Fluoride uptake characteristics of fly ash

Retention of fluoride ion in dynamic experiments on columns packed with fly ash was studied at 20 degrees C with a series of aqueous solutions containing 1, 5, 10, 20, 50, and 100 mg F-/L. The flow rate through a 450-9 bed was less than or equal to 2 mL/hr. At the lowest F- concentration (1 mg/L), the F- level in the effluent initially increased and then gradually decreased down to 0 mg/L after 120 hours. With higher F- concentrations in the feed solutions, the F- concentration in the effluent steadily decreased reaching 0 mg/L after 120-168 hours. We conclude that coal fly ash is an effective sorbent for F- ions, especially at high concentrations in water.