The dissertation is devoted to the creation of magnetic nanocomposite sorbents on mineral base (saponite, palygorskite and spondyle clay) for wastewater purifying from. According to the results of X-ray diffraction analysis the crystallites size of Fe3O4 nanoparticles in MC is in the range of 2-10 nm.
Comparative analysis of МС samples containing Fe3O4 in amount of 2-7% indicates an increase of specific surface area due to the development of mesoporous structure caused by the formation of nanosized layer of magnetic modifier on the surface of pores of clay matrix. It is shown that the synthesis of magnetic nanocomposites on mineral base by impregnation method allows to obtain mesoporous sorbents with predominant mesopore diameter of 4-5 nm.
On the basis of comparison of the sizes of magnetite crystallites in the MС and the values of their coercivity and specific magnetization of saturation, the following regularities were established. First, the crystallines of magnetite in the size of no more than 3 nm had a zero value of the coercive force. Secondly, for Fe3O4 with crystallite size not more than 10 nm, the increase of specific magnetization of saturation and coercivity proportionally depended on the size of crystallites. Third, the magnetite, which was characterized by the size of crystallites 17-18 nm, had a high value of specific magnetization at too low coercivity and magnetic induction. The established regularities are explained by the change in the mechanism of magnetization from the reorientation of magnetic moments (single domain state) to the displacement of the domain walls (polydomain state), which occurs approximately at the size of crystallites of 10 nm, and by the presence of magnetite particles in the size less than 3 nm in a superparamagnetic state. Therefore, magnetic modifier stabilized on mineral matrix was obtained in the form of nanoscale single-domain particles.
Investigation of MC by the Mossbauer spectroscopy method has shown that, in contrast to the spectra of clay minerals, in the MC spectra the intense expanded sextets, that are characteristic for nanosized magnetite with a particle size of not more than 10 nm, and the doublets inherent to magnetite particles in a superparamagnetic state were indicated. An increase in the intensity of sexettes and a decrease in the intensity of doublets at increasing the particle size and magnetite crystallites was found. Thus, it was confirmed that magnetite was stabilized on a clay mineral in the form of singledomain particles (5-10 nm in size) and particles with superparamagnetic properties whose contribution decreases with increasing Fe3O4 content in the composite.
It was established, that adsorption processes using synthesized magnetic nanocomposite sorbents compared with their separate phases are accompanied by a synergistic effect. Mathematical modeling of adsorption of pollutants of different genesis on MC and native clays using Langmuir, Freundlich, Temkin and Dubinin-Radushkevych models has shown that the adsorption of cationic dye is reliably described by the Langmuir adsorption equation (R2 ≈ 1), the removing of anionic surfactants and dyes occurs in accordance with the Langmuir and Temkin adsorption models (R2> 0,9), and the adsorption of polyphosphates is most correctly agreed with the models of Langmuir and Friedlich isotherms (R2> 0,9).
The experimental data of adsorption of dyes, surfactants and polyphosphates were analyzed in accordance with mathematical kinetic models of the pseudo-first and pseudo-second order and the Boyd-Adamson diffusion models. Since the determination coefficient for the pseudo-second order model in all cases was R2 ≈ 1, this mathematical model most accurately describes the adsorption process of pollutants of different genesis on the MC. It was found that the limiting stage of adsorption of dyes, surfactants and polyphosphates is the intermolecular interaction between sorbent and pollutant. The thermodynamic parameters ΔG0 (from -1 kJ/mol to -4 kJ/mol) and ΔН0 (-(15-23) kJ/mol) indicated the physical and exotherm nature of adsorption on MC. An increase of negative value of entropy change ΔS0 by modulus at least in 3 times for MC compared with clays confirmed the higher energy of electrostatic interaction between magnetic nanocomposites with polytutans of different genesis.
Based on the obtained data, the design of the magnetic settler and the algorithm for calculating its technical characteristics are proposed. The scheme of sorption purification of industrial wastewater with the use of magnetic nanocomposites is developed. A technologically efficient, economically profitable and environmentally safe way of disposal of spent magnetic nanocomposites in the form of ceramic bricks or clinker mineral additives for concrete is proposed. Magnetic nanocomposites were also tested in conditions close to industrial applications.
