The effect of desferrioxamine B on europium(III) interactions with gibbsite

Anthropogenic contamination of surface and subsurface environments has led to greater interest in the interactions of toxic metal ions with mineral surfaces. Toxic metal ions are a major form of soil and sediment contamination. They are released to the environment from numerous sources including industrial discharges and solid waste disposal, untreated sludge application, mining, pesticide and fertilizer use, and fly ash release and application to land. Also, high level radioactive waste processing and disposal sites are potential sources of radionuclide contamination. Many of these latter species exist as metallic cations.; The present study examines the interactions of Eu(III) (a luminescent probe and a surrogate for some trivalent actinides) with a prototypical soil mineral, solvated gibbsite (Al(OH)3). The adsorption of Eu(III) on gibbsite was investigated in the presence and absence of desferrioxamine B (DFB), a natural exocellular microbial ligand. Aqueous complexation of Eu(III) by DFB was also examined. The local coordination environment of the Eu(III) was assessed with steady-state and time-resolved luminescence spectroscopy and with extended x-ray absorption spectroscopy (EXAFS).; In homogeneous solutions, a 1:1 Eu-DFB complex was observed at a pH value of approximate 6. At pH values ≥9 luminescence and infra-red measurements suggest the formation of a different Eu-DFB complex involving an additional amino-group on the ligand.; In binary systems comprised of aqueous Eu(III) and gibbsite, adsorbed Eu(III) is present as inner-sphere surface complexes and the extent of adsorption is independent of ionic strength. In ternary systems containing Eu(III), gibbsite and DFB, the presence of DFB enhances Eu adsorption at low pH, due to the sorption of metal ligand complexes. In contrast, DFB inhibited the sorption of Eu sorption by gibbsite (relative to the binary system) at pH values ≥7.