Method for recovering platinum from failed platinum-containing solid residue

Abstract

The invention relates to a method for recovering platinum group metal (PGM) material comprising platinum from waste comprising spent solid residues comprising platinum and optionally palladium, said method comprising the following steps: a) subjecting said material to a leaching step in the presence of a suitable leaching agent, an oxidizing agent and an acidic medium; b) when the weight ratio of palladium to platinum in the leachate obtained in the previous step is less than about 1.1: 1, adding palladium to the leachate until the weight ratio of palladium to platinum is equal to or higher than about 1.1: 1; and c) subjecting the leachate comprising platinum and palladium to a reduction step to precipitate platinum group metal (PGM) material comprising platinum in metallic form from the leachate. The invention also relates to the use of palladium for recovering platinum from a leachate comprising platinum and palladium in a weight ratio equal to or higher than about 1.1: 1.

Description

[0001] This application claims priority to European patent application EP22382410.3 filed on April 28, 2022. Technical Field

[0002] The present invention relates to the field of recovery of platinum group metals (PGMs), and in particular to a process for recovering PGM materials containing platinum in the presence of palladium from waste solid residues containing PGMs, such as spent automotive catalysts. Background Art

[0003] Platinum group metals (PGMs) include six chemical elements, namely platinum, palladium, rhodium, ruthenium, iridium and osmium. PGMs have similar physical and chemical properties, such as high melting points, high heat resistance, and high corrosion resistance. PGMs tend to co-occur in the same deposits.

[0004] The main use of platinum and other PGMs is their catalytic properties. Therefore, PGMs have a wide range of applications in many industrial sectors, such as the automotive industry, the chemical industry and the petroleum refining industry. Therefore, PGMs have been identified by the European Commission as critical raw materials with significant economic importance and potential supply risks.

[0005] The greatest demand for platinum is in the automotive sector, particularly in three applications: automotive catalysts, sensors and spark plugs. The use of platinum in automotive catalysts accounts for more than 95% of the total automotive platinum demand. Automotive catalysts or vehicle catalytic converters (VCCs) are installed in the exhaust line of a vehicle and are used for vehicle emissions control, causing the unburned hydrocarbon, carbon monoxide and nitrogen oxide exhaust emissions to be completely burned to form less harmful carbon dioxide gas, nitrogen and water vapor.

[0006] Platinum is also required as a catalyst in both electrodes of a proton exchange membrane fuel cell (PEMFC), a device that uses hydrogen and oxygen as fuel and produces water as the main and only product, and is considered a viable alternative to fossil fuel-powered vehicles.

[0007] The reforming process using platinum catalysts is also very important in petroleum refining because it can greatly increase the octane number of naphtha and is more economical than any other refining process to produce high-octane gasoline.

[0008] Annual production of platinum is much smaller than that of gold or silver. Obtaining platinum and other PGMs is made more difficult by their scarcity on Earth and the large amounts of energy and water required in their extraction. As a result, PGMs are precious and fairly expensive. In contrast, PGM concentrations in secondary energy sources such as VCC are much higher. Recycling is therefore an attractive method of obtaining PGMs; while reducing supply risk and securing future PGM demand, recycling also significantly reduces the environmental impact of PGMs compared to primary energy sources.

[0009] Despite the urgent need to recycle PGMs, only 25% to 33% of global demand for palladium, platinum and rhodium was supplied by recycling between 2017 and 2019.

[0010] Traditionally, precious metals are recovered from ores or waste materials containing spent catalysts by pyrometallurgical processes, more specifically smelting, as these processes are effective in increasing the PGM content and thereby reducing the impurity content. However, pyrometallurgical processes are high temperature processes that require a lot of energy.

[0011] Over the past two decades, alternative technologies for pyrometallurgical processes have been evaluated with a focus on reducing environmental impact. Typically, pyrometallurgical processes are carried out using aqua regia, cyanide or chlorine in the presence of an oxidizing agent such as HCl, HNO 3 or H 2 SO 4 Hydrometallurgical dissolution of spent automotive catalysts using strong acids is the most commonly used dissolution method. Among them, cyanide leaching is widely implemented due to its high dissolution efficiency. However, it has been replaced by safer methods due to its severe toxicity and energy consumption.

[0012] Wiecka et al. (Separation and purification technology, 2021, vol. 280, 1-11) disclosed a four-stage hydrometallurgical method for recovering PGM from spent automobile converters, which includes: 1) leaching with an organic acid such as oxalic acid or lactic acid, 2) leaching with an inorganic acid from the catalyst remaining after the first stage, 3) followed by leaching with a quarternary ions or ammonium ions to extract PGM, and 4) thiourea in HCl and HNO 3 The PGM is recovered by back extraction.

[0013] In summary, the recoveries, efficiencies and purities of the proposed alternative hydrometallurgical methods are still insufficient to compete with the results obtained with the industrially used pyrometallurgical methods.

[0014] Among the reported technologies for separation and purification of PGMs from dissolution or leachate, the most used by global refineries are solvent extraction and multi-stage precipitation, regardless of the upstream process selected. In particular, solvent extraction is one of the preferred methods due to its high efficiency and high selectivity. Nevertheless, efforts continue to be made to find more environmentally friendly and safer organic extractants and organic diluents without losing the efficiency achieved.

[0015] PCT application WO2008155464 generally describes a method for recovering metals from a spent catalyst composition containing organic contaminants and catalytically active metals on a catalyst support. In the method, metals, cobalt, nickel, molybdenum, rhenium or precious metals, are leached from the spent catalyst composition by adding an ionic liquid comprising an ammonium compound and a hydrogen bond donor capable of forming hydrogen bonds with the ammonium compound.

[0016] EP3375895 discloses a method for extracting rare earth elements using a deep eutectic solvent, wherein the deep eutectic solvent consists of a mixture of a hydrogen bond acceptor (HBA) compound (A) and a hydrogen bond donor (HBD) compound (B) in a molar ratio of (A) to (B) of 1:10 to 10:1, wherein the deep eutectic solvent is capable of extracting at least 50 weight / weight % of one or more than one rare earth element contained in the starting solid product in less than 5 hours.

[0017] From what is known in the art, it can be concluded that there is still a need to find environmentally friendly, cost-effective and efficient methods for recovering PGMs, especially platinum, especially from spent platinum-containing solid residues to overcome the problems of the prior art. Summary of the invention

[0018] The inventors have developed a two-step method for recovering platinum group metal (PGM) materials containing platinum from waste materials containing PGMs, such as spent automobile catalysts, which method is capable of recovering PGMs with high recovery efficiency, particularly recovery efficiency greater than about 60%, typically concentrating Pt in solid form together with other PGMs such as Pd and Rh present in the initial material, and the PGMs have a purity greater than 85%.

[0019] The method developed by the inventors comprises a leaching step and a reduction step. The inventors have found that when the leachate contains a certain amount of palladium in addition to platinum, the amount of platinum and palladium recovered after the reduction step is significantly increased compared to the amount recovered when palladium is not present or not present in sufficient amount in the leachate. This is illustrated in the following examples.

[0020] The amount of palladium required in the leachate may have been obtained by leaching simultaneously the platinum and also the palladium still contained in the spent solid residue. Alternatively, palladium in metallic form may be added externally to the initial spent solid residue containing platinum in order to leach out a sufficient amount of palladium. Furthermore, part or all of the required amount of palladium may also be added directly to the leachate after the platinum (and other PGMs, if present) have been leached out. This makes the process very versatile and suitable from an industrial point of view, since the palladium may also be recovered after the reduction step and, if desired, may be reused again.

[0021] Furthermore, an advantage of the process of the present invention is that it can be carried out under very mild conditions, in particular using a deep eutectic solvent (DES) as the leaching agent, which is beneficial from an environmental point of view, since the deep eutectic solvent is biodegradable and can be reused and / or recycled. Furthermore, DES has a very low vapor pressure, thereby minimizing the effects of corrosion caused by gas release.

[0022] Thus, a first aspect of the present invention relates to a process for recovering a platinum group metal (PGM) material comprising platinum from a waste material comprising spent solid residues comprising platinum and optionally palladium, wherein the platinum and palladium are in metallic form, oxide form or alloy form, the process comprising the steps of:

[0023] a) subjecting the waste to a leaching step in the presence of a suitable leaching agent, an oxidizing agent and an acidic medium, thereby obtaining a leachate comprising the platinum and optionally the palladium initially contained in the waste in ionic form;

[0024] b) when the weight ratio of palladium to platinum in the leachate obtained in the previous step is lower than about 1.1:1, adding palladium in ionic form to the leachate until the weight ratio of palladium to platinum is equal to or higher than about 1.1:1; and

[0025] c) subjecting the leachate comprising platinum and palladium in a weight ratio equal to or greater than about 1.1:1 to a reduction step to precipitate a platinum group metal (PGM) material comprising platinum in metallic form from the leachate.

[0026] A second aspect of the present invention relates to the use of palladium for recovering platinum from a leachate, the leachate comprising platinum and palladium in a weight ratio equal to or greater than about 1.1: 1. If necessary, Pd can be added externally to increase the Pd / Pt ratio in the leachate and improve the recovery rate of Pt. DETAILED DESCRIPTION OF THE INVENTION

[0028] Unless otherwise specified, all terms used in this application should be understood as having their ordinary meanings known in the art. Other more specific definitions of certain terms used in this application are described below and are intended to apply throughout the specification and claims.

[0029] The term "about" or "approximately" as used herein refers to a numerical range of ±10% of a particular value. For example, the expression "about 10" or "approximately 10" includes 10±10%, ie, 9 to 11.

[0030] The term "platinum group metals (PGM)" refers to the group of the following substances: platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), and osmium (Os).

[0031] For the purposes of the present invention, the terms "metallic" and "metal" are used interchangeably to refer to substances that have metallic properties, i.e., materials that exhibit a shiny appearance when freshly prepared, polished, or fractured and that conduct electricity and heat relatively well. The term "oxide form" as used herein includes any oxide of a metal. For example, platinum in oxide form may be PtO or PtO 2 , palladium in the form of oxides can be PdO or PdO 2 . The term "alloy" as used herein refers to a substance having metallic properties and consisting of two or more chemical elements, at least one of which is a metal. The percentage of a particular metal in an alloy can be determined by standard procedures, for example, wet chemical analysis digestion of a sample followed by inductively coupled plasma (ICP) emission spectroscopy. Non-limiting examples of platinum alloys include alloys of platinum with rhodium, germanium, palladium, tin, indium, gallium, rhenium, lead, copper, gold, and the like. Non-limiting examples of palladium alloys include alloys of palladium with platinum, gold, tin, zinc, lead, nickel, rhodium, silver, and the like.

[0032] For the purposes of the present invention, the expression "leaching of metal" is understood to mean the dissolution process of extracting a metal, such as platinum, from a solid starting product, which is usually a spent catalyst, into a liquid, in particular a specific leaching agent used for extraction. The term "leaching" is also referred to herein as "extraction". There is no distinction in the use of the two terms.

[0033] As used herein, the term "leachate" refers to the liquid containing the extracted or leached metals initially contained in the solid starting product and the term "lixiviant" refers to any chemical medium capable of leaching one or more metals, particularly platinum, from the solid starting product.

[0034] The term "deep eutectic solvent" or "DES" refers to a solvent system formed by a eutectic mixture of a Lewis acid and a Lewis base or a Bronsted acid and a Bronsted base, which may contain various anionic and / or cationic species. When mixed in certain proportions, the melting point of the DES is much lower than the melting point of any of the individual components. Deep eutectic solvents have a wide liquid phase range and a low vapor pressure. DES do not react with water, are non-flammable and have relatively low cost. In addition, many of them are biocompatible and biodegradable.

[0035] The term "room temperature" used herein refers to a temperature of 15°C to 35°C, particularly a temperature of 20°C to 25°C.

[0036] As used herein, the term "wt%" (weight percent) of a component refers to the amount of an individual component relative to the total weight of the composition or, if specifically mentioned, to the total weight of another component.

[0037] For the purposes of the present invention, when palladium or platinum is not in metallic form but forms part of other compounds (for example, it is present in oxide form or in the form of a salt), the amounts of palladium or platinum referred to herein refer only to the amount of metal in these compounds as determined, for example, by inductively coupled plasma optical emission spectroscopy.

[0038] The term (C 1 -C n ) Alkyl refers to a saturated branched or straight hydrocarbon chain containing 1 to n carbon atoms and only single bonds. Non-limiting examples of alkyl include methyl, ethyl, propyl, butyl, isopropyl, 2-methylpropyl, pentyl, hexyl, octyl, decyl, etc. The alkyl referred to here may be substituted.

[0039] The term "halogen" as used herein refers to fluorine, chlorine, bromine and iodine.

[0040] As mentioned above, the present invention relates to a process for recovering platinum group metal (PGM) material comprising platinum from waste comprising waste solid residues containing platinum and optionally palladium, wherein the platinum and palladium are in metallic form, oxide form or alloy form.

[0041] According to one embodiment, optionally in combination with one or more features of the above or below embodiments, the platinum group metal (PGM) material comprises platinum and one or more species selected from palladium, ruthenium, rhodium, iridium and osmium.

[0042] The spent platinum-containing solid residue, also referred to herein as "spent solid residue", may generally be a scrapped product. For the purposes of the present invention, the term "end-of-life" (EOL) product refers to a product containing platinum in metallic form or in alloy form that has reached the end of its useful life. Examples of such EOLs that can be used in the process of the present invention include spent catalysts, in particular spent catalysts for purifying gases produced by diesel-powered engines and fuel-powered engines (autocatalysts), spent petroleum refining catalysts, spent proton exchange membrane fuel cells (PEMFCs) and spent catalysts for the chemical industry.

[0043] The terms "autocatalyst," "car catalyst," "automobile / automotive catalyst," "automobile / automotive catalytic converter," "vehicle catalytic converter (VCC)," or simply "converter" are used interchangeably herein.

[0044] Commercial automotive catalysts are divided into catalytic converters with ceramic supports (about 90% of automotive catalysts) and catalytic converters with metal supports (about 10%). The ceramic material or the metal material is usually coated with an alumina layer and is rich in PGMs, which are usually platinum, palladium and rhodium. The ceramic support of the catalytic converter usually consists of a support of cordierite (magnesium aluminum silicate), which is formed into a monolithic block with a honeycomb structure by extrusion. Waste converters can be obtained from scrap yards or automotive repair shops.

[0045] The starting materials used in the process of the present invention, also referred to herein as "waste materials", include waste solid residues comprising platinum in metallic form, oxide form or alloy form, in particular platinum in metallic form or oxide form.

[0046] In one embodiment, optionally in combination with one or more features of the above or below embodiments, the spent platinum-containing solid residue is selected from spent automotive catalysts, spent petroleum refining catalysts, spent proton exchange membrane fuel cells (PEMFCs), and spent catalysts for the chemical industry. More specifically, the spent platinum-containing solid residue is a spent motor vehicle catalyst.

[0047] Typically, the amount of platinum in the waste is at least about 3 mg, about 10 mg, 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 90 mg or about 100 mg per Kg of material. According to one embodiment, optionally in combination with one or more features of the above or below embodiments, the amount of platinum in the waste is 3 mg to 10000 mg per Kg of waste, more specifically 50 mg to 8000 mg or 150 mg to 7000 mg.

[0048] According to one embodiment, the spent solid platinum-containing residue further comprises one or more than one other PGM selected from palladium, ruthenium, rhodium, iridium and osmium. More specifically, the spent solid platinum-containing residue comprises platinum, palladium and rhodium. The spent solid platinum-containing residue may also contain other metals such as lanthanum (La), cerium (Ce), aluminum (Al), iron (Fe) or lead (Pb).

[0049] The waste material may therefore also contain palladium in metallic form, in oxide form or in alloy form, in particular palladium in metallic form or in oxide form, which is also leached out together with the platinum in the first step of the process. The palladium may be present in the spent platinum-containing solid residue in metallic form, in oxide form or in alloy form, as is customary in automotive catalysts, or may be added to the spent platinum-containing solid residue from the outside in metallic form, in oxide form or in alloy form.

[0050] Therefore, according to one embodiment, optionally in combination with one or more features of the above or below embodiments, the waste material comprises spent platinum-containing solid residue, the spent platinum-containing solid residue does not contain any palladium added from the outside, and further comprises palladium in metal form, oxide form or alloy form. More specifically, the waste material consists of spent platinum-containing solid residue, the spent platinum-containing solid residue further comprises palladium in metal form, oxide form or alloy form, in particular palladium in metal form or oxide form.

[0051] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the waste material comprises i) spent platinum-containing solid residues in the absence of palladium, and ii) palladium added from the outside in metal form, oxide form or alloy form, in particular palladium in metal form or oxide form. More specifically, the waste material consists of i) spent platinum-containing solid residues in the absence of palladium, and ii) palladium added from the outside in metal form, oxide form or alloy form, in particular palladium in metal form or oxide form.

[0052] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the scrap comprises i) a spent platinum-containing solid residue further comprising palladium in metal form, oxide form or alloy form, in particular palladium in metal form or oxide form, and ii) palladium in metal form, oxide form or alloy form, in particular palladium in metal form or oxide form, added from the outside. More specifically, the scrap consists of i) a spent platinum-containing solid residue further comprising palladium in metal form, oxide form or alloy form, in particular palladium in metal form or oxide form, and ii) palladium in metal form, oxide form or alloy form, in particular palladium in metal form or oxide form, added from the outside.

[0053] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the waste material comprises spent platinum-containing solid residues without palladium, without any palladium added from the outside. More specifically, the waste material consists of spent platinum-containing solid residues without palladium.

[0054] According to one embodiment, optionally in combination with one or more features of the above or below embodiments, when palladium is present in the waste, whether because palladium is present in spent platinum-containing solid residues and / or because palladium is added to the material from the outside, the amount of palladium in the waste is about 7 mg per Kg of material, more specifically at least about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 90 mg or about 100 mg.

[0055] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the amount of palladium in the waste is at least 7 mg to 10000 mg per Kg of material, more specifically 20 mg to 10000 mg, wherein the amount refers to palladium in metallic form or oxide form.

[0056] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the amount of platinum in the waste is at least about 3 mg, about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 90 mg or about 100 mg per Kg of material, and the amount of palladium in the waste is about 7 mg per Kg of material, more specifically at least about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 90 mg or about 100 mg.

[0057] As mentioned above, the desired amount of palladium in the leachate may have been obtained by leaching simultaneously the platinum and palladium also contained in the waste material. Thus, according to another embodiment, the amount of palladium in the spent platinum-containing solid residue of the starting material is such that the weight ratio of palladium to platinum in the leachate after the leaching step a) is equal to or higher than about 1.1:1, more specifically equal to or higher than about 1.2:1, about 1.3:1, about 1.4:1, about 1.5:1, about 1.6:1, about 1.7:1, about 1.8:1, about 1.9:1, about 2:1, about 2.1:1, about 2.2:1, about 2.3:1, about 2.4:1, about 2.5:1, about 2.6:1, about 2.7:1, about 2.8:1, about 2.9:1, about 3:1 1, about 2.7:1, about 2.8:1, about 2.9:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, about 15:1, about 20:1, about 25:1, about 30:1, about 40:1, about 50:1, about 60:1, about 70:1, about 80:1, about 90:1, about 100:1, about 110:1, about 120:1, about 130:1, about 140:1, about 150:1, and more specifically equal to or higher than about 2:1.

[0058] The efficiency of the process of the invention can be further improved by applying the leaching step to a homogeneous, particularly powdered spent solid platinum-containing residue. Thus, if necessary, the spent solid platinum-containing residue can be conveniently pretreated by methods well known in the art, including, for example, pretreatments aimed at size reduction, homogenization, surface cleaning, etc.

[0059] In one embodiment, optionally in combination with one or more features of the above or below embodiments, the spent platinum-containing solid residue has a powder form obtained by grinding and sieving using a 2 mm sieve.

[0060] Conventional physical pretreatment steps usually involve first disassembling the converter to separate the precious metal-containing support material from the precious metal-free steel shell, either by removing the shell for ceramic converters or by crushing for metal converters. This step is usually followed by a comminution step, such as crushing or grinding. Other pretreatments may also be applied, such as oxidation / reduction steps or calcination. For example, if the spent platinum-containing solid residue contains platinum or palladium in oxidized form (e.g., PtO 2 、PtO、PdO、PdO 2 ), a pre-reduction step using, for example, formic acid may be beneficial.

[0061] The method of the present invention comprises step a) subjecting the spent platinum-containing solid residue to a leaching step in the presence of a suitable leaching agent, an oxidant and an acidic medium, thereby obtaining a leachate containing platinum and optionally palladium initially contained in the platinum-containing material in ionic form.

[0062] Examples of suitable leaching agents that may be used include, but are not limited to, HCl and aqua regia (HNO 3 and HCl) and mixtures thereof, organic acids such as oxalic acid and lactic acid, inorganic bases such as NaOH, 4 Organic bases of OH, metal salts such as NaCl, halogens, cyanides and deep eutectic solvents.

[0063] Examples of oxidizing agents that may be used include, but are not limited to, hydrogen peroxide (H 2 O 2 ), NaNO 3 ,I 2 , KHSO 5 , Fenton's reagent (H 2 O 2 A mixture with iron, usually in the form of FeSO 4 in the form of ).

[0064] Furthermore, the leaching step is carried out in an acidic medium (pH <7). The acidic medium can be obtained by adding an acid, in particular one selected from sulfuric acid (H 2 SO 4 ), hydrochloric acid (HCl) and nitric acid (HNO 3 ), more specifically, for example, 37% by weight HCl or, for example, 6M HNO 3 .

[0065] According to one embodiment, optionally in combination with one or more features of the above or below embodiments, the oxidant is selected from hydrogen peroxide, NaNO 3 ,I 2 , KHSO 5 , Fenton's reagent and mixtures thereof, more specifically the oxidant is hydrogen peroxide, such as 35 wt % hydrogen peroxide.

[0066] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the acidic medium is obtained by adding an acid selected from sulfuric acid, hydrochloric acid, nitric acid and mixtures thereof, more specifically the acidic medium is hydrochloric acid.

[0067] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the leaching agent is selected from inorganic acids, organic acids, inorganic bases, organic bases, metal salts, halogens, cyanides and deep eutectic solvents, more specifically the leaching agent is a deep eutectic solvent as defined herein.

[0068] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the weight ratio of the leaching agent to the waste material is 3:1 to 50:1, more specifically 4:1 to 30:1, 5:1 to 20:1 or 6:1 to 10:1, even more specifically about 8:1.

[0069] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the weight ratio of oxidant to waste is 0.1:1 to 10:1, more specifically 0.15:1 to 7:1, 0.2:1 to 5:1 or 0.3:1 to 2:1, even more specifically about 0.75:1.

[0070] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the acidic medium is provided at a weight ratio of acid to waste of 0.1:1 to 10:1, 0.15:1 to 7:1, 0.2:1 to 5:1, or more specifically 0.3:1 to 2:1, even more specifically about 0.5:1.

[0071] When the leaching agent is a deep eutectic solvent, the leaching step may be performed at a temperature of 40°C to 130°C, more specifically 60°C to 120°C, for a time of 0.25h to 6h, more specifically 1h to 4h.

[0072] In one embodiment, optionally in combination with one or more features of the above or below embodiments, the leaching step a) is carried out in the presence of a deep eutectic solvent, particularly in a weight ratio of 3:1 to 50:1 relative to the waste, particularly in a weight ratio of 0.1:1 to 10:1 relative to the waste, and an acidic medium, and comprises the following steps: i) heating the deep eutectic solvent at a temperature of 40°C to 130°C, more particularly 60°C to 120°C; ii) adding an inorganic acid to the deep eutectic solvent and heating the mixture at a temperature of 40°C to 130°C, more particularly 60°C to 120°C; and iii) adding an oxidant and stirring for 0.25 to 6 hours, more particularly 1 to 4 hours.

[0073] Deep eutectic solvents

[0074] The deep eutectic solvent consists of a mixture of a hydrogen bond acceptor (HBA) compound (A) and a hydrogen bond donor (HBD) compound (B) as defined above.

[0075] The term "hydrogen bond acceptor" as used herein refers to a chemical structure having at least one electronegative atom, such as an oxygen atom or a nitrogen atom, which is capable of interacting with an electronegative hydrogen atom through a hydrogen bond. The term "hydrogen bond donor" as used herein refers to a chemical structure having at least one electronegative hydrogen atom, which is capable of interacting with an electronegative atom through a hydrogen bond.

[0076] In one embodiment, optionally in combination with one or more features of the above or below embodiments, the hydrogen bond acceptor compound (A) is selected from the following substances:

[0077] a) Type Cat + X - (I) wherein Cat + is selected from any ammonium ion, imidazole Ions and The cation of the ion, X - It is a Lewis base;

[0078] b) betaine or a salt thereof; and

[0079] c) Carnitine or a salt thereof.

[0080] In a more specific embodiment, optionally in combination with one or more features of the above or below embodiments, the hydrogen bond acceptor compound (A) is of formula Cat + X- (I) wherein Cat + is selected from ammonium ion, imidazole Ions and The cation of the ion, X - It is a Lewis base.

[0081] In another more specific embodiment, optionally in combination with one or more features of the above or below embodiments, in the cationic + In the present invention, the quaternary ammonium cation has the formula a), imidazole The cation has the formula b), The cation has formula c), wherein formula a), formula b) and formula c) are as follows:

[0082]

[0083] wherein each R substituent may be the same or different and is selected from H, phenyl optionally substituted with halogen, and (C 1 -C 18 ) alkyl, the substituent being selected from phenyl optionally substituted with halogen, halogen, OH, -OCO(C 1 -C 6 )alkyl, -OCOY, -COO(C 1 -C 6 )alkyl and COOH, wherein Y is halogen.

[0084] Non-limiting examples of ammonium cations include (2-hydroxyethyl)trimethylammonium (choline, Ch), ethyltrimethylammonium, ethylammonium, triethylammonium, triethylmethylammonium, benzyltriethylammonium, methylammonium, dimethylammonium, (2-chloroethyl)trimethylammonium, (2-fluoroethyl)trimethylammonium, (2-bromoethyl)trimethylammonium, ethyl(2-hydroxyethyl)dimethylammonium, benzyl(2-hydroxyethyl)dimethylammonium, bis(2-hydroxyethyl)dimethylammonium, benzyl-bis(2-hydroxyethyl)methylammonium, (2-chlorocarbonyloxyethyl)trimethylammonium, tetrabutylammonium, tetrapropylammonium, (2-hydroxyethyl)diethylammonium, benzyltrimethylammonium, benzyltriethylammonium, benzyl(2-hydroxyethyl)dimethylammonium, diethylammonium, and (2-acetoxyethyl)trimethylammonium.

[0085] Imidazole Non-limiting examples of cations include 1-ethyl-3-methylimidazole 1-Butyl-3-methylimidazole and 1-hexyl-3-methylimidazole

[0086] Non-limiting examples of cations include methyltriphenylphosphine Benzyltriphenylphosphine P-Carboxymethyl-tributyl Trihexyl(tetradecyl) Tributyl(tetradecyl) Tributyl (octyl) and tetrabutyl

[0087] In a specific embodiment, optionally in combination with one or more features of the above or below embodiments, the cation Cat in the salt of formula (I) + selected from the quaternary ammonium cations of formula a) as defined above and quaternary ammonium cations of formula c) cation; even more specifically, the cation Cat + is a quaternary ammonium cation of formula a).

[0088] In another embodiment, optionally in combination with one or more features of the above or below embodiments, in the above formula a), formula b) and formula c), more specifically in formula a) and formula c), even more specifically in formula a), each R is independently selected from H, benzyl and optionally substituted (C 1 -C 18 ) alkyl (more specifically (C 1 -C 14 )alkyl, even more specifically (C 1 -C 12 ) alkyl); more specifically, each R is independently selected from H, benzyl, and (C 1 -C 18 ) alkyl (more specifically (C 1 -C 14 )alkyl, even more specifically (C 1 -C 12 )alkyl), the substituent being selected from phenyl, halogen and OH.

[0089] In another embodiment, optionally in combination with one or more features of the above or below embodiments, in the above formula a), formula b) and formula c), more specifically in formula a) and formula c), even more specifically in formula a), each R is independently selected from benzyl; optionally substituted phenyl as defined above; and optionally substituted C as defined above. 1 -C 18 Alkyl (more specifically (C 1 -C 14 )alkyl, even more specifically (C 1 -C 12 )alkyl).

[0090] In another embodiment, optionally in combination with one or more features of the above or below embodiments, in the above formula a), formula b) and formula c), more specifically in formula a) and formula c), even more specifically in formula a), at least one R substituent is not H. In another specific embodiment, at least two R substituents are not H.

[0091] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the cation Cat in the salt of formula (I) + is selected from ethylammonium and choline. More specifically, the cation Cat + For choline.

[0092] In-style Cat + X - In the salt of (I), the anion X - Lewis base X is a Lewis base. For the purposes of the present invention, the term Lewis base refers to any nucleophilic substance that contains an unshared electron pair that can be shared with an acid. A Lewis base is therefore an electron pair donor. - Non-limiting examples of NO 3 - 、F - , Cl - Br - ,I - , BF 4 - , ClO 4 - , CN - 、SO 3 CF 3 - or COOCF 3 - .

[0093] In a specific embodiment, optionally in combination with one or more features of the above or below embodiments, the anion X in the salt of formula (I) - Selected from halides, especially Cl - or Br - .

[0094] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the salt of formula (I) Cat + X -Selected from choline chloride, choline nitrate, choline acetate, methylammonium chloride, dimethylammonium chloride, ethyl (2-hydroxyethyl) dimethylammonium chloride, ethylammonium chloride, triethylammonium chloride, triethylmethylammonium bromide, benzyltriethylammonium chloride, (2-chlorocarbonyloxyethyl) trimethylammonium chloride, (2-chloroethyl) trimethylammonium chloride, (2-fluoroethyl) trimethylammonium bromide, (2-bromoethyl) trimethylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrapropylammonium bromide, (2-hydroxyethyl)-diethylammonium chloride, benzyltrimethylammonium chloride, benzyltriethylammonium tetrafluoroborate, benzyl (2-hydroxyethyl) dimethylammonium chloride, bis (2-hydroxyethyl) dimethylammonium iodide, benzyl-bis (2-hydroxyethyl) methylammonium chloride, (2-acetoxyethyl) trimethylammonium chloride, 1-ethyl-3-methylimidazole Chloride, 1-butyl-3-methylimidazole Chloride, 1-hexyl-3-methylimidazole Chloride, Benzyltriphenyl chloride Methyltriphenylphosphine bromide Trihexyl(tetradecyl)chloride Tributyl(tetradecyl)chloride Tributyl(octyl) chloride and tetrabutyl chloride

[0095] In another embodiment, optionally in combination with one or more than one features of the above or below embodiments, the hydrogen bond acceptor compound (A) is selected from betaine or a salt thereof and carnitine or a salt thereof.

[0096] For the purposes of the present invention, betaine refers to N,N,N-trimethylglycine and carnitine refers to 3-hydroxy-4-N,N,N-trimethylaminobutyrate. In one embodiment, optionally in combination with one or more features of the above or below embodiments, carnitine is L-carnitine.

[0097] The salts of betaine and carnitine include salts with organic acids such as fumaric acid and inorganic acids such as hydrochloric acid. In one embodiment, optionally in combination with one or more than one feature of each of the above or below embodiments, the hydrogen bond acceptor compound (A) is selected from betaine, betaine hydrochloride, carnitine and carnitine hydrochloride.

[0098] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the hydrogen bond acceptor compound (A) is selected from carnitine or a salt thereof, betaine or a salt thereof, choline chloride and ethylammonium chloride. More specifically, the hydrogen bond acceptor compound (A) is choline chloride.

[0099] In the present invention, (C 1 -C 12 ) alcohol, (C1 -C 12 )aldehyde, (C 1 -C 18 ) carboxylic acid, (C 1 -C 6 )urea, (C 1 -C 12 )amide, (C 1 -C 12 ) nitrogen-containing compounds, (C 2 -C 12 ) amino acids and (C 1 -C 12 ) Sugar can be used as a hydrogen bond donor (HBD) compound (B).

[0100] Non-limiting examples of HBD include (C 1 -C 6 ) urea, for example urea, 1-(trifluoromethyl)urea, 1-methylurea, allylurea, 1,3-dimethylurea, 1,1-dimethylurea, thiourea, tetramethylurea; (C 1 -C 12 ) amides, such as N-methylacetamide, acetamide, benzamide, 2,2,2-trifluoroacetamide, salicylamide; (C 1 -C 12 ) alcohols, for example ethylene glycol, 9-anthracene methanol, ethanol, isopropanol, mannitol, 8-hydroxyquinoline, methyl and phenyl salicylate, triethanolamine, 2-chloroethanol, 4-hydroxy-3-methoxybenzaldehyde (vanillin), p-hydroxybenzaldehyde, benzyl alcohol, phenol, p-cresol, o-cresol, m-cresol, p-chlorophenol, p-aminophenol, xylenol, glycerol, ethylene glycol, triethylene glycol, 1,4-butanediol, 1,6-hexanediol; (C 1 -C 12 ) aldehydes, such as benzaldehyde; (C 2 -C 12 ) amino acids, such as glycine, alanine, lysine, and phenylalanine; (C 1 -C 12 ) sugars, such as fructose, lactose, saccharin, glucose, xylitol, sorbitol; (C 1 -C 18 ) carboxylic acids such as trifluoroacetic acid, glycolic acid, trichloroacetic acid, glycoronic acid, benzoic acid, citric acid, mandelic acid, valeric acid, tartaric acid, glutaric acid, m-nitrobenzoic acid, p-hydroxybenzoic acid, glutamic acid, m-aminobenzoic acid, malonic acid, p-toluenesulfonic acid, oxalic acid, benzoic acid, phenylacetic acid, phenylpropionic acid, itaconic acid, levulinic acid, propane-1,2,3-tricarboxylic acid (tricarballylic acid), salicylic acid, trans-cinnamic acid, 3,5-dinitrobenzoic acid, nicotinic acid, stearic acid, hippuric acid, oleic acid, terephthalic acid, adipic acid, malic acid, succinic acid, acetic acid, and lactic acid; and (C 1-C 12 ) Nitrogen-containing compounds, such as aniline, imidazole, hydroxylamine hydrochloride, diaminoethane, 1,2-diaminopropane, pyridine, benzylamine, triethylamine.

[0101] In a specific embodiment, optionally in combination with one or more features of the above or below embodiments, the hydrogen bond donor compound (B) is selected from (C 1 -C 12 ) alcohol, (C 1 -C 12 )aldehyde, (C 1 -C 18 ) carboxylic acid, (C 1 -C 12 )amide, (C 1 -C 12 ) nitrogen-containing compounds, (C 2 -C 12 ) amino acids and (C 1 -C 12 ) sugar, more specifically selected from (C 1 -C 12 ) alcohol, (C 1 -C 12 )aldehyde, (C 1 -C 18 ) carboxylic acid and (C 1 -C 12 )amide.

[0102] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the hydrogen bond donor compound (B) is (C 1 -C 6 )urea. More specifically, the hydrogen bond donor is (C 1 -C 6 ) urea selected from urea, 1-(trifluoromethyl)urea, 1-methylurea, allylurea, 1,3-dimethylurea, 1,1-dimethylurea, thiourea and tetramethylurea; even more specifically urea.

[0103] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the hydrogen bond donor compound (B) is (C 1 -C 18 ) carboxylic acid. More specifically, the hydrogen bond donor is (C 1 -C 18) carboxylic acid selected from trifluoroacetic acid, glycolic acid, trichloroacetic acid, glycoronic acid, benzoic acid, citric acid, mandelic acid, valeric acid, tartaric acid, glutaric acid, m-nitrobenzoic acid, p-hydroxybenzoic acid, glutamic acid, m-aminobenzoic acid, malonic acid, p-toluenesulfonic acid, oxalic acid, benzoic acid, phenylacetic acid, phenylpropionic acid, itaconic acid, levulinic acid, propane-1,2,3-tricarboxylic acid (tricarballylic acid), salicylic acid, trans-cinnamic acid, 3,5-dinitrobenzoic acid, nicotinic acid, stearic acid, hippuric acid, oleic acid, terephthalic acid, adipic acid, malic acid, succinic acid, acetic acid and lactic acid. Even more specifically, the hydrogen bond donor is (C 1 -C 9 ) carboxylic acid, even more specifically glycolic acid or lactic acid.

[0104] Typically, in the deep eutectic solvent, the molar ratio of (A) to (B) of the hydrogen bond acceptor compound (A) and the hydrogen bond donor (HBD) compound (B) is 1: 10 to 10: 1. In a specific embodiment, optionally in combination with one or more features of the above or below embodiments, the molar ratio of (A) to (B) of the hydrogen bond acceptor compound (A) and the hydrogen bond donor (HBD) compound (B) is 1: 5 to 5: 1, more specifically 1: 4 to 4: 1, even more specifically 1: 1 to 1: 5.

[0105] In a specific embodiment, optionally in combination with one or more features of the above or below embodiments, the molar ratio of (A) to (B) of the hydrogen bond acceptor compound (A) and the hydrogen bond donor (HBD) compound (B) is 1:1, 1:2, 1:3, 1:4 or 1:5, more specifically 1:2.

[0106] The deep eutectic solvent used in the method of the present invention may further comprise a second hydrogen bond donor (HBD) compound, thereby forming a ternary deep eutectic solvent. This component may be the same as or different from the HBD defined in the binary DES consisting of a mixture of a hydrogen bond acceptor compound (A) and a hydrogen bond donor (HBD) compound (B) as described above.

[0107] In a specific embodiment, optionally in combination with one or more than one feature of the above or below embodiments, the second hydrogen bond donor of the ternary DES is (C 1 -C 18 ) carboxylic acid. More specifically, the hydrogen bond donor is (C 1 -C 18) carboxylic acid selected from trifluoroacetic acid, glycolic acid, trichloroacetic acid, glycoronic acid, benzoic acid, citric acid, mandelic acid, valeric acid, tartaric acid, glutaric acid, m-nitrobenzoic acid, p-hydroxybenzoic acid, glutamic acid, m-aminobenzoic acid, malonic acid, p-toluenesulfonic acid, oxalic acid, benzoic acid, phenylacetic acid, phenylpropionic acid, itaconic acid, levulinic acid, propane-1,2,3-tricarboxylic acid (tricarballylic acid), salicylic acid, trans-cinnamic acid, 3,5-dinitrobenzoic acid, nicotinic acid, stearic acid, hippuric acid, oleic acid, terephthalic acid, adipic acid, malic acid, succinic acid, acetic acid and lactic acid. Even more specifically, the second hydrogen bond donor is (C 1 -C 9 ) carboxylic acid, even more specifically citric acid or malonic acid, even more specifically citric acid.

[0108] In a specific embodiment, optionally in combination with one or more features of the above or below embodiments, the second HBD in the ternary DES is present in an amount of 1 wt % to 40 wt %, more specifically 5 wt % to 20 wt %, even more specifically 10 wt % to 15 wt %, relative to the total weight of the DES.

[0109] In another specific embodiment, optionally in combination with one or more features of the above or below embodiments, the DES used in the method of the present invention is selected from the following substances, choline chloride: oxalic acid, choline chloride: lactic acid, betaine: lactic acid, choline chloride: citric acid, choline chloride: lactic acid and citric acid, choline chloride: lactic acid and oxalic acid, choline chloride: malonic acid, choline chloride: malic acid, tetrabutylammonium chloride: lactic acid, tetrabutylammonium chloride: acetic acid, tetrabutylammonium chloride: oxalic acid, betaine: oxalic acid, choline chloride: ethylene glycol, choline chloride: glycerol, choline chloride: p-toluenesulfonic acid, wherein betaine is optionally in the form of a hydrochloride salt.

[0110] In another embodiment, optionally in combination with one or more features of the above or below embodiments, the DES used in the method of the present invention is selected from the following substances:

[0111] - choline chloride:oxalic acid in molar ratios of 1:1, 1:1.5, 1:2 and 1:3

[0112] -85 wt% choline chloride:citric acid with a molar ratio of 1:1.4 + 15 wt% H 2 O

[0113] - 1:2 and 1:10 molar ratios of choline chloride:lactic acid

[0114] - Betaine:lactic acid at a molar ratio of 1:10

[0115] - Betaine: oxalic acid at a molar ratio of 1:1

[0116] -85% choline chloride:citric acid with a molar ratio of 1:1.4 + 15% H 2 O

[0117] -80% choline chloride:lactic acid and 20% citric acid in a molar ratio of 1:2

[0118] -70% choline chloride:lactic acid and 30% citric acid in a molar ratio of 1:3

[0119] - choline chloride:lactic acid and oxalic acid in molar ratios of 1:1:1, 1:1:2, 1:2:1, 1:3:1 and 1:4:2

[0120] - Choline chloride:malonic acid in a molar ratio of 1:2

[0121] - 1:1 molar ratio of choline chloride:malic acid

[0122] - choline chloride:glucose:water in a molar ratio of 5:2:5

[0123] - Tetrabutylammonium chloride:lactic acid in molar ratios of 3:2, 3:1 and 2:1

[0124] -Tetrabutylammonium chloride:acetic acid in molar ratios of 2:1, 1:1, 3:2

[0125] -Tetrabutylammonium chloride:oxalic acid in a molar ratio of 1:1

[0126] - Choline chloride:ethylene glycol in a molar ratio of 1:2

[0127] - Choline chloride: glycerol in a molar ratio of 1:2

[0128] DES are usually obtained by mixing a hydrogen bond acceptor (HBA) compound (A), in particular a quaternary ammonium salt, as defined above and a hydrogen bond donor (HBD) compound (B), such as an alcohol, a sugar or a carboxylic acid, as defined above, in the required amounts, preferably by heating at a suitable temperature, such as 60° C. to 80° C., for a suitable time, such as 0.5 hour to 4 hours.

[0129] The inventors have found that when DES is used as a leaching agent, the DES-based leachate can be reused to leach metals from fresh automotive catalyst powder, increasing the concentration of metals in the DES. This has the advantage of reducing the amount of DES required to recover a certain amount of Pt, and the increase in the Pt concentration in the leachate improves the recovery of Pt in the reduction step. Therefore, according to another embodiment, optionally in combination with one or more features of the above or below embodiments, the method for recovering platinum of the present invention comprises subjecting the material to a leaching step in the presence of a suitable leaching agent and optionally an oxidant, the leaching agent being a deep eutectic solvent, which has been previously used to recover platinum.

[0130] As described above, the method for recovering platinum of the present invention further comprises a reduction step, wherein platinum is precipitated in metallic form and thus recovered. In order to have a high recovery efficiency, it is required that the leaching solution subjected to the reduction step contains platinum and palladium in a weight ratio equal to or higher than about 1.1:1.

[0131] Thus, according to one embodiment, optionally in combination with one or more features of the above or below embodiments, step c) is performed by subjecting the leachate to a reduction step, the leachate comprising platinum and palladium in a weight ratio equal to or higher than about 1.1:1, more specifically equal to or higher than about 1.2:1, about 1.3:1, about 1.4:1, about 1.5:1, about 1.6:1, about 1.7:1, about 1.8:1, about 1.9:1, about 2:1, about 2.1:1, about 2.2:1, about 2.3:1, about 2.4:1, about 2.5:1 :1, about 2.6:1, about 2.7:1, about 2.8:1, about 2.9:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, about 15:1, about 20:1, about 25:1, about 30:1, about 40:1, about 50:1, about 60:1, about 70:1, about 80:1, about 90:1, about 100:1, about 110:1, about 120:1, about 130:1, about 140:1, about 150:1, and more specifically equal to or higher than about 2:1.

[0132] According to another embodiment, optionally in combination with one or more features of the above or below embodiments, the leachate used in step c) contains at least about 7 mg, more specifically at least about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 90 mg, about 100 mg, about 200 mg, about 300 mg, about 400 mg, about 500 mg, about 600 mg, about 700 mg, about 800 mg or about 900 mg of palladium per Kg of leachate, even more specifically, the leachate used in step c) contains about 820 mg of palladium per Kg of leachate.

[0133] According to another embodiment, optionally in combination with one or more features of the above or below embodiments, the leachate used in step c) contains at least about 1.4 mg, more specifically at least about 2 mg, about 5 mg, about 10 mg, about 15 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 85 mg, about 90 mg, about 95 mg, about 100 mg, about 110 mg, about 120 mg, about 130 mg, about 140 mg, about 150 mg, about 160 mg, about 170 mg, about 180 mg, about 190 mg, about 200 mg, about 210 mg, about 220 mg, about 230 mg, about 240 mg, about 250 mg, about 260 mg, about 270 mg, about 280 mg, about 290 mg, about 300 mg, about 310 mg, about 320 mg, about 330 mg, about 340 mg, about 350 mg, about 360 mg or about 370 mg of palladium per Kg of leachate.

[0134] According to another more specific embodiment, optionally in combination with one or more features of the above or following embodiments, when the concentration of platinum in the leachate is lower than about 40 mg / Kg of leachate, more specifically about 38 mg / Kg, about 35 mg / Kg, about 30 mg / Kg, about 25 mg / Kg, about 20 mg / Kg, about 15 mg / Kg, about 10 mg / Kg or about 5 mg / Kg; the weight ratio of palladium to platinum in the leachate is equal to or higher than about 2:1, about 2.1:1, about 2.2:1, about 2.3:1, about 2.4:1, about 2.5:1. 1, about 2.6:1, about 2.7:1, about 2.8:1, about 2.9:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, about 15:1, about 17:1, about 20:1, about 25:1, about 30:1, about 40:1, about 50:1, about 60:1, about 70:1, about 80:1, about 90:1, about 100:1, about 110:1, about 120:1, about 130:1, about 140:1 or about 150:1, more specifically equal to or higher than about 17:1.

[0135] According to another more specific embodiment, optionally in combination with one or more features of the above or below embodiments, when the concentration of platinum in the leachate is equal to or higher than about 40 mg / Kg leachate and lower than about 80 mg / K leachate, more specifically about 40 mg / Kg, about 45 mg / Kg, about 50 mg / Kg, about 55 mg / Kg, about 60 mg / Kg, about 65 mg / Kg, about 70 mg / Kg, about 75 mg / Kg or about 78 mg / Kg; the weight ratio of palladium to platinum in the leachate is equal to or higher than 1.8:1, about 1.9:1, about 2 ... .2:1, about 2.3:1, about 2.4:1, about 2.5:1, about 2.6:1, about 2.7:1, about 2.8:1, about 2.9:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, about 15:1, about 20:1, about 25:1, about 30:1, about 40:1, about 50:1, about 60:1, about 70:1, about 80:1, about 90:1, about 100:1, about 110:1, about 120:1, about 130:1, about 140:1 or about 150:1, more specifically equal to or higher than about 8:1.

[0136] According to another more specific embodiment, optionally in combination with one or more features of the above or below embodiments, when the concentration of platinum in the leachate is equal to or higher than about 80 mg / Kg of leachate, more specifically about 80 mg / Kg, about 85 mg / Kg, about 90 mg / Kg, about 95 mg / Kg, about 100 mg / Kg, about 110 mg / Kg, about 120 mg / Kg, about 130 mg / Kg, about 140 mg / Kg, about 150 mg / Kg, about 160 mg / Kg g / Kg, about 170mg / Kg, about 180mg / Kg, about 190mg / Kg, about 200mg / Kg, about 210mg / Kg, about 220mg / Kg, about 230mg / Kg, about 240mg / Kg, about 250mg / Kg, about 260mg / Kg, about 270mg / Kg, about 280mg / Kg, about 290mg / Kg, about 300mg / Kg, about 310mg / Kg, about 320mg / Kg, about 330mg / Kg g, about 340 mg / Kg, about 350 mg / Kg, about 360 mg / Kg or about 370 mg / Kg; the weight ratio of palladium to platinum in the leachate is equal to or higher than about 1.1:1, about 1.2:1, about 1.3:1, about 1.4:1, about 1.5:1, about 1.6:1, about 1.7:1, about 1.8:1, about 1.9:1, about 2:1, about 2.1:1, about 2.2:1, about 2.3:1, about 2.4:1, about 2.5:1, about 2.6:1, about 2.7:1 1, about 2.8:1, about 2.9:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, about 15:1, about 20:1, about 25:1, about 30:1, about 40:1, about 50:1, about 60:1, about 70:1, about 80:1, about 90:1, about 100:1, about 110:1, about 120:1, about 130:1, about 140:1 or about 150:1, more specifically equal to or higher than about 2:1.

[0137] When the weight ratio of palladium to platinum in the leachate obtained in the leaching step is equal to or higher than about 1.1:1, the reduction step can be directly performed, as described in detail herein.

[0138] Alternatively, when the weight ratio of palladium to platinum in the leachate obtained in the leaching step is low, in particular equal to or lower than about 0.9:1, the scheme of the present invention further comprises the step of adding palladium in ionic form until the weight ratio of palladium to platinum in the leachate is equal to or higher than about 1.1:1.

[0139] According to one embodiment, optionally in combination with one or more features of the above or below embodiments, the method of the present invention comprises a step b) of adding ionic palladium to the leachate until the ratio of palladium to platinum is equal to or greater than about 1.1:1; more specifically, the ionic palladium added to the leachate is a palladium salt, even more specifically a salt soluble in the leaching agent. Examples of palladium salts that can be used include, but are not limited to, PdCl 2 、Pd(OAc) 2 、Pd(NO 3 ) 2 、Pd(SO 4 ) 2 、Pd(NH 4 )Cl 2 、[Pd(NH 3 ) 4 ]Cl 2 , bis(acetylacetonate)palladium, etc.

[0140] The reduction step c) can be carried out by methods known in the art. In the case of using a deep eutectic solvent as a leaching agent, it is not necessary to add a reducing agent, especially when the DES is selected from the following substances, choline chloride: oxalic acid; choline chloride: lactic acid, betaine: lactic acid, choline chloride: citric acid, choline chloride: lactic acid and citric acid, choline chloride: lactic acid and oxalic acid, choline chloride: malonic acid, choline chloride: malic acid, tetrabutylammonium chloride: lactic acid, tetrabutylammonium chloride: acetic acid, tetrabutylammonium chloride: oxalic acid, betaine: oxalic acid, choline chloride: ethylene glycol, choline chloride: glycerol, choline chloride: p-toluenesulfonic acid, wherein betaine is optionally in the form of a hydrochloride. Otherwise, a reducing agent can be added.

[0141] In one embodiment, optionally in combination with one or more features of the above or below embodiments, the reducing step c) is performed by heating the leachate at a temperature of 100° C. to 120° C. for 1 to 8 hours.

[0142] Typically, platinum and palladium are recovered in solid form together with other PGMs that may be present in the starting material. Further separation steps and / or purification steps may be performed. Therefore, according to one embodiment, optionally in combination with one or more features of the above or below embodiments, the method of the present invention further comprises the following steps: d) separating the platinum group metal (PGM) material containing platinum in metallic form obtained in the previous step from the solvent, for example by using conventional filtration systems such as cartridge filters, filter presses, centrifugation, etc., e) optionally washing the precipitate, for example using H 2 O, and f) optionally drying the platinum group metal (PGM) material, for example, by using an oven to remove moisture from the solid. Generally, the drying step can be performed at any temperature above room temperature; the lower the temperature, the longer the time required.

[0143] Furthermore, the method may further comprise the step g) of separating platinum from the platinum group metal (PGM) material.

[0144] As described above, the method of the present invention can provide a platinum recovery efficiency of at least 60 wt / wt%. Therefore, according to a specific embodiment, optionally in combination with one or more features of the above or below embodiments, the method of the present invention uses a deep eutectic solvent to extract platinum of at least about 60 wt / wt%, about 70 wt / wt%, about 80 wt / wt%, about 85 wt / wt%, about 90 wt / wt%, about 95 wt / wt% or about 97 wt / wt%.

[0145] The percentage of extraction as defined above, also referred to herein as the efficiency or percentage of platinum recovery, can be determined by comparing i) the content of one or more platinum group metals (PGM) which have dissolved in the deep eutectic solvent after the starting product containing the PGMs has been contacted with the deep eutectic solvent (step a) for the above specified time, and ii) the content of the same PGM in the starting solid product which has been contacted with the DES in step a) of the process.

[0146] The above-mentioned content i) and content ii) can be measured by using inductively coupled plasma optical emission spectroscopy (ICP-MS), which is a well-known technique in the art. The technician will know how to perform the above-mentioned measurements. For example, these measurements can be performed under the conditions shown in the examples by using an ICP-MS spectrometer such as the Agilent 7900ICP / MS.

[0147] The extraction percentage or efficiency of the method of the present invention can be calculated by the following formula:

[0148] Efficiency = [(x*y) / 1000000] / [(z*w) / 1000000]*100

[0149] Where x is the concentration of each PGM in DES measured by ICP-MS (in ppm); y is the amount of DES sample used in the experiment, in g; z is the concentration of each PGM in the starting solid measured by ICP-MS (in ppm); w is the amount of starting solid sample used in the experiment, in g.

[0150] Throughout the specification and claims, the word "comprising" and its variants are not intended to exclude other technical features, additives, components or steps. In addition, the word "comprising" also includes the situation of "consisting of ...". Additional objects, advantages and features of the present invention will become obvious to those skilled in the art after reviewing the specification, or can be learned through the practice of the present invention. The following examples are provided by way of illustration and are not intended to limit the present invention. In addition, the present invention covers all possible combinations of the specific and preferred embodiments described herein. Example

[0151] Inductively Coupled Plasma Optical Emission Spectroscopy (ICP / MS)

[0152] The equipment used in the following experiments is Agilent 7900ICP / MS. The mass numbers used for each element are: 195Ptnm and 105Pd use 205Tl and 133C as internal standards. The measurement parameters are: repeated reading time: 10s; instrument stabilization delay 10s; repetition: 5; power 1.25kW; plasma flow rate 15L / min; auxiliary gas flow rate 1.5; nebulizer pressure 190kPa / Calibration parameters: curve type: linear, correlation coefficient limit: 0.999, maximum error: 10.

[0153]

[0154] The calibration standards used in a matrix of 5% hydrochloric acid are as follows:

[0155] Table 1

[0156]

[0157] The standard samples were prepared from the following substances: a Pt standard solution with an ICP concentration of 1000 mg / L (CPAchem); a Pd standard solution with an ICP concentration of 1000 mg / L (CPAchem).

[0158] Verify standard sample (maximum error: 10%).

[0159] Table 2

[0160] VS Pt(μg / L) 1 Pd(μg / L) 1

[0161] The standard samples used for the above verification are commercially available (6-component solutions: 100 mg / L each of Au, Ir, Pd, Pt, Rh, Ru, CPAchem).

[0162] Determination of palladium and platinum content in samples

[0163] 1) In the starting material or in the precipitated solid after reduction

[0164] The solid material was dissolved by microwave-assisted acid digestion using Milestone Ethos Up. In the first step, a representative sample of about 0.1 g was digested by microwave heating in 2 mL of concentrated nitric acid (65%), 6 mL of hydrochloric acid (37%), and 2 mL of hydrofluoric acid (48%). The sample and acid mixture were placed in an inert PTFE-sealed microwave container. The temperature profile was set to reach 230°C ± 10°C within 20 minutes. And continued at 230°C ± 10°C for 15 minutes. Afterwards, in the second step, 25 mL of 4% boric acid was added to complex the excess HF. The temperature profile was set to reach 180°C ± 10°C within 20 minutes and continued at 180°C ± 10°C for 15 minutes. After cooling, the contents of the container were diluted to 50 mL and analyzed by ICP-MS. The solution was diluted with 5% HCl to be within the calibration range.

[0165] 2) From the leachate solution

[0166] 0.5 g of the solution was diluted to 25 mL with 5% HCl and then diluted with 5% HCl to bring it within the calibration range before analysis by ICP-MS.

[0167] Conventional method for preparing DES

[0168] A sufficient amount of hydrogen bond donor and one or more hydrogen bond acceptors are placed in the same container and magnetically stirred at 80° C. for 2 hours. The initial solid mixture becomes a transparent and uniform fluid, i.e., a deep eutectic solvent.

[0169] According to the above conventional method, the following DES was obtained: choline chloride / oxalic acid 1:1.5.

[0170] Example 1 - Steps for recovering PGMs

[0171] Starting Materials

[0172] The palladium and platinum containing starting materials were automotive catalysts in powder form from scrap light-duty vehicles and scrap heavy-duty vehicles, with a particle size distribution and composition as shown in Table 3 below:

[0173] Table 3

[0174]

[0175] Step 1: Leaching of PGMs

[0176] Platinum group metals (PGMs) in different autocatalyst samples were leached using a deep eutectic solvent (DES) formed by mixing choline chloride / oxalic acid (DES) in a molar ratio of 1:1.5 as described above. First, the DES was heated at 60°C to facilitate its transfer from the storage container to the leaching reactor. The weight ratio of DES / autocatalyst in the reactor was 8:1. Next, 37 wt% HCl was added to the DES in a weight ratio of 0.5:1 acid / autocatalyst in the reactor. The resulting solution was stirred and heated to 80°C, and then the autocatalyst powder was added to the DES in the above-mentioned amount (DES / solid weight ratio was 8:1). Finally, 35 wt% HCl was added to the DES. 2 O 2 Slowly add to the mixture until the weight ratio of hydrogen peroxide / autocatalyst reaches 0.75:1. Once all the components are in the reactor, maintain a temperature of 80°C and stir well to keep the powder suspended for 3 hours to complete the leaching step. After this period, the solution is filtered at the same temperature to separate the undissolved solids from the leachate. The separated solids are washed with fresh (DES / HCl) leachate at 80°C. The washing solution is then added to the resulting leachate. The leached amount and recovery efficiency of PGM are determined using inductively coupled plasma.

[0177] Step 2: Reduction of PGMs in the leachate

[0178] After filtering the leachate, it was poured into the reactor again and the solution temperature was raised to 120°C for 4 hours. After this period, the solution was filtered before cooling it. The resulting solid (reduced PGM) was washed with water at room temperature to obtain a PGM concentrate with a purity of 80%. The amount of PGM precipitated and the purity of the solid were determined using inductively coupled plasma.

[0179] Step 3: Purification of reduced PGMs (optional)

[0180] The resulting PGM concentrate was further washed with a dilute sulfuric acid solution (0.1M to 0.5M) for at least 15 minutes, followed by room temperature washing and finally drying. The final washing step yielded a concentrate containing about 95% metallic PGMs. The purity of the solid was determined using inductively coupled plasma.

[0181] result

[0182] Table 4 below shows the concentrations of Pd and Pt in the leachate after the leaching step (initial leachate); the Pd / Pt ratio in the leachate after the leaching step; the concentrations of Pd and Pt in the leachate after the reduction step (final leachate); and the Pt recovered after the reduction step for each sample.

[0183] The percentage of recovery or efficiency is calculated by the following formula:

[0184] Efficiency = [(x*y) / 1000000] / [(z*w) / 1000000]*100

[0185] Where x is the concentration of each PGM in DES measured by ICP-MS (in ppm); y is the amount of DES sample used in the experiment, in g; z is the concentration of each PGM in the starting solid measured by ICP-MS (in ppm); w is the amount of starting solid sample used in the experiment, in g.

[0186] Table 4

[0187]

[0188] * In samples 6 and 23, 1.0 mg and 9.4 mg of PdCl were added to DES during the leaching process of the automotive catalyst powder samples, respectively. 2 To adjust the Pd in ​​the leachate.

[0189] ** In Sample 22 and Sample 29, the amount of Pd in ​​the starting material was adjusted by adding 37.1 mg and 442.7 mg of metallic Pd to the powder samples, respectively.

[0190] Example 2 - Reuse of DES-based leachate for PGMs recovery in different cycles

[0191] The Pt contained in the autocatalyst sample 1 shown in Table 3 was leached under the conditions shown in step 1 of the above-mentioned Example 1. Once the remaining solids were separated and washed as shown in step 1, a leachate (leachate of cycle 1) was obtained. Fresh autocatalyst powder was then leached under the same conditions, but using the leachate of cycle 1 instead of new DES to obtain a second leachate (leachate of cycle 2). The fresh autocatalyst powder was further leached using the resulting leachate (leachate of cycle 2) instead of new DES to obtain a third leachate (leachate of cycle 3). This operation was repeated for a total of up to 7 cycles.

[0192] Table 5 shows the concentrations of Pd and Pt in the leachate after each leaching cycle:

[0193] Table 5

[0194]

[0195] As can be seen, the results indicate that the DES leachate (DES obtained after leaching the autocatalyst powder) can be used again to leach metals from fresh autocatalyst powder, increasing the concentration of metals in the DES. In this way, the concentrations of Pt and Pd increase in each subsequent cycle. In addition, the purity of the PGM concentrated solids is similar when the reduction step is performed with the leachate obtained in cycle 7.

[0196] Reference List

[0197] -Wiecka Zuzanna et al.: "Recovery of platinum group metals from spent automotive converters by leaching with organic and inorganic acids and extraction with quaternary phosphonium salts", Separation and purification technology, 2021, vol.280, 1-11

[0198] -WO2008155464

[0199] -EP3375895

Claims

1. A method for recovering a platinum group metal (PGM) material comprising platinum from waste comprising spent solid residues containing platinum and optionally palladium, wherein the platinum and palladium are in metallic form, oxide form or alloy form, the method comprising the steps of: a) subjecting the waste to a leaching step in the presence of a suitable leaching agent, an oxidizing agent and an acidic medium, thereby obtaining a leachate comprising the platinum and optionally the palladium initially contained in the waste in ionic form; b) when the weight ratio of palladium to platinum in the leachate obtained in the previous step is lower than about 1.1:1, adding palladium in ionic form to the leachate until the weight ratio of palladium to platinum is equal to or higher than about 1.1:1; and c) subjecting the leachate comprising platinum and palladium in a weight ratio equal to or greater than about 1.1:1 to a reduction step to precipitate a platinum group metal (PGM) material comprising platinum in metallic form from the leachate.

2. The method according to claim 1, wherein the leaching agent is selected from the group consisting of inorganic acids, organic acids, inorganic bases, organic bases, metal salts, halogens, cyanides and deep eutectic solvents.

3. The method according to claim 2, wherein the suitable leaching agent is a deep eutectic solvent.

4. The method according to claim 3, wherein the deep eutectic solvent consists of a mixture of: (i) a hydrogen bond acceptor (HBA) compound (A) selected from a) Type Cat + X - (I) wherein Cat + is selected from any ammonium ion, imidazole Ions and Ion cation, And X - It is a Lewis base; b) betaine or its salts; and c) carnitine or a salt thereof; and (ii) a hydrogen bond donor (HBD) compound (B) selected from (C1-C 12 ) alcohol, (C1-C 12 )aldehyde, (C1-C 18 ) carboxylic acid, (C1-C6) urea, (C1-C 12 )amide, (C1-C 12 ) nitrogen-containing compounds, (C1-C 12 ) amino acids and (C1-C 12 )sugar, The molar ratio of (A) to (B) is 1:10 to 10:

1.

5. The method according to any one of claims 1 to 4, wherein the weight ratio of the leaching agent to the waste material is from 3:1 to 50:

1.

6. The method according to any one of claims 3 to 5, wherein the oxidizing agent is selected from hydrogen peroxide, NaNO3, I2, KHSO5, Fenton's reagent and mixtures thereof.

7. The process according to any one of claims 3 to 6, wherein the acidic medium is obtained by adding an acid selected from sulfuric acid, hydrochloric acid, nitric acid and mixtures thereof.

8. The method according to any one of claims 3 to 7, wherein the leaching step is carried out at a temperature of 40 to 130°C for a period of 0.25 to 6 hours.

9. The method according to any one of claims 1 to 8, wherein the leachate used in step c) comprises platinum and palladium in a weight ratio equal to or higher than about 2:

1.

10. The method according to any one of claims 1 to 8, wherein: i) the concentration of platinum in the leachate used in step c) is less than about 40 mg / kg leachate and the weight ratio of palladium to platinum is equal to or greater than about 2:1; or ii) the concentration of platinum in the leachate used in step c) is equal to or higher than about 40 mg / Kg leachate and lower than about 80 mg / Kg leachate, and the weight ratio of palladium to platinum is equal to or higher than about 1.8:1; or iii) the concentration of platinum in the leachate used in step c) is equal to or higher than about 80 mg / Kg leachate, and the weight ratio of palladium to platinum is equal to or higher than 1.1:

1.

11. The method according to any one of claims 1 to 10, wherein the reducing step c) is performed by heating the leachate at a temperature of 100 to 120°C for 1 to 8 hours.

12. The process according to any one of claims 1 to 11, further comprising the steps of d) separating the platinum group metal (PGM) material comprising platinum in metallic form obtained in the previous step from the solvent, e) optionally washing the material with water, and f) optionally drying the material obtained in the previous step.

13. The method according to any one of claims 1 to 12, wherein the material further comprises palladium in metallic form, oxide form or alloy form.

14. The method according to any one of claims 1 to 13, wherein the spent solid residue is selected from spent automotive catalysts, spent petroleum refining catalysts, spent proton exchange membrane fuel cells (PEMFCs) and spent catalysts for the chemical industry.

15. Use of palladium for the recovery of platinum from a leachate, wherein the leachate comprises platinum and palladium in a weight ratio equal to or higher than about 1.1:1.

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