Abstract
Mesoporous silica SBA-15 grafted with benzene-1,3,5-triamido-tetraphosphonic acid (SBA-15-BTATPA) was synthesized. After detailed characterization of the material using various analytical instrumentation, it was applied for the recovery of Nd3+ as a function of the contact time, ion concentration, and pH. The adsorption equilibria and kinetics were also examined. Under the optimal conditions, adsorption equilibrium was reached within 60 min of contact time, and the adsorption capacity of Nd3+ at room temperature and pH 6 was 129.8 mg g−1, which was higher than that by other rare earth element (REE) ions tested for comparison (Y3+, La3+, and Ce3+). The adsorbent showed excellent distribution coefficient for Nd3+ greater than 1.0 × 105 mL/g. The preferential order of adsorption in the ion mixture with equal ion concentrations was Y3+>Nd3+>Ce3+>La3+, which followed the sequence of their decreasing atomic size and increasing stability constant. The competing adsorption by transition metal ions, such as Cu2+, Ni2+, Co2+, and Zn2+, on the REEs recovery was negligible (<2%). The observed adsorption isotherms could be fitted well to a Langmuir model (correlation factor R2 > 0.99), whereas the adsorption kinetics could be described satisfactorily by a pseudo second order kinetic model. The material was reusable for up to 5 consecutive times with only a slight decrease in adsorption capacity.
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