Multivariate statistical and GIS-based approach to evaluate heavy metals behavior in mine sites for future reclamation

Abstract

Soil contamination by metals has become a widespread serious problem in many parts of the world. Two tailing ponds (Lirio and Gorguel) from an abandoned Pb–Zn mine for a future reclamation were selected, surface samples were taken and analyzed for waste properties and total, extractable by DTPA and water-soluble Pb, Cu, Zn and Cd content. Results showed that both ponds were polluted by Cd, Pb, and Zn. High total concentrations of Zn and Pb and high percentage of extractable-Cd in both ponds suggested high risk of mobility via plants uptake. Due to high concentrations of soluble Zn and percentages of soluble Cd, especially in Lirio pond, these metals could be mobilized by runoff water and reach streams or leach to waste deep layers and contaminate soil and even groundwater. Thus, the immobilization of these metals should be a priority in reclamation actions. Statistical analyses showed that, for Lirio pond, soluble Cd and Zn and extractable Cd, Zn and Pb concentrations were increased by the presence of organic matter, due likely to formation of soluble organic ligands. Clay and electrical conductivity also increased soluble and extractable Zn concentrations, which could be attributed to adsorption of metals for clays combined by the effect of competition for sorption sites with cations and metal-complexation with anions. Finally, soluble Pb was controlled by pH. Therefore, it is recommended the use of alkaline amendment, which will increase the pH and immobilize the metals preventing the effect of organic matter. However, in Gorguel pond, the concentration of soluble and extractable Zn, Pb and Cd were dependent on pH and salinity. Since the pH of this pond is high, it is not necessary to increase it. Oppositely, the reclamation program should include actions to reduce soluble salts generated by oxidation process, which would reduce heavy metal mobility. A GIS-based approach was adopted to identify highest risk sites, where main efforts of reclamation and monitoring should be realized. Three locations in the Lirio pond and two in the Gorguel pond were selected according to their environmental risk, north, south and west edges for Lirio and west and center for Gorguel.