High-purity ammonium metatungstate crystal may be prepared by neutralization-nanofiltration-crystallization coupling process. Among them, the coupling process of neutralization-nanofiltration was studied to know the effects of temperature, pH value, stirring rate, and membrane pressure on the coupling process. The neutralization-nanofiltration coupling process includes acid neutralization process to prepare AMT mixed solution and nanofiltration process of AMT mixed solution.
Neutralization-nanofiltration Coupling Process to Study Preparation Conditions of High-purity Ammonium Metatungstate Crystal
1. Test Materials and Devices
(1) Ammonium paratungstate (APT-0);
(2) Nitric acid (Industrial grade);
(3) Deionized water (Conductivity≥20kΩ•cm);
(4) Nanofiltration desalination device uses HDS-12-2# spiral membrane with a molecular weight cut off of 350 and a membrane area of 2.5m2.
2. Test Method
Step 1: Add dilute nitric acid into APT solution. APT is gradually converted to AMT under appropriate reaction conditions such as appropriate acidity and temperature.
Step 2: AMT solution is passed through a nanofiltration membrane device by concentration and washing to obtain pure AMT solution.
Step 3: During a certain time interval, the concentrations of tungsten and nitrate ions in feed liquid and permeate are sampled and analyzed; And permeate pressure is directly read by pressure gauge.
3. Analysis Method
The content of tungsten was analyzed by thiocyanate colorimetric method (in the form of WO3). And the content of nitrate ion was determined by ferrous sulfate-potassium dichromate titration.
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