A facile synthesis of sodium nonatitanate from anatase and evaluation of its strontium ion exchange properties

Sodium NonaTitanate (SNT) is an efficient inorganic ion exchanging material for removal of strontium and was extensively used for waste water clean-up in Fukushima reactor accident site. The requirement for larger volume of SNT for specific applications like decontamination of low-level nuclear waste solution or sites with accidentally dispersed radioactivity necessitates low cost and facile process for its synthesis. Herein, we have reported a facile hydrothermal method for preparation of SNT (Na 4 Ti 9 O 20 x H 2 O, x ~ 9) from anatase using an optimized concentration of alcohol. The nature and concentration of alcohol have been optimized to obtain SNT in high yield. The aqueous solution of alcohol was found to be crucial for dissociation of anatase under reaction conditions and hence formation of SNT phase. The product has been characterized by powder XRD, Thermogravimetric studies and SEM-EDX analysis, and the ion exchange capacity for Sr 2+ ion have been evaluated using ICP-AES. The Sr 2+ exchange kinetics follow pseudo second order rate equation and the ion exchange capacity for Sr 2+ at equilibrium is 2.16 mmol/g. Equilibrium Sr 2+ ion uptake data have been analysed using different isotherm models and a favourable Langmuir monolayer adsorption process is proposed. Besides, the electrostatic preferences favour for the fast and complete exchange of Na + by Sr 2+ ions. SNT shows high selectivity for Sr 2+ over Na + ions in low Na + ion concentration while the uptake is appreciably affected in presence of Ca 2+ and Y 3+ as well as in highly acidic condition. In addition, it is also shown that the Sr 2+ exchanged nonatitanate can be transformed conveniently to SrTiO 3 phase, which is a promising ceramic matrix for immobilization. This study demonstrated a protocol for synthesis of promising low-cost ion exchangers using low cost and abundant titanium precursors, like micron sized commercial crystalline anatase and subsequent development of waste immobilization matrix.