Preparation of ZrO2 and ZrO2–TiO2 microspheres by the sol–gel method and an experimental design approach to their strontium adsorption behaviours

ZrO2 and ZrO2–TiO2 mixed gel spheres were prepared via sol–gel process. The source sols of Zr and Zr–Ti (with 1:1 molar ratio) were prepared by the ammonia addition method starting from ZrOCl2 and TiCl4 solutions. A simple method, using a gelation column containing two phases (methyl isobutyl ketone and ammonia) as sphere forming and gelling medium, allowing to direct preparation of ZrO2 and ZrO2–TiO2 mixed gel spheres. The adsorption behaviours of each adsorbent towards strontium were determined by the experimental design method for the possible application to its removal from radioactive waste solutions. pH, temperature, strontium concentration and shaking time were chosen as independent variables and the efficiency of strontium removal as dependent output variable. Central composite design (CCD), with seven replicates at the centre points and thus a total of 31 experiments were employed in this study for each synthesized ZrO2 and ZrO2–TiO2 microspheres. Sorption data have been interpreted in terms of Freundlich, Langmuir and Dubinin–Radushkevich equations. Thermodynamic parameters for the sorption system have been determined. Each adsorbent were subjected to thermal treatment from 600 °C to 900 °C and were investigated by XRD, FTIR, DTA/TGA, SEM and BET surface area methods.