Anyun Zhang

Properties and mechanism of molybdenum and zirconium adsorption by a macroporous silica-based extraction resin in the MAREC process

Abstract To achieve effective separation of molybdenum and zirconium in the MAREC process, the adsorption properties and mechanism of Mo(VI) and Zr(IV) with a macroporous CMPO/SiO2‐P (CMPO: octyl(phenyl)‐N,N‐diisobutylcarbamoylmethylphosphine oxide) extraction resin have been studied. By investigating the influence of the aqueous concentrations of H+ and NO3 − on the adsorption of Mo(VI), the composition of complex of Mo(VI) and CMPO/SiO2–P is determined as H2MoO4 · 2CMPO/SiO2–P for dilute aqueous HNO3 and H2MoO3 (NO3)2 · 2CMPO/SiO2–P for concentrated aqueous HNO3, respectively. Similarly, the composition of Zr(IV) and CMPO/SiO2–P is determined as ZrO(NO3)2 · 2CMPO/SiO2–P or Zr(NO3)4 · 2CMPO/SiO2–P in 0.3–4.0 M HNO3, while ZrO2 · 2H2O · 2CMPO/SiO2–P is assumed for lower HNO3 concentration. Based on the compositions of Mo(VI) and Zr(IV) with CMPO/SiO2–P and the elution behavior of Mo(VI) and Zr(IV) by using 0.05 M diethylenetriaminepentaacetic acid (DTPA) at 0.01–1.0 M HNO3, a dynamic interconversion equilibrium between the complexes of Mo(VI) or Zr(IV) and CMPO/SiO2–P is demonstrated to take place in the elution process. To verify the adsorption mechanism, the adsorption and elution behavior of Mo(VI) and Zr(IV) with 0.05 M DTPA‐pH 2.0 was performed from a simulated high level radioactive liquid waste (HLLW) containing Pd(II), Gd(III), Y(III), Eu(III), Sm(III), Mo(VI), and Zr(IV). The results indicate that Mo(VI) and Zr(IV) not only can be efficiently eluted with 0.05 M DTPA‐pH 2.0, but also the elution efficiency is much better than that of 0.5 M H2C2O4 previously used in the MAREC process. The reverse equilibrium of complexes between Mo(VI) or Zr(IV) and CMPO/SiO2–P in high and low acidity was demonstrated, respectively.

Chromatographic Separation of Strontium (II) from a Nitric Acid Solution Containing some Typically Simulated Elements by a Novel Silica‐Based TODGA Impregnated Polymeric Composite in the MAREC Process

Abstract A new kind of macroporous silica‐based N,N,N′,N′‐tetraoctyl‐3‐oxapentane‐1,5‐diamide (TODGA) chelating polymeric adsorption material (TODGA/SiO2‐P) was developed and synthesized by impregnating TODGA molecules into the pores of ∼50 µm SiO2‐P particles to separate strontium effectively from high‐level liquid waste (HLLW). The adsorption of some typically simulated elements Na(I), K(I), Cs(I), Rb(I), Sr(II), Ba(II), and Ru(III) towards TODGA/SiO2‐P adsorbent was investigated by examining the influence of contact time and HNO3 concentration. It was found that with an increase in the HNO3 concentration, the adsorption of Sr(II) onto TODGA/SiO2‐P adsorbent increased quickly from 0.5 M to 2.0 HNO3 and then decreased. TODGA/SiO2‐P exhibited excellent adsorption ability and selectivity for Sr(II) over all of the tested elements, which showed almost no adsorption. Based on the batch experiments, the separation of Sr(II) from a 2.0 M HNO3 solution containing ∼5×10−3 M of the simulated elements was performed by TODGA/SiO2‐P packed column at 25°C and 50°C, respectively. Cs(I), K(I), Ru(III), Ba(III), Rb(I), and Na(I) were found to facilely elute out column and flow into effluent along with feed solution and 2.0 M HNO3 because of no adsorption. Sr(II) adsorbed towards TODGA/SiO2‐P was desorbed sufficiently by distilled water and separated completely from the simulated elements. Its recovery percentage was 100.2% at 25°C and 99.7% at 50°C. Furthermore, the leakage behavior of TODGA from its silica‐based adsorbent was investigated. It was found that the quantity of TODGA leaked was basically equivalent to its solubility in the corresponding HNO3 solution.

SPEC: A New Process for Strontium and Cesium Partitioning Utilizing Two Macroporous Silica-Based Supramolecular Recognition Agents Impregnated Polymeric Composites

Abstract To effectively separate two heat generators Cs(I) and Sr(II) from a highly active liquid waste (HLW), two macroporous silica-based polymeric composites (Calix[4]arene-R14 + M)/SiO2-P and (DtBuCH18C6 + M)/SiO2-P were synthesized. It was done by impregnating and immobilizing the supramolecular recognition agent, 1,3-[(2,4-diethylheptyl ethoxy)oxy]-2,4-crown-6-calix[4]arene (Calix[4]arene-R14) or 4,4′,(5′)-di-(tert-butylcyclo hexano)-18-crown-6 (DtBuCH18C6), into the pores of the macroporous SiO2-P particles with a mean diameter of 50 µm. It was found that in the first column packed with (Calix[4]arene-R14 + M)/SiO2-P, all of the tested elements were effectively eluted and separated into two groups: (1) Na(I), K(I), Sr(II), Ba(II), Rh(III), Ru(III), Pd(II), Zr(IV), RE(III) (La-Lu and Y), and Mo(VI) (Sr-containing group), and (2) Cs(I)-Rb(I) (Cs-group) by eluting with 4.0 M HNO3 and water, respectively, at 298 K. The heat emitting element Cs(I) flowed into the second group along with Rb(I), while Sr(II) showed no sorption and flowed into the Sr-containing group. In the second column packed with (DtBuCH18C6 + M)/SiO2-P, the Sr-containing group was separated into (1) Na(I), K(I), Rh(III), Ru(III), RE(III) (La-Lu and Y), Pd(II), Zr(IV), and Mo(VI) (non-sorption group), and (2) Sr(II)-Ba(II) (Sr-group), by eluting with 2.0 M HNO3 and water, respectively. The heat emitting element Sr(II) adsorbed by (DtBuCH18C6 + M)/SiO2-P flowed into the second group along with Ba(II). Based on the results, a new process entitled SPEC (Strontium/Cesium Partitioning from HLW by Extraction Chromatography) for heat generator partitioning from a simulated highly active liquid waste utilizing two macroporous silica-based supramolecular recognition composites has been developed.

Partitioning of Cesium from a Simulated High Level Liquid Waste by Extraction Chromatography Utilizing a Macroporous Silica‐Based Supramolecular Calix[4]arene‐Crown Impregnated Polymeric Composite

Abstract 1,3‐[(2,4‐Diethyl‐heptylethoxy)oxy]‐2,4‐crown‐6‐calix[4]arene (Calix[4]arene‐R14) is a supramolecular compound exhibiting Cs ion recognition in high level liquid waste (HLLW). To separate effectively Cs(I) from HLLW, a novel silica‐based Calix[4]arene‐R14 polymeric material (Calix[4]arene‐R14/SiO2‐P) was prepared. It was done through impregnating a mixture of Calix[4]arene‐R14 and tri‐n‐butyl phosphate (TBP), a molecular modifier, into the pores of macroporous SiO2‐P particles utilizing a vacuum sucking technique. The sorption of some typical fission product (FP) elements Na(I), K(I), Cs(I), Rb(I), Sr(II), and La(III) towards Calix[4]arene‐R14/SiO2‐P was investigated by examining the influence of contact time and the HNO3 concentration. It was found that with an increase in the HNO3 concentration from 1.0 M to 4.0, the sorption of Cs(I) towards Calix[4]arene‐R14/SiO2‐P increased quickly and then decreased with further increase of HNO3 concentration to 5.0 M. At the optimum HNO3 concentration of 4.0 M HNO3, the Calix[4]arene‐R14/SiO2‐P adsorbent exhibited excellent sorption ability and selectivity for Cs(I) over all of the tested elements, which showed very weak or almost no sorption except Rb(I). The chromatographic separation of Cs(I) from a simulated HLLW containing ∼5 mM of the FP elements and 4.0 M HNO3 was performed by Calix[4]arene‐R14/SiO2‐P packed column at 298 K. Na(I), K(I), Sr(II), and La(III) were found to elute facilely and flowed into the effluent along with 4.0 M HNO3. Cs(I) and Rb(I), adsorbed strongly onto Calix[4]arene‐R14/SiO2‐P, were desorbed sufficiently by water. The leakage behavior of Calix[4]arene‐R14 and TBP from Calix[4]arene‐R14/SiO2‐P was also investigated.

Association Behavior of 4-Acylpyrazolone Derivative and Tertiary Amine of High Molecular Weight in Antagonistic Synergistic Extraction of Palladium

To find an effective extraction and removal method for palladium(II), which is one of the main fission products from an acidic nuclear spent fuel solution, the extraction behavior of palladium(II) from a nitric acid medium by an acidic chelating extractant, 1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5-one (HPMTP) and a tertiary amine of high molecular weight, tri-n-octylamine (TOA), has been studied by spectrophotometry. A noticeable antagonistic extraction effect was observed in the extraction system under the given conditions. To understand this phenomenon, a preliminary investigation was performed to explain the mechanism of this reaction. According to the theory of corresponding solutions (TCS), the association reaction between HPMTP and TOA is proposed in the organic phase. An associated species, HPMTP·TOA, formed through hydrogen bonding in a chloroform medium might be the main reason why an antagonistic extraction effect occurred. The association constant between HPMTP and TOA was calculated to be 2.86±0.05.

Synthesis of a Novel Silica‐Based Macroporous Polymer Containing TODGA Chelating Agent and Its Application in the Chromatographic Separation of Mo(VI) and Zr(IV) from Diethylenetriaminepentaacetic Acid

Abstract A novel silica‐based N,N,N′,N′‐tetraoctyl‐3‐oxapentane‐1,5‐diamide (TODGA) chelating polymeric material (TODGA/SiO2‐P) was synthesized by impregnating TODGA into ∼50 µm of spherical SiO2‐P particles for separating Mo(VI) and Zr(IV) from a HNO3 solution containing 0.05 M diethylenetriaminepentacetic acid (DTPA) in minor actinides recovery by extraction chromatography (MAREC) process. The adsorption of TODGA/SiO2‐P for Mo(VI) and Zr(IV) was investigated by examining the influence of HNO3 and DTPA concentrations. It was found that HNO3 concentration from 0.3 M to 9 M either with or without 0.05 M DTPA had a strong effect on the adsorption of Mo(VI) and Zr(IV) towards TODGA/SiO2‐P. In the absence of 0.05 M DTPA, both the adsorption of Mo(VI) and Zr(IV) decreased with an increase in the concentration of HNO3 from 0.3 M to 3 M and then gradually increased. In the presence of 0.05 M DTPA, Zr(IV) showed scarcely any adsorption towards TODGA/SiO2‐P below 2 M HNO3 and was gradually adsorbed from 2 M to 3 M HNO3 while Mo(VI) showed almost no adsorption. In excess of 3 M HNO3, the adsorption curve of Mo(VI) or Zr(IV) fully overlapped with that of the absence of 0.05 M DTPA. This resulted from the dissociation of Mo(VI) or Zr(IV) from its complex with DTPA because of full protonation of DTPA in high HNO3 concentration and the strong complexation taking place simultaneously with TODGA/SiO2‐P. In terms of the batch experiments, the separation of Mo(VI) and Zr(IV) from a 3 M HNO3 solution containing 0.05 M DTPA was performed by employing the TODGA/SiO2‐P packed column at 50°C. Molybdenum(VI) was found to leak out of the column along with 3 M HNO3. Zirconium(IV) adsorbed by TODGA/SiO2‐P was effectively eluted by 0.5 M H2C2O4. The recovery was 101.6% for Mo(VI) and 94.8% for Zr(IV). This work was financially supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) under the framework of the “Development of Innovation Nuclear Technologies.”

Palladium Removal from the Simulated Nuclear Spent Fuel Solution Using a Silica‐Based SiPyR‐N3 Anion Exchanger

Abstract The ERIX process consists of electroreduction and anion exchange for reprocessing spent nuclear fuels, in which Pd removal from spent fuel solution is necessary in the first step, since Pd can deposit at the electrode in the metallic state and interfere with the electroreduction. In the present work, the possibility in selective removal of Pd using a porous silica‐supported anion exchanger, SiPyR‐N3, containing a pyridine group has been studied. Adsorption behavior of Pd(II) from a simulated solution using a SiPyR‐N3 packed column has been investigated. The elution of Pd(II) using 0.05 M DTPA and 0.2 M thiourea was examined and compared. The SiPyR‐N3 resin showed a significantly strong adsorption for Pd(II) from HNO3 solution. The unique adsorption was considered to result from the complex formation between Pd(II) and the resin which contains the soft‐atom N with a lone pair of electrons. U(VI) and some typical simulated fission products, La(III), Pr(III), and Sr(II), showed almost no or very weak adverse impact on the Pd(II) separation, except for Re(VII) and Ru(III). The results of column experiments demonstrated that the Pd can be selectively removed from the nuclear spent fuel solution, though further work is needed to improve Pd elution.

Adsorption and Chromatographic Separation of Mo(VI) and Zr(IV) Ions from a High-Concentration Oxalic Acid Solution by a Macroporous Silica-Based N,N,N′,N′-Tetraoctyl-3-Oxapentane-1,5-Diamide Polymeric Adsorbent

To separate Mo(VI) and Zr(IV) ions from a 0.5 M oxalic acid solution and from each other, a novel macroporous silica-based N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) chelating polymeric adsorbent (TODGA/SiO2-P) was synthesized by introducing the TODGA molecule into ca. 50-μm diameter SiO2-P particles by impregnation. The adsorption of Mo(VI) and Zr(IV) ions onto TODGA/SiO2-P was investigated by examining the influence of nitric acid and oxalic acid concentrations. It was found that the adsorption was strongly affected by increasing the HNO3 concentration from 0.5 M to 9.0 M either with or without the addition of 0.5 M H2C2O4. In the absence of 0.5 M H2C2O4, the distribution coefficients (Kd) of both Mo(VI) and Zr(IV) ions decreased with an increase in the HNO3 concentration from 0.5 M to 3.0 M, increased slowly when the concentration of HNO3 was increased further from 3.0 M to 6.0 M, and then increased gradually above 6.0 M concentration. Furthermore, the adsorption of Zn(IV) ions onto TODGA/SiO2-P was considerably greater than that of Mo(VI) ions. In the presence of 0.5 M H2C2O4, Zr(IV) ions showed no adsorption at HNO3 concentrations below 4.0 M, being partly adsorbed in the presence of 4.0–6.0 M HNO3 and fully adsorbed when the HNO3 concentration was greater than 6.0 M. In contrast, Mo(VI) ions showed a much lower adsorption at HNO3 concentrations below 2.0 M and no adsorption above this acid level. In the presence of HNO3 at a concentration above 6.0 M and containing 0.5 M H2C2O4, the adsorption of Zr(IV) ions overlapped that from a similar HNO3 solution which did not include 0.5 M H2C2O4. This was attributed to complete protonation of the C2O2−2 anion. On the basis of batch experiments, Mo(VI) and Zr(IV) ions were separated from a 6.5 M HNO3 solution containing 0.5 M H2C2O4 by means of a column packed with TODGA/SiO2-P at 50°C. The separate components, Mo(VI) and Zr(IV), could be effectively separated from each other by eluting with some selected eluants. The recovery percentage was 100.5% for Mo(VI) ions and 96.8% for Zr(IV) ions.

Adsorption Behavior of Sr(II) and some Typical Co‐existent Metals Contained in High Level Liquid Waste onto a Modified Macroporous Silica‐Based Polymeric DtBuCH18C6 Composite

To significantly reduce the bleeding of 4,4′,(5′)‐di(tert‐butylcyclohexano)‐18‐crown‐ 6 (DtBuCH18C6), an improved novel macroporous silica‐based polymeric composite (DtBuCH18C6+TBP)/SiO2‐P was synthesized. It was performed by impregnating and immobilizing DtBuCH18C6 into the pores of the SiO2‐P particles via the molecular modification of DtBuCH18C6 with a tri‐n‐butyl phosphate (TBP) through hydrogen bonding. The adsorption of a few typical simulated fission and non‐fission products Pd(II), La(III), Na(I), K(I), Sr(II), Ba(II), Ru(III), Cs(I), Mo(VI), and Y(III) onto (DtBuCH18C6+TBP)/SiO2‐P was investigated at 323 K. It was done by examining the effect of contact time and the HNO3 concentration in a range of 0.1–5.0 M. Sr(II), one of the main heat emitting nuclides, showed optimum adsorption onto (DtBuCH18C6+TBP)/SiO2‐P in 2.0 HNO3, while others showed very weak or almost no adsorption except a portion of Ba(II). The leaching of TBP and DtBuCH18C6 from (DtBuCH18C6+TBP)/SiO2‐P was evaluated. The average content of DtBuCH18C6, 298.7 ppm, leached from (DtBuCH18C6+TBP)/SiO2‐P in 2.0 M HNO3 at 323 K was obviously lower than that of 797.3 ppm leached from DtBuCH18C6/SiO2‐P at 298 K. The significant reduction of DtBuCH18C6 leaching from its macroporous silica‐based polymeric adsorbent was achieved. It is useful for the recycle operation of the silica‐based DtBuCH18C6 impregnated polymeric composite in chromatographic partitioning of Sr(II) from high level liquid waste (HLLW).

Preparation of a Novel Macroporous Silica-based Diglycolamide Derivative-impregnated Polymeric Composite and its Adsorption Mechanism for Rare Earth Metal Ions

Diethylenetriaminepentaacetic acid (DTPA), a multi-dentate acidic chelating agent containing five carboxyl and three amine groups all capable of protonation, is a pentabasic acid. To separate minor actinide [MA(III)] and rare earth [RE(III)] elements effectively from a HNO3 solution containing DTPA generated in the MAREC process, a functional polymeric composite impregnated with a novel macroporous silica-based diglycolamide compound, N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA), was prepared. Thus, the impregnated functional polymeric composite (TODGA/SiO2-P) was obtained by impregnating and immobilizing TODGA molecules in the pores of the SiO2-polymer (SiO2-P) particles (ca. 50 μm diameter) via a vacuum sucking technique. The effects of H+ ions within the concentration range 0.01–3.0 M and of NO3− ions within the range 0.1–3.115 M on the adsorption of RE(III) ions onto TODGA/SiO2-P were investigated at 298 K. It was found that in the presence of 0.05 M DTPA, the DTPA species strongly affected the adsorption of RE(III) ions. The adsorption capability of TODGA/SiO2-P depended on the competitive reactions of RE(III) ions with two species, viz. H4DTPA− and H2DTPA3−. The distribution coefficient (Kd) for RE(III) ions increased with increasing NO3− concentration, with one RE(III) ion reacting with two NO3− ions. The adsorption mechanism of RE(III) ions towards the TODGA/SiO2-P polymeric composite in HNO3 solution containing 0.05 M DTPA was suggested as: RE 3 + + H 4 DTPA - + 2 NO 3 - + 3 TODGA / SiO 2 - P ⇋ RE ( H 4 DTPA ) ( NO 3 ) 2 ⋅ 3 TODGA / SiO 2 - P The formation of H4DTPA− and RE(H4DTPA)(NO3)2 which are both capable of adsorbing with TODGA/SiO2-P was the main reason why RE(III) ions exhibited such significant adsorption in the presence of 0.05 M DTPA.