Competitive Defluorination Influenced by Chloride Ions by Nanofiltration Membrane in Advanced Drinkingwater
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 Cl- from the groundwater, and the relationship between the ions of F- and Cl- by the negatively charged nanofiltration membrane (NF) . The results showed that the rejection efficiency of F- was higher than that Cl- by NF. Selectivity coefficient (S) of F-/Cl- was prominent (S > 1.5). The F- concentrations in permeate were distributed in 0.5~1.0 mg/L with less than 3.7 mg/L of feed water. In addition, the F- rejection rates represented different characteristics affected by Cl-. It was calculated that about 10.0 mol ions of Cl- caused 1.1 mol ions of F- to penetrate NF. S value increased from 1.5 to 2.0 above with the increase of F- concentrations. The selectivity and competitive relationship existed between F- and Cl- during the defluorination by NF membrane.