Trace elements leaching from Pb-Zn mine waste (Plombieres, Belgium) and environmental implications

The geochemical and mineralogical characterization of mine waste provides essential information to understand the environmental and health impacts and to adequately manage present and historical mine waste sites. In the present study, mine waste samples from a former Zn-Pb mining site were subjected to different types of leaching tests, an in-vitro bioaccessibility test, and a mineralogical analysis. The samples were characterized by elevated pseudo-total Pb (up to 51,800 mg/kg), Zn (up to 60,100 mg/kg), Cd (up to 429 mg/kg), and As (up 3170 mg/kg) concentrations, and contained, among other minerals, cerussite (PbCO3) and galena (PbS). Lead is not only present in abundant concentrations, but also in highly bioaccessible forms, as determined from the in-vitro bioaccessibility test. This indicates the high risks posed in the case of ingestion of fine dust particles. The partial dissolution of the Pb-bearing minerals as a function of pH was modeled using PHREEQC geochemical software and was compared with experimental data. The high Pb release is mainly controlled by the dissolution of cerussite, even at natural pH values. X-ray diffraction analyses revealed that the amount of cerussite decreased (by >= 50%) in all samples as a consequence of leaching with water. Other Pb and Zn minerals present in the samples also dissolved when extracted with water, but not to the magnitude of cerussite. Although the mining site has been inactive for over 100 years, the high concentrations of metal(loid)s within the samples are still evident. Not only are the metals present in high concentrations, but also as mobile forms, especially when pH changes. This study proved to be essential in understanding the different parameters controlling metal(loid)s and in identifying the potential threats the mine waste poses to human health and the environment. From this overall assessment, proper methods for an effective recovery or reprocessing of the mine waste can be further evaluated.