Migration Behavior of ²²⁶Ra in Rock and Soil Media around a Typical Uranium Tailings Reservoir

Abstract

As the most concerning uranium decay product in environmental assessments of uranium tailings ponds, 226Ra urgently requires the determination of its migration behavior within the surrounding geotechnical medias. In this study, we took a uranium tailings pond in southern China as the research object, collected undisturbed soil columns of fully weathered mica schist, clay in the vadose zone and aquifer gravel through borehole sampling, and conducted static batch experiments to obtain the adsorption isotherms and distribution coefficients of 226Ra in different geotechnical medias. They also explained the adsorption mechanism of 226Ra from a microscopic perspective. Through dynamic soil column migration experiments and numerical simulations, the migration parameters of 226Ra in the three geotechnical medias were obtained. The results showed that calcite is an important adsorption phase for Ra, and the first-order rate constants ωph of the physical rate process of 226Ra in clay, fully weathered mica schist, and gravel are 7.3/h, 13.1/h, and 1.67E-11/h, respectively. The first-order rate constants αch of the chemical rate process are 0.001/h, 2.5E-04/h, and 7.5E-09/h, respectively, and the Kd values are 373.96mL/g, 265.49mL/g, and 418.57mL/g.