The principle of ammonium metatungstate electrodialysis is mainly based on electrodialysis technology. Under the action of a DC electric field, the electrolyte is separated from the water by using the permeation selectivity of the ion exchange membrane. The following is the detailed principle of the method:
Electric field action and ion migration
When a DC electric field is applied to the electrodialyzer, a directional electric field is formed in the membrane stack.
Under the action of this electric field, water molecules will dissociate to form H+ and OH- ions, and migrate to the salt chamber and the alkali chamber respectively.
Ion exchange and separation
During the electrodialysis process, specific ion exchange membranes (such as anion exchange membranes or cation exchange membranes) are used to control the migration of ions.
For the production of ammonium metatungstate, the key step is to circulate the ammonium tungstate anolyte with a pH of 9 through the electrodialyzer.
Under the action of voltage, ammonium ions (NH4+) will migrate to the cathode liquid through a specific ion exchange membrane and combine with other ions to form new compounds, such as ammonium sulfate.
pH change and compound formation
As the electrolysis process proceeds, ammonium ions in the anolyte continue to migrate out, causing the pH value to drop sharply.
When the pH value drops to a certain range (such as 8.7-8.3), the anolyte becomes turbid due to the formation of insoluble compounds. However, these compounds will dissolve again between pH values of 4-5.
When the pH value further drops to 3.0, the electrolysis process will stop.
Product recovery and purification
After the above process, the anolyte is clarified and evaporated into a thick slurry.
Coarse white ammonium metatungstate (AMT) crystals can be recovered from it, completing the entire process of preparing ammonium metatungstate by electrodialysis. This method has the advantages of short process, high direct recovery rate, low energy consumption and no pollution, so it has good application prospects in industrial production.
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