Ya-Lan Liu

Mesoporous silica SBA-15 functionalized with phosphonate and amino groups for uranium uptake

Mesoporous silicas have a very attractive ability of sorption and enrichment of metal ions due to their huge surface area and facile functionalization by organic ligands. In this work, phosphonate-amino bifunctionalized mesoporous silica SBA-15 (PA-SBA-15) as U(VI) sorbent was fabricated through post-grafting method. The obtained mesoporous silica was characterized by SEM, XRD, NMR and nitrogen sorption/desorption experiments, which revealed the existence of ordered mesoporous structure with uniform pore diameter and large surface area. The adsorptivity of PA-SBA-15 for U(VI) from aqueous solution was investigated using batch sorption technique under different experimental conditions. The preliminary results show that the U(VI) sorption by PA-SBA-15 is very quick with equilibrium time of less than 1 h, and the U(VI) uptake is as large as 373 mg/g at pH 5.5 under 95 °C. The sorption isotherm has been successfully modeled by the Langmuir isotherm, suggesting a monolayer homogeneous sorption of U(VI) in PA-SBA-15. The sorption is pH-dependent due to the pH-dependent charge of sorbent in the aqueous solution. The thermodynamics research shows that the sorption is a feasible and endothermic process. Based on these results, PA-SBA-15 could be a promising solid phase sorbent for highly-efficient removal of U(VI) ions from waste water and enrichment of U(VI) from a solution at a very low level.

Extraction of thorium from LiCl–KCl molten salts by forming Al–Th alloys: a new pyrochemical method for the reprocessing of thorium-based spent fuels

The co-reduction process of Th(IV) and Al(III) ions in the LiCl-KCl-AlCl3-ThO2 molten salts with different concentrations of AlCl3 was investigated at 800 K on the tungsten electrode. Cyclic voltammetry, square wave voltammetry and open-circuit chronopotentiometry techniques were used to study electrochemical behaviors of Al(III), Th(IV) and Al-Th alloy formation processes. The results showed that five kinds of Al-Th intermetallic compounds could be formed in the AlCl3 poor system, whereas only one kind of Al-Th compound formed in the AlCl3 rich system. Al-Th alloys were obtained by potentiostatic electrolysis on aluminum electrodes and by galvanostatic electrolysis on a tungsten electrode. All the Al-Th alloys were characterized by scanning electron microscopy ( SEM) with energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The XRD results showed that the Al-Th compound prepared in the AlCl3 rich system was

Electroreduction-based Tb extraction from Tb4O7 on different substrates: understanding Al-Tb alloy formation mechanism in LiCl-KCl melt

This work presents the electroreduction of Tb(III) ions, and formation mechanisms of Al–Tb alloys in molten chlorides by applying different types of cathodes: Mo, Al and Al-coated Mo. First, Tb(III) ions were successfully produced by the chlorination of Tb4O7 with AlCl3 in this work. Next, the mechanisms of electrode reactions were determined by various electrochemical techniques, such as cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and open circuit chronopotentiometry (OCP). On the Mo electrode, the reduction of Tb(III) to Tb(0) was determined to be reversible and a one-step process with three electrons exchanged, which was mainly controlled by the mass transport process of linear diffusion of Tb(III) in a chloride melt. In addition, the diffusion coefficient of Tb(III) was calculated to be (2.29 ± 0.01) ×10−5 cm2 s−1 by the Sand equation. According to electrochemical investigations, it was clear that Al–Tb alloy formation was feasible on both solid aluminum and Al-coated molybdenum electrodes. Three redox signals corresponding to the formation and dissolution of different kinds of Al–Tb intermetallic compounds were observed on the Al-coated Mo electrode, whereas only one redox signal was detected on the solid Al electrode. Finally, deposited Al–Tb alloy samples were prepared by potentiostatic electrolysis and characterized by scanning electronic microscopy coupled with energy dispersive spectrum (SEM-EDS) and X-ray diffraction (XRD). It was found that the intermetallic compound Al2Tb was formed by potentiostatic electrolysis at a potential of −1.6 V and at a temperature of 803 K. When the deposition temperature was elevated to 903 K, the intermetallic compound Al3Tb was then obtained by potentiostatic electrolysis.

Condition dependence of Zr electrochemical reactions and morphological evolution of Zr deposits in molten salt

This work presents a comprehensive study for the electrochemical behaviors of zirconium in LiCl-KCl eutectic. The effects of stirring, temperature and Zr concentration on the electrode reactions, the ZrCl4 sublimation from the melt, microcosmic morphologies of Zr deposits (ZrCl and Zr) obtained at different potential and temperature have been investigated. The behaviors of Zr(IV), on a large concentration range from 0.13% to 2.28% in melt, show a multiple-step reaction involving Zr(IV), Zr(II), ZrCl and Zr species. Temperature plays a crucial role on the changes of Zr(IV) reduction behavior on the solid electrode. The Zr(IV)/ZrCl couple is more easily observed at lower temperature and gradually diminishes with the increase of temperature. The Zr(IV)/Zr(II) and Zr(II)/Zr reactions are predominant on the W electrode at higher temperatures. At 673 K, a layered structure of insoluble ZrCl formed by potentiostatic electrolyses at 1.1 V was visualized by scanning electron microscopy-energy dispersive X-ray (SEM-EDS), while only Zr metal particles was observed at higher temperature than 773 K. An evolution of the Zr-based structure and size corresponding to the ZrCl and Zr metal based on different potentiostatic electrolysis was observed. The average particle size of the Zr metalparticles increases with the increase of temperature.

Kinetics process of Tb(III)/Tb couple at liquid Zn electrode and thermodynamic properties of Tb-Zn alloys formation

Electrochemical properties of rare-earth elements in the LiCl-KCl eutectic are important for the pyrometallurgical recycling process of spent nuclear fuels. In this work, the electrochemical properties of Tb (III)/Tb (0) couple were studied by the cyclic voltammetry (CV) at a liquid Zn pool electrode. The results showed that this electrochemical reaction is quasi-reversible with mixed reversible diffusion control and the charge transfer control. The diffusion coefficient of Tb (III) was determined to be in the order of ~10−5 cm2 s−1. Moreover, kinetic parameters, such as the standard rate constants (ks) and charge transfer coefficient (α) for the electroreduction of Tb (III) to Tb (0) at the liquid Zn electrode, were calculated by the Nicholson method at 873 K. Additionally, it was found that Tb-Zn intermetallic compounds were easily to be formed in the measurements. Hence, the reduction process of Tb (III)/Tb (0) couple on the Zn-coated Mo electrode was also studied to obtain more information of the Tb-Zn intermetallic compounds. Electrochemical signals stemming from various intermetallic compounds associated with TbZn12, Tb2Zn17, Tb13Zn58, Tb3Zn11, TbZn3, TbZn2 and TbZn, were observed. The thermodynamic data were thereafter estimated by applying the emf method at 823–923 K. The standard formation Gibbs energies and the standard equilibrium constant of each Tb-Zn intermetallic compounds were also calculated. Finally, enthalpies and entropies of formation and the apparent standard potentials of various Tb-Zn intermetallic compounds were also obtained.