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

Geochemical characterisations are implemented to get information about the composition of unknown samples but some elements occur in different oxidation states that can not be determined by established techniques without special efforts like sample dissolution or extra equipment. One example is sulphur with its most common species, sulphide and sulphate. Different approaches, based on WD-XRF routine measurements, provide simple alternatives for a quantitative speciation. A set of 100 synthetic samples has been prepared in different concentrations and were measured by a Panalytical Axios minerals spectrometer. The first approach is based on the shift of the Kα1,2 doublet. Sulphide peaks are located at 2309 eV, sulphates at 2310 eV and mixtures can be found on a linear regression of energy and sulphide amount. As opposed to sulphides, sulphates show sulphur Kβ’ satellite peaks. Another procedure is based on this difference because the intensity of S Kβ’ increases with increasing sulphate content. The amount of sulphide can be calculated by a linear regression based the quotient Kβ’/Kβ of the sulphur peak height or area. However, this method has two limitations: low sulphide concentrations (<10 g/kg sulphide in the sample) and interferences with lead (Pb Mβ peak). The WD-XRF based strategies provide simple and reliable methodologies for a quantitative speciation of sulphides and sulphates whereupon the matrix influence can be neglected. These approaches have been implemented in investigations of ore-containing samples from mining dumps in Saxony/Germany. These procedures can be applied to give previously not measurable data on solid samples containing different sulphur species.