Uranium contamination of fluvial systems. Mechanisms and processes. Part I : geochemical mobility of uranium along the water path, the Koekemoerspruit (South Africa) as a case study

Abstract

Tailings deposits from gold- and uranium mining usually contain elevated amounts of radioactive and chemotoxical heavy metals. By seepage dissolved uranium and other contaminants migrate from tailings deposits via groundwater into adjacent fluvial systems. The subsequent transport in streams and rivers is one of the most effective pathways of distributing contaminants throughout the biosphere. In a comparative study of mining areas in Germany, South Africa and Australia mechanisms of non-point stream-contamination and the aqueous transport of uranium were investigated. The study comprises geochemical analyses of samples from various sediment-water systems along the aqueous pathway as well real-time in situ-measurements in the fluvial system itself. In this paper geochemical data of water- and sediment samples from the Koekemoer Spruit as a typical example for a mining affected stream in South Africa - are analysed with respect to possible mechanisms of transport and immobilisation of uranium migrating in solution. Ratios between dissolved and solid phases of uranium for various water-sediment-systems along the aqueous pathway indicated, unexpectedly, significant lower mobility of uranium in stream and channel water than in the groundwater-floodplain system. Correlation of various geochemical parameters suggests co-precipitation of uranium along with calcium-carbonate and iron/manganese-compounds is the main reason for the higher immobilisation rate in the flowing water systems.