Leaching behaviour of Ra from uranium tailings and adsorption behaviour in geotechnical medias.

The leaching process of uranium tailings is a typical water-rock interaction. The release of Ra from uranium tailings depends on the nuclides outside the intrinsic properties of uranium tailings on the one hand, and is influenced by the water medium on the other. In this paper, a uranium tailings repository in southern China was used as a research object, and uranium tailings at different depths were collected by drilling samples and mixed to analyze the Ra occurrence states. Static dissolution leaching experiments of Ra under different pH conditions, solid-liquid ratio conditions, and ionic strength conditions were carried out, and the adsorption and desorption behaviours of Ra in five representative stratigraphic media were investigated. The results show that Ra has a strong adsorption capacity in representative strata, with adsorption distribution coefficient K values ranging from 1.07E+02 to 1.29E+03 (mL/g) and desorption distribution coefficients ranging from 4.97E+02 to 2.71E+03 (mL/g), but the adsorption is reversible. The Ra in uranium tailings exists mainly in the residual and water-soluble states, and the release of Ra from uranium tailings under different conditions is mainly from the water-soluble and exchangeable state fractions. Low pH conditions, low solid-liquid ratio conditions and high ionic strength conditions are favourable to the release of Ra from uranium tailings, so the release of Ra from uranium tailings can be reduced by means of adjusting the pH in the tailings and setting up a water barrier. The results of this research have important guiding significance for the management of existing uranium tailings ponds and the control of Ra migration in groundwater, which is conducive to guaranteeing the long-term safety, stability and sustainability of uranium mining sites.