Contamination assessment and availability of potential toxic elements from the Sidi Driss tailing pile (NW Tunisia) based on geochemical and geophysical methods

• Published in: Journal of African earth sciences (1994) Vol. 202; p. 104921
• Main Authors: Salhi, Rania, Durães, Nuno, Dhaoui, Mohamed, Patinha, Carla, Ferreira da Silva, Eduardo, Mlayah, Ammar
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-06-2023
• Subjects: Electrical resistivity tomography; Potential toxic elements; Selective chemical extractions; Tailings; Electrical resistivity tomography; Potential toxic elements; Tailings; Selective chemical extractions
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2023.104921

Mine wastes are of particular relevance, either because they represent a source of contamination by potential toxic elements (PTEs), or even because the high concentrations of some critical raw materials with economic interest can make their mining viable in the future.
This work presents mineralogical, geochemical, and geophysical data aimed at a detailed characterization of an old tailing pile of the Sidi Driss mine (northern Tunisia) that exploited Pb and Zn concentrates. The results obtained from four drilling boreholes, reaching a maximum depth of 11 m, show high concentrations of metal(loid)s in the tailings, namely As, Ba, Cd, Mn, Pb and Zn. Apart from barium, the higher concentrations of these PTEs were found between 3 and 8 m depth. The availability of such metal(loid)s is higher in deeper sections of the tailing pond than on the surface, which is explained by the reduction and oxidation environments prevailing at these depths, respectively. Thus, at surface sulphides are oxidised and several metal(loid)s are released and leached. This oxidation process generates acid mine drainage (AMD), causing the dissolution of carbonates, such as cerussite, from which Pb is released and leached underground. In deeper sections of the tailing pond, reduction conditions prevent sulphide oxidation and the prevalence of circumneutral pH values. In such environments, carbonates are not dissolved and Pb leached from the surface precipitates (e.g., as anglesite, an insoluble sulphate), as demonstrated by sequential selective chemical extraction.
Electrical resistivity tomography (ERT) showed low resistivity areas from surface to 8 m depth. This is a consequence of waterlogging on the surface (due to rainy events) and, on the subsurface, of high metal(loid) contents in tailings. High electrical resistivity was measured below this level (bedrock), but a connection between heavily contaminated horizons (tailings) and a subsequent layer of low resistivities (associated with groundwater) is observed, which is of particular concern.
•Tailing pile of Sidi Driss mine was studied by geochemical and geophysical methods.•As, Ba, Cd, Mn, Pb and Zn are the PTEs of greater environmental concern in the area.•Distribution and geoavailability of PTEs varies in depth and with redox conditions.•ERT allowed to delimit the contaminated region and its connection with groundwater.