Ti/Si ratio as a tool to tailor the microstructure of titanate-based crystalline phases able to selectively trap strontium over calcium

Abstract

The sitinakite structure is one of the most promising material to tackle down the problem of the treatment of wastewater contaminated with 90Sr. To provide a better insight on how the synthesis conditions can affect the properties of this crystalline silicotitanate (CST), the effect of the Ti/Si ratio in the starting gel was studied to produce more efficient materials. It was found that for the lower Ti/Si ratios, powders with the sitinakite structure were obtained. The specific surface area had a slow down effect on the strontium uptake kinetics below a threshold value between 50 and 100 m2.g−1. Higher ratios landed powders with the sodium nonatitanate structure, still relevant for this study as this layered phase is known for its affinity with Sr2+. Finally, sorption isotherms realized with a competitor ion to Sr2+, i. e. Ca2+, showed that only sitinakite structure was able to selectively catch Sr2+, with an initial molar ratio Ca/Sr of 49.6 in the liquid and a final ratio between 2.2 and 4.1 in the solid. This study therefore delineated the synthesis conditions leading to CST structures capable of depolluting strontium-contaminated aqueous outflows.