Immobilization Of Cesium Research Articles

Immobilization of cesium from aqueous solution using nanoparticles of synthetic calcium phosphates

The particularities of cesium incorporation into synthetic calcium phosphates with either apatite or whitlockite-type structures were investigated using the sorption process from aqueous solution and further heating to 700 °C. The nanoparticles for sorption were prepared by wet precipitation from aqueous solutions at a fixed molar ratio of Ca/P = 1.67 and two different ratios of CO32−/PO43− (0 or 1). The obtained substituted calcium phosphates and corresponding samples after the sorption of cesium from solutions with different molar concentrations (c(Cs+) = 0.05, 0.1 and 0.25 mol L−1) were characterized by powder X-ray diffraction, FTIR spectroscopy, scanning electron microscopy and elemental analysis. Based on the combination of X-ray diffraction and elemental analyses data for the powders after sorption, the cesium incorporated in the apatite- or whitlockite-type structures and its amount increased with its concentration in the initial solution. For sodium-containing calcium phosphate even minor content of Cs+ in its composition significantly changed the general principle of its transformation under annealing at 700 °C with the formation of a mixture of α-Ca3(PO4)2 and cesium-containing apatite-related phase. The obtained results indicate the perspective of using of complex substituted calcium phosphates nanoparticles for immobilization of cesium in the stable whitlockite- or apatite-type crystal materials.

Hot isostatic pressing of potassium-magnesium-phosphate materials for cesium immobilization

Hot isostatic pressing of potassium-magnesium-phosphate materials for cesium immobilization

Cesium immobilization in (Ba,Cr)-hollandites: Effects on structure

Hollandites with compositions Ba1.15−xCs2xCr2.3Ti5.7O16 (0 ≤ x ≤ 1.15) intended for the immobilization of cesium (Cs) from nuclear waste have been prepared, characterized, and analyzed for Cs retention properties. Sol-gel synthesized powders were used for structural characterization using a combination of X-ray, neutron, and electron diffraction techniques. Phase-pure hollandites adopting tetragonal (I4/m) or monoclinic symmetry (I2/m) were observed to form in the compositional range 0 ≤ x ≤ 0.4. Structural models for the compositions, x = 0, 0.15, and 0.25 were developed from Rietveld analysis of powder diffraction data. Refined anisotropic displacement parameters (βij) for the Ba and Cs ions in the hollandite tunnels indicate local disorder of Ba/Cs along the tunnel direction. In addition, weak superlattice reflections were observed in X-ray and electron diffraction patterns that were due to the compositional modulation i.e., ordering of ions and vacancies along tunnel direction. Our overall observations suggest the phase-pure hollandites studied assumed supercell structures with ordered tunnel cations, which in turn have positional disorder in individual supercells.

A new route to the stable capture and final immobilization of radioactive cesium

Radioactive Cs released from damaged fuel materials in the event of nuclear accidents must be controlled to prevent the spreading of hazardous Cs into the environment. This study describes a simple and novel process to safely manage Cs gas by capturing it within ceramic filters and converting it into monolithic waste forms. The results of Cs trapping tests showed that CsAlSiO4 was a reaction product of gas-solid reactions between Cs gas and our ceramic filters. Monolithic waste forms were readily prepared from the Cs-trapping filters by the addition of a glass frit followed by thermal treatment at 1000°C for 3h. Major findings revealed that the Cs-trapping filters could be added up to 50wt% to form durable monoliths. In 30–50wt% of waste fraction, CsAlSiO4 was completely converted to pollucite (CsAlSi2O6), which is a potential phase for radioactive Cs due to its excellent thermal and chemical stability. A static leaching test for 28 d confirmed the excellent chemical resistance of the pollucite structure, with a Cs leaching rate as low as 7.21×10−5gm−2/d. This simple scheme of waste processing promises a new route for radioactive Cs immobilization by synthesizing pollucite-based monoliths.

Cesium and Strontium Immobilization in Portland Cement Pastes Blended With Pozzolanic Additives

The effect of incorporation of pozzolanic additives on the immobilization of cesium and strontium ions in cementitious pastes was investigated. Pastes containing Portland cement together with ground granulated blast furnace slag (GGBFS) (50%, 75%), metakaolin (MK) (10%, 20%), or silica fume (SF) (20%), either in its densified or raw form, were prepared. The transport properties of the immobilized ions through the paste were evaluated using leaching tests. Single differential thermal analysis (SDTA) was used to estimate the extent of the pozzolanic reaction and the pozzolanic reactivity of the different formulations. For strontium ions, the best immobilization system was the 20% raw silica fume (RSF) paste, characterized by the highest relative pozzolanity (RP). However, for cesium ions the most effective additive was the densified silica fume (DSF), reducing the apparent diffusion coefficient by two orders of magnitude compared to the unblended paste.

Cesium and Strontium Retentions Governed by Aluminosilicate Gel in Alkali-Activated Cements.

The present study investigates the retention mechanisms of cesium and strontium for alkali-activated cements. Retention mechanisms such as adsorption and precipitation were examined in light of chemical interactions. Batch adsorption experiments and multi-technical characterizations by using X-ray diffraction, zeta potential measurements, and the N2 gas adsorption/desorption methods were conducted for this purpose. Strontium was found to crystalize in alkali-activated cements, while no cesium-bearing crystalline phases were detected. The adsorption kinetics of alkali-activated cements having relatively high adsorption capacities were compatible with pseudo-second-order kinetic model, thereby suggesting that it is governed by complex multistep adsorption. The results provide new insight, demonstrating that characteristics of aluminosilicate gel with a highly negatively charged surface and high micropore surface area facilitated more effective immobilization of cesium and strontium in comparison with calcium silicate hydrates.

The study on preparing absorbent of potassium nickel hexacyanoferrate (II) loaded zeolite for removal of cesium from radioactive waste solutions and stable solidification method for those spent absorbents

The development of cesium selective adsorbent is urgent subject for the decontamination of intermediate and high level water from nuclear facilities especially in nuclear accidents. For the selective adsorption and stable immobilization of radioactive cesium, K-Ni- hexacyanoferrate (II) loaded zeolite (FCzeolite) (synthesized zeolite of Hanoi University of Science and Technology) were prepared by impregnation/precipitation method. The ion exchange equilibrium of Cs+ for composites FC-zeolite was attained within 5 h and estimated to be above 97% in Cs+ 100mg/l solution at pH: 4-10. Ion exchange capacity of Cs+ ions (Qmax) for FC-zeoliteX was reached 158.7 and 98.0 mg/g in pure water and sea water respectively. Those values for FC-zeolite A was 103.1 and 63.7 mg/g. Decontamination factor (DF) of FC-zeolite X for 134Cs was 149.7 và 107.5 in pure water and sea water respectively. Initial radioactivity of 134Cs ion solution infect to decontamination factor. KNiFC-zeolite X after uptaked Cs (CsFC- zeolite X) was solidificated in optimal experimental conditions: Mixing CsFC-zeolite X with additive of Na2B4O7 (5%), temperature calcined 900oC for 2h in air. Solid forms was determined some of parameters: Cs immobilization, mechanical stability, volume reduction after calcination (%) and leaching rate of Cs+ ions in solution.

Mechanochemical processing K 2 CO 3 /Cs 2 CO 3 -cellulose and kaolinite for the formation of water-insoluble Cs-compound

Abstract The aim of this work is to develop a novel method for the immobilization of radioactive cesium (Cs) compound, and this can be applied to the treatment of real biomass items contaminated with Cs which had spread over a wide area from the Fukushima Daiichi Nuclear Power Station in March 2011 in Japan. In the same group of alkali metal Cs, potassium (K) was first used for optimizing experimental conditions. The chemical composition of Cs in the contaminated biomass is believed to be similar to Cs2CO3, so that K2CO3 was used as a model starting sample added to cellulose, called as CK mixture, and further with kaolinite, as CKK mixture. Both CK and CKK mixtures were separately ground by a planetary ball mill, and the ground products were heated at different temperatures in air. Heating both mixtures at 600 °C enables us to reduce their weights effectively, due to mainly decomposition of cellulose. Finally, the mixture containing cellulose, kaolinite and Cs2CO3, as CKC mixture was investigated under the optimized conditions. As a result, the formation of water-insoluble Cs compound in the calcined sample with kaolinite addition after milling operation was achieved.

A Potential Wasteform for Cs Immobilization: Synthesis, Structure Determination, and Aqueous Durability of Cs2TiNb6O18.

Cs2TiNb6O18 is a potential ceramic wasteform for the long-term immobilization of radioactive cesium. Cs2TiNb6O18 was synthesized using the aqueous precursor method and a solid-state reaction, and its crystal structure was determined from the Rietveld refinement of synchrotron X-ray and neutron powder diffraction data. The structure is a pyrochlore analogue, space group P3̅m1 with Cs in 9-fold coordination. The calculated bond valence sum from analysis of neutron diffraction data of 0.84 and high coordination number suggest that Cs has a strong bonding environment. The chemical aqueous durability was investigated using the MCC-1 and PCT-B standard test methods. The measured Cs leach rates of 3.8 × 10-3 and 2.1 × 10-3 g m-2 day-1 obtained via the MCC-1 and PCT-B methods, respectively, demonstrate good promise of a safe long-term immobilization material comparable to, if not better than, hollandite-the material in the multiphase titanate ceramics (Synroc) targeted for cesium sequestration.

Immobilization of cesium into mineral-like matrices of tridymite, kosnarite, and langbeinite structure

Cesium-containing phosphates CsMgPO4, CsZr2(PO4)3, and Cs2Mg0.5Zr1.5(PO4)3 of framework structure were synthesized. The chemical stability of the crystalline phosphates in neutral, acidic, and alkaline media was studied. Quantitative data on the chemical stability in a wide pH range and on the ion-exchange capacity of phosphates containing cesium, magnesium, and zirconium ions were obtained by potentiometric titration. The Cs leach rates from the ceramic samples upon long contact with water were from 3 × 10–4 to 4 × 10–6 g cm–2 day–1. The phosphates CsZr2(PO4)3 and Cs2Mg0.5Zr1.5(PO4)3 are thermally stable in the temperature range from–268 to 1000°C, and CsMgPO4 undergoes a low-temperature phase transition at–37°C without break of chemical bonds in the structure. The stability of ceramic and powdered samples of CsMgPO4, CsZr2(PO4)3, and Cs2Zr1.5Mg0.5(PO4)3 was studied in different aspects, and these materials proved to be promising for cesium consolidation. High cesium content of CsMgPO4 allows its use as a material of the active core of 137Cs/137mBa sources.

Solvent-free synthesis and application of nano-Fe/Ca/CaO/[PO4] composite for dual separation and immobilization of stable and radioactive cesium in contaminated soils

This study assessed the synthesis and application of nano-Fe/Ca/CaO-based composite material for use as a separation and immobilizing treatment of dry soil contaminated by stable (133Cs) and radioactive cesium species (134Cs and 137Cs). After grinding with nano-Fe/CaO, nano-Fe/Ca/CaO, and nano-Fe/Ca/CaO/[PO4], approximately 31, 25, and 22wt% of magnetic fraction soil was separated. Their resultant 133Cs immobilization values were about 78, 81, and 100%, respectively. When real radioactive cesium contaminated soil obtained from Fukushima was treated with nano-Fe/Ca/CaO/[PO4], approximately 27.3wt% of magnetic and 72.75% of non-magnetic soil fractions were separated. The highest amount of entrapped 134Cs and 137Cs was found in the lowest weight of the magnetically separated soil fraction (i.e., 80% in 27.3% of treated soil). Results show that 134Cs and 137Cs either in the magnetic or non-magnetic soil fractions was 100% immobilized. The morphology and mineral phases of the nano-Fe/Ca/CaO/[PO4] treated soil were characterized using SEM–EDS, EPMA, and XRD analysis. The EPMA and XRD patterns indicate that the main fraction of enclosed/bound materials on treated soil included Ca/PO4 associated crystalline complexes. These results suggest that simple grinding treatment with nano-Fe/Ca/CaO/[PO4] under dry conditions might be an extremely efficient separation and immobilization method for radioactive cesium contaminated soil.

Immobilization of cesium by zirconium phosphate

Mixtures of cesium nitrate and ammonium-ion type zirconium phosphate, NH4Zr2(PO4)3, with varying molar ratios were thermally treated at 600 or 750 °C, yielding partial cesium-ion type zirconium phosphates, CsxH1−xZr2(PO4)3 (x = 0.4, 0.6, 0.8). Immobilization of cesium on the CsxH1−xZr2(PO4)3 was examined. Leaching tests at 90 °C using pseudo-seawater as leachant revealed that the cesium leach rates of the materials with x = 0.4 and 0.6 were in the order of 10−2 g m−2 day−1, smaller than those reported for borosilicate glasses, the generally accepted first-generation waste form. This indicated the materials examined were better cesium immobilizers than borosilicate glasses.

Preferential removal and immobilization of stable and radioactive cesium in contaminated fly ash with nanometallic Ca/CaO methanol suspension

In this work, the capability of nanometallic Ca/CaO methanol suspension in removing and/or immobilizing stable (133Cs) and radioactive cesium species (134Cs and 137Cs) in contaminated fly ash was investigated. After a first methanol and second water washing yielded only 45% of 133Cs removal. While, after a first methanol washing, the second solvent with nanometallic Ca/CaO methanol suspension yielded simultaneous enhanced removal and immobilization about 99% of 133Cs. SEM-EDS analysis revealed that the mass percent of detectable 133Cs on the fly ash surface recorded a 100% decrease. When real radioactive cesium contaminated fly ash (containing an initial 14,040Bqkg−1134Cs and 137Cs cumulated concentration) obtained from burning wastes from Fukushima were reduced to 3583Bqkg−1 after treatment with nanometallic Ca/CaO methanol suspension. Elution test conducted on the treated fly ash gave 100BqL−1 total 134Cs and 137Cs concentrations in eluted solution. Furthermore, both ash content and eluted solution concentrations of 134Cs and 137Cs were much lower than the Japanese Ministry of the Environment regulatory limit of 8000Bqkg−1 and 150BqL−1 respectively. The results of this study suggest that the nanometallic Ca/CaO methanol suspension is a highly potential amendment for the remediation of radioactive cesium-contaminated fly ash.

酸化チタンによるセシウム安定閉じ込め

酸化チタンによるセシウム安定閉じ込め

Cesium Immobilization in Soil by Ball-Milling Treatment with Nanometallic Ca/CaO Additive

AbstractThis work assessed ball-milling treatment for remediation of cesium (Cs)-contaminated soil. The immobilization efficiency increases from 56.4% in the absence of treatment to 89.9, 91.5, 97.7, and 96.4% when the soil is ball milled for 30, 60, and 120 min, respectively. However, the addition of nanometallic Ca/CaO and NaH2PO4 increased the immobilization efficiency to approximately 96.4% compared with ball milling alone, even when the milling time was decreased to 60 min. Actually, with the addition of Ca/CaO and NaH2PO4, the leachable fraction of Cs was reduced in the soil after a short milling time. These promising results suggest that ball milling can be regarded as applicable for the remediation of cesium-contaminated soil in dry and water-free conditions. This treatment method requires no expensive reagent and does not generate exhaust gases. It requires only electricity with cheap and commercially available reagents. This treatment process is an environmentally friendly depollution technique.

Crystallographic Evaluation of Sodium Zirconium Phosphate as a Host Structure for Immobilization of Cesium and Strontium

Sodium zirconium phosphate (NZP) is a potential material for immobilization of nuclear effluents. It was observed up to ~7.16 wt% (~2.67 mol%) of strontium and ~14.46 wt% (~3.56 mol%) of cesium could be simultaneously loaded into NZP formulations without significant changes in the three‐dimensional framework structure. The crystal chemistry of Na1−x(Cs1.33Sr1)xZr2P3O12 (x = 0.1–1.0) has been investigated using General Structure Analysis System programming. The CsSrNZP phases crystallize in the space group R‐3c and Z = 6. Powder diffraction data have been subjected to Rietveld refinement to arrive at a satisfactory structural convergence of R‐factors.

Transformation and clustering of defects induced by electron irradiation in barium hollandite ceramics for radioactive cesium storage: Electron paramagnetic resonance study

Barium hollandite-type ceramics have been envisaged for the immobilization of radioactive cesium. To evaluate their stability under irradiation, a hollandite ceramic of composition Ba1.16Al2.32Ti5.68O16 was irradiated with electrons at a temperature close to room temperature to simulate the effect of β- and γ-decays of cesium. Ti3+ and O2- paramagnetic defects induced by electron irradiation [V. Aubin-Chevaldonnet et al., J. Phys.: Condens. Matter 18, 4007 (2006)] were detected by electron paramagnetic resonance. As the temperature in the bulk of the hollandite waste form could reach 300 °C at the beginning of the storage, the thermal stability of these paramagnetic defects was also studied. Isothermal annealing treatments at 300 °C and isochronal annealing treatments between 50 °C and 800 °C show that the irradiation induced Ti3+ (E1 and E2 centers) and O2− (H centers) do not recombine. Instead, they partially transform during annealing, respectively, into titanyl TiO+ centers (E3 centers) at the grain surface and into paramagnetic clusters of O2− of less than 10 nm size (G2 centers), trapped in the bulk of the grains. These oxygen-rich aggregates could prefigure the formation of molecular oxygen observed in electron irradiated glasses.

High immobilization of soil cesium using ball milling with nano-metallic Ca/CaO/NaH2PO4: implications for the remediation of radioactive soils

This report shows that cesium can be immobilized in soils with an efficiency of 96.4% by ball milling with nano-metallic Ca/PO4. In Japan, the major concern on 137Cs deposition and soil contamination due to the emission from the Fukushima Daiichi nuclear power plant showed up after a massive quake on March 11, 2011. The accident rated 7, the highest possible on the international nuclear event scale, released 160 petabecquerels (PBq) of iodine 131I and 15 PBq of 137Cs according to the Japanese Nuclear and Industrial Safety Agency. Both 137Cs and 131I radioactive nuclides are increasing cancer risk. Nonetheless, 137Cs, with a half-life of about 30 years compared with 8 days for 131I, is a major threat for agriculture and stock farming and, in turn, human life for decades. Therefore, in Japan, the 137Cs fixation and immobilization in contaminated soil is the most important problem, which should be solved by suitable technologies. Ball milling treatment is a promising treatment for the remediation of cesium-contaminated soil in dry conditions. Here, we studied the effect, factors and mechanisms of soil Cs immobilization by ball milling with the addition of nano-metallic Ca/CaO/NaH2PO4, termed “nano-metallic Ca/PO4.” We used scanning electron microscopy combined with electron dispersive spectroscopy (SEM/EDS) and X-ray diffraction. Results show that immobilization efficiency increases from 56.4% in the absence of treatment to 89.9, 91.5, and 97.7 when the soil is ball-milled for 30, 60 and 120 min, respectively. The addition of nano-metallic Ca/PO4 increased the immobilization efficiency to about 96.4% and decreased the ball milling time. SEM/EDS analysis allows us to observe that the amount of Cs decreased on soil particle surface. Use of nano-metallic Ca/PO4 over a short milling time also decreases Cs leaching. Therefore, ball milling with nano-metallic Ca/PO4 treatment may be potentially applicable for the remediation of radioactive Cs-contaminated soil in dry conditions.

A crystal-chemical approach in the development of phosphate materials as environmentally safe chemical forms of utilization of spent Cs-containing ferrocyanide sorbents

Crystalline materials are developed as environmentally safe forms of chemical binding of components of spent cesium-containing ferrocyanide sorbents. Data on cationic compositions of ferrocyanides are summarized. Using structural-chemical modeling, compositions based on orthophosphates of framework structure, crystallizing in the structural type of langbeinite mineral, are chosen for the immobilization of cesium and ferrocyanide cations. The cationic composition includes cesium, some bivalent d elements, iron (molar ratio 2: 3: 2), and the cations added. The substances synthesized are characterized by X-ray phase analysis, DSC, and IR spectroscopy. Upon heat treatment of the samples for 5 h at 800°C, cesium does not pass to the gas phase. The leaching rate on the fifth day at 90°C in the dynamic mode was R = 3 × 10−5 g cm−2 day−1. The results of thermal and hydrolytic tests show that the crystalline forms chosen enhance the safety barrier for the incorporated cesium in the course of prolonged storage with isolation from the biosphere.

Crystallographic evaluation of sodium zirconium phosphate as a host structure for immobilization of cesium

Sodium zirconium phosphate (NZP) is a potential material for immobilization of nuclear effluents. The existence of cesium containing NZP structure was determined on the basis of crystal data of solid solution. It was found that up to ~9.0 wt% of cesium could be loaded into NZP formulations without significant changes of the three-dimensional framework structure. The crystal chemistry of Na1−xCsxZr2P3O12 (x = 0.1–0.4) has been investigated using General Structure Analysis System programming. The CsNZP phases crystallize in the space group R-3c and Z = 6. Powder diffraction data have been subjected to Rietveld refinement to arrive at a satisfactory structural convergence of R-factors. The unit cell volume and polyhedral (ZrO6 and PO4) distortion increase with rise in the mole% of Cs+ in the NZP matrix. The PO4 stretching and bending vibrations in the infrared region have been assigned. SEM, TEM, and EDAX analysis provide analytical evidence of cesium in the matrix.