The origin and assignment of the complex main satellite X-ray photoelectron spectroscopy (XPS) features cations in ionic compounds have been subject extensive theoretical studies using different methods. There is agreement that within a molecular orbital model, one needs to take into account types configurations. Specifically, those where core electron removed, but no other configuration changes are made addition ionization, there also shake or charge-transfer configuration. However, strong...

This contribution is both a review of different aspects X‐ray photoelectron spectroscopy that can help one determine U oxidation states and personal perspective on how to effectively model the complicated mixed‐valence phases. After discussion valence band, focus lingers U4f region, where use binding energies, satellite structures, peak shapes discussed in some detail. Binding energies were shown be very dependent composition/structure consequently unreliable guides state, particularly...

A composite sorbent (GAC−QPVP) was prepared by coating poly(4-vinylpyridine) onto a granular activated carbon, followed cross-linking and quaternization processes. The characterized scanning electron microscopy, point of zero charge measurement, BET analysis. Batch experiments with variable pH, ionic strength, concentrations Cr(VI), sorbent, competing anions were conducted to evaluate the selective sorption Cr(VI) from aqueous solutions. results showed that rates could be described...

Carbonation reactions are central to the prospect of CO2 trapping by mineralization in geologic reservoirs. In contrast relevant aqueous-mediated reactions, little is known about propensity for carbonation key partner fluid: supercritical carbon dioxide containing dissolved water ("wet" scCO2). We employed situ mid-infrared spectroscopy follow reaction a model silicate mineral (forsterite, Mg2SiO4) 24 h with wet scCO2 at 50 °C and 180 atm. The results show dramatic dependence reactivity on...

Mercury (Hg) is a highly toxic element, and its contamination of groundwater presents significant threat to terrestrial ecosystems. Understanding the geochemical processes that mediate mercury transformations in subsurface necessary predict fate transport. In this study, we investigated redox transformation mercuric Hg (Hg[II]) presence Fe(II)/Fe(III) mixed valence iron oxide mineral magnetite. Kinetic spectroscopic experiments were performed elucidate reaction rates mechanisms. The...

This Critical Review reviews the origin and chemical rheological complexity of radioactive waste at U.S. Department Energy Hanford Site. The waste, stored in underground tanks, was generated via three distinct processes over decades plutonium extraction operations. Although close records were kept original disposition, tank-to-tank transfers conditions that impede equilibrium complicate our understanding chemistry, phase composition, rheology waste. Tank slurries comprise particles...

The interaction of anhydrous supercritical CO(2) (scCO(2)) with both kaolinite and ~1W (i.e., close to but less than one layer hydration) calcium-saturated montmorillonite was investigated under conditions relevant geologic carbon sequestration (50 °C 90 bar). molecular environment probed in situ using a combination three novel high-pressure techniques: X-ray diffraction, magic angle spinning nuclear magnetic resonance spectroscopy, attenuated total reflection infrared spectroscopy. We...

Reduction of U(VI) to U(IV) on mineral surfaces is often considered a one-step two-electron process. However, stabilized U(V), with no evidence U(IV), found in recent studies indicates can undergo one-electron reduction U(V) without further progression U(IV). We investigated pathways uranium by reducing electrochemically magnetite electrode at pH 3.4. Cyclic voltammetry confirms the U(V). Formation nanosize precipitates surface potentials and dissolution solids oxidizing are observed situ...

Shale formations play fundamental roles in large-scale geologic carbon sequestration (GCS) aimed primarily to mitigate climate change and smaller-scale GCS targeted mainly for CO2-enhanced gas recovery operations. Reactive components of shales include expandable clays, such as montmorillonites mixed-layer illite/smectite clays. In this study, situ X-ray diffraction (XRD) infrared (IR) spectroscopy were used investigate the swelling/shrinkage H2O/CO2 sorption Na(+)-exchanged montmorillonite,...

The origins of the complex Fe 2p X-Ray Photoelectron Spectra (XPS) hematite (α-Fe2O3) are analyzed and related to character bonding in this compound. This analysis provides a new novel view reasons for XPS binding energies (BEs) BE shifts, which deepens current understanding interpretation physical chemical significance XPS. In particular, many-body effects considered initial final, 2p-hole configuration wavefunctions. It is shown that one-body or one-configuration not sufficient many-body,...

High-resolution X-ray photoelectron spectroscopy was used to demonstrate that reduction of aqueous U6+ at ferrous mica surfaces 25 °C preserves U5+ as the dominant sorbed species over a broad range solution compositions. Polymerization with and U4+ is identified possible mechanism for how mineral circumvent rapid disproportionation U5+. The general nature this suggests could play an important, but previously unidentified, role in low-temperature chemistry uranium reducing, heterogeneous systems.

The stability of biogenic uraninite with respect to oxidation is seminal the success in situ bioreduction strategies for remediation subsurface U(VI) contamination. properties and hence are dependent on its size, structure, composition. In this study, local-, intermediate-, long-range molecular-scale structure nanoscale produced by Shewanella oneidensis strain MR-1 was investigated using EXAFS, SR-based powder diffraction TEM. products were found be structurally homologous stoichiometric UO2...

The heterogeneous reduction of UVI to UIV by ferrous iron is believed be a key process influencing the fate and transport U in environment. reactivity both sorbed structural FeII has been studied for numerous substrates, including magnetite. Published results from UVI-magnetite experiments have variable, ranging no clear evidence formation UIV. In this contribution, we used XAS high resolution (±cryogenic) XPS study interaction with nanoparticulate indicated that was partially reduced UV...

Geologic storage of CO2 requires that the caprock sealing rock is highly impermeable to CO2. Swelling clays, which are important components caprocks, may interact with leading volume change and potentially impacting seal quality. The interactions supercritical (sc) Na saturated montmorillonite clay containing a subsingle layer water in interlayer region have been studied by sorption neutron diffraction techniques. excess isotherms show maxima at bulk densities ≈0.15 g/cm3, followed an...

Reactions involving variably hydrated super critical CO(2) (scCO(2)) and a Na saturated dioctahedral smectite (Na-STX-1) were examined by in situ high-pressure X-ray diffraction at 50 °C 90 bar, conditions that are relevant to long-term geologic storage of CO(2). Both hydration dehydration reactions rapid with appreciable reaction occurring minutes near steady state within an hour. Hydration occurred stepwise as function increasing H(2)O the system; 1W, 2W-3W, >3W clay states stable from...

U(VI) doped hematite was synthesized and exposed to two different organic reductants with E(0) of 0.23 0.70 V. A combination HAADF-TEM EXAFS provided evidence that uranium incorporated in uranate, likely octahedral coordination. XPS indicated structurally reduced U(V), whereas non-incorporated U(IV). Specifically, the experiments indicate U(V) dominant oxidation state around Eh -0.24 -0.28 V pH 7.7-8.6 for at least up 5 weeks reaction time. but not U(IV), also detected +0.21 (pH 7.1-7.3)....

Sorption of contaminants onto mineral surfaces is an important process that can restrict their transport in the environment. In current study, uranium (U) uptake on magnetite (111) was measured as a function time and solution composition (pH, [CO3]T, [Ca]) under continuous batch-flow conditions. We observed, real-time situ, adsorption reduction U(VI) subsequent growth UO2 nanoprecipitates using atomic force microscopy (AFM) newly developed U LIII-edge grazing-incidence X-ray absorption...