Erbium adsorption from aqueous solutions using RSM-based optimization of the phosphate functional group in modified nano titania

Nano-titania was modified by nitrilotris(methylene)phosphonic acid (NTMP) as a new adsorbent and as a suitable linker for further performance to the adsorption of erbium from aqueous solutions. The adsorbent was characterized by different techniques analysis including FTIR, BET, SEM, XRD and XPS. The effects of adsorbent dose, pH, initial concentration of erbium and temperature were optimized by central composite design (CCD) and were analyzed and modeled by response surface methodology (RSM). Statistical analysis of variance (ANOVA) was carried out to identify the adequacy of the developed model, and revealed good agreement between the experimental data and proposed model. The adsorption capacity of erbium in pure nano titania, NTMP/nano titania and optimal adsorption conditions was 12.5 mg g⁻¹, 50 mg g⁻¹ and 106 mg g⁻¹, respectively. In this work, we showed that phosphate group from NTMP how could modified the adsorbent surface. Moreover, the kinetic and isotherm studies were conducted. Regarding to the calculation of ΔG°, ΔH° and ΔS°, it is observed that the nature of erbium ion sorption was endothermic, spontaneous, physisorptive and was favored at higher temperature. Furthermore, the desorption capacity of erbium ions by H₃PO₄, HCl, HNO₃, H₂SO₄, and EDTA was evaluated. Finally, the presence of competitive ions (La³⁺, Sm³⁺, and Dy³⁺ ions) on the erbium adsorption capacity was investigated using RSM. Considering all these, we show that the novel adsorbent can be effective for the removal of erbium from aqueous solutions using sorbent modified technique.