| 摘要 |
<p>PURPOSE:To remove fluoride ions efficiently by allowing water contg. fluoride ions to react with calcium ions and subjecting this to settling and separating then forming the precipitate of magnesium hydroxide and calcium carbonate and returning the precipitate. CONSTITUTION:Raw water is introduced through a raw water pipe 6 into a dissolving vessel 1, and further the precipitate in a settling vessel 5 is introduced therein through a return pipe 7. If necessary, an acid is added to this mixture through a feed pipe of chemicals 8 to control the pH to <=4 and to dissolve the returned precipitate. The outflow water from the vessel 1 is introduced into the 1st reaction vessel 2 where the pH is controlled to 5-8.5 in the presence of calcium ions to allow precipitate to form. The reacting liquid in the vessel 2 is subjected to solid-liquid sepn. in a settling tank 3. The supernatant is flowed out into the 2nd reaction vessel 4. In the vessel 4, the pH is controlled to >=9.5 in the presence of magnesium ions and carbonate ions to allow precipitate to form. The precipitate is returned through the pipe 7 into the vessel 1.</p> |
