Facile Synthesis of Nanolayered Manganese Oxide for the Efficient and Selective Removal of Strontium(II) from Nuclear Wastewater

Efficient and selective removal of radioactive ⁹⁰Strontium (⁹⁰Sr) from nuclear wastewater is a sustainable strategy for nuclear energy development and environmental protection due to its long half-life and high biochemical toxicity. Herein, a novel nanolayered manganese oxide material (Na_0.7MnO_2.05, Na-NLMO) is proposed and its application for Sr(II) capture in both simulated waste liquid and real natural water systems. Na-NLMO is tailored for Sr(II) adsorption through a simple and rapid solid-phase reaction, which has good chemical stability and a strong affinity for Sr(II) across the pH range of 1 to 8. The maximum adsorption capacity is 145.21 mg g^-1 taking advantage of the solid-liquid ratio of 0.67 g L^-1. The loaded Sr(II) is almost quantitatively recovered by dilute hydrochloric acid solution. Even after 4 adsorption-desorption cycles, it could still effectively adsorb more than 99.9% of Sr(II). Furthermore, the adsorption is unaffected by the excess presence of sodium(I), potassium(I), magnesium(II), and calcium(II). In real-world media such as tap water and river water, its distribution coefficients are 5.2 × 10⁵ and 5.6 × 10⁵ mL g^-1, respectively. More importantly, the distribution coefficient toward ⁹⁰Sr in seawater still achieved 2.5 × 10³ mL g^-1. The adsorption mechanism of electrostatic interaction and ion exchange is revealed by combining experimental results and spectroscopic analysis, such as Transmission Electron Microscope and X-ray diffraction. The results are expected to provide new insights into the development of innovative and practical technologies for the treatment and disposal of secondary nuclear waste.