Adsorption and regeneration of fluoride ion on a high alumina content bauxite

Adsorption of fluoride ion from aqueous solutions by using different silico-aluminous natural products was studied. Preliminary batch tests indicated how bauxite shows a high removal efficiency. Such optimum efficiency is due to the elevated presence of aluminium hydroxide (gibbsite) and aluminium oxide hydroxide (boehmite). Both batch and continuous experiments were performed: Freundlich equation well described batch equilibrium data. In continuous-flow column experiments, the effects of inlet fluoride concentration (5–50 mg L–1) and flow rate (up to 2.5 mL min–1) on breakthrough time and adsorption capacity were studied. Column studies showed that the dynamic adsorption capacity depends on the inlet fluoride concentration and the flow rate. After adsorption of fluorides, saturated bauxite, was regenerated by using two different solutions containing NaOH and H2SO4. Column tests indicated a different behaviour of original respect to regenerated bauxite.