Long-term assessment of remediation treatments applied to an area affected by a mining spill

Abstract

This study evaluates the effectiveness of remediation treatments in the long-term (twenty years later) in one of the largest mine spills in the world, the Aznalcóllar accident. Soil recovery was carried out through the application of different rates of organic (compost and manure) and inorganic amendments (materials rich in iron oxides and calcium carbonate). The different amendment combinations were grouped in four treatments (T1 to T4) and applied in different sectors depending on the soil properties and the degree of initial pollution. To assess the degree of soil recovery, the physicochemical properties, the total, soluble and bioavailable concentrations of the main pollutants (Pb, As, Zn and Cu) were determined over time. The applied treatments increased the pH, CaCO3 and organic carbon of the soils, reduced the EC and decreased the mobility of the pollutants, indicating that remediation treatments were efficient in the recovery of soils contaminated by potentially harmful elements. However, twenty years after the accident, total concentrations of Pb and As still exceed the intervention levels of the current regulations in certain areas. These areas are located in the sectors closest to the mine and where treatments T1 and T2 were applied; in these cases, the dose of organic amendment, materials rich in iron oxides and calcium carbonate were not effective enough, so the application of new treatments is recommended to complete the full recovery of the area.