The principle of preparing ammonium metatungstate hydrate by ion exchange method can be clearly divided into the following steps and points:
- Principle of preparing ammonium metatungstate hydrate by ion exchange method
Ion exchange method utilizes the ions in ion exchange resin to exchange with the ions in solution, so as to realize the separation and purification of specific ions. In the process of preparing ammonium metatungstate hydrate, the pH value of the solution is adjusted to make the ammonium ions in ammonium tungstate or ammonium sec-tungstate exchange with the hydrogen ions in the resin, thus generating ammonium metatungstate solution under specific conditions, and finally obtaining ammonium metatungstate hydrate through evaporation and crystallization.
Steps for the preparation of ammonium metatungstate hydrate by ion exchange method
Preparation of raw materials and resin
Raw material
Ammonium tungstate solution or ammonium sec-tungstate solution.
Resin
Strongly acidic or weakly acidic H+ type cation resin, such as commercially available Dulitecc3 resin or Amerliter IRC-84 resin.
pH Adjustment
Adjust the pH of the raw material solution to a range suitable for ion exchange, generally around pH 3.5. This is to promote effective exchange of ammonium ions with hydrogen ions in the resin.
Ion exchange
Hydrogen ions (H+) in the ion exchange resin are exchanged with ammonium ions (NH4+) in the raw material solution. In this process, the resin adsorbs ammonium ions and releases hydrogen ions into solution. The key to this step is the selectivity and exchange efficiency of the resin.
Cooking and Conversion
The exchanged solution is boiled at a certain temperature (e.g., 98°C), usually for 5 hours. The purpose of this step is to convert ammonium tungstate or ammonium sec-tungstate into a stable ammonium metatungstate solution under the action of hydrogen ions. The choice of boiling temperature and time has an important influence on the conversion efficiency and product quality.
Evaporation, concentration and crystallization
The boiled ammonium metatungstate solution is evaporated and concentrated to increase the solute concentration in the solution. Subsequently, ammonium metatungstate is precipitated from the solution to form crystals by cooling crystallization or spray drying. This step is one of the key steps in the preparation of ammonium metatungstate hydrate.
Filtration and Drying
The crystallized ammonium metatungstate hydrate is separated from the mother liquor using filtration equipment. The wet crystals are then dried to remove residual water and solvent to obtain the dried ammonium metatungstate hydrate finished product.
The principle of preparing ammonium metatungstate hydrate by ion exchange method is to use the selective adsorption and exchange performance of ion exchange resin to exchange ammonium ions in the raw material solution with hydrogen ions in the resin, thus generating ammonium metatungstate solution under specific conditions and obtaining the product by evaporation and crystallization. This method has the advantages of simple process, convenient control and high product purity, and is one of the important methods for the preparation of ammonium metatungstate hydrate.
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