Role of nano-goethite in controlling U(VI) sorption-desorption in subsurface soil

Abstract Iron oxide nanoparticles in natural soils and sediments can be nanoporous due to the aggregation of nanoparticles. Nanopores can greatly affect the sorption-desorption as well as reduction-oxidation behavior of U(VI) because of their high internal surface area and nanopore confinement effects. Batch U(VI) sorption-desorption experiments were conducted to understand the role of nano-goethite in controlling U(VI) sorption-desorption behavior in saprolite subsoil from Oak Ridge Field Research Center (ORFRC), Tennessee, a premier field research site for environmental remediation. The subsoil samples from ~ 6.5–8.5 m depth were nearly homogeneous in mineral composition (quartz, illite and smectite) and particle size distribution. The subsoil samples were characterized by a range of dithionite-citrate-bicarbonate (DCB) extractable Fe(III) oxide content (127–404 μM/g), BET surface area (25–38 m 2 /g), and nanoporosity (pore size  2 + and HCO 3 − . Sequential extraction of U(VI) pre-sorbed to saprolite subsoils with NaHCO 3 (1, 10, and 100 mM) exhibited more resistant U(VI) desorption from soils containing higher amount of nanoporous goethite. This study suggests that nano-crystalline goethite with nanoporous structure may exert a significant role in controlling the mobility and transport of U(VI) in subsurface environment where nanoporous minerals are ubiquitous and abundant.