| 摘要 |
PURPOSE:To efficiently remove fluorine from waste water contg. hexafluorosilicate ions by electrolyzing said waste water to form fluorine ions then bringing Ca ions into reaction therewith. CONSTITUTION:An alkali is added to the waste water contg. the hexafluorosilicate ions to adjust the pH thereof to preferably >=7, then such waste water mixture as an electrolyte is subjected to a DC electrolysis. The hexafluorosilicate ions are an anode and are dissociated to silicon ions and fluorine ions by such electrolytic reaction. Hardly soluble Ca fluoride is formed by the Ca ions from the waste water mixture in this state and the fluorine ions are removed. The formed slurry is subjected to a solid-liquid sepn. and if the fluorine ions remain in the liquid component, the above-mentioned operation is repeated. The liquid is neutralized and released if the fluorine ions in the liquid component attains a control value or above. Namely, the hexafluorosilicate ions, the removal efficiency of which have heretofore not been satisfactory with a Ca salt settling method are removed with high removal efficiency.
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