Desorption Of Cs Research Articles

Surface activation of n-type AlGaN with cesium and oxygen to enhance thermionic emission

The aim of this study is to enhance the characteristics of thermionic emission of AlGaN surface through surface control employing cesium (Cs) and oxygen. Cs-deposited AlGaN has significant applications in thermionic energy converters. However, as the emitter temperature increases, the thermal desorption of Cs from AlGaN surface increases, resulting in a decrease in the thermionic emission current. Therefore, focusing on the high affinity between Cs and oxygen, we investigated the possibility of suppressing thermal desorption by depositing Cs and oxygen on AlGaN surface. The thermionic emission current measured when Cs and oxygen were alternately deposited on AlGaN surface was 1.9 × 10−3 A cm−2 at 500 °C. The thermionic emission current was significantly higher than that obtained with Cs-only deposition (2.0 × 10−5 A cm−2). In addition, we attempted to reproduce the effect of dynamic surface changes on thermionic emission employing a new thermionic emission model (modified Richardson–Dushman model) that considers the correlation between a specific surface reconstruction phase and its thermionic emission component. The results suggest that the adsorbed component of Cs-deposited AlGaN exhibits three Cs adsorption sites with different desorption energies, while the adsorbed component of Cs/O2 co-deposited AlGaN exhibits at least four Cs adsorption sites with different desorption energies. It is suggested that the increase in adsorption components with higher desorption energies, caused by the deposition of oxygen, may have reduced the thermal desorption and improved Cs coverage and stability.

Influence of cations and low molecular weight organic acids on Cs(I) adsorption on montmorillonite and vermiculite

To predict the mobility of radiocesium (RCs) in the environment, it is essential to understand the adsorption and desorption processes. In this study, we focused on the effects of certain environmental factors, including typical cations (K+, Na+, and NH4+) and low molecular weight organic acids (LMWOAs) such as acetic acid, malic acid, and citric acid on the behavior of RCs on montmorillonite and vermiculite. The results showed that montmorillonite possesses the strongest adsorption capacity for Cs+ than that of vermiculite. Since K+ and NH4+ exhibit similar physicochemical properties to Cs+, there is a significant inhibition of Cs+ adsorption on montmorillonite and vermiculite during the competitive interaction with K+ and NH4+. Compared to NH4Cl, the desorption ratios of Cs+ on montmorillonite and vermiculite are higher in the presence of KCl as the background solution. Low molecular weight organic acids can cover the surfaces of montmorillonite and vermiculite to different extents, which effectively blocks the adsorption sites for Cs+, and leads to an obvious decrease in the adsorption and desorption of Cs+. Due to the high expandable performance, Cs+ is primarily reversibly adsorbed by montmorillonite. Nevertheless, the adsorption of Cs+ on vermiculite exhibits typical irreversible characteristics due to the interlayer collapse. After the adsorption of LMWOAs on montmorillonite and vermiculite, the irreversible adsorption of Cs+ is increased obviously, mainly due to the blocking effect of organic matters on the adsorption sites with high affinity to Cs+.

A comparative study on the Cs adsorption/desorption and structural changes in different clay minerals.

We investigated the structural changes in clay minerals after Cs adsorption and understood their low desorption efficiency using an ion-exchanger. We focused on the role of interlayers in Cs adsorption and desorption in 2:1 clay minerals, namely illite, hydrobiotite, and montmorillonite, using batch experiments and XRD and EXAFS analyses. The adsorption characteristics of the clay minerals were analyzed using cation exchange capacity (CEC), maximum adsorption isotherms (Qmax), and radiocesium interception potential (RIP) experiments. Although illite showed a low CEC value, it exhibited high selectivity for Cs with a relatively high RIP/CEC ratio. The Cs desorption efficiency after treatment with a NaCl ion exchanger was the highest for illite (74.3%), followed by hydrobiotite (45.5%) and montmorillonite (30.3%); thus, Cs adsorbed onto planar sites, rather than on interlayers or frayed edge sites (FESs), is easily desorbed. After NaCl treatment, XRD analysis showed that the low desorption efficiency was due to the collapse of the interlayer-fixed Cs, which tightly narrowed the interlayers' hydrobiotite due to the ion exchange of divalent cations (Mg2+ or Ca2+) into the monovalent cation (Na+). Moreover, EXAFS analysis showed that hydrobiotite formed inner-sphere structures after NaCl desorption, indicating that it was difficult to remove Cs from NaCl desorption due to the collapsed hydrobiotite and montmorillonite interlayers as well as the strong bonding in FESs of illite. In contrast, chelation desorption using oxalic acid effectively dissolved the narrowed interlayers of hydrobiotite (98%) and montmorillonite (85.26%), enhancing the desorption efficiency. Therefore, low desorption efficiency for Cs clays using an ion exchanger was caused by the collapsed interlayer due to the exchange between monovalent cation and divalent cation.

Adsorption structure deteriorating negative electron affinity under the H2O environment

Photocathodes with negative electron affinity (NEA) characteristics have various advantages, such as small energy spread, high spin polarization, and ultrashort pulsing. Nitride semiconductors, such as GaN and InGaN, are promising materials for NEA photocathodes because their lifetimes are longer than those of other materials. In order to further prolong the lifetime, it is important to better understand the deterioration of NEA characteristics. The adsorption of residual gases and back-bombardment by ionized residual gases shorten the lifetime. Among the adsorbed residual gases, H2O has a significant influence. However, the adsorption structures produced by the reaction with H2O are not comprehensively studied so far. In this study, we investigated adsorption structures that deteriorated the NEA characteristics by exposing InGaN and GaAs to an H2O environment and discussed the differences in their lifetimes. By comparing the temperature-programmed desorption curves with and without H2O exposure, the generation of CsOH was confirmed. The desorption of CsOH demonstrated different photoemission behaviors between InGaN and GaAs results. InGaN recovered its NEA characteristics, whereas GaAs did not. Considering the Cs desorption spectra, it is difficult for an NEA surface on InGaN to change chemically, whereas that for GaAs changes easily. The chemical reactivity of the NEA surface is different for InGaN and GaAs, which contributes to the duration of photoemission. We have attempted to prolong the lifetime of InGaN by recovering its NEA characteristics. We found that InGaN with NEA characteristics can be reused easily without thermal treatment at high temperatures.

Copolymerization of anthranilic acid and o-phenylenediamine by a free radical in the presence of nanoparticles of copper hexacyanoferrates for the removal of cesium ions in aqueous solutions

Core–shell nanocomposite of copper hexacyanoferrate copolymer of anthranilic acid with o-phenylenediamine (CHCF-poly-AA-co-OPD)) was synthesized and used as ion exchanger for the removal of cesium ions from wastewater. The nanocomposite was prepared by implantation of CHCF nanoparticles into the copolymer of poly(AA-co-OPD) during the polymerization process. By transmission electron microscope, scanning electron microscope and Brunauer–Emmett–Teller, the surface morphology and the porous structure were investigated. The physicochemical characterization of the prepared core–shell nanocomposite was carried out by FT-IR spectroscopy, XRD and thermogravimetric analysis. As a function in pH, metal ion concentration, shaking time and temperature, the capacity of the CSNC toward cesium ions and the behaviors of the process were studied. The results illustrated that the maximum capacity was recorded 1.35 mmol g−1 at pH 11, 10 mmol L−1 Cs+ and 25 °C. Also, Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D–R) isotherms models were studied, in which the data were well fitted with Langmuir model, suggesting that the uptake of Cs+ was monolayer and homogeneous. Also, the adsorption kinetics data were fitted well to pseudo-second-order model. Thermodynamic parameters were calculated in the temperature from 25 to 60 °C, and the data revealed that Cs+ sorption was endothermic, spontaneous and more favorable at higher temperature. Up to 92% desorption of Cs+ was completed with 2 M KCl.

Desorption of Cs from vermiculite by ultrasound assisted ion exchange.

Nuclear power plant accidents typically lead to the contamination of large volumes of soils with radioactive cesium. This element is hard to desorb from soil, especially when it is bound to mica minerals, and aggressive and energy-consuming techniques are often required. In this study, we investigated the use of ultrasound with Mg2+ cation exchange for the removal of a133Cs-contaminated vermiculite over a wide range of temperatures (20-200°C). At room temperature, ultrasound was found to significantly accelerate Cs desorption but only reversibly adsorbed Cs species were removed. Under hydrothermal conditions and ultrasonic irradiation in contrast, the removal efficiency after 1h was 50% at 100°C and more than 95% at 200°C, compared with only 50% without ultrasonication at 200°C. Cs contamination can therefore be nearly totally removed, even from collapsed vermiculite sites where sorption is considered irreversible. Ultrasound waves and high temperatures both make trapped Cs more accessible by spreading the sheets and improving mass transfer. Acoustic noise spectra show that even at high pressure and temperature, cavitation bubbles form, oscillate and collapse, with the desired physical effects. These results demonstrate the potential of synergistic ultrasound and hydrothermal treatment for soil remediation.

Influence of head group structure of cationic surfactants on the desorption of cesium from clays and clay minerals

The role of cationic surfactants head group for cesium (Cs) desorption from clays and clay minerals was investigated in this study by using two surfactants having similar hydrocarbon chain lengths but different head group types. Two surfactants used were dodecyltrimethylammonium bromide (DTAB) with linear structure and benzyldodecyldimethylammonium bromide (BDAB) containing bulkier head group. The results indicated that Cs desorption from bentonites using both surfactants was accompanied by interlayer expansion. In the case of Na-bentonite, BDAB showed higher Cs desorption efficiency than DTAB due to larger interlayer expansion after intercalation of BDAB. In contrast, the amount of desorbed Cs from Ca-bentonite was comparable, corresponding to the almost identical interlayer expansion after intercalation of both surfactants. It was because Ca ions present in Ca-bentonite must associate with two negatively charged interlayers, hence limiting its expansion. Cs desorption from kaolinite was more governed by surfactant micelles. When the surfactant micelles were formed earlier at low concentration, considerable desorption of Cs was achieved. In this regard, BDAB more efficiently desorbed Cs compared to DTAB owing to rapid formation of BDAB micelles at lower concentrations caused by the increase in head group size. For Cs desorption from illite, both surfactants even exhibited similar insignificant results with HCl used as a control of desorbent. Frayed edge sites in illite probably provoked strong Cs retention causing the difficulty in desorbing Cs. Furthermore, desorption kinetic data of Cs from all samples using both surfactants fitted well with pseudo-second order model, suggesting the occurrence of chemical desorption by involving ion-exchange mechanism.

Core\u2013shell polymer nanocomposite based on free radical copolymerization of anthranilic acid and o-amino phenol in the presence of copper hexacyanoferrates nanoparticles and its adsorption properties

Core–shell polymer nanocomposite (CSNC) of copper hexacyanoferrate-copolymer of anthranilic acid with o-aminophenol (CHCF-poly(AA-co-OAP)) was synthesized and used as ion exchanger for the sorption of cesium ions from aqueous solution. The nanocomposite was prepared by implantation of CHCF nanoparticles into copolymer of poly(AA-co-OAP) during the polymerization process. The surface morphology and the porous structure were investigated through transmission electron microscope (TEM), scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET). The characterization of the prepared (CSNC) was carried out by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Thermogravimetric (TGA). Which SEM and TEM images confirmed the nano-size of the prepared CSNC. The values of adsorption capacity of CSNC towards cesium ions and the factors influence on the removal of cesium from solutions were investigated as function in pH, metal ion concentration, temperature and contact time. The results illustrated that the highest value of sorption capacity of the prepared CSNC towards Cs+ ions was 2.1 mmol g−1 at pH 11, 10 mmol L−1 Cs+ and 25 °C. Four modeling include on Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) isotherms models were studied. According to the obtained data, Langmuir model considered the most suitable model, which suggest that the uptake of Cs+ was monolayer and homogeneous. Also, the adsorption kinetics data was fitted well to pseudo-second-order model. Thermodynamic parameters were calculated in the temperature from 25 to 60 °C and the data revealed that Cs+ sorption was endothermic, spontaneous, and more favorable at higher temperature. Up to 92% desorption of Cs+ was completed with 2 M KCl.

Desorption of Cs from Vermiculite by Ultrasound Assisted Ion Exchange

Desorption of Cs from Vermiculite by Ultrasound Assisted Ion Exchange

Desorption of Cs+ from contaminated biotite with a low molecular mass organic acid

Desorption of Cs+ from biotite using various organic and inorganic acids was evaluated considering the removal of Cs+ from contaminated soils. Oxalic acid was most effective in desorbing Cs+ from biotite. The desorption efficiency increased with heating temperature and time, and 94.8% desorption efficiency was obtained at 85 °C after 4 h. The contents of Al, Fe, and Mg in biotite decreased with the increasing heating time, and these contents decreased by 50%, 91%, and 95%, respectively after 4 h of oxalic acid treatment. In addition, X-ray diffraction could not detect biotite peaks after oxalic acid treatment. The results indicate that oxalic acid desorbed Cs+ from biotite by decomposing the biotite structure. Moreover, a desorption efficiency of Cs+ from biotite of > 95% was obtained using oxalic acid treatment even in the biotite with aging of 3 months. Since the research on effective desorption of Cs+ around the boiling point of water is limited, the results of this study are expected to contribute to the development of low energy and environment-friendly remediation of soil contaminated with radioactive species.

Behaviors of Desorption Agents During Removal of Cs From Clay Minerals and Actual Soil

The behaviors of various desorption agents were investigated during the desorption of cesium (Cs) from samples of clay minerals and actual soil. Results showed that polymeric cation exchange agents (polyethyleneimine (PEI)) efficiently desorbed Cs from expandable montmorillonite, whereas acidic desorption solutions containing HCl or PEI removed considerable Cs from hydrobiotite. However, most desorption agents could desorb only 54% of Cs from illite because of Cs’s specific adsorption to selective adsorption sites. Cs desorption from an actual soil sample containing Cs-selective clay mineral illite ( PEI > NH4+, and the highest Cs desorption amount achieved using HCl was 83%. Unlike other desorption agents with only cation exchange capabilities, HCl can attack minerals and induce dissolution of metallic elements. HCl’s ability to both alter minerals and induce H+/Cs+ ion exchange is expected to promote Cs desorption from actual soil samples.

Removal of cesium ions from A-type zeolites using sodium tetrakis(4-fluorophenyl)borate and sodium tetraphenylborate

With the ultimate aim of reducing the volume of radioactive-cesium-contaminated soil generated by the nuclear power plant accident in Fukushima Prefecture in 2011, this study focuses on the desorption of Cs+ ions from minerals that strongly adsorb Cs+, such as clay, using the ion-association reagents sodium tetrakis(4-fluorophenyl)borate hydrate (NaTFPB) and sodium tetraphenylborate (NaTPB) under mild conditions. A-type zeolite was selected as a representative aluminosilicate mineral with a high cesium adsorption capacity. NaTFPB exhibits stronger hydrophobic interactions with Cs+ and improved Cs+ compared to NaTPB; a desorption efficiency of 89.4% was achieved at a 10:1 NaTFPB/cesium molar ratio.

Cesium removal from a water system using a polysulfone carrier containing nitric acid-treated bamboo charcoal

Laboratory scale sorption and desorption experiments were performed to investigate the cesium (Cs) removal efficiency of a bead-shaped polysulfone carrier containing HNO3-treated bamboo charcoal (BC). The average Cs removal efficiency of BC only and of polysulfone carrier without BC after 1 h sorption reaction was 53 and 18%, respectively. However, the Cs removal efficiency for the polysulfone carrier with 5% HNO3-treated BC (P-5N-BC) after 1 h and 24 h reaction was 66 and 98%, respectively. The Cs removal efficiency after 24 h reaction remained >85% over a wide range of pH and temperature conditions, suggesting that using P-5N-BC as the Cs adsorbent is feasible in a variety of aquatic environments. The maximum Cs sorption capacity (qm) of P-5N-BC, as calculated from a Langmuir isotherm model, was 60.9 mg/g, which is much higher than those of other adsorbents from previous studies for 1 h of sorption time. The Cs desorption rate of P-5N-BC for 24 h desorption time was <17%, showing that the Cs was stably enough attached to the HNO3-treated BC for long-term use. The results of continuous column experiments showed that the total amount of treated water from the column packed with P-5N-BC increased more than nine times when compared with that from the only BC-granule-packed column. The P-5N-BC maintained more than 68% Cs removal efficiency after 90 pore volumes of flushing, suggesting that only 15 g of P-5N-BC (with only 0.75 g of HNO3-treated BC) could clean 5 L of Cs-contaminated water (initial Cs concentration: 1.0 mg/L; effluent concentration: < 0.09 mg/L). The present results demonstrate that P-5N-BC has remarkable potential for removal of Cs from diverse water systems.

Desorption mechanisms of cesium from illite and vermiculite

It is known that cesium ion, Cs+, is strongly sorbed to micaceous minerals. However, the desorption of Cs+ at a trace sorption level with time in the presence of different salt ions is not well understood. In this study, we conducted long-term sorption and desorption experiments of Cs+ with illite and vermiculite at room temperature to study the effects of sorption time and co-existing cations on the desorption. A small amount of Cs+ (50 nM Cs+ spiked with 900 Bq 137Cs) was sorbed to the illite and vermiculite in the presence of 1 mM K+ or Ca2+, or 1 mM K+ and 100 mM Ca2+ over 8 weeks, which was then desorbed in the presence of Prussian blue (PB) nanoparticles over 12 weeks. The PB nanoparticles were used to inhibit the re-sorption of desorbed Cs+. More than 90% of Cs+ was sorbed to the minerals in the presence of Ca2+; meanwhile, only 50–70% of Cs+ was in the presence of K+. For all samples other than the illite with Ca2+ (Ca-illite), more than 80% of Cs+ were desorbed within a few days, and almost all Cs+ was desorbed at the end of the experiment. The large and fast desorption of Cs+ indicated a large part of Cs+ sorbed to these minerals were indeed labile in the presence of a strong sorbent like PB nanoparticles. These desorption trends were hardly influenced by a change of the sorption time. The desorption of Cs+ from the Ca-illite was slow, taking more than one month before 80% desorption for the sample with 1-day sorption, and the desorption amount only reached less than 90%. This slow desorption of Cs+ from the Ca-illite became even slower with the sorption time from one day to two weeks, and only 70% of sorbed Cs+ was desorbed at the end of the experiment for the latter. The mechanisms of Cs+ desorption from the Ca-illite was quantitatively explained by fitting to a pseudo first-order desorption model, suggesting that 30–40% of Cs+ was sorbed to the peripheral region of the interlayer of the Ca-illite and diffused into the interior part. The rest of sorbed Cs+ can be desorbed relatively fast. As this Cs+ was most likely sorbed to frayed edge sites in the Ca-illite, these results suggested that a part of the sorbed Cs+ (70 - 60%) was labile. Thus, the expansion and collapse of the peripheral regions of the interlayers induced by co-existing cations and interlayer migration of Cs+ are important processes constraining the sorption and desorption of Cs+ to/from the micaceous minerals. In addition, compared with the desorption from the pure minerals examined in this study, the desorption of Cs+ from real soils was slower likely due to weathering and/or the formation of aggregates.

Desorption technologies for remediation of cesium-contaminated soils: a short review.

This review summarizes the mechanisms for desorbing and extracting cesium (Cs+) from clay minerals and soil. Most techniques use ion exchange with acids, cations, polymers, and surfactants. Some improve desorption of Cs+ from clay minerals, while surfactants and polymers expand the interlayer. Mixtures of acids/polymers, acids/surfactants, cations/polymers, and cations/surfactants are therefore more effective agents for desorption of Cs+ from clay minerals. Hydrothermal treatment plays a role similar to that of polymers and surfactants in expanding the interlayer of clay minerals. The primary desorption mechanism expands the interlayer and desorbs Cs+, but multiple sequential extractions based on these techniques can more effectively desorb Cs+ from clay minerals and field-contaminated soils. Desorption techniques for Cs+ based on multiple sequential extractions can reportedly achieve an efficiency greater than 90%, and such approaches are likely to be important technologies for remediation of Cs+-contaminated soils and industrial accident sites, as well as the dismantling of nuclear power plants.

Hydrothermal Desorption of Cs with Oxalic Acid from Hydrobiotite and Wastewater Treatment by Chemical Precipitation

A hydrobiotite (HBT) clay contains more cesium (Cs)-specific adsorption sites than illitic clay, and the capacity of frayed edge sites can increase as the weathering of micaceous minerals proceeds. Thus, Cs can be selectively adsorbed to HBT clay. In this study, we investigated the removal efficiency of non-radioactive (133Cs) and radioactive (137Cs) Cs from HBT, using oxalic acid. We found the minimum optimal concentration of 0.15 M oxalic acid removed more than 90% of Cs. Subsequently, cations and Cs ions were removed using Ca(OH)2 and sodium tetraphenylborate (NaTPB) to treat the washing wastewater generated at the optimum concentration of the desorbent (0.15 M oxalic acid). In order to remove cations and heavy metal ions in the waste solution, Ca(OH)2 was treated at a mass ratio of 0.025 g/mL and pH 9–10 to derive optimal conditions. As a final step, to remove Cs, NaTPB was treated with a mass ratio of 2 mg/mL and reduced to below 0.1 mg/L Cs to find the optimal dose. The novelty of this study is that the amount of radioactive waste can be drastically reduced by removing the non-radioactive cations and heavy metals separately in the first step and removing the remaining radioactive Cs in the second step.

Sequential removal of radioactive Cs by electrochemical adsorption and desorption reaction using core-shell structured carbon nanofiber–Prussian blue composites

137Cs is harmful to human health and the environment; hence, research on new techniques and development of materials for removing from contaminated water have attracted attention. Herein, we demonstrate that core-shell structured Prussian blue–carbon nanofiber (PB–CNF) composites, synthesized by electrodeposition, can be used to effectively remove radioactive 137Cs via electrochemical adsorption/desorption. PB nanoparticles with thicknesses of tens of nanometers were electrochemically formed on the CNF core with a diameter of approximately 100 nm; the exact weight of PB on CNF was 2.75 mg/cm2. The PB–CNF electrodes more efficiently adsorbed and desorbed the Cs ions than the existing PB–FTO electrode and PB–commercial carbon cloth. Transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses confirmed that the Cs ions removed from the solution were adsorbed on PB rather than on CNF. X-ray photoelectron spectroscopy analysis confirmed that the oxidation state of iron in PB changes depending on the Cs ion adsorption and desorption reaction. Cycling experiments of electrochemical adsorption and desorption using PB–CNF showed that radioactive 137Cs and non-radioactive Cs ions can be continuously removed from radioactive wastewater and accumulated in a specific solution. These results imply that the PB–CNF composite can efficiently remove radioactive Cs and significantly reduce secondary radioactive waste. Moreover, the composite is reusable and can aid the establishment of a low-cost alternative Cs removal process.

Hydrothermal-treatment desorption of cesium from clay minerals: The roles of organic acids and implications for soil decontamination

The adsorption and desorption of cesium (Cs) on clays of contaminated soil in a rhizosphere zone can be greatly affected by various biogeochemical processes, the timespans of which are usually months to years. Herein, we present several representative scenarios of the binding of Cs on diverse sites of vermiculitized biotite by controlled Cs adsorption to particles of different sizes. We investigated whether and how the fixed Cs in the different scenarios is desorbed by ambient and hydrothermal treatments with several low-molecular-weight organic acids (LMWOAs). The results showed that the sorbed Cs was discriminatively retained in the un-collapsed, partially collapsed, and thoroughly collapsed structures of vermiculites. The desorption of the sorbed Cs by hydrothermal LMWOAs extractions was easily realized in the un-collapsed structure, but was limited or minimal in the partially collapsed and thoroughly collapsed structures. The Cs desorption varied in accord with the LMWOA species applied and increased with the acid concentration, temperature, and number of treating cycles. The analysis of Cs-desorbed specimens confirmed their partial destruction and interlayer expansion, suggesting that the underlying mechanism of Cs removal by LMWOAs involves not only acid dissolution and complexation but also the accelerated weathering of clays within a short time under hydrothermal conditions. Our findings contribute novel insights into the mobility, bioavailability, and fate of Cs in contaminated soils and its removal from these soils for environmental restorations.

Analysis of the cesium distribution in the JT-60SA negative ion sources for steady long-pulse operation.

To realize stable negative ion beams for 100 s required in the neutral beam injector of JT-60SA, a physical model to control cesium (Cs) distribution inside the negative ion source has been developed in order to maintain the stable negative ion production at the plasma grid (PG) surface with Cs. In this work, to quantitatively evaluate Cs coverage on the PG, a three-dimensional Cs transportation code was introduced to consider the spatial Cs distribution in the source. The spatial temperature distribution of the chamber wall was also introduced in this model. As a result, the reasonable variation of the Cs coverage for 100 s was obtained, compared to that in the initial model. Based on the modified model, the operational temperature of the chamber wall was proposed to be less than 60 °C to suppress the desorption of Cs in the chamber wall and to sustain the stable negative ion production. In addition, it was also suggested that a slightly higher wall temperature before the operation leads to a decrease in the amount of Cs stored at the chamber wall, resulting in suppression of Cs consumption in the ion source.

Selective removal of radiocesium from micaceous clay for post-accident soil decontamination by temperature-controlled Mg-leaching in a column

The effective and efficient removal of radioactive Cs from contaminated soil is highly urgent for the nuclear post-accident remediation. In present study, we achieved rapid Cs desorption from both a typical micaceous clay (i.e., vermiculitized biotite, VB) and actually contaminated soil by high-speed ion exchange through temperature-controlled continuous leaching with Mg-solutions in a column reactor. Cs-sorbed VB was firstly employed as a soil surrogate to explore the macro-Cs desorption process and micro-mechanism in detail. Results showed that VB sandwiched the adsorbed Cs to its interlayers within collapsed structure (10.7 Å) and prevent Cs release even by abundant extraction with H2O at 250 °C or Mg2+ at 25 °C. However, Mg2+-extracted Cs desorption boosted significantly with elevating temperatures and 100 % of sorbed-Cs was removed from Cs-VB leached above 150 °C. Further structural and composition analysis of the leached specimen ensured that solvated Mg2+ preferentially entered into Cs+-collapsed interlayers at 150 °C than K+-interlayers above 200 °C, leading to prior complete Cs removal over K from VB at lower temperatures. By contrast, the Cs-contaminated soil reduced by ∼39 % but ∼82 % of its initial radioactivity after equally leaching with same volumes of Mg2+-solution at 150 and 200 °C, respectively. These temperature-controlled Cs desorption validated that radioactive Cs in actual soil indeed be tightly trapped by micaceous clays nearly in the Cs-K co-collapsed interlayers, to which its extraction by other cations can conditionally occur above enough high leaching temperatures. These superior features would inspire new insights for the design of novel practical technologies for treatment and decontamination of the nuclear post-accident soils.