99TcO4 − diffusion and sorption in compacted GMZ bentonite studied by capillary method

Sorption and diffusion of ⁹⁹TcO₄ ^? in compacted bentonite from Gaomiaozi county (Inner Mongolia, China) (denoted as GMZ bentonite) was studied by capillary method. The distribution coefficient (K _d) and diffusion coefficient (D _a) were calculated from diffusion curves of ⁹⁹TcO₄ ^? in compacted GMZ bentonite. The D _a and K _d values decreased with the increasing of the bulk dry density of the compacted bentonite. With increasing pH values, the D _a values increased whereas the K _d values decreased, which is attributed to the ion exchange and electrostatic repulsion between the negative surface charged bentonite and negative charged ⁹⁹TcO₄ ^? ions at high pH values. The diffusion and relative concentration distributions of ⁹⁹TcO₄ ^? in compacted bentonite after long aging time were simulated from the distribution and diffusion coefficients. Effect of aging time on the diffusion of ⁹⁹TcO₄ ^? in compacted bentonite was also calculated using the theoretical equation. The results indicated that ⁹⁹TcO₄ ^? was an easily mobile radionuclide in environment and the release of ⁹⁹TcO₄ ^? from the radioactive waste repository was dangerous to the environmental pollution.     

Effect of EDTA on the diffusion behavior of 99TcO4 − and ReO4 − in GMZ bentonite

Polyaminopolycarboxylate EDTA with powerful metal-binding property, which often presents in low and intermediate-level waste, can enhance the radionuclide migration. The effect of EDTA on the diffusion behavior of ⁹⁹TcO₄ ^? and ReO₄ ^? in Gaomiaozi (GMZ) bentonite was investigated by using through-diffusion method. For ⁹⁹TcO₄ ^? in present of EDTA, the D _e values was (1.2 ± 0.1) × 10^?11 m²/s, which was 4 times higher than that in absent of EDTA. It can be explained that the complexation between ⁹⁹TcO₄ ^? and EDTA might be formed. By contrast, the D _e values of ReO₄ ^? remained unchanged in present or absent of EDTA, indicating that ReO₄ ^? could not complex with EDTA. However, the diffusion of ReO₄ ^? could be increased in present of EDTA, the D _a value was found to be increased from 1.8 × 10^?10 to 5.4 × 10^?10 m²/s. It demonstrated that ReO₄ ^? need more drastic conditions to form the Re(VII)–EDTA complexes than those used for ⁹⁹TcO₄ ^?. For both ReO₄ ^? and ⁹⁹TcO₄ ^?, the rock capacity factor α is less than the total porosity ε _tot, indicating that they has little retention/sorption on the surface of bentonite.     

Experimental and numerical investigations of 99TcO4− diffusion in compacted SPV 200 bentonite

Journal of Radioanalytical and Nuclear Chemistry - Diffusion characteristics in bentonite are essential to quantify the transport of radionuclides through buffer/backfill materials in waste...     

Sorption of Am(Ⅲ) on Na-bentonite:Effect of pH,ionic strength,temperature and humic acid

Sorption of Am(Ⅲ) on Na-bentonite as a function of contact time,pH,ionic strength,humic acid(HA) and temperature was investigated under ambient conditions.The results showed that the sorption was strongly dependent on pH and ionic strength. Am(Ⅲ) sorption can be described well by pseudo-second-order model.The presence of HA takes a positive effect at low pH;but a negative influence under high pH range.Enthalpy,entropy and Gibbs free energy(i.e.,△H~0,△S~0 and△G~0) calculated from sorption isotherms suggested that sorption process of Am(Ⅲ) was spontaneous and endothermic.     

Adsorption of 99TcO4 − onto hydrotalcite and calcined hydrotalcite under basic conditions: influence of humic acids and anions

The remediation of technetium-99 (⁹⁹Tc) at contaminated sites remains a major challenge, as Tc high solubility and anionic nature under oxic conditions lead to high contaminant mobility. Hydrotalcite, a form of anionic clay, can strongly retain anions, especially upon mineral calcination. However, naturally occurring humic acids can also sorb onto hydrotalcite, therefore competing with TcO₄ ^? for sorption sites. This work explores the ability of hydrotalcite to retain TcO₄ ^? in presence of humic substances to evaluate the efficacy of hydrotalcite for Tc remediation in natural environment. Results show that calcined hydrotalcite can immobilize TcO₄ ^?, while the presence of 23 ppm humic acids has little influence on TcO₄ ^? uptake. However, additional monatomic and polyatomic anions in solution can compete with TcO₄ ^? for sorption sites on hydrotalcite.     

Complexation and sorption studies of Co(II) with γ-alumina-bound fulvic acid: effect of pH,ionic strength,fulvic acid and alumina concentration

The removal of heavy metal ion Co(II) from aqueous solution is studied using γ-Al₂O₃ by batch technique. The experiments are performed at T = 20 ± 2 °C, in 0.01 M NaNO₃ solutions and under aerobic conditions. The effect of pH, ionic strength, fulvic acid (FA) and alumina concentration on the sorption of Co(II) on alumina are also respectively investigated. The pH affects the sorption of Co(II) significantly as compared with the effect of FA and ionic strength. The results indicate that strong chemical bonds are formed between Co(II) and the bare or FA coated alumina surface, and a transition from the adsorption to surface-induced precipitation of Co(II) on alumina surface takes place. The addition sequences of Co/FA on Co(II) sorption is also studied and the results indicate that the sorption of Co(II) in ternary system is independent of addition sequences. The results also suggest that the sorption of metal ions on mineral surface depends on the nature of mineral, nature of organic ligand and nature of metal ion.     

Sedimentation–diffusion profiles and layered sedimentation of charged colloids at low ionic strength

We report the formation of strongly inflated sedimentation–diffusion concentration profiles for charged monodisperse colloidal spheres in absolute ethanol. Various additional experiments, such as light scattering, confirm that the very dilute supernatants, left behind by the majority of settling colloids, contain spheres that repel each other at distances of micrometers. We attribute these unusual profiles to a significant counter-ion contribution to the osmotic pressure and to the Debye screening length. An approximate osmotic equation-of-state at the level of the second virial coefficient for dispersions at very low ionic strength indeed implies an algebraic long-distance decay of sedimentation–diffusion profiles, together with significant lowering of the effective colloid mass by an entropic lift due to counter-ions. We have also observed that sedimenting dispersions sometimes demix into two layers, which are both disordered fluids. Since the colloids are clearly repulsive on the DLVO pair level, this layering possibly manifests a phase transition driven by many-body attractions.     

Sorption of radiocobalt on a novel γ-MnO2 hollow structure: effects of pH, ionic strength, humic substances and temperature

A novel γ-MnO₂ hollow structure has been synthesized using a simple chemical reaction between MnSO₄ and KMnO₄ in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. As an example of potential applications, γ-MnO₂ hollow structure was used as adsorbent in radionuclide ⁶⁰Co(II) treatment, and showed an excellent ability. The effect of pH, contact time, ionic strength, humic acid (HA)/fulvic acid (FA), and temperature was investigated using batch techniques. The results indicated that the sorption of ⁶⁰Co(II) on γ-MnO₂ was obviously dependent on pH values but independent of ionic strength. The presence of HA/FA enhanced the sorption of ⁶⁰Co(II) on γ-MnO₂ at low pH, whereas reduced ⁶⁰Co(II) sorption on γ-MnO₂ at high pH. The kinetic sorption of ⁶⁰Co(II) on γ-MnO₂ can be well fitted by the pseudo-second-order rate equation. The thermodynamic parameters (ΔH ⁰, ΔS ⁰, ΔG ⁰) were also calculated from the temperature dependent sorption isotherms, and the results suggested that the sorption of ⁶⁰Co(II) on γ-MnO₂ was a spontaneous and endothermic process. The sorption of ⁶⁰Co(II) on γ-MnO₂ was attributed to surface complexation rather than ion exchange.     

Effects of ionic strength, temperature and conformation on affinity interactions of β₂-glycoprotein I monitored by capillary electrophoresis

We have used CE to evaluate the interaction between β?-glycoprotein I (β?gpI) and heparin. β?gpI is a human plasma protein involved in the blood coagulation cascade. It is of interest to functionally characterize the interactions of β?gpI because the exact function is not entirely known and because circulating autoantibodies against β?gpI are associated with an increased risk of thrombotic events. The effect of the ionic strength, temperature, and conformation of the protein on the interaction between β?gpI and heparin has been studied. The CE procedure for this study is simple, fast, and automatic. β?gpI and heparin were allowed to interact during electrophoresis at different ionic strength buffers and at different capillary temperatures. To mimic perturbation of the conformation of β?gpI, different denaturing agents (SDS, ACN, and urea) were added to the BGE. While simple 1:1 binding isotherms were obtained at 22 °C, the data strongly suggest that at physiological temperature the binding stoichiometry is not 1:1 and/or that cooperative interactions begin to play a role. We found that (i) the K(D)-values differed by a factor of 60 at the ionic strengths studied (ii) β?gpI was resistant to denaturation with SDS and ACN, but was partially denatured by urea, and (iii) the K(D) for the β?gpI-heparin interaction in the presence of urea was ten times higher than the K(D) determined at the same conditions without urea added. Therefore, we conclude that the interaction between β?gpI and heparin is dependent on electrostatic interactions and on the conformation of β?gpI.     

Effect of pH, ionic strength, foreign ions, fulvic acid and temperature on 109Cd(II) sorption to γ-Al2O3

The sorption of Cd(II) from aqueous solution on γ-Al₂O₃ was investigated under ambient conditions. Experiments were carried out as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid and temperature. The results indicated that the sorption of Cd(II) was strongly dependent on pH and ionic strength. At low pH, the sorption of Cd(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on γ-Al₂O₃ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms at three different temperatures. The thermodynamic data (ΔG ⁰, ΔS ⁰, ΔH ⁰) calculated from the temperature dependent sorption isotherms suggested that the sorption of Cd(II) on γ-Al₂O₃ was an spontaneous and endothermic process.     

Effects of humic acids and microorganisms on decabromodiphenyl ether, 4,4′-dibromodiphenyl ether and anthracene transportation in soil

In this study, effects of humic acids (HA) and microorganisms on the migration of hydrophobic organic contaminants (HOCs), decabromodiphenyl ether (BDE-209), 4,4′-dibromodiphenyl ether (BDE-15) and anthracene, in soils were examined. More soil particles were dispersed into the colloidal phase (0.22-1 μm) in the presence of HA and/or microorganisms as a result of increased erosion and friction. The study suggested that PBDEs (BDE-209 and BDE-15) and anthracene in soils would be transported to other places by...     

Dissociation quotients of D-galacturonic acid in aqueous solution at 0.1 MPa to 1 molal ionic strength and 100°C

The molal dissociation quotients of D-galacturonic acid were measured potentiometrically in a newly-designed, hydrogen-electrode concentration cell from 5 to 100°C at four ionic strengths ranging from 0.1 to 1.0 mol-kg^–1 using sodium trifluoromethanesulfonate (NaF₃CSO₃) as the supporting electrolyte. These quotients were fitted in the all anionic (isocoulombic) form by an empirical equation incorporating three adjustable parameters. When combined with the known dissociation quotient for water in the same medium, this treatment yielded the following thermodynamic quantities for the acid dissociation equilibrium at 25°C and infinite dilution: log K_H=–3.490±0.011, H _H ⁰ =0.4±0.2 kJ-mol^–1, S _H ⁰ =–65±1 J-mol^–1-K^–1, and C _{p, H} ⁰ =–231±8 J-mol^–1-K^–1. Comparisons are made with the corresponding results of a limited number of previous studies carried out near ambient conditions.     

Evaluation of solubility and diffusion coefficients in polymer film–vapor systems by sorption experiments

Sorption experiments are commonly used to determine the equilibrium and kinetics of mass-transfer processes of vapors in polymeric materials. Electrogravimetry is recognized as a powerful technique. A discussion of the standard theoretical approach to determine solubility and diffusion coefficients is presented. The reduced mathematical expression commonly used for calculations of D values is discussed. A consistency test to check for common deviations caused by the experimental complexity is discussed and resolved.The sorption of hexanol and ethyl caproate into a metallocene polyethylene and an ionomer was measured by electrogravimetry. Transport was characterized through the solubility and the diffusion coefficients. The formalism presented was used in these experiments and is commented upon.     

Effect of grain size on the sorption and desorption of SeO4 2− and SeO3 2− in columns of crushed granite and fracture infill from granitic water under dynamic conditions

The sorption of 2 × 10^?5 mol/dm³ Na₂SeO₄ and Na₂SeO₃ dissolved in synthetic granitic water (SGW) were investigated in columns of crushed granite and fracture infill (clay minerals) of various grain sizes. Desorption was studied using pure SGW. The goal of study was the quantification of the effect of grain size on the retardation and distribution coefficients of SeO₄ ^2? and SeO₃ ^2?, as well as on the other transport parameters (Peclet number and hydrodynamic dispersion coefficient). A model based on the erfc-function, assuming a non-linear reversible equilibrium sorption/desorption isotherm, was used for evaluation of sorption/desorption and transport parameters. The determination of selenium was performed using an ICP-MS technique. The experimental breakthrough curves were fitted using non-linear regression procedure, in the course of which the parameters mentioned were sought. Summing up, no sorption was recorded in the case of SeO₄ ^2? under these conditions. The values of retardation coefficients were practically one for all studied grain sizes. On the other hand, significant sorption was found for SeO₃ ^2?: depending on the grain size, the retardation coefficients varied between 1.6–8.7 in pure granite and 1.8–37.2 in infill materials. These values correspond to distribution coefficients of 0.2–2.5 and 0.2–12.7 cm³/g, respectively. The both parameters have similar values in a case of desorption which reflects the reversible character of sorption process. It was found that retardation and distribution coefficients and sorption capacity for SeO₃ ^2? also increase with decreasing grain size.     

On the mechanism of diffusion and ionic transport in crystalline insoluble acid salts of tetravalent metals—II self diffusion of Na+ and K+ on microcrystals of Zr(NaPO4)2·3H2O and Zr(KPO4)2·3H2O

A modification of the Fick equation solution for diffusion in spherical particles from a well-stirred solution of limited volume that takes into account the non-uniformity of the particle-size has been developed. The equation obtained has been employed in a study of the self-diffusion rate of ²⁴Na⁺ and ⁴²K⁺ in Zr(NaPO₄)₂·3H₂O and Zr(KPO₄)₂·3H₂O, respectively. The self diffusion processes have been followed at different temperatures and the Arrhenius plot has been shown to hold. In the range of temperature studied the self-diffusion occurs in a single step and activation energies of 73 and 79 KJ/mole have been found for the sodium and potassium forms, respectively. The mobility data are compared with conductivity data available for the same ionic forms.     

Structural Effects on Defects and Growth in Crystals of Urea

1INTRODUCTIONThecrystalofureaisanonlinearopticalmaterial(13andcanbeprepareanopticalparameterocillator(OPO)element[2).LargeperfectcrystalshavebeengrownbysO.lutionmethod[3i,v!'athez-directionrestrictedgrowth..thed,thedirectionwiththehighestgrowthspeed.However,nodetailedinformationwasgivenondislocationsandstrainfeaturesrevealedbyX-raydiffractiontopography"'.Weconcentrateonstudyofthestructuraleffectsonthedefectiveformationandgrowthmorphology.foeureacrystalcrystallizesinthete-tragonalsystem"…     

Effects of hyperbranched and linear architecture on properties of polymers composed of poly(ɛ-caprolactone) and hydroxycinnamic acid

Photoreactive and degradable polymers with linear and hyperbranched architectures which composed of poly(?-caprolactone) and hydroxycinnamic acid or its substituted derivatives were synthesized by thermal melt-polycondensation. The chemical structures of the polymers were confirmed by FTIR and ¹H NMR measurements. The polymers showed good photoreactivities and fluorescent properties, and the hyperbranched polymers showed higher photoreactive speed and weaker fluorescence properties. These polymers had excellent thermal stabilities due to the rigid conjugated structures and the π-π strcking interaction of the cinnamoyl group, especially for the hyperbranched polymer. Moreover, the hydrolysis experiments and the XRD results revealed that the hyperbranched and linear polymers are amorphous and crystalline, respectively, and the degradation rate of amorphous polymers are faster than crystalline samples.