Factors affecting vanadium precipitation
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Factors affecting vanadium precipitation
Phenomenon
In industrial production, the pH value of the leaching solution is about 8-9. The precipitant ammonium chloride and concentrated sulfuric acid are added to adjust the pH value to between 2-2.5. Vanadium can be precipitated in the form of ammonium metavanadate, but the precipitation is affected by the following conditions.
Concentration of vanadium solution
The higher the concentration of vanadium in the stock solution, the faster the growth rate of the crystal nucleus during the hydrolysis of vanadium precipitation. The faster the precipitation rate, the faster the growth rate of the crystal nucleus, so the crystal structure is incomplete, the precipitated particles are not tight, the adsorbed impurities are more, the water is more, and the quality is poor. Sometimes it is easy to cause sticking if it is not well controlled. In short, the higher the concentration of vanadium, the faster the precipitation rate, and the lower the grade of the precipitate. In general, the concentration of the stock solution is controlled at 15-20g/L.
The influence of acidity
The experiment shows that the precipitation of vanadium begins when the pH value is 3.6. As the acidity increases, the reaction rate of vanadium becomes faster. However, as the acidity increases to a certain value, it is accompanied by the occurrence of side reactions, that is, the reverse dissolution of polyvanadate ammonium
The effect of ammonium salt amount
The addition method of ammonium salt is generally that ammonium salt is easy to decompose in alkaline solution. Therefore, in industry, the pH value of the solution is adjusted to between 4-5, and then ammonium salt is added. Then, under stirring, the pH is adjusted to about 1.9-2.1, and then heated for precipitation
The effect of precipitation time
When the ammonia addition coefficient is fixed at 0.65 and the pH value is equal to 2.2, the precipitation rate can reach more than 98% when the time reaches more than 25 minutes. In actual production, the precipitation rate can be guaranteed by controlling it for more than 30-40 minutes.
The effect of temperature
When the other conditions are exactly the same, the increase in temperature can accelerate the precipitation rate of vanadium from the solution. The temperature also has a great influence on the reverse precipitation rate, physical form, and the grade of polyvanadate ammonium. When precipitation is carried out at low temperature, the apparent particles of the precipitate are fine, the color is red, and the grade is high. The precipitate obtained at high temperature has large particles, dark color, and correspondingly low grade.
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Slightly soluble in water, insoluble in ethanol, soluble in strong acid, strong base. |
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