WO2012010766A1 - Wall for separating electrolytes for the selective transfer of cations through the wall, and associated manufacturing method and transfer method - Google Patents

Abstract

The invention relates to a wall for separating electrolytes, comprising an active layer (22) made of a material capable of developing intercalation and deintercalation reactions for the selective transfer of cations through the wall, and a supporting layer (21) which is made of a porous material and used as carrier for the active layer (22). A method for selectively transferring cations uses such a transfer wall (2). According to a method for manufacturing such a transfer wall (2), a solution including an active material in the form of a powder, a binder, and a solvent is prepared, and then the surface of a supporting layer (21) made of a porous material is coated with said solution and the solvent is evaporated.

Description

 Electrolytic separation wall for the selective transfer of cations through the wall, method of

 manufacturing and transfer process.

FIELD OF THE INVENTION

 The invention relates to an electrolyte separation wall for the selective transfer of cations through the wall, a method of manufacturing said wall and a method of selectively transferring cations through said wall. The invention further relates to an electrolytic type process for transporting cations, through a suitable wall, from a first electrolyte solution containing one or more classes of ions of the same charge or charge, to a second electrolytic solution.

 PRIOR ART

 A method of this type is already known using, as separating wall, a wall formed of molybdenum cluster chalcogenides, especially the Μθε β phases called Chevrel phases, described in international patent application WO 2009/007598. This process has also been the subject of the following publications:

- Electrochemical reactions of reversible intercalation in Chevrel compounds for cationic transfer - Principle and application on Co ²⁺ ion; S. Seghir, C. Boulanger, S. Diliberto, JM Lecuire, M. Potel, 0. Merdrignac-Conanec; in Electrochemistry Communications, 10, 2008, 1505-1508.

 Selective transfer of cations between two electrolytes using the intercalation properties of Chevrel phases; S. Seghir, C. Boulanger, S. Diliberto, M. Potel, JM. Cook it ; in Electrochimica Acta, 55, 2010, 1097-1106.

These documents state that cations may be transported through the wall of material of formula Μθε β (with X = S, Se, Te) called Phases de Chevrel where reversible redox systems of the type occur:

Mo ₆ Xs + xM ^{n +} + xn e ^" M _x Mo ₆ Xs

 x being a number typically ranging from 0 to 4.

These systems are diversified by the nature of the cation M ^{n +} , chalcogen X and stoichiometry x ternary.

 In an experimental setup implementing the selective transfer method, the transfer wall is placed between two compartments respectively comprising a platinum-plated electrode that operates in anode and a stainless steel electrode that operates as a cathode. The first compartment contains a first electrolyte which contains different cations of an effluent to be treated. The second compartment contains a second electrolyte for receiving the selected cations.

A continuous electric current is established between the anode and the cathode. In the overall electrochemical operation of all the two compartments, intercalation of the cation occurs at the interface M _x Mo ₆ Ss / first electrolyte (effluent to be treated, mixture of cations M ^{n +} , M ' ^{n +} , M'' ^{n +} different from each other for example), according to:

Mo ₆ Xs + xM ^{n +} + xn e- → M _x Mo ₆ Xs

The deintercalation of this same cation M ^{n +} at the interface M _x Mo ₆ Ss / second electrolyte (recovery solution of M ^{n +} for example) is carried out reciprocally according to

M _x Mo ₆ Xs → Mo ₆ X ₈ + xn e ^" + xM ^{n +}

The mobility of the metal cation in the Chevrel phase thus makes it possible to transfer the desolvated M ^{n +} cation from one medium to another without transferring any other chemical species from one or the other of the compartments.

A transfer wall in the form of a pellet is obtained by hot sintering a mixture of powder of composition adapted to the stoichiometry of the desired material. This produces discs of active material with a thickness of 2 to 5 millimeters.

The tests with walls composed of selenated and sulphurized phases have shown that in particular the cations of the following metals can be transferred from one electrolyte to another: iron, manganese, cobalt, nickel chromium, copper, zinc, cadmium. The limits of current densities obtained are between 10 and 20 A / m ² , with faradic yields greater than 90 ~ 6, or even greater than 98%, and very good selectivity.

 The tests also demonstrated that the transfer rate limit increased with decreasing wall thickness. However, the necessary mechanical strength of the wall limits the decrease in its thickness.

 Moreover, the lithium transfer could not be obtained with such walls. However, lithium is increasingly used industrially, especially for electric vehicle batteries.

 OBJECTIVES OF THE INVENTION

 The object of the invention is therefore to provide a selective transfer wall allowing a good transfer speed and with a wider choice of transferable cations.

 STATEMENT OF THE INVENTION

With these objectives in view, the invention relates to an electrolyte separation wall comprising a sealed active layer of a material capable of developing intercalation and deintercalation reactions for the selective transfer of cations through the wall, characterized in that it comprises a support layer made of a porous material serving as a support for the active layer. The inventors have succeeded in producing a wall with a porous support that provides mechanical strength and an active layer whose thickness can be very small. They found that the porous support did not interfere with the electrochemical reactions that occur at the level of the active layer. By decreasing the thickness of the active layer, the transfer speed reached is much greater than the speed limit according to the prior art, which is one of the objectives of the invention.

 The porous material is chosen for example from mullite, silica, fiberglass, quartz or a ceramic. These materials have the necessary qualities to fulfill the role of the wall, namely the mechanical strength, the resistance to the products contained in the electrolytes and the porosity.

 The porosity of the porous material is, for example, between 0.4 and 0.6. This value expresses the material ratio in relation to the volume occupied. It constitutes a good compromise between the volume of the electrolyte present in the porous support and the mechanical strength of said support.

 In particular, the material of the active layer is a binary or ternary material having a host array and having reversible cation-receiving properties according to a redox reaction. The inventors have found that the Chevrel phases are not the only materials that can develop intercalation / deintercalation reactions to form a selective transfer wall, but more generally host networks that are stable and where reaction reactions occur. redox.

 The material of the active layer is for example a metal chalcogenide.

In particular, the metal chalcogenide is a molybdenum cluster chalcogenide (Mo _n X _n + 2 or M _x Mo _n X _n + 2), X being a chalcogen selected from S (Sulfur), Se (Selenium) or Te (Tellurium), and M being a metal. The number n is chosen for example from 1; 1.5; 2; 3; 4; 5; 6 or 9.

 According to another composition, the material of the active layer is a lithium compound and a metal in the form of oxide, phosphate or fluoride or a combination of these forms, the metal being chosen from nickel, cobalt, iron, manganese, vanadium, titanium or chromium. It can be seen that these materials are capable of developing intercalation and deintercalation reactions, and of selectively transferring cations, in particular lithium.

 According to a method of manufacturing the transfer wall, a solution comprising an active material in the form of a powder, a binder and a solvent is prepared, then the surface is coated with a support layer of porous material with the said solution and evaporating the solvent to form a sealed active layer on the support layer.

 It is found that the active layer obtained is tight, which ensures that the electrolytes do not mix when the wall separates them. In addition, despite the initial powder formulation, the active layer is electrically conductive, showing that the grains are in contact with each other and allowing the oxidation-reduction reactions to develop over the entire surface of the layer. active. The layer obtained is very thin, in accordance with the objective initially set.

 The binder is, for example, polyvinylidene fluoride.

 The solvent is, for example, 1-methyl-2-pyrrolidone.

The result is already satisfactory when the powder material is present in a proportion of 80% mass off the solvent.

 The powder material has for example a particle size of between 30 and 100 μm.

 According to an improvement, the solution further comprises graphite powder. This makes it possible to complete the electrical conductivity of the active layer.

 According to an improvement, the active layer is polished until the support layer appears through the active layer. This reduces the thickness of the active layer. Despite this decrease, the watertightness is preserved and the performance of the wall is not affected. There is an increase in the limit value of the electrical current density.

 The subject of the invention is also a process for the selective extraction of cations by electrochemical transfer, characterized in that a transfer wall as described above is used as electrolyte separation wall, and cation transfer is ensured through said electrolyte transfer wall. transfer wall by generating a potential difference between firstly the first electrolyte, and secondly the second electrolyte or said transfer wall, so as to cause intercalation of the cations in the transfer wall on the first side electrolyte, a diffusion of the cations in it, and their deintercalation in the second electrolyte.

 According to other characteristics:

 at least one of the electrolytes is non-aqueous. The electrolytes may be different between the compartments, in particular by differentiation of the nature of the base salts, by the level of acidity, by the presence of complexing agents, by the nature of the solvents, in particular organic or inorganic non-aqueous solvents such as, for example, DMSO , DMF, ionic liquids, solid electrolytes, etc.

the transfer wall is electrically connected to a apparatus for measuring the potential between said wall and reference electrodes located respectively in each electrolyte and adjusting accordingly the potential applied between said electrolytes.

the difference in potential is generated between the first electrolyte and the transfer wall, and the deintercalation of the cations on the side of the second electrolyte is a chemical deintercalation by a chemical oxidant in the second electrolyte.

a succession of transfers of cations is ensured through transfer walls arranged successively between end electrolytes, and with one or more electrolytes intermediate between the different transfer walls.

the transferred metal is electrodeposited on the cathode. at least two transfer walls of different nature separate the first compartment of respective compartments in parallel for selective transfers of different cations with specific intercalation modulated electrolyses on each of the transfer walls engaged. Transfers to separate compartments allow the specific simultaneous recovery of each of the metals, for example for a source solution containing Cobalt and Lithium ions using an active layer in MoeSs for the transfer of cobalt and a second in LiMr ^ C ^ selective transfer of lithium.

BRIEF DESCRIPTION OF THE FIGURES

 The invention will be better understood and other features and advantages will appear on reading the description which follows, the description referring to the appended drawings among which:

Figure 1 is a sectional view of a transfer wall according to the invention; FIG. 2 is an X-ray diffraction analysis graph of the porous material for the manufacture of a wall according to FIG. 1;

 Figures 3 and 4 are schematic views of a test fixture for checking the porosity or tightness of the wall of Figure 1;

 Figure 5 is a block diagram of the device, Figure 6 illustrates an arrangement using a plurality of compartments and serial transfer walls;

 Figure 7 illustrates an arrangement using multiple compartments and parallel transfer walls.

 DETAILED DESCRIPTION

A transfer wall in the form of a tablet 2 according to the invention is formed of a porous support 21 on which a thin active layer 22 is deposited. The manufacture of sealed pellets is carried out in a first phase of manufacture of the porous support 21, and a second phase of application of the active layer 22 on the support 21.

 Elaboration of the porous support

The porous support 21 may be commercially available in mullite, quartz or ceramic. By way of example, an embodiment is detailed below, which is derived from the protocol given by the article by Garcia-Gabaldon et al. on the production of ceramic membranes based on kaolin and alumina developing a flexible porosity for their application as separation membranes in electrochemistry: Effect of porosit on the effective electrical conductivity of different ceramic membranes used as separators in electrochemical reactors, Journal of Membranes Sciences 280 (2006) 536-544. The protocol is as follows: initially a mixture provided for 5 g of material consists of:

2.52 g of Kaolin (hydrated aluminum silicate Al ₂ Si ₂ O ₅ (OH) 4,

3.80 g Alumina A1 ₂ 0 ₃

 1 g of commercial potato starch.

 The mixture of the powders is homogenized in a porcelain mortar and then wetted with a minimum volume of acetone to avoid the formation of aggregates. This mixture is dried in the open air for 14 hours. The powder obtained is then regrinded manually with the mortar for 10 minutes and then by fraction of about 1 g, it is shaped into a pellet by pressing into a matrix of 25 mm diameter at a pressure of 2 tons for 5 min. The compacted pellets form a disc 1 mm thick. The samples are subjected to two successive heat treatments.

A first heating at 300 ° C allows the air oxidation of potato starch. This organic binder is removed in 1 hour and thus creates porosity. An additional treatment at 1100 ° C for 8 to 24 hours ensures satisfactory mechanical strength. After this heat treatment, discs 24 mm in diameter and 1 mm in thickness are obtained. The surface is 4.5 cm ² .

 X-ray diffraction analysis was performed on the porous pellet (Figure 2). The recorded spectrum shows the absence of impurities as well as the formation of an alumina phase and a mullite phase.

The evaluation of the porosity of the pellet was tested using pH paper and nitric acid HNO ₃ in the following manner shown in the diagram of FIG. 3: the turning of the pH paper made it possible to confirm a good porosity of the pellet. The porosity checks give average values of 0.553 by volume for initial contents of 10% of starch and 0.501 for contents of 5%.

 Elaboration of the active layer

 The second phase of the manufacture of the pellet consists in the physical coating of a face of the porous support 21. In the example which is shown, the coating is carried out with a Chevrel phase suspension, of formula ΜθδΧβ, with X being a chalcogen, in a volatile solvent. The working electrode is prepared from MoeSs or MoeSes pulverulent compounds which constitutes the active mass. An addition of polyvinylidene fluoride, also called PVDF, acts as a binder.

 The MoeSes phase results from a ceramic synthesis starting from the mixture Mo ° + 2 Mo S e2 homogenized and cold-pressed in a cylinder at a pressure of 250 MPa, carried out in a furnace crucible sealed with an arc furnace, under partial pressure of argon, then heated for 50h at 1300 ° C. The same sieving milling treatment at 50 μιη is also applied to this compound.

 The purity of the synthesized powders is verified by their X-ray diffraction pattern obtained on a diffractometer.

 The synthesis of the Chevrel phase based on sulfur is carried out via a ternary phase with an intermediate metal such as for example CU3M06 S 8. The synthesis of this ternary compound is carried out in a sealed silica ampoule at 1000 ° C. for 50 hours. The initial mixture consists of micrometric powders of Cu, M0 S 2 and Mo homogenized in a ball mill for 30 minutes and compressed under cold pressure of 250 MPa.

The molybdenum powder is deoxidized under a stream of hydrogen at 1000 ° C. for 3 hours and the powder of MoS 2 is prepared in a sealed silica ampoule by progressive heating of the stoichiometric mixture of the elements. up to 800 ° C.

 The particle size of the powdered products involved is in a range of 30 to 100 micrometers.

The MoeSes phase results from a ceramic synthesis starting from the homogenized Mo + 2MoSe ₂ mixture and cold-pressed in a cylinder at a pressure of 250 MPa, carried out in a furnace sealed molybdenum crucible, under argon partial pressure, then heated for 50h at 1300 ° C. The purity of the reaction products obtained is verified by their X-ray diffraction pattern obtained on a diffractometer.

Application of the active layer on porous support by coating Case of the Chevrel phase matrix

 A suspension consisting of 95% phases of

Chevrel powder and 5% PVDF is formed in 1-methyl-2-pyrrolidone, hereinafter referred to as NMP, at the rate of 0.1 g of the solid Mo ₆ Xs phase, 0.005 g of PVDF dispersed in 1 mL of NMP. The whole is stirred for 2 hours.

 Using a pasteur pipette, a few drops of the ΜθεΧβ NMP-PVDF suspension are placed on the surface of the porous support disk to cover the entire surface evenly. Then the whole is put in the oven for 1h to remove the NMP solvent. Under these conditions, the resulting MoeSs or MoeSes film adheres to the surface of the disk with thicknesses of the order of 80 μm. In addition, the leakage tests according to FIG. 4 confirm the good occlusion of the pores of the porous disk, since the pH paper does not turn. Electrical conductance tests demonstrate good electrical contact between the grains.

Spinning coating techniques have also been practiced. They lead to coatings same configuration as before.

 For the synthesis of the MoeSs binary phase, chemical deintercalation of the copper electrochemically after the completion of the coating is carried out.

Case of the oxide matrix of Li _x M _y O _{z type}

According to another example, the wall is made with the active material a matrix corresponding to the general formula Li _x M _y O _z , in which y and z are integers, for example non-limiting Li _x CoO 2, LiMr ^ C ^ Li ^ Os, Li i02 or LiMn02- the active material may also comprise a mixture of metals M. the principle of development remains a coating of the porous support with a suspension of Li _x M _y O _z.

The coating solution is prepared from a Li _x M _y O _z powder mixture which constitutes the active material at 80% by weight, of 10% PVDF which acts as a binder and a 10% carbon which ensures electrical conductivity. The mixture is homogenized intimately in a mortar.

 A suspension is carried out in 1-methyl-2-pyrrolidone with stirring for 2 hours at a rate of 0.2 grams of powder mixture per 1 ml of NMP.

Using a pasteur pipette, a few drops of the Li _x M _y O _z NMP-PVDF suspension _{are placed} on the surface of the porous support disk to cover the entire surface evenly. This operation can also be done in a centrifugal distribution technique. Then the whole is put in the oven for 1h to remove the NMP solvent. Under these conditions, the resulting oxide film adheres to the surface of the disc with thicknesses of the order of 80 μm. In addition, the sealing tests confirm the good occlusion of the pores of the porous disk. Electrical conductance tests demonstrate good electrical behavior of the film. Whatever the type of matrix, to follow the interface potentials, it is necessary to set up an electrical contact around the pellet with the help of graphite lacquer 23. We paint the outline of the pellet and overflow on the face of the active layer 22.

 Selective transfer process

 The diagram of FIG. 5 shows a device for implementing a selective transfer method using transfer walls according to the invention. The device comprises a tank 1 having two compartments 11 and 12, adapted to receive an electrolyte and separated by a partition wall 13 in which is placed a transfer wall 2 consisting of a disc-shaped pellet 2, mounted in the partition 13 tightly.

 The device also comprises an anode A1 placed in the first compartment 11 and a cathode C2 placed in the second compartment 12. A potential difference ΔΕ can be applied between the anode A1 and the cathode C2 by means known per se, in order to impose and control a current i between electrolytes E1 and E2.

 The active layer 22 is placed on the side of the first compartment 11, even if the system also functions when it is on the side of the second compartment 12. A spring loaded contact system 44 provides an electrical connection with the contour of the covered chip 2 graphite lacquer, and makes it possible to connect it to a control apparatus, adapted in particular for measuring the interface potential Eil, Ei2 of the wafer with respect to reference electrodes 33, 34 respectively arranged in each compartment 11, 12 of the tank 1, as illustrated in FIG.

The implementation of the device is carried out typically as follows:

The compartments 11 and 12 are filled with the desired electrolyte, for example, and in no way limiting, 100 ml Na ₂ SO ₄ 0.5 M + M ₍ i) SO ₄ as the first electrolyte El in the first compartment 11, and 100 ml Na ₂ SO ₄ 0.5 M as the second electrolyte E 2 in the second compartment 12, with Μ ₍ υ being one or more metal cations which it is desired to separate, the anode A1 being placed in the first compartment 11 and the cathode C2 in the second compartment 12, and the contact 44 of the pellet is connected to potentiometric control means, connected to the reference electrodes 33, 34 immersed in the electrolytes E1 and E2. adjust accordingly the global potential ΔΕ applied between the anode A1 and the cathode C2, so as to obtain a current density relative to the operational surface of the transfer wall 2, or of all the transfer walls arranged s in parallel, for example between 2 and 200 A / m ² .

An overall intensiostatic regime is established between the anode A1 and the cathode C2. Let RH, for host network, be the material of the active layer 22. In the overall electrochemical operation of all the two compartments, the electrolyte E1 being an original solution to be treated comprising a mixture of the cations of different metals and of identical or different charges, M ^{n +} , M ' ^{n +} , M''^{n' +} for example, and one electrolyte E2 being a recovery solution of the metal M, it occurs:

The intercalation of the cation M ^{n +} at the interface of the active layer 22 with the electrolyte El, according to:

RH + xM ^{n +} + xn e ^" → M _X RH

the deintercalation of this same cation at the interface of the active layer 22 with the electrolyte E2 (recovery solution of M ^{n +} for example), which takes place reciprocally

M _X RH = ^ RH + xn e ^" + x M ^{n +}

The mobility of the metal cation in the host network thus allows the transfer of the desolvated M ^{n +} cation from one medium to another without transfer of any other chemical species from one or the other of the compartments.

 It will also generally be noted that the electrolytes placed in the two compartments 11, 12 comprising the anode A1 and the cathode C2 may be different, in particular by the nature of the base salts, by the level of acidity, by the presence of complexing agents, by the nature of the solvents, in particular organic or inorganic non-aqueous solvents (DMSO, DMF, ionic liquids, solid electrolytes, etc.). It is thus possible, for example, to carry out ionic transfer of a sulphate medium to a chloride medium without diffusion of said medium.

In the variant of Figure 6, the vessel has three compartments. The two end compartments 11 ', 12' are equivalent to the compartments 11 and 12 of the example shown in FIG. 1. An additional compartment 15 containing an electrolyte E3 is situated between the two compartments 11 'and 12' and separated therefrom. by partition walls 13 ', 13 "each having one or two transfer walls 2', 2" according to the invention. These transfer walls 2 ', 2 "can be of the same kind, simply to increase the selectivity of the transfer from the compartment 11' to the compartment 12 '.They can also be of a different nature, and can be managed differently by a specific control of the For example, two types of cations can be transferred from the compartment 11 'to the compartment 15, and only one from the compartment 15 to the compartment 12. Various combinations of pellets may be applied between the various compartments, for example to effect a separation of different cations. and transfer parameters can thus be used to perform desired separations and various treatments.

 In the case of the variant of FIG. 6, the intermediate electrolyte (s) E3 may also be identical or different from one or both electrolytes E1 or E2.

In another variant, illustrated in Figure 7, the vessel has three compartments. The central compartment 11 "is equivalent to the first compartment 11 of the example shown in FIG. 2. The left compartment 12" is equivalent to the second compartment 12 of the example shown in FIG. 2. An additional compartment 16 containing an electrolyte E3 is located to the right of the first compartment and separated from it by a partition wall 13 "'having one or more transfer walls 2"' according to the invention. These transfer walls 2 "'are different in nature depending on the partition wall 13, 13"', to selectively transfer a specific cation for each compartment. For example, the first electrolyte El is a source solution containing cobalt and lithium ions. The first transfer wall 2, between the first and the second compartment 11 ", 12", has an active material M0 ₆ S ₈ for the selective transfer of cobalt, while the second transfer wall 2 "', between the first and the third compartment 11 ', 16, has an active material LiMn ₂ 0 ₄ for the simultaneous selective transfer of lithium. The first compartment 11 "has an anode A1" so as to create a transfer current between said anode Al "and a cathode C2" in the second compartment, and another transfer current between said anode Al "and a cathode C3 in the second compartment. third compartment 16. Example 1

A porous pellet 21 coated with an active layer 22 based on sulphurous Chevrel phase is used as transfer wall 2, as described above, in an arrangement according to FIG. 5. The transfer of cations between the first compartment 11 containing the first electrolyte El (0.1 M M ²⁺ cation solution in Na ₂ S0 ₄ 0 1 M medium, H ₂ SO ₄ 0.1 M) and the second compartment 12 containing the second recovery electrolyte E 2 at 0, 1 M of Na ₂ SC> 4, and 0.1 M of H ₂ SO ₄ was studied for the two types of pellets based respectively on MoeSs and MoeSes, and at different current densities. The study aimed to verify for different cations M ^{n +} the faradic yields of the transfers, to determine the boundary conditions for porous MoeSs and MoeSes pellets and to evaluate the current density limit. The transfer process is based on pre-conditioning with a quantity of intercalated cation estimated from the mass Μθε β deposited for a stoichiometry of Μ _χ / ₂ Μθ6 8 · Tables 1 and 2 show the results obtained for an active material respectively MoeSs and MoeSes.

Table 2. It is found that faradic yields are interesting by being greater than 90% and that the current densities are much higher than those of the prior art (of the order of 16 A / m ² ).

For the sulphide phase, the quantitative transfer occurs at speeds between 2.10 ^-2 mol / h / m ² at low current density (3.2 A / m ² ) and 3 mol / h / m ² at high density. current (70 A / m ² ). This last value appears as a limit speed for connection thicknesses in MoeSs estimated at 80 μm. Concerning the MoeSes active material pellet, the transfer rates in these seleniated phases are in the same order of magnitude as for the sulphide phase: ie 5.10 ^-2 mol / h / m ² for 3.2 A / m ² and 4 mol / h / m ² for 70 A / m ² only for Cd ²⁺ , Zn ²⁺ , Mn ²⁺ , Cu ²⁺ and In ³⁺ cations. The following tables 3 and 4 specify for each element the transfer rates for a current density of 70 A / m ² .

 Table 3.

 Table 4.

selectivity

In the selective cation transfer process, the first electrolyte E1 contains a mixture of cations of which only one type is transferred through the wall. Selectivity results from the fact that during the electrolysis operation, the voltage applied between the two faces active layer 22 only allows intercalation and deintercalation of one type of cation. To transfer the other cations, a higher potential should be applied, which is not the purpose of the process. The type of cation that is transferred has a minimum intercalation potential and a maximum deintercalation potential that is expressed relative to the reference potential given by a saturated calomel electrode (SCE).

 Transfer experiments have been performed for synthetic mixtures of cations such as: Co / Ni, Cd / Zn, Cd / Ni, Zn / Mn, Cd / Co, Co / Fe, Ni / Fe and Cd / Co / Ni.

In the following examples, made from mixtures of two equimolar cations (0.1 M), the selectivity of the transfer is expressed by a transfer selectivity rate of the cation M ^{n +} represented by the ratio M _t ^{n +} / Σ Mi _t ^{n +} the quantity of transferred cations M _t ^{n +} for the species in question to the sum of the transferred cations of any species Mi _t ^{n +} in compartment 2, for example Co _t / (Co _t + Ni _t ) for the mixture Co ²⁺ + Ni ²⁺ .

 This ratio is therefore even closer to 100% that the selectivity is large and takes a value of 50% if no selectivity develops.

 Tables 5 and 6 summarize the selectivity levels obtained for the different mixtures with different current densities. The values indicated for the different current densities correspond to the average of the selectivity rates obtained every hour during the electrolysis of 1 to 7 hours.

Mixtures active material of the transfer wall: MO _O S _S

Cation Other Potential Potential Density of Density of transferred cations intercalation deintercalation maximum current current maximum 3.2 A / m ² 70 A / m ²

(mV / ECS) (mV / ECS) (%) (%)

Cd Zn -592 -327 93 93

Co Ni -624 -250 99 99 Cd Ni -582 -278 70 78

Zn Mn -814 -196 57 to 60

Cd Co -585 -373 47 89

Co Fe -751 -175 60 59

Neither Fe-756 -118 49 53

Cd Co / Ni -660 -250 63 77

In Cd / Zn / / / /

 Table 5.

 Table 6.

It can be seen that the selectivity rate depends on the current density. The selectivity is high for high current densities thus inducing high transfer rates. The nature of the active layer 22 of the wall plays an important role in selective cation transfer. The selectivity of the transfer of Cd ²⁺ or Zn ²⁺ in the presence of Ni ²⁺ is really improved up to 99% using a selenated matrix. The same observation can be made in the case of Cd ²⁺ in the Cd / Co mixture. The selectivity is not affected by the small thickness of the active layer 22.

 Example 2

In this example, the active layer 22 is made of LiCoO ₂ material with a thickness of about 80 μm. Such a material is exploited for example in the positive electrode of lithium ion batteries. The first electrolyte is an aqueous Li ⁺ solution at 1 M in Na ₂ SC> 4 1M medium. The second electrolyte which serves as a recovery solution is an aqueous solution of Na ₂ SC> 4 to 1M. The results are shown in Table 7.

 Table 7. Example 3

 This example is similar to Example 2, except that the second electrolyte which serves as a recovery solution is a solution of a propylene carbonate solvent and tetrabutyl ammonium perchlorate. The anode is in platinum titanium and the cathode in stainless steel. The results are shown in Table 8.

 Table 8. Example 4

From a film produced by depositing MoeSs-PVDF on a porous pellet according to the protocol presented above, the excess material is removed from the film by manual polishing, by abrasion to the SiC disk of particle size 2400 for a few seconds. until appearance of the color of the porous support. Thus, only part of the transfer materials are left in the pores. This operation practiced and tested in the same way as the previous experiments is indicated by much more advantageous transfer performance, with an applicable current density of about 80 A / m ² , greater than previously, without disturbing faradic yields.

Example 5 Transfer of Li ⁺ from a Li ₂ S0 ₄ and CoS0 ₄ Mixed Electrolyte

In this example, the active layer is made of LiMn ₂ 0 _{4 material} with a thickness of about 80 μm. The first electrolyte is an aqueous solution containing Li ⁺ (1M) and Co ²⁺ (0.5M) cations in sulfate medium. The second electrolyte that serves as a recovery solution is a solution of a ₂ S0 ₄ at a concentration of 1M. The results are shown in Table 9.

 Table 9.

Claims

Electrolytic separation wall comprising an active layer (22) sealed with a material capable of developing intercalation and deintercalation reactions for the selective transfer of cations through the wall, characterized in that it comprises a support layer (21) made of a porous material serving as a support for the active layer (22).  2. Wall according to claim 1, wherein the porous material (21) is selected from mullite, silica, fiberglass, quartz or a ceramic.  3. Wall according to claim 1, wherein the porosity of the porous material (21) is between 0.4 and 0.6.  4. Wall according to claim 1, wherein the material of the active layer (22) is a binary or ternary material having a host network and having reversible cation-receiving properties according to a redox reaction.  The wall of claim 4 wherein the material of the active layer (22) is a metal chalcogenide. The wall of claim 5, wherein the metal chalcogenide is a molybdenum cluster chalcogenide (Mo _n X _n + 2 or M _x Mo _n X _n + 2).  The wall of claim 4, wherein the material of the active layer (22) is a lithium compound and a metal in the form of oxide, phosphate or fluoride or a combination of these forms. metal being selected from nickel, cobalt, iron, manganese, vanadium, titanium or chromium. 8. A method of manufacturing a wall according to one of claims 1 to 7, wherein is prepared a solution comprising an active material in the form of powder, a binder and a solvent, then the surface is coated with a support layer (21) of porous material with said solution and the solvent is evaporated to form a sealed active layer (22) on the support layer (21). ).  9. The process of claim 8 wherein the binder is polyvinylidene fluoride.  The process of claim 8 wherein the solvent is 1-methyl-2-pyrrolidone.  11. The method of claim 8, wherein the powder material is present in a proportion of 80% by weight off the solvent.  12. The method of claim 8, wherein the powder material has a particle size of between 30 and 100 microns.  13. The method of claim 8, wherein the solution further comprises graphite powder.  The method of claim 8 wherein the active layer (22) is polished to expose the support layer (21) through the active layer (22).  15. A process for the selective extraction of cations by electrochemical transfer, characterized in that a transfer wall (2) according to one of claims 1 to 7 is used as the electrolyte separation wall, and cation transfer is ensured. through said transfer wall (2) by generating a potential difference (ΔΕ) between first electrolyte (El) and second electrolyte (E2) or transfer wall (2). , so as to cause intercalation of the cations in the transfer wall (2) on the side of the first electrolyte, a diffusion of the cations in the latter, and their deintercalation in the second electrolyte (E2). 16. The method of claim 15, wherein at least one of the electrolytes (E1, E2) is non-aqueous. 17. The method of claim 15, wherein the transfer wall (2) is electrically connected to a device for measuring the potential between said wall and reference electrodes (33, 34) located respectively in each electrolyte (E1, E2). ) and the potential applied between said electrolytes (E1, E2) is adjusted accordingly.  18. The method of claim 15, wherein the potential difference (ΔΕ) is generated between the first electrolyte (El) and the transfer wall (2), and the deintercalation of the cations on the side of the second electrolyte (E2) is a chemical deintercalation by a chemical oxidant in the second electrolyte.  19. A method according to claim 1, wherein a succession of transfers of cations through transfer walls (2) arranged successively between end electrolytes (E1, E2) and with one or more intermediate electrolytes (E3) is provided. ) between the different transfer walls.