Formation Mechanism and Structural Characterization of NaAl₁₁O₁₇ Based on Solid-State Reaction

As an aluminum rich mineral, NaAl₁₁O₁₇ is widely found in the by-products of the metallurgical industry, and it can be used as an alkali solidification phase in the harmless treatment of alkali-containing solid wastes due to its low formation temperature and strong stability. The formation mechanism, kinetics and structural characterization of NaAl₁₁O₁₇ were systemically studied based on the solid-state reaction in Na₂CO₃-Al₂O₃ system, and the reaction conditions that prevent the formation of NaAl₁₁O₁₇ were also established. The results show that NaAl₁₁O₁₇ is more feasible to form than NaAlO₂ when the Al₂O₃-to-Na₂O molar ratio (A/N) is > 11.0, and it almost completely transforms into NaAlO₂ when the A/N ratio decreases to 1.0. The formation kinetics of NaAl₁₁O₁₇ corresponds to the diffusion-controlled model of a 3D Ginstling-Brounstein model in the temperature range of 1000–1200°C. The conversion efficiency of NaAl₁₁O₁₇ is controlled by the phase boundary reaction model. Furthermore, the apparent activation energy and corresponding kinetic equation of NaAl₁₁O₁₇ formation were determined to be 46.89 kJ/mol and k = 1 × exp[–46.89/RT], respectively. The crystal structure characterization reveals that NaAl₁₁O₁₇ is formed by the doping of Na⁺ into [AlO₄] tetrahedron to form a solid solution.