Mineralogical characterization of a bentonite from Bravo mine, Boa Vista, Paraíba

Abstract

A bentonite sample from Bravo mine, Boa Vista District (Paraíba, NE Brazil), presenting the high Cation Exchange Capacity (CEC) of 106meq/100g, was thoroughly characterized, in order to find the best added- value application for it. Smectite, quartz, and jarosite have been identified in the run of mine (ROM) sample, whereas the size fraction under 10μm contains only smectite with traces of quartz. All the iron in the sample is Fe3+, as analysed by 57Fe Mössbauer Spectroscopy, and its sole carriers are smectite, exclusively in the octahedral layer, and goethite, around 30% (wt) in both samples. According to solid state 27Al Nuclear Magnetic Ressonance, only 1% of the aluminium is located in the tetrahedral layer of the smectite, whereas 99% of it is octahedral. The clay’s chemical composition and its spectroscopic signature classify the chocolate bentonite as an iron-rich montmorillonite. Thermal analysis, with an endothermic peak due to smectite dehydroxylation at 488.6°C, and FTIR (Fourier Transformed Infrared) Spectroscopy, confirm the classification.