WO2025238151A1

WO2025238151A1 - Process for electromediated metal stripping and recovery

Info

Publication number: WO2025238151A1
Application number: PCT/EP2025/063397
Authority: WO
Inventors: Maxime DUCREUX; Julien Leclaire; Adrien FOROT; Déborah ROMITO; Trevor Alan Hatton; Kai-Jher TAN
Original assignee: Mecaware; Centre National de la Recherche Scientifique CNRS; Universite Claude Bernard Lyon 1; Massachusetts Institute of Technology
Current assignee: Mecaware; Centre National de la Recherche Scientifique CNRS; Universite Claude Bernard Lyon 1; Massachusetts Institute of Technology
Priority date: 2024-05-16
Filing date: 2025-05-15
Publication date: 2025-11-20
Anticipated expiration: 2026-11-16
Also published as: EP4650469A1

Abstract

The present invention relates to an electromediated process for separating at least one first-row transition metal M1, such as nickel, from a liquid sample. The liquid sample preferably originates from a battery. The invention further relates to an electromediated process for regenerating copper and/or a primary amine from a complex comprising copper and said primary amine, an electromediated process for stripping a metal ion from a complex comprising said metal and a primary amine and an electromediated process for recovering at least one first-row transition metal M1 and/or at least one primary amine from a complex comprising said metal and said primary amine.

Description

PROCESS FOR ELECTROMEDIATED METAL STRIPPING AND RECOVERY

TECHNICAL FIELD

The present invention relates to a process for selectively extracting and recovering chemical elements from a liquid sample. Utilities used for extraction and recovery are managed by electrochemical means, thus minimizing the need of any additive and the amount of effluents. The process of the invention is thus advantageous in economic, environmental and ecological terms.

TECHNICAL BACKGROUND

Energy storage has become a global issue and a major challenge. Since the 1980s, the annual world consumption of oil has become greater than the quantities of new deposits discovered. It is therefore necessary to turn to other sources of energy, such as renewable energies, and to develop technologies for the storage of these energies in order to better manage these resources. Efforts to reduce oil consumption are particularly linked to the development of electric vehicles and batteries. While Lithium-ion batteries are now commonly used in computers and mobile phones, there remains some limitations for large-scale applications like electric vehicles. In particular, such applications require high amounts of strategic metals, such as cobalt or rare earth metals, which are expensive. The development of effective and selective recycling processes is therefore crucial in this field.

To date, few methods for capturing and separating strategic metals, such as those contained in batteries, have been developed.

Black mass is a black powder obtained after grinding and optionally heating the various cells used to store electrons. In the black mass, metals are present as oxides, which can be considered as basic when dissolved in water. Classical treatment and separation methods from black mass, such as hydrometallurgic separation methods, most involve the use of acidic conditions for leaching metals from the battery black mass. When extracting agents are used to extract the metals, acidic conditions are also implemented for separating the extracted metal from the extracting agent(s) (stripping). At the end of the recycling process, the metals are classically precipitated as salts in acidic or basic conditions.

Existing methods typically rely on acid for stripping. Such methods are impacting, due to the sue of acids. Other methods rely on metal recovery by direct electrowinning, which requests much energy. Both types of methods further represent a substantial operational cost.

In order to limit waste and/or effluents and optimize atom economy, it would be useful to use separating processes that can be implemented in basic medium, and which imply as little as possible generation of waste and/or effluents, such as the stripping of metals in absence of acid, and/or their recovery as basic salts. Implementation of continuous and/or cyclic processes would also be advantageous.

International patent application WO2023/242129 discloses a process for selectively capturing chemical elements from a polymetallic sample, said process involving the selective dissolution and/or precipitation of the different metals. Nickel and cobalt are prevented from precipitation by complexing with an amine, while other valuable metals are precipitated. Nickel and cobalt are further contacted with copper salts such as copper chloride or copper sulfate, generating copper ions to selectively liberate the metal from the complex (stripping), and finally precipitating the metal as a salt such as a carbonate or a hydroxide. Copper is the element of choice for complexing an amine, as it is known to have the highest affinity according to the Irving-Williams series. At the end of the process, the stripping agent, ie copper as cupric ions, is bound to the ligand/solubilizing agent, ie the amine, and further treatment is necessary to recover copper. Said process involves the use of different salts, at least for nickel stripping (use of copper salts such as copper chloride or copper sulfate), and for nickel or cobalt precipitation (use of sodium carbonate and/or sodium hydroxide salts), which generate saline byproducts.

Thus, there remains a need to provide processes allowing recovery of metals from polymetallic samples, such as black mass, which would not involve acidic steps and limit the generation of waste and/or effluents. Advantageously, such methods should also imply the use of no or very little additives, such as salts, so as to avoid pollution of the medium and/or the need for further separation and/or purification steps.

SUMMARY OF THE INVENTION

In this respect, the Inventors have unexpectedly evidenced that it was possible to use electrochemistry to efficiently separate and recover target transition metals, such as nickel, cobalt and/or zinc, from a liquid sample. In practice, cupric ions from a sacrificial anode are used to cleave a complex between an amine ligand and the target transition metal(s) (stripping) Copper is then recovered from the primary amine-copper complex by the use of electrochemistry. Actually, copper may be recovered as a copper deposit on the cathode electrode of a system, such as an electrochemical cell, from the primary aminecopper complex. Advantageously, copper recovery and/or primary amine recovery in the cathodic chamber are implemented simultaneously to precipitation of a salt of the target transition metal, such as nickel, cobalt and/or zinc, in the anodic chamber of the system, such as the anodic chamber of the electrochemical cell, by contacting a primary amine complex of the target transition metal with copper ions generated at the anode of the system. Ions such as carbonate and/or hydroxide ions are further used for the recovery as target transition metals. The used utilities that are cupric ions and carbonate and/or hydroxide ions may be generated and/or recycled by electrochemical means, without accumulating byproducts.

Thus, a first object of the present invention is a process for separating at least one first-row transition metal Ml from a liquid sample, said process comprising the steps of: a) Contacting the liquid sample with at least one primary amine and optionally CO 2, so as to obtain a first liquid phase; b) Contacting the first liquid phase with copper ions generated at the anode of a system, such as an electrochemical cell, so as to obtain a second liquid phase, c) Contacting said second liquid phase with a carbonate and/or a hydroxide, so as to obtain a third liquid phase and Ml in a solid form, d) Separating Ml in a solid form from the third liquid phase, and e) Depositing copper from the third liquid phase by reduction at the cathode of the system, such as the electrochemical cell.

The process for separating at least one first-row transition metal Ml according to the invention simultaneously allows separating Ml in a solid form, regenerating copper and regenerating the complexing primary amine. The use of electrochemistry allows limiting the need for additives and the produced effluents.

In some embodiments, steps b) and e) are implemented simultaneously to water electrolysis.

In some embodiments, Ml is selected from the group consisting of nickel, cobalt and zinc.

In some embodiments, the liquid sample comprises two first-row transition metals Ml and M2, each of Ml and M2 being independently preferably selected from the group consisting of nickel, cobalt and zinc.

In some embodiments, the process further comprises, between step a) and step b), a step of separating the first liquid phase from a first solid phase obtained at step a).

In some embodiments, Ml in a solid form recovered at step c) is a carbonate, a hydroxide or a combination thereof, of Ml.

In some embodiments, the primary amine is selected from the group consisting of ammonia, N- alkylethylene diamines, wherein the alkyl group is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec -butyl and tert-butyl groups, preferably isopropyl group, ethylene diamine, propane diamine, tris-(2-aminoethyl)amine, lysine, glycine, 2,3-diaminopropionic acid, 2,3- diaminosuccinic acid, 2,4-diaminobutyric acid, and 2,5 -diaminopentanoic acid, preferably it is ethylene diamine.

In some embodiments, the at least one transition metal Ml comprises cobalt, and step c) further comprises contacting the second liquid phase with a reducing agent, wherein said reducing agent is preferably an electron produced by electrochemistry.

In some embodiments, the liquid sample comprises two transition metals Ml and M2, wherein M2 is cobalt, and steps c)-d) comprise the following sub-steps: a) contacting said second liquid phase with a carbonate and/or a hydroxide, so as to obtain a liquid phase LI and Ml in a solid form,

P) recovering said Ml in a solid form, y) contacting said liquid phase LI with a reducing agent, so as to obtain the third liquid phase and M2 in a solid form, and

5) recovering said M2 in a solid form, wherein said reducing agent is preferably an electron produced by electrochemistry.

In some embodiments, step b) is implemented simultaneously to water reduction, and the hydroxide ions produced by water reduction are preferably used for implementing step c).

In some embodiments, step e) is implemented simultaneously to water oxidation, and the H⁺ ions produced by water oxidation are preferably used for leaching Ml from a solid sample before step a).

In some embodiments, Ml in a solid form is further purified, preferably by contacting Ml in a solid form with an aqueous ammonia solution, and treating the obtained mixture by electrolysis.

In some embodiments, the process is cyclically repeated or continuous, and at least one of the elements recovered at an iteration of the process is re-used in a further iteration of the process.

A second object of the present invention is a process for regenerating copper and/or a primary amine from a complex comprising copper and said primary amine, said process comprising depositing copper at the cathode of a system, such as an electrochemical cell, by electrolysis of a liquid phase comprising said complex comprising copper and said primary amine, and recovering at least one of the primary amine and the copper.

A third object of the invention is a process for stripping a metal ion from a complex comprising said metal and a primary amine, wherein the metal of the metal ion is a first-row transition metal Ml, said process comprising contacting a liquid phase comprising said complex comprising said metal and a primary amine with copper ions generated at the anode of a system, such as an electrochemical cell.

A fourth object of the invention is a process for recovering at least one first-row transition metal Ml and/or a primary amine from a complex comprising said metal and said primary amine, said process comprising electrolyzing a solution or a suspension comprising said complex in a system, such as an electrochemical cell, comprising an anode suitable for producing copper ions, and recovering at least one of Ml, the primary amine, and copper.

FIGURES

Figure 1 is a graph presenting cell energy requirements in the presence of different (a) anions (Cl-, NO f , and SO4² ) and (b) cations (Li⁺, Na⁺, and Mg²⁺), obtained from continuous and sequential two-electrode chronopotentiometry experiments in the order of ca. 10 and 50 A/m², with each current density held for 120 s. Each solution was comprised of 10 mM Ni²⁺ salt, 100 mM Na⁺ or SO4² salt, and 30 mM ethylenediamine, with the counter ions used for (a) and (b) being Na⁺ and SO4² , respectively.

Figure 2 is a graph presenting cell energy requirements in solutions containing 10 mM G1SO4 and 100 mM Na2SC>4 (grey), and 10 mM G1SO4, 100 mM Na2SC>4, and 20 mM ethylenediamine (black), obtained from continuous and sequential three -electrode chronopotentiometry experiments in the order of ca. -10 and -50 A/m², with each current density held for 120 s.

Figure 3 presents the results of electrochemical H-cell experiments with an anode chamber solution comprising 10 mM NiCU, 30 mM ethylenediamine, and 100 mM NaCl, and a cathode chamber solution comprising 100 mM NaCl. (a) UV-Vis spectra, (b) nickel recovery percentage, and (c) copper concentration of the anode chamber solution, before and after applied current densities of ca. 0, 25, 50, and 75 A/m² for 1930 s (0, 0.5, 1, and 1.5 theoretical copper equivalents).

Figure 4 presents the UV-Vis spectra of the cathode chamber solution, before and after an applied current density of ca. 75 A/m² for 1930 s (1.5 theoretical copper equivalents).

Figure 5 presents the results of electrochemical H-cell experiments with an anode chamber solution comprising 10 mM NiCh, 30 mM ethylenediamine, and 100 mM NaCl, and a cathode chamber solution comprising 10 mM CuCI 2. 20 mM ethylenediamine, and 100 mM NaCl. UV-Vis spectra of the (a) anode chamber solution and the (b) cathode chamber solution, and (c) copper concentrations of the anode and cathode chamber solutions, before and after an applied current density of ca. 75 A/m² for 1930 s (1.5 theoretical copper equivalents). Figure 6 presents the evolution of the UV spectra of the medium during monoelectronic reduction of Co(en)₃ ³⁺ into Coion) ;² at pH 4.

Figure 7 displays UV-Vis measurements before (black line) and after (grey line) electrochemical dissolution of copper by chronoamperometry.

Figure 8 displays the UV-Vis measurements performed during the chronoamperometry experiments over the Zn/Ni mixture, (a) almost entirely forming the amount of Cu(en)2 expected to selectively strip zinc and (b) achieving the amount of Cu(en)2 required for stripping nickel. Notably, the dotted lines stand for the Cu(en)2 formation via CuCU addition, while the continued black lines correspond to UV- Vis experiments of the anode chamber solution while the chronoamperometry occurred.

Figure 9 is a flowsheet of Ni and Co separation and recovery according to the invention by electrochemical management of cupric ions as stripping agents and carbonate ions as precipitating agents by electrochemical means without water splitting. EDA=ethylenediamine.

Figure 10 is a flowsheet of Ni and Co separation and recovery according to the invention by electrochemical management of cupric ions as stripping agents and carbonate ions as precipitating agents by electrochemical means with water splitting. EDA=ethylenediamine.

DETAILED DESCRIPTION OF THE INVENTION

Process for separating at least one first-row transition metal Ml

A first object of the invention is a process for separating at least one first-row transition metal Ml from a liquid sample, comprising steps a) to e).

The process involves applying an electrical potential to the anode and cathode in a system, such as an electrochemical cell, and flowing the liquid sample through the system.

The system comprises an anode, a cathode, and anodic chamber, a cathodic chamber, and preferably a membrane separator at least partially disposed between the anodic chamber and the cathodic chamber. The system preferably further comprises a solution comprising a primary amine, and an electrolyte. An electrolyte is a medium containing ions that are electrically conductive through the movement of those ions, but not conducting electrons.

Upon application of an electrical potential to the anode and cathode in the system, the primary amine may associate and/or dissociate with the first-row transition metal Ml and/or with metal ions. Each association and/or dissociation step is performed simultaneously to a complementary reaction at the other electrode, such as water oxidation (to produce H⁺ ions) or water reduction (to produce OH ions).

S Step a)

Step a) aims at complexing the at least one first-row transition metal Ml in the liquid sample with a primary amine.

The liquid sample on which the separating process according to the invention is carried out can be any type of liquid sample comprising the first-row transition metal Ml as defined herein. It can be a liquid sample of any origin. For instance, the liquid sample may be originating from a battery, wastes from batteries production, effluents from steel industry or dairy industry, red mud, ores, or fly ash. In a particular embodiment, the liquid sample is a sample originating from a battery, for instance a nickel- metal hydride or Li-ion battery, or a component thereof (such as a battery cathode). More specifically, the liquid sample may be obtained by solubilizing or leaching a solid sample comprising the first-row transition metal Ml as defined herein, said solid sample being typically from a battery, for instance a nickel-metal hydride or Li-ion battery, or a component thereof (such as a battery cathode).

In some embodiments, the liquid sample is obtained by contacting a solid sample originating from a battery with H⁺ ions obtained by an electrochemical process, such as water electrolysis.

Preferably, H⁺ ions are produced by water oxidation at the anode of the system, such as the electrochemical cell or fuel cell.

The solid sample may be of any one of the following formulae: La2NigCoMn, Al_xFe_yNi_zMnCoO with x and y being each independently from 0.1 and 10, and z is an integer from 1 to 8 (preferably 8), LiAl_wCuFeNikMnCoO with w being from 0.1 and 10 and k is an integer from 1 to 8 (preferably 8), or LiAlo iNio sCoo iMno iO.

In some embodiments, the process comprises preliminary steps, prior to step a), for removing at least part of other metals, such as copper, lithium, aluminum and/or manganese from the liquid sample. Suitable techniques for such removal steps are well known in the art. For instance, the process disclosed in WO2023/242129 may be used for removing aluminum and/or manganese. The liquid sample processed according to the invention may thus be exempt of such impurities or contain very low amounts thereof. The liquid sample may thus not comprise any copper and/or lithium and/or aluminum and/or manganese. When the liquid sample is obtained by contacting a solid sample originating from a battery with H⁺ ions obtained by water oxidation at the anode of the system, the preliminary removal steps may be implemented either before or after the contacting step with H⁺ ions.

Preferably, said liquid sample is an aqueous solution comprising the first-row transition metal Ml as defined herein. Ml in the liquid sample is typically in the form of cations.

The concentration of Ml in the liquid sample is advantageously equal to or less than 0.75 mol/L, for instance comprised between 0.05 and 0.55 mol/L, or between 0.25 and 0.55 mol/L.

The concentrations of each chemical element in the liquid sample (i.e. their initial concentration) can be determined by titration ICP (Inductively Coupled Plasma spectroscopy).

The first-row of transition metals comprises the ten following metals: Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), and Zinc (Zn). In some embodiments, Ml is selected from the group consisting of nickel, cobalt and zinc. More preferably, Ml is nickel.

“Ml in a solid form” refers to a solid, in particular a solid salt, comprising the chemical element ML Preferably, “Ml in a solid form” is a carbonate of Ml, a hydroxide of Ml or a combination thereof. A particular combination is a carbonate-hydroxide of ML

In some embodiments, the liquid sample comprises n first-row transition metals, n being at least equal to 2, referred to as Ml, M2, M3, . . . , Mn. In some embodiments, the liquid sample comprises exactly two first-row transition metals. In some embodiments, the liquid sample comprises nickel and cobalt. In some embodiments, the liquid sample comprises nickel and zinc. In some embodiments, the liquid sample comprises cobalt and zinc. In some embodiments, the liquid sample comprises more than two first-row transition metals, but only one or two of them (M 1 , or M 1 and M2) are separated with a process according to the invention.

The primary amine according to the invention is an amine comprising one or several primary amine NFL groups. The primary amine does not comprise any secondary amine group.

The primary amine according to the invention can be of general formula R2-NH2, in which R2 is selected from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl groups and aromatic groups, the hydrocarbon chain of which is optionally interrupted by at least one heteroatom chosen from N, O and S and which is optionally substituted by at least one substituent, which substituent preferably does not comprise an aldehyde CHO. In the present invention, an “alkyl group” denotes a linear or branched C1-C20, preferably Ci-Ce, in particular C1-C3, saturated hydrocarbon group. Preferably the alkyl group is chosen from methyl, ethyl, n-propyl, isopropyl, n butyl, sec-butyl, tert-butyl, n-pentyl and n-hexyl groups. The alkyl group can optionally be interrupted by at least one heteroatom chosen from N, O and S. The alkyl group can optionally be substituted, in particular by at least one group chosen from hydroxys (-OH), alkoxys (- OR), thiols (-SH), thioethers (-SR), carbonyls (-CHO or -C(O)R), carboxyls (-COOH or -COOR) and amines (-NH2), wherein R is preferably an unsubstituted alkyl group and comprises solely single bonds. An “alkenyl group” denotes an alkyl group as defined above, additionally comprising at least one C=C double bond.

An “alkynyl group” denotes an alkyl group as defined above, additionally comprising at least one C=C triple bond.

The cycloalkyl, cycloalkenyl and cycloalkynyl groups respectively represent cyclic alkyl, alkenyl and alkynyl groups.

An “aromatic group” is a group comprising at least one flat ring comprising a conjugated 71 system formed of double bonds and/or of lone pairs, in which each atom of the ring comprises a p orbital, the p orbitals overlap and the delocalization of the 71 electrons results in a decrease in the energy of the molecule. Preferably, an aromatic group is chosen from phenyl, pyridinyl, pyrimidinyl, pyrazinyl, triazinyl, furanyl, thiophenyl, pyrrolyl, imidazolyl, thiazolyl, oxazolyl and naphthyl groups. Preferably, the aromatic group is a phenyl.

In a particular embodiment, the primary amine comprises at least 2 primary amine groups, preferably at least 3, at least 4 or at least 5 primary amine groups. In particular, the primary amine is such that R2 is an alkyl group substituted by at least one NH₂ substituent, preferably substituted by a single NH2 substituent, more preferably terminated by a single NH2 substituent.

The primary amine may be a primary amine from a water-lean solvent, such as N,N- dimethylethylenediamine, N,N,N’,N’ -tetramethylethylenediamine or 1,3 -propanediamine.

In some embodiments, the primary amine is selected from the group consisting of ethylene diamine, propane diamine, tris-(2-aminoethyl)amine, lysine, glycine, 2,3-diaminopropionic acid, 2,3- diaminosuccinic acid, 2,4-diaminobutyric acid, and 2,5 -diaminopentanoic acid, preferably it is ethylene diamine.

In some embodiments, the primary amine is selected from the group consisting of ammonia, N- alkylethylene diamines, wherein the alkyl group is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl and tert-butyl groups, preferably isopropyl group, ethylene diamine, propane diamine, tris-(2-aminoethyl)amine, lysine, glycine, 2,3 -diaminopropionic acid, 2,3- diaminosuccinic acid, 2,4-diaminobutyric acid, and 2,5 -diaminopentanoic acid, preferably it is ethylene diamine.

The primary amine may be either water-miscible or non-water miscible.

The carbon dioxide used in the process of the invention (in particular in step a) and/or for generating the carbonate in step c)) can result from a human activity, of which it represents a waste product; for example, it can originate from combustion flue gases, refinery gas, cement works gas or blast furnace gas.

The liquid sample, the at least one primary amine and optional CO2 may be contacted in step a), simultaneously or successively. Advantageously, contacting step a) is carried out in water. More particularly, the liquid sample is typically an aqueous solution, and no additional solvent is used to carry out contacting step a). In such embodiments, the primary amine is preferably water-miscible.

The concentration of the primary amine in step a) may be comprised between 0.05 M and 15 M, preferably between 0.5 M and 10 M, and more preferably between 2 M and 5 M.

Preferably, step a) is implemented at room temperature. By "room temperature”, it is meant a temperature comprised between about 15 °C and 25 °C.

The capturing or recovering of the chemical elements of the process according to the invention is typically carried out after observation (or “detection”) of a precipitate after different components and/or reactants have been brought into contact. Advantageously, the detection additionally comprises the comparison of the sample obtained with a similar sample which does not comprise the chemical element and which can be denoted reference sample. Likewise, the detection can additionally comprise the comparison of the sample obtained with a similar sample which comprises the chemical element. The duration of each contacting step of the process of the invention can be suitably adjusted by the skilled artisan, and may in particular be determined by the period of time necessary for the complete formation of a precipitate after contacting the components and/or reactants. Step b)

Step b) aims at substituting the at least one first-row transition metal Ml with copper in the complex with the primary amine.

Step b) is implemented in a system, such as an electrochemical cell, or more simply a cell, which comprises copper working electrodes.

Step b) may be implemented by applying an electrical potential to the anode and cathode in the system. In some embodiments, the cell further comprises, between the anode and the cathode compartments, an anion exchange membrane. The anion exchange membrane helps limiting the issuance of parasitic reactions, in particular by preventing cupric cation from being transferred from the anode compartment to the cathode compartment. Parasitic reactions may actually affect the process performance.

The electrical potential to be applied at step b) and the duration of application may be determined by one skilled in the art from his general knowledge, depending among others on the nature of Ml and of the primary amine, on their respective concentration, and on the desired number of equivalents of copper ions.

The amount of copper ions in step b) is advantageously comprised between 1 and 3 molar equivalents, preferably between 1.5 and 2 equivalents, relative to the amount of Ml. As copper ions are generated at the anode, no counterion is introduced simultaneously to the copper ions, contrary to copper ions introduced via a chemical salt.

The electrical potential to be applied at step b) may be about +/-0.1 volts, about +/-0.2 volts, about +/- 0.3 volts, about +/-0.4 volts, about +/-0.5 volts, about +/-0.6 volts, about +/-0.7 volts, about +/-0.8 volts, about +/-0.9 volts, about +/-1.0 volts, about +/-1.1 volts, about +/-1.2 volts, about +/1.3 volts. Advantageously, the potential is about +/-0.6 volts or about +/-0.7 volts.

The electrical potential may be applied for instance with use of a first electrode, a second electrode, a potentiostat, and/or a power supply.

Advantageously, step b) is carried out in water. More particularly, the first liquid phase is typically an aqueous solution, and no additional solvent is used to carry out step b).

Advantageously, step b) is carried out at room temperature.

In some embodiments, in particular when Ml is cobalt, the process comprises an intermediate step b’) before or after step b) of contacting the first or the second liquid phase with a reducing agent as defined below.

Step c)

Step c) aims at precipitating Ml in a solid form.

Advantageously, step c) is carried out in water. More particularly, the second liquid phase is typically an aqueous solution, and no additional solvent is used to carry out step c).

As used herein, “a carbonate” refers to a carbonate CO ,² ion. In some embodiments, the carbonate ion may be introduced as a carbonate salt, such as a carbonate of an alkali metal (such as sodium carbonate, potassium carbonate, or lithium carbonate), or of an alkaline-earth metal (such as barium carbonate, calcium carbonate or magnesium carbonate). In other preferred embodiments, the carbonate ion may be introduced by reacting carbon dioxide with a hydroxide ion, preferably obtained by water reduction by electrolysis at the cathode of the system. The flowsheet of figure 9 represents a process according to the invention in absence of water splitting, and the flowsheet of figure 10 represents a process according to the invention with water splitting. In some embodiments, the carbonate ion may be introduced by reacting carbon dioxide with an amine, such as lysine.

The amount of carbonate in step c) is advantageously comprised between 0.5 and 5 molar equivalents, relative to the amount of Ml .

As used herein, “a hydroxide" refers to a hydroxide OH- ion. In some embodiments, the hydroxide ion may be introduced as a hydroxide salt, such as a hydroxide of an alkali metal (such as sodium hydroxide, potassium hydroxide, or lithium hydroxide), or of an alkaline-earth metal (such as barium hydroxide, calcium hydroxide or magnesium hydroxide). In other preferred embodiments, the hydroxide ion is obtained by water reduction by electrolysis at the cathode of the system.

When present, the amount of hydroxide in step c) is advantageously comprised between 0.5 and 1 molar equivalent, relative to the amount of Ml.

In a particular embodiment, the amount of carbonate is comprised between 1 and 5 molar equivalents relative to the amount of Ml, and the amount of hydroxide is comprised between 0.5 and 5 molar equivalents relative to the amount of Ml.

In a particular embodiment, the molar ratio of carbonate to hydroxide in step c) is comprised between 0.1 and 10, preferably between 0.5 and 2.

Step c) is preferably implemented at room temperature.

Step c) may be implemented in any pH conditions allowing precipitation of Ml in solid form. When Ml is nickel and Ml is precipitated as a carbonate, step c) is preferably implemented at a pH comprised between 8 and 9, preferably a pH of about 8.5. When Ml is zinc and Ml is precipitated as a carbonate, step c) is preferably implemented at a pH comprised between 6 and 7, preferably a pH of about 6.5.

When the liquid sample comprises more than one first-row transition metals to be recovered and/or separated, step c) may be implemented several times, in different conditions each allowing the selective precipitation of each first-row transition metals. In some embodiments, especially when the liquid sample comprises nickel and zinc and Ml and M2 are precipitated as carbonates, step c) is first implemented at a pH comprised between 6 and 7, and then step c) is implemented at a pH comprised between 8 and 9. When the pH is to be increased in the process according to the invention, such increase may be preferably implemented by producing hydroxide OH- ions by water reduction at the cathode of the system. Alternatively, the pH may be increased by addition of a base.

In some embodiments, especially when the liquid sample comprises two first-row transition metals Ml and M2 to be recovered and/or separated, M2 being cobalt, a step b’) of contacting the medium with a reducing agent, such as an electron produced by electrochemistry, may be implemented between both iterations of step c).

■ Step d)

Step d) aims at separating Ml from the third liquid phase and may be implemented with any suitable solid-liquid separation technique known in the art. Step d) may be for instance carried out by filtration, centrifugation, or reverse osmosis.

More generally, each recovering and/or separating step of the process of the invention may be independently carried out by filtration, centrifugation, or reverse osmosis.

Step d) is preferably implemented at room temperature.

In some embodiments, especially when the liquid sample comprises more than one first-row transition metals to be recovered and/or separated, step d) may be implemented several times after each iteration of step c).

In an embodiment, the liquid phase comprises at least two first-row transition metals Ml and M2, M2 being cobalt. In such an embodiment, steps c)-d) of the process of the invention may comprise: a) contacting said second liquid phase with a carbonate and optionally a hydroxide, so as to obtain a liquid phase LI and Ml in a solid form, preferably at a pH comprised between 8 and 9,

P) recovering said Ml in a solid form, y) contacting said liquid phase LI with a reducing agent, preferably at a pH comprised between 3 and 5, so as to obtain the third liquid phase and M2 in a solid form, and

5) recovering said M2 in a solid form.

Advantageously, steps a) and y) are carried out in water. More particularly, the second liquid phase and said liquid phase LI are typically aqueous solutions, and no additional solvent is used to carry out steps a) and y). Contacting step a) is advantageously carried out at room temperature. Contacting step y) is advantageously carried out at room temperature or under heating to a temperature T₄ above room temperature, T₄ being preferably comprised between 70 °C and 110 °C, more preferably at about 100 ° When the pH is to be decreased in the process according to the invention, such decrease may be preferably implemented by producing H⁺ ions by water oxidation at the anode of the system, or by bubbling CO2 in the medium. Alternatively, the pH may be decreased by addition of an acid.

The amount of carbonate in step a) is advantageously comprised between 0. 1 and 10 molar equivalents, relative to the amount of M2.

When present, the amount of hydroxide in step a) is advantageously comprised between 0.1 and 10 molar equivalents, relative to the amount of M2.

In a particular embodiment, the molar ratio of carbonate to hydroxide in step a) is comprised between 0.1 and 10 preferably between 0.5 and 2.

As used herein, a “reducing agent” refers to any chemical or physical species that is able to reduce (i.e. decrease the oxidation state of) ions of the chemical element M2 contained in the liquid phase LI in step y). Advantageously, the use of a reducing agent favors the decomplexation between M2 and the amine. In some embodiments, the reducing agent is a solid metal (i.e. having an oxidation state of 0) such as metallic cobalt (i.e. Co⁰), metallic iron (i.e. Fe°), or metallic copper (i.e. Cu°), CO2 or activated carbon. In a preferred embodiment, the reducing agent is an electron produced by electrochemistry. Such embodiment has the advantage of further limiting the effluents of the process in comparison with the use of chemical reducing agents.

The amount of reducing agent in step y) is advantageously comprised between 0.5 and 5 molar equivalents, relative to the amount of M2.

In a particular embodiment, step y) comprises contacting said liquid phase LI with a reducing agent, copper ions, optionally H⁺ ions preferably produced by water oxidation at the anode of the system, and optionally a carbonate and/or a hydroxide, so as to obtain the third liquid phase and M2 in a solid form. Advantageously, the copper ions from step b) present in the second liquid phase and/or those added in step y), in combination with the reducing agent, favor the decomplexation between M2 and the amine, and the formation (or “precipitation”) of M2 in a solid form.

The copper ions are preferably generated by the copper anode.

In steps a) and ), said Ml in a solid form is preferably a hydroxide, carbonate or carbonate-hydroxide of ML In a particular embodiment, Ml is nickel, and said Ml in a solid form is a carbonate of nickel.

In steps y) and 5), said M2 in a solid form is preferably a hydroxide, carbonate or carbonate-hydroxide of M2. In a particular embodiment, M2 is cobalt, and said M2 in a solid form is a carbonate of cobalt. In some embodiments, for instance when Ml is recovered as a carbonate and/or a carbonate-hydroxide, the process according to the invention comprises a further step of purifying the obtained Ml in a solid form. Low amounts of copper impurity may indeed be present in the recovered Ml in a solid form. The purification step may be implemented by contacting Ml in a solid form with an aqueous ammonia solution, and treating the obtained mixture by electrolysis. Metal purity may be increased thanks to this purification step, to reach battery grade. In some embodiments, this purification is implemented when Ml is nickel.

Step e)

Step e) aims at recovering the copper, which may be reduced upon exposure to an electrical potential at the cathode. Upon reduction of copper, the primary amine dissociates from the copper, generating free primary amine in solution in the cathodic chamber.

The electrical potential to be applied at step e) may be about +/-0.1 volts, about +/-0.2 volts, about +/- 0.3 volts, about +/-0.4 volts, about +/-0.5 volts, about +/-0.6 volts, about +/-0.7 volts, about +/-0.8 volts, about +/-0.9 volts, about +/-1.0 volts, about +/-1.1 volts, about +/-1.2 volts, about +/1.3 volts.

Step e) is preferably implemented at room temperature.

In some embodiments, step e) further comprises recovering the primary amine from the cathodic chamber.

In some embodiments, especially when the process comprises steps a) to 5), step e) may be performed in two steps, one between steps ) and y), and the other after step 5).

Of course, all embodiments disclosed with two transition metals in the present invention may be implemented by iterating steps if more than 2 transition metals are present in the liquid sample.

In some embodiments, the process for separating at least one first-row transition metal Ml from a liquid sample is cyclically repeated, or is continuous. By cyclically repeated, it is meant that the process is repeated at least 2 times, preferably at least 3, 4, 5, 6, 7, 8, 9 or 10 times. In such embodiments, the primary amine that is recovered at step e) may be re-used in step a) of the next iteration of the process. Furthermore, deposition of copper at the cathode may be performed simultaneously to water oxidation at the anode, thus generating H⁺ ions. Said H⁺ ions may be re-used in a further iteration of the process, especially for leaching the first-row transition metal(s) from a solid sample originating from a battery to the invention

The present invention encompasses all processes obtained by combination of the general and/or specific features disclosed above for each step of the process. The section below discloses specific embodiments of the process of the invention, which do not limit its scope.

In some embodiments, the liquid sample is obtained by contacting a solid sample originating from a battery with H⁺ ions obtained by water oxidation performed at the anode of a fuel cell. Step c) of the process involves hydroxide ions obtained by water reduction, and is advantageously performed at the cathode of the fuel cell. Water oxidation and water reduction correspond to water electrolysis. In such embodiments, steps b) and e) of the process may be implemented in a different electrochemical cell. Preferably, in such embodiments, Ml is nickel and/or the primary amine is ethylene diamine. Such embodiments allow a traceless metal recovery and primary amine regeneration.

In some embodiments, the liquid sample is obtained by contacting a solid sample originating from a battery with H⁺ ions obtained by water oxidation at the anode of a first electrochemical cell. Step e) of the process of the invention is advantageously performed at the cathode of the electrochemical cell. Steps b) and c) may be implemented in a second electrochemical cell, step c) involving hydroxide ions obtained by water reduction. Preferably, in such embodiments, Ml is nickel and/or the primary amine is ethylene diamine. Such embodiments allow a traceless metal recovery and primary amine regeneration.

In some embodiments, step b) is implemented in the anodic chamber of the electrochemical device, the generation of hydroxide ions to be used in step c) is implemented in the cathodic chamber of the electrochemical device, and the contents of both compartments are combined for implementing step c). Step d) is preferably implemented by filtration. Step e) is preferably implemented in the cathodic chamber of the electrochemical device, thus liberating the primary amine, and water reduction is implemented in the anodic chamber of the electrochemical device, thus regenerating H+ ions that may be re-used for obtaining the liquid sample from the solid sample originating from a battery. Such embodiments allow a traceless metal recovery and primary amine regeneration. In some embodiments, the liquid sample comprises two first-row transition metals Ml and M2, Ml being preferably nickel and M2 being cobalt, and the implementation of the process of the invention, wherein steps c)-d) comprise steps a) to 5), allows traceless separation and recovery of both first-row transition metals, and amine regeneration.

In some embodiments, the liquid sample comprises two first-row transition metals Ml and M2, Ml being preferably nickel and M2 being preferably zinc, and step c) is implemented twice at two different pH, allowing first the selective precipitation of M2 in a solid form (such as a carbonate), and then the precipitation of Ml in a solid form (such as a carbonate). Preferably, M2 is zinc and step c) is first implemented at a pH comprised between 6 and 7. Preferably, Ml is nickel and step c) is further implemented at a pH comprised between 8 and 9. Implementation of such process allows traceless separation and recovery of both first-row transition metals, and amine regeneration.

Process for regenerating copper and/or a primary amine

A second object of the invention is a process for regenerating copper and/or a primary amine from a complex comprising copper and said primary amine, said process comprising depositing copper at the cathode of a system, such as an electrochemical cell, by electrolysis of a liquid phase comprising said complex comprising copper and said primary amine, and recovering at least one of the primary amine and the copper.

In some embodiments, the complex comprising copper and said primary amine is obtained by contacting a complex comprising a first-row transition metal Ml and said primary amine with copper ions. Copper ions may originate either from a chemical compound, such as copper chloride, or preferably from a copper anode.

All features disclosed above for the global process, especially for step e) thereof, apply to the present process.

Process for stripping a metal ion

All features disclosed above for the global process, especially for step b) thereof, apply to the present process. Process for recovering a first-row transition metal Ml and/or a primary amine

All features disclosed above for the global process apply to the present process.

In the present application, the term "about" (or ca.) preceding a value is well-known to the skilled artisan and means that said value may vary to a certain extent depending on the context in which the term is used. If certain uses of this term are not clear to the skilled artisan depending on the context, then "about" means ± 20%, preferably ± 10% of said value.

Unless otherwise indicated, when a range is expressed by means of the expression "comprised between", the limit values are included within the range described.

The invention will also be described in further detail in the following examples, which are not intended to limit the scope of this invention, as defined by the attached claims.

EXAMPLES

Materials and methods

Electrochemical measurements were performed using a VersaSTAT 3 (Princeton Applied Research) or a SP- 150 (Bio-Logic) potentiostat in either batch cell or H-cell configurations under magnetically stirred conditions. Batch cell experiments were run in a ca. 20 mb cylindrical glass cell vial (BASi) using rectangular pieces of 110 copper shim stock (0.005” thickness, Trinity Brand Industries) as the working and counter electrodes, and a RE-5B MF-2052 Ag/AgCl (3 M NaCl) reference electrode (BASi) (if required), in 5 mb volume of solution. H-cell experiments were run in a ca. 10 mb (ca. 5 mb per electrode chamber) H-cell (Adams & Chittenden Scientific Glass Coop) fitted with a Fumasep FAS-30 anion exchange membrane (FuMA-Tech) using rectangular pieces of 110 copper shim stock (0.005” thickness, Trinity Brand Industries) as the working and counter electrodes, in 5 mb volume of solution per electrode chamber. Copper electrodes were generated by attaching each copper substrate to a copper wire with copper tape. Copper substrates were prepared with dimensions of either ca. 1 cm x 2.5 cm (for the batch cell) or ca. 0.5 cm x 3 cm (for the H-cell), and were immersed to a depth of either ca. 1 cm (for the batch cell) or ca. 2 cm (for the H-cell) in solution for a total submerged area of ca. 1 cm². In general, electrolyte solutions for the electrochemical experiments were prepared with 10 mM metal salt, 20 or 30 mM ethylenediamine, and 100 mM supporting electrolyte, unless otherwise specified. Samples were prepared for solution-phase characterization by passing them through a cellulose acetate syringe filter (25 mm diameter, 0.22 pm pore size, VWR) to remove any solid particles. Metal concentrations were quantified via inductively-coupled mass spectrometry (ICP-MS) measurements conducted on a 7900 ICP-MS system (Agilent). All calibration solutions and internal standards were prepared from TraceCERT ICP standards (Sigma- Aldrich) and 2 wt. % HNOs . Samples were diluted to lie within the concentration range of the calibrations, and both the calibration solutions and samples were spiked to contain 1 ppb rhodium as an internal standard. Prior to ICP-MS, each applicable sample (1 m ) was spiked with 100 pL of a solution containing 0.05 M NaOH and 0.1 M Na2COs, and subsequently incubated at room temperature for 24 h in order to precipitate any free nickel ions in solution. Ultraviolet-visible spectroscopy (UV-Vis) measurements were carried out on a Cary 60 UV- Vis spectrophotometer (Agilent) with a quartz cuvette. The electrochemical studies concerning nickel and zinc were performed using a AUT.MAC.S (Metrohm) potentiostat in H-cell configuration under magnetically stirred conditions. The experiments were run in ca. 400 m (200 mb per electrode chamber) using a Metrohm H-cell equipped with a bumasep FAS-30 anion exchange membrane using copper plates (size specified below for each case) as working electrodes, Ag/AgCl (D-Junction, Metrohm) as reference electrode and Pt sheet electrode (surface area ca. 1 mm², Metrohm) as counter electrode. Detailed amounts of electrolyte and starting solutions are described below for each experiment. Metal concentrations were quantified via ICP-OES 5800 VDV (Agilent) at a concentration of 500 ppb using a HNO3 5% matrix, with a relative standard deviation (RSD) <5%. Each sample has been analyzed three times at multiple wavelengths. All calibration solutions and internal standards were bought from Sigma- Aldrich. Samples were diluted to he within the concentration range of the calibrations. Ultraviolet-visible spectroscopy (UV-Vis) measurements were carried out on a UV-1900I spectrophotometer (Shimadzu) with a quartz cuvette.

Example 1. Formation of copper-amine complex in an electrolyzer

To evaluate the effect of the electrolyte on the copper oxidation reaction, a copper anode was subject to chronopotentiometry in the presence of various anions and cations. At current densities of ca. 10 and 50 A/m², the measured cell energies did not exhibit significant variation between different anions (CT, NOf , and SO4² ) or cations (Ei⁺, Na⁺, and Mg²⁺) (Figure 1). Contrastingly, the addition of ethylenediamine to cupric salt solutions resulted in larger energy requirements for sustaining cell operation at ca. -10 and -50 A/m², which was ascribed to the complexation between copper and ethylenediamine (Figure 2).

Formation of the copper-ethylene diamine complex in the electrolyzer is assessed by the cell energy required by the solution containing ethylene diamine and copper ions, in comparison with the energy required by the other solutions. Example 2. Recovery of nickel with a process according to the invention

The feasibility of the invention was, at first, tested by screening the counter ion effect on nickel recovery. Notably, 2X^_ = 2CT, SO4² and 2HCOO anions were investigated both in the cathodic (sodium salts as electrolyte) and anodic chambers (nickel salts as precursors).

Ni(en)s²⁺, 2X^_ complex solutions were prepared by loading a 500 m Erlenmeyer flask with a 50 mM aqueous solution of NiX2 nickel salt (17.5 mmol, 340 mL), followed by the dropwise addition of ethylenediamine en (3 eq, 52.5 mmol, 3.5 mL) completed to 350 mL with water.

Electrolyte solutions were prepared by loading a 500 mL Erlenmeyer flask with a 100 mM aqueous solution of sodium salt NaX (35 mmol, 350 mL).

The cathodic chamber of the H-cell system was loaded with the electrolyte solution and equipped with one graphite plate as counter electrode and a magnetic bar. The anodic chamber of the H-cell system was loaded with the Ni(en)s²⁺ complex solutions and equipped with one Copper plate as working electrode, an Ag/AgCl reference electrode and a magnetic bar. Before starting the chronoamperometry experiment, CO 2 was bubbled (100 mL/min) in the latter solution until the pH was lowered from ca. 10.09 to 6.55. While continuously bubbling CO2, a +0.7 V potential was applied for 6 hours at room temperature to promote the cupric ion formation in the anodic chamber. UV -vis experiments of the given solutions of the anodic chamber showed an absorbance band at ca. 560 nm, revealing the formation of the targeted Cu(en)_x ²⁺ complexes. A control UV-vis experiment of the solution in the cathodic chamber was additionally performed, proving the absence of copper or nickel species. At the end of the electrochemical experiment, the anodic solution was recovered and heated to reflux until basic pH was reached. The resulting suspension was filtered off and the solid dried in the oven overnight before characterization.

The H-cell configuration was also used to investigate the extent of nickel recovery as a function of the amount of copper supplied to the solution through variation of the current density. UV-Vis measurements revealed commensurately increasing peak absorbance readings at ca. 540 to 555 nm with the applied cell current in the anode chamber solution, and the absence of any such signals in the cathode chamber solution, thus illustrating the successful electrochemical release of cupric cations from the anode to the solvent to form copper-ethylenediamine complexes, and the role of the anion exchange membrane in inhibiting the transfer of copper to the cathode chamber, respectively (Figure 3a and Figure 4). The resulting solutions were carbonated to precipitate the liberated nickel cations as insoluble carbonates, after which the remaining nickel concentrations in the solution phase were measured to calculate the overall nickel extraction amounts. As expected, nickel removal rose with the amount of copper in the system, culminating in a 61% nickel recovery from a 10 mM NiCL solution at ca. 75 A/m² (1.5 theoretical copper equivalents added) (Figure 3b). The greater extent of copper oxidation at higher current densities was clearly evidenced by the heightened concentrations of copper detected in solution, and was facilitated at Faradaic efficiencies of ca. 60% (Figure 3c). Due to the reversible nature of the copper redox couple, both copper and ethylenediamine were also included in the cathode chamber to synthetically replicate the spent electrolyte after nickel extraction for the purpose of investigating intandem nickel and copper recovery as a single electrochemical stage. Applying a current density of ca. 75 A/m² (1.5 theoretical copper equivalents) under these conditions resulted in an increase and decrease in the copper concentrations of the anode and cathode chamber solutions from concomitant copper oxidation and reduction with efficiencies of 62% and 53%, respectively, which was confirmed both visually, as well as through UV-Vis (Figure 5a and Figure 5b) and ICP-MS (Figure 5c) solution-phase measurements.

Example 3: Proof of concept of implementing steps b) and c) with cobalt

In the present example, Ml is cobalt and a step b’) of contacting the first liquid phase with a reducing agent is implemented before step b) of contacting the liquid phase with copper ions. In the present proof of concept, copper ions are introduced as CuCI ₂. and it is clear for one skilled in the art that copper ions generated at an anode of a system would have the same technical effect.

Preparation of Leachates and CO2 buffer solution

CO(HCOO)2-2H₂0 was prepared according to the following synthetic procedure. To a suspension of CoCOs (14.42 g, 122 mmol, 1 eq) in water (48 mL), formic acid (1.27 mol, 48 mL, 10.4 eq) was slowly added. The mixture was heated to reflux for 1 hour, then cooled to room temperature. Acetone (70 mL) was then added, and the resulting pink suspension was filtered using hydrophobic membranes (PTFE, 10 pm) and the solid dried overnight at 90 °C. The resulting product was pure Co(HCOO)2 2H2O, obtained as a dark pink powder (analyzed by ICP-OES and ion chromatography).

Ni(HCOO)₂ 1.5H2O was prepared according to the following synthetic procedure. To a suspension of 2NiCO3-3Ni(OH)2’4H2O (100 g, 170 mmol, 1 eq) in water (200 mL), formic acid (3.18 mol, 120 mL, 18.7 eq) was slowly added. The mixture was stirred at room temperature for 2 hours, then acetone (200 mL) was added, and the resulting green suspension was filtered using hydrophobic membranes (PTFE, 10 pm) and the solid dried overnight at 90 °C. The resulting product was pure Ni(HC00)2 l.SELO, obtained as a green powder (analyzed by ICP-OES and ion chromatography).

Co(en)₃(HCOO)₃ was prepared as follows: To a solution of Co(HCOO)2 (1.494 g, 10 mmol, 1 eq) and ethylenediamine (1.81 g, 2.0 mL, 30 mmol, 3 eq) in water (100 mL, pH = 12.33), formic acid (660 mg, 0.377 mL, 10 mmol, 1 eq) was added. The resulting solution (pH = 9.15) was bubbled with compressed air for 4 hours and then heated under reflux for 12 hours. UV-Vis analysis confirmed the complete formation of Co(en)3(HCOO)3.

Co(en)3(HCOO)z solution was prepared by dissolving Co(HCOO)2 (647.4 mg, 3.5 mmol, 1 eq) and ethylenediamine (700 pL, 10.5 mmol, 3 eq) in water (70 mL, pH = 10.47). The solution was kept under an inert atmosphere.

Model Ni and Co solutions were prepared as follows: To a suspension of Ni(HC00)2 2H2O (36.95 g, 200 mmol, 1 eq) in water, ethylenediamine (40 mL, 600 mmol, 3 eq) and 10 mL of Co(en)3(HCOO)3 solution (2 mol/L, 0.1 eq) were added. The total volume was adjusted to 500 mL using a volumetric flask. UV-Vis spectroscopy was used to analyze the final solution, containing 400 mM Ni(en)3(HCOO)2 and 40 mM Co(en)3(HCOO)3.

The Real leachate used as starting material in the following paragraphs was prepared as follows: A blackmass powder (50 g), containing a lithiated nickel-manganese-cobalt oxide with a 811 ratio and graphite (40 wt%), was treated with a concentrated solution of formic acid (250 mL, 4.73 M, 4 molar equiv. of HCOOH vs n₀(Ni+Mn+Co)) at 80 °C for 3h to afford, after filtration over a hydrophobic membranes (0.45 pm), a colorless filtrate containing the lithium (2.058 M) and a black solid containing formates of nickel, manganese and cobalt, as well as graphite. The resulting black wet solid (125 g) was then suspended in water (400 mL) and subsequently treated with a concentrated solution of ethylenediamine (96 mL, 1.43 mol, 4.86 equiv. vs n₀(Ni+Mn+Co)) followed by CO2 injection (flow rate: 250 mL/min) for 2 h and heated to reflux for 4 hours. This led to the consequent recovery, after filtration over an hydrophobic membrane (PTFE, 0.45 pm), of graphite (20.78 g), MnCOs (1.18 g) as a beige solid, while the filtrated dark red solution (710 mL) stands for the real leachate containing Nickel (0.344 M) and Co (0.042 M).

The CO2 buffer solution used as alternative electrolyte in the following paragraphs was prepared as follows: To a suspension of L-lysine hydrochloride (10 g, 54.8 mmol, 1 eq) in distilled water (20 mL) vigorously stirred, KOH pellets (6.5 g, 115 mmol, 2.1 eq) were slowly added. The resulting yellow solution was added dropwise to a beaker containing 100 mL of ethanol cooled down to 0 °C. To get rid of the thus formed KC1, the suspension was filtered using a Buchner funnel, and the solvents evaporated in vacuo to remove ethanol. The concentration of the resulting K-Lysine aqueous solution was determined by ’H qNMR and acid titration using a 1 M HC1 solution.

Co(en)₃C13 and Co(en)2CO3Cl, en referring to ethylenediamine, were prepared beforehand. Co(en)₂CO3Cl was prepared according to the procedure disclosed in Springborg, J.; Schaffer, C. E.; Preston, J. M.; Douglas, B. Dianionobis(Ethylenediamine)Cobalt(III) Complexes. Inorganic Syntheses 2007, 63-77. Co(en)₃(CO3)i .5 was prepared according to the following synthetic procedure. To a solution of Co(en)₃C13 (3 g, 8.38 mmol, 1 eq) in distilled water (170 mL), Ag2SC>4 (3.92 g, 12.6 mmol, 1.5 eq) was added under vigorous stirring. The resulting suspension was stirred at 85 °C for 3 hours, then the system was allowed to cool down to room temperature and filtered. The solid was washed several times with distilled water, then the filtrate was concentrated in vacuo, to afford pure Co(en)₃(SO4)i 5 as an orange powder (3.17 g, 99.6% yield). The obtained solid was dissolved in 80 mL of distilled water, followed by the addition of Ba(OH)2 -H2O (2.4 g, 12.7 mmol, 1.5 eq) under vigorous stirring. The suspension was stirred at room temperature for 18 hours, then CO 2 was bubbled for 3 hours, and the system filtered. The resulting filtrate was concentrated in vacuo, to afford pure Co(en)3(CO3)i .5 as an orange powder (3.04 g, 92% yield). Example 3,1, Chemical reduction of CoIenHCH by FeCL

In a typical experiment, 0.7632g (2mmol) of Co(en)3C13.2H2O were added to 15mL of distilled water and the mixture was degassed with argon for 20 minutes. 0.3mL of a IM solution of NaOH were then added to reach a pH of 10.5 . A solution containing 0.3976g (2mmol, leq) of FeC12.4H2O in 5mL of distilled water was also prepared and degassed with argon for 20minutes, then added dropwise to the cobalt solution, while maintaining the pH at 10.5 by addition of a degassed IM NaOH (6.2mL added at the end of the addition of the FeCL solution). A brown precipitate was formed during the addition of the FeCL solution. The mixture was left under agitation and inert atmosphere for 1 hour at room temperature. During this time, a solution containing 0.5117g of CUCI2.2H2O (3mmol, 1.5eq) in 5mL of water was prepared and degassed. The iron/cobalt mixture was then filtered under inert atmosphere, affording a brown solid. The solid was dissolved in 37% HC1 solution, and analyzed by ICP-OES, which delivered a precipitation yield of 88.4% in Fe and 19.6% in Co.

The filtrate was transferred to the copper solution without any contact with air and left under agitation for 1 hour. 3.1mL of a IM NaOH solution were added to the mixture to rise the pH from 5.6 to 8.5, allowing for the precipitation of a blue solid. The solid was filtered on Whatman GF/F (<0.7pm) filter, dried, and analyzed by ICP-OES. Precipitation yield in cobalt was determined to be 48.4% in Co and the metallic purity, 53%, the main impurity being Copper.

The same procedure was applied to Co(en)2CO3Cl. Precipitation yield in cobalt was determined to be 47% in Co and the metallic purity, 28%, the main impurity being Copper. Example 3,2: Chemical reduction of CoIenHCH by N2H4

In a typical experiment, 0.7632g (2mmol) of Co(en)3C13.2H2O were added to 15mL of distilled water and the mixture was degassed with argon for 20 minutes. A solution containing 0.0798g (1.5mmol, 0.75eq) of N2H4.H2O and 0.240g (6mmol, 3eq) of NaOH in 5mL of distilled water was also prepared and degassed with argon for 20 minutes, then added dropwise to the cobalt solution. The mixture was brought to 70°C and left under agitation and inert atmosphere for 2 hours at room temperature. After 2 hours the mixture was filtered under inert atmosphere. The solid was washed with 20mL of 20% acetic acid in water, allowing for the dissolution of the Co(OH)₂ in the solid. The resulting solution was analyzed by ICP-OES, giving a precipitation yield of 42%. The remaining solid, corresponding to Co(0) was dissolved in 37% HC1 solution, and analyzed by ICP-OES, giving a precipitation yield of 48% in Co.

The same procedure was applied to Co(en)₂CO3Cl. Precipitation yield in cobalt was determined to be 75% in Co and the metallic purity, 100%.

S Example 3,3: Chemical reduction of CofenhCE by NH₂0H

In a typical experiment, 0.7632g (2mmol) of Co(en)3C13.2H₂O were added to 15mL of distilled water and the mixture was degassed with argon for 20minute. 0.1937g (3mmol, 1.5eq) of a 50% solution of NH₂0H in water was added in 5mL of distilled water, with 0.240g (6mmol, 3eq) of NaOH and degassed with argon for 20 minutes, then added dropwise to the cobalt solution. The mixture was brought to 70°C and left under agitation and inert atmosphere for 2 hours at room temperature. During this time, a solution containing 0.5117g of CUC1₂.2H₂O (3mmol, 1.5eq) in 5mL of water was prepared and degassed. The cobalt mixture was then filtered under inert atmosphere, allowing the obtention of a brown solid. The solid was dissolved in 37% HC1 solution, and analyzed by ICP-OES, giving a precipitation yield of 54.2% in Co.

The filtrate was transferred to the copper solution without any contact with air and left under agitation for 1 hour, allowing for the precipitation of a green solid. The solid was filtered, dried, and analyzed by ICP-OES, giving a precipitation yield in cobalt of 37.0% in Co and 12.4% in Cu, with a metallic purity of 66.5%, the main impurity being Copper. The total yield of the combined solids was determined to be 91.2% and the total purity 81%.

The same procedure was applied to Co(en)₂CO3Cl. Precipitation yield in cobalt was determined to be 84% in Co and the metallic purity, 78%, the main impurity being Copper.

S Example 3,4: Selective recovery of nickel and cobalt with a process according to the invention The H-cell configuration was used to investigate the extent of the selective recovery of nickel and cobalt as a function of the amount of copper supplied to the starting solution by applying an electric potential. At first, a stock solution of Ni(en)₂ 20 mM was prepared by adding 475 mg (2 mmol, 1 eq) of NiCl₂-6H₂O to a 100 mb volumetric flask. The flask was filled with 50 mb of distilled water, followed by the slow addition of 240 mg of ethylenediamine (267 pL, 4 mmol, 2 eq), eventually completing the volume with distilled water. A second stock solution of Co(en)3(CC>3)i .5 20 mM was prepared by adding 795 mg (2 mmol, 1 eq) of Co(en)₃(CO3)i .5 to a 100 mb volumetric flask, which was completed to volume with distilled water. The two solutions were added to the anode chamber, in the presence of 1.06 g of Na₂CC>3 (10 mmol, 10 eq) used as electrolyte, while the cathode chamber exclusively contained a 100 mM Na₂CC>3 solution in distilled water. The initial pH of the anode chamber solution was 10.8, which was adjusted to 7.0 by bubbling CO2 (flow rate: 0.1 mL/min) over one hour, to limit the concurrent formation of CuO_x, being favored at basic pH. Upon application of an electric potential of +0.6 V to a copper electrode (5 x 3.8 cm) dipped in the anode chamber solution, the effective electrochemical release of Cu²⁺ was detected by UV-Vis analysis (Figure 7). Notably, an increased absorbance at 590 nm could be observed within 18 hours, standing for the formation of Cu(en)₂.

In sharp contrast, the cathode chamber solution stayed colorless, addressing the role of the anion exchange membrane in inhibiting the transfer of Cu²⁺ to the cathodic chamber. The resulting anode chamber solution was treated with 212 mg of Na₂CO3 (2 mmol, 1 eq) and 1 mb of a 1 M NaOH solution (Immol, 0.5 eq), and the achieved suspension was filtered. The solid was then washed several times with distilled water, dried and analyzed by ICP-EOS (inductively coupled plasma optical emission spectroscopy). This resulted in a 22% nickel recovery from the starting 10 mM NiCl₂ solution, with a metal purity of 92%. Furthermore, ICP-EOS analysis of the remaining filtrate confirmed that 78% of nickel was left.

The investigation continued by attempting to selective deposit metallic copper, leaving Co(en)3(CO3)i .5 for its reduction and subsequent stripping. A fresh stock solution of Cu(en)₂ 20 mM was prepared by adding 341 mg (2 mmol, 1 eq) of CUC1₂-2H₂O to a 100 mb volumetric flask. The flask was filled with 50 mb of distilled water, followed by the slow addition of 240 mg of ethylenediamine (267 pL, 4 mmol, 2 eq), eventually completing the volume with distilled water. A second stock solution of Co(en)₃(CO3)i 5 20 mM was prepared by adding 795 mg (2 mmol, 1 eq) of Co(en)3(CC>3)i 5 to a 100 mb volumetric flask, which was completed to volume with distilled water. The two solutions were added to the cathode chamber, in the presence of 1.06 g ofNa₂CC>3 (10 mmol, 10 eq) used as electrolyte, while the anode chamber exclusively contained a 100 mM Na₂CC>3 solution in distilled water. The initial pH of the cathode chamber solution was 11.0, which was adjusted to 7.2 by bubbling CO₂ (flow rate: 0.1 mb/min) over one hour. Upon application of an electric potential of -0.7 V to a glassy carbon electrode (2.5 x 1.8 cm) dipped in the cathode chamber solution, the effective electrochemical deposition of metallic copper was detected by UV-Vis analysis. Notably, the decreased absorbance at 590 nm could be followed until no longer observed, after 20 hours of chronoamperometry measurement. The resulting metallic Cu° was collected from the working electrode, weighted, dried and analyzed by ICP-EOS, providing a metal recovery of 94.4% of copper with a corresponding purity of 98.9%.

The resulting filtrate, having a pH of 6.7, was treated with formic acid until a pH of 4.0 was achieved, then the system was poured into the cathode chamber of the H cell. Upon application of an electric potential of -0.7 V to a glassy carbon electrode (2.5 x 1.3 cm) dipped in the cathode chamber solution, the reduction of Co(en)₃(CO3)i 5 to Co(en)3CC>3 was followed by UV-Vis measurements (Figure 6). Notably, the decreased absorbance peak at 511 nm could be observed until complete disappearance, achieved after 20 hours of chronoamperometry experiment. The stripping of cobalt and consequent recovery in its carbonated form was attempted by adding Cu²⁺ ions in form of CuCl₂. The Co(II)- containing solution was treated with 512 mg (3 mmol, 1.5 eq) of CUCI2 2H2O upon vigorous stirring. The resulting mixture, having a pH of 2.7, underwent the addition of a 2 M Na2CO₃ solution until reaching a pH of 10. The corresponding suspension was fdtered, then the purple solid was washed several times with distilled water, dried at 90 °C for 18 hours and analyzed by ICP-EOS. This provided a precipitation yield of 78% and a metal purity of 70% for cobalt, aside with copper as major impurity. At last, the recovered fdtrate was poured in the cathode chamber and, upon application of an electric potential of -0.7 V for 24 hours, the entire recovery of metallic copper was achieved, being confirmed by ICP-EOS analysis of the Cu° collected on the glassy carbon electrode.

Example 4: Proof of concept - selective recovery of nickel and cobalt with and without water splitting Example 4,1: Selective recovery of Nickel

A) Using water splitting in cathodic chamber

The H-cell configuration was used to investigate the extent of the selective recovery of nickel as a function of the amount of copper supplied to the starting solution by applying an electric potential. At first, a stock solution of Ni(en)₃(HCOO)2 400 mM and Co(en)3(HCOO)3 40 mM was prepared from nickel and cobalt salts (see preparation above). The solution was added to the anode chamber (no additives as electrolyte were added because the ionic strength of the solution is self-sufficient for ionic transport), while the cathode chamber contained a IM NaHCOO solution in distilled water. The initial pH of the anode chamber solution was 10.8, which was adjusted to 7.0 by bubbling CO2 (flow rate: 0. 1 mL/min) over one hour. This helps limiting the concurrent formation of CuO_x, favored at basic pH. The anodic compartment is equipped with a copper electrode (5 x 5 cm) and a reference electrode (Ag/Ag/Cl) and the cathodic compartment with either a graphite or titanium electrode (5 x 5 cm). Upon application of an electric potential of +0.3 V to the copper electrode dipped in the anode chamber solution (with a continuous flow of CO2 (flow rate: 0.1 mL/min)), the effective electrochemical release of Cu²⁺ was followed by UV-Vis analysis. Notably, an increased absorbance at 590 nm could be observed within 24 hours, standing for the formation of Cu(en)2. In sharp contrast, the cathode chamber solution stayed colorless, addressing the role of the anion exchange membrane in inhibiting the transfer of Cu²⁺ to the cathodic chamber.

The resulting anode chamber solution has a pH of 7.63 and was refluxed 3 hours in order to remove CO 2 from the solution. After cooling down to room temperature the pH was at 8.80 and the suspension was filtered on hydrophilic membrane (0.45 um). The green solid was then washed several times with distilled water, dried and analyzed by ICP-EOS.

For model solution, this resulted in a 70-80% nickel recovery from the starting solution, with a metal purity of 70-80%. Furthermore, ICP-EOS analysis of the remaining filtrate confirmed that 20-30% of nickel was left. Implementation of a similar procedure from a real leachate resulted in a 80-85% nickel recovery with a metal purity of 70-75%. Furthermore, ICP-EOS analysis of the remaining filtrate confirmed that 15- 20% of nickel was left in the liquid phase.

B) Using water splitting in cathodic chamber with a CO? buffer

The H-cell configuration was used, replacing the aqueous formate solution in the cathodic chamber with an amine -containing aqueous solution, able to capture CO? while not depicting high chelating properties towards transition metals. Since this solution would be enriched with carbamates and HCO? anions, the latter ones could migrate to the anodic chamber during the electrochemical experiments instead of OH ions, generated by the water reduction. This was expected to favor a controlled precipitation of the targeted metal carbonate, as well as “buffering” the pH of the anodic chamber, which no longer required a continuous CO? bubbling to prevent the CuO_x formation. Specifically, a 200 mM aqueous solution of K-Lysine (350 m , see preparation above) underwent CO? loading by injecting pure CO? (flow rate: 50 mL/min) for 1 hour, lowering the pH from 12.1 to 8.2. The resulting solution was used in the cathodic chamber, while a model solution of Ni(en)₃(HCOO)? 50 mM with its pH lowered from 9.2 to 6.5 was placed in the anodic chamber. Similarly to the experimental conditions described in paragraph A, the anode chamber was equipped with a copper electrode (10 x 5 cm) and a reference electrode (Ag/AgCl). The cathodic compartment instead was loaded with a graphite electrode (10 x 5 cm). A +0.3 V was then applied for 21 h at r.t. while monitoring the electrodissolution of Cu²⁺ ions in the anodic chamber by UV-Vis measurements. As previously mentioned, CO? was bubbled in the anodic chamber for a few minutes only if the pH was higher than 8.2 (to limit the CuO_x formation on the copper electrode). After completion of the chronoamperometry experiment, the anode solution was heated to reflux for 1 hour to promote CO? desorption. The resulting suspension was filtered on hydrophilic membrane (0.45 pm), leading to a light green solid which was, then, washed with distilled water (5 x 30 m ), dried at 90 °C and analyzed by ICP-EOS. This analysis confirmed a nickel recovery of 95-98% from the starting model solution, with a metal purity of 90-93% and an associated faradic efficiency of 75-78%.

C) Without using water splitting in cathodic chamber

In the last described step, at the cathodic chamber were used a salty water solution in order to equilibrate charges and electrons transfer (water splitting). Other reactions can be done here such as copper reduction. After recovery of nickel and cobalt, the remaining solution contains Cu(en)?(HCOO)? Adding this solution to the cathodic chamber allows to perform both steps at the same time.

The same H-cell configuration was used. At first, a stock solution of Ni(en)₃(HCOO)? 130 mM was prepared from nickel salts (see preparation above). The solution was added to the anode chamber (no additives as electrolyte were added because the ionic strength of the solution is self-sufficient for ionic transport), while the cathode chamber contained a 200mM Cu(en)₂(HCOO)2 solution in distilled water. Both pH were about 10 and adjusted to 7.0 by bubbling CO2 (flow rate: 100 mL/min) over one hour). The anodic compartment is equipped with a copper electrode (5 x 5 cm) and a reference electrode (Ag/Ag/Cl) and the cathodic compartment with a graphite electrode (5 x 5 cm). Upon application of an electric potential of +0.3 V to the copper electrode dipped in the anode chamber solution (with a continuous flow of CO 2 (flow rate: 0.1 mL/min)), the effective electrochemical release of Cu²⁺ in the anodic compartment (Cu electrodeposition in the cathodic compartment) was detected by UV-Vis analysis. Notably, an increased/decreased absorbance at 590 run could be observed within 24 hours, standing for the formation/deposition of Cu(en)2. The resulting anode chamber solution was refluxed for 3 hours in order to remove CO2 from the solution. After cooling down to room temperature the suspension was filtered on hydrophilic membrane (0.45 um). The green solid was then washed several times with distilled water, dried and analyzed by ICP-EOS.

For model solutions, this resulted in a 70% nickel recovery from the starting solution, with a metal purity of 70%. Furthermore, ICP-EOS analysis of the remaining filtrate confirmed that 30% of nickel was left. ICP-EOS analysis and NMR analysis showed that no copper was left in the cathodic compartment and that 97% of initial en was left in solution.

S Example 4,2: Selective recovery of copper

The investigation continued by attempting to selective deposit metallic copper, leaving Co(en)₃(HCOO)3 for its reduction and subsequent stripping. Model and real leachate solutions were directly used or eventually some water was evaporated to adjust volume to the mono-cell (again, no additives as electrolyte were added because the ionic strength of the solution is self-sufficient for ionic transport). The mono-cell glass reactor is equipped with a graphite working electrode (5 x 5 cm), a reference electrode (Ag/AgCl) and a graphite or titanium counter electrode (5 x 5 cm) . Upon application of an electric potential of -0.7 V to the working electrode, the effective electrochemical deposition of metallic copper was detected by UV-Vis analysis. Notably, the decreased absorbance at 590 run could be followed until no longer observed, after 47 and 72 hours of chronoamperometry measurement for real leachate and model solution, respectively. For both experiments, the resulting metallic Cu° was collected from the working electrode, weighted, dried and analyzed by ICP-EOS, providing a metal recovery of 95-100% of copper with a corresponding purity of >95%. S Example 4,3: Selective recovery of cobalt

A) Under acidic pH

The H-cell configuration was used to investigate the extent of the recovery of cobalt. At first, a stock solution of Co(en)₃(HCOO)3 50 mM was prepared from cobalt salts (see preparation above). The solution was added to the cathode chamber (no additives as electrolyte were added because the ionic strength of the solution is self-sufficient for ionic transport), while the anode chamber contained a 0.5M HCOOH solution in distilled water (pH = 2). The initial pH of the cathode chamber solution was 9.6, which was adjusted to 3.7 by addition of 4 m HCOOH, to limit the concurrent oxidation of cobalt complexes under basic conditions. The anodic compartment was equipped with a copper electrode (5 x 5 cm), and the cathodic compartment with a graphite electrode (5 x 5 cm) and a reference electrode (Ag/AgCl). Upon application of an electric potential of -0.7 V to the graphite electrode, the effective electrochemical reduction of Co³⁺ was detected by UV-Vis analysis. Notably, the decreased absorbance peak at 511 nm could be observed until complete disappearance, achieved after 20 hours of chronoamperometry experiment. On the other side, the dissolution of copper was also detected by UV- Vis analysis (increased absorbance peak at 570 nm).

The resulting anode chamber solution was mixed with 150 mb of cathodic compartment. To the resulting solution was added sodium hydroxide (5 ,4g) and 5 mb of sodium carbonate (2M solution) for a final pH of 9.2. Then the suspension was filtered on hydrophilic membrane (0.45 um) and the solid dried and analyzed by ICP-EOS. Since cobalt was proven to still be in the filtrate, the same procedure was repeated once more, resulting in a 73% cobalt recovery in two steps (45% and 28%), with a metal purity of 97% and 88% (impurity being Cu).

A similar procedure to recover cobalt from a real leachate collected at the end of step 4.2, notably containing Ni(en)3(HCOO)3 78 mM and Co(en)3(HCOO)3 40 mM. The given solution (350 mb) was added to the cathodic chamber, while 350 mb of a IM NaHCOO solution in distilled water were placed in the anodic chamber. To promote the Co³⁺ reduction, the pH of the cathodic chamber solution was lowered from 8.9 to 5.2 by adding 17 mb of concentrated HCOOH. CO2 was bubbled in the cathodic chamber (flow rate: 30 mb/min) throughout the whole electrochemical experiment to prevent the subsequent oxidation of the Co²⁺ ions thus formed. Both chambers were equipped with graphite electrodes (10 x 5 cm), and a reference electrode (Ag/AgCl) was added to the cathodic chamber. The application of an electric potential of -0.7 V to the graphite working electrode allowed the Co³⁺ reduction, which was monitored by UV-Vis analysis.

The chronoamperometry experiment was interrupted after 24 hours - the graphite working electrode was replaced by a copper electrode (10 x 5 cm) - in order to proceed with the electrochemical Cu²⁺ ion formation and, thus, the selective stripping of Co(en)₃(HCOO)2. A +0.3 V was then applied to the copper electrode for 6h at r.t. and the formation of Cu(en)₂(HCOO)2 complex followed by UV-Vis analysis. The resulting suspension in the anodic chamber was, then, filtered on hydrophilic membrane (0.45 um), and the solid was dried at 90 °C and characterized by ICP-EOS analysis. This resulted in a 90% cobalt recovery and 59% nickel recovery from the starting solution, with a metal purity of 81% for nickel (the remaining impurity being copper). Finally, ICP-EOS analysis of the corresponding filtrate confirmed that 10% of cobalt and 38% of nickel from their initial concentration were left in the solution.

B) Cobalt complete reduction

The H-cell configuration was used to investigate the extent of the recovery of cobalt. At first, a stock solution of Co(en)3(HCOO)3 50 mM was prepared from cobalt salts (see preparation above). The solution was added to the cathode chamber (no additives as electrolyte were added because the ionic strength of the solution is self-sufficient for ionic transport), while the anode chamber contained a IM NaHCOO solution in distilled water. The initial pH of the cathode chamber solution was 8.97, which was adjusted to 7.0 by bubbling CO2 (flow rate: 0. 1 mL/min) over one hour). The cathodic compartment was equipped with a graphite electrode (5 x 5 cm) and a reference electrode (Ag/Ag/Cl) and the cathodic compartment with a graphite electrode (5 x 5 cm). Upon application of an electric potential of -0.7 V to the graphite electrode, the effective electrochemical deposition of metallic copper was detected by UV-Vis analysis. Notably, the decreased absorbance at 590 nm could be followed until no longer observed, after 20 hours of chronoamperometry measurement. The resulting graphite electrode coated with metallic copper was replaced by a new one and upon application of an electric courant of -0.3 A to the graphite electrode, the effective electrochemical deposition of metallic cobalt was detected by UV- Vis analysis. Notably, the decreased absorbance at 460 nm could be followed until no longer observed, after 22 hours of chronopotentiometry measurement. The resulting graphite electrode coated with metallic cobalt was added to a new anodic compartment composed by a 200mM triethylamine solution loaded with CO2 (pH = 6.9). The cathodic compartment was filled with IM NaHCOO solution in distilled water. The cathodic compartment was loaded with a reference electrode (Ag/AgCl) and the cathodic compartment with a graphite electrode (5 x 5 cm). Upon application of an electric potential of +0.8 V to the graphite electrode coated with cobalt, the effective electrochemical dissolution of cobalt was detected by UV-Vis analysis. Notably, the increased absorbance at 522 nm could be followed until no longer observed, namely after 23 hours of chronoamperometry measurement. The resulting anode chamber solution was refluxed for 3 hours in order to remove CO2 from the solution. After cooling down to room temperature the suspension was filtered on hydrophilic membrane (0.45 um). The purple solid was then washed several times with distilled water, dried and analyzed by ICP-EOS. This resulted in a 25% cobalt recovery from the starting solution, with a metal purity of 98%. Furthermore, ICP-EOS analysis of the remaining filtrate confirmed that less than 1% of cobalt was left in the filtrate. This leads to suggest that the remaining cobalt was not entirely recovered from the electrode. Example 5: Zinc recovery with a process according to the invention o Example 5.1: Recovery of zinc with a process accordins to the invention

The H-cell configuration was used to investigate, at first, the extent of zinc recovery as a function of the amount of copper supplied to the solution by varying the current density. A stock solution of Zn(en)₂ 5 mM was prepared by adding 136 mg (1 mmol, 1 eq) of ZnCl₂ to a 200 m volumetric flask. The flask was filled with 100 mb of distilled water, followed by the slow addition of 130 mg of ethylenediamine (133 pL, 2 mmol, 2 eq), eventually completing the volume with distilled water. The anode chamber solution contained Zn(en)₂ 5 mM and Na₂SC>4 10 mM (284 mg, 10 mmol) used as electrolyte, having an initial pH of 9.39, while the cathode chamber solution exclusively contained Na₂SC>4 10 mM in distilled water. In order to limit the copper oxidation to CuO_x (which is favored at basic pH), CO₂ was bubbled into the anodic chamber (flow rate: 0.1 mL/min) until a pH of 6.16 was reached. Upon application of a current of 5 mA to a copper electrode (1 cm x 1 cm) dipped in the anode chamber solution, the effective electrochemical release of Cu²⁺ was proved by UV-Vis measurements. Notably, an increasing absorbance at 590 nm could be observed within 16 hours, standing for the formation of Cu(en)₂

In sharp contrast, the cathode chamber solution stayed colorless, addressing the role of the anion exchange membrane in inhibiting the transfer of Cu²⁺ to the cathodic chamber. The resulting anode chamber solution was treated with 118 mg ofNa₂CO₂ (1.1 mmol, 1.1 eq), and the achieved suspension was filtered. The solid was then washed several times with distilled water, dried and analyzed by ICP- EOS. This resulted in a 87% zinc recovery from a starting 5 mM ZnCl₂ solution, with a metal purity of 99.5%. Furthermore, ICP-EOS analysis of the remaining filtrate confirmed that 11.8% of zinc was left. Given the reversible nature of the copper redox couple, the recovered filtrate containing Cu(en)₂ was placed in the cathodic chamber, in the presence of a glassy carbon electrode ( 1 cm x 1 cm) as working electrode. Upon application of a potential of -0.7 V for 24 hours promoted the partial consumption of Cu(en)₂, followed by UV-Vis analysis. These conditions promoted the electrochemical deposition of 23% of copper, as confirmed by ICP-EOS analysis of the solution. o Example 5.2: Proof of concept of selective recovery of zinc and nickel accordins to the invention In the given example, the isolated recovery of zinc and nickel has been investigated, by selectively stripping them upon addition of copper ions through electrochemical oxidation of a copper electrode. The concept was, at first, probed by adding the copper ions in form of CuCl₂.

■Z Example 5,2.1. Chemical addition of CuCl₂ for selective stripping

A stock solution of ZnCl₂ and NiCl₂-6H₂O 5 mM was prepared by adding 68 mg (0.5 mmol, 1 eq) and 119 mg (0.5 mmol, 1 eq) of the respective salts to a 100 mL volumetric flask. The flask was filled with 50 mL of distilled water, followed by the slow addition of 120 mg of ethylenediamine (133 pL, 2 mmol, 4 eq), eventually completing the volume with distilled water. The mixture was stirred at room temperature for 15 minutes, then an initial portion of 76 mg (0.45 mmol, 0.9 eq) of CuCh^ThO was added to exclusively strip zinc from the ethylenediamine. The system was treated with 64 mg (0.6 mmol, 1.2 eq) of Na2CO₃ under vigorous stirring, then filtered and the resulting solid washed with distilled water (3 x 25 mL) and dried at 90 °C for 18 hours, leading to 31 mg of a white solid. The chemical stripping continued by adding a second aliquot of 76 mg (0.45 mmol, 0.9 eq) of CUC12’2H2O to the filtrate, this time aiming at the stripping of nickel. Figure 8 (dotted lines) presents the corresponding UV-Vis measurements. The solution was stirred at room temperature for 15 minutes, followed by the addition of 20 mg (0.25 mmol, 0.5 eq) of NaOH and 53 mg (0.5 mmol, 1 eq) of Na₃CO₃ under vigorous stirring. The system was filtered and the corresponding solid washed with distilled water (3 x 25 mL), then dried at 90 °C for 18 hours, to achieve 48 mg of a dark green solid. Both the solids were analyzed by ICP-EOS, which provided for the white one a precipitation yield of 79.1% in zinc and 2.3% of nickel, and a resulting metal purity of 97.1% of zinc and 2.9 of nickel. For what concerns the dark green solid, precipitation yields of 8.2% of zinc, 32.8% of nickel and 3.3% of copper was obtained, thus affording a metal purity of 83.3% of nickel, 12.4% of zinc and 4.3% of copper.

S Example 5,2.2. Electrochemical addition of Cu ions for selective stripping

The H-cell configuration was used to investigate the extent of selective recovery of zinc and nickel as a function of the controlled amount of copper provided to the solution upon application of an electric potential. The anode chamber solution (200 mL) contained Zn(en)₂ 5 mM, Ni(en)2 5 mM and Na2SC>4 10 mM (284 mg, 10 mmol) used as electrolyte, which the cathode chamber was exclusively filled with Na2SC>4 10 mM in distilled water. The anodic chamber solution had an initial pH of 9.49, which was reduced to 6.07 by bubbling CO2 (flow rate: 0.1 mL/min), aiming at limiting the concurrent CuO_x formation, being strongly favored at basic pH. Upon application of a potential of +0.7 V, the effective electrochemical release of Cu²⁺ was estimated by UV-Vis measurements. Aiming at the selective stripping of zinc, UV-Vis analyses of the anodic chamber solution were performed during the experiment of chronoamperometry, until 0.9 eq of Cu(en)2 were estimated to be formed, thus the potential was applied for a global time of 18 hours. The resulting anodic chamber solution was treated with 118 mg of Na₂CO₃ (1.1 mmol, 1.1 eq), allowing the precipitation of a white solid, which was filtered, washed with distilled water (3 x 25 mL), dried and analyzed by ICP-EOS. This provided a precipitation yield of 42.9% and a metal purity of 98.7% for zinc, with nickel being the impurity (precipitated in 2.5% yield and purity of 1.3 %). The filtrate was again placed into the anodic chamber solution, and a chronoamperometry experiment was performed, applying a potential of +0.7 V for 22 h (estimated by UV-Vis analysis to correspond to 1.8 eq of Cu(en)₂ globally formed). Figure 8 (black lines) presents the corresponding UV-Vis measurements. Throughout the two measurements, the cathodic chamber stayed colourless, further validating the role of the anion exchange membrane to inhibit the transfer of Cu²⁺ to the cathodic chamber. The anodic chamber solution was treated with 40 mg of NaOH (0.5 mmol, 0.5 eq) and 105 mg of Na2COs (1 mmol, 1 eq), promoting the precipitation of a dark green solid, which was filtered, washed with distilled water (3 x 25 mL), dried and analyzed by ICP-EOS. This achieved a precipitation yield of 30.2% and a metal purity of 88.6% of nickel, with zinc and copper being the impurities (0.6% yield and 4.2% purity for zinc, 0.9% yield and 7.1% purity for copper).

Example 6: Zinc recovery with a process according to the invention

S Example 6,1: Recovery of zinc with a process according to the invention using water splitting in cathodic chamber with a CO 2 buffer

Similarly to the experimental procedure described above for nickel recovery, the aqueous formate solution traditionally used in the cathodic chamber as electrolyte was replaced by a 200 mM aqueous solution of K-Lysine (350 mL, see preparation above), treated by injection of pure CO 2 (flow rate: 50 mL/min) for 1 hour, to lower its pH from 12.1 to 8.2. The resulting solution was used in the cathodic chamber, while a model solution of Zn(en)₂(HCOO)2 50 mM was prepared from zinc salt precursor (see preparation above) with its pH lowered by bubbling pure CO 2 (flow rate: 50 mL/min) for 45 minutes, to lower the pH from 8.9 to 6.3. The H-cell configuration was equipped as previously described, with a copper electrode (10 x 5 cm) and a reference electrode (Ag/AgCl) in the anode chamber, and a graphite electrode (10 x 5 cm) in the cathodic chamber. The electrodissolution of Cu²⁺ ions in the anodic chamber was achieved by applying an electric potential of +0.3 V to the copper electrode, monitored by UV-Vis measurements. Analogously to the nickel recovery, CO 2 was bubbled in the anodic chamber for a few minutes, only if the pH was higher than 8.2 (to limit the CuO_x formation on the copper electrode). After 21 hours of chronoamperometry experiment, the anode solution was heated to reflux for 1 hour to promote CO2 desorption. The resulting suspension was filtered on hydrophilic membrane (0.45 urn) to afford a white solid which was, then, washed with distilled water (5 x 30 mL), dried at 90 °C and analyzed by ICP-EOS. This resulted in a zinc recovery of 94-99% from the starting model solution with a metal purity of 97-99% and an associated faradic efficiency of 60-65%. Example 6,2: Selective recovery of zinc in a zinc -nickel mixture according to the invention

Similarly to the studies performed for the selective nickel recovery, the H-cell configuration was additionally used to test the selective recovery of zinc and nickel from a zinc-nickel mixture, by controlling the amount of cuprate ions provided to the system upon application of an electric potential. Hence, a model solution containing 50 mM Ni(en)3(HCOO)2 and 50 mM Zn(en)₂(HCOO)2 (350 mL, see preparation above) was added to the anodic chamber, and its pH lowered from 9.4 to 6.2 by bubbling CO2 (flow rate: 50 mL/min) for 1 hour. The cathode chamber was filled with 350 mL of a 200 mM K- Lysine aqueous solution, treated with CO 2 injection (flow rate: 50 mL/min) for 1 hour to lower its pH from 12.1 to 8.2. The anode chamber was equipped with a copper electrode (10 x 5 cm) and a reference electrode (Ag/AgCl), while a graphite electrode (10 x 5 cm) was placed into the cathode chamber. Upon application of an electric potential of +0.3 V, the electrodissolution of Cu²⁺ ions was observed and controlled by UV-Vis measurements. Notably, after 18 hours, 1.1 equivalents of Cu(en)₂ were formed according to UV-vis analysis, which stands for a sufficient amount for the selective stripping of Zn(en)2(HCOO)2. The resulting anodic chamber solution was heated to reflux for 1 hour to afford a white solid, which was filtered, washed several times with distilled water (3 x 30 mL), dried at 90 °C and analyzed by ICP-EOS. This resulted in a zinc recovery of 98% and a metal purity of 98% (with the main impurity being copper), and an associated faradic efficiency of 55%. o Example 6,3: Selective recovery of nickel in a zinc -nickel mixture according to the invention

To pursue the collection of the nickel from the zinc-nickel mixture, the resulting filtrate of the above- mentioned 6.2 procedure was collected and placed again in the anode chamber. By means of CO 2 injection performed in both chambers of the H-cell (flow rate: 50 mL/min) for 1 hour, pH of the cathodic and the anodic chambers were lowered to 8.4 and 6.5, respectively. An electric potential of +0.3 V was then applied to the copper electrode for 24 h at room temperature, and the formation of Cu(en)₂ was followed by UV-Vis analysis. The CO₂ injection in the anodic chamber was performed for a few minutes throughout the experiment only if the pH was higher than 8.2. The anodic chamber solution was eventually heated to reflux for 1 hour to afford a green solid, which was filtered, washed several times with distilled water (3 x 30 mL), dried at 90 °C and analyzed by ICP-EOS.

This led to a nickel recovery of 88% and a metal purity of 89% (with the main impurity being copper), and the corresponding faradic efficiency is 61%. Finally, a ICP-EOS analysis of the remaining filtrate solution confirmed the presence of 10% nickel left in the solution.

Example 7: Further purification of nickel carbonate

Nickel carbonate obtained by a process according to the invention was further purified as follows.

In a 500 mL beaker was placed NiCOs (1.98 g, purity of 86.7 %) suspended in demineralized water (300 mL). The suspension was then treated with a concentrated ammonia solution (100 mL, 28-30 %w) and stirred with a magnetic stirrer at room temperature. The resulting pH was 12.16. The batch cell system was then loaded with one graphite plate as working electrode, one anodized titanium plate as counter electrode. A -0.7 V potential was eventually applied for 22 h at r.t.. After removing the electrochemical system from the beaker, the resulting blueish solution was heated to reflux for 3 h to desorb NH₃ and subsequently bring the pH of the solution to 10.20. The green suspension was filtered. The resulting light green solid was then washed with demineralized water (1x10 mL) and dried in an oven at 90 °C for 16 h, giving metallic purity in Nickel of 99.6% - the impurity being Copper.

Claims

1. Process for separating at least one first-row transition metal Ml from a liquid sample, said process comprising the steps of: a) Contacting the liquid sample with at least one primary amine and optionally CO 2, so as to obtain a first liquid phase; b) Contacting the first liquid phase with copper ions generated at the anode of a system, such as an electrochemical cell, so as to obtain a second liquid phase, c) Contacting said second liquid phase with a carbonate and optionally a hydroxide, so as to obtain a third liquid phase and Ml in a solid form, d) Separating Ml in a solid form from the third liquid phase, and e) Depositing copper from the third liquid phase by reduction at the cathode of the system, such as the electrochemical cell.

2. Process for separating at least one first-row transition metal Ml from a liquid sample according to claim 1, wherein steps b) and e) are implemented simultaneously to water electrolysis.

3. Process for separating at least one first-row transition metal Ml from a liquid sample according to claim 1 or claim 2, wherein Ml is selected from the group consisting of nickel, cobalt and zinc.

4. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 1 to 3, wherein the liquid sample comprises two first-row transition metals Ml and M2, each of Ml and M2 being independently preferably selected from the group consisting of nickel, cobalt and zinc.

5. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 1 to 4, wherein the process further comprises, between step a) and step b), a step of separating the first liquid phase from a first solid phase obtained at step a).

6. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 1 to 5, wherein Ml in a solid form recovered at step c) is a carbonate, a hydroxide or a combination thereof, of Ml .

7. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 1 to 6, wherein the primary amine is selected from the group consisting of ammonia, N-alkylethylene diamines, wherein the alkyl group is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl and tert-butyl groups, preferably isopropyl group, ethylene diamine, propane diamine, tris-(2-aminoethyl)amine, lysine, glycine, 2,3 -diaminopropionic acid, 2,3- diaminosuccinic acid, 2,4-diaminobutyric acid, and 2,5 -diaminopentanoic acid, preferably it is ethylene diamine.

8. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 1 to 7, wherein the at least one transition metal Ml comprises cobalt, and wherein step c) further comprises contacting the second liquid phase with a reducing agent, wherein said reducing agent is preferably an electron produced by electrochemistry.

9. Process for separating at least one first-row transition metal Ml from a liquid sample according to claim 8, wherein the liquid sample comprises two transition metals Ml and M2, wherein M2 is cobalt, and wherein steps c)-d) comprise the following sub-steps: a) contacting said second liquid phase with a carbonate and optionally a hydroxide, so as to obtain a liquid phase LI and Ml in a solid form,

10. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 2 to 7, wherein step b) is implemented simultaneously to water reduction, and wherein the hydroxide ions produced by water reduction are preferably used for implementing step c).

11. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 2 to 7 and 10, wherein step e) is implemented simultaneously to water oxidation, and wherein the H⁺ ions produced by water oxidation are preferably used for leaching Ml from a solid sample before step a).

12. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 1 to 11, wherein Ml in a solid form is further purified, preferably by contacting Ml in a solid form with an aqueous ammonia solution, and treating the obtained mixture by electrolysis.

13. Process for separating at least one first-row transition metal Ml from a liquid sample according to any one of claims 1 to 12, wherein the process is cyclically repeated or continuous, and at least one of the elements recovered at an iteration of the process is re-used in a further iteration of the process.

14. Process for regenerating copper and/or a primary amine from a complex comprising copper and said primary amine, said process comprising depositing copper at the cathode of an electrolyzer by electrolysis of a liquid phase comprising said complex comprising copper and said primary amine, and recovering at least one of the primary amine and the copper.

15. Process for stripping a metal ion from a complex comprising said metal and a primary amine, wherein the metal of the metal ion is a first-row transition metal Ml, said process comprising contacting a liquid phase comprising said complex comprising said metal and a primary amine with copper ions generated at the anode of an electrolyzer.

16. Process for recovering at least one first-row transition metal Ml and/or at least one primary amine from a complex comprising said metal and said primary amine, said process comprising electrolyzing a solution or a suspension comprising said complex in an electrolyzer comprising an anode suitable for producing copper ions, and recovering at least one of Ml, the primary amine, and copper.