Estimation of the mobility of heavy metals in tailing sediments

摘要

Realistic evaluation of the environmental contamination risks from uranium tailings requires an understanding of ways of binding or of the specific chemical forms of trace metals in the tailing materials and consequently their mobility and participation in the water cycle. For this purpose, samples were taken from the uranium tailings of Schneckenstein and were analysed by means of a seven-steps sequential chemical extraction. For the residual fraction, ICP-AES was used for the analysis of fifteen elements (Ba, Cr, Zn, Co, Cd, As, Mn, Fe, Pb, Ni, Al, V, Cu, U, and Th). For the other separation fractions, ICP-MS was used for all elements except for Fe where flame adsorption spectroscopy (FAAS) was utilised. The data analysis shows the near immobility of Al as well as of chromium and vanadium under all weathering conditions of the tailings environment. Whereas thorium and iron seems to be also low mobile, certain amounts of their total contents are exposed to mobilisation under reducing conditions. In addition, the most mass of Cu as well as of Mg, Pb and Zn are low mobile, while considerable amounts of their whole concentrations are exposed to mobilisation under the same above mentioned conditions. Nevertheless, certain portions are high mobile. Moreover, although the most amounts of elements such as As, Co, Mn, and Ni are inactive, considerable amounts are mobile under anoxic conditions, whereas little ones are high mobile. Furthermore, of their part Cd, Ba and U are considerably mobile but the anaerobic conditions increase the bioavailability of the last two mentioned elements.