Radium desorption behavior of riverine suspended sediment: Theoretical and experimental

Radium desorption from riverine or suspended sediment is an important source term of Ra isotopes in estuarine water, which is one of the significant factors affecting the source/sink material balance for Ra applications, such as estimating submarine groundwater discharge flux in coastal zones. In this paper, a theoretical model is proposed to study Ra desorption considering several influencing factors, including salinity, particle size and size distribution, alpha recoil range of atoms in the sediment grains, and grain surface roughness. The results of the model parameter sensitivity analysis show that the alpha-decay recoil can improve the number of total exchangeable Ra on grain surfaces, but it is more significant for sediment of small grain size. Sediment with large mean grain size may contain a considerable number of smaller particles, which may facilitate the Ra desorption quantity. Due to the relatively low concentrations of Ra in natural mineral, the Ra desorption quantity is not sensitive to the roughness of the sediment grain surfaces. The model fits well with the indoor experimental data, by fitting the experimental data or quoting the literature values, the desorption parameters (A, B, α, β) in the model can be determined to estimate the total number of exchangeable Ra of a sediment and also predict the Ra desorption of sediments in different conditions.