Metal deportment in Pb-Zn mine wastes from a historic tailings pond, Plombières, East Belgium

Abstract

The exploitation of mine waste materials as secondary resources requires in-depth mineralogical analyses, with metal deportment being of particular relevance for metal recovery. Using a combination of the Scanning Electron Microscope (SEM)-based Mineral Liberation Analyser (MLA) and Electron Probe Micro-Analyser (EPMA) methods, the deportment of lead and zinc in the historic Plombières mine site (East Belgium) was investigated. The mine site comprises four different materials: soil, metallurgical waste, brown and yellow tailings. The integration of the MLA and EPMA data allowed the identification and quantification of Pb- and Zn-bearing phases, including minerals present in low abundances as well as slag phases. Different slag types and Pb oxides phases are the main sources of lead in Plombières mine waste samples. These phases host 65 to 99 % of the Pb, the rest is distributed between cerussite (0 to 37 %), and/or anglesite (0 to 17 %). Approximately 95 % of Zn is hosted by different types of slags or by fraipontite, with minor amounts contributed by sphalerite (0.1 to 3 %), gahnite (1.0 to 2.4 %), willemite (0.1 to 2.9 %), and bannisterite (0 to 3 %). The MLA/EPMA measurements were validated by comparing calculated Pb and Zn grades with bulk grades measured by X-ray fluorescence spectroscopy. The coefficients of correlation between the measured and calculated values were found to be 0.89 for lead and 0.80 for zinc. Uncertainties on the metal deportments were estimated by bootstrap resampling and are typically low. The highest uncertainties are observed when the metal-bearing phases are present in low abundances, which is particularly noticeable in the yellow tailings. Considering the promising results, the integrated approach applied in this study should be applicable to other metals and waste deposits across the globe.