Weakly bound complexes of CF3Br molecules or of CF3Br and CH3OH were prepared in supersonic jet expansions and studied by photoionization mass spectrometry. Argon was present in the jet expansion to promote cooling of the complexes. Measured ionization potentials are CF3Br, 11.404±0.014 eV; (CF3Br)2, 11.10±0.02 eV; (CF3Br⋅CH3OH), 10.76±0.05 eV. The appearance potential of CF+3 from CF3Br was found to be 11.56±0.02 eV, and evidence is presented that this value is adiabatic. From this appearance potential, ΔH0f0(CF+3)=86.6±1.1 kcal mol−1. The magnitude of the spin–orbit splitting in X̃ 2E CF3Br+ into E1/2 and E3/2 states dominates any Jahn–Teller distortion. The effects of these phenomena on the stability of X̃ 2E CF3Br+ are discussed. The following dissociation channels were observed: CF+3 from X̃ 2E CF3Br+, CF2Br+ from Ã 2A1 CF3Br+, Br+ from B̃ 2A2 CF3Br+, and CF+2 from D̃ 2E CF3Br+. (CF3⋅CH3OH)+ is not produced from neutral dimers, but is created when a CF3Br moiety embedded in a trimer or larger cluster is ionized to Ã 2A1 CF3Br+. In contrast, (Br⋅CH3OH)+ does come from dimers as well as larger clusters. The cross sections for the production of (CF3Br)+2 and (CF3Br⋅CH3OH)+ from trimers or larger progenitors are enhanced when intracluster CF3Br is ionized to CF3Br+ in the B̃ or higher electronic states. Possible reasons for these state-specific reactions are given. Finally, a new method is presented for determining neutral cluster distributions in a molecular beam, and the method is shown to be in quantitative agreement with the near-threshold technique previously published by Grover et al. [J. Phys. Chem. 95, 6473 (1991)].

In-situ recovery (ISR) of uranium (U) from sandstone-type roll-front deposits is a technology that involves the injection of solutions that consist of ground water fortified with oxygen and carbonate to promote the oxidative dissolution of U, which is pumped to recovery facilities located at the surface that capture the dissolved U and recycle the treated water. The ISR process alters the geochemical conditions in the subsurface creating conditions that are more favorable to the migration of uranium and other metals associated with the uranium deposit. There is a lack of clear understanding of the impact of ISR mining on the aquifer and host rocks of the post-mined site and the fate of residual U and other metals within the mined ore zone. We performed detailed petrographic, mineralogical, and geochemical analyses of several samples taken from about 7 m of core of the formerly the ISR-mined Smith Ranch-Highland uranium deposit in Wyoming. We show that previously mined cores contain significant residual uranium (U) present as coatings on pyrite and carbonaceous fragments. Coffinite was identified in three samples. Core samples with higher organic (N 1 wt.%) and clay (N6-17 wt.%) contents yielded higher 234 U/ 238 U activity ratios (1.0-1.48) than those with lower organic and clay fractions. The ISR mining was inefficient in mobilizing U from the carbonaceous materials, which retained considerable U concentrations (374-11,534 ppm). This is in contrast with the deeper part of the ore zone, which was highly depleted in U and had very low 234 U/ 238 U activity ratios. This probably is due to greater contact with the lixiviant (leaching solution) during ISR mining. EXAFS analyses performed on grains with the highest U and Fe concentrations reveal that Fe is present in a reduced form as pyrite and U occurs mostly as U(IV) complexed by organic matter or as U(IV) phases of carbonate complexes. Moreover, U-O distances of~2.05 Å were noted, indicating the potential formation of other poorly defined U(IV/VI) species. We also noted a small contribution from U_O at 1.79 Å, which indicates that U is partially oxidized. There is no apparent U-S or U-Fe interaction in any of the U spectra analyzed. However, SEM analysis of thin sections prepared from the same core material reveals surficial U associated with pyrite which is probably a minor fraction of the total U present as thin coatings on the surface of pyrite. Our data show the presence of different structurally variable uranium forms associated with the mined cores. U associated with carbonaceous materials is probably from the original U mobilization that accumulated in the organic matter-rich areas under reducing conditions during shallow burial diagenesis. U associated with pyrite represents a small fraction of the total U and was likely deposited as a result of chemical reduction by pyrite. Our data suggest that areas rich in carbonaceous materials had limited exposure to the lixiviant solution, continue to be reducing, and still hold significant U resources. Because of t...

15We use uranium (U) isotope ratios to detect and quantify the extent of natural U reduction in 16 groundwater across a roll front redox gradient. Our study was conducted at the Smith Ranch-17 model that evaluates both the migration of U from the ore body and the extent of natural 27 attenuation due to reduction. We find that the pre-mining migration of U down-gradient of the 28 delineated ore body is minimal along eight transects due to reduction in or adjacent to the ore 29 body, whereas two other transects show little or no sign of reduction in the down-gradient 30 region. These results suggest that characterization of U isotopic ratios at the mine planning stage, 31 in conjunction with routine geochemical analyses, can be used to identify where more or less 32 post-mining remediation will be necessary. 33

Drill-core samples from a sandstone-hosted uranium (U) deposit in Wyoming were characterized to determine the abundance and distribution of uranium following in-situ recovery (ISR) mining with oxygen-and carbon dioxide-enriched water. Concentrations of uranium, collected from ten depth intervals, ranged from 5 to 1920 ppm. A composite sample contained 750 ppm uranium with an average oxidation state of 54% U(VI) and 46% U(IV). Scanning electron microscopy (SEM) indicated rare high uranium (~1000 ppm U) in spatial association with P/Ca and Si/O attributed to relict uranium minerals, possibly coffinite, uraninite, and autunite, trapped within low permeability layers bypassed during ISR mining. Fission track analysis revealed lower but still elevated