Ruiqin Liu

An advanced partitioning process for key elements separation from high level liquid waste

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 silica/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(II) from simulated HLLW was achieved. Tc(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/SiO2-P adsorbents over various FPs including Ln(III). The R-BTP adsorbents were fairly stable in 3 M HNO3, but instable against γ-irradiation-3M HNO3. An advanced partitioning 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.

Development of a simplified separation process of trivalent minor actinides from fission products using novel R-BTP/SiO2-P adsorbents

From a viewpoint of direct separation of trivalent minor actinides (MA: Am, Cm etc.) from fission products (FP) including rare earths (RE) in high level radioactive liquid waste, the authors have developed a simplified separation process using a single column packed with novel extraction adsorbents. Attention was paid to a new type of nitrogen-donor ligand, R-BTP (2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine, R: alkyl group) as an extractant because it has higher extraction selectivity for Am(III) than RE(III). Since the R-BTP ligands show different properties such as adsorbability and stability when they have different alkyl groups, several R-BTP extraction adsorbents were prepared by impregnating the R-BTP ligands with different alkyl groups (isohexyl-, isoheptyl- and cyheptyl-BTP) into a porous silica/polymer composite support (SiO2-P particles). This work investigated: (1) fundamental properties of the synthesized R-BTP/SiO2-P adsorbents, (2) adsorption and desorption properties of Am and FP in nitric acid solution and water using the adsorbents in a batch experiment, (3) radiolytic and chemical stabilities of the adsorbents, and (4) the possibility for developing a simplified separation process of MA using the most promising adsorbent (isohexyl-BTP/SiO2-P) under temperature control between 25 and 50°C.

Challenges to develop single-column MA(III) separation from HLLW using R-BTP type adsorbents

In order to directly separate trivalent minor actinides (MA: Am, Cm) from fission products (FP) containing rare earths (RE) in high level radioactive liquid waste (HLLW), the authors have challenged to develop a simplified MA separation process by extraction chromatography using a single column. Attention has been paid to a new type of nitrogen-donor ligands, R-BTP (2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl) pyridine, R: alkyl group) as an extractant because it shows high extraction selectivity for Am(III) over RE(III). It is known that the R-BTP ligands show different properties such as adsorbability and stability by having different alkyl groups. Therefore, some novel adsorbents were prepared by impregnating different types of R-BTP ligands (isohexyl-, isoheptyl- and cyheptyl-BTP) and a similar ligand to the R-BTP, ATP (2,6-bis(1-aryl-1H-tetrazol-5-yl)pyridines), into the porous silica/polymer support (SiO2-P particles). This work deals with comparison in adsorption and desorption properties of Am and some FP in HNO3 solution onto such R-BTP type adsorbents, as well as chemical and radiolytic stability of the adsorbents. Then the possibility of a single-column separation of MA from main FP was pursued by evaluating the results of column experiments using the most promising adsorbent (isohexyl-BTP/SiO2-P) under temperature control. In addition, elution behaviors of U and Pd were also estimated.

Evaluation of Me2-CA-BTP/SiO2-P adsorbent for the separation of minor actinides from simulated HLLW

A novel silica-based adsorbent Me2-CA-BTP/SiO2-P was prepared to separate minor actinides from fission products in high level liquid waste. Me2-CA-BTP/SiO2-P adsorption behavior towards 241Am(III) and main FP from HNO3 solutions were studied. The adsorbent exhibited much higher affinity for Am(III) over FP elements in a large HNO3 concentration range and possess good adaptability as HNO3 concentration changes. Dy(III), as a simulated element of MA(III), showed good adsorption properties and elution performance. Dy(III) adsorption kinetics and isotherm followed the pseudo-second-order rate law and Langmuir isotherm adsorption model, respectively. Adsorbed Dy(III) could be effectively eluted from Me2-CA-BTP/SiO2-P by H2O or dilute HNO3.

Evaluation study on a macroporous silica-based isohexyl-BTP adsorbent for minor actinides separation from nitric acid medium

Abstract To separate the long-lived minor actinides (MA = Am, Cm) from high level liquid waste (HLLW), we have been studying a partitioning technology named “MAREC” (Minor Actinides Recovery from HLLW by Extraction Chromatography) process which consists of two separation columns packed with silica-based adsorbents. In this work, we prepared the silica-based 2,6-bis(5,6-diisohexyl-1,2,4-triazin-3-yl)pyridine (isohexyl-BTP/SiO2-P) adsorbent used in the second column (0.01 ∼ 0.1 mol dm–3 HNO3) in the MAREC process for the separation of trivalent minor actinides (MA(III)) from trivalent rare earth elements (RE(III)) which are contained in HLLW. The content of extracting agent isohexyl-BTP in isohexyl-BTP/SiO2-P was as high as 33.3% of the total mass of the adsorbent. The adsorbent exhibited high affinity and selectivity for Am(III) over RE(III) not only in nitric acid solution but also in nitrate solution. Investigation showed that only a small part of isohexyl-BTP molecules inside isohexyl-BTP/SiO2-P leaked into 0.01 mol dm–3 HNO3 with or without γ-irradiation. The adsorption performance of isohexyl-BTP/SiO2-P did not evidently change after 120 d of contact with 0.01 mol dm–3 nitric acid. Furthermore, after γ-irradiated in 0.01 mol dm–3 HNO3 under the experimental conditions, isohexyl-BTP/SiO2-P exhibited higher adsorption for RE(III) than before γ-irradiation.

Electrochemical behavior and electrowinning of palladium in nitric acid media

In this study, the electrochemical behavior of Pd(II) in nitric acid media was investigated using various electrochemical techniques. By analyzing the cyclic voltammogram of Pd(II) recorded at Pt electrode, a series of electrochemical reactions associated with palladium were recognized, indicating that Pd(II) undergoes a single step two-electrons irreversible process. Electroreduction reaction of Pd(II) and auto-catalytic reactions of nitrous acid are supposed to play a leading role in low and high concentrations of nitric acid, respectively. Stirring could facilitate the reduction of Pd(II) in relatively low nitric acid concentration (⩽ 3 mol/L). The value of charge transfer coefficient was determined to be 0.18 for the measurements at 298 K. The diffusion coefficient of Pd(II) increased from 1.89 × 10−8 cm2/s at 288 K to 4.23 × 10−8 cm2/s at 318 K, and the activation energy was calculated to be 21.5 kJ/mol. In electrowinning experiments, SEM images of palladium obtained by electrolysis reveal the dendrite growth in all cases, which is uniform all over the entire surface of Pt electrode. The recovery ratios of Pd at different nitric acid concentrations are high, and the faradic efficiency of electrolysis decreases with increasing the nitric acid concentration. When stirring was introduced during electrolysis, the electrodeposition rate of Pd increased substantially.

Adsorption mechanism of silica/polymer-based 2,6-bis(5,6-diisohexyl-1,2,4-triazin-3-yl)pyridine adsorbent towards Ln(III) from nitric acid solution

ABSTRACT 2,6-Bis(5,6-diisohexyl-1,2,4-triazin-3-yl)pyridine (isoHexyl-BTP) is a nitrogen-donor chelating ligand which shows high extraction selectivity for minor actinides (MA) over lanthanides (Ln). We synthesized a macroporous sillica/polymer-based isoHexyl-BTP adsorbent (isoHexyl-BTP/SiO2-P) for the separation of MA(III) from Ln(III) in high-level liquid waste. The work focused on the isoHexyl-BTP/SiO2-P adsorption mechanism towards Ln(III) in nitric acid solution and the coordination chemistry between Ln(III) and isoHexyl-BTP/SiO2-P through batch adsorption experiments, extended X-ray absorption fine spectroscopy, acid-base titration and ion chromatography. It was found that both H+ and NO3− directly participated in the adsorption reaction. For the middle and heavy Ln(III), Ln(isoHexyl-BTP/SiO2-P)3(NO3)3·3HNO3 was supposed as the main product of the adsorption. The Ln(III)-N (Ln(isoHexyl-BTP/SiO2-P)33+) bond length of the first coordination layer decreased as the atomic number of Ln(III) increased, which explains the increased adsorption affinity of isoHexyl-BTP/SiO2-P towards middle and heavy Ln(III) in relatively high concentration nitric acid as the Ln(III) atomic number increased.

ESR signals from silk fabrics irradiated by UV -rays

ESR studies were done on UV-ray irradiated silk fabric samples at room temperature. Different types of UV lamps were used and similar ESR signals were observed. The results indicate that UV-rays can produce free radicals for graft-copolymerization of monomer onto silk fibers without external additives or co additives, Also, radicals in silk fabrics irradiated by UV-rays are purer than that irradiated by gamma-rays. The study suggests that UV-lights may be a better tool to improve properties of silk fabrics by grafting monomers onto the polymer chains.

Adsorption behavior of Me 2 -CA-BTP/SiO 2 -P adsorbent toward MA(III) and Ln(III) in nitrate solution

A porous Me2-CA-BTP/SiO2-P adsorbent was prepared to separate MA(III) from Ln(III) in high level liquid waste (HLLW). The adsorption behavior of Me2-CA-BTP/SiO2-P toward 241Am(III) and Ln(III) in 0.01 M HNO3-NaNO3 solution was studied. Me2-CA-BTP/SiO2-P showed high adsorption and selectivity toward 241Am(III) over Ln(III) fission products with the separation factor (SF) reaching to 557, 2355, 1952, 1082, 214, 105, 86, 14 for Y, La, Ce, Nd, Sm, Eu, Gd and Dy respectively in 0.01 M HNO3-0.99 M NaNO3 solution. The adsorption kinetics of both Dy(III) and Eu(III) on Me2-CA-BTP/SiO2-P was studied and followed pseudo-second-order rate equation indicating chemical sorption as the rate-limiting step of the adsorption, and the adsorption isotherm of Dy(III) and Eu(III) matched better with the Langmuir isotherm than the Freundlich isotherm with the adsorption amount around 0.22 and 0.20 mmol/g respectively. Thermodynamic study revealed that the adsorption of both Dy(III) and Eu(III) on Me2-CA-BTP/SiO2-P was spontaneous and endothermic processes with a positive entropy at 298, 308, 313 K.

Feasibility studies on the selective separation of fission palladium(II) by isoHex-BTP/SiO2-P adsorbent from HLLW

ABSTRACT Aiming at the selective recovery of fission palladium(II) from high-level liquid waste (HLLW), the silica/polymer (SiO2-P)-based isoHex-BTP adsorbent (isoHex-BTP/SiO2-P) was synthesized by impregnating complexing agent isoHex-BTP into the multiporous SiO2-P inert support. The feasibility of separation of Pd(II) from HLLW by isoHex-BTP/SiO2-P was evaluated by batch experiment method. The results showed that isoHex-BTP/SiO2-P exhibited much higher adsorption selectivity for Pd(II) than the other fission products, even Am(III) and Pu(IV) presented in HLLW. The ideal nitric acid concentration for the adsorption of Pd(II) by the adsorbent was shown to be ≥2 mol dm–3. The adsorption of Pd(II) fits well to the pseudo-second-order kinetic model and Langmuir isotherm model. Quantitative Pd(II) desorption was achieved by using 0.5 mol dm−3 SC(NH2)2 - 0.1 mol dm−3 HNO3 solution.