Abstract

Infrared spectra and X-ray diffractograms were obtained for Georgia palygorskite with merent contents of coordinated water. Interpretation of these results show that palygorskite starts to lose coordinated water at relatively low temperatures, causing the structure of the mineral to fold. Although the mineral is folded when 50 percent of the coordinated water is lost, the folding does not appear to be uniform. An ordered folded state is not reached until 65 percent of the water is lost. Rehydration from the folded state containing coordinated water is rapid. Removal of the last half of coordinated water is accompanied by loss of the structural hydroxyls.

Flushing palygorskite with ammonia removes the coordinated water and replaces it with ammonia coordinated to the Mg located at the channel edge. However, almost no ammonium is produced, indicating that the mineral contains few exchangeable cations. In the ammo-mated palygorskite, folding of the mineral occurs readily upon evacuation of the sample at ambient temperature. This suggests that six-fold coordination of each edge Mg is an important tactor in keeping palygorskite in the unfolded state.

Comparison of palygorskite to the analogous fibrous mineral sepiolite shows palygorskite to fold and dehydroxylate at lower temperatures. These characteristics parallel similar obser-va ions for other layer silicates, and have been attributed to differences between dioctahedral and trioctahedral minerals.

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