Process for separating metals by solvent extraction

Abstract

The present invention relates to a process for the recovery of Li and one or more of Ni, Mn and Co from acidic aqueous solutions, such as those obtained by leaching of Li-ion batteries or their waste. The process is based on the use of a saponified organic extractant. The extractant is saponified with LiOH instead of NaOH. This avoids the introduction of another alkali metal into the raffinate, which would interfere with the recovery of Li. The saponification is carried out under conditions suitable to obtain a homogeneous and clear microemulsion. Such emulsion is stable and thus particularly suitable for industrial applications. Ni, Mn and Co are extracted and can be recovered from the organic phase, while Li can be recovered from the aqueous phase. Part of the Li can be converted into LiOH and reused for the saponification.

Description

[0001] This invention relates to the field of recycling Li-ion batteries or their waste, and describes an efficient method for recovering lithium (Li) and one or more of nickel (Ni), manganese (Mn) and cobalt (Co) from an acidic aqueous solution.

[0002] The development of lithium-ion batteries, particularly the use of nickel-manganese-cobalt (NMC) cathode materials, has increased the demand for high-purity nickel sulfate, cobalt sulfate, and manganese sulfate, either in solid form or in solution. In terms of resource efficiency and environmental impact, recovering these raw materials from industrial waste and end-of-life products is preferable to primary mineral mining.

[0003] Streams originating from battery recycling typically contain lithium (Li). Li is an alkali metal and is difficult to separate from other metal ions, especially those with very similar chemical properties, such as sodium (Na). However, sodium hydroxide (NaOH) is the most common alkaline reagent used for neutralization operations in refining processes, including (hydrolysis) precipitation, solvent extraction, and ion exchange. Therefore, Li often ends up in process wastewater along with Na. Na-Li separation is necessary for the high-value utilization of Li from wastewater.

[0004] Commonly known methods for Li recovery are often based on precipitation, which are time-consuming, have low Li recovery rates, and produce low-quality lithium salts. Therefore, solvent extraction methods (also known as the SX method) have gained more attention for Li recovery.

[0005] Hung Shu-Hui et al. (“Recovery of metal ions from spent Lithium Ion Batteries (LIBs) using sodium salts of D2EHPA or P507: performance evaluation and life cycle assessment”, Research Journal of Chemistry and Environment, Vol. 18, 2014) described the extraction of Li, Co, Mn, and Ni from spent Li-ion battery solvents using sodium di(2-ethylhexyl)phosphate (Na-D2EHPA) and mono(2-ethylhexyl) ester (Na-P507) dissolved in kerosene. Both D2EHPA and P507 extractants were saponified with NaOH solution, and kerosene was used as a diluent. The extraction percentages of metal ions, including Li, Co, Mn, and Ni, increased with increasing equilibrium pH. NaOH was introduced, and Na ultimately existed as Na2SO4 in the raffinate, stoichiometrically exchanging the extracted metals.

[0006] JP2019169306 discloses a method for producing a battery electrode material in a slurry state, which is coated onto a sheet current collector and contains an aqueous binder and an electrode active material comprising electrolytically dissolved Mn dioxide. The method of kneading and mixing the electrode raw material with water as a solvent includes the steps of mixing the electrode active material, mixing the binder, and mixing with a neutralizing agent. This method uses LiOH as a neutralizing agent, but is not within the context of a hydrometallurgical refining method that uses solvent extraction as a technique for separating metals.

[0007] Han Zhejie et al. described a solvent extraction method using acidic solvents and systematically studied the extraction mechanism (“Recycling of lithium and fluoride from LiF wastewater from LiF synthesis industry by solvent extraction”, Journal of Environmental Chemical Engineering, Vol. 11, 2023). The results showed that Li was extracted via a cation exchange mechanism using D₂EHPA (di-2-ethylhexylphosphoric acid). A 99.72% Li recovery and a battery-grade LiCl solution (3.40 g / L) were achieved by mixing LiF (aqueous solution) with NaOH-saponified D₂EHPA at 25 °C for 6 minutes at pH 4.60. However, the Li-loaded solvent itself was not used for metal extraction.

[0008] US2021130927 teaches a method for extracting Li from a Ni(II) / Li(I) solution and optionally extracting Ni, thereby producing a lithium-lean solution. Such a method requires a Li-selective extractant to separate Li, rather than using a conventional system to extract impurities and concentrate Li in the raffinate stream.

[0009] WO23175157 discloses a method for processing black mass into battery chemicals. The black mass is leached, followed by the removal of impurities from a first process solution using LiOH to produce a second process solution. Li is then separated from the second process solution using chromatographic separation, yielding Li₂SO₄ and a third process solution. Finally, the method converts the resulting Li₂SO₄ into LiOH and H₂SO₄ via electrodialysis. LiOH is used as a neutralizing agent for hydrometallurgical refining via ion exchange technology based on chromatographic principles, but not in the specific context of solvent extraction.

[0010] JP2023100269 teaches a method for recovering metals from Li-ion battery waste by reducing the use of NaOH as a pH adjuster. Instead, pH correction is performed using a LiOH solution after leaching and during solvent extraction operations. The extraction includes separate steps for Mn extraction, Co extraction, and Ni extraction. An aqueous Li₂SO₄ solution is hydroxylated to obtain an aqueous LiOH solution, which is used for recovery and reuse in previous refining steps. There is no mention of reusing the regenerated LiOH solution for solvent saponification.

[0011] CN108517422 teaches a method for recovering Li from a lithium-containing multimetallic solution. The solution is adjusted to pH 3-7 and extracted with a saponified organic phase to obtain a lithium-rich raffinate. The saponified organic phase is obtained by mixing an organophosphorus extractant with a non-sodium saponifying agent.

[0012] "Saponification" is the process of converting the acidic form of an acidic extractant molecule into a neutral form. In the typical reaction with NaOH, the extractant protons are released and exchange with Na+ ions according to the following reaction: (Where R represents an organic extractant). Based on available technologies, the industrial applicability of LiOH as a neutralizing agent in solvent extraction methods is not apparent.

[0013] Saponifying organic solvents with LiOH solution may result in a two-phase system. The separation of the aqueous and organic phases can be achieved using various techniques, including coalescence devices, sedimentation devices, parallel plate separation, membrane filtration, and centrifugation. However, any such process step will obviously increase the overall cost of the process.

[0014] Another method is to directly inject NaOH or LiOH solution into the extraction reactor. Such a method can be chosen where direct pH control is preferred (e.g., to optimize selectivity), but it requires pH adjustment during the extraction process.

[0015] It appears that most refining processes utilize NaOH for neutralization, which inevitably leads to the mixing of Na and Li when processing Li-containing NMC streams.

[0016] In view of the problems described in the prior art, the object of the present invention is to provide an alternative method that uses solvent extraction and pre-saponification with LiOH to recover Li on the one hand, and one or more of Ni, Mn and Co on the other. This simplifies the existing refining process.

[0017] In this method, pre-saponification is performed, i.e., the organic solvent mixture is converted with LiOH solution. Neutralization using LiOH avoids Na ion contamination from NaOH. Pre-neutralization of the organic solvent mixture also eliminates the need for pH adjustment during the extraction step. Solvent flow rates, solubility, and the properties of the saponified organic extractant become more consistent and predictable, which is an advantage in industrial plants. Such a method is preferred in capacity-driven processes.

[0018] More specifically, in a separate reaction, an organic extractant in acidic form is mixed with LiOH to produce an emulsion, which is then used for neutralization.

[0019] During the process, any formation or separation of the aqueous phase will cause fluctuations in the input to the extraction reactor. The emulsion needs to remain stable when pumped from the saponification reactor to the extraction section of the industrial unit. Microemulsions (which are a single, stable, homogeneous, and clear organic phase) meet this requirement well.

[0020] The present invention is further described in detail in the following embodiments.

[0021] 1. A method for separating metals by solvent extraction, the method comprising the steps of:

[0022] A first aqueous phase is provided, the first aqueous phase comprising an acidic aqueous solution containing Li, and further comprising one or more of Ni, Mn and Co;

[0023] A first organic phase is provided, the first organic phase comprising an organic extractant in an acidic form and a diluent;

[0024] The second organic phase is obtained by at least partially saponifying the organic extractant by mixing the first organic phase with an aqueous solution containing LiOH.

[0025] Under conditions suitable for solvent extraction, the first aqueous phase is mixed with the second organic phase to obtain a third organic phase containing one or more of the major components of Ni, Mn, and Co, and a second aqueous phase containing the major component of Li; and,

[0026] Separate the third organic phase from the second aqueous phase;

[0027] The characteristic feature is that, in the saponification step, the first organic phase is mixed with an aqueous solution containing LiOH until a uniform and clear microemulsion is obtained.

[0028] 2. The method according to item 1, wherein the first organic phase further comprises a modifier.

[0029] 3. The method according to claim 1 or 2, wherein the organic extractant comprises an organic phosphonic acid of the formula bis(2,4,4-trimethylpentyl)phosphonic acid.

[0030] 4. The method according to any one of items 1 to 3, wherein the saponification step is carried out using an aqueous solution containing LiOH at a concentration of 90 to 120 g / L, preferably 100 to 110 g / L.

[0031] 5. The method according to any one of items 1 to 4, wherein the microemulsion is free of Na.

[0032] 6. The method according to any one of items 3 to 5, wherein the organic extractant contains more than 95% by weight of an organic phosphonic acid, and wherein the saponification level is 60% or less.

[0033] 7. The method according to any one of items 3 to 5, wherein the organic extractant contains less than 90% by weight of an organic phosphonic acid, and wherein the saponification level is 20% or less.

[0034] 8. The method according to any one of items 1 to 7, wherein the microemulsion comprises 1 to 10% by volume of water.

[0035] 9. The method according to any one of items 1 to 8, wherein the concentration of Ni in the first aqueous phase is less than 125 g / L.

[0036] 10. The method according to any one of items 1 or 9, wherein the concentration of Co in the first aqueous phase is less than 120 g / L.

[0037] 11. The method according to any one of items 1 to 10, wherein the concentration of Mn in the first aqueous phase is less than 130 g / L.

[0038] 12. The method according to any one of items 1 to 11, wherein the concentration of Li in the first aqueous phase is in the range of 0.1 to 35 g / L.

[0039] 13. The method according to any one of items 1 to 12, wherein the first aqueous phase is obtained by acid leaching of a Li-ion battery or its waste.

[0040] 14. The method according to any one of items 1 to 13, further comprising the step of: recovering one or more of Ni, Mn and Co from the third organic phase by stripping with an acidic aqueous solution, thereby obtaining a metal-containing aqueous phase and a metal-depleted organic phase.

[0041] 15. The method according to any one of items 1 to 14, further comprising the step of: electrodialysis of the second aqueous phase to obtain an acidic aqueous solution and an aqueous solution containing LiOH.

[0042] 16. The method of claim 15, wherein the acidic aqueous solution is used in the step of recovering one or more of Ni, Mn and Co according to claim 14.

[0043] 17. The method according to item 15, wherein the aqueous solution containing LiOH is used in the saponification step according to item 1.

[0044] The first embodiment relates to a method for separating metals by solvent extraction, comprising the steps of:

[0045] A first aqueous phase is provided, the first aqueous phase comprising an acidic aqueous solution containing Li, and further comprising one or more of Ni, Mn and Co;

[0046] A first organic phase is provided, the first organic phase comprising an organic extractant in an acidic form and a diluent;

[0047] The second organic phase is obtained by at least partially saponifying the organic extractant by mixing the first organic phase with an aqueous solution containing LiOH.

[0048] Under conditions suitable for solvent extraction, the first aqueous phase is mixed with the second organic phase to obtain a third organic phase containing one or more of the major components of Ni, Mn, and Co, and a second aqueous phase containing the major component of Li; and,

[0049] Separate the third organic phase from the second aqueous phase;

[0050] The characteristic feature is that, in the saponification step, the first organic phase is mixed with an aqueous solution containing LiOH until a uniform and clear microemulsion is obtained.

[0051] One particular embodiment relates to a method for separating metals by solvent extraction, comprising the steps of:

[0052] A first aqueous phase is provided, the first aqueous phase comprising an acidic aqueous solution containing Li, and further comprising one or more of Ni, Mn and Co;

[0053] A first organic phase is provided, the first organic phase comprising an organic extractant in an acidic form and a diluent;

[0054] The organic extractant is partially saponified by mixing the first organic phase with an aqueous solution containing LiOH, thereby obtaining the second organic phase;

[0055] Under conditions suitable for solvent extraction, the first aqueous phase is mixed with the second organic phase to obtain a third organic phase containing one or more of the major components of Ni, Mn, and Co, and a second aqueous phase containing the major component of Li; and,

[0056] Separate the third organic phase from the second aqueous phase;

[0057] In the saponification step, the first organic phase is mixed with an aqueous solution containing LiOH in the presence of an organic extractant based on an organophosphorus acid, until a saponification level of at least 1% and at most 60% is reached and a homogeneous phase containing a clear and transparent microemulsion is obtained.

[0058] Another specific embodiment relates to a method for separating metals by solvent extraction, comprising the steps of:

[0059] A first aqueous phase is provided, the first aqueous phase comprising an acidic aqueous solution containing Li, and further comprising one or more of Ni, Mn and Co;

[0060] A first organic phase is provided, the first organic phase comprising an organic extractant in an acidic form and a diluent;

[0061] The organic extractant is partially saponified by mixing the first organic phase with an aqueous solution containing LiOH, thereby obtaining the second organic phase;

[0062] Under conditions suitable for solvent extraction, the first aqueous phase is mixed with the second organic phase to obtain a third organic phase containing one or more of the major components of Ni, Mn, and Co, and a second aqueous phase containing the major component of Li; and,

[0063] Separate the third organic phase from the second aqueous phase;

[0064] In the saponification step, the first organic phase is mixed with an aqueous solution containing LiOH in an organic extractant containing more than 5% phosphine oxide, particularly an organic phosphine oxide, until a saponification degree of at least 1% and at most 20% is achieved and a homogeneous phase containing a clear and transparent microemulsion is obtained.

[0065] An "extractant" is a compound that can extract the active component of a metal species by chemically binding with it to form a metal-extractant complex, wherein the complex is more soluble in an organic phase than in an aqueous phase. Specifically, the extractant is an organic extractant. Organic extractants are particularly based on organophosphorus acids, including organophosphoric acids, organophosphonic acids, and organophosphonic acids. Suitable organic extractants include, for example, hypophosphonic acids. Since they contain organic substituents, they should more accurately be called organic hypophosphonic acids, but the term can be used synonymously as long as it actually refers to the same chemical compound. Examples include: bis(2,4,4-trimethylpentyl)hydantoin, sold under commercial names such as Cyanex 272, Ionquest 290, and C272; organophosphates, such as D2EHPA [bis(2-ethylhexyl)phosphonic acid]; and organophosphonic acids, such as PC88A [2-ethylhexylphosphonate mono-2-ethylhexyl ester], DIDA [diisopropyl dithiophosphonic acid], or versatic 10 acid [neodecanic acid]. These extractants can be used according to the invention, provided they are metered at concentrations that allow for the formation of homogeneous and clear microemulsions.

[0066] An important aspect of this invention is that the organic extractant, initially in its acidic form, is saponified before use. The term "saponification" refers to the replacement of the acidic proton of the acid with another cation. In this invention, the proton is replaced with a Li cation.

[0067] "Saponification level" is defined as the percentage (in %) of the extractant acidic protons replaced by an alkali metal (Li in this case), and is given as a molar percentage (mol%). The saponification level can be up to 20%, up to 50%, or up to 60%. Due to the risk of gel formation (which is undesirable in industrial processes), saponification levels above 60% are not recommended. As a lower limit, the saponification level is at least 1 mol%, or at least 5 mol%, particularly at least 10 mol% or 20 mol%, or 20% or less.

[0068] It should be noted that NaOH is the most commonly used alkali for saponification or other neutralization operations in refining processes. When the aim is to separate and recover Li, it is advantageous to avoid any contamination of the reaction solution with Na. Typically, Na and Li end up together in the same solution, and their separation is difficult or at least requires additional process steps. Therefore, using Li instead of Na for saponification results in a more efficient and shorter overall time. Furthermore, any Li used for saponification is not lost but contributes to the total amount of recoverable Li. This advantageous combination makes LiOH the most preferred saponifying agent in this method.

[0069] Another key aspect of this invention is obtaining an emulsion, and more specifically, a homogeneous and clear microemulsion. An "emulsion" is a mixture of two or more liquids that are generally immiscible but, under specific conversion methods, will exhibit a macroscopically homogeneous but microscopically heterogeneous state. In an emulsion, one liquid is dispersed within another. In this invention, the emulsion comprises a saponified organic acid combined with an aqueous phase. In this method, a clear microemulsion is obtained. A microemulsion is defined as a thermodynamically stable isotropic liquid mixture. Visually, a microemulsion presents as a single clear phase. This clear or transparent appearance is due to the small size of the dispersed droplets, typically smaller than the wavelength of light (400 to 800 nm), thus avoiding scattering. Such a small droplet size ensures the stability of the microemulsion and can enhance the reaction kinetics of the extraction process.

[0070] Solvent extraction, also known as SX, is a hydrometallurgical separation technique in which two immiscible phases (an organic phase and an aqueous phase) are brought into contact with each other. Under suitable conditions, a specific metal transfers between the two phases. Such suitable conditions for SX are well known to those skilled in the art.

[0071] In the above embodiments, the term "diluent" refers to an organic molecule or mixture of different organic molecules added to the organic phase to dilute the extractant and allow the dissolution of the metal complex, improve the physical properties of the organic phase (especially phase separation), and reduce its cost, as diluents are generally cheaper than extractants. Diluents are typically kerosene fractions, such as aliphatic or aromatic hydrocarbons and cycloalkanes, or mixtures thereof. Commercial products include ShellSol™, Elixore™, and Escaid™.

[0072] In any process step, the term "major portion containing a certain element" means that the element contains more than 50% by weight of the element relative to the total weight of the element entering the process step.

[0073] More specifically, the third organic phase preferably contains more than 80%, more preferably more than 90%, of one or more of Ni, Mn, and Co. The second aqueous phase preferably contains more than 80%, more preferably more than 90%, of Li.

[0074] In another embodiment, the first organic phase also contains a modifier. Modifiers are often added to improve the solubility of metal complexes in the organic phase, alter the physical properties of the solvent to prevent the formation of solid residues or a third phase. These phenomena are indeed undesirable in solvent extraction. Modifiers may also be added to prevent chemical degradation of the extractant or diluent. However, modifiers may impair the selectivity of the organic phase because they may participate in the formation of metal-extractant complexes.

[0075] In another embodiment, the organic extractant comprises an organophosphonic acid of the formula bis(2,4,4-trimethylpentyl)phosphonic acid. This extractant is particularly suitable for extracting Co and Mn from aqueous solutions.

[0076] In another embodiment, the saponification step is carried out using an aqueous solution containing 90 to 120 g / L, preferably 100 to 110 g / L, of LiOH. A more concentrated LiOH solution is generally preferred to limit the amount of water introduced into the system. Therefore, concentrations below 90 g / L are less advantageous. On the other hand, solutions exceeding 120 g / L of LiOH may reach their saturation limit. Clearly, the precipitation of Li crystals during saponification or in subsequent processes must be avoided.

[0077] In another embodiment, the microemulsion is Na-free. One of the objectives of this invention is to recover Li while avoiding contamination by other alkali metal elements such as Na. Therefore, neutralization or saponification with NaOH is preferably avoided.

[0078] In another embodiment, the microemulsion contains a limited amount of aqueous phase. This amount is preferably in the range of 1 to 10% by volume.

[0079] In another embodiment, the organosphinic acid has a purity exceeding 95%. Such an acid is available, for example, under the commercial name IONQUEST® 290. Using such a high-purity reagent, the saponification level can advantageously reach 60 mol%, while still obtaining a clear or transparent microemulsion. The saponification level is at least 1 mol%, or at least 5 mol%, particularly at least 10 mol%. After saponification, a step to separate excess water may be required.

[0080] In another embodiment, the organosphinic acid has a purity of less than 90%. Such an acid can be obtained, for example, under the commercial name CYANEX® 272. Using such a reagent, the saponification level can only reach 20 mol%, while still obtaining a clear or transparent microemulsion, particularly, a saponification level of at least 1 mol%, or at least 5 mol%, especially at least 10 mol%. Since the impurities present mainly consist of phosphine oxide or organosphinic oxide, a purity of less than 90% can be restated to mean that the organosphinic acid contains more than 5% and less than 10% phosphine oxide. This has the technical effect of obtaining a homogeneous phase containing a clear and transparent microemulsion. Therefore, in this case, the step of separating excess water is not required.

[0081] To ensure solution stability, it is preferable to keep the Ni concentration in the first aqueous phase less than 125 g / L. It is also preferable to keep the Co concentration in the first aqueous phase less than 120 g / L. Furthermore, it is preferable to keep the Mn concentration in the first aqueous phase less than 130 g / L. It is also advantageous if the cumulative concentrations of Ni, Co, and Mn in the first aqueous phase are less than 130 g / L. These maximum concentrations also correspond to concentrations typically expected when the first aqueous phase originates from the acid leaching step of a Li-ion battery or its waste.

[0082] The method of the present invention is particularly significant if the first aqueous phase contains an economically viable Li concentration, making its separation and recovery worthwhile. However, excessively high Li concentrations will again jeopardize the stability of the solution. Therefore, a Li concentration of 0.1 to 35 g / L in the first aqueous phase is preferred. The mentioned Li concentration range also corresponds to a range that can generally be expected when the first aqueous phase originates from the acidic leaching of Li-ion batteries or their waste.

[0083] Therefore, the method of the present invention is particularly suitable for treating solutions derived from the acidic leaching of Li-ion batteries or their waste.

[0084] "Li-ion batteries or their waste" refers to, for example, waste Li-ion batteries, used or scrapped batteries, production waste or battery waste, industrial waste, electrode materials or other pretreated battery materials.

[0085] Valuable metals such as Ni, Mn, and Co can be advantageously recovered from a metal-containing third organic phase via back-extraction. This is typically carried out using a 0.1 to 10 M acidic solution of HCl or H₂SO₄. Once in aqueous solution, these metals can be separated and refined according to common hydrometallurgical methods. These metals can then be reused in Li-ion battery cathodes. The back-extracted organic phase can then be used again as the first organic phase in this process.

[0086] Li can be advantageously recovered from the second aqueous phase, for example by electrodialysis, membrane electrolysis, solvent extraction, or ion exchange. A portion of this Li can be converted to LiOH and recovered in the saponification step as an aqueous solution containing LiOH. The remaining Li can be recovered for reuse in the cathode or anode of a Li-ion battery.

[0087] Preferably, the second aqueous phase is subjected to electrodialysis to obtain an acidic aqueous solution and an aqueous solution containing LiOH. The acidic aqueous solution can then be used in a step of recovering one or more of Ni, Mn, and Co by back-extraction. The aqueous solution containing LiOH can then be used in a step of saponifying an organic extractant in its acidic form.

[0088] The following examples illustrate the present invention.

[0089] Example 1

[0090] The stability of microemulsions containing 30% (v / v) Cyanex® 272 or Ionquest® 290 and LiOH was investigated. Escaid 110 (70% (v / v)) was used as the diluent. Saponification was performed with a 105 g / L LiOH solution. The reagents were stirred at 25°C for 15 minutes.

[0091] Table 1: Stability of different saponified emulsions prepared using Cyanex® 272 and Ionquest® 290

[0092]

[0093] A clarified microemulsion typically refers to a homogeneous and stable microemulsion, meaning that the water contained within it will not separate later, such as during the pumping of the solution. Any phase separation during processing alters the organic phase:water ratio (O / A ratio), which needs to be avoided.

[0094] It appears that a clear emulsion can be obtained for up to 60% of all saponification levels, particularly with Ionquest® 290; while for Cyanex® 272, the saponification level window is limited to 20% or less. This is presumably due to the difference in purity between these commercial products, which are 98% and 85% respectively.

[0095] Due to the risk of gel formation (which is undesirable in industrial processes), a saponification level higher than 60% is not recommended.

[0096] During saponification, excess water can form a separate phase. This does not alter the stability of the microemulsion itself. However, this aqueous phase needs to be separated from the microemulsion before use. For both compounds mentioned above, Cyanex can be used at a low saponification level of up to 20%. ® Beyond 272, this phase will always form, therefore it is preferable to use Cyanex at a low saponification level of at most 20%. ® 272.

[0097] Example 2

[0098] This example illustrates the use of 30% Cyanex by volume. ® Solvent extraction steps for 272 and 70% (v / v) Escaid 110. The solvent was pre-saponified with LiOH solution. The target solvent capacity was 10 g / L Mn, corresponding to a saponification level of 42.5%. For this purpose, 116 mL of 75 g / L LiOH solution was added per liter of organic solvent. To obtain a clear microemulsion, the diluted solvent and LiOH solution were mixed at 25°C for approximately 15 minutes.

[0099] The extraction was performed in six steps. In each step, the aqueous phase from the previous step was mixed with an equal volume of fresh saponified organic phase at an O / A ratio of 1. Therefore, a total of 702 mL of LiOH solution was added during the extraction process, resulting in a total raffinate volume of 1.70 L. The aqueous phase and microemulsion were stirred at 40 °C for 5 minutes to ensure equilibrium.

[0100] In the first five steps, the Li in the organic extractant is depleted: this leads to a slight decrease in pH and automatic termination of the extraction process. However, in the sixth step, the Mn in the aqueous phase is depleted. The pH remains at its nominal value of approximately 4.6.

[0101] In Table 2, the initial (first) aqueous phase is labeled "Feed" and the second aqueous phase is labeled "Raffinate". The feed originates from a pretreatment process that includes the bulk removal of Ni and Co (in sulfate form) and hydrolysis / neutralization. For use according to the invention, the feed is neutralized, for example, with LiOH, Li₂CO₃, Ca(OH)₂, or CaCO₃, but avoiding NaOH. The reported pH is the pH after this neutralization.

[0102] Table 2: Metal composition of feed and raffinate solutions before and after the six extraction steps using an organic phase containing 30% by volume of 42.5% saponified Cyanex-272.

[0103]

[0104] This example demonstrates excellent yields exceeding 99% for the extraction of Co and Mn. However, due to the selected working pH of approximately 4.5, which is not particularly suitable for Ni extraction, Ni exhibited a lower yield. This example also confirms that the pH of the aqueous phase remained exceptionally stable at approximately 4.5 during extraction. This characteristic is attributed to an ion exchange mechanism between the metals, specifically, in this example, an ion exchange mechanism between Mn and Li. This contrasts with the need for continuous neutralization when the extractant is used in its acidic form.

[0105] If higher Ni is required, the same extractant can be used at a slightly higher pH (such as 5.0 to 5.5).

Claims

1. A method for separating metals by solvent extraction, the method comprising the steps of: A first aqueous phase is provided, which comprises an acidic aqueous solution containing Li, further comprising one or more of Ni, Mn and Co; A first organic phase is provided, which comprises an organic extractant in acidic form, and a diluent; by mixing said first organic phase with an aqueous solution containing LiOH, thereby obtaining a second organic phase; Under conditions suitable for solvent extraction, the first aqueous phase is mixed with the second organic phase to obtain a third organic phase containing one or more of the major components of Ni, Mn, and Co, and a second aqueous phase containing the major component of Li; and, Separate the third organic phase from the second aqueous phase; In the saponification step, the first organic phase is mixed with an aqueous solution containing LiOH in the presence of an organic extractant based on an organophosphorus acid, until a saponification level of at least 1% and at most 60% is reached and a homogeneous phase containing a clear and transparent microemulsion is obtained.

2. The method according to claim 1, wherein the microemulsion has a dispersion droplet size of about 400 to about 800 nm.

3. The method according to claim 1 or 2, wherein the first organic phase further comprises a modifier.

4. The method according to any one of claims 1 to 3, wherein the first organic phase further comprises a modifier, said modifier being a phosphine oxide compound, particularly an organophosphine oxide compound.

5. The method according to any one of claims 1 to 3, wherein the first organic phase further comprises more than 5% of a phosphine oxide compound, particularly an organophosphine oxide compound, as a modifier.

6. The method according to any one of claims 1 to 5, wherein the organic extractant comprises an organic phosphonic acid, particularly an organic phosphonic acid according to the formula bis(2,4,4-trimethylpentyl)phosphonic acid.

7. The method according to any one of claims 1 to 6, wherein the saponification step is carried out using an aqueous solution containing LiOH at a concentration of 90 to 120 g / L, preferably 100 to 110 g / L and / or a relative amount of 1 vol% to 5 vol%, preferably 2 vol% to 4 vol%.

8. The method according to any one of claims 1 to 7, wherein the microemulsion is free of Na.

9. The method according to any one of claims 1 to 8, wherein the organic extractant contains more than 95% by weight of an organic phosphonic acid, and wherein the saponification level is 60% or less and at least 1%.

10. The method according to any one of claims 1 to 8, wherein the organic extractant contains less than 90 mol% of an organic phosphonic acid, and wherein the saponification level is 20% or less and at least 1%.

11. The method according to any one of claims 1 to 10, wherein the microemulsion comprises 1 to 10% by volume of water.

12. The method according to any one of claims 1 to 11, wherein the cumulative concentrations of Ni, Co and Mn in the first aqueous phase are less than 130 g / L.

13. The method according to any one of claims 1 to 12, wherein the concentration of Li in the first aqueous phase is in the range of 0.1 to 35 g / L.

14. The method according to any one of claims 1 to 13, wherein the first aqueous phase is obtained by acid leaching of a Li-ion battery or its waste.

15. The method according to any one of claims 1 to 14, further comprising the step of: One or more of Ni, Mn, and Co are recovered from the third organic phase by back-extraction with an acidic aqueous solution, thereby obtaining a metal-containing aqueous phase and a metal-depleted organic phase.

16. The method according to any one of claims 1 to 15, further comprising the step of: The second aqueous phase is subjected to electrodialysis to obtain an acidic aqueous solution and an aqueous solution containing LiOH.

17. The method of claim 16, wherein the acidic aqueous solution is used in the step of recovering one or more of Ni, Mn and Co according to claim 15.

18. The method of claim 16, wherein the aqueous solution containing LiOH is used in the saponification step of claim 1.

19. The method for separating metals by solvent extraction according to one or more of claims 1 to 18, the method comprising the steps of: A first aqueous phase is provided, the first aqueous phase comprising an acidic aqueous solution containing Li, and further comprising one or more of Ni, Mn and Co; A first organic phase is provided, the first organic phase comprising an organic extractant in an acidic form and a diluent; The organic extractant is partially saponified by mixing the first organic phase with an aqueous solution containing LiOH, thereby obtaining the second organic phase; Under conditions suitable for solvent extraction, the first aqueous phase is mixed with the second organic phase to obtain a third organic phase containing one or more of the major components of Ni, Mn, and Co, and a second aqueous phase containing the major component of Li; and, Separate the third organic phase from the second aqueous phase; In the saponification step, the first organic phase is mixed with an aqueous solution containing LiOH in an organic extractant containing more than 5% phosphine oxide, particularly an organic phosphine oxide, until a saponification degree of at least 1% and at most 20% is achieved and a homogeneous phase containing a clear and transparent microemulsion is obtained.

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