Method for producing high-crystal-yield and high-purity ammonium heptamolybdate by taking ammonium tetramolybdate as raw material

Abstract

The invention relates to a method for producing ammonium heptamolybdate with high crystal yield and high purity by taking ammonium tetramolybdate as a raw material, which comprises the following steps: adding pure water into a batching tank at room temperature, starting a stirrer, introducing liquid ammonia into the batching tank, then adding ammonium tetramolybdate, stirring and dissolving, heating to 65 DEG C, and stirring and dissolving for 1 hour at the constant temperature of 65-70 DEG C to obtain an ammonium molybdate mixed solution; refluxing, circulating and precisely filtering by a precise filter, pumping into a cooling crystallizing tank, adding nitric acid into the crystallizing tank while stirring at room temperature to adjust the pH value of the solution to 6.2-6.5, and continuously stirring for 30 minutes; and cooling the ammonium molybdate mixed solution in the cooling crystallization tank for 7 hours, cooling the temperature of the material in the crystallization tank to 10-12 DEG C, crystallizing and separating out an ammonium heptamolybdate product, centrifugally filtering, introducing air with the relative humidity of 40% and the temperature of 15-25 DEG C into a rotary roller dryer, and drying to obtain the ammonium heptamolybdate. The method has the advantages of simple and reasonable process, regular product crystal form, good crystallization yield and high purity.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal hydrometallurgical technology, and specifically relates to a method for producing high-crystallization-yield and high-purity ammonium heptamolybdate using ammonium tetramolybdate as raw material. Background Technology

[0002] Ammonium heptamolybdate belongs to the polyacid salt class and has the chemical formula (NH4)6Mo7O. 24 Ammonium heptamolybdate (AHMo) is an important inorganic compound widely used in the production of chemical catalysts, pigments, metal surface treatment agents, corrosion inhibitors, and trace element fertilizers. The purity requirements of AHMo significantly impact its application performance. For chemical catalysts, AHMo requires extremely high purity; insufficient purity can lead to impurities introduced into the catalyst, triggering various side reactions or reducing its activity, thus affecting the efficiency and product quality of the chemical reaction. Similarly, in other industries such as pigments and metal surface treatment agents, the purity of AHMo is crucial. Low-purity AHMo may cause color deviations in pigments, and its use as a metal surface treatment agent can weaken its performance, ultimately affecting the quality and effectiveness of the final product.

[0003] Currently, the most classic traditional process for producing ammonium heptamolybdate uses ammonium tetramolybdate as raw material. Ammonium tetramolybdate is dissolved in ammonia water at 50–60℃ to prepare a high-concentration ammonium molybdate mixed solution with a specific gravity of 1.34–1.36 g / mL (solution pH = 8.0–9.5, ammonia to molybdenum molar ratio of 1.1–1.2). After filtration and evaporation to concentrate the solution to a specific gravity of 1.42–1.44 g / mL, the product is obtained by cooling crystallization and centrifugation. This process uses traditional crystallizers, resulting in high energy consumption. Furthermore, during crystallization, a large amount of product often adheres to the bottom and walls of the crystallizer, requiring manual or mechanical cleaning. This reduces production efficiency and easily introduces impurities. Furthermore, under this process, the yield of ammonium heptamolybdate in a single crystallization is only 50-60%, the product has an irregular crystal form (indistinct crystal edges and uneven particle size distribution), and the crystal surface is dark white, resulting in poor clarity of the ammonium heptamolybdate aqueous solution. The product's various quality indicators can only meet the basic requirements of the GB / T3460-2007 quality standard, and cannot meet the requirements of a few high-end customers for higher purity and performance of ammonium heptamolybdate. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for producing high-crystallization-yield and high-purity ammonium heptamolybdate using ammonium tetramolybdate as raw material, which produces products with regular crystal form, good crystallization yield and high purity.

[0005] The technical solution of this invention is: A method for producing high-crystallization-yield, high-purity ammonium heptamolybdate from ammonium tetramolybdate, comprising the following specific steps: Step 1: Preparation of ammonium molybdate mixed solution: Add 6.6 ml of pure water to the mixing tank at room temperature. 3 Turn on the stirrer and introduce 135-153 kg of liquid ammonia into the mixing tank. Then add 3000 kg of ammonium tetramolybdate into the mixing tank and stir to dissolve for 10 minutes. Then heat the mixed solution in the mixing tank to 65°C and stir to dissolve at a constant temperature of 65-70°C for 1 hour to obtain the ammonium molybdate mixed solution. Step 2, Circulating Precision Filtration: The ammonium molybdate mixed solution prepared in step 1 is filtered through a precision filter under reflux to make the ammonium molybdate mixed solution clear and transparent, and then pumped into a cooling crystallization tank with a jacket. Step 3: Neutralize acid and adjust pH: Turn on the stirrer of the cooling crystallizer and add nitric acid to the crystallizer while stirring at room temperature to adjust the pH of the solution to 6.2-6.5. Continue stirring for 30 minutes. Step 4, Cooling and Crystallization: Open the cooling water inlet and outlet valves of the cooling crystallizer jacket, and circulate cooling water into the cooling crystallizer jacket. The cooling water temperature is 5℃. Cool the ammonium molybdate mixed solution in the cooling crystallizer for 7 hours. The material temperature in the crystallizer drops to 10-12℃, and the ammonium heptamolybdate product crystallizes out. Step 5: Centrifugal filtration: Turn on the centrifuge and control the centrifuge speed at 400 rpm. Open the discharge valve at the bottom of the cooling crystallization tank and control the centrifuge feeding amount at 300 kg / time. After feeding, increase the centrifuge speed to 1000 rpm. After centrifuging and filtering for 30 minutes, stop the machine and discharge the material to obtain ammonium heptamolybdate with a free water content ≤2.0%wt. Step 6: Product drying: Turn on the rotary drum dryer. The drying drum of the rotary drum dryer should be kept at a temperature of 500-1000 m³ / h. 3 Air with a relative humidity of 40% and a temperature of 15-25°C is introduced at a flow rate of / h to dry the product and obtain high-purity ammonium heptamolybdate.

[0006] Furthermore, in step 1, after constant temperature dissolution, the pH value of the ammonium molybdate mixed solution is 6.7–7.0.

[0007] Furthermore, in step 3, the stirring speed is 60 revolutions per minute.

[0008] Furthermore, in step 3, the flow rate of nitric acid added is 500–800 L / h.

[0009] Furthermore, in step 4, the cooling water flow rate is 20–30 m / s. 3 / h.

[0010] Furthermore, when drying products in a rotary drum dryer, the rotation speed of the drying drum is 6 revolutions per minute.

[0011] Furthermore, the free water content in the ammonium tetramolybdate is 2% to 3% wt.

[0012] The nitric acid is industrial nitric acid with a mass content of ≥98%.

[0013] The beneficial effects of this invention are: Through a precision filter circulating filtration process, solid particles and ammonia-insoluble impurities entrained in ammonium tetramolybdate are effectively removed, reducing impurity residues in ammonium heptamolybdate crystals. Strict control of the ammonia-molybdenum ratio in the ammonium molybdate mixed solution ensures the crystal form and purity of the ammonium heptamolybdate product. Before cooling and crystallization, the pH of the solution is adjusted with nitric acid to precisely control the free ammonia concentration and enhance the solubility of soluble impurities. Adjustments to the stirring speed, jacket cooling water flow rate, cooling water temperature, and cooling time ensure the particle size, particle size distribution, crystal regularity, crystallization yield, and product purity of ammonium heptamolybdate, preventing crystals from sticking to the walls. The product is dried using a low-temperature rotary drum dryer, which reduces energy consumption and costs while avoiding product contamination.

[0014] The process described in this invention is simple and reasonable, yielding ammonium heptamolybdate with high purity and excellent clarity and impurity content. The crystal regularity is significantly better than traditional processes; under a microscope, the product exhibits sharp edges, uniform particle size, and clear transparency. The crystallization yield is significantly improved compared to traditional processes, with a one-time crystallization yield exceeding 80% (compared to only 50-60% in traditional processes), achieving high efficiency for industrial-scale production. The product purity is above 99.5%, and all product indicators meet the requirements of the new national standard GB / T3460-2017 for Grade I products. Most indicators are close to the standards for chemical reagent-grade ammonium heptamolybdate (e.g., clarity and color ≤ 4#, reaching analytical purity levels). Attached Figure Description

[0015] Figure 1 This is a process flow diagram of the present invention; Figure 2 These are microscopic photographs of the crystal form and particle size distribution of the ammonium heptamolybdate product of the present invention (corresponding to Example 1); Figure 3 These are microscopic photographs of the crystal form and particle size distribution of the ammonium heptamolybdate product of the present invention (corresponding to Example 2); Figure 4 These are microscope images showing the crystal form and particle size distribution of ammonium heptamolybdate produced using traditional processes. Detailed Implementation

[0016] Example 1 Step 1: Preparation of ammonium molybdate solution: Add 6.6 ml of pure water to the ammonium molybdate mixing tank at room temperature. 3 Turn on the agitator of the ammonium molybdate mixing tank and stir. Pour 153 kg of liquid ammonia into the ammonium molybdate mixing tank, and then add 3000 kg of tetramolybdate (free water content of 2% to 3% wt, in this example, the free water content is 3% wt) into the ammonium molybdate mixing tank. After stirring and dissolving for 10 minutes, pass heating steam through the heating jacket of the ammonium molybdate mixing tank to heat the ammonium molybdate mixing tank. Stop heating when the material in the ammonium molybdate mixing tank reaches 65°C, and stir and dissolve at a constant temperature of 65 to 70°C for 1 hour. After the constant temperature is completed, use pH test paper to measure the pH value of the prepared ammonium molybdate mixed solution to be 7.0, and the ammonium molybdate mixed solution is obtained. Step 2, Circulating Precision Filtration: The ammonium molybdate mixed solution prepared in step 1 is filtered through a precision filter via reflux circulation. After the filtrate is clear and transparent, it is pumped into a cooling crystallization tank with a jacket. Step 3: Neutralize acid and adjust pH: Turn on the agitator of the cooling crystallization tank and set the stirring speed to 60 rpm. Add nitric acid (industrial grade nitric acid with a mass content of ≥98%) to the tank while monitoring the pH value to adjust the solution pH value. As the solution pH value approaches the pre-adjusted pH value, reduce the rate of nitric acid addition. During the entire process of adding nitric acid, control the nitric acid flow rate at 500-800 L / h to adjust the pH to 6.2. After the nitric acid addition is completed, continue stirring for 30 minutes. Step 4, Cooling and Crystallization: Open the cooling water inlet and outlet valves of the cooling crystallizer jacket to circulate cooling water into the jacket of the cooling crystallizer. The cooling water temperature should be 5℃, and the cooling water flow rate should be 20-30m / s. 3 / h, the ammonium molybdate mixed solution in the cooling crystallization tank is cooled down for 7 hours, and the temperature of the material in the tank drops to 10℃. At this time, a large amount of white ammonium heptamolybdate product crystallizes out in the cooling crystallization tank. Step 5: Centrifugal filtration: Turn on the centrifuge and control its speed at 400 rpm. Open the discharge valve at the bottom of the cooling crystallization tank and control the feeding rate of the centrifuge at 300 kg / time. After feeding, increase the centrifuge speed to 1000 rpm and centrifuge for 30 minutes before stopping the machine and discharging the product. The free water content in the ammonium heptamolybdate product after centrifugation should be ≤2.0%. The centrifuge operation is as follows: low-speed feeding at 400 rpm, medium-speed dehydration at 400-1000 rpm, and high-speed centrifugation at 1000 rpm. Step 6: Product drying: Turn on the rotary drum dryer. The drying drum of the rotary drum dryer should be kept at a temperature of 500-1000 m³ / h. 3 Air with a relative humidity of 40% and a temperature of 15-25°C is introduced at a flow rate of / h, and the product is dried at a drying drum speed of 6 rpm to obtain ammonium heptamolybdate.

[0017] Example 2 Step 1: Preparation of ammonium molybdate solution: Add 6.6 ml of pure water to the ammonium molybdate mixing tank at room temperature. 3 Turn on the agitator of the ammonium molybdate mixing tank and stir. Pour 147 kg of liquid ammonia into the ammonium molybdate mixing tank, and then add 3000 kg of tetramolybdate (free water content of 2% to 3% wt, in this example, the free water content is 3% wt) into the ammonium molybdate mixing tank. After stirring and dissolving for 10 minutes, pass heating steam through the heating jacket of the ammonium molybdate mixing tank to heat the ammonium molybdate mixing tank. Stop heating when the material in the ammonium molybdate mixing tank reaches 65°C, and stir and dissolve at a constant temperature of 65 to 70°C for 1 hour. After the constant temperature is completed, use pH test paper to measure the pH value of the prepared ammonium molybdate mixed solution to be 6.9, and the ammonium molybdate mixed solution is obtained. Step 2, Circulating Precision Filtration: The ammonium molybdate mixed solution prepared in step 1 is filtered through a precision filter via reflux circulation. After the filtrate is clear and transparent, it is pumped into a cooling crystallization tank with a jacket. Step 3: Neutralize acid and adjust pH: Turn on the stirrer of the cooling crystallization tank and set the stirring speed to 60 rpm. Add nitric acid (industrial grade nitric acid with a mass content of ≥98%) to the tank while monitoring the pH value to adjust the solution pH value. As the solution pH value approaches the pre-adjusted pH value, reduce the rate of nitric acid addition. During the entire process of adding nitric acid, control the nitric acid flow rate at 500-800 L / h to adjust the pH to 6.3. After the nitric acid addition is completed, continue stirring for 30 minutes. Step 4, Cooling and Crystallization: Open the cooling water inlet and outlet valves of the cooling crystallizer jacket to circulate cooling water into the jacket of the cooling crystallizer. The cooling water temperature should be 5℃, and the cooling water flow rate should be 20-30m / s. 3 / h, the ammonium molybdate mixed solution in the cooling crystallization tank is cooled down for 7 hours, and the temperature of the material in the tank drops to 10℃. At this time, a large amount of white ammonium heptamolybdate product crystallizes out in the cooling crystallization tank. Step 5: Centrifugal filtration: Turn on the centrifuge and control the centrifuge speed at 400 rpm. Open the discharge valve at the bottom of the cooling crystallization tank and control the centrifuge feeding rate at 300 kg / time. After feeding, increase the centrifuge speed to 1000 rpm. Centrifuge and spin dry for 30 minutes, then stop the machine and discharge the material. The free water content in the ammonium heptamolybdate product after spin drying is ≤2.0%. The centrifuge operation is as follows: low speed feeding at 400 rpm, medium speed dehydration at 400-1000 rpm, and high speed spin drying at 1000 rpm. Step 6: Product drying: Turn on the rotary drum dryer. The drying drum of the rotary drum dryer should be kept at a temperature of 500-1000 m³ / h. 3 Air with a relative humidity of 40% and a temperature of 15-25°C is introduced at a flow rate of / h, and the product is dried at a drying drum speed of 6 rpm to obtain ammonium heptamolybdate.

[0018] Example 3 Step 1: Preparation of ammonium molybdate solution: Add 6.6 ml of pure water to the ammonium molybdate mixing tank at room temperature. 3 Turn on the agitator of the ammonium molybdate mixing tank and stir. Pour 140 kg of liquid ammonia into the ammonium molybdate mixing tank, and then add 3000 kg of tetramolybdate (free water content of 2% to 3% wt, in this example, free water content of 3% wt) into the ammonium molybdate mixing tank. After stirring and dissolving for 10 minutes, pass heating steam through the heating jacket of the ammonium molybdate mixing tank to heat the ammonium molybdate mixing tank. Stop heating when the material in the ammonium molybdate mixing tank reaches 65°C, and stir and dissolve at a constant temperature of 65 to 70°C for 1 hour. After the constant temperature is completed, use pH test paper to measure the pH value of the prepared ammonium molybdate mixed solution to be 6.8, and obtain the ammonium molybdate mixed solution. Step 2, Circulating Precision Filtration: The ammonium molybdate mixed solution prepared in step 1 is filtered through a precision filter via reflux circulation. After the filtrate is clear and transparent, it is pumped into a cooling crystallization tank with a jacket. Step 3: Neutralize acid and adjust pH: Turn on the agitator of the cooling crystallization tank and set the stirring speed to 60 rpm. Add nitric acid (industrial grade nitric acid with a mass content of ≥98%) to the tank while monitoring the pH value to adjust the solution pH value. As the solution pH value approaches the pre-adjusted pH value, reduce the rate of nitric acid addition. During the entire process of adding nitric acid, control the nitric acid flow rate at 500-800 L / h to adjust the pH to 6.4. After the nitric acid addition is completed, continue stirring for 30 minutes. Step 4, Cooling and Crystallization: Open the cooling water inlet and outlet valves of the cooling crystallizer jacket to circulate cooling water into the jacket of the cooling crystallizer. The cooling water temperature should be 5℃, and the cooling water flow rate should be 20-30m / s. 3 / h, the ammonium molybdate mixed solution in the cooling crystallization tank is cooled down for 7 hours, and the temperature of the material in the tank drops to 12℃. At this time, a large amount of white ammonium heptamolybdate product crystallizes out in the cooling crystallization tank. Step 5: Centrifugal filtration: Turn on the centrifuge and control the centrifuge speed at 400 rpm. Open the discharge valve at the bottom of the cooling crystallization tank and control the centrifuge feeding rate at 300 kg / time. After feeding, increase the centrifuge speed to 1000 rpm. Centrifuge and spin dry for 30 minutes, then stop the machine and discharge the material. The free water content in the ammonium heptamolybdate product after spin drying is ≤2.0%. The centrifuge operation is as follows: low speed feeding at 400 rpm, medium speed dehydration at 400-1000 rpm, and high speed spin drying at 1000 rpm. Step 6: Product drying: Turn on the rotary drum dryer. The drying drum of the rotary drum dryer should be kept at a temperature of 500-1000 m³ / h. 3 Air with a relative humidity of 40% and a temperature of 15-25°C is introduced at a flow rate of / h, and the product is dried at a drying drum speed of 6 rpm to obtain ammonium heptamolybdate.

[0019] Example 4 Step 1: Preparation of ammonium molybdate solution: Add 6.6 ml of pure water to the ammonium molybdate mixing tank at room temperature. 3 Turn on the stirrer of the ammonium molybdate mixing tank and stir. Pour 135 kg of liquid ammonia into the ammonium molybdate mixing tank, and then add 3000 kg of tetramolybdate (free water content of 2% to 3% wt, in this example, the free water content is 3% wt) into the ammonium molybdate mixing tank. After stirring and dissolving for 10 minutes, heat the ammonium molybdate mixing tank by passing heating steam through the heating jacket. When the material in the ammonium molybdate mixing tank reaches 65°C, stop heating and stir and dissolve at a constant temperature of 65 to 70°C for 1 hour. After the constant temperature is completed, use pH test paper to measure the pH value of the prepared ammonium molybdate mixed solution, which is 6.7, to obtain the ammonium molybdate mixed solution. Step 2, Circulating Precision Filtration: The ammonium molybdate mixed solution prepared in step 1 is filtered through a precision filter via reflux circulation. After the filtrate is clear and transparent, it is pumped into a cooling crystallization tank with a jacket. Step 3: Neutralize acid and adjust pH: Turn on the agitator of the cooling crystallization tank and set the stirring speed to 60 rpm. Add nitric acid (industrial grade nitric acid with a mass content of ≥98%) to the tank while monitoring the pH value to adjust the solution pH value. As the solution pH value approaches the pre-adjusted pH value, reduce the rate of nitric acid addition. During the entire process of adding nitric acid, control the nitric acid flow rate at 500-800 L / h to adjust the pH to 6.5. After the nitric acid addition is completed, continue stirring for 30 minutes. Step 4, Cooling and Crystallization: Open the cooling water inlet and outlet valves of the cooling crystallizer jacket to circulate cooling water into the jacket of the cooling crystallizer. The cooling water temperature should be 5℃, and the cooling water flow rate should be 20-30m / s. 3 / h, the ammonium molybdate mixed solution in the cooling crystallization tank is cooled down for 7 hours, and the temperature of the material in the tank drops to 12℃. At this time, a large amount of white ammonium heptamolybdate product crystallizes out in the cooling crystallization tank. Step 5: Centrifugal filtration: Turn on the centrifuge and control the centrifuge speed at 400 rpm. Open the discharge valve at the bottom of the cooling crystallization tank and control the centrifuge feeding rate at 300 kg / time. After feeding, increase the centrifuge speed to 1000 rpm. Centrifuge and spin dry for 30 minutes, then stop the machine and discharge the material. The free water content in the ammonium heptamolybdate product after spin drying is ≤2.0%. The centrifuge operation is as follows: low speed feeding at 400 rpm, medium speed dehydration at 400-1000 rpm, and high speed spin drying at 1000 rpm. Step 6: Product drying: Turn on the rotary drum dryer. The drying drum of the rotary drum dryer should be kept at a temperature of 500-1000 m³ / h. 3 An air flow rate of 15-25°C with a relative humidity of 40% is introduced at a flow rate of / h, and the product is dried at a drying drum speed of 6 rpm to obtain ammonium heptamolybdate.

[0020] Table 1 Comparison of process parameters between Examples 1-4 of the present invention and traditional process parameters Table 2. Statistical table of ammonium heptamolybdate and crystallization mother liquor in Examples 1-4 of the present invention. Table 3. Detection results of ammonium heptamolybdate products after implementing process parameters in Examples 1-4 of the present invention and the traditional process. Table 4. Detection results of impurity control indicators during the production process of ammonium heptamolybdate products in Examples 1-4 of this invention (enterprise standard ppm). Note: Based on the molecular formula of ammonium heptamolybdate, the theoretical molybdenum content in the ammonium heptamolybdate product is 54.37%.

[0021] Test results of ammonium heptamolybdate products prepared in Examples 1-4 of this invention: (1) Data shows that the yield of ammonium heptamolybdate prepared by the process of the present invention is >80% in one crystallization. (2) Data shows that the quality indicators of the ammonium heptamolybdate product prepared by the process of the present invention have all met the quality requirements of the new national standard GB / T3460-2017 Grade I product; (3) Data description: According to the GB / T657-2011 reagent grade ammonium heptamolybdate product clarity test method, the product clarity and color are ≤4#, which has reached the quality index of reagent analytical grade ammonium heptamolybdate, indicating that the product purity is very high; (4) Microscopic images of ammonium heptamolybdate crystals show that the ammonium heptamolybdate crystals are regular, with distinct edges and corners, uniform particle size, and clear and transparent crystals, further proving that the ammonium heptamolybdate product has a very high purity.

[0022] The above are merely specific embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing high-purity ammonium heptamolybdate with high crystallization yield from ammonium tetramolybdate, characterized by the following steps: Step 1, preparation of ammonium molybdate mixed solution; Step 2, circulating precision filtration; circulating and filtering the ammonium molybdate mixed solution prepared in Step 1 with a precision filter to make the solution clear and transparent, and then pouring it into a cooling crystallization tank with a jacket; Step 3, acid neutralization and pH adjustment; turning on the agitator of the cooling crystallization tank, and adding nitric acid to the tank to adjust the pH of the solution to 6.2-6.5 while stirring at room temperature, and continuing to stir for 30 minutes; Step 4, cooling crystallization; opening the inlet and outlet valves of the cooling water jacket of the cooling crystallization tank, circulating cooling water into the jacket, cooling the ammonium molybdate mixed solution in the tank to a temperature of 10-12℃ for 7 hours, and then the ammonium heptamolybdate product crystallizes out; Step 5, centrifugal filtration; starting the centrifuge, controlling the speed at 400 rpm, opening the discharge valve at the bottom of the cooling crystallization tank, controlling the feeding amount of the centrifuge at 300 kg per time, increasing the speed to 1000 rpm after feeding is completed, and then stopping the centrifuge after 30 minutes of centrifugal filtration to obtain ammonium heptamolybdate with a free water content of ≤2.0%wt; Step 6, product drying. In Step 1, the pH of the ammonium molybdate mixed solution after constant temperature dissolution is 6.7-7.

0. Into the ingredient tank was added pure water 6.6 m 3 At room temperature, the stirrer was started and 135-153 kg of liquid ammonia was introduced into the ingredient tank. Then, 3000 kg of ammonium tetramolybdate was added into the ingredient tank. After stirring and dissolving for 10 minutes, the mixed solution in the ingredient tank was heated to 65°C and stirred at a constant temperature of 65-70°C for 1 hour to obtain an ammonium molybdate mixed solution. In Step 3, the stirring speed is 60 rpm. In Step 3, the flow rate of the added nitric acid is 500-800 L / h. When drying the product in a rotary drum dryer, the speed of the drying drum is 6 rpm. The nitric acid is industrial nitric acid with a mass content of ≥98%. The free water content in the ammonium tetramolybdate is 2-3%wt. ​ ​ ​ ​ The rotary drum dryer is started, and air with a relative humidity of 40% and a temperature of 15-25℃ is introduced into the drying cylinder of the rotary drum dryer at a flow rate of 500-1000 m 3 / h to dry the product, obtaining high-purity ammonium heptamolybdate.

2. The method for producing high crystallization yield and high purity ammonium heptamolybdate from ammonium tetramolybdate according to claim 1, characterized in that: ​ 3. The method for producing high crystallization yield and high purity ammonium heptamolybdate from ammonium tetramolybdate according to claim 1, characterized in that: ​ 4. The method for producing high crystallization yield and high purity ammonium heptamolybdate from ammonium tetramolybdate according to claim 1, characterized in that: ​ 5. The method for producing high crystallization yield and high purity ammonium heptamolybdate from ammonium tetramolybdate according to claim 1, characterized in that: In step 4, the cooling water is passed at a rate of 20 to 30 m 3 / h.

6. The method for producing high crystallization yield and high purity ammonium heptamolybdate from ammonium tetramolybdate according to claim 1, characterized in that: ​ 7. The method for producing high crystallization yield and high purity ammonium heptamolybdate from ammonium tetramolybdate according to claim 1, characterized by: ​ 8. The method for producing high crystallization yield and high purity ammonium heptamolybdate from ammonium tetramolybdate according to claim 1, characterized by: ​

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