Agents and processes for recycling batteries

Abstract

A deep eutectic solvent for separating a metal from a metal bearing material is disclosed, wherein the deep eutectic solvent is formed from choline chloride and acetic acid. Also disclosed is a process for separating a metal from a metal bearing material, wherein the process includes leaching the metal bearing material with a deep eutectic solvent formed from choline chloride and acetic acid.

Description

AGENTS AND PROCESSES FOR RECYCLING BATTERIESPRIORITY DOCUMENTS

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024901288 titled “AGENTS AND PROCESSES FOR RECYCLING BATTERIES” and fded on 3 May 2024, the contents of which are hereby incorporated by reference in their entirety.TECHNICAL FIELD

[0002] The present disclosure relates generally to agents and processes for separating a metal from a metal bearing material. In a particular form, the present disclosure relates to a deep eutectic solvent, an antisolvent, and a process for separating a metal from a cathode material.BACKGROUND

[0003] With the rapid development of modern society and industry, energy and environmental issues have gradually become one of the important issues affecting social development. The emergence of lithium ion batteries (LIBs) not only alleviates the energy crisis, but also makes up for the time and space constraints of renewable energy such as wind, solar and tidal energy.1In the past 30 years since the 1990s, LIBs have gradually become the pillar of modern energy and occupied a huge market share with their unique advantages of small volume, low weight, long cycle life and high energy density.2In order to reduce CO2 emissions as proposed by the Paris Agreement, the demand for batteries is intended to grow exponentially in the near future. In particular, the potential of applying lithium-ion batteries in electric vehicles and hybrid vehicles has been gradually stimulated. Electric vehicle sales have continued to increase globally since 2011, reaching 16.5 million units globally as of 2021, while an astonishing 6.6 million units were sold in 2021 alone.3The wide application of LIBS in many aspects also leads to the shortage of lithium, cobalt, and other resources. The life of LIBs in electric vehicles is only 5 to 10 years, and the battery life of small electronic products is only about three years.4It is estimated that there will be 11 million tons of scrapped LIBs in the world by 2030. The limited lithium and cobalt reserves will also impact the production of LIBs.5In addition, LIBs contain toxic electrolyte and non-degradable polymers. Disposal of spent LIBs directly in landfill will lead to a series of safety and environmental problems.6Therefore, achieving high levels of battery recycling will have strong benefits for resource sustainability and environmental protection.

[0004] The methods used for spent LIB recovery are mainly divided into pyrometallurgy, hydrometallurgy and direct recycling process. Pyrometallurgical technology is mature and simple to operate, but it faces many challenges in decreasing consumption of fossil fuels, reducing emission ofexhaust, and controlling lithium loss compared with other recovery methods.7 9Direct recycling processes can simplify the recovery steps, reduce recovery cost and reduce discharge of waste gases and wastewater.10However, in the regeneration process, impurities will be inevitably mixed into the recycled materials, resulting in the inability of the regenerated materials to achieve the same performance as the new cathode materials. At the same time, because it does not decompose the cathode materials into metal elements, there are many restrictions on its application after recovery.11The hydrometallurgical method generally includes three steps viz. 1) peeling of untreated cathode material from the spent cathode electrode, 2) leaching of untreated cathode material, and 3) selective extraction of valuable metals. Although hydrometallurgy is one of the most feasible recovery methods because of high metal leaching efficiency, strong corrosive solvents could cause damage to equipment and environment.12 14Organic acids that are expected to replace inorganic acids also need to add additional reducing agents or increase the temperature to accelerate the dissolution of metals.15, 16In this context, deep eutectic solvents (DES), regarded as a new class of green solvents, have been proposed as an efficient reducing agent and leaching agent in LIBs cathode leaching. DESs can provide good leaching ability of metal oxides, while the use of aggressive aqueous media and the emission of toxic and environmentally harmful gases can be avoided and water consumption and discharge of wastewater can potentially be reduced.

[0005] Another challenge in recovering LIBs is the selective separation and recovery of multiple elements in a cathode material. For lithium cobalt oxide (LCO) cathode materials, most publications propose to recover cobalt through chemical precipitation, and synthesise LCO materials by replenishing lithium. However, in this process, the extractant structure is destroyed due to the addition of precipitant and the extractant cannot be reused.17, 18For ternary cathode materials such as lithium nickel manganese cobalt oxides (NCM or NMC), chemical precipitation and solvent extraction methods have been used in combination to achieve separation of valuable metals. However, the extractant used at present is expensive and the separation process is cumbersome, which is not suitable for industrial production.

[0006] Chang et al. proposed to achieve efficient and selective separation of Ni, Mn and Co by adjusting the coordination environment of transition metal complexes in a DES based on choline chloride ( [Ch]Cl) : oxalic acid dihydrate.19However, the oxalic acid dihydrate based DES suffers from high viscosity, which in turn slows down mass transfer rates and presents a serious limitation for an efficient leaching process. During subsequent separation, dimethyl sulfoxide (DMSO) is used as a diluent to reduce the viscosity of DES, but use of the unrecyclable diluent increases the cost of battery recovery. Thus, separation of adjacent transition metals in the periodic table by a simple, efficient and low-cost method still needs further exploration.

[0007] Morina et al. suggested that a DES composed of choline chloride: lactic acid at a molar ratio of 2: 1.25The DES is liquid at room temperature and has a melting temperature well below -70 °C. It wasfound that the DES could leach Li, Mn, Co and Ni and thus could be used to recover valuable metals from spent lithium batteries. However, the DES is found not to be effective in leaching Li. Specifically, a treatment at 100 °C for 5 hours only achieved a leaching efficiency of 75% for Li.

[0008] Ma et al. prepared a choline chloride and L-(+)-tartaric acid (TA) DES at a molar ratio of 1:1 and investigated its application in recycling cathode material LiCoi / iNi i / ?Mn 1 / 3O2.26However, it was noted that the [Ch]Cl / TA with trace amounts of water at room temperature is a highly viscous liquid and, even at 70 °C, the viscosity of the [Ch]Cl / TA with a water content of 1% w / w is high (6840 mPa-s). Such viscosity will slow down mass transfer rates and make it a hurdle for an efficient leaching process.

[0009] There is a need for new or improved agents and processes that can be used to separate and / or recover one or more metals from a metal bearing material, for example spent lithium batteries. Alternatively, or in addition, there is a need for an alternative to known agents and processes that can be used to separate and / or recover one or more metals from a metal bearing material, for example spent lithium batteries.SUMMARY

[0010] According to a first aspect, there is provided a deep eutectic solvent for separating a metal from a metal bearing material, wherein the deep eutectic solvent is formed from choline chloride and acetic acid.

[0011] In some embodiments of the first aspect, the metal bearing material is a cathode material. In some further embodiments, the metal bearing material is a cathode material of an electrochemical device. In some further embodiments, the metal bearing material is a cathode material for an energy storage device, for example a secondary battery. In some further embodiments, the metal bearing material is a cathode material of an ion battery. In some further embodiments, the ion battery is selected from lithium ion batteries and sodium ion batteries.

[0012] In some embodiments of the first aspect, the metal comprises one or more selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In some further embodiments, the metal comprises or consists of one or more selected from the group consisting of lithium (Li), nickel (Ni), cobalt (Co) and manganese (Mn). In some further embodiments, the metal comprises or consists of lithium (Li) and one or more selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In some further embodiments, the metal comprises or consists of one or more selected from lithium (Li) and nickel (Ni) and one or more selected from cobalt (Co) and manganese (Mn).

[0013] In some embodiments of the first aspect, the metal bearing material comprises or consists of one or more material selected from the group consisting of lithium cobalt oxide (LiCoCL), lithium manganese oxide (LiMmCL), lithium nickel oxide (LiNiCL), lithium nickel cobalt oxides, lithium nickel manganese oxides, and lithium nickel manganese cobalt oxides. In some further embodiments, the metal bearing material comprises or consists of one or more material selected from lithium nickel manganese cobalt oxides. In even further embodiments, the lithium nickel manganese cobalt oxide is Li1.05Ni0.33Mn0.33Co0.33O2 (NC 111).

[0014] In some embodiments of the first aspect, choline chloride and acetic acid within the deep eutectic solvent are at a molar ratio of about 1:2 to about 1:5. In some further embodiments, the deep eutectic solvent consists of choline chloride and acetic acid at a molar ratio of about 1:2 to about 1:5. In some further embodiments, the deep eutectic solvent consists of choline chloride and acetic acid at a molar ratio of about 1:2.

[0015] According to a second aspect, there is provided use of choline chloride and acetic acid in separating a metal from a metal bearing material, wherein a deep eutectic solvent formed from choline chloride and acetic acid is used.

[0016] In some embodiments of the second aspect, the metal bearing material is a cathode material. In some further embodiments, the metal bearing material is a cathode material of an electrochemical device, such as a secondary battery. In some further embodiments, the metal bearing material is a cathode material of an ion battery. In some further embodiments, the ion battery is selected from lithium ion batteries and sodium ion batteries.

[0017] In some embodiments of the second aspect, the metal bearing material is leached by use of the deep eutectic solvent. In some further embodiments, for the leaching, the cathode material and the deep eutectic solvent are at a solid-to-liquid ratio (i.e. S / L ratio) of about 10 g / L to 50 g / L. In even further embodiments, the leaching is carried out at about 90 °C to 120 °C for about 8 to 12 hours, for example 10 hours. In even further embodiments, the leaching is carried out at about 120 °C for about 12 hours.

[0018] In some embodiments of the second aspect, the metal comprises one or more selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In some further embodiments, the metal comprises or consists of one or more selected from the group consisting of lithium (Li), nickel (Ni), cobalt (Co) and manganese (Mn). In some further embodiments, the metal comprises or consists of lithium (Li) and one or more selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In some further embodiments, the metal comprises or consists of one or more selected from lithium (Li) and nickel (Ni) and one or more selected from cobalt (Co) and manganese (Mn).

[0019] In some embodiments of the second aspect, the metal bearing material comprises or consists of one or more material selected from the group consisting of lithium cobalt oxide (LiCoCL), lithium manganese oxide (LiMmC ), lithium nickel oxide (LiNiCL), lithium nickel cobalt oxides, lithium nickel manganese oxides, and lithium nickel manganese cobalt oxides. In some further embodiments, the metal bearing material comprises or consists of one or more material selected from lithium nickel manganese cobalt oxides. In even further embodiments, the lithium nickel manganese cobalt oxide is Li1.05Ni0.33Mn0.33Co0.33O2 (NC 111).

[0020] In some embodiments of the second aspect, choline chloride and acetic acid within the deep eutectic solvent are at a molar ratio of about 1:2 to about 1:5. In some further embodiments, the deep eutectic solvent consists of choline chloride and acetic acid at a molar ratio of about 1:2 to about 1:5. In even further embodiments, the deep eutectic solvent consists of choline chloride and acetic acid at a molar ratio of about 1:2.

[0021] In some embodiments of the second aspect, acetone is used as antisolvent after leaching with the deep eutectic solvent. In some further embodiments, acetone is used as antisolvent to precipitate one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn). In some further embodiments, the acetone as antisolvent is introduced to the leachate obtained after leaching with the deep eutectic solvent at an initial organic-to-aqueous volumetric ratio (O / A) of about 2 to 20. In even further embodiments, the initial organic-to-aqueous volumetric ratio (O / A) is about 10.

[0022] According to a third aspect, there is provided a process for separating a metal from a metal bearing material, wherein the process includes leaching the metal bearing material with a deep eutectic solvent formed from choline chloride and acetic acid.

[0023] In some embodiments of the third aspect, the metal bearing material is a cathode material. In some further embodiments, the metal bearing material is a cathode material of an electrochemical device, such as a secondary battery and an ion battery. In some further embodiments, the ion battery is selected from lithium ion batteries and sodium ion batteries. In some further embodiments, for the leaching, the metal bearing material (such as the cathode material of the ion batteries) and the deep eutectic solvent are at a solid-to-liquid ratio (i.e. S / L ratio) of about 10 g / L to 50 g / L. In even further embodiments, the leaching is carried out at about 90 °C to 120 °C for about 8 to 12 hours, for example 10 hours. In even further embodiments, the leaching is carried out at about 120 °C for about 12 hours.

[0024] In some embodiments of the third aspect, choline chloride and acetic acid within the deep eutectic solvent are at a molar ratio of about 1:2 to about 1:5. In some further embodiments, the deep eutectic solvent consists of choline chloride and acetic acid at a molar ratio of about 1:2 to about 1:5. Insome further embodiments, the deep eutectic solvent consists of choline chloride and acetic acid at a molar ratio of about 1:2.

[0025] In some embodiments of the third aspect, the metal comprises or consists of one or more material selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In some embodiments, the metal comprises or consists of one or more selected from the group consisting of lithium (Li), nickel (Ni), cobalt (Co) and manganese (Mn). In some further embodiments, the metal comprises or consists of lithium (Li) and one or more selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In even further embodiments, the metal comprises or consists of one or more selected from lithium (Li) and nickel (Ni) and one or more selected from cobalt (Co) and manganese (Mn).

[0026] In some embodiments of the third aspect, the metal bearing material comprises or consists of one or more material selected from the group consisting of lithium cobalt oxide (LiCoCL), lithium manganese oxide (LiMmCL), lithium nickel oxide (LiNiCL), lithium nickel cobalt oxides, lithium nickel manganese oxides, lithium cobalt manganese oxides, and lithium nickel manganese cobalt oxides. In some further embodiments, the metal bearing material comprises or consists of one or more selected from lithium nickel manganese cobalt oxides. In even further embodiments, the lithium nickel manganese cobalt oxide is Li1.05Ni0.33Mn0.33Co0.33O2 (NCM111).

[0027] In some embodiments of the third aspect, the process includes, after the leaching, using acetone as antisolvent to separate one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) from the leachate. In some further embodiments, the acetone as antisolvent is introduced to the leachate at an initial organic-to-aqueous volumetric ratio (O / A) of about 2 to 20. In even further embodiments, the initial organic-to-aqueous volumetric ratio (O / A) is about 10.

[0028] In some embodiments of the third aspect, the process includes combining oxalic acid with the separation residue obtained through the separation by use of acetone as antisolvent to separate cobalt in the form of a cobalt containing precipitate and obtaining an oxalic acid solution. In some further embodiments, the process includes combining the oxalic acid solution with NaOH to separate manganese in the form of a manganese containing precipitate. In even further embodiments, the cobalt containing precipitate is calcinated to obtain CO3O4 and / or the manganese containing precipitate is calcinated to obtain M113O4.

[0029] In some embodiments of the third aspect, the process includes recovering acetone from the solution obtained through the separation by use of acetone as antisolvent. In some further embodiments, the process includes combining the solution obtained after acetone being recovered with sodium hydroxide (NaOH) to separate nickel in the form of a nickel containing precipitate and obtaining a NaOHsolution. In some further embodiments, the process includes combining the solution obtained after acetone being recovered with oxalic acid to separate nickel in the form of a nickel containing precipitate and obtaining an oxalic acid solution. In even further embodiments, the process includes combining the NaOH solution or the oxalic acid solution with sodium carbonate (NazCOs) and then introducing acetone thereto to separate lithium in the form of lithium carbonate (LizCOs).

[0030] In some embodiments of the third aspect, recovery efficiency of Li is about 97.1%, recovery efficiency of Mn is about 93.3%, recovery efficiency of Co is about 96.5% and / or recovery efficiency of Ni is about 96.1%. In some further embodiments, recovery efficiencies of Li, Mn, Co and Ni through the process are about 97.1%, about 93.3%, about 96.5% and about 96.1%.

[0031] According to a fourth aspect, there is provided a process for separating a metal from a metal bearing material, wherein the process comprises:(a) leaching the metal bearing material with formic acid and forming a first leachate and a first separation residue, and(b) leaching the first separation residue with a deep eutectic solvent formed from choline chloride and acetic acid.

[0032] In some embodiments of the fourth aspect, the process comprises:(a) leaching the metal bearing material with formic acid and forming a first leachate comprising lithium (Li) and a first separation residue comprising nickel (Ni) and one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn), and(b) leaching the first separation residue with a deep eutectic solvent formed from choline chloride and acetic acid and forming a second leachate comprising nickel (Ni) and one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn).

[0033] In some embodiments of the fourth aspect, the process comprises (c) using acetone as an antisolvent to precipitate from the second leachate one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn), and nickel (Ni) will remain in a solution after the precipitation (for example in a filtrate).

[0034] Embodiments for steps (b) and (c) of the fourth aspect and the subsequent steps may refer to those described herein in relation to the third aspect. Embodiments for step (a) of the fourth aspect may refer to those described herein in relation to the fifth aspect.

[0035] According to a fifth aspect, there is provided a process for separating a metal from a metal bearing material, wherein the process comprises(1) leaching the metal bearing material with formic acid and forming a first leachate and a first separation residue, and(2) leaching the first separation residue with a deep eutectic solvent formed from choline chloride and formic acid and forming a second leachate and, optionally, a second separation residue.

[0036] In some embodiments of the fifth aspect, the process comprises(1) leaching the metal bearing material with formic acid and forming a first leachate comprising lithium (Li) and a first separation residue comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, comprising nickel (Ni); and(2) leaching the first separation residue with a deep eutectic solvent formed from choline chloride and formic acid and forming a second leachate comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, a second separation residue comprising nickel (Ni).

[0037] In some embodiments of the fifth aspect, the process comprises (3) treating the second leachate with an anti-solvent such as an alcohol or a ketone so that cobalt (Co) and / or manganese (Mn) are removed in a solid form. In some embodiments, the alcohol used in step (3) is selected from C1-5 alcohol. In some embodiments, the alcohol used in step (3) is selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, glycerol, and a combination thereof. In some embodiments, the ketone used in step (3) is selected from the group consisting of acetone, butanone, 2-pentanone, 3-pentanone and a combination thereof. In some further embodiments, the process comprises (5) removing the alcohol or the ketone from the treated second leachate obtained from step (3) (for example through distillation) and, optionally, direct the alcohol or the ketone recovered to step (3) for reuse. In even further embodiments, the process comprises (6) reusing the deep eutectic solvent contained in the treated second leachate obtained from step (3) for step (2).

[0038] In some embodiments of the fifth aspect, for step (3), the volume of the alcohol or the ketone to be used and the volume of the deep eutectic solvent comprised in the second leachate are at a ratio of about 5 L / L to 25 L / L, for example about 10 L / L to 25 L / L, about 5 L / L to 20 L / L, about 10 L / L or about 15 L / L. In some further embodiments, for step (3), the second leachate is treated by the alcohol or the ketone at room temperature for about 6 hours.

[0039] In some embodiments of the fifth aspect, the process comprises (4) separating cobalt (Co) and manganese (Mn) in the solid form obtained from step (3) by use of oxalic acid so as to form a solution comprising manganese (Mn) and a precipitate comprising cobalt oxalate. In some further embodiments, the process comprises (7) separating manganese (Mn) out of the solution obtained from step (4) by use of sodium hydroxide and, optionally, recovering manganese (Mn) (for example as MnO(OH)).

[0040] In some embodiments of the fifth aspect, the metal bearing material is a cathode material of an electrochemical device. In some embodiments, the metal bearing material is a cathode material for an energy storage device, such as a secondary battery. In some further embodiments, the metal bearing material is a cathode material of an ion battery. In even further embodiments, the ion battery is selected from lithium ion batteries and sodium ion batteries.

[0041] In some embodiments of the fifth aspect, the metal comprises or consists of one or more material selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In some embodiments, the metal comprises or consists of one or more selected from the group consisting of lithium (Li), nickel (Ni), cobalt (Co) and manganese (Mn). In some further embodiments, the metal comprises or consists of lithium (Li) and one or more selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In even further embodiments, the metal comprises or consists of one or more selected from lithium (Li) and nickel (Ni) and one or more selected from cobalt (Co) and manganese (Mn).

[0042] In some embodiments of the fifth aspect, the metal bearing material comprises or consists of one or more material selected from the group consisting of lithium cobalt oxide (LiCoCL), lithium manganese oxide (LiMmCL), lithium nickel oxide (LiNiCL), lithium nickel cobalt oxides, lithium nickel manganese oxides, lithium cobalt manganese oxides, and lithium nickel manganese cobalt oxides. In some further embodiments, the metal bearing material comprises or consists of one or more selected from lithium nickel manganese cobalt oxides. In even further embodiments, the lithium nickel manganese cobalt oxide is Li1.05Ni0.33Mn0.33Co0.33O2 (NCM111).

[0043] In some embodiments of the fifth aspect, the formic acid used in step (1) is a formic acid having a purity of at least about 90%. In some further embodiments, the formic acid used in step (1) is a formic acid having a purity of at least about 94%, for example at least about 95%. In even further embodiments, the formic acid used in step (1) is a formic acid having a purity of at least about 98%.

[0044] In some embodiments of the fifth aspect, for the leaching of step (1), the metal bearing material (such as the cathode material of an ion battery) and the formic acid are at a solid-to-liquid ratio (i.e. S / L ratio) of about 30 g / L to 45 g / L, for example about 30 g / L and 35 g / L. In some further embodiments, the leaching of step (1) is carried out at about 40 °C to 70 °C, for example about 40 °C, 50 °C and 60 °C. Ineven further embodiments, the leaching of step (1) is carried out at about 60 °C. In even further embodiments, the leaching of step (1) is carried out until a desirable leaching result is achieved, for example for at least about 4 hours or at least 5 hours. In a specific embodiment, the leaching of step (1) is carried out at about 60 °C with the solid-to-liquid ratio (i.e. S / L ratio) being about 30 g / L.

[0045] In some embodiments of the fifth aspect, the deep eutectic solvent of step (2) consists of choline chloride and formic acid at a molar ratio of about 1:2 to 1:9. In some further embodiments, the deep eutectic solvent of step (2) consists of choline chloride and formic acid at a molar ratio of about 1:5.

[0046] In some embodiments of the fifth aspect, for the leaching of step (2), the first separation residue and the deep eutectic solvent are at a solid-to-liquid ratio (i.e. S / L ratio) of about 20 g / L to 60 g / L, for example about 20 g / L to 50 g / L or 30 g / L to 50 g / L, such as about 30 g / L, 35 g / L or 50 g / L. In some further embodiments, the leaching of step (2) is carried out at about 80 °C to 100 °C, for example about 90 °C. In even further embodiments, the leaching of step (2) is carried out for about 6 to 30 hours, for example about 6 to 24 hours or about 10 to 15 hours, such as about 12 hours or about 24 hours. In even further embodiments, the leaching of step (2) is carried out with the S / L ratio being about 50 g / L at about 90 °C for about 12 to 24 hours, for example 24 hours.

[0047] In some embodiments of the fifth aspect, for step (1), after leaching with formic acid, a solidliquid separation such as vacuum separation is conducted to form the first leachate and the first separation residue. In some further embodiments, the process further comprises step (8) recovering formic acid from the first leachate (for example through distillation). In even further embodiments, the process further comprises (9) reusing the formic acid recovered in step (8) for step (1).

[0048] In some embodiments of the fifth aspect, for step (2), after leaching with the deep eutectic solvent, a solid-liquid separation is conducted to form the second leachate and the second separation residue. In some further embodiments, the solid-liquid separation is a vacuum separation.

[0049] In some embodiments of the fifth aspect, for step (3), after treating with ethanol, a solid-liquid separation is conducted to form the treated second leachate and the solid comprising cobalt (Co) and / or manganese (Mn). In some further embodiments, the solid-liquid separation is a vacuum separation.

[0050] In some embodiments of the fifth aspect, for step (4), after separating by use of oxalic acid, a solid-liquid separation is conducted to form the solution comprising manganese (Mn) and the precipitate comprising cobalt oxalate. In some further embodiments, the solid-liquid separation is a vacuum separation.

[0051] According to a sixth aspect, there is provided a process for separating a metal from a metal bearing material, wherein the process comprises leaching the metal bearing material with a deep eutectic solvent formed from choline chloride and formic acid and forming a leachate comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, a separation residue.

[0052] In some embodiments of the sixth aspect, the separation residue comprises nickel (Ni).

[0053] According to a seventh aspect, there is provided a use of a deep eutectic solvent formed from choline chloride and formic acid as a leaching agent to separate a metal from a metal bearing material, wherein the metal bearing material comprises one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, comprises nickel (Ni).

[0054] Embodiments of the sixth and seventh aspects and the subsequent steps may refer to those described herein in relation to the fifth aspect.BRIEF DESCRIPTION OF FIGURES

[0055] Embodiments of the present disclosure will be discussed with reference to the accompanying figures wherein Figures 1 to 18 relate to the first to fourth aspects of the present disclosure and Figures 19 to 28 relate to the fifth to seventh aspects of the present disclosure.

[0056] Figure 1 shows DES (formed from choline chloride and acetic acid) leaching efficiency of Ei at different temperatures and lengths of time.

[0057] Figure 2 shows DES (formed from choline chloride and acetic acid) leaching efficiency of Mn at different temperatures and lengths of time.

[0058] Figure 3 shows DES (formed from choline chloride and acetic acid) leaching efficiency of Ni at different temperatures and lengths of time.

[0059] Figure 4 shows DES (formed from choline chloride and acetic acid) leaching efficiency of Co at different temperatures and lengths of time.

[0060] Figure 5 shows selective separation efficiency at different O / A ratios.

[0061] Figure 6 shows element mass ratio of Co in the 2ndseparation residue.

[0062] Figure 7 shows XRD of recovered Co in the 2ndseparation residue, wherein the characteristic peak is completely consistent with the peak of cobalt oxalate hydrate (PDF #00-014-0741).

[0063] Figure 8 shows element mass ratio of Mn in the 3rdseparation residue.

[0064] Figure 9 shows XRD of recovered Mn in the 3rdseparation residue, wherein the product corresponds to MmCL (PDF #00-001-1127).

[0065] Figure 10 shows an FTIR spectrum of recovered acetone.

[0066] Figure 11 shows element mass ratio of Ni in the 4thseparation residue.

[0067] Figure 12 shows XRD of recovered Ni in the 4thseparation residue.

[0068] Figure 13 shows the overall selective separation efficiency where oxalic acid was used for the separation of Ni and Li.

[0069] Figure 14 shows selective separation efficiency of LCO at different O / A ratios.

[0070] Figure 15 shows leaching ability of LCO spent cathode materials using original DES (formed from choline chloride and acetic acid) and regenerated DES (formed from choline chloride and acetic acid).

[0071] Figure 16 shows FTIR of the DES (formed from choline chloride and acetic acid) structure in the 1stleaching and the 3rdleaching.

[0072] Figure 17 shows an illustrative schematic diagram of a recycling process for Li-battery cathode materials which involves use of a deep eutectic solvent formed from choline chloride and acetic acid.

[0073] Figure 18 shows an illustrative schematic diagram of a recycling process for Li-battery cathode materials which involves use of formic acid and a deep eutectic solvent formed from choline chloride and acetic acid.

[0074] Figure 19 shows an illustrative schematic diagram of a recycling process for Li-battery cathode materials which involves use of formic acid and a deep eutectic solvent formed from choline chloride and formic acid.

[0075] Figure 20 shows recovery yield of Li by use of formic acid at different reaction temperatures and the S / L ratio of 30 g / L for 5 hours.

[0076] Figure 21 shows recovery yield of Li by use of formic acid with different S / L ratios at 60 °C and 5 hours.

[0077] Figure 22 shows recovery yield of Ni at different molar ratios of choline chloride and formic acid for the DES at 90 °C, 12 hours and the S / L ratio of 50 g / L.

[0078] Figure 23 shows recovery yield of Ni by use of the DES formed from choline chloride and formic acid with different S / L ratios at 90 °C, 12 hours.

[0079] Figure 24 shows recovery yield of Ni with different reaction times at 90 °C and 50 S / L.

[0080] Figure 25 shows recovery yields of Co and Mn by use of ethanol as an anti-solvent at differentEthanol / DES ratios.

[0081] Figure 26 shows the final recovery yields of Li, Mn, Co and Ni according to the method of the fifth aspect disclosed herein.

[0082] Figure 27 shows Fourier-transform infrared (FTIR) spectra of fresh ethanol and regenerated- ethanol.

[0083] Figure 28 shows FTIR spectra of fresh DES, DES after leaching, and R-DES (regenerated- DES), wherein the DES is formed from choline chloride and formic acid.DESCRIPTION OF EMBODIMENTS

[0084] The present disclosure arises from the inventors’ finding that a deep eutectic solvent formed from choline chloride and acetic acid was efficient to separate and recover one or more metal from a metal bearing material like lithium ion batteries, especially from a cathode material comprising one or more metal selected from lithium (Li), nickel (Ni), cobalt (Co) and manganese (Mn). It has also been surprisingly found by the inventors that, after leaching the cathode material of the lithium batteries with the deep eutectic solvent, use of acetone as antisolvent could help separate Li, Ni, Co and Mn in pairs (i.e. into a pair of Li and Ni and a pair of Co and Mn), and the pairwise separation of elements enables diverse options for subsequent separation of elements, for example by chemical precipitation, solvent extraction and electrochemical deposition. Furthermore, the addition of acetone as antisolvent did not destroy the structure of the leaching solution containing the deep eutectic solvent and multiple reuses of the deep eutectic solvent can be achieved.

[0085] The present disclosure also arises from the inventors’ finding that formic acid can be used to separate lithium from other metal(s) such as nickel (Ni), cobalt (Co) and / or manganese (Mn) comprised in a metal bearing material, especially in a cathode material of ion batteries. As a result, lithium may be present in a liquid form (for example, a first leachate) while other metals may be present in a solid form (for example, a first separation residue). It is favourable that the formic acid used is to be recovered and reused. It has also been surprisingly found by the inventors that, after leaching a metal bearing material such as a cathode material of lithium ion batteries with formic acid, a deep eutectic solvent formed from choline chloride and formic acid could be used to further separate other metal(s) such as nickel (Ni), cobalt (Co) and / or manganese (Mn). For example, when the first separation residue comprises nickel (Ni), cobalt (Co) and manganese (Mn), the deep eutectic solvent could be used to leach it so that Mn and Co will be present in a second leachate and Ni will be present in a second separation residue.

[0086] The term “deep eutectic solvent (DES)” used herein refers to a combination of two or more Lewis or Brpnsted acids and bases that, when mixed together at precise ratios, constitutes a liquid system with a melting point much lower (corresponding to the qualifier “deep”) than each individual component. DESs are formed by a hydrogen bonding acceptor (HBA) and a hydrogen bonding donor (HBD), making them liquid eutectic solvents. The hydrogen bonding acceptor (HBA) may be a quaternary ammonium salt such as choline chloride. The hydrogen bonding donor (HBD) may include carboxylic acids such as oxalic acid and lactic acid.

[0087] The term “antisolvent” used herein refers to a solvent that reduces the solubility of a solute.

[0088] The term “leach” used herein refers to dissolution of a metal from a metal bearing material(such as those derived from natural ores and spent ion batteries) into a liquid medium. The term “leachate” used herein represents the liquid phase obtained after a leaching operation. When leaching by use of a DES, the leachate may comprise the DES and the metal(s) dissolved in the DES. The metal may be present as a soluble salt in the liquid medium or form a complex (for example with a DES) and remain in the solution. A leaching operation may be accompanied by stirring, for example mechanical stirring or ultrasound agitation. Generally, higher leaching temperature and longer leaching time are helpful to accelerate the diffusion of ions and thereby enhance a leaching efficiency. The leaching efficiency may also be affected by the solid to liquid (S / L) ratio. Leaching parameters can be optimised to suit a specific situation by the person skilled in the art.

[0089] The term “electrochemical device” used herein refers to a device that can convert chemical energy into electrical energy through an electrochemical reaction. Types of electrochemical device include, but are not limited to, a battery, a supercapacitor, particularly an electrochemical device without use of a fuel. In some embodiments, the battery may be selected from a secondary battery, a flow battery, and a static battery.

[0090] It should be appreciated that there may be or may not be another step between the steps described herein. That is, in some circumstances, the sequential steps described herein may be conducted immediately after one another.

[0091] It should be understood that every maximum numerical limitation given throughout this disclosure is deemed to include each and every lower numerical limitation as an alternative, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this disclosure is deemed to include each and every higher numerical limitation as an alternative, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this disclosure is deemed to include each and every numerical range or number that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein. By way of example, the phrase from about 2 to about 4 includes the whole number and / or integer ranges from about 2 to about 3, from about 3 to about 4; each possible range based on real (e.g., irrational and / or rational) numbers, such as from about 2.1 to about 4.9, from about 2.1 to about 3.4 and so on; and the individual real numbers such as 2, 2.5, 3, 3.5, and 4.

[0092] Disclosed herein is a deep eutectic solvent (DES) for separating a metal from a metal bearing material, which is made from choline chloride and acetic acid.

[0093] In some circumstances, choline chloride ([Ch]Cl) as hydrogen bonding acceptor (HBA) and acetic acid or formic acid as hydrogen bonding donor (HBD) are combined to form a deep eutectic solvent. The formation involves the interaction of hydrogen bonds, which may be confirmed by the Fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance (NMR). It can be done by mixing [Ch] Cl and acetic acid, for example at a temperature of about 60 °C, with stirring until a homogeneous transparent liquid is formed. The [Ch] Cl and acetic acid can present a eutectic region at a molar ratio of about 1:2 to about 1:5. In some embodiments, the DES is formed with 1 mole [Ch] Cl and 2 mole acetic acid. The [Ch]Cl and formic acid can present a eutectic region at a molar ratio of about 1:2 to 1:9, for example about 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8 and 1:9. In some embodiments, the DES is formed with 1 mole [Ch]Cl and 2 mole acetic acid. [Ch]Cl is commercially available from Sigma-Aldrich, United States.

[0094] Acetic acid is available at a relatively lower cost, which makes the DES disclosed herein a promising solution for large-scale recycling of spent lithium ion batteries. Formic acid is commercially available from Sigma-Aldrich, United States. The amount of water within the acetic acid-based DES or the formic acid-based DES should be minimised. This is because the increase of water content will reduce the concentration of the acetic acid-based DES or the formic acid-based DES and affect the leaching efficiency. Moreover, the increase of water will affect the structure of acetic acid-based DES or the formic acid-based DES, which in turn could have unfavourable impact on the leaching efficiency. It ispreferred that the acetic acid-based DES and the formic acid-based DES disclosed herein are substantially free of water. In some cases, the water content within the acetic acid-based DES or the formic acid-based DES is no more than 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% by weight based on the total weight of the acetic acid-based DES. In some circumstances, it is recommended that no water or diluent is present in the DES disclosed herein.

[0095] The metal(s) comprised in a metal bearing material may include, but are not limited to, lithium, aluminium, and transition metals, such as nickel, cobalt, manganese and copper. Where the metal(s) to be separated comprise(s) or is / are one or more selected from lithium and nickel and one or more selected from cobalt and manganese, a leaching step using the DES disclosed herein may produce a liquid phase comprising the lithium and / or nickel and a solid phase comprising the cobalt and / or manganese.

[0096] The metal bearing material may be of natural origin (for example natural ores) or derived from a manufactured product (for example battery electrodes). In some embodiments, the metal bearing material includes a cathode material of an electrochemical device. In some further embodiments, the metal bearing material includes a cathode material of ion batteries or secondary batteries. The cathode material may be collected from ion batteries, such as lithium ion batteries and sodium ion batteries. For example, a cathode material of the lithium ion batteries may comprise lithium and one or more selected from nickel, cobalt and manganese, and a cathode material of the sodium ion batteries may comprise sodium and one or more selected from nickel, cobalt and manganese. In addition, the cathode material used herein may further comprise aluminium and / or copper. It is also possible for a cathode material to be doped, for example, Na-doped Li1.17Na0.03Ni0.13Mn0.54Co0.13O2 (Na-LNMC). For example, the metal bearing material (such as a cathode material of lithium ion batteries) may comprise or consist of one or more selected from the group consisting of lithium cobalt oxide (LiCoOz), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNO2), lithium nickel cobalt oxides, lithium nickel manganese oxides, lithium cobalt manganese oxides, and lithium nickel manganese cobalt oxides. Lithium nickel manganese cobalt oxides (NCM or NMC) are commonly used for fabricating the cathode of lithium ion batteries due to its considerable capacity and energy density. Therefore, recovery of the metals from spent lithium ion batteries could not only solve environmental problems but also compensate for the scarcity of metal resources. They have a general formula of LiNLMn.Co CL. The most important representatives have a composition with x + y + z that is near 1 , with a small amount of lithium on the transition metal site. Consideration may be given to Lii.o5Nio.33Mno.33Coo.3302(NCMlll), LiNio.5Coo.2Mno.3O2 (NCM 523), LiNio.6Coo.2Mno.2O2 (NCM 622), and LiNio.sCoo.1Mno.1O2 (NCM 811). Lithium cobalt oxide (LiCoO2) is a dark blue or bluish-grey crystalline solid. Lithium manganese oxide (LiMn2O4) is a cathode material with a spinel structure, which allows the material to be discharged at high rates. It would be appreciated that more than one cathode materials (i.e. mixed cathode materials) can be leached at the same time by use ofthe DES disclosed herein. In this regard, an illustrative example is a mixture of LiCoCL. LiMmCL and Li1.05Ni0.33Mn0.33Co0.33O2 (NC 111).

[0097] Spent batteries such as LIBs usually need to be discharged before recycled for the sake of safety. Spent batteries may need to be pre-processed (e.g. deactivate, disassemble or comminute) and the battery components be sorted for recycling. If needed, the cathode materials may be cleaned (for example, by ultrasonic cleaning) before any further treatment. The cathodes materials may be calcinated (for example at about 500 °C to 600 °C) to make cathode powders fall off Al foil and remove any residual carbon. Alternatively, cathode material may be separated from a current collector (such as Al foil) by keeping cathode plates in a solution of sodium hydroxide for a period under ultrasound with 10% (w / v) pulp density. The cathode material may then be subjected to deionized water for washing and later dried in an oven. The dried cathode material may be further crushed and sieved through a sieve (for example, a 74 pm sieve) to make fine powder. Cathode powders may be immersed in an alkaline NaOH solution to remove the small amount of Al in the powders. The composition of cathode powders to be leached may be analysed through X-ray powder diffraction (XRD) or inductive coupled plasma-optical emission spectrometry (ICP-OES).

[0098] Leaching is an interfacial reaction between the solid and the liquid, and the boundary area of the two phases can affect leaching efficiency. It is suggested that the cathode materials are grounded into fine powders, for example with a mean particle size of about 0.5 to 1 pm, to increase the contact surface area and to accelerate the leaching. Taking LiNii / sCoi / sM / sCL cathode material as an example, the mean particle size of the powders to be leached is about 0.5 pm. The mean particle size can be determined using a laser particle size analyser.

[0099] The acetic acid-based DES disclosed herein can be used to leach desirable metal(s) from the metal bearing material. For example, the leaching is carried out by combining the metal bearing material and the DES and making them contact with each other. A suitable temperature and a suitable leaching time can be chosen by the person skilled in the art. For example, when the acetic acid-based DES is used, the leaching may be performed at a temperature of about 60 °C to 120 °C for a certain period, for example 2 to 24 hours. In a preferable embodiment, the leaching is performed at about 90 °C to 120 °C for about 8 to 12 hours. This may be accompanied by stirring, for example mechanical stirring or ultrasound agitation. Taking a cathode material of lithium ion batteries as example, preferable leaching conditions may include a leaching temperature of about 120 °C, a leaching time of about 12 hours, and a solid-to- liquid ratio (i.e. cathode powders (mass) vs the acetic acid-based deep eutectic solvent (volume)) of about 10 g / L to 50 g / L. After the leaching, undissolved residues may be filtered off and a leachate comprising the acetic acid-based DES and the metal(s) is obtained. Alternatively, a leachate may be collected by centrifugation to remove any solid phase. The leachate may be subjected to an analysis by inductivelycoupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the concentration(s) of the metal(s). Results disclosed herein show that the leaching efficiencies of Li, Co, Ni, and Mn may reach almost 100% at 120 °C and 12 hours. The leaching efficiency is calculated as: r / i =1 DESX 100%, where r / i is leaching efficiency of I (=Co. Ni,Mn or Li) in the solution, V is leaching solution volume, mi is the mass of the initial amount of I in the metal bearing material.

[0100] After the leaching, any suitable separation techniques such as chemical precipitation, solvent extraction and / or electrochemical process may be chosen to separate and even recover each individual metal. In the case that the metal bearing material is a cathode material, such as a cathode material of lithium ion batteries, it may be possible to use antisolvents including, but not limited to, acetone, ethanol, methanol, isopropanol, ethylene glycol, acetonitrile, n-propanol, i-propanol, and isobutyl alcohol]. The amount of antisolvent to be used may vary in different situations. If acetone is used as antisolvent, an initial organic-to-aqueous volumetric ratio (O / A) of about 8 to about 10 might be considered. It has been advantageously found that acetone used as antisolvent does not chemically react with the acetic acidbased DES disclosed herein, which in turn would allow multiple reuses of the DES.

[0101] If needed, acetone is used as antisolvent to precipitate one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn). When the metal bearing material comprises Li, Ni, Co and Mn, such as lithium nickel manganese cobalt oxides, particularly Li1.05Ni0.33Mn0.33Co0.33O2, it has been surprisingly found that use of acetone as antisolvent allows separation of Li, Ni, Co and Mn in pairs (i.e. into a pair of Li and Ni and a pair of Co and Mn). Specifically, after introducing acetone as antisolvent to the leachate and conducting a separation, for example through filtration or centrifugation, Li and Ni stay in the solution (e.g. filtrate in the case of filtration) while Co and Mn enter into the separation residue (e.g. filtrant in the case of filtration). The pairwise separation of elements advantageously enables diverse options for subsequent separation of elements, for example by chemical precipitation and electrochemical deposition. When the metal bearing material is LiCoCL and acetone is used as antisolvent, the filtrate contains Li and the filtrant contains Co after introducing acetone to the leachate and conducting a filtration.

[0102] When the metal bearing material comprises Li, Ni, Co and Mn, such as lithium nickel manganese cobalt oxides, particularly Li1.05Ni0.33Mn0.33Co0.33O2, acetone as antisolvent may be introduced to the leachate at an initial organic-to-aqueous volumetric ratio (O / A) of, for example, about 2 to about 20, preferably about 10. The “organic” used here refers to acetone and the “aqueous” used here refers to the leachate comprising the DES. If the O / A ratio is as high as 12, a certain amount of Ni will precipitate together with Co and Mn from the leachate. If the O / A ratio is too low, a desirable precipitation of Co and Mn from the leachate will not be achieved. In the case that Li1.05Ni0.33Mn0.33Co0.33O2 is the metal bearingmaterial and leaching is performed with the DES, the separation residue by use of acetone antisolvent might be a complex formed by Co, Mn, and the acetic acid-based DES.

[0103] Many options are available to selectively separate a metal from the solution and the separation residue respectively after separation by use of antisolvent as stated above. For this purpose, known methods such as solvent extraction, ion-exchange and chemical precipitation may be adopted to treat. Given the different chemical properties of Li, Ni, Co and Mn, a chemical precipitation can be considered for selective separation. Before selective separation, the solution obtained after separation by use of antisolvent as stated above may contain a large amount of antisolvent. Therefore, it may be advantageous to recover the antisolvent for example acetone from the solution prior to the selective separation. For the purpose of illustration, acetone can be recovered by heating the solution (for example at about 80 °C) for a period of time and collecting the condensate produced thereby.

[0104] For example, when the separation residue comprises Co and Mn, oxalic acid can be used as a precipitant to allow Co to form cobalt oxalate hydrate as the precipitate. Then NaOH can be introduced to the remaining solution and make Mn precipitate as Mn(0H)2. The precipitates may be obtained through filtration or centrifugation. Following that, the precipitates may be subjected to calcination to produce valuable material, such as CO3O4 and MmCL.

[0105] When the solution comprises Li and Ni, Ni can be selectively precipitated as nickel oxalate hydrate by adding oxalic acid to the solution. Alternatively, the solution can be combined with sodium hydroxide (NaOH) to separate nickel in the form of a nickel containing precipitate and obtaining a NaOH solution. Following that, the oxalic acid solution obtained or the NaOH solution obtained can be combined with sodium carbonate (NazCOs) and then introducing acetone thereto to separate lithium in the form of lithium carbonate (LizCOs).

[0106] A suitable method known in the art can be selected to determine the composition of a solid phase or a liquid phase. Examples of the methods include, but are not limited to, X-ray powder diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), and Energy Dispersive Spectroscopy (EDS).

[0107] The process for separating a metal (for example, transition metals) from a metal bearing material (for example cathodes materials of lithium ion batteries) disclosed herein may be useful to produce high-purity products. By use of the DES, an effective separation of Co, Mn and Li, Ni from spent cathode materials can be achieved. Furthermore, subsequent separations including a separation with the aid of antisolvent could lead to a high selectivity and a good recovery rate of Mn, Co and Ni. For example, the purities of Ni, Co and Mn products recovered from NCM 111 cathode materials can be about 93.3%, about 96.5% and about 96.1% respectively. In addition, similar results can be obtained forLCO cathode materials. Another benefit is that the DES and anti-solvent are reusable. The recycling strategy of cathode materials (for example cathode materials of lithium ion batteries) proposed here may fundamentally deepen the understanding of the transition metal leaching process and have good prospects in recycling of spent battery cathodes.

[0108] Also disclosed herein is a process for separating a metal from a metal bearing material, wherein the process comprises:(1) leaching the metal bearing material with formic acid and forming a first leachate and a first separation residue, and(2) leaching the first separation residue with a deep eutectic solvent formed from choline chloride and formic acid and forming a second leachate and, optionally, a second separation residue.

[0109] The process can be particularly suitable for separating a metal from a cathode material of an electrochemical device, for example a cathode material of lithium ion batteries. In some circumstances, the process for separating a metal from a metal bearing material may comprise:(1) leaching the metal bearing material with formic acid and forming a first leachate comprising lithium (Li) and a first separation residue comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, comprising nickel (Ni); and(2) leaching the first separation residue with a deep eutectic solvent formed from choline chloride and formic acid and forming a second leachate comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, a second separation residue comprising nickel (Ni).

[0110] As stated above, the metal bearing material can be originated from spent batteries. The process disclosed herein may include pre-processing the spent batteries (e.g. deactivate, disassemble or comminute) and sorting battery components for recycling. The pre-processing can be done by any suitable process, for example, those known in the art. If needed, cathode materials of spent batteries may be cleaned (for example, by ultrasonic cleaning) before any further treatment. To achieve a satisfactory separation efficiency, it is favourable to employ powder or small pieces of a metal bearing material such as a cathode material. For the purpose of illustration, the particle size of a cathode powder may be less than about 0.5 pm, so as to increase contact surface area between the cathode powder and a leachant (such as formic acid and a deep eutectic solvent from choline chloride and formic acid) and to accelerate the leaching. The composition of a powder of the metal bearing material to be leached may be analysedthrough X-ray powder diffraction (XRD) or inductive coupled plasma-optical emission spectrometry (ICP-OES).

[0111] It is desirable for the formic acid used in step (1) to have a purity of at least about 90%, for example, at least about 92%, at least about 94%, at least about 95%, at least about 96%, or at least about 98%. In some circumstances, formic acid may be used in combination with another agent such as hydrogen peroxide. When hydrogen peroxide is also used, it is used as a reducing agent. The amount of H2O2 may be about 6 vol% based on the total amount of formic acid and H2O2. Formic acid is conventionally produced from methanol and is commercially available from Sigma- Aldrich, United States. In the situation that the metal bearing material comprises lithium (Li) and other metals such as cobalt (Co), nickel (Ni) and / or manganese (Mn), lithium could be selectively leached into solution using formic acid while other metals could be precipitated out. Similarly, when the metal bearing material comprises sodium (Na) and other metals such as nickel (Ni) and manganese (Mn), sodium could be selectively leached into solution using formic acid while other metals could be precipitated out. Any suitable solid-liquid separation method such as vacuum separation and centrifugation may be employed to facilitate or accelerate formation of a first leachate and a first separation residue. In this way, a first leachate comprising lithium and / or sodium and a first separation residue comprising other metal(s) is formed. In some circumstances, the first separation residue comprises nickel (Ni) and one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn). For the cathode material LiNii / 3Coi / 3Mni / 3O2(NCM 111), the reaction with formic acid is as follows, wherein M represents at least one of Ni, Co and Mn:2LiMOz+ 4HC00H - 2HCOOLi + (HC00)2M + 2HzO + MO2

[0112] For the leaching of step (1), the metal bearing material (such as the cathode material of an ion battery) and the formic acid can be used at a solid-to-liquid ratio (i.e. S / L ratio) of about 30 g / L to 45 g / L, for example about 30 g / L. The leaching by use of formic acid may be carried out at about 40 °C to 70 °C, for example at about 40 °C, 50 °C and about 60 °C. The leaching may be conducted for a period until a desirable leaching efficiency is reached, for example, for at least 4 hours or at least 5 hours. Taking a cathode material of lithium ion batteries as an example, leaching conditions may include a leaching temperature of about 60 °C, a leaching time of about 5 hours, and a solid-to-liquid ratio (i.e. cathode powder (mass) vs the deep eutectic solvent (volume)) of about 30 g / L.

[0113] The first leachate and the second leachate described in detail hereinafter may be subjected to an analysis by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the concentration(s) of the metal(s). Results disclosed herein show that the leaching efficiency of Li by use of formic acid may reach almost 98.7% at60 °C and 5 hours. The leaching efficiency is calculated as: r / i =1 DESX 100%, where r / i is leachingefficiency of I (=Li, Na, Ni, Co, or Mn) in the solution, V is leaching solution volume, mi is the mass of the initial amount of I in the metal bearing material.

[0114] Formic acid contained in the first leachate can be recovered (i.e. step (8)) by a suitable method known in the art, for example through distillation, and then be reused (i.e. step (9)) for the leaching in step (1). Specifically, the first leachate can be distilled for concentration, for example at a temperature of about 60 °C to about 80 °C (such as 60 °C), while stirring or vacuum heating to recover formic acid. In the case that a cathode material from lithium ion batteries is the metal bearing material, after distillation, a lithium rich solution is produced and formic acid is recovered. Recovery and reuse of formic acid contained in the first leachate can be readily achieved and reduce the costs of the process disclosed herein, which is of great importance from a commercial point of view. The lithium-rich solution comprising lithium formate can be further concentrated so as to allow lithium formate to precipitate out and the precipitate may be further processed for the purpose of recovery.

[0115] A deep eutectic solvent formed from choline chloride and formic acid will be used to leach the first separation residue and form a second leachate and a second separation residue (i.e. step (2)). The deep eutectic solvent used in step (2) may be formed from choline chloride and formic acid at a molar ratio of about 1:2 to about 1:9, for example at a molar ratio of about 1:5. The deep eutectic solvent can be prepared by mixing choline chloride and formic acid, for example at a molar ratio of about 1:5 and stirred at 60 °C ~ 80 °C until a uniform and transparent liquid is produced. Any suitable solid-liquid separation method such as vacuum separation and centrifugation may be employed to facilitate or accelerate formation of the second leachate and the second separation residue. In this way, a second separation residue comprising nickel is formed and a second leachate comprising other metal(s). When the first separation residue comprises nickel (Ni) and one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn), the second leachate will comprise one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and the second separation residue will comprise nickel (Ni). The second separation residue comprising nickel (Ni) may be further heated (for example at about 600 °C ~ 700 °C) to produce nickel oxide. For example, about 98.9% or even 99.2% of nickel (Ni) compared to the initial amounts thereof in the metal bearing material may be obtained.

[0116] For the leaching of step (2), the first separation residue and the deep eutectic solvent can be used at a solid-to-liquid ratio (i.e. S / L ratio) of about 20 g / L to 60 g / L, for example about 20 g / L to 50 g / L or about 30 g / L to 50 g / L, such as 20 g / L, 30 g / L or 50 g / L. The leaching by use of the deep eutectic solvent may be carried out at about 80 °C to 100 °C, for example at about 90 °C. The leaching of step (2) may be conducted for a period until a desirable leaching efficiency is reached. In some circumstances, the leaching is conducted for about 6 to 30 hours, for example 6 to 24 hours or 10 to 15 hours, such as 12hours or 24 hours. For example, leaching conditions may include a leaching temperature of about 90 °C, a leaching time of about 24 hours, and a solid-to-liquid ratio (i.e. the first separation residue (mass) vs the deep eutectic solvent (volume)) of about 20 g / L to about 50 g / L. In some embodiments, 97.8% of cobalt (Co) and 87.5% manganese (Mn) compared to the initial amounts thereof in the metal bearing material may be present in the second leachate. In some embodiments, 98.3% of cobalt (Co) and 98.6% manganese (Mn) compared to the initial amounts thereof in the metal bearing material may be present in the second leachate.

[0117] In some circumstances, the second leachate may be treated with an alcohol or a ketone so that other metals such as cobalt (Co) and / or manganese (Mn) are removed in a solid form (i.e. step (3)). The alcohol used in step (3) may be selected from C1-5 alcohol, such as methanol, ethanol, n-propanol, isopropanol, glycerol, and a mixture thereof. Examples of the ketone used in step (3) include, but are not limited to, acetone, butanone, 2-pentanone, and 3-pentanone. Then the treated second leachate will comprise the alcohol or the ketone and the deep eutectic solvent formed from choline chloride and formic acid. The ratio between the volume of the alcohol or the ketone to be used and the volume of the deep eutectic solvent comprised in the second leachate may be selected to improve separation efficiency of other metals such as cobalt (Co) and / or manganese (Mn). For example, the alcohol or the ketone and the deep eutectic solvent comprised in the second leachate are used at a volume ratio of about 5 L / L to 25 L / L, for example about 10 L / L to 25 L / L, about 5 L / L to 20 L / L, about 10 L / L or about 15 L / L. The temperature and the time for treating the second leachate by use of the alcohol or the ketone can be selected to further improve the separation efficiency. In some circumstances, the second leachate is treated by ethanol at room temperature for about 6 hours when the ratio between the volume of ethanol and the volume of the deep eutectic solvent comprised in the second leachate is about 10 L / L. It is possible to remove the alcohol especially ethanol or the ketone especially acetone from the treated second leachate and, if desirable, direct the alcohol or the ketone recovered to step (3) for reuse (i.e. step (5)), which can be done through distillation of the treated second leachate. In the case that the alcohol is ethanol, the treated second leachate may be subjected to a distillation at a temperature of about 70 °C, so that ethanol will evaporate and can be collected through a condenser. The deep eutectic solvent after being separated from the alcohol and recovered may be directed back to step (2) and be reused (i.e. step (6)). The reusability of alcohol and / or deep eutectic solvent makes the process disclosed herein more commercially applicable.

[0118] When the second leachate comprises cobalt (Co) and manganese (Mn) and a solid comprising cobalt (Co) and manganese (Mn) is obtained from step (3), cobalt (Co) and manganese (Mn) in the solid may be separated by use of oxalic acid so as to form a solution comprising manganese (Mn) and a precipitate comprising cobalt oxalate (i.e. step (4)). Then NaOH (for example, in the form of a solution) can be introduced to the solution comprising manganese (Mn) and make Mn precipitate for example asMnO(OH) (i.e. step (7)). Any suitable solid-liquid separation method such as filtration or centrifugation can be adopted to separate out the precipitates. Following that, the precipitates may be subjected to calcination to produce valuable material, such as CO3O4 and M113O4.

[0119] The process disclosed herein, especially the process with the usage of formic acid and a deep eutectic solvent formed from choline chloride and formic acid, could be operated as a full closed-loop recycling process. In particular, the process of the fifth aspect disclosed herein could advantageously recycle the deep eutectic solvent formed from choline chloride and formic acid that has been used and / or the formic acid that has been used. This can significantly reduce the cost of solvents and represent a very promising industry application.

[0120] It would be appreciated that a process for separating a metal from a metal bearing material is also disclosed, wherein the process comprises leaching the metal bearing material with a deep eutectic solvent formed from choline chloride and formic acid and forming a leachate comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, a separation residue. In some circumstances, the separation residue comprises nickel (Ni). Also disclosed herein is a use of a deep eutectic solvent formed from choline chloride and formic acid as a leaching agent to separate a metal from a metal bearing material, wherein the metal bearing material comprises one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, comprises nickel (Ni). Relevant details and steps may refer to those described hereinabove for the process with the usage of formic acid and a deep eutectic solvent formed from choline chloride and formic acid.EXAMPLESFormation of DES based on [ Ch] Cl and acetic acid

[0121] A DES was prepared by combining hydrogen bond accepter (1 mole choline chloride) and hydrogen bond donner (2 mole acetate acid) and stirring them at about 60 °C until a clear solution formed. Choline chloride and acetic acid were purchased from Sigma-Aldrich Chemical Co.Comparison of leaching efficiency

[0122] To optimise leaching conditions, lOOmg of spent Li1.05Ni0.33Mn0.33Co0.33O2 (NCM111) powder was added to 5ml of DES, and then operating conditions were changed by adjusting the leaching temperature and leaching time (see Figure 1 to Figure 4). Inductively coupled plasma mass spectra (ICP- MS) (Agilent 7900) was used to determine the leaching efficiency of various metal elements in the DES. The leaching of Li, Mn, Co, and Ni was significantly affected by leaching time and leaching temperature. At a low temperature for a short time, the leaching of the four metal elements did not achieve a desiredeffect. But with the increase of leaching temperature and leaching time, the leaching efficiency of each ofLi, Ni, Mn and Co reached almost 100% at 120 °C for 12 hours. It is considered that higher leaching temperature and longer leaching time can accelerate the diffusion of ions and increase the number of activated molecules.22Selective recovery of transition metals

[0123] The solubility of different elements in the DES environment was regulated by using acetone as antisolvent to selectively separate Li, Ni, Mn and Co. According to the optimal leaching conditions (120 °C, 12 hours) of the acetic acid-based DES for spent NCM111, lOOmg NCM111 was dissolved into 5ml the DES ([Ch]Cl: acetic acid= l :2 molar ratio). The leaching efficiency is shown in Figures 1 to 4. Next, the selective separation efficiency of metal elements was conducted by adding acetone as antisolvent into the leachate comprising the DES, and was further explored by adjusting different organic to aqueous (O / A) ratios, where organic is acetone and aqueous is the DES. Figure 5 shows the concentration of each element in the solution comprising the leachate and acetone under conditions that O / A ratio is between 1 and 12 and the reaction time is 6 hours. At the initial stage, with the increase of acetone ratio, the concentration of Li in the solution almost remained the same, but the concentration of Co and Mn gradually decreased, which proved that more Co and Mn were precipitated from the solution to produce precipitates. However, Ni precipitates slightly after acetone was added, and when O / A is raised to 12, only 80% of Ni is retained in the solution. Therefore, the optimisation result is that when O / A is 10, the consumption of antisolvent can be balanced, and better separation effect can be achieved. The results of ICP showed that 97.5% of Li and 96.3% of Ni in the 1stseparation did not produce precipitation in the solution, while 96.5% of Co and 94.7% of Mn were separated. The precipitate that was separated here is referred to as 1stseparation residue.

[0124] Since oxalic acid has been reported to react with cobalt to form cobalt oxalate precipitates without reacting with Mn, the 1stseparation residue was added to a 0.5M oxalic acid solution and heated at 70 °C with stirring for 3 hours. The final pink cobalt oxalate precipitate was recovered by vacuum filtration . The mass ratio of Co and Mn was determined by ICP (Figure 6). After the 2ndseparation, the elemental mass ratio of Co in the 2ndseparation residue reached 94.9%. As a small part of nickel remained in the 1stseparation residue, oxalic acid and nickel can also form nickel oxalate precipitation, which leads to 3.7% nickel being separated from the filtrate. Figure 7 shows the XRD characteristic peak of the 2ndseparation residue, which is completely consistent with the peak of cobalt oxalate hydrate (PDF #00-014-0741). In order to make the 2ndseparation residue more valuable, they were calcined at 600 °C for 3 hours to obtain CO3O4 (PDF #00-009-0418) powder (Figure 7). After Co being separated out, only the Mn element remained in the oxalic acid solution. For the recovery of single element Mn in the oxalic acid solution, a 2M NaOH solution was used to recover Mn.23A 2M NaOH solution was added dropwiseto the filtrate containing Mn with stirring until the pH reached 10 and stirring was continued for 2 hours to obtain 3rdseparation residue.23The separation efficiency of the 3rdseparation residue was measured by ICP, the elemental mass ratio of Mn reached 99.9% (Figure 8). Figure 9 shows the XRD of the recovered Mn(0H)2, but no characteristic peak is observed. This is because Mn(0H)2 is easily oxidised to MnOOH, and the oxidised precipitate may contain a mixture of amorphous manganese hydroxide, hydroxy-oxy- manganese, and other compounds. Therefore, there is no obvious characteristic peak in the XRD of the 3rdseparation residue. The 3rdseparation residue was calcined at 800 °C for 3 hours, and the product was Mn3O4(PDF #00-001-1127) according to XRD analysis (Figure 9).

[0125] On the other hand, Ni and Li were still present in the solution comprising the leachate and acetone. Due to the large amount of acetone added, it was desirable to recover acetone. Here, the solution comprising the leachate and acetone was heated to 80 °C and then the acetone was collected through a condenser. The FTIR result of the recovered acetone was compared with that of commercial acetone, and the structure did not show any change (Figure 10).

[0126] After recovery of acetone, the next step is to separate Ni and Li. For this purpose, oxalic acid and NaOH were used respectively to separate Li and Ni and to observe the impacts of different precipitants on the separation of Li and Ni.

[0127] In one experiment, oxalic acid equivalent to about 1.5 times (mole ratio) nickel is added to the solution comprising the DES after acetone being recovered. Figure 11 shows the element mass ratio of the 4thseparation residue by use of oxalic acid, wherein the mass ratio of Ni element is 91.8%. The 4thseparation residue was analysed. The characteristic peak of the 4thseparation residue is completely consistent with that of nickel oxalate hydrate (PDF #00-001-0299) according to XRD analysis (Figure 12). The 4thseparation residue was calcined at 600 °C for 3 hours, and the oxide obtained was identified as NiO (PDF #00-042-1319) by XRD characterization (Figure 12).

[0128] After recovery of Ni, Na2COs was added into the oxalic acid solution to allow Li ion to form Li2CC>3. Li2COs is insoluble in acetone, addition of acetone into the oxalic acid solution led to separation of Li as Li2CC>3.

[0129] In another experiment, oxalic acid was replaced with NaOH for the separation of Ni and Li, where the mass ratio of Ni obtained is 92.0%.

[0130] After calculation of each separation step, the final separation efficiency of four elements were finally obtained, where oxalic acid was used for the separation of Ni and Li, as shown in Figure 13. The selective separation efficiencies of Li, Mn, Co and Ni is 97.1%, 93.3%, 96.5% and 96.1%, respectivelybased on Ni and Li separated by oxalic acid. Or selective separate efficiency of Li, Mn, Co, Ni is 97.2%, 93.3%, 96.5% and 94.8%, based on Ni and Li separated by NaOH.Reuse of the spent DES

[0131] A key challenge in conventional hydrometallurgy recovery processes is that precipitants added to the solution for extracting metal elements can affect the structure of the leachate. In this work, the addition of antisolvent did not destroy the structure of the leachate and realized the reuse of DES after the leaching of spent cathode materials such as LCO. The 80mg LCO spent cathode materials were leached using 5ml DES ([Ch]Cl: acetic acid=l :2 molar ratio) at 120 °C and 10 hours. After the leaching, the solution was added with anti-solvent (acetone) and a separation through precipitation was observed. The best separation efficiency was achieved by adjusting the O / A ratio (Figure 14). After centrifugation, acetone was recovered from the solution comprising the leachate through distillation at 80 °C. The solution obtained after acetone was recovered was regenerated DES. Figure 15 compares the leaching effect of LCO spent cathode materials using original DES and regenerated DES, and the results show a slight but acceptable decrease in leaching efficiency. Furthermore, FTIR were used to reveal the structural changes of DES after regeneration (Figure 16). It was found from the FTIR analysis that the structure of each functional group of DES did not change significantly after several reuse, which provided the feasibility of reusing the spent DES.Exemplified process with the usage of formic acid and a deep eutectic solvent formed from choline chloride and formic acid

[0132] The entire process is illustrated in Figure 19, wherein spent cathode material powder Li1.05Ni0.33Mn0.33Co0.33O2 (NCM111) having a size of about 0.5pm was used. The extraction of Li by use of formic acid (95%) was investigated and optimised by varying reaction temperature for the purpose of leaching and the solid-to-liquid ratio. The recovery yield of Li with formic acid was determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (Agilent 7900). It was found that increasing the solid-to-liquid ratio gradually decreased the recovery efficiency of Li, whereas an increase in temperature enhanced Li recovery (Figure 20 and Figure 21). The optimal leaching conditions for Li were established at a reaction temperature of 70 °C and a solid-to-liquid ratio of 30, at 5 hours achieving a lithium recovery rate of 99.7% or even 100%. However, since the recovery yields of Li at 60 °C and 70 °C are very similar, in order to reduce energy consumption, a temperature of 60 °C may be considered.

[0133] Selective separation of Ni, Co, and Mn was performed using the DES formed from choline chloride and formic acid. The DES was prepared by combining 1 mole of choline chloride with 5 moles of formic acid and stirring at approximately 60 °C until a clear solution formed. The choline chloride and formic acid were sourced from Sigma- Aldrich Chemical Co. Experiments indicated that varying themolar ratios of DES influenced the selective recovery of Ni. As shown in Figure 22, increasing the amount of formic acid gradually increased the recovery yield of Ni, whereas the recovery yields of Co and Mn first decreased and then increased. Particularly, at a molar ratio of 1:5 (ChCl: Formic acid), the recovery yields of Co and Mn were only 4.2% and 1.2% respectively or only 4.8% and 6.8% respectively. The low recovery yields of Co and Mn at the DES molar ratio of 1 :5 facilitated the selective extraction of Ni. Furthermore, the solid-to-liquid ratio and reaction time were optimized under fixed molar ratios. As depicted in Figure 23, increasing the solid-to-liquid ratio generally raised the recovery yield of Ni, but also led to increased recovery rates of Co and Mn, potentially reducing the purity of Ni. Therefore, in addition to modifying the solid-to-liquid ratio, further studies on reaction time were conducted. With increasing reaction time, the recovery yield of Ni remained relatively stable, while the recovery yields of Co and Mn gradually decreased, significantly enhancing the separation efficiency of Ni and aiding in increasing its purity, Figure 24. After these experiments, it was determined that under conditions of a solid-to-liquid ratio of 50, a reaction time of 24 hours, and a temperature of 90 °C, the recovery yield of Ni reached 99.1% with a purity of 94.3% or the recovery yield of Ni reached 99.2% with a purity of 94.5%.

[0134] Since Ni was recovered in a precipitated form, Co and Mn remained in the DES as ions. To facilitate recycling and reuse of the DES, Co and Mn were co-precipitated using an anti-solvent method without destroying the DES structure. Ethanol was selected as the anti-solvent, and the liquid-to-liquid ratio of ethanol to DES was optimized for the co-precipitation of Co and Mn. As the amount of ethanol gradually increased, a slight decrease in the recovery rate of Co was observed, while the recovery rate of Mn significantly decreased (Figure 25). Ultimately, at a liquid-to-liquid ratio of 10, the highest recovery yields for Co and Mn were 98.3% and 96% (or 96.9%), respectively. Thus, Li, Ni, Mn, and Co were all recovered, with Co and Mn being recovered in a co-precipitated form. The final recovery yields of Li, Mn, Co, and Ni was 98.7%, 87.3%, 97.9%, and 98.8% respectively, or was 99.6%, 95.6%, 96.6%, and 99.2% respectively (Figure 26). Further selective separation of Co and Mn could be achieved through the methods described herein.

[0135] After recovery of all the metal elements, the DES containing ethanol was distilled at 70 °C to remove ethanol therefrom and recover DES. Comparisons were made between recovered ethanol and recovered DES with fresh ethanol and fresh DES through FTIR spectroscopy. Figure 27 and Figure 28 show that the structures of the recovered ethanol and the recovered DES were respectively similar to those of the fresh samples. It suggests that addition of ethanol did not alter the structure of the DES and that both recovered ethanol and recovered DES could be further recycled and reused. It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification is to be taken to be inclusive of features towhich the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0136] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0137] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and / or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.REFERENCES

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Claims

CLAIMS1. A process of separating a metal from a metal bearing material, wherein the process comprises:(1) leaching the metal bearing material with formic acid and forming a first leachate and a first separation residue, and(2) leaching the first separation residue with a deep eutectic solvent formed from choline chloride and formic acid and forming a second leachate and, optionally, a second separation residue.

2. The process according to claim 1, wherein the process comprises:(1) leaching the metal bearing material with formic acid and forming a first leachate comprising lithium (Li) and a first separation residue comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, comprising nickel (Ni); and(2) leaching the first separation residue with a deep eutectic solvent formed from choline chloride and formic acid and forming a second leachate comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, a second separation residue comprising nickel (Ni).

3. The process according to either claim 1 or claim 2, wherein the process comprises (3) treating the second leachate with an alcohol or a ketone so that cobalt (Co) and / or manganese (Mn) are / is removed in a solid form.

4. The process according to claim 3, wherein the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, glycerol, and a combination thereof, and the ketone is selected from the group consisting of acetone, butanone, 2-pentanone, 3-pentanone and a combination thereof.

5. The process according to either claim 3 or claim 4, wherein for step (3), the volume of the alcohol or the ketone to be used and the volume of the deep eutectic solvent comprised in the second leachate are at a ratio of about 5 L / L to 25 L / L, for example about 10 L / L to 25 L / L, about 5 L / L to 20 L / L, about 10 L / L or about 15 L / L.

6. The process according to any one of claims 1 to 5, wherein the process comprises (5) removing the alcohol or the ketone from the treated second leachate obtained from step (3) and, optionally, direct the alcohol recovered to step (3) for reuse.

7. The process according to any one of claims 1 to 6, wherein the process comprises (6) reusing the deep eutectic solvent contained in the treated second leachate obtained from step (3) for step (2).

8. The process according to any one of claims 1 to 7, wherein the process comprises (4) separating cobalt (Co) and manganese (Mn) in the solid form obtained from step (3) by use of oxalic acid so as to form a solution comprising manganese (Mn) and a precipitate comprising cobalt oxalate.

9. The process according to any one of claims 1 to 8, wherein the metal bearing material is a cathode material of an electrochemical device.

10. The process according to any one of claims 1 to 9, wherein the metal bearing material is a cathode material of a battery.

11. The process according to any one of claims 1 to 10, wherein the metal comprises one or more material selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn).

12. The process according to any one of claims 1 to 11, wherein the metal comprises or consists of lithium (Li) and one or more selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn).

13. The process according to any one of claims 1 to 12, wherein the metal bearing material comprises one or more material selected from the group consisting of lithium cobalt oxide (LiCoCL), lithium manganese oxide (LiMmCL), lithium nickel oxide (LiNiCL), lithium nickel cobalt oxides, lithium nickel manganese oxides, lithium cobalt manganese oxides, and lithium nickel manganese cobalt oxides.

14. The process according to any one of claims 1 to 13, wherein for the leaching of step (1), the metal bearing material and the formic acid are at a solid-to-liquid ratio (i.e. S / L ratio) of about 30 g / L to about 45 g / L.

15. The process according to any one of claims 1 to 14, wherein the leaching of step (1) is carried out at about 40 °C to 70 °C, for example about 60 °C.

16. The process according to any one of claims 1 to 15, wherein choline chloride and formic acid within the deep eutectic solvent of step (2) are at a molar ratio of about 1:2 to about 1:9, for example about17. The process according to any one of claims 1 to 16, wherein for the leaching of step (2), the first separation residue and the deep eutectic solvent are at a solid-to-liquid ratio (i.e. S / L ratio) of about 20 g / L to about 60 g / L, for example about 50 g / L.

18. The process according to any one of claims 1 to 17, wherein the leaching of step (2) is carried out at about 80 °C to about 100 °C, for example about 90 °C.

19. A process of separating a metal from a metal bearing material, wherein the process comprises leaching the metal bearing material with a deep eutectic solvent formed from choline chloride and formic acid and forming a leachate comprising one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, a separation residue.

20. Use of a deep eutectic solvent formed from choline chloride and formic acid as a leaching agent to separate a metal from a metal bearing material, wherein the metal bearing material comprises one or more metal selected from the group consisting of cobalt (Co) and manganese (Mn) and, optionally, comprises nickel (Ni).

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