143 research outputs found
Water-Exchange Study Revealed Unexpected Substitution Behavior of [(CO)2(NO)Re(H2O)3]2+ in Aqueous Media
No full textCopyright © 2006 American Chemical SocietyMarie-Line Lehaire, Pascal V. Grundler, Stefan Steinhauser, Niklaus Marti, Lothar Helm, Kaspar Hegetschweiler, Roger Schibli, and André E. Merbac
Mechanistic changeover for the water substitution on fac-[(CO)(3)Re(H(2)O)(3)](+) revealed by high-pressure NMR
No full textCopyright © 2004 American Chemical SocietyPascal V. Grundler, Bernadette Salignac, Sonia Cayemittes, Roger Alberto, and André E. Merbac
Cross section measurement of terbium radioisotopes for an optimized 155Tb production with an 18 MeV medical PET cyclotron.
No full text155Tb [t1/2 = 5.32 d, Eγ = 87 keV (32%); 105 keV (25%) (IAEA, 2021)] is a novel promising radionuclide for theranostic applications in nuclear medicine. Its physical properties make it suitable for single photon emission computed tomography (SPECT) imaging, while its chemistry allows it to be used as a diagnostic partner for therapeutic radiolanthanides or pseudo-radiolanthanides, such as 177Lu and 90Y. Moreover, 155Tb could be used as a precise diagnostic match for the β--emitter 161Tb, opening doors for the true theranostics concept. The availability of 155Tb in quantity and quality suitable for medical applications is an open issue and its production with medical cyclotrons via the 155Gd(p,n)155Tb and 156Gd(p,2n)155Tb nuclear reactions represents a possible but challenging solution. For this purpose, an accurate knowledge of the production cross sections is mandatory. In this paper, we report on the measurement of the production cross sections of 155Tb and other terbium radionuclides formed by proton irradiation of natGd2O3, 155Gd2O3 and 156Gd2O3 enriched targets, performed at the Bern University Hospital cyclotron laboratory. On the basis of the obtained results, the production yield and purity were calculated to assess the optimal irradiation conditions. The results of several production tests are also presented
Cross-section measurement of thulium radioisotopes with an 18 MeV medical PET cyclotron for an optimized 165Er production.
No full text165Er is a pure Auger-electron emitter with promising characteristics for therapeutic applications in nuclear medicine. The short penetration path and high Linear Energy Transfer (LET) of the emitted Auger electrons make 165Er particularly suitable for treating small tumor metastases. Several production methods based on the irradiation with charged particles of Er and Ho targets can be found in the literature. In this paper, we report on the study of 165Er indirect production performed via the 166Er(p,2n)165Tm →165Er reaction at the 18 MeV Bern medical cyclotron. Despite the use of highly enriched 166Er2O3 targets, several Tm radioisotopes are produced during the irradiation, making the knowledge of the cross sections involved crucial. For this reason, a precise investigation of the cross sections of the relevant nuclear reactions in the energy range of interest was performed by irradiating Er2O3 targets with different isotopic enrichment levels and using a method based on the inversion of a linear system of equations. For the reactions 164Er(p, γ)165Tm, 166Er(p,n)166Tm, 166Er(p, γ)167Tm, 167Er(p,3n)165Tm, 167Er(p, γ)168Tm, 168Er(p,2n)167Tm and 170Er(p,3n)168Tm, the nuclear cross section was measured for the first time. From the results obtained, the production yield and purity of the parent radioisotope 165Tm were calculated to assess the optimal irradiation conditions. Several production tests with solid targets were performed to confirm these findings
XAS evidence for the stability of polytellurides in hydrothermal fluids up to 599 degree(s) C, 800 bar
No full textAlthough the crustal abundance of tellurium (Te) is about half of that of gold (Au), several classes of Au deposits are highly enriched in Te. Our understanding of the nature of this Au-Te association is hampered by the lack of experimental studies of Te geochemistry at elevated temperature. We characterized the structure of polytelluride solutions from room temperature to 599ºC at 800 bar using in situ X-ray absorption spectroscopy. Both ab-initio XANES and EXAFS fits show that polytellurides are stable up to the highest temperature with planar structures (four-or threefold coordination of Te) giving way to linear chaines (e.g. Te2-ion) at temperatures above --200ºC. This is the first experimental confirmation of the thermal stability of polytelluride species. The data shows that polytellurides play an important role in Te transport in reduced S-rich or CO2-rich solutions and vapors.Joël Brugger, Barbara E. Etschmann, Pascal V. Grundler, Weihua Liu, Denis Testemale and Allan Pringhttp://www.minsocam.org/msa/ammin/toc/2012/AS12.htm
A novel pre-treatment of calaverite by hydrothermal mineral replacement reactions
No full textWe report a new method for pre-treatment of refractory gold-bearing tellurides employing the hydrothermal mineral replacement reactions. The method is illustrated by the replacement of calaverite by metallic gold at 150-250 °C under vapor saturated pressures. The influences of temperature, pH, and additional salts (NaCl and Na2SO4) on the conversion rate were investigated using the orthogonal array design method. The results indicate that temperature is the most significant factor, followed by pH, and then additional salts. The optimal condition for fast and low cost conversion is 200 °C, pH 6.0, 0.01 M NaCl, and <38 μm particle size. Under this condition, the conversion can be completed within 15 h. These preliminary results indicate that the hydrothermal mineral replacement reaction is a promising pre-treating step for gold-bearing tellurides processing. © 2009 Elsevier Ltd. All rights reserved.Jing Zhao, Fang Xia, Allan Pring, Joël Brugger, Pascal V. Grundler and Guorong Che
Copper(I) speciation in mixed thiosulfate-chloride and ammonia-chloride solutions: XAS and UV-Visible spectroscopic studies
No full textThiosulfate and ammonia mixtures may be more environmentally benign alternatives to cyanide for leaching Au from ores. In this method, the Cu(I)/Cu(II) couple acts as a redox mediator aiding in the oxidative dissolution of metallic Au. Information about the speciation of Cu(I) and Cu(II) in these lixiviant solutions is paramount to the optimization of gold ore processing conditions. With this in mind, we have carried out XANES, EXAFS and UV-Vis spectroscopic studies of the speciation of Cu(I) in mixed thiosulfate-chloride and ammonia-chloride solutions. In thiosulfate-chloride solutions, the EXAFS studies indicate that the geometry of the predominant Cu(I) complex is distorted trigonal (triangular planar), with an average of 2 sulfur atoms + 1 oxygen atom occupying the coordination sphere. This indicates that the stability of the [Cu(S2O3)3]5− complex is lower than previously proposed. Formation constants for Cu(I) thiosulfate complexes have been derived on the basis of systematic UV-Vis measurements of solutions with varying [S2O3]/[Cl] ratios. Only one mixed chloride-thiosulfate complex, [Cu(H2O)(S2O3)Cl]2−, was found to predominate over the range of conditions investigated. For Cu(I) in ammonia-chloride solutions, our results confirm the broad stability of [Cu(NH3)2]+ and we have also identified a stable mixed amminechlorocopper(I) complex, [CuCl(NH3)]+. XAS reveals that these two complexes share a linear geometry. This study demonstrates that combinations of methods are required to decipher the geometry and thermodynamic properties of transition metal complexes in mixed ligand chemical systems where many species may coexist. Our results allow more comprehensive predictions of solution speciation and contribute to efforts to design improved methods to process gold ore with thiosulfate and ammonia lixiviants.Barbara E. Etschmann, Jay R. Black, Pascal V. Grundler, Stacey Borg, Dale Brewe, D. C. McPhail, Leone Spiccia and Joël Brugge
Mechanism and kinetics of a mineral transformation under hydrothermal conditions: Calaverite to metallic gold
No full text© 2009 Mineralogical Society of AmericaThe transformation of calaverite to gold under hydrothermal conditions was studied experimentally by probing the effects of temperature (140 to 220 °C), pH (2-12), oxidant concentration, geometric specific surface area, and solid-weight to fluid-volume ratio on the sample textures and the reaction, kinetics. Under all of the experimental conditions explored, calaverite transformed to various extents to metallic gold. The replacement is pseudomorphic, as gold preserves the external dimensions of calaverite. The resulting elemental gold is porous; consisting of filament-shaped aggregates with diameters ranging from 200 to 500 nm and lengths up to 25 (.im. Gold crystals appear to be randomly oriented with respect to the twinned calaverite grains. The transformation proceeds via a, coupled calaverite dissolution-gold precipitation mechanism, with calaverite dissolution being rate-limiting relative to gold precipitation. Tellurium is lost to the bulk solution as Te(IV) complexes, and may further precipitate away from the dissolution site (e.g., autoclave walls) as TeO2(S). In contrast, gold precipitates locally near the calaverite dissolution site. Such local gold precipitation is facilitated by fast heterogeneous nucleation onto the calaverite surface. The dissolution of calaverite and the overall reaction are oxidation, reactions, and oxygen diffusion, through the porous metallic gold layer probably plays an important role in, sustaining the reaction. A similar disso lution- reprecipitation process may be responsible for the formation of mustard gold during the weathering of gold-telluride ores. At 220 °C, solid-state replacement of calaverite by gold is slow (months), but calaverite grains ~100 (J,m in, size are fully replaced in <24 h under hydrothermal conditions, providing a possible alternative to roasting as a pre-treatment of telluride-rich gold ores.Jing Zhao, Joël Brugger, Pascal V. Grundler, Fang Xia, Guorong Chen and Allan Prin
Bismuth speciation in hydrothermal fluids: an X-ray absorption spectroscopy and solubility study
No full textThe solubility of bismuth oxide (α-Bi2O3(s); bismite) in near-neutral sodium perchlorate solutions at 65 and 80°C, and pure water from 150 to 600°C, PSat to 800bar was studied using various batch-reactor techniques and in situ XAS spectroscopy. The solubility of Bi2O3(s) follows a similar trend to Sb2O3(s) (senarmontite), which has been interpreted in terms of a neutral Sb(OH)3(aq) complex. Thus a similar neutral complex, Bi(OH)3(aq), is inferred for Bi. XANES spectroscopy confirms that the Bi(OH)3(aq) complex carries a stereochemically active lone electron pair, and EXAFS data suggest that the geometry of the complex changes little over the temperature range 380-610°C at 800bar, with three oxygen neighbors at ∼2.08å. The solubility data obtained in this study are used in conjunction with thermodynamic properties for α-Bi2O3(s) to obtain thermodynamic parameters for Bi(OH)3(aq) within the framework of the revised Helgeson-Kirkham-Flowers (HKF) equation of state. Speciation calculations using these new properties indicate that, similarly to arsenic and antimony, bismuth is transported predominantly as a neutral hydroxide complex in a wide range of temperature, pressure, and fluid compositions. In contrast to arsenic and antimony, bismuth is much less soluble in typical hydrothermal fluids in the form of hydroxide complexes, and high temperatures (≥400°C) are required for significant Bi transport by aqueous fluids. These results are consistent with the common association between Bi mineralization and magmatism. © 2012 Elsevier Ltd.Blake Tooth, Barbara Etschmann, Gleb S. Pokrovski, Denis Testemale, Jean-Louis Hazemann, Pascal V. Grundler, Joël Brugge
Xocolatlite, Ca2Mn24+Te2O12 center dot H2O, a new tellurate related to kuranakhite: Description and measurement of Te oxidation state by XANES spectroscopy
No full textXocolatlite, Ca2Mn24+ Te2 6+ O12·H2O, is a rare new mineral from the Moctezuma deposit in Sonora, Mexico. It occurs as chocolate-brown crystalline crusts on a quartz matrix. Xocolatlite has a copper-brown streak, vitreous luster, and is transparent. Individual crystals show a micaceous habit. Refractive indices were found to be higher than 2.0. Density calculated from the empirical formula is 4.97 g/cm3, and immersion in Clerici solution indicated a density higher than 4.1 g/cm3. The mineral is named after the word used by the Aztecs for chocolate, in reference to its brown color and provenance. The crystallographic characteristics of this monoclinic mineral are space group P2, P2/m, or Pm, with the following unit-cell parameters refined from synchrotron X-ray powder diffraction data: a = 10.757(3) Å, b = 4.928(3) Å, c = 8.942(2) Å, β = 102.39(3)°, V = 463.0(3) Å, and Z = 2. The unavailability of a suitable crystal prevented single-crystal X-ray studies. The strongest 10 lines of the X-ray powder diffraction pattern are [d in Å (I) (hkl)]: 3.267(100)(012), 2.52(71)(303̄), 4.361(51) (002), 1.762(39)(323̄), 4.924 (34)(010), 2.244(32)(313̄), 1.455(24)(006), 1.996(21)(014), 1.565(20) (611), and 2.353(18)(411̄). XANES Te Lm-edge spectra of a selection of Te minerals (including xocolatlite) and inorganic compounds showed that the position of the absorption edge can be reliably related to the oxidation state of Te. XANES demonstrated that xocolatlite contains Te6+ as a tellurate group. Water has been tentatively included in the formula based on IR spectroscopy that indicated the presence of a small amount of water. Raman, IR, XANES, and X-ray diffraction data together with the chemical composition show a similarity of xocolatlite to kuranakhite. A possible series may exist between these two species, xocolatlite being the Ca-rich end-member and kuranakhite the Pb-rich one.Pascal V. Grundler, Joël Brugger, Nicolas Meisser, Stefan Ansermet, Stacey Borg, Barbara Etschmann, Denis Testemale and Trudy Boli
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