A method for preparing water-soluble ammonium dimolybdate using a continuous evaporation crystallizer

Abstract

A method for preparing water-soluble ammonium dimolybdate by using a continuous evaporation crystallizer, wherein ammonium tetramolybdate is added to pure water and industrial ammonia water, filtered by a precision filter, and sent to a crystallization evaporator for evaporation and crystallization. During evaporation and crystallization, the steam pressure of the crystallization evaporator is controlled at 0.2-0.4 MPa, and the material temperature of the evaporation chamber of the crystallization evaporator is controlled at 101-105°C. The crystallization evaporator is in a slightly negative pressure state of ‑50Pa-100Pa, and evaporation and concentration are started. The evaporation rate of the stock solution is 2.1-2.5m 3 / h, when the crystallinity of ammonium dimolybdate in the crystallization chamber of the crystallization evaporator reaches 30-35%, centrifugal filtration and drying are started to obtain water-soluble ammonium dimolybdate. The advantages are: simple process, easy operation, low cost, small particle size of ammonium dimolybdate product, good particle size distribution and regular product crystal form, and the water solubility of the obtained ammonium dimolybdate can reach 100%.

Description

Technical Field

[0001] The invention relates to a method for preparing water-soluble ammonium dimolybdate by utilizing a continuous evaporation crystallizer. Background Art

[0002] As one of the most important intermediate products for deep processing of molybdenum, ammonium dimolybdate is very popular among customers due to its uniform particle size, good fluidity, stable quality and stable quality of post-processing products such as molybdenum powder, molybdenum bars and molybdenum catalysts. Ammonium dimolybdate accounts for more than 70% of the total market share of ammonium molybdate products.

[0003] With the improvement of the quality of molybdenum deep-processing products and the expansion of molybdenum metal application areas, downstream customers have put forward higher quality requirements for ammonium dimolybdate products. In addition to meeting some of the original basic properties of ammonium dimolybdate, higher requirements are also put forward for the water solubility index of ammonium dimolybdate. It is required that after 42g of ammonium dimolybdate is dissolved in 100ml of pure water at 20-30℃ with stirring for 15 minutes, the ammonium dimolybdate must be 100% dissolved, and the dissolved liquid must be clear and transparent.

[0004] At present, the ammonium dimolybdate product obtained by the conventional ammonium dimolybdate production method has large crystal size, wide particle size distribution, irregular crystal structure, poor uniformity, etc., resulting in unqualified water solubility index of ammonium dimolybdate, solubility of ammonium dimolybdate product is about 40%, and the dissolved liquid is turbid. The solubility of ammonium molybdate can be improved to a certain extent by screening the product, and the screened part is regarded as water-soluble ammonium dimolybdate. The screening rate of the product is only about 30%, the product cost is high, and the product cannot reach 100% solubility, and the quality cannot meet customer requirements. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing water-soluble ammonium dimolybdate by using a continuous evaporation crystallizer, which has the advantages of simple process, easy operation, low cost, small particle size of ammonium dimolybdate product, good particle size distribution and regular product crystal form. The obtained water-soluble ammonium dimolybdate can reach 100%, thereby broadening the application field of molybdenum metal.

[0006] The technical solution of the present invention is:

[0007] A method for preparing water-soluble ammonium dimolybdate using a continuous evaporation crystallizer, the specific steps are as follows:

[0008] Step 1 Solution preparation:

[0009] Adding ammonium tetramolybdate to purified water and industrial ammonia water to obtain an ammonium tetramolybdate solution having a specific gravity of 1.30 to 1.32 g / mL and a pH value of 8.0 to 8.5;

[0010] Step 2: Fine filtration:

[0011] Filter the ammonium tetramolybdate solution through a precision filter;

[0012] Step 3: Evaporation and crystallization:

[0013] The ammonium tetramolybdate solution that has been precisely filtered is used as the stock solution to evaporate and crystallize in the crystallization evaporator. During evaporation and crystallization, the steam pressure of the crystallization evaporator is controlled at 0.2-0.4MPa, and the material temperature in the evaporation chamber of the crystallization evaporator is controlled at 101-105°C. The crystallization evaporator is in a slightly negative pressure state of -50Pa-100Pa, and evaporation and concentration begins. The evaporation rate of the stock solution is 2.1-2.5m 3 / h, when the crystallinity of ammonium dimolybdate in the crystallization chamber of the crystallization evaporator reaches 30-35%, centrifugal filtration and drying are started to obtain water-soluble ammonium dimolybdate.

[0014] Furthermore, the molybdenum content in the ammonium tetramolybdate solution in step 1 is 180-200 g / L.

[0015] Furthermore, the filtrate after centrifugal filtration is returned to the crystallization evaporator and continues to evaporate and crystallize with the precisely filtered ammonium tetramolybdate solution.

[0016] As a further preference, the feed weight of the filtrate after centrifugal filtration returned to the crystallization evaporator accounts for ≤20% of the total feed weight.

[0017] Furthermore, during centrifugal filtration, a centrifugal filter is used, the power of the centrifugal filter is 22KW, the speed of the centrifugal filter is 1000r / min, and the discharge temperature of ammonium dimolybdate is 40-50°C.

[0018] Furthermore, the drying temperature in step 3 is 105-110°C.

[0019] Furthermore, during precision filtration, the material temperature is 50-60°C, and the filtration pressure of the precision filter is ≤0.4MPa.

[0020] Furthermore, the ammonium dimolybdate has a crystallinity of 32-33%.

[0021] Furthermore, in step 1, the volume ratio of pure water to industrial ammonia water is 3:1, and the pH value of the ammonium tetramolybdate solution is 8.5.

[0022] The beneficial effects of the present invention are:

[0023] The process is simple, easy to operate, does not require high temperature and high pressure equipment, and has low production cost. By reasonably controlling the molybdenum content and free ammonia concentration (PH value) in the ammonium dimolybdate evaporation stock solution, the evaporation crystallization method is adopted, and the stock solution feeding speed, i.e., the stock solution evaporation speed and the crystallinity of ammonium dimolybdate are controlled, so as to obtain the uniform particle size, good particle size distribution and uniform crystal structure of the ammonium dimolybdate product crystal, which can meet the requirement that 42g of ammonium dimolybdate is dissolved in 100ml of pure water at 20-30℃ for 15 minutes, and at the same time, the physical and chemical properties of the ammonium dimolybdate product meet the requirements of GB / T3460-2017, and is suitable for industrial production. DETAILED DESCRIPTION

[0024] Example

[0025] Step 1 Solution preparation:

[0026] At room temperature, add the 3 (Φ2.6×3.5m), material: 304 stainless steel) plus pure water (16-18MΩ) 6m 3 , start stirring the preparation tank, add 2m 3 Industrial ammonia water (quality meets the requirements of GB / T631-2017), steam is passed through the jacket of the preparation tank for heating, when the temperature of the solution in the preparation tank rises to 40°C, 3000Kg of ammonium tetramolybdate is added to the tank, and the temperature is continued to rise to 60°C, and stirred at a constant temperature for 30 minutes until the ammonium tetramolybdate in the tank is completely dissolved. The specific gravity of the solution is 1.30g / mL measured by a hydrometer, and the pH value of the solution is 8.0-8.5 measured by pH test paper. After all the test indicators are qualified, stirring is stopped to obtain an ammonium tetramolybdate solution;

[0027] Step 2: Fine filtration:

[0028] Open the discharge valve at the bottom of the preparation tank and start the precision filter (0.1m 3 (Φ0.4×0.9m), material: 304 stainless steel) feed pump, start filtering, during precision filtering, the material temperature is 50-60℃, monitor the pressure gauge pressure on the precision filter at ≤0.4MPa during filtering to avoid clogging of the filter element of the precision filter, when the ammonium tetramolybdate solution in the preparation tank is put into the precision filter and the filtration is completed, stop the feed pump of the precision filter and the stirring on the preparation tank, and close the discharge valve at the lower end of the preparation tank;

[0029] Step 3: Continuous evaporation crystallization:

[0030] Total volume of ammonium dimolybdate evaporation crystallizer: 26m 3 , divided into two chambers, the upper end is the evaporation chamber 20m 3 (Φ2.9×3.0m), the lower end is the crystallization chamber 6m 3(Φ1.6×3.0m), all made of 304 stainless steel; open the material inlet valve of the ammonium dimolybdate evaporator crystallizer, start the feed pump of the ammonium dimolybdate continuous evaporator, feed the precisely filtered ammonium tetramolybdate solution to the ammonium dimolybdate continuous evaporator, start the circulation pump of the evaporation chamber of the ammonium dimolybdate evaporator, open the heating steam valve of the ammonium dimolybdate evaporator reboiler, open the material circulation pump of the crystallization chamber of the ammonium dimolybdate continuous evaporator, control the steam pressure of the heating reboiler at 0.2~0.4MPa, and control the material temperature of the evaporation chamber at 101~105℃, the crystallization evaporator is in a slightly negative pressure state of -50Pa~100Pa, start evaporation and concentration, and the evaporation rate of the stock solution is 2.1~2.5m 3 / h, when the degree of crystallization of ammonium dimolybdate in the ammonium dimolybdate crystallization chamber solution reaches 30-35%;

[0031] Step 4 Centrifugal filtration:

[0032] The solution is sent to a centrifugal filter for centrifugal filtration. The power of the centrifugal filtration is 22Kw, the speed of the centrifugal filtration is 1000r / min, the discharge temperature of ammonium dimolybdate is 40-50°C, the filter cake after centrifugal filtration is dried in a microwave drying furnace, and the filtrate after centrifugal filtration is returned to the crystallization evaporator to continue evaporation and crystallization with the precisely filtered ammonium tetramolybdate solution. The feed weight of the filtrate after centrifugal filtration returned to the crystallization evaporator accounts for 10% of the total feed weight;

[0033] Step 5 Drying:

[0034] The filter cake fed into the microwave drying furnace is dried in the microwave drying furnace at a drying temperature of 105-110° C. to obtain water-soluble ammonium dimolybdate.

[0035] The actual operation process control parameter statistics of the continuous evaporation crystallizer of Example 1 to Example 5 of the present invention are shown in Table 1:

[0036]

[0037] Table 1 Actual operation process control parameters of continuous evaporation crystallizer of Example 1-Example 5

[0038] Example 1

[0039] Step 1 Solution preparation:

[0040] At room temperature, add the 3 (Φ2.6×3.5m), material: 304 stainless steel) plus pure water (16-18MΩ) 6m 3 , start stirring the preparation tank, add 2m 3Industrial ammonia water (quality meets the requirements of GB / T631-2017), steam is passed through the jacket of the preparation tank for heating, and when the temperature of the solution in the preparation tank rises to 40°C, 3000Kg of ammonium tetramolybdate is added to the tank, and the temperature is continued to rise to 60°C, and stirred at a constant temperature for 30 minutes until the ammonium tetramolybdate in the tank is completely dissolved. The specific gravity of the solution is 1.30g / mL measured by a hydrometer, and the pH value of the solution is 8.5 measured by a pH test paper. After all the test indicators are qualified, stirring is stopped to obtain an ammonium tetramolybdate solution;

[0041] Step 2: Fine filtration:

[0042] Open the discharge valve at the bottom of the preparation tank and start the precision filter (0.1m 3 (Φ0.4×0.9m), material: 304 stainless steel) feed pump, start filtering, during precision filtering, the material temperature is 50-60℃, monitor the pressure gauge pressure on the precision filter at ≤0.4MPa during filtering to avoid clogging of the filter element of the precision filter, when the ammonium tetramolybdate solution in the preparation tank is put into the precision filter and the filtration is completed, stop the feed pump of the precision filter and the stirring on the preparation tank, and close the discharge valve at the lower end of the preparation tank;

[0043] Step 3: Continuous evaporation crystallization:

[0044] Total volume of ammonium dimolybdate evaporation crystallizer: 26m 3 , divided into two chambers, the upper end is the evaporation chamber 20m 3 (Φ2.9×3.0m), the lower end is the crystallization chamber 6m 3 (Φ1.6×3.0m), all made of 304 stainless steel; open the material inlet valve of the ammonium dimolybdate evaporator crystallizer, start the feed pump of the ammonium dimolybdate continuous evaporator, feed the precisely filtered ammonium tetramolybdate solution to the ammonium dimolybdate continuous evaporator, start the circulation pump of the evaporation chamber of the ammonium dimolybdate evaporator, open the heating steam valve of the ammonium dimolybdate evaporator reboiler, open the material circulation pump of the crystallization chamber of the ammonium dimolybdate continuous evaporator, control the steam pressure of the heating reboiler at 0.4MPa, and control the material temperature of the evaporation chamber at 105℃, the crystallization evaporator is in a slightly negative pressure state of -50Pa~100Pa, start evaporation and concentration, and the evaporation rate of the stock solution is 2.5m 3 / h, when the degree of crystallization of ammonium dimolybdate in the ammonium dimolybdate crystallization chamber solution reaches 32%, the solution is sent to a centrifugal filter for centrifugal filtration;

[0045] Step 4 Centrifugal filtration:

[0046] During centrifugal filtration in the centrifugal filter, the power of the centrifugal filtration is 22Kw, the speed of the centrifugal filtration is 1000r / min, the discharge temperature of ammonium dimolybdate is 40-50℃, the filter cake after centrifugal filtration is dried in a microwave drying furnace, the filtrate after centrifugal filtration is returned to the crystallization evaporator to continue evaporation and crystallization with the precisely filtered ammonium tetramolybdate solution, and the feed weight of the filtrate after centrifugal filtration returned to the crystallization evaporator accounts for 10% of the total feed weight;

[0047] Step 5 Drying:

[0048] The filter cake fed into the microwave drying furnace is dried in the microwave drying furnace at a drying temperature of 105-110° C. to obtain water-soluble ammonium dimolybdate. The test results of appearance, FSS particle size, microscopic observation results, bulk density, purity and water solubility of the water-soluble ammonium dimolybdate are shown in Table 2. The test results of the chemical composition of the water-soluble ammonium dimolybdate are shown in Table 3.

[0049] Example 2

[0050] Step 1 Solution preparation:

[0051] At room temperature, add the 3 (Φ2.6×3.5m), material: 304 stainless steel) plus pure water (16-18MΩ) 6m 3 , start stirring the preparation tank, add 2m 3 Industrial ammonia water (quality meets the requirements of GB / T631-2017), steam is passed through the jacket of the preparation tank for heating, and when the temperature of the solution in the preparation tank rises to 40°C, 3000Kg of ammonium tetramolybdate is added to the tank, and the temperature is continued to rise to 60°C, and stirred at a constant temperature for 30 minutes until the ammonium tetramolybdate in the tank is completely dissolved. The specific gravity of the solution is 1.30g / mL measured by a hydrometer, and the pH value of the solution is 8.5 measured by a pH test paper. After all the test indicators are qualified, stirring is stopped to obtain an ammonium tetramolybdate solution;

[0052] Step 2: Fine filtration:

[0053] Open the discharge valve at the bottom of the preparation tank and start the precision filter (0.1m 3 (Φ0.4×0.9m), material: 304 stainless steel) feed pump, start filtering, during precision filtering, the material temperature is 50-60℃, monitor the pressure gauge pressure on the precision filter at ≤0.4MPa during filtering to avoid clogging of the filter element of the precision filter, when the ammonium tetramolybdate solution in the preparation tank is put into the precision filter and the filtration is completed, stop the feed pump of the precision filter and the stirring on the preparation tank, and close the discharge valve at the lower end of the preparation tank;

[0054] Step 3: Continuous evaporation crystallization:

[0055] Total volume of ammonium dimolybdate evaporation crystallizer: 26m3 , divided into two chambers, the upper end is the evaporation chamber 20m 3 (Φ2.9×3.0m), the lower end is the crystallization chamber 6m 3 (Φ1.6×3.0m), all made of 304 stainless steel; open the material inlet valve of the ammonium dimolybdate evaporator crystallizer, start the feed pump of the ammonium dimolybdate continuous evaporator, feed the precisely filtered ammonium tetramolybdate solution to the ammonium dimolybdate continuous evaporator, start the circulation pump of the evaporation chamber of the ammonium dimolybdate evaporator, open the heating steam valve of the ammonium dimolybdate evaporator reboiler, open the material circulation pump of the crystallization chamber of the ammonium dimolybdate continuous evaporator, control the steam pressure of the heating reboiler at 0.35MPa, and control the material temperature of the evaporation chamber at 104℃, the crystallization evaporator is in a slightly negative pressure state of -50Pa~100Pa, start evaporation and concentration, and the evaporation rate of the stock solution is 2.4m 3 / h, when the degree of crystallization of ammonium dimolybdate in the ammonium dimolybdate crystallization chamber solution reaches 32%, the solution is sent to a centrifugal filter for centrifugal filtration;

[0056] Step 4 Centrifugal filtration:

[0057] During centrifugal filtration in the centrifugal filter, the power of the centrifugal filtration is 22Kw, the speed of the centrifugal filtration is 1000r / min, the discharge temperature of ammonium dimolybdate is 40-50℃, the filter cake after centrifugal filtration is dried in a microwave drying furnace, the filtrate after centrifugal filtration is returned to the crystallization evaporator to continue evaporation and crystallization with the precisely filtered ammonium tetramolybdate solution, and the feed weight of the filtrate after centrifugal filtration returned to the crystallization evaporator accounts for 10% of the total feed weight;

[0058] Step 5 Drying:

[0059] The filter cake fed into the microwave drying furnace is dried in the microwave drying furnace at a drying temperature of 105-110° C. to obtain water-soluble ammonium dimolybdate. The test results of appearance, FSS particle size, microscopic observation results, bulk density, purity and water solubility of the water-soluble ammonium dimolybdate are shown in Table 2. The test results of the chemical composition of the water-soluble ammonium dimolybdate are shown in Table 3.

[0060] Example 3

[0061] Step 1 Solution preparation:

[0062] At room temperature, add the 3 (Φ2.6×3.5m), material: 304 stainless steel) plus pure water (16-18MΩ) 6m 3 , start stirring the preparation tank, add 2m 3Industrial ammonia water (quality meets the requirements of GB / T631-2017), steam is passed through the jacket of the preparation tank for heating, and when the temperature of the solution in the preparation tank rises to 40°C, 3000Kg of ammonium tetramolybdate is added to the tank, and the temperature is continued to rise to 60°C, and stirred at a constant temperature for 30 minutes until the ammonium tetramolybdate in the tank is completely dissolved. The specific gravity of the solution is 1.30g / mL measured by a hydrometer, and the pH value of the solution is 8.5 measured by a pH test paper. After all the test indicators are qualified, stirring is stopped to obtain an ammonium tetramolybdate solution;

[0063] Step 2: Fine filtration:

[0064] Open the discharge valve at the bottom of the preparation tank and start the precision filter (0.1m 3 (Φ0.4×0.9m), material: 304 stainless steel) feed pump, start filtering, during precision filtering, the material temperature is 50-60℃, monitor the pressure gauge pressure on the precision filter at ≤0.4MPa during filtering to avoid clogging of the filter element of the precision filter, when the ammonium tetramolybdate solution in the preparation tank is put into the precision filter and the filtration is completed, stop the feed pump of the precision filter and the stirring on the preparation tank, and close the discharge valve at the lower end of the preparation tank;

[0065] Step 3: Continuous evaporation crystallization:

[0066] Total volume of ammonium dimolybdate evaporation crystallizer: 26m 3 , divided into two chambers, the upper end is the evaporation chamber 20m 3 (Φ2.9×3.0m), the lower end is the crystallization chamber 6m 3 (Φ1.6×3.0m), all made of 304 stainless steel; open the material inlet valve of the ammonium dimolybdate evaporator crystallizer, start the feed pump of the ammonium dimolybdate continuous evaporator, feed the precisely filtered ammonium tetramolybdate solution to the ammonium dimolybdate continuous evaporator, start the circulation pump of the evaporation chamber of the ammonium dimolybdate evaporator, open the heating steam valve of the ammonium dimolybdate evaporator reboiler, open the material circulation pump of the crystallization chamber of the ammonium dimolybdate continuous evaporator, control the steam pressure of the heating reboiler at 0.3MPa, and control the material temperature of the evaporation chamber at 103℃, the crystallization evaporator is in a slightly negative pressure state of -50Pa~100Pa, start evaporation and concentration, and the evaporation rate of the stock solution is 2.3m 3 / h, when the degree of crystallization of ammonium dimolybdate in the ammonium dimolybdate crystallization chamber solution reaches 33%, the solution is sent to a centrifugal filter for centrifugal filtration;

[0067] Step 4 Centrifugal filtration:

[0068] During centrifugal filtration, the centrifugal filtration power is 22Kw, the centrifugal filtration speed is 1000r / min, the ammonium dimolybdate discharge temperature is 40-50℃, the filter cake after centrifugal filtration is dried in a microwave drying furnace, the filtrate after centrifugal filtration is returned to the crystallization evaporator and continues to evaporate and crystallize with the precisely filtered ammonium tetramolybdate solution, and the feed weight of the filtrate after centrifugal filtration returned to the crystallization evaporator accounts for 10% of the total feed weight;

[0069] Step 5 Drying:

[0070] The filter cake fed into the microwave drying furnace is dried in the microwave drying furnace at a drying temperature of 105-110° C. to obtain water-soluble ammonium dimolybdate. The test results of appearance, FSS particle size, microscopic observation results, bulk density, purity and water solubility of the water-soluble ammonium dimolybdate are shown in Table 2. The test results of the chemical composition of the water-soluble ammonium dimolybdate are shown in Table 3.

[0071] Example 4

[0072] Step 1 Solution preparation:

[0073] At room temperature, add the 3 (Φ2.6×3.5m), material: 304 stainless steel) plus pure water (16-18MΩ) 6m 3 , start stirring the preparation tank, add 2m 3 Industrial ammonia water (quality meets the requirements of GB / T631-2017), steam is passed through the jacket of the preparation tank for heating, and when the temperature of the solution in the preparation tank rises to 40°C, 3000Kg of ammonium tetramolybdate is added to the tank, and the temperature is continued to rise to 60°C, and stirred at a constant temperature for 30 minutes until the ammonium tetramolybdate in the tank is completely dissolved. The specific gravity of the solution is 1.30g / mL measured by a hydrometer, and the pH value of the solution is 8.5 measured by a pH test paper. After all the test indicators are qualified, stirring is stopped to obtain an ammonium tetramolybdate solution;

[0074] Step 2: Fine filtration:

[0075] Open the discharge valve at the bottom of the preparation tank and start the precision filter (0.1m 3 (Φ0.4×0.9m), material: 304 stainless steel) feed pump, start filtering, during precision filtering, the material temperature is 50-60℃, monitor the pressure gauge pressure on the precision filter at ≤0.4MPa during filtering to avoid clogging of the filter element of the precision filter, when the ammonium tetramolybdate solution in the preparation tank is put into the precision filter and the filtration is completed, stop the feed pump of the precision filter and the stirring on the preparation tank, and close the discharge valve at the lower end of the preparation tank;

[0076] Step 3: Continuous evaporation crystallization:

[0077] Total volume of ammonium dimolybdate evaporation crystallizer: 26m 3, divided into two chambers, the upper end is the evaporation chamber 20m 3 (Φ2.9×3.0m), the lower end is the crystallization chamber 6m 3 (Φ1.6×3.0m), all made of 304 stainless steel; open the material inlet valve of the ammonium dimolybdate evaporator crystallizer, start the feed pump of the ammonium dimolybdate continuous evaporator, feed the precisely filtered ammonium tetramolybdate solution to the ammonium dimolybdate continuous evaporator, start the circulation pump of the evaporation chamber of the ammonium dimolybdate evaporator, open the heating steam valve of the ammonium dimolybdate evaporator reboiler, open the material circulation pump of the crystallization chamber of the ammonium dimolybdate continuous evaporator, control the steam pressure of the heating reboiler at 0.25MPa, and control the material temperature of the evaporation chamber at 102℃, the crystallization evaporator is in a slightly negative pressure state of -50Pa~100Pa, start evaporation and concentration, and the evaporation rate of the stock solution is 2.2m 3 / h, when the degree of crystallization of ammonium dimolybdate in the ammonium dimolybdate crystallization chamber solution reaches 33%, the solution is sent to a centrifugal filter for centrifugal filtration;

[0078] Step 4 Centrifugal filtration:

[0079] During centrifugal filtration in the centrifugal filter, the power of the centrifugal filtration is 22Kw, the speed of the centrifugal filtration is 1000r / min, the discharge temperature of ammonium dimolybdate is 40-50℃, the filter cake after centrifugal filtration is dried in a microwave drying furnace, the filtrate after centrifugal filtration is returned to the crystallization evaporator to continue evaporation and crystallization with the precisely filtered ammonium tetramolybdate solution, and the feed weight of the filtrate after centrifugal filtration returned to the crystallization evaporator accounts for 10% of the total feed weight;

[0080] Step 5 Drying:

[0081] The filter cake fed into the microwave drying furnace is dried in the microwave drying furnace at a drying temperature of 105-110° C. to obtain water-soluble ammonium dimolybdate. The test results of appearance, FSS particle size, microscopic observation results, bulk density, purity and water solubility of the water-soluble ammonium dimolybdate are shown in Table 2. The test results of the chemical composition of the water-soluble ammonium dimolybdate are shown in Table 3.

[0082] Example 5

[0083] Step 1 Solution preparation:

[0084] At room temperature, add the 3 (Φ2.6×3.5m), material: 304 stainless steel) plus pure water (16-18MΩ) 6m 3 , start stirring the preparation tank, add 2m 3Industrial ammonia water (quality meets the requirements of GB / T631-2017), steam is passed through the jacket of the preparation tank for heating, and when the temperature of the solution in the preparation tank rises to 40°C, 3000Kg of ammonium tetramolybdate is added to the tank, and the temperature is continued to rise to 60°C, and stirred at a constant temperature for 30 minutes until the ammonium tetramolybdate in the tank is completely dissolved. The specific gravity of the solution is 1.30g / mL measured by a hydrometer, and the pH value of the solution is 8.5 measured by a pH test paper. After all the test indicators are qualified, stirring is stopped to obtain an ammonium tetramolybdate solution;

[0085] Step 2: Fine filtration:

[0086] Open the discharge valve at the bottom of the preparation tank and start the precision filter (0.1m 3 (Φ0.4×0.9m), material: 304 stainless steel) feed pump, start filtering, during precision filtering, the material temperature is 50-60℃, monitor the pressure gauge pressure on the precision filter at ≤0.4MPa during filtering to avoid clogging of the filter element of the precision filter, when the ammonium tetramolybdate solution in the preparation tank is put into the precision filter and the filtration is completed, stop the feed pump of the precision filter and the stirring on the preparation tank, and close the discharge valve at the lower end of the preparation tank;

[0087] Step 3: Continuous evaporation crystallization:

[0088] Total volume of ammonium dimolybdate evaporation crystallizer: 26m 3 , divided into two chambers, the upper end is the evaporation chamber 20m 3 (Φ2.9×3.0m), the lower end is the crystallization chamber 6m 3 (Φ1.6×3.0m), all made of 304 stainless steel; open the material inlet valve of the ammonium dimolybdate evaporator crystallizer, start the feed pump of the ammonium dimolybdate continuous evaporator, feed the precisely filtered ammonium tetramolybdate solution to the ammonium dimolybdate continuous evaporator, start the circulation pump of the evaporation chamber of the ammonium dimolybdate evaporator, open the heating steam valve of the ammonium dimolybdate evaporator reboiler, open the material circulation pump of the crystallization chamber of the ammonium dimolybdate continuous evaporator, control the steam pressure of the heating reboiler at 0.2MPa, and control the material temperature of the evaporation chamber at 101℃, the crystallization evaporator is in a slightly negative pressure state of -50Pa~100Pa, start evaporation and concentration, and the evaporation rate of the stock solution is 2.1m 3 / h, when the degree of crystallization of ammonium dimolybdate in the ammonium dimolybdate crystallization chamber solution reaches 33%, the solution is sent to a centrifugal filter for centrifugal filtration;

[0089] Step 4 Centrifugal filtration:

[0090] During centrifugal filtration in the centrifugal filter, the power of the centrifugal filtration is 22Kw, the speed of the centrifugal filtration is 1000r / min, the discharge temperature of ammonium dimolybdate is 40-50℃, the filter cake after centrifugal filtration is dried in a microwave drying furnace, the filtrate after centrifugal filtration is returned to the crystallization evaporator to continue evaporation and crystallization with the precisely filtered ammonium tetramolybdate solution, and the feed weight of the filtrate after centrifugal filtration returned to the crystallization evaporator accounts for 10% of the total feed weight;

[0091] Step 5 Drying:

[0092] The filter cake fed into the microwave drying furnace is dried in the microwave drying furnace at a drying temperature of 105-110° C. to obtain water-soluble ammonium dimolybdate. The test results of appearance, FSS particle size, microscopic observation results, bulk density, purity and water solubility of the water-soluble ammonium dimolybdate are shown in Table 2. The test results of the chemical composition of the water-soluble ammonium dimolybdate are shown in Table 3.

[0093] Comparative Example 1

[0094] In this comparative example, when the degree of crystallinity of ammonium dimolybdate in the ammonium dimolybdate crystallization chamber solution reaches 45%, the solution is sent to a centrifugal filter for centrifugal filtration; the rest is the same as in Example 5.

[0095] Comparative Example 2

[0096] In this comparative example, the evaporation rate of the original liquid was controlled to be 3m 3 / h; the rest is the same as in Example 5.

[0097] Comparative Example 3

[0098] In this comparative example, the pH value of the ammonium tetramolybdate solution is 9.0; the other conditions are the same as those in Example 5.

[0099] Table 2 Quality test results of water-soluble ammonium dimolybdate of Example 1-Example 5

[0100]

[0101] The water solubility test of ammonium dimolybdate of the present invention is as follows: 42 g of ammonium dimolybdate is dissolved in 100 mL of pure water under stirring at 20-30° C. for 15 minutes, heating and stirring are stopped, and the mixture is left standing for 5 minutes. When 100% of the ammonium dimolybdate is dissolved and the solution is clear and transparent, the water solubility of the product is qualified.

[0102] Table 3 Test results of chemical composition of water-soluble ammonium dimolybdate of Example 1 to Example 5

[0103]

[0104] From Table 2 and Table 3, it can be seen that the analysis and detection results of water-soluble ammonium dimolybdate of Examples 1 to 5 of the present invention are as follows:

[0105] (1) The water-soluble ammonium dimolybdate of Examples 1 to 5 of the present invention complies with the GB / T3460-2017 standard in terms of both chemical composition index and physical quality requirements.

[0106] (2) The water-soluble ammonium dimolybdate of Examples 1 to 5 of the present invention has excellent appearance, FSS particle size, microscopic observation results, bulk density, purity and water solubility. The product solubility can reach 100%, which meets the actual application requirements.

Claims

1. A method for preparing water-soluble ammonium dimolybdate using a continuous evaporation crystallizer, characterized in that: Specific steps as follows: Step 1 Solution preparation: Adding ammonium tetramolybdate to purified water and industrial ammonia water to obtain an ammonium tetramolybdate solution having a specific gravity of 1.30-1.32 g / mL, a molybdenum content of 180-200 g / L, and a pH value of 8.0-8.5; Step 2: Fine filtration: Filter the ammonium tetramolybdate solution through a precision filter; Step 3: Evaporation and crystallization: The ammonium tetramolybdate solution that has been precisely filtered is used as the stock solution to evaporate and crystallize in the crystallization evaporator. During evaporation and crystallization, the steam pressure of the crystallization evaporator is controlled at 0.2-0.4MPa, and the material temperature in the evaporation chamber of the crystallization evaporator is controlled at 101-105°C. The crystallization evaporator is in a slightly negative pressure state of -50Pa-100Pa, and evaporation and concentration begins. The evaporation rate of the stock solution is 2.1-2.5m 3 / h, when the crystallinity of ammonium dimolybdate in the crystallization chamber of the crystallization evaporator reaches 30-35%, centrifugal filtration and drying are started to obtain water-soluble ammonium dimolybdate.

2. The method for preparing water-soluble ammonium dimolybdate by utilizing a continuous evaporation crystallizer according to claim 1, wherein: The filtrate after centrifugal filtration is returned to the crystallization evaporator to continue evaporation and crystallization with the precisely filtered ammonium tetramolybdate solution.

3. The method for preparing water-soluble ammonium dimolybdate by utilizing a continuous evaporation crystallizer according to claim 2, wherein: The feed weight of the filtrate after centrifugal filtration returned to the crystallization evaporator accounts for ≤20% of the total feed weight.

4. The method for preparing water-soluble ammonium dimolybdate by utilizing a continuous evaporation crystallizer according to claim 1, characterized in that: During centrifugal filtration, a centrifugal filter is used. The power of the centrifugal filter is 22KW, the speed of the centrifugal filter is 1000r / min, and the discharge temperature of ammonium dimolybdate is 40-50°C.

5. The method for preparing water-soluble ammonium dimolybdate by utilizing a continuous evaporation crystallizer according to claim 1, characterized in that: Step 3: The drying temperature is 105-110°C.

6. The method for preparing water-soluble ammonium dimolybdate by a continuous evaporation crystallizer according to claim 1, characterized in that: During precision filtration, the material temperature is 50-60°C and the filtration pressure of the precision filter is ≤0.4MPa.

7. The method for preparing water-soluble ammonium dimolybdate by a continuous evaporation crystallizer according to claim 1, characterized in that: The ammonium dimolybdate has a crystallinity of 32-33%.

8. The method for preparing water-soluble ammonium dimolybdate by a continuous evaporation crystallizer according to claim 1, characterized in that: The volume ratio of pure water to industrial ammonia water in step 1 is 3:

1.

9. The method for preparing water-soluble ammonium dimolybdate by utilizing a continuous evaporation crystallizer according to claim 8, characterized in that: The pH value of the ammonium tetramolybdate solution in step 1 is 8.5.

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