Caesium

The control of the cation composition of formamidinium (FA), methylammonium (MA), and cesium (Cs) has been used to engineer significant improvements in organic–inorganic perovskite solar cells. However, the thermal stability of mixed-cation perovskite solar cells is not fully understood. In this work, we present the results of an experimental study of the stability of double-cation perovskites [(FAPbI3)0.97(MAPbBr3)0.03] [(FAMA)-perovskite solar cells (PSCs)] and triple-cation based-perovskites [Cs0.05(FA0.95MA0.05)0.95Pb(I0.95Br0.05)3] [(CsFAMA)-PSCs] operated between 40 and 60°C. The thermally induced changes in the film microstructure are elucidated via scanning electron microscopy and x-ray diffraction analyses, and these are related to changes in optoelectronic properties, charge transport, and current–voltage characteristics of (FAMA)-PSCs and (CsFAMA)-PSCs. The implications of the observed degradation mechanisms are also discussed for the future development of efficient and s...

SummaryWe set out to study connected porosity of crystalline rock using X‐ray microtomography and scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM‐EDS) with caesium chloride as a contrast agent. Caesium is an important radionuclide regarding the final deposition of nuclear waste and also forms dense phases that can be readily distinguished by X‐ray microtomography and SEM‐EDS. Six samples from two sites, Olkiluoto (Finland) and Grimsel (Switzerland), where transport properties of crystalline rock are being studied in situ, were investigated using X‐ray microtomography and SEM‐EDS. The samples were imaged with X‐ray microtomography, immersed in a saturated caesium chloride (CsCl) solution for 141, 249 and 365 days and imaged again with X‐ray microtomography. CsCl inside the samples was successfully detected with X‐ray microtomography and it had completely penetrated all six samples. SEM‐EDS elemental mapping was used to study the location of caesium in the ...

Наведено результати дослідження умов окиснення озоном органічних компонентів рідких радіоактивних відходів (РРВ) на прикладі модельного розчину з імітованими розчинами щавлевої кислоти та динатрієвої солі етилендиамінтетраоцтової кислоти (ЕДТА). Установлено, що в процесі обробки органічних складових РРВ
озоном відбувається зменшення величини рН, що призводить до зниження ефективності їхньої деструкції. Утримання рН на рівні вихідних значень (11−12 одиниць) шляхом постійного підлуговування здатне підвищити ефективність деструкції органічних компонентів РРВ на 30 %. ЕДТА краще піддається деструкції озоном (озонолізу), ніж щавлева кислота. Деструкція органічних компонентів РРВ відбувається в два етапи: перший, більш швидкий, та другий, більш повільний. Максимальний ступінь деструкції ЕДТА в умовах експерименту становив 86 %, ступінь деструкції щавлевої кислоти — 51 %, максимальний ступінь деструкції органічних компонентів модельного розчину РРВ (ЕДТА, щавлева кислота, синтетичні поверхнево-активні
речовини) становив 67 %. За рахунок співосадження та адсорбції під час озонування розчину відбувається зменшення концентрації марганцю в модельному розчині РРВ на 94,3 %, знижується активність 137Cs на 26 %, а 90Sr на 15,7 %, концентрація кобальту зменшується лише на 6 %.

Вибір і впровадження ефективної й екологічно безпечної технології очищення рідких радіоактивних відходів (РРВ) українських АЕС є актуальним, оскільки діючана АЕС схема переробки РРВ має чимало суттєвих недоліків. Однією з таких технологій вважається сорбційно-осадова з використанням природних або модифіко-ваних мінеральних сорбентів, зокрема цеолітів, які мають молекулярно-ситові та сорбційно-селективні властивості до низки радіонуклідів. У статті наведено результати дослідження сорбції 90Sr і 137Cs природним, кислотно- та лужно-модифікованим цеолітами Сокирницького родовища з модельних розчинів РРВ та визначено форми знаходження сорбованих радіонуклідів. Основним мінералом у складі цеолітових порід є кліноптилоліт — 70 ± 3 мас. % із домішками кварцу та слюди у кількостях ~12 та ≤ 3 % відповідно. Показано, що в процесі модифікації цеоліту відбувається перерозподіл обмінних катіонів і вмісту катіонів у ґратці кліноптилоліту. Природний цеоліт належить до калій-кальцій-натрієвих кліноптилолітів, натрій модифікований цеоліт — натрій-калій-кальцієвих, а кислотно модифікований — калій-натрій-кальцієвих. Відношення Si/Al збільшується у ряду: цеоліт природний → цеоліт натріймодифікований→ цеоліт кислотно-модифікований. Установлено, що модифікація кліноптилоліту натрієм не лише підвищує температурну стійкість, але й збільшує адсорбцію радіонуклідів 90Sr і 137Cs з модельних розчинів РРВ. Ізотерми іонного обміну показують, що селективність натрієвої форми кліноптилоліту щодо досліджуваних радіонуклідів є вищою, ніж селективність природного і кислотно-модифіко-ваного кліноптилолітів. Максимальний ступінь сорбції 90Sr природним цеолітом протягом експерименту (14 діб) становить 55 %, 137Cs — 90 %, лужно-модифікованим для 90Sr — 62,2 %, а 137Cs — 98,78 %, кислотно-модифікованим 90Sr — 18 %, а 137Cs — 85 %. Аналіз отриманих результатів дає підстави рекомендувати цеоліт Сокирницького родовища і його натрієві форми як ефективні сорбенти радіонуклідів із РРВ у разі запровадження сорбційно-осадової технології.

The report presents the results of an experimental modelling of the influence of Са2+ ion concentration and the alkaline pH of a model solution on the sorption capacity of natural (NB) and sodium-modified (SMB-20) bentonites from the Cherkasy deposit for 137Cs and 90Sr. Based on the computer simulation data, it was found that small amounts of sediments, mainly oxides, hydroxides, Fe oxyhydroxides (hematite, goethite, limonite), and Ca carbonates (calcite, aragonite) were present in the model solution with the increase in Са2+ ion concentration (after adding CaCl2 solution) and alkaline pH. The obtained Cs and Sr sorption values indicate that the insoluble / sparingly soluble compounds do not block the interlayer surface of montmorillonite (the main mineral of bentonite clays), but are formed mainly on the basal surface, frayed edges and surface defects of the mineral grains of montmorillonite. The concentration of the main structural elements (Si, Al) in the bentonites practically does not change with increased pH and Ca2+ ion concentration in the model solution compared to the initial samples. This fact indicates the stability of the bentonites under these conditions. At the
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same time, an increase in the calcium concentration and a decrease in the sodium concentration were found in the ion-exchange complex of the bentonites, if compared to the NB. This results in the transformation of SMB 20 bentonite from Na, Ca form to Ca, Na form. The Cs and Sr sorption on NB is shown to proceed more effectively than on SMB-20. The results of this research may justify the bentonite clay application as a component of the isolating engineered barriers of radioactive waste disposal facilities.

Нині в Україні накопичено десятки тисяч метрів кубічних рідких радіоактивних відходів (РРВ), які зберігаються у сховищах тимчасового типу, що є значною проблемою екологічної безпеки. Сорбційно-осадова схема вилучення радіонуклідів для переробки трапних вод АЕС є перспективною. На основних етапах дезактивації трапних вод доцільно використовувати дешеві та доступні природні та модифіковані сорбенти–алюмосилікати: бентоніти та цеоліти. Для використання сорбційно-осадового методу вилучення доцільно провести руйнування органічних компонентів трапних вод (ЕДТА, щавлева кислота, СПАР) озоном, оскільки наявність даних речовин ускладнюють сорбційне вилучення 60Со і 54Мn.

In article shown results the chemical, mineral and granulometric composition of natural and modified by soda bentonite clays from Cherkas’ke deposit, the composition of exchange cations, diffractograms, differential heating curves, IR spectra and features of 137Cs sorption. It is determined that sorption degree for 137Cs on the modified samples exceeds 90%, for natural bentonite – about 85%. On both types of bentonite with increasing of contact time with model solution and pH, there is a redistribution of water-soluble, ion-exchange and fixed forms of radionuclides and the part of the latter that do not participate in migration processes increases, which indicates the ability of bentonites to effectively immobilize radionuclides for a long time. Investigated bentonite clays can serve as material for creating anti-migration barriers for surface/subsurface storage facilities for RW disposal.

The dissertation is submitted to the degree of Doctor of Philosophy in Technical Sciences by spatiality 21.06.01 – Ecological Safety. State Ecological Academy of Postgraduate Education and Management, Kyiv, 2021.
The dissertation is devoted to the study of the ecological safety of processes of removing radionuclides from multicomponent solutions. It is established that in the process of the destruction of organic substances – components of liquid radioactive waste (LRW) by ozone, a significant drop in pH value takes place as a result of a decrease in the destruction efficiency, and the process of the destruction of organic components occurs in two stages: fast and slow. It is determined that the highest efficiency of the destruction of organic components of LRW is achieved with constant alkalization of the solution and keeping the pH values at 11-12 units. It is shown that in the process of ozonation, precipitates of metal hydroxides and oxides are formed, on the surface of which radionuclides are fixed due to co-precipitation and adsorption. Thus, in the result of ozonation, the concentration of Mn2+ decreases by 94.3%, Co2+ – by 6%, the activity of 137Cs reduces by 26%, 90Sr – by 15.7%. It is found that in all parameters (degree of sorption, rate of establishment of sorption equilibrium, the prevalence of strongly fixed forms of sorption – acid-soluble and residual) Na-modified sorbents are the most effective among the studied sorbents: relative to 90Sr, Co2+, Mn2+ – Na-modified bentonite of the Cherkas’ke deposit PBA-20 (maximum sorption degree of 90Sr – 85%, Co2+ – 99%, Mn2+ – 99%); relative to 137Cs – an alkali-modified zeolite of the Sokyrnyts’ke deposit (the degree of 137Cs sorption – 99%). I.e. industrial modification of bentonites with soda and laboratory modification of zeolite with alkali (NaOH), significantly increases the degree of sorption of the studied radionuclides in comparison with their natural Ca-forms. It is determined that the sorption equilibrium upon adsorption of Co, Mn, Cs from the model LRW is established within from one to seven days, Sr – from two to fourteen days, the degree of sorption is practically independent of the initial pH of the solution, and the sorbents have a high buffering capacity. It is determined that it is more appropriate to use an alkali-modified zeolite as a sorbent under dynamic conditions. It is found that zeolites are characterized by high selectivity for 137Cs concerning its chemical analogue – 40К. It is shown that preliminary ozonation of the solution for 2 hours effectively destroys the organic components of LRW in such a way that the degree of sorption of the studied radionuclides is only 2 - 3% lower from the solution after ozonation in comparison with the control solution, which did not contain organic components. The adequacy parameters (MAPE, MPE, R2, R2adj, χ2, F, BIC, AIC) of mathematical models are calculated, and it is determined that the sorption model of the kinetics of complex chemical processes of all studied radionuclides (Co, Mn, Cs, Sr) with the most effective sorbents (PBA-20 bentonite and alkali-modified zeolite) is the most adequate and a universal model among those presented. Recommendations on the development of a scheme for LRW treatment by extracting radionuclides are presented, a conceptual block diagram of LRW treatment is given.

The main feature of bentonite clays is their highsorption capacity with respect to various radionuclides.The study of sorption kinetics of 137Cs was performed inthe static mode by natural and industrial soda modified(PBA‑20) samples of bentonite clays of Cherkasy depositof bentonite and paligorskite clays from groundwatermodel solutions of radioactive waste disposal facilitiesof “Vector” production complex under various pH andsolution mineralisation. The desorption of occludedsamples was studied in distilled water and acetate-ammoniumbuffer solution. The value of the degree ofsorption (S) for 137Cs on the modified samples exceeds90 %, for natural bentonite this indicator is lower (about83–85 %). On both types of bentonite with increasing timeof their contact with aqueous solution and pH, there is aredistribution of water-soluble,ion-exchange and fixedforms of radionuclide and the share of the latter, that is notparticipating in migration processes increases, indicatingthe ability of bentonites to immobilize effectively for along time. It is shown that Na-modified bentonite hashigher proportion of sorption in fixed form compared tonatural one and its application increases the probabilityof irreversible fixation of migrating radionuclides undernon-optimal conditions of sorption (high pH (>11) ofwater after prolonged contact with cement-concretecomponents of engineering barriers) and thus increasesthe environmental safety of the storage facility. It isshown that bentonite clays of the Cherkasy deposit canserve as an effective material for creating anti-migrationbarriers of I and II stages of surface/near-surface storagefacilities for radioactive waste disposal at the “Vector” production complex. At the same time, the issue of practical application of bentonite clays of Cherkasy deposit for accurate predictions of securing radioactive waste disposal of Chornobyl origin requires further study of sorption-desorption properties of bentonite clay with respect to other fission products and actinides.

The article presents the results of an experimental modelling of the influence of Са2+ ion concentration and pH of a model solution on the elemental composition and sorption capacity of natural (NB) and sodium-modified (SMB-20) bentonites from the Cherkasy deposit for 137Cs and 90Sr. The processes of the Cs and Sr sorption from multicomponent solutions with different pH, Eh and salt composition depend on the insoluble or sparingly soluble compounds precipitated on the bentonite surface. Based on the computer simulation data, it was found that small amounts of sediments, mainly oxides, hydroxides, Fe oxyhydroxides (hematite, goethite, limonite), and Ca carbonates (calcite, aragonite, dolomite) were present in the model solution with alkaline pH after adding CaCl2 solutions. Oxides and hydrated oxides of Fe, and calcium carbonates play an important role in the Cs and Sr sorption processes on bentonites. They can concurrently sorb radionuclides and block the sorption centres in montmorillonites. The concentration of the main structural elements (Si, Al) in the bentonites practically does not change with the increased pH and Ca2+ ion concentration in the model solution compared to the initial samples of NB and SMB-20, which indicates their structural stability. At the same time, an increase in the calcium concentration and a decrease in the sodium concentration were found in the ion-exchange complex of montmorillonite — the main bentonite mineral if compared to the initial samples. This can eventually lead to the transformation of SMB-20 bentonite from Na, Ca form to Ca, Na form. The 137Cs and 90Sr sorption on NB is shown to proceed more effectively, compared to SMB-20 in conditions of the increased pH and Ca2+ ion concentration. The results of this research may justify the bentonite clay application as a component of the isolating engineered barriers of radioactive waste disposal facilities.

Cesium radioactive isotopes (134Cs and 137Cs) are dangerous to human health due to their long half-life and high solubility in water. Nuclear experiments, wars, and nuclear plant accidents have been the main sources of Cs release into the environment. In recent years, several methods have been introduced for the elimination of Cs radioactive isotopes from contaminated water. This study provides an overview of the available published articles (2008–2016) regarding the remediation of waters polluted by Cs isotopes. The maximum adsorption capacity (MAC) of Cs isotopes corresponded to natural chabazite (273.24 mg Cs/g adsorbent), hollow Prussian blue (PB) nanoparticles (262 mg Cs/g adsorbent), and Prussian blue implemented non-woven fabric (260 mg Cs/g adsorbent). Using natural chabazite and PB adsorbents, along with another adsorbent (PB graphene oxide hydrogel), Cs radioactive isotopes can be effectively removed from the aqueous solutions.

The control of the cation composition of formamidinium (FA), methylammonium (MA), and cesium (Cs) has been used to engineer significant improvements in organic–inorganic perovskite solar cells. However, the thermal stability of mixed-cation perovskite solar cells is not fully understood. In this work, we present the results of an experimental study of the stability of double-cation perovskites [(FAPbI3)0.97(MAPbBr3)0.03] [(FAMA)-perovskite solar cells (PSCs)] and triple-cation based-perovskites [Cs0.05(FA0.95MA0.05)0.95Pb(I0.95Br0.05)3] [(CsFAMA)-PSCs] operated between 40 and 60°C. The thermally induced changes in the film microstructure are elucidated via scanning electron microscopy and x-ray diffraction analyses, and these are related to changes in optoelectronic properties, charge transport, and current–voltage characteristics of (FAMA)-PSCs and (CsFAMA)-PSCs. The implications of the observed degradation mechanisms are also discussed for the future development of efficient and s...

The cesium-137 is the most problematic radionuclide in the radioactive wastes. It belongs to the IA group of the periodic table, highly reactive towards water and has very high mobility. Due to beta and gamma radiation hazards of radiocesium its decontamination and disposal requires some special tools and techniques. In this study globules of clay material was used for the removal of cesium from low level liquid radioactive wastes and further processed for immobilization. The aim of this study was to assess the solidification and immobilization of secondary waste. The secondary waste, after sorption of cesium from the liquid radioactive waste generated at this institute, was found compatible to the cement matrix used for the cementation process. The procedure for immobilization of low level radioactive waste with cementation using vitreous clay material as an additive was developed.