Nickel, iron-containing clay minerals from Niquelândia deposit, Brazil: 1. Characterization

Two representative samples of Ni, Fe-containing clays from Niquelândia deposit, Goias, Brazil, have been characterized by different methods and techniques. X-ray diffraction (XRD) was used for the identification of the crystalline phases and to follow the structural modifications occurring upon thermal treatments. One of the samples (N4) is a pure smectite, while the second one (N7) is a mixture of 2:1 (smectite) and 1:1 (lizardite) phases. The thermoanalytical results [differential thermal analysis (DTA), thermogravimetric analysis (TGA)] are consistent with the XRD identification and the low nickel content of lizardite. Mِssbauer spectroscopy data allow to assign most of the iron contents to two octahedral sites. From those results and the chemical analysis data, structural formulas of the smectite are proposed. Both clays are montmorillonite-type with appreciable Al for Si tetrahedral substitutions.