The adsorption of methylene blue from model aqueous solutions on bentonite-like clay, hydroxyapatite, and a composite sorbent has been investigated. The kinetic and thermodynamic parameters of adsorption in the temperature range 298–333 К have been calculated. The process is found to obey Langmuir isotherm equation. It is spontaneous but slightly endothermic. The maximal sorption capacity of the composite sorbent toward methylene blue is 175.4 mg/g at 25 °С that is 1.3 times more than that for bentonite-like clay and 17.8 times more than that for hydroxyapatite. Kinetics of the process is due to the combination of external and internal diffusion and can be described better by the model of pseudo-second order reaction.
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.
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