Dear Chandra Kant Tewari, ...
Published by Marco Rognoni, Owner at WET, Water Edge Technologies
Dear Chandra Kant Tewari,
The precipitation of CaF2 may sound to be a good and cheap way. However I have to contradict Mr Comoglio.
CaF2 is rated "insoluble" because its solubility is very poor: about 16 ppm (out of which about 7 of F and about 9 of Ca).
The guideline of WHO is to accept F content below 1,5 ppm, hence the precipitation of CaF2 takes place for concentration which is much higher than recommended by WHO.
The minimum concentration achieved by combining Ca with F is therefore about 7 ppm (probably something more for temperature higher than 20°C). This limit is probably achieved naturally because the water is expected to have more than 9 ppm Ca++. Hence the addition of more Ca is useless because the limiting compound for the formation of CaF2 is F (not Ca).
Unfortunately there are no cheap techniques for the selective reduction of Fluorides, and costly plants are eventually necessary to treat the water in large quantities before distribution (non-selective desalination). In Tamil Nadu you may refer to GB Saline (part of GB Group) of Trichy.