Selective demineralization of water by nanofiltration application to the defluorination of brackish water

Nanofiltration is generally used to separate monovalent ions from divalent ions, but it is also possible to separate ions of the same valency by caref ul application of the transfer mechanisms involved. Analysis of the retenti on of halide salts reveals that small ions like fluoride are the best retai ned, and that this is even more marked under reduced pressure when selectiv ity is greatest. The selectivity desalination of fluorinated brackish water is hence feasible and drinking water can be produced directly at much lowe r cost than using reverse osmosis by optimizing the pressure for the type o f water treated. (C) 2001 Elsevier Science Ltd. All rights reserved.