EP4650469A1

EP4650469A1 - Process for electromediated metal stripping and recovery

Info

Publication number: EP4650469A1
Application number: EP24305764.3A
Authority: EP
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: 2024-05-16
Publication date: 2025-11-19
Also published as: WO2025238151A1

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

TECHNICAL FIELD

The present invention relates to a process for selectively extracting and recovering chemical elements from a liquid sample. Said extraction and recovery is implemented 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 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 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). At the end of the recycling process, the metals are classically precipitated as salts in basic conditions.
In order to limit waste, effluents and also the amount of atoms involved, 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. 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 precipitated by complexing with an amine, further contacting with copper chloride, generating copper ions to liberate the metal from the complex, 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, copper is complexed with 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 chloride), and for nickel or cobalt precipitation (use of carbonate and/or hydroxide salts).
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 recover copper from a 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 amine-copper complex. Advantageously, copper recovery and/or primary amine recovery in the cathodic chamber are implemented simultaneously to precipitation of a salt of a transition metal, such as nickel or cobalt, in the anodic chamber of the system, such as the anodic chamber of the electrochemical cell, by contacting a primary amine complex of the transition metal with copper ions generated at the anode of the system.
Thus, a first object of the present invention is a process for separating at least one first-row transition metal M1 from a liquid sample, said process comprising the steps of:

a) Contacting the liquid sample with at least one primary amine and optionally CO₂, 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 M1 in a solid form,
d) Separating M1 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 M1 according to the invention simultaneously allows separating M1, 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, M1 is selected from the group consisting of nickel, cobalt and zinc.
In some embodiments, the liquid sample comprises two first-row transition metals M1 and M2, each of M1 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, M1 in a solid form recovered at step c) is a carbonate, a hydroxide or a combination thereof, of M1.
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 at least one transition metal M1 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 M1 and M2, wherein M2 is cobalt, and steps c)-d) comprise the following sub-steps:

α) contacting said second liquid phase with a carbonate and/or a hydroxide, so as to obtain a liquid phase L1 and M1 in a solid form,
β) recovering said M1 in a solid form,
γ) contacting said liquid phase L1 with a reducing agent, so as to obtain the third liquid phase and M2 in a solid form, and
δ) recovering said M2 in a solid form,

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 M1 from a solid sample before step a).
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 M1, 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 M1 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 M1, the primary amine, and copper.

FIGURES

Figure 1 is a graph presenting cell energy requirements in the presence of different (a) anions (Cl^-, NO₃ ^-, and SO₄ ^2-) 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 SO₄ ^2- salt, and 30 mM ethylenediamine, with the counter ions used for (a) and (b) being Na⁺ and SO₄ ^2-, respectively.
Figure 2 is a graph presenting cell energy requirements in solutions containing 10 mM CuSO₄ and 100 mM Na₂SO₄ (grey), and 10 mM CuSO₄, 100 mM Na₂SO₄, 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 NiCl₂, 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 NiCl₂, 30 mM ethylenediamine, and 100 mM NaCl, and a cathode chamber solution comprising 10 mM CuCl₂, 20 mM ethylenediamine, and 100 mMNaCl. 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 Co(en)₃ 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 CuCl₂ addition, while the continued black lines correspond to UV-Vis experiments of the anode chamber solution while the chronoamperometry occurred.

DETAILED DESCRIPTION OF THE INVENTION

Process for separating at least one first-row transition metal M1

A first object of the invention is a process for separating at least one first-row transition metal M1 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 M1 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).

✔ Step a

Step a) aims at complexing the at least one first-row transition metal M1 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 M1 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 M1 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: La₂Ni₉CoMn, 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_wCuFeNi_kMnCoO with w being from 0.1 and 10 and k is an integer from 1 to 8 (preferably 8), or LiAl_0.1Ni_0.8Co_0.1Mn_0.1O.
In some embodiments, the process comprises preliminary steps, prior to step a), for removing at least part of other metals, such as 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.
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 M1 as defined herein. M1 in the liquid sample is typically in the form of cations.
The concentration of M1 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, M1 is selected from the group consisting of nickel, cobalt and zinc. More preferably, M1 is nickel.
"M1 in a solid form" refers to a solid, in particular a solid salt, comprising the chemical element M1. Preferably, "M1 in a solid form" is a carbonate of M1, a hydroxide of M1 or a combination thereof. A particular combination is a carbonate-hydroxide of M1.
In some embodiments, the liquid sample comprises n first-row transition metals, n being at least equal to 2, referred to as M1, 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 (M1, or M1 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 NH₂ 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 C₁-C₆, 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 π 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 π 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.
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 M1 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 M1 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 M1.
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 M1 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 M1 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 CO₃ ^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 amount of carbonate in step c) is advantageously comprised between 0.5 and 5 molar equivalents, relative to the amount of M1.
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 M1.
In a particular embodiment, the amount of carbonate is comprised between 1 and 5 molar equivalents relative to the amount of M1, and the amount of hydroxide is comprised between 0.5 and 5 molar equivalents relative to the amount of M1.
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 M1 in solid form. When M1 is nickel and M1 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 M1 is zinc and M1 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 M1 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 M1 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 M1 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 M1 and M2, M2 being cobalt. In such an embodiment, steps c)-d) of the process of the invention may comprise:

α) contacting said second liquid phase with a carbonate and optionally a hydroxide, so as to obtain a liquid phase L1 and M1 in a solid form, preferably at a pH comprised between 8 and 9,
β) recovering said M1 in a solid form,
γ) contacting said liquid phase L1 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
δ) recovering said M2 in a solid form.

Advantageously, steps α) and γ) are carried out in water. More particularly, the second liquid phase and said liquid phase L1 are typically aqueous solutions, and no additional solvent is used to carry out steps α) and γ). Contacting step α) is advantageously carried out at room temperature. Contacting step γ) 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 °C.
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 α) is advantageously comprised between 0.1 and 10 molar equivalents, relative to the amount of M2.
When present, the amount of hydroxide in step α) 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 α) 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 L1 in step γ). 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. Fe⁰), or metallic copper (i.e. Cu⁰), 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 γ) is advantageously comprised between 0.5 and 5 molar equivalents, relative to the amount of M2.
In a particular embodiment, step γ) comprises contacting said liquid phase L1 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 γ), 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 α) and β), said M1 in a solid form is preferably a hydroxide, carbonate or carbonate-hydroxide of M1. In a particular embodiment, M1 is nickel, and said M1 in a solid form is a carbonate of nickel.
In steps γ) and δ), 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.

✔ 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.
The electrical potential may be applied for instance with use of a first electrode, a second electrode, a potentiostat, and/or a power supply.
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 α) to δ), step e) may be performed in two steps, one between steps β) and γ), and the other after step δ).
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 M1 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

Specific embodiments of the process according 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, M1 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, M1 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 M1 and M2, M1 being preferably nickel and M2 being cobalt, and the implementation of the process of the invention, wherein steps c)-d) comprise steps α) to δ), 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 M1 and M2, M1 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 M1 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, M1 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 M1 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

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 M1, 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.
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 M1 and/or a primary amine

A fourth object of the invention is a process for recovering at least one first-row transition metal M1 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 M1, the primary amine, and copper.
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 mL 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 mL volume of solution. H-cell experiments were run in a ca. 10 mL (ca. 5 mL 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 mL 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 µm 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. % HNO₃. 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 mL) was spiked with 100 µL of a solution containing 0.05 M NaOH and 0.1 M Na₂CO₃, 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 mL (200 mL per electrode chamber) using a Metrohm H-cell equipped with a Fumasep 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 lie 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 (Cl^-, NO₃ ^-, and SO₄ ^2-) or cations (Li⁺, 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 H-cell configuration was 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 NiCl₂ 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 in-tandem 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, M1 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 CuCl₂, 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.
Co(en)₃Cl₃ and Co(en)₂CO₃Cl, en referring to ethylenediamine, were prepared beforehand. Co(en)₂CO₃Cl was prepared according to the procedure disclosed in Springbørg, J.; Schäffer, C. E.; Preston, J. M.; Douglas, B. Dianionobis(Ethylenediamine)Cobalt(III) Complexes. Inorganic Syntheses 2007, 63-77. Co(en)₃(CO₃)_1.5 was prepared according to the following synthetic procedure. To a solution of Co(en)₃Cl₃ (3 g, 8.38 mmol, 1 eq) in distilled water (170 mL), Ag₂SO₄ (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)_1.5 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 CO₂ was bubbled for 3 hours, and the system filtered. The resulting filtrate was concentrated in vacuo, to afford pure Co(en)₃(CO₃)_1.5 as an orange powder (3.04 g, 92% yield).

✔ Example 3.1. Chemical reduction of Co(en)₃Cl₃ by FeCl₂

In a typical experiment, 0.7632g (2mmol) of Co(en)₃Cl₃.2H₂O were added to 15mL of distilled water and the mixture was degassed with argon for 20 minutes. 0.3mL of a 1M solution of NaOH were then added to reach a pH of 10.5 . A solution containing 0.3976g (2mmol, 1eq) of FeCl₂.4H₂O 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 1M NaOH (6.2mL added at the end of the addition of the FeCl₂ solution). A brown precipitate was formed during the addition of the FeCl₂ 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 CuCl₂.2H₂O (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% HCl 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 1M 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 (<0.7µm) 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 Co(en)₃Cl₃ by N₂H₄

In a typical experiment, 0.7632g (2mmol) of Co(en)₃Cl₃.2H₂O 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% HCl 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%.

✔ Example 3.3: Chemical reduction of Co(en)₃Cl₃ by NH₂OH

In a typical experiment, 0.7632g (2mmol) of Co(en)₃Cl₃.2H₂O 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 NH₂OH 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 CuCl₂.2H₂O (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% HCl 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.

✔ 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 mL volumetric flask. The flask was filled with 50 mL of distilled water, followed by the slow addition of 240 mg of ethylenediamine (267 µL, 4 mmol, 2 eq), eventually completing the volume with distilled water. A second stock solution of Co(en)₃(CO₃)_1.5 20 mM was prepared by adding 795 mg (2 mmol, 1 eq) of Co(en)₃(CO₃)_1.5 to a 100 mL 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 Na₂CO₃ (10 mmol, 10 eq) used as electrolyte, while the cathode chamber exclusively contained a 100 mM Na₂CO₃ 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 × 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 mL of a 1 M NaOH solution (1mmol, 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. 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)_1.5 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 CuCl₂·2H₂O to a 100 mL volumetric flask. The flask was filled with 50 mL of distilled water, followed by the slow addition of 240 mg of ethylenediamine (267 µL, 4 mmol, 2 eq), eventually completing the volume with distilled water. A second stock solution of Co(en)₃(CO₃)_1.5 20 mM was prepared by adding 795 mg (2 mmol, 1 eq) of Co(en)₃(CO₃)_1.5 to a 100 mL 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 of Na₂CO₃ (10 mmol, 10 eq) used as electrolyte, while the anode chamber exclusively contained a 100 mM Na₂CO₃ 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 mL/min) over one hour. Upon application of an electric potential of -0.7 V to a glassy carbon electrode (2.5 × 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 Cu⁰ 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 × 1.3 cm) dipped in the cathode chamber solution, the reduction of Co(en)₃(CO₃)_1.5 to Co(en)₃CO₃ 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 CuCl₂·2H₂O 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 filtered, 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 filtrate 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 Cu⁰ collected on the glassy carbon electrode.

Example 4: Zinc

∘ Example 4.1: Recovery of zinc with a process according 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 mL volumetric flask. The flask was filled with 100 mL of distilled water, followed by the slow addition of 130 mg of ethylenediamine (133 µL, 2 mmol, 2 eq), eventually completing the volume with distilled water. The anode chamber solution contained Zn(en)₂ 5 mM and Na₂SO₄ 10 mM (284 mg, 10 mmol) used as electrolyte, having an initial pH of 9.39, while the cathode chamber solution exclusively contained Na₂SO₄ 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 × 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 of Na₂CO₃ (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 × 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.

∘ Example 4.2: Proof of concept of selective recovery of zinc and nickel according 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.

✔ Example 4.2.1. 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 µL, 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 CuCl₂·2H₂O 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 × 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 CuCl₂·2H₂O 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 Na₂CO₃ under vigorous stirring. The system was filtered and the corresponding solid washed with distilled water (3 × 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.

✔ Example 4.2.2. 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 Na₂SO₄ 10 mM (284 mg, 10 mmol) used as electrolyte, which the cathode chamber was exclusively filled with Na₂SO₄ 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 × 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 Na₂CO₃ (1 mmol, 1 eq), promoting the precipitation of a dark green solid, which was filtered, washed with distilled water (3 × 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).

Claims

Process for separating at least one first-row transition metal M1 from a liquid sample, said process comprising the steps of:
a) Contacting the liquid sample with at least one primary amine and optionally CO₂, 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 M1 in a solid form,

d) Separating M1 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.
Process for separating at least one first-row transition metal M1 from a liquid sample according to claim 1, wherein steps b) and e) are implemented simultaneously to water electrolysis.
Process for separating at least one first-row transition metal M1 from a liquid sample according to claim 1 or claim 2, wherein M1 is selected from the group consisting of nickel, cobalt and zinc.
Process for separating at least one first-row transition metal M1 from a liquid sample according to any one of claims 1 to 3, wherein the liquid sample comprises two first-row transition metals M1 and M2, each of M1 and M2 being independently preferably selected from the group consisting of nickel, cobalt and zinc.
Process for separating at least one first-row transition metal M1 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).
Process for separating at least one first-row transition metal M1 from a liquid sample according to any one of claims 1 to 5, wherein M1 in a solid form recovered at step c) is a carbonate, a hydroxide or a combination thereof, of M1.
Process for separating at least one first-row transition metal M1 from a liquid sample according to any one of claims 1 to 6, wherein 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.
Process for separating at least one first-row transition metal M1 from a liquid sample according to any one of claims 1 to 7, wherein the at least one transition metal M1 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.
Process for separating at least one first-row transition metal M1 from a liquid sample according to claim 8, wherein the liquid sample comprises two transition metals M1 and M2, wherein M2 is cobalt, and wherein steps c)-d) comprise the following sub-steps:
α) contacting said second liquid phase with a carbonate and optionally a hydroxide, so as to obtain a liquid phase L1 and M1 in a solid form,

β) recovering said M1 in a solid form,

γ) contacting said liquid phase L1 with a reducing agent, so as to obtain the third liquid phase and M2 in a solid form, and

δ) recovering said M2 in a solid form,

wherein said reducing agent is preferably an electron produced by electrochemistry.
Process for separating at least one first-row transition metal M1 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).
Process for separating at least one first-row transition metal M1 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 M1 from a solid sample before step a).
Process for separating at least one first-row transition metal M1 from a liquid sample according to any one of claims 1 to 11, 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.
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.
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 M1, 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.
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, 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 M1, the primary amine, and copper.