Adsorption of fluoride, chloride, bromide, and bromate ions on a novel ion exchanger.

A novel ion exchanger based on double hydrous oxide (Fe2O3Al2O3xH2O) was obtained by the original sol-gel method from easily available and cheap raw materials and employed for adsorption of F-, Cl-, Br-, and BrO-3 from simultaneous solutions. Adsorbent was characterized by potentiometric titration, zeta-potential, and poremetrical characteristics. A technologically attractive pH effect of F-, Br-, and BrO-3 sorption on the investigated double hydroxide of Fe and Al, which is capable of working in the pH range 3 to 8.5, was observed. Kinetic data on fluoride and bromide sorption fit well the pseudo-second-order model. Isotherms of fluoride, bromide, chlorine, and bromate ion sorption on Fe2O3Al2O3xH2O were obtained at pH 4. The isotherm of F- sorption fit well the Langmuir model; sorption affinity (K=0.52 L/mg) and sorption capacity (90 mg F/g) were high. In the competitive adsorption of bromide and bromate, bromide dominated at equilibrium concentrations of the ions >40 mg/L. The mechanism of fluoride adsorption to the surface of the model cluster of the sorbent synthesized and the geometry of the cluster itself were modeled with the HyperChem7 program using the PM3 method.