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.
Highlights
Uranium is a radioactive heavy metal, which is widely dispersed throughout the earth’s crust, with an average concentration in rocks and soils of 2-4 mg/kg.in the auriferous sediments of the Witwatersrand uranium is accumulated up to1000ppm, displaying average concentrations of about 100ppm
From 26 mines, which at one stage were feeding into 18 uranium recovery plants currently in 1995 only 3 mines and 4 plants are left, producing about 1500t U3O8 per year (CfG, 1998)
The results show that solute transfer of uranium from slimes dams is a major mechanism of contamination
Summary
Uranium is a radioactive heavy metal, which is widely dispersed throughout the earth’s crust, with an average concentration in rocks and soils of 2-4 mg/kg (ppm).in the auriferous sediments of the Witwatersrand uranium is accumulated up to1000ppm, displaying average concentrations of about 100ppm. Uranium is a radioactive heavy metal, which is widely dispersed throughout the earth’s crust, with an average concentration in rocks and soils of 2-4 mg/kg (ppm). In the auriferous sediments of the Witwatersrand uranium is accumulated up to. Compared to ore with Ugrades of 3-6% mined in Canada and Australia this is regarded as low-grade ore (CfG, 1998). In South Africa uranium was mainly produced as a by-product of gold, which already covers the mining costs. Between 1952 - when the first regular U-recovery plant was commissioned - and 1991 a total of 167,000t of U3O8 was produced (Waggitt, 1994). From 26 mines, which at one stage were feeding into 18 uranium recovery plants currently in 1995 only 3 mines and 4 plants are left, producing about 1500t U3O8 per year (CfG, 1998)
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