Solid-phase speciation of arsenic in abandoned mine wastes from the northern Puna of Argentina using X-ray absorption spectroscopy

摘要

This study investigates the solid-phase speciation of arsenic (As) in the abandoned sulfide mine wastes accumulated in La Concordia mine, northern Puna of Argentina. Samples were collected from the exposed walls of an oxidation profile formed in one of the tailing dams. Mineralogy was characterized by XRD and SEM/EDS. X-ray absorption fine structure spectroscopy (XAFS) was used to determine the arsenic oxidation state. The primary sources are As-bearing sulfides, such as arsenian pyrite and arsenopyrite. As-jarosite and Fe (hydrous)sulfates are the more abundant secondary As-bearing minerals. X-ray absorption near edge structure (XANES) analysis indicates that As+5 is the dominant oxidation state in the entire oxidation profile but minor proportions of As~(+3) are also observed in the bottom saturated layers. The in-depth distribution of the As redox species reveals that after 30 years of exposure, oxidation has affected almost the entire sedimentary column, eventhough signs of anoxic conditions are macroscopically observed.