Lithium recovery from slag

Abstract

Li-bearing slag is typically produced when Li batteries or their waste products are recycled on a smelter. Li recovery methods include: - a pulverization step in which the metal slugs are pulverized to a particle size distribution having a D50 of less than 100 μm; - contacting, in an aqueous medium, the Li-containing metal slag with an alkaline Ca compound, the alkaline Ca compound being provided in an amount selected so that the molar ratio of Ca in the alkaline Ca compound to Li in the slag is at least 0.75, thereby obtaining a suspension; - a heating step in which the suspension is heated to a temperature above 80°C for at least 30 minutes, thereby obtaining a leaching suspension; a separation step in which the solids are separated from the liquid in the leach suspension, thereby obtaining a leach solution containing most of the Li, and a solid residue containing Ca. This alkaline leaching process allows for the simple recovery of battery-grade LiOH from the leach solution while consuming fewer reagents than known acid leaching processes.

Description

[Technical Field]

[0001] The present invention relates to a method for the recovery of Li (lithium) contained in metal slag. Such slag is typically produced when Li batteries or their waste products are recycled using a smelting process. Relatively noble metals such as Cu, Co, and Ni are present in the alloy phase, while more easily oxidized elements such as Li are present in the slag phase. Both phases are discarded and discharged separately. [Background technology]

[0002] Due to the relative scarcity of Li, it has recently become economical to recover Li from slag. Known processes employ acid leaching to dissolve Li.

[0003] WO2022085222 discloses a process for recovering lithium from secondary battery materials. It teaches that ensuring an Al to Li mass ratio of 6 or less is essential. This requirement can be met by adjusting the amount of Al in the slag according to various schemes. The slag is leached using an acidic aqueous solution. A particle diameter of 0.5 to 5 mm is preferred. The leachate is then purified by adding an alkaline substance to raise its pH to 14. The mixture is filtered, and the lithium in the solution is precipitated as carbonate.

[0004] Georgi-Maschler et al. ("Development of a recycling process for Li-ion batteries", Journal of Power Sources, Vol. 207, pp. 173-182, 2012) describe at a very general level a hydrometallurgical method for the recovery of lithium from slag derived from waste batteries. Flue dust and crushed slag are subjected to leaching, but no details regarding the application conditions are given. Acid leaching with sulfuric acid is the preferred choice. Lithium is precipitated from this acid leachate with sodium carbonate.

[0005] JP2020029613 describes a combination of an aqueous leaching process and a reduction melting process for the recovery of valuable metals in waste lithium-ion batteries. The leaching process is performed on the slag prepared in the melting process to recover Li in the leaching solution. The slag is leached in slightly acidified water at a pH of 5-7 under atmospheric pressure at a temperature below 100°C. Pressure leaching is not required. A particle diameter of 0.5-5 mm is preferred. The pH of the solution is gradually increased to 11 or higher due to the dissolution of Li. This aids in the precipitation of any undesirable Ni, Co, Cu, and Fe in the solution. If the amount of Li is small, a water-soluble alkali may be added to the mixture to ensure a basic pH of 11 or higher. The mixture is then filtered.

[0006] According to the above literature, Li is leached under acidic conditions, which produces soluble salts such as LiCl or Li2SO4. This salt must be converted to the insoluble Li2CO3, or LiOH, which is then precipitated. The alkaline conditions reported are only relevant for the subsequent purification of the solution.

[0007] CN115784272 describes a process for recovering lithium, aluminum, and fluorine from fluorine-rich aluminum electrolytic slag using a multi-stage alkaline leaching method. The slag, containing compounds such as Na3AlF6, LiNa2AlF6, K2NaAlF6, and CaF2, is first crushed and sieved, then subjected to sodium hydroxide leaching, aging, and water leaching. Lithium is recovered as Li2CO3, and fluorine is precipitated as NaF. The slag chemistry differs significantly from slag derived from lithium-ion battery recycling, and the applied leaching method uses strongly alkaline conditions and is not selective. The focus is explicitly on dissolving and recovering both lithium and fluorine from aluminum smelting slag.

[0008] It has been found that Li in the slag can be selectively leached using a specific amount of alkaline Ca compound. Under optimized conditions, Li leaching yields of over 80% can be achieved. LiOH is formed during the leaching process, thus making the additional conversion of Li salts to LiOH redundant.

[0009] To produce battery-grade Li, the LiOH solution can be purified, for example, by precipitation of impurities, ion exchange, or using selective membranes. High-purity Li can be readily obtained using crystallization, such as evaporative crystallization to produce solid LiOH, or reactive crystallization with carbonate to produce solid Li2CO3. Summary of the Invention

[0010] In a first embodiment, a method for recovering Li from a Li-bearing metal slag is described, the method comprising: - a pulverization step of pulverizing said metal slag to a particle size distribution having a D50 of less than 100 μm, calculated from the cumulative undersize distribution by volume according to ISO 13320:2020; - contacting, in an aqueous medium, the Li-containing metal slag with an alkaline Ca compound, the alkaline Ca compound being provided in an amount selected so that the molar ratio of Ca in the alkaline Ca compound to Li in the slag is at least 0.75, thereby obtaining a suspension; - a heating step of heating the suspension to a temperature above 80°C for at least 30 minutes, thereby obtaining a leach suspension; a separation step in which solids are separated from the liquid in said leach suspension, thereby obtaining a leach solution containing most of the Li, and a solid residue containing Ca.

[0011] Metal slags are typically obtained by recycling lithium-ion batteries or their waste products using smelting. Such smelting processes produce slags containing Li in amounts of at least 0.2 wt. %, more typically greater than 1 wt. %, or even greater than 2.5 wt. %. These slags are suitable feedstocks for the present process.

[0012] According to stoichiometry, one mole of Ca would be expected to be sufficient to leach two moles of Li, resulting in a molar ratio of 0.5. Surprisingly, it has been observed that a significant excess of Ca is indeed required. This excess has been successfully quantified, resulting in a lower limit of 0.75 for the molar Ca to Li ratio, which corresponds to 150% of the stoichiometric amount.

[0013] To enable the formation of alloy and slag phases during melting, so-called slag formers or flow agents are used. Typical slag formers are, for example, CaO and SiO2. It should be noted that CaO in the slag must be considered non-reactive in the present Li leaching process. Therefore, alkaline Ca compounds such as CaO, Ca(OH)2, or CaCO3 should be added in the contacting step in the amounts specified above, regardless of the Ca in the slag.

[0014] The amount of Li in the metal slag can be determined by chemical analysis, and a person skilled in the art can then easily derive the amount of Ca compound required in the contacting step. The amount of Ca compound specified above for this process may be added all at once or, alternatively, may be added in stages.

[0015] The steps of contacting, heating, and solid-liquid separation together with leaching can be repeated on the solid residue to further increase Li yield. The amount of Ca compound specified above may then be distributed over the repeated contacting steps. Counter-flow configurations of aqueous solution and solid residue are particularly useful in the present disclosure because they reduce overall water consumption while optimizing Li leaching yield.

[0016] The process of the present invention can be operated in batch or continuous mode.

[0017] Heating time and reaction time may be somewhat correlated according to commonly known rules: a lower temperature may mean a longer reaction time to reach the optimum Li leaching yield, while a higher temperature may increase the reaction rate.

[0018] A "major portion" of an element means 50% or more of the amount of that element entering the process.

[0019] In another embodiment, the metal slag is derived from recycling lithium-ion batteries or waste thereof using a pyrometallurgical smelting process, which includes used or end-of-life batteries, waste from manufacturing, or battery components such as electrode foils, electrolytes, separators, casing materials, and electrode materials, or raw battery materials such as "black sludge," resulting in a highly complex waste stream.

[0020] In another embodiment, the slag is pulverized by grinding or atomization, which ensures faster and more complete dissolution of the Li. Pulverization by milling is the preferred option. Milling may be performed during the contacting step.

[0021] In another embodiment, the metal 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 the ISO 13320:2020 standard. D50 is the particle size in μm whereby the volume cumulative distribution reaches 50%. Reducing the particle size increases the exposure of Li compounds to Ca compounds in solution. Particles with a D50 between 5 and 30 μm have shown excellent Li leaching yields and kinetics. Further reducing the particle size increases the speed of the process but has limited impact on the overall leaching yield.

[0022] The order of addition of the slag, Ca compound, and aqueous medium in the contacting step is not important, for example, in one embodiment, the Ca compound is added to the metal slag before contacting the mixture with the aqueous medium.

[0023] In another embodiment, the Ca compound is added in an amount selected to provide a molar ratio of Ca in the Ca compound to Li in the slag of 1 to 1.5, preferably 1.1 to 1.3, and more preferably 1.1 to 1. These ratios provide good Li yields while avoiding excessive reactant costs.

[0024] In another embodiment, the Ca compound is CaO, Ca(OH), or CaCO. CaCO is the preferred choice, with CaO and Ca(OH) being more preferred.

[0025] In another embodiment, the Ca compound is in powder form, which facilitates reaction with the aqueous medium as well as with the slag.

[0026] In another embodiment, the contacting step is carried out using a solids to liquid ratio of 50 to 500 g / L, which ensures that the suspension of solids in the aqueous medium is provided with reasonable agitation power in the contacting and heating reactor(s).

[0027] In another embodiment, the heating step is carried out at 100-200°C, preferably 110-150°C. Higher reaction temperatures above 100°C have been found to substantially increase the Li yield. While operating at temperatures below 70°C may be feasible, this would require impractical reaction times to reach the desired Li yield of at least 50%. For economic reasons, higher temperatures in the range of 100-200°C are preferred. On the other hand, increasing the reactor temperature above 150°C no longer significantly improves the Li yield.

[0028] In another embodiment, the process is carried out in an aqueous medium containing dissolved salts, for example, dissolving 1 mol / L of Na2SO4 or NaOH, which raises the boiling point of the aqueous medium and allows the heating step to operate somewhat above 100°C while avoiding the use and cost of a pressure reactor.

[0029] In another embodiment, the heating step is carried out for 30 to 600 minutes, preferably 90 to 400 minutes, more preferably 180 to 360 minutes.

[0030] In another embodiment, the Ca compound is premixed with the metal slag prior to the contacting step, for example, the Ca compound may be added during the grinding of the slag.

[0031] In another embodiment, the solid residue obtained in the separation step of separating the solids from the liquid in the leach suspension is comminuted, which is useful when repeated steps of contacting, heating, and solid-liquid separation are applied.

[0032] In another embodiment, the metal slag further comprises 5-50 wt. % Al2O3, preferably 30-50 wt. Al is frequently present in metal slag because the casing or cathode foil of a lithium-ion battery is made of Al. Al is very easily oxidized and transferred entirely to the slag.

[0033] In another embodiment, the metal slag further comprises 2-50 wt. % SiO2, preferably 2-20 wt. % and more preferably 2-10 wt. SiO2 is often added to metal slag as a fluid to lower the melting point or make the slag less viscous. Silicon is very easily oxidized and is transferred entirely to the slag.

[0034] In another embodiment, the metal slag further comprises 10-70 wt. % MnO, preferably 10-40 wt. % MnO, more preferably 15-30 wt. % Mn is often present as an active component of the cathode. It is easily oxidized and is primarily transferred to the slag.

[0035] In another embodiment, the contacting step involves providing smelter fumes containing LiF and an additional alkaline Ca compound in an amount selected to provide a molar ratio of Ca in the additional Ca compound to Li in the fumes of 0.25 to 0.5. The Li fumes may contain different Li salts. Some, such as LiF, dissolve by consuming a stoichiometric amount of Ca compound, while others, such as LiBr, LiCl, and LiO, readily dissolve without the need for Ca. In contrast to the first embodiment, the additional amount of Ca for leaching LiF corresponds to an expected molar ratio of 0.5. However, this additional amount may be even lower, down to 0.25, especially if the amount of Ca compound used to leach Li in the slag is high, potentially resulting in a large amount of unreacted excess. For practical reasons, it is preferred that the same Ca compound be selected for leaching Li in the slag and the fumes.

[0036] In another embodiment, Li-bearing metal slag obtained from a first hot metal smelting process and Li-bearing smelter fumes obtained from the same or another hot metal smelting step are premixed, thereby obtaining a heterogeneous Li-enriched mixture.

[0037] In another embodiment, the solid residue is used as a cement substitute. The solid residue or leach residue is the insoluble portion left after the process of the present invention is carried out. It can be used as at least a partial cement substitute. DETAILED DESCRIPTION OF THE INVENTION

[0038] The following examples illustrate the invention.

[0039] Example 1: Effect of temperature Lithium 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 approximately 5-8 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 leach 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 75% yield. The elemental contents of the feed, the resulting leach solution, and the solid residue are shown in Table 1.

[0040] [Table 1]

[0041] This example was repeated at different temperatures, and the respective Li yields are shown in Table 1a.

[0042] [Table 2]

[0043] Lowering the reactor temperature to 70°C results in a poor Li yield of 36%. Increasing the reactor temperature to above 80°C significantly improves Li dissolution. Further increases in temperature above 120°C or 150°C have only limited effect.

[0044] Example 2: Effect of Ca / Li ratio 30 g of the ground slag according to Example 1, 125 mL of water, and 15.8 g of CaO are added to a pressure reactor. The molar ratio of Ca in the added CaO to Li in the slag is equal to 1.5. The reactor is heated to 150°C and maintained at this temperature for 90 minutes. The leach suspension is filtered, and the solid residue is washed and dried. A leach solution with a Li concentration of 9.82 g / L is obtained, with a yield of 78%. The elemental contents of the feed, the resulting leach solution, and the solid residue are shown in Table 2.

[0045] [Table 3]

[0046] This example was repeated using different Ca / Li ratios, with the respective Li yields shown in Table 2a.

[0047] [Table 4]

[0048] A Ca / Li ratio of 0.5 results in a poor Li yield of 37%. Increasing the Ca / Li ratio to 0.75 significantly improves the Li yield. The Li yield increases further with the addition of more Ca.

[0049] Example 3: Effect of Heating Time Using Pressure Leaching Lithium 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 approximately 5–8 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 min. The leach 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 elemental contents of the feed, the resulting leach solution, and the solid residue are shown in Table 3.

[0050] [Table 5]

[0051] This example was repeated using different leaching times, with the respective Li yields shown in Table 3a.

[0052] [Table 6]

[0053] Most of the Li is leached after 30 minutes. Longer times improve yields. These longer times may be useful when lower temperatures are selected or when coarser slag particles are processed.

[0054] Example 4: Effect of heating time at atmospheric pressure Lithium 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 5-8 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 min. The leach 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 59% yield. The elemental contents of the feed, the resulting leach solution, and the solid residue are shown in Table 4.

[0055] [Table 7]

[0056] This example was repeated using different leaching times, with the respective Li yields shown in Table 4a.

[0057] [Table 8]

[0058] Most of the Li is leached after 360 minutes at 90°C. Longer times improve yields. Compared to Example 3, lower temperatures are expected to require longer reaction times to leach most of the Li.

[0059] Example 5: Effect of particle size distribution A 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 leach 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.

[0060] [Table 9]

[0061] This example was repeated using different grinding conditions to produce slags with different particle size distributions, characterized primarily by D50. The respective Li yields are shown in Table 5a.

[0062] [Table 10]

[0063] At a D50 of 95.5 μm, a barely acceptable 52% of the Li dissolves. Further reduction in particle size to below 50 μm significantly increases the Li yield.

[0064] Example 6: Illustration of a two-step leaching process 30 g of the ground slag according to Example 1, 125 mL of water, and 13.2 g of CaO are added to a pressure reactor. The molar ratio of Ca in the added CaO to Li in the slag is equal to 1.25. The reactor is heated to 150°C and maintained at this temperature for 90 minutes. The first leach suspension is filtered, and the solid residue is washed and dried. A first leach solution is obtained with a Li concentration corresponding to a yield of 78%.

[0065] The dried leach residue, 165 mL of HO, and 2.6 g of CaO are added to a pressure reactor. This increases the overall process molar ratio of Ca in the added CaO to Li in the slag to 1.5. The reactor is heated to 150°C and maintained at this temperature for 90 minutes. The second leach suspension is filtered, and the solid residue is washed and dried. A second Li-loaded leach solution is obtained, increasing the overall process Li yield to 90%. The final residue is depleted in Li.

[0066] [Table 11]

[0067] The Li yield can be enhanced by repeating the leaching operation on the solid residue. The total amount of Ca added can then be distributed over the different leaching steps.

Claims

1. 1. A method for recovering Li from a Li-bearing metal slag, comprising: - a pulverization step in which the metal slugs are pulverized to a particle size distribution having a D50 of less than 100 μm, calculated from the cumulative undersize distribution by volume according to ISO 13320:2020; - contacting, in an aqueous medium, the Li-containing metal slag with an alkaline Ca compound, the alkaline Ca compound being provided in an amount selected so that the molar ratio of Ca in the alkaline Ca compound to Li in the slag is at least 0.75, thereby obtaining a suspension; - a heating step of heating said suspension to a temperature above 80°C for at least 30 minutes, thereby obtaining a leaching suspension; a separation step in which solids are separated from the liquid in the leach suspension, thereby obtaining a leach solution containing most of the Li, and a solid residue containing Ca.

2. 10. The method of claim 1, wherein the metal slugs are derived from recycling lithium ion batteries or waste thereof.

3. 3. The method according to claim 1 or 2, wherein the step of pulverizing the slag is carried out by grinding or atomization.

4. 4. The method of claim 3, wherein the comminuting is performed by milling, and the milling is performed during the contacting step.

5. 3. The method according to claim 1 or 2, wherein the metal slag has a particle size distribution with a D50 calculated from the cumulative undersize distribution by volume according to ISO 13320:2020 of less than 50 μm, preferably less than 25 μm, more preferably less than 15 μm.

6. 3. The method according to claim 1 or 2, wherein the Ca compound is provided in an amount selected so that the molar ratio between the Ca in the Ca compound and the Li in the slag is between 1 and 1.5, preferably between 1.1 and 1.

3.

7. The Ca compound is CaO, Ca(OH) ２ , or CaCO ３ The method according to claim 1 or 2, wherein

8. 3. The method of claim 1 or 2, wherein the contacting step is carried out using a solids to liquid ratio of 50 to 500 g / L.

9. 3. The method according to claim 1 or 2, wherein the heating step is carried out at a temperature of from 100 to 200°C, preferably from 110 to 150°C.

10. 3. The method of claim 1 or 2, wherein the heating step is carried out for a time period of from 30 to 600 minutes, preferably from 90 to 400 minutes, more preferably from 180 to 360 minutes.

11. 3. The method of claim 1 or 2, wherein the Ca compound is premixed with the metal slag prior to the contacting step.

12. 3. The method of claim 1 or 2, wherein the solid residue is comminuted.

13. The metal slag contains 5 to 50 wt. % Al ２ O ３ 3. The method according to claim 1 or 2, further comprising, preferably 30 to 50% by weight,

14. The metal slag contains 2 to 50% by weight of SiO ２ 3. The method of claim 1 or 2, further comprising preferably 2 to 20 wt. %, more preferably 2 to 10 wt. % of a hydroxybenzoate.

15. 3. The method according to claim 1 or 2, wherein the metal slag further comprises 10-70 wt.% MnO, preferably 10-40 wt.%, more preferably 15-30 wt.%.

16. 3. The method of claim 1, wherein in the contacting step, smelter fumes containing LiF and an additional alkaline Ca compound are provided in amounts selected so that the molar ratio of the Ca in the additional Ca compound to the Li in the fumes is 0.25 to 0.5.

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