Chemical analysis in the field by x-ray fluorescence spectroscopy, an example from the Lac Dasserat study, Quebec

Abstract

Two types of X-ray fluorescence (XRF) spectrometers were deployed on site to analyse stream and lake surface waters as well as lake sediment chemistry. Water and sediment samples were collected downstream of the abandoned Aldermac VMS mine, 15 km west of Rouyn-Noranda, Quebec. The goals of the study are to identify the spatial and temporal extent of metal contamination as a result of decades of acid mine drainage from the Aldermac site and to evaluate and compare rapid data collection in the field by XRF with laboratory-based inductively coupled plasma mass spectrometry (ICP-MS) for Cu, Zn and Mn. Water chemistry was determined by a Bruker S2 PICOFOX total reflection X-ray fluorescence (TXRF) spectrometer from filtered and acidified samples spiked with Ga as an internal standard. The instrument demonstrated high accuracy for the certified reference material (CRM), TMDA-51.3. Data obtained for Cu, Zn and Mn concentrations were within acceptable limits of the certified values. Analytical results by ICP-MS of lake and stream samples showed excellent correlation (r2 > 0.99) with field analysis by TXRF for the three metals. Lake sediment geochemistry was determined by a handheld Olympus Innov-X Delta Premium DP-4000 X-ray fluorescence spectrometer. Sample preparation in the field included drying and reducing samples to a powder. High accuracy of analytical results was obtained using CRM LKSD-1 for Cu, Zn and Mn. Comparison of Cu, Zn and Mn concentrations determined by handheld XRF with ICP-MS analyses of aqua-regia and four-acid digestions of sediment samples also yielded excellent correlations (r2 > 0.98). Results suggest that TXRF analysis of surface waters and handheld XRF analysis of lake sediments provide practical and accurate diagnostic tools for rapid field analysis of Cu, Zn and Mn concentrations. Overnight results allowed quick testing of scientific hypotheses (e.g., contaminant flowpaths, locations of potential control sites) without waiting for laboratory results (e.g., by ICP). Rapid data acquisition also provided guidance for and optimization of daily sampling strategies during field work. Rapid field-based analytical results from XRF spectrometry have the potential to provide efficiencies for environmental risk assessments conducted by industrial project proponents and environmental consultants.