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The present study focuses on soil washing enhancement via soil pretreatment with nanoscale zero-valent iron (nZVI) for the remediation of potentially toxic elements. To this end, soil polluted with As, Cu, Hg, Pb and Sb was partitioned into various grain sizes (500-2000, 125-500 and <125 μm). The fractions were pretreated with nZVI and subsequently subjected, according to grain size, to Wet-High Intensity Magnetic Separation (WHIMS) or hydrocycloning. The results were compared with those obtained in the absence of nanoparticles. An exhaustive characterization of the magnetic signal of the nanoparticles was done. This provided valuable information regarding potentially toxic elements (PTEs) fate, and allowed a metallurgical accounting correction considering the dilution effects caused by nanoparticle addition. As a result, remarkable recovery yields were obtained for Cu, Pb and Sb, which concentrated with the nZVI in the magnetically separated fraction (WHIMS tests) and underflow (hydrocyclone tests). In contrast, Hg, concentrated in the non-magnetic fraction and overflow respectively, while the behavior of As was unaltered by the nZVI pretreatment. All things considered, the addition of nZVI enhanced the efficiency of soil washing, particularly for larger fractions (125-2000 μm). The proposed methodology lays the foundations for nanoparticle utilization in soil washing operations.

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found pervasively in various environmental compartments, such as soils, water, air and sediments [2, 13, 68]. In this regard, several studies have demonstrated that the number of humans exposed to PAHs through soils is higher than through air or water [45, 51, 73]. Given that these compounds are carcinogenic, mutagenic, teratogenic and toxic to all living organisms, there is a need to monitor their concentration in soils [6, 56]. PAHs are listed as priority pollutants by the European Union and the United States Environmental Protection Agency [14, 20, 55], and they are becoming increasingly studied and tracked in soils worldwide [1, 11, 23, 64]. PAHs are often divided into 16 priority compounds. Among them, benzo[a]pyrene (BaP) is one of the most hazardous because of its carcinogenic and mutagenic properties and its persistence and bioaccumulation in the environment [66, 78]. Consequently, the European Union established in 2004 an atmospheric target value of 1 ng/m 3 for BaP [18]. Regarding soils, Spanish legislation set out Risk-Based Soil Screening Levels (RBSSLs) for organic contaminants, based on toxicity parameters and land use. In this regard, these limits for BaP in soils are: 2 mg•kg − 1 for industrial use; 0.2 mg•kg − 1 for urban use; and 0.02 mg•kg − 1 for other uses (those that are neither urban nor industrial and that are suitable for agricultural, forestry and livestock-raising activities as defined in [62]). PAHs can be natural or anthropogenic. Natural sources comprise incomplete natural combustion of carbon-containing fuel such as coal or wood (wildfires), or even volcanic eruptions and petroleum input in oil seeps [76]. On the other hand, energy production, industrial emissions, waste incineration, car exhausts, and biomass burning are common examples of anthropogenic sources [15, 74]. Another remarkable source of PAHs is coal mining since this activity involves the massive use of this fossil fuel for energy production in power stations and also coal waste accumulation and coal processing, which have also led to soil pollution by PAHs around the world [29, 30, 52]. Sources of PAHs can be studied using specific molecular ratios [33, 73]. In addition, multivariate statistical methods, such as hierarchical cluster analysis (HCA) and principal component analysis (PCA), can unravel relationships between inorganic and organic pollutants [47, 70]. Finally, geostatistical methods (e.g. kriging, inverse-distance weighting (IDW)) allow the characterization and

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