Method for recovering valuable elements and method for producing metals

Abstract

Provided is a valuable element recovery method that can recover not only valuable elements but also lithium. The recovery method involves: adding, to oxides including lithium and at least one element selected from the group consisting of nickel and cobalt, a reducing agent and a slag forming agent containing CaO and SiO2; and applying heat to the mixture to reduce the oxides. The CaO and SiO2 are contained in the slag forming agent at a mass ratio (CaO / SiO2) of 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 technology]

[0002] In recent years, the demand for lithium-ion batteries has been rapidly increasing due to the popularity of electric vehicles. In particular, the recent CO 2 From the perspective of reducing emissions, demand for electric vehicles, which do not use fossil fuels, is expected to continue to expand in the future, and the associated demand for lithium-ion batteries is also expected to continue to increase in the future.

[0003] Generally, the positive electrode material of a lithium-ion battery is made of an oxide (composite oxide) containing nickel (Ni), cobalt (Co), manganese (Mn), etc. A specific example of this composite oxide is LiNiO 2 , LiCoO 2 , LiMnO 2 etc. Metal elements such as Ni, Co, and Mn cannot be said to be abundant worldwide. For this reason, recovering these metal elements (valuable elements) from the positive electrode material of lithium-ion batteries is extremely beneficial from the perspective of efficient resource utilization.

[0004] A lithium ion battery is composed of a combination of components such as a positive electrode material, a negative electrode material, and a separator, and further contains an electrolyte solution and the like. For this reason, when recovering valuable elements from the positive electrode material of a lithium ion battery, preliminary treatment such as removal of the electrolyte, pulverization, and crushing is carried out prior to the recovery. After such pre-treatment, the positive electrode material is separated from the lithium-ion battery, and then valuable elements are recovered from the separated positive electrode material. The processes for recovering valuable elements are classified into two types: a wet process in which the positive electrode material is dissolved in acid, followed by solvent extraction and electrolytic refining, and a dry process in which the positive electrode material is heated together with a reducing agent and a slag-forming agent to reduce and generate valuable elements (e.g., Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-95628 [Patent Document 2] JP 2013-91826 A [Patent Document 3] JP 2012-224877 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the dry process, a composite oxide (LiNiO 2 , LiCoO 2 , LiMnO 2 ) is reduced to produce metals containing valuable elements (Ni, Co, Mn) as well as slag. Incidentally, Li may also be required in addition to valuable elements such as Ni, Co, and Mn. However, in dry processing, some of the Li may volatilize, which requires the Li to be recovered separately, which is cumbersome.

[0007] The present invention has been made in consideration of the above points, and an object of the present invention is to provide a method for recovering valuable elements that can recover not only valuable elements but also lithium. [Means for solving the problem]

[0008] As a result of extensive investigations, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention.

[0009] That is, the present invention provides the following [1] to [9]. [1] A method for producing a sintered body comprising an oxide containing at least one element selected from the group consisting of nickel and cobalt and lithium, a reducing agent, and CaO and SiO 2The oxide is reduced by heating the mixture to obtain CaO and SiO contained in the slag forming agent. 2 Mass ratio of CaO to SiO 2 ) is 0.50 or less. [2] The method for recovering valuable elements according to the above [1], wherein the temperature at which the oxide is heated is 1450°C or higher. [3] The method for recovering valuable elements according to the above [1] or [2], wherein the oxide is reduced to obtain a metal containing at least one element selected from the group consisting of nickel and cobalt. [4] The method for recovering a valuable element according to any one of the above [1] to [3], wherein the reducing agent is a carbon-containing substance. [5] The method for recovering valuable elements according to any one of the above [1] to [4], wherein the reducing agent is at least one iron-containing substance selected from the group consisting of metallic iron and iron oxide. [6] The method for recovering valuable elements according to the above [5], wherein the iron oxide is ferrous oxide. [7] The method for recovering valuable elements according to the above [5], wherein the iron-containing material is at least one selected from the group consisting of dust, scale, sludge and scrap. [8] The method for recovering a valuable element according to any one of the above [1] to [7], wherein the oxide is obtained from a lithium ion battery. [9] A method for producing a metal, comprising producing a metal containing at least one element selected from the group consisting of nickel and cobalt, by using the method for recovering a valuable element according to any one of the above items [1] to [8]. Effect of the Invention

[0010] According to the present invention, not only valuable elements but also lithium can be recovered. [Brief description of the drawings]

[0011] [Figure 1] 1 is a graph showing the results of a reduction experiment using a slag former A having a mass ratio (CaO / SiO2) of 1.50. [Diagram 2]1 is a graph showing the results of a reduction experiment using a slag former B having a mass ratio (CaO / SiO2) of 0.50. [Diagram 3] This is an Ellingham diagram (standard free energy change-temperature diagram). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Method of recovering valuable elements] The method for recovering a valuable element of the present invention (hereinafter, for convenience, also referred to as "the present recovery method") comprises the steps of: adding a reducing agent, CaO and SiO to an oxide containing at least one element selected from the group consisting of nickel and cobalt and lithium; 2 The oxide is reduced by heating the mixture to obtain CaO and SiO contained in the slag forming agent. 2 Mass ratio of CaO to SiO 2 ) is less than or equal to 0.50.

[0013] In summary, this recovery method is a method for recovering at least one element selected from the group consisting of nickel (Ni) and cobalt (Co) (hereinafter also referred to as "valuable element") from the positive electrode material (oxide) of a lithium-ion battery by dry processing. Furthermore, this recovery method also recovers lithium (Li).

[0014] <Findings Obtained by the Inventors> The cathode material of lithium-ion batteries is generally LiNiO 2 , LiCoO 2 , LiMnO 2 It is composed of oxides (composite oxides) such as: Considering the thermodynamics of dry processing, for example, LiNiO 2 and LiCoO 2 At high temperatures, it decomposes as follows to produce NiO and CoO, respectively: 2LiNiO 2 →Li 2 O+2NiO+1 / 2O 2 2LiCoO 2 →Li 2O+2CoO+1 / 2O 2

[0015] The standard free energy change (ΔG 0 ) are shown below, respectively. NiO→Ni+1 / 2O 2 :ΔG 0 =234900-84.68T[J] CoO → Co+1 / 2O 2 :ΔG 0 =235480-71.55T[J] Materials that have free energy change values ​​lower than these standard free energy change values ​​at any elevated temperature can be used as reducing agents.

[0016] When recovering valuable elements as metals from complex oxides by dry processing, calcium oxide (CaO) and silicon dioxide (SiO 2 ) is used as a slag forming agent. CaO and SiO contained in the slag former 2 Mass ratio of CaO to SiO 2 ) is also called basicity, and it has been conventionally considered that a basicity of 0.66 to 2.00 is preferable (Patent Documents 2 to 3). However, the present inventors conducted a reduction experiment described below and found that the mass ratio (CaO / SiO 2 It was found that valuable elements could be recovered as metals at a high reduction rate even when a low-basicity slag former with a ratio of 0.50 or less was used.

[0017] In the reduction experiment, the oxide to be reduced (positive electrode material for lithium-ion batteries) was heated in an argon gas atmosphere at 1650°C with the addition of coke (C) as a reducing agent and a slag-forming agent to produce metal and slag. The produced metal is called "produced metal" and the produced slag is called "produced slag".

[0018] In the reduction experiment, the slag forming agent was prepared by mixing CaO and SiO 2 ) is 1.50, or a slag former A having a mass ratio (CaO / SiO2 ) was 0.50.

[0019] The reduction rate (unit: mass%) of each metal element was calculated based on the following formula. Reduction rate = 100 x (amount of metal element contained in the produced metal [kg]) / (amount of metal element contained in the oxide to be reduced [kg])

[0020] Furthermore, the residual rate (unit: mass %) of each metal element in the produced slag was calculated based on the following formula. Residual rate in the produced slag = 100 × (amount of metal element contained in the produced slag [kg]) / (amount of metal element contained in the oxide to be reduced [kg])

[0021] Figure 1 shows the mass ratio (CaO / SiO 2 ) is a graph showing the results of a reduction experiment using a slag former A having a melting point of 1.50. Figure 2 shows the mass ratio (CaO / SiO 2 ) is a graph showing the results of a reduction experiment using a slag former B having a melting point of 0.50.

[0022] As shown in Figs. 1 and 2, even when a slag former B with low basicity was used, a high reduction rate of, for example, Ni exceeding 90 mass % could be achieved. In addition, when low-basicity slag former B was used, the reduction rate of Mn was lower than that when high-basicity slag former A was used, and Mn was able to remain in the slag (selective separation). Furthermore, when the residual rate of Li in the produced slag was examined, it was 80% by mass or less when high-basicity slag-former A was used, whereas it was a high value of 90% by mass or more when low-basicity slag-former B was used.

[0023] From the above results, the mass ratio (CaO / SiO 2 By using a slag former with a slag ratio of 0.50 or less, it was possible to obtain a slag containing a large amount of Li in addition to the produced metals containing the valuable elements Ni and Co. In other words, Li could be recovered simply and efficiently. The method for further recovering Li from the produced slag is not particularly limited, and various methods such as a method for recovering Li in the form of lithium carbonate by wet processing can be mentioned.

[0024] Next, the recovery method will be described in more detail. The following description also includes a description of the method for producing a metal of the present invention.

[0025] <Reduced object (oxide)> The object to be reduced in this recovery method is an oxide containing at least one element selected from the group consisting of nickel (Ni) and cobalt (Co) and lithium (Li), and specifically, for example, a positive electrode material for a lithium-ion battery. The oxide may further contain manganese (Mn). The positive electrode material (oxide) is obtained by carrying out pre-processing such as removing the electrolyte from the lithium-ion battery.

[0026] <Reducing Agent> Examples of the reducing agent include aluminum-containing substances such as metallic aluminum (Al); silicon-containing substances such as metallic silicon (Si) and FeSi; carbon-containing substances that contain carbon; and iron-containing substances.

[0027] Examples of carbon-containing substances include solid carbon-containing substances such as graphite, coke, and solid hydrocarbons; and gaseous carbon-containing substances such as carbon monoxide (CO) and hydrocarbon gases (eg, propane gas); and the like. When using a carbon-containing substance as a reducing agent, CO, CO 2 , H 2 This is preferable in that gases such as O are generated and the amount of slag generated is not increased.

[0028] The iron-containing substance is at least one selected from the group consisting of metallic iron (Fe) and iron oxide. The iron-containing substance as the reducing agent will be described below.

[0029] FIG. 3 is an Ellingham diagram (standard free energy change-temperature diagram). With reference to the above-mentioned standard free energy change and the Ellingham diagram (FIG. 3), the Fe / FeO equilibrium is less noble than the Ni / NiO equilibrium and the Co / CoO equilibrium, and reduction by Fe is considered possible. In addition, FeO / Fe 3 O 4 The equilibrium is less noble than the Ni / NiO equilibrium, but more noble than the Co / CoO equilibrium. For this reason, it is expected that Ni and Co can be selectively reduced (Ni is contained in the produced metal, and Co is contained in the produced 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]

[0030] In addition, the higher up on the Ellingham diagram (Figure 3), the more likely it is to become metallized. When Si or Al is used as a reducing agent, Mn also easily becomes metallized. Therefore, it is expected that by using Fe (or FeO) as a reducing agent, only Ni and Co will be metallized without metallizing Mn.

[0031] As metallic iron (Fe), for example, scrap or nuggets of iron used in steel mills may be used.

[0032] Iron oxide is generally classified as ferrous oxide (FeO), also known as wustite, or triiron tetroxide (Fe 3 O 4 ) and ferric oxide (Fe 2 O 3 ) are classified into three types: Of these, magnetite and hematite have a higher standard free energy change than that of wustite at the same temperature, and may be less likely to cause a reduction reaction. For this reason, ferrous oxide (wustite) is preferred as the iron oxide because it easily induces a reduction reaction. The iron oxide may be at least one of dust, scale, and sludge (hereinafter, for convenience, referred to as "dusts") that are generated as by-products in the iron-making process. The use of dust as iron oxide is preferable from the viewpoint of effectively utilizing by-products of the iron-making process and from the viewpoint of utilizing an inexpensive iron source.

[0033] Amount of reducing agent added The amount of the reducing agent added is preferably 1.0 equivalent or more, more preferably 1.2 equivalents or more, and even more preferably 1.4 equivalents or more, because this makes it easier to suppress insufficient reduction. The upper limit of the amount of the reducing agent to be added is not particularly limited. However, if the amount of the reducing agent to be added is too large, it may result in extra costs. Therefore, the amount of the reducing agent to be added is preferably 1.8 equivalents or less, more preferably 1.6 equivalents or less.

[0034] The amount of reducing agent required to reduce the oxides NiO and CoO to be reduced is called 1.0 equivalent. For example, the reducing agent may be metallic iron (Fe), ferrous oxide (FeO), metallic aluminum (Al), metallic silicon (Si), coke (C), and propane (C 3 H 8 ), reduction with one equivalent of reducing agent is shown as follows, respectively: Fe+(NiO,CoO)→(Ni,Co)+FeO 3FeO+(NiO,CoO)→(Ni,Co)+Fe 3 O 4 2Al+3(NiO,CoO)→3(Ni,Co)+Al 2 O 3 Si+2(NiO,CoO)→2(Ni,Co)+SiO 2 C+2(NiO,CoO)→2(Ni,Co)+CO 2 C 3 H 8+10(NiO,CoO) → 10(Ni,Co) + 3CO 2 +4H 2 O

[0035] When determining the amount of reducing agent to be added, first, the contents of NiO and CoO in the oxide to be reduced are obtained. Specifically, the Ni and Co contents in the object to be reduced (oxide) are measured and regarded as the NiO and CoO contents in the object to be reduced (oxide), respectively. The Ni and Co contents are measured using an energy dispersive X-ray analyzer (EDX).

[0036] <Slag former> As described above, in this recovery method, calcium oxide (CaO) and silicon dioxide (SiO 2 ) is used as a slag forming agent. CaO and SiO in the slag former 2 The content (total content) of 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.

[0037] 《Mass ratio (CaO / SiO 2 )》 As described above, in this recovery method, CaO and SiO 2 Mass ratio of CaO to SiO 2 ) is low, and a low basicity slag former is used. That is, the mass ratio of the slag forming agent used in this recovery method (CaO / SiO 2 ) is 0.50 or less, preferably 0.48 or less, more preferably 0.46 or less, even more preferably 0.44 or less, particularly preferably 0.42 or less, and most preferably 0.35 or less. On the other hand, the mass ratio of the slag former (CaO / SiO 2 The lower limit of is not particularly limited and is, for example, 0.15, preferably 0.20, more preferably 0.25, and even more preferably 0.30.

[0038] Amount of slag former to be added The amount of the slag former added is not particularly limited, but the mass ratio of the slag former to the oxide to be reduced (slag former / oxide) is preferably 0.40 to 1.00, more preferably 0.45 to 0.85, and even more preferably 0.50 to 0.80.

[0039] <heating> In this recovery method, the oxide to be reduced is heated in a state where a reducing agent and a slag-forming agent are added, whereby the oxide is reduced.

[0040] 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, because this makes it easier to suppress insufficient reduction. The upper limit of the heating temperature is not particularly limited and is appropriately set depending on the performance of the equipment (furnace) used for heating, but if the heating temperature is too high, it may result in extra costs. Therefore, the heating temperature is preferably 1800°C or less, more preferably 1700°C or less.

[0041] The atmosphere in which the oxide is heated (heating atmosphere) is, for example, nitrogen gas (N 2 Suitable examples of the atmosphere include an inert atmosphere such as a nitrogen gas (N) atmosphere, an argon gas (Ar) atmosphere, and a reducing atmosphere such as a carbon monoxide gas (CO) atmosphere.

[0042] The time for heating the 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. The upper limit of the heating time is not particularly limited. However, if the heating time is too long, it may result in extra costs. For this reason, the heating time is preferably 6 hours or less, and more preferably 5 hours or less.

[0043] 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 melting furnace, a low-frequency melting furnace, a rotary kiln, a vertical furnace, and a steelmaking furnace.

[0044] <Produced metal> A metal is produced by reducing an oxide to be reduced. In this recovery method, the metal obtained by reduction of the oxide (product metal) contains valuable elements (Ni, Co). Thus, the valuable elements (Ni, Co) contained in the oxide to be reduced are recovered as product metal. The product metal may be a metal containing only one of the valuable elements (Ni, Co) (or the proportion of one valuable element is greater than the proportion of the other valuable element).

[0045] <Resulting slag> By reducing the oxide to be reduced, slag is produced in addition to the metal. The slag obtained in this recovery method (produced slag) contains a large amount of Li, as described above. When an iron-containing substance is used as the reducing agent, the resulting slag contains FeO and the like. In addition, the produced slag may contain oxides of valuable elements (eg, MnO) that were not included in the produced metal. When reducing oxides containing Mn, the Mn / MnO equilibrium changes to Fe / FeO equilibrium and FeO / Fe 3 O 4 Since it is less noble than the equilibrium, it is possible to suppress the incorporation of Mn into the product metal obtained by reduction. When wet treatment is carried out, there are many different treatment methods depending on the form of Mn, which is troublesome. In contrast, the present recovery method using dry treatment is advantageous in that Mn can be retained in the generated slag. EXAMPLES

[0046] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples described below.

[0047] <Cathode material> First, a positive electrode material for a lithium-ion battery was prepared. Specifically, the lithium-ion battery was subjected to pretreatment such as disassembly, discharge, and removal of the electrolyte, and the positive electrode material was separated. The composition of the positive electrode material was Ni:Mn:Co=6:2:2 in molar ratio. The positive electrode material further contained Li.

[0048] <Reducing Agent> The reducing agents were aluminum metal (Al) powder, silicon metal (Si) powder, coke (C) powder, and propane gas (C 3 H 8 ) was prepared. Furthermore, as reducing agents, powder of metallic iron (Fe) obtained by atomization processing and powder of ferrous oxide (FeO) were prepared.

[0049] <Slag former> As slag formers, CaO and SiO 2 A slag former consisting of CaO and SiO 2 Mass ratio of CaO to SiO 2 Several types of slag formers with different melting points were prepared.

[0050] <Reduction of cathode material: Examples 1-6 and Comparative Examples 1-2> Next, the prepared cathode material was placed in an electric furnace with a heat size of 150 kg, a reducing agent and a slag-forming agent were added, and the mixture was heated. Thus, the cathode material was reduced to obtain a generated metal and a generated slag. The heating time was 3 hours, and the heating atmosphere was Ar. 30 kg of the slag former was added to 45 kg of the positive electrode material, i.e., the mass ratio of the slag former to the positive electrode material (slag former / positive electrode material) was about 0.67. The type and amount of reducing agent used (unit: equivalent weight), the mass ratio of the slag forming agent used (CaO / SiO 2 ) and the heating temperature (unit: °C) are shown in Table 1 below.

[0051] The reduction ratios of the metal elements Ni, Co, and Mn were calculated based on the above formula. The reduction ratios were converted from "mass %" to "mol %". Furthermore, the residual percentage of Li in the produced slag was calculated based on the above formula. The residual percentage in the produced slag was converted from "mass %" to "mol %". The results for both are shown in Table 1 below.

[0052] [Table 1]

[0053] <Summary of evaluation results> As shown in Table 1 above, the mass ratio (CaO / SiO 2 In the invention examples 1 to 8, the mass ratio (CaO / SiO 2 ) exceeding 0.50 was used, the residual rate of Li in the generated slag was higher.

[0054] In all of Examples 1 to 8, the reduction rates of Ni and Co were high, while the reduction rate of Mn was suppressed to 20% or less. In particular, in Examples 5 and 6 in which Fe or FeO was used as the reducing agent, the reduction rate of Mn could be further suppressed. In addition, the reduction rate of Co in Example 6 is lower than that in Example 5. This is thought to be because the free energy at the time of generating FeO is slightly lower than the free energy at the time of generating CoO (see FIG. 3). However, since FeO generates Fe by reduction, the reduction potential is higher than that of FeO. Overall, it has a certain degree of reduction potential, and it is thought that this result is reflected in the results.

[0055] Comparing Examples 1 to 6 with Examples 7 to 8, the mass ratio of the slag former (CaO / SiO 2 In Examples 7 to 8, in which the reduction ratio β was further reduced, the reduction ratio of Mn was further suppressed without causing a large decrease in the reduction ratios of Ni and Co, as compared with Examples 1 to 6.

Claims

1. An oxide containing lithium and at least one element selected from the group consisting of nickel and cobalt is mixed with a reducing agent, CaO and SiO ２ and heating the mixture to reduce the oxide, The CaO and SiO contained in the flux ２ Mass ratio (CaO / SiO ２ ) is 0.35 or less; Heating the oxide with the reducing agent and the slag forming agent added thereto; The method for recovering valuable elements, wherein the temperature when the oxide is heated is 1300° C. or higher.

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

3. 3. The method for recovering valuable elements according to claim 1, wherein the oxide is reduced to obtain a metal containing at least one element selected from the group consisting of nickel and cobalt.

4. 3. The method for recovering valuable elements according to claim 1, wherein the reducing agent is a carbon-containing substance.

5. 3. The method for recovering valuable elements according to claim 1, wherein the reducing agent is at least one iron-containing substance selected from the group consisting of metallic iron and iron oxide.

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

7. 6. The method for recovering valuable elements according to claim 5, wherein the iron-containing material is at least one selected from the group consisting of dust, scale, sludge and scrap.

8. 3. The method for recovering valuable elements according to claim 1 or 2, wherein the oxide is obtained from a lithium ion battery.

9. A method for producing a metal, comprising the steps of: producing a metal containing at least one element selected from the group consisting of nickel and cobalt, by using the method for recovering valuable elements according to claim 1 or 2.

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