title: The flotation tailings of the former Pb-Zn mine of Touiref (NW Tunisia): mineralogy, mine drainage prediction, base-metal speciation assessment and geochemical modeling.
abstract: The underground extraction of Pb-Zn mineralization in the Touiref area stopped in 1958. A large volume of flotation tailings (more than 500 Mt) containing sulfides were deposited in a tailings impoundment. The goals of this study are to evaluate the neutralization capacity of the unoxidized and oxidized tailings, to assess the speciation of metals between the different components of the tailings material, and to assess the mobility of metals and the secondary minerals' precipitation in pore waters using geochemical modeling. To accomplish these objectives, representative samples from both fresh and oxidized zones were collected along a vertical profile through the tailings pile. Physical, chemical (ICP-MS), and mineralogical characterization (X-ray diffraction (XRD), reflected light microscopy, scanning electron microscope (SEM)) of these samples was performed. Grain size analysis shows that the tailings are dominated by silt- to sand-sized fractions. The microscopic observation highlights the presence of pyrite, marcasite, galena, and sphalerite as primary minerals in a carbonated matrix. The study reveals also the presence of secondary minerals represented by cerussite, smithsonite, anglesite, and Fe oxi-hydroxides as important scavengers for trace elements. The static tests show that the presence of calcite in the tailing samples ensures acid-neutralizing capacity (ANC), which is significantly greater than the acidity potential (PA). The geochemical characterization of the unoxidized samples shows higher Cd, Pb, and Zn concentrations than the oxidized samples containing the highest values for Fe and SO4. Sequential extraction tests show that significant percentages of metals are distributed between the acid-soluble fractions (Cd, Pb, and Zn) and the reducible one (Zn). Pore water analysis indicates that Ca is the dominant cation (8,170 and 6,200 mg L(-1), respectively), whereas sulfate is the principal anion (6,900 and 5,100 mg L(-1), respectively). Saturation index (SI) calculations of minerals in pore water extracted from both the oxidized and unoxidized samples are indicative of gypsum (SI >0) and Fe(III) oxides (SI ≫0) precipitation. The latter controls the Fe concentration in solution.
authors.affiliation: Laboratoire de Ressources Minérale et Environnement, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092, Tunis, Tunisia, mohamedali.othmani@gmail.com.
authors.forename: Mohamed Ali
authors.initials: MA
authors.lastname: Othmani
authors.forename: Fouad
authors.initials: F
authors.lastname: Souissi
authors.forename: Hassan
authors.initials: H
authors.lastname: Bouzahzah
authors.forename: Bruno
authors.initials: B
authors.lastname: Bussière
authors.forename: Eduardo Ferreira
authors.initials: EF
authors.lastname: da Silva
authors.forename: Mostafa
authors.initials: M
authors.lastname: Benzaazoua
mesh_terms: D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000032:analysis*; D007220:Industrial Waste / Q000032:analysis*; D008670:Metals / Q000032:analysis*; D008903:Minerals / Q000032:analysis*; D008906:Mining; D008962:Models, Theoretical; D013431:Sulfates / Q000032:analysis*; D013440:Sulfides / Q000032:analysis*; D014416:Tunisia; D014961:X-Ray Diffraction
chemical_list: D004785:Environmental Pollutants; D007220:Industrial Waste; D008670:Metals; D008903:Minerals; D013431:Sulfates; D013440:Sulfides