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Incremental leach fraction of 137 Cs, 60 Co, and 152,154 Eu radionuclides from immobilized cement matrices as a function of time.
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Leaching characteristics of some radionuclides that are commonly encountered in radioactive waste streams from immobilized waste matrices in different cement-clay grouts have been assessed to investigate the influence of the clay additives on the leaching behavior of the solid waste matrices. The International Atomic Energy's Agency (IAEA) standard...
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Context 1
... A ( t ) is the cumulative radioactivity leached, A 0 the initial radioactivity present in specimen, V the volume of specimen (cm 3 ), and S is the exposed surface area of specimen (cm 2 ). The objective of performing the IAEA standard leach method is to measure the CLF that represents the leaching rate of some radionuclides of potential concern from immobilized waste matrix under continuously saturated conditions that represents the worst case. The result of this method is used to estimate the intrinsic mass transfer parameters such as the apparent diffusiv- ity of the studied radionuclides, which are used in conjunction with mathematical models to estimate the long-term leaching behavior. The influence of natural clay additives on the CLF of Cs, 60 Co, and 152,154 Eu from the studied immobilized waste matrices are depicted in Fig. 2. The examination of this figure indicates that: (a) The CLF is less than 5% for each of the studied cases. (b) The addition of 10% of natural clays decrease the CLF for the studied radionuclides, and this can be attributed to the low porosity of these additives that can reduce the overall porosity of the waste matrix when compared with that of plain cement matrix and also to the high sorption capacity of those natural clays for the studied radionuclides [18–20]. (c) The CLF from OPC–bentonite waste matrix is lower than that from OPC–red clay and this may be related to the higher sorption capacity of bentonite, towards all the studied radionuclides, than red clay. (d) 152,154 Eu has the smallest leachability; this can be attributed to the low solubility of lanthanides and actinides in the high pH environment of the hydrated cement. On the other hand, 137 Cs has the highest leachability because of its low field strength that keeps it substantially soluble in the high pH environment [8–10]. Various leaching studies assessed the effect of different additives on the leachability of 137 Cs from cement based matrices, a comparison between the performance of these matrices and the OPC–bentonite, and OPC–red clay matrices could be held by comparing the CLF of 137 Cs measured after 90 days in a static leach test using distilled water. It was found that the CLF (cm) from OPC–bentonite and OPC–red clay matrices are lower than that of OPC–zeolite (0.012) and OPC–tobermorite (0.014) [19,30]. In general, any leaching phenomena from cementitious material can be explained as a combination of the diffusion and dissolution mechanisms. Various studies in the literature, divide the leaching phenomena into three regions [19,21,30]. The first is controlled by the rapid release of dissolved soluble materials that exists on the surface of the waste matrix, which is known as surface wash-off. Following surface wash-off, the material release is controlled by diffusion through the pore space of the waste matrix. At the last region, the slow portion of dissolution control the leaching phenomena, in this case, the dissolution of materials from the surface proceeds faster that the diffusion through the pores. Both the rapid and slow portion of dissolution will result in the release of highly soluble materials but it will not cause depletion of material. The examination of the plot of incremen- tal leach fractions form the studied immobilized waste matrices loaded by 137 Cs, 60 Co, and 152,154 Eu expressed as cm/day on log scale versus time (Fig. 3), indicate that the leaching pattern can be divided into two regions. Region I shows initial rapid release of radionuclides within the first 5 days, then a drastic reduction in the release take place over a longer period of time. From this figure, it is clear that the leaching of the studied ...
Context 2
... the pores. Both the rapid and slow portion of dissolution will result in the release of highly soluble materials but it will not cause depletion of material. The examination of the plot of incremen- tal leach fractions form the studied immobilized waste matrices loaded by 137 Cs, 60 Co, and 152,154 Eu expressed as cm/day on log scale versus time (Fig. 3), indicate that the leaching pattern can be divided into two regions. Region I shows initial rapid release of radionuclides within the first 5 days, then a drastic reduction in the release take place over a longer period of time. From this figure, it is clear that the leaching of the studied radionuclides Table 2 Slope of the linear ...
Citations
... Further studies will focus on the evaluation of the retention capacity of radionuclides in the obtained cementoid systems by measuring the radiological activity of the leachate, using Cs 137 and Co 60 as radioactive isotopes [51][52][53]. ...
In this paper, we study the influence of densified microsilica and colloidal nanosilica admixtures on the mechanical strength and the microstructural characteristics of special mortars used for immobilizing radioactive concrete waste. The experimental program focused on the replacement of cement with micro- and/or nanosilica, in different proportions, in the basic composition of a mortar made with recycled aggregates. The technical criteria imposed for such cementitious systems, used for the encapsulation of low-level radioactive waste, imply high fluidity, increased mechanical strength and lack of segregation and of bleeding. We aimed to increase the structural compactness of the mortars by adding micro- and nanosilica, all the while maintaining the technical criteria imposed, to obtain a cement matrix with high durability and increased capacity for immobilizing radionuclides. The samples from all the compositions obtained were analyzed from the point of view of mechanical strength. Also, micro- and nanosilica as well as samples of the optimal mortar compositions were analyzed physically and microstructurally. Experimental data showed that the mortar samples present maximum compressive strength for a content between 6 and 7.5% wt. of microsilica, respectively, for a content of 2.25% wt. nanosilica. The obtained results suggest a synergistic effect of micro- and nanosilica when they are used simultaneously in cementitious compositions. Thus, among the analyzed compositional variants, the mortar composition with 3% wt. microsilica and 2.25% wt. nanosilica showed the best performance, with an increase in compressive strength of 23.5% compared to the control sample (without micro- and nanosilica). Brunauer–Emmett–Teller (BET) analysis and scanning electron microscopy (SEM) images highlighted the decrease in pore diameter and the increase in structural compactness, especially for mortar samples with nanosilica content or a mixture of micro- and nanosilica. This study is useful in the field of recycling radioactive concrete resulting from the decommissioning of nuclear research or nuclear power reactors.
... Studies by Cote et al. (1987), Seveque et al. (1992), Rahman et al. (2007), and El-Kamash et al. (2006) delved into leaching behaviour, mathematical modelling, and kinetics of specific radionuclides in cement matrices. Their models became crucial tools for predicting releases, aiding in assessing the long-term performance and stability of cement-based waste forms. ...
... Saleh et al. (2020a,b) qualified phytoremediated radioactive waste, examining long-term behaviour under leaching and weathering. Rahman et al. (2007) developed models predicting radionuclide leaching from cement-clay matrices. These studies enhance our understanding of cement-based solidification's extended-term performance, emphasizing diverse factors and environmental conditions. ...
This review paper provides a comprehensive analysis of cement-based solidification and immobilisation of nuclear waste. It covers various aspects including mechanisms, formulations, testing and regulatory considerations. The paper begins by emphasizing the importance of nuclear waste management and the associated challenges. It explores the mechanisms and principles in cement-based solidification, with a particular focus on the interaction between cement and nuclear waste components. Different formulation considerations are discussed, encompassing factors such as cement types, the role of additives and modifiers. The review paper also examines testing and characterisation methods used to assess the physical, chemical and mechanical properties of solidified waste forms. Then the paper addresses the regulatory considerations and compliance requirements for cement-based solidification. The paper concludes by critically elaborating on the current challenges, emerging trends and future research needs in the field. Overall, this review paper offers a comprehensive overview of cement-based solidification, providing valuable insights for researchers, practitioners and regulatory bodies involved in nuclear waste management.
... Cement waste forms mainly include waste, additives or enhancement materials, cement, and water (Abdel Rahman et al., 2013). Different enhancement materials are used to lessen the leaching tendency of problematic radionuclides such as 85 Sr, 60 Co, and 137 Cs and/or to enhance the mechanical performance of the waste form (Abdel Rahman et al., 2007;El-Kamash et al., 2006;Goni et al., 2006;Guerrero and Goni, 2002;Fernandez-Jimenz et al., 2005). Correspondingly, several works dealing with the radioisotopes immobilization with cement and cement-enhancement materials were carried out (Atkinson et al., 1985;Snoeck et al., 2012;Beushausen and Gillmer, 2014;Pourjavadi et al., 2013). ...
... Plotting the CFL values versus the cumulative time provides a straightforward graphical comparison of leaching data from the various solidified cementitious samples [55]. These results can be later used in modeling calculations to predict the long-term leaching behavior and the overall durability and performance of final waste forms [62]. ...
... The unsubstituted 11 B-containing ions and molecules can release from the cementitious matrix effectively when the solidified specimens get contacted with water (Fig. 10d). These phenomena are supported by the observations in Fig. 7, where after a rapid release of boron from the specimens' surface during the first day (surface wash-off), the abundance of released 10 B decreases in time, whereas the total boron leaching increases continuously due to the 11 B release [62,94]. ...
Boric acid is a significant radioactive waste generated during the operation of nuclear power plants. Cementitious materials have been widely studied for the immobilization of boric acid. The generally used natural boric acid has been replaced by enriched boric acid for geochemical reasons and are expected to have varied behaviors in cementitious matrices. Results showed that simulated enriched/natural boric acid liquid wastes mostly contain boron in $${\mathrm{B}(\mathrm{OH})}_{4}^{-}$$ B ( OH ) 4 - and $${{\mathrm{B}}_{5}{\mathrm{O}}_{6}(\mathrm{OH})}_{4}^{-}$$ B 5 O 6 ( OH ) 4 - ionic forms, but the mass ratio of these species is higher in enriched boric acid solutions. In function with the concentration of enriched/natural boric acid, the solidified cementitious materials show different mineralogy.
... Low and intermediate level radioactive wastes are generated in radiochemical laboratories, research reactors, radioisotopes of metallurgical laboratories, activation analysis units, nuclear medicine divisions in hospitals, universities, and research organizations, as well as in industrial activities [1,2]. The radionuclides released may be transported with water, adsorbed by inorganic particulate matter, and/ or deposited in bottom sediments, where they pose a threat to living beings. ...
Phytomass sorbent material (RM) was obtained as a by-product from the process of essential oil extraction. Its phosphoric acid-modified nano-form, N-RM, was used to absorb Sr(II) and Eu(III) from an aqueous solution. The pseudo-second-order is the better fitting model. Isotherm Langmuir and Freundlich models were fitted with a maximum capacity of qm 18.2, 60.4, 11.5, and 13.8 mg/g for Eu/RM, Eu/N-RM, Sr/RM, and Sr/N-RM, respectively. The packet technique promised to be applicable on a large scale for the treatment of contaminated water. Both RM and N-RM are effective eco-friendly adsorbents for the removal of Eu(III) and Sr(II).
... e fitting process was based on the equation of Fick's second law in a semi-infinite medium, and apparent diffusion coefficient (ADC) as well as the time for complete leaching of radionuclides were calculated [21,33,34]. In this study, the ADC of cations in the fly ash/cement waste forms was assumed to be constant. ...
The utilization of cement waste forms with high content of fly ash is a potential method in large-volume immobilization of low- and intermedium-level radioactive waste at near-surface. However, the migration behavior of radionuclides in fly ash/cement waste forms under geological environment is still unclear. This study researched the transformation of products, pore structure as well as the leachability of Ca²⁺, Na⁺, and simulated radioactive nuclides (Sr²⁺ and Cs⁺) in fly ash/cement waste forms under simultaneous effect through X-ray diffractometer (XRD), mercury intrusion porosimetry (MIP), and inductively coupled plasma optical emission spectroscopy (ICP-OES). Furthermore, the relationship between the decalcification and the leaching of Sr²⁺ and Cs⁺ was established by the fitting curves of apparent diffusion coefficient. The results indicated that the products of fly ash/cement waste forms were kept stable under simultaneous effect and the pore structure has excellent resistance to temperature. The increasing salt concentrations of leachant and temperature promoted the leaching of radionuclides while the protection layer formed at 60–80°C inhibited this phenomenon. The relationship of apparent diffusion coefficient between Sr²⁺ and Ca²⁺ was quadratic nonlinear, while the relationship between Cs⁺ and Ca²⁺ showed a linear relationship. Compared to cement waste forms, fly ash/cement waste forms were more stable. In addition, the long-term retention ability of fly ash/cement waste forms to Cs⁺ was more outstanding than Sr²⁺.
... These highmoisture waste resins are currently collected and stored in drums into long-term storage building that meet International Atomic Energy Agency (IAEA) standards for radioactive waste storage facilities; to deal with growing production rate, it remains extremely urgent to explore more efficient solidification paradigm. Although substantial studies have been conducted to understand how to reduce leachability of radionuclides from commonly used ordinary Portland cement (OPC) matrices, high leaching rates and package volume, swelling and cracking of the formulations remain the major drawbacks for solidification of resin wastes (Abdelrahman et al., 2007;Faiz et al., 2017;Li and Wang, 2006;Neji et al., 2015;Plecas et al., 2004;Saleh et al., 2020b;Wang and Wan, 2015). Therefore, the development of an efficient and promising technology for robust solidification of waste resins is highly imperative to ensure their stability for storage and ultimate disposal in seawater or groundwater environments. ...
... In this study, to simulate the leaching behavior in natural conditions at the Maamoura burial site, the leaching medium was conducted in deionized water (pH = 7.06 ± 0.02), sodium hydroxide solution (pH = 10 ± 0.02), and chloride acid solution (pH = 3 ± 0.05). The volume of the leaching medium was 10 times the exposed surface area of the package, forming a 2 cm on each side (Abdelrahman et al., 2007). The static leaching test is shown in Fig. S1(a-b). ...
... Along all leachates, the highest incremental leaching rate was recorded during the first and third days, which may be from the superficial surfaces of packages. This figure clearly shows that the Cs leaching mechanism from the studied packages was attributed to surface wash-off and diffusion mechanism, where the slow portion of Cs dissolution did not occur (Abdelrahman et al., 2007). Leaching rates for GePK-1, GePK-3 and GePK-6 at pH 7 were 1.23 × 10 −08 , 1.10 × 10 −08 and 8.91 × 10 −09 (cm/s), respectively, lower than that for OPC matrix (1.01 × 10 −07 (cm/s)) (Faiz et al., 2017), demonstrating the robustness of trapping 134 Cs using UPSderived geopolymer packages. ...
Nuclear–grade Spent Organic Resin (SOR) contains high concentrations of radioactive nuclides and metal contaminants, while phosphate sludge contains high amount of fine clayey particles and CO32−, both posing a major threat to the biosphere. In this study, a novel geopolymer package (GP) was proposed to directly solidify SOR loaded with 134Cs by incorporating uncalcined phosphate sludge (UPS) as feedstocks, activated by NaOH/KOH. The results showed that alkali-mixed reagents-activated GP is more advantageous in terms of chemical stability and mechanical properties than NaOH-activated GP, recording compressive strength values greater than the waste acceptance criteria and OPC. The 28–day compressive strength of solidified packages can exceed 31 MPa at the highest amount of 42 wt% UPS. The addition of NaF powder into the solidified packages generates more hybrid type gels, which are more conducive to partial dissolution and bonding UPS particles, thereby producing stable and stronger GP. Leaching results of solidified GP in presence of up to 13 wt% SORs showed that only 0.15 % of total 134Cs was leached, even under aggressive solutions. Solidification mechanism revealed that activation of UPS-MK blend forms N,K–A–S–H, (N,K,C)–A–S–H/C–S–H gels coexisting with unreacted particles, thereby solidify/stabilize metal contaminants and Cs+ by a synergetic immobilization action of hydration products via substitution and encapsulation. This study provides a promising paradigm for effective solidification of nuclear–grade resins and synergetic harmless treatment of industrial/phosphate mine solid wastes.
... Cement is used for the encapsulation of radioactive wastes due to its chemical, thermal, and radioactive stability; corrosion resistance; and beneficial compatibility with most varieties of waste [13][14][15][16]. Among the numerous types of cement, Portland cement is the most commonly used for the solidification of LLW/ILW and has high retention potential resulting from mechanisms such as sorption, ion exchange, characteristic phase formation, oxy/hydroxyl precipitation, and combinations as cementwaste interactions [7,17,18]. The physical and chemical immobilization of radioactive wastes minimizes radionuclide migration and provides sufficient structural stability [17,18]. ...
... Among the numerous types of cement, Portland cement is the most commonly used for the solidification of LLW/ILW and has high retention potential resulting from mechanisms such as sorption, ion exchange, characteristic phase formation, oxy/hydroxyl precipitation, and combinations as cementwaste interactions [7,17,18]. The physical and chemical immobilization of radioactive wastes minimizes radionuclide migration and provides sufficient structural stability [17,18]. ...
... In all cases, the LR significantly decreased during the early stages of leaching (<5 days) but then gradually decreased over time. Among the four nuclides, Cs had the highest LR because of its low field strength, making it substantially soluble under highly alkaline conditions [18,[49][50][51]. Soler [52] reported that the easy release of Cs from its cementitious waste form can be attributed to its high solubility in high pH (12.5-13.6) ...
Numerous low-level and intermediate-level radioactive wastes are generated from the decommissioning processes of nuclear power plants; these wastes are immobilized to prevent the release of radionuclides under disposal conditions. In this study, we investigated the leaching behavior of Cs, Sr, Co, and Eu, which are common in immobilized decommissioning wastes. Ordinary Portland cement (OPC) was used as an immobilization agent. During the test, leaching of the nuclides occurred in the order of Cs, Sr, Co, and Eu and decreased over time. The results showed that 41.4% of the total Cs leached over 90 days, although the other elements leached in quantities less than 1.5%. CaCO3 was precipitated by the release of cementitious materials, indicating carbonation of the leachate. The leachability indexes in all cases exceeded the acceptable criteria (>6). The results of the present study suggest that OPC can be effectively used as a binding material to immobilize nuclides (Cs, Sr, Co, and Eu) contained in decommissioning wastes.
... All the static LTs were executed on duplicate at ambient temperature. The ɤ values were calculated consistent with the subsequent equation [9,22,23]: ...
... The acquired data showed that the resistance of zeolite cement to γ-radiation is relatively reasonable as this material encompasses zeolitic phase in its structure which, in turn, speeds up the formation of hydration products that fill the pores in the hydrated cement paste and accordingly makes the hydrated paste more compact and has a low porosity [18]. The decrease in R s by increasing the radiation dose (R d ) may be attributed to the variation in the atomic displacement and dimensional stability of the solidified products as a result of particle interactions resulting from the radiolysis of loosely bound molecules [21,22]. The sharp decrease of compressive strength starting from 50 KGy may be due to two main reasons; the first is the failure of hydration products on using radiation up to this value [28] and the second owing to possible increases in the total porosity of the hardened pastes by irradiation [29]. ...
The development of cementitious materials remains a vital goal to produce valuable products with good mechanical, physical and chemical properties suitable for the safe disposal of concentrated radionuclides resulted from the treatment of contaminated solutions. In this paper, zeolite cement with good properties was laboratory synthesized from industrial by-products fly ash and characterized using various characterization techniques. The leaching characteristics of strontium and cobalt radionuclides from the synthesized zeolite cement were scrutinized conforming with the standard leaching methodology of International Atomic Energy Authority (IAEA). A mechanical strength assessment was executed to characterize the extent of immobilization process of the solidified matrices. The cumulative leaching fraction (ɤ) of the two studied radionuclides was found to be less than 5% in all examined conditions, which implies the applicability of the IAEA-recommended methodology for estimating the diffusion coefficient. The experimental leaching data were regressed nonlinearly to various mathematical kinetic models to assess the controlling leaching mechanism and to determine the leaching parameters. The regression results indicated that strontium (⁸⁵Sr) and cobalt (⁶⁰Co) leaching resulted from two succeeding mechanisms: as first order kinetic reaction, and then diffusion. The calculated values of leachability indices signify that the performance of each of the studied matrices is within an acceptable range. A simplified mathematical model, rooted in the first order reaction and diffusion mechanisms, was simulated to predict the radionuclides leaching rates from zeolite cement matrices. By comparing the synthesized zeolite cement with other cementitious materials, it can be concluded that the synthesized material can be classified as an efficient material suitable to immobilize ⁸⁵Sr and ⁶⁰Co from radioactive wastes. The acquired findings demonstrated that the studied immobilized waste matrices have acceptable mechanical effectiveness.
... The resulting wastes generated from the treatment of the spent solvents should be immobilized in suitable waste form prior for their disposal in radioactive waste disposal facilities. Cementbased materials have been largely practiced to immobilize sludge, concentrate, emulsified organic liquids, sorbents, and ashes (Drace et al., 2012;Abdel Rahman et al., 2014b;Abdel Rahman and Ojovan, 2016;Abdel Rahman and Zaki 2009Abdel Rahman et al., 2007). It should be noted that direct immobilization can affect the efficiency of ordinary Portland cement in containing these wastes; the use of emulsifier is required to increase the waste loading and enhance the containment performance. ...
Solvent extraction techniques are widely used in different
industries to extract specified compounds; the sustainability of
these techniques is challenged by the environmental impacts of
conventional solvents and the limitations of conventional contacting devices. Advances in research areas have been addressed
this point by proposing green solvents and synergetic applications via the use of solvent impregnated sorbent or liquid membrane. This research was not applied on the industrial scale,
especially in the field of radioactive waste management, where
most of the research was focused on material preparation and
testing to optimize the recovery/removal performance. Limited
research addresses the radiation stability of these materials, and
no research was found on the treatment of spent green solvents
and their immobilization
