Method for recovering valuable elements

Abstract

Provided is a valuable element recovery method, whereby it becomes possible to obtain a metal containing a valuable metal at a large content. The recovery method includes adding a reducing agent to an oxide containing at least one element selected from the group consisting of nickel and cobalt and heating the resultant mixture to reduce the oxide, in which the reducing agent contains at least one component selected from the group consisting of metal iron and iron oxide, and the amount of the reducing agent to be added is 1.3 equivalents or less.

Description

[Technical field]

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

[0002] In recent years, the demand for lithium-ion batteries has been rapidly increasing due to the widespread use of smartphones, personal computers, and electric vehicles. In particular, from the perspective of the recent need to reduce CO2 emissions, demand for electric vehicles that 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] In general, the positive electrode material of a lithium-ion battery is made of an oxide (composite oxide) containing nickel (Ni), cobalt (Co), and the like. Metal elements such as Ni and Co 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 used to recover valuable elements are classified into two types: wet processing, in which the positive electrode material is dissolved in acid followed by solvent extraction and electrolytic refining, and dry processing, in which the positive electrode material is heated together with a reducing agent to reduce and produce valuable elements.

[0005] Examples of reducing agents used in dry treatment (for example, Patent Document 1) include carbonaceous materials such as graphite; aluminum-containing materials such as metallic aluminum (Al); silicon-containing materials such as metallic silicon (Si) and FeSi; and the like. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-95628 Summary of the Invention [Problem to be solved by the invention]

[0007] In dry processing, when an Al-containing or Si-containing material is used as a reducing agent, slag is usually generated, which requires slag treatment costs, and the cost of the reducing agent itself is relatively high, resulting in high costs. In addition, when carbonaceous materials are used as reducing agents, the amount of CO2 generated is greater than when other reducing agents are used, which may go against the trend in reducing CO2 emissions.

[0008] As a result of the investigations conducted by the present inventors, it was found that metallic iron and iron oxide can be used as the reducing agent, which is less expensive than Al- or Si-containing materials and does not use carbonaceous materials, thereby reducing the amount of CO2 generated. However, further investigation by the inventors revealed that, depending on the amount of reducing agent used, the proportion of Fe may be high and the proportions of the valuable elements Ni and Co may be low in the metal (alloy) obtained by reducing the positive electrode material (oxide).

[0009] The present invention has been made in consideration of the above points, and has an object to provide a method for recovering valuable elements that can yield metals with a high proportion of valuable elements. [Means for solving the problem]

[0010] 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.

[0011] That is, the present invention provides the following [1] to [6]. [1] A method for recovering valuable elements, comprising adding a reducing agent to an oxide containing at least one element selected from the group consisting of nickel and cobalt, and heating the oxide to reduce the oxide, the reducing agent containing at least one element selected from the group consisting of metallic iron and iron oxide, and the amount of the reducing agent added is 1.3 equivalents or less. [2] The method for recovering valuable elements according to [1] above, wherein the oxide is obtained from a lithium ion battery. [3] The method for recovering valuable elements according to [1] or [2] above, wherein the iron oxide is ferrous oxide. [4] The method for recovering valuable elements according to any one of the above [1] to [3], wherein the reducing agent is at least one selected from the group consisting of dust, scale, sludge and scrap. [5] The method for recovering a valuable element according to any one of the above [1] to [4], wherein the temperature when the oxide is heated is 1450° C. or higher. [6] The method for recovering a valuable element according to any one of the above [1] to [5], wherein the oxide is reduced to obtain a metal containing iron and at least one element selected from the group consisting of nickel and cobalt. Effect of the Invention

[0012] According to the present invention, there is provided a method for recovering valuable elements, which is capable of obtaining metals having a high ratio of valuable elements. [Brief description of the drawings]

[0013] [Figure 1] This is an Ellingham diagram (standard free energy change-temperature diagram). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] [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 adding a reducing agent to an oxide containing at least one element selected from the group consisting of nickel and cobalt, which is obtained from a lithium ion battery, and heating the oxide to reduce the oxide, wherein the reducing agent contains at least one element selected from the group consisting of metallic iron and iron oxide, and the amount of the reducing agent added is 1.3 equivalents or less.

[0015] 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.

[0016] <Findings Obtained by the Inventors> The positive electrode material of a lithium-ion battery is generally made of an oxide (composite oxide) such as LiNiO2, LiCoO2, or LiMnO2. Considering the thermodynamics of dry processing, for example, LiNiO2 and LiCoO2 decompose at high temperatures as follows, producing NiO and CoO, respectively. 2LiNiO2 → Li2O+2NiO+1 / 2O2 2LiCoO2 → Li2O+2CoO+1 / 2O2

[0017] The standard free energy change (ΔG 0 ) are shown below, respectively. NiO→Ni+1 / 2O2:ΔG 0 =234900-84.68T[J] CoO→Co+1 / 2O2: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.

[0018] Conventionally, substances having strong reducing power, such as carbonaceous materials, Al-containing substances, and Si-containing substances, have been used as reducing agents. However, from the viewpoint of reducing CO2 emissions and cost, it is desirable to use a different reducing agent. Therefore, the present inventors have investigated substances that are not carbonaceous, are relatively inexpensive, and are not rare, as potential new reducing agents, and have found that metallic iron (Fe) or iron oxide is effective.

[0019] The standard free energy change (ΔG 0 ) is as follows: FeO→Fe+1 / 2O2:ΔG 0 =264430-64.73T[J] Fe3O4→3FeO+1 / 2O2:ΔG 0 =302370-108.15T[J]

[0020] Figure 1 is an Ellingham diagram (standard free energy change-temperature diagram). Referring to the above-mentioned standard free energy change and the Ellingham diagram (FIG. 1), 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, the FeO / Fe3O4 equilibrium is less noble than the Ni / NiO equilibrium, but more noble than the Co / CoO equilibrium. Therefore, it is expected that Ni and Co can be selectively reduced (Ni is recovered as metal, and Co remains in the slag). Specifically, the following reactions are expected. NiO+Fe→Ni+FeO:ΔG 0 =-29530-19.95T[J] CoO+Fe→Co+FeO:ΔG 0 =-28950-6.82T[J]

[0021] In addition, the higher up on the Ellingham diagram (Figure 1), 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.

[0022] However, elements contained in conventional reducing agents, such as C, Al, and Si, have very low standard free energy change values, and it is thought that when Fe is used, the reduction reaction is unlikely to occur (or even if it does occur, it is only in trace amounts).

[0023] Therefore, the present inventors carried out tests to confirm the possibility of reducing NiO and CoO with Fe and iron oxide (Test Examples 1 to 8). Specifically, first, powders of NiO, CoO, Fe and FeO were mixed in the powder composition (unit: molar ratio) shown in Table 1 below, and the resulting mixture was compacted. Thereafter, the obtained compact was placed in an electric resistance furnace and heated at 1400° C. for 3 hours in an argon gas atmosphere. The phases formed in the heated compact were evaluated by measurement using an electron probe microanalyzer (EPMA). Among the phases formed, the composition of the alloy phase is also shown in Table 1 below.

[0024] [Table 1]

[0025] As shown in Table 1 above, in Test Examples 1 to 4 in which Fe was added to NiO and CoO, NiO and CoO were reduced and melted together with the excess Fe added, and an Fe-Ni-Co alloy phase was confirmed. It was also confirmed that the smaller the amount of Fe added, the smaller the proportion of Fe in the resulting alloy, and the larger the proportions of Ni and Co.

[0026] Furthermore, as shown in Table 1 above, in Test Examples 5 to 8 in which FeO was added to NiO and CoO, NiO and CoO were reduced, and the Fe-Ni-Co alloy phase was confirmed. FeO was partially reduced to Fe, which existed as part of the alloy. At this time, the following reaction is considered to have occurred. 4FeO → Fe3O4 + Fe It was also confirmed that the smaller the amount of FeO added, the smaller the proportion of Fe and the larger the proportions of Ni and Co in the resulting alloy.

[0027] From the above results, it was confirmed that Fe and iron oxide can be used as reducing agents. Furthermore, it was confirmed that an alloy with a high proportion of Ni and Co could be obtained by reducing the amount of reducing agent added.

[0028] Next, the recovery method will be described in more detail.

[0029] <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 and cobalt, and specifically, for example, a positive electrode material for a lithium ion battery. The positive electrode material (oxide) is obtained by carrying out pre-processing such as removing the electrolyte from the lithium-ion battery.

[0030] <Reducing Agent> For the reasons mentioned above, in the present recovery method, a reducing agent containing at least one selected from the group consisting of metallic iron (Fe) and iron oxide is used. As metallic iron (Fe), for example, scrap or nuggets of iron used in steel mills may be used.

[0031] Iron oxide is generally divided into three types: ferrous oxide (FeO), also known as wustite; triiron tetroxide (Fe3O4), also known as magnetite; and ferric oxide (Fe2O3), also known as hematite. 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.

[0032] <Amount of reducing agent added> In this recovery method, the amount of reducing agent added is 1.3 equivalents or less, which results in a metal with a low proportion of Fe and a high proportion of valuable elements (Ni, Co).

[0033] The smaller the amount of reducing agent added, the higher the proportion of valuable elements (the lower the proportion of Fe) in the resulting metal, which prevents excess Fe from remaining in the metal without being used as a reducing agent. Furthermore, the smaller the amount of reducing agent added, the greater the proportion of Ni in the metal obtained, especially between Ni and Co. This is presumably because, as Ni is higher than Co in the Ellingham diagram (Figure 1), Ni is easier to metallize than Co, and Ni is reduced first by Fe (or iron oxide). For these reasons, the amount of reducing agent added is preferably 1.2 equivalents or less, more preferably 1.1 equivalents or less, even more preferably 1.0 equivalents or less, particularly preferably less than 1.0 equivalent, and most preferably 0.9 equivalents or less.

[0034] The lower limit of the amount of the reducing agent added is not particularly limited. However, from the viewpoint of suppressing insufficient reduction, the amount of the reducing agent added is preferably 0.1 equivalent or more, more preferably 0.3 equivalent or more, and even more preferably 0.5 equivalent or more.

[0035] The amount of reducing agent required to reduce the oxides NiO and CoO to be reduced is called 1.0 equivalent. For example, when the reducing agent is metallic iron (Fe) or ferrous oxide (FeO), the reduction with one equivalent of the reducing agent is shown as follows, respectively: Fe+(NiO,CoO)→(Ni,Co)+FeO 3FeO+(NiO,CoO)→(Ni,Co)+Fe3O4

[0036] 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).

[0037] <heating> In this recovery method, the oxide to be reduced is heated in a state where a reducing agent is added to the oxide, whereby the oxide is reduced. When heating, a flux such as CaO or SiO2 may be added in addition to the reducing agent.

[0038] 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.

[0039] Suitable atmospheres for heating the oxide (heating atmosphere) include, for example, inert atmospheres such as a nitrogen gas (N2) atmosphere and an argon gas (Ar) atmosphere; and reducing atmospheres such as a carbon monoxide gas (CO) atmosphere.

[0040] 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.

[0041] 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.

[0042] <Product> Metals are produced by reducing the oxide (cathode material) to be reduced. In other words, valuable elements (Ni, Co) contained in the oxide are recovered as metals.

[0043] In this recovery method, the metals obtained by reduction of the oxides (also called "product metals") contain, for example, iron (Fe) and valuable elements (Ni, Co). Such metals are sufficiently valuable as materials that they can be used, for example, in the iron-making process. It is preferable that the product metal has a low ratio of Fe and a high ratio of valuable elements (Ni, Co), which increases its value as an alloy. 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).

[0044] In addition to metals, slag may also be produced by reducing the oxide (cathode material). The slag (also called "produced slag") contains oxides such as FeO. In addition, the produced slag may contain oxides of valuable elements (eg, MnO) that were not included in the produced metal. When reducing an oxide containing Mn, the Mn / MnO equilibrium is less noble than the Fe / FeO equilibrium and the FeO / Fe3O4 equilibrium, so that it is possible to prevent Mn from being mixed into the product metal obtained by reduction. When wet processing is carried out, there are many different processing methods depending on the form of Mn, which is troublesome. In contrast, the present recovery method using dry processing is advantageous in that it allows Mn to be retained in the slag. EXAMPLES

[0045] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples described below.

[0046] <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 is shown in Table 2 below. As shown in Table 2 below, the composition of the positive electrode material was Ni:Mn:Co=6:2:2 in molar ratio.

[0047] [Table 2]

[0048] <Reducing Agent> As reducing agents, graphite (C) powder, metallic aluminum (Al) powder, and metallic silicon (Si) powder were prepared. As another reducing agent, powder of metallic iron (Fe) obtained by atomization processing and powder of ferrous oxide (FeO) were prepared. As further reducing agents, powders of dust, scale and scrap generated in the steelmaking process were prepared. The compositions of the dust, scale and scrap are shown in Table 3 below. In Table 3 below, "M.Fe" indicates the amount of metallic Fe.

[0049] [Table 3]

[0050] <Reduction of Cathode Material: Inventive Examples 1 to 23, Comparative Examples 1 to 10, and Reference Examples 1 to 6> Next, the prepared cathode material was placed in an electric furnace with a heat size of 50 to 80 kg, and any of the reducing agents described above and flux (CaO, SiO2) were added and heated. In this way, the cathode material was reduced. The heating time was 3 hours in each case. The type and amount of the reducing agent used (unit: equivalent), the heating temperature (unit: °C) and the heating atmosphere (Ar, N2 or CO) are shown in Table 4 below.

[0051] The composition of the metals produced by reduction of the positive electrode material was determined. In addition, the reduction rate (unit: mass%) was determined for each of the metal elements Ni, Co, and Mn. The reduction rate is the ratio of the amount of metal actually obtained to the theoretical amount of metal produced by the reduction reaction. For example, when the reduction rate of Co is 20 mol%, it means that 20 mol% of the Co contained in the positive electrode material is reduced to metal, and the remainder remains as oxide. The results are shown in Tables 4 to 6 below.

[0052] [Table 4]

[0053] [Table 5]

[0054] [Table 6]

[0055] <Summary of evaluation results> As shown in Tables 4 and 5 above, the metals produced in Examples 1 to 23, in which the amount of reducing agent added was 1.3 equivalents or less, had a lower proportion of Fe and a higher total proportion of Ni and Co than the metals produced in Comparative Examples 1 to 10, in which the amount of reducing agent added was more than 1.3 equivalents.

[0056] For example, see Examples 1 to 3 of the present invention. The smaller the amount of reducing agent added, the smaller the proportion of Fe in the produced metals, and the larger the total proportion of Ni and Co. In addition, there was a tendency that the proportion of Ni in the produced metal increased (and the proportion of Co decreased) as the amount of reducing agent added decreased. The same was true for Examples 4 to 6, 7 to 9, 10 to 12, 13 to 15, 16 to 17, 18 to 19, 20 to 21, and 22 to 23.

Claims

1. adding a reducing agent to an oxide containing at least one element selected from the group consisting of nickel and cobalt, and heating the resulting oxide to reduce it; the reducing agent contains at least one selected from the group consisting of metallic iron and iron oxide; The method for recovering a valuable element, wherein the amount of the reducing agent added is 0.1 equivalents or more and 0.9 equivalents or less, or 1.1 equivalents or more and 1.3 equivalents or less.

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

3. 2. The method for recovering valuable elements according to claim 1, wherein the iron oxide is ferrous oxide.

4. 2. 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.

5. 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.

6. The method for recovering valuable elements according to any one of claims 1 to 5, wherein the oxide is reduced to obtain a metal containing iron and at least one element selected from the group consisting of nickel and cobalt.

Images