Synergistic adsorption behavior of a silica-based adsorbent toward palladium, molybdenum, and zirconium from simulated high-level liquid waste

In this study, the synergistic adsorption behavior of palladium [Pd(II)], molybdenum [Mo(VI)], and zirconium [Zr(IV)] in simulated high-level liquid waste was systematically investigated based on various factors, such as the contact time, concentration of nitric acid, adsorption amount, and temperature using a silica-based adsorbent impregnated with N,N′-dimethyl-N,N′-di-n-hexyl-thiodiglycolamide (Crea) and 2, 2′, 2′ -nitrilotris[N,N-bis(2-ethylhexyl)acetamide] (TAMIA-EH). The adsorption rates of Pd(II), Mo(VI), and Zr(IV) in this synergistic adsorption system were high; thus, equilibrium states could be obtained in only 1 h with high uptake percentages of more than 90%. The adsorption abilities of Pd(II), Mo(VI), and Zr(IV) were only slightly affected by variation in the concentration of nitric acid in the range of 0.1–5 M and solution temperature in the range of 288–313 K. Selective stripping of the adsorbed Re(VII), Pd(II), Zr(IV), and Mo(VI) was successfully achieved under elution with 5 M HNO₃, 0.2 M Tu (pH 1), 50 mM DTPA (pH 2), and 50 mM DTPA dissolved in 0.5 M Na₂CO₃ (pH 11) solutions using the chromatography method. In addition, the adsorption performance in solid-state was studied using the particle-induced X-ray emission (PIXE) method; the obtained results were in good agreement with the results obtained via column separation.