Sorption characteristics and separation of tellurium ions from aqueous solutions using nano-TiO2

Titanium dioxide nanoparticles (nano-TiO2) 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-TiO2 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-TiO2. The kinetics and thermodynamics of the sorption of Te(IV) onto nano-TiO2 were also studied. The kinetic experimental data properly correlated with the second-order kinetic model (k2 = 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 ΔH0 and ΔG0 values indicated the exothermic and spontaneous nature of the sorption process, respectively. Finally, Nano-TiO2 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%).