Assessing uranium mobility in water-sediment system and diurnal stream chemistry

Abstract

Due to gold mining operations in the Witwatersrand Basin, rivers’ sediment has been polluted with uranium. In this study, we looked at factors that influenced uranium remobilisation by rewetting a dry sediment collected from a uranium polluted dam with rainwater and the daily changes in water chemistry were analysed. The rapid oxidation of uranium by oxygen led to the dissolution of uranium adsorbed by iron and carbonate while the presence of nitrate ensured that uranium was not completely immobilised eight hours after rewet. The result of the diurnal stream water chemistry indicated an increase in water pH and decrease in electrical conductivity during the day and vice-versa at night. This resulted in higher concentration of dissolved uranium at night than during the day. From the result, it can be concluded that dissolved uranium can be remobilised from dry polluted sediment by rainwater and uranium remobilisation is not linear due to the heterogeneity of sediment and the difference in solubility rate of each component of the sediment which uranium is adsorbed onto. Dissolved uranium released from sediment can remain in the water column for several hours even after rainfall, which can be harmful to the health of people that use the water for various purposes.