The chloride is one of the most common co-existing compound in drinking water. Therefore, it is significant to study the properties of selective removal of Fand Clfrom the groundwater, and the relationship between the ions of Fand Clby the negatively charged nanofiltration membrane (NF) . The results showed that the rejection efficiency of Fwas higher than that Clby NF. Selectivity coefficient (S) of F -/Clwas prominent (S > 1.5). The Fconcentrations in permeate were distributed in 0.5~1.0 mg/L

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... with less than 3.7 mg/L of feed water. In addition, the Frejection rates represented different characteristics affected by Cl -. It was calculated that about 10.0 mol ions of Clcaused 1.1 mol ions of Fto penetrate NF. S value increased from 1.5 to 2.0 above with the increase of Fconcentrations. The selectivity and competitive relationship existed between Fand Clduring the defluorination by NF membrane.