Sorption of Eu(III) on quartz at high salt concentrations

Abstract

Sorption of Eu(III) onto quartz from highly saline solutions (up to 5M NaCl) has been studied by sorption edges. The acid-base titrations of the solid surface suggest the rather unusual presence of two different sites that has been the object of recent discussions in the literature. Europium uptake results show the usual behaviour with a steep pH-edge and nearly complete removal at sufficiently high pH. Previous spectroscopic data on this system suggest the presence of two bidentate surface complexes with different proton stoichiometry. Based on this, a self-consistent Surface Complexation Model (SCM) was fitted to the full set of experimental data, from 0.1 to 5 M NaCl, using a coupled Pitzer/surface complexation approach. The Pitzer model was applied to aqueous species. A Basic Stern Model was used for interfacial electrostatics of the system, which includes ion-specific effects via ion-pair formation. Parameter fitting was done using the general parameter estimation software UCODE coupled to a modified version of FITEQL2 involving separate calculations of the respective ionic strength corrections. At high ionic strength (>1 M), the surface potential is strongly screened by ion-pair formation and the diffuse layer potential is negligibly low, which justifies the extension of the standard electrostatic model to these harsh conditions. Overall, our model is able to describe the full set of analysed data. It is expected that these first systematic data acquisition along with the detailed modelling can serve as a benchmark for the modelling of future studies on sorption in highly saline systems.

Adsorption of Strontium onto Synthetic Iron(III) Oxide up to High Ionic Strength Systems

“…We conclude that using such a combination is a robust approach to simulate contaminant uptake from highly saline solutions, given that the model is calibrated selfconsistently on a consistent set of experimental and solution speciation data. Previous models that used high salt levels [7,[27][28][29][30] were more complex (involving more sites and more adjustable parameters). The fact that the very simple adsorption model framework (1-site, 1-pK, Basic Stern model) with fewer adjustable parameters can also be combined with Pitzer approaches in aqueous solution lends credibility to the approach on a general level and, in particular, for nuclear waste management in geochemical settings that involve high salt concentrations.…”

“…For high salt levels, specific precautions must be taken to obtain meaningful data from electrode readings [25][26][27]. From our point of view, self-consistent and comprehensive data covering both titrations and the uptake of solutes in brine solutions have recently gained importance [7,28]. In the iron oxide-hydroxide systems, as well as in the work on clays [27,29,30], the associate potentiometric titrations to design the acid-base models were carried out up to 1 M concentration, while the titrations by Garcia et al [28] were carried out up to 5 M. The modelling in the above cited papers (involving self-consistent data) coupled non-electrostatic [27,29,30] or electrostatic [7,28] surface complexation models with the Pitzer or Specific ion Interaction Theory (SIT) approaches [31][32][33][34].…”

“…In the iron oxide-hydroxide systems, as well as in the work on clays [27,29,30], the associate potentiometric titrations to design the acid-base models were carried out up to 1 M concentration, while the titrations by Garcia et al [28] were carried out up to 5 M. The modelling in the above cited papers (involving self-consistent data) coupled non-electrostatic [27,29,30] or electrostatic [7,28] surface complexation models with the Pitzer or Specific ion Interaction Theory (SIT) approaches [31][32][33][34]. Garcia et al [28] also showed that the acid-base model involved strong shielding of the charge in the Stern layer, particularly at high salt levels, which results in very low diffuse layer potentials. As a consequence, the application of the Gouy-Chapman equation that is included in these models can be justified.…”

“…As a consequence, the application of the Gouy-Chapman equation that is included in these models can be justified. The previous electrostatic models that were applied up to the high salt levels [7,28] involved a surface complexation scheme with reaction equations that could, in principle, be linked to the mechanistic level. The non-electrostatic models applied in the high salt concentration context [27,29,30] might also be interpreted, to some extent, in this way.…”

Prediction of Europium Retention in Perovskite: Potential Candidates for an Engineering Barrier in the Disposal of Radioactive Waste

“…ese characteristics have allowed them to be used to create different types of materials by partial substituting of metals, obtaining modified perovskites that have been used in various photocatalytic applications [9][10][11]. On the other hand, perovskites, such as tausonite, have been used successfully in the retention of U 6+ and Eu 3+ , simulating the different isotopes of uranium and actinides (Ac 3+ ), which are produced in the burning and reprocessing of nuclear fuels [12,13].…”