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topic 4903

Nitric HF acid


I would like to know about the potential uses for spent Nitric-HF acid (6:1 Ratio) which is an acid mix typically used to etch silicon wafers for the production of microchips. What industries or companies can use spent Nitric-HF acid?

Tom Mackey
- Theodore, Alabama


The Si etching reaction can be expressed as follows: Si + 4HNO3 + 6HF --> H2SiF6 + 4NO2 + 4H2O Silicon is oxidized by rthe nitric acid and the resulting silicon oxide is dissolved by the HF acid.

Hexafluorosilicate and water are generated in the solution. The NO2 is gasified and treated. One possible use for the spent acid is fertilizer, but many fertilizer producers cannot handle the residual HF.

Tom Mackey
- Theodore, AL.

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