Recovery of Nickel and Cobalt from Spent Battery Cathode Materials

Abstract

The present invention belongs to the field of pyrometallurgy and discloses a method and slag suitable for recovering Ni and Co from Li-ion batteries or their waste, in particular from battery black powder. The slag composition is defined as follows: 25% <MnO<70%;Al2O3+0.5MnO<45%;SiO2> 5%; Li2O>1%; 0.5% <P2O5<10%;MnO+Li2O+Al2O3+CaO+SiO2+FeO+MgO+P2O5> 90%; and wherein (CaO+2Li2O+0.4MnO) / SiO2≥2.0. This composition is particularly suitable for limiting or avoiding wear or corrosion of furnaces lined with magnesia-containing refractory bricks.

Description

Technical Field

[0001] The present invention belongs to the field of pyrometallurgy and relates to the recovery of Ni and Co from Li-ion batteries or their waste, more particularly from battery black powder. Background Art

[0002] In recent years, driven in particular by new regulations in Europe and China, electric vehicles have experienced unprecedented growth, designed to gradually reduce the CO2 footprint of cars and limit urban air pollution. This growth is expected to continue in the coming decades. The adoption of electric vehicles depends largely on the performance of the batteries used to store electrical energy. To achieve the highest energy density while keeping costs under control, rechargeable Li-ion batteries are preferred. Many of these batteries contain positive electrodes based on the transition metals Ni, Mn, and Co, and are therefore also called NMC batteries. As the electric vehicle market grows, the demand for these metals is expected to increase significantly.

[0003] The demand for nickel and cobalt could even outstrip global production capacity. Cobalt is particularly critical because it is currently produced only as a by-product of the nickel and copper industries. The nickel market is significantly larger than the cobalt market. Most nickel is used in the production of stainless steel, where its purity is less important. However, high-purity nickel and high-purity cobalt metals or compounds are already in short supply. Given this, recovering nickel and cobalt from spent lithium-ion batteries or their waste is an attractive proposition, also known as the battery circular economy.

[0004] In particular, so-called "battery black" (BM) or "black matter" is a very interesting starting material for recycling. Although the term battery black is often used in industry, its exact composition can vary significantly depending on the manufacturer or application. Typically, scrapped batteries are disassembled and shredded, which may include separating the casing material, foil and / or negative electrode. Sometimes they are also pre-processed. Compared to the processing of intact batteries, the battery black resulting from this process is usually characterized by a relatively low aluminum content. On the other hand, it contains considerable amounts of lithium, manganese, cobalt and / or nickel.

[0005] Facilities used to recycle batteries and battery waste typically use hydrometallurgical processes to process battery black powder, producing salts or metal hydroxides. Pyrometallurgical refining processes are less common, and the combined pyro-hydrometallurgical process according to the present invention remains a rare exception.

[0006] The known pyrometallurgical process for recycling lithium-ion batteries reduces nickel, cobalt, and copper oxides to their respective metals in a furnace, concentrating them in an alloy phase at high temperatures. Other compounds, such as lithium and manganese, are oxidized to Li2O and MnO and collected in the slag.

[0007] Over time, operating this high-temperature process can cause wear or corrosion of the furnace walls. Typically, the furnace walls are made of refractory bricks. The most commonly used bricks are primarily magnesia. Typical magnesia bricks contain over 90% magnesia, while magnesia-chrome bricks contain 50% to 70%. It has been observed that magnesia is dissolved by ordinary slag during furnace operation. This wear or corrosion is a recurring problem, resulting in high maintenance costs due to the need to shut down the furnace and regularly replace refractory bricks. This problem becomes more pronounced at higher operating temperatures, such as above 1550°C. Summary of the Invention

[0008] The present invention therefore aims not only to provide an efficient method for recovering Ni and Co from Li-ion batteries or their waste, in particular from battery black powder, but also to increase the life of the furnace. This is achieved by operating with a dedicated slag system rich in MnO and Li2O, with a controlled composition designed to limit the corrosion of Mg-containing refractory bricks.

[0009] WO2017121663 describes the composition of slags produced in industrial processes and discloses the effects of MnO on slag viscosity and cobalt recovery. The main slag components described are CaO, SiO2, Al2O3, Li2O, and MnO or MnO2. The MnO concentrations in the slags disclosed are very low, and the teaching is limited to the amount of MnO in the slag.

[0010] Wittkowski et al. (Speciation of Manganese in a Synthetic Recycling Slag Relevant for Lithium Recycling from Lithium-Ion Batteries: Metals, Vol. 11(2), 2021, p. 188) analyzed the phase composition of different Li-containing slags relevant for Li-ion battery recycling. Battery black powder was not mentioned as a starting material. All reported slags were characterized by MnO contents much lower than those according to the present invention.

[0011] On the other hand, recent Li-ion batteries generally contain increased amounts of Mn. This results in slag compositions having higher MnO contents.

[0012] WO12140951, WO13080266, and WO20013294 propose methods for recycling Li-ion battery waste to recover Ni and Co while simultaneously fixing impurities such as Fe and P in the slag phase. Although it is stated that Mn may be a component of the resulting slag, no preferred range or specific effect of MnO in such slag is specified.

[0013] CN103924088 and EP3269832 describe bath smelting of spent batteries, producing alloys containing Co and / or Ni and slags rich in SiO2 and MnO. There is no mention of the Li content in these slags, nor of any effect of MnO or Li2O. There is no mention of battery black powder as a starting material.

[0014] CN105838895 and Xiao et al. (Recovery of Valuable Metals from Spent Lithium-Ion Batteries by Smelting Reduction Process Based on MnO-SiO2-Al2O3 Slag System: J. Sustain. Metall., Vol. 3, 2017, pp. 703-710) describe the composition of slag produced by smelting Li-ion batteries and a leaching process for extracting Li and Mn from the resulting slag. A method for extracting lithium and manganese from lithium-containing, manganese-rich slag is disclosed, without discussing specific slag properties. In all examples given, the typical slag is rich in MnO, SiO2, and Al2O3, while the Li2O content is quite low.

[0015] Vest et al. (Slag design for lithium recovery from spent batteries: Int. Work. Met. Interact., Vol. 9(93), 2010, pp. 93-106) describe theoretical calculations for different slag systems, some of which are also rich in MnO. However, with regard to lithium, the goal is to design a slag so that the Li distribution shifts towards the maximum concentration in the flue dust rather than in the slag. Therefore, one of the desired slag properties is a low capacity / solubility for Li2O.

[0016] EP21176046 describes a pyrometallurgical recycling process for Li-ion batteries, in which the batteries are fed into a smelting furnace equipped with a submerged injection mechanism for O2-containing gas to reduce the majority of the Ni and Co. The resulting slag is processed in a second reduction smelting step, where the remaining Ni and Co are extracted. The slag contains less than 20% MnO and has relatively high amounts of Al2O3, such as greater than 20% or even greater than 30%. No mention is made of wear or corrosion of the furnace walls.

[0017] The present invention achieves a significant reduction in the wear of magnesia-containing refractory bricks in pyrometallurgical processes, which contributes to the overall economic efficiency of the process. The following embodiments further describe the present invention. DETAILED DESCRIPTION

[0018] According to a first embodiment, a method for recovering Ni and Co from Li-ion batteries or their waste materials comprises the following steps:

[0019] - Provide a furnace lined with magnesia-containing refractory bricks;

[0020] - providing a feed comprising a slag forming agent and Li-ion batteries or waste thereof, wherein the Al content of the feed is less than 8%; and

[0021] - smelting the feed under reducing conditions to obtain an alloy containing a majority of Ni and Co and a Li-containing slag, wherein the slag has the following mass composition percentages:

[0022] 25% <MnO<70%;

[0023] Al2O3+0.5MnO<45%;

[0024] SiO2>5%;

[0025] Li2O>1%;

[0026] 0.5% <P2O5<10%;

[0027] MnO+Li2O+Al2O3+CaO+SiO2+FeO+MgO+P2O5>90%; and

[0028] Among them, (CaO+2Li2O+0.4MnO) / SiO2≥2.0.

[0029] "Slag former" means, for example, one or more of CaO, Al2O3 and SiO2. Other slag formers well known to those skilled in the art may also be present. The slag formers themselves may be added, or they may be obtained in situ from readily oxidizable metals present in the feed, such as aluminum.

[0030] A "furnace lined with magnesia-containing refractory bricks" is understood to mean a metallurgical furnace which is at least partially lined with such bricks, in particular in the areas which come into contact with the slag.

[0031] While the method described is suitable for processing Li-ion batteries or their waste, other materials can also be included in the metallurgical feed. For example, mixed hydroxide precipitate (MHP) can be added: this product typically contains useful concentrations of Co, Ni, and Mn, as well as Mg. The Co and Ni are recovered in the alloy, while the Mn and Mg are absorbed into the slag, where they serve the useful purpose of protecting the lining. Combining battery materials with MHP also optimizes overall energy consumption, as batteries tend to be exothermic during the smelting process, while MHP is endothermic. The total feed can advantageously contain up to 30% by weight of MHP.

[0032] In the total feed, compounds other than MHP not originating from Li-ion batteries or their waste should preferably be limited to less than 25%, more preferably less than 15%.

[0033] According to another embodiment, the Li-ion battery or its waste material is battery black powder.

[0034] The expression "battery black powder" is commonly used in the industry to describe an intermediate product derived from Li-ion batteries or their waste materials (such as new or spent Li-ion batteries, used or scrapped batteries, production or battery waste, electrode materials or other pre-processed battery materials). The batteries are usually disassembled. Thus, for example, Al, Fe and Cu are separated from the casing and cables. All of these battery materials are then chopped and sometimes pre-treated (for example by heat treatment) to remove residual electrolyte or graphite, thereby obtaining a powder or filter cake, which can be further processed into blocks or pellets. In the latter case, this may include mixing with other compounds that do not originate from Li-ion batteries or their waste materials to produce those blocks or pellets.

[0035] The battery black powder will still contain a considerable amount of Co and / or Ni, making the pyrometallurgical process economically efficient. The above characteristics make battery black powder a preferred feed material for the method.

[0036] "Major portion" of an element or compound means more than 50% by weight of the corresponding amount present in the feed. It may also include ranges having lower limits selected from 55%, 60%, 65%, 70%, and 75% and upper limits selected from 80%, 85%, 90%, 95%, and 100%.

[0037] According to another embodiment, the content of MnO in the slag is 30% or more, preferably 40% or more.

[0038] The content of MnO in the slag plays a key role in the present invention. At least 10% MnO is required in the slag to observe the effect of inhibiting the dissolution of MgO from the magnesium-containing refractory bricks in the furnace lining into the slag. At least 25% MnO in the slag fully shows the effect of inhibiting the dissolution of MgO. It is preferred that the slag has at least 30% MnO, more preferably at least 40%. When the method uses battery black powder as the starting feed and uses a minimum amount of slag-forming agent to save costs and keep the slag volume low, the amount of MnO in the slag will generally be higher than 25%.

[0039] Combining a MnO content of 25% to 70% with a relatively small volume of slag is beneficial as this is consistent with inhibiting MgO dissolution.

[0040] On the other hand, adding more flux, thereby increasing the overall volume of the slag and diluting the percentage of MnO to below 25%, gradually increases the amount of MgO dissolved from the refractory bricks and therefore has a negative effect.

[0041] The upper limit of 70% MnO in the slag helps to keep the melting point of the slag sufficiently low.

[0042] Mn in slag is represented by "MnO." The exact oxidation state of Mn in such slags is not always clearly defined. Therefore, manganese oxide ("MnO") can also correspond to a mixture of MnO monoxide and MnO2 dioxide. The MnO content is assumed to be significantly higher than 95%, particularly under the selected reduction reaction conditions.

[0043] MnO is usually green, while MnO2 is usually dark brown or dark gray, so it is called "manganese black". Green will only dominate when the content of monoxide is high enough.

[0044] The content of P2O5 in the slag is 0.5% <P2O5<10%。

[0045] Phosphorus typically originates from the electrolyte in Li-ion batteries and is incorporated into the slag in the form of P2O5.

[0046] Lithium iron phosphate (LFP) batteries typically contain more phosphorus than NMC batteries, but no cobalt and nickel. In an industrial setting, recyclers may have to process feed containing a mixture of such LFP batteries and NMC batteries, which would contribute to the overall phosphorus content in the slag.

[0047] According to another embodiment, the content of Al2O3 in the slag is less than 30%.

[0048] Too high a content of Al2O3, such as more than 30% or even more than 40%, increases the melting point of the slag. Heating to higher temperatures is less economical and increases refractory wear.

[0049] Battery black powder typically adds only limited amounts of Al2O3 to the slag. This is significantly different when starting with battery black powder rather than complete Li-ion batteries, which are typically rich in Al due to their outer shell.

[0050] The slag composition conforms to the formula Al2O3+0.5MnO<45%, which allows the slag to have a relatively high MnO content while limiting the amount of Al2O3.

[0051] According to another embodiment, the mass composition percentage of the slag is Al2O3+0.5MnO<30%. In this way, the amount of Al2O3 is further limited in the slag with a relatively high MnO content, which is beneficial to protecting the magnesia-containing refractory bricks.

[0052] According to another embodiment, the CaO content in the slag is 40% or less, preferably 30% or less.

[0053] CaO helps maintain sufficient fluidity in the slag and ensures ease of handling. CaO also helps inhibit the dissolution of MgO from magnesia-containing refractory bricks, as Ca and Mg have similar chemical sites in the slag. Operating the process at the preferred upper limit of 30% CaO helps keep the melting point of the slag below 1600°C. However, excessive amounts of CaO, such as above 40%, can increase the melting point of the slag and should be avoided.

[0054] On the other hand, an increase in the amount of MnO allows a reduction in the amount of CaO since they are similar in suppressing the dissolution of MgO from magnesia-containing refractory bricks.

[0055] According to another embodiment, the slag forming agent does not contain CaO.

[0056] MnO-rich feeds even allow to completely avoid CaO as a slag former. This opens the way to explore other slag systems besides the well-known ternary slag system Al2O3-CaO-SiO2 commonly used in the prior art.

[0057] The beneficial effects of the present invention can still be achieved in the absence of CaO, since MnO in the slag plays a key role in this regard.

[0058] According to another embodiment, the Li2O content in the slag is greater than 3%, preferably greater than 6%.

[0059] It was also observed that, in addition to MnO and CaO, Li2O can also inhibit the dissolution of Mg from Mg-containing refractory bricks. When recycling Li-ion batteries, the amount of Li2O in the slag is expected to be large.

[0060] In this context, ">3%" is to be understood as meaning, in particular, 3.1% or more, preferably 3.2% or more, 3.3% or more, 3.4% or more, and particularly also 3.5% or more, 4.0% or more, 4.5% or more, 5.0% or more, or 5.5% or more. Amounts greater than 3% allow for increased lithium content in the slag. However, since LiO also inhibits Mg dissolution, higher amounts (e.g., greater than 6%) are preferred not only for economic reasons but also because of the greater contribution to wear reduction. This is particularly true for amounts of 7% or more, 8% or more, 9% or more, or 10% or more.

[0061] SiO2 helps to lower the melting point of the slag. On the other hand, increasing the amount of SiO2 has a negative effect. Therefore, according to another embodiment, the amount of SiO2 in the slag is less than 20%.

[0062] In a preferred embodiment, the slag composition conforms to the formula (CaO+2Li2O+0.4MnO) / SiO2≥2.0.

[0063] According to another embodiment, the content of cobalt oxide in the slag is 0.05%. <CoO<1%。

[0064] Under the applied process conditions, most of the cobalt is incorporated into the alloy, while only a small amount remains in the slag. Typically, concentrations of less than 1% are achieved. Completely cobalt-free slags cannot be achieved in industrial Li-ion battery recycling.

[0065] According to another embodiment, the Fe content in the slag is 25% or less, preferably 10% or less. In FeO-rich slags containing greater than 10% FeO, or even greater than 25% FeO, CoO cannot be reduced to metallic Co without also transferring relatively large amounts of metallic Fe into the alloy phase. This significantly increases the cost of any subsequent hydrometallurgical processing of the resulting alloy and is therefore less than ideal. Furthermore, Fe-containing slags are corrosive to magnesia-containing refractory bricks at high temperatures.

[0066] Therefore, according to a preferred embodiment, the Fe content in the feed is 5% or less. This can be achieved, for example, by separating the Fe-containing casing material, or by keeping the amount of undesirable lithium iron phosphate (LFP) batteries in the feed sufficiently low.

[0067] Slag composition and operating temperature are key considerations for the methods described herein. The present invention achieves a balance between compounds that protect the furnace walls (e.g., MnO, CaO, LiO) and compounds that negatively impact the walls. Furthermore, the slag composition range allows for adequate slag fluidity and minimal overheating at the desired operating temperature. It is preferred that the temperature be as low as possible while still remaining above the melting point of the alloy.

[0068] This balance is reflected in the proposed process conditions as well as in the composition of the slag itself.

[0069] According to another embodiment, the step of melting the feed is carried out at a temperature of at least 1400°C to ensure complete melting of the metallurgical feed and at most 300°C above the liquidus point of the slag, preferably at most 100°C above the liquidus point of the slag. The lower limit is preferred to avoid that the produced alloy or slag is even partially solidified. The upper limit is preferred to avoid overheating the slag. Higher temperatures promote the dissolution of Mg from the Mg-containing refractory bricks. Therefore, lower temperatures are generally preferred in order to reduce wear and save energy. Overheating the slag has a negative impact on the dissolution of the Mg-containing refractory bricks by the slag.

[0070] The preferred operating temperature is below 1700°C, more preferably below 1650°C, even more preferably below 1600°C, and most preferably below 1550°C.

[0071] According to another embodiment, the smelting step comprises the further steps of:

[0072] - Sampling of slag;

[0073] - cooling the slag sample and evaluating its color; and

[0074] - in case the slag sample is green, terminating the smelting step; or

[0075] - In case the slag sample is not green, the smelting step is continued after adjusting the pO2 level to achieve more reducing conditions.

[0076] "Sampling the slag" means removing a small sample of the slag while continuing the method under selected conditions.

[0077] The evaluation of color can be easily performed visually. Compared with chemical analysis of the slag, monitoring the color change can quickly and effectively indicate that the slag contains a certain minimum percentage of MnO. As will be described in more detail below, it is further observed that the green color of the slag also indicates that most of the Co contained in the feed is reduced and thus merged into the alloy. Without being bound by theory, it is actually believed that the color changes to green due to the reduction of MnO2 to MnO, but also due to the reduction of the usually darker oxides such as Fe, Ni and Co.

[0078] Visual inspection is a quick and easy process control method that saves time and operating costs.

[0079] In the context of the present invention, "green" is defined as a color having hue, lightness, and chroma within the following ranges according to the ASTM D1535-14 (2018) standard:

[0080] - Tones range from 5GY to 5BG;

[0081] - Brightness: ≥3; and

[0082] - Chroma: ≥3.

[0083] An example of green is shown in the "Geological Rock Color Chart and Original Munsell Color Chart" produced by Munsell Color Company in 2009.

[0084] The operating conditions are selected so that most of the Mn is oxidized to slag and most of the Co and Ni are reduced to alloy. Preferably, more than 90%, more preferably more than 95%, and most preferably more than 98% of the Co and Ni are collected in the alloy. The pO2 level of the process of the present invention is easily adjusted to achieve these favorable yields.

[0085] According to another embodiment, the pO2 level is adjusted to 10 -7 >pO2>10 -12 , preferably adjusted to pO2<10 -8 , more preferably adjusted to pO2<10 -8.5 , preferably adjusted to pO2 < 10 -9 .

[0086] with 10 -7 Compared with the pO2 level of 10 -8 , 10 -8.5 and 10 -9 The preferred pO2 level and 10 -12 The limit actually represents stronger reducing conditions and is conducive to high reduction yields.

[0087] According to another embodiment, the color of the slag is green. During smelting of the charge material under reducing conditions, the color of the slag typically changes from dark grey or dark brown to green as the process proceeds.

[0088] According to another embodiment, the furnace is an electric furnace. Using an electric furnace or electric arc furnace (EAF) allows for greater flexibility in situations where higher operating temperatures are desired or required. Another advantage is that it allows for the use of off-peak electricity prices, or electricity produced from environmentally friendly green sources such as local wind farms.

[0089] Another embodiment describes a Li-containing metallurgical slag having the following weight percentage composition:

[0090] 25% <MnO<70%;

[0091] Al2O3+0.5MnO<45%;

[0092] SiO2>5%;

[0093] Li2O>3%;

[0094] 0.5% <P2O5<10%;

[0095] MnO+Li2O+Al2O3+CaO+SiO2+FeO+MgO+P2O5>90%; and

[0096] Among them, (CaO+2Li2O+0.4MnO) / SiO2≥2.0.

[0097] Another embodiment describes a Li-containing metallurgical slag, wherein the color of the slag is green. The green color indicates that the slag contains a certain minimum percentage of MnO, which is important for specific slag properties.

[0098] Another embodiment describes a Li-containing metallurgical slag, wherein the MnO content in the slag is 30% or more, preferably 40% or more. A higher content is beneficial for protecting the furnace wall.

[0099] Another embodiment describes a Li-containing metallurgical slag, wherein the content of Al2O3 in the slag is less than 30%. Limiting the amount to less than 30% is beneficial for achieving a lower melting point.

[0100] Another embodiment describes a Li-containing metallurgical slag, wherein the CaO content of the slag is 40% or less, preferably 30% or less. Slags with relatively high amounts of MnO, such as over 40% or even over 50%, allow for very low CaO contents. This includes slags that contain no CaO.

[0101] In all the above cases, the beneficial properties of the slag according to the invention of preventing wear or corrosion of the furnace walls or preventing the dissolution of MgO from magnesia-containing refractory bricks are maintained.

[0102] Another embodiment describes a Li-containing metallurgical slag, wherein the Fe content of the slag is 25% or less, preferably 10% or less. When the slag is reused in a new pyrometallurgical operation, the iron in the slag may be transferred to the alloy, which is undesirable because it makes any subsequent hydrometallurgical processing of the alloy more complicated and therefore costly.

[0103] Another embodiment describes the use of the Li-containing metallurgical slag as a slag-forming agent in a pyrometallurgical recovery process. The obtained metallurgical slag contains one or more of MnO, Al2O3, CaO and SiO2, and can therefore be used as a slag-forming agent in new operations.

[0104] Another embodiment describes the use of the Li-containing metallurgical slag as a slag forming agent in the method according to the first embodiment, thereby partially or completely replacing the slag forming agent in the step of providing a feed comprising the slag forming agent.

[0105] Reusing the resulting metallurgical slag in new operations allows for more flexible selection of operating conditions, such as the process's pO2 level. For example, when more oxidizing conditions are used, thereby sending more Co and / or Ni to the slag, these valuable metals can be recovered in subsequent operating cycles, where more reducing conditions can be used to recover more Co and / or Ni. Thus, another embodiment describes a Li-containing metallurgical slag, wherein the slag also contains cobalt.

[0106] When metallurgical slag is reused as a slag-forming agent in a new process cycle, it should be considered that the incoming battery or scrap material may contain additional amounts of compounds such as Al, Mn, or Li, which will eventually enter the slag after oxidation. Consequently, the amount of Al2O3, MnO, or Li2O in the slag will increase. Al2O3, in particular, has a direct impact on the melting point, so its accumulation in the slag needs to be monitored.

[0107] Due to the introduction of new compounds, the metallurgical slag according to the present invention can only be reused a limited number of times. To determine whether the slag can be further reused, the slag composition should be analyzed and compared to the compositional specifications described herein. Tapping and reusing at least a portion of the metallurgical slag, or diluting it with new slag-forming agents, are viable long-term options.

[0108] As mentioned above, the slag according to the present invention helps significantly inhibit the dissolution of MgO from magnesia-containing refractory bricks. However, this cannot be completely avoided. This leads to another positive side effect when recycling the slag. Any MgO that has accumulated in the slag during previous smelting operations, when combined with MnO, LiO, and CaO, tends to inhibit further corrosion of the refractory bricks. This makes reusing the slag particularly attractive.

[0109] Another embodiment describes the use of the Li-containing metallurgical slag in a lithium recovery process. Slags with a Li2O content exceeding 3% allow for the valorization of the contained lithium, with higher Li2O contents, such as exceeding 6% or even exceeding 8%, being preferred. Lithium recovery is particularly attractive when the slag is repeatedly reused, as each new cycle accumulates Li2O in the slag, easily reaching concentrations exceeding 8%, 10%, 12%, or 14%.

[0110] Li fuming is the preferred process for recovering lithium from such Li-containing metallurgical slags, as it ensures high recovery rates. For this purpose, the use of alkali metal or alkaline earth metal chlorides, such as CaCl2, has been described in WO2020104164.

[0111] Another embodiment describes the use of the Li-containing metallurgical slag in a cobalt recovery process. Reusing the slag as a slagging agent in the method according to the first embodiment or in other battery recycling processes allows for the recovery of residual cobalt. This is not only for economic reasons, but also for ecological reasons.

[0112] The CoO content in the slag will preferably be limited to less than 1%, more preferably less than 0.5%, thereby reducing losses of this valuable metal and producing a slag that can be safely disposed of in landfill once it is no longer used.

[0113] Example

[0114] The following examples are provided to further illustrate embodiments of the present invention.

[0115] Example 1

[0116] The dissolution of MgO from the walls of a magnesium-containing crucible was measured using several different slag compositions. Various compounds found in lithium-ion batteries or their waste, and their oxides such as FeO, Al2O3, Li2O, MnO, and P2O5, were melted in a 1L MgO crucible along with CaO and SiO2 as fluxes. The total weight of the added oxides was 1000 g.

[0117] The crucible was gradually heated using an induction furnace at a heating rate of 150°C / h. Once the slag was completely melted, the crucible was maintained at 1500°C or 1650°C. After heating for 2 hours, the molten slag was removed from the crucible and quenched with water. Table 1 lists the composition of the slag produced in this example.

[0118] Table 1: Composition of the produced slag

[0119]

[0120] The MgO concentration in the above slag is relatively low. This result shows that under the selected conditions, the dissolution of MgO from the crucible wall is well suppressed.

[0121] (CaO+2Li2O+0.4MnO) / SiO2 is 2.9 in slag 1-1, 2.2 in slag 1-2, and 9.0 in slag 1-3.

[0122] Experiments were conducted with slag compositions that did not contain Ni, Co or Cu, since the amounts of these metals in the final slag are typically very low and therefore do not substantially affect the slag properties.

[0123] Comparative Example 2

[0124] The dissolution of MgO from the walls of a magnesium-containing crucible was measured using different slag compositions. Various compounds found in lithium-ion batteries or their waste, and their oxides such as FeO, Al2O3, Li2O, MnO, and P2O5, were melted in a 1L MgO crucible along with CaO and SiO2 as fluxes. The total weight of the added oxides was 1000 g.

[0125] The crucible was gradually heated using an induction furnace at a heating rate of 150°C / h. Once the slag was completely melted, the crucible was maintained at 1500°C for 2 hours. After heating for 2 hours, the molten slag was removed from the crucible and quenched with water. Table 2 lists the composition of the slag produced in this example.

[0126] Table 2: Composition of the produced slag

[0127]

[0128] Compared to the slag used in Example 1, the MnO content in the slag was adjusted to less than 10%. The (CaO + 2Li2O + 0.4MnO) / SiO2 ratio was 1.2 in Slag 2-1 and 1.1 in Slag 2-2. The measured MgO concentrations in these slags were relatively high (9.0% to 15.7%), indicating that relatively large amounts of MgO were dissolved from the crucible into the corresponding slags. As in Example 1, the slags contained no Ni, Co, or Cu.

[0129] Discussion of Examples 1 and 2

[0130] The slag obtained in Example 1 contained less MgO than the slag obtained in Comparative Example 2. No significant degradation of the MgO crucible was observed under the conditions of Example 1, whereas the crucible wall became thinner under the conditions of Comparative Example 2. As shown in Example 1, the slag containing a relatively high concentration of MnO suppressed the dissolution of MgO. More specifically, when the MnO concentration was 25% or more, the dissolution of MgO into the slag was effectively suppressed.

[0131] Example 3

[0132] 500 kg of battery black powder was charged to a 1 m diameter furnace newly lined with 200 mm chrome-magnesia refractory bricks. Slag produced in an earlier smelting operation, with the composition shown in Table 3, was added along with the battery black powder and reused as a slag forming agent. The bath temperature was maintained between 1500°C and 1550°C, which was suitable for maintaining sufficient fluidity of the slag and alloy for easy tapping and handling. Heat was provided by oxidizing the Al and C in the battery using submerged O2 injection. The injection rate was selected to achieve strong reducing conditions, i.e., in this case, a pO2 of 10 -9Natural gas is added to compensate for heat losses in the furnace. After heating for 1 hour, the resulting alloy and slag are separated by tapping. During the process, a small amount of fumes is captured.

[0133] Table 3 shows the analysis of the input and output phases of the method.

[0134] Table 3: Input and output phases of the described method

[0135]

[0136] During battery processing, no significant degradation of the MgO-containing refractory bricks was observed. The resulting slag had a MgO concentration of only 1.4%, equivalent to a loss of 0.1 kg of MgO from the refractory bricks. This very small degradation is attributed to the high MnO content in the slag. Therefore, this slag effectively inhibits the wear of furnace walls made of MgO-containing refractory bricks.

[0137] General conclusions

[0138] The metallurgical slag according to the present invention is suitable for recovering valuable metals, such as Ni and Co, from Li-ion batteries or their waste, while minimizing the degradation of magnesia-containing refractory bricks of the furnace.

Claims

1. A method for recovering Ni and Co from Li-ion batteries or their waste, the method comprising the following steps: - Provide a furnace lined with magnesia-containing refractory bricks; - providing a feed comprising a slag forming agent and Li-ion batteries or waste thereof, wherein the Al content of the feed is less than 8%; and - smelting the feed under reducing conditions to obtain an alloy containing a majority of Ni and Co and a Li-containing slag, wherein the slag has the following composition percentages by weight: 25% <MnO<70%; Al2O3+0.5MnO<45%; SiO2>5%; Li2O>1%; 0.5% <P2O5<10%; MnO+Li2O+Al2O3+CaO+SiO2+FeO+MgO+P2O5>90%; and and Among them, (CaO+2Li2O+0.4MnO) / SiO2≥2.

0.

2. The method according to claim 1, wherein the content of MnO in the slag is 30% or more.

3. The method according to claim 1 or 2, wherein the content of Al2O3 in the slag is less than 30%.

4. The method according to claim 1 or 2, wherein the Li-ion battery or its waste material is battery black powder.

5. The method according to claim 1 or 2, wherein the content of CaO in the slag is 40% or less.

6. The method according to claim 1 or 2, wherein the content of Li2O in the slag is greater than 3%.

7. The method according to claim 1 or 2, wherein the content of cobalt oxide in the slag is 0.05% <CoO<1%。 8. The method according to claim 1 or 2, wherein the Fe content in the slag is 25% or less.

9. The method according to claim 1 or 2, wherein the content of Fe in the slag is 10% or less.

10. The method according to claim 1 or 2, wherein the content of Fe in the feed is 5% or less.

11. The method of claim 1 or 2, wherein the step of melting the charge is performed at a temperature of at least 1400°C and at most 300°C above the liquidus point of the slag, thereby avoiding overheating.

12. The method of claim 1 or 2, wherein the step of melting the charge is performed at a temperature of at least 1400°C and at most 100°C above the liquidus point of the slag, thereby avoiding overheating.

13. The method according to claim 1 or 2, wherein the smelting step comprises the following additional steps: - taking samples of the slag; - cooling the slag sample and evaluating its color; and - in case the slag sample is green, terminating the smelting step; or - In case the slag sample is not green, the smelting step is continued after adjusting the pO2 level to achieve more reducing conditions.

14. The method according to claim 1 or 2, wherein the furnace is an electric furnace.

15. A Li-containing metallurgical slag having the following composition by weight: 25% <MnO<70%; Al2O3+0.5MnO<45%; SiO2>5%; Li2O>3%; 0.5% <P2O5<10%; MnO+Li2O+Al2O3+CaO+SiO2+FeO+MgO+P2O5>90%; and and Among them, (CaO+2Li2O+0.4MnO) / SiO2≥2.

0.

16. The Li-containing metallurgical slag according to claim 15, wherein the content of MnO in the slag is 30% or more.

17. The Li-containing metallurgical slag according to claim 15 or 16, wherein the content of Al2O3 in the slag is less than 30%.

18. The Li-containing metallurgical slag according to claim 15 or 16, wherein the content of CaO in the slag is 40% or less.

19. The Li-containing metallurgical slag according to claim 15 or 16, wherein the Fe content in the slag is 25% or less.

20. The Li-containing metallurgical slag according to claim 15 or 16, wherein the Fe content in the slag is 10% or less.

21. The Li-containing metallurgical slag according to claim 15 or 16, wherein the slag further contains cobalt.

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