Ammonium Metatungstate Preparation -- Extraction Method
The extraction method is a preparation process that use ammonium tungstate with ammonium tungstate solution as raw material.
This method is also one of the processes for preparing Ammonium Metatungstate (AMT) at presnt. The extraction principle of ammonium metatungstate (AMT) extraction method is similar to that of ammonium tungstate extraction method, which needs to experience four stages including extraction, water washing and stripping. The whole extraction process is carried out in a box-type mixer-settlers, the difference is that in the reverse extraction operation, the concentration and dosage of the extractant are different.
In the process of production, using ammonium tungstate solution as raw material, ammonium metatungstate was extracted by solvent extraction, extraction of NH4+ ion from ammonium metatungstate solution by a cationic extractant, then, the solution of pH in the condition of 3~4, ammonium metatungstate solution was obtained by reverse extraction. This is a simple and economical method. Ammonium metatungstate solution obtained by solvent extraction, ammonium nitrate was prepared by concentrated crystallization or spray drying.
Some scholars used EPA-88-1 extractant to prepare ammonium tungstate from ammonium metatungstate solution.The most important feature of this method is that two product of ammonium tungstate and ammonium metatungstate can be obtained simultaneously by changing the pH value of different raffinate. The production cost is correspondingly reduced, the cycle is shortened, and the energy consumption is low, and the utility model is especially suitable for the technical transformation project of the existing ammonium tungstate factory.
Ammonium metatungstate has the same advantages as ion exchange method. It is simple, continuous and low cost. But the biggest weakness of the extraction method is that the solid substance is easy to cause emulsification during the extraction process. The whole process is easy to fail in some simple situations, and that's why it hasn't been as popular as ion exchange.
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