Sustainable synthesis of Na₂ZrO₃ from Zircaloy waste for CO₂ capture applications

Abstract

High-temperature Na2ZrO3 sorbents were synthesized for the first time via a solid-state route utilizing Zircaloy waste and NaOH. Thermochemical calculations combined with structural studies reveal a complex formation mechanism in which the in-situ oxidation of the alloy and the early formation of highly reactive Na-intermediates provide a significant thermodynamic advantage. Systematically controlling the synthesis parameters, such as the milling time of the reagents, the Na:Zr molar ratio and the calcination temperature, resulted in distinct Na2ZrO3 sorbents with specific structural and microstructural characteristics. The optimized Na2ZrO3 sorbent (5 h of milling, 2:1 Na:Zr ratio, 800 ◦C) exhibits a maximum uptake of 22 wt% (92% of theoretical) and the fastest sorption rate reported (0.236 gCO2/g.min), surpassing both traditional solid-state and sophisticated wet chemistry methods. Kinetic analysis using the Avrami model confirms a 2D nucleation and growth mechanism that becomes increasingly dominant during cycling, minimizing diffusion-limited stages. This enhanced reactivity is attributed to a structural activation and fragmentation process, which transforms monoclinic polyhedral crystals into an interconnected nanocrystalline network with a defect-rich structure. This study offers a viable, scalable strategy for valorizing industrial waste into high-performance Na2ZrO3 sorbent for practical CO2 capture applications.