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.     

Determination of gold and silver in dross using EDXRF technique

Gold and silver in dross were determined by energy‐dispersive X‐ray fluorescence technique. Sample was prepared by pressed pellet method using microcrystalline cellulose powder as binder, and a method of standard additions was used for quantification. L_β X‐ray of gold (11.4 keV) and K_β X‐ray of silver (24.9 keV) were used for analysis. The measured concentrations of gold and silver were 132 ± 8 and 1181 ± 84 mg kg^?1, respectively. The results were validated by instrumental neutron activation analysis technique. The t‐test indicated that there was no significant difference between results obtained by the two techniques. Energy‐dispersive X‐ray fluorescence is a simple, precise and accurate technique for the determination of gold and silver in dross. Copyright © 2014 John Wiley & Sons, Ltd.     

Quantitative speciation of manganese oxide mixtures by RIXS/RRS spectroscopy

Resonant inelastic X‐ray scattering, also named X‐ray resonant Raman scattering, was recently used to discriminate local chemical environments. By means of this novel technique, the speciation of samples could be attained in a variety of samples and experimental conditions. Until now, this discrimination methodology had been applied only to pure compounds, being the speciation possible by two different mathematical treatments. Nevertheless, the effectiveness/sensitivity of this technique has not been tested yet in samples containing mixtures of oxides of the same element. In this work, the first results of quantitative speciation of mixtures of manganese compounds, using resonant inelastic X‐ray scattering/X‐ray resonant Raman scattering spectroscopy, are presented. The results show that it is possible to discriminate and quantify oxide mixtures of the same element in slightly different proportions, allowing a quantitative speciation of compound mixtures in a variety of experimental conditions, presenting also several advantages over conventional spectroscopic techniques. Copyright © 2017 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.     

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.     

Mercury in archeological hair samples from Xiongnu burials (Noin‐Ula,Mongolia): SR XRF and CXRM analysis

A technique has been developed for determining mercury content in the concentration range of 1–1000 μg/g in hair samples by X‐ray fluorescence analysis using synchrotron radiation (synchrotron radiation X‐ray fluorescence, Siberian Synchrotron and Terahertz Radiation Center, Budker Institute of Nuclear Physics SB RAS). The mercury content was identified in archeological hair samples from an ancient burial of Xiongnu nobility (Mongolia, mound 22, 1^st century BC–1^st century AD); the content values were elevated (up to 1100 μg/g) in all the samples (n = 41). An X‐ray microanalysis using polycapillary lenses in a confocal scheme (confocal X‐ray microscopy station) was developed at the Synchrotron radiation X‐ray fluorescence to establish mercury distribution in a cross section of hair shaft with a spatial resolution of 5 μm. The findings of the study make it possible to assume exogenous income of mercury (from the burial environment) to the hair.     

The investigation of K‐shell fluorescence parameters of Zn–Fe alloys with different grain size and microstrain values

It is known that zinc alloys with iron group metals have better corrosion resistance than pure zinc. Owing to the corrosion resistance of these alloys, Zn–Fe coatings are widely used in automotive industry and have excellent mechanical performance. In this work, we investigated the relationship between the changes in the measured X‐ray fluorescence parameters (K_β/K_α, σ_Kα and σ_Kβ) and the changes in the structural parameters such as microstrain or grain size values for Zn–Fe alloys that were prepared with different pH values. To explain these changes, the K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values were calculated by three different ways for the elemental forms of Zn and Fe. The structural parameters, such as microstrain and grain size, were also calculated. We expect that the outer shell electronic distribution affects the structural parameters of the produced Zn–Fe alloys, changing the measured K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values. We also show that Zn–Fe alloy mi nimum microstrain value corresponds to the maximum changes in K_βX‐ray production cross‐section values of Fe and Zn. Copyright © 2017 John Wiley & Sons, Ltd.     

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.     

Distinction and quantification of inorganic sulfur species including thiosulfate by X‐ray fluorescence (WD‐XRF)

Sulfur occurs in a variety of inorganic and organic compounds with oxidation states from ?II up to +VI. Differentiation of these species in solid geochemical samples can be challenging because of oxidation processes during sample preparation by acidic digestion. Applying pressed powder pellets and an analysis by wavelength‐dispersive X‐ray fluorescence minimises reactions with oxidants and water. Main subjects of this work were five inorganic sulfur species, sulfide ?II, elemental sulfur 0, thiosulfate +II, sulfite +IV, and sulfate +VI, and the determination of their fluorescence energies in the sulfur X‐ray spectra. S Kα_1,2 and S Kβ₁ can be observed for all species, S Kβ′ satellites only for species with coordinated oxygen. The results are in good agreement with previously published data. Yet none of the 38 investigated papers from the past 90 years reported S Kα_1,2 of thiosulfate, which was determined as E = 2,309.12 eV in this work apparently for the first time. Binary mixtures of sulfur species are strongly differing in their ability of being quantitatively differentiated, as a reliable quantification requires a sufficient difference of the respective fluorescence energies. Regression equations for each mixture can be used to calculate the ratio of mass fractions of the investigated species from the evaluated fluorescence energy. If boundary conditions are considered, the presented approaches can be applied for analyses of geochemical samples or quality control of technical products. The main advantage of the described methods is the option of implementation to everyday X‐ray fluorescence lab routine without substantial additional effort.     

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.     

Determination of gold,platinum and uranium in South African ores by high‐energy XRF spectrometry

An automated energy‐dispersive x‐ray fluorescence spectrometer, called the AZTEC, was developed for the non‐destructive determination of gold, platinum and uranium in Witwatersrand ores, by utilizing the high‐energy spectral regions of the K x‐ray lines of these elements. It provides a viable alternative to fire assay, and measures gold concentrations down to <1 ppm. About 100 g of pulverized sample are presented for analysis in a 20 mm diameter tube, and the fluorescent x‐rays are detected by an array of up to 12 high‐purity germanium detectors. Count‐rates of up to 10⁶ counts per second per detector can be processed by the signal processing electronics. The AZTEC technique is a variant of the scattered radiation technique. Concentration is related to peak intensities corrected for background, matrix variations, density and line overlaps. Provided that the samples are finely pulverised, the AZTEC analyses compare well with those obtained by fire assay. Production instruments are being used mainly in the gold mining industry, where they have analysed over 10⁷ samples to date. Copyright © 2004 John Wiley & Sons, Ltd.     

Speciation of inclusions and precipitates in steel by means of XRF and LEEIXS

Fundamentals of x‐ray fluorescence spectrometry and X‐ray emission spectrometry in the case of electron probe x‐ray microanalysis and low‐energy electron induced x‐ray spectrometry are compared. The different aluminum and titanium compounds occurring in steel can be investigated by examining soft x‐ray spectra, arising from valence shell orbitals. The non‐metallic inclusions were isolated by galvanometric electrolysis. In the case of the speciation of titanium, direct electron bombardment of the sample is used to generate soft x‐rays. By investigating the Ti L lines, titanium carbide, nitride and sulfide can be distinguished. To specify aluminum compounds, the Kβ transition in the x‐ray fluorescence spectrum was examined. The concentration of aluminum oxide and nitride in precipitates of special steel qualities can be determined with a satisfactory determination limit. Finally, pre‐operational studies for the determination of different silicon inclusions using electron excitation were carried out. Copyright © 2003 John Wiley & Sons, Ltd.     

On the correlation between the X‐ray absorption chemical shift and the formal valence state in mixed‐valence manganites

Here the correlation between the chemical shift in X‐ray absorption spectroscopy, the geometrical structure and the formal valence state of the Mn atom in mixed‐valence manganites are discussed. It is shown that this empirical correlation can be reliably used to determine the formal valence of Mn, using either X‐ray absorption spectroscopy or resonant X‐ray scattering techniques. The difficulties in obtaining a reliable comparison between experimental XANES spectra and theoretical simulations on an absolute energy scale are revealed. It is concluded that the contributions from the electronic occupation and the local structure to the XANES spectra cannot be separated either experimentally or theoretically. In this way the geometrical and electronic structure of the Mn atom in mixed‐valence manganites cannot be described as a bimodal distribution of the formal integer Mn³⁺ and Mn⁴⁺ valence states corresponding to the undoped references.     

Utilization of standardless analysis algorithms using WDXRF and XRD for Egyptian iron ore identification

On the basis of fundamental parameter approaches, the validity of standardless wavelength dispersive X‐ray fluorescence (WDXRF) and X‐ray powder diffraction algorithms was confirmed for analyzing Egyptian iron ore samples collected from two different locations, Aswan and Baharyia. The studied Egyptian iron ores represent different depositional environments and consequently exhibit variable mineralogical and chemical compositions. In the case of WDXRF analysis, the ground powders of iron ore samples were mixed and pressed with low contamination binder in a mass ratio of wax: sample = 4: 0.9 g at 120 kN cm^?2. A standardless method for quantitative WDXRF was employed, which requires accurate determination of the amount of organic material in the sample. On the basis of differential thermal analysis, a new method is introduced for the determination of loss of ignition. With the application of the proposed method and standardless quantitative analysis, results for 12 elements in iron ores were obtained: Fe, Mn, Mg, Si, Al, Ca, Na, K, S, Ba, Zn, and Cl. The reliability and precision of the adopted procedure were tested against a standard reference material ‘Iron ore concentrate (SRM 690, NIST, USA)’. The quantitative analysis results of the certified reference material were found acceptable. Depending on the WDXRF results, the powder samples were directly introduced to X‐ray powder diffraction goniometry, and the phase compositions were quantitatively determined by using a standardless analysis program based on Rietveld method. The main phases of all iron ore samples are the hematite and goethite, whereas other phases are found with varying ratios, namely quartz, nordstrandite, rhodochrosite, kaolinite, todorokit, bassanit, andydrite, and hydroxyapatite. Copyright © 2012 John Wiley & Sons, Ltd.     

Application of Synchrotron X‐Ray Microbeam Spectroscopy to the Determination of Metal Distribution and Speciation in Biological Tissues

Abstract

Resolving the distribution and speciation of metal(loid)s within biological environmental samples is essential for understanding bioavailability, trophic transfer, and environmental risk. We used synchrotron x‐ray microspectroscopy to analyze a range of samples that had been exposed to metal(loid) contamination. Microprobe x‐ray fluorescence elemental mapping (µSXRF) of decomposing rhizosphere microcosms consisting of Ni‐ and U‐contaminated soil planted with wheat (Triticum aestivum) showed the change in Ni and U distribution over a 27‐day period, with a progressive movement of U into decaying tissue. µSXRF maps showed the micrometer‐scale distribution of Ca, Mn, Fe, Ni, and U in roots of willow (Salix nigra L.) growing on a former radiological settling pond, with U located outside of the epidermis and Ni inside the cortex. X‐ray computed tomography (CMT) of woody tissue of this same affected willow showed that small points of high Ni fluorescence observed previously are actually a Ni‐rich substance contained within an individual xylem vessel. µSXRF and x‐ray absorption near‐edge spectroscopy (XANES) linked the elevated Se concentrations in sediments of a coal fly ash settling pond with oral deformities of bullfrog tadpoles (Rana catesbeiana). Se distribution was localized within the deformed mouthparts, and with an oxidation state of Se (?II) consistent with organo‐Se compounds, it suggests oral deformities are caused by incorporation of Se into proteins. The range of tissues analyzed in this study highlight the applicability of synchrotron X‐ray microspectroscopic techniques to biological tissues and the study of metal(loid) bioavailability.     

X‐ray fluorescence determination of Cs,Ba, La,Ce, Nd,and Ta concentrations in rocks of various composition

The technique has been developed for the quantification of small tantalum, cesium, barium, lanthanum, cerium, and neodymium concentration in rocks with X‐ray wavelength dispersive spectrometer S8 TIGER (Bruker AXS, Germany). The optimum conditions have been chosen for registration of the analyzed elements characteristic radiation and background positions. To determine the concentrations of analyzed elements accurately, the contribution of overlapping lines to the experimental intensities of the analytical lines has been taken into account. The sample of mass about 1.2 g has been pressed into pellet by the hydraulic press. Metrological studies showed that the accuracy in the determination of the concentration of analyzed elements for the developed technique meets the requirements for methods of III accuracy class. The Ta detection limits calculated for TaL_β1‐analytical and CsL_α1‐analytical lines were 2.6 and 3.4 ppm, respectively. The detection limit of Ba, La, Ce, and Nd was (in ppm), respectively, 4.3, 2.7, 5.8, and 4.7. The metrological characteristics of the previously developed and adapted techniques were compared. Ta concentration in granite pegmatite samples has been quantified. The samples of the highest tantalum content have been investigated additionally by powder diffraction and X‐ray microprobe analysis. The X‐ray diffraction method turned out to be insensitive to the detection of mineral phase of tantalum niobates, while micro‐XRF allowed detecting its presence in tourmaline grains. Copyright © 2017 John Wiley & Sons, Ltd.     

Chemical speciation via X‐ray emission spectra

Since the early days of X‐ray spectrometry, X‐ray emission and fluorescence spectra have been used to investigate chemical speciation, e.g. the dependence on the formal oxidation state. Laboratory wavelength‐dispersive spectrometers have adequate resolution for these measurements. However, almost all studies have employed empirical methods to interpret the spectra. We aim to place such methods on a quantitative basis by means of efficient ab initio calculations of the X‐ray emission line shapes based on a self‐consistent, real‐space Green's function approach, as implemented in the X‐ray spectroscopy code FEFF8.2. Calculations are presented for the phosphorus K‐M_{2, 3}, and the chromium L‐series emission lines for a selection of simple compounds. These lines exhibit changes depending on the oxidation state and on the neighboring atoms in the compounds that can be observed with instruments available in many XRF laboratories. The calculated spectra, as modified by convolution with a model monochromator response function, are compared with measured spectra. Simulated and measured spectra are found to be in reasonable agreement, and show that the approach has the potential to yield quantitative information about the chemical state. Copyright © 2006 John Wiley & Sons, Ltd.     

Sample thickness and quantitative concentration measurements in Br K‐edge XANES spectroscopy of organic materials

While XANES spectroscopy is an established tool for quantitative information on chemical structure and speciation, elemental concentrations are generally quantified by other methods. The edge step in XANES spectra represents the absolute amount of the measured element in the sample, but matrix effects and sample thickness complicate the extraction of accurate concentrations from XANES measurements, particularly at hard X‐ray energies where the X‐ray beam penetrates deeply into the sample. The present study demonstrates a method of quantifying concentration with a detection limit approaching 1 mg kg^?1 using information routinely collected in the course of a hard X‐ray XANES experiment. The XANES normalization procedure unambiguously separates the signal of the absorber from any source of background. The effects of sample thickness on edge steps at the bromine K‐edge were assessed and an empirical correction factor for use with samples of variable mass developed.     

Manganese speciation in Diplodon chilensis patagonicus shells: a XANES study

X‐ray absorption near‐edge spectroscopy (XANES) at the Mn K‐edge was used to investigate the environment of Mn in situ within the growth increments of the long‐lived freshwater bivalve species Diplodon chilensis patagonicus. Single XANES spectra and Mn Kα fluorescence distributions were acquired at submillimetre resolution (up to 100 µm × 50 µm), at Mn concentrations below the weight percent range (100–1000 µg g^?1) in a high Ca matrix. The position and intensity of the pre‐edge feature in the shell spectrum resembles best that of the Mn(II)‐bearing reference compounds, suggesting that this is the oxidation state of Mn in the bivalve shells. By comparison with the XANES spectra of selected standard compounds, hypotheses about Mn speciation in the shell are also reported. In particular, different factors, such as provenance, ontogenetic age, variable Mn‐concentrations or seasonal shell deposition seem not to influence the speciation of the metal in this bivalve species.     

Study of absorption parameters around the K edge for selected compounds of Gd

The K shell absorption jump ratios, jump factors, effective atomic numbers, and electron densities were derived from the measured total mass attenuation coefficient using an energy dispersive X‐ray fluorescence spectrometer for Gd₂O₃, Gd₂(CO₃)₃H₂O, Gd₂(C₂O₄)₃H₂O, and Gd₂(SO₄)₃ compounds. The total mass attenuation coefficients were measured in the X‐ray energy range from 39.52 to 57.14 keV in a transmission geometry utilizing the Kα₂, Kα₁, Kβ₁, and Kβ₂ X‐rays from different secondary source targets excited by the 59.54‐keV photons from an Am‐241 annular source and detected by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. The energy gap, ionization energy, electron affinity, and global electrophilicity parameters of oxide, sulfate, oxalate, and carbonate ions were calculated using density functional theory (B3LYP). The experimental results are discussed based on these parameters. Copyright © 2015 John Wiley & Sons, Ltd.