Method for recovering platinum group metals from exhaust gas purification catalysts of scrapped automobiles

Abstract

The application provides a method for recovering platinum group metals from waste automobile exhaust catalysts, and belongs to the field of precious metal recovery. The method comprises the following steps: crushing and impurity removal pretreatment of the waste catalyst to obtain solid residue; mixing the obtained solid residue with lye and then performing hot-pressing activation to obtain active residue; using an acidic leaching system of hydrochloric acid-hydrogen peroxide-sodium chloride to leach the active residue to obtain a leaching solution rich in platinum group metals; adjusting the acidity of the leaching solution and then adding a first adsorption material to selectively adsorb platinum and palladium, and separating the supernatant and platinum / palladium enrichment material; adjusting the acidity of the supernatant and then adding a second adsorption material to selectively adsorb rhodium, and performing solid-liquid separation to collect rhodium enrichment material; and performing elution and refining on the platinum / palladium enrichment material and the rhodium enrichment material respectively to recover platinum, palladium and rhodium. Through the recovery method of optimized design of alkaline hot-pressing activation-mild acidic directional leaching-two-stage magnetic adsorption separation, the platinum, palladium and rhodium in the waste automobile exhaust catalysts are efficiently recovered.

Description

Technical Field

[0001] This invention belongs to the field of precious metal recycling technology, and specifically relates to a method for recovering platinum group metals from waste automobile exhaust purification catalysts. Background Technology

[0002] The platinum group metal content in automotive exhaust purification catalysts reaches 0.1%~0.3%. The waste catalysts generated after failure have become an important secondary resource. However, the platinum group metal content in waste catalysts is low, the occurrence state is complex, and they are often encapsulated by the carrier due to high-temperature sintering, making recycling difficult.

[0003] Existing recycling technologies are mainly divided into pyrometallurgical and hydrometallurgical processes. Traditional all-hydrometallurgical processes often use aqua regia or hydrochloric acid-chlorine systems, which are highly corrosive, produce toxic gases, and have poor selectivity, resulting in the leaching of large amounts of impurities such as aluminum and silicon, increasing the difficulty and cost of subsequent separation. Although the combined pyrometallurgical-hydrometallurgical process has a higher recovery rate, it suffers from problems such as high energy consumption, generation of harmful waste gases and residues, and significant environmental pressure.

[0004] In the wet separation process, traditional solvent extraction and ion exchange technologies suffer from problems such as long process time, unsatisfactory selectivity, and difficulty in separating and recovering adsorbents. Summary of the Invention

[0005] Therefore, the present invention aims to provide a method for recovering platinum group metals from waste automotive exhaust purification catalysts, in order to solve at least one of the technical problems in the background art.

[0006] This invention is implemented as follows:

[0007] This invention provides a method for recovering platinum group metals from waste automotive exhaust purification catalysts, the method comprising the following steps:

[0008] S1, the spent catalyst is crushed and removed before being treated to obtain solid slag;

[0009] S2, the obtained solid slag is mixed with alkaline solution and then hot-pressed to activate it, thus obtaining an active slag enriched with platinum group metals.

[0010] S3, the activated slag is leached using an acidic leaching system of hydrochloric acid-hydrogen peroxide-sodium chloride to obtain a leachate enriched with platinum group metals.

[0011] S4, after adjusting the acidity of the leachate, add the first adsorbent material to selectively adsorb platinum and palladium, and separate the supernatant and platinum / palladium enrichment material;

[0012] S5, after adjusting the acidity of the supernatant, add the second adsorbent material to selectively adsorb rhodium, separate the solid and liquid, and collect the rhodium-enriched material;

[0013] S6, the platinum / palladium enriched material and the rhodium enriched material are eluted and refined to recover platinum, palladium and rhodium;

[0014] The first adsorbent material comprises, from the inside out: a layer of superparamagnetic iron oxide nanoparticles, a silica coating layer, and a polyamide-amine dendritic macromolecular layer grafted onto the silica coating layer and having thiourea functional groups at the ends;

[0015] The second adsorbent material comprises, from the inside out: a cluster of superparamagnetic iron oxide nanoparticles and a modified silica coating layer; the modified silica refers to ordered mesoporous silica with amine and thiol bifunctional groups fixed by chemical bonds.

[0016] Further, S2 specifically includes: mixing the solid slag with an alkaline solution of 40%~70% at a solid-liquid ratio of 1:3~1:5, and reacting it at 150℃~250℃ and 0.5MPa~3.0MPa for 1h~5h;

[0017] The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

[0018] Furthermore, step S3 is as follows:

[0019] First, add 2 mol / L to 6 mol / L hydrochloric acid solution to the activated slag at a solid-liquid ratio of 1:5 to 10 to obtain a slurry.

[0020] After starting the stirring and heating to 70℃~90℃, slowly add hydrogen peroxide, accounting for 3%~8% of the total volume of the slurry, and add sodium chloride to maintain the total chloride ion concentration in the reaction system at 1mol / L~3mol / L;

[0021] Continue stirring and keeping the reaction at a constant temperature for 2 to 4 hours. After the reaction is complete, separate the solid and liquid phases to obtain a leachate enriched with platinum group metals.

[0022] Furthermore, the preparation method of the first adsorbent material in step S4 includes the following steps:

[0023] Provides superparamagnetic Fe3O4 nanoparticles;

[0024] Fe3O4@SiO2 nanoparticles were obtained by coating Fe3O4 nanoparticles with a silica intermediate layer using the Stöber method.

[0025] Fe3O4@SiO2 nanoparticles were pretreated with surface amination.

[0026] Fe3O4@SiO2@PAMAM is obtained by grafting polyamide-amine dendritic macromolecules of a target generation onto the surface of Fe3O4@SiO2 nanoparticles pretreated with amination by alternating Michael addition and amidation transfer reactions; the target generation is 1.0~5.0.

[0027] Fe3O4@SiO2@PAMAM reacts with isothiocyanate to graft thiourea functional groups onto the ends of dendritic macromolecules.

[0028] Furthermore, in step S4, the acidity of the leachate is adjusted to a hydrochloric acid environment of 1 mol / L to 3 mol / L; the temperature of the adsorption process is 40℃ to 60℃; the adsorption time is 60 min to 120 min; and the solid-liquid ratio of the first adsorbent to the leachate is 1:300 to 700.

[0029] Furthermore, the preparation method of the second adsorbent material in step S5 includes the following steps:

[0030] Provides superparamagnetic Fe3O4 nanoparticle clusters;

[0031] Using hexadecyltrimethylammonium bromide as a template agent, ordered mesoporous silica was coated onto Fe3O4 nanoparticle clusters via a sol-gel method, and the template agent was removed by extraction to obtain Fe3O4@mesoporous SiO2 microspheres.

[0032] The Fe3O4@mesoporous SiO2 microspheres are mixed with a silanizing agent in an inert organic solvent and subjected to a surface silanization reaction via a one-step or stepwise method, thereby simultaneously introducing amine functional groups and sulfur-containing functional groups onto the surface of mesoporous silica; the silanizing agent comprises silanes that can provide amine groups and silanes that can provide sulfur-containing functional groups.

[0033] Furthermore, the pore size of the mesoporous silica is 3nm~10nm.

[0034] Furthermore, in step S5, the acidity of the supernatant is adjusted to a hydrochloric acid environment of 3 mol / L to 6 mol / L; the temperature of the adsorption process is 50℃ to 70℃; the adsorption time is 90 min to 150 min; and the solid-liquid ratio of the second adsorbent to the supernatant is 1:200 to 400.

[0035] Further, in step S6, the platinum / palladium enriched material is eluted using a thiourea hydrochloric acid solution with a concentration of 0.3 mol / L to 0.7 mol / L.

[0036] Furthermore, in step S6, the rhodium-enriched material is eluted using a thiourea-sulfuric acid solution with a concentration of 0.05 mol / L to 0.15 mol / L.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. This invention achieves efficient recovery of platinum, palladium, and rhodium from waste automotive exhaust catalysts through an optimized alkaline hot-press activation-mild acidic directional leaching-two-stage magnetic adsorption separation method.

[0039] 2. This invention provides two adsorbent materials based on superparamagnetic materials and designed for specific metals. The thiourea functional group of the first-stage adsorbent targets Pt / Pd, while the amine-thiol group of the second-stage adsorbent targets Rh in a synergistic manner. They have little interference with each other and can accurately capture target elements from complex solutions.

[0040] 3. The two adsorbent materials of the present invention have good stability and can be recycled multiple times, reducing the cost of a single treatment.

[0041] 4. This invention uses a mild leaching system of hydrochloric acid and hydrogen peroxide, which completely avoids the use of aqua regia and the resulting toxic nitrogen oxide waste gas in traditional processes, and also eliminates the need for dangerous gases such as chlorine, resulting in high production safety.

[0042] 5. This invention uses an alkaline hot-pressing activation liquid to recycle aluminum, achieving synergistic resource recovery; the mild leaching system has high selectivity and low impurity dissolution, reducing the amount of waste residue and waste liquid generated and the difficulty of treatment from the source.

[0043] 6. Compared with the energy-intensive atmospheric pressure alkali roasting and pyrometallurgical smelting processes, the hot pressing activation and all-wet process of the present invention significantly reduces energy consumption. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] A method for recovering platinum group metals from waste automotive exhaust purification catalysts includes the following steps S1 to S6.

[0046] S1, the spent catalyst is crushed and removed before being treated to obtain solid slag;

[0047] Waste automotive exhaust purification catalyst (hereinafter referred to as waste catalyst) is removed from the vehicle exhaust pipe and mechanically crushed to a certain particle size (such as 100 mesh to 200 mesh) to increase the reaction surface area. Then, strong magnetic separation is used to remove most of the iron impurities from the waste catalyst tank and attached to it, reducing the impurity load of subsequent processes.

[0048] S2, the obtained solid slag is mixed with alkaline solution and then hot-pressed to activate it, thus obtaining an active slag enriched with platinum group metals.

[0049] Specifically, the solid slag is mixed with an alkaline solution (sodium hydroxide solution or potassium hydroxide solution) with a concentration of 40%~70% at a solid-liquid ratio of 1:3~1:5, and placed in a high-pressure reactor and reacted at 150℃~250℃ (preferably 180℃~220℃) and 0.5MPa~3.0MPa (preferably 1.0MPa~2.0MPa) for 1h~5h (preferably 2h~4h). After the reaction is completed, hot filtration is performed, and the solid residue is collected and thoroughly washed with hot water until neutral to obtain an active slag enriched with platinum group metals.

[0050] The purpose of this step is to dissolve the alumina (γ-Al₂O₃) in the support of the spent catalyst. Upon heating, this reacts with a strong alkali such as sodium hydroxide or potassium hydroxide to produce aluminates and water. The filtrate from the hot filtration (mainly containing aluminates) can be used to recover aluminum, for example, by adjusting the pH to prepare aluminum hydroxide.

[0051] S3, the activated slag is leached using an acidic leaching system to obtain a leachate enriched with platinum group metals;

[0052] The acidic leaching system is a synergistic system of hydrochloric acid, hydrogen peroxide, and sodium chloride. This step specifically involves:

[0053] S31. First, add 2 mol / L to 6 mol / L hydrochloric acid solution to the activated slag obtained in step S2 at a solid-liquid ratio of 1:5 to 10 to obtain a slurry;

[0054] S32. After starting the stirring and heating to 70℃~90℃, slowly add 3%~8% of the total volume of hydrogen peroxide (concentration of 30%), and add sodium chloride to maintain the total chloride ion concentration in the reaction system at 1mol / L~3mol / L;

[0055] S33. Continue stirring and keeping the temperature constant for 2-4 hours. After the reaction is complete, separate the solid and liquid phases to obtain a leachate enriched with platinum group metals.

[0056] The synergistic system of hydrochloric acid, hydrogen peroxide, and sodium chloride avoids the generation of chlorine gas and has a much lower corrosiveness than aqua regia. Since the carrier of the spent catalyst has been largely removed in the S2 step, acid consumption is significantly reduced, and the dissolution rate of impurities (such as Al, Si, Fe, Ca, etc.) is extremely low, achieving directional leaching of platinum group metals. Highly efficient and selective leaching of platinum group metals is achieved under relatively mild conditions; hydrogen peroxide, as a green oxidant, oxidizes the elemental metals into ions, and the chloride ions of sodium chloride provide ligands to form stable chloride anions (such as PtCl6). 2- (etc.), and then dissolve in the leachate.

[0057] S4, after adjusting the acidity of the leachate, add the first adsorbent material to selectively adsorb platinum and palladium, and separate the supernatant and platinum / palladium enrichment material;

[0058] The first adsorbent material comprises, from the inside out: a layer of superparamagnetic iron oxide nanoparticles, a silica coating layer, and a polyamide-amine dendritic material layer grafted onto the silica coating layer with thiourea functional groups at the ends.

[0059] The acidity of the leachate is adjusted to a hydrochloric acid environment of 1 mol / L to 3 mol / L; the adsorption temperature is 40℃ to 60℃; the adsorption time is 60 min to 120 min; the solid-liquid ratio of the first adsorbent to the leachate is 1:300 to 700; and continuous stirring is allowed during adsorption. The thiourea functional group and the chloride anion (PtCl6) 2- PdCl4 2- Strong selective coordination occurs between platinum and palladium, which are firmly captured in a dendritic macromolecular network. After adsorption, a powerful permanent magnet is placed outside the reaction vessel; the first adsorbent material, which has adsorbed platinum / palladium group metals, is rapidly attracted to the magnet, achieving complete separation from the solution. The supernatant is collected for further processing, and the solid is the platinum / palladium enriched material. The magnetically adsorbed platinum / palladium enriched material can be washed with dilute hydrochloric acid solution to remove physically adsorbed or weakly bound impurity ions. The washed liquid can be combined with the supernatant for further processing.

[0060] The preparation method of the first adsorbent material includes the following steps:

[0061] S41. Provides superparamagnetic Fe3O4 nanoparticles;

[0062] Superparamagnetic Fe3O4 nanoparticles can be commercially available or synthesized in-house, such as by a coprecipitation method. Specifically, FeCl3·6H2O and FeSO4·7H2O are dissolved in deoxygenated deionized water in a specific molar ratio, with the ratio of ferric iron to ferrous iron ranging from 1.5 to 2.5:1. Under an inert atmosphere (e.g., N2), the mixed solution is heated to 60°C–80°C, and an excess of concentrated ammonia (NH3·H2O) is rapidly added with vigorous stirring until the final concentration of ammonia in the reaction system reaches 0.5 mol / L–1.5 mol / L. The reaction continues for 30–60 minutes, during which a black precipitate is observed to form. The precipitate is separated using an external magnet and repeatedly washed with deionized water and ethanol until neutral to obtain superparamagnetic Fe3O4 nanoparticles.

[0063] S42. Fe3O4 nanoparticles were coated with a silica intermediate layer using the Stöber method to obtain Fe3O4@SiO2 nanoparticles;

[0064] Specifically, Fe3O4 nanoparticles prepared by S41 were dispersed in a solution of anhydrous ethanol, deionized water and concentrated ammonia, and ultrasonically dispersed to obtain a dispersion system. Under mechanical stirring, the precursor tetraethyl orthosilicate was slowly added dropwise to the dispersion system, with the mass-to-volume ratio of Fe3O4 nanoparticles to tetraethyl orthosilicate ranging from 1:2 to 6. The reaction was carried out at room temperature for 6 to 12 hours. The nanoparticles were then magnetically separated and washed with ethanol to obtain core-shell structured Fe3O4@SiO2 nanoparticles.

[0065] S43. Fe3O4@SiO2 nanoparticles were subjected to surface amination pretreatment;

[0066] Fe3O4@SiO2 nanoparticles prepared by S42 were dispersed in anhydrous toluene at a solid-liquid ratio of 1 g: 50 mL ~ 200 mL. Under inert atmosphere and mechanical stirring, a measured amount of (3-aminopropyl)triethoxysilane APTES (mass ratio of Fe3O4@SiO2 nanoparticles to APTES = 1:0.5~2) was slowly added dropwise. The mixture was heated to 100℃~120℃ and reacted under reflux for 12 h~24 h. After post-treatment, Fe3O4@SiO2 nanoparticles Fe3O4@SiO2-NH2 with surface amination pretreatment were obtained.

[0067] S44. By alternating Michael addition and amidation transfer reactions, Fe3O4@SiO2 nanoparticles pretreated with amination were grafted with polyamide-amine dendritic macromolecules of the target generation to obtain Fe3O4@SiO2@PAMAM-G. n The target algebra G n The value is 1.0~5.0, preferably 3.0~4.0.

[0068] Specifically, it includes:

[0069] (1) Michael addition reaction: Fe3O4@SiO2 nanoparticles with surface amination pretreatment prepared by S43 were dispersed in anhydrous methanol, and excess methyl acrylate was added (e.g., the mass-volume ratio of Fe3O4@SiO2-NH2 to methyl acrylate was 1g:5mL~20mL), thereby introducing ester end groups on the surface of Fe3O4@SiO2 nanoparticles; after the reaction, the product was washed to obtain G0.5 generation product.

[0070] (2) Amide transfer reaction: The above G0.5 generation product was dispersed in methanol, and excess ethylenediamine was added (e.g., the mass-volume ratio of G0.5 generation product to ethylenediamine was 1g:10mL~30mL) to introduce amine end groups on the surface. After the reaction, the product was washed to obtain the G1.0 generation product, namely, the magnetic microspheres Fe3O4@SiO2@PAMAM-G grafted with polyamide-amine dendritic macromolecules. 1.0 ;

[0071] (3) Repeat steps (1) and (2) with the product of step (2). By controlling the number of cycles, the products of generation G2.0, G3.0, G4.0 and G5.0 can be obtained in sequence.

[0072] S45.Fe3O4@SiO2@PAMAM-G n It reacts with isothiocyanates to graft thiourea functional groups onto the ends of dendritic macromolecules.

[0073] Specifically, this involves preparing Fe3O4@SiO2@PAMAM-G using S44. n Dispersed in acetonitrile or ethanol, with the addition of excess isothiocyanate (such as phenyl isothiocyanate or alkyl isothiocyanate, Fe3O4@SiO2@PAMAM-G) n The mass-to-volume ratio of isothiocyanate is 1g:0.5mL~3mL. The reaction is carried out at 40℃~60℃ for 12h~24h with stirring. The isothiocyanate reacts with the -NH2 group at the end of PAMAM to form a thiourea bond. After the reaction is completed, the mixture is magnetically separated and thoroughly washed with ethanol and deionized water in sequence. After drying, the first adsorbent material is obtained.

[0074] In the first adsorbent material, superparamagnetic iron(III) oxide forms the core, surrounded by silica as the intermediate layer, and polyamide-amine dendritic macromolecules with thiourea functional groups at their ends are grafted onto the intermediate layer. The superparamagnetic core ensures that the material can achieve rapid and complete separation through an external magnetic field; the dendritic macromolecules provide a highly branched three-dimensional structure, creating numerous binding sites; the sulfur and nitrogen atoms in the thiourea functional group act as soft bases, forming stable coordination bonds with Pt(II) and Pd(II) ions, which act as soft acids; in the acidic chloride ion system, thiourea exhibits a much higher selectivity for Pt and Pd chloride anions than other metal ions. In acidic leachate, the first adsorbent material selectively captures PtCl4 through the thiourea functional group. 2- and PdCl4 2- Plasma forms stable complexes, which are then used to enrich and separate Pt and Pd through magnetic separation.

[0075] S5, after adjusting the acidity of the supernatant, add the second adsorbent material to selectively adsorb rhodium and separate the supernatant and the rhodium enrichment material;

[0076] In practical applications, the rhodium content among the platinum group metals in spent catalysts is relatively low, and the first adsorbent material has a poor adsorption effect on rhodium chloride anions, resulting in rhodium being mainly concentrated in the supernatant. This invention employs a second adsorbent material for specific adsorption of rhodium.

[0077] The second adsorbent material comprises, from the inside out: a cluster of superparamagnetic iron oxide nanoparticles and a coating layer of modified silica; the modified silica refers to ordered mesoporous silica with amine and thiol bifunctional groups fixed by chemical bonds. The superparamagnetic iron oxide nanoparticle cluster structure provides strong magnetism, ensuring rapid and thorough separation; the ordered mesoporous silica structure provides preliminary physical sieving, facilitating the entry of Rh complex ions and excluding some macromolecular impurities; the amine groups, under acidic conditions, are protonated and positively charged, attracting negatively charged RhCl6 through electrostatic attraction. 3- The complex ion; the thiol group, as a strong coordinating group, forms a stable coordination bond with the Rh(III) ion; the amine-thiol group achieves a dual-function synergistic effect, with the amine group first enriching the Rh species near the material surface, and then the thiol group performing specific strong coordination to achieve efficient capture.

[0078] The pore size of mesoporous silica is 2nm~10nm, preferably 3nm~8nm.

[0079] The acidity of the supernatant was adjusted to a hydrochloric acid environment of 3 mol / L to 6 mol / L; the adsorption temperature was 50℃ to 70℃; the adsorption time was 90 min to 150 min; and the solid-liquid ratio of the second adsorbent to the supernatant was 1:200 to 400. Under optimized high-acidity conditions, the electrostatic attraction of amine groups was used to rapidly enrich rhodium complex ions, followed by the specific strong coordination of thiol groups to achieve precise anchoring and firm binding of rhodium. The two processes worked synergistically, and the mesoporous structure ensured efficient and selective recovery of rhodium from the liquid. After adsorption, a powerful permanent magnet was placed on the outer wall of the container; the second adsorbent material, which had adsorbed platinum group metal rhodium, aggregated, achieving solid-liquid separation, with the solid being the rhodium-enriched material. The magnetically adsorbed rhodium-enriched material could be washed with dilute hydrochloric acid solution to remove physically adsorbed or weakly bound impurity ions.

[0080] Specifically, the preparation method of the second adsorbent material includes the following steps:

[0081] S51. Provides superparamagnetic Fe3O4 nanoparticle clusters;

[0082] Superparamagnetic Fe3O4 nanoparticle clusters can be purchased commercially or synthesized in-house. For example, a solvothermal method can be used to obtain uniformly sized and more magnetically potent clusters. Specifically, FeCl3·6H2O, sodium citrate, and sodium acetate are dissolved in ethylene glycol. The mixed solution is then transferred to a high-pressure reactor lined with polytetrafluoroethylene and reacted at 150℃~250℃ for 8h~12h. After cooling, the nanoparticles are magnetically separated and washed with ethanol and water to obtain monodisperse Fe3O4 microspheres, which are essentially nanoparticle clusters.

[0083] S52. Coating with an ordered mesoporous silica layer;

[0084] The above-mentioned nanoparticle clusters were dispersed in an alkaline aqueous solution containing hexadecyltrimethylammonium bromide (CTAB) and ultrasonically dispersed evenly, with CTAB serving as a mesoporous template agent. Tetraethyl orthosilicate was slowly added dropwise under stirring. The reaction was carried out at 30°C to 50°C for 2 to 4 hours to allow silica to grow in an orderly manner outside the magnetic core. After the reaction was completed, the microspheres were magnetically separated and washed with ethanol. Then, the microspheres were refluxed in an acidic ethanol solution (such as an ethanol solution of hydrochloric acid) to completely remove the CTAB template agent, yielding magnetically ordered mesoporous silica microspheres.

[0085] S53. Silanization reaction; specifically including:

[0086] (1) The magnetic ordered mesoporous silica microspheres prepared by S52 were dispersed in anhydrous toluene or xylene at a solid-liquid ratio of 1:40~80 and ultrasonically treated for 20min~40min to obtain a dispersion system.

[0087] (2) Transfer the dispersion system to a three-necked flask equipped with a condenser, and under nitrogen protection, add two silane coupling agents, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH-791) and 3-mercaptopropyltrimethoxysilane (KH-590), with a mass ratio of silane coupling agent to silica microspheres of 0.5 mmol / g to 3.0 mmol / g;

[0088] (3) Heat the reaction system to 90℃~120℃ and stir vigorously under reflux for 12h~36h at this temperature to introduce amine and mercapto bifunctional groups on the silica layer;

[0089] (4) After the reaction is complete, cool to room temperature, perform magnetic separation, and wash thoroughly with toluene and ethanol in sequence. Dry under vacuum at 50℃~70℃ to obtain the second adsorbent material. In the second adsorbent material, superparamagnetic iron oxide nanoparticle clusters constitute the core, ordered mesoporous silica coats the core, and amine and thiol bifunctional groups are fixed on the ordered mesoporous silica layer by chemical bonds.

[0090] S6, the platinum / palladium enriched material and the rhodium enriched material are eluted and refined to recover platinum, palladium and rhodium;

[0091] Specifically, the platinum / palladium enrichment material was placed in a 0.3 mol / L to 0.7 mol / L thiourea hydrochloric acid solution and stirred and eluted at 35℃ to 45℃ for 50 to 70 minutes. After magnetic separation, a high-concentration Pt / Pd enrichment solution was obtained. The separated adsorbent material could be regenerated and reused. Saturated ammonium chloride solution was slowly added to the enrichment solution until no more yellow (NH4)2PtCl6 precipitate was formed. The solution was filtered, the precipitate was washed with ethanol, and calcined in a muffle furnace at 700℃ to 800℃ to obtain sponge platinum. The mother liquor after platinum separation was adjusted to pH 9 to 10 with ammonia water, filtered, and acidified with hydrochloric acid to pH=1 to obtain a pale yellow Pd(NH3)2Cl2 precipitate, which was then calcined to obtain sponge palladium.

[0092] Specifically, the rhodium-enriched material is placed in a thiourea-sulfuric acid solution with a concentration of 0.05 mol / L to 0.15 mol / L, and stirred and eluted at 55℃ to 65℃ for 85 min to 95 min. After magnetic separation, a high-concentration Rh-enriched solution is obtained. The separated adsorbent material can be regenerated and reused. The Rh-enriched solution is adjusted to a weakly alkaline state, heated to 85℃ to 95℃, and formic acid is slowly added to remove the Rh... 3+ After reduction, filtration, and washing, the material is calcined in a hydrogen atmosphere to obtain high-purity sponge rhodium.

[0093] Example 1

[0094] The specific steps for preparing the first adsorbent material include:

[0095] S41. Superparamagnetic Fe3O4 nanoparticles were prepared by dissolving 5.2 g FeCl3·6H2O and 2.0 g FeSO4·7H2O in approximately 150 mL of deoxygenated deionized water; under N2 protection, the mixed solution was heated to 60 °C, and 10 mL of concentrated ammonia was rapidly added with vigorous stirring; the reaction was continued for 60 min, and a black precipitate was observed to form; the precipitate was separated by an external magnet and repeatedly washed with deionized water and ethanol until neutral to obtain superparamagnetic Fe3O4 nanoparticles.

[0096] S42. Preparation of Fe3O4@SiO2 nanoparticles using the Stöber method: 5g of Fe3O4 nanoparticles obtained in the above steps were dispersed in a solution of anhydrous ethanol (1600mL), deionized water (400mL), and concentrated ammonia (40mL), and ultrasonically dispersed for 40min to obtain a dispersion system; under mechanical stirring, 20mL of precursor tetraethyl orthosilicate was slowly added dropwise to the dispersion system; the reaction was carried out at room temperature for 8h; magnetic separation was performed, and the nanoparticles were washed with ethanol to obtain core-shell structured Fe3O4@SiO2 nanoparticles.

[0097] S43. Disperse 10g of Fe3O4@SiO2 nanoparticles obtained in S42 in 1000mL of anhydrous toluene. Under an inert atmosphere and with mechanical stirring, slowly add 10g of (3-aminopropyl)triethoxysilane (APTES) dropwise using a syringe. Heat to 110℃ and continue the reaction under reflux for 24h. After the reaction is complete, allow the system to cool to room temperature, separate the product using an external magnetic field, wash three times with anhydrous toluene to remove physically adsorbed residual APTES, and then wash twice with anhydrous ethanol to replace the solvent. Place the product in a vacuum drying oven and dry at 60℃ for 10h to obtain Fe3O4@SiO2 nanoparticles with surface amination pretreatment.

[0098] S44. Take 10g of the surface-amined Fe3O4@SiO2 nanoparticles obtained in the above steps, disperse them in 500mL of anhydrous methanol, add 100mL of methyl acrylate, and carry out a Michael addition reaction at room temperature for 24 hours. After washing, the G0.5 product is obtained. Disperse the above G0.5 product in 500mL of methanol, add 200mL of ethylenediamine, and carry out an amidation transfer reaction at room temperature for 24 hours. After washing, the G1.0 product is obtained, namely, the magnetic microspheres Fe3O4@SiO2@PAMAM-G grafted with polyamide-amine dendritic macromolecules. 1.0 ;

[0099] S45. Disperse 10g of the product obtained from S43 in 50mL of acetonitrile, add 20g of phenyl isothiocyanate, and react at 50℃ for 24 hours to graft thiourea functional groups onto the ends of the dendritic macromolecules; after the reaction is completed, perform magnetic separation, and wash thoroughly with acetonitrile, ethanol and deionized water in sequence, and dry to obtain the first adsorbent material.

[0100] Example 2

[0101] The difference between this embodiment and Embodiment 1 is that S44 produces a G2.0 generation product, while the other conditions are the same as in Embodiment 1.

[0102] The specific steps of S44 are as follows: 10g of Fe3O4@SiO2 nanoparticles with surface amination pretreatment obtained in the above steps are dispersed in 500mL of anhydrous methanol, and 100mL of methyl acrylate is added. A Michael addition reaction is carried out at room temperature for 24 hours. After washing, the G0.5 generation product is obtained. The G0.5 generation product is dispersed in 500mL of methanol, and 200mL of ethylenediamine is added. An amidation transfer reaction is carried out at room temperature for 24 hours. After washing, the G1.0 generation product is obtained, namely, the magnetic microspheres Fe3O4@SiO2@PAMAM-G grafted with polyamide-amine dendritic macromolecules. 1.0Repeating the Michael addition and amidation transfer steps with the G1.0 product, and controlling the number of cycles, yielded the G2.0 product, Fe3O4@SiO2@PAMAM-G. 2.0 .

[0103] Example 3

[0104] The difference between this embodiment and Embodiment 1 is that S44 is prepared as G3.0 generation product, while other conditions are the same as in Embodiment 1.

[0105] The specific steps of S44 are as follows: 10g of Fe3O4@SiO2 nanoparticles with surface amination pretreatment obtained in the above steps are dispersed in 500mL of anhydrous methanol, and 100mL of methyl acrylate is added. A Michael addition reaction is carried out at room temperature for 24 hours. After washing, the G0.5 generation product is obtained. The G0.5 generation product is dispersed in 500mL of methanol, and 200mL of ethylenediamine is added. An amidation transfer reaction is carried out at room temperature for 24 hours. After washing, the G1.0 generation product is obtained, namely, the magnetic microspheres Fe3O4@SiO2@PAMAM-G grafted with polyamide-amine dendritic macromolecules. 1.0 The G1.0 product was subjected to repeated Michael addition and amidation transfer reactions, and the product was then recycled through the Michael addition and amidation transfer reactions to obtain the G3.0 product, Fe3O4@SiO2@PAMAM-G. 3.0 .

[0106] Example 4

[0107] The difference between this embodiment and Embodiment 1 is that S44 is prepared as a G4.0 generation product, while the other conditions are the same as in Embodiment 1.

[0108] The specific steps of S44 are as follows: 10g of Fe3O4@SiO2 nanoparticles with surface amination pretreatment obtained in the above steps are dispersed in 500mL of anhydrous methanol, and 100mL of methyl acrylate is added. A Michael addition reaction is carried out at room temperature for 24 hours. After washing, the G0.5 generation product is obtained. The G0.5 generation product is dispersed in 500mL of methanol, and 200mL of ethylenediamine is added. An amidation transfer reaction is carried out at room temperature for 24 hours. After washing, the G1.0 generation product is obtained, namely, the magnetic microspheres Fe3O4@SiO2@PAMAM-G grafted with polyamide-amine dendritic macromolecules. 1.0 The G1.0 generation product was subjected to repeated Michael addition and amidation transfer reactions. The product was then recycled through the Michael addition and amidation transfer reactions. By controlling the number of cycles, the G4.0 generation product, Fe3O4@SiO2@PAMAM-G, was obtained. 4.0 .

[0109] Example 5

[0110] The difference between this embodiment and Embodiment 1 is that S44 is prepared as a G5.0 generation product, while the other conditions are the same as in Embodiment 1.

[0111] The specific steps of S44 are as follows: 10g of Fe3O4@SiO2 nanoparticles with surface amination pretreatment obtained in the above steps are dispersed in 500mL of anhydrous methanol, and 100mL of methyl acrylate is added. A Michael addition reaction is carried out at room temperature for 24 hours. After washing, the G0.5 generation product is obtained. The G0.5 generation product is dispersed in 500mL of methanol, and 200mL of ethylenediamine is added. An amidation transfer reaction is carried out at room temperature for 24 hours. After washing, the G1.0 generation product is obtained, namely, the magnetic microspheres Fe3O4@SiO2@PAMAM-G grafted with polyamide-amine dendritic macromolecules. 1.0 The G1.0 generation product was subjected to repeated Michael addition and amidation transfer reactions. The product was then recycled through the Michael addition and amidation transfer reactions. By controlling the number of cycles, the G4.0 generation product, Fe3O4@SiO2@PAMAM-G, was obtained. 5.0 .

[0112] Comparative Example 1

[0113] The method for preparing the first adsorbent material in this comparative example differs from that in Example 3 in that S45 is omitted, i.e., thiourea functional group grafting is not performed, while other conditions are the same as in Example 3.

[0114] Comparative Example 2

[0115] The method for preparing the first adsorbent material in this comparative example differs from that in Example 3 in that S43-S45 are omitted, and only the Fe3O4@SiO2 nanoparticles prepared by S42 are used. Other conditions are the same as in Example 3.

[0116] Comparative Example 3

[0117] The method for preparing the first adsorbent material in this comparative example differs from that in Example 3 in that S42 to S45 are omitted, and only the superparamagnetic Fe3O4 nanoparticles prepared by S41 are used. Other conditions are the same as in Example 3.

[0118] Comparative Example 4

[0119] The method for preparing the first adsorbent material in this comparative example differs from that in Example 3 in that the superparamagnetic Fe3O4 nanoparticles of S41 are replaced with conventional Fe3O4, while the other conditions are the same as in Example 3.

[0120] Example 6

[0121] The specific steps for preparing the second adsorbent material include:

[0122] S51. Provide superparamagnetic Fe3O4 nanoparticle clusters: Dissolve 13.5g FeCl3·6H2O, 4.0g sodium citrate and 36.0g sodium acetate in 700mL ethylene glycol and stir until completely dissolved; transfer the mixed solution to a high-pressure reactor lined with polytetrafluoroethylene and react at 200℃ for 10h; after cooling, magnetic separation is performed, and the nanoparticles are washed with ethanol and water to obtain monodisperse superparamagnetic Fe3O4 nanoparticle clusters.

[0123] S52. Coating with an ordered mesoporous silica layer: Take 3g of the above-mentioned superparamagnetic Fe3O4 nanoparticle clusters and 5g of cetyltrimethylammonium bromide (CTAB) and disperse them in 1500mL of water. Then add 2.0g of sodium hydroxide, and ultrasonically disperse them evenly. Heat the mixture to 40℃. Under stirring and heat preservation, slowly add 15mL of tetraethyl orthosilicate and react for 2h. After the reaction is completed, magnetic separation is performed and the mixture is washed with ethanol. Then, the mixture is refluxed in an acidic ethanol solution (1000mL ethanol + 10mL concentrated hydrochloric acid) for 6h to completely remove the CTAB template agent. Magnetic separation and washing with ethanol are performed to obtain magnetically ordered mesoporous silica microspheres.

[0124] S53. Silanization reaction: 10g of magnetically ordered mesoporous silica microspheres prepared in S52 were dispersed in 50mL of anhydrous toluene and sonicated for 30 minutes to obtain a dispersion system. The dispersion system was transferred to a three-necked flask equipped with a condenser, and under nitrogen protection, two silane coupling agents, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH-791, 20mmol) and 3-mercaptopropyltrimethoxysilane (KH-590, 20mmol), were added simultaneously. The reaction system was heated to 110℃ and refluxed with vigorous stirring for 24h. After the reaction was completed, it was cooled to room temperature, magnetically separated, and thoroughly washed with toluene and ethanol in sequence. It was then vacuum dried at 60℃ to obtain the second adsorbent material.

[0125] Comparative Example 5

[0126] The method for preparing the second adsorbent material in this comparative example differs from that in Example 6 in that the superparamagnetic Fe3O4 nanoparticle clusters in S51 are changed to superparamagnetic Fe3O4 nanoparticles, while the other conditions are the same as in Example 3.

[0127] Specifically, in this comparative example, S51 was prepared as follows: 5.2 g of FeCl3·6H2O and 2.0 g of FeSO4·7H2O were dissolved in approximately 150 mL of deoxygenated deionized water; under N2 protection, the mixed solution was heated to 60 °C, and 10 mL of concentrated ammonia was rapidly added with vigorous stirring; the reaction was continued for 60 min, and a black precipitate was observed to form; the precipitate was separated by an external magnet and repeatedly washed with deionized water and ethanol until neutral to obtain superparamagnetic Fe3O4 nanoparticles.

[0128] Comparative Example 6

[0129] The method for preparing the second adsorbent material in this comparative example differs from that in Example 6 in that S53 is omitted, while the other conditions are the same as in Example 6.

[0130] Comparative Example 7

[0131] The method for preparing the second adsorbent material in this comparative example differs from that in Example 6 in that only KH-791 is added in S52, i.e. only amine grafting is performed, while other conditions are the same as in Example 6.

[0132] The silanization reaction of S53 in this comparative example was as follows: 10 g of magnetically ordered mesoporous silica microspheres prepared by S52 were dispersed in 50 mL of anhydrous toluene and sonicated for 30 minutes to obtain a dispersion system; the dispersion system was transferred to a three-necked flask equipped with a condenser, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH-791, 20 mmol) was added under nitrogen protection; the reaction system was heated to 110 °C and refluxed with vigorous stirring for 24 h. After the reaction was completed, it was cooled to room temperature, magnetically separated, and thoroughly washed with toluene and ethanol in sequence. It was then vacuum dried at 60 °C to obtain the second adsorbent material.

[0133] Comparative Example 8

[0134] The method for preparing the second adsorbent material in this comparative example differs from that in Example 6 in that only KH-590 is added in S52, i.e. only thiol grafting is performed, while other conditions are the same as in Example 3.

[0135] The silanization reaction of S53 in this comparative example was as follows: 10 g of magnetically ordered mesoporous silica microspheres prepared by S52 were dispersed in 50 mL of anhydrous toluene and sonicated for 30 minutes to obtain a dispersion system; the dispersion system was transferred to a three-necked flask equipped with a condenser, and 3-mercaptopropyltrimethoxysilane (KH-590, 20 mmol) was added under nitrogen protection; the reaction system was heated to 110 °C and refluxed with vigorous stirring for 24 h. After the reaction was completed, it was cooled to room temperature, magnetically separated, and thoroughly washed with toluene and ethanol in sequence, and then vacuum dried at 60 °C to obtain the second adsorbent material.

[0136] Example 7

[0137] This embodiment describes a method for recovering platinum group metals from waste automotive exhaust purification catalysts, which includes the following steps:

[0138] S1, the material is crushed into blocks with a particle size of less than 10mm by a jaw crusher; the material after coarse crushing is fed into a ball mill and ground into powder that can pass through a 100-mesh standard sieve, and then the waste catalyst tank and most of the attached iron impurities are removed by strong magnetic separation to obtain solid slag.

[0139] S2, the solid slag is mixed with a 50% sodium hydroxide solution at a solid-liquid ratio of 1:4 and placed in a high-pressure reactor. Stirring (200 rpm) and heating are started. The reaction is carried out at 200℃ and 1.5 MPa for 3 hours. After the reaction is completed, the temperature is allowed to drop below 80℃, the pressure is released and the material is discharged. Hot filtration is performed, and the solid residue is collected and washed thoroughly with hot water until neutral to obtain an active slag enriched with platinum group metals.

[0140] S3. First, add 4 mol / L hydrochloric acid solution to the activated slag obtained in step S2 at a solid-liquid ratio of 1:8 to obtain a slurry. After starting the stirring and heating to 80°C, slowly add 5% hydrogen peroxide (concentration of 30%) of the total volume of the slurry, and add sodium chloride to maintain the total chloride ion concentration in the reaction system at 2 mol / L. Continue stirring and keeping the temperature for 3 hours. After the reaction is completed, immediately perform vacuum filtration. The filter residue is mainly cordierite, and the filtrate is the leachate enriched with platinum group metals.

[0141] S4. First, the acidity of the leachate obtained in step S3 is adjusted to a 2 mol / L hydrochloric acid environment. The first adsorbent material is added at a solid-liquid ratio of 1:500 (as shown in Table 1). The solution is heated to about 50°C and kept at this temperature with stirring for 90 minutes. After adsorption is complete, a strong permanent magnet is placed outside the reaction vessel. The first adsorbent material, which has adsorbed platinum / palladium group metals, is quickly attracted to the magnet and completely separated from the solution. The supernatant is collected for subsequent processing, and the solid is the platinum / palladium enriched material. The magnetically adsorbed platinum / palladium enriched material is quickly washed with a dilute hydrochloric acid solution of about 1 mol / L. The washed liquid is combined with the supernatant for subsequent processing.

[0142] S5, adjust the acidity of the supernatant obtained in step S4 to a hydrochloric acid environment of 4 mol / L, and add the second adsorbent material (as shown in Table 1) at a solid-liquid ratio of 1:300; heat to about 60℃; keep warm and stir for 120 min for adsorption; after adsorption is completed, place a strong permanent magnet on the outer wall of the container; the second adsorbent material that has adsorbed the platinum group metal rhodium aggregates to achieve solid-liquid separation, wherein the solid is the rhodium enriched material.

[0143] S6. Platinum / palladium enriched material was placed in a 0.5 mol / L thiourea solution and eluted with stirring at 40°C for 60 min. After magnetic separation, a high-concentration Pt / Pd enriched solution was obtained. The separated adsorbent material could be regenerated and reused. Saturated ammonium chloride solution was slowly added to the enriched solution until no more yellow (NH4)2PtCl6 precipitate was formed. The solution was filtered, the precipitate was washed with ethanol, and calcined in a muffle furnace at 750°C to obtain sponge platinum. The mother liquor after platinum separation was rinsed with ammonia water. Adjust the pH to 9-10, filter, and acidify with hydrochloric acid to pH=1 to obtain a pale yellow Pd(NH3)2Cl2 precipitate, which is then calcined to obtain sponge palladium. Place the rhodium-enriched material in a 0.1 mol / L thiourea solution and elute with stirring at 60℃ for 90 min. After magnetic separation, a high-concentration Rh-enriched solution is obtained. The separated adsorbent material can be regenerated and reused. Adjust the Rh-enriched solution to weakly alkaline, heat to 85℃-95℃, and slowly add formic acid to remove Rh. 3+ After reduction, filtration, and washing, the material is calcined in a hydrogen atmosphere to obtain high-purity sponge rhodium.

[0144] Based on the different first and second adsorbent materials in Table 1, the recovery rate and purity of platinum group metals were calculated, and the results are shown in Table 1.

[0145] The platinum / palladium / rhodium recovery rate was calculated by dividing the mass of pure metal in the refined sponge metal by the theoretical mass of the same metal in the spent catalyst feedstock. The mass of pure metal was determined by multiplying the total mass of the refined product by its measured purity. The theoretical mass of the metal in the feedstock was determined by ICP-OES analysis of a representative feedstock sample after digestion.

[0146] The purity of the obtained platinum / palladium / rhodium was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) according to GB / T 1419-2015, GB / T 1420-2015, and GB / T 1421-2015 standards. The content of metallic impurities was determined by carbon-sulfur analyzer and oxygen-nitrogen-hydrogen analyzer. The purity of the main element was determined by subtraction method, that is, the total amount of all impurity elements measured after subtracting from 100%.

[0147] Table 1

[0148]

[0149] As shown in Table 1, the first adsorbent material prepared in Examples 1 to 5 of this invention, combined with the second adsorbent material prepared in Example 6, achieved efficient and high-purity integrated recovery of platinum, palladium, and rhodium. The first adsorbent material prepared in Example 3 exhibited the best recovery rate. This is because: insufficient functional group density due to low generation number (G1.0 / G2.0) and increased steric hindrance due to high generation number (G4.0 / G5.0) both resulted in a slight decrease in Pt / Pd recovery rate.

[0150] When the first adsorbent was replaced with Comparative Example 1, the first adsorbent was not modified with thiourea functional groups, which led to a significant decrease in the Pt / Pd recovery rate. Furthermore, the Pt / Pd leakage severely interfered with the second adsorbent, resulting in a simultaneous significant decrease in the Rh recovery rate and a severe deterioration in the product purity.

[0151] When the first adsorbent material was replaced with Comparative Example 2, the first adsorbent material was not grafted with PAMAM and only used Fe3O4@SiO2 nanoparticles. It had almost no adsorption capacity as a carrier, and the Pt / Pd recovery rate was extremely low, which also caused the Rh recovery to fail due to severe interference.

[0152] The first adsorbent material was replaced with Comparative Example 3. The first adsorbent material only used superparamagnetic Fe3O4 nanoparticles. The magnetic core without a protective layer was unstable and had the lowest recovery rate.

[0153] When the first adsorbent material was replaced with that of Comparative Example 4, and the superparamagnetic Fe3O4 nanoparticles in the first adsorbent material were replaced with conventional Fe3O4, the recovery rate decreased slightly.

[0154] When the second adsorbent was replaced with that in Comparative Example 5, and the superparamagnetic Fe3O4 nanoparticle clusters in the second adsorbent were replaced with superparamagnetic Fe3O4 nanoparticles, the recovery rate of rhodium decreased significantly. This was because the adsorption capacity was low and the separation performance was poor, resulting in direct rhodium loss.

[0155] When the second adsorbent was replaced with Comparative Example 6, and the coating layer of the second adsorbent was not grafted with amine and thiol groups, the recovery rate of rhodium decreased significantly, making it almost meaningless to recover, and the purity also decreased significantly.

[0156] When the second adsorbent was replaced with Comparative Example 7, and the coating layer of the second adsorbent was not grafted with thiol groups but only with amine groups, the recovery rate of rhodium decreased significantly and the purity also decreased slightly.

[0157] When the second adsorbent was replaced with Comparative Example 8, and the coating layer of the second adsorbent was not grafted with amine groups but only with thiol groups, the recovery rate of rhodium decreased significantly and the purity also decreased slightly.

[0158] Comparative Example 9

[0159] This comparative example describes a method for recovering platinum group metals from waste automotive exhaust purification catalysts. The difference between this example and Example 7 is the deletion of step S2. In this example, the first adsorbent material prepared in Example 3 and the second adsorbent material prepared in Example 6 are used. The other steps are the same as in Example 7.

[0160] Comparative Example 10

[0161] This comparative example describes a method for recovering platinum group metals from waste automotive exhaust purification catalysts. The difference between this method and Example 7 is that step S2 uses conventional alkaline roasting instead of hot pressing activation. In this method, the first adsorbent material prepared in Example 3 and the second adsorbent material prepared in Example 6 are used. The other steps are the same as in Example 7.

[0162] Step S2 of this comparative example specifically involves mixing the solid slag with sodium hydroxide solid at a solid-liquid ratio of 1:3, calcining it in a muffle furnace at 600°C for 4 hours, and then quenching it with water to obtain the activated slag.

[0163] Comparative Example 11

[0164] This comparative example describes a method for recovering platinum group metals from waste automotive exhaust purification catalysts. The difference between this method and Example 7 is that step S3 uses aqua regia leaching instead of mild acid leaching. In this method, the first adsorbent material prepared in Example 3 and the second adsorbent material prepared in Example 6 are used. The other steps are the same as in Example 7.

[0165] Step S3 of this comparative example is as follows: In a corrosion-resistant fume hood, 240 mL of concentrated hydrochloric acid and 80 mL of concentrated nitric acid are slowly mixed in a 2 L beaker to prepare aqua regia; 100 g of activated sludge is transferred to a 2 L corrosion-resistant reactor (equipped with a reflux condenser and tail gas absorption device), and the prepared aqua regia is slowly added. At this time, a large amount of reddish-brown toxic fumes containing nitrogen oxides will be produced. The solid-liquid ratio is maintained at approximately 1:8 (g / mL). If insufficient, deionized water is added. After starting the stirring and heating to 80°C, continue stirring and keep the reaction at this temperature for 4 hours. After the reaction is complete, the solid and liquid are separated, and the filtrate is the leachate. Transfer the leachate to a beaker, add small amounts of concentrated hydrochloric acid repeatedly and heat to evaporate until it is evaporated to a wet salt state to remove nitric acid. Dissolve the above wet salt residue with an appropriate amount of 4 mol / L hydrochloric acid solution and transfer it to a volumetric flask. Make up the volume to 1 L with 4 mol / L hydrochloric acid. This solution is the leachate for enriching platinum group metals prepared by the aqua regia leaching method.

[0166] Comparative Example 12

[0167] This comparative example describes a method for recovering platinum group metals from waste automotive exhaust purification catalysts. The difference between this method and Example 7 is that step S3 uses single hydrochloric acid leaching instead of the hydrochloric acid-hydrogen peroxide-sodium chloride system. In this method, the first adsorbent material prepared in Example 3 and the second adsorbent material prepared in Example 6 are used. The other steps are the same as in Example 7.

[0168] In this comparative example, step S3 is as follows: First, add 4 mol / L hydrochloric acid solution to the activated slag obtained in step S2 at a solid-liquid ratio of 1:8 to obtain a slurry; start stirring and heat to 80°C, then continue stirring and heat preservation reaction for 3 hours. After the reaction is completed, vacuum filtration is performed immediately. The filter residue is mainly cordierite, and the filtrate is the leachate enriched with platinum group metals.

[0169] The recovery rate and purity of platinum group metals in Comparative Examples 9 to 12 were tested using the same method as in Example 7. The results are shown in Table 2 and are compared with those in Group 3 of Example 7.

[0170] Table 2

[0171]

[0172] As can be seen from the data in Table 2, the recovery rate of platinum group metals in Comparative Example 9 without alkali activation was extremely low, with almost no recovery significance. This directly proves that the alkali activation step is indispensable for destroying the carrier structure and exposing the encapsulated platinum group metals. Because a large amount of carrier was not dissolved, the proportion of impurities in the dissolved part was relatively high, which in turn reduced the purity.

[0173] The recovery rate of platinum group metals in Comparative Example 10, which was calcined under normal pressure, decreased significantly and the purity also decreased substantially. The reason is that the hot pressing activation of the present invention, under liquid phase and relatively low temperature conditions, has higher reaction efficiency and metal recovery rate than traditional high temperature solid phase calcination. Calcination leads to sintering and secondary encapsulation, and the calcination process results in the formation of compound forms that are more difficult to handle.

[0174] The recovery rate and purity of platinum group metals in Comparative Example 11, leached with aqua regia, both decreased slightly. Among them, rhodium metal saw the largest decrease. This is because aqua regia indiscriminately dissolves a large number of impurities, which compete with Rh for adsorption sites of the second adsorbent material, leading to a decrease in Rh recovery rate. In subsequent refining steps, it is difficult to completely separate Rh, resulting in a decrease in the purity of the final sponge metal product.

[0175] The recovery rates of platinum group metals in Comparative Example 12, which were leached with hydrochloric acid alone, decreased significantly because without an oxidant, the metals could not be converted from a zero-valence state to a soluble ionic state.

[0176] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for recovering platinum group metals from waste automotive exhaust purification catalysts, characterized in that, The method includes the following steps: S1, the spent catalyst is crushed and removed before being treated to obtain solid slag; S2, the obtained solid slag is mixed with alkaline solution and then hot-pressed to activate it, thus obtaining an active slag enriched with platinum group metals. S3, the activated slag is leached using an acidic leaching system of hydrochloric acid-hydrogen peroxide-sodium chloride to obtain a leachate enriched with platinum group metals. S4, after adjusting the acidity of the leachate, add the first adsorbent material to selectively adsorb platinum and palladium, and separate the supernatant and platinum / palladium enrichment material; S5, after adjusting the acidity of the supernatant, add the second adsorbent material to selectively adsorb rhodium, separate the solid and liquid, and collect the rhodium-enriched material; S6, the platinum / palladium enriched material and the rhodium enriched material are eluted and refined to recover platinum, palladium and rhodium; The first adsorbent material comprises, from the inside out: a layer of superparamagnetic iron oxide nanoparticles, a silica coating layer, and a polyamide-amine dendritic macromolecular layer grafted onto the silica coating layer and terminated with thiourea functional groups; the preparation method of the first adsorbent material includes the following steps: Provides superparamagnetic Fe3O4 nanoparticles; Fe3O4@SiO2 nanoparticles were obtained by coating Fe3O4 nanoparticles with a silica intermediate layer using the Stöber method. Fe3O4@SiO2 nanoparticles were pretreated with surface amination. By alternating Michael addition and amidation transfer reactions, Fe3O4@SiO2 nanoparticles with a target generation of polyamide-amine dendritic macromolecules were grafted onto their surface after surface amination pretreatment to obtain Fe3O4@SiO2@PAMAM; the target generation was 1.0~5.

0. Fe3O4@SiO2@PAMAM reacts with isothiocyanate to graft thiourea functional groups onto the ends of dendritic macromolecules; The second adsorbent material comprises, from the inside out: a cluster of superparamagnetic iron oxide nanoparticles and a modified silica coating layer; the modified silica refers to ordered mesoporous silica with amine and thiol bifunctional groups fixed by chemical bonds; the preparation method of the second adsorbent material includes the following steps: Provides superparamagnetic Fe3O4 nanoparticle clusters; Using hexadecyltrimethylammonium bromide as a template agent, ordered mesoporous silica was coated onto Fe3O4 nanoparticle clusters via a sol-gel method, and the template agent was removed by extraction to obtain Fe3O4@mesoporous SiO2 microspheres. The Fe3O4@mesoporous SiO2 microspheres are mixed with a silanizing agent in an inert organic solvent and subjected to a surface silanization reaction via a one-step or stepwise method, thereby simultaneously introducing amine functional groups and sulfur-containing functional groups onto the surface of mesoporous silica; the silanizing agent comprises silanes that can provide amine groups and silanes that can provide sulfur-containing functional groups.

2. The method for recovering platinum group metals from waste automotive exhaust purification catalysts according to claim 1, characterized in that, S2 specifically includes: mixing the solid slag with an alkaline solution of 40%~70% at a solid-liquid ratio of 1:3~1:5, and reacting it at 150℃~250℃ and 0.5MPa~3.0MPa for 1h~5h; The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

3. The method for recovering platinum group metals from waste automotive exhaust purification catalysts according to claim 1, characterized in that, The S3 steps are as follows: First, add 2 mol / L to 6 mol / L hydrochloric acid solution to the activated slag at a solid-liquid ratio of 1:5 to 10 to obtain a slurry. After starting the stirring and heating to 70℃~90℃, slowly add hydrogen peroxide, accounting for 3%~8% of the total volume of the slurry, and add sodium chloride to maintain the total chloride ion concentration in the reaction system at 1mol / L~3mol / L; Continue stirring and keeping the reaction at a constant temperature for 2 to 4 hours. After the reaction is complete, separate the solid and liquid phases to obtain a leachate enriched with platinum group metals.

4. The method for recovering platinum group metals from waste automotive exhaust purification catalysts according to claim 1, characterized in that, In step S4, the acidity of the leachate is adjusted to a hydrochloric acid environment of 1 mol / L to 3 mol / L; the temperature of the adsorption process is 40℃ to 60℃; the adsorption time is 60 min to 120 min; and the solid-liquid ratio of the first adsorbent to the leachate is 1:300 to 700.

5. The method for recovering platinum group metals from waste automotive exhaust purification catalysts according to claim 1, characterized in that, The mesoporous silica has a pore size of 3 nm to 10 nm.

6. The method for recovering platinum group metals from waste automotive exhaust purification catalysts according to claim 1, characterized in that, In step S5, the acidity of the supernatant is adjusted to a hydrochloric acid environment of 3 mol / L to 6 mol / L; the temperature of the adsorption process is 50℃ to 70℃; the adsorption time is 90 min to 150 min; and the solid-liquid ratio of the second adsorbent to the supernatant is 1:200 to 400.

7. The method for recovering platinum group metals from waste automotive exhaust purification catalysts according to claim 1, characterized in that, In step S6, the platinum / palladium enriched material is eluted using a thiourea hydrochloric acid solution with a concentration of 0.3 mol / L to 0.7 mol / L.

8. The method for recovering platinum group metals from waste automotive exhaust purification catalysts according to claim 1 or 7, characterized in that, In step S6, the rhodium-enriched material is eluted using a thiourea-sulfuric acid solution with a concentration of 0.05 mol / L to 0.15 mol / L.

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