Abstract: Methods are presented for synthesis of composite materials based on resorcinol–formaldehyde polymer and phosphorus-containing vermiculite with simultaneous introduction of calcium carbonate into the reaction mixture. The composition and structure of sorbents have been determined by IR spectroscopy, X-ray powder diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, and positron annihilation spectroscopy. The sorption characteristics of the composites have been studied using the example of methylene blue adsorption and strontium extraction from aqueous solutions under static conditions. The results of strontium sorption have been calculated using the Freundlich, Langmuir, and Langmuir–Freundlich equations. The strontium distribution coefficients have been calculated at pH 6–7; it has been shown that the Kd of the sorbent with phosphorus-containing vermiculite and calcium carbonate is higher than the Kd of the known model resorcinol–formaldehyde sorbent. The degree of inhomogeneity of the sorbent surface, as well as the sorption constant and the maximum sorption value, have been determined. The dependence of the limiting sorption on the degree of inhomogeneity and the number of defects during positron annihilation (Ne+) have been demonstrated. The ionization constants and the capacity of surface functional groups have been determined by potentiometric titration. © 2022, Pleiades Publishing, Ltd.

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