Process for the recovery of precious metals from a heterogeneous catalyst containing precious metals

Abstract

The invention relates to a process for the recovery of precious metals from a heterogeneous catalyst comprising a solid support material and at least partially in elemental form palladium, platinum or rhodium, said process comprising the steps of: (a) converting the precious metal into an oxidation state > 0 by treating the heterogeneous catalyst with an oxidizing agent in the presence of hydrochloric acid to form a two-phase system A comprising an aqueous phase of hydrochloric acid A1 and a solid phase comprising the support material insoluble therein, (b) optionally at least partially separating the aqueous phase of hydrochloric acid A1 from the two-phase system A and adding a further aqueous phase to the remaining residue of the two-phase system A to form a two-phase system B comprising an aqueous phase of hydrochloric acid B1 and a solid phase comprising the support material insoluble therein, and (c) cathodic electrodeposition of the at least one precious metal from the aqueous phase of hydrochloric acid of the two-phase system.

Description

[0001] This invention relates to a method for recovering precious metals from heterogeneous catalysts containing precious metals.

[0002] The term “heterogeneous catalyst containing noble metals” or simply “heterogeneous catalyst” as used in this article should be understood as a support material equipped with catalytically active noble metals or containing catalytically active noble metal substances.

[0003] In many chemical processes, noble metals or substances containing noble metals are now used as catalysts, either in the form of homogeneous catalysts or heterogeneous catalysts. In homogeneous catalysis, the catalytically active noble metal is uniformly mixed with the reactants, for example, in solution, while in heterogeneous catalysis, the catalytically active noble metal exists on and / or within a support material that is at least substantially inert, and forms a heterogeneous mixture with the reactants. In many cases, heterogeneous catalysts are preferred because they can be removed from the reaction mixture in a simple manner, for example, by filtration. Many industrial chemical processes, such as reforming in monomer production for fuel production or polymer chemistry, use heterogeneous catalysts on a tonne scale. However, heterogeneous catalysts are also widely used for gas purification, such as in the treatment of exhaust gases or waste gas.

[0004] To ensure high catalytic activity, noble metals are typically finely distributed and applied to the inner and / or outer surfaces of at least substantially inert support materials in heterogeneous catalysts. These support materials are usually porous, allowing the catalytically active noble metal to be uniformly distributed over a large surface area.

[0005] After a certain operating time, the activity of both the precious metal-containing catalyst and the used catalyst must be replaced. Due to the high price of precious metals, the use of precious metal-containing catalysts is generally only economical if the precious metals used can be recovered.

[0006] For the purpose of precious metal recovery, used heterogeneous catalysts containing precious metals are typically subjected to hydrometallurgical methods, such as those described in EP 2985 354 A1. The heterogeneous catalyst containing precious metals is subjected to an oxidation step, in which the precious metal is rendered into a water-soluble form. Subsequently, the water-soluble precious metal is removed from the support material in multiple washing steps. The precious metal must then be recovered from the combined washing media, which requires handling large liquid volumes and energy-intensive and time-consuming steps. For example, US 7,166,145B1 describes how precious metals can be recovered from such combined washing media in a multi-stage process by final electrolytic deposition; previously, the components are separated into solid (support material) and liquid components (an aqueous phase containing the precious metal and the washing media).

[0007] The object of this invention is to find an efficient method for at least almost completely recovering noble metals (more precisely palladium and / or platinum and / or rhodium) from a heterogeneous catalyst containing noble metals, more precisely palladium and / or platinum and / or rhodium. In particular, providing a method that requires virtually no washing media is part of this object.

[0008] This objective can be achieved by a method for recovering noble metals from heterogeneous catalysts and / or recovering noble metals from heterogeneous catalysts, the heterogeneous catalysts comprising a solid support material and at least one noble metal selected from the group consisting of palladium (Pd), platinum (Pt), and rhodium (Rh) and present at least partially in elemental form, the method comprising the following sequential steps:

[0009] (a) A two-phase system A is formed by treating a heterogeneous catalyst with an oxidant in the presence of hydrochloric acid to convert at least one noble metal, which is at least partially present in elemental form, into an oxidation state >0, thereby forming a two-phase system A comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising a support material insoluble therein.

[0010] (b) Optionally, but preferably, the aqueous hydrochloric acid phase A1 is at least partially separated from the two-phase system A, and an additional aqueous phase is added to the remaining residue of the two-phase system A to form a two-phase system B comprising the aqueous hydrochloric acid phase B1 and a solid phase comprising a carrier material insoluble therein.

[0011] (b′) If step (b) has optionally been performed once or more, the hydrochloric acid aqueous phase is repeatedly separated at least partially from the two-phase system formed in the preceding steps, and an additional aqueous phase is added to form another two-phase system comprising the hydrochloric acid aqueous phase and a solid phase comprising a carrier material insoluble therein, and

[0012] (c)(c1) Cathodic electrodeposition of at least one noble metal from the hydrochloric acid aqueous phase A1 of the two-phase system A, or (c2) from the hydrochloric acid aqueous phase B1 of the two-phase system B, or (c3) from the hydrochloric acid aqueous phase of the last two-phase system formed in step (b′).

[0013] As used herein and as is known to those skilled in the art, the term "oxidation state" refers to the formal charge of an atom within a compound or the actual charge of a monatomic ion. By definition, an atom in an elemental state has an oxidation state of 0.

[0014] Throughout this paper, the two-phase system comprising an aqueous hydrochloric acid phase and a solid phase is repeatedly mentioned. The solid phase contains or is composed of a carrier material insoluble in the aqueous hydrochloric acid phase. The solid phase may be distributed in the two-phase system as a suspension, or it may partially settle at the bottom, or form the lower layer of the two phases. The latter is particularly true in a static state.

[0015] Steps (a), (b), (b′), and (c) are consecutive steps and may be directly consecutive steps without intermediate steps. Step (a) is performed before steps (b), (b′), and (c). In addition to step (b), which is optional but preferably performed, the method according to the invention may also include additional method steps performed before step (a), between steps (a) and (c), or after step (c). Step (b), which is preferably performed, may be followed by an optional step (b′), which is performed before step (c). If step (b′) is performed, steps similar to step (b) are performed once or more in that step, wherein in each case, at least a portion of the hydrochloric acid aqueous phase is separated from the relevant two-phase system, and an additional aqueous phase is added to the remaining portion of the relevant two-phase system. For example, a hydrochloric acid solution, hydrochloric acid, or water may be suitable as the additional aqueous phase to be added.

[0016] In one embodiment, the method according to the invention comprises successive steps (a) and (c), wherein step (c) is in a variant (c1) without steps (b) and (b′). In other words, there is then a method for recovering noble metals from and / or from a heterogeneous catalyst comprising a solid support material and at least one noble metal selected from the group consisting of palladium, platinum, and rhodium and present at least partially in elemental form, the method comprising the following successive steps:

[0017] (a) A two-phase system A is formed by treating a heterogeneous catalyst with an oxidant in the presence of hydrochloric acid to convert at least one noble metal, which is at least partially present in elemental form, into an oxidation state >0, thereby forming a two-phase system A comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising a support material insoluble therein.

[0018] as well as

[0019] (c) Cathodic electrodeposition of at least one noble metal from the hydrochloric acid aqueous phase A1 of the two-phase system A, without steps (b) and (b′). Cathodic electrodeposition from the hydrochloric acid aqueous phase A1 of the two-phase system A means that step (c) is performed in the presence of a solid support material insoluble in the hydrochloric acid aqueous phase A1. Here, the noble metal is recovered by cathodic electrodeposition electrolysis.

[0020] In a preferred embodiment, the method according to the invention comprises successive steps (a), (b), and (c), wherein step (c) is a variant (c2) without step (b′). In other words, there is then a method for recovering noble metals from and / or from a heterogeneous catalyst comprising a solid support material and at least one noble metal selected from the group consisting of palladium, platinum, and rhodium and present at least partially in elemental form, the method comprising the following successive steps:

[0021] (a) A two-phase system A is formed by treating a heterogeneous catalyst with an oxidant in the presence of hydrochloric acid to convert at least one noble metal, which is at least partially present in elemental form, into an oxidation state >0, thereby forming a two-phase system A comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising a support material insoluble therein.

[0022] (b) At least partially separating the aqueous hydrochloric acid phase A1 from the two-phase system A, and adding another aqueous phase to the remaining residue of the two-phase system A to form a two-phase system B comprising the aqueous hydrochloric acid phase B1 and a solid phase comprising a carrier material insoluble therein, and

[0023] (c) Cathodic electrodeposition of at least one noble metal from the hydrochloric acid aqueous phase B1 of the two-phase system B, without step (b′). Cathodic electrodeposition from the hydrochloric acid aqueous phase B1 of the two-phase system B means that step (c) is carried out in the presence of a solid support material insoluble in the hydrochloric acid aqueous phase B1. In step (b) of this preferred embodiment of the method according to the invention, the hydrochloric acid aqueous phase A1, which is at least partially separated, is further processed by conventional methods known to those skilled in the art (e.g., hydrometallurgical methods) to recover the noble metal dissolved therein. Preferably, the recovery of the noble metal from the at least partially separated hydrochloric acid aqueous phase A1 by cathodic electrodeposition is not performed. Overall, the recovery of the noble metal is carried out here partially non-electrolytically, for example by hydrometallurgy.

[0024] And it is carried out partially by electrolysis through cathode electrodeposition.

[0025] In yet another embodiment, the method according to the invention comprises successive steps (a), (b), (b′), and (c), wherein step (c) is a variant (c3). In other words, there is then a method for recovering noble metals from and / or from a heterogeneous catalyst comprising a solid support material and at least one noble metal selected from the group consisting of palladium, platinum, and rhodium and present at least partially in elemental form, the method comprising the following successive steps:

[0026] (a) A two-phase system A is formed by treating a heterogeneous catalyst with an oxidant in the presence of hydrochloric acid to convert at least one noble metal, which is at least partially present in elemental form, into an oxidation state >0, thereby forming a two-phase system A comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising a support material insoluble therein.

[0027] (b) Separate at least partially the aqueous hydrochloric acid phase A1 from the two-phase system A, and add another aqueous phase to the remaining residue of the two-phase system A to form a two-phase system B comprising the aqueous hydrochloric acid phase B1 and a solid phase comprising a carrier material insoluble therein.

[0028] (b′) Repeating this process once or more, at least partially separating the hydrochloric acid aqueous phase from the two-phase system formed in the preceding steps, and adding another aqueous phase to form another two-phase system comprising the hydrochloric acid aqueous phase and a solid phase comprising a carrier material insoluble therein, and

[0029] (c) Cathodic electrodeposition of at least one noble metal from the hydrochloric acid aqueous phase of the last two-phase system formed in step (b'). Cathodic electrodeposition from the hydrochloric acid aqueous phase of the last two-phase system formed in step (b') means that step (c) is carried out in the presence of a solid support material insoluble in the hydrochloric acid aqueous phase. In this embodiment of the method according to the invention, the hydrochloric acid aqueous phases A1 and B1, which are at least partially separated in steps (b) and (b'), and optionally the additional hydrochloric acid aqueous phase, which are at least partially separated in step (b'), can in each case be further processed independently or conveniently in combination with each other by conventional methods known to those skilled in the art (e.g., hydrometallurgical methods) to recover the noble metal dissolved therein. Preferably, the recovery of the noble metal from the at least partially separated hydrochloric acid aqueous phases A1 and B1 and optionally the additional hydrochloric acid aqueous phase, which are at least partially separated in step (b'), is not performed by cathodic electrodeposition. Overall, the recovery of the noble metal is carried out partially non-electrolytically, for example by hydrometallurgy, and partially electrolytically by cathodic electrodeposition.

[0030] For all three of the foregoing embodiments of the method according to the invention, it is important to the invention that the cathodic electrodeposition according to step (c) is advantageously carried out from the hydrochloric acid aqueous phase of the two-phase system under consideration, i.e., in each case in the presence of a solid carrier material insoluble in the relevant hydrochloric acid aqueous phase, or in other words, in all cases in the presence of the entire relevant two-phase system A or B or the last two-phase system formed in step (b′).

[0031] In the method according to the invention, the heterogeneous catalyst treated with an oxidant in the presence of hydrochloric acid comprises a solid support material and at least one noble metal, which is present at least partially in elemental form and selected from the group consisting of palladium, platinum, and rhodium; in other words, the heterogeneous catalyst comprises a solid support material and palladium and / or platinum and / or rhodium, which in each case is present at least partially in elemental form. The heterogeneous catalyst preferably does not contain any other noble metal besides palladium and / or platinum and / or rhodium. In one embodiment, the heterogeneous catalyst consists of a solid support material and palladium and / or platinum and / or rhodium, which in each case is present at least partially in elemental form. Any noble metal not present in elemental form may be present as a noble metal compound in a positive oxidation state, for example, as a noble metal oxide. The noble metal content of the heterogeneous catalyst formed from palladium, platinum, and / or rhodium may, for example, range from 0.02% by weight to 80% by weight. As described above, at least one noble metal present at least partially in elemental form is selected from the group consisting of palladium, platinum, and rhodium. The precious metals may exist in alloy form with each other. Preferably, these are platinum, which exists at least partially as an element, and / or palladium, which exists at least partially as an element.

[0032] In this document, reference is made to solid support materials. This is understood to mean solid supports that are virtually free of noble metals, which may be equipped with catalytically active noble metals or substances containing such noble metals. Suitable solid support materials are chemically at least largely inert to many different conditions or reaction conditions; this can also be ensured for carbon-based supports mentioned below. In particular, solid support materials are at least largely inert to acidic and oxidizing media, and preferably also to alkaline media. They are insoluble in aqueous media over a pH range of -1 to +7, and preferably also in the alkaline range. “Insoluble” should not be understood here as an absolute term; those skilled in the art will understand it as substantially insoluble or almost insoluble. Suitable support materials are commercially available or can be produced using conventional methods known to those skilled in the art. Examples of support materials are inorganic ceramic materials, such as pure oxide ceramics, such as alumina, zirconium oxide, titanium dioxide, and silicon dioxide, and mixed oxide ceramics, such as aluminum titanate and dispersed ceramics (Al2O3 / ZrO2). Support materials may be doped with other elements, such as rare earth metals. Other examples of carrier materials include non-oxide ceramics, such as silicon carbide, silicon nitride, aluminum nitride, boron carbide, and boron nitride. Other examples are silicate-based materials, particularly aluminum silicate, and very especially zeolites.

[0033] Another possible type of support material is a carbon-based material. As already mentioned, the support material must have at least some tolerance to the conditions that predominate under catalytic operating conditions and the conditions of the method according to the invention. If the support material is carbon, it is likely preferred that the carbon material has a high degree of graphitization. Suitable carbon-based support materials with a high degree of graphitization are also commercially available, for example, under the name... Purchased from Heraeus.

[0034] Generally speaking, in step (a) of the method according to the invention, the heterogeneous catalyst treated with an oxidant in the presence of hydrochloric acid is a material with a large surface area, for example, having a surface area of ​​10 m². 2 / g to 500m 2 / g, preferably 300m 2 / g to 500m 2 / g BET surface area. Generally, these are porous materials. BET surface area can be determined by BET measurement according to DIN ISO 9277 (according to Chapter 6.3.1, static volume measurement method, gas used: nitrogen). Unless otherwise stated, all standards cited herein are the current versions as of the priority date of this patent application in each case. Open porosity can be expressed by open pore volume. Open pore volume can be determined by mercury porosimetry or by measuring water absorption capacity. For example, it can be in the range of 0.2 ml / g to 1.2 ml / g. Porosity can be formed by pores of various orders of magnitude, such as mesopores and / or macropores. Pore size can be in the range of, for example, 5 nm to 10 μm.

[0035] Heterogeneous catalysts can exist in particulate form. The average particle size d50 of the support material can, for example, range from 3 μm to 100 μm. The average particle size d50 can be determined using a particle size analyzer by laser diffraction. However, heterogeneous catalysts can also be in the form of molded bodies. Examples of molded bodies include strands, cylinders, granules, rings, porous rings, spheres, saddles, wheels, chairs, foams, and honeycomb structures. Such molded bodies can have, for example, a height of 100 μm to a diameter of 50 cm at the thickest point. The heterogeneous catalyst can incidentally be pulverized, for example, by grinding, prior to step (a), regardless of whether it exists in particulate form or as a molded body of the shape defined.

[0036] Generally, in the method according to the invention, the heterogeneous catalyst treated with an oxidant in the presence of hydrochloric acid is a used heterogeneous catalyst. A used heterogeneous catalyst is one whose catalytic activity has decreased and is no longer sufficient after a certain operating time. Depending on the process of using the used heterogeneous catalyst, a noble metal substance modified relative to the original catalytic activity and / or another substance not originally present may be located on the support material. Therefore, before carrying out the method according to the invention, more precisely before carrying out step (a), in addition to the possible mechanical crushing described above, the heterogeneous catalyst may advantageously undergo a further pretreatment step. In this regard, the heterogeneous catalyst may be pretreated or has been pretreated accordingly before step (a). For example, pretreatment in the form of heat treatment or annealing may be advantageous. This is mainly advantageous if organic matter occupies the heterogeneous catalyst after its use and is removed by pyrolysis and / or combustion before step (a). If the heterogeneous catalyst does not contain noble metals in elemental form, but rather as noble metal substances in a higher oxidation state, a reduction pretreatment may advantageously be carried out, particularly advantageously in a reducing atmosphere. In particular, the pretreatment prior to step (a) may include heat treatment, reduction treatment, or heat treatment followed by reduction treatment.

[0037] In method step (a), at least one noble metal, which exists at least partially in elemental form, is converted to an oxidation state >0 by treating a heterogeneous catalyst with an oxidant in the presence of hydrochloric acid to form a two-phase system A comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising a support material insoluble therein.

[0038] During step (a) of the method, a reaction system comprising a heterogeneous catalyst, hydrochloric acid, and one or more oxidants is initially present. The heterogeneous catalyst comprises a support having at least one noble metal present at least partially in elemental form. After step (a) of the method is completed, a two-phase system A is obtained comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising a support material insoluble therein. The aqueous hydrochloric acid phase A1 contains the noble metal removed from the support and is now present in dissolved form in an oxidation state >0. The solid phase comprises the support material insoluble in the aqueous hydrochloric acid phase A1 and substantially free of the noble metal as particles and / or as a molded body.

[0039] The hydrochloric acid used in step (a) can be, for example, 1 mol to 12 mol of acid (H3O). + Concentration within the range of ) / liter.

[0040] The oxidant used in step (a) of method can be solid, liquid, or gaseous. Examples of available solid oxidants known to those skilled in the art include chlorates, nitrates, bromates, iodates, chlorites, bromates, iodates, hypochlorites, perchlorates, and peroxide compounds. Such oxidants may be present, in particular, as salts of alkali metals or alkaline earth metals. Suitable liquid oxidants are, for example, aqueous solutions of the aforementioned solid oxidant and / or hydrogen peroxide. Suitable gaseous oxidants are, in particular, chlorine and ozone. The oxidant can be used alone or in any combination.

[0041] The exposure time of at least one oxidant is not further limited. In a preferred embodiment, the exposure time can be from 5 minutes to 240 minutes, particularly preferably from 10 minutes to 120 minutes, and especially from 15 minutes to 60 minutes. The oxidation step can be carried out in a temperature range, for example, from 20°C to 80°C or even up to the boiling point.

[0042] After treatment with an oxidizing agent, at least one noble metal exists in an oxidation state >0. Preferably, for example, palladium exists as Pd(II) and / or Pd(IV), platinum exists as Pt(II) and / or Pt(IV), and rhodium exists as Rh(I) and / or Rh(III).

[0043] During step (a) of the method, at least one noble metal may be transferred at least partially, substantially or almost completely from the carrier material to the hydrochloric acid aqueous phase, thereby ultimately forming the hydrochloric acid aqueous phase A1.

[0044] In principle, when recovering precious metals from and / or recovering precious metals from used heterogeneous catalysts containing precious metals, it is desirable to almost completely remove the precious metals from the support material. Almost complete removal should be understood as meaning that after the removal of the precious metals, based on the total weight of the support material plus the remaining precious metals therein, the support material contains only ≤500 wt.ppm (weight ppm), preferably ≤100 wt.ppm of precious metals. The method according to the invention is a method for recovering precious metals from and / or recovering precious metals from the heterogeneous catalyst; more precisely, it is a method for recovering at least one precious metal from and / or recovering at least one precious metal from the heterogeneous catalyst selected from the group consisting of palladium, platinum, and rhodium. Preferably, the recovery is carried out in the manner described above, with almost complete removal from the support material.

[0045] The hydrochloric acid aqueous phase A1 of the two-phase system A can have, for example, up to 12 mol of acid (H3O) + The concentration can be 1 mol / L, especially in the range of 1 mol to 12 mol / L. The pH of the aqueous phase A1 of hydrochloric acid can be, for example, in the range of -1 to +3.

[0046] The hydrochloric acid aqueous phase A1 of the two-phase system A contains a portion of at least one noble metal converted from the carrier material in an oxidation state >0 and in dissolved form, in a quantitative proportion, for example, in the range of 0.1 g / L to 30 g / L.

[0047] The undissolved carrier material is present in the two-phase system A in a quantitative proportion, for example, in the range of 10 g / L to 1000 g / L of aqueous hydrochloric acid phase A1, preferably in an amount of 50 g / L to 100 g / L of aqueous hydrochloric acid phase A1.

[0048] The hydrochloric acid aqueous phase A1 of the two-phase system A surrounds the support material and is usually also present inside the support material, such as in pores.

[0049] The aqueous hydrochloric acid phase A1 may also contain other components, such as oxidants and / or residues from oxidation of reaction products that do not contain precious metals.

[0050] Optionally, diluting the hydrochloric acid aqueous phase A1 of the two-phase system A may be advantageous. Suitable diluents are, for example, hydrochloric acid solution, hydrochloric acid, or water.

[0051] In the foregoing preferred embodiments and further embodiments of the method according to the invention, step (b) is performed in which the aqueous hydrochloric acid phase A1 is at least partially separated from the two-phase system A and a further aqueous phase is added to the remaining residue of the two-phase system A to form a two-phase system B. The at least partial separation can be performed, for example, by decantation, filtration, or centrifugation. Suitable additional aqueous phases to be added are, for example, hydrochloric acid solution, hydrochloric acid, or water. The resulting two-phase system B comprises the aqueous hydrochloric acid phase B1 and a solid phase comprising a carrier material insoluble therein.

[0052] The hydrochloric acid aqueous phase B1 of the two-phase system B can have, for example, up to 12 mol of acid (H3O) + The pH of the aqueous phase B1 of hydrochloric acid can be, for example, in the range of -1 to +3.

[0053] The hydrochloric acid aqueous phase B1 of the two-phase system B contains at least one noble metal in an oxidation state >0 and in dissolved form, in a quantitative proportion, for example, in the range of 0.01 g / L to 30 g / L.

[0054] The undissolved carrier material is present in the two-phase system B in a quantitative proportion, for example, in the range of 10 g / L to 1000 g / L of aqueous hydrochloric acid phase B1, preferably in an amount of 50 g / L to 100 g / L of aqueous hydrochloric acid phase B1.

[0055] The hydrochloric acid aqueous phase B1 of the two-phase system B surrounds the support material and is usually also present inside the support material, such as in the pores.

[0056] The aqueous phase B1 of hydrochloric acid may also contain other components, such as oxidants and / or residues from oxidation of reaction products that do not contain precious metals.

[0057] Optionally, diluting the hydrochloric acid aqueous phase B1 of the two-phase system B may be advantageous. Suitable diluents are, for example, hydrochloric acid solution, hydrochloric acid, or water.

[0058] If step (b) is performed in the method according to the invention, as is preferably the case, an optional step (b′) may then be performed. This optional step is a step that is repeated once or multiple times, wherein in each case the hydrochloric acid aqueous phase is at least partially separated from the relevant two-phase system formed immediately following the aforementioned step, and an additional aqueous phase is added to form another two-phase system comprising the hydrochloric acid aqueous phase and a solid phase comprising a carrier material insoluble therein. In the case of only one instance or in the case of separation according to the first part of step (b′), the two-phase system formed immediately following the aforementioned step is the two-phase system B formed in step (b).

[0059] In step (c) of the method according to the invention, at least one noble metal is cathodically electrodeposited from the hydrochloric acid aqueous phase A1 of the two-phase system A, or from the hydrochloric acid aqueous phase B1 of the two-phase system B, or from the hydrochloric acid aqueous phase of the last two-phase system formed in step (b′), i.e., in each case, in the presence of a solid support material insoluble in the relevant hydrochloric acid aqueous phase. During step (c), the entire hydrochloric acid aqueous phase in question is depleted of at least one noble metal. "Entire hydrochloric acid aqueous phase" here means both its portion within (particularly, for example, within pores and cavities) and external to the solid support material.

[0060] In the context of the method according to the invention, cathodic electrodeposition is understood to mean a method in which a noble metal existing in an oxidation state >0 is electrochemically reduced and deposited as an element on or at the cathode.

[0061] During step (c), the solid support material can be uniformly distributed in the relevant two-phase system as a suspension, for example, as a result of stirring the two-phase system or flowing an inert gas through the two-phase system. In another embodiment, the solid support material can form the lower layer of the two phases and remain stationary, with only the upper aqueous hydrochloric acid phase moving, for example, by stirring. For example, cathodic electrodeposition can also be performed without stirring. The solid support material can also be partially suspended simultaneously, with the residue settling at the bottom.

[0062] Suitable electrode materials are known in principle to those skilled in the art. Electrodes made of graphite, titanium, or stainless steel have proven particularly suitable. According to the invention, the cathode can also be made of precious metals, particularly advantageously of such precious metals that are also recyclable. Electrodes with the largest possible surface area are particularly suitable. In principle, electrodes of any shape are suitable. The use of mesh or fan-shaped electrodes may be advantageous. In one embodiment, multiple cathodes may be used.

[0063] Cathodic electrodeposition can be carried out without spatial separation of the partial reaction. However, spatial separation of the partial reaction can also be advantageously achieved through membranes, diaphragms, or ion-exchange membranes. For example, an anode chamber filled with dilute sulfuric acid can be used in this way, and thus the generation of chlorine at the anode can be avoided.

[0064] It is particularly advantageous to operate at voltages in the range of 1.1V to 5V during cathode electrodeposition.

[0065] The current density during cathode electrodeposition can be, for example, 5 mA / cm². 2 Up to 300mA / cm 2 Within the range, preferably within 10 mA / cm 2 Up to 100mA / cm 2 Within the range, especially at 20 mA / cm 2 Up to 40mA / cm 2 Within the range.

[0066] Cathodic electrodeposition can be performed at room temperature, for example in the range of 15°C to 25°C, or even at higher temperatures, such as up to 90°C. In particular, when performing cathodic electrodeposition from an aqueous hydrochloric acid phase, it may be advantageous to operate at elevated temperatures, for example, in the range of 70°C to 90°C.

[0067] The duration of cathode electrodeposition is not further limited. It is based in particular on the size of the electrode surface area, the set current density, the concentration of the noble metal at the start of step (c), and the time it takes for the concentration of the noble metal in the hydrochloric acid aqueous phase to drop below the desired limit.

[0068] After step (c) is completed, the concentration of noble metals in the hydrochloric acid aqueous phase can be <50 wt.ppm, preferably <10 wt.ppm. For example, the concentration of noble metals can then be in the range of 0 wt.ppm to <50 wt.ppm, preferably in the range of 5 wt.ppm to <10 wt.ppm.

[0069] Method step (c) is typically performed under acidic conditions by cathodic electrodeposition of at least one noble metal from an aqueous hydrochloric acid phase, which may have a pH range of, for example, -1 to +3. All noble metals are cathodiically deposited here.

[0070] However, in some cases, it may be advantageous to raise the pH of the aqueous hydrochloric acid phase to, for example, an alkaline pH range of ≥8 to 14, preferably ≥8 to 11.5, and particularly ≥8 to 10, prior to cathodic electrodeposition; here, such an aqueous hydrochloric acid phase with the raised pH is referred to as an "alkaline-adjusted aqueous hydrochloric acid phase". In particular, if at least one noble metal contains palladium, or is particularly palladium, it may be advantageous to raise the pH of the aqueous hydrochloric acid phase to an alkaline pH range of, for example, ≥8 to 14, preferably ≥8 to 11.5, and particularly ≥8 to 10, prior to cathodic electrodeposition. In this case, step (c′) can therefore be performed immediately before step (c) to adjust the suitable alkaline pH value to, for example, a range of ≥8 to 14, preferably ≥8 to 11.5, and particularly ≥8 to 10. In this case, the relevant two-phase system A, B, or the last two-phase system formed in step (b′) is mixed with ammonium hydroxide plus optionally an additional base such as, for example, NaOH or KOH. Ammonium hydroxide can be added as an ammonia feed or preferably as an aqueous solution; alternatively, an ammonium salt that releases ammonium hydroxide under the influence of a strong base, such as NaOH or KOH, can also be added. The advantages of this alkaline adjustment of pH include reduced or avoided chlorine formation at the anode, and the ability to carry out step (c) at increased current densities while reducing hydrogen production. Electrochemical efficiency (the ratio of deposited palladium to current density) can be improved. This particular embodiment of the method according to the invention is a method for recovering palladium from and / or recovering palladium from a heterogeneous catalyst comprising a solid support material and palladium present at least partially in elemental form, the method comprising the following sequential steps:

[0071] (a) Palladium, which exists at least partially in elemental form, is converted to an oxidation state >0 by treating a heterogeneous catalyst with an oxidant in the presence of hydrochloric acid to form a two-phase system A comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising a support material insoluble therein.

[0072] (b) Optionally, but preferably, the aqueous hydrochloric acid phase A1 is at least partially separated from the two-phase system A, and an additional aqueous phase is added to the remaining residue of the two-phase system A to form a two-phase system B comprising the aqueous hydrochloric acid phase B1 and a solid phase comprising a carrier material insoluble therein.

[0073] (b′) If step (b) has optionally been performed once or more, the hydrochloric acid aqueous phase is repeatedly separated from the two-phase system formed in the preceding steps, at least partially, and an additional aqueous phase is added to form another two-phase system comprising the hydrochloric acid aqueous phase and a solid phase comprising a carrier material insoluble therein.

[0074] (c′) Using ammonium hydroxide, the alkalinity pH of the hydrochloric acid aqueous phase A1 of the two-phase system A, or the hydrochloric acid aqueous phase B1 of the two-phase system B, or the hydrochloric acid aqueous phase of the last two-phase system formed in step (b′), is adjusted to be ≥8 to 14, preferably ≥8 to 11.5, particularly ≥8 to 10.

[0075] (c) Cathodic electrodeposition of palladium from the hydrochloric acid aqueous phase of the alkaline-conditioned two-phase system in step (c′). Cathodic electrodeposition from the hydrochloric acid aqueous phase of the alkaline-conditioned two-phase system in step (c′) means that step (c) is performed in the presence of a solid support material insoluble in the alkaline-conditioned hydrochloric acid aqueous phase.

[0076] Step (c′) is performed using ammonium hydroxide; as described, various bases of ammonium hydroxide, such as sodium hydroxide or potassium hydroxide, may also be used. In particular, when adjusting the pH in the range of ≥8 to 10, pH adjustment can be performed using only ammonium hydroxide as the base.

[0077] After completing the method according to the invention, it may be advantageous to recover the carrier material, which is largely free of precious metals. This is especially true when the carrier material is in the form of an expensively produced molded body; for this purpose, the method according to the invention can be carried out gently on the molded body, and, for example, stirring can be omitted during the associated cathodic electrodeposition step.

[0078] Methods for further processing the elemental noble metal obtained in the relevant cathode electrodeposition step are known to those skilled in the art and depend on, for example, the type of noble metal, the method conditions, and / or the cathode used. For example, the deposited noble metal may adhere to the cathode; in this case, it can subsequently be separated from the cathode, for example, by mechanical processing, or the cathode, comprising the initial electrode material and the noble metal deposited on it, can be further processed as a whole. After electrochemical reduction, the noble metal may also not adhere to the cathode; it may exist, for example, in the form of powder or particles in a reaction space that is particularly advantageously separated, and can be separated by known methods.

[0079] Using the method according to the invention, precious metals, more specifically palladium, platinum, and / or rhodium, can be recovered from used heterogeneous catalysts in an environmentally friendly and resource-saving manner. On the one hand, direct electrolytic deposition requires a smaller reactor volume. Furthermore, since the volume of the washing medium or washing water has been reduced compared to methods according to the prior art, the process steps and incremental development steps that were previously necessary are eliminated, which means reduced energy and time consumption.

[0080] Exemplary Implementation

[0081] Example 1 :

[0082] 100 g of heterogeneous catalyst (spheres with a diameter of 3 mm; 0.511 wt% palladium on alumina) corresponding to 500 mg palladium was mixed with 1 L of 6N hydrochloric acid. Chlorine was flowed through the two-phase system at 10 Nl / h at 60 °C for 15 minutes with stirring. Chlorine was then removed by holding at 90 °C for 30 minutes. After settling of the solid components, 865 mL of liquid phase was removed. 476 mg palladium was recovered from the removed liquid phase by hydrometallurgical methods. The two-phase residue was diluted with 160 mL of water, and 7 g of ammonium chloride was added. Subsequently, 28 wt% ammonium hydroxide solution was added until a pH of 8.8 was reached. Elemental palladium was deposited at the cathode with an electrochemical efficiency of 25% in an electrolytic deposition at 4 V through a graphite electrode at 25 °C and a current density of 33 mA / cm². The overall palladium recovery yield was 99.5%. ICP-OES analysis of the support material showed a palladium residue content of <10 wt.ppm based on the total weight of the support material.

[0083] Example 2 :

[0084] 50 g of a heterogeneous catalyst (powder with a particle size of 100 μm to 1 mm; 2 wt% palladium on aluminum silicate) corresponding to 1000 mg palladium was heated at 800 °C for 5 h in air, followed by annealing at 500 °C for 2 h in H2 atmosphere, and then mixed with 1 L of 6N hydrochloric acid. Chlorine was continuously passed through the two-phase system at 6 N l / h at 60 °C for 15 min while stirring. Chlorine was then removed by holding at 85 °C for 30 min. After settling the solid components, 850 ml of liquid phase was removed. 890 mg palladium was recovered from the removed liquid phase by hydrometallurgical methods. The two-phase residue was diluted with 150 ml of water and 7 g of ammonium chloride was added. Subsequently, 28 wt% ammonium hydroxide solution was added until a pH of 8 was reached. The reaction was then carried out at 25 °C and 33 mA / cm². 2 Elemental palladium was deposited at the cathode with an electrochemical efficiency of 25% via electrolytic deposition through a graphite electrode at 4V. The overall palladium recovery yield was 99.5%. Palladium analysis of the support material by ICP-OES showed a residual palladium content of <10 wt.ppm based on the total weight of the support material.

[0085] Example 3 :

[0086] 100 g of heterogeneous catalyst (powder with a particle size of 100 μm to 1 mm; 0.5 wt% palladium and 0.5 wt% platinum on alumina) corresponding to 500 mg palladium and 500 mg platinum was mixed with 1 L of 6N hydrochloric acid. Chlorine was continuously passed through the two-phase system at 6 N l / h at 60 °C for 30 minutes with stirring. Chlorine was then removed by holding at 85 °C for 30 minutes. After settling the solid components, 850 ml of the liquid phase was removed. 470 mg palladium and 450 mg platinum were recovered from the removed liquid phase by hydrometallurgical methods. The two-phase residue was diluted with 150 ml of water. Subsequent hydrometallurgical treatment was carried out at 85 °C and 33 mA / cm². 2 At a current density of 12%, elemental palladium and elemental platinum were deposited at the cathode via electrolytic deposition through a graphite electrode at 1.8 V. The overall recovery yield of the precious metals (palladium and platinum) was 99.5%. ICP-OES analysis of the support material showed residual contents of <10 wt. ppm palladium and <10 wt. ppm platinum based on the total weight of the support material.

[0087] Example 4 :

[0088] 100 g of heterogeneous catalyst (spheres with a diameter of 3 mm; 0.511 wt% palladium on alumina) corresponding to 500 mg palladium was mixed with 1 L of 6N hydrochloric acid. Chlorine was continuously passed through the two-phase system at 10 N l / h at 60 °C for 15 minutes with stirring. Chlorine was then removed by holding at 90 °C for 30 minutes. After sedimentation of the solid components, 865 ml of the liquid phase was removed. 476 mg palladium was recovered from the removed liquid phase by hydrometallurgical methods. The two-phase residue was diluted with 150 ml of water. Subsequent hydrometallurgical treatment was carried out at 85 °C and 33 mA / cm². 2 Elemental palladium was deposited at the cathode with an electrochemical efficiency of 12% via electrolytic deposition through a graphite electrode at 1.8 V at a current density of [value missing]. The overall palladium recovery yield was 99.5%. Palladium analysis of the support material by ICP-OES showed a residual palladium content of <10 wt.ppm based on the total weight of the support material.

Claims

1. A method for recovering noble metals from a heterogeneous catalyst and / or recovering noble metals from a heterogeneous catalyst, said heterogeneous catalyst comprising a solid support material and at least one noble metal selected from the group consisting of palladium, platinum, and rhodium and present at least partially in elemental form, said method comprising the following sequential steps: (a) The at least one noble metal, which exists at least partially in elemental form, is converted to an oxidation state >0 by treating the heterogeneous catalyst with an oxidant in the presence of hydrochloric acid to form a two-phase system A comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising the support material insoluble therein. (b) Optionally, the aqueous hydrochloric acid phase A1 is at least partially separated from the two-phase system A, and an additional aqueous phase is added to the remaining residue of the two-phase system A to form a two-phase system B comprising the aqueous hydrochloric acid phase B1 and a solid phase comprising the carrier material insoluble therein. (b′) If step (b) has optionally been performed once or more, the hydrochloric acid aqueous phase is repeatedly separated at least partially from the two-phase system formed in the preceding steps, and an additional aqueous phase is added to form another two-phase system comprising the hydrochloric acid aqueous phase and a solid phase comprising the carrier material insoluble therein, and (c)(c1) Cathodic electrodeposition of the at least one noble metal from the hydrochloric acid aqueous phase A1 of the two-phase system A, or (c2) from the hydrochloric acid aqueous phase B1 of the two-phase system B, or (c3) from the hydrochloric acid aqueous phase of the two-phase system last formed in step (b′), wherein: Step (c1) is carried out in the presence of a solid support material that is insoluble in the aqueous phase A1 of hydrochloric acid; Step (c2) is carried out in the presence of a solid support material that is insoluble in the aqueous phase B1 of hydrochloric acid; Step (c3) is carried out in the presence of a solid carrier material that is insoluble in the aqueous phase of hydrochloric acid.

2. The method according to claim 1, wherein the additional aqueous phase is a hydrochloric acid solution or water.

3. The method according to claim 1, wherein the additional aqueous phase is hydrochloric acid.

4. The method according to claim 1, wherein the method comprises the sequential step (a) and (c) in a variant form (c1), without steps (b) and (b′).

5. The method according to claim 1, wherein the method comprises the successive steps (a), (b) and (c) in a variant form (c2), without step (b′).

6. The method according to claim 2, wherein the method comprises the successive steps (a), (b) and (c) in a variant form (c2), without step (b′).

7. The method according to claim 3, wherein the method comprises the successive steps (a), (b) and (c) in a variant form (c2), without step (b′).

8. The method according to claim 1, wherein the method comprises the successive steps (a), (b), (b′) and (c) in a variant form (c3).

9. The method according to claim 2, wherein the method comprises the successive steps (a), (b), (b′) and (c) in a variant form (c3).

10. The method according to claim 3, wherein the method comprises the successive steps (a), (b), (b′) and (c) in a variant form (c3).

11. The method according to any one of claims 1 to 10, wherein the heterogeneous catalyst is a used heterogeneous catalyst.

12. The method according to any one of claims 1 to 10, wherein the heterogeneous catalyst has undergone one or more pretreatment steps prior to step (a).

13. The method according to any one of claims 1 to 10, wherein the oxidant is selected from chlorates, nitrates, bromates, iodates, chlorites, bromates, iodates, hypochlorites, perchlorates, peroxides, chlorine and / or ozone.

14. The method according to any one of claims 1 to 10, wherein the precious metal recovery is carried out in a manner that removes almost completely from the carrier material.

15. The method according to any one of claims 1 to 10, wherein the cathode electrodeposition is performed under spatial separation of the partial reaction.

16. The method according to any one of claims 1 to 10, wherein the cathode electrodeposition is performed until a noble metal concentration of <50 wt.ppm is achieved in the hydrochloric acid aqueous phase.

17. A method for recovering palladium from a heterogeneous catalyst and / or recovering palladium from a heterogeneous catalyst, said heterogeneous catalyst comprising a solid support material and palladium present at least partially in elemental form, said method comprising the following sequential steps: (a) The palladium, which exists at least partially in elemental form, is converted to an oxidation state >0 by treating the heterogeneous catalyst with an oxidant in the presence of hydrochloric acid to form a two-phase system A comprising an aqueous hydrochloric acid phase A1 and a solid phase comprising the support material insoluble therein. (b) Optionally, the aqueous hydrochloric acid phase A1 is at least partially separated from the two-phase system A, and an additional aqueous phase is added to the remaining residue of the two-phase system A to form a two-phase system B comprising the aqueous hydrochloric acid phase B1 and a solid phase comprising the carrier material insoluble therein. (b′) If step (b) has optionally been performed once or more, the hydrochloric acid aqueous phase is repeatedly separated at least partially from the two-phase system formed in the preceding steps, and an additional aqueous phase is added to form another two-phase system comprising the hydrochloric acid aqueous phase and a solid phase comprising the carrier material insoluble therein. (c′) Using ammonium hydroxide, adjust the alkalinity pH of the hydrochloric acid aqueous phase A1 of the two-phase system A, or the hydrochloric acid aqueous phase B1 of the two-phase system B, or the hydrochloric acid aqueous phase of the last two-phase system formed in step (b′), within the range of ≥8 to 14. (c) Cathodic electrodeposition of the palladium from the hydrochloric acid aqueous phase of the two-phase system that has been alkaline-treated in step (c′).

18. The method of claim 17, wherein the heterogeneous catalyst is a used heterogeneous catalyst.

19. The method of claim 17, wherein the heterogeneous catalyst has undergone one or more pretreatment steps prior to step (a).

20. The method of claim 18, wherein the heterogeneous catalyst has undergone one or more pretreatment steps prior to step (a).

21. The method of claim 17, wherein the oxidant is selected from chlorates, nitrates, bromates, iodates, chlorites, bromates, iodates, hypochlorites, perchlorates, peroxides, chlorine and / or ozone.

22. The method of claim 18, wherein the oxidant is selected from chlorates, nitrates, bromates, iodates, chlorites, bromates, iodates, hypochlorites, perchlorates, peroxides, chlorine and / or ozone.

23. The method of claim 19, wherein the oxidant is selected from chlorates, nitrates, bromates, iodates, chlorites, bromates, iodates, hypochlorites, perchlorates, peroxides, chlorine and / or ozone.

24. The method of claim 20, wherein the oxidant is selected from chlorates, nitrates, bromates, iodates, chlorites, bromates, iodates, hypochlorites, perchlorates, peroxides, chlorine and / or ozone.

25. The method according to any one of claims 17 to 24, wherein palladium recovery is carried out in a manner that removes it almost completely from the carrier material.

26. The method according to any one of claims 17 to 24, wherein the cathode electrodeposition is performed under spatial separation of the partial reaction.

27. The method according to any one of claims 17 to 24, wherein the cathode electrodeposition is performed until a noble metal concentration of <50 wt.ppm is achieved in the aqueous hydrochloric acid phase.