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Abstract. The adsorption of fluoride from an aqueous solution onto a dolomite sorbent was studied. The surface morphology of the dolomite sorbent was evaluated, and it was found to have an un-smooth porous structure. The point of zero charge (PZC), specific surface area, and average pore size of the dolomite were observed at approximate pH 8.0-9.5, 1.17 m 2 /g, and 105.7 Å, respectively. The major mineral components of the dolomite sorbent were dolomite, calcite, and quartz. From a kinetic adsorption test, the dolomite sorbent required 12 hours of contact time to reach equilibrium with a fluoride adsorption capacity of 0.000581 mM/g, and the kinetic adsorption fitted well with a pseudo-second order kinetic reaction with a rate constant of 21.07 g/mM·min.

Abstract. The objective of this research was to study the effects of a pretreatment using activated carbon and cationic exchange resin on groundwater defluoridation by a reverse osmosis membrane. Actual groundwater containing a high fluoride concentration was collected and examined. Experiments were operated under controlled conditions: a transmembrane pressure of 0.6 MPa and temperature of 25 °C. The reverse osmosis system with activated carbon and cationic exchange resin pretreatments had higher fluoride removal than the one without the pretreatments, 97% compared to 95%, respectively. Additionally, the reverse osmosis system with the pretreatments also produced a higher permeate flux, 1.1 10 -5 compared 9.6 10 -6 m 3 /m 2 ·s without the pretreatment. When the reverse osmosis systems with and without pretreatments were fouled, they showed a decrease in fluoride rejection, as well as a permeate flux decline. After the fouled reverse osmosis membranes were chemically cleaned, the permeate flux recovery and the fluoride rejection of the osmosis system with the pretreatments improved. It could be concluded that the activated carbon and cationic exchange resin played an important role in improving the reverse osmosis system as they contributed to high fluoride rejection and high permeate flux.