A method for recovering tungsten, molybdenum and vanadium from waste SCR denitration catalyst

Abstract

This invention provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalysts. The method involves a pretreatment process of alkaline leaching, evaporation concentration and crystallization, and resolution to obtain a suitable extraction feed solution. Silicon and arsenic are then effectively removed through synergistic purification using aluminum, magnesium, and calcium sources. Subsequently, under specific pH conditions, a combination of operations including molybdate sulfidation, molybdenum-vanadium synergistic extraction, vanadium selective washing, molybdenum oxidation back-extraction, and tungsten fractional extraction is performed. This achieves stepwise separation and enrichment of three elements with similar chemical properties, making it particularly suitable for the separation and purification of valuable metals in complex alkaline feed systems containing high concentrations of impurities such as silicon and arsenic. The method provided by this invention achieves deep removal of silicon and arsenic, and efficient separation and purification of tungsten, molybdenum, and vanadium. The removal rates of silicon and arsenic, the recovery rates of tungsten, molybdenum, and vanadium, and the purity of the final product all reach high industrial levels, with product purity ≥96% and recovery rates of tungsten ≥96.3%, molybdenum ≥96.4%, and vanadium ≥95.4%.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgy and secondary resource recycling technology, specifically to a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalysts. Background Technology

[0002] Selective catalytic reduction (SCR) denitrification catalysts are core materials used in flue gas denitrification processes. Their role is to catalyze the removal of nitrogen oxides (NOx) from flue gas through a catalytic reaction. x It is converted into harmless nitrogen (N2) and water (H2O), thereby reducing air pollution.

[0003] SCR denitrification catalysts are widely used in flue gas denitrification treatment in industries such as thermal power generation and steel metallurgy. Their main components are active components such as V2O5, WO3, and MoO3 supported on a TiO2 carrier. As their service life ends, a large amount of spent SCR catalysts reach the end of their designed lifespan, facing the challenges of harmless disposal and resource recovery. The amount of waste SCR denitrification catalysts generated is increasing year by year. Direct disposal of strategically valuable metals such as tungsten, molybdenum, and vanadium contained within them not only wastes resources but also poses environmental risks. Therefore, developing economically feasible recovery technologies is of great significance.

[0004] Currently, the main processes for recovering valuable metals from spent SCR catalysts include alkaline leaching, acid leaching, and a combined roasting-leaching method. Among these, high-alkali leaching is widely used due to its high dissolution rate for active metals such as tungsten, molybdenum, and vanadium, and its relatively simple operation. However, during high-alkali leaching, in addition to the target valuable metals such as tungsten, molybdenum, and vanadium entering the solution, impurities such as silicon, arsenic, calcium, magnesium, and aluminum, which are present in large quantities in the spent SCR denitrification catalyst, are also dissolved under strongly alkaline conditions, resulting in an extremely complex composition of the leachate. Especially after the leachate is evaporated, concentrated, crystallized, and the crystals are redissolved, the concentrations of silicon and arsenic in the redissolved filtrate remain at high levels. The presence of these impurities severely affects the subsequent extraction and separation effects, leading to low metal recovery rates and substandard product purity. Existing methods use lime precipitation or aluminum salt precipitation to remove silicon or arsenic separately, but these methods have the problem of difficulty in achieving deep removal of silicon and arsenic simultaneously in the same process. Furthermore, tungsten, molybdenum, and vanadium are prone to co-precipitation during the impurity removal process, leading to the loss of these metals. Meanwhile, tungsten, molybdenum, and vanadium have similar chemical properties, resulting in poor separation selectivity in the extraction system, severe co-extraction, and difficulty in back-extraction, which poses significant challenges to subsequent stepwise recovery.

[0005] Therefore, it is of great significance to develop a technical method that can efficiently remove silicon and arsenic impurities and achieve deep separation and recovery of tungsten, molybdenum and vanadium. Summary of the Invention

[0006] To address the problems of high concentrations of silicon and arsenic in the existing technology for recovering tungsten, molybdenum, and vanadium from the high-alkali leaching crystallization resolution filtrate of spent SCR denitrification catalysts, as well as the poor separation selectivity of tungsten, molybdenum, and vanadium leading to poor separation and extraction effects and low recovery rates, this invention provides a method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalysts.

[0007] According to a first aspect of the present invention, a method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalysts is provided, comprising the following steps: S1. The waste SCR denitrification catalyst is mixed with the first alkaline solution, and the resulting alkaline slurry is filtered to obtain the first filtrate. The first filtrate is evaporated, concentrated and crystallized to obtain the crystallization mother liquor and filtered. The obtained mixed crystals are mixed with a solvent and filtered to obtain the redissolved filtrate. S2. Add aluminum source, magnesium source and calcium source to the redissolved filtrate to react, filter the first reaction solution to obtain the second filtrate; S3. Adjust the pH of the second filtrate to 7.5~8.0, add a sulfur-containing compound to react, filter the resulting second reaction solution to obtain the third filtrate; S4. Adjust the pH of the third filtrate to 8.5~9.0 and perform countercurrent extraction with the first organic extractant to collect the first aqueous phase containing tungsten and the first organic phase loaded with molybdenum and vanadium; S5. Adjust the pH of the first aqueous phase to 5.4~5.8, and use the second organic extractant to perform countercurrent extraction on the first aqueous phase to obtain the tungsten-loaded organic phase. Then, use the second alkaline solution to perform countercurrent back-extraction on the tungsten-loaded organic phase to obtain the tungsten-containing back-extraction solution. S6. The first organic phase is countercurrently washed with a first detergent to collect a second aqueous phase containing vanadium and a second organic phase loaded with molybdenum, wherein the first detergent includes a soluble chloride and an alkali metal hydroxide; S7. Adjust the pH of the second aqueous phase to 8.5~9.0 and control the temperature to 20~25℃. Then add ammonium salt, mix and stir to react. After aging and separation, ammonium metavanadate is obtained. S8. The second organic phase is subjected to countercurrent oxidation treatment using an oxidant, and then the second organic phase after countercurrent oxidation treatment is subjected to countercurrent back-extraction using a third alkaline solution to obtain a molybdenum-containing back-extraction solution.

[0008] The tungsten, molybdenum, and vanadium in the waste SCR denitrification catalyst are supported on the TiO2 support in the form of oxides or composite oxides.

[0009] In S1, a series of operations—alkali leaching, filtration, evaporation, concentration, crystallization, solid-liquid separation, resolution, and filtration—lay a solid foundation for the smooth implementation of the entire recovery process. First, the high-alkali leaching operation converts valuable metals such as tungsten, molybdenum, and vanadium into soluble tungsten, molybdenum, and vanadium salts, which are then efficiently transferred to the liquid phase. After solid-liquid separation, the valuable metals are separated from the insoluble residues (mainly TiO2 support and some aluminosilicates), avoiding wear on the extraction equipment and potential interference with separation efficiency caused by solid waste in subsequent processing steps. Second, the first filtrate obtained after solid-liquid separation (i.e., the high-alkali leachate) is evaporated, concentrated, and crystallized, allowing the valuable metals to precipitate in the form of mixed crystals. After solid-liquid separation, mixed crystals are obtained, while most impurities such as silicon and arsenic, due to their high solubility in the mother liquor or weak crystallization tendency, fail to enter the mixed crystals and are thus partially removed during the crystallization stage. This achieves a one-time physical separation of valuable metals and some impurities, while reducing reagent consumption and waste generation in subsequent deep silicon and arsenic removal processes. Furthermore, the mixed crystals are then redissolved in a solvent, and the resulting clarified reconstituted filtrate, after filtration, serves as the starting material for subsequent impurity removal and separation processes. This reconstituted filtrate increases the concentration of the target metal, and the filtration process after solvent redissolving ensures the clarity of the feed solution. This provides reliable feeding conditions for subsequent continuous extraction operations using precision equipment such as centrifugal extractors, which helps extend equipment maintenance cycles and ensures stable long-term operation. Through the pretreatment in step S1, the feed solution entering subsequent processes has a high concentration of valuable metals and a relatively low impurity content, and the material is homogeneous and stable. This provides a good raw material foundation for the separation efficiency and product purity of the entire recovery process.

[0010] In S2, by adding aluminum, magnesium, and calcium sources to the redissolved filtrate for reaction, the synergistic effect of the aluminum, magnesium, and calcium sources can efficiently remove silicon and arsenic, two impurity elements that seriously interfere with subsequent extraction operations, while minimizing the loss of co-precipitation of tungsten, molybdenum, and vanadium.

[0011] In step S3, the pH of the second filtrate is adjusted to 7.5-8.0. Under this pH condition, the added sulfur-containing compound can undergo a sulfidation reaction with the molybdate ions in the second filtrate, converting them into thiomolybdate ions with a high conversion rate. After sulfidation treatment, the binding force of molybdenum with the organic extractant in subsequent steps is significantly enhanced, and its retention capacity in the organic phase is significantly improved, while the binding force of vanadium with the organic extractant is basically unaffected. This difference allows vanadium to be efficiently eluted into the aqueous phase during the subsequent washing of the molybdenum and vanadium-containing organic phase with a detergent containing soluble chlorides and alkali metal hydroxides, while molybdenum is basically retained in the organic phase, thus achieving effective separation of molybdenum and vanadium. Simultaneously, the sulfidation reaction involved in step S3 has little effect on the tungsten in the filtrate, which retains its original chemical form, facilitating the subsequent stepwise separation of tungsten from molybdenum and vanadium. After the selective transformation described above, i.e., the conversion of molybdate to thiomolybdate, the difference in binding between molybdenum and vanadium with the organic extractant in the subsequent separation process is fully amplified, providing favorable conditions for the recovery of molybdenum and vanadium with high recovery rates and purity, respectively. In addition, after step S3, a small amount of insoluble matter is removed by filtration, and the resulting filtrate is a clear homogeneous solution, which meets the requirements of the subsequent extraction process for the clarity of the feed liquid.

[0012] In step S4, the pH of the third filtrate is adjusted to 8.5-9.0 before countercurrent extraction. Molybdenum and vanadium are efficiently extracted into the organic phase, achieving a high extraction rate. However, under these conditions, tungsten has a weak affinity for the organic extractant and remains mostly in the aqueous phase, resulting in a low co-extraction rate. This step effectively separates tungsten from molybdenum and vanadium. The tungsten-containing aqueous phase is sent to a subsequent process for acid adjustment and re-extraction to recover tungsten, while the molybdenum and vanadium-loaded organic phase is sent to a washing process for further separation of vanadium and molybdenum. This diversion operation assigns three elements with similar chemical properties to different material paths, facilitating their separate recovery in subsequent steps. Furthermore, the countercurrent extraction method in step S4 ensures thorough mass transfer between the organic and aqueous phases through multi-stage contact, guaranteeing complete extraction and stable separation. After step S4, molybdenum and vanadium are enriched in the organic phase, while tungsten remains in the aqueous phase. These three elements then proceed to different subsequent processing routes, laying the foundation for high-recovery rates of tungsten, molybdenum, and vanadium.

[0013] In step S5, by lowering the pH of the first aqueous phase from 8.5-9.0 to 5.4-5.8, the protonation degree of tungstate ions is altered, enhancing their binding force with the organic extractant. This allows for efficient extraction of tungsten by the organic phase, achieving a high extraction rate. After back-extraction of the resulting tungsten-loaded organic phase, tungsten is transferred to the aqueous phase to form a tungsten salt solution, with a high back-extraction rate and a significantly increased tungsten concentration in the resulting tungsten-containing back-extraction solution. Through the aforementioned pH adjustment, extraction, and back-extraction operations, tungsten can be effectively extracted from the complex first aqueous phase and enriched in the back-extraction solution. This back-extraction solution can be directly sent to subsequent processes for the preparation of tungsten salt products, achieving a high overall tungsten recovery rate and yielding a tungsten-containing back-extraction solution with high purity.

[0014] In step S6, under the action of a detergent containing soluble chlorides and alkali metal hydroxides, vanadium in the first organic phase is selectively displaced from the organic phase into the aqueous phase, achieving a high removal rate. The resulting vanadium-containing aqueous phase can be directly sent to the ammonium salt precipitation process for the preparation of ammonium metavanadate. Simultaneously, due to the strong binding force between thiomolybdate ions and the organic extractant, molybdenum remains largely unaffected during washing and continues to reside in the organic phase, achieving a high retention rate. Through this selective washing operation, vanadium enters the aqueous phase, while molybdenum remains in the organic phase. Vanadium and molybdenum, originally co-extracted in the same organic phase, are effectively separated and enter their respective recovery routes. The low molybdenum content in the vanadium-containing aqueous phase after washing is beneficial for obtaining a high-purity ammonium metavanadate product in the subsequent ammonium salt precipitation process; while the low vanadium content in the molybdenum-loaded organic phase after washing is beneficial for obtaining a high-purity molybdenum-containing product solution in the subsequent oxidative back-extraction process. Furthermore, this washing operation also removes trace impurities and residual liquid from the organic phase, resulting in a cleaner molybdenum-loaded organic phase entering subsequent processes. Through this treatment, vanadium and molybdenum are effectively separated within the same extraction system, with each metal entering different subsequent processing routes, laying the foundation for the separate recovery of vanadium and molybdenum with high purity.

[0015] In step S7, by adjusting the pH (8.5~9.0) and temperature (20~25℃), under the action of ammonium salts, vanadate ions in the vanadium-containing second aqueous phase combine with ammonium ions to form ammonium metavanadate precipitate. This precipitation reaction has high selectivity. A large amount of chloride ions, alkali metal ions, and trace amounts of other soluble impurities coexisting in the solution do not participate in the precipitation reaction and remain in the vanadium mother liquor. Vanadium and these impurity components can be effectively separated by solid-liquid separation operations such as filtration or centrifugation. After separation and washing, the ammonium metavanadate precipitate yields a high-purity solid product. Through this precipitation separation operation, the vanadium recovery rate can reach a high level. Simultaneously, since the selective washing in step S6 has effectively separated molybdenum from vanadium, the molybdenum content in the vanadium-containing second aqueous phase in step S7 is low, which also provides favorable conditions for maintaining the high purity of the ammonium metavanadate product. After the above treatment, vanadium is separated from the solution in the form of solid ammonium metavanadate. This product can be directly used as a vanadium recovery product, or it can be further processed by calcination or other post-treatment to convert it into other vanadium products such as vanadium pentoxide.

[0016] In step S8, under the action of the oxidant, thiomolybdate ions in the second organic phase are oxidized to molybdate ions, achieving a high conversion rate. This chemical transformation effectively reduces the binding force between molybdenum and the organic extractant. Molybdenum, originally tightly bound to the extractant in the form of thiomolybdate ions, exhibits significantly weakened affinity for the organic phase after conversion to molybdate, thus creating favorable conditions for subsequent alkaline back-extraction. The oxidized organic phase is then subjected to countercurrent back-extraction with an alkaline solution. Molybdate ions are converted into soluble molybdenum salts and enter the aqueous phase, achieving a high back-extraction rate and significantly increasing the molybdenum concentration in the resulting molybdenum-containing back-extraction solution. Through the aforementioned oxidation and back-extraction operations, molybdenum is effectively released from the second organic phase and enriched in the back-extraction solution. This back-extraction solution can be directly sent to subsequent processes for the preparation of molybdate products, achieving a high overall molybdenum recovery rate and yielding a molybdenum-containing back-extraction solution with high purity. Simultaneously, the back-extracted organic phase can be washed and regenerated, returning to the extraction section for recycling, reducing the consumption of organic phase and reagents and thus lowering operating costs. After the above treatment, molybdenum was recovered from the organic phase in the form of a molybdate solution, completing the resource recovery of molybdenum from the waste SCR denitration catalyst through leaching, extraction, washing, oxidation, and back-extraction.

[0017] In summary, this invention provides a complete process for separating and recovering tungsten, molybdenum, and vanadium from the high-alkali leaching, crystallization, and resolution filtrate of spent SCR denitrification catalysts. This method obtains a suitable extraction feed solution through pretreatment steps of alkaline leaching, evaporation concentration crystallization, and resolution. Silicon and arsenic are then effectively removed through synergistic purification using aluminum, magnesium, and calcium sources. Subsequently, under specific pH conditions, a combination of operations including molybdate sulfidation, molybdenum-vanadium synergistic extraction, vanadium selective washing, molybdenum oxidation back-extraction, and tungsten fractional extraction is performed. This achieves stepwise separation and enrichment of three elements with similar chemical properties, and is particularly suitable for the separation and purification of valuable metals in complex alkaline feed systems containing high concentrations of impurities such as silicon and arsenic. The method provided by this invention can achieve deep removal of silicon and arsenic, and efficient separation and purification of tungsten, molybdenum, and vanadium. The removal rates of silicon and arsenic, the recovery rates of tungsten, molybdenum, and vanadium, and the purity of the final product all reach high industrial levels, with product purity ≥96% and recovery rates of tungsten ≥96.3%, molybdenum ≥96.4%, and vanadium ≥95.4%.

[0018] Furthermore, the process route of this invention features seamless integration of each unit operation, a high degree of automation, and suitability for large-scale continuous production. The organic phase is recyclable, reagent consumption is reduced by 40%, and wastewater discharge is reduced by 50%. In addition, the method provided by this invention has advantages such as simple process, high metal recovery rate, high product purity, low cost, and environmental friendliness. At the same time, it avoids the equipment corrosion and environmental pollution problems caused by the large-scale use of strong acids and alkalis in traditional processes, which is in line with the development direction of green metallurgy.

[0019] Preferably, S2 satisfies at least one of the following conditions a to g: a. The aluminum source includes sodium aluminate; b. Calculated according to the molar ratio, the ratio of aluminum (Al) in the aluminum source to silicon (Si) in the redissolved filtrate is (1.5~2.5):1; c. The magnesium source includes magnesium oxide, with an activity ≥65%; d. Calculated according to the molar ratio, the ratio of magnesium (Mg) in the magnesium source to arsenic (As) in the redissolved filtrate is (1.1~1.2):1; e. The calcium source is lime milk (calcium hydroxide) with a solid content of 18-22%, prepared using water and calcium oxide. f. Calculated according to the molar ratio, the calcium element (Ca) in the calcium source : silicon element (Si) in the reconstituted filtrate = (2.5~3.5) : 1; g. The temperature for reacting aluminum, magnesium and calcium sources in the reconstituted filtrate is 90~95℃.

[0020] It should be noted that the activity of magnesium oxide (MgO) refers to the effective MgO content that can rapidly hydrate in aqueous solution to form magnesium hydroxide, and is directly related to crystal defect density, specific surface area, and crystal lattice integrity. Highly active MgO has a loose crystal lattice, many unsaturated surface bonds, and a large specific surface area (≥100 μm²). 2 / g), with a fast hydration rate; low-activity MgO has a dense lattice, high crystallinity, and strong surface inertness, resulting in a slow hydration rate or even difficulty in reaction.

[0021] The activity of MgO can be determined by the citric acid neutralization method (YB / T4019-2015): at 30℃, the shorter the reaction time of 10% citric acid with MgO to pH=3.0, the higher the activity. Among them, the activity of MgO ≥65% corresponds to a citric acid reaction time ≤40s, which belongs to the high activity level in industrial applications.

[0022] In step S2, sodium aluminate is used as the aluminum source, magnesium oxide with an activity ≥65% as the magnesium source, and lime slurry as the calcium source for the arsenic and silicon removal processes. This effectively removes arsenic and silicon from the redissolved filtrate. Magnesium oxide primarily removes arsenic, reacting with arsenate ions in the redissolved filtrate to form insoluble magnesium arsenate precipitate (3MgO + 2AsO4). 3- +3H₂O = Mg₃(AsO₄)₂↓ + 6OH⁻ - This process achieves arsenic removal from the reconstituted filtrate. Sodium aluminate and lime slurry synergistically remove silicon, with the following reaction: 3Ca(OH)2 + 2NaAlO2 + xNa2SiO3 + (4-x)H2O = 3CaO·Al2O3·xSiO2·(6-2x)H2O↓ + (2+2x)NaOH, where x is the silicon saturation coefficient, 0≤x≤3, and industrially x=1. Sodium aluminate provides aluminate ions in alkaline solution, while lime slurry provides calcium ions and hydroxide ions. Both react with silicate ions in the reconstituted filtrate to form insoluble hydrated calcium aluminosilicate precipitate. Through the combined action of sodium aluminate, activated magnesium oxide, and lime slurry, arsenic and silicon in the reconstituted filtrate can be simultaneously and efficiently removed, with a silicon removal rate ≥99% and an arsenic removal rate ≥98%, and tungsten, molybdenum, and vanadium losses ≤0.5%, thus solving the problem of interference from high-silicon and arsenic feed solutions on subsequent extraction.

[0023] Meanwhile, by controlling the amounts of aluminum, magnesium, and calcium sources within the aforementioned ranges and maintaining the reaction temperature between 90 and 95°C, the specific types, amounts, and reaction temperatures of the aluminum, magnesium, and calcium sources are coordinated to ensure that the silicon and arsenic removal reactions can proceed fully under suitable kinetic conditions. At the same time, the co-precipitation loss of tungsten, molybdenum, and vanadium is kept at a low level, thereby improving the removal rates of silicon and arsenic and providing a low-interference feed liquid environment for subsequent extraction processes.

[0024] Preferably, S2 includes the following operations: heating the redissolved filtrate to 90-95°C, controlling the stirring speed at 80-100 rpm, adding an aluminum source, adjusting the stirring speed to 120-150 rpm, reacting for 40-50 min, adding a magnesium source and stirring for 5-10 min, then adding a calcium source dropwise to the system and reacting at 90-95°C for 1-3 h, subsequently lowering the system temperature to 80-85°C, stopping stirring and maintaining the temperature for 1-3 h to obtain a first reaction solution, filtering the first reaction solution to obtain a second filtrate; wherein, the calcium source is added dropwise for 60-90 min.

[0025] In the silicon and arsenic removal process in step S2, the deep impurity removal effect is further optimized by controlling key process parameters such as reaction temperature, stirring speed, feeding sequence, and reaction time. Specifically, the reconstituted filtrate is first heated to 90-95℃. Under this temperature condition, the precipitation reaction of silicon and arsenic has a suitable kinetic rate, which is conducive to the full progress of the impurity removal reaction. Regarding the control of the feeding sequence and stirring speed, sodium aluminate is added first, and the stirring speed is controlled at 80-100 rpm. Under alkaline conditions without calcium hydroxide, sodium aluminate is basically dissolved in the reconstituted filtrate and reacts slowly with silicate ions. Since the arsenic content in the reconstituted filtrate is small, the stirring speed is increased to 120-150 rpm and reacted for 40-50 minutes before adding activated magnesium oxide. Activated magnesium oxide can react efficiently with arsenate ions to form magnesium arsenate precipitate. This segmented adjustment of the stirring speed helps the reactants to be quickly and uniformly dispersed in the system and fully contact the target impurities, improving the reaction efficiency. After the activated magnesium oxide is added, the mixture is stirred for 5-10 minutes. The addition of lime slurry provides sufficient reaction time for the magnesium arsenate precipitation reaction. Then, hydrated calcium aluminosilicate is gradually formed, and the resulting magnesium arsenate precipitate also acts as an adsorbent, promoting the precipitation of silicate ions. Controlling the addition time to 60-90 minutes maintains a low degree of supersaturation in the reaction system, preventing explosive nucleation of the precipitate due to excessively high local calcium ion concentrations, which could lead to the physical entrainment of valuable metals. After the lime slurry is added, the system is kept at 90-95°C for 1-3 hours to ensure the silicon precipitation reaction proceeds fully. The system temperature is then lowered to 80-85°C, and stirring is stopped while the system is aged for 1-3 hours. This combination of temperature reduction and static aging helps the already formed precipitate particles to grow further and their crystal form to become more perfect. Through the above-mentioned control measures, the removal rates of silicon and arsenic can both reach a high level. The content of silicon and arsenic in the purified feed solution entering the subsequent process is significantly reduced, providing feeding conditions with low impurity content for the subsequent extraction and separation process. At the same time, the co-precipitation loss of tungsten, molybdenum and vanadium is controlled within a low range, improving the retention rate of the target valuable metals.

[0026] Preferably, in S3, the sulfur-containing compound includes at least one of sodium sulfide nonahydrate and hydrogen sulfide.

[0027] Sodium sulfide nonahydrate and / or hydrogen sulfide are selected as sulfide oxidizing agents, which can provide sufficient sulfur ions in alkaline solutions to gradually convert molybdate into thiomolybdate.

[0028] Preferably, in S3, the molar ratio of sulfur (S) in the sulfur-containing compound to molybdenum (Mo) in the second filtrate is calculated as (3.5~4.5):1.

[0029] By controlling the amount of sulfur-containing compounds added within the aforementioned range, sufficient reactant supply for the sulfidation reaction is ensured, improving the conversion efficiency of molybdate, while avoiding the introduction of additional sulfide residues due to excessive sulfidating agent. Under pH conditions of 7.5–8.0, sodium sulfide nonahydrate within this range can sufficiently convert molybdate to thiomolybdate, while vanadium undergoes virtually no sulfidation under these conditions. After this treatment, molybdenum exhibits significantly stronger binding affinity to the organic extractant than vanadium during subsequent extraction and washing processes. This difference in binding affinity allows for effective elution of vanadium while molybdenum remains largely in the organic phase when using detergents containing sodium chloride and sodium hydroxide in the subsequent washing process. This provides a good separation basis for the selective recovery of vanadium and further purification of molybdenum.

[0030] Preferably, S3 includes the following operations: heating the second filtrate to 40~50℃, adding acid to adjust the pH to 7.5~8.0, adding a sulfur-containing compound, stirring at 100~150 rpm and keeping at 40~50℃ for 4~6 h to obtain a second reaction solution, filtering the second reaction solution to obtain a third filtrate.

[0031] In step S3, the second filtrate is heated to 40-50°C and the pH is adjusted to 7.5-8.0 before the sulfur-containing compound is added. This order of addition avoids the problem of decomposition or reduced reaction efficiency of the sulfur-containing compound due to instability under excessively high or low pH conditions, allowing the sulfation reaction to proceed in a suitable acid-base environment. Controlling the stirring speed at 100-150 rpm facilitates the rapid dispersion of the sulfur-containing compound in the solution and ensures sufficient contact with molybdate ions, promoting uniform reaction. Maintaining the reaction at a constant temperature of 40-50°C for 4-6 hours provides suitable kinetic conditions for the sulfation reaction, enabling efficient conversion of molybdate ions to thiomolybdate ions. After the reaction, filtration removes a small amount of insoluble matter, resulting in a clear, homogeneous solution that meets the clarity requirements of the feed solution in subsequent extraction processes. Through comprehensive control of the above reaction conditions, the sulfation reaction proceeds sufficiently, providing a good chemical basis for the selective separation of vanadium and molybdenum in the subsequent washing process.

[0032] Preferably, at least one of the following conditions a to b is satisfied in S4: a. The first organic extractant comprises 10-30 vol% trioctylmethylammonium chloride (Aliquat 336), 5-15 vol% sec-octanol and sulfonated kerosene; b. During the countercurrent extraction process, control O / A = 1:(2~4) and the number of extraction stages to be 5~6.

[0033] Trioctylmethylammonium chloride is used as the active component in the organic extractant. Its quaternary ammonium salt structure can undergo anion exchange reaction with thiomolybdate and vanadate under alkaline conditions, effectively capturing them from the aqueous phase to the organic phase. At the same time, 2-octanol is added as a phase modifier in the organic extractant, which helps to improve the phase separation performance during the extraction process and reduce the tendency to emulsify. Sulfonated kerosene is used as a diluent in the organic extractant, which can adjust the viscosity and density of the organic phase, giving it good fluidity and suitable phase adaptability.

[0034] The third filtrate was subjected to countercurrent extraction with the aforementioned organic extractant at a pH of 8.5–9.0, with an oil-to-water ratio controlled at 1:2–1:4 and 5–6 extraction stages. Within this pH range, trioctylmethylammonium chloride exhibited high extraction selectivity for thiomolybdate and vanadate ions, but weak affinity for tungstate ions. Therefore, molybdenum and vanadium were efficiently transferred to the organic phase, while tungsten remained primarily in the aqueous phase. Through the combination of the aforementioned organic extractant and extraction conditions, the separation of tungsten from molybdenum and vanadium could be achieved with relatively stable results. In the above countercurrent extraction process, if the O / A ratio is too small (e.g., O / A=1:5) and the extraction stage is too low (e.g., 4 stages), the amount of organic phase extracted will be too small, and molybdenum and vanadium cannot be effectively extracted. This will result in excessive molybdenum and vanadium residues in the first aqueous phase, affecting the subsequent extraction and purity of tungsten. If the O / A ratio is too large (O / A=1:1), the amount of extractant will also be too large, which will significantly co-extract tungsten and other impurities. Even if the extraction stage is increased (e.g., 7 stages), it will not be effectively reduced.

[0035] Preferably, S5 satisfies at least one of the following conditions a to e: a. The second organic extractant includes 10-30 vol% trioctylmethylammonium chloride (Aliquat336), 5-15 vol% sec-octanol and sulfonated kerosene; b. In the countercurrent extraction of the first aqueous phase using the second organic extractant, the O / A ratio is controlled to be 1:(2~4), and the number of extraction stages is 5~6. c. The second alkaline solution includes 3-5 mol / L sodium hydroxide; d. In the countercurrent back-extraction process of the tungsten-loaded organic phase using the second alkaline solution, the O / A ratio is controlled to be (1~2):(1~2), and the number of back-extraction stages is 5~7. e. Before countercurrent back-extraction of the tungsten-loaded organic phase using a second alkaline solution, the operation includes countercurrent washing of the tungsten-loaded organic phase using a second detergent, wherein the second detergent comprises 0.3~0.7 wt% sodium chloride, and during the countercurrent washing of the tungsten-loaded organic phase, the O / A ratio is controlled to be (2~3):1, and the number of washing stages is 1~2.

[0036] A second organic extractant with the same composition as the first organic extractant was used to extract the tungsten-containing aqueous phase under weakly acidic conditions (pH 5.4–5.8). Within this pH range, tungstate ions are protonated and more easily captured by the quaternary ammonium salt extractant (trioctylmethylammonium chloride), thus facilitating the transfer of tungsten from the aqueous phase to the organic phase. During this extraction process, the oil-to-water ratio of 1:2–1:4 and the 5–6 stages of extraction help ensure sufficient extraction. Simultaneously, the abundant sodium ions and cations such as calcium and magnesium present in the first aqueous phase are not extracted under these conditions and remain in the raffinate, achieving effective separation of tungsten from these abundant coexisting salt impurities. Before back-extraction, the tungsten-loaded organic phase is subjected to 1–2 stages of countercurrent washing with a second detergent containing 0.3–0.7 wt% sodium chloride. This helps remove small amounts of entrained impurities and residual feed from the organic phase, further reducing the impurity content in the subsequent back-extraction solution. The washed tungsten-containing organic phase is then subjected to countercurrent back-extraction with 3-5 mol / L sodium hydroxide solution under conditions of an oil-water ratio of 1:2-2:1 and 5-7 stages to obtain a tungsten-containing back-extraction solution. Through the above extraction, washing, and back-extraction operations, tungsten is effectively extracted from the complex first aqueous phase and enriched in the back-extraction solution. This back-extraction solution can be used directly or after further processing to prepare tungsten salt products.

[0037] In condition b, during the countercurrent extraction of the first aqueous phase using the second organic extractant, if the O / A ratio is too high (e.g., O / A = 1:1), the amount of extractant will be too large, and even if the number of extraction stages is increased, it will not be able to effectively enrich and utilize the impurities, and more impurities will be co-extracted. If the O / A ratio is too low (e.g., O / A = 1:5) and the number of extraction stages is too small, it will lead to incomplete tungsten extraction and a low extraction rate.

[0038] In condition e, during the countercurrent washing of the tungsten-loaded organic phase using the second detergent, if the amount of detergent used is large or the number of stages is high, it will lead to increased tungsten elution loss and unnecessary waste of reagents and equipment.

[0039] In condition d, during the countercurrent back-extraction of the tungsten-loaded organic phase using a second alkaline solution, if the number of back-extraction stages is too small (e.g., 4 stages), it will lead to incomplete back-extraction and a low primary recovery rate.

[0040] Preferably, S6 satisfies at least one of the following conditions a to b: a. The first detergent comprises 0.5~1.5 mol / L sodium chloride and 0.5~1.5 mol / L sodium hydroxide; b. During the countercurrent washing of the first organic phase using the first detergent, the O / A ratio is controlled to be (1~2):1, and the number of washing stages is 3~5.

[0041] Sodium chloride and sodium hydroxide are used as detergents, and their concentrations are controlled within the aforementioned range. Sodium chloride provides chloride ions (Cl...). - Sodium hydroxide provides hydroxide ions (OH-). - The system maintains a strongly alkaline environment. Under these washing conditions, chloride and hydroxide ions can undergo a displacement reaction with vanadate ions, which have relatively weak binding forces in the organic phase, allowing vanadium to enter the aqueous phase from the organic phase. Thiomolybdate ions, due to their stronger binding force with the quaternary ammonium salt extractant, remain largely in the organic phase. Maintaining an oil-to-water ratio of 1:1 to 2:1 and a washing stage of 3 to 5 ensures sufficient contact between the aqueous and organic phases during washing, facilitating complete vanadium removal. The resulting vanadium-containing aqueous phase has a low molybdenum content and can be directly introduced into the ammonium salt precipitation process for the preparation of ammonium metavanadate. The molybdenum-loaded organic phase, also with a low vanadium content, can be used in the subsequent oxidation back-extraction process for molybdenum recovery. Through the combination of the washing agent composition and washing conditions, vanadium and molybdenum are effectively separated in the same extraction system, creating conditions for the recovery of these two metals at high purity.

[0042] Preferably, S7 satisfies at least one of the following conditions a to b: a. Ammonium salts include at least one of ammonium chloride and ammonium bicarbonate; b. Ammonium ions (NH4+) in ammonium salts + The molar ratio of vanadium (V) in the first aqueous phase to that in the second aqueous phase is (2~4):1.

[0043] The pH of the vanadium-containing second aqueous phase is adjusted to 8.5-9.0, and the temperature is controlled at 20-25℃. Then, ammonium salt is added and stirred to react. Vanadate ions combine with ammonium ions to form ammonium metavanadate precipitate with low solubility. This precipitation reaction has high selectivity for vanadium. Sodium ions, chloride ions, and other soluble impurities present in the solution do not participate in this precipitation reaction and remain in the mother liquor. Ammonium metavanadate can be separated from these impurities by filtration or centrifugation. After washing, the residual mother liquor adhering to the particle surface of the obtained ammonium metavanadate solid is further removed, which helps to obtain a high-purity ammonium metavanadate product, which can be directly used as a vanadium recovery product.

[0044] Preferably, S8 satisfies at least one of the following conditions a to f: a. The oxidizing agent includes 5-7 wt% hydrogen peroxide; b. Calculated according to the molar ratio, the ratio of oxidant to molybdenum in the second organic phase is (16~18):1; c. In the process of countercurrent oxidation of the second organic phase using an oxidant, the O / A ratio is controlled to be (1~2):1, and the oxidation stage is 2~4. d. The third alkaline solution includes 3-5 mol / L sodium hydroxide; e. During the countercurrent back-extraction of the second organic phase after countercurrent oxidation treatment with a third alkaline solution, the O / A ratio is controlled to be (1~3):1, and the number of back-extraction stages is 3~5; f. After countercurrent back-extraction of the second organic phase treated by countercurrent oxidation, the process also includes countercurrent elution of the obtained lean organic phase using an eluent, wherein the eluent includes water, and during the countercurrent elution process, the O / A ratio is controlled to be (2~3):1, and the number of elution stages is 2~4.

[0045] It should be noted that the organic-poor phase refers to the organic solvent phase remaining after the effective substances have been extracted.

[0046] 5–7 wt% hydrogen peroxide was used as the oxidant, and its dosage was controlled within the aforementioned range. This dosage range ensured sufficient oxidant to fully react with thiomolybdate ions while avoiding unnecessary reagent consumption due to excessive oxidant. Countercurrent contact was performed under conditions of an oil-to-water ratio of 1:1–2:1 and 2–4 oxidation stages, allowing for a more complete conversion of thiomolybdate ions in the organic phase to molybdate ions, thereby reducing the binding force between molybdenum and the quaternary ammonium salt extractant. The oxidized organic phase was then subjected to countercurrent back-extraction using a 3–5 mol / L sodium hydroxide solution under conditions of an oil-to-water ratio of 1:1–3:1 and 3–5 back-extraction stages. Molybdate ions were transferred to the aqueous phase to form a molybdate solution, ensuring efficient transfer of molybdenum from the organic phase to the aqueous phase. Furthermore, the back-extracted organic phase could be recycled back to the extraction section after elution with pure water, reducing the consumption of fresh organic extractant and reagents, thus contributing to cost reduction. Through comprehensive control of the above oxidation and back-extraction conditions, molybdenum is effectively released from the second organic phase and enriched in the back-extraction solution, providing a raw material solution for the subsequent preparation of molybdate products.

[0047] In condition c, during the countercurrent oxidation of the second organic phase using an oxidant, if the O / A ratio is too high (e.g., 3:1) and the oxidation level is too low (e.g., level 1), the amount of oxidant used will be too small, which will lead to incomplete oxidation and affect the subsequent molybdenum back-extraction effect.

[0048] In condition e, during the countercurrent back-extraction of the second organic phase after countercurrent oxidation treatment with a third alkaline solution, if the O / A ratio is too high (e.g., 4:1) and the number of back-extraction stages is too low (e.g., stage 1), the back-extraction effect will be poor.

[0049] Preferably, in the countercurrent extraction, back-extraction, washing, and countercurrent oxidation processes involved in S1 to S8, a centrifugal extractor of ultragravity is used. The centrifugal extractor is a type 150 centrifugal extractor with a drum speed of 2000 to 3000 rpm and a separation factor of 500 to 1000.

[0050] The use of a centrifugal extractor with high gravity improves mass transfer efficiency by 3 to 5 times compared to traditional extraction equipment, reduces the number of extraction stages by 2 to 3, reduces the floor space by more than 60%, and reduces energy consumption by 30%. Attached Figure Description

[0051] Figure 1 This invention provides a complete process route diagram for the method of recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalysts. Detailed Implementation

[0052] The technical features of the technical solution provided by the present invention will be further clearly and completely described below with reference to specific embodiments. 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.

[0053] In the O / A ratios used in the following examples and comparative examples, O refers to the oil phase, A refers to the aqueous phase, and the O / A ratio refers to the oil-water volume ratio.

[0054] Example 1 A method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalysts, the complete process route of which is as follows: Figure 1 As shown, it includes the following steps: S1. Preparation of redissolved filtrate Waste SCR denitrification catalyst was mixed with a first alkaline solution (sodium hydroxide solution), and the resulting alkaline slurry was filtered to obtain a first filtrate. The first filtrate was evaporated, concentrated, and crystallized to obtain a crystallization mother liquor, which was then filtered. The resulting mixed crystals were mixed with a solvent and filtered to obtain 1000 L of redissolved filtrate. The pH value of the above redissolved filtrate is >13.5, and the specific components are as follows: calcium (Ca) 0.2740 g / L, magnesium (Mg) 0.1200 g / L, sodium (Na) 90.7000 g / L, potassium (K) 0.2320 g / L, silicon (Si) 15 g / L, vanadium (V) 5 g / L, arsenic (As) 0.4 g / L, tungsten (W) 28 g / L, molybdenum (Mo) 2.3 g / L, titanium (Ti) 0.1030 g / L, and aluminum (Al) 0.2730 g / L; S2. Deep removal of silicon and arsenic The reconstituted filtrate was heated to 92℃ and stirred at 90 rpm. 5 L of aluminum source (10% sodium aluminate solution) was added, and the stirring speed was increased to 130 rpm. After reacting for 45 min, 0.8 kg of magnesium source (active magnesium oxide with an activity ≥65%) was added and stirred for 8 min. Then, 30 L of calcium source (lime slurry with a solid content of 20%) was added to the system, and the addition time was controlled at 75 min. After the addition was completed, the stirring speed was increased to 100 rpm, and the reaction was carried out at 92℃ for 2 h. Subsequently, the system temperature was lowered to 82℃, stirring was stopped, and the temperature was maintained for 2 h to obtain the first reaction solution. The first reaction solution was filtered, and the filter cake was washed with 50 L of pure water. The washing liquid was combined with the clarified liquid to obtain 980 L of the second filtrate. The second filtrate was tested and found to contain ≤0.1 g / L silicon and ≤0.008 g / L arsenic. S3. Molybdate sulfation The second filtrate was introduced into the reaction vessel and kept at 45°C. The pH of the second filtrate was adjusted to 7.8 with dilute acid. 3.2 kg of sulfur-containing compound (sodium sulfide nonahydrate) was added (in three batches, with an interval of 30 min between each batch). The mixture was stirred at 130 rpm and kept at 45°C for 5 h. The second reaction solution was then filtered to obtain the third filtrate. S4. Preparation of pre-extraction solution and synergistic extraction of molybdenum and vanadium. Preparation of pre-extraction solution: Adjust the pH of the third filtrate to 8.8 with dilute acid, let it stand and filter to obtain 965 L of pre-extraction solution; Molybdenum-vanadium co-extraction: A 150-type centrifugal extractor was used to perform countercurrent extraction of the pre-extraction liquid with the first organic extractant (20% Aliquat 336 + 10% 2-octanol + 70% sulfonated kerosene). The O / A ratio was controlled at 1:3 and the number of extraction stages was 5. After the extraction was completed, the first aqueous phase containing tungsten (i.e., raffinate, which was sent to the subsequent tungsten pre-extraction liquid preparation process) and the first organic phase loaded with molybdenum and vanadium were collected. S5. Preparation of tungsten extraction pretreatment solution, tungsten extraction, tungsten washing, tungsten back-extraction, and elution and regeneration of the organic phase from tungsten extraction. The pH of the first aqueous phase was adjusted to 5.6 with dilute acid, and after standing and filtration, 950 L of tungsten extraction pre-extraction liquor was obtained, containing 27.6 g / L of tungsten. The pre-extraction liquor was subjected to countercurrent extraction using a second organic extractant (20% Aliquat 336 + 10% sec-octanol + 70% sulfonated kerosene), controlling the O / A ratio at 1:3 and with 6 extraction stages, yielding a tungsten-loaded organic phase. This phase was then countercurrently washed with a second detergent (0.5 wt% sodium chloride solution), controlling the O / A ratio at 2:1 and with 2 washing stages. Finally, the tungsten-loaded organic phase was countercurrently back-extracted using a second alkaline solution (4 mol / L sodium hydroxide solution), controlling the O / A ratio at 1:1 and with 7 back-extraction stages, yielding a tungsten-containing back-extraction solution containing 80.5 g / L of tungsten. g / L, the lean organic phase after back-extraction is eluted and regenerated, with O / A = 2:1, elution stage 2, and pure water as the eluent. The regenerated organic phase is returned to the extraction section for recycling. S6. Vanadium selective washing A 150-type centrifugal extractor was used to countercurrently wash the first organic phase with a first washing agent (a mixed solution of 1 mol / L sodium chloride and 1 mol / L sodium hydroxide), controlling the O / A ratio to 2:1 and the washing stage to 3 stages. The vanadium-containing second aqueous phase (i.e., the washing residue, containing 29.5 g / L of vanadium, which was sent to the subsequent ammonium salt precipitation process) and the molybdenum-loaded second organic phase were collected. S7. Ammonium salt vanadium precipitation The pH of the second aqueous phase was adjusted to 8.8 and the temperature was controlled at 23°C. Then, ammonium salt (ammonium chloride) was added, mixed and stirred, and after aging and separation, ammonium metavanadate was obtained. S8. Thiomolybdate oxidation, molybdenum back-extraction, and organic phase elution regeneration The second organic phase was subjected to countercurrent oxidation treatment using an oxidant (6 wt% hydrogen peroxide, added at a rate 17 times the molar amount of molybdenum in the second organic phase), with the O / A ratio controlled at 1.5:1 and the oxidation stage number 3. Then, the second organic phase after countercurrent oxidation treatment was subjected to countercurrent back-extraction using a third alkaline solution (4 mol / L sodium hydroxide solution), with the O / A ratio controlled at 2:1 and the back-extraction stage number 4, resulting in a molybdenum-containing back-extraction solution and a lean organic phase. The molybdenum-containing back-extraction solution was sent to the molybdenum salt preparation process to prepare molybdenum salt products. The lean organic phase was then eluted and regenerated, with the O / A ratio controlled at 2:1 and the elution stage number 2, using pure water as the eluent. The resulting regenerated organic phase was returned to the extraction section for recycling.

[0055] Example 2 This embodiment provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalyst. Compared with Example 1, the difference in composition is that in S2, the aluminum source, magnesium source, and calcium source are added in no particular order. The specific operation steps are as follows: S2. Deep removal of silicon and arsenic The reconstituted filtrate was heated to 92°C, and the stirring speed was controlled at 130 rpm. 5 L of aluminum source (10% sodium aluminate solution), 0.8 kg of magnesium source (active magnesium oxide), and 30 L of calcium source (lime slurry with a solid content of 20%) were added, with a total addition time of 85 min. After the addition was completed, the stirring speed was adjusted to 100 rpm, and the reaction was carried out at 92°C for 2 h. Subsequently, the system temperature was lowered to 82°C, stirring was stopped, and the temperature was maintained for 2 h to obtain the first reaction solution. The first reaction solution was filtered, and the filter cake was washed with 50 L of pure water. The washing liquid was added to the clarified liquid to obtain the second filtrate.

[0056] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are consistent with those in Example 1.

[0057] Example 3 This embodiment provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalyst. Compared with Example 1, the difference in configuration is that in S2, after the aluminum source is added, the stirring speed is not adjusted, and the stirring speed is maintained at 90 rpm.

[0058] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are consistent with those in Example 1.

[0059] Example 4 This embodiment provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalysts. Compared with Example 1, the difference in composition is that in S3, an equal amount of hydrogen sulfide is used to replace sodium sulfide nonahydrate as a sulfur-containing compound.

[0060] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are consistent with those in Example 1.

[0061] Example 5 This embodiment provides a method for recovering tungsten, molybdenum and vanadium from waste SCR denitrification catalyst. Compared with Example 1, the difference in composition is: (1) in S5, the second detergent used is pure water; (2) in S6, the first detergent used is a 2 mol / L sodium hydroxide solution.

[0062] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are consistent with those in Example 1.

[0063] Comparative Example 1 This comparative example provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalyst. The difference in composition compared to Example 1 is that in S3, the pH of the second filtrate is adjusted to 7.2 with dilute acid.

[0064] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are consistent with those in Example 1.

[0065] Comparative Example 2 This comparative example provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalyst. The difference in composition compared to Example 1 is that in S3, the pH of the second filtrate is adjusted to 8.5 with dilute acid.

[0066] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are consistent with those in Example 1.

[0067] Comparative Example 3 This comparative example provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalyst. The difference in composition compared to Example 1 is that in S4, the pH of the third filtrate is adjusted to 8.2 with dilute acid.

[0068] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are consistent with those in Example 1.

[0069] Comparative Example 4 This comparative example provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalyst. The difference in composition compared to Example 1 is that in S4, the pH of the third filtrate is adjusted to 9.2 with dilute acid.

[0070] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are consistent with those in Example 1.

[0071] Comparative Example 5 This comparative example provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalyst. The difference in composition compared to Example 1 is that in S5, the pH of the first aqueous phase is adjusted to 5.2 with dilute acid.

[0072] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are consistent with those in Example 1.

[0073] Comparative Example 6 This comparative example provides a method for recovering tungsten, molybdenum, and vanadium from waste SCR denitrification catalyst. The difference in composition compared to Example 1 is that in S5, the pH of the first aqueous phase is adjusted to 6.0 with dilute acid.

[0074] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are consistent with those in Example 1.

[0075] Test case This test example utilizes the methods provided in Examples 1-5 and Comparative Examples 1-6 to recover tungsten, molybdenum, and vanadium from the high-alkali leaching crystallization redissolution filtrate of waste SCR denitrification catalyst. The purity of the tungsten-containing back-extraction solution (sodium tungstate) obtained in step S5 and the total recovery rate of tungsten, the purity of ammonium metavanadate obtained in step S7 and the total recovery rate of vanadium, and the purity of the molybdenum-containing back-extraction solution (sodium molybdate) obtained in step S8 and the total recovery rate of molybdenum are detected and calculated.

[0076] (1) Total recovery rate The formulas for calculating the recovery rates of tungsten, molybdenum, and vanadium are as follows: η 总 =m 产品质量 / (V 原液 ×C 原液 )×100% In the formula: V 原液 Volume of original solution added, in L; C 原液 : Target metal concentration in the original solution, g / L; m 产品质量 Net weight of metals in the final product / semi-finished product, in grams.

[0077] The total recovery rate is calculated separately for each of the four stages (extraction → washing → oxidation → back-extraction): η 总 =η 萃取 ×η 洗涤 ×η 氧化 ×η 反萃 .

[0078] The formulas for the fractional recovery rate are as follows: Extraction recovery rate: η 萃取 =(V 负载有机 ×C 有机 ) / (V 料液 ×C 进料 )×100%, where C 有机 : Concentration of supported organic phase metal, g / L; V 负载有机 Organic phase volume, L; V 料液 Pre-extraction liquid volume, L; C 进料 Metal concentration in the pre-extraction solution, g / L.

[0079] Wash retention rate: η 洗涤 =(V 洗后有机 ×C 洗后有机 ) / (V 进洗有机 ×C 进洗有机 )×100%, where V 洗后有机 : Volume of organic phase after washing, L; C 洗后有机 : Concentration of organic phase metals after washing, g / L; V 进洗有机Organic phase volume before washing, L; C 进洗有机 : Concentration of organic phase metals before washing, g / L.

[0080] Oxidation retention rate: η 氧化 =(V 氧化后有机 ×C 氧化后有机 ) / (V 进氧化有机 ×C 进氧化有机 )×100%, where V 氧化后有机 Volume of the organic phase after oxidation, in L; C 氧化后有机 : Concentration of organic phase metal after oxidation, g / L; V 进氧化有机 Volume of organic phase before oxidation, in L; C 进氧化有机 : Concentration of organic phase metal before oxidation, g / L.

[0081] Back-extraction recovery rate: ηback-extraction = (Vback-extraction solution × Cback-extraction solution) / (Vinput back-extraction organic matter × Cinput back-extraction organic matter) 进反萃有机 )×100%, where V 反萃液 : Extraction liquid volume, L; C 反萃液 Metal concentration of the back-extraction solution, g / L; V 进反萃有机 Volume of organic phase before back-extraction, L; C 进反萃有机 : Concentration of organic phase metals before back-extraction, g / L.

[0082] (2) Purity The calculation formula is: Purity = (m L / m c ) × 100%.

[0083] In the formula, m L For the mass of the target metal (or metal salt) in the final product, L can be sodium tungstate, sodium molybdate, or ammonium metavanadate; m c For the quality of the final product (including the target metal or metal salt, and other impurities).

[0084] Table 1 Overall Recovery and Purity Results

[0085] The purity of the tungsten, molybdenum, and vanadium final products recovered from the high-alkali leaching crystallization resolution filtrate of the waste SCR denitrification catalyst using the methods provided in Examples 1-5 and Comparative Examples 1-6, as well as the total recovery rate of tungsten, molybdenum, and vanadium, are shown in Table 1.

[0086] As shown in Table 1: In the process of recovering tungsten, molybdenum, and vanadium from the high-alkali leaching crystallization redissolution filtrate of waste SCR denitrification catalyst using the method provided in Example 1, the pH of the second filtrate was adjusted to 7.5-8.0 with dilute acid in S3 before the sulfation reaction was carried out. In S4, the pH of the third filtrate was adjusted to 8.5-9.0 with dilute acid before countercurrent extraction was carried out. In S5, the pH of the first aqueous phase was adjusted to 5.4-5.8 with dilute acid before extraction was carried out. Finally, the total recovery rate of the three metals, tungsten, molybdenum, and vanadium, was all above 97.8%, and the purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate was all above 99.5%.

[0087] Compared to Example 1, in the process of recovering tungsten, molybdenum, and vanadium from the high-alkali leaching crystallization resolution filtrate of waste SCR denitrification catalyst using the methods provided in Comparative Examples 1 and 2, the total recovery rate of tungsten, molybdenum, and vanadium, as well as the purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate, were lower than in Example 1 when the pH of the second filtrate was adjusted to 7.2 and 8.5 respectively using dilute acid in S3. These results indicate that adjusting the pH of the second filtrate to 7.5-8.0 before adding the sulfide in S3 avoids the problem of decomposition or reduced reaction efficiency of sulfur-containing compounds due to instability under excessively high or low pH conditions. This allows the sulfidation reaction to proceed in a suitable acid-base environment, thereby improving the final total recovery rate of tungsten, molybdenum, and vanadium, as well as the purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate.

[0088] Compared to Example 1, in the process of recovering tungsten, molybdenum, and vanadium from the high-alkali leaching crystallization resolution filtrate of waste SCR denitrification catalyst using the methods provided in Comparative Examples 3 and 4, the pH value of the third filtrate was adjusted to 8.2 and 9.2 respectively in S4 with dilute acid. The total recovery rate of the three metals (tungsten, molybdenum, and vanadium) and the purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate were all lower than in Example 1. These results indicate that countercurrent extraction of the third filtrate with an organic extractant under pH conditions of 8.5–9.0 exhibits high extraction selectivity for thiomolybdate and vanadate ions within this pH range, but weak affinity for tungstate ions. Therefore, molybdenum and vanadium can be efficiently transferred to the organic phase, while tungsten mainly remains in the aqueous phase. The combination of the pH conditions with the organic extractant and extraction conditions allows for stable separation of tungsten from molybdenum and vanadium, thereby improving the final total recovery rate of the three metals and the purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate.

[0089] Compared to Example 1, in the process of recovering tungsten, molybdenum, and vanadium from the high-alkali leaching crystallization redissolved filtrate of waste SCR denitrification catalyst using the methods provided in Comparative Examples 5 and 6, the pH value of the first aqueous phase was adjusted to 5.2 and 6.0 respectively in S5 with dilute acid. The total recovery rate of the three metals (tungsten, molybdenum, and vanadium) and the purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate were all lower than in Example 1. These results indicate that extraction of the tungsten-containing first aqueous phase under weakly acidic conditions (pH 5.4–5.8) allows the tungstate ions to be protonated and more easily captured by the quaternary ammonium salt extractant (trioctylmethylammonium chloride), thus facilitating the transfer of tungsten from the aqueous phase to the organic phase. This improves the final total recovery rate of the three metals (tungsten, molybdenum, and vanadium) and the purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate.

[0090] By comparing the recovery rate and purity results of Examples 1 and 2, it can be seen that in step S2, adding aluminum source, magnesium source and calcium source to the redissolved filtrate in sequence for reaction can achieve deep removal of silicon and arsenic.

[0091] By comparing the recovery rate and purity results of Examples 1 and 3, it can be seen that in step S2, after the aluminum source is added, the stirring speed is increased to 120~150 rpm before the active magnesium oxide is added. The active magnesium oxide can react efficiently with arsenate to form magnesium arsenate precipitate. This segmented adjustment of the stirring speed helps the reactants to be quickly and uniformly dispersed in the system and to fully contact the target impurities, thereby improving the reaction efficiency and thus improving the total recovery rate of the three metals tungsten, molybdenum and vanadium, as well as the purity of the recovered sodium tungstate, ammonium metavanadate and sodium molybdate.

[0092] The recovery rate and purity results of Examples 1 and 4 demonstrate that, compared to hydrogen sulfide, adding sodium sulfide nonahydrate to the second filtrate in S3 for sulfidation reaction can, to a certain extent, improve the total recovery rate of the three metals tungsten, molybdenum, and vanadium, as well as the purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate.

[0093] The recovery rate and purity results of Examples 1 and 5 show that using sodium chloride solution as the second detergent in S5 and a mixed solution of sodium chloride and sodium hydroxide as the first detergent in S6 results in a higher overall recovery rate of tungsten, molybdenum, and vanadium, as well as higher purity of the recovered sodium tungstate, ammonium metavanadate, and sodium molybdate compared to using pure water as the second detergent and sodium hydroxide solution as the first detergent.

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalysts, characterized in that, Includes the following steps: S1. The waste SCR denitrification catalyst is mixed with the first alkaline solution, and the resulting alkaline slurry is filtered to obtain the first filtrate. The first filtrate is evaporated, concentrated and crystallized to obtain the crystallization mother liquor and filtered. The obtained mixed crystals are mixed with a solvent and filtered to obtain the redissolved filtrate. S2. Add aluminum source, magnesium source and calcium source to the reconstituted filtrate to react, filter the first reaction solution to obtain the second filtrate; S3. Adjust the pH of the second filtrate to 7.5-8.0, add a sulfur-containing compound to react, filter the resulting second reaction solution to obtain the third filtrate; S4. Adjust the pH of the third filtrate to 8.5~9.0 and perform countercurrent extraction with the first organic extractant to collect the first aqueous phase containing tungsten and the first organic phase loaded with molybdenum and vanadium; S5. Adjust the pH of the first aqueous phase to 5.4~5.8, and use the second organic extractant to perform countercurrent extraction on the first aqueous phase to obtain a tungsten-loaded organic phase. Then, use the second alkaline solution to perform countercurrent back-extraction on the tungsten-loaded organic phase to obtain a tungsten-containing back-extraction solution. S6. The first organic phase is countercurrently washed with a first detergent to collect a second aqueous phase containing vanadium and a second organic phase loaded with molybdenum, wherein the first detergent includes a soluble chloride and an alkali metal hydroxide; S7. Adjust the pH of the second aqueous phase to 8.5~9.0 and control the temperature to 20~25℃. Then add ammonium salt, mix and stir to react. After aging and separation, ammonium metavanadate is obtained. S8. The second organic phase is subjected to countercurrent oxidation treatment using an oxidant, and then the second organic phase after countercurrent oxidation treatment is subjected to countercurrent back-extraction using a third alkaline solution to obtain a molybdenum-containing back-extraction solution.

2. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 1, characterized in that, S2 satisfies at least one of the following conditions a to g: a. The aluminum source includes sodium aluminate; b. Calculated according to the molar ratio, the ratio of aluminum element in the aluminum source to silicon element in the redissolved filtrate is (1.5~2.5):1; c. The magnesium source includes magnesium oxide, and the activity of the magnesium oxide is ≥65%; d. Calculated according to the molar ratio, the ratio of magnesium in the magnesium source to arsenic in the redissolved filtrate is (1.1~1.2):1; e. The calcium source is lime milk with a solid content of 18-22%, prepared using water and calcium oxide; f. Calculated according to the molar ratio, the calcium element in the calcium source : the silicon element in the redissolved filtrate = (2.5~3.5) : 1; g. The temperature at which aluminum, magnesium, and calcium sources are added to the reconstituted filtrate for reaction is 90-95°C.

3. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 2, characterized in that, S2 includes the following operations: heating the reconstituted filtrate to 90-95°C, controlling the stirring speed to 80-100 rpm, adding an aluminum source, adjusting the stirring speed to 120-150 rpm, reacting for 40-50 min, adding a magnesium source and stirring for 5-10 min, then adding a calcium source dropwise to the system and reacting at 90-95°C for 1-3 h, then lowering the system temperature to 80-85°C, stopping the stirring and keeping it at that temperature for 1-3 h to obtain a first reaction solution, filtering the first reaction solution to obtain a second filtrate; The calcium source is added over a period of 60 to 90 minutes.

4. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 3, characterized in that: In S3, the sulfur-containing compound includes at least one of sodium sulfide nonahydrate and hydrogen sulfide, and / or, calculated by molar ratio, the sulfur element in the sulfur-containing compound: molybdenum element in the second filtrate = (3.5~4.5):

1.

5. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 1, characterized in that, S3 includes the following operations: heating the second filtrate to 40~50℃, adding acid to adjust the pH to 7.5~8.0, adding a sulfur-containing compound, stirring at 100~150 rpm and keeping at 40~50℃ for 4~6 h to obtain a second reaction solution, filtering the second reaction solution to obtain a third filtrate.

6. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 1, characterized in that: S4 satisfies at least one of the following conditions a to b: a. The first organic extractant comprises 10-30 vol% trioctylmethylammonium chloride, 5-15 vol% sec-octanol and sulfonated kerosene; b. During the countercurrent extraction process, control O / A = 1:(2~4) and the number of extraction stages to be 5~6.

7. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 1, characterized in that, S5 satisfies at least one of the following conditions a to e: a. The second organic extractant comprises 10-30 vol% trioctylmethylammonium chloride, 5-15 vol% sec-octanol and sulfonated kerosene; b. During the countercurrent extraction of the first aqueous phase using the second organic extractant, the O / A ratio is controlled to be 1:(2~4), and the number of extraction stages is 5~6. c. The second alkaline solution comprises 3-5 mol / L sodium hydroxide; d. During the countercurrent back-extraction of the tungsten-loaded organic phase using a second alkaline solution, the O / A ratio is controlled to be (1~2):(1~2), and the number of back-extraction stages is 5~7. e. Before countercurrent back-extraction of the tungsten-loaded organic phase using a second alkaline solution, the process includes countercurrent washing of the tungsten-loaded organic phase using a second detergent, wherein the second detergent comprises 0.3~0.7 wt% sodium chloride, and during the countercurrent washing of the tungsten-loaded organic phase, the O / A ratio is controlled to be (2~3):1, and the number of washing stages is 1~2.

8. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 1, characterized in that, S6 satisfies at least one of the following conditions a to b: a. The first detergent comprises 0.5~1.5 mol / L sodium chloride and 0.5~1.5 mol / L sodium hydroxide; b. During the countercurrent washing of the first organic phase using the first detergent, the O / A ratio is controlled to be (1~2):1, and the number of washing stages is 3~5.

9. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 1, characterized in that, S7 satisfies at least one of the following conditions a to b: a. The ammonium salt includes at least one of ammonium chloride and ammonium bicarbonate; b. The molar ratio of ammonium ions in the ammonium salt to vanadium in the second aqueous phase is (2~4):

1.

10. The method for recovering tungsten, molybdenum, and vanadium from spent SCR denitrification catalyst as described in claim 1, characterized in that: S8 satisfies at least one of the following conditions a to f: a. The oxidant comprises 5-7 wt% hydrogen peroxide; b. Calculated according to the molar ratio, the oxidant : molybdenum element in the second organic phase = (16~18) : 1; c. During the countercurrent oxidation of the second organic phase using an oxidant, the O / A ratio is controlled to be (1~2):1, and the oxidation stage is 2~4. d. The third alkaline solution comprises 3-5 mol / L sodium hydroxide; e. During the countercurrent back-extraction of the second organic phase after countercurrent oxidation treatment with a third alkaline solution, the O / A ratio is controlled to be (1~3):1, and the number of back-extraction stages is 3~5; f. After countercurrent back-extraction of the second organic phase treated by countercurrent oxidation, the process further includes countercurrent elution of the obtained lean organic phase using an eluent, wherein the eluent includes water, and during the countercurrent elution process, the O / A ratio is controlled to be (2~3):1, and the number of elution stages is 2~4.

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