Particulate platinoid-silicide- and silicon-carbide-containing mixture and anaerobic, thermal method for producing same

Abstract

The invention concerns the field of noble metal processing and relates to a platinoid-silicide- and silicon-carbide-containing mixture, which is recycled from platinoide- and SiC-containing materials, enriched, concentrated and / or cleaned, and to a method for producing same. The problem addressed by the present invention consists in specifying a platinoid-silicide- and silicon-carbide-containing mixture in which the platinoid-silicides are present at high yield and / or high purity and which is produced from platinoid- and SiC-containing materials by way of a simple and cost-effective method. The problem is solved by a platinoid-silicide- and silicon-carbide-containing mixture in which platinoids are present at a concentration of at least 1 mass % and in which, in addition to silicon carbide particles and silicon carbide particle agglomorates, the platinoids are present as platinoid silicide particles and / or as agglomerates of platinoid silicide particles, and or platinoid silicide particles bond the silicon carbide particles into an agglomerate and / or are arranged on the surface of the silicon carbide particles, wherein the silicon carbide of the silicon carbide particles is present as technically pure silicon carbide.

Description

[0001] Platinoid silicide and silicon carbide-containing mixture and process for its preparation

[0002] The invention relates to the fields of precious metal processing, technical ceramics and processing technology and relates to a platinoid silicide and silicon carbide-containing mixture which is recycled, enriched, concentrated and / or purified from platinoid and SiC-containing materials and can be industrially processed and reused as platinoids, and to a process for its production.

[0003] Automotive catalysts and industrial catalysts are used for exhaust gas aftertreatment from internal combustion engines and industrial exhaust gases, e.g., from chemical reactions or combustion processes. Other applications of industrial catalysts include influencing chemical reactions to improve conversion, yield, and selectivity. Automotive catalysts drastically reduce pollutant emissions in engine exhaust gases; industrial catalysts reduce the pollutant content in industrial exhaust gases; or improve the conversion of chemical reactions and their selectivity with regard to specific compounds. Many automotive and industrial catalysts essentially consist of ceramic carrier structures with catalytically active substances that are positioned on the ceramic carrier structures using adhesive materials.

[0004] The ceramic support structures often have the form of fillers, honeycombs, open-cell foams or wound structures and cordierite (Mg-Al silicate), tialite (Al titanate) or silicon carbide (SiC) are often used as materials for these ceramic support structures.

[0005] Silicon carbide (SiC) is a synthetic industrial mineral used in many industries due to its outstanding properties (hardness, high-temperature properties, chemical resistance). Its use in the form of special, highly pure, and narrowly fractionated fine powder grains (0.5 to approximately 250 pm) is particularly important in microelectronics / photovoltaics (wafer sawing), in ceramics production, for the production of ballistic protective ceramics for military technology, automotive environmental technology (diesel particulate filters), and as an abrasive material for high-quality surface finishing in all areas of mechanical engineering.

[0006] For vehicle and industrial catalysts, a coating consisting of a mixture of different metal oxides is usually applied as a washcoat to the ceramic support structures as an adhesive material for the catalytically active substances. This washcoat can consist in particular of gamma-aluminum oxide, cerium oxide and zirconium dioxide, or also of other materials such as zeolites.

[0007] Platinoids, especially platinum, palladium, rhodium and iridium, are primarily used as catalytically active substances or catalyst particles.

[0008] In many applications, these metals are used as extremely fine active particles, which are often used with other auxiliary materials.

[0009] In the context of the present invention, platinoids are to be understood as PGM (Platinum Group Metals) and PGE (Platinum Group Elements), i.e. the elements of groups 8 to 10 of the 5th period of the Periodic Table of Elements (PSE), i.e. the “light platinum metals”: ​​ruthenium (Ru), rhodium (Rh), palladium (Pd) and the elements of groups 8 to 10 of the 6th period of the PSE, i.e. the “heavy platinum metals”: ​​osmium (Os), indium (Ir), platinum (Pt).

[0010] According to the definition of a catalyst, the catalyst substance influences the reaction rate of a chemical reaction without being consumed itself (Wikipedia, keyword catalyst).

[0011] However, most catalytically active substances degrade during use due to various effects, rendering them unusable for catalysis. At this point, the vehicle and / or industrial catalysts must be replaced.

[0012] Such used catalysts, which have degenerated with regard to the catalytically active substances, generally have a high SiC content, usually more than 50 wt.%, and a typically low concentration of platinoids, usually less than 0.2 wt.% based on the SiC content. Typically, the platinoids are present as isolated particles in the form of metals or metal alloys, i.e., they possess the crystal structure and properties of the metal lattice, which may be slightly modified by alloying elements. The platinoid particles have particle sizes of < 50 nm.

[0013] Other substances from the production of the used catalysts are also present, e.g. so-called washcoats, which serve to anchor the platinoid particles and consist of, for example, very fine aluminum, cerium and zirconium oxide particles.

[0014] Furthermore, other substances from the application are present in the used catalysts, e.g. reaction products of the chemical processes in which the catalysts were used, or ash and soot particles in used diesel particulate filters.

[0015] Due to the intrinsic value of the catalytically active substances, these are recovered from used catalysts, for example, and reused to produce new catalysts.

[0016] Various processes are known for this. Typically, the catalysts are mechanically freed of adhering materials, such as metal containers (so-called canning in the case of automotive catalysts) and bearing mats. This can be followed by coarse grinding and fractionation to separate out further impurities and achieve the highest possible pre-concentration of platinoids. The material produced in this way is then usually treated using pyrometallic processes, which achieve a very high platinoid concentration. These platinoids are then separated and purified using further, usually hydrometallurgical, processes. In pyrometallic processes, the ground catalyst materials are mixed with fluxes and collector metals, such as Cu, Fe, Pb, and Ni, and the mixture is melted.The ceramics and washcoats contained in the crushed catalyst materials react with the fluxes to form silicate slags and can thus be separated from the metals.

[0017] An overview of these processes is given, for example, by I. Yakoumis et al, Cleaner Engineering and Technology 3 (2021 ) 100112, DOI: 10.1016 / j.clet.2O21.100112.

[0018] Since the introduction of the so-called 3-way catalyst in the 1970s, cordierite has been predominantly used as the catalyst substrate, which can be easily separated using the pyrometallurgical processes mentioned above.

[0019] Since the 2000s, catalysts using silicon carbide ceramics as substrates have been used in the automotive sector, but also in the chemical industry, e.g. as diesel particulate filters for cars and trucks.

[0020] For the purposes of the present invention, silicon carbide ceramics are understood to mean all ceramics that consist predominantly of silicon carbide, i.e., more than 70%. Other components may include silicon metal, silicate, nitride, oxynitride, or carbonaceous binder phases.

[0021] These silicon carbide ceramics are significantly more valuable than cordierite ceramics, as they are more complex to manufacture. In vehicle catalysts on SiC diesel particulate filters (including so-called cDPFs = catalyzed diesel particulate filters), the platinoid concentration is very low, ranging from only 0.2% (in older cDPFs) to 0.01% (in modern cDPFs). For example, with a typical 3:1 platinum and palladium mixture, this corresponds to a volume fraction of only 0.025 to 0.002% of platinoids in a SiC diesel particulate filter.

[0022] The concentration of platinoids in catalysts and used catalysts is determined by known analytical methods, such as XRF (X-ray fluorescence) or, particularly preferably, inductively coupled plasma optical emission spectrometry (ICP-OES) after wet chemical digestion.

[0023] In pyrometallurgical processes, these high silicon carbide contents are disruptive because the reducing nature of the carbide counteracts good slagging of the ceramic and thus its separation from the molten metal.

[0024] All known processes for recycling platinoids from SiC diesel particulate filters aim at processes in which the SiC is at least partially decomposed during the recovery of the platinoids from the catalyst materials.

[0025] JP 2011032510 A describes a two-stage process in which a metal recovery process is proposed for gold- or platinum-containing substances with a SiC content of >2.5%.

[0026] In the first step, alkali metal oxides, alkali metal carbonates, alkali metal hydroxides, and / or oxygen-containing components, and optionally metallic copper, are used to oxidize the material in a furnace process. This also converts a large amount of copper into slag, which is a significant process disadvantage. This disadvantage is remedied as far as possible in a second process step in a reducing atmosphere.

[0027] However, according to Wiraseranee et al. (The Japan Institute of Metals and Materials, Materials Transactions, Vol. 55, 1083-1090, 2014), this process is extremely complex and associated with significant losses of the gold- or platinum-containing substances to be recovered, particularly due to the use of alkali metal oxides. The slag produced in the first process step is alkaline, and the more alkaline it is, the greater the losses of the gold- or platinum-containing substances.

[0028] According to WO 2021 / 140012 A1, it is proposed to prepare a mixture of these catalyst materials with iron oxides for the recovery of platinoids from catalyst materials containing SiC, wherein iron oxides are to be added in such an amount that at least 65% of the SiC can be completely oxidized by means of iron oxide.

[0029] In a furnace process, a liquid iron melt and a liquid slag are then produced, with the iron melt containing the platinoids.

[0030] A disadvantage of the known processes is that high losses of platinoids occur, particularly when SiC is present in the platinoid-containing materials to be processed.

[0031] The object of the present invention is to provide a platinum silicide and silicon carbide-containing mixture in which the platinum silicides are present in high yield and / or high purity and are produced from platinum and SiC-containing materials using a simple and cost-effective process.

[0032] The object is achieved by the invention defined in the claims. Advantageous embodiments are the subject of the dependent claims, whereby the invention also includes combinations of the individual claims in the sense of an "and" connection, as long as they are not mutually exclusive.

[0033] In the platinoid silicide and silicon carbide-containing mixture according to the invention, platinoids are present in a concentration of at least 1 wt. %, and furthermore, in addition to silicon carbide particles and silicon carbide particle agglomerates, the platinoids are present as platinoid silicide particles and / or as agglomerates of platinoid silicide particles, and / or the platinoid silicide particles combine the silicon carbide particles to form an agglomerate and / or they are arranged on the surface of the silicon carbide particles, wherein the silicon carbide of the silicon carbide particles is present as technically pure silicon carbide. Advantageously, the platinoid silicide particles are present in island form on the surface of silicon carbide particles.

[0034] Further advantageously, the silicon carbide particles have an average grain size dso, measured by laser diffraction, of < 100 pm, advantageously an average grain size of 0.5 to 50 pm.

[0035] Also advantageously present as platinoid silicides are PtSi, PtSi2, PteSis, Pti2Sis, Pt2sSi?, PtsSi, Pt?Si2, Pt2Si, Pdo,84Sio,i6, PduSis, PdsSi, PdSi, SiPd2, SiRh2, SisRhs, RhSi, RhsSi4, Rh4Sis and / or mixed forms thereof.

[0036] And also advantageously, the silicon carbide particles have SiC contents of at least 95%, advantageously more than 98%.

[0037] It is also advantageous if the platinoids are present at a concentration of 2 to 10 wt.%, advantageously 5 to 8 wt.%.

[0038] It is also advantageous if, in addition to platinoid silicide particles and silicon carbide particles, impurities of less than 5 mass %, advantageously less than 2 mass %, are present in the mixture.

[0039] It is further advantageous if the mixture consists essentially of silicon carbide particles and platinoid silicide particles with or without impurities.

[0040] In the process according to the invention for producing a mixture containing platinoid silicide and silicon carbide, at least materials containing platinoid and silicon carbide are comminuted and analyzed at least with regard to their platinoid concentration. The comminuted materials are then subjected to a temperature treatment between 1400-2600 °C under vacuum or a non-oxidizing atmosphere with the addition of at least carbon and / or silicon to achieve a reaction of the oxides and silicates to CO and / or to achieve SiC formation and / or to achieve silicide formation of the platinoids. After the materials have been cooled, they are subjected to a mechanical treatment and fractionation into at least two fractions, wherein in one fraction at least platinoid silicide particles and silicon carbide particles are enriched in which the platinoids are present in a concentration of at least 1 Ma.-% and technically pure silicon carbide is present.

[0041] Advantageously, vehicle catalysts and / or industrial catalysts are used as materials containing at least platinoid and silicon carbide.

[0042] Furthermore, it is advantageous for materials containing at least platinoid and silicon carbide to be comminuted to an average grain size dso, measured by laser diffraction, of < 1000 pm.

[0043] Likewise advantageously, the comminution and / or mechanical treatment is carried out by applying a mechanical impulse, even more advantageously by mixing, grinding, autogenous grinding, by using eddy currents and / or ultrasound.

[0044] And also advantageously, the temperature treatment of the crushed composition is carried out at temperatures of 1,400 - 2,000 °C.

[0045] It is also advantageous if the temperature treatment of the crushed composition is carried out at temperatures of 2,000 - 2,600 °C.

[0046] Furthermore, it is advantageous if carbon and / or silicon are added before and / or during the temperature treatment, depending on the analysis of the platinoid and silicon carbide-containing materials, to realize a reaction of the oxides and silicates to CO and / or to realize SiC formation and / or to realize silicide formation of the platinoids.

[0047] It is also advantageous to add carbon in the form of soot, coke, or graphite, and silicon in the form of technically pure silicon or silicon dioxide. It is also advantageous to cool the materials after the heat treatment at a cooling rate of 10 to 1,000 K / min.

[0048] It is also advantageous if, after cooling and / or comminution and / or fractionation of the materials, one or more further temperature treatments are carried out, advantageously at temperatures between 800 and 1200 °C, under vacuum or in a non-oxidising atmosphere.

[0049] It is also advantageous if the fractionation of the crushed materials is carried out after temperature treatment and cooling by sieving, sifting, flotation, sedimentation, centrifugation and / or cyclone processes.

[0050] The present invention makes it possible for the first time to provide a platinoid silicide and silicon carbide-containing mixture in which the platinoid silicides are present in high yield and / or high purity, and which is produced from platinoid and SiC-containing materials using a simple and cost-effective process.

[0051] This is achieved by a platinoid silicide and silicon carbide-containing mixture in which platinoids are present at a concentration of at least 1 wt.%.

[0052] The concentration of platinoids in the platinoid silicide and silicon carbide-containing mixture according to the invention is preferably determined by ICP-OES. By specifying the platinoid concentration in the platinoid silicide and silicon carbide-containing mixture according to the invention, the elemental concentration of platinoids is determined, not the amount of platinoid silicides. Due to the different composition of the platinoid silicides, the proportion of platinoid silicides can vary depending on their silicon content. Therefore, specifying the platinoid concentration as a result of chemical analysis by ICP-OES is simpler and more accurate.In addition, for the recycling process and further processing of the platinoid silicide and silicon carbide-containing mixture according to the invention using known pyro- or hydrometallurgical processes, it is important to know the platinoid concentration and to compare it with the starting material in order to determine the quantitative and value-related loss or the recycling rate of platinoids.

[0053] The indication of the concentration of platinoids in the inventive platinoid-silicide- and silicon carbide-containing mixture expressly does not mean that platinoids are present in the inventive mixture as platinoid metal and / or platinoid-metal alloy; on the contrary, they are always present as platinoid-silicide compounds. In ICP-OES analysis, these silicides are dissolved by chemical digestion, and only then is the platinoid concentration determined.

[0054] Platinoid and silicon carbide-containing materials, in particular vehicle catalysts and / or industrial catalysts, were used as starting materials for producing the mixture according to the invention.

[0055] The production of the platinoid and silicon carbide-containing mixture according to the invention from these starting materials is particularly advantageous because the silicon carbide (SiC) present therein is already present in high purity and is not decomposed by the production process according to the invention and rendered unusable for further use.

[0056] Advantageously, the platinoids are present in the mixture according to the invention at a concentration of 2 to 10 wt.%, advantageously 5 to 8 wt.%.

[0057] Furthermore, in addition to the platinoid silicide particles and silicon carbide particles, impurities of less than 5 wt.%, advantageously less than 2 wt.%, are advantageously present in the mixture according to the invention.

[0058] According to the invention, in the platinoid silicide and silicon carbide-containing mixture, the silicon carbide particles are predominantly present in isolated form and / or as silicon carbide particle agglomerates, and the platinoids are present in isolated form as platinoid silicide particles and / or as agglomerates of platinoid silicide particles, and / or platinoid silicide particles combine with silicon carbide particles to form an agglomerate. Likewise advantageously, in the mixture according to the invention, the platinoid silicide particles are present in island form on the surface of the silicon carbide particles.

[0059] In the context of the present invention, agglomerates are understood to mean particles that are bonded together, which are loosely bonded to one another by electrostatic or van der Waals forces, but also firmly bonded particles that have arisen by sintering or intergrown crystallites or that adhere to one another by bonding with binding phases.

[0060] Also according to the invention, the silicon carbide in the silicon carbide particles of the mixture according to the invention is present as technically pure silicon carbide.

[0061] Advantageously, the silicon carbide particles have SiC contents of at least 95%, more advantageously more than 98%.

[0062] It is also advantageous if the silicon carbide particles in the mixture according to the invention have an average grain size dso, measured by laser diffraction, of < 100 pm, more advantageously from 0.5 to 50 pm.

[0063] It is also advantageous if PtSi, PtSi2, PteSis, Pti2Sis, Pt2sSi7, PtsSi, Pt?Si2, Pt2Si, Pdo,84Sio,i6, PduSis, PdsSi, PdSi, SiPd2, SiRh2, SisRhs, RhSi, RhsSi4, Rh4Sis and / or their mixed forms are present as platinoid silicides.

[0064] Furthermore, it is advantageous if the mixture according to the invention consists essentially of silicon carbide particles and platinoid silicide particles with or without impurities.

[0065] The platinoid silicide particles present according to the invention can be present either as individual particles or in island form on the surface of the silicon carbide particles with an average grain size d50 , measured by laser diffraction, of <100 pm, advantageously 0.5 to 50 pm. Average grain sizes d50 , measured by laser diffraction, of the silicon carbide particles of <20 pm are also advantageous. According to the invention, the platinoid silicide particles, whether isolated or adhering to the SiC particles, have a size of at least 0.5 pm, advantageously greater than 1 pm, and even more advantageously 5-10 pm, measured as the average grain size d50 (Sauter diameter) by image analysis on polished sections of the particle mixture.Thus, the platinoid silicide particles are at least 10 times larger, advantageously even 20 to 200 times larger, than the platinoid particles in the platinoid and silicon carbide-containing materials used as starting materials for the production of the platinoid-silicon carbide-containing mixture according to the invention, such as in particular in vehicle catalysts and / or in industrial catalysts.

[0066] Furthermore, it is important according to the invention that the platinoid silicides according to the invention are understood to be chemical compounds of the platinoids with silicon, which have their own crystal lattice and are therefore crystallographically distinct from pure precious metals and their alloys. The presence of platinoid silicides can be detected, for example, by X-ray diffraction methods. Furthermore, the platinoid silicides contain a discrete proportion of silicon, which can be detected, for example, by quantitative EDX analysis.

[0067] According to the invention, the platinoid silicide particles can also be located wholly or partially between silicon carbide particles, whereby they can also combine the silicon carbide particles to form an agglomerate.

[0068] Particularly advantageous platinoid silicide particles are PtSi, Pt2Si, and / or PdSi. Furthermore, the platinoid silicide particles can also contain small amounts of other elements, such as iron.

[0069] Furthermore, it is according to the invention that the concentration of platinoids in the mixture is > 1 wt.%, advantageously 2 - 10 wt.%, even more advantageously 5 - 8 wt.%.

[0070] Furthermore, it is advantageous if the amount of other impurities, i.e., everything that is not platinoid silicide particles and SiC particles, is < 5 mass %, even more advantageously < 2 mass %. The used catalysts used as starting materials, and in particular the used catalytically coated SiC diesel particulate filters, often still contain oxidic / silicate washcoats and contaminants, such as soot (carbon) and ash, such as zinc, calcium, phosphorus, and sulfur compounds. Furthermore, diesel particulate filters made of silicon carbide ceramic often contain so-called cements made of SiC particles, aluminosilicate fibers, and silicate binders.

[0071] Due to the inventive production process of the platinoid silicide and silicon carbide-containing mixture according to the invention, essentially all the components that do not consist of or contain SiC and platinoids are almost completely removed, so that only very small amounts of < 5 wt. %, advantageously < 2 wt. %, of impurities are present in the platinoid silicide and silicon carbide-containing mixture according to the invention.

[0072] It is a particular advantage of the present invention that after completion of the process according to the invention, a mixture according to the invention is present.

[0073] The mixture according to the invention can then be further processed using known methods and, in particular, pure platinoids can be produced from the platinoid silicides, which can be reused industrially with or without the implementation of further, known processing steps.

[0074] Furthermore, the object is achieved by a process for producing a mixture containing platinoid silicide and silicon carbide, in which at least materials containing platinoid and silicon carbide are comminuted.

[0075] It is particularly advantageous if vehicle catalysts and / or industrial catalysts are used as materials containing platinoid and silicon carbide.

[0076] Furthermore, it is advantageous if the platinoid- and silicon carbide-containing materials are comminuted to an average grain size d50 , measured by laser diffraction, of < 3000 pm, advantageously from 0.5 to 1000 pm, particularly advantageously from 0.5 to 500 pm. The comminution and / or mechanical treatment can advantageously be achieved by applying a mechanical impulse, advantageously by mixing, grinding, autogenous grinding, by using eddy currents and / or ultrasound.

[0077] Advantageously, the comminution and / or mechanical treatment can be carried out with an energy input between 0.1 and 5 MJ / kg.

[0078] After comminution of the platinoid and silicon carbide-containing materials as starting materials, according to the invention these are analyzed at least with regard to their concentration of platinoids and subsequently subjected to a temperature treatment between 1400-2600 °C under vacuum or non-oxidizing atmosphere.

[0079] It is advantageous if the temperature treatment of the crushed composition is carried out at temperatures of 1,400 - 2,000 °C.

[0080] It is also advantageous if the temperature treatment of the crushed composition is carried out at temperatures of 2,000 - 2,600 °C.

[0081] Advantageously, the addition of carbon and / or silicon can be carried out before and / or during the heat treatment, depending on the analysis of the platinoid and silicon carbide-containing materials, in order to realize a reaction of the oxides and silicates to CO and / or to realize SiC formation and / or to realize silicide formation of the platinoids.

[0082] It is also advantageous if the addition of carbon is realized in the form of soot or coke powder and the addition of silicon is realized in the form of metallic silicon or silicon oxide.

[0083] After the temperature treatment, the materials are cooled according to the invention.

[0084] It is advantageous if the materials are cooled after the heat treatment at a cooling rate of 10 to 1,000 K / min. Furthermore, according to the invention, after cooling, the materials are subjected to mechanical treatment and fractionation into at least two fractions.

[0085] In this case, the platinoid-silicide and silicon carbide-containing mixture according to the invention is formed in one fraction, in which the platinoids are present at a concentration of at least 1 mass % and the silicon carbide in the silicon carbide particles is present as technically pure silicon carbide.

[0086] It is also advantageous if the fractionation of the crushed materials is carried out after the temperature treatment and cooling by sieving, sifting, flotation, sedimentation, centrifugation and / or cyclone processes.

[0087] After comminution of the starting materials in the form of platinoid and silicon carbide-containing materials, these are analyzed according to the invention for their material composition, especially with regard to their concentration of platinoids, silicon carbide, carbon, silicon metal and other silicon compounds, such as Si oxides and silicates, as well as the total oxygen content.

[0088] Commonly known methods are used for the analysis, such as ICP-OES for the platinoids, quantitative X-ray diffraction (XRD with Rietfeld analysis for SiC), XRF (for total Si and other elements), as well as the inert gas melting method (oxygen) and the oxidation method with NDIR (free carbon).

[0089] The starting materials in the form of platinoid and silicon carbide-containing materials from used catalysts, preferably from used catalysts and especially from used catalytically coated SiC diesel particulate filters, can contain many different types and quantities of components other than SiC and platinoids. The exact amount and type of addition depends on the analytical results.

[0090] Depending on the analytical results, carbon and / or silicon additives are added to the ground starting materials to achieve a reaction of the oxides and silicates to form CO, SiC formation, and silicide formation of the platinoids. It is particularly advantageous to set a molar concentration of >50 mol% of silicon to platinoid with respect to the platinoid concentration; particularly advantageously, 50-75 mol%.

[0091] To realize these additions, metallic silicon powder, silicon dioxide powder and / or carbon, advantageously in the form of soot and / or coke powder, can be added to the crushed starting materials.

[0092] It has been found that the best approach for analyzing and adding carbon and / or silicon is to first use the analyzed oxygen and silicon content, and then calculate one mole of carbon per mole of oxygen and one mole of carbon per mole of silicon not bound in SiC and not required for the reaction of the platinoid metals to form platinoid silicides, and add these to the mixture. The amount of silicon required for the formation of the platinoid silicides is at least 1 mole per mole of platinoids, preferably 1-1.5 moles per mole of platinoids.

[0093] If the crushed feedstocks already contain free carbon, e.g., in the form of soot from used diesel particulate filters, this amount is deducted from the calculated amount. In the rare cases where the amount of carbon present in the crushed feedstocks is too high, silicon is added to the mixture in an amount of 1 mol per mole of carbon and at least 1 mol per mole of platinoids, preferably 1-1.5 mol per mole of platinoids.

[0094] It has also been shown that the processes involved in heat treatment are very complex, and surprisingly, almost all oxides, silicates, and other compounds other than SiC and platinoids are removed from the mixture. The oxides and silicates escape not only in the form of CO, but also as volatile compounds, such as Al2O, AlO, or SiO, while other components evaporate in their elemental form.

[0095] In this respect, the above-mentioned procedure of adding carbon and / or silicon is preferred, but not absolutely necessary.

[0096] Due to the high SiC content of the starting materials and the high temperature during the heat treatment according to the invention, the oxide components are always reduced. If the free carbon content is too low for this, this leads to partial decomposition of the SiC and the formation of CO and free silicon, which in turn promotes the formation of platinoid silicides.

[0097] The person skilled in the art can determine, with just a few tests, a desired or even optimal amount of carbon and / or silicon additives for an existing mixture, which results in a high SiC and platinoid silicide content.

[0098] It is merely preferable not to add too much carbon to the mixture than is necessary for the reduction of the oxides and silicates, since this would leave residual free carbon in the mixture and the formation of the platinoid silicides would not be complete.

[0099] Subsequently, according to the invention, the crushed material, optionally provided with additives, is subjected to a temperature treatment between 1400 - 2600 °C under vacuum or non-oxidizing atmosphere.

[0100] Technical protective gas atmospheres such as argon or nitrogen atmospheres with a residual oxygen content of < 100 ppm are used as non-oxidizing atmospheres.

[0101] However, mixtures with CO can also be used, for example, since these do not lead to the oxidation of the SiC.

[0102] The temperature treatment is possible under slight overpressure as well as under negative pressure, up to vacuum.

[0103] The heat treatment is advantageously carried out under an argon atmosphere. The heat treatment can be carried out in both batch furnaces and in continuous operation.

[0104] The residence times of the crushed and additive-containing material at the maximum temperatures used are advantageously between 10 minutes and 900 minutes, even more advantageously between 30 and 180 minutes, whereby this also depends on the volume of crushed materials to be treated and on the temperature.

[0105] During the thermal treatment of the crushed materials, at least platinoid silicides and technically pure silicon carbide are formed. After cooling the crushed materials, which is advantageously carried out at a cooling rate of 10 to 1,000 K / min, the invention then involves mechanical treatment and fractionation into at least two fractions, particularly with regard to the mass of platinoids.

[0106] By the procedure according to the invention, one of the fractions produced during the fractionation contains the platinoid-silicide and silicon carbide-containing mixture according to the invention with a concentration of at least 1 wt.% platinoids and technically pure silicon carbide.

[0107] The mechanical treatment can advantageously be carried out as already described. The mechanical treatment can advantageously be carried out with an energy input between 0.1 and 5 MJ / kg.

[0108] Fractionation into at least two fractions, particularly with regard to the mass of platinoids, can advantageously be achieved by physical separation of the crushed materials after heat treatment and cooling. Physical separation can be achieved, for example, by sieving, sifting, centrifugation, cyclone processes, sedimentation, or flotation. Due to the high density of platinoid silicides compared to silicon carbide, separation processes based on differences in density, such as sedimentation, sifting, and centrifugation, are particularly preferred.

[0109] For example, after physical separation, fractions containing, for example, three, four, or five powders with different platinoid masses can be obtained. Depending on the subdivision and composition of the powder groups, these are then advantageously assigned to two fractions: a fraction without platinoids and a fraction with platinoids.

[0110] It is readily possible for a person skilled in the art to separate the respective powder fractions into the two fractions according to the invention based on the mass of platinoids with just a few fractionation experiments and content analyses. Advantageously, the concentration of platinoids in one fraction is >40 times higher, and even more advantageously, by a factor of 80-300 times higher, than in the other fraction.

[0111] Relative to the concentration of the platinoids in the starting materials used, the concentration of the platinoids in the fraction containing the mixture according to the invention is higher by a factor of > 8, advantageously by a factor of 9 to 30.

[0112] Advantageously, the amount of the fraction with the high concentration of platinoid silicides is < 10%, even more advantageously < 5%, based on the total amount of material before fractionation.

[0113] In the context of the present invention, fraction is understood to mean a division of the composition after the temperature treatment and cooling with regard to its mass of platinoids, produced by physical separation.

[0114] A mechanical treatment as separation can cause the apparently brittle platinoid silicides to chip or break off, whereby they can be separated from the silicon carbide particle surfaces or interstices and further crushed during a further mechanical treatment.

[0115] It is further advantageous if, after cooling and / or after comminution and / or after fractionation of the materials, one or more further temperature treatments are carried out, advantageously at temperatures between 800 and 1200 °C, under vacuum or in a non-oxidising atmosphere.

[0116] It is advantageous if, after cooling the crushed material, it is subjected to one or more further temperature treatments at temperatures between 800-1200 °C under vacuum or non-oxidizing atmosphere, and the material is cooled again, advantageously at a cooling rate of 10 to 1,000 K / min, and only then does the mechanical treatment and fractionation take place.

[0117] It is also advantageous if, after the mechanical treatment and fractionation, one of the fractions is again subjected to one or more further temperature treatments at temperatures between 800-1200 °C under vacuum or non-oxidizing atmosphere, and the material is again cooled, advantageously at a cooling rate of 10 to 1,000 K / min, and this fraction is then again subjected to mechanical treatment and further fractionation.

[0118] By this procedure it is possible to increase the content of platinoid silicides in the platinoid silicide and silicon carbide-containing mixture according to the invention.

[0119] It is surprising according to the invention that the platinoid silicides, after the heat treatment, deposit in island form or as a layer on the surface of silicon carbide particles and / or between the silicon carbide particles.

[0120] It is known that the metallic impurities in SiC waste in the form of Fe, Va, Ti, Al, B, Mn, Wo, Cr, Ni form metal silicides during high-temperature treatment (WO 2021 / 152134 A1 ).

[0121] However, this could not be expected for platinoids, since the state of the art had to assume a non-separable change in the platinoids for the reaction of platinoids with silicon carbide at high temperatures, known as the Kirkendall effect. According to this theory, the reaction of silicon carbide with platinoids results in strip-like, alternating deposits of graphite and platinoid silicides forming on the silicon carbide particles, leading to a further fine distribution of the platinoid silicides, making their separation from the silicon carbide particles virtually impossible (for Pt: MRRijinders, et al: Solid State Ionics Vol. 95, 51-59, 1997; for Rh and Pd: Demkowicz, et al: Solid State Ionics, Vol. 179, 2313-2321, 2008).

[0122] Quite surprisingly, contrary to the Kirkendall effect, the platinoid silicides deposit in island-like forms and / or as a layer on or between the silicon carbide particles. At the same time, the platinoid silicide particles coarsen from their original size of just a few nanometers to platinoid silicide particles measuring up to a few micrometers. This makes the platinoid silicide particles at least 10 times larger than the platinoid particles in the starting materials used for used automotive or industrial catalysts, and advantageously by a factor of 20-200.

[0123] This allows the platinoid silicide particles to be separated relatively easily from the silicon carbide particles after cooling and fractionation.

[0124] With the solution according to the invention, platinoids from silicon carbide and platinoid-containing materials can be recycled comparatively easily and recovered in high concentrations.

[0125] In addition to this advantage, the solution according to the invention also recycles the at least technically pure, and usually even highly pure, silicon carbide contained in the platinoid and silicon carbide-containing materials.

[0126] This has not been possible with the current state of the art methods.

[0127] The at least one fraction enriched with platinoid silicide particles according to the invention can then be further subjected to conventional hydrometallurgical or melt-metallurgical purification processes to produce pure platinoid metals. Due to the high platinoid concentration in the platinoid silicide and silicon carbide-containing mixture according to the invention, conventional melt-metallurgical processes are then easier to carry out, for example, since significantly less disruptive SiC is introduced into the melt per precious metal concentration than with conventionally used platinoid catalysts.

[0128] The other fraction or fractions which are not enriched with platinoid silicide particles but consist essentially only of silicon carbide can be further processed with the usual further processing steps into typical silicon carbide powders which are used, for example, as powder for the production of technical ceramics or refractory products, as diesel particulate filters or as abrasives.

[0129] Overall, the advantage of the invention over the prior art is thus clear. With the material and process according to the invention, the amount of silicon carbide that interferes with pyro- or hydrometallurgical processes is reduced by 90-95%, and 90-95% of the silicon carbide contained in the used catalysts can be reused.

[0130] The invention is explained in more detail below using an exemplary embodiment.

[0131] Example 1

[0132] 50 kg of used catalytically coated diesel particulate filters from vehicles are pre-crushed with a jaw crusher and then crushed in a ball mill to an average particle size d50 of 600 pm, measured by laser diffraction.

[0133] This crushed material is analyzed and a content of 79 mass% SiC (analyzed by XRD), a total oxygen content of 6.8 mass% (analyzed by LECO oxygen analyzer), a free carbon content of 1.2 mass% (analyzed by LECO carbon analyzer), and a total silicon content of 47 mass% Si (analyzed by XRF) are determined. The total amount of silicon analyzed and the analyzed SiC content result in a content of 3.5 mass% silicon, which is not bound in SiC. Furthermore, trace elements such as aluminum, zinc, calcium, phosphorus, sulfur, cerium, and others in various compounds were analyzed by XRF as a total element content of 12 mass%, as well as a platinum content of 0.107 mass% and a palladium content of 0.036 mass% (a total platinoid content of 0.143 mass%) using ICP-OES.The particle size of the platinoid particles, present as platinoid metals, analyzed in a FESEM, is below 50 nm.

[0134] For the addition of carbon, a molar amount of 50 mol% carbon based on the existing molar mass of oxygen is calculated for the reaction of the total oxygen content with carbon to form CO, corresponding to a quantity of 2550 g of carbon based on the 50 kg total amount of crushed material. For the formation of platinoid silicides, a molar amount of 1 mol% silicon based on the molar amount of the platinoid content is calculated, corresponding to a quantity of 6.2 g of silicon based on the 50 kg total amount of crushed material. Of the available analyzed total amount of silicon of 3.5 mass%, which is not bound in SiC, corresponding to 1750 g of silicon, 1743.8 g of silicon remain after deducting the amount of 6.2 g required for platinoid formation, for which an addition of 1 mol of carbon per mole of silicon to form SiC is calculated as 1490 g of carbon.The total required amount of carbon is 4040 g, based on the 50 kg total amount of crushed material. Taking into account the 1.2 mass% free carbon already contained in the mixture, the amount is reduced accordingly and added in the form of 3440 g of coke powder with a grain size of < 63 pm and mixed in a tumbler mixer.

[0135] The crushed material is loosely filled into graphite crucibles. The graphite crucibles are heated in a protective gas furnace under an argon atmosphere at 10 K / min to 2500 °C and held at 2500 °C for 120 minutes.

[0136] After cooling at a rate of 20 K / min, the powdered crucible contents are removed from the crucibles, homogenized again in a ball mill and loosely filled into graphite crucibles and heated again in a protective gas furnace under argon atmosphere at 10 K / min to 1150°C and held at 1150°C for 30 min.

[0137] After further cooling at a rate of 15 K / min, the remaining material in the crucibles (43 kg of powdered contents) was determined by weighing. The material was removed from the crucibles and mechanically treated in an air mill at 0.1 MJ / kg. Subsequently, the powder was separated into two powder fractions with particle sizes of < 40 pm and > 40 pm by sifting. The amount of the powder fraction with particle sizes < 40 pm was 3460 g.

[0138] Before mechanical treatment in the air mill, the thermally treated powder exhibits numerous agglomerates of silicon carbide particles held together by the platinoid silicides. After mechanical treatment and the thermal treatment, the silicon carbide particles and platinoid silicide particles are predominantly present in isolated form.

[0139] After mechanical treatment in an air mill, the powder fraction with a particle size of < 40 pm has a SiC content of 98.5 wt.% SiC. The total impurities (Fe, Al, Ce), analyzed by XRF, are 1.5 wt.%. The platinoid content is 2.15 wt.%, measured by ICP-OES. XRD identified the diffraction lines of PtSi, in addition to the SiC polytypes 6H and 4H, and very small amounts of PdSi and Pt2Si. The particle size distribution, measured by laser diffraction, has a d50 value of 18 pm. The analysis in a FESEM on polished sections of the powder particles shows, in addition to the predominantly isolated SiC particles, predominantly isolated platinoid silicide particles, and island-shaped platinoid silicide particles adhering to SiC particles and platinoid silicide particles in the interstices between agglomerated SiC particles, whereby the platinoid silicide particles have particle sizes of approximately 1 - 8 pm.Using quantitative image analysis, the average particle size of the platinoid silicide particles was determined to be 5.2 pm, with a d50 value. Semi-quantitative EDX analysis demonstrated that the individual platinoid silicide particles contain a high platinum content of approximately 70 wt.%, palladium of approximately 20 wt.%, and silicon of approximately 8 wt.%, along with minor impurities of iron, nickel, and cerium.

[0140] After mechanical treatment in the air mill, the other powder fraction with a particle size of > 40 pm has a SiC content of 99.1 wt.%. The total impurities (Fe, Al, Ce), analyzed by XRF, are 1.5 wt.%. The platinoid content is 0.9 wt.%, measured by ICP-OES.

[0141] Platinoid concentration, measured by ICP-OES, is below 0.003 wt.%. The particle size distribution, measured by laser diffraction, has a d50 value of 93 pm.

[0142] Compared to the crushed starting material before heat treatment, mechanical treatment, and fractionation, the platinoid concentration in the powder fraction < 40 pm after thermal treatment, mechanical treatment, and fractionation is 14 times higher. For further processing of the powder fraction < 40 pm for platinoid recovery, the SiC content was reduced from 40 kg in the crushed starting material to 3.3 kg in the powder fraction < 40 pm, i.e., by approximately 92%. The SiC powder in the fraction > 40 pm is present in an amount of 37.7 kg of SiC with a purity of 99.1% as technically clean SiC, i.e., 94% of the SiC can be reused.

Claims

Patent claims 1. A mixture containing platinoid silicide and silicon carbide, in which platinoids are present in a concentration of at least 1 mass%, and in which, in addition to silicon carbide particles and silicon carbide particle agglomerates, the platinoids are present as platinoid silicide particles and / or as agglomerates of platinoid silicide particles, and / or the platinoid silicide particles combine the silicon carbide particles to form an agglomerate and / or are arranged on the surface of the silicon carbide particles, wherein the silicon carbide of the silicon carbide particles is present as technically pure silicon carbide.

2. Platinoid silicide and silicon carbide-containing mixture according to claim 1, wherein the platinoid silicide particles are present in island form on the surface of silicon carbide particles.

3. Platinoid silicide and silicon carbide-containing mixture according to claim 1, wherein the silicon carbide particles have an average grain size dso, measured by laser diffraction, of < 100 pm, advantageously an average grain size of 0.5 to 50 pm.

4. Platinoid silicide and silicon carbide-containing mixture according to claim 1, in which PtSi, PtSi2, PteSis, Pti2Sis, Pt2sSi7, PtsSi, Pt?Si2, Pt2Si, Pd0,84Sio,ie, PduSis, PdsSi, PdSi, SiPd2, SiRh2, SisRhs, RhSi, RhsSi4, Rh4Sis and / or mixed forms thereof are present as platinoid silicides.

5. Platinoid silicide and silicon carbide-containing mixture according to claim 1, wherein the silicon carbide particles have SiC contents of at least 95%, advantageously more than 98%.

6. Platinoid-silicide- and silicon carbide-containing mixture according to claim 1, wherein the platinoids are present at a concentration of 2 to 10 wt.%, advantageously 5 to 8 wt.%, of platinoids.

7. Platinoid silicide and silicon carbide-containing mixture according to claim 1, in which in addition to platinoid silicide particles and silicon carbide particles in the mixture Impurities of less than 5 mass%, advantageously less than 2 mass%, are present.

8. Platinoid silicide and silicon carbide-containing mixture according to claim 1, wherein the mixture consists essentially of silicon carbide particles and platinoid silicide particles with or without impurities.

9. A process for producing a mixture containing platinoid silicide and silicon carbide, in which at least materials containing platinoid and silicon carbide are comminuted and analyzed at least with regard to their concentration of platinoids, the comminuted materials are then subjected to a temperature treatment between 1400-2600 °C under vacuum or a non-oxidizing atmosphere with the addition of at least carbon and / or silicon to achieve a reaction of the oxides and silicates to form CO and / or to achieve SiC formation and / or to achieve silicide formation of the platinoids, and after the materials have been cooled, they are subjected to a mechanical treatment and fractionation into at least two fractions, one fraction being enriched in at least platinoid silicide particles and silicon carbide particles in which the platinoids are present in a concentration of at least 1 Ma.-% and technically pure silicon carbide is present.

10. The method according to claim 9, wherein vehicle catalysts and / or industrial catalysts are used as materials containing at least platinoid and silicon carbide.

11. A process according to claim 9, wherein at least platinoid- and silicon carbide-containing materials are comminuted to an average grain size d50, measured by laser diffraction, of < 1000 pm.

12. Method according to claim 9, wherein the comminution and / or mechanical treatment is carried out by applying a mechanical impulse, advantageously by means of mixing, grinding, autogenous grinding, by using eddy currents and / or ultrasound.

13. The method according to claim 9, wherein the temperature treatment of the comminuted composition is carried out at temperatures of 1,400 - 2,000 °C.

14. The method according to claim 9, wherein the temperature treatment of the comminuted composition is carried out at temperatures of 2,000 - 2,600 °C.

15. The method according to claim 9, wherein carbon and / or silicon are added before and / or during the temperature treatment depending on the analysis of the platinoid and silicon carbide-containing materials to realize a reaction of the oxides and silicates to CO and / or to realize SiC formation and / or to realize silicide formation of the platinoids.

16. A process according to claim 9, wherein carbon is added in the form of soot, coke or graphite and silicon is added in the form of technically pure silicon or silicon dioxide.

17. The method according to claim 9, wherein the cooling of the materials after the temperature treatment is carried out at a cooling rate of 10 to 1,000 K / min.

18. A process according to claim 9, wherein after cooling and / or after comminution and / or after fractionation of the materials, one or more further temperature treatments are carried out, advantageously at temperatures between 800 and 1200 °C, under vacuum or in a non-oxidising atmosphere.

19. A process according to claim 9, wherein the fractionation of the comminuted materials after the temperature treatment and cooling is carried out by sieving, sifting, flotation, sedimentation, centrifugation and / or cyclone processes.