Pellet silica-based titanate adsorbents with high selectivity for strontium removal from synthetic radioactive solutions

Abstract

The selective removal of strontium ion (Sr2+) from seawater has aroused great attention since the occurrence of the Fukushima nuclear accident. Inorganic ion adsorbents show promise in the treatment of large amounts of polluted water. Among of them, the titanates present a stability and selectivity towards strontium, but limited by poor mechanical and granulometric properties. In this work, a novel silica-based titanate (Na2TinO2n+1/SiO2) was synthesized by sol-gel method and then characterized by X-ray diffraction (XRD), thermal analysis (TG-DSC), XPS and BET. Characterization suggested that the crystal of the titanate was greatly affected by temperature, leading to the difference of the adsorption properties. The silica-based material showed a significant increase in specific surface area; and the adsorption process was found to be an ion-exchange reaction occurred inside these particles. Finally, the material calcined at 500 °C was selected to conduct the following batch experiments. Results suggested that the adsorption data of Sr2+ fitted the Langmuir adsorption model well; the pH from 3 to 10 contributed to a better Sr2+ adsorption behavior, with adsorption amount approaching 33.31 mg/g; the adsorption could reach equilibrium within 5 min with data fitted by the pseudo second kinetic model. And the selectivity coefficient revealed that this material had higher selectivity towards Sr2+ contrast to other alkali and alkaline-earth metals. Based on above static experimental results, the dynamic treatment was designed and carried out in a glass column. This test demonstrated that Na2TinO2n+1/SiO2 could remove the strontium from the simulated seawater effectively and efficiently with no leakage. Generally, this work provides an excellent material to removing Sr2+ from high salinity solution with good column compatibility.