Mineralogy and chemistry of a new bentonite occurrence in the eastern Amazon region, northern Brazil D.S. Moraes a, ⁎, R.S. Angélica b , C.E.F. Costa a , G.N. Rocha Filho a , J.R. Zamian a a UFPA — Universidade Federal do Pará, Instituto de Ciências Exatas e Naturais, Laboratório de Catálise e Oleoquímica, 66075-110, Belém, PA, Brazil b UFPA — Universidade Federal do Pará, Instituto de Geociências, 66075-110 Belém, PA, Brazil abstract article info Article history: Received 28 July 2009 Received in revised form 8 February 2010 Accepted 11 February 2010 Available online 19 February 2010 Keywords: Amazon Bentonite Brazil Montmorillonite Parnaíba Basin The Brazilian production of bentonite is approximately 300,000 t/year, with more than 88% of this production concentrated in small deposits located in the Paraíba state (northeast Brazil), which consequently are becoming exhausted. The objective of this paper is to present a new occurrence of bentonite from the eastern Amazon in northern Brazil, here referred to as Balsas bentonite. A selected sample of the material was characterized by XRD, TG/DTA, ICP-OES, FTIR, SEM-EDS, N 2 adsorption/desorption at 77 K and CEC. The main constituent of the bulk sample is montmorillonite. Kaolinite is completely absent, in contrast to some bentonites found in the famous Paraíba state. The results obtained from the mineralogical and chemical characterization confirm that this material, in comparison to some reference bentonites from the Clay Mineral Society Source Clays, has promise as an engineering material, indicating its possible use in various research and industrial applications. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Smectites are widespread in nature as the main components of ben- tonites. They are used in a large number of technical and geotechnical applications. World reserves of bentonites from different geological contexts have been well explored and documented in several countries. Although Brazil hosts huge mineral potential for metallic ores, few exploration programs for industrial minerals and clays have been carried out by government institutions or private companies. In the case of bentonite, Brazilian production is around 300,000 t/year, with over 88% of this production coming from relatively small deposits in Boa Vista municipality, Paraíba state, in northeast Brazil (DNPM, 2008). These bentonites were discovered in the early 1960s, and their geological origin is related to alterations of glassy material derived from volcanic ash (Gopinath et al., 1981). According to Amorim et al. (2004), they are composed of montmorillonite, illite, kaolinite and mixed layers of illite– montmorillonite and quartz. They are naturally polycationic and when treated with a concentrated sodium carbonate solution, they can be transformed into sodium bentonites with rheological properties in accordance with specifications of the American Petroleum Institute. These sodium bentonites are able to act as substitutes for natural sodium bentonites that are imported by Brazil (Luz and Lins, 2006). Most of the papers in Brazilian scientific literature address modifications and further applications of bentonites that are primarily from Boa Vista (Paraíba) (e.g., Pereira et al., 2005; Paiva et al., 2008, among others). After 40 years of exploitation, it is of great concern that production at the Boa Vista region is decreasing due to the exhaustion of reserves. New areas in Brazil should be immediately envisaged for exploration. Paleozoic sedimentary basins occupy more than 50% of the Brazilian territory by area, with sedimentary sequences that are hundreds of meters thick and an enormous potential to encompass bentonite deposits. In this study, a new occurrence of smectite-bearing “green shales” is described. The “green shales” are associated with the clays and siltstones of the Eopermian Pedra de Fogo Formation, Parnaíba Paleozoic Basin, in the Maranhão state, northeast Brazil. We call this new material “Balsas bentonite”, after the name of the main city in the vicinity. The main purpose of this study is to present reliable chemical and mineralogical characterization of these bentonites, with the future goal of establishing their use for adsorption and catalysis applications. 1.1. Geological setting The Parnaíba Basin is located in the western portion of northeastern Brazil. It covers an area of approximately 600,000 km 2 , comprising a total sedimentary section that is approximately 4000 m thick at its depocenter. A summary of the geological, geophysical, and geotectonic context of this and other Paleozoic basins in Brazil can be found in Góes and Feijó (1994) and Milani and Zalán (1999). According to these authors, the Pedra de Fogo Formation belongs to the Balsas Group, a Carboniferous–Triassic Supersequence made up of a clastic–evaporitic succession of sedimentary rocks with fine-to-medium-grained sand- stones, brown shales and subordinated limestones (Piauí Formation), Applied Clay Science 48 (2010) 475–480 ⁎ Corresponding author. E-mail address: dorsan@ufpa.br (D.S. Moraes). 0169-1317/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2010.02.009 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay