COMPOSITE MATERIAL USEFUL FOR PALLADIUM EXTRACTION, ITS PREPARATION PROCESS AND ITS USES

Abstract

The present invention relates to a composite material comprising a porous solid support and at least one malonamide non-covalently bonded to the surface of this porous solid support. The present invention also relates to a method for preparing such a material and its use for extracting palladium from an acidic leaching solution containing it.

Description

Title of the invention: COMPOSITE MATERIAL USEFUL FOR THE EXTRACTION OF PALLADIUM, ITS PREPARATION PROCESS AND ITS USES Technical field

[0001] The present invention belongs to the technical field of recycling precious metals such as palladium and more particularly to the technical field of recycling palladium involving solid / liquid extraction.

[0002] Indeed, the present invention relates to a composite material comprising a solid, porous, mineral or organic support, impregnated with extracting molecules from the malonamide family.

[0003] The present invention also relates to a process for preparing such a material as well as its uses, in particular for separating palladium from other metallic elements contained in an acid leaching solution, resulting in particular from the recycling of waste electrical and electronic equipment. STATE OF THE PRIOR ART

[0004] Palladium (Pd) belongs to the platinum group metals and has interesting catalytic properties and good corrosion resistance. It is mainly used in the manufacture of catalytic converters for automobiles. Other applications include electronics, the chemical industry, dental repair and jewelry. The growth in demand for palladium is mainly driven by the growth of the automotive market.

[0005] The supply of this metal remains strategic due to the geographical location of the deposits and, consequently, production, limited to a few countries. For this reason, recycling is an alternative of choice.

[0006] This recycling may correspond to the reprocessing of nuclear waste, palladium being one of the transition metals with the highest quantity in fission products. It may also concern catalytic converters, a homogeneous source of palladium, treated in a hydrochloric medium. The exploitation of new recycling channels should therefore be an area of ​​future economic interest. The recovery of waste electrical and electronic equipment (or WEEE), also known as "urban mining", is a rapidly growing topic. WEEE, and in particular multilayer ceramic capacitors from electronic cards that are particularly rich in palladium, represent a significant potential source of this metal.

[0007] Whatever the operating method for treating waste containing palladium, This metal is ultimately recovered hydrometallurgically from solutions containing palladium in the form of a metal cation. These solutions are generally very acidic, based on nitric acid. Two approaches are mainly used:

[0008] 1) liquid-liquid extraction which allows the palladium salt to be selectively extracted in organic phase, a technique which applies well to relatively concentrated solutions (> 100 mg / L approximately), and

[0009] 2) solid-liquid extraction which aims to fix the palladium salt on a material solid in contact with the solution, a technique which applies well to low concentration solutions (< 100 mg / L approximately).

[0010] Electrodeposition could constitute an interesting alternative by taking advantage of the relatively high reference potential of the Pd2+ / Pd couple Eo = +0.951 V (ESH, standard hydrogen electrode). However, palladium forms alloys with silver (Ag) whose reference potential is close: Ag+ / Ag Eo = +0.800 V (ESH). It is therefore expected that in the presence of silver, this process is not selective. Finally, the selectivity of this process with respect to iron and neodymium has not been demonstrated.

[0011] In the case of liquid-liquid extraction, the process requires the use of organic solvents, as well as a back-extraction step which makes it possible to i) recover the palladium by precipitation from a concentrated aqueous solution, and ii) regenerate the organic solvent. This method using malonamide-type molecules free of sulfur atoms as extractants has been the subject of two international applications WO 2016 / 008932 A1 [1] and WO 2019 / 048790 A1 [2],

[0012] In the case of solid-liquid extraction, the process requires a step of desorption of the palladium salt from the solid support (elution), but this step can prove tricky because the affinity of the solid for palladium must be very high to recover with a satisfactory yield the palladium present in low concentration in the aqueous solution. Generally speaking, the chemical functions allowing the separation of palladium(II) from other cations in acid solution are either sulfides or phosphorus derivatives. Thus, very effective grafted resins have been developed based on the use of phosphorus or sulfur functions.

[0013] An alternative to chemical grafting is impregnation with extractant molecules, which is simpler, less expensive, and more flexible in terms of the molecules chosen. Comparative studies show that, in certain cases, impregnation is superior to grafting in terms of total capacity, selectivity, or kinetics. The extractant molecule is immobilized on a commercial hydrophobic resin, designed for the capture of organic pollutants in aqueous media, most often polystyrene crosslinked with divinyl-benzene (e.g., the macroporous resin Am-bertlite® XAD-2). By deliberately saturating the resin with the extractant molecule, obtains a new material exhibiting the properties of the extractant molecule while retaining the solid and porous character of the resin. These solids are known in the English-language scientific literature as “solvent impregnated resin” (SIR). Impregnation is generally carried out by evaporating a suspension containing the resin, a volatile solvent and the non-volatile extractant molecule. This technique can be generalized to other porous supports, such as inverse silica gel, i.e. silica grafted with aliphatic carbon chains, generally with 8 or 18 carbon atoms.

[0014] The disadvantages of this technique derive mainly from the labile nature of the impregnated molecules, immobilized by physisorption: a more or less significant fraction is irremediably lost with each use, the quantity of extradant lost depending on its solubility in the medium to be treated. Strategies have been developed to counter this effect, in particular by wrapping the beads in a layer of porous polymer such as polyvinyl alcohol crosslinked with divinyl sulfone, improving stability at the cost of significantly slower kinetics and an additional cost due to this additional wrapping step.

[0015] If the affinity of the solid for palladium must be very high, it must however be reversible to allow its back-extraction by elution. Difficult elution will lead to a solution that is too dilute in palladium (< 1 g / L approximately) which will not allow the efficient isolation of a palladium salt by precipitation. This is typically the case for analytical applications (for example, seawater analysis) which have been developed for concentrations up to 0.1 mg / L maximum. In order to obtain concentrations higher than 1 g / L, an elution solution with high affinity for palladium must be used. Thiourea solutions in nitric or hydrochloric acid medium are typically used to demonstrate the reversibility of adsorption in laboratory scale studies. However, these studies do not show the recovery of palladium to its elemental or oxide form due to the high stability of the Pd-thiourea complex.Beyond its significant economic cost, thiourea has the disadvantage of slowly degrading into ammonium thiocyanate, which limits its recycling and generates odorous sulfur and nitrogen effluents.

[0016] When elution of the palladium salt proves impossible, the only way to recover the palladium is to calcine the resins. If the support contains sulfur or phosphorus, then a derivative of the palladium phosphate or palladium sulfide type is then obtained. The treatment of this derivative requires an additional treatment step to recover the palladium in metal form. This step can involve dissolution (phosphate) or calcination (sulfide) which then generates toxic gases (SO2).

[0017] There is therefore currently no simple process for selectively recovering palladium present in an acid leaching phase that would allow both a liquid-liquid extraction step and a low-concentration elution step to be avoided.

[0018] The inventors therefore set themselves the goal of solving such a technical problem and more particularly of proposing a material making it possible to solve this technical problem. Statement of the invention

[0019] The present invention makes it possible to achieve the aim set by the inventors since it concerns the use of a material in the form of a solid, porous, mineral or organic support, impregnated with extracting molecules of the malonamide type which can be exclusively composed of C, H, O and N atoms for the selective extraction of palladium from a complex acid leaching solution.

[0020] The inventors have shown that it is possible to achieve the same performance as the best selective sulfur derivatives of palladium by using a malonamide such as TetraHexylMalonamide (THMA) with a molar mass of 438.7 g / mol. Compared to existing applications, the invention is distinguished by the absence of recourse to sulfur or phosphorus extracting molecules. The selectivity of the material with respect to copper and nickel is also unique compared to processes which use extracting molecules, non-sulfur and non-phosphorus, i.e. extracting molecules of the amine type.

[0021] The malonamides used in the present invention have already been described in liquid / liquid extractions for extracting palladium from aqueous nitric solutions [1,2]. In this prior art, the back-extraction (elution) of palladium used an acidified thiourea solution with the drawbacks mentioned above. However, surprisingly, the inventors have shown that with the material which is the subject of the present invention, this elution can be carried out with a simple acidified saline solution (Example 3 below).

[0022] Regarding applicability and reliability, the synthesis of the malonamides used such as THMA is relatively simple and the starting materials are accessible and inexpensive. Furthermore, the inventors have shown that it is not necessary to use these malonamides in purified form to maintain good extraction performance (Example 4 below).

[0023] Furthermore, compared to chemical grafting, impregnation is a simple and inexpensive method. Note that the use of malonamides does not require an additional wrapping step.

[0024] The solid support used may be an organic support, palladium adsorbed on the composite material according to the invention can be recovered directly by incineration of the palladium-loaded material. Calcination and elution are also reliable and well-known methods for recovering palladium.

[0025] Thus, this sequence of simple and reliable steps is only made possible by the unique combination of the physicochemical properties of the malonamides used, such as THMA, namely good solubility in solvents, affinity for hydrophobic materials, excellent affinity for palladium, selectivity for other metals, and reversibility of adsorption or absence of non-volatile elements.

[0026] Therefore, the present invention relates to a composite material comprising a porous solid support and at least one malonamide fixed, non-covalently, to the surface of this porous solid support.

[0027] In a particular embodiment, said malonamide attached to the surface of the porous solid support included in the composite material according to the invention is a substituted diamide of formula (I): R1(R2)NC(=O)-CH(R3)-C(=O)-N(R4)R5 (I)

[0028] in which

[0029] - the radicals R1, R2, R4 and R5, identical or different, represent an alkyl radical, a heteroalkyl radical or an arylalkyl radical, and

[0030] - the radical R3 represents a hydrogen atom, an alkyl radical or a hetero radical roalkyl, and

[0031] - the total number of carbon atoms that the radicals R1, R2, R present together 3, R4 and R5 is greater than or equal to 20.

[0032] The solid support that the material according to the invention comprises is porous. In other words, this solid support may have macropores, mesopores and / or micropores. By "macropores" is meant pores or voids having an average diameter greater than 50 nm and in particular greater than 70 nm. By "mesopores" is meant pores or voids having an average diameter of between 2 nm and 50 nm and in particular between 2 nm and 20 nm. By "micropores" is meant pores or voids having a diameter less than 2 nm.

[0033] The porosity of the solid support included in the material according to the invention is advantageously an open porosity. By "open porosity" is meant a porosity comprising pores which, on the one hand, open onto the surface of the solid support and therefore communicate with the exterior of this solid support and which, on the other hand, communicate with other pores, themselves communicating or not with the exterior of this solid support.

[0034] It should be noted that the porosimetry of the solid support used in the material according to the invention, namely the distribution in diameter and volume of the pores, also plays a role in the maximum quantity of immobilized malonamides.

[0035] Indeed, in the material according to the present invention, the malonamide(s) such as that previously defined is(are) fixed on the entire external surface of the solid support and in particular at the level of the surface of the pores accessible by the external environment.

[0036] Typically, the solid support included in the material according to the invention is in the form of objects whose size is between 100 μm and 10 mm, in particular between 150 μm and 3 mm and, in particular, 200 μm and 600 μm. Such objects can be used in packed columns useful in extraction processes and can be in particular in the form of powders, particles, grains or beads. The solid support used can therefore be defined as a particulate or granular solid support.

[0037] As indicated above, the bond between the malonamide(s) and the surface of the solid support is not a covalent bond. Thus, this bond corresponds to a physical adsorption or physisorption via weak chemical bonds including electrostatic forces, Van der Waals forces, hydrogen bonding and hydrophobic bonds. Advantageously, the bond between the malonamide(s) and the surface of the solid support is a hydrophobic bond involving at least one of the radicals R1, R2, R3, R4 and R5 and the surface of the solid support. In fact, the surface of the solid support is hydrophobic, this hydrophobic character possibly being inherent to the material constituting this surface or due to a treatment making it possible to make this surface hydrophobic. An example of such a treatment is a functionalization of the surface of the solid support by aliphatic groups.

[0038] As the material according to the invention is particularly useful for extracting palladium from acidic leaching solutions, particularly nitric acid solutions containing it, the solid support must retain its integrity in such solutions.

[0039] This solid support may be organic and comprises or consists of one or more polymer(s) and / or one or more copolymer(s) notably chosen from the group consisting of polymers and copolymers manufactured from styrene, polymers and copolymers manufactured from ethylene, polymers and copolymers manufactured from propylene, polymers and copolymers manufactured from formaldehyde and phenol, polymers and copolymers manufactured from amide, polymers and copolymers prepared from acrylic acid, polymers and copolymers manufactured from vinyl chloride, polymers and copolymers manufactured from vinylidene fluoride and copolymers manufactured from ethylene and chlorotrifluoroethylene.

[0040] It is obvious that, in the case where the palladium is recovered by incineration, the polymer(s) and / or the copolymer(s) included in or constituting the solid support used will advantageously be composed of carbon, hydrogen, oxygen and nitrogen atoms. In this case, the polymer(s) and / or the copolymer(s) included in or constituting the solid support are chosen from the group consisting of polymers and copolymers made from styrene, polymers and copolymers made from ethylene, polymers and copolymers made from propylene, polymers and copolymers made from amide and polymers and copolymers prepared from acrylic acid.

[0041] In particular, the solid support of the material according to the present invention comprises or consists of one or more polymers and / or one or more polymers are chosen from the group consisting of polymers and copolymers manufactured from styrene. A particular example of an organic solid support which can be used in the context of the present invention is a polystyrene resin crosslinked with di-vinylbenzene such as, for example, the Amberlite® XAD-2 resin sold in particular by Supelco.

[0042] Alternatively, this solid support may be mineral and comprises or consists of silica functionalized by aliphatic chains and / or by aromatic chains. A particular example of a mineral solid support usable in the context of the present invention is a mesoporous silica, functionalized by aliphatic chains and / or by aromatic chains.

[0043] The malonamide(s) used in the context of the present invention are of formula (I): R1(R2)NC(=O)-CH(R3)-C(=O)-N(R4)R5 (I)

[0044] in which

[0045] the radicals R1, R2, R4 and R5, identical or different, represent an alkyl radical, a heteroalkyl radical or an arylalkyl radical,

[0046] the radical R3 represents a hydrogen atom, an alkyl radical or a heteroalkyl radical and

[0047] the total number of carbon atoms that the radicals R1, R2, R3, R4 and R5 present together is greater than or equal to 20.

[0048] In the context of the present invention, the term “alkyl radical” means a linear, branched or cyclic alkyl radical comprising from 1 to 20 carbon atoms, in particular from 1 to 18 carbon atoms and, in particular, from 1 to 15 carbon atoms.

[0049] In the context of the present invention, the term "heteroalkyl radical" means a linear, branched or cyclic heteroalkyl radical comprising from 1 to 20 carbon atoms, in particular from 1 to 18 carbon atoms and, in particular, from 1 to 15 carbon atoms, the heteroatom(s) possibly being a nitrogen atom, an oxygen atom, a sulfur atom or a phosphorus atom, in particular a nitrogen atom or an oxygen atom and, in particular, an oxygen atom. It is obvious that, in certain forms of implementation and in particular in the case where the palladium is recovered by incineration, no heteroatom present in a heteroalkyl radical is a sulfur atom or a phosphorus atom. The heteroatom(s) may in particular interrupt an alkyl chain and / or separate an alkylene chain and an alkyl chain. In particular, in the context of the present invention, a heteroalkyl radical is an alkyl radical as previously defined interrupted by an oxygen atom.

[0050] In the context of the present invention, the term "arylalkyl radical" means a linear, branched or cyclic alkyl radical comprising from 1 to 20 carbon atoms, in particular from 1 to 15 carbon atoms, in particular from 1 to 10 carbon atoms, said alkyl radical being substituted by an aryl radical. The term "aryl radical" means a mono- or polycyclic aromatic group having from 4 to 10 carbon atoms and, in particular, from 6 to 8 carbon atoms. In the context of the present invention, when at least one radical among the radicals R1, R2, R3 and R4 is an arylalkyl radical, this radical is attached to the nitrogen of the malonamide via its alkyl radical.

[0051] In accordance with the invention, the malonamide used is preferably chosen from malonamides in which the total number of carbon atoms that the radicals R1, R2, R3, R4 and R5 together have is greater than or equal to 22 and, in particular, greater than or equal to 24. Indeed, such malonamides have a hydrophobic character which makes it possible to increase their affinity for the solid support of the material according to the invention.

[0052] Thus, in a first embodiment, the malonamide used is of formula (II): Rla(R2a)NC(=O)-CH(R3a)-C(=O)-N(R4a)R5a (II)

[0053] in which the radicals Rla, R2a, R3a, R4a and R5a, identical or different, represent an alkyl radical or a heteroalkyl radical as previously defined.

[0054] In this first embodiment, the malonamide used is a malonamide of formula (II) as previously defined in which the radicals R1a and R5a are identical and the radicals R2a and R4a are identical, the radicals R1a and R4a possibly being identical or different.

[0055] In particular, the malonamide used in this first embodiment is a malonamide of formula (II) as previously defined in which the radicals R1a, R2a, R4a and R5a are as previously defined and in which the radical R3a is an alkyl radical or a heteroalkyl radical and in particular an alkyl radical interrupted by an oxygen atom.

[0056] More particularly, international application WO 2016 / 008932 A1 [1] describes particular examples of malonamides of formula (II) since the latter are free of sulfur atoms.

[0057] More particularly still, the malonamide of formula (II) used in the context of the present invention is free of sulfur atoms and phosphorus atoms and in particular consists only of carbon, hydrogen, oxygen and nitrogen atoms.

[0058] As advantageous examples, the malonamide used in this first embodiment is chosen from the group consisting of A,A'-dimethyl-A,A'-dibutyltetradecylmalonamide (or DMDBTDMA), AA'-dimethyl-A,N'-dioctylhexylethoxymalonamide (or DMDOHEMA), N,A'-dimethyl-A,N'-dioctyloctylmalonamide (or DMDOOMA), AA'-dimethyl-AA'-dioctylhexylmalonamide (or DMDOHxMA), A,A'-dimcthyl-A,A'-dioctylheptylmalonamide (or DMDOHpMA), AA'-dimethyl-AA'-dibutyl-dodecylmalonamide (or DMDBDDEMA) and AA'-dimethyl-AA'-dibutyl-tetradecylmalonamide (or DMDBTDEMA).

[0059] In a second embodiment, the malonamide used is of formula (III): Rlb(R2b)NC(=O)-CH2-C(=O)-N(R4b)R5b (III)

[0060] in which the radicals Rlb, R2b, R4b and R5b, identical or different, represent an alkyl radical comprising at least 5 carbon atoms, a heteroalkyl radical comprising at least 5 carbon atoms or an arylalkyl radical, said arylalkyl radical being as previously defined.

[0061] In formula (III) of the malonamides used in this second embodiment, the term “alkyl radical comprising at least 5 carbon atoms” means a linear, branched or cyclic alkyl radical comprising from 5 to 20 carbon atoms, in particular from 5 to 15 carbon atoms, in particular from 5 to 12 carbon atoms and, more particularly, from 5 to 10 carbon atoms.

[0062] In formula (III) of the malonamides used in this second embodiment, the term "heteroalkyl radical comprising at least 5 carbon atoms" means a linear, branched or cyclic heteroalkyl radical comprising from 5 to 20 carbon atoms, in particular from 5 to 15 carbon atoms, in particular from 5 to 12 carbon atoms and, more particularly, from 5 to 10 carbon atoms, the heteroatom(s) possibly being a nitrogen atom, an oxygen atom, a sulfur atom or a phosphorus atom, in particular, a nitrogen atom or an oxygen atom and, in particular, an oxygen atom. It is obvious that, in certain forms of implementation and in particular in the case where the palladium is recovered by incineration, no heteroatom present in a heteroalkyl radical comprising at least 5 carbon atoms is a sulfur atom or a phosphorus atom.The heteroatom(s) may in particular interrupt an alkyl chain and / or separate an alkylene chain and an alkyl chain. In particular, in the context of the present invention, a heteroalkyl radical comprising at least 5 carbon atoms is an alkyl radical comprising at least 5 carbon atoms as previously defined interrupted by an oxygen atom.

[0063] In this second embodiment, the malonamide of formula (III) used in this second embodiment is preferably chosen from malonamides in which the radicals Rlb, R2b, R4b and R5b, which may be identical or different, each advantageously have at least 6 carbon atoms. Typically, the total number of carbon atoms that the radicals Rlb, R2b, R4b and R5b together have is greater than or equal to 20, in particular greater than or equal to 22 and, in particular, greater than or equal to 24.

[0064] In particular, the malonamide used in this second embodiment is a malonamide of formula (III) as previously defined in which the groups R1b and R4b are identical and the groups R2b and R5b are identical, the groups R1b and R5b possibly being identical or different.

[0065] More particularly, international application WO 2019 / 048790A1 [2] describes particular examples of malonamides of formula (III) since the latter are free of sulfur atoms.

[0066] More particularly still, the malonamide of formula (III) used in the context of the present invention is free of sulfur atoms and phosphorus atoms and in particular consists only of carbon, hydrogen, oxygen and nitrogen atoms.

[0067] As advantageous examples, the malonamide of formula (III) used in this second embodiment is chosen from the group consisting of N,N,N',N' -tetrahexylmalonamide (or THMA), A,A,A',A'-tetraoctylmalonamide (or TOMA), A,A,A',A'-tetra(2-ethylhexyl)malonamide (or T2EMA), N,N' -dihexyl-N,N' -dibenzylmalonamide, N,N,N',N'-tetra(2-phenylethyl)malonamide and N,N' -dihexyl-N,N' -dicyclohexylmalonamide.

[0068] Typically, the malonamide used in the context of the present invention is THMA and TOMA.

[0069] The present invention also relates to the process for preparing the material as previously defined. This process comprises a step of impregnating the porous solid support as previously defined with a solution in which at least one malonamide as previously defined is solubilized.

[0070] Thus, the method for preparing the material according to the present invention comprises the steps of: a. dissolving at least one malonamide as previously defined in a suitable solvent whereby a solution containing at least one malonamide as previously defined is obtained; b. bringing the porous solid support as previously defined into contact with the solution obtained in step a); and c. subjecting the assembly to conditions allowing the evaporation of the solvent from the solution obtained in step a), whereby a material according to the invention is obtained,

[0071] prior to step b), the porous solid support may optionally be subjected to washing and then drying.

[0072] The solvent used during step a) of the preparation process according to the invention must have the following properties: (i) be capable of solubilizing the malonamides as previously defined, (ii) not solubilizing the porous solid support as previously defined and (iii) be able to evaporate easily. A solvent which can evaporate easily is typically a solvent whose boiling point is less than 100°C at normal atmospheric pressure.

[0073] Advantageously, the solvent used during step a) of the preparation process according to the invention is chosen from the group consisting of benzene, dichloromethane, isopropanol, toluene, ethanol, diethyl ether, ethyl acetate, heptane, cyclohexane, acetone and any of their mixtures.

[0074] It is easy for a person skilled in the art to determine the concentration of malonamide(s) to be used during step a) of the preparation process as a function of the quantity of malonamide(s) desired per unit of mass of solid support.

[0075] During step b) of the process according to the invention, which can be defined as an impregnation step, the contact between the porous solid support and the solution containing the malonamide(s) is typically carried out with stirring and has a duration of less than or equal to 2 h.

[0076] Prior to step b) of the process, it is possible to subject the porous solid support to washing with water such as deionized water followed by washing with a water-miscible and easily evaporable solvent such as ethanol, isopropanol, tetrahydrofuran or acetone and then to drying under vacuum.

[0077] During step c) of the preparation process according to the invention, a person skilled in the art will be able to choose, without inventive effort, the conditions allowing the evaporation of the solvent from the solution prepared in step a). This evaporation is typically carried out under vacuum.

[0078] At the end of step c) of the preparation process according to the invention, the porous solid support to the surface of which the malonamide(s) is / are fixed, in a non-covalent manner, can be recovered by filtration and then optionally washed in an aqueous solution such as water before being used in a palladium extraction process.

[0079] The present invention finally relates to the use of a material as previously defined for extracting palladium from an acid leaching solution containing it. This extraction therefore corresponds to a solid / liquid extraction.

[0080] In other words, the present invention relates to a method for extracting palladium from an acid leaching solution containing it, consisting of bringing into contact a material as previously defined or a material prepared by a preparation process as previously defined with an acid leaching solution containing palladium whereby a palladium-laden material is obtained.

[0081] The material obtained at the end of this contact is in the form of a porous particulate material, with open porosity, impregnated with at least one malonamide as previously defined and on the surface of which palladium is adsorbed, in particular in the form of complexes with said at least one malonamide.

[0082] In the context of the present invention, the acid leaching solution used is characterized by the presence of different metallic elements among which there is palladium and at least one other metallic cation and in particular at least one other metallic cation whose valence is greater than or equal to 2.

[0083] Any acid leaching solution containing different metallic elements including palladium and at least one other metallic cation whose valence is greater than or equal to 2 can be used in the context of the present invention. The acid leaching solution used in the context of the method according to the invention is advantageously an acidic aqueous solution, in particular nitric acid, resulting from the treatment of waste electrical and electronic equipment and, in particular, from the treatment of multilayer ceramic capacitors from electronic cards, which are particularly rich in palladium. The acid leaching solution can also be obtained from the treatment of technological scraps or unsold items, resulting from the manufacture of these capacitors, or even from the treatment of certain jewelry.

[0084] Thus, this acid leaching solution comprises not only palladium but also at least one metallic element chosen from the group consisting of iron (Fe), copper (Cu), zinc (Zn), aluminum (Al), lead (Pb), nickel (Ni), silver (Ag), cobalt (Co), neodymium (Nd), lanthanum (La), dysprosium (Dy), ytterbium (Yb) and chromium (Cr). The quantity of each of these metallic elements and in particular the quantity of palladium in the acid leaching solution will depend on the origin of the acid leaching solution and in particular on the nature of the waste electrical and electronic equipment and the treatment to which it has undergone.

[0085] Typically, waste electrical and electronic equipment is ground, possibly subjected to an acid attack, for example, by hydrochloric acid or sulfuric acid and then subjected to an oxidizing attack by nitric acid, in particular in an amount of between 3 mol.L-1 and 6 mol.L-1, in order to dissolve metallic elements such as gold, silver, palladium and certain lanthanides. The acid leaching solution used in the process according to the present invention therefore corresponds to the aqueous nitric solution obtained following such treatment, i.e. a leaching water from the ground waste electrical and electronic equipment.

[0086] The quantity of nitric acid in the acid leaching solution used in the process according to the invention is advantageously between 1 M and 6 M and in particular between 2 M and 4 M.

[0087] This acid leaching solution may possibly have undergone pretreatment to already remove certain metal cations. Indeed, depending on the process chosen, certain major elements such as copper or iron, or even gold for its high value, can be selectively extracted by conventional hydrometallurgical techniques.

[0088] Generally speaking and in particular with regard to the above, the palladium present in the acid leaching solution prior to the implementation of the preparation process is in oxidized form, i.e. in the form of Pd2+ cations. The latter may optionally be present in part in the form of a complex by the nitrate or chloride anions present in the solution.

[0089] In the extraction process according to the invention, the material as previously defined is placed in a column and the contact between the acid leaching solution containing palladium and the material is carried out by passing the solution over the material in the column. In this case, the extraction process according to the invention is a column process.

[0090] Alternatively, the extraction process according to the invention may be a batch process, i.e. a process involving contact between the material as previously defined and the acid leaching solution containing palladium and stirring of the whole.

[0091] A person skilled in the art will know how to choose the duration of the extraction process so that it is sufficient to exhaust the acid leaching solution of palladium.

[0092] In a particular embodiment, the extraction method according to the invention may, in addition, comprise a prior step of preparing the material according to the preparation method as previously defined.

[0093] In another particular embodiment, the extraction method according to the invention may, in addition, comprise a subsequent step of recovering palladium from the palladium-laden material obtained, following a possible step of washing said palladium-laden material.

[0094] In another particular embodiment, the extraction method according to the invention may, in addition, comprise a prior step of preparing the material according to the preparation method as previously defined and a subsequent step of recovering the palladium from the palladium-laden material obtained, following a possible step of washing said palladium-laden material.

[0095] The recovery step may correspond to a step of elution (or desorption) of the palladium carried out by bringing the material loaded with palladium into contact with a acidified saline solution to obtain an eluate comprising at least palladium, the latter being able to be subsequently concentrated by evaporation.

[0096] Furthermore, for eluates in which the palladium concentration is at least 0.3 M, it is possible to consider the precipitation of palladium with ammonium salts to obtain Pd(NH3)2Cl2, a conventional method described in the literature [3]. This salt is a key intermediate in palladium chemistry and can also be calcined via the method described below, to obtain palladium in metallic form.

[0097] Advantageously, the acidified saline solution used during the elution step is a sodium chloride (NaCl) solution acidified with hydrochloric acid (HCl). Typically, in this solution, the sodium chloride is in a concentration of between 0.05 M and 1 M and in particular in a concentration of the order of 0.9 M (i.e. 0.9 M ± 0.05 M) and / or the hydrochloric acid is in a concentration of between 0.05 M and 1 M and in particular in a concentration of the order of 0.1 M (0.1 M ± 0.05 M).

[0098] The contacting during the elution step of the process according to the invention can be carried out at a temperature greater than or equal to room temperature. By "room temperature" is meant a temperature of 23°C ± 5°C. Advantageously, this elution step is carried out at room temperature.

[0099] The contacting during the elution step of the process according to the invention lasts between 2 h and 3 days and in particular of the order of 48 h (i.e. 48°h ± 6°h).

[0100] The contact conditions during the elution step of the process according to the invention vary depending on whether the extraction process is a column process or a batch process.

[0101] For a column process, the elution solution is circulated in a closed loop in the column containing the material obtained in the extraction step.

[0102] For a batch process, the contacting consists of placing the material obtained in the extraction step in the elution solution and keeping the whole under stirring. In a batch process, the solid / liquid ratio, i.e. the ratio of material obtained in the dry extraction step in g / elution solution in mL, is between 1:1 and 1:5. In particular, this ratio is 1:2.

[0103] It is possible, following the extraction step and prior to the elution step, to subject the material obtained following the extraction step to one or more washes using a washing solution, identical or different for each wash. This washing step makes it possible to eliminate the elements that are little or not retained by the porous particulate material. The washing solution used is an acidic aqueous solution such as an aqueous solution of hydrochloric acid, nitric acid or sulfuric acid. Typically, in this aqueous solution, the acid is in a concentration between 0.01 M and 4 M and in particular in a concentration of the order of 0.05 M (i.e. 0.05 M ± 0.01 M) or, alternatively, in a higher concentration of the order of 1 M (i.e. 1 M ± 0.1 M). In a particular embodiment, this washing solution is a solution containing nitric acid at a concentration of the order of 0.05 M or of the order of 1 M. The acidity of the washing solution prevents the hydrolysis of the palladium, which would make its subsequent desorption impossible.

[0104] In a batch process, the solid material is recovered after the extraction step, after the elution step and / or after the washing step(s) either (i) by decantation followed by a filtration step or (ii) by skimming the surface of the solution in which it is found followed by a filtration step, depending on the density of the material.

[0105] After the elution step, it is possible to use the material obtained, i.e. a porous particulate material with open porosity, impregnated with at least one malonamide as previously defined, in another extraction process. In other words, it is possible to use the material according to the invention in several extraction / washing / elution cycles. Before use in another extraction process, the material according to the invention is typically washed with an acidic aqueous solution as previously defined and then with water.

[0106] As a variant of a method involving an elution step, the palladium recovery step may correspond to a calcination step of the palladium-laden material obtained at the end of the extraction. This calcination step is possible when the porous particulate material used is an organic material, in particular as defined above. Indeed, such a material can be entirely transformed into volatile elements C, H, O, and N by a heat treatment.

[0107] In a first embodiment, this calcination is carried out in air at a temperature less than or equal to 1050°C and in particular at a temperature between 750°C and 900°C which corresponds to the decomposition temperature of palladium oxide (PdO) into metallic palladium. Cooling must then take place in an anoxic atmosphere (nitrogen or argon for example) to avoid oxidation of the palladium.

[0108] In a second embodiment, this calcination is carried out at a temperature less than or equal to 550°C, the temperature at which the organic molecules are decomposed. The residue obtained is then essentially formed of palladium oxide and it is appropriate to use a reducing gas (H2 or CO) in order to reduce the oxide.

[0109] Other characteristics and advantages of the present invention will become apparent to those skilled in the art upon reading the examples below given for illustrative and non-limiting purposes, with reference to the appended figures. Brief description of the drawings

[0110] [Fig. IA] shows the adsorption-desorption isotherms of dinitrogen at 77K of the commercial resin before (XAD-2) and after impregnation with THMA (XAD-2 - 15% THMA).

[0111] [Fig. IB] shows the adsorption-desorption isotherms of dinitrogen at 77K of mesoporous silica before (SiC8) and after impregnation with THMA (SiC8 - 15% THMA).

[0112] [Fig.2] shows the evolution of the palladium load of the impregnated supports over time. The points represent experimental measurements, the continuous lines are drawn to guide the eye. The extraction is carried out at room temperature (20°C), under gravity stirring (35 RPM), with 40 mL of aqueous phase and 0.4 g of support. The solution is described in Table 2 below.

[0113] [Fig.3] is an X-ray diffractogram of the solid obtained after calcination of the XAD-2 - 31% THMA resin loaded with Pd at 1050°C in air for 3 h and cooling under N2. The 5 most important peaks correspond to the PDF-00-046-1043 sheet of palladium metal.

[0114] [Fig.4] is a micrograph of the solid by SEM of the XAD-2 resin - 31% THMA loaded with Pd (9 mg / g) after calcination at 1050°C in air for 3 h, cooling under N2.

[0115] [Fig.5] shows the evolution of the palladium load of the supports impregnated with pure THMA or unpurified THMA (THMA*) with equal quantity of extractant. The points represent experimental measurements, the continuous lines are drawn to guide the eye. The extraction is carried out at room temperature (20°C), under gravity stirring (35 RPM), with 40 mL of aqueous phase and 0.4 g of support. The solution is described in Table 2 below.

[0116] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0117] Example 1: Preparation of impregnated supports.

[0118] Mesoporous silica type support

[0119] On the one hand, mesoporous silica (CAS No. 112926-00-8, mesh 35-70, Sigma-Aldrich) is pre-functionalized with aliphatic chains according to the following protocol: the silica is suspended in a toluene solution (CAS No. 108-88-3, Sigma-Aldrich) containing triethoxy(octyl)silane (CAS No. 2943-75-1, Sigma-Aldrich). This suspension is heated at 200°C by microwave for 30 min. After cooling, the material is washed with ethanol for more than 48 hours using a Soxhlet-type assembly, to remove the reaction by-products, toluene and excess reagents.

[0120] Commercial resin type support

[0121] A commercial resin (Amberlite® XAD-2, divinyl benzene crosslinked polystyrene, CAS No. 9060-05-3, mesh 20-60, supplied by Supelco) is washed three times with ethanol of a purity >96% (20 g of resin, for three times 250 mL of ethanol) then dried under vacuum (rotary evaporator and vacuum ramp).

[0122] Impregnation

[0123] The preparation of THMA is described in international application WO 2019 / 048790A1 [2],

[0124] The impregnation is carried out according to the same method for both supports: a dichloromethane solution (CAS No. 75-09-2, CarloErba), containing purified THMA is added to the dry support. The quantity of impregnated ligand is chosen such that the ligand loading is QE = 15 + 0.5% or 31 + 1% (mass %), depending on the tests, or in quantity of material: 0.35 or 0.71 mmol / g. The suspension is stirred for 2 h by rotation of the reactor (approximately 90 RPM) at room temperature (approximately 20°C), before being evaporated under vacuum at 42°C. The impregnated resin is designated by XAD-2 - X% THMA (with X = 15 or 31), and the grafted and impregnated silica by SiC8 - 15% THMA.

[0125] The materials thus prepared are characterized by dinitrogen porosimetry (Figures 1A and 1B, Novatouch LX3 porosimeter, Quantachrome), and the particle size is verified by laser particle size analysis (Table 1, Mastersizer3000, Malvern Panalytical).

[0126] The specific surface area of ​​the resin measured by the BET method, initially 361 m2 / g, decreases to reach 137 m2 / g. As for the grafted silica, this is 347 m2 / g before impregnation and 222 m2 / g after. The shape of the adsorption isotherms (Figures 1A and 1B) shows that it is mainly the micropores which are filled by the THMA. The particle size of the materials is not significantly affected (Table 1).

[0127] [Tableauxl] Support Djo (qm) D50 (qm) D90 (qm) XAD-2 294 + 7,454 + 9,684 + 27 308+1470 +2708+6

[0128] Table 1: Characteristic volume diameters of the supports before and after impregnation determined by laser granulometry (Mie theory).

[0129] Example 2: Selective extraction of palladium.

[0130] The tests conducted in the laboratory were carried out with a representative synthetic solution, prepared from salts (nitrates) of the aforementioned metals. Its composition is given in Table 2.

[0131] The metal concentrations of this solution as well as those of the other solutions are measured by optical ICP after appropriate dilution (iCAP-OES 6400, matrix HN03 2%, axial measurements of the lines: Pd 340.458 nm, Ni 341.476 nm, Cu 224.700 nm, Fe 259.940 nm, averages of three repeated measurements).

[0132] [Tables2] Species Concentration hno3 2 ± 0.2 mol / L Pd 50 ± 0.5 mg / L Ni 500 ± 10 mg / L Cu 1000 ± 20 mg / L Fe 1000 ± 20 mg / L

[0133] Table 2: Composition of the treated synthetic solution

[0134] In a stirred reactor (50 mL tube) containing a given mass of material per volume of solution (0.4 g of impregnated support per 40 mL of solution), the extraction rate and the maximum Pd capacity of the materials were measured at room temperature. The palladium load of the support q, is calculated conventionally by difference with the initial solution according to the following equation:

[0135] [Math.l] q = V*—-

[0136] in which V is the volume of treated solution (in L), C the measured Pd concentration (in mg / L), C0 the initial concentration of the Pd solution (in mg / L) and m the mass of impregnated support.

[0137] The extraction kinetics observed, i.e. the time required to saturate the support with palladium, depends both on the initial support used and also on the quantity of ligand used for impregnation ([Fig.2]).

[0138] With grafted silica (SiC8), the extraction kinetics is of the order of a few hours, but the palladium desorbs after 24 h. Other supports may have a higher Pd capacity (for example, XAD-2 - 31% THMA), to the detriment of the adsorption speed. The amount of impregnated THMA plays a fundamental role here with respect to the maximum Pd load, as evidenced by the significant difference between the supports XAD-2 - 15% THMA and XAD-2 - 31% THMA.

[0139] In terms of selectivity and captured fraction, the results after 24 h of extraction are recorded in Table 3. The results should be taken with caution for the impurities (Ni, Cu and Fe) which are in large excess compared to Pd (eg, ratio mass Cu / Pd = 20), and whose concentration varies little over time.

[0140] [Tables 3] Pd Ni Cu Fe Support In % capture SiC8 - 15% THMA 59+1 3 + 3 1 + 3 2 + 3 XAD-2 - 15% THMA 10+1 2 + 3 3 + 3 4 + 3

[0141] Table 3: Data after 24 h of extraction. The uncertainty values ​​are given for a relative uncertainty of concentration measurement of 2%. Extraction carried out at room temperature (20°C), under gravity stirring (35 RPM), with 40 mL of aqueous phase and 0.4 g of support. The initial solution is described in Table 2 above.

[0142] For the two most efficient supports, the depletion of the Pd solution, between 59 and 82%, is appreciable for extraction in a stirred reactor. The adsorption coefficients Kd (in L / g) are presented for the four metals present in Table 4. They are calculated conventionally according to the following equation:

[0143] [Math.2] Kd-^

[0144] in which C is the measured concentration (mg / L), and q the load of the support (mg / g).

[0145] [Tables4] Support Kd Pd (L / g) Kd Ni (L / g) Kd Cu (L / g) Kd Fe (L / g) SiC8 - 15%THMA 1.44 x 10 1 2.80 x 103 8.74 x 104 2.28 x 103 1.81 x 103 5.09 x 103

[0146] Table 4: Kd values ​​after 24 h of extraction at room temperature (20°C).

[0147] The Kd values ​​for Pd are much higher (by an order of magnitude 100) than those of other metals, which demonstrates the selectivity of the impregnated supports for palladium. Thus, even under the most unfavorable conditions with palladium in a very small minority in solution, the supports selectively capture the latter.

[0148] Example 3: Recovery of palladium.

[0149] Given its superior kinetic performance, silica is chosen to illustrate the palladium recovery strategy by elution. Recovery by calcination of the support is moreover more suitable for polymeric resin, especially that its palladium capacity is higher.

[0150] Recovery by elution of the Pd adsorbed on the mineral support

[0151] To illustrate the performance of the mineral material (SiC8 - 15%THMA), and in order to reduce measurement uncertainties, the adsorption experiment is repeated by increasing the quantities involved.

[0152] Thus a mass of 4 g of support is added to a volume of 200 mL of a solution similar to that described in Table 2, but with an initial concentration of Pd C o = 25 mg / L. The suspension is stirred by gravity stirring (45 RPM) at room temperature (20°C) for 4 h. ICP analysis of the Pd remaining in solution reveals a charge of the support equal to q = 1.0 mg / g.

[0153] The suspension is filtered under vacuum, using a minimal volume of deionized water to collect the solid. The latter is placed in a new 500 mL flask, containing a nitric acid solution diluted to 0.05 mol / L for the washing step. The suspension contains approximately 4 g of solid, per 400 mL of solution; it is stirred by gravity stirring at 45 RPM for 1 h. The washing solution is filtered under vacuum, and the solid is transferred to a flask containing the elution solution.

[0154] The latter is composed of NaCl at 0.9 mol / L and HCl at 0.1 mol / L. The volume of solution is 8 mL, which corresponds to a solid-liquid ratio of 1:2 (in g of dry resin per mL of elution solution). After 48 h of stirring at room temperature, a sample of solution is taken and filtered on a syringe at 0.22 pm, for analysis by ICP (Table 5).

[0155] [Tables5] Concentrations in mg / L of the elution solution Material Pd Ni Cu Fe SiC8 - 15% THMA 292 + 6 <5 <5 57 + 2

[0156] Table 5: Metal concentrations in the elution solution (NaCl = 0.9 mol / L and HCl = 0.1 mol / L) after 48 h of gravity stirring (45 RPM) at room temperature (20°C). The quantification limit of the method is 5 mg / L for Ni, Cu, and Fe.

[0157] The Pd concentration obtained is 12 times higher than that of the initial solution. On the other hand, the Fe concentration was divided by 17. The Ni and Cu contents were too low to be detectable (< 5 mg / L).

[0158] This elution confirms the selectivity of the material for Pd with respect to other impurities. It also confirms the possibility of recovering concentrated Pd using a simple acidified saline solution. The recovery yield is around 58% at the end of this batch.

[0159] Recovery by calcination of the organic support

[0160] To demonstrate the possibility of recovering Pd in ​​metallic form from a charged resin, a batch of XAD-2 - 31% THMA resin is brought into contact with a synthetic palladium solution (Co = 1 g / L and HNO3 = 3 mol / L). After extraction of the Pd, the resin is rinsed on a filter and dried in an oven at 80°C overnight (18 h).

[0161] In an alumina crucible, a mass of approximately 1 g of dry resin is weighed to be transferred to a tubular furnace. Under an air flow, the crucible undergoes a temperature rise of the order of 10°C / min until reaching a plateau at 1050°C for a duration of 3 h. At the end of this plateau, the air flow is stopped to be replaced by a nitrogen flow of equivalent flow rate, allowing the system to cool to room temperature in an anoxic atmosphere.

[0162] The solid obtained (approximately 2.5 mg) is characterized by X-ray diffraction (XRD) ([Fig.3]) (Diffractometer D8, Bruker), and scanning electron microscopy (SEM) ([Fig.4]) (BRUKER).

[0163] The diffractogram obtained ([Fig.3]) confirms that the palladium was indeed reduced during the calcination protocol. The peaks of palladium oxide (PdO: palladinite) are not detected. The unassigned peaks do not correspond to palladium oxide, and are most likely related to impurities present in the calcination crucible.

[0164] A porous structure is observed in the SEM ([Fig.4]), with hollow assemblies, of the order of magnitude of the initial resin beads (ca. 200 pm) contracted by calcination. The residual Pd structure is a few pm thick (2-5 pm), with openings of similar sizes. These observations suggest a large specific surface area, and therefore a high reactivity, to be confirmed by other methods if the product obtained was used as is (for direct applications in fine chemistry for example).

[0165] Example 4: Extraction of palladium with pure THMA or unpurified THMA.

[0166] When prepared according to the process described in the international application WO 2019 / 048790A1 [2], the THMA ligand is found in a mixture with its unconsumed synthesis reagents, i.e. di-hexylamine, at 45 mol%, and ethyl malonate 5 mol%.

[0167] Based on these proportions and the molar masses of these species, a new material was prepared while retaining the total amount of extractants (0.35 mmol / g di-hexyl-amine + THMA + ethyl malonate), and noted XAD-2 - THMA*.

[0168] The performance of the material (capacity and kinetics) was studied as described in Example 2 and compared to that obtained with purified THMA. The results of the extraction kinetics are presented in [Fig.5]. It appears that the performance obtained with unpurified THMA, although lower, remains comparable.

[0169] It is therefore possible to use the THMA ligand in a mixture with its unconsumed synthesis reagents. Références

[0170] [1] Demande internationale WO 2016 / 008932 Al

[0171] [2] Demande internationale WO 2019 / 048790 A1

[0172] [3] Bourgeois et al, 2020, “A simple process for the recovery of palladium from wastes of printed circuit boards”. Hydrometallurgy 191, 105241

Claims

Claims

1. Composite material comprising a porous solid support and at least one malonamide fixed, non-covalently, to the surface of this porous solid support.

2. Composite material according to claim 1, characterized in that said malonamide is a substituted diamide of formula (I): R'(R2)NC(=O)-CH(R3)-C(=O)-N(R4)R5 (I) in which - the radicals R1, R2, R4 and R5, which may be identical or different, represent an alkyl radical, a heteroalkyl radical or an arylalkyl radical, and - the radical R3 represents a hydrogen atom, an alkyl radical or a heteroalkyl radical, and - the total number of carbon atoms that the radicals R1, R2, R3, R4 and R5 together have is greater than or equal to 20.

3. Material according to claim 1 or 2, characterized in that said solid support is in the form of objects whose size is between 100 pm and 10 mm, in particular between 150 pm and 3 mm and, in particular, 200 pm and 600 pm.

4. Material according to any one of claims 1 to 3, characterized in that the surface of said solid support is hydrophobic, this hydrophobic character being able to be inherent in the material constituting this surface or due to a treatment making it possible to make this surface hydrophobic.

5. Material according to any one of claims 1 to 4, characterized in that said solid support is organic and comprises or consists of one or more polymer(s) and / or one or more copolymer(s) in particular chosen from the group consisting of polymers and copolymers manufactured from styrene, polymers and copolymers manufactured from ethylene, polymers and copolymers manufactured from propylene, polymers and copolymers manufactured from formaldehyde and phenol, polymers and copolymers manufactured from amide, polymers and copolymers prepared from acrylic acid, polymers and copolymers manufactured from vinyl chloride, polymers and copolymers manufactured from vinylidene fluoride and copolymers manufactured from ethylene and chlorotrifluoroethylene.

6. Material according to any one of claims 1 to 4, characterized in that said solid support is mineral and comprises or consists of silica functionalized by aliphatic chains and / or by aromatic chains.

7. Material according to any one of claims 1 to 6, characterized in that said at least one malonamide is A,A,A',A'-tetrahexylmalonamide (or THMA) or A,A,A',A'-tetraoctylmalonamide (or TOMA).

8. A process for preparing a material as defined in any one of claims 1 to 7, characterized in that it comprises the steps of a. dissolving at least one malonamide in a suitable solvent whereby a solution containing at least one malonamide is obtained; b. contacting the porous solid support with the solution obtained in step a); and c. subjecting the assembly to conditions allowing the evaporation of the solvent from the solution obtained in step a) whereby a material as defined in any one of claims 1 to 7 is obtained, prior to step b), the porous solid support may optionally be subjected to washing and then drying.

9. Preparation process according to claim 8, characterized in that said solvent is chosen from the group consisting of benzene, dichloromethane, isopropanol, toluene, ethanol, diethyl ether, ethyl acetate, heptane, cyclohexane, acetone and any of their mixtures.

10. Use of a material as defined in any one of claims 1 to 7 for extracting palladium from an acid leaching solution containing it.

11. A method of extracting palladium from an acid leaching solution containing palladium comprising contacting a material as defined in any one of claims 1 to 7 with an acid leaching solution containing palladium, whereby a palladium-laden material is obtained.

12. Extraction method according to claim 11, characterized in that said acid leaching solution is an acidic aqueous solution, in particular nitric, resulting from the treatment of waste electrical and electronic equipment and, in particular, from the treatment of multilayer ceramic capacitors from electronic cards, particularly rich in palladium.

13. Extraction method according to claim 11 or 12, characterized in that said material is arranged in a column and the contact between the acid leaching solution and the material is carried out by passing the solution over the material in the column.

14. Extraction method according to any one of claims 11 to 13, characterized in that said method further comprises a subsequent step of recovering palladium from said palladium-laden material obtained, following a possible step of washing said palladium-laden material.

15. Extraction method according to claim 14, characterized in that said recovery step corresponds - either to a step of desorption of the palladium carried out by bringing the material loaded with palladium into contact with an acidified saline solution to obtain an eluate comprising at least palladium; and - or to a step of calcination of the material loaded with palladium obtained at the end of the extraction.

16. Extraction method according to claim 15, characterized in that said acidified saline solution is a sodium chloride (NaCl) solution acidified with hydrochloric acid (HCl).

Images