Identification of arsenic solid species in sulfide mine tailings from the Concordia Mine Argentina using X-ray absorption spectroscopy

NIEVA N.E.; BORGNINO, L.; GARCÍA M. G.,

Campinas

Encuentro; 26th annual Users meeting LNLS/CNPEM; 2016

LNLS

 When mine waste rich insulfides are exposed to the weathering agents and to the action ofmicroorganisms, a highly acidic drainage, rich in dissolved metal(oid)s andsulfate is generated. The main process involves the oxidation of the parentsulfide and the subsequent precipitation of secondary minerals. During suchprocess, elevated concentrations of arsenic are released to the water and thenincorporated into a cycle that includes the precipitation/dissolution ofAs-bearing minerals as well as adsorption/desorption from Fe or Al (hydr)oxidesites. The aim of this work is toanalyze the As solid speciation in sediments accumulated in the tailing dams ofLa Concordiamine, Argentina Puna.Samples were collected fromdifferent layers observed in the exposed walls of an oxidation profile formedin one of the tailing dams. Mineralogy was characterized by XRD and SEM/EDS. Arsenic K-edge spectra (11867 eV) were collected atbeamline XAFS1 at the Brazilian Synchrotron Light Laboratory (LNLS) inCampinas, Brazil along with some As reference material such as scorodite, Na2HAsO4.7H2O,As2S3, and NaAsO2.4H2O. The X-rayabsorption near edge structure (XANES) spectra were analyzed using the Athenaprogram [1].The main primary mineralsdetermined by XRD and SEM/EDS are quartz, K-feldspar, zircon, and illite, aswell as sulfides such as arsenical pyrite, arsenopyrite, some scarce grains ofgalena and polymetallic sulfides. The main secondary As minerals areAs-jarosite and Fe (hydrous)sulfates, which are more abundant in the uppermostlayers [2].According to the obtainedresults the As XANES spectra, all samples show characteristic edge featuresthat correspond to As5+ compounds. However, samples from the bottomlayers show pre-edge shoulders in the range of As+3 species. Theresults indicate that As5+-O compounds are dominant in all layers,but their percentages decrease with depth. In contrast, the proportion of theAs3+ species, As3+-S and As3+-O, increases indepth. Considering the samples mineralogy, As(V) species likely correspond toAs-jarosite, and arsenate ions sorbed onto ferric oxyhydroxides. On the otherhand, As3+-S species likely correspond to polymetallic sulfideswhile As3+-O could be assigned to arsenite ions sorbed onto ferricoxyhydroxides. The obtained resultsindicate that As5+ compounds predominate all along the tailingprofile, with minor contributions of As3+ species. The latter aremore abundant in the bottom layers. The results suggest that after 30 years ofexposure, oxidation has affected almost the entire profile. This has importantenvironmental implications, because As is mostly associated with the morelabile phases identified in the sediments.