Defluorination in High Fluoride-Bearing Water with Electric Field and Limestone

High F^- in water can be removed by Ca²⁺ in form of precipitation of CaF₂ in water when their ion activity production(IAP) reaches up to equilibrium dissolution constant of fluorite based on the precipitation theory of insoluble minerals. Self-designed tank is used to generate a large number of Ca²⁺ and CO₃^2- from dissolution of limestone under the effect of electric field, then the Ca²⁺ and F^- movement to the cathode and anode respectively leads to partial accumulation in certain area. When [Ca²⁺][ F^-]²>Ksp(CaF₂), CaF₂ precipitates. The effect of voltage (U), distance of cathode and anode (d) and time (t) is discussed, the primary experiment results show that F^- concentration can be reduced to 1 mg/L(upper limit for Fluorine in drinking water in China) with initial F^- concentration of 10 mg/L, and the optimal conditions are as following: U = 8V, d = 2cm, t = 90min.