Removal of strontium (Sr²⁺) from aqueous solutions with titanosilicates obtained by the sol-gel method

Titanosilicates (TiSis) were synthesized from pure and technical precursors by the sol-gel method. X-ray diffraction (XRD) studies of TiSi identified amorphous phases. The Brunauer, Emmett and Teller (BET) surface area of TiSis obtained from pure and technical precursors measured using the low-temperature nitrogen adsorption/desorption technique were 270.3 and 158.7m²g^-1, respectively. Micro-mesopore and micro- meso- macropore structures were attributed to TiSi prepared from pure and technical precursors, correspondingly. TiSis mass, solution pH, contact time, initial Sr²⁺ concentration, temperature and background solution were investigated for their effect on sorption properties. TiSis were observed to have a high affinity for strontium in the pH range of 4-12. Strontium adsorption isotherms were established and fitted to the Langmuir, Freundlich, Redlich-Peterson, Sips and Toth models. Pseudo-first and pseudo-second models were used to describe experimental kinetic data. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) data for TiSis were collected before and after adsorption. Heterophase was observed on the surfaces of both types of TiSi material after Sr²⁺ uptake. The mechanism of Sr²⁺ sorption on titanosilicates was suggested.