Sorption of Trace Elements or Radionuclides in Natural Systems Containing Groundwater and Sediments

Abstract

Sorption of radionuclides / Sorption ratio / Sorption mechanisms / Radioactive Cs + ¡Radioactive Sr 2+ /Radioactive Ce 3+ Summary A general formula for the sorption ratio that is observed experimentally in natural systems is presented taking into account three kinds of processes: sorption at the outer surface of the solid particles, sorption in porous particles and one-directional processes such as precipitation or coprecipitation. These various processes as well as the mechanisms and the kinetics of sorption are discussed.The sorption of radioactive Cs + , Sr 2+ and Ce 3+ is studied in two selected natural sediment/groundwater systems, one of low and one of high salinity, under various conditions. Cs + ions are mainly sorbed in clay minerals that are suspended in the groundwater with relatively high sorption ratios, Sr 2+ ions are mainly sorbed on the sediments with relatively low sorption ratios, and Ce 3+ is mainly found in form of colloids or in suspended particles or in coprecipitates. Coprecipitation leads to very high sorption ratios for Ce 3+ . The behaviour of Cs + , Sr 2+ and Ce 3+ is typical for all elements with similar properties.

Migration of U, Th and REE in an Intragranitic Hydrothermal System: Implications for the Mobility of Actinides Around a Radwaste Repository

“…Incorporation in the lattices of newly precipitated or recrystallized alteration minerals either as major constituents (e. g. coffinite, Th-REE carbonates, zirconosilicates) or substituted as traces (titanium oxide, carbonates, epidote and sphene). This process which obviously played a dominant role at Auriat, has already been discussed by LIESER et al [17,18,19]. …”

Radioactivity: A Tool to Explore the Past

“…This is of special interest in case of long-lived radionuclides [3,147,[181][182][183]] the transport of which may be appreciably retarded or even stopped, if the interaction is strong, particularly if the radionuclides are incorporated into the solids. Therefore, sorption of radionuclides on solids has been investigated extensively for materials in the neighbourhood of planned high-active waste repositories [3,184], Sorption of radionuclides on solids may be due to various kinds of interactions [185][186][187]: Fixation by predominantly ionic bonds (ion exchange), by mainly covalent bonds (chemisorption), by weak (van der Waals) bonds (physisorption); sorption on the outer surface of the solids (substantial quantity: outer surface area), sorption on inner surfaces (substantial quantity: inner surface area), sorption by ion exchange at positions within the solids, sorption by precipitation, coprecipitation, or incorporation (one directional processes). In all cases the surface and exchange properties of the solids, in particular the quality of the sorption and exchange sites, are important, as well as the knowledge of the species of the radionuclides in the aqueous system [137,185,[188][189][190][191][192][193][194][195][196][197], in order to understand the migration behaviour of radionuclides.…”

“…3,84,85,90,93,138,184,186,187,[201][202][203][204][205][206][207][208][209][210][211][212][213][214][215], and it has been found in all investigations that sorption and migration may vary considerably. They depend on the properties and the dispersal of the radionuclide species present in solution, the nature of the sorption sites, the surface area of the solids and the interference and the competition, respectively, of other species.…”

Sorption of metal cations on suspended bentonite: effects of pH, ionic strength and complexing anions

“…For strongly sorbing radionuclides, their association with the mobile colloids can impact the migration processes. Maximum transport of radionuclides sorbed on colloids is possible if the sorption process is irreversible and colloid retention is minimal in the system [7][8][9]. The weathering of the surrounding rocks in an EBS has an important bearing on the performance/safety assessment of the geological repository.…”