Mineralogical control on arsenic release during sediment-water interaction in abandoned mine wastes from the Argentina Puna

NIEVA N.E.; BORGNINO L; LOCATI F.; GARCÍA M. G

SCIENCE OF THE TOTAL ENVIRONMENT

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 550 p. 1141 - 1151

0048-9697

The sulfide-rich residues of La Concordia mine,Argentina Puna, are accumulated in tailing dams that remained exposed to theweathering agents for almost 30 years. In such period of time, a complexsequence of redox and dissolution/precipitation reactions occurred, leading tothe gradual oxidation of the wastes and the formation of weathering profiles.Sulfide oxidation also originated a typical acid mine drainage, rich indissolved metal(oid)s and sulfate, that leaks into La Concordia, the smallcreek that crosses the site. As a consequence, the water quality is stronglyaffected, as it shows acidic pH values (i.e., pH < 4) and concentrations ofmetals and arsenic that highly exceed the guidelines values for drinking water.The sources of arsenic in the wastes were analyzed by XRD and SEM/EDS analysiswhile a standardized sequential extraction procedure was followed to define solidAs associations. In addition, the release of As during sediment-water interactionwas analyzed in a period of 10 months. The results indicate that primary As-bearingminerals are arsenian pyrite and polymetallic sulfides. As-jarosite, schwertmannite,scorodite, beudantite and mimetite are the only secondary As-bearing mineralsidentified by XRD and SEM/EDS. The rapid release (i.e., <1 h) of arsenicfrom the studied sediments is assigned to the early stages of As-bearingjarosite and schwertmannite dissolution, while contributions from more solubleFe (hydrous)sulfates could be also considered. Lower inputs from less solublephases such as scorodite are also expected in longer periods of sediment-water contact.In constrast, near 30% in average of the total As remain adsorbed onto Fe(hydr)oxides and oxyhydroxysulfates. At the geochemical conditions thatdominate the study site, this fraction of As can be consider as immobile.