Mechanisms, material performance, and process challenges in adsorption-based removal of radio strontium from aqueous systems: A review

Radioactive strontium, particularly 90Sr, is a long-lived fission product with a half-life of approximately 28.8 y. It is one of the major radiological concerns due to its chemical similarity to calcium. Strontium, when liberated in an aquatic environment, can move in surface water and ground water systems and can be bioaccumulated. As a result, an environmentally important technology for the removal of aqueous Sr must be developed with the required reliability and selectivity. Given the various methods of treatment, including precipitation, membrane filtration, solvent extraction and ion exchange, adsorption has been the subject of constant study due to its adaptability to a variety of water chemistries and ease of operation. In recent years, research has focused on various adsorbents, including natural and synthetic zeolites, titanates, biochar-based materials, hydroxyapatite, ion-exchange resins, metal-organic frameworks, MXenes, and composite matrices. The present review aims to summarize adsorption-based removal of strontium ions, highlighting the adsorption mechanism, the performance of adsorption materials, the selectivity of the adsorption process in the presence of other ions, the regeneration process, and technological limitations. The review does not focus on a single superior material that performs well across all water matrices and conditions, but rather emphasizes that water chemistry and operating conditions significantly influence adsorption performance, suggesting that researchers should test materials under relevant water matrices. The reported capacities and selectivity data are strongly dependent on water chemistry and experimental conditions. The most important research needs are the development of selective parameters for Ca2+/Mg2+ rich waters, improved regeneration procedures, and pilot-scale validation.