Transport and transformation of uranium and heavy metals from uranium tailings under simulated rain at different pH

Abstract

Uranium tailings are radioactive and toxic solid wastes that could contaminate waters, soils and sediments. Actually the risk of contamination is poorly known due to the lack of knowledge on the mobility of contaminants, especially the influence of acid rain on leaching, transformation and speciation of contaminants. Here, we studied the effect of simulated rain at different pH on the transport and transformation of Mn, Sr, Pb and U from uranium tailings. Semi-dynamic leaching tests and sequential extraction were conducted for Mn, Sr, Pb and U to determine their leaching patterns and to determine their speciation in uranium tailings. Results show that Mn, Sr, Pb and U become more leachable with decreasing rain pH. The release of these metals is initially rapid and then reaches a near steady state. After leaching with simulated rain, concentrations of metal-exchangeable and metal-carbonate fractions in tailings are highly reduced. The process governing the leaching of Mn and U is mainly wash-off, whereas the leached Sr and Pb are dissolution-controlled.