Tuning the ion exchange behavior of cesium and strontium on sodium iron titanate

The sodium iron titanate (NaFeTiO) ion exchanger was synthesized by the hydrolysis of tetraethyl orthotitanate and ferric chloride solution using sodium hydroxide. The amount of Fe³⁺ present in the solution was varied to obtain different Ti/Fe mole ratios in the product ranging from 5 to 15. The ion exchanger obtained was characterized by Raman spectroscopy, X-ray diffraction, Thermogravimetry, SEM-EDX analysis and elemental composition. The ion exchange behavior of Cs⁺ and Sr²⁺ on sodium iron titanate was studied as a function of aqueous phase pH, equilibration time, initial concentration of Cs⁺ and Sr²⁺ and presence of interfering ions in aqueous phase. The rate of ion-exchange of Cs⁺ and Sr²⁺ was best fitted into pseudo-second order rate equation. Similarly, the loading behavior of Cs⁺ and Sr²⁺ on NaFeTiO and the data obtained were fitted into various adsorption models such as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevitch adsorption isotherms. From the statistics of the fitting, it was found that the experimental isotherm was explained well by Langmuir adsorption model. The ion-exchange capacity of 127, 115, 95 mg.g⁻¹ for Cs⁺ and 86,128,169 mg.g⁻¹ for Sr²⁺ were obtained on NaFeTiO with Ti/Fe mole ratios 5, 10, and 15 respectively. The results showed that the selectivity of NaFeTiO can be tuned either for Sr²⁺ exchange by keeping higher Ti/Fe mole ratio or for Cs⁺ exchange by keeping lower Ti/Fe mole ratio. In view of this, NaFeTiO compound can be regarded as the potential candidate for separating cesium or strontium selectively from alkaline wastes.