Automated Mineral Analysis of Mine Waste
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Mineral Liberation Analyzer (MLA) is an automated mineralogical system originally developed to characterize ore and mill feeds for the metallurgical processing industry. Its ability to quantitatively characterize solid and particulate material, including whole rock thin sections, waste rock, tailings, soil, and sediments, has led to increasing applications in other industries. The software uses back-scatter electron imagery and energy dispersive X-ray analysis to analyze each particle’s shape, size, and mineralogical information. Energy dispersive X-ray data are compared to a user-generated Mineral Reference Library consisting of known phases and corresponding EDS spectra to classify each particle. MLA is used in this study to provide quantitative assessments of mining-related environmental samples to answer questions regarding mineralogical controls on bioaccessibility, metal leaching/acid rock drainage potential, and anthropogenic influence. Six tailings samples from the New Calumet Mine in Quebec, Canada, were analyzed using MLA. Gastric Pb bioaccessibility testing and total metal content performed on these samples indicated that Pb bioaccessibility in the <250 micron size fraction was not directly correlated with the total Pb concentration. This suggested that there were mineralogical and/or physical controls on bioaccessibility. MLA was used to quantify the relative proportions of cerussite, a highly bioaccessible Pb carbonate, and galena, a lower bioaccessibility Pb sulfide. Liberation and particle size were also analyzed as controls on bioaccessibility. Sample GD-VEG1 (highest bioaccessibility) has the highest ratio of cerussite to galena, the smallest particle size, and the most liberated Pb-bearing particles. The New Calumet tailings were also analyzed using static testing, a suite of laboratory tests used by environmental scientists and mine operators to operationally define acid rock drainage and metal leaching potential. Modal mineralogy obtained from MLA analysis was used to calculate neutralization potential (NP) and acid potential (AP), taking into account the presence of iron carbonate minerals and iron-bearing sulfides other than pyrite. Results are within several units of those obtained by static testing. Two Ni-impacted soil samples collected from the region of Kalgoorlie, Australia were characterized using MLA. Previous studies had focused on bioaccessibility and sequential extraction testing and minor mineralogical work. Preliminary XANES characterization conflicted with mineralogy predicted from sequential extraction and EMPA and MLA were used to quantitatively characterize major Ni-bearing phases and resolve previous discrepancies.