Recovery of nickel and cobalt from li-ion batteries and their scrap

Abstract

The invention belongs to the field of pyrometallurgy and discloses a method and a slag suitable for the recovery of Ni and Co from Li-ion batteries or scrap thereof. The composition of the slag is defined as follows: 10% < MnO < 40%; (CaO + 1.5 x Li2O) / Al2O3 > 0.3; CaO + 0.8 x MnO + 0.8 x Li2O < 60%; (CaO + 2 x Li2O + 0.4 x MnO) / SiO2 > 2.0; Li2O > 1%; and Al2O3 + SiO2 + CaO + Li2O + MnO + FeO + MgO > 85%. This composition is particularly suitable for limiting or avoiding the corrosion of a furnace lined with refractory bricks containing magnesium oxide.

Description

Technical Field

[0001] This invention belongs to the field of pyrometallurgy, and more specifically relates to the recovery of Ni and Co from Li-ion batteries or their waste. Background Technology

[0002] In recent years, electric vehicles have experienced unprecedented growth, driven by new legislation in Europe and China aimed at phasing out CO2 emissions from vehicle fleets and limiting air pollution in cities. This growth is expected to continue for decades to come. The adoption of electric vehicles largely depends on the performance of the batteries used to store electrical energy. Rechargeable Li-ion batteries are currently the preferred choice for achieving the highest energy density while maintaining cost control. Many of these batteries contain cathodes based on the transition metals Ni, Mn, and Co, and are therefore also known as NMC batteries. As the electric vehicle market grows, the demand for these metals is also expected to increase significantly.

[0003] The demand for Ni and Co may even exceed global production capacity. Co is particularly important because it is currently produced only as a byproduct of the Ni and Cu industries. The market for nickel is significantly larger than that for cobalt. Most Ni is used in the production of stainless steel, where the purity of Ni is less critical. However, high-purity Ni and high-purity Co metals or compounds are already in short supply. Given the above, recovering Ni and Co from spent Li-ion batteries or their waste is an attractive proposition.

[0004] There are some known methods for recycling Li-ion batteries, in which oxides of nickel, cobalt, and copper are reduced to metals and concentrated in an alloy phase at high temperatures.

[0005] WO2017121663 describes slag compositions generated during industrial processes and discloses the effect of MnO on slag viscosity and cobalt recovery. The main slag components described are CaO, SiO2, Al2O3, Li2O, and MnO (MnO2). The disclosed MnO concentration in these slags is very low, and the above content aims to limit the MnO content in slags. Elwert et al. (Phase composition of high lithium slags from the recycling of lithium-ion batteries: World of Metallurgy - ERZMETALL, Vol. 65, No. 3, 2012, pp. 163-171) analyzed the phase composition of three different slags with the aim of developing possible slag beneficiation processes for lithium recovery. Hu et al. (Recovery of Co, Ni, Mn, and Li from Li-ion batteries by smelting reduction - Part II: A pilot-scale demonstration: Journal of Power Sources, Vol. 483, 2021, 229089) proposed a method for recovering Li-ion batteries by smelting the batteries using a flux at temperatures above 1500°C, thereby producing slag and an alloy containing Ni, Co, and Mn. Elwert and Hu both described slag compositions with MnO concentrations well below 10%.

[0006] On the other hand, recent Li-ion batteries typically contain increasing amounts of Mn. This makes the formation of slag containing small amounts of Mn more difficult, as it requires either adding large amounts of flux to dilute the Mn, or selecting more reducing conditions for such processes to deliver more Mn to the alloy phase rather than the slag phase. The former option increases flux consumption and the total amount of slag obtained, while the latter option increases the complexity of any subsequent hydrometallurgical treatment of the alloy due to its higher Mn content. Both options would significantly reduce the economics of the methods.

[0007] WO12140951, WO13080266, and WO20013294 propose methods for recovering Ni and Co by recycling Li-ion battery debris while immobilizing impurities such as Fe and P in the slag phase. Although it is noted that Mn may be the major component of the resulting slag, the preferred range or specific role of MnO in such slags is not clearly defined. Furthermore, WO12140951 and WO13080266 focus on low-melting-point Fe-rich slags.

[0008] Vest et al. (Friedrich Slag design for lithium recovery from spent batteries: Int. Work. Met. Interact., Vol. 9, No. 93, 2010, pp. 93-106) described theoretical calculations for MnO-rich slag. Wittkowski et al. (Speciation of Manganese in a Synthetic Recycling Slag Relevant for Lithium Recycling from Lithium-Ion Batteries: Metals, Vol. 11, No. 2, 2021, p. 188) analyzed the phase composition of different Li-containing slags during Li-ion battery recycling.

[0009] CN103924088 and EP3269832 describe a method for smelting waste batteries in a molten pool, which produces alloys containing Co and / or Ni and slag rich in SiO2 and MnO.

[0010] None of the aforementioned prior art proposes a slag composition according to the present invention.

[0011] Even when slags with relatively high MnO content were disclosed, none of the aforementioned literature described the current process conditions or the impact of the resulting MnO-rich slag composition on the furnace walls. Typically, the furnace walls are made of refractory bricks. The main component of these bricks is magnesia. Examples are magnesia bricks (with a magnesia content typically exceeding 90%) or magnesia-chrome bricks (with a magnesia content typically between 50% and 70%). It has been observed that during furnace operation, the magnesia in the furnace walls is dissolved by the common slag, leading to wear or corrosion of the furnace walls over time. This is a recurring problem, resulting in high maintenance costs because the furnace needs to be shut down and the refractory bricks need to be replaced periodically. The problem is particularly pronounced at higher operating temperatures, such as above 1550°C. Summary of the Invention

[0012] Therefore, the object of this invention is to provide a method for recovering Ni and Co from Li-ion batteries, which operates using a dedicated slag system rich in MnO and Li2O configured to minimize corrosion of the magnesium oxide-containing refractory bricks during operation, while simultaneously extending the furnace's service life. The resulting reduction in wear significantly contributes to the overall economic efficiency of the method of this invention.

[0013] According to the first embodiment, the method for recovering Ni and Co from Li-ion batteries or their waste includes the following steps:

[0014] - Provide furnaces lined with refractory bricks containing magnesium oxide;

[0015] - Provides a charge containing slagging agents and Li-ion batteries or their waste; and

[0016] - The charge is smelted under reducing conditions to obtain an alloy mainly containing Ni and Co, as well as slag;

[0017] The slag is characterized by having a composition conforming to the following mass percentage:

[0018] 10% <MnO<40%;

[0019] (CaO+1.5×Li2O) / Al2O3>0.3;

[0020] CaO+0.8×MnO+0.8×Li2O<60%;

[0021] (CaO+2×Li2O+0.4×MnO) / SiO2≥2.0;

[0022] Li2O ≥ 1%; and

[0023] Al2O3+SiO2+CaO+Li2O+MnO+FeO+MgO>85%.

[0024] "Slagging agent" refers to one or more of, for example, CaO, Al2O3, and SiO2. Other slagging agents familiar to those skilled in the art may also be present. The slagging compound itself can be added directly, or it can be obtained in situ from easily oxidizable metals such as aluminum present in the charge.

[0025] "Li-ion batteries or their waste" refers to, for example, new or discarded Li-ion batteries, used or scrapped batteries, generated or battery debris, electrode materials, or pre-treated battery materials, such as materials that have been crushed or sorted, including so-called "black lumps." However, these should still contain a considerable amount of Co and / or Ni.

[0026] The “major part” of an element or compound refers to more than 50% by weight of the corresponding amount present in the charge. It may also include a range having a lower limit selected from 55%, 60%, 65%, 70%, and 75% and an upper limit selected from 80%, 85%, 90%, 95%, and 100%.

[0027] The MnO content in the slag plays a crucial role in this invention. A MgO content of at least about 10% is required in the slag to achieve the effect of inhibiting the dissolution of MgO from the furnace lined with magnesia-containing refractory bricks into the slag. Preferably, it has at least 15% MnO. Furthermore, an MnO content of 10–40% in a relatively small amount of slag is beneficial because the reduction in slag volume supports the inhibition of MgO dissolution. On the other hand, adding more flux, thereby increasing the total slag volume and diluting the percentage of MnO, increases the amount of MgO dissolved from the refractory bricks, thus having a negative impact.

[0028] Furthermore, the upper limit of MnO in the slag is also important because it helps maintain a sufficiently low melting temperature. According to the invention, slag containing up to 40% MnO melts below 1500°C. The lower temperature, together with the MnO content, helps to suppress the dissolution of MgO from the magnesia-containing refractory bricks. An MnO content exceeding 40% will raise the slag's melting point to above 1500°C, especially when the slag also contains a relatively large amount of Al2O3, for example, above 50%, and is therefore less preferred.

[0029] According to another implementation, the MnO content in the slag is 30% or less.

[0030] The percentage of Mn in the slag is standardized as "percentage of MnO". However, the exact oxidation state of manganese in such slag is not always clear. Therefore, manganese oxide ("MnO") can also refer to a mixture of single-species MnO and manganese dioxide MnO2. However, the proportion of single-species MnO is assumed to be much higher than 95%, especially under the selected reduction reaction conditions.

[0031] MnO is typically green, while MnO2 is usually dark brown or grayish-black, hence its name "manganese black". The green color is only visible when the concentration of a single species is sufficiently high.

[0032] According to another embodiment, the CaO content in the slag is 15% or more, preferably 20% or more.

[0033] According to another embodiment, the CaO content in the slag is 50% or less, preferably 30% or less.

[0034] A CaO content of at least 15% ensures sufficient slag fluidity and ease of handling. Since CaO helps inhibit the dissolution of Mg in magnesia-containing refractory bricks, and because Ca and Mg have similar chemical positions in the slag, a higher CaO content, such as 20% or more, is preferred. Using a preferred upper limit of 30% CaO to operate the process helps maintain the slag melting temperature below 1600°C. Excessively high CaO content, such as above 50%, significantly increases the slag melting temperature and should therefore be avoided.

[0035] It was also observed that, in addition to MnO and CaO, Li₂O also inhibits the dissolution of Mg from magnesia-containing refractory bricks, while increasing the SiO₂ content has a negative impact. This is reflected in the formula (CaO + 2 × Li₂O + 0.4 × MnO) / SiO₂ ≥ 2.0. When recovering Li-ion batteries, the amount of Li₂O in the slag will be considerable.

[0036] According to another embodiment, the Al2O3 content in the slag is <50%, preferably <40%, because excessive Al2O3 will increase the melting point of the slag.

[0037] According to another embodiment, the Fe content in the slag is 25% or less, preferably 10% or less.

[0038] According to another embodiment, the sum of Al2O3, SiO2, CaO, Li2O, MnO, FeO and MgO is 90% or greater, preferably 95% or greater.

[0039] According to another implementation scheme, (CaO+2×Li2O+0.4×MnO) / (SiO2+0.2×Al2O3) is >1.5.

[0040] Slag composition and operating temperature are key considerations in the methods described herein. This invention achieves a balance between compounds that protect the furnace walls (e.g., MnO, CaO, Li₂O) and compounds that negatively impact the furnace walls, even if these compounds are unavoidable (e.g., Al₂O₃ derived from Al in the feed) or otherwise necessary (e.g., SiO₂ required to lower the slag melting point). Furthermore, the slag composition domains ensure appropriate slag fluidity and minimize overheating at the desired operating temperature. Preferably, the temperature is as low as possible while still maintaining a temperature above the alloy melting point.

[0041] This balance is reflected in the proposed process conditions and the composition of the slag itself.

[0042] According to another embodiment, the smelting and charging step is carried out at a temperature of at least 1400°C to ensure complete melting of the metallurgical charge, and is operated at a temperature up to 300°C above the slag liquidus point, preferably up to 100°C above the slag liquidus point. The lower limit is preferred to avoid the formation of alloys and uniform solidification of the slag. The upper limit is preferred to avoid slag overheating. Higher temperatures promote the dissolution of Mg from magnesia-containing refractory bricks. Therefore, lower temperatures are generally preferred to reduce wear and save energy. Slag overheating has an adverse effect on the dissolution of magnesia-containing refractory bricks by the slag.

[0043] The ratio of CaO and Li2O to Al2O3 in the slag helps to keep the melting point of the slag sufficiently low, preferably below 1700°C, more preferably below 1650°C, even more preferably below 1600°C, and most preferably below 1550°C.

[0044] Although they are beneficial to the service life of magnesium oxide-containing refractory bricks, it is equally important to limit the combined amount of CaO, MnO and Li2O in the slag, because when CaO + 0.8 × MnO + 0.8 × Li2O exceeds 60%, the melting point of the slag will be too high.

[0045] According to another implementation scheme, the smelting step includes other steps:

[0046] - Take samples of the slag;

[0047] - Cool the slag sample and evaluate its color; and

[0048] - If the slag sample is green, terminate the smelting step; or

[0049] - If the slag sample is not green, continue the smelting steps after adjusting the pO2 level to obtain more reducing conditions.

[0050] "Sampling of slag" refers to taking a small sample of the slag and evaluating its color while continuing the method under selected conditions.

[0051] Color evaluation can be easily performed visually. Compared to chemical analysis of slag, monitoring color changes can quickly and effectively indicate the presence of a specific minimum percentage of MnO in the slag. As described in more detail below, it has also been observed that the green color of the slag also indicates a reduction in the major portion of Co in the feed and its incorporation into the alloy. Without being bound by theory, it is indeed believed that the greening is due to the reduction of MnO2 to MnO, but it is also due to the reduction of oxides of typically darker materials such as Ni and Co.

[0052] Visual inspection is a quick and easy way to determine whether process conditions should be adjusted, optimized, and / or terminated, thus saving time and operating costs. Therefore, color-coding is a reliable indicator of the progress of metallurgical operations.

[0053] In this context, "green" refers to a color whose hue, brightness, and chromaticity fall within the following ranges according to ASTM D1535-14 (2018):

[0054] - Hue ranges from 5GY to 5BG;

[0055] - Brightness: ≥3; and

[0056] - Chromaticity: ≥3.

[0057] An example of green is shown in the "Geological Rock-Color Chart with Genuine Munsell Color Chips" created by Munsell Color in 2009.

[0058] By selecting suitable operating conditions, most of the Mn is oxidized to slag and most of the Co and Ni are reduced to alloys. Preferably, >90%, more preferably >95%, and most preferably >98% of the Co and Ni are collected in the alloys to make the method most economical. The pO2 level of this method is easily adjustable to achieve these favorable yields.

[0059] According to another implementation plan, the pO2 level is adjusted to 10. -7 >pO2>10 -12 Preferably, pO2 < 10 -8 More preferably, pO2 < 10 -8.5 The optimal value is pO2 < 10. -9 .

[0060] Therefore, with 10 -7 Compared to the pO2 level, 10 -8 10 -8.5 and 10 -9 The preferred pO2 level and 10 -12 The limit represents a more reducing condition.

[0061] According to another embodiment, the slag is green in color. During the smelting and charging process under reducing conditions, the slag color typically changes from dark gray or dark brown to green as the method progresses.

[0062] In another implementation, the furnace is an electric furnace. Using an electric furnace or electric arc furnace (EAF) provides greater flexibility when higher operating temperatures are desired or required. Another advantage is that it can profit from off-peak electricity prices or from electricity produced by environmentally friendly green energy sources such as local wind farms.

[0063] According to another embodiment, the Li-containing metallurgical slag comprises a composition in the following mass percentages:

[0064] 10% <MnO<40%;

[0065] (CaO+1.5×Li2O) / Al2O3>0.3;

[0066] CaO+0.8×MnO+0.8×Li2O<60%;

[0067] (CaO+2×Li2O+0.4×MnO) / SiO2≥2.0;

[0068] Li2O ≥ 1%; and

[0069] Al2O3+SiO2+CaO+Li2O+MnO+FeO+MgO>85%.

[0070] According to another implementation plan, the Li-containing metallurgical slag is green.

[0071] According to another implementation scheme, the MnO content in the Li-containing metallurgical slag is 30% or less.

[0072] According to another embodiment, the CaO content in the Li-containing metallurgical slag is 15% or more, preferably 20% or more.

[0073] According to another embodiment, the CaO content in the Li-containing metallurgical slag is 50% or less, preferably 30% or less.

[0074] According to another embodiment, the Al2O3 content in the Li-containing metallurgical slag is 50% or less, preferably 40% or less.

[0075] According to another embodiment, the Fe content in the Li-containing metallurgical slag is 25% or less, preferably 10% or less. In FeO-rich slags with FeO contents greater than 10% and FeO contents significantly greater than 20%, CoO cannot be reduced to metallic Co without transferring a relatively large amount of metallic Fe into the alloy phase. This significantly increases the cost of any subsequent hydrometallurgical processing of the resulting alloy, which is therefore undesirable.

[0076] According to another embodiment, Li-containing metallurgical slag is used as a slagging agent in a pyrometallurgical recovery process. The resulting metallurgical slag contains CaO and SiO2, thus enabling its use as a slagging agent in new operations.

[0077] According to another embodiment, Li-containing metallurgical slag is used as a slagging agent in the method according to the first embodiment, thereby partially or completely replacing the slagging agent in the step of providing a charge containing the slagging agent.

[0078] Reusing the resulting metallurgical slag in new operations allows for more flexible selection of operating conditions, such as the pO2 level of the process. For example, when more oxidizing conditions are used, thus feeding more Co and / or Ni into the slag, these valuable metals are not lost but are recovered in the new operating cycle, where more reducing conditions may be used to recover even more Co and / or Ni.

[0079] When this metallurgical slag is reused as a slag-forming agent in a new process or as starting slag for the same process, it should be considered that the feed cell or its waste may contain additional amounts of compounds such as Al, Mn, or Li, which will eventually enter the slag after their oxidation. Therefore, the respective amounts of Al₂O₃, MnO, or Li₂O in the slag will increase. The amount of Li₂O is considered less critical; the amounts of Al₂O₃ and MnO have a more direct impact on the melting temperature. In another embodiment, the preferred upper limit for MnO is 30%, so that the balance of fresh MnO is fed from the new charge.

[0080] Because new compounds are fed into the slag, the metallurgical slag according to the present invention can only be reused a limited number of times. To determine whether the slag can continue to be reused, its composition should be analyzed and compared with the composition specifications described herein. As a feasible long-term option, at least a portion of the metallurgical slag may be diffused and reused, diluted with a new slagging agent.

[0081] As described above, the slag according to the invention helps to significantly inhibit the dissolution of MgO in refractory bricks. However, this cannot be completely avoided. This leads to another positive side effect during slag recycling. The MgO dissolved in the refractory bricks (resulting from the small amount of MgO dissolved during the previous smelting process) accumulates in the slag, which, along with MnO, Li2O, and CaO, inhibits further corrosion of the refractory bricks. This makes the reuse of the resulting slag particularly attractive. Detailed Implementation

[0082] The following embodiments are provided to further illustrate the implementation of the present invention.

[0083] Example 1

[0084] The dissolution of MgO from the walls of a magnesium oxide-containing crucible was determined when using several different slag compositions. In a 1 L MgO crucible, various compounds contained in Li-ion batteries or their waste, and their corresponding oxides such as FeO, Al₂O₃, Li₂O, and MnO, were melted together with CaO and SiO₂ as fluxes. The total weight of the added oxides was 1000 g. The ratio of FeO, Al₂O₃, Li₂O, and MnO was selected to represent a typical composition of existing Li-ion batteries.

[0085] The crucible was gradually heated using an induction furnace at a heating rate of 150°C / h. When the slag was completely melted, the crucible temperature was maintained at 1400, 1450, or 1500°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 obtained in this example.

[0086] Table 1: Composition of the obtained slag

[0087]

[0088] The concentration of MgO in the slag was relatively low (0.9% to 3.9%). This result indicates that, under the selected conditions, the dissolution of MgO from the crucible wall was well suppressed.

[0089] The experiment was conducted using slag compositions that do not contain Ni, Co, or Cu, because the content of these metals in the final slag is usually very low, and therefore has little impact on slag properties.

[0090] Comparative Example 2

[0091] The dissolution of MgO from the walls of a magnesium oxide-containing crucible was determined when using different slag compositions. In a 1 L MgO crucible, various compounds contained in Li-ion batteries or their waste, and their corresponding oxides such as FeO, Al₂O₃, and MnO, were melted together with CaO and SiO₂ as fluxes. The total weight of the added oxides was 1000 g.

[0092] The crucible was gradually heated using an induction furnace at a heating rate of 150°C / h. When the slag was completely melted, the crucible was held at 1400 or 1450°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 obtained in this example.

[0093] Table 2: Composition of the obtained slag

[0094]

[0095] Compared to the slags 1-1 to 1-3 used in Examples 1, the SiO2 content in the slags here was adjusted to be higher, while the CaO, Li2O, and / or MnO contents were adjusted to be lower. The MgO concentration measured in the above slags was relatively high (8.7% to 13.2%), indicating that a relatively large amount of MgO in the crucible was dissolved in the respective slags.

[0096] Similar to Example 1, the slag does not contain Ni, Co, or Cu.

[0097] Discussion of Examples 1 and 2

[0098] The slag obtained in Example 1 contained less MgO than the slag obtained in Comparative Example 2. No visible degradation of the MgO crucible was observed under the conditions of Example 1, while the crucible walls thinned under the conditions of Example 2. As shown in Example 1, slag containing a relatively low concentration of SiO2 and a relatively high combined concentration of Li2O, CaO, and / or MnO inhibited the dissolution of MgO. More specifically, when the ratio CaO + 2Li2O + 0.4MnO / SiO2 was 2 or greater, the dissolution of MgO into the slag was effectively inhibited.

[0099] Example 3

[0100] 500 kg of spent rechargeable Li-ion batteries were fed into a 1 m diameter furnace lined with 200 mm thick chromium-magnesium oxide refractory bricks. 80 kg of limestone and 20 kg of sand were added along with the Li-ion batteries. The molten pool temperature was maintained at 1450–1500 °C, which is suitable for maintaining sufficient flow of slag and alloys for easy release and disposal. Heat was provided by the oxidation of Al and C in the batteries, using submerged O2 injection. The injection rate was selected to ensure strong reducing conditions, i.e., pO2 of 10. -9 Natural gas is added to compensate for heat loss in the furnace. After heating for 1 hour, the resulting alloy and slag are separated by venting. Table 3 shows the analysis of the input and output phases of the method.

[0101] Table 3: Input and Output of the Method

[0102]

[0103] No visible degradation of the magnesium oxide-containing refractory bricks was observed during battery processing. The MgO concentration in the resulting slag was only 1.2%, equivalent to a loss of 2.3 kg of MgO from the refractory bricks, which is considered low. The ratio (CaO + 2Li₂O + 0.4MnO) / SiO₂ was 4.3. Therefore, this slag effectively inhibited furnace wall wear.

[0104] Comparative Example 4

[0105] 500 kg of spent rechargeable Li-ion batteries were fed into a 1 m diameter furnace lined with 200 mm thick chromium-magnesium oxide refractory bricks. 50 kg of limestone and 50 kg of sand were added along with the Li-ion batteries. The molten pool temperature was maintained at 1450–1500 °C, which is suitable for maintaining sufficient flow of slag and alloys for easy release and disposal. Heat was provided by the oxidation of Al and C in the batteries, using submerged O2 injection. The injection rate was selected to ensure strong reducing conditions, i.e., pO2 of 10. -9 Natural gas is added to compensate for heat loss in the furnace. After heating for 1 hour, the resulting alloy and slag are separated by venting. Table 4 shows the analysis of the input and output phases of the method.

[0106] Table 4: Input and Output of the Method

[0107]

[0108] The MgO concentration in the resulting slag was 9.0%, which is equivalent to the loss of 19.8 kg of MgO in the refractory bricks, resulting in severe wear on the furnace wall.

[0109] The ratio (CaO+2Li2O+0.4MnO) / SiO2 is 1.7.

[0110] Example 5

[0111] 500 kg of spent rechargeable Li-ion batteries were fed into a 1 m diameter furnace lined with 200 mm thick chromium-magnesium oxide refractory bricks. 50 kg of limestone and 50 kg of sand were added along with the Li-ion batteries. The molten pool temperature was maintained at 1450–1500 °C, which is suitable for maintaining sufficient flow of slag and alloys for easy release and disposal. Heat was provided by the oxidation of Al and C in the batteries, using submerged O2 injection. The injection rate was selected to ensure strong reducing conditions, i.e., pO2 of 10. -9 Natural gas is added to compensate for heat loss in the furnace. After heating for 1 hour, the resulting alloy and slag are separated by venting. Table 5 shows the analysis of the input and output phases of the method.

[0112] Table 5: Input and Output of the Method

[0113]

[0114] The concentration of MgO in the resulting slag was 2.8%, equivalent to the loss of 7.4 kg of MgO in the refractory bricks. The ratio (CaO + 2Li₂O + 0.4MnO) / SiO₂ was 2.8.

[0115] Discussion of Examples 3, 4, and 5

[0116] In Example 3 and Comparative Example 4, batteries with the same quantity and composition were fed into the furnace, but the ratio of limestone to sand was different. Compared to slag 4, the resulting slag 3 contained a higher concentration of CaO and a lower concentration of SiO2.

[0117] The ratios (CaO + 2Li₂O + 0.4MnO) / SiO₂ in slag 3 and slag 4 were 4.3 and 1.7, respectively. Only 2.3 kg of MgO dissolved in slag 3, while a significantly higher amount of 19.8 kg of MgO dissolved in slag 4.

[0118] In Example 5, a battery with a higher concentration of Mn and Li was fed into a furnace while maintaining the same limestone and sand ratio as in Comparative Example 4. The resulting slag 5 contained a higher concentration of MnO and Li2O than slag 4.

[0119] The ratio (CaO + 2Li₂O + 0.4MnO) / SiO₂ was 2.8, while 7.4 kg of MgO dissolved in slag 5. Therefore, this example demonstrates that the combination of MnO and Li₂O has beneficial effects while all other reaction conditions remain the same.

[0120] As shown in Examples 3 and 5, slag containing lower concentrations of SiO2 and higher combined concentrations of Li2O, CaO, and MnO is more suitable for suppressing the dissolution of MgO.

[0121] Example 6

[0122] 500 kg of spent rechargeable Li-ion batteries were fed into a 1 m diameter furnace lined with 200 mm of newly formed chromium-magnesium oxide refractory bricks. 189 kg of slag from Example 3 was added along with the Li-ion batteries. The molten pool temperature was maintained at 1450–1500 °C, which is suitable for maintaining sufficient flow of the slag and alloys for easy release and disposal. Heat was provided by the oxidation of Al and C in the batteries, using submerged O2 injection. The injection rate was selected to ensure strong reducing conditions, i.e., pO2 of 10. -9 Natural gas is added to compensate for heat loss in the furnace. After heating for 1 hour, the resulting alloy and slag are separated by venting. Table 6 shows the analysis of the input and output phases of the method.

[0123] Table 6: Input and Output of the Method

[0124]

[0125] No visible degradation of the magnesium oxide-containing refractory bricks was observed during the battery processing. The MgO concentration in the produced slag was only 1.2%, equivalent to a loss of 1.4 kg of MgO from the refractory bricks, which is much less than the degradation observed in Example 3. The ratio (CaO + 2Li₂O + 0.4MnO) / SiO₂ was 6.8. Therefore, this slag effectively suppressed wear on the furnace walls made of magnesium oxide-containing refractory bricks.

[0126] Overall Conclusion

[0127] The metallurgical slag according to the invention is suitable for recovering valuable metals such as Ni and Co from Li-ion batteries or their waste while minimizing the deterioration of magnesium oxide-containing refractory bricks in the furnace.

Claims

1. A method for recovering Ni and Co from Li-ion batteries or their waste, comprising the following steps: - Provide furnaces lined with refractory bricks containing magnesium oxide; - Provides a charge containing slagging agents and Li-ion batteries or their waste; and - The charge is smelted under reducing conditions to obtain an alloy mainly containing Ni and Co, as well as slag; Its features are, The slag has the following mass percentage composition: 10% <MnO<40%; (CaO+1.5×Li2O) / Al2O3>0.3; CaO+0.8×MnO+0.8×Li2O<60%; (CaO+2×Li2O+0.4×MnO) / SiO2≥2.0; Li2O ≥ 1%; and Al2O3+SiO2+CaO+Li2O+MnO+FeO+MgO>85%.

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

3. The method according to claim 1 or 2, wherein the CaO content in the slag is 15% or more, and wherein the CaO content in the slag is 50% or less.

4. The method according to claim 1 or 2, wherein the content of Al2O3 in the slag is 50% or less.

5. The method according to claim 1 or 2, wherein the Fe content in the slag is 25% or less.

6. The method according to claim 1 or 2, wherein the sum of Al2O3, SiO2, CaO, Li2O, MnO, FeO and MgO is 90% or greater.

7. The method according to claim 1 or 2, wherein (CaO+2×Li2O+0.4×MnO) / (SiO2+0.2×Al2O3) is >1.

5.

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

9. The method according to claim 1 or 2, wherein the smelting step comprises other steps: - Take samples of the slag; - Cool the slag sample and evaluate its color; and - If the slag sample is green, then terminate the smelting step; or - If the slag sample is not green, the smelting step is continued after adjusting the pO2 level to obtain more reducing conditions.

10. The method of claim 9, wherein the pO2 level is adjusted to 10. -7 >pO2>10 -12 .

11. The method of claim 9, wherein the slag is green in color.

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

13. Li-containing metallurgical slag, said Li-containing metallurgical slag having a composition conforming to the following weight percentages: 10% <MnO<40%; (CaO+1.5×Li2O) / Al2O3>0.3; CaO+0.8×MnO+0.8×Li2O<60%; (CaO+2×Li2O+0.4×MnO) / SiO2≥2.0; Li2O ≥ 1%; and Al2O3+SiO2+CaO+Li2O+MnO+FeO+MgO>85%.

14. The Li-containing metallurgical slag according to claim 13, wherein the slag is green.

15. The Li-containing metallurgical slag according to claim 13 or 14, wherein the MnO content in the slag is 30% or less.

16. The Li-containing metallurgical slag according to claim 13 or 14, wherein the CaO content in the slag is 15% or more, and wherein the CaO content in the slag is 50% or less.

17. The Li-containing metallurgical slag according to claim 13 or 14, wherein the Al2O3 content in the slag is 50% or less.

18. The Li-containing metallurgical slag according to claim 13 or 14, wherein the Fe content in the slag is 25% or less.

19. Use of Li-containing metallurgical slag according to any one of claims 13 to 18, as a slag-forming agent in a pyrometallurgical recovery method.

20. Use of Li-containing metallurgical slag according to any one of claims 13 to 18, as a slagging agent in the method according to any one of claims 1 to 12, thereby partially or wholly replacing the slagging agent in the step of providing a charge containing the slagging agent.

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