Preparation of TiO2-SiO2 mixed gel spheres for strontium adsorption

A simple external gelation process, taking full advantage of the gelation features of titanium and silica, was developed to prepare TiO₂–SiO₂ mixed gel spheres suitable for strontium adsorption. The source solutions used for the process were prepared from different mixtures of 1 M TiCl₄ and 1 M Na₂SiO₃ solutions and converted into droplets in a gelation column. The suitable spheres for strontium adsorption were obtained using a hexone (methyl isobutyl ketone) solution as the drop formation medium and ammonia as the gelling agent. The mixed oxide gels were identified and characterized by DTA/TGA, FTIR and XRD analysis. The parameters affecting the strontium adsorption, such as weight ratio of TiO₂, pH, temperature, shaking time and selectivity towards competing ions were investigated. Sorption data have been interpreted in terms of Freundlich, Langmuir and Dubinin–Radushkevich equations. Thermodynamic parameters for the sorption system have been determined at four different temperatures. The value of ΔH° = 39.553 kJ/mol and ΔG° = −16.687 kJ/mol at 296 K prove that the sorption of strontium on mixed oxide gel is an endothermic and a spontaneous process.