment such as electric arc furnaces, submerged arc furnaces, resistance furnaces, high-frequency induction melting furnaces, low-frequency induction melting furnaces, rotary kilns, vertical furnaces, and steelmaking furnaces.

[0153] <Generate Metal>

[0154] By reducing the oxide to be reduced, a metal is generated.

[0155] As described above, in the present recovery method, the metal (product metal) obtained by reducing the oxide contains less Mn and more Ni and Co. Thus, Ni and Co, which are valuable elements contained in the oxide to be reduced, are selectively recovered as product metals.

[0156] The generated metal may be a metal containing only one of Ni and Co as valuable elements (or a metal containing one valuable element in a larger proportion than the other valuable element).

[0157] In the case of using an iron-containing substance as a reducing agent, the resulting metal may further contain iron (Fe).

[0158] <Generated slag>

[0159] By reducing the oxide to be reduced, slag is generated in addition to the metal.

[0160] When an iron-containing substance is used as a reducing agent, the generated slag contains FeO and the like.

[0161] In addition to this, the produced slag may contain oxides of valuable elements not contained in the produced metal (for example, MnO) and the like.

[0162] When reducing an oxide containing Mn, by using an iron-containing substance as a reducing agent, since the Mn / MnO balance is lower than the Fe / FeO balance and the FeO / Fe3O4 balance, it is possible to suppress the mixing of Mn into the product metal obtained by the reduction.

[0163] When wet treatment is performed, there are many treatment methods depending on the form of Mn, which is complicated. In contrast, according to the present recovery method based on dry treatment, Mn can be retained in the generated slag, which is beneficial.

[0164] Example

[0165] Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the Examples described below.

[0166] <Cathode Materials>

[0167] First, the positive electrode material for the lithium-ion battery was prepared.

[0168] Specifically, the lithium-ion battery is subjected to pretreatment such as decomposition, discharge, and removal of the electrolyte to separate the positive electrode material. The composition of the positive electrode material is Ni:Mn:Co=6:2:2 in molar ratio. It should be noted that the positive electrode material also contains Li.

[0169] The content of Mn in the positive electrode material was 11.3 mass %.

[0170] <Reducing Agent>

[0171] As a reducing agent, powdered coke (C) was prepared.

[0172] Furthermore, as reducing agents, powder of metallic iron (Fe) and powder of ferrous oxide (FeO) obtained by atomization were prepared.

[0173] <Slag-forming agent>

[0174] As a slag-forming agent, a slag-forming agent composed of CaO and SiO2 was prepared. A plurality of slag-forming agents having different mass ratios of CaO to SiO2 (CaO / SiO2) were prepared.

[0175] <Reduction of positive electrode material: Inventive Examples 1 to 4 and Comparative Examples 1 to 5>

[0176] Next, the prepared positive electrode material, reducing agent and slag-forming agent were loaded into a submerged arc furnace with a furnace capacity (heat size) of 150 kg, and they were energized using electrodes to heat them. At this time, a part of the reducing agent was arranged directly below the electrode. Thus, the positive electrode material was reduced to obtain the generated metal and the generated slag. The heating temperature was set to 1600°C, the heating time was set to 3 hours, and the heating gas atmosphere was set to Ar gas atmosphere.

[0177] 30 kg of the slag-forming agent was added to 45 kg of the positive electrode material. That is, the mass ratio of the slag-forming agent to the positive electrode material (slag-forming agent / positive electrode material) was set to about 0.67.

[0178] The types and addition amounts (unit: equivalent) of the reducing agents used, and the mass ratio (CaO / SiO2) of the slag-forming agents used are shown in Table 1 below.

[0179] In addition, the reduction rate of each metal element of Ni, Co and Mn was calculated|required based on the above formula. The unit of the calculated reduction rate was converted from "mass %" to "mol %".

[0180] In addition, the residual rate of Li in the generated slag was calculated based on the above formula. The unit of the calculated residual rate in the generated slag was converted from "mass %" to "mol %".

[0181] All the results are shown in Table 1 below.

[0182] Table 1

[0183]

[0184] <Summary of evaluation results>

[0185] As shown in Table 1, the reduction rates of Mn in Comparative Examples 1 and 2 in which only coke (C) was used as a reducing agent were high.

[0186] In addition, in Comparative Examples 3 to 5 in which only metallic iron (Fe) or ferrous oxide (FeO) was used as a reducing agent, although the reduction of Mn could be suppressed, the reduction of Ni and Co was insufficient.

[0187] In contrast, in Invention Examples 1 to 6 using metallic iron (Fe) or ferrous oxide (FeO) and coke (C) in combination as a reducing agent, the reduction of Mn was suppressed and high reduction rates were obtained for Ni and Co. That is, Ni and Co could be selectively recovered.

[0188] Comparing Invention Example 1 and Invention Example 2, in which the amount of coke (C) added as a carbon-containing material was set to 1.0 equivalent, a higher reduction rate was obtained for Ni and Co compared to Invention Example 1 in which the amount of coke (C) added as a carbon-containing material was set to 0.4 equivalent.

[0189] Comparing Invention Example 2 with Invention Examples 3-4, Invention Examples 3-4 using a slag-forming agent with a mass ratio (CaO / SiO2) of 0.50 can further suppress the reduction of Mn compared to Invention Example 2 using a slag-forming agent with a mass ratio (CaO / SiO2) of 1.50. In addition, the residual rate of Li in the generated slag can be further increased.

[0190] Comparing Invention Examples 3 to 4 with Invention Examples 5 to 6, compared with Invention Examples 3 to 4, Invention Examples 5 to 6 in which the mass ratio of the slag-forming agent (CaO / SiO2) is further reduced can further suppress the reduction of Mn without causing a significant decrease in the reduction rate of Ni and Co.

Claims

1. A method for recovering valuable elements, the method comprising: A reducing agent and a slag-forming agent containing CaO and SiO2 are added to an oxide containing at least one element selected from nickel and cobalt and manganese, and the mixture is heated to reduce the oxide. The reducing agent contains a carbon-containing substance and an iron-containing substance, wherein the iron-containing substance is at least one selected from metallic iron and iron oxide. The total amount of the carbon-containing substance and the iron-containing substance added is 1.0 equivalent or more and 1.5 equivalent or less.

2. The method for recovering valuable elements according to claim 1, wherein: The added amount of the carbon-containing material is 1.0 equivalent.

3. The method for recovering valuable elements according to claim 1 or 2, wherein: The oxide further contains lithium.

4. The method for recovering valuable elements according to any one of claims 1 to 3, wherein: The manganese content in the oxide is 3 mass % or more and 12 mass % or less.

5. The method for recovering valuable elements according to any one of claims 1 to 4, wherein: The mass ratio of CaO to SiO2 (CaO / SiO2) contained in the slag-forming agent is less than 0.

50.

6. The method for recovering valuable elements according to any one of claims 1 to 5, wherein: The temperature when the oxide is heated is 1450° C. or higher.

7. The method for recovering valuable elements according to any one of claims 1 to 6, wherein: The iron oxide is ferrous oxide.

8. The method for recovering valuable elements according to any one of claims 1 to 7, wherein: The iron-containing substance is at least one selected from dust, scale, sludge and scrap iron.

9. The method for recovering valuable elements according to any one of claims 1 to 8, wherein: By reducing the oxide, a metal containing iron and at least one element selected from nickel and cobalt is obtained.

10. The method for recovering valuable elements according to any one of claims 1 to 9, wherein: The oxide is obtained from lithium-ion batteries.

11. A method for manufacturing a metal, the method comprising: A metal containing iron and at least one element selected from nickel and cobalt is produced using the method for recovering valuable elements according to any one of claims 1 to 10.

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