Long‐term assessment of remediation treatments applied to an area affected by a mining spill in Spain

Abstract

This study evaluated the effectiveness of remediation treatments in the long-term (20 years) for one of the largest mine spills in the world, the Aznalcóllar accident. Soil recovery was carried out through the application of various rates of organic (compost and manure) and inorganic amendments (materials rich in iron oxides and calcium carbonate). 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 contamination. To assess the degree of soil recovery, physicochemical properties, total, water-soluble, and bioavailable concentrations of the main contaminants (Pb, As, Zn, and Cu) were determined over time. Applied treatments increased pH, calcium carbonate, and organic carbon content of soils, reduced electrical conductivity, and decreased mobility of contaminants, indicating that remediation treatments were efficient recovering soils contaminated by potentially harmful elements (PHEs).However, 20 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 added doses of organic amendments, iron oxide-rich soils, and carbonate amendments were not sufficiently effective, so the application of new treatments is recommended to complete the total recovery of the Guadiamar Green Corridor.

Application of Biochar for the Restoration of Metal(loid)s Contaminated Soils

“…The germination rate calculated for RA was very low (17.83 ± 3.54) respect to NC, suggesting the existence of phytotoxic concentrations of the metals in the soil that prevent plant emergence. In previous studies conducted in contaminated soils in the area, it was observed that the acidic pH value and the high concentration of metals resulted in a lack of available essential nutrients, a potential toxicity in soil solution, and an absence of vegetation [29,54]. Delgado-Caballero et al [67] found that low pH together with high concentrations of Cd, Pb and Zn could have increased the solubility and toxicity of these elements, inhibiting seed germination in Bouteloua dactyloides and Cynodon dactylon.…”

“…Despite the efforts for restoring the area, metal(loid)s contamination persists more than 20 years after the accident. This soil is classified as eutric Regosol [31] and characterized by the absence of vegetation (Figure 1C) due to the presence of residual pollution [29,32]. Soil samples were collected from the surface layer (0-10 cm) using the methodology described in Aguilar et al [33].…”

“…In this study we explore the effect of biochar as an organic amendment to immobilize metal(loid)s and promote the vegetation restoration of a highly contaminated soil from the Guadiamar Green Corridor (Seville, Spain), an area affected by the Aznalcollar's pyrite mining spill where residual pollution is still detected more than twenty years after the accident [29] due to the oxidation of the remaining tailing in the soil. For this purpose, a pot experiment under greenhouse conditions was carried out.…”

Technosols Derived from Mining, Urban, and Agro-Industrial Waste for the Remediation of Metal(loid)-Polluted Soils: A Microcosm Assay

“…The selection of these wastes is based on the needs of Technosols to cope with pollution; carbonated wastes (CW and MS) provide pH buffering capacity, organic wastes (WS, VC, and OL) support the recovery of biological activity, and iron-rich wastes (IO) promote the retention capacity of anionic metal(loid)s (e.g., As and Sb). The proportions of wastes in the different Technosols are based on the real doses applied in the field during the remediation actions [29]. The components of the Technosols were dried, sieved to <4 mm, and mixed manually in plastic trays.…”