Paratungstate B guanidine salt precipitation method is a method for separating molybdenum and tungsten.
It is known that there are three kinds of orthopolyacids, namely, paratungstic acid A, paratungstic acid B, paratungstic acid Z, the structure of B is the most special, and its chemical formula is Na10[H2W12O42], containing two H atoms, so the selectivity is strongest.
The key point of B guanidine precipitation method is how to convert A into B. Scholars have found that SiO2 has a significant catalytic effect on the transition reaction, and can shorten the conversion process to a few hours, which makes the feasibility of B guanidine salt precipitation method.
After the conversion of sec-tungstic acid A to paratungstic acid B, the pH of the solution was increased from 6.7 to 8.1, ensuring that Mo42- could be polymerized in a large concentration range, in order to use guanidine salt precipitation agent can effectively separate and in suitable conditions of pH tungsten and molybdenum, tungsten and molybdenum separation under (pH>7.5), only the formation of paratungstate B can guarantee the high precipitation rate of tungsten.
Recently, some scholars believe that guanidine nitrate is an ideal selective precipitant for B. The concentration of guanidine nitrate was 1.063 times -1.068 times, pH7.70-7.79 was 45 minutes, , stirring speed of 120 minutes and other precipitation conditions, molybdenum containing paratungstate B and guanidine nitrate solution in the precipitation process can fully realize the separation of tungsten and molybdenum, and, in the process of transformation, and the recovery of ammonium paratungstate guanidine nitrate preparation at the same time.
After verification, paratungstate B guanidine salt precipitation method has been confirmed as an effective method for separation of tungsten and molybdenum, as to why there is no large-scale application to the laboratory, reason unknown. But good wine is not afraid of deep alley. In the near future, more scholars will further improve the method of B guanidine salt precipitation. Make it easier to popularize.
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