Oxygen penetration and subsequent reactions in flooded sulphidic mine tailings: a study at Stekenjokk, northern Sweden

A study of O-2 penetration and pore water geochemistry of the flooded taili ngs at Stekenjokk has been performed. The results show that there is a diff usion of elements from the tailings pore water to the overlying water. The presence of elements such as Ca, Mg, S, Si, Ba and Sr are likely the result of diffusion of older process water trapped in the tailings. Oxygen concen trations in the tailings measured with microelectrodes show that there is O -2 available down to 16 to 17 mm depth in the tailings. Pore water analyses show that there are subsurface maxima for the elements Cu, Zn, Ni, Co and Cd at depths of 0.25 to 2.75 cm. The highest concentrations of almost all e lements were found where previously oxidised material was deposited before the flooding. Lower pH is measured in the uppermost part of the tailings co mpared with the pond water and the tailings pore water at depth. Oxidation of sulphides in the uppermost part of the tailings is probably occurring. A decrease in oxidation rate can be expected in the future due to deposition of organic material at the tailings surface. Flooding seems to be an effic ient remediation method at Stekenjokk. (C) 1999 Elsevier Science Ltd. All r ights reserved.