Method for leaching precious metal from waste catalyst containing precious metal

Abstract

The invention provides a method for leaching precious metal from a waste catalyst containing precious metal, which comprises the following steps: mixing hydrochloric acid and an oxidizing agent to obtain a leaching agent, and mixing the waste catalyst containing precious metal with the leaching agent to obtain mixed slurry; and performing ultrasonic-microwave synergistic leaching treatment on the mixed slurry, and performing solid-liquid separation to obtain filter residues and a precious metal-rich leachate. According to the method, the leaching agent prepared from hydrochloric acid and the oxidizing agent is used, the precious metal in the waste catalyst containing the precious metal can be activated without using the leaching agent such as aqua regia which is prone to generating nitrogen-containing waste gas, generation of toxic gas is avoided from the source, and green and environment-friendly processes are achieved; meanwhile, ultrasonic-microwave synergistic leaching is utilized, a physical barrier is broken through ultrasonic, a reaction interface is maximized, microwave provides efficient heat energy and activates molecules, the chemical reaction rate of the interface is greatly increased, the synergistic strengthening effect is generated, and then the leaching rate of precious metal, especially rhodium, is greatly increased.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology and relates to a method for leaching precious metals from waste catalysts containing precious metals. Background Technology

[0002] In modern industrial systems, precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) play an irreplaceable and crucial role due to their unique physicochemical properties. From automotive exhaust purification and petrochemical catalysis to precision manufacturing in the electronics and information industry and cutting-edge research in the new energy field, these precious metals are core materials. In automotive exhaust purification catalysts, the catalytic system composed of platinum, palladium, and rhodium can efficiently convert harmful gases such as carbon monoxide, hydrocarbons, and nitrogen oxides into carbon dioxide, water, and nitrogen, significantly reducing the pollution of automotive exhaust to the environment. With increasingly stringent global environmental standards, the demand for these precious metals in the field of automotive exhaust purification continues to rise.

[0003] However, these precious metals are extremely scarce on Earth. Statistics show that global reserves of platinum group metals (including platinum, palladium, and rhodium) are only about 66,000 tons, and these reserves are declining after years of mining. Faced with such a severe resource situation, recovering precious metals from spent catalysts has become an important way to alleviate resource shortages, reduce production costs, and decrease environmental pollution.

[0004] CN119800081A discloses a method for recovering precious metals, comprising the following steps: I. Crushing the waste catalyst and mixing it with sodium carbonate at a weight ratio of 1:(0.5~1.2), and calcining it at a temperature of 700~1000℃ for 0.5~3h to obtain the calcined product; II. Dispersing the calcined product with a weight ratio of (0.2~0.5):1 and sodium hydroxide in water at a temperature of 50~90℃, and leaching it by stirring at a speed of 80~320r / min for 5~20min, filtering it while it is hot after leaching, collecting the filter residue, washing it, and drying it to obtain the recovered precious metal.

[0005] CN120796714A discloses a non-aqua regia gold extraction agent and method for recovering precious metals from waste containing precious metals. The non-aqua regia gold extraction agent is composed of nitrates, metal chlorides, and a weak acid. By precisely controlling the concentrations of nitrate, chloride, and hydrogen ions in the non-aqua regia gold extraction agent, the precious metals in the waste containing precious metals can be oxidized and leached in a green, efficient, and selective manner under room temperature conditions. The precious metal ions in the leachate are then reduced to obtain pure precious metal products.

[0006] In the leaching methods described above, the leaching rates of precious metals all need to be improved, especially the leaching rate of rhodium, which is generally low, becoming a key bottleneck restricting recovery efficiency and economic benefits. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for leaching precious metals from spent catalysts containing precious metals. This invention uses a leaching agent prepared from hydrochloric acid and an oxidant, eliminating the need for leaching agents such as aqua regia that easily generate nitrogen-containing waste gases. This method effectively activates the precious metals in the spent catalysts, thus avoiding NO emissions at the source. x The generation of toxic gases is eliminated, thus achieving a green and environmentally friendly process. Simultaneously, ultrasonic-microwave synergistic leaching is utilized. Ultrasonic waves break down physical barriers, maximizing the reaction interface; microwaves provide efficient thermal energy and activate molecules, greatly accelerating the interfacial chemical reaction rate and producing a synergistic strengthening effect, thereby significantly increasing the leaching rate of precious metals, especially rhodium.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for leaching precious metals from spent catalysts containing precious metals, the method comprising the following steps:

[0010] A leaching agent is obtained by mixing hydrochloric acid and an oxidant, and a mixed slurry is obtained by mixing the waste catalyst containing precious metals with the leaching agent.

[0011] The mixed slurry was subjected to ultrasonic-microwave synergistic leaching treatment, and solid-liquid separation was performed to obtain filter residue and precious metal leachate.

[0012] In this invention, hydrochloric acid and an oxidizing agent are mixed beforehand to prepare a leachate. The chloride ions in the hydrochloric acid can form stable chloride anions (such as [PtCl6]) with noble metals. 2- [PdCl4] 2- [RhCl6] 3-Oxidants can oxidize noble metal elements or low-valence noble metal oxides into soluble high-valence ions. After mixing the spent catalyst containing noble metals with the leaching agent, an ultrasonic-microwave synergistic leaching treatment is employed. The strong shock waves and microjets generated by the cavitation effect of ultrasound in the liquid physically break down and erode the catalyst support (γ-Al2O3 coating and cordierite), completely breaking its encapsulation of platinum group metal particles and fully exposing the encapsulated metal active sites. The strong stirring effect generated by ultrasound greatly reduces the thickness of the diffusion boundary layer between the liquid and solid phases, accelerating the mass transfer rate of leaching agent ions to the particle surface and internal pores, as well as the diffusion rate of reaction products into the bulk solution. Microwaves provide rapid and uniform bulk heating of polar molecules (water, HCl), avoiding the thermal gradient problem of traditional heating methods and greatly improving thermal efficiency. Simultaneously, selective heating of certain substances may locally reduce the activation energy of the reaction. The non-thermal effects of microwaves (such as their influence on molecular polarization) may directly promote redox reactions and accelerate the formation of noble metal chloride complex ions. The two work synergistically, synchronously in time and space, promoting each other and jointly solving the industry problem of difficult rhodium leaching, and significantly shortening the reaction time.

[0013] Following the ultrasonic-microwave synergistic leaching treatment described in this invention, the slurry is cooled to room temperature and then filtered or centrifuged to obtain a leachate rich in precious metals and a leachate residue mainly composed of carrier residue. The leachate is then transported to subsequent processes (such as solvent extraction, ion exchange, and precipitation refining) for the separation and purification of platinum, palladium, and rhodium. The leachate residue, after washing, can be treated harmlessly as a raw material for building materials, etc.

[0014] Preferably, the molar concentration of the hydrochloric acid is 2 mol / L to 8 mol / L, for example: 2 mol / L, 4 mol / L, 5 mol / L, 6 mol / L or 8 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 4 mol / L to 6 mol / L.

[0015] Preferably, the oxidant includes sodium chlorate and / or hydrogen peroxide, with sodium chlorate being the most preferred.

[0016] This invention uses sodium chlorate as an oxidant, which has advantages such as strong oxidizing power, few by-products, and easy storage and addition.

[0017] Preferably, the precious metal in the precious metal-containing waste catalyst includes any one or a combination of at least two of platinum, palladium, or rhodium. Typical but non-limiting combinations include combinations of platinum and palladium, platinum and rhodium, or palladium and rhodium.

[0018] Preferably, the particle size of the precious metal-containing waste catalyst is 100 mesh to 400 mesh, for example: 100 mesh, 150 mesh, 200 mesh, 300 mesh or 400 mesh, etc., and more preferably 150 mesh to 250 mesh.

[0019] Preferably, the molar ratio of the precious metal in the precious metal-containing waste catalyst to the oxidant is 1:(1.5~3), for example: 1:1.5, 1:1.8, 1:2, 1:2.5 or 1:3, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the liquid-to-solid ratio of the precious metal-containing waste catalyst to the leaching agent is (4~15) mL / 1g, for example: 4mL / 1g, 6mL / 1g, 8mL / 1g, 10mL / 1g or 15mL / 1g, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the ultrasonic-microwave synergistic leaching treatment temperature is 70℃~98℃, for example: 70℃, 75℃, 80℃, 90℃ or 98℃, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable, preferably 85℃~95℃.

[0022] Preferably, the microwave power of the ultrasonic-microwave synergistic leaching treatment is 200W~800W, for example: 200W, 400W, 500W, 700W or 800W, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 400W~600W.

[0023] Preferably, the ultrasonic frequency of the ultrasonic-microwave synergistic leaching treatment is 20kHz to 60kHz, for example: 20kHz, 30kHz, 40kHz, 50kHz or 60kHz, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 25kHz to 40kHz.

[0024] Preferably, the ultrasonic power density of the ultrasonic-microwave synergistic leaching treatment is 0.2W / mL to 1.5W / mL, for example: 0.2W / mL, 0.5W / mL, 0.8W / mL, 1W / mL or 1.5W / mL, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.5W / mL to 1.0W / mL.

[0025] Preferably, the ultrasonic-microwave synergistic leaching treatment time is 10 min to 90 min, for example: 10 min, 20 min, 50 min, 70 min or 90 min, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable, preferably 20 min to 50 min.

[0026] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention uses a leaching agent prepared with hydrochloric acid and an oxidant, which can activate the precious metals in the waste catalyst containing precious metals without the need for leaching agents such as aqua regia that easily generate nitrogen-containing waste gas, thus avoiding NO from the source. x The generation of toxic gases is eliminated, achieving a green and environmentally friendly process. Simultaneously, ultrasonic-microwave synergistic leaching is utilized. Ultrasonic waves break down physical barriers, maximizing the reaction interface; microwaves provide efficient thermal energy and activate molecules, greatly accelerating the interfacial chemical reaction rate, producing a synergistic strengthening effect of "1+1>2," thereby significantly increasing the leaching rate of precious metals, especially rhodium.

[0029] (2) The method for leaching precious metals from waste catalysts containing precious metals described in this invention can achieve a platinum leaching rate of over 96.8%, a palladium leaching rate of over 97.2%, and a rhodium leaching rate of over 91.5%, thus realizing the leaching of multiple precious metals. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the process for leaching precious metals from spent catalysts containing precious metals, provided in an embodiment of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0032] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0033] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0035] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0036] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0038] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0039] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0040] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0041] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0042] The precious metal-containing waste catalyst used in the embodiments and comparative examples of this invention is a waste automobile exhaust purification three-way catalyst. The waste automobile exhaust purification three-way catalyst has a platinum mass content of 0.21%, a palladium mass content of 0.12%, and a rhodium mass content of 0.052%. The waste automobile exhaust purification three-way catalyst is mechanically crushed and then ball-milled to a particle size of 200 mesh.

[0043] Example 1

[0044] This embodiment provides a method for leaching precious metals from spent catalysts containing precious metals. A schematic flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0045] Hydrochloric acid with a molar concentration of 5 mol / L was mixed with 0.87 g of sodium chlorate to obtain a leaching agent. 100 g of waste automobile exhaust purification three-way catalyst was mixed with the leaching agent at a liquid-solid ratio of 6 mL / 1 g to obtain a mixed slurry.

[0046] The mixed slurry was placed in an ultrasonic-microwave synergistic reactor. The microwave power was controlled at 500W, the ultrasonic power density at 0.5W / mL, the frequency at 28kHz, and the reaction temperature at 90℃. After reacting for 30 minutes, the mixture was cooled, filtered, and washed to obtain the filter residue and the precious metal leachate.

[0047] Example 2

[0048] This embodiment provides a method for leaching precious metals from spent catalysts containing precious metals. A schematic flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0049] Hydrochloric acid with a molar concentration of 4 mol / L was mixed with 0.87 g of sodium chlorate to obtain a leaching agent. 100 g of waste automobile exhaust purification three-way catalyst was mixed with the leaching agent at a liquid-solid ratio of 15 mL / 1 g to obtain a mixed slurry.

[0050] The mixed slurry was placed in an ultrasonic-microwave synergistic reactor. The microwave power was controlled at 400W, the ultrasonic power density at 0.8W / mL, the frequency at 35kHz, and the reaction temperature at 85℃. After reacting for 40 minutes, the mixture was cooled, filtered, and washed to obtain the filter residue and the precious metal leachate.

[0051] Example 3

[0052] This embodiment provides a method for leaching precious metals from spent catalysts containing precious metals. A schematic flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0053] Hydrochloric acid with a molar concentration of 6 mol / L was mixed with 0.87 g of sodium chlorate to obtain a leaching agent. 100 g of waste automobile exhaust purification three-way catalyst was mixed with the leaching agent at a liquid-solid ratio of 4 mL / 1 g to obtain a mixed slurry.

[0054] The mixed slurry was placed in an ultrasonic-microwave synergistic reactor. The microwave power was controlled at 600W, the ultrasonic power density at 1W / mL, the frequency at 25kHz, and the reaction temperature at 95℃. After reacting for 20 minutes, the residue and precious metal leachate were obtained by cooling, filtration, and washing.

[0055] Example 4

[0056] The only difference between this embodiment and Embodiment 1 is that sodium hypochlorite is replaced with 20 mL of 30% hydrogen peroxide. All other conditions and parameters are exactly the same as in Embodiment 1.

[0057] Example 5

[0058] The only difference between this embodiment and Example 1 is that the molar concentration of hydrochloric acid is 8 mol / L, while the other conditions and parameters are exactly the same as in Example 1.

[0059] Example 6

[0060] The only difference between this embodiment and Example 1 is that the molar concentration of hydrochloric acid is 2 mol / L; all other conditions and parameters are exactly the same as in Example 1.

[0061] Example 7

[0062] The only difference between this embodiment and Embodiment 1 is that the microwave power of the ultrasonic-microwave synergistic leaching treatment is 200W, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0063] Example 8

[0064] The only difference between this embodiment and Embodiment 1 is that the microwave power of the ultrasonic-microwave synergistic leaching treatment is 800W, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0065] Example 9

[0066] The only difference between this embodiment and Embodiment 1 is that the ultrasonic frequency of the ultrasonic-microwave synergistic leaching treatment is 20kHz, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0067] Example 10

[0068] The only difference between this embodiment and Embodiment 1 is that the ultrasonic frequency of the ultrasonic-microwave synergistic leaching treatment is 60kHz, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0069] Comparative Example 1

[0070] The only difference between this comparative example and Example 1 is that only microwave leaching was performed; all other conditions and parameters are exactly the same as in Example 1.

[0071] Comparative Example 2

[0072] The only difference between this comparative example and Example 1 is that only ultrasonic leaching was performed; all other conditions and parameters are exactly the same as in Example 1.

[0073] Performance testing:

[0074] The precious metal content in the leachate was analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES), and the ancient metal leaching rate was calculated. The test results are shown in Table 1.

[0075] Table 1

[0076]

[0077] As can be seen from Table 1, and from Examples 1-10, the method for leaching precious metals from waste catalysts containing precious metals described in this invention can achieve a platinum leaching rate of over 96.8%, a palladium leaching rate of over 97.2%, and a rhodium leaching rate of over 91.5%, thus realizing the leaching of multiple precious metals.

[0078] A comparison of Examples 1 and 4 shows that in the method for leaching precious metals from waste catalysts containing precious metals described in this invention, the choice of oxidant affects the leaching rate of precious metals. This invention uses sodium chlorate as an oxidant, which has advantages such as strong oxidizing power, few by-products, and easy storage and addition. Moreover, it has a good leaching effect on rhodium. Hydrogen peroxide can also leach platinum and palladium well, but the leaching effect on rhodium is slightly reduced.

[0079] A comparison of Examples 1 and 5-6 shows that in the method for leaching precious metals from spent catalysts containing precious metals described in this invention, the molar concentration of hydrochloric acid affects the leaching effect. Controlling the molar concentration of hydrochloric acid between 4 mol / L and 6 mol / L significantly improves the leaching effect. If the molar concentration of hydrochloric acid is too low, there is insufficient chloride ion coordinating agent, failing to provide enough Cl⁻. - When the metal coordinates with noble metal ions, the leaching reaction cannot proceed completely, resulting in a significant decrease in the leaching rate. Insufficient acidity in the reaction system and a lack of sufficient H₂O hinder the leaching process. + It is a prerequisite for protonation and dissolution of the passivation layer on the oxide surface, while also inhibiting Rh 3+ Hydrolysis produces insoluble hydroxyl oxides. Insufficient acidity prevents the effective breaking of rhodium's chemical inertness, leading to a sharp decrease in its leaching rate. If the molar concentration of hydrochloric acid is too high, the oxidant decomposes and is lost ineffectively. Under high-concentration hydrochloric acid and microwave heating conditions, the strong oxidant sodium chlorate undergoes a violent self-decomposition reaction, preferentially reacting with large amounts of Cl-. - The reaction produces chlorine gas, which not only results in the ineffective consumption of the oxidant, leading to insufficient effective dosage for oxidizing precious metals, but also may cause problems such as operational safety, environmental leakage, and gas collection and treatment due to the large and rapid escape of chlorine gas.

[0080] A comparison of Examples 1 and 7-8 shows that in the method for leaching precious metals from spent catalysts containing precious metals described in this invention, the microwave power of the ultrasonic-microwave synergistic leaching treatment affects the leaching effect. Controlling the microwave power of the ultrasonic-microwave synergistic leaching treatment to 400W~600W significantly improves the leaching effect. If the microwave power of the ultrasonic-microwave synergistic leaching treatment is too low, it is impossible to rapidly and uniformly heat the reaction system in bulk, making it difficult to reach and maintain the optimal reaction temperature. A lower reaction temperature will significantly slow down the interfacial chemical reaction rate for precious metal dissolution, resulting in a slow and incomplete leaching process. Furthermore, insufficient power cannot effectively promote the rupture of the inert oxide film on the surface of the precious metal and the formation of chloride coordination ions, thus resulting in a low leaching rate for refractory precious metals such as rhodium. If the microwave power of the ultrasonic-microwave synergistic leaching treatment is too high, it will cause instantaneous localized overheating in the reaction system, especially on the surface of the catalyst particles, disrupting the stable reaction environment. Moreover, excessive power will waste energy and reduce the overall energy efficiency of the process.

[0081] A comparison of Examples 1 and 9-10 shows that in the method for leaching precious metals from spent catalysts containing precious metals described in this invention, the ultrasonic frequency of the ultrasonic-microwave synergistic leaching treatment affects the leaching effect. Controlling the ultrasonic frequency of the ultrasonic-microwave synergistic leaching treatment within the range of 25kHz to 40kHz significantly improves the leaching effect. If the ultrasonic frequency of the ultrasonic-microwave synergistic leaching treatment is too low, the cavitation bubble size becomes too large, leading to an imbalance between destructive force and selectivity: the lower the frequency, the larger the cavitation bubble size generated in the liquid, and the more intense the instantaneous high temperature and pressure generated upon collapse. Excessively violent impacts may indiscriminately and severely pulverize the catalyst support. If the ultrasonic frequency of the ultrasonic-microwave synergistic leaching treatment is too high, the period of the sound wave becomes shorter, and the cavitation bubbles do not have enough time to grow to a size capable of generating effective impact force before collapsing, resulting in a weakened cavitation effect. The intensity of the generated shock wave and microjets is insufficient to effectively peel off and break the dense support encapsulating the precious metal, preventing the encapsulated active sites of the precious metal from being fully exposed, and thus failing to maximize the leaching reaction interface.

[0082] Comparing Example 1 and Comparative Examples 1-2, it can be seen that the present invention employs a synergistic ultrasonic-microwave leaching treatment. The strong shock waves and microjets generated by the cavitation effect of ultrasound in the liquid physically break down and erode the catalyst support, completely breaking its encapsulation of platinum group metal particles. This fully exposes the encapsulated metal active sites. The strong stirring effect generated by ultrasound significantly reduces the thickness of the diffusion boundary layer between the liquid and solid phases, accelerating the mass transfer rate of leaching agent ions to the particle surface and internal pores, as well as the diffusion rate of reaction products into the bulk solution. Microwaves rapidly and uniformly heat polar molecules (water, HCl) in the bulk phase, avoiding the thermal gradient problem of traditional heating methods and greatly improving thermal efficiency. Simultaneously, selective heating of certain substances may locally reduce the activation energy of the reaction. The non-thermal effects of microwaves (such as their influence on molecular polarization) may directly promote redox reactions, accelerating the formation of noble metal chloride complex ions. The synergistic effect of both methods, occurring synchronously in time and space, mutually promotes each other, jointly solving the industry problem of difficult rhodium leaching and significantly shortening the reaction time.

[0083] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for leaching precious metals from spent catalysts containing precious metals, characterized in that, The method includes the following steps: A leaching agent is obtained by mixing hydrochloric acid and an oxidant, and a mixed slurry is obtained by mixing the waste catalyst containing precious metals with the leaching agent. The mixed slurry was subjected to ultrasonic-microwave synergistic leaching treatment, and solid-liquid separation was performed to obtain filter residue and precious metal leachate.

2. The method as described in claim 1, characterized in that, The molar concentration of the hydrochloric acid is 2 mol / L to 8 mol / L, preferably 4 mol / L to 6 mol / L.

3. The method as described in claim 1 or 2, characterized in that, The oxidant includes sodium chlorate and / or hydrogen peroxide, preferably sodium chlorate.

4. The method according to any one of claims 1-3, characterized in that, The precious metals in the precious metal-containing waste catalyst include any one or a combination of at least two of platinum, palladium, or rhodium. Preferably, the particle size of the precious metal-containing waste catalyst is 100 mesh to 400 mesh, and more preferably 150 mesh to 250 mesh.

5. The method according to any one of claims 1-4, characterized in that, The molar ratio of the precious metal to the oxidant in the precious metal-containing waste catalyst is 1:(1.5~3).

6. The method according to any one of claims 1-5, characterized in that, The liquid-to-solid ratio of the precious metal-containing waste catalyst to the leaching agent is (4~15) mL / 1g.

7. The method according to any one of claims 1-6, characterized in that, The ultrasonic-microwave synergistic leaching treatment temperature is 70℃~98℃, preferably 85℃~95℃.

8. The method according to any one of claims 1-7, characterized in that, The microwave power of the ultrasonic-microwave synergistic leaching treatment is 200W~800W, preferably 400W~600W.

9. The method according to any one of claims 1-8, characterized in that, The ultrasonic frequency of the ultrasonic-microwave synergistic leaching treatment is 20kHz~60kHz, preferably 25kHz~40kHz. Preferably, the ultrasonic power density of the ultrasonic-microwave synergistic leaching treatment is 0.2W / mL to 1.5W / mL, and more preferably 0.5W / mL to 1.0W / mL.

10. The method according to any one of claims 1-9, characterized in that, The ultrasonic-microwave synergistic leaching treatment time is 10 min to 90 min, preferably 20 min to 50 min.

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