Eudialyte of the Kola Peninsula Is a Promising Source for Obtaining Composite Zr–Ti–SiO2 Sorbents of Nonferrous Metals and Radionuclides

Composite zirconium–titanium–silica sorbents with SiO₂ content of 10–30 wt % were synthesized on the basis of products of hydrochloric acid decomposition of eudialyte concentrate and their surface modification into H⁺ and Na⁺ forms was carried out. All samples were studied by methods of chemical, X‑ray phase, Brunauer–Emmett–Teller (BET), and Barrett–Joyner–Halenda (BJH) analyses. It is shown that all obtained samples of silica-containing Zr–Ti–SiO₂ sorbents are mesoporous. The pores are predominantly wedge-shaped with open ends, and pores with a diameter of 10–50 nm (~50% of the total pore volume) have the maximum volume. Based on the obtained values of the specific capacity of the adsorption monolayer of the surface of SiO₂ samples and the value of Gibbs energy change (ΔG°) in the process of nitrogen sorption, it was concluded that the surface modification of synthesized Zr–Ti–SiO₂ sorbents does not affect the physicochemical properties of their surfaces and the mechanism of nitrogen sorption. The sorption activity of synthesized samples towards Cu²⁺, Co²⁺, and Sr²⁺ ions was studied by the static method. It was found that modification of the obtained samples into the H⁺ form has less influence on their sorption capacity than their conversion into the Na⁺ form, does not depend on their SiO₂ content in the range of 10–30%, and decreases in the Cu²⁺ → Co²⁺ → Sr²⁺ series.