Rare earth elements partitioning at solid-water interface: Impact on REE geochemical behaviour and tracing properties – SURFREE

The chemical properties of rare earth elements (REE) leads to characteristic REE signatures in waters where a process dominates, making of REE efficient l tracers. However, the theoretical basis is still lacking to relate a REE signature to a given process. It is recognized that REE distributions are controlled by interactions between solution and surface. However, REE partitioning mechanisms between solution and relevant mineral is little understood. Moreover, much less studies explored solids competition for REE adsorption. Although, this raises questions: Is additivity model valuable in all case? What is the reaction kinetic impact on surface competition for REE binding? This proposal is aimed to provide a better understanding of sorption processes and their kinetics on REE distribution. Our objective is to quantitatively investigate and model the REE sorption onto competitive solids and construct a thermodynamic model to predict REE speciation in solution when surfaces are in competition (natural environmental case). Therefore, an original methodology will be developed. The different solids will be fixed on inert supports and separately or together introduced in a REE solution. This technique will allow to test a number of scenarii, such as REE distribution between iron oxide and clay. Besides the understanding of REE distribution at solid interfaces, this proposal will provide valuable data for the modelling of REE competitive sorption. Two existing models - presenting various functionalities - will be modified. Experimental data will be modelled with WHAM VI. This model is focused on organic matter, and present a module, SCAMP, dedicated to adsorption. PHREEQC will be also used to model the reactions kinetic. By providing well-constrained sorption constants and a better understanding of the solid/water interface processes, this proposal will improve the datasets and knowledge basis required by a lot of REE studies. ...