Synchrotron XAS study on the As transformations during the weathering of sulfide-rich mine wastes

NIEVA, N.E.; BORGNINO, L.; GARCIA, M.G.; BIA, G.

THE SCIENCE OF TOTAL ENVIRONMENT

ELSEVIER SCI LTD

Año: 2019 vol. 669 p. 798 - 811

0048-9697

This paper describes the weathering processes that occurred across two tailing dumps in the Concordia mine (Puna of Argentina) with the purpose of evaluating the formation of secondary As-bearingminerals due to arsenopyrite alteration. After 30 years of exposure, the gradual oxidation of thewastes produced a number of secondary mineral phases containing As in different chemical arrangements. Synchrotron-based X-ray absorption spectroscopy was used to determine both, As and Fe solid speciation and to identify the formed As-bearing minerals.The results reveal that in the first stages of oxidation, As released from arsenopyrite is adsorbed/substituted in the jarosite structure partially inhibiting its dissolution. When pH values in the system slightly increase Asjarosite transforms into schwertmannite, where the released As could be re-adsorbed or co-precipitated. When the available adsorption sites become oversaturated with As, the precipitation of amorphous ferric arsenatesmay occur. The latter, likely constitute the more labile As fractions in the sediments and are therefore the main phases contributing As to the nearby environments. These amorphous and labile phases are more abundant in the uppermost layers of the profiles, where oxidation has taken place for a more prolonged time-lapse.The described transformations are enhanced by the acidic pH, the absence of minerals attenuating the acidity and the high sulfate and As concentrations in pore water