Mineralogy and geochemistry of mill tailings impoundments from Algares (Aljustrel), Portugal: Implications for acid sulfate mine waters formation

Fine fractions from mill tailing deposits and filtrated material from acid mine waters were mineralogical and geochemical studied. Siderotil, copiapite, rhomboclase, natrojarosite, gypsum, amorphous ferric oxyhydroxide were identified by X-ray diffraction (XRD). Schwertmannite was identified by Infra-red spectroscopy (ATR-IR). Stretching modes of S–O bonds were analyzed either for finest fractions or filtrated material. The presence of SO4 complexes identified either in bidentate or monodentate coordination affects the mobilization of bivalent metals (Me). Weak Me–SO4 bond was found for filtrated phases from acid waters.