Clays and Clay Minerals, Vol. 60, No. 3, 265–277, 2012.

Abstract

Bentonite deposits are rare in Brazil and most of their production comes from a single region. A new bentonite occurrence, the Formosa bentonite from northern Brazil, is described here. The occurrence is associated with altered Mesozoic volcanic rocks of the Parnaı´ba Sedimentary Basin, one of the largest continental flood basalt (CFB) provinces on Earth. The purpose of the present study was to evaluate the physical and chemical properties of a new smectite-bearing deposit in Brazil. Analysis has shown that the major mineral present in the Formosa bentonite is a dioctahedral smectite along with minor amounts of hematite, K-feldspar, and kaolinite. Quartz is absent. A Li+-saturation test (Hofmann-Klemen treatment) revealed a montmorillonite smectite; large interlayer-Mg2+ contents revealed by N2 adsorption/desorption and cation exchange capacity results suggested a Mg-bentonite. This characterization helped to explore the structure-functionality (reactivity) relationship and to develop index tests for industrial applications and the research of new materials. Use of this material as a desiccant-grade bentonite is envisaged (desiccant-grade bentonites contain Mg2+ and/or Ca2+ as the dominant exchangeable cations), or it could be activated with Na+ for use in many industrial applications (e.g. as a drilling fluid or for pelletizing iron ore). The large areal occurrence of the flood basalts suggests the possibility of very large deposits of these bentonites, a promising new exploration target for this class of industrial minerals in northern Brazil.