Synthesis and performance of zeolite microspheres for strontium adsorption, regeneration, and immobilization

In this study, zeolite microspheres (ZMSs) with a highly porous three-dimensional (3D) network structure exhibiting efficient Sr²⁺ adsorption properties were successfully prepared. The synthesis of these ZMSs involved the use of zeolite 4A (Z4A) derived from kaolinite, with the assembly process facilitated by the crosslinking interaction between sodium alginate (SA) and Ca²⁺. Zeolite was immobilized in polymers, which facilitated the adsorption and desorption operations of the adsorbent. Static adsorption results indicated that a favorable adsorption performance was achieved within the pH range of 3–8. The Langmuir isotherm fitting results revealed that the maximum saturated adsorption capacity was determined to be 51.6 mg/g. In addition, the adsorption capacity could reach 89.5 % of the equilibrium adsorption capacity within 1 h, demonstrating a relatively fast adsorption kinetics. Column tests demonstrated the effective performance of the material, with 668 mL of an effluent solution containing 100 mg/L Sr²⁺ reaching a 5 % breakthrough point. The recovery of the adsorbent can reach 58.73 % after five recycles when 0.02 M EDTA-2Na is used as the eluent. The leaching ratio of ZMSs ceramics sintered at 1100 °C in different leachates was found to follow the order: 0.1 M HCl >0.1 M NaOH >0.1 M NaCl > H₂O. These findings showed ZMSs had high adsorption efficiency, convenient operability, recyclability and stability, serving as a novel adsorbent for efficient Sr²⁺ removal and disposal in radioactive wastewater, suitable for large-scale low-level treatment.