Separation and Recovery of Cs from High Active Waste Simulant using Resorcinol Formaldehyde Polycondensate Resin: Batch and Column Studies

Resorcinol formaldehyde polycondensate resin has been extensively used for the separation of ¹³⁷Cs from low and medium active alkaline waste solutions. The present study examines the suitability of the resin for separation of Cs from high active solutions. Batch uptake of Cs by RFPR has been evaluated from test solutions containing varying Na (0.6–3.0 M) and Cs (1.00 × 10^?4 to 0.10 M) concentrations. Batch results have been used to establish Cs exchange isotherms of the resin and were found to follow Freundlich as well as Dubinin-Radushkevich (D-R) isotherm equations. The loading behavior of Cs on RFPR column has been evaluated by conducting five column runs using different Cs bearing solutions. Based on these results, it is concluded that the D-R equation can be used to predict saturated loading of Cs in the column. The saturation loading of Cs on 1 L bed was estimated to be as high as 13 g and 34 g from feed solution containing Cs concentration 2.57 × 10^?4 and 4.30 × 10^?3 mol/L respectively. Sequential elution of Na and Cs resulted in a high Cs bearing concentrate containing very low concentration of sodium. This study is relevant in the preparation of gamma source for radiation technology applications after immobilization of the concentrate in glass.     

Potassium hexacyanocobalt ferrate and ammonium molybdophosphate sorption bags for the removal of 137Cs from aqueous solutions and a simulated waste

In the present study, the removal and immobilization of ¹³⁷Cs from aqueous waste solutions and a simulated waste was investigated. Two inorganic ion‐exchange complexes: di‐potassium hexacyanocobalt(II)‐ferrate(II), K₂CoFe(CN)_6·xH₂O (KCFC), and ammonium‐12‐molybdophosphate [(NH₄)₃PMo₁₂O_40·aq] (AMP), were charged separately into porous nylon bags (sorption bags) of 5 µm pore diameter. The first complex (KCFC) was prepared in our laboratory. The second (AMP) was used for comparison. Easy handling and increased potential for reuse characterize the sorption bag technique. The KCFC complex was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA), porosity, infra‐red (IR) and X‐ray powder diffraction (XRD). The chemical and structural investigations revealed that the KCFC complex has adequate ion‐exchange capacity and high affinity for ¹³⁷Cs. The sorption bag technique showed promising results for the removal of ¹³⁷Cs from aqueous waste solutions. The KCFC bags showed the highest ¹³⁷Cs removal (～0.91 g g^?1), at pH 8.5; AMP bags gave the highest ¹³⁷Cs removal (～0.97 g g^?1) in 0.1 N HNO₃ and 1.5 N HNO₃, both with a waste: sorbent ratio of 80 cm³ g^?1. Sorption data for both KCFC and AMP revealed a good fit to the Freundlich sorption isotherm. To assess the potential of sorption bags, the used bags were regenerated in different leachants and reused in further sorption investigations. ¹³⁷Cs recovery from the used sorbents was ～0.46 g g^?1 using 6 N HCl as leachant for AMP, compared with ～0.253 g g^?1 for KCFC using 6 N NaCl. These results indicated stronger cesium immobilization in the KCFC complex. Copyright © 2003 Society of Chemical Industry     

Multiple Ion Exchange Column Tests for Cesium (CS+) Removal from Hanford Site Tank 241‐AW‐101 with SuperLig® 644 Resin

Abstract

Six cycles of loading, elution, and regeneration were performed to remove cesium (Cs⁺) from a Hanford Site tank waste sample using SuperLig^® 644 resin. The sample, which was retrieved from Tank 241‐AW‐101, was diluted to 5.09 M Na⁺ and processed through dual ion exchange columns to remove ¹³⁷Cs. Each column had an inside diameter of 1.45 cm and a height of 30 cm; and contained 15 mL of wet resin in the sodium form. The columns, designated as primary (lead) and polishing (lag), were connected in series during loading, but they were separated during elution and regeneration. The cesium loading on the primary column during the six cycles ranged from 160 to 225 bed volumes (BV) at <50% breakthrough. A gradual decline of the resin loading performances was observed as a function of number of loading cycles. For all cycles, the percent removal of cesium (¹³⁷Cs) was greater than 99.99% and the decontamination factors (DFs) achieved were higher than 1.0 × 10⁴. Elution of the resin with 0.5 M nitric acid at 25 ± 2°C was effective. Approximately 99% of the ¹³⁷Cs bound on the resin was eluted with less than 15 BV of the eluent (0.5 M nitric acid). The cumulative dose absorbed by the resin in the primary column was 1.99 × 10⁷ rad with a 20% loss of ion exchange capacity was at 50% breakthrough after completing six loading cycles.     

Adsorption of Radioactive Ions 137Cs+, 85Sr2+, and 60Co2+ on Natural Magnetite and Hematite

Abstract

Natural magnetite and hematite have been used as granular sorbents for ¹³⁷Cs⁺, ⁸⁵Sr²⁺, and ⁶⁰Co²⁺ at tracer concentration levels in aqueous solutions of constant pH (range 2–10) at 25°C. The kinetics of adsorption, up to the first 60 to 90 min, followed a first-order equation. At pH 6–8 about 50% Cs, 30% Co, and 18% Sr is removed from the solution with magnetite and 78% Co with hematite. The difference in the sorption capabilities of magnetite and hematite is discussed in terms of crystal structures of these oxides.     

Effect of particle size on cesium exchange kinetics by K-depleted phlogopite

Cation exchange mechanism and rate of Cs⁺ exchange were investigated in < 2 μm and 20–2 μm particle size fractions of K-depleted phlogopite (Na-phlogopite). The K-depleted phlogopite was prepared from a natural phlogopite by a potassium removal method using sodium tetraphenylborate (NaTPB) at room temperature. X-ray diffraction (XRD) patterns revealed that interlayer K⁺ ions were completely replaced with sodium ions after the potassium removal treatment. Ion exchange isotherms and kinetics were determined for Na⁺ → Cs⁺ exchange with two particle size fractions. The isotherms indicated that both particle size fractions showed high selectivity for Cs⁺. Based on the isotherm tests, ΔG^o values of < 2 μm and 20–2 μm particle fractions were − 6.83 kJ/mol and − 7.08 kJ/mol, respectively. Kinetics of Cs exchange revealed that the 20–2 μm particle size fraction of the K-depleted phlogopite took up more Cs⁺ ions than the < 2 μm particle size fraction. Various kinetic models were applied to describe Na⁺ → Cs⁺ exchange process. Elovich model described the kinetic data of the < 2 μm particle size fraction well, while the modified first-order model or parabolic diffusion model described the data of the 20–2 μm particle size fraction well.     

Long-term diffusion experiment at Mont Terri: first results from field and laboratory data

The diffusion of radionuclides is an important safety aspect for nuclear waste disposal in argillaceous host rocks. A long-term diffusion experiment, termed DI-A, is being carried out at the Mont Terri Rock Laboratory in the Opalinus Clay formation. The aim of this experiment is the understanding of the migration and sorption behaviour of cationic and anionic species in consolidated clays. This study reports on the experimental layout and the first results obtained from the DI-A experiment, which include the investigation of HTO, ²²Na⁺, Cs⁺, and I⁻ migration during a period of 1 year by analysing these tracers in the water circulating in the borehole. In addition, results obtained from through-diffusion experiments on small-sized samples with HTO, I⁻, and ³⁶Cl⁻ are presented.The decrease of tracer concentrations in the borehole is fastest for Cs⁺, followed by ²²Na⁺, HTO, and finally I⁻. The chemical composition of the artificial pore water in the borehole shows very little variation with time, thus indicating almost no chemical disturbance around the borehole.Through-diffusion experiments in the laboratory that were performed parallel to the bedding plane with two different methods yielded effective diffusion coefficients for HTO of 4–5×10⁻¹¹ m² s⁻¹ and significantly lower ones for anions Cl⁻ and I⁻ (0.7–1.6×10⁻¹¹ m² s⁻¹). The results indicate the importance of anion exclusion effects arising from the negatively charged clay surfaces. Furthermore, they demonstrate the anisotropic diffusion properties of the clay formation with significantly increased diffusion rates parallel to bedding relative to the perpendicular direction.The tracer data of the in situ experiment were successfully described with 2D diffusion models using diffusion and sorption parameters obtained from the above mentioned and other laboratory studies. The modelling results indicate that HTO and I⁻ diffused with no retardation. The retardation of Na⁺ and Cs⁺ could be described by empirical sorption expressions from previously derived batch sorption (Cs⁺) or diffusion (Na⁺) experiments.Overall, the obtained results demonstrate the feasibility of the technical concept to study the diffusion of non-sorbing and sorbing tracers in consolidated clays.     

Uptake of cesium and strontium cations by potassium-depleted phlogopite

Phlogopite mica was equilibrated with 1.0 N sodium chloride (NaCl)–0.2 N sodium tetraphenylborate (NaTPB)–0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at room temperature resulting in an almost complete removal (92%) of the mica's interlayer K. X-ray powder diffraction analysis provides additional evidence that hydrated Na⁺ ions had almost completely replaced the interlayer K⁺. Following equilibration, the c-axis spacing of the mica increased from 10.0 Å to approximately 12.2 Å. Cesium and Sr ion exchange isotherms indicate that K-depleted phlogopite is highly selective for both elements, the Cs⁺ exchange capacity is 1.26 meq/g or 65% of the theoretical cation exchange capacity and the Sr²⁺ exchange capacity is 1.94 meq/g or 100% of the theoretical exchange capacity of the mica. Kielland plots indicated that the mica was selective for Cs⁺ when the equivalent exchange capacity of Cs⁺ in the exchanger phase (X¯_Cs) was < 0.66 and selective for Sr²⁺ when X¯_Sr < 0.41. At equivalent fractions greater than these levels, layer collapse and/or steric effects limit the diffusion of these ions into the interlayers of the mica. Analysis of the Cs⁺ equilibrated mica utilizing XRD indicated that a collapse of the c-axis spacing had occurred. Based on the high selectivity of < 45-μm K-depleted phlogopite for Sr²⁺ and Cs⁺, this material may prove useful as an inorganic ion exchanger for these radioactive isotopes.     

Chitosan-ferrocyanide sorbents for concentrating Cs-137 from seawater

Chitosan-ferrocyanide sorbents (CFS) based on ferrocyanides Ni-K, Cu-K and Zn-K for concentrating Cs-137 from the seawater have been obtained. Sorbent CFS Zn-K can be used in sorption-regeneration cycle using 5 M solution of NH₄NO₃ as the eluent. In dynamic condition, the sorption efficiency of Cs-137 and the elution for the CFS Zn-K exceeds 95%. The two-staged scheme of Cs-137 concentrating from seawater is suggested. First stage is the removal of radionuclide from seawater by the CFS Zn-K sorbent, and the second stage is the sorption of Cs-137 from eluate by the CFS Ni-K sorbent.     

Simultaneous removal of the radiotoxic nuclides Cs and I from aqueous solution

The simultaneous removal of cationic and anionic radiotoxic nuclides such as Cs¹³⁷ and I¹²⁹ from radioactive liquid wastes has been studied. As an adsorbent material, the mixture of activated carbon and chabazite zeolite was used. The mixing ratio of 7:3 of activated carbon to chabazite in weight fraction was found to be optimum under the most conservative condition for the Cs⁺ and I⁻ concentration ratio. Experimental data and surface analysis indicated that Cs⁺ adsorbed onto the activated carbon surface caused a synergistic effect on the adsorption of I⁻. The effect of background electrolytes, namely Na⁺ and Cl⁻, on the Cs⁺ isotherm was minute over the whole range of equilibrium concentrations, whereas that on the I⁻ isotherm was greater at lower equilibrium concentrations. A dynamic model was proposed, based on surface diffusion and competitive adsorption. The breakthrough behaviors of Cs⁺ and I⁻ in the column, charged with the mixed adsorbent, were predicted satisfactorily by the proposed dynamic model.     

Use of chitosan derivatives as solid phase extractors for metal ions

This paper shows a comparative study between the two radiation grafted chitosan derivatives viz. cross-linked chitosan (CRC) and cross-linked chitosan after hydrolysis (CRCH). These chitosan derivatives were used as solid phase extractors for several radionuclides. The uptake of ¹³⁷Cs, ^85,89Sr, ¹⁵²Eu, ²⁴¹Am, ²³⁴Th and ²³³U by CRCH and CRC was studied using batch and column methods. The K_d, exchange capacity, breakthrough capacity for different metal ions with the functionalized polymers were determined. The uptake followed the following trend: UO₂²⁺>Th⁴⁺>Cs⁺>Eu³⁺>Am³⁺>Sr²⁺ for both sorbents. It was seen that CRCH has a greater uptake of metal ions compated to CRC but CRC was more selective of the two.     

Alginate and Algal-Based Beads for the Sorption of Metal Cations: Cu(II) and Pb(II)

Alginate and algal-biomass (Laminaria digitata) beads were prepared by homogeneous Ca ionotropic gelation. In addition, glutaraldehyde-crosslinked poly (ethyleneimine) (PEI) was incorporated into algal beads. The three sorbents were characterized by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX): the sorption occurs in the whole mass of the sorbents. Sorption experiments were conducted to evaluate the impact of pH, sorption isotherms, and uptake kinetics. A special attention was paid to the effect of drying (air-drying vs. freeze-drying) on the mass transfer properties. For alginate, freeze drying is required for maintaining the porosity of the hydrogel, while for algal-based sorbents the swelling of the material minimizes the impact of the drying procedure. The maximum sorption capacities observed from experiments were 415, 296 and 218 mg Pb g⁻¹ and 112, 77 and 67 mg Cu g⁻¹ for alginate, algal and algal/PEI beads respectively. Though the sorption capacities of algal-beads decreased slightly (compared to alginate beads), the greener and cheaper one-pot synthesis of algal beads makes this sorbent more competitive for environmental applications. PEI in algal beads decreases the sorption properties in the case of the sorption of metal cations under selected experimental conditions.     

Examination of the use of synthetic Zeolite NaA–X blend as backfill material in a radioactive waste disposal facility: Thermodynamic approach

The underground disposal of radioactive waste is based upon a multibarrier concept. For long-term performance assessment of radioactive repositories, knowledge concerning the sorption of radionuclides in backfill materials is required. As a part of the multibarrier system for effective isolation of radioactive waste in a repository, Zeolite NaA–X blend was prepared from fly ash, characterized, and evaluated to be used as a backfill material. In this concern, the sorption behavior of Cs⁺ on the prepared material as a function of pH, initial ion concentration and temperature was studied by batch technique. The sorption isotherm data was interpreted by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. The application of the Langmuir isotherm yielded monolayer capacity of 1546 mmol/kg at 298 K while the maximum sorption capacity predicted by D–R isotherm was of 2446 mmol/kg. Thermodynamic parameters for the sorption system were determined at three different temperatures. The enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) of sorption at 298 K were found to be 25.43 kJ/mol, 93 J/mol K and −2.316 kJ/mol, respectively. The positive value of ΔH° corresponds to the endothermic nature of the sorption process. The numerical value of ΔG° decreases with an increase in temperature indicating that the sorption was spontaneous and more favorable at higher temperatures.     

Effects of the orientation of smectite particles and ionic strength on diffusion and activation enthalpies of I and Cs ions in compacted smectite

The apparent diffusion coefficients (D_a) for I⁻ and Cs⁺ ions in compacted Na-smectite which is a major constituent clay mineral of bentonite were studied as a function of smectite's dry density (0.9–1.4 Mg/m³), ionic strength ([NaCl] = 0.01, 0.51 M), temperature (22–60 °C) and diffusion direction to the orientated direction of smectite particles. The Na-smectite was prepared by ion-exchanging with Na⁺ ions a Na-bentonite, Kunipia-F®, of which smectite content is over 99 wt.%. The D_a-values for both ions showed a tendency to be higher in the parallel direction than in the perpendicular direction to the orientated direction of smectite particles at a low-ionic strength of [NaCl] = 0.01 M. The D_a-values for I⁻ ions showed different trends depending on diffusion direction and dry density at a high-ionic strength of [NaCl] = 0.51 M. Namely, although the D_a-values for I⁻ ions showed a tendency to be higher in the parallel direction than in the perpendicular direction to the orientated direction of smectite particles at a high-dry density of 1.4 Mg/m³, these showed a reciprocal tendency at dry densities of 0.9–1.0 Mg/m³. The D_a-values for Cs⁺ ions uniformly increased with an increase of ionic strength in both diffusion directions. Considering electrostatic effect from smectite surface and the change in tortuosity on dry density, ionic strength and diffusion direction to the orientated direction of smectite particles, I⁻ ions are considered to mainly diffuse in interstitial pores. While, Cs⁺ ions can diffuse in both interlayer and interstitial pores, and the D_a-values are considered to have elevated by competing with Na⁺ ions. The activation enthalpies (ΔE_a) for I⁻ ions, slightly higher (ΔE_a = 19.8−20.0 kJ/mol) than that of the diffusion coefficient in free water (D^o) for I⁻ ions (ΔE_a = 17.36 kJ/mol) at a low-ionic strength of [NaCl] = 0.01 M, decreased with an increase of ionic strength, became of similar level to that of the D^o at a high-ionic strength of [NaCl] = 0.51 M, increased with an increase of dry density. On the contrary, the ΔE_a-values for Cs⁺ ions, clearly higher (ΔE_a = 25.6−28.4 kJ/mol) than that of the D^o for Cs⁺ ions (ΔE_a = 16.47 kJ/mol) even in low-dry density over the ionic strength, increased with an increase of dry density. The ΔE_a-values for Cs⁺ ions are considered to be due to the decrease in the activity of porewater in addition to the effect of ion exchange enthalpy between Cs⁺ and Na⁺ ions in smectite.     

Thermodynamics of Cesium Extraction from Acidic Media by HCCD and PEG

Abstract

In this study, details of cesium extraction from nitrate media using chlorinated cobalt dicarbollide (HCCD) dissolved in the polar phenyl trifluoromethyl sulfone (FS-13) diluent have been examined. It has been verified that Cs⁺ phase transfer is based solely on cation exchange (H⁺ for Cs⁺) that is, that a previously reported nitrate dependency arises from nonideal behavior of solute species. The enthalpy and entropy of the system calculated using appropriate corrections to the van't Hoff analysis are found to be in good agreement with independently measured calorimetry results. Finally, it is demonstrated that synergistic extraction of Cs⁺ by HCCD and PEG does not occur. Although there is a definite interaction between HCCD and PEG (and it is well established that this interaction is responsible for the extraction of Sr²⁺), this association is actually antagonistic to the extraction of Cs⁺.     

Recovery of 137Cs from Laboratory Waste using Solvent Extraction with Sodium Tetraphenylboron (TPB)

The paper describes a method for the recovery of ¹³⁷Cs from an aqueous radioactive laboratory waste solution containing ¹³⁷Cs (2 µg/mL) in the presence of high concentration of Na⁺ using solvent extraction technique. The method comprises of adjustment of pH to the acidic range (pH = 2), contacting the aqueous radioactive solution with sodium tetraphenylboron (TPB) in nitrobenzene, whereby ¹³⁷Cs binds with tetraphenylboron anions and gets separated. Results of this investigation indicate that ¹³⁷Cs could be efficiently and selectively extracted from an aqueous solution media containing high concentration of Na⁺ under mildly acidic pH into an organic phase and back extracted with small volume of 3 M HNO₃, thus enabling concentration. The proposed method was successfully applied in real samples.     

A new composite of crystalline silicotitanate for sequestration of 137Cs and 90Sr from low-level aqueous waste solution

ABSTRACT

A new composite of crystalline silicotitanate (CST) has been synthesized for the sequestration of Cs and Sr from low-level liquid waste generated in the nuclear industry. The product characterization using X-RAY DEFRACTION (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of CST crystals in the composite. Sorption studies carried out under various test conditions showed that the composite has high affinity for both Cs and Sr. Results of structural characterization of Cs and Sr-loaded CST indicated that the overall structural integrity remained intact after substitution of Na⁺ by Cs⁺ or Sr²⁺. The exceedingly good Cs and Sr sorption performance displayed by the CST composite will find applications in the treatment of nuclear waste.     

Preparation and near-infrared photothermal conversion property of cesium tungsten oxide nanoparticles

Cs_0.33WO₃ nanoparticles have been prepared successfully by a stirred bead milling process. By grinding micro-sized coarse powder with grinding beads of 50 μm in diameter, the mean hydrodynamic diameter of Cs_0.33WO₃ powder could be reduced to about 50 nm in 3 h, and a stable aqueous dispersion could be obtained at pH 8 via electrostatic repulsion mechanism. After grinding, the resulting Cs_0.33WO₃ nanoparticles retained the hexagonal structure and had no significant contaminants from grinding beads. Furthermore, they exhibited a strong characteristic absorption and an excellent photothermal conversion property in the near-infrared (NIR) region, owing to the free electrons or polarons. Also, the NIR absorption and photothermal conversion property became more significant with decreasing particle size or increasing particle concentration. When the concentration of Cs_0.33WO₃ nanoparticles was 0.08 wt.%, the solution temperature had a significant increase of above 30°C in 10 min under NIR irradiation (808 nm, 2.47 W/cm²). In addition, they had a photothermal conversion efficiency of about 73% and possessed excellent photothermal stability. Such an effective NIR absorption and photothermal conversion nanomaterial not only was useful in the NIR shielding, but also might find great potential in biomedical application.     

Rapid transformation from Cs-geopolymers to Cs-defined ceramics by microwave sintering

Cs-defined ceramics are considered to be ideal solidification forms for ¹³⁷Cs with high solubility, high volatility, and high mobility in Cs-containing nuclear wastes. In this study, a process consisting of low-temperature solidification and subsequent rapid microwave sintering was proposed to treat the simulated nuclide ¹³⁷Cs. Cs-geopolymer (CsGP) precursors were first prepared to form solidified forms containing simulated ¹³⁷Cs under ambient conditions. Afterwards, a rapid transformation from CsGP to Cs-defined ceramics was realized by microwave sintering below 1100 °C for 30 min, which could effectively avoid the Cs volatility while Cs entered into Cs-defined ceramic lattices under conventionally long-term and high-temperature sintering. As-prepared Cs-defined ceramics exhibited superior chemical durability, and the normalized Cs⁺ leaching rate was as low as 3.06 × 10⁻⁴ g/(m^2.d).     

Effect of cesium content on the structure and catalytic performances of heteropoly compounds in one-step synthesis of methylmethacrylate from methacrolein

Keggin-type heteropoly compounds (HPCs) H_3.2−x Cs _x Cu_0.25As_0.1PMo₁₁VO₄₀ (x, 0–2.5) were used as catalysts for coupling reaction of methylmethacrylate (MMA) from methacrolein (MAL) in this study. And the catalytic performance of the HPCs was investigated in the oxidation-esterification coupling reaction. Moreover, the HPCs were characterized by NH₃-TPD, TG-pyridine-adsorption/desorption, N₂-adsorption/desorption, ICP, TG-DSC, FT-IR, XRD and TPR. These reactive results have been correlated to the acidity, surface area and reducibility. With the increasing of Cs content, surface area of the HPCs increased, while the acidity and reducibility decreased. Difference of the quantity of acid sites originated from the hydration protons being substituted by Cs⁺. Effects of Cs⁺ content on the reducibility of the HPCs indicated that Cs⁺ changed the structural stability of V as coordinating atoms and the proportion of the different reducible states of Mo⁶⁺.     

Rates of Exchange of Cs+ and Sr2+ for Poorly Crystalline Sodium Titanium Silicate (CST) in Nuclear Waste Systems

The compound sodium titanium silicate, popularly known as CST, is highly selective for Cs⁺. It was synthesized for the purpose of removing ¹³⁷Cs from basic nuclear waste systems. This compound has a tunnel structure in which the Cs⁺ ion just fits but diffusion through the tunnels is relatively slow. CST loses its ability to sequester Cs⁺ in the strongly basic nuclear waste solutions. However, replacement of titanium with 25 mol% of niobium increases the selectivity to a satisfactory level. It has been found that producing a less crystalline form of Nb-CST greatly improves the rate of Cs⁺ removal. Additionally, the non-niobium CST is selective for strontium both as Sr²⁺ and Sr(OH)⁺. It is suggested that both radioisotopes of cesium and strontium may be efficiently extracted by a combination of a mixture of poorly crystalline CST and Nb-CST.