Method for recovering nickel and cobalt via natural deep eutectic solvent-based ion exchange separation

Abstract

The present invention relates to a method for recovering nickel and cobalt via natural deep eutectic solvent (DES)-based ion exchange separation, the method comprising the steps of: (a) mixing nickel oxide and cobalt oxide with a natural deep eutectic solvent and dissolving same; (b) speciating nickel or cobalt ions into cationic species or anionic species by mixing the solution obtained in step (a) with water and hydrating same; and (c) recovering or removing the cationic species or anionic species contained in the solution obtained in step (b) by using a cationic ion exchange resin or an anionic ion exchange resin. By combining the natural deep eutectic solvent and the ion exchange separation, nickel and cobalt can be recovered in an environmentally-friendly and efficient manner.

Description

Nickel and Cobalt Recovery Method via Natural Eutectic Solvent-Based Ion Exchange Separation

[0001] The present invention relates to a method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method, and more specifically, to a method for recovering nickel and cobalt in an environmentally friendly and efficient manner by combining a natural eutectic solvent and an ion exchange separation method.

[0002] As energy production, decommissioning, and material processing activities grow rapidly worldwide, the volume of hazardous waste is surging, and waste inventories are reaching critical levels. According to the IAEA, there are currently millions of cubic meters of radioactive waste globally, including Very Low Level Waste (VLLW), Low Level Waste (LLW), Intermediate Level Waste (ILW), and High Level Waste (HLW).

[0003] General waste contains radioactive isotopes (RI) and metals such as nickel (Ni) and cobalt (Co), which often occur as corrosion products of reactor components like stainless steel. In addition to their presence in nuclear waste, Ni and Co are essential for energy storage and electronic devices, particularly lithium-ion batteries (LIBs), and are critical materials for battery performance and lifespan. As both metals are expensive and becoming increasingly scarce, developing efficient methods to recover them from nuclear and industrial waste is of great economic and environmental importance.

[0004] Meanwhile, as the aforementioned waste management involves complex issues and high processing costs due to difficulties in reducing waste volume, decontamination, and disposal, there is an increasing need for sustainable and cost-effective solutions that extend beyond nuclear waste to broader applications such as battery recycling and resource recovery from mining and industrial waste.

[0005] In this regard, Korean Registered Patent No. 10-0772967 describes thiocyanate ions (SCN) in an aqueous solution containing cobalt ions and nickel ions. - A method for selectively separating cobalt ions from an aqueous solution containing cobalt and nickel ions is disclosed, comprising the step of adding a source and then passing the obtained separation solution through an ion exchange column filled with a cation exchange resin to selectively adsorb cobalt ions contained in the separation solution onto the cation exchange resin. However, a method for recovering nickel and cobalt efficiently and in an environmentally friendly manner by combining a natural eutectic solvent and an ion exchange separation method as in the present invention is not disclosed.

[0006] The objective of the present invention is to provide a method for recovering nickel and cobalt in an environmentally friendly and efficient manner by combining a natural eutectic solvent with an ion exchange separation method.

[0007] To achieve the above objective, the present invention provides a method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method, comprising: (a) mixing and dissolving nickel oxide and cobalt oxide with a natural eutectic solvent (Deep Eutectic Solvent, DES); (b) speciating nickel or cobalt ions into cationic or anionic species by mixing and hydrating the solution obtained in step (a) with water; and (c) recovering or removing the cationic or anionic species contained in the solution obtained in step (b) using a cationic ion exchange resin or anionic ion exchange resin.

[0008] In addition, according to the present invention, a method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method is provided, wherein in step (a), the natural eutectic solvent comprises a hydrogen bond acceptor (HBA) which is choline chloride (ChCl) and a hydrogen bond donor (HBD) which is p-toluenesulfonic acid (pTSA) or ethylene glycol (EG).

[0009] In addition, according to the present invention, a method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method is provided, wherein the molar ratio of the hydrogen bond acceptor and the hydrogen bond donor is 1:2 to 2:1.

[0010] In addition, according to the present invention, in step (b), the cation species is Ni 2+ or Co 2+ and, the above anionic species is NiCl4 2- or CoCl4 2- A method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method is provided.

[0011] In addition, according to the present invention, a method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method is provided, further comprising the step of recycling the natural eutectic solvent obtained in step (c) by reusing it in step (a).

[0012] The method for recovering nickel and cobalt through a natural eutectic solvent (DES)-based ion exchange separation method (IX) according to the present invention is a stable anionic complex (e.g., NiCl4) in which Ni and Co ions can be separated more efficiently than in a hydrated form in which they coordinate with chloride ions in DES. 2- and CoCl4 2-Since it forms a ) and combines DES with the IX process to selectively separate Ni and Co, it has the advantage of not requiring the harsh chemical reagents and high-temperature environments commonly used in conventional extraction methods, and operates under mild conditions.

[0013] In addition, according to the present invention, by efficiently separating Ni and Co metals from waste, the volume of waste to be treated can be reduced. Furthermore, by operating under mild conditions, costs are reduced, and dependence on corrosive chemical reagents is also reduced, thereby providing the advantage of treating waste in an environmentally friendly manner.

[0014] However, the effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description below.

[0015] FIG. 1 is a diagram showing the process of recovering nickel and cobalt according to one embodiment of the present invention.

[0016] FIG. 2 is a diagram showing the percentage of dissolution by pre-hydration of nickel and cobalt oxides according to one embodiment of the present invention.

[0017] Figure 3 is a UV-Vis spectrum result measuring the speciation of nickel and cobalt according to various hydration rates according to one embodiment of the present invention.

[0018] FIG. 4 is a diagram showing the removal percentage of nickel and cobalt according to various hydration rates according to one embodiment of the present invention.

[0019] FIG. 5 is a diagram showing the percentage of removal of nickel and cobalt according to various hydration rates according to another embodiment of the present invention.

[0020] The present invention will be described in more detail below with reference to the attached drawings.

[0021] One aspect of the present invention provides a method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method, comprising: (a) mixing and dissolving nickel oxide and cobalt oxide with a natural eutectic solvent (Deep Eutectic Solvent, DES); (b) speciating nickel or cobalt ions into cationic or anionic species by mixing and hydrating the solution obtained in step (a) with water; and (c) recovering or removing the cationic or anionic species contained in the solution obtained in step (b) using a cationic ion exchange resin or anionic ion exchange resin.

[0022] In the present invention, step (a) is a step of mixing and dissolving nickel oxide and cobalt oxide with a natural eutectic solvent (Deep Eutectic Solvent, DES).

[0023] More specifically, in the present invention, the natural eutectic solvent refers to a substance that exists as a solution at 40 to 50°C or lower, with a lowered melting point when two naturally derived substances (liquid / solid or solid / solid) are mixed in a certain molar ratio at room temperature.

[0024] The above natural eutectic solvent is generally composed of a mixture of a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), and the chemical and physical properties of the natural eutectic solvent are determined according to the combination of the HBA and HBD.

[0025] In the present invention, the hydrogen bond acceptor (HBA) is preferably choline chloride (ChCl), and the hydrogen bond donor (HBD) is preferably p-toluenesulfonic acid (pTSA) or ethylene glycol (EG).

[0026] In the present invention, the molar ratio of the hydrogen bond donor and the hydrogen bond acceptor may be, for example, 1:2 to 2:1, but is not limited thereto.

[0027] In the present invention, step (b) is a step of speciating nickel or cobalt ions into cation species or anion species by mixing the solution obtained in step (a) with water to hydrate it.

[0028] In the present invention, when mixed with water and hydrated as described above, the metal ions of nickel or cobalt in the solution undergo speciation, and for example, when hydrated to 100% (without DES), Ni 2+ or Co 2+ It speciates into, and at 0% hydration (100% DES), NiCl4 2- or CoCl4 2- It speciates into.

[0029] In the present invention, step (c) is a step of recovering or removing cationic species or anionic species contained in the solution obtained in step (b) using a cationic ion exchange resin or anionic ion exchange resin.

[0030] In the present invention, for example, the recovery or removal of metal ions contained in ChCl:pTSA or ChCl:EG DES is carried out by contacting the metal-DES solution with various IX media.

[0031] More specifically, according to the present invention, a cationic IX resin medium is contacted with a solution to form a metal (e.g., Ni) in ChCl:pTSA or ChCl:EG DES. 2+ and Co 2+ ) can be recovered or removed, and by contacting the solution with an anionic IX resin medium, metal (e.g., NiCl4) in ChCl:pTSA or ChCl:EG DES can be recovered or removed. 2- and CoCl4 2- ) can be recovered or removed.

[0032] Meanwhile, in the present invention, if metal species are recovered or removed from, for example, ChCl:pTSA or ChCl:EG DES through step (c), clean DES is obtained, so that this DES can be recycled by reusing it in step (a).

[0033]

[0034] The present invention will be explained in more detail below through examples. However, these examples are intended to illustrate the invention and the scope of the invention is not limited to these examples.

[0035]

[0036] Example 1: Experimental Method

[0037] 1-1 Reagents

[0038] Choline chloride (≥98%), p-toluenesulfonic acid (pTSA-ACS reagent, ≥98.5%), and ethylene glycol (anhydrous, 99.8%) were purchased from Sigma Aldrich. All metal oxides used in the dissolution and separation experiments were purchased from Sigma Aldrich (based on 99.9% trace metals). All nuclear-grade ion exchange resins, NRW150, NRW160, PFA445, and A555, were Purolite TM It was purchased from (see Table 1). The core grade indicates that no resin pretreatment is required. All reagents were used as is without further purification. The water used was purified using a Millipore system (18 ΩM).

[0039] Table 1

[0040]

[0041]

[0042] 1-2 Synthesis of DES

[0043] ChCl-pTSA DES was synthesized by mixing pTSA and ChCl in a molar ratio of 2:1. Subsequently, the mixture was heated to 60°C and mixed at 400 rpm for 2 hours to completely dissolve the components. Once the DES mixture was synthesized, it was cooled to room temperature before use for metal dissolution. ChCl:EG DES was synthesized using a similar method, with the molar ratio changed to 1:2. Both DES mixtures were prepared in an open bench without atmospheric control to mimic actual applications.

[0044]

[0045] 1-3 Sign language of DES

[0046] The water content was adjusted to modify the properties of DES. Adding water to DES allows for the use of a low-viscosity medium, facilitating the incorporation of IX resin. To investigate the effect of water content on metal dissolution, initial hydration percentage values ​​were selected at 0 wt% (pure DES), 20 wt%, 40 wt%, 60 wt%, and 80 wt%. Since the hydration step was performed after dissolving metal oxides in DES, 100 wt% (pure water) was omitted. It is noteworthy that almost no dissolution occurred when metal oxides were dissolved in 100 wt% water. After hydration, the hydrated DES medium was brought into contact with the selected IX resin.

[0047]

[0048] 1-4 Metal Melting and Separation

[0049] Metal oxides NiO and CoO were selected for dissolution. Subsequently, 0.1 g of the metal oxide was added to 5 mL of DES and stirred for 48 hours to ensure all metals were dissolved. Once dissolved, 0.1 g of IX resin (Purolite TMNRW150, NRW160, PFA445, and A555) were brought into contact with a DES-metal solution and shaken in an orbital shaker for 48 hours and left at room temperature. After 48 hours, the resins were separated from the DES solution by filtration using a syringe and syringe filter. All dissolution and separation experiments were repeated three times. Subsequently, the supernatant was stored and treated in 10 wt% nitric acid for inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis (ThermoScientific iCAP 6000 ICP spectrometer equipped with a CETAC ASX-520 autosampler).

[0050]

[0051] 1-5 Measuring Instruments

[0052] The chemical structures and successful synthesis of pTSA-ChCl and EG-ChCl DES were analyzed using Fourier transform infrared spectroscopy (FT-IR-TENSOR27) and UV-vis (Shimadzu UV-2600i). Scanning electron microscopy (SEM) and energy-dispersive X-rays (EDX) were used to confirm the presence of metal on the surface of the IX resin. All SEM and EDX analyses were performed using a FE-SEM 7800F Prime.

[0053]

[0054] Example 2: Results and Discussion

[0055] 2-1 DES Synthesis and Properties

[0056] Choline chloride-based p-toluenesulfonic acid (ChCl:pTSA) and ethylene glycol (ChCl:EG) DES were synthesized in ratios of 1:2 and 2:1, respectively. The purity and successful synthesis of each DES were confirmed by FTIR and UV-vis spectroscopic analysis of the synthesized DES, ChCl:pTSA, and ChCl:EG.

[0057]

[0058] 2-2 Metal Oxide Leaching

[0059] For initial testing, both ChCl:pTSA and ChCl:EG DES were pre-hydrated prior to metal oxide dissolution to evaluate dissolution efficiency. As shown in Figure 2, the dissolution percentage generally decreased with increasing moisture content, but the initial dissolution efficiency varied depending on whether the samples were pre-hydrated or anhydrous. For pre-hydrated DES (20-80% hydration), the initial dissolution efficiency was approximately 85% for both Ni and Co in the pTSA-based DES at 20% hydration. Similarly, for the EG-based DES, the initial dissolution efficiency was approximately 90% for Ni and 85% for Co.

[0060]

[0061] Efficient dissolution was observed during pre-hydration, which may be due to reduced metal viscosity and improved mass transfer in each DES. However, dissolution efficiency began to decrease when the hydration rate exceeded 20%, and at 100% hydration, metal oxides (metal oxides soluble only in water) were minimally dissolved or did not dissolve at all. In ChCl:pTSA, NiO dissolved less efficiently than CoO, whereas in ChCl:EG, NiO dissolved more efficiently than CoO. This may be because CoO dissolves more easily in more acidic media. However, complete dissolution was not achieved due to the solubility limit of oxides in water.

[0062]

[0063] However, when the metal oxide was dissolved in pure DES, complete dissolution was achieved (Fig. 2). Hydrating this metal-DES solution facilitated the next step IX. It is important to note that as the hydration level increases, the concentration of the metal oxide decreases, so it is necessary to normalize the ICP results to account for the addition of the IX resin and the lowered metal oxide concentration, thereby calculating the actual dissolution percentage.

[0064]

[0065] 2-3 Speciation of metal complexes due to hydration

[0066] The coordination chemistry of Ni and Co was significantly influenced by the solvation environment, resulting in different species in water and DES. Ni in 100% water 2+ Wa Co 2+ It exists as a hydrated cation, but in 100% DES, it mainly forms anionic chloride complexes. This difference in solvation not only determines chemical behavior but also affects electronic transitions that can be observed through UV-Vis spectroscopy.

[0067]

[0068] 2-3-1 Speciation in Pure Water

[0069] Ni in a pure aqueous solution environment 2+ Wa Co 2+ As expected, it is stabilized as a hydrated metal cation, and both ions form an octahedral complex in which six water molecules coordinate around the metal center, forming the major species Ni(H2O)6 2+ and Co(H2O)6 2+ It generated. The hydration of these ions occurred due to strong ion-dipole interactions between the metal cation and surrounding water molecules. At higher pH, [Ni(OH)] + or [Co(OH)] + Hydroxide complexes such as [the above] can be formed, but under neutral or weakly acidic conditions, hexaaqua complexes were maintained predominantly.

[0070]

[0071] 2-3-2 Speciation in Pure DES

[0072] Conversely, the DES environment promoted the formation of anionic chloride complexes due to high chloride ion concentrations. For example, in choline chloride-based DES, Ni 2+ and Co 2+ It coordinates with chloride ions to form [NiCl4] 2- and [CoCl4] 2-It formed complexes such as [CoCl4(H2O)2]. The tetrahedral coordination geometry stabilized by chloride ions was preferred due to ionic interactions between the metal center and the chloride ligand. Depending on the specific DES and moisture content, [CoCl4(H2O)2] 2- Mixed coordination species such as can also potentially be formed, which reflects the dynamic solvation characteristics of the hydrated DES system. For reference, Ni 2+ is Co 2+ Because it has a smaller ionic radius and higher charge density compared to [NiCl6], under certain conditions [NiCl6] 4- It can form higher coordination states such as.

[0073]

[0074] 2-3-3 UV-Vis: Coordination and Electronic Transitions

[0075] Ni and Co species in water and DES significantly influence the UV-Vis spectra, reflecting the different electronic environments of each solvent. Co in water 2+ wa Ni 2+ All of them exhibited characteristic dd transitions within the octahedral coordination structure. [Ni(H2O)6], a Ni hexaaqua complex 2+ It exhibited absorption bands at 390–430 nm and 600–700 nm (Figs. 3a and c). Co hexaaqua complex [Co(H2O)6] 2+ Is 4 T1g(F)→ 4 It absorbed weakly in the 510–530 nm range corresponding to the T1g(P) transition (Figs. 3b and d).

[0076] Ni in DES 2+ Wa Co 2+ The UV-Vis spectrum is dominated by ligand-metal charge transfer (LMCT) and dd transitions of chloride complexes. In the case of Ni, [NiCl4] 2-The morphology absorbs more strongly than water, and the absorption bands shifted at 700–800 nm and 500–600 nm, appearing yellowish-green (Figs. 3a and c). These stronger absorption bands and the rightward shift of the bands in DES occurred due to more permissible dd transitions in the tetrahedral geometry and strong coordination with chlorides. In the case of cobalt, [CoCl4] 2- The complex 4 A2(F)→ 4 Strong absorption in the 600–700 nm range was observed due to the T1(P) transition, resulting in a characteristic intense blue color (Figs. 3b and d).

[0077]

[0078] 2-3-4 Effects of Hydrolysis on Speciation in DES

[0079] The addition of water to DES introduced a competitive solvation environment, altering the coordination geometry and speciation of metal ions. As the hydration level increased, there was a gradual transition from chloride-coordinated species to hydrated species. For Co in EG-based DES, the change in speciation occurs at approximately 30% hydration, and Co(H2O)6 2+ Co was found to be the dominant species. On the other hand, Co of pTSA-based DES showed a similar conversion at about 40% hydration, indicating that potential differences in HBD components affect the stability of chloride complexes and the individual complexes formed.

[0080] Ni showed a similar trend, but the change in speciation was less pronounced, particularly in pTSA-based DES. These subtle changes in speciation due to hydration can be consistent in the separation process. For example, IX resin can be used to selectively separate Ni and Co based on coordination preference in these DES environments. This is because metal ions exhibit different affinities for chlorides versus physical ligands. While recent studies have highlighted this speciation using similar conditions, this invention focuses solely on speciation, and separation via speciation was performed by fixing the metal chloride concentration as the water content increased.

[0081]

[0082] Possibility of separating Co and Ni via 2-3-5 IX

[0083] Differences in the speciation of Ni and Co between water and DES, along with transitions following hydration, provide opportunities for selective separation strategies. IX resins can separate Ni from Co by leveraging the different binding affinities of metal species. For example, Ni forms chloride complexes that are more stable in DES compared to Co, allowing it to selectively adsorb to specific resins with the appropriate functional groups. Changes in coordination due to hydration selectively target the unique solvation environments of Ni and Co, thereby allowing Ni 2+ Wa Co 2+ Since it can remove ions, it further enhances the potential of customized separation processes.

[0084]

[0085] The distinct species of Ni and Co and their corresponding UV-Vis absorption characteristics in water and DES environments provide a basis for understanding their chemical behavior and interactions in these new DES solvents. Table 2 summarizes the differences in coordination species and UV-Vis absorption of Co and Ni in both water and DES.

[0086] Table 2

[0087]

[0088] 2-4 Single metal absorption using ion exchange resin

[0089] DES solutions containing Ni and Co were applied to batch-by-batch IX experiments using the following resin: Purolite TM NRW150 and NRW160, cation resins, PFA445 and A555 anion resins. Each IX resin was individually contacted with a metal oxide-DES solution for 48 hours, and each experiment was repeated three times. The percentage of metal species removal is shown in Figure 4.

[0090]

[0091] For cation exchange resins NRW150 and NRW160 (Figs. 4a and b), minimal removal of Ni and Co at 0% hydration was observed in both pTSA and EG-based DES. This is attributed to the speciation of Ni and Co, where at 0% hydration, the metals are mainly in anionic form ([NiCl4] 2- , [CoCl4] 2- It exists as ). As the hydration level increases, more cationic species (Ni 2+ , Co 2+ ) is generated, which can be effectively removed by the cation exchange resin. As the hydration level increased, 80–100% of Ni and Co were removed using cation exchange resins in both pTSA and EG DES, and EG showed slightly higher removal efficiency for both metals compared to pTSA.

[0092]

[0093] A similar trend was observed in anion exchange resins PFA445 and A555 (Figs. 4c and d). Anionic forms of Ni and Co ([NiCl4]) at 0% hydration. 2- , [CoCl4] 2-...was effectively removed. However, as hydration increased, the proportion of anionic species decreased, leading to a reduction in removal efficiency. The main reason for this is that the injection of water causes DES components to dissociate, generating more hydrated forms of Ni and Co that are incompatible with the anionic resin. Even at 0% hydration, Ni and Co could not be completely removed by the anionic resin. This is likely due to mass transfer limitations, as the high viscosity of unhydrated DES hinders the diffusion of metal species. The calculated maximum theoretical ion exchange capacities (IEC) for each resin—NRW150, NRW160, PFA445, and A555—were 46.95, 61.63, 41.08, and 32.28 g / L, respectively. This indicates that the amount of metal in the solution is less than the maximum capacity of the resin, suggesting that viscosity is causing issues. ChCl:EG showed a slight improvement in removal efficiency compared to ChCl:pTSA, which may be due to the lower viscosity of the former.

[0094]

[0095] 2-5 Multi-metal absorption using ion exchange resin

[0096] The separation, recovery, or removal of Ni and Co are all critical for the nuclear active and corrosion species, resource recovery of consumed LIB cathode materials, and general mining. Therefore, the feasibility of separating and recovering Ni and Co using DES-IX was investigated. Stock solutions of Ni and Co containing ChCl:pTSA and ChCl:EG DES were prepared by dissolving both Ni and Co in DES solutions. These solutions were prepared using Purolite, the same resin mentioned above. TM NRW150, NRW160, PFA445, and A555 were used for the batch-by-batch IX experiments. Each IX resin was individually contacted with a metal oxide-DES solution for 48 hours, and each experiment was repeated three times. The percentage of metal species removal is shown in Figure 5.

[0097]

[0098] Using cation and anion exchange resins in DES Co 2+ and Ni 2+ The selective absorption of ions is determined by factors such as hydration level, ion complexation, and resin type. These considerations influence how Co and Ni interact with the resin, depending on complex formation with DES components or chloride ions, and ion mobility within various hydration levels.

[0099]

[0100] 2-5-1 Ni of Cation Exchange Resin 2+ and Co 2+ absorption

[0101] In the case of cation exchange resins that directly adsorb positively charged species, Ni 2+ and Co 2+ The absorption is directly influenced by ion mobility and complex stability within DES. The viscosity of DES, driven by water content, plays an important role in regulating the transport of metal ions to the resin sites.

[0102]

[0103] At low hydration rates (0–30%), the high viscosity of the solution and strong coordination interactions between metal ions and DES components limit ion mobility, thereby restricting resin adsorption. Co may form less stable complexes in DES than Ni due to ligand field stabilization. In other words, Co is more readily available for exchange and may be adsorbed preferentially over Ni. However, chloride complexes ([NiCl4] 2- and [CoCl4] 2- ) is formed, so the cation exchange cannot be efficiently performed at a hydration rate of 0%. As the hydration rate increases above 0%, it can be observed that both Ni and Co are slightly removed from ChCl:pTSA and ChCl:EG (Figs. 5a-d).

[0104]

[0105] At moderate hydration levels (30–60%), viscosity decreases, leading to greater ion solvation and mobility. Figures 3b and c show that the speciation peak intensity of Co ions drops significantly in both ChCl:pTSA and ChCl:EG, and more Ni 2+ and Co 2+ Indicates that ions are formed. Ni 2+ and Co 2+ As ions are now more readily available for exchange, [NiCl4] 2- and [CoCl4] 2- The paper was less formed. However, Ni 2+ Since it has a higher charge density and a smaller ionic radius, it tends to form stronger interactions with the resin, so removal appears to converge toward Co removal. This change is due to Co as mobility constraints are relaxed. 2+ See Ni 2+ It makes absorption more favorable.

[0106]

[0107] At high hydration rates (60-80%), DES viscosity decreases significantly and metal ions are well solvated. Co 2+ wa Ni 2+ is easier to use for exchange again, but Ni 2+ Generally, due to charge density and affinity for the active site of the resin, Co 2+ It exhibits stronger bonding to the resin. Figures 5a and b show complete convergence of Ni and Co removal, indicating less competition between the two separate ions for sites on the IX resin at 80–100% hydration. Due to weak complexing, the cation exchange resin Co at low moisture content 2+ While showed a more favorable exchange with, Ni 2+ Absorption increased at high moisture levels where it binds more efficiently.

[0108]

[0109] 2-5-2 Absorption of anion exchange resin through anion complexes

[0110] In the case of anion exchange resins, the absorption of Co and Ni depends on the formation of anionic complexes, because these resins are designed to adsorb negatively charged species. In chloride-rich DES solutions, Co 2+ wa Ni 2+ is [NiCl4] 2- and [CoCl4] 2- It can form anionic species, which can be adsorbed onto the resin. The stability and solubility of these anionic complexes depend significantly on the moisture content of DES, which affects the competition between Co and Ni absorption.

[0111]

[0112] At low hydration rates (0-30%), high chloride concentrations are present, forming the anionic complex [NiCl4] 2- and [CoCl4] 2- It induces the formation of stable metal ions together. Ni generally forms more stable chloride complexes due to its higher charge density and tendency to coordinate strongly with chloride ions, resulting in [NiCl4] absorption by the resin as shown in Figs. 5e-h. 2- is preferred.

[0113]

[0114] At moderate hydration levels (30-60%), solvation is introduced, weakening the stability of the chloride complex. Nevertheless, Ni 2+ is Co 2+ Although Ni absorption is still likely to be preferred as it maintains a more stable complex with chlorides, the gap between Ni and Co absorption begins to narrow as solvation destabilizes the complex. This is primarily due to the increased dissociation of DES components.

[0115]

[0116] When the hydration rate is 60-80%, the chloride complex becomes destabilized as solvation competes with chloride coordination, so Co 2+ and Ni 2+The ions become more available as free-solvated cations. Since this resin is designed for anionic species, stable [NiCl4] 2- and [CoCl4] 2- Due to a lack of complexes, minimal absorption occurs as shown in Figures 5e-h.

[0117]

[0118] 2-5-3 Comparative Absorption

[0119] In DES solutions with low water content, the cation exchange resin is mainly Co 2+ While it captures [NiCl4], anion exchange resins [NiCl4] due to differences in complex formation stability. 2- It prefers complexes. As the hydration level increases, solvation reduces viscosity, enhances ion mobility, and promotes the dissociation of metal-chloride complexes. Due to these changes, the cation exchange resin Co 2+ See Ni 2+ While absorption is preferred, the anion exchange resin shows a decrease in overall absorption due to the destabilization of the necessary chloride complex.

[0120]

[0121] In general, cation exchange resins did not show a significant difference in removal efficiency between pTSA and EG DES. However, for anion exchange resins, particularly A555, high removal efficiency was observed for both Ni and Co up to 40–60% hydration. This indicates a change in species (Cl in DES) as hydration increases. - This can be explained by competition between the cationic and anionic forms of metal species that may be affected by availability. The delayed transition from anionic to cationic species as hydration increases may further explain the observed trend.

[0122]

[0123] 2-6 Conclusion

[0124] The present invention has successfully demonstrated the dissolution, speciation, and removal of Ni and Co using DES at various hydration levels. In initial tests, dissolution efficiency peaked at approximately 20% hydration, achieving over 75-80% for both metals using pre-hydrated DES. Furthermore, complete dissolution was achieved at 100% DES, and the resulting solution was hydrated, allowing the metals to be fully utilized in the subsequent IX process.

[0125]

[0126] The speciation of Ni and Co was significantly influenced by the hydration environment. In 100% water, both metals are hydrated cations [(Ni(H2O)6] 2+ and [Co(H2O)6] 2+ While it exists as ), in 100% DES, it mainly exists as anionic chloride complexes ([NiCl4] 2- and [CoCl4] 2- ... was formed. As the hydration level increased, the species coordinated to chloride was converted into a hydrated form, making selective separation strategies using IX resin easier.

[0127]

[0128] The present invention relates to a cation exchange resin that has Ni at a higher hydration level. 2+ and Co 2+ It was further confirmed that while effectively removing [the substance], the anion exchange resin initially captures anion species. However, as hydration increased, the stability of these anion complexes decreased, affecting removal efficiency. Overall, the results of the present invention demonstrated that a customized separation process utilizing the unique solvation environments of Ni and Co can minimize environmental impact by supporting circular economy principles through improved recovery and resource management efforts in various applications and enabling resource recycling and reuse.

[0129]

[0130] From the foregoing description, those skilled in the art to which the present invention pertains will understand that the present invention may be implemented in other specific forms without altering its technical concept or essential features. In this regard, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of the present invention should be interpreted as including all modifications or variations derived from the meaning and scope of the claims set forth below and their equivalents, rather than from the detailed description above.

Claims

1. (a) A step of mixing and dissolving nickel oxide and cobalt oxide with a natural eutectic solvent (Deep Eutectic Solvent, DES), (b) a step of speciating nickel or cobalt ions into cation or anion species by mixing the solution obtained in step (a) with water to hydrate it, and (c) a step of recovering or removing cationic species or anionic species contained in the solution obtained in step (b) using a cationic ion exchange resin or anionic ion exchange resin, a method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method.

2. In Paragraph 1, A method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method, wherein in step (a) above, the natural eutectic solvent comprises a hydrogen bond acceptor (HBA) which is choline chloride (ChCl) and a hydrogen bond donor (HBD) which is p-toluenesulfonic acid (pTSA) or ethylene glycol (EG).

3. In Paragraph 2, A method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method, wherein the molar ratio of the hydrogen bond acceptor and the hydrogen bond donor is 1:2 to 2:

1.

4. In Paragraph 1, In step (b) above, the cation species is Ni 2+ or Co 2+ and, the above anionic species is NiCl4 2- or CoCl4 2- Method for recovering nickel and cobalt through phosphorus, natural eutectic solvent-based ion exchange separation.

5. In Paragraph 1, A method for recovering nickel and cobalt through a natural eutectic solvent-based ion exchange separation method, further comprising the step of recycling the natural eutectic solvent obtained in step (c) by reusing it in step (a).

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