Physicochemical characterization and mercury speciation of particle-size soil fractions from an abandoned mining area in Mieres, Asturias (Spain)

Soils from old cinnabar mining areas usually exhibit high Hg contents, whose mobility depends on soil parameters and environmental conditions. This paper presents the study of the Hg speciation in soil samples from an abandoned Hg mine and metallurgical plant in Mieres (Asturias, Spain), in relation to their mineralogical and chemical composition and their particle-size distribution. A characterization of samples was made by X-Ray Diffraction Spectrometry, Scanning Electron Microscopy and Atomic Absorption and Emission Spectroscopy analyses. A sequential extraction method was applied to establish Hg mobility in the samples and their grain-size subsamples. The highest Hg mobility was found in well-developed soils, as a consequence of the adsorption processes by iron and manganese oxides, whereas in those more contaminated soils, a higher proportion of Hg was leached in the non-mobile fraction. A higher Hg mobility was found in the finest grain-size subsamples, probably due to the accumulation of clay minerals and oxides in these ranges.