Comparative interpretation of leach rate of137Cs and60Co from cement matrix

A technique for leaching¹³⁷Cs and⁶⁰Co from a cement matrix, using three methods based on theoretical equations, has been developed. These were: Method I, diffusion equation derived for a plane source model, Method II, rate equation for diffusion coupled with a first-order reaction. The leaching data were also analyzed by an empirical method employing a polynomial equation, Method III. Results presented in this paper are examples of data obtained in a cement testing project which will influence the design of the future radioactive waste storage center.     

A gravimetric study of water vapour sorption on hydrated cement pastes

To study the pore structure of hardened cement pastes water vapour sorption isotherms are measured in a gravimetric way. The accuracy appeared to be restricted by water vapour effects on the balance (a Cahn 2000 micro balance) and by the employed type of secondary fulcra. It takes several days before the total amount of water vapour is adsorbed or desorbed when the vapour pressure is changed. Therefore a method of extrapolation is employed to calculate the equilibrium amount from the course of the mass change with time.     

Diffusion of 99Tc in granite under aerobic and anoxic conditions

Summary  Vezetéknév     

Low-temperature crystal growth of Cs2LiLuCl6-II and Cs2KScCl6 under reducing conditions and their structural refinement

Cs₂LiLuCl₆ (form II, metastable at room temperature) and Cs₂KScCl₆ were obtained as single crystals from reaction of CsLu₂Cl₇: Li = 1:1 and Cs₃Sc₂Cl₉: K = 1:2 in arc-welded tantalum tubes at 500°C. They crystallize with the cubic face-centered K₂NaAlF₆-type structure (elpasolite, Fm3m, Z = 4) with a = 1040.9 pm, x(Cl) = 0.2483(4) [Cs₂LiLuCl₆-II] and a = 1087.3(3) pm, x(Cl) = 0.2263(6) [Cs₂KScCl₆].     

Sorption properties of chemically treated clinoptilolites with respect to Cs and Co

The sorption ability of clinoptilolite treated by NaOH solution has been studied. The distribution coefficients of¹³⁷Cs and⁶⁰Co were studied by the radiochemical method. The variation of distribution coefficients with pH was studied. Also the influence of competitive ions on distribution coefficients were investigated. The total cation exchange capacity and XRD analysis were also measured.     

聚羧酸共聚物侧链结构对水泥水化及硬化过程的影响

以聚乙二醇系列、丙烯酸、顺酐、丙烯酸羟乙酯为原料合成聚羧酸减水剂,讨论聚羧酸共聚物侧链长度对水泥分散性能和水化过程的影响,并测试掺加减水剂的混凝土性能.实验结果表明:通过调整聚羧酸共聚物中侧链链长的比例使其具有最佳的分散性.实验合成的聚羧酸共聚物聚乙二醇侧链为nPEG600∶nPEG400=1∶1时,分散效果最好,水泥浆体的流动度及分散力最佳,分别为289 mm和10.36.聚羧酸减水剂具有缓凝特性,能够显著延缓水泥水化及硬化过程,使水泥石的后期水化更充分、水化产物结构更紧密更有力量,各龄期混凝土抗压强度都有较大提高.在水泥中添加0.3%聚羧酸减水剂(PEG600∶400),32.5#水泥3 d,7 d和28 d的抗压强度分别提高了50.4%,40.8%,35.1%,42.5#水泥3 d,7 d,28 d的抗压强度分别提高了16.7%,31.0%和22.3%.     

Hydrated Cs+-exchanged MFI zeolites: location and population of Cs+ cations and water molecules in hydrated Cs6.6MFI from in and ex situ powder X-ray diffraction data as a function of temperature and other experimental conditions

Extending our previous investigation of dehydrated, Cs-exchanged MFI zeolites (J. Phys. Chem. B 2006, 110, 97-106) to hydrated analogues, we have determined the crystal structures of members of the Cs(6.6)H(0.3)MFI.xH(2)O series, for 0 < x < 28, from synchrotron-radiation powder diffraction data. In the fully hydrated phase, three independent Cs(+) cations and six water molecules are identified in difference Fourier maps. The populations of the cations amount to 2.79/3.40/0.41 Cs/unit cell (uc) for the Cs1/Cs2/Cs3 sites, respectively, and those of the water molecules to 4/4/4/4/8/4 H(2)O/uc for the Ow1/Ow2/Ow3/Ow4/Ow5/Ow6 sites, respectively. Close to water saturation, the Cs3 and Ow6 sites are near each other (approximately 1.44 A) and are not occupied simultaneously. At saturation, Cs cations and water molecules form three interconnected Cs(H(2)O)(n) clusters and one (H(2)O)(4) cluster in the MFI channel system: Cs2(H(2)O)(5) centered at x/y/z approximately -0.018/0.146/0.546 (midway between the intersection and the straight channels), Cs1(H(2)O)(4) centered at approximately 0.056/0.240/0.889 (the zigzag channel openings), Cs3(H(2)O)(2) centered at approximately 0.228/0.25/0.899 (in the zigzag channel), and the (H(2)O)(4) cluster (in the zigzag channel) bonded to Cs1 and Ow1. (H(2)O)(4) and Cs3(H(2)O)(2) exclude each other. The Cs2(H(2)O)(5) clusters are connected through weak Ow5...Ow5' hydrogen bonds (2.88 A) and form polymeric chains in the straight channel direction (010). During progressive hydration this Cs2 cation enlarges its hydration shell, stepwise, from Cs2(H(2)O)(2) to Cs2(H(2)O)(3), to Cs2(H(2)O)(4), and finally to a Cs2(H(2)O)(5) cluster. During the dehydration process, these extraframework species migrate, and it is shown that for varying total H(2)O/uc loadings the individual populations of the Cs(+) cations and H(2)O molecules strongly depend on experimental and measurement (in situ vs ex situ) conditions. The shapes of the channels change also; except for T > 150 degrees C, in all the Cs(6.6)H(0.3)MFI.xH(2)O phases, the straight channel D10R (double 10-ring) pore openings (1.16 < epsilon < 1.23) become strongly elliptical. The framework structure of all the investigated phases conforms to orthorhombic Pnma space group symmetry. Hydration and dehydration in Cs(6.6)MFI are fully reversible processes. From a knowledge of the Cs(+) locations, we are able to estimate, by computer simulations, the positions of H(2)O molecules in Cs(6.6)H(0.3)MFI.28H(2)O. The maximum theoretically possible water loading in an hypothetical and idealized cationless [Cs(6.6)H(0.3)]MFI structure amounts to 48 H(2)O/uc (nine independent water species), which is in fair agreement with existing high-pressure data (47 H(2)O/uc). This value is to be compared with the water saturation capacity obtained in a structural refinement of sealed-tube diffraction data of a proton-exchanged H(6.9)MFI.38H(2)O (seven independent water molecules). In the crystal structure of this H-ZSM-5 phase, the straight channel openings are almost circular (epsilon = 1.08). From this we conclude that the main factor responsible for the flexibility of the MFI framework is the presence of the Cs(H(2)O)(n)() clusters residing in, or close to, the straight channel double 10-rings.     

Correlation between pore structure and low-temperature dilatation of hydrated cement pastes and mortars

The pore structure and low-temperature dilatation behavior of traditional hydrated Portland cement paste compacted by different methods were investigated. The aim of the investigation was to demonstrate the influence of the water-cement ratio and the compacting conditions on the developing pore structure and the frost dilatation during the early stage of the hydration process. A low water-cement ratio and a high compacting pressure resulted in initially low porosity, but in coarser pore sizes. Vibration resulted in lower pore volumes as compared with those of cast cement pastes, but the pore size distributions were similar. In accordance with the pore size distribution, two frost dilatation effects were measured when macro- and mesopores also occurred in the hydrated cement pastes. In the samples compacted by high pressure, a single frost dilatation effect occurred in connection with the macropores present in the sample. The magnitude of the frost dilatation effect decreased with increasing curing time. The decrease is caused by a decrease in the volume of the pores and also by an increase in matrix strength.

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Zusammenfassung Es wurde die Porenstruktur und das Tieftemperaturdilatationsverhalten von herkömmlichem, hydratiertem, durch verschiedene Methoden verdichtetem Portland-Zementleim untersucht. Das Ziel der Untersuchung bestand im Nachweis des Einflusses des Wasser-Zement-Verhältnisses und der Verdichtungsbedingungen auf die entstehende Porenstruktur und die Frostdilatation in der frühen Periode des Hydratationsprozesses. Ein niedriges Wasser-Zement-Verhältnis und ein hoher Verdichtungsdruck liefert eine geringe Porösität, aber größere Porenmaße. Vibration liefert im Vergleich zu gegossenem Zementleim ein geringeres Porenvolumen, aber die Beiträge zur Porengröße waren ähnlich. In Übereinstimmung mit dem Porengrößeeinfluß wurden zwei Frostdilatationseffekte gemessen, wenn sowohl Makroals auch Mesoporen in den hydratierten Zementleimen vorkamen. In denjenigen Proben, die unter Hochdruck verdichtet wurden, tritt in Verbindung mit der Gegenwart von Makroporen in der Probe ein einfacher Frostdilatationseffekt auf. Die Höhe des Frostdilatationseffektes sinkt mit steigender Aushärtungszeit. Dieses Sinken wird durch eine Abnahme des Volumens der Poren verursacht und ebenfalls durch ein Ansteigen der Matrixfestigkeit.

     

Correlation between pore structure and low-temperature dilatation of hydrated cement pastes and mortars

The pore structure and low-temperature dilataion behaviour of a traditional hydrated Portland cement paste and a special cement paste of high initial strength were investigated.The aim of the investigation was to demonstrate the role of the cement type in developing the pore structure and frost dilatation during the hydration process. The lower porosity and the higher strength of the special hydrated cement paste resulted in smaller frost dilatation effects in comparison with those of the traditional cement paste in the early stage of hydration.

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Zusammenfassung An einem herkömmlich hydratierten Portland Zementleim und einem Spezialzementleim mit hoher Anfangsfestigkeit wurde die Porenstruktur und das Dilatationsverhalten bei niedrigen Temperaturen untersucht. Mit dieser Untersuchung sollte gezeigt werden, welche Rolle die Zementart wÄhrend des Hydratationsprozesses bei der Ausbildung der Porenstruktur und der Ausdehnung bei Frost spielt. Die geringere PorösitÄt und höhere Festigkeit des speziell hydratierten Zementleimes ergaben bezogen auf herkömmlichen Zementleim im frühen Stadium der Hydratation geringere Dilatationseffekte bei Frost.

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The author is grateful to Dr. Ludmilla Opoczky and Mr. Imre Horváth for the samples.     

Determination of Co and Cs by stopped-flow RFIA with the aid of multi-channel analyzer

Radiometric flow-injection analysis (RFIA) was used for the transport of carrier and sample solution. Radioactive nuclides⁶⁰Co and¹³⁷Cs were used as indicators and a NaI (Tl) scintillation detector coupled to a Canberra MCA for measuring the activity of¹³⁷Cs at 662 keV and⁶⁰Co at 1173 keV and 1332 keV. Experimental parameters related to RFIA were studied, too.     

Co2+ binding cysteine and selenocysteine: a DFT study

In this paper we report structural and energetic data for cysteine and selenocysteine in the gas phase and the effect of Co(2+) complexation on their properties. Different conformers are analyzed at the DFT/B3LYP level of both bound and unbound species. Geometries, vibrational frequencies, and natural population analysis are reported and used to understand the activity of these species. In particular, we have focused our attention on the role of sulfur and selenium in the metal binding process and on the resulting deprotonation of the thiol and seleniol functions. From the present calculations we are able to explain, both from electronic structure and thermochemical point of views, a metal-induced thiol deprotonation as observed in gas-phase experiments. A similar process is expected in the case of selenocysteine. In fact, cobalt was found to have a preferential affinity with respect to thiolate and selenolate functions. This can be related to the observation that only S and Se are able-in thiolate and selenolate states-to make a partial charge transfer to the cobalt thus forming very stable complexes. Globally, very similar results are found when substituting S with Se, and a very small difference in cobalt binding affinity is found, thus justifying the use of this substitution in X-ray absorption experiments done on biomolecules containing cysteine metal binding pockets.     

Migration of 99Tc in unsaturated Chinese loess under natural rainfall conditions: An in-situ test

The migration of ⁹⁹Tc in unsaturated Chinese loess was investigated in-situ with a tracer method. Quartz containing ³H (HTO) and ⁹⁹Tc (⁹⁹TcO₄ ^-) was introduced into the bottom of an experimental pit which was then backfilled at the field test site. Then core soil samples were taken and cut vertically into 1 cm long slices. The slice samples were analyzed by liquid scintillation techniques in the laboratory. The results indicate that the migration pattern of ⁹⁹Tc was quite similar to that of ³H and the vertical diffusion coefficients of ⁹⁹Tc and ³H were calculated as (4.7±0.4)^.10^-2 cm²/d and (7.8±0.4)^.10^-2 cm²/d, respectively.     

Redistribution of radicals under conditions of γ-irradiation (Co60)

Conclusions The possibility of a redistribution of radicals between germanium tetrachloride and tetraalkyltin under conditions of-irradiation (Co⁶⁰) at room temperature was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1381–1382, June, 1969.     

Highly effective removal of 22Na, 134Cs and 60Co from aqueous solutions by titanosilicate: a radiotracer study

Sorption of Na(I), Cs(I) and Co(II) radionuclides from aqueous solutions by titanosilicate have been investigated. The time dependent studies for metal ions showed relatively rapid sorption kinetics between 5 and 30 min to reach equilibrium. A batch adsorption model based on assumption of the pseudo-second-order mechanism was applied to predict the sorption rate, while the equilibrium capacity was calculated at different temperatures. The adsorption of different radionuclides onto titanosilicate was found to be favored at high ions concentrations and low temperature for Na⁺ and Co²⁺ while at high temperature for Cs⁺. Activation energy of adsorption was computed to be 2.35, 24.11 and 5.74 kJ/mol for adsorption of Na(I), Cs(I) and Co(II), respectively. The results revealed that the adsorption of Cs⁺ is the highest relative to Na⁺ and Co²⁺ at different conditions which may be attributed to its low hydration energy. Further, the equilibrium isotherm for the interested ions was analyzed and it was found to obey Frundlich equation.     

Cs2CO3-mediated decomposition of N-tosylhydrazones for the synthesis of azines under mild conditions

Research on Chemical Intermediates - A facile, environmentally and efficient Cs2CO3-mediated decomposition of N-tosylhydrazones reaction has been developed for the synthesis of functionalized...     

Determination of sorption capacity of fucoidic sands for Cs+ and Sr2+ under dynamic column conditions

In this paper, the sorption behavior of Cs⁺ and Sr²⁺ on column of fucoidic sands under dynamic flow conditions was investigated, and their sorption capacities (SC) towards these two cations were studied. The determination of SC is based on the construction of respective breakthrough curves using ¹³⁷Cs and ⁸⁵Sr radionuclides as isotopic indicators in laboratory experiments. The samples were taken from several parts of the borehole in the area of interest. Undisturbed cores of 5 cm in diameter and 10 cm long were put in the glass columns and the cores were perfectly tightened using acrylate resin. In this time-dependence study, the so-called cenoman background groundwater was used. A concentration of 10^?6 mol/dm³ of Cs⁺ and Sr²⁺ in liquid phase individually was established using neutral salts of CsNO₃ and Sr(NO₃)₂, respectively. The groundwater was introduced at the bottom of the columns by a multi-head peristaltic pump, at a constant flow-rate of about 4 cm³/h. The results show that the sorption capacity of the investigated fucoidic sands for ¹³⁷Cs and ⁸⁵Sr is 0.1–1.5 and 0.05–0.5 μmol/100 g, respectively, in dependence on the evaluation of corresponding breakthrough curves. Some differences in the behavior of the cores during the experiments have also been observed and explained.     

Fractionation of 137Cs and 60Co in soils by sequential extractions

Comparison of six sequential extraction schemes either widely used or specifically developed for speciation of ¹³⁷Cs and ⁶⁰Co in two types of soil (Chromic Luvisol and Eutric Fluvisol) is presented. The results from the comparison show that extractable radiocesium in Chromic Luvisol (14%) is about three times lower than in Eutric Fluvisol (39%). For Chromic Luvisol the total extractable radiocobalt varies from 42 to 78% while the variation for Eutric Fluvisol is not so substantial (55–83%). The results show that BCR and NIST schemes developed for heavy metals are not efficient for radiocesium fractionation, but give very good results in the case of radiocobalt. The efficiency of a scheme is dependant not only on the type of radionuclide but on the type of soil as well. The best reagent for evaluation of bioavailable cesium is NH₄NO₃ or other NH⁺ ₄-salt. Practically most of the radiocobalt is in extractable form in both soils (about 83%) and major part of radiocesium (more than 60% depending on the soil type) is strongly bound in the soils and not extractable.