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

Abstract

The sulfide-rich residues of La Concordia mine, Argentina Puna, are accumulated in tailing dams that remainedexposed to the weathering agents for almost 30 years. In such period of time, a complex sequence of redoxand dissolution/precipitation reactions occurred, leading to the gradual oxidation of the wastes and the formationof weathering profiles. The sources of arsenic in the wastes were analyzed by XRD and SEM/EDS analysiswhile a standardized sequential extraction procedure was followed to define solid As associations. In addition,the release of As during sediment?water interaction was analyzed in a period of 10 months. The results indicatethat primary As-bearing minerals are arsenian pyrite and polymetallic sulfides. As-jarosite and scarce arsenatesare the only secondary As-bearing minerals identified by XRD and SEM/EDS. However, the rapid release(i.e., b1 h) of arsenic from suspensions of the studied sediments in water, seems to be associated to the dissolutionof highly soluble (hydrous)sulfates, as it was determined in samples of the efflorescences that cover the entiresite. Contributions from the more abundant As-jarosite are also expected in longer periods of sediment?water interaction, due to its low rate of dissolution in acid and oxic conditions. Finally, near 30% of As remains adsorbed onto Fe (hydr)oxides thus representing a hazardous reservoir with the potential of mobilizing As intoporewaters and streamwaters if the acidic and oxidizing conditions that predominate in the region are altered.