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

Since large areas have been contaminated by mining activities, knowledge ab out the evolution of polluted sites and pollutant speciation are required f or environmental risk assessment. A mineralogical and chemical investigatio n was performed on the site of the Cheni's mine (France), where sulphide-ri ch tailings, containing large amounts of arsenic (As), were abandoned in 19 44. It revealed that most of S, Fe and As are no longer in sulphide forms i n the surface layer (0-2 m). Oxidation products are gypsum, epsomite and As -rich Fe hydroxides. Arsenic fixation was found to be reversible when leach ing conditions increase. We also attempted to provide an approach of the As -bearing phases using a normative calculation: average composition is [Fe2O 3](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 scienc es/Editions scientifiques et medicales Elsevier SAS.)