A kind of ammonium tetramolybdate and preparation method thereof

Abstract

The present application relates to the technical field of ammonium molybdate, and specifically discloses an ammonium tetramolybdate and a preparation method thereof, wherein the preparation method comprises the following steps: S1: after mixing an acidic mother liquor and a nitric acid solution evenly, adding roasted molybdenum concentrate and mixing evenly, heating the reaction, cooling, solid-liquid separation, washing, and obtaining a pre-treated material; S2: mixing the pre-treated material and ammonia water evenly, heating the reaction, cooling, solid-liquid separation, obtaining a leachate, and then adding magnesium nitrate and mixing evenly, after reaction, standing, solid-liquid separation, and obtaining an ammonium molybdate solution; S3: mixing the ammonium molybdate solution and ammonium sulfide evenly, after reaction, solid-liquid separation, and then adding modified porous silica gel, after reaction, standing and aging, solid-liquid separation, and obtaining a purified solution; S4: adjusting the pH of the purified solution to 2-2.5, crystallizing, solid-liquid separation, drying, and obtaining a crystallized mother liquor and ammonium tetramolybdate. The preparation method of the present application improves the leaching rate of molybdenum, the removal rate of impurities, and the purity of ammonium tetramolybdate.

Description

Technical Field

[0001] The present application relates to the technical field of ammonium molybdate, and more specifically, to ammonium tetramolybdate and a preparation method thereof. Background Art

[0002] Molybdenum is a rare metal with a high melting point, showing many outstanding properties. Its high melting point, low pressure and excellent elongation make it easy to process into ultra-thin foils and ultra-fine wires. At the same time, the hardness and strength limit of molybdenum are also quite high. These characteristics together form a solid foundation for molybdenum to be used in many fields.

[0003] In the field of metallurgy and smelting, it is an important alloying element and can be used to produce alloy steel, stainless steel, heat-resistant steel and alloy cast iron, etc. In terms of mechanical processing, its excellent performance makes it an ideal material for manufacturing various parts. In addition, molybdenum also plays a key role in the field of high-temperature resistant materials and can withstand extreme high temperature environments. In the field of electric light sources, molybdenum also shows unique application value. It is worth mentioning that molybdenum is also an indispensable trace element in organisms, which makes it also widely used in fields such as medicine and fertilizers. However, despite so many advantages of molybdenum, its abundance in the earth's crust is only 3×10 -4 %, and mainly coexists with other minerals in the form of molybdenum sulfide or molybdate. To make it into high-performance molybdenum products and apply it to various fields, it needs to go through a series of complex processes, including mining and ore enrichment, smelting, chemical purification, roasting and reduction, etc. In this process, ammonium tetramolybdate is an important intermediate product, and its quality has a decisive influence on the quality of subsequent molybdenum products and molybdenum products.

[0004] The production of ammonium tetramolybdate is based on roasted molybdenum concentrate, which is often called industrial molybdenum oxide, molybdenum roasted sand, high-soluble molybdenum oxide, etc. The main components are MoO 3 , and contains a certain amount of impurities such as silicon dioxide, iron, potassium, calcium, magnesium, phosphorus, copper, etc. Therefore, in the process of preparing ammonium tetramolybdate, these impurities may affect the purity and quality of the final product. Therefore, in the preparation process, it is necessary to take a variety of measures to remove or reduce the impact of these impurities to ensure the purity and quality of ammonium tetramolybdate.

[0005] The patent application document with publication number CN116395744A discloses a method for preparing ammonium molybdate, which prepares ammonium molybdate by subjecting raw molybdenum to the steps of roasting, acid leaching, ammonia leaching, acid precipitation and replacement.

[0006] In the patent application document, during the acid leaching process, due to the complex structure of the raw molybdenum after roasting, especially its internal density and possible impurities, the pH, ionic strength and other conditions of the solution are relatively simple during ordinary acid leaching, and the contact and reaction with the roasted molybdenum concentrate are not sufficient, resulting in some molybdenum being unable to be effectively dissolved, which not only affects the recovery rate of molybdenum, but may also have a negative impact on the purity of ammonium molybdate in subsequent steps. Summary of the invention

[0007] In order to improve the recovery rate of molybdenum and the purity of ammonium tetramolybdate, the present application provides ammonium tetramolybdate and a preparation method thereof.

[0008] In a first aspect, the present application provides a method for preparing ammonium tetramolybdate, using the following technical solution:

[0009] A method for preparing ammonium tetramolybdate comprises the following steps:

[0010] S1: acid salt pretreatment: after the acid mother liquor and nitric acid solution are mixed evenly, the pH is adjusted to 2-4, the roasted molybdenum concentrate is added and mixed evenly, the temperature is raised to 60-80°C, the reaction is carried out for 2-4 hours, the temperature is lowered to room temperature, the solid-liquid separation is carried out, and the pretreated material is obtained;

[0011] The acidic mother liquor is an ammonium tetramolybdate crystallization mother liquor, the content of molybdenum in the ammonium tetramolybdate crystallization mother liquor is 10 g / L to 20 g / L, and the mass concentration of the nitric acid solution is 30% to 45%;

[0012] S2: Ammonia leaching: Mix the pretreated material and ammonia water evenly, heat to 40-60°C, react for 4-7 hours, cool to room temperature, separate the solid and liquid, obtain the leachate, then add magnesium nitrate and mix evenly, react for 30-60 minutes, stand, separate the solid and liquid, and obtain the ammonium molybdate solution;

[0013] The ammonia water is added in three stages with increasing concentrations, and the mass concentrations of the ammonia water are: 10% to 15% in the first stage, 15% to 20% in the second stage, and 20% to 25% in the third stage;

[0014] S3: Evenly mix the ammonium molybdate solution and ammonium sulfide, react for 60 to 90 minutes, separate the solid and liquid, then add the modified porous silica gel, react for 60 to 90 minutes, stand for aging, separate the solid and liquid, and obtain a purified solution;

[0015] S4: adjusting the pH of the purified liquid to 2-2.5, crystallizing, solid-liquid separation, and drying to obtain a crystallization mother liquor and ammonium tetramolybdate.

[0016] Preferably, the mass ratio of the magnesium nitrate, ammonium sulfide, modified porous silica gel and roasted molybdenum concentrate is (0.003~0.005):(0.02~0.04):(0.04~0.06):1.

[0017] Preferably, the ratio of the volume of the ammonium tetramolybdate crystallization mother liquor to the mass of the roasted molybdenum concentrate is (1-3) ml / g.

[0018] Preferably, the ammonium tetramolybdate crystallization mother liquor may be the crystallization mother liquor in step S4.

[0019] Preferably, in step S1, the ratio of the volume of the nitric acid solution to the mass of the roasted molybdenum concentrate is (0.5-1.5) ml / g.

[0020] Preferably, the roasted molybdenum concentrate is passed through a 100-200 mesh sieve before use.

[0021] By adopting the above technical scheme, firstly, the ammonium tetramolybdate crystallization mother liquor is compounded with nitric acid solution for acid salt pretreatment, which can recover the molybdenum element remaining in the mother liquor on the one hand, and on the other hand, the molybdate ions contained in the mother liquor can promote the dissolution of molybdenum in the roasted molybdenum concentrate through ion effect, and can also dissolve most impurities such as iron, potassium, calcium, magnesium, phosphorus, copper, etc. in the roasted molybdenum concentrate into the liquid phase, and realize efficient separation from molybdenum. At the same time, this stage converts low-valent molybdenum oxide and molybdate into high-valent molybdenum oxide or molybdic acid, laying the foundation for subsequent ammonia leaching to increase the leaching rate of molybdenum.

[0022] Secondly, during the ammonia leaching process, MoO 3 , H 2 MoO 4 Etc. dissolution and leaching into NH 4 MoO 4 Entering the solution, the residual copper, phosphorus, potassium and calcium in the pretreated material are also leached and converted into Cu(NH 3 ) 3 2+ ,PO 4 3- , K + , Ca 2+ It also enters the solution, while impurities such as silicon dioxide and iron are insoluble in ammonia water and remain in the solid phase, thus achieving separation from molybdenum.

[0023] In this process, ammonia water is added in a step-by-step increasing concentration form, so that the gradual dissolution of molybdenum and the gradual increase of impurity precipitation form a dynamic balance, avoiding the excessive wrapping of unreacted molybdenum raw materials by initial precipitation (such as iron hydroxide, etc.), ensuring the continuous dissolution of molybdenum in the entire ammonia leaching process, and improving the leaching rate of molybdenum. At the same time, the impurity precipitation is more uniform, not easy to agglomerate, and is convenient for solid-liquid separation, further improving the purity of the product. Adding a small amount of magnesium nitrate to the leachate helps the impurity ions PO 4 3- The two phases are in full contact and begin to form fine precipitation nuclei, thus achieving the separation of phosphorus and molybdenum.

[0024] Finally, the ammonium molybdate solution leached from ammonia also contains Cu(NH 3 ) 3 2+ And a small amount of Fe 2+ 、Ni 2+ , K + , Ca 2+ After adding ammonium sulfide, Cu(NH 3 ) 3 2+ , Fe 2+ 、Ni 2+ With S 2- The water-insoluble CuS, FeS, NiS and other precipitates are generated, which play a role in preliminary impurity removal. Then, modified porous silica gel is added for deep impurity removal. The phosphonic acid groups on the surface of modified porous silica gel have a good adsorption effect on cations such as potassium and calcium. Through ion exchange and complexation, the content of impurity ions such as potassium and calcium in the solution can be effectively reduced. At the same time, the flocculation effect of functional groups such as hydroxyl and amino groups on suspended matter further purifies the solution and significantly improves the purity of ammonium tetramolybdate.

[0025] Preferably, the specific steps of adding ammonia water in a stepwise increasing concentration form are:

[0026] Mix 10%~15% ammonia water and pretreated materials evenly, heat to 40~50℃, react for 1~2h, add 15%~20% ammonia water, heat to 45~55℃, react for 1~2h, add 20%~25% ammonia water, heat to 50~60℃, react for 2~3h, cool to room temperature, separate solid and liquid, and obtain leachate.

[0027] Preferably, the ratio of the volume of the ammonia water with a mass concentration of 10% to 15%, the ammonia water with a mass concentration of 15% to 20%, and the ammonia water with a mass concentration of 20% to 25% to the mass of the pretreated material is (1.5 to 2.5) ml: (1 to 2) ml: (0.5 to 1.5) ml: 1 g.

[0028] By adopting the above technical solution, ammonia water is added in increasing concentrations in stages. In the early stage of ammonia leaching, ammonia water with a lower concentration can react gently with the pretreated material to prevent impurities from quickly aggregating and forming a coating layer on the surface of the pretreated material. As the reaction proceeds, the concentration of ammonia water is gradually increased. On the one hand, it can promote the full dissolution of insoluble molybdenum compounds in the material to ensure efficient leaching of molybdenum; on the other hand, ammonia water of different concentrations creates different reaction environments, so that impurities are precipitated or reacted in the most suitable form at the corresponding stage and removed. Through this staged and targeted impurity removal method, the impurity removal efficiency has been significantly improved, fundamentally ensuring the high purity of the final product and laying a solid foundation for the subsequent preparation of high-quality ammonium tetramolybdate products.

[0029] Preferably, in the ammonia leaching step, 1 to 3 ammonia leaching process operations can be selected, and the leaching solution in the previous stage can be used for leaching in the later stage.

[0030] Preferably, the method for preparing the modified porous silica gel comprises the following steps:

[0031] S11: Dispersing the monomer uniformly in the solvent, adding the initiator, and mixing uniformly to obtain a solution A;

[0032] S12: Under an inert atmosphere, the porous silica gel and solution A are mixed evenly, the temperature is raised to 70-90° C., the reaction is performed for 5-7 hours, the temperature is lowered to room temperature, the solution is washed, and the solution is dried to obtain a modified porous silica gel;

[0033] The monomers are composed of hydroxyethyl acrylate, acrylamide and vinyl phosphonic acid, and the mass ratio of the porous silica gel to hydroxyethyl acrylate, acrylamide and vinyl phosphonic acid is 1: (0.08-0.16): (0.04-0.08): (0.15-0.3);

[0034] The initiator is azobisisobutyronitrile.

[0035] Preferably, the amount of azobisisobutyronitrile used is 0.5% to 2% of the total mass of the monomers.

[0036] By adopting the above technical scheme, the functional groups such as hydroxyl, amide, phosphonic acid groups on the surface of modified silica gel can form stable complexes with cations such as potassium and calcium in the ammonium molybdate solution or adsorb them on the silica gel surface through ion exchange, while the molybdate and ammonium ions in ammonium molybdate are less adsorbed, thereby effectively removing impurities while retaining the content of ammonium molybdate to the greatest extent, thereby improving the purity of the ammonium molybdate product. In addition, the modified porous silica gel can also play a certain flocculation role. In the solution system, it can promote the suspended particles to approach each other, effectively aggregate, and finally precipitate, further optimizing the purification effect of the solution and ensuring the smooth progress of the subsequent process.

[0037] Preferably, in step S2, after adding magnesium nitrate and mixing evenly, the step of adding magnesium hydroxide is also included. After the magnesium hydroxide is added, the mixture is mixed evenly, reacted for 30 to 60 minutes, allowed to stand, and solid-liquid separation is performed to obtain an ammonium molybdate solution; the amount of the magnesium hydroxide used accounts for 0.1% to 0.3% of the mass of the roasted molybdenum concentrate.

[0038] By adopting the above technical solution, the magnesium hydroxide added after magnesium nitrate can guide the formed crystal nuclei to grow in an orderly manner on its surface, avoid excessive agglomeration of precipitation, make the precipitation more uniform, and the uniform precipitation particles are easier to filter and wash in the subsequent solid-liquid separation process, which can effectively improve the separation efficiency and effect, reduce the entrainment of impurities, and thus improve the purity of the subsequent ammonium molybdate.

[0039] Preferably, in step S2, after the magnesium hydroxide is added, the mixture is mixed evenly, reacted for 30 to 60 minutes, allowed to stand, and solid-liquid separation is performed, and the process further comprises the step of adding ammonium carbonate, wherein after the ammonium carbonate is added, the mixture is mixed evenly, reacted for 20 to 40 minutes, allowed to stand, and solid-liquid separation is performed to obtain an ammonium molybdate solution; and the amount of the ammonium carbonate used accounts for 0.12% to 0.16% of the mass of the roasted molybdenum concentrate.

[0040] By adopting the above technical scheme, under ammonia conditions, after adding ammonium carbonate, carbonate ions can combine with magnesium and calcium ions remaining in the solution to form precipitates, and are removed in the subsequent solid-liquid separation step, thereby reducing the impurity content in the ammonium molybdate solution and improving the purity of the subsequent ammonium tetramolybdate.

[0041] Preferably, in step S1, after the nitric acid solution, the step of adding ammonium heptamolybdate is further included, and the amount of the ammonium heptamolybdate is 0.7% to 1% of the mass of the roasted molybdenum concentrate.

[0042] By adopting the above technical solution, in the early stage of acid salt pretreatment, ammonium heptamolybdate is mixed with acid mother liquor and nitric acid, and the higher concentration of molybdate ions in the solution produces a common ion effect, which makes the molybdenum in the roasted molybdenum concentrate more easily dissolved. The combination of ammonium heptamolybdate and nitric acid solution can also adjust the acidity of the solution to a certain extent, which can not only ensure the full dissolution of molybdenum, but also enable some impurities to exist in a suitable form, which is convenient for subsequent separation and removal.

[0043] Preferably, in step S1, after the temperature is lowered to room temperature, a step of adding a hydrogen peroxide solution is further included, and after the hydrogen peroxide solution is added, the reaction is carried out for 40 to 60 minutes, and then the solid and liquid are separated to obtain the pretreated material.

[0044] Preferably, the mass concentration of the hydrogen peroxide solution is 10%-15%, and the ratio of the volume of the hydrogen peroxide solution to the mass of the roasted molybdenum concentrate is (0.08-0.1) ml / g.

[0045] By adopting the above technical solution, hydrogen peroxide can further process some impurities or incompletely reacted substances in the roasted molybdenum concentrate, oxidize some low-valent metal ions into high-valent states, and make them easier to separate or convert in subsequent steps.

[0046] In a second aspect, the present application provides ammonium tetramolybdate prepared by the above-mentioned preparation method of ammonium tetramolybdate.

[0047] In summary, this application has the following beneficial effects:

[0048] 1. The present invention uses roasted molybdenum concentrate as raw material, firstly pre-treating with acid salt to achieve efficient separation of most impurities from molybdenum, and at the same time converting low-valent molybdenum oxide and molybdate into high-valent molybdenum oxide or molybdic acid; secondly, adding ammonia water in the form of stepwise increasing concentration can better control the reaction process, improve the leaching rate of molybdenum and the removal rate of impurities, and adding magnesium nitrate to the leachate is helpful to remove PO 4 3- Finally, the ammonium molybdate solution was deeply purified by ammonium sulfide and modified porous silica gel, which further reduced the impurity content and significantly improved the purity of subsequent ammonium tetramolybdate.

[0049] 2. In the subsequent process of ammonia leaching, magnesium hydroxide and ammonium carbonate are added to the present application. Magnesium hydroxide can promote the growth of impurity precipitation particles through the seed effect, making the precipitation easier to separate, further improving the efficiency and thoroughness of impurity removal. In addition, the magnesium hydroxide precipitate formed during the precipitation process can also remove some other trace impurities that are difficult to remove by conventional precipitation methods through surface adsorption; and ammonium carbonate can effectively remove residual magnesium and calcium ions, and has the advantages of relatively simple operation and good impurity removal effect. It can effectively improve the purity of the solution, provide purer raw materials for subsequent processes such as the preparation of ammonium tetramolybdate products, and help improve the quality of the final product.

[0050] 3. In the initial stage of acid salt pretreatment, the present application adopts a mixture of acid mother liquor, ammonium heptamolybdate and nitric acid. The higher molybdate ion concentration can promote the molybdenum in the roasted molybdenum concentrate to dissolve more quickly and fully, thereby effectively improving the recovery rate of molybdenum. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a scanning electron microscope image of ammonium tetramolybdate in Example 1 magnified 100 times;

[0052] Figure 2 This is a scanning electron microscope image of ammonium tetramolybdate in Example 1 magnified 500 times;

[0053] Figure 3 This is a scanning electron microscope image of ammonium tetramolybdate in Example 1 magnified 2000 times;

[0054] Figure 4 This is a scanning electron microscope image of ammonium tetramolybdate in Example 1 magnified 4000 times. DETAILED DESCRIPTION

[0055] The present application is further described in detail below with reference to embodiments.

[0056] In the present application, when the molybdenum content of the roasted molybdenum concentrate is higher than 59.97%, the dosage of ammonia water, ammonium tetramolybdate crystallization mother liquor and nitric acid solution can be increased accordingly, and the increase is based on the existing volume dosage, according to the ratio of 10% to 15%.

[0057] Table 1 Analysis and testing indicators of roasted molybdenum concentrate

[0058]

[0059] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0060] Porous silica gel was purchased from Qingdao Ronghui Adsorption Materials Co., Ltd.;

[0061] Magnesium hydroxide was in the form of hexagonal flakes with a purity of 99.9% and a D50 particle size of 2-5 μm, and was purchased from Qinghe County Ruijiang Metal Materials Co., Ltd.

[0062] Preparation Examples 1~3 Modified Porous Silica Gel

[0063] Preparation Example 1

[0064] This preparation example provides a method for preparing modified silica gel, comprising the following steps:

[0065] S11: The monomer is uniformly dispersed in 500 ml of anhydrous ethanol, and 0.54 g of azobisisobutyronitrile is added, and the mixture is stirred and mixed to obtain a solution A;

[0066] S12: Under a nitrogen atmosphere, 100 g of porous silica gel and solution A were stirred and mixed uniformly, the temperature was raised to 70° C., reacted for 7 h, naturally cooled to room temperature, washed with anhydrous ethanol for 3 times, transferred to a vacuum drying oven, and dried at 70° C. to constant weight to obtain modified porous silica gel;

[0067] The monomers include 8 g hydroxyethyl acrylate, 4 g acrylamide and 15 g vinylphosphonic acid;

[0068] Before using the porous silica gel, first pass it through a 50-mesh sieve to get the material under the sieve, and then pass it through a 150-mesh sieve to get the material on the sieve.

[0069] Preparation Example 2

[0070] This preparation example provides a method for preparing modified silica gel, comprising the following steps:

[0071] S11: The monomer is uniformly dispersed in 500 ml of anhydrous ethanol, and 0.27 g of azobisisobutyronitrile is added, and the mixture is stirred and mixed to obtain a solution A;

[0072] S12: Under a nitrogen atmosphere, 100 g of porous silica gel and solution A were stirred and mixed uniformly, the temperature was raised to 90° C., reacted for 5 h, naturally cooled to room temperature, washed with anhydrous ethanol for 3 times, transferred to a vacuum drying oven, and dried at 70° C. to constant weight to obtain modified porous silica gel;

[0073] The monomers include 16 g hydroxyethyl acrylate, 8 g acrylamide and 30 g vinylphosphonic acid;

[0074] Before using the porous silica gel, first pass it through a 50-mesh sieve to get the material under the sieve, and then pass it through a 150-mesh sieve to get the material on the sieve.

[0075] Preparation Example 3

[0076] This preparation example provides a method for preparing modified silica gel, comprising the following steps:

[0077] S11: The monomer is uniformly dispersed in 500 ml of anhydrous ethanol, and 0.43 g of azobisisobutyronitrile is added, and the mixture is stirred and mixed to obtain a solution A;

[0078] S12: Under a nitrogen atmosphere, 100 g of porous silica gel and solution A were stirred and mixed uniformly, the temperature was raised to 80° C., reacted for 6 h, naturally cooled to room temperature, washed with anhydrous ethanol for 3 times, transferred to a vacuum drying oven, and dried at 70° C. to constant weight to obtain modified porous silica gel;

[0079] The monomers include 14 g hydroxyethyl acrylate, 6 g acrylamide and 25 g vinylphosphonic acid;

[0080] Before using the porous silica gel, first pass it through a 50-mesh sieve to get the material under the sieve, and then pass it through a 150-mesh sieve to get the material on the sieve.

[0081] An embodiment of a method for preparing ammonium tetramolybdate in the present application is as follows:

[0082] Example 1

[0083] This embodiment provides a method for preparing ammonium tetramolybdate, comprising the following steps:

[0084] S1: acid salt pretreatment: 1L of ammonium tetramolybdate crystal mother liquor with a molybdenum content of 10g / L and 0.5L of nitric acid solution with a mass concentration of 30% are mixed in a reactor, and the pH is adjusted to 4 with a nitric acid solution with a mass concentration of 10%, and then 1kg of roasted molybdenum concentrate is added and stirred to mix evenly, the temperature is raised to 60°C, and the reaction is stirred for 4h, and then naturally cooled to room temperature, filtered, and washed twice with deionized water to obtain a pretreated material;

[0085] S2: Transfer the pretreated material to the reactor, turn on the stirring device, and slowly add 1.5L of 10% ammonia water. After the addition is completed, heat it to 40°C, continue to stir and react for 2h, then slowly add 1L of 15% ammonia water. After the addition is completed, continue to heat it to 45°C, continue to stir and react for 2h, then add 0.5L of 20% ammonia water, continue to heat it to 50°C, continue to stir and react for 3h, stop stirring, naturally cool to room temperature, filter, and obtain a leachate; then add 3g of magnesium nitrate to the leachate, stir and mix evenly, continue to stir and react for 30min, let it stand for 3h, filter, and obtain an ammonium molybdate solution;

[0086] S3: Add 20g of ammonium sulfide to the ammonium molybdate solution and stir to mix evenly, react for 60min, filter, then add 40g of modified porous silica gel, stir to mix evenly, react for 60min, let stand for 12h, filter, and obtain a purified solution;

[0087] S4: Transfer the purified liquid to a crystallization kettle, adjust the pH of the purified liquid to 2-2.5 with a 10% nitric acid solution, control the temperature of the crystallization kettle between 15-20°C, continue stirring and crystallizing for 24 hours, and perform pH detection every 2-3 hours. If the pH value changes, add a small amount of 10% nitric acid solution for fine adjustment. After the crystallization is completed, let it stand for 2 hours, filter under reduced pressure to obtain a crystallization mother liquor and ammonium tetramolybdate crystals. Transfer the ammonium tetramolybdate crystals to a vacuum drying oven and dry them at 70°C to constant weight to obtain ammonium tetramolybdate.

[0088] Wherein, the ammonium tetramolybdate crystallization mother liquor comes from the crystallization mother liquor in step S4;

[0089] Before using the roasted molybdenum concentrate, first pass it through a 100-mesh sieve to get the undersize, then pass it through a 200-mesh sieve to get the oversize;

[0090] The modified porous silica gel is from Preparation Example 1.

[0091] Example 2

[0092] This embodiment provides a method for preparing ammonium tetramolybdate, comprising the following steps:

[0093] S1: acid salt pretreatment: 3L of ammonium tetramolybdate crystal mother liquor with a molybdenum content of 20g / L and 1.5L of nitric acid solution with a mass concentration of 45% are mixed in a reactor, and the pH is adjusted to 2 with a nitric acid solution with a mass concentration of 10%, and then 1kg of roasted molybdenum concentrate is added and stirred to mix evenly, the temperature is raised to 80°C, and the stirring reaction is continued for 2h, and then naturally cooled to room temperature, filtered, and washed twice with deionized water to obtain a pretreated material;

[0094] S2: Transfer the pretreated material to the reactor, turn on the stirring device, and slowly add 2.5L of 15% ammonia water. After the addition is completed, heat it to 50°C, continue to stir and react for 1h, then slowly add 2L of 20% ammonia water. After the addition is completed, continue to heat it to 55°C, continue to stir and react for 1h, then add 1.5L of 25% ammonia water, continue to heat it to 60°C, continue to stir and react for 2h, stop stirring, naturally cool to room temperature, filter, and obtain a leachate; then add 5g of magnesium nitrate to the leachate, stir and mix evenly, continue to stir and react for 60min, let it stand for 3h, filter, and obtain an ammonium molybdate solution;

[0095] S3: Add 40g of ammonium sulfide to the ammonium molybdate solution and stir to mix evenly, react for 90min, filter, then add 60g of modified porous silica gel, stir to mix evenly, react for 90min, let stand for 12h, filter, and obtain a purified solution;

[0096] S4: Transfer the purified liquid to a crystallization kettle, adjust the pH of the purified liquid to 2-2.5 with a 10% nitric acid solution, control the temperature of the crystallization kettle between 15-20°C, continue stirring and crystallizing for 24 hours, and perform pH detection every 2-3 hours. If the pH value changes, add a small amount of 10% nitric acid solution for fine adjustment. After the crystallization is completed, let it stand for 2 hours, filter under reduced pressure to obtain a crystallization mother liquor and ammonium tetramolybdate crystals. Transfer the ammonium tetramolybdate crystals to a vacuum drying oven and dry them at 70°C to constant weight to obtain ammonium tetramolybdate.

[0097] Wherein, the ammonium tetramolybdate crystallization mother liquor comes from the crystallization mother liquor in step S4;

[0098] Before using the roasted molybdenum concentrate, first pass it through a 100-mesh sieve to get the undersize, then pass it through a 200-mesh sieve to get the oversize;

[0099] The modified porous silica gel is from Preparation Example 2.

[0100] Example 3

[0101] This embodiment provides a method for preparing ammonium tetramolybdate, comprising the following steps:

[0102] S1: acid salt pretreatment: 2L of ammonium tetramolybdate crystal mother liquor with a molybdenum content of 15g / L and 1L of nitric acid solution with a mass concentration of 40% are mixed in a reactor, and the pH is adjusted to 3 with a nitric acid solution with a mass concentration of 10%, and then 1kg of roasted molybdenum concentrate is added and stirred to mix evenly, the temperature is raised to 70°C, and the stirring reaction is continued for 3h, and then naturally cooled to room temperature, filtered, and washed twice with deionized water to obtain a pretreated material;

[0103] S2: Transfer the pretreated material to the reactor, turn on the stirring device, and slowly add 2L of 12% ammonia water. After the addition is completed, heat it to 45°C, continue to stir and react for 1.5h, then slowly add 1.5L of 17% ammonia water. After the addition is completed, continue to heat it to 50°C, continue to stir and react for 1.5h, then add 1L of 22% ammonia water, continue to heat it to 55°C, continue to stir and react for 2.5h, stop stirring, naturally cool to room temperature, filter, and obtain a leachate; then add 4g of magnesium nitrate to the leachate, stir and mix evenly, continue to stir and react for 50min, let it stand for 3h, filter, and obtain an ammonium molybdate solution;

[0104] S3: Add 30g of ammonium sulfide to the ammonium molybdate solution and stir to mix evenly, react for 80min, filter, then add 50g of modified porous silica gel, stir to mix evenly, react for 80min, let stand for 12h, filter, and obtain a purified solution;

[0105] S4: Transfer the purified liquid to a crystallization kettle, adjust the pH of the purified liquid to 2-2.5 with a 10% nitric acid solution, control the temperature of the crystallization kettle between 15-20°C, continue stirring and crystallizing for 24 hours, and perform pH detection every 2-3 hours. If the pH value changes, add a small amount of 10% nitric acid solution for fine adjustment. After the crystallization is completed, let it stand for 2 hours, filter under reduced pressure to obtain a crystallization mother liquor and ammonium tetramolybdate crystals. Transfer the ammonium tetramolybdate crystals to a vacuum drying oven and dry them at 70°C to constant weight to obtain ammonium tetramolybdate.

[0106] Wherein, the ammonium tetramolybdate crystallization mother liquor comes from the crystallization mother liquor in step S4;

[0107] Before using the roasted molybdenum concentrate, first pass it through a 100-mesh sieve to get the undersize, then pass it through a 200-mesh sieve to get the oversize;

[0108] The modified porous silica gel is from Preparation Example 3.

[0109] Example 4

[0110] The difference between this embodiment and embodiment 3 is that:

[0111] S2: First ammonia leaching: transfer the pretreated material to the reactor, turn on the stirring device, and slowly add 2L of 12% ammonia water. After the addition is completed, heat it to 45°C, continue stirring and reacting for 1.5h, then slowly add 1.5L of 17% ammonia water. After the addition is completed, continue to heat it to 50°C, continue stirring and reacting for 1.5h, then add 1L of 22% ammonia water, continue to heat it to 55°C, continue stirring and reacting for 2.5h, then stop stirring, naturally cool to room temperature, filter, and obtain the first leachate and the first filter residue;

[0112] Second ammonia leaching: transfer the first filter residue to a new reactor, turn on the stirring device, and slowly add 2L of the first leaching solution. After the addition is completed, heat it to 55°C, continue stirring and react for 2.5 hours, stop stirring, cool naturally to room temperature, and filter to obtain the second leaching solution and the second filter residue;

[0113] The third ammonia leaching: transfer the second filter residue to a new reactor, turn on the stirring device, and slowly add 2L of the first leaching solution. After the addition is completed, heat it to 55°C, continue stirring and react for 2.5 hours, stop stirring, cool naturally to room temperature, and filter to obtain the third leaching solution and the third filter residue;

[0114] The second leachate, the third leachate and the remaining first leachate are combined to obtain a leachate, 4 g of magnesium nitrate is added, and the mixture is stirred and mixed evenly, and then 1 g of magnesium hydroxide is added and stirred and mixed evenly, and the mixture is reacted for 30 min, allowed to stand for 3 h, and filtered to obtain an ammonium molybdate solution;

[0115] The rest is the same as in Example 3.

[0116] Example 5

[0117] The difference between this embodiment and embodiment 4 is that:

[0118] In step S2, 4 g of magnesium nitrate is added to the leachate, and after stirring and mixing, 2 g of magnesium hydroxide is added and stirred and mixed, reacted for 50 min, allowed to stand for 3 h, filtered, and then 1.2 g of ammonium carbonate is added and stirred and mixed, reacted for 20 min, allowed to stand for 2 h, filtered, and an ammonium molybdate solution is obtained;

[0119] The rest is the same as Example 4.

[0120] Example 6

[0121] The difference between this embodiment and embodiment 5 is that:

[0122] S1: acid salt pretreatment: 2L of ammonium tetramolybdate crystal mother liquor with a molybdenum content of 15g / L, 1L of nitric acid solution with a mass concentration of 40% and 7g of ammonium heptamolybdate are mixed in a reactor, and the pH is adjusted to 3 with a nitric acid solution with a mass concentration of 10%, and then 1kg of roasted molybdenum concentrate is added and stirred to mix evenly, the temperature is raised to 70°C, and the reaction is stirred for 3h, then naturally cooled to room temperature, filtered, and washed twice with deionized water to obtain a pretreated material;

[0123] In step S2, 4 g of magnesium nitrate is added to the leachate, and after stirring and mixing, 3 g of magnesium hydroxide is added and stirred and mixed, reacted for 60 min, allowed to stand for 3 h, filtered, and then 1.4 g of ammonium carbonate is added and stirred and mixed, reacted for 30 min, allowed to stand for 2 h, filtered, and an ammonium molybdate solution is obtained;

[0124] The rest is the same as Example 5.

[0125] Example 7

[0126] The difference between this embodiment and embodiment 6 is that:

[0127] S1: acid salt pretreatment: 2L of ammonium tetramolybdate crystal mother liquor with a molybdenum content of 15g / L, 1L of nitric acid solution with a mass concentration of 40% and 8g of ammonium heptamolybdate are mixed in a reactor, and the pH is adjusted to 3 with a nitric acid solution with a mass concentration of 10%, and then 1kg of roasted molybdenum concentrate is added and stirred to mix evenly, the temperature is raised to 70°C, and the stirring reaction is continued for 3h, and then naturally cooled to room temperature, and then 0.08L of hydrogen peroxide solution with a mass concentration of 10% is added and stirred to mix evenly, and after reacting for 40min, it is filtered and washed twice with deionized water to obtain a pretreated material;

[0128] In step S2, 4 g of magnesium nitrate is added to the leachate, and after stirring and mixing, 2 g of magnesium hydroxide is added and stirred and mixed, reacted for 50 min, allowed to stand for 3 h, filtered, and then 1.6 g of ammonium carbonate is added and stirred and mixed, reacted for 40 min, allowed to stand for 2 h, filtered, and an ammonium molybdate solution is obtained;

[0129] The rest is the same as Example 6.

[0130] Example 8

[0131] The difference between this embodiment and embodiment 7 is that:

[0132] S1: acid salt pretreatment: 2L of ammonium tetramolybdate crystal mother liquor with a molybdenum content of 15g / L, 1L of nitric acid solution with a mass concentration of 40% and 10g of ammonium heptamolybdate are mixed in a reactor, and the pH is adjusted to 3 with a nitric acid solution with a mass concentration of 10%, and then 1kg of roasted molybdenum concentrate is added and stirred to mix evenly, the temperature is raised to 70°C, and the stirring reaction is continued for 3h, and then naturally cooled to room temperature, and then 0.1L of hydrogen peroxide solution with a mass concentration of 15% is added and stirred to mix evenly, and after reacting for 60min, it is filtered and washed twice with deionized water to obtain a pretreated material;

[0133] The rest is the same as Example 6.

[0134] Comparative Example 1

[0135] The difference between this comparative example and Example 1 is:

[0136] S2: Transfer the pretreated material to the reactor, turn on the stirring device, and slowly add 1.5L of 13.3% ammonia water. After the addition is completed, heat it to 40°C, continue to stir and react for 2h, then slowly add 1L of 13.3% ammonia water. After the addition is completed, continue to heat it to 45°C, continue to stir and react for 2h, then add 0.5L of 13.3% ammonia water, continue to heat it to 50°C, continue to stir and react for 3h, stop stirring, naturally cool to room temperature, filter, and obtain a leachate; then add 3g of magnesium nitrate to the leachate, stir and mix evenly, continue to stir and react for 30min, let it stand for 3h, filter, and obtain an ammonium molybdate solution;

[0137] The rest is the same as in Example 1.

[0138] Comparative Example 2

[0139] The difference between this comparative example and Example 1 is:

[0140] S3: Add 20g of ammonium sulfide to the ammonium molybdate solution and stir to mix evenly, react for 60min, filter, then add 40g of porous silica gel, stir to mix evenly, react for 60min, let stand for 12h, filter, and obtain a purified solution;

[0141] Before using the porous silica gel, first pass it through a 50-mesh sieve to get the material under the sieve, and then pass it through a 150-mesh sieve to get the material on the sieve.

[0142] The rest is the same as in Example 1.

[0143] Performance testing

[0144] The molybdenum content (referred to as Mo) in the ammonium tetramolybdate in Examples 1 to 8 and Comparative Examples 1 to 2 was analyzed and tested according to the testing standard GB / T3460-2017. The test results are shown in Table 2, including the Fsss particle size (referred to as particle size) and the bulk density (referred to as density) of ammonium tetramolybdate.

[0145] Table 2 Molybdenum content and impurity content test data of ammonium tetramolybdate in Examples 1 to 8 and Comparative Examples 1 to 2

[0146]

[0147] From the analysis of Table 2, we can see that:

[0148] It can be seen from Example 1 and Comparative Examples 1-2 that, in the ammonia leaching process, adding ammonia water in the form of stepwise increasing concentration can better adapt to the dissolution characteristics of the pretreated material at different reaction stages, avoid the excessively rapid formation of a product layer on the surface of the molybdenum ore to hinder subsequent reactions, thereby improving the leaching rate of molybdenum.

[0149] The porous silica gel is modified and specific functional groups are introduced to enhance the ability to remove impurities, achieving more precise impurity separation without affecting the recovery of molybdenum.

[0150] It can be seen from Examples 1 to 3 that by optimizing the reagent dosage and reaction conditions in each step, the molybdenum content and impurity removal rate in ammonium tetramolybdate are maintained within a good range.

[0151] It can be seen from Examples 3 to 4 that magnesium hydroxide is added after magnesium nitrate, and the magnesium hydroxide may react with certain impurities in the solution and guide the formation and separation of magnesium ammonium phosphate precipitate, further increasing the molybdenum content in ammonium tetramolybdate and the impurity removal rate.

[0152] It can be seen from Examples 4 to 5 that by adding ammonium carbonate after magnesium hydroxide, the ammonium carbonate can form an insoluble carbonate precipitate with the metal ions remaining in the solution, further reducing the concentration of impurity ions in the solution, thereby increasing the molybdenum content in the subsequent ammonium tetramolybdate.

[0153] It can be seen from Examples 5 to 6 that adding ammonium heptamolybdate after the nitric acid solution may promote the entire molybdenum leaching reaction system to proceed in the direction of generating the target product, thereby improving the conversion rate and selectivity of the reaction. At the same time, the molybdate ions in the ammonium heptamolybdate form complexes with the impurity ions, thereby changing the properties of the impurity ions and making them easier to remove.

[0154] It can be seen from Examples 6 to 8 that in step S1, after cooling to room temperature, a hydrogen peroxide solution is added, and hydrogen peroxide can oxidize some low-valent metal ions to high-valent states, and high-valent metal ions are more easily precipitated or removed, thereby increasing the removal rate of impurities in ammonium tetramolybdate and improving product quality.

[0155] Combining Example 1 and Figure 1~Figure 4 Analysis shows that Example 1 provides the key chemical composition data of ammonium tetramolybdate, with a molybdenum content of 55.89%. At the same time, the contents of impurity elements such as Si, Fe, K, Ca, Mg, P, and Cu are at a relatively low level. These data lay the foundation for purity judgment.

[0156] Through electron microscope scanning images of different magnifications, the sample prepared in Example 1 can be deeply observed and analyzed.

[0157] In the 100x scanning electron microscope image, the overall distribution state of the particles in the sample within a larger field of view can be preliminarily observed. At this time, although there are particles of different sizes, they are dispersed relatively evenly, and there is no local aggregation of a certain type of special form or suspected impurity particles. As the magnification increases to 500 times, many particles that are approximately spherical or ellipsoidal can be seen more clearly, and these particles maintain relatively uniform gaps between each other, further indicating that the sample also has good distribution uniformity at the microscopic scale. When the magnification increases to 2000 times, it presents a larger block with cracks, bumps and fine particles attached to the surface, but from the perspective of structural association, this block structure can be reasonably inferred to be formed by the aggregation of many previously observed fine particles. When the magnification is further increased to 4000 times, the finer flake or petal-like structures on the particle surface can be clearly observed, and no abnormal structures that are significantly different from the main particles in terms of morphology, size, grayscale, etc. and appear out of place are found.

[0158] During the entire observation process from low to high magnification, no suspected impurity particles were found that were significantly and abruptly different from the main particles in terms of shape, size, grayscale, etc. Based on the observation results at different magnifications above, it can be judged that the sample prepared in Example 1 presents a relatively uniform phase. This phenomenon largely reflects that the sample has a high purity, the main component occupies a dominant position in the sample, and the impurity component content is relatively low.

[0159] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for preparing ammonium tetramolybdate, characterized in that: The steps include: S1: acid salt pretreatment: after the acid mother liquor and nitric acid solution are mixed evenly, the pH is adjusted to 2-4, the roasted molybdenum concentrate is added and mixed evenly, the temperature is raised to 60-80°C, the reaction is carried out for 2-4 hours, the temperature is lowered to room temperature, the solid-liquid separation is carried out, and the pretreated material is obtained; The acidic mother liquor is an ammonium tetramolybdate crystallization mother liquor, the content of molybdenum in the ammonium tetramolybdate crystallization mother liquor is 10 g / L to 20 g / L, and the mass concentration of the nitric acid solution is 30% to 45%; S2: Ammonia leaching: Mix the pretreated material and ammonia water evenly, heat to 40-60°C, react for 4-7 hours, cool to room temperature, separate the solid and liquid, obtain the leachate, then add magnesium nitrate and mix evenly, react for 30-60 minutes, stand, separate the solid and liquid, and obtain the ammonium molybdate solution; The ammonia water is added in three stages with increasing concentrations, and the mass concentrations of the ammonia water are: 10% to 15% in the first stage, 15% to 20% in the second stage, and 20% to 25% in the third stage; S3: Evenly mix the ammonium molybdate solution and ammonium sulfide, react for 60 to 90 minutes, separate the solid and liquid, then add the modified porous silica gel, react for 60 to 90 minutes, stand for aging, separate the solid and liquid, and obtain a purified solution; S4: adjusting the pH of the purified liquid to 2-2.5, crystallizing, solid-liquid separation, and drying to obtain a crystallization mother liquor and ammonium tetramolybdate; The modified porous silica gel is prepared by modification with hydroxyethyl acrylate, acrylamide and vinylphosphonic acid.

2. The method for preparing ammonium tetramolybdate according to claim 1, wherein The mass ratio of the magnesium nitrate, ammonium sulfide, modified porous silica gel and roasted molybdenum concentrate is (0.003-0.005): (0.02-0.04): (0.04-0.06):

1.

3. The preparation method of ammonium tetramolybdate according to claim 1, characterized in that: The ratio of the volume of the ammonium tetramolybdate crystallization mother liquor to the mass of the roasted molybdenum concentrate is (1-3) ml / g.

4. The method for preparing ammonium tetramolybdate according to claim 1, wherein In step S1, the ratio of the volume of the nitric acid solution to the mass of the roasted molybdenum concentrate is (0.5-1.5) ml / g.

5. The method for preparing ammonium tetramolybdate according to claim 1, wherein The specific steps of adding ammonia water in the form of increasing concentration in three stages are: uniformly mixing ammonia water with a mass concentration of 10% to 15% with the pretreated material, heating to 40 to 50° C., reacting for 1 to 2 hours, adding ammonia water with a mass concentration of 15% to 20%, heating to 45 to 55° C., reacting for 1 to 2 hours, adding ammonia water with a mass concentration of 20% to 25%, heating to 50 to 60° C., reacting for 2 to 3 hours, cooling to room temperature, separating the solid and the liquid, and obtaining a leachate.

6. The method for preparing ammonium tetramolybdate according to claim 5, characterized in that: The ratio of the volume of the ammonia water with a mass concentration of 10% to 15%, the ammonia water with a mass concentration of 15% to 20%, and the ammonia water with a mass concentration of 20% to 25% to the mass of the pretreated material is (1.5 to 2.5) ml: (1 to 2) ml: (0.5 to 1.5) ml: 1 g.

7. The method for preparing ammonium tetramolybdate according to claim 1, characterized in that: The preparation method of the modified porous silica gel comprises the following steps: S11: Dispersing the monomer uniformly in the solvent, adding the initiator, and mixing uniformly to obtain a solution A; S12: Under an inert atmosphere, the porous silica gel and solution A are mixed evenly, the temperature is raised to 70-90° C., the reaction is performed for 5-7 hours, the temperature is lowered to room temperature, the solution is washed, and the solution is dried to obtain a modified porous silica gel; The monomer is composed of hydroxyethyl acrylate, acrylamide and vinyl phosphonic acid, and the mass ratio of the porous silica gel to hydroxyethyl acrylate, acrylamide and vinyl phosphonic acid is 1: (0.08-0.16): (0.04-0.08): (0.15-0.3); the initiator is azobisisobutyronitrile.

8. The method for preparing ammonium tetramolybdate according to claim 1, characterized in that: In step S2, after adding magnesium nitrate and mixing evenly, the step of adding magnesium hydroxide is also included. After the magnesium hydroxide is added, the mixture is mixed evenly, reacted for 30 to 60 minutes, allowed to stand, and solid-liquid separation is performed to obtain an ammonium molybdate solution; the amount of the magnesium hydroxide used accounts for 0.1% to 0.3% of the mass of the roasted molybdenum concentrate.

9. The method for preparing ammonium tetramolybdate according to claim 8, characterized in that: In step S2, after the magnesium hydroxide is added, the mixture is mixed evenly, reacted for 30 to 60 minutes, allowed to stand, and after solid-liquid separation, the process further includes the step of adding ammonium carbonate. After the ammonium carbonate is added, the mixture is mixed evenly, reacted for 20 to 40 minutes, allowed to stand, and solid-liquid separation is performed to obtain an ammonium molybdate solution. The amount of the ammonium carbonate used accounts for 0.12% to 0.16% of the mass of the roasted molybdenum concentrate.

10. Ammonium tetramolybdate prepared by the method for preparing ammonium tetramolybdate according to any one of claims 1 to 9.

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