Kinetic model for radionuclide sorption

A mathematical kinetic model is developed for sorption of radionuclides, occurring via transition of the sorbate atoms initially to the subsurface layer of the particles of a polydisperse sorbent with a known particle size distribution function ?(R), and then to the bulk of these particles. The variance of the function ?(R) was demonstrated to have a considerable effect on the sorption rate. The simulated results are compared with the experimental data on the sorption of ⁹⁰Sr from an aqueous medium on polydisperse calcium carbonate in the forms of calcite and vaterite.     

Structure and hydrogenation features of mechanically activated LaNi5-type alloys

The effect of short-term mechanical activation in a ball mill on the thermodynamics of interaction with hydrogen and the structure of intermetallic and hydride phases was studied for a series of AB₅ type alloys from the standpoint of their use as filler in metal-polymer membranes. It was found that the activation processing leads, as expected, to a decrease in the size of coherent scattering domains and an increase in the lattice strain, while the phase composition and unit cell parameters remain unaffected. Despite this, there is a significant change in the pressure-composition isotherms, a reduction of the total capacity ad the plateau region. XRD study of the hydride phases evidences smaller volume expansion of the intermetallic crystal lattice at hydrogen absorption for the alloys subjected to mechanical activation. Analysis of the obtained thermodynamic and structural data allows us to consider the mechanically activated LaNi_4.8Al_0.2 as the most appropriate for low-pressure and low-temperature application in the hydrogen separation composite membranes. La_0.7Ce_0.3Ni_4.5Cu_0.5 and LaNi₅ with maximum activation treatment of 3 min are more promising for use at elevated pressures.     

Factors in the Physicochemical Activity of Solids in Heterogeneous Systems

Recent works dealing with the physicochemical activity of solids are surveyed. The physicochemical activity of solids is understood as their ability to sorb components of their environment, participate in chemical reactions (including catalytic ones), cause radiation effects, etc. Quantitative characterization of physicochemical activity is attempted. Equations are derived to relate physicochemical activity to experimentally determinable properties of solids.     

Novel process for preparation of metal-polymer composite membranes for hydrogen separation

In the present work, a new preparation method for metal-polymer composite materials for hydrogen separation which consist of hydride-forming intermetallic compound LaNi₅ and polyethylene was developed. According to this technique, the mechanical activation of the initial powder mixtures was employed to provide good interface between the phases. A series of composite membranes with various filler concentrations was synthesized and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The gas transport properties of the obtained materials in relation to H₂, O₂, N₂, CO₂ and CH₄ were tested. The results indicate that the addition of the hydride-forming intermetallic compound to the barrier polymer leads to significantly improved selectivity with respect to hydrogen. The proposed method can be considered as a promising approach to producing of high performance composite membranes for hydrogen separation.     

Sorption of 90Sr and 90Y with the Vaterite Modification of Calcium Carbonate

Highly dispersed vaterite, a metastable modification of CaCO₃, can efficiently sorb ⁹⁰Sr²⁺ and ⁹⁰Y³⁺ ions from neutral aqueous solutions. The sorption proceeds in two stages. The first, rapid, stage (15-20 min) consists in adsorption of the radionuclide ions at active surface sites. The second, slow, stage (3-4 days) consists in irreversible capture of the radionuclides in the bulk upon transition of vaterite to calcite by the recrystallization mechanism.     

Hollow Alumina Macrotubes

Poorly crystallized Al₂O₃macrotubes 50 m to 6 cm in length, 10 to 300 m in outer diameter, and 2 to 60 m in inner diameter were obtained by heating partially hydrolyzed AlCl₃powder to 170–220°C in a flowing inert gas or air. The tubes were characterized by electron microscopy, atomic-force microscopy, IR spectroscopy, x-ray diffraction, and electron probe microanalysis.     

Sorption of <Superscript>90</Superscript>Sr and <Superscript>90</Superscript>Y with stable and metastable modifications of calcium carbonate

A comparative study of sorption of ⁹⁰Sr²⁺ and ⁹⁰Y³⁺ cations from aqueous solutions saturated with respect to calcium carbonate on the metastable CaCO₃ modifications (aragonite and vaterite) and also on the stable CaCO₃ modification (calcite) was carried out at 20°C. The sorption of these radionuclides from the solutions containing Sr(NO₃)₂ carrier and without it was studied. Aragonite shows the highest sorption capacity for ⁹⁰Sr²⁺, and these parameters are the lowest for calcite. All the CaCO₃ metastable modifications irreversibly sorb ⁹⁰Sr²⁺ and ⁹⁰Y³⁺ cations and therefore show promise for sorptive decontamination of water from ⁹⁰Sr.