Caracterização química, mineralógica e aplicações potenciais da bentonita associada a basaltos intemperizados da Formação Mosquito, Bacia do Parnaíba, Sul do Maranhão

Abstract

In the city of Formosa da Serra Negra (Maranhão state, northern Brazil), extensive outcrops of weathered basalts are found, which show enough clay contents to be a potential bentonitic material. The basalts are related to the Jurassic Mosquito Formation (Parnaíba Sedimentary Paleozoic Basin). In this work these saprolites were referred as Formosa bentonite, and the main purpose was to characterize their mineralogical and chemical composition for further potential applications. X-ray diffraction results show that montmorillonite is the main mineral present along with minor amounts of hematite, K-feldspar, magnetite and kaolinite. The Formosa Bentonite was compared with four reference bentonites: Chocolate and Bofe (from the famous Paraiba state deposits), SWy-2 and SAz-1 (from the Clay Mineral Society). Although these bentonites have showed a wide chemical, mineralogy and texture variation, common for such material, the similarities were convincing to increase the expectations of a new Brazilian bentonite. The present montmorillonite was successfully pillared with aluminium polyhydroxications. Results showed that the pillarization process increased the basal spacing of the natural clay from 15.3 to 18.7 Å and the surface area from 55.9 to 180.3 m2/g, proper for catalytic and adsorption applications. Adsorption tests were also carried out for Cu2+ in aqueous solution using the natural and pillared Formosa Bentonite. Surprisingly, in the three evaluated process variables (pH, contact time and adsorption equilibrium) the natural bentonite exhibited a better adsorptive capacity in comparison with the pillarized one. This is of special value if one intends to use these bentonites in natura, for instance, for wastewater treatment. They are environmentally correct, economically viable and assure low cost.