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.