| 摘要 |
PROBLEM TO BE SOLVED: To maintain a stable and efficient treatment of water for a long period by efficiently removing scale forming components without necessitating ion exchange treatment to effectively prevent the problems due to the scale of calcium fluoride on a RO membrane surface in a deionization in a RO membrane filter device by mixing industrial water or city water containing calcium ion with recovered water containing fluorine ion. SOLUTION: Calcium carbonate crystal and phosphoric acid and/or a phosphate are added into raw water adjusted to pH>=8 to produce hardly soluble fluoroapatite and the fluoroapatite is separated and removed with membrane filtration using a UF membrane or a MF membrane and the filtrate is deionized.
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