Preparation method of low-potassium ammonium molybdate

Abstract

The invention belongs to the technical field of ammonium molybdate preparation, and particularly relates to a preparation method of low-potassium ammonium molybdate. The preparation method comprises the following steps: step 1, complexing modification of a molybdic acid solution: leaching industrial roasted molybdenum with sulfuric acid, and then mixing with a citric acid-tartaric acid mixed complexing agent to form a stable complex solution; 2, gradient temperature control crystallization: transferring the complex solution into a crystallization kettle, carrying out temperature control crystallization in two stages, separating out coarse crystals in the first stage, separating out fine crystals in the second stage, and carrying out centrifugal collection; and 3, dynamic countercurrent washing: combining the coarse crystal and the fine crystal, and carrying out countercurrent gradient washing by using an ethanol-deionized water mixed solution to remove potassium ions adsorbed on the surface. According to the method, the lattice potassium removal limit is broken through, potassium ions are inhibited from being embedded into lattices through complexing competition, surface potassium is directionally enriched in combination with gradient crystallization, the content of potassium ammonium molybdate is smaller than or equal to 30 ppm, and the lattice potassium proportion is smaller than 5%; and a clean production path is reconstructed, and a pure water phase process without resin / organic solvent is adopted, so that the discharge amount of wastewater is reduced, and no toxic by-product is generated.

Description

Technical Field

[0001] The present invention belongs to the technical field of ammonium molybdate preparation, and particularly relates to a method for preparing low-potassium ammonium molybdate. Background Art

[0002] As the core intermediate in the molybdenum metallurgy industrial chain, the purity of ammonium molybdate directly determines the upper limit of the performance of subsequent high-end materials such as molybdenum powder and molybdenum targets. The factors that have a greater impact on its purity are alkali metal impurities such as potassium and sodium. In recent years, with the breakthrough of semiconductor chip manufacturing processes to nodes below 3nm and the popularization of high-resolution display panels, the potassium content requirement for ammonium molybdate used in sputtering targets has been increased from traditional industrial grade (<500ppm) to electronic grade (<50ppm). Therefore, the process requirements for preparing ammonium molybdate have been correspondingly improved.

[0003] The traditional ammonium molybdate preparation processes mainly include: Acid crystallization method: Adjust the pH of the nitric acid leaching solution of molybdenum concentrate with ammonia water for crystallization. However, potassium ions are easily incorporated into the ammonium molybdate lattice through isomorphous substitution, and the potassium content in the final product > 300ppm; Ion exchange method: Use cation resin to adsorb potassium ions. Although the potassium residue can be reduced (<100ppm), the resin needs to be regenerated frequently and the wastewater treatment cost is high; Solvent extraction method: Use tributyl phosphate (TBP) to extract and separate potassium. However, the residue in the organic phase is likely to contaminate the product, and the process is complex.

[0004] In the above process methods, the acid crystallization method has no effective means to inhibit the doping of potassium in the lattice, and the potassium removal efficiency is low; the ion exchange method is carried out in separate sections and a large amount of acid and alkali are required to regenerate the resin; the solvent extraction method is carried out in separate sections and a large amount of organic reagents are consumed; the traditional processes are difficult to balance low potassium content, low cost and environmental protection requirements, and especially cannot meet the preparation requirements of electronic grade ammonium molybdate (potassium content < 50ppm). Summary of the Invention

[0005] In order to overcome the three core defects of difficult removal of lattice-doped potassium, high pollution in the refining process and non-continuous process in the prior art, the present invention provides a method for preparing low-potassium ammonium molybdate.

[0006] The present invention is achieved by the following technical solutions: A method for preparing low-potassium ammonium molybdate, comprising the following steps: Step 1, complex modification of molybdic acid solution: Leach industrial molybdenum roasting sand with sulfuric acid, mix the leaching solution with a citric acid-tartaric acid mixed complexing agent, and stir for 30 minutes to form a stable complex solution; Step 2, gradient temperature-controlled crystallization: Transfer the complex solution into a crystallization kettle and perform temperature-controlled crystallization in two stages. Coarse crystals with a particle size of 50 - 100 μm are precipitated in the first stage. After centrifugal separation, the mother liquor is retained. Fine crystals with a particle size of 10 - 20 μm are precipitated in the second stage and collected by secondary centrifugation. Step 3, dynamic countercurrent washing: Combine the coarse crystals and fine crystals, and perform countercurrent gradient washing with a mixed solution of ethanol - deionized water at a flow rate of 2 L / min for 3 times to remove the potassium ions adsorbed on the surface.

[0007] Preferably, in Step 1, the leaching solution is mixed with a citric acid - tartaric acid mixed complexing agent, and the mixing ratio is based on the molybdenum content in the leaching solution, and is mixed at a molar ratio of Mo:CA:TA = 1:0.4:0.1.

[0008] Further, in Step 2, the specific method for precipitating coarse crystals in the first stage is that the complex solution is maintained at 40 °C, and ammonia water is slowly added dropwise until the pH is in the range of 2.0 - 2.5.

[0009] Further, in Step 2, the specific method for precipitating fine crystals in the second stage is that the mother liquor is cooled to 10 °C, and ammonia water is added to make up until the pH is in the range of 5.0 - 5.5.

[0010] Preferably, the ethanol - deionized water mixed solution is composed of anhydrous ethanol with a content of more than 99.5% and deionized water mixed at a volume ratio of 1:3.

[0011] This preparation method further includes Step 4, drying: Put the washed coarse crystals and fine crystals into a hot oven, maintain the temperature at 80 °C, and the drying time is 6 h to finally obtain solid ammonium molybdate.

[0012] The beneficial effects of the present invention are as follows: 1. The present invention breaks through the limit of lattice potassium removal, inhibits the embedding of potassium ions into the lattice through complexation competition, combines gradient crystallization to directionally enrich surface potassium, and realizes that the potassium content in ammonium molybdate is ≤ 30 ppm, where the proportion of lattice potassium is < 5%; reconstructs the clean production path, adopts a pure water phase process without resin / organic solvent, reduces the wastewater discharge and has no toxic by-products.

[0013] 2. The present invention adopts the method of double complexation to synergistically shield potassium ions. Citric acid and tartaric acid jointly complex molybdate ions to block the embedding of potassium ions into the lattice, thereby greatly reducing the potassium content in the final product of ammonium molybdate.

[0014] 3. The present invention adopts the method of stepwise gradient crystallization, realizes the differential distribution of potassium impurities in coarse / fine crystals through temperature - pH regulation, preferentially separates high - potassium coarse crystals, and gradient crystallization directionally enriches surface potassium, which is conducive to the subsequent washing to remove potassium impurities.

[0015] 4. The present invention uses countercurrent washing gradient to strengthen the removal of potassium impurities, and uses ethanol to reduce the dielectric constant of the solution and improve the elution efficiency of potassium ions. Detailed implementation mode

[0016] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0018] The reagents and raw materials used in the embodiments and comparative examples of the present invention can be obtained through commercial channels without special instructions.

[0019] The reagents involved in the present invention are as follows: Sulfuric acid: industrial grade concentrated sulfuric acid (98wt%), diluted to 20 - 30wt% for use; Citric acid (CA): analytical pure (≥99.5%), prepared into a 20wt% aqueous solution; Tartaric acid (TA): chemically pure (≥99.0%), prepared into a 15wt% aqueous solution; Ammonia water: the solution concentration is 25wt%, diluted to 10wt% for pH adjustment.

[0020] Example 1 A method for preparing ammonium molybdate with low potassium content includes the following steps: Step 1: Complex modification of molybdic acid solution 100 g of industrial molybdenum roasting sand is leached with 1000 mL of 25wt% sulfuric acid, where the Mo content in the industrial molybdenum roasting sand is 55wt%, and the Mo content in the obtained leaching solution is 80 g / L.

[0021] The leaching solution is mixed with a citric acid - tartaric acid mixed complexing agent in a molar ratio of Mo:CA:TA = 1:0.4:0.1, and stirred for 30 minutes to form a stable complex, shielding the active sites of potassium ions.

[0022] Among them, the citric acid-tartaric acid mixed complexing agent is formed by mixing citric acid (CA) and tartaric acid (TA) at a molar ratio of CA:TA = 0.4:0.1, and it is prepared and used immediately. The leaching solution is mixed with the citric acid-tartaric acid mixed complexing agent based on the molybdenum content in the leaching solution, and the molar ratio is Mo:CA:TA = 1:0.4:0.1.

[0023] Step 2: Gradient temperature-controlled crystallization Transfer the solution obtained in Step 1 to a crystallization kettle and carry out temperature-controlled crystallization in two stages: The first stage: Heat the solution to 40 °C and keep it at this temperature. Slowly add ammonia water until the pH is in the range of 2.0 - 2.5, and coarse crystals will precipitate. The particle size of the coarse crystals is 50 - 100 μm. After centrifugal separation, keep the mother liquor. The second stage: Cool the mother liquor to 10 °C, add ammonia water to adjust the pH to the range of 5.0 - 5.5, and fine crystals will precipitate. The particle size of the fine crystals is 10 - 20 μm. Collect the crystals by secondary centrifugation.

[0024] Step 3: Dynamic countercurrent washing Combine the coarse crystals and the fine crystals, and carry out countercurrent gradient washing with an ethanol-deionized water mixed solution at a flow rate of 2 L / min for 3 times to remove the potassium ions adsorbed on the surface.

[0025] Among them, the ethanol-deionized water mixed solution is prepared by mixing absolute ethanol and deionized water at a volume ratio of 1:3, and the purity of absolute ethanol is ≥99.5%.

[0026] Step 4: Drying Put the washed coarse crystals and fine crystals into a hot oven, keep the temperature at 80 °C, and the drying time is 6 h. Finally, 99.3 grams of ammonium molybdate are obtained.

[0027] Detect the finally obtained ammonium molybdate solid substance, measure the potassium content by ICP-MS detection method. Among them, the potassium content is 10 ppm, achieving an ultra-low potassium content in the final product; the molybdenum recovery rate is ≥98%, the recovery rate in the process is high, the wastewater discharge is reduced, and there is no organic waste liquid, which is an environmentally friendly process; no ion exchange resin or extractant is required, the raw material cost is reduced, and the process is economical and applicable.

[0028] Comparative Example 1 This comparative example relates to a method for preparing ammonium molybdate, which is different from Example 1 in that no citric acid-tartaric acid mixed complexing agent is used, and it includes the following steps: Step 1: Pretreatment of molybdic acid solution Leach 100 g of industrial molybdenum roasting sand with 1000 mL of 25 wt% sulfuric acid. Among them, the Mo content in the industrial molybdenum roasting sand is 55 wt%, and the Mo content in the obtained leaching solution is 80 g / L.

[0029] Step 2: Gradient temperature-controlled crystallization Transfer the solution obtained in Step 1 to a crystallization kettle and control the temperature for crystallization in two stages: First stage: Heat up the solution and maintain it at 40 °C. Slowly add ammonia water until the pH is in the range of 2.0 - 2.5, and coarse crystals will precipitate. The particle size of the coarse crystals is 50 - 100 μm. After centrifugal separation, retain the mother liquor; Second stage: Cool the mother liquor to 10 °C, add ammonia water to make the pH in the range of 5.0 - 5.5, and fine crystals will precipitate. The particle size of the fine crystals is 10 - 20 μm. Centrifuge twice to collect the crystals.

[0030] Step 3: Dynamic countercurrent washing Combine the coarse crystals and fine crystals, and carry out countercurrent gradient washing with an ethanol - deionized water mixed solution at a flow rate of 2 L / min for 3 times to remove the potassium ions adsorbed on the surface.

[0031] Among them, the ethanol - deionized water mixed solution is prepared by mixing absolute ethanol and deionized water at a volume ratio of 1:3.

[0032] Step 4: Drying Put the washed coarse crystals and fine crystals into a hot oven, maintain the temperature at 80 °C, and the drying time is 6 h. Finally, 107 grams of ammonium molybdate are obtained.

[0033] Detect the finally obtained ammonium molybdate solid substance, and measure the potassium content by ICP - MS detection method. The potassium content is 320 ppm.

[0034] Comparative Example 2 This comparative example provides a method for preparing ammonium molybdate, which is different from Example 1 in that it does not perform fractional crystallization and includes the following steps: Step 1: Complex modification of molybdic acid solution Leach 100 g of industrial molybdenum roasting sand with 1000 mL of 25 wt% sulfuric acid. The Mo content in the industrial molybdenum roasting sand is 55 wt%, and the Mo content in the obtained leaching solution is 80 g / L.

[0035] Mix the leaching solution with a citric acid - tartaric acid mixed complexing agent at a molar ratio of Mo:CA:TA = 1:0.4:0.1, and stir for 30 minutes to form a stable complex, shielding the potassium ion active sites.

[0036] Among them, the citric acid - tartaric acid mixed complexing agent is prepared by compounding citric acid (CA) and tartaric acid (TA) at a molar ratio of CA:TA = 0.4:0.1 and used immediately. The leaching solution is mixed with the citric acid - tartaric acid mixed complexing agent based on the molybdenum content in the leaching solution, and the molar ratio is Mo:CA:TA = 1:0.4:0.1.

[0037] Step 2: Temperature - controlled crystallization Transfer the solution obtained in Step 1 to a crystallization kettle, gradually reduce the solution temperature from 50 °C to 10 °C, slowly add ammonia water dropwise until pH = 5, precipitate crystals, and collect by centrifugation.

[0038] Step 3: Dynamic countercurrent washing The crystals are subjected to countercurrent gradient washing with an ethanol-deionized water mixture at a flow rate of 2 L / min for 3 times to remove the potassium ions adsorbed on the surface.

[0039] Among them, the ethanol-deionized water mixture is prepared by mixing absolute ethanol and deionized water at a volume ratio of 1:3.

[0040] Step 4: Drying Put the washed coarse crystals and fine crystals into a hot oven, keep the temperature at 80 °C, and the drying time is 6 h. Finally, 90 grams of ammonium molybdate are obtained.

[0041] Detect the finally obtained ammonium molybdate solid substance, and measure the potassium content by ICP-MS detection method, and the potassium content is 50 ppm.

[0042] Comparative Example 3 This comparative example provides a method for preparing ammonium molybdate, which is different from Example 1 in that deionized water is used for washing in Step 3, and the steps are as follows: Step 1: Complex modification of molybdic acid solution Leach 100 g of industrial molybdenum roasting sand with 1000 mL of 25 wt% sulfuric acid, where the Mo content in the industrial molybdenum roasting sand is 55 wt%, and the Mo content in the obtained leachate is 80 g / L.

[0043] The leachate is mixed with a citric acid-tartaric acid mixed complexing agent at a molar ratio of Mo:CA:TA = 1:0.4:0.1, and stirred for 30 minutes to form a stable complex, shielding the potassium ion active sites.

[0044] Among them, the citric acid-tartaric acid mixed complexing agent is prepared by compounding citric acid (CA) and tartaric acid (TA) at a molar ratio of CA:TA = 0.4:0.1, and is prepared and used immediately. The leachate is mixed with the citric acid-tartaric acid mixed complexing agent based on the molybdenum content in the leachate, and the molar ratio is Mo:CA:TA = 1:0.4:0.1.

[0045] Step 2: Gradient temperature-controlled crystallization Transfer the solution obtained in Step 1 to a crystallization kettle, and carry out temperature-controlled crystallization in two stages: The first stage: The solution is heated and maintained at 40 °C, ammonia water is slowly added dropwise until the pH is in the range of 2.0 - 2.5, coarse crystals are precipitated, the particle size of the coarse crystals is 50 - 100 μm, and the mother liquor is retained after centrifugal separation; Second stage: Cool the mother liquor to 10°C, add ammonia water to adjust the pH to the range of 5.0 - 5.5, fine crystals will precipitate, the particle size of the fine crystals is 10 - 20 μm, and the crystals are collected by secondary centrifugation.

[0046] Step 3: Countercurrent washing Combine the coarse crystals and fine crystals, and perform countercurrent gradient washing with deionized water at a flow rate of 2 L / min for 3 times.

[0047] Step 4: Drying Put the washed coarse crystals and fine crystals into a hot oven, keep the temperature at 80°C, and the drying time is 6 h. Finally, 110 grams of ammonium molybdate are obtained.

[0048] Detect the finally obtained solid ammonium molybdate substance, and measure the potassium content by ICP-MS detection method. The potassium content is 120 ppm.

[0049] From the above Example 1 and Comparative Examples 1 - 3, it can be seen that the potassium content in Example 1 is the lowest, indicating that by complexing molybdate ions with citric acid and tartaric acid together, blocking the embedding of potassium ions into the crystal lattice, combining gradient crystallization to enrich potassium on the surface directionally, and using ethanol to reduce the dielectric constant of the solution to improve the elution efficiency of potassium ions, thereby greatly reducing the potassium content in the final product of ammonium molybdate.

[0050] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of ammonium molybdate with low potassium content, characterized in that, It includes the following steps: Step 1, complex modification of molybdic acid solution: Leach industrial molybdenum roasting sand with sulfuric acid, mix the leaching solution with a citric acid-tartaric acid mixed complexing agent, and stir for 30 minutes to form a stable complex solution; Step 2, gradient temperature-controlled crystallization: Transfer the complex solution to a crystallization kettle, control the temperature for crystallization in two stages. In the first stage, coarse crystals with a particle size of 50-100 μm are precipitated, and the mother liquor is retained after centrifugal separation; In the second stage, fine crystals with a particle size of 10-20 μm are precipitated and collected by secondary centrifugation; Step 3, dynamic countercurrent washing: Combine the coarse crystals and fine crystals, and carry out countercurrent gradient washing with an ethanol-deionized water mixed solution at a flow rate of 2 L / min for 3 times to remove the potassium ions adsorbed on the surface.

2. A method for preparing ammonium molybdate with low potassium content according to claim 1, characterized in that, In Step 1, when the leaching solution is mixed with the citric acid-tartaric acid mixed complexing agent, the mixing ratio is based on the molybdenum content in the leaching solution, and the mixing is carried out at a molar ratio of Mo:CA:TA = 1:0.4:0.

1.

3. A method for preparing ammonium molybdate with low potassium content according to claim 1, characterized in that, In Step 2, the specific method for precipitating coarse crystals in the first stage is that the complex solution is maintained at 40 °C, and ammonia water is slowly added dropwise until the pH is in the range of 2.0-2.

5.

4. A method for preparing ammonium molybdate with low potassium content according to claim 3, characterized in that, In Step 2, the specific method for precipitating fine crystals in the second stage is that the mother liquor is cooled to 10 °C, and ammonia water is added to make the pH in the range of 5.0-5.

5.

5. A method for preparing ammonium molybdate with low potassium content according to claim 1, characterized in that, The ethanol-deionized water mixed solution is composed of absolute ethanol and deionized water mixed in a volume ratio of 1:

3.

6. A method for preparing ammonium molybdate with low potassium content according to claim 1, characterized in that, It also includes Step 4, drying: Put the washed coarse crystals and fine crystals into a hot oven, keep the temperature at 80 °C, and the drying time is 6 h to finally obtain solid ammonium molybdate.