Preparation of highly stable zeolite-alginate foam composite for strontium(90Sr) removal from seawater and evaluation of Sr adsorption performance.

Alginate bead is a promising strontium (Sr) adsorbent in seawater, but highly concentrated Na ions caused over-swelling and damaged the hydrogel bead. To improve the mechanical stability of alginate bead, flexible foam-type zeolite-alginate composite was synthesized and Sr adsorption performance was evaluated in seawater; 1-10% zeolite immobilized alginate foams were prepared by freeze-dry technique. Immobilization of zeolite into alginate foam converted macro-pores to meso-pores which lead to more compact structure. It resulted in less swollen composite in seawater medium and exhibited highly improved mechanical stability compared with alginate bead. Besides, Sr adsorption efficiency and selectivity were enhanced by immobilization of zeolite in alginate foam due to the increase of Sr binding sites (zeolite). In particular, Sr selectivity against Na was highly improved. The 10% zeolite-alginate foam exhibited a higher log Kd of 3.3, while the pure alginate foam exhibited 2.7 in the presence of 0.1 M Na. Finally, in the real seawater, the 10% zeolite-alginate foam exhibited 1.5 times higher Sr adsorption efficiency than the pure alginate foam. This result reveals that zeolite-alginate foam composite is appropriate material for Sr removal in seawater due to its swelling resistance as well as improved Sr adsorption performance in complex media.

Highly stable and magnetically separable alginate/Fe3O4 composite for the removal of strontium (Sr) from seawater.

In this study, a highly stable alginate/Fe3O4 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 Fe3O4 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 Fe3O4. The alginate/Fe3O4 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 Kd value from 3.7 to 2.4 at the 0.01 M Ca. The alginate/Fe3O4 composite could be completely regenerated using 0.1 M HCl and CaCl2. In real seawater spiked with 50 mg/L of Sr, the alginate/Fe3O4 composite showed 12.5 mg/g of Sr uptake, despite the highly concentrated ions in seawater. The adsorption experiment for radio-active 90Sr revealed a removal efficiency of 67% in real seawater, demonstrating the reliability of the alginate/Fe3O4 composite.