Highly stable and magnetically separable alginate/FeO composite for the removal of strontium (Sr) from seawater.

In this study, a highly stable alginate/FeO composite was synthesized, and systematically investigated for the practical application of strontium (Sr) removal in complex media, such as seawater and radioactive wastewater. To overcome the drawbacks of the use of alginate microspheres, high contents of alginic acid and FeO were used to provide a more rigid structure with little swelling and facile separation, respectively. The synthesized composite was optimized for particle sizes of <400 μm and 1% content of FeO. The alginate/FeO composite showed excellent Sr uptake (≈400.0 mg/g) and exhibited outstanding selectivity for Sr among various cations (Na, Mg, Ca and K). However, in diluted Sr condition (50 mg/L), Ca significantly affected Sr adsorption, resulting in a decrease of K value from 3.7 to 2.4 at the 0.01 M Ca. The alginate/FeO composite could be completely regenerated using 0.1 M HCl and CaCl. In real seawater spiked with 50 mg/L of Sr, the alginate/FeO composite showed 12.5 mg/g of Sr uptake, despite the highly concentrated ions in seawater. The adsorption experiment for radio-active Sr revealed a removal efficiency of 67% in real seawater, demonstrating the reliability of the alginate/FeO composite.