Optimization of zeolite LTA formation from kaolin using fusion/hydrothermal method: Crystallization parameters and Box-Behnken experimental design

Using the fusion/hydrothermal approach, the effects of NaOH/kaolin ratio, the crystallization temperature and the crystallization time of the reaction system on the synthesis of zeolite A from natural kaolin have been methodically investigated. The study aimed to enhance crystallinity of the obtained zeolite by employing optimization curves generated from a three-level Box-Behnken Design (BBD) simulation. Using XRD, SEM/EDS, FTIR, XPS and TEM/SAED, the synthesis products` phase, composition and morphology were described. The morphological analysis and elemental characterization confirm that the NaOH/kaolin treated at 550 °C has the necessary Si/Al ratio and structural transformation to support LTA zeolite synthesis. The XRD analysis reveals that optimal conditions for synthesizing high-purity Zeolite A include a NaOH concentration of 3 M, 5 h of agitation, 12 h of crystallization, and a crystallization temperature of 90 °C. Higher NaOH concentrations and crystallization temperatures can lead to unwanted phases like sodalite, while longer times do not significantly improve crystallinity. From the statistical results, the optimal conditions identified 90 °C, a NaOH/kaolin weight ratio of 0.9, and a crystallization duration of 12.50 h resulted in a significant increase in crystallinity, reaching 88.60 %. These findings underscore the importance of carefully controlling synthesis parameters to achieve high-quality zeolite products through the fusion/hydrothermal process. In addition, the validation of the response surface methodology (RSM) model confirmed its effectiveness in optimizing the synthesis parameters for Zeolite A, achieving a crystallinity of 91.10 % under the ideal conditions of a NaOH/kaolin weight ratio of 1.06, crystallization temperature of 92.99 °C, and crystallization time of 12.69 h. The results, supported by SEM analysis, demonstrated improved crystallinity and uniform particle size, aligning closely with predicted values. This successful validation emphasizes the model`s reliability and potential for enhancing production efficiency while maintaining high-quality zeolite A. Its economic viability for industrial-scale applications was demonstrated by the projected $0.95/kg cost of producing zeolite A from Algerian kaolin using the fusion/hydrothermal technique.