PROPRIEDADES FÍSICO-QUÍMICAS DE ARGILAS E DE ZEÓLITAS DO ESTADO DO MARANHÃO

Abstract

The State of the Maranhão, Northeast of Brazil, has large occurrences of clays and zeolites. Nevertheless, these materials are not commercially exploited, due to lack of studies on its mineralogical and chemical composition. In this context, the objective this paper has as to study the physico-chemical features, particularly textural and structural properties and surface acidity of some natural clays and zeolites from the State of Maranhão. Thirteen samples of clays and four of zeolites were collected in Governador Edson Lobão, Montes Altos, Barra do Corda, Presidente Dutra, Grajaú, Codó and Carolina. All materials were characterized by X ray diffraction (XRD), X ray fluorescence (XRF), thermal analysis (TGA/DTA/DSC), N2 and n-butylamine adsorption/desorption. The obtained results revealed that the clays are, under a mineralogy view point, constituted by, basically, smectites and kaolinites, being some of these solid composites for 100% of sand and another one for a mixture of minerals of iron and clay, showing diversified chemical compositions and specific areas which varying from 2 m2/g until 85 m2/g. The zeolites showed to be structurally similar with a mixed mineralogical composition, presenting stilbite phases as well as smectite, with quite low specific areas (5 m2/g until 13 m2/g). Zeolites revealed to be more acidic than the clays. However, it should be emphasized that the surface acidity of all clays is also significant, being characterized by strong acid sites. In the particular case of the smectites, mainly of A5 sample, it was verified that the chemical activation, through acid treatment, modified its crystalline structure and increased its specific area for 136,53 m2/g. The adsorption capacity of the acid-activated clays had been more of natural clays and in some cases, these values had been similar to those gotten when using commercial clays. In a general way, this study indicates that the evaluated solids can be applied as adsorbents, as catalysts and as raw materials for refractory and ceramics production.