In situ migration of tritiated water and iodine in Grimsel granodiorite,part II: assessment of the diffusion coefficients by TDD modelling

Diffusive transport of iodine (I) and tritiated water (HTO) in granodiorite is studied in the framework of the long term diffusion project (LTD) at the Grimsel Test Site, Switzerland. In this paper we modelled the tracer profiles measured in a long term (780 days) in situ diffusion test was carried out as part of LTD. The main outcome of the modelling tends to prove that the in situ apparent diffusion coefficients of I and HTO are close to the reference apparent diffusion coefficient determined in the laboratory (D _a = 3 × 10⁻¹⁰ m² s⁻¹).

     

Water sorption by poly(tetrahydrofurfuryl methacrylate‐co‐2‐hydroxyethyl methacrylate). I. A mass‐uptake study

Cylindrical samples (≈5 mm × 20 mm) of poly(2‐hydroxyethyl methacrylate) and copolymers of 2‐hydroxyethyl methacrylate and furfuryl methacrylate were prepared, and the sorption of water into these cylinders was studied by the mass‐uptake method and by the measurement of the volume change at equilibrium. The equilibrium water content and volume change for the cylinders both varied systematically with the copolymer composition. The diffusion of water into the cylinders followed Fickian behavior, with the diffusion coefficients, dependent on the copolymer composition, varying from 2.00 × 10⁻¹¹ m²s⁻¹ for poly(2‐hydroxyethyl methacrylate) to 5.00 × 10⁻¹² m²s⁻¹ for poly(2‐hydroxyethyl methacrylate‐co‐tetrahydrofurfuryl methacrylate) with a 1 : 4 composition. The polymers that were rich in 2‐hydroxyethyl methacrylate were characterized by a water‐sorption overshoot, which was attributed to a slow reorientation of the polymer chains in the swollen rubbery regions formed after water sorption. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1939–1946, 2000     

Multi-scale study of the mineral porosity of veined gneiss and pegmatitic granite from Olkiluoto,Western Finland

The purpose of this work was to support the long-term experiments for investigation of rock matrix retention properties at the spent nuclear fuel repository site ONKALO, in Olkiluoto, Western Finland. Towards this end, rock samples were characterised in terms of porosity connected to mineralogy, with emphasis on pore sizes, and fillings. Both filled and unfilled pores were found with unfilled pores being majority in the pegmatitic granite veins of the mostly veined gneiss samples. It was found that the fillings were often connected to local alteration and the alteration caused variation in the range of pore sizes.     

Effects of pH and Concentration on Cs Ions Sorption and Diffusion in Crushed Granite by Using Batch and Modified Capillary Method

A comprehensive evaluation of Cs ions sorption to and diffusion in crushed granite was conducted in this study. The sorption capacity of crushed granite suggested by the Langmuir model was 5.48 × 10^?6 mol‐Cs/g‐granite. The distribution coefficient (Kd) was around 7.5 mL/g and pH independent. By using an in‐diffusion method with a modified capillary column, some diffusion relevant parameters of Cs ions in crushed granite were derived. The apparent diffusion coefficient (Da) seemed unaffected by Cs concentration (1.15 × 10^?10 to 2.82 × 10^?10 m²/s, at 10^?7 and 10^?3 M, respectively). The determined effective diffusion coefficients (De) were located in the window from 8.59 × 10^?10 (10^?7 M) to 1.69 × 10^?9 (10^?3 M) m²/s. Under various pH environments, pH independent Da (9.0 × 10^?9 m²/s) and De (1.0 × 10^?9 m²/s) values were observed. Under current systems, consistently higher De than Da implied the diffusion of Cs ions was governed by surface diffusion phenomenon. Whereas the pH insensitive feature indicated the Cs sorption to crushed granite was mainly through ion‐exchange reaction. Moreover, further SEM/EDS mapping clearly showed the adsorbed Cs ions were highly concentrated on the fracture surface of biotite.     

Cd(II) and Pb(II) extraction and transport modeling in SLM and PIM systems using Kelex 100 as carrier

The extraction and transport of Cd(II) and Pb(II) in two different membrane systems (SLM and PIM) using Kelex 100 as carrier was studied, proposing the corresponding chemical models of transport. A two-species transport model is proposed for Cd(II), according to solvent extraction (SX) data. Experimental SLM permeabilities are 9.7×10⁻⁵ m s⁻¹, while measured PIM permeabilities are 5×10⁻⁵ m s⁻¹. Values for the aqueous boundary layer thickness and for the diffusion coefficient of the metal cation-carrier complexes in the membrane phase were calculated from numerical fitting of experimental data using the proposed transport models. A highly selective Pb(II) separation was achieved in PIM systems based on the nature of the chemical equilibria involved in Cd(II) and Pb(II) membrane transport.     

Modelling of mass transfer in facilitated supported liquid membrane transport of copper(II) using MOC-55 TD in Iberfluid

The transport of copper(II) through a supported liquid membrane using MOC-55 TD (oxime derivative), dissolved in Iberfluid, as a carrier has been studied. A physico-chemical model is derived to describe the transport mechanism which consists of: diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction and diffusion through the membrane. The experimental data can be explained by mathematical equations describing the rate of transport. The mass transfer coefficient was calculated from the described model as 2.8×10⁻³ cm s⁻¹, the thickness of the aqueous boundary layer as 2.6×10⁻³ cm⁻¹ and the membrane diffusion coefficient of the copper-containing species as 1.2×10⁻⁸ cm² s⁻¹.     

Enhanced mass transfer during solid–liquid extraction of gamma-irradiated red beetroot

The exposure to gamma-irradiation pretreatment increases cell wall permeabilization, resulting in loss of turgor pressure, which led to the increase of extractability of betanin from red beetroot. The degree of extraction of betanin was investigated using gamma irradiation as a pretreatment prior to the solid–liquid extraction process and compared with control beetroot samples. The beetroot subjected to different doses of gamma irradiation (2.5, 5.0, 7.5, 10.0 kGy) and control was dipped in an acetic acid medium (1% v/v) to extract the betanin. The diffusion coefficients for betanin as well as ionic component were estimated considering Fickian diffusion. The results indicated an increase in the diffusion coefficient of betanin (0.302×10⁻⁹–0.463×10⁻⁹ m²/s) and ionic component (0.248×10⁻⁹–0.453×10⁻⁹ m²/s) as the dose rate increased (from 2.5 to 10.0 kGy). The degradation constant was found to increase (0.050–0.079 min⁻¹) with an increase gamma-irradiation doses (2.5–10.0 kGy), indicating lower stability of the betanin as compared to control sample at 65 °C.     

Comparative study on retardation behavior of Cs in crushed and intact rocks: two potential repository host rocks in the Taiwan area

This study investigates sorption and diffusion of Cs in two potential host rocks (granite from Kinmen Island and basalt from Penghu Island) by using batch and through-diffusion methods in order to establish a reliable safety assessment methodology. These methods were applied to crushed and intact rock samples to investigate the actual geological environment. According to solid-phase analysis, including X-ray diffraction, elemental analysis, auto radiography, and polar microscopy, the sorption component primarily contained iron?Cmagnesium (Fe?CMg) minerals in basalt and granite. Moreover, the distribution coefficient (K _d) of Cs in various concentrations (~10^?2?C10^?7?M) obtained from batch tests indicated a higher sorption capacity in basalt than that in granite because of the 10% Fe?CMg mineral content. The diffusion of Cs in both crushed granite and basalt reached steady state after 110?days, and the apparent diffusion coefficients (D _a) were 2.86?×?10^?11 and 1.82?×?10^?12?m²/s, respectively. However, the value of D _a for Cs in intact rocks was estimated to be 1.45?×?10^?12?m²/s in granite and 0.56?×?10^?12?m²/s in basalt, lower than the values obtained using crushed rocks. In addition to the microporous structure (major sorption minerals), it showed that the major retardation of Cs depended on the porosity (??) of compacted media, according to through-diffusion tests. In fact, the solid/liquid (S/L) ratio decreased as is the case when switching from batch to column experiments and the sorption effect on minerals became even more negligible in retardation of radionuclide migration.     

Diffusion of ferrocene methanol in super-cooled aqueous solutions using cylindrical microelectrodes

The diffusion of ferrocene methanol in super-cooled aqueous solutions containing sucrose has been studied, using disk and cylindrical microelectrodes, over a wide viscosity range. The solution viscosity and the reduced temperature T/T_g (T_g being the glass transition temperature) were varied by changing the sucrose concentration and the temperature of the system. The voltammetric limiting current obtained with a disk microelectrode and the i(t) response on a cylindrical microelectrode after a potential step were used to determine diffusion coefficients from 7 × 10⁻⁶ cm² s⁻¹ down to 2 × 10⁻¹¹ cm² s⁻¹. The electrochemical procedure described in this work allows a simple and accurate measurement of the dynamics of electroactive solutes in glass-forming liquids.     

Electron excitation coefficients of neutral and ionic levels of krypton in Townsend discharges

In this paper, we present experimental results for excitation coefficients of krypton atoms to several Kr and Kr⁺ excited levels for E/N (electric field to gas particle number density ratio usually in units of Townsend, 1 Td = 10^− 21 V m²) values from 7 × 10^− 20 V m² to above 1 × 10^− 17 V m². The data have been obtained in two different parallel plate self-sustained Townsend discharge drift tubes. The spatial distribution of the emission intensities were recorded and then normalized to give excitation coefficients at the anode, by using the electron flux at this point. The values of these coefficients are placed on an absolute scale by using a standard tungsten ribbon lamp calibrated against a primary blackbody radiation standard. The ionization rates at different E/N are obtained from the spatial emission profiles.The data for atomic krypton levels 2p₂, 2p₃, 2p₅, 2p₆, 2p₇, 2p₈, 3p₅ and 3p₆ (in Paschen notation) were converted to excitation coefficients by using quenching coefficients from the literature. The emission coefficients of eight 4s²4p⁴ (³P)5p levels of Kr⁺ have also been measured for E/N values from about 1 × 10^− 18 V m² up to nearly 8 × 10^− 18 V m².     

Theoretical study of sorption-induced bending of polypyrrole films

Polypyrrole films containing perchlorate were electrochemically synthesized and the bending and recovery motion of the films obtained has been investigated. It was found that the thickness of the film and ambient relative humidity (RH) were crucial to the motion of film: An increase of the film thickness decreased the displacement of the bending but increased the bending stress. On the other hand, an increase of the ambient RH decreased both functions. The motion of film was caused by the difference of expansion on both sides of the film owing to anisotropic sorption of water vapor, which could be expressed by the diffusion-limited bending model. The diffusion coefficients calculated from the bending and recovery motion at 25°C, RH 50% were 12.2 × 10⁻⁸ cm² s⁻¹ and 3.5 × 10⁻⁸ cm² s⁻¹, respectively. The maximum expansion of the film surface calculated from the bending curve was about 0.36%. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2237–2246, 1998     

Sorption of U(VI) on granite

The sorption-desorption of uranium (VI) on Grimsel granite of Switzerland was studied under oxidizing conditions with an initial uranium concentration range of between 9.7·10^–7 and 4.5·10^–4M, using a batch technique. The sorption coefficients varied between 8.0 and 0.4 ml/g and sorption was not fully reversible. The data could be fitted to a Freundlich isotherm. By fitting the data with the Dubinin-Radushkevich equation, a mean energy of sorption of 10.7 kJ/mol was calculated, which corresponds to the energy of ion exchange reactions. The kinetic data could be interpreted by assuming diffusion into the crushed granite particles. The calculated pore diffusion coefficient was between 2.0·10^–11–7.7·10^–11 m²/s.     

Synthesis of organically bridged trialkoxysilanes bearing acetoxymethyl groups and applications to reverse osmosis membranes

New bridged trialkoxysilanes bearing acetoxymethyl groups were synthesized by double hydrosilylation of 1,6‐diacetoxy‐2,4‐butadiyne, using two equivalents of triethoxysilane and a metal catalyst. With a Ru catalyst, the reaction proceeded via anti‐addition to provide BTES‐Ac‐a as a single isomer, while a similar reaction with a Pt or Rh catalyst provided an isomeric mixture of syn ‐adducts BTES‐Ac‐b. Reverse osmosis (RO) silica membranes were prepared by the sol–gel process with BTES‐Ac‐a and BTES‐Ac‐b and the membranes were examined with respect to water desalination using a 2000 ppm NaCl aqueous solution. NaCl rejection of the membranes increased to reach 96% at the early stage of the RO experiments. However, the rejection decreased gradually to 85% after 70 and 200 h for BTES‐Ac‐a and BTES‐Ac‐b, respectively, due to hydrolytic decomposition of the silica network during the experiments. In contrast, a membrane prepared from copolymerization of BTES‐Ac‐a with ethane‐bridged bistrialkoxysilane (BTES‐E1) showed improved stability towards hydrolysis with stable NaCl rejection of 96% with higher water permeance (3.5 × 10⁻¹³ m³ m⁻² s⁻¹ Pa⁻¹) than that of a membrane prepared by homopolymerization of BTES‐E1 (2.7 × 10⁻¹⁴ m³ m⁻² s⁻¹ Pa⁻¹) reported previously.     

Microstructural and gas separation properties of CVD modified mesoporous γ-alumina membranes

Chemical vapor deposition (CVD) was used to modify 4 nm pore, sol–gel derived, γ-alumina membranes supported on macroporous α-alumina. Aluminum oxide was deposited in the pores of the γ-alumina membrane by alternating additions of trimethylaluminum (TMA) and water vapor. By reducing the pore size, the permeance of non-condensable gasses was reduced much more than the permeance of condensable gasses due to capillary condensation or preference adsorption of water vapor. The modified membrane that exhibited the best separation properties had a water vapor permeance ranging from 1.5×10⁻⁶ to 3.0×10⁻⁷ mol/m² s Pa, an oxygen permeance ranging from 1.7×10⁻⁷ to 1.5×10⁻⁹ mol/m² s Pa, and a separation factor as high as 140 at room temperature. The microstructure of the pores contained some irregularities which were attributed to an atomic layer CVD (ALCVD) mechanism modified by homogeneous reactions. The effect of the modified ALCVD was higher permeances than would be expected. P-type zeolite membranes were also made and found to have similar separation properties to the more heavily modified γ-alumina membranes.     

Comparison of thoron (220Rn) content and gamma radiation level in high background radiation area of Kollam district in Kerala,India

In order to map the thoron prone areas of the coastal region of Kollam district, a well known HBRA of south India, comparative study of radon and thoron exhalation rate was conducted. The in situ measurement of radon and thoron exhalation has been taken. These studies were correlated with the gamma radiation level. The average value of thoron exhalation is found to 5.55 ± 1.35 Bq m⁻² s⁻¹ along the coastal areas and the radon exhalation rate is found to 107.6 ± 32 Bq m⁻² h⁻¹. The value of thoron exhalation was found 12 times greater than the global values in Neendakara and Chavara region and about 6 times greater in the Alappad region.

     

Silica–zirconia membranes for nanofiltration

Inorganic nanofiltration membranes were fabricated from silica–zirconia composite colloidal sol (molar ratio Si/Zr=9/1) using a sol–gel process. Molecular weight cut-off (MWCO) was successfully controlled between 200 and 1000 Da by regulating the colloidal diameters of sol solutions in the final coating stage. The pure water permeabilities ranged from 0.15×10⁻¹¹ to 1.5×10⁻¹¹ m³ m⁻² s⁻¹ Pa⁻¹. Pore size and pore size distribution were estimated based on the dynamic method of humid air permeation, and found to be from 1.0 to 2.9 nm. The MWCO obtained from NF experiments using neutral organic solutes corresponds well with the pore diameters estimated from the dynamic permeation method. Silica–zirconia membranes were found to be stable in aqueous solution for periods in excess of four months.     

Neutron bombardment of lithium bis(oxalato) borate: LiBOB

Lithium bis(oxalato) borate (LiBOB) was neutron bombarded with a flux of 2.40 × 10¹² n cm⁻² s⁻¹ for 1, 2, 3 and 4 h. The neutron damaged LiBOB was studied by FT-IR and Raman spectroscopy as well as by DSC (Differential Scanning Calorimetry). It is shown that the neutron bombardment causes the radiolysis of the oxalate ligand of LiBOB producing boric acid. The kinetics of LiBOB radiolysis under neutron bombardment was fitted according to the pseudofirst order kinetics law using either the FT-IR data or the decomposition enthalpy data leading in both cases to a rate constant of 9.2 × 10⁻⁵ s⁻¹. Pristine LiBOB is not a paramagnetic solid but after neutron bombardement it gives a very clear and stable ESR signal attributed to trapped spins in the radiolysis products.

     

Effects of ionic strength and humic acid on 99TcO4 ? sorption and diffusion in Beishan granite

In terms of pre-safety assessment of a potential site for high-level radioactive wastes disposal in China, the geochemical behavior of key radionuclides which tend to be released from the repository must be thoroughly investigated. ⁹⁹Tc is a long-lived fission product with appreciable productivity in nuclear fuel, and Tc (+7) has unlimited solubility in near-field geochemical environments. In this study, the effects of ionic strength and humic acid on ⁹⁹TcO₄ ^? sorption and diffusion in Beishan granite were investigated with through-diffusion and batch sorption experiments. Results indicated that the effective diffusion coefficients (D _e) of ⁹⁹TcO₄ ^? in Beishan granite varied from 1.07?×?10^?12 to 1.28?×?10^?12?m²/s without change with ionic strength, while the distribution coefficients (K _d) negatively correlated with ionic strength of the rock/water system. This study also indicates that there is no evident influence of humic acid concentration on the diffusion behavior of ⁹⁹TcO₄ ^? in Beishan granite, due to the limited interaction between humic acid and ⁹⁹TcO₄ ^?.     

The States,Diffusion, and Concentration Distribution of Water in Radiation‐Formed PVA/PVP Hydrogels

Abstract

Hydrogels with various compositions of polyvinyl alcohol (PVA) and poly(1‐vinyl‐2‐ pyrrolidinone) (PVP) were prepared by irradiating mixtures of PVA and PVP in aqueous solutions with gamma‐rays from ⁶⁰Co sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T₂ relaxation measurements and the kinetics of water diffusion in the hydrogels were studied by sorption experiments and NMR imaging. The DSC endothermic peaks in the temperature range ?10 to +10°C implied that there are at least two kinds of freezable water present in the matrix. The difference between the total water content and the freezable water content was referred to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with F_VP=0.19 has been estimated to be g_H2O/g_Polymer=0.375. From water sorption experiments, it was demonstrated that the early stage of the diffusion of water into the hydrogels was Fickian. A curve‐fit of the early‐stage experimental data to the Fickian model allowed determination of the water diffusion coefficient, which was found to lie between 1.5×10^?11 m² s^?1 and 4.5×10^?11 m² s^?1, depending on the polymer composition, the cross‐link density, and the temperature. It was also found that the energy barrier for diffusion of water molecules into PVA/PVP hydrogels was ≈24 kJ mol^?1. Additionally, the diffusion coefficients determined from NMR imaging of the volumetric swelling of the gels agreed well with the results obtained by the mass sorption method.     

Study of the reactions of OH with HCl,HBr, and HI between 298 K and 460 K

The reactions between OH radicals and hydrogen halides (HCl, HBr, HI) have been studied between 298 and 460 K by using a discharge flow-electron paramagnetic resonance technique. The rate constants were found to be k_HCl(298 K) = (7.9 ± 1.3) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ with a weak positive temperature dependence, k_HBr (298-460 K) = (1.04 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_HI(298 K) = (3.0 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The homogeneous nature of these reactions has been experimentally tested.