Iron and manganese in an anaerobic leachate plume

In the strongly anaerobic part of the leachate plume at the Grindsted Landfill very high concentrations of dissolved iron and manganese have been observed consistently; for example iron was found in concentrations exceeding 200 mg/l. Samples carefully obtained from the plume have been characterized in terms of colloidal content (cross flow filtration) and free ferro-ion activity (ion exchange resin technique). The results surprisingly suggest that more than 70% of the measured iron concentrations are due to free ferro-ions. This suggests strongly supersaturated conditions in the plume and currently the thermodynamic data for siderite (FeCO3)is being revisited and supplementary measurements made.