| 摘要 |
PROBLEM TO BE SOLVED: To recover hydrofluoric acid of a desired concentration and to reduce the amounts of desalting liquid discharged outside a system and chemicals such as hydrofluoric acid supplied by making the concentration of an alkali supplied to a neutralization process exceed a specified value in normal. SOLUTION: Waste liquid of nitric acid and hydrofluoric acid is supplied from a raw liquid storage tank 1 to a pH adjustment tank 2 through a channel 3. The waste liquid in the tank 2 is neutralized by the addition of potassium hydroxide of concentration exceeding a prescribed value, or 1.0 N. In this process, metal compounds such as Fe(OH)3 , Cr(OH)3 , Ni(OH)2 precipitate as metal sludge, and the filtrate (KF and KNO3 ) is supplied to the desalting chamber 13 of a bipolar membrane apparatus 4. The supplied filtrate is ionized in the chamber 13, hydrofluoric acid and nitric acid are separated into the acid line 8 of the apparatus 4, and potassium hydroxide is separated into an alkali line 9. Hydrofluoric acid and nitric acid separated from the acid line 8 are returned to an acid wash tank 11 and the raw liquid storage tank 1. |
