X‐ray fluorescence determination of sulfur chemical state in sulfide ores

This paper describes the X‐ray fluorescence technique for estimation of the ratio between sulfide and total sulfur in sulfide ores using the influence of sulfur chemical state on positions and intensities of lines (SKα_1,2, SKβ_1,3) and satellites (SKβ′, SKα_3,4) of the sulfur X‐ray emission spectra measured by the wavelength‐dispersive X‐ray fluorescence spectrometer. The samples to be analyzed were prepared as pressed powder pellets on boric acid substrate. The SKα_1,2 line chemical shift is the most appropriate parameter for sulfur chemical state estimation because spectral lines in this field are intensive and are almost not affected by spectral overlap of lead spectrum lines. The ratios of line intensities SKβ′/SKβ_1,3, SKα_3,4/SKα_1,2 and SKβ_1,3/SKα_1,2 were also used as analytical parameters. Forty‐one samples of sulfide ores collected in the Russian Far East and Southern Ural deposits have been analyzed. The results of estimation of sulfur chemical state by gravimetric and proposed X‐ray fluorescence techniques agree fairly well. Copyright © 2016 John Wiley & Sons, Ltd.     

Monitoring synchrotron X‐ray‐induced radiolysis effects on metal (Fe,W) ions in high‐temperature aqueous fluids

Radiolysis‐induced effects on aqueous tungsten ions are observed to form a precipitate within seconds upon exposure to a synchrotron X‐ray micro‐beam in a WO₃ + H₂O system at 873 K and 200 MPa. In situ Fe K‐edge energy‐dispersive X‐ray absorption spectroscopy (ED‐XAS) measurements were made on Fe(II)Cl₂ aqueous solutions to 773 K in order to study the kinetics of high‐temperature reactions of Fe²⁺ and Fe³⁺ ions with transient radiolysis species. The radiolytic reactions in a fluid sample within a hydrothermal diamond anvil cell result in oxidation of the Fe²⁺ ion at 573 K and reduction of Fe³⁺ at temperatures between 673 and 773 K and of the Fe²⁺ ion at 773 K. The edge‐energy drift evident in the ED‐XAS data directly reflects the kinetics of reactions resulting in oxidation and/or reduction of the Fe²⁺ and Fe³⁺ ions in the aqueous solutions at high temperatures. The oxidation and reduction trends are found to be highly consistent, making reliable determinations of reaction kinetics possible.     

Chromium speciation in mildly heated Cr(VI)‐doped latosol soil

Cr(VI) chemical reduction in natural organic matter (NOM)‐bearing latosol soil was investigated under various heating conditions at ≤378 K. An enhanced Cr(VI) reduction rate has been observed for the reaction at 353–378 K. The effect of Fe(II) naturally occurring in the latosol soil on Cr(VI) chemical reduction is negligible compared with the effect of NOM. Cr(OH)₃ was quantitatively specified by X‐ray absorption spectroscopy to be the key chromium species (～80%) after ～90% of Cr(VI) was chemically reduced by NOM at 353–378 K. This study indicates a potential strategy for using the heat extracted from industrial flue gas with a heat exchanger to chemically reduce Cr(VI) in NOM‐bearing or organics‐amended soils that contain Cr(VI).     

X‐ray spectroscopy for chemistry in the 2‐4 keV energy regime at the XMaS beamline: ionic liquids,Rh and Pd catalysts in gas and liquid environments,and Cl contamination in γ‐Al2O3

The 2–4 keV energy range provides a rich window into many facets of materials science and chemistry. Within this window, P, S, Cl, K and Ca K‐edges may be found along with the L‐edges of industrially important elements from Y through to Sn. Yet, compared with those that cater for energies above ca. 4–5 keV, there are relatively few resources available for X‐ray spectroscopy below these energies. In addition, in situ or operando studies become to varying degrees more challenging than at higher X‐ray energies due to restrictions imposed by the lower energies of the X‐rays upon the design and construction of appropriate sample environments. The XMaS beamline at the ESRF has recently made efforts to extend its operational energy range to include this softer end of the X‐ray spectrum. In this report the resulting performance of this resource for X‐ray spectroscopy is detailed with specific attention drawn to: understanding electrostatic and charge transfer effects at the S K‐edge in ionic liquids; quantification of dilution limits at the Cl K‐ and Rh L₃‐edges and structural equilibria in solution; in vacuum deposition and reduction of [Rh^I(CO)₂Cl]₂ to γ‐Al₂O₃; contamination of γ‐Al₂O₃ by Cl and its potential role in determining the chemical character of supported Rh catalysts; and the development of chlorinated Pd catalysts in `green' solvent systems. Sample environments thus far developed are also presented, characterized and their overall performance evaluated.     

Quantitative analysis of sulphides and sulphates by WD‐XRF: Capability and constraints

In the course of geochemical characterisations, total sulphur analyses are common practice although a differentiated quantification of sulphur species could provide valuable additional information, particularly when samples from unclear or changing redox environments are investigated. Unfortunately, a likewise simple distinct determination of just sulphide and sulphate already requires considerable efforts as sample dissolution or extra equipment. Two comparatively convenient strategies based on extended routine wavelength dispersive X‐ray fluorescence spectrometry measurements were adapted and optimised for a reliable quantitative sulphur speciation whereupon the matrix influence can be neglected. About 100 synthetic samples with different concentration ratios of sulphides and sulphates have been prepared and analysed using a WD‐XRF spectrometer. The first approach to differentiate between oxidation states and their quantification takes advantage of the Kα_1,2 doublet shift. Sulphide lines are located at 2309 eV, sulphate lines at 2310 eV, and mixtures can be quantified by a regression curve of fluorescence energy versus sulphide amount. Secondly, the amount of sulphide can be calculated by a regression curve based on the quotient Kβ′/Kβ of the sulphur peak heights or areas. In contrast to sulphides, sulphates show sulphur Kβ′ satellite peaks, and the intensity of S Kβ′ increases with the increasing sulphate content. However, the applicability of this second method is limited by the lower detection limit of sulphide (10 g kg^?1 sulphide in the sample) and interferences with lead (Pb Mβ line). Both approaches are validated by an independent method, Electrothermal Vaporisation Inductively Coupled Plasma Optical Emission Spectrometry, and already employed in investigations of ore‐containing mining dumps in Saxony/Germany. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of the possible origins of sulfur in 19th century salted paper photographs by x‐ray fluorescence spectroscopy

An X‐ray fluorescence method to determine whether sulfur is present in 19th century photographs due to intentional toning or to environmental deterioration is proposed. In the 19th century salted paper print photographic process, AgCl formed on the surface of a sheet of paper was exposed to sunlight in contact with a negative, leading to the printing out of a Ag image that was fixed by immersing it in a sodium thiosulfate solution or hypo. The improper execution of the fixing in these photographs may result in the presence of sulfur, mostly manifested in image fading, irregular staining, and discoloration. Also, 19th century artists produced salted paper prints with a variety of image tonalities, for example, by using an artificially aged thiosulfate bath. The presence of sulfur in photographs may also be due to sulfur‐containing environmental pollutants. Therefore, knowledge about the location and amounts of sulfur is important to understand the artistic technique and/or the deterioration processes. In this study, the amounts of sulfur and the silver to sulfur signal ratios were determined for a salted paper print made in the laboratory following a 19th century procedure and for two artistic salted paper photographs using X‐ray fluorescence and standards prepared with different amounts of retained hypo and quantified by inductively coupled plasma atomic emission spectroscopy. The amounts of sulfur and the normalized silver to sulfur ratios for the artistic photographs were evaluated based on the results obtained in the samples prepared in the laboratory and in the context of the 19th century practices. Copyright © 2016 John Wiley & Sons, Ltd.     

A setup for synchrotron‐radiation‐induced total reflection X‐ray fluorescence and X‐ray absorption near‐edge structure recently commissioned at BESSY II BAMline

An automatic sample changer chamber for total reflection X‐ray fluorescence (TXRF) and X‐ray absorption near‐edge structure (XANES) analysis in TXRF geometry was successfully set up at the BAMline at BESSY II. TXRF and TXRF‐XANES are valuable tools for elemental determination and speciation, especially where sample amounts are limited (<1 mg) and concentrations are low (ng ml^?1 to µg ml^?1). TXRF requires a well defined geometry regarding the reflecting surface of a sample carrier and the synchrotron beam. The newly installed chamber allows for reliable sample positioning, remote sample changing and evacuation of the fluorescence beam path. The chamber was successfully used showing accurate determination of elemental amounts in the certified reference material NIST water 1640. Low limits of detection of less than 100 fg absolute (10 pg ml^?1) for Ni were found. TXRF‐XANES on different Re species was applied. An unknown species of Re was found to be Re in the +7 oxidation state.     

A high‐temperature furnace for in situ synchrotron X‐ray spectroscopy under controlled atmospheric conditions

A high‐temperature furnace with an induction heater coil has been designed and constructed for in situ X‐ray spectroscopic experiments under controlled atmospheric conditions and temperatures up to 3275 K. The multi‐purpose chamber design allows working in backscattering and normal fluorescence mode for synchrotron X‐ray absorption and emission spectroscopy. The use of the furnace is demonstrated in a study of the in situ formation of Cr oxide between 1823 K and 2023 K at logPO₂ values between ?10.0 and ?11.3 using X‐ray absorption near‐edge spectroscopy. The set‐up is of particular interest for studying liquid metals, alloys and other electrically conductive materials under extreme conditions.     

Investigation of cadmium accumulation mechanism in hepatopancreas of Patinopecten yessoensis by synchrotron radiation X‐ray absorption fine structure and synchrotron radiation X‐ray fluorescence analyses

Chemical state of cadmium in a hepatopancreas of a scallop (Patinopecten yessoensis) was studied by means of synchrotron radiation‐based X‐ray analytical techniques. X‐ray absorption fine structure (XAFS) and X‐ray fluorescence (XRF) imaging were used to identify the chemical state and the distribution of cadmium in the hepatopancreas, respectively. The results of in vivo Cd K‐edge XAFS suggested that the neighboring atoms of the cadmium in the hepatopancreas are of sulfur. Therefore, we propose that cadmium was accumulated by a metalloprotein with sulfur. Micro XRF imaging of thin sections of the hepatopancreas showed that cadmium is distributed on the surface of intestinal epithelia and concentrated in the internal tissue of the hepatopancreas. These results indicated that scallops accumulate cadmium inside the hepatopancreas through the intestinal epithelium.     

Effects of organic ligands on Pb absorption and speciation changes in Arabidopsis as determined by micro X‐ray fluorescence and X‐ray absorption near‐edge structure analysis

Pb can pass through the food chain via plants and threaten human health, which has attracted widespread attention. Changes in Pb speciation affect its bioavailability in soils and water. However, whether organic ligands can change the uptake and mobility of Pb in plants and increase or decrease Pb bioavailability remains uncertain. To reveal the roles of organic and inorganic Pb in Pb metabolism in plants, the localization and speciation changes of Pb in Arabidopsis thaliana plants grown in organic and inorganic Pb were characterized by synchrotron radiation micro X‐ray fluorescence and X‐ray absorption near‐edge structure, respectively. These results demonstrated that Arabidopsis absorbed more Pb from Pb(NO₃)₂ than Pb(CH₃COO)₂ at the same exposure concentration. A higher percentage of Pb‐citrate was found in Arabidopsis exposed to inorganic Pb solution, which suggested that Pb‐citrate was the main complex for root‐to‐shoot transportation in Arabidopsis exposed to inorganic Pb solutions. Pb complexed with the organic ligand CH₃COO^? significantly inhibited primary root growth and lateral root development, while, at the same time, Pb was blocked by root hairs, which represented another way to reduce Pb absorption and protect the plant from biotoxicity.     

Nature of chemical states of sulfur embedded in atomic‐layer‐deposited HfO2 film on Ge substrate for interface passivation

Sulfur was embedded in atomic‐layer‐deposited (ALD) HfO₂ films grown on Ge substrate by annealing under H₂S gas before and after HfO₂ ALD. The chemical states of sulfur in the film were examined by S K‐edge X‐ray absorption spectroscopy. It was revealed that the valences of S‐ions were mostly –2 at Ge/HfO₂ interface (GeS_x or HfO_2–yS_y to passivate the interface), while they were mostly +6 in HfO₂ layers (sulfates; HfO_2–z(SO₄)_z). The leakage current density in post‐deposi‐tion‐treated film was lower than that in pre‐deposition‐treated one. This suggests that the passivation of defects in oxide layer by sulfate ions is more effective to lower the leakage current rather than the interface defect passivation by S^2– ions. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Optimization of L‐shell X‐ray fluorescence detection of lead in bone phantoms using synchrotron radiation

Closely related toxicity and retention mechanisms of lead (Pb) in the human body involve the bone tissues where Pb can accumulate and reside on a time scale ranging from years to tens of years. In vivo measurements of bone Pb can, therefore, play an important role in a comprehensive health risk assessment of Pb exposure. In vivo L‐shell X‐ray fluorescence (LXRF) measurement of bone Pb was first demonstrated over 4 decades ago. Implementation of the method, however, encountered challenges associated with low sensitivity and calibration procedure. In this study, the LXRF measurement was optimized by varying the incident photon energy and the excitation‐detection geometry. The Canadian Light Source synchrotron radiation was used to compare 2 different excitation‐detection geometries of 90^° and 135^° using 3 different X‐ray photon energies: 15.8, 16.6, and 17.5 keV. These energies optimized excitation of the L₃ subshell of Pb and simulated the most intense K‐shell emissions of zirconium, niobium, and molybdenum, respectively. Five rectangular plaster‐of‐Paris bone phantoms with Pb concentrations of 0, 7, 17, 26, and 34 μg/g, and one rectangular 3.1‐mm‐thick resin phantom mimicked the X‐ray attenuation properties of human bone and soft tissue, respectively. Optimal LXRF detection was obtained by the 15.8‐keV energy and the 90^° and 135^° geometries for the bare bone and the bone and soft tissue phantoms, respectively.     

Synchrotron study of oxygen depletion in a Bi‐2212 whisker annealed at 363 K

Direct evidence is reported of structural and electronic effects induced on a single Bi₂Sr₂CaCu₂O_8+δ (Bi‐2212) whisker during a progressive annealing process. The crystal was investigated by micro X‐ray diffraction (µ‐XRD), micro X‐ray fluorescence and electrical characterization at the European Synchrotron Radiation Facility, during a series of three in situ thermal processes at 363 K. Each step increased the sample resistivity and decreased its critical temperature, up to a semiconducting behaviour. These data correlate with µ‐XRD analysis, which shows an increase of the c‐axis parameter from 30.56 Å to 30.75 Å, indicating an oxygen depletion mechanism. Mild temperature annealing could be an effective process to modulate the intrinsic Josephson junctions' characteristics in Bi‐2212 whiskers.     

Multivariate curve resolution alternating least squares in the quantitative determination of sulfur using overlapped S(Kα)–Mo(Lα) emission peaks by wavelength dispersive X‐ray fluorescence spectrometry

Spectral line overlap is a serious problem in quantitative X‐ray fluorescence analysis. In this study multivariate curve resolution alternating least squares (MCR‐ALS) approach was used to resolve the effect of overlapping S(K_α)–Mo(L_α) emission lines generated by standard‐less software of a wavelength dispersive X‐ray fluorescence spectrometer (WDXRF) for the quantitative monitoring of sulfur in mineral samples. Scan channel set contained Ge crystal, 550‐µm collimator, flow detector (Ar + CH₃) and rhodium (Rh) tube. The 18 calibration and 10 validation samples contain 0.00%–10.98% sulfate (SO₃) and 0.00%–92.40% MoO₃. The digitized spectral data were extracted in the range between 109° and 113.9° (2θ) at every 0.1 degree. Lack of fit percentage (LOF%) for experimental data and the variance explained at the optimum condition () were 2.32 and 99.94, respectively. The values of the root mean square error of prediction (RMSEP) for analyzing of sulfur were 0.23. MCR‐ALS was also compared with partial least squares (PLS) method for determination of sulfur in the presence of molybdenum. To evaluate the resolution and quantification performance of MCR‐ALS procedure, the method was used to determine sulfur in presence of molybdenum in two synthetic soil samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Measurement of the X‐ray mass attenuation coefficients of silver in the 5–20 keV range

The X‐ray mass attenuation coefficients of silver were measured in the energy range 5–20 keV with an accuracy of 0.01–0.2% on a relative scale down to 5.3 keV, and of 0.09–1.22% on an absolute scale to 5.0 keV. This analysis confirms that with careful choice of foil thickness and careful correction for systematics, especially including harmonic contents at lower energies, the X‐ray attenuation of high‐Z elements can be measured with high accuracy even at low X‐ray energies (<6 keV). This is the first high‐accuracy measurement of X‐ray mass attenuation coefficients of silver in the low energy range, indicating the possibility of obtaining high‐accuracy X‐ray absorption fine structure down to the L₁ edge (3.8 keV) of silver. Comparison of results reported here with an earlier data set optimized for higher energies confirms accuracy to within one standard error of each data set collected and analysed using the principles of the X‐ray extended‐range technique (XERT). Comparison with theory shows a slow divergence towards lower energies in this region away from absorption edges. The methodology developed can be used for the XAFS analysis of compounds and solutions to investigate structural features, bonding and coordination chemistry.     

A microfocus X‐ray fluorescence beamline at Indus‐2 synchrotron radiation facility

A microfocus X‐ray fluorescence spectroscopy beamline (BL‐16) at the Indian synchrotron radiation facility Indus‐2 has been constructed with an experimental emphasis on environmental, archaeological, biomedical and material science applications involving heavy metal speciation and their localization. The beamline offers a combination of different analytical probes, e.g. X‐ray fluorescence mapping, X‐ray microspectroscopy and total‐external‐reflection fluorescence characterization. The beamline is installed on a bending‐magnet source with a working X‐ray energy range of 4–20 keV, enabling it to excite K‐edges of all elements from S to Nb and L‐edges from Ag to U. The optics of the beamline comprises of a double‐crystal monochromator with Si(111) symmetric and asymmetric crystals and a pair of Kirkpatrick–Baez focusing mirrors. This paper describes the performance of the beamline and its capabilities with examples of measured results.     

In vivo time‐resolved X‐ray fluorescence mapping measurements of Egeria densa immersed in Cr(VI) aqueous solution

In vivo time‐resolved Cr and Ca X‐ray fluorescence (XRF) mapping measurements were performed in a laboratory over a period of 69 days on a living common aquatic plant Egeria densa that was immersed in 5 mM K₂CrO₄ aqueous solution. The time and spatial resolution for each time‐resolved XRF map were ~1.6 days and 1 × 1 mm², respectively. The obtained XRF maps exhibited characteristic localized Cr and Ca areas where the XRF signals were especially strong (‘hot spots’), and this indicated the necessity of preliminary millimeter‐resolution surveying in XRF microscopy. Ca hot spots were detected prior to Cr(VI) immersion and nearly disappeared after immersion in deionized water for 2 weeks and the Cr(VI) solution for 1 week. After these immersions, a Cr hot spot was formed at approximately the same location of the missing Ca hot spot, which suggests that the original Ca‐accumulated regions were substituted for the isolation of Cr species when they were introduced. The sizes and intensity distributions of the Cr hot spots were sensitive to the Cr(VI) exposure approximately 1 week prior to each XRF measurement. This sensitivity suggests potential applications of E. densa as a Cr(VI) biomonitor in aquatic environments. Copyright © 2014 John Wiley & Sons, Ltd.     

Sulfur Immobilized in Hierarchically Porous Structured Carbon as Cathodes for Lithium–Sulfur Battery with Improved Electrochemical Performance

In order to overcome the main obstacles for lithium–sulfur batteries, such as poor conductivity of sulfur, polysulfide intermediate dissolution, and large volume change generated during the cycle process, a hard‐template route is developed to synthesize large‐surface area carbon with abundant micropores and mesopores to immobilize sulfur species. The microstructures of the C/S hybrids are investigated using field emission scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, nitrogen adsorption–desorption isotherms, and electrochemical impedance spectroscopy techniques. The large surface and porous structure can effectively alleviate large strain due to the lithiation/delithiation process. More importantly, the micropores can effectively confine small molecules of sulfur in the form of S_2–4, avoiding loss of active S species and dissolution of high‐order lithium polysulfides. The porous C/S hybrids show significantly enhanced electrochemical performance with good cycling stability, high specific capacity, and rate capability. The C/S‐39 hybrid with an optimal content of 39 wt% S shows a reversible capacity of 780 mA h g^?1 after 100 cycles at the current density of 100 mA g^?1. Even at a current density of 5 A g^?1, the reversible capacity of C/S‐39 can still maintain at 420 mA h g^?1 after 60 cycles. This strategy offers a new way for solving long‐term reversibility obstacle and designing new cathode electrode architectures.     

K‐edge XANES analysis of sulfur compounds: an investigation of the relative intensities using internal calibration

Sulfur K‐edge XANES (X‐ray absorption near‐edge structure) spectroscopy is an excellent tool for determining the speciation of sulfur compounds in complex matrices. This paper presents a method to quantitatively determine the kinds of sulfur species in natural samples using internally calibrated reference spectra of model compounds. Owing to significant self‐absorption of formed fluorescence radiation in the sample itself the fluorescence signal displays a non‐linear correlation with the sulfur content over a wide concentration range. Self‐absorption is also a problem at low total absorption of the sample when the sulfur compounds are present as particles. The post‐edge intensity patterns of the sulfur K‐edge XANES spectra vary with the type of sulfur compound, with reducing sulfur compounds often having a higher post‐edge intensity than the oxidized forms. In dilute solutions (less than 0.3–0.5%) it is possible to use sulfur K‐edge XANES reference data for quantitative analysis of the contribution from different species. The results show that it is essential to use an internal calibration system when performing quantitative XANES analysis. Preparation of unknown samples must take both the total absorption and possible presence of self‐absorbing particles into consideration.