Method for recovering metal molybdenum and tungsten in waste hydrofining catalyst

Abstract

The invention discloses a method for recovering metal molybdenum and tungsten in a waste hydrofining catalyst, which comprises the following three steps: pretreating a hydrogenation catalyst containing molybdenum and tungsten, preparing a leaching solution, and refining and extracting the metal molybdenum and tungsten, and comprises the following steps: sorting the waste catalyst containing molybdenum and tungsten to remove impurities such as porcelain balls and the like; the method comprises the following steps: carrying out ball-milling grinding, sodium modification oxygen-enriched roasting, water leaching, filtering, leaching, refining and the like, carrying out sodium modification roasting on the ground material in an alkaline medium to remove impurities such as deposited carbon, colloid and asphaltene in a catalyst pore channel, and then carrying out water leaching to separate organic matters; finally, efficient separation, extraction and recovery of diamond tungsten in the waste catalyst are achieved in the mode that vanadium is extracted firstly, then molybdenum is extracted and then tungsten is extracted, and an acid method total leaching technology is adopted, the recovery method protected by the invention is simple in technology, little in pollution and high in metal tungsten recovery rate, byproducts of ammonium metavanadate and nickel aluminum powder can be further separated in a gradient mode, and the method is suitable for industrial production. And nickel sulfate and aluminum hydroxide products are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of waste catalyst recycling, and particularly relates to a method for recycling metals molybdenum and tungsten in waste hydrofining catalysts. Background Art

[0002] After crude oil is processed by atmospheric and vacuum distillation for the first time, and then through secondary processing or refining, clean gasoline, diesel, aviation kerosene and other refined oil products that meet the standard requirements are finally obtained, or raw materials such as olefins and aromatics required by chemical plants are provided. As is well known, the development of the refining industry depends on the progress of catalysts. The quality of gasoline and diesel in China from National Standard III to National Standard VI is closely related to the development of catalysts. The development of catalysts not only means the progress of preparation technology, but also will inevitably bring a substantial increase in the quantity and variety of catalysts, and at the same time means the continuous growth of the quantity of waste catalysts. It is estimated that the annual output of waste catalysts in the petrochemical industry in China is about 4 million tons. The metal components in waste catalysts hardly suffer losses, and their grades are much higher than those of ores. They are important secondary resources and have high recycling value.

[0003] In the prior art, refining waste catalysts are mainly generated in the main processing stages such as catalytic cracking, hydrofining, hydrocracking / hydro-upgrading, and catalytic reforming. In recent years, with the development of heavy oil utilization technology, residue hydrotreating units have been continuously built, and the quantity of residue hydrotreating waste catalysts has increased significantly. Different from the long service life (about 6 years) of gasoline and diesel hydrofining catalysts, the catalysts of residue hydrotreating units have the problems of large consumption, short service life (about 1.5 years), and frequent replacement. These several types of catalysts such as catalytic cracking, hydrofining, hydrocracking / hydro-upgrading, catalytic reforming, and residue hydrotreating account for more than 90% of the total amount of refining catalysts. The above-mentioned waste catalysts are all hazardous wastes of category HW50 refined petroleum products manufacturing specified in the National Hazardous Waste List (2021 Edition), and have toxicity (Toxicity, T) that is harmful to the ecological environment and human health. Therefore, enterprises with qualifications are required to complete the transportation, regeneration or recycling of waste catalysts.

[0004] Hydrofining catalysts are mainly applied to devices such as gasoline hydrofining, diesel hydrofining, residue hydrotreating, and aviation kerosene hydrofining in the refining process. Most of them are prepared with oxidized states of molybdenum and nickel as active components and activated alumina as carriers. Before use, the oxidized metal compounds are converted into sulfide states by a sulfiding agent. Waste hydrofining catalysts contain a certain amount of metals such as molybdenum and nickel, and also contain flammable substances such as benzene, polycyclic aromatic hydrocarbons, sulfur, and carbon. The metals are mainly the active components Ni, Mo, Wo, etc. of the catalyst itself, and part of them are the deposition and adsorption of harmful substances in the feedstock oil during the hydrogenation process on the catalyst, such as V, Ni, As, etc. According to the difference in the service life of the catalyst, they are generally divided into two categories, one is a conventional hydrofining catalyst, and the other is a residue hydrotreating catalyst. Summary of the Invention

[0005] The object of the present invention is to provide a method for recovering molybdenum and tungsten metals from spent hydrofining catalysts, which selects a product coupling cascade separation technology for the problems of difficult separation of similar metals such as vanadium, molybdenum and tungsten in multi-metal spent catalysts and low product purity.

[0006] To achieve the above object, the technical solution involved in the present invention is: a method for recovering molybdenum and tungsten metals from spent hydrofining catalysts, characterized in that: The recovery method includes three major steps: pretreatment of molybdenum- and tungsten-containing hydrofining catalysts, preparation of leaching solution, and refined extraction of molybdenum and tungsten metals. The specific steps are as follows: S1: Pretreatment of molybdenum- and tungsten-containing hydrofining catalysts: The spent catalyst is ground, and after grinding, it is subjected to oxygen-enriched roasting treatment to remove moisture, carbon deposits and organic substances in the raw material; the oxygen-enriched roasting treatment is carried out through an oxygen-enriched roasting device, and the reaction temperature of the gas-solid two-phase is regulated to make the material fully contact with oxygen and burn thoroughly, reducing the formation of insoluble tailings in side reactions. After the oxygen-enriched roasting treatment, fine materials are obtained; then, the fine materials after the above oxygen-enriched roasting treatment are dissolved with inorganic salts, and inorganic salts are added for oxygen-enriched inorganic salt medium roasting to convert acid oxides that are insoluble in water into oxygen-containing salts that are soluble in water, which is beneficial to the subsequent leaching of metals; S2: Preparation of leaching solution: Take the material roasted in step S1 above, dilute it with H2O at 40°C to form a slurry, and inorganic salts of vanadium, molybdenum, tungsten and a small amount of aluminum dissolve in water and enter the leaching solution; S3: Refined extraction of molybdenum and tungsten metals: S301: First-stage cascade vanadium precipitation: Add NH4Cl to the leaching solution obtained in S2, stir and let stand to precipitate vanadic acid; S302: Second-stage cascade molybdenum precipitation: Add one of HBr, HCl and H2SO4 to the filtrate from which vanadium is extracted in S301 at 40 - 80°C to adjust the PH value and precipitate molybdic acid; S303: Third-stage cascade tungsten precipitation: Add one of HBr, HCl and H2SO4 to the filtrate from which molybdenum is extracted in S302 at 40 - 80°C to adjust the PH value and precipitate tungstic acid, and further extract to obtain high-purity tungsten element.

[0007] Preferably, the specific steps of the pretreatment of molybdenum- and tungsten-containing hydrofining catalysts are as follows: S101: Grind the clover-columnar multi-metal spent catalyst into particles below 300 mesh; S102: Feed the catalyst ground in the above S101 into an oxygen-enriched roasting furnace wrapped in a NaHCO3 medium. A flame injector is installed at the furnace outlet. The heat source is natural gas, with a flame length of 3 - 8 meters. Roast for 3 - 8 hours, and control the roasting temperature at 500 - 700 °C under normal pressure to remove moisture, carbon deposits, and organic substances in the raw materials. S103: In S102, a small part of the carbon that is not completely roasted forms carbon slag, which forms sediment during the sedimentation process. Preferably, in the oxygen-enriched inorganic salt medium roasting in S1, the inorganic salt added is one or two of NaCO3, K2CO3, and NaHCO3.

[0008] Preferably, the specific steps for the refined extraction of molybdenum and tungsten metals are as follows: First, take the first-stage cascade leaching solution, add the extractant NH4Cl, and the addition ratio is that the ratio of the filtrate to NH4Cl is 5:1. After stirring and standing, vanadium precipitates in the form of ammonium metavanadate, and the acid gas is absorbed by the alkali solution. Second, take the second-stage cascade vanadium precipitation solution, add HBr at 60 °C, and the addition ratio is that the first-stage filtrate:HBr is 3:1. Adjust the pH value to 0.5 - 2, and molybdenum precipitates in the form of molybdic acid, and the acid gas is absorbed by the alkali solution.

[0009] Finally, take the third-stage cascade molybdenum precipitation solution, add HCl at 70 °C, and the addition ratio is that the second-stage filtrate:HCl is 4:1. Adjust the pH value to 0.5 - 2.5, and tungsten precipitates in the form of tungstic acid, and the acid gas is absorbed by the alkali solution.

[0010] The advantages and beneficial effects of the present invention are as follows: The present invention provides a method for recovering molybdenum and tungsten metals in a multi-metal waste hydrogenation catalyst, which is aimed at the characteristics of multi-metal components in the waste catalyst. The "oxygen-enriched mild roasting - enhanced leaching for efficient separation of vanadium and molybdenum and product cascade conversion technology" is selected to recover the total vanadium, molybdenum, and tungsten metals in the waste catalyst, improving the recovery rate and metal purity. Overall, the present invention adopts a process of grinding first and then roasting. During the roasting process, the amount of soot and the loss of metals with soot can be significantly reduced, the consumption of ball mill steel balls and the return material amount can be reduced. At the same time, for the materials that have been thoroughly roasted, metals are extracted. The subsequent gradient leaching solution has a high recovery rate and high purity, providing high-quality new materials for fields such as aviation, aerospace, electronic information, and medical treatment. Specific Embodiments

[0011] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same and similar parts among the embodiments, reference can be made to each other.

[0012] The present invention protects a method for recovering metal molybdenum and tungsten from waste hydrofining catalysts. The recovery method includes three major steps: pretreatment of molybdenum- and tungsten-containing hydrofining catalysts, preparation of leaching solution, and refining and extraction of metal molybdenum and tungsten. In this process, after the waste molybdenum- and tungsten-containing catalysts are sorted to remove impurities such as porcelain balls, they are ground by ball milling, subjected to sodium-rich oxygen roasting, water leaching, filtration, dissolution leaching, refining, etc. The ground material is subjected to sodium-rich roasting in an alkaline medium to remove impurities such as carbon deposits, gums, and asphaltenes in the catalyst pores, and then water leaching is carried out to separate the organic phase. The primary liquid is first subjected to vanadium precipitation with an ammonium salt, filtered under pressure to separate the filtrate and filter residue, and the aluminum residue is recovered for aluminum. The filtrate enters the secondary liquid tank and acid is added for molybdenum precipitation, filtered under pressure to obtain molybdic acid, and the aluminum residue is recovered. The filtrate is then introduced into the tertiary liquid tank and acid is added for tungsten precipitation. Finally, tungstic acid is obtained through ion exchange resin adsorption and desorption.

[0013] In this application, the present invention adopts an acid full-leaching process of first extracting vanadium, then molybdenum, and finally tungsten to achieve efficient separation, extraction, and recovery of diamond tungsten in waste catalysts. The process is simple, has less pollution, a high recovery rate of metal tungsten, and by-products ammonium metavanadate and nickel-aluminum powder can be further separated in a cascade manner to obtain nickel sulfate and aluminum hydroxide products.

[0014] The three major steps involved in the process of the present invention, namely pretreatment of molybdenum- and tungsten-containing hydrofining catalysts, preparation of leaching solution, and refining and extraction of metal molybdenum and tungsten, are specifically as follows: S1: Pretreatment of molybdenum- and tungsten-containing hydrofining catalysts: Grind the waste catalysts, and after grinding, conduct oxygen-rich roasting treatment to remove moisture, carbon deposits, and organic substances in the raw materials; the oxygen-rich roasting treatment is carried out through oxygen-rich roasting equipment, and the reaction temperature of the gas-solid two phases is regulated to enable the material to fully contact with oxygen and burn thoroughly, reducing the formation of insoluble tailings in side reactions; then take the fine material after the above pretreatment and dissolve it with inorganic salts, and conduct oxygen-rich inorganic salt medium roasting by adding inorganic salts. The inorganic salts added are one or two of Na2CO3, K2CO3, and NaHCO3, so that acidic oxides that are insoluble in water are converted into oxygen-containing salts that are soluble in water, facilitating the subsequent leaching of metals; In the waste hydrofining catalysts, molybdenum and tungsten exist as oxidized metals and are insoluble in water. After pretreatment grinding and oxygen-rich roasting, we add Na2CO3 to convert these insoluble oxidized metals into oxygen-containing salts that are soluble in water. That is, during the oxygen-rich roasting process, Na2CO3 reacts with V2O5, MoO3, and WO3 to form sodium vanadate, sodium molybdate, and sodium tungstate salts. The chemical reaction equations are as follows:

[0015] S2: Preparation of leaching solution: Take the material roasted in step S1 above, add H2O at 40 °C to dilute it into a slurry, and inorganic salts of vanadium, molybdenum, tungsten, and a small amount of aluminum dissolve in water and enter the leaching solution; S3: Refined extraction of molybdenum and tungsten metals: S301: First-stage cascade vanadium precipitation: Add NH4Cl to the leaching solution obtained in S2, stir and let stand, and vanadic acid will precipitate out; S302: Second-stage cascade molybdenum precipitation: Add one of HBr, HCl, and H2SO4 to the filtrate from which vanadium is extracted in S301 at 40 - 80 °C, adjust the pH value, and molybdic acid will precipitate out; S303: Third-stage cascade tungsten precipitation: Add one of HBr, HCl, and H2SO4 to the filtrate from which molybdenum is extracted in S302 at 40 - 80 °C, adjust the pH value, and tungstic acid will precipitate out. After further extraction, high-purity tungsten element is obtained. The extraction method is an existing technology. For example, I use solvent extraction method as the extraction method, and tungsten element can be selectively extracted from the aqueous phase through an organic solvent.

[0016] In this application, the specific steps for the pretreatment of the molybdenum-tungsten-containing hydrogenation catalyst are as follows: S101: Grind the clover-columnar multi-metal waste catalyst into particles smaller than 300 mesh; S102: Send the catalyst ground in S101 above into an oxygen-enriched roasting furnace wrapped in a NaHCO3 medium. A flame injector is installed at the furnace outlet, the heat source is natural gas, the flame length is 3 - 8 meters, roast for 3 - 8 hours, and control the roasting temperature at 500 - 700 °C under normal pressure to remove moisture, carbon deposits, and organic substances in the raw materials; S103: In the part where a small amount of carbon in S102 is not completely roasted, carbon slag is formed, and sediment is formed in the sedimentation process.

[0017] In this application, the specific steps for the refined extraction of molybdenum and tungsten metals are as follows: First, take the first-stage cascade leaching solution, add the extractant NH4Cl, and the addition ratio is that the ratio of the filtrate to NH4Cl is 5:1. After stirring and letting stand, vanadium precipitates in the form of ammonium metavanadate, and the acid gas is absorbed by the alkaline solution; Second, take the second-stage cascade vanadium precipitation solution, add HBr at 60 °C, and the addition ratio is that the first-stage filtrate:HBr is 3:1. Adjust the pH value to 0.5 - 2, and molybdenum precipitates in the form of molybdic acid, and the acid gas is absorbed by the alkaline solution.

[0018] Finally, take the third-stage cascade molybdenum precipitation solution, add HCl at 70 °C, and the addition ratio is that the second-stage filtrate:HCl is 4:1. Adjust the pH value to 0.5 - 2.5, and tungsten precipitates in the form of tungstic acid, and the acid gas is absorbed by the alkaline solution.

[0019] In the present application, the pretreatment of the molybdenum-tungsten hydrogenation catalyst includes two major steps: grinding and oxygen-enriched roasting. The oxygen-enriched roasting is to control the gas-solid two-phase reaction temperature through oxygen-enriched roasting equipment, so that the material is fully in contact with oxygen and burns thoroughly, reducing the formation of insoluble tailings from process side reactions, and then roasting in an oxygen-enriched inorganic salt medium, that is, the fine material after oxygen-enriched roasting is dissolved with an inorganic salt, and the inorganic salt can be one or two of Na2CO3, K2CO3 and NaHCO3, so that the acidic oxides that are insoluble in water are converted into oxygen-containing acid salts that are easily soluble in water, which is beneficial to the subsequent leaching of metals.

[0020] In this application, in the process of refining and extracting metal molybdenum and tungsten, one of HBr, HCl and H2SO4 can be used to adjust the pH value, precipitate tungstic acid, and further extract to obtain high-purity tungsten element. The principle of using one of HBr, HCl and H2SO4 to adjust the pH value is as follows, taking HBr as an example: Hydrogen bromide (HBr) is an inorganic compound with the chemical formula HBr. It is miscible with water and can be miscible in ethanol, acetic acid, etc. It is a strong acid with a pungent odor. Hydrogen bromide is mainly used to manufacture various bromine compounds, and can also be used in industries such as medicine, dyes, and fragrances. In the roasting process of the pretreatment of molybdenum-containing tungsten hydrogenation catalyst, the waste catalyst needs to be roasted, and HBr solvent is preferably used to leaching molybdenum. Hydrogen bromide (HBr) and sodium molybdate (Na2MoO4) will undergo an oxidation-reduction reaction under acidic conditions. Hydrogen bromide (HBr) reacts with sodium molybdate (Na2MoO4) to generate molybdic acid, in which hydrogen bromide acts as a reducing agent and the molybdenum (Mo) in sodium molybdate is reduced. The specific reaction equation is as follows:

[0021] Finally, through the above steps, molybdenum metal can be extracted from the waste catalyst. During the extraction process, HBr not only serves as a reaction medium, but also participates in the chemical reaction to generate soluble molybdates, thereby achieving the extraction of molybdenum.

[0022] In the present application, the process of leaching molybdenum (Mo) in the spent catalyst using hydrogen bromide (HBr) and subsequently converting it into molybdic acid (HMo0) involves the following principle: The molybdenum in the spent catalyst usually exists in the form of oxides (such as Mo0) or sulfides. HBr, as a strong acid and reducing agent, dissolves molybdenum through the following reaction: The dissolution chemical equation of Mo03 in an acidic environment is: MoO3+2HBr→MoO2 2+ +2Br - +H2O; if Mo(IV) or MoS2 is present, HBr further reduces and dissolves the chemical equation: MoS2+4HBr →Mo 4+ +2H2S+4Br - , then, Mo 4+It is oxidized to MoO₂ under oxidative conditions (such as air). 2+ . The dissolved molybdenum (existing in the form of MoO₂ 2+ or HMoO₄ - ) is converted into insoluble molybdic acid by adjusting the pH: MoO₂ 2+ + 2H₂O → H₂MoO₄↓ + 2H + or HMoO₄ - + H⁺ → H₂MoO₄↓.

[0023] Example 1: Step 1: Take the above-mentioned cascade leaching solution, add the extractant NH₄Cl, and the addition ratio is that the ratio of the filtrate to NH₄Cl is 5:1. After stirring and standing, vanadium precipitates out as ammonium metavanadate, and the acid gas is absorbed by the alkaline solution.

[0024] Step 2: Take the above-mentioned cascade vanadium precipitation solution, add HCl at 60°C, and the addition ratio of the filtrate to HCl is 3:1. Adjust the pH value to 1.5, and molybdenum precipitates out as molybdic acid.

[0025] Step 3: Take the above-mentioned cascade molybdenum precipitation solution, add H₂SO₄ at 70°C, and the addition ratio of the filtrate to H₂SO₄ is 4:1. Adjust the pH value to 2, and tungsten precipitates out as molybdic acid. After the acid gas is washed with water, it is absorbed by adding NaOH.

[0026] Example 2: Step 1: Take the above-mentioned cascade leaching solution, add the extractant NH₄Cl, and the addition ratio is that the ratio of the filtrate to NH₄Cl is 5:1. After stirring and standing, vanadium precipitates out as ammonium metavanadate, and the acid gas is absorbed by the alkaline solution.

[0027] Step 2: Take the above-mentioned cascade vanadium precipitation solution, add HBr at 60°C, and the addition ratio of the filtrate to HBr is 3:1. Adjust the pH value to 1.2, and molybdenum precipitates out as molybdic acid.

[0028] Step 3: Take the above-mentioned cascade molybdenum precipitation solution, add HCl at 70°C, and the addition ratio of the filtrate to HCl is 4:1. Adjust the pH value to 2, and tungsten precipitates out as molybdic acid. After the acid gas is washed with water, it is absorbed by adding NaOH.

[0029] Example 3: Step 1: Take the above-mentioned cascade leaching solution, add the extractant NH₄Cl, and the addition ratio is that the ratio of the filtrate to NH₄Cl is 5:1. After stirring and standing, vanadium precipitates out as ammonium metavanadate, and the acid gas is absorbed by the alkaline solution.

[0030] Step 2: Take the above-mentioned cascade vanadium precipitation solution, add H₂SO₄ at 60°C, and the addition ratio of the filtrate to H₂SO₄ is 3:1. Adjust the pH value to 1.5, and molybdenum precipitates out as molybdic acid.

[0031] Step 3: Take the above-mentioned stepped molybdenum-precipitating solution, add HBr at 70 °C, and the addition ratio of the filtrate to HBr is 4:1. Adjust the pH value to 2. Tungsten precipitates out as molybdic acid. After the acid gas is washed with water, it is absorbed by adding NaOH.

[0032] The experimental results are shown in the following table:

[0033] In the above three examples, the second example has the best recovery rate and purity of molybdenum and tungsten obtained from the leaching solution.

[0034] In this application, molybdate (MoO4 2- ) and tungstate (WO4 2- ) have similar basic units in chemical structure. However, since molybdenum (Mo) and tungsten (W) belong to the same group (Group 6), both exist in the form of single acid radicals with a tetrahedral structure (XO4 2- , X = Mo / W) under simple conditions. The central atom (Mo 6+ or W 6+ ) coordinates with four oxygen atoms to form a symmetric tetrahedral geometric configuration. This is the same point. However, due to the property differences between them, there are some key differences in their oxygen-containing acid radicals: Molybdate is more likely to form various isopolyacid radicals (such as [Mo7O 24 6- , [Mo8O 26 4- , etc.). Especially in acidic conditions, molybdenum tends to form a polynuclear polymer structure by sharing oxygen atoms. The polymerization tendency of tungstate is stronger. Especially at low pH, it is easy to form complex isopolyacid radicals, and the size and stability of its polymers are usually higher than those of molybdenum. Secondly, in the pH-dependent behavior, molybdate mainly exists as MoO4 2- in neutral or weakly alkaline solutions; polymerization begins when pH < 6, forming polymolybdates. Tungstate remains as WO4 2- monomers in a wider pH range, but rapidly polymerizes into large molecular clusters such as metatungstate under acidic conditions (pH < 4).

[0035] ​​Due to the above differences between the two, the selection of leaching solvents is also different. First, the solvent used for leaching molybdenum is HBr. Using hydrogen bromide (HBr) as a solvent to extract molybdic acid (such as MoO4 or molybdates) from waste catalysts has the following potential advantages: Molybdic acid dissolution: Molybdenum in waste catalysts often exists in the form of oxides (MoO3) or sulfides (MoS2). As a strong acid, HBr can dissolve MoO4 to form soluble molybdenum-oxygen-bromine complexes. At the same time, the reducibility of HBr may contribute to the oxidative dissolution of MoS2. Impurity separation: HBr has low solubility for certain metal impurities (such as Fe, Ni, Al). By adjusting the acid concentration or adding oxidants (such as Br2), molybdenum can be selectively dissolved, reducing co-dissolved impurities and simplifying subsequent purification steps. Low temperature and high efficiency: Compared with traditional alkali fusion (requiring high temperature) or strong oxidizing acids (such as HNO3 + H2SO4), HBr can achieve efficient leaching of molybdenum at a relatively low temperature (such as 80 - 100°C), reducing energy consumption and the risk of equipment corrosion. The solvent used for leaching tungsten is HCl. As a solvent for extracting tungsten from waste catalysts, HCl has the following significant advantages: Hydrochloric acid can effectively dissolve tungsten oxides (such as WO3) or tungstates, and at the same time has selectivity for other metal impurities (such as iron, nickel, etc.) in the waste catalyst, reducing co-dissolution and simplifying subsequent purification steps. Hydrochloric acid is a commonly used strong acid in industry, with low price and stable supply, suitable for large-scale treatment of waste catalysts, and its economy is superior to special solvents such as hydrofluoric acid. High-efficiency leaching of tungsten can be achieved under normal pressure or moderate heating (60 - 90°C), without the need for high-temperature and high-pressure equipment, reducing energy consumption and equipment requirements. The dissolved tungsten (such as H2WO4 or WO4 2- ) can be directly precipitated as tungstic acid (H2WO4) by adjusting the pH, or further purified by ion exchange / solvent extraction, and the process connection is smooth.

[0036] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for recovering molybdenum and tungsten metals from waste hydrofining catalysts, characterized in that: The recovery method includes three major steps: pretreatment of molybdenum- and tungsten-containing hydrofining catalysts, preparation of leaching solution, and refined extraction of molybdenum and tungsten metals. The specific steps are as follows: S1: Pretreatment of molybdenum- and tungsten-containing hydrofining catalysts: The waste catalyst is ground, and after grinding, it is subjected to oxygen-enriched roasting treatment to remove moisture, carbon deposits, and organic substances in the raw material; the oxygen-enriched roasting treatment is carried out through oxygen-enriched roasting equipment, and the gas-solid two-phase reaction temperature is regulated to make the material fully contact with oxygen and burn thoroughly, reducing the formation of insoluble tailings in side reactions. After the oxygen-enriched roasting treatment, fine materials are obtained; then, the above-mentioned fine materials after oxygen-enriched roasting treatment are dissolved with inorganic salts, and inorganic salts are added for oxygen-enriched inorganic salt medium roasting to convert acid oxides insoluble in water into oxygen-containing salts soluble in water, which is beneficial to the subsequent leaching of metals; S2: Preparation of leaching solution: Take the material roasted in step S1 above, dilute it with H2O at 40°C to form a slurry, and vanadium, molybdenum, tungsten inorganic salts, and a small amount of aluminum dissolve in water and enter the leaching solution; S3: Refined extraction of molybdenum and tungsten metals: S301: First-stage stepwise vanadium precipitation: Add NH4Cl to the leaching solution obtained in S2, stir and let stand to precipitate vanadic acid; S302: Second-stage stepwise molybdenum precipitation: Add one of HBr, HCl, and H2SO4 to the filtrate from which vanadium is extracted in S301 at 40 - 80°C to adjust the PH value and precipitate molybdic acid; S303: Third-stage stepwise tungsten precipitation: Add one of HBr, HCl, and H2SO4 to the filtrate from which molybdenum is extracted in S302 at 40 - 80°C to adjust the PH value and precipitate tungstic acid, and high-purity tungsten elements are obtained after further extraction; 2. The method for recovering molybdenum and tungsten metals from waste hydrofining catalysts according to claim 1, characterized in that: The specific steps of the pretreatment of molybdenum- and tungsten-containing hydrofining catalysts are as follows: S101: Grind the clover-columnar multi-metal waste catalyst into particles below 300 meshes; S102: Send the catalyst ground in S101 above into an oxygen-enriched roasting furnace wrapped in a NaHCO3 medium. A flame injector is installed at the furnace outlet, the heat source is natural gas, the flame length is 3 - 8 meters, roast for 3 - 8 hours, and control the roasting temperature at 500 - 700°C under normal pressure to remove moisture, carbon deposits, and organic substances in the raw material; S103: In S102, a small amount of carbon that is not completely roasted forms carbon slag, which forms sediment in the sedimentation process.

3. The method for recovering molybdenum and tungsten metals from waste hydrofining catalysts according to claim 1, characterized in that: In the oxygen-enriched inorganic salt medium roasting in S1, the added inorganic salt is one or two of Na2CO3, K2CO3, and NaHCO3.

4. The method for recovering molybdenum and tungsten metals from waste hydrofining catalysts according to claim 1, characterized in that: The specific steps of the refined extraction of molybdenum and tungsten metals are as follows: First, take the first-stage stepwise leaching solution, add the extractant NH4Cl, and the addition ratio is that the ratio of the filtrate to NH4Cl is 5:

1. After stirring and standing, vanadium precipitates in the form of ammonium metavanadate, and the acid gas is absorbed by an alkaline solution; Secondly, take the secondary cascade vanadium precipitation solution, add HBr at 60 °C, and the addition ratio is primary filtrate:HBr = 3:

1. Adjust the pH value to 0.5 - 2, and molybdenum precipitates in the form of molybdic acid, and the acid gas is absorbed by the alkaline solution.

5. Finally, take the tertiary cascade molybdenum precipitation solution, add HCl at 70 °C, and the addition ratio is secondary filtrate:HCl = 4:

1. Adjust the pH value to 0.5 - 2.5, and tungsten precipitates in the form of molybdic acid, and the acid gas is absorbed by the alkaline solution.

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