Be2+ hydration in concentrated aqueous solutions of BeCl2.

Neutron diffraction experiments were carried out on concentrated aqueous solutions of beryllium chloride at three concentrations: 1.5, 3, and 6 molal. By working with a specific ("null") mixture of heavy water (D2O) and water (H2O), information on the local structure around Be2+ ions was extracted directly. For all three BeCl2 solutions, the results show that the Be2+ ion has a well-defined 4-fold coordination shell that is dominated by oxygen atoms. There is also a relatively small probability (10-15%) that there are direct contacts between Be2+ and Cl- at a distance of approximately 2.2 angstroms. The oxygen atoms of the highly structured Be2+ first hydration shell are found to be situated at 2.6 angstroms apart, and form a pyramidal structure, in agreement with recent MD simulation results. The Cl- ions have approximately seven oxygen atoms (water molecules) in their hydration shells sited at 3.2 angstroms.

Determination of the Cd-bearing phases in municipal solid waste and biomass single fly ash particles using SR-microXRF spectroscopy.

By using an excitation energy of 27.0 keV, synchrotron radiation-induced micro-X-ray fluorescence (SR-microXRF) is employed to extract information regarding the composition and distribution of Cd-bearing phases in municipal solid waste (MSW) and biomass fly ashes. Significance of observation is based on statistics of totally more than 100 individual MSW and biomass fly ash particles from a fluidized bed combustion (FBC) plant. Cd concentrations in the parts-per-million range are determined. In general, although previous leaching studies have indicated Cd to be predominant in the smaller-size ash particles, in the present study Cd is more evenly distributed throughout all the particle sizes. For MSW fly ashes, results indicate the presence of Cd mainly as CdBr2 hot-spots, whereas for biomass fly ashes, which exhibit lower CdX2 concentration, a thin Cd layer on/in the particles is reported. For both ashes, Ca-containing matrixes are found to be the main Cd-bearing phases. Support for this observation is found from independent first-principles periodic density functional theory calculations. The observations are condensed into a schematic mechanism for Cd adsorption on the fly ash particles.

Optimized end station and operating protocols for reflection extended x-ray absorption fine structure (ReflEXAFS) investigations of surface structure at the European Synchrotron Radiation Facility beamline BM29.

The development of the capability to engineer the surface properties of materials to match specific requirements demands high quality surface characterization techniques. The ideal tool should provide chemically specific structural characterization as well as surface sensitivity and depth profiling. Ideally the characterization method should also be applicable to systems both with and without long range order. X-ray absorption spectroscopy fine structure, when using the standard transmission detection system, provides all this information with the significant exception of surface sensitivity. In contrast, by detecting the reflected instead of the transmitted beam, it encompasses all these requirements because when the incident beam impinges onto a sample surface at glancing angles, in conditions close to the total reflection, only the outermost regions of the system under study are sampled. Such a technique provides information about the local structure as a function of depth as well as thin layer structure in the case of layered samples. Although it is potentially the ideal tool to study surface modified materials, experimental difficulties have hampered its widespread use in the fields of surface and materials sciences. As a solution to the experimental challenges, we provide a detailed description of an appropriate experimental station, the sample requirements, the measuring protocols, and software routines needed to optimize the collection of the data. To illustrate the capabilities of the technique the results obtained for a model multilayer sample are presented and analyzed under the total external reflection approximation.

A route to the brightest possible neutron source?

We review the potential to develop sources for neutron scattering science and propose that a merger with the rapidly developing field of inertial fusion energy could provide a major step-change in performance. In stark contrast to developments in synchrotron and laser science, the past 40 years have seen only a factor of 10 increase in neutron source brightness. With the advent of thermonuclear ignition in the laboratory, coupled to innovative approaches in how this may be achieved, we calculate that a neutron source three orders of magnitude more powerful than any existing facility can be envisaged on a 20- to 30-year time scale. Such a leap in source power would transform neutron scattering science.

Microextended X-ray absorption fine structure studies of cadmium speciation within single municipal solid waste fly ash particles.

The local chemical structure of trace amounts of cadmium within microvolumes of highly inhomogeneous municipal solid waste fly ash particles was successfully monitored by means of micro-EXAFS. A new quantification procedure was developed for the evaluation of the micro-EXAFS data sets obtained from each individual particle based on a reverse Monte Carlo simulation. Evidence has been presented for the existence of cadmium silicate and cadmium chloride, with the cadmium silicate being the dominant form, and it has been demonstrated that the cadmium exists in both crystalline and amorphous states within the microspots analyzed.

Direct determination of cadmium speciation in municipal solid waste fly ashes by synchrotron radiation induced mu-X-ray fluorescence and mu-X-ray absorption spectroscopy.

Cadmium is a toxic metal that causes environmental concern in connection with utilization and land filling of ash from combustion of municipal solid waste (MSW). Collecting information about the chemical associations of Cd in ash is fundamental since this affects its solubility and leachability from the ash material. In the work presented here, the content, distribution, and chemical forms of toxic metals especially of Cd on/in individual Municipal Solid Waste (MSW) fly ash particles have been investigated in situ by synchrotron radiation induced mu-X-ray fluorescence and absorption spectrometry. The use of an excitation energy of 27 keV made it possible to detect trace metals, such as Cd, present at ppm levels routinely. Changing the excitation energy in the vicinity of the absorption edge of Cd (26.71 keV), the absorption spectra of this element were measured for the first time in this high energy range in micron-sized spots of individual fly ash particles. The measurements indicated Cd to be preferably concentrated in some small areas ("hot-spots") with high concentration (up to 200 ppm) rather than in a homogeneous distribution or as a thin coating on the whole particle surface, making the surface-reaction the most probable mechanism of Cd enrichment during MSW combustion processes. Comparisons of XAS spectra of fly ashes and reference compounds showed that in the particles studied Cd is present in the oxidation state +2. Analyses of linear combinations of standard spectra allowed estimating the Cd presence within fly ash particles as an admixture of primarily CdSO4, CdO, and CdCl2 as well as an unidentified compound not included as a standard.