Is nanoremediation an effective tool to reduce the bioavailable As, Pb and Sb contents in mine soils from Iberian Pyrite Belt?

Abstract

São Domingos mine is one of the most important abandoned mines in the Iberian Pyrite Belt (IPB) (SE, Portugal), which has large amounts of waste deposited in tailings. Weathering causes sulphide oxidation, acid mine drainage, leaching of high levels of potentially hazardous elements (PHEs) and, consequently, environmental degradation in surrounding areas.The use of nanoparticles (NPs) to recover contaminated soils from IPB can be an effective tool compared to the use of traditional amendments, due to small size, high specific surface and reactivity of NPs. The combination of nanoremediation techniques, together with the current phytoremediation techniques carried out in the IPB, could improve the immobilisation and decrease the availability of PHEs in these soils.In this research was assessed whether the use of hydroxyapatite (HANPs), hematite (HMNPs) and maghemite (MNPs) nanoparticles are effective for recovery degraded soils. Extractable contents of As, Pb and Sb were determined in soils treated (with NPs) and non-treated. Three different extractants based on CaCl2 (0.01 M), low molecular weight organic acids (LMWOA - 10 mM) and ultrapure water (UPW) were used. Extractable contents of Pb, As and Sb in the soil samples treated with NPs decreased; and HANPs were those that most bioavailable Pb retained. In addition, the NPs were characterised in shape, size and elemental composition before and after being applied to the soil samples using High Resolution Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy (HR-TEM/EDS). After treatment, the NPs associated to As, Pb and Sb were identified in the mine soils. The great decrease of PHEs bioavailability was possible due to the association of PHEs with the NPs, which reduce considerably the mobility of PHEs in mine soils.