Geochemical behaviour of rare earth elements in mining environments under non-acidic conditions

The rare earth elements (REE) were determined in water and solid samples at the abandoned mine of Ingurtosu (Sardinia, Italy). Research was performed to evaluate the main factors that control the geochemical behaviour of REE in near-neutral pH mining environments. REE show the highest concentrations (13-100 μg/l) in drainages from mine tailings, especially when water sampling was carried out under high flow conditions. Positive correlations between ΣREE and Zn and Pb were observed, possibly indicating REE sorption on Zn- and Pb-rich fine particles (<0.4 μm). Fractionation processes were observed normalizing REE in waters with respect to REE in mining-related residues. The Naracauli waters show an enrichment in HREE, probably due to the high stability of dissolved HREE(CO3)2- complexes in the studied waters. REE fractionation was not observed during hydrozincite bioprecipitation.