Assessment of soil heavy metal pollution: a case study of the abandoned mine of Ichmoul, Algeria

This study aimed to assess and evaluate heavy metal contamination in the soil and sediment surrounding the Ichemoul lead mine northeast of Algeria. Soil and sediment samples were analyzed to determine the pH, particle size, organic matter (OM) content, and heavy metal (HM) concentration. The total HM concentration was determined by digestion in a mixture of strong acids. Flame atomic absorption spectrophotometry (FAAS) was used to determine the copper (Cu), lead (Pb), and zinc (Zn) contents in the obtained solutions. Major elements were analyzed by X-ray fluorescence spectrometry (XRF). X-ray diffraction (XRD) was used to determine the mineralogy of processing tailings, lead concentrates inside the abandoned plant, and the soil surrounding the mine. The potential environmental contamination was assessed by comparing the concentrations of Cu, Zn, and Pb with the geochemical background and using the following pollution indices: enrichment factor (EF), geoaccumulation index (I_geo), and Nemerow pollution index (NPI). Most soil samples had Cu, Pb, and Zn concentrations significantly exceeding local and regional background values. Spearman correlation, variance coefficient (VC), and HM spatial distribution suggested anthropic contamination in this area due to the storage of ore-rich sulfide minerals and ore extraction and processing. The EF showed that the soil was significantly enriched in Pb. The I_geo and NPI showed that the soil near the old abandoned plant was severely contaminated. The mineralogical and chemical composition of the concentrate showed the presence of galena, anglesite, barite, and chalcopyrite, with 78% of the lead as a product of the flotation processes prevalent at that time. Its presence under weathering processes has contributed significantly to the soil contamination surrounding the treatment plant with heavy metals, especially Pb. The chemical composition of ore processing waste indicated a deficiency in heavy metals, so it does not provide an environmental risk. The spatial interpolation results of the HMs indicate that high concentrations of these elements are closer to sources of contamination. The hotspots with high HMs concentrations are limited and localized due to the carbonate environment, neutral to alkaline pH, and fine soil fractions.