Evolution of sulphides-rich mine tailings and immobilization of As and Fe

Since large areas have been contaminated by mining activities, knowledge about the evolution of polluted sites and pollutant speciation are required for environmental risk assessment. A mineralogical and chemical investigation was performed on the site of the Cheni's mine (France), where sulphide-rich tailings, containing large amounts of arsenic (As), were abandoned in 1944. It revealed that most of S, Fe and As are no longer in sulphide forms in the surface layer (0-2 m). Oxidation products are gypsum, epsomite and As-rich Fe hydroxides. Arsenic fixation was found to be reversible when leaching conditions increase. We also attempted to provide an approach of the As-bearing phases using a normative calculation: average composition is [Fe2O3](5)[As2O5](4). 30 H2O nearby the reduced original material, and [Fe2O3](3)[As2O5](2). 18 H2O in more leached material. ((C) 1999 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.)