From the silicon treatment foul solution you recover and reuses nitric acid the manner

摘要

PURPOSE: To improve recovering efficiency by removing silicon dioxide deposited on a cooling condensing part by dissolving with fluoric acid and recovering nitric acid by distillation when recovering nitric acid from a washing waste liquid or the like of poly crystalline silicon or the like. ;CONSTITUTION: A waste water bottle 11 in a oil bath 10 is connected to a cooling part 13 and a collecting vessel 14 with a branching pipe 12 and is connected to a fluoric acid supply pipe 15. And the waste water is heated to equal or above b.p. of a fluoric acid water and a nitric acid water, usually 100-125°C, and is distilled. Water-fluoric acid group is distilled on a low b.p. side. In the process, hydrosilicofluoric acid is decomposed and silicon fluoride is distilled with fluoric acid and reacts with water to deposit silicon dioxide in the cooling part 13. And distilled fluoric acid flows down to the cooling part 13 through the supply pipe 15 to dissolve and remove silicon dioxide. Supply of fluoric acid is stopped when deposition is out. And when the distillation on the side of low b.p. group is completed, the distillation is transferred to the side of high b.p. group for distilling nitric acid to recover nitric acid.;COPYRIGHT: (C)1993,JPO&Japio