Layers rich in Fe- and Mn-oxyhydroxides formed at the tailings-pond water interface, a possible trap for trace metals in flooded mine tailings

Geochemical field studies of the flooded sulphide-rich mine tailings at Stekenjokk in northern Sweden have been performed. Minor diffusion of elements from the tailings to the pond water is occurring. The diffusion rate is higher where tailings that were oxidised before the flooding have been deposited. Layers rich in Fe-and Mn-oxyhydroxides have been developed close to the tailings surface, and a layer of natural sediments rich in organic material have developed on the tailings surface since the flooding. The oxyhydroxides adsorb and/or co-precipitate metals and function as a trap for released metals at the tailings-pond water interface, thereby decreasing the diffusion rate from the tailings pore water to the pond water at the sediment-water interface. This study shows that it is possible for a deposit of flooded tailings to reach a state when it almost functions as a natural lake in northerly areas, with Fe-and Mn-oxyhydroxide layers controlling the diffusion of metals into the overlying pond water, within a relatively short time after remediation. (C) 2001 Elsevier Science B.V. All rights reserved.