A method for preparing high-purity ammonium molybdate from waste metal molybdenum products

Abstract

This application relates to a method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate, belonging to the field of non-ferrous metal secondary resource recycling and hydrometallurgical technology. The method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate includes the following steps: 1. Cleaning and degreasing the molybdenum waste to expose the molybdenum matrix; 2. First, electrochemically decomposing the molybdenum waste, then filtering the molybdenum-containing electrolyte obtained from the electrochemical decomposition step to remove impurities, evaporating and concentrating the purified ammonium molybdate solution until crystallization, stopping evaporation and cooling when the crystallization rate reaches 70%, separating the solid and liquid, and drying to obtain the ammonium molybdate product; 3. Tail gas absorption. This method is applicable to the extraction of molybdenum from waste molybdenum products, with a short process, high degree of process control, high product purity and stable quality, high molybdenum metal recovery rate, low auxiliary material consumption, and no wastewater generation, exhibiting significant environmental advantages and low cost.

Description

Technical Field

[0001] This application relates to the fields of secondary resource recycling and hydrometallurgical technology of non-ferrous metals, and in particular to a method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate. Background Technology

[0002] Molybdenum is an important strategic metal with wide applications in metallurgy, electronics, aerospace, and other fields. Waste molybdenum materials such as scrap molybdenum wire used in heating elements, wire-cut molybdenum wire from electrical discharge machining, used residual molybdenum electrodes, molybdenum mandrels, molybdenum wafers, and sputtering residue are all readily recyclable secondary resources of molybdenum. They share a common characteristic: they are all high-purity molybdenum metal, typically containing over 95% molybdenum, giving them extremely high recycling value.

[0003] Currently, the main technical routes for recovering molybdenum from waste molybdenum products include chemical leaching and roasting (alkali leaching). Chemical leaching typically uses strong acid systems such as nitric acid, aqua regia, or concentrated sulfuric acid to dissolve metallic molybdenum. However, these strong acid systems present problems such as severe equipment corrosion, difficulty in waste acid treatment, and environmental pollution from acid mist. Roasting (alkali leaching) requires oxidizing and roasting the waste molybdenum products at high temperatures, resulting in high energy consumption and the generation of large amounts of smoke and dust. In recent years, chemical leaching methods using ionic liquid media in conjunction with ammonia and hydrogen peroxide have also been reported, but these processes are complex and require expensive ionic liquids, hindering industrial-scale application.

[0004] In the electrochemical dissolution of metallic molybdenum, existing technologies mainly focus on the selective dissolution of molybdenum-copper alloy waste in NaOH-NaCl electrolytes, and the separation and recovery of molybdenum from nickel-based superalloy electrochemical dissolution solutions. Regarding the purification and impurity removal of ammonium molybdate, chelating resins have been applied to remove impurity metal ions from ammonium molybdate solutions, capable of removing ppm-level impurity metal ions. However, no reports have been published on a complete technical route from waste molybdenum wire / crucible to high-purity ammonium molybdate products, organically integrating the electrochemical dissolution of waste metallic molybdenum parts with a deep impurity removal process using chelating resins.

[0005] Domestic and international scientists have conducted extensive research on the recovery of Mo from molybdenum waste. The main technological methods include pyrometallurgical processes, hydrometallurgical processes, and combined pyrometallurgical and hydrometallurgical processes. Pyrometallurgical processes have long reaction times, incomplete oxidation, and low recovery rates; hydrometallurgical processes have low unit production capacity, easily generate waste liquid and waste gas, have high energy consumption, and also have low recovery rates; combined pyrometallurgical and hydrometallurgical processes have long process flows, easily generate waste liquid and waste gas, and have relatively high energy consumption.

[0006] Chinese Patent Publication No. CN115446322A discloses a method for recycling waste molybdenum targets to prepare molybdenum powder. This method includes the following steps: electrochemically dissolving the waste molybdenum targets in a sodium hydroxide solution to obtain a mixed solution A; adding an aqueous polyacrylamide solution to mixed solution A for coagulation, followed by filtration to obtain solution B; adsorbing solution B using a cation exchange resin to obtain filtrate C; adding ammonium chloride to filtrate C, heating to concentrate and crystallize to obtain crystal D; and finally reducing crystal D with hydrogen to obtain molybdenum powder. The molybdenum content in the waste molybdenum targets is above 80%, and sodium hydroxide solution is the preferred electrolyte system. This method combines electrochemical dissolution with cation exchange resin adsorption to achieve the recycling of waste molybdenum targets and the final preparation of molybdenum powder. Chinese Patent Publication No. CN112939080A discloses a method for preparing high-purity ammonium molybdate using an exchange resin. This method involves a pretreatment step of obtaining an ammonium molybdate solution through chemical leaching, followed by filtration and chelation resin exchange of the ammonium molybdate solution. The main steps include: filtering the ammonium molybdate solution; passing the treated ammonium molybdate solution through a resin exchange device containing chelating resin; and removing various impurities such as metal ions from the outlet of the resin exchange device. The initial step of this method is chemical leaching, while electrochemical dissolution is the key differentiating feature of this invention. A published article in *China Molybdenum Industry* (2011, No. 03) describes a method for purifying ammonium molybdate solution using ion exchange resin. The JC-1 chelating resin used effectively purifies impurity metal ions in the ammonium molybdate solution, resulting in a divalent metal ion content of approximately less than 1 mg / kg after purification. Simultaneously, the purity of the prepared tetramolybdate is improved, and the crystal morphology remains unchanged compared to ordinary ammonium molybdate. This method provides a technical reference for the subsequent purification of ammonium molybdate solutions prepared by chemical methods, but it does not involve the integrated process of electrochemical dissolution and chelating resin impurity removal.

[0007] In summary, the existing technologies mainly have the following problems: (1) Pyrometallurgical processes have long reaction times, insufficient oxidation, low recovery rates, high energy consumption, and serious dust pollution. (2) Hydrometallurgical processes (such as strong acid leaching and ammonia + hydrogen peroxide chemical leaching) have low unit production capacity, strong acid corrosivity, large equipment wear, difficult waste acid treatment, acid mist pollution, safety hazards in the storage and use of strong oxidants such as hydrogen peroxide, complex process flow, and are not conducive to continuous industrial production. (3) The pyrometallurgical-hydrometallurgical combined process is lengthy, generates a large amount of wastewater and waste gas, and has high energy consumption. (4) In terms of electrochemical dissolution, the existing technologies mainly focus on the selective dissolution of molybdenum-copper alloy waste in NaOH-NaCl electrolyte and the separation and recovery of molybdenum and rhenium in the electrochemical dissolution solution of nickel-based high-temperature alloys. However, there is little research on the electrochemical dissolution of pure metal molybdenum waste such as high-purity molybdenum crucibles and molybdenum wires, and there is a lack of effective integration with the deep impurity removal process of chelating resin. The electrochemical dissolution system used in the Chinese patent with publication number CN115446322A is sodium hydroxide solution, which is fundamentally different from the ammonia system used in this application, and the final product targets are also different (molybdenum powder vs. high-purity ammonium molybdate). (5) There is no systematic solution to how existing electrochemical dissolution technology can effectively suppress anodic passivation under the condition of high concentration of ammonium molybdate, and how to efficiently remove impurities from the solution after dissolution to meet the requirements of high-purity ammonium molybdate products. Summary of the Invention

[0008] In view of this, this application provides a method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate. This application uses electrolysis to oxidize and dissolve molybdenum in the waste molybdenum products to obtain an ammonium molybdate solution. After ion exchange to remove impurities, the solution is concentrated and crystallized to form pure ammonium molybdate crystalline solid. This method is suitable for the extraction of molybdenum from waste molybdenum products. The process is simple, the production process is highly controlled, the product has high purity and stable quality, the molybdenum metal recovery rate is high, the auxiliary material consumption is low, and no wastewater is generated. It has obvious environmental advantages and low cost, and can effectively overcome the defects of the above-mentioned existing technology, such as strong corrosiveness, large environmental pollution, and difficulty in meeting the requirements of high-purity products by chemical dissolution method.

[0009] This application provides a method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate, comprising the following steps:

[0010] 1. Alkali washing of waste molybdenum metal: The waste molybdenum is cleaned and degreased to expose the molybdenum metal matrix;

[0011] II. Decomposition of Pure Molybdenum Waste and Product Preparation: First, the molybdenum waste is electrochemically decomposed. Then, the molybdenum-containing electrolyte obtained from the electrochemical decomposition step is filtered to remove impurities. The purified ammonium molybdate solution obtained after impurity removal is evaporated and concentrated until crystallization. When the crystallization rate reaches 70%, evaporation is stopped, cooling is performed, solid-liquid separation is carried out, and drying is carried out to obtain the ammonium molybdate product.

[0012] 3. Tail gas absorption: The tail gas generated by electrochemical decomposition is connected to a two-stage absorption tank containing deionized water through an exhaust pipe. When the pH in the first-stage tank is greater than 9, the absorbent in the absorption tank is returned to the circulation tank to be used as a supplementary electrolyte. The second-stage solution is transferred to the first stage, and then fresh deionized water is added to the second stage.

[0013] Preferably, in step one, the specific process of cleaning and degreasing is as follows: alkaline washing water is injected into the cleaning tank, the basket containing molybdenum waste is placed in the cleaning tank, compressed air is introduced into the cleaning tank for cleaning for 10-30 minutes, and then the basket is placed in two-stage deionized water tanks for cleaning, compressed air is introduced into each tank for 1-3 minutes. After the two-stage deionized water cleaning is completed, the basket discharge valve is opened to fill the molybdenum waste into the electrolytic cell.

[0014] Preferably, the alkaline washing water is prepared by diluting industrial-grade NaOH with deionized water to a mass concentration of 1-5%.

[0015] Preferably, in step two, the specific process of electrochemical decomposition is as follows: the cleaned molybdenum waste is used as the anode of the electrolytic cell, a stainless steel plate is used as the cathode, and a mixed solution of ammonium molybdate solution containing 15~30 g / L of molybdenum and ammonia water containing 30~180 g / L is used as the electrolyte. A DC power supply is connected to carry out electrochemical dissolution. During the electrolysis process, metallic molybdenum is oxidized and dissolved at the anode to generate ammonium molybdate, which enters the electrolyte. The concentration of molybdenum ions in the electrolyte gradually increases. When the concentration of molybdenum ions in the electrolyte reaches ≥60 g / L, the electrolyte is extracted and sent to the subsequent impurity removal process, and fresh electrolyte is added to maintain the reaction.

[0016] Preferably, the specific conditions for the electrochemical dissolution are: an electrochemical dissolution temperature of 40~80℃, a pH value controlled at 9.0~11.0, and a current density controlled at 800~1500 A / m. 2 .

[0017] Preferably, in step two, the specific process of filtration is as follows: the filtrate flows sequentially through a chelating resin exchange device, so that the impurity metal ions in the solution are selectively adsorbed by the resin, and the effluent is a purified ammonium molybdate solution.

[0018] Preferably, the chelating resin is an aminocarboxylic acid or aminophosphonic acid chelating resin.

[0019] Preferably, the chelating resin is MTS9300 or D860.

[0020] Preferably, the specific adsorption conditions are as follows: the adsorption conditions are a temperature ≤70℃, a flow rate of 5~20 BV / h, and the Ca concentration is monitored by taking an instantaneous post-exchange liquid sample every hour. When the Ca concentration in the post-exchange liquid is >0.5mg / l, the adsorption is stopped. The resin is washed with deionized water until the column contains trace amounts of molybdenum. The resin is then desorbed with 5~10% hydrochloric acid. After desorption, the resin is washed with water and a new round of adsorption can be performed.

[0021] Preferably, the desorption control flow rate is 5~20 BV / h.

[0022] Compared with the prior art, this application has the following advantages:

[0023] (1) This application replaces the traditional strong acid chemical dissolution method with an electrochemical method, which eliminates the need for strong oxidants, avoids strong acid corrosion and acid mist pollution, and significantly improves production safety.

[0024] (2) The electrolyte can be recycled and supplemented with ammonia water, so almost no wastewater is generated, which is in line with the green and environmentally friendly development direction of metallurgy.

[0025] (3) The current density and voltage can be precisely adjusted, and the reaction rate can be flexibly controlled to meet the needs of different scales of waste molybdenum raw material processing.

[0026] (4) The process is highly continuous, which is suitable for large-scale continuous industrial production and solves the limitation of traditional chemical leaching methods that can only be operated in batches.

[0027] (5) The product can directly meet the national standard MSA-0 high-purity ammonium molybdate index requirements, realizing the high-value recycling and utilization of waste molybdenum. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a schematic flowchart of the method for preparing high-purity ammonium molybdate from the recovery of molybdenum from waste molybdenum products according to this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] Unless otherwise specified, the experimental methods used in the embodiments of this application are all conventional methods.

[0032] In the following examples, unless otherwise specified, all raw materials can be obtained by commercial purchase or conventional methods.

[0033] like Figure 1 As shown in the embodiments of this application, a method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate is provided, comprising the following steps:

[0034] I. Alkaline washing of waste molybdenum metal

[0035] Waste molybdenum crucibles or waste molybdenum wires are cleaned and degreased to expose the metallic molybdenum matrix.

[0036] Specifically, NaOH (Sichuan Jinlu Resin, meeting the national standard GB / T 209-2018 industrial grade, liquid alkali NaOH mass fraction: 30%) is diluted with deionized water to an alkaline washing water concentration of 1~5%. A certain volume of alkaline washing water is injected into the cleaning tank, and the basket of molybdenum waste is placed in the cleaning tank. Compressed air is introduced into the cleaning tank for cleaning for 10~30 minutes. Then, the basket is placed in two stages of deionized water tanks for cleaning, and compressed air is introduced into each tank for 1~3 minutes. After the two stages of deionized water cleaning are completed, the basket discharge valve is opened to fill the waste into the electrolytic cell.

[0037] II. Decomposition of Pure Molybdenum Waste and Product Preparation

[0038] (a) Electrochemical decomposition of pure molybdenum waste:

[0039] The cleaned waste molybdenum products were used as the anode of the electrolytic cell, with a stainless steel plate as the cathode. The electrolyte was a mixture of ammonium molybdate solution (containing 15-30 g / L molybdate) and ammonia solution (containing 30-180 g / L ammonia). (The pre-added ammonium molybdate formed a suitable oxide film on the anode surface, effectively inhibiting the passivation of pure molybdenum in the alkaline electrolyte, allowing for long-term, continuous, and stable electrochemical dissolution). A DC power supply was used for electrochemical dissolution. The electrolyte temperature was 40-80℃, the pH was controlled at 9.0-11.0, and the current density was controlled at 800-1500 A / m. 2During electrolysis, metallic molybdenum undergoes oxidation and dissolution at the anode, generating ammonium molybdate which enters the electrolyte, gradually increasing the concentration of molybdenum ions in the electrolyte. When the molybdenum ion concentration in the electrolyte reaches ≥60 g / L, the electrolyte is extracted and sent to the subsequent impurity removal process, and fresh electrolyte is added to maintain the reaction. The fresh electrolyte is composed of a mixture of concentrated ammonia, ammonium molybdate crystallization mother liquor, and deionized water.

[0040] The reaction at the anode during electrolysis is as follows:

[0041] Mo + 8OH - -6e=MoO4 2- +4H2O;

[0042] The reaction at the cathode during electrolysis is as follows:

[0043] 6H₂O + 6e = 3H₂↑ + 6OH⁻ - .

[0044] (II) Purification of ammonium molybdate solution and preparation of ammonium molybdate products:

[0045] The molybdenum-containing electrolyte obtained from the electrochemical decomposition step is filtered. The filtrate flows sequentially through a chelating resin exchange unit, where impurity metal ions such as Fe, Cu, Ca, Mg, Si, Ti, Ta, Ni, and Cr are selectively adsorbed by the resin. The effluent is a purified ammonium molybdate solution. (The molybdenum-containing solution obtained from the electrochemical dissolution is directly introduced into the chelating resin purification unit (without prior ammonia removal or pH adjustment), utilizing the chelating resin to adsorb Fe...) 3+ Cu 2+ Ca 2+ The chelating resin exhibits strong adsorption of metal cations but almost no adsorption of molybdate anions, achieving highly efficient separation with "impurity removal without molybdenum loss." The purified impurity content is all <0.1 mg / L, laying the foundation for the preparation of MSA-0 grade products. The chelating resin is an aminocarboxylic acid or aminophosphonic acid chelating resin, and the adsorption conditions are: temperature ≤70℃, flow rate 5~20 BV / h. Ca concentration is monitored by taking samples of the post-exchange solution every hour. Adsorption is stopped when the Ca concentration in the post-exchange solution is >0.5 mg / L. The resin is washed with deionized water until the column effluent contains trace amounts of molybdenum. Desorption is then performed using 5~10% hydrochloric acid at a controlled flow rate of 5~20 BV / h. After desorption, the resin is washed with water and ready for a new round of adsorption. The molybdenum concentration in the post-adsorption solution remains almost unchanged. The impurities such as Fe, Cu, Ca, Mg, Si, Ti, Ta, Ni, and Cr in the ammonium molybdate solution flowing out after adsorption are less than 0.1 mg / L. This solution can be used to prepare pure ammonium molybdate with a molybdenum metal recovery rate of over 99%.

[0046] Unlike conventional anion exchange resins (such as 201×7) used for impurity removal and transformation, this application employs chelating resins (such as MTS9300 and D860) which exhibit extremely high selectivity. These resins are effective for Cu... 2+ Fe 3+ Ca 2+ It has a strong chelating ability for metal cations, while it is more effective at chelating MoO4. 2- Molybdenum in its anionic form hardly adsorbs. Therefore, this step can efficiently remove other metallic impurities that enter the solution during the electrochemical dissolution process, while all molybdenum remains in the solution, achieving the ideal separation effect of "impurity removal without molybdenum loss," which is key to obtaining high-purity ammonium molybdate.

[0047] The purified ammonium molybdate solution obtained from the impurity removal step is evaporated and concentrated until crystallization. When the crystallization rate reaches 70%, evaporation is stopped, cooling is performed, solid-liquid separation is carried out, and drying is carried out to obtain ammonium dimolybdate (ADM) product that meets the requirements of MSA-0 grade in GB / T 3460-2017 standard. The mother liquor separated by centrifugation is returned to the electrolysis step to replenish the electrolyte.

[0048] III. Exhaust Gas Absorption

[0049] The tail gas generated by electrolysis is introduced into a two-stage absorption tank containing deionized water through an exhaust pipe. When the pH in the first-stage tank is greater than 9, the absorbent in the absorption tank is returned to the circulation tank to be used as a supplementary electrolyte. The second-stage solution is transferred to the first stage, and then fresh deionized water is added to the second stage.

[0050] Example 1:

[0051] 30% industrial-grade NaOH was diluted with deionized water to a mass concentration of 3% and then injected into the cleaning tank. The basket containing pure molybdenum waste (molybdenum content > 99%) was placed in the cleaning tank, and compressed air was introduced into the cleaning tank for 10 minutes. Then, the basket was placed in two stages of deionized water tanks for cleaning, and compressed air was introduced into each tank for 1 minute. After the two stages of deionized water cleaning were completed, the basket discharge valve was opened to fill the waste into the electrolytic cell.

[0052] An electrolyte containing 18.54 g / L molybdenum and approximately 170 g / L ammonia, with a volume of approximately 20 L, was prepared. Molybdenum was added in the form of ammonium molybdate, and ammonia was added in the form of concentrated ammonia solution. The electrolyte was injected into the electrolytic circulation tank, the circulation pump was started, and the electrolytic tank voltage was set to 9.0 V, and the current density to 800 A / m³. 2Set the current and connect the power supply to the electrolytic cell. During electrolysis, maintain the temperature between 40 and 80°C and the pH between 10 and 11 (add concentrated ammonia as needed). Electrolysis continues for 85 hours. When the molybdenum concentration reaches 75.6 g / L, extract a portion of the electrolyte and send it to the impurity removal process, while replenishing with fresh electrolyte to maintain the reaction. After electrolysis, the weight of the residual molybdenum wire at the anode is 1061.8 g, with a total dissolved molybdenum content of 518.2 g, and an average dissolution rate of 6.10 g / h. The anode current efficiency, calculated according to Faraday's law, has an average value of 75%–85%.

[0053] The molybdenum-containing electrolyte obtained from the electrolysis step was filtered, and the filtrate was sequentially passed through a chelating resin exchange device. D860 resin was selected as the chelating resin, and the adsorption conditions were: temperature ≤70℃ and flow rate 5 BV / h. Adsorption was stopped when the Ca concentration in the exchanged solution was >0.5 mg / L. After treatment with the chelating resin, the Ca concentration in the solution decreased from 3.3 mg / L to 0.1 mg / L, Mg from 2.14 mg / L to 0.06 mg / L, and Ti from 5.0 mg / L to <0.1 mg / L. The molybdenum recovery rate reached 99.3%.

[0054] The purified liquid was evaporated and concentrated until crystallization occurred. Evaporation was stopped when the crystallization rate reached 70%, and the liquid was allowed to cool naturally. After solid-liquid separation, the liquid was dried to obtain a white crystalline powder product. Testing showed that the product fully met all the technical requirements of MSA-0 grade (ammonium dimolybdate, ADM) in GB / T 3460-2017 standard: MoO3 content 82.1%; W content 0.001%; ​​and the content of all impurity elements met the standards for MSA-0 grade (ammonium dimolybdate, ADM) in GB / T 3460-2017 standard. The molybdenum recovery rate throughout the process reached 99.3%.

[0055] Example 2:

[0056] Industrial-grade NaOH (wt: 30%) was diluted with deionized water to a mass concentration of 2% and then injected into the cleaning tank. A basket containing pure molybdenum waste (molybdenum content > 99%, waste molybdenum crucible fragments, approximately 1600g) was placed in the cleaning tank. Compressed air was introduced into the cleaning tank for 20 minutes. The basket was then placed in two stages of deionized water tanks for cleaning, with compressed air introduced for 2 minutes in each stage. After the two stages of deionized water cleaning were completed, the basket discharge valve was opened to fill the waste into the electrolytic cell.

[0057] An electrolyte containing 30 g / L molybdenum and approximately 100 g / L ammonia was injected into the electrolytic circulation tank. The circulation pump was started, and the electrolytic tank voltage was set to 9.0 V, the current density to 1000 A / m², and the power supply to the electrolytic tank was turned on. The temperature was controlled at 50-60℃ during electrolysis. When the molybdenum concentration in the electrolyte reached 94.2 g / L, a portion of the electrolyte was extracted and sent to the impurity removal process, and fresh electrolyte was added to maintain the reaction. The total electrolysis time was 72 hours. After electrolysis, the mass of residual molybdenum waste at the anode was 726.4 g, and a total of 873.6 g of metallic molybdenum was dissolved, with an average dissolution rate of 12.13 g / h. The anode current efficiency was calculated according to Faraday's law, with an average value of 76-86%.

[0058] The molybdenum-containing electrolyte obtained from the electrolysis step was filtered, and the filtrate was sequentially passed through a chelating resin exchange device. MTS9300 resin was selected as the chelating resin, and the adsorption conditions were: temperature ≤70℃ and flow rate 10 BV / h. Adsorption was stopped when the Ca concentration in the exchanged solution was >0.5 mg / L. After treatment with the chelating resin, the Ca concentration in the solution decreased from 3.1 mg / L to 0.1 mg / L, Mg from 2.8 mg / L to 0.1 mg / L, and Ti from 4.6 mg / L to <0.1 mg / L.

[0059] The purified liquid was evaporated and concentrated until crystallization occurred. Evaporation was stopped when the crystallization rate reached 70%, and the liquid was allowed to cool naturally. After solid-liquid separation, the liquid was dried to obtain a white crystalline powder product. Testing showed that the product fully met all quality requirements of MSA-0 grade (ammonium dimolybdate, ADM) in GB / T 3460-2017 standard. The overall molybdenum recovery rate reached 99.4%.

[0060] Example 3:

[0061] Industrial-grade NaOH (wt: 30%) was diluted with deionized water to a mass concentration of 5% and then injected into the cleaning tank. A basket containing pure molybdenum waste (molybdenum content > 99%) was placed in the cleaning tank, and compressed air was introduced into the cleaning tank for 30 minutes. The basket was then placed in two stages of deionized water tanks for cleaning, and compressed air was introduced into each tank for 3 minutes. After the two stages of deionized water cleaning were completed, the basket discharge valve was opened to fill the waste into the electrolytic cell.

[0062] An electrolyte containing 25 g / L molybdenum and approximately 140 g / L ammonia was injected into the electrolytic circulation tank. The circulation pump was started, and the electrolytic tank voltage was set to 9.0 V, the current density to 1200 A / m², and the power supply to the electrolytic tank was turned on. During electrolysis, when the molybdenum concentration in the electrolyte reached 79.8 g / L, a portion of the electrolyte was extracted and sent to the impurity removal process, and fresh electrolyte was added to maintain the reaction. The total electrolysis time was 64 hours. After electrolysis, the mass of residual molybdenum waste at the anode was 612.2 g, and a total of 987.8 g of metallic molybdenum was dissolved, with an average dissolution rate of 15.43 g / h. The anode current efficiency was calculated according to Faraday's law, with an average value of 77-87%.

[0063] The molybdenum-containing electrolyte obtained from the electrolysis step was filtered, and the filtrate was sequentially passed through a chelating resin exchange device. MTS9300 resin was selected as the chelating resin, and the adsorption conditions were: temperature ≤70℃ and flow rate 10 BV / h. Adsorption was stopped when the Ca concentration in the exchanged solution was >0.5 mg / L. After treatment with the chelating resin, the Ca concentration in the solution decreased from 2.8 mg / L to 0.1 mg / L, Mg from 1.8 mg / L to 0.2 mg / L, and Ti from 4.5 mg / L to <0.1 mg / L.

[0064] The purified liquid was evaporated and concentrated until crystallization occurred. Evaporation was stopped when the crystallization rate reached approximately 70%, and the liquid was allowed to cool naturally. After solid-liquid separation, the liquid was dried to obtain a white crystalline powder product. Testing showed that the product fully met all the technical requirements of MSA-0 grade (ammonium dimolybdate, ADM) in GB / T 3460-2017 standard. The overall molybdenum recovery rate reached 99.2%.

[0065] Test case

[0066] 20 L of electrolyte was collected, with a molybdenum concentration of 94.2 g / L and an ammonia concentration of 30.78 g / L. After filtration to remove suspended solids, the electrolyte was passed through an exchange column packed with aminocarboxylic acid chelating resin (resin volume 2 L) at a flow rate of 10 BV / h. After adsorption by the chelating resin, the concentration of the main impurity metal ions in the solution was significantly reduced. The specific purification effect of Example 2 is shown in Table 1.

[0067] Table 1

[0068]

[0069] Table 1 shows the liquid phase composition data of the electrolyte before and after purification with chelating resin:

[0070] 1) The molybdenum concentration decreased from 94.2 g / L to 93.62 g / L, with extremely low molybdenum loss; the molybdenum retention rate was approximately 99.38% (93.62 ÷ 94.2). The ammonia concentration remained essentially unchanged. This demonstrates that the aminocarboxylic acid chelating resin in this application effectively chelates molybdate anions (MoO4). 2-It adsorbs almost nothing, achieving the core effect of removing impurities without losing molybdenum.

[0071] 2) Impurities such as Ti, Ca, and Mg were significantly removed. Ti decreased from 5.0 mg / L to <0.1 mg / L, Ca decreased from 3 mg / L to 0.2 mg / L, and Mg decreased from 2 mg / L to 0.1 mg / L. Silicon was removed to some extent, but the removal was limited.

[0072] 3) Under the conditions of high molybdenum and ammonia-containing alkaline electrolyte in this system, the chelating resin can selectively adsorb cationic metal impurities and is suitable for electrochemically dissolved ammonium molybdate electrolyte. It does not require pre-adjustment of pH or removal of ammonia and can be directly fed for impurity removal.

[0073] The product underwent full testing according to GB / T 3460-2017 standard. The results of Example 2 are shown in Table 2.

[0074] Table 2

[0075]

[0076] Table 2 shows the full test results of the ammonium dimolybdate product obtained after purification, concentration and crystallization according to GB / T 3460-2017. This proves that the entire process of "electrochemical dissolution + chelating resin deep impurity removal + evaporation crystallization" in this application can directly produce high-purity ammonium dimolybdate product of national standard MSA-0 grade. This proves that the entire process route is complete and feasible, and can realize high-value recycling of waste molybdenum products.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate, characterized in that, Includes the following steps:

1. Alkaline washing of waste molybdenum metal: The waste molybdenum is cleaned and degreased to expose the molybdenum metal matrix; II. Decomposition of Pure Molybdenum Waste and Product Preparation: First, the molybdenum waste is electrochemically decomposed. Then, the molybdenum-containing electrolyte obtained from the electrochemical decomposition step is filtered to remove impurities. The purified ammonium molybdate solution obtained after impurity removal is evaporated and concentrated until crystallization. When the crystallization rate reaches 70%, evaporation is stopped, cooling is performed, solid-liquid separation is carried out, and drying is carried out to obtain the ammonium molybdate product.

3. Tail gas absorption: The tail gas generated by electrochemical decomposition is connected to a two-stage absorption tank containing deionized water through an exhaust pipe. When the pH in the first-stage tank is greater than 9, the absorbent in the absorption tank is returned to the circulation tank to be used as a supplementary electrolyte. The second-stage solution is transferred to the first stage, and then fresh deionized water is added to the second stage.

2. The method for preparing high-purity ammonium molybdate from waste molybdenum products according to claim 1, characterized in that, In step one, the specific process of cleaning and degreasing is as follows: alkaline washing water is injected into the cleaning tank, the basket containing molybdenum waste is placed in the cleaning tank, compressed air is introduced into the cleaning tank for 10-30 minutes, and then the basket is placed in two-stage deionized water tanks for cleaning, compressed air is introduced into each tank for 1-3 minutes. After the two-stage deionized water cleaning is completed, the basket discharge valve is opened to fill the molybdenum waste into the electrolytic cell.

3. The method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate according to claim 2, characterized in that, The alkaline washing water is prepared by diluting industrial-grade NaOH with deionized water to a mass concentration of 1-5%.

4. The method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate according to claim 1, characterized in that, In step two, the specific process of electrochemical decomposition is as follows: the cleaned molybdenum waste is used as the anode of the electrolytic cell, a stainless steel plate is used as the cathode, and a mixed solution of ammonium molybdate containing 15~30 g / L of molybdenum and ammonia water containing 30~180 g / L is used as the electrolyte. A DC power supply is connected to carry out electrochemical dissolution. During the electrolysis process, metallic molybdenum is oxidized and dissolved at the anode to generate ammonium molybdate, which enters the electrolyte. The concentration of molybdenum ions in the electrolyte gradually increases. When the concentration of molybdenum ions in the electrolyte reaches ≥60 g / L, the electrolyte is extracted and sent to the subsequent impurity removal process, and fresh electrolyte is added to maintain the reaction.

5. The method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate according to claim 4, characterized in that, The specific conditions for the electrochemical dissolution are as follows: electrochemical dissolution temperature of 40~80℃, pH value controlled at 9.0~11.0, and current density controlled at 800~1500 A / m. 2 .

6. The method for preparing high-purity ammonium molybdate from waste molybdenum products according to claim 1, characterized in that, In step two, the specific filtration process is as follows: the filtrate flows sequentially through a chelating resin exchange device, so that the impurity metal ions in the solution are selectively adsorbed by the resin, and the effluent is a purified ammonium molybdate solution.

7. The method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate according to claim 6, characterized in that, The chelating resin is an aminocarboxylic acid or aminophosphonic acid chelating resin.

8. The method for recovering molybdenum from waste molybdenum products to prepare high-purity ammonium molybdate according to claim 6, characterized in that, The chelating resin is MTS9300 or D860.

9. The method for preparing high-purity ammonium molybdate from waste molybdenum products according to claim 6, characterized in that, The specific adsorption conditions are as follows: the adsorption conditions are temperature ≤70℃, flow rate 5~20 BV / h, and Ca concentration is monitored by taking an instantaneous post-exchange liquid sample every hour. When the Ca concentration in the post-exchange liquid is >0.5mg / l, the adsorption is stopped. The resin is washed with deionized water until the column contains trace amounts of molybdenum. Desorption is performed with 5~10% hydrochloric acid. After desorption, the resin is washed with water and a new round of adsorption can be performed.

10. The method for preparing high-purity ammonium molybdate from waste molybdenum products according to claim 9, characterized in that, The desorption control flow rate is 5~20 BV / h.

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