[en] In this study, sorption experiments of trivalent lanthanide elements (Ln)-chemical analogs of trivalent An-onto illite in the presence of DIC were performed. The obtained sorption distribution coefficients (K_d) as a function of pH and DIC concentrations were interpreted using a thermodynamic sorption model. Additionally, time-resolved laser fluorescence spectroscopy (TRLFS) was performed to investigate the chemical form of Eu sorbed on illite. The TRLFS data were subjected to parallel factor analysis (PARAFAC) and compared with the predictions of the thermodynamic sorption model. The experiments, except for instrumental analyses, were performed in a N₂-filled glove box. The illite was pretreated to remove impurities and replace exchangeable cations with Na⁺. Batch sorption experiments were performed as follows: the illite suspension, NaCl, and NaHCO₃/Na₂CO₃ solutions were mixed to a given concentration, then aliquots of a Eu or Sm stock solution were added to the suspension and allowed to react until sorption equilibrium was reached. After the reaction period, solid-liquid separation was performed by centrifugation, and the concentration of Eu or Sm in the supernatant was measured by inductively coupled plasma-mass spectrometry to calculate the K_d values. The obtained K_d values were modeled with the 2-site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model. Samples for TRLFS measurements were prepared in a similar way, but with higher initial Eu concentration than the batch experiments to obtain sufficient signal intensity; the solid phase was collected by centrifugation and dried. TRLFS measurements were performed by irradiating the samples with a 394-nm laser at room temperature. Fluorescence spectra were collected by a time-gated charge-coupled device camera. The data were smoothed and background subtracted, then arranged in a three-dimensional array (solution conditions x wavelength x time) and processed by PARAFAC using the N-way Toolbox for MATLAB. The experimental results are explained

[en] The results of U(VI) were also compared with those of two trivalent lanthanides (Eu(III) and Sm(III)), which are common chemical analogs of trivalent actinides. Sorption experiments of U(VI) on illite in the presence of DIC were conducted under ambient conditions. Aliquots of NaCl, carbonate, and NaOH stock solutions were added into the centrifuge tubes first, followed by adding aliquots of an acidified U(VI) stock solution little by little, and then the residual desired carbonate stock solutions. Afterward, the weighed pretreated illite was added into the tube, followed by adjusting the pH value. The tubes were then shaken for seven days, followed by pH measurement, centrifugation and filtration. The U(VI) concentrations were analyzed by using an inductively coupled plasma - mass spectrometry instrument. The residual solids were freeze-dried and subsequently analyzed by using the Nd:YAG laser with an excitation wavelength of 360 nm at near liquid Helium temperature. The fluorescent decay spectra with different delay times were recorded. The shape and decay lifetime of the normalized spectra after background subtraction were analyzed and compared. Those spectra were also combined and analyzed by using the PARAFAC method embedded in the N-way Toolbox for MATLAB. The obvious inhibition effect of DIC on U(VI) sorption was revealed from the macroscopic batch experimental results, which was also observed for Eu(III)/Sm(III) sorption. The updated 2-site protolysis non-electrostatic surface complexation and cation exchange model considering the formation of two uranyl-carbonate sorption complexes was able to reproduce the experimental results well. The variation of the sorption species as a function of the DIC level was also provided by the modeling process. Based on the PARAFAC analysis on the cryo-TRLFS spectra, three components were differentiated. In addition, there is clear correspondence in the variation of the sorption species between the modeling and spectroscopic analysis results. The formation of ternary uranyl-carbonate sorption complexes was successfully identified. As for the modeling of Eu(III) sorption, it was also necessary to consider the formation of Eu-carbonate sorption complexes, which was confirmed by the PARAFAC analysis on the TRLFS spectra at room temperature. Identification of the sorption species adds more credibility to the predictive sorption model, which provides more confidence in the safety assessment of deep geological disposal. In addition, these results help better understand the fate and transport of radionuclides in natural environments

[en] The surface and sorption properties of kaolinite were analyzed as a function of silicate. Batch experiments indicate that the U(VI) sorption is promoted by the addition of silicate at low pH while is depressed at high pH. The sorption was acceptably predicted by the formation of a ternary silicate surface complex under the experimental conditions. The pseudo-second order kinetic model fit the sorption kinetics better. The sorption isotherms are more in accordance with Langmuir model and the thermodynamic parameters indicate a spontaneous and endothermic sorption process. (author)

[en] The surface property of attapulgite was investigated by N₂-BET surface area and zeta potential analysis in this paper. Solution pH had a remarkable effect on the sorption process, indicated an inner-sphere complexation. Humic acid (HA) in the solution enhanced U(VI) sorption significantly at pH < 5.0, while decreased U(VI) sorption obviously at pH > 9.0. The characteristic fluorescence changes of HA indicated that a strong chemical reaction occurred between the functional groups in HA and UO₂²⁺. The sorption was a spontaneous and endothermic process with increased entropy, and the increase in temperature would benefit the sorption. (author)

[en] This study explored the sorption behavior and mechanism of U(VI) on sericite. The surface properties of sericite were investigated, and the effects of several environmental factors on U(VI) sorption to sericite were evaluated. The experimental data were simulated by different isotherm models and kinetic models. Humic acids affects U(VI) sorption obviously while silicate promotes the process in the whole pH range. The sorption-desorption hysteresis suggests an irreversible sorption process. Spectroscopic analyses indicate that the -OH groups have an important effect in the U(VI) sorption. (author)