Chemical reactivity of natural peat towards U and Ra.

Peat is a complex material with several organic constituents that contribute to its high capacity to retain metals. In the context of uranium mining, peat can accumulate high concentrations of uranium and its decay products such as radium. Hence, interaction with peat appears to be a key factor in the understanding of the geochemical mechanisms controlling the fate of these products. This study aims to determine the sorption properties of two trace elements, U(VI) and 226Ra, on natural organic matter from peat. The presented method was applied to both natural peat samples originating from a mining context, with various contents of organic matter (from 40 to 70%) and detrital loads, and wetland peat with a more than 98% composition of organic matter. In the present study, considering peat material as a sorbent, its reactivity towards metals and other contaminants can be described as that of an ion-exchanger. A relatively simple model of ion-exchange based on the sorption properties of carboxylic sites has been applied with success to describe the sorption of uranium and radium. In the general overview of the different mechanisms able to control the mobility of these radionuclides in a uranium mining context, organic matter is likely one of the main contributors to radionuclide scavenging even under oxic conditions.