Sapo-34 Obtained from Amazonian Flint Kaolin: Influence of Impurities of “Oxidized Fe/Ti” in Synthesis and Its Application in the Removal of Cationic Dye from Water

• Published in: Processes 2023-03, Vol.11 (3), p.662
• Main Authors: Pinheiro, Darllan R, Pinheiro, Alice P, Pontes, Fabio A, Soares, João Vitor K, Neves, Roberto F, Paz, Simone P. A
• Format: Article
• Language: English
• Subjects: Acids; Adsorbents; Adsorption; Adsorptivity; Aluminum; Aqueous solutions; Cationic dyes; Chemical synthesis; Chemisorption; Clay; Crystallinity; Degree of crystallinity; Dyes; Environmental impact; Impurities; Iron; Kaolin; Methylene blue; Mines; Molecular sieves; pH effects; Surface properties; Thermal stability; Titanium; Zeolites
• ISSN: 2227-9717; 2227-9717
• DOI: 10.3390/pr11030662

Non-processed kaolin (flint kaolin) from a mine located in the Capim area (Amazon region, northern Brazil), usually considered as waste, was selected as a source of silicon and aluminum in the synthesis of SAPO-34. This is a molecular sieve and cationic exchanger chosen for tests focusing on the removal of methylene blue in aqueous solutions, which is a cationic dye widely used by textile industries in Brazil. The results revealed that the SAPO-34 has been successfully synthesized with typical cubic morphology, good crystallinity (>90%), and thermal stability (~998 °C). Although the oxidized Fe/Ti impurities contained in the flint kaolin affect the degree of crystallinity of the zeolitic product, its adsorptive properties are not significantly affected, which demonstrates the excellent adsorption results (pH = 11; % removal > 90%). It proved to be an adsorbent with considerable adsorption capacity (9.83 mg·g−1). The pH test confirmed the acidic surface characteristics (pH solution 2–4; ↓ removal), and the kinetic model that best fitted the experimental data was pseudo-second-order, with R2 = 0.998 (kinetics controlled by chemisorption).