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In the goal of finding efficient scavengers for radioiodide in conditions (pH, pE) close to those encountered in deep geological sites, sorption of iodide ions on cuprous sulfide minerals (especially roxbyite, Cu1.75S) has been studied. Surface analysis by X-ray photoelectron spectroscopy has shown that commercial cuprous sulfides are covered by an oxidized overlayer (mainly in the form of CuSO4). Therefore, a synthetic procedure to get roxbyite (typically by mixing Na2S with an aqueous suspension of commercial Cu2O) was applied to produce pure samples with clean surfaces. Batch equilibration of cuprous sulfide particles suspended in aqueous solutions containing iodide species has revealed significant consumption of iodide. The sorption mechanism involves the formation of a surface complex via the exchange of surface hydroxyl groups by iodide anions, as highlighted by a transient pH increase during the immobilization process. Other copper and mixed copper–iron sulfides (e.g. CuS, CuFeS2), which are stable over wide pH and potential ranges are also likely to accumulate iodide species. Because of the specific interaction between iodide and copper(I) centers on the minerals, high distribution coefficients (>1000 ml/g) were observed. [Copyright &y& Elsevier]

Competition between selenium (IV) and silicic acid for the hematite (α-Fe2O3) surface has been studied during this work. Single batch experiments have been performed to study separately the sorption of selenium (IV) and silicic acid as a function of the pH. With the help of the 2-pK surface complexation model, experimental data have been fitted using the FITEQL 4.0 program. Two monodentate inner-sphere surface complexes have been used to fit selenite ions retention, and :inf loc="post">3. In order to fit sorption of silicic acid, the two following surface complexes, namely f loc="post">3SiO4, and , have been used. Using the surface complexation constants coming from these two binary systems, prediction curves of the effect of silicic acid on the retention of selenium (IV) onto hematite have been obtained. Finally, performed experiments showed a competition between selenium (IV) and silicic acid for the surface sites of hematite. Experimental data matched DDLM predictions, confirming the ability of the surface complexation model to predict quantitatively and qualitatively the ternary system selenium (IV)/H4SiO4/hematite. [Copyright &y& Elsevier]

Abstract: Sorption of selenium(IV) and silicic acid onto magnetite (Fe3O4) was investigated in binary systems, with concentrations of silicic acid under the solubility limit of amorphous silica. Using the double diffuse layer model (DDLM), surface complexation constants of selenium(IV) and H4SiO4 onto magnetite were extracted using Fiteql 4.0. Then, prediction curves of the sorption of selenium(IV) in the presence of silicic acid onto magnetite were obtained, using the calculated surface complexation constants. Finally, laboratory experiments were performed and showed a competition between selenium(IV) and silicic acid for the surface sites of magnetite. Experimental results matched the model predictions, confirming its ability to model qualitatively and quantitatively the ternary system. [Copyright &y& Elsevier]

Abstract: The sorption of europium(III) species from EuCl3 solution at pH=5.4 onto dickite particles is investigated using spectroscopic methods. Thanks to the neutrality of phyllosilicate sheets of dickite, cation exchange is prevented. X-ray photoelectron spectroscopy reveals that chloride atoms probably remain in the ligand sphere of the europium(III) cation. The edge site-specific reactivity is evidenced by epifluorescence microscopy and Raman spectroscopy. Comparison between dickite/europium(III) samples rinsed or not with distilled water shows that the surface processes not only involve inner-sphere complex formation, but also either outer-sphere complex or surface precipitation. Raman spectra also indicate that europium(III) surface complexes are preferentially localised at the edge of tetrahedral silica sheets. [Copyright &y& Elsevier]

Sorption of H4SiO4 (including experiments as a function of time, Kd measurement with different m/v ratios and sorption edges) onto different iron (hydro)oxides as goethite (α-FeOOH), hematite (α-Fe2O3), and magnetite (Fe3O4) has been studied with concentration of silicates under solubility limit. A surface complexation model has been used to account for sorption edge of silicates onto these iron oxide surfaces. It reveals that two types of surface complex namely ≡ FeH3SiO4 and ≡ FeH4SiO− 4, are needed to describe properly the experimental observations. [Copyright &y& Elsevier]

The aim of this study is to understand the sorption of tributyltin (TBT) onto natural quartz sand by classical batch experiments and spectroscopic surface analyses. At pH<6, the major species of TBT is the cation TBT+. Due to the presence of both the cationic part and the butyl chains, TBT should present amphiphilic properties. For concentrations lower than 40 μM, TBT sorption occurs as a homovalent 1:1 cation exchange between either H+ or Na+ and TBT+. The increasing affinity of TBT with respect to the different materials follows the series kaolinite≪natural sand. From XPS analyses, where the chemical environment of Sn did not change, indicating possible complete reversibility of the TBT sorption, it seems that inner-sphere surface complexes could be formed due to the increase in the 3d-level binding energy. At TBT concentrations higher than 100 μM, we showed by flotation experiments and XPS analysis that the surface becomes hydrophobic. After one monolayer was formed, the TBT sorption could thus be due to hydrophobic interaction between the butyl chains of the sorbed TBT and those of the TBT still available from the bulk solution. This mechanism is consistent with surface condensation and the shape of the sorption isotherm. [Copyright &y& Elsevier]