The ability of natural and modified montmorillonite clays from Belgorod oblast to sorb Cs, Sr, U, and Pu radionuclides was studied. The clays were modified by treatment with metal (Li + , Na + , K + , Mg 2+ , Ca 2+ , Fe 2+ , Zn 2+ ) chloride solutions or aqueous HCl. The natural and modified clays studied show high performance in sorption treatment of solutions to remove Cs radionuclides. The natural clay and the Na and Mg forms of clays show the best sorption characteristics with respect to Cs. The distribution coefficient K d of 137 Cs in sorption on the above samples from a 0.1 M NaNO 3 solution is (1.1-1.4) × 10 4 cm 3 g -1 , which is 4-5 times higher compared to natural clinoptilolite. The Sr, U, and Pu radionuclides are sorbed on the examined clay samples to a considerably lesser extent. The K d values in sorption of these radionuclides from tap water are lower by 2-3 orders of magnitude than in sorption of Cs. Addition of clay materials in the course of cementation of liquid radioactive wastes, including NPP bottom residues, allows the rate of radiocesium leaching from the hardened cement compounds to be decreased by a factor of 5-16. The most efficient sorption additive in cementation of NPP bottom residues is natural montmorillonite clay.

A comprehensive study of the material composition of clay raw materials of the al-Najaf field (Iraq), which belongs to the sedimentary deposits of the Dammam formation, is conducted. The features of the chemical and phase composition of the rock are determined using x-ray phase, energy dispersive, microrentgenospectral, electron microscopic and thermogravimetric methods of analysis. The presence of titanium as an impurity element is detected in the studied clay along with the typical element composition of aluminosilicates using energy-dispersion-spectral analysis. At the same time, a high total content of oxides of alkaline and alkaline earth metals (Cao, Na2O, K2O) is recorded, amounting to more than 5.0 wt. %. It is found that the sample under study has a polymineral composition, the main rock-forming minerals are kaolinite, illite and montmorillonite. The total percentage of the clay component is more than 82 wt.%. Content of clay particles belonging to high-and medium-dispersed fractions (size 10 microns or less) it is more than 60% by weight. The average size of the particles composing the studied clay is about 32.0 microns. Based on the data on the chemical, mineralogical and granulometric composition of the sample, a conclusion is made about the potential suitability of the studied clay as a sorption-active material, as well as in the production of Portland cement and coarse ceramics.

Phase formation of calcium monoaluminate and calcium dialuminate in the СаО–Al2О3 system in the range 230–1450°C was studied using a model powder mixture comprising aluminum and calcium hydroxides. The onset of formation of an intermediate phase Ca12Al14O33 (С12А7) was observed at 430°С. At 1100°С, the appearance of CaAl4O7 (CA2) and the presence of κ-Al2O3 were observed. The onset of intense formation of the CaAl2O4 (СА) phase is at 1170°С. In the range 1250–1400°С, the CA amount increases notably, while the СА2 proportion remains almost unchanged. The final formation of the CA and CA2 target phases occurs in 2 h at 1450°С. The syntheses of CA and CA2 is controlled by Ca2+ diffusion inward the aluminum-enriched cores of spherulites. Energy dispersive X-ray spectroscopy elucidated the CA and CA2 distribution in the form of concentric layers.

No abstract

The results of studying the process of fine grinding of α-Al2O3 in the presence of polyethylene glycol (PEG) and an antistatic composition are presented. It is shown that the main reason for the agglomeration of fine particles is the effect of the appearance of an electrostatic surface charge. The introduction of PEG prevents the appearance of a «pseudo-viscous grinding medium», removing the excess electrostatic charge on the surface of newly formed ultrafine particles, and also intensifies the process of abrasion of primary alpha-alumina crystals. The antistatic composition successfully neutralizes the surface electrical charge, but does not have the effect of a grinding aid.