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

Abstract

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 Kα1,2 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)

“…The fluorescence energies as presented in Table are in good agreement with previously published data from the last 90 years (Figure ). All mean values with the only exception of S Kβ 1 for sulfite (Table ) are within the confidence intervals calculated from the previously published data .…”

“…The fluorescence energies as presented in Table are in good agreement with previously published data from the last 90 years (Figure ). All mean values with the only exception of S Kβ 1 for sulfite (Table ) are within the confidence intervals calculated from the previously published data . For a better comparability of respective fluorescence energies and the possible impact of the historic development of XRF instrumentation, this big amount of 38 data sets was categorised to four time periods: 1920–1949, 1950–1979, 1980–1999 and 2000–2016.…”

“…Energies of X‐ray fluorescence lines for sulfur in different oxidation states: A comparison of values from this work (mean value ± range of dispersion) and previously published data…”

“…Mixtures of sulfides and sulfates of copper, iron, and zinc were comprehensively analysed . Respective results are transferrable to sodium compounds, of which Na 2 S and Na 2 SO 4 show a good differentiability (Figure ).…”

“…Particularly in case of substantial sulfur concentrations, this demands for determination of oxidation states. Although XRF is generally not considered an appropriate method for such purposes, sulfur is one of the few exceptions: Kα 1,2 fluorescence energies for sulfates of barium, potassium, sodium, copper, iron, and zinc do not show significant differences whereas sulfides display a distinctly lower sulfur Kα 1,2 energy as compared to sulfur in sulfates . The electron shell structure of the—in terms of XRF—comparatively small sulfur atom is prone to observable changes of inner electron energy levels depending on the particular kind of the atom's chemical bondings.…”