This paper presents the synthesis of iron(III)-aluminum(III) mixed oxide with some of its physicochemical characteristics and fluoride adsorption behavior thereon. Results showed that the optimum initial pH for fluoride adsorption is 4.0-10.0, and the equilibrium time required is 1.5 h. The isotherm data follow the order Redlich-Peterson g Langmuir > Freundlich > Temkin. The Langmuir monolayer adsorption capacity of the adsorbent is determined to be 17.73 mg/g, which is higher than that of either of the pure oxides. The enthalpy change (∆H°) and entropy change (∆S°) for the adsorption reaction are +29.31 kJ/mol and +116.75 J mol -1 K -1 , respectively. The adsorption is endothermic in nature. The kinetics follows a pseudo-second-order rate equation, and the reaction rate is a multistage-controlled diffusion process. The activation energy for this adsorption reaction is 6.35 kJ/mol.

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Characterization of synthetic Fe(III)−Zr(IV) mixed oxide (NHIZO) by the X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses confirmed the material as agglomerated nanocrystallite particles (16−21 nm) which was used for As(III) sorption from water. The optimum pH and equilibrium time (As(III) concentrations (mgL−1), 5.0 and 10.0; NHIZO dose, 2 g·L−1; temperature, 303 K) were 7.0 ± 0.2 and 2.0 h, respectively. The kinetic and equilibrium data described, respectively, the pseudo-second-order equation and the Langmuir as well as the Redlich−Peterson isotherm models very well. The Langmuir capacity was 65.5 ± 1.0 mg·g−1 at 303 K, which increased with increasing temperature. The positive enthalpy (ΔH°) and negative free energy (ΔG°) changes indicated the endothermic and spontaneous nature of the reaction, respectively. The sorption energy (4.64−5.20 kJ·mol−1) and Fourier transform infrared (FTIR) analyses suggested physissorption of As(III) by NHIZO. The sorbed arsenic could be desorbed (∼80%) by 2.0 M alkali. The toxicity leaching characteristic procedure test marked As(III)−NHIZO as nonhazardous waste.