Sorption of caesium by complex hexacyanoferrates iii. a study of the sorption properties of potassium copper ferrocyanide

Commercially available potassium copper ferrocyanide (KCuFC) has been studied for caesium sorption. An effective capacity of 2.25 ± 0.06 mmol g^?1 can be achieved at a caseium concentration of 0.015m. The presence of 0.82m, magnesium nitrate reduces the effective capacity to 2.04 ± 0.06 mmol g^?1. The cyanoferrate also shows high caesium uptake in various simulated process solutions relevant to the treatment of radioactive wastes. KCuFC also possesses a high selectivity for caesium in high salt concentration solution. However, the cyanoferrate is not stable in acidic solution of pH < 3. Desorption of the sorbed caesium at various nitric acid concentrations has been investigated and it is concluded that caesium is eluted by a chemical reaction step as a consequence of the oxidation of the cyanoferrate.     

Arbuscular mycorrhizal fungi mediated uptake of 137Cs in leek and ryegrass

In a first experiment of soil contaminated with 137Cs, inoculation with a mixture of arbuscular mycorrhizae enhanced the uptake of 137Cs by leek under greenhouse conditions, while no effect on the uptake by ryegrass was observed. The mycorrhizal infection frequency in leek was independent of whether the 137Cs-contaminated soil was inoculated with mycorrhizal spores or not. The lack of mycorrhizae-mediated uptake of 137Cs in ryegrass could be due to the high root density, which was about four times that of leek, or due to a less well functioning mycorrhizal symbiosis than of leek. In a second experiment, ryegrass was grown for a period of four cuts. Additions of fungi enhanced 137Cs uptake of all harvests, improved dry weight production in the first cut, and also improved the mycorrhizal infection frequencies in the roots. No differences were obtained between the two fungal inoculums investigated with respect to biomass production or 137Cs uptake, but root colonization differed. We conclude that, under certain circumstances, mycorrhizae affect plant uptake of 137Cs. There may be a potential for selecting fungal strains that stimulate 137Cs accumulation in crops. The use of ryegrass seems to be rather ineffective for remediation of 137Cs-contaminated soil.     

Sorption of caesium by complex hexacyanoferrates. v. a comparison of some cyanoferrates

The properties of copper cyanoferrates and potassium cobalt ferrocyanide prepared at Imperial College and similar commercial products for caesium sorption have been investigated. Copper and cobalt based cyanoferrates have different chemical compositions and appear to be good adsorbers for the removal of caesium in aqueous solutions. Different caesium sorption mechanisms were observed for these cyanoferrates. A conventional ion exchange reaction, physical adsorption and a combination of the two processes were observed. The difference in caesium sorption mechanism also reflects the kinetics of the sorption process. Potassium copper ferrocyanide has the highest effective capacity but the caesium sorption rate is the slowest, whilst potassium cobalt ferrocyanide possesses faster kinetics but considerably lower effective capacity. Copper ferrocyanide tends to have better mechanical stability and moderate sorption kinetics and caesium uptake.     

Selective oxidation of propane over alkali-doped Mo–V–Sb–O catalysts

Alkali metal-doped MoVSbO catalysts have been prepared by impregnation of a MoVSbO-mixed oxide (prepared previously by a hydrothermal synthesis) and finally activated at 500 or 600 °C in N₂. The catalysts have been characterized and tested for the selective oxidation of propane and propylene. Alkali-doped catalysts improved in general the catalytic performance of MoVSbO, resulting more selective to acrylic acid and less selective to acetic acid than the corresponding alkali-free MoVSbO catalysts. However, the specific behaviour strongly depends on both the alkali metal added and/or the final activation temperature. At isoconversion conditions, catalysts activated at 600 °C present selectivity to acrylic acid higher than that achieved on those activated at 500 °C, both K-doped catalysts presenting the highest yield to acrylic acid. The changes in the number of acid sites as well as the nature of crystalline phases can explain the catalytic behaviour of alkali-doped MoVSbO catalysts.     

Rural areas affected by the Chernobyl accident: Radiation exposure and remediation strategies

Main objectives of the present work were to develop an internationally agreed methodology for deriving optimized remediation strategies in rural areas that are still affected by the Chernobyl accident, and to give an overview of the radiological situation in the three affected countries, Belarus, Russia and Ukraine. Study settlements were defined by having in 2004 less than 10,000 inhabitants and official dose estimates exceeding 1 mSv. Data on population, current farming practices, contamination of soils and foodstuffs, and remedial actions previously applied were collected for each of such 541 study settlements. Calculations of the annual effective dose from internal radiation were validated with extensive data sets on whole body counter measurements. According to our calculations for 2004, in 290 of the study settlements the effective dose exceeded 1 mSv, and the collective dose in these settlements amounted to about 66 person-Sv. Six remedial actions were considered: radical improvement of grassland, application of ferrocyn to cows, feeding pigs with uncontaminated fodder before slaughter, application of mineral fertilizers for potato fields, information campaign on contaminated forest produce, and replacement of contaminated soil in populated areas by uncontaminated soil. Side effects of the remedial actions were quantified by a ‘degree of acceptability’. Results are presented for two remediation strategies, namely, Strategy 1, in which the degree of acceptability was given a priority, and Remediation Strategy 2, in which remedial actions were chosen according to lowest costs per averted dose only. Results are highly country-specific varying from preference for soil replacement in populated areas in Belarus to preference for application of ferrocyn to cows in Ukraine. Remedial actions in 2010 can avert a large collective dose of about 150 person-Sv (including averted doses, which would be received in the following years). Nevertheless, the number of inhabitants in Belarusian and Russian settlements with annual doses exceeding 1 mSv remains large. Compared to international values for the cost-effectiveness of actions to reduce occupational exposures, the recommended remediation strategies for rural areas affected by the Chernobyl accident are quite cost-effective (about 20 k€/person-Sv).     

锶和铯在粉碎花岗岩柱中的迁移研究

研究了锶、铯在粉碎花岗岩上的吸附和迁移性能。设计了小型吸附柱,用氚水和~(125)I~-作示踪剂分别测定了自由柱体积FCV,完成了含有小量载体的~(85,89)Sr和~(134)Cs示踪剂淋洗曲线的测定,计算出柱法和批式法的吸附比R_d值,并进行比较。结果表明:所设计的吸附柱能满足碎岩柱实验要求。用氚水或用~(125)I~-测定的FCV本质上没有差別。锶、铯淋洗曲线仅出现单个的宽的淋洗曲线峰,未发现存在不可逆吸附现象。本实验使用的花岗岩对锶的吸附比在较高锶浓度(10~(-3)～10~(-5)mol/l)时随锶浓度而变化。当柱法和批式法两种实验体系中锶量对花岗岩重量比接近时,两种方法测出的R_d值也相近。     

Identification of cationic and oxidic caesium species in basic Cs-overloaded BEA zeolites

A parent acidic H-BEA with crystallites very small in size and high external surface area was used to prepare a series of materials loaded with increasing Cs⁺ contents by firstly ion-exchange and then impregnation with CsOH solutions. The monitoring of the ion-exchange process by chemical analysis and by IR spectroscopy in presence of CO or NH₃ reveals that a relevant amount of Brønsted acid sites in dehydrated H-BEA is related to framework Al sites that, in aqueous solution, turn into partially extraframework Al species unable to act any longer as sites of cationic exchange. This limits the exchange capacity in solution and higher levels of ion-exchange are attained by subsequent impregnation and calcination. A possible explanation for such a behaviour is proposed. The formation of carbonates by adsorption of CO₂, monitored by IR, confirms that the basic character induced on framework oxygen atoms by exchange of H⁺ with Cs⁺ is significantly weaker than that reached upon Cs-overloading. For the latter, the strong basicity is related to the presence of Cs₂O-like nanoparticles (also detected by EXAFS), dispersed within the zeolite pores (as shown by pore volume and TEM/EDX measurements). IR spectroscopy of adsorbed CO shows that Cs⁺ as countercations or as surface sites of occluded Cs₂O-like species exhibit a similar Lewis acid strength. Noticeably, in Cs-overloaded BEA, pairs of Cs⁺ sites (formed by two countercations and/or one countercation and a Cs⁺ at the surface of Cs₂O-like particles) are present, where CO can be adsorbed in a head–tail form, producing a distinct ν_CO band at 2145 cm⁻¹.     

Accumulation of potassium, rubidium and caesium (Cs and Cs) in various fractions of soil and fungi in a Swedish forest

Radiocaesium (¹³⁷Cs) was widely deposited over large areas of forest in Sweden as a result of the Chernobyl accident in 1986 and many people in Sweden eat wild fungi and game obtained from these contaminated forests. In terms of radioisotope accumulation in the food chain, it is well known that fungal sporocarps efficiently accumulate radiocaesium (¹³⁷Cs), as well as the alkali metals potassium (K), rubidium (Rb) and caesium (Cs). The fungi then enhance uptake of these elements into host plants. This study compared the accumulation of these three alkali metals in bulk soil, rhizosphere, soil-root interface, fungal mycelium and sporocarps of mycorrhizal fungi in a Swedish forest. The soil-root interface was found to be distinctly enriched in K and Rb compared with the bulk soil. Potassium concentrations increased in the order: bulk soil < rhizosphere < fungal mycelium < soil-root interface < fungal sporocarps; and Rb concentration in the order: bulk soil < rhizosphere < soil-root interface < fungal mycelium < fungal sporocarps. Caesium was more or less evenly distributed within the bulk soil, rhizosphere and soil-root interface fractions, but was actively accumulated by fungi. Fungi showed a greater preference for Rb and K than Cs, so the uptake of ¹³⁷Cs could be prevented by providing additional Rb or K at contaminated sites. The levels of K, Rb, and Cs found in sporocarps were at least one order of magnitude higher than those in fungal mycelium. These results provide new insights into the use of transfer factors or concentration ratios. The final step, the transfer of alkali metals from fungal mycelium to sporocarps, raised some specific questions about possible mechanisms.     

Heteropolyanions based catalysts for paraffins isomerization

n-Hexane isomerization was carried over Cs_xH_3−xPW₁₂O₄₀ catalysts promoted with Pt by mechanical mixing with a Pt on alumina catalyst. Different parameters as caesium and platinum content in the catalyst, temperature and atmosphere of heteropolyacids pre-treatment were optimized. The catalytic performances of the best catalyst were compared with those of industrial Pt promoted mordenite. 0.3 wt.% Pt-promoted Cs₂H₁PW₁₂O₄₀ pre-treated under hydrogen flow at 473 K showed the highest conversion and selectivity. Its performances are very close to those of the industrial zeolitic catalyst in the same reaction conditions. The gain in dibranched isomers selectivity is really promising for the future. With this catalyst, the reaction proceeds by a non-ideal bifunctional mechanism resulting from the superposition of a monofunctional acid and a bifunctional metal–acid mechanism.     

微生物与铯的相互作用及其在放射性核素污染环境修复中的应用潜力

含放射性核素的废物在排放前必须进行有效的处理。铯是核电站排放的放射性物质之一。现有的除铯技术，如沸石吸附、离子交换等方法成本较高。利用微生物技术去除铯是目前可以考虑的替代方案，铯具有的独特化学性质决定了铯与微生物之间的相互作用机理不同于其它金属／放射性核素。据报道，自然界中存在大量的微生物可以吸收铯，但不同种类的微生物，其吸收量差别很大，微生物对铯的吸收量受一些环境因素的影响，如操作系统(分批式或连续流)、菌体的固定化、pH值，特别是其它单价阳离子(如K^ 、Na^ )存在与否等。微生物对铯吸收量的差别可能与其单价阳离子转移系统对铯的亲合力有关，通过现代生物技术手段可以分离筛选出对铯具有高度亲合力的微生物。此外，控制微生物的生理状态也可以改变其对铯的亲合力。微生物方法去除铯在放射性核素污染环境的生物修复中具有实用潜力。