CN112875753A - Preparation method of low-sodium low-ammonium high-purity molybdic acid - Google Patents
Preparation method of low-sodium low-ammonium high-purity molybdic acid Download PDFInfo
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Abstract
The invention relates to a preparation method of high-purity molybdic acid for catalyst industry, which comprises the following steps: the preparation method comprises the steps of adding water into high-purity molybdenum trioxide to prepare slurry, slowly adding solid sodium hydroxide, adjusting the pH value of a solution to 6-12, and filtering the mother liquor to obtain clear mother liquor, wherein the mother liquor is a sodium molybdate solution; slowly adding a nitric acid solution into the clarified mother liquor to adjust the pH acidity of the solution, and heating until molybdic acid crystals are precipitated; thirdly, solid-liquid separation is carried out on the mixed solution containing the crystalline molybdic acid, and the high-purity molybdic acid is obtained by drying and screening the solid at the temperature of 60-95 ℃. The method has scientific and reasonable design and excellent application effect, selects single molybdenum concentrate as a raw material, and obtains a high-purity molybdic acid product by a two-stage purification process of ammonium tetramolybdate and high-purity molybdenum trioxide, wherein the high-purity molybdenum trioxide is dissolved in specific sodium hydroxide, the solution of the high-purity molybdenum trioxide is acidified by nitric acid to reach a certain pH value, crystals of molybdic acid are separated out from the solution, and the high-purity molybdic acid product is obtained by solid-liquid separation, drying and screening.
Description
Technical Field
The invention belongs to the field of chemical production, relates to a catalyst production technology, and particularly relates to a preparation method of low-sodium low-ammonium high-purity molybdic acid.
Background
Molybdic acid is an inorganic acid, is an oxyacid of molybdenum, and is weak in oxidizing property. The catalyst is used as a main effective component for manufacturing a high-end catalyst for residual oil hydrogenation in the petroleum processing process, and plays a key role in bearing. The preparation method of common molybdic acid mainly adopts a method of nitric acid acidification of solution containing molybdate recovered from waste catalyst. Therefore, only the molybdic acid product with low purity is taken as the raw material for producing low-quality ammonium tetramolybdate or sodium molybdate in the molybdenum industry market in China at present and is supplied to molybdenum chemical enterprises for use. The final composition is not pure molybdic acid, and is usually a mixture of molybdic acid and ammonium molybdate.
The existing production process uses the recovered industrial molybdenum waste to produce molybdic acid, wherein the existence of ammonium salt and sodium salt has great influence on the processing of high-end catalysts. NH in molybdic acid4The content requirement is not higher than 0.05%, and a high-purity molybdic acid product which can meet the use requirement of the catalyst does not exist in China so far.
In addition, when the ammonium molybdate content in molybdic acid is more than 1%, the physical properties of the finished product are changed, namely, molybdic acid with low purity generates extremely fine crystal particles, has high viscosity, is difficult to filter, and generates agglomeration after drying, thereby bringing difficulty to subsequent processing procedures.
Through the search of the prior published patent documents, the following published patent documents similar to the method technology of the invention exist:
a preparation method of high-purity molybdic acid (CN106698517A) is disclosed, and the preparation method comprises the steps of adding flaky sodium hydroxide into a molybdate solution for pretreatment, evaporating, dissolving with pure water after crystals appear, adding nitric acid for acidification, performing solid-liquid separation, and drying to obtain the high-purity molybdic acid. The disadvantages of the patent are that:
1. raw materials: the molybdate solution is ammonium molybdate, the raw material source contains a large amount of ammonium, and great difficulty is brought to subsequent impurity removal; 2. removing ammonium: according to the method, all ammonium is added into flaky sodium hydroxide and evaporated to remove free ammonium salt under a high-alkalinity condition, and tests show that the removal effect is poor, the ammonium residue phenomenon is serious, and the product is caked; 3. according to the method, a large amount of flaky sodium hydroxide is added to remove ammonium, but a large amount of sodium ions are introduced in the ammonium removal process, so that a new problem is brought to the subsequent purification of molybdic acid; 4. the method is characterized in that 98% nitric acid is adopted for acidification, the solution is acidified, molybdate radicals in the solution are precipitated through acidification, however, practice shows that the requirement of high-concentration nitric acid in the storage and transportation process is high, after the solution is added, the whole reaction system is carried out at high temperature due to the fact that a large amount of heat is released through neutralization reaction of strong acid and strong base, impurity removal is very unfavorable, a large number of impurities cannot be removed, the product is sticky and separated out at high temperature, and the product is bound after being dried, so that the method has a subsequent crushing process, and the three points cause inconvenience to downstream production enterprises and need to be solved urgently.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a preparation method for obtaining a high-purity molybdic acid product by dissolving and acidifying high-purity molybdenum trioxide by sodium hydroxide through the purification processes of ammonium tetramolybdate and high-purity molybdenum trioxide by using single molybdenum concentrate as a raw material.
The technical problem to be solved by the invention is realized by adopting the following technical scheme:
a preparation method of low-sodium low-ammonium high-purity molybdic acid comprises the following steps:
the preparation method comprises the steps of adding water into high-purity molybdenum trioxide to prepare slurry, slowly adding solid sodium hydroxide, adjusting the pH value of a solution to 6-12, and filtering the mother liquor to obtain clear mother liquor, wherein the mother liquor is a sodium molybdate solution;
slowly adding a nitric acid solution into the clarified mother liquor to adjust the pH of the solution to acidity, and heating until molybdic acid crystals are separated out;
thirdly, solid-liquid separation is carried out on the mixed solution containing the crystalline molybdic acid, and the high-purity molybdic acid is obtained by drying and screening the solid at the temperature of 60-95 ℃.
Moreover, the high-purity molybdenum trioxide is prepared by calcining ammonium tetramolybdate at high temperature.
Moreover, the preparation method of the high-purity molybdenum trioxide comprises the following steps: the method comprises the steps of selecting molybdenum concentrate with more than 50% of molybdenum content to produce ammonium tetramolybdate; and calcining the ammonium tetramolybdate at the high temperature of 300-600 ℃ to generate high-purity molybdenum trioxide.
And the weight ratio of the high-purity molybdenum trioxide to the water is 1: 2-3.
Moreover, the concentration of the nitric acid solution is 40-80%.
And in the step three, the heating temperature is 60-95 ℃, and the heating time is 15-60 min.
The high-purity molybdenum trioxide is produced by roasting and ammonia leaching molybdenum concentrate with the concentration of more than 50%, removing impurities, precipitating nitric acid and then calcining at high temperature.
The invention has the advantages and positive effects that:
1. according to the method, more than 50% of molybdenum concentrate is used as a raw material to produce ammonium tetramolybdate, the ammonium tetramolybdate is calcined at a high temperature of 300-600 ℃ to generate high-purity molybdenum trioxide, compared with a molybdate/ammonium mixed solution, the problem of high ammonium content is solved in advance, a subsequent ammonium removing process is not needed, the ammonium content of a finished product is low, and meanwhile, environmental pollution is avoided.
2. According to the method, alkaline conditions are required to be provided for dissolving molybdenum trioxide, high-purity molybdenum trioxide is mixed with water to form slurry, then solid sodium hydroxide is slowly added, the pH value of the solution is adjusted to 6-12, too strong alkaline conditions are not required, the addition amount of the solution sodium hydroxide is effectively controlled, a large amount of sodium impurities in a finished product are avoided, and the purity of molybdic acid is effectively improved.
3. According to the method, 40-80% nitric acid is slowly added into the clarified mother liquor, the acidic condition of the solution is adjusted until molybdic acid crystals are precipitated, as the concentration of the nitric acid is low, a large amount of heat is not released in the reaction, the molybdic acid is not caked, the concentration and crushing steps are not needed, the concentration of the nitric acid is low, the production cost is effectively reduced, and compared with the high-concentration acidification crystals, the method has the advantages of large fineness of the finished product, low viscosity and loose physical properties, and can meet the requirements of customers.
4. The method has scientific and reasonable design and excellent application effect, selects single roasted molybdenum concentrate as a raw material, and obtains a high-purity molybdic acid product through a two-stage purification process of ammonium tetramolybdate and high-purity molybdenum trioxide, wherein the high-purity molybdenum trioxide is dissolved in specific sodium hydroxide, the solution of the high-purity molybdenum trioxide is acidified by nitric acid to reach a certain pH value, and molybdic acid crystals are separated out from the solution, and the high-purity molybdic acid product is obtained through solid-liquid separation, drying and screening.
Detailed Description
The present invention is further illustrated by the following specific examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.
The method selects single roasted molybdenum concentrate as a raw material, and comprises the two-stage purification process of ammonium tetramolybdate and high-purity molybdenum trioxide, wherein the high-purity molybdenum trioxide is dissolved in sodium hydroxide, the solution is acidified by nitric acid to obtain a solution with the pH value of 1-4, molybdic acid crystals are separated out, and a high-purity molybdic acid product is obtained through solid-liquid separation, drying and screening.
A preparation method of low-sodium low-ammonium high-purity molybdic acid comprises the following steps:
a first part: source of high purity molybdenum trioxide
(1) Selecting single molybdenum concentrate to produce ammonium tetramolybdate, and specifically using high-solubility molybdenum trioxide obtained by roasting more than 50% of molybdenum concentrate as a raw material to produce ammonium tetramolybdate;
(2) the ammonium tetramolybdate is calcined at a high temperature of 300-600 ℃, a rotary furnace is adopted for calcination, namely dynamic calcination, and is particularly suitable for ammonium volatilization in the calcination process, the ammonium tetramolybdate is calcined at stages and gradient temperatures, such as 300-plus-400 ℃, 400-plus-600 ℃, 600-plus-500 ℃ and 500-plus-400 ℃, the ammonium can be sufficiently removed after the stage-by-stage calcination, and the ammonium can be insufficiently removed in other methods, so that secondary ammonium removal is not required in the subsequent production process, and the high-purity molybdenum trioxide can be generated.
A second part: production of molybdic acid
(1) Adding water into high-purity molybdenum trioxide with the purity of 99.5% to prepare slurry according to the proportion of (1: 2-3), slowly adding solid sodium hydroxide to adjust the pH value of the solution to be within 6-12, and filtering the mother solution to obtain clear mother solution; the mother liquor is sodium molybdate solution.
After adding solid sodium hydroxide, molybdenum trioxide reacts with sodium hydroxide to form sodium molybdate, which does not need to be subjected to a strong alkaline environment, so that the invention does not need to generate a large amount of sodium which is difficult to remove, and the pH value of the invention does not need to be an extremely high alkaline environment, so that the sodium content of the invention in the product index is only 0.2%, while the pH environment of the step in the prior art CN106698517A is required to be 14, and the step in which the high alkaline environment is required to be maintained is used for removing ammonium, so that the invention has great progress for the step.
(2) Slowly adding nitric acid (40-80%) into the clarified mother liquor to adjust the pH of the solution to be 1-4, heating to 60-95 ℃, and carrying out 15-60min until molybdic acid crystals are precipitated;
in the prior art, CN106698517A adopts 98% concentrated nitric acid, the concentration is fuming nitric acid, the heat release is serious in the use process, the separated molybdic acid is sticky along with the increase of the heat release, and the molybdic acid is seriously caked after being dried and cannot form powder. The invention adopts nitric acid with low concentration, does not relate to exothermic reaction, slowly separates out crystals under stirring at the temperature of 60-95 ℃, and after separation, molybdic acid crystals with large particles and uniform granularity form uniform powder after drying without crushing.
(3) Solid-liquid separation of the mixed solution containing the crystalline molybdic acid, drying the solid at 60-95 ℃, and sieving to obtain high-purity molybdic acid, wherein the molybdic acid product is powder, almost white powder, and the average particle size of the molybdic acid product is 40-60 meshes.
The detection results of the quality indexes of the high-purity molybdic acid obtained by the method are as follows:
| item (%) | Mo | Fe | Cu | Mg | W | K | Na | Ca | Pb | NH4 |
| Analysis results | 59.4 | 0.001 | 0.005 | 0.001 | 0.01 | 0.01 | 0.2 | 0.001 | 0.0006 | 0.005 |
The content of NH4 in the molybdic acid product is 0.005%, which is far superior to the customer standard, and the content of Na is 0.2%, and the molybdic acid with low sodium content is realized for the first time through process improvement.
The invention fills the blank that the molybdenum industry at home and abroad does not have high-purity molybdic acid products,
although the embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that: various substitutions, changes and modifications are possible without departing from the spirit and scope of the invention and the appended claims, and therefore the scope of the invention is not limited to the embodiments disclosed.
Claims (9)
1. A preparation method of low-sodium low-ammonium high-purity molybdic acid is characterized by comprising the following steps: the method comprises the following steps:
the preparation method comprises the steps of adding water into high-purity molybdenum trioxide to prepare slurry, slowly adding solid sodium hydroxide, adjusting the pH value of a solution to 6-12, and filtering the mother liquor to obtain clear mother liquor, wherein the mother liquor is a sodium molybdate solution;
slowly adding a nitric acid solution into the clarified mother liquor to adjust the pH value of the solution to 1-4, and heating to 60-95 ℃ until molybdic acid crystals are precipitated;
thirdly, solid-liquid separation is carried out on the mixed solution containing the crystalline molybdic acid, and the high-purity molybdic acid is obtained by drying and screening the solid at the temperature of 60-95 ℃.
2. The process of preparing low-sodium low-ammonium high-purity molybdic acid according to claim 1, wherein: the high-purity molybdenum trioxide is prepared by high-temperature calcination.
3. The process for preparing low-sodium low-ammonium high-purity molybdic acid according to claim 1 or 2, wherein: the preparation method of the high-purity molybdenum trioxide comprises the following steps: selecting ammonium tetramolybdate produced from molybdenum concentrate with molybdenum content of more than 50%; and calcining the ammonium tetramolybdate at the high temperature of 300-600 ℃ to generate high-purity molybdenum trioxide.
4. The process for preparing low-sodium low-ammonium high-purity molybdic acid according to claim 1 or 2, wherein: the high-purity molybdenum trioxide is mixed with water to form slurry, and the weight ratio of the high-purity molybdenum trioxide to the water is 1: 2 to 3.
5. The process of preparing low-sodium low-ammonium high-purity molybdic acid according to claim 1, wherein: the concentration of the nitric acid solution is 40-80%.
6. The process of preparing low-sodium low-ammonium high-purity molybdic acid according to claim 1, wherein: in the step three, the heating temperature is 60-95 ℃, and the heating time is 15-60 min.
7. The process of preparing low-sodium low-ammonium high-purity molybdic acid according to claim 1, wherein: the high-purity molybdenum trioxide is produced by using high-solubility molybdenum trioxide, which is obtained by roasting more than 50% of single molybdenum concentrate, as a raw material to produce ammonium tetramolybdate and then calcining at a high temperature (300-600 ℃).
8. The process of preparing low-sodium low-ammonium high-purity molybdic acid according to claim 1, wherein: and slowly adding a nitric acid solution into the clarified mother liquor to adjust the pH of the solution to 1-4.
9. The process of preparing low-sodium low-ammonium high-purity molybdic acid according to claim 1, wherein: the purity of the high-purity molybdenum trioxide is 99.5%.
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