Sorption characteristics and separation of tellurium ions from aqueous solutions using nano-TiO 2

Abstract

Titanium dioxide nanoparticles (nano-TiO 2) were employed for the sorption of Te(IV) ions from aqueous solution. A detailed study of the process was performed by varying the sorption time, pH, and temperature. The sorption was found to be fast, equilibrium was reached within 8 min. When the concentration of Te(IV) was below 40 mg L −1, at least 97% of tellurium was adsorbed by nano-TiO 2 in the pH range of 1–2 and 8–9. The sorbed Te(IV) ions were desorbed with 2.0 mL of 0.5 mol L −1 NaOH. The sorption data could be well interpreted by the Langmuir model with the maximum adsorption capacity of 32.75 mg g −1 (20 ± 0.1 °C) of Te(IV) on nano-TiO 2. The kinetics and thermodynamics of the sorption of Te(IV) onto nano-TiO 2 were also studied. The kinetic experimental data properly correlated with the second-order kinetic model ( k 2 = 0.0368 g mg −1 min −1, 293 K). The overall rate process appeared to be influenced by both boundary layer diffusion and intra-particle diffusion. The mean energy of adsorption was calculated to be 17.41 kJ mol −1 from the Dubinin–Radushkevich (D–R) adsorption isotherm at room temperature. Moreover, the thermodynamic parameters for the sorption were estimated, and the Δ H 0 and Δ G 0 values indicated the exothermic and spontaneous nature of the sorption process, respectively. Finally, Nano-TiO 2 as sorbent was successfully applied to the separation of Te(IV) from the environmental samples with satisfactory results (recoveries >95%, relative standard deviations was 2.0%).