Defluoridation by freshly prepared aluminum hydroxides

The exposure to fluoride via drinking water is a great issue globally. This study investigates the adsorptive capability of the freshly prepared aluminum hydroxide, i.e., in-situ Al2O3·xH2O, towards fluoride. The maximum adsorption of above 110 mg F/g Al is observed in pH ranges from 5.0 to 7.2. The adsorption equilibrium is achieved within 120 min, and pseudo-second-order model may well describe the adsorption kinetics (R2 = 0.999), indicating the involvement of chemisorptions in. The characteristics of low particle diameter, high surface area, and the surface reactivity of the amorphous in-situ Al2O3·xH2O enables its superior to remove fluoride for the in-situ Al2O3·xH2O. pH impacts the distribution of Al species and the quantity of solid-state Al available for fluoride. The ratios of monomeric Al, i.e., Ala, are below 4% in pH from 6 to 8, and then increase to 19.2% at pH 4 and to 28.9% at pH 10. Alc, showing adverse trends to Ala, is the main species for fluoride removal. In cases that the amount of in-situ Al2O3·xH2O available is the same, surface charge is dominant to affect the removal of fluoride. FTIR indicates the replacement of surface hydroxyl groups by fluoride.

The removal of fluoride by the in-situ Al2O3·xH2O was observed to be positively correlated with the surface charge of the in-situ Al2O3·xH2O, and the higher zeta potential contributes to the more significant removal of fluoride. The introducing of negatively charged ions such as phosphate and sulfate decreases the zeta potential, and inhibites the removal of fluoride accordingly.Figure optionsDownload as PowerPoint slideHighlights
► The adsorption capability of above 110 mg F/g Al is observed for in-situ Al2O3·xH2O.
► The low particle diameter and fresh reactivity enable its high adsorption capability.
► pH impacts Al species distribution, solid-state Al quantity and fluoride removal.