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International audienceInteraction of aqueous Se(IV) with pyrite was investigated using persistently stirred batch reactors under O2-free (<1 ppm) conditions at pH ranging from 4.5 to 6.6. Thermodynamic calculations, an increase in pH during the experiments, and spectroscopic observation indicate that the reduction of aqueous Se(IV) by pyrite is dominated by the following reaction: FeS2 + 3.5HSeO3− + 1.5H+ = 2SO42− + Fe2+ + 3.5Se(0) + 2.5H2O. The released Fe(II) was partitioned between the bulk solution and pyrite surface at pH ≈ 4.5 and 4.8, with the Fe2+ density at pyrite-solution interface about 4 orders of magnitude higher than that in the bulk solution, while iron oxyhydroxide precipitated at pH ≈ 6.6, resulting in the decrease of dissolved iron. In the Se(IV) concentration range of the experiments, aqueous Se(IV) reduction rate follows the pseudofirst order which is in the form of ln mSe(IV) = −k′t + ln mSe(IV)0, where k′ is apparent rate constant combining the rate constant k and pyrite surface area to mass of solution ratio (A/M). And the aqueous Se(IV) reduction rate constant for a standard system (k) with 1 m2 pyrite surface area per 1 kg solution was obtained to be 1.65 × 10−4 h−1, 3.28 × 10−4 h−1, and 4.76 × 10−4 h−1 at pH around 4.5, 4.8, and 5.1, respectively. The positive correlation between reaction rate and pH disagrees with the theories that protons are consumed when HSeO3− is reduced to Se0, and negative charge density on pyrite surface increases as pH increases. Thus, a ferrous iron mediated electron transfer mechanism is proposed to operate during the reduction of aqueous Se(IV) by pyrite. pH and iron concentration affect significantly on Se(IV) reaction rate and reaction product

7 O 15 ] (TPKBUO-3), were synthesized under high-temperature/high-pressure conditions. In all three compounds, the U/B ratio exceeds 1. Boron exhibits BO 3 coordination only, which is different from other uranyl borates prepared at room temperature or under mild hydrothermal conditions. A rare uranium(VI) tetraoxide core UO 4 O 2 , which is coordinated by two BO 3 groups, is observed in the structure of TPKBUO-1. Both structures of TPKBUO-1 and TPKBUO-3 contain three different coordination environments of uranium, namely, UO 4 O 2 , UO 2 O 4 , and UO 2 O 5 and UO 2 O 4 , UO 2 O 5 , and UO 2 O 6 bipyramids in TPKBUO-1 and TPKBUO-3, respectively.

COMMUNICATION Albrecht-Schmitt et al.Complex clover cross-sectioned nanotubules exist in the structure of fi rst uranium borate phosphate An actinide borate phosphate was prepared via a high temperature solid-state reaction. This phase exhibits unprecedented complex inorganic nanotubular fragments with an external diameter of B2 Â 2 nm. The nanotubular aggregates are based on borate tubes where the exterior of the tubes is decorated with UO 2 (PO 4 ) 3 moieties to form a complex shape with a cross-section similar to the clover cross.

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The simultaneous incorporation of IO3(-) and NpO2+ into Ba3(UO2)2(HPO4)2(PO4)2 (BaUP), which serves as a model for uranyl alteration phases, was investigated. LA-ICP-MS data demonstrate that the incorporation of both of these species is significantly enhanced when they are present together. The most probable explanation is that charge balance is obtained by the coupled substitutions of NpO2+ <--> UO2(2+) and IO3(-) <--> HPO4(2-). According to the LA-ICP-MS results, in the absence of iodate as much as 2.91 +/- 0.14 to 3.44 +/- 0.25% of the uranium in BaUP can be replaced by neptunium. When iodate is present in the reaction, the amount of uranium substitution by neptunium increases to 6.05 +/- 0.65% to 7.93 +/- 0.83%. The net increase for neptunium is 116 +/- 0.30% to 225 +/- 0.25%. Similarly, in the absence of NpO2+, iodate incorporation into BaUP reaches an I/U level of 0.0021 +/- 0.0004 to 0.0038 +/- 0.0005; whereas in its presence there is an increase to as much as 100 +/- 0.11% to 0.0042 +/- 0.0008.

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