Ammonium Metatungstate Preparation -- Nanofiltration Method
Ammonium Metatungstate (AMT) is an important compound product in tungsten smelting process.It is widely used in areas.
The common methods of preparing ammonium metatungstate include thermal degradation and ion exchange, extraction, nanofiltration, electrodialysis and neutralization.
Nanofiltration membrane is a new type of pressure driven separation membrane developed since 1980s. Nanofiltration method is a membrane separation technique, which is independent from reverse osmosis membrane technology.
Filter membrane is the main focus of nanofiltration. The separation performance of nanofiltration membrane is between reverse osmosis and ultrafiltration membrane. It has a good removal effect on low molecular weight substances, high valence ions, low valence cations and anions. Therefore, some scholars used the nanofiltration method to prepare ammonium metatungstate (AMT) from the original solution of ammonium paratungstate (APT) crystallization.
The separation of chloride ions from the crystallization mother liquor by nanofiltration can overcome the shortcoming of the difficulty in removing the chloride ions in the crystallization liquor of the APT process by ion exchange. At the same time the use of nanofiltration membrane acid anion NO3-, but also the main material of the tungsten does not wear, to achieve the purpose of producing pure AMT crystal.
It is important to note that when APT crystallization liquor is dealt by nanofiltration method, the appropriate hydrochloric acid is added to neutralize and adjust the acid, and then the impurity is removed by nanofiltration. The quality of the obtained AMT is better.After the industrial proof, our country's nanofiltration membrane production technology has made great progress. Nanofiltration method has no pollution, high impurity removal efficiency, and has been able to control costs, and has the potential for popularization.
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