Method for recovering silver from invalid ethylene oxide catalyst

Abstract

The invention relates to the technical field of metallurgy and solid waste recycling, in particular to a method for recovering silver from a spent ethylene oxide catalyst, which comprises the following steps: crushing and drying the spent catalyst, and mixing with copper concentrate, calcium oxide, silicon dioxide and carbon powder according to a specific proportion; placing the mixed material in a microwave heating device, carrying out sulfonium-making smelting at a specific microwave frequency, and controlling the smelting temperature and time so that silver in the catalyst is selectively captured in a generated sulfonium phase; and after smelting is finished, the sulfonium phase and the slag phase are separated, and silver-rich sulfonium is obtained. According to the method, efficient enrichment and recovery of silver are achieved through the microwave external field enhanced reaction, the method has the advantages of being low in energy consumption, rapid in reaction and high in silver recovery rate, meanwhile, the problem of environmental pollution of a wet process is avoided, and resource utilization of the carrier aluminum oxide is achieved.

Description

Technical Field

[0001] This invention relates to the field of metallurgy and solid waste resource utilization technology, specifically to a method for recovering silver from degraded ethylene oxide catalysts. Background Technology

[0002] Ethylene oxide (EO) is a crucial organic chemical raw material and product in the ethylene industry, second only to polyethylene, and is widely used in pharmaceuticals, automobiles, and electronics. Silver catalysts are precious metal catalysts with silver as the active component, and are the only industrial catalyst used in the oxidation of ethylene to produce ethylene oxide. They are typically silver (Ag) supported on α-alumina (α-Al₂O₃), with a global annual demand exceeding 8,000 tons. After a certain period of use, silver catalysts become ineffective due to decreased activity, resulting in a large amount of high-silver-content degraded catalyst. Silver is a precious metal with high economic value; efficient recovery has significant economic benefits and resource recycling significance.

[0003] Existing methods for silver recovery from spent ethylene oxide catalysts commonly involve dissolving silver using cyanide leaching and nitric acid leaching, followed by recovery through displacement, precipitation, or electrolysis. The main problems include: high reagent consumption and high cost. Cyanide is highly toxic and poses significant environmental pressure; strong acid leaching severely corrodes equipment, limiting leaching rates. The Al₂O₃ support consumes acid, and silver particles may be encapsulated or form insoluble compounds, affecting leaching efficiency. Wastewater treatment is difficult, generating large amounts of wastewater containing cyanide, acid, or heavy metals, with high treatment costs and environmental risks. Aluminum resources are not utilized; the Al₂O₃ support is typically treated as solid waste, failing to achieve resource recovery.

[0004] Traditional pyrometallurgical methods commonly employ direct smelting and matte-forming smelting. Direct smelting involves directly melting degraded catalysts at high temperatures, resulting in silver enrichment in the metallic phase. However, it suffers from extremely high energy consumption, silver volatilization losses at high temperatures, significant silver entrainment losses due to high slag viscosity caused by high Al₂O₃ content, and the need for a strong reducing atmosphere. Matte-forming smelting is an effective pyrometallurgical method for capturing precious metals, selectively capturing them by forming a matte phase with a strong affinity for Ag. However, conventional fuel-heated or electric arc-heated matte-forming smelting methods, when applied to high-alumina degraded catalysts, face problems such as high energy consumption, slow reaction kinetics, prominent slag phase issues, and strong dependence on additives. Furthermore, Al₂O₃ readily forms high-melting-point compounds with slag-forming agents such as CaO, deteriorating slag properties.

[0005] Microwave external field heating has advantages such as selective heating, fast heating speed, high energy utilization, and easy control. Microwave external field enhanced matte smelting can form a clear matte-slag two-phase structure in a short time, providing conditions for favorable thermodynamic distribution and rapid kinetic migration of silver. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recovering silver from a spent ethylene oxide catalyst. The method involves mixing catalyst powder with copper concentrate, slagging agent and carbon powder, and then using a microwave field for matte smelting to selectively enrich silver in the matte phase, thereby achieving efficient, low-consumption and clean recovery.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0008] A method for recovering silver from degraded ethylene oxide catalysts includes the following steps:

[0009] S1: The degraded ethylene oxide catalyst is pretreated to obtain catalyst powder;

[0010] S2: The catalyst powder is mixed with copper concentrate, calcium oxide, silicon dioxide and carbon powder to obtain a mixture.

[0011] S3: The mixture is placed in a microwave heating device and smelted under the action of a microwave field to selectively capture silver in the formed matte phase;

[0012] S4: After smelting, the matte phase and slag phase are separated to obtain silver-rich matte.

[0013] Furthermore, in step S1, the pretreatment includes: crushing the degraded ethylene oxide catalyst to a particle size of less than 74 micrometers and drying it to a water content of no more than 1 wt%.

[0014] Furthermore, in step S2, based on the total dry weight of the mixture, the content of each component is as follows:

[0015] Copper concentrate: 50wt%~70wt%;

[0016] Depleted ethylene oxide catalyst powder: 9wt%~25wt%;

[0017] Total content of calcium oxide and silicon dioxide: 12wt%~25wt%;

[0018] Toner: 0.5wt%~2wt%.

[0019] Furthermore, in step S2, the mass ratio of calcium oxide to silicon dioxide (CaO / SiO2) is controlled to be between 0.3 and 1.2.

[0020] Furthermore, the mass ratio of CaO / SiO2 is 0.8.

[0021] Furthermore, the copper concentrate contains, by mass percentage, 15% to 25% copper, 20% to 30% iron, and 6% to 20% sulfur.

[0022] Furthermore, in step S3, the process conditions for matte smelting are as follows: microwave frequency is 2.45 GHz; smelting temperature is 1150℃~1350℃; and the holding time at the smelting temperature is 40 min~120 min.

[0023] Furthermore, the melting temperature is 1300°C.

[0024] Furthermore, in step S4, the separation includes: after the smelting is completed, the mixture is allowed to stand for 5 to 20 minutes, and then the matte phase and slag phase are mechanically separated.

[0025] On the other hand, the present invention provides a silver-rich matte product, which is prepared by the above method;

[0026] The silver content in the silver-rich matte product is not less than 250g / t;

[0027] Furthermore, the ratio of silver content in the silver-rich matte product to silver content in the smelting slag produced in the method is greater than 10:1.

[0028] The beneficial effects of this invention are:

[0029] This invention utilizes the strong affinity of matte for silver. By combining a depleted catalyst with copper concentrate, a slagging agent, and carbon powder, and smelting under a microwave field, silver is selectively captured in the matte phase. Controlling the proportion of copper concentrate in the furnace charge to 50wt%-70wt% ensures the formation of a sufficient quantity and stable composition of the matte phase, providing a thermodynamically stable enriched phase for silver. The bulk heating characteristics of microwaves and the sensitizing effect of carbon powder promote rapid and uniform heating and mass transfer of the materials, overcoming the extraction kinetic limitations caused by the encapsulation of silver particles by the Al2O3 carrier. Simultaneously, by adjusting the CaO / SiO2 mass ratio, a low-viscosity calcium aluminosilicate slag system with low silver solubility is obtained, ensuring clear separation of the matte and slag phases based on density difference, significantly reducing silver loss caused by slag entrainment. Examples show that the silver content in the silver-rich matte obtained by this method is not less than 250 g / t, the matte / slag silver partition ratio is greater than 10:1, and the silver recovery rate exceeds 97%, verifying its efficient silver capture and separation capabilities.

[0030] This invention employs direct microwave heating instead of traditional external heating, achieving rapid internal heating through the absorption of microwave energy by molecules, ions, and conductive phases within the material. Trace amounts of carbon powder act as sensitizers, preferentially heated in the low-temperature range, thereby initiating and accelerating the overall matte-forming and melting reactions. This significantly shortens the time to reach the target melting temperature, thus reducing overall energy consumption. The rapid and uniform microwave heating also avoids reaction imbalances caused by temperature gradients, allowing matte-forming, slag phase formation, and silver migration processes to be completed efficiently and synergistically within a shorter holding time. Comparative examples demonstrate that, under the same formulation and conditions, microwave heating yields higher-grade silver-rich matte and lower silver content in the slag compared to traditional electric heating, showcasing its significant advantages in enhancing reaction kinetics and improving energy efficiency.

[0031] This invention eliminates wet processes such as cyanidation and strong acid leaching, thus preventing the use of highly toxic chemicals and the generation of cyanide- and acid-containing wastewater at the source. In the pyrometallurgical process, sulfur is mainly fixed in the stable matte and slag phases, resulting in low sulfur content in the flue gas. This sulfur can be introduced into an acid production system for resource recovery, avoiding sulfur pollution. For Al2O3, the main component of the degraded catalyst, CaO and SiO2 slagging agents are added to transform it into stable calcium aluminosilicate slag during smelting. This slag phase can be comprehensively utilized as a building material raw material, thereby transforming the carrier Al2O3 from a waste to a potentially valuable byproduct. Simultaneously, it achieves the recovery of precious metal silver and the synergistic utilization of aluminum resources, meeting the requirements of clean production and resource recycling.

[0032] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the overall process of the present invention;

[0035] Figure 2 This is a schematic diagram of the smelting products. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] A method for recovering silver from a spent ethylene oxide catalyst, as described in this embodiment, includes: uniformly mixing pretreated spent catalyst powder with copper concentrate, calcium oxide, silica, and carbon powder. The uniformly mixed charge is then loaded into a microwave-safe high-purity alumina crucible and placed within the reaction chamber of a microwave melting furnace. Silver-rich matte phase, slag, and smelting flue gas are obtained through matte-forming smelting. The entire smelting process is simple and efficient, consumes relatively little energy, and achieves clear separation of the slag and matte phases. This invention provides a broad scope for the efficient and low-energy recovery of this type of resource.

[0038] The present invention achieves the capture of silver in degraded ethylene oxide catalysts through microwave matte smelting using the following technical solution, including the following steps:

[0039] S1: Raw material preparation: copper concentrate and degraded ethylene oxide catalyst are selected as raw materials for matte smelting, calcium oxide and silicon dioxide are used as slag-forming agents, and carbon powder is used as a combustion aid.

[0040] S2: Select materials according to the following percentage content:

[0041] Copper concentrate 60%–70%;

[0042] 15%–18% of ethylene oxide catalysts have failed.

[0043] Excipients: 12%–25%;

[0044] The excipients are calcium oxide, silicon dioxide, and carbon powder;

[0045] S3: Ball mill the main raw materials and auxiliary materials to make them evenly mixed, then put them into a crucible, and then put the crucible into a microwave melting furnace to melt at 1150~1350℃ for 40~120 minutes.

[0046] In this embodiment, the melting temperature in step S3 is selected as 1300℃, and the raw material is ball-milled to between 200-300 mesh using a sample mill.

[0047] S4: Adjust the mass ratio of the degraded catalyst powder, copper concentrate, calcium oxide, silicon dioxide, and carbon powder to achieve a Ca / SiO2 ratio of 0.3-1.2 during the batching process.

[0048] In this embodiment, Ca / SiO2 = 0.8 in step S4.

[0049] S5: After smelting, a clearly separated slag-matte two-phase mixture and smelting flue gas are obtained, among which the smelting flue gas can be used for the next step of acid production and recovery.

[0050] In this embodiment, after the smelting is completed in step S4, silver-rich matte and smelting slag are obtained respectively, and their mass is weighed and their element content is detected.

[0051] This invention utilizes microwave matte smelting to capture silver from degraded ethylene oxide catalysts. The smelting product, after further processing, allows for the efficient separation and extraction of the precious metal silver. The smelting flue gas and slag can be recycled and reused. This invention provides a more energy-efficient and effective method for capturing silver from degraded ethylene oxide catalysts, improving the utilization rate of secondary resources.

[0052] Smelting products such as Figure 2 As shown, a clear two-phase structure of silver-rich matte and smelting slag appears.

[0053] Example 1

[0054] A method for recovering silver from a degraded ethylene oxide catalyst, as described in this embodiment, includes:

[0055] S1: Raw material selection: The main raw material, copper concentrate, contains 15.52 wt% copper, 20.58 wt% iron, 6.47 wt% sulfur, 4.11 wt% CaO, and 8 wt% SiO2. The degraded ethylene oxide catalyst contains 15 wt% silver.

[0056] S2: Weigh out 50g of copper concentrate (main raw material), 9g of depleted ethylene oxide catalyst, and 7.91g of 98% analytical grade calcium oxide powder, 9.89g of 98% analytical grade silicon dioxide powder, and 1g of 300-mesh carbon powder. After batching, the proportion of copper concentrate is 64.3wt%, the proportion of depleted ethylene oxide catalyst is 11.6wt%, and the proportion of slagging agent is 24.2wt%. Control the calcium-silicon ratio at 0.8.

[0057] S3: Use a sample preparation machine to ball mill the main material and auxiliary material to a mesh size of 200-300. After mixing them evenly, put them into a corundum crucible. Then, put the crucible into a microwave melting furnace with a microwave field of 2.45 GHz and melt it at 1300℃ for 60 minutes.

[0058] S4: After smelting, remove the crucible, break it, and observe the layering. The phase with metallic luster is the silver-rich matte phase, and the phase without metallic luster is the slag phase. After smelting, keep it at a constant temperature to obtain silver-rich matte and smelting slag. Weigh and test the mass of each.

[0059] The contents of various metals in the silver-rich matte phase and smelting slag were obtained as follows:

[0060]

[0061] Example 2

[0062] A method for recovering silver from a degraded ethylene oxide catalyst, as described in this embodiment, includes:

[0063] S1: Raw material selection. The composition of the copper concentrate in this embodiment differs from that in Example 1. The main raw material copper concentrate contains 20.72 wt% copper, 27.71 wt% iron, 16.63 wt% sulfur, 1.92 wt% CaO, and 10 wt% SiO2. The degraded ethylene oxide catalyst contains 16.8 wt% silver.

[0064] S2: Weigh out 50g of copper concentrate (main raw material), 15g of depleted ethylene oxide catalyst, and 7.91g of 98% analytical grade calcium oxide powder, 9.89g of 98% analytical grade silicon dioxide powder, and 1g of 300-mesh carbon powder. After batching, the proportion of copper concentrate is 59.7wt%, the proportion of depleted ethylene oxide catalyst is 17.9wt%, and the proportion of slagging agent is 21.2wt%. Control the calcium-silicon ratio at 0.8.

[0065] S3: Use a sample preparation machine to ball mill the main material and auxiliary material to a mesh size of 200-300. After mixing them evenly, put them into a corundum crucible. Then, put the crucible into a microwave melting furnace with a microwave field of 2.45 GHz and melt it at 1300℃ for 60 minutes, and hold it for 60 minutes.

[0066] S4: After smelting, remove the crucible, break it, and observe the layering. The phase with metallic luster is the silver-rich matte phase, and the phase without metallic luster is the slag phase. After smelting, keep it at a constant temperature to obtain silver-rich matte and smelting slag. Weigh and test the mass of each.

[0067] The contents of various metals in the silver-rich matte phase and smelting slag were obtained as follows:

[0068]

[0069] Example 3

[0070] This embodiment will use a traditional electrothermal heating method for matte smelting, and compare it with a microwave heating method for matte smelting, including:

[0071] S1: Raw material selection: The main raw material, copper concentrate, contains 15.52 wt% copper, 20.58 wt% iron, 6.47 wt% sulfur, 4.11 wt% CaO, and 8 wt% SiO2. The degraded ethylene oxide catalyst contains 15 wt% silver.

[0072] S2: Weigh out 50g of copper concentrate (main raw material), 9g of depleted ethylene oxide catalyst, and 7.91g of 98% analytical grade calcium oxide powder, 9.89g of 98% analytical grade silicon dioxide powder, and 1g of 300-mesh carbon powder. After batching, the proportion of copper concentrate is 64.3wt%, the proportion of depleted ethylene oxide catalyst is 11.6wt%, and the proportion of slagging agent is 24.2wt%. Control the calcium-silicon ratio at 0.8.

[0073] S3: Use a sample preparation machine to ball mill the main material and auxiliary material to a mesh size of 200-300. After mixing them evenly, put them into a corundum crucible and then melt them in a conventional resistance furnace at 1300℃ for 60 minutes and hold for 60 minutes.

[0074] S4: After smelting, remove the crucible, break it, and observe the layering. The phase with metallic luster is the silver-rich matte phase, and the phase without metallic luster is the slag phase. After smelting, keep it at a constant temperature to obtain silver-rich matte and smelting slag. Weigh and test the mass of each.

[0075] The contents of various metals in the silver-rich matte phase and smelting slag were obtained as follows:

[0076]

[0077] Example 4

[0078] A method for recovering silver from a degraded ethylene oxide catalyst, as described in this embodiment, includes:

[0079] S1: Raw material selection. The composition of the copper concentrate in this embodiment differs from that in Example 1. The main raw material, copper concentrate, contains 23.11 wt% copper, 22.71 wt% iron, 14.63 wt% sulfur, 2.01 wt% CaO, and 8 wt% SiO2. The degraded ethylene oxide catalyst contains 13.3 wt% silver.

[0080] S2: Weigh out 50g of copper concentrate (main raw material), 20g of spent ethylene oxide catalyst, and 7.91g of 98% analytical grade calcium oxide powder, 9.89g of 98% analytical grade silicon dioxide powder, and 1g of 300-mesh carbon powder. After batching, the proportion of copper concentrate is 56.3wt%, the proportion of spent ethylene oxide catalyst is 22.5wt%, and the proportion of slagging agent is 20.0wt%. Control the calcium-silicon ratio at 0.8.

[0081] S3: Use a sample preparation machine to ball mill the main material and auxiliary material to a mesh size of 200-300. After mixing them evenly, put them into a corundum crucible. Then, put the crucible into a microwave melting furnace with a microwave field of 2.45 GHz and melt it at 1300℃ for 60 minutes, and hold it for 60 minutes.

[0082] S4: After smelting, remove the crucible, break it, and observe the layering. The phase with metallic luster is the silver-rich matte phase, and the phase without metallic luster is the slag phase. After smelting, keep it at a constant temperature to obtain silver-rich matte and smelting slag. Weigh and test the mass of each.

[0083] The contents of various metals in the silver-rich matte phase and smelting slag were obtained as follows:

[0084]

[0085] The results of the above embodiments show that the process of using a microwave melting furnace to process copper concentrate, slag-forming agent, and depleted catalyst, along with the addition of carbon powder with good wave absorption characteristics, to form matte and capture the precious metal silver from the depleted catalyst is feasible. After melting, the silver content of the silver-rich matte is above 254.56 g / t, and the silver recovery rate from the depleted catalyst is above 97%, achieving efficient and low-consumption recovery of precious metals and reducing precious metal loss. Comparative experiments using ordinary electrothermal melting provide a practical and feasible method for efficiently and effectively recovering the precious metal silver from depleted ethylene oxide catalysts.

[0086] In summary, this invention proposes a method for recovering silver from spent ethylene oxide catalysts, comprising: crushing and drying the spent catalyst, then mixing it with copper concentrate, calcium oxide, silica, and carbon powder in a specific ratio; placing the mixture in a microwave heating device and performing matte smelting at a specific microwave frequency, controlling the smelting temperature and time to selectively capture silver in the generated matte phase; after smelting, separating the matte phase from the slag phase to obtain silver-rich matte. This invention utilizes microwave-enhanced reaction to achieve efficient silver enrichment and recovery, offering advantages such as low energy consumption, fast reaction, and high silver recovery rate, while avoiding the environmental pollution problems of wet processes and realizing the resource utilization of the alumina support.

[0087] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method of recovering silver from a spent ethylene oxide catalyst, characterized by, Includes the following steps: S1: The degraded ethylene oxide catalyst is pretreated to obtain catalyst powder; S2: The catalyst powder is mixed with copper concentrate, calcium oxide, silicon dioxide and carbon powder to obtain a mixture. S3: The mixture is placed in a microwave heating device and smelted under the action of a microwave field to selectively capture silver in the formed matte phase; S4: After smelting, the matte phase and slag phase are separated to obtain silver-rich matte.

2. The method of claim 1, wherein, In step S1, the pretreatment includes: crushing the degraded ethylene oxide catalyst to a particle size of less than 74 micrometers and drying it to a water content of no more than 1 wt%.

3. The method of claim 1, wherein, In step S2, based on the total dry weight of the mixture, the content of each component is as follows: Copper concentrate: 50wt%~70wt%; Depleted ethylene oxide catalyst powder: 9wt%~25wt%; Total content of calcium oxide and silicon dioxide: 12wt%~25wt%; Toner: 0.5wt%~2wt%.

4. The method of claim 1 or 3, wherein, In step S2, the mass ratio of calcium oxide to silicon dioxide (CaO / SiO2) is controlled to be between 0.3 and 1.

2.

5. The method of claim 4, wherein, The mass ratio of CaO / SiO2 is 0.

8.

6. The method of claim 1, wherein, The copper concentrate contains, by mass percentage, 15% to 25% copper, 20% to 30% iron, and 6% to 20% sulfur.

7. The method of claim 1, wherein, In step S3, the process conditions for matte smelting are as follows: microwave frequency is 2.45 GHz; smelting temperature is 1150℃~1350℃; and the holding time at the smelting temperature is 40 min~120 min.

8. The method of claim 7, wherein, The melting temperature is 1300℃.

9. The method of claim 1, wherein, In step S4, the separation includes: after smelting, letting it stand for 5 to 20 minutes, and then performing mechanical separation of the matte phase and the slag phase.

10. A silver-rich matte product characterized in that, It is prepared by the method described in any one of claims 1 to 9; The silver content in the silver-rich matte product is not less than 250g / t; Furthermore, the ratio of silver content in the silver-rich matte product to silver content in the smelting slag produced in the method is greater than 10:1.

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