| 摘要 |
PROBLEM TO BE SOLVED: To obtain sludge excellent in dewaterability by returning a crystal having a small particle diameter to be used for reaction to grow the crystal and separating to take out the crystal having large particle diameter and uniform particle size. SOLUTION: Fluorine-containing water 11 is reacted with a calcium compound in a reaction vessel 2 to deposit calcium fluoride, flocculated in a flocculating vessel 3, solid-liquid separated in a solid-liquid separating vessel 4 and the separated sludge 15 is classified in a classification device 21, the sludge containing the crystal relatively large in particle diameter is discharged to the outside of the system and the sludge containing the crystal relatively small in particle diameter is returned to a mixing vessel 6 to be mixed with a calcium compound and supplied to the reaction vessel 2 to be reacted.
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