Technetium retention by gamma alumina nanoparticles and the effect of sorbed Fe2+

Technetium (Tc) retention on gamma alumina nanoparticles (gamma-Al2O3 NPs) has been studied in the absence (binary system) and presence (ternary system) of previously sorbed Fe2+ as a reducing agent. In the binary system, gamma-Al2O3 NPs sorb up to 6.5% of Tc from solution as Tc(VII). In the ternary system, the presence of previously sorbed Fe2+ on gamma-Al2O3 NPs significantly enhances the uptake of Tc from pH 4 to pH 11. Under these conditions, the reaction rate of Tc increases with pH, resulting in a complete uptake for pHs > 6.5. Redox potential (Eh) and X-ray photoelectron spectroscopy (XPS) measurements evince heterogeneous reduction of Tc (VII) to Tc(IV). Here, the formation of Fe-containing solids was observed; Raman and scanning electron microscopy showed the presence of Fe(OH)(2), Fe(II)-Al(III)-Cl layered double hydroxide (LDH), and other Fe(II) and Fe(III) mineral phases, e.g. Fe3O4, FeOOH, Fe2O3. These results indicate that Tc scavenging is predominantly governed by the presence of sorbed Fe2+ species on gamma-Al2O3 NPs, where the reduction of Tc(VII) to Tc(IV) and overall Tc retention is highly improved, even under acidic conditions. Likewise, the formation of additional Fe solid phases in the ternary system promotes the Tc uptake via adsorption, co-precipitation, and incorporation mechanisms.