Is pXRF a suitable analytical technique for mining prospection and geochemical characterisation of contaminated sites?

Portable X-Ray fluorescence analyzers (pXRF) are widely used for elemental analysis on several matrices in a variey of scientific and industrial fields such as environmental geochemistry, mining, archaeometry and metallurgy. Although its versatility and ready-to-use merits during both field campaigns and in the laboratory, pXRF should be used for quantitative analysis only following a careful validation of accuracy (via CRM analyses) or comparability with confirmatory samples (e.g., analysed by means of ICP-AES or ICP-MS). The reference method used to establish data quality includes three levels: definitive > quantitative > qualitative [1]. In this study, several samples collected at two mining district of Friuli Venezia Giulia region (Italy) were analyzed by an OlympusTM analyzer (VCA) using both “Soil” and “Geochem” methods. Results were compared with ICP-MS for metal(loid) content and DMA-80TM for total Hg determination . Differences of comparability between grounded and ungrounded samples were evaluated to evaluate the efficiency of the pXRF analysis on heterogeneous samples, in order to minimize time-consuming operations. Results indicate that low concentrations and interferences are the main source of error in pXRF measurements. Samples from the Cu-Sb mine site of the Mt. Avanza reached the quantitative level for the majority of the selected elements, due to relatively elevated concentrations of the analytes and minor levels of interfering elements such as Pb. Conversely, at the Raibl Pb-Zn mining site, the high amounts of Pb (>1%) interfere seriously with As, and natural low-concentrations of e.g., Cr, Cu, Hg and Sb make undetectable such elements due to the geochemical characteristics of the host-rock and the ore minerals. False positives occur in the determination of some elements indicating that spectral analysis is always needed before using the pXRF data. [1] United States Environmental Protection Agency (US EPA), 1998. http://nepis.epa.gov/Adobe/PDF/30003LR0.pdf