Solid material that can be used to extract palladium and / or rhodium and / or silver, method for preparing same and uses thereof

Abstract

The present invention relates to a material in the form of porous polymer beads with open porosity, characterised in that said material comprises at least one dialkyl sulphide possibly combined with at least one alkyl aniline in at least a portion of the pores of said polymer beads. The present invention also relates to a method for preparing such a material and to the use thereof for extracting palladium and / or rhodium and / or silver from a solution containing same.

Description

[0001] SOLID MATERIAL USEFUL FOR THE EXTRACTION OF PALLADIUM AND / OR RHODIUM AND / OR SILVER, ITS PREPARATION PROCESS AND ITS USES

[0002] TECHNICAL FIELD

[0003] The present invention belongs to the technical field of metal recycling and more particularly to the technical field of palladium and / or rhodium and / or silver recycling involving solid / liquid extraction.

[0004] Indeed, the present invention relates to a solid material in the form of porous polymer beads in the pores of which are trapped extracting molecules from the family of dialkyl sulfides and possibly other extracting molecules from the family of alkyl anilines.

[0005] The present invention also relates to a process for preparing such a material as well as its uses, in particular for separating palladium and / or rhodium and / or silver from other metallic elements contained in solutions comprising these elements, for example solutions resulting from the reprocessing of spent nuclear fuels, solutions of fission products, or solutions resulting from the leaching of conventional ores (production from ores) or unconventional ores (metals resulting from recycling processes, for example, waste electrical and electronic equipment).

[0006] STATE OF THE PRIOR ART

[0007] Palladium (Pd) and rhodium (Rh) belong to the platinum group metals and have interesting catalytic properties and good corrosion resistance. They are 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 and rhodium is mainly driven by the growth of the automotive market. The supply of these metals remains strategic due to the geographical location of the deposits and, consequently, production, limited to a few countries. For this reason, recycling is a preferred alternative.

[0008] This recycling may involve the reprocessing of spent nuclear fuels, as palladium is one of the transition metals with the highest quantity in fission products. It may also involve catalytic converters, a homogeneous source of palladium and rhodium, treated in a hydrochloric environment. Waste electrical and electronic equipment (WEEE), also known as "urban mining," contains palladium and rhodium; their recycling represents significant potential sources of palladium and rhodium.

[0009] Recycling studies include two axes: pyrochemistry / pyrometallurgy and hydrometallurgy. Regarding hydrometallurgy, different technologies can be used, such as liquid-liquid extraction, electrochemistry, precipitation, supported liquid membranes, or ion exchange resins.

[0010] On an industrial scale, the separation of palladium and rhodium from acidic ore leaching solutions (primary or secondary) is achieved using liquid-liquid extraction (LLE) or precipitation.

[0011] ELL requires the use of extractant molecules capable of trapping the metal to be recovered, diluted in an organic phase. Several extractant molecules have been studied for the extraction of palladium and / or rhodium from acidic solutions such as hydrochloric or nitric solutions.

[0012] Thus, dialkyl sulfides or dialkyl-sulfides, available on an industrial scale, such as, for example, dioctyl-sulfide (or DOS) and dihexyl-sulfide (or DHS), have a remarkable selectivity for palladium in nitric medium and have been studied, in mixture with an alkyl aniline or alkyl-aniline, in the context of a co-extraction of palladium and rhodium [1,2]. To be used in an ELL process, this mixture is diluted in an organic solvent consisting of aromatic molecules to limit the passage of the dialkyl sulfide and alkyl aniline mixture to the aqueous phase containing palladium and / or rhodium. Thus, ELL remains an effective technique but can be expensive to implement because it requires the use of significant equipment and the use of one or more extracting molecule(s) diluted in an organic phase.The extracting molecules and the organic phase must be slightly soluble in the aqueous phase in which the palladium and rhodium are initially found, otherwise the process becomes more complex. ELL also involves the use of solvent, often in large quantities.

[0013] Also, the inventors set themselves the goal of providing a material and a method which, while making it possible to efficiently and selectively separate and purify the palladium and / or rhodium contained in a solution such as an aqueous nitric solution containing palladium and / or rhodium in a mixture with other cations such as metal cations, are free from the drawbacks mentioned above.

[0014] STATEMENT OF THE INVENTION

[0015] The present invention makes it possible to achieve the goal set by the inventors since the latter have shown that it is possible to trap, coat, encapsulate extracting molecules of the dialkyl sulfide type, possibly associated, combined with extracting molecules of the alkyl aniline type in the pores of porous polymer beads with open porosity. Thus, the use of porous polymer beads forming a porous shell protects the extracting molecules and greatly reduces their passage into the aqueous phase while allowing the passage of metal ions such as palladium and rhodium, which can come into contact with the extracting molecules in the pores of the porous beads.

[0016] Furthermore, this porous bead type system loaded with extracting molecules can be prepared by an easily industrializable process involving suspension polymerization.

[0017] Finally, the inventors have shown that this system of porous beads loaded with extracting molecules can be used not only to efficiently and selectively extract palladium and / or rhodium but also only to efficiently and selectively extract silver.

[0018] Therefore, this system of porous beads loaded with extracting molecules can be used to extract palladium and / or rhodium and / or silver from solutions containing them such as nitric solutions, without using solvent unlike ELL. This extraction can be implemented on a compact column-type device as illustrated in examples 3 and 4 below.

[0019] Thus, the present invention relates to a material in the form of porous polymer beads with open porosity, said material comprising at least one dialkyl sulfide in at least part of the pores of said polymer beads.

[0020] The material according to the invention is a solid material which can be defined as a composite material since it comprises, on the one hand, beads made of organic (co)polymers and, on the other hand, extracting molecules.

[0021] By "polymer bead" or "(co)polymer bead", the two expressions being usable interchangeably, is meant a particulate, spherical structure, consisting of crosslinked organic polymers and / or copolymers. The polymer beads used in the present invention are porous with open porosity.

[0022] The pores of the polymer beads used in the present invention have an average diameter of approximately 45 nm to 250 nm according to observations made using a scanning electron microscope.

[0023] By "open porosity" is meant a porosity comprising pores which, on the one hand, open onto the surface of the porous beads of the material and communicate with the exterior of these beads and which, on the other hand, communicate with other pores, themselves communicating or not with the exterior of the porous beads of the material.

[0024] Furthermore, the polymer beads used in the present invention have an average diameter of between 10 pm and 1 mm, in particular between 50 pm and 500 pm and, in particular, of the order of 100 pm (i.e. 100 pm ± 40 pm).

[0025] Since the material according to the invention is particularly useful for extracting palladium and / or rhodium and / or silver from acid solutions, particularly nitric acid solutions containing them, the polymers and / or copolymers constituting the polymer beads of this material must retain their integrity in such solutions. Consequently, the polymers and / or copolymers constituting the polymer beads of the material according to the invention are particularly chosen from the group consisting of polymers and copolymers made from styrene, polymers and copolymers made from urea, polymers and copolymers made from divinylbenzene, polymers and copolymers made from alginate, polymers and copolymers made from chlorophenylsulfone and polymers and copolymers containing amide groups.In particular, the polymers and / or copolymers constituting the polymer beads of the material according to the invention are chosen from the group consisting of polymers and copolymers manufactured from styrene and polymers and copolymers manufactured from styrene and divinylbenzene.

[0026] The material according to the present invention comprises extracting molecules. By "extracting molecule" is meant a molecule which, in the presence of palladium and / or rhodium and / or silver, is capable of forming a non-covalent complex with a palladium cation and / or a rhodium cation and / or a silver cation.

[0027] In a porous bead of the material according to the invention, only certain pores may have one or more extracting molecule(s). In a particular embodiment, in a porous bead of the material according to the invention, substantially all the pores may have one or more extracting molecule(s).

[0028] The extracting molecules are trapped, encapsulated in pores of the porous beads. In other words, one or more extracting molecule(s) is / are maintained in the space formed by a pore of a porous bead, this maintenance not involving any covalent bond between an atom of an extracting molecule and an atom at the periphery of the pore, i.e. an atom of the wall materializing a pore.

[0029] In the context of the present invention, the extracting molecules used are dialkyl sulfides. By "dialkyl sulfide" is meant a molecule of general formula RSR' with R and R', identical or different, representing an alkyl group.

[0030] By "alkyl group" is meant, in the context of the present invention, a linear, branched or cyclic alkyl group, comprising from 4 to 20 carbon atoms, in particular from 4 to 16 carbon atoms and in particular, from 5 to 12 carbon atoms.

[0031] In a particular embodiment, the dialkyl sulfide(s) used are of general formula (C n H2n+i)2S with 6 <n<10. Dans un mode de réalisation plus particulier, le sulfure de dialkyle mis en œuvre est du sulfure de dioctyle (ou dioctyl sulfure).

[0032] Furthermore, the dialkyl sulfide(s) used in the material according to the invention may be used combined with one or more alkyl anilines. In other words, the material according to the invention further comprises at least one alkyl aniline in at least part of the pores of said polymer beads.

[0033] By "alkyl aniline" is meant a molecule of general formula R"(CeH4)NH2 with R'' representing an alkyl group as previously defined.

[0034] In a particular embodiment, the alkyl aniline(s) used are of general formula (Cn-Fbn'+iHCeH^NFh with 6 <n'<10. Dans un mode de réalisation plus particulier, l'aniline d'alkyle mise en œuvre est l'aniline d'octyle (ou octylaniline).

[0035] In this variant involving extractant molecules of the dialkyl sulfide type and of the alkyl aniline type, a dialkyl sulfide and an alkyl aniline may be present in the same pore of a porous bead and / or in two distinct pores of this porous bead.

[0036] The present invention also relates to the process for preparing the material as previously defined. This process comprises a suspension polymerization step known per se.

[0037] By "suspension polymerization" is meant a polymerization in a dispersed medium with compartmentalization of the reaction medium. Thus, in a suspension polymerization, there are two immiscible phases with (i) a dispersed phase comprising the monomer(s), precursors of a (co)polymer and a polymerization initiator and (ii) a dispersing continuous phase, typically aqueous, comprising a stabilizing agent. More particularly, a suspension polymerization makes it possible to produce polymer beads (called dispersed phase) within an aqueous continuous phase. The process consists of dispersing one or more monomers, relatively insoluble in water, in the form of liquid droplets under the effect of vigorous stirring which is maintained during the polymerization within a dispersing phase. Initiators soluble in the liquid monomer phase are used in this process to trigger the polymerization reaction.

[0038] The process for preparing the material according to the present invention comprises the steps of: a) preparing an aqueous phase comprising a stabilizing agent; b) preparing an organic phase comprising at least one radically polymerizable monomer, at least one polymerization initiator, at least one dialkyl sulfide and optionally at least one alkyl aniline; c) contacting the organic phase prepared in step b) with the aqueous phase prepared in step a) under stirring, whereby the organic phase forms droplets in the aqueous phase; and d) maintaining stirring and subjecting the assembly to conditions allowing the formation of radical species from said at least one polymerization initiator present in the organic phase, whereby the polymerization of said at least one radically polymerizable monomer is initiated and a material according to the invention is obtained.

[0039] Any stabilizing agent known in the field of suspension polymerization can be used during step a) of the preparation process according to the invention; the latter is useful for stabilizing a suspension and preventing the coalescence of organic phase droplets during steps c) and d). Typically, this stabilizing agent is chosen from the group consisting of polyvinyl alcohol, starch, gelatin, calcium phosphate, polyacrylic acid salts, gum arabic and gum tragacanth. Advantageously, the stabilizing agent used during step a) of the preparation process according to the invention is gum arabic. In the aqueous phase prepared in step a) of the process according to the invention, the stabilizing agent is present in an amount of between 0.5% and 5% by mass relative to the total volume of the aqueous phase and in particular of the order of 2% (i.e. 2% ± 0.5%) by mass relative to the total volume of the aqueous phase.

[0040] In addition, the aqueous phase used during step a) of the process according to the invention is advantageously acidic to promote the existence of the acid forms of the extracting molecules. Typically, the pH of this aqueous phase is between 0.5 and 4 and in particular of the order of 1.5 (i.e. 1.5 ± 0.5). To obtain such a pH, an acid such as hydrochloric acid is present in the aqueous phase.

[0041] The solvent of the organic phase prepared during step b) of the process according to the invention is an organic solvent chosen from polar or aliphatic organic solvents, the use of which has already been proposed for carrying out suspension polymerization. In particular, this organic solvent is chosen from the group consisting of cyclopentane, pentane, cyclohexane, n-hexane, cycloheptane, n-heptane, n-octane, isooctane, nonanes or dodecanes, linear or branched (such as n-dodecane), hexadecane, petroleum ether, benzene, n-butylbenzene, isobutylbenzene, sec-butylbenzene, tert-butylbenzene, p-cymene, triisopropylbenzene, toluene, xylene, cumenes, kerosene, hydrogenated tetrapropylene (or TPH), diethyl ether, n-butyl acetate, isopropyl myristate and mixtures thereof. More particularly, the solvent of the organic phase prepared during step b) of the process according to the invention is toluene.

[0042] In the organic phase prepared in step b) of the process according to the invention, the organic solvent is present in an amount of between 45% and 65% by mass relative to the total mass of the organic phase and in particular of the order of 55% (i.e. 55% ± 5%) by mass relative to the total mass of the organic phase.

[0043] Any radically polymerizable monomer, soluble in the organic phase and therefore only slightly or not at all soluble in the aqueous phase and from which a polymer or copolymer as previously defined can be obtained by radical polymerization, can be used during step b) of the process according to the invention. In particular, the radically polymerizable monomer present in the organic phase prepared in step b) of the process according to the invention is styrene.

[0044] In the organic phase prepared in step b) of the process according to the invention, the radically polymerizable monomer(s) is / are present in an amount of between 10% and 30% by mass relative to the total mass of the organic phase and in particular of the order of 20% (i.e. 20% ± 3%) by mass relative to the total mass of the organic phase.

[0045] In addition to the radically polymerizable monomer(s), the organic phase prepared in step b) of the process according to the invention may contain a crosslinking agent. The latter promotes the crosslinking of the (co)polymer obtained by radical polymerization of the polymerizable monomer(s) present in the organic phase. In particular, the crosslinking agent present in the organic phase prepared in step b) of the process according to the invention is a divinylbenzene.

[0046] When the organic phase prepared in step b) of the process according to the invention contains a crosslinking agent, the latter is present in an amount of between 6% and 18% by mass relative to the total mass of the organic phase and in particular of the order of 12% (i.e. 12% ± 1%) by mass relative to the total mass of the organic phase.

[0047] In addition, the organic phase prepared in step b) of the process according to the invention contains one or more chemical polymerization initiator(s). Indeed, it is also possible to act on the chemical environment of the radically polymerizable monomer(s) by adding to the organic phase one or more chemical initiator(s) whose stability is less great than that of the radically polymerizable monomer(s) under the chosen environmental conditions. This or these initiator(s) evolve(s) in an unstable form which acts on the radically polymerizable monomer(s) and generate(s) the formation of radical entities from the latter.

[0048] There are many chemical initiators for radical polymerization. Typically, within the scope of the invention, the polymerization initiator(s) is / are chosen from the group consisting of thermal initiators which, under the action of heat, dissociate into free radicals and photochemical or radiochemical initiators which are excited by radiation triggered by irradiation and produce free radicals.In particular, within the scope of the invention, the polymerization initiator(s) is / are chosen from the group consisting of halogenated initiators, compounds having very labile covalent bonds with halogens and generally corresponding to bonds established between a heteroatom, such as N, S or O, and a halogen, potassium persulfate (K2S2O8), ammonium persulfate ((NF hS^s), 2,2'-azobisisobutyronitrile (AIBN) and peroxidized compounds such as benzoyl peroxide, tert-butyl peroxide, cumyl peroxide, tert-butyl perbenzoate, tert-butyl hydroperoxide. It is obvious that the polymerization initiator(s) used in the present invention must be soluble in the organic phase prepared during step b) of the method according to the invention.More specifically, the polymerization initiator present in this organic phase is a thermal initiator and in particular 2,2'-azobisisobutyronitrile (AIBN).

[0049] In the organic phase prepared in step b) of the process according to the invention, the polymerization initiator(s) is / are present in an amount of between 0.5% and 2% by mass relative to the total mass of the organic phase and in particular of the order of 1% (i.e. 1% ± 0.2%) by mass relative to the total mass of the organic phase.

[0050] The extracting molecules present in the organic phase prepared in step b) of the process according to the invention, i.e. the dialkyl sulfide(s) and the alkyl aniline(s), are present in a total quantity of between 5% and 20% by mass relative to the total mass of the organic phase and in particular of the order of 12% (i.e. 12% ± 1%) by mass relative to the total mass of the organic phase.

[0051] During the preparation of the organic phase, the above-mentioned compounds may be added to the organic solvent all at once, in groups or one after the other. Advantageously, the above-mentioned compounds are added to the organic solvent one after the other and typically in the following order: the radically polymerizable monomer(s), the optional crosslinking agent(s), the polymerization initiator(s) and the extracting molecules with addition of the dialkyl sulfide(s) and then optionally the alkyl niline(s).

[0052] During step c) of the process according to the invention, the contact between the aqueous phase and the organic phase consists of injecting the organic phase into the aqueous phase with stirring and typically at a constant flow rate.

[0053] During step d) of the process according to the invention, the conditions allowing the formation of radical species from the polymerization initiator(s) present in the organic phase depend on this or these polymerization initiator(s). Typically, they are chosen from thermal conditions and irradiations. In particular, these conditions are thermal conditions. As a particular example, when the polymerization initiator is a thermal initiator such as AIBN, the mixture comprising the aqueous phase in which the organic phase is in the form of droplets is brought to a temperature above 50°C, in particular between 60°C and 90°C and, in particular, of the order of 80°C (i.e. 80°C ± 5°C).

[0054] During step d) of the preparation process according to the invention, a person skilled in the art will be able to choose, without inventive effort, the duration of stirring and application of the conditions allowing the formation of radical species depending on the polymerization initiator(s) present in the organic phase. As a particular example, when the polymerization initiator is a thermal initiator such as AIBN, the stirring and the thermal conditions as defined above are maintained for a duration of between 1 h and 10 h and in particular of the order of 5 h (i.e. 5 h ± 1 h).

[0055] At the end of step d) of the preparation process according to the invention, the porous beads with open porosity containing extracting molecules can be recovered by filtration and then optionally washed in an aqueous solution such as water before being used in a process for extracting palladium and / or rhodium.

[0056] The present invention finally relates to the use of a material as previously defined for extracting palladium and / or rhodium and / or silver from a solution containing it. These extractions therefore correspond to solid / liquid extractions.

[0057] In other words, the present invention relates to a method for extracting palladium and / or rhodium and / or silver from a solution containing them, consisting of bringing into contact a material as previously defined or a material prepared according to the preparation method as previously defined with a solution containing palladium and / or rhodium and / or silver, whereby a material loaded with palladium and / or rhodium and / or silver is obtained.

[0058] This contacting allows the palladium and / or rhodium and / or silver to migrate from the solution into the pores: this can be referred to as a fixation step. Thus, the material obtained at the end of this contacting is in the form of porous polymer beads with open porosity containing, in at least part of the pores of the beads, on the one hand, extracting molecules of the dialkyl sulfide type possibly associated with extracting molecules of the alkyl aniline type and, on the other hand, palladium and / or rhodium and / or silver.

[0059] The solution containing palladium and / or rhodium and / or silver typically in the form of a palladium salt and / or a rhodium salt and / or a silver salt from which it is desired to extract the palladium and / or rhodium and / or silver is typically a nitric aqueous phase containing different metallic elements among which there are palladium and / or rhodium and / or silver and at least one other metallic cation.

[0060] Any solution containing palladium and / or rhodium and / or silver may be treated by the extraction process according to the invention. This solution may comprise palladium alone, rhodium alone, silver alone, palladium and rhodium, palladium and silver, rhodium and silver or palladium, rhodium and silver.

[0061] Advantageously, the solution implemented within the framework of the extraction process according to the invention is a nitric aqueous phase resulting from the treatment of spent nuclear fuels or resulting from the leaching of ores or resulting from the treatment of waste electrical and electronic equipment. Thus, the solution implemented within the framework of the extraction method according to the invention comprises not only palladium and / or rhodium and / or silver but also at least one metallic element chosen from the group consisting of iron (Fe), copper (Cu), zinc (Zn), aluminum (Al), lead (Rb), nickel (Ni), cobalt (Co), neodymium (Nd), lanthanum (La), dysprosium (Dy), ytterbium (Yb), cerium (Ce), ruthenium (Ru), zirconium (Zr), molybdenum (Mo), rhenium (Re), technetium (Te), gadolinium (Gd), vanadium (V) and chromium (Cr).The quantity of each of these metallic elements and in particular the quantity of palladium and / or rhodium and / or silver in the aqueous nitric phase will depend on the origin of the aqueous nitric phase and in particular on the nature of the elements treated, the ore treated or the nature of the waste electrical and electronic equipment treated and, overall, on the previous treatment undergone.

[0062] Typically, waste electrical and electronic equipment is crushed, 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 a quantity of between 3 mol.L 1 and 6 mol.L 1and this, in order to dissolve metallic elements such as gold, silver, palladium and certain lanthanides. In this case, the nitric aqueous phase used in the process according to the present invention therefore corresponds to the solution obtained following such treatment, i.e. leaching water from ground electrical and electronic equipment waste.

[0063] Generally speaking and in particular with regard to the above, the palladium and / or rhodium and / or silver present in the aqueous nitric phase prior to the implementation of the extraction process are in oxidized form, i.e. in the form of Pd cations. 2+ , of Rh cations 3+ and Ag cations + These cations may possibly be present partly in the form of complexes with the nitrate, chloride or sulfate anions present in the solution.

[0064] In the extraction process according to the invention, the material as previously defined is placed in a column and the contact between the solution containing palladium and / or rhodium and / or silver 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.

[0065] 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 solution containing palladium and / or rhodium and / or silver with stirring of the whole.

[0066] 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.

[0067] In another particular embodiment, the extraction method according to the invention may, in addition, comprise a subsequent step of recovering palladium and / or rhodium and / or silver from the material loaded with palladium and / or rhodium and / or silver obtained.

[0068] 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 and / or rhodium and / or silver from the material loaded with palladium and / or rhodium and / or silver obtained.

[0069] The recovery step may correspond to a step of desorption of the palladium and / or rhodium and / or silver carried out by bringing the material loaded with palladium and / or rhodium and / or silver into contact with an aqueous solution to obtain an eluate comprising at least palladium and / or rhodium and / or silver, the latter being subsequently able to be concentrated by evaporation. This step, also referred to as the “desorption step”, makes it possible to migrate the palladium and / or rhodium and / or silver in the opposite direction, i.e. from the inside of the beads to the aqueous solution.

[0070] The aqueous solution used during the desorption step, hereinafter referred to as "desorption solution" or "elution solution", is a dilute acid solution such as a dilute solution of hydrochloric acid, nitric acid or sulfuric acid. Typically, in this aqueous solution, the acid is in a concentration of between 0.1 M and 0.5 M and in particular in a concentration of the order of 0.3 M (0.3 M ± 0.05 M).

[0071] In a particular embodiment of this desorption step, the desorption solution contains a palladium and / or rhodium and / or silver complexing agent capable of facilitating the migration into the aqueous phase of the palladium and / or rhodium and / or silver contained in the porous beads.

[0072] Advantageously, this complexing agent is chosen from the group consisting of sulfur-based compounds such as thiourea, thiocyanate or thiosulfate salts, sodium or potassium metabisulfite; chloride-based compounds such as hydrochloric acid or alkali metal chloride solutions; nitrogen compounds such as ammonia, hydrazine salts, hydroxylamine salts and mixtures thereof; ammonium chloride; chelating compounds derived from polycarboxylic acids such as oxalic acid, EDTA, HEDTA and mixtures thereof. Typically, in the desorption solution, the complexing agent is in a concentration of between 0.1 M and 1 M and in particular in a concentration of the order of 0.5 M (0.5 M ± 0.1 M).

[0073] For example, the desorption solution may contain nitric acid at a concentration of about 0.3 M and thiourea at a concentration of about 0.5 M.

[0074] The contacting during the desorption step of the process according to the invention can be carried out at a temperature above room temperature. By "room temperature" is meant a temperature of 23°C ± 5°C. Advantageously, this desorption step is carried out at a temperature between 30°C and 60°C and in particular of the order of 45°C (i.e. 45°C ± 5°C).

[0075] The contact conditions during the desorption step of the process according to the invention vary depending on whether the extraction process is a column process or a batch process.

[0076] For a column process, the desorption solution is circulated in a closed loop in the column containing the material obtained in the extraction step. This circulation can last from 30 min to 3 h and in particular around 2 h (2 h ± 15 min). For a batch process, the contacting consists of placing the material obtained in the extraction step in the desorption solution and keeping the whole thing stirred.

[0077] It is possible, following the extraction step and prior to the desorption 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 polymer beads. The washing solution used is a dilute acid solution such as a dilute solution of hydrochloric acid, nitric acid or sulfuric acid. Typically, in this aqueous solution, the acid is in a concentration of between 0.1 M and 0.5 M and in particular in a concentration of the order of 0.3 M (0.3 M ± 0.05 M). In a particular embodiment, this washing solution is a solution containing nitric acid at a concentration of the order of 0.3 M.

[0078] After the desorption step, it is possible to use the material obtained, i.e. porous beads with open porosity containing, in at least part of the pores of the beads, extracting molecules of the dialkyl sulfide type, possibly associated, combined with extracting molecules of the alkyl aniline type, in another extraction process. In other words, it is possible to use the material according to the invention in several successive fixation / washing / elution cycles. By "other extraction process", we mean both an extraction process carried out on an eluate obtained at the end of an extraction process as previously defined and an extraction process carried out on a new solution containing palladium and / or rhodium and / or silver.

[0079] As a variant of a method involving a desorption step, the recovery step may correspond to a step of calcining the material loaded with palladium and / or rhodium and / or silver obtained at the end of the fixing step. Indeed, the (co)polymer forming the porous beads with open porosity can be entirely transformed into gas by a heat treatment. After this calcination step, a solid concentrated in palladium and / or rhodium and / or silver is obtained. 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.

[0080] BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 is a diagram of the assembly used for the synthesis of the material which is the subject of the present invention.

[0082] Figure 2 is a diagram of the material of the present invention with a capsule or ball composed of a shell of polymers or copolymers containing a dialkyl sulfide optionally combined with an alkyl aniline.

[0083] Figure 3 is an optical microscope photograph of beads formed from a shell of styrene / divinylbenzene copolymers containing a mixture of dioctyl sulfide and octyl aniline.

[0084] Figure 4 is a schematic of the experimental setup used in Example 3.

[0085] Figure 5 is a schematic of the experimental setup used in Example 4.

[0086] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0087] Example 1: Preparation of the material according to the invention

[0088] The manufacture of polymer beads containing the extractant(s) is carried out in a reactor equipped with a sealed lid allowing the reactor head to be inerted by a continuous flow of nitrogen. The reactor used is made of glass and has a useful volume of 250 mL. It is equipped with four 316L steel counter-blades, a 316L steel stirring propeller, with 4 blades inclined at 45°, placed halfway up the liquid and a double jacket connected to a thermostatically controlled bath (Figure 1).

[0089] The injection of the organic phase is carried out via a chromatography capillary with an internal diameter of 0.250 mm at 60 mL / h. The reactor is filled with 211 mL of 2% gum arabic solution in water and 8.5 mL of 1M hydrochloric acid. This solution is left stirring for at least one night in the reactor under nitrogen flushing.

[0090] The organic phase is prepared by adding, one by one, the following products into a flask:

[0091] - for a material comprising only a dialkyl sulfide

[0092] 8.2 g of toluene, 2.7 g of styrene, 1.8 g of divinylbenzene (DVB), 0.13 g of 2,2'-azobisisobutyronitrile (AIBN) and 0.98 g of dioctyl sulfide.

[0093] - for a material comprising a dialkyl sulfide and an alkyl aniline

[0094] 8.2 g of toluene, 2.7 g of styrene, 1.8 g of divinyl benzene (DVB), 0.13 g of 2,2'-azobisisobutyronitrile (AIBN), 0.96 g of dioctyl sulfide and 0.75 g of octyl aniline.

[0095] The organic phase is injected into the reactor at a constant flow rate while stirring. Approximately 10 minutes after the end of the injection, external water circulation increases the temperature in the reactor to 80°C. The reactor is left stirring at this temperature for 5 hours.

[0096] The heating device is then stopped so that the reactor contents return to room temperature. The styrene / DVB copolymer beads containing dioctyl sulfide and octyl aniline that have formed in the reactor are then recovered by filtration, washed with water and can be used directly for the extraction of palladium and / or rhodium. The beads can be dried at 50°C overnight for dry storage pending use.

[0097] The formed beads have a structure as shown in Figure 2. They are spherical and have an average size of approximately 100 pm (Figure 3).

[0098] Example 2:

[0099] The experiment consisted of bringing into contact 120 ± 1 mg of polymer beads containing only dioctyl sulfide produced according to the protocol of example 1 with 2 mL of aqueous phase whose composition is provided in Table 1 below. Table 1: Elemental composition of the solutions used in the fixing step of example 2.

[0100] The experiment is carried out with 3 aqueous phases having the same elemental composition (see Table 1) but nitric acid concentrations equal to 0.9 M; 1.9 M; 3.9 M respectively. The three tubes are fixed on a stirring device rotating at 18 rpm, itself placed in an enclosure whose temperature is regulated at 25°C ± 0.1°C.

[0101] After 19 h of stirring, the contents of the tubes were centrifuged and the aqueous phase was removed and filtered using a syringe filter with a cut-off threshold of 0.45 μm. The filtrate was diluted and then analyzed by inductively coupled plasma equipped with an atomic emission spectrometer (ICP-AES). The measured concentrations are given in Table 2.

[0102] Table 2: Elemental composition of the solutions after the fixing step of example 2.

[0103] Comparison of the concentrations in Table 1 and Table 2 shows that 100% of the palladium is captured by the beads as well as more than 96% of the silver.

[0104] The beads from the extraction step are then placed in contact with 4 mL of a solution containing 0.2 mol / L of nitric acid and 0.5 mol / L of thiourea. The three tubes are again attached to a stirring device rotating at 18 rpm, itself placed in an enclosure whose temperature is regulated at 25°C ± 0.1°C.

[0105] After 3 h of stirring, the contents of the tubes are centrifuged and the aqueous phase is removed and filtered using a syringe filter with a cut-off threshold of 0.45 µm. The filtrate is diluted and then analyzed by ICP-AES. The measured concentrations are given in Table 3.

[0106] Table 3: Elemental composition of the solutions after the elution step of example 2.

[0107] The results in Table 3 show that the elution step allows 46 to 56% of the palladium fixed in the beads to be transferred into the aqueous phase.

[0108] Example 3:

[0109] A cylindrical column of 6.6 mm diameter as shown in Figure 4 is filled with 1 g of polymer beads containing dioctyl sulfide and octylaniline, produced according to the protocol of Example 1 and dried at 50°C overnight. The test carried out comprises three successive stages: fixation, washing and then elution. At each stage, a different solution is injected into the column.

[0110] At the fixation step, 48 mL of a solution containing 1.8 mol / L of nitric acid and the metal concentrations given in Table 4 below are injected into the column at a constant flow rate (20 mL / h).

[0111] Table 4: Composition of the solution introduced in the fixing step of example 3.

[0112] In the washing step, 30 mL of a 0.3M nitric acid solution is introduced at 20 mL / h into the column to remove elements that are poorly or not at all retained by the microbeads and thus purify the palladium and / or rhodium and / or silver.

[0113] In the elution step, 8 mL of an aqueous solution containing 0.3 mol / L nitric acid and 0.5 mol / L thiourea is introduced at 10 mL / h into the column to migrate the palladium and / or rhodium out of the capsules. The palladium and / or rhodium are then collected in the recovery bottle.

[0114] In the fixation step, 88% of the palladium and 72% of the silver are retained inside the beads. In the washing step, the palladium and silver remain fixed in the beads. In the elution step, 98.5% of the palladium fixed in the microbeads is recovered in the solution exiting the column. The composition of this solution is given in Table 5. Silver is also recovered.

[0115] Table 5: Composition of the solution leaving the column at the elution step of example 3.

[0116] The technique allows palladium to be concentrated by a factor of 5 compared to the solution introduced in the fixation step. The other elements are present in low concentration except silver, which is the least well separated by this technique, i.e. it is also recovered at the same time as the silver.

[0117] The test was conducted voluntarily until the palladium breakthrough to estimate the material capacity. There was no palladium leakage up to 25 mL injected. On the other hand, a large volume of solution was introduced during washing to see its impact on the silver. This test having shown that the impact of washing on silver is very low, a wash with 5 mL of solution would have been sufficient.

[0118] Example 4:

[0119] A cylindrical column of 6.6 mm diameter as shown in Figure 5 is filled with 1 g of polymer beads containing dioctyl sulfide and octylaniline, produced according to the protocol of Example 1 and dried at 50°C overnight. The test carried out comprises three successive stages: fixation, washing and then elution. At each stage, a different solution is injected into the column.

[0120] In the fixation step, 60 mL of a solution containing 1.8 mol / L nitric acid and the metal concentrations given in Table 6 below are injected into the column at a constant flow rate (60 mL / h). Just before introduction into the column, 0.15 mol / L sodium nitrite was added to the solution.

[0121] Table 6: Composition of the solution introduced in the fixation step of Example 4. As shown in Figure 5, the solution is pumped into a bottle (called a “pot” in the diagram of Figure 5) to be sent to the column and the solution leaving the column is returned to the same bottle. After 24 hours of closed-loop circulation, the measured concentrations are reported in Table 7.

[0122] Table 7: Composition of the solution after the fixing step of example 4.

[0123] The data in Table 7 show that 48% of the rhodium was fixed inside the microbeads and that the other elements were little or not retained by them.

[0124] In the washing step, 4 mL of a 0.3M nitric acid solution are introduced at 40 mL / h into the column to remove elements that are poorly or not retained by the m. In the elution step, 20 mL of an aqueous solution maintained at 45°C containing 0.3 mol / L of nitric acid and 0.5 mol / L of thiourea are placed in the pot. After 2 hours of closed-loop circulation, the rhodium concentration in the solution represents 71% of the amount of rhodium present in the beads at the end of the fixation step. The composition of this solution is given in Table 8.

[0125] Table 8: Composition of the solution after the fixing step of example 4.

[0126] The technique allows for a solution containing fewer impurities than the initial solution to be obtained in a compact device. This support can be reused.

[0127] An alternative is to calcine the microbeads after the fixation step because the copolymer can be completely converted into gas by heat treatment. After this, a rhodium-concentrated solid can be recovered.

[0128] Furthermore, if we compare the results observed for examples 3 and 4, it appears that nevertheless the chemical affinity of the material according to the invention for palladium and for silver is much higher than that for rhodium. In addition, the fixation of palladium and silver on the material is much faster than that of rhodium. Nevertheless, a joint recovery of the three metals is possible, it is only necessary to put a sufficient quantity of material. Indeed, when the solution passes, the palladium and the silver will be quickly fixed and, if the solution devoid of palladium and silver is in contact with the material, it is the rhodium which will be fixed. The palladium, the silver and the rhodium will therefore be fixed in very distinct zones of the column but will nevertheless be fixed in the same column.

[0129] References

[0130] [1] Tatarchuk et al, 2006, "Kinetics of Rhodium Extraction from Nitric Acid Solutions with a Mixture of Dihexyl Sulfide and Alkylanilinium Nitrate", Russian Journal of Inorganic Chemistry, vol. 51, pages 1977-1981.

[0131] [2] Tatarchuk et al, 2012, "Thiourea Stripping of Rhodium from Organic Phases Resulting from Extraction with a Mixture of Dialkyl Sulfide and Alkylanilinium Nitrate from Acid Nitrate-Nitrite Aqueous Solutions of Triaquatrinitrorhodium(lll)", Russian Journal of Inorganic Chemistry, vol. 57, pages 1398-1404.

Claims

CLAIMS 1. Process for preparing a material in the form of porous polymer beads with open porosity, and comprising at least one dialkyl sulfide in at least part of the pores of said polymer beads, said process comprising a suspension polymerization step.

2. Method according to claim 1, characterized in that said polymer beads have an average diameter of between 10 pm and 1 mm, in particular between 50 pm and 500 pm and, in particular of the order of 100 pm (i.e. 100 pm ± 40 pm).

3. Method according to claim 1 or 2, characterized in that the polymers and / or copolymers constituting said polymer beads are chosen from the group consisting of polymers and copolymers manufactured from styrene and polymers and copolymers manufactured from styrene and divinylbenzene.

4. Process according to any one of claims 1 to 3, characterized in that said at least one dialkyl sulfide is of general formula (C n H2n+i)2S with 6 <n<10 et, notamment, est du sulfure de dioctyle.

5. Method according to any one of claims 1 to 4, characterized in that said material further comprises at least one alkyl aniline in at least a portion of the pores of said polymer beads.

6. Process according to claim 5, characterized in that said alkyl aniline is of general formula (C n -H2n'+i)(C6H4)NH2 with 6 <n'<10 et, notamment, est de l'aniline d'octyle.

7. Preparation process according to any one of claims 1 to 6, characterized in that it comprises the steps consisting of: a) preparing an aqueous phase comprising a stabilizing agent; b) preparing an organic phase comprising at least one radically polymerizable monomer, at least one polymerization initiator, at least one dialkyl sulfide and optionally at least one alkyl aniline; c) bringing the organic phase prepared in step b) into contact with the aqueous phase prepared in step a) while stirring, whereby the organic phase forms droplets in the aqueous phase;and d) maintaining stirring and subjecting the assembly to conditions allowing the formation of radical species from said at least one polymerization initiator present in the organic phase, whereby the polymerization of said at least one radically polymerizable monomer is initiated and a material in the form of porous, open-porosity polymer beads, and comprising at least one dialkyl sulfide in at least part of the pores of said polymer beads is obtained.; 8. Preparation process according to claim 7, characterized in that said organic phase further contains a crosslinking agent.

9. Preparation process according to claim 7 or 8, characterized in that said polymerization initiator is a thermal initiator.

10. A method for extracting palladium and / or rhodium and / or silver from a solution containing them, comprising preparing a material in the form of porous, open-porosity polymer beads and comprising at least one dialkyl sulfide in at least part of the pores of said polymer beads according to a preparation method as defined in any one of claims 1 to 9; contacting a material thus prepared with a solution containing palladium and / or rhodium and / or silver, whereby a material loaded with palladium and / or rhodium and / or silver is obtained.

11. Extraction method according to claim 10, characterized in that said solution containing palladium and / or rhodium and / or silver is an aqueous nitric phase resulting from the treatment of spent nuclear fuels or resulting from the leaching of ores or resulting from the treatment of waste electrical and electronic equipment.

12. Extraction method according to claim 10 or 11, characterized in that said material is arranged in a column and the contact between the solution containing palladium and / or rhodium and / or silver and the material is carried out by passing the solution over the material in the column.

13. Extraction method according to any one of claims 10 to 12, characterized in that said method further comprises a subsequent step of recovering palladium and / or rhodium and / or silver from said material loaded with palladium and / or rhodium and / or silver obtained.

14. Extraction method according to claim 13, characterized in that said recovery step corresponds to: - either in a step of desorption of palladium and / or rhodium and / or silver carried out by bringing the material loaded with palladium and / or rhodium and / or silver into contact with an aqueous solution to obtain an eluate comprising at least palladium and / or rhodium and / or silver; and - either at a stage of calcination of the material loaded with palladium and / or rhodium and / or silver to obtain a solid concentrated in palladium and / or rhodium and / or silver.

Images