A method for comprehensive utilization of waste catalyst

Abstract

This application relates to the technical field of hazardous waste utilization, specifically to a method for the comprehensive utilization of spent catalysts. Specifically, the spent catalyst is subjected to sequential oxidative roasting, wet ball milling, and pressure leaching to obtain a first leachate and leaching residue. The first leachate is then extracted using multi-stage countercurrent extraction, where molybdenum and tungsten are extracted. After back-extraction, a back-extraction solution containing molybdenum and tungsten is obtained. The back-extraction solution is then subjected to sequential static degreasing, evaporation and concentration, and multi-stage countercurrent extraction to remove vanadium, yielding a raffinate and a vanadium-containing back-extraction solution. The raffinate mainly contains molybdate and tungsten ions. The separation method is determined based on the different molar ratios of molybdenum and tungsten. The leaching residue is acidically leached using sulfuric acid solution at room temperature and pressure to obtain a second leachate. Extraction is performed using cobalt and nickel extractants, respectively, followed by back-extraction, evaporation, and crystallization to obtain cobalt sulfate and nickel sulfate products. The method provided in this application can recover vanadium, tungsten, cobalt, molybdenum, nickel, and other metal resources from spent catalysts.

Description

Technical Field

[0001] This application relates to the technical field of hazardous waste utilization, and in particular to a method for the comprehensive utilization of spent catalysts. Background Technology

[0002] In the production of petrochemical products, vanadium, tungsten, cobalt, molybdenum, and nickel-based spent catalysts are used extensively. For example, when ethylene and propylene obtained from petroleum hydrocarbon cracking are used as polymerization feedstocks, they must first undergo selective hydrogenation. The hydrogenation catalysts used are generally cobalt, molybdenum, and nickel active components supported on alumina. Other examples include the use of hydrogenation catalysts in the refining of cracked gasoline; cobalt-molybdenum shift catalysts in methanol production; tungsten and nickel-based catalysts in cracking reactors; and vanadium-tungsten-based catalysts in flue gas purification.

[0003] Catalysts lose their activity after a certain period of use and need to be replaced. According to the "National Hazardous Waste List," the replaced spent catalysts belong to category HW50 and must be treated as hazardous waste. The common method is safe landfill disposal, but this method results in resource waste. Alternatively, metal resources in spent catalysts can be recovered. However, recovery typically targets only a specific metal or a single type of catalyst and is not applicable to the recovery and utilization of spent catalysts containing multiple metals, such as vanadium, tungsten, cobalt, molybdenum, and nickel.

[0004] Therefore, in order to further improve the recovery efficiency of metal resources in spent catalysts, it is urgent to find a method to simultaneously recover multiple types of metals from spent catalysts. Summary of the Invention

[0005] This application provides a method for the comprehensive utilization of spent catalysts. The method provided by this application can recover metal resources such as vanadium, tungsten, cobalt, molybdenum, and nickel from spent catalysts. This method is applicable to the treatment of single-type or multi-type spent catalysts, as well as spent catalysts in which various metals coexist. It has a high recovery rate, high product purity, and a wide range of applications.

[0006] Firstly, this application provides a method for the comprehensive utilization of spent catalysts, employing the following technical solution:

[0007] A method for the comprehensive utilization of spent catalysts, the method specifically includes the following steps:

[0008] The spent catalyst is subjected to oxidative roasting, wet ball milling, and pressure leaching in sequence to obtain a first leachate and a leaching residue; the first leachate is used for the recovery of molybdenum, tungsten, and vanadium; the leaching residue is used for the recovery of nickel and cobalt.

[0009] For the first leachate:

[0010] The first leachate is extracted using a multi-stage countercurrent extraction method, in which molybdenum and tungsten are extracted, and then back-extracted to obtain a back-extract containing molybdenum and tungsten; the back-extract is then subjected to static deoiling, evaporation and concentration, and multi-stage countercurrent extraction to remove vanadium, to obtain raffinate and a vanadium-containing back-extract.

[0011] The raffinate mainly contains molybdate and tungstate ions; different separation methods are determined according to different molar ratios of molybdenum and tungsten, specifically:

[0012] A. When the molybdenum content is close to the tungsten content, i.e., the molar ratio of the two is 0.2-5: Evaporation and concentration are first employed, allowing the higher content of tungsten to crystallize first in the form of ammonium paratungstate. At this stage, the ammonium paratungstate crystals still contain a small amount of ammonium molybdate, which needs to be further purified through a dissolution-ion exchange step. Then, after evaporation and crystallization, a pure ammonium paratungstate product can be obtained. Simultaneously, the concentrated mother liquor from the first evaporation and concentration process is mainly ammonium molybdate, containing a small amount of ammonium paratungstate. This concentrated mother liquor is then extracted to remove tungsten before being evaporated and crystallized again to obtain a pure ammonium molybdate product.

[0013] B. When the molybdenum content is much greater than the tungsten content, that is, the molar ratio of the two is greater than 5: the tungsten is removed directly by extraction, and then evaporated and crystallized to obtain a pure ammonium molybdate product;

[0014] C. When the molybdenum content is much less than the tungsten content, i.e. the molar ratio of the two is less than 0.2: directly use ion exchange to remove molybdenum, and then carry out evaporation and crystallization to obtain pure ammonium paratungstate product;

[0015] For the leaching residue: the leaching residue is acidically leached with sulfuric acid solution at room temperature and pressure to obtain a second leachate; it is then extracted with cobalt extractant and nickel extractant respectively, and after back-extraction, evaporation and crystallization, cobalt sulfate product and nickel sulfate product are obtained.

[0016] Optionally, the spent catalyst contains any one or more of molybdenum, tungsten, vanadium, nickel, and cobalt.

[0017] Optionally, the concentration of V2O5 in the raffinate can be reduced to below 0.01 g / L.

[0018] Optionally, the vanadium removal rate in the raffinate reaches 99% or higher.

[0019] Optionally, (NH4)2SO4 is added to the vanadium-containing back-extraction solution under pH 8-9 conditions to induce a metathesis reaction and obtain ammonium metavanadate crystals.

[0020] Optionally, the second leachate is first extracted with the cobalt extractant, and after back-extraction and evaporation crystallization, a cobalt sulfate product is obtained; then, the raffinate obtained after back-extraction is extracted with a nickel extractant, and after back-extraction and evaporation crystallization, a nickel sulfate product is obtained.

[0021] Optionally, an appropriate extractant may be selected based on the nickel and cobalt content in the second leachate.

[0022] Optionally, when the Co / Ni content is greater than 1 / 5, the extractant used is P204; when the Co / Ni content is less than 1 / 5, the extractant used is P507; and when the Co / Ni content is less than 1 / 10, the extractant used is Cyanex272.

[0023] In summary, this application includes at least one of the following beneficial technical effects:

[0024] 1. The comprehensive utilization method of waste catalyst in this application has a wide range of applications. It can be applied not only to the treatment of single-metal waste catalysts, but also to the treatment of waste catalysts containing multiple metals such as vanadium, tungsten, cobalt, molybdenum and nickel. It has a high metal recovery rate and high product purity.

[0025] 2. Using a combination of alkaline leaching / acid leaching and other methods to leach different metals separately can reduce subsequent separation costs, improve product purity, and avoid mutual interference between metals during separation and recovery.

[0026] 3. The extraction performance of different extractants for molybdenum, tungsten, vanadium, nickel and cobalt was evaluated. The extractant with the highest overall efficiency was determined, and various extraction indicators were optimized. By combining chamber extraction or tubular extraction equipment and precisely controlling reaction parameters, the goal of separating precious metal elements in complex multi-metal solutions step by step was achieved, thereby improving the recovery rate.

[0027] 4. Washing the acid leaching filter residue and the purification residue can further improve the recovery rate. At the same time, the washing liquid of the purification residue can also be used to wash the acid leaching residue and finally return it to the acid leaching reactor for treatment.

[0028] 5. By alkali leaching and extracting molybdenum from spent molybdenum-tungsten-vanadium catalysts, the low-vanadium raffinate is converted into sodium hydroxide through causticization. The sodium salt is then returned to high-pressure alkali leaching, forming a closed-loop cycle of aqueous phase based on "leaching-extraction-crystallization". This improves the recycling rate of water, alkali, and ammonia. The alkali conversion rate of the low-vanadium raffinate reaches over 80%, and the ammonia recycling rate reaches over 70%, reducing wastewater generation and lowering production costs. Attached Figure Description

[0029] Figure 1 A flowchart illustrating the comprehensive utilization method of the spent catalyst provided in this application. Detailed Implementation

[0030] Before describing the embodiments of this application in detail, it should be understood that the terminology used herein is for the purpose of describing a particular embodiment only. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the term pertains.

[0031] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0032] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] In this application, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0034] This application provides a method for the comprehensive utilization of spent catalysts. The spent catalysts are sequentially subjected to oxidative roasting, wet ball milling, and pressure leaching to obtain a first leachate and leaching residue. The first leachate is used for the recovery of molybdenum, tungsten, and vanadium; the leaching residue is used for the recovery of nickel and cobalt.

[0035] For the first leachate:

[0036] The first leachate is extracted using a multi-stage countercurrent extraction method, in which molybdenum and tungsten are extracted, and then back-extracted to obtain a back-extract containing molybdenum and tungsten; the back-extract is then subjected to static deoiling, evaporation and concentration, and multi-stage countercurrent extraction to remove vanadium, to obtain raffinate and a vanadium-containing back-extract.

[0037] The raffinate mainly contains molybdate and tungstate ions; different separation methods are determined according to different molar ratios of molybdenum and tungsten, specifically:

[0038] A. When the molybdenum content is close to the tungsten content, i.e., the molar ratio of the two is 0.2-5: Evaporation and concentration are first employed, allowing the higher content of tungsten to crystallize first in the form of ammonium paratungstate. At this stage, the ammonium paratungstate crystals still contain a small amount of ammonium molybdate, which needs to be further purified through a dissolution-ion exchange step. Then, after evaporation and crystallization, a pure ammonium paratungstate product can be obtained. Simultaneously, the concentrated mother liquor from the first evaporation and concentration process is mainly ammonium molybdate, containing a small amount of ammonium paratungstate. This concentrated mother liquor is then extracted to remove tungsten before being evaporated and crystallized again to obtain a pure ammonium molybdate product.

[0039] B. When the molybdenum content is much greater than the tungsten content, that is, the molar ratio of the two is greater than 5: the tungsten is removed directly by extraction, and then evaporated and crystallized to obtain a pure ammonium molybdate product;

[0040] C. When the molybdenum content is much less than the tungsten content, i.e. the molar ratio of the two is less than 0.2: directly use ion exchange to remove molybdenum, and then carry out evaporation and crystallization to obtain pure ammonium paratungstate product;

[0041] For the leaching residue: the leaching residue is acidically leached with sulfuric acid solution at room temperature and pressure to obtain a second leachate; it is then extracted with cobalt extractant and nickel extractant respectively, and after back-extraction, evaporation and crystallization, cobalt sulfate product and nickel sulfate product are obtained.

[0042] In one specific implementation, such as Figure 1 As shown, a method for the comprehensive utilization of spent catalysts specifically includes the following steps:

[0043] (1) Oxidative roasting

[0044] Waste catalysts (including those containing molybdenum, tungsten, vanadium, nickel, and cobalt) are transferred from the temporary storage warehouse to the raw material intermediate warehouse. Heavy oil and other organic matter on the surface of the waste catalysts are removed by direct combustion in a rotary kiln at a temperature of 600-700℃ for 1.5-2.5 hours.

[0045] The flue gas generated from the combustion of heavy oil on the surface of the spent catalyst enters the secondary combustion chamber, where it undergoes secondary combustion using natural gas as fuel. The combustion temperature is 1050-1150℃, and the residence time is greater than 2 seconds, ensuring complete combustion of the flue gas. The flue gas, after undergoing secondary high-temperature combustion, is then desulfurized using a dual-alkali method and discharged through the exhaust stack in compliance with emission standards.

[0046] The specific reaction equations involved in the above-mentioned oxidative roasting are as follows: 2MoS2+7O2=2MoO3+4SO2; NiS+3O2=2NiO+2SO2; 2CoS+3O2=2CoO+2SO2.

[0047] (2) Ball milling-pressure alkaline leaching

[0048] The waste catalyst processed in step (1) is transferred to the silo, and then enters the wet ball mill for wet ball milling. The ball-milled slurry flows by gravity to the batching tank, and then an appropriate amount of water and alkali (such as sodium hydroxide and sodium carbonate, with a weight ratio of (1-2):1 and a total concentration of 30%) are added. The liquid-solid ratio is (5-10):1. Then the mixture is pumped to the leaching kettle for heating and leaching, and the leaching residue is discharged.

[0049] The leachate flows by gravity into the leachate storage tank and is then pumped to subsequent molybdenum, tungsten, and vanadium recovery processes.

[0050] The leaching residue is used in subsequent nickel and cobalt recovery processes.

[0051] (3) Molybdenum, tungsten and vanadium recovery

[0052] This step includes alkaline extraction, washing, preparation of the back-extraction agent, and back-extraction.

[0053] 1) Molybdenum-tungsten extraction

[0054] The leachate obtained in step (2) is sent to an extraction tank and subjected to multi-stage countercurrent extraction. Molybdenum in the leachate is preferentially extracted; impurities such as phosphorus, silicon, and most of the vanadium remain in the raffinate; if tungsten is present in the solution, it is extracted along with the molybdenum. The loaded organic phase is washed with pure water, and the wash water is combined with the raffinate. The washed loaded organic phase is then subjected to multi-stage countercurrent back-extraction to obtain a molybdenum-containing back-extraction solution and a back-extraction organic phase.

[0055] 2) Vanadium removal by extraction: The molybdenum-containing back-extraction solution obtained from molybdenum-tungsten extraction is first allowed to stand and de-oil in a back-extraction solution storage tank, and then concentrated by evaporation in a multi-effect evaporator to cause the molybdate and vanadate in the solution to undergo a hybridization reaction; after multi-stage countercurrent extraction, the vanadium removal rate is over 99%, and the V2O5 concentration in the raffinate can be reduced to below 0.01 g / L.

[0056] 3) Molybdenum-tungsten separation: The raffinate mainly contains molybdate and tungstate ions. Different separation methods are determined based on the different molar ratios of molybdenum and tungsten.

[0057] A. When the molybdenum content is close to the tungsten content, i.e. the molar ratio of the two is 0.2-5: direct extraction to remove tungsten is less efficient. Instead, evaporation and concentration are used first, so that the tungsten content, which is higher, crystallizes out as ammonium paratungstate. At this time, the ammonium paratungstate crystals still contain a small amount of ammonium molybdate, which needs to be further removed by dissolution-ion exchange. After evaporation and crystallization, pure ammonium paratungstate product can be obtained.

[0058] Meanwhile, the concentrated mother liquor in the first step of the evaporation and concentration process is mainly ammonium molybdate (containing a small amount of ammonium paratungstate). After the mother liquor is extracted to remove tungsten, it is then evaporated and crystallized to obtain a pure ammonium molybdate product.

[0059] B. When the molybdenum content is much greater than the tungsten content, that is, the molar ratio of the two is greater than 5: the tungsten can be removed directly by extraction, and then evaporated and crystallized to obtain a pure ammonium molybdate product.

[0060] C. When the molybdenum content is much less than the tungsten content, i.e., the molar ratio of the two is less than 0.2, the molybdenum can be removed directly by ion exchange. After removing the molybdenum, the product can be evaporated and crystallized to obtain pure ammonium paratungstate.

[0061] (4) Ammonium molybdate and ammonium paratungstate crystals

[0062] Ammonium molybdate solution is pumped into a crystallizer, where it is concentrated by evaporation and then cooled for crystallization. Molybdenum in the solution crystallizes out as ammonium dimolybdate. The crystallized slurry is then filtered through a tipping-bucket filter to obtain wet MSA and evaporation crystallization mother liquor. The wet MSA is transferred to a drying process, while the evaporation crystallization mother liquor flows into a mother liquor storage tank. The reaction is as follows:

[0063] (NH4)2MoO4+H2O=(NH4)2MoO7·2H2O+2NH3.

[0064] The mother liquor from the evaporation crystallization process is pumped into an acid precipitation crystallization reactor. Sulfuric acid is added to the reactor while stirring to adjust the pH to 2-3. Molybdenum in the solution crystallizes out as ammonium tetramolybdate. The precipitate is then filtered through a tilting bucket filter to obtain wet ammonium tetramolybdate and the mother liquor. The reaction is as follows:

[0065] 4(NH4)2MoO4+3H2SO4=(NH4)2Mo4O 13 ·2H2O+3(NH4)2SO4+H2O.

[0066] The ammonium tetramolybdate obtained by acid precipitation is dissolved in a redissolution reactor to obtain an ammonium molybdate solution, which is then returned to the evaporation and crystallization process. The mother liquor from the acid precipitation enters the recycling process.

[0067] (5) Vanadium precipitation

[0068] The residual liquid from molybdenum extraction is fed into a vanadium precipitation reactor. At pH 8-9, the vanadium in the solution mainly exists as V₄O₂. 12 4- (VO3 - It exists in the form of (NH4)2SO4. Adding (NH4)2SO4 to a vanadium solution will trigger a double displacement reaction, as shown in the following equation:

[0069] 2NaVO3+(NH4)2SO4=2NH4VO3+Na2SO4.

[0070] During this process, factors such as the amount of ammonium salt added (ammonium addition coefficient) and the pH value of vanadium precipitation are controlled to obtain white or light yellow ammonium metavanadate (PFSA) crystals.

[0071] (6) Nickel-cobalt recovery (acid leaching-pressure filtration-purification)

[0072] The leaching residue obtained in step (2) mainly contains nickel and cobalt, and acid leaching is required to recover nickel and cobalt.

[0073] After being leached with an acidic solution of approximately 10% sulfuric acid at normal pressure and temperature, nickel and cobalt ions are mainly present in the leachate. After filtration, separation, washing, and purification, a solution containing nickel and cobalt with relatively few impurities is obtained.

[0074] (7) Cobalt extraction

[0075] The leachate obtained in step (6) was extracted with a cobalt extractant, and then back-extracted and evaporated to crystallize to obtain cobalt sulfate product.

[0076] (8) Nickel extraction

[0077] The raffinate obtained in step (7) was extracted with a nickel extractant, and then back-extracted and evaporated to crystallize to obtain nickel sulfate product.

[0078] To save on extraction reagent costs, the following extraction agents were selected for different cobalt / nickel ratios: when the Co / Ni content > 1 / 5, P204 was used; when the Co / Ni content < 1 / 5, P507 was used; and when the Co / Ni content < 1 / 10, Cyanex272 was used.

[0079] To ensure both product purity and separation effectiveness while also considering usage costs, different extractants were selected based on the above conditions.

[0080] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0081] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0082] The present application will be further described in detail below with reference to the embodiments and test results.

[0083] Example 1

[0084] This embodiment provides a method for the comprehensive utilization of spent catalysts. The catalyst used is a spent catalyst containing molybdenum, tungsten, vanadium, nickel, and cobalt, weighing 100 kg. Specifically, the molybdenum content is 5 kg, the tungsten content is 0.5 kg, the vanadium content is 1 kg, the nickel content is 2 kg, and the cobalt content is 1 kg.

[0085] The above-mentioned comprehensive utilization method for spent catalysts specifically includes the following steps:

[0086] (1) Oxidative roasting

[0087] The spent catalyst was transferred from the temporary storage warehouse to the raw material intermediate warehouse, and heavy oil and other organic matter on the surface of the spent catalyst were removed by direct combustion in a rotary kiln at a temperature of 65°C for 2 hours.

[0088] The flue gas generated from the combustion of heavy oil on the surface of the spent catalyst enters the secondary combustion chamber, where it undergoes secondary combustion using natural gas as fuel. The combustion temperature is 1100℃, and the residence time is greater than 2 seconds, ensuring complete combustion of the flue gas. The flue gas, after undergoing secondary high-temperature combustion, is then desulfurized using a dual-alkali method and discharged through the exhaust stack in compliance with emission standards.

[0089] (2) Ball milling-pressure alkaline leaching

[0090] The waste catalyst processed in step (1) is transferred to the silo, and then enters the wet ball mill for wet ball milling. The ball-milled slurry flows by gravity to the batching tank, and 700 kg of water and 300 kg of alkali (150 kg each of sodium hydroxide and sodium carbonate) are added. Then it is pumped to the leaching kettle for heating and leaching, and the leaching residue is discharged.

[0091] The leachate flows by gravity into the leachate storage tank and is then pumped to subsequent molybdenum, tungsten, and vanadium recovery processes.

[0092] The leaching residue is used in subsequent nickel and cobalt recovery processes.

[0093] (3) Molybdenum, tungsten and vanadium recovery

[0094] 1) Molybdenum-tungsten extraction

[0095] The leachate obtained in step (2) is sent to an extraction tank and subjected to multi-stage countercurrent extraction. Molybdenum in the leachate is preferentially extracted; impurities such as phosphorus, silicon, and most of the vanadium remain in the raffinate; if tungsten is present in the solution, it is extracted along with the molybdenum. The loaded organic phase is washed with pure water, and the wash water is combined with the raffinate. The washed loaded organic phase is then subjected to multi-stage countercurrent back-extraction to obtain a molybdenum-containing back-extraction solution and a back-extraction organic phase.

[0096] 2) Vanadium removal by extraction: The molybdenum-containing back-extraction solution obtained from molybdenum-tungsten extraction is first allowed to stand and de-oil in a back-extraction solution storage tank, and then concentrated by evaporation in a multi-effect evaporator to cause the molybdate and vanadate in the solution to undergo a hybridization reaction; after multi-stage countercurrent extraction, the vanadium removal rate is over 99%, and the V2O5 concentration in the raffinate can be reduced to below 0.01 g / L.

[0097] 3) Molybdenum-tungsten separation: The raffinate mainly contains molybdate and tungstate ions. Different separation methods are determined based on the different molar ratios of molybdenum and tungsten.

[0098] A. When the molybdenum content is close to the tungsten content, direct extraction to remove tungsten is less efficient. Instead, the process involves evaporation and concentration to allow the more abundant tungsten to crystallize as ammonium paratungstate. At this point, the ammonium paratungstate crystals still contain a small amount of ammonium molybdate, which needs to be further removed by a dissolution-ion exchange step. After evaporation and crystallization, a pure ammonium paratungstate product can be obtained.

[0099] Meanwhile, the concentrated mother liquor in the first step of the evaporation and concentration process is mainly ammonium molybdate (containing a small amount of ammonium paratungstate). After the mother liquor is extracted to remove tungsten, it is then evaporated and crystallized to obtain pure ammonium molybdate product.

[0100] B. When the molybdenum content is much greater than the tungsten content, the extraction method can be used directly to remove the tungsten. After removing the tungsten, the product can be evaporated and crystallized to obtain pure ammonium molybdate.

[0101] C. When the molybdenum content is much lower than the tungsten content, ion exchange can be used directly to remove molybdenum. After removing molybdenum, evaporation and crystallization can be carried out to obtain pure ammonium paratungstate product.

[0102] In this embodiment, the molybdenum content is 5 kg and the tungsten content is 0.5 kg, which belongs to category B, that is, when the molybdenum content is much greater than the tungsten content, the extraction method can be used directly to remove the tungsten. After removing the tungsten, the product is evaporated and crystallized to obtain a pure ammonium molybdate product.

[0103] (4) Ammonium molybdate and ammonium paratungstate crystals

[0104] Ammonium molybdate solution is pumped into a crystallizer, where it is concentrated by evaporation and then cooled to crystallize, causing molybdenum in the solution to crystallize out as ammonium dimolybdate. After crystallization, the slurry is filtered through a tipping filter to obtain wet MSA and evaporation crystallization mother liquor. The wet MSA is then transferred to a drying process, while the evaporation crystallization mother liquor flows into a mother liquor storage tank.

[0105] The mother liquor from the evaporation crystallization process is pumped into an acid precipitation crystallization vessel. Sulfuric acid is added to the vessel while stirring to adjust the pH to 2-3. The molybdenum in the solution will crystallize out as ammonium tetramolybdate. The solution is then filtered through a tipping filter to obtain wet ammonium tetramolybdate and the mother liquor from the crystallization process.

[0106] The ammonium tetramolybdate obtained by acid precipitation is dissolved in a redissolution reactor to obtain an ammonium molybdate solution, which is then returned to the evaporation and crystallization process. The mother liquor from the acid precipitation enters the recycling process.

[0107] The final yield was: 10 kg of ammonium molybdate product; and 0.81 kg of ammonium paratungstate product.

[0108] Specifically as follows:

[0109] Ammonium molybdate has a molecular weight of 196 and a vanadium content of 48.98%. The raw material is 5 kg of molybdenum, with a yield of 98%, which is 4.9 kg, corresponding to 10 kg of ammonium metavanadate.

[0110] Ammonium paratungstate has a molecular weight of 3132 and a tungsten content of 58.75%. The raw material tungsten is 0.5 kg, and the yield is 95%, which is 0.475 kg, corresponding to a mass of 0.81 kg of ammonium paratungstate.

[0111] (5) Vanadium precipitation

[0112] The residual liquid from molybdenum extraction is fed into a vanadium precipitation reactor. At pH 8-9, the vanadium in the solution mainly exists as V₄O₂.12 4- (VO3 - It exists in the form of ammonium metavanadate (PFSA). Adding (NH4)2SO4 to a vanadium solution will cause a metathesis reaction. Controlling the amount of ammonium salt added (ammonium addition coefficient) and the pH value for vanadium precipitation during this process yields white or pale yellow ammonium metavanadate (PFSA) crystals, 2.2 kg.

[0113] Specifically as follows:

[0114] Ammonium metavanadate has a molecular weight of 117 and a vanadium content of 43.59%.

[0115] 1 kg of vanadium raw material yields 96% (0.96 kg), corresponding to 2.2 kg of ammonium metavanadate.

[0116] (6) Nickel-cobalt recovery (acid leaching-pressure filtration-purification)

[0117] The leaching residue obtained in step (2) mainly contains nickel and cobalt, and acid leaching is required to recover nickel and cobalt.

[0118] After being leached with an acidic solution of approximately 10% sulfuric acid at normal pressure and temperature, nickel and cobalt ions are mainly present in the leachate. After filtration, separation, washing, and purification, a solution containing nickel and cobalt with relatively few impurities is obtained.

[0119] (7) Cobalt extraction

[0120] The leachate obtained in step (6) was extracted with cobalt extractant (P204), and then back-extracted, evaporated and crystallized to obtain cobalt sulfate product, 2.55 kg.

[0121] Specifically as follows:

[0122] Cobalt sulfate has a molecular weight of 155 and a cobalt content of 38%.

[0123] 1 kg of cobalt raw material yields 97% (0.97 kg), which corresponds to 2.55 kg of cobalt sulfate.

[0124] (8) Nickel extraction

[0125] The raffinate obtained in step (7) was extracted with nickel extractant (P204), and after back-extraction and evaporation crystallization, 5.16 kg of nickel sulfate product was obtained.

[0126] Specifically as follows:

[0127] Nickel sulfate has a molecular weight of 154 and a nickel content of 37.6%.

[0128] 2 kg of raw nickel was used, with a yield of 97%, which is 1.94 kg, corresponding to 5.16 kg of nickel sulfate.

[0129] Comparative Example

[0130] This comparative example provides a method for the comprehensive utilization of spent catalysts. The catalyst used is a spent catalyst containing molybdenum, tungsten, vanadium, nickel, and cobalt, weighing 100 kg. Specifically, the molybdenum content is 5 kg, the tungsten content is 0.5 kg, the vanadium content is 1 kg, the nickel content is 2 kg, and the cobalt content is 1 kg.

[0131] The above method specifically includes the following steps:

[0132] Direct leaching with 10% sulfuric acid was used to extract and separate molybdenum, tungsten, vanadium, nickel, and cobalt from the leachate, with corresponding recovery rates of 85%, 88%, 82%, 90%, and 91%, respectively; however, the product purity could not meet the standards.

[0133] As can be seen from the above, the comprehensive utilization method for spent catalysts provided in this application has a significantly higher recovery efficiency for each metal than the methods in the prior art used in the comparative examples. Specifically, the recovery rate of each metal in the comprehensive utilization method of this application is greater than 95%, and the purity meets relevant product standards. Simultaneously, in the ammonium molybdate solution, the removal rate of vanadium and tungsten reaches over 99%, the vanadium and tungsten concentration is less than 0.01 g / L, and the direct molybdenum recovery rate is greater than 95%.

[0134] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for the comprehensive utilization of spent catalysts, characterized in that, The method specifically includes the following steps: The spent catalyst is subjected to oxidative roasting, wet ball milling, and pressure leaching in sequence to obtain a first leachate and a leaching residue; the first leachate is used for the recovery of molybdenum, tungsten, and vanadium; the leaching residue is used for the recovery of nickel and cobalt. For the first leachate: The first leachate is extracted using a multi-stage countercurrent extraction method, in which molybdenum and tungsten are extracted, and then back-extracted to obtain a back-extract containing molybdenum and tungsten; the back-extract is then subjected to static deoiling, evaporation and concentration, and multi-stage countercurrent extraction to remove vanadium, to obtain raffinate and a vanadium-containing back-extract. The raffinate mainly contains molybdate and tungstate ions; different separation methods are determined according to different molar ratios of molybdenum and tungsten, specifically: A. When the molybdenum content is close to the tungsten content, i.e., the molar ratio of the two is 0.2-5: Evaporation and concentration are first employed, allowing the higher content of tungsten to crystallize first in the form of ammonium paratungstate. At this stage, the ammonium paratungstate crystals still contain a small amount of ammonium molybdate, which needs to be further purified through a dissolution-ion exchange step. Then, after evaporation and crystallization, a pure ammonium paratungstate product can be obtained. Simultaneously, the concentrated mother liquor from the first evaporation and concentration process is mainly ammonium molybdate, containing a small amount of ammonium paratungstate. This concentrated mother liquor is then extracted to remove tungsten before being evaporated and crystallized again to obtain a pure ammonium molybdate product. B. When the molybdenum content is much greater than the tungsten content, i.e. the molar ratio of the two is greater than 5: the tungsten is removed directly by extraction, and then evaporated and crystallized to obtain a pure ammonium molybdate product; C. When the molybdenum content is much less than the tungsten content, i.e. the molar ratio of the two is less than 0.2: directly use ion exchange to remove molybdenum, and then carry out evaporation and crystallization to obtain pure ammonium paratungstate product; For the leaching residue: the leaching residue is acidically leached with sulfuric acid solution at room temperature and pressure to obtain a second leachate; it is then extracted with cobalt extractant and nickel extractant respectively, and after back-extraction, evaporation and crystallization, cobalt sulfate product and nickel sulfate product are obtained.

2. The method for comprehensive utilization of spent catalysts according to claim 1, characterized in that, The concentration of V2O5 in the raffinate can be reduced to below 0.01 g / L.

3. The method for comprehensive utilization of spent catalysts according to claim 1, characterized in that, The vanadium removal rate in the raffinate reached over 99%.

4. The method for comprehensive utilization of spent catalysts according to claim 1, characterized in that, The vanadium-containing back-extraction solution was subjected to a double decomposition reaction by adding (NH4)2SO4 at pH 8-9 to obtain ammonium metavanadate crystals.

5. The method for comprehensive utilization of spent catalysts according to claim 1, characterized in that, First, the second leachate is extracted using the cobalt extractant, and after back-extraction and evaporation crystallization, cobalt sulfate product is obtained; then, the raffinate obtained after back-extraction is extracted using the nickel extractant, and after back-extraction and evaporation crystallization, nickel sulfate product is obtained.

6. The method for comprehensive utilization of spent catalysts according to claim 1, characterized in that, Select the appropriate extractant based on the nickel and cobalt content in the second leachate.

7. The method for comprehensive utilization of spent catalysts according to claim 6, characterized in that, When the Co / Ni content is greater than 1 / 5, the selected extractant is P204; when the Co / Ni content is less than 1 / 5, the selected extractant is P507; when the Co / Ni content is less than 1 / 10, the selected extractant is Cyanex272.

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