| 摘要 |
Recovering acid from a spent aqueous etching mixture used to purify polycrystalline silicon, comprising hydrofluoric, nitric, hexafluorosilicic and nitrous acids, comprises distilling of the first 20-50 wt.% of the mixture as dilute acid containing more than 90% of the hexafluorosilicic acid, thereby reducing the water content of the mixture to 10-30 wt.%, and then distilling off a second fraction to leave a residue of 1-5 wt.%, which is disposed of. An independent claim is also included for purifying polycrystalline silicon with an aqueous etching mixture containing hydrofluoric and nitric acids, where the spent etching mixture is processed as above to give a mixture of hydrofluoric and nitric acids with a nitric acid content of more than 55 wt.% and a silicon content of less than 1 wt.%, which is added to the the etching mixture for primary purification. |
