The main reasons for adding nitric acid during the tungsten smelting precipitation process are as follows:
Promote the dissolution and extraction of tungsten
Nitric acid is oxidizing and can extract tungsten from the ore. To obtain free acid, one part of tungsten ore is mixed with four parts of carbonate oxaline, and then nitric acid is added, and tungstic acid is precipitated in a solid state. This shows the key role of nitric acid in promoting the dissolution and extraction of tungsten during tungsten smelting.
Control the pH value and reaction conditions of the solution
The addition of nitric acid can affect the pH value of the solution, and then affect the existence form and reaction rate of ions in the solution. The addition of nitric acid helps to adjust the solution to a pH range suitable for tungsten precipitation.
Eliminate interfering ions
During the smelting process, other ions may exist in the solution, which may interfere with the precipitation of tungsten. The addition of nitric acid can react with these interfering ions and convert them into a form that does not interfere with precipitation, thereby improving the purity of tungsten precipitation.
Participate in the precipitation process as a reactant
Nitric acid directly participates in the precipitation process of tungsten as a reactant. For example, in the process of generating tungstic acid, nitric acid reacts with tungsten compounds in tungsten ore to generate precipitable tungstates.
Improving precipitation efficiency and purity
The addition of nitric acid can accelerate the formation of precipitation and improve precipitation efficiency. At the same time, due to the oxidizing and selectivity of nitric acid, it can improve the purity of precipitation and reduce the impurity content.
Advantages compared with hydrochloric acid
Although hydrochloric acid can also be used in the smelting process of tungsten, nitric acid is less corrosive and causes less damage to equipment. Therefore, it is more economical and safe to use nitric acid when a large amount of tungsten-containing solution needs to be treated for a long time.
In summary, nitric acid is added to the tungsten smelting precipitation process to promote the dissolution and extraction of tungsten, control the pH value and reaction conditions of the solution, eliminate interfering ions, participate in the precipitation process as a reactant, improve precipitation efficiency and purity, and have lower corrosiveness and higher economy compared with hydrochloric acid.
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