A subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts

Abstract

This invention relates to the field of solid waste resource utilization and nickel-molybdenum catalyst recovery technology, specifically to a subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts. To address the problems of high energy consumption and significant resource waste in current waste nickel-molybdenum catalyst recovery processes, this invention provides a highly efficient subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts. It achieves complete oxidation of organic components and selective leaching of molybdenum through alkaline subcritical water reaction, utilizes a multi-stage flash evaporation unit to achieve cascaded heat utilization and water reuse, and employs acidic subcritical water for selective nickel extraction. This invention uses subcritical water as the main reaction medium to achieve efficient leaching of valuable metals and harmless treatment of organic components, solving the problems of heavy pollution, high energy consumption, and low recovery rates associated with traditional recovery processes.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and nickel-molybdenum catalyst recovery technology, specifically to a subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts. Background Technology

[0002] As the petrochemical industry transforms towards cleaner and more efficient processes, a large amount of waste nickel-molybdenum catalysts are generated. These catalysts are typical urban minerals due to their adsorption of complex hydrocarbon organic matter and the presence of high-value metals such as nickel and molybdenum in sulfide form. However, the complex composition of waste nickel-molybdenum catalysts also presents significant challenges to their recycling. Their stable metal sulfide crystal structure makes direct and efficient leaching with conventional acids and alkalis difficult. Therefore, efficient recovery of the valuable metals from these catalysts is of great significance for ensuring the security of my country's strategic metal resources and promoting the development of a circular economy.

[0003] Currently, the mainstream method for industrial recycling of spent nickel-molybdenum catalysts is the pyrometallurgical roasting-wet leaching process. Pyrometallurgical roasting requires oxidative roasting at temperatures above 600℃ to remove organic matter and convert sulfides into oxides. This process is energy-intensive and inevitably produces SO₂. x NO x Greenhouse gases like molybdenum are difficult to treat, and the costs are exorbitant. More importantly, high temperatures easily cause molybdenum oxide (MoO3) to volatilize and react with the alumina support to form insoluble aluminum molybdate (Al2(MoO4)3), resulting in irreversible molybdenum loss and creating a significant ceiling on its recovery rate. The roasted material is typically processed using wet methods, and molybdenum recovery usually involves alkaline leaching (such as sodium carbonate or sodium hydroxide solutions). However, overcoming the dissolution resistance of the conversion products often requires high-concentration alkaline solutions, high temperatures, and long reaction times, leading to high alkali consumption. Furthermore, the strongly alkaline environment can easily cause partial dissolution of the alumina support, introducing aluminum impurities and increasing the difficulty and cost of subsequent solution purification.

[0004] In summary, current traditional processes are characterized by long routes, high resource and energy consumption, and significant emissions of waste, with low metal recovery rates and economic viability, failing to meet the requirements of current green, low-carbon, and circular economic development. Summary of the Invention

[0005] To address the problems of high energy consumption, high pollution, and insufficient recovery of components associated with traditional nickel-molybdenum catalyst recovery methods, this invention provides a subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts. This invention aims to develop a clean recovery technology that avoids high-temperature roasting at the source, achieving integrated harmless treatment of organic matter and efficient selective extraction of metals. This technology has urgent practical significance and important industrial value for overcoming existing technological bottlenecks, improving the recovery rate of strategic metal resources, and alleviating environmental pressure.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] This invention provides a subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts, comprising a subcritical reaction unit, a multi-stage flash evaporation unit, and a molybdenum liquid treatment unit.

[0008] The subcritical reaction unit includes a first subcritical reaction unit and a second subcritical reaction unit. The first subcritical reaction unit includes an alkaline subcritical reaction device, the inlet of which is connected to a slurry preheater and an oxidant tank, respectively, for leaching metallic molybdenum from the slurry. The second subcritical reaction unit includes an acidic subcritical reaction device, for separating metallic nickel from other impurities. The inlet of the acidic subcritical reaction device is connected to the outlet of a solid-liquid separator.

[0009] The multi-stage flash evaporation unit includes a first-stage flash evaporator and an n-stage flash evaporator connected in sequence; the material inlet of the first-stage flash evaporator is connected to the outlet of the alkaline subcritical reaction device through a first-stage back pressure valve and a pressure damper; the material outlet of the n-stage flash evaporator is connected to the inlet of the solid-liquid separator through a three-stage control valve; and the steam outlet of the first-stage flash evaporator is connected to the slurry preheater through a pressure relief valve.

[0010] The molybdenum solution treatment unit includes a membrane concentrator, an evaporator, an acid processor, and an ammonia solvent purifier. The steam outlet of the n-stage flash evaporator is connected to the slurry preheater via an n1-stage pressure relief valve, and the steam outlet of the n-stage flash evaporator is connected to the evaporator via an n2-stage pressure relief valve. The outlet of the evaporator is connected to the inlet of the acid processor for leaching the concentrated material in the acid processor and then filtering it. The inlet of the acid processor is connected to an acid storage tank. The material outlet of the acid processor is connected to the material inlet of the ammonia solvent purifier, and the inlet of the ammonia solvent purifier is connected to an ammonia storage tank for redissolving the solid material and then repurifying and recovering it.

[0011] Preferably, the liquid phase outlet and solid phase outlet of the solid-liquid separator are respectively connected to the molybdenum liquid treatment unit and the second subcritical reaction unit.

[0012] Preferably, the subcritical reaction unit includes a first subcritical reaction unit and a second subcritical reaction unit. The first subcritical reaction unit is used to leach metallic molybdenum from the slurry. The first subcritical reaction unit includes a raw material storage tank, a slurry mixing tank, an alkali storage tank, a slurry pump, a slurry preheater, an oxidant tank, and an alkaline subcritical reaction device. The raw material storage tank and the alkali storage tank supply materials to the slurry mixing tank to form a mixed slurry. The slurry mixing tank is connected to the alkaline subcritical reaction device through the slurry pump and the slurry preheater. The oxidant tank is connected to the alkaline subcritical reaction device and supplies oxidant to it.

[0013] This invention utilizes a mixed slurry that is pressurized and heated in a slurry pump and a slurry preheater before entering an alkaline subcritical reactor. An oxidant tank is connected to the alkaline subcritical reactor and supplies it with an oxidant, creating a micro-oxidation environment within the reactor to completely and harmlessly degrade the organic matter encapsulating the nickel-molybdenum catalyst. An alkaline solution storage tank supplies an alkaline solution, such as sodium hydroxide solution, to the slurry mixing tank to adjust the pH of the mixed slurry entering the alkaline subcritical reactor to 9-12, thereby reducing molybdenum in the nickel-molybdenum catalyst material to soluble metal ions.

[0014] Preferably, the reaction conditions of the alkaline subcritical reactor are: temperature of 200℃~400℃, pressure of 5MPa~8MPa, reaction time of 1h~4h, and pH=9~12.

[0015] In this invention, the pressure in the first subcritical reaction unit is provided by a slurry pump, which pumps the mixed slurry into the alkaline subcritical reaction device, and the pressure in the alkaline subcritical reaction device is maintained in the range of 5MPa to 8MPa by a primary back pressure valve.

[0016] This invention can adapt to the recovery of nickel-molybdenum catalysts with different contents by flexibly adjusting parameters such as the temperature, pressure and residence time of subcritical water, and has strong material adaptability and process scalability.

[0017] Preferably, the second subcritical reaction unit includes an acidic subcritical reaction device, a filter tank, and a purification crystallizer; the material inlet of the acidic subcritical reaction device is connected to the solid phase outlet of the solid-liquid separator; the acidic subcritical reaction device is used to dissolve solid materials using an acidic solution and carry out a subcritical reaction.

[0018] Preferably, the reaction conditions of the acidic subcritical reactor are: temperature of 200℃~250℃, pressure of 2MPa~4MPa, reaction time of 2h~3h, and pH=2~4.

[0019] Preferably, the outlet of the acid processor is connected to the inlet of the acidic subcritical reaction device to provide an acidic solution; the outlet of the acidic subcritical reaction device is connected to a filter tank; the liquid phase outlet of the filter tank is connected to a purification crystallizer, and the solid phase outlet of the filter tank is connected to a third product collector to recover reusable solid materials after the reaction; the outlet of the purification crystallizer is connected to a second product collector to recover high-purity nickel sulfate crystals.

[0020] Preferably, the oxidant includes, but is not limited to, at least one of oxygen, ozone, oxygen-enriched air, and hydrogen peroxide solution. More preferably, if hydrogen peroxide solution is used, its concentration is 5 wt% to 15 wt%.

[0021] In this invention, the amount of gaseous oxidant used is evaluated based on the partial pressure of oxygen. If oxygen or ozone is used, the total pressure of the system = initial reactor pressure + oxygen partial pressure. For example, at 250°C, if the pressure inside the alkaline subcritical reactor is 4.0 MPa, and 1.0 MPa of oxygen is introduced, then the total pressure will be 4.0 MPa + 1.0 MPa = 5.0 MPa.

[0022] In this invention, the pressure of the alkaline subcritical reactor is maintained at 5MPa to 8MPa. Its core function is to maintain the special physicochemical properties of subcritical water. Higher pressure can also accelerate the reaction rate. The residual pressure after the reaction can be used for energy recovery in subsequent processes.

[0023] In this invention, the pressure damper is used to control the pressure drop of the first-stage back pressure valve and provide resistance to prevent cavitation in the first-stage back pressure valve; the number of the n-stage flash evaporators is designed according to specific system requirements, the n1-stage pressure relief valve discharges high-grade steam to the slurry preheater, and the n2-stage pressure relief valve discharges low-grade steam to the evaporator concentrator; the steam generated by the multi-stage flash evaporation unit is connected to the slurry mixing tank for water reuse after heat recovery.

[0024] Preferably, the liquid phase outlet of the solid-liquid separator is connected to the membrane concentrator, the concentrated liquid outlet of the membrane concentrator is connected to the material inlet of the evaporator, and the solution outlet of the membrane concentrator is connected to the slurry mixing tank for water reuse.

[0025] More preferably, the liquid phase outlet of the solid-liquid separator is a crude sodium molybdate solution, and the solid phase outlet is a nickel-containing filter cake; the membrane concentrator uses a nanofiltration membrane or a reverse osmosis membrane, which can remove most of the water and some monovalent salts from the crude molybdate solution.

[0026] In this invention, the second subcritical reaction unit includes an acidic subcritical reaction device, a filter tank, and a purification crystallizer; the material inlet of the acidic subcritical reaction device is connected to the solid phase outlet of the solid-liquid separator; the acidic subcritical reaction device adjusts the pH to 2-4 through an acidic solution and provides the required temperature and pressure conditions for the subcritical reaction, and the nickel in the solid material is redissolved into metal ions; the material outlet of the acidic subcritical reaction device is connected to the inlet of the filter tank.

[0027] Further preferably, the acidic solution required by the acidic subcritical reactor is sourced from external supply and reused acid solution filtered by an acid processor; the outlet of the acidic subcritical reactor is connected to a filter tank; the liquid phase outlet of the filter tank is connected to a purification crystallizer, and the solid phase outlet of the filter tank is connected to a third product collector to recover alumina-rich slag whose main component is alumina after the reaction; the outlet of the purification crystallizer is connected to a second product collector to recover high-purity nickel sulfate crystals.

[0028] Preferably, the oxidant required for the first subcritical reaction unit includes, but is not limited to, at least one of oxygen, ozone, oxygen-enriched air, and hydrogen peroxide solution; the acidic solution in the second subcritical reaction unit includes, but is not limited to, at least one of sulfuric acid and hydrochloric acid; and the reagent in the ammonia storage tank is preferably ammonia water.

[0029] Preferably, the solid content of the mixed slurry is 10% to 40%. For example, 10%, 15%, or 20%. This invention does not specifically limit the solid content of the mixed slurry; the solid content of the mixed slurry can be selected according to actual needs.

[0030] Preferably, the solution outlet of the ammonia purifier is connected to the deep water processor, and the solution outlet of the purification crystallizer is connected to the deep water processor for acid-base neutralization and deep purification of the waste liquid. The water outlet of the deep water processor is connected to the slurry mixing tank.

[0031] Preferably, the liquid phase outlet and solid phase outlet of the solid-liquid separator are respectively connected to the molybdenum liquid treatment unit and the second subcritical reaction unit.

[0032] This invention significantly improves overall energy efficiency by constructing a highly efficient closed-loop energy and material cycle. Through multi-stage flash evaporation units, heat is utilized in a cascade manner, achieving waste heat recovery and reducing external energy input. Simultaneously, the outlet solution of the membrane concentrator, the recycled steam from the multi-stage flash evaporation units, and the water recovered by the deep water processor are all connected to the slurry mixing tank, achieving system water recovery and reducing external water input.

[0033] The beneficial effects of this invention are: 1. This invention uses green subcritical water as the main reaction medium, utilizing its unique properties of low dielectric constant, high ion product, and high diffusion coefficient. Coupled with a controllable green oxidant, it not only achieves highly efficient subcritical wet oxidation of degradable organic matter and metal sulfides in the catalyst, but also realizes the conversion of organic matter into carbonates and metal sulfides into sulfate. This invention abandons the roasting process in traditional recovery methods and eliminates the need for desulfurization and dust removal. It has the comprehensive advantages of mild reaction conditions, low energy consumption, low raw material costs, and low environmental pressure, successfully solving the inherent problems of high energy consumption, high pollution, and low metal recovery rate of the traditional "pyrometallurgical roasting-wet leaching" process.

[0034] 2. Compared to the traditional atmospheric pressure alkaline leaching process, this invention fully utilizes the alkaline catalytic properties of water in the subcritical hydrothermal system, enabling the system to achieve high OH- ion concentrations. - The concentration is increased to 100 to 1000 times that at normal pressure, and the amount of alkali added is relatively less; at the same time, the higher hydrothermal reaction temperature promotes the reaction, further reducing the dependence on strong alkalis and other external strong chemical reagents, thus reducing chemical consumption and the generation of high-salt wastewater from the source.

[0035] 3. This invention employs a multi-stage flash evaporation unit to recover and utilize the thermal energy of the reacted materials in stages, which is used for preheating the feed and driving evaporation and concentration, significantly reducing the overall energy consumption of the system. The system achieves deep recovery of valuable components through a combination of processes such as membrane concentration and evaporation crystallization, and recovers and utilizes most of the system's water and acid, realizing a closed-loop cycle of materials and energy. Attached Figure Description

[0036] Figure 1 This is a flowchart of a subcritical hydrothermal system for recovering valuable metals from a nickel-molybdenum catalyst, as described in an embodiment of the present invention.

[0037] Explanation of reference numerals in the attached figures: 1. Raw material storage tank; 2. Slurry mixing tank; 3. Alkali storage tank; 4. Slurry pump; 5. Slurry preheater; 6. Oxidant tank; 7. Alkaline subcritical reactor; 8. Pressure damper; 9. Multi-stage flash evaporator; 9-1. First-stage flash evaporator; 9-n. n-stage flash evaporator; V1. First-stage back pressure valve; Vn. n-stage control valve; V3. Third-stage control valve; V2. Pressure relief valve; Vn1. n1-stage pressure relief valve; Vn2. n2-stage pressure relief valve; 10. Solid-liquid separator; 11. Membrane concentrator; 12. Evaporator concentrator; 13. Acid storage tank; 14. Acid processor; 15. Ammonia storage tank; 16. Ammonia solvent purifier; 17. First finished product collector; 18. Acidic subcritical reactor; 19. Filter tank; 20. Purification crystallizer; 21. Second finished product collector; 22. Third finished product collector; 23. Deep water processor. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0039] Compared to the traditional high-energy-consuming and high-polluting pyrometallurgical roasting-wet leaching process, subcritical water, due to its low dielectric constant and high ion product, possesses OH- oxidative properties. - The high concentration of subcritical water allows for the efficient leaching of valuable metals such as molybdenum without the addition of large amounts of strong alkali, significantly reducing wastewater generation and chemical reagent consumption at the source. Furthermore, the thermochemical properties of the subcritical water environment provide conditions for the oxidative degradation of organic matter in the catalyst. Therefore, subcritical hydrothermal technology, as an environmentally friendly novel recovery strategy, has significant potential application value for the recovery of valuable metals from nickel-molybdenum catalysts.

[0040] In summary, addressing the problems of high energy consumption, high pollution, and insufficient recovery of components in traditional nickel-molybdenum catalyst recovery technologies, this invention combines the potential advantages of subcritical water with the gap in metal recovery process solutions to provide a subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts. This is of great significance for improving resource recycling and promoting the sustainable development of the new energy industry.

[0041] This invention discloses a subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts. The system includes a subcritical reaction unit, a multi-stage flash evaporation unit, and a molybdenum liquor treatment unit. The subcritical reaction unit comprises a first subcritical reaction unit and a second subcritical reaction unit. The first subcritical reaction unit can achieve slurry preparation and harmless degradation of organic components, as well as leaching metallic molybdenum from the slurry. The second subcritical reaction unit is used to separate and recover high-value nickel sulfate and alumina products. The multi-stage flash evaporation unit is used to depressurize and recover heat gradients from the outlet material of the alkaline subcritical reactor. The molybdenum liquor treatment unit can separate and recover high-purity ammonium molybdate products. This invention innovatively uses subcritical water as the main medium, and by precisely controlling its physicochemical properties, it reduces chemical consumption and waste generation at the source and achieves high-value recovery and utilization of valuable components in nickel-molybdenum catalysts.

[0042] The technical solution of the present invention will be further described below through specific embodiments. Unless otherwise specified, the methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0043] like Figure 1 A subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts includes a subcritical reaction unit, a multi-stage flash evaporation unit, and a molybdenum liquid treatment unit.

[0044] The subcritical reaction unit includes a first subcritical reaction unit and a second subcritical reaction unit. The first subcritical reaction unit is used to leach metallic molybdenum from the slurry. The first subcritical reaction unit includes a raw material storage tank 1, a slurry mixing tank 2, an alkali storage tank 3, a slurry pump 4, a slurry preheater 5, an oxidant tank 6, and an alkaline subcritical reaction device 7. The outlets of the raw material storage tank 1 and the alkali storage tank 3 are respectively connected to the inlet of the slurry mixing tank 2. The raw material storage tank 1 and the alkali storage tank 3 together supply materials to the slurry mixing tank 2 and mix them to form a mixture. The slurry mixing tank 2 is connected in sequence to the slurry pump 4 and the slurry preheater 5 for pressurizing and heating the mixture. The slurry preheater 5 is connected to the alkaline subcritical reaction device 7 for feeding the mixture into the alkaline subcritical reaction device 7 for reaction. The inlet of the alkaline subcritical reaction device 7 is connected to the outlet of the oxidant tank 6 to provide a micro-oxidation environment, so that the organic components can be completely degraded harmlessly and the molybdenum element in the nickel-molybdenum catalyst material can be reduced to soluble metal ions.

[0045] Specifically, the solid content of the mixed slurry is 10% to 40%. For example, 10%, 15%, 20%, 30%, and 40%. This invention does not specifically limit the solid content of the mixed slurry; the solid content can be selected according to actual needs.

[0046] The outlet of the alkaline subcritical reactor 7 is connected to a multi-stage flash evaporation unit for depressurization and heat recovery of the outlet material; the outlet of the multi-stage flash evaporation unit is connected to a solid-liquid separator 10 for component separation of the material; the liquid phase outlet of the solid-liquid separator 10 is connected to a molybdenum liquid treatment unit for recovering metallic molybdenum; the solid phase outlet of the solid-liquid separator 10 is connected to a second subcritical reactor unit for recovering metallic nickel and other valuable components.

[0047] Specifically, this invention mainly utilizes a slurry pump 4 to pump the mixed slurry into an alkaline subcritical reactor 7 and maintain the pressure environment within the alkaline subcritical reactor 7; an oxidant tank 6 is used to provide an oxidant to the alkaline subcritical reactor 7 to form a micro-oxidation environment, which harmlessly degrades the organic components encapsulating the nickel-molybdenum catalyst in a subcritical water environment; and an alkaline solution storage tank 3 is used to provide an alkaline solution to the material. For example, a sodium hydroxide solution with a concentration of 2 mol / L can generally be used to maintain the pH of the mixed slurry in the alkaline subcritical reactor 7 in the range of 9 to 12, providing an alkaline environment for the alkaline subcritical reactor 7, thereby reducing molybdenum in the nickel-molybdenum catalyst material to soluble metal ions.

[0048] Specifically, the reaction conditions within the alkaline subcritical reactor 7 are: temperature 200℃~400℃, pressure 5MPa~8MPa, reaction time 1h~4h; pH=9~12; the oxidant is at least one of oxygen, ozone, and hydrogen peroxide solution. If hydrogen peroxide solution is used, its concentration is 5wt%~15wt%. The amount of gaseous oxidant is evaluated based on the partial pressure of oxygen. If oxygen or ozone is used, the total pressure of the system = initial reactor pressure + oxygen partial pressure. For example, at 250℃, if the pressure inside the alkaline subcritical reactor is 4.0MPa, and 1.0MPa of oxygen is introduced, then the total pressure will be 4.0MPa + 1.0MPa = 5.0MPa.

[0049] The pressure within the alkaline subcritical reactor 7 is provided by the slurry pump 4, which pumps the prepared mixture into the alkaline subcritical reactor 7. The pressure within the alkaline subcritical reactor 7 is maintained within the range of 5 MPa to 8 MPa via a primary back pressure valve V1. Specifically, maintaining the pressure within the alkaline subcritical reactor 7 at 5 MPa to 8 MPa serves the core purpose of preserving the unique physicochemical properties of subcritical water. Higher pressure can also accelerate the reaction rate, and the residual pressure after the reaction can be used for energy recovery.

[0050] The solid-liquid separator 10 is mainly used for solid-liquid separation of a mixed slurry, in which metallic molybdenum is mainly present in the liquid phase, while metallic nickel and other components are mainly present in the solid phase. The liquid phase outlet and solid phase outlet of the solid-liquid separator 10 are respectively connected to the molybdenum solution treatment unit and the second subcritical reaction unit. Specifically, the liquid phase outlet of the solid-liquid separator 10 is a crude sodium molybdate solution, and the solid phase outlet is a nickel-containing filter cake.

[0051] The molybdenum solution treatment unit includes a membrane concentrator 11, an evaporator 12, an acid storage tank 13, an acid processor 14, an ammonia storage tank 15, and an ammonia purifier 16; the concentrator 11, evaporator 12, acid processor 14, ammonia purifier 16, and a first finished product collector 17 are connected in sequence. After separation from the solid-liquid separator 10, the liquid phase material enters the membrane concentrator 11 for preliminary filtration and purification. The material outlet of the membrane concentrator 11 is connected to the evaporator 12. The heat required for the evaporator 12 comes from the low-grade heat recovered by the n-stage flash evaporator 9-n. The concentrated material from the evaporator 12 first enters the acid processor 14 for acid leaching and then filtration. The solid material then enters the ammonia purifier 16 for redissolution, recrystallization, purification, and recovery. The resulting finished product enters the first finished product collector 17. Specifically, the membrane concentrator 11 uses a nanofiltration membrane or a reverse osmosis membrane, which can remove most of the water and some monovalent salts from the crude molybdate solution.

[0052] The multi-stage flash evaporation unit includes a primary flash evaporator 9-1, a pressure damper 8, an n-stage flash evaporator 9-n, a slurry preheater 5, and an evaporator concentrator 12. The material inlet of the primary flash evaporator 9-1 is connected to the outlet of the alkaline subcritical reaction device 7 via a primary back pressure valve V1 and a pressure damper 8. The material outlet of the n-stage flash evaporator 9-n is connected to the inlet of the solid-liquid separator 10 via a tertiary control valve V3. The steam outlet of the primary flash evaporator 9-1 is connected to the slurry preheater 5 via a pressure relief valve V2. The steam outlet of the n-stage flash evaporator 9-n is connected to the slurry preheater 5 via an n1-stage pressure relief valve Vn1 and to the evaporator concentrator 12 via an n2-stage pressure relief valve Vn2.

[0053] The pressure damper 8 is used to control the pressure drop of the first-stage back pressure valve V1 and provide resistance to prevent cavitation of the first-stage back pressure valve V1; the number of the n-stage flash evaporators 9-n is designed according to specific system requirements, the n1-stage pressure relief valve Vn1 discharges high-grade steam to the slurry preheater 5, and the n2-stage pressure relief valve Vn2 discharges low-grade steam to the evaporator 12; the steam generated by the multi-stage flash evaporation unit is connected to the slurry mixing tank 2 through pipelines for water reuse after heat recovery.

[0054] Specifically, the power required for the molybdenum liquid treatment unit is provided by the residual pressure of the multi-stage flash evaporation unit. The third-stage control valve V3 is mainly used to regulate the liquid level of the n-stage flash evaporator 9-n to ensure its flash evaporation function. The n-stage control valve Vn is used to regulate the liquid level of the first-stage flash evaporator 9-1 to ensure its flash evaporation function. Here, n is an integer greater than 0.

[0055] Specifically, pressure relief valve V2 is used to control the pressure in the first-stage flash evaporator 9-1, and pressure relief valves Vn1 and Vn2 are used to control the pressure in the n-stage flash evaporator 9-n. When the multi-stage flash evaporator 9 has a large number of stages, the flash evaporators with earlier stages mainly open the n1-stage pressure relief valve Vn1 to recover steam with higher heat, while the flash evaporators with later stages mainly open the n2-stage pressure relief valve Vn2 to recover steam with lower heat.

[0056] The second subcritical reaction unit includes an acidic subcritical reactor 18, a filter tank 19, and a purification crystallizer 20, which are connected in sequence. The material inlet of the acidic subcritical reactor 18 is connected to the solid phase outlet of the solid-liquid separator 10. The acidic subcritical reactor 18 is used to dissolve solid materials using an acidic solution and carry out a subcritical reaction. For example, the acidic subcritical reactor 18 uses an acidic solution to adjust the pH of the reactor to 2-4 to convert nickel in solid impurities into soluble metal ions. The reaction conditions of the acidic subcritical reactor are: temperature of 200℃-250℃, pressure of 2MPa-4MPa, reaction time of 2h-3h, and pH of 2-4. The outlet of acid processor 14 is connected to the inlet of acidic subcritical reactor 18 to provide acidic solution; the outlet of acidic subcritical reactor 18 is connected to filter tank 19; the liquid phase outlet of filter tank 19 is connected to purification crystallizer 20 to remove heavy metals from the filtrate and crystallize nickel sulfate; purification crystallizer 20 is connected to second product collector 21 to recover high-purity nickel sulfate crystals; the solid phase outlet of filter tank 19 is connected to third product collector 22 to recover reusable solid materials after the reaction, such as aluminum-rich slag whose main component is alumina.

[0057] Specifically, the acidic solution required for the acidic subcritical reactor 18 is sourced from external supply and reused acid solution filtered by the acid processor 14. The reagents in the acidic subcritical reactor 18 include, but are not limited to, at least one acidic solution selected from sulfuric acid and hydrochloric acid, and the H₂O of the acidic solution used... + The concentration is generally 2 mol / L; the reagent in the ammonia storage tank 15 is preferably ammonia water, and the mass concentration of the ammonia water used is generally 25% to 28%.

[0058] Specifically, the solution outlet of the ammonia purifier 16 is connected to the deep water processor 23, and the solution outlet of the purification crystallizer 20 is also connected to the deep water processor 23. The deep water processor 23 is used to neutralize the waste liquid with acid and alkali and to perform deep purification. The purified water is then reused in the slurry mixing tank 2.

[0059] This invention significantly improves overall energy efficiency by constructing a highly efficient closed-loop energy and material cycle. Through multi-stage flash evaporation units, heat is utilized in a cascade manner, achieving waste heat recovery and reducing external energy input. Simultaneously, the outlet solution of the membrane concentrator 11, the recycled steam from the multi-stage flash evaporation units, and the water recovered by the deep water processor 23 are all connected to the slurry mixing tank 2, achieving system water recovery and reducing external water input.

[0060] In summary, the subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts provided by the embodiments of the present invention mainly includes five stages in the process of recovering valuable components from nickel-molybdenum catalysts: The first stage is the pretreatment stage, which mainly includes two parts: slurry preparation and high-pressure conveying. Slurry preparation takes place in slurry mixing tank 2, where the waste nickel-molybdenum catalyst is mixed with an alkaline solution provided by alkaline storage tank 3, adjusting the mixture to a solid content of 10%–40%. High-pressure conveying involves pumping the prepared slurry into the alkaline subcritical reactor 7 via slurry pump 4.

[0061] The second stage is the subcritical hydrothermal reaction stage, carried out in the alkaline subcritical reactor 7, with the temperature controlled at 200℃~400℃ and the pressure at 5MPa~8MPa. An oxidant (such as oxygen, ozone, or hydrogen peroxide) is introduced, and the reaction lasts for 1h~4h, achieving the oxidative degradation of organic components and fully exposing the nickel-molybdenum materials to the environment (destroying the organic matter covering the catalyst surface). Under subcritical conditions, the dielectric constant of water decreases to 10~30 (at room temperature 80℃), and the ion product increases to 10. -11 ~10 -12 This gives it a solubility similar to organic solvents and allows it to self-ionize and generate large amounts of OH-. - .

[0062] The third stage is the energy recovery stage, mainly including the recovery and utilization of thermal and pressure energy. The first-stage flash evaporator 9-1 and the earlier n-stage flash evaporators 9-n reuse high-grade heat steam to the slurry preheater 5, while the later n-stage flash evaporators 9-n reuse low-grade heat steam to the evaporator concentrator 12. The n-stage control valve Vn and the third-stage control valve V3 are used to control the liquid level within the flash evaporators to adapt to subsequent environmental conditions. This third stage fully utilizes the system's waste heat and pressure, achieving low energy consumption outside the multi-stage flash evaporation units.

[0063] The fourth stage is the molybdenum recovery stage, which mainly includes filtration purification, acid leaching, and ammonia leaching purification processes. In the ammonium molybdate recovery process, most of the water and some monovalent salts in the crude molybdate solution are first removed by membrane concentrator 11. After concentration in evaporator concentrator 12, the solution enters acid processor 14 for acid leaching. The crystalline material then enters ammonia leaching purifier 16 for redissolution, purification, and crystallization to form ammonium molybdate product. Subsequently, the product enters the first finished product collector 17.

[0064] The fifth stage is the nickel recovery stage, which mainly includes acidic subcritical reaction and impurity removal processes. The material from the solid phase outlet of the solid-liquid separator 10 enters the acidic subcritical reaction device 18, where the nickel oxide is dissolved by acid washing with an acidic solution and reacted under subcritical conditions. The reacted material enters the filter tank 19, and after filtration, the solid (alumina) enters the third product collector 22; the liquid enters the purification crystallizer 20, where it is concentrated and purified to remove heavy metal ion impurities from the solution and obtain nickel sulfate as the finished product. Finally, the nickel sulfate enters the second product collector 21.

[0065] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts, characterized in that, It includes a subcritical reaction unit, a multi-stage flash evaporation unit, and a molybdenum liquid treatment unit; The subcritical reaction unit includes a first subcritical reaction unit and a second subcritical reaction unit. The first subcritical reaction unit includes an alkaline subcritical reaction device, the inlet of which is connected to a slurry preheater and an oxidant tank, respectively, for leaching metallic molybdenum from the slurry. The second subcritical reaction unit includes an acidic subcritical reaction device, for separating metallic nickel from other impurities. The inlet of the acidic subcritical reaction device is connected to the outlet of a solid-liquid separator. The multi-stage flash evaporation unit includes a first-stage flash evaporator and an n-stage flash evaporator connected in sequence; the material inlet of the first-stage flash evaporator is connected to the outlet of the alkaline subcritical reaction device through a first-stage back pressure valve and a pressure damper; the material outlet of the n-stage flash evaporator is connected to the inlet of the solid-liquid separator through a third-stage control valve; and the steam outlet of the first-stage flash evaporator is connected to the slurry preheater through a pressure relief valve. The molybdenum solution treatment unit includes a membrane concentrator, an evaporator, an acid processor, and an ammonia solvent purifier. The steam outlet of the n-stage flash evaporator is connected to the slurry preheater via an n1-stage pressure relief valve, and the steam outlet of the n-stage flash evaporator is connected to the evaporator via an n2-stage pressure relief valve. The outlet of the evaporator is connected to the inlet of the acid processor for leaching the concentrated material in the acid processor and then filtering it. The inlet of the acid processor is connected to an acid storage tank. The material outlet of the acid processor is connected to the material inlet of the ammonia solvent purifier, and the inlet of the ammonia solvent purifier is connected to an ammonia storage tank for redissolving the solid material and then repurifying and recovering it.

2. The subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 1, characterized in that, The first subcritical reaction unit includes a raw material storage tank, a slurry mixing tank, an alkali storage tank, a slurry pump, a slurry preheater, an oxidant tank, and an alkaline subcritical reaction device. The outlets of the raw material storage tank and the alkali storage tank are respectively connected to the inlet of the slurry mixing tank to supply materials to the slurry mixing tank and form a mixed slurry. The slurry mixing tank is connected to the alkaline subcritical reaction device through the slurry pump and the slurry preheater. The oxidant tank is connected to the alkaline subcritical reaction device to provide oxidant.

3. The subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 2, characterized in that, The reaction conditions of the alkaline subcritical reactor are: temperature of 200℃~400℃, pressure of 5MPa~8MPa, reaction time of 1h~4h, pH=9~12; and the solid content of the mixed slurry is 10%~40%.

4. The subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 2, characterized in that, The second subcritical reaction unit includes an acidic subcritical reaction device, a filter tank, and a purification crystallizer; the material inlet of the acidic subcritical reaction device is connected to the solid phase outlet of the solid-liquid separator; the acidic subcritical reaction device is used to dissolve solid materials using an acidic solution and carry out a subcritical reaction.

5. The subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 4, characterized in that, The reaction conditions of the acidic subcritical reactor are: temperature 200℃~250℃, pressure 2MPa~4MPa, reaction time 2h~3h, pH=2~4.

6. The subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 4, characterized in that, The outlet of the acid processor is connected to the inlet of the acidic subcritical reactor to provide an acidic solution; the outlet of the acidic subcritical reactor is connected to a filter tank; the liquid phase outlet of the filter tank is connected to a purification crystallizer, and the solid phase outlet of the filter tank is connected to a third product collector to recover reusable solid materials after the reaction; the outlet of the purification crystallizer is connected to a second product collector to recover high-purity nickel sulfate crystals.

7. The subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 4, characterized in that, The oxidant is at least one of oxygen, ozone, oxygen-enriched air, and hydrogen peroxide solution; the acidic solution is at least one of sulfuric acid and hydrochloric acid; and the reagent in the ammonia storage tank is ammonia water.

8. The subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 1, characterized in that, The liquid phase outlet of the solid-liquid separator is connected to the membrane concentrator, the concentrated liquid outlet of the membrane concentrator is connected to the material inlet of the evaporator, and the solution outlet of the membrane concentrator is connected to the slurry mixing tank.

9. The subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 1, characterized in that, The solution outlet of the ammonia purifier is connected to the deep water processor, and the solution outlet of the purification crystallizer is also connected to the deep water processor. These are used to neutralize the waste liquid with acid and alkali and to perform deep purification. The water outlet of the deep water processor is connected to the slurry mixing tank.

10. A subcritical hydrothermal system for recovering valuable metals from nickel-molybdenum catalysts according to claim 1, characterized in that, The liquid phase outlet and solid phase outlet of the solid-liquid separator are respectively connected to the molybdenum liquid treatment unit and the second subcritical reaction unit.

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