Synthesis of zeolite a from metakaolin and its application in the adsorption of cationic dyes

The present work reports the synthesis of zeolites from two metakaolins, one derived from the white kaolin and the other derived from the red kaolin, found in a deposit in the city of São Simão (Brazil). The metakaolins were prepared by calcination of the kaolins at 600 ◦C; zeolite A was obtained after alkali treatment of the metakaolins with NaOH. The resulting solids were characterized by powder X-ray diffraction, thermal analysis, scanning electron microscopy, and nitrogen adsorption/desorption at −196 ◦C, which confirmed formation of zeolite A. The zeolites were applied as adsorbents to remove methylene blue, safranine, and malachite green from aqueous solutions. The zeolites displayed high adsorption capacity within short times (between one and five minutes); qt was 0.96 mg/g. The equilibrium study showed that the zeolites had higher adsorption capacity for malachite green (qe = 55.00 mg/g) than for the other two cationic dyes, and that the Langmuir isotherm was the model that best explained the adsorption mechanism.The Spanish authors thank the Spanish Ministry of Economy and Competitiveness (MINECO)_x000D_ and the European Regional Development Fund (ERDF) for joint financial support (grant MAT2013–47811–C2–R_x000D_ and MAT2016-78863-C2-R). The Brazilian group acknowledges the support from the Brazilian research funding_x000D_ agencies Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (311767/2015–0, 2012/08618-0,_x000D_ 2013/19523-3, and 2016/01501–1), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES),_x000D_ and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). Both groups thank the Spain–Brazil_x000D_ Interuniversity Cooperation Grant, jointly funded by the Spanish Ministry of Education, Science and Sports_x000D_ (PHBP14/00003) and CAPES (317/15)