New processes for the production of ammonium metatungstate are mainly focused on improving product quality, reducing energy consumption and production costs, as well as ensuring safe and environmentally friendly operations. Below are figures and information about several new processes for the production of ammonium metatungstate.
Improved process based on evaporation crystallization method
This method is based on the conventional evaporative crystallization method, but with process improvements.
Evaporative crystallization
The conventionally produced ammonium metatungstate solution is fed into an evaporation crystallization (concentration) tank and indirectly heated to evaporate and crystallize at the boiling temperature. During the evaporation process, the PH value of the feed solution is controlled between 2.0 and 5.5 by adding nitric acid. When the density of the material liquid reaches 2.5g/cm³ or the crystallization rate reaches 80%, the heating is stopped and cooled down, and then the ammonium metatungstate crystal material containing free water is filtered.
Free water removal
Send the above materials into the far-infrared steel belt heating furnace, in the temperature range of 50 ~ 70 ℃ from low to high, gradually increase the temperature, dehydration treatment for 40 ~ 80 minutes, until the water content of free water in the material is 3 ~ 5wt%.
- Drying, packaging: the dehydrated material will be sent to the far-infrared steel belt heating furnace, in the temperature range of 100 ~ 170 ℃ from low to high, gradually increase the temperature, drying treatment 50 ~ 90 minutes. After cooling, sieving and packing, ammonium metatungstate powder is obtained.
Neutralization method
Ammonium metatungstate is prepared from ammonium sec-metatungstate and nitric acid.
Add ammonium sec-metatungstate to deionized water and ammonium citrate to form a slurry containing WO₃ 12%-30% concentration.
According to the ratio of ammonium paratungstate: nitric acid = 1:20, add 3% to 5% of dilute nitric acid to ammonium paratungstate slurry, control the solid-liquid ratio of 1: (3 ~ 4), Ph value of 2 ~ 4, heating and dissolution, so that the relative density of the solution reaches 1.18 ~ 1.20.
Heating to 80 ~ 90 ℃, constant temperature and volume control Ph value, stirring reaction for 4 hours, aging a few hours, the clear liquid concentration to WO3 content in about 50%, filtration to remove insoluble matter, the clear liquid continue to concentrate, cooling crystallization, to 80 ℃ drying system.
Tungstic acid method
Dissolve tungstic acid with ammonia, add it to boiling deionized water, and heat it with stirring to make Ph=8.
Add acetic acid in the case of boiling solution, and then adjust the Ph value of 2 ~ 4 with dilute nitric acid, continue to heat and concentrate to the relative density of 1.5 ~ 2, stop heating, cooling and filtration.
The filtrate was added with ethanol and stirred thoroughly, then filtered after settling, and the crystals were dried and crushed at 80℃ to obtain the product.
These new processes aim to improve the purity, yield and production efficiency of ammonium metatungstate through fine control of process parameters, optimization of operation steps, and adoption of new technologies and equipment, as well as to reduce production costs and environmental pollution. In practical application, suitable process methods can be selected according to factors such as raw material sources, product quality requirements and production conditions.
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