Modified anion exchange resin for removal of metals from spent lithium-ion batteries and process thereof

Abstract

The present invention discloses ligand-modified anion exchange resins for the selective removal of lithium, cobalt, nickel, and manganese from acid-leached spent lithium-ion batteries. The resins are synthesized through in-situ modification of styrene–divinylbenzene matrices using sodium salts of selected ligands in a deoxygenated ethanol–water medium. The developed process enables efficient sorption and separation of target metals under competitive leachate conditions. Batch continuous and fixed-bed column studies confirm the high removal efficiency, sequential selectivity, and stable performance of the ligand-modified resins. The synergistic chelation–exchange mechanism imparts enhanced selectivity and robustness compared to unmodified resins. The invention provides a scalable and sustainable method for strategic metal removal, supporting circular economy objectives in lithium-ion battery recycling.

Description

FIELD OF THE INVENTIONThe present invention relates to the field of ion exchange resins. More specifically,the present invention provides a ligand modified anion exchange resins and processfor preparing the ligand modified anion exchange resins. The present invention alsoprovides a method for the removal of metals from spent lithium-ion batteries usingthe ligand modified anion exchange resins.BACKGROUND OF THE INVENTIONThe global energy transition is driving unprecedented demand for lithium-ionbatteries (LIBs), primarily due to their superior energy density, long cycle life, andfavourable weight-to-volume ratio. LIBs have become indispensable in portableelectronics and electric vehicles (EVs), where electrification of transport is a centralstrategy for mitigating greenhouse gas emissions, reducing urban air pollution, andlowering dependence on fossil fuels. Between 2021 and 2022 alone, the globaldemand for LIBs grew by 65%, increasing from 330 GWh to 550 GWh, largelydriven by a 55% surge in EV sales. Forecasts suggest that demand will rise nearlyseven-fold by 2030, reaching about 4.7 TWh. Correspondingly, the generation ofspent lithium-ion batteries (SLIBs) is expected to escalate, with an estimated 12.85million tons of EV batteries reaching end-of-life by 2030. This will necessitate thesupply of more than 10 million tons of critical metals such as lithium (Li), cobalt(Co), nickel (Ni), and manganese (Mn) for new LIB production.A typical LIB consists of a graphite anode, lithium metal oxide cathode (such asLiCoO₂ or NMC-based materials), polymer separator, organic electrolyte, andcopper / aluminium current collectors. Recycling these components is essential forensuring resource security, environmental sustainability, and reduction of relianceon primary mining of critical metals. To address this need, three principal recyclingmethods have been developed: pyrometallurgical, hydrometallurgical, and directrecycling (Larouche et al., Progress and status of hydrometallurgical and directrecycling of Li-ion batteries and beyond, Materials (2020) 13(3), 801).Pyrometallurgical processes employ high-temperature smelting (>1500°C) torecover metals such as cobalt, nickel, and copper in alloy phases. However, thismethod suffers from substantial drawbacks, including loss of lithium andaluminium to slag, high energy intensity, significant greenhouse gas emissions, andinefficiencies in recovering lighter metals (Lee et al., Pyrometallurgical recyclingof end-of-life lithium-ion batteries, International Journal of Minerals, Metallurgyand Materials (2024),31, 1554-1571). Hydrometallurgical processes, in contrast,utilize aqueous solutions commonly mineral acids such as H₂SO₄, HCl, or HNO₃combined with reducing agents like H₂O₂ to leach valuable metals from shreddedbatteries. Although hydrometallurgy achieves high metal removal efficiencies(often exceeding 90%) and is scalable, it generates secondary liquid waste, requirescostly reagents, and involves complex pH control (Premathilake et al., Advancinghydrometallurgical recycling of spent lithium-ion batteries: An AI-based readinessand sustainability assessment. RSC Sustainability (2025)). Direct recyclingmethods, aimed at reconditioning intact cathode materials through relithiation andstructural repair, are environmentally promising but remain confined to laboratoryscale research due to technical limitations such as accurate battery sorting and theabsence of standardized recycling protocols (Ji et al., Fundamentals, status andchallenges of direct recycling technologies for lithium-ion batteries, ChemicalSociety Reviews (2023), 52(23), 12345-12378).Given these limitations, there is a growing emphasis on alternative, sustainablerecycling technologies that enable selective and efficient removal of critical metalsfrom SLIBs. Ion exchange technology (IXT) has emerged as a promising methodand operates on the principle of exchanging target metal ions in leachates with ionsbound to a solid resin matrix, thereby enabling high selectivity in metal removal.Compared to conventional methods such as chemical precipitation, solventextraction, and electrochemical separation, IXT offers several advantages such asreduced chemical consumption, resin reusability, and minimized generation ofsecondary waste (Kumar & Kumar, Solvent extraction / ion exchange for metalseparation and recovery, National Metallurgical Laboratory (2021)). Moreover,IXT systems can be integrated into existing hydrometallurgical circuits forenhanced process efficiency. Typically, SLIBs are subjected to mechanicalseparation, thermal pretreatment, and subsequent hydrometallurgical leaching usinginorganic or organic acids, with or without reducing agents, to extract metals suchas Li, Co, Ni, and Mn. Traditional downstream processes for metal separationincluding chemical precipitation and solvent extraction often lack selectivity andincrease environmental burden. By contrast, ion exchange resins provide greaterselectivity, reusability, and process sustainability, thereby reducing both operationalcosts and ecological impact. Several more prior arts in the related technology havebeen listed below.WO2024034327A1 discloses a treatment method for obtaining a solution of nickeland / or cobalt, from a waste battery. It discloses application of sodium hydroxide foralkali leaching of the solution of waste battery followed by reduction of the alkalileachate using an acid solution and a reducing agent. Further discloses the acidsolution can be of hydrochloric acid. The method further discloses a sulfidation stepof adding a sulfidizing agent to the reduction leachate, wherein the sulfidizing agentcan be sodium sulfide (Na2S). Furthermore, there is an oxidation neutralization stepinvolved wherein sodium hydroxide (NaOH) is used as a neutralizing agent forprecipitating and removing valuable metals from the waste. The neutralization stepis followed by an ion-exchange step for separating by adsorption onto the ionexchange resin and obtain an ion-exchanged solution containing Ni and / or Co.US7504036B2 discloses a method for impregnating metal complexes into anionexchange materials to provide modified anion exchange resins for effectively andefficiently removing or recovering various metals from process solutions, effluentsand aqueous solutions. The method comprises steps of loading an anionic substancecomprising a metal containing complex onto an anion exchange material followedby immobilizing at least a portion of the metal of the metal containing complexinside the anion exchange material. Further discloses application of NaOH andNa2S for activating the anion exchange resin so that the hydroxide and sulfide anioncomponents will break the metal complexes present in the process solutions andprecipitate or immobilize the metals inside the anion exchange resin. Furthermore,the process disclosed therein is capable of loading transition metals such as Fe, Cu,Mn, Zn.JP2019099874A discloses a method for recovering Li from manufacturing processwastewater containing lithium and aluminum of positive electrode material forlithium secondary battery using a weakly acidic cation exchange resin having asulfonic acid group and a modified resin with functional group of sodium salt type.IN393640B discloses a synthesis method for hybrid iron sulfide impregnated anionexchanger for selective removal of hexavalent chromium from contaminated water.The process discloses an anion exchange resin containing styrene-divinyl benzenematrix and quaternary ammonium functional group are kept in contact with Na2Ssolution in an orbital shaking incubator for dispersing sulfide within anion exchangeresin. Further discloses, sulfide dispersed anion exchange resin on contacting witha solution containing metal ions facilitates in-situ metal nanoparticle loading insidethe resin matrix. Further discloses, the preconditioning of anion exchange resindisclosed therein involves successive rinsing of the resin with NaOH and HClsolutions. Furthermore, the disclosed process for selective removal of hexavalentchromium from contaminated water involves application of both the parent anionexchanger and the modified anion exchanger in sulfide form.Despite the advantages associated with IXT, large scale application of ion exchangein SLIB recycling faces several challenges as certain resins exhibit preferentialaffinity for specific ions, leading to incomplete removal or co-extraction ofunwanted metals. Also, organic contaminants and particulates in leachates mayblock active sites of the resin, decreasing efficiency and service life. High ionicstrength and the presence of multiple metal species complicate selective separation.Although reusable, resins require periodic regeneration with harsh chemicals,producing additional waste streams. Further, industrial adoption requires carefuloptimization of IX conditions and seamless integration into hydrometallurgicalleaching circuits.Therefore, there exists a strong need for innovation in this domain. Advances inresin material science, hybrid systems, and improved pretreatment protocols canovercome current limitations. Optimizing the hydrometallurgical leaching stage andcoupling it with ion exchange for selective and efficient removal of cobalt, nickel,lithium, and manganese from SLIBs holds the potential to significantly improveindustrial feasibility, reduce environmental impact, and contribute to circulareconomy goals in battery manufacturing.To overcome the limitations of the prior arts, the present invention focusses on thedevelopment of ligand modified anion exchange resins and the use of modifiedanion exchange resins in removing valuable metals like cobalt, nickel, manganese,and lithium from the acid-leached solution of SLIBs.OBJECTIVES OF THE INVENTIONThe main objective of the present invention is to provide a ligand modified anionexchange resinsAnother objective of the present invention is to provide a ligand modified anionexchange resins for the removal of valuable metals including cobalt (Co), nickel(Ni), manganese (Mn), and lithium (Li), from spent lithium-ion batteries.Another objective of the present invention is to provide a process for the preparationof ligand-modified anion exchange resins, wherein the ligands include carbonate,citrate, hydroxide, nitrite, oxalate, sulfide and phosphate.Another objective of the present invention is to provide a continuous batch processfor the removal of metals including cobalt (Co), nickel (Ni), manganese (Mn), andlithium (Li), from spent lithium-ion batteries.Another objective of the present invention is to provide a continuous fixed-bedprocess for the removal of metals including cobalt (Co), nickel (Ni), manganese(Mn), and lithium (Li), from spent lithium-ion batteries.SUMMARY OF THE INVENTIONThis summary is provided to introduce a set of concepts, in a simplified format, thatwill be further explained in the detailed description of the invention. This summaryis neither intended to identify the main concepts or key concepts of the invention,nor is it intended to describe the scope of the invention.The present invention provides a modified anion exchange resin, comprising:-a polymer matrix functionalised with amine group; and-a ligand,wherein the anion exchange resin is modified by incorporating the ligand inthe polymer matrix.The present invention also provides a process of preparing a modified anionexchange resin, process comprising:a) preconditioning an anion exchange resin with 0.05 to 0.1 Mhydrochloric acid solution;b) contacting 10 to 20 g of the preconditioned anion exchange resinwith a ligand salt solution prepared in a deoxygenated solventmixture of ethanol and water under an inert atmosphere, at atemperature in a range of 29 to 31°C to obtain a resin solutionmixture, wherein ethanol and water are present in a ratio in the rangeof 30:70 to 40:60 % v / vc) subjecting the resin solution mixture to rotation at 100 to 120 rpmfor a time period in a range of 3 to 4 hours at a temperature in a rangeof 29 to 31°C to obtain a suspension; andd) allowing the suspension to settle and separating a sediment bydecanting followed by washing and drying at a temperature in arange of 45 to 50°C under the inert atmosphere to obtain themodified anion exchange resin.The present invention further provides a method for removing metals from spentlithium-ion battery, comprising:-extracting a black mass from spent lithium-ion battery;-subjecting the black mass to acid leaching with an inorganic acid followedby treatment with an oxidising agent to obtain dissolved metal containingacid leachate; and-contacting the metal containing acid leachate with a modified anionexchange resins as defined herein or a combination thereof for removal ofmetals, wherein the metals are cobalt (Co+2), nickel (Ni+2), manganese(Mn+2), and lithium (Li+2).BRIEF DESCRIPTION OF THE DRAWINGSThe following figures form part of the present specification and are included tofurther illustrate aspects of the present disclosure. The disclosure may be betterunderstood by reference to the figures in combination with the detailed descriptionof the specific embodiments presented herein.Figure 1 depicts performance of parent anion exchange resins and ligand modifiedanion exchange resins for the removal of cobalt, nickel, manganese and lithiumfrom synthetic solution.Figure 2 depicts performance of parent anion exchange resins and ligand modifiedanion exchange resins for the removal of cobalt, nickel, manganese and lithiumfrom acid leached spent lithium-ion batteries.Figure 3 depicts schematic of reactor set up for the continuous batch study for theremoval of cobalt, nickel, manganese and lithium.Figure 4 depicts the overall removal efficiency and overall uptake capacity oflithium, cobalt, nickel and manganese during continuous batch study for (a).Reactor 1 (b). Reactor 2 and (c). Reactor 3.Figure 5 depicts schematic of reactor set up for the continuous fixed bed columnstudy for the removal of cobalt, nickel, manganese and lithium.Figure 6 depicts breakthrough curve of cobalt, nickel, manganese and lithium in acontinuous fixed bed column reactor.DETAILED DESCRIPTION OF THE INVENTIONFor convenience, before further description of the present disclosure, certain termsemployed in the specification, and examples are delineated here. These definitionsshould be read in light of the remainder of the disclosure and understood as by aperson of skill in the art.The terms used herein have the meanings recognized and known to those of skill inthe art, however, for convenience and completeness, particular terms and theirmeanings are set forth below. The articles "a", "an" and "the" are used to refer toone or to more than one (i.e., to at least one) of the grammatical object of the article.The terms "comprise" and "comprising" are used in the inclusive, open sense,meaning that additional elements may be included. It is not intended to be construedas "consists of only". The term "at least one" is used to mean one or more and thusincludes individual components as well as mixtures / combinations. Throughout thisspecification, unless the context requires otherwise the word "comprise", andvariations such as "comprises" and "comprising", will be understood to imply theinclusion of a stated element or step or group of element or steps but not theexclusion of any other element or step or group of element or steps. The term"including" is used to mean "including but not limited to". "including" and"including but not limited to" are used interchangeably.Unless defined otherwise, all technical and scientific terms used herein have thesame meaning as commonly understood by one of ordinary skill in the art to whichthis disclosure belongs. Although any methods and materials similar or equivalentto those described herein can be used in the practice or testing of the disclosure, thepreferred methods and materials are now described.The present disclosure is not to be limited in scope by the specific embodimentsdescribed herein, which are intended for the purposes of exemplification only.Functionally equivalent products, compositions, and methods are clearly within thescope of the disclosure, as described herein.The present invention provides ligand modified anion exchange resins, wherein themodification is achieved by incorporating functional ligands capable of facilitatingselective interaction and precipitation of target metal ions, cobalt (Co), nickel (Ni),manganese (Mn), and lithium (Li), within the anion exchange resin matrix.The present invention provides a process for the preparation of ligand modifiedanion exchange resins, wherein the resin, comprising a styrene-divinyl benzenematrix with benzyl trimethyl amine functional groups, is first preconditioned bysuccessive rinsing with HCl to remove impurities. The preconditioned resin is thentreated with a deoxygenated water-ethanol mixture containing a solution of sodiumcarbonate, sodium citrate, sodium hydroxide, sodium nitrite, sodium oxalate,sodium sulfide or sodium phosphate, separately, in an orbital shaking incubator.Following this treatment, the ligand modified anion resin is separated, thoroughlywashed, and subsequently dried under nitrogen. Optionally, the dried resin may bestored in ethanol solution under airtight conditions to preserve its functionality.The present invention provides an individual batch process employing ligandsupported modified anion exchange resins for the removal of cobalt (Co), nickel(Ni), manganese (Mn), and lithium (Li). The ligand modified anion exchange resinsinclude carbonate-modified anion exchange resin, citrate-modified anion exchangeresin, hydroxide-modified anion exchange resin, nitrite-modified anion exchangeresin, oxalate-modified anion exchange resin, sulfide-modified anion exchangeresin, and phosphate-modified anion exchange resin. The performance of the ligandmodified anion exchange resins is assessed using both synthetic solutionscontaining equivalent concentrations of individual metals, cobalt (Co), nickel (Ni),manganese (Mn), and lithium (Li), to replicate the composition of SLIBs leachatesand acid-leached solutions of SLIBs. By employing these different ligands modifiedanion exchange resins, the invention enables a systematic assessment of theirperformance in terms of metal ion interaction, selective precipitation, and removalefficiency. This novel approach provides a comprehensive understanding of thesuitability of ligand modified anion exchange resins for efficient removal ofvaluable metals.The modified anion exchange resin is the ligand modified anion exchange resin.In an aspect, the present invention provides a modified anion exchange resin,comprising:-a polymer matrix functionalised with amine group; and-a ligand,wherein the anion exchange resin is modified by incorporating the ligand inthe polymer matrix.In an embodiment of the present invention, the amine group is selected from thegroup consisting of benzyl trimethyl amine, benzyl triethyl amine, dimethylethanolamine, diethyl ethanolamine, ethylenediamine, triethylenetetramine,imidazole, and combinations thereof, and wherein the amine functional group is ina concentration in a range of 1.1 to 1.8 meq / g of the polymer matrix.In an embodiment of the present invention, the polymer matrix is made of acopolymer of styrene and divinylbenzene.In an embodiment of the present invention, the ligand is selected from carbonate,citrate, hydroxide, nitrite, oxalate, sulfide and phosphate, and wherein the ligandgroup is in a concentration in a range of 1.1 to 1.8 meq / g of the total exchangecapacity of the polymer matrix.In another aspect, the present invention provides a process of preparing amodified anion exchange resin, process comprising:a) preconditioning an anion exchange resin with 0.05 to 0.1 Mhydrochloric acid solution;b) contacting 10 to 20 g of the preconditioned anion exchange resinwith a ligand salt solution prepared in a deoxygenated solventmixture of ethanol and water under an inert atmosphere, at atemperature in a range of 29 to 31°C to obtain a resin solutionmixture, wherein ethanol and water are present in a ratio in the rangeof 30:70 to 40:60 % v / v;c) subjecting the resin solution mixture to rotation at 100 to 120 rpmfor a time period in a range of 3 to 4 hours at a temperature in a rangeof 29 to 31°C to obtain a suspension; andd) allowing the suspension to settle and separating a sediment bydecanting followed by washing and drying at a temperature in arange of 45 to 50°C under the inert atmosphere to obtain themodified anion exchange resin.In an embodiment of the present invention, the ligand salt solution is selected froma solution of sodium carbonate in a concentration in a range of 0.2 to 0.7 M, sodiumcitrate in a concentration in a range of 0.1 to 0.5 M, sodium hydroxide in aconcentration in a range of 0.2 to 0.7 M, sodium nitrite in a concentration in a rangeof 0.2 to 0.5 M, sodium oxalate in a concentration in a range of 0.2 to 0.7 M, sodiumsulfide in a concentration in a range 0.1 to 0.4 M and sodium phosphate in aconcentration in a range 0.2 to 0.7 M.In a further aspect, the present invention provides a method for removing metalsfrom spent lithium-ion battery, comprising:-extracting a black mass from spent lithium-ion battery;-subjecting the black mass to acid leaching with an inorganic acid followedby treatment with an oxidising agent to obtain dissolved metal containingacid leachate; and-contacting the metal containing acid leachate with a modified anionexchange resin as defined in claim 1 or a combination thereof for removalof metals, wherein the metals are cobalt (Co+2), nickel (Ni+2), manganese(Mn+2), and lithium (Li+2).In an embodiment of the present invention, the inorganic acid is selected from thegroup consisting of sulphuric acid, phosphoric acid, hydrochloric acid, and aquaregia, and wherein the oxidising agent is selected from the group consisting ofhydrogen peroxide, potassium permanganate, sodium hypochlorite, sodiumpersulfate, sodium chlorate, and combinations thereof.In an embodiment of the present invention, the acid leaching with sulphuric acid ina concentration in a range of 0.5 to 1 M gives metal dissolution efficiency in a rangeof 92 to 99.6 %.In an embodiment of the present invention, a sequential combination of citratemodified anion exchange resin, phosphate-modified anion exchange resin, andcarbonate-modified anion exchange resin has a Lithium (Li+1) removal efficiencyof 99.71%, Cobalt (Co+2) removal efficiency of 99.85%, Nickel (Ni+2) removalefficiency of 99.94%, and Manganese (Mn+2) removal efficiency of 99.97%,In an embodiment, the present invention provides a continuous batch system for theremoval of metals from a solution containing metals from SLIBs or selected froma group comprising cobalt, nickel, manganese, and lithium or a combination thereofusing the citrate-modified anion exchange resin, phosphate-modified anionexchange resin and carbonate-modified anion exchange resin. In the first stage, themetal containing solution is contacted with citrate-modified anion exchange resinin a primary reactor, resulting in the formation of a treated liquid phase, referred toas supernatant A. Supernatant A is then transferred to a second reactor, where it isbrought into contact with phosphate-modified anion exchange resin to furtherdecrease dissolved metal concentrations, yielding supernatant B. The processcontinues by passing supernatant B into a third reactor, wherein it is treated with acarbonate-modified anion exchange resin. This final stage produces supernatant C,characterized by significantly very low levels of targeted metals. This sequentialreactor system, employing citrate-modified anion exchange resin, phosphatemodified anion exchange resin and carbonate-modified anion exchange resin incombination provides a highly efficient and systematic approach for multi-metalremoval from metal contaminated solutions.In an embodiment, the present invention provides a continuous fixed-bed systemfor the removal of metals from a solution containing metals selected from a groupcomprising cobalt (Co), nickel (Ni), manganese (Mn), and lithium (Li) or acombination thereof using citrate-modified anion exchange resin, phosphatemodified anion exchange resin, oxalate-modified anion exchange resin andhydroxide-modified anion exchange resins. In this configuration, the solutioncontaining the target metals is continuously passed through a two-column setuparranged in series. The first column is packed with citrate-modified anion exchangeresin and phosphate-modified anion exchange resin, which initiates the removal ofmetal contaminants. The partially treated effluent is then directed to the secondcolumn containing oxalate-modified anion exchange resin and hydroxide-modifiedanion exchange resin, where additional purification is achieved through selectiveion exchange and precipitation. This dual fixed-bed system, integrating citratemodified anion exchange resin, phosphate-modified anion exchange resin, oxalatemodified anion exchange resin and hydroxide-modified anion exchange resin,provides a robust and scalable treatment method with high efficiency for multimetal selective removal in a continuous flow mode.EXAMPLES:Example 1. Preparation of ligand modified anion exchange resins.The present invention provides a process for the preparation of ligand modifiedanion exchange resins such as carbonate-modified anion exchange resin (C-AX),citrate-modified anion exchange resin (Ci-AX), hydroxide-modified anionexchange resin (H-AX), nitrite-modified anion exchange resin (N-AX), oxalatemodified anion exchange resin (O-AX), sulfide-modified anion exchange resin (SAX), and phosphate-modified anion exchange resin (P-AX) through an in-situsynthesis process and the process comprises the following steps are discussedbelow:i. Preconditioning of anion exchange resin.The parent anion exchange resin / anion exchange resin (AX) [Commercial Name:INDION GS 300, Chemical and physical properties are in Table 1] employedcomprises a styrene-divinylbenzene matrix functionalized with benzyl trimethylamine groups. Prior to use, the anion exchange resin is subjected to apreconditioning step to ensure removal of impurities and activation of the ionexchange sites. The resin is treated with 0.05 to 0.1 M hydrochloric acid (HCl)solution, allowing effective displacement of residual ions and surface contaminants.Following this acid treatment, the resin is thoroughly rinsed with deionized water.Table 1. Chemical and physical properties of INDION GS 300.ii.Selection of solvent medium.A deoxygenated ethanol-water mixture is employed as the reaction medium duringthe modification steps, as it provides both resin swelling and ligand stability. Theinclusion of ethanol promotes swelling of the resin beads, thereby enhancing theaccessibility of internal functional groups within the polymer matrix, while thedeoxygenated condition, maintained by sparging nitrogen gas, prevents oxidativedegradation of ligands. To balance these requirements with the need for solubilityand stability of sodium carbonate, sodium citrate, sodium hydroxide, sodium nitrite,sodium oxalate, sodium sulfide and sodium phosphate, which are readily soluble inwater but less so in ethanol, the ethanol-water ratio is optimized. The preferred ratioranges from 30:70 to 40:60 (ethanol: water, v / v), with 30:70 being the most suitable,as it provides sufficient ethanol content to induce swelling without compromisingsolubility and ionic mobility of the modifying agents. Ratios above 50:50 tend toreduce solubility and hinder ion diffusion, whereas ratios below 20:80 diminish theswelling benefit imparted by ethanol.iii. Process of dispersing ligands within anion exchange resin.For the preparation of ligand modified anion exchange resins, whereinpreconditioned anion exchange resins are subjected to controlled ligandincorporation under inert and optimized reaction conditions. The modification isachieved by contacting the preconditioned resin with sodium salts of selectedligands in a deoxygenated ethanol-water medium, thereby ensuring efficient ionexchange and stable incorporation of the ligand ions.Briefly, 20 g of preconditioned anion exchange resin is contacted with 100 mL ofligand salt solution prepared in an optimized deoxygenated ethanol-water mixture(30:70 v / v) under an inert atmosphere, at a temperature in a range of 29 to 31°C.The resin-solution mixture is transferred into a 250 mL batch reactor and subjectedto orbital shaking at 100 rpm for a duration of 3 - 4 hours, while maintaining atemperature of 30 ± 0.5°C to obtain a suspension. Throughout the process,continuous purging with nitrogen gas is applied to provide an inert atmosphere andto preserve the stability of ligand ions during exchange. This configuration ensuresuniform mixing, strict temperature control, and reproducible modificationconditions.The novelty of this invention resides in the optimization of ligand saltconcentrations for each selected ligand, which maximizes the uptake efficiency offunctional ligand ions while reducing reagent wastage and preventing theaccumulation of unbound residues. The optimized concentrations are determined asfollows: sodium carbonate, 0.4 M (range 0.2-0.7 M); sodium citrate, 0.3 M (range0.1-0.5 M); sodium hydroxide, 0.5 M (range 0.2-0.7 M); sodium nitrite, 0.3 M(range 0.2-0.5 M); sodium oxalate, 0.5 M (range 0.2-0.7 M); sodium sulfide, 0.2M (range 0.1-0.4 M); and sodium phosphate, 0.3 M (range 0.2-0.7 M). Within theseoptimized ranges, the chloride ions originally present in the resin matrix are fullydisplaced by the corresponding ligand ions, resulting in chemically stable andreproducible ligand-supported resins. Successful incorporation is visuallyconfirmed through a distinct colour change of the resin beads, serving as a practicalindicator of modification.By maintaining all reaction conditions constant except for the type and optimizedconcentration of ligand salt the invention provides a generalized yet adaptablepreparation method applicable across a range of ligands. This standardizationensures comparability between different ligand systems, reproducibility of the resinmodification process, and suitability for selective removal of cobalt, nickel, andmanganese ions from complex aqueous matrices, including synthetic solutions andspent lithium-ion battery (SLIB) leachates.iv. Separation, washing and storage.Upon completion of the modification, the ligand modified anion exchange resin isin the form of suspension and is allowed to settle down and sediments are separatedfrom the reaction medium by decantation. The separated resin is subsequentlywashed with distilled or deionized water to ensure removal of residual, and anyreaction byproducts. This washing step is repeated until a neutral pH of the washsolution is achieved, thereby confirming complete elimination of excess reagents.Following the washing stage, the resin is subjected to controlled drying atapproximately 50°C under a nitrogen atmosphere. The inert atmosphere minimizesthe risk of atmospheric contamination or moisture uptake, thereby preserving thefunctional integrity of the modified anion exchange resin. Optionally, the dried resinmay be stored in ethanol solution within an airtight container, which furtherenhances the stability of the modified form during long-term storage and preventsoxidative degradation.Application of Modified Anion Exchange ResinsExample 2. Removal of metals from spent lithium-ion batteriesThe method for removal of metals from lithium-ion batteries is as follows:1. Preparation of Spent Lithium-Ion Battery Black Mass.Black mass, a carbon-rich powder containing high-value metals, was recoveredfrom SLIBs following a systematic pre-treatment protocol. The SLIBs were firstfully discharged by immersion in a 5 - 10 wt.% NaCl solution for 72 hours, wherethe residual charge was utilized to drive electrolysis and ensure safe handling. Afterdrying, the external casings were carefully dismantled to minimize the risk of shortcircuits and thermal runaway. The electrode assemblies were then unrolled, andcathode sheets-comprising lithium metal oxides coated on aluminium foils-wereselectively separated owing to their high metal content. These cathode sheets weretreated with 5 -10 wt.% NaOH at 60°C for 4 hours, resulting in the detachment ofthe active material as a sludge. The sludge was subsequently washed, dried at 105°C for 24 hours, and the resulting black powder, referred to as black mass, wascollected. The metal composition of the black mass was characterized using an Xray fluorescence (XRF) spectrometer. The analysis revealed cobalt (Co) andmanganese (Mn) as the predominant metals, accounting for 44% and 40% of thetotal metal content, respectively. Nickel (Ni) was present in smaller amounts at10.85%, while aluminium (Al), attributed to residual foil or impurities, contributedless than 3%. Lithium (Li), though present, could not be accurately quantified byXRF due to its low fluorescent yield and the long-wavelength nature of itscharacteristic radiation. Therefore, Inductively Coupled Plasma Mass Spectrometry(ICP-MS) was employed, which determined the lithium content to beapproximately 4% by weight. The overall composition of the recovered black massaligns with that of cathode materials commonly used in lithium-ion chemistries,including LiCoO2, Li(NiMnCo)O2, and LiMn2O4.2. Acid Leaching of Black Mass.The black mass derived from SLIBs was subjected to an acid leaching process torender the contained transition metals into soluble ionic forms suitable for selectiveremoval by ligand modified ion exchange resins. A predetermined quantity of blackmass was placed in a 500 mL glass reactor, followed by the addition of an inorganicacid of defined concentration together with an oxidising agent, such as hydrogenperoxide (H2O2), to facilitate dissolution. The reactor was maintained undercontrolled hydrodynamic conditions using a magnetic stirrer equipped with a hotplate and temperature sensor, enabling precise regulation of agitation speed andthermal input. After a defined contact period, the slurry was filtered to obtain aliquid leachate containing dissolved cationic metals, including lithium, cobalt,nickel, and manganese, and a solid residue comprising the undissolved fraction ofthe black mass.Systematic studies were conducted to evaluate the influence of acid type,concentration, and temperature on the dissolution efficiency of the black mass. Fouracids were tested sulfuric acid (H2SO4), phosphoric acid (H3PO4), hydrochloric acid(HCl), and aqua regia each at a concentration of 0.5 M, under controlled operatingconditions of 30°C, 60°C, and 90°C with agitation at 100 rpm for 120 minutes.The efficiency of the leaching process was assessed by quantifying the solid residueafter filtration, which served as an indicator of incomplete dissolution. Among thetested lixiviants, H2SO4 consistently produced the least residue, followed by H3PO4,while HCl and aqua regia left substantial undissolved mass. At 90°C and 0.5 Mconcentration, H2SO4 achieved a dissolution efficiency of 92%, establishing it asthe most effective lixiviant under comparable conditions. The observed temperaturedependence confirmed that dissolution is kinetically controlled, with elevatedtemperatures enhancing both solubility and leaching kinetics of the transitionmetals.Further optimization of the process focused on increasing the concentration ofH2SO4 to achieve near-complete dissolution. When the concentration was increasedfrom 0.5 M to 1 M at 90°C, the solid residue decreased from approximately 0.4 gto less than 0.01 g, corresponding to leaching efficiencies of 92% and 99.6%,respectively. This improvement is attributed to enhanced proton activity at higheracid concentrations, which promotes lattice breakdown of cathode materials andstabilizes metal ions in solution through sulfate complexation. The comparativeefficiencies of the acids were determined to follow the order: H2SO4 (1 M, 99.6%)> H2SO4 (0.75 M, 98%) > H2SO4 (0.5 M, 92%) > H2PO4 (0.5 M, 76%) > Aqua regia(0.5 M, 40%) > HCl (0.5 M, 24%). These results confirm H2SO4 as the preferredlixiviant due to its superior ability to simultaneously deliver proton-drivendissolution and stable complexation of transition metals.Under the optimized leaching conditions of 1 M sulfuric acid at 90°C, the blackmass was efficiently transformed into a homogeneous ionic solution enriched withLi⁺, Co²⁺, Ni²⁺, and Mn²⁺. The corresponding concentrations were lithium (2.09g / L), cobalt (6.74 g / L), nickel (3.54 g / L), and manganese (15.65 g / L). Among these,manganese exhibited the highest solubility, followed by cobalt and nickel, whilelithium showed comparatively lower dissolution. This outcome confirms theeffectiveness of H2SO4 in extracting transition metals from the black mass andproducing a feed solution hereinafter referred to as the feed leachate directlycompatible with the multi-reactor ion-exchange configuration of the presentinvention.Performance of ligand modified anion exchange resinTo validate the inventive concept of ligand-modified anion exchange resins, theperformance of the ligand-modified anion exchange resins for the removal oflithium, manganese, cobalt and nickel was compared against parent cationresin / cation exchange resin (CX) and parent anion resin (AX). Batch adsorptionstudies were conducted first with synthetic multicomponent metal concentrationsequivalent to SLIB leachates, followed by acid-leached SLIB matrices to assessreal-world applicability. Controlled experimental conditions (solution volume 100mL, resin dosage 8 g, 90°C, 100 RPM, 1 - 2 h) were maintained across all trials toensure comparability.a. Performance in synthetic solutions and acid-leached SLIBs.Unmodified resins, CX and AX resin, exhibited only baseline activity. CX showedmoderate uptake of Mn²⁺ (92.8 mg / g), Ni²⁺ (90.2 mg / g), and Co²⁺ (86.0 mg / g), butminimal Li⁺ removal (12.2 mg / g). AX showed uniformly low uptake across all ions(15 - 31 mg / g), confirming the limited applicability of unmodified AX systems. Bycontrast, ligand-modified anion exchange resin demonstrated enhanced capacitiesand distinct ion selectivity. For example, C-AX, P-AX nearly doubled Mn²⁺ uptakecapacity, 196.8 mg / g and 194.0 mg / g, respectively compared to parent AX, withsignificant Co²⁺ and Ni²⁺ binding. S-AX and N-AX preferentially targeted Mn²⁺,while H-AX displayed clear affinity for Ni²⁺ uptake capacity as 78.4 mg / g. O-AXdemonstrated balanced uptake of Ni²⁺ (75.1 mg / g) and Co²⁺ (91.4 mg / g). Ci-AXshowed the highest overall performance, with 231.7 mg / g Mn²⁺, 125.2 mg / g Co²⁺,55.3 mg / g Ni²⁺, and a unique Li⁺ uptake of 48.2 mg / g, a capability not observed inother resins (Figure 1).When tested with real acid-leached SLIBs (Figure 2), overall uptake capacitiesmoderately declined due to multi-ion competition, altered speciation, and leachateacidity. Nonetheless, ligand-functionalized systems retained their relativeselectivity patterns and superiority over unmodified resins. C-AX and P-AXachieved Mn²⁺ uptake values of 131.2 mg / g and 130.2 mg / g, respectively, withreduced Co²⁺ (61.8-63.2 mg / g) and Ni²⁺ (24-27 mg / g) capacities. S-AX and N-AXmaintained Mn²⁺ preference (85.5-109.6 mg / g) but with diminished efficienciescompared to synthetic solutions. H-AX continued to favour Ni²⁺ (40.9 mg / g), whileO-AX showed dual affinity toward Ni²⁺ (28.0 mg / g) and Co²⁺ (60.9 mg / g). Mostnotably, Ci-AX preserved its superior performance under competitive SLIBconditions, recording 143.0 mg / g for Mn²⁺, 67.7 mg / g for Co²⁺, 35.7 mg / g for Ni²⁺,and 28 mg / g for Li⁺.Direct comparison between Figures 1 and 2 confirms that synthetic solutionsrepresent the maximum potential of ligand-metal interactions, while real SLIBleachates introduce competitive suppression. Unmodified CX and AX showeddrastic declines under SLIB conditions (<40 mg / g for Mn²⁺, <20 mg / g for Ni²⁺ andCo²⁺), while ligand-functionalized systems preserved selective binding throughsynergistic ion-exchange and ligand chelation. Among all, Ci-AX remained themost robust, retaining high capacities across all ions, including lithium.The inventive ligand modification transforms conventional anion exchangers intohighly selective dual-function sorbents capable of removing Mn, Co, Ni, and Lifrom complex SLIB matrices. The citrate-modified resin demonstrated the greatestadvantage, maintaining high uptake and selectivity under both synthetic and realleachate conditions. This establishes the invention as a technically significantadvancement for hydrometallurgical removal, offering enhanced selectivity,operational stability, and potential for scalable application in spent lithium-ionbattery recycling.b. Ligand modified anion exchange resin in continuous batch systemThe present disclosure describes a continuous batch system designed for theselective and sequential removal of cobalt, nickel, manganese, and lithium ionsfrom metal-containing acid leachates of SLIBs. The process employs three typesof ligand-modified anion exchange resins namely, citrate-modified anion exchangeresin, phosphate-modified anion exchange resin, and carbonate-modified anionexchange resin in a reactor sequence, ensuring maximum efficiency of removalthrough staged treatment under optimized operating conditions. The schematics ofthe reactor configuration is provided in Figure 3 and details of the reactor situationis discussed below.i.Reactor 1 (Treatment with Citrate-Modified Anion Exchange Resin):A pre-leached acidic solution containing dissolved metals (Co, Ni, Mn, Li) isintroduced into a first batch reactor maintained at 50 ± 2°C under continuousstirring at 100 rpm to ensure uniform contact. The solution is brought into contactwith a measured quantity of citrate-modified anion exchange resin (4 g), and theinfluent flow is continued until resin saturation is achieved. Saturation occurswithin approximately 60 minutes from the start of contact, beyond which noadditional removal of cobalt, nickel, manganese, or lithium is observed. The treatedeffluent is recovered as Supernatant A, which exhibits significantly reducedconcentrations of the target metals relative to the influent solution.ii.Reactor 2 (Treatment with Phosphate-Modified Anion Exchange Resin):Supernatant A is immediately transferred into a second reactor containingphosphate-modified anion exchange resin. The reactor is maintained similarly at 50± 2°C under continuous stirring (100 rpm) to facilitate resin-solute interactions.Metal removal progresses until equilibrium saturation is achieved, which istypically observed after 90 minutes of contact time in the second reactor. After thisstage, no further reduction of metal concentration is observed. The resulting treatedsolution is collected as Supernatant B, containing substantially lower levels ofdissolved metals compared to Supernatant A.iii. Reactor 3 (Treatment with Carbonate-Modified Anion Exchange Resin):Supernatant B is subsequently passed into a third batch reactor containingcarbonate-modified anion exchange resin. The system is again maintained at 50 ±2°C with C under continuous stirring (100 rpm) to facilitate resin-soluteinteractions. Contact is continued until equilibrium is reached, requiringapproximately 60 minutes. This final stage is particularly critical since the acidleached solution entering this reactor (Supernatant B) still contains residual cobalt,nickel, manganese, and lithium at concentrations sufficient for further removal.Following this treatment, the resulting effluent, Supernatant C, is obtained, whichis characterized by markedly low residual concentrations of all targeted metals.Performance of Ligand modified anion exchange resinIn the reactor 1, after 60 minutes of operation at 50 ± 2°C under continuous stirring,the resin achieved saturation. The resin exhibited selective removal of the targetmetals with removal efficiencies of 45.9% for lithium, 43.7% for cobalt, 41.8% fornickel, and 39.6% for manganese. The corresponding uptake capacities werecalculated as 24 mg / g, 72.1 mg / g, 37 mg / g, and 155 mg / g, respectively (Figure 4a).The results demonstrate that the citrate-functionalized resin shows comparativelyhigher affinity toward cobalt and manganese, attributable to stronger complexationof these divalent transition metal ions. Although not achieving complete removal,this step effectively reduced the initial metal load and prevented prematuresaturation of subsequent resins.In the second stage reactor, the partially treated effluent (Supernatant A) wassubjected to treatment with phosphate-modified anion exchange resin. After 90minutes of contact under identical conditions, the resin reached equilibrium.Removal efficiencies of 67.3% for lithium, 64.7% for cobalt, 73.7% for nickel, and59.3% for manganese were obtained, corresponding to uptake capacities of 19mg / g, 60 mg / g, 38 mg / g, and 140 mg / g of resin, respectively (Figure 4b). Comparedto the citrate-modified resin, the phosphate-modified resin demonstrated enhancedand more balanced removal performance across all metals, with particularlysignificant improvement in nickel uptake. This enhanced performance is attributedto the strong coordination potential of phosphate groups with divalent transitionmetals through electrostatic attraction and inner-sphere complexation.The third reactor, employing carbonate-modified anion exchange resin, proved tobe the most effective step in the sequence. Upon 60 minutes of contact at 50 ± 2°C,near-complete elimination of residual metals from Supernatant B was achieved. Theremoval efficiencies were 98.4% for Li, 99.2% for Co, 99.6% for Ni, and 99.9% forMn, corresponding to uptake capacities of 9.1 mg / g, 32.5 mg / g, 13.5 mg / g, and 96mg / g of resin, respectively (Figure 4c). The outstanding performance of thecarbonate-modified resin is attributed to its strong affinity for transition metalsthrough inner-sphere complexation and potential precipitate-like interactions underacidic conditions. Notably, even lithium typically more difficult to remove wascaptured with very high efficiency (98.4%), underscoring the broad-spectrumremoval capability of the resin.The sequential three-stage treatment employing ligand-modified anion exchangeresins has demonstrated outstanding effectiveness in the removal of lithium, cobalt,nickel, and manganese from SLIBs. Starting with high initial concentrations (Li:2090 mg / L, Co: 6594 mg / L, Ni: 3542 mg / L, Mn: 15,645 mg / L), the staged processprogressively reduced metal levels to near-complete elimination, with final effluentconcentrations of 6 mg / L (Li), 10 mg / L (Co), 2 mg / L (Ni), and 5 mg / L (Mn). Thiscorresponds to total removal efficiencies of 99.71%, 99.85%, 99.94%, and 99.97%,respectively.The success of this approach is rooted in the strategic deployment of distinct ligandfunctionalities at each stage. The citrate-modified resin provided the first barrier,reducing the overall metal load and preventing downstream resin saturation. Thephosphate-modified resin, with strong affinity for transition metals, ensuredsubstantial secondary removal, further lowering concentrations. Finally, thecarbonate-modified resin functioned as a polishing step, exploiting bothcomplexation and precipitation-like interactions to capture residual metals withnear-quantitative efficiency.An important aspect of this system is that no pH adjustment or additional reagentswere required, allowing the process to operate under the intrinsic conditions of theacid-leached solution. This not only simplifies the treatment scheme but alsoenhances sustainability by avoiding secondary waste generation. Moreover, thestaged configuration enhances selectivity and efficiency by distributing theadsorption burden across multiple resins, ensuring each operates under favourablebinding conditions.The outcome is a highly purified effluent (Supernatant C), suitable for directdischarge under environmental compliance standards or as a purified feedstock forstrategic metals. Beyond its technical efficiency, the process demonstratesreproducibility, scalability, and adaptability to continuous operation, making it apromising candidate for industrial deployment in sustainable lithium-ion batteryrecycling.c. Ligand modified anion exchange resin in a continuous column systemThe fixed-bed continuous column experiment was designed using two Plexiglascolumns arranged in series (Figure 5), each with a bed height of 8 cm and an EBCTof 25 minutes. The first column was packed with citrate-modified and phosphatemodified anion exchange resins. The effluent from this first stage was then directedinto the second column, which was filled with oxalate-modified and hydroxidemodified anion exchange resins. The influent acid-leached liquor containinglithium, nickel, cobalt, and manganese at high concentrations, was pumped throughthe system using a microprocessor-based peristaltic pump at 0.3 mL / min, ensuringsteady flow and a constant head across both columns.The breakthrough curves obtained from the study (Figure 6) followed acharacteristic sigmoidal pattern, typical of fixed-bed adsorption systems. Initially,all four metals were completely retained, as evidenced by the absence of detectableconcentrations in the effluent up to about 200 minutes. Beyond this point, lithiumwas the first species to appear in the effluent, indicating that its affinity for themodified ligands was comparatively weaker than the transition metals. Nickelfollowed soon after, while cobalt began to elute at later times. Manganese exhibitedthe strongest retention, with breakthrough observed only after prolonged operation.This sequential appearance reflects the competitive binding behaviour of theligands and the relative stabilities of the metal-ligand complexes formed within thepacked beds.A more quantitative analysis using the practical 5% of influent concentration as thebreakthrough criterion provides further clarity. Lithium reached its 5%breakthrough at approximately 260 minutes, which corresponds to 5.2 bed volumesof treated liquor. Nickel followed at 300 minutes (6.0 bed volumes), cobalt at 340minutes (7 bed volumes), and manganese at 420 minutes (8.5 bed volumes). Thissequential breakthrough order clearly shows that the resin system preferentiallyretains transition metals, particularly manganese and cobalt, while lithium isremoved to a lesser extent.The total metal removal capacity of the two-column system was estimated byintegrating the difference between the influent and effluent concentrations over thecourse of the experiment. The system removed approximately 195 mg of lithium,366 mg of nickel, 849 mg of cobalt, and 2,421 mg of manganese before saturationof the resins occurred. When normalized to the packed bed volume of 15 g, thecorresponding adsorption capacities were about 13 g / kg bed for lithium, 24 g / kgbed for nickel, 57 g / kg bed for cobalt, and 161 g / kg bed for manganese. Thesevalues confirm that the ligand-modified resins are highly effective for transitionmetal removal, while lithium is less effectively captured. The superior retention ofmanganese and cobalt is attributed to their strong complexation with oxalate ligandsand the formation of hydroxide precipitates within the second column, whichfurther prolongs their retention.The reasons for this behaviour lie in the chemistry of the ligands used. Citrate andphosphate in the first column promote complexation with multivalent cations butbind weakly to lithium, which explains its early breakthrough. Oxalate in the secondcolumn forms particularly stable complexes with nickel, cobalt, and manganese,while hydroxide modification enhances removal by generating localized pHincreases that trigger precipitation of transition metal hydroxides. This combinedmechanism prolongs the retention of cobalt and manganese, which is why theybreak through only at later stages. The strong preference for transition metals isadvantageous when the goal is to purify lithium streams by removing contaminants,but it is less effective if lithium capture itself is desired.In summary, the continuous fixed-bed study successfully demonstrated sequentialand selective removal of metals from an acid-leached liquor. Lithium, with theweakest interaction, broke through earliest, followed by nickel and cobalt, whilemanganese was strongly retained due to combined chelation and precipitationeffects. The results clearly highlight the effectiveness of ligand-modified anionexchange resins for transition-metal capture, while also identifying the limitationsof lithium removal under the tested conditions.Advantages of the modified anion exchange resin of the present invention:1. Ligand driven selectivity: Functional groups, carbonate, phosphate, hydroxide,oxalate, citrate, sulfide and nitrite, provided tailored affinity, enablingdifferential removal of Mn, Ni, Co, and Li.2. Chelation exchange synergy: Unlike conventional resins, ligand-modifiedsystems operate via dual pathways; electrostatic ion exchange and coordinationdriven binding yielding both higher capacity and selectivity.3. Robustness in real leachates: Even under high competition and acidity of SLIBleachates, ligand-functionalized systems, especially Ci-AX, preservedefficiency, validating their industrial applicability.

Claims

1. A modified anion exchange resin, comprising: -a polymer matrix functionalised with amine group; and -a ligand, wherein the anion exchange resin is modified by incorporating the ligand in the polymer matrix.

2. The modified anion exchange resin as claimed in claim 1, wherein the amine group is selected from the group consisting of benzyl trimethyl amine, benzyl triethyl amine, dimethyl ethanolamine, diethyl ethanolamine, ethylenediamine, triethylenetetramine, imidazole, and combinations thereof, and wherein the amine functional group is in a concentration in a range of 1.1 to 1.8 meq / g of the polymer matrix.

3. The modified anion exchange resin as claimed in claim 1, wherein the polymer matrix is made of a copolymer of styrene and divinylbenzene.

4. The modified anion exchange resin as claimed in claim 1, wherein the ligand is selected from carbonate, citrate, hydroxide, nitrite, oxalate, sulfide and phosphate, and wherein the ligand group is in a concentration in a range of 1.1 to 1.8 meq / g of the total exchange capacity of the polymer matrix.

5. A process of preparing a modified anion exchange resin, process comprising: a) preconditioning an anion exchange resin with 0.05 to 0.1 M hydrochloric acid solution; b) contacting 10 to 20 g of the preconditioned anion exchange resin with a ligand salt solution prepared in a deoxygenated solvent mixture of ethanol and water under an inert atmosphere, at a temperature in a range of 29 to 31°C to obtain a resin solutionmixture, wherein ethanol and water are present in a ratio in the range of 30:70 to 40:60 % v / v c) subjecting the resin solution mixture to rotation at 100 to 120 rpm for a time period in a range of 3 to 4 hours at a temperature in a range of 29 to 31°C to obtain a suspension; and d) allowing the suspension to settle and separating a sediment by decanting followed by washing and drying at a temperature in a range of 45 to 50°C under the inert atmosphere to obtain the modified anion exchange resin.

6. The process as claimed in claim 5, wherein the ligand salt solution is selected from a solution of sodium carbonate in a concentration in a range of 0.2 to 0.7 M, sodium citrate in a concentration in a range of 0.1 to 0.5 M, sodium hydroxide in a concentration in a range of 0.2 to 0.7 M, sodium nitrite in a concentration in a range of 0.2 to 0.5 M, sodium oxalate in a concentration in a range of 0.2 to 0.7 M, sodium sulfide in a concentration in a range 0.1 to 0.4 M and sodium phosphate in a concentration in a range 0.2 to 0.7 M.

7. A method for removing metals from spent lithium-ion battery, comprising: -extracting a black mass from spent lithium-ion battery; -subjecting the black mass to acid leaching with an inorganic acid followed by treatment with an oxidising agent to obtain dissolved metal containing acid leachate; and -contacting the metal containing acid leachate with a modified anion exchange resin as defined in claim 1 or a combination thereof for removal of metals, wherein the metals are cobalt (Co+2), nickel (Ni+2), manganese (Mn+2), and lithium (Li+2).

8. The method as claimed in claim 7, wherein the inorganic acid is selected from the group consisting of sulphuric acid, phosphoric acid, hydrochloricacid, and aqua regia, and wherein the oxidising agent is selected from the group consisting of hydrogen peroxide, potassium permanganate, sodium hypochlorite, sodium persulfate, sodium chlorate, and combinations thereof.

9. The method as claimed in claims 7 and 8, wherein acid leaching with sulphuric acid in a concentration in a range of 0.5 to 1 M gives metal dissolution efficiency in a range of 92 to 99.6 %.

10. The method as claimed in claim 7, wherein a sequential combination of citrate-modified anion exchange resin, phosphate-modified anion exchange resin, and carbonate-modified anion exchange resin has a Lithium (Li+1) removal efficiency of 99.71%, Cobalt (Co+2) removal efficiency of 99.85%, Nickel (Ni+2) removal efficiency of 99.94%, and Manganese (Mn+2) removal efficiency of 99.97%.