Removal of fluoride from drinking water by natural stilbite zeolite modified with Fe(III)

Stilbite zeolite (STI), a natural zeolite with high crystallinity and an open pore system, was modified with FeCl3 solution for the removal of fluoride from drinking water. The parent STI and modified STI (Fe(III)-STI) were characterized by FTIR, scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Adsorption of fluoride on modified STI (Fe(III)-STI) was studied as a function of contact time, adsorbent dose, initial concentration, pH and coexisting ions. Fluoride concentration can be reduced down to the lower level of 1 mg L−1 under the optimum condition (with solid/solution ratio of 1:100 and the contact time of 2 h and pH 6.94) when initial fluoride concentration of 10 mg L−1 is employed. The fluoride adsorption on Fe(III)-STI zeolite is well described by the Langmuir adsorption model, and the maximum fluoride adsorption capacity is 2.31 mg g−1. The kinetic result indicates that the adsorption of fluoride on the modified natural zeolite follows pseudo-first-order model. The possible mechanism on fluoride adsorption on Fe(III)-STI zeolite is also discussed.

Research highlights
► The natural STI zeolite was modified by Fe(III) ion to obtain a fluoride adsorbent.
► Fluoride concentration can be reduced down to 1 mg L−1 under the optimum conditions.
► Fluoride sorption may be a diffusion controlled process combined with chemisorption.
► It is an economical and efficient way for fluoride removal.