High Selectivity For Cs Research Articles

Immobilization of Cs, Cd, Pb and Cr by synthetic zeolites from Spanish low-calcium coal fly ash

This report describes a study of the immobilization of Cs +, Cd 2+, Pb 2+ and Cr 3+ by synthetic zeolites formed as a result of the hydrothermal treatment of Spanish class F coal fly ash in a 1 M solution of NaOH. The majority zeolite formed at 150 °C was a gismondine-type P1-Na species (Na 6Al 6Si 10O 32·12H 2O), which at 200 °C transformed into analcime-C zeolite (Na(Si 2Al)O 6H 2O). The shift in pore size distribution towards pores with diameters of about 2.2 nm observed after the zeolites were washed entailed an increase in the specific surface area, to values nearly double the figures recorded prior to washing. With a high selectivity for Cs, the gismondine type Na zeolite P was found to be the best candidate for immobilizing radioactive waste. Gismondine and analcime-C zeolites also exhibited high Cd selectivity.

Microwave-hydrothermal synthesis of Al-substituted tobermorite from zeolites

Here, we report the rapid synthesis of Al-substituted tobermorites from zeolites under microwave-hydrothermal (M-H) conditions. The synthesized phases were characterized by powdered XRD analysis, SEM and selective Cs exchange determination. Zeolites served as aluminosilicate sources and M-H conditions yielded highly crystalline Al-substituted tobermorites in 2 h at 180°C and they showed high selectivity for Cs. For example, an Al-substituted tobermorite synthesized from phillipsite showed Cs exchange K d of 2161±465 and 118,589±44,928 from 0.02N NaCl and 0.02N CaCl 2 solutions (both contained 0.0002N CsCl), respectively. Al-substituted tobermorites are expected to be useful for the selective separation of radioactive Cs and tobermorites can be incorporated in cement and/or concrete matrix for Cs immobilization.

Neutron Powder Diffraction Study of Ti2(OH)2OSiO4·1.5H2O

The proton form of the exchanger Na{sub 2}Ti{sub 2}O{sub 3}(SiO{sub 4}){center_dot}2H{sub 2}O exhibits a high selectivity for Cs{sup +} even in acid solutions. A neutron diffraction study was carried out to locate the position of the exchangeable protons. The structure contains cubane-like Ti{sub 4}O{sub 4} clusters bridged by silicate groups. The acidic proton is located on the cubane oxygens which make them four-coordinate, being bonded to three titaniums and one proton. The unit cell is tetragonal. There are six water molecules per tunnel and two tunnels per unit cell. Thus, the empirical formula is Ti{sub 2}(OH){sub 2}OSiO{sub 4}{center_dot}1.5H{sub 2}O. The water molecules are H-bonded to the framework oxygens and to each other. Although the tunnels are filled with water molecules, framework sites normally occupied by Na{sup +} are empty. The high selectivity for Cs{sup +} apparently stems from the ability to form a thermodynamically stable eight-coordinate complex by replacement of the hydroxyl protons.

Cs+ Ion Exchange Kinetics in Complex Electrolyte Solutions Using Hydrous Crystalline Silicotitanates

TAM-5 is a hydrous crystalline sodium silicotitanate inorganic ion exchanger with a high selectivity for Cs+. The kinetics of Cs+−Na+ ion exchange using TAM-5 in multicomponent electrolyte solutions were determined using batch experiments. For the powder, which is composed of crystals, a single-phase, homogeneous model fit the data best. For the granules, which were prepared from the powder, a two-phase, heterogeneous model resulted in an excellent fit of the data. Macropore and crystal diffusivities were determined by fitting the model to experimental data collected on the powder and the granules. Intracrystalline diffusivities were concentration dependent and were on the order of 10-19 m2/s. Macropore diffusivities were on the order of 10-10 m2/s. Resistance to diffusion in the macropores was not significant for granules with diameters less than 15 μm. A two-phase, homogeneous model, where liquid within the pores is in equilibrium with the solid, was also evaluated for the granules. Surprisingly, for the granules, an excellent fit of the data was obtained; however, the effective macropore diffusivity was 1.1 × 10-11 m2/s, an order of magnitude smaller than the macropore diffusivity found using the two-phase, heterogeneous model.

Formation of Highly Selective Cesium-Exchange Sites in Montmorillonites

AbstractIon-exchange sites with very high selectivity for Cs (ΔGCa2+Cs+ = 40 kJ/eq) similar to illite were generated in a controlled way in montmorillonites b. (1) repeated wetting-drying cycles and b. (2) charge reduction using the Hofmann-Klemen effect. An almost continuous range of sites with selectivities varying from ln KCa2+Cs+ = 33 to 5 was observed.

Contribution a l'etude des echangeurs inorganiques: Echangeurs a base de plomb(II)

Sorption properties of Pb2+ compounds (fluoride, ferrocyanide, oxyde) have been investigated by tracers methods and batch equilibrium study. The fluoride exibits high selectivity and capacity values for REE and the ferrocyanide, high selectivity for Cs and transition ions. The great solubility of the oxyde in acidic ambients limits its analytical value. Adsorption on lead fluoride seems to be governed by the formation of a low solubility product while on ferrocyanide ion exchange phenomenons are predominant.

Cæsium–Sodium Ion Exchange on Clinoptilolite

Clinoptilolite is a natural zeolite that has a high selectivity for Cs. The sorption of Cs and Na ions on clinoptilolite is determined, and exchange sorption isotherms are determined for Cs-Na exchange on clinoptilolite at 50 and 75 deg C. (T.F.H.)