Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The use of copper canisters in the Swedish KBS-3 concept for spent nuclear fuel disposal could result in the formation of copper-bearing uranyl phases should a canister suffer from defects or if the containment were to fail before reducing conditions are established in the repository. Most uranyl species would be expected to display higher solubility than the original uranium(IV) dioxide fuel, leading to enhanced release, though this would depend on the phase and prevailing groundwater conditions. Secondary alteration products may also be poorly crystalline or even amorphous, making characterization difficult during the pre-closure period owing to the high radiation field close to the canister. Vandenbrandeite, [CuUO2(OH)4], is a rare mineral in nature but known to form by alteration of primary uraninite through interaction with oxidizing groundwater containing dissolved copper. Consequently, an attempt has been made to characterize two vandenbrandeite specimens of varying crystallinity by luminescence and multiple-laser Raman spectroscopy; techniques amenable to remote, robotic deployment and which have proved useful in discriminating other uranyl oxy-hydroxides, silicates, and phosphates. The first reported luminescence emission and excitation spectra for vandenbrandeite revealed near-negligible luminescence, with a slightly enhanced signal for the specimen displaying poorer crystallinity. This observation agrees well with density functional theory calculations. The simulated projected density of state and band structure show an unlikely transition from the U f-orbitals to Cu d-orbitals, or O states, would be required for luminescence to be detectable; this probably improves for poorly crystalline specimens as the spatial overlap between the orbitals increases. Furthermore, negligible differences in the number of peaks and peak positions were detected in the laser wavelength-dependent Raman spectra although again, variation in background noise and peak shape was observed based on the degree of crystallinity. Good agreement was obtained between experimental and simulated Raman spectra, particularly with the environmentally sensitive axial uranyl stretching modes, validating the crystal system derived in this study. The findings of this study suggest luminescence spectroscopy, when combined with Raman spectroscopy, may be able to both identify vandenbrandeite and distinguish between crystalline and amorphous forms based on their relative luminescence intensity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The frequent occurrence of chlorides and carbonates in the form of microinclusions of melts or high-density fluid (HDF) in diamonds and igneous minerals of kimberlites worldwide generates genuine interest in their phase diagrams under pressure. Here, we present the first experimental results on the phase relations in the NaCl-CaCO3 and NaCl-MgCO3 systems at 6 GPa in the range 1000–1600 °C performed using a multi-anvil press. We found that both systems have the eutectic type of phase diagrams. The subsolidus assemblages are represented by halite + aragonite and halite + magnesite. Halite-aragonite eutectic is situated just below 1200 °C and has a composition of 40 wt% NaCl and 60 wt% CaCO3. Halite-magnesite eutectic is located at 1300 °C and has a composition of 72 wt% NaCl and 28 wt% MgCO3. The halite melting point was established at 1500 °C. Complete miscibility between carbonate and chloride liquids was observed up to 1600 °C. The results support the hypotheses that saline HDF is either a low-temperature derivative or precursor of mantle carbonatite HDF. The data also do not exclude an alternative hypothesis, according to which saline HDF are formed as a result of the reduction of the carbonate component of chloride-containing carbonatite melts to diamond.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This issue of New Mineral Names provides a summary of five new species: pohlite, muonionalustaite, medvedevite, gysinite-(La), and nioboheftetjernite.</jats:p>