Commercial-grade zeolite A synthesis from natural stellerite and clinoptilolite for exceptional Sr2+ removal performance

Abstract

The expansion of nuclear energy has increased the demand for sustainable and economically viable technologies for treating radioactive wastewater containing radionuclides such as 90Sr2+. In this work, we develop a low-temperature, energy-efficient solid-phase alkali activation strategy to upcycle abundant natural clinoptilolite and stellerite into highly crystalline zeolite A (HEU-LTA and STI-LTA). Activation at 100–200°C significantly reduces energy input and processing costs compared with conventional high-temperature routes, improving life-cycle sustainability and scalability. Crystallization mechanisms and the evolution of ring building units were elucidated using UV-Raman spectroscopy and solid-state MAS NMR. Both materials satisfy first-class commercial standards, with static water adsorption capacities of 26.0–26.2 wt.%. In Sr2+ removal tests, HEU-LTA and STI-LTA achieved >99.7% removal efficiency at a low solid-to-liquid ratio of 1:1000 g⋅mL−1, high adsorption capacities (271.0–316.5 mg g−1, rapid kinetics, wide pH tolerance (4–13), and strong selectivity. This approach provides a cost-effective, scalable, and resource-efficient pathway for producing high-performance zeolitic adsorbents for radioactive wastewater remediation.