Neptunium (Np(V)) sorption onto a purified illite is investigated as a function of pH (3-10) and [Np V O 2 + ] tot (3 Â 10 À8 -3 Â 10 À4 M) in 0.1 M NaCl under Ar atmosphere. After about one week reaction time, only insignificant variation of Np sorption is observed and the establishment of reaction equilibrium can be assumed. Surprisingly, solid-liquid distribution ratios (R d ) are clearly higher than those measured for Np(V) sorption onto illite under aerobic conditions. The observation that R d increases with decreasing pe (pe = Àlog a eÀ ) suggests partial reduction to Np(IV), although measured redox potentials (pe values) at a first glance suggest the predominance of Np(V). Reduction to Np(IV) at the illite surface could indeed be confirmed by X-ray absorption near-edge spectroscopy (XANES). Np speciation in presence of the purified Na-illite under given conditions is consistently described by applying the 2 sites protolysis non-electrostatic surface complexation and cation exchange model. Measured pe data are taken to calculate Np redox state and surface complexation constants for Np(IV) are derived by applying a data fitting procedure. Constants are very consistent with results obtained by applying an existing linear free energy relationship (LFER). Taking Np(IV) surface complexation constants into account shifts the calculated Np(V)/ Np(IV) redox borderline in presence of illite surfaces by 3-5 pe units (0.2-0.3 V) towards redox neutral conditions. Our study suggests that Np(V) reduction in presence of a sorbing mineral phase is thermodynamically favored.

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Extremely arsenic-rich acid mine waters have developed by weathering of native arsenic in a sulfide-poor environment on the 10th level of the Svornost mine in Jáchymov (Czech Republic). Arsenic rapidly oxidizes to arsenolite (As2O3), and there are droplets of liquid on the arsenolite crust with high As concentration (80,000-130,000 mg·L(-1)), pH close to 0, and density of 1.65 g·cm(-1). According to the X-ray absorption spectroscopy on the frozen droplets, most of the arsenic is As(III) and iron is fully oxidized to Fe(III). The EXAFS spectra on the As K edge can be interpreted in terms of arsenic polymerization in the aqueous solution. The secondary mineral that precipitates in the droplets is kaatialaite [Fe(3+)(H2AsO4)3·5H2O]. Other unusual minerals associated with the arsenic lens are běhounekite [U(4+)(SO4)2·4H2O], štěpite [U(4+)(AsO3OH)2·4H2O], vysokýite [U(4+)[AsO2(OH)2]4·4H2O], and an unnamed phase (H3O)(+)2(UO2)2(AsO4)2·nH2O. The extremely low cell densities and low microbial biomass have led to insufficient amounts of DNA for downstream polymerase chain reaction amplification and clone library construction. We were able to isolate microorganisms on oligotrophic media with pH ∼ 1.5 supplemented with up to 30 mM As(III). These microorganisms were adapted to highly oligotrophic conditions which disabled long-term culturing under laboratory conditions. The extreme conditions make this environment unfavorable for intensive microbial colonization, but our first results show that certain microorganisms can adapt even to these harsh conditions.

Colloids ColloidsG 2000 XAFS and LIBD Investigation of the Formation and Structure of Colloidal Pu(IV) Hydrolysis Products. -The structures of Pu(IV) oxyhydroxide eigen-colloids formed upon increasing the pH of an aqueous Pu(IV) solution are characterized by XAFS and laser induced breakdown detection (LIBD). A model of colloid formation is proposed, which leads to a face-centered cubic Pu sublattice having cation defects. The solubility for Pu(IV) measured with LIBD is close to the lower limit of the solubility curve from previously reported data. -(ROTHE, J.; WALTHER, C.; DENECKE*, M. A.; FANGHAENEL, T.; Inorg. Chem. 43 (2004) 15, 4708-4718; Inst. Nukl. Entsorgungstech., Forschungszent.