Method for recovering precious metal from a plating layer

Abstract

Process for recovering a precious metal from a plating layer. This application relates to a process for recovering a precious metal present in a plating layer covering all or part of the surface of an object, comprising (i) contacting said object with an aqueous solution having a pH of 4 to 11 and comprising from 0.01 mol.L-1 to 1 mol.L-1 of dihydrogen phosphate and / or hydrogen phosphate ions, and from 0.1 mol.L-1 to 2 mol.L-1 of hypochlorite ions, such that at least a portion of the precious metal present in the plating layer dissolves in the aqueous solution, and (ii) separating the solution obtained at the end of step i) from the object, so as to recover, on the one hand, the object, and on the other hand, the aqueous solution containing the precious metal. Figure for abstract: none

Description

Title of the invention: Method for recovering a precious metal from a plating layer

[0001] The present invention relates to a method for recovering a precious metal, in particular gold, present in a plating layer of a manufactured object.

[0002] The extraction of precious metals, such as gold, contained in small quantities in ores is widely documented. It is carried out on an industrial scale on very large quantities of ore, despite a very low precious metal content (for example, a few grams of gold per ton of ore). To do this, the ores are finely crushed to release the metal trapped in a gangue, and then the metal is dissolved by an oxidizing reagent. In the case of gold, highly toxic reagents such as cyanides or highly corrosive reagents such as chlorine in an acidic environment are used. Environmental problems associated with the use of these reagents are well known and problematic insofar as they completely prevent the development of new facilities in Western countries such as France. The recent controversies surrounding the 'Montagne d'Or' project in French Guiana are a perfect illustration of this.Numerous alternatives have been studied, but none have been implemented to date due to their lower efficiency (lower yields, slow kinetics, etc.).

[0003] Manufactured goods, particularly waste electrical and electronic equipment (WEEE), constitute an alternative source of precious metals. Many of these goods are coated with a thin layer of precious metal, also known as a "plating layer." In most cases, the metal used is gold or a gold-based alloy. It can also be palladium or rhodium. The high value of these metals is now leading to consideration of their recovery for recycling in the manufacture of new goods.

[0004] However, recovering these precious metals presents several problems. The presence of other metals (iron, copper, zinc, etc.) or alloys (brass, etc.) complicates the recovery process. These other metals or alloys are also attacked, often first, leading to very high reagent consumption. Ultimately, despite a precious metal content often much higher than that of the ore (up to a few kg per ton of waste), no effective process has yet achieved widespread acceptance.

[0005] Gold-rich and fusible (copper-based) waste can be efficiently treated by pyrometallurgy. However, this technique is incompatible with the presence of certain alloys such as Kovar® or Zamak®, or certain other materials. organic supports generating dioxins during pyrolysis / combustion and / or inorganic supports generating unusable residues.

[0006] Hydrometallurgical techniques have been developed to treat small quantities of waste. They most often rely on a first step of total dissolution of the base metals (iron, copper, zinc, etc.) in order to limit the amount of reagents needed in a second step to dissolve the precious metals. However, it is known that hydrometallurgical processes are difficult to implement, notably much more complicated than the processing of gold ore.

[0007] Despite numerous alternative approaches studied, few processes available today offer a satisfactory precious metal recovery yield considering the quantity and cost of the reagents used. Consequently, much waste remains untreated, and the precious metals it contains are not recovered.

[0008] Among all precious metals, gold is the most commonly used for plating. However, being ductile, gold-based plating layers are not very wear-resistant. Furthermore, depending on the base metal used, the underlying metal can migrate into the plating layer and alter its properties. Therefore, a nickel underlayer is most often used, which provides both mechanical support to the plating layer and acts as a diffusion barrier for the base metal. However, nickel oxidizes much more easily than gold. Consequently, it is impossible, using current processes, to recover the gold without first extracting the nickel.

[0009] Thus, none of the current demetallization techniques allows for the selective recovery of precious metals present in a plating layer, without simultaneously extracting other metals present in the treated object.

[0010] The present invention therefore aims to provide a process for selectively recovering the precious metal or metals present in a plating layer of an object, without recovering any other metals that may be present.

[0011] In particular, in the case of an object comprising a layer of gold-based plating, the present invention aims to provide a process for recovering the gold, while preserving the nickel underlayer. Summary of the invention

[0012] The invention relates to a method for recovering a precious metal present in a plating layer covering all or part of the surface of an object, comprising:

[0013] (i) bringing said object into contact with an aqueous solution having a pH of 4 to 11 and comprising from 0.01 mol.L⁻¹ to 1 mol.L⁻¹ of dihydrogen phosphate and / or hydrophosphate ions, and from 0.1 mol.L⁻¹ to 2 mol.L⁻¹ of hypochlorite ions, so that at least a portion of the precious metal present in the plating layer dissolves in the aqueous solution, and

[0014] (ii) the separation of the solution obtained at the end of step i) and of the object, so as to recover, on the one hand, the object, and on the other hand, the aqueous solution comprising the precious metal.

[0015] Preferably, the precious metal is chosen from the group consisting of gold, palladium, platinum, rhodium and mixtures thereof, preferably gold.

[0016] Preferably, the plating layer covers at least 70% of the surface of the object, preferably at least 80%, more preferably at least 90%, advantageously at least 95%.

[0017] According to one embodiment, the object further has a nickel underlayer located between the surface of the object and the plating layer.

[0018] According to one embodiment, the aqueous solution further comprises at least one alkali metal chloride, preferably sodium chloride.

[0019] Preferably, the object also has an external plastic coating layer and the process includes a preliminary step of incinerating or dissolving said plastic coating layer.

[0020] Preferably, the recovery rate of the precious metal is greater than or equal to 80% by weight, preferably greater than or equal to 90% by weight, more preferably greater than or equal to 95% by weight.

[0021] Advantageously, the aqueous solution is obtained by acidification of a solution comprising hypochlorite ions, optionally followed by the introduction of dihydrogenophosphate and / or hydrogenophosphate ions.

[0022] Preferably, the acidification of the solution is carried out by the addition of phosphoric acid.

[0023] Preferably, the solution is prepared by diluting a bleach concentrate, preferably a bleach concentrate comprising at least 9.6% by weight of active chlorine. General description

[0024] The invention relates to a method for recovering a precious metal present in a layer of plating covering all or part of the surface of an object.

[0025] For the purposes of this invention, "precious metal" means a metallic chemical element of limited availability and significant economic value. The precious metal to be extracted is typically chosen from the group consisting of gold, palladium, platinum, rhodium, and mixtures thereof. Preferably, the precious metal to be extracted is gold.

[0026] The precious metal to be extracted is present in a layer of plating covering all or part of the outer surface of an object.

[0027] For the purposes of this invention, "plating layer" means a coating layer comprising at least one metallic element, in particular at least one element chosen from among the precious metals listed above.

[0028] The plating layer can be made of a single pure precious metal or a mixture of several precious metals. It can also consist of an alloy of several metals, at least one of which is a precious metal.

[0029] Preferably, the plating layer has a precious metal content greater than or equal to 30% by mass, relative to the total mass of the plating layer, more preferably greater than or equal to 50% by mass, advantageously greater than or equal to 70% by mass.

[0030] More preferably, the plating layer has a precious metal content greater than or equal to 37% by mass, relative to the total mass of the plating layer, advantageously greater than or equal to 58% by mass, more advantageously greater than or equal to 75% by mass.

[0031] Preferably, the veneer layer has a thickness greater than or equal to 10 nm, preferably greater than or equal to 40 nm.

[0032] Advantageously, the thickness of the plating layer is 50 nm to 5 pm.

[0033] For the purposes of this invention, "object" means a manufactured object resulting from human activity and comprising at least one coating layer comprising at least one precious metal as defined above. The nature of the object to be treated is not particularly limited, the only requirement being that the object comprise at least one coating layer comprising a precious metal.

[0034] The object to be processed may, for example, consist of a metal part covered with a layer of plating, such as a lid, or an electrical component, such as a contact pin. It may also be a spare part from an electrical or electronic device, in particular waste electrical and electronic equipment (WEEE). The object to be processed may also consist of a piece of jewelry, particularly one that is flat or in the form of a ring.

[0035] The process of the invention is particularly suited to the treatment of defective or end-of-life objects. In this case, it makes it possible to recover the metal or precious metals for recycling, particularly for the manufacture of new industrial objects.

[0036] Preferably, the object to be treated has at least one of its dimensions greater than or equal to 0.5 mm, preferably greater than or equal to 2 mm.

[0037] Preferably, the largest dimension of the object to be treated is less than or equal to 1 m, preferably less than or equal to 30 cm.

[0038] The method of the invention is advantageous in that it can be applied to small objects, typically to objects in which the largest dimension is less than or equal to 1cm, for example ranging from 0.5 mm to 1 cm.

[0039] By "aspect ratio" in the context of the invention, we mean the ratio of the dimension the longest dimension of the object over the shortest dimension of the object.

[0040] Preferably, the object has an aspect ratio of 1 to 1000, more preferably of 1 to 100.

[0041] By "covering all or part of the surface", for the purposes of the invention it is understood that the veneer layer covers at least part of the outer surface of the object.

[0042] Advantageously, the plating layer covers at least 70% of the outer surface of the object, preferably at least 80%, more preferably at least 90%, advantageously at least 95%.

[0043] According to one embodiment, the object to be treated also has, under the plating layer, an underlayer of a metal distinct from the precious metals defined above.

[0044] Preferably, according to this embodiment, the underlayer comprises at least one metallic element selected from the group consisting of nickel, cobalt, copper, iron, and any of their mixtures.

[0045] More preferably, the sub-layer is nickel-based or a nickel-based alloy.

[0046] The process of the invention is then advantageous in that it allows the metal or precious metals present in the plating layer to be dissolved while preserving the underlayer.

[0047] According to a particular embodiment, the object to be treated may also include a protective layer of plastic material, specifically intended to protect the precious metal plating layer. This protective layer then takes the form of an outer coating layer covering all or part of the plating layer. Such a protective layer is sometimes also referred to as a "varnish layer".

[0048] The object to be treated then has a plurality of coating layers deposited one on top of the other. In particular, the object comprises a veneer layer as defined above on which a protective layer of plastic material is deposited. Optionally, the object to be treated may also further comprise an underlayer as defined above, deposited between the object and the veneer layer.

[0049] For the purposes of this invention, "plastic material" means a polymer-based material that can be applied in a thin layer and, upon drying, forms a solid, adherent, and durable film. The plastic material can also be strengthened by chemical crosslinking, in particular by exposure to ultraviolet radiation.

[0050] Preferably, the plastic material is a synthetic varnish, more preferably an acrylic-type varnish. Examples include varnishes derived from acrylic acid and / or its esters, varnishes derived from methacrylic acid and / or its esters, and mixtures thereof.

[0051] In the case where the object is covered with a protective layer, and before proceeding To recover the metal or precious metal(s) present in the plating layer, it is necessary to carry out a preliminary step of removing the protective layer.

[0052] Thus, and depending on the object to be treated, the process according to the invention may include an optional preliminary step of removing the protective layer.

[0053] The technique for removing the protective layer is determined by a person skilled in the art using their general knowledge and with regard to the nature of the protective layer and possibly its thickness.

[0054] According to a first embodiment, the protective layer is removed by incineration.

[0055] To do this, the object to be treated is introduced into an oven in which it is heated to a temperature greater than or equal to 100°C, preferably greater than or equal to 200°C, for example ranging from 250°C to 500°C.

[0056] The precise incineration temperature depends on the chemical nature of the protective layer as well as its thickness. Its precise determination can be made using the general knowledge of a person skilled in the art.

[0057] The incineration time must also be adjusted according to the chemical nature and thickness of the protective layer. Typically, the incineration time ranges from 1 minute to 2 hours, preferably from 5 minutes to 30 minutes. The optimal incineration time is determined by a person skilled in the art, depending on the object being treated.

[0058] According to a second embodiment, the protective layer is removed by dissolution.

[0059] Preferably, according to this second embodiment, the object to be treated is brought into contact with a solution capable of dissolving the protective layer. This contact step can be carried out by immersing the object in the solution or by spraying the solution onto its surface.

[0060] The solution consists, for example, of an aqueous solution of sodium hydroxide (caustic soda) with a concentration typically ranging from 1 mol.L to 10 mol.L*. The solution may also consist of an organic solvent, in particular chosen from the group consisting of acetone, methyl ethyl ketone (butanone), aromatic solvents and mixtures thereof.

[0061] The solution is typically chosen according to the chemical nature of the coating layer. Selecting the appropriate solution falls within the general knowledge of a person skilled in the art.

[0062] The process of the invention comprises a first step of contacting the object with an aqueous solution, such that at least a portion of the precious metal or metals present in the plating layer dissolves in the aqueous solution. Then, in a second step, the aqueous solution recovered at the end of the first step is used to dissolve the object. The step is separated from the object, so as to recover, on the one hand, the object, and on the other hand, the aqueous solution containing the metal or precious metals.

[0063] The aqueous solution comprises dihydrogen phosphate ions H2PO4 and / or hydrogen phosphate ions HPO42.

[0064] In the context of the invention, the term "(di)hydrogenophosphate" is used to designate dihydrogenophosphate ions, hydrogenophosphate ions, and any mixture comprising both dihydrogenophosphate ions and hydrogenophosphate ions.

[0065] The presence of (di)hydrogen phosphate ions helps stabilize metals not belonging to the precious metal family, particularly nickel. In particular, they allow for the selective recovery of precious metals present in the plating layer. Furthermore, they limit the amount of hypochlorite ions required to dissolve the precious metal(s).

[0066] The aqueous solution typically has a pH ranging from 4 to 11. The pH value of the solution ensures the presence of (di)hydrogen phosphate ions in the aqueous solution. At a pH that is too acidic, particularly below 2, the (di)hydrogen phosphate ions are transformed into phosphoric acid (H3PO4). Conversely, at a pH that is too basic, particularly above 12, the (di)hydrogen phosphate ions are transformed into phosphate ions (PO43).

[0067] Preferably, the pH of the aqueous solution is from 4 to 8, preferably from 5 to 7.

[0068] The aqueous solution typically has a concentration of dihydrogen phosphate and / or hydrogen phosphate ions ranging from 0.01 mol.L 1 to 1 mol.L *, preferably from 0.02 mol.L 1 to 0.1 mol.L *.

[0069] According to one embodiment, the (di)hydrogenophosphate ions are essentially in the form of dihydrogenophosphate ions.

[0070] Preferably, according to this embodiment, the aqueous solution has a concentration of dihydrogen phosphate ions ranging from 0.01 mol.L 1 to 1 mol.L *, preferably from 0.02 mol.L 1 to 0.1 mol.L *.

[0071] The aqueous solution also includes hypochlorite ions to oxidize the metal or precious metal(s) present in the plating layer in order to cause their dissolution in the aqueous solution.

[0072] The aqueous solution typically has a concentration of hypochlorite ions ranging from 0.1 mol.L 1 to 2 mol.L *, preferably from 0.5 mol.L 1 to 1 mol.L *.

[0073] The aqueous solution may also further comprise at least one alkali metal chloride. The presence of chloride ions helps to stabilize the precious metals oxidized as cations in the aqueous solution.

[0074] Preferably, the alkali metal chloride is chosen from the group consisting of lithium chloride, sodium chloride, potassium chloride and one of any of their mixtures.

[0075] Advantageously, the alkali metal chloride is sodium chloride.

[0076] When present, the concentration of alkali metal chlorides in the aqueous solution will, preferably, be from 0.1 mol.L 1 to 2 mol.L *, preferably from 0.5 mol.L 1 to 1 mol.L *.

[0077] The first step (step i) of bringing the object into contact with an aqueous solution can be carried out by simply spraying the aqueous solution onto the surface of the object. It can also be carried out by soaking or immersing the object to be treated in a bath of the aqueous solution.

[0078] Preferably, the first step is carried out by soaking / immersion.

[0079] Advantageously, the first step is carried out at room temperature, preferably at a temperature ranging from 5°C to 40°C, more preferably from 10°C to 30°C, typically from 15°C to 25°C.

[0080] Preferably, the object to be treated is kept in contact with the aqueous solution for a period of at least 1 minute, typically from 1 minute to 1 hour, and advantageously from 1 minute to 10 minutes.

[0081] The process of the invention may also include a preliminary step of preparing the aqueous solution implemented in step i).

[0082] Preferably, the hypochlorite ions are introduced into the aqueous solution in the form of a solution of alkali metal hypochlorite, preferably chosen from the group consisting of sodium hypochlorite, lithium hypochlorite, potassium hypochlorite and any of their mixtures.

[0083] Advantageously, hypochlorite ions are introduced into the aqueous solution in the form of a sodium hypochlorite solution.

[0084] Even more advantageously, the hypochlorite ions are introduced in the form of a bleach solution.

[0085] The pH of the aqueous solution is fixed by adding an acid selected from the group consisting of nitric acid, citric acid, acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid, and any mixture thereof, preferably selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, and any mixture thereof. Advantageously, the pH of the aqueous solution is fixed by adding phosphoric acid.

[0086] The use of phosphoric acid is advantageous in that it allows at the same time the pH of the solution to be adjusted and the (di)hydrogen phosphate ions to be introduced.

[0087] Alternatively, the (di)hydrogen phosphate ions can be added in the form of a phosphate buffer solution. In this case, the pH of the buffer solution is adjusted by adding an acid chosen from the group consisting of nitric acid, citric acid, acetic acid, hydrochloric acid, sulfuric acid, phos- phoric acid and any of their mixtures, preferably chosen from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid and any of their mixtures.

[0088] According to a preferred embodiment, the aqueous solution is obtained by acidification of a solution comprising hypochlorite ions, optionally followed by a step of introducing (di)hydrogen phosphate ions.

[0089] Preferably, the hypochlorite ion solution is prepared by diluting a bleach concentrate.

[0090] For the purposes of this invention, "bleach concentrate" means a solution obtained by implementing the bleach process. The bleach process is known to those skilled in the art and allows the preparation of an equimolar aqueous solution of sodium chloride and sodium hypochlorite (also called "bleach") from chlorine gas and sodium hydroxide (NaOH).

[0091] Concentrated bleach with varying levels of active chlorine is commercially available.

[0092] Preferably, the aqueous solution of the invention is prepared from a bleach concentrate comprising at least 9.6% by weight of active chlorine.

[0093] The acidification of the hypochlorite ion solution is then carried out by adding an acid chosen from the group indicated above.

[0094] Preferably, acidification and the introduction of (di)hydrogenophosphate ions are carried out simultaneously by introducing hypochlorite ions of phosphoric acid into the solution.

[0095] Advantageously, phosphoric acid is introduced in the form of an aqueous solution of dilute phosphoric acid, preferably with a content ranging from 5 to 40% by weight of phosphoric acid, more preferably ranging from 10% to 20% by weight.

[0096] The use of a dilute aqueous solution of phosphoric acid is indeed preferable for the safety of operators.

[0097] Although bleach contains sodium chloride, the resulting total chloride ion content may be insufficient to stabilize the precious metal or metals in solution. In this case, the preparation of the aqueous solution includes an additional step of diluting an alkali metal chloride, in particular sodium chloride, in the hypochlorite ion solution.

[0098] In this case, the dissolution step is preferably carried out before the acidification of the solution.

[0099] The second step (step ii) of the process consists of separating the aqueous solution obtained at the end of step i) from the object, and thus recovering, on the one hand, the object, and on the other hand, the aqueous solution comprising the precious metal or metals.

[0100] Preferably, the second step of the process of the invention is carried out by filtration.

[0101] The process of the invention thus allows the recovery on one side of an aqueous solution rich in precious metals, and on the other side the object whose initial plating layer has been depleted in precious metal.

[0102] Preferably, the process of the invention makes it possible to recover at least 80% by weight of the metal or precious metals present in the plating layer of the treated object, preferably at least 90% by weight, even more preferably at least 95% by weight.

[0103] The process of the invention may further include one or more post-treatment steps of the aqueous solution rich in metal or precious metals and / or of the object depleted in precious metal.

[0104] For example, the resulting aqueous solution can be subjected to one or more purification steps to remove any impurities. It is also possible to carry out one or more (selective) precipitation steps to recover the precious metal(s) in solid form.

[0105] The treated object may itself undergo one or more additional treatment steps intended to recover one or more of the materials still present in the treated object, with a view to their recycling.

[0106] The process of the invention is based on the surprising discovery made by the inventors that the presence of dihydrogen phosphate and / or hydrogen phosphate ions during the dissolution step of the metal or precious metals makes it possible to improve the resistance to oxidation of metals other than precious metals, in particular the resistance to oxidation of nickel.

[0107] This capacity of dihydrogenophosphate and / or hydrogenophosphate ions has, according to the inventors, never been reported in the literature.

[0108] The process of the invention is thus advantageous in that it allows the metal or precious metals present in a plating layer of an object to be selectively recovered, in particular without recovering the other metals.

[0109] In particular, and in the case of an object comprising a layer of gold-based plating deposited on a nickel-based underlayer, the process of the invention makes it possible to recover the gold without the nickel.

[0110] Furthermore, the process of the invention makes it possible to considerably reduce the amount of reagent required for the recovery of precious metals. Since the presence of (di)hydrogen phosphate ions improves the oxidation resistance of metals other than precious metals, they are not oxidized during the process of the invention. Thus, all the hypochlorite ions present in the aqueous solution can be used to oxidize the precious metal or metals, thereby allowing their transfer into the aqueous solution. Examples [YES] Example 1:

[0112] A solution is prepared by dissolving 2.4 g of sodium hypochlorite and 1.5 g of sodium chloride in 100 mL of demineralized water. The solution is brought to a pH of 5 by the gradual addition, while stirring, of an aqueous solution of phosphoric acid at a concentration of 1 mol / L.

[0113] The resulting solution is used to treat metallic micro-lids with a length of 3 mm, a width of 2 mm, and a thickness of 1 mm. The micro-lids are coated with a layer of gold with a thickness of 60 nm to 100 nm. The micro-lids also have a nickel sub-layer, placed directly beneath the gold layer, with a thickness of 0.5 µm to 2 µm. The elemental composition of the micro-lids is approximated by completely dissolving a sample of the lids in aqua regia. The micro-lids then have the following composition: 50% by mass copper, 44% zinc, 5.5% nickel, and 0.1% gold, the remainder being impurities.

[0114] The resulting solution is then poured into a beaker containing 20 g of the metal micro-lids to be treated.

[0115] The assembly is placed under agitation for 6 hours.

[0116] The dissolving of gold is monitored by inductively coupled plasma emission spectrometry (ICP-OES) using a SPECTRO ARCOS spectrometer marketed by AMETEK.

[0117] The mixture is then filtered, and the residual solid is removed.

[0118] The resulting solution is analyzed by inductively coupled plasma emission spectrometry (ICP-OES). The solution has a gold concentration of 1070 mg / L. It also contains 1.23 g / L of copper and 231 mg / L of nickel.

[0119] The gold present in the plating layer is thus recovered quantitatively. A small amount of nickel and copper is also recovered in solution. These amounts correspond to 2% by weight of the nickel and 1.2% by weight of the copper present in the starting object.

[0120] Example 2:

[0121] A solution is prepared by diluting 40 mL of a 12.5% ​​(w / w) sodium hypochlorite solution in 60 mL of demineralized water. 1.5 g of sodium chloride are added to this solution. The resulting solution is stirred and its pH is adjusted to 5.8 by gradually adding approximately 3 mL of a 10% (w / w) aqueous phosphoric acid solution.

[0122] The resulting solution is used to treat chemical sensors consisting of metal cylinders embedded in a plastic support. The metal cylinders have a diameter of 8 mm and a height of 1 mm. The metal cylinders are coated with a layer of gold with a thickness of 60 nm to 80 nm. The cylinders also have a nickel underlayer, placed directly under the gold layer, with a thickness of 5 pm to 6 pm.

[0123] The elemental composition of the chemical sensors is approximated by completely dissolving a sample of the sensors in aqua regia. The sensors then have the following composition: 53% by mass iron, 6.6% nickel, 0.3% copper, and 0.1% gold, the remainder being plastic material. The resulting solution is then poured into a beaker containing 20 g of the chemical sensors.

[0124] The assembly is placed under agitation and the dissolution of the gold is monitored by inductively coupled plasma emission spectrometry (ICP-OES).

[0125] After 5 min, the gold concentration measured in the solution is 223 mg / L, indicating that all the gold present in the plating layer has been dissolved.

[0126] The mixture is then filtered, and the residual solid is recovered.

[0127] The residual solution containing gold is analyzed by inductively coupled plasma emission spectrometry (ICP-OES). The solution then exhibits a nickel concentration of 198 mg / L, corresponding to 1.5% of the amount of nickel present in the initial chemical sensors. The concentrations of copper, zinc, and iron are below the detection limit (0.02 mg / L).

[0128] Thus, only the gold surface of the chemical sensors was attacked. All the base metals (copper, iron, zinc) were not dissolved in the solution and are still present on the sensors after the end of the process.

Claims

Demands

1. A method for recovering a precious metal present in a plating layer covering at least 70% of the surface of an object having a nickel underlayer located between the surface of the object and the plating layer comprising: (i) bringing said object into contact with an aqueous solution having a pH of 4 to 11 and comprising from 0.01 mol.L 1 to 1 mol.L 1 of dihydrogenophosphate and / or hydrogenophosphate ions, and from 0.1 mol.L 1 to 2 mol.L 1 of hypochlorite ions, such that at least a part of the precious metal present in the plating layer dissolves in the aqueous solution, and (ii) separating the solution obtained at the end of step i) from the object, so as to recover, on the one hand, the object, and on the other hand, the aqueous solution comprising the precious metal; and in which the recovery rate of the precious metal is greater than or equal to 80% by weight.

2. A method according to claim 1, wherein the precious metal is chosen from the group consisting of gold, palladium, platinum, rhodium and mixtures thereof, preferably gold.

3. A method according to claim 1 or according to claim 2, wherein the plating layer covers at least 80% of the surface of the object, more preferably at least 90%, advantageously at least 95%.

4. A process according to any one of claims 1 to 3, wherein the aqueous solution is obtained by acidification of a solution comprising hypochlorite ions, optionally followed by the introduction of dihydrogen phosphate and / or hydrogen phosphate ions.

5. A method according to claim 4, wherein the acidification of the solution is carried out by the addition of phosphoric acid.

6. A process according to any one of claims 4 or 5, wherein the solution is prepared by diluting a bleach concentrate, preferably a bleach concentrate comprising at least 9.6% by weight of active chlorine.

7. A method according to any one of the preceding claims, wherein the aqueous solution further comprises at least one alkali metal chloride, preferably sodium chloride.

8. A method according to any one of the preceding claims, wherein the article further has an external coating layer made of

9. plastic and wherein the process includes a preliminary step of incinerating or dissolving said plastic coating layer. Process according to any one of the preceding claims, wherein the recovery rate of the precious metal is greater than or equal to 90% by weight, more preferably greater than or equal to 95% by weight.