Release of technology critical metals during sulfide oxidation processes: the case of the Poderosa sulfide mine (south-west Spain)

Abstract

Environmental contextNatural weathering of rocks may release technology critical elements (TCEs) to the environment, and anthropogenic activities can noticeably increase TCE release rates. We investigated acid mine drainage outflows from an underground sulfide mine in south-west Spain, reporting TCE concentrations orders of magnitude higher than those observed in natural waters. The findings improve our knowledge on mobility of TCEs in different geological settings. AbstractExtensive extraction of technology critical elements (TCEs) from the lithosphere and their use results in a growing dispersion and remobilisation of these elements within the environmental compartments. We investigated the concentration and mobility of different TCEs (rare earth elements (REEs), Sc, Y, Ga and Tl) in acid mine drainage (AMD) outflows from a massive sulfide underground mine in south-west Spain for around 2 years. High levels of TCEs were observed; average concentrations of 8.2mgL−1 of REEs, 1.5mgL−1 of Y, 80µgL−1 of Ga, 53µgL−1 of Sc and 42µgL−1 of Tl were reported, several orders of magnitude higher than those observed in natural waters. The TCEs source in the study site is primarily accessory minerals in the host rocks, although the contribution of Ga and Tl by sulfides cannot be discarded. A seasonal variability in TCEs is observed in AMD waters, although their maximum concentrations do not coincide with those of sulfide-related elements. TCEs seem not to be controlled by the precipitation of secondary minerals, but by the intensity of chemical weathering inside the mined zone. A positive correlation between REEs and the Si/Na+K ratio seems to indicate that these elements are linked to resistant minerals to weathering.