Valuable element recovery method and metal production method

Abstract

Provided is a method for recovering valuable elements, whereby not only valuable elements but also lithium can be recovered. In the recovery method, a reducing agent and a slag former containing CaO and SiO2 are added to an oxide containing lithium and at least one element selected from the group consisting of nickel and cobalt, and heating is performed to reduce the oxide. The mass ratio (CaO / SiO2) of CaO and SiO2 contained in the slag former is 0.50 or less.

Description

Technical Field

[0001] The present 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 cathode material is dissolved in an acid and then subjected to solvent extraction and electrolytic refining, and dry treatment in which the cathode material is heated together with a reducing agent and a sludge 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

[0014] Patent Document 2: Japanese Patent Application Publication No. 2013-91826

[0015] Patent Document 3: Japanese Patent Application Publication No. 2012-224877 Summary of the invention

[0016] Problems to be solved by the invention

[0017] In the dry process, by reducing the composite oxides (LiNiO2, LiCoO2, LiMnO2), slag is generated in addition to metals containing valuable elements (Ni, Co, Mn).

[0018] However, in addition to valuable elements such as Ni, Co, and Mn, Li is sometimes required.

[0019] However, in the dry treatment, a part of Li may volatilize. In this case, Li needs to be recovered separately, which is complicated.

[0020] 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 that can recover not only valuable elements but also lithium.

[0021] Solutions to the problem

[0022] 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.

[0023] That is, the present invention provides the following [1] to [9].

[0024] [1] A method for recovering valuable elements, the method comprising: reducing the oxide by adding a reducing agent and a slag-forming agent containing CaO and SiO2 to the oxide and heating the oxide, wherein the oxide contains at least one element selected from nickel and cobalt and lithium, and the mass ratio of CaO to SiO2 (CaO / SiO2) contained in the slag-forming agent is less than 0.50.

[0025] [2] The method for recovering valuable elements according to [1] above, wherein the temperature at which the oxide is heated is 1450° C. or higher.

[0026] [3] The method for recovering valuable elements according to [1] or [2] above, comprising reducing the oxide to obtain a metal containing at least one element selected from nickel and cobalt.

[0027] [4] The method for recovering valuable elements according to any one of [1] to [3] above, wherein the reducing agent is a carbonaceous substance containing carbon.

[0028] [5] A method for recovering valuable elements according to any one of [1] to [4] above, wherein the reducing agent is at least one iron-containing substance selected from metallic iron and iron oxides.

[0029] [6] The method for recovering valuable elements according to [5] above, wherein the iron oxide is ferrous oxide.

[0030] [7] The method for recovering valuable elements according to [5] above, wherein the iron-containing material is at least one selected from dust, scale, sludge and scrap iron.

[0031] [8] The method for recovering valuable elements according to any one of [1] to [7] above, wherein the oxide is obtained from a lithium ion battery.

[0032] [9] A method for producing a metal, the method comprising: producing a metal containing at least one element selected from nickel and cobalt using the valuable element recovery method described in any one of [1] to [8] above.

[0033] Effects of the Invention

[0034] According to the present invention, not only valuable elements but also lithium can be recovered. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a graph showing the results of a reduction experiment when a slag-forming agent A having a mass ratio (CaO / SiO2) of 1.50 was used.

[0036] Figure 2 This is a graph showing the results of a reduction experiment when a slag-forming agent B having a mass ratio (CaO / SiO2) of 0.50 was used.

[0037] Figure 3 It is the Ellingham diagram (standard free energy change-temperature curve). DETAILED DESCRIPTION

[0038] [Methods for recovering valuable elements]

[0039] In the method for recovering valuable elements of the present invention (hereinafter also referred to as "the present recovery method" for convenience), 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 lithium and heated to reduce the above-mentioned oxide, and the mass ratio of CaO to SiO2 (CaO / SiO2) contained in the above-mentioned slag-forming agent is less than 0.50.

[0040] In summary, the present recovery method is a method for 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.

[0041] Furthermore, in the present recovery method, lithium (Li) is also recovered.

[0042] <Understandings Obtained by the Present Invention>

[0043] The positive electrode material of a lithium-ion battery is generally formed of oxides (complex oxides) such as LiNiO2, LiCoO2, and LiMnO2.

[0044] 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.

[0045] 2LiNiO2→Li2O+2NiO+1 / 2O2

[0046] 2LiCoO2→Li2O+2CoO+1 / 2O2

[0047] The standard free energy change (ΔG 0 ) are shown below respectively.

[0048] NiO→Ni+1 / 2O2:ΔG 0 =234900-84.68T[J]

[0049] CoO→Co+1 / 2O2:ΔG 0 =235480-71.55T[J]

[0050] 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.

[0051] In the case of recovering valuable elements in the form of metals from the composite oxide by dry treatment, a slag-forming agent containing calcium oxide (CaO) and silicon dioxide (SiO 2 ) is used.

[0052] The mass ratio of CaO and SiO2 contained in the slag-forming agent (CaO / SiO2) is also called basicity, and has been preferably 0.66 to 2.00 in the past (Patent Documents 2 to 3).

[0053] However, the present inventors have found, through the reduction experiment described below, that even when a slag-making agent with a low basicity having a mass ratio (CaO / SiO2) of 0.50 or less is used, valuable elements can be recovered in the form of metals at a high reduction rate.

[0054] In the reduction experiment, the oxide to be reduced (positive electrode material of lithium ion battery) was heated in an argon atmosphere at 1650° C. in the presence of coke (C) as a reducing agent and a slag-forming agent, thereby generating metal and slag.

[0055] The generated metal is referred to as “generated metal”, and the generated slag is referred to as “generated slag”.

[0056] In the reduction experiment, slag-forming agent A having a mass ratio (CaO / SiO2) of 1.50 or slag-forming agent B having a mass ratio (CaO / SiO2) of 0.50 was used as the slag-forming agent.

[0057] Based on the following formula, the reduction rate (unit: mass %) of each metal element was calculated.

[0058] 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])

[0059] Furthermore, the residual rate (unit: mass %) of each metal element in the generated slag was calculated based on the following formula.

[0060] 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])

[0061] Figure 1 This is a graph showing the results of a reduction experiment when a slag-forming agent A having a mass ratio (CaO / SiO2) of 1.50 was used.

[0062] Figure 2 This is a graph showing the results of a reduction experiment when a slag-forming agent B having a mass ratio (CaO / SiO2) of 0.50 was used.

[0063] like Figure 1~Figure 2 As shown in FIG. 1 , even when a slag-forming agent B having a low basicity is used, for example, a high reduction rate exceeding 90 mass % can be achieved for Ni.

[0064] In addition, when the slag-forming agent B having a low basicity is used, the reduction rate of Mn is lower than when the slag-forming agent A having a high basicity is used, and Mn can be left in the slag (selective separation).

[0065] In addition, as for Li, the residual rate in the generated slag is found to be 80 mass % or less when the slag-forming agent A with high basicity is used, whereas it shows a high value of 90 mass % or more when the slag-forming agent B with low basicity is used.

[0066] According to the above results, by using a slag-making agent with a mass ratio (CaO / SiO2) of 0.50 or less, in addition to the generated metal containing Ni and Co as valuable elements, a generated slag containing a large amount of Li is obtained. That is, Li can be easily recovered with good efficiency.

[0067] 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.

[0068] Next, the present recovery method will be described in more detail.

[0069] It should be noted that the following description also serves as a description of the method for producing the metal of the present invention.

[0070] <Reduction target (oxide)>

[0071] The reduction target in the present recovery method is an oxide containing at least one element selected from nickel (Ni) and cobalt (Co) and lithium (Li), specifically, for example, a positive electrode material of a lithium ion battery.

[0072] The oxide may further contain manganese (Mn).

[0073] The positive electrode material (oxide) is obtained by subjecting the lithium ion battery to pretreatment such as removal of the electrolyte.

[0074] <Reducing Agent>

[0075] Examples of the reducing agent include aluminum-containing substances such as metal aluminum (Al); silicon-containing substances such as metal silicon (Si) and FeSi; carbon-containing substances containing carbon; iron-containing substances; and the like.

[0076] Examples of the carbon-containing substance include solid carbon-containing substances such as graphite, coke, and solid hydrocarbons; and gaseous carbon-containing substances such as carbon monoxide (CO) and hydrocarbon gas (for example, propane gas).

[0077] When a carbon-containing substance is used as a reducing agent, it is preferable that gases such as CO, CO 2 , and H 2 O are generated after reduction, which does not increase the amount of generated slag.

[0078] 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.

[0079] Figure 3 It is the Ellingham diagram (standard free energy change-temperature curve).

[0080] 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.

[0081] In addition, although the FeO / Fe3O4 balance is lower than the Ni / NiO balance, it is higher than the Co / CoO balance.

[0082] 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.

[0083] NiO+Fe→Ni+FeO:ΔG 0 =-29530-19.95T[J]

[0084] CoO+Fe→Co+FeO:ΔG 0 =-28950-6.82T[J]

[0085] It should be noted that in Ellingham Figure 3 ), the higher it is, the easier it is to metalize.

[0086] If Si or Al is used as a reducing agent, Mn is also easily metallized.

[0087] 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.

[0088] As the metallic iron (Fe), for example, scrap iron or granular iron used in an ironworks or the like can be used.

[0089] Iron oxides are generally classified into three types: ferrous oxide (FeO) called wutrite, ferrosoferric oxide (Fe3O4) called magnetite, and ferric oxide (Fe2O3) called hematite.

[0090] 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.

[0091] Therefore, from the reason that a reduction reaction is easily induced, ferrous oxide (wüstite) is preferable as the iron oxide.

[0092] 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.

[0093] 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.

[0094] 《Amount of reducing agent added》

[0095] From the viewpoint of easily suppressing reduction failure, the amount of the reducing agent added is preferably 1.0 equivalent or more, more preferably 1.2 equivalent or more, and even more preferably 1.4 equivalent or more.

[0096] The upper limit of the amount of reducing agent added is not particularly limited. However, if the amount of reducing agent added is too much, it may cost too much. Therefore, the amount of reducing agent added is preferably 1.8 equivalents or less, and more preferably 1.6 equivalents or less.

[0097] The amount of the reducing agent required to reduce the oxides NiO and CoO to be reduced is referred to as 1.0 equivalent.

[0098] For example, when the reducing agent is metallic iron (Fe), ferrous oxide (FeO), metallic aluminum (Al), metallic silicon (Si), coke (C) and propane (C3H8), the reduction using 1 equivalent of the reducing agent is as shown below.

[0099] Fe+(NiO, CoO)→(Ni, Co)+FeO

[0100] 3FeO+(NiO, CoO)→(Ni, Co)+Fe3O4

[0101] 2Al+3(NiO, CoO)→3(Ni, Co)+Al2O3

[0102] Si+2(NiO, CoO)→2(Ni, Co)+SiO2

[0103] C+2(NiO, CoO)→2(Ni, Co)+CO2

[0104] C3H8+10(NiO, CoO)→10(Ni, Co)+3CO2+4H2O

[0105] 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.

[0106] 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.

[0107] The contents of Ni and Co were measured using an energy dispersive X-ray analyzer (EDX).

[0108] <Slag-forming agent>

[0109] As described above, in the present recovery method, a slag-forming agent containing calcium oxide (CaO) and silicon dioxide (SiO2) is used.

[0110] 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.

[0111] 《Mass ratio (CaO / SiO2)》

[0112] As described above, in the present recovery method, a low-basicity slag-forming agent having a low mass ratio of CaO to SiO 2 (CaO / SiO 2 ) is used.

[0113] That is, the mass ratio (CaO / SiO2) of the slag-forming agent used in the present recovery method is 0.50 or less, preferably 0.48 or less, more preferably 0.46 or less, further preferably 0.44 or less, particularly preferably 0.42 or less, and most preferably 0.35 or less.

[0114] On the other hand, 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.

[0115] 《Amount of slag-forming agent added》

[0116] 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.

[0117] <Heating>

[0118] In the present recovery method, the oxide to be reduced is heated in a state where a reducing agent and a slag-forming agent are added to the oxide, thereby reducing the oxide.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] The equipment used for heating the oxide is not particularly limited, and examples thereof include conventionally known equipment such as an electric furnace, a resistance furnace, a high-frequency induction melting furnace, a low-frequency induction melting furnace, a rotary kiln, a vertical furnace, and a steelmaking furnace.

[0125] <Generate Metal>

[0126] By reducing the oxide to be reduced, a metal is generated.

[0127] In the present recovery method, the metal (product metal) obtained by reducing the oxide contains valuable elements (Ni, Co). Thus, the valuable elements (Ni, Co) contained in the oxide to be reduced are recovered as product metals.

[0128] The generated metal may be a metal containing only one of the valuable elements (Ni, Co) (or a metal containing one valuable element in a larger proportion than the other valuable elements).

[0129] <Generated slag>

[0130] By reducing the oxide to be reduced, slag is generated in addition to the metal. As described above, the slag obtained in the present recovery method (generated slag) contains a large amount of Li.

[0131] When an iron-containing substance is used as a reducing agent, the generated slag contains FeO and the like.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] Example

[0136] Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the Examples described below.

[0137] <Cathode Materials>

[0138] First, the positive electrode material for the lithium-ion battery was prepared.

[0139] 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.

[0140] <Reducing Agent>

[0141] As reducing agents, powder of metal aluminum (Al), powder of metal silicon (Si), powder of coke (C), and propane gas (C3H8) were prepared.

[0142] Furthermore, as reducing agents, powder of metallic iron (Fe) and powder of ferrous oxide (FeO) obtained by atomization were prepared.

[0143] <Slag-forming agent>

[0144] 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.

[0145] <Reduction of positive electrode materials: Inventive Examples 1 to 6 and Comparative Examples 1 to 2>

[0146] Next, the prepared positive electrode material was added to an electric furnace with a furnace capacity (heat size) of 150 kg, and a reducing agent and a slag-forming agent were added and heated. Thus, the positive electrode material was reduced to obtain a generated metal and a generated slag. The heating time was 3 hours, and the heating gas atmosphere was set to an Ar gas atmosphere.

[0147] 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 about 0.67.

[0148] The type and addition amount (unit: equivalent) of the reducing agent used, the mass ratio (CaO / SiO2) of the slag-forming agent used, and the heating temperature (unit: °C) are shown in Table 1 below.

[0149] In addition, the reduction rate of each metal element of Ni, Co and Mn was calculated based on the above formula. The unit of the calculated reduction rate was converted from "mass %" to "mol %".

[0150] 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 %".

[0151] All the results are shown in Table 1 below.

[0152]

[0153] <Summary of evaluation results>

[0154] As shown in Table 1 above, the residual rate of Li in the generated slag is higher in Invention Examples 1 to 8 using a slag-forming agent with a mass ratio (CaO / SiO2) of less than 0.50 than in Comparative Examples 1 to 2 using a slag-forming agent with a mass ratio (CaO / SiO2) exceeding 0.50.

[0155] Inventive Examples 1 to 8 all had high reduction rates of Ni and Co, and on the other hand, all were able to suppress the reduction rate of Mn to 20% or less.

[0156] In particular, in Inventive Examples 5 and 6 in which Fe or FeO was used as the reducing agent, the reduction rate of Mn was further suppressed.

[0157] It should be noted that the reduction rate of Co in Invention Example 6 is lower than that in Invention Example 5. This is considered to be because the free energy of FeO generation is slightly lower than the free energy of CoO generation (see Figure 3 ). However, it is considered that since FeO is reduced to generate Fe, its reduction potential is higher than that of FeO, and that it has a certain degree of reduction potential, which is reflected in the results.

[0158] By comparing Invention Examples 1 to 6 with Invention Examples 7 to 8, it can be seen that Invention Examples 7 to 8, which further reduce the mass ratio of the slag-forming agent (CaO / SiO2), can further suppress the reduction rate of Mn compared to Invention Examples 1 to 6 without causing a significant decrease in the reduction rate of Ni and Co.

Claims

1. A method for recovering valuable elements, the method comprising: The oxide is reduced by adding a reducing agent and a slag-forming agent containing CaO and SiO2 to the oxide and heating the oxide, wherein the oxide contains at least one element selected from nickel and cobalt and lithium, The mass ratio of CaO to SiO2 (CaO / SiO2) contained in the slag-forming agent is less than 0.

50.

2. The method for recovering valuable elements according to claim 1, wherein: The temperature when heating the oxide is 1450° C. or higher.

3. The method for recovering valuable elements according to claim 1 or 2, the method comprising: By reducing the oxide, a metal containing at least one element selected from nickel and cobalt is obtained.

4. The method for recovering valuable elements according to any one of claims 1 to 3, wherein: The reducing agent is a carbonaceous substance containing carbon.

5. The method for recovering valuable elements according to any one of claims 1 to 4, wherein: The reducing agent is at least one iron-containing substance selected from metallic iron and iron oxides.

6. The method for recovering valuable elements according to claim 5, wherein: The iron oxide is ferrous oxide.

7. The method for recovering valuable elements according to claim 5, wherein: The iron-containing substance is at least one selected from dust, scale, sludge and scrap iron.

8. The method for recovering valuable elements according to any one of claims 1 to 7, wherein: The oxide is obtained from lithium-ion batteries.

9. A method for manufacturing a metal, the method comprising: A metal containing 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 8.

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