Synergic identification of heavy metal contaminants in mining tailings, waste rocks, and soil using laser-induced breakdown spectroscopy and x-ray fluorescence spectroscopy

Abstract:

Contamination due to heavy metal contaminants such as arsenic, cadmium, copper, lead, zinc in mining tailings, waste rocks, and contaminated soil/sediments from the hard-rock mining in the Upper Clark Fork River Basin (UCFRB) in Montana, USA, including the Flint Creek watershed, can be widely distributed and inhomogeneous because of large flood events and emission from the Anaconda Smelter stack. Identification of the contaminants using hand-held laser-induced breakdown spectroscopy (LIBS) is quick and accurate. Compared to x-ray fluorescence (XRF), LIBS has no risk of radiation and can be safer. In this study, we sampled sediments, soil, hard rocks in UCFRB and Black Mine area near Phillipsburg, Montana, and used LIBS and XRF to measure heavy metal contaminant concentrations, after a comprehensive calibration of candidate contaminants (arsenic, cadmium, lead, copper, and zinc) using about forty reference rock samples with known chemical compositions from inductively coupled plasma (ICP) mass spectrometry analysis. The agreement and disparity between the measurements by LIBS and XRF analyzers were analyzed. Relationship between the measured concentrations by the two analyzers for each potential contaminant was derived through machining learning techniques. To validate the results, 30 samples of tailings and soil were analyzed in the laboratory using Montana Tech’s inductively coupled plasma-optical emission spectrometry (ICP-OES) instrument and the spectroradiometer, respectively.