Ammonium Metatungstate Preparation -- Electrodialysis Method
Ammonium Metatungstate (AMT) is an important compound product in the process of tungsten smelting and it is widely used.
The common methods of preparing ammonium metatungstate include thermal degradation and ion exchange, extraction, electrodialysis and neutralization.
Electrodialysis is the process of separating the electrolyte from the water by the selective conductivity of the ion exchange membrane under the action of the DC electric field. Under the action of the voltage, ammonium ion is used to form ammonium sulfate solution in the cathode solution of the circulation through anion exchange membrane. Electrodialysis method circulating pH = 9 ammonium metatungstate anode solution through the electrodialysis. Under the action of the voltage, the ammonium ion exchange membrane generates an ammonium sulfate solution through the anion in the circulating catholyte. The excess of ammonium ions in the anolyte begins to mass transfer, causing the pH to drop sharply due to the removal of the "associated" ions. At pH 8.7-8.3, the anode becomes turbid due to the insoluble compounds, but the compounds dissolve between pH4-5. At pH3.0, the process stops.
The anodic liquid is clarified and evaporated to a thick slurry, from which the coarse-grained white AMT crystals can be recycled. The final product recycle rate is higher than 99%.
Electrodialysis method is an effective way to obtain ammonium metatungstate. Its advantage is that AMT is prepared with high purity and high recycle rate. It has the potential of research and development.
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