Adsorção do corante azul de metileno em caulinita natural e intercalada com acetato de potássio provenientes da região de Bom Jardim de Goiás – GO

Abstract

Clays have been used since ancient times by mankind for the production of ceramic objects, such as bricks and tiles, and more recently in various technological applications. The possibility of chemical modification of clay minerals allows the development of its use for various types of technological applications, adding value to this abundant natural resource. This work describes the characterization of kaolinite, from of Bom Jardim de Goiás region - GO, in natural and intercalated form, to possible application in the adsorption processes. The samples were characterized by X-ray diffraction, X-ray fluorescence, thermal analysis, scanning electron microscopy and infrared, aiming their applicability as adsorbents for the removal of pollutants, in the case studied, the methylene blue dye. Part of the natural kaolinite sample was intercalated with organic compound, potassium acetate by milling method, whose intercalation resulted in an increase in basal spacing of 7.16 Å to 13.76 Å. Chemical analysis of the natural sample showed that the silicon content (41.97%) and aluminum (33.76%) are consistent with the percentage of ideal kaolinite, although the analysis have showed high contents in iron (6.56%), magnesium (2.17%) and potassium (1.38%), which was attributed to the presence of illite associated to sample. In the intercalated sample, the chemical analysis revealed an increase in potassium content of 1.38% for 14.12%, and other changes such as loss in the content of silicon and aluminum. The infrared spectra of the natural sample showed characteristic bands to kaolinite in 472, 541 and 1011cm-1 , while the intercalated sample showed additional bands in the region of 1408 and 1604 cm-1 attributed to stretching vibrational CH3COOof potassium acetate. The thermal behavior of the natural sample was very close to theoretical kaolinite, showing endothermic peaks in 53°C and 500°C, attributable to the elimination of water molecules and dehydroxylation, respectively. The last peak corresponds to the endothermic reaction in which occurs the transformation of kaolinite to metakaolinite. Adsorption studies were realized in the samples to evaluate the adsorptive capability of them, using the batch method. The models used for this study were the Langmuir, Freundlich and Sips. The adsorption of the dye was favorable in pH 9.0 for natural sample, and pH 7.0 for the intercalated sample. The model that best fitted the experimental data was the Sips for both samples. For kinetic studies were tested three models, Pseudo-first order, Pseudo-second order, and Avrami. For both clays, the model of Avrami was that best fit to the experimental data. The contact time required for the system to reach equilibrium was 90 and 120 minutes for the sample natural and intercalated, respectively. The maximum adsorption capacity reached by the intercalated clay was 79.34 mg g-1 , while by the natural sample was 72.14 mg g-1 . These values show that both samples of kaolinite are considered to be good adsorbents in the removal of methylene blue dye in aqueous solutions.