Enhanced Sr²⁺ Sequestration in Fe-Modified Sodium Titanate: Adsorption Performance and Mechanisms

The sequestration of Sr²⁺ remains a significant challenge in the treatment of radioactive liquid waste. In this work, we studied the synthesis and characterization of sodium titanate (NTO) and Fe-modified sodium titanate (Fe-NTO) for the removal of Sr²⁺ from complex aqueous environments. The introduction of Fe species was accompanied by an expanded interlayer spacing of the sodium titanate phase, which may improve Sr²⁺ accessibility and influence adsorption behavior. Adsorption kinetics and isotherms of Fe-NTO could be described by the pseudo-second-order model and the Langmuir equation, respectively, giving an enhanced capacity of 173.92 mg g^-1 as compared to pristine NTO (151.03 mg g^-1). In complex solution matrices, Fe-NTO maintained effective Sr²⁺ uptake in simulated seawater, although the Sr/Ca discrimination was modest. In simulated waste liquid of the thorium molten salt reactor nuclear energy system (TMSR), Fe-NTO exhibited strong Sr²⁺ adsorption with a high distribution coefficient of 1.47 × 10⁵ mL g^-1, while also showing strong uptake of other multivalent ions. Combined Raman, XPS, postadsorption XRD, and ICP-OES analyses support that Sr²⁺ sequestration involves electrostatic attraction, Na⁺/Sr²⁺ ion exchange, and weak interactions with oxygen-containing sites in the titanate structure. These findings demonstrate the potential of Fe-NTO for effective Sr²⁺ sequestration in complex aqueous matrices, including simulated TMSR-related waste liquid, while underscoring the need for further optimization of ion selectivity in multicomponent systems.