The principle of solvent extraction for the preparation of ammonium metatungstate hydrate is mainly based on the difference in solubility or partition coefficient of a substance in two immiscible (or slightly soluble) solvents. The following is a detailed description of the principle:
Solvent extraction principle
The difference in solubility or partition coefficient of a substance in two immiscible (or slightly soluble) solvents is utilized to transfer a solute substance from one solvent to another. This is the basic principle of solvent extraction, which is widely used in chemical, metallurgical, food and other industries.
Solvent extraction of ammonium metatungstate
Take ammonium tungstate solution as raw material, use organic extractant such as di(2-ethylhexyl) phosphate (D₂EHPA) or tributyl phosphate (TBP) and kerosene solvent to form organic phase.
During the extraction process, the extractant in the organic phase reacts with the ammonium ions in the ammonium tungstate solution to transfer the ammonium ions from the aqueous phase to the organic phase, thereby reducing the pH of the solution to 2-4.
Reverse extraction and generation of ammonium metatungstate
In the solution after extraction, ammonium ions are re-transferred from the organic phase to the aqueous phase by adjusting the conditions, such as pH, to generate ammonium metatungstate solution.
In this process, the solvent extractant acts as a mediator to help transfer the ammonium ion between the two solvents.
Subsequent treatment
The generated ammonium metatungstate solution is concentrated and crystallized, impurities are removed by filtration and separation, and then dried to produce ammonium metatungstate hydrate product.
The principle of preparing ammonium metatungstate hydrate by solvent extraction method is to make use of the difference of solubility of substances in different solvents to transfer ammonium ions from ammonium tungstate solution to ammonium metatungstate solution through the process of extraction and counter-extraction, and then through the subsequent treatments such as concentration and crystallization, and then drying, the product of ammonium metatungstate hydrate is finally produced. This method has the advantages of simple operation, low cost and high efficiency, and is one of the important processes for the preparation of ammonium metatungstate hydrate.
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