Simulated High Level Liquid Waste Research Articles

An ultrastable luminescent covalent organic polymer for selective Pd2+ detection in strong acid

AbstractThe low natural abundance of palladium (10 ppb) in the Earth's crust highlights its considerable potential as a valuable resource, especially given that spent nuclear fuel contains approximately 1–2 kg of Pd per ton. However, the detection and separation of Pd2+ from high‐level liquid waste (HLLW) present significant challenges due to high acidity (2–5 M HNO3) and intense radiation conditions inherent in spent fuel reprocessing. We present a cyano‐olefin‐linked covalent organic polymer (COP‐TnPp) that exhibits remarkable stability in strong acidic environments and resilience to radiation. Thanks to its olefin linkage, which facilitates π‐electron conjugation, COP‐TnPp exhibits strong luminescence, whose intensity remains stable across a range of 1–5 M nitric acid solutions. Pd2+ ions can effectively quench the fluorescence of COP‐TnPp in 1 and 5 M HNO3 solutions with detection limits of 0.37 and 0.63 μM, respectively. Additionally, COP‐TnPp demonstrates exceptional selectivity for Pd2+ ions, even amidst 22 other interfering ions in a simulated HLLW solution (5 M HNO3), with the detection limit remaining at 0.697 μM. This work not only marks an advancement in the development of materials for detecting Pd2+ in extreme acidic conditions but also offers new insights into the detection of other radionuclides under similarly challenging environments.

Influence of temperature and flow rate on alteration layer structure and leaching properties of simulated sulfur-containing borosilicate HLW glass under multi-field coupling effects

During long-term deep geological disposal process, high-level liquid waste (HLW) glass may be exposed to “Thermodynamics-Hydrodynamics-Mechanics-Chemistry” (THMC)multi-field coupling effects. The leaching properties of sulfur-containing borosilicate HLW glass at different temperatures (40–150 °C) and different flow rates (0.01–0.10 mL/min) under THMC coupling effects were studied in this work. The alteration layer structure of waste glass surface was also characterized. The results show that honeycomb-shaped phyllosilicate alteration layer forms after leaching in simulated groundwater and white block-shaped BaSO4 crystals appear on the glass surface at 90 °C after 28 d. The amount of BaSO4 crystals increases obviously at 150 °C. The leaching rates of B, Si, Cs and U elements increase with increasing temperature and flow rate. Particularly, the leaching rates of B, Si, Cs, and U under THMC coupling effects (90 °C, 0.01 mL/min, 10 MPa, pH=8.05) after 28 d in the simulated groundwater are 1.10 × 10–1, 1.73 × 10–1, 2.91 × 10–1, 3.79 × 10–1 g·m-2·d-1, respectively.

Silica-Reinforced AMP-Calcium Alginate Beads for Efficient and Selective Removal of Cesium from a Strong Acidic Medium.

Due to the significant selectivity for Cs+, ammonium molybdophosphate (AMP) possesses potential to uptake radiocesium from high-level liquid waste (HLLW), whereas its micro-crystalline structure and fine powder morphology limit its industrial application. Although the granulation method with alginate is prospective for the preparation of an AMP exchanger, the mechanical strength of obtained beads may be insufficient for application. In this context, we prepared silica-reinforced AMP-calcium alginate (ACS) beads and evaluated their performance for Cs+ removal from strong acidic solutions. It was found that the addition of silica in the fabrication significantly improved the mechanical strength of the beads in comparison to those without silica. Notably, the beads with an AMP/silica mass ratio of 1.0 exhibited an exceptional mechanical strength, surpassing that of ACS beads composed of other components. The batch experiment results indicated that the Cs+ adsorption follows a non-linear pseudo-second-order rate equation. The distribution coefficient of Cs+ was high even in extreme acidic conditions (∼1.6 × 102 mL/g in 8.0 mol/L HNO3 solution). The Cs+ adsorption can be well fitted with the Langmuir model, and the estimated maximum exchange capacity in 3.0 mol/L HNO3 could reach 23.9 mg/g. More importantly, ACS beads showed excellent selectivity toward Cs+ uptake over eight co-existing metal ions in simulated HLLW, with separation factor values all above 145. The column experiment exhibited that the beads can serve as the stationary phase in columns to effectively remove Cs+. The findings of this study are significant as they provide insights into the development of efficient materials for radiocesium removal from high-level liquid waste. The results demonstrate the potential of silica-reinforced ACS beads for Cs+ adsorption, with promising applications in industrial settings.

Research on calcination thermal decomposition process of simulated high-level liquid waste based on two-step vitrification

The two-step vitrification process involves converting high-level waste from a liquid to a solid state through calcination, followed by melting the calcines with glass matrix material to form glassy wasteforms. The calcination process is a critical stage in the vitrification process. This study investigated the thermal decomposition performance and phase evolution of power reactor simulated high-level waste during the calcination process. As the calcination temperature increased from 100 to 900 °C, the resultant waste calcines showed increasingly darker color and smaller general particle sizes. Below 600 °C, the waste experienced thermal decomposition of nitrate and formate compounds, leading to an approximate 40 wt% weight reduction. At 600 °C, the waste's weight remained constant, and crystalline phases such as ZrxM1-xO2 (M = Ce, Pr, Nd), BaMoO4, CeO2, and GdxCe1-xO2 were observed.

Demonstration of Mixer-Settlers Runs for Separation of Uranium and Neptunium by TBP Vis-a-Vis DHOA Under a Legacy Waste Condition

ABSTRACT Separation of neptunium from an acidic feed containing 0.063 mol/L uranium in 3 mol/L HNO3 was demonstrated in counter-current extraction in mixer-settlers with TBP (tri-n-butyl phosphate) and DHOA (N,N’-dihexyl octanamide) as the organic extractants. With a feed solution of 0.063 mol/L uranium (in the absence of neptunium) and at an organic to aqueous phase ratio (O/A) = 1, >99.9% uranium could be extracted into the organic phase in 6 stages with the raffinate containing <10−5 mol/L of uranium. The extraction results with TBP and DHOA were comparable. However, stripping of uranium with 0.01 mol/L HNO3 from the loaded organic phase was better with DHOA vis-a-vis TBP phase. From the DHOA phase, loaded with 0.063 mol/L uranium, the entire metal ion could be stripped in 6 stages at an O/A = 1. However, ca. 17% uranium remained in the TBP phase even after 6 stages of stripping. With these preliminary results, the extraction of neptunium was systematically studied in mixer-settlers from feed containing uranium, and from simulated high level liquid waste. Our results of neptunium extraction in the presence of 0.021 mol/L uranium yielded excellent result. Similarly, the extraction of neptunium from simulated high level liquid waste was also demonstrated with good extraction efficiency.

Efficient and Selective Removal of Palladium from Simulated High-Level Liquid Waste Using a Silica-Based Adsorbent NTAamide(C8)/SiO2-P.

In order to realize the effective separation of palladium from high-level liquid waste (HLLW), a ligand-supported adsorbent (NTAamide(C8)/SiO2-P) was prepared by the impregnation method in a vacuum. The SiO2-P carrier was synthesized by in situ polymerization of divinylbenzene and styrene monomers on a macroporous silica skeleton. The NTAamide(C8)/SiO2-P adsorbent was fabricated by impregnating an NTAamide(C8) ligand into the pore of a SiO2-P carrier under a vacuum condition. The adsorption performance of NTAamide(C8)/SiO2-P in nitric acid medium has been systematically studied. In a solution of 0.2 M HNO3, the distribution coefficient of Pd on NTAamide(C8)/SiO2-P was 1848 mL/g with an adsorption percentage of 90.24%. With the concentration of nitric acid increasing, the adsorption capacity of NTAamide(C8)/SiO2-P decreases. Compared to the other 10 potential interfering ions in fission products, NTAamide(C8)/SiO2-P exhibited excellent adsorption selectivity for Pd(II). The separation factor (SFPd/other metals > 77.8) is significantly higher than that of similar materials. The interference of NaNO3 had a negligible effect on the adsorption performance of NTAamide(C8)/SiO2-P, which maintained above 90%. The adsorption kinetics of Pd(II) adsorption on NTAamide(C8)/SiO2-P fits well with the pseudo-second order model. The Sips model is more suitable than the Langmuir and Freundlich model for describing the adsorption behavior. Thermodynamic analysis showed that the adsorption of Pd(II) on NTAamide(C8)/SiO2-P was a spontaneous, endothermic, and rapid process. NTAamide(C8)/SiO2-P also demonstrated good reusability and economic feasibility.

Understanding the extraction behavior of Eu(III) from acidic medium and the feasibility of separation of simulated high level liquid waste compositions using a phosphonium ionic liquid containing diglycolamide extractant

Liquid-Liquid extraction behavior of trivalent lanthanides (by taking Eu(III) as a representative) in a strongly hydrophobic phosphonium based ionic liquid (IL) in conjunction with a diglycolamide (DGA) based extractant was perused in detail to emphasize the extraction pathway and coordination behavior. Trihexyl(tetradecyl)phosphonium nitrate (Cyphos nitrate: [P66614][NO3]) was chosen as IL solvent phase containing N,N,N’,N’-tetra-(2-ethylhexyl)diglycolamide (T2EHDGA) (a well-known DGA ligand) as the extractant.The extraction behavior of Eu(III) was furnished at different experimental parameters such as the concentration of initial nitric acid, concentration of ligand, equilibration time and experimental temperature to explore the extractability of the proposed IL system. The extraction showed an increasing trend with an increase in the feed acidity followed by attaining a plateau region at higher acid concentration inferring the occurrence of a neutral solvation type coordination mechanism. The mixture of T2EHDGA/[P66614][NO3] was implemented on the extraction of Fast Reactor Simulated High Level Liquid Waste (FR-SHLLW) solution spiked with Am(III) and the results were promising with respect to efficacy of the proposed IL phase. All the trivalent Ln(III) and Am(III) were selectively separated from some of the co-extracting fission products using a suitable holding agent in the feed phase. IL composition chosen for the study was radiation stable exhibiting comparable extraction behavior for SHLLW metal ions. The present study uses only dilute nitric acid as the stripping agent without adding any aqueous phase complexing agent which is a major underscore as far as the economic and environmental benefits are concerned.

Precise recognition and efficient recovery of Pd(II) from high-level liquid waste by a novel aminothiazole-functionalized silica-based adsorbent

Efficient recognition, separation and recovery of palladium from high-level liquid waste (HLLW) not only helps the safe, green and environmentally friendly disposal of nuclear waste, but also is an essential important supplement to overcome the growing shortage of natural palladium resources. Herein, a novel silica-based functional adsorbent named 2AT-SiAaC was prepared by a two-step method, i.e., grafting of 2-aminothiazole (2AT) via the amidated reaction after in-situ polymerization of acrylic monomers on porous silica. SEM, EDS, TG-DSC, BET and PXRD all proved the successful preparation of 2AT-SiAaC, and it exhibited ultrahigh adsorption selectivity for Pd(II) (Kd (distribution coefficient) ≥ 10,344.2 mL/g, SFPd/M (separation factor) ≥ 613.7), fast adsorption kinetics with short equilibrium time (t ≤ 1 h) and good adsorption capacity (Q ≥ 62.1 mg Pd/g). The dynamic column experiments shows that 2AT-SiAaC achieved efficiently separation of Pd(II) from simulated HLLW, and the enrichment coefficients (C/C0) of Pd(II) was as high as about 14 with the recovery rate nearly 99.9% and basically kept the same performance in three adsorption-desorption column cycle experiments. The adsorption mechanism was analyzed by FT-IR, XPS and DFT calculations, and the ultrahigh selectivity of 2AT-SiAaC was attributed to the preferred affinity of the soft N-donor atoms in 2AT for Pd(II). NO3− ions participated in the adsorption reaction to keep charge balance, and the frontier orbital electron density distribution diagram shows the charge transfer in the process of material preparation and adsorption. To sum up, 2AT-SiAaC adsorbent provided a new insight for precise recognition and efficient separation of Pd(II) from HLLW.

Effect of metallic redox ions on the corrosion behavior of GTAW weldment of type 304L stainless steel in simulated non-radioactive PUREX and HLLW medium

Nuclear-spent fuel reprocessing and high-level liquid waste (HLLW) storage containers possess various inorganic higher valance oxidizing metallic ions and fission products, further influencing nitric acid corrosion through the PUREX route. This study evaluated the effect of nitric acid corrosion on gas-tungsten arc weldment (GTAW) of stainless steel (SS) 304 L in simulated reprocessing and HLLW medium in non-radioactive conditions. The effect of oxidizing metallic cations, which were present as the major amount in the mark-I spent fuel of fast breeder test reactors (FBTR) in India; these are Cs+1, Nd+3, Mo+6, Fe+3, and V+5 as a surrogate redox system for Pu(VI)/Pu(IV) and Np(VI)/Np(V) system was evaluated by the electrochemical corrosion test method in 2 M, 6 M, and 8 M nitric acid solutions. The resistance of polarization (Rp) value decreases with the nitric acid concentration, and the effect of oxidizing ions in different nitric acid concentrations also changes. The three-phase corrosion (boiling liquid, vapor, and condensate phase) resistance behavior in different concentrations (6 M and 8 M) of the nitric acid medium, without and with redox ions, has been evaluated. The corrosion rate is higher in the liquid phase compared to the vapor and condensate phases. On the other hand, it is relatively higher for the inorganic metallic redox ions containing solutions.

Selective Separation of Zr(IV) from Simulated High-Level Liquid Waste by Mesoporous Silica.

The efficient separation of Zr(IV) ions from strong acidic and radioactive solutions is a significant challenge, especially in the context of the aqueous reprocessing of nuclear fuels. The complexity of such solutions, which are often characterized by high acidity and the presence of radioactive elements, poses formidable challenges for separation processes. Herein, several mesoporous silicas (HMS, MCM-41, KIT-6, and SiO2-70 Å) with excellent acid and radiation resistance properties were employed as sorbents to remove Zr(IV) ions from simulated high-level liquid waste. The batch experiments were designed to investigate the influence of adsorption time, HNO3 concentration, initial Zr(IV) concentration, adsorbent dosage, and temperature on the adsorption behavior of Zr(IV). The results indicate that the adsorption equilibrium time of mesoporous silica materials was approximately 8 h, and all the adsorption processes followed the pseudo-second-order kinetics equation. The isotherms of Zr(IV) adsorption by KIT-6 exhibited good agreement with the Langmuir model, while the Freundlich model could be utilized to fit the adsorption on HMS, MCM-41, and SiO2-70 Å. The adsorption capacity of MCM-41 for Zr(IV) in 3 mol/L HNO3 was 54.91 mg/g, which is three times the adsorption capacity reported for commercial silica gel (17.91 mg/g). The thermodynamic parameters indicate that the adsorption processes for zirconium are endothermic reactions. Furthermore, the mesoporous silicas exhibited a pronounced selectivity in the adsorption of Zr(IV) within a simulated high-level liquid waste containing 10 co-existing cations (3 mol/L HNO3). This suggests that mesoporous silicas have great potential for Zr(IV) removal in actual radioactive liquids with high acidity during spent fuel reprocessing.

Study on Dynamic Column Behavior and Complexation Mechanism of DBS-Modified Crown Ether-Based Silica to 90Sr.

A crown ether-loaded hybrid adsorbent suitable for the separation and enrichment of strontium from high-level liquid waste was synthesized. 4',4'(5″)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) and its modifiers dodecyl benzenesulfonic acid (DBS) and 1-dodecanol were impregnated into silica-based polymer support. The hybrid adsorbent exhibited excellent Sr(II) selectivity ability, and effective chromatographic separation and recovery of Sr(II) from simulated high-level liquid waste could be achieved with a (DtBuCH18C6 + DBS + dodec)/SiO2-P packed column. The recovery rate of Sr(II) calculated based on the mass balance was approximately 99% and over 80% for the other coexisting metal ions. An appropriate increase in the concentration of Na-DTPA eluent was favorable to improve the efficiency of the elution process because of the increased complexation capacity of [DTPA]5- to Sr(II). The developed theoretical model can simulate the dynamic breakthrough curves of the material on the basis of short column data, thereby predicting the scale-up column of the practical operation. Density functional theory calculation was used to explore the action mechanism of DBS modifiers on the Sr(II) complexation process of crown ether groups. Two Sr(II) complexation isomeric models of DtBuCH18C6 were established, and the calculation results revealed a similar complexation ability. DtBuCH18C6 could form a stable Sr(II) complexation structure with DBS coordination, which further indicated that DBS could be a ligand to promote the Sr(II) adsorption ability of crown ether materials.

Precipitation behaviour of simulated high-level liquid waste during the denitration process based on two-step vitrification

In the two-step vitrification process, it is necessary to first reduce the acidity of the waste before calcination. In this study, the influence of formic acid as a denitration agent on the precipitation behavior of a simulated high-level liquid waste during denitration was investigated. The denitration process was conducted at a temperature of 90℃, and the denitration ratio ranged from 1.0 to 2.0. The denitration products were analyzed using various techniques including ICP-OES, XRF, SEM-EDS, Raman, and XRD. The results revealed a significant decrease in nitrate content after denitration when the denitration ratio was between 1.0 and 2.0. As the denitration ratio increased, the nitrate content progressively decreased, while the formic acid content increased. A denitration precipitate containing elements such as Zr, Mo, La, Ce, Nd, Fe, Te, Pr, Cs, Sm, Sr, Y, Co, and Ni was observed. The content of each component and the morphology of the precipitate were found to be correlated with the denitration ratio. Crystallization of MoO2 and Ln2Zr3(MoO4)9 (Ln = La, Ce, Nd, Pr, Sm) in the precipitation occurred when the denitration ratio was between 1.0 and 1.2. On the other hand, predominantly rod-shaped particles (Ln(HCOO)3, Ln = La, Ce, Pr, Nd, Sm) were formed when the denitration ratio was 1.4 or higher.

Adsorption behavior of platinum-group metals and Co-existing metal ions from simulated high-level liquid waste using HONTA and Crea impregnated adsorbent

The volume and toxicity of radioactive waste can be decreased by separating the components of high-level liquid waste according to their properties. An impregnated silica-based adsorbent was prepared in this study by combining N,N,N′,N′,N″,N″-hexa-n-octylnitrilotriacetamide (HONTA) extractant, N′,N′-di-n-hexyl-thiodiglycolamide (Crea) extractant, and macroporous silica polymer composite particles (SiO2–P). The performance of platinum-group metals adsorption and separation on prepared (HONTA + Crea)/SiO2–P adsorbent was then assessed together with that of co-existing metal ions by batch-adsorption and chromatographic separation studies. From the batch-adsorption experiment results, (HONTA + Crea)/SiO2–P adsorbent showed high adsorption performance of Pd(II) owing to an affinity between Pd(II) and Crea extractant based on the Hard and Soft Acids and Bases theory. Additionally, significant adsorption performance was observed toward Zr(IV) and Mo(VI). Compared with studies using the Crea extractant, the high adsorption performance of Zr(IV) and Mo(VI) is attributed to the HONTA extractant. As revealed from the chromatographic experiment results, most of Pd(II) was recovered from the feed solution using 0.2 M thiourea in 0.1 M HNO3. Additionally, the possibility of recovery of Zr(IV), Mo(VI), and Re(VII) was observed using the (HONTA + Crea)/SiO2–P adsorbent.

Silica-based covalent organic framework composite for efficient separation and enrichment of palladium and its heterogeneous catalysis application

Considering the necessity and challenge in palladium recovery from high-level liquid waste and hydrogen energy development, the first attempt was made to adsorb Pd(II) from simulated high-level liquid waste firstly, then to achieve in situ reduction by a simple method and followed by using it directly for efficient hydrogen production through the catalytic decomposition of formic acid. In this work, a composite of covalent organic framework and SiO2 (Tp-Azo-COF/SiO2) was prepared by wet impregnation method using SiO2 as a carrier. The characteristics of the composite were examined by SEM, EDS, BET, TG, XRD, etc. The results showed that Tp-Azo-COF/SiO2 exhibited regular silicon-based spherical shapes in microscopic form and good heat resistance. In batch experiments, Tp-Azo-COF/SiO2 was demonstrated excellent adsorption and selectivity for Pd(II) at a wide range of HNO3 acidity (1–5 M), and the separation factor was as high as 2653 at 3 M HNO3. Tp-Azo-COF/SiO2 was able to reach a maximum adsorption capacity of 85.40 mg/g at 120 min at 298 K in 3 M HNO3. FT-IR and XPS analysis show that the adsorption mechanism of Pd(II) by the composite occurs mainly on the C-NH of Tp-Azo-COF, and NO3– is also involved in the coordination. In dynamic column experiments, Tp-Azo-COF/SiO2 was demonstrated a nearly complete separation and recovery of Pd(II) with good reusability, and the enrichment coefficients all maintained at about 30. Finally, an efficient and environmentally friendly process was proposed to achieve the in situ reduction of Pd(II)-loaded Tp-Azo-COF/SiO2. Pd-loaded Tp-Azo-COF/SiO2 was demonstrated better decomposition performance than commercial Pd-based catalysts hydrogen production by the catalytic decomposition formic acid.

A functionalized ionic compound for the extraction of ReO4−/TcO4− from highly acidic environment

Selective extraction of TcO4− from high-level liquid waste (HLLW) is essential for spent fuel reprocessing but most of the available extractants can't effectively extract TcO4− from highly acidic environment. In this manuscript, a functionalized ionic compound (I-TPyam) that contains the amide group was synthesized, which can efficiently extract ReO4− from highly acidic environment. 0.3 M I-TPyam solution can extract 97.3 % and 88.0 % of ReO4− from ReO4− solutions that contains 1 M and 3 M nitric acid. Even in more realistic simulated HLLW that contains 22 metal ions and 2.5 M HNO3, it can still extract 87.0 % of the Re. This performance can be further improved by two-stage extraction or denitration treatment, with extraction efficiency increased to 94.9 % and 96.4 %, respectively. Besides, this extractant can also effectively extract Re from neutral ReO4− solution and simulated LAW, with distribution ratio reached 10,468 and 246, respectively. A small portion of Mo will be co-extracted but can be selectively stripped in the stripping process. Our XPS experiments, along with DFT simulations highlighted the predominate role of pyridinium and amide groups in Re (Tc) extraction, revealed the driving forces and explained why I-TPyam prefer to extract ReO4− instead of NO3−.

Vitrification of simulated high-level liquid waste by laser

Vitrification of simulated high-level liquid waste by laser

Fast removal of strontium from nitric acid solution using an acid-resistant silica-based adsorbent

To efficiently separate strontium (Sr) from simulated high level liquid waste (HLLW), a novel acid-resistant inorganic-organic hybrid adsorbent, named as HEMAP/SiO2-P, was prepared by loading 2-hydroxyethyl-2-methyl-2-propenoate phosphate (HEMAP) into styrene-divinylbenzene modified silica (SiO2-P) with vacuum impregnation method. The experimental results showed that the adsorbent exhibited good adsorption selectivity with the SFSr/metal ions over 64.2 in 3 M HNO3 simulated HLLW. In addition, the adsorption of Sr by the adsorbent was in accordance with the pseudo-second-order kinetic model and the Langmuir isotherm model, and the adsorption equilibrium was obtained within 1 min with the saturation adsorption capacity of 61.2 mg/g. The adsorption of Sr was not markedly changed with increasing temperature. Furthermore, the results of adsorption experiments, characterization analysis, extraction experiments and density functional theory (DFT) calculations revealed that two organic ligand molecules were coordinated with one Sr molecule and simultaneously involved two nitrate molecules to maintain the charge balance during the adsorption process.

Cyclohexyl substituted diglycolamide ligands for highly efficient separation of strontium: Synthesis, extraction and crystallography studies

A series of novel diglycolamide (DGA) ligands containing cyclohexyl substituent on the amidic N atom were investigated for their solvent extraction and complexation ability toward Sr2+ in HNO3 solution. Compared with the most commonly used N,N,N′,N′-tetraoctyldiglycolamide (TODGA), the introduction of cyclohexyl substituent into the DGA skeleton can significantly enhance the extractability toward Sr2+ in the case of toluene as the diluent. And the more cyclohexyl substituents there are, the more significant the effect is. About 8−80 fold increase of the Sr2+ distribution value for LI−LVI ligands can be achieved than that for TODGA at 2.0 mol/L HNO3. The extractability of these cyclohexyl substituted DGA ligands follows the order of LI ≈ LIII > LII > LIV > LV > LVI > > TODGA. Meanwhile, for the DGA ligands with the same number of cyclohexyl substituents, LIII with moderate alkyl chain length (n-butyl) has higher extractability than LII with short chain (n-ethyl) and LIV with long chain (n-octyl). Slope analysis reveals the formation of 1:3 metal-ligand extracted species during the extraction process, which is also confirmed by the results obtained from ESI-MS, FT-IR and single-crystal X-ray diffraction analyses. Furthermore, the single crystal of DGA ligand with Sr(NO3)2 was obtained for the first time, and the analysis of its structure indicates that each DGA molecule participates in the complexation with the 9-fold coordinated Sr2+ through two amide carbonyl O atoms and one ether O atom, accompanied by two free NO3− in the outer coordination sphere. The extraction of Sr2+ by the novel DGA ligand is a spontaneous and exothermic process of increasing entropy, and follows neutral complexing extraction model. In addition, an extraction test of Sr2+ from simulated high level liquid waste was also carried out and demonstrates a highly efficient and selective separation of Sr2+ over the other co-existing ions.

Efficient separation of strontium in different environments with novel acid-resistant silica-based ion exchanger

Radioactive strontium (90Sr) is widespreadly concerned due to its high biochemical toxicity, relatively long half-life, high fission yield and potential special applications in heat source and medical field. Herein, a novel acid-resistant silica-based adsorbent Sb2O5/SiO2 was prepared by a two-step method, i.e. vacuum impregnation followed by oxidation. The adsorbent was characterized by XRD, SEM, TEM, EDS, BET, FT-IR and XPS techniques, which revealed its characterization of small particle size (75–150 μm), abundant functional groups and well-crystallized structure. The experimental results revealed Sb2O5/SiO2 exhibited good adsorption selectivity for Sr in pH 9–3 M HNO3 solution, the adsorption equilibriums were obtained within 5 min in pH 6 solution and 30 min in 1 M HNO3 solution with the adsorption capacities of 160.6 mg/g and 51.8 mg/g, respectively. Moreover, it also demonstrated good application potential in medical isotope preparation area as efficient strontium-yttrium (Sr-Y) separation was achieved with the separation factor over 7769 in pH 6 solution. Furthermore, the column experiments confirmed that Sr could be effectively removed both in seawater and simulated high level liquid waste (HLLW), and the purity of Y could reach to 99.7 % in Sr-Y separation. Finally, density functional theory (DFT) calculations confirmed that the adsorption mechanism was ion exchange between Sr(II) and H+ (in Sb-OH), and the adsorption was accompanied by the transfer of charge and the decrease of adsorption energy.

Efficient separation of palladium from nitric acid solution by a novel silica-based ion exchanger with ultrahigh adsorption selectivity

Palladium (Pd) in high level liquid waste (HLLW) is a valuable alternative resource besides its natural reserves. On the other hand, the presence of Pd has extremely negative impacts on the vitrification process of HLLW. To separate Pd from HLLW, a novel silica-based adsorbent named HEMAP/SiO2-P was designed and prepared by using 2-hydroxyethyl-2-methyl-2-propenoate phosphate as the functional group donor, dichloromethane as the diluent and styrene–divinylbenzene modified silica particle as the carrier. The experimental results reveal that HEMAP/SiO2-P possesses excellent adsorption selectivity (SFPd/other metals > 183.2) and large adsorption capacity (393.4 mg/g) towards Pd in 1 M HNO3 solution. Moreover, column experiments show that the adsorbent can effectively separate Pd from other coexisting metal ions in simulated HLLW with the recovery yield of 99.4%. The experimental and characterization analyses as well as DFT calculations confirm that the adsorption mechanism involves ion exchange between Pd(II) and H+ (in P-OH) accompanied by the transfer of charge.