Uranyl hydroxide

Abstract: Incorporation of Oxidized Uranium into Fe (hydr)oxides during Fe(II) Catalyzed Remineralization Peter S. Nico 1* , Brandy D. Stewart 2† , and Scott Fendorf 2 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; 510- 486-7118; 510-486-5686 (fax); psnico@lbl.gov Environmental Earth System Science, Stanford University, Stanford, CA 94305 Present address: Chemical and Biological Engineering, Montana State University, Bozeman, MT 59717 Abstract The form of solid phase U after Fe(II) induced anaerobic remineralization of ferrihydrite in the presence of aqueous and absorbed U(VI) was investigated under both abiotic batch and biotic flow conditions. Experiments were conducted with synthetic ground waters containing 0.168 mM U(VI), 3.8 mM carbonate, and 3.0 mM Ca 2+ . In spite of the high solubility of U(VI) under these conditions, appreciable removal of U(VI) from solution was observed in both the abiotic and biotic systems. The majority of the removed U was determined to be substituted as oxidized U (U(VI) or U(V)) into the octahedral position of the goethite and magnetite formed during ferrihydrite remineralization. It is estimated that between 3% and 6% of octahedral Fe(III) centers in the new Fe minerals were occupied by U(VI). This site specific substitution is distinct from the non-specific U co-precipitation processes in which uranyl compounds, e.g. uranyl hydroxide or carbonate, are entrapped with newly formed Fe oxides. The prevalence of site specific U incorporation under both abiotic and biotic conditions and the fact that the produced solids were shown to be resistant to both extraction (30 mM KHCO 3 ) and oxidation (air

Abstract: We determined the association of uranium with bacteria isolated from the Waste Isolation Pilot Plant (WIPP), Carlsbad, New Mexico, and compared this with known strains of halophilic and non-halophilic bacteria and archaea. Examination of the cultures by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) showed uranium accumulation extracellularly and/or intracellularly to a varying degree. In Pseudomonas fluorescens and Bacillus subtilis uranium was associated with the cell surface and in the latter it was present as irregularly shaped grains. In Halobacterium halobium, the only archeon studied here, uranium was present as dense deposits and with Haloanaerobium praevalens as spikey deposits. Halomonas sp. isolated from the WIPP site accumulated uranium both extracellularly on the cell surface and intracellularly as electron-dense discrete granules. Extended X-ray absorption fine structure (EXAFS) analysis of uranium with the halophilic and non-halophilic bacteria and archaea showed that the uranium present in whole cells was bonded to an average of 2.4′0.7 phosphoryl groups at a distance of 3.65′0.03 A. Comparison of whole cells of Halomonas sp. with the cell wall fragments of lysed cells showed the presence of a uranium bidentate complex at 2.91′0.03 A with the carboxylate group on the cell wall, and uranyl hydroxide with U-U interaction at 3.71′0.03 A due to adsorption or precipitation reactions; no U-P interaction was observed. Addition of uranium to the cell lysate of Halomonas sp. resulted in the precipitation of uranium due to the inorganic phosphate produced by the cells. These results show that the phosphates released from bacteria bind a significant amount of uranium. However, the bacterially immobilized uranium was readily solubilized by bicarbonate with concurrent release of phosphate into solution.

Abstract: The solubility of uranyl hydroxide and uranyl carbonate and the formation constants of the complexes present in the supematant Solution were determined at 25°C in 0.1 M NaClOi solutions. The solubility products were found to be logA^,p= —22.21 and log/Csp= — 13.29. respectively. In the pH ränge from 4.5 to 5.5 the hydroxo complexes (U02)2(0H)r (lg/? = 22.16), and (U02)3(0H)5^ (lg^ = 53.05) were found. Under the condition 11 < l g ( C 0 3 \" ) < 6 three mononuclear uranyl carbonate complexes. UO2CO3 (lg/J = 8.70), U02(C03) r (lg^= 16.33), and U02(C03)r (Ig/? = 23.92) exist.