To design novel phenanthroline-derived soft ligands for selectively separating minor actinides from lanthanides, four tetradentate phenanthroline-derived heterocyclic ligands(BTPhen, BPyPhen, BPzPhen, and BBizPhen) were constructed and their complexation behaviors with Am(ⅡI) and Eu(ⅡI) were systematically investigated by density functional theory(DFT) coupled with relativistic small-core pseudopotential. In all the 1:1-type species, the metal ion is in the center of the cavity and coordinates with two nitrogen atoms(N1 and N1′) of the phenanthroline skeleton and the other two nitrogen atoms(N2 and N2′) of the auxiliary groups. The bond lengths of Am–N are comparable to or even shorter than those of Eu–N bonds because the ionic radii of Am(ⅡI) are larger than those of Eu(ⅡI). Additionally, the negative ΔΔGAm/Eu value for the reaction of [M(H2O)4-(NO3)3] + L → ML(NO3)3 + 4H2 O indicates that the complexation reaction of Am(ⅡI) is more energetically favorable than that of Eu(ⅡI); this can be considered as an important design criterion to screen phenanthroline-derived ligands for MA(ⅡI) extraction. According to this criterion, the selectivity of tetradentate phenanthroline-derived ligands for separating Am(ⅡI) over Eu(ⅡI) follows the order of BTPhen > BBizPhen > BPyPhen > BPzPhen.
Separation of trivalent minor actinides(MA(ⅡI): Am(ⅡI), Cm(ⅡI)) from fission products(FP) in high-level liquid waste(HLLW) is an important task in advanced nuclear-fuel reprocessing systems. For this purpose, an advanced aqueous partitioning process based on extraction chromatography method was studied. Because R-BTP extractants(R-BTP: 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine, R = alkyl group) exhibit high selectivity for MA(ⅡI) over trivalent rare-earth elements(RE(ⅡI)), a novel adsorbent isoHex-BTP/SiO2-P was prepared by impregnating isoHex-BTP extractant into the macroporous SiO2-P support with a mean diameter of 60 μm. The stability of isoHex-BTP/SiO2-P against nitric acid and γ-irradiation was investigated. It was found that isoHex-BTP/SiO2-P adsorbent shows good adsorption affinity to Dy(ⅡI). The hydrolytic and radiolytic stability of isoHex-BTP/SiO2-P adsorbent in 0.01 mol/L HNO3 was fairly promising. However, the adsorption amount Q of Dy(ⅡI) decreased dramatically in 3 mol/L HNO3 with the increase of the absorbed dose and became nearly zero at the absorbed dose over 46 kGy. These results suggest that with the synergetic effect of radiation and acidic hydrolysis, the adsorbent instantly loses its efficacy.
A macroporous silica-based silver loaded adsorbent was synthesized by grafting the silver complexes of thiourea(Ag(tu)3NO3) into a silica-based copolymer support(Si O2-P). The adsorbent was used to uptake iodide anions(I–) by batch and column techniques. The kinetic and saturated adsorption experiments were carried out by varying the shaking times and initial concentration of I–. Experimental results shown that the kinetic adsorption of I–was controlled by a pseudo second order model and the saturated adsorption of I–was controlled by the chemisorption mechanism, which followed a Langmuir adsorption equation. The breakthrough curve of I–had a S-shaped profile. The column efficiency was estimated to be over 90%.
To separate MA （Am, Cm） and some fission product elements （FPs） such as Tc, Pd, Cs and Sr from high level liquid waste （HLLW） systematically, we have been studying an advanced aqueous partitioning process, which uses selective adsorption as the separation method. For this process, we prepared several novel adsorbents which were immobilized in a porous sili- c^polymer composite support （SiO2-P）. Adsorption and separation behavior of various elements was studied experimentally in detail. Small scale separation tests using simulated HLLW solutions were carried out. Pd（II） was strongly adsorbed by the AR-01 anion exchanger and effectively eluted off by using thiourea. Successful separation of Pd（ll） from simulated HLLW was achieved. Te（VII） also exhibited strong adsorption on AR-01 and could be eluted off by using U（IV） as a reductive eluent. Am（Ⅲ） presented significantly high adsorbability and selectivity onto R-BTP/SiOz-P adsorbents over various FPs including Ln（Ⅲ）. The R-BTP adsorbents were fairly stable in 3 M HNO3, but instable against 7-irradiation-3M HNO3. An advanced par- titioning process consisting of three separation columns for the target elements separation from HLLW was proposed and the obtained experiment results indicated that the proposed process is essentially feasible.
The extraction chromatography–electrodeposition(EC–ED) process was proposed for the quantitative recovery of palladium from high-level liquid waste(HLLW) in this study. The process coupled the extraction chromatography method to obtain the decontamination of Pd(II) from HLLW with the electrochemical method to recover metallic palladium from the concentrated solution.Separation of Pd(II) from a nitric acid medium by extraction chromatography using iso Bu-BTP/SiO_2-P adsorbent and the electrochemical behavior of Pd(II) in nitric acid solution in the presence of thiourea(TU) were investigated.iso Bu-BTP/SiO_2-P exhibited a high selectivity for Pd(II)over other fission products(FPs), and Pd(II) could be desorbed by TU from loaded BTP/SiO_2-P. The adsorbent performed good stability against HNO_3 because the adsorption performance kept Pd(II) after extended contact with HNO_3 solution. The column experiment achieved the separation of Pd(II) from simulated HLLW successfully.The electrochemical behavior of Pd(II) in palladium desorption solution containing TU and nitric acid was investigated at a platinum electrode by cyclic voltammetry. A weak reduction wave at-0.4 V was due to the reduction in Pd(II) to Pd(0), and the deposition process wasirreversible. In electrowinning experiments, a maximum of92% palladium could be obtained.
The adsorption behavior of241Am(Ⅲ) and Eu(Ⅲ) by silica/polymer-based iso Hex-BTP adsorbent(iso HexBTP/Si O2-P) was investigated by a batch experiment method. iso Hex-BTP/Si O2-P exhibited high affinity and selectivity for241Am(Ⅲ) over152Eu(Ⅲ) in 2–4 mol/dm3 nitric acid solutions. Within the experimental contact time range of 0.5–24 h, iso Hex-BTP/Si O2-P showed high selectivity for241Am(Ⅲ) compared to152Eu(Ⅲ) in3 mol/dm3 nitric acid solution. However, the adsorption kinetics of241Am(Ⅲ) and152Eu(Ⅲ) was slow. Eu(Ⅲ)adsorption followed the pseudo-second-order kinetic model, indicating chemical adsorption as the rate-limiting step of the adsorption process. And the adsorption agreed well with the Langmuir adsorption model at various temperatures. The adsorption kinetics and isotherm data indicated that the equilibrium adsorption capacity, the adsorption rate, the maximum adsorption capacity and the adsorption affinity, increased with temperature. The thermodynamic parameters, negative change in Gibbs free energy, and positive change in enthalpy and entropy,suggested that the adsorption of Eu(Ⅲ) was spontaneous and endothermic process with an increase of entropy.
Palladium（II） and chloride ions tend to form complexes in aqueous solution. Both theoretical and experimental （by UV spec- trum） results indicate that there are four complexes formed in aqueous solution containing 3 mol/L hydrochloric acid and 20 mmol/L PdC12. This work evaluates the kinetics of electrochemical deposition of palladium on a Platinum electrode. For this purpose, palladium electrodeposition was investigated by means of cyclic voltammetry （CV）, potentiostatic current-time tran- sients （CTTs） and Tafel curve. By CTTs curves, the regions corresponding to the charge transfer control, mixed control and diffusion control were identified. In the diffusion control region, palladium electrodeposition mechanism was characterized as progressive nucleation with three-dimensional （3D） growth under diffusion control; as for the mixed control region, an adsorp- tion （1Ads）, ion transfer （liT）, and nucleation and growth （ING） model were proposed to analyze the current-time transients quan- titatively, which could separate the IAds, lit and IN~ perfectly.
The electrochemical behavior of Pd(Ⅱ) and Rh(Ⅲ) in [EMIm]NTf2ionic liquid has been studied on Pt working electrodes at 298 K by cyclic voltammetry(CV), polarization curve and galvanostatic transient techniques.Cyclic voltammogram of Pd(II) in [EMIm]NTf2consists of two cathodic current peaks located at 1.37 V(E pc2),corresponding to Pd2+/Pd+, and at 0.69 V(E pc1) corresponding to Pd+/Pd. The transfer coefficient α was calculated by the Tafel extrapolation from the polarization curves to be 0.306, which is in agreement with the value reported in an aqueous solution system. For Rh(Ⅲ) in [EMIm]NTf2, a cathodic current peak(E pc) was observed at-0.39 V, corresponding to Rh3+/Rh, and two oxidation peaks were observed at-0.13 V(E pa1) and0.37 V(E pa2) during the reverse scan. A significantly negative shift in the cathodic peak potential was observed with the increase of the scan rate, indicating that the reduction of Pd(II) and Rh(Ⅲ) on the Pt electrode involves kinetic complications. By using the galvanostatic transient technique, the diffusion coefficients of Pd(II) and Rh(Ⅲ) in [EMIm]NTf2ionic liquid solution were found to be ～ 10-7cm2/s. The potential difference between the reduction of Pd(II) to Pd and the reduction of Rh(Ⅲ) to Rh obtained from the CV curves of the Pd(II) and Rh(Ⅲ) co-existing [EMIm]NTf2solution is found to be about 0.74 V, which makes it possible to electrodeposit Pd(II) and Rh(Ⅲ) separately.
The unique physical and chemical properties of room-temperature ionic liquids(RTILs) have recently received increasing attention as solvent alternatives for possible application in the field of nuclear industry, particularly in liquid-liquid separations of radioactive nuclides. We investigated solvent extraction of U(VI) from aqueous solutions into a commonly used ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([C4mim][NTf2]) using trioctylphosphine oxide(TOPO) as an extractant. The effects of contact time, TOPO concentration, acidity, and nitrate ions on the U(VI) extraction are discussed in detail. The extraction mechanism was proposed based on slope analysis and UV-Vis measurement. The results clearly show that TOPO/[C4mim][NTf2] provides a highly efficient extraction of U(VI) from aqueous solution under near-neutral conditions. When the TOPO concentration was 10 mmol/L, the extraction of 1 mmol/L U(VI) was almost complete(> 97%). Both the extraction efficiency and distribution coefficient were much larger than in conventional organic solvents such as dichloromethane. Slope analysis confirmed that three TOPO molecules in [C4mim][NTf2] bound with one U(VI) ion and one nitrate ion was also involved in the complexation and formed the final extracted species of [UO2(NO3)(TOPO)3]+. Such a complex suggests that extraction occurs by a cation-exchange mode, which was subsequently evidenced by the fact that the concentration of C4mim+ in the aqueous phase increased linearly with the extraction percent of U(VI) recorded by UV-Vis measurement.
