||Equilibrium Fluoride Capacity of Activated Alumina. Determination of the Effects of pH and Competing Ions.
Singh, Gurinderjit ;
Clifford, Dennis A. ;
||Houston Univ., TX.;Municipal Environmental Research Lab., Cincinnati, OH.
Chemical equilibrium ;
Water treatment ;
Potable water ;
Activated alumina ;
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This report describes research on the determination of the equilibrium fluoride adsorption capacity of small columns of acid pretreated activated alumina (Alcoa F-1 grade). The experimental observations verified the expectation that fluoride is very favorably adsorbed in preference to the common anions: sulfate, chloride and bicarbonate. However, the adsorption capacities were found to be four to five times higher than what has been reported in the early literature for municipal defluoridation processes. Fluoride adsorption capacity is significantly affected and is decreased with an increase in pH beyond seven. The alumina selectivity sequence determined by experiments was the same as has been reported in the early literature, OH(-1) greater than F(-1) greater than SO4(-2) greater than Cl(-1) greater than HCO3(-1). Although fluoride anions are preferred over sulfate ions, the sulfate ions compete significantly at the levels found in ground water supplies. Experiments with high ionic strength ranging up to 56 millimoles per liter (5600 ppm as CaCO3) indicate that the total adsorption capacity increases slightly. Fluoride adsorption capacity decreases only slightly with the very significant increases in the concentrations of the other anions. These equilibrium data will prove useful in utilizing the maximum adsorption capacity of activated alumina in municipal defluoridation processes.