Method useful for selectively solubilizing a nickel-based layer of a multilayer stack

Abstract

Method useful for selectively solubilizing a nickel-based layer of a multilayer stack The present invention primarily relates to a method useful for selectively solubilizing a nickel-based layer (35) of a multilayer stack (5) arranged on the surface of a flat inert support (15), said stack comprising, in addition to said nickel-based layer (35), at least one copper-based layer (25), and its use for recovering the noble metal from a plating layer (46) arranged on the surface of the nickel-based layer (36) of a plated multilayer stack (6) arranged on the surface of a flat inert support (16). Figure for abstract: None

Description

Title of the invention: Method useful for selectively solubilizing a nickel-based layer of a multilayer stack Technical field

[0001] The present invention relates to the field of recycling, in particular the recovery of noble metal plating layers, in particular gold, for example, present in a smart card. More specifically, it relates to a method useful for selectively solubilizing the nickel-based layer of a multi-layer stack and a method for recovering the noble metal from a plating layer of a multi-layer stack. Prior art

[0002] Many manufactured objects are covered with a thin layer of noble metal, generally called plating, in order to improve their properties, in particular their appearance, their conduction properties, their mechanical strength, etc. Most of the time, the noble metal used is gold, or a gold-based alloy, silver, or a silver-based alloy, or other noble metals such as palladium, platinum, or rhodium, possibly in the form of alloys.

[0003] Due to the high value of these noble metals, their recovery is generally sought in order to reuse them in the manufacturing process of new objects.

[0004] By analogy, the recovery of noble metals from ores is widely documented. It is generally carried out on an industrial scale on very large quantities of ores in which the noble metals are contained in small quantities, typically of the order of a few grams of gold per ton of ore. Thus, it is known to recover the noble metal by finely grinding the ores in order to release the metal trapped in a gangue, then by obtaining the dissolution of the metal using a generally oxidizing reagent. In the case of gold, highly toxic reagents such as cyanides or highly corrosive reagents such as chlorine in an acid medium are used. However, these reagents pose significant environmental problems, which also prevent the development of new noble metal recovery units in Western countries such as France.

[0005] Furthermore, these methods are difficult to implement for the more specific treatment of industrial waste. Indeed, other metals such as iron, copper, zinc, nickel, aluminum, cobalt, or alloys such as brass are present in most industrial waste, and are also attacked by the reagent, often first. This has the effect of leading to excessive consumption of reagents and complicate the process.

[0006] For example, hydrometallurgical techniques have been developed to recover noble metal from small quantities of waste. These techniques propose dissolving the noble metals, in order to then recover them selectively. They are most often based on a first step of total dissolution of the base metals, i.e., those distinct from the noble metals, such as iron, copper, or zinc, followed by a subsequent step of dissolving the noble metals.

[0007] It is also known that gold-rich waste and waste such as fuses, particularly copper-based, can be effectively treated by pyrometallurgy. However, this technique is incompatible with certain alloys such as kovar or zamak, or with certain supports. For example, organic supports generate dioxins during pyrolysis or combustion, while inorganic supports generate unusable residues.

[0008] Thus, to the inventors' knowledge, there is no consensus on any effective process for industrial waste, despite a mass content of noble metal often much higher than that of an ore, up to a few kg of noble metal per tonne of waste. As a result, many wastes are not treated, and the noble metals they contain are lost.

[0009] Despite numerous alternatives studied, few of them allow a recovery yield of noble metals from industrial waste that is satisfactory in terms of the quantity and cost of the reagents used.

[0010] As stated above, the invention is particularly concerned with the recovery of noble metals present in plating layers such as those appearing in particular on smart cards.

[0011] Generally, these manufactured objects comprise a noble metal-based plating layer deposited on the surface of a metallic ancillary layer or most often a stack of several layers of metals distinct from a noble metal, for example iron, nickel and copper, which can be called base metals. For example, chips such as those implemented in smart cards are generally formed from a stack of several metal layers, with in general the upper layer being made of noble metal, deposited on a layer of nickel itself deposited on the support, generally formed of copper.

[0012] Among the known approaches for recovering the noble metal from a plating, some propose to recover the noble metal by dissolving the layer or all of the layers based on associated base metals. Thus, Gontijo et al. [1] describes a method for recovering the gold present on connection pins by successively dissolving all the metals present in the underlying layers, to ultimately obtain several respective solutions of all the base metals to the solute state and gold in the solid state.

[0013] However, it would also be beneficial during such an operation to be able to recover some of these base metals, which are also expensive, in a non-solubilized state, such as copper, for example. For this purpose, document WO 2020 / 245736 describes a process based on electrodissolution of nickel in order to selectively recover the plating metal and the base metal which may be copper-based. However, this process requires a specific installation, which is difficult to control because the parts to be treated must be placed in a conductive basket connected to the anode of a generator. In addition, parts on a non-conductive support such as a plastic support cannot be treated by this method.

[0014] Consequently, there is a need for a method that is simple to implement and not limited in terms of the nature of the support, making it possible to selectively solubilize a base metal, in particular nickel, when a layer thereof is implemented in a form associated with a layer of copper, so as to allow the preservation of a significant quantity of this copper in a non-solubilized form.

[0015] There is also a need to be able to take advantage of this process for the purpose of recovering noble metals present in platings combined with juxtaposed layers of nickel and copper. Statement of the invention

[0016] Thus, the present invention relates to a method useful for selectively solubilizing a nickel-based layer of a multilayer stack arranged on the surface of a flat inert support, said stack comprising, in addition to said nickel-based layer, at least one copper-based layer, one face of which is in contact with all or part of one face of said nickel-based layer and being at least partly intercalated between said inert support and said nickel-based layer, characterized in that said method comprises bringing at least said nickel-based layer and preferably said multilayer stack into contact with an aqueous treatment solution comprising at least 10% by weight of sulfuric acid relative to its total weight and at least 2% to 6% by weight of oxidizing agent relative to its total weight,to selectively solubilize nickel from said nickel-based layer and preserve copper integral with said inert support and, where appropriate, recover said support containing copper after said solubilization.

[0017] As exemplified below, the method of the invention makes it possible to solubilize at least 50% by weight of the nickel in the nickel-based layer and preserve at least 70% by weight of the copper in the copper-based layer.

[0018] The invention further relates to the use of a method according to the invention for recovering the noble metal from a plating layer arranged on the surface of the layer based on nickel of a plated multilayer stack arranged on the surface of a flat inert support.

[0019] The invention also relates to a method for recovering the noble metal from a plating layer of a plated multilayer stack arranged on the surface of a flat inert support, said stack comprising, in addition to said plating layer, at least one nickel-based layer, one face of which is in contact with all or part of one face of said plating layer and at least one copper-based layer, one face of which is in contact with all or part of one face of said nickel-based layer and being at least partly interposed between said inert support and said nickel-based layer, characterized in that said method comprises at least the steps consisting of: i) Contacting at least said nickel-based layer of said plated multilayer stack and in particular said plated multilayer stack with an aqueous treatment solution comprising at least 10% by weight of sulfuric acid relative to its total weight and at least 2% to 6% by weight of oxidizing agent relative to its total weight to selectively solubilize an effective amount of nickel from said nickel-based layer and preserve copper integral with said inert support and ii) recovering from said treatment solution said noble metal detached from said stack and, if necessary, isolating said support provided with copper.

[0020] According to an advantageous embodiment, the plating layer comprises more than 75%, in particular more than 95% by weight of a noble metal chosen from gold, silver, platinum, rhodium and palladium, preferably from gold, silver and palladium, and more preferably gold, in pure or alloy form.

[0021] In particular, the plating layer considered according to the invention appears on the surface of a plated multilayer stack of a smart card, for example a bank card, a printed circuit or a planar connector used in electronic cards.

[0022] As illustrated in the following examples, such a method proves to be particularly advantageous for separating the plating layer and recovering the copper-coated support.

[0023] Furthermore, the method and the use according to the invention can advantageously be implemented whatever the nature of the flat support, provided that it is inert.

[0024] Other characteristics, variants and advantages of the objects of the invention will become more apparent upon reading the description, examples and figures which follow, given for illustrative and non-limiting purposes of the invention.

[0025] In the rest of the text, the expressions “between ... and ...”, “ranging from ... to ...” and “varying from ... to ...” are equivalent and are intended to mean that the limits are included, unless otherwise stated.

[0026] For the sake of clarity in the drawings, the proportions of the various constituent elements multilayer stacks are not shown to scale. Brief description of the drawings

[0027] [Fig. 1] schematically illustrates a side view of a first example of a multilayer stack (5) which can be implemented in the method according to the invention.

[0028] [Fig.2] schematically illustrates a side view of a second example multilayer stack (6) which can be implemented in the methods or use according to the invention. Detailed description Multi-layer stacking

[0029] For the purposes of the invention, a first face is said to be “in contact with all or part” of a second face when at least part of the surface of the first face touches at least part of the surface of the second face.

[0030] The multilayer stack is arranged on the surface of the flat inert support. It comprises layers secured to each other and is secured to the flat inert support.

[0031] In a multilayer stack according to the invention, the nickel-based layer is in particular in contact with the copper-based layer.

[0032] As for the copper-based layer, it is at least partly interposed between the nickel-based layer and the inert support. It may or may not be in contact with the inert support. Preferably, one face of said copper-based layer is in contact with all or part of one face of said inert support.

[0033] By flat support is meant that the support comprises at least one flat face in contact with the multilayer stack, preferably with the copper layer. In particular, the support comprises at least two flat faces substantially parallel to each other. Preferably, the flat face in contact with the stack is the face of the multilayer support with the largest area.

[0034] Preferably, the multilayer stack has a planar geometry. In particular, the layers extend over the planar face of the support or of the adjacent layer by their longitudinal faces. Preferably, all the layers of a multilayer stack of planar geometry comprise planar longitudinal faces. In particular, all the layers of the multilayer stack comprise two planar longitudinal faces substantially parallel to the planar face of the support in contact with the multilayer stack.

[0035] The longitudinal faces of a layer may be connected to each other by at least lateral faces. The lateral faces of all the layers of the multilayer stack may be aligned.

[0036] The nickel-based layer may be contacted with the treatment solution by at least one surface of one of its faces. In particular, at least one surface of the side faces can be brought into contact with the treatment solution, and preferably constitutes the point of contact of the treatment solution with the nickel-based layer.

[0037] In particular, at least one, and preferably all, of the lateral faces of a multilayer stack can be viewed. Preferably, the lateral face of the nickel layer can be viewed. When all the lateral faces can be viewed, it is in particular possible to view the superposition of the different layers constituting the multilayer stack. Preferably, the lateral faces of the nickel-based layer, and more preferably the lateral faces of all the layers of the multilayer stack, are not coated with another solid material.

[0038] In particular, the multilayer stack secured to the support comprises a succession of layers superimposed and joined to each other in the following order: the inert support, the copper-based layer and the nickel-based layer.

[0039] An example of a multilayer stack 5 that can be implemented in the method according to the invention is shown in [Fig.l] and comprises a nickel-based layer 35 and a copper-based layer 25 secured to a flat inert support 15, the flat inert support 15 comprising a flat face 45 in contact with a face of the copper layer 25, and the nickel-based layer 35 comprising a lateral face 55 that can be brought into contact with the treatment solution.

[0040] According to a particular embodiment, the multilayer stack is a plated multilayer stack further comprising a plating layer. As its description indicates, the plating layer is the surface layer of the stack. The plating layer is in particular arranged on the surface of the nickel-based layer.

[0041] In a plated multilayer stack, one face of the nickel-based layer is in contact with all or part of one face of said plating layer. Preferably, the nickel layer of a plated multilayer stack is at least partly interposed between the plating layer and the copper layer.

[0042] In particular, the multi-layer stack plated integral with the support comprises a succession of superimposed and joined layers organized in the following order: the inert support, the copper-based layer, the nickel-based layer, and the plating layer.

[0043] An example of a plated multilayer stack 6 that can be implemented in the method according to the invention is shown in [Fig.2], comprising a plating layer 46, a nickel layer 36 and a copper layer 26 secured to an inert support 16, the inert support 16 comprising a flat face 46 in contact with a face of the copper layer 26, and the nickel-based layer 36 comprising a lateral face 56 which can be brought into contact with the treatment solution.

[0044] The multilayer stack, in particular the plated multilayer stack, has in particular a classic architecture of the stacks considered for chips.

[0045] For the purposes of the invention, a layer “based” on a metal is a layer comprising at least 50% by weight of said metal, in particular at least 80% by weight, more particularly at least 95% by weight of said metal, relative to the weight of said layer, or even consisting of said metal.

[0046] For the purposes of the invention, a “copper layer” or a “nickel layer” correspond respectively to a copper-based layer or a nickel-based layer.

[0047] For example, a nickel-based layer comprises more than 50% by weight of nickel, in particular more than 80% by weight, and advantageously consists of nickel. Preferably, the nickel layer comprises less than 5% by weight of iron relative to its total weight, and more preferably is free of an alloy of nickel and iron. The thickness of the nickel base layer can range from 0.1 μm to 100 μm, preferably from 1 μm to 10 μm.

[0048] A copper-based layer may comprise more than 60% by weight of copper, in particular more than 80% by weight, and advantageously consists of copper. The copper-based layer may comprise a brass-type alloy. The thickness of the copper-based layer may range from 100 μm to 10 mm, preferably from 100 μm to 1 mm.

[0049] As regards the plating layer, it is based on a noble metal, in particular a precious metal. It may comprise a noble metal chosen from gold, platinum, rhodium, palladium, and silver. In particular, it comprises more than 70%, in particular more than 80% by weight of a noble metal chosen from gold, silver, and palladium, preferably from gold and palladium, in pure or alloy form. Preferably, the plating layer comprises gold or a gold-based alloy, in particular comprises more than 90%, more particularly more than 95%, or even more than 99%, by weight of gold, and more preferably is made of gold. Examples of gold-based alloys include gold alloys containing 0.1 to 3% of cobalt or nickel. An example of a palladium-based alloy is the 20% nickel palladium-nickel alloy.

[0050] In particular, the multilayer stack is devoid of an iron or aluminum-based layer, or of a layer based on an iron or aluminum alloy. Inert support

[0051] By "inert support" is meant that the support is inert in the treatment solution, i.e. it does not react in the treatment solution.

[0052] The support may be made of plastic or wood, preferably of plastic. Among plastic materials, organic polymers including resins can be mentioned.

[0053] Preferably, it comprises more than 60%, in particular more than 75%, or even more than 90%, by weight of organic polymer, or even consists of organic polymer. It may in particular be an organic polymer chosen from PVC, polypropylene, polyethylene, epoxy resins and their mixtures, in particular polyethylene. Inorganic fillers may be incorporated into the polymer, in particular in order to modify its physical, thermal and mechanical properties. As inorganic filler, mention may be made of glass fibers, graphite and calcium carbonate. The polymer support may be flexible or rigid. Treatment solution

[0054] The treatment solution is aqueous and comprises at least 10% by weight of sulfuric acid relative to the total weight of the solution and at least 2% to 6% by weight of oxidizing agent relative to the total weight of the solution.

[0055] The treatment solution may comprise at least 20%, preferably from 20% to 30%, and more preferably from 23% to 27% by weight of sulfuric acid relative to its total weight. The sulfuric acid concentration may of course be adjusted according to the multilayer stack and the desired dissolution kinetics. For example, if the concentration is too high, the reaction may be violent, which is not desired, while if the concentration is too low, the reaction may be too slow.

[0056] In particular, the oxidizing agent is chosen from hydrogen peroxide, dioxygen, a peracid, in particular peracetic acid, a persulfate, in particular ammonium persulfate, a permanganate, in particular oxidized manganese, a potassium salt, in particular oxone, and mixtures thereof, in particular from hydrogen peroxide, dioxygen, a peracid, in particular peracetic acid, a persulfate, in particular ammonium persulfate, and mixtures thereof. The dioxygen may be introduced into the aqueous solution by bubbling, in particular continuously during contact.

[0057] Preferably, the oxidizing agent is hydrogen peroxide.

[0058] The treatment solution may comprise at most 4%, preferably from 2% to 4%, and more preferably from 2.5% to 3.5% by weight of oxidizing agent, in particular hydrogen peroxide, relative to its total weight.

[0059] The treatment solution may further comprise at least one additional acid chosen from mineral acids other than sulfuric acid, oxidizing acids and mixtures thereof at a concentration of less than or equal to 20% by weight, in particular less than or equal to 10% by weight, or even less than or equal to 5% by weight relative to the total weight of the solution. Preferably, the additional acid may be chosen from hydrochloric acid, formic acid, acetic acid, phosphoric acid, nitric acid and mixtures thereof. In particular, the treatment solution comprises less than 1% by weight of additional acid relative to the total weight of the solution.

[0060] Advantageously, the treatment solution comprises less than 5% by weight of hydrochloric acid, preferably less than 1% by weight, relative to the total weight of the treatment solution, or even is free of hydrochloric acid.

[0061] According to a preferred embodiment, the treatment solution is an aqueous solution comprising from 23% to 27% by weight of sulfuric acid relative to its total weight and from 2.5% to 3.5% by weight of hydrogen peroxide relative to its total weight. Contact stage

[0062] According to an advantageous variant, the method according to the invention consists of a single treatment step, namely the contacting step defined according to the invention. In other words, the multilayer stack has not undergone any prior chemical treatment dedicated to impacting its integrity, such as, for example, contact with another acid, in an oxidizing or non-oxidizing medium, for example hydrochloric acid.

[0063] The contact required according to the invention aims to establish contact between the treatment solution and the nickel of said stack in order to solubilize the latter.

[0064] To do this, the treatment solution is brought into contact with at least one side face of the nickel layer.

[0065] Contacting can be achieved by immersing the multilayer stack in the treatment solution, or by continuously spraying the treatment solution onto the multilayer stack.

[0066] Preferably, the contacting is carried out by immersing the multilayer stack or even the stack and support assembly in said treatment solution. The mass concentration of the stack and support assembly in the treatment solution may be at least 50 g / L, preferably at least 100 g / L, or even from 150 g / L to 250 g / L, relative to the total volume of the treatment solution.

[0067] Upon contact with the treatment solution, an alteration of its nickel-based layer is observed at the level of the multilayer stack due to the progressive solubilization of the nickel constituting it.

[0068] When the multilayer stack comprises a plating layer, this solubilization phenomenon then initiates a phenomenon of detachment of the plating superimposed on this nickel layer. It delaminates. When this reaction is carried out via the immersion of all or part of the stack in the treatment solution, the delamination phenomenon generally materializes by the appearance of flakes of the delaminated noble metal in dispersion in the treatment solution. These flakes are then easily isolated, in particular by filtration. In particular, the noble metal detached from the stack is in the form of flakes.

[0069] It is also observed at the level of the multilayer stack, as illustrated in examples, that the copper remains visible on the surface of the support. Thus, copper from said copper layer remains attached to said inert support. In particular, the majority of the copper is not dissolved by contact with the solution.

[0070] The contacting is advantageously effective for solubilizing at least 50% by weight of the nickel in the nickel-based layer and preserving at least 70% by weight of the copper in the copper-based layer. Preferably, it is effective for solubilizing at least 60% by weight of the nickel in the nickel-based layer and preserving at least 80% by weight of the copper in the copper-based layer.

[0071] The contacting can be carried out at a temperature ranging from 10°C to 60°C, preferably from 15°C to 40°C, and more preferably from 15°C to 30°C. It can be carried out for a duration of at least 1 h, preferably at least 4 h, or even ranging from 18 h to 72 h. The temperature and duration of the contacting can advantageously be adjusted to control the dissolution kinetics and the proportion of nickel dissolved during this contacting step.

[0072] According to a particular embodiment, all or part of the oxidizing agent of the treatment solution can be added gradually, in portions or continuously, in particular dropwise, during the reaction with the multilayer stack. Recovery step

[0073] After the step of bringing the multilayer stack into contact with the treatment solution, the support on which copper remains is recovered.

[0074] Preferably, the support provided with recovered copper comprises less than 40% by weight of nickel, preferably less than 20% by weight, or even is nickel-free.

[0075] Copper can be recovered from the copper-coated support.

[0076] As for the noble metal detached from a multi-layer stack comprising a plating layer, it is recovered from the treatment solution. It can be recovered by solid-liquid separation, for example by filtration, decantation, centrifugation. Preferably, the noble metal detached from the stack is recovered by filtration of said treatment solution.

[0077] The solid recovered by solid-liquid separation advantageously comprises at least 10% by weight of the noble metal, preferably at least 40% by weight, or even at least 50% by weight relative to the weight of the solid recovered.

[0078] The recovered solid may also comprise copper. In particular, it comprises less than 50% by weight, preferably less than 20% by weight of copper relative to the weight of the recovered solid.

[0079] Advantageously, the recovered solid is in the form of noble metal flakes, or noble metal sheets, preferably in the form of metal flakes noble, with the noble metal being at least 50% or even at least 90% pure.

[0080] Advantageously, the recovered solid can be directly used as a secondary raw material in existing processes, in particular without subsequent treatment. In particular, it can be refined. For example, it can be directly used to refine it and then put it in the form of a noble metal ingot. For example, when it is a gold plating layer, the recovered flakes can directly undergo refining and be put in the form of a gold ingot. Examples

[0081] The modules from the electronics industry used in the examples below are formed from the following successive layers:

[0082] - support made of polyethylene plastic material with a thickness of 0.2 mm;

[0083] - copper layer with a thickness of 100 μm comprising at least 95% by weight of copper ;

[0084] - nickel layer with a thickness of 6 μm comprising at least 95% by weight of nickel;

[0085] - gold layer with a thickness of 1 μm comprising at least 95% by weight of gold.

[0086] Recovery of gold from a plating layer according to the invention.

[0087] 13 mL of a 96% by weight aqueous sulfuric acid solution and 5 mL of a 30% by weight aqueous hydrogen peroxide solution are successively added to 20 mL of demineralized water. Demineralized water is then added to the mixture to obtain 50 mL of a 25% by weight sulfuric acid solution and 3% by weight hydrogen peroxide. This solution is introduced into a beaker containing 10 g of modules from the electronics industry as detailed above. The delamination of the gold is observed visually over time. Samples of the solution constituting the treatment bath are taken after 4 hours and 48 hours of immersion, these samples and the treated module are visually characterized, and the solid recovered by filtration of the sample is analyzed by scanning electron microscopy in X-ray dispersion mode (SEM-EDX).

[0088] Table 1 below shows the results obtained.

[0089] [Tables 1] 4h immersion 48 b. immersion. Visual observation Most of the gold is present in the form of flakes on the surface of the treatment bath Characterization of the treatment bath sample - 62% of the nickel and 16% of the copper initially present on the modules are dissolved in the solution ~ For is not detected * all of the nickel and only 17% of the copper are dissolved in the solution - gold is not detected Characterization of the solid material recovered by filtration It is formed of pure gold at approximately 50% by weight, mixed with copper Visual characterization of the support Presence of copper on the support Presence of copper on the support confirmed by SEM-EDX List of cited documents

[0090] [1] Gontijo et al., Hydrometallurgy 196 (2020) 105432.

Claims

Claims

1. A method useful for selectively solubilizing a nickel-based layer (35) of a multilayer stack (5) arranged on the surface of a flat inert support (15), said stack comprising, in addition to said nickel-based layer (35), at least one copper-based layer (25), one face of which is in contact with all or part of one face of said nickel-based layer (35) and being at least partly interposed between said inert support (15) and said nickel-based layer (35), characterized in that said method comprises bringing at least said nickel-based layer (35) and preferably said multilayer stack (5) into contact with an aqueous treatment solution comprising at least 10% by weight of sulfuric acid relative to its total weight and at least 2% to 6% by weight of oxidizing agent relative to its total weight,to selectively solubilize nickel from said nickel-based layer and preserve copper integral with said inert support (15) and, where appropriate, recover said support provided with copper after said solubilization.,

2. A method according to the preceding claim wherein the contacting is effective to solubilize at least 50% by weight of the nickel in the nickel-based layer and preserve at least 70% by weight of the copper in the copper-based layer.

3. Method according to claim 1 or 2 in which the contacting is carried out at a temperature ranging from 10°C to 60°C, preferably from 15°C to 40°C, and more preferably from 15°C to 30°C.

4. Method according to any one of the preceding claims, in which the contacting is carried out for a duration of at least 1 h, preferably at least 4 h, or even ranging from 18 h to 72 h.

5. Method according to any one of the preceding claims in which the oxidizing agent is chosen from hydrogen peroxide, dioxygen, a peracid, in particular peracetic acid, a persulfate, in particular ammonium persulfate, and mixtures thereof, preferably is hydrogen peroxide.

6. A method according to any one of the preceding claims wherein said treatment solution comprises at least 20%, preferably from 20% to 30%, and more preferably from 23% to 27% by weight of sulfuric acid relative to its total weight.

7. A method according to any preceding claim wherein said treatment solution comprises at most 4%, preferably from 2% to 4%, and more preferably from 2.5% to 3.5% by weight of oxidizing agent, in particular hydrogen peroxide, relative to its total weight.

8. Method according to any one of the preceding claims in which the contacting is carried out by immersing the stack or even the stack and support assembly in said treatment solution.

9. A method according to any preceding claim, wherein one face of said copper-based layer is in contact with all or part of one face (45) of said inert support.

10. A method according to any preceding claim wherein said support is made of plastic or wood, preferably plastic.

11. Method according to any one of the preceding claims in which said stack further comprises a plating layer arranged on the surface of the nickel-based layer, comprising more than 75%, in particular more than 95% by weight of a noble metal chosen from gold, silver, platinum, rhodium and palladium, preferably from gold, silver and palladium, and more preferably gold, in pure or alloy form.

12. Use of a method according to any one of the preceding claims for recovering the noble metal from a plating layer (46) arranged on the surface of the nickel-based layer (36) of a plated multilayer stack (6) arranged on the surface of a flat inert support (16).

13. Use according to the preceding claim in which said plating layer comprises more than 75%, in particular more than 95% by weight of a noble metal chosen from gold, silver, platinum, rhodium and palladium, preferably from gold, silver and palladium, and more preferably gold, in pure or alloy form.

14. Use according to claim 12 or 13 wherein said plating layer appears on the surface of a plated multilayer stack of a smart card, for example a bank card, a printed circuit or a planar connector used in electronic cards.

15. Method for recovering the noble metal from a plating layer (46) of a plated multilayer stack (6) arranged on the surface of a flat inert support (16), said stack comprising, in addition to said plating layer, at least one nickel-based layer (36), one face of which is in contact with all or part of one face of said layer of plating and at least one copper-based layer (26), one face of which is in contact with all or part of one face of said nickel-based layer and being at least partly interposed between said inert support (16) and said nickel-based layer (36) characterized in that said method comprises at least the steps of i) bringing at least said nickel-based layer of said plated multi-layer stack (6) and in particular said plated multi-layer stack (6) into contact with an aqueous treatment solution comprising at least 10% by weight of sulfuric acid relative to its total weight and at least 2% to 6% by weight of oxidizing agent relative to its total weight to selectively solubilize an effective amount of nickel from said nickel-based layer and preserve copper integral with said inert support (16) and ii) recovering from said treatment solution said noble metal detached from said stack and where appropriate,insulate said support with copper.,

16. A method according to claim 15 wherein the contacting i) is carried out according to any one of claims 2 to 10.

17. A method according to any one of claims 15 to 16 wherein said plating layer comprises more than 75%, in particular more than 95% by weight of a noble metal chosen from gold, silver, platinum, rhodium and palladium, preferably from gold, silver and palladium, and more preferably gold, in pure or alloy form.

18. A method according to any one of claims 15 to 17 wherein said noble metal detached from the stack is recovered by solid-liquid separation, preferably by filtration of said treatment solution.

19. Method according to any one of claims 15 to 18 in which said noble metal separated from the stack is in the form of flakes.

20. Method according to any one of claims 15 to 19 in which said plating layer appears on the surface of a plated multilayer stack of a smart card, for example a bank card, a printed circuit or a planar connector used in electronic cards.

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