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US 5,346,557 AGranted
Process for cleaning silicon mass and the recovery of nitric acid
AssigneeHi-Silicon Co., Ltd.
InventorsHideo Ito, Mitsutoshi Narukawa, Kazuhiro Sakai
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Abstract
In a process for cleaning a silicon mass with a acid washing solution, a waste solution containing a mixed acid composed of nitric acid and hydrofluoric acid is introduced to a distillation step, and hydrofluoric acid is introduced to a distillation cooling portion to prevent precipitation of silicon dioxide. The waste cleaning liquor is distilled to recover nitric acid.
Claims18
A process comprising:
- sufficiently heating a liquid waste solution "obtained from cleaning a polycrystalline silicon mass" has been inserted after which comprises nitric acid, hydrofluoric acid, hydrosilicofluoric acid, and water so as to boil off a hydrofluoric acid containing vapor;
- transmitting said hydrofluoric acid containing vapor, said heating being effective to remove the hydrosilicofluoric acid to a condensation region;
- condensing said vapor in said condensation region to form a liquid condensate;
- and
- recovering said nitric acid as a substantially pure solution;
- wherein liquid hydrofluoric acid is added to said condensation region during said condensing step.
3 more elements
Dependencies are inferred from the claim text.