Iron and aluminium based mixed hydroxides: A novel sorbent for fluoride removal from aqueous solutions

In our previous studies, iron and aluminium based mixed hydroxides were prepared in different molar ratios and fluoride removal efficiencies were evaluated. It was found that the Fe/Al sample with 1:1 molar ratio exhibited maximum adsorption capacity for fluoride. In the present work detailed studies were carried out to understand the effect of fluoride concentration on kinetics, adsorbent dose and competing anion concentrations. Characterisation studies on the adsorbent by XRD, TGA, SEM-EDX, TEM and FT-IR analysis before and after fluoride adsorption were carried out to understand the adsorption mechanism. The particles were irregular in shape, <0.5 μm in size, highly porous and showed specific surface area of 268 m2 g−1. XRD and FT-IR studies revealed significant changes after fluoride adsorption and showed formation of new complexes on adsorbent surface. Applicability of different sorption kinetic models was studied. The surface sites are heterogeneous in nature and followed heterogeneous site binding model. The presence of phosphate, sulphate and arsenate showed adverse effect on fluoride removal efficiency of Fe/Al adsorbent. The efficiency of material towards ground water samples treatment was tested with and without adjusting pH, and the results are discussed.