Mineral sequestration of CO(2) by aqueous carbonation of coal combustion fly-ash.

The increasing CO(2) concentration in the Earth's atmosphere, mainly caused by fossil fuel combustion, has led to concerns about global warming. A technology that could possibly contribute to reducing carbon dioxide emissions is the in-situ mineral sequestration (long term geological storage) or the ex-situ mineral sequestration (controlled industrial reactors) of CO(2). In the present study, we propose to use coal combustion fly-ash, an industrial waste that contains about 4.

Arsenate incorporation in gypsum probed by neutron, X-ray scattering and density functional theory modeling.

The ability of gypsum, a common sulfate mineral, to host arsenic atoms in its crystalline structure, is demonstrated through experimental structural studies of the solid solutions formed upon synthetic coprecipitation of gypsum (CaSO4 x 2 H2O) and arsenic. Neutron and X-ray diffraction methods show an enlargement of the gypsum unit cell proportional to the concentration of arsenic in the solids and to the pH solution value. The substitution of sulfate ions (SO4(2-)) by arsenate ions is shown to be more likely under alkaline conditions, where the HAsO4(2-) species predominates.

Hydration of Hg2+ in aqueous solution studied by neutron diffraction with isotopic substitution.

The structural parameters of Hg2+ hydration were studied in 0.225 mol/L solutions of Hg2+ in DNO3/D2O by means of neutron diffraction with isotopic substitution of 199Hg for natHg. It was found that Hg2+ is hydrated by a first solvation shell of six water molecules.

Chemical forms of selenium in the metal-resistant bacterium Ralstonia metallidurans CH34 exposed to selenite and selenate.

Ralstonia metallidurans CH34, a soil bacterium resistant to a variety of metals, is known to reduce selenite to intracellular granules of elemental selenium (Se(0)). We have studied the kinetics of selenite (Se(IV)) and selenate (Se(VI)) accumulation and used X-ray absorption spectroscopy to identify the accumulated form of selenate, as well as possible chemical intermediates during the transformation of these two oxyanions. When introduced during the lag phase, the presence of selenite increased the duration of this phase, as previously observed.

Zn speciation in the organic horizon of a contaminated soil by micro-X-ray fluorescence, micro- and powder-EXAFS spectroscopy, and isotopic dilution.

Soils that have been acutely contaminated by heavy metals show distinct characteristics, such as colonization by metal-tolerant plant species and topsoil enrichment in weakly degraded plant debris, because biodegradation processes are strongly inhibited by contamination. Such an organic topsoil, located downwind of an active zinc smelter and extremely rich in Zn (approximately 2%, dry weight), was investigated by X-ray diffraction, synchrotron-based X-ray microfluorescence, and powder- and micro-extended X-ray absorption fine structure (EXAFS) spectroscopy for Zn speciation and by isotopic dilution for Zn lability. EXAFS spectra recorded on size fractions and on selected spots of thin sections were analyzed by principal component analysis and linear combination fits.

Accumulation forms of Zn and Pb in Phaseolus vulgaris in the presence and absence of EDTA.

The internalized speciation of Zn and Pb in roots and leaves of Phaseolus vulgaris grown in zinc sulfate, zinc EDTA, lead nitrate, and lead EDTA solutions were studied by electron microscopy (Zn) and extended X-ray absorption fine structure (EXAFS) spectroscopy (Zn and Pb). Zn was predominantly present as Zn phosphate dihydrate in the roots and leaves of the plant regardless of its form in solution. Pb was predominantly found in the leaves as cerussite (lead carbonate) when the plant was grown in Pb nitrate solution and as a mixture of PbEDTA and an undetermined species in contact with PbEDTA solution.

Influence of Anionic Layer Structure of Fe-Oxyhydroxides on the Structure of Cd Surface Complexes.

The nature of crystallographic reactive sites on the lepidocrocite (gammaFeOOH) surface has been determined by atomic force microscopy (AFM) and extended X-ray absorption fine structure (EXAFS) spectroscopy and compared to the surface bonding properties of goethite. To this end, the specific surface areas of lepidocrocite particles, and of their crystal faces, were calculated from the size and shape of individual particles determined by AFM, and the structure of Cd surface complexes was determined from Cd-Fe EXAFS distances. The combined results show that Cd forms solely mononuclear surface complexes, even at 100% surface coverage, and that hydrated Cd octahedra sorb on basal {010} and lateral {hk0}, {h0l} faces of lepidocrocite platelets by sharing edges with surface Fe octahedra.