Sequential chemical extraction and mineralogical bonding of metals from Styrian soils

Geogenic metal contaminations in soils are intensely discussed in waste management, as the recyclability of excavated soil is regulated by limit values for pseudo-total contents in Austria. However, the use of pseudo-total contents overestimates the release of some contaminants such as metals into the environment. Sequential extraction provides an empiric tool to better assess the mobility of metals and predicts their bonding type in individual fractions, but the relation between the obtained fractions and the exact mineralogical bonding is often unclear. Electron microprobe analyses provide detailed mineralogical insights, but do not yield direct information about the mobility of elements. A combination of both methods has been used a few times in soil sciences in general, but never to Styrian soils. Thus, six geogenic contaminated Styrian soils and one compost soil were investigated by a method combination of sequential chemical extraction and electron microprobe analyses. Sequential extraction suggested that Cr in five substrates and As and Ni in one substrate each are bound in stable crystalline minerals, whereas Pb in four samples and Cu in two samples are adsorbed to iron and manganese hydroxides. Elemental mappings obtained by electron microprobe analyses confirmed sequential chemical extraction results and specified that Cu and Pb are bound to manganese (hydr)oxides, As to Fe–Cu–Sb–S compounds, Cr to spinels and Ni to olivine. In summary, the current study gives new information about the mobility and mineralogy of metals in six Styrian soils which is relevant for their possible recycling despite exceeded limit values for pseudo-total content.