Method for preparing ammonium dimolybdate from ammonium heptamolybdate

Abstract

The invention provides a method for preparing ammonium dimolybdate from ammonium heptamolybdate, and belongs to the technical field of chemical product preparation. The method comprises the following steps: weighing ammonium heptamolybdate and an ammonium source in a container according to a molar ratio, adding deionized water, stirring while heating until solids are completely dissolved, then cooling and crystallizing the solution, filtering after the crystallization is finished, and drying the filtered crystal substance to obtain ammonium dimolybdate; the ammonium source is one or more of ammonium bicarbonate, ammonium carbonate and ammonia water, and the molar ratio of the ammonium heptamolybdate to the ammonium source is equal to 1: (1.0-1.3) in terms of total ammonium in the ammonium heptamolybdate and the ammonium source. The method is short in technological process, low in energy consumption and relatively simple in preparation means, and the prepared ammonium dimolybdate product is low in impurity content and stable in quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical product preparation, in particular to a preparation method of ammonium dimolybdate. BACKGROUND

[0002] Ammonium dimolybdate, abbreviated as ADM, has a chemical formula of (NH4)2Mo2O7 or H8Mo2N2O7, and a theoretical Mo content of 56.45%. It is easily soluble in alkali and water, and insoluble in alcohol and acetone. At normal temperature and pressure, it is relatively stable. Ammonium dimolybdate is widely used as a raw material for preparing molybdenum oxide, molybdenum powder, catalysts, ceramic pigments and other molybdenum compounds due to its single crystal composition, uniform particle size and good fluidity.

[0003] Currently, there are two main methods for producing ammonium dimolybdate: evaporation crystallization and double decomposition reaction. In the evaporation crystallization method, the main raw material is ammonium molybdate solution or tetramolybdate ammonium. The ammonium molybdate solution is obtained through molybdenum concentrate roasting-leaching-extraction processes, which contains many impurities and has a high content. The crystallization rate needs to be controlled at a low level to obtain a product that meets the national standard requirements. Tetramolybdate ammonium [(NH4)2Mo4O7] is mainly prepared by adjusting the pH of ammonium molybdate solution to 1.5-2.0 using nitric acid as an acid precipitant and then acid precipitating and crystallizing. This process has problems such as high consumption of nitric acid and difficulty in treating NH4NO3 wastewater. In addition, tetramolybdate ammonium contains a certain amount of NO-3, which results in the presence of NO-3 in ammonium dimolybdate prepared by this method, ultimately causing problems such as ammonium salt caking and crystal hardening. In addition, tetramolybdate ammonium has low water solubility and a small ammonia molybdenum ratio (1:2), and a large amount of ammonia water is consumed during the ammonia dissolution process, which not only increases the cost of reagents but also increases the burden of subsequent wastewater treatment. The double decomposition reaction method is a gas-solid reaction, and the reaction process is slow. It still has the problems caused by tetramolybdate ammonium as a raw material. 13 SUMMARY

[0004] In view of the technical problems existing in the existing preparation methods of ammonium dimolybdate, the purpose of the present application is to provide a method for preparing ammonium dimolybdate from heptamolybdate ammonium, which has a short process flow, low energy consumption, relatively simple preparation means, and low impurity content in the prepared ammonium dimolybdate product.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: ​The application discloses a method for preparing ammonium dimolybdate by using ammonium heptamolybdate, which comprises the following steps: weighing ammonium heptamolybdate and an ammonium source in a container according to a molar ratio, adding deionized water, heating and stirring at the same time, increasing the temperature to 70-80 DEG C until the solid is completely dissolved, then transferring the solution into a cooling crystallizer to perform cooling crystallization, filtering after the end, drying the filtered crystalline substance, and obtaining ammonium dimolybdate; the ammonium source is one or more of ammonium bicarbonate, ammonium carbonate and ammonia water, and the molar ratio of the ammonium heptamolybdate and the ammonium source is converted into ammonium heptamolybdate: total ammonium in the ammonium source = 1:1.0-1.3.

[0006] Generally, the mass ratio of ammonium heptamolybdate to deionized water should be no less than 108:100, which can ensure that the deionized water can completely dissolve the ammonium heptamolybdate at 70-80 DEG C.

[0007] Further, the filtered crystalline mother liquor is returned and mixed with the solution to be transferred into the cooling crystallizer, and then the solution is continuously transferred into the cooling crystallizer to perform cooling crystallization, so as to prepare ammonium dimolybdate.

[0008] Further, the concentration of the ammonia water is 25-28 wt.%.

[0009] Further, during the cooling crystallization process of the solution in the cooling crystallizer, the cooling rate is 20-50 DEG C / h, the stirring rate is 100-300 r / min, the final cooling temperature is 5-10 DEG C, and the final temperature holding time is 0.5-2 h.

[0010] Further, the drying temperature of the crystalline substance is 75-85 DEG C, and the drying time is 4-10 h.

[0011] By using the method, ammonium dimolybdate is prepared by evaporation crystallization of ammonium heptamolybdate, the solubility of ammonium heptamolybdate [(NH4)6Mo7O 24 4H2O] in the aqueous solution is higher than that of ammonium dimolybdate, and the solubility of both decreases with the decrease of the temperature. According to the difference and characteristics of the solubility, ammonium heptamolybdate can be dissolved at a relatively high temperature (70-80 DEG C) and the ammonium source can be added to perform an ammonium supplement reaction, and then ammonium dimolybdate can be prepared by cooling crystallization at a low temperature. Compared with the prior art, the process flow is significantly shortened, the energy consumption is low, the preparation means is relatively simple, the product quality problem caused by impurities is greatly reduced, the influence of impurities such as NO- 3, Cl - , S 2- , etc. in the upstream process of the ammonium molybdate solution or the acid precipitating agent can be effectively avoided, the purity and quality stability of the final product ammonium dimolybdate can be ensured, the prepared ammonium dimolybdate product meets the requirements of the MSA-0 grade product in GB / T3460-2017, the mother liquor after crystallization can be returned and mixed with the solution to be cooled and crystallized to continuously prepare ammonium dimolybdate, and the raw material utilization rate is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Phase diagram obtained by X-ray diffractometer for Example 1; Figure 2 Phase diagram obtained by X-ray diffractometer for Example 2; Figure 3 Phase diagram obtained by X-ray diffractometer for Example 3. DETAILED DESCRIPTION

[0013] In order to facilitate the understanding of the present application, the present application will be described in more detail below in conjunction with and preferred embodiments. Example 1

[0014] A method for preparing ammonium dimolybdate from ammonium heptamolybdate, 1600g of ammonium heptamolybdate and 102g of ammonium bicarbonate were taken in a beaker (molar ratio, ammonium heptamolybdate: total ammonium in ammonium source = 1:1), 2000mL of deionized water was added, the beaker was placed in a constant temperature water bath for stirring and heating to 75℃, until the solid was completely dissolved, to obtain the required solution, then the solution was slowly transferred to a cooling crystallizer to start cooling crystallization, the cooling rate of the cooling crystallizer was controlled at 30℃ / h, the stirring rate of the stirring mechanism of the cooling crystallizer was 150r / min, the final cooling temperature was 8℃, and the final temperature was kept for 1h. After crystallization, filtration was carried out, the crystallization mother liquor filtered out was recovered and returned to mix with the solution to be transferred to the cooling crystallizer in the next batch, and the cooling crystallization was continued to prepare ammonium dimolybdate. The crystalline product filtered out was placed in a constant temperature drying oven at 75℃ for drying for 10h, and ammonium dimolybdate product was obtained after drying. The molybdenum (Mo) content was detected by thiocyanate colorimetry, and the molybdenum content in the product was 56.35%. Figure 1 The phase diagram obtained by X-ray diffractometer for the crystalline product, from the diagram, it can be seen that each diffraction peak corresponds to PDF#37-0379, and the product is single-phase ammonium dimolybdate. Example 2

[0015] A method for preparing ammonium dimolybdate from ammonium heptamolybdate, take 1600g of ammonium heptamolybdate and 80.8g of ammonium carbonate in a beaker (according to the molar ratio, ammonium heptamolybdate: total ammonium in ammonium source = 1:1.3), add 2000mL of deionized water, place the beaker in a constant temperature water bath and stir and heat to 70℃ until the solid is completely dissolved, obtain the required solution, then slowly transfer the solution to a cooling crystallizer to start cooling crystallization, control the cooling rate of the cooling crystallizer at 20℃ / h, the stirring rate of the stirring mechanism of the cooling crystallizer at 100r / min, the final cooling temperature at 5℃, and the final temperature holding time at 1h. After crystallization, filter, recover the crystallization mother liquor, return to the solution to be transferred to the cooling crystallizer in the next batch, continue to transfer to the cooling crystallizer for cooling crystallization, and prepare ammonium dimolybdate. Dry the filtered crystalline material in a constant temperature drying oven at 75℃ for 8h, and obtain ammonium dimolybdate product after drying. The molybdenum (Mo) content of the product is 56.64% by thiocyanate colorimetry. Figure 2 The phase diagram of the crystalline product is detected by X-ray diffractometer, and from the diagram it can be seen that each diffraction peak corresponds to PDF#37-0379, and the product is single-phase ammonium dimolybdate. Example 3

[0016] A method for preparing ammonium dimolybdate from ammonium heptamolybdate, take 1600g of ammonium heptamolybdate and 80.8g of ammonium carbonate in a beaker (according to the molar ratio, ammonium heptamolybdate: total ammonium in ammonium source = 1:1.3), add 2000mL of deionized water, place the beaker in a constant temperature water bath and stir and heat to 70℃ until the solid is completely dissolved, obtain the required solution, then slowly transfer the solution to a cooling crystallizer to start cooling crystallization, control the cooling rate of the cooling crystallizer at 20℃ / h, the stirring rate of the stirring mechanism of the cooling crystallizer at 100r / min, the final cooling temperature at 5℃, and the final temperature holding time at 1h. After crystallization, filter, recover the crystallization mother liquor, return to the solution to be transferred to the cooling crystallizer in the next batch, continue to transfer to the cooling crystallizer for cooling crystallization, and prepare ammonium dimolybdate. Dry the filtered crystalline material in a constant temperature drying oven at 75℃ for 8h, and obtain ammonium dimolybdate product after drying. The molybdenum (Mo) content of the product is 56.64% by thiocyanate colorimetry. Figure 3 The phase diagram of the crystalline product is detected by X-ray diffractometer, and from the diagram it can be seen that each diffraction peak corresponds to PDF#37-0379, and the product is single-phase ammonium dimolybdate. Example 4

[0017] A method for preparing ammonium dimolybdate from ammonium heptamolybdate, take 1600g of ammonium heptamolybdate, 60g of ammonium bicarbonate, and 60mL of ammonia water (according to the molar ratio, ammonium heptamolybdate: total ammonium in ammonium source = 1:1.2) in a beaker, add 2000mL of deionized water, place the beaker in a constant temperature water bath and stir and heat to 75℃ until the solid is completely dissolved, obtain the required solution, then slowly transfer to a cooling crystallizer to start cooling crystallization, control the cooling rate of the cooling crystallizer at 20℃ / h, the stirring rate of the stirring mechanism of the cooling crystallizer at 300r / min, the final cooling temperature at 8℃, the final temperature holding time at 0.5h, after the end of the process, filter, recover the crystallization mother liquor filtered out, return to the solution to be transferred to the cooling crystallizer in the next batch, continue to transfer to the cooling crystallizer for cooling crystallization, and ammonium dimolybdate is prepared. The crystalline material filtered is placed in a constant temperature drying oven at 75℃ for 6h, and ammonium dimolybdate product is obtained after drying. The molybdenum content in the product is 56.67% by thiocyanate colorimetry. Example 5

[0018] A method for preparing ammonium dimolybdate from ammonium heptamolybdate, take 1600g of ammonium heptamolybdate, 60g of ammonium bicarbonate, and 60mL of ammonia water (according to the molar ratio, ammonium heptamolybdate: total ammonium in ammonium source = 1:1.2) in a beaker, add 2000mL of deionized water, place the beaker in a constant temperature water bath and stir and heat to 75℃ until the solid is completely dissolved, obtain the required solution, then slowly transfer to a cooling crystallizer to start cooling crystallization, control the cooling rate of the cooling crystallizer at 20℃ / h, the stirring rate of the stirring mechanism of the cooling crystallizer at 300r / min, the final cooling temperature at 8℃, the final temperature holding time at 0.5h, after the end of the process, filter, recover the crystallization mother liquor filtered out, return to the solution to be transferred to the cooling crystallizer in the next batch, continue to transfer to the cooling crystallizer for cooling crystallization, and ammonium dimolybdate is prepared. The crystalline material filtered is placed in a constant temperature drying oven at 75℃ for 6h, and ammonium dimolybdate product is obtained after drying. The molybdenum content in the product is 56.67% by thiocyanate colorimetry.

[0019] As can be seen from the results of the examples, the preparation method of the application can prepare ammonium dimolybdate with high purity and stable quality, and the product meets the requirements of MSA-0 grade product in GB / T3460-2017.

[0020] The raw materials used in the method of the application, ammonium heptamolybdate, ammonium bicarbonate, ammonium carbonate and ammonia water, can be purchased on the market. The mass concentration of commercially available ammonia water is 25-28wt.% as commonly marked.

[0021] The cooling crystallizer and constant temperature drying oven used in the application are all prior art devices.

[0022] The above merely describes the preferred embodiments of the present application, and is not intended to limit the scope of protection of the present application. It should be noted that, for those skilled in the art, the technical parameter changes and equivalent technical means replacement without departing from the scope of the present application defined in the claims, all belong to the protection scope of the present application.

Claims

1. A method for preparing ammonium dimolybdate from ammonium heptamolybdate, characterized in that, The method involves weighing ammonium heptamolybdate and ammonium source in a container by molar ratio, adding deionized water, heating and stirring simultaneously, raising the temperature to 70℃~80℃ until the solid is completely dissolved, then transferring the solution to a cooling crystallizer for cooling and crystallization, filtering after completion, and drying the filtered crystals to obtain ammonium dimolybdate; the ammonium source is one or more of ammonium bicarbonate, ammonium carbonate, and ammonia water, and the molar ratio of ammonium heptamolybdate to ammonium source is converted to ammonium heptamolybdate: total ammonium in ammonium source = 1: 1.0~1.

3.

2. The method for preparing ammonium dimolybdate from ammonium heptamolybdate according to claim 1, characterized in that, The filtered mother liquor is returned to be mixed with the solution to be transferred to the cooling crystallizer, and then transferred to the cooling crystallizer for cooling crystallization to prepare ammonium dimolybdate.

3. A method for preparing ammonium dimolybdate from ammonium heptamolybdate according to claim 1 or 2, characterized in that, The concentration of the ammonia water is 25~28 wt.%.

4. A method for preparing ammonium dimolybdate from ammonium heptamolybdate according to claim 1 or 2, characterized in that, The solution is cooled and crystallized in a cooling crystallizer at a cooling rate of 20~50℃ / h, a stirring rate of 100~300r / min, a final cooling temperature of 5~10℃, and a final temperature holding time of 0.5~2h.

5. A method for preparing ammonium dimolybdate from ammonium heptamolybdate according to claim 1 or 2, characterized in that, The drying temperature of the crystals is 75~85℃, and the drying time is 4~10h.

6. A method for preparing ammonium dimolybdate from ammonium heptamolybdate according to claim 4, characterized in that, The drying temperature of the crystals is 75~85℃, and the drying time is 4~10h.

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