LAUSR

The synthesized phases with chemical composition M62+Al3OH18A+SO4212H2O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left[ {{\text{M}}^{2 + }_{6} {\text{Al}}_{3} \left( {\text{OH}} \right)_{18} } \right]\left[ {{\text{A}}^{ + } \left( {{\text{SO}}_{4} } \right)_{2} } \right]12{\text{H}}_{2} {\text{O}}$$\end{document} (M2+ = Mn, Mg, Zn; A+ = Li, Na or K) were evaluated in relation to their thermal behavior by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). In the shigaite (M2+ = Mn), natroglaucocerinite (M2+ = Zn) and motukoreaite (M2+ = Mg) phases, the TGA measurements indicated that all samples were dehydrated up to 200 °C in two steps, followed by dehydroxylation above 300 °C. After the thermal treatment at 1000 °C, formation of oxides/spinels were observed for the shigaite and natroglaucocerinite phases, while for motukoreaite, oxides, spinels and MgSO4 were detected. XRD indicated a reduction in the basal distance from around 11 Å for the fully hydrated phases to around 7 Å for the dehydrated phases. The thermal treatments of some samples at 100 °C, 150 °C and 200 °C indicated that in all phases, intercalated sulfate and alkaline metal ions can be dehydrated and rehydrated. As indicated by FTIR, at 200 °C sulfate could be grafted to the layers and at 300 °C, for all the phases, a stable mixture of amorphous materials was obtained, which could not be rehydrated.