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.