Recovery of key elements from spent lithium-ion batteries using supported membrane solvent extraction

Abstract

Single-stage and multi-stage systems and methods are provided for recovering key elements from lithium ion batteries in substantially pure form. The systems and methods include supported membrane solvent extraction using a permeable hollow fiber with an immobilized organic phase within the pores of the fiber. The permeable hollow fiber is in contact with a feed solution on one side and a stripping solution on the other side to provide simultaneous extraction and stripping of elements from a dissolved lithium ion cathode material while rejecting other elements from the feed solution. The single- and multi-stage systems and methods can selectively recover cobalt, manganese, nickel, lithium, aluminum, and other elements from used battery cathodes and are not limited by equilibrium constraints compared to traditional solvent extraction processes.

Description

[0001] This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention. TECHNICAL FIELD

[0002] The present invention relates to the recovery of key elements from spent lithium ion batteries in their pure form, and in particular, the recovery and separation of cobalt, nickel, manganese, lithium and / or other elements using supported liquid membrane solvent extraction. BACKGROUND

[0003] In recent years, lithium ion batteries have gained worldwide attention due to their widespread use in portable electronic products and electric vehicles. Lithium ion batteries are smaller, lighter, have no memory effect, and provide more energy per unit volume than conventional nickel-cadmium (Ni-Cd) or nickel-metal hydride (NiMH) batteries.

[0004] Cobalt is considered a critical material and is used in large and increasing amounts in lithium ion batteries. Currently, the world's land-based cobalt resources are estimated to be about 25 million tons. The richest sources of cobalt are primarily in the Democratic Republic of Congo. Cobalt mining is done in the Congo, which currently supplies 54% of the world's cobalt demand, while China, Russia, and Australia each contribute about 5% of the world's cobalt demand. 30% of the current cobalt supply is consumed by the lithium ion battery industry. Therefore, lithium ion batteries are considered an important secondary resource for cobalt extraction and recovery. Further, the presence of metal contaminants in waste generated from used lithium ion batteries can adversely affect the environment.

[0005] Conventional solvent extraction methods have been used commercially to recover cobalt from primary, secondary, and spent battery cathode materials. However, conventional processes have limitations such as high solvent inventory, emulsion formation, and multi-step operations including stripping and washing. A non-dispersive solvent extraction method using supported liquid membranes with known extractants such as Cyanex 272 and Cyanex 301 has been proposed for the separation of cobalt in the presence of nickel and manganese. Swain et al. (Chemical Engineering Journal, 2015. 271, p. 61-70) investigated the separation of cobalt by supported hollow fiber and flat sheet liquid membrane solvent extraction using Cyanex 272 as the extractant. The feed solution used in this study was a salt of cobalt and lithium dissolved in sulfuric acid, such as cobalt sulfate and lithium sulfate. However, the chemistry of cobalt in lithium ion batteries is much more complex than divalent cobalt salts.

[0006] Accordingly, there remains a need for improved methods and systems for the recovery of cobalt and other elements from lithium ion batteries using supported liquid membrane solvent extraction. In particular, there remains a need for improved methods and systems for the selective recovery of constituent elements in substantially pure form from LiCo02and LiNiCoMn02(nickel-manganese-cobalt or NMC) cathodes in spent lithium ion batteries. SUMMARY

[0007] A method and system for the recovery of elements in substantially pure form from lithium ion batteries is provided. The method and system includes supported membrane solvent extraction using an organic phase immobilized within the pores of permeable hollow fibers for the selective extraction of elements from a feed solution having a regulated pH. The permeable hollow fibers are contacted on one side with an aqueous feed solution and on the other side with a stripping solution to provide simultaneous extraction and stripping of elements from a dissolved lithium ion cathode material while rejecting other elements from the feed solution.

[0008] In one embodiment, the method includes wetting the pores of a plurality of hollow fibers with an organic phase having a cationic liquid extractant and an organic solvent. The method then includes moving an aqueous feed solution along one side of the hollow fibers, the aqueous feed solution including a dissolved cobalt-containing battery material, such as LiCo02or LiNiCoMn02. The method includes simultaneously moving a stripping solution along the other side of the hollow fibers, the aqueous feed solution being pressurized (about 2 psig) relative to the stripping solution such that the ionic liquid extractant in the pores of the plurality of hollow fibers continuously extracts Co(II) from the aqueous feed solution for recovery by the stripping solution.

[0009] In another embodiment, the system includes a membrane module, a feed reservoir, and a stripping reservoir. The membrane module includes a plurality of hollow fibers, and the pores of the hollow fibers are wetted (pre-impregnated) with an immobilized organic phase. The feed reservoir and the stripping reservoir include an aqueous feed solution and a stripping solution, respectively, which are passed through the membrane module in continuous recirculation. The aqueous feed solution is directed along the lumen side of the hollow fibers, and the stripping solution is directed along the shell side of the hollow fibers, optionally in a cross-flow direction. In other embodiments, the aqueous feed solution is directed along the shell side of the hollow fibers and the stripping solution is directed along the lumen side of the hollow fibers. The aqueous feed solution includes a cobalt-containing battery material, and is pressurized relative to the stripping solution. The organic phase within the pores of the hollow fibers includes an organic solvent and a cationic extractant, such as Cyanex 272 or Cyanex 301, selected to continuously extract cobalt (e.g., Co(II)) from the aqueous feed solution for recovery by the stripping solution.

[0010] The methods and systems of the present invention can facilitate the simultaneous stripping and stripping of cobalt and other elements from lithium-ion cathode materials using an organic phase immobilized within the pores of hollow fibers. For example, the multi-stage systems discussed herein can selectively recover cobalt, manganese, nickel, and lithium from used battery cathodes. In comparison to traditional solvent extraction processes, the systems and methods discussed herein are not limited by equilibrium constraints. The present inventors have demonstrated in laboratory examples a non-dispersive solvent extraction method using supported liquid membranes with cationic extractants to recover key elements in substantially pure form, and including a pre-treatment of the cathode and anode prior to the supported membrane solvent extraction.

[0011] These and other features and advantages of the present invention will become apparent from the following description of the invention, when viewed in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Illustration of a membrane module according to the systems and methods of the present invention.

[0013] Figure 2 Illustration of a single-stage system including a membrane module Figure 1 .

[0014] Figure 3 Illustration of a two-stage system including a membrane module Figure 1 .

[0015] Figure 4 Illustration of a three-stage system including a pre-treatment process and a membrane solvent extraction process including a membrane module Figure 1 .

[0016] Figure 5 Illustration of a three-stage system including a membrane module Figure 1 .

[0017] Figures 6(A)-6(E) illustrate Co recovery from LiCoO2for Example 1. Figure 6(A) depicts the concentration of the feed solution; Figure 6(B) depicts the concentration of the stripping solution; Figure 6(C) depicts the purity (%) of Co in the feed and stripping; Figure 6(D) depicts Co recovery over time; and Figure 6(E) depicts Co extraction rate over time.

[0018] Figures 7(A)-7(E) illustrate Co recovery from LiCoO2at higher initial concentrations of Co than depicted in Figures 6(A)-6(E) for Example 2. Figure 7(A) depicts the concentration of the feed solution; Figure 7(B) depicts the concentration of the stripping solution; Figure 7(C) depicts the purity (%) of Co in the feed and stripping; Figure 7(D) depicts Co recovery over time; and Figure 7(E) depicts Co extraction rate over time.

[0019] FIGS. 8(A)-8(E) illustrate the first stage recovery of Co from NMC for Example 3. FIG. 8(A) depicts the concentration of the feed solution; FIG. 8(B) depicts the concentration of the stripping solution; FIG. 8(C) depicts the purity of Co in the feed and stripping (%); FIG. 8(D) depicts the recovery of Co over time; and FIG. 8(E) depicts the extraction of Co over time.

[0020] FIGS. 9(A)-9(E) illustrate the second stage recovery of Co from NMC for Example 3. FIG. 9(A) depicts the concentration of the feed solution; FIG. 9(B) depicts the concentration of the stripping solution; FIG. 9(C) depicts the purity of Co in the feed and stripping (%); FIG. 9(D) depicts the extraction of Co; and FIG. 9(E) depicts the extraction of Co over time.

[0021] FIGS. 10(A)-10(E) illustrate the first stage separation of Co and Mn from Ni and Li for Example 4. FIG. 10(A) depicts the stripping solution concentration over time; FIG. 10(B) depicts the feed solution concentration over time; FIG. 10(C) depicts the Co purity in the feed and stripping solutions over time (%); FIG. 10(D) depicts the recovery of Co over time; and FIG. 10(E) depicts the extraction of Co over time.

[0022] FIGS. 11(A)-11(E) illustrate the second stage separation of Co from Mn for Example 4. FIG. 11(A) depicts the stripping solution concentration over time; FIG. 11(B) depicts the feed solution concentration over time; FIG. 11(C) depicts the Co purity in the feed and stripping solutions over time (%); FIG. 11(D) depicts the recovery of Co over time; and FIG. 11(E) depicts the extraction of Co over time.

[0023] FIGS. 12(A)-12(E) illustrate the third stage separation of Ni from Li for Example 4. FIG. 12(A) depicts the stripping solution concentration over time; FIG. 12(B) depicts the feed solution concentration over time; FIG. 12(C) depicts the Ni purity in the feed and stripping solutions over time (%); FIG. 12(D) depicts the recovery of Ni over time; and FIG. 12(E) depicts the extraction of Ni over time.

[0024] Figure 13 Scanning electron microscope (SEM) images of cobalt oxide separated from cathode material in Example 4.

[0025] Figure 14 Energy dispersive x-ray spectroscopy (EDS) of cobalt oxide separated from cathode material in Example 4.

[0026] Figure 15This includes X-ray diffraction (XRD) of cobalt oxide isolated from the cathode material in Example 4. Detailed Implementation

[0027] The inventions considered and disclosed herein include methods and systems for recovering constituent elements from lithium-ion batteries via membrane-assisted solvent extraction. Generally, the method includes the following steps for single-stage or multi-stage extraction of one or more constituent elements: a) providing a membrane module comprising a plurality of porous hollow fibers; b) wetting the plurality of porous hollow fibers with an organic phase comprising a cationic extractant and an organic solvent; c) applying a continuous flow rate of an acidic aqueous feed solution of a predetermined pH along the lumen side or shell side of the plurality of porous hollow fibers; and d) applying a continuous flow rate of an acidic back-extraction solution of a predetermined pH along another lumen side or shell side of the plurality of porous hollow fibers. The step of wetting the plurality of porous hollow fibers (step (b)) is performed prior to the steps of applying the feed solution flow rate and the back-extraction solution flow rate (steps (c) and (d)). The steps of applying the feed solution flow rate and the back-extraction solution flow rate are generally simultaneous. These steps are discussed below in conjunction with single-stage separation (Part I) and multi-stage separation (Part II).

[0028] I. Single stage separation

[0029] Membrane modules typically include a plurality of hollow or tubular fibers extending between opposing tube sheets. As an illustration, a membrane module containing fiber bundles, such as... Figure 1 As shown and typically designated as 10, membrane module 10 includes a housing 12, which includes a feed inlet port 14, a feed outlet port 16, a back-extraction inlet port 18, and a back-extraction outlet port 20. A suitable membrane module may include a membrane module area of ​​1.4 m². 2 Hydrophobic polypropylene membrane modules (Membrana GmbH) Or Membrana-Charlotte, LLC Multiple hollow fibers 22 are fitted at their opposite ends to first and second tube sheets 24, 26, such that the fibers 22 extend in a common direction. Each fiber 22 includes a lumen side 28 and a shell side 30. The lumen side 28 is... Figure 1 In the diagram, it is shown as exposed to the feed solution; however, in other embodiments, the lumen side 28 is exposed to the back-extraction solution. Similarly, the shell side 30 is... Figure 1The lumen side is exposed to the stripping solution in FIG. 1, however in other embodiments the shell side 30 is exposed to the feed solution. As used herein, the "lumen side" includes the inner surface defining a passage extending longitudinally through the length of the hollow fiber, while the "shell side" includes the outer surface of the fiber, such that the lumen side and the shell side are separated from one another by the thickness of the membrane sidewall. The side in contact with the feed solution is defined as the "feed interface," and the side in contact with the stripping solution is defined as the "stripping interface." The lumen side is the feed interface in some embodiments, and the stripping interface in other embodiments. Similarly, the shell side is the stripping interface in some embodiments, and the feed interface in other embodiments.

[0030] The hollow fibers 22 are porous to hold the organic phase therein, and are formed of a material capable of withstanding the acidic conditions in the feed solution and the stripping solution. The hollow fibers 22 can be formed of a hydrophobic material, which assists in preventing the fibers from being wetted by the aqueous feed solution, and also prevents the organic phase from migrating into the stripping solution. The hydrophobic material can include, for example, polypropylene, polyethylene, polyvinylidene fluoride, polyether ether ketone, polysulfone, or polyethersulfone. The pore size is selected such that the organic phase containing the extractant does not migrate due to contact with the pressurized feed solution at a pressure of about 2 psi greater than the pressure on the stripping side of the fiber, optionally less than 5 psi greater than the pressure of the stripping solution. In some embodiments, the hollow fibers include an average pore size of less than 0.1 microns, while in other embodiments the average pore size is between 0.01 microns and 0.1 microns, inclusively. The hollow fibers include an average inner diameter of between 0.1 mm and 1.0 mm, inclusively, further optionally between 0.2 mm and 0.3 mm, inclusively. The hollow fibers include an average outer diameter of between 0.1 mm and 1.0 mm, inclusively, further optionally between 0.6 mm and 0.7 mm, inclusively. The hollow fibers have an average sidewall thickness of between 0.01 mm and 0.1 mm, inclusively, further optionally between 0.02 mm and 0.03 mm, inclusively.

[0031] Wetting the plurality of porous fibers with the organic phase generally includes directing the organic phase through the feed input port 14 for a predetermined period of time (e.g., 1 hour) to saturate the fibers with the organic phase. Flow of the organic phase is stopped after a sufficient period of time to produce immobilized organic phase within the pores of the plurality of fibers. After wetting, distilled water is circulated through both input ports 14, 18 to flush excess organic phase from the membrane module 10. The immobilized organic phase includes a cationic extractant (discussed below) and an organic solvent. The organic solvent includes a synthetic isoparaffin solvent, such as Isopar-L (Exxon Mobile Corporation). Other immobilized organic phases can be used in other embodiments if desired. Optionally, the immobilized organic phase includes tri-butyl phosphate (TBP), however TBP is not required and in some embodiments the immobilized organic phase is free of TBP. This is because TBP is conventionally used in solvent extraction processes to prevent the formation of a third phase, which is the separation of the organic phase into two liquids, as observed in an emulsion. The third phase is generally attributed to limited solubility of the extractant in the organic diluent and high acid strength used in the feed and stripping solutions. There is no third phase formation in the present membrane solvent extraction process because the amount of organic phase that is embedded in each pore of the hollow fiber membrane is very low. Additionally, dilute acid solutions are used in the membrane solvent extraction process, which prevents emulsion formation. Thus, the organic phase does not necessarily include TBP and in many embodiments TBP is not used.

[0032] When used in accordance with the systems and methods described herein, the extractant can be selected to recover certain elements while rejecting others. For example, the extractant can include bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272, Cytec Inc.) or methylpentyl dithiophosphinic acid (Cyanex 301, Cytec Inc.). The extractant can include Cyanex 272 to extract Co and Mn while substantially rejecting Ni and Li from a feed solution having a pH between 4.0-6.0, inclusive, further optionally 5.0-6.0, inclusive. By way of further example, the extractant can include Cyanex 272 to extract Co while substantially rejecting Li from a feed solution having a pH between 5.0-6.0, inclusive, more specifically about 5.9. By way of further example, the extractant can include Cyanex 272 to extract Ni while substantially rejecting Li from a feed solution having a pH between 6.0-7.5, inclusive, more specifically 6.0-6.5, inclusive. By way of further example, the extractant can include Cyanex 301 to extract Co while substantially rejecting Mn from a feed solution having a pH of 1.5 or less. By way of further example, the extractant can include Cyanex 301 to extract Co and Ni while substantially rejecting Li from a feed solution having a pH between 1.0-3.0, inclusive. An acetate buffer, such as sodium acetate, is added during the extraction process to maintain high extraction rates by controlling the decrease in pH in the feed solution. As used herein, "substantially rejecting" means that the molar concentration of the rejected element (moles per liter of solution) in the receiving solution is less than 1% of the molar concentration of the rejected element (moles per liter of solution) in the donor solution after 1 hour of membrane solvent extraction, unless otherwise specified.

[0033] Directing a continuous flow rate of an acidic aqueous feed solution along the lumen side or shell side of the plurality of porous hollow fibers includes directing the acidic aqueous feed solution through the feed input port 14. The acidic aqueous feed solution includes a cathode material dissolved from a post-consumer lithium ion battery, such as LiCo02cathode material and LiNiCoMn02(NMC) cathode material. The pH of the feed solution is selected based on the extractant. For Cyanex 272, the pH of the feed solution can be 5.5-6.0, inclusive, which can be achieved by dissolving the cathode material in 0.2-4 M H2S04and up to 5 vol% H202as a reducing agent to convert Co(III) to Co(II), which is more soluble than Co(III). For Cyanex 301, the pH of the feed solution can be 1.2-3.0, inclusive, which can be achieved by dissolving the cathode material in 0.2-4 M H2S04and up to 5 vol% H202as a reducing agent to convert Co(III) to Co(II). An acetate buffer, such as sodium acetate, is added to maintain a high extraction rate by setting the initial pH of the feed solution, which is adjusted to be within a predetermined range by intermittent addition of the buffer (e.g., sodium acetate) and / or base (e.g., ammonium hydroxide) during the membrane solvent extraction. The feed solution can alternatively include the cathode material dissolved in HN03or HC1 at a desired molar concentration. As Figure 1 shown, the feed solution can be directed through the module 10 along the lumen side 28 of each of the plurality of porous hollow fibers 22. Alternatively, the feed solution can be directed through the module 10 along the shell side 30 of each of the plurality of fibers 22.

[0034] Directing a continuous flow rate of an acidic aqueous stripping solution along the lumen side or shell side of the plurality of permeable fibers for stripping includes directing the stripping solution through the stripping input port. The stripping solution is suitable for stripping Co(II) or other constituent elements from the feed interface to the stripping interface. The stripping solution can include, for example, H2S04, HN03, or HC1 at a higher molar concentration than the feed solution. That is, a concentration gradient, and thus a chemical potential gradient, is generally formed between the feed solution and the stripping solution. As shown above, Figure 1 the stripping solution is directed through the module 10 along the shell side 30 of each of the plurality of fibers 22, optionally in a direction generally transverse to the flow of the feed solution within the fibers 22. Alternatively, the stripping solution can be directed through the interior of the hollow fibers 22 to contact the lumen side 28 thereof.

[0035] To further illustrate the circulation of the feed solution and the stripping solution, Figure 2A system for membrane assisted solvent extraction is illustrated in FIG. 4 and generally designated 40. System 40 includes a feed reservoir 42, a strip solution reservoir 44, membrane module 10, a feed line 46, a feed return line 48, a strip line 50, and a strip return line 52. The feed solution is contained within feed reservoir 42 and is kept in constant agitation with a mechanical stirrer to ensure uniform concentration. Feed line 46 includes a pump 54, such as a peristaltic pump, to ensure that the feed line pressure is slightly greater than the strip line pressure. In some applications, the feed can be pressurized up to and including 2 psig, optionally less than 5 psig, while the strip can be kept at atmospheric pressure. Strip line 50 also includes a pump 56, such as a peristaltic pump, to ensure continuous flow of the strip solution through module 10. The feed solution and the strip solution are in continuous recirculation. However, in other embodiments, the feed line and / or the strip line form an open circuit.

[0036] The method can further include filtering, drying, and / or annealing the strip solution to recover high purity cobalt. For example, the strip solution can be precipitated out with oxalic acid or ammonium hydroxide, then filtered, dried at room temperature, and annealed. The optional annealing characteristics can include 750 °C for two hours. However, the steps of filtering, drying, and annealing the strip solution are optional and can be replaced or modified as needed depending on the intended use of the recovered cobalt. The strip solution can alternatively be recovered through support membrane solvent extraction module 10 or a second support membrane solvent extraction module.

[0037] II. Multi-stage separation

[0038] A two-stage system for cobalt recovery is illustrated in FIG. 5 and generally designated 60. System 60 includes a feed reservoir 62, a strip solution reservoir 64, membrane module 10, a feed line 66, a feed return line 68, a strip line 70, and a strip return line 72. The feed solution is contained within feed reservoir 62 and is kept in constant agitation with a mechanical stirrer to ensure uniform concentration. Feed line 66 includes a pump 74, such as a peristaltic pump, to ensure that the feed line pressure is slightly greater than the strip line pressure. In some applications, the feed can be pressurized up to and including 2 psig, optionally less than 5 psig, while the strip can be kept at atmospheric pressure. Strip line 70 also includes a pump 76, such as a peristaltic pump, to ensure continuous flow of the strip solution through module 10. The feed solution and the strip solution are in continuous recirculation. However, in other embodiments, the feed line and / or the strip line form an open circuit. Figure 3As shown and typically designated 60. In this system, a first-stage recovery of Co and Mn is performed using a first membrane module 10, and a second-stage recovery of Co is performed using a second membrane module 10'. The first-stage recovery includes a first feed reservoir 62, a first membrane module 10, a feed pump 64, a back-extraction pump 66, and a first back-extraction reservoir 68. The second-stage recovery includes a second feed reservoir 70, a second membrane module 10', a feed pump 72, a back-extraction pump 74, and a second back-extraction reservoir 76. The first membrane module 10 includes hollow fibers pre-impregnated with a first fixed organic phase adapted to recover Co and Mn (e.g., Cyanex 272) from dissolved NMC cathode material. The second membrane module 10' includes a second fixed organic phase adapted to recover Co from a second feed solution containing Co and Mn from the first back-extraction solution. More specifically, the first membrane module 10 includes a stationary organic phase comprising Cyanex 272 in Isopar-L, while the second membrane module 10' includes a stationary organic phase comprising Cyanex 301 in Isapar-L. In the current embodiment, the pH of the first feed solution is between 5.5 and 6.0, and the pH of the second feed solution is optionally adjusted to about 2.0 with ammonium hydroxide.

[0039] A three-stage method for recovering and separating Li, Ni, Co, and Mn from used cathode materials, such as... Figure 4 As shown, the method includes a pretreatment process 100 and a multi-stage membrane solvent extraction process 102. The used cathode material 104 in this embodiment comprises an active material and an aluminum support. The active material generally contains Li, Ni, Co, and Mn in fine powder form. The fine powder is aggregated using a polyvinylidene fluoride (PVDF) binder and a carbon raiser. The cathode material is then pressed together onto an Al support and subsequently incorporated into a lithium-ion battery. Although not shown, this method can also be used to recover copper (Cu) from the battery anode, which generally comprises the active material on a copper support. Additionally, Cu and Al present in the cathode material can also be separated and recovered using supported membrane solvent extraction with extractants such as ACORGAM 5640 and Cyanex 801.

[0040] To first remove the PVDF binder and carbonizer, the cathode plate undergoes heat treatment 106, acid dissolution 108, and vacuum filtration 110. The cathode plate is heated in an inert atmosphere to a temperature above 500°C to decompose the PVDF, allowing for easy removal of the cathode material from the Al support. Additionally, the carbon black present in the cathode material to increase the conductivity of the oxide cathode undergoes a redox reaction with the active cathode material at approximately 550°C. This results in partial reduction of the transition metals present in the cathode powder, thereby reducing the amount of H₂O₂ required during acid dissolution 108. Since the melting point of Al is approximately 650°C, the heat treatment 106 includes a temperature range between 550°C and 650°C (inclusive) (as used in this disclosure, "inclusive" includes both the lower and upper limits). More specifically, the cathode plate is heated in a nitrogen atmosphere to 570°C by gradually increasing the temperature at a rate of 10°C / min, held at 570°C for 25 minutes, and then gradually reduced to room temperature. The cathode plate is then washed with water to separate the Al support from the cathode powder. After the cathode powder is dissolved in acid, vacuum filtration 110 is used to remove the carbon raiser present in the cathode material.

[0041] Multi-stage membrane solvent extraction process 102 Figure 5 As shown, the process includes a first-stage separation of Co and Mn from Li and Ni, a second-stage separation of Co and Mn, and a third-stage separation of Ni and Li. The first-stage separation includes a first feed reservoir 112, a first membrane module 114, and a first back-extraction reservoir 116. The first feed reservoir 112 includes a feed solution comprising cathode material 104 dissolved in a strong acid (e.g., H2SO4) and a reducing agent such as up to 5% by volume of H2O2 from the pretreatment process 100. The feed solution has a pH stable between 4.0 and 6.0 (inclusive) and includes an acetate buffer, such as a sodium acetate buffer solution. The first membrane module 114 comprises hollow fibers pre-impregnated with a first fixed organic phase comprising a cationic extractant (e.g., 1M Cyanex 272) and an organic solvent (e.g., Isopar-L). The organic phase may include 33 vol% Cyanex 272, 5 vol% TBP, and the balance Isopar-L; however, TBP may be omitted without affecting the separation and recovery in the first stage. For back-extraction, the first back-extraction reservoir 116 comprises a strong acid, such as 0.75 M H₂SO₄, which continuously flows through the first membrane module 114. Due to H₂... + The transfer of ions from the back-extraction solution causes a decrease in the pH of the feed solution, which is mitigated by intermittent addition of a buffer (e.g., sodium acetate) and / or a base (e.g., ammonium hydroxide) to adjust the pH of the feed solution to between 4.0 and 6.0 (inclusive), and optionally further to 5.5. The concentrations of Co and Mn in the back-extraction solution increase over time, while the transfer of Li and Ni is negligible.

[0042] The second stage separation includes a second feed reservoir 118, a second membrane module 120, and a second stripping reservoir 122. The second feed reservoir 118 includes a second feed solution having Co and Mn concentrations recovered from the first stripping reservoir 116. The second membrane module 120 includes a second immobilized organic phase adapted to recover Co from the second feed solution while substantially rejecting Mn. The pH of the feed solution is stabilized at 1.5 or less, such as 1.2, with the addition of a buffer (such as sodium acetate) and / or a base (such as ammonium hydroxide). The second membrane module 120 includes hollow fibers pre-impregnated with the second immobilized organic phase, which includes a cationic extractant (such as 1 M Cyanex 301) and an organic solvent (such as Isopar-L). The second stripping reservoir 122 includes a strong acid, such as 1 M H2SO4, which is continuously moved through the second membrane module 120 to strip Co from the organic phase. The Co concentration in the stripping solution increases over time, with negligible transfer of Mn.

[0043] The third stage separation includes a third feed reservoir 124, a third membrane module 126, and a third stripping reservoir 130. The third feed reservoir 124 includes a third feed solution having Li and Ni concentrations recovered from the first feed reservoir 112. The third membrane module 126 includes a third immobilized organic phase adapted to recover Ni from the first feed solution while substantially rejecting Li. The pH of the feed solution is stabilized between 6.0-6.5 with the addition of a buffer (such as sodium acetate) and / or a base (such as ammonium hydroxide). The third membrane module 126 includes hollow fibers pre-impregnated with the third immobilized organic phase, which includes a cationic extractant (such as 1 M Cyanex 272) and an organic solvent (such as Isopar-L). The third stripping reservoir 130 includes a strong acid, such as 0.75 M H2SO4, which is continuously moved through the third membrane module 126 to strip Ni from the organic phase. The Ni concentration in the stripping solution increases over time, with negligible transfer of Li.

[0044] Accordingly, the method and system provide recovery and separation of substantially pure cobalt, manganese, nickel, and lithium as part of a continuous and scalable recovery process. The method and system can overcome removal limitations caused by equilibrium effects and can recover key elements in highly pure form, as shown in the following examples, which are intended to be non-limiting.

[0045] Example 1

[0046] In one embodiment, an aqueous feed solution was prepared by dissolving 10 gm LiCo02(Li = 663.86 ppm; Co = 5826.06 ppm) in 750 mL of 0.2 M H2S04and 2 vol% H202was used as a reducing agent. A 250 mL of 3 M sodium acetate buffer solution with a pH of 5.2 was used to stabilize the pH of the feed solution and the final feed solution concentration was 10 gm / L of LiCo02. The organic phase was 33 vol% (1 M) Cyanex 272, 5 vol% tri-butyl phosphate (TBP) and the balance Isopar-L. The stripping solution was 1 L of 0.75 M H2S04. The initial pH of the feed was adjusted to 5.02 using ammonium hydroxide. The separation performance of Co is shown in Figures 6(A)-6(E). The Co content in the stripping solution increased with time and the recovery of Co reached 92% while maintaining minimal Li passage into the stripping solution (see Figure 6(B)). Using Cyanex 272 as the extractant in the organic phase contained in the porous membrane support, 99.6 wt% pure Co was recovered from the membrane solvent extraction (see Figure 6(D)). Due to the H + The transfer of ions from the stripping solution, the pH of the feed solution decreased from 5.02 to 4.66. As the Co concentration in the feed solution decreased, the extraction of Co decreased over time (see Figures 6(A), 6(C) and 6(E)).

[0047] Example 2

[0048] In another embodiment, the feed solution included a higher initial concentration of LiCo02. In particular, the feed solution included 20,000 ppm LiCo02(Li = 1486.25 ppm; Co = 11532.325 ppm) dissolved in 0.5 M H2S04and 2.5 vol% H202. The stripping solution included 0.75 M H2S04. To the feed solution was added 250 mL of sodium acetate buffer for pH stabilization. The initial pH of the feed solution was adjusted to 5.5. To prevent the extraction from decreasing over time as the pH decreased, ammonium hydroxide was added intermittently to the feed solution to maintain the pH in the range of 5.5-6.0. The separation performance of Co is shown in Figures 7(A)-7(E). The Co concentration in the stripping solution increased with negligible transfer of Li and the recovery of cobalt reached 91% (see Figures 7(B) and 7(D)). Using Cyanex 272 as the extractant in the organic phase, 99.5 wt% pure Co was recovered from the membrane solvent extraction (see Figure 7(C)).

[0049] Example 3

[0050] In this embodiment, a two-stage membrane solvent extraction process is used to separate and recover Co from NMC. In the first stage ( Figure 3 Module 1), Cyanex 272, was used to separate Co and Mn because it facilitates the selective extraction of Co and Mn within a pH range of 5.5–6.0. ​​In the second stage ( Figure 3 Module 2), Cynex 301 is used to separate Co and Mn at feed pH values ​​below 2.

[0051] NMC with a Ni:Co:Mn ratio of 1:1:1 was used as the feedstock for the membrane solvent extraction process. 20 g / mL of NMC (Li = 1402.89 ppm; Co = 3698.89 ppm; Mn = 3626.08 ppm; Ni = 3630.82 ppm) dissolved in 750 mL of 0.5 M H₂SO₄ and 2 vol% H₂O₂ were used as a reducing agent to remove insoluble Co. 3+ Converted to soluble Co 2+ Valence state. The pH of the feed solution was stabilized using 250 mL of a 3M sodium acetate buffer solution at pH 5.2, resulting in a final feed solution concentration of 20 g / L NMC cathode material. The extractant used in the first stage was 1 M Cyanex 272 in Isopar L. The back-extraction solution used was 1 L of 0.75 M H₂SO₄. The initial pH of the feed solution was adjusted to 5.5 using ammonium hydroxide. The Co and Mn contents in the back-extraction solution increased over time, and Co recovery reached 92% while minimizing the ingress of Ni and completely repelling the non-ingress of Li (see Figure 8(B)). To prevent the extraction rate from decreasing with pH over time, ammonium hydroxide was intermittently added to the feed solution to maintain the pH in the range of 5.0–5.5. The separation and recovery of Co in the first stage are shown in Figures 8(A)–8(E).

[0052] To further purify Co, the final stripping solution obtained in the first stage was used as feed solution for the second stage separation. The pH of the second stage feed solution was adjusted to 1.34 using ammonium hydroxide. The extractant used in this stage was 1 M Cyanex 301 in Isopar-L. The stripping solution used was 1 L of 1 M H2SO4. Cyanex 301 selectively extracted both Co and Ni while minimizing the co-extraction of Mn at feed pH values < 2. However, the concentration of Ni in the feed solution prepared from the stripping solution was negligible. Therefore, the second stage was used to separate and recover Co from the solution of Co and Mn. The Co content in the stripping increased with time and the recovery of Co reached 54% in two hours while keeping the Mn passage into the stripping solution to a minimum. 99.12% pure Co was recovered from the membrane solvent extraction using Cyanex 301 as the extractant in the organic phase contained in the membrane carrier. The feed pH value decreased to 1.04 during the experiment, however, the extraction efficiency of Co was not affected by this change in pH value. The separation performance of Co in this second stage is shown in Figures 9(A)-9(E).

[0053] Example 4

[0054] In this example, substantially pure Ni, Li, Co, and Mn were recovered from a used Chevrolet Volt lithium ion battery using a three stage membrane solvent extraction process. About 60 gm of cathode powder mixed with partially oxidized carbon black was obtained using a heat treatment. A first stage feed solution was prepared by dissolving 40 gm of cathode material in 750 mL of 4 M H2SO4. The insoluble carbon black was separated from the feed solution using vacuum filtration. 2 vol% H2O2 was used as a reducing agent to convert partially reduced Co(III) to soluble Co(II) valence state. The carbonaceous additive present in the cathode material was insoluble in H2SO4. A 250 mL solution of 3 M sodium acetate buffer solution at pH 5.6 was used to stabilize the pH of the feed solution. A feed solution concentration of about 30 gm / L of used cathode material was obtained. The feed solution comprised 1 L of 30,000 ppm used cathode in 4 M H2SO4, 2 vol% H2O2, and 250 mL of 3 M sodium acetate buffer solution. The initial composition of the feed solution comprised Li (1005.0 ppm), Co (3663.9 ppm), Ni (4363.7 ppm), and Mn (9721.2 ppm), with no Al detected. The cationic extractant comprised 1 M Cyanex 272 in Isopar-L. The stripping solution comprised 1 L of 0.75 M H2SO4. The initial pH of the feed solution was adjusted to 4.9 using ammonium hydroxide. To prevent the extraction yield from decreasing over time as the pH decreased, ammonium hydroxide was added intermittently to the feed solution to maintain a pH range of 4.5-5.0, inclusively, during the run. Within this feed pH, Cyanex 272 extracted both Co and Mn while preventing the co-extraction of Ni and Li. The Co and Mn content in the stripping solution increased over time, and the recovery of Co reached 98.4% while preventing the passage of Ni and Li into the stripping solution. The separation and recovery of Co in Stage 1 is shown in FIGS. 10(A)-10(E).

[0055] To further purify Co from Mn, a second stage separation was performed using the final stripping solution from the first stage separation as the feed solution. The pH of the feed solution was adjusted to 1.2 using ammonium hydroxide. The composition of the feed solution for the second stage comprised Co (2853.6 ppm) and Mn (7844.3), with no Li or Ni detected. The decrease in Co and Mn concentration was due to the addition of ammonium hydroxide to the feed solution for pH adjustment. The extractant used in this stage was 1 M Cyanex 301 (50% vol / vol) in Isopar-L. The membrane module area was 1.4 m2, and the flow rate was 0.5 L / min. The feed solution was pumped through the membrane module at a flow rate of 0.5 L / min. The extractant was pumped through the membrane module at a flow rate of 0.5 L / min. The stripping solution was pumped through the membrane module at a flow rate of 0.5 L / min. The pH of the feed solution was adjusted to 1.2 using ammonium hydroxide. The composition of the feed solution for the second stage comprised Co (2853.6 ppm) and Mn (7844.3), with no Li or Ni detected. The decrease in Co and Mn concentration was due to the addition of ammonium hydroxide to the feed solution for pH adjustment. The extractant used in this stage was 1 M Cyanex 301 (50% vol / vol) in Isopar-L. The membrane module area was 1.4 m 2The back-extraction solution used was 1 L of 1M H₂SO₄. Cyanex 301 selectively extracted both Co and Ni while minimizing Mn co-extraction at a feed pH less than 1.5. However, the Ni concentration in the feed solution prepared from the first-stage back-extraction solution was almost zero, indicating that Ni was not extracted from the organic phase. Therefore, a second stage was used to separate and recover Co from the Co and Mn solution. The Co content in the back-extraction increased over time, and the cumulative Co recovery reached 94.3% within 4 hours while preventing Mn from entering the channels of the back-extraction solution. 100% pure Co was recovered from the membrane solvent extraction using Cyanex as the extractant in the organic phase contained in the membrane pores. The feed pH decreased to 1.13 during this experiment. However, the Co extraction rate was unaffected by this pH change. The separation performance of the second stage is shown in Figures 11(A)–11(E).

[0056] To separate Ni and Li present in the first-stage feed solution, a third-stage separation was performed using the same feed solution remaining after the first stage. The pH of the third-stage feed solution was adjusted to 6.3 using ammonium hydroxide. The feed solution composition included Li (744.5 ppm) and Ni (3467.1 ppm), with no detected Co, Mn, or Al. The decrease in Ni and Li concentrations was due to the addition of ammonium hydroxide to the feed solution for pH adjustment. The extractant used in this stage was 1 M Cyanex 272 (50% v / v) in Isopar-L. The back-extraction solution contained 1 L of 0.75 M H₂SO₄. The membrane module area was 1.4 m². 2 Cyanex 272 selectively extracts Ni while minimizing Li co-extraction within a feed pH range of 6.0–6.5. The Ni content in the back-extraction solution increases over time, and the cumulative Ni recovery reaches 89.7% within 6 hours, with minimal Li translocation into the back-extraction solution. Using Cyanex 272 as the extractant in the organic phase contained within the membrane pores, 96.1% of pure Ni is recovered from membrane solvent extraction. During the test run, the feed pH was maintained within the range of 6.0–6.5. The separation performance of the third stage is shown in Figures 12(A)–12(E).

[0057] The recovered cobalt was precipitated with oxalic acid and annealed at 760 °C. The cobalt oxide was then characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Figure 13 The image shows a SEM image of Co3O4 powder. The Co3O4 powder contains rod-shaped particles with a size of 20-40 μm. The EDS spectrum of Co3O4 recovered from the cathode material is shown below. Figure 14The characteristic peaks of Co304were only observed in the EDS spectrum. No peaks of any other constituent elements of the cathode material were observed except for cobalt, strongly suggesting that cobalt was in pure form separate from other constituent elements of the cathode material (Li, Ni, Mn). Finally, Figure 15 X-ray diffraction (XRD) including Co304separated from the cathode material.

[0058] The above description is that of the current embodiments of the application. Various alterations and changes can be made without departing from the spirit and more broad aspects of the application as defined in the appended claims, which are to be interpreted in the light of the patent law principles including but not limited to the doctrine of equivalents. Any reference to claimed or inventive subject matter is not intended to be limiting of the scope of the application, but is to be read as a mere description drawn in language for the prior art basepoint that enables others skilled in the art to make or use the application.

Claims

1. A method for recovering cobalt from a lithium ion battery, the method comprising: dissolving a battery material containing Co, Mn, Ni, and Li in an acid to form a feed solution, the feed solution comprising Co and Li; providing a membrane module comprising a plurality of hollow fibers, the plurality of hollow fibers comprising a porous sidewall defining a lumen side separated from a shell side; wetting the porous sidewall of the plurality of hollow fibers with an organic phase, the organic phase comprising a cationic extractant and an organic solvent, wherein the organic phase is free of tri-butyl phosphate; performing membrane solvent extraction by moving the feed solution along one of the lumen side or the shell side of the plurality of hollow fibers while simultaneously moving a stripping solution along the other of the lumen side or the shell side of the plurality of hollow fibers, the stripping solution comprising a pH less than the pH of the aqueous feed solution; maintaining the pH of the feed solution within a predetermined range of 4.0 to 6.0, inclusive, by intermittently introducing a buffer or a base to the feed solution during membrane solvent extraction; wherein wetting the porous sidewall of the plurality of hollow fibers with the organic phase is performed prior to moving the feed solution and moving the stripping solution, and wherein the cationic extractant in the porous sidewall continuously extracts Co and Mn from the aqueous feed solution for recovery by the stripping solution while substantially rejecting Li and Ni.

2. The method of claim 1, wherein the feed solution comprises a positive pressure differential between 1 psi - 5 psi relative to the stripping solution.

3. The method of claim 1, wherein the feed solution and the stripping solution are moved through the membrane module in continuous recirculation for at least 30 minutes.

4. The method of claim 1, further comprising separating the battery material from a used battery cathode, wherein separating the battery material from a used battery cathode comprises heat treating, acid dissolution, and vacuum filtering the used battery cathode.

5. A method for recovering battery material, the method comprising: dissolving a battery material containing Co, Mn, Li, and Ni in an acid to form a first feed solution, and adjusting the pH of the first feed solution between 4-6, inclusive; providing a first membrane module comprising a first plurality of hollow fibers, the first plurality of hollow fibers each comprising a lumen side and a shell side; wetting the first plurality of hollow fibers with a first organic phase, the first organic phase comprising a first cationic extractant and being free of tri-butyl phosphate; and after wetting the first plurality of hollow fibers, moving an aqueous feed solution along one of the lumen side or the shell side of the plurality of hollow fibers while simultaneously moving a stripping solution along the other of the lumen side or the shell side of the plurality of hollow fibers; wherein the first cationic extractant continuously removes Co and Mn from the aqueous feed solution as a first stage membrane solvent extraction while substantially rejecting Li and Ni, and wherein the stripping solution continuously strips Co and Mn from the first organic phase.

6. The method of claim 5, wherein adjusting the pH of the first feed solution comprises intermittently adding a buffer or a base to maintain the pH between 4-6, inclusive.

7. The method of claim 5, wherein the first feed solution comprises a positive pressure differential between 1 psi and 5 psi relative to the first stripping solution.

8. The method of claim 5, wherein moving the first feed solution and moving the first stripping solution comprises continuously recirculating the first feed solution and the first stripping solution through the first membrane module for at least 1 hour.

9. The method of claim 5, further comprising performing a second stage membrane solvent extraction on the first stripping solution as a second feed solution to recover Co while substantially rejecting Mn, and adjusting the pH of the second feed solution to be less than or equal to 1.

5.

10. The method of claim 9, wherein the second stage membrane solvent extraction comprises: providing a second membrane module comprising a second plurality of hollow fibers, the second plurality of hollow fibers comprising a lumen side and a shell side; wetting the second plurality of hollow fibers with a second organic phase, the second organic phase comprising a second cationic extractant; and moving the second feed solution along one of the lumen side or the shell side of the second plurality of hollow fibers and simultaneously moving a second stripping solution along the other of the lumen side or the shell side of the second plurality of hollow fibers; wherein the second cationic extractant continuously extracts Co from the second feed solution while substantially rejecting Mn, and wherein the third stripping solution continuously strips Co from the second organic phase.

11. The method of claim 9, further comprising subjecting the first solution as a third feed solution to a third stage of membrane solvent extraction to recover Ni while substantially rejecting Li and adjusting the pH of the third feed solution to between 6.0 and 6.5, inclusive.

12. The method of claim 11, wherein the third stage membrane solvent extraction comprises: providing a third membrane module comprising a third plurality of hollow fibers, the third plurality of hollow fibers comprising a lumen side and a shell side; wetting the third plurality of hollow fibers with a third organic phase, the third organic phase comprising a third cationic extractant; and moving the third feed solution along one of the lumen side or the shell side of the third plurality of hollow fibers and simultaneously moving a third stripping solution along the other of the lumen side or the shell side of the third plurality of hollow fibers; wherein the third cationic extractant continuously extracts Ni from the third feed solution while substantially rejecting Li, and wherein the third stripping solution continuously strips Ni from the third organic phase.

13. The method of claim 5, wherein the first plurality of hollow fibers is formed from a hydrophobic material.

14. The method of claim 5, further comprising separating the battery material from a used battery cathode, wherein separating the battery material from the used battery cathode comprises heat treating, acid digesting, and vacuum filtering the used battery cathode.

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