Method for regenerating ion exchange resins containing metal IONS and products and uses of the regenerated resins

Abstract

The present disclosure is in the field of ion exchange resins, in particular, but not exclusively, resins comprising metal ions, more in particular coming from an electrochemical method such as an electropolishing method; and is directed to methods for washing such resins and using the so regenerated resins, for example, in an electrochemical method, a water treatment method or for the production of recycled objects, e.g., using conventional (such as injection, extrusion, and molding) and advanced (such as three-dimensional printing) processing techniques.

Description

[0001] METHOD FOR REGENERATING ION EXCHANGE RESINS CONTAINING METAL

[0002] IONS AND PRODUCTS AND USES OF THE REGENERATED RESINS

[0003] TECHNICAL FIELD

[0004] The present disclosure is in the field of ion exchange resins, more in particular, but not exclusively, resins comprising metal ions, and is particularly directed to methods for washing such resins and using the so regenerated resins, for example, in an electrochemical method, a water treatment method or for the production of recycled objects, e.g., using conventional (such as injection, extrusion, and molding) and advanced (such as three-dimensional printing) processing techniques.

[0005] BACKGROUND

[0006] Ion exchange resins are useful in numerous chemical processes and are often used for the removal of metals in the form of metal ions in, e.g., electrochemical methods such as electropolishing methods, and water treatment methods, to name a few.

[0007] Typically, once ion exchange resins have completed a cycle of use, the resins can be regenerated for using them in the same processes or in other processes for a certain number of cycles. However, after several cycles, the resins are damaged, e.g., being the main damage mechanisms the collapse and closure of the pre-existing porosity, and usual treatments do not suffice for them to be reused in the same processes, which marks the end of their useful life. Resins at the end of their useful life are usually disposed of by, e.g., burning, thereby being an environmental burden.

[0008] To reduce waste streams and costs, it is therefore of interest to prolong the useful life of ion exchange resins as much as possible and to use them in as many cycles as possible in, e.g., ion exchange methods. Furthermore, the materials contained in the ion exchange resins, e.g., a matrix of a polymeric nature and / or metal ions trapped therein, make them attractive as materials for the production of recycled objects. However, the presence of metal ions in the resins make them unsuited for certain applications.

[0009] The removal of metal ions from used ion exchange resins is therefore important for their subsequent reutilization, be it, e.g., for providing regenerated resins that can find use in new cycles of ion exchange methods they may be used in, and / or for providing recycled objects from the resins. Similarly, it may be of interest reusing, e.g., components, such as metals, extracted from the used ion exchange resins.

[0010] Methods for washing and regenerating ion exchange resins used in the treatment of water have been described by, e.g., suppliers of ion exchange resins for the treatment of water. Such methods conventionally include washes with aqueous solutions of salts, bases, or acids. Washes with strong acids such as sulfuric acid (H2SO4) or hydrochloric acid (HCI), may be of choice in order to reintroduce protons into the resins. Strong acids may be used in concentrations, e.g., from 1 to 10 wt.% of acid based on the total weight of aqueous solutions. However, such strong acid washes result in damages of the resin, in particular the porosity of the resin may be adversely affected and their effectiveness may drop considerably for their subsequent use as ion exchange resins. Also, the acidification of ion exchange resins by such washes may make them unsuited, e.g., in the preparation of recycled objects for certain applications.

[0011] In certain applications, when the ion exchange resin to be recovered originates from an electrochemical method, such as surface finishing processes including electropolishing methods that employ the ion exchange resin as conductive solid particles, in addition to comprising metal ions the ion exchange resin may comprise other metallic residues, such as salts, that may become embedded within the solid structure of the resin. This embedding may occur as a result of localized fusion, degradation, or softening of the resin, triggered by, e.g., the Joule effect generated during the transmission of electric current. The regeneration of ion exchange resins used in such electrochemical methods is particularly problematic and has never been studied up to date, where the previously commented effect would not be easily overcome by conventional methods, presenting limitations on the reuse of said resins for the same or for other applications.

[0012] SUMMARY

[0013] It has now been found that ion exchange resins comprising metal ions can be suitably washed with an aqueous solution comprising an inorganic salt to provide a regenerated ion exchange resin. The so regenerated ion exchange resins have also been found to be suitably reusable in methods such as, for example, methods where ion exchange resins are used for the removal of metal ions or for the production of recycled objects. Also, one or more components found in the ion exchange resins to be washed may be extracted and also be reusable.

[0014] The present disclosure relates to a method at least comprising the following steps: a. providing an ion exchange resin comprising metal ions; and b. washing the ion exchange resin with an aqueous solution of an inorganic salt.

[0015] The method may, thus, provide a regenerated ion exchange resin.

[0016] The method has been found to be, in some embodiments, simple, effective for the extraction of at least some metal ions from the resin to obtain a regenerated ion exchange resin, and it can be conducted in a cost-effective manner; concerning the latter, the method may be conducted without using expensive reagents. The method is also environmentally friendly as waste streams can be suitably processed or even reused. For instance, the resins may be used to provide recycled objects and the extracted metal ions may suitably provide metal ion extracts which can also be used subsequently in other applications and processes. Since at the end of their useful life ion exchange resins are often disposed of by burning, methods as described herein may also reduce carbon emissions, as the need of disposing of the resins may be eliminated or postponed.

[0017] The present disclosure further relates to regenerated ion exchange resins and to metal ion extracts obtainable by the above-mentioned method.

[0018] The term regenerated ion exchange resin as used herein refers to an ion exchange resin which has been previously used, e.g., in a water treatment method or an electrochemical method such as an electropolishing method, and which has been subjected to a washing step in a method as described herein. The regenerated resin may be conditioned for its subsequent use, as also described in more detail below.

[0019] The present disclosure also relates to a method using the regenerated ion exchange resins in a process, such as, for example but without limitation, an electropolishing method, a water treatment method, or the manufacturing of a recycled object. The present disclosure also relates to recycled objects comprising the regenerated ion exchange resins.

[0020] The present disclosure also relates to catalytic applications of metal ions obtainable from or by methods like the above-mentioned one, and to catalysts comprising metal ions extracted by such methods.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as examples of how the disclosure can be carried out. The drawings comprise the following figures:

[0023] Figure 1 : Extracted amount of metal ions (mg Fe / L) with aqueous solutions having different concentrations of inorganic salt (NaCI) by mixing at 25 °C for 45 minutes without agitation (A) according to Example 1 and with agitation (B) according to Example 2.

[0024] Figure 2: Extracted amount of metal ions (mg Fe / L) with aqueous solutions having different concentrations of inorganic salt (NaCI) by mixing at 70 °C for 45 minutes without agitation (A) according to Example 3 and with agitation (B) according to Example 4.

[0025] Figure 3: Extracted amount of metal ions (mg Fe / L) with an aqueous solution having a concentration of inorganic salt (NaCI) of 0, 2 and 5 M by mixing at 50 °C for 45 minutes with agitation using one (1) washing cycle according to Example 5.

[0026] Figure 4: Extracted amount of metal ions (mg Fe / L) with an aqueous solution having a concentration of inorganic salt (NaCI) of 5 M by mixing at 50 °C for 45 minutes with agitation with an increasing number of washing cycles (N) according to Example 6.

[0027] Figure 5: Example of an electropolishing method, including methods described in

[0028] WO 2017 / 186992 A1. Figure 6: Extracted amount of metal ions (mg Fe / L) as function of the reaction time, using different inorganic salt (NaCI) concentrations of 1 , 2, 3, 4 and 5 M and at different temperatures of 30 °C (A), 60 °C (B) and 70 °C (C), corresponding to Examples 7-11 , 12- 16 and 17-18, respectively.

[0029] Figure 7: Extracted amount of metal ions (% extracted Fe) mixed at 70 °C for 45 minutes with agitation, as function of the concentration of inorganic salt (NaCI) of 1 , 2, 3, 4 and 5 M, according to Examples 19 - 23.

[0030] Figure 8: Evolution of current trough time at 25 V during (A) an electropolishing process with a virgin ion exchange resin comprising metal ions and (B) after the electropolishing method and subsequently washing the ion exchange resin according to Example 24.

[0031] Figure 9: Images of a resin (A) before an electropolishing method and (B) after the electropolishing method and subsequently washing the ion exchange resin according to Example 24.

[0032] DETAILED DESCRIPTION

[0033] As indicated above, a first aspect of the present disclosure relates to a method at least comprising the following steps: a. providing an ion exchange resin comprising metal ions; and b. washing the ion exchange resin with an aqueous solution of an inorganic salt.

[0034] With the method, at least some metal ions from the ion exchange resin are extracted, thereby obtaining a regenerated ion exchange resin.

[0035] It has been found that regenerated ion exchange resins may be obtained having physical properties which are very similar to those of the original ion exchange, e.g., before use in the ion exchange process which provided the ion exchange resin comprising metal ions. Such physical properties may include the porosity, density and ion exchange activity as disclosed in more detail below.

[0036] The washing may be conducted by mixing the ion exchange resin with the aqueous solution of the inorganic salt.

[0037] Providing an ion exchange resin comprising metal ions of step (a), may be performed by means known in the art. For instance, ion exchange resins comprising metal ions may be provided by using ion exchange resins in processes wherein metals are captured by the ion exchange resins or provided as waste streams from such processes.

[0038] For instance, ion exchange resins may be used for the removal of metals in the form of metal ions in, e.g., electrochemical methods such as electropolishing method, or water treatment methods, such as the treatment of wastewater from the ore and / or mining industry. Accordingly, in some embodiments, providing an ion exchange resin comprising metal ions of step (a), may comprise using an ion exchange resin in an electrochemical method such as an electropolishing method or a water treatment method, preferably using an ion exchange resin in an electrochemical method and more preferably in an electropolishing method. Such methods may be used for the removal of metals from, e.g., an object to be polished or the water to be treated, preferably from an object to be polished, in the form of metal ions.

[0039] In several embodiments, using the ion exchange resin in an electropolishing method may comprise electropolishing at least one surface of an object with a medium comprising the ion exchange resin to extract metal ions from the at least one surface, thereby providing the ion exchange resin comprising the metal ions.

[0040] The object may be, e.g., a metallic object or a ceramic object, including manufactured objects and, in particular, 3D printed objects), and it may preferably be a metallic object. A metallic object may be, e.g., a pure metal or a metal alloy. In particular the metallic or ceramic object may comprise a transition metal selected from, e.g., iron (Fe), copper (Cu), cobalt (Co), chromium (Cr), aluminium (Al), titanium (Ti), nickel (Ni), silver (Ag), gold (Au), and tungsten (W), and ions thereof. Ceramic objects that may be used in an electropolishing method may, e.g., have at least 0.1 wt.% metallic component and up to 99.9 wt.% of ceramic content. Metals present in the ceramic objects may be the same as detailed above for the metallic objects. Suitable examples of ceramic objects may include, for instance, a ceramic filled in a metallic binder.

[0041] The medium may typically be a fluid and may be non-conductive, mildly conductive, or conductive. In some embodiments, the medium used in the electropolishing method may further comprise a plurality of abrasive particles introduced therein.

[0042] Electropolishing may be performed by methods known in the art. Reference is made to, for instance, the International Application No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1), which describes a method for smoothing and polishing metals via ion transport by means of free solid bodies, and the solid bodies that are electrically conductive for carrying out said method. Such an example of an electropolishing method is illustrated in Figure 5. In such an example the method may comprise, e.g., the connection of the parts 1 , e.g., a metal part, to the positive pole of a current generator, by means of a securing element 2 associated with a device, and the subjecting thereof to friction with particles 4 of free solid bodies which are electrically conductive and included in a receptacle 3 with a gaseous environment occupying the interstitial space 5, and which contact electrically with the negative pole (cathode) of the current generator, via the receptacle 3 directly or via a ring acting as a cathode. The solid bodies may be particles 4 with the porosity and affinity to retain electrolyte liquid, e.g., below the saturation level, and have an electrical conductivity. Reference is also made to the International Application No. PCT / ES2021 / 070065 (published as WO 2022 / 123096 A1) which describes the treatment of metallic surfaces and refers to an electrolytic medium comprising solid particles and a non- conductive fluid, the process that uses said medium, and the device for carrying out the process.

[0043] Accordingly, in some embodiments in a method as described therein, the ion exchange resin comprising metal ions provided in step (a) may be an ion exchange resin used in an electrochemical method, e.g. an electropolishing method. Such electropolishing method may be as described above and in particular according to Application No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1) or International Application No. PCT / ES2021 / 070065 (published as WO 2022 / 123096 A1). The ion exchange resin recovered after a washing in a method as described herein can then be reused for the same application, e.g., in an electropolishing method, or for any other application.

[0044] In several embodiments, using the ion exchange resin in a water treatment method may comprise contacting a water comprising metal ions and an ion exchange resin to extract metal ions from the water, thereby providing the ion exchange resin comprising the metal ions. A water treatment may comprise treating water with ion exchange resins for water demineralization, to remove, e.g., metals (metal ions in particular) such as calcium (Ca2+) and / or magnesium (Mg2+) from water, thereby reducing the hardness of water. A water treatment may comprise contacting wastewaters with ion exchange resins or removing metal ions, preferably heavy metal ions, from wastewaters. For instance, in some examples a wastewater may be from the mining industry (arsenic (As), copper (Cu), lead (Pb)), metal smelting (As, Cu, Pb), recycling plants (cadmium (Cd)), textile and steel industries (Cr), paints (mercury (Hg), zinc (Zn)), the pulp and paper industry (Hg), oil refinery (Hg), rubber processing (Hg), fertilizer (Hg), batteries (Hg, Pb), medicines (Hg), pesticides (Hg, Zn), steel (Pb), automotive (Pb), cosmetics (Zn), pigments (Zn) and galvanizing (Zn) sectors, the main metal present in wastewaters of each application being indicated between brackets.

[0045] Alternatively providing an ion exchange resin comprising metal ions of step (a), may comprise providing a waste stream comprising an ion exchange resin comprising metal ions. Such a waste stream may be, e.g., from a process using an ion exchange resin in an electropolishing method, or in a water treatment method, preferably in an electropolishing method. The ion exchange resin of the waste stream may also be separated from the medium by, e.g., filtration (including filtration with or without vacuum) or other known separation methods.

[0046] Accordingly, in some embodiments in a method as described therein, the ion exchange resin comprising metal ions provided in step (a) may be an ion exchange resin used in a water treatment method, e.g., as described above. The ion exchange resin recovered after washing in a method as described herein can then be reused for the same application, e.g., in a water treatment method, or for any other application. In some embodiments, e.g., preferably where the ion exchange resin is used in an electrochemical method such as an electropolishing method wherein the ion exchange resin is used in combination with a non-conductive medium, the ion exchange resin may be subjected to acleaning step prior to a the washing step (b) in a process as described herein, e.g., as part of the step (a), also referred to as a pre-cleaning step or previous cleaning step. Such pre-cleaning step may increase the regeneration efficiency of the ion exchange resin and reduce the reaction time and number of washing cycles. A previous cleaning step may comprise rinsing or immersing the ion exchange resin comprising metal ions with or in a cleaning solution of organic solvents. A cleaning solution of organic solvents can include, e.g., polar protic solvents like ethanol or methanol, which may contribute to the removal polar residues; polar aprotic solvents such as acetone or dimethyl sulfoxide (DMSO), which may contribute to the removal of a wider range of compounds; non-polar solvents like hexane or toluene, which may contribute to the removal if oils and hydrophobic residues; chlorinated solvents like dichloromethane (DCM), which may contribute to the removal of stubborn deposits; and specialty solvents such as ethyl acetate, which may be particularly suited for environmentally friendly and versatile applications. Using a specific cleaning solution in such pre-cleaning step may allow tailoring the cleaning process to specific residue characteristics and operational constraints.

[0047] In certain embodiments, alkaline agents can also be used in the pre-cleaning step to enhance the removal of organic residues prior to the washing step (b) of a method as described herein.

[0048] Examples of alkaline agents that may be used in a pre-cleaning step include, e.g., sodium carbonate (Na2CO3), which may contribute to removing fatty and oily residues by, e.g., neutralizing acids, emulsifying oils, and saponifying fats. Similarly, sodium metasilicate (Na2SiO3), provides strong alkaline action which may contribute to dissolving grease and removing stubborn residues, making it particularly suitable for ion exchange resins used in an electrochemical process, such as electropolishing processes. Other effective alkaline agents include sodium hydroxide (NaOH) and potassium hydroxide (KOH), which may contribute to saponifying grease and emulsifying organic deposits, and trisodium phosphate (TSP), which may contribute to remove grease and dirt by suspending particles in solution. Other alkaline agents such as sodium bicarbonate (NaHCO3) offers mild abrasiveness and acid-neutralizing properties, while ammonium hydroxide (NH40H), a weak base, is effective against polar organic residues like fats and proteins.

[0049] Such alkaline agents may be used in an aqueous solution or can be combined with organic solvents, to provide a solution of the alkaline agent in an organic solvent. The organic solvent may be selected from, e.g., acetone, ethanol, and dichloromethane. The use of an organic solvent in the pre-cleaning step may provide enhanced efficiency in removing diverse residues.

[0050] In some embodiments, the pre-cleaning step comprises rinsing or immersing the ion exchange resin comprising metal ions with or in an alkaline agent, e.g., in an aqueous solution or in combination with organic solvents.

[0051] The ion exchange resin comprising metal ions provided in step (a) may be wet or dry, depending on the method on which it is used, whether a pre-cleaning step as described above has been performed, and whether it has been allowed to dry or not and to which extent. As a mode of example, an ion exchange resin provided in a, e.g., electrochemical method such as an electropolishing method may be separated from the electropolishing medium, by filtration, providing a wet resin, or at least a partially wet resin. Similarly, a resin provided in a, e.g., water treatment method may also be separated from its medium (i.e. , water) by filtration providing a wet resin, or at least a partially wet resin. In several embodiments, the ion exchange resin comprising metal ions to be dried before subjecting it to the washing step (b) to remove solvent comprised in the resin. In some cases, the ion exchange resin comprising metal ions provided may be partially dry or partially wet. However, it may be preferred for the resin to be wet, or at least partially wet, to avoid the need of, e.g., swelling during or prior to the washing steps.

[0052] The amount of solvent, e.g. water, present in the resin may be expressed by the swelling degree. The swelling degree may be expressed as the percentage increase in weight or volume, preferably weight, of the resin when exposed to a specific solvent, e.g., water or an aqueous solution.

[0053] Resins provided in step (a) may have a swelling of 20 to 85 % of weight increase, e.g., from 25 to 75 % of weight increase, in particular from 30 to 70 %, more in particular from 35 to 65 %, yet more in particular from 58 to 65 % of weight increase, based on the weight increase of the resin as used in step (a), compared to the dry-weight of the ion change resins used. In several embodiments the swelling may be of, e.g., about 50%, and in in several other embodiments of about 60 %.

[0054] Ion exchange resins may be defined by one or more of the following: the type of ions being exchanged (e.g., cations and / or anions); the nature of the active groups of the resins (i.e., the chemical groups present in the resins responsible for the ion exchange also referred to as functional groups); and the nature of the material of the resins onto which such active groups are bound (generally polymeric materials with the active groups hanging from them).

[0055] Suitable resins may be cationic and / or anionic resins. In some embodiments, cation exchange resins, which bind to cations, i.e., positively charged ions. Since metal ions may typically be cations, ion exchange resins used in methods as described herein may suitably be cationic. Suitable resins may be acidic, basic and / or chelating ion exchange resins. Chelating ion exchange resins may themselves be acidic and / or basic. In some embodiments, ion exchange resins as used herein may be selected from acidic ion exchange resins. In some embodiments, ion exchange resins as used herein may be selected from chelating ion exchange resins.

[0056] In several embodiments acidic ion exchange resins, may be selected from strong acidic and weak acidic resins. Strong cation exchange resins may comprise, e.g., sulfonic acid groups or the corresponding salts, also referred to in the art as sulfonic or sulfonated ion exchange resins and referred to herein as sulfonic ion exchange resins. Some specific examples include sodium polystyrene sulfonate or poly(2-acrylamido-2-methyl-1- propanesulfonic acid) (also referred to as polyAMPS) ion exchange resins. Weak acid functional groups, such as ion exchange resins comprising carboxylic acid groups.

[0057] In several embodiments basic ion exchange resins may be selected from strong basic resins and weak basic resins. Strong basic ion exchange resins may comprise, e.g., quaternary amino groups, for example, trimethylammonium groups such as N-propyl- trimethylammonium groups, including, e.g., poly(acrylamido-N-propyltrimethylammonium chloride) (referred to as polyAPTAC). Weak basic ion exchange resins may comprise, e.g., primary, secondary, and / or tertiary amino groups, such as polyethylene amine.

[0058] In several embodiments chelating ion exchange resins may comprise acidic groups, such as iminodiacetic acid (IDA) groups, amino diacetic acid groups, aminophosphonic acid groups, such as aminomethyl phosphonic acid (AMPA), phosphoric acid, and carboxylic acid groups; and / or basic groups, such as thiourea groups, and 2-picolylamine groups; and / or the corresponding salts of said acidic and / or basic groups. Other chelating groups, e.g., comprising sulphur (S) donor atoms, such as thiol and thiouronium groups may also be used.

[0059] Ion exchange resins may be preferably selected from acidic ion exchange resins and more preferably from sulfonic ion exchange resins. It may be preferred for the ion exchange resin to be a sulphonic ion exchange resin.

[0060] The material of the ion exchange resins, also referred to in the art as the matrix of the resin, may vary widely and may include polymeric materials such as polystyrene (such as polystyrene divinylbenzene resins such as sulphonic resins or cholestyramine), polyacrylic resins (such as polymethacrylic acid including resins referred to as polacrilex or polacrilin), polyethylene, polypropylene, polyvinylchloride (high density polyvinylchloride), polyamide, and cellulose fiber. Other materials, such as zeolites (e.g., manganese zeolite) or activated carbon (e.g., granular activated carbon) may also be used as ion exchange resins.

[0061] The cross-linking degree of the ion exchange resins may vary from, e.g., 1 to 25 %, in particular from 2 to 20 %. In some embodiments resins may have a cross-linking degree from 1 to 10 %, e.g. about 2 % or about 5-6 %, and in other embodiments from 10 to 25 %, e.g., about 12 %. The cross-linking degree may be defined the percentage of polymer chains that are interconnected in the ion exchange resin. The cross-linking degree may be known from the supplier of the ion-exchange resin. The cross-linking degree may also be determined by means known in the art.

[0062] Ion exchange resins may typically be in the form of beads (e.g., spherical particles). The ion exchange resins may be defined by the particle size of the beads. They may have, e.g., a monomodal, bimodal and / or multimodal particle size distribution. The particle size may be known from the provider or may be measured by methods known in the art. For instance, using Laser Scanning Confocal Microscopy (LSCM) system, a laser diffraction particle measurement system (PMS) (such as the MasterSizer), Scanning Electron Microscopy (SEM) system or an Optical Microscopy (OM) system, among other optical, laser and / or interferometric techniques. The particle size data may be statistically processed using methods known in the art such as Ulrn and Constantinides method. This method may typically start with the correct representation of the ion exchange resin diameter measurement data, e.g., registered one or more of the systems indicated above, directly obtained from an image software (such as Image J public domain software) and subsequently statistical deconvolute the results. The deconvolution technique may start with the generation of the experimental cumulative distribution function (CDF). Then, the distribution of the ion exchange resin particle size distribution for each particle size can be approximated by a Gaussian distribution, identified by the mean value and standard deviation of the ion exchange resin particle size distribution obtained by using this methodology. In this way, the ionic exchange particle size distribution values can be fitted to CDF using a sigmoid shape error function. Finally, this entire statistical process (deconvolution, fitting and the subsequent simulation of the experimental Gaussian curves over the experimental data) for each ion exchange resin particle size under study has been done using a mathematical software. Reference is made to, e.g., Ulrn et al., “Statistical Indentation Techniques for Hydrated Nanocomposites: Concrete, Bone, and Shale.” Journal of the American Ceramic Society. Vol. 90 (2007) pp. 2677-2692; Constantinides et al., “On the use of nanoindentation for cementitious materials.”, Materials and Structures. Vol. 36 (2003) pp. 191-196; and Constantinides, et al. “Grid indentation analysis of composite microstructure and mechanics: Principles and validation.”, Materials Science and Engineering A. Vol. 430 (2006) pp. 189-202.

[0063] Different particle sizes and particle size distributions may be preferred depending on the application and use of the same. As a mode of example, ion exchange resins as described herein may have a particle size from, e.g., 50 to 2000 .m, in particular from 300 to 1200 .m measured by using the LSCM and / or SEM techniques (achieving the equivalent results) and statistically treated by using the Ulrn and Constantinides method. Depending on the internal structure of the beads, ion exchange resins may be classified as microporous (having pore diameters of less than 2 nm), mesoporous (having pore diameter between 2 and 50 nm) or macroporous (having pore diameters of greater than 50 nm).

[0064] The properties of the beads of the ion exchange resins together with the functional group’s nature and cross-linking degree of the resin, may influence its ion-exchange behavior, and may vary depending on the use made of the ion exchange resin.

[0065] Morphologically, ion exchange resins may be classified as gel-type (also referred to as micro reticular, typically including microporous or mesoporous resins) or porous-type (also referred to as macroreticular typically including microporous resins). Porous-type resins have stable macropores in the dry state and their appearance is opaque. The beads have a porous multi-channeled structure which provides them with a high effective surface area. Porous-type resins may have a cross-linking degree of, e.g., above 10 %, e.g., from 10 to 25 %, in particular from 11 to 20%.

[0066] Gel-type resins rely on swelling and have a three-dimensional (3D) porous structure when swollen, with a solvent evenly dispersed through it. When the solvent is removed, the gel shrinks, and its porosity is not appreciable in the dry state. This type of resins presents heterogeneous micropores (ranging between 0.7 and 2 nm) and a cross-link degree from 1 to 10 %, in particular from 2 to 9 %, and more in particular from 3 to 8 %. Visually, they may have a translucid aspect.

[0067] The diameter or slit width, e.g., in nm, may be used to define porous sizes of ion exchange resins. The diameter of the entrance of a pore may be used, e.g., to define pores with cylindrical or conic shape and the slit width of the entrance of a pore for pores with slit shape. For pores with other shapes the diameter or slit width may be simply used as is the largest dimension of the entrance of the pore. The diameter or slit width may be generally known from the ion exchange resin supplier. The diameter or slit width may also be determined by methods known in the art. For instance, the determination of the pore size distribution may be carried out by methods known in the art such as the gas adsorption and / or mercury intrusion methods. The gas adsorption method may be used to measure pore sizes, e.g., from 0.35 to over 100 nm. On the other hand, the mercury intrusion method may be used for measuring pores sizes from 3.2 nm to larger than 400 .m accessible from the surface of a material is generally. Classic methods exist to determine pore size distributions, for instance the BJH method (named after the scientists Barret, Joyner, Helenda) may be used to describe mesopores, while the HK method (named after the scientists Horvath and Kawazoe) may be used to describe micropores. Modern methods such as DFT (Density Functional Theory) or GCMC (Grand Canonical Monte Carlo) based molecular similaritons may also be applied. Pore sizes as defined herein may preferably measured using the BJH method. The surface area of the resin, e.g., the BET (Brunauer-Emmett-Teller) surface area in m2 / g, may also be a useful parameter to define the porosity of the resin and it is generally known from the ion exchange resin supplier. The surface area, and in particular the BET specific surface area may be determined by methods known in the art. For instance, the BET specific surface area is based on the physical adsorption of gas molecules on a solid surface and is determined by methods known in the art and allows to determine the internal porosity of the resin. For instance, the ISO 9277 standard may be used for calculating the specific surface area of solids is based on the BET method.

[0068] In certain applications, when the ion exchange resin to be recovered originates from an electrochemical method, such as surface finishing processes including electropolishing methods that employ the ion exchange resin as conductive solid particles, in addition to comprising metal ions the ion exchange resin may comprise other metallic residues, such as salts, e.g., form the acids and metals present in the electropolishing method such as metal sulphates, metanosulphates, phosphates, nitrates etc. Such salts may become embedded within the solid structure of the resin. This embedding may occur as a result of localized fusion, degradation, or softening of the resin, triggered by, e.g., the Joule effect generated during the transmission of electric current. Such salts may block the porous of the ion exchange resin and reduce, e.g., its BET surface area. Regenerating an ion exchange resin by washing in a method as described herein may also improve the BET surface area of the regenerated ion exchange resin compared to the BET surface area of the ion exchange resin comprising metal ions prior to the washing.

[0069] Due to the presence of such salts, to date, these types of ion exchange resin have been disregarded for subsequent reuse. It has now surprisingly been found that a washing method as described herein provides a regenerated ion exchanged resin which may be conditioned (e.g., subjected to drying, or swelling with water or appropriate electrolyte solutions) and be subsequently used in other applications as described herein, including a further electrochemical surface treatment process including electropolishing. By adjusting the electrochemical parameters (such as the voltage) of the process using a regenerated ion exchanged resin by a method as described herein, conditions may be achieved which may be suited for electrochemical surface treatment processes or even provide properties equivalent to those of where virgin ion exchange resins are used.

[0070] The term virgin ion exchange resin, or virgin resin, as used herein refers to an ion exchange resin which has not been yet used, e.g., a commercial resin as provided by the supplier, or conditioned for its subsequent use but not yet used.

[0071] The term conditioned ion exchange resin, or conditioned resin, as used herein refers to a regenerated or virgin ion exchange resin which is subjected to a treatment to adequate it to its subsequent use, e.g., subjected to drying, or swelling with water or appropriate electrolyte solutions as described in detail elsewhere herein. Macroporous ion exchange resins may be defined by pore sizes with a diameter or a slit width of 50 nm or above. Macroporous ion exchange resins advantageously have a high effective surface area, facilitating the ion exchange process, may give access to the exchange sites for larger ions than, e.g., microporous resins, and may be suitably used with a wide range of solvents, with little or no change in volume. The beads of macroporous ion exchange resins may be more rigid than those of microporous resins facilitating ease of removal from the reaction system. Macroporous resins may have a BET specific surface area of, e.g., 8 to 20 m2 / g, in particular from 10 to 18 m2 / g, and more in particular from 12 to 16 m2 / g. Beads of macroporous resins may, e.g., have size expressed as the mean D50 diameter from 300 to 1200 pm, in particular from 400 to 1000 pm.

[0072] Mesoporous ion exchange resins have intermediate pore sizes with a diameter or a slit width from 2 to 50 nm. Mesoporous resins may have a surface specific area of, e.g., 6 to 12 m2 / g.

[0073] Microporous ion exchange resins (also referred to as gel-type) may be defined to have a diameter or slit width of 2 nm or less. Microporous ion exchange resins may not have discrete pores, and solute ions diffuse through the particle to interact with exchange sites. Compared to macroporous ion exchange resins, microporous ion exchange resins may advantageously be less fragile, requiring, e.g., less care in handling, may react faster in certain applications and / or may possess higher loading capacities. Microporous resins may have a BET specific surface area of, e.g., 4 to 10 m2 / g, in particular from 5 to 9 m2 / g. As indicated above, the surface area may be known from the supplier or may be determined by means known in the art. Beads of microporous resins may, e.g., have size expressed as the mean D50 diameter from 300 to 1200 pm, in particular from 400 to 1000 pm.

[0074] Ion exchange resins may preferably be macroporous.

[0075] The type of resin may be chosen for a specific ion exchange method, e.g., considering the type of metal ions that it may retain and procedural aspects, such as speed of the ion exchange and handling of the resin.

[0076] In several particular embodiments, ion exchange resins may be selected from sulfonic ion exchange resins, yet more in particular the ion exchange resins may be a polystyrene divinyl benzene sulfonic ion exchange resin, and even more in particular a macroporous polystyrene divinyl benzene sulfonic ion exchange resin.

[0077] An ion exchange resin comprising metal ions provided in step (a), may be an ion exchange resin comprising active groups wherein at least part of its active groups are bonded to metal ions. In several embodiments, an ion exchange resin may be partially substituted with metal ions. In several embodiments, an ion exchange resin may be totally substituted with metal ions, also referred to as saturated with metal ions, meaning that the ion exchange resin is no longer capable to bonding to additional metal ions under typical processing conditions. The weight amount of metals present in the ion exchange resin may depend on the type of ion metal, owing to the specific weight of the metal retained in the ion exchange resin. The number of metal ions retained may also depend on the valence of the metal, accordingly the weight amount may also depend on or the valence of the ion metal. As a mode of example, an ion exchange resin may comprise e.g., based on the total weight of metal ion expressed as the ratio between the grams of extracted metal ions and the volume of resin expressed in liters, 7.8-19.5 g / L for titanium group metals; 19.5 - 39.1 g / L for iron group of metals; 19.5 - 39.1 g / L for cobalt and chromium group metals; 19.5 - 39.1 g / L for nickel group metals; and 23.4-46.9 g / L for copper group metals. The amount of metal ions retained in the ion exchange resin may be known or may be measured by means known in the art. For instance, from the known theoretical ion exchange capacity of the resin and the level of saturation of the resin. As a mode of example in an electropolishing method the level of saturation may be determined by the level of intensity in the service conditions. When the intensity starts to decrease, the resin starts to be saturated, and when it reaches a minimum threshold value, it may be considered to be fully saturated.

[0078] A method of the present disclosure enables to reuse, one or more times, ion exchange resin at least partially substituted with metal ions, and in some embodiments totally substituted.

[0079] An ion exchange resin comprising metal ions provided in step (a), may be an ion exchange resin at the end of its useful life as an ion exchange resin or may be at the end of a cycle during its useful life as an ion exchange resin.

[0080] Typically, an ion exchange resin at the end of its useful life as an ion exchange resin can no longer be effectively used as an ion exchange resin, e.g., in typical processing conditions. This may be due to structural changes of the ion exchange resin, e.g., in its internal structure, for example, it may have lost at least part of its porosity. The porosity, or in other words, the level of porosity of the regenerated resin influences the capacity of such resin to further comprise metal ions like, for example, metal ions to be absorbed by the resin during, e.g., an electropolishing method. Therefore, the regenerated resin may not be effectively reused as an ion exchange resin when the porosity is lower than a certain amount, as quantified by, e.g., the specific surface area as determined by BET. Such resins may be processed in a method as described herein, to extract metal ions therefrom and to provide a regenerated ion exchange resin that can be subsequently used in other applications and / or processes, such as in the manufacture of recycled objects, as discussed in further detail below.

[0081] An ion exchange resin at the end of a cycle during its useful life as an ion exchange resin, may no longer be suitably used in another ion exchange cycle. This may be due to the resin being saturated in metal ions. Furthermore, its internal structure and in particular its porosity may also be detrimentally affected but without considerably decreasing its porosity, e.g., beyond a predetermined porosity threshold. Such resins may be processed in a method as described herein, to extract metal ions therefrom and to provide a regenerated ion exchange resin that can be subsequently used in a new cycle as an ion exchange resin, as discussed in further detail below.

[0082] The number of metal ions present in the resin, or the density of metal ions with respect to, e.g., the weight of polymer particles of the resin can also determine the reusability of the resulting resin since a high number of metal ions in the regenerated resin allows a lower number of metal ions to be absorbed by the resin before reaching the saturation level, thus reducing the efficiency of the resin to accumulate further metal ions and losing effectiveness in, e.g., an electropolishing process.

[0083] The number of times that the resin can be reused in an ion exchange cycle, may depend upon the level of porosity of the regenerated resin and / or the amount of metal ions that remain after being subjected to a method as described herein, particularly, the washing of the ion exchange resin comprising the metal ions.

[0084] The metal ions comprised in the ion exchange resin may vary depending on the type of metal ions has encountered the ion exchange resin in the processes wherein it has been used prior to or during step (a). By way of example, the metal atoms of a surface finished object that may have been transferred from at least one surface thereof to the ion exchange resin in the form of metal ions, and as a result, the at least one surface has been surface finished, e.g., by means of an electrochemical process such as an electropolishing method.

[0085] The nature and the total accumulated number of metal ions present at one time or another in the resin and / or the particles or solutions (e.g., acid) that the resin contacts during its use may also influence the porosity of the ion exchange resin provided in step (a), but also of the final regenerated ion exchange resin.

[0086] The metal ions comprised in the ion exchange resin may be transition metals, from groups 3-12 of the periodic table. The metal ions may be from a single type of metal or a combination of metals. The charge of the metals comprised in the ion exchange resin may also be the same or different.

[0087] Metal ions comprised in the ion exchange resin provided in step (a), may be selected from, e.g., iron, copper, cobalt, chromium, aluminium, titanium, nickel, silver, gold, tungsten, calcium, magnesium, sodium, manganese, zinc and heavy metal ions such as lead, cadmium, arsenic and mercury ions, preferably from iron, copper, cobalt, chromium, aluminium, titanium, nickel, silver, gold, and tungsten ions. For instance, the ion exchange resin may comprise metal ions selected from: Fe2+, Fe3+, Cu2+, Co2+, Co3+, Cr2+, Cr34, Al3+, Ti4+, Ni2+, Ni4+, Ag+, Au+, W64, Ca2+, Mg2+, Na+, Mn2+, Zn2+, Pb2+, Cd2+, As3+, and Hg2+. Preferably, metal ions may be selected from Fe2+, Fe3+, Cu2+, Co2+, Co3+, Cr2+, Cr3+, Al3+, Ti4+, Ni2+, Ni4+, Ag+, Au+, and W64.

[0088] In some embodiments, e.g., in particular when in step (a) the ion exchange resin is provided from a water treatment method, the ion exchange resin comprises metal ions selected from: calcium (Ca2+), magnesium (Mg2+), sodium (Na+), iron (Fe2+ / Fe3+), manganese (Mn2+), and heavy metal cations including lead (Pb2+), cadmium (Cd2+), and mercury (Hg2+).

[0089] In some embodiment, e.g., in particular when in step (a) the ion exchange resin is provided from an electrochemical method such as an electropolishing method, the metal ions may be preferably selected from iron (Fe2+ / Fe3+), copper (Cu2+), cobalt (Co2+ / Co3+), chromium (Cr2+ / Cr3*), aluminium (Al3+), titanium (Ti4+), nickel (Ni2+ / Ni4+), silver (Ag+), gold (Au+), and tungsten (W5*).

[0090] In several embodiments, e.g., when step (a) comprises providing an ion exchange resin used in a water treatment, i.e., previously used in or by performing a water treatment as described above, also referred to herein as water treatment resins, the ion exchange resin may comprise a plurality of different types of metal ions, e.g., at least 2 or at least 3 or even at least 4 different types of metal ions. The type of metal ions and the distribution of the concentrations of the different types of metal ions present in the ion exchange resin will vary depending on the metal content in the water that was treated in the water treatment, and the type. In some embodiments, whilst the concentration of each type of metal ion present in the ion exchange resin may be different, the metal ion present in the highest concentration may not be very far from the metal ion present in the second highest concentration, third and fourth highest concentration, resulting in a distribution of the concentration of the different metals in the resin that is relatively homogeneous. The most common metal ions present in water treatment resins may typically be calcium (Ca2+), magnesium (Mg2+), sodium (Na+), iron (Fe2+ / Fe3+), manganese (Mn2+). and heavy metal cations including lead (Pb2+), cadmium (Cd2+), and mercury (Hg2+). In some embodiments water treatment resins, in addition to one or more metal ions may additionally comprise non- metal ions such as ammonium (NH4+), chloride (Cl"), sulfate (S042-), nitrate (NO3“), bicarbonate (HCO3“), fluoride (F“), silicates (SiO32-), phosphate (P043-), as well as organic anions such as humic and fulvic acids.

[0091] In several embodiments, step (a) comprises providing an ion exchange resin used in an electrochemical process, such as an electropolishing process, i.e., previously used in processes as described above, also referred to herein as electropolishing resins. In such cases, the ion exchange resin may also comprise a plurality of different types of metal ions, e.g., at least 2 or at least 3 or even at least 4 different types of metal ions. However, the concentration of each type of metal ions are not distributed in a homogeneous proportion, as their distribution depends on the alloy being surface finished or polished in the electrochemical process. For instance, electropolishing may be performed on materials preferably selected from steel, stainless steel, cobalt chrome, aluminum, brass, copper alloys, Inconel, tungsten carbide, titanium alloys, and cast iron. Electropolishing of steel may typically provide ion exchange resins comprising iron (Fe2+, Fe3+) as main metal ions and traces of manganese ions (Mn2+). Electropolishing of stainless steel may typically provide ion exchange resins mainly comprising chromium (Cr34, Cr®+), nickel (Ni2+), iron (Fe2+, Fe3+), and traces of molybdenum (Mo6+). Electropolishing of cobalt chrome may typically provide ion exchange resins mainly comprising in cobalt (Co2+, Co3+) and chromium (Cr34, Cr®+). Electropolishing of aluminum may typically provide ion exchange resins mainly comprising aluminum (Al3+) ions. Electropolishing of brass may typically provide ion exchange resins mainly comprising zinc (Zn2+) and copper (Cu+, Cu2+). Electropolishing of copper alloys may typically provide ion exchange resins mainly comprising copper (Cu+, Cu2+) ions. Inconel may typically provide ion exchange resins mainly comprising nickel (Ni2+), chromium (Cr34, Cr®+), and molybdenum (Mo6+). Electropolishing of tungsten carbide may typically provide ion exchange resins mainly comprising tungsten (W®+) ions. Electropolishing of titanium alloys may typically provide ion exchange resins mainly comprising titanium (Ti3+, Ti4+) ions, and electropolishing of cast iron may typically provide ion exchange resins mainly comprising iron (Fe2+, Fe3+) and traces of carbon-related impurities. Accordingly, in an electropolishing ion exchange resin one type of metal ion may be present in a significantly higher concentration (i.e. the main metal or metals of the alloy being treated) than other types of metal ions present in the resin (i.e., metals being present in trace amounts). In some embodiments, two or three types of metal ions may be present in a significantly higher concentration than other types of metal ions present in the resin.

[0092] Depending on the origin of the ion exchange resin provided in step (a), a precleaning step as discussed above may be optionally performed in step (a) and the washing step (b) may be fine-tuned based on the specific ions present and their corresponding concentration distribution for each element. This adjustment ensures that the cleaning process effectively prepares the resin to meet the precise requirements of the application in which it will be used, whether for water purification, industrial deionization, or specialized purposes such as recycling materials for urban furniture.

[0093] Washing the ion exchange resin with an aqueous solution of an inorganic salt of step (b), thereby extracting at least some of the metal ions from the ion exchange resin and obtaining a regenerated ion exchange resin, may for instance be performed by mixing the ion exchange resin with the aqueous solution of the inorganic salt.

[0094] The washing of the ion exchange resin with the aqueous solution of the inorganic of step (b) salt may influence the amount of metal ions present in the resulting resin, and it may also influence the porosity of the resulting resin. In this sense, the configuration of the washing step may contribute to improving the characteristics of the regenerated resin.

[0095] In several embodiments the aqueous solution of the inorganic salt of step (b) may have an inorganic salt concentration of from 0.5 to 6 M, in particular from 1 to 5 M, more in particular from 2 to 4 M, yet more in particular from 2 to 3 M. Such concentrations provide a good balance on the amount of metal ions that can be extracted and the speed of the extraction. Higher concentrations may lead to a quick extraction of the metallic ions, in particular for the iron metallic ions, and as a consequence saturating the media, which tends to reduce the extraction ability and speed. Lower concentrations may slow down the extraction of metal ions.

[0096] The inorganic salt of the aqueous solution for washing the ion exchange resin may be selected from a chloride, a nitrate and / or a sulfate salt of an alkali metal or an alkaline earth metal, a lanthanide metal or ammonium. Alkali metals may be selected from sodium and potassium. Alkaline earth metals may be selected from calcium, magnesium, and strontium. A lanthanide metal may be, e.g., cerium.

[0097] Metal ions present in the inorganic salt are typically different from the metal ions originally comprised in the provided ion exchange resin. As indicated above metal ions comprised in the provided ion exchange resin may be transition metal ions, whereas metals of the inorganic salt may be alkali, alkaline earth, or lanthanide metal ions.

[0098] In several embodiments, the inorganic salt of the aqueous solution may be a chloride salt, more in particular the inorganic salt may be a chloride salt selected from sodium chloride, potassium chloride and calcium chloride, yet more in particular the inorganic salt may be selected from sodium chloride and potassium chloride, and even more in particular the inorganic salt may be sodium chloride, as sodium chloride is widely available and economical. Such salts have been found to advantageously work in a suitable range of extraction conditions and provide adequate extraction times.

[0099] In several embodiments, the inorganic salt of the aqueous solution may be a sulphate salt, in particular a cesium salt.

[0100] In particular realizations of the invention are selected, for example but without limitation, from: NaCI, KCI, NaHCO, NaHCCh, and KHCO3, preferably from NaCI, KCI, and NaHCO.

[0101] Washing may be performed by methods and means known in the art. For instance, a washing may be performed in a suitable container that allows mixing the ion exchange resin with the aqueous solution of the inorganic salt. In several embodiments, a suitable a container may provided with mixing means or may be a container that may be suitably shaken. A suitable container may also be provided with means for temperature control and / or means for phase separation.

[0102] Mixing the ion exchange resin with the aqueous solution of the inorganic salt may be performed by methods known in the art. As a mode of example mixing may be performed by simply adding the ion exchange resin to the aqueous solution or vice versa, adding the aqueous solution to the ion exchange resin, e.g., in a suitable container. Mixing may be performed without or with agitation, e.g., by stirring, e.g., by using a container provided with agitation (stirring) means such as a stirrer, and / or by shaking, e.g., by using container that may be suitably shaken. Mixing with agitation, e.g., by stirring, may be preferred as it may accelerate extraction of the metal ions. Mixing may also be performed by using, e.g., recirculation methods. As an exemplification, but without limitation, in some embodiments a method as described herein comprises steps of recirculation of an aqueous solution of an inorganic salt through an ion exchange resin comprising metal ions provided in step (a). In several embodiments, mixing may be performed at a mixing temperature at which, e.g., the inorganic salt is fully dissolved in aqueous solution. As a mode of example, the mixing temperature may be from, e.g., 20 °C to 100 °C, in particular from 25 °C to 95 °C, in particular from 30 to 90 °C, more in particular from 35 to 85 °C, and yet more in particular from 40 to 80 °C. A temperature from 65 to 75 °C, e.g., of about 70 °C may be preferably used. Such temperatures have been found to provide suitable solubility of the inorganic salts and salts resulting from extracted metal ions in water and to provide adequate extraction times. Lower temperatures may not provide good solubility and may slow down the extraction of the metal ions. Higher temperatures may adversely degrade the polymer of the ion exchange resin. In several embodiments, mixing may preferably be performed at a mixing temperature below the melting point of the ion exchange resin and more preferably below the glass transition temperature of the ion exchange resin. The melting point and the glass transition temperature of the ion exchange resin may be known from the supplier. The glass transition temperature and melting point may also be determined by methods known in the art, for instance, by thermal analysis, and in particular by using thermogravimetric analysis (TgA). The analysis may be carried out in the temperature range of 20 - 1000°C in the so-called high-resolution mode with a heating rate of 10 K min’1under nitrogen and / or air atmosphere. In several embodiments mixing is performed at a temperature from 65 to 75 °C using an aqueous solution of an inorganic salt, e.g., of NaCI, at a concentration from 2 to 3 M.

[0103] The washing of step (b) may be performed using a proportion of mass of ion exchange resin per volume of aqueous solution of inorganic salt from 1 to 1000 g of resin to 1 L of aqueous solution, in particular from 5 to 500 g of resin to 1 L of aqueous solution, more in particular from 10 g 100 g of resin to 1 L of aqueous solution. These masses of ion exchange resin per volumes of aqueous solution of inorganic salt have been found to provide suitable amounts of metal being extracted and, in some embodiments, in adequate extraction times.

[0104] Washing may be performed by mixing the ion exchange resin with the aqueous solution of the inorganic salt for a suitable amount of time to extract an amount of metals, preferably the maximum amount of metals, under the mixing conditions (e.g., a specific temperature and concentration of the aqueous solution). Generally, mixing may be performed from 30 seconds to 3 hours, in particular from 1 minute to 2 hours, more in particular from 5 minutes to 1.5 hours, and yet more in particular from 15 minutes to 1 hour. Such times may also be referred to as extraction times. Such extraction times are adequate as they provide an adequate level of extraction of metal ions in a reasonable time for industrial application.

[0105] In several embodiments, the washing time time is adjusted to reach the desired efficiency or performance depending on the final application of a regenerated resin. In particular embodiments, an amount or percentage of material extracted from the resin as a function of time will adopt a different logarithmic evolution through time depending on the previously selected parameters, such as temperature, salt concentration, salt used, stirring power, aqueous solution-to-resin ratio, metals to be recovered, initial saturation level of the resin with metal ions, etc. The previously mentioned condition can also be understood as a different % of ion recovery logarithmic evolution is obtained from a resin, at a given reaction time, as a function of the selected parameters, which can be tuned or selected depending on the user and the final application requirements, as illustrated in , e.g., Figure 6, Figure 7 and Figure 8, based on experimental examples as detailed below. .

[0106] Depending on the final application of the recovered ion exchange resin, a different final ion exchange capacity may be required, and the washing process may be adapted to provide the required final ion exchange capacity, which can be linked to the amount of ion metals recovered, and thus removed, from the ion exchange resin. In some realizations of the invention, the washing time may be varied and adjusted to recover, e.g., from 40 % to 100 % of the metal ions present in the ion exchange resin, in particular from 60 % to 99% of metal ions, more in particular from 80 % to 95 % of metal ions.

[0107] In several embodiments washing times of step (a) according to a method as described herein are, for example but without limitation, from 1 to 300 minutes, in particular from 10 to 120 minutes, more in particular from 45 to 90 minutes.

[0108] In some embodiments, in particular where the resin to be recovered comes from an electrochemical method such as an electropolishing method using them as conductive solid particles, a metallic residue, such as a salt, can be incrusted to the solid structure of the resin as a result of a localized fusion, degradation or softening of said resin triggered by the joule effect experimented during the current transmission. This tribological modification of the resin surface can alter the performance under working conditions when reused in electropolishing methods. For instance, the absorption capacity of the resin may be reduced, and upon conditioning for an electropolishing process, less of the electrolytic solution can be absorbed. This effect can be observed in, e.g., Figure 9 the where regenerated resin (9-B) after a washing step (b) as described herein presents higher humidity on the surface compared to the virgin ion exchange resin prior to its use in the electropolishing method (9-A), under the same moisture conditions according to the example 24. This change in absorbing properties may result in a higher humidity on the surface of the regenerated resin which may trigger an increase on the current as observed in, e.g., see Figure 8-B) when the regenerated resin is subjected to same electropolishing conditions (e.g., 25 V) to those subjected to the corresponding virgin ion exchange resin (see Figure 8-A). Indicating that the regenerated ion exchange resin may behave differently when compared to the virgin ion exchange resin. Nonetheless, the difference in properties and behavior is not necessarily detrimental to the subsequent use of the regenerated ion exchange resin. For instance, several parameters, such as the conditioning of the resin or the working conditions of the resin, may be adjusted to adapt the regenerated resin to its final application. As a mode of example, a difference in the output current for a given potential (e.g., as seen at 25 V in the examples and figures 8A and 8B) may be compensated by changing the potential of the electrochemical process so that the regenerated resin provides a similar output current (e.g., 5 V in figure 8B when compared to figure 8A). Other parameters such as an increase of electropolishing time or an increase of the working temperature may also be adjusted to obtain a desired performance of the regenerated ion exchange resin. As a result, an ion exchange resin presenting similar properties than before the electropolishing method may be obtained.

[0109] Accordingly, regenerated ion exchange resins obtained after washing in a process as described herein, can be successfully used in, e.g., a subsequent electrochemical process. Similarly, the regenerated resin can be conditioned and reused not only for electrochemical processes, but also for other purposes, such as water depuration and urban furniture construction.

[0110] A washing step (b) according to the present invention may be performed under mixing, e.g., under conventional stirring conditions, or other recirculation methods. As an exemplification, but without limitation, in some embodiments a method as described herein comprises steps of recirculation of an aqueous solution of an inorganic salt through an ion exchange resin comprising metal ions provided in step (a).

[0111] The washing of step (b) may be performed more than once, in particular twice or more, more in particular may be performed three times or more. It may be preferred for the washing step to be performed three times. Generally, a washing step may comprise mixing the ion exchange resin with the aqueous solution for a specific amount of time thereby extracting at least some of the metal ions from the ion exchange resin. The aqueous solution comprising extracted metal ions may then be separated from the ion exchange resin. The separated ion exchange resin may then be washed in a subsequent washing step with a new aqueous solution of inorganic salt, to extract further metal ions from the resin. In some embodiments, a majority of metal ions may be extracted from the ion exchange resin in a first washing step. The amount of metal ions extracted may be increased by subjecting the ion exchange resin to one or more additional washing steps. It has been found that three washing steps may, in some embodiments, remove most of the metal ions that may be removed by washing with an aqueous solution of an inorganic salt. Generally, more than three washing steps may not substantially increase the extraction of metal ions to justify the expense and waste of performing such additional steps. However, a method as described herein may in several embodiments allow the removal of virtually all metal ions originally present in the ion exchange resin in a single step.

[0112] In several embodiments, from 70 to 100% of the metal ions originally present in the resin may be extracted with one or more washing steps, e.g., a single washing step, two washing steps or three washing steps. In several embodiments, at least 90 %, in particular at least 95 %, more in particular at least 99 %, and yet more in particular substantially all metal ions, and even mor in particular 100 % or metal ions may be extracted with one or more washing steps.

[0113] The extraction of the metal ions may be determined by methods known in the art, such as photometric methods to measure the amount of metal ions in the aqueous solution after the washing step, and any subsequent washing steps. Quantification of the amount of specific metal ions in the washing solution may be performed by, e.g., inductively coupled plasma optical emission spectrometry (ICP-OES) whereby different ions present in, e.g., an aqueous solution, may be identified and quantified. Briefly, the ICP-OES technique is based on the steaming, dissociation, ionization and excitation of the different chemical elements of a sample in a plasma. Due to the high temperatures generated in the plasma, the analytes are atomized and ionized generating atomic emission spectra of characteristic lines. The spectra are scattered by the diffraction grating and the light-sensitive detector measures the line intensities. Furthermore, numerous standard tests are commercially available for different metal ions and can be performed following the supplier instructions. By way of example, the amount of iron ions extracted from an ion exchange resin comprising iron ions (Fe2+) may be established by photometric determination with 1 , 10-phenanthroline. T ests for determining the amount of iron ions in aqueous solutions are commercially available and can be simply executed following the supplier instructions. An example of a commercially available test is, e.g., Nanocolor® Standard test for Iron available from Macherey-Nagel (in particular Test 1-36 for concentrations of 0.01-15 mg / L of Fe of reference 91836), yet other tests can also be used instead, and they also fall within the scope of the present disclosure.

[0114] The quantified amount of metal ions extracted can be compared to the theoretical amount of metal ions that may be present in a saturated ion exchange resin, based on the amount of resin and the theoretical number of active sites that may bond to metal ions per, e.g., gram of resin (generally known form the supplier of the ion exchange resin). When the solution obtained from a wash does not contain measurable amounts of metal ions originally present in the resin, it may be considered that all metal ions originally present in the ion exchange resin have been extracted.

[0115] The amount and type of metal ions present in the ion exchange resin, e.g., prior to and / or after being subjected to one or more washing steps, may also be quantified by methods known in the art, such as, Scanning Electron Microscopy - Energy Dispersive X- ray spectroscopy (SEM-EDX). For instance, a sample may be placed over a carbon tape and subsequently placed inside the SEM equipped with an EDX system to allow for the chemical analysis of the metallic traces.

[0116] In a method as described herein, washing the ion exchange resin may further comprise obtaining a metal ion extract. Accordingly, a second aspect of the present disclosure is a metal ion extract obtainable by a method according to the first aspect. For instance, a metal ion extract may be obtained by mixing the ion exchange resin with the aqueous solution of an inorganic salt, whereby the metal ions may be extracted from the ion exchange resin into the aqueous solution, providing an aqueous solution comprising metal ions. The aqueous solution may also comprise ions of the inorganic salt, as some of the ions of the inorganic salt will have replaced the metal ions in the ion exchange resin but some ions may still remain in the aqueous solution. The metal ions and the ions of the inorganic salt may be dissolved in the aqueous solution and may additionally be in the form of a precipitate or in suspension in the aqueous solution. The aqueous solution comprising metal ions may as such be a metal ion extract or comprise a metal ion extract. The aqueous solution may be separated from the ion exchange resin to provide an isolated metal extract and / or may also be further processed to provide a metal extract. For instance, the aqueous solution comprising the metal extract may be concentrated, e.g., using physical, chemical or thermic methods.

[0117] A metal ion extract may be subsequently used to manufacture a catalyst. Accordingly, a method as described herein may further comprise manufacturing a catalyst using the metal ion extract. A third aspect of the present disclosure relates to a method of manufacturing a catalyst using a metal ion extract, for instance an extract according to the first or second aspects.

[0118] Manufacturing a catalyst may comprise, e.g., dissolving and / or crystallizing one or more extracted metal ions from the metal ion extract. Dissolving may comprise mixing the metal ion extract with, e.g., a strong acid such as H2SO4. Crystallizing may comprise a purification process though physical methods to be able to separate each constitutive metallic ions present in, e.g., a solution of the metal ions.

[0119] Manufacturing a catalyst may comprise processing the metal extract or metal ions dissolved and / or crystallized from metal extract with other components. For instance, a metal extract or crystallized metal ions as described herein may be mixed with ceramic materials to provide ceramic catalysts scaffolds. Ceramic materials may include advanced ceramic materials, comprising, for instance, alumina (AI2O3) and / or calcium carbonate (CaCCh), which may be commercially available as such or extracted from natural sources. As a mode of example CaCCh may be extracted from eggshells. Metal ions from the metal extract, e.g., crystallized therefrom, may also be purified and concentrated. Another aspect of the present disclosure relates to a catalyst, e.g., obtained with the method of the first aspect or the third aspect, comprising metal ions.

[0120] Such catalyst may include, for instance, catalyst for industrial processes such the dehydrogenation of ethanol to obtain acetaldehyde (C2H5OH C2H4O + H2), ethanol production, hydrolysis, esterification, and the water-gas shift (WGS) reaction, among others. A preferred process may be the dehydrogenation of ethanol to acetaldehyde.

[0121] The metal ion extract or catalyst as described herein may have a purity from 5 to 99% and in particular from 40 to 99% after being purified by using physical, chemical and / or thermal routes, i.e.: density, pyrolysis, etc. The purity may be measured, for example, by way of X-ray diffraction or by SEM-EDX.

[0122] A method as described with reference to the first aspect provides a regenerated ion exchange resin which may also be suitably subsequently used. Accordingly, another aspect of the present disclosure further relates to a regenerated ion exchange resin obtainable by a method as described therein.

[0123] The regenerated ion exchange resin may be used as such or may be further processed for a particular use. In some embodiments, after the washing step (a) with the aqueous inorganic salt solution, comprising one or more washing steps or cycles as described above, the washed ion exchange resin (or regenerated ion exchange resin) may be subsequently further cleaned, e.g., by rinsing with a solvent such as water, and / or conditioned to adequate it to its desired use, e.g., dried or swelled with water, e.g. for use in a subsequent water treatment method or with an appropriate acid solution, e.g., for use in a subsequent electropolishing method.

[0124] For instance, in some embodiments, the regenerated ion exchange resin may be subsequently washed with an acidic aqueous solution (e.g., a strong acid such as H2SO4; or HCI. Such acidic aqueous solutions may typically have a concentration from 0.5 to 60%, in particular from 1 to 10%. The mass of regenerated ion exchange resin per volume of acidic aqueous solution, may be similar to that used for the washes of the ion exchange resin comprising metal ions with the aqueous solution of the inorganic salt. Using a wash with an acidic aqueous solution any ions from the inorganic salt (e.g., alkaline or alkaline earth metal ions or ammonium ions) comprised in the regenerated ion exchange resin may be substituted by protons, which may act more effectively in an ion exchange process than the cations of the inorganic salt. Accordingly, if the ion exchange resin is to be used, e.g., in an ion exchange process, it may be preferred for the regenerated resin to be subjected to a wash with an acidic aqueous solution. In several other embodiments the regenerated ion exchange resin may be lixiviated, by washing the resin with, e.g., water, before, for instance, being used for obtaining recycled objects therefrom.

[0125] It has been found that using a method as described herein, wherein an ion exchange resin comprising metal ions is washed with an aqueous inorganic salt solution, may increase the useful life of the resin as an ion exchange resin, by increasing the number of cycles that the ion exchange resin may be used in an ion exchange method. In particular, the number of cycles may be increased when compared to ion exchange resins that have been directly washed with aqueous acid solutions.

[0126] The regenerated ion exchange resin may have a low (e.g., below a certain threshold) amount of metal ions originally present in the resin or may be substantially free of metal ions originally present in the resin. As discussed, since ions of the inorganic salt may substitute the metal ions originally present in the ion exchange resin, the regenerated ion exchange resin after washing with the aqueous solution of inorganic salt may comprise ions of the inorganic salt (e.g., alkaline or alkaline earth metal ions, lanthanide metal ions or ammonium ions).

[0127] The regenerated ion exchange resin may have a varying porosity. The porosity may vary, e.g., depending on the porosity of the starting ion exchange resin provided in step (a) of the method and / or the way the ion exchange resin may be affected by the washing of step (b). By way of example, a regenerated ion exchange resin may have a porosity defined in terms of the BET specific surface area from 0.5 to 20 m2 / g, in particular from 0.75 to 15 m2 / g, more in particular from 1 to 10 m2 / g.

[0128] In several embodiments, the porosity may be below a predetermined porosity threshold. In several alternative embodiments, the porosity may be above a predetermined porosity threshold. Such porosity threshold may be expressed as the BET specific surface area and may be, e.g., from 0.5 to 5 m2 / g, in particular from 0.75 to 4 m2 / g, and more in particular from 1 to 3 m2 / g.

[0129] For example, the predetermined porosity threshold may be a 20 % of the initial porosity of the resin. As a mode of example, for an ion exchange resin having an initial BET specific surface area, e.g., from 7 to 14 m2 / g, a porosity threshold value, in terms of the surface area may be from 1 .4 to 2.8 m2 / g, and, in several embodiments, ion exchange resins with surface area below such threshold values can be considered unsuited for further use as in ion exchange methods.

[0130] In some embodiments, the regenerated ion exchange resin may be used in an electropolishing method. In several particular embodiments an electropolishing method using the regenerated ion exchange resin by, e.g.: introducing the regenerated ion exchange resin into a medium; and electropolishing at least one surface of an object with the medium having the resin introduced therein to extract metal ions from the at least one surface.

[0131] Such electropolishing methods may be known. As a mode of example reference is made to., e.g., International Application No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1), and International Application No. PCT / ES2021 / 070065 (published as WO 2022 / 123096 A1) as discussed above. In some embodiments, the medium may further comprise a plurality of abrasive particles introduced therein.

[0132] Accordingly, a method as described herein may further comprise using the obtained regenerated ion exchange resin in an electropolishing method. Another aspect of the present disclosure relates to a method comprising using a regenerated ion exchange resin in an electropolishing method.

[0133] In some embodiments, the regenerated ion exchange resin may be used in a water treatment method. In some embodiments, a water treatment method may comprise using the regenerated ion exchange resin by, e.g.: contacting a water comprising metal ions and the obtained regenerated ion exchange resin to extract metal ions from the water.

[0134] The water may be, for example but without limitation, wastewater, including also wastewater selected from the ore and / or mining industry.

[0135] Accordingly, a method as described herein may further comprise using the obtained regenerated ion exchange resin in a water treatment method. Another aspect of the present disclosure relates to a method comprising using a regenerated ion exchange resin in a water treatment method. In some embodiments, a regenerated resin used in an electropolishing method or in a water treatment method may have a porosity above a predetermined porosity threshold, e.g., expressed as the BET specific surface area and may be as defined above.

[0136] In some embodiments, the regenerated ion exchange resin may be used in manufacturing a recycled object, e.g., to form at least part of the recycled object. In some embodiments, manufacturing a recycled object may further comprise using an elastomer and / or a thermoelastic material in combination with the regenerated ion exchange resin to form at least part of the recycled object. Accordingly, a method as described herein may further comprise manufacturing a recycled object comprising using the regenerated ion exchange resin to form at least part of the recycled object. Another aspect of the present disclosure relates to a method comprising using a regenerated ion exchange resin in manufacturing a recycled object, in particular to form at least part of the recycled object. In some embodiments, a regenerated resin used for manufacturing a recycled object may have a porosity below a predetermined porosity threshold, e.g., expressed as the BET specific surface area and may be as defined above.

[0137] Manufacturing a recycled object as described herein may be performed using conventional (such as injection, extrusion, and molding) and advanced (such as three- dimensional printing) processing techniques.

[0138] Manufacturing a recycled object comprising using the regenerated ion exchange resin may comprise, e.g., cleaning the regenerated ion exchange resin with, for instance, water. Manufacturing a recycled object may further comprise mixing the regenerated ion exchange resin, which may be optionally clean, with other materials, e.g., other polymeric materials and / or advanced ceramic materials, employed as, e.g., polymeric matrices and ceramic scaffolds respectively. Other materials may be useful to enhance the properties of the regenerated ion exchange properties and to make them suitable for a specific application.

[0139] Further aspects of the present disclosure relate to a recycled object obtainable by methods as described herein and to a recycled object comprising a regenerated ion exchange resin as described herein.

[0140] In some embodiments, a recycled object as described herein or from a method as described herein may be selected, for example, from an acoustic panel ora sound absorber; a piece of furniture, e.g., urban furniture; a pavement, e.g., a urban pavement, such urban pavements may be useful for, e.g., absorption of plastic deformation; and a tunnel fan. In some embodiments the recycled object may be a 3D-printed object.

[0141] In this text, the term “includes”, “comprises” and derivations thereof (such as “including”, “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0142] On the other hand, the disclosure is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.

[0143] EXAMPLES

[0144] A polystyrene divinylbenzene sulfonic ion exchange resin was used in the electropolishing of stainless-steel pieces until saturation of its active sites, by immersing the stainless-steel pieces in a bucket with macroporous ionic exchange resin, in particular macroporous polystyrene divinyl benzene sulfonic ion exchange resin comprising an aqueous solution of sulfuric acid and moving the stainless-steel piece in relation to the ion exchange resin. The process was repeated until the electrical intensity of the electropolishing process decreased and / or the brightness of the dry-electropolished specimen was considerable decreased, which was indicative of the full saturation of the ion exchange resin particles. In the present examples a useful working time of the resin was found to be of around 100 h, reaching the end of its useful life. However, depending on the amount of ion exchange resin used for electropolishing, the useful working time of the ion exchange resin may be of, e.g., from at least 50 h to, e.g., several months depending on the industrial scale of the specific post-processing method.

[0145] The ion exchange resin was saturated with metal ions (mainly iron ions) extracted from the stainless-steel pieces. At the end of the electropolishing process, the solid ionic exchange resin filled with the metallic ions coming from the electrochemical polishing process of stainless steel, was washed to remove the iron ions from the ionic exchange resin.

[0146] Experiments were conducted on samples of the ion exchange resin comprising iron ions. 10 g of ion exchange resin was mixed with 20 mL of aqueous solution of sodium chloride (NaCI) in distilled water at different concentrations, a blank solution comprising water only (0 M NaCI concentration), and aqueous solutions of NaCI at increasing concentrations of 1 M, 2 M, 3 M, 4 M, 5 M and 6 M.

[0147] Tests were conducted for washing with a mixing (extraction) time of 45 minutes in some cases (Examples 1 to 5), at different temperatures, and with and without agitation, i.e. , with and without stirring.

[0148] In other examples the washing or extraction time was varied from 15 to 75 min for different concentrations and temperatures (Examples 7-16).

[0149] The extraction of the metal ions (in this case iron ions) was followed by determining the amount of iron dissolved in the aqueous solution after a given extraction time using photometric determination with 1 ,10-phenathroline compared to a blank sample using the Nanocolor® Standard test for Iron available from Macherey-Nagel (Test 1-36 for concentrations of 0.01-15 mg / L of Fe, reference 91836) and following the supplier instructions and an spectrophotometer to measure the absorbance of the different solutions measured. Samples having concentrations of iron higher than the range of the test were suitably diluted prior to the measurement, and the concentration of the sample was calculated from the dilution used. The amount of iron ions extracted from the resin using different conditions (e.g., aqueous inorganic salt concentration, temperature number of washing cycles) was established in mg of Fe per liter of aqueous solution used (mg Fe / L).

[0150] Examples 1-5: Extraction of metals from an ion exchange resin using washing steps with different inorganic salt concentrations.

[0151] Extraction of metal ions was performed by using a single washing cycle by mixing the ion exchange resin with aqueous solutions of NaCI of different concentrations at a temperature of 25 °C for 45 minutes, without agitation for example 1 and with agitation for example 2, and at a temperature of 70 °C for 45 minutes, without agitation for example 3 and with agitation for example 4. The amount of iron for each washing cycle was measured by triplicate and the average was recorded as the extracted iron in mg Fe / L based on the mass of iron per volume of the aqueous solution. The results are shown in the table below (Table 1) and in Figure 1A and B for examples 1 and 2 respectively, and in Figure 2A and B for examples 3 and 4 respectively. Table 1

[0152] Even though good extractions are obtained using concentrations of NaCI from 1 to 5 M, it can be seen that concentrations from 3 to 5 M show the highest level of extraction in a single mixing step. A higher temperature and the use of agitation (stirring) have been found to contribute to further increase the metal ion extraction.

[0153] Example 6: Extraction of metals from an ion exchange resin using multiple washing cycles Extraction of metal ions was performed by using a single set of conditions as indicated in the table below, using an increasing number of washing cycles, in order to evaluate the effect of an increasing number of washing steps on iron extraction. The extracted iron is measured in triplicate as explained above and the results are shown in the table below (Table 2) and in Figure 4.

[0154] Table 2 As can be appreciated from example 6, the amount of iron ions extracted decreases with each washing cycle. The highest amount of metal ions is removed in the first washing step (after 1 washing cycle). With a second washing cycle, significant amounts of metal ion are still being removed. The amount of metal ions extracted with a third washing cycle is measurable but lower than with previous washing cycles. The amount of metal ions removed with a fourth washing cycle could not be measured.

[0155] Examples 7 - 11 : Extraction of metals from an ion exchange resin using washing steps with different inorganic salt concentrations and different washing times at 30 °C.

[0156] Extraction of metal ions was performed by using a single washing cycle by mixing the ion exchange resin with aqueous solutions of NaCI of different concentrations at a temperature of 30 °C for 15, 30, 45, 60 and 75 minutes, with agitation. The amount of iron for each washing cycle was measured by triplicate and the average was recorded as the extracted iron in mg Fe / L based on the mass of iron per volume of the aqueous solution of NaCI. The results are shown in the table below (Table 3) and in Figure 6A.

[0157] Table 3

[0158] As can be appreciated from examples from 7 to 11 and from Figure 6A, at 30 °C there is a gap on the extraction speed using higher concentrations than 1M. In all cases, increasing the reaction time implies an increase of the extracted Fe ions during the cleaning process.

[0159] Examples 12 - 16: Extraction of metals from an ion exchange resin using washing steps with different inorganic salt concentrations and different washing times at 60 °C.

[0160] Extraction of metal ions was performed by using a single washing cycle by mixing the ion exchange resin with aqueous solutions of NaCI of different concentrations at a temperature of 60 °C for 15, 30, 45, 60 and 75 minutes, with agitation. The amount of iron for each washing cycle was measured by triplicate and the average was recorded as the extracted iron in mg Fe / L based on the mass of iron per volume of the aqueous solution.

[0161] The results are shown in the table below (Table 4) and in Figure 6B.

[0162] Table 4

[0163] As can be appreciated from examples from 12 to 16 and from Figure 6B, at 60°C there is also a gap on the extraction speed using higher concentrations than 1 M. In all cases, increasing the reaction time implies an increase of the extracted Fe ions during the cleaning process. Increasing the temperature from 30 to 60 °C, the amount of extracted Fe ions during the cleaning process has considerably increased, as well as the slope of the extraction curve with time.

[0164] Examples 17 and 18: Extraction of metals from an ion exchange resin using washing steps with different inorganic salt concentrations and different washing times at a and temperature of 70 °C.

[0165] Extraction of metal ions was performed by using a single washing cycle by mixing the ion exchange resin with aqueous solutions of NaCI of different concentrations at a temperature of 70 °C for 15, 30, 45, 60 and 75 minutes, with agitation. The amount of iron for each washing cycle was measured by triplicate and the average was recorded as the extracted iron in mg Fe / L based on the mass of iron per volume of the aqueous solution. The results are shown in the table below (Table 5) and in Figure 6C up to 120 minutes. Table 5 As can be appreciated from examples from 17 and 18 and from Figure 6C, at 70 °C there is also a gap on the extraction speed using concentrations higher than 1 M. In all cases, increasing the reaction time implies an increase of the amount of extracted Fe ions during the cleaning process. Increasing the temperature from 60 to 70 °C, the extracted Fe ions during the cleaning process has considerably increased, even more so when compared to the increase of the amount of Fe ions observed with the increase of temperature from 30 to 60 °C. The slope of the extraction curve with time has also been observed to increase with the increase of temperature.

[0166] Examples 19 - 23: Extraction of metals from an ion exchange resin using washing steps with different inorganic salt concentrations, for 45 min and at 70 °C.

[0167] Extraction of metal ions was performed by using a single washing cycle by mixing the ion exchange resin with aqueous solutions of NaCI of different concentrations at a temperature of 70 °C for 45 minutes, with agitation. The amount of iron for each washing cycle was measured by triplicate and the percentage (%) of extracted iron was calculated from the average was recorded as the extracted iron in mg Fe / L based on the mass of iron per volume of the aqueous solution of NaCI, with respect to the extracted iron in mg Fe / L extracted under the same conditions (70 °C for 45 minutes) with the 5 M solution (which was considered as the 100% of extraction). The results are shown in the table below (Table 6) and in Figure 7.

[0168] Table 6

[0169] From the results obtained on Figure 7 of examples 19 - 23, the best results have been obtained washing at 70 °C with a concentration of NaCI from 2 to 3 M.

[0170] Example 24: Ion exchange resin worked under an electrochemical polishing process, washed, reconditioned and reworked under an electrochemical polishing application.

[0171] An ion exchange resin has been prepared for being used as a solid electrolyte for an electrochemical polishing (electropolishing) process. The solid electrolyte comprises 15 L of: o 80 % in volume of electrically conductive particles made of:

[0172] • 79.66 wt.% of spherical macroporous particles with a heterogeneous particle size distribution ranging between 0.3 - 1.1 mm in diameter of sulfonated styrene divinylbenzene particles (Mitsubishi Relite CFS / FB) in an acid format after being dried up to get a constant moisture of around 33 wt. % with respect to the total weight of the solid bodies.

[0173] • 20.34 wt.% of methanesulfonic acid at a concentration of 70 wt.%, comprised within the solid bodies. o 20 % in volume of electrically conductive particles made of:

[0174] • 95.87 wt.% of spherical macroporous particles with monodispersed particle size around 0.28 mm in diameter of sulfonated styrene divinylbenzene particles (Purolite PCR 145K) in an acid format after being dried up to get a constant moisture of around 50 wt. % with respect to the total weight of the solid bodies.

[0175] • 4.13 wt.% of sulfuric acid at a concentration of 98 wt.%, comprised within the solid bodies.

[0176] The final aspect of the virgin ion exchange resin, prepared as described here above, is shown with a picture taken with DeltaPix DPX M6000 digital microscope in Figure 9A, presenting a brown aspect and no humidity above the liquid saturation limit of the resin.

[0177] The mentioned solid electrolyte was used for electropolishing a metal part consisting of a rectangular piece of austenitic stainless steel comprising chromium, nickel and molybdenum (AISI 316L SSL) with dimensions of 22 x 50 x 2 mm.

[0178] The austenitic stainless-steel sample was subjected to one pole of a power supply, was immersed in a 20 L capacity cylindrical receptacle comprising a mesh of platinated titanium, subjected to a second pole of a power supply. The receptacle was filled with 15L of the described solid electrolyte, fully covering the metal part to be treated, applying to said metal part a circular orbital motion of an amplitude of 3 cm radius at a frequency of 60 R.P.M.

[0179] The austenitic stainless-steel sample was electropolished at 25V, using a symmetric voltage with 1000 ms of anodic and cathodic polarization with a duty cycle of 100 ms between each polarity time. The sample was polished during 100 h after which the lifespan of the solid electrolyte was considered to reach its end, as metal ions extracted from the sample were found to saturate the resin. The evolution of current through time was recorded and provided an indication of the polishing performance of the system at 25 V, displaying a constant current value of about 0.5 A with time (see Figure 8A).

[0180] The used resin was washed according to Example 21. After the washing step performed to the resin, the solid electrolyte was prepared by mixing with methanesulfonic acid and sulfuric acid as described above, showing the final aspect as shown with a picture taken with DeltaPix DPX M6000 digital microscope in Figure 9B. The aspect of the solid electrolyte after being regenerated is dissimilar to the virgin ion exchange resin (of Figure 9A), presenting a whiter aspect and a higher level of humidity above the liquid saturation limit of the resin.

[0181] A similar austenitic stainless-steel sample was polished under the same conditions. The evolution of current through time was recorded and provided an indication of the polishing performance of the system at different voltages (5V, 10 V and 25V), displaying a constant current value of about 5 - 6 A at 25V (see Figure 8B). The higher current value obtained at 25V may be linked to the resulting different final humidity above the liquid saturation limit of the resin as observed in Figure 9B of the regenerated ion exchange resin when compared to the virgin resin.

[0182] A different current may result in a different performance of the electropolishing process and a different polishing effect in the metal piece being polished. Nonetheless, the output current can be adjusted by different methods, such as properly selecting the final water added to the ion exchange resin or by changing the voltage of the current applied to the electropolishing method. As it can also be seen in Figure 8B, the working voltage was adjusted from 25 to 5 V to obtain a similar current to that of Figure 8A, of about 0.5 A.

Claims

CLAIMS1 . A method comprising the following steps: a. providing an ion exchange resin comprising metal ions; b. washing the ion exchange resin with an aqueous solution of an inorganic salt thereby extracting at least some of the metal ions from the ion exchange resin and obtaining a regenerated ion exchange resin, wherein washing is performed by mixing the ion exchange resin with the aqueous solution of the inorganic salt.

2. The method of claim 1 , wherein the ion exchange resin is selected from an acidic ion exchange resin, a basic ion exchange resin, and / or a chelating ion exchange resin in particular the ion exchange resin may be selected from a sulphonic ion exchange resin.

3. The method of claim 1 or 2, wherein in particular the ion exchange resin may be a polystyrene resin, in particular a polystyrene divinylbenzene resin; a polyacrylic resin, in particular a polymethacrylic acid resin; a polyethylene resin; a polypropylene resin; a polyvinylchloride resin, in particular a high density polyvinylchloride; a polyamide resin; and a cellulose fiber; a zeolite, in particular a manganese zeolite; or an activated carbon in particular a granular activated carbon.

4. The method of any one of claims 1 to 3, wherein mixing is performed at a mixing temperature from 20 °C to 100 °C, in particular from 25 °C to 95 °C, in particular from 30 to 90 °C, more in particular from 35 to 85 °C, yet more in particular from 40 to 80 °C, and even more in particular from 65 to 75 °C.

5. The method of any one of claims 1 to 4, wherein mixing is performed from 30 seconds to 3 hours, in particular from 1 minute to 2 hours, more in particular from 5 minutes to 1.5 hours, and yet more in particular from 15 minutes to 1 hour.

6. The method of any one of claims 1 to 5, wherein the inorganic salt selected from a chloride, a nitrate and / or a sulfate salt of an alkali metal, an alkaline earth metal, a lanthanide or ammonium, in particular the inorganic salt is a chloride salt, more in particular the inorganic salt is a chloride salt is selected from sodium chloride, potassium chloride, calcium chloride, yet more in particular is selected from sodium chloride and potassium chloride and even more in particular is sodium chloride.

7. The method of any one of claims 1 to 6, wherein the aqueous solution of the inorganic salt has an inorganic salt concentration of from 0.5 to 6 M, in particular from 1 to 5 M, more in particular from 2 to 4 M, and yet more in particular from 2 to 3 M.

8. The method of any one of claims 1 to 7, wherein the proportion of mass of ion exchange resin per volume of aqueous solution of inorganic salt is from 1 to 1000 g of resin to 1 L of solution, in particular from 5 to 500 g of resin to 1 L of solution, more in particular from 10 g to 100 g of resin to 1 L of solution.

9. The method of any one of claims 1 to 8, wherein the washing of step (b) is performed more than once, in particular twice or more, and more in particular is performed three times.

10. The method of any one of claims 1 to 9, wherein the metal ions comprised in the ion exchange resin are transition metal ions.

11. The method of any one of claims 1 to 9, wherein the metal ions comprised in the ion exchange resin are selected from iron, copper, cobalt, chromium, aluminium, titanium, nickel, tungsten, calcium, magnesium, sodium, manganese, zinc and heavy metal ions such as lead, cadmium, arsenic and mercury ions, and are preferably selected from iron, copper, cobalt, chromium, aluminium, titanium, nickel, silver, gold, and tungsten ions..

12. The method of any one of claims 1 to 11 , wherein- the ion exchange resin comprising metal ions provided in step (a) is an ion exchange resin used in an electropolishing method or in a water treatment method; or- providing the ion exchange resin of step (a) comprises using an ion exchange resin in an electropolishing method or a water treatment method.

13. The method of claim 12, wherein using the ion exchange resin in an electropolishing method comprises electropolishing at least one surface of an object with a medium comprising the ion exchange resin to extract metal ions from the at least one surface, thereby providing the ion exchange resin comprising the metal ions.

14. The method of claim 12, wherein using the ion exchange resin in a water treatment method comprises contacting a water comprising metal ions, in particular a wastewater, and an ion exchange resin to extract metal ions from the wastewater, thereby providing the ion exchange resin comprising the metal ions.

15. The method of any one of claims 1 to 14, wherein washing the ion exchange resin further comprises obtaining a metal ion extract.

16. The method of any one of claims 1 to 15, further comprising using the obtained regenerated ion exchange resin in an electropolishing method by: introducing the obtained regenerated ion exchange resin into a medium; and electropolishing at least one surface of an object with the medium having the resin introduced therein to extract metal ions from the at least one surface.

17. The method of any one of claims 1 to 15, further comprising using the obtained regenerated ion exchange resin in a water treatment method by: contacting a water comprising metal ions, in particular a wastewater and more in particular a wastewater from the ore and / or mining industry, and the obtained regenerated ion exchange resin to extract metal ions from the wastewater.

18. The method of any one of claims 1 to 15, further comprising manufacturing a recycled object comprising using the regenerated ion exchange resin to form at least part of the recycled object.

19. The method of claim 18, wherein manufacturing further comprises using an elastomer and / or a thermoelastic material in combination with the regenerated ion exchange resin to form at least part of the recycled object.

20. The method of any one of claims 18 or 19, wherein the regenerated ion exchange resin used in manufacturing has a porosity that is below a predetermined porosity threshold, the predetermined porosity threshold preferably being defined in terms of the GET specific surface area and being from 0.5 to 5 m2 / g, in particular from 0.75 to 4 m2 / g, and more in particular from 1 to 3 m2 / g.

21. The method of any one of claims 15 to 20, further comprising manufacturing a catalyst using the metal ion extract.

22. The method of claim 21 , wherein the manufacturing comprises crystallizing one or more extracted metal ions from the metal ion extract.

23. A regenerated ion exchange resin obtainable by a method of any one of claims 1 to 15, or a recycled object obtainable by any one of claims 18 or 19.

24. A metal ion extract obtainable by a method of claim 15 or a catalyst obtainable by a method of any one of claims 21 or 22.

25. A catalyst comprising metal ions extracted by a method according to any one of claims 1 to 15 or 22.

26. A method comprising using a regenerated ion exchange resin of claim 23 in an electropolishing method or a water treatment method.

27. A method comprising using a regenerated ion exchange resin of claim 23 in the manufacturing of a recycled object.

28. The method of claim 26 wherein using the regenerated ion exchange resin in an electropolishing method comprises: introducing the regenerated ion exchange resin into a medium; and electropolishing at least one surface of an object with the medium having the resin introduced therein to extract metal ions from the at least one surface.

29. A recycled object comprising a regenerated ion exchange resin according to claim 23.

30. The recycled object of any one of claims 23 and 29 or the method of any one of claims 17, 18, and 26 wherein the recycled object is selected from an acoustic panel or a sound absorber, a piece of furniture, a pavement, a tunnel fan, and a 3D-printed object.

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