Dehydration and dehydroxylation of nontronites and ferruginous smectite

Differential thermal analysis and thermogravimetry have been used to compare the dehydration and dehydroxylation behaviour of a series of nontronites including two newly discovered nontronites from Uley, South Australia. A comparison is made with the thermal behaviour of ferruginous smectite. Three dehydration endotherms were found at around 60°C, 100°C and 160°C. A strong dehydroxylation endotherm for all samples was found at ∼430°C. The nontronites from Hohen-Hagen and Garfield show well-defined steps for dehydroxylation whereas the two Uley nontronites showed continuous dehydroxylation. The intensities of the infrared spectra of the hydroxyl-stretching region showed excellent correlation with the nontronite dehydroxylation endotherms. The infrared spectra of the water bending region showed two bands centred at ∼1630 and 1670 cm−1. These bands are attributed to adsorbed water and coordinated water.