Synthesis of a low-silica CHA zeolite with exceptional selectivity for radioactive 137Cs+

Abstract

¹³⁷Cs⁺ is the predominant radionuclide in nuclear wastewater. The efficient and quick removal of radioactive Cs⁺ from wastewater is significant for the safe use of nuclear energy and human health. Herein, we reported a green and facile one-pot synthesis of a low-silica CHA zeolite with a Si/Al ratio of 2.06, in which no OSDAs or seeds are needed. The resultant Na forms a CHA zeolite (Na-CHA), which has exceptional selectivity and a deep removal ability for the capture of ppt (parts per trillion)-level radioactive ¹³⁷Cs⁺ from real nuclear power wastewater with a ¹³⁷Cs⁺ radioactive activity of 1587.22 Bq L⁻¹ (corresponding to the mass concentration of 0.496 ppt) and high concentrations of H₃BO₃ and NaOH as well as other radionuclides such as ⁶⁰Co²⁺ and ⁹⁰Sr²⁺. After treating with a solid/liquid ratio of 1/1000 in g mL⁻¹, the resultant ¹³⁷Cs⁺ radioactive concentration was as low as 7 Bq L⁻¹, corresponding to a distribution coefficient (K_d) of 2.26 × 10⁵ mL g⁻¹. The obtained Na-CHA zeolite also showed fast adsorption kinetics (ca. 5 min), a high capture capacity (442.48 mg g⁻¹), a broad working pH range (4–12), and excellent radiation resistance (the crystallinity and performance of the Na-CHA zeolite were not affected by 1000 KGy ⁶⁰Co²⁺ irradiation). More importantly, the synthesis was scaled-up to the order of 100 L with readily available raw materials and the performance of the resultant products was the same as that of the products synthesized at the lab scale. The superior selectivity, coupled with the ultra-low cost and environmentally benign nature, makes the Na-CHA zeolite an ideal candidate in nuclear wastewater management.