Lithium recovery from slag

Abstract

When recovering lithium batteries or waste thereof on a smelting furnace, Li-containing slag is typically produced. The Li recovery process comprises the following steps: powdering the metallurgical slag into a particle size distribution with D50 of less than 100 [mu] m; -contacting the Li-containing metallurgical slag with a basic Ca-compound in an aqueous medium provided in an amount selected to obtain a molar ratio of Ca in said Ca-compound to Li in said slag of at least 0.75, thereby obtaining a suspension; -heating the suspension to a temperature exceeding 80 DEG C for at least 30 minutes, thereby obtaining a leached suspension; and-separating the solids from the liquid in the leached suspension, thereby obtaining a leached solution containing the majority of Li and a solid residue containing Ca. The alkaline leaching process allows direct recovery of battery grade LiOH from the leach solution while consuming less reagent than known acidic leaching processes.

Description

[0001] The present invention relates to a method for recovering lithium (Li) contained in metallurgical slag. This type of slag is typically produced when lithium batteries or their waste are recycled using smelting methods. Relatively noble metals, such as Cu, Co, and Ni, are reported as an alloy phase, while more readily oxidizable elements, such as Li, are reported as a slag phase. Both phases are decanted and discharged separately.

[0002] Due to the relative scarcity of Li, its recovery from slag has recently become an economical initiative. Known methods employ acid leaching to dissolve Li.

[0003] WO2022085222 discloses a method for recovering lithium from secondary battery materials. It teaches that ensuring an Al to Li mass ratio of 6 or less is crucial. This requirement is met by adjusting the amount of Al in the slag according to various protocols. The slag is leached using an acidic aqueous solution. Particle diameters between 0.5 and 5 mm are preferred. The leachate is then subjected to a purification step by adding an alkaline substance to raise its pH to a maximum of 14. The mixture is filtered, and the Li in the solution is precipitated as carbonate.

[0004] JP2020029613 describes a combination of a reduction smelting step and an aqueous leaching step to recover precious metals from spent Li-ion batteries. The leaching step is carried out on the slag produced in the smelting step, with the aim of recovering Li in the leach solution. The slag is leached in slightly acidified water with a pH of 5 to 7 at atmospheric pressure at a temperature below 100°C. Pressure leaching is said to be unnecessary. A particle diameter of between 0.5 and 5 mm is preferred. Due to the dissolution of Li, the pH of the solution is said to gradually increase to 11 or higher. This helps to precipitate any unwanted Ni, Co, Cu and Fe in the solution. When the amount of Li is small, a water-soluble base can be added to the mixture to ensure an alkaline pH of 11 or higher. The mixture is then filtered.

[0005] According to the above document, Li is leached under acidic conditions, resulting in soluble salts such as LiCl or Li2SO4. This salt must be converted into insoluble Li2CO3 or LiOH and then precipitated. The alkaline conditions reported only concern the subsequent purification of the solution.

[0006] It has been found that Li can be selectively leached from slag using a specific amount of alkaline Ca compounds. Under optimized conditions, Li leaching yields of 80% or more can be achieved. LiOH is formed during the leaching step, making the additional conversion of Li salts to LiOH unnecessary.

[0007] To produce battery-grade Li, LiOH solution can be purified by, for example, precipitation of impurities, ion exchange, or by using selective membranes. High-purity Li can be readily obtained using crystallization, such as evaporative crystallization to produce solid LiOH, or reactive crystallization with carbonates to produce solid Li2CO3.

[0008] In a first embodiment, a method for recovering Li from a Li-containing metallurgical slag is described, the method comprising the following steps:

[0009] - pulverizing the metallurgical slag to a particle size distribution with a D50 of less than 100 μm, the D50 being calculated from the cumulative distribution of undersize by volume according to ISO 13320:2020;

[0010] - contacting the Li-containing metallurgical slag with an alkaline Ca-compound in an aqueous medium, provided in an amount chosen to obtain a molar ratio of Ca in the Ca-compound / Li in the slag of at least 0.75, thereby obtaining a suspension;

[0011] - heating the suspension to a temperature exceeding 80° C. for at least 30 minutes, thereby obtaining a leached suspension; and,

[0012] - Separating the solids from the liquid in the leached suspension, thereby obtaining a leaching solution containing the majority of Li and a solid residue containing Ca.

[0013] Metallurgical slags are typically obtained by recycling Li-ion batteries or their waste using smelting. Such smelting processes produce slags containing Li in amounts of at least 0.2 wt%, but more typically greater than 1 wt%, or even greater than 2.5 wt%. These slags are suitable raw materials for the present method.

[0014] According to stoichiometry, one mole of Ca would be sufficient to leach two moles of Li, resulting in a molar ratio of 0.5. Surprisingly, it has been observed that a large excess of Ca is actually required. This excess can be quantified, resulting in a lower limit of 0.75 for the molar ratio of Ca to Li. This lower limit corresponds to 150% of the stoichiometric amount.

[0015] To enable the formation of alloy and slag phases during smelting, so-called slag formers or fluxes are used. Typical slag formers include, for example, CaO and SiO2. It is important to note that in this Li leaching process, the CaO in the slag is considered non-reactive. Therefore, a specified amount of an alkaline Ca compound, such as CaO, Ca(OH)2, or CaCO3, is added during the contacting step, regardless of the Ca content in the slag.

[0016] The amount of Li in the metallurgical slag can be determined by chemical analysis. The skilled person can then easily deduce the amount of Ca-compound required in the contacting step.

[0017] The specified amount of Ca-compound for this process can be added all at once or, alternatively, in steps.

[0018] The contacting, heating, and solid-liquid separation steps, which jointly achieve leaching, can be repeated on the solid residue to further improve the Li yield. A specific amount of Ca-compound can then be distributed among the repeated contacting steps. Countercurrent flow of the aqueous solution to the solid residue is particularly useful here, as it reduces overall water consumption while optimizing the Li leaching yield.

[0019] The process of the present invention can be operated in batch or continuous mode.

[0020] According to well-known rules, there may be a certain correlation between heating and reaction time: lower temperature may mean longer reaction time to achieve the optimal Li leaching yield, while higher temperature may improve kinetics.

[0021] By "majority" of an element is meant 50% or more of the amount of the element entering the process.

[0022] In another embodiment, the metallurgical slag is derived from the recycling of Li-ion batteries or their waste using pyrometallurgical smelting methods. Li-ion batteries or their waste include used or scrapped batteries, production scrap, or battery components (such as electrode foil, electrolyte, separator, casing material, and electrode material) or pre-processed battery materials (such as "black"), resulting in a very complex waste stream.

[0023] In another embodiment, the slag is powdered by pulverization or atomization. This will ensure faster and more complete dissolution of the Li. Pulverization by grinding is a preferred option. Grinding can be performed during the contacting step.

[0024] In another embodiment, the metallurgical slag has a particle size distribution with a D50 of less than 50 μm, preferably less than 25 μm, and more preferably less than 15 μm. The particle size distribution is measured by laser diffraction according to ISO 13320:2020. D50 is the particle size in μm at which the volume cumulative distribution reaches 50%. With a small particle size, the Li compounds are more exposed to the Ca compounds in the solution. Particles with a D50 of 5 to 30 μm show excellent Li leaching yield and kinetics. Further reducing the particle size will increase the kinetics of the process, but will only have a limited impact on the overall leaching yield.

[0025] The order in which the slag, the Ca-compound and the aqueous medium are added in the contacting step is not critical. For example, in one embodiment, the Ca-compound is added to the metallurgical slag and their mixture is then contacted with the aqueous medium.

[0026] In another embodiment, the Ca-compound is added in an amount selected so that the molar ratio of Ca in the Ca-compound / Li in the slag is 1 to 1.5, preferably 1.1 to 1.3, and more preferably 1.1 to 1. These ratios will provide good Li yields while avoiding excessive reactant costs.

[0027] In another embodiment, the Ca-compound is CaO, Ca(OH) 2 or CaCO 3. CaCO 3 is a preferred choice, while CaO and Ca(OH) 2 are even more preferred.

[0028] In another embodiment, the Ca compound is in powder form. This will facilitate the reaction with the aqueous medium and with the slag.

[0029] In another embodiment, the contacting step is performed using a solid to liquid ratio of 50 to 500 g / L. This will ensure suspension of the solids in the aqueous medium and reasonable stirring power in the contacting and heating reactors.

[0030] In another embodiment, the heating step is carried out at 100 to 200°C, preferably 110 to 150°C. It has been found that higher reaction temperatures above 100°C will significantly increase the Li yield. Operating at temperatures below 70°C may be feasible, but this will require impractical reaction times to reach the desired Li yield of at least 50%. For economic reasons, higher temperatures in the range of 100°C to 200°C are preferred. On the other hand, increasing the reactor temperature above 150°C will no longer significantly improve the Li yield.

[0031] In another embodiment, the method is carried out in an aqueous medium containing a dissolved salt. For example, 1 mol / L dissolved Na2SO4 or NaOH will raise the boiling point of the aqueous medium, allowing the heating step to be carried out at slightly above 100°C while avoiding the use and cost of a pressure reactor.

[0032] In another embodiment, the heating step is performed for a period of 30 to 600 minutes, preferably 90 to 400 minutes, and more preferably 180 to 360 minutes.

[0033] In another embodiment, the Ca-compound is premixed with the metallurgical slag before the contacting step.For example, the Ca-compound can be added during comminution of the slag.

[0034] In another embodiment, the solid residue obtained in the step of separating the solids from the liquid in the leached suspension is ground. This is useful when the contacting, heating and solid-liquid separation steps are repeated.

[0035] In another embodiment, the metallurgical slag further comprises 5 to 50 wt% Al2O3, preferably 30 to 50 wt%. Since the casing or cathode foil of Li-ion batteries is made of Al, Al is often present in metallurgical slag. Al is very easily oxidized and is fully reported as slag.

[0036] In another embodiment, the metallurgical slag further comprises 2 to 50 wt % SiO2, preferably 2 to 20 wt %, and more preferably 2 to 10 wt %. SiO2 is often added to metallurgical slag as a flux to lower the melting point of the slag or make it less viscous. Si is very easily oxidized and is fully reported as slag.

[0037] In another embodiment, the metallurgical slag further comprises 10 to 70 wt % MnO, preferably 10 to 40 wt %, and more preferably 15 to 30 wt %. Mn is typically present as an active component of the cathode. It is easily oxidized and is primarily reported as slag.

[0038] In another embodiment, during the contacting step, smelter flue gas containing LiF and additional alkaline Ca-compound are provided in an amount selected to achieve a molar ratio of Ca in the additional Ca-compound to Li in the flue gas of 0.25 to 0.5. The Li flue gas may contain different Li salts. Some, such as LiF, require a stoichiometric amount of Ca-compound to dissolve, while most other Li salts, such as LiBr, LiCl, and Li2O, dissolve readily without any need for Ca. Compared to the first embodiment, the additional amount of Ca used to leach LiF corresponds to a desired molar ratio of 0.5. However, this additional amount can be even lower, as low as 0.25, particularly when the amount of Ca-compound used to leach Li from the slag is on the high side, resulting in a large unreacted excess. For practical reasons, it is preferred to select the same Ca-compound to leach Li from both the slag and the flue gas.

[0039] In another embodiment, the Li-containing metallurgical slag obtained from the first pyrometallurgical smelting process is premixed with Li-containing smelter flue gas obtained from the same or another pyrometallurgical smelting step to obtain a heterogeneous Li-rich mixture.

[0040] In another embodiment, the solid residue is used as a cement substitute. The solid residue or leached residue is the insoluble portion remaining after carrying out the method of the present invention. It can be used, at least in part, as a cement substitute.

[0041] The following examples illustrate the invention.

[0042] Example 1: Effect of Temperature

[0043] Li slag containing 4.35 wt% Li, 21.4 wt% Al, 21.7 wt% Si, 17.6 wt% Ca, 1.12 wt% Mn, 1.30 wt% Mg and 0.74 wt% Fe was ground to a particle size distribution with a D50 of about 5 to 8 μm. 30 g of this slag, 125 mL of water and 10.5 g of CaO were added to a pressure reactor. The molar ratio of Ca in the added CaO to Li in the slag was equal to 1. The reactor was heated to 120°C and maintained at this temperature for 90 minutes. The leached suspension was filtered and the solid residue was washed and dried. A leach solution with a Li concentration of 8.98 g / L was obtained, corresponding to a yield of 75%. The element contents of the feed, the resulting leach solution and the solid residue are shown in Table 1.

[0044] Table 1: Mass balance (g) for the leaching process at 120 °C (base case)

[0045]

[0046] This example was repeated at different temperatures and the corresponding Li yields are shown in Table 1a.

[0047] Table 1a: Li yield as a function of heating temperature

[0048]

[0049] Lowering the reactor temperature to 70°C resulted in an insufficient Li yield of 36%. Increasing the reactor temperature to 80°C or higher significantly improved Li dissolution. Further increasing the temperature to above 120 or above 150°C had only limited effect.

[0050] Example 2: Effect of Ca / Li ratio

[0051] 30 g of ground slag from Example 1, 125 mL of water, and 15.8 g of CaO were added to a pressure reactor. The molar ratio of Ca in the added CaO to Li in the slag was 1.5. The reactor was heated to 150°C and maintained at this temperature for 90 minutes. The leached suspension was filtered, and the solid residue was washed and dried. A leach solution with a Li concentration of 9.82 g / L was obtained, corresponding to a yield of 78%. The elemental contents of the feed, the resulting leach solution, and the solid residue are shown in Table 2.

[0052] Table 2: Mass balance (g) for the leaching process at a Ca / Li ratio of 1.5 (base case)

[0053]

[0054] This example was repeated using different Ca / Li ratios. The corresponding Li yields are shown in Table 2a.

[0055] Table 2a: Li yield as a function of Ca / Li ratio

[0056]

[0057] A Ca / Li ratio of 0.5 resulted in an insufficient Li yield of 37%. Increasing the Ca / Li ratio to 0.75 significantly improved the Li yield. When even more Ca was added, the Li yield increased further.

[0058] Example 3: Effect of heating time when using pressure leaching

[0059] Li slag containing 4.1 wt% Li, 20.1 wt% Al, 7.0 wt% Si, 15.5 wt% Ca, 6.6 wt% Mn, 1.99 wt% Mg and 0.90 wt% Fe was ground to a particle size distribution with a D50 of about 5 to 8 μm. 20 g of this slag, 125 mL of water and 10.5 g of CaO were added to a pressure reactor. The molar ratio of Ca in the added CaO to Li in the slag was equal to 1.5. The reactor was heated to 150°C and maintained at this temperature for 270 minutes. The leached suspension was filtered and the solid residue was washed and dried. A leach solution with a Li concentration of 6.84 g / L was obtained, corresponding to a yield of 88%. The element contents of the feed, the resulting leach solution and the solid residue are shown in Table 3.

[0060] Table 3: Mass balance (g) for a 270-minute leaching process (base case)

[0061]

[0062] This example was repeated using different leaching times. The corresponding Li yields are shown in Table 3a.

[0063] Table 3a: Li yield as a function of leaching time

[0064]

[0065] Most of the Li is leached out after only 30 minutes. Longer times lead to increased yields. Such longer times may be useful when lower temperatures are selected, or when processing coarser slag particles.

[0066] Example 4: Effect of heating time at atmospheric pressure

[0067] Li slag containing 4.3 wt% Li, 16.8 wt% Al, 4.5 wt% Si, 17.7 wt% Ca, 11 wt% Mn, 1.3 wt% Mg and 2.5 wt% Fe was ground to a particle size distribution with a D50 of approximately 5 to 8 μm. 200 g of this slag, 1000 mL of water and 140 g of Ca(OH)2 were added to a pressure reactor. The molar ratio of Ca in the added Ca(OH)2 to Li in the slag was equal to 1.5. The reactor was heated to 90°C and maintained at this temperature for 360 minutes. The leached suspension was filtered and the solid residue was washed and dried. A leach solution with a Li concentration of 4.2 g / L was obtained, corresponding to a yield of 59%. The elemental contents of the feed, the resulting leach solution and the solid residue are shown in Table 4.

[0068] Table 4: Mass balance (g) for a 270-minute leaching process (base case)

[0069]

[0070] This example was repeated using different leaching times. The corresponding Li yields are shown in Table 4a.

[0071] Table 4a: Li yield as a function of leaching time

[0072]

[0073] At 90°C, most of the Li was leached after 360 minutes. Longer times resulted in increased yields. Compared to Example 3, the lower temperature, as expected, required longer reaction times to leach most of the Li.

[0074] Example 5: Effect of particle size distribution

[0075] Li slag containing 4.41 wt% Li, 19.8 wt% Al, 6.48 wt% Si, 23.8 wt% Ca, 0.93 wt% Mn, 1.30 wt% Mg, and 0.81 wt% Fe was ground to a particle size distribution with a D50 of approximately 9.8 μm. 200 g of this slag, 1 L of water, and 107 g of CaO were added to a pressure reactor. The molar ratio of Ca in the added CaO to Li in the slag was equal to 1.5. The reactor was heated to 150°C and maintained at this temperature for 10 hours. The leached suspension was filtered, and the solid residue was washed and dried. A leach solution with a Li concentration of 7.5 g / L was obtained, corresponding to a yield of 85%. The elemental contents of the feed, the resulting leach solution, and the solid residue are shown in Table 5.

[0076] Table 5: Mass balance (g) for the leaching process of slag with a D50 of 9.8 μm (base case)

[0077]

[0078] The example was repeated using different grinding conditions to produce slags with different particle size distributions. The main characteristic of these slags is their D50. The corresponding Li yields are shown in Table 5a.

[0079] Table 5a: Li yield as a function of particle size distribution

[0080]

[0081] When the D50 was 95.5 μm, 52% of the Li was dissolved, which was barely acceptable. Further reducing the particle size to below 50 μm significantly increased the Li yield.

[0082] Example 6: Description of a 2-step leaching process

[0083] 30 g of ground slag from Example 1, 125 mL of water, and 13.2 g of CaO were added to a pressure reactor. The molar ratio of Ca in the added CaO to Li in the slag was 1.25. The reactor was heated to 150°C and maintained at this temperature for 90 minutes. The suspension from the first leachate was filtered, and the solid residue was washed and dried. A first leachate solution with a Li concentration corresponding to a yield of 78% was obtained.

[0084] The dried leach residue, 165 mL of HO, and 2.6 g of CaO were added to the pressure reactor. This increased the overall process molar ratio of Ca from the added CaO to Li from the slag to 1.5. The reactor was heated to 150°C and maintained at this temperature for 90 minutes. The suspension from the second leach was filtered, and the solid residue was washed and dried. A second Li-containing leach solution was obtained, thereby increasing the overall process Li yield to 90%. The final residue was depleted of Li.

[0085] Table 6: Material balance of the 2-step leaching process (g)

[0086]

[0087] The Li yield can be increased by repeating the leaching operation on the solid residue. The total amount of added Ca can then be distributed among the different leaching steps.

Claims

1. A method for recovering Li from Li-containing metallurgical slag, the method comprising the following steps: - pulverizing the metallurgical slag to a particle size distribution with a D50 of less than 100 μm, the D50 being calculated from the cumulative distribution of undersize by volume in accordance with ISO 13320:2020; - contacting the Li-containing metallurgical slag with an alkaline Ca-compound in an aqueous medium, provided in an amount chosen to obtain a molar ratio of Ca in the Ca-compound / Li in the slag of at least 0.75, thereby obtaining a suspension; - heating the suspension to a temperature exceeding 80° C. for at least 30 minutes, thereby obtaining a leached suspension; as well as, - Separating the solids from the liquid in the leached suspension, thereby obtaining a leaching solution containing the majority of Li and a solid residue containing Ca.

2. The method according to claim 1, wherein the metallurgical slag is derived from the recycling of Li-ion batteries or their waste.

3. The method according to claim 1 or 2, wherein the pulverization of the slag is performed by pulverization or atomization.

4. The method according to any one of claims 1 to 3, wherein the metallurgical slag has a particle size distribution with a D50 below 50 μm, preferably below 25 μm, more preferably below 15 μm, the D50 being calculated from the cumulative distribution of undersize by volume according to ISO 13320:2020.

5. The method according to any one of claims 1 to 4, wherein the Ca-compound is provided in an amount selected to obtain a molar ratio of Ca in the Ca-compound / Li in the slag of 1 to 1.5, preferably 1.1 to 1.

3.

6. The method according to any one of claims 1 to 5, wherein the Ca-compound is CaO, Ca(OH)2 or CaCO3.

7. The method according to any one of claims 1 to 6, wherein the contacting step is performed using a solid-liquid ratio of 50 to 500 g / L.

8. The method according to any one of claims 1 to 7, wherein the heating step is performed at a temperature of 100 to 200°C, preferably 110 to 150°C.

9. The method according to any one of claims 1 to 8, wherein the heating step is performed for a period of 30 to 600 minutes, preferably 90 to 400 minutes, and more preferably 180 to 360 minutes.

10. The method according to any one of claims 1 to 9, wherein the Ca-compound is premixed with the metallurgical slag before the contacting step.

11. The process according to any one of claims 1 to 10, wherein the solid residue is ground.

12. The method according to any one of claims 1 to 11, wherein the metallurgical slag further comprises 5 to 50 wt.-% Al2O3, preferably 30 to 50 wt.-%.

13. The method according to any one of claims 1 to 12, wherein the metallurgical slag further comprises 2 to 50 wt% SiO2, preferably 2 to 20 wt%, more preferably 2 to 10 wt%.

14. The method according to any one of claims 1 to 13, wherein the metallurgical slag further comprises 10 to 70 wt% MnO, preferably 10 to 40 wt%, and more preferably 15 to 30 wt%.

15. The method according to any one of claims 1 to 14, wherein in the contacting step, the smelter flue gas comprising LiF and the additional basic Ca-compound are provided in amounts selected to obtain a molar ratio of Ca in the additional Ca-compound / Li in the flue gas of 0.25 to 0.5.

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