Concentration and chemical bonding conditions of metal(loid)s in mining contaminated subaquatic sediments of the Hüttenteich near Berthelsdorf, Saxony, Germany

Significant amounts of sediments are stored in natural lakes and dams. In the Erzgebirge, Germany, these sediments were eroded from surrounding areas and are often contaminated by metal(loid)s. This leads to a potential risk for water quality. The sediments themselves reduce the water storage capacity of these reservoirs. Decreasing capacities of landfills necessitate comprehensive treatment and recycling strategies to reduce the solid concentrations of the main contaminants (As, Pb, Cd, Cu, Zn). The aim of the study was to determine the spatial and fractional distribution of concentration and chemical bonding conditions of these metal(loid)s in the sediments of the investigation area to derive effective treatment technologies. For this, the total solid concentration, and the leaching behaviour of the metal(loid)s have to be determined. Therefore, representative samples were studied under reducing conditions using ‘aqua regia digestions’, sequential extractions with the fine grained fraction (≤ 0.063 mm), and elution tests with precipitation water and ultrapure water. The results show that pH, grain size and metal(loid) concentrations of the eluate and the solid depend on catchment areas, flow conditions, deposition conditions within the dam, and sediment depth. Maximal solid concentrations were detected between 30 cm and 60 cm sediment depth. There is no significant difference in solid concentration of the metal(loid)s between the fine grained fraction and the coarse grained fraction (> 0.063 mm, ≤ 2 mm). The main contaminants are bound in different proportions to non-residual compounds, thus less to silicates. The dissolved concentrations of the metal(loid)s, determined by the elution tests with the two solvents considered, do not differ significantly from each other. The study shows that mobilization may be an effective treatment option for these subaquatic sediments, but its evaluation requires further investigation.