Elena V. Fomenko

Influence of the composition and structure of the glass-crystalline shell of cenospheres on helium permeability

We studied the interrelation between the composition, morphology, and helium permeability of the shell of narrow fractions of nonmagnetic nonperforated cenospheres extracted from cenosphere concentrates of fly ash of the sialic type with the use of technological stages of hydrodynamic, magnetic separation, sizing, and aerodynamic classification. For the interval of variation of Al2O3 content from 20 to 38 wt %, the regression equation [SiO2]/[Al2O3] = 5.06 − 0.1[Al2O3] is established, with the correlation coefficient equal to −0.98. It is found that, together with the growth in the concentration of Al2O3 in the indicated interval, the content of the originally mullite phase increases from 1.3 to 42.4 wt %, and this is accompanied by the growth of the helium permeability of the glass-crystalline shell of the cenospheres.

A novel layered zirconium molybdate as a precursor to a ceramic zirconomolybdate host for lanthanide bearing radioactive waste

Novel layered zirconium molybdates (Mo/Zr = 2) in Na+- and NH4+-exchanged forms with a defective crystalline structure and a specific surface area of up to 100 m2 g−1 were synthesized under mild hydrothermal treatment conditions (150 °C, 3 days) without structure-directing reagents. The NH4+- zirconomolybdate material was tested for its ability to immobilise aqueous radioactive waste containing rare earth elements by a sorption/impregnation–crystallization process using simulant Nd3+/Ln3+ bearing solutions. The motivation for tailoring (Ln,Zr,Mo)-ceramics was the utilization of sediment-forming components of spent nuclear fuel processing solutions, such as Mo and Zr, for immobilization of transuranium radionuclides or an actinide–lanthanide (An–Ln) fraction of high-level effluents. The target (Ln,Zr,Mo)-phase acceptable for incorporation of actinides and lanthanides, Ln2Zr3(MoO4)9 (Ln = La–Tb), was selected on the basis of studying the phase formation in triple oxide systems Ln2O3–ZrO2–MoO3 (Ln = La–Lu, Y, Sc) and analysis of the known promising host phases being developed in the world for the actinide immobilization. X-ray diffraction and thermal analysis methods were used in the study of the thermochemical conversion of the Nd3+/Ln3+-zirconomolybdates resulting from loading the layered NH4+-zirconomolybdate precursor with different quantities of Nd3+/Ln3+. The results on Nd3+ immobilization by the sorption–crystallization route reflected the influence of the acidity of the simulant solutions on the content of the target phase in the solidified (Nd,Zr,Mo)-ceramics. The impregnation/sorption–crystallization procedure provided poly-phase composites including Nd2Zr3(MoO4)9, ZrxNdy(MoO4)2 and ZrO2, the quantity of the target phase depending on the Nd3+ loading. The solidification of the Ln bearing simulant solution at 16% Men+ loading resulted in nearly mono-phase ceramics of the Nd2Zr3(MoO4)9 structural type.

Gas permeation properties of hollow glass-crystalline microspheres

Permeation of He, H2 and Ne was studied for hollow glass-crystalline microspheres. Microspheres demonstrated high permeability to helium with high selectivity for He/H2 and He/Ne owing to the composition and structure of their shells.

Single-Stage Aerodynamic Separation of Fly Ash Produced after Pulverized Combustion of Coal from the Ekibastuz Basin

The single-stage separation of fly ash from field 1 of the electrostatic precipitator of Reftinskaya GRES (Regional Thermal Power Plant), which burns coal from the Ekibastuz Basin, was performed by aerodynamic classification with the use of a flow of air. It was found that, at a constant airflow rate of 50 m3/h, the morphologically uniform fractions of small spherical particles with a narrow distribution, for which dmax was 2, 3, and 4 μm and d90 was 4, 6, and 8 μm, can be separated by decreasing the speed of the classifier rotor from 22000 to 10000 rpm. At a minimum speed of 2000 rpm, the target product of separation was a narrow fraction containing large particles, which were characterized by dmax of 109 μm and d90 of 205 μm. It was established that SiO2 and Al2O3 were the basic chemical components of the fractions obtained, and the total concentration of these components was as high as 86–91 wt %. With increasing the size of fractions with dmax from 2 to 116 μm, a decrease in the concentration of SiO2 and an increase in the amounts of Al2O3 and Fe2O3 were observed. The dependence of phase composition on the particle size was established for the small fractions: as dmax was increased in a range of 2–25 μm, a monotonic decrease in the concentration of a quartz phase and an increase in the concentration of mullite were observed; the concentration of a Fe-containing spinel phase also increased.

Microsphere Zirconomolybdate Sorbents for Extraction of Lanthanides (III) from Aqueous Solutions

Micromesoporous zirconomolybdates with a specific surface area of 200 m2/g and pore sizes in the range of 10-40 Å (Dmax~15 Å) were synthesized under hydrothermal conditions (150 °С, 72 h). Microsphere composites were prepared by deposition of the zirconomolybdates on a microsphere hollow carrier with a macroporous shell (Dpore ~ 2-10μm) resulted from the NH4F-HCl-H2O etching of a cenosphere narrow fraction (-0,08+0,071 mm) separated from coal fly ash of Reftinskaya power station. The morphological type “cenospheres with a porous shell and a smooth surface” predominates in the fraction. The sorption properties of zirconomolybdates and microsphere composites with different Mo/Zr ratio were studied regarding Nd3+ cations as a surrogate of trivalent actinides. It was established that the thin-layer mode of zirconomolybdate deposition on the carrier and the increasing of a Mo/Zr ratio in its composition provides the enhanced distribution coefficient (up to 104 ml/g) and efficiency of Nd3+ sorption (up to 85 %).