Immobilization Of Cesium Research Articles

Zirconosilicate Sorbent Based on Waste Fly Ash Cenospheres for Cesium Immobilization in a Ceramic Form

Zirconosilicate Sorbent Based on Waste Fly Ash Cenospheres for Cesium Immobilization in a Ceramic Form

Advancements in immobilization of cesium and strontium radionuclides in cementitious wasteforms—A review

AbstractThe safe and secure encapsulation or immobilization of nuclear waste, particularly low to intermediate‐level waste (accounting for ∼97% of the total volume of nuclear waste), has been a significant concern. Consequently, numerous studies have been conducted on various materials such as ordinary Portland cement‐based, bitumen, and ceramics for the purpose of waste encapsulation/immobilization. However, these studies generally offer a broad overview of materials performance without focusing on specific radioisotopes of concern. Cesium (Cs) and strontium (Sr) are important radioactive nuclides to consider for encapsulation, but the existing studies on immobilizing these elements are fragmented and lack a comprehensive understanding. This critical review article offers a thorough qualitative and quantitative analysis to uncover the primary trends/knowledge gaps within the field. It comprehensively delves into waste classifications/management and leaching assessments, followed by an exploration of the immobilization performance and durability issues of various traditional and advanced cementitious materials including low‐temperature chemically bonded ceramics such as alkali‐activated matrices and Mg‒K phosphates for the immobilization of Cs and Sr. Furthermore, the review article provides fresh insights and perspectives, including recommendations for improvements, novel technologies, and future trends in this domain.

Cesium stabilization by engineered alkaline attack of glass for pharmaceutical containers

An innovative method for immobilizing cesium has been developed through the alkali activation of boro-alumino-silicate glass. Glass powders from discarded pharmaceutical vials, suspended in CsOH-based activating solutions yield cementitious matrices upon drying at nearly room temperature. Solid blocks are formed through bridging of adjacent particles by condensation reactions in hydrated surface layers. Silicates, borates, and aluminates released into the solution, along with atmospheric CO2 interact with Cs+ and NH4+ ions, forming additional phases, with various chemical stability. When exposed to boiling water the blocks are stable. Boro-pollucite (CsBSi2O6) formed as the result of chemical reactions in the system is stable and does not dissolve. However, boiling results in dissolution of cesium carbonate. A mixed attack by CsOH-NH4OH instead of CsOH reduces the formation of cesium carbonate, maximizing the immobilization of cesium in a stable matrix.

New approach to niobia-modified borosilicate glasses for Cs waste immobilization

The use of nuclear materials is increasing in energy production, medicine, and environmental sectors. Following this trend, the generation of radioactive wastes is also increasing in the whole production cycle and use of this kind of materials. Among these, the 137Cs radionuclide presents a potential risk to human health due to its half-life time (30,2 years), high-level activity (1 TBq) and easiness to contaminate rivers, soil, and air. The immobilization of 137Cs in solid matrices has been an available option researched by several countries. In this context a new glass composition based on aluminoborosilicate glass modified with niobium (Nb) was used for the immobilization of cesium through adding Cs-loaded zeolite. Homogeneous vitreous wasteforms were improved with the growth of Nb content in the compositions. All compositions were able to keep up to 5.9 wt% Cs2O, previously adsorbed by zeolite A, and the immobilization efficiency was around 53%. Their structural analyses by Raman revealed a depolymerized and complex network structure, due to the presence of several cations including Cs. In turn, Nb reflected positively on the chemical resistance and thermal properties, by changing the distribution of silicate species. The wasteforms presented good glass forming ability and thermal stability up to 520 °C. Through the thermal treatment for devitrification, Cs atoms were stabilized into the Pollucite phase (CsAlSi2O6). Besides that, the wasteforms, preferably the one containing 8.0 mol% Nb, showed low elemental releases and leaching rates for Cs (1 × 10−3 g m2.day−1), after the leaching experiments at 90 °C for 7 days in static conditions, verified by the neutron activation analysis (NAA).

Novel cesium immobilization by alkali activation and cold consolidation of waste pharmaceutical glass

A new method of cesium immobilization has been successfully developed by combining alkali activation of boro-alumino-silicate glass and viscous flow sintering. Powdered glass from discarded pharmaceutical vials, suspended in a 2.5 M CsOH aqueous solution, underwent surface hydration as well as partial dissolution. Condensation reactions occurring at hydrated surface layers upon drying at 40 °C over 7 days resulted in welding of adjacent particles, forming a network that trapped newly formed gel and crystal phases. The newly formed phases including crystalline boro-pollucite (CsBSi2O6), were derived mostly from Cs+ ions reacting with the products of glass dissolution and exhibited a high chemical stability. Further stabilization was achieved through viscous flow sintering at 700 °C, resulting in the incorporation of Cs+ ions in a glass matrix. The effectiveness of the immobilization was confirmed by leaching test using the Materials Characterization Center-1 Standard (MCC-1). This innovative approach not only enhances the chemical stability of cesium waste forms, but also aligns with principles of cleaner production by repurposing pharmaceutical glass waste, promoting sustainable materials management.

Low temperature fabrication of Ba0.9Cs0.3Cr2.1Ti5.9O16 ceramic waste form for cesium immobilization using Bi2O3 as sintering aid

In this paper, we present a productive low-temperature fabrication of Cs-hollandite ceramics by adding Bi2O3 as a sintering aid to achieve high cesium retention. The effects of Bi2O3 addition on the phase composition, crystal structure and aqueous stability of the stoichiometric Ba0.9Cs0.3Cr2.1Ti5.9O16 ceramic waste form were investigated. It was found that adding Bi2O3 can effectively reduce the sintering temperature and promote densification of Cs-containing hollandite products. The Cs-hollandite ceramic with 2 wt% Bi2O3 sintered at 1000 °C showed a single phase with > 98 % cesium retention, which was ∼ 200 °C lower and ∼ 11 % retention rate higher than those of reported Cs-bearing hollandite. Moreover, the leached sample remained stable tetragonal structure, the LRCs was in the order of 10-3 g·m-2·d-1 after 28 days and the leaching indexes > 8, exhibiting good aqueous stability. This route can be considered as a promising solution to prevent cesium loss for incorporating the cesium waste in ceramic hosts.

Cesium immobilization of high pH and low pH belite-rich cement under varying temperature

Low-pH cement is being studied in radioactive waste repositories. The belite-rich cement (BRC) recently gained attention due to its higher CO2 sequestration and low pH attainment under carbonation exposure. Therefore, this study evaluated the effects of pH and temperature on cesium immobilization of BRC. High pH (12.6) and low pH (9.9) BRC were produced via air curing and carbonation treatment, respectively. The high and low pH BRC samples were placed in a leaching environment at 25 °C and 45 °C for 90 days. An inverse correlation between pH and cesium mobilization of BRC was observed. The high pH BRC achieved the lowest effective diffusion coefficient (4.05E-09 cm2/s), whereas the highest value (2.64E-07 cm2/s) was achieved in case of low pH BRC. The physicochemical and morphological properties unveiled the decrease in Si/Ca ratio of gel, precipitation of Ca2+ ions in calcite formation, and increment in pore structure connectivity (pore size > 100 nm) in low pH BRC. However, the high pH BRC demonstrated the high Si/Ca ratio in C-S-H gel, hydroxide phases and higher disconnected pores. Thermodynamic modeling revealed the presence of significant carbonated phases beyond 15% CO2 uptake. The findings contributed to the BRC’s feasibility in developing nuclear waste storage facility.

Facile formation of pollucite in geopolymers: Implications for radioactive Cs immobilization

Pollucite, CsAlSi2O6, is one of the few naturally occurring cesium minerals, and is considered as an efficient phase for long-term immobilization of radioactive cesium. The occlusion of cesium ions within pollucite structure is conventionally achieved via solid state syntheses, requiring temperatures exceeding 1000 °C, or hydrothermal processes which are typically preformed at 200–300 °C and elevated pressures. The current paper reports on the formation of pollucite within Cs-bearing geopolymers at near-ambient temperatures and pressures. By combining data from X-ray powder diffraction and 133Cs solid-state NMR measurements we are able not only to identify the various phases that are formed within crystalline-amorphous geopolymer matrices, but also follow changes in the distribution of cesium between the various phases as a function of geopolymer formulation. Based on these data we were able demonstrate that the extent of pollucite formation increases with the Si2O:Al2O3 ratio in the geopolymer formulation. The formation of crystalline pollucite domains within composite crystalline-amorphous geopolymer matrices may have important implications for the immobilization of radioactive cesium.

Kinetics of in-situ pollucite crystallization in relation to cesium immobilization in the fly ash-based geopolymers

Kinetics of in-situ pollucite crystallization in relation to cesium immobilization in the fly ash-based geopolymers

Preliminary Study of Cesium Immobilization in a Geopolymer Matrix

Geopolymers are modern synthetic materials that have many beneficial characteristics, e.g. excellent mechanical properties, fire- and heat-resistance, minimal shrinkage and can be molded into shape. Given their aforementioned characteristics, geopolymers could be applicable as conditioning materials, e.g. to handle hazardous waste and radioactive materials. However, their long-term applicability needs to be investigated.The aim of this study is to investigate the mobility of Cs-137 radionuclides in embedding materials. Different geopolymeric matrices - namely kaolinite, bentonite, zeolites and red mud - were tested. The leach test was performed according to the ASTM C1308-08(2017) standard and the activity concentration of Cs-137 isotopes was measured by gamma spectrometry using a high-purity germanium (HPGe) semiconductor detector. According to our preliminary results, the matrices that resulted in the most significant immobilization effect were those in which bentonite, cement, fly ash and 8M NaOH were used, releasing approximately 10% of the cesium.

Cesium immobilization from aqueous solution by struvite synthesis

ABSTRACT To demonstrate the validity of the Cs decontamination process by synthesizing Cs-struvite (CsMgPO4·6 H2O) from a waste solution containing multiple cations, synthesis tests and tests confirming structural stability were performed. The synthesis test was conducted in a solution containing Na, K, Cs, Mg, and P. After 0.5 h stirring, Cs, Mg, and P were recovered, and the sample structure was confirmed as Cs-struvite. With the TG-DTA analysis, the absence of Cs vaporization was confirmed up to 1200°C. The gamma irradiation resistance of Cs-struvite was confirmed. Gamma irradiation using the Co-60 as the radiation source with a maximum radiation dose of 300 kGy caused no loss of Cs or structural changes. The elution test, in which samples were left to stand in distilled water for 7 days, showed that Cs-struvite had a higher water resistance than CsMgPO4, indicating that it is desirable to compress Cs-struvite directly after synthesis to obtain a solidified body with higher water resistance. The results demonstrated the feasibility of Cs removal by Cs-struvite synthesis and the stability of Cs-struvite.

Composite metal phosphates for selective adsorption and immobilization of cesium, strontium, and cobalt radionuclides in ceramic matrices

Zr–Ca–Mg composite phosphates of various chemical compositions were prepared by facile heterogeneous synthesis and their adsorption properties towards 137Cs, 85,90Sr, 60Co radionuclides were studied. The obtained composites showed a high efficiency for 137Cs, 85,90Sr, and 60Co adsorption (Kd > 104 mL/g) from model 0.1M NaNO3 aqueous solution. A sharp decrease in adsorption properties was found against 0.01M CaCl2 and seawater background, due to a decrease in the adsorbents selectivity. Zr–Ca–Mg phosphates exhibited high efficiency of radionuclides immobilization during metal ions leaching in water (desorption efficiency ∼10%). At the same time, the desorption rate of radionuclides in seawater solutions increased by 4–8 times. Calcination of saturated adsorbents at 1000 °C led significantly to increase in the efficiency of radionuclides immobilization. Thus, the activity of 60Со and 85Sr radionuclides in seawater solutions after exposure for 28 days did not exceed the lower detection limit, and the desorption efficiency of 137Cs was less than 4%. This was due to the formation of mixed Cо0.5Zr0.5(PO4), SrZr4(PO4)6 phosphates, characterized by high efficiency of radionuclides immobilization. The obtained Zr–Ca–Mg composite phosphates are promising materials for the adsorption and immobilization of 137Cs, 85,90Sr, and 60Co radionuclides.

A novel approach for rice straw agricultural waste utilization: Synthesis of solid aluminosilicate matrices for cesium immobilization

A new approach to the use of rice straw as a difficult-to-recycle agricultural waste was proposed. Potassium aluminosilicate was obtained by spark plasma sintering as an effective material for subsequent immobilization of 137Cs into a solid-state matrix. The sorption properties of potassium aluminosilicate to 137Cs from aqueous solutions were studied. The effect of the synthesis temperature on the phase composition, microstructure, and rate of cesium leaching from samples obtained at 800–1000 °C and a pressure of 25 MPa was investigated. It was shown that the positive dynamics of compaction was characteristic of glass ceramics throughout the sintering. Glass ceramics RS-(K,Cs)AlSi3O8 obtained by the SPS method at 1000 °C for 5 min was characterized by a high density of ∼2.62 g/cm3, Vickers hardness ∼ 2.1 GPa, compressive strength ∼231.3 MPa and the rate of cesium ions leaching of ∼1.37 × 10−7 g cm−2·day−1. The proposed approach makes it possible to safe dispose of rice straw and reduce emissions into the atmosphere of microdisperse amorphous silica, which is formed during its combustion and causes respiratory diseases, including cancer. In addition, the obtained is perspective to solve the problem of recycling long-lived 137Cs radionuclides formed during the operation of nuclear power plants into solid-state matrices.

Cesium immobilization in porous silica and [formula omitted]Cs self-heating simulations

The interest to immobilize 137Cs can pursue different aims. When it is separated from spent nuclear fuels, it is possible to reduce the thermal loading of the host glass and increase the waste loading capacity of the matrix. Also, the separated 137Cs can be used to produce radioactive sealed sources useful in industrial and medical applications. If reprocessing is not envisaged after the generation of electrical energy, the spent nuclear fuel is the most important radioactive waste generated in the nuclear fuel cycle. In this case, aqueous solutions obtained from the chemical dissolution of spent nuclear fuels are high-level wastes. Short-lived fission products, such as 90Sr and 137Cs, constitute the main source of heat generation from beta decay, causing self-heating of the glassy matrix. It is well known that vitrification is the main used technology, capable to immobilize these wastes during hundreds of years generating a waste form with proved structural stability, thermal shock resistance, and high chemical durability. In this article we present in an analogous way the immobilization of an specific amount of stable cesium in a porous Si-rich glass matrix through adsorption and sintering. Sintering requires lower temperature than that required in immobilization by melting. The leaching behavior of the waste form obtained was studied from the procedure described by the MCC-1 test method. Considering 137Cs only for simulations, this work also includes the thermal evolution calculation of a simulated silica glass block loaded with 2 wt.% of 137Cs.

Recovery and immobilization of cesium from aqueous solution after hydrothermal treatment using functional porous glass

ABSTRACT Fukushima Daiichi Nuclear Power Station accident caused a large amount of waste contaminated with radioactive Cs. Decontamination of radioactive Cs from soil and its safe disposal are required. Functional porous glass (FPG) is effective for removal of Cs from aqueous solution, and vitrification can subsequently be done in a stepwise process. To demonstrate the validity of this proposed decontamination process, adsorption, elution, and vitrification experiments were carried out. First, the adsorption of Cs on FPG was governed by a pseudo second-order kinetic model and the adsorption isotherm was in accord with the Langmuir model. The adsorption experiments targeted 11 elements, which represent the components after hydrothermal treatment of contaminated soil; Cs showed the highest adsorption selectivity. Second, the vitrification tests of the FPG with CsCl revealed that no loss of Cs was observed at temperatures up to 1200°C The elution experiments showed the lowest normalized leaching (NLCs) values at a low temperature of 800°C without Na addition, or at 1200°C with Na addition, indicating that the melting of the pores and glass matrix, retention within the aluminosilicate structure were the key experimental factors. The feasibility of removal and vitrification of Cs via FPG was demonstrated.

Immobilization of strontium and cesium by aluminosilicate ceramics derived from metakaolin geopolymer-zeolite A composites via 1100 °C heating treatment

In this work, K-based metakaolin geopolymer-zeolite A composites doped with strontium and cesium radionuclides have been subjected to 1100 °C to prepare aluminosilicate ceramic waste forms. Serial analysis of mineral characterization, physical properties and leaching resistance have been adopted to investigate the immobilization performance of aluminosilicate ceramic waste forms for strontium and cesium radionuclides. Compared to geopolymer-zeolite A composites, the obtained ceramic waste forms exhibit preferable mechanical property and leaching resistance (in deionized water, brine solutions and silicate solutions). The compressive strengths of aluminosilicate ceramic waste forms (Sr/Cs-loaded matrix) are both above 80 MPa, which are far higher than that of geopolymer-zeolite composites solidification matrices. Owing to the viscous sintering under 1100 °C heating treatment, even compact and dense ceramic waste forms have been successfully synthesized, accompanied by the main crystalline phase transformation in monoliths from zeolite A to leucite. Cs-leucite and Sr-feldspar also have been detected by XRD and TEM analyses, which are conducive to capturing strontium and cesium radionuclides in ceramic monoliths. All findings have proven that the ceramics waste forms derived from metakaolin geopolymer-zeolite A composites could be an ideal option for nuclear wastes immobilization.

Cesium immobilization in metakaolin-based geopolymers elucidated by 133Cs solid state NMR spectroscopy

Geopolymers are promising candidates for nuclear-waste immobilization, and more specifically for the immobilization of radioactive cesium. Low-Si metakaolin-based geopolymers cured at temperatures of 40 °C in the presence of Cs ions generate a mixture of amorphous and crystalline phases including a Cs-bearing zeolite F phase. Using a combination of 133Cs solid-state NMR and X-ray powder diffraction measurements we were able to show that Cs preferentially binds to zeolite F even when zeolite F is not the dominant phase in the matrix. Moreover, post-leaching NMR experiments indicate that zeolite F binds Cs more efficiently than the remaining crystalline or amorphous phases. Tailoring geopolymer formulations so that a large fraction of zeolite F is generated may therefore be a promising route for the production of immobilization matrices for cesium.

Evaluation on migration and transformation of trace nuclides in thermal degradation for low-level radioactive waste

The migration and transformation of trace nuclides (cobalt, cesium and strontium) during pyrolysis and gasification of low-level radioactive waste (plastic, glove, coverall, paper towel, sawdust and mixture) were evaluated based on two lab-scale fixed-bed reactors and chemical equilibrium calculation. Co and Cs mobilities in plastic were both higher than that of glove at the same pyrolysis temperature. From the test of cesium migration, the mobilities of cesium in plastic and glove due to the addition of ZrO2 (wt.1%) during thermal treatment almost reduced by one half or above, indicating that ZrO2 was a favorable agent for immobilization of cesium. Phosphorus and sulphur in low-level radioactive waste could resist the migration of Co. The pyrolysis temperature for the mixture should be kept below 509 ºC to prevent the cesium migration. Chlorine in the samples could increase the migration of Cs. The gasification temperature should be kept below 1200 ºC to prevent cobalt and strontium migration. Negative micro-pressure operation did not impact greatly the migration of the trace nuclides. CsOH (g) in plastic and CsCl (g) in mixture decreased both by about 91% by increasing the pressure from 0.1 MPa to 1.0 MPa, indicating that lifting the pressure could effectively resist the migration of the trace nuclides.

Selective removal and immobilization of cesium from aqueous solution using sludge functionalized with potassium copper hexacyanoferrate: a low-cost adsorbent

Selective removal and immobilization of cesium from aqueous solution using sludge functionalized with potassium copper hexacyanoferrate: a low-cost adsorbent

Insight into cesium immobilization in contaminated soil amended with biochar, incinerated sewage sludge ash and zeolite

Radioactive cesium (Cs) in the soil represents a severe threat to human health and the environment. Plant uptake is an important pathway for the migration of Cs to the human food chain. It is therefore essential to find effective amendments for reducing the phytoavailability of Cs. In this study, we aimed to evaluate the effectiveness and possible mechanisms of biochar (BC), incinerated sewage sludge ash (ISSA) and zeolite (ZL) on the immobilization of Cs in the contaminated soil. Greenhouse pot experiment was conducted using Napier grass ( Pennisetum purpureum ) to investigate the effects of BC, ISSA and ZL (10% application rate, w/w) on the soil properties, plant biomass, the accumulation and distribution of Cs in the grass grown on the contaminated soil added with Cs as a rate of 100 mg kg −1 . The results showed that all amendments enhanced the grass growth, with the maximum biomass recorded in the ISSA treatment. The concentrations of Cs in the leaf blade, leaf sheath and root of grass significantly decreased with all amendment applications. Especially the BC application showed the lowest Cs concentration in grass, decreased by up to 95% compared to control (no amended soil). Moreover, the obtained results in terms of pH, cation exchange capacity, surface charge, specific surface area and potassium concentration of amendments and potting soils highlighted the remarkable efficiency of biochar to adsorb Cs and reduce the plant uptake of Cs providing key evidences for Cs immobilization. • Cs immobilization in soil amended with three sorbent materials was investigated. • The additions of BC, ISSA and ZL significantly restricted the Cs transfer to plant. • The BC showed the most significant inhibition effect on the plant uptake of Cs. • Cs was immobilized by BC due to its high sorption capacity and K concentration.